The effect of surface oxides and grain sizes on the deuterium permeation behavior of niobium membranes

Abstract

Group 5 transition metal niobium is considered as the promising hydrogen separation membrane material because of its theoretical highest atomic hydrogen permeability, good mechanical strength, low price and easy shaping. However, the permeability of hydrogen in the dense metal membrane is affected by surface oxides, gain sizes, defects and so on. In this paper, the effect of surface oxides and grain sizes on the permeation behavior of deuterium through niobium membranes is studied. The niobium membranes with micro- and nanocrystalline were first treated by mechanically or electro-polished to remove the surface oxides, and then the deuterium permeability tests were performed in the temperature range of 600–800 ℃ at the driving pressures of 50 kPa by gas-driven permeation method. Results showed that the niobium membrane with nanocrystalline and “clean” surface had the highest deuterium permeation than that with microcrystalline or unclean surface. More importantly, grain size and grain boundary had a greater influence on the deuterium permeation behavior of niobium membranes than the thin surface oxides. These results shed new light on the enhancement of hydrogen and its isotopes permeation in the niobium-based hydrogen separation membranes. Further work is to study the plasma-driven permeation of deuterium through nanocrystalline niobium membrane in order to obtain the super-permeation rate.