JPH06146047A - Anode for generating oxygen and its production - Google Patents

Abstract

PURPOSE:To develop the insoluble anode having excellent durability in an acidic plating bath of sulfuric acid by providing an electrode active layer consisting of a mixture composed of IrO2 and Ta2O5 via an intermediate layer consisting of a thin film of a mixture composed of SiO2 and Ta on the surface of a base body made of a valve metal. CONSTITUTION:The surface of the base body made of the valve metals, such as Ti, Ta, Nb and Zr, as the insoluble anode to be used at the time of plating a material to be plated as cathode with Sn, Zn, Cr, etc., by using an acidic plating liquid consisting of sulfuric acid contg. metal ions of Sn, Zn, Cr, etc., is provided with the intermediate layer consisting of the thin film of the mixture composed of the SiO2 and the Ta by a physical vapor growth method, such as sputtering method, and thereafter, a soln. prepd. by dissolving salts of Ir and Ta into ethyl alcohol, etc., is applied thereon and after the coating is dried, the base body is heated to 380 to 500 deg.C in air or oxygen-contg. atmosphere to thermally decompose the metal salts, by which the electrode active layer consisting of 30 to 8Omol% IrO2 and 20 to 70mol% Ta2O5 is formed. The insoluble anode having a long life is obtd. without being attacked by the acidic plating liquid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insoluble anode used in a sulfuric acid acidic bath for electroplating a steel sheet with oxygen, particularly tin, zinc, chromium or the like, and a method for producing the same. .

[0002]

2. Description of the Related Art Lead or lead alloy is currently used as an anode used for electroplating steel sheets with tin, zinc, chromium, etc. However, lead is relatively rapidly consumed and is caused by molten lead. There are problems such as contamination of the plating solution and deterioration of the plating film. Platinum-plated anodes and platinum foil clad anodes have been investigated as alternative anodes, but platinum has been exhausted and has not been solved yet. For this reason, various insoluble anodes have been proposed which use noble metals and oxides thereof, which consume less, as an electrode catalyst.

However, in an electrode which is widely used in terms of economical efficiency and workability and which is simply coated with an electrocatalyst using titanium and its alloy as a substrate, an electrode catalyst layer is formed by oxygen generated from the anode during use. A non-conductive oxide layer is formed between the substrates, and even if the remaining amount of the electrode catalyst is sufficient, the function as an electrode is lost, and finally the electrode catalyst layer is peeled off and becomes unusable. Occurs. For this reason, the coating amount of the electrode catalyst tends to be increased, but the utilization efficiency is not so high considering the use of expensive noble metal. Therefore, many improvement means have been proposed which provide an intermediate layer of various substances between the substrate and the electrode catalyst layer to protect the substrate and improve the durability of the electrode.

For example, in Japanese Patent Publication No. 51-19429, platinum is used as an intermediate layer between a conductive support substrate and an electrode active material coating.
Iridium alloy, cobalt, manganese, palladium,
We are trying to prevent the passive state of the electrode by providing an oxygen impermeable layer made of oxides of lead and platinum. However, since the intermediate coating material itself has a catalytic activity for oxygen generation, it reacts with the permeating electrolytic solution to cause an oxygen generation reaction in the intermediate layer, and the adhesion of the electrode coating and the passivation preventing effect were not sufficient.

Further, in JP-A-57-192281, an electrode having a base of titanium or a titanium alloy and having an electrode coating made of a metal oxide has a conductive oxide layer of tantalum and / or niobium as an intermediate layer. Although an electrolysis electrode provided with oxygen generation provided is proposed, the tantalum or niobium oxide layer is not sufficient to prevent passivation.

The present inventors have found that the intermediate coating layer containing titanium oxide containing a non-stoichiometric compound represented by TiOx (x is 1.5 or more and less than 2.0) and silica is a titanium base material. Was found to be effective in preventing the immobilization of the above-mentioned, and filed a patent application (JP-A-3-271386). This coating requires a thermal spraying method, the resulting coating contains some air bubbles, and it is impossible to completely shield the substrate from the electrolyte solution, but the life of the electrode has been increased It wasn't enough.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an oxygen generating anode having sufficient catalytic activity for oxygen generation and having sufficient durability for electrolysis in a sulfuric acid acidic solution. It is in.

