Viscosity of RE-Mg-Si-O-N(RE = Y, Gd, Nd and La) melts

Viscosities of the molten RE-Mg-Si-O-N(RE = Y, Gd, Nd and La) glasses have been measured using a newly-developed rotational viscometer with gas tight furnace. Effects of nitrogen and rare-earth additives on the viscosities of RE-Mg-Si-O-N melts have been investigated systematically at elevated temperature (∼1873 K). The viscosities of molten RE-Mg-Si-O-N glasses exponentially increased with nitrogen content, which indicates that the substitution of nitrogen for oxygen in the melts may lead to a high average coordination of nonmetal atoms, and that the increase of cross-linking produces a more rigid network structure. The viscosities of RE-Mg-Si-O-N melts were found to decrease in the order of cationic radius of rare-earth elements, which suggests that larger rare-earth elements behave as a stronger network modifier of complex silicate or silicon-oxynitride anions in elevated temperature melts. Additionally, the viscosity of the smaller rare earth containing oxynitride melt indicated more sensitive increase with nitrogen content.