In order to increase the corrosion resistance in a dilute uranium alloy, aftereffects of plating were investigated in two ways; the effect of thickness and porosity in the Ni-film electroplated, and that of process itself, electroplating, in pre-treatment and in post-treatment. Series of corrosion tests were performed in a dilute NaCl solution ($50ppm Cl^-$), in a doubly distilled pure water at 18℃, and in a relative humidity 80% at 70℃. Changes in the weight of specimens were measured periodically after the start of the tests.
Thicker the coating layer, less the total corrosion rate. This was attributed to the decrease in porosity. However the local corrosion rate was increased at the pore site in contrast as the coating becomes thicker.
Protection was satisfactory only in a heavily etched specimen. It was found that heavy etching in the pre-treatment prevents the increase on the corrosion rate and that it decreases the distance between roots in the surface, which in turn stops the increase of the porosity. Further, corrosion rate was kept constant regardless of the solution heat treatment or of the caustic soaking. The post-treatment to increase the mechanical properties, vacuum degassing, was found to increase the corrosion rate.
Ni-coating offered an excellent protection to RH 80% at 70℃ and to distilled water at 18℃.
