Physico-Geometrical Kinetics of Solid-State Reactions in an Undergraduate Thermal Analysis Laboratory

Abstract

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 twodimensional 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.

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

“…The thermal decomposition of a solid is the chemical process initiated by nucleation on the reactant surfaces and subsequently advancing at as-generated reaction interfaces. [1][2][3][4] Thus, the fundamental kinetic equation generally comprises terms expressing the temperature dependence of the reaction rate like the Arrhenius-type equation and the change in the reaction rate as the reaction advances. The change in the overall reaction rate as advancing the reaction is caused by variation of the effective area of the reaction interface in the scheme of the linear advancement of the reaction interface controlled by a ratelimiting step.…”

“…5,6 This behavior is usually expressed by a function of the fractional reaction α, i.e., f(α), termed the kinetic model function. [1][2][3][4] In addition to the physico-geometrical feature of the heterogeneous chemical kinetics in the solid state, the evolution of a gaseous product is another characteristic of the thermal decomposition of solids. When the product gas presented in the reaction atmosphere causes a distinguishable effect on the reaction rate of the thermal decomposition, an accommodation function (AF) 7 is needed in the fundamental kinetic equation.…”

Universal Kinetic Description for Thermal Decomposition of Copper(II) Hydroxide over Different Water Vapor Pressures

“…The thermal decomposition of solids, for example, A(s) ⇄ B(s) + C­(g), is characterized by specific heterogeneous features attributed to the physico-geometrical events that occur during the reaction site formation via nucleation on the surface of reactant solid, A(s), and the advancement of an as-produced reaction interface recognized as a zone of locally enhanced reactivity. − Product gas C­(g) removal by diffusion from the reacting site via the solid product B(s) surface layer and gas desorption from the reacting solid surface are also relevant physicochemical events that control the overall reaction rate. Crystal growth of B(s) in the as-produced surface product layer controls gaseous product diffusion path formation.…”

Kinetic characterization of multistep thermal oxidation of carbon/carbon composite in flowing air

“…9b) [58][59][60]: From the above kinetic observations, it is apparent that a further detailed kinetic approach to the oxidation reaction requires the separation of the component reaction steps.…”