Ceramic sintered body and electrode for generating plasma

Abstract

This invention relates to ceramic sintered bodies and electrodes for plasma generation. The ceramic sintered body comprises: a first specific element, which is composed of five or six elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); a second specific element, which is composed of one element selected from yttrium (Y) and aluminum (Al); and carbon (C). The total content of the first specific element, the second specific element, and carbon in the ceramic sintered body is 98 at% or more, the content of the second specific element in the ceramic sintered body is 3000 atppm or less, the content of carbon in the ceramic sintered body is 45 at% or more and 55 at% or less, and the ceramic sintered body has a single-phase structure in which the first specific element is dissolved.

Description

Technical Field

[0001] This invention relates to ceramic sintered bodies and electrodes for plasma generation. Background Technology

[0002] Previously, there were known ceramic sintered bodies for electrodes used in plasma generation (e.g., Patent Document 1 and Non-Patent Document 1).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent No. 6929755

[0006] Non-patent literature

[0007] Non-Patent Literature 1: Shiro Shimada, Michio Inagaki, Kunihito Matsui, "Oxidation Kinetics of Hafnium Carbide in the Temperature Range of 480° to 600°C", Journal of the American Ceramic Society, Volume 75, Issue 10, October 1992, Pages 2671-2678, [Searched May 9, 2023], URL <https: / / doi.org / 10.1111 / j.1151-2916.1992.tb05487.x> Summary of the Invention

[0008] The problem the invention aims to solve

[0009] However, even with existing technologies such as Patent Document 1 and Non-Patent Document 1, there is still room for improvement in the techniques for enhancing the oxidation resistance of ceramic sintered bodies.

[0010] The purpose of this invention is to provide a technique for improving the oxidation resistance of sintered ceramic bodies.

[0011] Solution for solving the problem

[0012] The present invention was made to solve at least a part of the above-mentioned problems and can be implemented in the following manner.

[0013] (1) According to one aspect of the present invention, a ceramic sintered body is provided. The ceramic sintered body comprises: a first specific element, which is composed of five or six elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta) and tungsten (W); a second specific element, which is composed of one element selected from yttrium (Y) and aluminum (Al); and carbon (C), wherein the sum of the first specific element, the second specific element and carbon contained in the ceramic sintered body is 98 at% or more, the second specific element contained in the ceramic sintered body is 3000 atppm or less, and the carbon contained in the ceramic sintered body is 45 at% or more and 55 at% or less, and the ceramic sintered body has a single-phase structure in which the first specific element is dissolved.

[0014] According to this composition, the ceramic sintered body has a single-phase structure with a first specific element dissolved in solid solution. The first specific element is composed of five or six elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten. This improves the oxidation resistance of the ceramic sintered body.

[0015] (2) In the ceramic sintered body of the above manner, the aforementioned first specific element may include zirconium. According to this configuration, the ceramic sintered body includes zirconium as the first specific element, whose ionic radius is larger than that of any one of titanium, vanadium, niobium, molybdenum, hafnium, tantalum, or tungsten. Consequently, the strain of the lattice of the single-phase structure in which the first specific element is dissolved increases. Therefore, the ceramic sintered body becomes less susceptible to oxidation, thus further improving its oxidation resistance.

[0016] (3) In the ceramic sintered body of the above-described manner, the iron (Fe) content in the ceramic sintered body can be 800 atppm or less. Based on this configuration, since the iron concentration in the ceramic sintered body is 800 atppm or less, the precipitation of iron-based particles is suppressed. Therefore, the melting of the ceramic sintered body as the temperature rises is suppressed, thereby suppressing the weight loss of the ceramic sintered body due to use.

[0017] (4) According to another aspect of the present invention, a plasma generating electrode is provided. This plasma generating electrode comprises a ceramic sintered body as described above. According to this configuration, the plasma generating electrode comprises a ceramic sintered body having a single-phase structure in which a first specific element is dissolved, thereby improving the oxidation resistance of the plasma generating electrode. Consequently, the lifespan of the plasma generating electrode can be extended.

[0018] It should be noted that the present invention can be implemented in various ways, such as by a method for manufacturing a ceramic sintered body, an apparatus having a ceramic sintered body, or a method for controlling an apparatus having a ceramic sintered body. Attached Figure Description

[0019] Figure 1 This is a cross-sectional view of the plasma generating electrode of the ceramic sintered body according to the first embodiment.

[0020] Figure 2 Figure 1 illustrates the preparation conditions for the ceramic sintered body sample.

