JPH08199384A - Electrode for electrolysis and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] [Structure] (a) 3 to 7 mol% of iridium oxide and 93 to 97 mol are provided on the surface layer of a titanium substrate having a surface layer made of an alloy of titanium and tantalum.
% Tantalum oxide first intermediate layer, (b) 10-
A second intermediate layer consisting of 30 mol% iridium oxide and 70-90 mol% tantalum oxide, and (c) 60-98 mo
An electrode for electrolysis, wherein an outer layer composed of 1% iridium oxide and 2-40 mol% tantalum oxide is sequentially provided. [Effect] It has excellent durability and is particularly useful as an anode in electrolysis such as surface treatment of a metal accompanied by generation of oxygen in the anode, metal foil production, and recovery.

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 bubble 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, a new layer (hereinafter referred to as an intermediate layer) is provided between the electrode substrate and the catalyst layer,
A method of protecting the electrode substrate is taken. Sufficient corrosion resistance to this intermediate layer; sufficient electrical conductivity; good adhesion to the electrode substrate;
Good adhesion with the catalyst layer; layer without cracks; low electrochemical activity;
It is required to have characteristics such as low manufacturing cost. As a condition that satisfies such conditions,
Method for forming an intermediate layer composed of two or more kinds of bubble metal oxides having different valences, and forming an intermediate layer composed of a bubble metal oxide and a platinum group metal or an electrically conductive platinum group metal oxide A method, a method of forming a bubble metal or its alloy by a thermal spraying method, an ion plating method or the like has 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 tetravalent valence on a 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 iridium oxide, platinum metal and tantalum oxide containing 40 to 90 mol% of iridium, 0.1 to 30 mol% of platinum and 50 to 10 mol% of tantalum on a conductive substrate. There is proposed an oxygen generating electrode in which an iridium oxide layer or an iridium oxide-tantalum oxide layer containing at most 50 mol% of tantalum is provided as an upper layer through the underlayer. 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. 5-2875752, 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 underlying layer of iridium oxide and tantalum oxide containing 4 mol% and 86 to 91.6 mol% of tantalum. There has been proposed an oxygen generating electrode provided with an upper layer 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 Patent Laid-Open No. 5-171483, plasma spraying of metal tantalum and / or its alloy powder on a conductive substrate made of titanium or its alloy in a non-oxidizing atmosphere under reduced pressure is carried out. 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 an electrode active substance is coated on a conductive metal substrate made of a bubble metal or its alloy, 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 also been proposed. However, a thin film intermediate layer formed by these methods has a conductive property. Although it has the effect of suppressing the permeation of the electrolytic solution into the substrate,
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 or for the production of metal foils.
An object is to provide a sufficiently durable electrode for electrolysis and a method for producing the same.

[0010]

The present inventors have conducted various studies to develop a durable electrode for electrolysis, in particular, an electrode that can be used as an anode for a long period of time in electrolysis with oxygen generation in the anode. As a result of stacking, it was discovered that the alloy layer of titanium metal and tantalum metal has a higher corrosion resistance than titanium alone, and a corrosion resistant first intermediate layer is formed on the alloy layer of titanium and tantalum to protect the alloy layer. Durability by forming a second intermediate layer having good corrosion resistance and conductivity on the first intermediate layer, and further providing an outer layer that is an oxygen-generating active substance on the second intermediate layer. The inventors have found that an extremely excellent electrode for electrolysis can be obtained and completed the present invention.

Thus, according to the present invention, (a) 3 to 7 mol% of iridium oxide and 93 to 9% of (a) iridium oxide are provided on the surface layer of a titanium substrate having a surface layer made of an alloy of titanium and tantalum.
A first intermediate layer consisting of 97 mol% tantalum oxide,
(B) 10 to 30 mol% of iridium oxide and 70 to 9
A second intermediate layer consisting of 0 mol% tantalum oxide, and (c) 60-98 mol% iridium oxide and 2-40 m
It is intended to provide an electrode for electrolysis, which is characterized in that an outer layer made of ol% tantalum oxide is sequentially provided.

