JP2002129371A - Electrode for electrolysis and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for electrolysis with adequate durability, even when used for water treatment, metal surface treatment, or the like, for which a polarity-switching current waveform is imposed, and to provide a manufacturing method therefor. SOLUTION: The electrode for electrolysis comprises (a) a base substance consisting of titanium, (b) an alloy layer of titanium and tantalum provided on the base substance, (c) a porous tantalum layer formed on the alloy layer, and (d) platinum supported in the porous tantalum layer.

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, and more particularly, to electrolysis in water treatment, metal surface treatment, etc., which is excellent in durability, and in particular, is provided with a current waveform in which polarity is switched. The present invention relates to a useful electrode for electrolysis and a method for producing the electrode.

[0002]

2. Description of the Related Art Conventionally, electrodes in which a platinum group metal, a platinum group metal oxide and a valve metal oxide are coated on a substrate made of titanium or a titanium alloy are used in many fields of the electrolytic industry. However, in the fields of water treatment, metal surface treatment, and the like, in which a current waveform that switches polarity is applied,
Electrodes coated with platinum, which are relatively stable against polarity switching, are used. However, in environments where the current density is high and H + generated on the noble potential side stays in the vicinity of the electrode, the potential is low. When the transition to, corrosion of the titanium substrate proceeds, an oxide layer having poor conductivity is formed at the titanium substrate interface, and even if the amount of the remaining electrode catalyst substance is sufficient, the function as an electrode is lost, There is a problem that the adhesion strength of the remaining electrode catalyst material is reduced, the electrode catalyst material is dropped, and the consumption rate is accelerated.

[0003] An object of the present invention is to solve the above-mentioned problems of the conventional electrolysis electrode, and to use the electrode as an electrolysis electrode for water treatment, metal surface treatment, or the like to which a current waveform that switches polarity is applied. And a durable electrolytic electrode and a method for producing the same.

[0004]

SUMMARY OF THE INVENTION The present inventors have developed a long-lasting electrolysis electrode, particularly an electrolysis electrode for water treatment, metal surface treatment, or the like, to which a current waveform that switches polarity is applied. As a result of various studies to develop an electrode that can be used over a wide range, this time, the intermediate layer consisting of an alloy layer of titanium and tantalum and a porous tantalum layer formed on the alloy layer has much higher corrosion resistance than titanium alone. It has been found that by carrying platinum, which is an electrode catalyst substance, on this intermediate layer, an electrode for electrolysis with extremely excellent durability can be obtained, and the present invention has been completed. .

Thus, the present invention relates to (a) an electrode substrate made of titanium, (b) an alloy layer of titanium and tantalum provided on the surface of the electrode substrate, and (C) a porous tantalum formed on the alloy layer. And (d) platinum supported on the porous tantalum layer.

The present invention also provides a method of forming a titanium-tantalum alloy layer by dispersing tantalum on the surface of a titanium substrate by electric discharge coating, and eluting a part of the titanium in the alloy surface layer to form a titanium alloy on the titanium substrate. After forming a porous tantalum layer via an alloy layer of titanium and tantalum, and then supporting platinum on the porous tantalum layer.

Hereinafter, the electrode for electrolysis of the present invention and the method for producing the same will be described in more detail.

[0008]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, titanium is used as an electrode substrate. It is desirable that the titanium substrate to be used is pre-treated in advance, as is usually done.
Specific examples of such preprocessing include, for example, the following.

First, after the surface of the titanium substrate is degreased by washing with alcohol and / or electrolysis in an alkaline solution, hydrofluoric acid having a hydrogen fluoride concentration of 1 to 20% by weight or hydrofluoric acid and nitric acid are used. By treating with a mixed acid with another acid such as sulfuric acid, an oxide film on the surface of the titanium base is removed and the surface of the titanium crystal grain boundary unit is roughened. The acid treatment is carried out at room temperature to about 40 ° C. depending on the surface condition of the titanium substrate.
The reaction can be carried out at a temperature of ° C. for several minutes to over ten minutes. Note that blasting may be used in combination to sufficiently perform surface roughening.

Next, the surface of the titanium substrate thus treated with acid is contacted with concentrated sulfuric acid to roughen the inner surface of the titanium crystal grain boundary into fine protrusions, and to form a titanium hydride layer on the surface of the titanium substrate. Is formed. The concentration of the concentrated sulfuric acid used is generally 40 to 80% by weight, preferably 50 to 60% by weight. If necessary, a small amount of sodium sulfate may be used for the purpose of stabilizing the treatment. Other sulfates and the like may be added. The contact with the concentrated sulfuric acid can be usually performed by immersing the titanium substrate in a concentrated sulfuric acid bath, and the bath temperature at that time is generally about 100.
To about 150 ° C., preferably about 110 to about 130 ° C., and the immersion time is usually about 0.
Five to about ten minutes, preferably about one to about three minutes, is sufficient. By this sulfuric acid treatment, the inner surface of the titanium crystal grain boundary is finely roughened into a projection shape, and the surface of the titanium substrate is coated with a very thin titanium hydride to prevent reoxidation in the air until the next step. Can be formed.
The surface of the titanium substrate thus treated with acid is washed with water and dried.

