JP2004323955A - Electrode for electrolysis, and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for electrolysis, which can be used for high-speed zinc plating, and has durability particularly to a counter current. <P>SOLUTION: The electrode for electrolysis comprises a substrate of a valve metal, an intermediate layer of metallic iridium covering the substrate surface, iridium oxides covering the surface of the intermediate layer, and a catalytic layer containing a stabilizer for a metallic oxide. The electrode for electrolysis is used as an anode 18 in a metal plating apparatus 11, and then even when the counter current flows and cathodic polarization occurs during the electrolysis, the electrode has the durability to the counter current given by the intermediate layer of the metallic iridium, has an electrode performance improved by the stabilizer for the metallic oxide, and enables a stable operation for a long term. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrode for electrolysis and a method for manufacturing the same, and more particularly, to an anode for electrolysis used for industrial electrolysis and a method for manufacturing the same, and more particularly, to high-speed electrogalvanization in which a reverse current may flow during electrolysis. The present invention relates to an anode for electrolysis which is most suitable for use and a method for producing the anode.
[0002]
[Prior art]
As an anode for electrolysis typified by a high-speed galvanizing electrode, a metal such as zinc as a plating substance has been used. Here, a method is employed in which the metal is deposited as a plating layer at the cathode while replenishing the metal from the anode to the electrolytic solution. Since both the cathodic reaction and the anodic reaction are the same, the plating solution is theoretically always constant. The zinc anode has been widely used because of the fact that the theoretical decomposition voltage becomes zero and energy saving can be achieved.
However, in practice, the theoretical dissolution occurs at the anode, but the electrodeposition of the cathode does not necessarily proceed as expected, the metal concentration in the electrolyte tends to increase, and the anode is consumed. Accordingly, there is a problem that the inter-electrode distance increases, the power consumption always changes, and the inter-electrode distance must be constantly adjusted to maintain a constant voltage. Therefore, in recent years, a method has been adopted in which an insoluble electrode having no dimensional change is used and the adjustment of the electrolytic solution and the energization are performed separately.
[0003]
In other words, initially, a stable and inexpensive copper alloy was used as the insoluble anode, but the copper alloy elutes to some extent, and the eluted copper leads to contamination of products and plating equipment, and furthermore, the electrolytic solution itself is also contaminated. was there. In particular, copper is a controlled substance as a heavy metal, and its elution has been a serious environmental problem.
As a measure against this problem, an electrode called a so-called DSA in which a valve metal such as titanium or a titanium alloy is used as a base material and the surface thereof is coated with a platinum group metal oxide has come to be used. When this DSA is used for anodic oxygen generation, iridium oxide is used as the platinum group metal oxide, whereby substantially no change in the shape of the electrode itself is obtained, and stable current / voltage characteristics can be obtained. Now you can. Electrodes using iridium oxide as an electrode material enable high-current electrolysis for a long time and are widely used.
[0004]
This kind of electrode has been widely used industrially because of its high stability particularly at high current density, and is now used as standard from the viewpoint of practical value.
However, this type of electrode exhibits extremely excellent characteristics as long as it is used continuously as an anode.However, when a reverse current flows in an acid, that is, it functions as a cathode even partially or for a short time, hydrogen When the generated reaction occurs, there is a problem in that the electrode is greatly consumed and the life of the electrode is shortened. As a means for improving this, Japanese Patent Application Laid-Open No. 2002-275697 proposes an electrode that is resistant to reverse current by increasing the thermal decomposition temperature during production. Although this technique is useful for stabilizing the electrode material, it is used for producing an electrode by crystal growth by thermal decomposition. In other words, it is a mechanism in which the precursor (compound such as chloride) is thermally decomposed and a part of the volatile substance or solvent is replaced with oxygen while being blown off by heat, and a new crystal is formed at that time. Since the product is not a melt, homogenization does not occur after the product is formed, and the material is necessarily porous. Therefore, as long as it is manufactured by the thermal decomposition method, it becomes porous, and the protection of the base material becomes insufficient, and the conventional thermal decomposition method (oxide method) is disadvantageous in this point.
