Characteristics of the deposits and oxide films formed on 316L stainless steel in situ tested on a boiler of 1000 MW pulverized coal-fired power plant for 150 h were examined. The results show that the deposits are mainly composed of outer fly ash, middle sulfate, and chloride and fluoride in the inner layer. Oxide films are mainly Fe₂O₃ and Fe₃O₄. Two models of coupling mechanism of dew point corrosion and viscous ash deposits at different temperature ranges are proposed to instruct engineering application.

This paper shows how the last algebraic matricial form can be obtained when the finite element method is used to approximate the potential distribution of a cathodic protection system that includes low conductivity irregularities in the electrolyte away from, close to and directly on the cathode. In order to study the influence of the resistivity of these irregularities on the possibilities of steel protection, five conductivities were analysed. The numerical results, validated with COMSOL® Multiphysics, show the importance of considering irregularities in the domain in order to prevent systems from becoming unprotected. The experimental data agrees with the theoretical data.

Steam cracking is a petrochemical process that cleaves a broad range of hydrocarbon feed molecules into a variety of light olefinic products, including the highly desirable ethylene. Over the course of a cracking operation using a feed mixture of a saturated hydrocarbon and steam around 900–1000 °C in tubular alloy coils located in fired heaters, coke inevitably forms on the inside surfaces of the furnace tubes and must be burned off and/or spalled off periodically using steam or a steam–air mixture. Furnace tube materials are predominantly based on chromia-forming alloys; such alloys can degrade by carburization and oxide–carbide conversion in such a mixed carburizing–oxidizing environment. These hurdles have been largely overcome by using an alumina-forming material that provides superior corrosion and coking resistance. Cracking hydrocarbons at much higher temperatures results in high selectivity to acetylene, which can be converted into many petrochemical products including ethylene. The desired hydropyrolysis reaction from hydrocarbons to acetylene can be realized in a reverse-flow reactor operating above 1500 °C in a scaleable manner. The reactor elements include ceramic components that are placed in the hottest regions of the reactor, and must withstand temperatures in the range of 1500–2000 °C. Moreover, the materials in the hot zone are exposed alternately to a regeneration (heat addition) step that is mildly oxidizing and a pyrolysis (cracking) step that is strongly reducing with a correspondingly high carbon activity. This paper addresses the thermodynamic stability of selected ceramic materials based on alumina, zirconia, and yttria for such an application. Results from laboratory tests involving the exposure of these ceramic materials to simulated process conditions followed by their microstructural characterization are compared with expectations from thermodynamic predictions.

Mechanistic study of stress corrosion cracking of carbon steel in fuel-grade ethanol was made using slow strain rate testing and constant tensile load testing at yield strength stress level of the steels. Characterization of the fracture surface was made using SEM and SEM–EDS. Selective dissolution of ferrite from pearlite phase was observed. Crack initiation took place preferably from pearlite phase. Corroded zones consisting of crystallographic pits were found from fracture surfaces.

We have created an accelerated corrosion environment for sintered Nd–Fe–B magnets in e-motor applications. E-motor working conditions are complex, and standard magnet corrosion tests only cover a small subset of possible parameters (e.g., samples are usually tested in the demagnetized state). In this work magnetized and demagnetized sintered Nd–Fe–B magnets were placed in gearbox oil, and exposed to temperature cycles (θ_max = 130 °C) using an autoclave. Beforehand the magnets were pre-immersed in saturated water-based salt solution to account for water and de-icing salt that might interfuse gearbox oil over time. The corrosive behavior was studied for two commercial magnet grades, “high grade” (8.9 wt% dysprosium) and “low grade” (3.1 wt% dysprosium); and monitored by weight loss, structural analysis (scanning electron microscopy and energy dispersive X-ray) as well as magnetic characterization. The magnetized samples corroded significantly faster than their demagnetized counterparts. Strong differences in the corrosion rates of the “low grade” and “high grade” material are discussed. We concluded that the magnetization state is one key parameter that needs to be considered in corrosion tests for e-motor applications.

Sulfuric acid doped nano-polyaniline was prepared by direct mixed oxidation in two different systems. A novel approach for preparing polyaniline (PANI) in FeCl₂/H₂O₂ system was developed. The PANI possessed an excellent dispensability. Corrosion protection of epoxy coatings containing two kinds of polyaniline (PANI) on Q235 steel was studied by electrochemical impendance spectroscopy (EIS) technique and Tafel polarization test in 3.5 wt% sodium chloride (NaCl) aqueous solution. The results indicated that the epoxy coating containing PANI obtained in FeCl₂/H₂O₂ system had the best performance of the corrosion protection among three systems under investigation. The possible protective mechanism of PANI was discussed.

A new quaternary Ti–20Nb–10Zr–5Ta alloy was thermo-mechanically processed; applying a stress of 10 ton-forces after heat treatment at 1000 °C it resulted a very homogeneous, fine microstructure characterized by the best mechanical properties: low Young's modulus (60 GPa) and high tensile strength and hardness. The corrosion behaviour of this processed alloy after long-term soaking (5000 h) in simulated human fluid (Ringer solution) was studied. SEM micrographs of as-cast and processed alloy after immersion proved that their surfaces were covered with a layer with a porous microstructure. EDX analysis detected Ca, P, and O as constituent elements of this porous layer. XPS determined the presence of the protective TiO₂, Nb₂O₅, ZrO₂, and Ta₂O₅ oxides and of the hydroxyapatite deposited from solution. All electrochemical parameters exhibited more favourable values for the processed alloy indicating the beneficial influence of the applied treatment. Impedance parameters revealed a nobler behaviour of the processed alloy than of the as-cast one. EIS spectra showed a passive film with two layers: a compact, inner, electronically conducting, barrier layer and an outer, porous layer.

The aim of this study was to monitor the dissolution of violin, viola, and violoncello strings in order to monitor the release of metal ions during their usage. The concentration of dissolved metal ions in corrosive solution (nitric acid) is discussed. The concentration determined are decreasing in the following order: Fe³⁺>Cu²⁺>Al³⁺>Cr³⁺>Si⁴⁺>Mn²⁺>Ni²⁺>Zn²⁺>Mo²⁺>Sb²⁺>V²⁺>W²⁺>Sn²⁺. Among all investigated metal ions, nickel is far the most allergenic. The results have shown that majority of investigated samples contained nickel in their composition, in amounts that are higher than prescribed limits of 0.05%. Therefore, those items could induce contact allergic dermatitis in musicians sensitive to nickel allergy, presenting a potential threat to their health.

The corrosion performance of Zn–Mg(1–2%)–Al(1–2%) (ZMA) coatings has been compared to zinc–iron alloy (galvannealed, GA) and zinc–aluminum coating (Zn–5Al, Galfan) as well as to conventional zinc coatings produced by hot-dip galvanization (HDG) and electrogalvanization (EG). For this purpose, cosmetic samples (painted and uncoated) and hem-flange panels were produced. Their corrosion performance was compared in three different accelerated corrosion tests, as regularly used by the automotive industry, e.g., VDA621-415, N-VDA (VDA233-102), and Volvo STD 423-0014. As can be concluded from our results, the behavior of ZMA coatings was strongly dependent on the testing conditions as well as on the configuration of the samples. The advantageous effect of ZMA coating was more pronounced in open situations than in confined ones, irrespective of the testing conditions. ZMA coatings provided a significant improvement in comparison to conventional coatings in tests involving a significant salt load such as VDA621-415 or neutral salt spray especially on cosmetic configurations. By contrast, the beneficial effect of ZMA coatings was less obvious in tests with lower salt load (VDA233-102, Volvo STD423-0014), particularly when considering cosmetic corrosion on painted samples and corrosion in confinement. Interestingly, no significant differences were observed between samples with varying Al and Mg content in the metallic coating (1–2% each). The results were compared to data from field exposure at stationary sites.

Aluminum materials roll-plated on both sides are combinations of metals, which consist of clad layers on a core. To document the long term behavior of roof profiles of Alclad 3004 after long term exposure of about 40 years, evaluations were made at three locations in Germany with different climatic conditions. Locations with typical rural-urban, coastal-urban, and industrial climates were selected. The corrosion progress as a function of time and climatic type could be characterized by cross-sections of roof specimens. To interpret the protective mechanism of the clad layer, the corrosion behavior of Alclad 6025 was characterized by electrochemical investigations. The results show that the passive clad material easily undergoes pitting in media containing specific amounts of chlorides. In case of contact of both cladding and core with an electrolyte the core alloy was protected because of the pitting corrosion of the cladding. This guarantees long-time corrosion protection of constructions like facades or roofs under different atmospheric conditions.

The galvanic corrosion behaviors of NiC filled conductive silicon rubber (CSR) with different resistivity coupled to magnesium alloys were investigated in 3.5% sodium chloride solution at different temperatures. Such investigations were carried out by means of electrochemical measurement, weight-loss determination, and surface characterization. The results indicated that the changes of CSRs' resistivity and the temperature of the electrolyte would affect the Tafel slope, cathodic corrosion current, and linear polarization resistance of the cathodic branch of the polarization curve. The lower the resistivity, the larger the average galvanic corrosion current density and the average galvanic corrosion rate of Mg alloys at the same temperature. The corrosion morphology revealed that the greater the corrosion current density, the more serious the corrosion on the surface of Mg alloys.

01570 aluminum alloy was cold rolled and annealed at different temperatures, and their microstructure, mechanical properties, pitting and stress corrosion cracking (SCC) behaviors were observed and determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), immersion test, slow strain rate tensile (SSRT), and constant loading tests. The results reveal that the dislocations within the grains of alloy 01570 are transformed from dislocation tangles to dislocation walls and subgrains as the treatment varies from the cold rolled temper to the annealed tempers; at the same time, the tensile strength and SCC resistance of alloy 01570 are increased and the elongation is decreased, whereas the corrosion rate is negligibly influenced by the annealing treatments. Therefore, the annealed at 300 °C temper can be selected as the optimum heat treatment for the practical application of alloy 01570.

Stress corrosion cracking of carbon steel in aerated ethanol–gasoline blend was studied using notched slow strain rate testing. Characterization of the fracture surface was made using SEM and SEM–EDS. Intergranular stress corrosion cracking (SCC) was produced in ethanol–gasoline blend with 15.5 wt% ethanol that was produced by evaporation of light C4 and C5 fractions from the ethanol–gasoline blend with 10.4 wt% of ethanol. Chloride concentration of 2 mg/L was found to cause transition from intergranular SCC to fully transgranular SCC in ethanol-gasoline blend with 85 wt% of ethanol. Transgranular SCC was found to initiate mainly at the pearlite phase and intergranular SCC initiated equally on the pearlite and ferrite phases. Chloride caused localized crystallographic pitting on the transgranular SCC fracture surfaces near the lamellar cementite left on the steel surface due to selective dissolution of ferrite from pearlite.

The determination of critical pitting temperatures (CPT) in various test solutions like ferric chloride solution according to ASTM G48 or “Green Death” solution is a common test method for the comparative assessment of the pitting corrosion resistance of highly alloyed steels and NiCrMo alloys. In addition to the well-known disadvantages of standard methods, like long test times, subjective examination, and large scatter, for the highest alloyed NiCrMo alloys no stable pitting corrosion can initiate even at the highest test temperatures. This paper describes the limitations of standard test methods and shows how these problems can be solved by an alternative test solution and an adjusted test method. By capturing and examining the current noise under potentiostatic conditions during continuous heating in a 4.5 M calcium chloride solution the transition from metastable to stable pitting corrosion as a criterion for CPT can be detected in a reproducible way.

The microstructure of light element containing Al₂₅Ti₂₅Ga₂₅Be₂₅ equi-molar composition alloy was investigated by X-ray diffractometry and scanning electron microscopy, while the corrosion behavior was tested in 1 M sulfuric acid solution (H₂SO₄) at ambient temperature (298 K). The results show that the alloy displays good general corrosion resistance. The influence of the microstructure and morphology of the constituent phases is also evaluated.

A comparative study of the corrosion properties of an AlZnMgCu alloy subjected to simulate age-forming (SAF) and traditional aging was performed. The samples pretreated at 160 °C for 24 h using SAF and traditional aging, were immersed in 3.5 wt% sodium chloride solution for up to 96 h, the process of which was monitored by in situ electrochemical impedance spectroscopy (EIS). Optical profilometry measurement shows that the sample subjected to SAF has deeper pits and larger localized corrosion compared with the traditionally aged sample. EIS results suggest that corrosion rate changes with increasing time of immersion, and age forming makes the AlZnMgCu alloy hard to form effective passive film. The larger precipitate and wider precipitate free zone of the sample subjected to simulate age forming were thought to be responsible for the poor corrosion resistance during the immersion test. Additionally, these results suggest that stress during age-forming increases the grain aspect ratio, which is harmful to intergranular corrosion resistance of the AlZnMgCu alloy.

Natural hydroxyapatite (HA) was coated on NiTi alloy using electrophoretic deposition method to improve the corrosion resistance and biocompatibility. Coating process was performed at 120 s in various applied voltages of 40, 60, and 80 V. Sintering process was done at 800 °C under inert gas for 2 h. Electrochemical behavior of the coated samples was investigated in simulated body fluid by using electrochemical impedance spectroscopy and polarization tests. Furthermore, the nickel ions release from NiTi and HA coated-NiTi samples were analyzed by atomic absorption analysis. Ultimately, scanning electron microscopy micrographs and X-ray diffraction patterns were used to evaluate the morphology and phase analysis of HA coatings. The results show that the sample coated at 60 V reveals a uniform, dense coating accompanied with a higher corrosion resistance. Moreover, after 4 weeks, nickel ions release was reduced to 0.205 µg/cm² for coated sample at 60 V.

