INFLUENCE OF VELOCITY ON CORROSION OF COPPER IN ALKALINE CHLORIDE SOLUTIONS

It has been reported previously that the mechanism for the erosion-cor rosion of copper (Cu) in seawater is the removal of protective layers by hydrodynamic shear. This hypothesis was tested by studying the anod ic dissolution of Cu in aerated 3.5 wt% sodium chloride (NaCl) solutio ns using a system designed to isolate the effect of surface shear stre ss. The experimental apparatus consisted of an axisymmetric impinging jet and disk electrode coupled with a scanning ellipsometer. This allo wed a phenomenon occurring at a critical shear stress, such as removal of protective films, to be seen at a corresponding radial position. E nhancement of the corrosion rate, as measured electrochemically, was l ess than would have been caused by an increase in overall convective t ransport. The ellipsometer did not indicate the presence of any critic al radius, even though the shear stress at the Cu electrode was an ord er of magnitude higher than the critical shear stress reported in the literature. Therefore, the critical shear stress previously reported i n the literature could not be attributed to removal of protective laye rs by hydrodynamic shear.