JPH08109490A - Production of anode for generating oxygen - Google Patents

Abstract

PURPOSE: To produce an anode for generating oxygen having excellent durability by providing the surface of a conductive base body of metal Ti subjected to surface roughening to specific roughness with an electrode active material coating layer contg. a platinum metal oxide via an intermediate layer of Ta. CONSTITUTION: The surface of the conductive metallic base body consisting of the metal Ti or its alloy and having a prescribed shape is subjected to surface roughening by a blasting treatment and is further subjected to degreasing and is formed with fine ruggedness by chemical etching treatment, by which the center line average height Ra thereof is specified to a range of 3 to 8μm. The intermediate layer consisting of the Ta or its alloy is thereafter formed by a sputtering method on the surface of the base body at a thickness of 1 to 5μm. This layer is then provided thereon with the electrode active material coating layer contg. the platinum metal oxide. A mixture composed of 10 to 97wt.% (in terms of metal) platinum metal oxide and 90 to 3% valve metal oxide of Ti, Ta, Nb, Zr, etc., is preferable as the electrode active material. As a result, the passivation of the base body is prevented and the electrode having the excellent durability even under severe service conditions is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for producing an insoluble anode used in an electrolysis process involving generation of oxygen, mainly in electroplating zinc, tin, chromium or the like and surface treatment of stainless steel.

[0002]

2. Description of the Related Art Lead or a lead-based alloy has been conventionally used as an anode for galvanizing steel sheets, but it has had problems such as contamination of a plating solution due to eluted lead and deterioration of film quality. As an alternative anode, various insoluble anodes have been proposed in which a base body made of a valve metal such as titanium is coated with an electrode active material containing a noble metal oxide. However, in an electrode in which the surface of the substrate is simply coated with an electrode active material, the electrolytic solution penetrates through the cracks present in the electrode active material layer, and an insulating passivation film is formed and remains at the coating layer-substrate interface. Even if the amount of the active material is sufficient, there is a disadvantage that the function as an electrode is lost.

In order to suppress such passivation of the substrate, JP-A-48-40676 discloses a metal such as titanium, tantalum or the like which has durability under an electrolytic environment on an electrode substrate by plasma spraying or the like. There has been proposed a coated electrode in which an electrode active material is deposited on the surface by thermal spray coating. Further, Japanese Patent Application Laid-Open No. 56-112458 proposes an electrode in which a metal such as tantalum is plasma sprayed on a titanium substrate and then irradiated with an electron beam or the like to form a ruthenium oxide by a thermal decomposition method. There is. However, since the thermal spray coating of titanium, tantalum, etc. is generally a sparse structure, it is difficult to prevent the electrolyte solution from entering the interface of the substrate, and it is also recognized that it lacks durability in long-term use.

In order to solve such a problem, JP-A-53-95180 discloses that a titanium substrate is coated with a tungsten / tantalum mixed film by a method such as vapor deposition, ion plating, and cathode sputtering, and a rhodium thin film is further formed. Electrodes deposited by vapor deposition have been proposed. In addition, Japanese Unexamined Patent Publication
JP-A-2828491 describes that an electrode in which a metal tantalum intermediate layer is formed by sputtering and further coated with an electrode active material is effective for preventing passivation of a substrate. Although these electrodes have a relatively dense intermediate layer formed by the various vapor deposition methods described above and having a high corrosion resistance, they are sufficiently durable for practical use. Since the composition of the electrode active material coated on the layer has not been studied in detail, the concealment ratio of the intermediate layer, the adhesion to the substrate, and the anchor effect on the electrode active material are insufficient, resulting in a more dense and pinhole-like structure. There was still room for improving the durability by forming a coating layer having a small amount.

[0005]

The object of the present invention is to prevent the passivation of a substrate, which is a problem in electrolysis with oxygen generation, and insoluble electrodes which are mainly studied as anodes for electroplating, and to prevent severe use. It is to provide a method for producing an electrode having excellent durability even under conditions.

[0006]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that in an oxygen generating anode, after a substrate is roughened to an average roughness in a specific range by blasting and then chemically etched. The present invention has been completed by finding that it is extremely effective to solve the above problems by sputtering tantalum or its alloy to form an intermediate layer.

