Influence of structure of palladium and nickel based membranes on hydrogen permeation

The effects of Ni, Pd and Pd77Ag23 alloy membrane microstructures on hydrogen permeation have been investigated using the electrochemical permeation method. Deformation, annealing and electrodeposition have been used to modify the membrane microstructure.; The delay for hydrogen permeation in palladium is increased when the degree of deformation increases. The annealing of deformed palladium and Pd 77Ag23 at 250°C or 850°C accelerates hydrogen diffusion. The annealed metals release hydrogen more rapidly than the deformed metals. The Pd77Ag23 alloy needs more time to release hydrogen. The solubility increases in both palladium and Pd77Ag23 when deformation increases. A hydrogen-trapping model has been developed, which allows the prediction of trends in the experimental data.; The nickel electrodeposits exhibit fiber texture with two components (100) and (110). Low current densities yield a dominant (100) texture. High current densities develop a strong (110) fiber texture. There is a texture transition region between 30 and 50A/dM2. After annealing at 800°C for lh, the (100) texture is transformed to (111) texture. Diffusion coefficients increase as texture is transformed from (001) to (011) and (111). The diffusion coefficient of a sample without a dominant texture is lower than the values measured for the samples with (001), (110) and (111) textures. Diffusion coefficients of (001) and (011) polycrystalline membranes are higher than (001) and (011) single crystal membranes. However, in both cases the (011) diffusion coefficient is greater than the (001). By using absorption energies of (001), (011) and (111), the three basic planes in nickel, adsorption energies for other orientations have been estimated using the weighted average method. Absorption energies for different orientations have been shown in the form of an inverse pole figure.; The diffusivity of hydrogen increases six times from single crystal membranes to polycrystalline membranes, and increases six times again from polycrystalline membranes to nanocrystalline membranes. When nanocrystalline nickel membranes have been annealed between 200°C and 900°C, they yield a texture change in the nickel membrane from (100) fiber texture to a mixture of (100) fiber texture and (111) texture, and then only one recrystallization (111) texture component is observed. During annealing from 200°C to 900°C, a slight increase in the number of high angle (45°--65°) grain boundaries occurs and a percentage of the low (0°--15°) and middle angle (30°--45°) grain boundaries decreases slightly. After annealing at 800°C and 900°C, changes in the grain size do not affect the rate of diffusion of hydrogen.; There are four major microstructural factors: deformation defects, grain size, texture and grain misorientation, which affect hydrogen permeation in metals. In the polycrystalline materials studied, the importance of crystal defects, grain size, texture and grain misorientation on hydrogen permeation has been established.; In the developed multilayer membranes when hydrogen charging is from the nano-Ni side of the nano-Ni and poly-Ni composite membrane, the permeation current rises rapidly. When hydrogen charging is from the poly-Ni side of the same composite membrane, the permeation current gradually rises and it takes longer to reach a steady state. The permeability of the nano-poly-Ni membranes charging from the nano-Ni side is eight times higher than that of the same composite membrane charging from the poly-Ni side. The diffusivity of the nano-poly-Ni membranes charging from the nano-Ni side is two times higher than that of the same composite membrane charging from the poly-Ni side. The nano-poly-Ni membranes charging from the nano-Ni side release hydrogen faster than the same composite membrane charging from the opposite side. The diffusivity and permeability of the nano-poly-Ni membrane are smaller than those for a single...