Chromium electroplating bath using trivalent chromium - with complex forming chemicals such as hypophosphites and glycine

摘要

Process for prepg. an aq. bath for the electrodeposn. of chromium, comprises (a) making an aq. soln. with pH 2.5-5 contg. min. 0.1 N dissolved triavelent Cr ions plus at least sufficient weak complex former to form a complex with all the Cr; (b) maintaining the pH value for >=5 mins.; (c) adding an acid to lower the pH to 1-4. The complex former is pref. selected from hypophosphites, glycine, gluconates, glycolates, formates, or formamide, and in step (b) the soln. may be heated and/or held =60 hrs. at pH 2.5-5. Several pref. baths are listed including compsn.: 0.1-2 M Cr3+, with 0.1-6 M. complex former and 0.03-1 M boric acid or borate. Bath avoids the use of hexavalent Cr which involves serious effluent problems, but is less costly than other trivalent Cr solns.