DE10243139A1 - Alloy for decorative or functional purposes e.g. as a coating material for buttons and sliding clasp fasteners and absorbing layers in solar cells contains tin, copper, bismuth and oxidic oxygen - Google Patents

Abstract

Alloy contains 1-15 % tin, 19-60 % copper, 30-80 % bismuth and 0-10 % oxidic oxygen. Independent claims are also included for the following: (1) Coated object comprising a substrate and a layer made from the above alloy; (2) Electrolyte composition containing an ionogenic tin compound, an ionogenic copper compound and an ionogenic bismuth compound; and (3) Electrolytic process for the production of dark alloy layers comprising preparing a substrate to be coated as cathode, preparing the above electrolyte composition, electrolytically depositing a dark alloy layer onto the substrate and optionally post-treating the alloy layer.

Description

The present invention relates to dark bismuth-tin-copper alloys, ionic bismuth, tin, and electrolyte compositions containing copper compounds and a method of making the alloys. The invention relates Moreover the use of alloys for decorative and functional Purposes.

It has long been known to have metal surfaces or electrochemically deposited layers by treatment with chemical Colored solutions to change. This process is called "coloring" [non-metallic Inorganic coatings, W. Machu, Springer Verlag, Vienna, 1952; Recipes for metal coloring and Metal covers without Power source, O.P. Chandler, Eugen G. Leuze Verlag, Saulgau, 1994]. In the past the one for decorative Applications mostly desired gray or black hue achieved with different methods. For example, the black coloring of copper, brass or Bronze with a solution made of copper nitrate (so-called "black flame"), with a solution Potassium hydroxide and potassium persulfate (so-called "persulfate stain") or with one selenium-containing dyeing process blackening of iron with a solution from arsenic trioxide and iron sulfate in hydrochloric acid (so-called "arsenic coloring") and the black coloring of Silver through the so-called "sulfur boar staining".

The disadvantage of these conventional dyeing processes is that that through the superficial chemical Conversion of the to be colored Only a thin substrate superficial Color layer is generated, both in the layer thickness to be achieved as also in adhesive strength or durability, e.g. with mechanical stress, is limited. Another disadvantage is the high reactivity of the staining solutions, which only allows short downtimes and complicates automation.

In addition to coloring through chemical treatment the one to be colored surface are electrolytic processes for the production of layers with gray or black self-coloring known, such as black nickel, black zinc, black chrome, black ruthenium or tin-nickel alloys.

In EP-B-0 808 921 describes the electrolytic production of a Sn-Cu-Pd alloy with a white luster and its use for decorative purposes.

In JP-A-59023895 describes the electrolytic generation of a black coating from a ternary Sn-Ni-Cu alloy.

The electrolytic coloring of anodized aluminum with metal salt solutions containing one or more metal salts selected from nickel, cobalt and tin is described in US-A-4,022,671 or US-A-4,066,816 described.

These procedures sometimes require complicated process control, a high energy requirement or the use of expensive materials. Also exist despite improvements in layer thickness and against the adhesive strength through superficial Chemical conversion layers still created disadvantages in terms of of consistency compared to the layers created mechanical stress, e.g. through use or cleaning of the coated objects. A well-known phenomenon is e.g. peeling the color layers of zippers or Button at To wash.

The object of the invention was therefore based on a coating material and a method for the same To provide manufacturing, which avoided the problems mentioned can be.

Surprisingly it was found that this problem is solved by an alloy, which contains certain amounts of tin, copper and bismuth.

Been in the past ternary alloys made of bismuth, copper and tin or alloys, among others contain these metals.

The properties of these materials vary greatly with the proportions of the metals.

So in US-A-5,368,814 describes a lead-free solder metal with a low solidus line, which mainly consists of bismuth and tin (ie in each case approx. 50%, based on the total amount of bismuth and tin) and in addition an effective amount of a third component which enhances the physical and mechanical properties, such as indium , Copper, silver or combinations thereof (eg 4% copper). The alloy is described as a particularly useful joining material in microelectronic applications.

A scratch-resistant bronze alloy based on copper as the main component, which also contains 1-13% by weight of tin, not more than 18% by weight of zinc, 0.5-6% by weight of bismuth, 0.05-3% by weight of antimony contains than 1 wt .-% phosphorus and less than 4 wt .-% lead is in US-A-6,419,766 described.

