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Chrome layer has good hardness, wear resistance, corrosion resistance and decorative appearance, it is not only for decorative coating, also used extensively for functional coatings. Currently, chrome plating industry has become the most widely used types of plating one. For a long time, use of hexavalent chrome plating, hexavalent chromium toxicity, are carcinogenic. The toxicity of trivalent chromium is only one percent of hexavalent chromium sulfate system trivalent chromium plating anodes only precipitated oxygen, no precipitation of harmful gases, so the ratio of trivalent chromium chloride system is more environmentally friendly. This paper studies the trivalent chromium plating Sulfate process, and sulfate system cathodic deposition process mechanism was preliminarily. By orthogonal experiments and single-factor test done on the original process optimization, through the Hull cell test piece bright range of specimen thickness and polarization curves of the test to study the bath content of each component. And the effects of pH value, temperature, current density and plating time and other process conditions. Good coverage of the bath, up to 95% or more, about 86% dispersion capacity, good bath life, good stability. Rare little effect on the deposition rate, Fe2 deposition rate can be increased, but increased iron content in the coating, the coating color dark. Since trivalent chromium plating on impurity ions is more sensitive, we study Cu2, Ni2, Cl-and Zn2 impurity ions such as the impact of the bath, and the absorbance measured through a bath of hexavalent chromium formation rate, the findings indicate that , because the bath with the presence of stabilizers, hexavalent chromium electroplating pre-generated slowly, until stabilizer depleted, hexavalent chromium generate faster. Trivalent chromium plating sulfate plating time with the increase of the coating thickness, the coating morphology of the microporous type into micro-cracks, micro-cracks, compared with hexavalent chromium, trivalent chromium plating Sulphate microcracks smaller. Through a variety of electrochemical measurements and copper accelerated acetic acid salt spray test (CASS) studied the plating time Trivalent chromium sulfate corrosion resistance of the coating, the test results show that when the plating time was 10min, the corrosion resistance of the coating Preferably, the corrosion resistance of the coating with chromium rather. A variety of rare earth on the corrosion resistance of the coating has little effect. By cathodic polarization curves and cyclic voltammetry studies Sulphate trivalent chromium ion cathodic deposition process, studies show that the deposition of trivalent chromium ions in two steps, and are irreversible process. The potential of the reaction step according to the literature the theoretical values.
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