JP2013216550A - Method for manufacturing silicon carbide sintered body, and silicon carbide sintered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon carbide sintered body having a high bulk density and improved corrosion resistance, and to provide a method for manufacturing the silicon carbide sintered body.SOLUTION: A method for manufacturing a silicon carbide sintered body has a mixing step S20 for mixing silicon carbide powder with a nonmetallic sintering aid, and a pressure sintering step S50 for pressure sintering a mixture of the mixing silicon carbide powder and the nonmetallic sintering aid under a non-oxidizing atmosphere, wherein the nonmetallic sintering aid includes a silicon-modified phenol resin.

Description

  The present invention relates to a mixing step of mixing silicon carbide powder and a nonmetallic sintering aid, and a pressure sintering step of pressure sintering a mixture of silicon carbide powder and a nonmetallic sintering aid. And a method for producing a silicon carbide sintered body and a silicon carbide sintered body.

  Conventionally, a mixing step of mixing silicon carbide powder and a nonmetallic sintering aid, a pressure sintering step of pressure sintering a mixture of silicon carbide powder and a nonmetallic sintering aid, A method for producing a silicon carbide sintered body having a slag is widely known (see, for example, Patent Document 1).

  In the manufacturing method described above, since a nonmetallic sintering aid is used, the content of metal contained in the silicon carbide sintered body is small. For this reason, the silicon carbide sintered body manufactured by the above-described manufacturing method can be suitably used as a component for a semiconductor manufacturing apparatus in which metal is an impurity.

JP-A-10-67565

  In the method for producing a silicon carbide sintered body described above, a part of the nonmetallic sintering aid remains as free carbon (that is, free carbon). Due to this free carbon, fine pores (pores) were generated in the silicon carbide sintered body. For this reason, the silicon carbide sintered body obtained by the above-described manufacturing method has a smaller bulk density than the silicon carbide sintered body in which no pores are generated.

  In addition, since pores are likely to become a starting point of corrosion, for example, when a silicon carbide sintered body is exposed to plasma, the silicon carbide sintered body obtained by the above-described manufacturing method is not subjected to silicon carbide sintering. The surface of the silicon carbide sintered body was worn rather than the bonded body.

  Accordingly, the present invention has been made in view of such circumstances, and provides a silicon carbide sintered body having a large bulk density and improved corrosion resistance, and a method for producing the silicon carbide sintered body. With the goal.

  In order to solve the above-mentioned problems, the present inventors have conducted extensive research and found that the use of silicon-modified phenolic resin as a non-metallic sintering aid can reduce free carbon and complete the present invention. I let you.

  The present invention is characterized by a mixing step (mixing step S20) in which silicon carbide powder and a nonmetallic sintering aid are mixed, and in a non-oxidizing atmosphere, the silicon carbide powder and the nonmetallic sintering aid. A pressure sintering step (pressure sintering step S50) for pressure sintering the mixture with the agent, and a method for producing a silicon carbide sintered body, wherein the non-metallic sintering aid includes The gist is that a silicon-modified phenol resin is contained.

  Further, the mass ratio of the silicon-modified phenol resin to the non-metallic sintering aid may be 50% or more.

  In addition, a silicon compound that is liquid at room temperature, an organic amine or ammonia synthesized as a catalyst, an organic compound that is liquid at room temperature that produces carbon by heating, and a polymerization catalyst or a crosslinking catalyst that is dissolved in the organic compound are mixed. And a step of generating a mixture (mixture generation step S12) and a step of heating the mixture under a non-oxidizing atmosphere to generate the silicon carbide powder (silicon carbide generation step S14). .

  Another feature of the present invention is that free carbon is less than 1% and volume resistivity is less than 1 Ω · cm.

  According to the present invention, it is possible to provide a silicon carbide sintered body having a large bulk density and improved corrosion resistance, and a method for producing the silicon carbide sintered body.

FIG. 1 is a flowchart for explaining a method for manufacturing a silicon carbide sintered body according to the present embodiment. FIG. 2 is a flowchart for explaining the method for producing the silicon carbide powder according to the present embodiment.

  An example of a method for producing a silicon carbide sintered body and a silicon carbide sintered body according to the present invention will be described with reference to the drawings. Specifically, (1) a method for producing a silicon carbide sintered body, (2) operational effects, (3) comparative evaluation, and (4) other embodiments will be described.

  In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. It should be noted that the drawings are schematic and ratios of dimensions and the like are different from actual ones. Accordingly, specific dimensions and the like should be determined in consideration of the following description. It goes without saying that the drawings include parts having different dimensional relationships and ratios.

(1) Manufacturing method of silicon carbide sintered body The manufacturing method of the silicon carbide sintered body which concerns on this embodiment is demonstrated, referring FIG.1 and FIG.2. FIG. 1 is a flowchart for explaining a method for manufacturing a silicon carbide sintered body according to the present embodiment. FIG. 2 is a flowchart for explaining the method for producing the silicon carbide powder according to the present embodiment.

  As shown in FIG. 1, the silicon carbide sintered body manufacturing method according to the present embodiment includes a preparation step S10, a mixing step S20, a forming step S30, a temperature raising step S40, and a pressure sintering step S50. And have.

(1.1) Preparation step S10
The preparation step S10 is a step of preparing silicon carbide powder and a nonmetallic sintering aid.

