JP3422885B2 - Electrode substrate - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode used as an anode in an acidic electrolytic solution in which oxygen is generated as an anodic reaction, and is particularly suitable for high current density electrolysis in high-speed galvanizing or electrolytic copper foil production. It relates to the anode used.

[0002]

2. Description of the Related Art Lead anodes have been used for high-speed galvanizing of steel sheets and production of electrolytic copper foils. The reason is that the electrolytic bath contains sulfuric acid as a main component, it is extremely corrosive, and there is almost no stable conductive substance other than lead, the electrolytic current density is large, and moreover, lead is Because it is relatively inexpensive. Another reason is that lead easily forms alloys with other metals and has excellent workability. However, even when using a lead alloy that consumes little, the amount consumed during electrolysis is a few mg /
Ah, which can pollute the environment,
In addition, there is a problem that it is contained in the plated layer or the foil, which is a product, and has an adverse effect. Therefore, so-called dimensionally stable electrodes have been used in which the surface of a thin film forming metal such as titanium, a valve metal, or an alloy thereof is coated with an electrode catalyst layer of a platinum group metal or its oxide. . This electrode is used as a chlorine generation electrode when sodium hydroxide and chlorine are produced by electrolysis of salt.

Although the components of the electrode catalyst coating of such an electrode were changed and used for oxygen generation, there was a problem in that oxygen was transferred into the coating layer and passivated by surface oxidation of titanium as a substrate. was there. To solve this problem, the inventors have made various efforts. For example, in order to retain conductivity even if passivation occurs in a part,
The base metal surface is previously made an oxide containing another metal,
For example, a non-stoichiometric oxide containing a small amount of oxygen is formed in advance so as to give conductivity close to that of a semiconductor and not lose conductivity even when reacting with oxygen transferred from the electrode surface.

Further, titanium is not always chemically stable in sulfuric acid, which is an electrolytic bath used for these purposes, and therefore tantalum is coated on the surface and then the coating is formed, and the vitreous intermediate layer is formed. It is also practiced to coat the titanium completely. However, the formation of a semiconductor oxide coating on the substrate surface is not always completely formed as in the case of making electronic components,
It is possible that the electrode base body is rendered nonconductive before the coating layer of the electrode catalyst reaches the end of its life, and the corrosion resistance is not necessarily high. This was also the case with a material containing a conductive material such as platinum in order to maintain conductivity in the coating. On the other hand, in the substrate coated with tantalum, tantalum itself has sufficient corrosion resistance, but due to the difference in expansion coefficient between tantalum and titanium, the electrode catalyst layer is formed by thermal decomposition of the compound coated with the electrode catalyst substance. In the process, volume expansion occurs, which causes separation from titanium, which is the substrate. Therefore, there is a problem that the conditions for forming the electrode catalyst substance are extremely limited, and a good effect cannot always be expected.

Further, there is a problem that the vitreous coating does not necessarily have good conductivity, and the adhesiveness between the electrode catalyst substance and the vitreous coating is not good. That is, usually, the electrode catalyst substance and the substrate form a chemical bond, but in the case of a glassy coating, the chemical bond cannot be expected. Although various improvements have been made in this way, it cannot be said that the problems have been sufficiently solved. Further, although a technique of spraying a corrosion resistant substance has been proposed, even if the sprayed layer itself has sufficient corrosion resistance, since the thickness of the intermediate layer of the electrode is about 100 μm, the through hole can be completely formed. It was extremely difficult to prevent. If a corrosive electrolyte enters between the thermal spray layer and the substrate through these slight through holes, the substrate will not polarize even during electrolysis, and the interface may corrode, resulting in sufficient durability. I couldn't say that there was anything.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a long-life insoluble electrode that can be used as an anode in an acidic electrolyte in which an oxygen evolution reaction occurs as an anodic reaction.

