Dispersion electrolyte for graphite-containing layers

Abstract

To provide an electrolyte for electrodepositing a tin layer, a nickel layer or a tin-nickel layer having improved tribological properties and low contact resistance, which can be used safely and in an environmentally responsible manner. To provide an electrodeposition method of a tin layer, a nickel layer or a tin-nickel layer, a metal substrate coated with the tin layer, the nickel layer or the tin-nickel layer, and use of an electrolytic solution.SOLUTION: This is achieved by a dispersion electrolyte for electrodepositing a graphite-containing tin layer, a graphite-containing nickel layer or a graphite-containing tin-nickel layer, a method for electrodepositing the graphite-containing layer using the electrolyte, a metal substrate coated with the graphite-containing layer, and the use of the dispersion electrolyte.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a dispersion electrolyte for electrodepositing a tin, nickel or tin-nickel layer containing graphite, a method for electrodepositing said graphite-containing layer using said electrolyte, a metal substrate coated with said graphite-containing layer, and the use of the dispersion electrolyte. [Background technology]

[0002] As an alternative to hard chromium layers, tin-nickel layers with comparable physical properties and particularly high hardness levels have been described, for example, in WO 2016 / 131916 A1. For the electrodeposition of such tin-nickel layers, electrolytes have been used which, for environmental and health reasons, are far more advantageous than those for hard chromium layers, which use chromium(VI) compounds and, more generally, hexafluorosilicic acid, which can also release toxic hydrogen fluoride at low pH values.

[0003] Like hard chromium layers, the tin-nickel layers described in WO 2016 / 131916 A1 have high hardness levels, for example, HV 750 (HV = Vickers hardness) or higher. Furthermore, hard tin-nickel layers are characterized by very good corrosion resistance to acids and bases and can be machined using grinding, turning, milling, and similar processes. Due to the tin-nickel layer's certain degree of embrittlement, it is also possible to re-strip worn layers from the component.

[0004] Due to their properties, hard tin-nickel layers, like hard chromium layers, are commonly used as the "final layer", ie the outer layer of a component, primarily to protect said component.

[0005] In principle, there is also a need to provide electronic components such as contacts or electrodes with a corrosion-resistant protective layer. In any case, the need for components that are reliable, long-lasting, and as efficient as possible, i.e., with as few losses as possible, in the course of expanding electrification has recently placed ever-increasing demands on the sustainability of such components. In addition, during their production, substances and processes that are harmful to health and the environment should be avoided as much as possible.

[0006] Thus, for example, corrosion-resistant protective layers for electrical contacts and also for electrodes of batteries or fuel cells are desired which, in addition to good corrosion resistance, also have low electrical contact resistance (boundary resistance) and improved tribological properties, in particular wear resistance, compared to conventional hard tin-nickel layers.Therefore, there is a need for electrolytes capable of electrolytically depositing layers having this combination of advantageous properties.

[0007] It is also desirable to improve these properties with tin and nickel layers which can also serve as protective layers against corrosion. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] WO2016 / 131916A1 Summary of the Invention [Problem to be solved by the invention]

[0009] It is therefore an object of the present invention to provide an electrolyte for electrodepositing a tin, nickel or tin-nickel layer having improved tribological properties and low contact resistance, which can be used safely and environmentally responsibly. Other objects of the present invention are to provide a method for electrodepositing such a tin, nickel or tin-nickel layer, a metal substrate coated with such a tin, nickel or tin-nickel layer, and uses of the electrolyte. [Means for solving the problem]

[0010] These objects are achieved by a dispersion electrolyte for electrodepositing a graphite-containing tin layer, a graphite-containing nickel layer or a graphite-containing tin-nickel layer, a method for electrodepositing said graphite-containing layer using said electrolyte, a metal substrate coated with said graphite-containing layer, and the use of the dispersion electrolyte, as set out in the independent claims. Preferred configurations are given in the dependent claims and below. [Brief explanation of the drawings]

[0011] [Figure 1] 1A and 1B are photographs showing coated substrates of Comparative Example 1 (FIG. 1a), Comparative Example 2 (FIG. 1b), and Example 2 (FIG. 1c). [Figure 2] 1 is a scanning electron microscope photograph of Comparative Example 1. [Figure 3] 1 is a scanning electron microscope photograph of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention provides a dispersion electrolyte for electrodepositing a graphite-containing tin layer, a graphite-containing nickel layer, or a graphite-containing tin-nickel layer, the dispersion electrolyte comprising: - Sn at concentrations from 2 to 50 g / L 2+ ions (tin ions) and / or Ni at concentrations of 0.2 to 70 g / L 2+ ions (nickel ions) and - graphite particles in a concentration of 5 to 200 g / L; - at least one anionic dispersant in a concentration of from 1 to 25 g / L; - Sn 2+ and Ni 2+ a complexing agent for the ions; - a conductive salt; - Water and Includes:

[0013] The pH of the dispersion electrolyte according to the present invention is from 4 to 7. The dispersion electrolyte is also abbreviated below as "electrolyte".

[0014] The inventors have surprisingly found that the dispersion electrolyte according to the present invention allows for the formation of graphite-containing layers by electrodepositing graphite particles together with a metal layer. Furthermore, they have surprisingly found that incorporating graphite particles into a tin, nickel, or tin-nickel layer improves the contact resistance (boundary resistance) and triboelectric properties, particularly wear resistance, compared to the corresponding layer without graphite particles. The improved triboelectric properties are also accompanied by improved durability of the coating due to reduced brittleness. Therefore, the dispersion electrolyte allows for the formation of protective layers that, due to their low contact resistance, reduce electrical energy losses, thereby extending the operating time, i.e., the service life, so that the overall component is more sustainable. Furthermore, the graphite-containing layer has excellent corrosion resistance against acids and bases. Therefore, the electrolyte allows for the production of reliable protective layers with low corrosion losses.

[0015] Thus, it is possible to achieve this advantageous combination of properties in one layer using a dispersion electrolyte. Until now, it has at best been possible to achieve this combination of properties using multiple layers fabricated separately.

