Gibbs free energy of formation of Cu2In2O5 ternary phase determined by E.M.F. method

Abstract

Employing electrochemical cells with the solid zirconia electrolyte: Cu2O,CuO/O2-/air Cu2In2O5, In2O3,Cu2O/O2-/air In,In2O3/O2-/Ni, NiO Gibbs free energy of formation of solid Cu2In2O5 phase as well as that for In2O3 and CuO oxides was determined in the temperature range from 973 K to 1372 K. The results obtained in this study were used to derive Gibbs free energy change of the reaction of formation of the ternary compound from respective oxides: 2CuO + In2O3 = Cu2In2O5 which is equal to: ?Gf0,Cu2In2O5 = 33905 ? 41.50T (?3600) Jmol?1. Standard enthalpy of formation from elements ?H0f,298 and standard enthalpy ?S0298 derived for Cu2In2O5 phase by Second Law sigma plot are -1211 (?15) kJ mol-1 and 493.20 (?10) J (K-1 mol-1). Oxygen potential diagrams for the Cu-In-O system are also given at two temperatures.