Passivating surface of zinc to improve corrosion resistance etc. - using bath contg. chromium ion, hydrogen peroxide and sulphuric acid, gives blue tint to treated zinc

摘要

The surface of zinc is passivated (chromated) by treatment with an aq. acid soln. of a Cr (III) cpd. contg. H2O2 or a H2O2-releasing cpd., and H2SO4. Use of H2O2 and H2SO4 in the passivating baths gives a desired decorative blue colouration to the treated Zn surface. The formation of the colour is not affected by the presence of Zn ions, as in previous processes, and is achieved without the use of hazardous chemicals such as chormate ion or prechlorates. The treated Zn has improved corrosion resistance and improved adhesion to paints and plastics.