KR20140033424A - Electrolyte and its use for the deposition of black ruthenium coatings and coatings obtained in this way - Google Patents

Abstract

The present invention relates to a ruthenium electrolyte suitable for electrodeposition of decorative and industrial layers having a certain blackness. The invention also relates to the use of the electrolyte solution of the invention in a process for electrodepositing decorative and industrial layers of ruthenium (“black ruthenium”) having a certain blackness in jewels, ornaments, consumer goods and industrial products. The invention therefore also relates to corresponding layers and articles coated in this way. The electrolyte is characterized in that it operates in a weak acid to alkaline pH range.

Description

ELECTROLYTE AND ITS USE FOR THE DEPOSITION OF BLACK RUTHENIUM COATINGS AND COATINGS OBTAINED IN THIS WAY}

The present invention relates to a ruthenium electrolyte suitable for electrodeposition of decorative and industrial layers having a certain blackness. The invention also relates to the use of the electrolyte solution of the invention in a process for electrodepositing decorative and industrial layers of ruthenium (“black ruthenium”) having a certain blackness on jewels, ornaments, consumer goods and industrial products. The invention therefore also relates to corresponding layers and articles coated in this way.

Consumer and industrial products, jewellery and adornments are coated with thin layers of oxide-stable metals to prevent corrosion and / or improve optical quality. These layers should be mechanically stable and should not fade or wear even with relatively long use. Proven methods for making such layers include electroplating, in which a number of metal layers and alloy layers can be obtained in high quality form. Examples well known in everyday life are bronze and brass layers deposited on door handles or knobs, chrome coatings on automotive parts, gold plating of zinc-plated tools or wristbands.

A particular challenge in the field of electroplating is the production of metal layers that are stable to oxidation and mechanically strong with black, which is of interest not only in the decoration and jewelry sectors, but also in industrial applications, for example in the field of solar technology. It is becoming. Only a few metals are available for producing black layers that are stable to oxidation. In addition to ruthenium, rhodium and nickel are suitable. The use of precious metal rhodium is limited to the jewelry sector due to high raw material costs. Low-cost nickel and nickel-containing alloys can be used in particular in the jewelry and consumer sector, with strict regulations only in special cases, since the nickel and nickel-containing metal layers are contact allergens. The use of ruthenium has become an attractive alternative in all the applications described.

Electrolytes for the production of black ruthenium layers in electroplating processes are known in the art. The most widely used baths contain ruthenium in complex form with amidosulfonic acid or ruthenium as nitridochloro or nitridobromo complex (US 6117301, US 3576724, JP 6325909, WO 2001/011113, DE 19741990, US 4375392, JP 2054792, EP 1975282). The pH of the baths is often present in the acid range.

DE 1959907 describes the use of the binuclear ruthenium complex [Ru ₂ NCl _x Br _{8 -x} (H ₂ O) ₂ ] ^3- in an electroplating bath. In one embodiment, a nitrile chloro complex [Ru ₂ NCl ₈ (H ₂ O) ₂ ] ^3- is used. JP 56119791 contains 1-20 g / l ruthenium together with at least one compound selected from dicarboxylic acids, tricarboxylic acids, benzenesulfonic acids, N-containing aromatics and amino acids or derivatives of these compounds mentioned and from 0.01 to A 10 g / l thio compound relates to a ruthenium electrolyte further used as a blackening additive.

In order to improve the quality of jewelry and upholstery, the black layers should have not only good mechanical adhesive strength but also defect free optical quality. They should be able to be produced, if necessary, in a clear or cloudy form and with a very dark black color. This applies to applications in the industrial sector, in particular in solar technology. Black layers for improving the quality of consumer goods must also meet the requirements for mechanical stability. In particular, they should not show any black wear, even if used frequently over a long period of time.

Ruthenium baths and processes described in the prior art that meet the above requirements should use toxicologically problematic compounds such as thio compounds as blackening additives, or may require additional transition metals to ensure the required mechanical adhesive strength. Which makes it difficult to maintain the bath during the electrodeposition process. In addition, acid baths are capable of electrodeposition only to metals having relatively precious metal properties.

