Enthalpy of formation of a solid soluion in the Cr-S system.

概要

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Enthalpy changes of combustion (ΔHc) of nonstoichiometric chromium sulfides; trigonal-Cr2S3 (t-Cr2S3) and rhombohedral-Cr2S3 (r-Cr2S3), were measured by using a Tian-Calvet type twin-calorimeter. The enthalpy change of phase transformation from t-Cr2S3 to r-Cr2S3 (CrS1.471 to CrS1.478) was found to be; ΔHT/kJ·mol-1=-83.16. In the nonstoichiometric t-Cr2S3 phase (CrS1.402-CrS1.471), the ΔHc value stayed unchanged at about-840kJ·mol-1 in the compositional range of CrS1.450-CrS1.471, while it increased with decreasing sulfur composition (x in CrSx) up to c. a. -420kJ·mol-1 at CrS1.402, suggesting that the crystal lattice of CrSx becomes more stable at lower sulfur compositions in the t-Cr2S3 phase. The enthalpies of the foration of solid slution (ΔHss)in the t-Cr2S3 phase were also estimated by assuming CrS1.478 (sulfurrich end of the t-Cr2S3 phase) as the standard state and that the more sulfur deficient compositions than CrS1.478 were considered to be formed by the dissolution of Cr atoms into CrS1.478. ΔHss was almost zero in the compositional range of CrS1.450-CrS1.471, while it increased with decreasing sulfur composition x in x < 1.450. It went through a maximum of c. a. 370kJ·mol-1 at CrS1.440 and then decreased.
日本熱測定学会の論文