The present invention also provides a titanium substrate having a surface layer consisting of an alloy of titanium and tantalum, on said surface layer.
(A) Ir / T containing an iridium compound and a tantalum compound
After applying a solution containing a in a molar ratio of a of 3/97 to 7/93, a heat treatment is performed in an oxidizing atmosphere to obtain 3 to 7 mol% of iridium oxide and 93
A first intermediate layer consisting of ˜97 mol% of tantalum oxide is formed, and (b) an iridium compound and a tantalum compound are added on the first intermediate layer at a molar ratio of Ir / Ta in terms of metal of 1/9 to 3/3 / After applying a solution containing it at a ratio of 7 to 10 by heating in an oxidizing atmosphere,
A second intermediate layer composed of 30 mol% iridium oxide and 70 to 90 mol% tantalum oxide is formed, and then (c) the iridium compound and the tantalum compound are converted to Ir / Ta metal on the second intermediate layer. Molar ratio 60/40
After applying a solution containing it at a ratio of ~ 98/2,
By heat treatment in an oxidizing atmosphere, 60 to 98
The present invention provides a method for producing an electrode for electrolysis, which comprises forming an outer layer made of mol% iridium oxide and 2 to 40 mol% tantalum oxide.

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

In the electrode of the present invention, titanium is used as the substrate. The titanium substrate used is preferably pretreated in advance, as is customary. Preferred specific examples of such pretreatment include those described below. First, after degreasing the surface of the titanium substrate by washing with alcohol or the like and / or by electrolysis in an alkaline solution according to a conventional method, the hydrogen fluoride concentration is 1 to 20% by weight.
The treatment with hydrofluoric acid or a mixed acid of hydrofluoric acid and other acids such as nitric acid and sulfuric acid removes the oxide film on the surface of the titanium substrate and roughens the titanium crystal grain boundary units. 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 acid-treated is washed with water and dried.

One of the features of the present invention is that the surface of the titanium substrate is modified to form a surface layer made of an alloy of titanium and tantalum and excellent in corrosion resistance on the titanium substrate.

The surface layer made of an alloy of titanium and tantalum can be formed, for example, by using the titanium substrate as a cathode and using tantalum as an electrode rod to scan the surface of the titanium substrate for electrical discharge machining. It is generally desirable to carry out the electric discharge machining in a non-oxidizing atmosphere, for example, an argon atmosphere.

The diameter of the tantalum electrode rod used for electric discharge machining can be selected within the range of usually 1 to 10 mm, but a diameter of 4 mm or more is generally preferable from the viewpoint of work efficiency and the like.

Further, the discharge conditions differ depending on the diameter of the tantalum electrode rod used. For example, when a tantalum electrode rod having a diameter of 6 mm is used, the electrode discharge pulse is 200-60.
0 Hz and the capacitance of the capacitor can be 100 to 400 μF.

In this way, electric discharge machining is performed for 5 to 30 minutes per 1 dm ² to form an alloy layer of titanium and tantalum on the surface of the titanium substrate. The surface of the alloy layer of titanium and tantalum thus formed is generally roughened, and the roughness measured by a surface roughness meter (SEF-30D, a surface roughness / contour shape measuring instrument manufactured by Kosaka Laboratory Ltd.). Value is usually 50 ~
It is about 200 μm.

The alloy layer of titanium and tantalum formed as described above is at least 10 μm, preferably 30 μm.
It can have the above thickness. The thickness of the alloy layer is 1
If it is less than 0 μm, it is generally impossible to impart sufficient corrosion resistance to the titanium substrate. On the other hand, the upper limit of the thickness of the alloy layer is not particularly limited, but even if it is made thicker than necessary, the effect accompanying it cannot be obtained and it is rather economically disadvantageous. Therefore, it is usually 150 μm or less, preferably Is suitably 100 μm or less.