(1.1A) Silicon carbide powder Examples of the silicon carbide powder according to the present embodiment include α-type, β-type, amorphous, and a mixture thereof. In particular, β-type silicon carbide powder is preferably used. There is no particular limitation on the grade of the β-type silicon carbide powder. For example, commercially available β-type silicon carbide powder can be used. The particle size of the silicon carbide powder is preferably small from the viewpoint of densification. The particle size of the silicon carbide powder is preferably 0.01 or more and 10 μm or less, more preferably 0.05 or more and 1 μm or less. When the particle size of the silicon carbide powder is 0.01 μm or more, it becomes easy to handle in processing steps such as weighing and mixing. When the particle size of the silicon carbide powder is 10 μm or less, the specific surface area is large. That is, when the particle size of the silicon carbide powder is 10 μm or less, the contact area with the adjacent silicon carbide powder becomes large, and thus a high-density silicon carbide sintered body can be obtained.

A silicon carbide powder having a particle size of 0.05 to 1 μm, a specific surface area of 5 m ² / g or more, free carbon 1% or less, and oxygen content 1% or less is preferably used. Further, the particle size distribution of the silicon carbide powder used is not particularly limited. In the production of a silicon carbide sintered body, from the viewpoint of improving the packing density of the powder and the reactivity of silicon carbide, it is possible to use silicon carbide powder having a particle size distribution having two or more maximum values. it can.

  In order to obtain a high-purity silicon carbide sintered body, it is preferable to prepare a high-purity silicon carbide powder.

  The high-purity silicon carbide powder can be produced, for example, by a production method having a mixture production step S12 and a silicon carbide production step S14.

(1.1A.1) Mixture generation step S12
The mixture production step S12 is a step of producing a mixture by mixing a silicon compound that is liquid at normal temperature, an organic compound that is liquid at normal temperature that produces carbon by heating, and a polymerization catalyst or a crosslinking catalyst that is solubilized in the organic compound. .

  As a silicon compound that is liquid at room temperature, for example, a polymer of alkoxysilane (mono-, di-, tri-, tetra-) and tetraalkoxysilane is used as a liquid compound. Among the alkoxysilanes, tetraalkoxysilane is preferably used. Specific examples include methoxysilane, ethoxysilane, propoxysilane, butoxysilane and the like. From the viewpoint of handling, ethoxysilane is preferably used as the silicon compound. Examples of the tetraalkoxysilane polymer include a low molecular weight polymer (oligomer) having a degree of polymerization of about 2 to 15 and a silicate polymer having a higher degree of polymerization, which are liquid.

  A silicon compound that is solid at normal temperature may be used together with a silicon compound that is liquid at normal temperature. Examples of the solid silicon compound that can be used in combination with the liquid silicon compound at room temperature include silicon oxide. In the present invention, silicon oxide includes silica sol (a colloidal ultrafine silica-containing liquid containing OH groups and alkoxyl groups inside), silicon dioxide (silica gel, fine silica, quartz powder) and the like in addition to SiO.

  From the viewpoint of good homogeneity and handling properties, tetraethoxysilane oligomers and mixtures of tetraethoxysilane oligomers and fine powder silica are preferably used as the silicon compound. These silicon compounds are preferably highly pure. The initial impurity content of the silicon compound is preferably 20 ppm or less, and more preferably 5 ppm or less.

  The organic compound that is liquid at room temperature that produces carbon by heating has a high residual carbon ratio and is preferably an organic compound that is polymerized or cross-linked by a catalyst or heating. Examples of such an organic compound include monomers and prepolymers of resins such as phenol resin, furan resin, polyimide, polyurethane, and polyvinyl alcohol. Liquid substances such as cellulose, sucrose, pitch, and tar can also be used as the organic compound. In particular, a resol type or novolac type phenol resin having a high residual carbon ratio and excellent workability is preferable. A solid organic compound that generates carbon by heating may be used together with an organic compound that is liquid at normal temperature.

  In the presence of organic amine or ammonia as a catalyst, the resol type phenol resin useful in the present embodiment includes monovalent or divalent phenols such as phenol, cresol, xylenol, resorcin, bisphenol A, formaldehyde, acetaldehyde, It can be synthesized by reacting with aldehydes such as benzaldehyde.

  The organic amine may be any of primary, secondary, and tertiary amines. As the organic amine, dimethylamine, trimethylamine, diethylamine, triethylamine, dimethylmonoethanolamine, monomethyldiethanolamine, N-methylaniline, pyridine, morpholine and the like can be used. It is preferable that the catalyst does not contain an impurity element.

  It is possible to synthesize a resol-type phenol resin by adding 1 to 3 moles of aldehydes and 0.02 to 0.2 moles of organic amine or ammonia to 1 mole of phenols and heating to 60 to 100 ° C. it can.

  As a method of synthesizing a resol type phenol resin by reacting phenols and aldehydes in the presence of an organic amine or ammonia, a conventionally known method can be adopted.

  On the other hand, the novolak type phenolic resin useful in the present embodiment is a mixture of monovalent or divalent phenols and aldehydes similar to those described above, and acids containing no impurity elements (specifically, hydrochloric acid, sulfuric acid, p. -Toluenesulfonic acid or oxalic acid can be used as a catalyst for the synthesis.

