Diffusion of uranium in molybdenum, niobium, zirconium and titanium

Abstract

An investigation was made of the diffusion of uranium in molybdenum, niobium, zirconium and titanium. The diffusion coefficients were established by measuring the integral activity of the residue of the sample, using the α-radiation of uranium enriched up to 90 per cent with ²³⁶U, at temperatures of 1500–2000°C (for molybdenum and niobium) and 915–1200°C (for zirconium and titanium).

The temperature dependence of the diffusion coefficients was presented as $\text{D}{}_{\mathrm{Mo}}{}^{\mathrm{U}}\text{= 7.60 × 10}{}^3\text{exp(− 76400/RT)cm}{}^2\text{/sec;}$$\text{D}{}_{\mathrm{Nb}}{}^{\mathrm{U}}\text{= 8.90 × 10}{}^{\mathrm{-2}}\text{exp(− 76800/RT)cm}{}^2\text{/sec;}$$\text{D}{}_{\mathrm{Zr}}{}^{\mathrm{U}}\text{= 7.77 × 10}{}^{\mathrm{-5}}\text{exp(− 25800/RT)cm}{}^2\text{/sec;}$$\text{D}{}_{\mathrm{Ti}}{}^{\mathrm{U}}\text{= 4.90 × 10}{}^{\mathrm{-4}}\text{exp(− 76400/RT)cm}{}^2\text{/sec;}$

The substantial differences between the diffusion mobility and activation energy values of molybdenum and niobium on the one hand and zirconium and titanium on the other are probably due to defects in the crystal lattice, such as excess vacancies in zirconium and titanium due to polymorphic transformation.