[0021] Figure 3 Figure 2 illustrates the preparation conditions for the ceramic sintered body sample.

[0022] Figure 4 Figure 1 illustrates the characteristics of the sample of the sintered ceramic body.

[0023] Figure 5 This is Figure 2, which illustrates the characteristics of the sample of the sintered ceramic body.

[0024] Explanation of reference numerals in the attached figures

[0025] 1…Electrode head (ceramic sintered body)

[0026] 10…Electrodes for plasma generation Detailed Implementation

[0027] <First Embodiment>

[0028] Figure 1 This is a cross-sectional view of a plasma generating electrode 10 equipped with the electrode head 1 (ceramic sintered body) of this embodiment. The plasma generating electrode 10 of this embodiment is used to generate, for example, oxygen plasma in plasma-using cutting machines, surface treatment apparatuses, spraying apparatuses, etc. The plasma generating electrode 10 includes an electrode head 1 serving as a plasma generating cathode and a head support portion 2 supporting the electrode head 1.

[0029] Electrode head 1 is a sintered ceramic body comprising: a first specific element, consisting of five or six elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); a second specific element, consisting of one element selected from yttrium (Y) and aluminum (Al); and carbon (C). The total content of the first specific element, the second specific element, and carbon in electrode head 1 is 98 at% or more, and the content of the second specific element is 3000 atppm or less. The total content of the first specific element, the second specific element, and carbon can be 100 at%, and the content of the second specific element can be 0 atppm. The carbon content in electrode head 1 is 45 at% or more and 55 at% or less. The concentrations of the first specific element and carbon in electrode head 1 are determined using energy-dispersive X-ray spectroscopy (EDS). The determination of the second specific element and the measurement of its concentration in electrode head 1 were performed using an inductively coupled plasma (ICP) emission spectrometer.

[0030] The electrode head 1 of this embodiment has a single-phase structure with a first specific element dissolved in it. In this embodiment, the presence of a single-phase structure with a first specific element dissolved in it is determined by X-ray diffraction using an X-ray diffraction apparatus. Specifically, in the crystal structure analysis of the electrode head 1 using X-ray diffraction with CuKα1 rays, when the 2θ is measured at 20° to 80°, if only one peak exists in each of the <111>, <200>, <220>, <311>, and <222> directions originating from the NaCl-type structure in the ranges of 30.0° to 37.2°, 34.8° to 43.1°, 50.2° to 62.3°, 59.7° to 74.4°, and 62.7° to 78.5°, then the electrode head 1 is determined to have a single-phase structure. It should be noted that when two or three peaks are observed in any of the ranges of 30.0°~37.2°, 34.8°~43.1°, 50.2°~62.3°, 59.7°~74.4°, or 62.7°~78.5°, it is judged to have multiphase structure.

[0031] The electrode head 1 of this embodiment contains five elements—titanium, zirconium, niobium, hafnium, and tantalum—as a first specific element. Preferably, the electrode head 1 contains a combination of titanium, zirconium, hafnium, and tantalum as the first specific element. As a combination of the first specific elements, the electrode head 1 preferably contains zirconium and hafnium; more preferably, it contains zirconium, hafnium, and tantalum; and even more preferably, it contains zirconium, hafnium, tantalum, and titanium. The concentration of zirconium in the electrode head 1 reaches 8.43 at%, making it resistant to oxidation in an atmosphere containing oxygen plasma. The ceramic sintered body of the electrode head 1 contains yttrium as a second specific element.

[0032] The electrode head 1 in this embodiment contains iron as an unavoidable impurity. In this embodiment, the iron (Fe) content in the electrode head 1 is 800 atppm or less. Alternatively, the iron content in the electrode head 1 can be 0 atppm.

[0033] The electrode head 1 of this embodiment has a single-phase structure with a first specific element dissolved in it, thus forming a dense ceramic sintered body with few pores. The density of the ceramic sintered body is expressed by the calculated relative density, which is calculated using the theoretical density value obtained based on the lattice constant obtained from Rietveld analysis, and the specific gravity and porosity measured according to JISR 1634. The relative density of the electrode head 1 of this embodiment is greater than 97%.

[0034] In the electrode head 1 of this embodiment, the concentration difference between the first specific elements is less than 5 at%, thus easily forming a solid solution single-phase structure. In this embodiment, the concentration difference between the first specific elements is determined based on the results calculated using energy-dispersive X-ray spectroscopy to determine the composition ratio in the grains.

