Abstract
High‐purity polycrystalline MgO and Al2O3 were thermally grooved at 1500° and 1600°C. Accurate techniques were developed for following the growth of a single groove. For high‐purity samples growth kinetics were essentially similar to those reported in the literature but were determined to be controlled by volume diffusion. Specimens for thermal grooving were prepared from Al2O3 to which transition metal oxides (Fe2O39, MnO, and TiO2), which are known to accelerate shrinkage and sintering of Al2O3 powder compacts, had been added; the rate of groove growth was increased remarkably by minor amounts of these additives. Control of partial pressure indicated that Fe2+ and Ti4+ are the species active in promoting groove growth. Substantial evidence was found for volume diffusion as the mechanism controlling groove formation.
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