JP2010037570A - Diamond electrode, method for producing diamond electrode, and ozone-generating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diamond electrode which has an electroconductive diamond film with adequate adhesiveness formed on the surface of a substrate metal, and inhibits the electroconductive diamond film from being peeled off from the electrode substrate; a production method therefor; and an ozone-generating device which can generate ozone of high concentration for a long period of time, by using the diamond electrode as an anode. <P>SOLUTION: This diamond electrode includes the electrode substrate which is formed from the substrate metal selected from pure Ti, a Ti alloy, pure Nb and pure Ta, and the electroconductive diamond film which is formed by doping boron into the surface of the electrode substrate; and has a hydride of substrate metal species formed in the interface of the electrode substrate and the electroconductive diamond film. An intensity ratio of a main peak of the hydride to a main peak of the substrate metal, which are obtained from X-ray diffraction measurement, is 0.1 to 3.0. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a diamond electrode, a method of manufacturing the diamond electrode, and an ozone generator, and more particularly, a diamond electrode used as an anode of an ozone generator that electrolyzes water to generate ozone, and the diamond The present invention relates to an electrode manufacturing method, and further to an ozone generator using the diamond electrode as an anode.

Ozone (O ₃ ) is a highly oxidizable substance, and sterilization, decolorization, and deodorization derived from its properties are industrially used in a wide range of fields such as semiconductors, medical care, and foods. Although ozone itself is an unstable substance, it can be decomposed into oxygen (O ₂ ) naturally and there is no concern about secondary pollution such as air pollution. Under such a premise, in order to generate ozone with high efficiency, various research and development, such as the development of a new ozone generator, has been conducted.

  In particular, an electrolysis method in which an electrolysis cell is constructed by sandwiching a solid polymer membrane between an anode and a cathode, and water is allowed to flow through the electrolysis cell is excellent in that the device can be downsized and high-concentration ozone can be generated. It has become the mainstream of development.

  As an electrode material used for an ozone generator using this electrolysis method, it is desired to form an electrode using a material having high catalytic performance for ozone generation. In addition, since ozone is generated most efficiently at the three-phase interface with the electrode (anode), the solid molecular film, and water, it is desirable to use an electrode having a mesh or porous form.

  From the above viewpoints, lead dioxide and platinum formed in a net-like or porous shape are currently most frequently used as electrode materials. However, when lead dioxide or platinum is used as an electrode material, it has been pointed out that there are the following problems.

  One of the problems when using lead dioxide as an electrode material is that there is concern about toxicity when dissolved. In addition, lead dioxide is not a stable substance, and once power generation (ozone generation, anodic polarization) is stopped, ozone generation ability (catalytic performance) is significantly reduced. There is also a problem that it is necessary to keep the current flowing.

  When platinum is used as an electrode material, there is a problem that platinum is gradually dissolved and consumed when a large current and a large voltage are applied. In addition, since the dissolved platinum ions are clogged in the solid molecular film, there is a problem that proton permeability is lowered and ozone generation efficiency is lowered. Furthermore, there is a fact that platinum is expensive because it is a noble metal.

  When lead dioxide or platinum is used as an electrode material, there are situations where there are various problems as described above, and a diamond electrode with conductivity that does not have such problems is used as an electrode of an ozone generator. It has been proposed. Since diamond itself has no conductivity, a diamond electrode doped with an element having a valence different from carbon, such as boron (B), and imparted with conductivity is used.

  Diamond electrodes do not decompose, oxidize, dissolve, etc. under potential application conditions necessary for ozone generation, and have excellent stability as a substance. Ozone generation has catalytic performance equivalent to that of platinum. It is thought that it can be used suitably as an electrode of a generator.

  As this diamond electrode, Patent Document 1 discloses an electrode composed of a self-stereoscopic conductive diamond plate having a thickness of 0.8 mm, in which a diamond is formed by a microwave plasma CVD method and a large number of holes are opened by a laser. Patent Document 2 proposes an ozone electrode coated with diamond doped with C, and Patent Document 3 discloses an electrode in which a conductive diamond film is embedded in a metal surface.