[0035] The head support portion 2 is a bottomed cylindrical member, which can be formed, for example, by machining a copper rod-shaped member. A hole 2b is formed in the bottom 2a of the head support portion 2, and the electrode head 1 is inserted therein. By inserting the electrode head 1 into the hole 2b of the head support portion 2, the plasma generation electrode 10 of this embodiment is completed.

[0036] Next, the manufacturing method of electrode head 1 will be described. As a method for manufacturing electrode head 1, firstly, weighed metal powder and ethanol are added together to a bead mill and mixed and pulverized for 20 hours to prepare a metal powder mixture. The weighed metal powders are titanium carbide powder (average particle size: 1.7 μm), zirconium carbide powder (average particle size: 2.4 μm), niobium carbide powder (average particle size: 1.1 μm), hafnium carbide powder (average particle size: 0.7 μm), and tantalum carbide powder (average particle size: 1.0 μm), each weighed at 20 mol% in the prepared metal powder mixture. Next, 0.4 wt% of zirconium oxide (hereinafter referred to as "3YSZ") partially stabilized with 3 mol% yttrium oxide (Y₂O₃) is added to the metal powder mixture, and the mixture is further mixed and pulverized for 20 hours to prepare a slurry. The prepared slurry is dried using a hot water bath to prepare a dried powder. The dried powder is passed through a sieve with a pore size of 100 μm to obtain granulated powder. The granulated powder is then put into a hot pressing mold and pressed and fired in a vacuum atmosphere at a temperature of 1900℃ and a pressure of 30 MPa to complete electrode head 1.

[0037] Next, we will describe the relevant evaluation tests on the ceramic sintered body used as the electrode head for plasma generation. In this evaluation test, multiple ceramic sintered bodies were fabricated under different fabrication conditions, and the influence of the fabrication conditions on the properties of the ceramic sintered bodies was evaluated.

[0038] Figure 2 Figure 1 illustrates the preparation conditions for the ceramic sintered body sample. Figure 3 Figure 2 illustrates the preparation conditions for the ceramic sintered body samples. In this evaluation experiment, 29 samples (samples 1 to 29) were prepared as ceramic sintered body samples. The preparation conditions for each of samples 1 to 29 are as follows: Figure 2 and Figure 3The document shows the types of "main raw materials" and their respective molar percentages, the types of "additives" and their respective weight percentages, as well as the "firing method," "temperature" (unit: °C), and "pressure" (unit: MPa) as "firing conditions."

[0039] First, the first specific element contained in the ceramic sintered body, namely the "main raw material," will be described. In samples 1 to 29, such as... Figure 2 and Figure 3 As shown, samples 1-21 and 24-29 were prepared using 1-8 materials selected from titanium carbide, vanadium carbide, zirconium carbide, niobium carbide, molybdenum carbide, hafnium carbide, tantalum carbide, and tungsten carbide as "main raw materials". Samples 1-21 and 24-29 were prepared using powders of the "main raw materials" with the average particle sizes shown below.

[0040] Titanium carbide powder: 1.7μm

[0041] Vanadium carbide powder: 1.8μm

[0042] Zirconium carbide powder: 2.4μm

[0043] Niobium carbide powder: 1.1μm

[0044] Molybdenum carbide powder: 1.8μm

[0045] Hafnium carbide powder: 0.7μm

[0046] Tantalum carbide powder: 1.0μm

[0047] Tungsten carbide powder: 1.1μm

[0048] Next, the second specific element contained in the ceramic sintered body, namely the "additional substance," will be explained. For example... Figure 2 and Figure 3 As shown, samples 1-21 and 24-29 used either 3YSZ or alumina (Al2O3) as an "additive". It should be noted that samples 1-21 and 24-29 used powders of the "additive" with the average particle size shown below. It should also be noted that sample 24 used 0.4 wt% zirconium oxide (ZrO2) as an "additive". Details of the raw materials used in the preparation of samples 22 and 23 will be described later.

[0049] 3YSZ: 1.0μm

[0050] Al2O3: 0.3μm

[0051] In the preparation of samples 1-21 and 24-29, the metal powder mixture was prepared in the same manner as that used for electrode head 1. In the preparation of the metal powder mixture, the molar percentage of the "main raw material" in the metal powder mixture was weighed out. Figure 2 or Figure 3 The values ​​shown were added together with ethanol to a ball mill and mixed and pulverized for 20 hours. In sample 25, equal amounts of titanium carbide, vanadium carbide, and niobium carbide were weighed to make the total amount of the main raw materials approximately 100 mol%, and added together with ethanol to a ball mill and mixed and pulverized for 20 hours. In samples 1–21 and 25–29, an amount equivalent to the weight of the prepared metal powder mixture was added. Figure 2 or Figure 3 The amounts of "additives" shown were further mixed and pulverized for 20 hours to prepare a slurry. In sample 24, 0.4 wt% of zirconium oxide, equivalent to the amount of the metal powder mixture, was added as an "additive," and the mixture was further mixed and pulverized for 20 hours to prepare a slurry. In samples 1–21 and 24–29, the prepared slurries were dried in a hot water bath to prepare dried powders. The dried powders were then passed through a sieve with a pore size of 100 μm to obtain granulated powders.

