Sintered ceramic body and electrode for plasma generation

Abstract

The invention relates to a ceramic sintered body and an electrode for plasma generation. The sintered ceramic body contains: a first specific element comprising five or six elements selected from the group consisting of titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); a second specific element comprising one element selected from the group consisting of yttrium (Y) and aluminum (Al); and a carbon element (C), the sum of the first specific elements, the second specific elements, and the carbon element being 98 at% or more, the ceramic sintered body having a plurality of structures having different compositions from each other, and one of the plurality of structures having a solid solution containing at least three or more elements among the first specific elements.

Description

Technical Field

[0001] The present invention relates to a ceramic sintered body and an electrode for plasma generation. Background Art

[0002] Conventionally, a ceramic sintered body for an electrode for plasma generation has been known (for example, Patent Document 1).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent No. 6929755 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] However, even with the prior art such as Patent Document 1, there is still room for improvement in the technology of improving the durability against thermal stress in the ceramic sintered body.

[0008] An object of the present invention is to provide a technology for improving the durability against thermal stress in a ceramic sintered body.

[0009] Solutions for Solving the Problems

[0010] The present invention is made to solve at least a part of the above problems and can be achieved in the following manner.

[0011] (1) According to one aspect of the present invention, there is provided a ceramic sintered body. The ceramic sintered body includes: a first specific element composed of 5 or 6 elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); a second specific element composed of 1 element selected from yttrium (Y) and aluminum (Al); and carbon element (C), and the sum of the first specific element, the second specific element, and the carbon element is 98 at% or more. The ceramic sintered body has a plurality of structures with different compositions, and one of the plurality of structures has a solid solution containing at least 3 or more elements of the first specific element.

[0012] According to this configuration, the ceramic sintered body contains 98 at% or more of a first specific element, a second specific element, and a carbon element. The first specific element is composed of 5 or 6 elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten. One of the various structures possessed by the ceramic sintered body has a solid solution containing at least 3 or more of the first specific elements. Since the solid solution containing 3 or more of the first specific elements contains elements with a lower melting point than hafnium carbide, for example, a dense ceramic sintered body can be produced even by a method such as hot pressing. Therefore, the strength of the ceramic sintered body is increased, and the durability against thermal stress can be improved.

[0013] (2) In the ceramic sintered body of the above-described manner, spinodal decomposition can occur in another one of the various structures. According to this configuration, spinodal decomposition has occurred in another one of the various structures. As a result, the resistance between the structures becomes smaller, and heat generation of the ceramic sintered body can be suppressed. Therefore, consumption of the ceramic sintered body due to heat generation can be suppressed.

[0014] (3) In the ceramic sintered body of the above-described manner, another one of the various structures can have a solid solution containing at least 2 or more of the first specific elements. According to this configuration, another one of the various structures has a solid solution containing at least 2 or more of the first specific elements. As a result, the ceramic sintered body becomes denser, and therefore the strength of the ceramic sintered body can be further increased.

[0015] (4) In the ceramic sintered body of the above-described manner, the second specific element contained in the ceramic sintered body can be 3000 atppm or less. According to this configuration, since the second specific element contained in the ceramic sintered body is 3000 atppm or less, pore formation between the structures is suppressed. As a result, the ceramic sintered body becomes denser, and therefore the strength of the ceramic sintered body can be further increased.

[0016] (5) In the ceramic sintered body of the above-described manner, the carbon element contained in the ceramic sintered body can be 45 at% or more and 55 at% or less. According to this configuration, since the carbon element contained in the ceramic sintered body is 45 at% or more and 55 at% or less, precipitation of the metal phase of the first specific element can be suppressed, and precipitation of free carbon can be suppressed. As a result, the strength of the ceramic sintered body can be further increased.

[0017] (6) In the ceramic sintered body in the above-described manner, the iron element (Fe) contained in the ceramic sintered body may be 800 atppm or less. According to this configuration, since the concentration of the iron element in the ceramic sintered body is 800 atppm or less, precipitation of iron-based particles is suppressed. Thereby, melting of the ceramic sintered body with an increase in temperature is suppressed, and thus consumption of the ceramic sintered body due to heat generation can be further suppressed.

[0018] (7) According to another aspect of the present invention, there is provided an electrode for plasma generation. The electrode for plasma generation includes the ceramic sintered body in the above-described manner. According to this configuration, the electrode for plasma generation includes a ceramic sintered body having a first structure that is a solid solution containing at least three or more elements among the first specific elements. Thereby, durability against thermal stress of the electrode for plasma generation can be improved, and thus the life of the electrode for plasma generation can be extended.

[0019] It should be noted that the present invention can be implemented in various ways. For example, it can be implemented as a method for manufacturing a ceramic sintered body, a device including a ceramic sintered body, a control method for a device including a ceramic sintered body, and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a cross-sectional view of an electrode for plasma generation including the ceramic sintered body of the first embodiment.

[0021] Figure 2 is a cross-sectional SEM image of the ceramic sintered body of the first embodiment.

[0022] Figure 3 is a first diagram illustrating production conditions of a sample of the ceramic sintered body.

