ToF-SIMS of polyphosphate glasses

The increasing interest in phosphate glasses is due to the fact that they are considered to be bioactive functional materials in applications such as hard and soft tissue engineering and also that they possess interesting optical properties. These include low dispersion, high refractive index and high transparency for ultraviolet light. They have also been found to be responsible for the good anti-wear properties of phosphorus-based engine-oil additives. More recently, the low processing temperature of zinc and iron phosphates, as well as their chemical durability, has opened the possibility for new applications, such as the immobilization of nuclear wastes. Understanding the surface chemistry of such glasses turns out to be a key step for inferring their underlying mechanisms of action. In this work, zinc phosphate and iron phosphate glasses of different chain lengths were synthesized and characterized by means of time-of-flight secondary ion mass spectroscopy (ToF-SIMS). ToF-SIMS was able to successfully differentiate between the samples of different composition. A characteristic pattern of phosphate fragments was observed in the negative-mode ToF-SIMS spectra. The most intense peaks could be assigned to the phosphate fragments PO⁻, PO₂⁻, PO₃⁻ and PO₄⁻. Toward higher masses, fragments containing up to four phosphorus atoms with a periodicity of PO₂ were observed: FePO₃⁻, ZnPO₃⁻, FePO₄⁻, ZnPO₄⁻, FeP₂O₆⁻, ZnP₂O₆⁻, FeP₂O₇⁻, ZnP₂O₇⁻; FeP₃O₈⁻, ZnP₃O₈⁻, FeP₃O₉⁻ and ZnP₃O₉⁻. This pattern characterizes the spectra of all the glasses under investigation. For the first time, a method is proposed that allows the discrimination between polyphosphates of different chain lengths, by comparing the intensities of the relevant ToF-SIMS peaks. Copyright © 2012 John Wiley & Sons, Ltd.