JPS62108770A - Silicon carbide sintered body and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a high-grade silicon carbide sintered body having high density, oxidation resistance, and IL-temperature properties, and a method for producing the same.

Silicon carbide sintered bodies have extremely attractive chemical and mechanical properties, so they are used particularly in gas turbine parts, high-temperature heat exchangers, and other filter structures used under harsh conditions. This material is suitable for such uses.

[Conventional technology]

By the way, silicon carbide has been known as a material that is difficult to sinter. In other words, until recently, it has been difficult to obtain a high-density sintered body of this material using the pressureless sintering method, which is commonly used to produce oxide ceramics, in which the material is molded at room temperature and then sintered under no pressure. there were.

However, recently, various pressureless sintering methods have been reported in which a mixed powder containing silicon carbide leaves, a carbonaceous additive, and a carbonaceous additive is formed and sintered in a non-oxidizing atmosphere.

For example, JP-A-50-78609 discloses [(a) silicon carbide in an amount corresponding to 0.3 to 3.0% by weight of boron! M elementary gold-containing compound, and 0.1 to 1.0 fKt
forming a homogeneous dispersion of submicron powder consisting of a carbonaceous additive corresponding to % carbon (b
) shaping the powder mixture into a green object; and (0)
A high-density silicon carbide ceramic comprising a stage Wi is sintered in an inert atmosphere at a humidity of 1900-2100 C for a time sufficient to obtain a ceramic article having a density of at least 85% of the theoretical density. An invention related to "a method for manufacturing" is disclosed.

JP-A-54-67599 discloses that [organosilicon polymer compounds containing silicon and carbon gold as main skeleton components are thermally decomposed at a temperature of 1,600 to 2,200 C in a total vacuum or an inert gas atmosphere to mainly form β- A powder containing 5ic 2 as the main component is obtained, and this powder is heated to a temperature of 500 to 500°C in an oxidizing atmosphere, and then treated with an acid containing at least hydrofluoric acid to dissolve and remove impurities to obtain high purity β-3iC. After adding carbon and boron to the raw material powder using this powder until the content of each becomes 0.1 to 5% by weight in the mixture, and shaping the mixture into a predetermined shape. , in vacuum, in CO gas atmosphere, 2000~2300 in inert gas atmosphere.
The patent discloses a method for producing a sintered silicon carbide body, which comprises sintering at a humidity of C for a time sufficient to achieve a density of at least 2.609/min.

JP-A-56-1FI9181 describes ``a method for manufacturing a silicon carbide sintered body in which fine silicon carbide powder, a boron-containing additive, and a carbonaceous additive are mixed, molded, and then sintered without pressure. 100 parts by weight of silicon carbide fine powder consisting essentially of 85% by weight or more of crystalline silicon carbide and the remainder being 2H-type crystalline silicon carbide, and a boron-containing addition of 0.1 to 3.0 parts by weight in terms of boron content. A first step of homogeneously mixing the additive and a carbonaceous additive of more than 1.0 parts by weight and less than 4.0 parts by weight in terms of fixed carbon content; a second step of molding the homogeneous mixture into an arbitrary product shape; Step: The formed body is treated with argon, helium,
2050 in a gas atmosphere consisting of at least one selected from neon, krypton, xenon, and hydrogen.
3rd step of sintering at ~2200 C; consists of a combination of the above 1st to 3rd steps, with β-type crystals at 50-85% by weight and residual free carbon exceeding 1.0% by weight and 3.0% by weight or less Contains
3.097CI'13 or higher density manufacturing method for high-strength silicon carbide sintered body" is disclosed.

[Problems to be Solved by the Invention 1] By the way, according to the invention described in JP-A-50-78609, boron is used as an auxiliary agent in a concentration of 0.3 to 3.0 to silicon carbide. It is necessary to contain it in a relatively large amount (by weight%), and the resulting sintered body has a disadvantage that it has poor oxidation resistance.

