JP6046989B2 - Method for producing sintered silicon carbide - Google Patents

Description

The present invention relates to a method for producing a silicon carbide sintered body.

  Silicon carbide is a highly conductive semiconductor compound and is used as a heating element because it has excellent thermal and chemical stability in terms of material. In general, a heating element made of silicon carbide is manufactured by mixing a silicon carbide raw material powder with an organic binder, forming it into a predetermined shape, and then converting the structure into recrystallized silicon carbide by sintering. Yes. And since silicon carbide has a wide band gap of about 3 eV, it is necessary to reduce the electrical resistance to a level at which electricity can be passed. For this purpose, means for dissolving or dispersing a trivalent element or pentavalent element in silicon carbide is effective.

  Silicon carbide becomes a p-type semiconductor when a trivalent element is dissolved, and becomes an n-type semiconductor when a pentavalent element is dissolved. Among them, the carrier of the p-type semiconductor is a hole, and the carrier of the n-type semiconductor is an electron. However, since the electron generally has a higher mobility than the hole, the pentavalent element is dissolved to form an n-type semiconductor. This is more effective for reducing the specific resistance. Examples of pentavalent elements that can be dissolved in silicon carbide include nitrogen group elements such as nitrogen, phosphorus, arsenic, antimony, or bismuth, and vanadium, niobium, and tungsten. Of these, nitrogen is the most solid element. It is easy to dissolve and has a high solid solution limit. For this reason, attempts have been proposed to dissolve nitrogen in the structure for the purpose of reducing the electrical resistance of silicon carbide.

  For example, Patent Literature 1 discloses a method of sintering silicon carbide in a nitrogen atmosphere, and Patent Literature 2 discloses a method of hot-press sintering silicon carbide in a nitrogen atmosphere. However, simply by sintering in nitrogen gas, the solid solution of nitrogen does not proceed smoothly, and the specific resistance cannot be reduced sufficiently. Patent Document 3 describes a method for forcibly solidifying nitrogen by increasing the nitrogen gas pressure during sintering of silicon carbide to 80 to 500 atm in order to increase the solid solubility of nitrogen. According to this method, since the amount of nitrogen solid solution increases, it becomes possible to effectively reduce the electrical resistivity of silicon carbide. To ensure the nitrogen gas pressure under the above conditions, for example, a hot isostatic press ( An expensive apparatus such as HIP) has to be applied, and there is a problem as an industrial means in terms of equipment and cost.

  Furthermore, in Patent Document 4, as a simple means for increasing the degree of nitrogen solid solubility in silicon carbide, a specific amount of nitride and carbon powder was mixed with the silicon carbide raw material powder during the production of the heating element, and further specified. When sintering is performed under conditions, the amount of solid solution of nitrogen can be effectively increased without the need for special equipment, and the specific resistance of the silicon carbide heating element can be reduced without deteriorating the material strength. It is described that can be.

  Examples of trivalent elements that can be dissolved in silicon carbide include boron, aluminum, gallium, and indium. Aluminum is considered to be either in solid solution, dispersed, or both in silicon carbide.

  However, these silicon carbide heating elements (sintered bodies) have been required to have improved strength. On top of that, high density has been studied to give strength, but there are problems such as sacrificing other factors (for example, resistance value when conductivity is given). .

Japanese Patent Publication No.57-18682 Japanese Patent Laid-Open No. 52-110499 Japanese Patent Publication No. 64-4312 JP-A-6-92733

This invention is made | formed in view of the said actual condition, and makes it a subject to provide the manufacturing method which can give high intensity | strength to a silicon carbide sintered compact.

  In order to solve the above-mentioned problems, the present inventor has made studies of the method for producing a silicon carbide sintered body, and as a result, has reached the present invention.

A method for producing a silicon carbide sintered body of the present invention is a method for producing a silicon carbide sintered body having a step of firing a raw material comprising a mixed powder of silicon carbide powder, silicon powder, and carbon powder. The silicon carbide contained in the raw material has fine silicon carbide powder whose particle size distribution satisfies the conditions of (D90) / (D10) ≦ 10, (D50) / (D10) ≦ 5, and the porosity is 40 It is characterized by being manufactured to be -55% .

  The method for producing a silicon carbide sintered body of the present invention has a fine silicon carbide powder showing a sharp particle size distribution peak in a raw material containing silicon carbide, and is excellent in Young's modulus and bending strength by firing this raw material. This demonstrates the effect of producing a silicon carbide sintered body.

