JPH0533177A - Production of anode for generating oxygen - Google Patents

Abstract

PURPOSE:To prevent the generation of the passivation of an insoluble anode for metal plating by thermally spraying an intermediate layer of a Ta metal on a Ti substrate, then forming a Ta2O5 layer contg. IrO2, thereon at the time of producing this insoluble anode. CONSTITUTION:The surface of an anode base body consisting of metal Ti, Ti-Ta-Nb alloy or the like is roughened by sand blasting, etc., and thereafter Ta or Ta alloy is thermally sprayed thereto as the insoluble anode for generating oxygen to be used at the time of electroplating Sn, Zn, Cr, etc., onto the surfaces of a steel sheet. An aq. soln. of a compsn. contg. 20mol% IrO2 and consisting of the balance Ta2O5 is applied on the surface of the thermally sprayed layer of the Ta metal and is heated to 360 to 550 deg.C in an oxidation atmosphere to form an electrode active layer consisting of the IrO2-contg. Ta2O5. The insoluble anode having the excellent durability is obtd. without passivation of the anode during the electrolysis or plating.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing an oxygen generating anode. In particular, it relates to an oxygen generating anode used for electroplating tin, zinc, chromium or alloys thereof.

[0002]

2. Description of the Related Art Lead or lead alloys are currently used as anodes for plating steel sheets of tin, zinc, chromium, etc. However, lead is consumed relatively quickly, and the plating solution is contaminated by the eluted lead and the plating film. There is a problem such as deterioration of. Platinum-plated anodes and platinum foil clad anodes have been studied as alternative anodes, but platinum also has the drawback of being considerably consumed, and therefore oxygen generation using noble metals and their oxides, which consume less, as electrode active substances. Various anodes for use have been proposed.

However, in the case of an electrode in which titanium and its alloy, which are widely used from the viewpoint of economy and workability, are simply coated with an electrode active substance, the electrode coating layer is formed by oxygen generated in the anode during use. A non-conductive oxide layer is formed between the substrates, and even if the amount of remaining electrode active substance is sufficient, the function as an electrode is lost, and eventually the electrode coating layer peels off and becomes unusable. (Kenichiro Ota et al., Electrochemistry, 57, No
1, P.I. 71-75 (1989)).

For this reason, the amount of the electrode active substance deposited tends to be increased, but it cannot be said that the utilization efficiency is high in view of using an expensive noble metal. In order to solve this problem, Japanese Patent Laid-Open No. 59-38394 discloses an oxide of at least one metal selected from titanium and tin having a valence of 4 on the substrate and a pentavalent atom. 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 valent tantalum and niobium having a valency is provided, and the intermediate layer is coated with an electrode active substance. In this case, the intermediate layer has no oxygen generation activity,
The electrical conductivity is considered to be obtained based on the valence control theory based on the generally known tetravalent and pentavalent metals.
Its conductivity is not sufficient.

JP-A-59-150091 proposes that platinum is dispersed in this intermediate layer for the purpose of imparting conductivity, but platinum itself is consumed in an electrolytic solution, especially in a sulfuric acid acidic solution. Since it is large, the durability of the intermediate layer is limited. Further, in this case, since the intermediate layer itself has an oxygen generating activity, passivation eventually occurs.

In Japanese Patent Laid-Open No. 62-174394, a porous platinum layer formed by electroplating is described as an intermediate layer, but even in this case, the fundamental solution has not been reached for the same reason as above.

Further, JP-A-57-192281 discloses an electrode having titanium or a titanium alloy as a base material and an electrode coating made of a metal oxide, and a conductive oxide layer of tantalum and / or niobium as an intermediate layer thereof. Although an electrode for electrolysis involving the generation of oxygen is proposed, the oxide layer of tantalum or niobium cannot be said to be sufficient to prevent the passivation phenomenon due to oxygen.

[0008]

The object of the present invention is to provide tin,
An object of the present invention is to provide an electrode having a long life by preventing passivation of a substrate, which is a problem in an insoluble anode for oxygen generation, which is being studied as an anode for electroplating of zinc, chromium, etc., in an economically advantageous manner. .

