Process for preparing nickel electrolyte and application thereof in electroplating process

Abstract

The invention relates to a nickel plating bath. The invention also relates to the use of the nickel plating bath in an electroplating process for the production of nickel plated substrates, in particular for electrical applications such as batteries and electrolysis devices.

Description

TECHNICAL FIELD

[0001] The present invention relates to a nickel plating bath comprising an aqueous nickel electrolyte and a process for preparing such electrolyte. The invention further relates to the use of the electrolyte for producing nickel plated substrates, in particular for electrical applications such as batteries and electrolytic devices. BACKGROUND

[0002] The world is facing huge challenges in terms of environmental changes. In order to reduce climate change, a significant reduction of greenhouse gases is needed. One of these greenhouse gases is carbon dioxide and it is released during the combustion of fossil fuels. The main user of fossil fuels is the transportation industry, in particular the automotive industry. One way to reduce the consumption of fossil fuels is the electrification of the automotive industry, which would mean a huge increase in the electrical storage capacity of cars in order to have the desired range for electric cars to be a promising alternative to combustion engine cars. Another way to reduce the consumption is the switch to an economy based on hydrogen as fuel instead of fossil fuels.

[0003] Both options, the electrification of the transportation industry and the economy based on hydrogen fuel, require the use of a large amount of nickel plated steel. The nickel plated steel is used in batteries to protect the battery against corrosion or to act as part of the electrical circuit in the battery. Nickel plated steel is used to produce hydrogen in electrolytic devices.

[0004] Depending on the application or battery type, the steel substrate, which is usually provided in the form of a (coiled) strip or sheet, is provided on one or both main sides (“top” and “bottom”) of the steel substrate. Most batteries have a cylindrical or prismatic shape, including components of batteries in the automotive industry, and the material used for the battery case is usually a steel strip or sheet substrate with a nickel coating on one or both sides. The nickel coating is usually applied by an electroplating process in a continuous electroplating line.

[0005] In view of the above environmental challenges, the demand for nickel plated steel will increase. The current production of nickel plated steel is expected to be insufficient to meet this increasing demand, requiring additional production capacity. The scale of the current nickel plated steel production lines does not comply with the expected demand and cannot easily be increased by increasing the existing capacity based on the existing plating technology.

[0006] Nickel plated steel strip or sheet is usually manufactured from a sulphate based electroplating bath, a chloride electroplating bath or an aminosulphonate based electroplating bath by plating a nickel layer onto the strip or sheet. In the electroplating process, nickel ions are consumed at the cathode. This can be done by adding fresh electrolyte to the plating bath. The continuous addition of fresh electrolyte is expensive and requires careful storage of large quantities of these chemicals. Another problem with nickel plating baths is that the maximum available current density during plating limits their usability for high speed electroplating processes. An alternative is to generate nickel ions for deposition at the anode, i.e. the anode is made of some form of nickel, for example nickel pellets stacked in an inert titanium basket to ensure good electrical contact between the individual pellets. The dissolution of the nickel anode material in the plating bath is a limiting factor for this type of electroplated nickel on steel substrates, limiting the production capacity of such plating lines. In EP 0 892 087-A2, electroplating of a nickel layer based on nickel salts is disclosed and also the option of using a soluble nickel anode is disclosed.

[0007] A problem associated with the use of all current standard nickel plating electrolytes is that they are not easily scalable. Most electrolytes contain chlorides that generate toxic chlorine gas at the anode, or the electrolytes have a limited conductivity that limits the deposition rate of nickel, or the electrolytes decompose, such as aminosulphonate electrolytes.

[0008] Object of the invention

[0009] It is an object of the present invention to provide a process for preparing a nickel ion containing solution in water that can be used as an electrolyte in a nickel electroplating process.

[0010] It is also an object of the present invention to provide an electrolyte that avoids the generation of toxic or environmentally harmful by-products, such as chlorine or unwanted metal ions.

[0011] It is also an object of the present invention to provide a process for preparing a nickel ion containing solution in water that can be used as an electrolyte in a continuous high speed nickel electroplating process.

[0012] It is also an object of the present invention to provide an apparatus for using the electrolyte in a continuous high speed nickel electroplating process. SUMMARY

[0013] This object is achieved by a process for preparing a nickel plating bath, said process comprising the steps of:

[0014] (a) nickel (metal),

[0015] (b) methanesulphonic acid, and

[0016] (c) an oxygen releasing compound

[0017] in an aqueous solution.