  However, the diamond electrode described in Patent Document 1 has a problem that it is very poor in productivity and is brittle and difficult to handle because it is a self-stereoscopic diamond. In addition, although the diamond electrodes described in Patent Document 2 and Patent Document 3 have initial characteristics, they do not consider the adhesion between the diamond and the base material, so that the diamond can be easily peeled off and dropped, resulting in durability. There is a problem of being inferior.

JP 2005-3336607 A JP-A-9-268395 JP 2005-532472 A

  The process of forming a conductive diamond film on the surface of an electrode substrate made of a substrate metal by a thermal CVD (chemical vapor deposition) method is performed in a high temperature range of 650 ° C to 900 ° C. Since diamond has a coefficient of thermal expansion different from that of the base metal, the thermal stress caused by the difference in the thermal expansion coefficient is observed when the film is cooled to room temperature after film formation at a high temperature range of 650 ° C. to 900 ° C. At the interface.

Examples of thermal stress generated at the interface between the diamond and the base metal when the conductive diamond film is formed on the surface of the electrode base made of pure Ti at 800 ° C. and then cooled to room temperature are as follows. When the linear expansion coefficient of titanium (Ti) is 8.4 × 10 ⁻⁶ (° C. ⁻¹ ), the linear expansion coefficient of diamond is 0.8 × 10 ⁻⁶ (° C. ⁻¹ ), and the Young's modulus is 1050 GPa, at room temperature. A thermal stress of about 6.2 GPa is generated at the interface between the diamond and the base metal. Thus, since a big thermal stress generate | occur | produces in the interface of a diamond and a base metal, a diamond and base metal cannot obtain favorable adhesiveness.

  In addition, since diamond is poor in ductility, if the electrode is deformed by external pressure during use, cracks will occur in the conductive diamond film. Due to the occurrence of the crack, the conductive diamond film is peeled off from the base metal and the base metal is exposed.

  When ozone is generated using the electrode with the base metal exposed as the anode of the ozone generator, corrosion proceeds from the exposed base metal to the interface between the diamond and the base metal, and conductive diamond. Helps peel the film. Thus, the generation efficiency of ozone will fall because peeling of a conductive diamond film is accelerated.

  The present invention has been made to solve the above conventional problems, and can form a conductive diamond film on the surface of a base metal with good adhesion, and the conductive diamond film is made of a base metal. Electrode that can be prevented from being peeled off, a method for producing the diamond electrode, and an ozone generator that can generate high-concentration ozone over a long period of time by using the diamond electrode as an anode It is a problem to provide.

  According to the first aspect of the present invention, an electrode base material made of one or more base metals selected from the group consisting of pure Ti, Ti alloy, pure Nb, and pure Ta, and boron on the surface of the electrode base material are doped. The hydride of the base metal species is formed at the interface between the electrode base material and the conductive diamond film, and is obtained by X-ray diffraction measurement. The strength ratio of the main peak of the hydride and the main peak of the base metal constituting the electrode base material (main peak of hydride / main peak of base metal) is 0. It is a diamond electrode characterized by being 1 or more and 3.0 or less.

  The invention according to claim 2 is the diamond electrode according to claim 1, wherein the film thickness of the conductive diamond film is 1 μm or more and less than 5 μm.

The invention according to claim 3 is characterized in that the electrode base material is formed of a wire, and a cross-sectional area of a cross section perpendicular to the longitudinal direction of the wire is 0.1 mm ² or more and 10.0 mm ² or less. The diamond electrode according to claim 1 or 2.

  A fourth aspect of the present invention is the diamond electrode according to the third aspect, wherein there are a plurality of the wires, and the wires do not overlap each other.

The invention according to claim 5 is characterized in that the electrode base material is an expanded metal, and the cross-sectional area of the cross section perpendicular to the longitudinal direction of the strand portion is 0.1 mm ² or more and 10.0 mm ² or less. The diamond electrode according to claim 1 or 2.

