JPH10102300A - Method for controlling plating solution for plating iron-containing metal using insoluble anode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for controlling the composition of a plating soln. for stabilization in the iron-contg. metal plating using an insoluble anode. SOLUTION: A plating soln. contg. >=1 kind among ferrous ion, sulfate ion, chlorine ion and sulfamic acid ion and urea or a pH regulator, if necessary, an insoluble anode and the cathode of a metallic material to be plated are used in this method for plating an iron-contg. metal using the cathode of a metallic material to be plated. Namely, a plating bath is brought into contact with metallic iron, >=7 one kind among ferrous sulfate, ferrous chloride and ferrous sulfamate are added to the soln., and the ferrous ion concn. in the bath is controlled to a desired value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for managing a plating solution when a metal material is plated with an iron-containing metal (iron or iron alloy) using an insoluble anode.

[0002]

2. Description of the Related Art At present, iron and iron alloys represented by iron and steel are widely used as various structural materials and industrial products.
It is a very important material both in quality and quantity industrially. on the other hand,
Iron coatings manufactured using the electrodeposition method are used for repairing steel parts, manufacturing iron foil, manufacturing high-purity iron, and have relatively limited uses such as magnetic materials and magnetic shielding materials that use the ferromagnetism. It is only used for

[0003] In recent years, there has been a growing demand for improved fuel efficiency of automobiles in terms of global environmental protection including global warming.
Along with this, the transition from cast iron to aluminum alloy has become remarkable in order to reduce the weight of constituent materials of internal combustion engines. Aluminum alloy materials are not only lightweight,
Because of its excellent heat dissipation characteristics, it is effective for improving the efficiency of the internal combustion engine and has an excellent effect of being inexpensive. Aluminum alloy piston for internal combustion engine,
When used as sliding members such as cylinders, hydraulic pumps, pneumatic pumps, and rotary compressors, the aluminum alloy itself has poor wear and seizure resistance, so its surface must be coated with a material that is harder than the aluminum alloy itself. It is.

[0004] Specific examples of such a high hardness coating material include hard chromium plating and Ni plating in which SiC or the like is dispersed. The former has a problem that the wettability with lubricating oil is poor and the oil retaining effect is inferior, and the wastewater treatment cost increases because the plating wastewater contains hexavalent chromium ions. In addition, the latter is excellent in seizure resistance, but has a problem that the wear resistance is inferior. Therefore, in order to solve these problems, several methods for forming an electric iron plating film on the surface of an aluminum alloy have been proposed.

In order to improve abrasion resistance and seizure resistance, a plating film having high hardness is required. JP-A-51-
No. 126935 discloses that an iron-phosphorus alloy plating base material layer containing 0.015 to 10% by weight of phosphorus contains a particle diameter of 0.1 to 10% by weight.
Means for solving the above problem by dispersing a solid lubricant of 30 μm or a high-hardness solid is described. Also, Japanese Patent Publication No. 56-18678 discloses that
Electroplating is performed using an aqueous solution in which one or more compounds containing carbon, boron, phosphorus, nitrogen or sulfur are mixed and contained in a water-soluble iron salt, and one or more of the above elements are contained in the formed iron film. A method is described in which a trace amount of eutectoid is deposited, and then the iron film is heat-treated. In these prior arts, a non-polluting plating solution that does not contain chromium is used, and a low-cost iron or iron alloy film with excellent wear resistance and seizure resistance can be obtained, and a longer life for sliding members has been achieved. You can do it.

In the above prior art, iron is used as an anode. However, when a soluble metal such as iron is used as an anode (anode), the shape of the anode changes due to its consumption, so that precise plating is difficult. And also
There are major drawbacks, such as the need to perform maintenance frequently in response to the consumption of the anode. Therefore, it is desirable to use an insoluble anode material as the anode. When an anode made of an insoluble material is applied to an iron plating solution, the following two oxidation reactions (1) and (2) occur on its surface. 2H ₂ O → O ₂ + 4H ⁺ + 4e (e: electron) (1) Fe ²⁺ → Fe ³⁺ + e (2)