It is a figure which shows the particle size distribution of the silicon carbide powder containing SiC (fine particle-A). It is a figure which shows the particle size distribution of the silicon carbide powder containing SiC (fine particle-B). It is a figure which shows the measurement result of the bending strength of each sample of an Example. It is a figure which shows the measurement result of the Young's modulus of each sample of an Example.

(Method for producing silicon carbide sintered body)
The method for producing a silicon carbide sintered body of the present invention includes a step of firing a raw material containing silicon carbide.

  And the manufacturing method of the silicon carbide sintered body of the present invention is that the silicon carbide contained in the raw material has a particle size distribution satisfying the conditions of (D90) / (D10) ≦ 10, (D50) / (D10) ≦ 5. Has fine silicon carbide powder to fill.

  In the production method of the present invention, a silicon carbide heating element can be produced by firing a raw material containing silicon carbide. Further, since the raw material contains fine silicon carbide powder and this raw material is fired, a non-dense (porous) heating element can be produced.

  In the production method of the present invention, silicon carbide contained in the raw material has fine silicon carbide powder whose particle size distribution satisfies the conditions of (D90) / (D10) ≦ 10, (D50) / (D10) ≦ 5. . By having fine silicon carbide powder in which silicon carbide satisfies predetermined conditions at the same time, the Young's modulus and bending strength of the manufactured silicon carbide sintered body can be increased. Here, (D90), (D50), and (D10) indicate values of 90, 50, and 10%, respectively, when the particle size distribution of the fine silicon carbide powder is measured.

  In the production method of the present invention, silicon carbide contained in the raw material has fine silicon carbide powder showing a sharp peak in particle size distribution. That is, a fine silicon carbide powder is formed only with fine particles with small variations in particle size. For this reason, by not containing particles having a relatively large particle size, the sinterability is high and not only can be fired (sintered) in a short time, but also the strength of the manufactured silicon carbide sintered body is increased. be able to.

  Furthermore, in the production method of the present invention, a large amount of fine powder particles composed only of fine particles are present between the raw material particles containing the fine powder. And by baking in this state, the neck of the sintered compact of a silicon carbide powder is formed in large quantities, and the intensity | strength of the silicon carbide sintered compact manufactured as a result is made high.

  (D90) / (D10) indicates the broadening of the peak width of the particle size distribution, and when (D90) / (D10) ≦ 10, the particle size distribution of the fine silicon carbide powder shows a sharp peak and is produced. The effect of increasing the Young's modulus and bending strength of the silicon carbide sintered body is exhibited. When (D90) / (D10) exceeds 10, the particle size distribution of the fine silicon carbide particles becomes wide, and the above effects cannot be sufficiently exhibited. Preferred (D90) / (D10) is 5 or less, and more preferred (D90) / (D10) is 2 or less.

  (D50) / (D10) indicates the broadening of the peak in the particle size distribution, and when (D50) / (D10) ≦ 5, the particle size distribution of the fine silicon carbide powder (width of (D50) and (D10) ) Shows a sharp peak, and exhibits the effect of increasing the Young's modulus and bending strength of the manufactured silicon carbide sintered body. When the value of (D50) / (D10) exceeds 5, the particle size distribution of the fine silicon carbide particles becomes wide, and the above effects cannot be sufficiently exhibited. Preferred (D50) / (D10) is 3.3 or less, and more preferred (D50) / (D10) is 2.5 or less.

  In the production method of the present invention, the fine silicon carbide powder is preferably a powder showing a peak corresponding to the smallest particle size when the particle size distribution of silicon carbide (powder) contained in the raw material is measured. Since the fine silicon carbide powder corresponds to the peak with the smallest particle size, the fine silicon carbide powder is located between the particles of the mixed powder such as silicon carbide powder having a larger particle size, A neck can be formed. Here, the peak corresponding to the smallest particle size means a peak having a peak height that can be recognized as a peak when the particle size distribution is measured. Noise and extremely small peaks are applicable. do not do.

  When the particle size distribution is measured, if the peak corresponding to fine silicon carbide overlaps with the peak of other silicon carbide powder, the peak corresponding to fine silicon carbide is the profile fitting method. The peaks identified (separated) by can be used. In the present invention, the peaks identified (separated) by this profile fitting method can be adopted even for the peaks of silicon carbide other than fine silicon carbide.