[0018] A nickel plating bath is understood to be an aqueous solution containing nickel ions (Ni 2+ ) for electroplating nickel onto a metal substrate. The plating bath can also be referred to as electrolyte or electroplating bath. An example of a nickel plating bath or electrolyte is an aqueous solution of nickel methanesulfonate.

[0019] In the context of the present invention, the oxygen releasing compound is a chemical compound which can be dissolved in an aqueous solution. The compound releases oxygen from the compound. Without being bound by this theory, it is believed that the released oxygen is so-called active oxygen or atomic oxygen, but not molecular oxygen (O2). The oxygen is then able to react with other compounds in the aqueous solution thereby producing the nickel plating bath. The reaction is preferably exothermic.

[0020] In a preferred embodiment of the present invention, the process of preparing a nickel plating bath comprises the following steps:

[0021] (a) nickel (metal),

[0022] (b) methane sulfonic acid, and

[0023] (c) hydrogen peroxide and / or ozone

[0024] are combined in an aqueous solution.

[0025] In another embodiment of the present invention, the process of preparing a nickel plating bath comprises the following steps:

[0026] (a) nickel (metal),

[0027] (b) methane sulfonic acid, and

[0028] (c) ozone

[0029] are combined in an aqueous solution.

[0030] In another embodiment of the present invention, the process of preparing a nickel plating bath comprises the following steps:

[0031] (a) nickel (metal),

[0032] (b) methane sulfonic acid, and

[0033] (c) sodium peroxoborate

[0034] are combined in an aqueous solution.

[0035] In an electroplating process for preparing a nickel coating, the nickel methanesulfonate solution has the advantage that the conductivity of the solution is rather high, so that a high deposition rate is possible.

[0036] A simple process to prepare a nickel methanesulfonate solution is to dissolve nickel metal (nickel (metal)) in methanesulfonic acid. However, nickel is not soluble in methanesulfonic acid. Surprisingly, however, the active oxygen released from an oxygen releasing compound such as hydrogen peroxide (H2O2), ozone (O3) or sodium peroxoborate (NaH2BO4) in an aqueous methanesulfonic acid solution oxidizes nickel very rapidly and clean to nickel ions (Ni 2+

[0037] It has surprisingly been found that the speed of preparing nickel methanesulfonate from metallic nickel in water by means of an oxidation process with a suitable oxygen releasing compound is very rapid and clean.

[0038] The temperature of the solution or water also influences the speed of dissolution of the nickel metal. It has been found that the temperature of the solution is preferably between 20°C and 80°C. The dissolution is particularly fast at temperatures above 40°C, for example between 50 and 70°C. A suitable maximum dissolution temperature is 68°C. Preferably, the temperature is between 55°C and 65°C. In order to avoid misunderstanding, it is noted that the temperature of the solution or water is the temperature during the preparation of the nickel methanesulfonate solution.

[0039] The following intermediate reaction takes place between hydrogen peroxide and nickel:

[0040]

[0041] NiO is the intermediate reaction product that dissolves immediately in methanesulfonic acid. The overall reaction is as follows:

[0042]

[0043] The following reaction takes place between ozone and nickel:

[0044]

[0045] The overall reaction is as follows:

[0046]

[0047] Sodium peroxoborate undergoes hydrolysis upon contact with water, resulting in hydrogen peroxide (H2O2) as the reaction of formula (1). Due to the hydrolysis, boric acid (B(OH)3) can also be formed.

[0048] As can be seen from the above formula (2), only water is formed and O2 and water are formed as by-products from formula (4). The reaction can be accelerated by increasing the surface area of the metallic nickel and by increasing the temperature of the aqueous solution, for example by using smaller pellets, thin strips or even nickel powder. The advantage of using hydrogen peroxide as the oxygen releasing compound is that it is available as a liquid and is therefore easier to handle than gaseous ozone. Ozone is preferably added as a gas, preferably by bubbling ozone gas through the aqueous solution. ​

[0049] Furthermore, it has been surprisingly found that the addition of boric acid and / or taurine significantly increases the maximum current density that can be used in the nickel plating process when using these nickel plating baths. The use of sodium perborate as oxygen releasing compound can already provide boric acid to the solution.

[0050] From a practical point of view, the use of hydrogen peroxide and / or ozone is preferred because it produces a pure nickel methanesulfonate solution and it does not produce boric acid to the solution, which is advantageous if a nickel methanesulfonate solution is chosen that is only added with taurine (and not with boric acid).

