Filter pressing and sintering of fine spinel and yttrium oxide powders

Magnesium-aluminium spinel (MgAl₂O₄) and yttrium oxide (Y₂O₃, yttria) materials have regular crystal structure so they can be transparent for infrared and visible light. The materials can be applied as IR windows or domes or as hosts in solid state lasers. Manufacturing and processing of such materials has been known for a long time, but there are still some issues such as application of fine i.e. submicron and nanometric powders and obtaining of fine-grained microstructure. Smaller grain size should improve mechanical parameters of such materials. The work presents results of investigations on shaping of fine spinel and yttrium oxide powders using filter pressing method of their aqueous suspensions followed by cold isostatic pressing of green samples. Homogeneity of microstructure of such materials was tested by mercury porosimetry. The samples were sintered in air and vacuum at various temperatures. The materials with the highest densities were subjected to such studies as microstructure observation using SEM microscopy, Vickers hardness measurements, and IR transmition measurements. Results of the investigations showed that the most important factor affecting preparation of transparent and fine-grained materials was agglomeration state of the used fine powders. (author)