Nanocrystalline copper oxide (CuO) powder of varying sizes (22, 25, 28 and 36 nm) have been successfully synthesized by hybrid electrochemical method using aqueous sodium nitrate electrolyte with Cu electrodes under galvanostatic mode at room temperature. The as-synthesized CuO sample was calcined for an hour at temperatures ranging from 60 to 900 °C. The crystallite size, morphology, and chemical state of the synthesized powders were characterized by powder XRD, XPS, SEM/EDAX, TEM, and UV–Vis spectral methods. The effect of calcination temperature on crystallite size and morphology was studied. The TEM result revealed that, the particles are hexagonal and the sizes are in 30–50 nm in diameter and 120–200 nm in length. The band gap values are 5.60 and 5.54 eV. The crystallite size increased with increase of calcination temperature. The CuO nanopowder is used to fabricate Zn–Ni–CuO composite thin films and its corrosion behaviour was analysed by Tafel extrapolation and electrochemical impedance spectroscopy. The results indicate that the Zn–Ni–CuO composite thin films provided good corrosion protection.

Binary magnesium–silver (Mg–Ag) alloys were designed as antibacterial material to treat infections in an implant site. The mechanical and electrochemical measurements were performed on three casting Mg–Ag alloys under cell culture conditions. The composition and distribution of the corrosion layer was analyzed by microscopy and X-ray photoelectron spectroscopy. In cell culture media, Mg–Ag alloys show higher, but still acceptable general corrosion rates while less susceptibility to pitting corrosion than pure Mg with increasing content of silver. This study indicates that Mg–Ag alloys have satisfactory corrosion properties and much better mechanical properties than pure magnesium as a functional biodegradable material.

Modified hydrotalcites (MTHs) represent a group of technologically promising materials for addition to concrete to improve its durability in aggressive environment, owing to their low cost, relative simplicity of preparation, and plenty of unique composition variables that may be adopted. Up to date, a lot of academic work and commercial interest on MHTs have been invested, but relatively few studies focus on cementitious materials, particularly in exploiting their potential applications in corrosion protection of reinforced concrete structures. In this article, the mechanism of corrosion in reinforced concrete and concrete properties that affect corrosion of reinforcement are briefly introduced. In addition, the existing knowledge with regard to synthesis and characterisation methods of MHTs, ion exchange within the MHT structure as well as the application of MHTs in the cementitious materials were reviewed accordingly. As a new emerging class of smart additive of reinforced concrete, MHTs are expected to contribute to the effort of searching for effective measures to improve the durability of reinforced concrete.

Significantly changed intergranular corrosion (IGC) and exfoliation corrosion (EFC) behaviors of the equal-channel-angular-pressed (ECAPed) Al–Cu alloy were discovered through immersion test, electrochemical measurements, and microstructure observation. The ECAPed alloys with ultra-fine grained (UFG) α(Al) matrix and extremely refined θ-phase particles displayed obvious decreased IGC sensitivity, but deteriorated susceptibility to EFC. The decreased IGC sensitivity of ECAPed alloys presented decreased IGC propagation depths in immersion test in NaCl + H₂O₂ solutions and increased polarization resistance in electrochemical impedance spectrum test in MIL-H-600 solution. The reason for the decreased IGC sensitivity was the breakage of the net structure of θ phase during ECAP process, which destroys the continuity of IGC propagation channel. The deteriorated susceptibility to EFC of ECAPed alloys in EXCO solution presented gradual evolution from serious IGC attack into obvious lamellar EFC, and finally complete dissolution of surface grains. Meanwhile, the EFC propagation depths were sharply decreased with the increasing ECAP passes. This phenomenon was caused by the aspects ratio evolution of deformed grains and the gradually decreased IGC sensitivity of the ECAPed alloys.

A new method of preparing water-based sol–gel containing titania nanoparticles for the protection of aluminum alloy AA2024 against corrosion was presented and performance of the coating in Harrison's solution was studied. The coating was prepared using alkoxysilanes, tetraethylorthosilicate (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS), and in additional metal alkoxide, titanium(IV) tetrapropoxide (TPOT), as a source of titania particles. Poly(ethylene imine) (PEI) polymer was utilized to create cross-linking and also to improve the coating quality. In addition, the molar ratios and amount of components and factors affecting performance were assessed to improve coating properties and its performance. Potentiodynamic scan (PDS) and electrochemical impedance spectroscopy (EIS) measurements were performed to evaluate the corrosion protection performance of coatings. Also, scanning electron microscopy (SEM) was employed to investigate surface morphology. The stability of the best prepared coating and its corrosion protective effects on the alloy were evaluated in Harrison's solution up to 15 days. The results revealed that this new sol–gel coating provides significant protection against corrosion of the AA2024 alloy in Harrison's solution.

The potential effects of seawater ingress into 316L lined pipes during subsea tie-in operations on corrosion performance were investigated. Immersion and accelerated corrosion tests were conducted on 316L in different mixtures of treated seawater. In particular, we examined the effect of oxygen and microorganisms in seawater on the performance of the alloy at the different mixtures of treated seawater to assess the risk of localized corrosion in the event of seawater ingress into pipelines. Results showed that oxygen has a negative impact on the biocidal and oxygen scavenging efficiency of the chemical treatments and a detrimental effect on pitting corrosion.

Biocorrosion is also known as microbiologically influenced corrosion (MIC). It is often caused by sulfate reducing bacteria (SRB) biofilms. More effective biocide treatment methods are desired due to environmental regulations and increasing costs. Recently, several publications revealed that some D-amino acids are signaling molecules for bacterial biofilm dispersal. In this work, tetrakis hydroxymethyl phosphonium sulfate (THPS) was combined with D-methionine for the mitigation of Desulfovibrio vulgaris (ATCC 7757) biofilm in the full ATCC 1249 medium and a modified medium with only four ingredients, i.e., magnesium sulfate, sodium lactate, ferrous ammonium sulfate hexahydrate, and yeast extract at concentrations 1/4 of those in the full medium, as well as MIC pitting of C1018 carbon steel. D-Methionine alone even at a concentration of 1000 ppm w/w and 50 ppm (active concentration) THPS alone were both found ineffective. However, a synergistic biocide combination consisting of 50 ppm THPS and 100 ppm D-methionine was highly effective and even better than 500 ppm THPS used alone. Although D-methionine alone has no biocidal effects, its biofilm dispersal effect can convert sessile cells to planktonic cells under a biocide stress. This is very useful in biofilm treatment because planktonic cells are much easier to treat than sessile cells using biocides.

The influence of a magnetic field yielding high magnetic flux densities and high flux density gradients on the free corrosion behavior of iron in a low concentrated acidic solution with and without chloride ions is studied by long time exposure experiments and electrochemical impedance spectroscopy (EIS). A decrease of the corrosion rate in electrode surface regions of high magnetic flux density is detected. This decrease of the dissolution rate is significantly stronger in the presence of chloride ions. The observed effects are discussed on the basis of the magnetically induced forces acting on the ions present in the solution, the surface coverage fraction of adsorbed species, and the stability of these adsorbed species.

The critical characteristics of corrosion product film (CPF) were investigated, and the mechanism of flow-accelerated corrosion (FAC) was discussed by improving the multiple reference frame method (MRF) using the space temporary coordinate system. The improved MRF was used to accomplish fluid structure interaction (FSI) numerical simulation for FAC testing machine with a pre-filming specimen. The new numerical method for the simulation of the critical characteristics of the CPF was proposed by coupling FSI and contact analysis in COMSOL Multiphysics software based on Hertz theory, which was used to calculate the critical characteristics of the specimen. The results reveal that the deformation and stress of the CPF increased with increasing temperature and flow velocity. The critical flow velocity was higher than the pre-filming flow velocity and increased with increasing temperature. The calculation results are consistent with those of the linear polarization experiment.

This project focused on investigations on the effect of chloride contaminations on the general corrosion and crack initiation behavior of low-alloy steel (German reactor pressure vessel steel 22NiMoCr3 7) in oxygenated high-temperature water (HTW). Therefore, tests were performed in oxygenated HTW without chloride and at different chloride contamination levels up to 50 ppb. Chloride was added either permanently or temporarily to simulate a chloride transient during plant operation. During these tests, electrochemical noise (EN) and electrochemical impedance spectroscopy (EIS) measurements were performed to monitor the electrochemical behavior depending on the adjusted environment conditions, especially the effect of chloride on the degradation of low-alloy steel. After the tests, the specimens were examined macroscopically and microscopically. In addition, the oxide layer thickness was determined using the focused ion beam (FIB) technique and different surface analysis techniques as, e.g., TOF-SIMS were performed to analyze the composition of the oxide layer. A change of the corrosion behavior of the tested specimens was revealed by the applied electrochemical methods EN and EIS during high-temperature testing. In addition, the applied post-test investigations showed a decrease in the oxide layer thickness due to permanently increased chloride concentrations in the HTW. Temporary transients, however, did not cause a long-term memory effect as shown by both, the electrochemical and the metallographic post-test investigations.

Alumina-chrome bodies were prepared by slip casting route. Slip casted bodies were sintered in the temperature range of 1550–1650 °C in reducing atmosphere with 2 h soaking time at peak temperature. Highly dense alumina-chrome body with bulk density 4.24 g/cc and almost zero apparent porosity were obtained at 1650 °C. The hot corrosion test of alumina-chrome crucible against borosilicate glass was carried out in static condition at 1200 °C for 4 h. The study of the glass–refractory interface after static corrosion test was done by scanning electron microscopy, energy dispersive X-ray spectroscopy analysis and X-ray diffraction (XRD) analysis. The XRD pattern of glass–refractory interface does not show formation of any new phases. Elemental mapping of glass–refractory interface indicates corrosion up to a depth of 70 µm has taken place in the form of ion migration.

The naphthenic acid corrosion (NAC) behaviors of SA210C and A335-P5 steel at different temperatures and flushing angles were investigated by a high-temperature high-flow-rate naphthenic acid corrosion simulation device. It was found that temperature and flushing angle could greatly influence the corrosion rate of SA210C and A335-P5, and temperature was the most important factor. Metallographic observations of SA210C and A335-P5 showed that perlites in ferrite steels would be dissolved preferentially when NAC occurred, and the ferrites would not be corroded remarkably before the perlites were dissolved completely. When the ferrites were corroded, the corrosion proceeded from grain boundary to inner grain. The subsurface would not be corroded before the perlites and ferrites vanished completely on the surface.

The effect of carbonation process on the passivating layer of zinc in Ca(OH)₂ saturated solution was studied. The investigation was performed by means of corrosion potential, corrosion current density, and impedance measurements. To analyze the changes in the passivating layer, X-ray diffraction, Raman spectroscopy and scanning electron microscopy (SEM) were utilized. The results obtained indicate that the layer of calcium hydroxyzincate (Ca[Zn(OH)₃]₂ · 2H₂O) (CHZ), which determines the passivity state of zinc both in Ca(OH)₂ saturated solution and in concrete, is destroyed by the carbonation process, in agreement with previous results obtained for galvanized steel embedded in concrete. X-ray diffractometry and Raman spectroscopy showed that CHZ reaction with CO₂ leads to the formation of Zn₅(CO₃)₂(OH)₆ (hydrozincite) and CaCO₃ (calcite). SEM observation confirms the deep transformation in the passivating layer caused by carbonation. Corrosion potential and corrosion current density measurements show that zinc maintains its passive state also after carbonation. However, impedance measurements indicate that hydrozincite has lower passivating properties than calcium hydroxyzincate in the carbonated solution.

A scratch test is used to measure the adhesion between corrosion product film (CPF) and carbon steel in deionized water under different pH and temperatures. The fuzzy feature model is modified to minimize errors between calculation and scanning electron microscopy (SEM) results. Findings illustrate that the maximum error decreases to 11%. The adhesion between CPF and substrate increases with rising temperature and pH of deionized water. The Poisson's ratio and Young's modulus of CPF are in the ranges [0.34 and 0.45] and [0.08 and 0.11 GPa], respectively, as temperature and pH change.

Aluminium composite materials reinforced with amorphous iron borides (Fe/B) have been manufactured following a powder metallurgical (PM) route. Aluminium particles were mixed with 20% (by wt.) Fe/B particles (obtained by mechanical alloying during 36 h from iron and boron powders, 50% by wt. mixture). Mixes were uniaxially pressed and sintered at different temperatures (ranging from 650 to 1100 °C). The effect of sintering temperature on the corrosion resistance of those materials has been studied and related to the formed microstructures. Moreover, those materials were compared to a wrought and a PM plain aluminium. Their behaviour is studied through cyclic anodic polarization curves in chloride media. In the Al + 20%Fe/B composites, low sintering temperatures (650–950 °C) exert a negative effect. However, when the material was sintered at high temperature (1000–110 0°C) its behaviour was very similar to the pure sintered aluminium.

Ni–P matrix, ternary Ni–W–P and Ni–P–ZrO₂ coatings, and quaternary Ni–W–P–ZrO₂ coatings were deposited using electroless method from a glycine bath. Their corrosion resistance was evaluated by electrochemical impedance spectroscopy (EIS) for various immersion times in a 3.5% NaCl solution. From among the investigated coatings, the ternary Ni–W–P coatings show the highest resistance to corrosion in the first hour of exposure to the 3.5% NaCl medium. An addition of ZrO₂ adversely affects the performance of both the Ni–P coatings and the Ni–W–P coatings. For all the coatings, including the ones containing tungsten, a marked decrease in pore resistance (R_por) over time is observed. This means that their corrosion resistance and capacity to protect the substrate decline. On the other hand, after 24 h immersion in the 3.5% NaCl solution the Ni–W–P coating shows the highest low-frequency impedance modulus (|Z|_{f = 0.01 Hz}). As regards corrosion resistance, the Ni–P coatings and the Ni–W–P coatings perform best.