Furthermore, according to the invention described in JP-A-54-67599, the method uses extremely expensive β-8C powder obtained by thermally decomposing an organosilicon polymer compound as a starting material. The disadvantage is that it is difficult to use widely as a material.

The invention described in JP-A-56-169181 is an invention filed by the present applicant, and its purpose is to improve a silicon carbide pressureless sintered body and to obtain a high-strength sintered body. By adding the quality additive in excess of the amount required by the oxygen content of the silicon carbide fine powder and actively incorporating it in the form of free carbon into the silicon carbide sintered body, the
This suppresses the phase transformation to type crystals, prevents the coarsening of the crystals due to conversion of β-type crystals to α-type crystals, and makes them fine crystals. However, the effect of suppressing phase transformation due to free actual temperature in the invention described in the above publication is not so sufficient (in particular, it is difficult to produce a high-density sintered body in which most of the silicon carbide is composed of β-type crystals). Ta.

The present invention eliminates the drawbacks of the previously known pressureless sintering methods for silicon carbide as described above, and is particularly suitable for use under harsh conditions such as gas turbine parts, high temperature heat exchangers, and furnace structural materials. The object of the present invention is to provide an atmospheric pressureless sintered body of silicon carbide mainly composed of β-type crystals that has high density and excellent oxidation properties, and a method for using the same.

[Ninth way to solve the problem]

From this point of view, the present inventors have conducted various studies on pressureless silicon carbide sintered bodies, and have found that at least 6
0% by weight consists of β-type crystals, and the average particle size is 0.05-5
50 weight i
Silicon carbide powder containing t% or more has excellent sinterability,
It can be sintered with the addition of a very small amount of densification aid, and the phase change S from β-type crystal to α-type crystal can be achieved.
We have newly found that it is possible to produce a high-density silicon carbide sintered body by the pressureless sintering method without causing almost any sintering, and have completed the present invention.

The present invention contains boron and free carbon, and contains at least 2
．． A silicon carbide sintered body having a density of 99/CIIL3, wherein at least 60% of the silicon carbide is a β-type crystal, and the boron content is 0.01 to 0.25 wt%. The present invention relates to a sintered body and a method for manufacturing the same.

Next, the silicon carbide sintered body of the present invention will be explained in detail.

The silicon carbide sintered body of the present invention contains at least 60% of silicon carbide.
% is required to be β-type crystal.

The reason for this is that β-type crystals are iragonal crystals and do not exhibit anisotropy in their coefficient of thermal expansion. Therefore, a sintered body in which at least 60% of silicon carbide is β-type crystals is sintered at a high temperature of, for example, 2000C or higher. This is because no residual stress is generated inside the sintered body even in the cooling process after sintering, so that a silicon carbide sintered body with extremely high strength can be obtained, and it is particularly preferable that the strength is 95% or more.

The silicon carbide sintered body of the present invention has a boron content of 0,01
~0.25% by weight is required. The reason for this is that a sintered body with a boron content of less than 0.01% by weight is extremely pure, and it is considered that phase transformation from β-type crystal to α-type crystal is extremely likely to occur. The content is 4 less than o, oi weight%, and V! ! 5 summer is 2
．． This is because it is substantially difficult and impractical to obtain a high-density sintered body with a density of 92/- or more.On the other hand, when the boron content is 0.
This is because boron contained in the sintered body lowers the melting point of the surface of the sintered body when the amount is more than 25% by weight, resulting in poor oxidation resistance of the sintered body. The content of is preferably less than 0.15% by weight.

The silicon carbide/sintered body of the present invention has at least 2.92/α
However, if particularly high strength is required, it is preferable to have a density of at least 3.097α3.

The silicon carbide sintered body of the present invention contains Na, K, Ca, M
g.

