JPWO2010128641A1 - Oxygen generating anode - Google Patents

Abstract

In insoluble anodes used in electrolysis processes involving oxygen generation, by extending sufficient electrode durability, not only positive polarization but also electrolysis with negative polarization, the electrode usage period can be extended, electrode repair, replacement, etc. Reduce work. In order to realize this, an active substance holding body made of a porous metal sheet such as an expanded metal, a punching metal, an interdigital or a net-like metal is joined to a conductive metal which is an electrode structure to constitute an electrode base. An electrode active substance mainly composed of iridium oxide is coated on the holding body bonding surface of the electrode base. An oxygen generating anode exhibiting excellent resistance to the cathodic phenomenon can be obtained.

Description

  The present invention relates to an oxygen generating anode used as an insoluble anode in an electrolysis process involving oxygen generation, mainly electroplating of zinc, tin or copper, surface treatment of stainless steel, and electrowinning of metals.

  Conventionally, lead or lead-based alloys have been used for electroplating zinc, tin, etc. on steel sheets, but have had problems such as contamination of the plating solution by the eluted lead and deterioration of film quality. As an alternative anode, various insoluble anodes have been proposed in which an electrode active layer containing a platinum group metal or an oxide thereof, for example, iridium oxide, as an electrode active material is formed on an electrode substrate. However, this type of electrode is intended to be used as an anode, and electrolysis involving not only positive polarization but also negative polarization has the drawback that the electrode life is significantly shortened compared to electrolysis with only positive polarization.

  Usually, in the electroplating of a steel plate, two anodes are used so as to face both sides of the steel plate in order to plate both sides of the steel plate, and the width of the two anodes arranged facing each other (perpendicular to the traveling direction of the steel strip). The dimension in the right direction) is set in accordance with the maximum width of the steel strip because there are many kinds of widths of the steel strip passing between them. For this reason, when a steel strip having a width smaller than the maximum width passes (a portion through which the steel strip passes is referred to as a plate path), the electrodes are directly opposed at the side end portions on both sides of the anode. When the front and back plating amounts of the steel plates are different, there is a difference in the potential of the two anodes with respect to the steel plate. It has been found that the outer portion of the plate potential on the lower potential side works as a cathode (anode cathodic phenomenon). At the side edge of the anode where the cathodic phenomenon occurs, the consumption of the electrode active material always proceeds more rapidly than the central part facing the steel strip, and the rapid consumption of the electrode active material at this side edge is the entire anode. It is supposed to dominate life.

  In order to extend the life of this type of electrode as a cathode, an electrode in which an intermediate layer of two layers of a platinum layer and an oxide layer is provided between a conductive electrode substrate and an electrode active material layer is disclosed in Patent Document 1. Has been proposed. Although this electrode has an effect of extending the life as a cathode, the platinum layer and the oxide layer have inherently poor adhesion, and the life of the plate path portion of the anode and the outer portion of the plate path in the electroplating of the steel plate is the same. It has not yet reached.

  As another countermeasure, a tantalum oxide coating layer to which platinum metal is added is provided on a conductive electrode substrate, and a coating layer made of iridium oxide and tantalum oxide is formed thereon as an intermediate layer. Patent Document 2 proposes an electrode provided with an upper layer made of iridium oxide. Although an improvement in durability can be seen by providing an upper layer, the significant wear inherent in platinum when acting as an anode cannot be suppressed, and the durability when acting as a cathode intermittently is insufficient.

  Under such circumstances, it is an important technical problem in the insoluble anode to effectively suppress the consumption of the electrode active material associated with the anode cathodic phenomenon, and one of the means for solving this technical problem is the cathode This is to make the thickness of the electrode active material layer thicker than the thickness of other portions in the portion where the crystallization phenomenon occurs (Patent Document 3). While increasing the thickness of the electrode active material layer is effective, increasing the thickness of the electrode active material layer is accompanied by a significant increase in cost. That is, the electrode active material layer is formed in a predetermined layer thickness by repeating so-called baking coating in which an electrode coating solution is applied, dried and baked. In order to increase the layer thickness, it is necessary to increase the number of times the baking coating is repeated, and not only the amount of expensive electrode active material used is increased, but also the number of work steps is remarkable.

