Abstract
The aim of this work was to identify parameters that could influence the conversion of kaolinite into metakaolinite. To this end, the dehydroxylation of four kaolinites, using controlled rate thermal analysis (CRTA) and thermogravimetric analysis (TGA), was investigated. X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) were used to confirm the kaolinitic nature of the samples. Their crystallinity was evaluated using the Hinckley index from the XRD patterns and transmission electron microscopy (TEM) was used for morphological observation of the clay platelets. The thermal analyses of the samples indicate, for all samples, low defects as revealed by the low amount of adsorbed water on the clay surface. The dehydroxylation temperature from both techniques was influenced by the sample crystallinity and particle size. It was observed from both techniques that increase crystallinity resulted in highdehydroxylation temperature. Also, the influence of the clay platelets size on the dehydroxylation temperature, is proposed. All the results indicate that crystallinity and particle size are parameters that could be used to control the temperature for the conversion of kaolinite to metakaolinite.
 Keywords: Kaolinite; Crystallinity, Dehydroxylation; Thermal analysis
Highlights
Clays are minerals, widely used in industries for various applications including building materials, fillers in plastics, paper, polymer-clay composite (De Carvalho et al, 2001; Harvey and Lagaly, 2006; Ekosse, 2010; Nkoumbou et al, 2009; Fadil-Djenabou et al, 2015; Gul et al, 2016)
The geological deposits for smectites clay are scarce in comparison to kaolinites, which are ubiquitous clays largely exploited as industrial minerals in various domains including paper, plastics, rubber, fiber glass, pesticides, building or ceramics (Murray, 2000; Harvey and Lagaly, 2006)
The spectra are typical of kaolinitic clays with the stretching bands of O-H bonds, in the kaolinite structure, at 3697, 3666, 3651 and 3620 cm-1(Frost et al, 2001; Mbey et al, 2013)
Summary
Widely used in industries for various applications including building materials, fillers in plastics, paper, polymer-clay composite (De Carvalho et al, 2001; Harvey and Lagaly, 2006; Ekosse, 2010; Nkoumbou et al, 2009; Fadil-Djenabou et al, 2015; Gul et al, 2016). The geological deposits for smectites clay are scarce in comparison to kaolinites, which are ubiquitous clays largely exploited as industrial minerals in various domains including paper, plastics, rubber, fiber glass, pesticides, building or ceramics (Murray, 2000; Harvey and Lagaly, 2006). Despite their reduced expandability, they are regarded as potential candidates for polymer-clay composites making (Chen and Evans, 2005; Mbey et al, 2012; Mbey et al, 2013; Mbey and Thomas, 2015)
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