Electrolyte bath for depositing a palladium-tin alloy

Abstract

The invention relates to an electrolyte bath for the cathodic deposition of binary palladium-tin alloys, a composition for such an electrolyte bath, the use of such an electrolyte bath, a method for coating with such an electrolyte bath, a coating, and an article coated with the coating. The electrolyte bath is intended for the deposition of a binary alloy consisting of at least 70 wt.% Pd and at most 30 wt.% Sn, wherein the electrolyte bath is an aqueous-alkaline solution with a pH of 7.0 to pH 9.0, preferably pH 7.5 to pH 8.0, containing ammonium ions, and containing 0.5 g / l to 10 g / l Pd ions, 1 g / l to 20 g / l Sn ions, at least one wetting agent, at least one complexing agent, and at least one brightening agent. The coating can be deposited crack-free in layer thicknesses up to 10 µm, exhibits good abrasion resistance, good corrosion resistance, and a whiteness of L* 3 82 in the CIELAB color space.

Description

[0001] The invention relates to an electrolyte bath for the deposition of binary palladium-tin alloys, a composition for such an electrolyte bath, the use of such an electrolyte bath, a method for coating with such an electrolyte bath, a coating and an article coated with the coating.

[0002] Electroplated palladium coatings are used in many areas. For example, palladium coatings are used in fashion jewelry. One advantage of palladium coatings for this application is their light color, with L* = 82 - 86 in the CIELAB color space. Palladium coatings are also used in industrial applications, particularly in the electronics industry, due to their low contact resistance.

[0003] Various electrolyte baths are known for the production of palladium alloy coatings.

[0004] For example, cyanide baths are disclosed in JPH10204677 and JPH 06293990. However, cyanide baths are highly toxic, and the use of cyanides should be avoided.

[0005] GB1468580 discloses a sulfite bath for the deposition of palladium and palladium alloys. The bath contains between 1 and 200 g / l of sulfite. The color of the deposit of palladium alloys from sulfite electrolyte baths is often darker. Furthermore, sulfite electrolyte baths often have stability problems.

[0006] US 2003047460 discloses palladium and palladium alloy baths, where palladium is added as a special ethylenediamine complex. The pH of the bath is acidic and ranges between 3 and 5. Only thin-layer palladium alloys can be deposited from these electrolytic baths.

[0007] The object is therefore to provide an electrolyte bath from which a crack-free coating with a high layer thickness can be deposited, which is more cost-effective in particular compared to pure palladium and which has high abrasion resistance and good corrosion resistance, wherein the coating is particularly shiny and has a light color, preferably of L* ≥ 82 in the CIELAB color space.

[0008] This object is achieved by an electrolyte bath for the cathodic deposition of a binary Pd / Sn alloy with at least 70 wt.% Pd and at most 30 wt.% Sn, wherein the electrolyte bath is present as an aqueous solution with pH 7.0 to pH 9.0, preferably pH 7.5 to pH 8.0, containing ammonium ions, and containing 0.5 g / l to 10 g / l Pd ions, 1 g / l to 20 g / l Sn ions, at least one wetting agent, at least one complexing agent and at least one brightening agent.

[0009] A binary palladium-tin alloy can be deposited from such an electrolyte bath, which is abrasion-resistant and exhibits good corrosion resistance. A coating deposited from the electrolyte bath according to the invention is just as corrosion-resistant as a pure palladium coating of the same layer thickness.

[0010] The electrolyte bath is also suitable for producing coatings with high layer thicknesses. Good adhesion is achieved. The coating is not brittle and does not exhibit cracking. Due to the alloying with tin, which is more cost-effective than palladium, the deposited coating is more cost-effective to produce than a pure palladium coating. The coating is glossy and has a light color with L* ≥ 82 in the CIELAB color space.

[0011] 0.5 g / l to 10 g / l Pd ions correspond to 0.0047 mol / l to 0.0940 mol / l Pd ions, 1 g / l to 20 g / l Sn ions correspond to 0.0084 mol / l to 0.1685 mol / l Sn ions.

[0012] Advantageous features are described below, and in particular in the dependent claims: The pH value can be adjusted with ammonia water. This simplifies bath operation.

[0013] An electrolyte bath with 5 g / l to 7 g / l Pd ions is particularly suitable.