  Moreover, it is preferable that the peak corresponding to fine silicon carbide shows an independent peak when the particle size distribution is measured. Since the peaks corresponding to fine silicon carbide become independent peaks, D10, D50, and D90 of fine silicon carbide can be measured (confirmed). Here, the independent peak of fine silicon carbide indicates a state in which another peak cannot be confirmed between D10 and D90.

In the method for producing a silicon carbide heating element of the present invention, the raw material is a mixed powder of silicon carbide powder, silicon powder, and carbon powder . Since the raw material is composed of these mixed powders, the silicon carbide heating element can be produced by firing (sintering) by firing the raw material.

  In the method for manufacturing a silicon carbide heating element of the present invention, as described above, the silicon carbide powder has fine silicon carbide powder. When silicon carbide containing fine silicon carbide is fired (sintered), a silicon carbide sintered body can be produced.

  Furthermore, silicon powder and carbon powder contained in the raw material (mixed powder) produce silicon carbide during firing. The generated silicon carbide also bonds silicon carbide to increase the strength of the silicon carbide heating element (sintered body).

  The particle size distribution of silicon carbide contained in the raw material shows a peak of the fine silicon carbide powder and one or more peaks different from the fine silicon carbide powder. The silicon carbide contained in the raw material has one or more peaks. Among them, D10 of the closest peak on the large diameter side of the fine silicon carbide powder peak satisfies the condition of (D10) / (D90) ≧ 1 with respect to D90 of the fine silicon carbide powder peak. preferable.

That is, when the particle size distribution of silicon carbide is measured, D90 (D90 _fine ) of the peak of fine silicon carbide powder and D10 (D10 _large ) of the other silicon carbide peak are (D10 _large ) / By satisfying the condition of (D90 _fine ) ≧ 1, it becomes possible to clearly distinguish the peak of the fine silicon carbide powder from the peak of the silicon carbide powder having a larger particle diameter. Furthermore, when this condition is satisfied, the fine silicon carbide powder does not contain a large silicon carbide powder, and the effect of using the fine silicon carbide powder can be sufficiently exhibited.

  In the production method of the present invention, silicon carbide (silicon carbide powder) contained in the raw material has fine silicon carbide powder and coarse silicon carbide powder having a median diameter (D50) larger than that of the fine silicon carbide powder. Is preferred. By forming a mixed powder of fine silicon carbide powder and coarse silicon carbide powder, a silicon carbide sintered body with improved strength can be produced. Further, by mixing fine silicon carbide powder and coarse silicon carbide powder, a mixed powder can be easily manufactured, and a silicon carbide sintered body can be easily manufactured. Here, the coarse silicon carbide powder corresponds to a powder for showing one or more peaks different from the fine silicon carbide powder described above (in claim 3) when the particle size distribution is measured.

  The coarse silicon carbide powder is not particularly limited as long as it is a coarse silicon carbide powder having a median diameter (D50) larger than that of the fine silicon carbide powder.

  That is, the coarse silicon carbide powder may be either a powder showing one peak or a powder showing a plurality of peaks when the particle size distribution is measured. Further, the peak may be either a broad peak or a sharp peak.

  The coarse silicon carbide powder is preferably a powder that causes a peak to appear in a particle size larger than the D90 of the peak of the fine silicon carbide powder when the particle size distribution is measured. Thereby, the cumulative value of the particle size distribution at the peak of the particle size distribution of the fine silicon carbide powder can be obtained.

  When the particle size distribution of the silicon carbide powder is measured, it is preferable that the peak corresponding to the fine silicon carbide powder is independent of the peak for the coarse silicon carbide powder. When coarse silicon carbide powder shows a plurality of peaks, it is preferable that each shows an independent peak.

  The silicon carbide powder is preferably a mixed powder of a plurality of types of silicon carbide having different particle size distribution characteristics. Since the silicon carbide powder is composed of a plurality of mixed powders, a silicon carbide powder having desired characteristics can be easily produced. Moreover, the silicon carbide to be mixed can be easily changed, and the particle size distribution characteristics of the silicon carbide powder can be easily adjusted.

  The silicon carbide powder is preferably a mixed powder of two types of silicon carbide having different average particle diameters (or median diameters (D50)). That is, it is preferably a mixed powder obtained by mixing fine silicon carbide powder and coarse silicon carbide powder.

  In the silicon carbide powder, the average particle size (or median diameter (D50)) of the fine silicon carbide powder and the coarse silicon carbide powder is preferably 5 to 30. When the particle size ratio is within this range, fine silicon carbide powder particles are sintered between coarse silicon carbide powder particles, and the strength of the manufactured sintered body is increased.

