JPH07315933A - Silicon carbide-based refractory and its production - Google Patents

Abstract

PURPOSE:To obtain an SiC-based refractory having improved oxidation resistance by incorporating a specified percentage or more of a glassy or crystalline SiO2 phase into grain boundary bonding parts made of Al2O3, mullite or a mixture of them. CONSTITUTION:A blend is prepd. so that it is composed of 70-85wt.% SiC particles having a prescribed particle size distribution and the balance Al2O3 particles and/or mullite particles having a particle size distribution in which particles having 6-6.5mum average particle diameter account for 2-6wt.% and particles having 0.6-1mu average particle diameter account for 9-28wt.%. A clay mineral contg. glassy or crystalline SiO2, e.g. kaolin is added to the blend by >=3wt.%, especially about 4-6wt.% (expressed in terms of SiO2) of the amt. of the blend. After blending, dispersant added water is further added by the required amt. and they are molded by vibration press molding or other method. The resultant molded body is fired at 1,300-1,500 deg.C for about 2-5hr in an oxidizing atmosphere to obtain the objective SiC-based rafractory having about >=2.7g/cm<3> density and contg. SiC grains bonded in grain boundary bonding parts and coated with surface orotecting coating films of SiO2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SiC refractory having excellent oxidation resistance and high temperature strength and a method for producing the same. SiC refractory is an important material in ceramic technology used for baking shelves, jigs, sheaths, and the like.

[0002]

2. Description of the Related Art Conventionally, SiC-based refractory materials have been manufactured by combining SiC aggregate particles with clay minerals or the like and firing them. However, since clay minerals having a low refractory degree are used as a binder, they are used. There is a problem that softening and oxidation are likely to occur at high temperatures inside.

In recent years, in order to solve this poor high-temperature performance, SiC particles and a small amount of metallic Si are mixed and fired in a nitrogen atmosphere, so that SiC having silicon nitride as a joint is used.
Quality refractories have been proposed (US Pat. No. 2,752,2)
No. 58). A method has also been proposed in which a mixture of SiC particles and a small amount of metallic Si is baked in a nitrogen atmosphere and then further oxidized (Japanese Patent Laid-Open No. 4-114968). The main phase of the grain boundary joint formed by this treatment is Si3 N4 or S
i2 ON2, and cristobalite exists as a subphase.

[0004]

However, when used for a long period of time, deterioration of Si--N due to oxidation occurs, and there is still a need for improvement in terms of durability and life of SiC refractories. Therefore, an object of the present invention is to provide a SiC refractory having improved room temperature and high temperature strength and oxidation resistance during long-term use, and a method for producing the same.

[0005]

The present invention is characterized in that grain boundary joints in SiC refractory are bonded with alumina and / or mullite, and oxidation resistance is obtained by molding and firing by a predetermined method. The main idea is to improve the strength and high temperature strength as compared with conventional ones.

According to the present invention, the SiC aggregate particles are 70-
85 wt%, preferably 75-85 wt%, to a SiC-based refractory bonded by a grain boundary bonding part with the balance being alumina and / or mullite having an average particle size in the range of 6.5 to 0.6 μm. Provided is an alumina- and / or mullite-bonded SiC refractory characterized in that glassy or crystalline SiO2 is contained in the grain boundary bonding portion in an amount of 3 wt% or more in an external amount.

In the present invention, the compounding amount of alumina and / or mullite in the grain boundary bonding part is 100 when the total amount with SiC is 100.
If the balance is 30% by weight, the balance becomes
The strength as a C-type refractory is reduced, and the compounding amount is 1
If it is less than 5% by weight, the filling property of the particles is deteriorated and the characteristics are deteriorated. A preferred blending amount is 15 to 25 wt%
Is. The SiC refractory thus obtained is excellent in oxidation resistance because alumina and mullite are oxides, and oxidation does not proceed to the center due to the dense SiO2 film on the surface. Further, since the particle filling property is good, this SiC refractory is excellent in high temperature strength.