  Heating when forming the electrode active material layer from the viewpoint that the very fast consumption of the electrode active material during negative polarization is due to selective dissolution of the valve metal oxide added as a binder, for example, tantalum oxide Method of preventing dissolution during negative polarization by improving the crystallinity of tantalum oxide or other valve metal oxide as a binder by making the temperature from 650 ° C. to 850 ° C. Has been proposed (Patent Document 4). However, if a valve metal such as titanium metal is exposed to a high temperature of 650 ° C. or higher in air for a long time, the titanium substrate is oxidized and the electrode becomes unusable.

  As yet another countermeasure, Patent Document 5 proposes a method of forming an electrode active material layer on an electrode substrate in which fine titanium particles are sintered on a titanium plate in a vacuum or in an inert atmosphere as an electrode that can withstand negative polarization. Sintering requires strict temperature control and atmosphere control at high temperatures, and the cost of manufacturing a sintered base becomes very high.

Japanese Patent Laid-Open No. 5-230682 Japanese Patent Laid-Open No. 11-302892 Japanese Patent Laid-Open No. 10-287998 JP 2002-275697 A JP 2006-188742 A

  The object of the present invention is to provide an oxygen generating anode that has sufficient durability not only in anodic polarization but also in electrolysis with negative polarization, thereby extending the use period of the anode, repairing and replacing the anode, etc. This is to reduce the manufacturing cost of the oxygen generating anode.

  By the way, when an insoluble anode is used only for anodic polarization, there is a symptom that iridium oxide, which is an electrode active substance, is gradually consumed, and that the consumption becomes severe at the end of the electrode. The life of the electrode in this case is determined by the rate of embrittlement of the electrode active layer rather than the consumption of the electrode active material. In contrast, when used for electrolysis involving not only positive polarization but also negative polarization, the consumption of the electrode active material is much faster than when using only positive polarization, and the life before the electrode active layer becomes brittle is shortened. I knew it would reach.

  Based on such facts, the present inventors diligently studied and examined a method for suppressing the consumption of the electrode active substance when used for electrolysis with negative polarization. As a result, porous metal sheets such as expanded metal (expanded metal) and punched metal (punched metal) are bonded as a physical support for the electrode active substance on the conductive metal that is the electrode structure from the electrode structural surface. It has been found that the use of the electrode substrate is an effective means for extending the lifetime of the portion where negative polarization occurs.

  More specifically, when an insoluble anode is used for electrolysis with only positive polarization, the porous metal sheet on the conductive metal that is the electrode structure does not affect the life of the anode. That is, the porous metal sheet does not contribute to extending the life of the electrode active material and does not function as a physical holding body. However, when used for electrolysis with negative polarization, the porous metal sheet contributes to the extension of the anode life. This fact means that when used for electrolysis with negative polarization, the porous metal sheet contributes to the extension of the life of the electrode active material and functions as a physical holding body or holding accelerator. .

  The oxygen generating anode of the present invention has been completed on the basis of such knowledge, and in the oxygen generating anode formed by coating the surface of the electrode substrate with an electrode active material, the surface of the conductive metal that is an electrode structure is provided. An electrode base is formed by bonding an active substance holding body made of a porous metal sheet or an active substance holding promoting body to an electrode active substance mainly composed of iridium oxide on the holding body bonding surface of the electrode base. Is an anode for oxygen generation that is resistant to cathodic phenomenon.

  There is a conventional method for increasing the strength of the binder added to the active material by increasing the thickness of the electrode active material layer or raising the sintering temperature because the consumption rate of the electrode active material increases when the cathodic phenomenon occurs However, in the oxygen generating electrode of the present invention, the resistance to the cathodic phenomenon is improved by a mechanism different from the conventional method, ie, physical retention of the electrode active material. The mechanism is known to be inherent to electrolysis with negative polarization as described above, but the details of active substance retention are unknown. For example, in the case of an electrode substrate obtained by bonding an expanded metal to a plate-like conductive metal, the present inventors have found that the thickness of the electrode active material layer because the catalyst coating solution is unevenly distributed in the gap of the bonding portion or the intersecting portion of the expanded metal. Is thicker but partially, it is more resistant to cathodicization than a uniformly coated plate-like electrode substrate, which is believed to contribute to the extension of anode life in electrolysis with negative polarization. .

