Electrolyte for deposition of smokeless carbon / black rhodium / ruthenium alloy layer

Abstract

The present invention is directed to an electrolyte that allows for the electrolytic production of black metal layers consisting of rhodium and ruthenium. The invention also relates to a method for producing a corresponding article and to the use of the electrolyte.

Description

Technical Field

[0001] The present invention is directed to an electrolyte that enables the electrolytic production of a ferrous metal layer composed of rhodium and ruthenium. The corresponding method for producing an article and the use of the electrolyte are likewise the subject of the present invention.

Background Art

[0002] Consumer goods, technical articles, jewelry, and ornaments are finished with a thin oxidation-stable metal layer to protect them from corrosion and / or for optical enhancement. These layers must be mechanically stable and should not show any signs of discoloration or wear even in the case of long-term use. An effective means for producing such layers is the galvanic method, which can obtain a plurality of high-quality metal and alloy layers. Examples well-known in daily life are the galvanic bronze and brass layers on door latches or doorknobs, the chrome coating on vehicle parts, zinc-plated tools, or the gold coating on watch straps.

[0003] A particular problem in the field of galvanic finishing is the production of a black metal layer that is oxidation-stable, conductive, and mechanically elastic, which may be of interest not only in the decorative and jewelry sectors but also, for example, in the field of solar technology or for technical applications as contact materials. Only a few metals are available for producing an oxidation-stable black layer. In addition to ruthenium, rhodium, palladium, chromium, and nickel are also suitable. The use of the precious metal rhodium is limited to the jewelry sector due to high raw material costs. The use of low-cost nickel and nickel-containing alloys, especially in the jewelry and consumer goods sectors, is only possible in exceptional cases and when strict requirements are met because nickel and nickel-containing metal layers are contact allergens.

[0004] Electrodeposition of a black ruthenium layer (black ruthenium) on a conductive substrate is most well-known (German Patent Application Publication No. 102011115802 (A1), International Publication No. 2012 / 171856 (A2), International Publication No. 2008 / 226545 (A1), and the documents cited therein). It is also possible to electrochemically generate a black rhodium deposit (black rhodium) (European Patent Application Publication No. 171091 (A2), Application Publication No. 4154988 (A2), Application Publication No. 61104097 (A2), Application Publication No. 61084393 (A2), Application Publication No. 61084392 (A2), https: / / ep.umicore.com / de / produkte-3 / produktfinder / rhoduna-470-black-rhodium-elektrolyt- / -Rhoduna® 470 Black).

[0005] Electrodeposition of a rhodium-ruthenium metal layer has already been described, for example, in German Patent Application Publication No. 2429275 (A) and International Publication No. 2010 / 057573 (A1). Application Publication No. S57101686 (A) describes an electrolyte that can obtain a metal layer of rhodium and ruthenium that can be dark blue, gray, or black depending on the conditions. However, the layers produced with the electrolytes described here do not have the blackness or abrasion resistance required in the market.

Summary of the Invention

Problems to be Solved by the Invention

[0006] Therefore, it was still an object to identify improved possibilities for metal deposition that better meet the requirements of market participants. Specifically, it should be possible to reproducibly produce a metal layer with an attractive black color tone, regardless of the presence or absence of a blue tint, in a simple and cost-effective manner. The resulting metal layer should be as crack-free and abrasion-resistant as possible since it can serve as a contact material, a decorative metal article, especially as a jewelry piece. For an industrial process, it should be possible to perform the deposition in an appropriately effective manner.

Means for Solving the Problems

[0007] These and further objects arising from the prior art in a manner obvious to a person skilled in the art are achieved by the specification of the electrolyte according to the features of claim 1. A particular use is described in claim 3. Claim 8 is directed to a method for electroplating a metal layer using the electrolyte according to the invention. The corresponding dependent claims relate to preferred embodiments of claims 1, 3, and 8.

[0008] In that an aqueous acidic electrolyte is provided for producing a dark-colored metal layer on a conductive material - 0.5 to 15.0 g / l of a soluble rhodium compound (with respect to the metal), and - 0.5 to 10.0 g / l of a soluble ruthenium compound (with respect to the metal), and - 5 to 150 g / l of an acid, and - phosphonic acid and dicarboxylic acid, and having the proposed objects are achieved.

