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

Customized porous Al 2 O 3 -ZrO 2 -mullite composites were designed and prepared by reaction sintering of zircon (ZrSiO 4 ) and alumina (Al 2 O 3 ) 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 ZrSiO 4 and Al 2 O 3 were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDS). The results indicate that ZrSiO 4 and Al 2 O 3 react and form ZrO 2 and mullite . Sintering temperature has an important effect on the reaction process. At 1400 °C, Al 2 O 3 reacts directly with SiO 2 of ZrSiO 4 to form mullite and ZrO 2 , which reduces the decomposition temperature of ZrSiO 4 and promotes the decomposition of ZrSiO 4 . However, at 1600 °C, ZrSiO 4 first decomposes to form SiO 2 and ZrO 2 , 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 ZrO 2 . Therefore, increasing the proportion of ZrSiO 4 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 ZrSiO 4 to Al 2 O 3 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.