JPH05331696A - Iron-based electroplating method - Google Patents

Abstract

PURPOSE:To perform a high quality plating at a high plating current efficiency by using an electrode having an iridium oxide covering layer as an insoluble anode and performing an iron electroplating at a high anode current density, thereby suppressing the energazing-oxidization of Fe<2+> ions. CONSTITUTION:The iron-based electroplating is performed by using an insoluble and in a sulfuric acid-acidic electrolytic plating bath. In such a case, the electrode formed by providing an iridium oxide-contg. covering layer provided on a conductive substrate, such as titanium, is used as the insoluble anode and simultaneously the anode current density is kept to >=50A/dm<2>. Thus, the rate of energazing-oxidization of the Fe<2+> ions can be maintained at a low level and the increase in the Fe<3+> ions can be suppress. Consequently, the replenishing of the Fe<2+> ions and the reduction load of the Fe<3+> ions are reduced, thereby enabling the reduction in cost and the accurate control of the plating liquid as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an iron-based electroplating method, and more particularly to an iron-based electroplating method capable of suppressing the electro-oxidation of Fe ²⁺ ions in a plating bath.

[0002]

[Field of Industrial Application] For example, in iron-based electroplating using a conventional lead-based insoluble anode, Fe ²⁺ in the plating bath is used.
Ions are electro-oxidized by a reaction of Fe ²⁺ → Fe ³⁺ + e ^−, which is one of the anodic reactions, and gradually become F 2 in the plating bath.
e ³⁺ increases. As described above, when Fe ³⁺ ions increase in the plating bath, the plating current efficiency and the plating quality deteriorate, and workability is significantly impaired.

Also in the conventional iron-based electroplating method, Fe ³⁺ ions in the plating bath are partially reduced and reduced when the metallic iron is dissolved due to the supply of Fe ²⁺ ions. .. However, in the conventional iron-based electroplating method, there is a large amount of Fe ³⁺ ion conduction oxidation as described above,
In order to reduce the Fe ³⁺ ion concentration, it is necessary to excessively dissolve metallic iron, which makes it difficult to control the Fe ²⁺ and Fe ³⁺ ion concentrations and is disadvantageous in terms of cost.

In order to carry out stable iron-based electroplating, it is necessary to control the Fe ³⁺ ion concentration to be low and the Fe ²⁺ ion concentration to be within a certain concentration range. ^It is necessary to reduce the amount of electro-oxidation of ²⁺ ions.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems in iron-based electric plating, and suppresses the electric oxidation of Fe ²⁺ ions in the plating bath. It is an object of the present invention to provide a ferrous electric plating method.

[0006]

In the iron-based electroplating method according to the present invention, an electrode having an iridium oxide-based coating layer on a conductive substrate is used as an insoluble anode, and the anode current density is 50 A / dm. ^By setting it to ² or more,
It is characterized by suppressing the electric oxidation of Fe ²⁺ ions in the plating bath.

In the present invention, an electrode having an iridium oxide-based coating layer on a conductive substrate is used as the insoluble anode. As the conductive substrate, for example, a metal such as titanium, tantalum, zirconium, niobium, or an alloy of two or more kinds of metals selected from these is used. Further, the iridium oxide-based coating layer may be a coating layer made of only iridium oxide, but iridium oxide may be used in an appropriate amount with one or more metals or compounds such as platinum, tantalum, ruthenium, palladium, titanium and cobalt. It may be added. The shape of such an iridium oxide-based coating layer (hereinafter referred to as an iridium oxide electrode) may be any of a plate shape, a mesh shape, a perforated plate shape, and the like.

FIG. 1 shows the change over time in the Fe ³⁺ ion concentration in the bath during iron-zinc plating. The plating conditions are as follows. FeSO ₄ .7H ₂ O: 400 g / l ZnSO ₄ .7H ₂ O: 10 g / l H ₂ SO ₄ : 10 g / l Anode current density: 70 A / dm ^{2 When} using a conventional lead-based alloy as an insoluble electrode In comparison with the case of using an iridium oxide electrode according to the present invention, there is a clear difference in the change in Fe ³⁺ ion concentration during plating. That is, according to the present invention, the use of the iridium oxide electrode suppresses the increase in the Fe ³⁺ ion concentration in the bath.

