JPS5893886A - Electroplating method - Google Patents

Abstract

PURPOSE:To electroplate iron at high current density with good efficiency by separating an anode chamber installed therein with an insoluble anode from a plating bath chamber by means of anion exchange membrane or an amphoteric ion exchange membrane and maintaining the sulfuric acid soln. in the anode chamber at a high concn. CONSTITUTION:In a plating cell 1, an insoluble anode 5 such as lead is installed in an anode chamber 4 separated from a plating bath chamber 3 by means of an anion or amphoteric ion exchange membrane 2. The anode 5 and a cathode 6 of iron are connected to an electric power source 7. Sulfuric acid of a prescribed concn. is circulated and supplied by a pump 9 from a storage tank 8 for sulfuric acid soln. into the chamber 4 to maintain the concn. of the sulfuric acid in the chamber 4 at >=50g/l. The plating bath is prepared in a dissolving tank 10 and after the pH, concn., etc. thereof are controlled in a controlling tank 12, the plating soln. is supplied from a storage tank 14 for plating soln. into the chamber 3 by a pump 15. Electroplating is accomplished without any trouble at <=70 deg.C bath temp. and >=35A/dm<2> current density by maintaining the concn. of the sulfuric acid in said chamber 4 at >=50g/l.

Description

[Detailed description of the invention] The present invention relates to a method for electroplating iron.

Conventionally, various electroplating methods have been implemented and developed for the purpose of preventing rust, corrosion, and improving weldability of iron. Particularly in the industrial electroplating method for railway cars, it is desired to increase the current density in order to downsize the equipment, for example by reducing the number of plating tanks in the plating line.

Generally, a soluble anode or an insoluble anode is used as an anode in an electroplating method. Among these, when using an insoluble anode, various methods have been proposed in which the anode is installed in an anode chamber separated from the plating bath by a diaphragm of an ion exchange membrane. An alloy plating method using an anion exchange membrane is described.

However, since ion-exchange membranes generally have a limiting current density, if a current is applied above this density, at the membrane interface on the ion-supplied side (desalination side) of the ion-exchange membrane,
This results in the splitting of water (H+ and 0H-). Therefore, if scale components are present, OH- may cause problems such as precipitation, and in anion exchange membranes, OH-
As a result of passing through the membrane, alkali burning occurs, and the membrane performance rapidly deteriorates, making it unusable. therefore,
Even in the electroplating method using an anion exchange membrane, it is difficult to increase the current density.

As a result of extensive research into a method for electroplating iron tubes using four metal tanks installed in an anode chamber in which an insoluble anode is separated from the plating bath by an ion exchange membrane, the present inventors have found that the sulfuric acid concentration in this anode chamber can be increased beyond a specified level. When the current density is increased, the present invention has been completed by discovering that electroplating can be performed without any problem even if the current density is increased.

In the electroplating of steel, the present invention is characterized in that an insoluble anode is installed in an anode chamber separated from the plating bath by an anion exchange membrane or an amphoteric ion exchange membrane, and the sulfuric acid concentration in this anode chamber is maintained at 50g713 or more. This is an electroplating method.

Embodiments of the method of the present invention will be described below with reference to the drawings. The plating bath 1 is separated into a plating bath 6 and an anode chamber 4 by an anion or amphoteric ion exchange membrane (hereinafter referred to as an ion exchange membrane) 2. An insoluble anode 5 is provided in the anode chamber 4, and the insoluble anode 5 and the object to be plated (iron 9@) 6 are connected to a power source 7. Sulfuric acid at a predetermined concentration is supplied to the anode chamber 5 from a sulfuric acid solution storage tank 8 by a pump 9 . The plating bath prepared in the dissolution tank 1o is sent to an adjustment tank 12 by a pump 11, and after adjusting the concentration and pH of the solution, is sent to a plating solution storage tank 14 by a pump 13, and then sent to a re-plating bath by a pump 15. 6.

The sulfuric acid in the anode chamber 5 and the sulfuric acid solution storage tank 8 can be circulated,
Furthermore, the sulfuric acid in the sulfuric acid solution storage tank 8 can be sent to the dissolution tank 1° and used for preparing a plating bath. At this time, Fe'
If S+ is present, it is preferable to remove Fe by reduction treatment, a chelating agent, or the like.

The plating bath contains a sulfate of the plating metal, and the sulfate concentration varies depending on the metal to be plated, but is generally 1 to 3 mol/1, preferably 2 to 3 mol/1. The anode chamber 4 is filled with sulfuric acid having a concentration of 50 g or more, preferably 609/-6 or more. Next, electroplating is performed by a conventional method.

When a plating voltage is applied between the insoluble electrode 5 and the steel cylinder 6, discharge of metal ions dissociated in the plating bath occurs, and metal is deposited on the surface of the steel 60. On the other hand, sulfuric acid ions (SOZ-) in the plating bath pass through the ion exchange membrane 2 and move into the anode chamber 4, and react with hydrogen ions generated on the surface of the insoluble anode 5 to produce sulfuric acid. As a result, the sulfate corresponding to the deposited metal disappears in the plating bath 6, and the corresponding sulfuric acid is generated in the anode chamber 4.

