JP2574699B2 - Oxygen generating anode and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an electrolytic process involving the generation of oxygen, in particular, tin, zinc,
It relates to an insoluble anode of electroplating of chromium or the like.

(Prior art) Currently, lead or lead alloy is used as an anode for electroplating copper plates such as tin, zinc, chromium, etc., but lead is relatively fast consumed, and contamination of the plating solution by dissolved lead. And problems such as deterioration of the plating film.

Platinum-plated anodes and platinum-foil clad anodes are being studied as alternatives to this, but platinum has been exhausted and has not been solved. For this reason, various insoluble anodes using noble metals and oxides thereof, which are less consumed, as electrode active substances have been proposed.

However, in the case of an electrode simply coated with an electrode active material using titanium or its alloy as a base, which is widely used in terms of economy and workability, the oxidizing power of the oxidizing power generated from the anode during use causes the generation of oxygen. A nonconductive oxide layer is formed between the electrode coating layer and the substrate, and even if the amount of the remaining electrode active substance is sufficient, the electrode function is lost, and eventually the electrode coating layer is peeled off and used. The inconvenience of being disabled is caused. For this reason, the coating amount of the electrode active material tends to be increased, but its use efficiency cannot be said to be good considering the use of expensive noble metals.

In order to solve this problem, JP-A-59-38394 discloses an oxide of at least one metal selected from titanium and tin having tetravalent valence and a pentavalent valence on a substrate. There has been proposed an electrode in which an intermediate layer made of a mixed oxide with an oxide of at least one metal selected from tantalum and niobium is provided, and the intermediate layer is coated with an electrode active material. In this case, the intermediate layer has no oxygen generating activity,
It is considered that the electric conductivity can be obtained based on a generally known valence control theory using tetravalent and pentavalent metals, but the electric conductivity is not sufficient.

Japanese Patent Application Laid-Open No. Sho 59-15091 proposes a method in which platinum is dispersed in this intermediate layer for the purpose of further imparting conductivity. However, platinum itself is greatly consumed in an electrolytic solution, particularly in a sulfuric acid solution, so that an intermediate layer is used. There is a limit to the durability of the layer. In this case, since the intermediate layer itself has the ability to activate oxygen generation, passivation occurs soon. Japanese Patent Application Laid-Open No. Sho 62-174394 describes a porous platinum layer formed by electroplating as an intermediate layer. However, in this case, a fundamental solution has not been reached for the same reason as described above.

Japanese Patent Application Laid-Open No. 57-192281 discloses an electrode having an electric coating made of a metal oxide on a base material of titanium or a titanium alloy, in which a tantalum and / or niobium conductive oxide layer is provided as an intermediate layer. Electrolytic electrodes involving oxygen generation have been proposed, but the tantalum or niobium oxide layer is not sufficient to prevent the passivation phenomenon due to oxygen.

(Problems to be Solved by the Invention) The passivation of the substrate, which is a problem in the insoluble anode for generating oxygen, which is being studied as the anode for electroplating tin, zinc, chromium, etc., of the present invention, is economically possible. An advantage is to provide an electrode that has a long life and prevents it in an advantageous manner.

(Means for Solving the Problems) In the insoluble anode for generating oxygen, the present inventors have found that tantalum metal or its alloy has a sufficient resistance to passivation due to oxygen generated by an electrode active material in the intermediate layer. Developing a long-life electrode that uses these metals as a protective layer thinned on the electrode substrate, economically preventing passivation of the electrode substrate, and improving the use efficiency of the electrode active material did.

That is, the present invention relates to an electrode in which an electrode active material containing a platinum group metal or an oxide thereof is coated at a pyrolysis temperature of 350 to 550 ° C. on a conductive metal substrate made of a valve metal or an alloy thereof. An oxygen-generating anode characterized in that a thin film intermediate layer having a thickness of 1 to 3 μm and containing, as a main component, crystalline metal tantalum formed by a sputtering method is provided between the coating layer and the coating layer.

The conductive metal medium used for the electrode substrate of the present invention is a valve metal forming a passive film such as titanium, zirconium, niobium, hafnium, tungsten, aluminum, molybdenum, bismuth, antimony or a metal thereof. Titanium, zirconium and niobium are particularly preferred.

Although the intermediate layer does not completely cover the surface of the electrode substrate, the protective effect of the substrate can be considerably obtained, but a thickness of 1 micron or more is required to achieve the object of the present invention. Usually, a thickness of 3 microns or less is sufficient. The intermediate layer itself does not need to be porous.

Next, an electrode coating layer having electrochemical activity is provided on the substrate on which the intermediate layer having no electrode activity is provided in this manner. As the electrode active substance suitable for electrolysis accompanied by oxygen generation, a platinum group metal or its oxide is preferable, or a mixed oxide of these with a valve metal such as titanium or tantalum is preferable. Typical examples are iridium oxide,
Iridium-tantalum mixed oxide, iridium-titanium mixed oxide, iridium-ruthenium mixed oxide, iridium-ruthenium-tantalum mixed oxide, iridium-ruthenium-titanium mixed oxide, ruthenium-titanium mixed oxide, ruthenium-tantalum mixed Oxides and the like.

Thermal decomposition is used as a method for coating such an electrode active material. That is, these metal salt solutions are applied and dried several times, and finally heat-treated at a temperature of 350 to 350 ° C. Thus, the electrode of the present invention having the intermediate layer mainly composed of tantalum metal can be obtained. As the shape of the electrode, various shapes such as a plate shape, a rod shape, an expanded shape, a perforated plate shape, and the like are possible.

