High-Temperature Oxidation of alpha Nickel-Silicon. 1: Reaction Kinetics; Thermogravimetry

摘要

The reaction kinetics of the high-temperature oxidation of alpha binary nickel-silicon alloys and the thermocouple alloy Nisil was studied. Rates of oxidation at temperatures in the range from 850 to 1250 C were measured by thermogravimetric methods under both isothermal and cyclic temperature conditions for periods of up to 164 h. Silicon in the alloys provides enhanced protection against high-temperature oxidation. Of the alloys studied, Nisil - a nickel-silicon-magnesium alloy - exhibited the greatest resistance to high-temperature oxidation. The agreement of the kinetic data with a simple parabolic rate law was assessed. For the low-silicon alloy Ni-0.9Si, the parabolic rate constant showed little variation throughout 164 h oxidation tests, whereas the rate constants for higher-silicon alloys generally decreased with time. This behavior is discussed in terms of the diffusion of reactants through the growing oxide scales, whose composition and mechanical integrity may vary with time. An activation energy of 175 + or - 21 kJ per mol was derived for the high-temperature oxidation of Ni-0.9Si.