Slurry for plasma spraying, method for producing sprayed film, aluminum oxide sprayed film, and sprayed member

Abstract

SOLUTION: To manufacture a spray coating film through plasma spray coating by using slurry for plasma spray coating that contains 20-80 mass% of aluminum oxide particles of 15 μm or less in maximum particle size (D100), includes one or two kinds or more selected between water and an organic solvent as a dispersant, and is 90% or less in supernatant transmissivity at a room temperature after being put in a 1 L container of 193 mm by 700 mL and left as it is for 168 hours.EFFECT: Slurry for plasma spray coating according to the present invention is used to stably form, on a base material, a spray coating film which has a low porosity, a sufficient film thickness, and small variation in electric resistance per volume with temperature, and includes aluminum oxide, and a spray coating member comprising such a spray coating film is useful for an electrostatic chuck.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a slurry for plasma spraying containing aluminum oxide, a method for producing a sprayed film using the slurry for plasma spraying, an aluminum oxide sprayed film, and a sprayed member. [Background technology]

[0002] Aluminum oxide has a wide range of applications due to its high electrical insulation and ability to form highly hard films and sintered bodies. For example, in the case of electrostatic chucks used in semiconductor manufacturing equipment, a conventional method has been to use a ceramic spray material made of a binary aluminum oxide / titanium oxide system formed by atmospheric plasma spraying (Patent Document 1: JP 2008-277862 A). However, the porosity of the sprayed film is high, ranging from 5% to 15% (Patent Document 2: JP 2014-156651 A). This results in a porous surface, which increases the specific surface area. Depending on the operating environment, this can accelerate deterioration due to corrosion of the dielectric layer.

[0003] Recently, with improvements in coating technologies such as thermal spraying, coatings that are close to sintered bodies have been developed, and in order to solve the above problems, coatings using the aerosol deposition method (AD method) and suspension plasma spraying method (SPS method) have been proposed.

[0004] For example, in the suspension plasma spraying method, by using particles with an average particle size D50 of 1 μm or more and 5 μm or less as a slurry for spraying, it has become possible to obtain a rare earth oxyfluoride coating with a porosity of 1% or less and a film thickness of approximately 100 μm (Patent Document 3: International Publication No. 2018 / 012454).

[0005] This rare earth oxyfluoride film has a thickness of about 100 μm. However, when applied to an electrostatic chuck, it is desirable for the film to be as thick as possible in order to ensure insulation against the voltage applied to attract the substrate (Patent Document 4: JP 2007-251124 A), and therefore an aluminum oxide film having a thickness exceeding 100 μm has been desired.

[0006] Furthermore, when applied to electrostatic chucks, in order to suppress fluctuations in electrical stress that occur when the temperature rises during etching processing, an aluminum oxide film is required that is not only thick but also has small temperature-dependent changes in electrical resistance. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-277862 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-156651 [Patent Document 3] International Publication No. 2018 / 012454 [Patent Document 4] Japanese Patent Application Laid-Open No. 2007-251124 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above-mentioned problems, and has an object to provide a slurry for plasma spraying that can produce an aluminum oxide coating that has low porosity, a sufficient film thickness, and little change in electrical resistance per volume with temperature, a method for producing a sprayed film using the slurry for plasma spraying, an aluminum oxide sprayed film, and a sprayed member. [Means for solving the problem]

[0009] As a result of extensive research into solving the above-mentioned problems, the present inventors have found that when 700 mL of a thermal spray slurry containing 20% ​​by mass or more and 80% by mass or less of aluminum oxide having a maximum particle size (D100) of 15 μm or less and using one or more dispersion media selected from water and organic solvents is placed in a 1 L container with a height of 193 mm and left to stand at room temperature for 168 hours, and the supernatant is collected, the transmittance of the supernatant is 90% or less, and the obtained slurry provides an excellent thermal sprayed component having an aluminum oxide thermal sprayed film on a substrate, which led to the present invention.

