Control of Oxide Particle Size by Oxygen Pressure for Internally Oxidized Silver Base Alloys

Abstract

Silver base alloys containing 11.3Cd, 11.4Cd-0.24Ni, 7.62Zn-0.45Te, 6.13Zn-0.97Sn-0.48Te, and 6.05Zn-1.03Sn-0.99In-0.47Te(at%) were internally oxidized at 1023, 1073 and 1123 K under continuously changed oxygen pressures and in the air. The control of oxide particle size by oxygen pressure has been investigated.
(1) In order to have the same size of dispersed oxide particles in all the regions of internal oxidation layers, the oxygen pressure P should be controlled with time t as P=K⁴P_a²t²⁄4X_a⁴, where K is the velocity constant of internal oxidation at a constant oxygen pressure P_a and X_a is the distance from the surface. The value of K depends on the composition of specimens and the temperature of internal oxidation. (2) The activation energy for internal oxidation is smaller than 92 kJ/mol estimated from the diffusion of oxygen in silver by Eichenauer and Müller. (3) The diffusivity of oxygen in internally oxidized layers and its activation energy are evaluated as being smaller than those in silver.