[0005]
On the other hand, an electroplating method has been proposed for depositing a metal. When this electroplating method is used, a denser electrode material layer can be obtained than in the above-mentioned pyrolysis method. That is, in the electroplating method, the metals are connected to each other and grow, so that although the problem of electrodeposition distortion remains, the whole can be covered relatively densely. Further, when the thermal decomposition method is performed using a metal instead of an oxide, the oxide tends to be porous similarly to the oxide, and very small precipitated particles are obtained by reduction, and the particles are active and have a metal structure on the metal. Since it grows with habits, it becomes denser than oxide, and since it is a metal, it is more stable than oxide at the time of negative polarization, so that it is advantageous as an electrode in which reverse current easily occurs.
In addition to the above, JP-A-9-125290 proposes a practical electrode in which an oxide layer is formed by plasma spraying in the middle.
The mechanism by which the reverse current affects the electrode wear is not clear, and therefore the effect of the technology proposed in the above publication is based only on results, and has not been theoretically elucidated, but is probably the base metal at the time of negative polarization It can be estimated that it depends on the properties of titanium. In other words, titanium becomes corrosive in an acid, and easily absorbs hydrogen to cause embrittlement. As a result, corrosion occurs, leading to wear of the electrode material.
[0006]
[Patent Document 1]
JP-A-6-293999 (Claims, paragraphs 0022 to 0030, Example 1)
[0007]
[Problems to be solved by the invention]
In order to solve the above-mentioned problems, particularly problems relating to electrodes using iridium oxide as a catalyst, for example, as disclosed in Patent Document 1, an electrode in which a metal iridium layer is inserted between a substrate and an iridium oxide layer, That is, an electrode having a laminated structure of a base material, a metal iridium layer, and an iridium oxide layer has been proposed. In this proposal, coating of the iridium oxide layer is performed by ion plating.
If the metal iridium oxide layer is not present during the coating of the iridium oxide layer by ion plating, that is, if the iridium oxide layer is formed directly on the surface of the substrate, the metal on the surface of the substrate, such as titanium, is slightly oxidized to a small extent. Titanium oxide may be formed at the interface between the material and the iridium oxide layer, which may impede energization. As described in Patent Literature 1, when a metal iridium layer exists between the base material and the iridium oxide layer, oxidation of the base material surface is suppressed, and conduction inhibition is prevented.
[0008]
However, the electrode manufactured by ion plating in this way prevents oxidation of the substrate surface, but according to the present inventors' studies, it is easy for distortion to occur, the surface area does not increase, and the electrolytic voltage is high. However, there is a drawback that wear is severe.
Therefore, although the electrode having the laminated structure of the metal iridium layer and the iridium oxide layer is a useful electrode from the viewpoint of preventing oxidation of the substrate surface, it is compared with an electrode having the substrate surface coated with a single layer of iridium oxide. As a result, the performance deteriorated too much, and could not be put to practical use at all. In addition, ion plating is disadvantageous in that it is iridium oxide alone, cannot be combined with another stabilizer, and cannot be sufficiently stabilized in that aspect.
Therefore, the present invention improves the electrode in which the above-mentioned substrate surface is coated with a laminated structure of a metal iridium layer and an iridium oxide layer, and suppresses deterioration of performance such as generation of distortion and high electrolytic voltage as much as possible, thereby oxidizing the surface of the substrate. It is an object of the present invention to provide an electrode for electrolysis having a resistance to reverse current by suppressing the occurrence of a reverse current and a method for producing the same.
