Platinum Electrolyte

Abstract

The present invention relates to a platinum electrolyte containing certain additives and to a method for electrolytically depositing a platinum layer using the electrolyte according to the invention.

Description

[Technical Field]

[0001] explanation The present invention relates to a platinum electrolyte containing a specific additive, and to a method for electrolytically analyzing a platinum layer using the electrolyte according to the present invention. [Background technology]

[0002] Platinum electroplating and electroforming are widely used in the manufacture of ornaments and jewelry not only for the bright luster and aesthetic appeal of platinum, but also for its high chemical and mechanical inertness. Therefore, platinum can also function as a coating for plug connections and contact materials.

[0003] A galvanic bath is a solution containing a metal salt that can deposit an electrochemical metal precipitate (coating) onto a substrate (object). This type of galvanic bath is often also called an "electrolyte." Therefore, aqueous galvanic baths will be referred to as "electrolytes" below.

[0004] Acidic and alkaline baths or electrolytes based on platinum(II) and platinum(IV) compounds are used for platinum electrodeposition. The most important bath types contain diaminodnitritoplatinum(II) (P-salt), sulfatodnitritoplatinic acid (DNS), or hexahydroxoplatinic acid, or their alkaline salts.

[0005] International Publication No. 2013104877(A1) proposes a platinum electrolyte containing platinum ion sources and borate ion sources that is more stable over longer periods. The bath generally exhibits good thermal stability. The bath can also be used over a wide range of pH values. In certain embodiments, the bath yields a bright, lustrous precipitate.

[0006] European Patent Publication 737760(A1) describes a platinum electrolyte containing up to 5 g / l of free amidosulfonic acid (ASS, sulfamidic acid, sulfamic acid, amidosulfonic acid) and a strong acid with a pH value of less than 1 between 20 and 400 g / l. The platinumamine sulfamate complex used therein proved remarkably stable in a strongly acidic bath without free amidosulfonic acid. The bath did not show precipitate formation, even when considering long electrolysis times. The amidosulfonic acid released during platinum precipitation is hydrolyzed and therefore does not accumulate in the electrolyte. However, hydrolysis is relatively slow in less acidic baths and at normal electrolysis temperatures.

[0007] German Patent No. 1256504(B) proposes an acidic platinum electrolyte capable of producing a strongly adhering platinum layer. To achieve specific overpotential characteristics of the anode thus produced, the electrolyte should contain more than 20 mg / l of bismuth. The electrolyte contains hydrochloric acid. In-house experiments have shown that higher bismuth concentrations in the electrolyte negatively affect the precipitation results. For example, at 100 mg / l, a dark-colored platinum precipitate is obtained.

[0008] U.S. Patent Application Publication No. 20100176001(A1) specifically refers to a platinum electrolyte that should contain citric acid in addition to bismuth. Its purpose is to obtain nanometer particles of platinum or platinum alloy that can function as a catalyst. It does not explain why it is advantageous to add transition metals to the electrolyte at concentrations of 0.1 micromol / l to 100 mol / l. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] International Publication No. 2013104877(A1) [Patent Document 2] European Patent Publication No. 737760(A1) [Patent Document 3] German Patent No. 1256504(B) [Patent Document 4] U.S. Patent Application Publication No. 20100176001(A1) [Overview of the project] [Problems that the invention aims to solve]

[0010] For the manufacture of contact materials, achieving high throughput rates in electrolytic coatings is particularly important to enable the lowest possible manufacturing costs per component. These throughput rates are achieved, among other things, by selecting very high current densities in the coating to provide rapid deposition of platinum. However, the use of high current densities during the deposition of platinum from acidic electrolytes, particularly with platinum amine sulfamate complexes (similar to European Patent No. 737760(A1)), produces cloudy black platinum particles that accumulate in the electrolyte, are incorporated into the platinum layer, or adhere to the deposited platinum surface. This results in uneven deposition as it grows. These have unfavorable properties in terms of gloss, corrosion resistance, and wear resistance. Therefore, to obtain a defect-free layer from these platinum electrolytes, deposition must be carried out at low current densities. [Means for solving the problem]

