JPH08225977A - Electrode for electrolysis and its production - Google Patents

Abstract

PURPOSE: To manufacture the electrode that has excellent durability and is used as an anode where oxygen is generated by forming an intermediate layer and an outer layer each of which consists of IrO2 and Ta2 O5 but has a different composition from the other on a Ti-Pt-Ta alloy layer formed on the surface of a Ti base body. CONSTITUTION: In this manufacture, a Pt layer having an about 0.05 to 2.0μm thickness is formed on the surface of a Ti base body by electroplating the surface with Pt or coating the surface with a Pt compound and thereafter subjecting the Pt compound on the surface to thermal decomposition and then, the resulting Ti base body is subjected to electric discharge machining by using a Ta electrode to form a Ti-Pt-Ta alloy layer having an about 10 to 150μm thickness on the surface of this base body. Subsequently, this alloy layer is coated with a solution contg. an Ir compound and a Ta compound and dried and thereafter, calcined at about 400 to 700 deg.C in an oxidizing atmosphere to form an intermediate layer that consists of 5 to 30mol% IrO2 and 70 to 95mol% Ta2 O5 and has an about 0.5 to 10g/m<2> coating weight on the Ti-Pt-Ta alloy layer. Then, similarly, an outer layer that consists of 60 to 98mol% IrO2 and 2 to 40mol% Ta2 O5 and has an about NO to 60g/m<2> coating weight is formed on this intermediate layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for electrolysis and a method for producing the same. The present invention relates to an electrode for electrolysis useful as an anode and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, an electrode in which a platinum group metal, a platinum group metal oxide or a valve metal oxide is coated on a substrate made of titanium or a titanium alloy has been used in many fields of the electrolytic industry. However, in the field of high-speed metal plating and metal foil production operated under high current density, a non-conductive oxide layer is formed on the surface layer of the substrate during use, and the amount of remaining electrode catalyst substance is insufficient. Even if there is, there is a disadvantage that the function as an electrode is lost. It is considered that the formation of such a non-conductive oxide is due to the chemical corrosion of the substrate surface due to the permeation of oxygen and the electrolytic solution generated in the catalyst layer.

In order to solve this problem, conventionally, a method of protecting the electrode substrate by providing a new layer (hereinafter referred to as an intermediate layer) between the electrode substrate and the catalyst layer has been adopted. Sufficient corrosion resistance with respect to this intermediate layer; Sufficient electrical conductivity; Good adhesion bondability with the electrode substrate; Good adhesion bondability with the catalyst layer; It is required to have characteristics such as a layer without cracks; low electrochemical activity; low manufacturing cost. To satisfy such conditions, conventionally, a method of forming an intermediate layer composed of two or more kinds of valve metal oxides having different valences, a valve metal oxide and a platinum group metal, or an electrically conductive platinum A method of forming an intermediate layer made of a group metal oxide, a method of forming a valve metal or an alloy thereof by a thermal spraying method, an ion plating, or the like have been proposed.

As a specific example thereof, Japanese Patent Laid-Open No. 59-3839.
No. 4 discloses an oxide of at least one metal selected from titanium and tin having a valence of 4 on the substrate and 5
There has been proposed an electrode in which an intermediate layer made of a mixed oxide with an oxide of at least one metal selected from tantalum and niobium having a valency of valency is provided, and an electrode active material is coated thereon. However, although the intermediate layer has no oxygen generation activity, it has a problem of insufficient electric conductivity.

Further, in JP-A-57-192281, in an electrode having titanium or titanium alloy as a base material and an electrode coating made of a metal oxide, a conductive oxide of tantalum and niobium is used as an intermediate layer. A layer-provided electrode for electrolysis involving oxygen generation has been proposed, but this intermediate layer has good corrosion resistance but insufficient electric conductivity.

JP-A-1-301876 discloses that 40 to 90 mol% of iridium and 0.1 to 0.1 of platinum are formed on a conductive substrate.
An iridium oxide layer or at most 50 mol% via an underlying layer consisting of iridium oxide, platinum metal and tantalum oxide containing 30 mol% and 50 to 10 mol% tantalum.
There has been proposed an oxygen generating electrode provided with an iridium oxide-tantalum oxide layer containing tantalum as an upper layer. Although the underlayer of this electrode has good electric conductivity, it has a problem that the substrate becomes passivated eventually due to poor corrosion resistance and oxygen-activating activity.