[0009]
[Means for Solving the Problems]
The present invention relates to an electrolytic solution comprising a valve metal substrate, a metal iridium intermediate layer coated on the surface of the substrate, and a catalyst layer containing iridium oxide and a metal oxide stabilizer coated on the surface of the intermediate layer. The electrode is a metal oxide stabilizer such as titanium oxide, tantalum oxide, and tin oxide. Further, the method of the present invention comprises applying an iridium compound-containing liquid containing a reducing agent to the surface of the valve metal substrate, forming a metal iridium intermediate layer on the valve metal substrate by thermal decomposition, and forming a metal iridium intermediate layer on the surface of the metal iridium intermediate layer. A method for producing an electrode for electrolysis, comprising applying an iridium-containing liquid and performing thermal decomposition in an oxidizing atmosphere to form a catalyst layer containing iridium oxide.
[0010]
Hereinafter, the present invention will be described in detail.
It is known that metal iridium is stable even in a metal state at the time of anodic polarization, and is not as active as iridium oxide.
In the electrode for oxygen generation electrolysis of the present invention having a laminated structure of a valve metal base material-a metal iridium intermediate layer-an iridium oxide-containing catalyst layer, the catalyst layer is brought into contact with the electrolytic solution as much as possible to increase the electrolysis efficiency. It is usually porous. Therefore, when the metal iridium intermediate layer is not present, the electrolyte comes into contact with the base material, and the base material is easily corroded, whereas in the present invention, the presence of the metal iridium intermediate layer causes the electrolyte solution to come into contact with the base material. Is prevented. Or a mode in which the metal iridium intermediate layer is made porous to some extent to improve the affinity with the iridium oxide layer, and the surface is substantially sealed with a catalyst layer containing iridium oxide, and the actual surface area as an electrode is extremely large. In this case, there is a possibility that the electrolytic solution comes into contact with the base material. In this case, however, the noble metal iridium protects the base material. This prevents the base material from being hydrogenated, and furthermore, the metal iridium is stable and the coating is less likely to be consumed even when a reverse current flows and the electrode is negatively polarized.
When the metal iridium intermediate layer is made porous, the degree of porosity is smaller than when the metal oxide is made porous, and a more dense structure can be obtained. In other words, metal oxides are usually produced by thermal decomposition coating, and in this thermal decomposition method, the solvent is volatilized, and the constituents of the precursor (for example, chlorine atoms of the metal chloride) are replaced by oxygen, which inevitably results in a porous material. The degree of is increased. On the other hand, the metal iridium intermediate layer of the present invention is formed by a metal-metal bond. In the case of metal, the metal iridium easily diffuses with each other, so that a denser porous layer can be formed. That is, the metal iridium intermediate layer of the present invention becomes a dense porous film when the coating is formed, and is effective for improving the affinity or adhesion to the catalyst layer formed on the surface.
[0011]
As described above, the problems of the conventional oxygen generating electrode are solved by the present invention, and an electrode for electrolysis having the following characteristics can be provided.
1) Prevent corrosion of the substrate by the electrolyte.
2) The metal iridium intermediate layer has durability against both forward current and reverse current, and almost completely prevents corrosion of the base material when a reverse current occurs.
3) Since the electrolysis is performed on the iridium oxide layer on the surface, the consumption is extremely small and effective. Since the surface area of iridium oxide can be increased, the load on the electrode material at the time of reverse current can be reduced, thereby further reducing electrode consumption.
[0012]
However, as described above, an electrode for electrolysis having a laminated structure of a valve metal substrate, a metal iridium layer, and an iridium oxide layer (catalyst layer) manufactured by an ion plating method has sufficient durability against a reverse current, Distortion is likely to occur, the surface area is not easily increased, the electrolysis voltage is likely to be increased, and further, there is a drawback that exhaustion is severe, and it is hard to be a practical electrode for electrolysis.
The present inventors have studied two types of techniques in order to eliminate the disadvantages of this electrode.
The first is to improve the electrode material by adding another metal oxide (metal oxide stabilizer) to the iridium oxide layer on the surface. Second, the laminated structure is the same as the conventional valve metal base. That is, a laminated structure is formed by using a material, a metal iridium intermediate layer, and an iridium oxide layer by a thermal decomposition method instead of the ion plating method.
