Thermotransport of Hydrogen in Niobium and Tantalum as a Function of Hydrogen Concentration

摘要

Transport of hydrogen in Nb and Ta has been measured in an extended hydrogen concentration range up to 0.3 (H/M) atomic ratio. In these high concentrations where the activity coefficient is not constant with concentration, the heat of transport is defined based on an activity ratio. Using the square root of the hydrogen pressure versus hydrogen concentration curves extrapolated from the curves measured by Veleckis and Edwards, the activity ratios were calculated from the measured concentrations. The absolute thermoelectric power of Nb and Ta has been measured in the same hydrogen concentration range in order to check the relationship, which was predicted by Huntington, between the absolute thermoelectric power and the heat of transport. The heat of transport based on the activity ratio, Q*(a/sub H//a/sub C/), decreased as the hydrogen concentration increased in both Nb and Ta. The heat of transport based on the hydrogen concentration ratio, Q*(C/sub H//C/sub C/), decreased in Ta but increased in Nb as the hydrogen concentration increased. The absolute thermoelectric power of Nb and Ta increased as the hydrogen concentration increased. (ERA citation 09:018751)