[0009] The electrolyte according to the invention presented herein enables the electroplating of a metal layer onto a conductive material, and the metal layer has very high wear resistance with good conductivity, and thus is intended for use as a contact material. Similarly, the attractive, dark-colored, and neutral hue color of the metal layer is also advantageous for use as a decorative element. It was not expected that this could be achieved with the electrolyte presented herein.

[0010] All materials that a person skilled in the art would have considered for this purpose are suitable as current-conductive materials on which a metal layer can be deposited according to the invention. Preferred are those selected from the group consisting of contact materials such as jewelry pieces, bathroom articles, metal consumer goods in the kitchen and living area, switches, plug connections, relays, and many more.

[0011] The rhodium compounds used in the electrolyte according to the present invention can be selected at the discretion of those skilled in the art. These are based on the required solubility in the acidic aqueous electrolyte, the precipitation ability associated with the ruthenium compounds used, and their selection with respect to the cost of the rhodium compounds.

[0012] In the electrolyte according to the present invention, rhodium exists in the form of its ions in a dissolved form. It is preferably introduced in the form of a water-soluble salt selected from the group of pyrophosphates, carbonates, hydroxycarbonates, bicarbonates, sulfites, sulfates, phosphates, nitrites, nitrates, halides, hydroxides, oxide hydroxides, oxides, or combinations thereof. Embodiments in which the metal in the form of a salt having ions is optionally used from the group consisting of pyrophosphates, carbonates, sulfates, hydroxycarbonates, oxide hydroxides, hydroxides, and bicarbonates are highly particularly preferred. It is absolutely preferred to be used in the electrolyte in the form of salts of mineral acids such as rhodium sulfate or rhodium phosphate. However, in the bath according to the present invention, it can also be used as a salt of an organic acid such as rhodium alkanesulfonate, for example, rhodium methanesulfonate or rhodium sulfamate, or as a mixture of these compounds. The trivalent rhodium compound used is more highly particularly preferably selected from rhodium(III) fluoride, rhodium(III) chloride, rhodium(III) bromide, rhodium(III) iodide, rhodium(III) oxide hydrate, and rhodium(III) sulfate.

[0013] The ruthenium compounds used in the electrolyte are selected, for example, from ruthenium(III) fluoride, ruthenium(III) chloride, ruthenium(III) bromide, ruthenium(III) iodide, ruthenium(III) nitrosyl nitrate, ruthenium(III) acetate, ruthenium isonitrile complex, ruthenium nitride-hydroxy complex, and ruthenium nitride-oxalato complex.

[0014] The ruthenium source for the electrolyte according to the present invention is more preferably prepared in situ. Next, this can be obtained in a complexed form containing ruthenium in an acidic aqueous solution based on a ruthenium(III) compound, amidosulfuric acid, and / or ammonium sulfamate, preferably as a binuclear complex. It is common to have an electrolyte bath or a preparation concentrate containing 1 to 10 g / l of amidosulfuric acid and / or ammonium sulfamate per 1 g / l of ruthenium. For this purpose, for example, a mixture containing a ruthenium(III) compound, amidosulfuric acid, and / or ammonium sulfamate is heated for a certain period of time, whereby 3- a salt is formed (X represents a monovalent anion). Ammonium ions or sodium ions or potassium ions can preferably be used as counterions (International Publication No. 2015 / 173186 (A1) or International Publication No. 12171856 (A2) or International Publication No. 2008 / 116545 (A1), and related documents cited therein).

[0015] Ruthenium is very particularly preferably used in the form of a binuclear, anionic nitride-halogen complex compound of the formula 3- [Ru2N(H2O)2X8], where X is a halide ion such as chloride, bromide, or iodide. In this context, the chloro complex 3- [Ru2N(H2O)2Cl8] is particularly preferred.