[0007]

According to the present invention, in an electrode substrate for an anode in which an oxygen generating reaction occurs as an anodic reaction, a layer containing a platinum group metal or an oxide thereof is formed on a metal substrate and then a conductive It is an electrode substrate on which a sprayed layer of titanium oxide is formed. Further, the above-mentioned electrode base body in which the platinum group metal is platinum and the oxide of the platinum group metal is palladium oxide. Further, the conductive titanium oxide is at least one selected from rutile type titanium oxide which becomes conductive by plasma spraying, a composite oxide of titanium oxide and other oxides, or titanium oxide which is made conductive by doping. It is an electrode substrate.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION That is, the electrode substrate of the present invention is
A thin film-forming metal such as titanium or an alloy thereof is used as an electrode substrate for generating oxygen as an anodic reaction, and a layer containing a platinum group metal or its oxide is formed on a substrate such as titanium, and then platinum is formed. Substrate for an anode that can be used for producing an anode that can be used in an acidic electrolyte in which an oxygen generation reaction occurs in which conductive titanium oxide is coated by plasma spraying on a layer containing a group metal or its oxide Is. Since the electrode substrate of the present invention has a layer of platinum group metal or platinum group metal oxide formed even when the electrolytic solution penetrates the layer formed by plasma spraying conductive titanium oxide, The surface of the electrode substrate is not corroded or passivated, and it is possible to manufacture a long-life electrode.

The metal substrate such as titanium used for manufacturing the electrode substrate of the present invention is roughened by sandblasting or the like and then cleaned by acid cleaning or the like. Since the sprayed layer of titanium oxide formed on the electrode substrate after cleaning has a thickness of several tens of μm, the surface roughness of the substrate metal is preferably JIS Rmax = 50 to 150 μm, which is comparable to this. A coating of a platinum group metal or metal oxide is formed on the cleaned metal substrate. The platinum group metal or metal oxide may be a single metal or a plurality of metal oxides. Specific examples include oxides of metals such as platinum and gold, and metals such as palladium and rhodium, and oxides of titanium or tantalum may be added to these metals or metal oxides.

The formation of the platinum group metal or metal oxide layer is carried out by thermal decomposition of a compound containing the platinum group metal,
It can be formed by a method such as plating or vapor deposition, but it is preferably formed by thermal decomposition. The thermal decomposition is performed by applying a solution containing a platinum group metal compound,
Firing is performed at a temperature of ~ 600 ° C to form a metal or oxide layer. The firing atmosphere can be appropriately selected depending on the material used and the layer to be formed.

The conductive titanium oxide layer formed on the platinum group metal or oxide layer is preferably formed by spraying titanium oxide particles. Titanium oxide particles that can be used are, in addition to those to which conductivity is imparted by dope or the like,
Even purified rutile particles and commercially available titanium oxide or rutile particles for plasma spraying can be used because they are partially reduced during plasma spraying and show conductivity. Regarding the size of the particles used, those having an average particle size of 10 to 200 μm are preferable, and 20 to 100 μm.
Particularly preferred is m.

The sprayed layer is uniformly deposited on the platinum group metal or its compound layer and has a thickness of 20 to 20.
It is preferably 0 μm. For plasma spraying, it is preferable to use a mixed gas of argon and hydrogen as the plasma gas.

The electrode substrate obtained as described above includes
An electrode catalyst coating can be formed by applying a solution containing an electrode catalyst substance and thermally decomposing it, but a protective layer consisting of tantalum oxide and titanium oxide is formed on the electrode substrate before forming the electrode catalyst layer. Layers can be formed. In particular, various electrode catalyst coatings can be formed, but it is preferable to form a coating containing iridium oxide and tantalum oxide.

[0014]

EXAMPLES The present invention will be described below by showing Examples of the present invention. Example 1 A titanium plate was blasted with # 120 iron grit to have a surface roughness of JIS Rmax = 110 μm, and then pickled in 25% sulfuric acid at 85 ° C. to remove the grit remaining on the surface and to activate it. did. Then, an isopropyl alcohol solution of chloroplatinic acid was applied to the surface of the titanium plate with a brush and kept at room temperature for 10 minutes, and then heated at 300 ° C. for 10 minutes while feeding a gas containing 15% hydrogen in air. It was disassembled. This operation was repeated 4 times to form a platinum layer of ² g / m ² .

Next, an average particle size of 50 μm which has been subjected to reduction treatment in a mixed gas of carbon monoxide and carbon dioxide at 1000 ° C.
m titanium oxide was sprayed on the entire surface by plasma spraying to form a sprayed layer having a thickness of 100 μm. A plasma spray gun (manufactured by Metco) was used for spraying the particles, the spraying conditions were a current of 500 A, a voltage of 60 to 70 V, the plasma gas was a mixed gas of argon and hydrogen, and the raw material supply rate was 20 g /
Min, pitch 5 mm, and the distance between the spray gun and substrate is 1
It was 00 mm.

