The Effect of Varied Amounts of LiF Sintering Aid on the Transparency of Alumina Rich Spinel Ceramic with the Composition MgO · 1.5 Al2O3

Magnesium aluminate spinel with the alumina rich composition MgO · 1.5 Al2O3 has been prepared as a transparent polycrystalline ceramic with average in-line transmission at 550 nm of 83.3 ± 0.9% and >80% throughout the visible spectrum. This finding significantly increases the compositional range over which polycrystalline magnesium aluminates can be prepared as fully dense ceramics with high transparency to visible light. Starting powders are prepared from combinations of high purity Mg(OH)2 and γ-Al2O3 thoroughly mixed in an aqueous slurry, and the solids are collected, dried, calcined, mixed with LiF 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. The crucial parameter for forming highly transparent MgO · 1.5 Al2O3 ceramic from this procedure is to hold the amount of LiF to 0.25 wt%.