Dissolution of alumina in mold fluxes

The solubility and rate of dissolution of alumina in a range of mold fluxes in the CaO-Al2O3-SiO2-Na2O-CaF2 system have been measured at 1530 °C using the rotating finger method. The solubilities were approximately 38 pct for all fluxes studied. The kinetics of dissolution were correlated with the Levich-Chochran equation for a rotating disc and used to determine the effective diffusivity of alumina. The effective diffusivity was inversely proportional to the viscosity of the flux and showed excellent agreement with previous work on CaO-Al2O3-SiO2 slags. This is in keeping with either the Eyring relation or the Stokes-Einstein relation. The value obtained for the size of the diffusing unit when the Stokes-Einstein relation was used, 1.81 Å, was more reasonable, which is not normally expected for silicate slags. This result is explained by the low level of polymerization in these fluxes.