Characteristics of Amorphous, Nanocrystalline, and Crystalline Membrane Alloys

The alloys intended for membrane technologies for producing high-purity hydrogen and the methods of their synthesis are analyzed. Both traditional Pd-based alloys and the alloys based on cheaper Group V and VIII metals are considered using binary Nb–Ni, V–Ni, and Ta–Nb alloys with Ti, Zr, Mo, Hf and W as an example. The kinetic and strength characteristics, thermal stability, wear resistance, and stable functionality of membrane amorphous and nanocrystalline alloys with alternative compositions based on Group V elements are considered. The problems of intermetallic and hydrogen embrittlement during long-term hydrogen selection processes are considered. A solution to these problems is proposed by designing new alloys based on Group V and VIII metals alloyed with elements Ti, Mo, Hf, and W, by limiting the temperature range from 473 to 673 K, and by limiting the maximum permissible hydrogen concentrations H/M to at most 0.22. Membrane alloys of Nb(V, Ta)–Ti–Ni solid solutions with a duplex matrix structure, namely, eutectic phases and primary phases {bcc (Nb, Ti) + TiNi} + {Nb(V, Ta), Ti}, respectively, and the NiTi and NiTi2 compounds stabilizing and protecting the matrix structure against brittle destruction are also analyzed. The proposed alternative alloys make it possible to produce high-purity gaseous hydrogen using new compositions instead of expensive membranes based on Pd–Au/Ag/Cu alloys.