Design and characterizations of novel Nb-ZrCo hydrogen permeation alloys for hydrogen separation applications

Abstract

Novel Nb–ZrCo hydrogen permeable alloys are developed as potential membrane materials for hydrogen separation applications. Microstructures, hydrogen permeation behavior and the resistance to hydrogen embrittlement of NbxZr(95-x)/2Co(105-x)/2 (x = 15 … 40) alloys are studied. Three different microstructures are found in these alloys, particularly (a) the primary ZrCo phase and eutectic {bcc-(Nb, Zr) + B2-ZrCo} for x < 25, (b) the fully eutectic for x = 25 and (c) the primary bcc-(Nb,Zr) and eutectic for x > 25. Alloys with Nb content between 20 and 30 at.% present higher permeation results. Increase in Nb content lead to higher hydrogen permeability (Φ), but poorer embrittlement resistance, which can be attributed to an increase in hydrogen solubility. Nb25Zr35Co40 exhibits an appropriate balance between hydrogen permeability and embrittlement resistance. Permeability is improved apparently and hydrogen embrittlement resistance is also further strengthened for directionally solidified (DS) Nb25Zr35Co40, which is mainly attributed to a decrease in hydrogen solubility and the significant increment of hydrogen diffusivity. The present work demonstrates that the newly developed alloys could be used as potential candidate for hydrogen separation applications.