A method of electroplating a crack-free hard chromium deposit comprises having present in the electroplating bath a complex halogen-containing compound which disassociates in an aqueous solution while maintaining the bond of a halogen in the complex. A plating voltage is used which periodically superimposes high voltage pulses on the base voltage.

Process for the treatment of metal surfaces by electro-deposition of metal coatings at high current densities

Desirable electrodeposition of bright chromium plate can be made onto a substrate from a portable plating device having an absorbent mass containing chromic plating medium. The medium contains a complex, water-soluble chromic compound for plating, which compound contains carboxylic acid constituents and halogen constituents. A uniform, bright chromium plate can be readily obtained on the substrate at a desirable current density that avoids the problems accompany ying portable plating at elevated temperature.

Chromium plating medium for a portable plating device

A bright decorative chromium plate of good appearance and durability is electrodeposited from a bath prepared from a solution containing trivalent chromic-compound. More particularly the bath is made from a preformed complex, or such complex is made in situ, and is a water-soluble trivalent chromic compound containing carboxylic acid constituents and halogen constituents. The prepared bath provides for excellent plating speed in the low current density region thus offering enhanced chromium thickness in recessed and difficult to plate areas.

Preparing plating bath containing chromic compound

The process and the improved black chromium plating produced thereby comprising electroplating chromium from an aqueous bath containing hexavalent chromium, trivalent chromium and a lower aliphatic carboxylic acid such as acetic acid. The hexavalent chromium compound is present in a range equivalent to 150-425 grams per liter of chromic acid anhydride; the trivalent chromium is present in an amount 8-30 grams per liter; and the total carboxylic acid, in both acid and carboxylate form, is in the range of 170-350 grams per liter of acid. The electroplating is conducted at 60-85* F. and with a cathode current density of 751000 amperes per sq. ft. The trivalent chromium concentration given above not only permits reproducable lustrous black chromium plating but also greatly decreases the break-in period for the bath. A further addition of ferric ions of up to 25 grams per liter further decreases or completely eliminates the break-in period and also increases the maximum operating temperature of the plating bath to 105* F. When iron is utilized, the combined concentration of trivalent chromium and iron should not exceed 35 grams per liter.

Process of black chromium plating

A bright decorative plating process for electroplating chromium on a basis metal, characterized by high coverage and throwing power, utilizes a chromic acid plating bath containing the anion of an organic carboxylic acid or a halogenated organic carboxylic acid. The baths are of unprecedentedly high CrO 3 to sulfate ratio, 600-3000:1. They may be of the self-regulating type. They contain a fluoride or complex fluoride as an auxiliary catalyst. The carboxylic acid anion may be added by introducing into the bath the acid itself, or a soluble salt of the acid, or the acid anhydride. The anions of the aliphatic dicarboxylic acids such as adipic acid and succinic acid anhydride are preferred. The concentration of the carboxylic acid anion is preferably from 0.5 to 32 grams per liter.

Fred Aoun

Papers

Method of electroplating chromium and compositions therefor