JP3463966B2 - Manufacturing method of electrode for electrolysis - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electrode for electrolysis, and more particularly, to excellent electrolysis under a high current density and excellent durability under a low potential environment. More particularly, the present invention relates to a method for producing an electrode for electrolysis useful as an anode in electrolysis such as surface treatment of a metal accompanied by oxygen generation on the anode, production of metal foil, and recovery. 2. Description of the Related Art Conventionally, an electrode in which a platinum group metal or a platinum group metal oxide and a valve metal oxide are coated on a substrate made of titanium or a titanium alloy has been used in many fields of the electrolytic industry. ing. However, in the field of high-speed metal plating and metal foil production operated under a high current density, an oxide layer having no conductivity is formed on a substrate surface layer during use,
Even if the amount of the electrode catalyst material remains sufficiently, there is a disadvantage that the function as an electrode is lost. It is considered that the formation of such an oxide having no conductivity is due to chemical corrosion of the substrate surface due to permeation of oxygen or an 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 has been adopted. The intermediate layer has sufficient corrosion resistance; has sufficient electric conductivity; has good adhesion to the electrode substrate; has good adhesion to the catalyst layer; It is required that the layer has characteristics such as a layer having no cracks; a low electrochemical activity; and a low manufacturing cost. Conventionally, a method for forming an intermediate layer composed of two or more types of valve metal oxides having different valences, a valve metal oxide and a platinum group metal or a conductive platinum There have been proposed a method of forming an intermediate layer made of a group III metal oxide, a method of forming a valve metal or an alloy thereof by thermal spraying, ion plating, or the like. As a specific example, Japanese Patent Application Laid-Open No. 59-3839 is disclosed.
Japanese Patent Application Publication No. 4 (1999) -1995 discloses that on a substrate, an oxide of at least one metal selected from titanium and tin having tetravalent valence and 5
An electrode has been proposed 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 valence of two is provided, and an electrode active material is coated thereon. However, although this intermediate layer has no oxygen generation activity, there is a problem that the electric conductivity is not sufficient. Japanese Patent Application Laid-Open No. 57-192281 discloses a conductive oxide of tantalum and niobium as an intermediate layer in an electrode having a titanium or titanium alloy base material and an electrode coating made of a metal oxide. Although an electrode for electrolysis accompanied by oxygen generation provided with a layer has been proposed, the intermediate layer has good corrosion resistance but insufficient electric conductivity. Japanese Patent Application Laid-Open No. Hei 1-301876 discloses that 40 to 90 mol% of iridium and 0.1
Through an underlayer of iridium oxide, platinum metal and tantalum oxide containing up to 30 mol% and 50 to 10 mol% of tantalum, the iridium oxide layer or at most 50
An electrode for oxygen generation has been proposed in which an iridium oxide-tantalum oxide layer containing mol% tantalum is provided as an upper layer, but the underlayer of this electrode has good electrical conductivity but is inferior in corrosion resistance. Due to the ability to activate oxygen, there is a problem that the substrate is eventually passivated. [0007] Further, Japanese Patent Application Laid-Open No. Hei 5-287572 discloses that a conductive substrate is coated with iridium 8.4 to 1 in terms of metal.
