JP3224401B2 - Electrodeposition method of metal coating - Google Patents

Abstract

A process for electrodepositing a metallic coating, mainly composed of a nickel-cobalt alloy, on a surface of an object, in particular a strip-iron, by means of an electrolysis bath wherein at least one insoluble anode is arranged in a substantially chloride-free electrolyte solution which comprises at least nickel sulfate, cobalt sulfate, boric acid and sulfuric acid, according to which process at least said surface is immersed in the electrolyte solution and an electric tension of such a value is applied between said anode and the object acting as cathode that near said surface, a current density of at least 30 A/dm<2> is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a method for coating a surface of an object, especially the surface of an iron of a strip, with a metal coating mainly composed of a nickel-cobalt alloy, comprising substantially at least nickel sulfate, cobalt sulfate and boric acid. Using an electrolytic bath in which at least one anode is placed in a solid electrolyte solution, immersing at least the surface in the electrolyte solution, and applying a voltage between the anode and the object serving as the cathode. It relates to a method for electrodeposition.

Such a process is described in the paper "les bains de nickel-cobalt brillants" (bright nickel-cobalt bath) published in the periodicals "Galvano" n ° 401, pp. 487-491, June 1970. Is disclosed. This paper,
Some examples of electrolytic baths for simultaneous electrodeposition of nickel and cobalt are described. Electrolysis is at most 10A / dm
It operates at a low current density of ² and utilizes a soluble anode to deposit nickel and cobalt. In this article, only the SCHEER bath contains a solution containing nickel sulfate, cobalt sulfate and boric acid. The SCHEER bath contains 110 g / 1 nickel sulfate, 390 g / 1 cobalt sulfate, 25 g / 1 boric acid, and additionally 7.5 mg / 1 potassium cyanide sulfate. The electrolysis is performed at a temperature of 60-80 ° C. and with a current density of 10 A / dm ² .

A problem that arises when using a SCHEER bath is that the nickel content of the nickel-cobalt alloy electrodeposited on the surface is low as a result of the nickel being more readily precipitated than cobalt. Therefore, to solve this problem, the electrolyte solution is required to contain a relatively high concentration of cobalt to ensure that the cobalt content of the electrodeposited coating is adequate. However, this solution is not economical and inefficient.

[0004] It is an object of the present invention to provide a method of depositing cobalt in a satisfactory manner without hindering nickel deposition and without having to increase the cobalt concentration in the electrolyte solution.

To this end, the method according to the invention comprises carrying out the electrolysis in an electrolyte solution to which sulfuric acid has been added,
And the voltage applied between the cathode and the substantially insoluble anode is at least 30 A /
The voltage is a value such that a current density of dm ² is realized. By using high current densities in the above-mentioned baths, good quality nickel-cobalt deposits are simultaneously obtained. By using a current density of at least 30 A / dm ² , the deposition process proceeds in a faster and more efficient direction. The surprising effect of applying a higher current density is that it guarantees that cobalt is already present throughout the deposited coating even at low cobalt contents in the electrolyte solution, because the cobalt is more easily deposited. . This higher current density requires the use of an insoluble anode. Sulfuric acid
Added to the electrolytic bath to increase the conductivity of the bath.

In a preferred embodiment of the method according to the invention, the applied voltage is such that the current density is between 50 and 300 A / dm ^2.
In particular, the voltage has a value of 240 to 250 A / dm ² . The best quality of precipitates is current density between 240 and 2
It was found that it could be obtained at 50 A / dm ² . In fact, a homogeneous coating was obtained at these current densities.

[0007] Preferably, a solution having a sodium sulfate concentration up to the limit of solubility is used as the electrolyte solution.
This maximum is imposed by the solubility of the sodium sulfate in the bath. Exceeding this value will have a negative effect on the appearance of the precipitate.

Preferably, the concentration of boric acid is about 30 to 60 g.
/ 1, preferably about 50 g / 1 and a sulfuric acid concentration of about 5 to 15 g / 1, more preferably about 10 g / 1, is used as the electrolyte solution. A sulfuric acid concentration of 10 g / 1 has a very favorable effect on the conductivity, but does not have a negative effect on the Faraday efficiency.

A preferred embodiment of the process according to the invention is characterized in that the electrolysis is carried out at a temperature of from 50 to 80 ° C., preferably at a temperature of about 70 ° C. In this temperature range, the object is not subject to high thermal constraints.

[0010] Preferably, the surface of the object and the anode are arranged in a substantially parallel relation to each other;
The electrolyte solution is then injected between this surface and the anode. This makes it possible to obtain a good stirring state of the electrolyte in the bath.

[0011] Other features and advantages of the present invention will become apparent from the following description of a method for electrodepositing a nickel-cobalt alloy according to the present invention. This description is given for the sake of example only, without limiting the scope of the invention. In the following, the invention will be described with reference to FIG. 1, which shows a schematic sectional view of an electrolytic cell for applying the method according to the invention.

