JPH0261083A - Anode for generating oxygen and production thereof - Google Patents

Abstract

PURPOSE:To impart corrosion resistance to an oxygen impermeable intermediate layer and to improve the electrical conductivity thereof as well as to prevent the damage of a surface layer by providing the intermediate layer and surface layer consisting of specific ratios of the oxide of Ti, Ta, Sn, etc., and iridium oxide onto a conductive metallic base body. CONSTITUTION:The insoluble anode for electroplating of Sn, Zn, Cr, etc., which generates O2 is produced by forming a) the conductive intermediate coating layer consisting of the oxide mixture composed of 85 to 95mol% the metal oxide of >=1 kinds of the Ti, Ta, Sn, Nb, and Zr and 15 to 5mol% IrO2 and b) the surface coating layer which consists of the oxide mixture composed of 20 to 70mol% metal oxide which is the same as in the above-mentioned (a) and 80 to 30mol% IrO2 and has O2 generating power on the conductive metallic base body. The intermediate coating layer and surface coating layer of this anode consist of the common components, contain the many crystals of the common rutile structure and are analogous in unit lattice volume to each other and, therefore, the adhesive property of both to each other is secure and the anode is strong against the erosion by the produced gas.

Description

[Detailed description of the invention] (Industrial application field) The present invention is directed to electrolytic processes involving oxygen evolution, particularly tin.

It relates to insoluble anodes used for electroplating of zinc, chromium, etc.

(Problems to be solved by conventional techniques and inventions) Tin,
Lead or lead alloys are currently used as anodes for electroplating of zinc, chromium, etc., but lead wears out quickly during mating and is eluted into the plating solution, causing problems such as contamination of the plating solution and deterioration of the plating film. I was disappointed.

Platinum plated anodes and platinum foil clad anodes are being considered as alternative anodes, but platinum consumption is large and no solution has yet been reached. For this reason, various insoluble anodes with low consumption have been proposed.

In JP-A No. 59-38394, at least one metal oxide selected from T1 and sn having a valence of 4 and Ta and Nb having a valence of 5 are deposited on a conductive metal substrate. They have proposed an electrode in which an intermediate layer made of a mixed oxide with at least one type of oxide selected from the above is provided to impart conductivity, and an electrode active material is coated on the intermediate layer.

The intermediate layer is a mixture of oxides of tetravalent metals and pentavalent metals, and is thought to be an N-type semiconductor based on the generally known valence control principle, but it still has insufficient electrical conductivity. The sex wasn't showing.

Japanese Patent Publication No. 51-19429 discloses that a Pt-1r alloy is used as an intermediate layer between a conductive support base material and an electrode active material coating. Co, Mn,
An oxygen-impermeable layer made of oxides of Pd, Pb, and Pt was established
Attempts are being made to prevent the electrode from becoming passivated. However, since the intermediate coating material itself has a catalytic activity for oxygen generation, it reacts with the permeating electrolyte and an oxygen generation reaction occurs in the intermediate layer, so that the adhesion of the electrode coating and the effect of preventing passivation were insufficient. .

In JP-A-59-150091, JP-A-59-3
No. 8394 proposes an electrode in which PT is dispersed in the intermediate layer. In other words, since there is a limit to the carrier concentration in the semiconductor intermediate layer, Pt is dispersed in order to provide further conductivity, but Pt itself dissolves little by little during electrolysis in an electrolytic solution, especially an acidic sulfuric acid solution, and does not last for a long time. There were limits to its use.

In JP-A-60-184691, an oxide of a metal selected from Ti and Sn and AI, Ga, and Fe are used as an intermediate layer between a conductive metal substrate and an electrode active material.

An intermediate layer in which Pt is dispersed in a mixed oxide with an oxide of at least one metal selected from Co, Ni, and TI is proposed. This intermediate layer is made by dispersing Pt in a mixed oxide of a tetravalent metal and a divalent or trivalent metal, and the oxide becomes a P-type semiconductor based on the valence control principle and has good conductivity. It was thought that high electronic conductivity was imparted by the Pt dispersed in the Pt. 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.

