JPH02175900A - Method for decreasing ferric ion in iron-based plating solution - Google Patents

Abstract

PURPOSE:To reduce Fe<3+> to Fe<2+> and to improve the performance of an iron- based plating soln. by connecting the soluble anode of Fe or a metal baser than Fe and the insoluble cathode of a metal nobler than Fe with a conductor in an Fe-based plating soln. contg. Fe<3+> ion, and allowing the plating soln. close to the cathode to flow rapidly. CONSTITUTION:An iron-based plating soln. 2 contg. 1-30g/l of Fe<3+> ion and consisting essentially of Fe<2+> ion is charged into a vessel 1. A soluble anode 3 of Fe or a metal baser than Fe and an insoluble cathode 4 of a metal nobler than Fe such as Pt are dipped in the soln., both electrodes 3 and 4 are connected with a conductor 5 of a Cu wire, etc., an agitator 7 such as a magnetic stirrer is arranged close to the cathode 4 to agitate the soln. 2 to increase the flow velocity of the soln. in the vicinity of the cathode 4, hence Fe<3+> is reduced to Fe<2+> to decrease the amt. of Fe<3+> ion, and the performance of the Fe-based plating soln. is restored.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to Fe3+ generated in the iron-based plating solution in the iron-based electroplating process using an insoluble anode in the electrolytic bath.
The present invention relates to a method for reducing trivalent iron ions in an iron-based plating solution suitable for reducing ions to Fe'* ions and returning the ions to an electrolytic cell of an iron-based plating apparatus for use.

[Conventional technology]

In recent years, the mainstream of industrial iron-based electroplating has been to use an insoluble anode as an anode. However, the biggest drawback of this plating method is that Fe" ions in the iron-based plating solution are exposed to external air. In addition to being oxidized, 02 gas generated at the anode and electrolytic oxidation at the anode are oxidized to Fe3+ ions, and Fe"" ions in the iron-based plating solution increase.
When a portion of the Fe1 ions at the cathode are reduced to Fe'' ions, excess power is consumed and the current efficiency of the cathode is reduced.

Generally, even if Fe3'' ions are present in trace amounts, they tend to become hydroxides and precipitate.

Since hydroxides are easily incorporated into the plating film and extremely reduce the ductility of the film, the following method of reducing Fe34 ions to Fe'' ions has been proposed.

1. A method in which the electrolytic cell is divided into an anode chamber and an lla electrode chamber by an ion exchange membrane, and electrolytic reduction is carried out while flowing a conductive liquid into the anode chamber and an iron-based plating solution into the cathode chamber.

2. A method in which metal particles are introduced into a reduction reaction tank, and an iron-based plating solution is passed through the reduction reaction tank to be reduced by the metal particles.

However, the method of the follower uses only 1 plating power for electrolytic reduction.
．． The processing cost is high because 5 to 2.5 times more power is required, and the conductive liquid must be passed through the anode chamber, making its management very complicated.

On the other hand, in the latter method, in addition to the reduction reaction of Fe3° ions to Fe'' ions by metal particles as shown in equation (1) below, the reaction between metal particles and the acid in the iron-based plating solution as shown in equation (2) is performed. A reaction also occurs.

Me + nFe - Ma + nFe" - (1) M
e + n H" = Me" + -H,
↑---------(2) However, since Me is a reducing metal such as Fe or Zn, it has the disadvantage that hydrogen gas is generated on the surface of the metal particles and changes the pH of the Fe ion-containing solution. Not only does this occur, but the ρ11 of the solution dynamically increases due to the generation of hydrogen gas, and a hydroxide film is formed on the surface of the metal particles, so the effective contact area of the surface of the metal particles with the iron-based plating solution gradually decreases. This has the disadvantage that the rate of reduction of Fe3'' ions to Fe28 ions decreases.This disadvantage is that simply stirring the iron-based plating solution causes the hydroxide film formed on the surface of the metal particles to deteriorate. This was a drawback that could not be solved because it could not be removed.

Therefore, as a method of suppressing the reaction of the above equation (2), it is possible to reduce the surface area of the metal particles, but the above (
There is a drawback that the reaction rate of formula 1) is also slow.

Alternatively, it is possible to increase the reduction efficiency by adding a reduction reaction accelerator or by introducing metal particles together with an insoluble metal such as platinum to preferentially cause the reaction of formula (1) above. Addition increases the cost of reduction, and adding metal particles together with insoluble metals such as platinum has the disadvantage that handling becomes complicated because the respective metals are mixed.

