JPH05156480A - Production of oxygen generating anode - Google Patents

Abstract

PURPOSE:To economically produce a durable oxygen generating anode by thermally spraying Ta on a Ti substrate, applying a soln. of the compds. of Ir, Ti, Nb, Zr, Sn, etc., and heating the soln. in an oxidizing atmosphere. CONSTITUTION:A wire of metallic Ta and/or its alloy is thermally sprayed on a conductive metallic substrate consisting of Ti or its alloy to provide an intermediate layer consisting essentially of the metallic Ta and/or its alloy. Arc spraying or plasma spraying is exemplified as the thermal spraying. A soln. of a metallic compd. of at least one kind among Ti, Nb, Zr and Sn and an Ir compd. and the soln. of a Ta compd. if necessary, are applied on the intermediate layer and heated at 360-550 deg.C in an oxidizing atmosphere. By this treatment, an electrode active layer consisting of >=20mol% IrO2 and the balance Ti, Nb, Zr and Sn or further at least one kind of metal oxide of Ta is formed. Consequently, passivation of the substrate is prevented, and a durable electrode is obtained with the dissolution and falling reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. 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 a lead alloy is currently used as an anode for plating steel sheets of tin, zinc, chromium, etc. Lead is consumed relatively quickly, and the plating solution is contaminated by the eluted lead.
There are problems such as deterioration of the plating film. Platinum-plated anodes and platinum foil clad anodes are being considered as alternative anodes, but platinum also has the drawback of being considerably worn out.
Therefore, various anodes for oxygen generation have been proposed which use noble metals and oxides thereof, which are less consumed, as electrode active substances.

However, in 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 material, an 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 Ohta 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 the utilization efficiency cannot be said to be good 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 material. 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.

Japanese Patent Laid-Open No. 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, particularly 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 also has an oxygen generating activity, passivation eventually occurs.

In JP-A-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 is not 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 a long-life electrode by preventing the passivation of a substrate, which is a problem in an insoluble anode for oxygen generation, which is being studied as an anode for electroplating zinc, chromium, etc., in an economically advantageous manner. ..

[0009]

In the insoluble anode for oxygen generation, the present inventors have sprayed a metal tantalum and / or tantalum alloy wire on a substrate to form an intermediate layer having a small oxygen content and fine pores. The present invention has been completed by finding that the formation of the above makes it possible to obtain an anode having a sufficient resistance to passivation by oxygen generated on the electrode active substance and having a long life. That is, the present invention provides an intermediate layer mainly composed of metal tantalum and / or its alloy by spraying a wire of metal tantalum and / or its alloy on a conductive substrate made of titanium or its alloy. Titanium,
A solution containing at least one metal compound selected from niobium, zirconium, and tin and an iridium compound is applied, and heated to 360 to 550 ° C. in an oxidizing atmosphere to give 20 mol% or more of iridium oxide. The method for producing an oxygen generating anode is characterized in that an electrode active layer made of an oxide of at least one metal selected from titanium, niobium, zirconium, and tin is provided as a balance.
Further, according to the present invention, a solution containing a tantalum compound in addition to the above metal compound is applied on the intermediate layer, and the same heat treatment is performed. A method for producing an oxygen generating anode, which is characterized in that an electrode active layer is formed.

A method of spraying tantalum metal on a metal substrate has been proposed so far. For example, JP-A-48-
In Japanese Patent No. 40676 and Japanese Patent Application Laid-Open No. 56-112458, a corrosion resistant metal powder such as tantalum is sprayed on a metal substrate by plasma spraying, and an electrode active material is coated thereon. 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, it is considered that the sprayed coating is a state in which powders in a molten state are gathered together, and microscopically holds a particle diameter of several tens of μm. 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 retains microporosity with a particle diameter of several tens of μm and is therefore subject to 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 film by a thermal decomposition method, it was unexpectedly surprising. It was also found that the tantalum film has little oxidation, can obtain good adhesion to the noble metal oxide film, and has a long life.

