An investigation of CaO-MgO-Al2O3-SiO2 liquids by nuclear magnetic resonance spectroscopy, vibrational spectroscopy, and ion dynamics simulation

A multi-directional approach has been taken in order to investigate the structural and dynamic properties associated with liquid phases in the system CaO-MgO-Al2O3-SiO2 (CMAS). Using a newly developed high temperature 27Al Nuclear Magnetic Resonance (NMR) spectroscopic technique, which involves simultaneously levitating and heating the sample with a CO2 laser, direct structural and dynamic information on refractory aluminate and aluminosilicate liquids has been obtained at temperature of 2000 K and above. From this technique, measured isotropic chemical shifts and NMR linewidths of the liquids exhibit systematic trends with variations in composition which can be associated with the static and relaxation behavior of the structural environment about aluminum. Structural information of the liquids is time-averaged due to the rapid motional averaging characteristic of these liquids at the timescale of the NMR experiment. Comparison of these results with those of corresponding glasses both from solid state NMR and vibrational spectroscopic experiments allows for a more detailed interpretation of the structural makeup of these liquids. Combined with results and next-nearest-neighbor environments allows for a more quantitative estimation of the melts investigated suggest greater proportions of high coordinate aluminum species (AlO5 and AlO6 units) compared to existing data compiled for corresponding glasses. Finally, in-situ high temperature Raman spectra have been obtained which show direct experimental evidence for the presence of distinct molecular species in these refractory liquids, and also indicate structural changes as a function to temperature