JP7340783B1 - Manufacturing method and electrode material for ozone generation electrode material - Google Patents

Abstract

[Problem] A method for manufacturing an electrode material that has chemical and physical durability that can be used in harsh environments and that can demonstrate stable performance over a long period of time, especially applicable to the production of electrode materials of various shapes and dimensions. A method and a manufactured electrode material are provided. [Solution] A method for manufacturing an electrode material with BDD particles fixed thereto, in which boron-containing diamond (BDD) particles are fixed on a metal substrate and conductivity is established as a whole. A laser beam is scanned and irradiated onto the surface of the surface to locally and instantaneously heat the base material on the surface to melt the surface layer, and BDD particles are supplied and arranged while the part is in a fluid state, and after cooling the part, the diamond particles are is recovered as a composite held by solidified metal. It is particularly effective to carry out this series of operations in an argon atmosphere. [Selection diagram] Figure 1

Description

The present invention is an electrode material for ozone generation, especially for the purpose of ozone water generation and purification of contaminated water on various scales, and has a unique structure derived from a unique manufacturing method using conductive diamond particles suitable for water treatment equipment. The present invention relates to an electrode material having the following, and a manufacturing method.

BACKGROUND ART In industrial wastewater treatment, a treatment process that generates ozone through water electrolysis and utilizes its chemical properties is widely used. Electrodes used in such environments are required to meet severe conditions, such as being able to withstand harsh environments and continuously exhibiting sufficient functionality under such environments. One way to construct electrode materials with high chemical resistance is to use silicon, niobium, tantalum, or other metals as a base material, and vapor-phase synthesize a diamond film containing boron (B) on the surface to impart conductivity. The method of forming by CVD (CVD) is widely used.

Another established method for constructing electrodes for electrolysis is to distribute and fix conductive diamond particles on a metal electrode substrate. For example, Patent Document 1 describes a configuration in which conductive diamond particles are bonded onto a conductive substrate using a conductive brazing material, and gaps between the diamond particles are filled with an insulating material.

Alternatively, Patent Document 2 discloses a technique for firmly bonding BDD particles onto a transition metal plate such as Ti via a transition metal carbide using ultra-high pressure technology, and Patent Document 3 discloses a technique in which BDD particles are firmly bonded to a transition metal plate such as Ti via a transition metal carbide. An electrode material for water electrolysis having BDD powder supported thereon is disclosed.

On the other hand, in the production of tools that use diamond particles as abrasive grains, in the field of manufacturing tools for cutting and other purposes, the surface of the base metal is irradiated with high-energy rays (e.g. laser light), and diamond particles are used as abrasive particles at the melted parts of the base metal. It is known to supply and fix diamond abrasive grains (for example, Patent Document 4).
Further, Non-Patent Document 1 discloses a method of fixing diamond particles as grinding abrasive grains on a metal material by using fiber laser light in particular for laser light irradiation for such applications. Laser light is irradiated onto the base metal of the tool, and diamond particles are placed on argon gas and supplied to tiny spots in the partially melted metal, which is then embedded and fixed.

With this technology, processing at each minute location can be completed in an extremely short time, so by scanning laser light irradiation on the base metal, it is expected to be applicable to diamond particle fixation in the production of diamond tools with large tool areas. can. Although the heating by laser irradiation used in this method generates high heat exceeding 3000℃, the irradiation time required is very short, so it is considered to be an effective method that does not involve graphitization or deterioration of diamond abrasive grains. It will be done.

Japanese Patent Application Publication No. 2005-325417 JP2022-069974 Publication Patent No. 7010529 (restated WO2020/171238) JP 2020-040138 (Patent No. 7012276) Publication

Journal of the Abrasive Processing Society vol.66 No.5 pp.263-268 (2022)

In an electrode configuration in which boron (B)-containing diamond particles are fixed on a substrate, in general, when manufacturing the material, the packing density of the diamond particles arranged on the electrode surface is made as high as possible, and at the same time, in order to prevent the diamond particles from falling off. Strong bonds based on chemical bonds have been required between the particles and the substrate surface.

The reason for this is to maximize the performance of the electrode, prevent deterioration in electrode performance due to the metal oxide film derived from the base metal exposed on the electrode surface, and ensure that the arrangement of diamond particles is essentially a single layer. This is because a strong bonding force is required between the surface of the base metal and the diamond crystal plane.