FIG. 2 shows the electro-oxidation rate of Fe ²⁺ ions.
The plating conditions are as follows. FeSO ₄ .7H ₂ O: 400 g / l ZnSO ₄ .7H ₂ O: 10 g / l H ₂ SO ₄ : 10 g / l Fe ³⁺ : 6000 ppm Anode current density: 70 A / dm ² Also, electric oxidation of Fe ²⁺ ions The rate was defined as 100% when 5.79 g of Fe ³⁺ ions were generated at an electric charge of 1 × 10 ⁴ coulombs.

The electro-oxidation rate of Fe ²⁺ ions is 75% when a conventional lead alloy is used as the anode, whereas it is 60% when an iridium oxide electrode is used according to the present invention. Is. As described above, it is not always clear why the use of the iridium oxide electrode as the anode lowers the current oxidation rate of Fe ²⁺ ions.
The anode reaction of the iron-based electric plated using an insoluble ^{electrode, Fe 2+ → Fe 3+ + e} - ... (1) H 2 O → 2H + + (1/2) O 2 + 2e - ... second (2) The reason for this is that when these electrodes compete with each other, the reaction of (2) above tends to occur when an iridium oxide electrode is used as the anode.
In fact, the oxygen evolution potential on the iridium oxide electrode in pure zinc plating solution is much lower than that on the lead-based alloy electrode, as shown in FIG. That is, on the iridium oxide electrode, since the reaction of (2) above occurs at a low overvoltage,
It is considered that the reaction of (1) is relatively reduced in iron-based electroplating.

Next, as shown in FIG. 4, which shows the relationship between the current oxidation rate of Fe ²⁺ ions and the anode current density, the anode current density is 5
When it is less than 0 A / dm ² , even when an iridium oxide electrode is used as the anode, the current-induced oxidation rate of Fe ²⁺ ions is considerably high. The reason is that the anodic reaction (1) and
Comparing (2), the reaction potential of (2) is higher,
In the case of low anode overvoltage (that is, low anode current density), the anode potential does not reach the reaction potential of (2), and only the reaction of (1) occurs. Even if the anode potential reaches the reaction potential of (2),
When the anode overvoltage (anode current density) is low, the reaction (1) may occur preferentially. Thus, it is preferable that the anode current density is high, and according to the present invention, by setting the anode current density to 50 A / dm ² or more, the current oxidation rate of Fe ²⁺ ions can be suppressed low.

In the present invention, the iron-based electric plating bath is a sulfuric acid bath. The plating layer is not limited as long as it is iron-based, and examples thereof include iron-zinc, iron-phosphorus, and iron-nickel.

[0013]

The present invention will be described below with reference to examples.
The present invention is not limited to these examples. Using an electrode made of titanium coated with iridium oxide as an anode, a current density of 130 A / dm ² and a plating flow rate of 1.2 m / in a plating bath having the composition shown below.
Iron-zinc electroplating was performed at a stripping speed of 80 m / min for 2 seconds. Plated bath composition _{FeSO 4 · 7H 2 O: 400g} / l ZnSO 4 · 7H 2 O: 10g / l H 2 SO 4: 10g / l Fe 3+: 7g / l Bath temperature: 60 ° C. Fe ²⁺ energized ions The oxidation rate is shown in Table 1.

[0014]

[Table 1]

[0015]

As described above, according to the method of the present invention, an electrode having an iridium oxide-based coating layer on a conductive substrate is used as an insoluble anode, and the anode current density is 5%.
By setting it to 0 A / dm ² or more, F in the plating bath is increased.
Effectively suppresses electro-oxidation of e ²⁺ ions, and reduces F in the plating solution.
Since it is possible to suppress the increase of e ³⁺ ions, Fe ²⁺
The supply of ions and the reduction load of Fe ³⁺ ions can be reduced, thus reducing the cost and controlling the plating solution accurately.

[0016]

[Brief description of drawings]

FIG. 1 is a graph showing changes with time in Fe ³⁺ ion concentration in a bath during plating.

FIG. 2 is a graph showing a current oxidation rate of Fe ²⁺ ions when a lead-tin alloy electrode and an iridium oxide electrode are used as an anode.

FIG. 3 is a graph showing an oxygen generation potential of an anode in a pure zinc plating solution.

FIG. 4 is a graph showing the relationship between the electro-oxidation rate of Fe ²⁺ ions and the anode current density.

Claims (1)

[Claims] 1. An electrode comprising an iridium oxide-based coating layer provided on a conductive substrate is used as an insoluble anode, and the anode current density is 50 A / dm ² or more.
An iron-based electroplating method, which comprises suppressing the electro-oxidation of Fe ²⁺ ions in the plating bath.