Abstract
Solid solution magnesium aluminate spinel with the alumina‐rich composition MgO·1.2 Al2O3 has been prepared as a transparent polycrystalline ceramic with average in‐line transmission at 550 nm of 84.8 ± 2.7% and >82% throughout the visible spectrum. Starting powders are prepared from mixtures of high purity Mg(OH)2 and γ‐Al2O3 thoroughly mixed in an aqueous slurry. Water is removed by rotary evaporation. The solids are collected, dried, calcined, mixed with LiF (as a sintering aid), and sieved. The powders are sintered into dense ceramics by hot pressing at 1600°C under vacuum and 20 MPa uniaxial load followed by hot isostatic pressing at 1850°C under 200 MPa Ar. Final grain sizes ranged between 300 and 1000 μm. Samples exhibited flexural strength of 176.8 ± 46.2 MPa; hardness of 12.3 ± 0.2 GPa; and elastic modulus of 292.9 ± 7.5 GPa. Control samples of stoichiometric magnesium aluminate spinel (MgO·Al2O3) were prepared with the same procedure and exhibited comparable values for transmission and physical properties.
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