[0009]

DISCLOSURE OF THE INVENTION The inventors of the present invention have sprayed a metal tantalum and / or tantalum alloy wire on a substrate in an insoluble anode for oxygen generation, and have a low oxygen content.
The present invention has been completed by discovering that by forming a microporous intermediate layer, it is possible to obtain an anode having sufficient resistance to the passivation by oxygen generated on the electrode active material and having a long life. It is a thing. That is, the present invention is to spray metal tantalum and / or its alloy wire onto a conductive metal substrate made of titanium or its alloy to spray metal tantalum and / or metal tantalum.
Alternatively, an intermediate layer containing the alloy as a main component is provided, and a solution containing a tantalum compound and an iridium compound is applied to the intermediate layer, and heated to 360 to 550 ° C. in an oxidizing atmosphere to obtain 20% by weight of iridium oxide. A method for producing an oxygen generating anode is characterized in that an electrode active layer having the above-mentioned balance and made of tantalum oxide is provided.

Methods for spraying a coating of tantalum metal onto a metal substrate have been previously proposed. For example, JP-A-48-40676 and JP-A-56-11245.
No. 8 discloses that a corrosion resistant metal powder such as tantalum is sprayed on a metal substrate by plasma spraying, and an electrode active material is coated on the metal substrate. However, in this method, the thermal spray material is a metal powder, and it is known that its particle size is generally about 10 to 100 μm. Therefore, the sprayed coating is in a state in which powders in a molten state are gathered together, and microscopically, it is considered that the particle diameter of several tens of μm is retained. When a noble metal oxide is pyrolytically coated on a coating of such tantalum powder plasma-sprayed at a temperature of 360 to 550 ° C., the tantalum coating is strongly oxidized and the oxidized tantalum coating is brittle and easily peels off from the metal substrate. It is considered that this is because the tantalum film has a microporosity with a particle diameter of several tens of μm and undergoes severe oxidation. In the above publication, the life is increased by alloying with the substrate by heat treatment in a vacuum or irradiation with an electron beam or plasma arc, but sufficient results have not yet been obtained.

When the present inventors did not use powder for thermal spraying of metal tantalum and / or its alloy, but performed arc spraying or plasma spraying with a wire, and coated a noble metal oxide on the coating by a thermal decomposition method, it was unexpectedly surprising. It was also found that the tantalum coating has little oxidation, can obtain good adhesion to the noble metal oxide coating, and can be a long-life electrode.

When tantalum wire and / or its alloy wire is sprayed, it is not clear to what extent the wire material is melted, but it is several tens to several hundreds compared to the powder material used in plasma spraying. It is considered to be twice as large, and for that reason, it is considered that embrittlement due to oxidation of the tantalum intermediate layer is small in the thermal decomposition step when forming the surface coating layer.

Titanium or its alloy used in the metal substrate of the present invention includes titanium metal, titanium-tantalum-niobium,
It is a titanium-based alloy such as titanium-palladium, and can have various shapes such as a plate shape, a rod shape, an expanded shape, and a perforated plate shape.

The intermediate layer formed on the surface of the metal substrate takes in some oxygen during thermal spraying and becomes a thermal sprayed layer of metal tantalum and its oxide and / or tantalum alloy and its oxide. The thermal spraying methods include flame spraying, plasma spraying, arc spraying, explosive spraying and the like, and particularly stable coating can be obtained by performing arc spraying or plasma spraying. The surface of the substrate is subjected to grid blasting, shot blasting or sand blasting as a pretreatment for thermal spraying. Alumina, silicon carbide, sand or the like is used as the blast material, and the particle size is 20
About 0 to 1000 μm is suitable.

In the arc spraying used in the present invention, a voltage is applied between two metal wires to generate an electric arc between the metal wires at the tip of the spray gun, and the arc melts the metal wires. The molten metal is deposited on the metal substrate with a high-speed compressed gas. In addition, plasma spraying using a metal wire uses a metal wire for spraying as an electrode when heating an inert gas such as nitrogen or argon to a high temperature with an electric arc,
As the gas passes through the electric arc, it is ionized into a plasma stream. At this time, the metal wire is melted and deposited on the metal substrate.