[0023] Figure 4 is a second diagram illustrating production conditions of a sample of the ceramic sintered body.

[0024] Figure 5 is a first diagram illustrating characteristics of a sample of the ceramic sintered body.

[0025] Figure 6 is a second diagram illustrating characteristics of a sample of the ceramic sintered body.

[0026] Figure 7 is a third diagram illustrating characteristics of a sample of the ceramic sintered body.

[0027] Figure 8 is a fourth diagram illustrating characteristics of a sample of the ceramic sintered body.

[0028] Explanation of Reference Signs

[0029] 1…Electrode tip (ceramic sintered body)

[0030] 10…Plasma generating electrode Detailed implementation mode

[0031] <First implementation mode>

[0032] Figure 1 It is a cross-sectional view of the plasma generating electrode 10 equipped with the electrode tip 1 (ceramic sintered body) of this implementation mode. The plasma generating electrode 10 of this implementation mode is used to generate, for example, oxygen plasma in a plasma cutter, a surface treatment device, a spraying device, etc. that use plasma. The plasma generating electrode 10 includes an electrode tip 1 as a plasma generating cathode and a tip support portion 2 that supports the electrode tip 1.

[0033] The electrode tip 1 is a ceramic sintered body, which contains: a first specific element composed of 5 or 6 elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); a second specific element composed of 1 element selected from yttrium (Y) and aluminum (Al); and carbon element (C). The sum of the first specific element, the second specific element, and the carbon element contained in the ceramic sintered body as the electrode tip 1 is 98 at% or more. The sum of the first specific element, the second specific element, and the carbon element can be 100 at%, and the second specific element can be 0 atppm. The second specific element contained in the electrode tip 1 is 3000 atppm or less, and the carbon element is 45 at% or more and 55 at% or less. The concentration of the first specific element and the carbon element in the electrode tip 1 is measured by energy dispersive X-ray analysis (EDS). The determination and concentration measurement of the second specific element in the electrode tip 1 are carried out using an inductively coupled plasma (ICP) emission spectroscopic analysis device.

[0034] The ceramic sintered body as the electrode tip 1 has a variety of structures with different compositions from each other. As one of the variety of structures of the ceramic sintered body as the electrode tip 1 of this implementation mode, it has a solid solution containing at least 3 or more elements among the first specific elements, and another of the variety of structures has a solid solution containing at least 2 or more elements among the first specific elements. Another of the variety of structures of the ceramic sintered body as the electrode tip 1 of this implementation mode has undergone spinodal decomposition.

[0035] Figure 2 It is a cross-sectional SEM image of the ceramic sintered body of the first implementation mode. Figure 2 It is a diagram schematically showing an image (cross-sectional SEM image) obtained by photographing the cross-section of the electrode tip 1 after thermal etching treatment using a scanning electron microscope (SEM). Figure 2 A variety of structures (crystals) are shown therein.Figure 2 Among the various structures shown, the first structure C1 is a solid solution containing at least three or more elements among the first specific elements. In the electrode tip 1, the first structure C1 is grains of a carbide represented by the compositional formula (HfZrTaVW)C containing hafnium, zirconium, tantalum, vanadium, and tungsten. In the first structure C1, the entire structure is solid-solved. The second structure C2 forms a solid solution containing two elements among the first specific elements. In the electrode tip 1, the second structure C2 is grains of a carbide represented by the compositional formula (VW)C containing vanadium and tungsten. As Figure 2 shown, spinodal decomposition has occurred in the second structure C2. In the second structure C2, as Figure 2 shown, spinodal decomposition has occurred in the entire structure. In the present embodiment, an X-ray diffraction method using an X-ray diffractometer is used to identify whether the ceramic sintered body of the electrode tip 1 has multiple structures, and whether one of the multiple structures forms a solid solution containing at least two or three or more elements among the first specific elements. Specifically, in the analysis of the crystal structure of the electrode tip 1 using the X-ray diffraction method using CuKα1 radiation, when two or more peaks in the <111>, <200>, <220>, <311>, <222> directions derived from the NaCl-type structure are present during measurement with 2θ ranging from 20° to 80°, or when at least one peak derived from the NaCl-type structure and at least one peak derived from the hexagonal crystal structure are present, it is determined that the electrode tip 1 has multiple structures. The composition of the structure possessed by the ceramic sintered body is identified by an analysis combining a cross-sectional SEM image and an analysis of the cross-sectional SEM image and energy dispersive X-ray analysis (EDS). Regarding whether spinodal decomposition has occurred in one of the multiple structures possessed by the ceramic sintered body of the electrode tip 1, it is determined by small-angle X-ray scattering measurement based on the cross-sectional SEM image observation as Figure 2 shown.

[0036] The ceramic sintered body possessed by the electrode tip 1 of the present embodiment contains yttrium as the second specific element. The yttrium contained in the ceramic sintered body of the electrode tip 1 is 145 atppm and is 3000 atppm or less.

[0037] The ceramic sintered body possessed by the electrode tip 1 of the present embodiment contains iron element as an inevitable impurity. The iron element (Fe) contained in the ceramic sintered body of the electrode tip 1 is 537 atppm and is 800 atppm or less. It should be noted that the iron element contained in the ceramic sintered body of the electrode tip 1 can be 0 atppm.