[0052] For the preparation of samples 1-19, 21, and 24-29 among samples 1-21 and 24-29, the following methods were used: Figure 2 and Figure 3 The firing was carried out using the hot pressing (HP) method as shown in the "Firing Method" section of the "Firing Conditions". In the preparation of samples 1-19, 21, and 24-29, the obtained granulated powder was added to a square hot pressing mold with dimensions of 30mm × 30mm, with the sample thickness being 20mm. Figure 2 and Figure 3 Under the "temperature" and "pressure" conditions in the "firing conditions", firing is carried out in a vacuum atmosphere.

[0053] For the preparation of sample 20 among samples 1-21 and 24-29, the following was used: Figure 3 The sample was fired using the Spark Plasma Sintering (SPS) method as described in the "Firing Conditions" section. In the preparation of sample 20, the obtained granulated powder was fed into a 10 mm diameter mold for spark sintering with a sample thickness of 10 mm, and fired in a vacuum atmosphere at a firing temperature of 1900 °C and a pressure of 70 MPa.

[0054] In the preparation of samples 22 and 23, hafnium oxide (HfO2), zirconium oxide (ZrO2), titanium oxide (TiO2), tantalum oxide (Ta2O5), and niobium oxide (Nb2O5), as well as carbon (C), were used as raw materials. Powders of the raw materials having the average particle size shown below were used in the preparation of samples 22 and 23.

[0055] Hafnium oxide powder: 2.0μm

[0056] Zirconia powder: 1.0μm

[0057] Titanium oxide powder: 1.0μm

[0058] Tantalum oxide powder: 3.0μm

[0059] Niobium oxide powder: 1.0μm

[0060] Carbon powder: 5.0μm

[0061] In the preparation of sample 22, the above raw materials were weighed to achieve the composition (HfZrTiTaNb). 0.6 C 0.4 In the preparation of sample 23, the above raw materials were weighed to achieve the composition (HfZrTiTaNb). 0.4 C 0.6 In the preparation of samples 22 and 23, the weighed raw materials were mixed using a ball mill, and the mixed powder was heat-treated in a vacuum atmosphere at a temperature of 1600℃ for 3 hours. Then, the heat-treated powder was put into a square hot-pressing mold with a size of 30mm×30mm, with the sample thickness being 20mm, and sintered in a vacuum atmosphere at a sintering temperature of 1900℃ and a pressure of 30MPa.

[0062] Figure 4 Figure 1 illustrates the characteristics of the sample of the sintered ceramic body. Figure 5 This is Figure 2, illustrating the characteristics of the ceramic sintered body samples. For samples 1-16, Figure 4 The table shows the number of elements belonging to the first specific element and the characteristics obtained through various measurements. For each sample 17–29, Figure 5 The number of elements belonging to the first specific element and the properties obtained through various measurements are shown. Here, for Figure 4 and Figure 5 The method for determining the characteristics of the samples shown is explained. In this evaluation test, mirror-polished samples were used for characteristic determination. It should be noted that, for... Figure 4 and Figure 5 For each characteristic shown, items that were not measured are marked as "-", and items whose measurement results are below the detection limit are marked as "ND".

[0063] Regarding the "degree of single-phase formation," X-ray diffraction using an X-ray diffraction apparatus was employed to identify the crystal phase of the sample, thereby determining whether single-phase formation had occurred. Specifically, similar to the determination method used for electrode head 1, in the analysis of the sample's crystal structure based on X-ray diffraction using CuKα1 rays, if only one peak from each of the <111>, <200>, <220>, <311>, and <222> directions originating from the NaCl-type structure exists in each of the ranges of 30.0°–37.2°, 34.8°–43.1°, 50.2°–62.3°, 59.7°–74.4°, and 62.7°–78.5°, then the sample is considered to have undergone single-phase formation. For samples identified as single-phase, the "relative density" is calculated using the theoretical density value derived from the lattice constant obtained through Rietveld analysis, and the specific gravity and porosity measured according to JIS R1634.

