Interstitial Diffusion of Copper and Silver in Lead

Abstract

The diffusivities D of copper and silver in high-purity lead have been measured by a radioactive tracer technique. They are described by DCu/Pb = 7.9×10−3e−(8020/RT) cm2 sec−1, DAg/Pb = 4.6×10−2e−(14 440/RT) cm2 sec−1. These results, in combination with those of Seith and Keil and Ascoli et al., show that the rates of diffusion of the noble metals in lead are several orders of magnitude greater than the self-diffusion rate of lead DPb. We have found that DPb is not measurably affected by the dissolution of either gold, in agreement with Seith and Keil, or of copper. The results indicate that neither the vacancy, interstitialcy, nor exchange mechanisms are predominant in the diffusion of these solutes. It is concluded that the noble metals are dissolved in lead at least partially in the interstitial state and that they diffuse almost wholly by an interstitial mechanism.