Effects of Additives and Temperature on Dissolution Rate and Diffusivity of Lime in Al^sub 2^O^sub 3^-CaO-SiO^sub 2^ Based Slags

The dissolution rate of dense lime specimens in calcium aluminosilicate based melts was measured at 1430 °C to 1600 °C in air, using a rotating disk/cylinder technique. The measured dissolution rates were strongly dependent on the rotation speed with the results indicating mass transfer in the slag phase to be a rate-limiting step. At a given rotation speed, the slag chemistry and temperature had strong effects on the dissolution rate. The diffusivity of CaO in the slag was calculated from the dissolution rate and solubility data, using known mass-transfer correlations. Addition of CaF^sub 2^ MnO^sub x^, FeO^sub x^, and TiO^sub 2^ to the slag increased the CaO diffusivity, while SiO^sub 2^ had an opposite effect. Addition of CaF^sub 2^ had the strongest effect and increased the diffusivity by a factor of 3 to 5 in the temperature range of 1500 °C to 1600 °C. The deduced activation energy for diffusion of CaO in these slags ranged from about 53 to 246 kJ/mole, depending on the concentration of additives used. [PUBLICATION ABSTRACT]