  Examples of the porous metal sheet bonded to the surface of the conductive metal that is the electrode structure can include expanded metal, punching metal, interdigital or net-like metal, bondability to the conductive metal surface, availability, From the viewpoint of mechanical strength and the like, an expanded metal or a punching metal is particularly preferable.

  The material of the conductive metal constituting the electrode substrate and the porous metal sheet bonded thereto is preferably a valve metal such as titanium, tantalum, niobium, tungsten or zirconium, and further titanium-tantalum, titanium-tantalum-niobium, titanium. -Titanium-based alloys such as palladium or tantalum-coated titanium are suitable, and the surface of the metal substrate may be oxidized, nitrided, borated or carbonized. The shape of the conductive metal as the electrode structure can be a desired shape such as a flat plate shape, a net shape, a rod shape, or a porous plate shape, but a flat plate shape or a porous plate shape is particularly preferable.

  The thickness of the porous metal sheet is preferably 0.2 mm or more and 4.0 mm or less. When the porous metal sheet is too thin, a problem occurs in the retention of the electrode active material. On the contrary, even if the porous metal sheet is thickened, the effect is small and the economic efficiency is only deteriorated.

  In the porous metal sheet, the aperture ratio is important together with the thickness. The opening ratio, that is, the ratio of the opening area to the total area is preferably 5 to 85%, particularly preferably 30 to 50%. When the aperture ratio is too small, the retention ability of the electrode active material and the effect of extending the anode life due to this decrease. Similarly, when the aperture ratio is too large, the ability to hold the electrode active material and the effect of extending the anode life due to this decrease. In addition, there is a problem in workability of joining to the conductive metal that is the electrode structure. The specifications for each type of porous metal sheet are as follows.

  LW (distance between the centers in the mesh long direction) and thickness are important for the dimensions of the expanded metal, and LW: 4 to 40 mm, thickness: 0.5 to 4.0 mm are desirable, and LW: 8 is more preferable. ˜20 mm thickness: 1.0 to 2.5 mm is preferable. The openings in the punching metal may be in a staggered arrangement of 45, 60, and 90 degrees, the ratio of the opening area to the total area is preferably 5 to 85%, and the hole diameter of the opening is 1.5 to 25 mm, particularly 2 10 mm is preferred.

  As a method for joining expanded metal, punching metal, interdigital or net-like metal, which is a porous metal sheet, to a conductive metal, welding, screwing or the like is used. However, when applying a large current density, for example, spot welding, TIG A welding method such as welding is preferred. Two or more of the expanded metal, punching metal, interdigital or reticulated metal may be bonded to the surface of the conductive metal. It is also possible to join two or more different shapes.

  The above is the description of the porous metal sheet which is a holding body for the electrode active material. Next, the electrode active material will be described. As a result of intensive research and investigation by the present inventors on the method of suppressing the consumption of the electrode active substance when used for electrolysis with negative polarization, from the aspect of the electrode active substance, the oxygen generating catalyst which is the main material is platinum. Group metal oxides, particularly iridium oxide, are desirable, and for binders added to the main material, the amount of valve metal oxide, for example tantalum oxide, is reduced from the viewpoint of giving priority to suppression of wear over prevention of embrittlement, It has been found effective to increase the relative amount of iridium oxide as the main material.

  Based on this knowledge, as the electrode active material to be coated on the electrode substrate, a main material that is an oxygen generation catalyst is used as a main component, and a mixture obtained by adding a binder to this is used. Use iridium oxide, which has excellent ability as a generation catalyst. As the binder, an oxide of one or more metals selected from the group consisting of valve metals such as titanium, tantalum, niobium, tungsten, zirconium, and tin is preferable. Typical examples of the electrode active material include iridium-tantalum mixed oxide, iridium-tantalum-titanium mixed oxide, and iridium-tantalum-niobium mixed oxide.