  By adding 0.5 to 0.9 mole of aldehyde and 0.02 to 0.2 mole of an inorganic or organic acid not containing an impurity element to 1 mole of phenol, and heating to 60 to 100 ° C. A novolac type phenolic resin can be synthesized.

  In addition, a conventionally well-known method can also be employ | adopted also for the synthesis | combination of a novolak-type phenol resin.

  The purity of the organic compound can be appropriately controlled and selected depending on the purpose. In particular, when high-purity silicon carbide powder is required, it is desirable to use an organic compound that does not contain 5 ppm or more of each metal.

  Examples of the polymerization catalyst or the crosslinking catalyst (hereinafter abbreviated as “catalyst”) that are solubilized in the organic compound include, for example, saturated or unsaturated carboxylic acids, dicarboxylic acids, aromatic carboxylic acids, among them saturated aliphatic dicarboxylic acids, Saturated aliphatic carboxylic acids and derivatives thereof are preferred. Specific examples of preferred catalysts include maleic acid (pKa = 1.75), acrylic acid (pKa = 4.26), oxalic acid (pKa1 = 1.04, pKa2 = 3.82), itaconic acid (pKa1). = 3.85, pKa2 = 5.45), malonic acid (pKa1 = 2.62, pKa2 = 5.28), succinic acid (pKa1 = 4.00, pKa2 = 5.24) and the like. Of these, at least one selected from maleic acid and derivatives thereof is preferred from the viewpoint of pKa and solubility in water. Examples of maleic acid derivatives include maleic anhydride. Examples of the aromatic carboxylic acid include salicylic acid (pKa = 2.81), phenoxyacetic acid (pKa = 2.99), and phthalic acid (pKa = 2.75).

  The catalyst is preferably a compound composed of only carbon atoms, hydrogen atoms and oxygen atoms. Since such a catalyst is composed of only carbon atoms, hydrogen atoms and oxygen atoms, it does not contain sulfur atoms in the molecule. Therefore, no harmful sulfur compound is generated even in the pressure sintering step S50.

  From the viewpoint of improving reactivity, the catalyst is preferably a compound containing a carboxyl group. In the present invention, “uniformly solubilized with an organic compound” means that the organic compound is uniformly dispersed at the molecular level by mixing.

  Maleic acid (1) has a pKa value almost comparable to toluene sulfonic acid (pKa = 1.4) (pKa = 1.75) and has acid strength. (2) Both unsaturated bonds and carboxyl groups are molecules Because it is included in the hydrophobic part, it has affinity between the hydrophobic part and the hydrophilic part, and it is easy to uniformly mix the silicon compound and the organic compound. (3) Since the reaction itself is not a strong exothermic reaction, the curing reaction is slow. In addition, since the reaction rate can be controlled by the amount of the catalyst added, it can be suitably used as a catalyst.

  As a compounding ratio of the silicon compound, the organic compound, and the catalyst, for example, the organic compound is preferably about 40 to 60 parts by weight and the catalyst is about 5 to 10 parts by weight with respect to 100 parts by weight of the silicon compound. The catalyst can also be blended by dissolving in a solvent that does not contain impurities. For example, a saturated solution obtained by saturating the above catalyst in water, acetone or the like can be used as the catalyst. It is important that the silicon compound, the organic compound and the catalyst are homogeneously mixed in order to cause a uniform reaction in the subsequent steps. For this reason, you may add surfactant to a mixture suitably according to the homogeneity degree of a mixture. Examples of the surfactant that can be used here include Span 20, Tween 20 (trade name, manufactured by Kanto Chemical Co., Inc.), and the addition amount is 5 to 10% by weight based on the total amount of the mixture. It is preferable that it is a grade.

  A silicon compound, an organic compound and a catalyst are mixed. It is preferable to add the catalyst after sufficiently stirring and mixing the silicon compound and the organic compound. When a silicon compound, an organic compound, and a catalyst are mixed and sufficiently stirred, the mixture is solidified. This solidification includes the mixture becoming a gel-like substance.

  After adding the catalyst, the mixture may be heated. Moreover, you may carbonize a solid substance by heating a solid substance for 30 to 120 minutes at the temperature of 800 to 1000 degreeC in non-oxidizing atmosphere formation, such as nitrogen and argon, as needed.

  The ratio of carbon to silicon in the present invention (hereinafter abbreviated as C / Si ratio) is defined by elemental analysis of a carbide intermediate obtained by carbonizing the mixture at 1000 ° C. Stoichiometrically, free carbon in the silicon carbide powder should be 0% when the C / Si ratio is 3.0. However, in practice, free carbon is generated when the C / Si ratio is low due to volatilization of SiO gas generated simultaneously with silicon carbide. It is important to determine the formulation in advance so that the amount of free carbon in the silicon carbide powder does not become an amount that is not suitable for use in manufacturing a sintered body or the like. Usually, in the firing at 1600 ° C. or higher near 1 atm, free carbon can be suppressed when the C / Si ratio is set to 2.0 to 2.5, and thus this range can be suitably used. When the C / Si ratio is 2.5 or more, free carbon significantly increases. However, since this free carbon has an effect of suppressing grain growth, it may be appropriately selected according to the purpose of grain formation. However, when the mixture is fired at a low or high atmospheric pressure, the C / Si ratio for obtaining pure silicon carbide varies, and in this case, it is not necessarily limited to the range of the C / Si ratio. is not.