[0051] Various compounds can be added to the nickel methanesulfonate solution to prepare a suitable nickel plating bath for nickel electroplating. These compounds can be, but are not limited to, buffers, brighteners, stress control agents, etc. Their addition, the effect of the addition and the suitable amount to be added are well known in the art.

[0052] The reaction of hydrogen peroxide or ozone with nickel has a 100% efficiency because both react with water or oxygen and do not form unwanted, toxic or environmentally harmful by-products such as chlorine gas. The process according to the present invention produces a nickel plating bath that does not contain compounds or unwanted metal ions that can lead to the production of toxic or environmentally harmful by-products such as chlorine or bromine.

[0053] Furthermore, the dissolution of nickel in the acidic aqueous solution of methanesulfonic acid with hydrogen peroxide and / or ozone is very fast, making the process usable in combination with high speed continuous electroplating processes.

[0054] The process according to the present invention has the great advantage that the amount of nickel needed to produce the nickel methanesulfonate solution of the electrolyte is far smaller in volume than the alternatives.

[0055] For example, 1000 kg of metallic nickel exhibits a volume of 112.2 dm3 3 , while the same amount of nickel from nickel carbonate exhibits a volume of 460.6 dm3 3 . When using nickel carbonate as nickel source, a volume that is 4.5 times larger needs to be handled. Also, from a health and safety point of view and from a logistical point of view, the handling, transport and storage of salts is more challenging than the handling of metallic nickel. This compound has been identified as a potentially carcinogenic and toxic compound (see e.g. www.ilo.org for nickel carbonate and nickel (II) oxide). Therefore, the costs and safety hazards associated with this method are higher than the method of the present invention.

[0056] The mechanism to produce a nickel methanesulfonate solution based on nickel carbonate (NiCO3), nickel hydroxide (Ni(OH)2) or NiO with appropriate safety precautions is as follows:

[0057]

[0058] Subsequently

[0059]

[0060] However, this is more cumbersome from a health and safety perspective, from a handling perspective and from a cost perspective compared to the process of the present invention.

[0061] In one embodiment, the process of preparing a nickel plating bath (nickel methanesulfonate solution in water) according to the present invention comprises the following steps:

[0062] (a) nickel (metal)

[0063] (b) methanesulfonic acid, and

[0064] (c) hydrogen peroxide and / or ozone

[0065] are combined in an aqueous solution to obtain a nickel methanesulfonate solution in water.

[0066] This means that nickel, methanesulfonic acid and hydrogen peroxide, or as an alternative, nickel, methanesulfonic acid and ozone, or as an alternative, nickel, methanesulfonic acid, hydrogen peroxide and ozone, are combined in an aqueous solution to react, i.e. the ingredients react in the aqueous solution.

[0067] The aqueous solution is preferably water or an aqueous solution of one or two of the other ingredients (a), (b) and (c). The water can be distilled water or demineralized water or simply tap water. All orders of addition of the ingredients (a), (b) and (c) are possible. This means, for example, that methanesulfonic acid and hydrogen peroxide are added to water or that methanesulfonic acid and hydrogen peroxide are combined as an aqueous solution and then nickel is added to the resulting aqueous solution. As an alternative, for example, nickel is added to water or one of the ingredients (b) or (c) and the other ingredients are added to the resulting aqueous solution. When the ingredients (a), (b) and (c) are combined, they react with each other. Nickel is oxidized by hydrogen peroxide and / or ozone to Ni 2+ ions and the anion of methanesulfonic acid forms the counter ion of the Ni 2+ ions.

[0068] In case sodium perborate is used, the conditions of the aqueous solution must be such that the perborate hydrolyzes to hydrogen peroxide and boric acid. Higher temperatures of the aqueous solution favor this hydrolysis. Sodium perborate releases oxygen rapidly at temperatures above 55°C. In order to make it active at lower temperatures (40-55°C), a suitable activator can be used.

[0069] Nickel is added as a metal and can be in any form. In order to enhance the dissolution of nickel in water by oxidation with hydrogen peroxide and / or ozone, the surface of the nickel should be as large as possible. In a preferred embodiment of the application, the nickel is in the form of metal pellets or metal powder. The average size of the pellets or powder particles is preferably less than 10 mm, more preferably less than 5 mm, further preferably less than 1 mm, even more preferably less than 0.1 mm, and most preferably 0.001-0.1 mm. When using thin strips of nickel, the thickness of the strips is preferably less than 1 mm, even more preferably less than 0.1 mm, and most preferably 0.001-0.1 mm. The advantage of being able to use nickel as a metal is that the storage of the raw material is simple and requires little space. The storage of nickel metal does not pose any safety problems.