Casting alloys based on copper, which contain small amounts of bismuth and tin, for example in US-A-5,487,867 (0.1 - 7% by weight bismuth and optionally 2 - 6% by weight tin), US-A-4,789,094 (1 .5 - 7 wt .-% bismuth and 1 - 12 wt .-% tin) and in US-A-5,330,712 (0.1 - 7 wt .-% bismuth and up to 16 wt .-% tin).

However, there is no indication in the publications mentioned that an alloy containing 1-15% by weight of tin, 19-60% by weight of copper, 30-80% by weight of bismuth and 0-10% by weight oxidi have oxygen, the task at hand solves.

The object of the invention is thus an alloy comprising a) 1-15 % By weight of tin, b) 19-60 % Copper, c) 30 - 80 % By weight bismuth and d) 0-10 Gewoxidischen oxygen and their use to decorative or functional purposes.

The subject of the invention is furthermore a coated article comprising a substrate and a layer an alloy according to the present Invention.

The subject of the invention is furthermore an electrolyte composition for producing the alloy according to the invention, comprising a) at least one ionogenic tin compound, b) at least one ionogenic copper compound, and c) at least one ionic bismuth compound.

The invention also relates to an electrolytic A method of making dark alloy layers, comprising the steps a) providing a substrate to be coated as cathode, b) providing an electrolyte composition according to the invention, c) electrolytic deposition of a dark one according to the invention Alloy layer on the substrate, and d) optionally aftertreatment the dark alloy layer produced in step c).

The alloy according to the invention comprises 1-15% tin, 19-60 % Copper, 30 - 80 % Bismuth and 0-10 % oxidic oxygen. All alloy related information should mean% by weight below.

The alloys of the present Invention are characterized by a dark color. The dark Color can vary depending on the exact composition of the alloy vary between brown, gray, dark blue, gray-blue and black. By increase The color of the oxygen content can also be varied (e.g. gray / anthracite: 0% 0; dark gray - black: 1 - 2% 0).

The alloys of the present Invention can also small amounts of other metals, e.g. Iron or aluminum contain. Here, the term “small amounts” is understood to mean amounts which are not more than 5% by weight, preferably 2% by weight and particularly preferably 0.5% by weight.

In a preferred embodiment the alloy consists essentially of 1 - 15% tin, 19 - 60% copper, 30-80 % Bismuth and 0 - 10% oxidic oxygen and inevitable impurities. such Impurities can e.g. from the manufacturing process or the raw materials used resulting impurities, such as nitrogen, phosphorus, carbon. Typically, these contaminants are present in the alloy in amounts which are not more than 3.0% by weight. Preferably lie such impurities in amounts that do not exceed 1.0% by weight and particularly preferably not more than 0.5% by weight. Accordingly is the amount of inevitable impurities in the alloys of the present invention about 0 to about 3.0% by weight, preferably 0 to 1.0% by weight and particularly preferably 0 to 0.5% by weight.

In a further preferred embodiment In the invention, the alloy is essentially free of one or selected from multiple items Nickel, lead, selenium, chrome, and antimony. It is particularly preferred that the alloy is essentially free of at least two elements, more preferred free of at least three of these elements and most preferred free from all enumerated Elements.

The expression "essentially free of" means here that the amount of these elements in the alloy is less than 2% by weight is. The amount is preferably less than 1% by weight, particularly preferably less than 0.5% by weight and most preferred less than 0.1% by weight.

The alloys of this embodiment have the additional Benefit on having no toxic or allergenic elements included and accordingly also the use of toxic or allergy-causing substances can be avoided in the manufacture of the alloys.

In another preferred embodiment the alloy is essentially free of one or more elements selected made of silver, gold, palladium, platinum, ruthenium, rhodium or iridium.

The expression "essentially free of" is as above Are defined.

The alloys of this embodiment have the additional Advantage on that they are particularly inexpensive to manufacture.

In a further preferred embodiment the alloy is essentially free of zinc, the expression “essentially free of "as above is defined. The alloys of this embodiment are characterized by a special one resistance across from mechanical stress.

In the alloys of the present Invention is the amounts of tin 1-15 %, preferably 1-10 % and particularly preferably 1-2 %.

