Intrinsic diffusion coefficients and the vacancy flow factor in Dilute Cu-Zn Alloys
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I.
INTRODUCTION
INFORMATION on the relative magnitudes of the jump frequencies of an impurity and the neighboring host atoms can be provided by the correlation factorf for the diffusion of the impurity in otherwise pure metal. ~ It is difficult to determine f, in connection with the isotope effect on the impurity diffusion, because the value of the kinetic energy factor AK, for impurity diffusion must be known. 2 Recently, Heumann 3 has shown that the vacancy flow factor, which is related theoretically to the five jump frequencies of a vacancy neighboring an impurity atom, can be determined from the intrinsic diffusion coefficient of the solvent atom in the infinite dilution of solute and tracer diffusion coefficients of solute and solvent in the pure metal. Knowing the values of the vacancy flow factor defined by the ratio of the phenomenological coefficients of flux equations in the state of infinite dilution, G = (LaB/LBB)Na=o,and the solute enhancement factor of solvent diffusivity, the correlation factor can be estimated independent of data on the isotope effect. 4'5 A study on the isotope effect and the solute enhancement effect for solvent diffusivity in Cu-Zn alloys has been carried out by Peterson and Rothman; 6 tracer diffusion and thermodynamic data in Cu-Zn alloys 8'9 are also available. Although interdiffusion and the Kirkendall effect in Cu-Zn alloys has been studied by many workers, ~~ experimental data on the intrinsic diffusion coefficients in dilute Cu-Zn alloys have been insufficient to estimate the intrinsic diffusion coefficient of copper in infinite dilution of zinc. In the present work, the interdiffusion coefficient,/), and the intrinsic diffusion coefficients of Zn and Cu, Dz, and Dcu, in the dilute alloys at 1168 K have been determined with semi-infinite couples using Darken's relation? 3 In addition, the Kirkendall effect in thin plate couples at 1168 K KAZUTOMO HOSHINO, formerly Graduate Student, Tohoku University, is now with Materials Science Division, Argonne National Laboratory, Argonne, IL 60439. YOSHIAKI IIJIMA, Instructor, and KEN-ICHI H|RANO, Professor, are both with the Department of Materials Science, Faculty of Engmeering, Tohoku Umverslty, Sendal 980, Japan. Manuscript submitted June 22, 1981 METALLURGICAL TRANSACTIONS A
has been examined using Heumann's method 14'15 to determine the ratio of the intrinsic diffusion coefficients, Dz,/Dcu, in very dilute alloys. Using the value of the intrinsic diffusion coefficient of copper in the alloy at infinite dilution of zinc, Dcu(0), determined by extrapolation, the vacancy flow factor has been calculated. The correlation factor for the impurity diffusion of zinc in copper has been estimated by combining the experimental value of the vacancy flow factor, G, with that of the enhancement factor, b.6 Comparing the correlation factor thus obtained with that based on the isotope effect 6 permits an estimate of the value of the kinetic energy factor for impurity diffusion.
II.
EXPERIMENTAL P R O C E D U R E
A pure copper rod was made
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