A binder such as a clay mineral is contained as an external distribution with the total amount of SiC and alumina and / or mullite being 100% by weight, and the glassy or crystalline substance contained in the clay mineral in the binder. 3% by weight of SiO2
That is all. If the external amount of SiO2 is less than 3 wt%, a sufficiently uniform SiO2 oxide film cannot be formed on the surface of the fired SiC refractory during firing or during use. SiO
The externally distributed amount of 2 is preferably 4 to 6 wt%. When one or two kinds of alumina and mullite are mixed with coarse particles and fine particles, the latter can be filled in the particle gaps of the former and the density of the entire SiC refractory can be further increased. That is,
Specifically, it is preferable that the first particles having an average particle size of 6 to 6.5 μm are 2 to 6 wt% and the second particles having an average particle size of 0.6 to 1 μm are 9 to 28 wt%. .

A clay mineral such as kaolin or an organic binder is added as a molding binder in an amount of 10 wt% or less, preferably 5 to 8 wt%, and a dispersant is added to a mixture of these SiC, alumina and mullite. Water is added in an amount necessary for molding, for example, 6 to 10 wt% by external distribution, and molding is performed by a method such as press molding or extrusion molding, and vibration press molding is most preferable. By firing these molded articles, a fired article of refractory having a high density can be obtained. Note that S
The density of the iC fired body can be 2.7 g / cm @ 3 or more. The above-mentioned molded product was subjected to 130 in an oxidizing atmosphere.
When baked at 0 to 1500 ° C., an oxide film is formed on the surface of the molded body film. The heating time is preferably 2 to 5 hours.
The oxidizing atmosphere is preferably air. The thickness of the oxide film is preferably 500 to 1000 μm.

FIG. 1 shows the results of measuring the density of a fired body obtained by molding and firing a mixture of alumina and SiC having different grain sizes. From this, it is predicted that the density of the grain boundary joint changes with the grain size. can do. In FIG. 1, the weight ratio is SiC: Al2 O3 = 8: 2, and the average particle diameter of alumina is 0.6 μm, 6.5 μm, 55 μm, 100 μm.
These are the results of four types of experiments. This experiment shows that the density of the SiC refractory depends on the average particle size of alumina. Further, as a result of conducting various experiments by mixing aluminas having different average particle sizes, 4 to 5 wt% of alumina having an average particle size of 6.5 μm and 15 to 2 having an average particle size of 0.6 μm were used.
It was found that a high temperature strength can be obtained at 0 wt%.

When a SiC refractory filled with alumina and / or mullite at a high density is fired in an oxidizing atmosphere, the SiC is oxidized and a dense oxide protective film is formed on the surface of the fired body. Is significantly improved. Incidentally, SiO2 contained in the binder is also present in this film, which contributes to the improvement of the oxidation resistance. Therefore, even when the SiC refractory material according to the present invention is used as a baking shelf for a long time, it hardly deforms or swells. Hereinafter, the present invention will be described in more detail with reference to Examples.

[0012]

[Examples] SiC and alumina having the particle size distribution shown in Table 1 were compounded as shown in the table (total amount 100 wt%), and kaolin was further compounded (Table 1 shows the SiO2 conversion compounding amount). . In these formulations, Examples 1, 2,
3 is a composition within the scope of claim 1. In addition, Example 1
No. 3 has a particle size distribution of SiC aggregate particles of 1000 to 3600 μ.
m of 15 to 25 wt%, 1000 to 350 μm of 23 to 30 wt%, and less than 350 μm of 23
It was changed so as to be ˜30 wt%. Comparative Example 1 is Si
Examples in which the amount of C aggregate particles exceeds the upper limit of the present invention and the particle size distribution of alumina is the lower end of the present invention, Comparative Examples 2 and 3 are examples in which the amount of alumina exceeds the upper limit of the present invention. These compositions were fired in air at 1400 ° C. for 5 hours. The characteristic values of the fired body are shown. In addition, the rate of increase in weight is based on the amount of S
It is a measured value after heating the iC refractory material at a temperature of 1000 ° C. in the atmosphere for 336 hours.

