Abstract
Kinetically frozen samples of flash calcined kaolinite (rapidly heated to 1000 °C, maintained at that temperature for a variable residence time and then rapidly cooled) have been produced in a laboratory calciner. Time resolution of the structural changes occurring has been achieved by following 27Al (78.15 MHz) and 29Si (59.58 MHz) magic angle spinning nuclear magnetic resonance (MAS NMR) spectra as a function of residence time. 29Si spectra can be deconvoluted into a minimum of four Gaussian components with shifts ranging from mullite-like (–90 ppm) to Q4(–110 ppm) Si environments. 27Al spectra show peaks for four-co-ordinate and six-co-ordinate Al. The derived picture of flash calcination is progressive transformation of kaolinite to a single product which undergoes little further chemical reaction during its short time in the calciner.
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