JP3257872B2 - Electrode substrate for electrolysis and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a durable electrode substrate for electrolysis and a method for producing the same, and more particularly to a durable and fluorine-resistant electrode used at a high current density and mainly used for an oxygen generation reaction. The present invention relates to an electrode substrate for electrolysis having resistance to current reversal and a method for producing the same.

[0002]

2. Description of the Related Art Industrial electrolysis, particularly electrolysis mainly using inorganic acids, is performed in a very wide range such as electrolytic smelting of metals, electroplating, and electrolytic synthesis of organic and inorganic substances. These electrodes for electrolysis, particularly lead or lead alloy electrodes, platinum-plated titanium electrodes, carbon electrodes, etc., have been proposed as anodes, but all of these electrodes have drawbacks and are not used for electrolysis in a wide range of applications. For example, a lead electrode is formed on its surface with lead dioxide, which is relatively stable and has good conductivity. However, this lead dioxide also has the drawback that several mg / AH is dissolved under ordinary electrolysis conditions, and the overvoltage is large. Platinum-plated titanium electrodes are expensive and have a short life, and if the anodic reaction is an oxygen generating reaction, the carbon electrode reacts with the generated oxygen to consume itself as carbon dioxide and has poor conductivity. There is. Dimensionally stable electrodes (DSE) have been proposed and widely used to overcome the disadvantages of each of these electrodes.

[0003] As long as this DSE is used as an anode with a valve metal represented by titanium as a base, the surface is passivated and functions as a chemically extremely stable long-life electrode.
However, when the DSE is also used as a cathode and is subjected to negative polarization, it reacts with the generated hydrogen to become hydride, which weakens the substrate itself or peels off the surface coating due to corrosion, thereby significantly shortening the electrode life. In particular, this is a major drawback when using DSE for electrolysis where the polarity is reversed, that is, the current direction is reversed. Furthermore, when electrolysis is performed in a solution in which certain halogen ions such as fluorine and fluoride are present, or in the presence of organic substances such as alcohols and aldehydes, abnormal corrosion of the base or active dissolution occurs even in a small amount thereof. Therefore, there is a problem that the electrode material formed on the surface is peeled off, and it becomes impossible to conduct electricity in a short time.

When used at an extremely large current density of 10 to ²⁰ KA / m ² , the interface between the electrode material and the substrate becomes inactive, and there is a problem that the current cannot be supplied finally, and this problem is solved. In order to achieve this, the present inventors provided a thin layer of platinum as an oxygen barrier layer on the surface of the substrate, or modified the surface of the substrate so that it became a semiconductive oxide in advance, even if it was passivated. We have proposed an electrode that has a structure that makes it possible or that has an intermediate layer that is extremely stable in an oxidized state such as tin oxide and does not lose conductivity.

It has been confirmed that these electrodes are extremely effective and have an electrode life 2 to 10 times or more as long as electrodes which do not modify the intermediate layer or the substrate. However, under such a large current density, even though the modified layer and the intermediate layer are provided, the passivation layer is formed on the substrate side with a thickness of several μm through them to maintain the activity of the electrode material. In some cases, it is often impossible to conduct electricity, and there has been a demand for a more effective surface modification method and an intermediate layer forming method for a longer life and more effective use of the electrode material. Also, depending on the electrolysis conditions, a reverse current may inevitably occur,
In this case, for example, tin oxide is instantaneously reduced and desorbed, and the modified layer also has a problem that the electrode material is easily dropped off.

Further, these intermediate layers and modified layers have resistance to the above-mentioned organic substances and certain corrosive halides, but are not sufficient. There was a problem in that it relied on its own corrosion resistance. In order to prevent the above-mentioned disadvantages of the prior art, in particular, passivation of the intermediate layer, there has been proposed a method of forming an intermediate layer by spraying a tantalum wire (Japanese Patent Laid-Open No. 5-156480).
issue). It is reported that this tantalum spraying forms an intermediate layer composed of a partial oxide in which metal tantalum and tantalum oxide are mixed. However, tantalum is liable to be oxidized, that is, passivation is more likely to occur than other metals, and it cannot be expected to have a long life especially under severe conditions. are doing.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems associated with the conventional electrode substrate, particularly a substrate such as DSE, and provides sufficient durability and chemical stability under a high current density and electrolysis with positive / negative reversal. An object of the present invention is to provide an electrode substrate for electrolysis which is stable for use under negative polarization and can be used for a long period of time, and a method for producing the same.

