The effect of powders homogenisation conditions on the synthesis of yttrium aluminium garnet (YAG) by a solid-state reaction

The work presents results of research on the influence of the state of homogenisation of reagent powders i.e. aluminium oxide and yttrium oxide on the synthesis of yttrium aluminium garnet. Fine powders of commercial aluminium oxide and yttrium oxide were mixed in the same manner in a laboratory ball mill but under four different conditions. Three batches of powders were prepared in water of various pH values, selected on the basis of the zeta potential measurements, and one batch was prepared in propanol. They were consolidated by filter pressing and then sintered in air at a temperature from 900 °C to 1700 °C for 1 h, with heating rate of 5 °C/min. Samples were subjected to dilatometric studies, phase composition determination, measurement of apparent density and pore size distribution, as well as a microscopic examination. Mixing environment affected, to a given extent, almost all the features of green, and partially sintered materials as well as course changes of linear dimensions. As a result, the relative densities of samples sintered at a maximum temperature ranged from 58.31% to 98.25%. The highest density was achieved for the material originating from the suspension having a pH of 9.5, in which heterocoagulation occurred.