[0016] Therefore, using the dispersion electrolyte according to the present invention, it is possible to achieve electrodeposition (i.e., electrolytic deposition) of a graphite-containing tin layer, a graphite-containing nickel layer, or a graphite-containing tin-nickel layer having advantageous properties on a metal substrate. In this context, "graphite-containing" means that spectroscopically detectable graphite is present in the form of graphite particles. Therefore, the graphite-containing layer represents a graphite particle-containing layer and is a composite layer.

[0017] With respect to the "tin layer," substantially only tin atoms (e.g., at least 95% by weight, particularly at least 98% by weight) are deposited as metal. In this case, the underlying electrolyte is Sn 2+ Contains Ni ions 2+Similarly, a "nickel layer" refers to a layer in which substantially only nickel atoms (e.g., at least 95% by weight, specifically at least 98% by weight) are deposited as metal. In this case, the underlying electrolyte is Ni 2+ Contains ions, but Sn 2+ With respect to the "tin-nickel layer," substantially only tin and nickel atoms (e.g., at least 95% by weight, particularly at least 98% by weight) are deposited as metals. Thus, the electrolyte is Sn 2+ and Ni 2+ It must contain ions.

[0018] The dispersion electrolyte is very flexible in handling and allows for a wide range of electrodeposition conditions to be selected. Because the pH of the dispersion electrolyte is between 4 and 7, i.e., slightly acidic, it can be used safely without generating dangerous hydrofluoric acid (hydrogen fluoride, HF). At low pH values, i.e., below 3.5, if the electrolyte contains fluoride ions, the amount of hydrogen fluoride generated may increase.

[0019] The dispersion electrolyte is Sn 2+ and / or Ni 2+ ions, i.e., dissolved tin and / or nickel salts. In principle, all suitable tin and / or nickel salts can be used. It is preferred to use chloride salts, i.e., SnCl2·nH2O and NiCl2·nH2O, because they are cheap, easy to handle, and contain chloride ions (Cl - ) to increase the conductivity of the electrolyte. Anhydrous salts or salts containing water of crystallization, designated by the additional designation "nH2O" (where n is typically 0 to 6), can be used. SnCl2·2H2O and / or NiCl2·6H2O are preferably used in the electrolyte because these salts are storable and inexpensive.

[0020] Whether the dispersion electrolyte is used to deposit a graphite-containing tin layer or a graphite-containing tin-nickel layer, the electrolyte typically contains Sn at a concentration of 5 to 45 g / L, preferably 20 to 30 g / L, and more preferably 23 to 27 g / L. 2+ For graphite-containing nickel layers and graphite-containing tin-nickel layers, Ni 2+ The concentration of the ions is specifically 10 to 65 g / L, preferably 50 to 65 g / L, and more preferably 50 to 60 g / L.

[0021] According to a preferred embodiment, the graphite-containing tin-nickel layer is deposited at a 1:1 molar ratio of tin to nickel, such that the nickel content relative to the tin and nickel metals is approximately 35% by weight. As explained below, the nickel content can be varied by process conditions such that the graphite-containing tin-nickel layer can contain 30 to 40% by weight, preferably 30 to 38% by weight, more preferably 32 to 37% by weight, and even more preferably 35% by weight, relative to the tin and nickel metals. For the graphite-containing tin-nickel layer, the electrolyte preferably contains 20 to 30 g / L, more preferably 23 to 27 g / L, of Sn. 2+ ions, preferably at a concentration of 50 to 65 g / L, more preferably 50 to 60 g / L. 2+ The nickel content in the electrolyte is usually higher than the tin content because nickel is less noble than tin and therefore does not deposit as easily. 2+ Ion: Ni 2+ The mass ratio of the ions is preferably from 1:1 to 1:4, more preferably from 1:2 to 1:3.

[0022] Surprisingly, it has been found that the nickel content in the graphite-containing tin-nickel layer can also be significantly reduced compared to the usual 1:1 ratio described above. According to this embodiment, the nickel content is 10 to 20 wt. % relative to the metallic tin and nickel, preferably 13 to 18 wt. %, and even more preferably 14 to 17 wt. %. To achieve a significantly lower nickel content, the mass ratio of tin to nickel in the electrolyte should be 8:1 or greater, specifically 10:1 or greater.

[0023] The dispersion electrolyte of the present invention contains 5 to 200 g / L of graphite particles dispersed therein, and the graphite particle content in the electrolyte is preferably 20 to 150 g / L, more preferably 40 to 100 g / L, to achieve the above-mentioned effects.

[0024] Generally, the Sn in the dispersion electrolyte 2+ ions and / or Ni 2+ For low ion content, low graphite particle content is also used. 2+ ions and / or Ni 2+ When the ion content is high, a large amount of graphite particles is preferably used. In the dispersion electrolyte, the Ni:graphite mass ratio is preferably 1:0.5 to 1:2, more preferably 1:0.5 to 1:1, and / or the Sn:graphite mass ratio is preferably 1:0.5 to 1:5, more preferably 1:1.5 to 1:2.5. The graphite content of the graphite-containing layer can also be changed by changing the graphite concentration in the electrolyte.

[0025] The type of graphite used is not limited in principle; natural or synthetic graphite types can be used. The median (d50) particle size of the graphite particles is typically within the range of 20 nm to 20 μm, preferably 1 to 10 μm, and more preferably 1.5 to 8 μm. The particle size can be measured, for example, by laser diffraction in accordance with ISO 13320:2020 using a HELOS (Helium-Neon Laser Optical System) spectrometer. Generally, the particle size should be equal to or less than the desired layer thickness of the graphite-containing layer. The particle size can be adjusted by conventional milling and / or screening processes that can separate excessively large or small particles. Suitable graphite particles are also commercially available.

[0026] Smaller graphite particles, specifically those with a median particle size of 20 nm to 0.5 μm, tend to provide moderately improved tribo-properties and even lower contact resistance in relatively hard layers. Graphite particles with a median particle size of 1.5 to 8 μm tend to provide very good tribo-properties and significantly reduced contact resistance, despite providing somewhat lower hardness levels than comparable nickel or tin-nickel layers without graphite particles.

