Residual carbon impurities in Zr-2.5Nb and their effect on deuterium pickup

The presence of residual carbon in Zr-2.5Nb at parts per million (ppm) levels affects the alloy's rates of oxide film growth and deuterium absorption (in 573 K lithiated heavy-water). Pickup rates increase with increasing carbon concentrations between 40 and 300 ppm with a possible inflection in the kinetic curves in the vicinity of 120 ppm. Increased rates are likely due to enhanced development of an inter-connected, large-scale, pore network within the oxide film. Oxides on Zr-2.5Nb containing 145 ppm carbon appear to be fully stoichiometric with a well developed network of large pores, while the oxide on the 85 ppm C alloy contains a high density of fine pores and is likely sub-stoichiometric