[0038] In the ceramic sintered body included in the electrode head 1 of the present embodiment, the concentration difference between the first specific elements is 1.33 at%, which is less than 5 at%. Accordingly, a solid solution is likely to be formed in the first structure C1. In the present embodiment, the concentration difference between the first specific elements is obtained based on the result of the composition ratio in the crystal grains calculated by energy dispersive X-ray spectroscopy.

[0039] The head support portion 2 is a bottomed cylindrical member, and can be formed, for example, by processing a copper rod-shaped member. A hole 2b for inserting the electrode head 1 is formed in the bottom portion 2a of the head support portion 2. By inserting the electrode head 1 into the hole 2b of the head support portion 2, the plasma generation electrode 10 of the present embodiment is completed.

[0040] Next, a method for manufacturing the electrode head 1 will be described. As a method for manufacturing the electrode head 1, first, vanadium carbide powder (average particle diameter: 1.8 μm), zirconium carbide powder (average particle diameter: 2.4 μm), niobium carbide powder (average particle diameter: 1.1 μm), hafnium carbide powder (average particle diameter: 0.7 μm), and tungsten carbide powder (average particle diameter: 1.1 μm) are weighed so as to be 20 mol% each in the ceramic sintered body. Each of the weighed metal powders is put into a bead mill together with an acetone solvent and pulverized for 10 hours in a circulation mode. Five kinds of slurries obtained by pulverizing with the bead mill are respectively put into a ball mill in a predetermined amount and mixed. Next, 0.4 wt% of zirconia partially stabilized with 3 mol% yttria (Y2O3) (hereinafter referred to as "3YSZ", average particle diameter: 1.0 μm) is added to the mixed slurry, and ball mill mixing is performed for 8 hours to produce a mixed slurry. The obtained mixed slurry is put into a heated vacuum container, and the slurry is dried under reduced pressure while heating to 60°C to produce dried powder. The obtained dried powder is passed through a sieve with a pore diameter of 100 μm to obtain granulated powder, which is put into a hot press die in a predetermined amount and fired (HP method) in a vacuum atmosphere under the conditions of a firing temperature of 1800°C and a firing pressure of 60 MPa. Thus, the electrode head 1 is completed.

[0041] Next, a related evaluation test of the ceramic sintered body used as the electrode head of the plasma generation electrode will be described. In this evaluation test, a plurality of ceramic sintered bodies with different production conditions were produced, and the influence of the production conditions on the characteristics of the ceramic sintered body was evaluated.

[0042] Figure 3 is FIG. 1 for explaining the production conditions of the sample of the ceramic sintered body. Figure 4 is FIG. 2 for explaining the production conditions of the sample of the ceramic sintered body. In this evaluation test, as samples of the ceramic sintered body, 24 kinds of samples 1 to 24 were produced. As the production conditions of each of the samples 1 to 24, Figure 3 andFigure 4 The types and respective molar percentages of the "main raw materials", the types and respective weight percentages of the "additives", and the "firing method", "temperature" (unit: °C), and "pressure" (unit: MPa) as the "firing conditions" are shown.

[0043] First, the "main raw materials" that are the first specific elements contained in the ceramic sintered body will be described. Among Samples 1 to 24, as Figure 3 and Figure 4 shown, five or six materials out of titanium carbide, vanadium carbide, zirconium carbide, niobium carbide, molybdenum carbide, hafnium carbide, tantalum carbide, and tungsten carbide were used as the "main raw materials" in the production of Samples 1 to 18, Sample 21, and Sample 22. Powders of the "main raw materials" with the average particle sizes shown below were used in the production of Samples 1 to 18, Sample 21, and Sample 22.

[0044] Titanium carbide powder: 1.7 μm

[0045] Vanadium carbide powder: 1.8 μm

[0046] Zirconium carbide powder: 2.4 μm

[0047] Niobium carbide powder: 1.1 μm

[0048] Molybdenum carbide powder: 1.8 μm

[0049] Hafnium carbide powder: 0.7 μm

[0050] Tantalum carbide powder: 1.0 μm

[0051] Tungsten carbide powder: 1.1 μm

[0052] Next, the "additives" that are the second specific elements contained in the ceramic sintered body will be described. As Figure 3 and Figure 4 shown, either 3YSZ or alumina (Al2O3) was used as the "additive" in the production of Samples 1 to 18, Sample 21, and Sample 22. Powders of the "additives" with the average particle sizes shown below were used in the production of Samples 1 to 18, Sample 21, and Sample 22.