[0014] It has proven particularly advantageous if the Pd ions are present in divalent form, with the Pd ions being present in particular in the form of palladium chloride, palladium tetramine sulfate, palladium diaminodinitrite, palladium diaminodichloride.

[0015] Furthermore, an electrolyte bath containing 3 g / l to 6 g / l Sn ions is preferred.

[0016] It is particularly suitable if the Sn ions are in divalent form.

[0017] The following compounds have proven particularly suitable: tin(II) chloride, tin(II) sulfate, tin oxalate, tin pyrophosphate.

[0018] In the context of the present invention, it has proven particularly advantageous if both palladium and tin are added to the bath in divalent form. An electrolyte bath with 5 g / l to 7 g / l Pd ions and 3 g / l to 6 g / l Sn ions is particularly preferred.

[0019] Suitable wetting agents are cationic and amphoteric surfactants. Cationic surfactants that are particularly suitable as wetting agents are quaternary ammonium compounds such as benzalkonium chloride. Amphoteric surfactants that are particularly suitable as wetting agents are betaines or sulfobetaines.

[0020] In addition, other wetting agents may be included, in particular alkyl ether sulfonates, alkyl ether phosphates, or preferably fatty alcohol alkoxylates.

[0021] Various complexing and chelating agents known in the chemical industry can be used as complexing agents. Examples include phosphonates, gluconates, citrates, nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), ethylene glycol bis(aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), and ethylenediaminedisuccinic acid (EDDS).

[0022] The brightening agent is advantageously a brightening agent from the group of substituted aromatic N-heterocycles, or from a mixture of substituted aromatic N-heterocycles.

[0023] It may also contain a tension reducer, particularly saccharin or an organic sulfonate.

[0024] To simplify bath management, conducting salts and / or pH stabilizers may be included, in particular ammonium, sodium or potassium phosphate, oxalate, pyrophosphate, sulfate, nitrate, chloride, citrate, tartrate or succinate.

[0025] To achieve a particularly glossy coating, the electrolyte bath should be a clear solution, particularly free of precipitates. The concentration of the metal salts, wetting agents, brightening agents, and additional ingredients should be selected so that the electrolyte solution is clear and remains clear throughout the coating process. The resulting coating is particularly glossy, adheres well, is crack-free, and is abrasion- and corrosion-resistant.

[0026] An electrolyte bath with the following composition is particularly suitable for this purpose: 0.5 - 10 g / l palladium ions from palladium diaminodichloride 1 - 20 g / l tin ions from tin pyrophosphate 30 - 150 g / l ammonium sulfate 0.1 - 10 g / l betaine 20 - 100 g / l nitrilotriacetic acid 0.01 - 1 g / l brighteners, especially substituted aromatic N-heterocycles.

[0027] A particularly advantageous composition of an electrolyte bath comprises 6 g / l Pd ions from palladium diaminodichloride, 4 g / l Sn ions from tin pyrophosphate, 60 g / l ammonium sulfate, 80 g / l ammonium dihydrogen phosphate, 4 g / l betaine as a wetting agent, 30 g / l nitrilotriacetic acid, 0.2 g / l fatty alcohol ethoxylate as a further wetting agent, 2 g / l saccharin as a voltage reducer, 4 ml / l of a mixture of substituted aromatic N-heterocycles, for example pyridine or pyrimidine derivatives, as a brightening agent, wherein the pH is adjusted to 8.0 with ammonia water.

[0028] The invention further relates to the use of a previously described electrolyte bath for the electroplating of an object with an electrically conductive surface, wherein a binary Pd / Sn alloy containing at least 70 wt.% Pd and at most 30 wt.% Sn is cathodically deposited. The alloy therefore consists exclusively of 70 wt.% to <100 wt.% Pd and >0 wt.% to 30 wt.% Sn.

[0029] This results in a coating with high abrasion resistance and good corrosion resistance, which is cost-effective to produce and has a favorable light color. The electrolytic bath is particularly easy to operate. The electrolytic bath is suitable, for example, for an object made of a metal, a metal alloy, or a plastic pretreated for electroplating. The electrolytic bath is particularly suitable for the deposition of layers with a thickness of 0.1 to 10 µm, especially 0.5 to 5 µm. The deposited layers are glossy and do not crack.

