Effects of Transition Metal Oxides on Thermal Conductivity of Mould Fluxes

Abstract

The thermal conductivity of the mould fluxes containing transition metal oxides was measured by hotline method at different temperatures. The relationship between the thermal conductivity of mold fluxes and the contents of transition metal oxides was discussed. The synthetic slags were composed of 30.0% — 35.4% CaO, 34.7% — 38.6% SiO2, 6% Al2O3, 9% Na2O, 14.4% CaF2, 0–4% Cr2O3 and 0–8% MnO in mass percent. The results indicated that Cr2O3 and MnO had a negative effect on thermal conductivity of mold fluxes. The thermal conductivity of mold fluxes was about 0.25 — 0.55 W/(m K) when the temperature reached 1300 °C, and it increased sharply to about 1.32–1.99 W/(m K) when the temperature reduced from 1300 to 1000 °C. The thermal conductivity of mold fluxes containing Cr2O3 and MnO was 10%—25% lower than those of original fluxes. The decrease in thermal conductivity was attributed to the change of molecular structure of mold fluxes. In addition, the poor integrity and regulation of polycrystal structure, complexity of crystal structure, and effects of impurities in the boundary and lattice distortion leaded to the reduction in the thermal conductivity. Na2CrO4, Mn2SiO4 and other minor phases were also found in the samples containing Cr2O3 and MnO, respectively.