EP2609232B1 - Electrolytic bath for electroplating and process thereof - Google Patents

Abstract

An electrolytic bath for electrodeposition includes nickel salt, phosphoric acid, phosphonic acid, and boric acid in solution. A method for producing an electrolytic bath includes the steps of mixing a nickel salt, phosphoric acid, phosphonic acid, and boric acid, and adding nickel carbonate in order to increase the pH value.

Description

The invention relates to an electrolytic bath for the electrodeposition and a process for its production, in particular for a galvanic deposition of a nickel-phosphorus layer.

The galvanic deposition of a nickel-phosphorus (NiP) layer on substrates is interesting for many applications, since a NiP layer has a high hardness and good anti-wear properties. In addition to galvanic nickel plating, chemical nickel plating is also known.

An electrolytic bath preferably allows a high quality coating at a high current density and deposition rate, and it is as cost effective as possible.

The WO 99/02765 A1 shows an electrolytic bath for NiP coating. The bath contains nickel carbonate, phosphoric acid, hypophosphorous acid (H ₃ PO ₂ ) or phosphorous acid (H ₃ PO ₃ ), and methanesulfonic acid.

It is an object of the invention to provide a novel electrolytic bath for electrodeposition and a process for its production.

According to the invention, the object is achieved by an electrolytic bath according to claim 1, a method according to claim 10 and a use according to claim 12. Such an electrolytic bath is stable, allows a high current density, a high deposition rate, the generation of a good nickel-phosphorus Layer, and it is inexpensive. Preferably, saccharin is added in the process.

Further details and advantageous developments of the invention will become apparent from the hereinafter described, in no way as a limitation of the invention to be understood embodiments, and from the dependent claims. A typical electroplating plant has a bath in which there is a bath (electrolyte, galvanic bath). The substrate to be coated (eg cylinder liner of an engine block) is surrounded in the electrolyte and by a dimensionally stable, insoluble anode or a soluble anode. A DC power source is connected to the anode with the plus terminal and the substrate (cathode) with the minus terminal, and the current is used to electrodeposit the layer on the substrate. A circulation pump ensures a uniform distribution of the bath, and there may be a rotation of the substrate in the electrolyte. This is only an illustrative example, and other electroplating equipment may be used.

Among other things, the composition of the bath determines what current densities and thus deposition rates are possible in the coating, and baths are available on the market for many applications.

Composition of the NiP bath

It is proposed a bath that is well suited for the galvanic coating with a layer of nickel and phosphorus and possibly other constituents, which is why the bath is referred to below as NiP bath. A nickel-phosphor coating has a higher hardness compared to a pure nickel coating and thus opens up additional fields of application. The nickel content in the nickel-phosphorus layer also affects the anti-wear properties and the corrosion properties of the alloy. The phosphorus content in the layer determines the hardness, and a common mass fraction is e.g. 6-8% by weight of phosphorus, but depending on the requirements, higher mass fractions of e.g. 12 wt .-% may be required.

• Nickelsalz
• Phosphorsäure (H₃PO₄)
• Phosphonsäure (H₃PO₃)
• Borsäure (H₃BO₃)

Preferably, a NiP bath is used with a composition containing in solution:

• nickel salt
• Phosphoric acid (H ₃ PO ₄ )
• Phosphonic acid (H ₃ PO ₃ )
• Boric acid (H ₃ BO ₃ )

The nickel or more precisely the nickel ions are present in the solution predominantly as nickel (II) or Ni ²⁺ , but other oxidation states may also occur.

In addition, the NiP bath may also contain saccharin and / or other additives. An addition of H ₃ PO ₂ (phosphinic acid) is also possible, but has not led to a better result in the experiments.

The combination of the constituents phosphoric acid, phosphonic acid and boric acid has proved to be advantageous, since the finished bath with this combination has proved to be relatively stable, in particular with regard to the pH. The combination also allows a high current density and thus a high deposition rate. In addition, the ingredients are relatively cheap.

The pH of the final bath preparation is preferably in the range of 1.6 to 2.3, more preferably in the range of 1.8 to 2.2.

