Physico-Geometrical Kinetic Modeling of the Thermal Decomposition of Magnesium Hydroxide

The thermal decomposition of Mg­(OH)2 was selected to realize an integrated kinetic understanding of the thermal decomposition of inorganic solids by correlating the physico-geometrical mechanisms and the effect of the product gas presented in the reaction atmosphere. Herein, the mechanistic features of the reaction, as revealed by a systematic kinetic study on a reaction in flowing dry N2 gas, were reported as the first part of the study. In spite of the smooth mass loss under various heating conditions, the formal kinetic analysis based on an assumption of single-step reaction indicated a possible multistep reaction comprising the surface reaction (SR) and subsequent internal phase boundary-controlled reaction (PBR). Two physico-geometrical models were applied to find the mechanistic features of the overall reaction. One is a single reactant-body model with an assumption of independent SR and PBR. The other is based on the physico-geometrical consecutive SR–PBR model in the assemblage of reactant particles. Through the stepwise kinetic analyses on these models, the SR and PBR were characterized by the first-order kinetic law with an activation energy (E a) of approximately 130 kJ mol–1 and two- or three-dimensional interface shrinkages with an E a value of approximately 248 kJ mol–1, respectively.