[0016] Which compounds of the metal are introduced into the electrolyte in what amounts can also potentially determine the color of the resulting coating and can be adjusted according to the customer's requirements. As shown, the metal to be deposited is present in ionic dissolved form in the electrolyte for applying a decorative coating to jewelry articles, consumer goods, and technical articles. Rhodium is preferably present in the electrolyte at a concentration of 1 g / l to 10 g / l, more preferably 2 g / l to 7 g / l. The ruthenium concentration is preferably 1 g / l to 8 g / l, more preferably 2 g / l to 6 g / l. The amounts shown are each related to the amount of the metal.

[0017] The electrolyte according to the invention functions particularly well within a very acidic pH range. The pH value range is specified below. Preferably, an inorganic acid is used to adjust the pH value. However, alternatively, an organic acid such as a sulfonic acid may be used for this purpose. Particularly preferably, an acid selected from the group consisting of sulfuric acid, hydrochloric acid, methanesulfonic acid, toluenesulfonic acid, benzenesulfonic acid, and sulfuric acid is most preferably used.

[0018] The black coloring of the galvanically produced rhodium-ruthenium layer is achieved by selectively suppressing the deposition rate from the galvanic bath. As inhibitors, and thus particularly as blackening additives for ruthenium, one or more phosphonic acid derivatives are present in the electrolyte according to the invention. The use of the compounds aminophosphonic acid AP, 1-aminomethylphosphonic acid AMP, aminotris(methylenephosphonic acid) ATMP, 1-aminoethylphosphonic acid AEP, 1-aminopropylphosphonic acid APP, (1-acetylamino-2,2,2-trichloroethyl)phosphonic acid, (1-amino-1-phosphonononanactyl)phosphonic acid, (1-benzoylamino-2,2,2-trichloroethyl)-phosphonic acid, (1-benzoylamino-2,2-dichlorovinyl)phosphonic acid, (4-chlorophenyl-hydroxymethyl)phosphonic acid, diethylenetriaminepenta(methylenephosphonic acid) DTPMP, ethylenediaminetetra(methylenephosphonic acid) EDTMP, 1-hydroxyethane-(1,1-diphosphonic acid) HEDP, hydroxyethyl-amino-di(methylenephosphonic acid) HEMPA, hexamethylenediaminetetra(methylenephosphonic acid) HDTMP, ((hydroxymethylphosphonomethyl-amino)-methyl)phosphonic acid, nitrilotris(methylenephosphonic acid) NTMP, 2,2,2-trichloro-1-(furan-2-carbonyl)aminoethylphosphonic acid, salts derived therefrom, or condensates derived therefrom, or combinations thereof, is preferred.

[0019] Particularly preferred is the use of one or more compounds selected from the group consisting of aminotris(methylenephosphonic acid) ATMP, diethylenetriaminepenta(methylenephosphonic acid) DTPMP, ethylenediaminetetra(methylenephosphonic acid) EDTMP, 1-hydroxyethane-(1,1-diphosphonic acid) HEDP, hydroxyethyl-amino-di(methylenephosphonic acid) HEMPA, hexamethylenediaminetetra(methylenephosphonic acid) HDTMP, salts derived therefrom, condensates derived therefrom, or combinations thereof.

[0020] Aminotris(methylenephosphonic acid) ATMP, ethylenediaminetetra(methylenephosphonic acid) EDTMP, and 1-hydroxyethane-(1,1-diphosphonic acid) HEDP, and salts or condensates derived therefrom, or combinations thereof, are particularly well-suited for coatings of decorative articles and consumer goods.

[0021] The amount of phosphonic acid can be selected by those skilled in the art. Those determinations will be based on the fact that the phosphonic acid is sufficient and shows the corresponding effect in the context of the present invention. The phosphonic acid is preferably used in an amount of 0.5 to 20 g / l in the electrolyte. In this context, more preferably, it is 1 to 10 g / l, and most preferably, it is 1 to 5 g / l.

[0022] Dicarboxylic acids that function as blackening additives, especially for rhodium deposition, are also present in the electrolyte. Suitable dicarboxylic acids are all acids that are convenient for those skilled in the art for the stated purposes, especially those that are available at low cost and dissolve sufficiently in an aqueous acidic electrolyte. These may be alkyl, alkenyl dicarboxylic acids or aryl dicarboxylic acids, and the acid groups should preferably be capable of forming internal anhydrides. The two acid groups can be assumed to form a bidentate complex compound together with the metal to be deposited, especially rhodium, where a 5- or 6-membered ring is formed with the metal atom. This is surprising since the dissociation of the dicarboxylic acid is low and any complexation occurs even slightly in an acidic environment. Nevertheless, this addition has an advantageous effect on the final metal deposition in the sense of the present invention.