The thickness of the intermediate layer of tantalum and its oxide and / or tantalum alloy and its oxide sprayed by these methods is about 5 to 500 μm. Since this intermediate layer is formed by thermal spraying, it has many pinholes and the porosity is in the range of 0.5 to 15%. Therefore, when performing electroplating on a substrate made of titanium or its alloy as an anode, the plating solution penetrates through the intermediate layer and is exposed to the plating solution. However, although the reason is not clear, even in the above-mentioned state, the titanium or titanium alloy of the base metal does not oxidize, the voltage does not rise, and the titanium base does not corrode. In order to prevent the oxidation of the substrate from progressing, it is effective that the intermediate layer has a thickness of 10 μm or more.

Further, as described above, it is not preferable that the porosity is small and the porosity is too porous. Further, since tantalum is a metal which is about 20 times more expensive than titanium, it is economically preferable to have a thickness of 500 μm or less. The intermediate layer formed by thermal spraying contains metal tantalum and / or its alloy as a main component, and contains these oxides and the oxidation rate or the oxide content depending on the ratio of the main strength measured by the X-ray diffraction method. The amount is 1 to 30% by weight, 15 to 30% by weight in the case of flame spraying, 1 to 7% by weight in the case of plasma spraying, and explosion spraying and arc spraying are in the middle thereof. It is believed that the oxides of this tantalum oxide and / or its alloys prevent the oxidation of the substrate during electroplating as well as the metal tantalum and / or its alloys.

The electrode active layer formed on the surface of the intermediate layer is composed of a mixture of iridium oxide and tantalum oxide, wherein iridium oxide is 20 mol% or more, preferably 20 to 95 mol% and tantalum oxide is 80 mol% or less, preferably Is 80
~ 5 mol%. Iridium oxide 3 is particularly preferable.
It is 0 to 90 mol% and tantalum oxide 70 to 10 mol%. If only iridium oxide is used, peeling and detachment during electroplating will occur frequently and the life of the electrode will be shortened. The presence of tantalum oxide in the electrode active layer has a good effect on the adhesion strength with the intermediate layer.

The electrode active layer is prepared by dissolving a metal salt of iridium chloride, iridium chloride, tantalum chloride or the like in a solvent such as ethyl alcohol, butyl alcohol or propyl alcohol to prepare a mixed solution having a predetermined composition, and brushing or rolling. It is formed by applying it by a method such as spray coating or dipping and performing a thermal decomposition treatment. After coating, it is dried at 100 to 150 ° C. for about 10 to 20 minutes in order to evaporate the solvent, and 360 to 550 in an electric furnace in an air or oxygen atmosphere.
C., preferably 380 to 500.degree. C. for 10 to 30 minutes for thermal decomposition treatment. If the heat treatment temperature is less than the above range, thermal decomposition does not completely occur, and if the heat treatment temperature exceeds the above range, oxidation of tantalum or a tantalum alloy forming an intermediate layer with the titanium substrate is promoted and damaged. The electrode active layer coated in this way is 5 g / m
^{When it is 2} or more, both catalytic ability and life for oxygen generation are improved.

The anode according to the present invention is preferably used with a current density of 10 A / dm ² or more during electroplating, and can be used up to 300 A / dm ² .

[0021]

In the anode according to the present invention, basically, the intermediate layer contains metal tantalum as a main component, so that the anode has good conductivity. Since this intermediate layer is formed by thermal spraying of a metal wire rod, it is considered that its moderate porosity enhances the adhesion to the electrode active layer and protects the metal substrate sufficiently. To be

[0022]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples. Example 1 A commercially available titanium plate (1 × 10 × 0.1 cm) was degreased with trichlorethylene and then blasted at a pressure of 4 kg / cm ² using an alumina grid (4). Next, a tantalum wire having a wire diameter of 1.2 mm was used to perform thermal spraying with an arc sprayer to obtain a thermal sprayed layer (intermediate layer) having a thickness of 50 μm. Examination of the chemical structure of the film by X-ray diffraction revealed that Ta and Ta ₂ O
₅ was formed and the oxidation rate was 11%.

A solution having the following composition was applied to the surface thereof. Tantalum pentachloride 0.47 g Iridium chloride 1.0 g Hydrochloric acid 1.0 ml Butyl alcohol 15 ml This was dried at 120 ° C. for 20 minutes, then in an electric furnace at 450 ° C. for 20 minutes, then in an electric furnace at 450 ° C. By pyrolyzing for 20 minutes, an electrode having a film made of a mixed oxide of Ta ₂ O ₅ (40 mol%) and IrO ₂ (60 mol%) was obtained. This operation was repeated several times to obtain an electrode active layer containing 10 g / m ^{2 of} iridium oxide. The adhesion between the electrode active layer and the thermal spray layer was very good.

