Reaction diffusion in the vanadium-zirconium system

Abstract

Reaction diffusion in the vanadium-zirconium system has been studied in the temperture range 1273 to 1473 K by use of two types of semi-infinite couples, (pure V)-(pure Zr) and (pure V)-(Zr-13.5 at% V alloy) and a sandwich type couple, (pure V)-(pure Zr foil of 50 to ~ 200μm)-(pure V). In all three types of couples diffused above 1373 K parabolic growth of the V₂Zr phase layer has been observed after respective incubation times. At 1473 K, the incubation time in the (pure V)-(pure Zr) couple is 24 h, however, it is 1 h in the (pure V)-(pure Zr foil of 50μm)-(pure V) couple and nearly zero in the (pure V)-(Zr-13.5 at% V alloy) couple. This suggests that for nucleation of the V₂Zr phase during the reaction diffusion, the concentration at the interface of the phase boundary between theβ-phase (Zr-rich solid solution) and theγ-phase (V-rich solid solution) is required to reach the nearly equilibrium one. It has been found that at the lower diffusion temperature the uphill diffusion of vanadium from theβ-phase contributes in part to growth of the V₂Zr layer. In addition to the V₂Zr phase, another phase, VZr, unexpected from the equilibrium phase diagram of the V-Zr system has been formed in the (pure V)-(pure Zr) couple diffused at 1473 K for more than 230 h.