Quantitative studies on the microstructure of ternary CaO–Al2O3–SiO2 glasses by Raman spectroscopy, 27Al MAS NMR and quantum chemistry ab initio calculation
Abstract
In order to investigate the structural behaviors of Al 3+ in aluminosilicate system, the microstructural characteristics of CaO-SiO 2 -based glassy samples with various Al 2 O 3 contents were examined quantitatively by Raman spectroscopy and 27 Al MAS NMR. Sequence of multiple cluster models of aluminosilicate system modified with Ca 2+ and Na + cations have been designed, and Raman spectral simulation were carried out after geometric optimization by quantum chemistry (QC) ab initio calculation. The functional relationship between Raman scattering cross section (RSCS) and stress index of silicon-oxygen tetrahedron (SIT) for aluminosilicates was established, which was applied to the calibration of experimental Raman spectra successfully. Some five-fold coordinated aluminum (Al Ⅴ , around 5%) and less than 2% six-fold coordinated aluminum (Al Ⅵ ) were detected by 27 Al MAS NMR, while most of aluminum remained in tetrahedral sites (Al Ⅳ ). The ever-finer quantitative results of Raman spectroscopy and NMR showed a gradually production of Al Ⅳ with the addition of Al 2 O 3 , along with the significant adjustment of Q i species distribution, in which Q 1 , Q 2 decreased and fully polymerized Q 4 increased while Q 3 showed a nonmonotonic variation and obtained the maximum at Al 2 O 3 =18 mole%. Furthermore, the effects of aluminum to bridging oxygen bond types (T-O b , T=Si, Al) and the degree of polymerization were also discussed in detail. These structural features related to composition are essential theoretic foundation to understand their properties.
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