The invention according to claim 6 is a method for producing a diamond electrode in which a conductive diamond film is formed on a surface of a base metal made of pure Ti or a Ti alloy by vapor phase synthesis in a mixed gas atmosphere of hydrocarbon gas and hydrogen gas. In this method, hydrogen gas is introduced into a chamber containing the base metal, the hydrogen gas pressure in the chamber is set to 1.2 × 10 ³ Pa or more, and 30 ° C./min or more, 100 ° C. / A temperature raising step of heating the base metal and absorbing hydrogen on the surface thereof by raising the temperature in the chamber to a temperature of 650 ° C. or higher and 900 ° C. or lower at a speed of min or less, and the temperature rise after step, the hydrocarbon volume ratio of gas is 8% or less of a gas mixture of hydrocarbon gas and hydrogen gas is introduced into the chamber, the mixed gas pressure of 1.33 × 10 ³ P in the chamber And above, a method for manufacturing a diamond electrode, characterized by comprising a film forming step of forming a conductive diamond film doped with boron on the surface of the electrode substrate.

The invention according to claim 7 is a method for producing a diamond electrode in which a conductive diamond film is formed on a surface of a base metal composed of pure Nb or pure Ta by vapor phase synthesis in a mixed gas atmosphere of hydrocarbon gas and hydrogen gas. In this method, hydrogen gas is introduced into a chamber containing the base metal, the hydrogen gas pressure in the chamber is set to 1.2 × 10 ³ Pa or more, and 20 ° C./min or more, 60 ° C. / A temperature raising step of heating the base metal and absorbing hydrogen on the surface thereof by raising the temperature in the chamber to a temperature of 650 ° C. or higher and 900 ° C. or lower at a speed of min or less, and the temperature rise after step, a mixed gas of volume ratio of 8% or less of the hydrocarbon gas and hydrogen gas of a hydrocarbon gas is introduced into the chamber, the mixed gas pressure of 1.33 × 10 3 ^Pa or more in the chamber And to a method for manufacturing a diamond electrode, characterized by comprising a film forming step of forming a conductive diamond film doped with boron on the surface of the electrode substrate.

  The invention according to claim 8 is the method for producing a diamond electrode according to claim 6 or 7, wherein the hydrocarbon gas is methane.

  A ninth aspect of the invention is an ozone generator characterized in that the diamond electrode according to any one of the first to fifth aspects is used as an anode.

  According to the diamond electrode of the present invention, the conductive diamond film is formed on the surface of the base metal with good adhesion, and the conductive diamond film can be prevented from peeling off from the electrode base made of the base metal. .

  Moreover, according to the method for producing a diamond electrode of the present invention, a conductive diamond film can be formed on the surface of a base metal with good adhesion, and the conductive diamond film is peeled off from an electrode base made of the base metal. This can be prevented.

  Furthermore, according to the ozone generator of the present invention, since the conductive diamond film is composed of electrodes formed on the surface of the base metal with good adhesion, high concentration ozone is generated over a long period of time. Can be made.

  The inventors have advanced research and development in order to use a diamond electrode as an anode of an ozone generator. A problem when a diamond electrode is used as an anode of an ozone generator is that the conductive diamond film is easily peeled off from the electrode substrate. As a result of research and development, in order to suppress the peeling of the conductive diamond film from the electrode substrate, it is effective to reduce the thermal stress generated at the interface between the diamond and the substrate metal. As a means, it has been found that it is effective to form a hydride at the interface between diamond and the base metal by forming a solid solution of hydrogen on the surface of the base metal in the film forming step of forming a conductive diamond film.

  The mechanism by which the conductive diamond film can be prevented from peeling from the electrode substrate by forming a hydride at the interface between the diamond and the substrate metal is not necessarily clear, but can be considered as follows.

  When hydrogen is absorbed from the surface of the base metal forming the electrode base material in a high temperature range (650 ° C. to 900 ° C.), the hydrogen concentration in the electrode base material is high on the surface side and low toward the center. Concentration distribution occurs, and the base metal expands in volume with the absorption of hydrogen. That is, the surface metal of the electrode base material tends to increase in volume as the surface side of the electrode base material increases, but the volume expansion is constrained by the inner side of the electrode base material where the volume expansion is small. Compressive stress will be generated.

