The Effect of the Rate of Cooling on the Allotropic Transformation Temperatures of Uranium

Abstract

Allotropic transformation in uranium has been studied over a range of cooling rates from 5 to about 8000°C/sec. The transformation temperatures of both gamma‐to‐beta and beta‐to‐alpha were found to decrease continuously with increasing rates of cooling. The extent of the beta‐range increased with increasing cooling rates. For rates of cooling up to 1000°C/sec, recalescence was observed in both transformations. For higher cooling rates, there was usually no recalescence. In most of the recorded cooling curves, a small but definite thermal arrest was observed, between the two main arrests which correspond to the two known phase transformations. This additional thermal arrest was also present in a heating curve, where it occurred at about 740°C, compared with 666 and 771°C for the two known phase transformations. Possible explanations of the additional arrest are discussed.