[0013]

[Table 1] Example Comparative Example 1 2 3 1 2 3 SiC 3360 ~ particle size distribution 1000 μm 20 23 18 30 25 20 (wt%) 1000 ~ 350 μm 25 30 33 30 20 20 350 μm less than 30 23 30 30 20 20 alumina Particle size distribution Average 6.5 μm 5 5 4 0 35 20 (wt%) Average less than 0.6 μm 20 19 15 10 0 20 Kaolin (external amount) wt% SiO2 conversion 3 4 5 3 4 2 Density (g / cm3) 2.83 2.85 2.80 2.57 2.63 2.51 Bending strength Room temperature 432.8 473.3 451.6 257.5 236.1 280.2 (kgf / cm2) 1400 ℃ 310.3 351.1 325.5 153.3 138.4 141.2 Weight increase rate (%) 0.21 0.20 0.21 0.23 0.25 0.29

As is clear from the table, the embodiment has a higher density than that of the comparative example, and the room temperature and high temperature strengths are increased by about two times accordingly. In addition, in the case of the comparative example, the weight increase rate was also increased because the oxidation proceeded to the center of the test piece. This indicates that the characteristics are not improved when the content of alumina is outside the range of the present invention.

[0015]

Action and effect of the invention SiC according to claim 1 of the present invention
Since the refractory material is made of alumina and / or mullite whose grain boundary bonding part is specified as the average grain size, the filling of the grain boundary material is improved, and since the SiO2 content in the binder is 3 wt% or more, the high temperature strength is high. It has excellent oxidation resistance and is industrially useful. In addition, since the structure of the surface coating film is specified in claim 3, the oxidation resistance is further improved. According to the fourth aspect, since a coarse grain and a fine grain of alumina or the like are mixed to form a grain boundary joint portion, a higher density can be obtained.

Further, the method of claim 5 of the present invention is the method of Si
C is bonded with alumina and / or mullite mixed in a predetermined particle size distribution, and the temperature is 1300 to 1500 ° C in an oxidizing atmosphere.
The SiC refractory produced by this method can have improved mechanical and thermal properties by having good particle packing properties and by forming a silica film on the fired surface. . That is, the SiC refractory according to the manufacturing method of the present invention has no swelling or deformation due to heating, and the durability is significantly improved.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the average particle size of alumina and the density of a SiC refractory after firing.

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[Procedure amendment]

[Submission date] June 6, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 1

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[Name of item to be corrected] Claim 3

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[Name of item to be corrected] Claim 6

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[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

In recent years, in order to solve this poor high-temperature performance, SiC particles and a small amount of metallic Si are mixed and fired in a nitrogen atmosphere, so that SiC having silicon nitride as a joint is used.
Quality refractories have been proposed (US Pat. No. 2,752,2)
No. 58). A method has also been proposed in which a mixture of SiC particles and a small amount of metallic Si is baked in a nitrogen atmosphere and then further oxidized (Japanese Patent Laid-Open No. 4-114968). The main phase of the grain boundary bonding portion formed by this treatment is Si ₃ N ₄ or S
i ₂ ON ₂ , and cristobalite exists as a subphase.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

According to the present invention, the SiC aggregate particles are 70-
85 wt%, preferably 75-85 wt%, to a SiC-based refractory bonded by a grain boundary bonding part with the balance being alumina and / or mullite having an average particle size in the range of 6.5 to 0.6 μm. Provided is an alumina- and / or mullite-bonded SiC refractory, characterized in that glassy or crystalline SiO ₂ is contained in the grain boundary bonding portion in an amount of 3 wt% or more in an external amount.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

In the present invention, the compounding amount of alumina and / or mullite in the grain boundary bonding part is 100 when the total amount with SiC is 100.
If the balance is 30% by weight, the balance becomes
The strength as a C-type refractory is reduced, and the compounding amount is 1
If it is less than 5% by weight, the filling property of the particles is deteriorated and the characteristics are deteriorated. A preferred blending amount is 15 to 25 wt%
Is. The SiC refractory thus obtained is excellent in oxidation resistance because alumina and mullite are oxides, and oxidation does not proceed to the center due to the dense SiO ₂ film on the surface. Further, since the particle filling property is good, this SiC refractory is excellent in high temperature strength.