[Problem to be solved by the invention]

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to inexpensively and easily convert Fe2°+ ions generated in the iron-based plating solution in the iron-based electroplating process using an insoluble anode in the electrolytic bath. It is an object of the present invention to provide a method for reducing trivalent iron ions in an iron-based plating solution, which is suitable for reducing the iron-based plating solution to ions and returning it to an electrolytic cell of an iron-based plating apparatus for use.

[Means to solve the problem]

As a result of various experimental studies to solve the above problems, the present inventors have found that iron or a soluble metal that is a component of iron-based plating that is baser than iron and an insoluble metal that is nobler than iron are connected by a conductor, and the soluble metal side the anode.

An iron-based plating solution is placed in a container with the insoluble metal side serving as the cathode.As shown in the following equations, the soluble metal on the anode side becomes metal ions in the iron-based plating solution containing Fe ions. We focused on the reaction in which Fe' ions are reduced to Fe' ions on the cathode side, which is made of an insoluble metal, while being dissolved.

Anode side Me −ne + Me”− (3) Cathode side Fe5th+ e −+ Fe”= =
...(4) Overall Me+nFe”→Me”+n
Fc"i5) However, Me is iron or a soluble metal less base than iron. Equation (5) is a cathode reaction. The rate is determined by equation (4), and the reaction of this equation (4) is Fe" near the cathode. The rate is determined by the rate of ion diffusion.

Therefore, at least F to the vicinity of the insoluble metal of the cathode
e" The supply rate of ions can be increased by stirring strongly with a Starcy device, stirring the iron-based plating solution by circulating it with a pump, etc., applying mechanical vibration to the insoluble metal of the cathode, or If the reaction of equation (5) is promoted by applying motion such as rotation, Fe3" ions generated in the iron-based plating solution in the iron-based electroplating process can be easily and cheaply removed. to F
The present invention was developed based on the discovery that it is effective as a method for reducing trivalent iron ions in an iron-based plating solution, which is suitable for reducing to e'' ions and returning them to the electrolytic cell of an iron-based plating device. was completed.

In this way, F at least near the insoluble metal of the cathode
What is the reason for increasing the supply rate of e3'' ions?

The reaction of equation (3) occurs instantaneously, but since the supply of Fe3+ ions cannot keep up with the reaction of equation (5), the reduction reaction from Fe3' ions to Fe1 ions becomes extremely slow and cannot be carried out industrially. Because it is impossible.

Then, using this method, Fe' in the iron-based electroplating solution was
The present inventors have confirmed from numerous experimental results that when reducing ions to Fe2+ ions, the Fe3 ion concentration must be 1 to 30 g/Q. This is because when the Fe3'' ion concentration in the iron-based electroplating solution is less than 1 g/l, the current flowing through the conductor connecting the anode made of a soluble metal and the cathode made of an insoluble metal is small; As a result, the reaction in equation (3) above does not proceed and a decrease in Fe3'' ions cannot be expected because Fe'' ions increase due to air oxidation caused by increasing the flow rate of the iron-based plating solution by stirring etc. Also, the Fe3° ion concentration in the iron-based electroplating solution is 30
g/l does not occur during normal iron-based electroplating, and even if such
When using iron-based plating solution with high ion concentration, F at the cathode
A phenomenon occurs in which some of the e3+ ions are reduced to Fe'' ions, which consumes extra power and lowers the current efficiency of the cathode, making it impossible to carry out industrial iron plating. This is because hydroxides based on the above are produced and incorporated into the plating film, resulting in an extreme decrease in the ductility of the film, which is undesirable.

〔Example〕

Example and Comparative Example 1 As shown in the cross-sectional explanatory diagram of one example of the apparatus suitable for carrying out the method of the present invention in FIG. insoluble metal 4
The soluble metal 3 and the insoluble metal 4 are connected by a conductor 5 made of copper wire, and an ammeter 6 is interposed in the middle of the conductor 5.
A magnetic stirrer 7 was placed directly below the insoluble metal 4 in the container 1. A chloride-based iron-based plating solution 2 with an Fe'+ ion concentration of 30 gIQ is poured into the container 1 immediately after bath preparation, and the magnetic stirrer 7 is driven to remove the iron-based plating solution 1 near the insoluble metal 4. Figure 2 shows the results of measuring the changes over time in the concentration of F, 34 ions in the iron-based plating solution by increasing the flow rate of the iron-based plating solution. A total of 6 measured values (
(current density, which is the current value flowing per unit cathode area)
is shown in Figure 3 with a mark.

On the other hand, as a comparative example, we measured the change over time in the Fe3'' ion concentration in the iron-based plating solution when the magnetic stirrer 7 was not driven, and the results are shown in Figure 4. The measured value (current density) of the ammeter 6 with respect to the Fe3+ ion concentration in the sample is shown as a 0 mark in FIG.

