Morphology, Chemical Composition and Phase Transformation of Hydrothermal Derived Sodium Titanate


  • This study was financially supported by National Science Council of Taiwan, in the Project no. 98-2218-E-006-238.

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This study intends to clarify the discrepancies on the effect of precursor size, chemical composition, and thermal behavior of Na-titanate obtained through a conventional hydrothermal reaction of anatase in a highly concentrated aqueous NaOH solution. According to experimental results, as well as that presented in related literatures, ultrafine anatase precursor favors nanofiber formation, whereas larger-particle anatase precursor forms nanotubes. The formation mechanism, in correlation with the precursor size and the resulting morphology of the obtained titanate product, is described in detail. According to X-ray Diffraction and Raman analyses, the as-formed Na-titanate is considered a quasi-disordered structure that allows the occupation of a wide range of Na into the titanate structure. An increased Na/Ti ratio is observed with increased temperature, which simultaneously results in a distortion of the titanate structure. Moreover, the as-synthesized Na-titanate is thermally unstable and tends to degrade into amorphous clusters after heat treatment at 300°C. Rod-like Na2Ti6O13 is recrystallized from the amorphous cluster at 700°C–800°C and becomes plate-like after annealing at 900°C via a parallel assembly of Na2Ti6O13 rods. An additional Na2Ti3O7 phase appears at high temperatures, exhibiting a relatively higher Na/Ti ratio.