The internal oxidation of Mg in Ag-1.12at%Mg was studied at 450 to 825C under various O partial pressures. Measurements of O weight gain and oxidation-front velocity showed that, at 450C, the rate of O penetration into the alloy was some 400 times slower than O diffusion in pure Ag. At 825C, this factor decreased until it was some 60 times slower. A comparison of these results with calculations based upon a model of internal oxidation indicated that the O diffusivity in pure Ag was almost identical to O diffusivity in the alloy. The decreased O penetration rate in the alloy was attributed to O uptake by the Mg species, which were able to capture super-stoichiometric amounts of O. The O fixation proceeded according to the predictions of the model. The oxidation rate increased with partial pressure, due to an increased O activity gradient. However, below about 600C and at 0.08atm partial pressure, O fixation progressed at a rate which was notably faster than that predicted by the model. This was attributed to a change in the Mg-O fixation stoichiometry; such that smaller amounts of O were absorbed and permitted the oxidation front to proceed more rapidly.

Oxygen Diffusion and Internal Oxidation of Mg in Ag/1.12at%Mg. B.C.Prorok, K.C.Goretta, J.H.Park, U.Balachandran, M.J.McNallan: Physica C, 2002, 370[1], 31-8