According to the present invention, the surface of a conductive metal substrate made of titanium metal or an alloy thereof is roughened by blasting and then chemically etched so that the center line average roughness Ra is in the range of 3 to 8 μm. After that, an intermediate layer made of tantalum or its alloy is provided by a sputtering method, and an electrode active material coating layer containing a platinum group metal oxide is provided on the surface of the intermediate layer, which is a method for producing an oxygen generating anode.

As the electrode substrate of the present invention, titanium-based alloys such as metallic titanium and titanium-tantalum, titanium-tantalum-niobium and titanium-palladium are suitable, and their shapes are plate-like, net-like, rod-like and porous. Any desired shape such as a plate shape can be used.

Grit blasting, shot blasting or sand blasting is applied to physically roughen the metal substrate. Alumina, zirconia, silicon carbide, steel, sand and the like are used as these blast materials, and the particle size thereof is preferably about 200 to 1000 μm. The surface roughness after blasting is an important factor for the durability of the electrode, and the center line average roughness Ra is 3 to 8.
It is necessary to have unevenness of μm, preferably 4 to 6 μm, and the peak count Pc at that time is 40 to 60 / c.
About m is desirable.

For chemical etching performed after blasting, at least one selected from hydrochloric acid, oxalic acid, sulfuric acid, and hydrofluoric acid is used.
An aqueous solution containing some inorganic acid is used, in some cases 60
The effect can be further enhanced by raising the temperature to not less than ° C. It is preferable that this chemical etching treatment not only cleans the surface of the substrate after blasting, but also forms minute irregularities due to erosion in addition to relatively large irregularities due to blasting. After this treatment, it is necessary to sufficiently wash with water, and ultrasonic cleaning with purified water or the like is effective. At that time, the center line average roughness Ra is 3 to 8 μm, preferably 4
~ 6 μm is required, and the peak count Pc
Is about 80 to 120 / cm. When Ra is less than the lower limit value of the above range, the anchor effect on the intermediate layer and the electrode active material coating layer becomes insufficient, and when it exceeds the upper limit value, the coating layer is uneven due to protrusions more than necessary. In addition, the electrode active material on the tip of the protrusion is selectively worn during electrolysis, resulting in a shorter life.

The thin film of tantalum or its alloy forming the intermediate layer of the electrode according to the present invention is formed on the pretreated substrate by the sputtering method. As the sputtering, both high frequency sputtering and DC bipolar sputtering are possible, and magnetron sputtering is more preferable. It is desirable that the film thickness of tantalum be 1 to 5 μm, and if it is less than 1 μm, the film cannot be sufficiently covered in relation to the grit treatment, and if it exceeds 5 μm, problems such as difficulty in sputtering processing occur. Since the degree of vacuum during sputtering affects the film formation speed and film quality,
It is necessary to sufficiently remove the residual gas in the apparatus that holds the substrate, and in this respect also, degreasing cleaning by chemical etching is the most effective pretreatment.

Finally, an electrode active layer containing an electrochemically active platinum group metal oxide is provided on the surface of the intermediate layer having no electrode activation ability. Platinum group metal oxides or mixed oxides of these with valve metals such as titanium, tantalum, niobium, tungsten, and zirconium are suitable as electrode active materials suitable for electrolysis involving oxygen generation. Typical examples are iridium-tantalum mixed oxide, iridium-titanium mixed oxide, iridium-ruthenium mixed oxide, iridium-ruthenium-titanium mixed oxide, ruthenium-titanium mixed oxide, ruthenium-tantalum mixed oxide, Examples thereof include iridium-platinum-tantalum mixed oxide. At this time, the platinum group metal is 10-9 in terms of metal.
A mixed oxide coating consisting of 7 wt% and valve metal of 90 to 3 wt% has excellent durability. The platinum group metal content in the electrode active layer is preferably ¹ to 300 g / m ² in terms of metal.

Particularly preferred is a mixed oxide composed of iridium oxide and tantalum oxide. At this time, the mixing ratio of iridium and tantalum has a great influence on the life of the electrode, and under the conditions of a large amount of bubbles generated in a galvanizing line and severe flow conditions, iridium 60-9 can be calculated as metal.
A mixed oxide coating containing 5% by weight and 40 to 5% by weight of tantalum has excellent durability, but further 70 to 90% by weight of iridium and 30 to 10% by weight of tantalum in terms of metal.
The mixed oxide coating containing is particularly durable.
The amount of iridium metal contained in the electrode active layer is 2 to 20.
0 g / m ² is preferred. The mixed oxide layer having the above composition is confirmed to be a dense film with particularly few cracks and voids by observing a cross section with a scanning electron microscope (SEM), and has an affinity with an intermediate layer made of tantalum or its alloy. Since it is also good, a stable potential is exhibited for a long time and the utilization rate of the active layer is high.