[0013]
While iridium oxide alone tends to cause the above-mentioned disadvantages depending on the production method as described above, when other metal oxides such as titanium oxide, tantalum oxide and tin oxide are added to iridium oxide, this metal At least one of the effects that the oxide functions as a stabilizer to stabilize iridium oxide, reduce distortion, increase surface area, reduce electrolysis voltage, and minimize consumption. Can be achieved.
Then, when the valve metal base material-metal iridium intermediate layer-iridium oxide layer is manufactured by a thermal decomposition method, unlike the case of the ion plating method, the metal iridium intermediate layer becomes dense and hardly generates distortion, and furthermore, the base material It is possible to provide sufficient protection.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
As the valve metal base material used in the present invention, JIS Class 1 or 2 pure titanium is most preferably used, but a valve metal having higher corrosion resistance such as tantalum or niobium may be used depending on the conditions of the electrolytic solution. It is. In addition, when used as an anode, the valve metal oxidizes the surface even as it is, so it becomes a so-called passive body, and it becomes difficult to conduct electricity from the electric resistance of the surface oxide, and as a cathode, conductivity occurs due to the action as a metal That is, it is named because it functions as a valve that can or cannot be energized depending on the direction of electricity, and metals of Group 4 and Group 5 such as titanium, zirconium, tantalum, and niobium are known. Have been. Also, alloys of these metals have the same characteristics as valve metals.
The shape of the base material may be determined according to the purpose. For example, a plate-like base material is used in high-speed zinc continuous plating (EGL), but a mesh or a perforated plate is used in other applications.
[0015]
A pretreatment may be applied to a substrate made of a metal or an alloy having such characteristics as required. The pretreatment is not particularly limited, but it is preferable to roughen the surface of the base material to increase the actual surface area, and to activate and remove acid deposits and blast residues by pickling.
Next, a metal iridium intermediate layer is formed on the surface of the substrate. This intermediate layer may be formed by electroplating, but is usually formed by a thermal decomposition method. For example, a coating solution is prepared by adding a reducing agent such as lavender oil to an alcohol solution of an iridium compound such as iridium chloride, and the coating solution is applied to the substrate surface, dried, and then substantially dried using a gas burner or the like. In this case, thermal decomposition (flame pyrolysis) is performed while reducing the temperature to a reducing atmosphere to deposit a metal iridium intermediate layer on the substrate surface. The thermal decomposition may be performed in a heating furnace such as an atmosphere furnace. In this case, it is desirable to take measures such as placing an inner box in the furnace so as to cut off oxygen as much as possible and flowing an inert gas therein.
[0016]
Alternatively, the above solution or an alcohol solution of iridium resinate may be applied to a substrate, dried and then thermally decomposed in a muffle furnace or the like to precipitate as metal iridium. For example, an ethanol solution of iridium mercaptan is applied to the surface of the substrate, dried, and then thermally decomposed at 450 to 600 ° C. The coating-pyrolysis is repeated about three to ten times to form a metallic iridium intermediate layer having metallic luster.
The metal iridium precipitated in this manner almost completely covers the surface of the base material, probably because the metal iridium bonds to each other while decomposing the compound groups around the metal iridium to form a metal iridium intermediate layer. Furthermore, since iridium hardly transmits hydrogen, even if hydrogen is generated on the surface of the metal iridium intermediate layer, it hardly reaches the substrate. Furthermore, metal iridium is chemically stable and does not substantially corrode in a plating solution containing a common inorganic acid, thereby providing good protection of the valve metal substrate.