[0064] "Difference in atomic concentration" represents the concentration difference between the first specific elements contained in the sample. "C concentration" represents the concentration of carbon in the sample. Both "difference in atomic concentration" and "C concentration" are calculated based on the composition ratio in the grains using energy-dispersive X-ray spectroscopy.

[0065] "Zr concentration", "Y concentration", "Al concentration", and "Fe concentration" represent the concentrations of zirconium, yttrium, aluminum, and iron in the sample, respectively. In this evaluation experiment, inductively coupled plasma atomic emission spectrometry was used to confirm the presence of yttrium or aluminum in the sample, and the "Zr concentration", "Y concentration", "Al concentration", and "Fe concentration" were measured respectively.

[0066] "Oxidation resistance" was measured using a high-frequency plasma etching apparatus. Specifically, the sample was etched by irradiating it with a high-frequency plasma of 100W for 30 minutes in a reduced oxygen atmosphere with the oxygen content adjusted to 30 Pa. The composition ratio of the etched sample was calculated using energy-dispersive X-ray spectroscopy, and the evaluation was based on the changes in carbon and oxygen content before and after treatment. The evaluation criteria for the sample's "oxidation resistance" are as follows.

[0067] "◎": Carbon reduction of 2 at% or more, or oxygen increase of 4 at% or more.

[0068] "0": Carbon reduction of 3 at% or more, or oxygen increase of 6 at% or more.

[0069] "△": Carbon reduction of 4 at% or more, or oxygen increase of 8 at% or more.

[0070] "×": Carbon reduction of 6 at% or more, or oxygen increase of 10 at% or more.

[0071] "Waste resistance" indicates the degree of consumption when a ceramic sintered body sample is used as an electrode for plasma generation. Specifically, an evaluation electrode was fabricated by machining a ceramic sintered body sample into a diameter of 1 mm × length of 10 mm. This electrode served as the cathode, with the anode grounded and connected to a DC pulse power supply. A plasma discharge of 300 W was conducted for 3 hours in an atmosphere containing a mixture of nitrogen and oxygen. After discharge, the weight reduction of the evaluation electrode was measured, and the consumption amount was calculated. In this evaluation test, the "consumption amount" for samples 1–21 and 25–29 shows a relative value when the consumption amount of sample 20 is set to 100. That is, Figure 4 and Figure 5 The lower the "durability" value shown, the less likely it is to be consumed.

[0072] Figure 4 The samples 1-16 shown all contain 5 or 6 of the first specific elements, indicating that single-phase formation has clearly occurred. Furthermore, the relative density of samples 1-16 is greater than 97%, and the difference in atomic concentration is less than 5 at%. Moreover, the carbon concentration in samples 1-16 is between 45 at% and 55 at%, and the concentration of yttrium or aluminum is less than 3000 atppm.

[0073] Samples 1 through 16 all contain zirconium, such as Figure 4 As shown, the oxidation resistance is indicated by either "◎" or "〇". Therefore, it can be concluded that, as discussed later... Figure 5 Compared to samples 17-29, the samples shown exhibit superior oxidation resistance. A comparison of samples 1-3 and 8-16 with higher zirconium concentrations among samples 1-16 with samples 4-7 with lower zirconium concentrations reveals that samples 1-3 and 8-16 with higher zirconium concentrations show further improved oxidation resistance.

[0074] Samples 1-16 all contained iron as an impurity, but its concentration was below 800 atppm. The wear resistance of samples 1-16 all reached a relatively low value below 40, which is consistent with... Figure 5 Compared to samples 17-29, the samples shown are less prone to consumption. A comparison of samples 1-3 and 8-16 (with lower iron concentrations) with samples 4-7 (with higher iron concentrations) shows that samples 1-3 and 8-16 (with lower iron concentrations) exhibit further improved resistance to consumption.

[0075] Figure 5 Samples 17–29 are inferior to samples 1–16 in terms of oxidation resistance and wear resistance. Here, the differences between the characteristics of samples 17–29 and those of samples 1–16 will be explained.

[0076] Sample 17 was fired at 1700°C, a lower firing temperature than samples 1–16 (refer to...). Figure 3 No single-phase formation occurred. Therefore, sample 17 has low oxidation resistance, and oxidation is likely to occur when used as a plasma generation electrode for generating oxygen plasma. Consequently, the lifespan of sample 17 as a plasma generation electrode may be shortened.