  In addition, the hydrogen absorbed in the electrode base material in the high temperature range exists in a solid solution in the base metal and in the form of a hydride with the base metal, and the ratio is Although it is expected that the temperature varies depending on the temperature of the electrode substrate, these ratios are not particularly problematic because they have the same volume expansion in any existing state. In addition, when the conductive diamond film is formed and then cooled to room temperature, most of the hydrogen is considered to exist in a hydride state. In particular, a large amount of the hydride is present on the surface side of the electrode substrate, that is, on the interface between the electrode substrate and the conductive diamond film.

  In this way, before film formation of the conductive diamond film (or before the completion of diamond nucleation), hydrogen is absorbed into the electrode base material, and compressive stress is applied to the surface of the electrode base material. The thermal stress (tensile stress) generated at the interface due to the difference in thermal expansion coefficient between the base metal and diamond can be relaxed, and as a result, good adhesion can be obtained.

  Next, a heating process for absorbing hydrogen into the electrode base material before the formation of the conductive diamond film and a film forming process after the heating process will be described.

  As a method for industrially producing diamond, there is a thermal CVD (chemical vapor deposition) method in which heat decomposition is performed in a high temperature range of 650 ° C. to 900 ° C. in a mixed gas atmosphere (reducing atmosphere) of hydrocarbon gas and hydrogen gas. . As the heating method, a hot filament method or a microwave heating method can be employed.

  In the present invention, after the temperature raising step to a desired temperature of 650 ° C. to 900 ° C. is performed in a hydrogen gas atmosphere to absorb hydrogen into the electrode substrate, a mixed gas of hydrocarbon gas and hydrogen gas is added to the chamber. By introducing into the electrode, a conductive diamond film doped with boron is formed on the surface side of the electrode substrate.

  Next, the metal seed | species of the base metal used for an electrode base material is demonstrated. A metal species that easily forms carbide is suitable as a metal species for forming a conductive diamond film. Moreover, since it is used for an ozone generator, the metal species are required to have excellent corrosion resistance. From the above viewpoint, examples of the metal species of the base metal used for the electrode base material include pure Ti, Ti alloy, pure Nb, and pure Ta. Among these metal species, pure Ti and Ti alloys are more suitable as metal species for the base metal used for the electrode base material because they easily absorb hydrogen.

  As described above, since the hydrogen absorption efficiency varies depending on the metal species of the base metal used for the electrode substrate, the temperature raising conditions in the temperature raising step described above are different.

When the base metal used for the electrode base material is pure Ti and Ti alloy, the hydrogen gas pressure in the chamber is set to 1.2 × 10 ³ Pa or higher and the temperature is increased at a rate of 100 ° C./min or lower. However, when the temperature is raised at less than 30 ° C./min, the electrode base material becomes brittle and the required strength cannot be ensured, so a temperature raising rate of 30 ° C./min or more is required.

Also, if the base metal used for the electrode base material was changed to pure Nb and pure Ta, since hardly absorbs hydrogen from pure Ti and Ti alloy described above, the hydrogen gas pressure in the chamber 1.2 × 10 ³ Pa The temperature may be increased at a rate of 60 ° C./min or less. However, when the temperature is raised at less than 20 ° C./min, the electrode base material becomes brittle and the required strength cannot be ensured, so a temperature raising rate of 20 ° C./min or more is required.

  Specific examples of the base metal used for the electrode base material include 1 to 4 types of pure Ti specified in JIS H 4600, Ti alloys such as Ti-6Al-4V, etc., and pure specified in JIS H 4701. Examples include Ta wrought material and pure Nb. By using such a base metal as an electrode base material, a diamond electrode having excellent adhesion can be produced. In the case of these alloys and pure metals, inevitable impurities are allowed to be mixed. For example, Nb is 99.9% by mass or more as pure Nb, and Nb containing Fe: 0.001% by mass and Ta: 0.06% by mass as inevitable impurities can be exemplified.

  In order to suppress peeling of the conductive diamond film, the ratio of the hydride of the base metal species on the surface of the electrode base material (also referred to as an interface between the electrode base material and the conductive diamond film in this specification) is Higher is preferred. The amount of hydride formed can be measured by X-ray diffraction (XRD). In order to suppress the peeling of the conductive diamond film, the main peak of the hydride obtained by XRD measurement and the electrode substrate are used. The strength ratio of the base metal of the constituent metal to the main peak (hydride main peak / base metal main peak) needs to be 0.1 or more.

