Abstract
The theory of diffusion in melts is outlined. The inter-diffusion (or mutual diffusion) coefficient D_<12> in a binary molten mixture can be divided into two contributions: one factor arises from concentration fluctuations related to stability of the mixture and the other one can be written in terms of self-diffusion coefficients of the respective components. The concept of the velocity autocorrelation function and the memory function is briefly described, and comparisons between theory and experiment are shown for diffusion properties of liquid metals. It is emphasized that microgravity experiments are very important in the studies of diffusion in melts, since they are free from the effects of convection and gravity inevitable in the experiments made on the earth.
