Abstract
Various kinds of black chromium plating baths have hitherto been reported in literatures. However, the bath composition is not yet established in actual practice at present. Physical and chemical properties of these deposits and the mechanism of their coloration are not also thoroughly researched.The authors examined black chromium plating baths in the literatures and found out that the bath containing hydrogen silicofluoride gave the plating with least powdery deposit and strongest adhesion; but its unevenness in color was most enormous among the platings from these kinds of baths.Plating conditions for the most even black color were researched and the following results were obtained.(1) The optimum composition of bath and plating conditions were as follows:CrO3 300g/l Bath temperature above 10°CH2SiF6 above 1g/l DK 30-50amp./dm2(2) Sulfuric acid should completely by removed, because its presence limited the range of black color. Hydrogen silicofluoride should be supplied to the bath according to its electrolytic comsumption.(3) Higher throwing power was obtained by coating the substrate with copper or nickel, and then, immediately plating black chromium on that coating.
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