Technique for Measuring Vacancy Concentrations in Metals at the Melting Point

A technique is described for measuring vacancy concentrations at the melting point by measuring the difference between the linear thermal expansion and the lattice thermal expansion. The method uses small specimens to facilitate eventual study of alloys and involves separate measurements of length change and lattice parameter change, the former by an interferometric technique and the latter by a diffractometer technique. The results of a study of 99.995% pure aluminum agree closely with the earlier measurements of Simmons and Balluffi, giving a vacancy concentration at the melting point of 8.7±1.2×10−4.