Thermodynamics of copper sulfides II. Heat capacity and thermodynamic properties of synthetic covellite, CuS, from 5 to 780.5 K. Enthalpy of decomposition

The heat capacity of CuS has been measured by adiabatic shield calorimetry from 5 to 840 K. The heat capacity increases regularly up to about 750 K and then more strongly as the decomposition temperature (780.5 K) of covellite into high-digenite and sulfur is approached. The molar enthalpy and molar entropy of decomposition are 2149.3R[middle dot]K and 2.755R. Above 780.5 K the uptake of sulfur in the high-digenite causes a further rise in the heat capacity. The low-temperature values increase more strongly than expected from the Debye relation with a Debye temperature estimated from the intermediate-temperature behavior. This phenomenon as well as a small bump in the heat capacity around 55 K are discussed. The resulting molar enthalpy and molar entropy at 298.15 and 825 K are 1136.6R[middle dot]K, 8.101R, and 6744.2R[middle dot]K, 17.393R, respectively.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27002/1/0000569.pd