Impurity Diffusion of Fourth Period Solutes (Fe, Co, Ni, Cu and Ga) and Homovalent Solutes (In and Tl) into Molten Aluminum

Abstract

In order to clarify the relative importance of various factors controlling the diffusion in liquid metals, the measurements of impurity diffusion coefficients have been carried out over the temperature range of 980 to 1320 K. Aluminum which can be regarded as a trivalent simple metal was chosen as a solvent. On the other hand, homovalent elements (Ga, In and Tl) and the fourth period elements (Fe, Co, Ni, Cu and Ga) have been chosen as the solutes. The results obtained can be summarized as follows:(1) The diffusion coefficients of homovalent solutes are in the order of DGa>DIn>DTl, that is, the diffusion coefficient increases as radius and mass of solute element decrease.(2) The apparent activation energy for diffusion of the solute belonging to the fourth period in the periodic table increases with decreasing valence of the solute. This may be due to the coulombic interaction between the solvent and the solute atoms caused by the excess charge locating on the solute atom. By assuming the Hartree self-consistent potential for the charge screening potential, the activation energies for diffusion were calculated. The calculated values agreed well with the observed apparent activation energies.(3) The diffusion coefficients of solutes in molten aluminum calculated on the basis of the hard sphere theory originally derived by Enskog are slightly smaller than those observed. The apparent energy obtained from the temperature dependence of the calculated diffusion coefficients are also smaller than the measured ones. The difference between the calculated and observed apparent activation energies for diffusion can be explained in terms of the coulombic interaction between the solute and the solvent atoms.