[0070] The application is also embodied in a nickel plating bath or electrolyte, which can be obtained by the process of the application as described above.

[0071] In an embodiment, the nickel plating bath comprises in water:

[0072] (a) 26-316 g / l nickel methanesulfonate,

[0073] (b) 10-100 g / l boric acid and / or 10-70 g / l taurine.

[0074] In a preferred embodiment, the nickel plating bath comprises in water:

[0075] (a) 26-285 g / l nickel methanesulfonate,

[0076] (b) 10-100 g / l boric acid and / or 10-70 g / l taurine.

[0077] The temperature of the solution or water also influences the dissolution rate of the nickel metal. It has been found that the temperature of the solution is preferably between 20°C and 80°C. The dissolution is particularly fast at temperatures above 40°C, for example between 50 and 70°C, a suitable maximum dissolution temperature being 68°C. Preferably, the temperature is between 55°C and 65°C.

[0078] The exact dissolution rate of the nickel metal in the solution depends on the exact composition of the solution and its exact temperature and can easily be determined using simple laboratory means. When nickel is added to the solution at 60°C, the value of the dissolution rate of the nickel was found to be in the range of about 0.05 and about 0.2 kg / m 2 .min, wherein the solution was made from 80 g / l of 30% H2O2 and 129 g / l of 70% methanesulfonic acid solution. For the sake of argument, a value of 0.1 kg / m 2The dissolution time for 1 kg of nickel pellets with an average size of about 5 mm is about 150 min. For an average particle size of 0.5 mm, the dissolution time is about 15 min, and for an average particle size of 0.01 mm, the dissolution time for 1 kg of particles is about 20 seconds.

[0079] The concentration of hydrogen peroxide in the solution is preferably 4 to 15 wt.-% H2O2, more preferably 7 to 12 wt.-% H2O2, most preferably 8 to 10 wt.-% H2O2, based on the total weight of the solution. The total weight of the solution includes water, hydrogen peroxide and methane sulfonic acid, but not the nickel metal. The concentration of methane sulfonic acid is preferably 15 to 35 wt.-%, more preferably 20 to 30 wt.-%, based on the total weight of the solution. These concentrations result in a high nickel dissolution rate.

[0080] In a preferred embodiment of the present application, the molar ratio of methane sulfonic acid to hydrogen peroxide in the solution is 2 : (0.90 to 1.10), preferably 2 : (0.95 to 1.05), more preferably 2 : (0.98 to 1.02), most preferably 2 : (0.995 to 1.005).

[0081] Nickel can be added in excess, but it is preferably added in stoichiometric amounts. The molar ratio of nickel : methane sulfonic acid : hydrogen peroxide is preferably (0.90 to 1.10) : 2 : (0.90 to 1.10), preferably (0.95 to 1.05) : 2 : (0.95 to 1.05), more preferably (0.98 to 1.02) : 2 : (0.98 to 1.02), most preferably (0.995 to 1.005) : 2 : (0.995 to 1.005). Ozone is added as a gas until the above amounts given for hydrogen peroxide have reacted.

[0082] Even if the molar ratio of nickel : methane sulfonic acid : hydrogen peroxide or ozone is exactly 1 : 2 : 1, the chemical reaction is never completely, so that the solution can still contain traces of hydrogen peroxide or ozone. However, the inventors have found that these traces do not significantly influence the plating performance nor the properties or composition of the nickel plated layer.

[0083] It has been found that the nickel plating bath according to the present application is particularly suitable for the preparation of an electrolyte used in a nickel electroplating process, in particular a high speed nickel electroplating process.

[0084] The present application therefore also relates to a nickel plating bath obtainable by the process of the present application, said process comprising the steps of:

[0085] (a) nickel,

[0086] (b) methane sulfonic acid, and

[0087] (c) oxygen-releasing compounds, such as

[0088] The ingredients are combined in water or an aqueous solution to obtain a solution of nickel methanesulfonate in water. The oxygen-releasing compound can be hydrogen peroxide or ozone or sodium perborate or a combination thereof.

