Alloying Effects on the Hydrogen Diffusivity during Hydrogen Permeation through Nb-Based Hydrogen Permeable Membranes

Abstract

The hydrogen solubility and the hydrogen permeability have been measured for Nb-based alloys in order to investigate the alloying effects on the hydrogen diffusivity during hydrogen permeation. The hydrogen diffusion coefficient during hydrogen permeation is estimated from a linear relationship between the normalized hydrogen flux, , and the difference of hydrogen concentration, C, between the inlet and the outlet sides of the membrane. It is found that the hydrogen diffusion coefficient during the hydrogen permeation is increased by alloying ruthenium or tungsten into niobium. On the other hand, the activation energy for hydrogen diffusion in pure niobium under the practical permeation condition is much higher than the reported values measured for dilute hydrogen solid solutions. It is interesting that the activation energy for hydrogen diffusion decreases by the addition of ruthenium or tungsten into niobium.

Alloying Effects on Hydrogen Solubility and Hydrogen Permeability for V-Based Alloy Membranes

“…Following the concept for alloy design proposed by Yukawa et al, 15,16,21) the alloying elements should be selected from two points of view. First, in order to reduce the hydrogen concentration, the alloying elements should have lower affinity for hydrogen than niobium or vanadium.…”

“…15,16) On the other hand, the hydrogen permeability of metal membrane is generally discussed by hydrogen permeation coefficient, ), which is the product of the hydrogen diffusion coefficient, D, and the hydrogen solubility constant, K. However, for non Pd-based alloys such as vanadium and its alloys, the Sievelts' law is not applicable under ordinary hydrogen permeation conditions (i.e., temperature and H 2 pressures), indicating that the hydrogen permeation coefficient, ), is not a good measure to show the hydrogen permeation ability of them.…”