Diffusion of liquid uranium into foils of tantalum metal and tantalum-10 wt% tungsten alloy up to 1350 °C

Abstract

Immersion experiments have been performed to investigate the diffusion of liquid uranium into 0.3 mm thick foils of tantalum metal and tantalum-10 wt% tungsten alloy in the temperature range of 1160 °C to 1350 °C, for reaction times up to 20 h, in zirconia crucibles. The original and uranium-reacted foils have been studied microscopically (SEM-EDAX) and a multilayer structure is revealed in the reacted foils. Layers identified for tantalum immersed in uranium: uranium-tantalum (U/Ta ~ 1), precipitated columnar tantalum (< 1 wt% U), inner uranium, and inner tantalum (with grown grains and uranium along grain boundaries). Layers identified for Ta-10 wt% W alloy immersed in uranium: uranium-tantalum (U/Ta~1, 0.3 wt% W), precipitated tantalum (< 1 wt% U, down to 1–2 wt% W), and inner Escher-type grains of tantalum-tungsten (up to 18 wt% W) and of uranium (< 2 wt% Ta, < 0.4 wt% W). A mechanism for the multilayer formation and the intrusion of liquid uranium into the solid foils is proposed and substantiated.