The influence of ageing on consolidation and sinterability of a sub-micron alumina powder

A commercial sub-micron alumina powder was used for investigation of the influence of exposure to atmospheric humidity on powder characteristics, consolidation behaviour, densification and final microstructure of alumina ceramics. A significant uptake of atmospheric water by inadequate storage confirmed by thermal analysis, XPS, and FTIR, resulted in decreased sinterability of the powder, although no significant influence on the mean size of alumina grains was observed. In addition, the effect of low temperature heat treatment (drying at 120 °C and calcination at 700 °C) was also studied. The sinterability of pre-dried powder increased if a wet consolidation method (pressure filtration) was used, but a negative effect of pre-drying was observed in case of dry forming (axial pressing). The calcination decreased the ability of the powder to adsorb water. The presence of aggregates formed by calcination markedly decreased the green and sintered densities in compacts consolidated by axial pressing.