[0030] Surprisingly, it was found that alloys with 73 to 77 wt.% palladium and 23 to 27 wt.% tin exhibit maximum abrasion resistance.

[0031] The invention further relates to a method for producing a coating using a previously described electrolyte bath. This method can involve immersing the object to be coated in the electrolyte bath, and applying a voltage to the electrodes, with a current density between 0.01 A / dm 2 and 5 A / dm 2 . The object is connected as the cathode. The method can be carried out particularly advantageously if the bath is maintained at a temperature of 25 °C to 65 °C.

[0032] Various insoluble anodes can be used for the process. Such insoluble anodes are preferably made of a material selected from the group consisting of platinized titanium and iridium transition metal mixed oxide, or combinations of these materials. Platinized titanium anodes are particularly preferred.

[0033] If the coating is carried out using the drum coating process, a current density of 0.05 to 0.5 A / dm 2 is particularly suitable.

[0034] If the production is carried out using the rack coating process, a current density of 0.2 to 5 A / dm 2< , in particular a current density of 0.25 to 1 A / dm 2< , is particularly suitable.

[0035] The invention further relates to a coating, in particular produced or producible using a method described above, wherein the coating consists of a binary alloy comprising at least 70 wt.% Pd and at most 30 wt.% Sn, in particular 73 to 77 wt.% Pd and 23 to 27 wt.% Sn. The coating advantageously has a whiteness of L* ≥ 82 in the CIELAB color space.

[0036] The coating can be deposited in high layer thicknesses without cracks, offers improved abrasion resistance compared to pure palladium, and is at least as corrosion-resistant. Its light color makes it particularly suitable for costume jewelry.

[0037] The coating can be used as the outermost final layer because it has high abrasion resistance and a particularly elegant appearance.

[0038] A coating with a layer thickness between 0.1 and 10 µm is particularly advantageous.

[0039] The coating can also be applied as an intermediate layer in a multi-layer coating system. At a layer thickness of 0.5 to 2 µm, the coating is particularly well-suited as a diffusion barrier layer in a multi-layer coating system. Such a diffusion barrier layer can prevent the diffusion of copper ions from the copper underlayer commonly used in fashion jewelry items into the outermost final layer, thus preventing tarnishing of the final layer. A coating with a thickness of 0.1 to 5 µm, and especially 2 µm, is particularly suitable as a corrosion protection layer.

[0040] According to the invention, an article, in particular a costume jewelry or decorative article, is also coated with a coating described above.

[0041] Such an item, especially a piece of costume jewelry, exhibits good durability even with prolonged and frequent use. The coating eliminates the need for nickel-containing coatings, making such an item particularly physiologically compatible.

[0042] The object can be made of brass, zinc, iron, steel, or their alloys, for example. It is also possible to coat plastics prepared for electroplating.

[0043] For costume jewelry items, it is particularly suitable if the article is coated with a coating system, wherein the coating system has a base layer of copper, wherein the previously described coating is arranged over the copper layer, and wherein a final layer comprising at least one precious metal, in particular gold, rhodium, ruthenium, platinum or alloys thereof, is arranged over the coating. Since the previously described coating has a bright, shiny color, wherein the color of the outermost final layer and the color of the coating are very similar, damage to the final layer that extends into the coating is hardly visible. The costume jewelry item therefore largely retains its appearance, even with prolonged and frequent wear, and therefore has increased durability.

[0044] In order to obtain a particularly shiny costume jewelry item, it can be provided that a bronze layer, in particular made of a Cu / Sn / Zn alloy, is arranged between the copper layer and the previously described coating.

[0045] To increase the adhesion of an outer layer arranged over the previously described coating, an adhesive gold layer can be arranged directly over the coating. Such an adhesive gold layer can have a thickness of 0.05 to 0.3 µm.

[0046] A costume jewelry item has proven particularly advantageous with a coating system comprising a base layer of copper, in particular a bronze layer arranged directly thereabove, a previously described coating arranged thereabove, and an outermost final layer arranged directly above the coating made of a, preferably binary, alloy comprising at least one metal selected from the group comprising platinum, rhodium, ruthenium and gold. An outermost final layer consisting of a platinum-rhodium alloy, in particular a binary Pt / Rh alloy with 70 to 90 wt.% Pt, preferably with 80 wt.% Pt, has a particularly similar color tone. Such a costume jewelry item can be produced particularly cost-effectively and is highly durable.

