Methods and Applications for the Study of the Thermal Decomposition Kinetics of Evaporite Minerals
Date Issued
2007
Date
2007
Author(s)
Lin, Shu-Hong
DOI
zh-TW
Abstract
ABSTRACT
Kinetic research of minerals has been a very important area in the research of geology. In this research, three kinetic methods ─ Master Curve Model (MCM), Ozawa method and Avrami Equation method ─ have been used to analyze and predict the thermal decomposition reactions of five evaporite minerals.
The research consists of three parts: First is to prepare the five high-purity synthetic evaporite minerals powders, including gypsum, calcite, chalcanthite, nitratine and hydromagnesite, and to verify their phases and purities by XRD. Second is to conduct a series of thermal decomposition experiments of the powders by TGA at various heating rates and isothermal condition. Third is to analyze the weight loss data by the three kinetic methods. The application limitations of MCM, Ozawa method and Avrami Equation on the study of thermal decomposition reactions will be discussed on the basis of the experimental results.
From the experimental results, constant heating rate experiments show a significant deviation of the data due to the possible temperature-measuring errors inside the Thermal Gravitometry Analyzer. Fortunately, isothermal experiments can effectively reduce the uncertainty of the data and thus derive adequate results. In this research, MCM demonstrates that it is excellent in the prediction of reaction process. The effect of grain size on reaction rate is shown in this work that smaller grain size samples may lead to a higher reaction rate, as a result of the “surface-area effect.” The final part of this research is to propose a new concept of “geothermometer,” which is based on the modeling of the kinetic reactions, and it may become a powerful tool to find out the possible temperature and time conditions of many geological processes.
To sum up, the research contributes in three aspects: First, using three kinetic models to characterize the thermal decomposition reactions and the thermal stability of five evaporate minerals, and most importantly to derive the quantitative relationship of the reaction percentage and the reaction time and temperature. Second, learning the applicability, the limitation and possible error levels of MCM, Ozawa method and Avrami Equation, based on the analysis results. Finally, proposing a new concept of “geothermometer,” and which may be very useful in geologic research. The results of this preliminary study may be extended to other kinetic reactions of various minerals.
Subjects
蒸發岩礦物
熱分解反應
動力學
尺寸效應
地質溫度計
evaporite mineral
thermal decomposition
kinetics
size-effect
geothermometer
Type
thesis
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