High-temperature reaction calorimetry of solid and liquid phases in the quasi-binary system Ag/sub 2/S-Sb/sub 2/S/sub 3/
High temperature reaction calorimetry has been applied in a thermochemical study of solid and liquid phases in the quasi-binary system Ag/sub 2/S-Sb/sub 2/S/sub 3/. Direct synthesis calorimetry of stibnite, Sb/sub 2/S/sub 3/, at 880 K and 768 K, from the elements yields a mean value for the standard enthalpy of formation, ..delta..H/sub f,stibnite,298 K//sup 0/ = -129.72 +- 3.75 kJ mol/sup -1/; this value is about 12 kJ mol/sup -1/ less exothermic than a previously reported value obtained by fluorine combustion calorimetry. The enthalpies of formation at 298 K of the sulfosalts ..cap alpha..-miargyrite (AgSbS/sub 2/) and hexagonal pyrargyrite (Ag/sub 3/SbS/sub 3/) from their endmember component sulfides (Ag/sub 2/S and Sb/sub 2/S/sub 3/) were determined to be -4.1 +- 2.3 kJ mol/sup -1/ and -7.8 +- 0.8 kJ mol/sup -1/, respectively. The enthalpy of transformation of ordered monoclinic ..cap alpha..-miargyrite to disordered cubic ..beta..-miargyrite at 298 K was determined to be +8.7 +- 1.4 kJ mol/sup -1/. If the equilibrium temperature for this transformation is equal to 650 K, this implies an entropy of transformation of about +13.3 JK mol. Liquid mixtures of solid Ag/sub 2/S and liquid Sb/sub 2/S/sub 3/ at 880 K were studied by solid-liquid reaction calorimetry and by dilution calorimetry, with pure liquid Sb/sub 2/S/sub 3/.
- Research Organization:
- Univ. of Chicago, IL (USA)
- OSTI ID:
- 7222737
- Journal Information:
- Geochim. Cosmochim. Acta; (United States), Vol. 52:1
- Country of Publication:
- United States
- Language:
- English
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