Among them, in the chemical reaction (1), oxygen is generated, and hydrogen ions remain in the plating solution, so that the pH of the plating solution drops. On the other hand, the chemical reaction (2) oxidizes ferrous ions and causes ferric ions formed thereby to accumulate in the plating solution. Therefore,
In order to cope with the change in bath composition due to these two reactions (1) and (2) in the plating solution, it is most common to bring metallic iron into contact with the plating solution. That is, by using metallic iron, a reaction of reducing hydrogen ions to increase pH as shown in the following formula (3),
It is possible to utilize the reaction of reducing ferric ions and returning them to ferrous ions as shown in the following formula (4). In addition, these reactions (3) and (4) can be performed together with replenishment of ferrous ions consumed by plating. Fe + 2H ⁺ → Fe ²⁺ + H ₂ (3) Fe + 2Fe ³⁺ → 3Fe ²⁺ (4)

[0008] For example, the technique described in Japanese Patent Application Laid-Open No. 58-151489 is directed to zinc-iron alloy plating, in which a plating solution is circulated through a filling tank filled with a metal filler. Thus, ion supply and suppression of accumulation of ferric ions are realized, and as the metal filler, a metal filler to be dissolved and a metal filler having a more electrochemically noble potential are used. It is disclosed that the use of a coexisting one is more effective. The technique described in JP-A-59-126799 is based on a technique in which a powdery or granular metal is added to a reaction tank connected to a plating tank and circulating a plating solution to supply a plating metal ion and a second step. In the case of performing the reduction of ferrous ions, by collecting unreacted metal powder or particles that carry over from the reaction tank, and by recycling this to the reaction tank,
The purpose is to increase the utilization efficiency of metal powder or granules.

As described above, several techniques have been disclosed for using an insoluble anode for iron or iron alloy plating by bringing metallic iron into contact with a plating solution. Equations (3) and (4) have been disclosed. There is no example referring to the reaction rate of the chemical reaction as shown in FIG. Simply contacting the metallic iron with the plating solution only causes the equations (3) and (4) to occur at a certain rate, but cannot control the reaction rate thereof. The decrease in pH due to the reaction (1) not only lowers the current efficiency of the plating, but also has adverse effects such as promoting pit formation and decreasing the ductility of the film. The formation and accumulation of ions not only lowers the plating current efficiency, but also causes a precipitate to form in the plating solution and be taken into the film, and if this reaction becomes excessive, the plating solution itself becomes suspended. There is a risk that the continuation of the operation may become impossible. According to the experience of the present inventors, when an insoluble anode is applied to many iron plating baths, the reaction ratio of the reaction (1) and the reaction (2) is represented by 40 to 80% in terms of the participation ratio of electrons. Since this ratio fluctuates depending on various conditions, the reaction (3) and the reaction (4) are taken as measures to prevent this fluctuation.
If it cannot be controlled in a timely manner, stable operation of iron or iron alloy plating is impossible. Furthermore, the dissolution rate of metallic iron is also a major problem. Generally, the rate of dissolution of a metal by an acid is much slower than that of dissolving a salt thereof. Therefore, if the supply of ferrous ions depends only on metallic iron, an extremely large metallic iron melting facility is required, resulting in a disadvantage that the facility cost becomes enormous.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to simplify the equipment for dissolving metallic iron by individually controlling the drop of pH and the accumulation of ferric ions in iron-containing metal plating using an insoluble anode. The object of the present invention is to provide a method for managing a plating solution for iron-containing metal plating using an insoluble anode, which enables the formation of a stable quality iron-containing metal plating film by enabling the stable management of the plating solution composition. It is assumed that.

[0011]

Means for Solving the Problems The present inventors have intensively studied to solve the technical problems of the prior art, and as a result, a step of bringing a plating solution into contact with metallic iron; It has been found newly that the above object can be achieved by simultaneously performing both steps of adding a ferrous salt of an anion such as chloride ion and sulfate ion to the plating solution, thereby completing the present invention.

