An improved process for the pickling of copper and copper based alloys

Abstract

Auto catalytic decomposition of hydrogen peroxide (A.C.D.) in sulphuric acid solution (10% sulphuric acid +1.5% hydrogen peroxide) has been studied in the presence of different concentrations of copper ions and certain stabilizers. Copper ions presence of different A.C.D at lower a well as at higher temperatures. Some organic molecules which form complexes with copper are found to inhibit A.C.D. of H2O2 very effectively. The best effect has been observed with inmidazole and benzotriazole. The decomposition is found to increase with passage of time but the rate is lower in stabilized solution. NML developed stabilizer based on organic polymeric compound provides maximum inhibition at 0.25% of its concentration. At higher concentration, the decomposition is found to increase. The stabilized solution is found to have good pickling properties towards copper having mill scale but it creates the problem of redeposition of copper during the pickling of brass. This behaviour has been explained in light of super-imposed E-pH Pourbaix diagram for copper and zinc. This super effective pickling of brass in sulphuric acid-peroxide mixture.