The corrosion properties were investigated for extruded Mg–3Al–1Zn (AZ31) alloy in alkaline NaCl solution which was manufactured by adding 0.5 wt% CaO without SF₆ protective gas. The results of electrochemical tests showed that the addition of 0.5 wt% CaO drastically increased the pitting potential and charge transfer resistance of the specimen, indicating that CaO addition enhances the film stability of AZ31 alloy. As results of electron probe X-ray microanalysis (EPMA), Al₂Ca phase and CaO was observed on the CaO-added specimen. The Al₂Ca phase was precipitated by the reduction of CaO, and was known as an effective corrosion barrier and hinders the corrosion propagation. Also, the CaO raw particle was observed, and could be remained after reduction as Al₂Ca phase. Meanwhile, the Mg₁₇Al₁₂ phase was not recognized due to the low content of Al in the AZ31 Mg alloy. The results of X-ray diffraction (XRD) showed that Ca(OH)₂ and Al₂Ca phase was observed on the CaO-added AZ31 Mg alloy after immersion for 5 days, which increased the protectiveness of Mg(OH)₂ film of the CaO-added specimen.

The present study describes the inhibition of aluminium in 1 N HNO₃ with different concentrations of 1, 2, 4-triazine precursors 4-amino-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one (AMTDT) and 4-amino-6-benzyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one (ABTDT) using electrochemical impedance spectroscopy adsorption studies and quantum chemical calculations at 298 K. As the electron density around the inhibitor molecule increases due to substitution, the inhibition efficiency also increases correspondingly. Quantum chemical approach was used to calculate some electronic properties of the molecule to ascertain the correlation between inhibitive effect and molecular structure of the inhibitor. The corrosion inhibition efficiencies of these molecules and the global chemical reactivity relate to some parameters, such as E_HOMO, E_LUMO, gap energy (ΔE), electronegativity (χ), global hardness (η), and the fraction of electrons transferred from the inhibitor molecule to the metallic atom (ΔN). In addition, the local reactivity has been analyzed through the Fukui function and condensed softness indices.

The life of a concrete structure exposed to deicing compounds or seawater is often been limited by chloride induced corrosion of the steel reinforcement. A complete assessment of the potential benefits afforded by new candidate rebar alloys must address both the lateral and radial corrosion propagation behavior in comparison to conventional steel as well as other factors that might affect the risk of corrosion-induced concrete cracking. The radial (depth) and lateral (length) corrosion propagation behavior of 18% Cr + 2.8% Mo (S31653) stainless steel, 21% Cr (S32101) duplex stainless steel, and 9% Cr steel compared to plain ASTM A615 carbon steel were characterized in saturated Ca(OH)₂ solution. Radial pit growth was found to be Ohmically controlled for all materials but repassivation occurred more readily at high applied potentials for 18% Cr + 2.8% Mo and 21% Cr stainless steels. Conversely, pit growth on plain steel propagated at all applied anodic potentials and did not repassivate until deactivation by cathodic polarization. Stainless steel also showed the highest resistance to lateral corrosion propagation from an active site during microelectrode array testing. 21% Cr duplex stainless and 9% Cr steel showed similar radial propagation behavior and corrosion morphology, which was intermediate to that of plain steel and S31653 stainless steel. Based on an existing concrete cracking model, it is expected that 9–21% Cr and 18% Cr + 2.8% Mo corrosion resistant rebar materials would require a greater depth of corrosion attack than carbon steel before damaging concrete via corrosion product formation.

Utilization of various types of multi-walled carbon nanotubes (MWCNTs) in zinc-rich paints (ZRPs) is presented addressing percolation and porosity related phenomena of traditional ZRPs. Hybrid paint coatings were formulated with 3.21 wt% polypyrrole (PPy) deposited alumina-MWCNT inhibitor particles (PDAMIPs) and 70 wt% zinc contents. Corrosion protection behavior of the hybrid coatings was investigated by electrochemical impedance spectroscopy (EIS), glow-discharge optical emission spectroscopy (GD OES), X-ray photoelectron spectroscopy (XPS), and FT-Raman spectroscopy. Immersion and salt-spray chamber tests gave evidence of improved galvanic protection and barrier nature of the hybrid coatings over the conventional ZRPs, whereas inhibited zinc corrosion and ignorable steel corrosion took place besides lower degradation of the binder. Zinc-rich hybrid paints with either high relative amount of polyelectrolyte-modified or low proportion of functionalized MWCNTs afforded enhanced corrosion prevention. This result is partly attributed to the nanotube volume fractions around the threshold of infinite cluster formation contributing to electrical percolation and galvanic action of the hybrids. Experimental results are discussed in a broader context on the basis of structure related findings of the PDAMIPs (described in Part I) and in the light of recent literature data. From the newly developed inhibitor particles, some of them are respected as worthy additives for application in hybrid coatings featuring high performance corrosion prevention functionality.

In part 1 of this work, preparation, structure, spectroscopic, and electrochemical characteristics of the polypyrrole (PPy) deposited alumina/multi-walled carbon nanotubes (MWCNTs) inhibitor particles (PDAMIPs) are presented. TEM observations evidenced uniform deposition of thin PPy film on the functionalized nanotubes, whereas co-deposition of PPy and polystyrene sulfonic acid (PSS) lead to thick polymer coverage on hydrated alumina. Modification with polymer complexes resulted in moderately dispersed PDAMIPs, which is due to the various degrees of aggregation and coalescence. FTIR revealed compact and dense PPy structure on the functionalized MWCNTs while it was not the case on alumina and the PSS modified nanotubes. Closer interaction of PPy with the MWCNTs resulted in enhanced charge mobility, whereas greater electroactivity and reversibility of PPy were noted to samples containing functionalized nanotubes and low amount of PSS. Rheological study verified moderate micron-scale dispersity and the modification caused various degrees of aggregations of the PDAMIPs. These were recognized to be valid in the suspensions at a solid phase concentration with component contents similar to the corrosion tested hybrid coatings. Rheological percolation of the nanotubes (with anisotropic factor of ∼100) was confirmed at volume fractions of 3.30 × 10⁻³ and 6.0 × 10⁻⁴ which were under the dilute/semi-dilute boundary type theoretical and experimental thresholds. This is related to the extensive interconnection of the nanotube-supported filaments. Thus, overlapping of the nanotubes should contribute to the electrical percolation thereby galvanic corrosion prevention function of the zinc-rich hybrid coatings, which is discussed in the 2nd part.

This article investigates the initial stages of corrosion phenomena on zinc and magnesium promoted by chlorine contamination by means of an environmental scanning electron microscope (ESEM). In particular, the corrosion of the substrates was promoted in situ in the ESEM chamber by modifying the relative humidity, thus promoting the condensation of water on the metal surface. The metal surfaces were previously contaminated with sodium chlorides. The corrosion morphologies obtained in the ESEM chamber were compared to the degradation promoted by exposing zinc and magnesium samples in the humidostatic chamber.

The need of corrosion protection for metals in aggressive environments is an issue of prime importance for widespread applications. In this article, we demonstrate the properties of oxide coatings prepared in molybdate/silicate and aluminate/silicate composite electrolytes via plasma electrolytic oxidation (PEO) on Mg–Li alloy. To understand the nature of the two coatings, the surface and cross-sectional morphologies, phase composition, and chemical composition of the coatings are studied by scanning electron microscopy (SEM), electron dispersion X-ray spectroscopy (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The corrosion resistances of oxide films are evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 3.5 wt% NaCl solution. In contrast to Mg–Li alloy substrate, the anti-corrosion properties of the two coated alloys are both remarkably improved. Furthermore, molybdate instead of aluminate as an additive in the electrolyte brings forth a denser and compact coating, which can provide longer corrosion protection for Mg–Li alloys. Thereby a surface protection method based on PEO in molybdate/silicate electrolyte is a promising means for producing a dark brown ceramic coating on the surface of Mg–Li alloys with the capability to corrosion protection.

Previous laboratory studies reported in the literature and field experience have revealed the accelerating effect of the heavy metals lead and zinc on the corrosion behaviour of materials used in waste incineration plants. The major problem is that heavy metal containing chloride and sulphate salts usually have relatively low melting points, often below the metal temperature of the boiler surfaces. While the negative influence of lead and zinc is well-known, copper is another heavy metal that can occur in high amounts of up to 2000 mg/kg in refuse-derived fuel, which is the fuel produced by shredding and dehydrating solid municipal waste that is burned in modern waste-to-energy plants. The impact of copper additions on the corrosion behaviour of one iron-based austenitic alloy 1.4952 and three nickel-based alloys 2.4856 (alloy 625), 2.4633 (alloy 602 CA), 2.4605 (alloy 59), which are often used in waste incineration plants was investigated. The results of these studies clearly show the strong corrosive effect of copper content in salt mixtures on the corrosion of steels and nickel-based alloys.

The effect of diethanolamine (DEA) and hexamethylenetetramine (HMTA) on the corrosion of carbon steel (CS) in concentrated aqueous solution of ammonium nitrate and urea (ANU) was studied by weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy. Both amines showed high inhibition efficiency >99% above a concentration of 0.5 wt% at 25 and 50 °C. The addition of 0.1–0.5 wt% sebacic acid to the tested solution containing amines did not enhance the inhibition efficiency. A positive synergistic effect was observed when 0.1–0.5 wt% of cinnamic acid was added to the ANU solution containing 0.3–1 wt% of amines. These results clearly demonstrate the potential of using CS for storage and transport of ANU solutions under ambient conditions.

The influence of Nd and Gd additions on the microstructure, hardness and oxidation of AM50 magnesium alloy was investigated. Nd and Gd formed Al₂Nd, Al₂Gd, AlMnNd and AlMnGd intermetallics and reduced the amount of β-phase. Grain size and hardness did not change significantly with the addition of Nd or Gd. For all the alloys, surface degradation was negligible at temperatures below 370 °C. However, at 410 °C, severe oxidation was observed and hardness values decreased by ∼30% due to grain coarsening. At this temperature, the modified alloys revealed oxidation rates between ∼2.3 and 20 times smaller than the unmodified alloy.

Thermal barrier coatings of nanostructured and microstructured yttria stabilized zirconia (YSZ) were deposited on GH4049 substrate by air plasma spray, respectively. Hot corrosion behaviors of both coatings were evaluated in comparative aspects. Results revealed that the nanostructured YSZ displayed higher resistance to the hot corrosion attack by Na₂SO₄ and V₂O₅. It was also shown, through X-ray diffraction quantitative phase analysis, that the nanostructured YSZ had good resistance to the tetragonal-monoclinic phase transformation during the hot corrosion process.

Electrochemical noise (EN) enables corrosion research and monitoring in real time and with high sensitivity. In the case of submicroscopic nucleation events of pitting corrosion it has been observed that the cathodic process plays a decisive role in the mechanism as well as in the origin of EN signals, which depend not only on the metallic dissolution reaction but also on the electron-consuming process. EN signals arising from the nucleation process of localized corrosion on stainless steels can only be recorded due to the inhibition effect on the cathodic process achieved by the spontaneous formation of the passive layer. In consequence, passive layer stability becomes a significant factor in influencing EN signals. The way in which the passive layer stability affects the acquisition and analysis of EN signals arising from pitting corrosion on stainless steels is discussed in detail.

The acquisition of electrochemical noise is always connected with the question of appropriate measuring devices. The noise measurement system shall allow to process the apparent fluctuations in an electrochemical cell in the low millivolt or microampere range and to record them without any changes. The measurement amplifier is an essential part of the measurement system, but its behavior in the chain of signal processing is difficult to define by a corrosion expert. The present article shows possibilities for the determination of the performance of a noise measurement amplifier. A dummy cell model is often used to get a realistic approach to the sources of electrochemical noise. This article introduces a model describing the generation of single transients from the basic electrochemical corrosion reactions. The model determines fluctuations in the potential which can be measured as voltage fluctuations on a real dummy cell circuit. With the help of a special arbitrary signal generator, artificial noise transients based on this description are applied to a commercial noise measurement system. The acquired signals are compared with the original signals from the signal source and the influences of the noise amplifier on the signals are discussed.

The intercrystalline corrosion, exfoliation corrosion (EXCO), and stress corrosion cracking (SCC) of Al–Zn–Mg–Sc–Zr alloy were investigated by means of constant temperature immersion corrosion method, optical microscopy, transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS). The results show that intercrystalline corrosion, and EXCO susceptibility of Al–Zn–Mg–Sc–Zr alloy decrease gradually with increasing of aging time. Corrosion susceptibility order from low to high is as follows: OA > PA > UA > NA. The SCC susceptibility index of PA temper is more than OA temper at the same strain rate. According to TEM observation, with aging time prolonging, a part of η′ phases transform to η equilibrium phases, which become coarse gradually. The distribution discontinuity of the grain boundary precipitates increases. In addition, for Al–Zn–Mg–Sc–Zr alloy without EXCO, the EIS is comprised by a capacitive impedance arc at high frequency and an inductive impedance arc at low frequency. Once EXCO occurs, the EIS is composed of two capacitive impedance arcs at high frequency and at low frequency, respectively.

Two kinds of cathodic shielding phenomena of the sacrificial anode cathodic protection systems, which are caused by a metal barrier, were investigated by numerical simulations and experiments in this paper. The results show that if the cathode current is completely shielded by the barrier, one side of the barrier would act as the anode leading to the occurrence of serious corrosion, while the protected components and the other side of the barrier would act as cathode being protected. However, if the cathode current is only partially shielded, both the metal components and the barrier would act as cathodes. Furthermore, this non-full shielding effect of the barrier would be weakening by decreasing the mass transfer resistance between the sacrificial anode and the cathodically protected component.

