Influence Of Element Y On High Temperature Of Hydrogen Permeation Process Of Pd-V-Pd Composite Membranes

V-based alloys have higher hydrogen permeability and lower cost than pure Pd.It is currently one of the most promising hydrogen separation alloys.In order to accelerate the dissociation of hydrogen molecules and the combination of hydrogen atoms,it is necessary to coat the surface of the V-based alloys film with a thin layer of Pd.V-based alloys also have certain problems at the same time,for example V has a higher hydrogen dissolution and can easily lead to hydrogen embrittlement.Hydrogen dissolution can be reduced ay alloying and increasing the working temperature.It has been found that element interdiffusion occurs between the surface Pd film and the V substrate when the V-based alloy film works at a temperature higher than 400?,resulting in the deterioration of the hydrogen permeability.Recent studies have shown that adding Y element to V85Ni15 alloy can effectively inhibit the diffusion between Pd and V.However,the effect of different amounts of Y added on the properties of the alloy and the effect of Y on the properties of other alloys are unclear.The effects of different amount of addition on V85Ni15 and V90Fe5Al5 alloys are studied in this paper.The as-cast and annealed V85-x Ni15Yx(x=0,0.2,0.8)alloys and V90-x Fe5Al5Yx(x=0,0.2,0.8)alloys were designed to investigate the effect of Y on the microstructure and high temperature hydrogen permeation.The results of XRD,SEM and EDS analysis of V85-x Ni15Yx(x=0,0.2,0.8)and V90-x Fe5Al5Yx(x=0,0.2,0.8)show that V85Ni15 alloy and V90Fe5Al5 alloy are single-phase solid solution group of bcc-V.After the addition of trace element Y different contents of Ni Y or Y3Al2 compounds phases were found.Y is a strong grain boundary segregation element and a very active lanthanon,so it easily reacts with other elements in the alloy to form macromolecular compounds.The as-cast and annealed V85-x Ni15Yx(x=0,0.2,0.8)alloys were subjected to a high temperature(753K)long-term hydrogen penetration test and high temperature heat treatment under vacuum conditions.The hydrogen permeation flux of the as-cast and annealed V85Ni15 alloys decreases rapidly with the prolonging of the test time,and the addition of the element Y improves the high temperature hydrogen permeation stability of the alloy to some extent.The stability of V84.8Ni15Y0.2 alloy is higher than that of V84.2Ni15Y0.8 alloy,while the stability of hydrogen penetration of annealed V84.8Ni15Y0.2 alloy is better than that of as-cast alloy under the same conditions.After the high temperature heat treatment test,the surface of the annealed V84.8Ni15Y0.2 alloy is relatively clean,with only a few pinholes and cracks.The line scan results show that the V component of the alloy composition diffuses to the surface of the Pd film at a minimum.It is considered that when the Y element content is 0.2 at%,the binding energy between the Y element and the V grain boundary is higher than the binding energy between the Y element and the Ni element,so more Y element segregates to the V grain boundary,thus impede the diffusion between Pd and V.However,when the Y content is 0.8 at%,the binding energy between the Y element and the Ni element is higher than the binding energy between the Y and the V grain boundary.Therefore,although the amount of the Y element increased,the Y content segregated to the V grain boundary decreased.After annealing,more Y elements in the alloy with Y content of 0.2 at% fully diffused into the V grain boundary to maintain the Pd film.Therefore,the annealed V84.8Ni15Y0.2 alloy has the best high-temperature hydrogen permeation stability.The influence of Y element on the high temperature hydrogen permeation stability of V90Fe5Al5 alloy was further investigated.For comparison with V-Ni alloys,the as-cast and annealed V90-x Fe5Al5Yx(x=0,0.2,0.8)alloys were subjected to a high temperature(753K)long-term hydrogen penetration test and high temperature heat treatment under vacuum conditions.The experimental results show that the high-temperature hydrogen permeation flux of the annealed V84.8Fe5Al5Y0.2 alloy is still stable with the extension of the experimental time.After the heat treatment experiment,a large number of pinholes and cracks were formed on the surface of the Pd film containing Y,while the pinholes and cracks on the surface of the alloy with Y addition of 0.2 at% were relatively few.It is considered that the result is due to the difference in binding energy between the Y element and the Al element and the V grain boundary.When more Y element segregates to the grain boundary,the hydrogen permeation flux of the alloy remains stable,and the Pd film plays a very good catalytic role.However,the hydrogen permeation stability of the annealed V84.8Fe5Al5Y0.2 alloy is better than that of the as-cast V84.8Fe5Al5Y0.2 alloy under the same conditions,but the maximum permeation flux is less than the as-cast V84.8Fe5Al5Y0.2 alloy.