  The particle size of the silicon carbide powder is not limited, and a fine silicon carbide powder having an average particle size (or median diameter (D50)) of 0.4 to 0.8 μm and an average particle size (or median). A mixed powder of coarse silicon carbide powder having a diameter (D50) of 10 to 15 μm is preferable.

  The fine silicon carbide powder is preferably contained in an amount of 10 to 50 mass% when the mass of the silicon carbide contained in the raw material is 100 mass%. The fine silicon carbide powder forms a large amount of necks between the silicon carbide particles of the silicon carbide powder during firing, and by including within this range, the effect of adding the fine silicon carbide powder can be sufficiently exhibited. . When the content of the fine silicon carbide powder is less than 10 mass%, the fine silicon carbide powder becomes too small and the neck is not sufficiently formed, and the effect of improving the strength of the silicon carbide sintered body is sufficiently obtained. Disappear. When the content exceeds 50 mass%, the number of fine particles increases and the sintered body to be produced becomes a dense body, which increases the weight (mass). For example, when used as a heating element The electric capacity of the battery becomes larger and the temperature is less likely to rise. A preferable ratio is 12 to 45 mass%, and a more preferable ratio is 15 to 40 mass%.

The production method of the present invention is produced so that the porosity is 40 to 55% . By producing the porosity to be 40 to 55%, for example, a sintered body that does not hinder the flow of gas can be produced. If the porosity is less than 40%, the manufactured sintered body becomes a dense body, which increases the weight (mass). For example, the electric capacity when used as a heating element increases and the temperature does not easily rise. If it exceeds 55%, the strength of the sintered body produced becomes low. A preferable porosity is 42 to 53%, and a more preferable porosity is 45 to 50%.

  It is preferable that the silicon powder and the carbon powder contained in the raw material contain more carbon moles than silicon moles. When carbon is contained in a larger number of moles than silicon, all silicon becomes silicon carbide when carbon and silicon produce silicon carbide. That is, no silicon remains in the manufactured silicon carbide heating element. If silicon remains in the silicon carbide heating element, the remaining silicon affects the characteristics of the silicon carbide sintered body. In particular, when a silicon carbide sintered body is used for a silicon carbide heating element, desired strength and electrical resistivity cannot be obtained. Here, the number of moles of carbon and silicon are the number of moles in terms of pure carbon and pure silicon, respectively. And in the manufacturing method of this invention, the molar ratio (Si / C) of silicon of silicon powder and carbon of carbon powder contained in the raw material is 0.5 to 1.0.

  The raw material preferably contains a compound having an element that can lower the electrical resistance when dissolved or dispersed in silicon carbide. By containing this compound in the raw material, when the raw material is fired, the silicon carbide sintered body to be produced comes to have this element dissolved or dispersed in the silicon carbide sintered body. That is, conductivity can be imparted to the manufactured silicon carbide sintered body. Furthermore, when the mixed powder contains this element, generation and dispersion of silicon carbide proceed in one step of firing.

  Here, a trivalent element can be mentioned as an element which can reduce an electrical resistance when it dissolves or disperses in silicon carbide. And as a trivalent element which can be dissolved in silicon carbide, 1 or more types chosen from boron, aluminum, gallium, and indium can be mention | raise | lifted.

  The element that can lower the electrical resistance when dissolved or dispersed in silicon carbide is preferably a trivalent element. That is, the mixed powder preferably contains a compound having a trivalent element. Further, the trivalent element is preferably aluminum from the viewpoint of ease of handling.

  In the present invention, the compound having an element capable of reducing the electric resistance is preferably mixed with the raw material in a powder state. When this compound is mixed with the raw material in a powder state, it can be uniformly mixed in the raw material and is uniformly dissolved in the silicon carbide sintered body. That is, there is no partial variation in the resistance value characteristics of the manufactured silicon carbide sintered body.

  The raw material preferably contains an aluminum compound. In the silicon carbide sintered body produced by firing the raw material containing the aluminum-based compound, the atomic aluminum derived from the aluminum-based compound is dissolved or dispersed in the silicon carbide sintered body. That is, conductivity can be imparted to the manufactured silicon carbide sintered body. Furthermore, since the raw material contains an aluminum-based compound, generation of silicon carbide and dispersion of atomic aluminum proceed in one step of firing.

