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Examining the kinetics of solids’ thermal decomposition with multiple overlapping steps is of growing interest in many fields, including materials science and engineering. Despite the difficulty of describing the kinetics for complex reaction processes constrained by physico-geometrical features, the kinetic deconvolution analysis (KDA) based on a cumulative kinetic equation is one practical method of obtaining the fundamental information needed to interpret detailed kinetic features. This article reports the application of KDA to thermal decomposition of clay minerals and indigo−clay mineral hybrid compounds, known as Maya blue, from ancient Mayan civilization. Maya blue samples were prepared by heating solid mixtures of indigo and clay minerals (palygorskite and sepiolite), followed by purification. The multistep thermal decomposition processes of the clay minerals and Maya blue samples were analyzed kinetically in a stepwise manner through preliminary kinetic analyses based on a conventional isoconversional method and mathematical peak deconvolution to finally attain the KDA. By comparing the results of KDA for the thermal decomposition processes of the clay minerals and the Maya blue samples, information about the thermal decomposition steps of the indigo incorporated into the Maya blue samples was extracted. The thermal stability of Maya blue samples was interpreted through the kinetic characterization of the extracted indigo decomposition steps.

Thermal decomposition of solids often includes simultaneous occurrence of the overlapping processes with unequal contributions in a specific physical quantity variation during the overall reaction (e.g., the opposite effects of decomposition and evaporation on the caloric signal). Kinetic analysis for such reactions is not a straightforward, while the applicability of common kinetic calculation methods to the particular complex processes has to be justified. This study focused on the critical analysis of the available kinetic calculation methods applied to the mathematically simulated thermogravimetry (TG) and differential scanning calorimetry (DSC) data. Comparing the calculated kinetic parameters with true kinetic parameters (used to simulate the thermoanalytical curves), some caveats in the application of the Kissinger, isoconversional Friedman, Vyazovkin and Flynn−Wall−Ozawa methods, mathematical and kinetic deconvolution approaches and formal kinetic description were highlighted. The model-fitting approach using simultaneously TG and DSC data was found to be the most useful for the complex processes assumed in the study.

In this laboratory experiment, a guided inquiry exploring the physicochemical principles of the dissolution of Ca(OH)[subscript 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)[subscript 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)[subscript 2](s), for determining the enthalpy of the Ca(OH)[subscript 2](s) solution, development of an energy diagram composed of several paths of a reaction that involve the dissolution of Ca(OH)[subscript 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)[subscript 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.

This study focuses on students' understandings of a liquid-gas system with liquid-vapor equilibrium in a closed system using a pressure-temperature (P-T) diagram. By administrating three assessment questions concerning the P-T diagrams of liquid-gas systems to students at the beginning of undergraduate general chemistry course, lack of understanding of the fundamental concepts concerning liquid-vapor equilibria, the ideal gas law, and boiling points was identified. A learning program for liquid-gas systems was then designed for students at the undergraduate general chemistry level to address this issue. It consists of a laboratory experiment and postlaboratory exercise and is intended to provide integrated student understanding. During the learning program, students actively used the related concepts to explain the physical chemistry of a liquid-gas system and integrated the concepts to explain practical systems in their daily lives using a P-T diagram. An outline of the learning program is reported on the basis of our educational practice. [ABSTRACT FROM AUTHOR]

An undergraduate kinetic experiment of the thermal decomposition of solids by microscopic observation and thermal analysis was developed by investigating a suitable reaction, applicable techniques of thermal analysis and microscopic observation, and a reliable kinetic calculation method. The thermal decomposition of sodium hydrogen carbonate is selected as the suitable reaction for the student experiments, because its physico-geometrical reaction mechanism is approximately described by the two-dimensional phase boundary controlled model, and its reaction kinetics are less sensitive to the measurement conditions of thermal analyses. On the basis of simple microscopic observations of this reaction, development of the physico-geometrical reaction model and derivation of the kinetic model function are imposed on students. The kinetic analysis is also performed using the kinetic rate data recorded by a single thermogravimetric run under modulated temperature conditions. This reduces the time spent in the laboratory and enables the application of a two-step kinetic calculation that provides reliable kinetic results. From the results, students can interpret the kinetics, which are closely related to the physico-geometrical characteristics of the reaction. A one-day undergraduate course in a thermal analysis laboratory is proposed from research and trials conducted in our university. [ABSTRACT FROM AUTHOR]

An inquiry-based laboratory exercise is described to determine the chemical composition of sodium percarbonate (SPC), which is a major component of domestic oxygen bleach. The students' knowledge of the chemical properties and reactions of sodium carbonate (SC) and hydrogen peroxide (HPO) is used to determine the chemical composition of SPC because SPC is the adduct of SC and HPO. If the hypothetical composition is assumed to be xNa2CO3⋅yH2O2, the composition can be determined by selecting one experimental method from the range of methods available. Synthetic SPC crystals or commercially available granular SPC can be used as the sample in the experiment. Because many choices involving different experimental methods are available, various learning programs can be designed to match the objectives and students' knowledge stage. This inquiry-based laboratory exercise is suitable for a high school chemistry course or a college introductory chemistry course and requires three hours. [ABSTRACT FROM AUTHOR]

Presents microscopic studies and introductory experiments to the kinetics of solid-state reactions. Theory of solid-state reactions; Kinetics of solid-state decompositions; Rate equations; Kinetics of nucleation and nuclear growth; Nucleus dimensions; Kinetics of established reaction; Microscopic studies of crystal dehydrations.