Transparent spinel by reactive sintering of different alumina modifications with MgO

Transparent spinel MgAl2O4 was prepared by reactive sintering of - Al2O3, - Al2O3 or - Al2O3 mixed with MgO by ball milling in ethyl alcohol. After drying the powders were pressed, sintered in air and hot isostatically pressed (HiP) from 1440°C to 1650°C. It turned out that the transparency depends both on the used modification of Al2O3 and on the HiP-Regime. In the visible range the highest real in-line transmission (85% at 4 mm thickness) was achieved with corundum (-Al2O3) and MgO after sintering at 1520°C and with a HiP-temperature of 1750°C.