[0012] The method for managing a plating solution for iron-containing metal plating using an insoluble anode according to the present invention comprises ferrous ions and at least one anion selected from sulfate, hydrochloric and sulfamate. A method for forming an iron-containing metal plating film on a surface of the metal material by performing an electrolytic treatment using an anode made of an insoluble electrode material and a cathode made of a metal material as a plating solution, wherein (1) Contacting metallic iron, and at the same time, (2) adding at least one ferrous salt selected from ferrous sulfate, ferrous chloride and ferrous sulfamate to the plating solution, The present invention is characterized in that the concentration of ferrous ions in a plating solution is controlled to a desired value.

[0013] In the plating solution management method of the present invention, the amount of ferric ion contained in the plating solution and the amount of ferrous ion that is consumed in the reduction reaction of the ferric ion out of the metallic iron in contact with the plating solution is determined. It is desirable to control to 20 to 100% of the total weight of metallic iron. In the plating solution management method, it is preferable that the plating solution further contains urea. Further, in the plating solution management method, the pH value of the plating solution can be adjusted using at least one selected from hydroxides of alkali metals and ammonia. Further, in the plating solution management method of the present invention, in the plating solution, a concentration of at least one anion selected from sulfate ions, chloride ions, and sulfamic acid ions, and a concentration selected from alkali metal ions and ammonium ions. It is preferable to dilute the plating solution so that at least one concentration does not exceed a predetermined upper limit.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The plating solution management method of the present invention is applied to a plating method using an insoluble electrode material as an anode. Examples of such insoluble electrode materials include graphite, lead and platinum. Further, in order to suppress the generation of ferric ions in the plating solution as much as possible, as an insoluble electrode material, a material having a low oxygen overvoltage,
For example, it is also preferable to use an electrode or the like in which a noble metal oxide is coated on a titanium alloy substrate.

The present invention cannot be realized without introducing metallic iron into the plating bath among the chemical reactions (3) and (4) essential for the plating method for iron or iron alloy plating using an insoluble anode. The reaction is based on reaction (4). Conversely, if the reaction (4) can be preferentially caused by other means, it is possible to reduce dependence on metallic iron which is difficult to handle in dissolving workability and the like. That is, in the present invention, the problem of insufficient supply of ferrous ion which occurs when the reaction (4) by metallic iron is prioritized is solved by the addition of ferrous salts of sulfuric acid, hydrochloric acid and sulfamic acid, which are easily dissolved. It will be resolved. Of course, these additives may be prepared in a high concentration aqueous solution in advance, and such an aqueous solution is convenient for automatic replenishment using a pump or the like.

Specifically, the ratio of the amount of metallic iron involved in the reaction (4) to the total amount of metallic iron charged is 20 to 1
It is preferably 00%, more preferably 50 to 100%. If it is less than 20%, the simple dissolution reaction of metallic iron of reaction (3) becomes dominant, and therefore, the concentration of ferrous ion in the plating solution becomes excessive, which is not preferable. Generally, in such a plating solution, the ferrous ion concentration is operated at a high concentration near the solubility upper limit, so that an excess of ferrous ion causes precipitation and precipitation of ferrous salt to prevent it. Requires a large amount of plating solution, which is economically disadvantageous. Furthermore, since reaction (3) involves the consumption of hydrogen ions, near metallic iron
There is a risk that a pH rise occurs and precipitates are generated in the plating solution. For this reason, it is not preferable that the ratio of the amount of metal iron which contributes to the reaction (3) is too large.

In order to control the ratio of the amount contributing to the reaction (4) in the total amount of the metallic iron to 20 to 100% as described above, it is empirically determined that the metallic iron and the plating solution are mixed. Measures may be taken to increase the contact reaction rate. In other words, as the metallic iron, using the finest possible shape, for example, iron powder, for the metal-containing plating solution,
It is to give as strong stirring as possible. Since the particle size of the iron powder depends on the stirring method and equipment factors such as its strength, it cannot be strictly defined, but it is preferable to use iron powder of at least 100 mesh under, whereby the ratio is reduced. It is possible to maintain 50% or more.

Since the ratio can be increased by increasing the reaction rate of metallic iron, it is possible to reduce the scale of the equipment for dissolving metallic iron, It is possible to obtain a favorable effect on plating operation, for example, it is possible to prevent precipitation or the like from occurring by alleviating a rise in pH in the vicinity of iron. Also, excessive input of metallic iron is clearly not preferred. That is, the addition of excess metallic iron causes the disappearance of the ferric ions to be reduced, whereby all the remaining metallic iron contributes to the reaction (3), and therefore the ratio of the contribution to the reaction (4) is It will be less than 20%.