  In the production method of the present invention, the aluminum compound preferably has a molar ratio in terms of aluminum atom contained in the aluminum compound to silicon carbide contained in the raw material of 0.1 to 5%. That is, the value (%) represented by [(number of moles of aluminum contained in aluminum compound) / (number of moles of raw material silicon carbide)] × 100 is 0.1 to 5%. By setting the molar ratio of aluminum to 0.1 to 5%, the silicon carbide sintered body has excellent resistance characteristics as a heating element. If the amount is less than 0.1%, the effect of improving conductivity is not obtained because the amount of aluminum is too small. If the amount exceeds 5%, the strength of silicon carbide (silicon carbide in which aluminum is dispersed) forming a silicon carbide sintered body is increased. The strength of the sintered body itself cannot be obtained sufficiently. In particular, when it was excessive as 10%, it became difficult to mold and could not be used for experiments. A preferable molar ratio is 0.5 to 5%, and a more preferable molar ratio is 0.5 to 2%.

  The aluminum compound is preferably alumina. The aluminum compound only needs to be able to disperse aluminum in an atomic state in silicon carbide produced during firing. That is, it may be pure aluminum (a state in which an oxide film is formed on the surface), alumina, or aluminum nitride, and it is preferable to use alumina for ease of handling. The aluminum-based compound is preferably a powder of aluminum powder, alumina powder, aluminum nitride powder or the like, and the form of particles of these powders is not particularly limited, and can be appropriately determined depending on the blending ratio, firing conditions, and the like. .

  The raw material preferably contains 55 to 95 mass% of silicon carbide (silicon carbide powder) contained in the raw material when the whole is taken as 100%. The whole shows the whole raw material. By including silicon carbide powder at 55 to 95 mass%, the manufactured silicon carbide sintered body can have sufficient strength. When the silicon carbide powder is less than 55 mass%, it is difficult to obtain sufficient strength. On the other hand, when the silicon carbide powder exceeds 95 mass%, the reaction-sintered silicon carbide produced from silicon and carbon is too little, and the formation of the bond neck is not sufficiently performed. A preferable ratio is 60 to 90 mass%, a more preferable ratio is 75 to 90 mass%, and a further preferable ratio is 85 to 90 mass%.

  In the production method of the present invention, the specific adjustment method is not limited as long as the step of preparing the raw material (mixed powder) is a step capable of preparing the raw material (mixed powder). For example, thoroughly mixing each powder of silicon carbide powder, silicon powder, carbon powder, etc., dispersing each powder of silicon carbide powder, silicon powder, carbon powder, etc. in a solvent (for example, water) with additives and kneading The process of performing etc. can be mention | raise | lifted. In order to obtain moldability in the subsequent steps, it is preferable to disperse each powder in a solvent and knead.

  As described above, the raw material mixed powder in the present invention indicates that each powder is mixed, and not only shows the powder state, but also the clay (or alternatively, the mixed powder is dispersed in a solvent) Including slurry).

  In the production method of the present invention, the raw material (mixed powder) is formed in the shape of the silicon carbide sintered body, that is, after the step of forming the raw material (mixed powder) is performed, the baking step is performed. It is preferable. If the process of shape | molding a raw material (mixed powder) is a process which can shape | mold a raw material (mixed powder) in a defined shape, a specific shaping | molding method will not be limited. For example, a step of extruding a clay-like raw material (mixed powder), a step of forming a slurry-like raw material (mixed powder) using a predetermined mold, and a step of compacting a powdery raw material (mixed powder) , Can be given.

  The step of forming the raw material (mixed powder) is preferably a step of extruding the clay-like raw material (mixed powder). Here, in the extrusion molding, it is preferable to use a vacuum kneading molding machine in order to prevent the molded body from being cracked by heating. The extruded molded body is preferably dried by a micro dryer when the shape retention is low, or a rotary dryer or the like when it is cylindrical. Moreover, you may dry with warm air or hot air at the time of drying, or may combine with another drying method.

  The molded body is preferably dried immediately after molding. When the shape-retaining property of the molded body is low, the molded body is deformed by its own weight, and the dimensional accuracy of the manufactured silicon carbide sintered body is deteriorated (becomes a defective product). In order to suppress the deformation of the molded body, it is preferable that the molded body is immediately dried.

