Microstructure And Hydrogen Permeation Properties Of V-Cr-Pd-Cu Alloy

Metal membrane is very important for separation and purification of hydrogen.Developing low-cost new-type metal membranes with excellent resistance to hydrogen embrittlement,with high permeability of hydrogen and with less or without Pd attracts much attention.In the present study,the influence of elements Cr and Pd on the microstructures and hydrogen-separation properties of V-based alloy are investigated to optimize concentrations of V-Cr-Pd alloy.Based on the idea of "multiphases and functions shared",a quaternary alloy,VCr-Pd-Cu,is designed.The formation of fcc-?Cu?solution phase is expected during solidification.By means of scanning electron microscopy?SEM?,X ray diffraction?XRD?,self-developed Sieverts-type apparatus,High precision hydrogen permeation equipment analysis and testing means.As-cast V-Cr-Pd alloy is composed of single bcc-?V?solid solution phase.The elements Cr and Pd uniformly dissolve in the alloy.The lattice is compressed because the atom V is replaced by the atom Cr.With the content of Cr being increased,the compression degree of lattice is increased.SEM results show that phase morphology of bcc-?V?changes from bulk type to worm type.With the dissolution of both Cr and Pd in the bcc-?V?phase,the addition of Pd can,to some extent,release the compression degree of the lattice.When the added amount of Pd and Cr is proper,such as V-5Cr-5Pd,the compression of lattice can be almost eliminated and the lattice parameters of bcc-V are similar to that of pure V.PCT curves show that since the dissolution of hydrogen is exothermic in the solid-solution alloys,the solubility of hydrogen in the metal membranes decreases with increasing temperature.At low equilibrium pressure,the temperatures obviously affect the hydrogen solubility.With the addition of Cr and Pd,both the amount of hydrogen absorption and the hydrogen diffusion coefficient K decrease.The more the amount of Cr and Pd dissolved,the larger the decreasing extent.The elements Cr and Pd play different roles in lowering the hydrogen solubility.The ability of Pd to reduce the hydrogen dissolution is stronger than that of Cr.The hydrogen permeation experiments of V-Cr-Pd show that although the hydrogen permeation rate of V-7Cr-3Pd is higher,a large amount of hydrogen is absorbed,leading to the membranes ruptured because of hydrogen embrittlement.The as-cast microstructure and hydrogen transmission performance of V₃₀Cu_70-xCr_x alloy show that the microstructure of Cu-V is reasonable and is similar to that of superconductive Cu-Nb alloy.In the two-phase structure,bcc-?V?phase is for hydrogen permeation?hydrogen diffusion channel?and fcc-?Cu?phase for supporting.By testing and analyzing the hydrogen dissolution and hydrogen diffusion properties of Cu₇₀V₃₀ and Cu₆₀V₃₀Cr₁₀alloys,we can see that as the supporting phase,fcc-?Cu?phase does not affect the properties of bcc-?V?phase.Based on V-5Cr-5Pd alloy,?V-5Cr-5Pd?₉₀-Cu₁₀ alloy is developed to introduce fcc-?Cu?phase.It is found that even if the content of Cu is low,the desirable two-phase structure still exists.?V-5Cr-5Pd?₉₀-Cu₁₀ alloy is characterized with excellent hydrogen permeation properties and resistance to hydrogen embrittlement.