At, Fe, Cr, Cu, Ti, Ni (
7) It is preferable that the content of at least xM of such selected elements is 0.5% by weight or less and 1% or less. The reason for this is that sintered bodies with a content of more than 0.5% of the envy elements described above tend to undergo phase transformation from β-type crystals to α-type crystals (from β-type crystals to α-type crystals). This is because coarse plate-like crystals are formed during the phase transformation and the strength is significantly deteriorated, making it difficult to apply the material to applications that require high toughness, especially at high temperatures.

Next, a method for manufacturing a silicon carbide sintered body of the present invention will be explained.

The second invention of the present invention contains boron and free carbon, and contains at least 2. In the method for producing a silicon carbide sintered body having a density of 'l/c1n, at least 60% of the silicon carbide is composed of β-type crystals, the average grain size is within the range of 0.05 to 5 μm, and the average grain size of the powder is Silicon carbide powder 10 containing 50% or more of powder having a particle size within ±50% of the diameter value
0 parts by weight and 0.01 to 0.2 in terms of boron content
A raw material composition consisting of 5 parts by weight of a boron-containing additive and 0.3 to 5.0 parts by weight of a carbonaceous additive in terms of fixed carbon is homogeneously mixed, and the formed product is molded into a non-containing material. A method for producing a silicon carbide sintered body, characterized in that the silicon carbide sintered body is heated to a conductivity of 1800 to 2300 C in an oxidizing atmosphere to form a silicon carbide sintered body in which at least 60% of silicon carbide is composed of β-type crystals. be.

According to the present invention, at least 60% of silicon carbide is composed of β-type crystals, and the average particle size is within the range of 0.05 to 5 μm,
It is also necessary to use a silicon carbide powder containing 50% by weight or more of powder having a particle size within ±50% of the average particle size of the powder.

In the silicon carbide powder, at least 60% of the silicon carbide is β.
The reason why it is necessary that it is made of type crystals is that β
Crystals mixed in silicon carbide, which is mainly composed of type crystals, are 2H type crystals that are more stable at lower temperatures than β type crystals, or α type crystals such as 4H type crystals, 6H type crystals, and 15R type crystals, which are more stable at higher temperatures than β type crystals. However, the 2H type crystal is extremely unstable in the temperature range where a normal sintering reaction occurs, and tends to cause abnormal grain growth during sintering.On the other hand, the 4H type crystal,
If α-type crystals that are stable in high temperature ranges, such as 6H-type crystals and 15R-type crystals, are contained, the phase transformation from β-type crystals to α-type crystals will be promoted during sintering, and the α-type crystals will become coarser as the α-type crystals change. If the content of β-type crystals is less than 60%, it will be difficult to obtain a high-strength sintered body with high density and uniform microstructure, since plate-like crystals will be generated and hinder densification. This is because silicon carbide is a silicon carbide having 95% or more of β-type crystals.

The crystal system of silicon carbide in the present invention is specified by α
The data obtained by X-ray diffraction were substituted into Domura's equations (1), (2), and (3) shown below.

(1) Ratio of β-type crystal to 2H-type crystal I: d=2
．． 51A Peak intensity value 't 100 Peak intensity value of d=2.67A.

However, Vβ is the customer type % of the β type crystal, and 2H is the volume % of the 2H type crystal.

(2) Ratio I of β-type crystal, 4H-type crystal and 6H-type crystal
A: d=2.51Anopeak degree value 'elO(1-
IB: d=2.51A nopic intensity value Th
When a=2.100. Peak intensity value of ssA.

However, ■β is the customer type % of the β type crystal, ■6H is the customer type % of the 6H type crystal, and V4H is the customer type % of the 4H type crystal.

(3) Ratio IA of β-type crystal, 6H-type crystal, and 15R-type crystal: peak intensity value of d-=2.62A when the peak intensity value of d=2.51A is set as 100.

IB: d=2. Peak intensity value of d = 2.58A when the peak intensity value of slA is set to 100.

