The mechanism of kaolinite dehydroxylation followed by high resolution 27Al and 29Si NMR

Structural reorganisations occurring during calcination of kaolinite have been followed using high resolution magic-angle-spinning 27Al and 29Si NMR spectroscopies. Calcines produced by both industrial 'soak calcination' and by 'flash calcination' (in He and He/water vapour mixtures) have been studied. The spectra enable discussion of structural rearrangements in terms of the degree of segregation of Si into Q4 and mullite-like environments as a function of calcination conditions. In the case of flash calcines, increasing H2O content of the calciner atmosphere increases the degree of segregation for calcines of similear specific gravity. (author). 15 refs.; 5 figs