[0053] 3YSZ: 1.0 μm

[0054] Al2O3: 0.3 μm

[0055] In the production of Samples 1 to 18, Sample 21, and Sample 22, similar to the manufacturing method of the electrode tip 1, weighing was first performed so that the molar percentage of the "main raw materials" became Figure 3 or Figure 4For the numerical values shown, each weighed metal powder is put into a bead mill together with an acetone solvent and pulverized in a circulation mode for 10 hours. Five or six kinds of slurries obtained by pulverization using the bead mill are put into a ball mill in a specified amount and mixed, and then "additives" are added to the mixed slurries so that the weight percentage becomes Figure 3 or Figure 4 the numerical values shown, and ball milling and mixing are carried out for 8 hours to produce a mixed slurry. The obtained mixed slurry is put into a heated vacuum container, and the slurry is dried under reduced pressure while being heated to 60 °C to form a dried powder, and the dried powder is passed through a sieve with a sieve pore of 100 μm, thereby obtaining a granulated powder. The obtained granulated powder is put into a hot pressing mold in a specified amount and fired under specified conditions (firing temperature: 1800 °C, firing pressure: 60 MPa, treatment atmosphere: vacuum) to obtain Samples 1 to 18, Sample 21, and Sample 22.

[0056] In the production of Samples 19 and 20, raw materials of various metal oxides and carbon raw materials are weighed so as to have the same composition ratio as that of Sample 1. Specifically, for Sample 19, raw materials of various metal oxides and carbon raw materials are weighed so that the ratio of the total metal element amount (ME) to carbon (C) becomes ME:C = 0.6:0.4. For Sample 20, raw materials of various metal oxides and carbon raw materials are weighed so that the ratio of the total metal element amount (ME) to carbon (C) becomes ME:C = 0.4:0.6. In the production of Samples 19 and 20, the weighed raw materials of metal oxides and carbon raw materials are mixed with a ball mill to obtain a powder, and the powder is heat-treated under specified conditions (treatment temperature: 1600 °C, treatment time: 3 hours, treatment atmosphere: vacuum). The heat-treated powder is put into a hot pressing mold in a specified amount and fired under specified conditions (firing temperature: 1800 °C, firing pressure: 60 MPa, treatment atmosphere: vacuum) to obtain Samples 19 and 20. As raw materials, zirconia (ZrO2), tantalum oxide (Ta2O5), niobium oxide (Nb2O5), vanadium oxide (V2O5), tungsten oxide (WO3) as metal oxides, and carbon (C) are used. In the production of Samples 19 and 20, powders of raw materials having the average particle sizes shown below are used.

[0057] Zirconia powder: 1.0 μm

[0058] Tantalum oxide powder: 3.0 μm

[0059] Niobium oxide powder: 1.0 μm

[0060] Vanadium oxide powder: 5.0 μm

[0061] Tungsten oxide powder: 0.7 μm

[0062] Carbon powder: 5.0μm

[0063] Sample 23 was fabricated into a single-phase sintered body of HfC using the spark plasma sintering method (SPS method). Specifically, hafnium carbide powder (average particle size: 0.7μm) was introduced into a square SPS mold with a size of 35×35 mm such that the thickness of the ceramic sintered body became 5 mm, and sintering was carried out under specified conditions (firing temperature: 1900°C, firing pressure: 70 MPa, processing atmosphere: vacuum) to fabricate Sample 23.

[0064] Sample 24 was fabricated using zirconium carbide (average particle size: 2.4μm), hafnium carbide (average particle size: 0.7μm), and tantalum carbide (average particle size: 1.0μm) as the "main raw materials". Sample 24 was fabricated through the same steps as Samples 1 to 18, Sample 21, and Sample 22. In this evaluation test, Samples 1 to 24 fabricated by the above method were processed into samples with dimensions of 3×4×35 mm.

[0065] Figure 5 It is the first figure illustrating the characteristics of the samples of the ceramic sintered body. Figure 6 It is the second figure illustrating the characteristics of the samples of the ceramic sintered body. Figure 5 and Figure 6 show the "composition", "particle size", and "proportion" of each of the two or three types of tissues contained in Samples 1 to 24.

[0066] For Figure 5 and Figure 6 the "composition" shown, similar to the ceramic sintered body of the electrode head 1 of the present embodiment, the samples after thermal etching treatment were photographed, and energy dispersive X-ray analysis targeting the range of the obtained cross-sectional SEM image was used to identify the composition of the tissue (grain). Figure 5 and Figure 6 the "particle size" shown represents the particle size obtained as follows: after the samples after the strength test described below were mirror-polished with diamond abrasive grains and the mirror-polished samples were thermally etched under specified conditions (processing atmosphere: vacuum, processing temperature: 1800°C, processing time: 5 minutes), the average particle size of the tissue was obtained using the intercept method based on the secondary electron image with a magnification of 2000 times taken by a scanning electron microscope. The "spinodal decomposition" of the "second tissue" indicates whether spinodal decomposition has occurred in the second tissue. Regarding whether spinodal decomposition has occurred in the second tissue, for the second tissue of each sample, similar to the ceramic sintered body of the electrode head 1 of the present embodiment, it was determined by small-angle X-ray scattering measurement based on cross-sectional SEM image observation.Figure 5 and Figure 6 The "ratio" shown is a value obtained by identifying the "composition" within the range of the cross-sectional SEM image taken and calculating the area ratio of each tissue within the SEM image range in the cross-sectional SEM image.