[0027] To efficiently disperse the graphite particles in the electrolyte and to uniformly incorporate the graphite particles in the graphite-containing layer, the dispersion electrolyte according to the present invention contains an anionic dispersant. The anionic dispersant typically has a sulfate group (-OSO3-), a sulfonate group (-SO3-), a carboxylate group (-CO2-), or a carboxyl group (-CO2H), which can then exist as an anion in aqueous solution. An alkali metal ion, preferably Na + , and ammonium anion (NH4 + ) are usually used as counterions because they provide good water solubility, increase conductivity, and do not adversely affect electrodeposition. Sulfate and sulfonate groups are in dissociated form at the pH of the dispersion electrolyte, i.e., they are not in protonated form. In contrast, carboxy and carboxylate groups can be in equilibrium with each other.

[0028] The anionic dispersant is preferably at least one selected from the group consisting of sulfate compounds having alkyl, aralkyl, or aromatic groups each having 6 to 24 carbon atoms; sulfonate compounds having alkyl, aralkyl, or aromatic groups each having 6 to 24 carbon atoms; and polymers containing carboxylate or carboxy groups. Combinations of different anionic dispersants can be used. "Sulfate compounds" herein refer to organic sulfate group-containing compounds. Similarly, "sulfonate compounds" are understood to mean organic sulfonic acid group-containing compounds.

[0029] Specifically, the anionic dispersant is preferably at least one selected from the group consisting of sulfate compounds having an alkyl group with 6 to 24 carbon atoms; aromatic sulfonate compounds whose base aromatic groups each have 6 to 14 carbon atoms; and polymers containing poly(meth)acrylic acid and salts thereof.

[0030] Very particularly preferably, the dispersant is a sulfate compound having an alkyl group having 6 to 24 carbon atoms selected from the group consisting of aliphatic alcohol sulfates, aliphatic alcohol polyether sulfates, aliphatic alcohol aryl polyether sulfates, and combinations thereof, and / or a polymer having aromatic sulfonic acid groups, where the base aromatic groups each have 6 to 14 carbon atoms, and the aromatic sulfonic acid groups are preferably derived from phenylsulfonic acid, phenolsulfonic acid, or naphthylsulfonic acid. In this case, the alkyl group having 6 to 24 carbon atoms originates from an aliphatic alcohol. The polyether group is specifically a polyethylene glycol group. The polymer having aromatic sulfonic acid groups is, for example, a condensation product of an aromatic sulfonate compound, such as phenylsulfonic acid, phenolsulfonic acid, or naphthylsulfonic acid, with formaldehyde. Fatty alcohol sulfates and aliphatic alcohol polyglycol ether sulfates containing alkyl groups having 6 to 20 carbon atoms, specifically 8 to 18 carbon atoms, are more preferably present as sulfate compounds.

[0031] Furthermore, a combination of at least one preferred sulfate compound and at least one preferred sulfonate compound is particularly preferred as an anionic dispersant, preferably used in a weight ratio of 1:10 to 10:1, specifically 1:8 to 3:1.

[0032] Examples of anionic dispersants are Sokalan® (BASF SE, poly(meth)acrylate-containing polymers or salts thereof), e.g. Sokalan® SR, sodium-phenolsulfonic acid condensates, sodium-phenylsulfonic acid condensates, sodium-naphthalenesulfonic acid condensates, Disponil® APE (BASF SE, alkyl polyglycol ether sulfate) and fatty alcohol sulfates having 6 to 20 carbon atoms, such as 2-ethylhexyl sulfate (e.g. sodium methsulfate), lauryl sulfate, oleyl sulfate, stearyl sulfate and sulfates of mixed fatty alcohols, in particular the corresponding sodium salts thereof.

[0033] The anionic dispersant is used in the dispersion electrolyte at a concentration of 1 to 25 g / L. Preferably, it is present in the electrolyte at a concentration of 2 to 20 g / L, preferably 4 to 10 g / L. Typically, a lower amount of anionic dispersant is used for a lower concentration of graphite particles, and similarly, a higher amount is used for a higher concentration of graphite particles.

[0034] As described above, the anionic dispersant effectively disperses graphite particles in the electrolyte, enabling the graphite particles to be uniformly incorporated into the graphite-containing layer. Advantageously, the graphite particles do not necessarily need to be dispersed in advance; rather, they can usually be incorporated into the electrolyte in powder form. Advantageously, homogenizing the electrolyte in an ultrasonic bath to achieve this goal is not necessary, reducing the preparation effort and enabling the dispersion electrolyte to be used economically and in large volumes. Furthermore, phosphate and pyrophosphate can also be dispersed in the dispersion electrolyte according to the present invention, thereby improving the solubility of tin and / or nickel salts.

[0035] Further components of the dispersion electrolyte are necessary to form a uniform graphite-containing layer with good deposition rate in the solution. 2+ and / or Sn 2+The complexing agent serves to stabilize salts and facilitate their transfer. In principle, any known complexing agent used in tin and nickel electrolytes can be used as the complexing agent. Preferably, the complexing agent is a water-soluble organic compound with chelating properties having at least three functional groups selected from amino, carboxy, and carboxylate groups. Preferably, at least two functional groups are amino groups. The amino groups are selected from primary, secondary, and tertiary amino groups. More preferably, the complexing agent contains one or more secondary and / or tertiary amino groups. The functional groups available for coordination are usually spaced apart by two or three carbon atoms to form a stable chelate complex.

[0036] Particularly preferably, the complexing agent is at least one selected from the group consisting of EDTA, DETA, DOTA, and DOTATOC. EDTA means ethylenediaminetetraacetic acid. DETA means diethylenetriamine. DOTA means 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid. DOTATOC means a DOTA-derived complexing agent (specifically, Phe-Cys-Tyr-Lys-Thr-Cys-Thr) in which a DOTA molecule is bound to the N-terminus of an octapeptide via an amine bond.

[0037] The amount of complexing agent used is determined by the amount of Sn in the dispersion electrolyte. 2+ and / or Ni 2+ Typically, the complexing agent is present in the electrolyte at a concentration of 5 to 70 g / L, preferably 10 to 65 g / L, more preferably 40 to 60 g / L, based on the concentration of the ions.

