Solubility and diffusion of cobalt in alumina

Abstract

Diffusion of Co in alumina was carried out between 1403 and 1873 K in air with or without the presence of a spinel phase. The penetration profiles were obtained by the secondary-ion mass spectrometry (SIMS) technique and at the highest temperature by tracer measurement. The Arrhenius relation D(1403-1873K) = 6.2 × 10⁹exp (-333kJmol^minus;1) m² s^minus;1/RT describes the temperature dependence of the diffusion coefficient obtained by both methods. The formation of the spinel phase CoAl₂O₄ was observed when the experiments were carried out at temperatures lower than 1673 K. The formation of the spinel phase offered a good opportunity to calibrate the SIMS signal and the solubility of Co in alumina was found to be about (2–4) × 10^minus;3 metal atom fraction in the temperature range 1403–1623 K.