• Nickel(II): 90 - 130 g/l
• Phosphorsäure: 60 - 90 g/l
• Phosphonsäure: 20 - 40 g/l
• Borsäure: 30 - 40 g/l
• Saccharin: 0 - 4 g/l

In the following, preferred ranges are given for the individual constituents of the composition with which the electrodeposition works well (high deposition rate and good quality nickel-phosphorus layer) and in which the phosphorus content in the deposited layer meets the requirements:

• Nickel (II): 90-130 g / l
• Phosphoric acid: 60-90 g / l
• Phosphonic acid: 20-40 g / l
• Boric acid: 30 - 40 g / l
• Saccharin: 0-4 g / l

Since the constituents in the (aqueous) solution are partially dissociated, it is better to verify other ranges for measuring the concentration of the constituents.

• Sulfat: 147 - 213 g/l

Dieser Bereich der Konzentration des Sulfats kann z.B. auch durch Zugabe von Schwefelsäure erreicht bzw. beeinflusst werden.The nickel salt is preferably added in the form of nickel sulfate in aqueous solution (NiSO ₄ .6H ₂ O or nickel (II) sulfate hexahydrate). The concentration of sulphate (SO ₄ ^2- ) in this case is for the upper range of nickel (II):

• Sulfate: 147 - 213 g / l

This range of the concentration of the sulfate can be achieved or influenced, for example, by adding sulfuric acid.

• Phosphat: 58 - 88 g/l
• Phosphit: 19 - 39 g/l

The phosphoric acid and phosphonic acid are substantially completely dissociated in the solution, so that the concentration of the phosphoric acid or phosphonic acid according to the above ranges can also be indicated by the concentration of the phosphate (PO ₄ ^3- ) or phosphite (PO ₃ ^3- ) :

• Phosphate: 58-88 g / l
• Phosphite: 19 - 39 g / l

The boric acid is incompletely dissociated in the solution. Dissolved molecules (H ₃ BO ₃ ) are thus in equilibrium with ions (3 H ⁺ + BO ₃ ^3- ). A bath according to the above boric acid concentration range contains boron (partly as a constituent of borate and partly as a constituent of boric acid) at a concentration in the range of 5.2 to 7.0 g / l.

With the NiP bath it is possible to coat different substrates. Thus, e.g. Copper, steel or stainless steel to be coated. Prior to coating, degreasing, activation and pickling of the substrate preferably takes place, as is known to the person skilled in the art.

Performed experiments

A variety of experiments were carried out with different bath compositions for the deposition of NiP. In the experiments exemplified below, a NiP layer could be produced by electrodeposition. The deposited NiP layer was nonporous, homogeneous, charcoal gray shiny and amorphous, whereby a recrystallization by annealing is possible. The substrate used was a copper stud which had been pretreated (degreasing, activation and pickling). The temperature was about 65 ° C, and the current density was up to 30 A / dm ² . The deposition rate is Depending on the current density, typical deposition rates of 0.5 μm / min to more than 2 μm / min were achieved, these values representing no technical limits. Successful tests were carried out with layer thicknesses of up to 100 μm.

Examples I to V

The NiP bath was composed as follows: attempt Nickel (II) phosphoric acid phosphonic boric acid saccharin I 100 g / l 75 g / l 30 g / l 35 g / l 2.6 g / l II 100 g / l 75 g / l 30 g / l 35 g / l 0g / l III 100 g / l 75 g / l 40 g / l 30 g / l 2.6 g / l IV 100 g / l 60 g / l 30 g / l 30 g / l 2.6 g / l V 100 g / l 45 g / l 10 g / l 30 g / l 2.6 g / l

The concentration of phosphoric acid or phosphonic acid can also be specified by the concentration of the phosphate (PO ₄ ^3- ) or phosphite (PO ₃ ^3- ). For example, 75 g / l phosphoric acid corresponds to 73 g / l phosphate and 30 g / l phosphonic acid corresponds to 29 g / l phosphite.

The use of saccharin is at NiP layer thicknesses of e.g. 5 - 10 microns not required, but has proved particularly at layer thicknesses of more than 40 microns as advantageous.

