Thermal Dehydration of Monohydrocalcite: Overall Kinetics and Physico-geometrical Mechanisms

Abstract

Monohydrocalcite (CaCO(3)·H(2)O: MHC) is similar in composition and synthetic conditions to hydrated amorphous calcium carbonate (ACC), which is focused recently as a key intermediate compound of biomineralization and biomimetic mineralization of calcium carbonate polymorphs. Detailed comparisons of the physicochemical property and reactivity of those hydrated calcium carbonates are required for obtaining fundamental information on the relevancy of those compounds in the mineralization processes. In the present study, kinetics of the thermal dehydration of spherical particles of crystalline MHC was investigated in view of physico-geometrical mechanism. The reaction process was traced systematically by means of thermogravimetry under three different modes of temperature program. A distinguished induction period for the thermal dehydration and cracking of the surface product layer on the way of the established reaction were identified as the characteristic events of the reaction. By interpreting the kinetic results in association with the morphological changes of the reactant particles during the course of reaction, it was revealed that nucleation and crystal growth of calcite regulate the overall kinetics of the thermal dehydration of MHC. In comparison with the thermal dehydration of hydrated ACC, which produces anhydrous ACC as the solid product, the kinetic characteristics of the thermal dehydration of MHC were discussed from the viewpoint of physico-geometry of the component processes.

Impact of atmospheric water vapor on the thermal decomposition of calcium hydroxide: a universal kinetic approach to a physico-geometrical consecutive reaction in solid–gas systems under different partial pressures of product gas

“…65,66,68,69,[78][79][80] Application of the Arrhenius-type plot based on eqn (8) is justified when zero-order kinetics with f (α IP ) = 1 is assumed for the IP process 78 or when the value of a IP with the average conversion rate (t IP -1 ) is assumed to be invariant for IP processes at the various temperatures being fulfilled by an isoconversional relationship. 65,66,68,69,80 In Fig Introducing an accommodation function in the form of eqn (5) is a possible primary approach. [1][2][3]7…”

“…16,52,58 In some cases, a significant induction period (IP) is also observed prior to the surface reaction (SR). [63][64][65][66][67][68][69] Such heterogeneous characteristics of the reaction and any significant impact of the mass and heat transfer phenomena are responsible for the numerous observations induced by atmospheric gases. Therefore, in addition to having a universal kinetic description for these processes under various p(C(g)) conditions, investigation into the impact of p(C(g)) on each component physico-geometrical reaction step must be explored separately in order to gain further insights into the fundamental problems of reaction kinetics that are often encountered in solid-gas systems.…”

Constant rate thermal analysis of a dehydrogenation reaction

“…The use of the CRTA procedure is not limited to first order reactions, but it can be employed independently of the kinetic model followed by the reaction, and for this reason has been used to study the kinetics of thermal decomposition of different materials. 25,[41][42][43][44] Moreover, this method has been successfully employed for the kinetic analysis of complex solid state reactions with overlapping processes, such as the thermal dehydroclorination of poly(vinyl chloride) and the quantitative characterization of multicomponent polymers. 27,45 The proposed kinetic mechanism was further checked by comparing the calculated f(α) with the most used conversion functions in literature, 46 which are normalized at α = 0.5 to better distinguish between the different models (Figure 5b).…”

A Promising approach to the kinetics of crystallization processes: The sample controlled thermal analysis

“…14,29,30 It has also been used for the thermal analysis of a wide range of reactions, such as dehydrations and dehydroxylations, [31][32][33][34] denitrations, 35 and decarbonations. 36,37 Moreover, CRTA experiments have been included in kinetic studies of thermal decomposition of materials, mainly carbonates, 4,11,[38][39][40][41][42] polymers, 13,[43][44][45] polymer nanocomposites, 46 but also other compounds, [47][48][49] to clarify the kinetic model followed by the reactions. Interestingly, SCTA has also applications in quantitative characterization, 16,50 and even has been used in sintering studies.…”