According to US 4082625, ruthenium electrodeposits of bright colors in the alkali range can also be obtained. US 350049 describes a ruthenium electrodeposition process in the range of pH 9-10. Ruthenium is maintained in solution in the pH range by complexing anions (EDTA, NTA, CDTA). A stable but brightly colored ruthenium electrodeposition is obtained.

Nitridochloro complexes of ruthenium are also used in the non-acidic aqueous bath for electrodeposition of ruthenium described in US Pat. No. 4,297,178. In addition, it contains oxalic acid or oxalate anion. However, it is doubtful whether the electrodepositions prepared in this manner have adequate blackness.

In view of the prior art cited herein, it is an object of the present invention to provide a stable electrolyte and its use, whereby the use of such electrolytes can yield ruthenium electrodeposits as durable and as black as possible on metal products. . In addition, electrodepositions on products which are not stable under a strong acidic environment are also possible.

This object and a further object which can be inferred in a clear manner from the prior art are achieved by an electrolyte having the characteristic features of claim 1. Advantageous embodiments of the electrolyte of the present invention are specified in claims 2 to 9. The use of the electrolyte solution of the invention in the process of the invention is described in claims 10 to 19. Electrodeposited layers are described in claims 20 to 24. Claim 25 relates to products coated in this manner.

With the provision of an electrolyte having a pH ≧ 5 to 12 for electrodepositing decorative and industrial layers of ruthenium with a certain blackness, having the following components, the above-mentioned objects are extremely effective, simple and advantageously achieved:

a) dissolved ruthenium at a concentration of 0.2 to 20 g (g / l) per liter based on the electrolyte, when calculated as ruthenium metal;

b) at least one dicarboxylic acid, tricarboxylic acid or tetracarboxylic acid anion at a concentration of 0.05 to 2 moles per liter;

c) one or more sulfur heterocycles;

d) at least one cationic surfactant, in particular surfactants based on quaternary ammonium salts.

The electrolyte provides a highly resistant and extremely black ruthenium electrodeposit on conductive, especially metallic products. Electrodeposition of black ruthenium coatings on conductive, especially metallic products, has only been possible so far with strong acidic electrolytes. In order to avoid attack on the substrate in the case of base metals to be coated, corrosion resistant intermediate layers (gold, palladium or palladium / nickel etc.) had to be provided for them before coating. However, the electrolyte of the present invention also makes it possible to work without an intermediate coating in a medium capable of plating substrates composed of die-cast zinc, brass or bronze.

Ruthenium is used in the form of a water-soluble compound known to those skilled in the art, preferably as a heteronuclear anionic nitrile of the formula [Ru ₂ N (H ₂ O) ₂ X ₈ ] ^3- where X is a halide ion. . Chloro complex [Ru ₂ N (H ₂ O) ₂ Cl ₈ ] ^3- is particularly preferred. The amount of the complex in the electrolyte solution of the present invention may be preferably selected such that the concentration of ruthenium calculated as ruthenium metal after the compound is completely dissolved is 0.5 to 10 g per liter based on the electrolyte solution. The finished electrolyte contains particularly preferably 1 to 8 g, very particularly preferably 3 to 6 g of ruthenium per liter based on the electrolyte. It is preferable that only ruthenium is electrodeposited from the electrolyte solution of this invention. In this case, the electrolyte does not contain additional transition metal ions other than ruthenium.