Furthermore, when an oxide layer is formed directly on the surface of a valve metal substrate, as described above, valve metals such as titanium are easily oxidized, and in many cases, electricity cannot be supplied by electrolysis for a short period of time. On the other hand, in the present invention, the metal iridium intermediate layer is formed on the surface of the valve metal base, and in this case, unlike the oxidizing atmosphere in the case of forming a metal oxide, it is performed in a substantial reducing atmosphere. The surface of the valve metal substrate is not substantially oxidized and does not adversely affect the current flow.
[0017]
Next, the catalyst layer containing iridium oxide is coated on the surface of the metal iridium intermediate layer thus formed.
The oxide constituting the catalyst layer may be iridium oxide alone as described above, but in that case, the metal iridium intermediate layer and the catalyst layer are formed by a thermal decomposition method.
When the catalyst layer contains iridium oxide and a metal oxide stabilizer, the production method is not limited, but here, the production method will be described using a thermal decomposition method as an example.
A typical combination of iridium oxide and a metal oxide stabilizer is a composite oxide of iridium oxide and tantalum oxide, and their composition ratio is not particularly limited, but iridium oxide: tantalum oxide = 1: 4 to 4: 1 (molar ratio) is desirable, and 1: 1 to 4: 1 is particularly desirable.
[0018]
To form the catalyst layer, first, a coating liquid having such a composition ratio is prepared. As this coating solution, for example, a solution obtained by dissolving a predetermined amount of iridic acid in a 10% hydrochloric acid solution of tantalum chloride or a tantalum alkoxide alcohol solution such as butyl tantalate is acidified with a slight amount of hydrochloric acid. And a solution obtained by dissolving a predetermined amount of iridic acid chloride.
These coating solutions may be selected according to the purpose. In general, in the case of high-speed galvanizing, the acid concentration is comparatively low, and the corrosiveness due to the acid is small. Therefore, it is desirable to use a solution containing an alkoxide. . On the other hand, when used in an electrolytic solution having a high acid concentration, such as for the production of copper foil, it is desirable to use a chloride solution which contains few volatile substances and can be expected to form a denser coating.
[0019]
Next, such a coating liquid is applied to the surface of the metal iridium intermediate layer, and the metal compound is converted into a metal oxide by thermal decomposition. The thermal decomposition conditions are such that iridium oxide is stable IrO ₂ As long as the tantalum component is partially dissolved in iridium oxide, or a state in which tantalum oxide is present as an amorphous type may be formed.Typically, the coating solution is applied and dried, and then dried. Thermal decomposition at 450 ° C. to 550 ° C. for about 5 to 15 minutes in an oxidizing atmosphere to obtain a black oxide coating. By repeating this coating and thermal decomposition, a catalyst layer composed of an oxide can be obtained during stabilization. In the course of the coating and thermal decomposition, a catalyst layer containing iridium oxide is obtained, and the surface of the underlying metal iridium intermediate layer is oxidized to form a more stable catalyst layer having excellent adhesion.
[0020]
Next, an example in which the electrode for electrolysis of the present invention is used for metal plating will be described with reference to the accompanying drawings.
FIG. 1 is a schematic vertical sectional view illustrating a metal plating apparatus equipped with an electrode for electrolysis of the present invention, and FIG. 2 is a view taken along line AA of FIG.
[0021]
The metal plating apparatus 11 contains a plating solution 13 for dissolving a metal compound for plating in a metal plating tank 12. The base end side of the sheet to be plated 14 is wound around a feed roll 15, fed out of the roll 15 into a plating solution 13, guided by a pair of rollers 16 and 17, and formed into a plate-shaped anode 18 and a cathode 19. Through the gap, the metal compound is subjected to the cathodic reduction to deposit metal on the cathode 19 side of the sheet to be plated 14 and plated, and the sheet to be plated 14 is wound up by a take-up roll 20 to complete the plating. The anode 18 is constituted by coating a metal iridium intermediate layer on a valve metal base material, and further covering a surface thereof with a catalyst layer composed of a composite oxide of iridium oxide and a metal oxide stabilizer.
