Preparation and Characteristics of ZrO2/ZrW2O8 Composites with Low Thermal Expansion

The ZrO2/ZrW2O8 ceramic matrix composites have been prepared by the two different processes: (1) ZrO2 and ZrW2O8 powders were mixed directly as raw material, then compacted by cold isostatic pressing under 200MPa, and finally, the ceramic matrix composites with low thermal expansion can be prepared by use of heat-pressing sintering or atmospheric sintering at temperature 1215oC. (2) ZrO2 (with excess mass) and WO3 powers were mixed as raw material, then compacted by cold isostatic pressing under 200MPa, and finally, the ZrO2/ZrW2O8 ceramic matrix composites can be made by use of heat-pressing sintering or atmospheric sintering at temperature 1215 oC after ZrW2O8 were synthesized by in-situ reaction of ZrO2 and WO3 powders at the same temperature. The microstructure, density, ZrW2O8 decomposition degree and the thermal expansion coefficient were compared among the sintered samples fabricated by the above two different methods, and affected by the different process parameters. The results show that the ceramic matrix composites with low thermal expansion are really composed of ZrO2, ZrW2O8 and WO3, and their relative densities are all more than 95%. Compared with the composites prepared by in-situ reaction, the densities, ZrW2O8 decomposition degree and the thermal expansion coefficient of the composites made by direct mixing are higher, less and smaller, respectively.