[0008]

According to the present invention, a sprayed layer having a thickness of 50 to 200 μm, which is a partial oxide containing metal titanium and titanium oxide, is formed on a conductive metal substrate which has been roughened in advance. An electrode substrate for electrolysis characterized by being formed and a method for producing the same.

Hereinafter, the present invention will be described in detail. When a sprayed layer containing titanium metal and titanium oxide is formed on a metal substrate according to the present invention, the sprayed layer has a dense and substantial surface area unique to arc spraying or plasma spraying, and has a substantial current density when used in electrolysis. The conductive oxide formed due to the lack of oxygen in the partial oxide caused by a large amount of metal can be secured, and the good conductivity of the metal and the strong adhesion between the sprayed layer and the base metal can be secured. Thus, an electrode base for electrolysis having good halogen resistance and reverse current resistance including fluorine produced by the method is obtained, and furthermore, progress of passivation is suppressed due to oxidation resistance under normal electrolysis conditions of titanium, and the Can be used.

The conductive metal substrate used in the present invention is not particularly limited as long as it is conductive because it is isolated by a sprayed layer formed on the surface when used as an electrode. There is a possibility that pinholes sometimes exist at a maximum of about 200 μm.For example, when used as an anode in a strong acid, it is desirable to use a valve metal represented by titanium having relatively high corrosion resistance. Is good,
It is desirable to use relatively inexpensive titanium or titanium alloy. Of course, in other electrolysis, a corrosion-resistant alloy such as nickel, stainless steel, or trade name Hastelloy can be used according to the purpose.

Prior to forming a thermal spray layer on the metal substrate, the surface of the substrate is roughened. Since the thermal spray layer has a thickness of 50 to 200 μm as a surface layer, it has an anchor effect for holding the thermal spray layer and obtaining stronger adhesion and a strong chemical bond between the base material and the thermal spray layer. The surface is roughened in order to obtain. Typical surface roughening methods include a physical method and a chemical method. This roughening is performed with care so that no impurities remain on the surface of the substrate after the roughening and a chemically unstable processed layer does not remain. Although the degree of surface roughening is not particularly limited, JISR _a = 10 to 20 μm, JISR _max = 50
About 200 μm is desirable.

As a physical method of the above-mentioned roughening, for example, there is a roughening by blasting, and the surface of the base material is polished with a ceramic sand such as alumina to form irregularities. In the case of this blasting method, it is preferable to use alumina or silica which is resistant to acid or alkali as the blast powder in consideration of the possibility that the electrolytic solution penetrates to the substrate surface of the electrode finally formed. If alumina or the like is used, even if the powder remains on the surface of the base material, the electrode can be used stably without causing abnormal elution as an electrode. Of course, it is more desirable to carry out pickling treatment or the like in order to prevent the residue of these powders that have penetrated the surface.

The above-mentioned chemical surface roughening method is a method of forming irregularities on the surface of a substrate with a chemical to roughen the surface. For example, when using titanium or a titanium alloy as a base material, about 85 to 90 ° C.
By immersing the previously washed substrate in a 20% hydrochloric acid aqueous solution and holding it for several hours, intergranular corrosion occurs to roughen the surface. If the substrate is titanium or stainless steel, 40-60
By immersing the base material in an aqueous solution of iodic acid of about 10% of about 10 ° C., so-called pitting corrosion is caused to roughen the surface.

Next, a sprayed layer containing metallic titanium and titanium oxide is formed on the roughened base material surface by arc spraying, plasma spraying, or the like to obtain an electrode substrate. The particle size of the spray powder to be used may be selected according to the purpose, but it is of course desirable that the surface area is large as long as the electrode substrate is used. The surface roughness of the electrode substrate is almost JISR _max ≧ 100 μm, J
It is desirable that ISR _a ≧ 10 μm. In order to achieve this surface roughness, it is preferable to use thermal spray powder having a particle size of 20 to 100 μm, but it is also possible to thermally spray a wire. If the particle size is less than 20 μm, a dense sprayed layer can be formed, but the surface roughness becomes small and oxidation during spraying may proceed too much. On the other hand, if it exceeds 100 μm, it becomes difficult to form a dense thermal sprayed layer without through holes. When only the metal is used as the thermal spray material, the thermal spray layer can be formed by using a metal wire as a raw material by the arc thermal spraying method. in this case,
Although the density is inferior to plasma spraying by about 5 to 10%, it has a feature that the surface unevenness is correspondingly large, so that it can be selected according to the application.