In the present work, nitrogen ion implantation (original method) to enhance the corrosion performance and cytocompatibility of biomedical pure titanium (CP Ti) and Ti–6Al–4V alloy has been studied. Different characterization methods were used to investigate the corrosion resistance of the nitrided Ti and Ti–6Al–4V samples such as anodic polarization, electrochemical impedance spectroscopy, monitoring of the open circuit potentials and corresponding gradients, evaluation of corrosion rates. Further, cell viability, initial cell spreading and osteoblast proliferation were tested in order to assess cytocompatibility of modified Ti and Ti–6Al–4V alloy. In severe functional conditions, the main electrochemical parameters for nitrided biomaterials presented better values, revealing nobler behaviour than un-nitrided samples; these more favourable values assure a very good corrosion resistance for long term of the treated biomaterials. The results of biological performance evaluation indicated that nitrided Ti and Ti–6Al–4V represent suitable biomaterials for the adhesion and proliferation of human osteoblasts in vitro. All these findings demonstrate that nitrided biomaterials exhibited a very good improvement of their corrosion resistance and biocompatibility, characteristics which recommend them as potential candidates for bone implants.

The electrochemical noise (EN) measurement technique is one of the most promising tools for continuous in situ corrosion monitoring in technical systems with a certain potential to be used for the detection of stress corrosion cracking (SCC). To evaluate the suitability of the EN technique for the detection of SCC initiation, a small but systematic test programme was started, performing EN measurements on type 304 austenitic stainless steel during constant extension rate tensile tests in aqueous thiosulphate solution at room temperature. SCC could be detected by EN measurements, which was verified by interruptions of the experiments at different stages, by testing steel with different degrees of sensitisation and by post-test fractography in the scanning electron microscope. Conclusions on the cracking mechanism could be drawn based on the current noise signal pattern.

Using the microwaves energy new organic polymers were synthesized by radicalic polymerization. These new organic compounds have anti-corrosive and anti-scale properties and for this reason, were used for cooling water systems protection. We presume that, these new organic polymers inhibit corrosion of carbon steel by a protective mechanism, forming insoluble iron complexes and repairing the porous oxide layers. The methods employed were potentiodynamic polarization, electrochemical impedance spectroscopy, and metallurgical microscopy techniques. The inhibition efficiency was high in all the studied cases. The corrosion parameters obtained from polarization curves and from EIS spectra are in good concordance and point out the inhibitory action of these new organic polymers. The adsorptions of the organic compounds on the carbon steels surface obeyed Langmuir's isotherm. Using FT-IR it was proved the adsorption of organic inhibitors and the formation of corrosion products on the carbon steels surface. The inhibition process was attributed to the formation of the adsorbed film on the metal surface that protects the metal against corrosive agents. The EIS measurements have confirmed this protection and pointed out the formation of adsorption layers on the electrode surface.

Parameters extracted from the wire beam electrode (WBE) galvanic current maps have been used in conjunction with electrochemical noise patterns to directly quantify the degree of localised corrosion inhibition provided by inhibitors and to understand the mechanism of localised corrosion inhibition. The behaviour of two traditional localised corrosion inhibitors has been assessed by their effects on the maximum anodic current density (i_max), total anodic current density (i_tot), the number of anodic sites (N_a) and the localised corrosion intensity index (LCII). Typical experiments are presented to illustrate the application of these parameters in providing useful information on the efficiency and mechanism of localised corrosion inhibition.

The aim of this study is to investigate the corrosion behaviour of three ZrTi alloys (denoted with Zr5Ti, Zr25Ti, and Zr45Ti) in 0.9% NaCl solution. For comparison, cp-Ti was also investigated. In order to study the localized corrosion resistance and corrosion behavior at open circuit potential versus time, the open circuit potential (E_OC) was recorded, and the cyclic potentiodynamic polarization (CPP) and electrochemical impedance spectroscopy (EIS) were performed. Scanning electron microscopy (SEM) observations were made following the CPP tests. The Zr5Ti alloy was the most susceptible to localized corrosion. The Zr25Ti alloy presents a dangerous breakdown potential but have a sufficiently negative zero corrosion potential that the difference between them is sufficiently to provide a higher localized corrosion resistance in comparison with Zr5Ti. Among ZrTi alloys subjected to investigation, the Zr45Ti alloy had a much larger passive range in the polarization curve and was the most resistant to localized corrosion. For used test conditions, the localized corrosion was not found for the cp-Ti. The EIS tests show that both investigated ZrTi alloys and cp-Ti exhibit passivity after 168 h immersion in 0.9% NaCl solution, at open circuit potential.

The effects of molybdenum (Mo), manganese (Mn) and tungsten (W) on the corrosion behavior and hardness of iron-based metallic glasses (MG) were investigated by using electrochemical measurements, X-ray photoelectron spectroscopy, and micro-hardness tester. The results showed that the alloying elements (Mo, Mn, and W) have great influence on the corrosion behavior and hardness. Corrosion resistance of the MG increased with Mo and W content to a critical value (9.4 and 3.2 at%, respectively) and then decreased, while kept increasing with Mn. The corrosion behavior is dependent on the composition of the passive film. The protective Mo(IV), Mn(IV), and W(VI) oxide film on the surface attributes to the enhanced stability of the film. The hardness of the MG is not sensitive to the Mn content, but increased with the Mo and W content. Little influence on the hardness is found when the Mo content is higher than 9.4 at%. Based on the above mentioned influence of alloying elements, corrosion, and wear resistance can be balanced to meet the service of marine pump that served in both corrosive and erosive environments.

An important possibility to improve the corrosion behaviour of magnesium alloys is the application of protective coatings. The quality of such coatings depends mainly on the pretreatment and the exposure conditions after pretreatment. Since magnesium surfaces change much faster under atmospheric conditions than those of almost any other technical material, it is necessary to pay special attention to this particular feature. The activity of acid-pickled surfaces of the magnesium alloys AZ31 and AZ91 in dependence on the exposure time and the humidity conditions was investigated with electrochemical noise (EN) measurements. In addition to pickling, plasma chemical vapour deposition processes open new possibilities for an economical, as well as ecologically quite safe, pretreatment. The results of EN investigations after acid pickling as well as specific plasma oxidation treatments of the two magnesium alloys after exposure to air with different humidities are presented.

Pitting corrosion is one of the most common mechanisms of surface damage on stainless steels. Electrochemical methods have been preferentially applied for the evaluation of the pitting corrosion resistance of stainless steels in the laboratory. Nevertheless, some of them are not reliable enough and in general the application of electrochemical methods in the field becomes difficult because of required deep understanding of corrosive phenomena and measurement technology. Therefore, new approaches for the evaluation of the pitting corrosion susceptibility of stainless steel surfaces in the laboratory as well as in the field are necessary. In the present paper two novel strategies including electrochemical noise measurements under anodic polarization for laboratory testing, and an indicator test to assess the susceptibility of stainless steel surfaces to pitting corrosion in the field are introduced. Experimental results concerning the influence of surface treatments on the pitting corrosion resistance on stainless steels have confirmed that final surface condition has a significant effect on their future pitting corrosion susceptibility. In addition, the pitting corrosion resistance of stainless steel surfaces was observed being specifically dependent on the achieved surface topography and in some cases independent on the roughness parameters of the surface.

In order to replace the hazardous chromate-based surface treatment, a new cerium chemical conversion coating was developed on 316L stainless steel through a mixed solution of hydrated cerium nitrate, citric acid, and hydrogen peroxide. The chemical composition was characterized by energy-dispersive spectroscopy, X-ray photoelectron spectroscopy and atomic force microscope. The dense conversion coating is composed of CeO₂ with a small amount of Ce₂O₃ and has small grain size lower than 50 nm. Its thickness is about 47.4 nm as determined by spectroscopic ellipsometry analysis. Potentiodynamic polarization was used to study the corrosion behavior of the coatings in the concentrated artificial seawater at 72 °C. In comparison with the conventional nitric acid-chromate passivated specimens, the cerium conversion coatings show much higher pitting potentials. It is suggested that the cerium conversion treatment is more effective than the nitric acid-chromate passivation to improve the pitting resistance of 316L stainless steel used in the hot seawater environments.

In this research, the corrosion behavior of different types of (NiTiC) coatings produced by high velocity oxy-fuel (HVOF) technique was studied. NiTiC and Ni(Ti,W)C composite powders were produced by self-propagation high temperature synthesis (SHS). These powders as feedstock were thermally sprayed on steel substrates in comparison with a conventional powder mixture of Ni + TiC. The microstructures of the produced coatings were characterized using SEM micrographs. The presence of different phases in the microstructure was investigated using EDS analysis and XRD patterns. Also, the behavior of the coatings against a corrosive media was studied using Tafel polarization tests. The results show that the NiTiC and Ni(WTi)C coatings exhibited better corrosion resistance than conventional Ni + TiC mixture coating due to the increment of the homogeneity of the structure and the decrement of the porosity level. In addition, the presence of W in the microstructure of Ni(WTi)C coating provided the least pitting and highest general corrosion.

Nanocrystalline Fe₃O₄ and α-Fe₂O₃ particles were successfully synthesized by hybrid electrochemical-thermal method. The as-prepared compound was calcined for an hour at different temperature. The crystallite size, morphology, and chemical state of the synthesized powders were characterized by powder XRD, TG-DTA, XPS, SEM/EDAX, TEM, FT-IR, and UV–Vis spectral techniques. Rietveld refinement of X-ray data of the calcined compound exhibits rhombohedral (hematite) structure with space group of R3c (No. 167). The thermal behavior of as-prepared compound was examined. Scanning electron photomicrographs show uniform, randomly oriented hexagonal and spherical like morphology and EDAX measurement showed its chemical composition. The TEM result revealed that the particle morphology was hexagonal with spherical in nature and sizes were in the order of 40–60 nm in diameter and 120–200 nm in length. The absorption and blue shift were noticed in UV–Vis absorption spectra and the band gaps were found to be 4.22–4.29 eV. The electrochemically generated Fe₃O₄ and α-Fe₂O₃ nanoparticles were used to fabricate ZnCoαFe₂O₃ composite thin films and its corrosion behavior was analyzed by anodic polarization, Tafel extrapolation, and electrochemical impedance spectroscopy (EIS). The results indicate that the ZnCoαFe₂O₃ composite thin films have potential applications to corrosion protection.

According to ASTM G50-76, materials have been exposed to atmospheres of Saudi Arabia. Environmental factors such as temperature, relative humidity and deposition rates of pollutants (Cl⁻ and SO₂) were investigated. X-ray diffraction was used for characterization. Corrosion rates were determined by weight loss. As per ISO 9223, aggressivity classification was made. The results obeyed well with the empirical kinetics equation of the form C = Ktⁿ, where K and C are the corrosion losses in mg/cm² after 1 and t years of the exposure, respectively, and n is constant. Based on n values, the corrosion mechanisms of samples are predicted.

The corrosion behaviors of AA6061 alloy in ethylene glycol (EG)–water solution were investigated by weight-loss test and electrochemical measurement. The surface morphology observation and composition analysis were performed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. After weight-loss test, the pH of EG–water solution increased. The presence of glycolic acid (GA) enhanced the corrosion susceptibility of AA6061 alloy. The higher pH value intensified the aggressive action of GA to AA6061 alloy. GA forms a complex with aluminum ions and its negative charge centers of oxygen atom plays a key role for the complex formation.

In this study, IN625 and a NiCrAlY coated IN625 were tested in high density and low density supercritical water for 500 h. The NiCrAlY coating was applied using plasma spray method. The surfaces were finely polished before testing to assist microstructure observation after testing. The NiCrAlY coated samples were additionally heat treated in air furnace to encourage alumina formation. SEM and XRD analyses were carried out to determine surface microstructure changes, particularly oxide formation. The results showed that when tested under high density supercritical water, the bare IN625 sample suffered from intergranular attacking while low density supercritical water did not have the same effect. Both as-sprayed NiCrAlY and heat treated NiCrAlY did not show any signs of intergranular attack or pitting after being tested in high density and low density supercritical water.

The susceptibility of girth welds to sulphide stress cracking (SSC) and hydrogen embrittlement (HE) were evaluated for API grade X80 and X56 steels, both for similar (X80/X80) and dissimilar (X80/X56) joints. Slow strain rate (SSR) and hydrogen permeation tests were performed at room temperature using sodium thiosulphate solutions at different pH levels. The SSR tests showed that the majority of the welded joints studied, though approved by the API 1104 standard's criteria, did in fact suffer a reduction in ductility and showed indications of susceptibility to sulphide stress cracking and to hydrogen embrittlement in the form of secondary longitudinal and internal transverse cracks. This was true regardless the welding process used.

In the present study, a new welding procedure was developed according to the welding difficulties of mechanical clad pipe. The effect of temperature on the corrosion product layer of stainless steel welded joints exposed to a CO₂-containing solution was investigated. The measurement techniques, such as scanning electron microscopy with energy dispersive spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy, were used to systematically characterize the morphology and composition of the corrosion product layer. The corrosion rates were calculated by weight loss method. The corrosion mechanisms are studied and discussed. The results showed that temperature is an important factor in the corrosion rate of mechanical clad pipe welded joints.

The characteristics of Ti6Al4V alloy subjected to thermal oxidation in air atmosphere at 650 °C for 48 h and its corrosion behavior in 0.1 and 4 M HCl and HNO₃ medium are addressed. When compared to the naturally formed oxide layer (∼4–6 nm), a relatively thicker oxide scale (∼7 µm) is formed throughout the surface of Ti6Al4V alloy after thermal oxidation. XRD pattern disclose the formation of the rutile and oxygen-diffused titanium as the predominant phases. A significant improvement in the hardness (from 324 ± 8 to 985 ± 40 HV_0.25) is observed due to the formation of hard oxide layer on the surface followed by the presence of an oxygen diffusion zone beneath it. Electrochemical studies reveal that the thermally oxidized Ti6Al4V alloy offers a better corrosion resistance than its untreated counterpart in both HCl and HNO₃ medium. The uniform surface coverage, compactness and thickness of the oxide layer provide an effective barrier towards corrosion of the Ti6Al4V alloy. The study concludes that thermal oxidation is an effective approach to engineer the surface of Ti6Al4V alloy to increase its corrosion resistance in HCl and HNO₃ medium.