(1.1A.2) Silicon carbide production step S14
The silicon carbide production step S14 is a step of producing a silicon carbide powder by heating the mixture in a non-oxidizing atmosphere.

  The mixture produced | generated by the said mixture production | generation process S12 turns into silicon carbide (silicon carbide powder) by heating at 1350 degreeC-2000 degreeC for about 30 minutes-3 hours, for example in argon atmosphere. The heating temperature and the heating time can be appropriately selected according to characteristics such as a desired particle size. In order to produce efficiently, the heating temperature is preferably 1600 to 1900 ° C.

  Moreover, the impurity of a silicon carbide powder can further be removed by heat-processing at 2000-2100 degreeC for 5 to 20 minutes at the time of the above-mentioned baking. Thereby, the silicon carbide powder with higher purity can be produced.

  The non-oxidizing atmosphere means an atmosphere in which no oxidizing gas exists. For example, the mixture is heated in an inert atmosphere (a rare gas such as helium or argon, nitrogen, or the like) or in a vacuum atmosphere.

  When sintering the produced silicon carbide powder, the particle size of the silicon carbide powder is preferably small from the viewpoint of increasing the density. For this reason, when using silicon carbide powder as a raw material for the sintered body, firing is performed so that the particle size of the silicon carbide powder is about 0.01 to 20 μm, and further about 0.05 to 2.5 μm. Is desirable. When the particle size of the silicon carbide powder is less than 0.01 μm, handling in processing steps such as weighing and mixing becomes difficult. When the particle size of the silicon carbide powder exceeds 20 μm, the specific surface area becomes small. That is, since the contact area with the adjacent powder becomes small and it becomes difficult to increase the density, the particle size of the silicon carbide powder is desirably 20 μm or less.

  In addition, by this baking, the carbon contained in the mixture becomes a reducing agent and the following reaction occurs.

SiO ₂ + C → SiC
Through the above steps, silicon carbide powder is obtained. When the obtained silicon carbide powder contains carbon, a so-called decarburization treatment may be performed by heating the silicon carbide powder at a temperature of 700 ° C. using an atmospheric furnace.

  In order to reduce the particle size of the silicon carbide powder, the silicon carbide powder may be pulverized using a jet mill so that the center particle size becomes 1 to 2 μm.

(1.1B) Nonmetallic sintering aid A nonmetallic sintering aid containing a silicon-modified phenolic resin is prepared as the nonmetallic sintering aid.

  The silicon-modified phenol resin is obtained by modifying a phenol resin with silicon. Silicon modified phenolic resin can be manufactured by a well-known manufacturing method. A commercially available silicon-modified phenol resin may be used.

  The mass ratio of the silicon-modified phenol resin to the non-metallic sintering aid (the mass of the silicon-modified phenol resin / the mass of the non-metallic sintering aid) is preferably 50% or more. The mass ratio is more preferably 80% or more. More preferably, the mass ratio is 100%, that is, the nonmetallic sintering aid is made of only a silicon-modified phenolic resin. In addition, it is the value remove | excluding the mass of the impurity regarding the mass ratio of the silicon | silicone modified phenol resin with respect to a nonmetallic sintering auxiliary agent.

  As the non-metallic sintering aid other than the silicon-modified phenol resin, a so-called carbon source that generates carbon by heating is used. Specifically, the organic compound which produces | generates carbon by heating, or the silicon carbide powder (particle diameter: about 0.01-1 micrometer) by which the surface was coat | covered with these are mentioned. From the viewpoint of the effect as a sintering aid, an organic compound that generates carbon by heating is preferably used.

  Specific examples of organic compounds that generate carbon by heating include coal tar pitch, pitch tar, phenol resin, furan resin, epoxy resin, phenoxy resin, monosaccharides such as glucose, sucrose, and the like with a high residual carbon ratio. Various saccharides, such as saccharides, polysaccharides, such as a cellulose and starch, are mentioned. For the purpose of homogeneously mixing silicon carbide powder and non-metallic sintering aid, those that are liquid at room temperature, those that dissolve in a solvent, those that soften by heating, such as thermoplasticity or heat melting, or A liquid is preferably used. A phenol resin having a high strength of the obtained molded body, particularly a resol type phenol resin is preferably used.

  When this organic compound is heated, it produces inorganic carbon compounds such as carbon black and graphite. This oriented carbon-based compound is considered to act effectively as a sintering aid.

  When obtaining a mixture of the silicon carbide powder and the nonmetallic sintering aid, it is preferable to mix the nonmetallic sintering aid dissolved or dispersed in a solvent. It is preferable to select a solvent suitable for the compound used as the nonmetallic sintering aid. Specifically, lower alcohols such as ethyl alcohol, ethyl ether, acetone, and the like can be selected for the phenol resin and silicon-modified phenol resin, which are organic compounds that generate carbon by suitable heating. It is preferable to use a non-metallic sintering aid and a solvent having a low impurity content.

  If the amount of the non-metallic sintering aid mixed with the silicon carbide powder is too small, the density of the sintered body will not increase, and if it is too large, free carbon contained in the sintered body may increase. For this reason, although it depends on the type of nonmetallic sintering aid used, generally, the amount of carbon derived from the nonmetallic sintering aid is 10% by weight or less, preferably 2-5. It is preferable to adjust the amount of addition of the nonmetallic sintering aid so that the weight percentage is achieved. The amount of carbon derived from the nonmetallic sintering aid is determined in advance by quantitatively determining the amount of silica (silicon oxide) on the surface of the silicon carbide powder using hydrofluoric acid, and stoichiometrically sufficient for the reduction. Can be determined by calculating.

