Nonstoichiometric Copper Sulfide Research Articles

Metastable equilibria in the system copper sulphidesulphuric acidammoniawater at 25°C

Potential-pH metastable equilibria diagrams for the system Cu 2− x SH 2SO 4NH 3H 2O at 25°C have been elaborated. New equations describing the potential of the nonstoichiometric copper sulphide electrode are presented. Potentiometric measurements were carried out on electrodes made of synthetic deficient chalcocite in solution of ammoniacal ammonium salts with a variable concentration of Cu(II) ions, free ammonia and environmental pH. Good agreement was found between the obtained experimental results and the relations established thermodynamically. On the basis of potentiometric measurements carried out in acidic solutions the value of the Gibbs standard free energy of the formation of djurleite Cu 1.965S was determined as − 20.33 kcal/mol.