However, the present inventors found that the base metal oxide can be substantially removed by exposing it to a reducing region during electrolysis, that a current-carrying path must be secured from the base to the diamond particles, and that a strong chemical bond is essential. I found out that this is not a requirement.

From the viewpoint of fully exhibiting the performance as an electrode, it is desirable that boron-containing diamond be disposed over the entire surface of the electrode. For example, a boron-containing diamond film formed by the CVD method on a substrate such as a titanium substrate is composed of a polycrystalline aggregate of densely packed diamond crystals, so the substrate surface is exposed to a strong oxidizing atmosphere containing ozone. It is understood that the probability of this occurring is low and that it can withstand long-term operation.

On the other hand, with an electrode configuration in which boron-containing diamond particles are arranged on a substrate, it is virtually impossible to fill the gaps between diamond particles with diamond particles, and it is impossible to avoid exposing the substrate surface to an oxidizing atmosphere at the anode. do not have.

However, in an electrolytic process that uses an electrode whose surface is covered with a metal oxide as a cathode, it has been found that the interference caused by the metal oxide (the phenomenon of increased electrical resistance) is eliminated, and furthermore, an electrode with the same structure It has been found that if the membranes are placed facing each other through a proton-conducting membrane (for example, Nafion (registered trademark) membrane) and the polarity is reversed every certain period of time, for example, every 1 to 5 minutes, it can withstand long-term electrolysis operations. did.

The subject of the present invention is a method for producing electrode materials that have chemical and physical durability that can be used in harsh environments and that can demonstrate stable performance over a long period of time, and is particularly applicable to the production of electrode materials of various shapes and dimensions. An object of the present invention is to provide a possible method and a manufactured electrode material.
The present inventors have conducted research on various cases based on the above-mentioned findings, and have completed the present invention as a result.

The gist of the present invention is to provide a method for manufacturing an electrode material in which boron-containing diamond (BDD) particles are fixed on a metal substrate and conductivity is established as a whole, in which a laser beam is scanned on the surface of the metal substrate. Irradiation was applied to locally and instantaneously heat the base material on the surface to melt the surface layer, and while the part was in a fluid state, BDD particles were supplied and arranged, and after the part was cooled, the diamond particles were held by the solidified metal. The present invention provides a method for producing a BDD particle-fixed electrode material, which is recovered as a composite, and is characterized in that a series of these operations is performed in an argon atmosphere.

The gist of the present invention is also that a part of the surface of the diamond electrode material produced by the above method, particularly the metal base, shows a partial melting history after processing, and boron-containing diamond (BDD) particles are integrated in the melting history part. The electrode material is produced by the method according to claim 1, wherein the diamond particles are fixed and the side surfaces (the surfaces in the direction perpendicular to the thickness of the substrate) of the diamond particles are held by a part of the base metal.

In the present invention, when producing a conductive electrode material, conductive diamond particles can be fixed on a wide range of materials by instantaneous heating based on laser irradiation, without substantially turning the diamond into graphite, resulting in stable performance. It is possible to manufacture various electrode materials in a short time.

In the electrode material of the present invention, the metal base material can be selected from a wide range of metal materials whose main component is a metal with a melting point of 2000° C. or less. Such metals may particularly include transition metals of groups 4, 5, and 6 of the periodic table as well as metals of the iron group, preferably one selected from Ti, Zr, Si, Fe, Ni, Co, and Cr. .

In the present invention, a fiber laser capable of local heating can be particularly used as a means for heating and melting the metal substrate, so the heat of the melted part is quickly diffused to the surroundings, so the reaction time for fixing the diamond particles is shortened. It is characterized by being extremely short, only a few seconds at most. Therefore, the process is completed within the induction time when diamond begins to graphitize.

On the other hand, metals with melting points exceeding 2000℃ (such as niobium), even among the metals listed above, require a relatively long time to melt when heating microscopic parts using a fiber laser, and the diamond particles are exposed to high temperatures. It is not suitable for the present invention because the exposure time is extended and graphitization becomes unavoidable.

According to the experience of the present inventors, graphitization of diamond is significantly promoted by the presence of oxygen, and therefore, it is necessary to heat the diamond particles at high temperature in an oxygen-free atmosphere. Oxygen barrier methods include establishing a work area surrounded by a barrier and filling it with inert gas, especially argon gas, which has a higher specific gravity than outside air, rather than spraying with a protective gas, and laser heating in the work space with an inert gas atmosphere. It is preferable to perform diamond fixing by.

