Phase Diagram of a Nickel‐Zinc Ferrite of Composition Ni0.685Zn0.177Fe2.138O4+γ

Abstract
The oxygen content of Ni0.685Zn0.177Fe2.138O4+γ was determined gravimetrically at atmospheric pressure in varying Po2, 3.5 × 10−4 to 1.0 atm at 600° to 1450°C. The phase boundary associated with the precipitation of α‐Fe2O3 was determined from the change in slope of γ vs T plots observed on heating. Metastability is particularly evident for curves observed on cooling. Isacompositional lines (0.002 < γ < 0.045) are shown on a plot of log PO2 vs 1/T. An enthalpy of ‐21.6 kcal/mol is calculated for the oxidation of Fe2+.