The oxidation behavior of Ag–5.08Sn–3.15Sb and Ag–6.84Sn–1.25Sb alloy powders was investigated in air at 800 °C. The thermal gravimetric analysis (TGA) results confirmed that the starting oxidation temperature of Ag–5.08Sn–3.15Sb and Ag–6.84Sn–1.25Sb alloy powders was 670 and 720 °C, respectively. The oxidation kinetic results suggested that the oxidation behavior of Ag–Sn–Sb alloy followed a parabolic rate and the oxidation rate of Ag–5.08Sn–3.15Sb alloy powders was 3.2 times larger than that of Ag–6.84Sn–1.25Sb alloy powders. XRD results indicated that the formed Sb₂O₃ would react with the Ag matrix forming AgSbO₃. SEM–EDS observations indicated that the formed oxides were primarily distributed on the grain boundaries and the formed AgSbO₃ particles nailed into the SnO₂ particles. In addition, the oxidation mechanism of Ag–Sn–Sb alloy powders and the effect of Sb on oxidation behavior of Ag–Sn alloy powders were also discussed.

The electrodeposition behavior of aluminum on TiB₂/A356 composite from AlCl₃–NaCl–KCl molten salt was studied in this paper. The surface morphology, microstructure, and phase composition of aluminum coating were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The phase composition of the composite was examined by X-ray diffraction technique. The polarization curves were measured and the corrosion current densities were obtained. The results indicated that the aluminum coating was preferentially electrodeposited on the surface of TiB₂ and Si phases. This phenomenon could be largely attributed to the different surface energies of TiB₂, Si, and Al phases. With the increasing of deposition time, a continuous, dense, and faceted aluminum coating was finally obtained. It was inferred that the growth of aluminum coating on the surface of the composite was mainly through two-dimensional spreading. However, three-dimensional growth could also be seen. The corrosion current density of the aluminum-coated TiB₂/A356 composite (1 min) decreased by an order of magnitude as compared with that of TiB₂/A356 composite, and was close to that of A356 alloy, and also in the same order of magnitude with that of pure aluminum. It is evident that, the coverage of TiB₂ and Si phases by aluminum coating (1 min) can effectively improve the corrosion resistance of TiB₂/A356 composite. In combination with SEM and EDS results, the behavior can be characterized as preferential electrodeposition.

An automated corrosion monitoring system using the electrical resistance technique was applied for assessment of the corrosivity towards carbon steel and zinc in different phases of a complex accelerated corrosion test recently introduced by VDA, an association of German car makers. It comprises salt spray, wet, dry, and freezing phases. The developed small and battery-driven atmospheric corrosion loggers provided high sensitivity allowing for sub-angstrom (<10⁻¹⁰ m) measurements of corrosion depth and good accuracy. The actual corrosion rate was affected by the exposure history due to a limited rate of wetting/drying and oxygen and ion transport to the reaction interface under a layer of corrosion products. The hysteresis was particularly strong for carbon steel. Except the freezing phase, the steel corrosion rate varied in a narrow range from 0.2 to 0.6 µm/h. For zinc, the corrosion rate varied from 0.001 to 0.1 µm/h in particular phases of the cycle with the maximum in the salt spray phase. Seventy-five percent of the metal corroded in the salt spray phase and in the following drying period representing only 13% of the total test time. The obtained data suggest that the proposed test cycle allowed for rather efficient drying of the zinc surface, which is believed to be crucial for the formation of corrosion products with certain protective ability observed also in field conditions.

The corrosion behaviors of 1420 Al–Li alloy under 4 µl MgCl₂ drops with initial concentration of 0.1–1.0 M in relative humidity (RH) 33% were studied using a Kelvin Probe. In all cases, the equilibrium MgCl₂ concentration was 4.9 M. The corrosion was highly dependent on the initial MgCl₂ concentration. After equilibration with the environment RH, the whole available cathodic limiting current associated with oxygen reduction was decreased with increasing the initial MgCl₂ concentration. Accordingly, the corrosion rate was decreased. Under the MgCl₂ drops with initial 0.1 and 0.3 M concentrations, the main corrosion form was filiform-like corrosion. While, as the initial concentration was increased to 1.0 M, the main corrosion form was meta-stable pitting corrosion. In the case of 0.1 and 0.3 M initial concentrations, along the Volta potential baseline at −0.7 to −0.8 V_SHE, there existed many potential transients in the form of rapid increase followed by immediate drop, which should be associated with the filiform-like corrosion growth stop and initiation. In the case of 1.0 M initial concentration, much more potential transients appeared in the form of sudden drop followed by a recovery, which was associated with the initiation and re-passivation of meta-stable pits.

The effect of benzotriazole (BTA) on the corrosion of a new type copper-manganese-aluminium (CMA) alloy in artificial seawater was investigated using dynamic electrochemical impedance spectroscopy (DEIS), linear polarization resistance, and Tafel extrapolarization methods. Measurement results obtained from those three methods showed that corrosion rates decreased while BTA concentration increased. This clearly indicates that BTA inhibits the corrosion rate of CMA in artificial seawater. Although there are consistent results obtained from all these three methods, the results of the percent inhibition efficiency, IE (%), values obtained from DEIS method should be calculated from the charge transfer resistance (R_ct) values obtained after 5 h.

In order to obtain a high quality protective plating coating on Mg–16Li–5Al–0.5RE alloy, a zinc dipping technique at room temperature was investigated. The zinc dipping technique included two immersion processes, the primary immersion process and the secondary immersion process. Primary zinc transition layers (PZTLs) and secondary zinc transition layers (SZTLs) were obtained after the primary and secondary immersion processes, respectively. The polarization curves, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to characterize PZTLs and SZTLs. The results indicated that immersion time had obvious effects on PZTLs and SZTLs, the optimum primary immersion time and secondary immersion time were 5 min and 30 s, respectively. Then nickel-plating coating deposited on the SZTL of Mg–16Li–5Al–0.5RE alloy was investigated via EDS, SEM, polarization curves, and EIS. The results demonstrated that the nickel-plating coating obviously improved corrosion resistance of Mg–16Li–5Al–0.5RE alloy and had good adherence property with the alloy because of the presence of zinc transition layer on the alloy.

To improve the mechanical properties, the castability as well as the corrosion resistance of magnesium alloys, aluminium is frequently employed. As a rule, technically relevant alloys contain between 3 and 9 wt% aluminium. Normally, aluminium contents under 3 wt% is said to have no corrosion reducing effect. In order to investigate the influence of specific additions of aluminium, various methods are employed in practice and different electrolytes or concentrations of saline solutions are used as testing media. In doing this, it is rarely possible to compare the results. For this reason, the current work both discusses the influence of aluminium and the effect of different saline solutions on the corrosion behaviour of low alloy magnesium–aluminium alloys as well as compares two different measuring procedures (electrochemical and gravimetric).

The electrodeposition of polypyrrole and polyaniline has been performed in aqueous solutions of sodium saccharinate and sulphuric acid, respectively. The coatings were obtained by voltamperometric and galvanostatic methods. The corrosion behaviour of polypyrrole and polyaniline coated stainless steel (SS) in sulphuric acid medium was investigated by linear polarisation, open circuit potential and electrochemical impedance spectroscopy. The polyaniline coatings doped with sulphate anions (SO) showed more resistance to protect SS to corrosion than the polypyrrole coatings doped with saccharinate anions (C₇H₄NO₃S⁻).

The corrosion behavior of an Al–0.63Mg–0.28Si alloy under MgCl₂ solution droplets with different initial concentration in environments of 33, 75, and 88% relative humidity (RH) was studied using a Kelvin probe. The available cathodic limiting current associated with oxygen reduction was highly dependent on the environment RH and initial concentration. In the 33% RH environment, metastable pitting was the main form of corrosion. In some cases at 75 and 88% RH, the potential baseline decreased slowly by hundreds of mV and remained at the lower value, indicating stable filiform-like corrosion grew. The initiation time of the stable corrosion was determined by the environment RH and initial concentration. With increasing initial concentration or decreasing environment RH, the available cathodic limiting current decreased, stable corrosion was difficult to occur. The stable corrosion could occur outside the drop and/or inside the drop, which was dependent on not only the cathodic limiting current but also the environment RH.

Immersion tin is widely used as a lead free surface finish in the printed circuit board technology. Tin prevents the underlying copper from corrosion and preserves its solderability during a long storage and lead-free assembly processes. Investigated immersion tin coatings were deposited on copper foil from thiourea-type baths with hydrochloric acid addition (SnHCl coatings) or methanesulfonic acid addition (SnMSA coatings). Obtained coatings were investigated in the as deposited state and after aging (4 h at 155 °C, in air). The scanning electron microscopy studies revealed differences in structure of tin samples deposited from different baths. Results of polarization and impedance investigations indicated that as deposited SnHCl coatings had better corrosion resistance in 0.5 M NaCl solution than SnMSA coatings. The aging resulted in the improvement of the corrosion resistance of thinner coatings (0.2 and 0.5 µm thick SnHCl and 0.3 µm thick SnMSA), which were thoroughly converted into Sn–Cu intermetallic (IMC) phases. In contrary, thicker coatings exhibited some worsening of the corrosion resistance upon aging. The solderability of all as-deposited tin coatings was acceptable, but decreased after aging, especially for thinner coatings, showing the through conversion into Sn–Cu IMC phases.

The non-destructive inspection method of scale on the inner wall of the ferritic steel and austenitic steel of high temperature boiler tube and the application effect were introduced in our work. The risk of scale exfoliation on the inner wall was also assessed. The risk of tube burst caused by scale exfoliation and accumulation, was reduced greatly, or even avoided by means of the change or treatment of high-risk tube confirmed by non-destructive inspection method.

This paper discusses the sulphidation/oxidation protection offered by multilayer CrAlYN/CrN coatings etched by Cr, CrAl and Y ions, deposited by a combined high power impulse magnetron sputtering (HIPIMS)/unbalanced magnetron sputtering (UBM) technique on a Ti–45Al–8Nb alloy (at%). The test was performed at 750 °C in an environment of H₂/H₂S/H₂O yielding low oxygen (10⁻¹⁸ Pa) and high sulphur (10⁻¹ Pa) partial pressures for up to 1000 h. The results show that all the exposed materials underwent uneven degradation; some places developed a thin protective oxide scale (Al,Cr)₂O₃ with a tiny sulphur content, whilst others developed a porous non-protective TiO₂ + Al₂O₃ scale as well with a tiny sulphur content.

The main problem limiting the application of magnesium alloys as biodegradable implant material is its high degradation rate. In order to slow down the corrosion rate an extrusion process and specific coating systems based on plasma-chemical oxidation (PCO) and organic dip coating with poly(L-lactid-co-caprolacton) (PLLC) were applied on Mg–1Ca magnesium alloy. The additional PLLC coating is used to delay the start of substrate corrosion, while the purpose of the PCO coating is to decrease the substrate corrosion rate. The corrosion behaviour was investigated in synthetic body fluid (SBF) through measurement of the hydrogen evolution rate in long term tests and polarisation and electrochemical noise measurements in short term tests. The results showed significant differences between the cast and extruded alloys and a decrease of the corrosion rate due to corrosion product formation. The combination of both coating systems resulted in a significant delay of metal substrate corrosion and all coating systems showed good correlation between short and long term tests. The combination of the three investigation methods provides the possibility to gain more information about the degradation behaviour and break down of protective coatings.

Aluminum alloys of the 7XXX series are widely used in aircraft applications. During the manufacturing of aeronautic components, the parts pass through four production phases (milling/drilling, deburring/adjustment, non-destructive testing, and surface treatment) and come into contact with several kinds of fluids such as degreasing and cleaning solutions, which can lead to the occurence of surface defects due to localized corrosion, then requiring reworking or scrapping. The present study aimed at studying the influence of process parameters in the deburring/adjustment stage on the development of surface defects in 7075 alloy parts. The methodology consisted of design of experiments, immersion and drying tests, and surface analysis for quantification of corrosion damage. The results showed that the degreasing bath concentration and temperature, the immersion time of the aluminum parts in the degreasing solution, and the use of solvent pre-cleaning had no significant influence on the quantity of surface defects. Therefore, these factors do not need to be rigorously controlled in the process. Clean washing water must be preferred and the parts must be dried in the stove at 110 °C in order to ensure a surface free of defects. The immersion and electrochemical tests showed that the occurrence of surface defects is lower in aged degreasing solution than in recently prepared solution.

In this work, a new ternary Ti–25Ta–5Zr alloy (with nontoxic alloying elements) was obtained and used to develop a thermo-mechanical procedure in order to optimize the balance strength – elastic modulus. Data about structural (by SEM) and mechanical properties are investigated. Also, its electrochemical behaviour in Ringer–Brown and Ringer solutions of different pH values (simulating severe functional conditions of an implant) was studied by cyclic potentiodynamic and linear polarization and electrochemical impedance spectroscopy (EIS). From cyclic potentiodynamic polarization curves it resulted the nobler behaviour of the thermo-mechanical treated alloy than as-cast alloy due to the favourable influence of the applied processing. Impedance spectra were fitted with one time constant equivalent circuit characterizing a very stable, resistant oxide passive film. The values of the open circuit potentials for the treated alloy are nobler than of the as-cast alloy and tended to more positive values in time, proving that the passive film on its surface is more compact and thickened in time.

