Microstructure of CaO-SiO2-based glassy samples with various Al2O3 contents were examined
quantitatively by Raman spectroscopy and 27Al MAS NMR (magic-angle spinning nuclear magnetic
resonance). Sequence of multiple cluster models of aluminosilicate system modified with Ca2+ and
Na+ cations have been designed, and Raman spectra simulation were carried out after geometric
optimisation 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. Some five-fold coordinated aluminium (AlV, around 5 per cent) and less than 2 per cent sixfold
coordinated aluminium (AlVI) were detected by 27Al MAS NMR, while most of aluminium
remained in tetrahedral sites (AlIV). The hyperfine quantitative results of Raman spectroscopy and
NMR showed a gradually production of AlIV with addition of Al2O3, along with the significant
adjustment of Qi species distribution, in which Q1, Q2 reduced and fully polymerised Q4 increased
while Q3 showed a non-monotonic variation and obtained the maximum at Al2O3 = 18 mol per cent.
Furthermore, the effects of aluminium to bridging oxygen bond types (T-Ob, T = Si, Al) and the degree
of polymerisation were also discussed in detail. The evolution of microstructure and its correlation
with the viscosity of CaO-SiO2 based melts, incorporating various Al2O3 additives, have been
investigated by employing in situ high temperature Raman spectroscopy at 1823 K and viscosity
model. These structural features related to composition are essential theoretic foundation to
understand their properties. The average Qi evolution culminates in an overall enhancement of the
degree of polymerisation. Viscosity was determined utilising a rigorously selected viscosity model,
elucidating a consistent upward trajectory as Al2O3 content is incrementally added. Furthermore, a
quantitative analysis of the relationship between viscosity and structure was conducted based on
the average number of non-bridging oxygen per network-forming tetrahedron (NBO/T). It provides
valuable insights for examining and predicting viscosity behaviour of aluminosilicate systems.