[0010] Therefore, the present invention provides the following slurry for plasma spraying, method for producing a sprayed film, aluminum oxide sprayed film, and sprayed member. 1. A slurry for plasma spraying, characterized in that it contains 20% by mass or more and 50% by mass or less of aluminum oxide particles with a maximum particle size (D100) of 12 μm or less, and 0.1% by mass or more and 3% by mass or less of one or more fine particle additives selected from rare earth oxides, aluminum oxide, and titanium oxide, which have an average particle size D50 of 0.3 μm or less, and uses one or more dispersion media selected from water and organic solvents, and when 700 mL of the slurry is placed in a 1 L container with a height of 193 mm and left to stand at room temperature for 168 hours, the transmittance of the supernatant is 90% or less. 2. A slurry for plasma spraying according to 1, characterized in that the aluminum oxide particles have an average particle diameter D50 of 2 μm or more and 8 μm or less, a crystallite size of 350 nm or more and 600 nm or less, and the aluminum oxide particles have an α-type aluminum oxide crystal structure. 3. A slurry for plasma spraying according to 2, wherein the aluminum oxide particles have an average particle size D50 of 5 μm or less. 4. A slurry for plasma spraying according to any one of 1 to 3, characterized in that the rare earth is one or more selected from the group consisting of yttrium (Y), gadolinium (Gd), holmium (Ho), erbium (Er), ytterbium (Yb), and lutetium (Lu). 5. A method for producing a thermal sprayed film, characterized by using a slurry for plasma thermal spraying according to any one of 1 to 4. 6. The method for producing a thermal sprayed film according to 5, characterized in that atmospheric thermal spraying is used. 7. The porosity is 1% or less, the film thickness is 100 μm or more, and (Volume resistivity at 23°C) / (Volume resistivity at 200°C) An aluminum oxide sprayed film characterized in that the value of the temperature variable represented by the formula (1) is 1 or more and 20 or less. 8 .7 A thermally sprayed member comprising the thermally sprayed film according to claim 1. 9. The thermally sprayed member according to 8, which is an electrostatic chuck. [Effects of the Invention]

[0011] By using the slurry for plasma spraying of the present invention, it is possible to stably form a sprayed film containing aluminum oxide on a substrate, which has low porosity, a sufficient film thickness, and little change in electrical resistance per volume with temperature, and a sprayed member having such a sprayed film is useful for an electrostatic chuck. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is an X-ray diffraction chart of the aluminum oxide particles of Example 1. [Figure 2] 1 is an X-ray diffraction chart of the thermal sprayed film of Example 1. [Figure 3] 1 shows the distribution of gray values ​​in a cross-sectional image of a thermal sprayed film. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in further detail below. In the present invention, aluminum oxide particles are sprayed as a slurry. The slurry of the present invention contains aluminum oxide particles. The maximum particle size (D100 (D100 in the present invention is the maximum particle size in the volume-based particle size distribution)) of the aluminum oxide particles is preferably 15 μm or less, more preferably 12 μm or less. If D100 exceeds 15 μm, clogging may occur between the slurry supply device and the thermal spray gun. The slurry of the present invention preferably does not contain particles with a particle size exceeding 15 μm. The content of aluminum oxide particles in the slurry of the present invention is preferably 20 mass% or more, more preferably 25 mass% or more, even more preferably 30 mass% or more, and preferably 80 mass% or less, more preferably 60 mass% or less, even more preferably 50 mass% or less.

[0014] The average particle diameter D50 of the aluminum oxide particles (D50 in the present invention is the cumulative 50% diameter (median diameter) in the volume-based particle diameter distribution) is preferably 2 μm or more, particularly 3 μm or more, and is preferably 8 μm or less, particularly preferably 5 μm or less.

[0015] The specific surface area (BET specific surface area) of aluminum oxide particles is 3m 2 / g or less, especially 1m 2 The lower limit of the specific surface area (BET specific surface area) of the aluminum oxide particles is not particularly limited, but is preferably 0.1 m 2 / g or more is preferred.

