JPH02232387A - Oxygen generating anode and production thereof - Google Patents

Abstract

PURPOSE:To provide the oxygen generating anode having durability by coating the surface of an intermediate coating layer consisting of a mixture composed of specific mol% of an oxide of metal such as titanium and rhodium oxide with a mixture composed of specific mol% of an oxide of metal such as titanium and iridium oxide. CONSTITUTION:The intermediate coating layer and a surface coating layer having oxygen generating catalytic ability is formed on a conductive metallic base body. The intermediate coating layer is formed of the oxide mixture composed of 85 to 90mol% oxide of at least one kind of the metals selected from Ti, Ta, Sn, Nb, and Zr and 5 to 15mol% rhodium oxide. The surface coating layer is formed of the oxide mixture composed of 23 to 70mol% metal oxide of at least one kind of the metals selected from Ti, Ta, Sn, Nb, and Zr and 30 to 80mol% iridium oxide. The conductive metal base body is composed of the metal selected from Ti, Ta, Nb, and Zr and the alloy thereof. The anode which is hardly dissolved by electrolysis in a sulfuric acid soln. is provided in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an insoluble anode used in electrolytic processes involving oxygen generation, particularly in electroplating of tin, zinc, chromium, etc.

[Conventional technology and problems to be solved] Currently, lead or lead alloys are used as anodes for electroplating of continuous steel strips such as tin, zinc, chromium, etc., but lead is consumed relatively quickly and is not suitable for plating. It dissolves into the solution, causing problems such as contamination of the plating solution and deterioration of the plating film. Platinum plated anodes and platinum foil clad anodes are being considered as alternative anodes, but platinum consumption is too great and the problem has not yet been resolved.

For this reason, various insoluble anodes with low consumption have been proposed.

For example, in JP-A No. 59-38394, at least one metal oxide selected from tetravalent titanium and tin and pentavalent tantalum and niobium are deposited on a conductive metal substrate. An electrode has been proposed in which an intermediate coating layer made of a mixed oxide with at least one metal oxide selected from the following is provided to impart conductivity, and an electrode active material is coated on the intermediate coating layer.

This intermediate coating layer contains a mixture of tetravalent metals and pentavalent metals, and is considered to be an N-type semiconductor based on the generally known valence control principle, but it still has insufficient electrical conductivity. Not obtained.

Furthermore, in Japanese Patent Publication No. 51-19429, an oxygen-impermeable layer made of a platinum-iridium alloy or an oxide of cobalt, manganese, palladium, lead, or platinum is provided as an intermediate layer between the conductive substrate and the electrode active material coating, and then An electrode consisting of a solid solution type outer coating that has corrosion resistance against electrolytes has been proposed. According to this, the catalyst in the intermediate layer is itself catalytically active for oxygen generation, and the solid solution type outer coating (judging from the examples, a solid solution of ruthenium oxide and titanium oxide) is even more catalytically active. . However, among the middle class,
Oxides of cobalt, manganese, palladium, lead, and platinum are relatively rapidly depleted in sulfur 1' solution. Furthermore, a solid solution of ruthenium oxide and titanium oxide also has poor durability in an acidic sulfuric acid solution, making it difficult to use it industrially.

Also, in JP-A-59-150091, JP-A-59-38
No. 394 proposes an electrode in which platinum is dispersed in an intermediate coating layer. In other words, since there is a limit to the carrier concentration in the semiconductor intermediate layer, platinum itself is used to impart further conductivity, but platinum itself gradually disintegrates during electrolysis in an electrolytic solution, especially in a sulfuric acid acidic solution, making it a limit for long-term use. There is.

JP-A No. 60-184691 discloses that an oxide of a metal selected from titanium and tin, and aluminum, potassium, iron, cobalt,
An intermediate layer in which platinum is dispersed in a mixed fluoride with an oxide of at least one metal selected from nickel and thallium has been proposed. This intermediate layer consists of a tetravalent metal and a divalent or trivalent metal.
Platinum is dispersed in a mixed oxide with a valence of gold, and this oxide becomes a P-type semiconductor based on the valence control principle, and not only has good electrical conductivity, but also has high electron resistance due to the dispersed platinum. It was thought to impart electrical conductivity. However, platinum itself gradually dissolves in the sulfuric acid acidic electrolyte, and the dissolution is accelerated during electrolysis, so a sufficient lifespan cannot be expected.

JP-A-62-174394 discloses that a porous platinum layer is provided on a conductive substrate by electroplating, and then at least one oxide selected from ruthenium oxide, palladium M oxide, and iridium oxide is deposited on the porous platinum layer by thermal decomposition. An electrode has been proposed in which a platinum plating layer and an oxide layer are repeatedly formed in an electrode provided with a metal layer. In this case as well, the problem of the platinum porous layer gradually dissolving in the sulfuric acid acidic electrolyte during electrolysis remains unsolved.