As a method of isolating a work space from outside air and creating an inert (neutral) gas atmosphere, a method is generally used in which atmospheric gas is injected toward the processing location. However, with the injection method, it is impossible to completely avoid the risk of entrainment of surrounding air. To establish an oxygen-free working space (area) for laser processing, it is effective to surround it with a dam at a certain height from the surface of the electrode substrate material and to fill it with an inert gas with a high specific gravity. The height of the dam depends on the size of the electrode material base, but it needs to be at least 10 mm above the base and surround the entire 360° circumference. As the filling gas, argon is preferable since its specific gravity relative to air is 1.4.

Furthermore, as for the particle size of the BDD particles used in the electrode material of the present invention, commercially available sized particles with a _D50 average particle size in a wide range of 10 to 300 μm can be used. For fine particles of 10 μm or less, there is noticeable loss due to an increase in the amount of particles carried by argon gas scattering around the melting point, and for coarse particles exceeding 300 μm, the three components of diamond particles, proton conductive membrane, and water come together. This is not preferable because the electrolytic performance deteriorates significantly due to a decrease in the number of electrode working points. A more preferred particle size is within the range of 20-100 μm.

In the present invention, scanning irradiation is performed with a heat input of 50 to 350W. The laser heating device to be used is not limited to a fiber laser, and various other devices can be used as long as it has a function of pinpoint irradiation to a desired minute portion.

As mentioned above, in electrode materials with conductive diamond particles fixed to them, oxides of the base metal may adhere to the surface of the particles during use, but even in such conditions, conductive diamond particles of the same composition are attached to both electrodes. By using electrodes and automatically switching the polarity of the electrode pair, it is possible to reduce or eliminate the influence of the oxide film.

In fixing boron-containing diamond particles by the method of the present invention, the particles fall into a pool of substrate metal melted by laser heating, are cooled and solidified, and are held in a state where they are tightened from the surroundings by the contracted metal component. In a fixed state, if at least 1/2 of the particle surface area is in contact with the metal component, it is sufficient for electrode use, and a current-carrying path can be secured.

A photograph (Example 1) showing the state of the surface of an electrode material produced according to the present invention. The results of Raman analysis conducted on the electrode material produced according to the present invention (Example 1).

#270/325 boron-doped diamond (BDD) abrasive grains (manufactured by FACT Inc., average grain size approximately 50 μm) were fixed on a titanium plate with a diameter of 80 mm and a thickness of 1 mm by fiber laser welding. For processing, an ALP-DI-4Axis-450 laser processing machine manufactured by Muratani Machinery Co., Ltd. was used. This device has a structure that focuses three laser beams onto one point, and the sending of the laser beams during scanning was controlled by the moving speed of the sample stage.

Diamond particles were supplied onto a titanium plate from a hopper above the sample stage together with argon gas to a laser beam focusing section, and in this operation example, they were continuously supplied at a constant rate of about 20 mg per minute. The irradiation was performed under the conditions of a laser light output of 50 W, a laser head feed rate of 2.5 mm/s, and an irradiation pitch of 0.25 mm, scanning 40 rows and fixing diamond particles in an area of 10 mm x 13 mm.

The irradiation area was surrounded by a dam with an inner diameter of 100 mm and a height of 15 mm, which was filled with argon gas in advance and a separate circuit was used to supply argon gas to prevent air from entering. The work was carried out in the argon pool thus formed to obtain a diamond particle layer fixed on the titanium plate with a width of approximately 0.2 mm. The time required for the fixing operation was about 4 minutes.

An 8 mm x 8 mm electrode material sample was cut out from the obtained BDD-fixed titanium plate by wire cutting. Raman analysis was performed on this sample, and a sharp peak at 1333 cm ^-1 attributed to diamond was obtained (Figure 2). On the other hand, the peak at around 1580 cm ^-1 attributed to graphite was weak, indicating that graphitization of diamond due to laser heating was at a negligible level.

