Studies on the phase diagram of Pb–Fe–O system and standard molar Gibbs energy of formation of ‘PbFe5O8.5’ and Pb2Fe2O5

Partial phase diagram of Pb–Fe–O system has been established by phase equilibration studies over a wide temperature range coupled with high temperature solid electrolyte based emf cells. Ternary oxides are found to coexist with liquid lead only at temperatures above 900 K. At temperatures below 900 K, iron oxides coexist with liquid lead.Standard molar Gibbs energy of formation of ternary oxides ‘PbFe5O8.5’ and Pb2Fe2O5 were determined by measuring equilibrium oxygen partial pressures over relevant phase fields using emf cells and are given by the following expressions: ΔfGmo‘PbFe5O8.5’±1.0(kJmol-1)=-2208.1+0.6677(T/K)(917⩽T/K⩽1117)ΔfGmoPb2Fe2O5±0.8(kJmol-1)=-1178.4+0.3724(T/K)(1050⩽T/K⩽1131).