Thermogravimetric analysis of InCl3 sublimation at atmospheric pressure

• Thermogravimetric analysis (TGA) is used to measure properties of InCl3.
• InCl3 vapor pressure is measured as function of temperature.
• Standard-state InCl3 sublimation enthalpy is measured.
• Very low levels of H2O lead to residual oxidation products.

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.