As a result, in the case of the embodiment of the method of the present invention in which the magnetic stirrer 7 was driven, as is clear from FIG.
Compared to the comparative example, the Fe ion concentration decreases rapidly and the current density decreases by only about 4 g/l even after 900 minutes without driving the magnetic stirrer 7. It was confirmed that the method of the present invention exerts a remarkable effect.

Comparative Example 2 Using the same equipment as in the above example, an experiment was conducted using an iron-based plating solution with an Fe' + ion concentration of 0.8 g/Q while driving the magnetic stirrer 7, and the iron-based plating was carried out. Changes in Fe''' ion concentration in the liquid over time were measured and the results are shown in FIG.

As is clear from Fig. 5, Fe'
Almost no decrease in the + ion concentration was observed, and the measured value (current density) of the ammeter 6 was approximately 0.04 A/d rrr, which was a very small amount of Fe'+ due to the flow of electricity.
Although there was a decrease in ions, it was confirmed that air oxidation was promoted by stirring the iron-based plating solution.

[Operation and effect of the invention]

As detailed above, the method for reducing trivalent iron ions in an iron-based plating solution according to the present invention is to use an iron-based plating solution containing 1 to 30 g/ff of Fe''' ions to reduce iron or an iron less noble than iron. A soluble metal, which is a component of system plating, and an insoluble metal nobler than iron are connected by a conductor, and introduced into a container in which the soluble metal side is used as an anode and the insoluble metal side is used as a cathode, and at least near the insoluble metal side in the container. This is a very simple method that rapidly reduces Fe3" ions in the iron-based plating solution to Fe" ions by increasing the flow rate of the iron-based plating solution. This method does not require electricity to perform electrolytic reduction, unlike the method in which electrolytic reduction is performed by dividing the anode chamber and cathode chamber into an anode chamber and a cathode chamber, and flowing a conductive liquid in the anode chamber and an iron-based plating solution in the cathode chamber. Therefore, it is cheap and easy to implement, and Fe3 in iron-based plating solution is
This is an innovative method that can be implemented industrially because the reduction of "ions to Fe" + ions occurs rapidly, and this method also improves plating in the iron-based electroplating process that uses an insoluble anode in the electrolytic bath. It is also useful for replenishing consumed Fe1 ions, and has high industrial value.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional explanatory diagram showing one embodiment of an apparatus suitable for carrying out the method of the present invention, and Fig. 2 shows the change over time of the Fe3+ ion concentration in the iron-based plating solution in an embodiment of the method of the present invention. Figure 3 shows the relationship between the current density and the Fe3+ ion concentration in the iron-based plating solution in Examples of the method of the present invention and Comparative Example 1 in which the flow rate of the iron-based plating solution near the insoluble metal side is not increased. Figure 4 is a diagram showing the change over time in the Fe3'' ion concentration in the iron-based plating solution of Comparative Example 1 in which the flow rate of the iron-based plating solution near the insoluble metal side is not increased, and Figure 5 is a comparison diagram. FIG. 3 is a diagram showing changes over time in the Fe3'' ion concentration in the iron-based plating solution in Example 2. In the drawing l...Container 2...Iron-based plating liquid 3...Soluble metal 4...Insoluble metal 5...Conductor 6...Ammeter 7...・Magnetic stirrer Fig. 1-6: Fig. 2 Time (min) Fig. 3 F♂+I Off #K (91 breaths) Fig. Time (min)

Claims (1)

[Claims] 1. An iron-based plating solution containing 1 to 30 g/l of Fe^3^+ ions is applied to iron or a soluble metal that is a component of iron-based plating that is baser than iron and an insoluble metal that is nobler than iron. and are connected by a conductor to introduce the iron-based plating solution into a container in which the soluble metal side is used as an anode and the insoluble metal side is used as a cathode, and the flow rate of the iron-based plating solution at least near the insoluble metal side in the container is increased. Therefore, the Fe^3^+ ions in the iron-based plating solution are replaced with Fe^2^
A method for reducing trivalent iron ions in an iron-based plating solution, which is characterized by rapid reduction to + ions. 2. The trivalent iron of the iron-based plating solution according to claim 1, wherein the flow rate of the iron-based plating solution at least near the insoluble metal side in the container is increased by stirring strongly or by circulating it with a pump or the like. Ion reduction method. 3. The method according to claim 1, wherein the flow velocity of the iron-based plating solution at least near the insoluble metal side in the container is increased by applying mechanical vibration to the insoluble metal of the cathode or by applying movement such as rotation to the insoluble metal of the cathode. A method for reducing trivalent iron ions in iron-based plating solutions.