The thickness of the sprayed layer to be formed is suitably from 50 to 200 μm, and if it is less than 50 μm, there is a great risk that through holes will remain. If it exceeds 200 μm, the sprayed layer becomes too heavy and tends to peel off. In some cases, there is a problem that the electric resistance increases. When a thermal spray is formed by ordinary plasma spraying, the thermal spray itself is in a strong reducing atmosphere,
In this atmosphere, no oxide is generated, but during the actual coating formation, the metal is easily converted to oxide in the cooling process, and an oxide surface may be formed. Conventionally, in order to prevent this oxide formation, an inert gas such as nitrogen or argon is used as a seal gas to suppress oxidation.

On the other hand, in the present invention, a phenomenon in which this oxide is formed positively is utilized, and a part of the sprayed titanium is converted into titanium oxide only by spraying metallic titanium to form a non-stoichiometric composition. It is intended to form a thermal spray layer containing a conductive oxide. However, the method of the present invention is not limited to this method, but includes the following two other methods, namely, a method using an oxidizing sealing gas and a method using a sprayed oxide particle to generate an oxide.

According to ordinary thermal spraying conditions, a metal titanium powder or a wire is sprayed on a roughened substrate surface using a mixed gas of argon and helium as a plasma gas. At this time, if the surrounding seal gas is an oxidizing gas, a part of the sprayed titanium is oxidized to form a mixed sprayed layer which is a partial oxide containing the sprayed titanium and the titanium oxide. The amount of oxide generated varies depending on the conditions. For example, if the oxidizing gas is air and the particle size of the sprayed titanium is 30 to 60 μm, 20 to 30% of the sprayed titanium is converted to titanium oxide, and the sprayed titanium is 70 to 80%. A mixed spray layer is formed, which is a partial oxide containing titanium and 30-20% titanium oxide. When the oxygen content is increased to about 50%, the oxide amount also increases to about 50%. However, if the amount of titanium oxide is further increased, an insulating oxide may be formed and the conductivity may be impaired, and there is a risk of explosive oxidation. Therefore, the oxygen content in the seal gas should be about 50% at the maximum. .

In addition to the above-mentioned metal titanium particles or wires as a sprayed material, a titanium oxide powder or wire is mixed and sprayed under the same spraying conditions to obtain a partial oxide containing metal titanium and titanium oxide at a predetermined ratio. Certain mixed sprayed layers are formed. In some cases, it may be desirable to add a small amount of tantalum or niobium to the partial oxide for the purpose of, for example, improving the halogen resistance. In this case, the method of using this oxide powder as a part of the sprayed powder is very convenient because the ratio of each metal and the ratio of the sprayed metal and the sprayed oxide can be set to a predetermined value. It becomes possible to apply.

An electrode is formed by forming a coating of an electrode substance containing, for example, iridium oxide on an electrode substrate having a coating layer made of only a conductive oxide formed on the surface of the substrate, and using the electrode as an anode in an aqueous acid solution to conduct electrolysis. When this is done, oxygen ions diffuse into the electrode simultaneously with the generation of oxygen, and a passive oxide is formed between the substrate and the electrode coating, so that electricity cannot be supplied. In the above-described electrode substrate of the present invention, the sprayed layer formed on the substrate by thermal spraying is partially converted into an oxide, and this partial oxide extremely effectively prevents the transfer of the oxygen ions and delays the passivation. As a result, the substantial electrode life is extremely long.

The electrode substrate according to the present invention has a minimum of 3 when used as an anode even in a bath containing a fluoride ion, when compared with an electrode substrate having only a metal sprayed layer.
The service life can be expected to be doubled. This is presumably because the formation of the partial oxide causes the entire coating to function as a conductive oxide. Further, when a current in the reverse direction is applied, the life is extended by at least about twice, and it can be seen that the device has resistance to the reverse current.

