Accession Number : ADA140866

Title :   High-Temperature Oxidation of Alpha Nickel-Silicon. I. Reaction Kinetics - Thermogravimetry,


Personal Author(s) : Palmer,L D

PDF Url : ADA140866

Report Date : Feb 1984

Pagination or Media Count : 43

Abstract : This report presents the results of a study of the reaction kinetics of the high-temperature oxidation of alpha binary nickel-silicon alloys and the thermocouple alloy Nisil. Rates of oxidation at temperatures in the range from 850 to 1250 deg 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 behaviour 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 mol-1 was derived for the high temperature oxidation of Ni-0.9Si.

Descriptors :   *Nickel alloys, *Silicon alloys, *Oxidation, *Reaction kinetics, High temperature, Thermogravimetric analysis, Thermocouples, Resistance, Mechanical properties, Diffusion, Foreign technology, Australia

Subject Categories : Properties of Metals and Alloys

Distribution Statement : APPROVED FOR PUBLIC RELEASE