[Means to solve the problem]

The present inventors have developed an insoluble anode for use in a 1M sulfur electrolyte by imparting corrosion resistance to the oxygen-impermeable intermediate layer and increasing conductivity, and by imparting oxygen generation catalytic activity to the surface layer to provide a mechanism for preventing gas generation. We have developed a long-life electrode that can prevent physical damage.

That is, the present invention provides a mixed oxide of 85 to 95 mol% of at least one metal oxide selected from titanium, tantalum, tin, niobium, and zirconium and 5 to 15 mol% of rhodium oxide on a conductive metal substrate. b) 20 to 70 mol% of an oxide of at least one metal selected from titanium, tantalum, tin, niobium, and zirconium and 30 to 80 mol% of iridium oxide; The present invention relates to an oxygen generating anode characterized in that a surface coating layer made of a mixed oxide and having a catalytic ability to generate hydrogen is formed, and a method for producing the same.

The conductive substrate used in the present invention includes titanium, tantalum,
Materials that form passive films include niobium, zirconium, and alloys thereof. Titanium and/or its alloys are usually used from the viewpoint of economy, electromechanical properties, workability, etc. The electrode can take various shapes such as a plate, a rod, an expanded band, and a perforated plate.

The intermediate coating layer is a mixed oxide layer consisting of 85 to 95 mol% of one or more oxides of titanium, tantalum, tin, niobium, and zirconium and 5 to 15 mol% of rhodium oxide, and the rhodium oxide content is 5 mol. If it is less than 15 mol %, the electron conductivity will be low, and if it exceeds 15 mol %, the oxygen generation catalytic ability will be strong, impairing the oxygen impermeability function and shortening the life. If an oxide layer of one or more of titanium, tantalum, tin, niobium, and zirconium is formed without rhodium oxide in the intermediate N layer, the life of the accelerated electrolytic test will be rather shortened. The cause is not clear, but in this case, even if the intermediate coating layer can sufficiently prevent oxygen permeation, the potential barrier between the substrate and the intermediate coating layer becomes high, which causes the voltage to rise quickly in the electrolytic life test. it is conceivable that.

The surface coverage consists of a mixed oxide layer consisting of 20 to 70 mol% of one or more oxides of titanium, tantalum, tin, niobium, and zirconium and 30 to 80 mol% of iridium oxide, and if iridium oxide is less than 30 mol%, The catalytic ability to generate oxygen deteriorates, and if it exceeds 80 mol%, the adhesion of the film will be impaired.

The coating layer of the electrode of the present invention is formed as follows.

The surface of the conductive metal substrate is roughened by etching with acid treatment, blasting, etc., and metal salts such as titanium chloride, tantalum chloride, stannous chloride, niobium chloride, zirconium oxychloride, and rhodium chloride are etched. is dissolved in a solvent such as ethyl alcohol or butyl alcohol to prepare a mixed solution of a predetermined composition, and applied by means such as brush coating, roll coating, spraying, or dipping. After coating, it is dried at 100 to 150°C for several tens of minutes to evaporate the solvent, and then thermally decomposed in an electric furnace in an air or oxygen atmosphere at 300 to 700°C for 10 to 20 minutes. If the heat treatment temperature is less than 300°C, thermal decomposition will not occur completely, and if it exceeds 700°C, the oxidation of the metal-cured substrate will progress and the substrate will be damaged. In order for the intermediate coating layer to have the ability to prevent oxygen permeation, the coating amount must be 3. 0(I
I/rri or more is good, and less is less effective.

The surface coating layer is a mixed solution of a predetermined composition by dissolving iridic acid chloride and metal salts such as titanium chloride, butyl titanate, tantalum chloride, niobium chloride, zirconium chloride, and stannous chloride in a solvent such as ethyl alcohol or butyl alcohol. and coated in the same manner as the intermediate layer. If the amount of catalyst in the coating layer is 10(]/m or more in terms of metallic iridium, both the catalytic ability for oxygen generation and the life span will be good.

The present invention will be explained in detail with reference to Examples below. All composition percentages in the examples are on a molar basis unless otherwise specified.

Example 1 Comparative Examples 1 and 2 A commercially available titanium plate (IX10XO.iCm) was degreased with acetone, etched in a 10% by weight hot oxalic acid solution, and a solution having the following composition was applied to its surface.

T a CJls 2. Og petyl ditanate 3.9g? hCi3・
3 H2 0 0. ! M thick}
{CI! l. ■Id! n-butyl alcohol 20 m This is 120
℃ for 20 minutes, then in an electric furnace at 500℃ for 10 minutes.
Ta20s30%, TiQ2
A film consisting of a mixed oxide of 60% Rh2 03 and 10% Rh2 03 was obtained. Repeat this operation 4 times and 3. 09/'
A rd intermediate coating layer was obtained. Next, a solution having the following composition was applied onto this intermediate coating layer.

