Transparent Solid Solution Magnesium Aluminate Spinel Polycrystalline Ceramic with the Alumina‐Rich Composition <scp> <scp>MgO</scp> </scp> ·1.2 <scp> <scp> Al ₂ O ₃ </scp> </scp>

Abstract

Solid solution magnesium aluminate spinel with the alumina‐rich composition MgO ·1.2 Al 2 O 3 has been prepared as a transparent polycrystalline ceramic with average in‐line transmission at 550 nm of 84.8 ± 2.7% and &gt;82% throughout the visible spectrum. Starting powders are prepared from mixtures of high purity Mg(OH) 2 and γ‐Al 2 O 3 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 · Al 2 O 3 ) were prepared with the same procedure and exhibited comparable values for transmission and physical properties.