  On the other hand, as the hydride of the base metal species on the surface of the electrode base material increases, the ratio of the hydride inside the electrode base material increases and the electrode base material becomes brittle. In order to obtain the required strength of the electrode base material itself, the strength ratio between the main peak of the hydride and the main peak of the base metal constituting the electrode base material (main peak of hydride / base The main peak of the material metal needs to be 3.0 or less.

  Further, when the conductive diamond film is thin, pinholes may remain, and the necessary corrosion resistance and durability may not be obtained. Therefore, the film thickness of the conductive diamond film needs to be 1 μm or more, and in this case, pinholes can be reliably prevented from remaining. On the other hand, cracks tend to occur when the film thickness is large. In order to prevent the occurrence of cracks, the film thickness of the conductive diamond film may be less than 5 μm. Therefore, the film thickness of the conductive diamond film is preferably 1 μm or more and less than 5 μm. However, considering productivity, it is more preferable to set it as 1 micrometer or more and 4 micrometers or less.

  In order to prevent the peeling of the conductive diamond film and the generation of cracks due to the external force during use of the diamond electrode, an electrode structure and strength that do not deform by the external force are required.

  Moreover, when the diamond electrode is formed of a plurality of wires, there is a possibility that the wires overlap each other. If there is an overlap between the wires, when an external force is applied, a gap is generated at the overlapping portion, a crack is generated in the conductive diamond film due to friction, and the conductive diamond film may be peeled off. Therefore, when the diamond electrode is formed of a plurality of wires, it is preferable that the wires do not overlap each other.

In addition, when the cross-sectional area of the wire constituting the diamond electrode is small and does not have sufficient strength, it is easily deformed by an external force applied during use, and peels off by generating a crack in the conductive diamond film. there is a possibility. Therefore, the cross-sectional area of the wire constituting the diamond electrode needs to be at least 0.1 mm ² or more, more preferably 0.15 mm ² or more. On the other hand, when the cross-sectional area of the wire is too large, when the diamond electrode is used in an ozone generator, the area of the three-phase interface between the diamond electrode, the solid polymer film, and water decreases, and the ozone generation efficiency decreases. It will be. Therefore, it is preferable that the cross-sectional area of the wire is to be 10.0 mm ² or less, more preferably may be a 5.00 mm ² or less.

Here, as shown in FIG. 1, the cross-sectional area of the wire means an area of a cross section (AA ′ cross section) obtained by cutting the wire in a direction orthogonal to the longitudinal direction. The electrode base material shown in FIG. 1 is an expanded metal obtained by processing a rolled material, and although it is not a wire material in detail, the strand portion is assumed to be a wire material and used for explanation of the cross-sectional area. The cross-sectional area of the expanded metal strand portion is preferably 0.1 mm ² or more and 10.0 mm ² or less as in the case of the wire. Note that the expanded metal is obtained by processing a rolled material and not formed by overlapping the wires, so that there is no peeling of the conductive diamond film and generation of cracks caused by the overlapping portion.

  In addition, the shape of the electrode base material is not particularly defined, and a lath net shape, a porous net plate such as an expanded metal (a plate having punch holes formed therein), or a circular bar arranged so as not to overlap each other, etc. Can be adopted.

  Examples of the present invention will be described below. It should be noted that the present invention is not limited to this embodiment, and can be implemented with appropriate modifications within a range that can be adapted to the gist of the present invention, all of which fall within the technical scope of the present invention. included.

<Example 1>
A 10 mm × 10 mm × 1 mm (thickness) pure Ti plate and pure Nb plate were used as substrates, respectively. The surface of the substrate was scratched with diamond abrasive grains, and the substrate was placed in a chamber of a microwave heating CVD apparatus. Then, after evacuating the chamber to 0.3 Pa, hydrogen gas having a pressure (hydrogen gas pressure) shown in Table 1 was introduced into the chamber, and microwave output corresponding to the temperature increase rate shown in Table 1 was made. Was applied to raise the temperature.