According to the present invention, an alloy layer of titanium and tantalum is provided on the surface of the titanium substrate appropriately pretreated as described above.

The formation of an alloy layer in which tantalum is dispersed in titanium can be performed, for example, by performing discharge coating by scanning the surface of the titanium substrate using the titanium substrate as a cathode and tantalum as an anode bar. The diameter of the tantalum anode rod used for the electric discharge coating process can be usually selected within a range of 1 to 10 mm, but a diameter of 4 mm or more is generally preferable from the viewpoint of working efficiency and the like.

The discharge coating conditions vary depending on the diameter of the tantalum anode rod used. For example, when a tantalum anode rod having a diameter of 6 mm is used, the discharge pulse is 200 to 6 μm.
00Hz, and the capacitor capacity is 100-400μ
F. Thus, 5 per dm ²
By performing discharge coating for up to 30 minutes, a titanium alloy layer in which tantalum is dispersed can be formed on the surface of the titanium substrate. At this time, the very thin titanium hydride coating on the titanium substrate surface generated in the concentrated sulfuric acid as described above is decomposed by the heat generated during the discharge coating process.

The titanium-tantalum alloy layer formed as described above has a thickness of at least 20 μm, preferably 60 μm.
It is desirable that the thickness be not less than m. If the thickness of the alloy layer is less than 20 μm, it is difficult to obtain a thickness of the alloy layer that can sufficiently prevent corrosion of the titanium substrate after the concentrated sulfuric acid treatment before coating with platinum. On the other hand, the upper limit of the thickness of the alloy layer is not particularly limited. However, even if the alloy layer is thicker than necessary, the effect associated therewith cannot be obtained and it is economically disadvantageous. 120 μm or less is appropriate.

The titanium substrate on which the alloy layer of titanium and tantalum is formed is then brought into contact with concentrated sulfuric acid to form a thin oxide film on the surface of the alloy layer with a depth of several μm to about 50 μm and a thickness of the alloy layer. The titanium in the alloy layer of 1/2 or less is eluted to form a porous tantalum layer on the titanium substrate via an alloy layer of titanium and tantalum.

The concentration of the concentrated sulfuric acid used is generally 40 to 80% by weight, preferably 50 to 60% by weight. If necessary, a small amount of sulfuric acid may be used for the purpose of stabilizing the treatment. Sodium and other sulfates may be added. The contact with the concentrated sulfuric acid can be usually carried out by immersing the titanium substrate in a concentrated sulfuric acid bath, and the bath temperature is generally about 100 to about 150 ° C, preferably about 11 ° C.
The temperature can be in the range of 0 to about 130 ° C, and the immersion time is usually about 5 seconds to several minutes, preferably about 0.5 to about 1 minute.

As described above, a porous tantalum layer is formed on the titanium base via the alloy layer of titanium and tantalum. This layer enhances the bonding property with the platinum coating described later.

The platinum is supported on the porous tantalum layer formed as described above. This loading is performed, for example, by allowing an alcohol solution containing a platinum compound to penetrate the porous tantalum layer with the solution on the surface of the porous tantalum layer, and drying the porous tantalum layer, which is thus impregnated with the solution, usually by drying. After that, it is thermally decomposed.

The platinum compound used herein is a compound which can be converted to platinum by decomposition under the following pyrolysis conditions, and specific examples thereof include platinum chloride, chloroplatinic acid and dinitrodiammineplatinum. Among them, dinitrodiammineplatinum is preferred. On the other hand, as a solvent for dissolving these platinum compounds, lower alcohols are particularly suitable, and for example, methanol, ethanol, propanol and the like are advantageously used.

Since dinitrodiammineplatinum does not directly dissolve in lower alcohols, it is convenient to first dissolve in nitric acid aqueous solution, concentrate the aqueous solution to dryness, and then dissolve in lower alcohols. The concentration of nitric acid in the aqueous nitric acid solution at that time can be generally in the range of 100 to 600 g · dm ⁻³ , preferably in the range of 200 to 500 g · dm ⁻³ .
If dinitrodiammine platinum is difficult to dissolve in an aqueous nitric acid solution at room temperature, it may be used at about 70 to about 100 ° C, preferably about 80 ° C.
It can be dissolved by heating to a temperature in the range of ~ 95 ° C.

