Removal of Lead from Fe–Pb Mixtures by Evaporation in Stagnant Argon at 1 448 K and the Determination of the Lead Vapor-Argon Interdiffusivity

Lead, considered as a tramp element in steel, was successfully removed from a 50% Fe–50% Pb mixture by evaporation in argon at 1448 K. The progress of the removal shows that it takes 5 h to completely remove the lead from the mixture, the nonvolatile iron (solid) being left behind in the crucible (alumina). Results point toward a diffusion-controlled evaporation, and the system, which closely simulates Stefan's tube for studying evaporation of a liquid through a stagnant gas film, allowed the measurement of the interdiffusivity of lead and argon (DPb–Ar). Since this study dealt with a pseudosteady state diffusion, rather than the steady state one for which the diffusion flux equation is well established, the required pseudosteady state equation was first developed, and, subsequently, utilized with the help of the rate data to find the DPb–Ar at 1448 K. The measured value, which is 1.766(±0.378) cm2/s, compares very well with the estimated value of 1.774 cm2/s.