Next, the management method of the present invention is more effective for an iron or iron alloy plating solution to which urea is added. The reason is that when the pH of the plating solution drops, urea in the plating solution is hydrolyzed to release carbon dioxide gas, leaving ammonium ions in the plating solution. That is, the urea decomposition reaction occurs preferentially in a portion where pH is locally lowered (due to the reaction (1)), such as in the vicinity of an insoluble anode, and the pH is adjusted by introducing an alkali metal hydroxide or aqueous ammonia described later. The same pH adjustment is performed automatically. Therefore, in the case of an iron or iron alloy plating solution containing urea, the drop in pH caused by using an insoluble anode is automatically eliminated by urea, so that there is no need for a step of intentionally adjusting the pH. The urea addition amount for obtaining the above effects is preferably in the range of 0.1 to 2.5 mol / liter, and 0.3 to 2.0 mol / liter.
More preferably, it is liter.

On the other hand, when urea is added to the iron or iron alloy plating solution, the plating film formed on the metal material (cathode) is given a luster or has an increased hardness. May change physical properties.
In order to avoid this, when urea is not added, the pH of the plating solution is adjusted to a desired value by adding an alkali metal hydroxide and / or aqueous ammonia against the pH drop caused by the above-mentioned reaction (1). Value can be adjusted.

As the above-described plating step proceeds, as a result, the concentration of pH adjusting components such as alkali metal ions and ammonium ions and the concentrations of anions such as sulfate ions, chloride ions and sulfamate ions gradually increase. The increase in these concentrations is rather preferable in plating operation because it increases the electrical conductivity of the plating solution.However, when the concentration of these chemicals exceeds the upper limit of the solubility, the excess only causes precipitation, so far. It becomes impossible to adjust the effective chemical concentration for the plating solution described above. Therefore, in order to regulate these concentrations so as not to exceed the upper limit, the plating solution may be diluted with water. At this time, if necessary
A part of the plating solution may be discarded out of the system. This plating solution may be partially discarded at a fixed rate. Actually, at the end of plating, the amount of the plating solution that adheres to the metal material for plating and is taken out of the system should be taken into consideration. Therefore, the amount of waste is determined according to the amount of the taken-out solution. This means that at the same time, some of the second ions, which are not preferable for the plating operation, are discarded out of the system, so that the burden on the reduction reaction of metallic iron is reduced.

[0022]

The method of the present invention will be specifically described with reference to the following examples and comparative examples.

Example 1 A 2 liter iron plating bath having the following composition was prepared:
A continuous operation test of iron plating was performed using an insoluble anode (an electrode coated with iridium oxide on a titanium substrate) as an anode and a copper plate (target area: 25 cm ² ) as a cathode. At this time, the temperature of the plating bath was 60 ° C.
And the cathode current density was set to 50 A / dm ² . Plating bath composition Ferrous sulfate heptahydrate 400 g / L Urea 90 g / L Ammonium sulfate 50 g / L (Adjust pH to 2.0 using sulfuric acid)

When the amount of electricity becomes 20 k coulombs / liter, the concentration of ferric ion in the bath rises to about 8 g / l. Therefore, an appropriate amount of iron powder is charged and stirred to remove ferric ions in the bath. The solution was reduced to ions and the plating solution was analyzed at the same time, and the concentrations of other components were adjusted in accordance with the analysis results.
This operation was repeated until the total amount of electricity passed became 500 kC / L. For energization at 20 k coulomb / liter, three plating substrates were prepared, and this energization was performed three times.