Via an underlayer of iridium oxide and tantalum oxide containing 4 mol% and 86 to 91.6 mol% of tantalum, containing 80 to 99.9 mol% of iridium and 0.1 to 20 mol% of tantalum in terms of metal There has been proposed an oxygen generation electrode provided with an upper layer made of iridium oxide and tantalum oxide. Although the underlying layer of this electrode has a certain degree of corrosion resistance and electrical conductivity, penetration of oxygen from the electrolyte and the catalyst layer into the substrate is unavoidable, and eventually the substrate becomes passivated. It has a problem and has not yet reached a fundamental solution to the above problem. On the other hand, Japanese Patent Application Laid-Open No. Hei 5-171483 discloses that a metal tantalum and / or an alloy thereof is plasma-sprayed on a conductive substrate made of titanium or its alloy in a non-oxidizing atmosphere under reduced pressure. 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 on the intermediate layer, and heated to 360 to 550 ° C. in an oxidizing atmosphere. Discloses a method for producing an oxygen-generating anode comprising forming an electrode active layer containing at least 20% by weight of iridium oxide and a balance of tantalum oxide. The above-mentioned intermediate layer is formed by plasma spraying to be a porous layer having irregularities, and has excellent adhesion to the electrode active layer, but as described in Japanese Patent Publication No. 5-57159, 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. In addition, tantalum and its alloy also contain oxygen generated in the catalyst layer. In addition, there is a problem that chemical corrosion is caused by contact with the electrolyte and the electrolyte and eventually the passivation of the intermediate layer occurs, and the above problem has not yet been fundamentally solved. Further, Japanese Patent Application Laid-Open No. 2-282149 discloses an electrode in which an electrode active material is coated on a conductive metal substrate made of a valve metal or an alloy thereof, and a metal is provided between the substrate and the electrode active material layer. An oxygen generating anode provided with a thin film intermediate layer mainly containing tantalum and its alloy is disclosed. The thin film intermediate layer is formed by applying a solution containing an organic tantalum compound or a tantalum chloride and heating the solution in a non-oxidizing atmosphere. The permeation of the liquid occurs and the passivation of the conductive substrate occurs. [0010] Further, methods of forming an intermediate layer by a vacuum deposition method, a sputtering method, an ion plating method, an ion implantation method or a vapor phase plating method have been proposed. Although it has the effect of suppressing the penetration of the electrolytic solution into the conductive substrate, the adhesion to the electrode active substance coating layer is not sufficient, and the equipment is large and the productivity is poor, so that there is a problem in industrial use. Further, in high-speed plating of metal, double-sided plating or single-sided plating is performed on a steel plate. When operations such as single-sided plating are performed, a non-energized anode is polarized and exposed to a base potential environment. However, there is a problem that the consumption of the catalyst is increased. The main object of the present invention is to solve the above-mentioned problems of the conventional electrode for electrolysis and to sufficiently use it as an anode for high-speed plating of metal operated at a high current density or for production of metal foil. It is another object of the present invention to provide a method for manufacturing a durable electrolytic electrode. The present inventors have developed a durable electrode for electrolysis, particularly an electrode that can be used as an anode for a long time in electrolysis in which oxygen is generated at the anode. As a result of various studies, this time, discharge scanning was performed on a titanium substrate using an alloy of a valve metal selected from titanium, tantalum, niobium, zirconium and tungsten and a metal selected from iridium, ruthenium and tin as an electrode material. Thereby forming an alloy layer on the surface of the titanium substrate, and then providing a coating layer composed of iridium oxide and tantalum oxide on the alloy layer,
The present inventors have found that an electrode for electrolysis which is extremely excellent in durability and stable even under a low potential environment can be obtained, and the present invention has been completed. Thus, the present invention relates to a method for producing at least one metal selected from the group consisting of titanium, tantalum, niobium, zirconium and tungsten in an amount of 50 to 96% by weight and at least one metal selected from iridium, ruthenium and tin in an amount of 50 to 96% by weight.
By using the alloy consisting of 4% by weight as an electrode material and performing discharge scanning on the surface of the titanium substrate, an alloy layer is formed on the surface of the titanium substrate, and then the iridium compound and the tantalum compound are contained on the surface layer. An object of the present invention is to provide a method for producing an electrode for electrolysis, comprising forming a coating layer composed of iridium oxide and tantalum oxide by applying a solution and then performing a heat treatment in an oxidizing atmosphere. Hereinafter, the method for manufacturing the electrode for electrolysis and the method of the present invention will be described in more detail. In the present invention, titanium is used as an electrode base material. It is desirable that the titanium substrate to be used is pre-treated in advance, as is usually done. Preferable specific examples of such pretreatment include, for example, a method described below. First, the surface of the titanium substrate is degreased by a conventional method, for example, washing with alcohol or the like and / or electrolysis in an alkaline solution, and then the concentration of hydrogen fluoride is 1 to 20.