The electrolyte contains certain organic compounds having at least one carboxylic acid group. These are especially dicarboxylic acids, tricarboxylic acids or tetracarboxylic acids. These are well known to those skilled in the art and can be found, for example, in Beyer-Walter, Lehrbuch der Organischen Chemie, 22nd edition, S. Hirzel-Verlag, p. 324 ff. In this context, particular preference is given to acids selected from the group consisting of oxalic acid, citric acid, tartaric acid, succinic acid, maleic acid, glutaric acid, adipic acid, malonic acid, malic acid. The acids are naturally present in anionic form in the electrolyte at the pH set. The carboxylic acid mentioned herein is added to the electrolyte at a concentration of 0.05 to 2 mol / l, preferably 0.1 to 1 mol / l and very particularly preferably 0.2 to 0.5 mol / l. This applies in particular to the use of oxalic acid, which is believed to also act as a conductive salt in the electrolyte.

Certain sulfur compounds are also present in the electrolyte in the present invention. These are in particular one or more sulfur compounds containing one or more sulfur atoms in the heterocyclic ring system (sulfur heterocycle) (Beyer-Walter, Lehrbuch der Organischen Chemie, 22nd edition, S. Hirzel-Verlag, p. 703 ff) ). These are optionally aromatic or fully or partially saturated five or six member rings or corresponding fused ring systems based on carbon containing one or more sulfur atoms and / or one or more additional heteroatoms, for example nitrogen Can be. The sulfur heterocycle used is preferably sufficiently water soluble so that it can be effectively used in an appropriate concentration range in the electrolyte. Preferred compounds are 3- (2-benzothiazolyl-2-mercapto) propanesulfonic acid sodium salt, saccharin sodium salt, saccharin-N-propylsulfonate sodium salt, 6-methyl-3,4-dihydro-1, 2,3-oxathiazin-4-one 2,2-dioxide, benzothiazole, 2-mercaptobenzothiazole, thiazole, isothiazole and derivatives thereof. While not being bound by the theory presented herein, it is believed that sulfur heterocycles affect dark blackening in the electrodeposition of ruthenium. Sulfur heterocycles are used in electrolytes at concentrations of 0.001 to 4 mol / l, preferably 0.002 to 1 mol / l and very particularly preferably 0.004 to 0.01 mol / l.

One or more surface-active substances of the cationic surfactant type are also present in the electrolyte. Possible surfactants of this type are in particular quaternary ammonium salts. These are well known to those skilled in the art (see Beyer-Walter, Lehrbuch der Organischen Chemie, 22nd edition, S. Hirzel-Verlag, p. 251 ff). Octyltrimethylammonium bromide, octyltrimethylammonium chloride, decyltrimethylammonium bromide, decyltrimethylammonium chloride, dodecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, From the group consisting of hexadecyltrimethylammonium chloride, ethyldimethylhexadecylammonium bromide, ethyldimethylhexadecylammonium chloride, benzyldimethyldecylammonium chloride, benzyldimethyldodecylammonium chloride, benzyldimethyltetradecylammonium chloride and benzyldimethylhexadecylammonium chloride Preferred ammonium salts are preferred. Cationic surfactants contemplated herein are used in electrolytes at concentrations of 0.1 to 20 mmol / L, preferably 0.5 to 10 mmol / L and very particularly preferably 1 to 5 mmol / L, which are also electrodeposited. It is important for the darker black of the layer.

The pH of the electrolyte is preferably only in the range of slightly acidic to alkaline. The pH is preferably set to a value in the range of 5 to 12. The pH of the electrolyte during use is more preferably in the range of 6-9, particularly preferably 7-8. Particularly preferred is set to a pH of about 7.5. The pH is kept constant by the addition of buffer material. These are well known to those skilled in the art (Handbook of Chemistry and Physics, CRC Press, 66th Edition, D-144 ff). Preferred buffer systems are borate, phosphate and carbonate buffers. The compound for preparing such a buffer system may be selected from the group consisting of boric acid, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, potassium bicarbonate and dipotassium carbonate. The buffer system is used at concentrations of 0.08 to 1.15 mol / l, preferably 0.15 to 0.65 mol / l and very particularly preferably 0.2 to 0.4 mol / l (on anionic basis).

Naturally, further additives advantageous for electrodeposition may be added to the electrolyte under consideration here. These are well known to those skilled in the art. Preference is given to those selected from the group consisting of conductive salts, further blackening additives, brighteners (Praktische Galvanotechnik, 5th edition, Eugen G. Leuze Verlag, Bad Saulgau, p. 39 ff).