[0038] The dispersion electrolyte further contains a conductive salt. A conductive salt is understood to mean a water-soluble salt that increases the conductivity of the electrolyte. Preferably, the conductive salt is at least one selected from the group consisting of sodium chloride, potassium chloride, ammonium chloride, sodium acetate, potassium acetate, ammonium acetate, ammonium fluoride, ammonium bifluoride, sodium fluoride, and potassium fluoride. The electrolyte preferably contains at least one conductive salt selected from ammonium fluoride, ammonium bifluoride, and ammonium acetate. Advantageously, the conductive salt also increases the solubility of tin and / or nickel salts.

[0039] Preferably, the dispersion electrolyte for electrodepositing the graphite-containing tin-nickel layer contains at least one fluoride (F), especially when the nickel content is 32 to 37% by weight, for example 35% by weight. - )-containing conductive salts, which may, but need not, be combined with other conductive salts. It is speculated that the fluoride ions may stabilize the dinuclear tin and nickel complex, thereby supporting the formation of a very consistent alloy ratio of the tin-nickel layer in a 1:1 molar ratio.

[0040] The conductive salt is typically present in the electrolyte at a concentration of 5 to 70 g / L, preferably 10 to 65 g / L, and more preferably 40 to 60 g / L.

[0041] According to a preferred embodiment, the dispersion electrolyte comprises: - Sn at concentrations of 5 to 45 g / L, especially 20 to 30 g / L 2+ ions, and / or Ni at a concentration of 10 to 65 g / L, especially 50 to 65 g / L 2+ Ions and - graphite particles with an average particle size of 1 to 10 μm, in particular 1.5 to 8 μm, in a concentration of 20 to 150 g / L, in particular 40 to 100 g / L; - at least one anionic dispersant in a concentration of from 2 to 20 g / L, in particular from 4 to 10 g / L, a complexing agent chosen from EDTA, DETA, DOTA and DOTATOC, in a concentration of between 10 and 65 g / L; - a conductive salt in a concentration of 10 to 65 g / L; - Water and Includes:

[0042] In this case, the anionic dispersant is at least one selected from the group consisting of sulfate compounds having an alkyl group having 6 to 24 carbon atoms; aromatic sulfonate compounds, wherein the aromatic groups on which they are based each have 6 to 14 carbon atoms; and polymers containing poly(meth)acrylic acid and salts thereof, and is preferably a combination of at least one sulfate compound and at least one sulfonate compound, for example, in the ratio described above.

[0043] According to a particularly preferred embodiment, the dispersion electrolyte comprises: - Sn at concentrations of 20 to 30 g / L, especially 23 to 27 g / L 2+ ions, and / or Ni at concentrations of 50 to 65 g / L 2+ Ions and - graphite particles with an average particle size of 1.5 to 8 μm, in a concentration of 40 to 100 g / L; - at least one anionic dispersant in a concentration of 4 to 10 g / L; a complexing agent chosen from EDTA, DETA and DOTA, in a concentration of from 10 to 65 g / L, in particular from 40 to 60 g / L, a complexing agent containing or consisting of a fluoride-containing conductive salt in a concentration of 10 to 65 g / L, in particular 40 to 60 g / L, - Water and Includes:

[0044] In this case, the anionic dispersant is preferably at least one selected from the group consisting of aliphatic alcohol sulfates and aliphatic alcohol polyether sulfates, in which the alkyl group of the aliphatic alcohol moiety has 6 to 24 carbon atoms, specifically 6 to 20 carbon atoms, and preferably 8 to 18 carbon atoms, and polymers having aromatic sulfonic acid groups, in which the basic aromatic groups each have 6 to 14 carbon atoms, and the aromatic sulfonic acid groups are preferably derived from phenylsulfonic acid, phenolsulfonic acid, or naphthylsulfonic acid. Particularly preferably, in this case, the at least one anionic dispersant is a combination of an aliphatic alcohol sulfate or an aliphatic alcohol polyglycol ether sulfate containing an alkyl group of 6 to 20 carbon atoms, in particular 8 to 18 carbon atoms, with a phenylsulfonic acid polymer (phenylsulfonic acid condensate), a phenolsulfonic acid polymer (phenolsulfonic acid condensate) or a naphthylsulfonic acid polymer (naphthylsulfonic acid condensate), for example in the ratios mentioned above.

[0045] Furthermore, the dispersion electrolyte may contain conventional additives such as those known from conventional electrolytes for the electrodeposition of tin, nickel and tin-nickel layers. In addition to the anionic dispersants described above, other dispersants may also be added to the electrolyte. However, preferably, only anionic dispersants are used.

[0046] The dispersion electrolyte can be formed by mixing or dissolving tin and / or nickel salts and other components, i.e., conductive salts, complexing agents, anionic dispersants, graphite powder, and water. The graphite powder can be added as a solid without the need to disperse it beforehand or to treat the mixture with ultrasound for dispersion. Stirring is preferred when forming the electrolyte, and, if required, mild heating is used to accelerate the dissolution of the components. The pH can be adjusted, for example, by adding hydrochloric acid, sodium hydroxide, ammonia, potassium hydroxide, or aqueous solutions thereof. The dispersion electrolyte of the present invention can advantageously be produced in large quantities, making it suitable for industrial use. The electrolyte can be stored, and stirring can be used to redisperse any graphite particles that may have settled.

[0047] The present invention further provides a method for electrodepositing a graphite-containing tin layer, a graphite-containing nickel layer, or a graphite-containing tin-nickel layer. The method comprises electrodepositing a graphite-containing layer onto a metal substrate using a dispersion electrolyte according to at least one embodiment described herein. The method is carried out at a temperature in the range of 50 to 85°C, preferably 55 to 70°C. The dispersion electrolyte is heated to this temperature.

[0048] The above method can be carried out using all conventional equipment for the electrodeposition of tin-nickel layers. When the electrolyte contains a fluoride salt, a plastic container is preferred over a glass container. The electrolyte is usually thoroughly mixed during deposition, for example by stirring.