[Procedure Amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

A binder such as a clay mineral is contained as an external distribution with the total amount of SiC and alumina and / or mullite being 100% by weight, and the glassy or crystalline substance contained in the clay mineral in the binder. The amount of SiO ₂ distributed is 3 wt%
That is all. If the external amount of SiO ₂ is less than 3 wt%, a sufficiently uniform SiO ₂ oxide film is not formed on the surface of the SiC fired refractory body during firing or during use. SiO
The externally distributed amount of ₂ is preferably 4 to 6 wt%. When one or two kinds of alumina and mullite are mixed with coarse particles and fine particles, the latter can be filled in the particle gaps of the former and the density of the entire SiC refractory can be further increased. That is,
Specifically, it is preferable that the first particles having an average particle size of 6 to 6.5 μm are 2 to 6 wt% and the second particles having an average particle size of 0.6 to 1 μm are 9 to 28 wt%. .

[Procedure Amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

A clay mineral such as kaolin or an organic binder is added as a molding binder in an amount of 10 wt% or less, preferably 5 to 8 wt%, and a dispersant is added to a mixture of these SiC, alumina and mullite. Water is added in an amount necessary for molding, for example, 6 to 10 wt% by external distribution, and molding is performed by a method such as press molding or extrusion molding, and vibration press molding is most preferable. By firing these molded articles, a fired article of refractory having a high density can be obtained. Note that S
The iC fired body can have a density of 2.7 g / cm ³ or more. The above-mentioned molded product was subjected to 130 in an oxidizing atmosphere.
When baked at 0 to 1500 ° C., an oxide film is formed on the surface of the molded body film. The heating time is preferably 2 to 5 hours.
The oxidizing atmosphere is preferably air. The thickness of the oxide film is preferably 500 to 1000 μm.

[Procedure Amendment 10]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

FIG. 1 shows the results of measuring the density of a fired body obtained by molding and firing a mixture of alumina and SiC having different grain sizes. From this, it is predicted that the density of the grain boundary joint changes with the grain size. can do. In FIG. 1, the weight ratio is SiC: Al ₂ O ₃ = 8: 2, and the average particle diameter of alumina is 0.6 μm, 6.5 μm, 55 μm, 100 μm.
These are the results of four types of experiments. This experiment shows that the density of the SiC refractory depends on the average particle size of alumina. Further, as a result of conducting various experiments by mixing aluminas having different average particle sizes, 4 to 5 wt% of alumina having an average particle size of 6.5 μm and 15 to 2 having an average particle size of 0.6 μm were used.
It was found that a high temperature strength can be obtained at 0 wt%.

[Procedure Amendment 11]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

When a SiC refractory filled with alumina and / or mullite at a high density is fired in an oxidizing atmosphere, the SiC is oxidized and a dense oxide protective film is formed on the surface of the fired body. Is significantly improved. In addition, SiO ₂ contained in the binder is also present in this film, which contributes to the improvement of oxidation resistance. Therefore, even when the SiC refractory material according to the present invention is used as a baking shelf for a long time, it hardly deforms or swells. Hereinafter, the present invention will be described in more detail with reference to Examples.