In the alloys of the present Invention is the amounts of copper 19 - 60 %, preferably 29-60 % and especially 39 - 60 %.

In the alloys of the present Invention is the amounts of bismuth 30 - 80 %, especially 35 - 70 % and particularly preferably 39-60 %.

The metals that make up the alloy, i.e. Tin, copper and bismuth, as well as any other metals, can also exist in oxidic form. Accordingly, the amount is of oxidic oxygen in the alloys according to the invention 0-10% by weight, preferably 0-5 % and particularly preferably 0-2 %.

The alloys of the invention are obtainable by electrolytic deposition from an electrolytic solution. This will start with a substrate to be coated is provided and connected as a cathode.

The substrate is not limited and can be from an electrically conductive but also from an electrically non-conductive material. In the latter case it is it is preferred to first coat the material to be coated with a coating an electrically conductive material, e.g. a metal like palladium or copper.

As electrically conductive substrates tin, copper, zinc or alloys are suitable, for example these metals, e.g. Bronze or brass.

As electrically non-conductive substrates For example, different types of plastic, ceramic are suitable Materials or glass.

The alloy components are in Form provided an electrolyte composition, the at least an ionogenic tin compound, at least one ionogenic copper compound and contains at least one ionic bismuth compound.

In addition, the electrolyte composition a suitable solvent or solvent mixture exhibit. An aqueous electrolyte composition is particularly preferably used.

The ionogenic tin, copper and Bismuth compounds are in no way limited as long as they are suitable for electrolytic deposition. typically, be for that preferred compounds that are in the selected solvent let solve.

Compounds are preferably used as the tin compound used in which tin in the oxidation levels +2 and / or +4 is present. Compounds are preferably used as the copper compound used in which copper in the oxidation states +1 and / or +2 is present. Compounds are preferably used as bismuth compounds used in which bismuth in the oxidation states +3 and / or +5 is present.

The ionogenic tin compound will particularly preferably from tin sulfates, tin chlorides, tin sulfonates, Tin oxalates, sodium stannates, potassium stannates and mixtures thereof selected.

The ionogenic copper compound will preferably from copper sulfates, copper chlorides, copper sulfonates, Copper oxalates, copper oxides and copper cyanides, complex copper compounds and mixtures thereof selected.

The ionic bismuth compound will preferably from bismuth nitrates, bismuth carbonates, bismuth citrates, complex bismuth compounds and mixtures thereof selected.

Others optionally in the alloy contained metals are also preferably in the form of their Salts used.

usual Additives can be added to the electrolyte composition as needed. there May be pH adjustment aids such as alkalis (e.g. potassium, sodium or ammonium hydroxide), inorganic acids (e.g. hydrochloric acid, sulfuric acid, phosphoric acid or boric acid) and their salts, buffers or organic acids (e.g. hydroxycarboxylic acids, citric acid or their Salts) act. Also conductive salts (e.g. alkali salts of hydrochloric acid, sulfuric acid, phosphoric acid), complexing agents (e.g. EDTA), wetting agents (e.g. anionic, cationic or zwitterionic Surfactants) or brighteners (e.g. organic nitrogen compounds such as polymeric reaction products of epichlorohydrin and amines) can after Need be added.

The electrolyte compositions can, for example from alkaline (cyanide-containing or cyanide-free), acidic or neutral electrolyte compositions can be selected.

• a) 0,05 – 5 g/l Kupfer als ionogene Kupferverbindung,
• b) 5 – 50 g/l Zinn als ionogene Zinnverbindung,
• c) 0,05 – 5 g/l Bismut als ionogene Bismutverbindung,
• d) 10 – 200 g/l Kalium- oder Natriumhydroxid,
• e) 10 – 200 g/l Komplexbildner
• f) 5 – 50 g/l einer Cyanidverbindung
• g) 0,1 – 10 g/l Glanzbildner und
• h) 0,1 – 10 g/l Netzmittel

aufweisen.An alkaline, cyanide-containing electrolyte composition according to the invention can, for example

• a) 0.05 - 5 g / l copper as an ionogenic copper compound,
• b) 5-50 g / l tin as an ionogenic tin compound,
• c) 0.05 - 5 g / l bismuth as an ionic bismuth compound,
• d) 10-200 g / l potassium or sodium hydroxide,
• e) 10-200 g / l complexing agent
• f) 5-50 g / l of a cyanide compound
• g) 0.1-10 g / l brightener and
• h) 0.1 - 10 g / l wetting agent

exhibit.