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 with 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 for 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 take 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 grit 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 with 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 unknown, even in the above-described 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, it is preferable that the porosity is small as described above, and it is not preferable that the porosity is too porous. Further, since tantalum is a metal that 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, but contains an oxide of these and X
The oxidation rate or its oxide content based on the ratio of the main strength measured by the line diffraction method is 1 to 30% by weight, 15 to 30% by weight in the case of flame spraying, and 1 in the case of plasma spraying.
~ 7 wt%, explosion spraying, arc spraying are in the middle. It is believed that this tantalum oxide and / or its alloy oxides prevent the oxidation of the substrate from proceeding during the electroplating of the steel sheet, similar to metal tantalum and / or its alloys.

The electrode active layer formed on the surface of the intermediate layer is a mixture of iridium oxide and an oxide of at least one metal selected from titanium, niobium, zirconium and tin, or a mixture of these and tantalum oxide. Iridium oxide is 20 mol% or more, preferably 20 to 95.
Mol%, at least one metal oxide selected from titanium, niobium, zirconium and tin, or a mixture of these and tantalum oxide is 80 mol% or less, preferably 80 mol% or less.
~ 5 mol%. Particularly preferred is iridium oxide 3
It is in the range of 0 to 90 mol% and other metal oxides of 70 to 10 mol%. If only iridium oxide is used, peeling and detachment during electroplating will occur frequently, shortening the life of the electrode. The presence of at least one metal oxide selected from titanium, niobium, zirconium and tin is considered to have a good effect on the adhesion strength to the thermal spraying intermediate layer mainly composed of metal tantalum and / or its alloy. Be done. Further, the presence of tantalum oxide in these further promotes the above effect. In this case, the mixing ratio of tantalum oxide and at least one metal oxide selected from titanium, niobium, zirconium, and tin is not particularly limited, but if tantalum oxide is 10 mol% or more, the above effect is large. Is.

The electrode active layer is made of an alcohol-soluble metal salt such as iridium chloride, iridium trichloride, tantalum pentachloride, titanium tetrachloride, zirconium oxychloride, niobium pentachloride, stannous chloride, ethyl alcohol, butyl alcohol, It is dissolved in a solvent such as propyl alcohol to prepare a mixed solution having a predetermined composition, which is applied by a method such as brush coating, roll coating, spray coating or dipping. After coating, it is dried at 100 to 150 ° C. for about 10 to 20 minutes to evaporate the solvent, and then 360 to 5 in an electric furnace in an air or oxygen atmosphere.
The thermal decomposition treatment is performed at 50 ° C., preferably 380 to 500 ° C. for 10 to 30 minutes. If the heat treatment temperature is less than the above range, thermal decomposition does not occur completely, 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 proceeds and damages. The electrode active layer coated in this way is 5 g
When it is / m ² or more, the 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]

As a result of the introduction of the intermediate layer, the anode according to the present invention delays the passivation of the titanium substrate, and can be used up to about 90% or more of the iridium oxide coating layer of the electrode active layer, without such an intermediate layer. In this case, there is a large difference from the case where the voltage increases when 20 to 30% of the coating layer is used. This is particularly remarkable when the current density is 100 A / dm ² or more.

Basically, since the intermediate layer of the anode according to the present invention contains metal tantalum as a main component, it has good conductivity. Since this intermediate layer is formed by thermal spraying of a metal wire,
It is considered that the reasonably porous structure enhances the adhesion to the electrode active layer and protects the metal substrate sufficiently. The oxide of a metal selected from titanium, niobium, zirconium and tin in the electrode active layer has a rutile type or rutile type similar crystal structure similar to iridium oxide, and also improves the adhesion to the intermediate layer.

