THE MEASUREMENT AND PREDICTION OF THE CORROSION POTENTIAL OF COPPER IN CHLORIDE SOLUTIONS AS A FUNCTION OF OXYGEN CONCENTRATION AND MASS-TRANSFER COEFFICIENT

Steady-state corrosion potentials of copper in O-2-containing NaCl sol ution have been measured using three types of electrode: a rotating-di sc electrode, an electrode covered by a porous nylon membrane and an e lectrode covered by a layer of compacted Na-bentonite clay. Mass-trans fer coefficients for these electrodes vary from 10(-2) cm s(-1) in bul k solution to 10(-7) cm s(-1) for the clap-covered electrode. Solution s were equilibrated with atmospheres of air, 2% O-2/N-2, 0.2% O2N2, or were nominally deaerated. In aerated bulk solution, the anodic reacti on is mass-transfer limited and the cathodic reaction is kinetically c ontrolled. With decreasing [O-2], the cathodic reaction becomes partia lly mass-transfer limited. Both reactions are essentially mass-transfe r controlled for the membrane- and clay-covered electrodes. A mixed-po tential model is developed for predicting E(Corr) over a wide range of mass-transfer conditions and [O-2], under circumstances where either reaction may be under joint kinetic/mass-transfer control.