In the method of the present invention, the sulfuric acid concentration in the anode chamber 4 is set to 50 g/
It is extremely important to maintain the ratio at 43 or higher, especially at 609/13 or higher. As a result, electroplating can be carried out without any problem at a current density of 55% m2 or more. Industrially 40 to 200 A/dm", preferably 50 to 150
It is carried out at A/dm2. On the other hand, when electroplating was performed with the sulfuric acid concentration in the anode chamber lower than 5011/43, as the current density was increased, the color tone of the anion exchange membrane changed to alkaline, and Membrane strength and performance are reduced. Therefore, if the anion exchange membrane is damaged, the plating bath and anolyte will mix, causing an abnormal change in the pH of the plating bath, and Fe2+ in the plating bath will migrate to the anode chamber and be oxidized. This results in an increase in Fe3+. An increase in Fe not only promotes corrosion of Fe on the back side of the plated object (nickel plating on conductor rolls, etc.) in the plating bath, but also causes problems in terms of plating bath management, as it becomes ferric hydroxide at pH 6 or higher. It is.

In the electroplating method of the present invention, the current density can be increased (the reason why it is possible is unclear, but anions are not completely baked into the exchange membrane with alkali), so the limiting current density may be very high, or In other words, anion exchange membranes generally have the property of being easily permeable to H, but in the present invention, by increasing the sulfuric acid concentration in the anode chamber. Accordingly, it has been confirmed that the H+ generated in the anode chamber permeates into the plating bath through the anion exchange membrane, resulting in a decrease in the sulfuric acid production efficiency.Therefore, the H+ permeation effect in the anion exchange membrane is - It is assumed that the critical current density becomes thicker (or disappears).In addition, when an amphoteric ion exchange membrane is used in the present invention, the H+ permeation effect is equivalent to or greater than that of an anion exchange membrane. Perhaps because of this, the current density can be increased even if the sulfuric acid concentration in the anode chamber is somewhat lower than when using an anion exchange membrane. The cation exchange capacity is 10 out of the total exchange capacity of
~40% is preferred.

Generally, in electroplating, Joule heat is generated and the liquid temperature rises, so the heat is removed by a heat exchanger or the like, and the liquid temperature is maintained at a temperature that is optimal for plating and economical for heat removal. In the present invention, when electroplating is performed by increasing the current density, the amount of heat removed from the solution also increases, but in particular, heat generation of the ion exchange membrane used becomes a problem. When performing electroplating with the temperature of the plating bath and the sulfuric acid solution in the anode chamber of the present invention generally being 70°C or higher and the current density being particularly 50 A/dm2 or higher, thermal sintering occurs in the ion exchange membrane. Performance degradation may occur.

Therefore, in the electroplating method of the present invention, the liquid temperature is
It is preferable to maintain the temperature below 0°C.

The anion exchange membrane used in the present invention includes a strongly basic exchange membrane containing a quaternary ammonium salt, such as N-benzyltrimethylammonium salt, and a weakly basic exchange membrane containing a -class to tertiary amino group. Either is fine. Anion exchange membranes with excellent mechanical strength, heat resistance, and oxidation resistance are commercially available and can be easily obtained.

Further, an amphoteric ion exchange membrane can be obtained, for example, by treating the above-mentioned anion exchange membrane with sulfuric acid or the like to introduce a sulfone group.

As an insoluble anode, it has excellent durability, is inexpensive, and is advantageous.

In addition, the surface of a metal such as titanium, niobium, or tantalum may be coated with an oxide of a platinum group metal such as iridium or palladium, or may be plated with platinum. The insoluble electrode preferably has a shape that suppresses an increase in electrical resistance due to generated gas, such as a flat plate, a mesh, a lath, or a rod.

In particular, when a lead-based metal is used as the insoluble anode, impurities mixed in the sulfuric acid in the anode chamber 4 tend to deteriorate the performance of the ion exchange membrane. In such a case, in order to maintain the performance of the ion exchange membrane, it is preferable to reduce the sulfuric acid. As a reduction treatment method, generally used is a method in which sodium sulfite, acidic sodium sulfite, hydrazine, ascorbic acid, etc. are added to sulfuric acid.

It is also effective to treat sulfuric acid with activated carbon.

According to the electroplating method of the present invention, since the current density can be increased, plating can be performed in a short time. Therefore, especially when continuously electroplating iron edges, coils, or plates, the number of plating tanks in the plating line can be reduced, which is extremely advantageous from an industrial perspective.

The electroplating method of the present invention can be used for single metal plating such as iron and zinc, and alloy plating such as zinc-nickel, zinc-iron, and zinc-cobalt. The method of the present invention includes
Iron products such as mild steel, steel, and ferrous alloys can be targeted.