Further, in Japanese Unexamined Patent Publication (Kokai) No. 5-287572, iridium 8.4 to 1 in terms of metal is formed on a conductive substrate.
Containing 80 to 99.9 mol% of iridium and 0.1 to 20 mol% of tantalum in terms of metal through an underlayer consisting of iridium oxide and tantalum oxide containing 4 mol% and tantalum 86 to 91.6 mol% There has been proposed an oxygen generating electrode provided with an upper layer made of iridium oxide and tantalum oxide. Although the underlayer of this electrode has a certain degree of corrosion resistance and electrical conductivity, the permeation of oxygen from the electrolytic solution and the catalyst layer into the substrate is unavoidable, and the passivation of the substrate eventually occurs. It has a problem and has not reached the fundamental solution to the above problems.

Further, in Japanese Unexamined Patent Publication (Kokai) No. 5-171483, plasma spraying of powder of metal tantalum and / or its alloy is performed on a conductive substrate made of titanium or its alloy in a non-oxidizing atmosphere under reduced pressure. By providing an intermediate layer containing metal tantalum and / or an alloy thereof as a main component, a solution containing a tantalum compound and an iridium compound is applied onto the intermediate layer, and heated to 360 to 550 ° C. in an oxidizing atmosphere. Disclosed is a method for producing an oxygen generating anode provided with an electrode active layer containing iridium oxide in an amount of 20% by weight or more and the balance being tantalum oxide. Since the above-mentioned intermediate layer is a porous layer having irregularities as compared with the thermal spraying surface layer, it has excellent adhesive bondability with the electrode active layer, but is disclosed in JP-B-5-571.
As described in JP-A-59-59, since the porous layer usually has about 3 to 25% of pores, it is difficult to completely control the permeation of the electrolytic solution into the conductive substrate, and tantalum and tantalum and The alloy also has a problem that chemical corrosion occurs due to contact with oxygen generated in the catalyst layer or the electrolytic solution, and eventually the intermediate layer also becomes passivated, and the above problems have not been fundamentally solved. .

Further, in JP-A-2-282491, in an electrode in which a conductive metal substrate made of a valve metal or its alloy is coated with an electrode active substance, metal tantalum is provided between the substrate and the electrode active substance layer. And an oxygen generating anode provided with a thin film intermediate layer containing an alloy thereof as a main component. This thin film intermediate layer is formed by applying a solution containing an organic tantalum compound or tantalum chloride and heating it in a non-oxidizing atmosphere. Penetration occurs and passivation of the conductive substrate occurs. Further, a method of forming an intermediate layer by a vacuum vapor deposition method, a sputtering method, an ion plating method, an ion implantation method, or a vapor phase plating method has been proposed, but a thin film intermediate layer formed by these methods has a conductive property. Although the effect of suppressing the permeation of the electrolytic solution into the substrate grows,
Adhesion with the electrode active substance coating layer is not sufficient, and productivity is poor even when the equipment is large, and there is a problem in industrial use.

The object of the present invention is to solve the above problems of conventional electrodes for electrolysis and to use them as an anode for high-speed plating of metals operated under high current density and for the production of metal foils.
An object is to provide a sufficiently durable electrode for electrolysis and a method for producing the same.

[0011]

The inventors of the present invention have conducted various studies to develop an electrode for electrolysis with oxygen generation that can be used for a long period of time, and as a result, an alloy layer of titanium metal, platinum and tantalum metal has been obtained. Was found to have better corrosion resistance than titanium alone, and after providing an intermediate layer having corrosion resistance on the alloy layer of titanium, platinum and tantalum to protect the alloy layer, an oxygen generating active substance is formed on the intermediate layer. It was found that a durable electrode for oxygen generation electrolysis can be obtained by providing the outer layer, and the present invention has been completed.