[0011] The achievement of the presented objective is quite remarkable, yet nevertheless advantageous, in that an aqueous cyanide-free electrolyte for the deposition of platinum or platinum alloys onto a conductive substrate is provided, containing one or more ions from the group consisting of Ir, Bi, Sb, Se, and Te, and without containing hydrochloric acid, with Bi, Sb, Se, and Te present at a maximum concentration of 100 mg / l of the electrolyte and Ir present at a maximum concentration of 1000 mg / l of the electrolyte (each relative to the metal). Even under high current densities, the deposition of platinum or platinum alloys can occur very rapidly without the formation of a black cloud of platinum particles in the electrolyte that would hinder deposition. This results in improved productivity, and therefore lower manufacturing costs, as well as defect-free layers. [Modes for carrying out the invention]

[0012] Platinum electrolytes known to those skilled in the art can be used as electrolytes for this purpose. Advantageously, such Pt electrolytes having platinum sulfamate complexes can be used. The latter can be selected from the group consisting of H2[Pt(NH2SO3)2SO4], H2[Pt(NH2SO3)2SO3], H2[Pt(NH2SO3)2Cl2], [Pt(NH3)2(NH2SO3)4], and [Pt(NH3)2(NH2SO3)2]. H2[Pt(NH2SO3)4] and [Pt(NH3)2(NH2SO3)2] can also be used particularly advantageously. The molar ratio of ligand to platinum can be varied accordingly. Such electrolytes are known to those skilled in the art from the prior art. One is cited, for example, in European Patent No. 737760(A1). Such electrolytes are also commercially available (PLATUNA® H1; PLATUNA® S1; PLATUNA® N1 Platinum Electrolyte Electroplating from Umicore Galvanotechnik GmbH (umicore.com)).

[0013] In the deposition of platinum from an electrolyte according to the present invention, one or more ions from the group consisting of Bi, Sb, Se, Ir, and Te can be co-deposited to a certain extent. The resulting precipitate then has 1 ppm to 5000 ppm, preferably 100 to 2000 ppm, of the correspondingly used metal. This also applies to the deposition of platinum alloys. As further alloying metals, all that are suitable for the purposes of the present invention from the perspective of those skilled in the art are considered. The alloying metals are preferably the PGM noble metals Rh, Pd, Ru, Re, and more preferably non-noble metals such as Ni, Co, In, Cu, Fe, etc., with Rh being particularly preferred from this viewpoint. Even in the case of a PtRh alloy electrolyte having a Pt complex, black clouds are formed during electrolytic deposition at high amperages, which can be avoided by the use of one or more ions from the group consisting of Ir, Bi, Sb, Se, and Te according to the present invention.

[0014] Suitable conductive substrates are those that can be coated with the electrolyte according to the present invention in an acidic pH range. These are preferably noble metal-containing substrates or corresponding coatings on base metal substrates. This relates, for example, to iron materials coated with nickel plating or copper plating followed by optionally gold plating, palladium pretreatment, platinum pretreatment, or silver pretreatment. Thus, the intermediate layer for nickel plating or copper plating may also be made from the corresponding alloy electrolyte (e.g., NiP, NiW, NiMo, NiCo, NiB, Cu, CuSn, CuSnZn, CuZn, etc.). Further substrate materials may be wax cores pre-coated (electroformed) with conductive silver lacquer.

[0015] Water-soluble compounds containing Bi, Sb, Se, Ir, and Te atoms in ionic form are considered suitable additives to help prevent the formation of free platinum in the electrolyte during precipitation. These can be used individually or in optional combinations in the electrolyte. The amounts of the additives Bi, Sb, Se, and Te should be such that the electrolyte concentration does not exceed 100 mg / l. Concentrations of less than 50 mg / l are advantageous, and the concentration of these additives in the electrolyte is particularly preferably 5 to 20 mg / l. In this case, the concentration is related to the metal. An exception here is iridium, which is added at concentrations up to 1000 mg / l, i.e., 100 to 1000 mg / l, preferably 200 to 700 mg / l, and very particularly preferably 300 to 600 mg / l.

