Abstract

The diffusion coefficients of iron, using ${\mathrm{Fe}}^{59}$ as the radioactive tracer, and the isotope-effect parameter, using ${\mathrm{Fe}}^{55}$ and ${\mathrm{Fe}}^{59}$ as tracers, have been measured in vanadium over a temperature range of more than 800\ifmmode^\circ\else\textdegree\fi{}C by standard sectioning and counting techniques. The diffusion of ${\mathrm{Fe}}^{59}$ in vanadium exhibits the anomalous behavior of having not one but two straight lines in a plot of $\mathrm{ln}D$ versus $\frac{1}{T}$, with a change of slope occurring near 1350\ifmmode^\circ\else\textdegree\fi{}C. The data have been analyzed into the sum of two exponentials: $D=2280$ $\mathrm{exp}(\ensuremath{-}\frac{101500}{\mathrm{RT}})$ at high temperatures, and $D=0.0936$ $\mathrm{exp}(\ensuremath{-}\frac{67600}{\mathrm{RT}})$ at low temperatures. The values of the isotope-effect parameter for the ${\mathrm{Fe}}^{59}$ and ${\mathrm{Fe}}^{55}$ isotopes are approximately constant near 0.7 at low temperatures, but decrease rapidly with increasing temperature above 1350\ifmmode^\circ\else\textdegree\fi{}C. The measurements are interpreted to indicate that two mechanisms of diffusion operate in vanadium. The mechanism predominant at low temperatures is identified as motion of a single vacancy; that at high temperatures is probably motion of divacancies.

Full Text
Paper version not known

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call