Structure-property relationships of mullite-SiC-Al2O3–ZrO2 composites developed during carbothermal reduction of aluminosilicate minerals

Abstract

Evolution of SiC and ZrO2 in the matrix of Al2O3 or mullite have been reported to enhance a higher toughness, good thermal shock resistance (lowering thermal expansion and improving thermal conductivity) and improved creep resistance of composite materials. In this study, the structure-property relationships of mullite-Al2O3 matrix composites have been investigated in conjunction with the evolution of reinforcing phases such as SiC–ZrO2 by an economical heat treatment process called carbothermal reduction of inorganic minerals (Kaolinite, Andalusite, Zircon). The influence of starting materials in relation with the variation in molar ratio of C/SiO2 on the phase composition, microstructures, physical and mechanical properties have been studied. Light microscopy has been supplemented with scanning electron microscopy, XRD analysis, differential thermal and thermal gravity analysis to follow the structure-property relationships. The experimental results show that with increasing of C/SiO2 ratio in starting materials, very fine SiC whiskers have been formed in the microstructures. Moreover, the densification and strength are considerable higher for ZrO2 + SiC containing composites in comparison to that of only SiC added ones. Furthermore, it has been found that the appropriate ratio of C/SiO2 with the associated firing temperature to develop a higher densification and SiC crystallization have been related to the 3.5, 1550 °C for kaolinite, 3.5, 1450 °C for zircon and 5.5, 1600 °C for andalusite containing composite samples, respectively.