Phase Stability of Iron Oxides on Palladium-Iron Alloy at Elevated Temperatures and Its Application to High Temperature Oxidation

Phase stability of iron-oxides as a function of alloy composition in Pd-Fe-O system has been examined by emf measurement with solid electrolyte of CaO-stabilized zirconia at the temperature ranging from 973 to 1123 K. Phase boundary between the alloy and iron-oxide was determined with six alloys in which Fe-composition is ranging from 1 to 64 at%. The boundary composition of wustite lies in between 34 at% Fe and 54 at% Fe and hematite was expected to be formed at the alloy composition less than 1 at% Fe. Thickness of iron oxide was estimated from the amount of consumed Fe in the alloy, which is given by the difference of initial and final composition at the temperature and oxygen partial pressure. Estimated thickness of iron oxide was in good agreement of that obtained from high temperature oxidation of Pd-Fe alloy. Emf measurement gives useful information to obtain single-phase iron-oxide with the expected thickness on Pd-Fe alloy by high temperature oxidation.