ELECTROLYTE AND METHOD FOR PRODUCING CHROMIUM LAYERS

Abstract

Disclosed is an electrolyte for the electrolytic deposition of chromium as a metal, comprising (a) a chromium (III) salt and (b) metallic chromium, the use of the electrolyte for producing chromium layers on rotationally symmetrical components, in particular gravure printing cylinders, and methods, in which this electrolyte is used.

Claims

1. An electrolyte for the electrolytic deposition of chromium as a metal, comprising (a) a chromium(III) salt and (b) metallic chromium.

2. The electrolyte according to claim 1, wherein the metallic chromium is available in the form of one or more molds in the electrolyte.

3. The electrolyte according to claim 1 or 2, wherein the electrolyte further contains (c) a sulfate.

4. The electrolyte according to any one of claims 1 to 3, further comprising: (d) a compound of the formula (I) ##STR00003## wherein R stands for NH.sub.2, OH or SO.sub.3H and n is an integer ranging from 1 to 3, and/or its salts, in particular, salts with monovalent cations such as Na.sup.+ and/or K.sup.+ or bivalent cations, and/or (e) formic acid and/or its salts, in particular, salts with monovalent cations such as Na.sup.+ and/or K.sup.+ or bivalent cations.

5. The electrolyte according to any one of the preceding claims, wherein the chromium(III) salt includes an inorganic and/or organic chromium(III) salt, in particular, wherein the inorganic chromium(III) salt is selected from potassium chrome alum, ammonium chrome alum, chromium sulfate, chromium sulfamate (amido sulfonate), chromium bromide, chromium iodide, chromium phosphate, chromium pyrophosphate (diphosphate), chromium phosphonate, chromium hydroxy sulfate (alkali chromium sulfate), chromium chloride and mixtures of two or more of them, or wherein the organic chromium(III) salt is selected from chromium citrate, chromium formate, chromium oxalate, chromium methanesulfonate, chromium dimethanesulfonate and mixtures of two or more of them.

6. The electrolyte according to any one of the preceding claims, wherein the electrolyte includes (f) a common additive, for example, a complexing agent and/or a wetting agent.

7. Use of the electrolyte according to any one of claims 1 to 6 for producing chromium layers on rotationally symmetrical components.

8. The use according to claim 7, wherein the rotationally symmetrical component is a gravure cylinder.

9. A method for producing a chromium layer by electrolytic deposition of chromium from an electrolyte by means of direct current and the use of an anode and a cathode, wherein the electrolyte is used according to any one of claims 1 to 6.

10. The method according to claim 9, wherein the metallic chromium is available in the form of one or more molds in the electrolyte.

11. The method according to claim 9 or 10, wherein the metallic chromium is placed in the electric field of the anode and cathode.

12. The method according to any one of claims 9 to 11, wherein the metallic chromium has contact to the anode.

13. The method according to any one of claims 9 to 12, wherein the anode is a precious metal containing mixed oxide anode.

14. The method according to any one of claims 9 to 13, wherein the surface of the metallic chromium includes 1% to 50% of the surface of the anode.

15. A method for keeping the chromium(III) content in an electrolyte constant during electrolysis, wherein the electrolysis is performed by using an electrolyte according to any one of claims 1 to 6.

16. A method for preventing the formation of chromium(IV) during and after the electrolytic deposition of chromium, wherein an electrolyte according to any one of claims 1 to 6 is used.

Description

EXAMPLE 1

[0049] An electrolyte with the following composition was provided: [0050] chromium(III) sulfate (density=1.26 g/ml; 3% Cr(III)->37.8 g/l->0.727M) 18.61 [0051] Na sulfoacetate (8.3%->104.6 g/l->0.568M) 6.27 kg [0052] Na formate (8%->100.8 g/l->1.482M) 6.05 kg [0053] Na sulfate, 1.7%->21.4 g/l->17 mM) 1.29 kg

[0054] One liter of electrolyte in a beaker was heated to 40° C. with constant stirring and a pH value of 3.1 was set. Thereafter, the electrodes were inserted into the beaker in parallel opposite to one another and connected to a power source. The anode was a mixed oxide coated (MMO) titanium expanded metal. As the cathode, a copper metal strip was used. The cathode surface was selected such that the working current density was, given a current of 3 ampere, approximately 20 A/dm.sup.2. The anode surface equals to the cathode surface. Furthermore, a metallic chromium nugget was mounted on the anode so that it is conductively connected to the anode.

COMPARATIVE EXAMPLE 2

[0055] Comparative example 2 was conducted similar to example 1, with the difference that a chromium nugget was not used.

[0056] Results

[0057] At the points in time 0, 2, 4, 6 and 8 hours, a 1.0 ml sample was taken in each case and the Cr(III) amount determined. It was noted that the Cr(III) amount decreased significantly quicker in comparative example 2 than in example 1. This suggests that the metallic chromium dissolves. This was confirmed by a gravimetric examination of the cathode and of the chromium nuggets before and after electrolysis.