[0049] The metal substrate is connected as a cathode. This may be, for example, a metal component, a connecting component, a switch, or an electrode. Preferably, the graphite-containing layer is formed on the metal substrate as the final layer, i.e., as the outer layer. "Metal substrate" is also understood to mean a metal layer that can be electrolytically coated, i.e., for example, a pre-metallized plastic. Examples of metals are, inter alia, copper, nickel, noble metals such as palladium or platinum, steel, stainless steel, brass, and bronze. The surface to be coated may be previously cleaned using conventional methods, for example, degreased.

[0050] A nickel anode may be used as the anode, for example, which allows for easy control of the nickel ion content in the electrolyte, and multiple anodes may also be used.

[0051] Furthermore, the method allows for a great improvement in the flexibility of carrying out the method. Preferably, the deposition is carried out at a rate of 0.1 to 10 A / dm 2 , preferably 0.5 to 5 A / dm 2 The current density can be used to influence, for example, the graphite content and, in the case of graphite-containing tin-nickel layers, the nickel content. In principle, the higher the current density, the higher the graphite content in the graphite-containing layer. 2 Such current densities make it possible to increase the nickel content of the graphite-containing tin-nickel layer.

[0052] It has also been found that the higher the tin concentration in the electrolyte, the lower the nickel content in the graphite-containing tin-nickel layer. Similarly, the lower the nickel concentration in the electrolyte, the lower the nickel content in the graphite-containing tin-nickel layer. For example, a tin / nickel ratio of 8:1 or greater, specifically 10:1 or greater, allows the nickel content in the graphite-containing tin-nickel layer to be set at 10 to 20 wt.%.

[0053] In some cases, the pH of the electrolyte can also affect the nickel content of the graphite-containing tin-nickel layer, with higher pH tending to result in somewhat higher nickel content.

[0054] In principle, the method can be used to produce graphite-containing layers of any desired thickness. Typically, the graphite-containing layers are deposited with a thickness of 4 to 30 μm, preferably 5 to 20 μm, and more preferably 5 to 12 μm. The layer thickness is measured by X-ray fluorescence spectroscopy according to DIN EN ISO 3497 (2001-12), for example, using a Fischerscope XDAL X-ray fluorescence spectrometer.

[0055] The present invention further provides a coated metal substrate obtainable by the method described herein using the dispersion electrolyte described herein, whereby the metal substrate is coated with a graphite-containing tin layer, a graphite-containing nickel layer, or a graphite-containing tin-nickel layer, where the graphite-containing layer contains 0.1 to 8 wt. % graphite, based on the total weight of the graphite-containing layer.

[0056] Preferably, the graphite-containing layer contains 0.5 to 3 wt %, more preferably 0.8 to 2.3 wt %, of graphite, based on the total weight of the graphite-containing layer.

[0057] As mentioned above, the graphite-containing layer has lower contact resistance and improved tribo-properties compared to a corresponding layer that does not contain graphite particles.

[0058] According to one embodiment, the graphite-containing layer is a graphite-containing tin layer. By nature, tin layers are very flexible and malleable. Surprisingly, it has been found that even with such a layer, the tribological properties, in particular the wear resistance, can be significantly increased. Likewise, it has been found that the contact resistance can be significantly reduced once again. The graphite-containing tin layer is particularly suitable for use in plug-in and sliding contacts.

[0059] According to another embodiment, the graphite-containing layer is a graphite-containing nickel layer. It has been found once again that the incorporation of graphite particles into the nickel layer significantly improves the tribological properties and contact resistance compared to a corresponding nickel layer without added graphite. Consequently, the brittleness of the nickel layer is also reduced, providing extended durability. At the same time, it is possible to achieve good hardness in the graphite-containing nickel layer, even without a subsequent hardening step.

[0060] According to a preferred embodiment, the graphite-containing nickel layer has an average friction coefficient of 0.4 or less, preferably 0.3 or less, even more preferably 0.2 or less, and / or a hardness of at least HV300 (Vickers hardness), preferably at least HV350, more preferably at least HV400. The average friction coefficient and hardness are measured using the methods described below. In particular, these properties can be adjusted through the graphite content in the layer and also through the size of the graphite particles.

[0061] The graphite-containing nickel layer is particularly suitable as a protective layer and for electrode coatings, plug-in connections, and contact surfaces. It can be a cheaper alternative to tin-nickel layers when the corrosion resistance requirements are not as high. A dense, well-adherent oxide layer forms on the as-deposited nickel layer, providing good protection against corrosion by dilute acids and bases. While conventional nickel layers have high contact resistance due to the oxide layer, this property is improved in the nickel layer according to the present invention through the introduction of graphite.

[0062] According to another embodiment, the graphite-containing layer is a graphite-containing tin-nickel layer. The graphite-containing tin-nickel layer typically has a nickel content of 10 to 40% by mass. In this case, the nickel content is preferably in the range of 13 to 18% by mass or 30 to 38% by mass, based on the metallic tin and metallic nickel.

[0063] Surprisingly, it has been found that it is possible to electrolytically deposit graphite-containing tin-nickel layers in which the nickel ratio is much lower than the conventional molar ratio of 1:1 (approximately 35% by weight). When the nickel content relative to the metallic tin and nickel is 13 to 18% by weight, specifically 14 to 17% by weight, the graphite-containing tin-nickel layers have very good tribological properties and low contact resistance. Increasing the amount of tin incorporated into the layer once again significantly reduces the contact resistance. The graphite-containing tin-nickel layers according to this embodiment are particularly suitable for plug-in connections, switching contacts, and as a replacement for silver layers.

[0064] In another configuration, the nickel content of the graphite-containing tin-nickel layer is preferably 30 to 38 wt. % based on the metallic tin and nickel, more preferably 32 to 37 wt. % (e.g., 35 wt. %). Compared to a corresponding tin-nickel layer without graphite, the tribological properties are improved and the contact resistance is reduced. Surprisingly, it has been found that these properties can also be combined with good hardness. Thus, the hardness of the graphite-containing tin-nickel layer is preferably HV 200 or higher, more preferably HV 300 or higher.

[0065] The graphite-containing tin-nickel layer preferably has an average coefficient of friction of 0.4 or less, preferably 0.2 or less.