  Here, the amount of carbon derived from the nonmetallic sintering aid is the carbon derived from the nonmetallic sintering aid according to the following chemical reaction formula, as determined by the above method. It is a value obtained in consideration of the residual carbon ratio after pyrolysis of the nonmetallic sintering aid (ratio of generating carbon in the nonmetallic sintering aid) and the like.

SiO ₂ + 3C → SiC + 2CO
Moreover, in the silicon carbide sintered body of the present invention, the total of carbon atoms derived from silicon carbide and nonmetallic sintering aids contained in the silicon carbide sintered body exceeds 30% by weight. 40% by weight or less is preferable. When the silicon carbide sintered body does not contain any impurities, the content of carbon atoms in the silicon carbide sintered body is theoretically 30% by weight. That is, when the proportion of impurities contained in the silicon carbide sintered body is increased, the content of carbon atoms in the silicon carbide sintered body is not preferable because it is 30% by weight or less. On the other hand, if the carbon atom content exceeds 40% by weight, the density of the obtained sintered body is lowered, and various properties such as strength and oxidation resistance of the sintered body are deteriorated.

(1.2) Mixing step S20
The mixing step S20 is a step of mixing the silicon carbide powder and the nonmetallic sintering aid.

  The silicon carbide powder prepared by the above-described preparation step S10 and the nonmetallic sintering aid are mixed.

  In order to mix the silicon carbide powder and the nonmetallic sintering aid homogeneously, as described above, for example, a phenol resin that is a nonmetallic sintering aid is dissolved in a solvent such as ethyl alcohol, It is preferable to mix well with the silicon carbide powder. It can mix by a well-known mixing means, for example, a mixer, a planetary ball mill, etc. The mixing is preferably performed for 10 to 30 hours, particularly 16 to 24 hours. After thorough mixing, the solvent is removed at a temperature compatible with the physical properties of the solvent, for example, 50-60 ° C. in the case of ethyl alcohol mentioned above.

The mixture obtained by removing the solvent is evaporated to dryness, and then sieved to obtain a raw material powder of the mixture. From the viewpoint of high purity, it is preferable that the material of the ball mill container and the ball is a synthetic resin containing as little metal as possible. In drying, a granulator such as a spray dryer may be used.

(1.3) Molding step S30
The molding step S30 is a step of obtaining a molded body by heating and pressing a mixture of the silicon carbide powder and the nonmetallic sintering aid disposed inside the molding die.

  First, the mixture is placed inside a molding die. In order to improve the density of the molded body, it is preferable to use a vibration filling method at the time of arrangement.

  From the viewpoint of the purity of the obtained silicon carbide sintered body, is the molding die used a graphite material for part or all of the molding die so that the mixture and the metal part of the die are not in direct contact with each other? Alternatively, a Teflon (registered trademark) sheet or the like is preferably interposed inside the molding die. The same applies to a temperature raising step S40 and a pressure sintering step S50 described later.

Once the mixture is placed inside the mold, the mixture is heated and pressurized. It is preferable to adjust the heating temperature, pressure, and pressurization time so that the density of the molded body is 1.5 g / cm ³ or more, preferably 1.9 g / cm ³ . Although the conditions differ depending on the characteristics of the nonmetallic sintering aid, the heating temperature is preferably in the range of 80 to 300 ° C, more preferably in the range of 120 to 140 ° C. The pressure is preferably in the range of 60 to 100 kgf / cm ² . The pressurization time is preferably 5 to 60 minutes, more preferably 20 to 40 minutes.

  A molded body obtained by heating and pressurizing the mixture may be disposed, and a mixture of silicon carbide powder and a nonmetallic sintering aid may be disposed inside the molding die. By heating and pressurizing the arranged molded body and the mixture, a molded body having a large thickness can be obtained.

  By arranging the formed body and the mixture and heating and pressurizing the formed body and the mixture a plurality of times, a silicon carbide sintered body having a high density and a large thickness can be finally produced.

In addition, when the average particle diameter of the powder constituting the mixture is about 0.5 μm, the density of the molded body is preferably 1.5 g / cm ³ or more. When the average particle diameter of the powder constituting the mixture is about 1 μm, the density of the compact is preferably 1.8 g / cm ³ or more. By satisfying this condition, a high-density silicon carbide sintered body can be produced.

  Before performing the next temperature raising step S40 and the pressure sintering step S50, the obtained molded body is cut so that the molded body fits the molding die used in the temperature raising step S40 and the pressure sintering step S50. May be.

(1.4) Temperature raising step S40
The temperature raising step S40 is a step of heating the mixture of the silicon carbide powder and the nonmetallic sintering aid under vacuum. In the present embodiment, the temperature raising step S40 includes a first temperature raising step S42 and a second temperature raising step S44.

  In the temperature raising step S40 and the pressure sintering step S50, not only the mixture of the silicon carbide powder and the nonmetallic sintering aid but also the molded body of the molding step S30 and the non-silicon carbide powder. It is called a mixture with a metal-based sintering aid.

