Progress in fabrication and characterization of mullite whiskers

Mullite has an orthorhombic crystal structure, with various advantages, such as high mechanical strength, and stable chemical and physical properties. Especially, mullite whiskers have been widely acknowledged to be potential candidates as reinforcing elements in the fabrication of ceramic-matrix composites. Various strategies have been developed to synthesize mullite whiskers, such as catalytic methods, liquid-phase reaction, molten salt reaction, solid-state reaction and high-energy ball milling process. In different synthesis methods, the underlying mechanisms governing the anisotropic grain growth of mullite grains vary. This paper aims to offer an overview on the progress in fabrication of mullite whiskers with different methods, and the perspectives on these special materials are briefly discussed.

Preparation of lightweight corundum-mullite thermal insulation materials by microwave sintering

Lightweight corundum-mullite thermal insulation materials were successfully prepared by microwave sintering at low temperature. The effects of sintering temperatures, PMMA microspheres and SiC particles on structure and properties of as-prepared corundum-mullite materials were investigated. The SiC became a hot spot under the action of microwave field, and these local high temperature areas promoted the formation and growth of mullite whiskers. The PMMA microspheres were burn out, leaving pores which could provide space for the growth of mullite whiskers. It was found that the optimal sintering temperature was 1400?C and corresponding porosity, density and bending strength of the samples were 71.2%, 0.99 g/cm3 and 3.85MPa, respectively. The thermal conductivity was from 0.201 to 0.313W/(m?K) between 30?C and 950?C. This work demonstrated that lightweight corundum-mullite materials with low density, high porosity, good thermal shock resistance and excellent thermal insulation properties could be successfully prepared by microwave sintering.