100 100α""
'v6H=1+, :1+,/'1+α10β 100β V15=-1+α+β However, ■β is the volume of the β-type crystal, ■6Ii is the volume of the 6H-type crystal, V15Rk'! 15 This is the volume of the R-type crystal.

In addition, is the peak intensity value of Rigaku Rotaflex? The area method was used to derive data obtained under the following X-ray diffraction conditions.

Scanning 5peed 1/4 〉Ch
art Bpeed l cm/wmTime
Con5tant 55ecFull 5ca
le 2 x 10 Cps load
40 KV, 100 mA @The reason why it is necessary that the average particle size of silicon carbide powder is within the range of 0.05 to 5 degrees is that silicon carbide powder whose average is smaller than o, os P'L is a bottleneck. This is because it is difficult to obtain such fine silicon carbide powder, and on the other hand, if silicon carbide larger than 5 μm is used as a starting material, it is difficult to sinter. This is because there are fewer locations where necks are initially formed, and shrinkage during sintering becomes uneven.

The silicon carbide powder has an average particle diameter value of ±
The reason why it is necessary to contain 50% by weight or more of powder having a particle size within the range of 50 cm is that the powder has a particle size within ±50% of the average particle size value. Powders with a powder content as low as 50% or less have a large difference in the amount of energy held by each powder particle, so the necks that are formed in the initial stage of sintering tend to be uneven in their locations. This is because it is difficult to produce a high-density sintered body, and it is particularly advantageous for the content to be 70% by weight or more.

According to the present invention, the @silicon carbide powder has β-type crystals (11
It is preferable that the half width of the X-ray diffraction peak in 1) is 0.35 degrees or less, and the degree of symmetry is within the range of 0.7 to 1.1. The reason for this is that the half-width of the X-ray diffraction peak at (111) in the β-type crystal is as large as 0.35 degrees.
Silicon carbide powder with a symmetry degree outside the range of 0.7 to 1.1 has a large amount of energy held by the powder particles themselves, and the crystals are unstable, and the phase changes from β-type crystal to α-type crystal during sintering. This is because not only is it difficult to obtain a high-density sintered body because transformation and abnormal grain growth of crystals are likely to occur, but also it is difficult to produce a silicon carbide sintered body with excellent mechanical properties. Yes, especially in the (111) vc of β-type crystals
The half width of the line diffraction peak is 0.30i or less, and the degree of symmetry is 0.
．． Advantageously, the silicon carbide powder is within the range of 8 to 1.0.

In addition, the half width of the peak at (111) of the β type crystal in the present invention is the width of the peak at a height of 1/2 of the peak intensity obtained by X-ray diffraction using α rays in Cu-, and is expressed in degrees. It will be done. Also, is the degree of symmetry the half width of the above peak? This is the ratio of the width on the low angle side to the width on the high angle side when divided at the highest point position, and is expressed by the following formula.

According to the invention, the silicon carbide fine powder has an oxygen content of 0.
Advantageously, it is between 1 and 1.0″ILt%.

Oxygen contained in the silicon carbide fine powder reacts with carbon during sintering and is removed by a mechanism as shown in the following equation.

5i02 + C-* Si○+Co (1
)SiO+ 20 → SiC+ Go (2
) Therefore, if the oxygen is present in an amount greater than 1.0 direct quantity, not only will it be necessary to use a large amount of carbonaceous additive, but also boron as a sintering aid will be oxidized.
This is because sintering becomes difficult, as Go gas is generated in the large leaves, making it necessary to vent gas during sintering. On the other hand, is it possible to obtain fine silicon carbide powder containing less than 0.1 direct quantity of oxygen by treating it with a mixed acid of hydrofluoric acid and nitric acid? It is active and easily oxidizes even at room temperature when dried in an air atmosphere, so in order to maintain a low oxygen content, it is necessary to use an atmosphere after acid treatment. This is because it is not practical because it must be maintained in a non-oxidizing state.