[0016] The crystalline structure of the aluminum oxide particles contained in the slurry of the present invention is preferably the α-type. Although there are other crystalline phases of aluminum oxide besides the α-type, such as the η-type, κ-type, δ-type, χ-type, γ-type, and θ-type, the high-temperature α-type is preferred because it has good stability in the slurry.

[0017] Furthermore, the crystallite size of the aluminum oxide particles, determined using the WPPD (Whole Powder Pattern Decomposition) method of X-ray diffraction in the 2θ range of 10° to 70°, is preferably 350 nm or more, more preferably 400 nm or more, and is preferably 600 nm or less, more preferably 500 nm or less.

[0018] Regarding the settling of particles contained in the slurry, when 700 mL of the slurry of the present invention is placed in a 1 L container having a height of 193 mm, such as a polypropylene container, and allowed to stand at room temperature for 168 hours, the transmittance of the supernatant liquid is preferably 90% or less, and more preferably 80% or less.

[0019] The slurry of the present invention contains a large number of minute spray particles, and as a result, although not particularly limited, it is presumed that a thick, dense sprayed coating can be stably produced.

[0020] The dispersion medium for the slurry is one or more selected from water and organic solvents. The dispersion medium may be water alone, a mixture of water and an organic solvent, or an organic solvent alone. The organic solvent is preferably selected taking into consideration its toxicity and environmental impact, and examples include alcohols, ethers, esters, and ketones. More specifically, preferred organic solvents include monohydric or dihydric alcohols having 2 to 6 carbon atoms, ethers having 3 to 8 carbon atoms such as ethyl cellosolve, glycol ethers having 4 to 8 carbon atoms such as dimethyl diglycol (DMDG), glycol esters having 4 to 8 carbon atoms such as ethyl cellosolve acetate and butyl cellosolve acetate, and cyclic ketones having 6 to 9 carbon atoms such as isophorone. From the standpoints of flammability and safety, water-soluble organic solvents that can be mixed with water are particularly preferred.

[0021] The slurry of the present invention may contain one or more particulate additives selected from rare earth oxides, aluminum oxide (preferably α-type aluminum oxide), and titanium oxide. The average particle size (D50 (volume basis)) of the particulate additive is preferably 0.3 μm or less, more preferably 0.2 μm or less. The content of the particulate additive in the slurry is preferably 3 mass% or less, particularly preferably 1 mass% or less, and more preferably 0.1 mass% or more, particularly preferably 0.2 mass% or more.

[0022] In the present invention, the rare earth element is preferably one or more selected from yttrium (Y), gadolinium (Gd), holmium (Ho), erbium (Er), ytterbium (Yb), and lutetium (Lu). The rare earth element preferably includes any of yttrium, gadolinium, ytterbium, and lutetium, and more preferably the rare earth element is composed of only yttrium, or yttrium as the main component (e.g., 90 mol % or more), with the balance being ytterbium or lutetium.

[0023] The specific surface area (BET specific surface area) of the particulate additive is preferably 80 m 2 / g or less, more preferably 60m 2 The lower limit of the specific surface area (BET specific surface area) of the particulate additive is not particularly limited, but is preferably 1 m 2 / g or more.

[0024] The slurry of the present invention may contain an anti-aggregation agent composed of an organic compound, particularly a water-soluble organic compound, to prevent aggregation of aluminum oxide particles. Surfactants and the like are suitable as anti-aggregation agents. Because aluminum oxide has a positive zeta potential, anionic surfactants are preferred, and polyethyleneimine-based anionic surfactants and polycarboxylic acid polymer-based anionic surfactants are particularly preferred. When the dispersion medium contains water, anionic surfactants are preferred, but when the dispersion medium is an organic solvent only, nonionic surfactants can also be used. The content of the anti-aggregation agent in the slurry is preferably 3% by mass or less, particularly 1% by mass or less, and more preferably 0.01% by mass or more, particularly 0.03% by mass or more.