[0021]

EXAMPLES Next, examples of the production of an electrode substrate according to the present invention will be described, but the examples do not limit the present invention.

[0022]

Example 1 A commercially available JIS type 2 pure titanium plate having a length of 100 mm, a width of 100 mm and a thickness of 3 mm was used as a base material, and its surface was sandblasted to break the surface structure. Annealing was performed at 2 ° C. for 2 hours. The grain size on the titanium surface was equivalent to JIS No. 6. The titanium plate was pickled in a 20% hydrochloric acid aqueous solution at 85 ° C. for 2 hours, and the surface was roughened by intergranular corrosion. The surface roughness is R _max =
It was about 150 μm.

Argon and helium as plasma gases
Using a gas mixed at 70:30, while spraying air as a seal gas, a titanium metal powder having a particle size of 40 to 60 μm is plasma-sprayed on the sample surface so that the spray thickness becomes 100 μm on average, and a reducing atmosphere is used. Cooled in. The surface roughness of the generated plasma sprayed sample is R _max = 180 μm, R _a = 15
μm. The surface of the sample exhibited a pale blue to dark blue color, indicating the presence of titanium oxide. Observation of the state of the sprayed layer by X-ray diffraction revealed that about 20 parts of rutile-type titanium oxide existed for about 80 parts of titanium metal. Several other unidentifiable diffraction lines were observed, which are considered to be lower order oxides.

A metal paste is applied to the surface of the sample,
When the resistance in the thickness direction of the layer was measured using this as an electrode, it was about 4 × 10 ⁻⁴ Ωcm, and the electrical resistance was slightly higher than that of metal titanium, although it had conductivity. A coating solution containing an electrode substance consisting of iridium: tantalum = 60: 40 (molar ratio) was applied to the sample and baked at 530 ° C.
This was repeated 10 times, and the coating amount was 8 g-iridium / m ^2.
Was used as the electrode sample. Using a copper wire cutter, a sample for electrolysis of 20 × 40 mm was cut out from the electrode sample and subjected to an electrolysis test. The electrolysis is performed in an aqueous solution of 150 g / liter-sodium sulfate + 100 g / liter-sulfuric acid at 60 ° C.
A positive current and a reverse current were applied at intervals of 2 minutes in the forward direction and 1 minute in the reverse direction at a current density of 0 A / dm ² . Stable electrolysis could be continued even after lapse of 2000 hours.

[0025]

Comparative Example 1 Thermal spraying was carried out in the same manner as in Example 1 except that no oxide was formed by performing thermal spraying by a reduced pressure plasma method without using a seal gas at the time of thermal spraying, and forming an electrode material. And an electrolysis test. In the electrode sample containing no oxide of the present comparative example, the voltage started to increase in 350 hours, and after about 1600 hours, the current was not supplied.

[0026]

Example 2 Using the same titanium substrate as in Example 1, blasting was performed using alumina sand having an average particle size of 1.2 mm. As a result, the surface roughness was R _max = 150 μm, R
_a = 15 μm This titanium substrate was degreased with acetone using an ultrasonic cleaner. Particle size range 40-70 on this surface
A mixture of titanium metal of μm and purified rutile ore (titanium oxide) having the same particle size equivalent to 10% thereof was sprayed under the same conditions as in Example 1 to obtain a sample. As the seal gas, a mixed gas obtained by mixing argon and oxygen at a ratio of 1: 1 was used.

As a result, a deep blue sprayed layer having an average coating thickness of 80 to 120 μm and a surface roughness of R _max 160 μm was obtained. The result of X-ray diffraction showed that titanium: titanium oxide = 1: 1. In addition, it turned out that titanium oxide is mainly a rutile type crystal layer. Since this is conductive, it can be inferred that it is a Magneli phase oxide.