The silicon carbide fine powder of the present invention is a raw material composition containing carbon powder and silica powder in a predetermined molar ratio, and includes Ca, M
g, At, Fe, Cr, Cu, Ti, Ni
The content of at least one element selected from the following is 0.2% by weight or less.
oxidation reaction and heating in a non-oxidizing atmosphere with a nitrogen gas partial pressure of 40 mHg or less to reach a finishing temperature of 1750 to 2300 C, or a nitrogen gas partial pressure of 4Q+w)i
1 by heating in a non-oxidizing atmosphere maintained above 1 g.
By reaching a finishing temperature of 850-2500 C, at least 600i! It can be produced by a method for producing silicon carbide powder in which β-type crystal silicon carbide is formed.

The C/SiO2 molar ratio between the carbon powder and the silica powder is preferably within the range of 3.0 to 4.5. According to the present invention, the boron-containing Additives converted to boron content: 0.01 to 0
．． It is necessary to add 1 part of 25ii.

The boron content of the boron-containing additive is 0.0
The reason for setting 1 to 0.25 parts by weight is that if it is less than 0.01 parts by weight, the adhesive effect during neck formation is insufficient and it is difficult to achieve high density.On the other hand, if it is more than 0.25 parts by weight, This is because boron remaining in the sintered body lowers the melting point of the silica layer on the surface of the sintered body, thereby degrading the oxidation resistance of the sintered body. As the boron-containing additive, it is advantageous to use, for example, at least one selected from boron, boron carbide, or a mixture thereof.

According to the present invention, a silicon carbide sintered body particularly excellent in oxidation resistance can be obtained when the amount of the boron-containing additive added is less than 0.15 parts by weight in terms of boron content.

According to the present invention, the carbonaceous additive is converted into a fixed carbon content of 0.3 to 5.0 parts by weight per 100 parts by weight of silicon carbide fine powder.
0i! [Additional addition is necessary. The carbonaceous additive is used to remove oxygen contained in the silicon carbide fine powder and to be interposed between the silicon carbide particles to optimize the diffusion of S1C. Therefore, carbonaceous additives contain oxygen
It is advantageous to add at least a suitable amount, and further add a sufficient amount so that it is uniformly interposed between silicon carbide particles. The reason why the amount of the carbonaceous additive added should be 0.3 to 5.01 parts by weight in terms of fixed carbon content is that if it is less than 0.3 parts by weight, most of the carbonaceous additive will be converted to oxygen. This is because the effect of optimizing the diffusion of SIG cannot be exerted because it is consumed, and on the other hand, if the amount exceeds 5.0 parts by weight, excessive carbon exists between silicon carbide particles, significantly inhibiting sintering. It is from.

Advantageously, the carbonaceous additive has a specific surface area of at least 100 min at the start of sintering. The reason is that the specific surface area at the start of sintering is 100 m2/
If the value is smaller than g, the effect of optimizing the diffusion of SiC is weak, so in order to fully exhibit the effect of optimizing the diffusion of SiO, a large amount must be added, and the inclusion layer in the sintered body is This is because, as a result, it is difficult to obtain a high-strength sintered body.

As the carbonaceous additive, any material that can cause carbon to be present at the start of sintering can be used, such as phenol 14.
various organic substances such as fat, lignin sulfonate, polyvinyl alcohol, consp f−+ MU+ coal tar pitch, alginate, polyphenylene, or carbon black.

Pyrolytic carbon such as acetylene black can be advantageously used.

According to the present invention, silicon carbide powder, a boron-containing additive, and a carbonaceous additive are homogeneously mixed, then molded into a formed body having an arbitrary shape, and then heated to a temperature of 1,800 to 2
A silicon carbide sintered body is produced by sintering at 300 C and having a density of 2.9 g/cm3 or more.

