Preparation of microporous mullite ceramics by foaming for high temperature thermal isolation

To satisfy the need of thermal isolation in high temperature industry, microporous mullite ceramics with nest-like structures have been fabricated by foaming with kyanite and Al(OH)(3) as raw materials, cement as the foam stabilizer. The effects of solid loading on viscosities of slurries, properties and microstructure of samples have been systematically investigated. It is found that foams can be stabilized by the hydration of cement in aqueous ceramic slurries, and then, they convert into pores in samples through curing and heating. With increasing solid loading, the number and size of pores decrease, but the mechanical strength and thermal conductivity increase. Meanwhile, a great amount of needle-like mullites are grown in-suit on pore walls, they interwoven into interlocked network structures, making the effective pore size and thermal conductivity smaller, while the mechanical strength stronger. In addition, to efficiently investigate the thermal insulation properties of samples at high temperature, a new thermal conductivity model has been built up, which combines the complexity of pore structure and thermal radiation, showing that the thermal radiation has an effect on the effective thermal conductivity at high temperature, and the experiment datas fit well with the model when d(1)=3, k'=0.3 and a=5 x 10(-11) W/mK(4). (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.