Reaction mechanisms and properties of in situ porous Al2O3-ZrO2-mullite composites

Abstract

Customized porous Al2O3-ZrO2-mullite composites were designed and prepared by reaction sintering of zircon (ZrSiO4) and alumina (Al2O3) at sintering temperatures from 1400 to 1600 °C for 3 h. The mechanical properties, microstructural evolution, and reaction mechanisms of the composites were investigated. The reactions between ZrSiO4 and Al2O3 were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDS). The results indicate that ZrSiO4 and Al2O3 react and form ZrO2 and mullite. Sintering temperature has an important effect on the reaction process. At 1400 °C, Al2O3 reacts directly with SiO2 of ZrSiO4 to form mullite and ZrO2, which reduces the decomposition temperature of ZrSiO4 and promotes the decomposition of ZrSiO4. However, at 1600 °C, ZrSiO4 first decomposes to form SiO2 and ZrO2, and then generates mullite by the diffusion of Si. The migration of Si is the key factor for the formation of mullite. The thermal shock resistance of the composites can be significantly improved by phase transformation toughening of in-situ ZrO2. Therefore, increasing the proportion of ZrSiO4 can significantly improve the mechanical properties of sample. The residual ratio of the flexural strength after thermal shock exceeded 90%, when the mass ratio of ZrSiO4 to Al2O3 was 3:1. Besides, the addition of polymethyl methacrylate could improve the porosity of materials and has a direct effect on the thermal conductivity of composites.