Abstract
Abstract The dehydroxylation of kaolinite and its subsequent transformation to cubic Al-spinel and mullite has been studied under water vapour atmospheres up to 0·8 atm pressure. Dehydroxylation, as determined by XRD, FTIR and solid state MAS NMR, can be accomplished at low temperatures (ca 500°C) under water vapour atmospheres, the efficiency increasing with increasing water vapour pressure. The subsequent thermal transformations to crystalline products are also facilitated by water vapour atmospheres, which also enhance the mechanical properties of the fired kaolinite (crushing strength and softening coefficient) by 3–4 times. These effects are discussed in terms of proton attack on the Si–O bonds followed by polycondensation of the resulting silanol groups to siloxane, facilitating the nucleation of mullite from amorphous aluminosilicate and strengthening the chemical bonds between the grains.
Published Version
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