By treating with a hydrofluoric acid or a mixed acid of hydrofluoric acid and other acids such as nitric acid and sulfuric acid, the oxide film on the surface of the titanium substrate is removed and the surface of the titanium grain boundary unit is roughened. Do. The acid treatment can be performed at 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 treated with acid is washed with water and dried. One feature of the present invention is that a surface of a titanium substrate is subjected to a modification treatment so that the titanium substrate is provided with one or more valve metals selected from titanium, tantalum, niobium, zirconium and tungsten, and iridium, ruthenium and tin. In forming a surface layer having excellent corrosion resistance made of an alloy with one or more metals selected from the group consisting of: One or more metals selected from titanium, tantalum, niobium, zirconium and tungsten (hereinafter referred to as “metals”).
An alloy composed of 50 to 96% by weight of a valve metal) and one or more metals selected from iridium, ruthenium and tin (hereinafter, referred to as a second metal) is obtained by a method known per se, for example, Plasma arc melting,
Although it can be manufactured by a powder sintering method or the like, the powder sintering method is particularly preferable. Thereafter, polishing, machining and cutting are performed to obtain an alloy electrode rod. The surface layer made of an alloy of a valve metal and a second metal is formed by, for example, scanning the surface of a titanium base using a titanium base as a cathode and an alloy of a valve metal and a second metal as an electrode rod. It can be performed by electrical discharge machining. Here, in the alloy composed of the valve metal and the second metal, when the content of the valve metal is less than 50% by weight and exceeds 96% by weight, an electrode having excellent durability and stability is formed. It is difficult. The valve metal content in the alloy is preferably between 60 and 90% by weight. The electric discharge machining is generally desirably performed in a non-oxidizing atmosphere, for example, an argon atmosphere. The diameter of the electrode rod used for electric discharge machining can be usually selected within a range of 2 to 12 mm.
Generally, those having a diameter of 4 mm or more are preferable from the viewpoint of work efficiency and the like. The discharge conditions can be changed depending on the diameter of the electrode rod used, the material of the electrodes, and the like. In general, the discharge conditions can be selected so that the electrode discharge pulse is 100 to 600 Hz and the capacitor capacity is 100 to 400 μF. When the melting point of the electrode alloy for discharge is higher than the melting point of titanium, the three alloy layers of titanium of the titanium base, the valve metal and the second metal are formed. If done at a temperature of
There is a tendency to form a coating layer of the alloy of the valve metal and the second metal. In this manner, electric discharge machining is performed for 5 to 30 minutes per 1 dm ^2, and an alloy layer of titanium, a valve metal and a second metal or an alloy of a valve metal and a second metal on the titanium substrate surface is formed. Form a coating layer. The surface of the alloy layer or the alloy coating layer formed in this manner is generally roughened, and a surface roughness meter [Surface Roughness / Contour Measuring Instrument SE, manufactured by Kosaka Laboratory Co., Ltd.]
F-30D] is usually 50.
200 μm. The titanium base and the alloy layer of the valve metal and the second metal or the alloy coating layer of the valve metal and the second metal of the titanium substrate formed as described above have a thickness of at least 10 μm, preferably 30 μm or more. Can be provided. When the thickness of the alloy layer or the alloy coating layer is less than 10 μm, generally, sufficient corrosion resistance cannot be imparted to the titanium substrate. The upper limit of the thickness of the alloy layer or the alloy coating layer is not particularly limited. However, even if the alloy layer or the alloy coating layer is thicker than necessary, the effect associated therewith cannot be obtained, and it is economically disadvantageous.