Thus, the present invention provides the surface of an alloy layer of a titanium substrate having an alloy layer of titanium, platinum and tantalum.
Iridium oxide 5-30 mol% and tantalum oxide 70-9
Iridium oxide 60 via the intermediate layer consisting of 5 mol%
The invention provides an electrode for electrolysis, which is characterized in that an outer layer composed of ˜98 mol% and tantalum oxide of 2 to 40 mol% is provided.

According to the present invention, (a) a titanium substrate provided with a platinum layer on its surface is subjected to electric discharge machining using a tantalum electrode to form an alloy layer of titanium, platinum and tantalum on the surface of the titanium substrate, and (b) ) A solution containing an iridium compound and a tantalum compound is applied to the surface of the alloy layer of a titanium substrate and then heat-treated in an oxidizing atmosphere to give 5 to 30 mol% of iridium oxide and 70% of tantalum oxide.
Iridium oxide 60 is formed by forming an intermediate layer composed of ˜95 mol%, and (c) subsequently applying a solution containing an iridium compound and a tantalum compound on the intermediate layer, and then performing heat treatment in an oxidizing atmosphere. The present invention provides a method for producing the electrode for electrolysis of the present invention, which comprises forming an outer layer composed of about 98 mol% of tantalum oxide and 2 to 40 mol% of tantalum oxide.

The electrode of the present invention and the method for manufacturing the same will be described in more detail below.

In the present invention, an alloy layer of titanium, platinum and tantalum is first provided on the surface of a titanium substrate as an electrode substrate. One formation of this alloy layer can be carried out by electrical discharge machining using a tantalum electrode on the surface of a titanium substrate on which a platinum layer is provided. The platinum layer can be formed by, for example, an electroplating method or a method of applying a solution containing a platinum compound and then performing a heat treatment at a temperature equal to or higher than the decomposition temperature of the platinum compound.

When a platinum layer is formed on the surface of a titanium substrate by electroplating, the titanium substrate is usually pretreated by the method described below and then platinum is electroplated.

First, the surface of the titanium substrate is subjected to
For example, after washing with alcohol and / or degreasing by electrolysis in an alkaline solution, the hydrogen fluoride concentration is 1 to 20.
By treating with hydrofluoric acid of weight% or a mixed acid of hydrofluoric acid and other acids such as nitric acid and sulfuric acid, the oxide film on the surface of the titanium substrate is removed and the titanium grain boundary units are roughened. To do. The acid treatment can be carried out at a temperature of room temperature to about 40 ° C. for several minutes to several tens of minutes depending on the surface condition of titanium. The acid-treated titanium surface is brought into contact with concentrated sulfuric acid to finely roughen the inner surface of the titanium crystal grain boundaries into protrusions and form a thin layer of titanium hydride on the titanium surface. Concentrated sulfuric acid to be used generally has a concentration in the range of 40 to 80% by weight, preferably 50 to 60% by weight, and if necessary, a small amount of sulfuric acid may be used for the purpose of stabilizing the treatment. You may add sodium or other sulfates. The contact with the concentrated sulfuric acid can be carried out by immersing the titanium substrate in a bath of concentrated sulfuric acid, and the bath temperature at that time is generally about 100 to about 15.
The temperature may be in the range of 0 ° C, preferably about 110 to about 130 ° C, and the immersion time is usually about 0.5 to about 1.
0 minutes, preferably about 1 to about 3 minutes is sufficient. By this sulfuric acid treatment, the inner surface of the titanium crystal grain boundary can be finely roughened in a projection shape, and a very thin titanium hydride film can be formed on the surface of titanium.

The sulfuric acid-treated titanium substrate is taken out of the sulfuric acid bath and rapidly cooled in an atmosphere of an inert gas such as nitrogen or argon to lower the surface temperature of titanium to about 60 ° C. or lower. For this rapid cooling, it is appropriate to use a large amount of cold water also for cleaning.

A titanium substrate having a very thin coating layer of titanium hydride formed on its surface in this manner is used in a dilute hydrofluoric acid or dilute fluoride solution (for example, sodium fluoride,
The titanium hydride coating is grown by dipping treatment in potassium fluoride or the like) to homogenize and stabilize the coating. The concentration of hydrogen fluoride in the dilute hydrofluoric acid or dilute fluoride aqueous solution that can be used here can be generally in the range of 0.05 to 3% by weight, preferably 0.3 to 1% by weight. The temperature during the immersion treatment with these solutions can be generally in the range of 10 to 40 ° C, preferably 20 to 30 ° C. The treatment can be carried out until a uniform film of titanium hydride having a thickness of usually 0.5 to 10 μm, preferably 1 to 3 μm is formed on the surface of titanium.

