Creep and oxygen diffusion in magnetite

The creep rate of polycrystalline Fe₃O₄ has been measured as a fonction of stress and oxygen partial pressure in the temperature range 480–1100°C. A regime of power law creep is found at high stress, with a stress exponent of ≈- 3.1 and an activation energy of 264 kJ/mol. A regime of diffusional flow is found at lower stresses and is interpreted as Nabarro-Herring creep. The data for the two regimes are combined to deduce an oxygen diffusion coefficient of ≈-10⁻⁵ exp(−264 kJ/mol/RT) m²s⁻¹, with oxygen vacancies suggested as the mobile species.