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Thermal transformations of kaolinite were studied by zgsi-and ZVA1-MAS/NMR and ESR techniques. In metakaolin, Si is still dominantly in the Q3 state (three Si atoms bonded to an Si-O4 tetrahedron) and A1 detectable by NMR is in both 4-coordination and 6-coordination. Coordination polyhedra around A1 or Fe replacing A1 are much distorted. Metakaolin crystallizes into y-alumina and mullite exothermically at ~ 980 ~ this crystallization being preceded by a faint endothermic reaction. The latter is due to segregation of SiO2 and A1203, which results in an increase of Si in the Q4 state and an increase of 6-coordinated A1203 .Kaolin minerals dehydroxylate at ~600~ this process corresponding to an intense endothermic peak on the DTA curve. The resultant anhydrous phase, called metakaolin or metakaolinite, is amorphous to X-rays. y-alumina plus mullite develop from the amorphous phase at ~ 980~ and this reaction is represented by a combination of a faint endotherm and a sharp and intense exotherm. The mechanism of this series of reactions has been studied from various standpoints, as reviewed by Brindley & Nakahira (1959), Tsuzuki (1971) andBrindley (1976). X-ray diffraction, electron microscopy, and X-ray fluorescence, IR absorption and M6ssbauer spectroscopy have all been used to study these reactions. Recent developments in high-resolution magic-angle-spinning MAS/NMR spectroscopy have allowed a new approach to this problem, Komarneni et al. (1985), MacKenzie et al. (1985b) and Brown et al. (1985) being forerunners in the application of this method to metakaolin and high-temperature phases of kaolinite. This paper gives the results of examination of a kaolinite heated to various temperatures, using 29Si-and 27A1-MAS/NMR and ESR techniques. Some new data are presented on the thermal transformation of kaolinite.

High-resolution solid state 29Si-NMR spectra and EPR spectra have been examined on twelve natural philosilicates. It has been found that presence of paramagnetic impurities is markedly effective in shortening the 29Si spin-lattice relaxation times (10 to 1000 ms), and in broadening the linewidths and is favorable for the use of solid state high-resolution 29Si NMR as a tool for structural studies of inorganic materials.

Low-energy electron energy loss spectroscopy (LEELS) has been used to study the electronic structure of margarite. The results show that the electronic structure of margarite is determined principally by local atomic arrangement and also the usefulness of LEELS as a powerful technique to investigate the depth profiling of the electronic structure of a material.

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