  With respect to the specific composition of the electrode active material, the content of the binder is reduced and the content of the oxygen generating catalyst as the main material is increased from the viewpoint of giving priority to the suppression of wear over the prevention of embrittlement. Specifically, a mixture of metal oxides containing 50 to 95% by weight of iridium in terms of metal and 50 to 5% by weight of one or more kinds of valve metals in terms of metal is preferable. A more preferable electrode active material is a mixture of metal oxides in which one type of valve metal is tantalum and iridium is contained at a weight percentage of at least twice that of tantalum in terms of metal. A particularly preferred electrode active material is an iridium-tantalum mixed oxide containing 70% by weight or more of iridium in terms of metal and the remaining metal component being tantalum.

  If the content of iridium oxide in the electrode active material is reduced, there is a drawback that the electrode active layer has insufficient oxygen generation capability and becomes porous. Moreover, the content of the binder is relatively increased, and the resistance to the cathodic phenomenon is lowered. On the other hand, when the iridium oxide content in the electrode active material is excessive, the content of the binder is relatively reduced, and from this point, the electrode active material is dropped, and the performance deterioration due to this becomes remarkable.

  Conventionally used thermal decomposition methods, powder sintering methods and the like can be applied as the electrode active substance coating method, but the thermal decomposition method is preferred. That is, these metal salt solutions are applied, dried, and fired in air at a temperature of 410 ° C. to 550 ° C. Application, drying, and baking operations are performed several to several tens of times to form a necessary amount of the electrode active layer.

  The oxygen generating anode of the present invention has a portion that is off the plate path of the anode due to the negative polarization phenomenon when zinc metal or the like is plated on the both sides of the steel plate with different coating widths for various plate widths. The problem that the life is shorter than the part that always faces the steel plate at the center is that by bonding a porous metal sheet such as expanded metal or punching metal on the conductive metal that is the electrode structure as a support for the electrode active material This can be effectively solved by constituting an electrode substrate and coating it with an electrode active substance mainly composed of a platinum group metal, particularly iridium. In addition, since it is not necessary to particularly increase the coating amount of the electrode active material or to increase the firing temperature when forming the electrode active material layer, the manufacturing cost can be kept low.

  Therefore, the oxygen generating anode of the present invention is particularly suitable for use in an insoluble anode for electroplating in which a cathodic phenomenon occurs, or in a portion in which the cathodic phenomenon of an insoluble anode for electroplating occurs.

  Embodiments of the present invention will be described below.

  An active substance holder made of a porous metal sheet is joined to one or both sides of the working surface of a flat conductive metal that is an electrode structure to constitute an electrode substrate. The active substance holding body is for physically holding the electrode active substance on the surface of the electrode substrate, which is an electrode structure. More precisely, the electrode active substance is applied to the surface of the electrode base in electrolysis with negative polarization. By physically holding, it contributes to the extension of anode life. Specifically, the porous metal sheet is made of expanded metal, punching metal, interdigital or net-like metal, and is joined to the surface of the conductive metal by welding or the like. These materials are made of valve metal, and titanium is preferable in terms of price and performance.

  When the electrode substrate is produced, the electrode active substance is coated on the active substance holding member bonding surface. The electrode active substance is a mixture of an oxygen generation catalyst as a main material and a binder, and specifically, a mixed oxide mainly composed of iridium as an oxygen generation catalyst. Specifically, the iridium content is 50% by weight or more, preferably 70% by weight or more in terms of metal. The metal component of the binder is a valve metal, preferably tantalum. The method for coating the electrode active material is the same as in the past.

  The produced oxygen generating anode is used in an insoluble anode in an electroplating line of a steel strip, particularly an insoluble anode in which a cathodic phenomenon occurs at the side edge, or a side edge in which the cathodic phenomenon of the insoluble anode occurs. Its durability is remarkably superior to conventional insoluble anodes that do not have an active substance holder.

Next, the present invention will be described more specifically with reference to examples and comparative examples.
Example 1
An electrode structure composed of a 30 mm × 30 mm × 10 mm flat plate made of titanium and an expanded metal made of titanium (30 mm × 30 mm square plate, LW is 8.0 mm, SW (mesh short) The distance between the centers in the eye direction) was 3.6 mm, the thickness was 1.2 mm), and the titanium base material was joined by spot welding. A titanium round bar having a diameter of 8 mm was welded perpendicularly to the center of the back surface of the titanium base material to obtain a power supply lead for energization. This was degreased by ultrasonic cleaning in acetone, and then the expanded metal surface was blasted at 0.6 MPa for about 10 minutes using No. 24 alundum. The titanium base material after the blast treatment was washed in running water for a whole day and night and dried to use as an electrode base.