[0021] The concentration of dinitrodiammineplatinum in nitric acid solution is generally 1-200 g · dm ^-3 in terms of a metal, preferably in the range of 20 to 150 g · dm ^-3. When the platinum concentration is lower than 1 g · dm ⁻³ , the efficiency of the enrichment operation deteriorates. When the platinum concentration exceeds 200 g · dm ⁻³ , dinitrodiammine platinum tends to be difficult to dissolve in the nitric acid aqueous solution.

The nitric acid aqueous solution of dinitrodiammine platinum thus prepared can be concentrated at about 50 to about 100 ° C, preferably about 70 to about 90 ° C. May be performed. Concentration can be performed until substantially dry.

The metal concentration of the platinum compound in the lower alcohol solution is generally 20 to 200 g · dm ⁻³ , preferably 4 to 200 g · dm ⁻³ .
It can be in the range of 0 to 150 g · dm ^-3 . The terms of metal concentration is low and the electrode catalyst carrying efficiency is worse than 20 g · dm ^-3, also 200 g · dm ^-3 electrode catalyst tends to aggregate exceeds, catalytic activity, carrying strength, uniformity, etc. loading amount Problems can arise.

The substrate having the porous tantalum layer impregnated with the platinum compound solution is dried, if necessary, at a temperature in the range of about 20 to about 100 ° C., and then thermally decomposed in an oxygen-containing gas atmosphere, for example, in the air. I do. Pyrolysis is carried out in a suitable heating furnace such as an electric furnace, a gas furnace, an infrared furnace, etc., generally at about 300 ° C.
To about 500 ° C, preferably from about 350 to about 450 ° C.

If necessary, the steps of solution permeation-drying-pyrolysis can be repeated to carry a predetermined amount of platinum. The amount of platinum supported is not strictly limited, but is usually 0.02 to ² g · dm ⁻² , preferably 0.1 to ² g · dm ⁻² .
It can be in the range of 0.5 g · dm ^-2 .

Hereinafter, the present invention will be described more specifically with reference to examples.

[0027]

EXAMPLE 1 A titanium plate material (t5 × 100 × 100 mm) equivalent to JIS 2 was degreased and washed with ethyl alcohol, and then 8% by weight at 20 ° C.
Treated in aqueous hydrofluoric acid for 2 minutes, then 120 ° C
In a 60% by weight aqueous sulfuric acid solution for 3 minutes. Then
The titanium substrate was taken out of the aqueous sulfuric acid solution, sprayed with cold water in a nitrogen atmosphere, quenched, and then dried. Next, using the titanium substrate as a cathode, a tantalum rod anode having a diameter of 6 mm was used to discharge for 15 minutes in an argon atmosphere.
A tantalum alloy layer was formed.

Further, a treatment is performed for 10 seconds in a 60% by weight sulfuric acid aqueous solution at 120 ° C. to elute titanium in the alloy layer up to a depth of about 5 μm from the surface, and an alloy layer of titanium and tantalum is formed on the titanium substrate. To form a porous tantalum layer.

Next, 0.4 cm ^{3 of} an ethanol solution of dinitrodiammineplatinum adjusted to a platinum concentration of 50 g · dm ^-3 was weighed, penetrated into the porous tantalum layer, and dried at room temperature for 10 minutes. The platinum compound was thermally decomposed by heating in the air at 350 ° C. for 10 minutes. This infiltration-drying-pyrolysis was repeated 9 times, and 0.2 g of platinum was supported on the porous tantalum layer to prepare Example electrode-1.

Further, after pretreating the titanium substrate in the same manner as in the above example, 0.2 g of platinum was electroplated to prepare a comparative example electrode-1.

Table 1 shows the consumption rate of platinum after electrolysis of the electrode thus obtained under the following conditions for 100 hours and further after treatment with an ultrasonic cleaner for 2 minutes. <Electrolysis conditions> Electrolyte solution: 1 MH ₂ SO ₄ ^-1 M Na ₂ SO ₄ Current density: 100 A · dm ⁻² Counter electrode: Pt Distance between electrodes: 10 mm

[0032]

[Table 1]

From the results shown in Table 1 above, it can be seen that the electrode of Example 1 of the present invention prevents deterioration of the interface with the titanium substrate even under conditions of high current density, and is an electrode having stable adhesion strength even after electrolysis. . Example 2 A titanium plate material (t5 x 100 x 100 mm) corresponding to JIS 2 was degreased and washed with ethyl alcohol, and then 8% by weight at 20 ° C.
Treated in aqueous hydrofluoric acid for 2 minutes, then 120 ° C
In a 60% by weight aqueous sulfuric acid solution for 3 minutes. Then
The titanium substrate was taken out of the aqueous sulfuric acid solution, sprayed with cold water in a nitrogen atmosphere, quenched, and then dried. Next, the titanium substrate was used as a cathode, and discharge was performed in the atmosphere for 20 minutes using a tantalum rod anode having a diameter of 6 mm to form an alloy layer having a thickness of about 100 μm in which tantalum was dispersed on a titanium substrate surface layer.