[0066] The contact resistance of the graphite-containing tin-nickel layer associated with the gold contact at 25° C. is specifically 50 mΩ (mOhm) or less, preferably 40 mΩ or less, and even more preferably 30 mΩ or less. The contact resistance is measured according to the method mentioned below.

[0067] The hardness, average coefficient of friction and contact resistance of the tin-nickel layer can be adjusted in particular through the graphite content in the layer and also through the size of the graphite particles.

[0068] The graphite-containing layer formed by the electrolyte according to the invention is suitable for various applications, as described above, especially for electronic components having low contact resistance and good durability due to their triboelectric properties and resistance to corrosion from acids and bases. The present invention also provides the use of the dispersion electrolyte described herein for producing an electronic component having a graphite-containing tin layer, a graphite-containing nickel layer, or a graphite-containing tin-nickel layer. Preferably, the dispersion electrolyte is used to produce a graphite-containing tin-nickel layer as a protective or final layer on a contact or electrode. The electrode can be used, for example, in batteries, electrolyzers, or fuel cells. Further application areas are electrical connector technology and catalyst layers. [Example]

[0069] The present invention is illustrated below by examples, without being limited to these examples.

[0070] Measurement method The following measurement methods were used:

[0071] 1) Layer thickness The layer thickness was measured using an XDAL X-ray fluorescence spectrometer from Fischerscope in accordance with DIN EN ISO 3497 (2001-12). This method is used for layer thicknesses up to 20 μm. For layer thicknesses above 20 μm, the layer thickness is measured microscopically on a cross section of the layer. Average measurements are mentioned.

[0072] 2) Composition The alloy composition (i.e., tin and nickel) was also analyzed by X-ray fluorescence spectroscopy using the above-mentioned equipment in accordance with DIN EN ISO 3497 (2001-12). The measured values ​​were obtained with an accuracy of better than ±2% by weight. The corresponding contents are given for the metals in the deposited layer.

[0073] The graphite content of the entire cross section of the graphite-containing layer was determined using glow discharge optical emission spectroscopy (GDOES) in accordance with DIN ISO 11505 (2018-02), the content being referred to for the entire graphite-containing layer.

[0074] 3) Tribology Tribological and average friction coefficient studies were carried out by the "Forschungsinstitut Edelmetalle + Metallchemie (fem)", Schwabisch Gmund (Germany) as pin-on-disk tribology tests according to test specification SOP 4CP1. A CSEM pin-on-disk tribometer machine was used as the test equipment. The counterbody was a sphere with a diameter of 6 mm made of alloy 100 Cr6, material no. 1.3505. The following parameters were used: Normal load: 5N Speed: 500 minutes -1 Sliding speed: 52.4mm / s Temperature: 23℃±2℃ Relative humidity: 50%±6% RPM: 10,000

[0075] The average coefficient of friction was measured in a long-term test of 10,000 cycles (number of revolutions). The average coefficient of friction (μ) is dimensionless.

[0076] 4) Contact resistance According to specification MIL-DTL-81706B (ContRes-ConCoat-001 from "Forschungsinstituts Edelmetalle + Metallchemie (fem)", Schwabisch Gmund (Germany)) with a contact pressure of up to 2 N The contact resistance associated with the gold contacts was measured in a four-point measurement at 25° C. A Keithley Instruments INC. Model 2410, 4393118, C34 was used as the measuring device.

[0077] 5) Vickers hardness The surface hardness of each deposited layer was tested after optional polishing (i.e., conditioning) according to DIN EN ISO 14577-1(2015-11). Vickers hardness is referred to using the unit "HV". The test load used of 0.005 corresponds to 0.049 N (multiplied by the proportionality constant 0.102). Vickers hardness is dimensionless.

[0078] 6) Amount of hydrogen fluoride released Hydrogen fluoride release was measured using a Drager accuro device and for contents between 0.5 and 15 ppm using a Drager hydrogen fluoride test tube 0.5 / a.

[0079] The MAK value (2001) of hydrogen fluoride is 2 ppm.

[0080] Preparation of metal substrate A steel sheet (DC03) measuring 50 × 120 × 1-2 mm was used as the metal substrate. Pretreatment was carried out as follows.

[0081] [Table 1]

[0082] Slotoclean AK 160 (containing NaOH and disodium metasilicate), Slotoclean EL DCG (containing NaOH, disodium metasilicate and sodium carbonate), and Slotoclean BEF30 (containing but-2-yn-1,4-diol and ethoxylated isotridecanol) are products of Dr. Ing. Max Schlotter GmbH.

[0083] reagent Among these, the following reagents were used in the experiments: VP 11 2571: Bath additive from Dr. Ing. Max Schlotter containing ammonium bifluoride (15 to 20% by weight) as conductive salt and polyamine (15 to 20% by weight) as complexing agent. VP 11 2572: Bath additive from Dr. Ing. Max Schlotter containing the sodium salt of a polymer of aromatic sulfonic acid (20 to 25% by weight) as an anionic dispersant. VP 11 2573: Bath additive from Dr. Ing. Max Schlotter containing, as anionic dispersant, sodium sulfate salts (15 to 20% by weight) of aliphatic alcohols having 6 to 20 carbon atoms.

[0084] Culmo AN 11-1 Additive: A bath additive from Dr. Ing. Max Schlotter containing ethoxylated, propoxylated 2-propylheptanol, (15 to 25% by weight).

[0085] Tin Bath Additive SAT311: A bath additive from Dr. Ing. Max Schlotter containing ethoxylated, propoxylated 2-propylheptanol (15 to 25% by weight) and 1,2-dihydroxybenzene (1 to 7% by weight).

[0086] Nickel bath additive SLOTONIK M: A bath additive from Dr. Ing. Max Schlotter containing C12-14 alkyl ether sulfate with EO sodium salt (3 to 5% by weight).

[0087] Asbury Carbons, Inc. Synthetic Graphite (40nm) and High Conductivity Synthetic Graphite (40nm).