[0077] Sample 18 was pressurized at 10 MPa during firing, a lower pressure than that of samples 1–16 (refer to...). Figure 3 Therefore, compared to samples 1-16, sample 18 has more pores and a lower relative density. Consequently, sample 18 is prone to heating due to resistance, and its lifespan as an electrode for plasma generation may be shorter.

[0078] Sample 19 uses only hafnium carbide as the "main raw material" (see reference). Figure 3 In an oxygen atmosphere, hafnium carbide is easily oxidized even at relatively low temperatures, therefore its oxidation resistance is rated as "×". Furthermore, hafnium carbide is a high-melting-point material and is therefore difficult to sinter using hot pressing (see reference). Figure 3 Sample 19, made from a sample with numerous pores and relatively low density, cannot be densely formed. Therefore, sample 19 has low durability and is easily consumed.

[0079] Similar to sample 19, sample 20 uses only hafnium carbide as the "main raw material," but it is manufactured using the "SPS (Electrically Sintered Pulsed) method" (see reference). Figure 3 Therefore, sample 20 is formed more densely than sample 19, with a higher relative density, thus improving its wear resistance compared to sample 19. However, as mentioned above, since hafnium carbide is easily oxidized, its oxidation resistance is "×".

[0080] The composition of sample 21 is (Hf 0.1 Zr 0.225 Ti 0.225 Ta 0.225 Nb 0.225 C. Thus, the atomic concentration difference is 6.5 at%, which is higher than the upper limit of the atomic concentration difference (5 at%) for samples 1 to 16. When the atomic concentration difference is greater than 5 at%, it is difficult to form a solid solution single-phase structure. Therefore, when used as a plasma generation electrode for generating oxygen plasma, oxidation is easy to occur, and the lifespan of the plasma generation electrode may be shortened.

[0081] Sample 22 was formed using an oxide of the first specific element and carbon as raw materials, with the composition (HfZrTiTaNb). 0.6 C 0.4The carbon concentration in sample 22 is 42.5 at%, which is lower than the lower limit of carbon concentration (45 at%) for samples 1–16. Therefore, a metallic phase of the first specific element readily precipitates in sample 22. The melting point of the metallic phase is lower than that of the carbide, so it easily melts at the temperature at which it is used as an electrode for plasma generation. Therefore, the lifespan of the electrode for plasma generation may be shortened.

[0082] Sample 23 was formed using an oxide of the first specific element and carbon as raw materials, with the composition (HfZrTiTaNb). 0.4 C 0.6 The carbon concentration in sample 23 was 57.2 at%, higher than the upper limit (55 at%) for samples 1–16. Therefore, free carbon easily precipitates out, and when used as an electrode for plasma generation, the temperature of the electrode itself rises due to the increased discharge initiation voltage, making it prone to melting. Consequently, the lifespan of the electrode as a plasma generator may be shortened.

[0083] Sample 24 was prepared using zirconium oxide instead of 3YSZ or Al2O3 as an additive. Therefore, Sample 24 does not contain yttrium or aluminum. When yttrium and aluminum are not present, the electrode used for plasma generation becomes more prone to melting due to the increased discharge initiation voltage, which may shorten its lifespan.

[0084] Sample 25 has the composition (TiNbV)C. That is, unlike samples 1-16, which contain 5 or 6 elements of the first specific element, sample 25 contains 3 elements. Furthermore, the iron concentration in sample 25 is 1340 atppm%, which is higher than the upper limit of iron concentration (800 atppm) for samples 1-16. When the iron concentration exceeds 800 atppm, coarse iron-based particles tend to precipitate. Iron-based particles have low melting points and easily melt at the temperature used as electrodes for plasma generation. Therefore, the lifespan of the electrode used for plasma generation may be shortened.

[0085] Sample 26 has the composition (HfTiTaNbVWMo)C. That is, unlike samples 1 to 16, which have 5 or 6 elements of the first specific element, sample 26 has 7 elements, and no single-phase formation has occurred. Therefore, similar to sample 17, when sample 26 is used as the plasma generation electrode for generating oxygen plasma, oxidation is easy to occur, and the lifetime of the plasma generation electrode may be shortened.

[0086] Sample 27 has the composition (HfZrTiTaNbVWMo)C. That is, unlike samples 1 to 16, which have 5 or 6 elements of the first specific element, sample 27 has 8 elements, and no single-phase formation has occurred. Therefore, similar to sample 26, when sample 27 is used as the plasma generation electrode for generating oxygen plasma, oxidation is easy to occur, and the lifetime of the plasma generation electrode may be shortened.

