RU2623514C2 - Electrolyte for galvanic sedimentation of nickel-aluminium coatings - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: electrolyte contains a eutectic mixture of choline chloride and urea, the eutectic mixture being prepared by mixing the components in a molar ratio of 1:2 in which nickel chloride and aluminium chloride are dissolved in an amount of g/l solution: nickel chloride 3.2- 33.0, aluminium chloride 12.5-144.0.

EFFECT: obtaining high-quality thin non-porous coatings and reducing the toxicity of the electrolyte by using environmentally friendly components.

1 cl

Description

The present invention relates to the field of electroplating and may find application in the electronic industry, mechanical engineering and other fields requiring the production of thin protective films or the deposition of a nickel-aluminum sublayer.

The invention relates to the field of applying high-quality thin coatings of nickel-aluminum by an electrolytic method from an ionic electrolyte based on a eutectic mixture of choline chloride and urea. A wide potential window and high stability of the electrolyte make it possible to use it for applying high-quality thin coatings well adhered to the base. The electrolyte, due to the low cost and availability of components, along with low toxicity, can be widely used for coating, providing temperature and corrosion protection of machine parts, as well as in areas requiring thin films or applying a nickel-aluminum sublayer.

Recently, ionic liquids are widely used as electrolytes for current sources. However, their high cost and toxicity do not allow their use as electrolytes for the deposition of films of metals and alloys.

The articles containing information on electrodeposition of nickel using eutectic based on an ionic liquid [1] and [2] describe the possibility of galvanic deposition of a nickel coating from an electrolyte based on a eutectic mixture of choline chloride and urea in a molar ratio of 1: 2 containing nickel chloride ( II) 48 g / l and 124 g / l, respectively.

In an article containing information about an electrolyte for precipitating aluminum from an eutectic-based electrolyte [3], an electrolyte for precipitating aluminum from an electrolyte based on the above-described eutectic in a molar ratio of 1: 1 containing 50 g / l of aluminum (III) chloride is described. The process is carried out at a temperature of 80-95 ° C.

The above methods do not allow the formation of a nickel-aluminum coating at one time. The disadvantages of these electrolytes include the need for the deposition process at high temperatures, which is due to the use in the latter case of a eutectic with a molar ratio of choline chloride and urea equal to 1: 1, which crystallizes at temperatures below 75 ° C.

A known method of forming an iron-aluminum alloy [4] from an electrolyte based on an ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethyl sulfonate ([Py _1,4 ] TfO), containing, g / l: iron (II) chloride 12.7 and chloride aluminum (III) 367.1.

The disadvantage of this electrolyte is the need to carry out the process at a high temperature (100 ° C), the need and complexity of controlling the pH of the medium, the very high cost and use of highly toxic components, which negatively affects the environment.

In the application US 20120189778 A1 (publ. 26.07.2012) electrolytes for galvanic deposition of coatings [5] - aluminum, ionic liquids, including: 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, 1-butyl- 1-methylpyrrolidinium bis (trifluoromethylsulfonyl) amide, 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) amide, trihexyl-tetraadecyl phosphonium bis (trifluoromethylsulfonyl) amide or mixtures thereof.

These electrolytes, as the closest analogues, can be taken as a prototype.

The disadvantages of such electrolytes is the need for precise control of the pH of the medium and its concentration, which requires additional costs and can lead to a deterioration in the quality of the coating. In addition, electrolytes have a very high cost, and the use of highly toxic components negatively affects the environment.

The technical problem to be solved by the claimed invention is directed is the production of thin high-quality non-porous nickel-aluminum coatings from the electrolyte due to the wide potential window, high stability, good leveling ability of the electrolyte at low current efficiency, and also a significant reduction in its cost and toxicity.

This problem is solved due to the fact that the inventive electrolyte for galvanic deposition of nickel-aluminum coatings is a eutectic mixture of choline chloride and urea in a molar ratio of 1: 2, in which nickel chloride and aluminum chloride are dissolved in an amount, g / l of solution: chloride nickel 3.2-33; aluminum chloride 12.5-144.

The technical result provided by the given set of features is the possibility of forming high-quality nickel-aluminum coatings from electrolytes based on ionic liquids, which significantly reduces the cost and toxicity of the electrolyte. A mixture of choline chloride and urea is a eutectic with a melting point of 12 ° C. The use of this eutectic mixture as the basis for the electrolyte is due to its good electrical conductivity, electrochemical inertness in a wide range of potentials, thermal stability, low cost and environmental safety. The use of a eutectic mixture of choline chloride and urea allows one to significantly shift the potentials for the release of aluminum and nickel due to the formation of complex complex ions, due to which there is a joint deposition of these metals, which is observed in the potential range 1200-1400 mV (relative to the silver reference electrode). The use of inert anodes (carbon or platinum) allows you to control the concentration of the main potential-determining ions, which makes it possible to maintain the current output of the metal at a low level to obtain the highest quality and uniform coating. Thus, the use of the eutectic mixture of choline chloride with urea as the basis for the electrolyte contributes not only to obtaining high-quality thin non-porous nickel-aluminum coatings, but also significantly reduces the cost and toxicity of the electrolyte through the use of environmentally friendly components.