Further, it is treated for 1 minute in a 60% by weight aqueous sulfuric acid solution at 120 ° C.
Titanium in the alloy layer was eluted to a degree, and a porous tantalum layer was formed on the titanium substrate via an alloy layer of titanium and tantalum.

Then, 0.4 cm ^{3 of} an ethanol solution of dinitrodiammineplatinum adjusted to a platinum concentration of 50 g · dm ^-3 was weighed, penetrated into the porous tantalum layer, and dried at room temperature for 10 minutes. The platinum compound was thermally decomposed in the air at 400 ° C. for 10 minutes. This infiltration-drying-pyrolysis was repeated 9 times, and 0.2 g of platinum was supported on the porous tantalum layer to prepare Example electrode-2.

Further, a titanium substrate was pre-treated in the same manner as in the above embodiment to prepare an ethanol solution of dinitrodiammineplatinum adjusted to a platinum concentration of 50 g · dm ^-3 , and this coating solution was used in the above embodiment. The same process as described above was repeated 9 times to produce Comparative Example Electrode-2.

Further, after the titanium substrate was degreased with acetone, it was etched with oxalic acid at 80 ° C. for 12 hours.
Then TaCl ₅ 0.50 g, conc. HCl 1.0 cm ^3, was applied an alcohol solution of tantalum liquid composition of n- butyl alcohol 10.0 cm ^3. This was placed in an electric furnace, and the atmosphere in the furnace was replaced with argon gas. After that, the temperature was raised to 100 ° C. at a temperature rising rate of 10 ° C. · min ⁻¹ and held for 10 minutes, and further raised to 490 ° C. for 15 minutes. It was kept at 490 ° C. for 20 minutes and fired. This operation was repeated five times to form an intermediate layer of metal tantalum on the titanium substrate.
After preparing an ethanol solution of dinitrodiammineplatinum adjusted to dm ^-3 , the same steps as in the above example were repeated nine times using this coating solution to prepare comparative example electrode-3.

The electrode life obtained when the electrode thus obtained was electrolyzed together with the electrode of Example 1 under the following conditions is shown in Table 2.
Shown in <Electrolysis conditions> Electrolyte solution: 1 MH ₂ SO ₄ -1 M Na ₂ SO ₄ Current waveform: After electrolysis at +100 A · dm ⁻² for 80 seconds, −1
Repetition of electrolysis at 0 A · dm ^-2 for 20 seconds Counter electrode: Pt Distance between electrodes: 10 mm

[0039]

[Table 2]

From the results shown in Table 2, it can be seen that the electrode of the embodiment having excellent corrosion resistance has a long life even when exposed to a low potential environment in an acidic solution in which corrosion of the titanium base is apt to proceed. .

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C25F 7/00 C25F 7/00 S (72) Inventor Keisuke Sawada 2-12-30 Aoyagi, Soka City, Saitama Prefecture Research Department, Soka First Plant, Ishifuku Kinzoku Kogyo Co., Ltd. 2-12-30 Aoyagi, Soka City Ishifuku Kin Sangyo Kogyo Co., Ltd. Soka 1st Factory Research Department F-term (reference) 4D061 DA01 DA10 DB20 EA02 EB02 EB30 EB31 EB35 4K011 AA11 AA13 AA21 AA26 AA31 DA01 4K044 AA06 AB02 BA02 BA08 BB13 BB13 CA35 CA53 CA64

Claims (2)

[Claims] 1. An electrode substrate made of titanium, (b) an alloy layer of titanium and tantalum provided on the surface of the electrode substrate, (C) a porous tantalum layer formed on the alloy layer, and d) An electrode for electrolysis, comprising platinum supported on the porous tantalum layer. 2. An alloy layer of titanium and tantalum is formed by dispersing tantalum on the surface of a titanium substrate by electric discharge coating to form an alloy layer of titanium and tantalum, and eluting titanium in the alloy surface layer. A method for producing an electrode for electrolysis, comprising forming a porous tantalum layer through a layer, and then supporting platinum on the porous tantalum layer.