This electrode was used as an anode in a 100 g / l sodium sulfate aqueous solution (pH 1.2) at 50 ° C., a platinum wire was used as a cathode, and a test was conducted at a current density of 200 A / dm ² until the cell voltage increased by 2V. Was determined as the life of the electrode. As a result, the usable time was 5150 hours. As a result of a fluorescent X-ray analysis, the residual iridium oxide was 0.8 g / m ² , and the utilization rate was 92%.

Examples 2 to 5, Comparative Examples 1 and 2 Coating of the thermal sprayed layer was performed in the same manner as in Example 1, and the composition of the electrode active layer was changed as shown in Table 1 to obtain 10 iridium oxide.
An anode containing g / m ² was prepared, and the same electrolytic test was carried out to obtain the results shown in Table 1.

[0026]

[Table 1]

Comparative Example 3 A commercially available titanium plate (1 × 10 × 0.1) that has been blasted
cm) with tantalum powder (particle size: 20 to 50 μm) and plasma spraying using argon gas as the plasma gas to obtain a sprayed layer having a thickness of 50 μm. Then, iridium oxide was added thereto in the same manner as in Example 1 to obtain 10 g / cm ² (I
Although an electrode active layer of rO ₂ : Ta ₂ O ₅ = 70: 30 molar ratio) was obtained, the tantalum sprayed layer was strongly oxidized, and the adhesion between the tantalum sprayed layer and the electrode catalyst layer was extremely poor. The test showed that the anode had a life of 830 hours.

Example 6 A commercially available titanium material (1 × 10 × 0.1 cm) was blasted with alumina grit (# 30), a tantalum wire (wire diameter 1.2 mm) was used, and argon gas was used as a plasma gas. Performs plasma spraying with a wire plasma sprayer using
A sprayed layer having a thickness of 100 μm was obtained. When the film was examined by X-ray diffraction, Ta and Ta ₂ O ₅ were formed, and the oxidation rate by X-ray diffraction was 5%. Then, Ta ₂ O ₅ (40 mol%) and IrO ₂ (6) were added in the same manner as in Example 1.
An electrode active layer composed of a mixed oxide with 0 mol%) was obtained.
The adhesion between the electrode active layer and the tantalum sprayed layer was good. When the same test as in Example 1 was conducted, the life of the anode was 5100 hours, and the residual iridium oxide was 0.5.
It was g / m ² , and the utilization rate of iridium oxide was 95%.

Comparative Example 4 A commercially available titanium plate (1 × 10 × 0.1 cm) was blasted in the same manner as in Example 1. Tantalum was sputtered thereon to a thickness of 1 μm using a high-frequency sputtering device (10 ⁻² Torr, argon gas, applied voltage: 2 KV). The same coating solution as in Example 1 was applied to the surface, and Ta ₂ O ₅ (40 mol%) was applied in the same manner.
An electrode having a film (10 g / m ² ) made of a mixed oxide of bismuth and IrO ₂ (60 mol%) was obtained. When a test was performed using this electrode under the same conditions as in Example 1, the life of the anode was 680 hours, and the residual iridium oxide was 7.0 g.
/ M ² , and the utilization rate was 30%.

[0030]

In the oxygen generating anode according to the present invention,
The intermediate layer formed by thermal spraying using a metal tantalum and / or tantalum alloy wire rod prevents electrolytic oxidation of the titanium or titanium alloy base material and has a strong corrosion resistance of the metal tantalum and / or tantalum alloy itself. It has resistance to electrolytic oxidation and good conductivity. In addition, the electrode active layer that is pyrolytically coated on the intermediate layer maintains good adhesion with the intermediate layer,
It has a large catalytic activity for oxygen generation and, like the intermediate layer, has excellent corrosion resistance to a sulfuric acid solution.