  When the molded body is dried by heating, it is preferably performed under drying conditions (heating temperature, heating time, temperature increase rate) such that deformation and cracking of the molded body do not occur. If the drying conditions are too gentle (such as when the heating temperature is low), the progress of drying of the molded body is slowed, and the molded body is likely to be deformed. Also, if the drying conditions are too severe (such as when the heating temperature is too high), the surface is dried while the inside of the molded body is wet, and as a result, the surface of the molded body is cracked. Thus, it is preferable that the dry conditions of a molded object are conditions of the grade which does not produce a malfunction in the molded object after drying.

  In the step of forming the mixed powder, the shape to be formed is not particularly limited. That is, it is preferable that the silicon carbide sintered body produced by the production method of the present invention is molded into a shape when used.

  In the production method of the present invention, the step of firing the molded body is a process capable of firing the molded body (sintering silicon carbide powder and generating silicon carbide from silicon powder and carbon powder). The specific adjustment method is not limited.

  In the step of firing the molded body, the firing conditions are not particularly limited, and the molded body is fired (silicon carbide powder is sintered and silicon carbide is generated from the silicon powder and the carbon powder). The temperature and time can be adjusted. The same applies to conditions such as the heating rate. When the firing conditions are within these ranges, the silicon carbide heating element has excellent resistance characteristics.

  It is preferable that calcination is carried out in an inert gas atmosphere. In the production method of the present invention, when baking is performed with aluminum powder mixed in the raw material (mixed powder), aluminum is dissolved or dispersed while forming silicon carbide. That is, it is no longer necessary to include aluminum that contributes to the improvement of conductivity in the firing atmosphere. That is, by performing firing in an inert gas atmosphere, damage to the firing furnace in which firing is performed can be suppressed. The inert gas at the time of baking is not specifically limited, It is preferable to use argon gas.

  It is preferable that the firing is performed in a nitrogen gas atmosphere. Nitrogen gas is poorly reactive and functions like an inert gas. The nitrogen gas may be a mixed gas with an inert gas (argon gas). In the case of a mixed gas, the mixing ratio is not limited and can be determined as appropriate.

  In the production method of the present invention, the step of firing the molded body may be a step of firing in a state in which an element imparting conductivity (the above-described trivalent element) is included in the atmosphere. In this case, it is preferable that a molded object (mixed powder) does not contain the element (aluminum compound) which provides electroconductivity.

  In the production method of the present invention, it is preferable to have an oxidation step of firing the sintered body fired in the firing step in an oxidizing atmosphere.

  The oxidation step is a step of firing in an oxidizing atmosphere, and the carbon remaining in the sintered body is removed, and the surface can be oxidized to be a stable substance.

  The oxidation step is preferably a step of heating in an oxidizing atmosphere. By heating in an oxidizing atmosphere, carbon can be removed at a lower temperature than in the firing step. That is, the oxidation step is preferably heated at a temperature lower than the firing temperature of the firing step. Specifically, it may be in a range that does not cause cracks due to thermal shock.

  In the production method of the present invention, the raw material powder (molded body) subjected to the sintering step is preferably subjected to a degreasing step. By performing the degreasing step, it is possible to improve the manufacturing efficiency and to prevent the firing furnace that performs sintering from being damaged. A degreasing process is not specifically limited, It is preferable that it is a process heated in inert atmosphere. Examples of the inert gas include nitrogen gas and argon gas, and argon gas is more preferable. Moreover, it is preferable that heating temperature shall be a temperature at which degreasing proceeds. Further, the amount of degreasing is not particularly specified as well, but it is better to degrease more than half.

(Silicon carbide sintered body)
The silicon carbide sintered body (hereinafter referred to as the silicon carbide sintered body of the present invention ) is produced by the method for producing a silicon carbide sintered body of the present invention .

  The silicon carbide sintered body of the present invention is a sintered body produced by the production method described above, and exhibits the effects of the production method described above. That is, the sintered body is excellent in strength (Young's modulus and bending strength).

And the silicon carbide sintered compact of this invention can have the silicon carbide produced | generated from carbon and silicon. In this case, silicon carbide generated from carbon and silicon is likely to have an element (trivalent element, aluminum) imparting conductivity therein. By arranging the aluminum compound in the mixed powder, the characteristics can be changed. That is, by having silicon carbide generated from carbon and silicon, the characteristics of the silicon carbide heating element of the present invention can be easily adjusted.

  The silicon carbide sintered body of the present invention is preferably a silicon carbide heating element. As described above, the silicon carbide sintered body can be used as a heating element. And since the sintered compact of this invention is excellent in intensity | strength, the effect which becomes a heat generating body excellent in intensity | strength is exhibited.