[0022]
In the metal plating apparatus 11, as shown in FIG. 2, when the width of the sheet to be plated 14 supplied to the apparatus 11 is substantially equal to the width of the anode 18 (solid line), it is slightly smaller than the width of the anode 18. There are various cases such as a short case (dotted line) and a case where the width is about half the width of the anode 18 (dashed line). In the case of the solid line in FIG. 2, almost no reverse current flows, but in the case of the dotted line and the dashed line, the width of the sheet to be plated 14 is narrower than the width of the anode 18 and overlaps with the sheet to be plated 14. Since the portion of the anode 18 which does not contribute to the current supply, no current flows, and the reverse current easily flows due to the negative polarization contrary to the normal case.
Conventional plating electrodes have poor durability against a reverse current, and when the reverse current flows, the catalyst material is peeled off or eluted, resulting in an extremely short electrode life. On the other hand, the illustrated anode 18 has the above-described configuration and has excellent durability against the reverse current, so that the operation can be performed for a long time even when the anode 18 is continuously used in an environment where the reverse current occurs.
[0023]
Next, examples of the electrode for electrolysis of the present invention will be described, but the examples do not limit the present invention.
[0024]
[Example 1]
A titanium plate having a thickness of 1 mm was roughened by grid blasting to have an average roughness of JIS Ra = 10 μm, and the surface was activated by an acid treatment with boiling 20% hydrochloric acid to obtain a valve metal substrate.
A coating solution was prepared by dissolving lavender oil in the same amount as the iridic acid chloride in a butyl alcohol solution of iridic acid chloride. This coating solution was applied to the surface of the valve metal substrate, dried at room temperature for 10 minutes, and then heated with a butane gas burner. Heating and thermal decomposition from the surface. The heating was performed for twice the time from the start of heating to the time when the surface of the base material became black and white. This coating-heating was repeated 10 times to obtain a coating of a slightly blackish white metal iridium intermediate layer having an apparent thickness of 2 μm.
Next, using a dilute hydrochloric acid aqueous solution of iridium chloride and tantalum chloride mixed so that Ir (iridium) / Ta (tantalum) = 2/1 as a coating solution, the solution is applied to the surface of the metal iridium intermediate layer, and dried at room temperature. After drying at 60 ° C. for 10 minutes, thermal decomposition was performed for 10 minutes in a muffle furnace through which air at 510 ° C. was passed. After cooling, the same operation was repeated. By repeating 15 times, a coating of a composite oxide composed of iridium oxide and tantalum oxide was formed on the surface to form an electrode for electrolysis. The thickness of the composite oxide layer thus produced was apparently 3 μm, and was 5 μm in total with the metal iridium intermediate layer.
[0025]
Using this electrode for electrolysis as a sample electrode, an electrolysis test was performed under the following conditions.
An aqueous solution having a pH of 1.8 by adding sulfuric acid to a 150 g / liter sodium sulfate solution at 60 ° C. was used as an electrolyte. A platinum plate was used as a counter electrode, the sample electrode was used as an anode, and the current density was 3 A / cm. ² The electrolysis was performed by reversing the current every 5 hours for 10 minutes. The electrolysis voltage was 5.8V. Thus, electrolysis could be performed for 2800 hours (total electrolysis time) before the anode could not be energized.
[0026]
[Comparative Example 1]
A substrate was prepared in the same manner as in Example 1, and instead of the metal iridium intermediate layer, a composite oxide coating having a titanium / tantalum ratio of 8/1 was directly formed on the surface of the substrate to form an intermediate layer. did. The same iridium oxide / tantalum oxide composite oxide layer as in Example 1 was formed on the surface of this intermediate layer to obtain a sample electrode. The operation for coating was repeated 25 times so that the total amount of iridium coating per unit area was the same.
When an electrolysis test was performed using the sample electrode under the same conditions as in Example 1, the electrolysis voltage was 5.9 V, which was almost the same as in Example 1, but the life of the electrode was 1200 hours.