  Next, a mixed gas of methane and hydrogen mixed at a mixing ratio (methane / hydrogen ratio) shown in Table 1 was introduced into the chamber so as to have a predetermined pressure (mixed gas pressure) shown in Table 1. Table 1 The conductive diamond film was formed at the film formation temperature and film formation time shown in FIG. After completion of the formation of the conductive diamond film, the microwave output was turned off and at the same time the supply of the mixed gas was stopped and the mixture was cooled to room temperature (25 ° C.).

  First, the amount of hydride formed was evaluated. X-ray diffraction (XRD) measurement was performed on each sample on which the conductive diamond film was formed. At that time, measurement was performed using a Cu—Kα ray under conditions of a tube voltage of 40 kV, a scanning angle range (2θ) of 30 ° to 100 °, and a scanning speed of 2 ° C./min.

From the obtained spectral data, the peak height due to the plane orientation indicating the main peak of the hydride and the main peak of the base metal is read, and the main peak of the hydride and the main metal of the base metal are read. The strength ratio to the peak (hydride main peak / base metal main peak) was calculated. The calculation results are shown in Table 1 as peak ratios. In the case of a titanium base material, the intensity ratio (peak ratio) was calculated using TiH ₂ (110) and αTi (101), and in the case of a niobium base material, NbH ₂ (111) and Nb (110), respectively. .

  Further, the surface of each sample on which the conductive diamond film was formed was observed with a scanning electron microscope (SEM). Observation was carried out at 5 magnifications with 5 fields of view, and the presence or absence of pinholes and cracks was judged. The case where no pinholes and cracks were recognized was judged as “good”, and the case where pinholes and cracks were found respectively was judged as “bad”. The observation results are shown in Table 1.

  Furthermore, the adhesion between the conductive diamond film and the electrode substrate was evaluated by an indent test. A diamond indenter with a diameter of 0.4 mm was pressed against the surface of each sample on which a conductive diamond film was formed with a predetermined load from the vertical direction, and the periphery of the indentation was observed with an optical microscope (500 times magnification). The presence or absence of peeling of the conductive diamond film was observed.

  Observation of the presence or absence of peeling of the conductive diamond film was started when the indentation load was 10N. If peeling of the conductive diamond film is not recognized, the indentation load is further increased by 10N, and the same test is performed. If no delamination is observed, the indentation load is further increased by 10N and the same test is performed. In a manner, the test was performed by increasing the indentation load up to 200N. By this test, the maximum indentation load at which peeling of the conductive diamond film does not occur is obtained. When the load is 100 N or more, the adhesion is “good”, and when the indentation is less than 100 N, the adhesion is “ It was determined as “bad” and shown in Table 1. Table 1 also shows the maximum load at which peeling was not observed.

  Sample No. 1-4 are examples in which diamond electrodes were formed under the production conditions satisfying claim 6; 6 is an example in which a diamond electrode is formed under manufacturing conditions satisfying claim 7. In these examples, the film thickness of the formed conductive diamond film is in the range of 1 μm or more and less than 5 μm, and the strength ratio between the main peak of the hydride and the main peak of the base metal (hydrogen The main peak of the compound / main peak of the base metal was also in the range of 0.1 to 3.0.

  As a result, sample no. In each of Examples 1 to 4 and 6, neither pinholes nor cracks were observed on the surface of each sample on which the conductive diamond film was formed. Sample No. 1-4, no peeling of the conductive diamond film was observed even when the indentation load was 200 N. In No. 6, no peeling of the conductive diamond film was observed until the indentation load was 150N.

  On the other hand, sample No. No. 5 is a comparative example, sample No. 7 is a comparative example in which the manufacturing conditions of claim 7 are different from the heating rate. Sample No. No. 5, the thickness of the formed conductive diamond film is less than 1 μm, and the strength ratio of the hydride main peak to the base metal main peak (hydride main peak / base metal) The main peak) was also less than 0.1. Sample No. In No. 7, although the film thickness of the formed conductive diamond film was in the range of 1 μm or more and less than 5 μm, no hydride was observed and the main peak of the hydride and the main peak of the base metal The strength ratio (main peak of hydride / main peak of base metal) was 0.

