Nb–Ni- and V–Ni-Based Membranes for High-Purity Hydrogen Production

Membrane separation of high-purity hydrogen is now one of the most effective technologies mainly due to the alternative replacement of expensive Pd–Ag membrane alloys with cheaper ones based on the Group VB bcc metals (V, Nb, Ta, etc.) with an amorphous or nanocrystalline structure and a permeability exceeding that of fcc palladium alloys. Although hydrogen selection membrane alloys made of bcc metals Co, V, Cr, Ta, and Nb exhibit a very high hydrogen permeability, they undergo brittle fracture because of excess hydrogen absorption. The hydrogen kinetics in titanium-alloyed membrane binary alloys Nb–Ni and V–Ni is analyzed and compared according to criteria such as strength characteristics, thermal stability, and hydrogen embrittlement resistance. The dissolution of Ni and Ti in niobium and vanadium phases increases the critical temperature of β hydride formation from 473 to 673 K. In addition, Ni–Ti and NiTi2 compounds stabilize the matrix structure of membrane alloys and prevent hydride formation.