Estimation of Liquidus Temperatures for Multicomponent Silicates from Activation Energies for Viscous Flow

This article considers the viscous-flow phenomenon in molten silicate melts in the vicinity of their liquidus temperatures. An agglomeration of ionic species occurs in the liquid slag with decreasing temperatures and results in an increase in the viscosity and the activation energy for viscous flow. The latter was found to be nonlinear, increasing rapidly as the temperature is approached wherein a solid phase is likely to separate from the liquid. The second derivative of the activation energy for viscous flow with respect to temperature was found to show a discontinuity in the vicinity of the liquidus temperature. This has been verified in the case of viscous flow for both pure water and CaO-SiO2 melts. Experimental data for the viscosities of complex silicate melts and mold fluxes have also demonstrated the occurrence of a discontinuity in the second-derivative function, which is in accordance with the liquidus temperature as determined by differential thermal analysis (DTA). Thus, the second derivative offers a useful way of estimating the liquidus temperatures of multicomponent silicates, which are often difficult to determine due to upercooling effects.