[0023]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples. Example 1 and Comparative Example 1 A commercially available titanium plate (1 × 10 × 0.1 cm) was degreased with trichloroethylene and then blasted using an alumina grit (# 24) at a pressure of 4 Kg / cm ² . 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.
When the crystal structure of the film was examined by X-ray diffraction, Ta and Ta ₂ O ₅ were formed and the oxidation rate was 11%.

A solution having the following composition was applied to the surface thereof. Niobium pentachloride 0.35 g Iridium chloride 1.0 g Hydrochloric acid 1.0 ml Butyl alcohol 15 ml This was dried at 120 ° C. for 20 minutes and then pyrolyzed in an electric furnace at 450 ° C. for 20 minutes to give Nb ₂ O
An electrode having a film made of a mixed oxide of 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 sprayed 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 5050 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%. On the other hand, as a comparison, the sprayed layer was omitted, an electrode active layer was formed on the substrate in the same manner as above, and the same test was performed. The life of the anode was 560 hours.

Examples 2 to 5, Comparative Examples 2 and 3 The 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 oxides.
An electrode containing g / m ² was prepared, and the same electrolytic test was carried out to obtain the results shown in Table 1.

[0027]

[Table 1]

Example 6, Comparative Example 4 An electrode was prepared and subjected to an electrolytic test in the same manner as in Example 1 except that the coating solution for forming the electrode active layer had the following composition. Tantalum pentachloride 0.23 g Niobium pentachloride 0.17 g Iridium chloride 1.0 g Hydrochloric acid 1.0 ml Butyl alcohol 15 ml The composition of the electrode active layer is Ta ₂ O ₅ (20 mol%), Nb ₂
O is ₅ (20 mol%) and IrO ₂ (60 mol%). As a result of the electrolytic test, the usable time of the electrode was 5100 hours, and as a result of the fluorescent X-ray analysis, the residual iridium oxide was 0.8 g / m ² , which was a utilization rate of 92%. On the other hand, as a comparison, the sprayed layer was omitted, an electrode active layer was formed on the substrate in the same manner as above, and the same test was performed. The life of the anode was 560 hours.

Examples 7 to 10 and Comparative Example 5 The coating of the thermal sprayed layer was carried out in the same manner as in Example 1, and the composition of the electrode active layer was changed as shown in Table 2 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 2.

[0030]

[Table 2]

Examples 11 to 13 Commercially available titanium plates (1 x 10 x 0.1 cm) were placed on an alumina paste.
Tantalum wire after blasting with # 30
(Wire diameter 1.2 mm), argon gas as plasma gas
Wire plasma spraying is performed using 100 μm thick
A sprayed layer was obtained. When the film was examined by X-ray diffraction, T
a and Ta₂O_FiveHas been formed and oxidation by X-ray diffraction
The rate was 5%. On top of this, the coating solution of Example 1
Instead of niobium, titanium tetrachloride 0.24 g, respectively
Zirconium xylchloride 0.42 g, stannous chloride 0.2
The same coating solution and heat treatment method were used except that 4 g was added.
TiO₂(40 mol%)-IrO₂(60 mol
%), ZrO₂(40 mol%)-IrO₂(60 mol
%) And SnO ₂(40 mol%)-IrO₂(60 mol
%) For each electrode active layer of 10 g / m²(Oxidation
(As iridium) and the same test,
The life of the pole and the utilization rate of iridium oxide are as shown in Table 3.
there were.

[0032]

[Table 3]

Comparative Example 6 A commercially available titanium plate (1 × 10 × 0.1) which has been blasted.
cm) with tantalum powder (particle size: 20 to 50 μm) and plasma spraying using argon gas as a plasma gas to obtain a sprayed layer having a thickness of 50 μm. Then, 10 g / m ² (Ir) of iridium oxide was added in the same manner as in Example 1.
Although an electrode active layer of O ² : Nb ₂ O ₅ = 60: 40 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 life of the anode was 790 hours.