The present invention relates to a method for electrodepositing a metal coating mainly composed of a nickel-cobalt alloy on the surface of an object, in particular on an iron or iron plate of a strip. This electrolysis comprises, for example, two anodes 2, 3 which are preferably plate-shaped anodes arranged horizontally and in a substantially parallel relation to each other as schematically illustrated in FIG. This is carried out using the electrolytic cell 1 during which the electrolyte solution 5 is injected according to the arrow 4 using the injection device 12 at a speed in the range of 3 m / s. The electrolytic cell 1 also includes chutes 6 and 7 for collecting the electrolyte solution 5, which can then be thickened and then injected again between the two anodes 2 and 3. When thickening the electrolyte solution, at least nickel sulfate and cobalt sulfate are added to keep the bath composition substantially constant.

The iron 8 of the strip is guided between the two anodes 2 and 3 in the direction indicated by the arrow 9 by means of rollers 10 and 11 constituting conductors. Roller 1
The iron of the strip in direct electrical contact with 0 and 11 thus constitutes the cathode. The voltage is applied to a cathode and anodes 2 and 3 composed of strip iron 8 such that a predetermined current density is achieved on both sides of the strip iron 8 using a DC power supply not shown in the figure. Is applied between
If necessary, this voltage, and thus the current density, can be separated on each side of the strip iron 8, so that different amounts of nickel-cobalt alloy are deposited on both sides of the strip iron 8. Good. The electrolytic cell may also include a single anode that deposits a nickel-cobalt alloy on only one side of the strip iron.

The anodes 2 and 3 used are substantially insoluble anodes, for example composed of a lead-silver anode or a titanium anode coated with a noble metal such as ruthenium or iridium. Since such an anode does not supply any nickel or cobalt, the electrolyte solution must contain all the nickel and cobalt to be electrodeposited. Furthermore, the electrolyte solution must be virtually free of chlorides, in particular to prevent corrosion of the anode.

The use of the method according to the invention makes it possible to electrodeposit a good quality metal coating on the iron 8 of the strip. For this purpose, according to the invention, a chloride-free solution comprising at least nickel sulphate, cobalt sulphate, boric acid and sulfuric acid is used, and this is combined with a cathodic current density of at least 30 A / dm ² . Comparative tests have shown that, due to this combination, it is possible to obtain homogeneous precipitates with a fine grain structure, especially after tempering high-quality metal precipitates, which are meant here.

Compared to the theory developed in the state of the art, a cathodic current density of 0 to 13 A / dm ² is applied, since cobalt is more easily deposited by applying a high cathodic current density. It has been found that the cobalt content in the nickel-cobalt alloy increases as compared to a coating deposited by a known method of co-precipitating cobalt. According to the state of the art, at low current densities in this range, it is known that increasing the current density reduces the cobalt content in the deposited nickel-cobalt alloy. However, substantial use of insoluble anodes in accordance with the present invention, and by applying a current density of. 30 to 300A / dm ^2, cobalt content in the deposited alloy is more, by increasing cathodic current density It has been found that the more cobalt the higher the content.

In a preferred embodiment of the method according to the invention, 5
A current density of 0-300 A / dm ² , preferably 150-300 A / dm ² is applied. A current density of at least 150 A / dm ² has the advantage that cobalt deposits very easily, so that a low cobalt content in the electrolyte solution does not cause any problems in obtaining a homogeneous nickel-cobalt alloy. provide. For example, applying a cathodic current density of 240-250 A / dm ² and obtaining a deposited nickel-cobalt alloy coating having a cobalt content of about 2% by having the electrolyte solution contain 0.2% cobalt sulfate. Can be. To enable such high current densities, the electrolyte solution used must meet certain conditions, such as, for example, those relating to conductivity.
To achieve high quality deposits, it is also necessary to combine the specific composition of the electrolytic bath with these high current densities.

Thus, in a preferred embodiment of the present invention,
An electrolyte solution containing about 30-60 g / 1, preferably 50 g / 1 boric acid and about 5-15 g / 1, preferably 10 g / 1 sulfuric acid is used. By using boric acid and sulfuric acid together, it is possible to combine good conductivity with good Faraday efficiency. In fact, the sulfuric acid used has a positive effect on conductivity but negatively on Faraday efficiency, while boric acid has a positive effect on Faraday efficiency but slightly reduces conductivity. .

Furthermore, the Faraday efficiency is also affected by the temperature of the electrolyte solution during the electrolysis, which is equal to 50-80 ° C., preferably substantially equal to 70 ° C. As this temperature rises, it has a beneficial effect on Faraday efficiency,
The rise in temperature is limited as a result of the technical constraints of the substance. Stirring the electrolyte solution by injecting the electrolyte solution between the two anodes also increases Faraday efficiency. In addition, sodium sulphate, more precisely an amount up to the limit of the solubility of sodium sulphate, may be added to the electrolyte solution. The addition of sodium sulfate also increases the conductivity of the electrolyte solution. That said,
The amount of sodium sulphate added should not be too high, as too much will negatively affect the appearance of the precipitate.