(1.4.1) First temperature raising step S42
The first temperature raising step S42 is a step of heating the mixture of the silicon carbide powder and the nonmetallic sintering aid to 700 ° C. under vacuum.

  A mixture of silicon carbide powder and a nonmetallic sintering aid is placed in a molding die. The molding die in which the mixture is placed is placed in a high temperature furnace. The molding die includes not only a metal mold but also a graphite mold.

The inside of the high-temperature furnace is evacuated and heated gently from room temperature to 700 ° C. Here, when it is difficult to control the temperature of the high temperature furnace, the temperature may be continuously increased to 700 ° C. The inside of the high-temperature furnace is set to 10 ⁻⁴ torr, the temperature is gradually raised from room temperature to 200 ° C., and the temperature is maintained at 200 ° C. for a certain time. Thereafter, the temperature is further gradually raised and heated to 700 ° C. Further, it is held for a certain time at a temperature of around 700 ° C. Thereby, the water | moisture content and organic solvent which are adsorb | sucking to a mixture are desorbed. Furthermore, carbonization by thermal decomposition of the nonmetallic sintering aid is performed. A suitable range of the time for maintaining the temperature at around 200 ° C. or around 700 ° C. is selected depending on the size of the sintered body. Whether or not the holding time is sufficient can be determined by a time point when the decrease in the degree of vacuum is reduced to some extent. By holding at 200 ° C. and 700 ° C. for a certain time, impurities can be removed and the nonmetallic sintering aid can be sufficiently carbonized. Furthermore, there are no cracks or voids in the mixture.

As an example, for a sample of about 5 to 10 g, the temperature is raised slowly from room temperature to 200 ° C. at 10 ⁻⁴ torr and held at 200 ° C. for about 30 minutes. Thereafter, the temperature is further gradually raised and heated to 700 ° C. The time from room temperature to 700 ° C. is about 6 to 10 hours, preferably about 8 hours. Furthermore, it is preferable to hold at about 700 ° C. for about 2 to 5 hours.

(1.4.2) Second temperature raising step S44
The second temperature raising step S44 is a step of heating the mixture of the silicon carbide powder and the nonmetallic sintering aid to 1500 ° C.

  The mixture is further heated in vacuum from 700 ° C. to 1500 ° C. If it is the conditions mentioned above, it will heat up over about 6 to 9 hours, and will hold | maintain at the temperature of 1500 degreeC for about 1 to 5 hours. In this step, it is considered that a reduction reaction of silicon dioxide and silicon oxide is performed. In order to remove oxygen bonded to silicon, it is important to complete the reduction reaction sufficiently. The holding time at a temperature of 1500 ° C. is a vacuum in the vicinity of 1300 ° C., which is a temperature before the start of the reduction reaction, until the generation of carbon monoxide as a by-product by this reduction reaction is completed, that is, the decrease in the degree of vacuum decreases. It is necessary to do until it recovers every time. By the reduction reaction in the second temperature raising step S44, silicon dioxide that adheres to the surface of the silicon carbide powder and inhibits densification and causes large grain growth is removed. The gas containing SiO and CO generated during the reduction reaction is accompanied by an impurity element. However, these generated gases are continuously discharged out of the high temperature furnace and removed by the vacuum pump. For this reason, it is preferable to sufficiently hold this temperature from the viewpoint of high purity.

(1.5) Pressure sintering step S50
The pressure sintering step S50 is a step of pressure sintering a mixture of silicon carbide powder and a nonmetallic sintering aid in a non-oxidizing atmosphere. In this embodiment, a mixture of silicon carbide powder and a nonmetallic sintering aid is placed in a molding die. The molding die in which the mixture is placed is placed in a high-temperature furnace, and heated and pressurized (so-called hot press) in a non-oxidizing atmosphere at a temperature of 2000 to 2400 ° C. and a pressure of 300 to 700 kgf / cm ² .

Sintering begins when the temperature rises above 1500 ° C. During sintering, in order to suppress abnormal grain growth, pressurization is started with about 300 to 700 kgf / cm ² as a guide. Thereafter, an inert gas is introduced to make the inside of the high-temperature furnace into a non-oxidizing atmosphere. Nitrogen or argon is used as this inert gas, but it is desirable to use argon gas because it is non-reactive even at high temperatures.

After making the inside of a high-temperature furnace into a non-oxidizing atmosphere, it is heated and pressurized so that the temperature is 2000 to 2400 ° C. and the pressure is 300 to 700 kgf / cm ² . The pressure at the time of pressing can be selected according to the particle size of the raw material powder. When the raw material powder has a small particle size, a suitable sintered body can be obtained even if the pressure during pressurization is relatively small. In addition, the temperature rise from 1500 ° C. to the maximum temperature of 2000 to 2400 ° C. is performed over 2 to 4 hours, but the sintering proceeds rapidly at 1850 to 1900 ° C. Further, the sintering is completed at this maximum temperature for 1 to 3 hours.

If the maximum temperature is 2000 ° C. or higher, the silicon carbide sintered body can be made sufficiently dense. When the maximum temperature is 2400 ° C. or lower, the silicon carbide sintered body does not sublime (decompose), and therefore a good silicon carbide sintered body can be obtained. Moreover, if pressurization conditions are 500 kgf / cm < ² > or more, a silicon carbide sintered compact can be made into a sufficiently high density. If the pressurizing condition is 700 kgf / cm ² or less, the molding die such as the graphite die is not damaged, and thus the silicon carbide sintered body can be produced efficiently.