In this investigation nano-zinc oxide-containing polyurethane-based coatings were prepared by incorporating 3 wt% nano-ZnO in the electrocoating composition. The paint films were deposited on phosphated steel panels through electrodeposition. The films were then rinsed by DI water and baked for 20 min at 165 °C in an electrical laboratory oven. The cured films were exposed to ultraviolet (UV) radiation under humid condition. Variation of chemical nature, color, surface roughness, gloss, and corrosion resistance of the coatings were investigated as a function of UV exposure period. It was found that in presence of nano-ZnO particles, photodegradation reactions of the aromatic polyurethane network are delayed for a longer time. Specular gloss and surface roughness values of the exposed films are in accordance to this observation too. It was found that deep cracks are formed in the films in which no nano-ZnO is present. The higher electrical resistance value of the nano-ZnO stabilized films was found to be due to the protective effect of the particles against photodegradation of the polyurethane binder.

This article describes the findings of an investigation on cracking of ethylene furnace pressure transmitter tapping lines made of stainless steel type 304H. A detailed failure analysis using several characterisation techniques such as visual and metallographic examinations, SEM/EDX, XRF/C&S as well as finite element analysis uncovered that the cracking was caused by polythionic acid stress corrosion cracking that took place due to presence of condensate, sulphides and oxygen in contact with sensitised material. Several corrective measures to prevent similar failures are discussed.

Application of corrosion inhibitors is one of the most common practices for the protection of steel structures and their alloys in industry. Since metallic corrosion is a major cause of economic losses in the oil industry, the use of natural inhibitors is an alternative for sustainable technological development. In the present study the effectiveness of the hydroalcoholic extract of the plant species Croton cajucara Benth (CC) dissolved in a microemulsion system (MES-CC) as well as in dimethyl sulfoxide (DMSO-CC) was evaluated as corrosion inhibitor on carbon steel AISI 1020 in saline medium. Surface tension measurements of the MES-CC confirmed micelle formation, and rheological data showed that viscosity varies with temperature. According to potentiodynamic technique and Tafel extrapolation, maximum inhibition efficiencies were effective (93.84% for MES-CC and 64.73% for DMSO-CC) with predominant control of cathodic reaction. The adsorption of MES-CC on carbon steel surface obeys Langmuir adsorption isotherm, while DMSO-CC was found to follow the Frumkin isotherm.

The corrosion behaviour of the twin belt cast EN AW 7075 alloy is governed by intermetallic phases, namely Al₁₂(Fe,Cr,Mn)₃Si, Mg₂Si and CuAl₂, and by Mg(Zn,Cu,Al)₂ precipitates. The former are responsible for pitting activities while the Mg(Zn,Cu,Al)₂ precipitates play a key role in intergranular corrosion. The very fine dispersion of Mg(Zn,Cu,Al)₂ precipitates in samples aged to peak hardness undergo coarsening, particularly along the grain boundaries, when the hot band samples are overaged. Overageing improves the resistance to intergranular corrosion while the samples in T6 temper suffer heavy attack along grain boundaries. While ageing treatments hardly produce any change in the features of the intermetallic particles, they nevertheless seem to impact the pitting response. This may be accounted for also by the precipitation activities which in turn, change the chemistry of the solid solution matrix. Overageing to the T73 temper implies a higher purity matrix and thus changes the microgalvanic effects when exposed to neutral chloride solutions.

An organic compound, 1,3-bis-dibutylaminopropan-2-ol (BDAP) was prepared and tested experimentally as inhibitor for reinforcement steel in simulated concrete pore solution. The electrochemical behavior of carbon steel electrodes immersed in simulated pore solutions with different concentration of BDAP was investigated by electrochemical measurements. Adsorption isotherm was determined based on the inhibition efficiency. The surface composition was evaluated via X-ray photoelectron spectroscopy (XPS) as well in order to verify the presence and adsorption property of BDAP. The results showed that BDAP could effectively suppress the anodic process of carbon steel corrosion and the inhibition efficiency was improving with the increase of inhibitor concentration. BDAP could adsorb on carbon steel surface according to Langmuir adsorption isotherm. XPS spectrum certified the existence of BDAP on the steel surface.

The conservation of archaeological marine iron artefacts requires chloride ions removal. In this study, the removal of chloride ions was undertaken by two electrochemical methods: the electrolytic and the galvanic reduction in alkaline media. The results were compared with those obtained by the washing and the sulphite reduction methods, under identical conditions. The experiments were performed on samples coming from an 18th century cast iron cannon-ball, found in the archaeological context of a shipwreck, l'Océan, which sank near the southern Portuguese coast, in 1759. The extraction of chloride ions was monitored by ionic chromatography (IC). The results allow to conclude that the sulphite reduction experiments using the mixture 0.5 M NaOH/0.5 M Na₂SO₃ presents the higher efficiency in the first week, being further overcome by both electrochemical methods. After 40 days of treatment, the electrolytic reduction is the most efficient method.

The goal of this study is to compare the corrosion behaviour of selected ternary nickel titanium (NiTi)-based alloys (Ni₄₅Ti₅₀Cu₅, Ni₄₇Ti₅₀Fe₃ and Ni₃₉Ti₅₀Pd₁₁) with a binary, pseudoelastic Ni_50.7Ti_49.3 alloy. We examine the influence of the ternary elements on the corrosion behaviour using standard electrochemical techniques. All measurements were done in a physiological solution (0.9% NaCl) simulating a body temperature of 37 ± 1 °C. The influence of Cu and Pd addition on the surface oxide film was characterised by X-ray photoelectron spectroscopy (XPS). The results revealed that, the localised corrosion resistance of these ternary alloys is lower than the binary NiTi alloy. By comparing the different NiTi-based alloys, the following relation has been proposed for their localised corrosion resistances: NiTiCu < NiTiFe < NiTiPd < NiTi. Depth profiling by XPS showed that the surface oxide film on all the investigated NiTi-based alloys is mainly of TiO₂, however, the NiTiPd and NiTiCu alloys showed metallic ternary element distributed within TiO₂ layer.

In this work it is presented a methodology applied by Companhia Siderúrgica Nacional (CSN, Brazil) in order to assess its blast furnace 3 carbon refractory hearth lining conditions. The aim of the investigation was the gathering of critical data base for blast furnace refractories life cycle follow up and eventual repair decision taking.

The sample drilling locations were chosen around the tap holes and hearth bottom areas. The advancing drilling depths were based on local temperature profiles. The isotherm limit of 500 °C was elected as a control parameter to assess the critical carbon refractory condition. The guidelines for sampling and testing as well as the results obtained through the physical and chemical characterizations of the cored samples are presented. The condition of the refractory lining is discussed under the light of the different known wear mechanisms of blast furnace hearth carbon refractories.

TiO₂/vanadium pentoxide (V₂O₅) and TiO₂–V₂O₅ coatings were prepared on type 304 stainless steel substrates via a sol–gel method, respectively. The TiO₂/V₂O₅ coating is compared with the TiO₂–V₂O₅ coating in terms of the photo-electrochemical performance. The two coatings can be stored with photogenerated electrons under UV irradiation in 3 wt% aqueous NaCl. The self-discharging time of the TiO₂/V₂O₅ coating is slower than that of the TiO₂–V₂O₅ coating. The slow discharging may be suitable for an anti-corrosion application for stainless steel. In the case while the two coatings are electrochemically charged under UV irradiation for 1 h, the TiO₂/V₂O₅ coating can maintain a good cathodic protection for type 304 stainless steel for 6 h in the dark, while the TiO₂–V₂O₅ coating can only maintain a good cathode protection for 0.5 h in the dark.

The present paper investigates two different titanium alloys: Ti6Al7Nb – a well-established implant biomaterial and Ti6Al4Zr – a relatively new titanium alloy. Roughness is evaluated with atomic force microscopy (AFM) and the hydrophilic/hydrophobic balance by contact angle measurements. Furthermore, an extensive characterization was done in order to evaluate and compare the electrochemical behaviour for both titanium alloys in artificial Fusayama and Afnor saliva, at different immersion times, and consisted of Tafel plots, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Also, metals ions release was measured using inductively coupled plasma mass spectrometry (ICP-MS). In both studied artificial saliva, Ti6Al4Zr alloy presents a better electrochemical behaviour according to corrosion rates from both electrochemical techniques and ICP-MS.

In the present paper, the isothermal oxidation behavior of alloy HK40 in H₂H₂O atmosphere in the temperature range 850–950 °C was systematically investigated by means of TGA, XRD, SEM, and EDS. The results demonstrated that the oxidation of alloy HK40 under low oxygen partial pressure obeyed a cubic instead of parabolic rate law. The values of the oxidation rate constant k at 850, 900, and 950 °C were 0.0079, 0.01886 and 0.04031 mg³/(cm⁶ h) at 850, 900, and 950 °C, respectively. The scales were composed of MnCr₂O₄ and Cr₂O₃. MnCr₂O₄ mainly existed in the form of blades in the outer part of the scale and its amount gradually increased with increasing temperature. In addition, there were silica particles along the scale/metal interface and indications were found that they contribute to the improvement of scale spallation resistance at high temperature as found by scratch tests.

The long-term oxidation performance of an alloy is critically linked to the early-stage oxidation behavior of high-temperature alloys. This study investigates early-stage oxidation behavior in terms of oxidation kinetics, scale evolution, and residual stresses developed within a scale of the commercially available cobalt-rich alloys: HAYNES® 188, 6B, 25, and HR-160® and a newly developed nitride-dispersion strengthened NS-163® alloy (HAYNES®, HR-160®, NS-163® are registered trademarks of Haynes International, Inc). Short-term isothermal oxidation exposures were conducted in flowing air at 982 °C for durations of 1–50 h. Oxidation kinetics was assessed by weight-change behavior, which showed that 188 alloy exhibited the lowest weight-gain, while for similar times HR-160 alloy underwent weight-loss. SEM/EDS analysis was performed to characterize oxides formed in these alloys, while stresses developed in the oxides of different alloys were measured using synchrotron X-ray radiation. The results in this paper clearly demonstrated the effects of alloy composition on the scale evolution and the amount of stresses developed in oxides.

The self-organized titanium dioxide (TiO₂) nanotube arrays on titanium mesh were prepared by electrochemical anodization with the neutral electrolyte containing ammonium sulfate and ammonium fluoride in a two-electrode electrochemical cell. The effects of the fluoride ion concentration, the anodic potential, and the oxidation time on the formation of the titanium dioxide nanostructures on titanium mesh with complex geometry were investigated. The anodized titanium mesh was characterized by field emission scanning electron microscope and in situ high temperature X-ray diffraction. The results show that the titanium dioxide nanotube arrays are grown in a radially outward direction around the titanium wire. The optimized anodization condition for preparing titanium dioxide nanotube arrays with superior architecture on the titanium mesh is 0.5 wt% of ammonium fluoride, 20 V of applied potential, and 20 min of oxidation time. The amorphous titanium dioxide nanotubes on titanium mesh turn to anatase phase at 400 °C and further to rutile phase at 650 °C.

The effect of cerium ion on the formation, morphology, composition, and corrosion behavior of Ni–cerium oxide coatings was investigated by SEM, FESEM, XRD, EDS, XPS, EIS, and potentiodynamic polarization. The extremely highest corrosion resistant coating was obtained when the cerium ion concentration in the plating bath was 16 mM. It has been observed that the presence of cerium ion in the plating bath led to changes in the morphology of the coating from pyramid nodular structure to coaxial structure. By adding cerium ion to the plating bath, a considerable grain refinement in the nanometer region was observed.

The current work investigated the impact of surface condition on the metal dusting behavior of chromia forming alloys. Five commercial alloys were included in the study, wrought 800H, 353MA, and cast G4859, G4852 Micro, and ET45 Micro, these alloys have a chromium and nickel content in the range of 20–35 wt% and 32–45 wt%, respectively. The wrought alloys were tested in a pickled state and the cast alloys with a machined surface, all the alloys were tested using a laboratory ground surface condition for comparison. The exposures were performed using a gas with a composition of 44 vol% CO, 52 vol% H₂, 2 vol% CO₂, and 2 vol% H₂O at a temperature of 600 °C and a pressure of 5.5 bar. The samples were periodically characterized by measuring the mass loss, pit density, pit size, and pit depth. The results show that the pickled surfaces were sensitive toward metal dusting attack while the machined and the ground surfaces had better resistance. This shows that the surface pre-treatment plays a crucial role.

This work aims to improve the corrosion rate of Ti6Al7Nb alloy and to increase its biocompatibility at the same time, obtaining polymer composite films based on polypyrrole/polyethylene glycol (PPy/PEG). The elaboration method was electrodeposition. FT-IR analysis was performed in order to emphasize the formation of the PPy-PEG composite film by incorporating PEG into the polymer structure. The paper is focussed on PEG (400 molecular weight) effect on the corrosion in bioliquids (as tested electrochemical bioliquid was chosen Hank's balanced salt solution) and on the biocompatibility properties. The PPy film significantly improves the biocompatibility of the Ti6Al7Nb alloy. The PEG presence in the polymerization solution leads to more stable composite polymer films on the titanium alloy surface with a better corrosion resistance and a more hydrophilic behaviour comparing with the PPy film. The increase of cell viability and proliferation potential as compared to the PPy film is not important.

The density functional theory at the B3LYP/6-311G++(d,p) basis set level calculations were performed on two thiophene derivatives used as corrosion inhibitors, namely 2-methylthiophene and 2-(aminomethyl)thiophene, to investigate the correlation between its molecular structure and the corresponding inhibition efficiency (IE%). Quantum chemical parameters such as the highest occupied molecular orbital energy (E_HOMO), the lowest unoccupied molecular orbital energy (E_LUMO), energy gap (ΔE), dipole moment (µ), electronegativity (χ), hardness (η), and the fraction of electrons transferred from the inhibitor molecule to the metal surface (ΔN), have been calculated. A good correlation between the theoretical data and the experimental results was found.

