JPH05209299A - Insoluble electrode and its production - Google Patents

Abstract

PURPOSE:To provide an insoluble electrode, excellent in corrosion resistance even in the case of electrolysis with high current density and durable in a long use, and the producing method thereof. CONSTITUTION:A valve metal layer 2 is formed on the surface of an electrode base material 1 and the insoluble electrode has a valve metal 2 heat-treated at 400-800 deg.C for >=0.5hr and <=10hr and an Ir oxide layer 7 between the valve metal layer 2 and IrO2 coating film layer 4, and the IrO2 coating film layer 4 is a dense layer or two layers of the dense layer and a porous layer. As a result, the valve metal and the Ir oxide layer increase the adhesive strength between both layers of the metal layer and the IrO2 layer and the oxidation progress of the valve metal layer from the boundary surface of the coating film is suppressed. Thus, the electrode is durable in a long use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insoluble electrode and a method for manufacturing the same.

[0002]

2. Description of the Related Art Generally, in electroplating a metal material, an insoluble electrode is used in an electroplating bath to electroplate a metal such as Zn, Sn, or Ni on the surface of a metal material to be plated which is a cathode. ing.

In electrorefining of metals, insoluble electrodes are used in a refining bath to electrorefine metals such as Mn and Zn.

The most commonly used insoluble electrode at this time is a Pb-based alloy.

This electrode is used for electroplating bath, electrorefining bath,
Particularly, in a sulfuric acid solution, PbO ₂ is formed on the surface of the solution during energization.

Although PbO ₂ exhibits the function of an insoluble electrode, the generated PbO ₂ and Pb have a weak adhesive force and are mixed in the electrolytic solution to cause defective plating or refining metal containing impurities.

Therefore, as a countermeasure, an electroplating bath, an electric smelting bath, especially IrO ₂ , which is a platinum group oxide, which is the most electrochemically stable in a sulfuric acid solution, is used as a base material for a valve metal (Ti, Ta, (A metal such as Zr that forms an insulating oxide layer on the surface and stops energization when energized)
An electrode coated on a layer is disclosed in JP-B-48-3954.

Further, it suppresses the oxidation of the valve metal layer.
In order to improve adhesion,₂O_FiveEtc.
The added film is formed and Ir is formed on the film. O₂Formed layers
The method of using an insoluble electrode is Japanese Patent Publication No. 46-21884.
Japanese Patent Laid-Open No. 63-235493
It

FIG. 1 shows the electrode structure. 1 is a SUS electrode base material, 2 is a valve metal layer, 3 is IrO ₂ —Ta ₂ O ₅
Layers 4 are IrO ₂ layers.

The method of applying the layers 3 and 4 is a so-called coating baking method in which a solution which becomes an oxide is applied to the valve metal layer and the baking is repeated at a temperature where it becomes an oxide. .

[0011]

[Problems to be Solved by the Invention] Japanese Patent Publication No. 46-2188
No. 4, JP-A-63-235493, an insoluble electrode having a layer mainly composed of IrO _{2 formed} by a coating and baking method has a low current density (up to 100 A / d).
m ² ), it can be used for a long time, but when conducting an electrical corrosion test under a high current density, especially in a sulfuric acid solution at 150 A / dm ² , a sharp voltage rise occurs in 3000 to 4000 hours and the electrode becomes unusable. Become.

The corrosion mechanism of this electrode will be described with reference to FIG. Since the IrO ₂ -containing layers 3 and 4 are formed by heat treatment of the solution, pores due to volatilization of the solution components are generated, and a hexagonal crack 5 is generated in the coating film due to the difference in thermal expansion between the valve metal layer and the IrO ₂ layer. ing.

Therefore, the porosity of the coating is as large as 5 to 30%, the specific surface area is large, and the current density per unit area is low, so that the melting loss speed is slow, but the pores and cracks cause the formation of the valve metal layer 2. Direct energization occurs, the insulating oxide film 6 is formed on the surface of the valve metal layer, and further the oxidation of the valve metal layer progresses through the interface between the valve metal layer and the film,
The voltage rises and the electrode function is lost. As a countermeasure against this, it is necessary to produce a homogeneous coating film without pores and cracks.

Conventional Japanese Patent Publication No. 46-21884, Journal of the Photographic Society of Japan [Vol51, No. 1, p3 (198
8)], a reactive sputtering method and a reactive vapor deposition method are shown as a method of sputtering Ir metal and oxidizing it near the substrate to obtain a uniform coating film having almost no cracks or pores.

However, the IrO ₂ film (hereinafter referred to as IrO ₂ reactive sputter film or IrO ₂ reactive vapor deposition film) produced by this reactive sputtering method or reactive vapor deposition method is 100.
There is a drawback that energization is stopped in a short time due to energization at a low current density of A / dm ² .

