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

Abstract

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.