期刊
ACTA PHYSICA POLONICA A
卷 131, 期 3, 页码 562-565出版社
POLISH ACAD SCIENCES INST PHYSICS
DOI: 10.12693/APhysPolA.131.562
关键词
81.70. Pg; 81.05. Je; 81.05. Mh; 81.70. Pg; 81.30. Mh; 07.85. Nc
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 20 degrees C min(-1). The 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): g(x) = [-ln(1-X)] (2/3)) also called Avrami-Erofeev equation of order 2/3. The values of the activation energy E-A and of the pre-exponential factor K are 157 kJmol(-1) and 7.58 x 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 (F-2 : g(x) = (1-x)-1-1), under the applied conditions. The activation energy E-A and pre-exponential factor K correspond to 243 kJ mol(-1) and 3.73 x 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 E-A and K were determined to be around 296 kJ mol(-1) and 1.82 x 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 degrees C in 200 degrees C steps.
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