Influence of anions on the passivity behavior of copper in alkaline solutions

Abstract

The competitive effect of the inorganic anions OH -, Cl -, Br -, I -, ClO - 4, NO - 3, SO 2- 4, CO 2- 3 and phosphates on the behavior of copper in alkaline aqueous solutions at pH 12 was investigated. The nature of changes occurring on the copper surface was analyzed by potentiodynamic and potentiostatic methods in conjunction with different instrumental surface analysis techniques. The influence of these anions on the anodic dissolution of copper was classified into three distinct categories. In the first group, comprising NaCl, NaBr and NaI solutions, copper(I) salts form insoluble, nonprotective films on the metal surface and the copper is expected to dissolve via the formation of CuA( n - 1)- n complexes. In the second group, comprising NaClO 4, Na 2 SO 4 and NaNO 3 solutions, substantial dissolution of copper is caused by the formation of easily soluble Cu 2+ salts, and copper (II) ions precipitate as hydroxides and oxides. In the third group, the hydroxide, phosphate and carbonate passivate the copper surface. In some solutions the phosphate and carbonate inhibit the anodic dissolution of copper. The aggressive nature of the anions investigated against the passivity of copper increases in the order SO 2- 4 < Cl - < Br - < NO - 3 < ClO - 4 < I -.