[0025] The slurry of the present invention can be produced by mixing predetermined amounts of aluminum oxide particles and a dispersion medium, and, if necessary, other components such as an anti-agglomerating agent and particle additives. In particular, to avoid excessive pulverization of solid components such as aluminum oxide particles, it is preferable to use, for example, a resin ball mill and resin balls (e.g., 10 mmφ or larger). In this case, the mixing time can be, for example, 1 hour or more and 6 hours or less. Furthermore, in order to break down agglomerated particles and remove impurities, it is effective to pass the mixed slurry through a sieve of 500 mesh (openings 25 μm) or smaller.

[0026] The slurry of the present invention is suitable for plasma spraying in an atmosphere containing an oxygen-containing gas, particularly for atmospheric suspension plasma spraying in which plasma is formed in the atmosphere. In the present invention, atmospheric suspension plasma spraying refers to a case in which the ambient gas in which plasma is formed is the atmosphere. The pressure in the field in which plasma is formed may be normal pressure such as atmospheric pressure, or may be pressurized or reduced pressure. Furthermore, HVOF spraying may also be used.

[0027] The substrate is selected from stainless steel, aluminum, nickel, chromium, zinc and alloys thereof, alumina, aluminum nitride, silicon nitride, silicon carbide, quartz glass, etc., and is appropriately selected depending on the application of the thermal sprayed member.

[0028] The plasma gas for forming the plasma is preferably a mixed gas of two or more gases selected from argon gas, hydrogen gas, helium gas, and nitrogen gas, and particularly preferably a mixed gas of two gases consisting of argon gas and nitrogen gas, a mixed gas of three gases consisting of argon gas, hydrogen gas, and nitrogen gas, or a mixed gas of four gases consisting of argon gas, hydrogen gas, helium gas, and nitrogen gas.

[0029] Specifically, the spraying operation involves, for example, first filling a slurry containing aluminum oxide particles into a slurry supply device, and then using a piping (powder hose) to supply the slurry of the present invention to the tip of the plasma spray gun with a carrier gas (usually argon gas).

[0030] The piping preferably has an inner diameter of 2 mm to 6 mm. By providing a sieve of 500 mesh (opening 25 μm) or less, preferably 100 mesh (opening 149 μm) at any point in the piping, for example, at the slurry supply port to the piping, clogging of the piping and the plasma spray gun can be prevented.

[0031] The thermal sprayed film can be formed by scanning a predetermined area on the substrate surface using an automated machine (robot) or by hand while moving the liquefied flame left and right or up and down along the substrate surface. The thickness of the thermal sprayed film is preferably 100 μm or more, more preferably 150 μm or more, and preferably 300 μm or less, more preferably 250 μm or less.

[0032] There are no particular limitations on the spraying conditions for suspension plasma spraying, such as spraying distance, current value, voltage value, gas type, and gas supply rate, and conventionally known conditions can be applied and may be appropriately set depending on the substrate, the slurry containing aluminum oxide particles, the application of the resulting sprayed member, etc. Alternatively, a layer of a rare earth oxide, rare earth fluoride, rare earth oxyfluoride, or the like having a thickness of about 50 μm to 300 μm may be formed on the substrate as a base film by, for example, atmospheric plasma spraying or atmospheric suspension plasma spraying at normal pressure, and then the sprayed film of the present invention may be formed thereon.