This titanium hydride (TiHy, where y is a number from 1.5 to 2) exhibits a grayish brown to a blackish brown color depending on the degree of hydrogenation, so that the titanium hydride coating having a thickness within the above range is used. Formation can be empirically controlled by changing the color tone of the surface of the substrate by contrasting the brightness with a standard color source. The titanium substrate having the titanium surface roughened and the titanium hydride coating thus formed is appropriately washed with water and then coated with a platinum layer by electroplating.

Examples of plating baths that can be used in this electroplating method include H ₂ PtCl ₆ and (NH ₄ ) ₂ PtC.
l _6, the _{K 2 PtCl 6, Pt (NH} 3) 2 (NO 2) a platinum compound such as _2, the sulfuric acid solution (pH 1-3) or aqueous ammonia, 2 to 20 g in terms of platinum / l, in particular 5~10g /
Dissolve to a concentration of 1 and, if necessary, to stabilize the bath sodium sulfate (in the case of acid bath), sodium sulfite, sodium sulfate (in the case of alkaline bath)
An acidic or alkaline plating bath to which a small amount of etc. is added can be used.

In platinum electroplating using a plating bath having such a composition, in order to suppress decomposition of the titanium hydride coating film formed on the surface of the titanium substrate as much as possible, a high speed plating method such as so-called strike plating is used for about 30 to about It is desirable to carry out at a relatively low temperature within the range of 60 ° C. By this electroplating, a platinum coating layer having excellent physical adhesion strength can be formed on the titanium hydride coating on the titanium substrate.

In this case, the plating thickness of platinum on the titanium substrate can be generally in the range of 0.05 to 2.0 μm. If the platinum plating thickness is less than 0.05 μm, the sufficient improvement effect of platinum plating cannot be seen, and conversely, even if the platinum plating thickness exceeds 2.0 μm, the effect of just increasing the thickness is It may not be obtained, and it may be uneconomical. The platinum plating thickness is usually sufficient within the range of 0.2 to 1.5 μm. Here, the film thickness of platinum in the platinum layer is a value obtained as follows using a fluorescent X-ray analysis method. That is, the platinum plating amount of various thickness platinum coating layers formed by the above method on the titanium substrate pretreated as described above was quantified by the wet analysis method and the fluorescent X-ray analysis method, and the analysis values by both methods were obtained. Is plotted on a graph to prepare a standard calibration curve, and then an actual sample is subjected to fluorescent X-ray analysis to determine the platinum film thickness from the analysis value and the standard calibration curve.

The platinum layer can also be formed by applying a solution containing a platinum compound on the surface of a titanium substrate and heat-treating at a temperature not lower than the decomposition temperature of the platinum compound. When the platinum layer is formed in this manner, it is desirable to pretreat the titanium substrate by the method described below.

First, the surface of the titanium substrate was subjected to
For example, after washing with alcohol and / or degreasing by electrolysis in an alkaline solution, the hydrogen fluoride concentration is 1 to 20.
By treating with hydrofluoric acid of weight% or a mixed acid of hydrofluoric acid and other acids such as nitric acid and sulfuric acid, the oxide film on the surface of the titanium substrate is removed and the titanium grain boundary units are roughened. To do.

The acid treatment can be carried out at a temperature of room temperature to about 40 ° C. for several minutes to several tens of minutes depending on the surface condition of the titanium substrate. The surface of the titanium substrate thus treated with acid is usually washed with water and dried.

Next, a platinum compound is applied onto the surface-treated titanium substrate surface, dried and then baked.

Examples of the platinum compound used here include dinitrodiammineplatinum, chloroplatinic acid, and platinum chloride, and dinitrodiammineplatinum is preferable.

