ON THE ANOMALOUS SELF-DIFFUSION IN BODY-CENTERED CUBIC ZIRCONIUM

Abstract

Results of recent diffusion studies in the BCC phase of Zr give unusually low values of the parameters Q and D0 in the expression for the diffusion coefficient D = D0 exp(−Q/RT). Measurements in the high-temperature range show a marked departure from linearity in a plot of log D vs. 1/T. A simple model is proposed to account for these results based on the assumption that excess vacancies introduced by impurities (probably oxygen) predominate in the low-temperature region. It is found that for zirconium the measured diffusion coefficient can be represented over the whole temperature range by D = 1.34 exp (−65,200/RT) + 8.5 × 10−5 exp (−27,700/RT) cm2/sec. The calculated concentration of excess vacancies is 0.038 atomic per cent.