Forming Mullite-Ceramics Reinforced With ZrO2-t Starting From Mullite-ZrO2-t and Kyanite-Al2O3-ZrO2-t Mixtures

Abstract

Mullite-ceramics reinforced with 8 and 10 vol. % YZT were prepared starting from two different powder mixtures. The first one was a mixture of pure mullite and YZT, and the other was a mixture of kyanite, alumina and YZT. The production of ceramics consisted of the pressureless-sintering of mixtures powders which were thoroughly mixed under high energy ball-milling. During sintering, kyanite and alumina of the second mixture react between them to form mullite. Measurements of density, microhardness and KIC were carry out in all produced materials, from it was obtained that samples produced with pure mullite reach major densities, microhardness and toughness in comparison with the values displayed for samples prepared with kyanite and alumina. The reason of this has its explanation since during sintering of the kyanite and alumina samples; there is a competition between two phenomena; the reaction to form mullite and the sintering of the product. As the reaction occurs at low temperature and has high energy consumption, the activation energy necessary for diffusion during sintering is not reached; therefore this phenomenon is the controlling agent during the processing.