Variation in viscosity of aluminosilicate melts with MgO/CaO molar ratio: Influence of five-fold coordinated aluminum

Viscosity of aluminosilicate melts is important for estimating transport phenomena in industrial processes. Viscosity variations with increasing MgO/CaO molar ratio have been reported for CaO-MgO-SiO2 (CMS) and CaO-MgO-Al2O3-SiO2 (CMAS) systems; however, the viscosity variation was not clearly correlated with the change in the melt structure. The present study investigated the influence of the MgO/CaO molar ratio on the viscosity of CMAS melts at temperatures higher than the liquidus using the rotating crucible method. The vis-cosity decreased with increasing substitution of CaO by MgO in the chosen CMAS system, whereas the opposite behavior has been reported for the CMS system. Aluminum-27 magic-angle spinning nuclear magnetic resonance spectra of the CMAS glasses show that the fraction of aluminum atoms in five-fold coordination ([5]Al) increased with increasing substitution of CaO by MgO. Our findings indicate that the formation of [5]Al reduces the vis-cosity of aluminosilicate melts.

Automated summary

The viscosity of CMAS melts decreases with increasing MgO/CaO molar ratio and the formation of [5]Al reduces the viscosity of aluminosilicate melts.