In JP-A No. 62-174394, a porous Pt layer is provided on a conductive substrate by electroplating, and at least one layer selected from ruthenium oxide, palladium oxide, and iridium oxide is formed on the porous Pt layer by thermal decomposition. We have proposed an electrode made of an oxide layer, which is formed by repeating a Pt plating layer and an oxide 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 for Solving the Problems) In an insoluble anode used in a sulfuric acid acidic electrolyte, the present inventors provided corrosion resistance to an oxygen-impermeable intermediate layer, increased conductivity, and oxygen generation in the surface layer. By preventing mechanical damage to catalyst activity and gas generation, we have achieved a long-life electrode.

That is, the present invention provides a method of forming a mixed oxide of 85 to 95 mol% of at least one metal oxide selected from titanium, tantalum, tin, niobium, and zirconium and 15 to 5 mol% of iridium oxide on a conductive metal substrate. and b) titanium, tantalum, tin, and niobium on the intermediate coating layer.

Oxygen characterized by forming a surface coating layer having oxygen generation catalytic ability consisting of a mixed oxide of 20 to 70 mol% of at least one metal oxide selected from zirconium and 80 to 30 mol% of iridium oxide. A generation anode and its manufacturing method.

The conductive metal substrate of the present invention includes a material that forms a passive film, such as a metal selected from titanium, tantalum, niobium, and zirconium, or an alloy thereof. Usually, titanium and/or
or its alloys are used. Various electrode shapes are possible, such as a plate, a rod, an expanded band, and a perforated plate.

The intermediate coating layer of the present invention is titanium, tantalum, and tin.

85 to 90 mol% of at least one oxide selected from niobium and zirconium and 15 to 5 mol% of iridium oxide
If the iridium oxide content is less than 5 mol%, the electronic conductivity will be low, and if it exceeds 15 mol%, the oxygen generation catalytic ability will be strong and the oxygen impermeable function will be lost. Because it is damaged, its lifespan is shortened.

When a mixed oxide film of at least one selected from titanium, tantalum, tin, niobium, and zirconium is formed without containing iridium oxide in the intermediate coating layer, the life of the accelerated electrolytic test is rather shortened. Although the cause is not clear, it is thought that although this intermediate coating layer can sufficiently protect against oxygen permeation, the potential barrier between the substrate and the intermediate layer becomes high, and as a result, the voltage increases quickly in the electrolytic life test.

The surface coating layer of the present invention is made of titanium, tantalum, or tin.

A mixed oxide having an oxygen generation catalytic ability of 20 to 70 mol% of at least one oxide selected from niobium and zirconium and 80 to 30 mol% of iridium oxide, with less than 30 mol% of iridium oxide. If the content exceeds 80 mol%, the adhesion of the film will be impaired.

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

After etching and roughening the surface of the conductive metal substrate using methods such as acid treatment and blasting, titanium chloride, titanium chloride,
Metal salts such as tantalum chloride, stannous chloride, niobium chloride, zirconium oxychloride or iridium chloride are dissolved in a solvent such as edyl alcohol or butyl alcohol to form a mixed solution of a predetermined composition, which is applied by brushing, rolling, It is applied by means such as spraying or dipping. then 100
It is dried at ~150°C for several minutes, and then subjected to thermal decomposition treatment at 300-700'C for 10-20 minutes in an electric furnace in an air or oxygen atmosphere.

If the heat treatment temperature is less than 300°C, thermal decomposition will not occur completely;
Further, if the temperature exceeds 700° C., oxidation of the metal substrate progresses and the substrate is damaged.

The thickness of the intermediate coating layer is preferably 3.0 g/m or more in order to exhibit oxygen permeation prevention ability, and if it is less than that, the effect will be low. Also, if the thickness of the surface coating layer is 10.0 g# or more,
Both the catalytic ability for oxygen generation and the lifespan are improved.

(Effects of the Invention) The intermediate coating layer and the surface coating layer in the anode of the present invention are made of common components, contain many crystals having a common rutile structure, and have similar unit cell volumes, so the mutual Adhesion is extremely strong, and it has characteristics such as being resistant to erosion due to generated gas. Generally speaking, the intermediate coating layer and the surface coating layer have a unique effect of having different functions of conductivity and oxygen generation catalytic ability by having different contents of the same iridium oxide.