(Effect) The effect of suppressing the passivation of the intermediate layer, that is, the thin film layer mainly composed of tantalum metal, in the electrode of the present invention is not necessarily clear logically. When performed, almost no diffraction pattern of tantalum and pentavalent tantalum oxide (Ta ₂ O ₅ ), which is generally considered most stable, is found at the interface between the surface coating layer and the intermediate layer in X-ray diffraction. That is, it is considered that tetravalent tantalum oxide (TaO ₂ ) having a rutile-type structure having metallic conductivity is generated at this interface, and is maintained in a chemically stable state with the electrode active material. Further, since the intermediate layer itself is almost in a state of metal tantalum, it is considered that the intermediate layer has good conductivity different from that of a pentavalent tantalum oxide having a poor conductor and a non-rutile structure.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

Example 1 and Comparative Example 1 A commercially available titanium plate having a thickness of 1 mm and a size of 30 mm × 10 mm was degreased with acetone and then etched with oxalic acid at 80 ° C. for 12 hours to obtain an electrode substrate.

After drying the titanium plate, it was treated for 1 hour using a high-frequency sputtering device (up to 10 ^-4 Torr / argon gas, high-frequency applied voltage of 2 KV) to obtain 40 g / m ^{2 of} tantalum,
An intermediate layer mainly composed of metal tantalum having an α-type crystal structure and having a thickness of 3 μm was formed on the substrate.

Further, an electrode coating wave having a liquid composition as shown below was adjusted and applied on the tantalum thin film intermediate layer.

_{TaCl 3 0.32g H 2 IrCl 6 ·} 6H 2 O 1.00g after drying 10 min conc. HCl 1.0 ml n-butyl alcohol 10.0ml which at 120 ° C., and calcined in an electric furnace maintained at 490 ° C. 20 min. This electrode active material coating operation was repeated eight times to produce an electrode using iridium oxide containing 10 g / m ² of iridium as the electrode active material (the composition of the electrode active coating layer was IrO ₂ (70% by weight) -Ta). ₂ O ₅ (30% by weight)
It is estimated to be).

For comparison, an electrode for comparison was prepared in the same manner except that the tantalum thin film intermediate layer was not provided.

After partially sealing the covered portion of these electrodes to make the effective portion of the electrode 10 mm × 10 mm, the anode was used as an anode in a sulfuric acid electrolytic solution at 50 ° C and 100 g /, and a platinum plate was used as a cathode and the current density was 200 A.
The accelerated electrolysis test was carried out under the conditions of / dm ^2.

In the electrode without the tantalum thin film intermediate layer, a sharp rise in the cell voltage was observed 70 hours later, and the electricity could not be supplied.
When the thickness of the electrode active material coating layer was measured at the time of this rise using a beta-ray film thickness type, the thickness was 80% of the thickness measured at the time of fabrication, and a result of 20% consumption was obtained.

On the other hand, in the electrode provided with the tantalum thin film intermediate layer, a stable electrolysis was still possible after 200 hours, although a rise of about 1 V was observed as compared with the initial cell voltage. At this point, the consumption of the electrode active material obtained from the thickness measurement is
It was 40%, indicating that the use efficiency of the electrode active material during electrolysis was improved by the tantalum thin film intermediate layer.

Comparative Example 2 The same titanium plate was degreased and etched in the same direction as in Example 1 to obtain an electrode substrate. An alcohol solution of tantalum having the following liquid composition was applied to the electrode substrate.

TaCl ₃ 0.50 g Concentrated HCl 1.0 ml n-butyl alcohol 10.0 ml This is put into an electric furnace, and heated to 100 ° C. at a rate of 10 ° C./min in an air atmosphere, that is, an oxidizing atmosphere, and then held for 10 minutes. Perform the drying process and in another 15 minutes
The temperature was raised to 490 ° C., and was kept as it was for 20 minutes. This operation was repeated five times to form an intermediate layer mainly containing 7 g / m ² of tantalum oxide as tantalum.

A diffraction pattern of Ta ₂ O ₅ was obtained by X-ray diffraction on the surface of the intermediate layer. Further, an electrode coating solution having the following liquid composition was prepared and applied on the intermediate layer.

After _{H 2 IrCl 6 · 6H 2 O} 1.00g of concentrated HCl 1.0 ml n-butyl alcohol 10.0ml This was dried for 10 minutes at 120 ° C., and calcined in an electric furnace maintained at 490 ° C. 20 min. This coating operation of the electrode active substance was repeated five times to produce an electrode using iridium oxide containing 7 g / m ² of iridium as the electrode active substance.

When the obtained electrode was subjected to an accelerated electrolysis test under the same electrolysis conditions as in Example 1, the electrode having an intermediate layer of Ta ₂ O ₅ had a life of 35 hours.

(Effects of the Invention) As described above, the electrode of the present invention is provided with a thin film intermediate layer containing tantalum metal as a main component, so that the passive state generated between the electrode substrate and the electrode active material layer, which has conventionally been regarded as a problem, is provided. Thus, the efficiency of use of the electrode active substance can be improved, and the utility value of the anode as an anode for industrial electrolysis, for example, as an anode for generating oxygen such as a sulfuric acid solution is great.

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Claims (1)

(57) [Claims] 1. An electrode comprising a conductive metal substrate made of a valve metal or an alloy thereof coated with an electrode active material containing a platinum group metal or an oxide thereof at a pyrolysis temperature of 350 to 550 ° C.
An oxygen-generating anode, comprising a thin-film intermediate layer having a thickness of 1 to 3 μm and comprising, as a main component, crystalline metal tantalum formed by a sputtering method between the substrate and the electrode active coating layer.