The electrodeposition works e.g. good at a temperature of about 65 ° C. There are also higher temperatures of e.g. 80-90 ° C possible, wherein when using organic additives such. Saccharin whose temperature sensitivity is to be considered.

It was reproducibly coated at current densities up to 30 A / dm ² . The measured current efficiency was about 50-55%. At a current density of 10 A / dm ² , a deposition rate of about 1 μm / min was achieved.

In the experiments carried out as mass fraction of phosphorus in the nickel-phosphorus layer up to 12 wt .-% was measured.

The experiments have shown that a higher nickel (II) concentration in the bath allows a higher current density, the concentration being limited by the saturation limit.

A layer of NiP is a binary alloy with the components Ni and P. However, other components to be deposited can also be added to the NiP bath. For example, it is also possible to deposit a ternary (Ni-XP, eg Ni-Co-P) or quaternary alloy, or it is also possible to deposit a dispersion layer in which additional particles are embedded in the NiP layer, eg silicon carbide (SiC ), Boron nitride (BN), boron carbide (B ₄ C), titanium nitride (TiN), silicon nitride (Si ₃ N ₄ ), titanium carbide (TiC), tungsten carbide (WC) and / or alumina (Al ₂ O ₃ ).

Analysis of the NiP bath

A prerequisite for commercial electrodeposition is the ability to analyze the bath composition. While the nickel (II) concentration is measurable by titration, and the concentration of phosphoric acid and the phosphonic acid by measuring the concentration of the phosphate (PO ₄ ^3- ) or phosphite (PO ₃ ^3- ) is possible by means of ion chromatography, the Determination of the concentration of boric acid in the specified NiP bath more difficult or expensive. Since a titration to determine the concentration of boric acid due to the similar pks values of boric acid, phosphoric acid and phosphonic acid is difficult or impossible, the determination of the concentration of boric acid by other methods such as AAS (atomic absorption spectrometry) or for accurate Measurements are made using the more expensive ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry).

Production of the NiP bath Example VI

• 100 g/l Ni²⁺
• 64 g/l H₃PO₄
• 30 g/l H₃PO₃
• 35 g/l H₃BO₃
• 2,6 g/l Saccharin

pH-Wert = 1,8As an example, the preparation of a NiP bath having the following composition is described:

• 100 g / l Ni ²⁺
• 64 g / l H ₃ PO ₄
• 30 g / l H ₃ PO ₃
• 35 g / l H ₃ BO ₃
• 2.6 g / l saccharin

pH = 1.8

Step 1

• 425,4 g/l Nickel(II)-sulfat-Hexahydrat in wässriger Lösung
• 2,6 g/l Saccharin

Das Nickel(II)-sulfat-Hexahydrat (NiSO₄ · 6 H₂O) in wässriger Lösung wird z.B. von der Fa. IPT International Plating Technologies GmbH, Stuttgart, als NDC Make Up & Maintenance angeboten. Dies ist eine Nickel(II)-sulfat-Hexahydrat-Lösung mit einer Konzentration von 114,5 g/l Nickel. Für die oben angegebene Menge des Nickel(II)-sulfat-Hexahydrats muss 0,675 I NDC Make Up & Maintenance zugegeben werden. Die angegebene Menge führt zu einer Konzentration von ca. 95 g/l Nickel(II).In the first step, in the case of the optional addition of saccharin, mixed:

• 425.4 g / l nickel (II) sulfate hexahydrate in aqueous solution
• 2.6 g / l saccharin

The nickel (II) sulfate hexahydrate (NiSO ₄ .6H ₂ O) in aqueous solution is offered, for example, by IPT International Plating Technologies GmbH, Stuttgart, as NDC Make Up & Maintenance. This is a nickel (II) sulfate hexahydrate solution with a concentration of 114.5 g / l nickel. For the above amount of nickel (II) sulfate hexahydrate, 0.675 I NDC Make Up & Maintenance must be added. The stated amount leads to a concentration of about 95 g / l nickel (II).