The anode of the present invention has excellent durability, such as plating of steel material in sulfuric acid solution, that is, tin.

Effectively used for electroplating of zinc, chromium, etc.

The present invention will be described in more detail below with reference to Examples. 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 (1xlOxO, 1cm) was degreased with acetone and etched in a 10% by weight hot oxalic acid solution, and a solution having the following composition was applied to the surface by brushing.

Taα52. ICI Butyl Titanate 4. O〃H2I rcj
! a ・6H201,On concentrated hydrochloric acid 1.0 d n-butyl alcohol 15〃 After drying this at 120'C for 20 minutes, it was heated in an electric furnace at 500 °C.
By baking at °C for 10 minutes, Ta20s30%
A film made of a mixed oxide of 60% T i 0 and 10% IrQ was obtained. Repeat this operation 4 times and 3. (X
An intermediate coating layer of l/TIt was obtained.

Next, a solution having the following composition was applied by brushing onto the intermediate coating layer.

Ta(lfso, 47gH2I
r(j!e ・6H201, Ott concentrated hydrochloric acid 1
．． 0 d n-butyl alcohol 15 rd! This is 12
By drying at 0°C for 20 minutes and then firing at 500°C for 10 minutes in an electric furnace, Ta20s40% and Ir0260
% of mixed oxide was obtained.

This operation was repeated 10 times to obtain a surface coating layer of 10.0 (1/tri).

This electrode was used as an anode in a 100(]/N sulfuric acid solution at 50°C, and the platinum wire was used as a cathode at a current density of 200 A/d.
When an accelerated electrolytic test was conducted at m2, it could be used for 320 hours.

On the other hand, as Comparative Example 1, an anode was prepared in the same manner as in Example 1, except that C1s was not added to the surface coating layer coating solution, and as Comparative Example 2, it was the same as in Example 1, except that no intermediate coating layer was formed. As a result of testing the anode produced in Example 1 in the same manner as in Example 1, the lifespan was 85 hours and 35 hours, respectively, indicating that the electrode of the present invention had a much longer lifespan.

Examples 2 to 4 Comparative Examples 3 and 4 Anodes were produced in the same manner as in Example 1, except that the composition ratio of the intermediate coating layer (4 times coated, 3.0 Mm) was changed as shown in Table 1, and the The results of the test conducted in the same manner as in Example 1 are shown in Table 1.

For comparison, the intermediate coating layer (4 coats, 3.0 (+/
An anode was prepared in the same manner as in Example 2 except that the composition ratio of (G) was changed as shown in Table 1, and the results of testing in the same manner as in Example 2 are also shown in Table 1. The results show that the effect of the intermediate coating layer is not sufficient when the IrO2 content of the intermediate coating layer is 3% or 20%.

Table 1 Examples 5 to 8 Comparative Examples 5 and 6 Anodes were produced in the same manner as in Example except that the composition ratio of the surface coating layer (coated 10 times, 10.OMTIt) was changed as shown in Table 2. The results of testing in the same manner as in Example 1 are shown in Table 2.

For comparison, the surface coating layer (coated 10 times, io, o
A positive plate was prepared in the same manner as in Example 5, except that the composition ratio of ct/butt was changed as shown in Table 2, and the results of testing in the same manner as in Example 5 are also shown in Table 2. Ta.

The results show that the IrO2 content of the surface coating layer is preferably 30% or more, and that when it becomes 90%, the life becomes extremely short.

Examples 9 to 12 Comparative Examples 7 to 10 The composition ratios of the intermediate coating layer (coated 4 times, 3.OMTri) and the surface coating layer (coated 10 times, io, oa/go) were changed as shown in Table 3. An anode was produced in the same manner as in Example 1 except for the above, and the test results are shown in Table 3.

Table 2 Table 3 As a result, the electrode of the present invention provided with an intermediate coating layer containing IrO2 has much better durability than the electrode provided with an intermediate coating layer not containing IrO2. I understand.

Claims (4)

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