According to the present invention, the formed body is heated at a temperature of 1800 to 2300C.
It is necessary to heat it to a temperature of . The reason is ml
When the temperature is lower than 1800 C, the object of the present invention 2
, 9j;? It is difficult to obtain a sintered body having a density of /Crn3 or higher, and on the other hand, if the density is higher than 2300 C, the coarsening of crystal grains due to the phase transformation from β-type crystal to α-type crystal is significant, and the physical properties of the sintered body, such as This is because the mechanical strength decreases, and a temperature range of 1900 to 2200 C is particularly advantageous in obtaining a sintered body with a uniform microstructure and high strength.

By the way, according to the present invention, it is important to suppress the phase transformation from β-type crystal to α-type crystal during sintering. It is advantageous to sinter within a temperature range of, for example, 1800 to 2100 C. In a maintained atmosphere, sintering can be performed in a higher temperature range, and if the partial pressure of at least one of the above-mentioned ♀ elementary gas or CO gas is maintained higher than 11111 Hg, the temperature range is 1900 to 2300 Hg.
It should be possible to sinter within the range of C.

According to the present invention, it is advantageous that the non-oxidizing atmosphere is normally a gas atmosphere consisting of at least one selected from argon, helium, and hydrogen, and if necessary, the above-mentioned nitrogen or Co may be added. It is also possible to use a mixed gas atmosphere.

According to the present invention, one of the heating steps leading to the sintering temperature
500 to 170011: Maintain the CO gas partial pressure in the temperature range lower than l [Pa for a sufficient period of time to allow the silica film removal reaction to proceed quickly and the neck formation reaction to occur uniformly. It is advantageous to do so.

According to the present invention, the green body can be relatively easily densified by charging the green body into a container that can rapidly prevent outside air from entering and firing it. The reason for this is thought to be that the volatilization of SiG from the formed body during firing can be sufficiently suppressed and the evaporation and recondensation of SiC can be promoted, so that neck growth can occur uniformly. . It is advantageous to use, for example, a graphite container as the container that can quickly block the intrusion of outside air.

Example 1 Silica powder (8102-99,
100 parts by weight of 8-weight tJ), 76 parts by weight of petroleum coke powder (G-98, 7-weight 1llt) with an average particle size of 29 μm, and high pitch powder (Ci-5) with an average particle size of 39 μm.
0.4 weight t%) 71m! A portion was blended and mixed for 10 minutes in a vertical screw mixer. While spraying a 0.2% aqueous solution of polyvinyl alcohol onto the blended raw materials, the raw materials were molded using a pan-type granulator, and after sieving and sieving, 150C
The average particle size was IQ, 5 m, and the bulk specific gravity was 0.
．． 6Of; //CWr3, C/5i02% Le ratio is 4
．． 0 granular raw material was obtained.

Kono granular raw material contains 0.05% by weight of AL and ¥0.0 Fe.
9-layer chest, Ti total 0.003% by weight, Ca 0.02%
t amount%, Mg total 0.005% by weight, Na 0.0
It contained 1''!1% and 0.01% by weight of K. No other impurity elements were detected.

This granular raw material was charged from the upper raw material charging port of the indirect heating furnace described in Japanese Patent Publication No. 57-48485, and brought into the heating zone where the set temperature in the reaction vessel was controlled at 1900 CK.
After carrying out the SiC conversion reaction for about 1 hour, the reactor was allowed to fall under its own weight into a cooling zone, and the reaction product was discharged from a sealable outlet.

The obtained reaction product was purified and classified for particle size to prepare silicon carbide fine powder.

The silicon carbide fine powder has 97% by weight of β-type crystals and the remainder is 2H.
Consisting of type crystals, o, 32gg% free carbon, 0.18
Contains heavy tSO oxygen, including Na, K, At, Fe,
Or.

(The total content of impurity elements such as u, Ti, Ni, G2Lk and MgO was about 0.11% by weight. Other properties are shown in Table 1.

