Viscosities of CaO-SiO₂-Al₂O₃-(R ₂O or RO) melts

The effect of adding R₂O (R=Li, Na and K) or RO (R=Ba, Mg) on the viscosities of CaO-SiO₂-Al₂O₃ (CaO/SiO ₂=0.67, 1.00 or 1.22, Al₂O₃=20 mass%) melts has been measured by rotating crucible viscometer. In addition, structural characterizations of these quenched vitreous samples have been investigated by ²⁷Al and ²⁹Si MAS-NMR spectra. The viscosities of CaO-SiO₂-Al₂O₃-R₂O quaternary melts decreased with increasing the additive content of Li₂O or Na ₂O. However, the viscosity of the melts increased with increasing the additive content of K₂O. In the case of CaO-SiO₂-Al ₂O₃-RO quaternary melts, the viscosities of the melts with CaO/SiO₂=0.67 decreased with increasing the additive content of BaO or MgO, however, the viscosities of the melts with CaO/SiO₂=1.00 and 1.22 increased with increasing the additive content of BaO. In the case of CaO-SiO₂-Al₂O₃-R₂O, the analysis of ²⁷Al MAS-NMR spectra and ²⁹Si MAS-NMR spectra indicated that the degree of polymerization of silicate anions in the glasses decreased with the addition of Li₂O or Na₂O, and that the degree of polymerization of aluminosilicate anions in the glasses increased with the addition of K₂O. It was estimated from the results that the increase in viscosities of CaO-SiO₂-Al₂O₃-K₂O melts was dependent on increase of aluminosilicate anions in the melts with the addition of K₂O. In the case of CaO-SiO₂-Al ₂O3-RO, the analysis of ²⁷Al MAS-NMR spectra and ²⁹Si MAS-NMR spectra indicated that the degree of polymerization of silicate and aluminosilicate anions in the glasses decreased with the addition of MgO. The degree of polymerization of aluminosilicate anions in the glasses increased with the addition BaO. It was estimated from the results that the increase in viscosities of CaO-SiO₂-Al₂O₃-BaO melts was dependent on increase of aluminosilicate anions in the melts with the addition of BaO.