In the first embodiment, the amount of electricity supplied is 20 k
For every coulomb / liter plating, 50 ml of the plating solution is discarded out of the system, water is added to adjust the level of the solution, and 5 g of iron (Fukuda Metal Fe-S-200: 200
The liquid composition was adjusted by adding 13 g of ferrous sulfate heptahydrate and 6.5 g of urea. This operation could be repeated without any abnormality until the total amount of electricity passed was 500 kC / L. The final solution composition of the plating bath is ferric ion concentration: 79.1 g
/ Liter (at the time of bathing: 80.4 g / l), urea concentration: 87.3 g / l (at the time of bathing: 90 g / l), sulfate ion concentration: 189 g / l (at the time of bathing:
175 g / l) and ammonium ion concentration:
The amount was 20.7 g / liter (at the time of bathing: 13.7 g / liter), and the continuous operation could be completed without a large variation in composition as compared with the composition at the time of bathing. The dissolving operation of the iron powder in these experiments was completed in about 1 hour. From the analysis results of the ferric ion before and after the introduction of the iron powder, the amount of the iron powder involved in the reaction (3) (reduction of ferric ion) was determined. The calculated ratio was 80%.

Example 2 The same continuous operation test as in Example 1 was performed. However, instead of the iron powder used in Example 1, iron particles having a larger particle size (FEEO1GA manufactured by Kojundo Chemical Laboratory: iron particles of 0.5 to 1 mm) were used. After discarding 80 ml of plating solution out of the system for every plating of 20 k coulombs / liter of electricity,
Water was added to adjust the liquid level, and 10 g of iron powder (Fe-S-200 manufactured by Fukuda Metal: iron powder of 200 mesh),
The liquid composition was adjusted by adding 5 g of ferrous sulfate heptahydrate and 9.1 g of urea. Also in Example 2, the plating operation was performed with a total energized electricity amount of 500 kC /
It could be repeated without any abnormalities until it reached liters. The final liquid composition is as follows: ferric ion concentration: 88 g / liter (at the time of building bath: 80.4 g / liter), urea concentration: 92.3
g / l (90 g / l at bath), sulfate ion concentration: 179 g / l (175 g / l at bath) and ammonium ion concentration: 14.1 g / l (13.7 g / l at bath). As a result, there was no large variation in the composition compared to the liquid composition at the time of the bathing, and the continuous operation could be completed. In the case of the experiment of the present Example 2, the dissolving operation of the iron powder was required for about 4 hours. From the analysis results of the ferric ion before and after the introduction of the iron powder, the reaction (3) (the ferric ion The ratio of the amount of iron powder involved in the reduction) was calculated to be about 40%.

Example 3 A continuous operation test similar to that of Example 1 was performed. However, a plating bath obtained by removing urea from the plating bath of Example 1 was used. The energization at 20 k coulomb / liter was performed three times, and the pH after each plating was measured to be 1.8.
Since the pH had dropped to the extent, the plating bath pH was adjusted to 2.0 using aqueous ammonia. After discarding 40 ml of the plating solution out of the system every time 20 k coulombs / liter is supplied, water was added to adjust the liquid level, and 5 g of iron powder (Fe-S-200: 200 mesh of Fukuda Metal Co., Ltd. (Iron powder) and 13 g of ferrous sulfate heptahydrate to adjust the liquid composition. This operation can be repeated without any abnormality until the total amount of supplied electricity reaches 500 kC / L, and the final liquid composition is a ferric ion concentration of 80.6 g / liter.
Liter (at the time of bathing: 80.4 g / l), sulfate ion concentration: 165 g / l (at the time of bathing: 175 g / l), and ammonium ion concentration: 12.8 g / l (at the time of bathing: 13.7 g / l) Thus, there was no large variation in the composition compared to the liquid composition at the time of building the bath, and the continuous operation could be completed. The dissolving operation of the iron powder in these experiments was completed in about one hour, and based on the analysis results of the ferric ion before and after the introduction of the iron powder, the ratio of the amount of the iron powder involved in the reaction (3) (reduction of ferric ion) Was calculated to be 75%.