On the other hand, a lower alcohol is suitable as a solvent for dissolving these platinum compounds.
Methanol, ethanol, propanol, butanol, or a mixture thereof are advantageously used. In addition, since dinitrodiammine platinum is not directly dissolved in lower alcohol, it is first dissolved in a nitric acid aqueous solution, and the platinum metal
After adjusting to 50 to 450 g / l, it is desirable to dissolve in lower alcohol. The metal concentration of the platinum compound in the lower alcohol solution can be generally in the range of 40 to 200 g / l, preferably 60 to 150 g / l. If the metal concentration is less than 40 g / l, the platinum loading efficiency tends to be poor, and if it exceeds 200 g / l, platinum tends to agglomerate, and problems such as non-uniform loading strength and loading amount tend to occur. .

The substrate obtained by applying the platinum compound on the surface-treated titanium substrate surface is optionally dried at a temperature within the range of about 20 to 150 ° C., and then in a non-oxidizing atmosphere or a reducing atmosphere and containing oxygen. The firing can be performed in any of the gas atmospheres. For example, when firing in a non-oxidizing atmosphere (for example, in nitrogen gas or argon gas), the firing can be performed at a temperature in the range of about 300 to 550 ° C, and in a reducing atmosphere (for example, hydrogen). When firing in a gas or in a mixture of hydrogen gas and nitrogen gas or argon gas), firing can be performed at about 100 to 200 ° C., and further firing in an oxygen-containing gas atmosphere, for example, in the atmosphere, Firing is generally about 450-650
The heating can be carried out by heating to a temperature in the range of 0 ° C., but it is preferably carried out in a non-oxidizing atmosphere in order to suppress the oxidation of the titanium substrate surface.

The heating can be carried out using a suitable heating furnace known per se, such as an electric furnace, a gas furnace or an infrared furnace. The heating time can be approximately 3 minutes to 30 minutes depending on the size of the substrate to be fired. By this firing, platinum can be supported on the surface of the titanium substrate. When a sufficient amount of platinum film thickness cannot be obtained by one loading operation, the steps of solution permeation- (drying) -firing can be repeated a desired number of times. At this time, the platinum film thickness on the titanium substrate can be in the range of 0.05 to 2.0 μm. If the platinum film thickness is less than 0.05 μm, the sufficient improvement effect due to the formation of the platinum layer cannot be seen. Conversely, even if the platinum film thickness exceeds 2.0 μm, the effect of merely increasing the thickness is obtained. However, the number of steps of repeating the process of permeating the solution- (drying) -firing increases, which may be uneconomical. Usually, with a film thickness within the range of 0.2 to 1.5 μm, it is sufficient that the number of times of repeating the steps of solution permeation- (drying) -firing is 1 to 5 times. Here, the platinum film thickness of the platinum layer is a value obtained using the fluorescent X-ray analysis method as described above.

The titanium substrate provided with the platinum layer in this manner is then subjected to electric discharge machining by scanning the surface of the titanium substrate using the titanium substrate as a cathode and tantalum as an electrode rod. Generally, the atmosphere for electric discharge machining is preferably a non-oxidizing atmosphere, and for example, an argon atmosphere can be used. The tantalum electrode rod used for electrical discharge machining has a diameter of 1 to
Although the diameter within the range of 10 mm can be used, the diameter is usually preferably 4 mm or more from the viewpoint of work efficiency and the like. The discharge conditions vary depending on the diameter of the tantalum electrode used, but when using an electrode rod having a diameter of 6 mm, the current pulse is within the range of 200 to 600 Hz, and the capacitor capacity is within the range of 100 to 400 μF. can do. In this way, electrical discharge machining is performed for 5 to 30 minutes per 1 dm ² to form an alloy layer of titanium, platinum and tantalum from the substrate on the surface of the titanium substrate. The surface of the alloy layer of titanium, platinum, and tantalum thus formed is roughened, and the roughness value measured by a surface roughness meter (Kosaka Laboratory's surface roughness / contour profile measuring instrument SEF-30D) is The thickness is usually about 50 to 200 μm, and an alloy of titanium, platinum and tantalum can form a layer having a thickness of 10 μm or more. Here, the thickness of the alloy layer is 10
If it is less than μm, it is not sufficient to impart corrosion resistance, and it is preferable to form a layer having a thickness of 30 μm or more. The upper limit of the thickness of the alloy layer is not particularly limited, but since tantalum is an expensive metal like the platinum group metal, it is preferably 150 μm or less. As a result, a roughened alloy layer made of titanium, platinum and tantalum, which has better corrosion resistance than titanium alone, can be formed on the surface of the titanium substrate.