[0089] The solution of nickel methanesulfonate in water obtainable by the process of the present invention preferably comprises a solution of nickel methanesulfonate in water, which contains 10 -6 to 0.1 wt.-% hydrogen peroxide and / or 10 -6 to 0.01 wt.-% ozone, preferably 10 -5 to 0.05 wt.-% hydrogen peroxide and / or 10 -5 to 0.005 wt.-% ozone. The pH is preferably 1 to 4. More preferably, the pH is below 3. Even more preferably, the pH is 1.5 to 2.5, most preferably 1.6 to 2.2.

[0090] The present invention also relates to the use of the nickel plating bath according to the present invention in a process of nickel electroplating. The use is the use of the nickel plating bath as electrolyte in a process of preparing a nickel coating, in particular a process of preparing a nickel coating by electroplating an article, preferably a steel sheet. Electroplating is also known as electrodeposition or electrocoating.

[0091] In a preferred embodiment of this use, the solution of nickel methanesulfonate in water is used to prepare an electrolyte for high-speed nickel electroplating, preferably electroplating with a dimensionally stable anode. Such a dimensionally stable anode is preferably made of a metal oxide, more preferably a mixed metal oxide, for example on a titanium support. The metal oxide is preferably iridium oxide, osmium oxide, ruthenium oxide, rhodium oxide, palladium oxide, platinum oxide or a mixture thereof.

[0092] When using the solution of nickel methanesulfonate in water as a nickel plating bath, a maximum current density of about 100 A / dm 2 (Ampere per square decimeter) is possible. In the course of the present invention, it was surprisingly found that the addition of boric acid (H3BO3) and / or taurine (2-aminoethanesulfonic acid) enhances the maximum current density that can be used to up to 140 A / dm 2 , while a solution of nickel methanesulfonate in water without the addition of boric acid or taurine has the above-mentioned maximum current density of about 100 A / dm 2 . This improves the efficiency and usability of the nickel plating bath for high-speed plating processes.

[0093] The present invention therefore also relates to a nickel plating bath for electroplating nickel, which comprises in water:

[0094] (a) 26-316 g / l nickel methanesulfonate

[0095] (b) 10-100 g / l boric acid and / or 10-70 g / l taurine.

[0096] This means that the nickel plating bath preferably comprises 26-316 g / l nickel methanesulfonate, 10-100 g / l boric acid and / or 10-70 g / l taurine and the balance water, prepared by the process of the present application. The nickel plating bath can additionally comprise typical electrolytic additives.

[0097] In a preferred embodiment, the nickel plating bath comprises in water:

[0098] (a) 26-285 g / l nickel methanesulfonate,

[0099] (b) 10-100 g / l boric acid and / or 10-70 g / l taurine.

[0100] The nickel plating bath according to the present application comprises 26-316 g / l nickel methanesulfonate, preferably 26-285 g / l nickel methanesulfonate, more preferably 80-200 g / l nickel methanesulfonate, even more preferably 105-160 g / l nickel methanesulfonate. The given amount of nickel methanesulfonate corresponds to about 10-120 g / l nickel, preferably about 10-110 g / l, more preferably about 30-75 g / l, even more preferably about 40-60 g / l nickel, dissolved in ionic form.

[0101] The amount of boric acid in the nickel plating bath according to the present application is 10-100 g / l boric acid, preferably 30-70 g / l boric acid, more preferably 40-60 g / l boric acid. The amount of taurine according to the preferred embodiment is 10-70 g / l taurine, preferably 30-60 g / l taurine, more preferably 40-60 g / l taurine.

[0102] The above-mentioned amounts can be combined in any combination. This means that preferred embodiments of the present application are nickel plating baths comprising in water, for example:

[0103] (a) 26-316 g / l nickel methanesulfonate

[0104] (b) 30-70 g / l boric acid and / or 30-60 g / l taurine,

[0105] or a nickel plating bath comprising in water:

[0106] (a) 80-285 g / l nickel methanesulfonate

[0107] (b) 10-100 g / l boric acid and / or 10-70 g / l taurine

[0108] or a nickel plating bath comprising in water:

[0109] (a) 80-200 g / l nickel methanesulfonate

[0110] (b) 10-100 g / l boric acid and / or 10-70 g / l taurine.

[0111] Both boric acid and taurine act as buffering and complexing agents. Taurine is biodegradable and thus preferred from an environmental point of view. A preferred embodiment of the present invention comprises taurine as component (b).

[0112] Another preferred embodiment of the present invention is the use of the nickel plating bath according to the present invention in a nickel electroplating process.