The implementation of the invention

The basis for the presented electrolyte is a eutectic mixture of choline chloride and urea, which is prepared by mixing the components in a certain molar ratio of 1: 1.5-1: 4 with little heating. A decrease in the urea content in the solution leads to the formation of a eutectic that crystallizes at temperatures below 75 ° C, which makes it impossible to use an electrolyte at room temperature. The upper boundary is due to the solubility limit of one component in another.

The optimal ratio of choline chloride and urea was 1: 2, at which the widest electrochemical potential window was observed (2.4 V for a platinum electrode).

Based on this eutectic mixture, several electrolytes of various concentrations were prepared for aluminum (III) and nickel (II) chlorides, the ratio between which was taken equal to 3: 1.

In this case, aluminum (III) chloride was added in the range of 12.5-144.0 g / L. The upper limit corresponds to the maximum solubility of aluminum (III) chloride in the eutectic, the lower limit is due to the minimum noticeable rate of the process of deposition of aluminum.

The content of Nickel (II) chloride in the proposed electrolyte is in the range of 3.2-33.0 g / l. The upper limit corresponds to the maximum viscosity of the electrolyte. When the content of Nickel (II) chloride is less than 3.2 g / l, the performance of coatings is significantly deteriorated.

The electrodeposition process was carried out at a temperature of 25-30 ° C and current density j = 0.2-2.5 A / dm ² . The lower current limit is due to the onset of the co-precipitation of aluminum and nickel at j = 0.2 A / dm ² . At a cathodic current density above j = 2.5 A / dm ² , local destruction of the electrolyte occurs in the cathode region, the coating forms poor quality, poorly adhered to the substrate.

As a cathode, a copper plate was used, the covered area of which was 5 cm ² . A graphite electrode served as an anode. The surface of the copper plates was carefully prepared, degreased and polished before application. For the application process, direct current was used. The thickness of the coatings was calculated by the standard weight method.

A prototype was made in which an electrolyte prepared as follows was used to apply high-quality nickel-aluminum coatings.

Choline chloride and eutectic in a molar ratio of 1: 2 were mixed in a container and kept with insignificant heating for 3 hours. To obtain 100 ml of eutectic, 64 g of choline chloride and 55.6 g of urea were taken. Then, in the obtained 100 ml of eutectic, 7.4 g of aluminum (III) chloride and 1.7 g of nickel (II) chloride were dissolved at a temperature of 80-90 ° C for 8 hours. The resulting electrolyte was a homogeneous transparent viscous (~ 4310 mPa⋅s) green solution. The conductivity of the solution at a temperature of 25 ° C ~ 610 μS / cm, the electrochemical potential window relative to the silver electrode is 1.27- + 1.34 V.

From the resulting solution at a temperature of 25 ° C and current density j = 0.5 A / dm ² for 1 hour, high-quality non-porous nickel-aluminum coatings 300–400 nm thick were obtained, which have good adhesion to the substrate and have high corrosion and thermal barrier properties .

Using the proposed electrolyte allows you to get high-quality thin films of Nickel-aluminum; carry out the process in low temperature conditions; minimize cost and toxicity.

Information sources:

1. Abbott A.R., El Ttaib K., Ryder K.S. and Smith E.L. // Electrodeposition of nickel using eutectic based ionic liquids / Transactions of the Institute of Metal Finishing, V. 86, No. 4, p. 234-240, 2008.

2. Liana Anicail, Andreea Floreal and Teodor Visan Studies // Regarding the Nickel Electrodeposition from Choline Chloride Based Ionic Liquids / Applications of Ionic Liquids in Science and Technology, p. 261-286, 2011.

3. Thanh-Cong Huynhl, Quang PD Dao and etc. // Electrodeposition of Aluminum on Cathodes in Ionic Liquid Based Choline Chloride / Urea / AlCl ₃ / Environment and Pollution, V. 3, No. 4, p. 59-69 2014.

4. Giridhar P., Weidenfeller B. // Electrodeposition of iron and iron-aluminum alloys in an ionic liquid and their magnetic properties / Phys. Chem. Chem. Phys., No. 16, p. 9317-9324, 2014.

5. Application US 20120189778 A1 (publ. 26.07.2012) Electrolytes for galvanic deposition of coatings (prototype).

Claims (1)

An electrolyte for galvanic deposition of a nickel-aluminum coating containing a eutectic mixture of choline chloride and urea obtained by mixing the components in a molar ratio of 1: 2, in which nickel chloride and aluminum chloride are then dissolved in an amount, g / l of solution: nickel chloride 3 2-33.0; aluminum chloride 12.5-144.0.