An electrode active substance coating solution having the following liquid composition was prepared and applied to the expanded metal bonding surface of the produced electrode substrate. After coating, the coating was dried at 100 ° C. for 10 minutes and then baked in an electric furnace maintained at 450 ° C. for 20 minutes. This electrode active material coating operation (coating, drying, firing) was repeated 10 times to produce an oxygen-generating anode having iridium oxide as the electrode active material on the electrode substrate surface. The electrode active material coating layer has a metal weight composition ratio of Ir / Ta = 7/3, an iridium content ratio of 70% by weight, and more than twice the tantalum content ratio (30% by weight). The amount of iridium metal was 30 g / m ² .

TaCl ₅ : 3.2 g
_{H 2 IrCl 6 · 6H 2 O} : 10.0g
35% HCl: 10 ml
n-CH ₃ (CH ₂ ) ₃ OH: 100 ml

  Only the surface (30 mm × 30 mm) of the electrode active material coating layer in this oxygen generating anode was left, and the other part was sealed and used as the anode for the polarity reversal life test.

The electrolytic bath used for the polarity reversal lifetime test was 100 g / L Na2 SO4 aqueous solution (pH was adjusted with sulfuric acid) at pH = 1.2, the temperature was 60 ° C., and the flow rate was 2 m / sec. Moreover, the platinum plate was used for the counter electrode. As an electrolysis method, forward and reverse energization is repeated by repeating forward energization (positive polarization) for 10 minutes at a current density of 100 A / dm ² and reverse energization (negative polarization) for 10 minutes at 30 A / dm ^2. The electrode life was defined as when the cell voltage increased by 5 V compared to the starting voltage. This polarity reversal electrode life acceleration test evaluates the durability of the electrode against cathodic phenomenon. The test results are shown in Table 1.

Example 2
An oxygen generating anode was prepared in the same manner as in Example 1 except that the composition of the electrode active material coating solution was as follows. The metal weight composition ratio of the electrode active material coating layer is Ir / Ta / Nb = 6.3 / 2.6 / 1.1, and the iridium content ratio is 63 wt%, but the tantalum content ratio (26 % By weight). The amount of iridium metal was 30 g / m ² . A polarity reversal electrode life acceleration test similar to that in Example 1 was performed. The test results are shown in Table 1.

TaCl ₅ : 9.9 g
_{H 2 IrCl 6 · 6H 2 O} : 32.5g
NbCl ₅ : 6.3 g
35% HCl: 15 ml
_{n-CH 3 (CH 2)} 3 OH: 240ml

Example 3
Titanium punching metal (30 mm x 30 mm square plate, opening at 60 degrees staggered, hole diameter, 30 mm x 30 mm x 10 mm titanium flat plate, which is an electrode structure, as a porous metal sheet for the active substance holder Of 3.0 mm, the hole center pitch of 5.5 mm, and the thickness of 1.5 mm) were joined by spot welding to obtain a titanium base material. A titanium round bar having a diameter of 8 mm was welded perpendicularly to the center of the back surface of the titanium base material to obtain a power supply lead for energization. Subsequent treatment of the titanium base material and formation of the electrode active material coating layer were performed in the same manner as in Example 1. The electrode active material coating layer has a metal weight composition ratio of Ir / Ta = 7/3, an iridium content ratio of 70% by weight, and more than twice the tantalum content ratio (30% by weight). The amount of iridium metal was 30 g / m ² . A polarity reversal electrode life acceleration test similar to that in Example 1 was performed. The test results are shown in Table 1.

Example 4
A 30 mm × 30 mm × 10 mm titanium flat plate, which is an electrode structure, and a titanium expanded metal (30 mm × 30 mm square plate, LW is 10.0 mm, SW is 5. 5 mm) as a porous metal sheet for an active substance holder. A titanium electrode substrate was prepared in the same manner as in Example 1 except that 0 mm and a thickness of 0.5 mm were joined by spot welding. An electrode active material coating layer having the same composition and coating amount as in Example 1 was formed on the surface of the produced electrode substrate, and then a polarity reversal electrode life acceleration test similar to that in Example 1 was performed. The test results are shown in Table 1.

