AbstractsEngineering

An electrochemical permeation cell has been used to test the influence of microstructural characteristics of metal specimens and electrochemical processing parameters on electrochemical hydrogen diffusion. The affect of intercrystalline volume, entry surface roughness, cathodic charging current density and different cold working conditions on hydrogen diffusion through polycrystalline metals was tested. Nanocrystalline specimens of pure nickel and of 80%-Nickel 20%-Iron were tested to determine the affect of intercrystalline volume on hydrogen breakthrough diffusion. Specimens of pure palladium were tested to determine the influence of entry surface roughness, cathodic charging current density, different cold working and texture conditions on hydrogen permeation. A series of permeation tests performed on nanocrystalline nickel were used to optimize the measurement conditions. Experiments performed on 80/20 Ni-Fe thin foils determined that the hydrogen breakthrough diffusion coefficient drops dramatically with increasing grain size in the range of 20 – 40 nanometers. Above 40 nanometers, the breakthrough diffusion coefficient reaches a steady-state level. This decrease in breakthrough diffusion coefficient is thought to be due to a decrease in intercrystalline volume. Tests performed on palladium showed that the hydrogen effective diffusion coefficient increased logarithmically with increasing cathodic charging current density. These experiments also demonstrated that the optimum charging current density for palladium is 0.1 mA/cm2. Other tests on palladium determined that the surface roughness, on the entry side of the specimens, had no influence on the effective diffusion coefficient, processing efficiency or hydrogen subsurface entry concentration. Experiments on cold rolled palladium sheets determined that cold working dramatically lowers both the hydrogen subsurface entry concentration and effective diffusion coefficient. The lowering of the effective diffusio