Thermogravimetric analysis of InCl₃ sublimation at atmospheric pressure

This paper presents a thermogravimetric approach to evaluate the vapor pressure of low-volatility inorganic compounds such as CuCl and InCl₃ under atmospheric conditions. The thermogravimetric analysis (TGA) approach is inherently more straightforward than alternatives such as torsion studies and mass spectrometry. Vapor pressures are evaluated using the Clausius-Clapeyron relationship between the vapor pressure and sublimation (or vaporization) enthalpy at a given temperature. Despite the relative simplicity of TGA, the highly hygroscopic nature of InCl₃ demands some caution in the data analysis. Especially at high temperature, a solid-phase oxidation product In₂O₃ remains as a residual mass. Water is found to be the oxidation agent, with the residual proceeding through a solid-phase InOCl intermediate. However in the relatively low temperature range of interest oxidation is found to be negligible, with the gas-phase sublimation product being In₂Cl₆. This paper reports sublimation enthalpies and vapor pressures as functions of temperature in the range 570 ≤ T ≤ 640 K and atmospheric pressure.