Zirconia-mullite composites consolidated by spark plasma reaction sintering from zircon and alumina

Mullite-ZrO2 composites have been fabricated by attrition milling a powder mixture of zircon, alumina, and aluminum metal with MgO or TiO2 as sintering additives, heating at 1100 degrees C to oxidize the aluminum metal, and consolidation by spark plasma sintering (SPS). The influence of the SPS temperature on the formation of mullite, and the density and the mechanical properties of the resulting composites have been studied. For the mullite-zirconia composites without sintering additives, the mullite formation was accomplished at 1540 degrees C. In contrast, for the composites having MgO and TiO2, the formation temperature dropped to 1460 degrees C. The composites without sintering additives were almost fully dense (99.9% relative density) and retained a larger amount of tetragonal zirconia. Those materials attained the best mechanical properties (E = 214 GPa and K-IC = 6 MPa - m(1/2)). To highlight the advantages of using the SPS technique, the obtained results have been compared with the characteristics of a mullite-zirconia composite prepared by the conventional reaction-sintering process.