Abstract
A relationship between corrosion potential and surface finish of Invar (Ni36%-Fe bal. alloy) etched in ferric chloride solutions was studied.
The Invar was attached to a rotating disk electrode equipment. The rotation rate was set at 1600rpm in order to approximate the actual etching process. A principal ingredient of etchants was FeCl3. The concentration of FeCl3, FeCl2, free HCl and Ni2+ were 40 to 48mass%, 1.87±0.08mass%, 0.20±0.04m (molality) and 0.43±0.02m, respectively. The temperature was maintained at 60 to 80°C.
We found a strong correlation between the surface finish and corrosion potential of Invar. When it was more noble than 200mV (SHE), the surface finish was smooth, while a rough finish was observed at less noble than 150mV. The difference of surface finish was shown distinctly in SEM photographs.
