Electrolyte for the deposition of anthracite/black rhodium/ruthenium alloy layers

Abstract

The present invention is directed toward an electrolyte which allows for electrolytically producing a black metal layer consisting of rhodium and ruthenium. The present invention also relates to a method for producing a corresponding article, and to the use of the electrolyte.

Claims

1. An aqueous, acidic electrolyte for producing dark metal layers on conductive materials, comprising: 0.5-15.0 g/l of a soluble rhodium metal; 0.5-10.0 g/l of a soluble ruthenium metal; 5-150 g/l of an acid; and a phosphonic acid and a dicarboxylic acid.

2. The electrolyte according to claim 1, wherein the soluble ruthenium metal is present in the form of a binuclear complex.

3. A method of producing an electrodeposited metal layer on an article, said electrodeposited metal layer comprising rhodium and ruthenium metals in a wt %-based composition of from 40:60 to 90:10, based on the sum of the weights of both metals, the metal layer having an L* value of less than 65 and an a* value of from −3 to +3 according to DIN EN ISO 11664-4 (effective version as of Apr. 8, 2019), which comprises contacting the electrolyte according to claim 1 with the article in the presence of a current thereby depositing the electrodeposited metal layer on the article.

4. The method according to claim 3, wherein the electrodeposited metal layer has a b* value between −7 and +7.

5. The method according to claim 3, wherein the electrodeposited metal layer serves as an underlayer for a first electrodeposited metal layer of rhodium, said first electrodeposited metal layer having a thickness of 0.05-0.5 μm.

6. The method according to claim 5, wherein the L* value of the underlayer and the first electrodeposited metal layer combined is below 50.

7. The method according to claim 3, wherein the electrodeposited metal layer has an abrasion resistance of less than 0.75 μm/1000 strokes as measured by a test known as “the Bosch-Weinmann test”.

8. A method for electrodepositing a metal layer on a conductive material, which comprises: a) contacting the conductive material as a cathode with the aqueous, acidic electrolyte according to claim 1; b) contacting an anode with the aqueous, acidic electrolyte; and c) establishing a current flow between the cathode and the anode.

9. The method according to claim 8, wherein the current flow has a current density of 0.1-50 A/dm.sup.2.

10. The method according to claim 8, wherein the pH value of the aqueous, acidic electrolyte is between 0.2 and 2.

11. The method according to claim 8, wherein the aqueous, acidic electrolyte has a temperature between 20° C. and 65° C.

12. The method according to claim 8, and wherein steps (a)-(c) result in the metal layer, and said method further comprises (d) subjecting the metal layer to an anodic post-treatment.

Description

EXAMPLE 1

(1) An electrolyte according to the invention which, in addition to 1.5 g/l of rhodium [dirhodium trisulfate], also contained 0.5 g/l of ruthenium as [Ru.sub.2NCl.sub.8(H.sub.2O).sub.2].sup.3−, 4 g/l of ethylene diamine tetra (methylene phosphonic acid) EDTMP, and 11 g/l of potassium hydrogen phtalate as a blackening agent in water, and 10 g/l of sulfuric acid, was used for producing black, well-conductive, and abrasion-resistant layers on consumer goods. The temperature of the electrolyte was 45° C.; the pH around 1.0.

(2) In a rack coating process, suitable substrates were finished at a set current density of 0.25 to 5 A/dm.sup.2. The obtained layers had very good mechanical stability and exhibited a black, very appealing neutral hue in the color range (a* and b* value).

(3) The color values are visible in the appended diagrams (FIGS. 1-3). The electrolyte according to the invention is referred to as RA black.

(4) Ruthuna® 490 and Ru 479 are commercially available black ruthenium electrolytes. Rhoduna® 470 and 471 are commercially available black rhodium electrolytes (https://ep.umicore.com/en/products/productfinder).

EXAMPLE 2

(5) An electrolyte according to the invention which, in addition to 1.0 g/l of rhodium [dirhodium trisulfate], also contained 1.0 g/l of ruthenium as [Ru.sub.2NCl.sub.8(H.sub.2O).sub.2].sup.3−, 5 g/l of ethylene diamine tetra (methylene phosphonic acid) EDTMP, and 7.5 g/l of potassium hydrogen phtalate as a blackening agent in water, and 10 g/l of sulfuric acid, was used for producing particularly black and abrasion-resistant layers on consumer goods. The temperature of the electrolyte was 45° C.; the electrolyte had a pH value of about 1.2.

(6) In a rack coating process, suitable substrates were pre-coated at a set current density of 0.75 to 2 A/dm.sup.2. A thin cover layer of a very dark (L*=47) black rhodium electrolyte (e.g. Rhoduna® 470) was then applied. It was anodically post-treated in a solution containing 10 g/l of potassium hydrogen phtalate at 4 volts. The post-dip solution was tempered at 30° C. The obtained layers showed a deep black hue and had very good mechanical stability.