[0008]

The present inventors have found that the conductive intermediate coating of vitreous silica and metallic tantalum is used to prevent the oxidation of titanium substrates commonly used in insoluble anodes used in sulfuric acid electrolytes. Layer, complete the anode that can be used until the electrode catalyst of the surface layer does not remain,
This is what makes it possible to extend the service life.

That is, according to the present invention, a thin film intermediate layer made of a mixture of silica and tantalum is provided on a conductive metal substrate made of a valve metal or its alloy, and 30 to 80 mol% of iridium oxide and 20 to 70 of tantalum oxide are provided thereon. The present invention relates to an oxygen generating anode and a method for producing the same, in which an electrode active layer made of a mixed oxide with mol% is provided.

The conductive metal substrate is a valve metal or its alloy forming a passive film such as titanium, tantalum, zirconium, niobium, etc. Usually, titanium or titanium is used from the viewpoint of economy, electromechanical properties and workability. / Or alloys thereof are preferred. The electrode may have various shapes such as a plate shape, a rod shape, an expanded shape, and a punching shape.

The surface of the substrate is grid-blasted, shot-blasted or sand-blasted. Alumina, silicon carbide, sand or the like is used as the blast material, and the particle size is 100 to 1000 μm (coarse-grain MAX # 30 to 20).
0) is suitable. After blasting, ultrasonic cleaning may be used to clean the surface.

The thin film intermediate layer made of a mixture of silica and tantalum is formed by physical vapor deposition.
osition method), that is, a sputtering method, an ion plating method, or a vacuum evaporation method. The sputtering method is particularly preferable. The thickness of the thin film intermediate layer is 0.
A thickness of 5 microns or more, preferably 1 micron or more is required, and a thickness of 5 micron or less, particularly 3 micron or less is sufficient. In order to improve the conductivity, the tantalum content should be 10 mol% or more.

The electrode active layer formed on the surface of the intermediate layer is composed of a mixture of iridium oxide and tantalum oxide, and the iridium oxide content is 30-80 mol%, preferably 40-80.
Mol% and tantalum oxide are in the range of 20 to 70 mol%, preferably 20 to 60 mol%. Iridium oxide is 30
If it is less than 80% by mole, the catalytic ability of oxygen generation deteriorates.
If it exceeds, the adhesion of the film will be poor and peeling during electrolysis,
Many of them fall off, which shortens the life of the electrode.

The electrode active layer is formed by adding a metal salt such as iridium chloride, iridium chloride or tantalum chloride to ethyl alcohol,
It is formed by dissolving it in a solvent such as butyl alcohol or propyl alcohol to prepare a mixed solution having a predetermined composition, applying it by a method such as brush coating, roll coating, spray coating, or dipping, and performing thermal decomposition treatment. After application, the solvent is evaporated to dry at 100 to 150 ° C. for about 10 to 20 minutes, and then 360 to 550 in an electric furnace of air or oxygen atmosphere.
C., preferably 380 to 500.degree. C. for 10 to 30 minutes for thermal decomposition treatment. If the heat treatment temperature is less than the above range, almost no thermal decomposition occurs, and if it exceeds the above range, the tantalum or tantalum alloy forming the intermediate layer with the base metal is oxidized and damaged. The electrode catalyst layer coated in this way was 5 g / m ²
If it is above, the catalytic ability and life for oxygen generation will be good.

The anode of the present invention is preferably used with a current density of 10 A / dm ² or more during electroplating, and can be used up to 300 A / dm ² .

[0016]

Since the intermediate layer of the anode of the present invention can be formed by a physical vapor deposition method such as a sputtering method, an ion plating method or a vacuum vapor deposition method, the fact that silica is vitreous The film becomes extremely dense.
That is, the porosity of the intermediate layer is almost zero and does not reach several percent to several tens percent as in the case of the thermal spraying method. Therefore, the base metal is almost completely protected from the electrolytic solution and no corrosion damage occurs. In particular, the higher the current density, the greater the effect of the intermediate layer according to the present invention.

[0017]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples.