It is apparent from the above-mentioned Examples and Comparative Examples that the above effects are particularly remarkable as compared with the anode in which the intermediate layer is formed by a method other than the thermal spraying of the tantalum wire and / or the tantalum alloy wire. As described above, according to the present invention, a long-life oxygen generating anode that is less likely to be dissolved or dropped during electrolysis in a sulfuric acid-based solution and can use most of the iridium oxide catalyst is obtained by a relatively simple manufacturing method.

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[Procedure amendment]

[Submission date] April 8, 1991

[Procedure Amendment 1]

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[0009]

DISCLOSURE OF THE INVENTION The inventors of the present invention have sprayed a metal tantalum and / or tantalum alloy wire on a substrate in an insoluble anode for oxygen generation, and have a low oxygen content.
The present invention has been completed by discovering that by forming a microporous intermediate layer, it is possible to obtain an anode having sufficient resistance to the passivation by oxygen generated on the electrode active material and having a long life. It is a thing. That is, the present invention is to spray metal tantalum and / or its alloy wire onto a conductive metal substrate made of titanium or its alloy to spray metal tantalum and / or metal tantalum.
Alternatively, an intermediate layer containing the alloy as a main component is provided, and a solution containing a tantalum compound and an iridium compound is applied on the intermediate layer, and heated to 360 to 550 ° C. in an oxidizing atmosphere to obtain 20 mol % of iridium oxide. A method for producing an oxygen generating anode is characterized in that an electrode active layer having the above-mentioned balance and made of tantalum oxide is provided.

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[0010] The method of the skin film of tantalum metal sprayed on the metal substrate, have been proposed so far. For example, JP-A-48-40676 and JP-A-56-1124.
In JP 58, a corrosion resistant metal powder such as tantalum is sprayed on a metal substrate by plasma spraying, and an electrode active substance is coated on the metal substrate. However, the thermal spray material of this method is a metal powder, and it is known that its particle size is generally about 10 to 100 μm. Therefore, the sprayed skin is a state in which melted powder is gathered together, and microscopically, it is considered that the particle size is maintained at several tens of μm. When such a noble metal oxide on tantalum powder plasma spray rinds <br/> film pyrolyzed coating at a temperature of three hundred sixty to five hundred and fifty ° C., severe oxidation of the tantalum-coated tantalum skin film oxidized brittle, metal substrate Easier to peel off. It is believed that the tantalum skin layer is subjected to severe oxidation at microporous number 10μm particle size. In the above publication, the life is increased by alloying with the substrate by heat treatment in a vacuum or irradiation with an electron beam or plasma arc, but sufficient results have not yet been obtained.

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The present inventors have without the use of powder spraying metal tantalum and / or alloys thereof, and arc spraying or plasma spraying at a wire, when a noble metal oxide coated pyrogenically on its skin layer, surprisingly to less oxidation of tantalum skin film is also,
It is possible to obtain a noble metal oxide skin film and good adhesion was found that an electrode of the long life.

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[0017] A further towards the porosity is less as described above
Good rather, it is not desirable is too porous. Also, tantalum is a metal that is about 20 times more expensive than titanium,
Economically, the thickness is preferably 500 μm or less. The intermediate layer formed by thermal spraying contains metal tantalum and / or its alloy as a main component, and contains these oxides and the oxidation rate or the oxide content depending on the ratio of the main strength measured by the X-ray diffraction method. The amount is 1 to 30% by weight, 15 to 30% by weight in the case of flame spraying, 1 to 7% by weight in the case of plasma spraying, and explosion spraying and arc spraying are in the middle thereof. It is believed that the oxides of this tantalum oxide and / or its alloys prevent the oxidation of the substrate during electroplating as well as the metal tantalum and / or its alloys.

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[0026]

[Table 1]

Claims (2)

[Claims] 1. An intermediate layer containing metal tantalum and / or its alloy as a main component is formed by spraying a wire of metal tantalum and / or its alloy on a conductive metal substrate made of titanium or its alloy. A solution containing a tantalum compound and an iridium compound is applied onto the layer, and the solution is applied in an oxidizing atmosphere.
The iridium oxide is heated to 0 to 550 ° C.
A method for producing an oxygen generating anode, which comprises providing an electrode active layer containing 0% by weight or more and the remainder being tantalum oxide. 2. The method for producing an oxygen generating anode according to claim 1, wherein the thermal spraying is arc spraying or plasma spraying.