A diffusion solution for the melting/dissolution of a solid at constant temperature and its use for measuring the diffusion coefficient in liquids

A general solution to the diffusion equation is obtained for the composition in two phases when one phase dissolves and the other grows at constant temperature. The relevance of the derivation to melting is discussed. The exact solution is used to examine the condition when diffusion may be considered to occur in only one phase. Experiments have been carried out using the analysis to obtain solute diffusion coefficients in liquid succinonitrile-water alloys. The method relies on an interface displacement measurement and does not require the composition to be measured as a function of position as is usually necessary with a diffusion couple.