The statement "g / l metal compound" refers to in of the present invention on the amount of metal atom in the compound in g, counter ions are not included.

The copper compound is preferably made from Sulfates, chlorides, sulfonates, oxalates or oxides selected.

As a tin compound is preferred Potassium or sodium stannate used.

A bismuth compound is preferably used Nitrate, carbonate or citrate compound used.

The preferred cyanide compound is sodium or potassium cyanide is used.

As wetting agents and brighteners, for example Resistant surfactants in the corresponding media, e.g. cationic Surfactants, polyhydric alcohols, e.g. Glycol or organic nitrogen compounds, e.g. polymeric reaction products from epichlorohydrin and amines used become.

The pH of the electrolyte composition is preferably set to a strongly alkaline range (e.g. pH 11-13).

• a) 0,05 – 5 g/l Kupfer als ionogene Kupferverbindung,
• b) 5 – 50 g/l Zinn als ionogene Zinnverbindung,
• c) 0,05 – 5 g Bismut als ionogene Bismutverbindung,
• d) 10 – 200 g/l Kalium- oder Natriumhydroxid,
• e) 10 – 200 g/l Komplexbildner,
• f) 0,1 – 10 g/l Glanzbildner und
• g) 0,1 – 10 g/l Netzmittel

aufweisen.An alkaline, cyanide-free electrolyte composition according to the invention can, for example

• a) 0.05 - 5 g / l copper as an ionogenic copper compound,
• b) 5-50 g / l tin as an ionogenic tin compound,
• c) 0.05 - 5 g bismuth as an ionogenic bismuth compound,
• d) 10-200 g / l potassium or sodium hydroxide,
• e) 10-200 g / l complexing agent,
• f) 0.1-10 g / l brightener and
• g) 0.1 - 10 g / l wetting agent

exhibit.

As a tin compound is preferred Sodium or potassium stannate used.

A copper compound is preferably used Sulfate, chloride, oxalate or oxide compound used.

A bismuth compound is preferably used Nitrate, citrate or carbonate compound used.

As wetting agents, for example, in the corresponding Media resistant Surfactants, e.g. cationic surfactants, polyhydric alcohols, e.g. glycol and as a brightener, organic nitrogen compounds, e.g. polymeric Reaction products from epichlorohydrin and amines can be used.

Organic, for example, can be used as complexing agents acids and their salts, phosphonic acids, Phosphonates, gluconates, glucoheptonic acids, glucoheptonates and ethylenediaminetetraacetic acid are used become.

The pH of the electrolyte composition is preferably set strongly alkaline (e.g. pH 11 - 13).

• a) 0,05 – 5 g/l Kupfer als ionogene Kupferverbindung,
• b) 5 – 50 g/l Zinn als ionogene Zinnverbindung,
• c) 0,05 – 5 g/l Bismut als ionogene Bismutverbindung,
• d) 1 – 50 g/l Kalium- oder Natriumhydroxid,
• e) 10 – 200 g/l Komplexbildner,
• f) 0,1 – 10 g/l Glanzbildner und
• g) 0,1 – 10 g/l Netzmittel

aufweisen.A neutral electrolyte composition according to the invention can, for example

• a) 0.05 - 5 g / l copper as an ionogenic copper compound,
• b) 5-50 g / l tin as an ionogenic tin compound,
• c) 0.05 - 5 g / l bismuth as an ionic bismuth compound,
• d) 1-50 g / l potassium or sodium hydroxide,
• e) 10-200 g / l complexing agent,
• f) 0.1-10 g / l brightener and
• g) 0.1 - 10 g / l wetting agent

exhibit.

A copper compound is preferably used Sulfate, chloride, sulfonate, oxalate or oxide compound used.

As a tin compound is preferred a sulfate or chloride compound or sodium or potassium stannate used.

A bismuth compound is preferably used Nitrate, citrate or carbonate compound used.

Suitable as a complexing agent, for example Tetrasodium pyrophosphate.

