The Tracer Diffusivity of Oxygen in Wustite and Cobaltous Oxide

Abstract

The tracer diffusivity of oxygen in Fe1−xO and CoO has been determined from measurements of the depth profile of 18O by secondary ion mass spectrometry. The tracer diffusivity in Fe1−xO was evaluated, by taking into account the surface reaction of oxygen, as D⁄m2·s−1=(1.17±0.78)×10−1exp[−(375±23kJ⁄mol)⁄RT] between 1093 and 1455 K for pco2⁄pco=1.00. The tracer diffusivity in Fe1−xO increased with increasing x. The surface reaction rate constant was expressed as K⁄m·s−1=(48.3±27.5)exp[−(293±14kJ⁄mol)⁄RT]. The tracer diffusivity in CoO was estimated, by taking account of evaporation of CoO, as D⁄m2·s−1=(8.76±5.67)×10−8exp[−(287±18kJ⁄mol)⁄RT] between 1273 and 1573 K for po2=21.3 kPa (0.21 atm). The evaporation rate was expressed as V⁄m·s−1=(2.65±1.59)exp[−(167±16kJ⁄mol)⁄RT].