The silicon carbide fine powder has a specific surface area of 99.85 N and 27.8
150 d of acetone was added to a mixture of m2/II boron carbide powder 0.15', F and 4°Ol of novolak type phenolic resin with a fixed carbon content of 51.6 ffit%, and the mixture was heated using a vibration mill for 2 hours. Mixed treatment. The mixture slurry was discharged from the vibration mill and spray-dried to obtain an average particle size of Q, Q9rls, and a powder bulk density of 35% (1,1
21/Crn3) granules were obtained.

A suitable amount was taken from the granules and pressed with a metal mold to give a 0.
Temporary molding was carried out at a pressure of 15 t/crn2, and then molding was carried out at a pressure of 1.8 t/crn2 using a hydrostatic press machine. The density of the formed body obtained by the above molding is 61 inches (1,
951/cm3).

The formed body was placed in a Tammann type sintering furnace and sintered in an argon gas stream under atmospheric pressure. Temperature rising process high-K
After holding at 1650 C for 40 minutes at 5 C/m1n1.1650 CK, the temperature was further increased at 5 C/min and held at a maximum temperature of 2060 r for 60 minutes. C during sintering
o Gas partial pressure is from room temperature to 1650 C, 5 KPa or less, 1
6501. 0.5KPa or less, 1650 when holding
The argon gas flow rate was adjusted appropriately so that the temperature was 5 KPa or less in the temperature range higher than C.

The obtained sintered body was 3.05L (relative theoretical density rate 95
．． It had a density of 0%). Also, powder X of this sintered body
As a result of line diffraction measurement, it was found that 93.0% of the silicon carbide in this sintered body was β-type crystal.

The sintered body was processed into a plate shape of 30 x 30 x lwm and washed with acetone to prepare a sample for oxidation resistance test. The sample was treated in a heating furnace maintained in an air atmosphere at 1400 C for 20 hours, and the weight increase before and after the treatment was measured, and it was 0.025 my/cm compared to before the treatment.
2, and it was recognized that the oxidation resistance was excellent. It was also found that the obtained sintered body had a higher electrical resistance than a silicon carbide sintered body obtained using a conventional densification aid in a relatively large amount.

Example 2, Comparative Example 1 Silicon carbide powder was obtained in substantially the same manner as in Example 1, except that the set temperature in the reaction vessel was changed as shown in Table 1.

Next, a sintered body was obtained in the same manner as in Example 1.

Table 1 shows the properties of the silicon carbide powder obtained and the percentage properties of the sintered body obtained using the powder.

Example 3 The silicon carbide powder obtained in Example 1 was further classified to
Silicon carbide powder having an average particle size and particle size distribution as shown in the table was obtained.

Next, the same method as in Example 1 was used, but the addition of boron carbide was reduced to 0. II, and the maximum temperature during sintering is 2010
A sintered body having the characteristics shown in Table 1 was obtained by changing the temperature to G.

It is almost the same as Example 1, but the set temperature in the reaction vessel and the nitrogen gas partial pressure in the atmosphere are different. Silicon carbide powder was obtained by setting the values as shown in Table 1.

Next, a sintered body was obtained in the same manner as in Example 1.

The properties of the obtained silicon carbide powder and the properties of the sintered body obtained using the powder are shown in Table 1.

Example 5 The silicon carbide powder obtained in Comparative Example 1-1 was charged into a Tammann-type heating furnace, and the set temperature in the heating furnace and the partial pressure of ♀ elemental gas in the atmosphere were set to the values shown in Table 2. After heat treatment, a sintered body was obtained in the same manner as in Example 1.

The properties of the silicon carbide powder obtained by heat treatment and the sintered body obtained using the powder are shown in Table 2.

Example 6 Sintered bodies were obtained in substantially the same manner as in Example 2-2, except that the amount of boron carbide added was changed as shown in Table 3.