[0023] Aromatic dicarboxylic acids capable of forming a 5- or 6-membered ring having a complexed metal atom, especially dicarboxylic acids selected from the group consisting of benzene, naphthol, and indenedicarboxylic acids, are particularly preferred. Phthalic acid and its salts are especially preferred.

[0024] The amount of dicarboxylic acid can be selected by those skilled in the art. Their determination will be based on the fact that the dicarboxylic acid is sufficient and still shows a corresponding effect in the sense of the present invention. The dicarboxylic acid is preferably used in an amount of 0.5 to 25 g / l in the electrolyte. In this context, more preferably, it is 1 to 20 g / l, and most preferably, it is 4 to 12 g / l.

[0025] This electrolyte is used, in particular, to produce an article having an electrodeposited metal layer containing metals rhodium and ruthenium in a composition based on weight percentages of 40:60 to 90:10 based on the total weight of both metals, and the metal layer has an L value of less than 65 and an a value of -3 to +3 according to the Cielab color system (EN ISO 11664-4, the latest version at the filing date). * value and an a * value. The b * value is advantageously -7 to +7.

[0026] The Cielab color system uses a three-dimensional color space where the lightness value L * is orthogonal to the color plane (a * , b * ). L * a * b * The most important characteristics of the color model include device independence and perceptual relationships. That is, color is defined as what is perceived by a normal observer under standard lighting conditions regardless of how they are generated or rendered. The color model is standardized in EN ISO 11664-4, "Colorimetry - Part 4: CIE 1976 L * a * b * Colour Space". Each color within the color space is defined by a color position with Cartesian coordinates {L * , a * , b *}. The a * b * coordinate plane is constructed based on the complementary color theory. Green and red are located on opposite sides of each other on the a * axis, and the b * axis extends between blue and yellow. The complementary hues are 180° opposite in each case, and gray is at their center (coordinate origin a * = 0, b * = 0). The L* axis represents the lightness (luminance) of colors with values from 0 to 100. In the illustration, this is at the zero point orthogonal to the a * b * plane. Since all achromatic colors (gray tones) are included between the endpoints of black (L * = 0) and white (L * = 100), it is sometimes called the neutral gray axis. The a * axis represents the green or red portion of the color, with negative values indicating green and positive values indicating red. The b * axis represents the blue or yellow portion of the color, with negative values indicating blue and positive values indicating yellow.

[0027] As described above, this electrolyte can be used to produce a reproducible dark to black layer that, in some cases, has a characteristic blue color tone, which best meets the market requirements in the consumer goods and jewelry sectors with respect to wear resistance and hue. b * Regarding the value, it should be noted that it should not deviate excessively from zero in order to achieve a clear black and cold color tone. In this article, b * the value is advantageously -5 to +5, preferably -3 to +3, particularly preferably -2 to +2. The preferred L * value is a value less than 65, very preferably less than 60. L * The value should be kept as low as possible. a * Regarding the value, a value of -2 to +2, very preferably a value of -1 to +1, is advantageously achieved.

[0028] The composition of the electrodeposited metal layer can vary within the scope of the claims. A person skilled in the art can control the amount, for example, based on the metal content in the electrolyte. The decision of a person skilled in the art will be directed towards the intended use of the deposited metal layer. The electrodeposited metal layer preferably has a composition of 55:45 to 90:10, very preferably 70:30 to 80:20, with respect to metals Rh and Ru.

[0029] The thickness of the metal layer deposited with the electrolyte according to the present invention can be determined by a person skilled in the art based on their respective requirement profiles. Usually, the thickness ranges from 0.5 to 1.5, preferably 0.25 to 0.75, very preferably 0.1 to 0.5 μm. It should be mentioned that with the electrolyte according to the present invention, a corresponding thick layer can also be electrodeposited without cracks occurring in the metal deposition. This is very surprising because brittle rhodium has a tendency to already have such cracks during electrodeposition when a smokeless coal / black layer is given.

