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

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.本研究通过筛选适配的反应体系、热分析与显微观测的适用技术路径，以及可靠的动力学计算方法，开发了一套基于显微观测与热分析的固体热分解本科动力学实验方案。本实验选用碳酸氢钠（sodium hydrogen carbonate）的热分解反应作为教学反应体系，原因在于其物理几何反应机理（physico-geometrical reaction mechanism）可近似通过二维相边界控制模型（two-dimensional phase boundary controlled model）描述，且反应动力学对热分析测试条件的敏感性较低。基于该反应的简易显微观测环节，要求学生完成物理几何反应模型的构建与动力学模型函数的推导。动力学分析亦可基于单次调制温度（modulated temperature）条件下热重测试（thermogravimetric run）采集的动力学速率数据开展。该方案可缩短实验室实验耗时，同时支持采用可获得可靠动力学结果的两步动力学计算方法。通过该实验结果，学生可深入理解与该反应物理几何特性紧密关联的动力学规律。基于本校开展的研究与教学实践，本工作提出了一个时长为一天的热分析实验室本科课程方案。