Microstructure and Room‐Temperature Mechanical Properties of Hot‐Pressed Magnesium Aluminate as Described by Quadratic Multivariable Analysis

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Abstract
Polycrystalline spinel (MgA12O4), hot‐pressed in graphite dies, yielded densities ranging from ∼64 to ≊100% of theoretical. Average grain size of compacts varied from 4 to 125μ depending on hot‐pressing conditions. Room‐temperature mechanical properties also varied widely; average strengths for the 15 experimental combinations ranged from 3500 to 34,000 psi in bending and from 21,700 to 389,000 psi in compression, and Young's modulus ranged from 0.54 X lo7 to 3.5 X 107 psi. Variations in bulk density, average grain size, room‐temperature transverse and compressive strengths, and Young's modulus of elasticity were separately expressed as multiple quadratic regressions in terms of 1/T (temperature), In t (time), and P(pressure) over the hot‐pressing range 1227’to 1750°C, 5 to 320 min, and 1000 to 3000 psi. From these regressions, empirical equations expressing mechanical properties in terms of regression solutions of density and grain size were derived which statistically indicate a principal dependence on density and only a minor grain size dependence.

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