[0088] (Examples 1 to 7 and Comparative Examples 1 and 2) For Examples 1 to 7 and Comparative Examples 1 and 2 ("CE1" and "CE2"), a tin-nickel electrolyte solution having the components shown in Table 1 was placed in a plastic beaker. To achieve this goal, SnCl2·2H2O and NiCl2·6H2O were first dissolved in a mixture of distilled water and bath additives at 55°C with stirring (250 rpm). Then, for Examples 1 to 7 and Comparative Example 2, the corresponding graphite powder was slowly added and dispersed with stirring (250 rpm). The median (d50) particle size of the graphite particles is given in parentheses as the particle size in Table 1. The pH was optionally adjusted by adding hydrochloric acid. The volume of the electrolyte was 2 L.

[0089] The above steel sheets were pretreated and then electrolytically coated under the conditions shown in Table 1. The electrolyte was thoroughly mixed using a (40 mm) stirring rod (250 rpm). Each steel rod was connected as a cathode and immersed in the electrolyte to a depth of 10 cm. Two Ni electrodes (50 × 120 × 5 mm), placed parallel to the cathode and 4 cm apart on either side, acted as anodes. The immersion depth of the anodes was also 10 cm. The two parallel-connected anodes were connected in the order of the electrolyte, cathode, and DC power supply.

[0090] The nickel content and graphite content were measured and the thickness of the deposited layer was measured.

[0091] [Table 2]

[0092] In Examples 1 to 7 and Comparative Examples 1 and 2, tin-nickel layers were electrolytically deposited on copper substrates with good adhesive strength. In Examples 1 to 7, the metal was uniformly deposited in the layer, and the graphite particles were uniformly incorporated, regardless of the particle size. In Comparative Example 2, when no anionic dispersant was added, there was no visible graphite incorporated into the tin-nickel layer, and the graphite content was significantly less than 0.1% by mass.

[0093] Figure 1 shows photographs of the coated substrates of Comparative Examples 1 and 2 and Example 2. The graphite incorporation in Comparative Example 2 (Figure 1b) was so low that it was visually indistinguishable from Comparative Example 1 (Figure 1a), which was produced without graphite particles throughout. In contrast, the good graphite incorporation in Example 2 made it possible to observe a black tin-nickel layer (Figure 1c).

[0094] Figure 2 shows scanning electron micrographs of the tin-nickel layer of Comparative Example 1. A uniform layer was observed at both 100x magnification (Figure 2a) and 30,000x magnification (Figure 2b).

[0095] Figure 3a shows the graphite-containing tin-nickel layer of Example 2 at 100x magnification. A uniform layer was observed, with no noticeable agglomerations of graphite particles. Figure 3b shows the same layer at 30,000x magnification. Due to the graphite particles, the surface is rougher than the tin-nickel layer of Comparative Example 1. The graphite particles and the surface of the graphite-containing tin-nickel layer are now clearly distinguishable.

[0096] The hardness, tribological properties (friction coefficient), and contact resistance of the tin-nickel layers formed in Examples 1 to 7 and Comparative Examples 1 and 2 were investigated. The above-described methods were used to achieve this goal. The results are summarized in Table 1 above.

[0097] The conventional tin-nickel layer of Comparative Example 1 is characterized by a high hardness level. Furthermore, the contact resistance associated with the gold contacts was measured to be 75.7 mΩ, and the average coefficient of friction was measured to be 0.57. Due to the low or absent amount of graphite incorporated, the physical properties of Comparative Example 1 were similar to those of Comparative Example 2.

[0098] In Examples 1 to 7, it was possible to significantly improve both the tribological properties and the contact resistance of the tin-nickel layer compared to Comparative Examples 1 and 2. These examples therefore demonstrate that the successful incorporation of graphite particles into the electrolytically deposited tin-nickel layer makes it possible to improve the durability and electrical conductivity compared to tin-nickel layers without the incorporation of graphite. Furthermore, it is noteworthy that it was possible to obtain layers with significantly higher hardness levels, regardless of the incorporation of graphite.

[0099] Furthermore, it was found that lower average friction coefficients and contact resistances tended to be measured when the graphite particles were large (Examples 1 to 3). Smaller graphite particles and lower amounts of incorporated graphite tended to result in somewhat higher average friction coefficients as well as somewhat higher hardness levels (Examples 4 to 6). Example 7, with a nickel content of only 16% by mass, also resulted in very good tribological properties, i.e., a low average friction coefficient and low contact resistance. A high tin content of approximately 84% by mass was associated with lower hardness levels.

[0100] Example 8 Example 2 was repeated, with the pH set to 4.0 and the bath temperature set to 60° C. The amount of hydrogen fluoride released was measured according to the method described above.

[0101] The amount of hydrogen fluoride released was below the detection limit, i.e., less than 0.5 ppm. Therefore, the dispersion electrolyte can be used safely.

[0102] (Examples 9 and 10 and Comparative Examples 3 and 4) The same procedures as in Examples 1 and 7 and Comparative Example 1 were carried out. For Example 9 and Comparative Example 3 (CE3), no nickel salt was used to prepare the tin layer. Similarly, for Example 10 and Comparative Example 4 (CE4), no tin salt was used to prepare the nickel layer. The composition of the electrolyte, the electrodeposition conditions, and the composition of the formed layer are summarized in Table 2.

[0103] In Comparative Examples 3 and 4, conventional tin or nickel layers were electrolytically deposited. As shown in Examples 9 and 10, it was also possible to produce graphite-containing tin or nickel layers without any problems using the dispersion electrolyte according to the invention. No significant modification of the dispersion electrolyte (except for the nickel or tin salt) was required to achieve this.

[0104] Furthermore, substantial improvements in tribological properties (lower average friction coefficient) and contact resistance were observed for both the softer tin layer and the harder, more brittle nickel layer (Table 2: Example 9 compared to Comparative Example 3, and Example 10 compared to Comparative Example 4). Thus, it was also possible to improve the durability and conductivity of the electrolytically deposited tin or nickel layer.

[0105] [Table 3]

Claims

1. 1. A dispersion electrolyte for electrodepositing a graphite-containing tin layer, a graphite-containing nickel layer, or a graphite-containing tin-nickel layer, comprising: - Sn at concentrations from 2 to 50 g / L 2+ ions and / or Ni at concentrations of 0.2 to 70 g / L 2+ Ions and - graphite particles in a concentration of 5 to 200 g / L; - at least one anionic dispersant in a concentration of from 1 to 25 g / L; - Sn 2+ and Ni 2+ a complexing agent for the ions; - a conductive salt; - Water and Including, pH between 4 and 7, Dispersion electrolyte.