The present invention also relates to the use of the electrolyte solution of the present invention. In such applications, those skilled in the art will immerse the conductive, in particular metallic, product to be coated as cathode in the electrolyte and allow current to flow between the anode and the cathode. The use of the electrolyte solution of the present invention is preferably carried out in the same advantageous embodiments described above for the electrolyte solution. The flow of current should be sufficient to electrodeposit the black ruthenium coating on conductive, especially metallic products, within the acceptable time range. Those skilled in the art will know the strength of the electric field to be set for this. A current density of 0.1 to 10 A / dm ² is preferably set. The current density is particularly preferably 0.2 to 5 A / dm ² and very particularly preferably 0.5 to 2 A / dm ² .

The temperature of the electrolyte during electrodeposition can be appropriately set by those skilled in the art. The range of temperature to be set is advantageously 10 to 80 ° C. The temperature is preferably set at 50 to 75 ° C and particularly preferably at 60 ° and 70 ° C. It may be advantageous to stir the electrolyte during electrodeposition.

In the case of an anode, it is also possible for the skilled person to select the aspects to be considered for this purpose. It is preferable to use an anode made of a material selected from the group consisting of titanium platinum, graphite, iridium-transition metal mixed oxides and certain carbon materials ("diamond-type carbon", DLC) or combinations thereof. Insoluble anodes consisting of titanium platinum or iridium-transition metal mixed oxides have been found to be advantageous. Particular preference is given to using an anode consisting of platinum platinum.

The present invention also provides black ruthenium layers obtainable by the process of the present invention. The layers have a thickness of 0.1 to 3 μm, preferably 0.2 to 1.5 μm and very particularly preferably 0.3 to 1.3 μm. The layer of the invention comprises 3% to 6% by weight, preferably 3.1% to 5% by weight and particularly preferably 3.2% by weight in the outer region (viewed inwardly from the visible surface) of about 1.1 (± 0.2) μm Sulfur content of% to 4.5% by weight. The sulfur content is particularly preferably about 4% by weight. The ruthenium layer also has a carbon content in the outer region of 1% to 2% by weight, preferably 1.1% to 1.8% by weight and very particularly preferably 1.15% to 1.5% by weight. The value is particularly preferably about 1.2% by weight. The ruthenium layer has an oxygen content of from 15% to 20% by weight, preferably from 16% to 19% by weight and particularly preferably from 17% to 18.5% by weight in the outer region. The oxygen content here is particularly preferably about 18% by weight. It seems particularly advantageous to have a gradient with a concentration in which the concentration of sulfur in the layer under consideration increases from outside to inside. Thus, it is often measured that the concentration of about 2% by weight of sulfur at the surface can increase up to 5% by weight inwardly. The values measured herein are GDOES method (Glow Discharge Optical Emission Spectrometry; R. Kenneth Marcus, Jose Broekaert: Glow Discharge Plasma in Analytical Spectroscopy, Wiley ISBN 0-471-60699-5 and Thomas Nelis, Richard Payling: Glow Discharge Optical Emission Spectroscopy-A Practical Guide, Royal Society of Chemistry, ISBN 0-85404-521-X.

The invention further provides certain products such as ornaments, consumer goods and industrial products having a layer according to the invention. Particular preference is given to products in which the corresponding electrodeposition in the acid range is not possible due to the base metal properties of the products.