On the surface layer made of an alloy of titanium and tantalum of the titanium substrate formed as described above, three layers respectively made of iridium oxide and tantalum oxide, the iridium oxide content increasing as the layers get higher. That is, the first intermediate layer, the second intermediate layer and the outer layer are sequentially coated.
Here, iridium oxide is substantially crystalline Ir.
It consists of O ₂ . In addition, tantalum oxide is an amorphous oxide.
It is represented by Ta ₂ O ₅ , and strengthens the binding property of the coating under the conditions of oxidation described later.

The first intermediate layer comprises 3 to 7 mol%, preferably about 5 mol% iridium oxide and 93 to 97 mol%, preferably about 95 mol% tantalum oxide,
It covers the roughened convexes and concaves of the surface layer made of an alloy of titanium and tantalum of the titanium substrate, and contributes to the improvement of the corrosion resistance of the substrate. The coverage of the first intermediate layer is generally 0.1-5.
0 g / m ^2, preferably be in the range of 0.5 to 3.0 g / m ^2.

The formation of the first intermediate layer will be specifically described below.

A solvent solution containing an iridium compound and a tantalum compound, preferably a lower alcohol solution, is applied on a surface layer of a titanium substrate made of an alloy of titanium and tantalum, and then dried to deposit the iridium compound and the tantalum compound. . 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 these iridium compound and tantalum compound include methanol, ethanol, propanol, isopropanol, butanol or a mixture thereof.

The ratio of the iridium compound to the tantalum compound in the above solution is 3 in terms of Ir / Ta metal conversion molar ratio.
It can be in the range of / 97 to 7/93, preferably about 5/95.

The application of the solution onto the alloy layer of the titanium substrate can be carried out, for example, by a spraying method, a brush coating method, a dipping method, etc., and thus a lower alcohol solution of the iridium compound and the tantalum compound is applied. The titanium substrate is dried at a relatively low temperature in the range of about 20 to about 150 ° C. and then fired in an oxidizing atmosphere, usually in the atmosphere.

The treatment described above can be repeated until the coating amount reaches the above range. The calcination is generally about 400 to about 700 ° C., preferably about 450 to about 400 in a suitable heating furnace such as an electric furnace, a gas furnace, an infrared furnace.
This can be done by heating to a temperature in the range of about 600 ° C. The heating time at that time can be approximately 5 minutes to 2 hours depending on the size of the substrate to be fired. By this firing, the iridium compound and the tantalum compound are changed to iridium oxide and tantalum oxide, respectively, to form the first intermediate layer.

On the first intermediate layer consisting of iridium oxide and tantalum oxide coated as described above, 1
0-30 mol%, preferably 15-25 mol% iridium oxide and 70-90 mol%, preferably 75-85 mol%
A second intermediate layer of tantalum oxide is provided. In the second intermediate layer, the content of iridium oxide is 10 mo.
If it is less than 1%, the electric conductivity tends to be deteriorated, while if it exceeds 30 mol%, the oxygen generating activity is increased and the corrosion resistance may be deteriorated.

The second intermediate layer is formed by adjusting the Ir / Ta metal conversion molar ratio of the iridium compound and the tantalum compound in the coating solution to 10/90 to 30/70, preferably 15/85 to 25/75. The formation can be performed in the same manner as the formation of the first intermediate layer, except that the change is made within the range. The coating amount of the second intermediate layer is generally 0.5 to 10.0.
g / m ^2, and preferably from to to be within the range of 1.0 to 5.0 g / m ^2.

As described above, the second intermediate layer having corrosion resistance and electrical conductivity can be formed, and the corrosion-resistant titanium substrate-modified layer on which the alloy layer of titanium and tantalum is formed can be used as the corrosion-resistant first layer. By forming the first intermediate layer and further the second intermediate layer having corrosion resistance and electrical conductivity, an electrode having epoch-making high durability can be obtained.

On the second intermediate layer composed of iridium oxide and tantalum oxide formed as described above, 60 to 98 mol%, preferably 70 to 95 m is further added.
ol% iridium oxide and 2-40 mol%, preferably 5
An outer layer of ˜30 mol% tantalum oxide is provided. In this outer layer, the content of iridium oxide is 60 mol%
If less than 98 mol%, when used at a high current density, the oxygen generation activity is insufficient and the electrode life tends to be shortened.
If it exceeds 1%, the consumption of the electrode catalyst (outer layer) tends to increase.

