VISCOSITY AND STRUCTURE OF QUATERNARY ALUMINOSILICATE MELTS

In the present work, the effects of R2O (R=Li, Na and K) or RO(R=Ba, Mg) additives on the viscosities of CaO-SiO2-Al2O3 (CaO/SiO2=0.67, 1.00 or 1.22, Al2O3=20mass%) melts have been measured by using rotating crucible viscometer. In addition, structural characterizations of these quenched vitreous samples have been investigated by 27Al MAS-NMR. The viscosities of CaO-SiO2-Al2O3-R2O quaternary melts decreased with the addition of Li2O or Na2O. However, the viscosity of the melts increased with the addition of K2O. In the case of CaO-SiO2-Al2O3-RO quaternary melts, the viscosities of the melts with CaO/SiO2=0.67 decreased with the addition of BaO or MgO, however, the viscosities of the melts with CaO/SiO2=1.00 and 1.22 increased with the addition of BaO. In the case of CaO-SiO2-Al2O3-R2O, 27Al MAS-NMR spectra indicated that the amount of Al3+ in tetrahedral coordination (Al3+(4)), which behaved as a network-former, was increased with addition of R2O. However, no significant difference in quantity of Al3+(4) was observed among the glasses containing different kind of additives (Li2O, Na2O or K2O). In the case of CaO-SiO2-Al2O3-RO, the analysis of 27Al MAS-NMR spectra indicated that the amount of Al3+(4) was not changed from CaO-SiO2-Al2O3 ternary glass. These results suggest that the increase in viscosity of CaO-SiO2-Al2O3-K2O or CaO-SiO2-Al2O3-BaO is not dependent on the increase of Al3+(4). It is estimated from the results that the polymerization degree of aluminosilicate anion have been affected by the kind of charge compensating cations.