Electrodeposition of black ruthenium coatings on conductive, in particular metallic articles according to the invention may be carried out in an exemplary manner as follows, taking into account what has been described above:

In the electrolytic use of black ruthenium layers, fragments (collectively referred to as substrates) of jewelry, ornaments, consumer goods or industrial products are immersed in the electrolyte of the present invention to form a cathode. For example, anodes made of platinum platinum (product information for PLATINODE ^® from Umicore Galvanotechnik GmbH) are also immersed in the electrolyte. Subsequently, a current is appropriately flowed between the anode and the cathode. In order to adhere the homogeneous layers tightly, the maximum current density should not exceed 10 amperes per square decimeter [A / dm ² ]. In excess of this value, amorphous ruthenium moieties may be electrodeposited. As a result, the layers may not be homogeneous and dark abrasion will appear under mechanical stress. The current density chosen is also determined by the type of coating process. In the barrel plating process, preferred current densities range from 0.1 to 1 A / dm ² . In a rack plating process, a current density of 0.5 to 5 A / dm ^{2 results} in optically defect black ruthenium layers.

The ruthenium electrolytes provided by the present invention are particularly suitable for processes for electrodeposition of decorative dark black layers and optionally bright layers, for example, on jewelry and decorative articles. Such articles are also provided by the present invention. The electrolyte can be preferably used in the barrel plating process and the rack plating process. The electrolyte described herein enables the production of particularly dense and dark black electrodeposits (L up to 50) on suitable materials (see FIG. 1 showing the comparative example and the results of Example 1 according to the invention). . Moreover, when using the electrolyte solution, it is possible to work in the weakly acidic to alkaline range, which is the first to allow electrodeposition of a black ruthenium coating on the base metal without providing the base metal with a precious metal interlayer in advance. This was not obvious at all in terms of known prior art.

Five samples were examined. Preparation of the samples can be taken from the examples.

It can be clearly seen that a relatively good L ^* value is obtained by the process in the alkali range (the electrolyte according to the invention). In addition, blackening is promoted by adding a cationic surfactant as a humectant.

Color values were measured in the layers formed using a standard color measurement instrument according to the CIE-L * a * b * system.

The layers were also examined by glow discharge optical emission spectroscopy (GDOES). Specimens are "sputtered-off" and excited on an approximately planar surface in an argon plasma to emit specific radiation. The radiation is detected with an optical spectrometer. Concentrations and depths are calculated by multimatrix calibration tests.

Example :

General method:

The brass sheet is immersed in the electrolyte having the composition described below.

Comparative Example-Formulations According to US 4297178:

Example 1 According to the Invention (Type I)

Example 2: According to the Invention (Type II)

Example 3: Sulfur Heterocycle Free (Type III)

Claims (25)

