The mineral composition of kaolin is mainly composed of kaolinite, which was widely used in the production of ceramics and refractory materials. In this paper, terahertz time-domain spectroscopy is used to study the optical properties of kaolinite group clay minerals and the absorption coefficient and refractive index of calcined kaolin, washed kaolin and metakaolin were characterized in the terahertz band. The experimental results show that when the type, composition proportion and particle size of kaolin changed, the time-domain signal, absorption coefficient and refractive index of the terahertz wave will show regular changes. Through qualitative and quantitative analysis, the difference which is kaolin of different types, different particle sizes and different concentrations can be effectively distinguished. The research results show that the time-domain terahertz spectroscopy technology can be effectively applied to the mineral component analysis and has important significance in geoscience research.
Montmorillonite plays an important role in mineral research, pharmaceutical research and treatment of polluted wastewater. The purpose of this study is to detect different porosity, thickness, calcined products of montmorillonite and to distinguish different types of montmorillonite by terahertz time-domain spectroscopy combining with other conventional analytical methods. In addition, optical parameters such as absorption coefficient, phase difference and refractive index can significantly characterize different porosity, thickness and calcination temperature. Therefore, it is of great significance to use terahertz time-domain spectroscopy for nondestructive testing of montmorillonite.
Using terahertz time-domain spectroscopy (THz-TDS) to characterize the shale is significant for geological research. This paper adopts the transmission THz-TDS system which is composed of a femtosecond laser, terahertz radiation generation device, corresponding detection device, and time delay control system. It can also further explore the application potential of THz-TDS in rock mineralogy. The method of shale powder tablet is used to make sample suitable for test and confirm the appropriate proportion that the shale mixed with PTFE under the condition of THz-TDS. Matlab software is used to extract the phase shift and amplitude curve of the sample, and then the refractive index and absorption coefficient of the sample are extracted from the time domain data. In addition, it is feasible to use the characteristic peak in the absorption coefficient to identify minerals in similar shales. The mineral composition of shales which cannot be directly determined by THz-TDS is determined by X-ray fluorescence (XRF) and X-ray diffraction (XRD). The experimental results show that the refractive index can be used to distinguish two kinds of similar black shales: oil shale which is rich in organic matter and ordinary shale. THz-TDS can be used as a supplement to traditional testing methods, which provide a new method for the study of the rock mineralogical characteristics of shale and make the characterization system of shale more perfect.
As a traditional mineral medicine, Lapis Chloriti has attracted much attentions in recent years. Based on the components determined by the X-ray diffraction, the Lapis Chloriti were characterized by the terahertz time domain spectroscopy. Results show that the absorption of sample has positive correlation with concentration. The more mass with Lapis Chloriti, the more absorption. And the absorption becomes more intense with the particle size increasing. In addition, the absorption influenced by other factors are also compared and discussed.
The characteristics of Calamines has been firstly analyzed by terahertz time-domain spectroscopy. Results show that the main composition of the Calamine is calcite. And the terahertz absorption much relates with the particle size, sample thickness, as well as the proportion of polytetrafluorethylene mixed in the sample.
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