A Study Of Raman Spectra Of Aluminosilicate Minerals, Glass And Melts

Silicate melts and minerals are widely applied to metallurgy, material science and geology. Thus studies on the structure and properties of silicate minerals, glasses and melts are of great importance in these fields. Raman spectroscopy and high-temperature Raman spectroscopy (HTRS) have widely been recognized as one of the most effective methods to study silicate microstructure, especially structure of silicate melts. Many significant research achievements have been obtained.This dissertation is supported by the Key Project of the National Natural Science Foundation of China "High-temperature Raman Spectroscopy (HTRS) and the Structure and Properties of Substance in High-temperature", which are jointly carried out by Shanghai University, China University of Geosciences (Beijing) and Peking University. The research intends to conduct studies on microstructure of silicate minerals and melts by using Raman and high-temperature Raman spectroscopy, including measuring Raman spectra of silicate and aluminosilicate minerals, glass and melts, calculating structure models by quantum mechanics and ab initio calculation of quantum chemistry and then comparing both experimental and calculating results. It aims to get better understanding about the role of Al³⁺ (including four-coordinate, six-coordinate) in silicate microstructure and its effects on the characteristics of Raman spectra of aluminosilicates, and to provide a hint in methodology for study of melt structure of silicates as well.Raman spectra of eleven typical aluminosilicate minerals were measured. By employing Dmol³ Density Functional Theory (DFT) software in Materials Studio3.1 packet, corresponding modeling was also conducted and then compared with the experimental results. Aluminosilicate glass samples with different compositions and mole ratios in K₂O-Al₂O₃-SiO₂ system were prepared and then measured with Raman spectrometer and High-temperature Raman spectrometer to get Ramam spectra for glass and melts, respectively. Meanwhile, polymerization models with various combinations of (Si, Al)-0 tetrahedrons were calculated by using software Gaussian 98W, i.e., ab-initio calculation of the quantum chemistry, and Compared with experimental results. The following conclusions can be reached on the basis of studies mentioned above.1. Similarities of Raman spectra among aluminosilicate crystals, glass and melts have been found. While frequencies of the characteristic peaks considerably decrease within the range of 800-1200 cm^-1, intensities of vibration increase within the range of 700-800 cm^-1 with increasing content of four-coordinated Al cations. While Raman scattering bands in the former range are assigned to Si-O_nb symmetric stretching vibrations, those in the range of 700-800 cm^-1 attributed to Al-O_nb symmetric stretching vibrations. The Raman bands within the range of 800-1200 cm^-1 shift to higher frequency if Al are six-coordinated cations as network modifiers.