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The condensed-state reaction between single crystals of A1203 and MgO was conducted in air at 156OOC. Spinel formed as two product layers which were shown to agree with the proposed mechanism. The crystallographic orientation of the parent crystals had no effect on the rate of spinel growth. The orientation of the spinel grown from sapphire was the same as that found by other investigators for isomorphic crystals. The orientation of spinel grown from periclase was largely dependent on the transport mechanism across the periclase-spinel interface.

The description of the elastic behavior of composite materials by mathematical expressions presently in the literature is restricted by the microstructural models on which they were based. An extension has been made to one of these expressions in which the shape of the included phase is considered as well as the moduli of the individual phases. The results allow a more general application of the theoretical expressions to composite materials in which the included phase is contained at low concentrations.

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