On the alloy layer of the titanium substrate on which the alloy layer of titanium, platinum and tantalum of the titanium substrate has been formed as described above, 5 to 30 mol% of iridium oxide, preferably 8 to 25 mol% and oxidation of iridium oxide are then formed. An intermediate oxide layer consisting of 70-95 mol% tantalum, preferably 75-92 mol% is coated. This intermediate oxide layer covers the roughened concave portions or convex portions of the alloy layer of the titanium substrate, and serves to improve the corrosion resistance without impairing the electrical conductivity. The coverage of the oxide layer is generally 0.5 to 10 g / m ² , preferably 1
It is suitable to be in the range of ~ 5 g / m ² .

The formation of the intermediate oxide is necessary, for example, after applying a solvent solution containing an iridium compound and a tantalum compound, preferably a lower alcohol solution, on the alloy layer on the titanium substrate formed as described above. It can be carried out by adhering the mixture of the iridium compound and the tantalum compound by drying depending on the method, and then heat treating in an oxidizing atmosphere. Examples of the iridium compound and tantalum compound that can be used here include compounds soluble in a lower alcohol solvent that can be thermally decomposed under the firing conditions described below to be converted into iridium oxide and tantalum oxide, respectively. Examples of such iridium compounds include iridium chloride, iridium chloride, potassium iridium chloride, and the like, and examples of tantalum compounds include tantalum chloride, tantalum ethoxide, and the like.

On the other hand, examples of the lower alcohol capable of dissolving the iridium compound and the tantalum compound include methanol, ethanol, propanol, isopropanol, butanol and the like, or a mixture thereof.

The solution containing the iridium compound and the tantalum compound can be applied by a method known per se, for example, a method such as brush coating, spray coating or roll coating. The titanium substrate thus applied with the lower alcohol solution of the iridium compound and the tantalum compound is usually dried at a relatively low temperature within the range of about 20 to about 150 ° C., and then calcined in the atmosphere.

The treatment described above can be repeated until the amount of the intermediate oxide coated reaches the above range.

The calcination is generally carried out in a suitable heating furnace such as an electric furnace, a gas furnace, an infrared furnace or the like, and is generally about 400 to about 700.
C., preferably about 450 to about 600.degree. C., by heating at a temperature in the range. The heating time at that time is about 5 minutes to 2 depending on the size of the substrate to be fired.
It can be about an hour. By this firing, the iridium compound and the tantalum compound are converted to iridium oxide and tantalum oxide, respectively, and an intermediate oxide is formed.

As described above, on the intermediate layer composed of iridium oxide and tantalum oxide, 60 to 98 mol% of iridium oxide, preferably 70 to 95% is further added.
Mol% and tantalum oxide 2-40 mol%, preferably 5
An outer layer consisting of -30 mol% is provided. If the iridium oxide content is less than 60 mol% in the outer layer, the oxygen generation activity may be insufficient and the electrode life may be shortened when used at high current densities, while if it exceeds 98 mol%, the electrode catalyst ( The consumption of the outer layer) tends to increase. The formation of the outer layer having the above components and composition can be performed in the same manner as described above for the formation of the intermediate oxide. The coating amount of the outer layer is generally 10 to 60 g / m ² , preferably 30 to
It is suitable to set it within the range of 50 g / m ² .

The electrode of the present invention manufactured as described above does not easily passivate at the titanium interface even when used for a long time under a high current density, has a long life, and is operated under a high current density. It can be preferably used as an anode for high-speed plating of metals and for manufacturing metal foils.

[0041]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but these examples are not intended to limit the scope of the present invention.

Example 1 Titanium plate material equivalent to JIS Class 2 ( ^t 3.0 × ^w 100 × ^l 10
0 mm) is degreased and washed with trichlorethylene, and then 20
Heat treatment with 8 wt% HF aqueous solution at ℃ for 2 minutes, then 12
It was treated in a 60% by weight H ₂ SO ₄ solution at 0 ° C. for 3 minutes. Then, the titanium substrate was taken out from the sulfuric acid solution and rapidly cooled by spraying cold water in a nitrogen atmosphere. Further 0.3% by weight at 20 ° C
It was immersed in an aqueous HF solution for 2 minutes and then washed with water.