The formation of the outer layer also has a molar ratio of Ir / Ta of the iridium compound and the tantalum compound in the coating solution in terms of metal of 60/40 to 98/2, preferably 70.
It can be performed in the same manner as the formation of the first intermediate layer, except that the change is made within the range of / 30 to 95/5.

The coating amount of the outer layer is generally 10 to 60 g /
It is suitable to set it to be m ² , preferably in the range of 30 to 50 g / m ² .

The electrode of the present invention manufactured as described above does not easily passivate the titanium interface even when used for a long time under high current density, has a long life, and operates under high current density. It can be suitably used as an anode for high-speed plating of metal and for producing metal foil.

[0036]

The present invention will be described in more detail with reference to the following examples, which do not limit the scope of the present invention.

Examples 1 to 6 and Comparative Examples 1 to 8 A titanium plate material corresponding to JIS type 2 ( ^t 3.0 × ^w 100 ×
(100 mm) was washed with alcohol, treated in 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 electric discharge machining was performed for 10 minutes in a glow box in which a tantalum electrode having a diameter of 6 mm was used and the atmosphere was replaced with argon. After that, the titanium plate on which tantalum was subjected to electric discharge machining was cut with a fine cutter into ^t 3.0 × ^w 10 × ^l 10 mm. EP
Elemental analysis of the cross section of the titanium plate subjected to electric discharge machining was performed by MA (electron probe microanalyzer), and an alloy layer in which tantalum metal was dispersed in titanium metal was confirmed. The thickness of this alloy layer is 30 to 50 μm.
m. A solution of iridium chloride in butanol and a solution of tantalum chloride in ethanol are mixed to obtain Ir2.8 g / l.
And Ta 50.0 g / l (molar blending ratio: 5Ir-95Ta) were prepared, and 3.0 μl per 1 cm ² was weighed with a micropipette, and the alloy of titanium and tantalum produced as described above was prepared. After coating on the modified layer of the titanium substrate on which the layer was formed, the layer was vacuum dried at room temperature for 30 minutes and further baked in the atmosphere at 500 ° C. for 10 minutes. This step 2
Repeated times.

Then, in order to obtain a second intermediate layer, a butanol chloride iridate butanol solution and a tantalum chloride ethanol solution are mixed to obtain Ir 9.37 g / l and Ta 50.0 g / l.
After preparing a coating solution containing 1 (molar compounding ratio: 15Ir-85Ta), the same steps as above were repeated three times using this coating solution.

Next, in order to obtain an outer layer, a butanol solution of iridium chloride and an ethanol solution of tantalum chloride are mixed, and coating containing Ir50.0 g / l and Ta20.2 g / l (molar blending ratio: 70 Ir-30Ta) is applied. After preparing the liquid,
Using this coating solution, the same steps as those described above were repeated 8 times to prepare Example electrode-1.

In the same manner as in the above-mentioned Example electrode-1, Example electrodes-2 to 6 and Comparative example electrodes-1 to 8 in which the composition of the coating layer was changed as shown in Table-1 were prepared.

[0041] on the modified layer of Comparative Example 9-11 Example electrode -1 similar ^t 3.0 to form an alloy layer of titanium and tantalum in the methods of × ^w 10 × ^l 10mm titanium substrate, H ₂ PtCl ₆ Was dissolved in butanol at a concentration of 10 g / l of platinum metal with a micropipette, 3.0 μl per cm ² was weighed, applied onto the above substrate, vacuum dried at room temperature for 30 minutes, and further in air at 500 ° C. 1
Bake for 0 minutes. This process was repeated 5 times. Next, an outer layer having the same composition as that of Example electrode-1 was formed by the same method as that of Example electrode-1 to prepare Comparative electrode-9.