[0067] Figure 7 It is Figure 3 showing the characteristics of the sample of the ceramic sintered body. Figure 8 It is Figure 4 showing the characteristics of the sample of the ceramic sintered body. Figure 7 and Figure 8 show the "Y concentration", "Al concentration", "Fe concentration", "C concentration", "atomic concentration difference of the first specific element", "relative density", "strength", "ON-OFF durability", and "consumption amount" of each of Samples 1 to 24.

[0068] Figure 7 and Figure 8 The "Y concentration", "Al concentration", "Fe concentration", and "C concentration" shown respectively represent the concentrations of yttrium element, aluminum element, iron element, and carbon element contained in the sample. In this evaluation test, for the sample after thermal etching treatment, quantitative analysis in energy dispersive X-ray analysis (EDS) targeting the range of the cross-sectional SEM image taken at a magnification of 500 times was used to measure the "Y concentration", "Al concentration", "Fe concentration", and "C concentration".

[0069] Figure 7 and Figure 8 The "atomic concentration difference of the first specific element" shown represents the concentration difference between the first specific elements contained in the sample. The "atomic concentration difference of the first specific element" is calculated using the concentration of the first specific element measured by quantitative analysis based on energy dispersive X-ray analysis.

[0070] Figure 7 and Figure 8 The "relative density" shown represents the degree of densification of the ceramic sintered body. The "relative density" is calculated using the specific gravity and open porosity measured for the sample by the method of JIS R1634, and the specific gravity of the mixture of carbide powders at the time of sample production. The specific gravity of the mixture of carbide powders at the time of sample production is calculated using the specific gravity of each carbide powder weighed at the time of sample production and its mixing ratio in the sample. The "strength" represents the value measured in the three-point bending strength test based on JIS R1601.

[0071] Figure 7 and Figure 8The so-called "on-off durability" refers to the degree of resistance to breakage when the sample is repeatedly energized and de-energized, indicating the durability against thermal stress. In this evaluation test, first, the sample is processed into φ1mm×L10mm, and the evaluation electrodes are fabricated. The fabricated evaluation electrodes are used as the cathodes, and the anodes are grounded. In a state connected to a DC pulse power supply, a plasma test of discharging in a mixed gas of nitrogen and oxygen is carried out (electric power: 200W, on-off cycle: discharging for 1 minute and stopping discharging for 10 seconds). In this plasma test, the length of the cumulative time until the sample is damaged is classified into "A", "B", "C", and "D" as follows. After the plasma test is carried out for a certain period of time, the damage state of the sample is visually confirmed.

[0072] A: No damage occurs even when the cumulative time reaches 5 hours or more.

[0073] B: Damage occurs when the cumulative time is more than 3 hours and less than 5 hours.

[0074] C: Damage occurs when the cumulative time is more than 30 minutes and less than 3 hours.

[0075] D: Damage occurs when the cumulative time is less than 30 minutes.

[0076] Figure 7 and Figure 8 The so-called "consumption amount" refers to the degree of consumption when the sample of the ceramic sintered body is used as the plasma generation electrode, indicating the wear resistance. The "consumption amount" is a value calculated using the value obtained by measuring the weight reduction of the evaluation electrode after the test in the above plasma test. The "consumption amount" shows the relative value when the "consumption amount" of sample 24 is set to 100. That is, the smaller the value, the less the consumption amount.

[0077] As Figure 3 or Figure 4 shown, Samples 1 to 22 each contain a first specific element composed of 5 or 6 elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten, a second specific element composed of 1 element selected from yttrium and aluminum, and a carbon element. In addition, in Samples 1 to 22, the total of the first specific element, the second specific element, and the carbon element is 98 at% or more, and as Figure 5 and Figure 6 shown, they have a first structure and a second structure with different compositions from each other. Furthermore, the first structure possessed by Samples 1 to 22 is a solid solution containing at least 3 or more elements of the first specific element.

[0078] In terms of "relative density", it was confirmed that Samples 1 to 22 had values equal to or greater than those of Sample 23, which is a single-phase sintered body of HfC. In addition, it was confirmed that the "strength" of Samples 1 to 22 was greater than that of Sample 23, and the "on-off durability" was also high. Furthermore, it was confirmed that the "consumption amount" of Samples 1 to 22 was smaller than that of Sample 24, in which the first structure is a solid solution containing two elements. From these, it can be confirmed that Samples 1 to 22 form a ceramic sintered body that is denser than or equal to Sample 23, thereby improving the strength, enhancing the durability against thermal stress compared to Sample 23, and being less consumable compared to Sample 24.

[0079] In addition, Sample 23 contains hafnium carbide and is fabricated by the spark plasma sintering method (SPS method). On the other hand, Samples 1 to 22 contain elements with a melting point lower than that of hafnium carbide. Therefore, it was confirmed that a dense ceramic sintered body can be fabricated even by the hot pressing method (HP method).

[0080] Samples 1 to 22 and Sample 24 were selected with the first specific element that forms two or more structures, namely the first structure and the second structure, as the main raw material. Thus, in each of the two or more structures, the grain growth of the grains can be suppressed, and therefore a ceramic sintered body with higher strength can be fabricated.