The electrolyte solution used in a preferred embodiment is
It contains about 200-270 g / 1, preferably 222-242 g / 1 nickel sulphate. It is particularly preferred that the amount of nickel sulfate is about 232 g / 1. This solution further contains cobalt sulfate starting from the lowest concentration of about 0.1% of the electrolyte solution. It has been found that by combining such a particular electrolyte solution having a relatively low nickel sulfate content with the high current densities described above, high quality deposits can be obtained. Another advantage of the higher current density is that the deposition proceeds at a faster rate.

With regard to the quality of the metal deposits obtained by applying the method according to the invention, it has been determined experimentally that a uniform metal deposit which is very finely divided due to the high current density can be obtained. Was found. Due to the fine grain structure, the deposits are very resistant to corrosion and bright due to the high density of the coating. As a result of the uniform growth of the coating during the electrolysis, a homogeneous layer of substantially uniform thickness is deposited. Thus, even the smallest thicknesses, possibly less than 0.5 μm, are already sufficient to deposit a good corrosion resistant metal coating. A considerable amount of the metal to be deposited in this way can be saved by using the method according to the invention. This method further increases the electrical performance of the metal deposit. The presence of cobalt in the deposited coating has a positive effect on the corrosion resistance and hardness of the deposit without reducing the possibility of stamping. In addition, cobalt increases the melting temperature of the nickel-cobalt alloy, and this significantly reduces the problem of sticking together when quenching the iron rolls of the strip.

It will be apparent that various modifications of the above-described embodiments of the method according to the invention may be made without departing from the scope of the invention.

In this way, the metal coating can be applied not only to the iron of the strip but also to other objects, possibly even objects of another material, for example a material previously coated with copper. . Other substances that also affect the deposited metal coating can be added to the electrolyte solution. Examples of these substances are brighteners.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an electrolytic cell for applying a method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electrolysis tank 2 ... Anode 3 ... Anode 5 ... Electrolyte solution 8 ... Target object 12 ... Electrolyte solution injection apparatus

Continuation of the front page (56) References JP-A-62-56591 (JP, A) JP-A-57-29599 (JP, A) JP-A-3-20492 (JP, A) JP-A-52-153834 (JP) , A) JP-B-58-43469 (JP, B2) JP-B-56-22958 (JP, B2) JP-B-59-9637 (JP, B2) Plating Technology Handbook Editing Committee, "Plating Technology Handbook" (Showa July 20, 1958), see Nikkan Kogyo Shimbun, page 37, “Electrolytic Bath Concentration”, Plating Association of Japan, “Practical Plating for Field Engineers (III)” (Showa 63.5) 25), Maki Shoten, p. 24 (58) Fields surveyed (Int. Cl. ⁷ , DB name) C25D 7/06 C25D 3/56 C25D 5/26

Claims (16)

(57) [Claims] 1. A method for electrodepositing a metal coating mainly composed of a nickel-cobalt alloy on a surface of a cathode using an electrolytic bath, wherein the electrolytic bath comprises a chloride containing nickel sulfate, cobalt sulfate and boric acid. An electrolyte solution having no electrolyte, at least one insoluble anode, and immersing a surface of the cathode in the electrolyte solution;
Adding sulfuric acid to the electrolyte solution, and applying a voltage between the at least one insoluble anode and the cathode so as to achieve a current density of at least 30 A / dm ² near the surface of the cathode. Electrodeposition method of metal coating. 2. The method according to claim 1, wherein the cathode is an iron strip. 3. The current density is 50 to 300 A / dm2.
The electrodeposition method of a metal coating according to claim 1, wherein 4. The current density is 150 to 300 A / dm.
4. The method according to claim 3, wherein the thickness is in the range of ² . 5. The current density is 240 to 250 A / dm.
^The method for electrodepositing a metal coating according to claim 4, wherein the value is within the range of ² . 6. The method of claim 1, wherein the electrolyte solution has a concentration of sodium sulfate up to a solubility limit. 7. The method according to claim 1, wherein the concentration of the nickel sulfate in the electrolyte solution is in a range of 200 to 270 g / l. 8. The method according to claim 7, wherein the concentration of the nickel sulfate in the electrolyte solution is in a range of 222 to 242 g / l. 9. The method according to claim 8, wherein the concentration of the nickel sulfate in the electrolyte solution is 232 g / l. 10. The method according to claim 1, wherein the concentration of the boric acid in the electrolyte solution is in a range of 30 to 60 g / l. 11. The method according to claim 1, wherein the concentration of the boric acid in the electrolyte solution is in a range of 50 g / l.
0. The method for electrodeposition of a metal coating according to 0. 12. The method according to claim 1, wherein the concentration of the sulfuric acid in the electrolyte solution is in the range of 5 to 15 g / l. 13. The method according to claim 12, wherein the concentration of the sulfuric acid in the electrolyte solution is in a range of 10 g / l.
3. The method for electrodepositing a metal coating according to claim 1. 14. The temperature of the electrolyte solution is 50 to 8 degrees Celsius.
The method according to claim 1, wherein the angle is within a range of 0 degrees. 15. The method according to claim 14, wherein the temperature of the electrolyte solution is in a range of 70 degrees Celsius. 16. The method according to claim 1, wherein the at least one insoluble anode is a lead-silver anode.