μm or less, preferably 100 μm or less is appropriate. On the surface of the titanium substrate formed as described above comprising the alloy layer of titanium, valve metal and second metal or the alloy coating layer of valve metal and second metal, iridium oxide and oxide A tantalum coating layer is formed. In forming the coating layer composed of iridium oxide and tantalum oxide, in order to protect the corrosion resistance of the alloy layer or the alloy coating layer formed on the titanium surface,
Generally, the formation of a coating layer composed of iridium oxide and tantalum oxide is performed in two or more steps. For example, after forming an intermediate layer composed of iridium oxide and tantalum oxide having a low iridium oxide content in advance, the iridium oxide content is reduced. It is preferable to coat an outer layer composed of iridium oxide and tantalum oxide having a high content. Here, iridium oxide may be made of substantially crystalline IrO ₂ , and tantalum oxide may be made of substantially amorphous Ta ₂
O ₅ can be used to enhance the bonding property of the coating according to the oxidation conditions described below. The intermediate layer is 5 to 30 mol%, preferably 8 to 30 mol%.
It can be composed of 25 mol% of iridium oxide and 70 to 95 mol%, preferably 75 to 92 mol% of tantalum oxide. Coating contributes to improving the corrosion resistance of the substrate. The coating amount of the intermediate layer is generally from 0.5 to 1
0.0 g / m ^2, preferably be in the range of 1.0 to 5.0 g / m ^2. Hereinafter, the formation of the intermediate layer will be specifically described. The iridium compound and the tantalum compound are adhered by applying a solvent solution containing an iridium compound and a tantalum compound, preferably a lower alcohol solution, on the surface layer composed of the alloy layer or the alloy coating layer of the titanium base, and then drying. Let me know. The iridium compound and the tantalum compound that can be used herein include compounds soluble in a lower alcohol solvent that can be thermally decomposed and converted to iridium oxide and tantalum oxide, respectively, under the calcination conditions described below. Examples of such an iridium compound include iridium chloride, iridium chloride, and potassium iridium chloride. Examples of the tantalum compound include tantalum chloride and tantalum ethoxide. On the other hand, examples of the lower alcohol that can dissolve these iridium compounds and tantalum compounds include methanol, ethanol, propanol, isopropanol, butanol and mixtures thereof. The ratio of the iridium compound to the tantalum compound in the above solution is 5/95 to 30/70, preferably 8/92 to 25/7, in terms of a metal ratio of Ir / Ta in terms of metal.
5 can be set. The application of the solution onto the alloy layer of the titanium substrate can be performed by, for example, a spraying method, a brush coating method, an immersion method, and the like. Thus, a lower alcohol solution of an iridium compound and a tantalum compound is applied. The dried 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 above-described treatment can be repeatedly performed until the coating amount reaches the above range. The calcination is generally carried out in a suitable heating furnace such as an electric furnace, a gas furnace, an infrared furnace, etc., generally at about 400 to about 700 ° C, preferably at about 450 to
This can be done by heating to a temperature in the range of about 600 ° C. The heating time at that time can be about 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 an intermediate layer. As described above, by forming an intermediate layer having corrosion resistance and electric conductivity on a titanium substrate modified layer comprising the above-mentioned alloy layer or alloy coating layer having low hydrogen overvoltage and corrosion resistance, an epoch-making process is achieved. Thus, an electrode having high durability can be obtained. On the intermediate layer composed of iridium oxide and tantalum oxide formed as described above, 60-98 mol%, preferably 70-95 mol%, of iridium oxide and 2-40 mol%, preferably Is 5-30m
An outer layer of ol% tantalum oxide is provided. In this outer layer, when the content of iridium oxide is less than 60 mol%, when used at a high current density, the oxygen generating activity becomes insufficient and the electrode life tends to be shortened. On the other hand, 98 mol%
When the value exceeds, the consumption of the electrode catalyst (outer layer) tends to increase. The formation of the outer layer also depends on the metal-to-metal molar ratio of Ir / Ta of the iridium compound and the tantalum compound in the solution to be applied being 60/40 to 98/2, preferably 70/40.
