Viscosities of CaO-SiO2-Al2O3 (R2O 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/SiO2=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 Al-27 and Si-29 MAS-NMR spectra. The viscosities of CaO-SiO2-Al2O3 R2O quaternary melts decreased with increasing the additive content of Li2O or Na2O. However, the viscosity of the melts increased with increasing the additive content of K2O. In the case of CaO-SiO2Al2O3 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-SiO2Al2O3 R2O, the analysis of Al-27 MAS-NMR spectra and Si-29 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-Al2O3K2O melts was dependent on increase of aluminosilicate anions in the melts with the addition of K2O. In the case of CaO-SiO2 Al2O3RO, the analysis of Al-27 MAS-NMR spectra and Si-29 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.