[0027]
[Example 2]
A sample electrode was prepared under the same conditions as in Example 1 except that the iridium oxide layer (catalyst layer) was formed using only the same molar amount of iridium oxide instead of coating the composite oxide composed of iridium oxide and tantalum oxide. Produced.
When an electrolysis test was performed using this sample electrode under the same conditions as in Example 1, the electrolysis voltage was 6.2 V and the life of the electrode was 400 hours.
[0028]
[Comparative Example 2]
Iridium was put in the crucible, melted and evaporated by an electron beam, and further ionized at 50 V and 10 A with an ionization electrode immediately above the crucible.
Then, the same base material as in Example 1 was placed facing iridium, and a iridium film was formed in a vacuum at a bias voltage of 500 V and a film forming speed of 10 μm / sec to form a metal iridium intermediate layer having a thickness of 2 μm. Next, 8 × 10 ^-4 A sample electrode was formed by coating iridium oxide with Torr. The film formation temperature was 500 ° C. for both the metal iridium intermediate layer and the iridium oxide coating.
When an electrolysis test was performed using the sample electrode under the same conditions as in Example 1, the electrolysis voltage was 6.3 V and the life of the electrode was 220 hours.
[0029]
[Example 3]
A sample electrode was produced under substantially the same conditions as in Example 1 except that the substrate was tantalum instead of titanium.
However, since tantalum is easily oxidized, the oxidation of the substrate was prevented during the first five coats of metal iridium by shifting to the next coat formation when the color of the coat changed to black and white. When the coating was completed 10 times, annealing was performed in a muffle furnace at 510 ° C. for 1 hour. The coating liquid for forming the composite oxide layer had the same molar ratio of iridium and tantalum as in Example 1, but the raw materials were iridium chloride and butyl tantalate, and the solvent was butyl alcohol. The thermal decomposition temperature was 500 ° C.
When an electrolysis test was performed using the obtained sample electrode under the same conditions as in Example 1, the electrolysis voltage was 5.6 V and the life of the electrode was 3,200 hours.
[0030]
[Example 4]
A dilute hydrochloric acid solution of titanium chloride and tantalum chloride was applied to the surface of the base material prepared in the same manner as in Example 1, dried, and then thermally decomposed in a muffle furnace at 540 ° C. for 10 minutes. This operation was repeated four times, and the surface of the base material was coated with titanium oxide / tantalum oxide = 9: 1 (molar ratio) in an amount of about 1 g / m 2 in terms of titanium metal and tantalum metal. ² The composite oxide layer was formed by thermal decomposition so that
A solution obtained by diluting iridium resinate manufactured by Daiken Kogyo using a 1: 1 mixture of ethyl alcohol and turpentine as a solvent is used as a coating solution, and this coating solution is applied to the surface of the composite oxide layer, and after drying, Pyrolysis was performed in a muffle furnace at 500 ° C., and a slightly grayish coating was obtained. This was repeated six times to form the same amount of metal iridium intermediate layer as in Example 1.
On this surface, a composite oxide film of iridium oxide / tantalum oxide was formed under the same conditions as in Example 1.
When an electrolysis test was performed using the obtained sample electrode under the same conditions as in Example 1, the electrolysis voltage was 5.7 V and the life of the electrode was 2450 hours.
[0031]
[Example 5]
A sample electrode was prepared in the same manner as in Example 4, except that the composition of the electrode material on the surface was changed to iridium / tantalum = 8/2 (molar ratio).
When an electrolysis test was performed using the obtained sample electrode under the same conditions as in Example 1, the electrolysis voltage was 5.6 V and the life of the electrode was 2550 hours.