[0033] The thermal sprayed film of the present invention is an oxide thermal sprayed film, and this oxide is an oxide consisting of aluminum oxide when the slurry contains only aluminum oxide, or an oxide consisting mainly of aluminum oxide with small amounts of components derived from the particulate additives (such as oxides or composite oxides of rare earth elements or titanium) when the slurry contains rare earth oxides or titanium oxide as particulate additives. In the present invention, the oxide constituting the aluminum oxide thermal sprayed film includes both oxides consisting of aluminum oxide and oxides consisting mainly of aluminum oxide with small amounts of components derived from the particulate additives. The aluminum oxide thermal sprayed film of the present invention has a porosity of 1% or less, and a temperature variable of volume resistivity, calculated by dividing the volume resistivity at 23°C by the volume resistivity at 200°C, of ​​1 or more and 20 or less, showing low temperature dependence of volume resistivity, making it useful for electrostatic chucks.

[0034] To use a sprayed member having the sprayed coating of the present invention as an electrostatic chuck, a sufficient electrostatic adsorption force can be obtained by reducing the surface roughness. If the electrostatic adsorption force cannot be obtained due to high surface roughness, polishing the surface of the sprayed coating is also effective. To facilitate surface polishing, a small surface roughness is preferable, and a surface roughness Ra of 3.5 μm or less is preferred.

[0035] Aluminum oxide ceramics are known to have high hardness and excellent wear resistance. Similarly, it is preferable that the thermally sprayed aluminum oxide film also has high hardness, with a Vickers hardness of 700 HV or more being preferred. [Example]

[0036] EXAMPLES The present invention will be specifically explained below by showing examples and comparative examples, but the present invention is not limited to the following examples.

[0037] [Examples 1 to 4, Comparative Example 1] [Production of Slurries for Thermal Spraying in Examples 1 to 4 and Comparative Example 1] For Examples 1 to 4, aluminum oxide particles (α-type aluminum oxide particles), a particulate additive, and an anti-agglomerating agent (surfactant) were weighed in the proportions shown in Table 1, and then a dispersion medium was prepared so as to achieve the contents shown in Table 1. These were placed in a nylon pot containing 15 mmφ nylon balls and mixed for approximately 6 hours, and the resulting mixture was passed through a 500 mesh (25 μm) sieve to obtain a slurry containing aluminum oxide particles. The thermal spray slurry of Comparative Example 1 was produced in the same manner as Example 1, except that the D50, D100, BET specific surface area, and crystallite size of the aluminum oxide particles used were different, and no particulate additive was used.

[0038] [Production of Thermal Sprayed Films (Thermal Sprayed Members) of Examples 1 to 4 and Comparative Example 1] The thermal spray coating (thermal sprayed component) was produced by degreasing the surface of a 100 mm square (5 mm thick) A5052 aluminum alloy substrate with acetone, roughening one side of the substrate using corundum abrasive (#60), and then using the thermal spraying conditions shown in Table 2.

[0039] [Evaluation of Slurry for Thermal Spraying] The evaluation results of the thermal spraying slurry are shown in Table 1.

[0040] (Measurement of particle size) The D100 and D50 values ​​of the aluminum oxide particles and the D50 values ​​of the particulate additive used in the thermal spray slurries of Examples 1 to 4 and Comparative Example 1 were measured by laser diffraction using a particle size distribution analyzer MT-3300 manufactured by Microtrac after preparing slurries by adding the aluminum oxide particles and the particulate additive to pure water and subjecting the prepared slurries to ultrasonic treatment at 40 W for 1 minute.

[0041] (BET specific surface area measurement) The specific surface areas of the aluminum oxide particles and the fine particle additives used in the slurries for thermal spraying in Examples 1 to 4 and Comparative Example 1 were measured using a fully automatic specific surface area measuring device, Macsorb HM model-1280, manufactured by Mountec Co., Ltd.

[0042] (X-ray diffraction measurement and crystallite size measurement) The X-ray diffraction of the aluminum oxide particles used in the slurries for thermal spraying in Examples 1 to 4 and Comparative Example 1 was measured using an X-ray diffractometer (PANalytical, X-Part Pro MPD, CuK α The crystallite size was calculated from the X-ray diffraction measurement results obtained using the WPPD (Whole Powder Pattern Decomposition) method at 2θ = 10° to 70°. Figure 1 shows the X-ray diffraction measurement results for the aluminum oxide particles of Example 1.

