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

Article abstract of DOI:10.1016/0021-9614(87)90057-7

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*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*K, 8.101R, and 6744.2R*K, 17.393R, respectively.