Effect of CaO Impurity on Mullite Formation from SiO2 Gel and Al2O3 Powders

To broaden the application of SiO2sol-bonded castables, using micro-or nano-Al2O3powder and SiO2gel powder as the main raw materials, the effects of CaO impurity on the formation of mullite by the reaction of Al2O3and SiO2at different temperatures(1 350, 1 400, 1 500, and 1 600 ℃) in different atmospheres(oxidation atmosphere and reduction atmosphere) were studied. The results show that in the oxidizing atmosphere, the introduction of CaO can promote the formation of mullite. When the temperature increases from 1 350 ℃ to 1 600 ℃, the amount of mullite formed gradually increases. In the reducing atmosphere, the introduction of CaO is not conducive to the formation of mullite, and the amount of mullite decreases with the increasing temperature. The smaller the particle size of Al2O3, the more easily it reacts with SiO2gel powder to form mullite.