Preparation And Properties Of High Temperature Structural Materials Based On The AlF₃-SiO₂System Gas-phase Reaction

High-temperature structural materials with light weight and high porosity wereextensively concerned in the high-temperature application field. Mullite was alwaysused as high temperature structural material. In this work, mullite fibers/whiskerscomposite structural material and mullite inter-locked structural material wereprepared based on the AlF3-SiO2system gas-phase reaction. The structure formationmechanism and the related characteristics/properties of the materials were analyzed inthis paper.Mullite inter-locked structural material was prepared by TBA (tertbutylalcohol)-based gel-casting and heat-treating method. In the structure formationprocess, topaz rod-like grains first formed in the AlF3-SiO2system gas-phase reaction,then the topaz grains transformed into tassel-like mullite grains which were composedof needle-like mullite grains. The tassel-like mullite grains formed inter-lockedstructure. The volume density, apparent porosity, specific surface area andcompression strength of the samples were tested to be0.530~0.586g/cm3,82.1~76.1%,12.293~4.645m2/g, and1.6~3.6MPa, indicating that this material could be used ashigh temperature catalyst supporter.Mullite fibers/whiskers frameworks were prepared by mixed-slurry-filtration andheat-treating method. In this material, the main structure were formed by thelap-jointing of the short mullite fibers, and a mass of mullite whiskers uniformly grewon the mullite fibers through the AlF3-SiO2system gas-phase reaction, leading to theformation of the hierarchical fibers/whiskers structure. The unfixed lap-jointing pointsof the mullite fibers were acted by the intersected mullite whiskers. The materialpossessed low volume density (<0.6g/cm3), high apparent porosity (>79%) and lowthermal conductivity (<0.2W/m·k). Moreover, the compression-resilience tests under0.4MPa showed good resilience performance of the material. Thus, this kind ofmaterial could be used as high-temperature heat-insulation material.In the extensive experiments, corundum/mullite platelets’ inter-locked structuralmaterial was prepared by using the preparation method of the mullite inter-lockedstructural material and changing the raw material mole ratio. Corundum plateletsintersected or jointed with each other to form the inter-locked structure, and small amount of mullite formed in the structure at higher temperature. The volume density,apparent porosity, specific surface area, and compression strength of the materialwere tested to be0.469~0.561g/cm3,83.1~79.8%,1.556~0.524m2/g and0.21~0.56MPa, respectively. This kind of material could also be used ashigh-temperature catalyst supporter. Meanwhile, the microstructure of thealumina-silica fibers was modified by the AlF3-SiO2system gas-phase reaction.Besides, silica-fiber-woven/mullite-whiskers composite structural material andmullite fibers/whisker/whiskers multilevel structural material were also preparedbased on the AlF3-SiO2system gas-phase reaction. These researches had potentialsignificance for improving the related performances of the materials.