Study On Electrochemical Palladium Plating Technology And Deuterium Permeation Performance On Niobium Surface

The dense metal films have important applications in the separation of hydrogen and its isotopes.Palladium and its alloy membranes are commonly used in industrial hydrogen separation and purification of membrane materials,but their high prices limit their large-scale industrial applications.The refractory metal niobium has the characteristics of good mechanic a 1 strength,low price and high intrinsic permeability coefficient However,due to the weak ability of Nb metal to dissociate hydrogen molecules and the formation of a dense oxide film on the surface,the permeability of hydrogen is greatly reduced.The advantages of the two methods can be fully utilized by removing the oxide layer on the surface and then covering the palladium film.Pd/Nb/Pd composite films were prepared by depositing a palladium film on the surface of niobium foil after removing the oxide layer by electrochemical polishing.The results show that:1.The majority of oxide film on niobium foil surface can be removed by mechanical grinding(residual thickness is about 30 nm),and then the oxide film can be completely removed by electrochemical polishing for 15 min in a mixed acid electrolyte with a DC voltage of 17 V and a hydrofluoric acid:concentrated sulfuric acid:lactic acid volume ratio of 1:3:6.The niobium foil removed from the oxide film was placed in the atmosphere again,and a thin oxide layer was rapidly formed on the surface.After about two days,the oxidation rate became extremely slow,indicating the ability to keep relatively clean.2.With optimized electroplating parameters,the surface of niobium foil with micron grain can be deposited to obtain palladium film with full coverage and no obvious holes.At the temperature of 723 K,the permeability coefficient of the obtained composite membrane reaches 1.25×10 8 mol·m-1·s-1 Pa-0.5,which is in the same magnitude as that of palladium(1×10-8 mol·m-1·s-1·Pa-0.5),and has great engineering application value.The mechanism is as follows:both electrochemical polishing and nanocrystalline samples can increase the deuterium permeability of niobium foil samples,and the latter can increase the deuterium permeability even more.In addition,the deposited palladium film can prevent the continuous oxidation of niobium surface,and the film itself will not be oxidized during the infiltration process,which is of great help to the infiltration of niobium foil.3.In the process of high temperature permeation,β-Nb2O5 oxide formed on the niobium film surface at the initial high temperature will not decompose,and α-Nb2O5 oxide formed at room temperature will decompose into low-priced niobium oxide.In addition,during this process,oxygen atoms in the oxide layer will further diffuse into the matrix,forming a very small amount of NbO oxide.