From the results shown in Tables 1, 2, and 3, the silicon carbide powders of this example all have excellent sinterability and can achieve high density with an extremely small amount of boron-containing additive. However, it is clear that a sintered body with high strength can be obtained.

Example 7 Sintered bodies were obtained in substantially the same manner as in Example 1, except that the sintering temperature and the partial pressure of nitrogen gas or CO gas in the atmosphere were varied as shown in Table 4.

The properties of the obtained sintered body are shown in Table 4.

Example 8 A sintered body was obtained in substantially the same manner as in Example 1, except that all the silicon carbide powder obtained in Example 5-3 was used and the sintering conditions were as shown in Table 4.

The properties of the obtained sintered body are shown in Table 4.

From the results shown in Table 4, it is recognized that nitric gas and CO gas present in the firing atmosphere are extremely effective in suppressing the formation of the α-type crystal.

〔Effect of the invention〕

As mentioned above, the silicon carbide sintered body of β-type crystalline produced with an extremely small amount of the densification aid of the present invention is particularly excellent in thermal shock resistance and high-temperature strength, and has excellent thermal shock resistance and high-temperature strength. It is extremely suitable as a material for parts and heat exchangers, and is extremely uniform. @ Due to its fine crystal structure, it is extremely excellent as a wear-resistant material, and can be used not only in combination with silicon carbide sintered bodies, but also various other metals; various synthetic resins such as fluororesin; and nitrides and oxides. It is extremely suitable as a material for bearings in mechanical seals used in combination with various ceramics such as, and is extremely useful industrially.

Claims (1)

[Claims] 1 Contains boron and free carbon, at least 2.9 g
A silicon carbide sintered body having a density of /cm^3, wherein at least 60% of the silicon carbide is β-type crystal and the boron content is 0.01 to 0.25% by weight. Sintered body. 2. The silicon carbide sintered body according to claim 1, wherein at least 95% of the silicon carbide is a β-type crystal. 3. The silicon carbide sintered body according to claim 1, having a density of at least 3.0 g/cm^3. 4. The silicon carbide sintered body according to claim 1, wherein the boron content is less than 0.15% by weight. 5 Na, K, Ca, Mg, Al, Fe, Cr, Cu,
The silicon carbide sintered body according to claim 1, wherein the content of at least one element selected from Ti and Ni is 0.5% by weight or less. 6 containing boron and free carbon, at least 2.9 g
In the method for producing a silicon carbide sintered body having a density of /cm^3, at least 60% of the silicon carbide is composed of β-type crystals, the average particle size is within the range of 0.05 to 5 μm, and the average particle size of the powder is within the range of 0.05 to 5 μm. Silicon carbide powder 100 containing 50% by weight or more of powder having a particle size within ±50% of the diameter value
Part by weight and 0.01 to 0.25 in terms of boron content
Part by weight of boron-containing additive and 0 in terms of fixed carbon content
．． A raw material composition consisting of 3 to 5.0 parts by weight of a carbonaceous additive is homogeneously mixed, and the molded product is heated to a temperature of 1800 to 2300°C in a non-oxidizing atmosphere to remove at least the silicon carbide. A method for producing a silicon carbide sintered body, characterized in that the silicon carbide sintered body is made of 60% β-type crystals. 7. The silicon carbide powder contains at least 95% of silicon carbide.
7. The manufacturing method according to claim 6, wherein is a β-type crystal. 8 The silicon carbide powder contains Na, K, Ca, Mg, Al
7. The manufacturing method according to claim 6, wherein the content of at least one element selected from among , Fe, Cr, Cu, Ti, and Ni is 0.5% by weight or less. 9. The silicon carbide powder is characterized in that the half width of the (111) X-ray diffraction peak of the β-type crystal is 0.35 degrees or less, and the degree of symmetry is within the range of 0.7 to 1.1. The manufacturing method described in Section 6.