Example 1 In the plating apparatus shown in the drawings, the plating bath 3 was filled with a zinc plating solution of pH 2 with a concentration of zinc sulfate (heptahydrate) of 2509/43 and sodium sulfate of 10 og/l, and an anion exchange membrane 2 ( Platinum was placed as an anode 5 in an anode chamber 4 separated by Neocepta ACH-45T (manufactured by Tokuyama Soda Co., Ltd.), and the anode chamber 4 was filled with 100 fi/43 sulfuric acid. 12 while keeping the sulfuric acid concentration in the anode chamber 4 constant.
A steel plate to be plated was continuously plated with zinc at a current density of 0 A/dIn2.

As a result, even after more than one month, no abnormalities such as alkali burn occurred on the anion exchange membrane, and F
The concentration of Fe ion gradually increased due to elution from the back side of the object to be plated, but reached an equilibrium state at about 100 ppm, and the Fe ion concentration was suppressed to several ppm, resulting in good zinc plating.

Comparative Example 1 Same as Example 1, except that the sulfuric acid concentration in the anode chamber 4 was changed to 4.
Zinc plating was performed at 0g/,,e. the result,
After 24 hours, the anion exchange membrane showed a change in color due to alkali burn, and as a result, the membrane strength decreased and some damage was observed.

Example 2 The plating bath 3 was treated with zinc sulfate heptahydrate 15og/-e, ferrous sulfate heptahydrate zsog/-g-, and sodium sulfate 1oo
, 9/-g, a platinum anode is installed in the anode chamber 4, which is filled with an iron-zinc plating solution of pH 2 and separated by an anion exchange membrane 2. fulfilled. 5 while maintaining the sulfuric acid concentration in the anode chamber 4.
Continuous iron-zinc plating was performed on the steel plate 6 at a current density of 5 A/am2.

As a result, we were able to keep Fe''+ in the plating bath below several tens of ppm at all times, and a stable alloy coating of 20% iron and 80% zinc was obtained.Also, uneven color tone and decrease in current efficiency were prevented. No alkali burning of the anion exchange membrane was observed even after one month of operation, and there was only a slight change in performance.

Comparative Example 2 The sulfuric acid concentration in the anode chamber in Example 1 was set to 40 to 454/A.
It was carried out under the same conditions as in Example 1, except that

As a result, Fe3+ in the plating bath was constantly at several tens of p for two days.
Although the sulfuric acid production efficiency in the anode chamber gradually decreased, two days later a sudden abnormal change in the pH of the plating bath and an increase in Fe were observed. When the anion exchange membrane was inspected, it was found that it had changed in color due to alkali burn, became brittle, and was partially damaged.

Example 3 A paste obtained by mixing 20 parts of polyvinyl chloride powder, 4 parts of styrene, 6 parts of 4-vinylpyridine, 0.7 parts of divinylbenzene, 2 parts of dioctyl phthalate, and 0.1 part of benzoyl peroxide was converted into polychlorinated It was applied to a vinyl cloth and polymerized in an autoclave at a temperature of 90°C to form a thick film.The thick film was then sulfonated with concentrated sulfuric acid at a temperature of 60°C for 5 hours, and then sulfonated with methyl iodide for 4 hours. The cation exchange capacity of the obtained amphoteric ion exchange membrane was measured, and the cation exchange capacity of the total ion exchange capacity was 31%.

Zinc sulfate heptahydrate 25-09/13 and sodium sulfate 100 were added to the plating bath 6 separated by this amphoteric ion exchange membrane 2.
Fill the anode chamber 4 with a pH 2 galvanizing solution at a concentration of g/A, fill the anode chamber 4 with sulfuric acid at a concentration of 1.259/-13, install a platinum anode 5, and continue zinc plating at a current density of 100 A/6 m2. I did it.

As a result, the amphoteric ion-exchange membrane did not show any abnormalities such as alkali burn after more than one month, and the Fe2+ concentration in the plating bath gradually increased due to elution from the back side of the object to be plated. ．． Although the concentration reached an equilibrium state of approximately Oppm, the generation of FoS+ was suppressed to a few ppm, and plating could be performed satisfactorily.

[Brief explanation of drawings]

The drawings are process diagrams for explaining embodiments of the present invention, in which symbol 1 is a plating tank, 2 is an ion exchange membrane, 3 is a plating bath, 4 is an anode chamber, 5 is an insoluble anode, and 6 is an object to be plated. shows. 9 applicants: Tokuyama Soda Co., Ltd. and 1 other representative: patent attorney Masao Kobayashi, +7

Claims (1)

[Claims] 1. In iron electroplating, an insoluble anode is installed in an anode chamber separated from the plating bath by an anion exchange membrane or an amphoteric ion exchange membrane, and the sulfuric acid concentration in this anode chamber is maintained at 509,743 or higher. An electroplating method characterized by: 2. The electroplating method according to claim 1, which is carried out at a current density of 55 A/am" or higher. 3. The electroplating method is carried out at a liquid temperature of 70° C. or lower. The method described in item 1 of the scope.