[0016] Bismuth can also be added to electrolytes by compounds known to those skilled in the art. Bismuth is preferably present in an oxidized (III) state. Compounds advantageous in this regard are selected from bismuth(III) oxide, bismuth(III) hydroxide, bismuth(III) fluoride, bismuth(III) chloride, bismuth(III) bromide, bismuth(III) iodide, bismuth(III) methanesulfonate, bismuth(III) nitrate, bismuth(III) tartrate, bismuth(III) citrate, and especially bismuth ammonium citrate.

[0017] Selenium or tellurium compounds used in electrolytes can be appropriately selected by those skilled in the art within the framework of the above-mentioned concentrations. Preferred selenium and tellurium compounds are those in which selenium or tellurium is present in an oxidation state of +4 or +6. Selenium and tellurium compounds are advantageously used in electrolytes in which selenium or tellurium in an oxidation state of +4 is present. Selenium and tellurium compounds are preferably selected particularly from tellurite, selenite, tellurous acid, selenous acid, telluric acid, selenic acid, selenocyanate, tellurocyanate, and selenate and tellurate. Generally, it is more preferable to use tellurium compounds than selenium compounds here. It is particularly preferable to add tellurium to the electrolyte in the form of a salt of tellurous acid, for example, in the form of potassium tellurite.

[0018] Suitable iridium compounds that can be added to electrolytes are compounds in various oxidation states. The following iridium compounds are available, for example, iridium(III) chloride, iridium(IV) chloride, hexachloroiridium(III) acid, hexachloroiridium(IV) acid, [Na, K, ammonium] hexachloroiridate(III), [Na, K, ammonium] hexachloroiridate(IV), iridium(III) bromide, iridium(IV) bromide, hexabromoiridium(III) acid, hexabromoiridium(IV) acid, [Na, K, ammonium] hexabromoiridate(III), [Na, K, ammonium] hexabromoiridate(IV), iridium(III) sulfate, iridium(IV) sulfate. In addition, there are the corresponding iodides. Iridium chloro compounds, more preferably iridium sulfate, are preferably used.

[0019] Antimony compounds that can be added to the electrolyte are known to those skilled in the art. These can be selected from the group of antimony(III) compounds consisting of antimony(III) fluoride, antimony(III) chloride, antimony(III) oxide, sodium antimony(III) tartrate oxide, together with sugar alcohols (such as glycerol, sorbitol, mannitol, etc.). Antimony(III) oxide and sodium antimony(III) tartrate oxide are preferably used. Antimony(III) oxide is very particularly preferably used for the purposes of the present invention.

[0020] In this electrolyte, depending on the application, anionic and non-ionic surfactants, such as polyethylene glycol adducts, fatty alcohol sulfates, alkyl sulfates, alkyl sulfonates, aryl sulfonates, alkylaryl sulfonates, heteroaryl sulfates, betaines, fluorinated surfactants, and salts and derivatives thereof, can typically be used (see also Kanani, N: Galvanotechnik; Hanser Verlag, Munich Vienna, 2000; pp. 84 ff). Wetting agents are also, for example, substituted glycine derivatives commercially available as Hamposyl®. Hamposyl® consists of N-acyl sarcosinates, i.e., condensation products of fatty acid acyl residues and N-methylglycine (sarcosine). The silver coatings deposited in these baths are white and shiny to highly shiny. The wetting agent results in a non-porous layer. More advantageous wetting agents are those selected from the following group.

[0021] Anionic humectants, such as n-dodecanoyl-n-methylglycine, (N-lauroyl sarcosine) sodium salt, alkyl collagen hydrolysates, 2-ethylhexyl sulfate sodium salt, lauryl ether sulfate sodium salt, 1-naphthalene sulfonate sodium salt, 1,5-naphthalenedisulfonate sodium salt, monoalkyl sulfate sodium, such as tetradecyl sulfate sodium, dodecyl sulfate sodium, ethylhexyl sulfate sodium, decyl sulfate sodium, octyl sulfate sodium, and mixtures thereof are particularly advantageous; Nonionic wetting agents, such as β-naphthol ethoxylate potassium salt, fatty alcohol polyglycol ether, polyethyleneimine, polyethylene glycol, and mixtures thereof. Wetting agents having a molecular weight of less than 2,000 g / mol; Cationic wetting agents, such as 1H-imidazolium-1-ethenyl (or 3-methyl)-methyl sulfate homopolymers.

