High-Pressure Oxidation of Metals, Nickel in Oxygen

Abstract

The oxidation of Mond nickel was studied between 1000 ~ and 1200~ at oxygen pressures from 6.5 x 10 -3 to 20.4 arm. The oxidation rate was controlled by diffusion through the oxide and had a gross activation energy of 50 _ 4 kcal/mole. Least squares straight line fitting over the entire pressure range indicated the rate was proportional to Po21/5. However, the rates above 1 arm appeared insensitive to pressure. On this basis, the measured rates below 1 atm more closely follow the PO21/4 dependence expected from electrical conductivity studies in NiO. The oxide oriented in a preferred manner with 100 planes parallel to the polycrystalline nickel base.In the early work of Wagner and Griinewald (1) on the oxidation of nickel, the observed parabolic rate was derived on the basis of diffusion of nickel ions by a vacancy exchange mechanism through a uniform layer of NiO. Below 1000~ the parabolic relation has been observed by other investigators (2-4). The role of cation vacancies has been confirmed by electrical and thermoelectric studies on NiO (5-7), which is a p-type semiconductor, and by the close correspondence of the activation energies for oxidation and for diffusion of radioactive nickel in NiO (8,9). Nevertheless, there are some anomalies. Gulbransen and Andrew (10) have observed that at 900~ and higher, parabolic rate law plots of the data show increasing values of the rate constant with time. The dissociation of two electron holes from each cation vacancy and a resulting oxidation rate and electrical conductivity dependence on Poe 1/6 which was assumed by Wagner and Griinewald are not clearly supported by electrical conductivity measurements or oxidation rate measurements.

On the oxidation mechanism of pure tungsten in the temperature range 600–800°C

“…This coincides with some studies reported in the literature [14,15,18 21,26]. Nevertheless, other authors have described the formation of a protective dark layer [15,20,21,26]. Discrepancies could result from the different expo sure times used in these works.…”

Point defect diagrams for pure and doped nickel oxide $$ {\hbox{N}}{{\hbox{i}}_{{1} - \delta }}{\hbox{O}} $$ in the temperature range of 1,173–1,673 K (II)

“…The studies on the chemical diffusion [19][20][21][29][30][31][32][33][34][35][36][37][38][39][40][41] and of the self diffusion of nickel [19,[41][42][43][44][45][46], performed mainly at higher oxygen pressures, indicate that the matter transport in Ni 1Àd O occurs generally via double ionized nickel vacancies. A similar conclusion could be obtained from the relation between the concentration of defects, the diffusion coefficients, and the parabolic rate constants of nickel oxidation [21,[47][48][49][50][51].…”

The effect of elevated air pressure on the oxidation properties of the nickel-based superalloy, RR1000, at 650°C with different surface modifications

“…The effects of exposures of chromia forming alloys to low pressures have been reported in the literature [10][11][12][13], but very little information is available on the effect of high pressure. Work by Baur, Bartlett [14] on pure nickel found that the oxidation rate of nickel is insensitive to pressure above atmospheric pressure. However, on advanced alloys under CO2 atmospheres Pint, Brese [15] found a complex dependence on pressure in that alloys of similar composition to RR1000 showed a decrease in the gravimetric oxidation rate at 125 bar pressure compared with 1 bar pressure.…”