[0081] In Samples 1 to 22, the "first structure" has a solid solution containing at least three or more elements among the first specific elements. Thus, a ceramic sintered body that is less consumable even when heated by energization can be fabricated. It should be noted that the more types of components contained in the grains, the smaller the consumption amount caused by the generation of plasma in the high-temperature region.

[0082] Regarding the "consumption amount" of Samples 1 to 16, it was confirmed that Samples 2, 8, 11, 15, and 16 showed smaller values, all reaching values less than 20. The "second structure" of Samples 2, 8, 11, 15, and 16 has spinodal decomposition. Since the "second structure" has spinodal decomposition, the resistance between the structures (grain boundaries) becomes smaller, so the heat generation caused by energization can be suppressed. Thus, the consumption caused by heat generation can be suppressed.

[0083] Regarding the "strength" of Samples 1 to 16, it was confirmed that Samples 1 to 4 and Samples 7 to 16, in which the "second structure" has a solid solution containing two or more elements among the first specific elements, showed larger values than Samples 5 and 6, in which the "second structure" has a solid solution containing one element among the first specific elements. The "second structure" in Samples 1 to 4 and Samples 7 to 16 has a solid solution containing at least two or more elements among the first specific elements. Since the "second structure" has a solid solution containing at least two or more elements among the first specific elements, the grain growth of the "first structure" is suppressed, and thus a ceramic sintered body with high strength can be produced. It should be noted that the more types of components contained in the grains of the "second structure", the more effectively the grain growth in the "first structure" can be suppressed, and thus the strength can be further increased.

[0084] Regarding the "strength" of Samples 1 to 18, Samples 21, and Samples 22, it was confirmed that Samples 1 to 18 with a "Y concentration" or "Al concentration" of 3000 ppm or less were superior to Samples 21 or 22 with a "Y concentration" or "Al concentration" greater than 3000 ppm. In Samples 21 and 22, the "Y concentration" or "Al concentration" is greater than 3000 ppm, so the densification of the ceramic sintered body is hindered, and pores are likely to form between the structures. Therefore, Samples 21 and 22 have low strength and are easily damaged. On the other hand, Samples 1 to 18 with a "Y concentration" or "Al concentration" of 3000 ppm or less can have a certain level of strength because pores are less likely to form between the structures.

[0085] Regarding the "strength" of Samples 1 to 20, it was confirmed that Samples 1 to 18 with a carbon element content of 45 at% or more and 55 at% or less showed larger values than Sample 19 with a carbon element content greater than 55 at% and Sample 20 with a carbon element content less than 45 at%. If the carbon element concentration in the ceramic sintered body is greater than 55 at%, free carbon will precipitate, and the free carbon appears between the structures in the form of a brittle phase, so the strength of the ceramic sintered body decreases. If the carbon element concentration in the ceramic sintered body is less than 45 at%, the metal contained in the second structure precipitates in the form of a metal phase. The melting point of the precipitated metal phase is lower than that of the carbide, so the durability of the ceramic sintered body at high temperatures decreases. On the other hand, by making the carbon element concentration in the ceramic sintered body 45 at% or more and 55 at% or less, the generation of free carbon and the precipitation of the metal phase can both be suppressed.

[0086] Regarding the "consumption amount" of Samples 1 to 16, it was confirmed that Samples 1 to 8 and Samples 11 to 16 with iron element of 800 atppm or less showed smaller values than Samples 9 and 10 with iron element greater than 800 atppm, and all reached values less than 40. Although the ceramic sintered body contains iron element in the form of impurities, if the concentration of the iron element is greater than 800 atppm, relatively large iron-based particles will precipitate. Since the melting point of the iron-based particles is low, the durability of the ceramic sintered body at high temperatures is reduced. On the other hand, by making the concentration of the iron element in the ceramic sintered body 800 atppm or less, the precipitation of the iron-based particles can be suppressed.

[0087] In a plasma cutter or a surface treatment device using plasma, a high melting point metal material such as hafnium carbide is sometimes used as the electrode for plasma generation. However, hafnium carbide is difficult to sinter, so it is difficult to obtain a dense ceramic sintered body. For this reason, the ceramic sintered body formed of hafnium carbide can only be manufactured by the electric current sintering method. The electric current sintering method is a method of sintering a ceramic compact by, for example, installing electrodes at both ends of a cylindrical ceramic compact and applying a high voltage to conduct electricity through the ceramic compact. However, for example, when manufacturing a relatively large ceramic sintered body, a large voltage needs to be applied, increasing the equipment cost and the manufacturing cost. In addition, the electric current sintering method is difficult to sinter a ceramic compact having a thickness uniformly, and the degree of freedom in shape is also low. Furthermore, even if a relatively dense ceramic sintered body can be manufactured using hafnium carbide, the strength of the ceramic sintered body is low due to the presence of minute pores in the grain boundaries. When the ceramic sintered body with low strength is used for the electrode tip of the electrode for plasma generation, if operations such as the generation and stop of plasma are repeated, the ceramic sintered body formed of hafnium carbide will be damaged due to the thermal stress caused by repeated on-off.

