A Model for Transitions in Oxidation Regimes of ZrB2

摘要: A mechanistic model that interprets the transition in oxidation behavior of zirconium diboride as temperature is varied from 600°C to 2500°C presented. Available thermodynamic data and literature for vapor pressures, oxygen permeability boria, viscosity boria were used evaluate model. Three regimes temperatures between them identified. In intermediate regime, viz., 1000°C 1800°C, good correspondence was obtained theory experiments weight gain, recession, scale thickness functions partial pressure. this rate-limiting step diffusion dissolved through a film liquid capillaries at base product. At lower temperatures, an external forms, but it not found contribute significantly resistance. Comparison with on recession very good, gain predicted be higher than experimentally observed unless flow viscous included. lost by evaporation, rate limited molecular nearly columnar blocks oxide MO2.; regime soon followed rapid acceleration due vaporization MO2 itself.