  As a result, sample no. In No. 5, pinholes were observed, and there was no peeling of the conductive diamond film. The indentation load was up to 60N, and the exfoliation of the conductive diamond film was observed when the indentation load was 70N. Sample No. In No. 7, pinholes and cracks were not observed, but the conductive diamond film was not peeled off. The indentation load was up to 30N, and the exfoliation of the conductive diamond film was observed when the indentation load was 40N.

<Example 2>
An expanded metal obtained by processing a rolled titanium material into a wire diameter having a predetermined cross-sectional area (cross-sectional area of the strand portion) shown in Table 2 was cut into a size of 100 × 150 mm ² and used as an electrode base material. The surface of the substrate was scratched with diamond abrasive grains and placed in a chamber of a microwave heating CVD apparatus. Then, after evacuating the chamber to 0.3 Pa, hydrogen gas having a pressure (hydrogen gas pressure) shown in Table 2 was introduced into the chamber, and a microwave output corresponding to the temperature increase rate shown in Table 2 was made. Was applied to raise the temperature.

  Next, a mixed gas of methane and hydrogen mixed at a mixing ratio (methane / hydrogen ratio) shown in Table 2 was introduced into the chamber so as to have a predetermined pressure (mixed gas pressure) shown in Table 2. Table 2 The conductive diamond film was formed at the film formation temperature and film formation time shown in FIG. After completion of the formation of the conductive diamond film, the microwave output was turned off and at the same time the supply of the mixed gas was stopped and the mixture was cooled to room temperature (25 ° C.). This sample is designated as sample A.

  A sample obtained by cutting a rolled material before expanding into a size of 10 mm × 10 mm was also prepared, and a conductive diamond film was formed in the same manner as described above. This sample is designated as sample B.

  First, the amount of hydride formed was evaluated. This evaluation was performed on Sample B. X-ray diffraction (XRD) measurement was performed on each sample on which the conductive diamond film was formed. At that time, measurement was performed using a Cu—Kα ray under conditions of a tube voltage of 40 kV, a scanning angle range (2θ) of 30 ° to 100 °, and a scanning speed of 2 ° C./min.

From the obtained spectral data, the peak height due to the plane orientation indicating the main peak of the hydride and the main peak of the base metal is read, and the main peak of the hydride and the main metal of the base metal are read. The strength ratio to the peak (hydride main peak / base metal main peak) was calculated. The calculation results are shown in Table 2 as peak ratios. The intensity ratio (peak ratio) was calculated using TiH ₂ (110) and αTi (101).

  Next, as shown in FIG. 2, a sample A having a conductive diamond film formed on an expanded metal base is used as an anode, and an electrode obtained by subjecting a titanium base to platinum plating is used as a cathode, with a thickness of 300 μm. An electrolytic cell was prepared by sandwiching the solid polymer film between an anode and a cathode, and an ozone generation test was performed using an ozone generator using the electrolytic cell.

  Water with a water temperature of 20 ° C. was passed through the anode at 3.0 liters / min and the cathode at 0.5 liters / min, a direct current of 15 A was applied, and the ozone generation concentration at that time was measured. The ozone concentration at the start of operation and after the continuous operation for 100 hours was measured, respectively, and if the measured value was 7 mg / liter or more at the start of operation and after the continuous operation for 100 hours, it was judged as acceptable. The ozone concentration was measured by an iodine coulometric titration method using an ozone counter ZC-300 manufactured by Hiranuma Sangyo. The measurement results are shown in Table 2.

  Sample No. Examples 8 and 9 are examples in which diamond electrodes were formed under manufacturing conditions satisfying claim 6. In these examples, the film thickness of the formed conductive diamond film is in the range of 1 μm or more and less than 5 μm, and the strength ratio between the main peak of the hydride and the main peak of the base metal (hydride) Of main peak / base metal main peak) was in the range of 0.1 to 3.0.

  As a result, sample no. In each of Examples 8 and 9, the ozone concentration was 7 mg / liter or more both at the start of operation with the ozone generator and after 100 hours of continuous operation. It can be seen that by using 8 and 9 respectively, it is possible to generate ozone at a high concentration for a long time. This is the sample No. The conductive diamond film formed on the surface side of 8 and 9 has excellent adhesion to the electrode base material and does not peel off after a long period of operation.