Comparative Example 7 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 Nb ₂ O ₅ (40 mol%) was applied in the same manner.
An electrode having a film (10 g / m ² as iridium oxide) of an electrode active layer made of a mixed oxide of —IrO ₂ (60 mol%) was obtained. When an electrolytic test was conducted using this electrode under the same conditions as in Example 1, the life of the anode was 680 hours, the residual iridium oxide was 7.0 g / m ² , and the utilization rate was 30%.

Examples 14 to 16 The coating of the sprayed layer was carried out in the same manner as in Examples 11 to 13, and
In place of the niobium pentachloride of the coating solution of Example 6
Titanium chloride 0.12 g, zirconium oxychloride 0.2
Same application except 1g and stannous chloride 0.12g
Depending on the liquid and heat treatment method, Ta₂O_Five(20 mol%)-
TiO₂(20 mol%)-IrO₂(60 mol%), T
a₂O_Five(20 mol%)-ZrO₂(20 mol%)-I
rO₂(60 mol%) and Ta₂O_Five(20 mol%)-
SnO₂(20 mol%)-IrO ₂From (60 mol%)
10g / m for each electrode active layer²(Iridium oxide
As a result of the same test, the life of the anode
The utilization rates of iridium oxide and iridium oxide are shown in Table 4.

[0036]

[Table 4]

Comparative Example 8 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 a plasma gas to obtain a sprayed layer having a thickness of 50 μm. Then, 10 g / m ² (Ir) of iridium oxide was added in the same manner as in Example 1.
O ₂ : Ta ₂ O ₅ : Nb ₂ O ₅ = 60: 20: 20 molar ratio) was obtained, but the tantalum sprayed layer was strongly oxidized and the adhesion between the tantalum sprayed layer and the electrode active layer was extremely poor.
When the same test as in Example 1 was performed, the life of the anode was 8
It was 10 hours.

Comparative Example 9 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 liquid as in Example 6 was applied to the surface, and Ta ₂ O ₅ (20 mol%) was applied in the same manner.
-Nb ₂ O ₅ (20 mol%) - IrO ₂ (60 mol%)
An electrode having a film (10 g / m ² as iridium oxide) of the electrode active layer made of the mixed oxide of was obtained. When an electrolytic test was conducted using this electrode under the same conditions as in Example 1, the life of the anode was 660 hours, the residual iridium oxide was 7.0 g / m ² , and the utilization rate was 30%. ..

[0039]

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

It is clear from the above 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 tantalum wire and / or 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 removed during electrolysis in a sulfuric acid solution and can use most of the iridium oxide catalyst is obtained by a relatively simple manufacturing method.

Claims (3)

[Claims] 1. An intermediate layer containing metal tantalum and / or an alloy thereof as a main component is formed by spraying a wire of metal tantalum and / or an alloy thereof on a conductive metal substrate made of titanium or an alloy thereof. Iridium oxide is obtained by applying a solution containing at least one metal compound selected from titanium, niobium, zirconium, and tin and an iridium compound onto the layer, and heating at 360 to 550 ° C. in an oxidizing atmosphere. At least 1 selected from titanium, niobium, zirconium, and tin with 20 mol% or more
A method for producing an oxygen generating anode, characterized in that an electrode active layer made of a metal oxide of one kind is provided. 2. At least one selected from titanium, niobium, zirconium and tin on the intermediate layer according to claim 1.
A solution containing a seed metal compound, a tantalum compound, and an iridium compound is applied, and 360 to 550 is applied in an oxidizing atmosphere.
20 mol% of iridium oxide by heating to ℃
A process for producing an oxygen generating anode, characterized in that an electrode active layer comprising the tantalum oxide and at least one metal oxide selected from titanium, niobium, zirconium and tin is provided as the balance. 3. The method for producing an oxygen generating anode according to claim 1, wherein the thermal spraying is arc spraying or plasma spraying.