  The silicon carbide heating element of the present invention can have an excellent resistance value from a low temperature (normal temperature) to a high temperature (several hundred degrees). That is, when a voltage is applied to the silicon carbide heating element, the heating element generates heat at any temperature from low temperature (room temperature) to high temperature (several hundred degrees). For this reason, the silicon carbide heating element is preferably used for removing a gas or the like containing a volatile organic compound (VOC). Further, it is preferably used for purifying exhaust gas from the internal combustion engine.

  That is, the silicon carbide heating element of the present invention preferably has a honeycomb structure in which a flow path through which a gas containing a component to be purified (heated gas) flows is defined. The shape of the honeycomb is not limited, and examples thereof include a columnar shape, an elliptical columnar shape, and a prismatic shape.

Hereinafter, the present invention will be described using examples.
As an example of the present invention, a silicon carbide sintered body (silicon carbide heating element) was manufactured.

Example 1
(Manufacture of silicon carbide heating elements)
First, the raw materials shown in Table 1 were weighed and prepared in the proportions shown in Table 2.

  First, coarse silicon carbide powder (shown in the table as SiC (coarse particles)), fine silicon carbide powder (shown in the table as SiC (fine particles-A) or SiC (fine particles-B)), silicon powder Conductivity imparting compound powder, dispersant, binder, and water, which are mixed powders of (Si), carbon powder (C), and alumina powder (Al 2 O 3), were weighed and prepared in the proportions shown in Table 1. Here, in the conductivity imparting compound powder, the silicon powder and the carbon powder are prepared such that the molar ratio of silicon to carbon is 0.84 to 0.89. Furthermore, in the conductivity-imparting compound powder, the alumina powder is prepared such that the molar ratio with respect to the total of the silicon carbide powder, the carbon powder, and the silicon powder is 1.00 to 1.75.

  The particle size distribution of the silicon carbide powder in a state where SiC (coarse particles) and SiC (fine particles) were mixed was measured, and the measurement results are shown in FIGS. 1 and 2 show the frequency (%) and the cumulative value (%) at the same time. FIG. 1 (a) shows the particle size distribution of the silicon carbide powder of sample 1 (SiC (fine particles-A) only), FIG. 1 (b) shows the particle size distribution of the silicon carbide powder of sample 2, and FIG. ) Shows the particle size distribution of the silicon carbide powder of the sample 3, and FIG. 1 (d) shows the particle size distribution of the silicon carbide powder of the sample 4 (SiC (coarse particles) only). Similarly, FIG. 2 (a) shows the particle size distribution of SiC (fine particles-B) only, FIG. 2 (b) shows the particle size distribution of the silicon carbide powder of Sample 5, and FIG. FIG. 2 (d) shows the particle size distribution of SiC (coarse particles), respectively. The particle size distribution was measured using a microtrack.

As shown in FIG. 1 (a) and FIG. 2 (a), SiC (fine particles-A) has D10: 0.198 (μm), D50: 0.513 (μm), D90: 1.127 ( μm) and (D90) / (D10): 5.69, (D50) / (D10): 2.591. SiC (fine particles-B) is D10: 0.243 (μm), D50: 2.164 (μm), D90: 9.278 (μm), (D90) / (D10): 38.18, (D50) / (D10): 8.91.
Moreover, SiC (coarse particle) was D10: 9.05 (micrometer), D50: 13.75 (micrometer), D90: 21.64 (micrometer).

As shown in FIGS. 1B to 1C showing the particle size distribution, the silicon carbide powder used in Samples 2 to 3 can confirm two independent peaks. Since there is a region with a frequency of 0% between the two peaks, it can be confirmed that the two peaks are completely independent. Here, the ratio (D10 _large ) / (D90 _fine ) between D10 (D10 _large ) of SiC (coarse particles) and D90 (D90 _fine ) of SiC (fine particles-A) was 8.03. .

On the other hand, the silicon carbide powder used for Samples 5-6 has one large peak and a portion where the particle size of the peak is small as shown in FIGS. 2 (b) to (c) showing the particle size distribution. It can be confirmed that a gentle bulge is located. It can be seen that this is due to the particle size distribution of SiC (fine particles). That is, SiC (fine particles-A) used for Samples 2 to 3 has a particle size distribution that shows one sharp peak (FIG. 1A). On the other hand, SiC (fine particles-B) used in Samples 5 to 6 has a particle size distribution that shows two broad connected peaks (FIG. 2A). Here, the ratio (D10 _large ) / (D90 _fine ) between D10 (D10 _large ) of SiC (coarse particles) and D90 (D90 _fine ) of SiC (fine particles-B) was 0.975. .