[0047] The invention is described with reference to the following figures and examples without limiting the inventive concept: Fig. 1shows the whiteness L* depending on the alloy composition. Fig. 2 shows the abrasion depending on the alloy composition. Example 1: Different alloy compositions

[0048] Various alloy compositions were investigated using electrolyte baths with the following composition: 0.5 g / l to 10 g / l Pd ions from palladium diaminodichloride, 1 g / l to 20 g / l Sn ions from tin pyrophosphate, 60 g / l ammonium sulfate, 80 g / l ammonium dihydrogen phosphate, 4 g / l betaine as a wetting agent, 0.2 g / l fatty alcohol ethoxylate as a further wetting agent, 30 g / l nitrilotriacetic acid as a complexing agent, 2 g / l saccharin as a voltage reducer, 4 ml / l of a mixture of substituted aromatic N-heterocycles, for example pyridine or pyrimidine derivatives, as a brightening agent, the pH being adjusted to 8.0 with ammonia water.

[0049] To prepare the baths, water was added and the salts were stirred in and dissolved one after the other, with the metal salts being added last.

[0050] Surprisingly, it was found that for deposits from electrolyte baths with palladium alloy concentrations of at least 70 wt.%, the whiteness L* is ≥ 82. This is shown in Table 1. Fig. 1 shows that at a concentration of <70 wt% palladium there is an unexpected, sudden drop in the L* values, whereby the whiteness in this case becomes unsuitable for costume jewelry. Table 1 Pd [wt.%] Sn [wt.%] Wisdom L* 100 0 86 93 7 84 86 14 84 80 20 83 75 25 83 70 30 82 0 100 92* * The pure tin was deposited from an acid bath, so the color is not comparable.

[0051] Fig. 2 shows the abrasion resistance of the alloys in the Taber Abraser test. The abrasion resistance does not behave linearly with the alloy composition as expected. This is evident from Fig. 2and Table 2. Surprisingly, it was found that the deposited coating exhibits maximum abrasion resistance at a palladium alloy concentration of approximately 75 wt.%. Such an alloy can be obtained by deposition from an electrolyte bath containing 6 g / l Pd ions and 4 g / l Sn ions. Table 2 Pd [wt.%] Sn [wt.%] Layer thickness loss [µm / 25 revolutions] 100 0 0,2078 93 7 0,1900 86 14 0,1681 80 20 0,1441 75 25 0,1377 70 30 0,1427 0 100 0,4472

[0052] Due to its good durability and light color, the coating shown here is particularly well-suited for any metallic white, decorative coating, such as costume jewelry. Due to their good corrosion resistance, high abrasion resistance, and crack-free nature, these alloys are also particularly well-suited for industrial applications, particularly in the electronics industry. Example 2: Coating a brass jewelry blank

[0053] A brass jewelry blank was coated with an exemplary electrolytic bath.

[0054] The electrolyte bath used included: 6 g / l Pd from palladium diaminodichloride 3 g / l Sn from tin-II-sulfate 60 g / l ammonium sulfate 100 g / l ethylene glycol bis(aminoethyl ether)-N,N,N',N'-tetraacetic acid 4 g / l wetting agent PF Sn (betaine, product of Ing. W. Garhöfer GesmbH) 0.2 g / l fatty alcohol ethoxylate 2 g / l saccharin 4 ml / l brightener: "Brightener PF Sn" (mixture of substituted aromatic N-heterocycles, product of Ing. W. Garhöfer GesmbH)

[0055] The pH value was adjusted to 8.0 using ammonia water.

[0056] The specification of g / l Pd refers to palladium ions, likewise the specification of g / l Sn refers to tin ions.

[0057] The brass jewelry blank to be coated was electrolytically degreased in a weakly alkaline, cyanide-free cleaner ("Degreasing 1018", product of IWG Ing. W. Garhöfer GesmbH) at 25 °C for 30 s at 10 A / dm 2<.

[0058] The jewelry blank was then rinsed in deionized water and pickled in a 5% sulfuric acid solution for 30 seconds. In an acidic copper bath containing 50 g / l Cu and 60 g / l sulfuric acid ("Cudega ®< pure 650", a product of IWG Ing. W. Garhöfer GesmbH), 20 µm of copper was deposited to a flattening and high-gloss finish at 4 A / dm 2< and 25 °C. The blank was rinsed again.