Examples of the coating method of the electrode active material include a thermal decomposition method, an electrochemical oxidation method, a powder sintering method, a vapor phase growth method including sputtering, and the like, but the thermal decomposition method is preferable. That is, these metal salt solutions are applied to the surface of an intermediate layer formed on a metal substrate that has been subjected to a predetermined pretreatment, dried, and then heat-treated at 350 to 600 ° C. in an air atmosphere. The target electrode active material coating layer can be obtained by repeating the above steps tens of times.

[0015]

In the past, when the electrode active material layer was formed on the metal substrate by the sputtering method, the surface was usually cleaned by chemical etching and the surface was slightly roughened. This is mainly because the thickness of the layer formed by sputtering is an extremely thin layer of about 0.1 μm, and if the roughening is increased by a physical method such as blasting, sufficient coating cannot be performed. Is. However, when the intermediate layer is formed by sputtering like the electrode according to the present invention, the film thickness is required to be 1 μm or more, and the roughening of the surface of the substrate is not only performed by chemical etching, but the average roughness is kept within a certain range. By carrying out the blast treatment in this way, an intermediate layer with few pinholes is formed, and even after coating with this intermediate layer, the surface of the substrate exhibits three-dimensional unevenness exhibiting an excellent anchoring effect on the electrode active material. As a result, the adhesion with the electrode active material is improved, and a highly durable anode having sufficient resistance to passivation by oxygen generated on the electrode active material can be obtained.

[0016]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples. All percentages in the examples are on a weight basis. Example 1 and Comparative Examples 1 and 2 Commercially available titanium plates (10 × 50 × 1.5 mm) were degreased with acetone, and then grit blasted at a pressure of 4 kgf / cm ² using alumina grit with a grain size of # 30. This was etched with a 10% oxalic acid solution kept at 90 ° C. for 3 hours, washed in running water for 24 hours, and dried to obtain an electrode substrate. When the roughness of the substrate surface was measured by a stylus type surface roughness measuring device, the center line average roughness Ra was 5.2 μm. As Comparative Example 1, the commercially available titanium plate was used without being blasted and only subjected to etching treatment. Further, as Comparative Example 2, the same blasting and etching processes as in Example 1 were performed using alumina grit with a grain size of # 10.

Next, each titanium plate was mounted in a chamber of a DC bipolar sputtering apparatus, a tantalum target was used, a vacuum degree of 1 × 10 ^-2 mbar, and an input power of 6
Sputter coating of tantalum was performed for about 1 hour under conditions of ˜7 kW and Ar flow rate of 600 sccm. By this treatment, a tantalum film having a thickness of about 2 μm was formed on the substrate. A solution having the following liquid composition was applied to this substrate. TaCl ₅ 185 mg H ₂ IrCl ₆ · 6H ₂ O 1000 mg 35% HCl 1 ml n-CH ₃ (CH ₂ ) ₃ OH 10 ml This was dried at 120 ° C. for 10 minutes and then calcined in an electric furnace kept at 490 ° C. for 20 minutes. did. This coating operation of the electrode active material was repeated tens of times to obtain an electrode active layer containing about 30 g / m ² of iridium oxide (weight composition ratio was I
r / Ta = 8/2).

Using these electrodes as anodes and zirconium plates as cathodes, a current density of 300 was obtained in a sulfuric acid aqueous solution containing a bath temperature of 80 ° C., pH 1.6 and sodium sulfate 100 g / l.
An accelerated life test was performed by an A / dm ² constant current electrolysis method. In this test, the time until the cell voltage increased by 5 V was determined as the electrode life. The results obtained are shown in Table 1.
The center line average roughness Ra of each sample shown in the table is the result of measuring the titanium substrate surface at the time when the pretreatment of sputtering is completed. As is clear from the results shown in Table 1, in the examples of the present invention in which the blasting and etching treatments were performed so that the surface roughness of the substrate was set within the limited range, high temperature, high current density, and severe electrolysis conditions were used. Nevertheless, it can be seen that the electrode life has been extended significantly.