[0043] (Turbidity and transmittance measurements) The thermal spray slurries of Examples 1 to 4 and Comparative Example 1 were stirred and dispersed until uniform, and then 700 mL of each was filled into a 1 L container (Kenis Co., Ltd., JK-PP bottle, wide mouth, 1000 mL) with a height of 193 mm and allowed to stand for 168 hours. The turbidity of the supernatant was then measured midway between the bottom of the container and the slurry surface. The turbidity was measured using a digital turbidity meter TBD700 manufactured by AS ONE Corporation.

[0044] For transmittance measurements, the samples were left to stand for 168 hours, as in the turbidity measurements, and then the supernatant liquid was collected from the middle between the bottom of the container and the slurry surface into a quartz cell. Transmittance measurements were performed using a PerkinElmer LAMBDA 750 (light source D2 tungsten) spectrophotometer at wavelengths of 250 nm to 850 nm, with a data interval of 1 nm and a scan speed of 256.75 nm / min. The transmittance at a wavelength of 550 nm was then read from the results.

[0045] [Evaluation of thermal sprayed coating] The evaluation results of the thermal sprayed coating are shown in Table 3.

[0046] (X-ray diffraction measurement) The sprayed film was scraped off from the obtained sprayed member and analyzed by X-ray diffraction. For X-ray diffraction, an X-ray diffractometer (PANalytical, X-Part Pro MPD, CuK α 2 shows the results of X-ray diffraction measurement of the thermal sprayed coating of Example 1.

[0047] (Measurement of the thickness of thermal sprayed coating) The thickness of the resulting coating was measured using an eddy current type coating thickness meter (LH-300 model, manufactured by Kett).

[0048] (Measurement of surface roughness Ra of thermal spray coating) The surface roughness Ra of the resulting sprayed film was measured using a surface roughness measuring instrument HANDYSURF E-35A manufactured by Tokyo Seimitsu Co., Ltd.

[0049] (Measurement of Vickers hardness of thermal spray coating) The hardness of the sprayed coating surface was measured 10 times using a micro Vickers hardness tester HMV-G31-XY-S manufactured by Shimadzu Corporation under measurement conditions of HV0.1 (980.7 mN) and 10 seconds hold, and the average value was used as the measured value.

[0050] (Measurement of porosity of thermal sprayed coating) A test piece of the thermal sprayed material was embedded in resin, and a cross section was cut out. The cross section was mirror-finished (Ra = 0.1 μm), and then a cross-sectional image (magnification: 200x) was taken using a scanning electron microscope (SEM). Ten fields of view (photographed area of ​​one field: 0.017 mm) were taken. 2 After photographing the specimen, the images were processed using the image processing software "Photoshop" (Adobe Systems Incorporated), and the porosity was quantified using the image analysis software "Scion Image" (Scion Corporation). The average porosity over 10 fields of view was evaluated as a percentage of the total image area.

[0051] Cross-sectional images taken with an electron microscope are backscattered electron images and are displayed in 8-bit grayscale. The cross-sectional image expresses the light intensity (gray value) for each pixel in 256 levels, ranging from 0 (absolute no light: black) to 255 (maximum light output). In the cross-sectional image of the sprayed coating, the void areas are closer to black than the entire sprayed coating, and have a relatively low gray value. The distribution of gray values ​​in the cross-sectional image of the sprayed coating is shown in Figure 3.

[0052] A threshold was determined for the cross-sectional image of the sprayed coating and binarized. The gray value of the void area was converted to 0, and the gray value of the entire sprayed coating was converted to 255. The ratio of the total number of pixels in the void area to the total number of pixels in the cross-sectional image was defined as the porosity.