The reason for this is that the IrO ₂ reactive sputter coating and the IrO ₂ reactive vapor deposition coating are easily peeled off by increasing the film thickness, and the optimum film thickness for production is several hundred to several thousand Å, which is very thin. This is because the specific surface area is smaller than that of the baked IrO ₂ coating, the current density per unit area is large, and the melting speed is fast.

The present invention provides an insoluble electrode having excellent corrosion resistance even when electrolysis is carried out at a high current density of 150 A / dm ² or more and capable of withstanding long-term use, and a method for producing the same.

[0018]

The first invention of the present invention is as follows:
A valve metal layer as a first layer, a valve metal and Ir oxide layer as a _second layer, and IrO ₂ as a third layer on the surface of the electrode base material.
A second aspect of the present invention is an insoluble electrode having a layer, wherein the first invention is a valve metal layer and a second layer is a first layer on the surface of the electrode base material.
The insoluble electrode is characterized by having a valve metal and an Ir oxide layer as a layer, a dense IrO ₂ layer as a third layer, and a porous IrO ₂ layer having a porosity of 5 to 30% as a fourth layer.

A third invention is a method for producing an insoluble electrode according to the first invention and the second invention, wherein the oxide layer of the second layer in the insoluble electrode is 500 to 800 ° C., 0.5 hr to 10 hr. The method for producing an insoluble electrode is characterized in that the third layer is formed after heating within.

[0020]

The electrode structure examples of the first and second inventions of the present invention are shown in FIGS.

The electrode of the first invention is Ir as shown in FIG.
The valve metal and Ir formed by heat treatment between the O ₂ film (for example, prepared by coating and baking) and the valve metal layer
It has an O ₂ diffusion layer 7.

Therefore, the valve metal layer and IrO₂Between layers
Has high adhesion strength, and oxidation of valve metal layer progresses from the interface
Is suppressed, 150 A / dm² Electrolysis at higher current density
It has excellent corrosion resistance and can be used for a long time.
Have signs.

As shown in FIG. 4, the electrode of the second invention comprises a thin film dense IrO ₂ layer 8 formed on the valve metal layer by a reactive sputtering method, a vapor deposition method or the like, and a valve metal layer formed by heat treatment. oxidation progression of valve metal layer from a very high interfacial adhesion strength of the valve metal layer and the IrO ₂ film layers to have the diffusion layer 7 of the IrO ₂ film is suppressed.

Further, since a porous (porous) coating produced by coating and baking is provided as an upper layer of the coating, the current density per area is low and the coating is less likely to be melted.

Therefore, even if electrolysis is performed at a high current density of 150 A / dm ² or more, it has excellent corrosion resistance and can withstand a longer period of use than the electrode of FIG.

[0026]

[Examples] In the following, the method of preparing the test sample, the evaluation method and the result will be described in detail.

First, a method for preparing a test sample will be described. 1) Cleaning the surface of 100 × 100 × 20 mm Ti base material with oxalic acid

2) An IrO ₂ film is formed on the base material by the reactive sputtering method, the reactive vapor deposition method or the IrO ₂ coating and baking method, and the method for forming the film by each method will be described below.

2-1) Reactive Sputtered Coating A base material Ti plate was placed in vacuum (8 × 10 ⁻⁴ torr) so as to face the Ir plate. Ar pressure 1 × 10 ^-1 to 2 in the vacuum chamber
× to 10 ^-2 torr, by applying 1kV potential to target hammered the Ir atom devoted to Ir plate discharges the Ar ions, the O ₂ gas onto the substrate at a gas pressure of 4.5 × 10 ^-4 torr An IrO ₂ reactive sputter coating 1000 Å was formed on the surface of the Ti base material at a spraying film formation rate of 2 Å / sec.

2-2) Reactive Vapor Deposition Coating A base material Ti plate was placed in vacuum (8 × 10 ⁻⁴ torr) so as to face the Ir plate.

This Ir plate was heated with an electron beam at 200 W to evaporate Ir, and the gas pressure was 6.5 × 10 ⁻⁴ to.
An O ₂ gas was introduced at rr to form an IrO ₂ reactive vapor deposition film 1000 Å on the surface of the Ti base material at a film forming rate of 2 Å / sec.

2-3) Coating baking coating A coating baking coating solution prepared by dissolving H ₂ IrCl ₆ which becomes IrO ₂ by thermal decomposition in butanol to adjust the Ir metal concentration to 60 g / l is coated with a brush, After drying, put in an electric furnace and bake at 450 ° C. about 8 times to make IrO
₂ Coating and baking method A coating film of about 50 μm was formed.

3) In this test, after the IrO ₂ film was formed, the test sample was heat-treated. The heating was performed in the air or Ar atmosphere, and the temperature at this time was measured on the electrode surface.