[0087] 1.5 wt% of 3YSZ was added to sample 28 as an additive (refer to...). Figure 3 Therefore, the yttrium concentration in sample 28 reached 3958 atppm, exceeding the upper limit of yttrium concentration (3000 atppm) for samples 1–16. Sample 29 contained 0.3 wt% alumina as an additive (see reference). Figure 3 Therefore, the aluminum concentration in sample 29 reached 4013 atppm, higher than the upper limit of aluminum concentration (3000 atppm) for samples 1-16. When the concentration of yttrium or aluminum exceeds 3000 atppm, yttrium and aluminum tend to precipitate at the grain boundaries of the ceramic sintered body, and the concentration of elements contained in the solid solution single-phase structure is prone to deviation. Therefore, when used as a plasma generation electrode for generating oxygen plasma, oxidation is easily carried out, and the lifespan of the plasma generation electrode may be shortened.

[0088] The zirconium concentration in sample 28 was 18.08 at%, higher than the 15 at% concentration in samples 1–16. When the zirconium concentration in the ceramic sintered body exceeds 15 at%, a multiphase structure containing zirconium is formed, and the concentration distribution of the first specific element within the particles of the single-phase structure becomes uneven. Therefore, when used as a plasma generation electrode for generating oxygen plasma, oxidation is easily carried out, and the lifespan of the plasma generation electrode may be shortened.

[0089] In plasma cutting machines or surface treatment devices, high-melting-point metals such as hafnium, zirconium, and tungsten are sometimes used as electrodes for plasma generation. However, due to the high plasma arc current causing heat generation of the electrodes themselves, and oxidation caused by the type of plasma gas such as oxygen, the electrodes are easily consumed, potentially shortening their lifespan. Therefore, hafnium carbide, with its higher melting point, is sometimes used as the electrode material for plasma generation. However, as explained for samples 19 and 20 above, hafnium carbide is easily oxidized even at low temperatures in an oxygen atmosphere, raising concerns that oxidation in an oxygen-containing plasma atmosphere could reduce its lifespan. Furthermore, hafnium carbide is difficult to sinter; therefore, obtaining large-sized sintered bodies requires high voltage, and only by using an electric current sintering method, which increases equipment and manufacturing costs, can a dense sintered body be obtained. Additionally, electric current sintering makes uniform sintering difficult and results in low shape freedom.

[0090] The ceramic sintered body of the electrode head 1 in this embodiment includes: titanium, zirconium, niobium, hafnium, and tantalum as first specific elements; yttrium as a second specific element; and carbon. By forming a solid solution that monolithically comprises the five first specific elements, oxidation can be suppressed even in an atmosphere containing, for example, oxygen plasma. Furthermore, since the first specific elements include elements with lower melting points than hafnium carbide, a dense ceramic sintered body can be produced even using sintering methods such as hot pressing. Therefore, the ceramic sintered body of the electrode head 1 in this embodiment can have a complex shape while reducing device and manufacturing costs. Moreover, compared to hafnium or hafnium carbide, the lifespan of the electrode head 1 can be extended.

[0091] The ceramic sintered body of the electrode head 1 described above has a single-phase structure in which a first specific element is dissolved in solid solution. The first specific element is composed of five or six elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten. This improves the oxidation resistance of the ceramic sintered body of the electrode head 1.

[0092] Furthermore, in the ceramic sintered body of the electrode head 1 in this embodiment, the first specific element includes zirconium. As a result, the strain of the lattice of the single-phase structure in which the first specific element is dissolved increases. Therefore, the ceramic sintered body of the electrode head 1 becomes less susceptible to oxidation, thus further improving the oxidation resistance of the ceramic sintered body.

[0093] Furthermore, in the ceramic sintered body of the electrode head 1 of this embodiment, the concentration of iron is 800 atppm or less, thus suppressing the precipitation of coarse iron-based particles. Consequently, melting of the ceramic sintered body as the temperature rises is suppressed, thereby preventing weight loss due to use. Therefore, the lifespan of the electrode head 1 can be extended.

[0094] Furthermore, the electrode head 1 of this embodiment includes a ceramic sintered body, which has a single-phase structure in which a first specific element is dissolved in solid solution. The first specific element is composed of five or six elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten. This improves the oxidation resistance of the electrode head 1, thereby extending the lifespan of the plasma generating electrode.