In order to evaluate the characteristics of the obtained electrode substrate, a hydrochloric acid aqueous solution of titanium tetrachloride and tantalum pentachloride containing 85 mol% of titanium and 15 mol% of tantalum is applied to the surface of the electrode substrate and the temperature is 560 ° C. in air. Heated for 15 minutes. This operation was repeated 3 times. Further, a coating solution prepared by dissolving iridium chloride in an ethyl alcohol solution of tantalum butoxide so as to be iridium: tantalum = 70: 30 (molar ratio) was applied to the surface, and baked in air at 530 ° C. for 10 minutes. . This operation was repeated 15 times to prepare an electrode. The obtained electrode was subjected to an immersion test at 75 ° C. in 20% by weight sulfuric acid. When the sample was taken out after 1000 hours, the electrode of this example showed a slight weight loss, but no other change was observed.

When electrolysis was carried out at a current density of 200 A / dm ^{2 using} 20% by weight of sulfuric acid as an anode at 75 ° C., the voltage increased 2150 hours after the start of energization and the electrolysis could not be continued. It was When the substance on the electrode substrate was analyzed after the completion of electrolysis, it could be confirmed that the electrode catalyst substance was consumed.

Comparative Example 1 An electrode was prepared and tested in the same manner as in Example 1 except that the platinum layer was not provided. In the immersion test, the titanium portion was corroded. Moreover, when an electrolysis test was conducted, the voltage increased in 1520 hours, and the electrolysis could not be continued. After the electrolysis was completed, the coating on the electrode substrate was examined, and it was found that there was corrosion between the sprayed layer and the substrate metal. In addition, about 30% of the electrode catalyst substance remained, and it was confirmed that corrosion was the cause of the short life.

Example 2 A 30% by weight hydrochloric acid solution of palladium chloride was applied to the surface of a titanium plate, and after drying, air was passed through the titanium plate at 520 ° C. for 10 hours.
It was heated and baked for 1 minute. The operations of coating, drying and heating and firing were repeated 4 times to form a coating layer containing 3 g / m ² of palladium oxide. The obtained coating layer contained about 10% by weight of titanium oxide, which is considered to be due to the elution of the titanium plate of the substrate, with respect to palladium. 1 at 650 ° C
After heating and stabilizing for a period of time, plasma spraying was performed in the same manner as in Example 1 to form a sprayed layer having a thickness of 50 μm. 5 × 10 ^-2 Ωcm containing 15 wt% tantalum oxide for thermal spraying
Average particle size of 50μm and maximum particle size of 150μm
The particles of the titanium oxide sintered body were used. When a coating of an electrode catalyst substance was formed on the obtained electrode substrate in the same manner as in Example 1 and an immersion test was conducted in the same manner as in Example 1, no change was observed. Further, when an electrolysis test was conducted in the same manner, it was possible to perform electrolysis 2300 hours after the start of energization.

Comparative Example 2 An electrode was prepared and tested in the same manner as in Example 2 except that the palladium oxide layer was not provided. In the immersion test, the coating layer peeled off. In addition, the titanium portion was corroded. Moreover, when an electrolysis test was performed,
At 00 hours, the voltage increased and it became impossible to continue electrolysis. After the electrolysis was completed, the coating on the electrode substrate was examined, and it was found that there was corrosion between the sprayed layer and the substrate metal.

[0021]

EFFECT OF THE INVENTION In the electrode substrate of the present invention, a conductive titanium oxide sprayed layer is formed after forming a coating of a platinum group metal or its oxide on a metal substrate. Even when it is used as a base body of an anode for oxygen generation, corrosion between the base body and a conductive titanium oxide sprayed layer hardly occurs, and a long-life anode can be obtained.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C25D 17/10 101 C25D 17/10 101A // C25D 1/04 311 1/04 311 (58) Fields investigated (Int.Cl. ⁷ , DB name) C25D 17/12 C23C 4/10 C23C 28/00 C25B 11/10 C25C 7/02 307 C25D 17/10 101

Claims (3)

(57) [Claims] 1. In an electrode substrate for an anode in which an oxygen generation reaction occurs, a layer containing a platinum group metal or its oxide is formed on a metal substrate, and then a sprayed layer of conductive titanium oxide is formed. And an electrode substrate. 2. The electrode substrate according to claim 1, wherein the platinum group metal is platinum, and the platinum group metal oxide is palladium oxide. 3. The conductive titanium oxide is at least selected from rutile type titanium oxide which becomes conductive by plasma spraying, a composite oxide of titanium oxide and another oxide, or titanium oxide which is made conductive by doping. The electrode substrate according to claim 1, which is one kind.