Characterisation of Mullite – ZrO2 Ceramics Prepared by Various Methods

Mullite - ZrO2 ceramics was sintered from variously prepared powder mixtures - different time milled and hydrothermal synthesized. As sintering aid 8 wt. % illite clay for one part of starting mixtures was added. Two sintering routes was applied for consolidation of powder – spark plasma sintering (SPS) technique and conventional sintering reactions in air. It is shown that the structure of sintered samples for SPS was completed at at 1250C and by conventional - at 1300C. The developed microstructure both conventional and SPS can be characterized by mullite matrix with evenly distributed ZrO2 grains. For conventually prepared and sintered samples corundum and ZrO2 tetragonal grains are observed, but for SPS dominates ZrO2 cubic The microstructure of ceramic samples from hydrothermal synthesized powders and consolidated by SPS is amorphous like with xenomorfic crystals of mullite and inclusions of grains of ZrO2 cubic. It is stated that additive of illite clay promotes the densification and at conventional sintering prevents the transformation of ZrO2 tetragonal to ZrO2 monoclinic by cooling of samples, but for SPS promotes formation of ZrO2 cubic. Sintered samples are characterized by pressure strength by value for SPS sintered samples processed from conventionally milled powder mixture