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

Abstract

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.

Revealing the effect of water vapor pressure on the kinetics of thermal decomposition of magnesium hydroxide

“…The Mg(OH)2 sample used in this study is a chemical reagent (special grade, > 99.5%, Wako, Japan) identical to that used in our previous study. 71 The characteristics of the sample, as revealed by the powder X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry (TG)differential thermal analysis (DTA) coupled with mass spectrometry (MS) of the evolved gas, and morphological characterization using scanning electron microscopic (SEM) observation and the Brunauer-Emmett-Teller (BET) specific surface area (SBET) measurement, were already reported in our previous study. 71 In summary, the sample contained agglomerated particles of approximately 50 μm in diameter (SBET = 34.1 ± 0.3 m 2 g -1 ), constructed by submicron-sized crystalline particles.…”

“…(3) Retardation of the overall reaction rate of the thermal decomposition of Mg(OH)2 by atmospheric water vapor was experimentally demonstrated by Horlock et al 48 and L'vov et al 49 Many previous reports for the thermal decomposition 45, were carefully reviewed and the detailed comparison was described in our previous article. 71 Thereafter, the physico-geometrical kinetic features of the thermal decomposition of Mg(OH)2 under a stream of dry N2 gas were investigated systematically. 71 The reaction involved a major mass-loss process and a subsequent reaction tail.…”

“…71 Thereafter, the physico-geometrical kinetic features of the thermal decomposition of Mg(OH)2 under a stream of dry N2 gas were investigated systematically. 71 The reaction involved a major mass-loss process and a subsequent reaction tail. Because the reaction tail was interpreted as the removal of trapped water molecules from the poorly crystalline solid product, i.e., MgO, accompanied by its crystal growth on further heating, 57 the major mass-loss process was subjected to a kinetic study of the chemical reaction.…”

Thermal Dehydration of Lithium Sulfate Monohydrate Revisited with Universal Kinetic Description over Different Temperatures and Atmospheric Water Vapor Pressures

“…The physico-geometrical consecutive process comprising the initial SR and subsequent PBR, i.e., the Mampel-type model, is a possible explanation for the sigmoidal mass-loss behavior. 41,42,44,[46][47][48]65,[92][93][94][95][96][97] In the scheme of the consecutive SR-PBR model, the variation in the mechanistic feature with the p(H2O) value, as appearing in the sigmoidal shape of the mass-loss curves, is…”

Improvements of Developed Graphite Based Composite Anti-Aging Agent on Thermal Aging Properties of Asphalt

“…The MH nanoparticle, as a kind of high efficient flame retardant, has strong thermal stability and smoke suppression property [ 19 , 20 ]. MH nanoparticles show the volume effect and quantum size effect after nano crystallization, which improves the compatibility between MH and asphalt.…”