After washing with water, dinitrodiaminoplatinum was dissolved in a sulfuric acid solution to carry out plating at 30 mA / cm ² for about 9 minutes in a platinum plating bath adjusted to have a Pt content of 5 g / l, pH≈2 and 50 ° C. To deposit Pt. The Pt plating thickness was 1.0 μm.

Then, a Pt-plated titanium plate was used as a cathode, and a tantalum electrode having a diameter of 6 mm was used to perform electrical discharge machining for 10 minutes in a glow box in which argon was substituted. After that, the titanium substrate on which tantalum was electric discharge machined was cut into ^t 3.0 × ^w 10 × ^l 10 mm with a fine cutter. E
PMA (electron probe microanalyzer)
At that time, elemental analysis of the cross section subjected to electric discharge machining revealed that it was an alloy layer in which tantalum metal and platinum were dispersed in titanium metal. The thickness of this alloy layer was 30 to 50 μm.
Ir 4.6 g / l prepared by mixing a butanol solution of iridium chloride and an ethanol solution of tantalum chloride on the alloy layer of the titanium substrate on which the alloy layer of titanium, platinum and tantalum thus formed is formed. And Ta50.0 g / l (molar compounding ratio: 8Ir-92Ta)
The coating solution containing was weighed at 3.0 μl per cm ² with a Micropipette, coated, dried in vacuum at room temperature for 30 minutes, and baked in the atmosphere at 500 ° C. for 10 minutes.
This process was repeated 3 times.

Then, in order to obtain an outer layer, Ir of 50.0 g / l and Ta prepared by mixing a solution of iridium chloride in butanol and a solution of tantalum chloride in ethanol.
Using the coating liquid containing 20.2 g / l (molar blending ratio: 70 Ir-30Ta), the same steps as above were repeated 8 times to prepare Example electrode-1.

Next, in the same manner as in Example electrode-1, Example electrodes-2 to 4 in which the composition of the coating layer was changed were prepared.

Further, in the same manner as in the above-mentioned Examples, Comparative Electrodes-1 and 2 whose composition of the coating layer was out of the range specified by the present invention were prepared.

Example 2 Titanium plate material equivalent to JIS type 2 ( ^t 3.0 × ^w 100 × ^l 1
(00 mm) was washed with alcohol, treated in an 8 wt% hydrofluoric acid aqueous solution at 20 ° C. for 2 minutes, washed with water and dried. Then, a dinitrodiammine nitric acid solution having a platinum concentration of 300 g / l was dissolved in butanol to prepare a solution having a platinum concentration of 75 g / l.

7.3 μl per cm ^{2 of} this solution was weighed with a micropipette on the surface of an acid-treated titanium substrate, allowed to penetrate, and then dried at room temperature for 30 minutes, and further 550
Firing was performed in the air at 0 ° C. for 10 minutes. This permeation-drying-firing process was repeated 4 times to make the Pt thickness 1.0 μm.

Then, a titanium plate on which a platinum layer was formed by heat treatment was used as a cathode, and a tantalum electrode having a diameter of 6 mm was used to perform electric discharge machining in a glow box in which argon was replaced.
Minutes. After that, the titanium plate on which tantalum was electric discharge machined was cut into ^t 3.0 × ^w 10 × ^l 10 mm with a fine cutter. Elemental analysis of the cross section subjected to electric discharge machining was carried out by EPMA (electron probe microanalyzer) to find that it was an alloy layer in which tantalum metal and platinum were dispersed in titanium metal. The thickness of this alloy layer is 30-50μ
It was m.

On the alloy layer of the titanium substrate on which the alloy layer of titanium, platinum and tantalum thus formed is formed,
In the same manner as in Example electrode-1, Example electrodes-5 to 8 in which the composition of the coating layer was changed were prepared.

Further, in the same manner as in the above-mentioned examples, comparative electrodes -3 to 4 in which the composition of the coating layer was out of the range specified by the invention were prepared.