Example 1, Comparative Example 1 A commercially available titanium plate (1 × 10 × 0.1 cm) was degreased with acetone and then blasted with alumina grit (# 30) at a pressure of 4 kg / cm ^2. It was Using this as a substrate, a high-frequency magnetron sputtering device (up to 3 x 10
^-3 Torr, argon gas frequency 13.56 MHZ, applied voltage 2 kV), and 55 mol% SiO ₂ -4
Sputtering was performed using a 5 mol% Ta target to form a 3 micron thick tantalum-containing silica intermediate coating layer on the titanium substrate. A solution having the following composition was applied to the surface. Tantalum pentachloride 0.32 g Iridium chloride 1.00 g Hydrochloric acid 0.5 ml Butyl alcohol 10 ml

After coating, this was dried at 120 ° C. for 20 minutes and then heat-treated in an electric furnace at 450 ° C. for 20 minutes to mix Ta ₂ O ₅ (30 mol%)-IrO ₂ (70 mol%). A film made of oxide was obtained. This operation 1
By repeating 0 times, an electrode active layer containing 12 g / m ^{2 of} iridium oxide was obtained. The adhesion between the electrode active layer and the intermediate layer was good. For comparison, an electrode was prepared in the same manner except that the intermediate layer was not provided.

An accelerated electrolysis test was conducted under the conditions of a current density of 200 A / dm ² using a platinum plate as a cathode and a sulfuric acid solution of 100 g / l at 50 ° C. as these electrodes. The time until the cell voltage increased by 5 V was determined as the electrode life. The electrode of the present invention could be used for 1330 hours, while the electrode without the intermediate layer had a life of 70 hours.

Comparative Example 2 A titanium substrate which had been subjected to the same blasting treatment as in Example 1 was subjected to silica gel (50 wt%) having a particle size of 20 to 30 μm and a particle size of 2
A uniform mixed powder of titanium oxide (50% by weight) of 0 to 30 μm was sprayed with a plasma spray gun to a thickness of 100 μm, and an electrode active layer similar to that of Example 1 was provided thereon. When this electrode was subjected to the same accelerated electrolysis test as in Example 1, the result was 760.
It was a lifetime of time.

Examples 2 to 6, Comparative Examples 3 and 4 The coating of the intermediate layer was performed in the same manner as in Example 1 except that the composition of the electrode active layer was changed as shown in Table 1 to obtain 12 g of iridium oxide.
An electrode containing / m ² was produced and the same test as in Example 1 was performed. From Table 1, it can be seen that the IrO ₂ composition of the electrode active layer is preferably 30 mol% or more, and when it is 90 mol%, the life becomes short.

[0023]

[Table 1]

[0024]

In the anode of the present invention, a dense thin film intermediate layer made of a mixture of silica and tantalum is formed on a valve metal substrate by a method such as sputtering, ion plating or vacuum deposition. The liquid hardly penetrates into the liquid and is not corroded by the sulfuric acid acidic electrolyte. Therefore, when the intermediate layer is coated with an electrode active layer and used as an anode for oxygen generation, corrosion damage of the base metal does not occur and the life of the anode is determined only by the reduction of the electrode catalyst. Therefore, it is possible to maximize the use of the electrode catalyst, and it is possible to extend the life of the anode.

Claims (4)

[Claims] 1. A thin film intermediate layer made of a mixture of silica and tantalum is provided on a conductive metal substrate made of a valve metal or its alloy, and 30 to 80 mol% of iridium oxide and 20 to 70 mol% of tantalum oxide are provided thereon. An oxygen generating anode comprising an electrode active layer made of a mixed oxide of 2. The oxygen generating anode according to claim 1, wherein the valve metal or its alloy is a metal selected from titanium, tantalum, niobium and zirconium, or an alloy thereof. 3. A thin film intermediate layer made of a mixture of silica and tantalum is deposited on a conductive metal substrate made of a valve metal or its alloy by physical vapor deposition, and 30 to 80 mol of iridium oxide is deposited thereon. % And tantalum oxide 20-
A method for producing an oxygen generating anode, characterized in that an electrode active layer comprising a mixed oxide of 70 mol% is deposited by thermal decomposition of a metal salt of iridium and tantalum. 4. The physical vapor deposition method is a sputtering method,
An ion plating method or a vacuum vapor deposition method.
The method for producing an oxygen generating anode according to 1.