[0113] The present invention also relates to the use of the nickel plating bath according to the present invention in a nickel electroplating process, preferably for electroplating nickel on steel, more preferably for electroplating nickel on steel sheet. A preferred embodiment of the present invention is the use of the nickel plating bath according to the present invention in the production of a battery case or an electrolytic device component. The process comprises electroplating nickel on a steel sheet and then using the resulting steel sheet having a nickel layer on the surface for the production of a battery case. Said using especially comprises known steps such as cutting the nickel-coated steel sheet and forming the sheet.

[0114] The nickel-plated steel sheet thus produced can also be used for other applications and is not necessarily limited to battery or electrolytic device components.

[0115] In the use of the nickel plating bath according to the present invention, i.e. the electroplating process, the temperature of the nickel plating bath in the nickel electroplating process is preferably 40-70 °C, more preferably 50-60 °C. The pH is preferably 1-4, more preferably 1-3. The pH is preferably 1 to 4. More preferably the pH is below 3. Even more preferably the pH is 1.5 to 2.5, most preferably 1.6-2.2.

[0116] The present invention also relates to a nickel electroplating process, wherein nickel is electrodeposited on an article, preferably a steel sheet or steel strip, in a nickel plating bath produced according to the present invention. The current density is preferably 40 to 140 A / dm 2 and the temperature of the plating bath is as described above.

[0117] The substrate used for nickel-plated metal substrate applications in batteries and electrolytic devices is typically a low-carbon steel strip. The strip is produced by cold rolling. The strip is usually provided in the form of a coil, but the strip can also be cut into smaller parts, called sheets. Wide coils can be slit into narrower strips and then rewound or cut into sheets.

[0118] For plating processes, it is preferred to plate a strip rather than a separate sheet. The production rate of a plating process is much higher and can be performed in a continuous plating line. After cold rolling, the steel strip is very hard and usually has to be annealed in order to soften or recrystallize the microstructure of the steel, enabling further processing such as deep drawing to produce a battery. The annealing can be performed before or after plating of the nickel. When plating is performed after annealing, then the metal substrate will have a layer of nickel on top of the steel substrate. If plating is performed before annealing, then the nickel will start to diffuse into the steel substrate and the iron will start to diffuse into the nickel layer. Depending on the nickel layer thickness, the annealing temperature, the annealing time and the type of annealing (batch or continuous annealing), the degree of interdiffusion can vary. If the annealing temperature is not very high or the annealing time is very short, then the degree of diffusion can be very limited (so-called shallow annealing). In this way, the surface of the nickel layer will still be only nickel, but a diffusion layer will be formed at the nickel-steel interface. The longer the annealing, the thinner the nickel plate and the higher the annealing temperature, the more mixing of nickel and iron, until the point where the iron starts to move to the surface of the plated layer. For some applications, this is very important and it is often reported that the Ni:Fe value on the surface is 1 : 1. The choice of annealing temperature and time also depends on the desired microstructure of the steel substrate after annealing. Post processing of the annealed and plated strip can be performed (in any order), such as temper rolling or tension levelling. This heat treatment can be performed in several ways, such as batch annealing, continuous annealing, normalizing and rapid annealing. All heat treatments will give the heat treated material certain desired mechanical properties. The main differences between the heat treatments are the heating rate, the maximum temperature and the duration at that maximum temperature. The heating can be performed by gas fire, electric heating or any other method, raising the temperature of the nickel plated steel substrate in a controlled way.

[0119] Figure 8 A series of nickel plated steel (Fe) substrates is shown, where on the left hand side the structure in cross section is shown schematically and on the right hand side a schematic of the nickel concentration is shown, where the left side of the graph is the surface. Figure 8 a shows a nickel plated steel strip without any diffusion. This is a steel substrate plated with a nickel layer after annealing of the steel substrate or without any annealing of the substrate. Figure 8 b shows a nickel plated steel strip that has been subjected to a shallow annealing. The diffusion of nickel into the steel substrate and of iron into the nickel layer is minimal and the iron has not yet reached the surface. The surface of the nickel plated layer is still 100% nickel. Figure 8 c shows a nickel plated steel strip that has been subjected to a more pronounced annealing. The diffusion of nickel into the steel substrate and of iron into the nickel layer is quite pronounced and the iron has reached the surface. The surface of the plated layer is about 70% Ni and 30% Fe. The more pronounced the annealing (in time or temperature) or the thinner the nickel layer, the higher the Fe content at the surface. By controlling the annealing and the plated layer thickness, the composition of the surface can be controlled. Example

[0120] The following examples provide preferred embodiments according to the present application and further illustrate the present application.

