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%) have internally been oxidized at 1023, 1073 and 1123 K under continuously changing pressure of oxygen and in air. The size of oxide particles has been controlled by oxygen pressure.
(1) In order to disperse the same size of oxide particles in all internal oxidation layers, the oxygen pressure P should be controlled with time t as P=K4Pa2t2⁄4Xa4, where K is the velocity constant of internal oxidation at a constant oxygen pressure Pa, and Xa 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 energies for internal oxidation of the alloys are smaller than 92 kJ/mol estimated from the diffusion of oxygen in silver. (3) The diffusivity of oxygen in internal oxidation layers and its activation energy are evaluated to be smaller than those in silver.