[0095] Furthermore, the electrode head 1 in this embodiment is manufactured by hot pressing. As a result, compared with plasma generating electrodes made of hafnium or hafnium carbide manufactured by electro-sintering, the electrode head 1 can have a complex shape while reducing device cost and manufacturing cost.

[0096] <Modifications of this embodiment>

[0097] This invention is not limited to the above-described embodiments and can be implemented in various ways without departing from its spirit, for example, the following modifications can be made.

[0098] [Variation Example 1]

[0099] In the above embodiment, the ceramic sintered body of the electrode head 1 includes five elements—titanium, zirconium, niobium, hafnium, and tantalum—as the first specific element. It is sufficient to include five or six elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten.

[0100] [Variation Example 2]

[0101] In the above embodiment, the electrode head 1 contains a combination of titanium, zirconium, hafnium, and tantalum as a first specific element. However, the preferred combination of the first specific element is not limited to this. A combination of zirconium, hafnium, and tantalum is also preferred, and a combination of hafnium and tantalum can further improve the oxidation resistance of the electrode head 1.

[0102] [Variation Example 3]

[0103] In the above embodiment, the concentration of zirconium in the electrode head 1 is 8.43 at%. However, the first specific element included in the electrode head 1 to improve its oxidation resistance is not limited to zirconium. Hafnium, tantalum, titanium, etc., can be included instead of zirconium, thereby improving the oxidation resistance of the electrode head 1.

[0104] [Variation Example 4]

[0105] In the above embodiment, the iron (Fe) content in the ceramic sintered body of the electrode head 1 is 800 atppm or less. The iron content can also be greater than 800 atppm, but if the iron concentration increases, the precipitated iron particles will melt, leading to a shorter lifespan. Therefore, a lower iron concentration is preferred. In measurements using an inductively coupled plasma atomic emission spectrometry (ICP-AES) analyzer, the iron concentration can also be below the measurement limit.

[0106] [Variation Example 5]

[0107] The ceramic sintered body described in the above embodiment is included in the electrode head 1. The technical field of applying the ceramic sintered body is not limited to this. It can also be used in technical fields requiring oxidation resistance and wear resistance.

[0108] The present invention has been described above based on embodiments and variations. However, the embodiments described above are for the purpose of facilitating understanding of the present invention and are not intended to limit the present invention. The present invention can be modified and improved without departing from its spirit and claims, and equivalent solutions are included in the present invention. Furthermore, if a technical feature is not described as an essential feature in this specification, it may be appropriately deleted.

[0109] <Application Example 1>

[0110] A ceramic sintered body, characterized in that it comprises:

[0111] The first specific element is composed of five or six elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W);

[0112] The second specific element consists of one element selected from yttrium (Y) and aluminum (Al); and

[0113] Carbon (C)

[0114] The total content of the aforementioned first specific element, the aforementioned second specific element, and carbon in the aforementioned ceramic sintered body is 98 at% or more.

[0115] The aforementioned second specific element contained in the aforementioned ceramic sintered body is below 3000 atppm.

[0116] The carbon content in the aforementioned ceramic sintered body is between 45 at% and 55 at%.

[0117] The aforementioned ceramic sintered body has a single-phase structure with the aforementioned first specific element dissolved in it.

[0118] <Application Example 2>

[0119] The ceramic sintered body according to Application Example 1 is characterized in that,

[0120] The first specific element mentioned above includes zirconium.

[0121] <Application Example 3>

[0122] The ceramic sintered body according to Application Example 1 or Application Example 2 is characterized in that,

[0123] The iron (Fe) content in the aforementioned ceramic sintered body is below 800 atppm.

[0124] <Application Example 4>

[0125] An electrode for generating plasma, comprising a ceramic sintered body as described in any one of Application Examples 1 to 3.

Claims

1. A ceramic sintered body, characterized in that, It includes: The first specific element is composed of five or six elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W). The second specific element, which consists of one element selected from yttrium (Y) and aluminum (Al); and Carbon element C, The total content of the first specific element, the second specific element, and carbon in the sintered ceramic body is 98 at% or more. The second specific element contained in the ceramic sintered body is below 3000 atppm. The carbon content in the sintered ceramic body is more than 45 at% and less than 55 at%. The sintered ceramic body has a single-phase structure in which the first specific element is dissolved.

2. The ceramic sintered body according to claim 1, characterized in that, The first specific element includes zirconium.

3. The ceramic sintered body according to claim 1 or 2, characterized in that, The iron (Fe) content in the sintered ceramic body is below 800 atppm.

4. An electrode for generating plasma, comprising a ceramic sintered body according to any one of claims 1 to 3.

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