Published online by Cambridge University Press: 28 February 2011
Controlled oxygen diffusion bonding experiments have shown that the formation of nickel aluminate spinel by solid state reaction between metallic Ni and α-A12O3 requires a certain oxygen activity, which is less than that of the Ni-NiO equilibrium. Under high vacuum bonding conditions the source of the oxygen required for spinel interphase formation was found to be oxygen initially dissolved in solution in the Ni. Equilibrium thermodynamic calculations confirmed the threshold oxygen activity dependence of spinel formation at the Ni/A12O3 interface, indicating ∼200 at. ppm oxygen is required in Ni before spinel can form at typical bonding temperatures. The predicted spinel layer thickness based on the calculated reaction equilibrium agrees extremely well with the measured thickness, further supporting the analysis.