As wetting agents, for example, in the corresponding Media resistant Surfactants, e.g. cationic surfactants, polyhydric alcohols, e.g. glycol and as a brightener, organic nitrogen compounds, e.g. polymeric Reaction products from epichlorohydrin and amines can be used.

The pH of the electrolyte composition is preferably set to a neutral range (pH 6-8).

• a) 0,05 – 5 g/l Kupfer als ionogene Kupferverbindung,
• b) 5 – 50 g/l Zinn als ionogene Zinnverbindung,
• c) 0,05 – 20 g Bismut als ionogene Bismutverbindung,
• d) 10 – 200 g/l Kalium- oder Natriumhydroxid,
• e) 10 – 200 g/l Komplexbildner,
• f) 0,1 – 10 g/l Glanzbildner und
• g) 0,1 – 10 g/l Netzmittel

A further neutral electrolyte composition according to the invention can, for example

• a) 0.05 - 5 g / l copper as an ionogenic copper compound,
• b) 5-50 g / l tin as an ionogenic tin compound,
• c) 0.05-20 g of bismuth as an ionic bismuth compound,
• d) 10-200 g / l potassium or sodium hydroxide,
• e) 10-200 g / l complexing agent,
• f) 0.1-10 g / l brightener and
• g) 0.1 - 10 g / l wetting agent

exhibit.

As a tin compound is preferred Sodium or potassium stannate used.

A copper compound is preferably used Sulfate, chloride, oxalate or oxide compound used.

A bismuth compound is preferably used Nitrate, citrate or carbonate compound used.

As wetting agents and brighteners, for example Resistant surfactants in the corresponding media, e.g. cationic Surfactants, polyhydric alcohols, e.g. Glycol or organic nitrogen compounds, e.g. polymeric reaction products from epichlorohydrin and amines used become.

Organic, for example, can be used as complexing agents acids and their salts, phosphonic acids, Phosphonates, gluconates, glucoheptonic acids, glucoheptonates and ethylenediaminetetraacetic acid are used become.

The pN value of the electrolyte composition is preferably set to a neutral range (pH 6-8).

• a) 0,005 – 0,5 g/l Kupfer als ionogene Kupferverbindung,
• b) 5 – 50 g/l Zinn als ionogene Zinnverbindung,
• c) 0,5 – 15 g/l Bismut als ionogene Bismutverbindung,
• d) 10 – 200 g/l Carbonsäure,
• e) 0,1 – 10 g/l Glanzbildner,
• f) 0,1 – 10 g/l Netzmittel

aufweisen.An acidic electrolyte composition according to the invention can, for example

• a) 0.005-0.5 g / l copper as an ionogenic copper compound,
• b) 5-50 g / l tin as an ionogenic tin compound,
• c) 0.5-15 g / l bismuth as an ionogenic bismuth compound,
• d) 10-200 g / l carboxylic acid,
• e) 0.1-10 g / l brightener,
• f) 0.1 - 10 g / l wetting agent

exhibit.

A copper compound is preferably used Sulfate, chloride, sulfonate, oxalate or oxide compound used.

As a tin compound is preferred a sulfate or chloride compound or sodium or potassium stannate used.

As a bismuth compound is preferred a nitrate, citrate or carbonate compound is used.

The pN value of the electrolyte composition is preferably adjusted to an acidic range (e.g. pH 1 to 5).

The ratio of metals in the alloy can in a manner known to those skilled in the art through the ratio of the metals in the electrolyte composition, by the type and amount of any other additives and through the deposition parameters, such as current density, temperature or flow rate to be influenced.

Anodes can be used as the counter electrode from insoluble Materials such as platinized titanium or graphite can be used. Also possible are soluble Bismuth, copper, tin or alloys made from these metals.

The temperature during electrodeposition is preferably chosen so that this is in a range of about 20-70 ° C, preferably in a range from 50 - 60 ° C.

The current density in the electrolyte solution is preferably set to a range of approximately 0.1-5 A / dm ² , preferably 0.2-0.5 A / dm ² .

The deposition rates preferably move in a range of approximately 0.01-0.5 μm / minute, preferably at 0.05-0.1 μm / minute.

With the method, layer thicknesses of 0.005 - 5 µm, preferably of 0.5 - 1 μm.

