Partial phase diagram of Bi-Fe-O system and the standard molar Gibbs energy of formation of Bi2Fe4O9

Abstract

Partial phase diagram of Bi-Fe-O system has been established by phase equilibration studies over a wide temperature range. On increasing the dissolved oxygen concentration in liquid bismuth in equilibrium with iron metal, iron oxides would precipitate first as the coexisting phases. With further increase in oxygen concentration, Bi2Fe4O9 would appear as the first ternary compound stable in liquid bismuth. Standard molar Gibbs energy of formation of Bi2Fe4O9 has been determined over a wide temperature range by measuring the equilibrium oxygen partial pressure in the Bi-Bi2Fe4O9-Fe2O3 phase field using solid electrolyte based emf cell and is given by the following expression:ΔfGmο < Bi2Fe4O9> ± 0.6 kJ = −2196.2 + 0.7679 (T/K) (T: 799–1023 K).