Fabrication and properties of mullite thermal insulation materials with in-situ synthesized mullite hollow whiskers

Abstract In this study, mullite thermal insulation materials with in-situ synthesized mullite hollow whiskers were prepared by a solid-state reaction method using industrial alumina and silica as raw materials and tungsten-containing compounds as catalysts. The phase transition, microstructures, and effects of in-situ formed hollow whiskers on morphologies and properties of mullite thermal insulation materials were investigated by TG-DTA, XRD, SEM, TEM, thermal conductivity and compressive strength tests. The formation mechanism of mullite hollow whiskers was also studied. The results show that Al–Si–O agglomerations adsorbed on the surface of Al2(WO4)3 columnar particles which were formed at about 900 °C, then the decomposition of Al2(WO4)3 columnar particles and mullitization of Al–Si–O agglomerations led to the formation of mullite hollow whiskers at about 1200 °C. The mullite thermal insulation materials (prepared at 1500 °C) with in-situ formed hollow whiskers exhibit a low thermal conductivity of 0.329 W/(m∙K) to 0.396 W/(m∙K) and a sufficient cold compressive strength of 5.22 MPa. The physical and mechanical properties were controlled by the width and aspect ratio of mullite hollow whiskers. The research of this work provides a new insight into the development of mullite thermal insulation materials used at high temperatures.