Title: Chromium electroplating baths and method of electrodepositing chromium

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Claims: Having now particularly described and ascertained our said invention and in what manner the same is to be performed, we declare that what we claim is:

1. A bath for the electroplating of chromium comprising an aqueous acidic hexavalent chromium solution containing 200 to 550 g/l chromium trioxide, 1 to 18 g/l strontium sulfate, 2 to 30 g/l potassium silicofluoride, 2 to 8 g/l potassium dichromate, and as a synergetic additive 4 to 50 g/l 2,2-dichloromalonic acid or a salt thereof.

2. A bath for the electroplating of chromium according to claim 1, wherein said synergetic additive is potassium 2,2-dichloromalonate.

3. A bath for the electroplating of chromium according to claim 1, wherein said synergetic additive is 2,2-dichloromalonic acid admixed with potassium 2,2-dichloromalonate.

4. A bath for the electroplating of chromium according to claim 1, wherein the amount of potassium silicofluoride is from 2 g/l to 20 g/l.

5. A bath for the electroplating of chromium according to claim 1, wherein the amount of strontium sulfate is from 1 g/l to 10 g/l.

6. A method for the electro-deposition of chromium coating on a metal workpiece, comprising using a bath according to claim 1, and including the step of operating the bath at a temperature range of 45.degree. to 60.degree.C and a current density of 40 to 500 amp/dm.sup.2.

7. A method according to claim 6, wherein the bath is operated at a current density of 50 to 200 amp/dm.sup.2 and a working temperature of 53.degree. .+-. 2.degree.C.

8. A method according to claim 6, including the steps of removing an oxide film from the metal workpiece and preventing the formation of a new oxide film by means of inhibitors until the workpiece is placed in the bath.

9. A method according to claim 6, wherein the plating conditions are effective to form an iron-chromium carbide zone on the surface of the workpiece so that the binding of the chromium coating upon the workpiece is of a molecular type.

10. A method according to claim 6, wherein the rate of circulation of the electrolyte is at least 8 times the volume of the bath per hour.
Other info:

Inventors: Studer, Walter (Olten, CH)

Application Number: 542385
Filing Date: 1975-01-20
Publication_date: 1976-04-20
Assignee: Rotel-Holding AG (Basel, CH)
Primary Class(es): 205/148 205/208, 205/286
Other Classes:
US Patent Ref:

3108933	Oct, 1963	Johnson	204/51.
3282812	Nov, 1966	Brown et al.	204/51.
3505183	Apr, 1970	Seyb et al.	204/51.

Other Refs:
Primary Examiner: Kaplan, G. L.
Assistant Examiner:
Attorney: Woodhams, Blanchard and Flynn