[0053] If the threshold value is fixed in the binarization process, it is difficult to properly separate voids because the brightness and contrast vary from image to image. Therefore, it is necessary to determine the threshold value according to the brightness and contrast. In general image binarization methods, the threshold value is determined by focusing on the valleys that appear in the gray value distribution, but this assumes that the gray value distribution is bimodal. However, as shown in Figure 3, the gray values ​​of thermal spray coatings have a unimodal distribution, so general image binarization methods cannot be applied.

[0054] In this invention, to quantify brightness and contrast, the distribution of gray values ​​was approximated by a normal distribution expressed by the following formula. x is the gray value, y is the number of pixels, a is the maximum value of the normal distribution, b is the gray value at the maximum value, and c is the width of the normal distribution. Fitting was performed using the nonlinear least squares method, and the gray value x was varied from 0 to 255. The fitting parameters a, b, and c that minimized the residual sum of squares of the number of pixels y were numerically analyzed using an iterative method. The initial values ​​were set to 10,000 for a, 100 for b, and 10 for c. The initial conditions were set to a greater than or equal to 0, b between 0 and 255, and c greater than or equal to 0.

[0055]

number

[0056] The threshold value t was defined using the following formula, with normal distribution fitting parameters b and c. This formula is a floor function, with the integer part being the threshold value. Since b corresponds to brightness and c corresponds to contrast, the threshold value is determined according to brightness and contrast. When evaluating a thermally sprayed aluminum oxide film, m was set to 5.35 and n to -62.9.

[0057]

number

[0058] (Measurement of specific volume resistivity of thermal sprayed coating) Using a digital ultra-high resistance / microcurrent meter Model 8340A (manufactured by ADC Corporation), volume resistance was measured at room temperature of 23°C and 200°C in accordance with the test standard ASTM (D257:2007), and the volume resistivity was calculated based on the film thickness data. Note that the "temperature variable" in Table 3 is a value calculated from (volume resistivity at 23°C) / (volume resistivity at 200°C), and the closer the temperature variable is to 1, the smaller the temperature change in volume resistivity.

[0059] From the obtained X-ray diffraction results, the crystallite size of the aluminum oxide particles of Example 1, determined by the WPPD (Whole Powder Pattern Decomposition) method, was 455 nm. The crystallite sizes of the aluminum oxide particles of Examples 2 to 4, determined by the same method, were 430 nm, 460 nm, and 420 nm, respectively. On the other hand, the crystallite size of the aluminum oxide particles of Comparative Example 1, determined by the same method, was 250 nm.

[0060] Suspension spraying was performed using the slurries for thermal spraying of Examples 1 and 2, which used water as a dispersion medium, contained aluminum oxide particles having a D100 of 15 μm or less and crystallite sizes of 455 nm and 430 nm, with the content being 30% by mass and 50% by mass, respectively, relative to the total amount of the slurry for thermal spraying, and further contained 0.1% by mass and 0.3% by mass of aluminum oxide fine particles having a D50 of 150 nm as a fine particle additive. 700 mL of the slurries was placed in a 1-L polypropylene container with a height of 193 mm, and after standing at room temperature for 168 hours, the transmittance of the supernatant was 46.1% and 75.7%, respectively. The resulting coating thicknesses were 153 μm and 213 μm, the surface roughnesses were 2.88 μm and 2.82 μm, the porosities were 0.42% and 0.32%, and the 23°C / 200°C ratios of electrical resistivity per volume (temperature variable) were 8.0 and 1.3, respectively.

[0061] The slurry for thermal spraying of Example 3 was used in suspension spraying. The slurry contained aluminum oxide particles with a D100 of 15 μm or less and a crystallite size of 460 nm, with a content of 30 mass% relative to the total amount of the slurry for thermal spraying, and further contained 0.3 mass% of Y2O3 fine particles with a D50 of 20 nm as a fine particle additive. 700 mL of the slurry was placed in a 1 L polypropylene container with a height of 193 mm and a capacity of 1 L. After leaving the slurry at room temperature for 168 hours, the supernatant liquid had a transmittance of 62.3%. The resulting slurry had a film thickness of 200 μm, a surface roughness of 3.07 μm, a porosity of 0.96%, and a 23°C / 200°C ratio (temperature variable) of electrical resistance per volume of 3.2.