  Also in the pressure sintering step S50, from the viewpoint of maintaining the purity of the sintered body to be obtained, a high-purity graphite raw material is used for the molding die (graphite mold), the high-temperature furnace heat insulating material, etc. used here. preferable. As the graphite raw material, high-purity processed material is used. Specifically, a graphite raw material that is sufficiently baked at a temperature of 2500 ° C. or more and does not generate impurities at the sintering temperature is desirable. Furthermore, it is preferable to use a high-purity product with few impurities for the inert gas to be used.

  The silicon carbide sintered body can be manufactured through the above steps. A silicon carbide sintered body having a free carbon of less than 1% and a volume resistivity of less than 1 Ω · cm can also be produced.

(2) Effects The silicon carbide powder manufacturing method according to the present embodiment includes a mixing step S20 in which silicon carbide powder and a nonmetallic sintering aid are mixed, and silicon carbide powder in a non-oxidizing atmosphere. And a pressure sintering step S50 for pressure-sintering a mixture of the non-metallic sintering aid, and the non-metallic sintering aid includes a silicon-modified phenol resin.

  The silicon-modified phenol resin contained in the nonmetallic sintering aid generates free carbon, for example, like the phenol resin. However, it is considered that silicon contained in the silicon-modified phenol resin reacts with free carbon to produce silicon carbide. The silicon carbide produced by the reaction between the silicon-modified phenol resin and free carbon improves the bulk density of the silicon carbide sintered body. Furthermore, since free carbon remaining in the silicon carbide sintered body is reduced, generation of pores due to free carbon can be suppressed. As a result, the corrosion resistance of the silicon carbide sintered body is improved.

  Thus, according to the method for manufacturing a silicon carbide sintered body according to the present embodiment, a silicon carbide sintered body having a large bulk density and improved corrosion resistance can be manufactured.

  Further, the mass ratio of the silicon-modified phenol resin to the nonmetallic sintering aid is preferably 50% or more. Thereby, since free carbon remaining in the silicon carbide sintered body can be sufficiently suppressed, it is possible to further improve the bulk density and the corrosion resistance.

  Also, a silicon compound that is liquid at normal temperature, an organic amine or ammonia synthesized as a catalyst, an organic compound that is liquid at normal temperature that produces carbon by heating, and a polymerization catalyst or a crosslinking catalyst that is dissolved in the organic compound are mixed, A step of producing a mixture, and a step of heating the mixture in a non-oxidizing atmosphere to produce silicon carbide powder.

  Since the organic compound that is liquid at room temperature that generates carbon by heating is synthesized using an organic amine or ammonia as a catalyst, the produced silicon carbide sintered body contains nitrogen atoms. Thereby, since the volume resistivity of a silicon carbide sintered compact becomes small, a silicon carbide sintered compact can be processed precisely by electric discharge machining.

  The silicon carbide sintered body has a free carbon of less than 1% and a volume resistivity of less than 1 Ω · cm. Since the volume resistivity is less than 1 Ω · cm, it can be precisely processed by electric discharge machining.

(3) Comparative evaluation In order to confirm the effect of the present invention, the following comparative evaluation was performed. In addition, this invention is not limited to a following example.

(3.1) Examples and Comparative Examples (3.1A) Example 1
Add 10.5 g of silicon-modified phenolic resin (Asahi Organic Materials Industries Co., Ltd .: AV Light SK087) and 100 g of ethanol to 89.5 g of silicon carbide powder (manufactured by Bridgestone), and use a ball mill to form a slurry. A mixture of was made. The produced mixture was granulated using a spray drying method to obtain a granule for sintering.

A φ30 carbon mold was filled with 10 g of the obtained granule for sintering. Hot press sintering was performed for 4 hours under the conditions of 2300 ° C., 500 kg / cm ² and an argon atmosphere. Thereby, a silicon carbide sintered body was obtained. Both surfaces of the obtained silicon carbide sintered body were ground. The thickness of the silicon carbide sintered body after grinding was 1.5 t.

(3.1B) Example 2
89.5 g of silicon carbide powder (manufactured by Bridgestone), 8.4 g of silicon-modified phenolic resin (Asahi Organic Materials Co., Ltd .: AV Light SK087) and 2.1 g of unmodified phenolic resin (manufactured by Airwater: SK) Lite SR-101) and 100 g of ethanol were added, and a slurry-like mixture was prepared using a ball mill.

  Other steps are the same as those in the first embodiment.

(3.1C) Example 3
89.5 g of silicon carbide powder (manufactured by Bridgestone), 5.25 g of silicon-modified phenolic resin (Asahi Organic Materials Co., Ltd .: AV Light SK087) and 5.25 g of unmodified phenolic resin (manufactured by Air Water: SK) Lite SR-101) and 100 g of ethanol were added, and a slurry-like mixture was prepared using a ball mill.

  Other steps are the same as those in the first embodiment.

(3.1D) Comparative Example 1
Add 10.5 g of unmodified phenolic resin (manufactured by Airwater: SK Light SR-101) and 100 g of ethanol to 89.5 g of silicon carbide powder (manufactured by Bridgestone), and use a ball mill to slurry. A shaped mixture was prepared.

  Other steps are the same as those in the first embodiment.