This electrode material was used as the anode side, and an electrode material (CVD electrode) in which boron-doped diamond was deposited on a niobium plate by the CVD method was used for the cathode side. An electrode set with fixed electrode surfaces facing each other was manufactured. The obtained electrode set was installed in a 1L beaker containing 600mL of deionized water, the power supply was set to a constant current of 0.2A aiming to generate 1ppm ozone, and continuous operation was performed while replenishing deionized water. The changes in voltage were observed. The additional voltage, which was 8.16V at the start of operation, increased to 10.6V after 140 hours and 17.3V after 258 hours.

The ozone concentration generated immediately after the start of energization was 1.10 ppm, 0.98 ppm just before the end of energization, and remained at 1 ppm throughout the operation. The ozone concentration generated was measured by using a pack test to determine the amount of ozone dissolved in water after 20 minutes of electricity, which was conducted approximately every 24 hours.

White powder was found adhering between the diamond particles on the surface of the BDD electrode taken out, and titanium oxide with a TiO composition was identified by X-ray diffraction. This white powder could be removed with a toothbrush without causing the abrasive grains to fall off, and the applied voltage after removal was reduced to 9.33V, and the generated ozone concentration increased to 1.15ppm.

In an attempt to suppress the production of titanium oxide, a reverse voltage was applied to the electrode set of Example 1, and the same operation was repeated.
The current is started using the BDD electrode as the anode, and when a voltage of 20.3V is required to flow a current of 0.2A, the polarity is reversed, with the BDD electrode as the cathode and the CVD diamond-coated electrode as the anode. When a current of A was applied, the applied voltage decreased to 11.0V 1 minute after starting the current flow, and reached a steady state of 10.2V after 5 minutes.

Furthermore, we returned the BDD electrode to the anode and the CVD electrode to the cathode, continued energization until the additional voltage rose to 15V, and then reversed the polarity again, which resulted in a steady state at approximately 10V, confirming reproducibility and long-term continuous operation. The possibility of

Two types of steel plates, SUS304 and SUS430, each having a diameter of 70 mm and a thickness of 1 mm were used as electrode substrate materials, and the operations in the above example were repeated. The conditions were the same as in Example 1 except that the laser light output was 250W.
Despite the increased output, the graphitization of diamond due to laser heating was negligible.

A 10 mm x 10 mm section was cut out from the obtained BDD welded SUS substrate using a wire cut and used as an electrode material. An electrode set was constructed with the SUS substrate electrode on the anode side and the CVD electrode on the cathode side, and electricity was applied to perform electrolysis. By applying a current of 10 V and 0.2 A, ozone concentrations of 0.93 ppm for the SUS304 substrate and 1.12 ppm for the SUS430 substrate were obtained, confirming that both steel types function as ozone generating electrodes. At the same time, a voltage increase of 5V due to the appearance of an oxide film was observed after 10 minutes of energization.

The two types of SUS substrate electrodes used above were arranged facing each other with a Nafion membrane interposed between them to form an electrode set. This electrode set was connected to a 15V constant voltage power source, and continuous operation was performed by reversing the polarity every minute. During continuous operation all day and night, the current value remained within the range of 0.2A to 0.3A, giving the prospect of long-term operation.

Claims (8)

In a manufacturing method for an electrode material in which boron-containing diamond (BDD) particles are fixed on a metal substrate and conductivity is established as a whole, the surface of the metal substrate is scanned and irradiated with laser light to locally improve the surface of the substrate material. Then, a series of operations are carried out in which the surface layer is melted by instantaneous heating, BDD particles are supplied and arranged while the part is in a fluid state, and after the part is cooled, the diamond particles are recovered as a composite held by solidified metal. A method for manufacturing a BDD particle-fixed electrode material, the method being carried out in an argon atmosphere isolated from the surroundings. 2. The method according to claim 1, wherein the metal substrate material contains as a main component one selected from transition metals of groups 4, 5, and 6 of the periodic table and iron group metals. The method according to claim 1 or 2, wherein the base material contains a metal species having a melting point of 2000°C or less as a main component. 2. The method according to claim 1, wherein the base material contains one selected from Ti, Zr, Si, and iron group metals as a main component. 2. The method according to claim 1, wherein the base material contains one selected from Fe, Ni, Co, and Cr as a main component. The method according to claim 1, wherein the diamond particles are sized particles having a D ₅₀ average particle size of 10 to 300 μm. The method according to claim 1, wherein the laser light irradiation is performed by a fiber laser. The method according to claim 1, wherein the laser light irradiation is performed by a fiber laser with an output of 50 to 350W.

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