[0062] The slurry for thermal spraying of Example 4 was used in water as a dispersion medium, and contained aluminum oxide particles having a D100 of 15 μm or less and a crystallite size of 420 nm, with a content of 30 mass% relative to the total amount of the slurry for thermal spraying. The slurry also contained 0.3 mass% TiO particles having a D50 of 50 nm as a particulate additive, and 0.1 mass% polyethyleneimine as a surfactant. 700 mL of the slurry was placed in a 1 L polypropylene container with a height of 193 mm and a volume of 1 L. After allowing to stand at room temperature for 168 hours, the supernatant had a transmittance of 75.5%. Suspension spraying was performed using the slurry for thermal spraying of Example 4, which had a film thickness of 176 μm, a surface roughness of 2.93 μm, a porosity of 0.69%, and a 23°C / 200°C ratio (temperature variable) of electrical resistance per volume of 1.9.

[0063] On the other hand, when suspension spraying was performed using the slurry of Comparative Example 1, which used water as a dispersion medium, contained aluminum oxide particles with a D100 of 18.5 μm and a crystallite size of 250 nm, and whose content was 30 mass% relative to the total amount of the slurry for thermal spraying. 700 mL of the slurry was placed in a 1 L polypropylene container with a height of 193 mm and left to stand at room temperature for 168 hours, the supernatant liquid had a transmittance of 97.4%. The obtained film had a thickness of 87 nm, which was thinner than that of the Examples. The surface roughness was 3.83 μm, which was greater than that of Examples 1 to 4. Furthermore, the porosity was 1.5%, which was greater than that of Examples 1 to 4 and exceeded 1. The ratio of electrical resistance per volume at 23°C / 200°C (temperature variable) was 28.5, which was more than three times higher than that of Examples 1 to 4.

[0064] [Table 1]

[0065] [Table 2]

[0066] [Table 3]

Claims

1. 1. A slurry for plasma spraying, comprising: 20% by mass or more and 50% by mass or less of aluminum oxide particles having a maximum particle size (D100) of 12 μm or less; and 0.1% by mass or more and 3% by mass or less of one or more fine particle additives selected from rare earth oxides, aluminum oxide, and titanium oxide, the fine particle additives having an average particle size D50 of 0.3 μm or less; and one or more dispersion media selected from water and organic solvents.

2. A slurry for plasma spraying, comprising: 700 mL of the slurry in a 1 L container having a height of 193 mm; and ...

2. 2. The slurry for plasma spraying according to claim 1, wherein the aluminum oxide particles have an average particle diameter D50 of 2 μm or more and 8 μm or less, a crystallite size of 350 nm or more and 600 nm or less, and a crystal structure of α-aluminum oxide.

3. 3. The slurry for plasma spraying according to claim 2, wherein the aluminum oxide particles have an average particle diameter D50 of 5 μm or less.

4. 4. The slurry for plasma spraying according to claim 1, wherein the rare earth element is one or more selected from the group consisting of yttrium (Y), gadolinium (Gd), holmium (Ho), erbium (Er), ytterbium (Yb), and lutetium (Lu).

5. A method for producing a thermal sprayed film, comprising using a slurry for plasma spraying according to any one of claims 1 to 4.

6. 6. The method for producing a thermal sprayed film according to claim 5, wherein the method is an atmospheric thermal spraying method.

7. The porosity is 1% or less, the film thickness is 100 μm or more, and (Volume resistivity at 23°C) / (Volume resistivity at 200°C) An aluminum oxide sprayed film characterized in that the value of the temperature variable represented by the following formula is 1 or more and 20 or less.

8. A sprayed component characterized by having the sprayed film described in claim 7.

9. The thermal spray-coated member according to claim 8, which is an electrostatic chuck.

Images