After depositing the desired layer thickness can optionally subjecting the alloys to a post-treatment step to further stabilize the color of the alloy. The alloy layer is covered with an oxygen-releasing Substance treated. The coated substrate is preferred into a solution immersed in this substance. Suitable as oxygen-releasing substances peroxide or persulfate compounds such as hydrogen peroxide or ammonium persulfate.

The concentration of the after-treatment solution is preferably 0.01 g / l - 5 g / l. Typical diving times are between 1 and 20 minutes.

The alloys according to the invention have a characteristic blue-gray to black color and are suitable for Use for decorative purposes, e.g. as covering material for clothing accessories, such as buttons or Zippers. Draw the covers through good durability across from Wear from mechanical stress or cleaning. The dark alloy layers but also for functional purposes, e.g. as absorbent layers be used in solar applications. In preferred embodiments the invention, the alloys are also free of toxic or expensive fabrics and offer further advantages in terms of economy and usability.

The invention is illustrated by the following examples explained. However, the invention is not based on the preferred ones listed therein embodiments limited.

EXAMPLES

example 1

An alkaline, cyanide-containing electrolyte has the following composition:
0.35 g / l copper as copper cyanide
3 g / l tin as sodium stannate
0.5 g / l bismuth as ammonium bismuth citrate
20 g / l dipotassium tartrate
10 g / l potassium cyanide
2 ml / l methylene tetramine
0.1 ml / l polyethyleneimine

At 60 ° C and 0.5 A / dm ² , a brown-black alloy layer can be deposited with this electrolyte. The color can be additionally stabilized with the after-treatment listed under Example 6.

Example 2

An alkaline electrolyte has the following composition
22 g / l tin as sodium stannate
0.5 g / l bismuth as ammonium bismuth citrate
0.2 g / l copper as copper sulfate
100 ml / l 1-hydroxyethylene (1,1-diphosphonic acid)
120 g / l potassium hydroxide
0.2 ml / l methylene tetramine

At 60 ° C and 0.5 A / dm ² , a blue-gray-black alloy layer can be deposited with this electrolyte. The deposition rate was approximately 0.05 μm / minute. The color can be additionally stabilized with the after-treatment listed under Example 6.

Example 3

A neutral electrolyte has the following composition
22 g / l tin as sodium stannate
0.5 g bismuth as ammonium bismuth citrate
0.2 g / l copper as copper sulfate
100 ml / l tetrasodium diphosphate
Potassium hydroxide to adjust the pH to 8 +/- 1
0.2 ml / l methylene tetramine

At 60 ° C and 0.5 A / dm ² , a black alloy layer can be deposited with this electrolyte. The deposition rate was approximately 0.05 μm / minute. The color can be additionally stabilized with the after-treatment listed under Example 6.

Example 4

An acidic electrolyte has the following composition
22g / l tin as sodium stannate
10 mg / l copper as copper sulfonate
2.5 g / l bismuth as ammonium bismuth citrate
2.5 ml / l methylene tetramine
1 ml / l surfactant

At 60 ° C and 0.5 A / dm ² , a black alloy layer can be deposited with this electrolyte. The pH of the electrolytes was 2.5 +/- 0.5. The color can be additionally stabilized with the aftertreatment listed under Example 5.

Example 5

Another neutral electrolyte has the following composition
10 g / l bismuth as bismuth citrate
0.75 g / l copper as copper sulfate
22 g / l tin as sodium stannate
100 ml / l 1-hydroxyethylene (1,1-diphosphonic acid)
50 g / l potassium hydroxide
2 ml / l methylene tetramine
20 ml / l cationic surfactants

At 50 to 60 ° C and 0.3 A / dm ² , a gray, anthracite-colored alloy layer can be deposited with this electrolyte. The deposition rate was approximately 0.05 μm / minute. There was no further stabilization of the color by post-treatment.

Example 6

The aftercare was done with

3 g / l perhydrite (e.g. Merck) = 0.1% H ₂ O ₂

With a treatment time of 5 to 10 minutes at 20 - 25 ° C Color of the alloys obtained in Examples 1 to 4 further be stabilized.

