The diffusion of Nb 95 and Ta 182 in tantalum

Abstract

Diffusion constants were obtained for Nb 95 and Ta 182 in tantalum over the temperature range 920–2500°C making use of lathe, grinding, and anodic film sectioning techniques. Over this temperature range, the lattice diffusion coefficients were observed to vary from about 2.5 × 10 −19cm 2/sec to about 4 × 10 −9cm 2/sec for Nb 95 in tantalum. The Ta 182 diffusion coefficients were about half those for Nb 95 at all temperatures. The apparent variation in the activation energy for Nb 95 diffusion in tantalum was about 6000 cal/mole over the whole temperature range; thus the Arrhenius relationship was seen to apply exceptionally well to this system. The expression D = 0.23 exp( −98,700 RT )cm 2/sec describes the data within 20%.