  On the other hand, sample No. 10 is a comparative example in which the production conditions of claim 6 and the rate of temperature increase are different. In this comparative example, the thickness of the formed conductive diamond film is less than 1 μm, and the strength ratio between the main peak of the hydride and the main peak of the base metal (the main peak / base of the hydride). The main peak of the metal material was also less than 0.1.

  As a result, although ozone with a good concentration can be generated at the start of operation of the ozone generator, a significant decrease in ozone concentration after a long operation is observed.

It is a principal part enlarged plan view which shows the electrode base material formed using the expanded metal which processed the rolling material. It is explanatory drawing which shows the ozone generator used for the ozone generation test of Example 2. FIG.

Claims (9)

An electrode base material made of one or more base metals selected from the group consisting of pure Ti, Ti alloy, pure Nb, and pure Ta;
It consists of a conductive diamond film formed by doping boron on the surface of the electrode base material,
A hydride of the base metal species is formed at the interface between the electrode base and the conductive diamond film,
Strength ratio between the main peak of the hydride obtained by X-ray diffraction measurement and the main peak of the base metal constituting the electrode base material (main peak of hydride / main base metal base) A diamond electrode having a peak) of 0.1 or more and 3.0 or less.   The diamond electrode according to claim 1, wherein the conductive diamond film has a thickness of 1 μm or more and less than 5 μm. The electrode base material is formed of a wire, and a cross-sectional area of a cross section perpendicular to the longitudinal direction of the wire is 0.1 mm ² or more and 10.0 mm ² or less. Diamond electrode.   The diamond electrode according to claim 3, wherein the wire includes a plurality of wires, and the wires do not overlap each other. The electrode substrate is expanded metal, the strand cross-sectional area of the cross section perpendicular to the longitudinal direction, 0.1 mm ² or more, according to claim 1, wherein a is 10.0 mm ² or less Diamond electrode. A method for producing a diamond electrode, wherein a conductive diamond film is formed on a surface of a base metal made of pure Ti or a Ti alloy by vapor phase synthesis in a mixed gas atmosphere of a hydrocarbon gas and a hydrogen gas,
Hydrogen gas is introduced into the chamber containing the base metal, the hydrogen gas pressure in the chamber is set to 1.2 × 10 ³ Pa or more, and at a rate of 30 ° C./min or more and 100 ° C./min or less. Raising the temperature in the chamber to 650 ° C. or higher and 900 ° C. or lower, thereby heating the base metal and absorbing hydrogen on the surface thereof; and
After the temperature raising step, a mixed gas of hydrocarbon gas and hydrogen gas having a volume ratio of hydrocarbon gas of 8% or less is introduced into the chamber, and the mixed gas pressure in the chamber is adjusted to 1.33 × 10 ^3. A method for producing a diamond electrode, comprising: a film forming step of forming a conductive diamond film doped with boron on the surface of the electrode base material at Pa or higher. A method for producing a diamond electrode, wherein a conductive diamond film is formed on a surface of a base metal composed of pure Nb or pure Ta by vapor phase synthesis in a mixed gas atmosphere of hydrocarbon gas and hydrogen gas,
Hydrogen gas is introduced into the chamber containing the base metal, the hydrogen gas pressure in the chamber is set to 1.2 × 10 ³ Pa or more, and at a rate of 20 ° C./min or more and 60 ° C./min or less. Raising the temperature in the chamber to 650 ° C. or higher and 900 ° C. or lower, thereby heating the base metal and absorbing hydrogen on the surface thereof; and
After the temperature raising step, a mixed gas of hydrocarbon gas and hydrogen gas having a volume ratio of hydrocarbon gas of 8% or less is introduced into the chamber, and the mixed gas pressure in the chamber is adjusted to 1.33 × 10 ^3. A method for producing a diamond electrode, comprising: a film forming step of forming a conductive diamond film doped with boron on the surface of the electrode base material at Pa or higher.   The method for producing a diamond electrode according to claim 6 or 7, wherein the hydrocarbon gas is methane.   6. An ozone generator using the diamond electrode according to claim 1 as an anode.

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