[Procedure Amendment 12]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

[0012]

EXAMPLE SiC and alumina having the particle size distribution shown in Table 1 were compounded as shown in the same table (total amount 100 wt%), and kaolin was further compounded (Table 1 shows the SiO ₂ conversion compounding amount). ). In these formulations, Examples 1, 2,
3 is a composition within the scope of claim 1. In addition, Example 1
No. 3 has a particle size distribution of SiC aggregate particles of 1000 to 3600 μ.
m of 15 to 25 wt%, 1000 to 350 μm of 23 to 30 wt%, and less than 350 μm of 23
It was changed so as to be ˜30 wt%. Comparative Example 1 is Si
Examples in which the amount of C aggregate particles exceeds the upper limit of the present invention and the particle size distribution of alumina is the lower end of the present invention, Comparative Examples 2 and 3 are examples in which the amount of alumina exceeds the upper limit of the present invention. These compositions were fired in air at 1400 ° C. for 5 hours. The characteristic values of the fired body are shown. In addition, the rate of increase in weight is based on the amount of S
It is a measured value after heating the iC refractory material at a temperature of 1000 ° C. in the atmosphere for 336 hours.

[Procedure Amendment 13]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

[0013]

[Table 1] Example Comparative Example 1 2 3 1 2 3 SiC 3360 ~ particle size distribution 1000 μm 20 23 18 30 25 20 (wt%) 1000 ~ 350 μm 25 30 33 30 20 20 350 μm less than 30 23 30 30 20 20 alumina Particle size distribution Average 6.5 μm 5 5 4 0 35 20 (wt%) Average less than 0.6 μm 20 19 15 10 0 20 Kaolin (external amount) wt% SiO ₂ conversion 3 4 5 3 4 2 Density (g / cm ³ ) 2.83 2.85 2.80 2.57 2.63 2.51 Bending strength Room temperature 432.8 473.3 451.6 257.5 236.1 280.2 (kgf / cm ² ) 1400 ℃ 310.3 351.1 325.5 153.3 138.4 141.2 Weight increase rate (%) 0.21 0.20 0.21 0.23 0.25 0.29

[Submission date] June 6, 1995

[Procedure Amendment 14]

[Document name to be amended] Statement

[Name of item to be corrected] 0015

[Correction method] Change

[Correction content]

[0015]

Action and effect of the invention SiC according to claim 1 of the present invention
Since the quality refractory is made of alumina and / or mullite whose grain-boundary bonding part is specified as the average grain size, the filling of the grain-boundary material is improved, and since the SiO ₂ content in the binder is 3 wt% or more, the high temperature It has excellent strength and oxidation resistance and is industrially useful. In addition, since the structure of the surface coating film is specified in claim 3, the oxidation resistance is further improved. According to the fourth aspect, since a coarse grain and a fine grain of alumina or the like are mixed to form a grain boundary joint portion, a higher density can be obtained.

Claims (6)

[Claims] 1. A grain boundary bond of one or two of alumina and mullite, which contains 70 to 85 wt% of SiC aggregate particles and has a particle size distribution in which the average particle size falls within the range of 6.5 to 0.6 μm. A SiC refractory bonded by parts, wherein the vitreous or crystalline SiO2 phase is contained in the grain boundary joint in an amount of 3 wt% or more in an external amount. 2. The SiC refractory according to claim 1, wherein the glassy or crystalline SiO2 phase is a constituent oxide of clay mineral. 3. The method according to claim 1 or 2, wherein the surface protective film is substantially composed of SiO2.
The SiC-based refractory described. 4. One or two of said alumina and mullite.
2-6 wt of first particles of seed having average particle size of 6-6.5 μm
%, Second particles having an average particle diameter of 0.6 to 1 μm of 9 to 2
The SiC refractory material according to claim 1, which comprises 8 wt%. 5. A method for producing a SiC refractory material, which comprises firing the composition according to claim 1 or 4 at a temperature of 1300 to 1500 ° C. in an oxidizing atmosphere. 6. The method for producing a SiC refractory according to claim 5, wherein the glassy or crystalline SiO2 is contained in kaolin.