(3.1E) Comparative Example 2
A silicon carbide sintered body (manufactured by Covalent Materials) manufactured using a CVD method was prepared.

(3.2) Bulk density measurement The bulk density of the silicon carbide sintered bodies according to Examples and Comparative Examples was measured using Archimedes method. The results are shown in Table 1.

(3.3) Plasma resistance measurement The plasma resistance of the silicon carbide sintered bodies according to Examples and Comparative Examples was measured using a plasma generator (manufactured by Denki Giken). Under the conditions of an output of 500 W, a pressure of 50 Pa, and CF ₄ / O ₂ = 100/100 sccm, the wear amount of the silicon carbide sintered body after 5 hours was measured. The results are shown in Table 1.

  In addition, it shows that plasma resistance is excellent, so that a numerical value is small.

(3.4) Free carbon measurement The ratio of the free carbon of the silicon carbide sintered bodies according to Examples and Comparative Examples was measured using a thermal analyzer (Rigaku: TG8120). Under a condition of air 10 ml / min and 10 ° C./min, a weight loss rate of 1150 ° C. was measured. The results are shown in Table 1.

(3.5) Volume Resistance Measurement The volume resistivity of the silicon carbide sintered bodies according to the examples and comparative examples was measured using a resistance measuring instrument (Mitsubishi Chemical: Loresta). The results are shown in Table 1.

(3.6) Results

  As shown in Table 1, the silicon carbide sintered body according to the example was found to have a larger bulk density than Comparative Example 1.

  Further, as shown in Table 1, it was found that the silicon carbide sintered body according to the example was superior in plasma resistance as compared with Comparative Example 1. Furthermore, it was found that the silicon carbide sintered bodies according to Examples 1 and 2 were superior in plasma resistance as compared with Comparative Example 2. That is, it was found that the mass ratio of the silicon-modified phenol resin to the nonmetallic sintering aid is preferably 80% or more.

  As shown in Table 1, it was found that the silicon carbide sintered body according to the example had less free carbon than Comparative Example 1. It is considered that free carbon contained in the silicon carbide sintered body has decreased due to the reaction between silicon and free carbon contained in the silicon-modified phenol resin. It is considered that the generation of pores was suppressed by the reduction of free carbon, and as a result, the plasma resistance was improved. In addition, it is considered that the bulk density of the silicon carbide sintered body is improved by the formation of silicon carbide by the reaction between silicon and free carbon.

  In addition, as shown in Table 1, the silicon carbide sintered body according to the example has a smaller volume resistivity than that of Comparative Example 2. Specifically, the volume resistivity of the silicon carbide sintered body according to Examples 1 to 3 is less than 1 Ω · cm, whereas the volume resistivity of the silicon carbide sintered body according to Comparative Example 2 is 100Ω. -It is cm or more. For this reason, the silicon carbide sintered body of Comparative Example 2 cannot be subjected to electric discharge machining, whereas the silicon carbide sintered body according to the present example can be subjected to electric discharge machining. Since electric discharge machining is excellent in precision machining, it was found that the silicon carbide sintered body according to the present example can be machined precisely.

(4) Other Embodiments Although the contents of the present invention have been disclosed through the embodiments of the present invention, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. The present invention includes various embodiments not described herein.

  For example, in the above-described embodiment, the method for manufacturing a silicon carbide sintered body includes the forming step S30, but is not necessarily limited thereto. The method for manufacturing the silicon carbide sintered body may not include the forming step S30.

  In the above-described embodiment, the silicon carbide sintered body is manufactured by performing the pressure sintering step S50 after the first temperature raising step S42 and the second temperature raising step S44 are completed. Not limited to. The pressure sintering step S50 may be performed without performing the first temperature raising step S42 and the second temperature raising step S44.

  In the above-described embodiment, the resol-type phenol resin is exemplified as the organic compound that is synthesized using organic amine or ammonia as a catalyst and is a liquid organic compound that generates carbon by heating, but is not necessarily limited thereto.

  As described above, the present invention includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

  S10 ... Preparation step, S12 ... Mixture generation step, S14 ... Silicon carbide generation step, S20 ... Mixing step, S30 ... Molding step, S40 ... Temperature raising step, S42 ... First temperature raising step, S44 ... Second temperature raising step, S50: Pressure sintering process

Claims (4)

A mixing step of mixing the silicon carbide powder and the nonmetallic sintering aid;
A pressure sintering step of pressure sintering a mixture of the silicon carbide powder and the nonmetallic sintering aid in a non-oxidizing atmosphere, and a method for producing a silicon carbide sintered body,
The method for producing a silicon carbide sintered body, wherein the nonmetallic sintering aid includes a silicon-modified phenol resin.   2. The method for producing a silicon carbide sintered body according to claim 1, wherein a mass ratio of the silicon-modified phenol resin to the nonmetallic sintering aid is 50% or more. A mixture of a silicon compound which is liquid at normal temperature, an organic amine or ammonia synthesized as a catalyst, an organic compound which is liquid at normal temperature which produces carbon by heating, and a polymerization catalyst or a crosslinking catalyst which is dissolved in the organic compound. Generating
The method for producing a silicon carbide sintered body according to claim 1, further comprising: heating the mixture in a non-oxidizing atmosphere to produce the silicon carbide powder. Free carbon is less than 1%,
A silicon carbide sintered body having a volume resistivity of less than 1 Ω · cm.

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