In this study, the mechanism and the kinetic parameters of the thermal decomposition of gibbsite Al(OH)3 were studied by differential thermogravimetry technique under non-isothermal conditions, between room temperature and 1200 K at heating rates of 5, 10, 15 and 20The obtained differential thermogravimetry curves show clearly three distinct peaks. The first peak is due to the partial dehydroxylation of gibbsite. Among the 32 types of differential equations of non-isothermal kinetics, we have found that the most suitable mechanism is (A 3/2 :2/3 ) also called Avrami-Erofeev equation of order 2/3. The values of the activation energy EA and of the pre-exponential factor K are 157 kJ mol −1 and 7.58 × 10 15 s −1 , respectively. The second peak corresponds to the decomposition of gibbsite to boehmite. Decomposition is controlled by the rate of second-order reaction (F2: g(x) = (1 − x) −1 − 1), under the applied conditions. The activation energy EA and pre-exponential factor K correspond to 243 kJ mol −1 and 3.73 × 10 22 s −1 , respectively. The third peak is due to transformation of boehmite to alumina. However the mechanism for such transformation is better described by the 3/2 rate order reaction (F 3/2 : g(x) = (1 − x) −1/2 − 1). In addition, the values of EA and K were determined to be around 296 kJ mol −1 and 1.82 × 10 19 s −1 , respectively. The results of differential thermogravimetry were supplemented by the differential thermal analysis. X-ray powder diffraction analysis was carried out for samples of gibbsite treated at different temperatures between 200 and 1200• C in 200• C steps.

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In the present study, the kinetics of meta-kaolinite (Al2O3·2SiO2) formation from Algerian Tamazarte kaolin was investigated by using differential thermal analysis. The differential thermal analysis and the thermogravimetric experiments were carried out on samples between room temperature and 1400• C, at heating rates from 10 to 40• C min −1 . X-ray diffraction was used to identify the phases present in the samples. The activation energies measured by differential thermal analysis from isothermal and non-isothermal treatments using Johnson-MehlAvrami methods with Ligero approximation and using Kissinger-Akahira-Sunose methods were around 145 and 159 kJ/mol, respectively. The Avrami parameter n which indicates the growth morphology parameters were found to be almost equal to 1.60, using non-isothermal treatments, and equal to 1.47 using isothermal treatments. The numerical factor which depends on the dimensionality of crystal growth was 1.60 obtained using Matusita et al. equation. The frequency factor calculated using the isothermal treatment is equal to 1.173 × 10 7 s −1 . Analysis of the results have shown that bulk nucleation was dominant during kaolinite transformation, followed by three-dimensional growth of meta-kaolinite with polyhedron-like morphology, controlled by diffusion from a constant number of nuclei.

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The effect of CaO on cordierite formation from kaolin-MgO-CaO powder mixtures, milled for 5 h and reaction sintered for 2 h in the temperature range 900-1400?C, was investigated. Phases formed in the developed materials were characterized by x-ray powder diffraction method (XRD) and Raman spectroscopy. Non-isothermal differential thermal analysis (DTA) and thermogravimetric (TG) experiments were performed from room temperature to 1400?C, at heating rates from 20 to 40?C/min. Activation energies were determined using Kissinger method. It was found that sintering the stoichiometric kaolin-magnesia mixture led to the nucleation and growth of monolithic cordierite; while cordierite along with anorthite were present in the other two samples where 4 or 8 wt% of CaO was added. The increase in CaO decreased cordierite formation temperature and increased the activation energy, which ranged from 445 to 619 kJ/mol for ?-cordierite and from 604 to 1335 kJ/mol for ?-cordierite.

In the present study the mechanism and kinetic parameters of allotropic transformation (α → β) of the quartz of Algerian clay from Al-maathed was studied by dilatometric analysis technique. The activation energies measured by both isothermal (Johnson-Mehl-Avrami theory using Ligero method) and non-isothermal (Kissinger methods) treatments were 980 and 1050 kJmol −1 , respectively. The growth morphology parameters n (Avrami parameter) which indicates the crystallization mode were found to be almost equal to 1.5, using non-isothermal treatments, and equal to 1.4 using isothermal (Ligero method). The numerical factor which depends on the dimensionality of crystal growth m obtained by Matusita et al. equation was 1.50. Analysis of the results shows that the bulk nucleation is the dominant mechanism in β-quartz crystallization and the three-dimensional growth of β-quartz crystals with polyhedron-like morphology occurs, controlled by diffusion from a constant number of nuclei.