Further, the titanium plate was washed with a hot oxalic acid aqueous solution, and the first intermediate layer, the second intermediate layer and the outer layer having the same composition as that of the example electrode-2 were formed on the titanium plate similarly to the example electrode-2. The electrode of Comparative Example 10 was manufactured by the method described above.

Further, the titanium plate was washed with a hot oxalic acid aqueous solution, and a butanol solution of iridium chloride and an ethanol solution of tantalum chloride were mixed on the titanium plate to obtain Ir 5.90 g /
1 and Ta 50.0 g / l (molar blending ratio: 10 Ir-90Ta)
After preparing a coating solution containing
3.0 μl per cm ^{2 is} weighed and applied, then at room temperature for 30
It was vacuum dried for 10 minutes and then baked in the air at 500 ° C. for 10 minutes. This process was repeated 4 times. Then, in order to obtain the outer layer, a solution of iridium chloride in butanol and a solution of tantalum chloride in ethanol are mixed to obtain Ir50.0 g / l and T
After preparing a coating solution containing a 5.23 g / l (molar compounding ratio: 90 Ir-10Ta), the same steps as above were repeated 8 times using this coating solution to prepare Comparative Example electrode-11.

Tables 1 and 2 show the electrode life when each of the electrodes thus obtained was electrolyzed under the following conditions.

<Electrolysis conditions> Electrolyte solution: 1 MH ₂ SO ₄ -1M Na ₂ SO ₄ Current density: 4 A / cm ² Counter electrode: Pt Distance between electrodes: 10 mm From the results shown in Tables 1 and 2, the example electrodes Shows that the electrode has a long life.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

As described above, according to the electrode for electrolysis of the present invention, a titanium-tantalum alloy layer having good corrosion resistance is formed on the surface of a titanium substrate by electric discharge machining using a tantalum electrode, and the alloy layer is formed on the alloy layer. The titanium-tantalum alloy layer is roughened by forming the first intermediate layer having good corrosion resistance and further forming the second intermediate layer having good corrosion resistance and electrical conductivity on the alloy layer. By providing excellent adhesion between the layer and the first intermediate layer and the second intermediate layer, suppressing passivation of the titanium substrate, and forming an outer layer which is a catalyst layer on the second intermediate layer. It is possible to provide an electrode for electrolysis that can be used for a long time.

Claims (2)

[Claims] 1. A titanium substrate having a surface layer made of an alloy of titanium and tantalum, having (a) 3 to 7 mol% of iridium oxide and 93 to 97 m.
a first intermediate layer consisting of ol% tantalum oxide, (b) 10-30 mol% iridium oxide and 70-9
A second intermediate layer consisting of 0 mol% tantalum oxide, and (c) 60-98 mol% iridium oxide and 2-40.
An electrode for electrolysis, wherein an outer layer composed of mol% tantalum oxide is sequentially provided. 2. An iridium compound and a tantalum compound (a) Ir / T are provided on the surface layer of a titanium substrate having a surface layer made of an alloy of titanium and tantalum.
After applying a solution containing a in a molar ratio of a of 3/97 to 7/93, a heat treatment is performed in an oxidizing atmosphere to obtain 3 to 7 mol% of iridium oxide and 93
A first intermediate layer made of ˜97 mol% tantalum oxide is formed, and (b) an iridium compound and a tantalum compound are provided on the first intermediate layer in a molar ratio Ir / Ta in terms of metal of 1/9.
After applying a solution containing it in a ratio of 3/7, heat treatment is performed in an oxidizing atmosphere to obtain 10 to 30 mol.
% Iridium oxide and 70 to 90 mol% tantalum oxide are formed on the second intermediate layer, and then (c) the iridium compound and the tantalum compound are provided on the second intermediate layer in a molar ratio of Ir / Ta in terms of metal. Is 60/40
After applying a solution containing it at a ratio of ~ 98/2,
By heat treatment in an oxidizing atmosphere, 60 to 98
2. The method for producing an electrode for electrolysis according to claim 1, wherein an outer layer composed of mol% iridium oxide and 2 to 40 mol% tantalum oxide is formed.