Solubility and diffusion of cobalt in alumina

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(1403-1873 K) = 6.2 x 10(9) exp(-333 kJ mol(1)/RT) m(2) s(1) 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) x 10(3) metal atom fraction in the temperature range 1403-1623 K.