Examples 2, 3 and Comparative Examples 3, 4 An electrode was prepared in the same manner as in Example 1 except that the etching conditions were as follows. (Example 2) 1.5% to a 43% sulfuric acid solution kept at 65 ° C.
Time immersion (Example 3) 2 in a 17.5% hydrochloric acid solution kept at 70 ° C
Time Immersion Next, an electrode was produced in the same manner as in Example 1 except that the following treatment was performed instead of the etching treatment in Example 1. (Comparative Example 3) No etching treatment (Comparative Example 4) Atmospheric oxidation treatment for 1 hour in an electric furnace at 450 ° C The same accelerated life test as in Example 1 was performed on the above electrodes. Table 1 shows the results. As shown in Table 1, it can be seen that the examples of the present invention in which the etching treatment is performed after the blast show a longer life.

Example 4 An electrode was prepared in the same manner as in Example 1 except that the commercially available titanium plate was chemically etched using a 30% aqueous solution of hydrofluoric acid at 25 ° C. for 15 minutes. The same accelerated life test as in Example 1 was performed on this electrode.
The results are shown in Table 1.

Examples 5, 6, 7, 8 Of the composition of the coating liquid used for forming the electrode active material, T
Substituting 185 mg of aCl ₅ for 39, 82, 13 respectively
Electrodes were produced in the same manner as in Example 1 except that the amounts were changed to 1,317 mg, and the electrodes were set as Examples 5, 6, 7, and 8, respectively. The same accelerated life test as in Example 1 was performed on this electrode. The results are shown in Table 1.

Example 9 A commercially available titanium plate surface was blasted with alumina grit having a grain size of # 36, and 185 mg of TaCl ₅ was contained in the composition of the coating solution used for forming the electrode active material.
An electrode was produced in the same manner as in Example 1 except that the amount was changed to 493 mg. The same accelerated life test as in Example 1 was performed on this electrode. The results are shown in Table 1.

[0023]

[Table 1]

[0024]

According to the present invention, a thin film intermediate layer of tantalum or its alloy, which is dense and has few pinholes, can be formed on a metal substrate of an electrode by blasting and chemical etching. Further, the roughening of the substrate by blasting mainly brings about an anchoring effect of the substrate with respect to the electrode active material coating layer, and peeling and dropping of the active material coating layer are extremely small,
Further, this also makes it possible to prolong the life by weighting the electrode active material. Further, due to the uniform film structure with few cracks and voids, it exhibits high resistance to a large amount of gas generation and erosion of the electrolytic solution under flowing conditions. Therefore, the anode according to the present invention can be used for a long time in an electrolytic solution having a strong corrosive property (a condition in which the bath temperature and the acid concentration are high) and an electrolysis with a large flow rate of the solution and a large amount of oxygen generation due to a high current density. It can maintain its function over time.

Claims (5)

[Claims] 1. A surface of a conductive metal substrate made of metallic titanium or its alloy is roughened by blasting and then subjected to chemical etching to obtain a center line average roughness Ra of 3 to 3.
A method for producing an oxygen generating anode, characterized by providing an intermediate layer made of tantalum or an alloy thereof by a sputtering method after setting the thickness to 8 μm, and providing an electrode active material coating layer containing a platinum group metal oxide on the surface thereof. 2. The method for producing an oxygen generating anode according to claim 1, wherein the intermediate layer made of tantalum or its alloy has a thickness of 1 to 5 μm. 3. The electrode active material is a mixed oxide composed of a platinum group metal oxide and an oxide of one or more kinds of valve metals selected from the group consisting of titanium, tantalum, niobium and zirconium metals. Item 3. A method for producing an oxygen generating anode according to Item 1 or 2. 4. The platinum-group metal as the electrode active material is 1 in terms of metal.
The method for producing an oxygen generating anode according to claim 3, which comprises a mixture of a platinum group metal oxide containing 0 to 97% by weight and a valve metal of 90 to 3% by weight, and a valve metal oxide. 5. The electrode active material is iridium 60 in terms of metal.
5. A mixture of iridium oxide and tantalum oxide containing .about.95% by weight and 40-5% by weight tantalum.
The method for producing an oxygen generating anode according to 1.