Zirconia transformation in multi-phases ceramic composites

Low cost composite ceramics based on zircon-mullite-zirconia-alumina phases were prepared by reaction sintering of boehmite (AlOOH) and zircon (ZrSiO4) powders. Boehmite to zircon weight ratios of the starting powders were varied (10 to 90 wt. %). The green compacts were made by uniaxial pressing at 7 MPa followed by cold isostatic pressing at 250 MPa. A reactive sintering in air of these compacts was made at different temperatures between 1400 and 1600 degrees C during 2 hours. A quantitative evaluation of the present phases was based on XRD. Dilatometric tests on the reaction-sintered composites were carried out in order to study the zirconia phase's transformations and their thermal expansion coefficient (alpha). In addition, the effects of both boehmite/zircon ratios and sintering conditions on the mechanical properties (Hardness Hv, Elastic modulus E and fracture toughness K-IC) of the obtained composites were characterized by Vickers indentation.