Claims (21)

Alloy comprising a) 1 - 15% tin b) 19-60 % Copper and c) 30-80 % Bismuth d) 0-10 % oxidic oxygen. The alloy of claim 1, wherein the alloy is a has dark color. Alloy according to claim 1 or 2, wherein it essentially free of one or more elements selected from nickel, lead, selenium, Is chrome and antimony. Alloy according to one of claims 1 to 3, wherein it essentially free of one or more elements selected from silver, gold, palladium, Is platinum, ruthenium, rhodium or iridium. Alloy consisting essentially of a) 1 - 15% tin b) 19-60 % Copper c) 30 - 80% bismuth d) 0-10 % oxidic oxygen as well as possibly unavoidable Impurities. Coated article comprising a substrate and a layer of an alloy according to any one of claims 1 to 5th An electrolyte composition comprising a) at least an ionogenic tin compound, b) at least one ionogenic copper compound, and c) at least one ionic bismuth compound. An electrolyte composition according to claim 7, comprising a) 0.05 - 5 g / l copper as an ionogenic copper compound, b) 5 - 50 g / l Tin as an ionogenic tin compound, c) 0.05 - 5 g / l bismuth as ionogenic bismuth, d) 10-200 g / l potassium or sodium hydroxide, e) 10-200 g / l complexing agent f) 5 - 50 g / l of a cyanide compound, g) 0.1-10 g / l brightener and H) 0.1-10 g / l wetting agent. An electrolyte composition according to claim 7, comprising a) 0.05 - 5 g / l copper as an ionogenic copper compound, b) 5 - 50 g / l Tin as an ionogenic tin compound, c) 0.05 - 5 g bismuth as an ionogenic bismuth compound, d) 10-200 g / l potassium or sodium hydroxide, e) 10-200 g / l complexing agent, f) 0.1-10 g / l brightener and g) 0.1 - 10 g / l wetting agent. An electrolyte composition according to claim 7, comprising a) 0.05 - 5 g / l copper as an ionogenic copper compound, b) 5 - 50 g / l Tin as an ionogenic tin compound, c) 0.05 - 20 g / l bismuth as ionogenic bismuth, d) 1-50 g / l potassium or sodium hydroxide, e) 10-200 g / l complexing agent, f) 0.1-10 g / l brightener and g) 0.1 - 10 g / l wetting agent. Electrolyte composition according to claim 7, comprising a) 0.005-0.5 g / l copper as ionogenic copper compound, b) 5-50 g / l tin as ionogenic tin compound, c) 0.5 - 15 g / l bismuth as an ionogenic bismuth compound, d) 10 - 200 g / l carboxylic acid, e) 0.1 - 10 g / l brightener, f) 0.1 - 10 g / l wetting agent. Electrolyte composition according to one of claims 7 to 11, the ionogenic tin compound consisting of tin sulfates, tin chlorides, Tin sulfonates, tin oxalates, sodium stannates, potassium stannates and mixtures thereof selected is. Electrolyte composition according to one of claims 7 to 12, the ionogenic copper compound consisting of copper sulfates, copper chlorides, Copper sulfonates, copper oxalates, copper oxides, copper cyanides, complex copper compounds and mixtures thereof is selected. Electrolyte composition according to one of claims 7 to 13, the ionic bismuth compound consisting of bismuth nitrates, bismuth carbonates, Bismuth citrates, complex bismuth compounds and mixtures thereof selected is. Electrolyte composition according to one of claims 7 to 14, further comprising a suitable solvent or solvent mixture. Electrolytic process for the production of dark Alloy layers comprising the steps a) Provide a substrate to be coated as a cathode, b) Provide an electrolyte composition according to any one of claims 7 to 15 c) electrolytic deposition of a dark alloy layer according to one of the claims 1 to 5 on the substrate, and d) if necessary aftertreatment the dark alloy layer produced in step c). The method of claim 16, wherein step c) in a temperature of 20 to 70 ° C is carried out. Method according to one of claims 16 or 17, wherein step c) is carried out at a current density of about 0.1 to 5 A / dm2. A method according to any one of claims 16 to 18, wherein step d) treating the dark alloy layer produced in step c) with an oxygen-releasing substance. The method of claim 19, wherein the oxygen-donating Substance made from peroxide compounds and persulfate compounds and mixtures selected from it is. Use of the alloy according to one of claims 1 to 5 for decorative or functional purposes.