When the electrical resistance of the sprayed layer was measured in the same manner as in Example 1, it was found to be 3 × 10 ⁻³ Ωcm in the thickness direction, which was considerably large. An iridium-tantalum phase was formed on the sample in the same manner as in Example 1 to obtain an electrode sample. This electrode sample was electrolyzed at 160 A / dm ² in a sulfuric acid aqueous solution at 60 ° C in which sodium fluoride was added to 15% sulfuric acid so as to contain 20 ppm of fluorine ions. Met.

[0029]

Comparative Example 2 Using the electrode sample produced in Comparative Example 1, an electrolytic test was performed under the same conditions as in Example 2, and the sample containing only metal as a sprayed layer was tested for its resistance to fluorine ions. The voltage began to rise 360 hours after the start of electrolysis, and the sprayed layer was peeled off at 390 hours, making it impossible to conduct electricity.

[0030]

Example 3 A sprayed layer and an electrode material were formed on a substrate under the same conditions as in Example 1 except that air was not used as a sealing gas and cooling was performed in an oxidizing atmosphere (air). An electrode sample was prepared and an electrode test was performed. The sample surface on which the sprayed layer was formed exhibited a pale blue to dark blue color, indicating the presence of titanium oxide. Further, even after 1000 hours from the start of electrolysis, there was no increase in voltage, and electrolysis could be continued.

[0031]

According to the present invention, a sprayed layer having a thickness of 50 to 200 μm, which is a partial oxide containing metallic titanium and titanium oxide, is formed on a conductive metal substrate which has been previously roughened. The electrode substrate for electrolysis described above. The electrode substrate according to the present invention has a sprayed layer containing titanium metal and titanium oxide. When the electrode substrate is coated with an electrode material and used for electrolysis as an electrode, the above-mentioned sprayed material partially converted into an oxide is formed. The layers are
It prevents the movement of oxygen ions generated at the anode during electrolysis and delays passivation. As a result, the substantial electrode life is extremely long.

In the partial oxide, the sprayed layer becomes a conductive oxide due to lack of oxygen, and as a result, good halogen resistance and reverse current resistance can be obtained. In the first method of manufacturing the electrode substrate according to the present invention, the formation of the sprayed layer composed of the partial oxide is achieved by spraying the metal titanium powder or the wire in an oxidizing atmosphere. An oxidizing gas such as air existing in the spraying atmosphere converts a part of the metallic titanium to titanium oxide to obtain a partially oxidized sprayed layer. The sprayed layer prevents the transfer of oxygen ions as described above. Electrode life and
It has good halogen resistance and reverse current resistance due to its conductivity.

In the second method for manufacturing an electrode substrate according to the present invention, a sprayed layer containing the above-mentioned partial oxide is formed by mixing a titanium oxide powder or a wire with a metal titanium powder or a wire used for thermal spraying. . The sprayed layer formed from the inclusion of titanium metal and titanium oxide in the sprayed powder or wire naturally also consists of a partial oxide which is a mixture of these, and the sprayed layer has the function as described above.

In the third method of manufacturing the electrode substrate according to the present invention, the cooling after the formation of the sprayed layer is performed in an oxidizing atmosphere. Form a partial oxide.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C25C 1/00-7/08 C25C 4/00-6/00 C25B 11/00-11/20

Claims (4)

(57) [Claims] 1. A thickness which is a partial oxide containing titanium metal and titanium oxide on a conductive metal base material which has been roughened in advance.
An electrode substrate for electrolysis, wherein a sprayed layer of 50 to 200 μm is formed. 2. A method of spraying metallic titanium in a oxidizing atmosphere on a previously roughened conductive metal base material to obtain a partial oxide containing sprayed titanium and titanium oxide having a thickness of 50 to 200 μm. A method for producing an electrode substrate for electrolysis, characterized by forming a sprayed layer of (1). 3. Spraying metallic titanium and titanium oxide on a conductive metal base material which has been roughened in advance to obtain a partial oxide containing titanium and titanium oxide having a thickness of 50 or less.
A method for producing an electrode substrate for electrolysis, comprising forming a sprayed layer of 200 μm. 4. A method of spraying metallic titanium onto a conductive metal base material which has been roughened in advance and cooling it in an oxidizing atmosphere to form a partial oxide containing sprayed titanium and titanium oxide having a thickness of 50%. A method for producing an electrode substrate for electrolysis, comprising forming a sprayed layer having a thickness of 200 μm from the above.