Viscosity evaluation of CaO-SiO₂-R₂O (R=Li, Na and K) based multi-phase fluxes

Viscosity of CaO-SiO₂-R₂O system at elevated temperature has been systematically evaluated with a rotating-crucible viscometer over the wide range of temperature, which includes the region of solid-liquid coexistence, so called "multi-phase". It was found that the viscosities of CaO-SiO₂-R₂O melts increased with temperature decrease, and were described with Arrehnius type temperature dependence between 20-100°C range of temperature below the liquidus. The rheological characterization Of CaO-SiO₂-R₂O melts had a transition from Newtonian to non-Newtonian fluid at a given temperature, which was classified as Bingham fluid according to the relationship between the shear rate and the shear stress calculated based on the experimental condition and the viscosity data. It was unveiled that the crystallization behavior controlled the changes in the Bingham yield stress τ_B Of CaO-SiO ₂-K₂O multi-phase fluxes with temperature decrease. The gradual increase of τ_B was attributed to the crystallization of the super-cooled melt with the dispersed fine grains. The devitrification with the course dentritic crystals caused the steep increase of τ_B.