Thermal treatment of anhydrous chromium (III) chloride: Thermodynamic study

Anhydrous CrCl3∙εH2O exhibited, under helium stream (6 L h–1, 5 K min–1), several transformations between room temperature and (1175 ± 2) K. The compound loses the physisorbed water molecules between (300 ± 2) K and (400 ± 2) K and the hydration degree (ε) was determined by thermogravimetry to be 0.14. However, using mass spectrometry, we were able to detect the transformation of CrCl3(cr) into CrCl3(g) at T = (776.00 ± 0.01) K. In this context, ΔsubH (776 K) value was estimated using some literature data and the Clausius-Clapeyron relation to be (245.20 ± 0.01) kJ mol–1. This value was corrected at (298.15 ± 0.01) K and (0.105 ± 0.01) MPa, resulting in (254.93 ± 0.01) kJ mol–1. Our thermodynamic calculations revealed that CrCl3(g) is decomposed into CrCl2(cr) and Cl2(g) within two distinct temperature ranges: (776 ± 2) to (860 ± 2) K and (950 ± 2) K to (1050 ± 2) K. Between (860 ± 2) and (950 ± 2) K, the evaporation of CrCl2(cr) in the form of CrCl4(g) takes place due to the presence of Cl2(g). However, at higher temperatures (T > 1050 K), residual CrCl2(cr) is evaporated and a final mass loss of 94 % is obtained.