[0022] The electrolyte according to the present invention is used in an acidic pH range, but can also be operated in a different pH range, for example, up to pH 9. Optimal results can be obtained when the pH value of the electrolyte is between 4 and 0.1. Those skilled in the art know how to adjust the pH value of the electrolyte. This is preferably in a strongly acidic range, and more preferably <2. It is very advantageous to select strongly acidic precipitation conditions where the pH value is less than 2, and in some cases even less than 1, or in boundary cases even further down to 0.5.

[0023] In principle, the pH value can be adjusted as needed by those skilled in the art. However, those skilled in the art will follow the idea of ​​introducing as few additional substances as possible into the electrolyte that could adversely affect the precipitation of the alloy in question. In particularly preferred embodiments, the pH value is adjusted solely by adding an acid. Thus, from the point of view of those skilled in the art, all compounds suitable for the corresponding application can be used. Those skilled in the art prefer to use a strong acid, particularly methanesulfonic acid or mineral acid, such as sulfuric acid or orthophosphoric acid, for this purpose.

[0024] In addition to the substances described above, the platinum electrolyte according to the present invention contains as few other substances as possible, because the risk of precipitate degradation increases with each additional additive. In addition to the above components, only conductive salts such as sodium sulfate, potassium sulfate, or the corresponding phosphates can be added to the electrolyte. In preferred embodiments, the electrolyte according to the present invention contains no citric acid at all.

[0025] The electrolyte of the present invention provides a lustrous precipitate that gives a silvery appearance. The precipitated platinum layer preferably has an L* value greater than +82. According to the Cielab color system (EN ISO 11664-4, latest version as of the filing date), the a* value is preferably -1 to 1, and the b* value is +2 to +9. The values ​​were determined using a Konica Minolta CM-700d.

[0026] The subject of the present invention is a method for similarly depositing a platinum or platinum alloy layer on a conductive substrate, wherein the electrolyte according to the present invention is used, and the substrate to be coated as an anode and cathode is brought into contact with the electrolyte, thereby establishing an electric current between the anode and the cathode.

[0027] The temperature that is advantageous during platinum deposition can be selected as desired by those skilled in the art. Thus, those skilled in the art will consider, on the one hand, a sufficient deposition rate and an applicable current density range, and on the other hand, economic considerations or electrolyte stability. It is advantageous to set the electrolyte temperature to 20°C to 90°C, preferably 40°C to 70°C, and particularly preferably 45°C to 65°C.

[0028] As already shown, the electrolyte according to the present invention is of the acidic type. Fluctuations in the pH value of the electrolyte may occur during electrolysis. Therefore, in a preferred embodiment of this method, those skilled in the art will monitor the pH value during electrolysis and, if necessary, adjust the pH value to a set value. This method is known to those skilled in the art.

[0029] Layer thicknesses in the range of 0.1 to 10 μm are typically used in rack operations for technical and decorative applications, with a load capacity of 1 to 5 A / dm².2 It is deposited using a current density within the range of. For technical applications, a layer thickness of up to 25 μm may be deposited. In a continuous system that is preferentially used for the electrolyte according to the present invention, a relatively wide range of layer thicknesses from about 0.5 to about 5 μm is deposited at the highest possible deposition rate, and thus, for example, 0.5 to 10 A / dm 2 is deposited at the highest possible current density. In addition, there are special applications, for example in electroforming, where relatively high layer thicknesses from several tens of μm to a maximum of several millimeters are deposited.

[0030] Instead of a direct current, a pulsed direct current can also be applied. Thereby, the current is interrupted for a certain period of time (pulse plating). With simple pulse conditions, for example, a current for 1 second at the average current density (t on ) and a pulse pause of 0.5 seconds (t off ), etc., a homogeneous, shiny, white coating was obtained.

[0031] The current density established in the electrolyte between the cathode and the anode during the deposition process can be selected by those skilled in the art based on the efficiency and quality of the deposition. Depending on the application and the type of coating system, the current density in the electrolyte is advantageously set to 0.2 to 50 A / dm 2 . If necessary, the current density can be increased or decreased by adjusting system parameters such as, for example, the design of the coating cell, the flow rate, the relationship between the anode or cathode. A current density of 0.5 to 50 A / dm 2 is advantageous, 1 to 25 A / dm 2 is preferred, and 5 to 20 A / dm 2 is particularly preferred.