As an electrolytic solution having a pH ≧ 5 to 12 for electrodepositing decorative and industrial layers of ruthenium with a certain blackness,
a) ruthenium dissolved at a concentration of 0.2 to 20 g (g / l) per liter based on the electrolyte, calculated as a ruthenium metal;
b) at least one dicarboxylic acid, tricarboxylic acid or tetracarboxylic acid anion at a concentration of 0.05 to 2 moles per liter;
c) one or more sulfur heterocycles;
d) An electrolyte solution having at least one cationic surfactant. The dinuclear anionic ruthenium nitrile of the formula [Ru ₂ N (H ₂ O) ₂ X ₈ ] ^3- wherein X is a halide ion, is also present as a halo complex. Electrolyte solution. The electrolyte according to claim 1 and / or 2, characterized in that the concentration of ruthenium after complete dissolution of the compound ranges from 2 to 8 g per liter based on the electrolyte. The electrolyte solution according to any one of claims 1 to 3, wherein the electrolyte solution does not contain additional transition metal ions. The method according to claim 1, wherein the carboxylic acid is selected from the group consisting of oxalic acid, citric acid, tartaric acid, succinic acid, maleic acid, glutaric acid, adipic acid, malonic acid, malic acid. Electrolyte solution. 6. The sulfur heterocycle according to claim 1, wherein the sulfur heterocycle is 3- (2-benzothiazolyl-2-mercapto) propanesulfonic acid sodium salt, saccharin sodium salt, saccharin N-propylsulfonate sodium Salt, 6-methyl-3,4-dihydro-1,2,3-oxathiazin-4-one 2,2-dioxide, benzothiazole, 2-mercaptobenzothiazole, thiazole, isothiazole And derivatives thereof, the electrolyte solution. The method according to claim 1, wherein the surfactant is octyltrimethylammonium bromide, octyltrimethylammonium chloride, decyltrimethylammonium bromide, decyltrimethylammonium chloride, dodecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, Tetradecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, ethyldimethylhexadecylammonium bromide, ethyldimethylhexadecylammonium chloride, benzyldimethyldecylammonium chloride, benzyldimethyldodecylammonium chloride Electrolytic, characterized in that it is selected from the group consisting of benzyldimethyltetradecylammonium chloride and benzyldimethylhexadecylammonium chloride and mixtures thereof liquid. The electrolyte solution according to any one of claims 1 to 7, wherein the pH of the electrolyte solution is in the range of 7 to 8. The electrolyte of claim 1, wherein the electrolyte comprises a buffer system selected from the group consisting of borate, phosphate and carbonate buffers. As a cathode, the use of an electrolyte in a process for electrodepositing a black ruthenium coating on a product by immersing a conductive, in particular metallic product, to be coated as a cathode in an electrolyte and flowing a current between the anode and the cathode,
Use, characterized in that the electrolyte solution claimed in one or more of claims 1 to 9 is selected. The dinuclear anionic ruthenium nitrile of the formula [Ru ₂ N (H ₂ O) ₂ X ₈ ] ^3- wherein X is a halide ion, is also present as a halo complex. Usage. Use according to claim 10 and / or 11, characterized in that the concentration of ruthenium after complete dissolution of the compound ranges from 2 to 8 g per liter based on the electrolyte. Use according to one or more of claims 10 to 12, characterized in that the electrolyte does not contain additional transition metal ions. The method of claim 10, wherein the carboxylic acid is selected from the group consisting of oxalic acid, citric acid, tartaric acid, succinic acid, maleic acid, glutaric acid, adipic acid, malonic acid, malic acid. Use. The sulfur heterocycle of claim 10, wherein the sulfur heterocycle is a 3- (2-benzothiazolyl-2-mercapto) propanesulfonic acid sodium salt, saccharin sodium salt, saccharin-N-propylsulfonate. Sodium salt, 6-methyl-3,4-dihydro-1,2,3-oxathiazin-4-one 2,2-dioxide, benzothiazole, 2-mercaptobenzothiazole, thiazole, isothia Use, characterized in that it is selected from the group consisting of sol and derivatives thereof. The method according to claim 10, wherein the surfactant is octyltrimethylammonium bromide, octyltrimethylammonium chloride, decyltrimethylammonium bromide, decyltrimethylammonium chloride, dodecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, Tetradecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, ethyldimethylhexadecylammonium bromide, ethyldimethylhexadecylammonium chloride, benzyldimethyldecylammonium chloride, benzyldimethyldodecylammonium chloride , Benzyldimethyltetradecylammonium chloride and benzyldimethylhexadecylammonium chloride and mixtures thereof . Use according to one or more of claims 10 to 16, characterized in that a current density of 0.1 to 10 A / dm ² is set. Use according to one or more of claims 10 to 17, characterized in that a temperature of 10 to 80 ° C is set. 19. An insoluble anode made of a material selected from the group consisting of titanium platinum, graphite, iridium-transition metal mixed oxides and certain carbon materials and combinations of these anodes is used. Use, characterized by. A black ruthenium layer obtainable as claimed in one or more of claims 10-19. The ruthenium layer of claim 20, wherein the thickness is from 0.1 to 3 μm. The ruthenium layer according to claim 20, wherein the layer has a sulfur content of 3 wt% to 6 wt% in the outer region of 1 μm. The ruthenium layer according to claim 20, wherein the layer has a carbon content of 1 wt% to 2 wt% in the outer region of 1 μm. The ruthenium layer according to claim 21, wherein the layer has an oxygen content of 15 wt% to 20 wt% in the outer region of 1 μm. 25. An article having a ruthenium layer as claimed in one or more of claims 20-24.

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