Mass spectrometric studies of the decomposition and the heat of formation of CuInS2(s)

The equilibrium vaporization of CuInS2(s) was studied by Knudsen cell mass spectrometric techniques in the temperature range 902 - 1110 K. Based on these and independent congruency studies, CuInS2(s) decomposes under steady-state conditions according to the reaction 2CuInS2(s) = Cu2S(s) + In2S(g) + S2(g). During the initial transient period of the vaporization of CuInS2, the ion intensities of In2S+ and S2+ change and assume steady-state values after some time. A second-law evaluation of intensity versus temperature data, obtained under steady-state conditions, yielded a value for the heat of the above decomposition reaction (2 moles of CuInS2) of δH0298 = 630.9+-26 kJ. With this quantity and auxiliary thermochemical data, the enthalpy of formation of CuInS2(s) was computed to be δH0/sub 298.s/ = -221.7+-13 kJ/mol. (author)