Precipitation Law of Hexavalent Chromium of Dacromet Coating in Different Mediums

Precipitation law of hexavalent chromium from dacromet coating containing Cr in NaCl, distilled water, Na₂SO₄ and NH₄Cl solutions, respectively, were studied by visible spectrophotometry. The results show that when the dacromet coating was immersed in the different-concentration NaCl or Na₂SO₄ solutions at 40℃ for 13 d, the hexavalent chromium precipitated slightly, with the maximum precipitated mass of 2.25 μg·cm^-2 and 8.56 μg·cm^-2, respectively. When immersed in distilled water and different-concentration NH₄Cl solution at 40℃ for 13 d, the precipitated mass of the hexavalent chromium was nearly zero, indicating an excellent stability of the coating.