[0032]
【The invention's effect】
The present invention relates to an electrolytic solution comprising a valve metal substrate, a metal iridium intermediate layer coated on the surface of the substrate, and a catalyst layer containing iridium oxide and a metal oxide stabilizer coated on the surface of the intermediate layer. An electrode, and an iridium compound-containing liquid containing a reducing agent is applied to the surface of the valve metal base material, a metal iridium intermediate layer is formed on the valve metal base material by thermal decomposition, and the iridium-containing liquid is applied to the surface of the metal iridium intermediate layer. Is applied and thermally decomposed in an oxidizing atmosphere to form a catalyst layer containing iridium oxide.
[0033]
The present invention can provide an electrode for electrolysis having a metal iridium intermediate layer.
Industrial electrolysis with oxygen generation at high current density, that is, reverse current or current reversal when cutting current, which is often a problem with anodes used in high speed galvanizing and high speed electrolysis for copper foil production, even if it is not reverse current In industrial electrolysis under a strong corrosive atmosphere, corrosion of the base material is a major problem.
When the electrode for electrolysis of the present invention is used, the corrosion is almost completely eliminated by the metal oxide stabilizer in the catalyst layer or by the high density of the metal iridium intermediate layer in the electrode for electrolysis produced by the method of the present invention. In addition, it is possible to provide an electrode for electrolysis having a sufficiently long life even under a high current density by using an oxide-based stable electrolytic substance (catalyst layer).
[0034]
Further, in the production of an electrode for electrolysis by a conventional pyrolysis method, the coating layer was easily peeled off by oxidation during the formation of the coating, but in the present invention, the metal iridium as the intermediate layer functions as an appropriate reducing agent. In addition, the protection of the base material becomes more reliable, and the oxide coating of the catalyst layer on the surface can be formed under optimal conditions.
As described above, the present invention can provide an electrode for electrolysis that can withstand a reverse current and has a long life even when used in a corrosive atmosphere.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view illustrating a metal plating apparatus equipped with an electrode for electrolysis of the present invention.
FIG. 2 is a view taken along line AA of FIG.
[Explanation of symbols]
11 Metal plating equipment
12 Metal plating tank
13 Plating solution
14 Sheet to be plated
18 Anode
19 cathode

Claims (10)

Electrolysis comprising a valve metal substrate, a metal iridium intermediate layer coated on the surface of the substrate, and a catalyst layer containing iridium oxide and a metal oxide stabilizer coated on the surface of the intermediate layer. Electrodes. The electrode for electrolysis according to claim 1, wherein the metal oxide stabilizer is at least one oxide selected from the group consisting of titanium oxide, tantalum oxide, and tin oxide. The electrode for electrolysis according to claim 1 or 2, wherein the valve metal of the valve metal base material is selected from titanium, a titanium alloy, tantalum, and a tantalum alloy. The electrode for electrolysis according to any one of claims 1 to 3, wherein the valve metal base has a thin oxide layer on the surface. The electrode for electrolysis according to any one of claims 1 to 4, wherein the metal iridium intermediate layer is a porous layer. The electrode for electrolysis according to any one of claims 1 to 5, wherein the metal oxide stabilizer is tantalum oxide, and the tantalum oxide and iridium oxide form a composite oxide. An iridium compound-containing liquid containing a reducing agent is applied to the surface of the valve metal base material, a metal iridium intermediate layer is formed on the valve metal base material by thermal decomposition, and the iridium-containing liquid is applied to the metal iridium intermediate layer surface. And producing a catalyst layer containing iridium oxide by performing thermal decomposition in an oxidizing atmosphere. The method for producing an electrode for electrolysis according to claim 7, wherein after the pretreatment of the valve metal base material, an iridium compound-containing liquid containing a reducing agent is applied. 9. The method for producing an electrode for electrolysis according to claim 8, wherein the pretreatment of the valve metal base material is to roughen the surface of the base material by blasting, and remove surface deposits and activate the surface by pickling. The method for producing an electrode for electrolysis according to claim 8 or 9, wherein the formation of the metal iridium intermediate layer is performed by flame pyrolysis after applying an iridium compound-containing liquid containing a reducing agent.

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