A STUDY OF THE CORROSION PRODUCTS OF ALUMINUM BRASS FORMED IN SODIUM-SULFATE SOLUTION IN THE PRESENCE OF CHLORIDES

The surface film forming on Al brass specimens immersed in stagnant Na//2SO//4 solutions containing chlorides at pH values 3. 0-7. 25 was examined by using chemical, electrochemical and X-ray techniques. In the absence of chlorides the surface film consists of oxides (CuO, Cu//2O) and cupric basic sulfates Cu//3(SO//4)//2. 4H//2O, stable in the whole range of pH; the surface film is quite homogeneous and no dezincification or localized corrosion occurs. In the presence of chlorides, the surface film consists also of cuprous chloride (CuCl) and of cupric left bracket Cu(OH,Cl)//2. 2H//2O right bracket and aluminum oxychlorides left bracket Al//4//5O//4//5(OH)//4//5Cl right bracket and aluminum oxides left bracket Al(OH)//3 right bracket . In the most acidic solutions the surface film is physically and chemically extremely unhomogeneous, thus favouring the occurrence of dezincification or localized corrosion phenomena.