[0030] For certain applications, it has proven advantageous to electrolytically apply a thin top layer of black rhodium deposited with the electrolyte according to the invention onto the metal layer. The metal deposit, probably thicker, deposited with the electrolyte according to the invention thus preferably subsequently functions as a sublayer of a further electrodeposited metal layer of rhodium, which latter has a thickness of 0.005 to 1 μm, preferably 0.025 to 0.75, and very preferably 0.05 to 0.5 μm. This final black rhodium layer can be applied with known electrolytes (published application No. 4154988 (A2), published application No. 61104097 (A2), published application No. 61084393 (A2), published application No. 61084392 (A2), https: / / ep.umicore.com / de / produkte-3 / produktfinder / rhoduna-470-black-rhodium-elektrolyt / -Rhoduna® 470 Black). It is thus possible to obtain more cost-effectively an article having a corresponding wear resistance, no cracks, and a darker metal layer, which was extremely surprising. The subject matter of the invention thus also relates to an article produced in a similar manner, comprising a sublayer deposited according to the invention, containing metallic rhodium and ruthenium in a composition based on weight percentages of 40:60 to 90:10 based on the total weight of both metals, and preferably an electrodeposited top layer of only black rhodium. A preferred L value of less than 50, more preferably less than 47 * The value is the result for the continuous layer described above. a * The value of a is from -2 to +3, very preferably from 0 to +2, and most preferably from 0 to +1. b * The value of b is from -1 to +6, very preferably from 1.5 to +4. The preferred properties of the sublayer as specified above also apply, with the necessary modifications, to the combinations of layers considered here.

[0031] The metal depositions discussed herein (for both the Rh / Ru layer and the continuous layer) have very high wear resistance, which has been found to be particularly advantageous for both the jewelry sector and technical applications (e.g., as contact materials). In what is known as the Bosch-Weinmann test (Bosch-Weinmann, A.M. Erichsen GmbH, publication 317 / D-V / 63, or Weinmann K., Farbe und Lack 65 (1959), pp. 647-651), the metal deposition achieves a value of less than 2.0 μm per 1000 strokes with the electrolyte according to the invention. More preferably, values of less than 1.0 μm per 1000 strokes, and very preferably even less than 0.75 μm per 1000 strokes can be achieved. In the case of the deposition of such wear-resistant metals, the composition of the rhodium-ruthenium layer is more preferably 50:50 to 80:20, most preferably 60:40 to 80:20.

[0032] The subject of the invention is also a method for electrodepositing a metal layer on a conductive material, comprising: a) the conductive material as the cathode is in contact with an aqueous acidic electrolyte according to the invention, b) the anode is in contact with the electrolyte, c) a sufficient current flow is established between the cathode and the anode.

[0033] It should be noted that the electrolyte and the preferred embodiments mentioned for its use are also applicable mutatis mutandis to the methods dealt with herein. The current density established in the electrolyte between the cathode and the anode during the deposition process can be selected by a person skilled in the art according to the deposition efficiency and the quality of the deposition. Depending on the application and the type of coating facility, the current density in the electrolyte is preferably set to 0.1 to 50 A / dm 2 ². If necessary, the current density can be increased or decreased by adjusting system parameters, such as the design of the coating cell, the flow rate, the condition of the anode or cathode, etc. A current density of 0.2 to 25 A / dm 2 is usually advantageous, preferably 0.25 to 15 A / dm 2, particularly preferably 0.25 to 10 A / dm 2 . Most preferably, the current density is within 0.5 to 6 A / dm 2 .

[0034] Typically, a thin layer thickness in the range of 0.1 to 0.3 μm is generated by rack operation. A low current density in the range of 0.25 to 5 A / dm 2 is thereby used. A further application of low current density is in drum or vibration technology, for example when coating contact pins. Here, a layer about 0.25 to 0.5 μm thick is applied at a current density in the range of 0.25 to 0.75 A / dm 2 . A layer thickness in the range of 0.1 to 1.0 μm is typically deposited by rack operation at a current density in the range of 0.5 to 5 A / dm 2 for mainly decorative purposes.