The formation can be carried out in the same manner as the formation of the intermediate layer, except that it is changed so as to fall within the range of / 30 to 95/5. The coating amount of the outer layer is generally 10 to 60 g /
m ² , preferably within the range of 30 to 50 g / m ² . The electrode of the present invention manufactured as described above has a long life, hardly causes passivation of the titanium interface even when used for a long time at a high current density, and has a long life. Since the hydrogen layer has a low hydrogen overvoltage and suppresses the consumption of the catalyst even in one-sided plating, it can be suitably used as a high-speed plating of a metal operated under a high current density or as an anode for producing a metal foil. Next, the present invention will be described in more detail with reference to examples, but the scope of the present invention is not limited by these examples. Examples 1 to 9 and Comparative Examples 1 to 7 A titanium plate material equivalent to JIS type 2 was used ( ^t 3.0 × ^w 100 ×
⁽ 100 mm) was washed with alcohol, treated in an aqueous solution of 8% by weight of hydrofluoric acid at 20 ° C. for 2 minutes, washed with water and dried. Next, 250 g of powder obtained by weighing a commercially available titanium powder and a ruthenium powder so as to have a weight ratio of 70:30, respectively, were mixed for 1 hour using a V-type mixer. Diameter 10
24 g of the mixed powder was inserted into each hole of a carbon die having 10 mm holes, and both ends were fixed with carbon punches, and a predetermined amount in a discharge plasma sintering machine (DR. SINTER) manufactured by Sumitomo Coal Mining Co. Installed in position. Thereafter, the inside of the sintering machine was set to an argon atmosphere, and a pressure of about 35 was applied.
Sintering was performed under the conditions of 0 kgf / cm ² , a pulse application voltage of 4 V, a pulse application current of 3500 A, a sintering temperature of 800 ° C., and a sintering time of 5 minutes. Thereafter, the surface was polished to obtain a 70 wt% Ti-Ru discharge coating electrode having a diameter of about 10 mm and a length of about 50 mm. Next, using the titanium plate from which the oxide film was removed as a cathode, electric discharge machining was performed for 10 minutes in a glove box purged with argon using a 70 wt% Ti-Ru electrode. Thereafter, the titanium plate subjected to the electric discharge machining was cut into ^t 3.0 × ^w 10 × ^l 10 mm with a fine cutter. EPMA
(Electron probe microanalyzer)
Elemental analysis of the cross section of the titanium plate subjected to electrical discharge machining revealed an alloy layer of titanium and ruthenium. In addition, when the surface of the electric discharge machined surface was subjected to component analysis by comparative measurement with a discharge electrode using a fluorescent X-ray analyzer, it was confirmed that the titanium component was increased. The thickness of this alloy layer was 30 to 50 μm. A butanol solution of iridium chloride and an ethanol solution of tantalum chloride were mixed, and Ir 5.9 g / l
And a coating solution containing 50.0 g / l of Ta (molar compounding ratio: 10Ir-90Ta) and 1 cm ² with a micropipette.
3.0 μl of the titanium-palladium alloy layer was applied to the titanium-palladium alloy layer formed as described above, and then vacuum-dried at room temperature for 30 minutes. Baked in the oven for 10 minutes. This step was repeated three times. Next, in order to obtain an outer layer, a butanol solution of iridium chloride and an ethanol solution of tantalum chloride are mixed, and a coating containing Ir 50.0 g / l and Ta 11.8 g / l (molar compounding ratio: 80 Ir-20 Ta) is used. After preparing the liquid,
Using this coating solution, the same process as described above was repeated eight times to produce Example electrode-1. Further, the component composition of the discharge electrode is shown in Table 1 below.
