Kinetics study on the dehydroxylation and phase transformation of Mg3Si2O5(OH)(4)

摘要

Determination of the decomposition mechanism and phase transformation of lizardite [Mg3Si2O5(OH)(4)] within laterite was carried out using thermal analysis kinetics during the heat-treatment process. Non-isothermal kinetic heating experiments at temperatures ranging from room temperature to 1273 K showed two characteristic peaks at approximately 898 K and 1094 K, corresponding to dehydroxylation and a phase transformation, respectively. Generalized master plots were used as a straightforward approach for determining the kinetic models. The Avrami-Erofeev reaction model was found to provide the best fit to the dehydroxylation process, and diffusion patterns with an apparent activation energy of 219 kJ mol(-1) are discussed. The results indicated that dehydroxylation was controlled by a constant nucleation rate and two-dimensional diffusion. In addition, the crystalline transformation of lizardite presented a reaction process-dependent evolution of the apparent activation energy, which decreased rapidly with increasing extent of the conversion. Based on the analyses, the phase transformation of lizardite may belong to reactions complicated by diffusion. (C) 2017 Elsevier B.V. All rights reserved.