Low‐Temperature TiO2‐SnO2 Phase Diagram Using the Molten‐Salt Method

Abstract

The molten‐salt method has been used for low‐temperature synthesis of ceramic compounds. It has been used in the present work to determine the phase diagram of the TiO2‐SnO2 system down to 400°C, which is not possible by the conventional solid‐state annealing method. LiCl‐KCl eutectic has been used as the molten salt. The experimental procedure consists of annealing powder of the TiO2‐SnO2 solid solution in the molten‐salt eutectic for a sufficient length of time at the temperature of interest. The a and c lattice parameters have been determined for the decomposed phases by X‐ray diffractometry. The phase diagram determined in the present work has been compared with that determined by conventional solid‐state annealing methods. The phase diagram determined in the present work exhibits a wider miscibility gap compared to the gap determined by the solid‐state annealing method. This is attributed to sluggish solid‐state kinetics at lower temperatures. The phase diagram determined in the present work agrees well with a regular solution model, except for a slight deviation in the SnO2‐rich portion of phase diagram above 1200°C. Scanning electron microscopy has been used to study the particle‐growth morphology. The solubility has been estimated from particle‐growth kinetics as well as from the direct‐current plasma technique. The results indicate that a modest solubility is sufficient to enhance the kinetics in the molten salt and, thereby, facilitate the determination of low‐temperature phase equilibria in ceramics.