Kinetics of the Growth of Spinel on Alumina Using Rutherford Backscattering Spectroscopy

The kinetics of the initial stage of the formation of a nickel aluminate spinel on the surface of alumina substrates has been studied. The NiO layer was formed by evaporating a thin film Ni onto the surface of single‐crystal alumina substrates and oxidizing the specimens in air at 700°C. This method gave a thin layer of NiO film that was uniform in thickness on top of the alumina substrates. The alumina surfaces studied include (0001), [1120], [1102], and [1100]. After the initial oxidation, the samples were annealed in air at 1020°C. The interaction of the thin‐film and the single‐crystal substrates was examined using Rutherford back‐scattering spectroscopy. The crystallography of the alumina substrates was found to influence greatly the kinetics of the spinel formation. For example, the rate of the spinel formation reaction is fastest for the lsqb;1102rsqb; and lsqb;1100rsqb; orientations and slowest for the (0001) orientation. The roughness of the surface of the alumina substrate has also been shown to influence directly the rate of the spinel formation. The presence of surface scratches accelerated the spinel formation. Copyright © 1987, Wiley Blackwell. All rights reserved