[0032] In the context of the present invention, the low, medium, and high current density ranges are defined as follows. Low current density range: 0.1 to 0.75 A / dm 2 , Medium current density range: 0.75 A / dm 2 exceeding ~ 2 A / dm 2 , High current density range: 2A / dm 2 Super.

[0033] The electrolyte and method according to the present invention can be used for the electrolytic emission of platinum coatings for technical applications, such as electrical plug connectors and printed circuit boards, as well as for decorative applications such as jewelry and watches. For technical applications, it is preferable to use a continuous system.

[0034] When using electrolytes, various anodes can be used. Therefore, only insoluble anodes are usable. Preferred insoluble anodes 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 ("diamond-like carbon," DLC), or combinations thereof. Platinum-plated titanium or titanium coated with mixed metal oxides are advantageous insoluble anodes, and the mixed metal oxides are preferably selected from iridium oxide, ruthenium oxide, tantalum oxide, and mixtures thereof. Iridium-transition metal mixed oxide anodes, consisting of iridium-ruthenium mixed oxide, iridium-ruthenium-titanium mixed oxide, or iridium-tantalum mixed oxide, are also advantageous for carrying out the present invention. Further information can be found in Cobley, AJ et al. (The use of insoluble anodes in acid sulfate copper electrodeposition solutions, Trans IMF, 2001, 79(3), pp. 113 and 114).

[0035] According to the present invention, the term "electrolyte bath" is understood to mean an aqueous electrolyte placed in a corresponding container and used with the anode and cathode under an electric current flow for electrolysis.

[0036] The electrolyte according to the present invention is aqueous. The compound is preferably a salt or complex soluble in the electrolyte. Therefore, the terms "soluble salt" and "soluble complex" refer to salts and complexes that dissolve in the electrolyte at the working temperature. In this case, the working temperature is the temperature at which electrolysis is performed. In the context of the present invention, a substance is considered soluble if at least 1 mg / l of it dissolves in the electrolyte at the working temperature. [Examples]

[0037] The electrolyte for precipitation was prepared as follows: First, 400 ml of deionized water was placed in a 1 L beaker. Then, while vigorously stirring, the corresponding amounts of acid, platinum, wetting agent, and finally the corresponding additive were added. Next, deionized water was added to this solution to make a final volume of 1 L. 0.2 dm³ pre-coated with nickel and gold. 2 Brass sheets of the specified dimensions were coated under the movement of electrolyte and product. Precipitation occurred at 1-20 A / dm 2 The experiment was conducted over the specified current density range. Particle formation in the electrolyte was evaluated. The results are recorded in the table below.

[0038] [Table 1-1] [Table 1-2] [Table 1-3]

[0039] Compared to Experiment 1 (no additives), particle formation due to additives in the electrolyte was significantly minimized during precipitation.

Claims

1. A water-based cyanide-free electrolyte for depositing platinum or platinum alloy on a conductive substrate, The electrolyte contains one or more ions from the group consisting of Ir, Bi, Sb, Se, and Te, does not contain hydrochloric acid, Bi, Sb, Se, and Te are present at a concentration of 5 to 100 mg / l of the electrolyte, Ir is present at a concentration of 50 to 1000 mg / l of the electrolyte, the electrolyte contains a platinum sulfamate complex, and platinum in the platinum sulfamate complex is present at a concentration of 5 to 20 g / l of the electrolyte, The electrolyte is characterized in that it has a pH of less than 2 and a current density of 1 to 15 A / dm² during precipitation.

2. The electrolyte according to claim 1, characterized in that the electrolyte does not contain citric acid.

3. A method for depositing a platinum or platinum alloy layer on a conductive substrate, A method characterized in that the electrolyte described in claim 1 or 2 is used, the substrate to be coated as an anode and cathode is brought into contact with the electrolyte, and an electric current is established between the anode and the cathode.

4. The method according to claim 3, characterized in that the temperature of the electrolyte during precipitation is 20 to 90°C.

5. The method according to claim 3 or 4, characterized in that the precipitation is carried out in a continuous system.

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