2. The electrolyte has a concentration of 5 to 45 g / L, preferably 20 to 30 g / L, of Sn 2+ ions, and / or Ni at a concentration of 10 to 65 g / L, preferably 50 to 65 g / L. 2+ 10. The dispersion electrolyte of claim 1, containing ions.

3. 3. The dispersion electrolyte according to claim 1 or 2, wherein the electrolyte contains graphite particles in a concentration of from 20 to 150 g / L, preferably from 40 to 100 g / L.

4. 4. The dispersion electrolyte according to claim 1, wherein the mass ratio of Ni:graphite in the electrolyte is from 1:0.5 to 1:2, preferably from 1:0.5 to 1:1, and / or the mass ratio of Sn:graphite in the electrolyte is from 1:0.5 to 1:5, preferably from 1:1.5 to 1:2.

5.

5. 5. The dispersion electrolyte according to any one of claims 1 to 4, wherein the graphite particles have a median (d50) particle size of 20 nm to 20 μm, preferably 1 to 10 μm, more preferably 1.5 to 8 μm.

6. 6. The dispersion electrolyte according to claim 1, wherein the dispersing agent is at least one selected from sulfate compounds having alkyl, aralkyl, or aromatic groups each having 6 to 24 carbon atoms; sulfonate compounds having alkyl, aralkyl, or aromatic groups each having 6 to 24 carbon atoms; and polymers containing carboxy or carboxylate groups.

7. 7. The dispersion electrolyte of claim 6, wherein the sulfate compound having an alkyl group having 6 to 24 carbon atoms is selected from aliphatic alcohol sulfates, aliphatic alcohol polyether sulfates, and combinations thereof, and / or the sulfonate compound is a polymer having aromatic sulfonic acid groups, the base aromatic groups each having 6 to 14 carbon atoms.

8. 8. The dispersion electrolyte according to claim 1, wherein the dispersant is present in the electrolyte in a concentration of from 2 to 20 g / L, preferably from 4 to 10 g / L.

9. 9. The dispersion electrolyte according to claim 1, wherein the complexing agent is an organic compound having at least three functional groups selected from amino groups, carboxy groups and carboxylate groups, preferably at least two functional groups being amino groups selected from primary, secondary and tertiary amino groups, and more preferably the complexing agent is at least one selected from EDTA, DETA, DOTA and DOTATOC.

10. 10. The dispersion electrolyte according to any one of claims 1 to 9, wherein the complexing agent is present in the electrolyte at a concentration of from 5 to 70 g / L, preferably from 10 to 65 g / L, more preferably from 40 to 60 g / L.

11. 11. The dispersion electrolyte according to any one of claims 1 to 10, wherein the conductive salt is at least one selected from sodium chloride, potassium chloride, ammonium chloride, sodium acetate, potassium acetate, ammonium acetate, ammonium fluoride, ammonium bifluoride, sodium fluoride and potassium fluoride, and in the case of electrodeposition of graphite-containing tin-nickel layers preferably contains a fluoride-containing conductive salt.

12. 12. The dispersion electrolyte according to any one of claims 1 to 11, wherein the conductive salt is present in the electrolyte at a concentration of from 5 to 70 g / L, preferably from 10 to 65 g / L, more preferably from 40 to 60 g / L.

13. 13. A method for electrodeposition of a graphite-containing tin layer, a graphite-containing nickel layer, or a graphite-containing tin-nickel layer, comprising electrodeposition of a graphite-containing layer onto a metal substrate using the dispersion electrolyte of any one of claims 1 to 12 at a temperature of from 50 to 85°C.

14. Deposition is from 0.1 to 10 A / dm 2 , preferably 0.5 to 5 A / dm 2 14. The method of claim 13, wherein the current density is

15. 15. The method according to claim 13 or 14, wherein the graphite-containing layer is deposited with a layer thickness of from 4 to 30 μm, preferably from 5 to 20 μm, more preferably from 5 to 12 μm.

16. 1. A coated metal substrate, comprising a metal substrate coated with a graphite-containing tin layer, a graphite-containing nickel layer, or a graphite-containing tin-nickel layer, wherein the graphite-containing layer contains 0.1 to 8% by weight of graphite, based on the total weight of the graphite-containing layer.

17. 17. The coated metal substrate of claim 16, wherein the graphite-containing layer contains 0.5 to 3 wt. %, preferably 0.8 to 2.3 wt. %, of graphite, relative to the total weight of the graphite-containing layer.

18. 18. The coated metal substrate of claim 16 or 17, wherein the graphite-containing layer is a graphite-containing nickel layer having an average coefficient of friction of 0.4 or less and a Vickers hardness of at least HV300.

19. 18. The coated metal substrate according to claim 16 or 17, wherein the graphite-containing layer is a graphite-containing tin-nickel layer having a nickel content of 10 to 40% by weight, preferably 13 to 18% by weight or 30 to 38% by weight, based on the tin metal and the nickel metal.

20. 20. The coated metal substrate of claim 19, wherein the graphite-containing tin-nickel layer has a nickel content of 32 to 37% by weight based on the tin metal and the nickel metal, and a Vickers hardness of at least HV200.

21. 21. The coated metal substrate according to claim 19 or 20, wherein the graphite-containing tin-nickel layer has an average coefficient of friction of 0.4 or less, preferably 0.3 or less.

22. 22. The coated metal substrate of any one of claims 19 to 21, wherein the contact resistance of the graphite-containing tin-nickel layer associated with a gold contact at 25°C is 50 milliohms (mOhm) or less, preferably 40 mOhms or less, and even more preferably 30 mOhms or less.

23. 13. Use of the dispersion electrolyte according to any one of claims 1 to 12 for producing an electronic component having a graphite-containing tin layer, a graphite-containing nickel layer or a graphite-containing tin-nickel layer.

24. 24. Use according to claim 23, wherein the electrolyte is used to produce a graphite-containing tin-nickel layer as a protective layer on a contact or electrode.

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