Example 4 A continuous operation test similar to that of Example 1 was conducted. However, in the plating bath composition, sulfamic acid was used instead of sulfuric acid as a supporting anion used in the bath of Example 1. Plating bath composition 40% Ferrous sulfamate 850 g / L Urea 90 g / L Sulfamic acid 15 g / L 28% ammonia water 24 g / L (Fine adjustment to 2.0 using ammonia water)

After discarding 50 ml of plating solution out of the system for every plating of 20 k coulombs / liter of supplied electricity, water was added to adjust the liquid level, and 6 g of iron powder (Fukuda Metal Fe-S The liquid composition was adjusted by adding -200: 200 mesh iron powder), 41 g of a 40% ferrous sulfamate solution, and 6.5 g of urea. This operation could be repeated without any abnormality until the total amount of electricity passed was 500 kC / L. The final liquid composition is ferric ion concentration: 61.2 g / liter (at the time of bathing: 56 g)
/ Liter), urea concentration 85.7 g / liter (at the time of building bath: 90 g / liter), sulfamate ion concentration:
220 g / l (at the time of building bath: 208 g / l) and ammonium ion concentration: 11.5 g / l (at the time of building bath: 7 g / l), and there was no large change in composition compared to the bath composition at the time of building bath. , Could end the continuous operation. The dissolving operation of the iron powder in these experiments was completed in about one hour, and based on the analysis results of the ferric ion before and after the introduction of the iron powder, the ratio of the amount of the iron powder involved in the reaction (3) (reduction of ferric ion) Was 85%.

Comparative Example 1 The same continuous operation test as in Example 1 was performed. However, 20k
In the adjustment of the composition of the plating bath for each electric current of coulomb / liter, the plating solution was not discarded and ferrous sulfate was not added. That is, every time 20k coulombs / liter is energized,
5.3 g of iron powder (Fe-S-200: 200 manufactured by Fukuda Metal)
(Mesh iron powder) and 2 g of urea only. As a result, when the plating bath was cooled to room temperature when the total amount of electricity passed was 240 kC / L, precipitation of crystallized substances was observed, and the liquid composition at that time was a ferric ion concentration of 97 g / liter.
Liter (at the time of bathing: 80.4 g / l), urea concentration 88 g / l (at the time of bathing: 90 g / l), sulfate ion concentration: 241 g / l (at the time of bathing: 175 g / l)
Liter) and ammonium ion concentration: 28.5 g
/ Liter (at the time of building bath: 13.7 g / liter), and particularly the concentrations of sulfate ion and ammonium ion were abnormally high.

Comparative Example 2 The same continuous operation test as in Comparative Example 1 was performed. However, the plating solution was discarded in order to prevent excessive amounts of sulfate ions and ammonium ions. However, as in Comparative Example 1, the addition of ferrous sulfate was not performed. That is, 50 ml of the plating solution is discarded out of the system every time a current of 20 kC is applied, water is added to adjust the level of the solution, and 5 g of iron powder (Fe-S-200: 200 manufactured by Fukuda Metal) is added. (Mesh iron powder) and 6 g of urea only. As a result, when the total amount of electricity passed was 180 kC / L, the current efficiency of iron plating was less than 50% (at the time of bathing: about 70%).
%), And the appearance of the plated product was deteriorated due to generation of many pits. The liquid composition at that time was ferric ion concentration: 6
0 g / l (at the time of bathing: 80.4 g / l), urea concentration: 82 g / l (at the time of bathing: 90 g / l), sulfate ion concentration: 148 g / l (at the time of bathing:
175 g / l) and ammonium ion concentration:
It was 17.3 g / liter (at the time of building bath: 13.7 g / liter), and particularly the concentrations of ferrous ion and sulfate ion were abnormally low.

Comparative Example 3 A continuous operation test similar to that of Example 1 was performed. However, instead of the iron powder used in Example 1, iron particles having a larger particle size (FEEO3GA manufactured by Kojundo Chemical Laboratory: iron particles of 5 to 10 mm) were used. After discarding 50 ml of plating solution out of the system for every plating of 20 k coulombs / liter of supplied electricity, water was added to adjust the level of the solution, and 27 g of iron particles were further added.
And the liquid composition was adjusted by adding 6.5 g of urea. As a result, when the plating solution was cooled at the time of 40 k coulomb / liter, precipitation of a crystallized product was observed. At this time, the liquid composition was as follows: ferric ion concentration: 117 g / l (at the time of building bath: 80.4 g / l), urea concentration: 91.
6 g / l (at the time of building bath: 90 g / l), sulfate ion concentration: 202 g / l (at the time of building bath: 175 g / l), and ammonium ion concentration: 14.6 g / l
Liters (at the time of bathing: 13.7 g / liter)
In particular, ferrous ions were excessive. In the case of the experiment of Comparative Example 3, the dissolving operation of iron powder was required for about 6 hours, and was involved in the reaction (3) (reduction of ferric ion) based on the analysis results of ferric ion before and after the introduction of iron powder. The calculated ratio of the iron powder content was about 15%. As described above, the amount of the plating solution to be discarded in order to prevent the ferrous ion in the plating bath from becoming excessive is calculated to be 200 ml (10% of the plating solution).
Therefore, such a method is not practically usable because it is economically useless.