This paper discusses new conceptual and mathematical models for blistering propagation especially useful for coating life assessment. It proposes new equations governing blister development that combines fracture mechanics and diffusion based concepts. The fracture mechanics concept is used to treat blister growth as crack propagation, while the diffusion concept is used to treat the ionic transport that eventually causes corrosion and blistering to occur. The new equations are expected to be useful in coating development as well as coating life assessment. Furthermore, with little modification, the equations are also beneficial for other surface engineering methods.

In the present study, a nanoceramic hexafluorozirconic acid was used as an eco-friendly conversion coating, which is free of the conventional phosphate salts. The effect of practical parameters on morphology and corrosion resistance of the coating was studied. Anti-corrosion behavior of the nanoceramic-based conversion coating on cold rolled steel substrates was evaluated at different solution pH and temperatures, utilizing the electrochemical impedance spectroscopy and direct current polarization. Moreover, the morphology of thin films was studied using field emission scanning electron microscopy (FE-SEM). The results revealed that the conversion thin films formed at a dipping temperature of 20 °C and pH 4.5 showed best anti-corrosion performance. SEM images indicated that increasing solution temperature resulted in micro-cracks creation and lack of consistency on the surface of the conversion coating. Moreover, the morphological structure changed with increasing pH value.

The degradation behaviour of an Mg-1Ca alloy is investigated in vitro to figure out the possibilities of influencing the degradation behaviour of such an alloy by applying heat treatment as well as the use of a coating system based on plasma-chemical oxidation. It is shown that an optimised solution annealing (T4-heat treatment) can reduce the degradation rate while an additional ageing between 240 and 300 °C (T6-heat treatment) increases it. A coating generated by plasma-chemical oxidation reduces the degradation rate in the immersion test. Its effect is depending on the former heat treatment of the Mg-1Ca alloy as well as on the parameter during plasma-chemical oxidation.

Long-term corrosion resistance of carbon steels grade API L80 and API Q125 has been evaluated by means of electrochemical measurements and exposure tests in the Molasse Basin, one of the most important geothermal fluids in Europe. In addition, the localized corrosion resistance of the duplex stainless steel alloy 2205 and the austenitic stainless steel grade 316L was determined at 100 and 150 °C. In general, investigated materials showed a remarkable resistance to uniform and localized corrosion. Their corrosion behaviour at service conditions is discussed in this paper.

A FeCrMoMnWBCSi amorphous metallic coating was prepared by using high-velocity oxy-fuel spray. The influence of processing parameters on microstructure, porosity level, amorphous phase fraction and corrosion behaviour of the coatings was characterised by scanning electron microscopy, X-ray diffraction, differential scanning calorimeter and electrochemical methods. The results indicated that the microstructures of the coatings were sensitive to the spray parameters considerably. Porosity and unmelted particle proportion decreased with the oxygen/fuel (O/F) ratio and increased with the powder feed rate. The trend of oxides content was opposite to the porosity and unmelted particle proportion. The coatings obtained with higher O/F ratio and lower powder feed rate exhibited higher hardness. The low coating hardness was mainly due to the high porosity especially when the porosity was higher than 1.21%. The spraying parameters strongly affected the amorphous phase fraction. There was a critical passive current density for balancing the porosity and the amorphous phase fraction. Corrosion resistance is dominant by the amorphous phase fraction when the porosity is less than 1.21%, while by porosity when it is higher than that. Open-circuit potential, potentiodynamic polarisation and electrochemical impedance spectroscopy results showed that the coatings obtained with the O/F ratio of 4.2 and the powder feed rate of 40 g/min exhibiting the best corrosion resistance in 1 wt% sodium chloride solution.

The corrosion inhibition behavior of benzotriazole (BTA) on a brazing alloy, CuP in the non-welded and welded conditions in 17 wt% (0.534 mol/L) tetra-n-butylammonium bromide (TBAB) aerated aqueous solution was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy/energy dispersive X-ray spectroscopy techniques. The experimental results showed that BTA could protect effectively copper alloys in aqueous TBAB solution. The inhibition efficiency of BTA increased with increasing inhibitor concentration from 0.1 to 6 g/L, attaining efficiencies of up to 96% calculated according to different methodologies. Corrosion current densities were lower after the melting process. Galvanic studies showed that copper behaved as the anode when coupled to its alloys. The addition of BTA caused an increase in charge transfer resistance and a decrease in the capacitance of the double layer. Adsorption of BTA in 17 wt% TBAB solution on the copper alloys' surface was found to obey the Langmuir adsorption isotherm.

The present work reports a simple and safe two-step process to render magnesium (Mg) alloy surfaces superhydrophobic via primary cell corrosion and subsequently cover it with a fluoroalkylsilane (FAS) film. The surfaces were characterized by scanning electron microscopy (SEM), optical microscopy, energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectrophotometry (FTIR), X-ray diffraction (XRD), and optical contact angle measurements. The power generated via the primary cell corrosion of copper and Mg alloys was also measured using a digital multimeter. The results show that micro/nanometer-scale binary rough structures and an FAS film with a low surface energy were present on the Mg alloy surfaces, both of which confer good superhydrophobicity with a water contact angle of 162.8° and a tilting angle of 2°. The micro/nanometer-scale binary rough structures consisted of micrometer-scale grains, cluster-like structures composed of nanometer-scale needles, and network-like structures composed of nanometer-scale sheets. Superhydrophobicity was analyzed by the Cassie–Baxter theory. Findings show that only about 6.3% of the water surface was in contact with the Mg alloy substrates, while the remaining 93.7% was in contact with the air cushion. The unique advantage of the proposed method is that power can be generated during the machining process of the superhydrophobic surfaces on the Mg alloy substrates.

We report on the corrosion of austenitic (AISI304) and duplex (2205) stainless steels in H₂O/KOH 50% at 120 °C. The research is based on a combination of electrochemical, structural and compositional analyses, aimed at assessing the surface modifications resulting from anodic attack and their impact on corrosion resistance. Linear sweep voltammetry and electrochemical impedance spectrometry measurements were carried out in an air-tight high-temperature cell. In-plane and cross-sectional SEM micrography, X-ray diffractometry and EDX profiling were used to characterise samples attacked under electrochemically controlled conditions. Electrochemical results have shown that AISI304 exhibits a complex passivating behaviour, while the anodic electrokinetics of the duplex is characterised by mixed kinetic control. AISI304 was found to fail by intergranular corrosion and to be covered: in passive conditions by acicular compounds and in transpassive conditions by a compact layer of corrosion products. Duplex samples, instead, exhibit an uniform form of corrosion morphology and bear a compact layer of corrosion products both in passive and in transpassive conditions.

Power plants are one of the major industries suffering from severe erosion–corrosion (E-C) problems resulting in substantial losses. One way of tackling this problem is by the use of thermal spray coatings. In the current investigation a new emerging technique i.e. cold spray coating process was used to deposit Ni-20Cr and Ni-50Cr powder on SA 516 (grade 70) boiler steel. The bare as well as the coated steels were subjected to cyclic experimental studies, in the superheater zone of a coal fired boiler. Weight change, thickness loss, XRD, FE-SEM/EDS and X-ray mapping techniques were used to analyse the eroded-corroded specimens. The uncoated steel showed weight gain after exposure in the actual boiler environment, whereas, for the coated steels there was initial weight loss followed by negligible weight change. Based upon thickness loss data the cold-sprayed Ni-50Cr coating was found to provide better E-C resistance than the Ni-20Cr coating.

In this paper, water uptake, porosity and corrosion behaviours of two-pack polyurethane coatings separately loaded with two types of silica nanoparticles (i.e. hydrophilic and hydrophobic silica nanoparticles) are presented. Water uptake of such coatings was measured by the aid of electrochemical impedance spectroscopy whereas porosity of the coatings was determined according to the ASTM D 6583 standard. Transmission electron microscopy and Fourier transform infrared spectroscopy were also utilised to examine morphology and chemical structure of the nanoparticles filled coatings. These techniques show that the hydrophobic SiO₂ nanoparticles could be easily dispersed throughout the polyurethane matrix while negatively influence the curing process of the coatings. The results reveal that the incorporation of both hydrophilic and hydrophobic silica nanoparticles into the polyurethane matrix, generally, reduces the percent porosity of the resultant coatings. However, obtained results show that the type and content of silica nanoparticles influence the capacitance and therefore water uptake of the coatings to various extents.

One of the most common corrosion protection methods in reinforcing concrete bars is the application of fusion-bonded epoxy coatings. Although considerable research has been carried out on the performance of epoxy-coated bars (ECR), there are still many uncertainties about their performance in cracked concrete. In this experimental program, reinforcing steel bars with six types of epoxy coatings embedded in concrete slabs with a 0.4 mm wide preformed crack intersecting the reinforcing steel at right angles were tested. Results of corrosion potentials, corrosion current density, coating adhesion tests, chloride content, and visual examination after 68 months of exposure to a simulated marine environment are reported. Results revealed that under the studied conditions the ECR did not provide total protection of steel reinforcement in cracked concrete. Their use however, tended to reduce significantly the damage caused by the chloride-induced corrosion when compared with the uncoated bars embedded in concrete with similar characteristics.

Six wear-resistant alloys based on nickel, containing 30 wt.% Cr and from 2.5 to 5.0 wt.% C, were elaborated by foundry and subjected to oxidation by air at 1000, 1100, and 1200 °C, for evaluating the oxidation behavior of hard bulk alloys. Their microstructures are rich in chromium carbides, eutectic, or pro-eutectic, and they also contain graphite for the highest carbon contents of interest. All the studied alloys obviously display a chromia-forming behavior, despite the initial low chromium content in the matrix. During oxidation, carbides disappear over an increasing distance from the oxidation front, with the consequence of the enrichment of the neighbor matrix in chromium. The minimal chromium content on the surface after oxidation decreases when the alloy is richer in carbon and increases with the oxidation temperature. The carbide-free zone tends to be deeper when the oxidation temperature increases, and also when the alloy's carbon content increases, in contrast with low-C Ni-30Cr alloys previously studied. The disappearance of carbides means a carbon loss as gaseous oxidized species. This probably disturbs the oxide scales growing on the external surface and may influence the oxidation behavior of the alloys. When present, graphite does not deteriorate dramatically the oxidation resistance of the alloys. The hardness of the alloys are lowered by the exposures to high temperature and by the presence of graphite.

Aging study of 1441 and 8090 AlLiCuMg alloys exhibited characteristic precipitation hardening phenomena. Potentiodynamic polarisation studies carried out on various tempers of the 1441 and 8090 AlLiCuMg alloys in 3.5% NaCl, with a small amount of H₂O₂, and in 3.5% NaCl solution with pH 10 and 12 showed the shifting of open circuit potential (OCP) towards more negative potential and higher corrosion rate, with the increase of aging time. The OCP value has shifted anodically with addition of H₂O₂ in 3.5% NaCl solution. Further, passivity phenomenon has been observed for all the alloy tempers in 3.5% NaCl solution at pH 10 and 12. The observation of OCP shift towards more negative potential and the higher corrosion rate with the increase of aging time has been attributed to the presence of higher amounts of anodic δ (AlLi), S′ (Al₂CuMg) and T₁ (Al₂CuLi) phases, studied by TEM, XRD and DSC methods.

Corrosion in the presence of CO₂ was studied under supercritical conditions (high pressure and moderate temperature) using different carbon steels and various corrosion resistant alloys (CRA's). An objective of this work was, among others, to put the results in perspective relative to various CO₂ corrosion models that have been developed and published over the years. In particular, the NORSOK, FREECORP, and OLI models were used for comparison, while others were discussed as well. The systems investigated were (a) supercritical CO₂ (SC CO₂) saturated with water (no separate water phase), (b) a water mist phase in equilibrium with SC CO₂, (c) a water/brine phase in equilibrium with SC CO₂. It was found that the OLI model best simulates the experimental corrosion rates observed in system (c) where coupons were corroded in the aqueous phase at high velocities in the rotating cage. The varying susceptibility of different carbon steels to corrosion under these conditions is highlighted. CRA steels are comparatively more resistant.

The electrochemical techniques, that is, polarization resistance (R_p) and potentiodynamic polarization curves, were used in order to determine the effect of turbulent flow on the corrosion inhibiting effect of 2-mercaptobenzimidazole (2-MBI) on API 5L X52 grade steel samples immersed in a 3% NaCl aqueous solution saturated with CO₂ at 60 °C. Turbulent flow conditions were controlled using a rotating cylinder electrode (RCE). An inhibition efficiency of 98% was measured at a concentration of 10 ppm of 2-MBI at a rotation rate of 5000 rpm. This efficiency value is similar to those efficiency values measured at 25 and 40 ppm 2-MBI and at the same rotation rate. These observations suggest that as the turbulent flow conditions increase the corrosion inhibiting effect of 2-MBI is enhanced. 2-MBI follows a Langmuir adsorption isotherm. The calculated values of adsorption equilibrium constant (K_ads) and adsorption free energy () suggest that the adsorption process taking place is chemical. The polarization curves indicate that the 2-MBI does not modify the electrochemical mechanism of the anodic (Fe dissolution) and cathodic (hydrogen evolution) reactions. It is suggested that 2-MBI decreases the rate at which these reactions occur, blocking the active sites on the steel surface.