[0121] Example 1. A nickel methanesulfonate solution (nickel plating bath) was prepared from 50 x 50 mm nickel pieces, which were immersed in a mixture of 80 g of 30 wt% H2O2 and 192 g of 70 wt% methanesulfonic acid solution at 60 °C. Nickel was dissolved at a rate of about 0.01 g / cm 2 / minute, which corresponds to 0.1 kg / m 2 .min.

[0122] The nickel pieces were removed when 50 g / l Ni was reached, and the resulting solution contained only nickel methanesulfonate and traces of H2O2. This solution was used for a nickel electroplating process, using a rotating cylinder electrode, on blackplate (low carbon, cold rolled steel). This rotating cylinder method allows an accurate simulation of industrial plating processes and industrial plating conditions.

[0123] The experimental conditions were as follows:

[0124] • Current density: 10, 20, 40, 60, 80 and 100 A / dm 2

[0125] • Plating time: 10 seconds

[0126] • Rotational speed of the cylinder: 400 rpm (revolutions per minute), which corresponds to a linear speed of 100 m / min.

[0127] • Temperature: 50 and 60 °C

[0128] • Gap between anode / cathode: 15 mm

[0129] The above conditions resulted in a very efficient nickel coating on steel (efficiencies of more than 90% were reached). The experiments showed that the solution according to the present application can be effectively used for high speed nickel electroplating processes.

[0130] Example 2. The maximum current density that can be used with the nickel plating bath of example 1 is about 100 A / dm 2 To the plating bath of example 1, boric acid was added in amounts of 15, 30 and 45 g / l and electroplating was performed at T = 60 °C, 400 rpm and t = 10 s. Current densities of up to 140 A / dm 2 were possible and the nickel layers obtained on the steel sheets had an excellent appearance over the whole current density range.

[0131] Example 3. Adhesion test

[0132] Nickel electroplating with the above nickel plating bath with and without boric acid was performed at a temperature of 35 °C, 40 °C, 50 °C, 60 °C and 70 °C at a line speed of 75 m / min to 150 m / min with a plating time of 5, 10 and 20 s with a hydrogen peroxide concentration of 0, 0.1 and 0.5 wt.%. The current density was 100 A / dm 2 The samples were subjected to adhesion tests (NEN EN ISO 2409:2013, Erichsen Dome Test, 5 mm, followed by tape (Gitterschnitt test)). None of the samples showed any peeling.

[0133] Example 4. Taurine addition

[0134] The maximum current density that can be used with the nickel plating bath of example 1 is about 100 A / dm 2 To the plating bath of example 1, 30 g / l taurine was added and electroplating was performed at T = 60 °C, 400 rpm and t = 10 s. Current densities up to 140 A / dm 2 were possible and the nickel layers obtained on the steel sheet had an excellent appearance over the entire current density range. BRIEF DESCRIPTION OF DRAWINGS

[0135] The application will now be illustrated by the following non-limiting drawings.

[0136] Figure 1 shows the relationship between the dissolution time (in minutes) of 1 kg of nickel pellets and the nickel pellets diameter (in mm) based on a hypothetical nickel dissolution rate of 0.1 kg / m 2 .min.

[0137] Figure 2 shows the relationship between the revolutions per minute of a rotating cylindrical electrode (RCE) and the line speed of an industrial plating line.

[0138] Figure 3 shows the thickness (in pm) of nickel layers deposited by a methanesulfonic nickel solution with 100 g / l Ni at 60 °C with an RCE at 400 rpm as a function of the current density (in A / dm 2 for different deposition times (5 s (lower curve), 10 s and 20 s (upper curve)).

[0139] Figure 4 shows the thickness (in pm) of nickel layers for a Ni = 50 g / l, 30 g / l methanesulfonic nickel solution with boric acid at 60 °C for a plating time of 10 s as a function of the current density (in A / dm2 as a function of the current density (in A / dm

[0140] Figure 5 shows the influence of the boron acid concentration on the coating thickness, for a plating time of 10 s, at 400 rpm9for 15 g / l (top curve), 30 g / l and 45 g / l boron acid (lower curves), as a function of the current density (in A / dm 2 as a function of the current density (in A / dm

[0141] Figure 6 shows the plating efficiency of a 50 g / l nickel methanesulfonate solution with 30 g / l boron acid as a function of the pH value. The plating efficiency increases sharply from a value below 50% at a pH below 1 to a value above 70% at a pH above 1. A higher efficiency of more than 90% is obtained from a pH value of 1.5 (for the sake of clarity: a higher pH value means that the solution is less acidic).

