The kinetics of the thermal decomposition of CaCO3 is significantly influenced by atmospheric and self-generated CO2 due to the reversibility of the reaction. More detailed understanding of this well-known phenomenon is desired for establishing an effective Ca-looping in the CaO–CaCO3 system for energy storage and CO2 capture. This article shows the universal kinetics of the thermal decomposition of CaCO3 over different temperatures and partial pressures of CO2 (p(CO2)) with the aid of an accommodation function (AF) composed of p(CO2) and equilibrium pressure. An analytical form of AF with exponents (a, b) was derived based on the kinetic considerations for the consecutive elementary steps of the surface nucleation and interfacial reaction. The overall kinetics of the thermal decomposition of CaCO3 were described universally over different temperatures and p(CO2) values by introducing the AF, in views of the isoconversional and isothermal kinetic relationships using the extended Friedman and experimental master plots, respectively. The universal kinetic description was extended to the kinetic modeling based on the physico-geometrical consecutive process comprising an induction period (IP), a surface reaction (SR), and a phase boundary-controlled reaction (PBR). The proposed kinetic approach enables parameterizing the CO2 effect via the optimized (a, b) and tracking changes in the CO2 effect as the physico-geometrical reaction step advanced from IP to PBR via SR. Furthermore, using the established universal kinetic description across different temperatures and p(CO2) values, a challenge was set to quantify the contributions of atmospheric and self-generated CO2 on the kinetics.

In this study, we investigated the mechanisms of variations in the overall kinetic behavior of the physico-geometrical consecutive process of the surface reaction (SR) and phase boundary-controlled reaction (PBR) in solid−gas systems with varying particle size of the reactants. Thermal decomposition of potassium hydrogen carbonate (KHCO 3 ) was selected as a suitable model reaction owing to the significant changes in its kinetic behavior with particle size and less sensitivity to experimental conditions for recording kinetic data. The reaction was characterized by an induction period (IP) accompanied by the formation of a gelatinated surface layer. The subsequent mass-loss process was indicated by the consecutive SR and PBR, which was accompanied by the nucleation and growth of solid products in the gelatinated layer and inward advancement of the reaction interface, respectively. Formal kinetic analyses of systematically recorded kinetic data revealed variations in the overall kinetic behaviors with the sample particle size, including changes in the variation trend of isoconversional activation energy values as the reaction progressed and the shape of the experimental master plot. The kinetics of each reaction step in the physico-geometrical consecutive process was investigated using an advanced kinetic approach based on an IP−SR−PBR model. The results revealed variations in the overall kinetic behaviors of the thermal decomposition of KHCO 3 with particle size, owing to changes in the reactivity of the reactant surface in IP, overlapping degree of SR and PBR, and total migration length of the reaction interface in PBR.

This study aims to parametrize the effect of selfgenerated gas on the thermal decomposition of inorganic solids in an inert gas atmosphere. The kinetics of reversible thermal decomposition should be described as a function of the temperature and partial pressure of the gaseous product in the reaction atmosphere; however, the partial pressure of evolved gas at the specific reaction site is difficult to measure because of the heterogeneous reaction nature. Extrapolation of the universal kinetic relationship established over different temperatures and partial pressures of the gaseous product in the reaction atmosphere to a reaction condition in an inert gas atmosphere is proposed as a possible method for estimating the effect of self-generated gas on such reactions in an inert gas atmosphere. This idea was practically demonstrated, as exemplified by the thermal decomposition of ZnCO 3 and CaCO 3 in a stream of dry N 2 and air. By setting the effective partial pressure of CO 2 (p(CO 2 )) as a weighted sum of the atmospheric and self-generated p(CO 2 ), a universal kinetic description of these thermal decomposition reactions across different temperatures and p(CO 2 ) values including those in an inert gas atmosphere was achieved, and the contribution of self-generated p(CO 2 ) was parametrized. Furthermore, the change in the contribution of self-generated p(CO 2 ) as the reaction advanced was evaluated by using consecutive surface and phase-boundarycontrolled reaction models. The proposed kinetic analysis approach addresses many issues in the conventional kinetic analysis approach and provides detailed kinetic insight into the reversible thermal decomposition of solids.

The effect of water vapor on the thermal decomposition of five different CaCO 3 samples was investigated to reveal the origin of the acceleration effect caused by water vapor. Biomineralized CaCO 3 samples decomposed at a relatively low temperature and were limitedly sensitive to variations in atmospheric water vapor pressure (p(H 2 O)). During the thermal decomposition of the mineral and synthetic CaCO 3 samples, an acceleration effect of water vapor was observed; however, the degree of the effect differed among the samples. A sample with smaller specific surface area and larger particle size (mineral aragonite) decomposed at higher temperatures but exhibited more significant reaction temperature reduction with increasing p(H 2 O). The kinetic analysis of the thermal decomposition of CaCO 3 (mineral aragonite) under different p(H 2 O) values revealed a variation in the surface reaction (SR) kinetics with p(H 2 O), indicating the enhancement of the SR at greater p(H 2 O). The subsequent reaction proceeded through a contracting geometry scheme, during which the CaO crystal growth and pore formation in the surface product layer were enhanced by the effect of water vapor. A universal kinetic analysis for the thermal decomposition of CaCO 3 under different temperatures and p(H 2 O) values was demonstrated by introducing an accommodation function (AF) of p(H 2 O), obtaining a single set of kinetic triplets and the exponent in the AF. The effect of water vapor on the kinetics was parameterized by the exponent in the AF, which can be a potential tool for evaluating the thermal decomposition of CaCO 3 in the Ca-looping system for CO 2 absorption and energy storage.

In this laboratory experiment, a guided inquiry exploring the physicochemical principles of the dissolution of Ca(OH)2(s) in water is proposed for laboratory classes in university and high school. As part of students’ inquiry, two experimental approaches are used. One is the change in solubility with temperature revealed by measuring the pH values of the suspended solution of Ca(OH)2(s) at various temperatures, which is then extended to its thermodynamic relationship via examining the temperature dependence of the solubility constant. The other method is to determine the enthalpy of solution using the calorimetric measurements. Due to the poor solubility of Ca(OH)2(s), for determining the enthalpy of the Ca(OH)2(s) solution, development of an energy diagram composed of several paths of a reaction that involve the dissolution of Ca(OH)2(s) as a component process and using Hess’s law are essential. A combination of these experimental approaches yields a stepwise students’ inquiry for revealing the source of the changes in Ca(OH)2(s) solubility with temperature, which may be flexibly adapted as an appropriate program depending on the targeted students. The two experimental procedures are presented by critically examining the experimental results. Based on the results of educational practices, typical guided inquiry constructions suited for the university and high school chemistry courses are proposed.