step 2

• 44 ml/l Phosphorsäure 85%ig
• 30 g/l Phosphonsäure
• 35 g/l Borsäure

Die Phosphonsäure und die Borsäure sind Feststoffe, die als solche oder aber auch in Lösung zugesetzt werden können. Das Bad hat in diesem Zustand einen pH-Wert im Bereich von unter 1. Im Falle der Zugabe von Saccharin erfolgt diese bevorzugt in die Nickelsalzlösung und vor der Zugabe der Säuren.In the second step are added to the bath:

• 44 ml / l phosphoric acid 85%
• 30 g / l phosphonic acid
• 35 g / l boric acid

The phosphonic acid and the boric acid are solids which can be added as such or else in solution. The bath in this state has a pH in the range of below 1. In the case of the addition of saccharin, this is preferably carried out in the nickel salt solution and before the addition of the acids.

step 3

Subsequently, in the third step or in the first and / or second step, nickel carbonate (NiCO ₃ ) is added until the pH is increased to about 1.8. This can be done, for example, by continuously measuring the pH during the addition of the nickel carbonate and stopping the addition as soon as the desired pH is reached. As a result, on the one hand additional nickel is supplied (about 5 g / l Ni ²⁺ ), and on the other hand, the current efficiency is significantly increased by the increased pH. Increasing the pH by adding nickel carbonate works well up to a pH of about 2.2. At a higher pH, saturation may occur in the bath.

The increase in the pH takes place according to the following reaction equation:

2 H ⁺ + NiCO ₃ → CO ₂ ↑ + H ₂ O + Ni ²⁺

The carbon dioxide (CO ₂ ) escapes as gas.

The increase in the pH can e.g. also by adding alkalis (e.g., sodium hydroxide (NaOH)). The use of nickel carbonate to increase the pH has the advantage that no cations of additional elements enter the bath, but the concentration of the nickel (II), which may have been lowered by the electrodeposition, is increased again.

Step 4

In the fourth step or in the first, second and / or third step, the electrolytic bath is filled with demineralised water (deionized water) to the desired volume.

The preparation of the NiP bath works e.g. good at a temperature of about 40-65 ° C, which are not absolute limits.

Naturally, various modifications and modifications are possible within the scope of the present invention.

For example, other nickel salts or combinations of nickel salts are possible (eg nickel sulfate and nickel chloride (NiCl ₂ )), preferably at least 50% of the nickel (II) comes from the nickel sulfate in the preparation of the bath, more preferably at least 70%.

By heat treatment of the coated substrate (tempering), a further increase in hardness can be achieved.

Claims (12)

1. An electrolytic bath for electrodeposition, comprising in solution:

   a) nickel salt

   b) phosphoric acid

   c) phosphonic acid

   d) boric acid.
2. The electrolytic bath according to claim 1,
   comprising in solution phosphoric acid with a concentration in the range of 60-90 g/l.
3. The electrolytic bath according to claim 1 or 2,
   further comprising in solution phosphonic acid with a concentration in the range of 20-40 g/l.
4. The electrolytic bath according to one of the preceding claims,
   further comprising in solution boric acid with a concentration in the range of 30-40 g/l.
5. The electrolytic bath according to one of the preceding claims,
   further comprising in solution nickel(II) with a concentration in the range of 90-130 g/l.
6. The electrolytic bath according to one of the preceding claims,
   further comprising in solution 0-4 g/l saccharine.
7. The electrolytic bath according to one of the preceding claims,
   having a pH in the range from 1.6 to 2.3.
8. The electrolytic bath according to one of the preceding claims,
   wherein the nickel salt comprises nickel sulfate and wherein more than 50% of the nickel(II) in the bath comes from the nickel sulfate.
9. The electrolytic bath according to one of the preceding claims,
   further comprising in solution sulfate with a concentration in the range of 147-213 g/l.
10. A method for producing an electrolytic bath, the method comprising the steps of:

    A) mixing a nickel salt, phosphoric acid, phosphonic acid, and boric acid; and

    B) adding nickel carbonate to raise the pH.
11. The method according to claim 10,
    wherein the pH of the bath is measured and wherein nickel carbonate is added to raise the pH until a predetermined pH is reached, the predetermined pH being situated preferably in the range from 1.6 to 2.3.
12. A use of an electrolytic bath according to one of claims 1 to 9 for electrodeposition of a nickel-containing layer onto a workpiece.