TaCJls. 0.47gH
2Irαs ・6t-ho 1.0(]1!HC
Fl! 1.0 ml of n-butyl alcohol (15 ml) was dried at 120° C. for 20 minutes, and then fired in an electric furnace at 500° C. for 10 minutes to obtain a film consisting of a mixed oxide of 40% Ta20s and 260% irQ. Repeat this operation 10 times. A surface coating layer of 1/771 was obtained.

This N-electrode was used as an anode in a 100 MfJ sulfuric acid solution at 50° C., and an accelerated electrolytic test was conducted at a current density of 20 OA/dm 2 with a distance between the electrodes of about 4 Cm and a platinum wire as a cathode.

The initial voltage is 8V, and it gradually increases, but after 320 hours, it suddenly increases to about 10V. This time is defined as the life of the electrode. On the other hand, for comparison, T was added to the surface coating layer coating solution.
When an accelerated electrolytic test was conducted under the same conditions as above using an anode prepared in the same manner except that aα5 was not added and an anode prepared in the same manner except that the intermediate coating layer was omitted, the life of the electrode was 110%. It was 35 hours.

Examples 2 to 4 Comparative Examples 3 and 4 Surface coating layer of Example 1 (coated 10 times, 10.0 [1
/m) in the same way as the intermediate coating layer (4 coats, 3.Oq.
/77f> except that the composition ratio was changed as shown in Table 1.
An anode was produced in the same manner as in Example 1. Example 1
Table 1 also shows the results of an accelerated electrolytic test conducted under the same conditions as above.

] As shown in the table above, the Rh203 content of the intermediate coating layer is 3%,
In the case of 20%, the R life of the electrode is short, and the effect of inserting the intermediate coating layer is not obtained.

Examples 5 to 8 Comparative Example 4.5 The intermediate N layer was the same as in Example 1, except that the composition ratio of the surface coating layer (coated 10 times, 10.0g/7rt) was changed as shown in Table 2. An anode was produced in the same manner as in Example 1. This was subjected to an accelerated electrolytic test under the same conditions as in Example 1, and the results are also shown in Table 2.

As shown in Table 2 and above, the Ir02 content of the surface-coated decoy is preferably 30% or more, and if it is 90% or more, the life will be shortened.

Examples 9-12 Comparative Examples 6-9 Intermediate coating layer (4 coats, 3.
OM rtt ) and surface coating layer (10 coats, 10,
0 (J/resistance), anodes were prepared by changing the composition materials as shown in Table 3, and an accelerated electrolysis test was conducted under the same conditions as in Example 1. The results are also listed in Table 3.

As described above, it can be seen that the electrode of the present invention having two intermediate coating layers containing Rh203 has superior durability compared to the electrode having an intermediate coating layer not containing Rt1203.

(Effects of the Invention) The anode of the present invention has a mixed oxide layer of rhodium oxide having oxygen permeation prevention ability and one or more of titanium, tantalum, tin, zirconium, and niobium oxides as an intermediate coating layer,
Provided as a surface coating layer is a mixed oxide layer of iridium oxide, which is catalytically active against oxygen generation and is hardly dissolved by electrolysis in a sulfuric acid solution, and one or more of the oxides of the metals listed below. Therefore, it is useful as a durable oxygen generating anode.

Claims (4)

[Claims] (1) On a conductive metal substrate, a) 85 to 95 mol% of an oxide of at least one metal selected from titanium, tantalum, tin, niobium, and zirconium and 5 to 15% of rhodium oxide;
an intermediate coating layer consisting of a mixed oxide with mol% and b) an oxide of at least one metal selected from titanium, tantalum, tin, niobium, and zirconium 20
1. An oxygen-generating anode characterized in that a surface coating layer having an oxygen-generating catalytic ability is formed of a mixed oxide of ~70 mol% and 30-80 mol% of iridium oxide. (2) The anode according to claim 1, wherein the conductive metal substrate is a metal selected from titanium, tantalum, niobium, zirconium, or an alloy thereof. (3) A solution containing at least one metal salt selected from titanium, tantalum, tin, niobium, and zirconium and a metal salt of rhodium is applied to a conductive metal substrate, and then heat-treated in an oxidizing atmosphere to form titanium. , an intermediate coating layer made of a mixed oxide of 85 to 95 mol % of at least one metal oxide selected from tantalum, tin, and niobium and 5 to 15 mol % of rhodium oxide, and then the same method as above. to form a surface coating layer made of a mixed oxide of 20 to 70 mol% of at least one metal oxide selected from titanium, tantalum, tin, niobium, and zirconium and 30 to 80 mol% of iridium oxide. Characteristic manufacturing method of anode for oxygen generation. (4) Heat treatment temperature in oxidizing atmosphere is 300 to 70
4. The method according to claim 3, wherein the temperature is 0<0>C.