The diffusion of gold in lead single crystals

Abstract

The diffusion of radioactive ¹⁹⁸Au and ¹⁹⁹Au has been measured in 99·999% pure lead single crystals over the temperature range of 190°c to 320°C. The final distribution of the solute, which was initially evaporated as a thin film on the surface of the lead specimens, could be represented in most cases by c(x, t)=S ₀[πDt]^−1/2exp—[x ²/4Dt], although departures from this were occasionally noted. The temperature dependence of the diffusion coefficient was found to be D=8·7 × 10⁻³ exp—[10 000/RT] cm²/sec. A number of models that could account for the unusually rapid diffusion of gold in lead are examined. It is concluded that the present results, and those of others for related phenomena, can be rationalized by assuming that gold enters and diffuses through the lead in two states of solution, substitutional and interstitial.