²⁷ Al and ²⁹ Si MAS NMR Study of Kaolinite Thermal Decomposition by Controlled Rate Thermal Analysis

Abstract

The processing of kaolinite under controlled rate thermal analysis conditions (CRTA) provides homogeneously transformed samples at defined dehydroxylation rates. The kaolinite‐to‐metakaolinite transformation has been monitored by solid‐state NMR and X‐ray diffraction. The metakaolinite product is an amorphous material with no resolved XRD pattern and is based on a disordered polymerized silicon/aluminum network in which aluminum preferably occupies four‐ and five‐fold structural positions in the ratio 60% Al VI , 30% Al V , and 10% Al VI . This complex dehydroxylation process has been viewed at different scales, with the aluminum NMR tracing a site‐by‐site destructon of the octahedral sheet and the silicon NMR and XRD following a more rapid destruction of the longrange order.