[0088] According to the ceramic sintered body included in the electrode tip 1 of the present embodiment described above, it contains 98 at% or more of a first specific element, a second specific element, and a carbon element, wherein the first specific element is composed of 5 or 6 elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten, and the first structure C1 in the various structures included in the ceramic sintered body has a solid solution containing at least 3 or more elements of the first specific element. Since the solid solution containing 3 or more first specific elements contains elements with a lower melting point than hafnium carbide, for example, a dense ceramic sintered body can be manufactured even by a method such as hot pressing. Therefore, the strength of the ceramic sintered body is increased, and the durability against thermal stress can be improved.

[0089] In addition, according to the ceramic sintered body included in the electrode tip 1 of the present embodiment, the first structure C1 has a solid solution containing at least 3 or more elements of the first specific element. Thereby, the consumption of the ceramic sintered body itself caused by heat generation due to energization can be suppressed.

[0090] In addition, in the ceramic sintered body included in the electrode head 1 according to the present embodiment, spinodal decomposition has occurred in the second structure C2. As a result, the resistance between the structures becomes smaller, and heat generation of the ceramic sintered body can be suppressed. Therefore, consumption of the ceramic sintered body due to heat generation can be suppressed.

[0091] In addition, in the ceramic sintered body included in the electrode head 1 according to the present embodiment, the second structure C2 has a solid solution containing at least two or more elements among the first specific elements. As a result, the ceramic sintered body becomes denser, and thus the strength of the ceramic sintered body can be further improved.

[0092] In addition, in the ceramic sintered body included in the electrode head 1 according to the present embodiment, the first specific elements are selected such that the composition of the first structure C1 and the composition of the second structure C2 are different from each other. As a result, grain growth of each of the first structure C1 and the second structure C2 is suppressed, and a ceramic sintered body with higher strength can be obtained.

[0093] In addition, in the ceramic sintered body included in the electrode head 1 according to the present embodiment, since the content of the second specific element in the ceramic sintered body is 3000 atppm or less, formation of pores between the structures is suppressed. As a result, the ceramic sintered body becomes denser, and thus the strength of the ceramic sintered body can be further improved.

[0094] In addition, in the ceramic sintered body included in the electrode head 1 according to the present embodiment, since the content of carbon element in the ceramic sintered body is 45 at% or more and 55 at% or less, precipitation of the metal phase of the first specific element can be suppressed, and precipitation of free carbon can be suppressed. As a result, the strength of the ceramic sintered body can be further improved.

[0095] In addition, in the ceramic sintered body included in the electrode head 1 according to the present embodiment, since the concentration of iron element in the ceramic sintered body is 800 atppm or less, precipitation of iron-based particles is suppressed. As a result, melting of the ceramic sintered body as the temperature rises is suppressed, and thus consumption of the ceramic sintered body due to heat generation can be further suppressed.

[0096] In addition, in the plasma generation electrode 10 according to the present embodiment, the plasma generation electrode includes a ceramic sintered body having a first structure C1, and the first structure C1 is a solid solution containing at least three or more elements among the first specific elements. As a result, the durability of the plasma generation electrode against thermal stress can be improved, and thus the life of the plasma generation electrode can be extended.

[0097] <Modifications of the present embodiment>

[0098] The present invention is not limited to the above-described embodiment, and can be implemented in various ways without departing from its gist. For example, the following modifications can also be made.

[0099] [Modification Example 1]

[0100] In the above-described embodiment, the ceramic sintered body included in the electrode head 1 contains five elements, i.e., hafnium, zirconium, tantalum, vanadium, and tungsten, as the first specific elements. It is sufficient to contain five or six elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten.

[0101] [Modification Example 2]

[0102] In the above-described embodiment, spinodal decomposition occurred in the entire structure of the second structure C2 included in the ceramic sintered body. Spinodal decomposition may not occur in the various structures included in the ceramic sintered body, but by causing spinodal decomposition in the structure, the resistance between the structures becomes smaller, and heat generation of the ceramic sintered body can be suppressed.

[0103] [Modification Example 3]

[0104] In the above-described embodiment, the second structure C2 is a crystal grain represented by the composition formula (VW)C containing vanadium and tungsten, and is a solid solution containing at least two or more elements among the first specific elements. The various structures included in the ceramic sintered body may not be a solid solution containing at least two or more elements among the first specific elements. When the structure is a solid solution containing at least two or more elements among the first specific elements, the ceramic sintered body becomes dense, and thus the strength of the ceramic sintered body can be improved.

[0105] [Modification Example 4]

[0106] In the above-described embodiment, the yttrium contained in the ceramic sintered body of the electrode head 1 is 145 atppm. The concentration of yttrium contained in the ceramic sintered body is not limited to this, and is preferably 3000 atppm or less. If the concentration of yttrium is 3000 atppm or less, the formation of pores between the structures is suppressed. Thereby, the ceramic sintered body becomes dense, and thus the strength of the ceramic sintered body can be improved. In addition, the second specific element contained in the ceramic sintered body may be aluminum. In this case, the aluminum contained in the ceramic sintered body is preferably 3000 atppm or less.

