The Electrochemical Behavior of α,β′-Brass in Basic NaNO3 Solutions

Abstract

The electrochemical behavior of an α,β′-brass CuZn40Pb2 (CW617N) was studied in basic nitrate solutions with various basic pHs and nitrate ion concentrations. In all the chosen experimental conditions, corrosion at the open circuit potential proceeded by the galvanic coupling of the α and β′ phases, leading to a surface dezincification of the β′ phase. The study showed that the extent of the dezincification was affected by the presence of lead in the alloy but the pH was the major parameter. During polarization tests, a pseudo-passive or a passive stage followed by a breakdown was observed: corrosion phenomena mainly involved copper and zinc dissolution from the β′ phase. At pH 11, a Cu2O/PbO layer was efficient in achieving passivity of the brass. At pH 12, a Cu(OH)2-rich surface layer was formed: it was not protective enough, and complete dissolution of the β′ phase was observed leading to the removal of lead particles.