In this test sample preparation, the heat treatment was carried out after the coating and baking coating was formed. However, the same effect can be obtained by forming the homogeneous IrO ₂ coating by the reactive sputtering method or the vapor deposition method or during the preparation of the coating and baking coating. Got

Table 1 shows the constitution and heat treatment conditions of the samples tested this time.

[0036]

[Table 1]

[0037]

[Table 2]

The durability evaluation of the prepared electrode was performed by the following method, and the result is shown in FIG.

Using a conventional product, a comparative product and the present invention as the anode and a platinum plate as the cathode, an electrical corrosion test was performed at a current density of 150 A / dm ² in a 5 wt% sulfuric acid solution at 60 ° C., and the change in voltage was measured.

As a result of the energization test, the conventional product is 3000 to 40.
At 00 hours, the voltage suddenly increased and the electrode became unusable.

It is considered that this is because the corrosion of the valve metal progressed from the interface between the IrO ₂ film and the valve metal layer.

Comparative products 2, 3, 4, and 5 are also 3000 to 300.
After 4000 hours, the voltage suddenly increased and the electrode became unusable.

This is because when the heating time is as short as 0.1 hr and the heating temperature is as low as 500 ° C., the valve metal layer and I
It is considered that, since diffusion does not occur between the rO ₂ coatings and there is no heat treatment effect, when the heating temperature is as high as 800 ° C. or when the heating is performed in Ar, IrO ₂ is reduced to Ir metal and the corrosion resistance is reduced.

Comparative products 9, 10, 11, 12, 1
In Nos. 6, 17, 18 and 19, a sharp voltage increase occurred between 12,000 and 14,000 hours and the electrodes became unusable.

The life of this electrode is superior to that of the conventional product, although it is not affected by heat treatment, but it is considered that it has a homogeneous thin film having a strong adhesive force with the valve metal under the coating and has an effect of suppressing the corrosion of the valve metal layer. Be done.

On the other hand, in the products 6, 7 and 8 of the present invention, 180
00 to 20000 hours, 13, 14, 15, 20, 2
It was found that in Nos. 1 and 22, a voltage rise occurred in 22,000 to 24,000 hours and the device could withstand long-term use.

In the products 6, 7 and 8 according to the present invention, the valve metal layer and the IrO ₂ coating diffusion layer were provided, and the valve metal layer and Ir were provided.
Oxidation of the valve metal layer from the interface of the O ₂ coating is difficult to proceed, so that in the products 13, 14, 15, 20, 21, and 22 of the present invention, there is no through hole to the valve metal layer,
It is considered that this is because the valve metal layer has a diffusion layer of the rO ₂ coating and the oxidation of the valve metal layer from the interface between the valve metal layer and the IrO ₂ coating does not proceed further.

The products 8, 15, and 22 of the present invention were subjected to a heat treatment for a long time, but the durability was not particularly improved, and it is considered that the heat treatment for a long time is not effective from the economical viewpoint.

[0049]

The insoluble electrode of the present invention is 150 A / dm
^It has excellent corrosion resistance even when electrolysis is performed at a high current density of ² or more, and can withstand long-term use, and is extremely useful as an electrode for other applications as well as an electrode for electroplating.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing an example of a conventional electrode structure.

FIG. 2 is an explanatory diagram of a corrosion mechanism of a conventional electrode example.

FIG. 3 is a cross-sectional view showing an example of the electrode structure of the present invention.

FIG. 4 is a cross-sectional view showing an example of the electrode structure of the present invention.

FIG. 5 is a diagram showing the results of a galvanic corrosion test of a conventional electrode example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 SUS electrode base material 2 Valve metal layer 3 IrO ₂ —Ta ₂ O ₅ coating baking coating 4 IrO ₂ coating baking coating 5 crack 6 insulating oxide 7 Ti—IrO ₂ diffusion layer 8 IrO ₂ reactive sputter coating

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[Procedure amendment]

[Submission date] March 10, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 3

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0019

[Correction method] Change

[Correction content]

A third aspect of the present invention is the method for producing an insoluble electrode according to the first and second aspects of the invention, wherein the oxide layer serving as the third layer in the insoluble electrode is 500 to 800 ° C. for 0.5 h.
The method for producing an insoluble electrode is characterized in that the second layer is formed by heating for not less than r and not more than 10 hours.

Claims (3)

[Claims] 1. An insoluble electrode having a valve metal layer as a first layer, a valve metal and Ir oxide layer as a _second layer, and an IrO ₂ layer as a third layer on the surface of an electrode base material. 2. A valve metal layer as the first layer, an oxide layer of valve metal and Ir as the _second layer, a dense IrO ₂ layer as the third layer, and a porosity of 5 to 3 as the fourth layer on the surface of the electrode base material.
An insoluble electrode having a 0% porous IrO ₂ layer. 3. The second oxide layer is 500 to 800 ° C.,
A method for producing an insoluble electrode, which comprises heating for 0.5 hr or more and within 10 hr, and then forming three layers.