[0059] Then, from the provided electrolyte bath with the above-mentioned composition, 2 µm of a palladium-tin alloy with 20.7 wt.% tin and 79.3 wt.% palladium were deposited at 45 °C and 1 A / dm 2< within 6 min.

[0060] Finally, the electroplated jewelry piece was rinsed in deionized water and dried. Visual assessment:

[0061] The resulting electroplated jewelry piece, or rather its surface, was white and highly lustrous. Its whiteness, measured according to CIELAB, was L* = 84. Corrosion resistance according to DIN 50018:

[0062] The corrosion resistance of the galvanized jewelry piece was tested according to DIN 50018, Testing in alternating condensation climates with sulfur dioxide-containing atmospheres, June 1997.

[0063] The corrosion resistance of the palladium-tin alloy was equally good in the SO 2 test compared with a coating made of a pure palladium electrolyte (Pallega ®< pure TS, product of IWG Ing. W. Garhöfer GesmbH), produced on the same base material. Abrasion resistance using the Taber Abraser test:

[0064] A brass disc was coated in the electrolyte bath described above using the process described above. For comparison, a brass disc was coated with 2 µm palladium in a pure palladium electrolyte (Pallega ®< pure TS, a product of IWG Ing. W. Garhöfer GesmbH). Both discs were then abraded. The pure palladium was abraded through significantly sooner than the palladium-tin alloy. Example 3: Coating of a die-cast zinc object

[0065] A zinc die-cast jewelry blank was coated. The electrolyte bath used included: 6 g / l Pd from tetramine palladium chloride 4 g / l Sn from tin pyrophosphate 60 g / l ammonium sulfate 80 g / l NTA 4 g / l wetting agent PF Sn (betaine, product of Ing. W. Garhöfer GesmbH) 0.2 g / l fatty alcohol ethoxylate 2 g / l saccharin 4 ml / l brightener: "Brightener PF Sn" (mixture of substituted aromatic N-heterocycles, product of Ing. W. Garhöfer GesmbH) pH value: 8.0 adjusted using ammonia water

[0066] The jewelry blank was electrolytically degreased in a weakly alkaline, cyanide-free cleaner (Degreasing 1018, a product of IWG Ing. W. Garhöfer GesmbH) at 25 °C for 30 s at 10 A / dm 2<. The jewelry blank was then rinsed in deionized water, and 5 µm of copper was deposited in an alkaline cyanide pre-copper bath containing 22 g / l Cu and 34 g / l KCN ("Cudega ®< pure 80", a product of IWG Ing. W. Garhöfer GesmbH) at 1 A / dm 2< and 50 °C. The pre-copper-plated jewelry blank was then pickled in a 5% sulfuric acid solution for 30 s. In an acidic copper bath containing 50 g / l Cu and 60 g / l sulfuric acid ("Cudega ®< pure 650", product of IWG Ing. W. Garhöfer GesmbH), 15 µm of copper were deposited in a flattening and high-gloss manner at 4 A / dm 2< and 25 °C. The copper-plated article was rinsed and pre-immersed in a 10% KCN solution. Then, from a bronze electrolyte bath ("Cudega ®< blend Sn white 15, product of IWG Ing. W.Garhöfer GesmbH) 2 µm bronze alloy was deposited from the electrolyte at 60 °C and 1 A / dm 2 within 10 minutes. It was then rinsed in deionized water and pickled in a 5% sulfuric acid solution.

[0067] On the thus pretreated object, 2 µm palladium-tin with the composition 24.8 wt.% tin and 75.2 wt.% palladium were deposited from the electrolyte bath provided with the above-mentioned composition at 50 °C and 1 A / dm 2< within 6 min.

[0068] After further rinsing and acid immersion, the resulting piece of jewelry was coated with 0.1 µm adhesive gold from a weakly acidic electrolyte containing 2.5 g / l Au ("Aurega ®< pure 218", a product of IWG Ing. W. Garhöfer GesmbH) at 1.5 A / dm 2< and 35 °C. It was then thoroughly rinsed in demineralized water, pickled in a 5% sulfuric acid solution, and coated with 0.2 µm platinum-rhodium (80 wt.% platinum, 20 wt.% rhodium) from an electrolyte containing 1.4 g / l Pt and 0.6 g / l Rh and 70 g / l sulfuric acid ("Platega ®< blend Rh", a product of IWG Ing. W. Garhöfer GesmbH) at 3 A / dm 2< and 50 °C for 4 min.

