Mass Transport in Stationary Contact Points

Recent experimental work with direct current on aluminum-aluminum contacts has demonstrated that the electron flow through the narrow areas of real contact is accompanied by a flow of atoms. Three possible atomic transport mechanisms are considered: electromigration, thermotransport, and diffusion. Their relative contributions to the mass flow are derived based upon accepted models for spatial distribution of current and temperature close to the contact point. When applying material parameters as for aluminum, electromigration appears to be the dominating effect. The migration rate varies strongly with temperature and is also expected to be far higher along grain boundaries, dislocations, etc., than for volume migration through the metal lattice. The process of current-induced mass transport through the contact points is, according to the derived model, nonstationary and may be significant to the electrical properties of the contact.