Comparative Example Titanium plate material equivalent to JIS Class 2 ( ^t 3.0 × ^w 100 × ^l 1
(00 mm) was washed with alcohol, treated with an 8 wt% aqueous solution of hydrofluoric acid at 20 ° C. for 2 minutes, washed with water and dried.
Then, the titanium plate from which the oxide film was removed was used as a cathode, and a tantalum electrode having a diameter of 6 mm was used to perform electric discharge machining for 10 minutes in a glow box in which argon was substituted. The thickness of this alloy layer was 30 to 50 μm.

On the alloy layer of the titanium substrate on which the alloy layer of titanium and tantalum thus formed was formed, an intermediate layer and an outer layer having the same intermediate layer composition and outer layer composition as those of Example electrode-1 were provided on the example electrode. It was formed by the same method as that of -1 to obtain a comparative electrode-5.

Pretreatment and P were carried out in the same manner as in Example electrode-1.
Comparative Example Electrode 6 was prepared by forming an intermediate layer and an outer layer having the same intermediate layer composition and outer layer composition as in Example Electrode 1 on a t-plated titanium substrate in the same manner as in Example Electrode 1.

Further, the same pretreatment as in Comparative Example electrode-5 was performed on the titanium substrate, and the intermediate layer and outer layer having the same intermediate layer composition and outer layer composition as in Example electrode-1 were prepared in the same manner as in Example electrode-1. The comparative electrode-7 formed in Step 3 was manufactured.

Tables 1 and 2 show the electrode life when each of the electrodes thus obtained was electrolyzed under the following conditions. As is clear from the results shown in Table 1 and Table 2, the electrode life of the example electrodes is long.

<Electrolysis conditions> Electrolyte solution: 1MH ₂ SO ₄ -1M Na ₂ SO ₄ Current density: 4A / cm ² Counter electrode: Pt Distance between electrodes: 10mm

[0059]

[Table 1]

[0060]

[Table 2]

[0061]

As described above, according to the electrode for electrolysis of the present invention, when the surface of the titanium substrate is coated with platinum and the electrical discharge machining is performed using the tantalum electrode, titanium having good corrosion resistance is obtained.
An alloy layer of platinum-tantalum is formed, and by forming an intermediate layer having good corrosion resistance and electrical conductivity on the alloy layer,
Since the titanium-platinum-tantalum alloy layer suppresses the passivation of the titanium substrate and has a roughened surface, it has excellent adhesion between the alloy layer and the intermediate layer, and on the intermediate layer. By forming the outer layer, which is the catalyst layer, on the electrode, an electrode for electrolysis that can be used for a long time can be provided.

Claims (4)

[Claims] 1. Iridium oxide 5 to 5 is formed on the surface of an alloy layer of a titanium substrate having an alloy layer of titanium, platinum and tantalum.
An electrode for electrolysis, comprising an outer layer composed of 60 to 98 mol% of iridium oxide and 2 to 40 mol% of tantalum oxide via an intermediate layer composed of 30 mol% and tantalum oxide 70 to 95 mol%. 2. A titanium base having a platinum layer on its surface is subjected to electric discharge machining using a tantalum electrode to form an alloy layer of titanium, platinum and tantalum on the surface of the titanium base, and (b) a titanium base. After applying a solution containing an iridium compound and a tantalum compound to the surface of the alloy layer of
By heat treatment in an oxidizing atmosphere, an intermediate layer composed of 5 to 30 mol% of iridium oxide and 70 to 95 mol% of tantalum oxide is formed. (C) Next, an iridium compound and a tantalum compound are formed on the intermediate layer. After applying the containing solution, by heat treatment in an oxidizing atmosphere,
Iridium oxide 60-98 mol% and tantalum oxide 2-4
The method for producing an electrode for electrolysis according to claim 1, wherein an outer layer of 0 mol% is formed. 3. The method according to claim 2, wherein the platinum layer is formed by electroplating. 4. The method according to claim 2, wherein the platinum layer is formed by applying a solution containing a platinum compound on the surface of the titanium substrate and then heat-treating at a temperature equal to or higher than the decomposition temperature of the platinum compound.