CONNECTION BETWEEN DIFFUSIVITY AND ACTIVITY-COEFFICIENT

On the basis of linear nonequilibrium thermodynamics, the connection b etween diffusivity and activity interaction coefficients in melts was delineated and this relation can be expressed as the following mathema tic formula: [GRAPHICS] ities show that the mass transfer is also infl uenced by a convective transport mechanism overlaying diffusion. The i nterfacial convection, known as the Marangoni effect, is considered to be the reason for this convection at the phase boundary. The dependen ce of the mass transfer on the basicity, the initial sulphur content o f the bath, and the addition of a CaF2 mass content of 2.5% has been i nvestigated. A computer calculated match of theoretical concentration plots with the data measured yields the interdiffusivity of S2- and Fe 2+ within the slag, the average velocity of the convective material tr ansport normal to the phase boundary, and the equilibrium sulphur cont ents. The value of the average velocity increases exponentially with d ecreasing slag viscosity. The relation between the mass transfer coeff icients and both the diffusion coefficient in the bath and the interdi ffusivity in the slag, familiar from the surface renewal theory, follo ws as a consequence of the mass conservation law.