Isothermal oxidation of nickel in the thin film region at several oxygen pressures
Hanson, Wayne Edward
Akers, W. W.
Master of Science
An apparatus for the study of the oxidation of nickel in pure oxygen at temperatures from 400°C to 1050°C and pressures from 0.10 mm Hg to 20.0 cm Hg was designed and constructed. The problem of stopping convection current interference was solved and continuous readings were taken as the nickel was oxidized. Runs were made at 0.130 mm Hg, 1.0 mm Hg, 2.0 cm Hg, and 10.6 cm Hg oxygen pressure at 719°C. The results were analyzed in terms of oxygen pressure and oxide thickness. The oxidation growth law was found to change from a logarithmic law to a quartic law at the two lower pressures when the oxide thickness reached 90-100 ug/cm2. At the two higher pressures, the mechanism changed from a logarithmic to a near parabolic at 90 ug/cm2 and finally to the absolute parabolic at about 300 ug/cm2. In the logarithmic region the rate of oxidation varied with the oxygen pressure to the 0.27 power up to 2.0 cm Hg. At pressures above 2.0 cm Hg the rate seemed to be independent of the oxygen pressure. The theoretical model of Grimley and Trapnell, which assumes cation diffusion to be the rate controlling step, was used to Interpret the experimental data.