[0035] It is also possible to use pulsed direct current instead of direct current. Thereby, the current is interrupted for a certain time (pulse plating). In reverse pulse plating, the polarity of the electrode changes, thereby causing partial anodic stripping of the coating. In this way, the layer accumulation is controlled by the continuous alternation with the cathode pulse. By using simple pulse conditions, for example, a current of 1 second at medium current density (t on ) and a pulse pause of 0.5 second (t off ), etc., a homogeneous coating was obtained.

[0036] Suitable substrate materials typically used herein are copper-based materials such as pure copper, brass, or bronze, iron materials such as iron or stainless steel, nickel, gold, and silver. The substrate material may also be a multilayer system coated either directly or by another coating technique. This relates, for example, to a circuit board base material or an iron material that is nickel-plated or copper-plated and then optionally gold-plated or pre-silver-coated. Another substrate material is, for example, a wax core pre-coated with a silver conductive varnish (electroforming).

[0037] As already shown, the electrolyte according to the invention is of the acidic type. The pH value should be 2 or less and should not be below 0.2. The pH value is preferably from 0.5 to 1.5. During electrolysis, the pH value of the electrolyte may change. Therefore, in a preferred embodiment of the method, the person skilled in the art continues to monitor the pH value during electrolysis and adjusts it to the nominal value if necessary. The acid used in the electrolyte is advantageously used to adjust the pH value.

[0038] The temperature that is predominant during the deposition of the rhodium-ruthenium metal layer can be selected as desired by the person skilled in the art. Thus, they are determined on the one hand according to a sufficient deposition rate and applicable current density range, and on the other hand according to economic aspects or the stability of the electrolyte. It is advantageous to set the temperature at 20 °C to 65 °C, preferably 30 °C to 60 °C, particularly preferably 40 °C to 55 °C.

[0039] When using the electrolyte according to the invention, the use of an insoluble anode may be preferred. Preferred for use as an insoluble anode are those made from materials selected from the group consisting of platinum-plated titanium, graphite, mixed metal oxides, glassy carbon anodes, and special carbon materials (DLC, "diamond-like carbon"), or combinations of these anodes. An insoluble anode of platinum-plated titanium or titanium coated with a mixed metal oxide is advantageous, and the mixed metal oxide is preferably selected from iridium oxide, ruthenium oxide, tantalum oxide, and mixtures thereof. Also advantageously used in the practice of the present invention is a mixed oxide anode consisting of iridium-transition metal oxide-mixed oxide, more preferably an iridium-ruthenium mixed oxide, an iridium-ruthenium-titanium mixed oxide, or an iridium-tantalum mixed oxide. Further information can be found in Cobley, A.J. et al. (The use of insoluble Anodes in Acid Sulphate Copper Electrodeposition Solutions, Trans IMF, 2001, 79(3), pp. 113 and 114).

[0040] To optimally produce a dark layer, it is advantageous to perform a post-anodization treatment (see European Patent Application Publication No. 171091 (B1) or https: / / en.wikipedia.org / w / index.php?title=Anodizing&oldid=888700538). This post-treatment, known to those skilled in the art, can further enhance the wear resistance and darken the rhodium-ruthenium layer or the continuous layer addressed herein. Thus, the tendency to form cracks can also be counteracted. For anodization, the articles produced according to the invention are introduced into a post-treatment solution and anodized (stainless steel cathode).

Brief Description of the Drawings

[0041]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0042] The present invention will be described in the following examples.

[0043] Example 1: In addition to 1.5 g / l of rhodium [rhodium trisulfate], also [Ru2NCl8(H2O)2] 3- as 0.5 g / l of ruthenium, 4 g / l of ethylenediaminetetra(methylenephosphonic acid) EDTMP, and 11 g / l of potassium hydrogen phthalate as a blackening agent in water, and 10 g / l of sulfuric acid, an electrolyte according to the invention was used to produce a black and highly conductive and wear-resistant layer on consumer goods. The temperature of the electrolyte was 45 °C and the pH was approximately 1.0.