Comparative Example 4 In the same manner as in Example 3, a continuous operation test using a bath containing no urea was conducted. However, the pH was not adjusted with ammonia water after each plating operation. As a result, when the pH was measured after the electricity flow of 20 k coulombs / liter, the pH was reduced to about 1.5, and the current efficiency of the iron plating at that time was reduced to 50% or less.
It was recognized that many cracks and pits were generated in the obtained plating film.

As is evident from the results of Examples 1 to 4, by performing the plating operation controlled by the method of the present invention, each component in the plating solution can be used for bathing even after passing a large amount of electricity. The composition was maintained substantially the same as in the above, and the plating solution was managed smoothly.

On the other hand, as shown in Comparative Example 1, unless the plating solution is discarded or ferrous ions are added by ferrous salts other than metallic iron, sulfate ions and ammonium ions become excessive. It was confirmed that their solubility could not be maintained. In addition, even if the plating solution was discarded as shown in Comparative Example 2, if the addition of ferrous salt was not used together with the adjustment of the ferrous ion concentration, the ferrous ion concentration in the plating bath would be conversely increased. It was confirmed that the content decreased and satisfactory plating could not be performed.

Further, as shown in Comparative Example 3, when the ratio of the amount contributing to the reaction (3) (reduction of ferric ion) of the introduced metallic iron is less than 20% by weight, the first in the plating bath is reduced. It has been confirmed that the iron ion concentration becomes excessive, and in order to prevent it, it is necessary to discard a large amount of plating solution which is economically unrealistic. In such a case, it takes a long time to dissolve the metallic iron, and the working efficiency is significantly reduced. Furthermore, in an iron plating bath to which urea is not added, it is necessary to adjust the direction of increasing the pH during the plating operation, and if this is neglected as in Comparative Example 4, the pH of the plating bath drops, Satisfactory plating becomes impossible.

[0037]

By applying the control method of the present invention, it is possible to stably operate iron or iron alloy plating using an insoluble anode even with simple equipment.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takehiro Nito 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation

Claims (5)

[Claims] An anode made of an insoluble electrode material, a cathode made of a metal material, and a plating solution containing ferrous ions and at least one anion selected from sulfate ions, hydrochloride ions and sulfamate ions. A method of forming an iron-containing metal plating film on the surface of the metal material by performing electrolytic treatment using (1) contacting metallic iron with the plating solution, and (2) adding sulfuric acid to the plating solution at the same time. At least one ferrous salt selected from ferrous iron, ferrous chloride and ferrous sulfamate is added to thereby control the concentration of ferrous ion in the plating solution to a desired value. A method for managing a plating solution for iron-containing metal plating using an insoluble anode. 2. A method according to claim 1, wherein the plating solution contains ferric ions, and the amount of the ferrous ions coming into contact with the plating solution consumed in the reduction reaction of the ferric ions is 20% of the total weight of the metallic iron. The plating solution management method according to claim 1, wherein the plating solution is controlled to 100%. 3. The plating solution management method according to claim 1, wherein urea is further contained in the plating solution. 4. The plating solution management method according to claim 1, wherein the pH value of the plating solution is adjusted using at least one selected from hydroxides of alkali metals and ammonia. 5. The plating solution according to claim 1, wherein a concentration of at least one kind of anion selected from a sulfate ion, a chloride ion and a sulfamate ion and a concentration of at least one kind of an alkali metal ion and an ammonium ion are selected. The plating solution management method according to claim 1, wherein the plating solution is diluted so as not to exceed a predetermined upper limit.