  The weighed and prepared SiC (coarse particles), SiC (fine particles), and conductivity-imparting compound powder were put in a bag and mixed well, and then kneaded with a binder, a dispersant, and water in a pressure kneader.

The obtained clay-like mixed powder was formed into a cylindrical shape by extrusion using an extrusion molding apparatus. The obtained molded body was in the form of a pipe having an outer diameter: 6 mm, an inner diameter: 4 mm, and a length: 150 mm.
Next, the molded body was immediately dried.
The dried molded body was degreased by heating under an inert gas atmosphere (nitrogen gas atmosphere).
Then, it was sintered (fired) under an inert gas atmosphere (argon gas atmosphere).
The sintered body was heated and heat-treated in an oxidizing gas atmosphere (air).
After the heat treatment, it was allowed to cool to produce a pipe-like silicon carbide heating element (heating elements of Samples 1 to 6).
The porosity of the manufactured heating elements of Samples 1 to 6 was measured and shown in Table 1.

(Evaluation)
Bending strength and Young's modulus were measured as evaluations of the heating elements of Samples 2 to 3 and 5 to 6 manufactured.

(Bending strength)
The bending strength was measured by a three-point bending test with a distance between fulcrums of 4 cm using an electronic universal testing machine. The measurement results are shown in Table 2 and FIG.

(Young's modulus)
The Young's modulus was measured using the same measuring device as the above bending strength. The measurement results are shown in Table 2. Also shown in FIG.

  As shown in Table 2, the heating elements of Samples 2 to 3 using SiC (Fine Particles-A) for SiC (Fine Particles) are the heating elements of Samples 5 to 6 of SiC (Fine Particles-B). In comparison, both the bending strength and Young's modulus are high. That is, it was confirmed that the strength of the silicon carbide heating element (sintered body) was increased by using SiC (fine particles-A).

That is, when the particle size distribution is measured, the heating elements of Samples 2 to 3 using the silicon carbide powder that shows two independent peaks are the samples 5 to 6 in which the particle size distribution peak of the silicon carbide powder does not show two peaks. It was confirmed that the strength was higher than that of the heating element.
(Resistivity)

  Next, when the resistance value characteristics (specific resistance) of the heating elements of Samples 2 and 5 were measured, it was confirmed that both heating elements had the same specific resistance as the heating element. . That is, the heating element of each sample corresponding to the present invention can generate heat by energization.

Claims (6)

A method for producing a silicon carbide sintered body comprising a step of firing a raw material comprising a mixed powder of silicon carbide powder, silicon powder, and carbon powder ,
The silicon carbide contained in the raw material has fine silicon carbide powder whose particle size distribution satisfies the conditions of (D90) / (D10) ≦ 10, (D50) / (D10) ≦ 5 ,
A method for producing a silicon carbide sintered body, wherein the porosity is 40 to 55% . The particle size distribution of silicon carbide contained in the raw material shows a peak of the fine silicon carbide powder and one or more peaks different from the fine silicon carbide powder,
Among the one or more peaks, silicon carbide contained in the raw material has a peak D10 closest to the large diameter side of the peak of the fine silicon carbide powder with respect to D90 of the peak of the fine silicon carbide powder. The method for producing a silicon carbide sintered body according to claim 1, wherein the condition of (D10) / (D90) ≧ 1 is satisfied. Silicon carbide contained in the raw material, the a fine silicon carbide powder, the fine and large coarse silicon carbide powder be a median size (D50) of the more silicon carbide powder, according to claim 1 or 2 consisting of mixed powder of The manufacturing method of the silicon carbide sintered compact in any one. The production of a silicon carbide sintered body according to any one of claims 1 to 3 , wherein the fine silicon carbide powder is contained in an amount of 10 to 50 mass% when the mass of the silicon carbide contained in the raw material is 100 mass%. Method. The method for producing a silicon carbide sintered body according to any one of claims 1 to 4 , wherein a molar ratio of silicon of the silicon powder contained in the raw material to carbon of the carbon powder is 0.5 to 1.0. . The said raw material is a manufacturing method of the silicon carbide sintered compact in any one of Claims 1-5 containing an aluminum type compound.

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