[0044] In a rack coating process, a suitable substrate was at 0.25 - 5 A / dm 2It was finished at the set current density. The obtained layer has very good mechanical stability and shows a very attractive neutral hue in the color range (a * value and b * value), being black.

[0045] The color values are visible in the attached chart (Figures 1 to 3). The electrolyte according to the present invention is called RA black.

[0046] Ruthuna® 490 and Ru479 are commercially available black ruthenium electrolytes. Rhoduna® 470 and 471 are commercially available black rhodium electrolytes (https: / / ep.umicore.com / en / products / productfinder).

[0047] Example 2 In addition to 1.0 g / l of rhodium [rhodium trisulfate], 1.0 g / l of ruthenium as [[Ru2NCl8(H2O)2]] 3- , 5 g / l of ethylenediamine tetra(methylenephosphonic acid) EDTMP, and 7.5 g / l of potassium hydrogen phthalate as a blackening agent in water, and 10 g / l of sulfuric acid. The electrolyte according to the present invention was used to produce a particularly black and wear-resistant layer on consumer goods. The temperature of the electrolyte was 45 °C, and the electrolyte had a pH value of about 1.2.

[0048] In the rack coating process, a suitable substrate was pre-coated at a set current density of 0.75 - 2 A / dm 2 . Next, a thin cover layer of a very dark (L * = 47) black rhodium electrolyte (e.g., Rhoduna® 470) was applied. It was post-treated anodically in a solution containing 10 g / l of potassium hydrogen phthalate at 4 volts. The solution after immersion was tempered at 30 °C. The obtained layer showed a dark black hue and had very good mechanical stability.

Claims

1. An aqueous acidic electrolyte for producing a dark metal layer on a conductive material, - 0.5 to 15.0 g / l of a soluble rhodium compound (with respect to metallic rhodium), and - 0.5 to 10.0 g / l of a soluble ruthenium compound (with respect to metallic ruthenium), and - 5 to 150 g / l of an acid, and - 0.5 to 20 g / l of a phosphonic acid, and - 0.5 to 25 g / l of an aromatic dicarboxylic acid, comprising An aqueous acidic electrolyte, wherein the pH value of the electrolyte is 0.5 to 1.

5.

2. The electrolyte according to claim 1, characterized in that ruthenium is present as a binuclear complex in the electrolyte.

3. Use of the electrolyte according to claim 1 or 2 for the production of an article having an electrodeposited metal layer containing rhodium and ruthenium in a composition based on weight percentages of 40:60 to 90:10 based on the total weight of both metals, wherein the metal layer has an L ＊ value of less than 65 and an a ＊ value of - 3 to + 3 according to the Cielab color system (EN ISO 11664 - 4, latest version at the filing date).

4. The use according to claim 3, characterized in that the b ＊ value of the electrodeposited metal layer is - 7 to + 7.

5. The use according to claim 3 or 4, characterized in that the electrodeposited metal layer functions as a lower layer for a further electrodeposited metal layer of rhodium, and the further electrodeposited metal layer of rhodium has a thickness of 0.05 to 0.5 μm.

6. The use according to claim 5, characterized in that the L ＊ value of the continuous layer of the electrodeposited metal layer and the further electrodeposited metal layer of rhodium is less than 50.

7. The continuous layer of the electrodeposited metal layer, or the electrodeposited metal layer and a further electrodeposited metal layer of rhodium, has a wear resistance of less than 0.75 μm per 1000 strokes (in the Bosch-Weinmann test), characterized in that the use according to any one of claims 3 to 6.

8. A method for electrodepositing a metal layer on a conductive material, comprising: a) the conductive material as a cathode is in contact with the aqueous acidic electrolyte according to claim 1 or 2; b) the anode is in contact with the electrolyte; c) a sufficient current flow is established between the cathode and the anode.

9. The current density in the electrolyte is 0.1 to 50 A / dm ２ , characterized in that the method according to claim 8.

10. The temperature during electrolysis is 20°C to 65°C, characterized in that the method according to claim 8 or 9.

11. The deposited metal layer is subjected to anodic post-treatment, characterized in that the method according to any one of claims 8 to 10.

Images