The discharge electrodes were prepared under the conditions for sintering, and the discharge machining was performed in the same manner as in Example electrode-1, and the composition of the coating layer was changed as shown in Table 1. Example electrodes-2 to 9 and comparative example electrodes-1 to 7 were produced. Comparative Example 8 A titanium plate material equivalent to JIS Class 2 ( ^t 3.0 × ^w 100 × ^l 1
00 mm) was degreased and washed with trichloroethylene,
Treated in an 8% by weight hydrofluoric acid solution at 0 ° C. for 2 minutes and then in a 60% by weight sulfuric acid solution at 120 ° C. for 3 minutes. The titanium substrate was taken out of the sulfuric acid solution and cooled rapidly by spraying cold water in a nitrogen atmosphere. Further, the resultant was immersed in a 0.3% by weight hydrofluoric acid solution at 20 ° C. for 2 minutes and then washed with water. After washing with water, dinitrodiaminoplatinum was dissolved in a sulfuric acid solution, and Pt content was adjusted to 5 g / l, pH was adjusted to about 2, and the temperature was adjusted to 50 ° C., and plating was performed at 30 mA / cm ² for about 9 minutes to form Pt. Was deposited. On this platinum plating layer, an intermediate layer and an outer layer having the composition shown in Table 1 were provided.
Comparative Example Electrode-8 was formed in the same manner as in the above. Comparative Example 9 A titanium plate material equivalent to JIS Class 2 ( ^t 3.0 × ^w 100 × ^l
100mm) after washing with alcohol, 8% by weight at 20 ° C
After a treatment in a hydrofluoric acid aqueous solution for 2 minutes, an intermediate layer and an outer layer having the compositions shown in Table 1 were formed on a titanium substrate washed with water and dried in the same manner as in Example electrode-1. 9 was produced. Table 1 shows the electrode life when each electrode obtained as described above was electrolyzed under the following conditions. <Electrolysis conditions> Electrolyte solution: 1 MH ₂ SO ₄ -1 M Na ₂ SO ₄ Current density: 4 A / cm ² Counter electrode: Pt Distance between electrodes: 10 mm Table 1 shows that the amount of consumption at the time of performing is 15% or less as ○ 16 to 30% or less and Δ 31% or more as x. <Electrolysis conditions> Electrolyte: 1 MH ₂ SO ₄ -1 M Na ₂ SO ₄ Current density Positive electrolysis: 2.0 A / cm ² , 80 seconds Reverse electrolysis: 0.1 A / cm ² , 20 seconds pulse electrolysis Counter electrode: Pt Distance between the electrodes: 10 mm Electrolysis time: 500 hours As is clear from the results shown in Table 1, the electrode of the example has a long electrode life and consumes little catalyst even in pulse electrolysis. [Table 1] As described above, according to the present invention, the surface of the titanium substrate is coated with at least one metal selected from the group consisting of titanium, tantalum, niobium, zirconium and tungsten.
The electric discharge machining is performed by using an electrode rod having a high hydrogen overvoltage composed of 0 to 96% by weight and a balance of at least one metal selected from iridium, ruthenium and tin, and a rough surface having corrosion resistance more than titanium on the titanium substrate. Formed alloy layer, and formed thereon a coating layer composed of iridium oxide and tantalum oxide, it has excellent adhesion to the coating layer, has durability against a low potential environment, and has a long An electrode for electrolysis that can be used can be provided.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI C25C 7/02 307 C25C 7/02 307 C25D 17/12 C25D 17/12 B (72) Inventor Shigeki Tsuchiya 2 Aoyagi, Soka City, Saitama Prefecture No. 12-30, Ishifuku Metal Industries Co., Ltd. Soka No. 1 Plant (56) References JP-A-6-200391 (JP, A) JP-A 5-33178 (JP, A) (58) Fields surveyed ( Int.Cl. ⁷ , DB name) C25D 17/10 101 C22C 14/00 C23C 26/00 C25B 11/06 C25B 11/10 C25C 7/02 307 C25D 17/12

Claims (1)

(57) Claims 1. 50 to 96% by weight of at least one metal selected from titanium, tantalum, niobium, zirconium and tungsten and at least one metal selected from iridium, ruthenium and tin By using an alloy consisting of 50 to 4% by weight as an electrode material and performing discharge scanning on the surface of the titanium substrate, an alloy layer is formed on the surface of the titanium substrate, and then an iridium compound and a tantalum compound are formed on the surface layer. A method for producing an electrode for electrolysis, comprising forming a coating layer composed of iridium oxide and tantalum oxide by applying a solution to be contained and then performing a heat treatment in an oxidizing atmosphere.