Flow-accelerated corrosion (FAC) is the most common failure in nuclear power plants. The FAC rate conforms to the experimental results in lab, which are calculated by some other FAC rate prediction models. However, when these models are employed to calculate the FAC rate of the elbow, the result is opposite to actual situation of failure of the elbow. In this paper, a new prediction model is proposed to calculate the flow accelerated corrosion (FAC) rate in the elbow, which combine the steady-state mass transfer model of electrochemical theory and one-dimensional galvanic corrosion model. Firstly, the distribution of velocity in the elbow is counted by FLUENT. Secondly, the free corrosion potential and the free corrosion current density are calculated by steady-state mass transfer model. At last, the novel model is used to obtain the FAC rate of the elbow. The result will show that the FAC rate of the outward bend of the elbow is two-orders than the inward bend of the elbow. The outward bend of elbow is the defective position, which accords with the statistical result of Kuen Ting et al.

Different quantities of silicon and calcium were added to Mg–6%Zn–1%Mn alloy and its effect on corrosion behavior investigated. AC and DC polarization were carried out on the extruded rods, which contain different quantities of silicon and calcium. The phases present in the alloys have been identified by optical microscopy and TEM. Four different phases were found, i.e., intermetallics containing Si–Mn, Mg–Si, Mg–Zn, and Mg–Si–Ca phase. The corrosion behavior of the studied alloys were influenced by the amount and distribution of the second phases.

This article has been retracted due to a substantial overlap with a previously published article in another journal.

This paper provides a brief review of research aimed at characterising the steel–concrete interfacial zone (SCIZ) and its influence on the susceptibility of the metal to pitting corrosion when concrete is exposed to environments that cause ingress of chloride ions accompanied by leaching of hydroxyl ions. For reinforced concrete made from Portland cements, exposed to aqueous solutions of sodium chloride, the buffering effect of solid calcium hydroxide (portlandite) at pH ∼12.6 has been shown to restrain the gradual decline in the hydroxyl ion concentration of the concrete pore solution phase at depths corresponding to the embedded steel. When the concrete is produced under laboratory conditions that are carefully controlled to exclude macroscopic defects from the SCIZ and the steel is cleaned before being embedded, this can lead to observed chloride threshold levels being consistently greater than 1% chloride by mass of cement. The buffering action of cement hydration products formed in the SCIZ is believed to be partly responsible for this high tolerance to chloride-induced corrosion because it counters the generation of ‘anodic acidity’ that is a necessary condition for stable growth of pits to occur. Translating this behaviour of laboratory specimens to the performance of full-scale reinforced concrete structures has often proved difficult in the past and there is a need for further research in this area, particularly in relation to the role of non-traditional cements.

Methods for service life prediction of reinforced concrete structures exposed to chloride-bearing environments require, amongst other parameters, the knowledge of the chloride threshold for pitting corrosion initiation (Cl_th). Nowadays, although the main factors influencing the chloride threshold are well known, it is often difficult to quantify a value of the chloride threshold, partly because of its intrinsic high variability, and partly because of the different test methods that have been used to measure it. All the experimental tests rely on the detection of steel depassivation and simultaneous measurement of chloride content or steel potential. This paper deals with the methods that can be used to detect steel depassivation in relation with the determination of the chloride threshold. Tests in concrete-pore-simulating solutions as well as tests in concrete will be considered, and advantages and limitations will be discussed.

Electrochemical impedance spectroscopy (EIS) and polarisation curves assisted by Raman spectroscopy were used to study the corrosion behaviour and to characterise the corrosion products of reinforcing steel embedded in fly ash mortars with and without chloride pollution. Two alkaline solutions with different soluble silica contents were utilised to activate the fly ash. After 720 days of experimentation the reinforcing steel embedded in fly ash mortar without chlorides remained passive, while the specimens in fly ash polluted with chloride ions (0.4 and 2%) yielded current density values of the order of 2 × 10⁻⁵ A/cm², typical of an active state. The main corrosion products identified on the steel surface were less crystallised phases of iron oxyhydroxide hydrates and goethite (α-FeOOH) or lepidocrocite (γ-FeOOH).

High chromium white irons are important candidate materials for use in alumina refineries to combat wear and corrosion. The effect of exposure time on the formation of oxide films was studied in a 23% Cr white cast iron exposed at 260 °C in 110 g/l caustic soda solutions. It was found that whilst well-formed octahedral M(II)O.M(III)₂O₃ spinel type oxides initially formed and spread across the surface of the material, these were gradually replaced by a background oxide with a higher Cr/Fe ratio and the morphology of the octahedral crystals became less well formed. Also, the oxidation was found to be predominantly in the matrix material, leaving carbide particles unsupported on the surface and in the later stages, significant corrosion was found along the carbide/matrix phase boundary.

Hot alkaline solutions, such as potassium/sodium carbonate solutions, have been used for carbon dioxide removal and capture processes. This survey summarizes the available corrosion data of steels in the solution with carbon dioxide dissolved. Plant operating experiences and laboratory testing results are considered. The corrosion mechanisms, important factors, inhibitor effects, and corrosion cracking are analyzed.

The electrochemical and tribocorrosion behaviors of Ti–6Al–4V, 316 stainless steel and Monel K500 alloys sliding against Al₂O₃ in artificial seawater are investigated in this paper. It can be observed that the open circuit potential drops down to more negative values due to the removal of passive film. And a rapid dissolution occurs in the wear track compared with the unworn area. The wear loss polarized in cathodic potential is lower than that in anodic potential and open circuit potential conditions, because the material deterioration is enhanced by corrosive attack. The wear volumes of 316 stainless steel are much higher than the ones measured for Ti–6Al–4V and Monel K500 alloys. Friction coefficients are significant large in cathodic polarization compared with anodic polarization for all alloys. Moreover, the 316 stainless steel exhibits large friction coefficients compared with Ti–6Al–4V and Monel K500 alloys.

Ti–22Nb–xZr and Ti–22Nb–xMo (x = 0, 2, 4, 6, in atom percent) were prepared by an arc melting method. The alloys were solution-treated at 1073 K for 1.8 ks followed by quenching them into ice water, and the electrochemical corrosion behavior in a 0.9% NaCl solution at 25 °C and neutral pH range of the solution-treated alloys was evaluated by using electrochemical impedance spectroscopy, polarization curves and an equivalent circuit analysis. It was found that the microstructure of the solution-treated Ti–22Nb alloy mainly contains β phase with small amount of α″ phase, and the addition of Zr or Mo to a Ti–22Nb alloy is efficient to stabilize the β phase. The resulting impedance parameters and passive current densities indicated that the corrosion resistance of the Ti–22Nb alloy was promoted significantly with the addition of Zr and Mo.

The inhibitive effect of Ce(III) and Ce(IV) ammonium nitrate inhibitors on the corrosion behavior of aluminium alloy AA2024 in 3.5% NaCl solution has been investigated. Four different concentrations (10⁻², 10⁻³, 10⁻⁴, and 10⁻⁵ M) of the inhibitors were studied. Ce³⁺ and Ce⁴⁺ ions are introduced into the corrosive medium with similar anionic compositions – (NH₄)₂Ce(NO₃)₅ and (NH₄)₂Ce(NO₃)₆. The inhibition efficiency (IE%) of the ions has been evaluated by using electrochemical methods – linear voltammetry (LVA) and electrochemical impedance spectroscopy (EIS). Moreover, the inhibitive ability has been investigated at different duration after addition of these salts into the corrosive media. It is established that the pH of the solutions plays an important role on the inhibition process for both cations. The results revealed that at relatively similar conditions, the cerium (III) ions showed higher inhibition efficiency than cerium (IV) ions, when they were compared to the case without inhibitor.

The influence of the weld metal chemistry on the susceptibility of AISI 444 ferritic stainless steel (FSS) weldment to stress corrosion cracking (SCC) in hot chloride was investigated by constant load tests and metallographic examination. Two types of filler metal of austenitic stainless steel (E316L and E309L) were used in order to produce fusion zones of different chemical compositions. The SCC test results showed that the interface between the fusion zone (FZ) and the heat affected zone (HAZ) was the most susceptible region to SCC. Results also showed that the AISI 444 stainless steel weldment with E309L weld metal presented the best SSC resistance. Microstructural examinations indicated that the cracks initiated in the weld metal and propagated to the HAZ of the AISI 444 FSS, where the fracture occurred and it was observed a considerable amount of precipitates. Additionally, the higher SCC resistance of the AISI 444 FSS weldment with E309L weld metal may be attributed to the presence of a discontinuous delta-ferrite network in its microstructure, which acted as a barrier to cracks propagation from the fusion zone to the HAZ/fusion zone interface of AISI 444 FSS. Fractrography analyses showed that the transgranular quasi-cleavage fracture mode was predominant in the AISI 444 weldment with E316L weld metal and the mixed fracture mode was the predominant in the AISI 444 weldment with E309L weld metal.

The main purpose of this paper is to systematically evaluate the anti-corrosion property of N,N-bis(2-benzimidazolylmethyl)amine (IDB), which is a novel good thermal stabilized inhibitor in acidic medium. Results obtained from electrochemical tests and corrosion surface morphology analyses reveal that IDB performs excellently as corrosion inhibitor for Q235 steel in 1 mol/L hydrochloric acid corrosive solution. Potentiodynamic polarization measurements show that IDB inhibits both the anodic and cathodic processes of corrosion and exhibits as a mixed-type inhibitor. Besides, the inhibiting efficiency (IE%) and consequently the degree of surface coverage (θ) increase with the inhibitor concentration rising. And when the concentration is 20 × 10⁻⁵ mol/L, the corrosion inhibition effect is best to reach 96.39%. The adsorption of inhibitor on Q235 steel is found to obey the Langmuir adsorption isotherm, and the calculated Gibbs free energy demonstrates that IDB spontaneously adsorbs and forms a protective chemisorbed film on Q235 steel to restrain its corrosion. Hereby, IDB will become a promising corrosion inhibitor in further.

Ceramic coatings with thickness of 27 µm were fabricated on Mg–7Li alloy in Na₂SiO₃–C₆H₁₈O₂₄P₆ solution by microarc oxidation (MAO). The morphology and phase composition of MAO coatings were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion behavior of the bare and MAO coated Mg–7Li alloy was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Results showed that the MAO coatings were composed of MgO, Li₂O, and Mg₂SiO₄, and there existed some micropores on the coating surface with a diameter of 3–20 µm. The corrosion potential (E_corr) and corrosion current density (I_corr) of the MAO coated alloy were about −1.4761 V and 7.204 × 10⁻⁷ A/cm², respectively. The E_corr of the MAO coated alloy increased by 109.6 mV and its I_corr decreased by three orders compared with that of the bare Mg–7Li alloy. The EIS plots indicated that the impedance of the MAO coated alloy was 15 times higher than that of the bare alloy. The fitting parameters showed that the resistance of the MAO coatings was far greater than that of the bare alloy. The dense intermediate layer and the transition layer of the MAO coatings acted as a barrier to hinder the proceeding of solution permeation, remarkably improving the corrosion resistance of the Mg–7Li alloy.

The aim of this work was to investigate the anti-corrosive properties of nanocomposite ZnNi coatings containing Al₂O₃ nanoparticles, prepared from alkaline commercial electrolytes (pH 13), (PERFORMA 280.5, COVENTYA S.A.S, France), by electrodeposition on carbon steel (OL37). The corrosion resistance of the coatings prepared with different concentrations of Al₂O₃ (5, 10, and 15 g/L) was evaluated in 0.2 g/L Na₂SO₄ solution (pH 5) by open circuit potential (OCP) measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. The results of electrochemical measurements were corroborated with those obtained by using X-ray diffraction analysis. The obtained results show that the introduction of Al₂O₃ nanoparticles in the plating bath generally brings an increase in corrosion resistance of ZnNi layers and put in evidence the existence of an optimal Al₂O₃ concentration. Under the examined conditions, the optimal concentration determined from polarization measurements was proven to be 5 g/L Al₂O₃. The highest value of the polarization resistance, R_p, obtained from impedance measurements corresponds also to ZnNi with 5 g/L Al₂O₃, which is in agreement with the results obtained from polarization and XRD measurements.

Poly(3-octylthiophene) (P3OT) was synthesized by direct oxidation of the 3-octylthiophene monomer using ferric chloride (FeCl₃) as an oxidant. Using the drop-casting technique, P3OT coatings were deposited onto 304 type stainless steel electrodes. For the purpose of determining the effect of thermal annealing on the corrosion protection of stainless steel with P3OT coatings, the coated electrodes were thermally annealed for 30 h at two different temperatures, 55 and 100 °C. The corrosion behavior of P3OT coated stainless steel was investigated in 0.5 M sulfuric acid (H₂SO₄) at room temperature using potentiodynamic polarization curves (PPC), linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS). The results indicated that the thermally treated P3OT coatings improved the corrosion resistance of the stainless steel in 0.5 M H₂SO₄. The best corrosion protection was obtained by the P3OT coating annealed at 100 °C. In order to study the temperature effect on the morphology of the coatings before and after the corrosive environment and compare it with corrosion protection, atomic force microscopy (AFM) and scanning electronic microscopy (SEM) were used.

The silicone-epoxy and polyurethane topcoats applied in a simulated sea splash environment were studied according to ISO20340 standard, and their properties were analyzed by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectrum (EIS). Glass transition temperature (T_g) of silicone-epoxy polymer is 7.7 °C higher than that of polyurethane polymer. Measurement of gloss and color difference demonstrates that anti-ageing property of silicone-epoxy topcoat is better than that of polyurethane topcoat. It is known from SEM and XPS analysis that silicone-epoxy topcoat can retain the good morphological structure and ageing resistance after accelerated cycle ageing test. The results from EIS analysis indicate that the silicone-epoxy topcoat has good anti-corrosion properties. Measurement of contact angles indicates that surface tension of silicone-epoxy topcoat is smaller than that of polyurethane topcoat before and after corrosion test.