Black chromium plating bath useful for solar reflecting coatings
AssigneeCouncil of Scientific and Industrial Research
InventorsVatia K. W. Grips, Indira Rajagopal, Sundarapandium Rajagopalan
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Abstract
The composition disclosed is an improved black chromium plating bath useful for solar selective coatings. The bath comprises an aqueous solution of sulphate-free chromic acid containing ions of nitrate, borate and fluosilicate. Being a room temperature black chromium bath, good quality black chromium deposite is obtained in the temperature range of 30.degree. C. to 50.degree. C. which is quite coherent and whose selectivity is better than 8.
Claims23
A black chromium plating bath which comprises 2-20 grams per liter of nitrate ions, 3-40 grams per liter of borate ions, 0.5-5 grams per liter of fluosilicate ions and the balance being an aqueous, solution of sulphate-free chromic acid, wherein said bath is substantially free of oxalic acid which forms carbonaceous impurities in said black chromium.
A black chromium plating bath which consists essentially of 2-20 grams per liter of nitrate ions, 3-40 grams per liter of borate ions, 0.5-5 grams per liter of fluosilicate ions and the balance being an aqueous solution of chromic acid.
A black chromium plating bath which consists of 2-20 grams per liter of nitrate ions, 3-40 grams per liter of borate ions, 0.5-5 grams per liter of fluosilicate ions and the balance being an aqueous solution of sulphate free chromic acid.
A black chromium plating bath consisting essentially of an aqueous solution of sulphate-free chromic acid and a sufficient amount of at least one catalyst compound to permit the formation of a black chromium coating having a solar selectivity value of at least about 4.
A process for the electrolytic deposition of a black chromium coating useful as a solar coating which comprises formulating the bath of claim 26 and effecting electrolysis of the bath at a temperature of about 30.degree. to 50.degree. C. at a current density of about 80 to 300 amps per square foot to deposit a black chromium coating upon a substrate.
Dependencies are inferred from the claim text.