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

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 Al 2 (WO 4 ) 3 columnar particles which were formed at about 900 °C, then the decomposition of Al 2 (WO 4 ) 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.