[0142] Figure 7 gives an impression of the quality of the coating that can be obtained for a plating time of 10 s at a plating temperature of 60 °C for nickel methanesulfonate solutions obtained at different current densities with the process of the invention. All show an excellent visual appearance.

[0143] Figure 8 shows a series of plated nickel (Fe) substrates at various stages of the diffusion annealing described above.

[0144] Figure 9 shows a device consisting of one or more dissolving tanks (D) for dissolving metallic nickel in methanesulfonic acid. One or more buffer tanks (B) can be used to store nickel methanesulfonate baths, for simple storage or for fine-tuning the composition of the bath by adding boronic acid or taurine, if required, and any other required additives. The solutions can be pumped from these buffer tanks to the plating tanks (here only two tanks are drawn, but there can be more). In a continuous plating process, a roll of metal substrate can be unwound and fed into the plating tank and plated, after which the plated substrate is rewound for further processing. The pre- or post-treatment of the plated strip, such as cleaning or annealing of the cold-rolled strip (before or after plating), is not shown. Neither are the piping, pumps and plating peripherals. Furthermore, the way in which the nickel metal and other required chemicals are supplied is not shown.

Claims

1. Process for the preparation of a nickel plating bath, comprising the following steps: (a) nickel (metal), (b) methane sulfonic acid, and (c) an oxygen releasing compound in combination in an aqueous solution.

2. Process according to claim 1, comprising the following steps: (a) nickel (metal), (b) methane sulfonic acid, and (c) hydrogen peroxide and / or ozone in combination in an aqueous solution.

3. Process according to claim 2, wherein the following intermediate reaction takes place: wherein NiO is the intermediate reaction product which is immediately dissolved in methane sulfonic acid, and wherein the overall reaction is as follows: or wherein NiO is the intermediate reaction product which is immediately dissolved in methane sulfonic acid, and wherein the overall reaction is as follows: resulting in an aqueous nickel methane sulfonic acid solution.

4. Process according to one of the preceding claims, characterized in that, The temperature of the aqueous solution is from 20°C to 80°C, preferably from 50°C to 70°C.

5. Process according to one of the preceding claims, characterized in that, The concentration of hydrogen peroxide is from 4 to 15 wt.-%, based on the total weight of the solution, and / or the concentration of methane sulfonic acid is from 15 to 25 wt.-%, based on the total weight of the solution.

6. Process according to one of the preceding claims, characterized in that, Methane sulfonic acid and / or hydrogen peroxide are used in the form of an aqueous solution.

7. Process according to one of the preceding claims, characterized in that, Nickel (metal) is used in the form of metal pellets or metal powder.

8. The process according to claim 7, characterized in that, The average size of the pellet or powder particles is less than 10 mm, preferably from 0.001 to 1 mm.

9. The process according to any one of claims 1 to 8, characterized in that, The molar ratio of methane sulfonic acid to hydrogen peroxide is 2 : (0.95 to 1.05), preferably 2 : (0.98 to 1.02).

10. Nickel plating bath, obtainable by the process of any one of claims 1 to 9.

11. The nickel plating bath according to claim 10, characterized in that which further contains 10 to 100 g / l boric acid and / or 10 to 70 g / l taurine.

12. Nickel plating bath according to claim 10 or 11, comprising in water 26 to 316 g / l nickel methane sulfonic acid, 10 to 100 g / l boric acid and / or 10 to 70 g / l taurine.

13. Nickel plating bath according to claim 12, comprising in water 80 to 200 g / l nickel methane sulfonic acid, 30 to 70 g / l boric acid and / or 30 to 60 g / l taurine.

14. Nickel plating bath according to claim 12 or 13, comprising in water: 80 to 200 g / l nickel methane sulfonic acid, and 30 to 60 g / l taurine.

15. Use of a nickel plating bath according to any one of claims 9 to 14 in a nickel electroplating process, preferably in a process for electroplating nickel on steel strip or sheet, preferably in a continuous electroplating process.

16. Use according to claim 15 for the production of nickel plated substrates, in particular for electrical applications, such as batteries and electrolytic devices.

Images