The influence of surface corrosion on microstructure and hydrogen permeability of Nb-Hf-Co dual-phase alloys

Abstract

Nb-HfCo quasi-binary alloys are prospective hydrogen separation membrane materials due to their price advantage and excellent hydrogen permeation performance. However, a small amount of acidic gas (e.g. CO2 and H2S) is often mixed in the feed gas, which corrodes the surface of the alloy membrane in the process of their application. Up to now, the corrosion behaviours and the corresponding influencing factors have not been studied yet, and the relationship between the microstructure and corrosion resistance has yet to be established. To this end, NbxHf(100−x)/2Co(100−x)/2 (x = 40.60) dual-phase alloys were prepared by arc melting and then corroded using an electrochemical workstation, and their microstructure, corrosion resistance and hydrogen permeability before and after corrosion were systematically studied. The results show that an oxide layer (Nb2O5, HfO2, CoO) is formed around the alloy surface after corrosion, and the order of corrosion resistance of these alloys is as follows: Nb60Hf20Co20 < Nb40Hf30Co30 < Nb50Hf25Co25 < Nb45Hf27.5Co27.5. The Nb45Hf27.5Co27.5 alloy, with the strongest corrosion resistance, exhibits a high hydrogen permeability of 6.70 × 10−8 mol H2 m−1 s−1 Pa−1/2 at 673 K after corrosion, which is the highest value reported in this alloy system up to now. In addition, the hydrogen permeation mechanism for Nb-based alloy membranes in a corrosive environment, is proposed for the first time. The present work demonstrates that Nb45Hf27.5Co27.5 alloy is an attractive candidate for hydrogen separation in an acidic corrosive environment.