Example 5
A 30 mm × 30 mm × 10 mm titanium flat plate, which is an electrode structure, and a titanium expanded metal (30 mm × 30 mm square plate, LW is 10.0 mm, SW is 5. 5 mm) as a porous metal sheet for an active substance holder. A titanium electrode substrate was prepared in the same manner as in Example 1 except that 0 mm and a thickness of 1.5 mm were joined by spot welding. An electrode active material coating layer having the same composition and coating amount as in Example 1 was formed on the surface of the produced electrode substrate, and then a polarity reversal electrode life acceleration test similar to that in Example 1 was performed. The test results are shown in Table 1.

Comparative Example 1
A titanium electrode substrate was prepared in the same manner as in Example 1 except that a titanium flat plate of 30 mm × 30 mm × 10 mm was used as the titanium substrate material. An electrode active material coating layer having the same composition and coating amount as in Example 1 was formed on this surface, and then the polarity inversion electrode life acceleration test similar to that in Example 1 was performed. The test results are shown in Table 1.

  The oxygen generating anodes of Examples 1 to 5 using an electrode base body in which a titanium expanded metal and a punching metal are joined to a titanium plate as an electrode structure are used for oxygen generation using simple plate-like titanium as an electrode base body. Compared with the anode, the electrode life was extremely excellent in the polarity reversal electrode life acceleration test.

Reference Examples 1-6
Oxygen generating anodes similar to those prepared in Examples 1 to 5 and Comparative Example 1 were prepared, and an electrode life acceleration test was performed on these. These are designated as Reference Examples 1-6.

The electrolytic bath used for the electrode life acceleration test was a pH = 1.4, 100 g / L Na2 SO4 aqueous solution (pH was adjusted with sulfuric acid), the temperature was 70 ° C., and the flow rate was 2 m / sec. A zirconium plate was used for the counter electrode. As an electrolysis method, the current density was 200 A / dm ² continuous positive energization (positive polarization), and when the cell voltage increased by 5 V compared to the starting voltage, the electrode life was defined. The results are shown in Table 2.

As can be seen from Reference Examples 1 to 6, when an acceleration test of only positive polarization was performed with continuous positive current, both the oxygen generation anodes of Examples 1 to 5 and the oxygen generation anode of Comparative Example 1 had an electrode life. There was no significant difference. As is clear from this, the active substance holder in the oxygen generating anodes of Examples 1 to 5 cooperates with the electrode active substance mainly composed of iridium to improve the durability of the electrode in electrolysis with negative polarization. Demonstrate the effect.

Claims (9)

  In an oxygen generating anode in which an electrode active material is coated on the surface of an electrode substrate, the electrode substrate is configured by bonding an active material holding member made of a porous metal sheet to the surface of a conductive metal that is an electrode structure. An oxygen-generating anode that is resistant to cathodic phenomena, wherein the holding surface of the electrode substrate is coated with an electrode active material mainly composed of iridium oxide.   2. The oxygen generating anode according to claim 1, wherein the porous metal sheet is an expanded metal, a punching metal, an interdigital or a reticulated metal.   The electrode active material is a mixture of metal oxides containing 50 to 95% by weight of iridium in terms of metal and 50 to 5% by weight of one or more kinds of valve metals in terms of metal. The anode for oxygen generation as described.   4. The oxygen generating anode according to claim 3, wherein one type of valve metal is tantalum, and the iridium content (% by weight) in terms of metal is at least twice the tantalum content (% by weight).   5. The oxygen generating anode according to claim 4, wherein the iridium oxide content in the electrode active material is 70% by weight or more in terms of metal, and the remaining metal oxide is tantalum oxide.   6. The oxygen generating electrode according to claim 1, which is used as an insoluble anode for electroplating in which a cathodic phenomenon occurs.   The electrode for generating oxygen according to any one of claims 1 to 5, which is used in a portion where the cathodic phenomenon of an insoluble anode for electroplating occurs.   8. The oxygen generating anode according to claim 1, wherein the conductive metal and the porous metal sheet are made of a valve metal.   9. The oxygen generating anode according to claim 8, wherein the valve metal is a metal selected from titanium, tantalum, niobium, tungsten, and zirconium.