[0069] Finally, the galvanized part was rinsed in deionized water and dried. Visual assessment:

[0070] The resulting electroplated jewelry piece, or rather its surface, was pure white and highly lustrous. Its whiteness, measured according to CIELAB, was L* = 89.4. Corrosion resistance according to DIN 50018:

[0071] The electroplated piece of jewelry performed equally well in the corrosion tests as a piece of jewelry coated using the same process but with pure palladium.

Claims

1. Electrolyte bath for the cathodic deposition of a binary Pd / Sn alloy with at least 70 wt.% Pd and at most 30 wt.% Sn, wherein the electrolyte bath is present as an aqueous alkaline solution with a pH of 7.0 to 9.0, in particular of 7.5 to 8.0, containing ammonium ions, and containing 0.5 g / l to 10 g / l Pd ions, 1 g / l to 20 g / l Sn ions, at least one wetting agent, at least one complexing agent and at least one brightening agent.

2. Electrolyte bath according to claim 1, containing 5 g / l to 7 g / l Pd ions.

3. Electrolyte bath according to claim 1 or 2, wherein the Pd ions are present in divalent form, wherein the Pd ions originate in particular from palladium chloride, palladium tetramine sulfate, palladium diaminodinitrite, palladium diaminodichloride.

4. Electrolyte bath according to one of claims 1 to 3, wherein 3 g / l to 6 g / l of Sn ions are contained.

5. Electrolyte bath according to one of claims 1 to 4, wherein the Sn ions are present in divalent form, wherein the Sn ions originate in particular from Sn-II sulfate, Sn-II chloride, Sn-II oxalate, Sn-II pyrophosphate.

6. Electrolyte bath according to one of claims 1 to 5, wherein a cationic surfactant, in particular a quaternary ammonium compound, and / or an amphoteric surfactant, in particular betaines or sulfobetaines, is contained as wetting agent.

7. Electrolyte bath according to one of claims 1 to 6, wherein one or more complexing agents are included, selected from the group comprising phosphonates, gluconates, citrates, nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), ethylene glycol bis(aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) and ethylenediaminedisuccinic acid (EDDS).

8. Electrolyte bath according to one of claims 1 to 7, wherein the brightener is a brightener from the group of substituted aromatic N-heterocycles.

9. Electrolyte bath according to one of claims 1 to 8, wherein a voltage reducer is contained, in particular saccharin or an organic sulfonate.

10. Electrolyte bath according to one of claims 1 to 9, wherein conductive salts and / or pH stabilizers are contained, in particular ammonium, sodium or potassium phosphate, oxalate, pyrophosphate, sulfate, nitrate, chloride, citrate, tartrate or succinate.

11. Electrolyte bath according to one of claims 1 to 10, wherein the electrolyte bath is present as a clear solution, wherein the solution is in particular free from precipitates.

12. Use of an electrolyte bath according to one of claims 1 to 11 for the galvanic coating of an article with an electrically conductive surface, wherein a binary Pd / Sn alloy with at least 70 wt.% Pd and at most 30 wt.% Sn, in particular with 73 to 77 wt.% Pd and 23 to 27 wt.% Sn, is deposited cathodically.

13. A method for producing an article with a coating of a binary Pd / Sn alloy with at least 70 wt.% Pd and at most 30 wt.% Sn using an electrolyte bath according to one of claims 1 to 11, wherein it is provided in particular that the article to be coated is immersed in the electrolyte bath, a voltage is applied to the electrodes, wherein a current density between 0.01 A / dm 2 and 5 A / dm 2 and wherein the bath is kept at a temperature of 35 °C to 65 °C.

14. Coating, in particular produced in a process according to claim 13, wherein the coating consists of a binary alloy of at least 70 wt.% Pd and at most 30 wt.% Sn, in particular of 73 to 77 wt.% Pd and 23 to 27 wt.% Sn, and a whiteness of L* 3 82 in the CIELAB color space.

15. An article coated with a coating according to claim 14 or with a coating produced according to claim 13.

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