[0107] [Modification Example 5]

[0108] In the above-described embodiment, the carbon element contained in the ceramic sintered body of the electrode head 1 is 45 at% or more and 55 at% or less. The concentration of the carbon element contained in the ceramic sintered body is not limited thereto, and is preferably in the range of 45 at% or more and 55 at% or less. If the concentration of the carbon element in the ceramic sintered body is greater than 55 at%, free carbon will precipitate, and the free carbon will appear as a fragile phase between the tissues, so the strength of the ceramic sintered body will decrease. If the concentration of the carbon element in the ceramic sintered body is less than 45 at%, the metal contained in the second tissue will precipitate in the form of a metal phase. Since the melting point of the precipitated metal phase is lower than that of the carbide, the durability of the ceramic sintered body at high temperatures will decrease. Therefore, by making the concentration of the carbon element in the ceramic sintered body 45 at% or more and 55 at% or less, it is possible to suppress both the generation of free carbon and the precipitation of the metal phase.

[0109] [Modification Example 6]

[0110] In the above-described embodiment, the iron element (Fe) contained in the ceramic sintered body provided in the electrode head 1 is 800 atppm or less. The iron element can also be greater than 800 atppm, but if the concentration of the iron element becomes high, the precipitated iron-based particles will melt, resulting in a short lifespan. Therefore, a low concentration of the iron element is preferred. The concentration of the iron element can also be below the detection limit in the quantitative analysis by energy dispersive X-ray analysis (EDS).

[0111] [Modification Example 7]

[0112] The ceramic sintered body of the above-described embodiment is provided in the electrode head 1. The technical field to which the ceramic sintered body is applied is not limited thereto. It can also be used in technical fields that require durability against thermal stress and wear resistance.

[0113] The above description has been made based on the embodiments and modification examples. However, the embodiments of the above-described method are for facilitating the understanding of the solution of the present method and do not limit the present method. The present method can be changed and improved without departing from its gist and the claims, and the present method includes its equivalent solutions. In addition, if the technical feature is not described in the form of an essential feature in this specification, it can be appropriately deleted.

[0114] <Application Example 1>

[0115] A ceramic sintered body, characterized in that it comprises:

[0116] A first specific element composed of 5 or 6 elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W);

[0117] A second specific element, which is composed of one element selected from yttrium (Y) and aluminum (Al); and

[0118] a carbon element (C),

[0119] the sum of the aforementioned first specific element, the aforementioned second specific element, and the carbon element is 98 at% or more,

[0120] the aforementioned ceramic sintered body has a plurality of structures with different compositions from each other,

[0121] one of the plurality of aforementioned structures has a solid solution containing at least three or more elements of the aforementioned first specific element.

[0122] <Application Example 2>

[0123] The ceramic sintered body according to Application Example 1, characterized in that

[0124] spinodal decomposition has occurred in another one of the plurality of aforementioned structures.

[0125] <Application Example 3>

[0126] The ceramic sintered body according to Application Example 1 or Application Example 2, characterized in that

[0127] another one of the plurality of aforementioned structures has a solid solution containing at least two or more elements of the aforementioned first specific element.

[0128] <Application Example 4>

[0129] The ceramic sintered body according to any one of Application Examples 1 to 3, characterized in that

[0130] the aforementioned second specific element contained in the aforementioned ceramic sintered body is 3000 atppm or less.

[0131] <Application Example 5>

[0132] The ceramic sintered body according to any one of Application Examples 1 to 4, characterized in that

[0133] the carbon element contained in the aforementioned ceramic sintered body is 45 at% or more and 55 at% or less.

[0134] <Application Example 6>

[0135] The ceramic sintered body according to any one of Application Examples 1 to 5, characterized in that

[0136] the iron element (Fe) contained in the aforementioned ceramic sintered body is 800 atppm or less.

[0137] <Application Example 7>

[0138] A plasma generation electrode includes the ceramic sintered body described in any one of Application Examples 1 to 6.

Claims

1. A ceramic sintered body, characterized in that, It includes: A first specific element composed of 5 or 6 elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); A second specific element composed of 1 element selected from yttrium (Y) and aluminum (Al); and Carbon element C, The sum of the first specific element, the second specific element, and the carbon element is 98 at% or more. The ceramic sintered body has a plurality of structures with different compositions from each other. One of the plurality of structures has a solid solution containing at least 3 or more elements of the first specific element.

2. The ceramic sintered body according to claim 1, wherein Spinodal decomposition has occurred in another one of the plurality of structures.

3. The ceramic sintered body according to claim 1 or 2, wherein Another one of the plurality of structures has a solid solution containing at least 2 or more elements of the first specific element.

4. The ceramic sintered body according to claim 1 or 2, wherein The second specific element contained in the ceramic sintered body is 3000 atppm or less.

5. The ceramic sintered body according to claim 1 or 2, wherein The carbon element contained in the ceramic sintered body is 45 at% or more and 55 at% or less.

6. The ceramic sintered body according to claim 1 or 2, wherein The iron element Fe contained in the ceramic sintered body is 800 atppm or less.

7. A plasma generation electrode comprising the ceramic sintered body according to any one of claims 1 to 6.

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