JPH07187785A - Sic refractory - Google Patents

Abstract

PURPOSE:To obtain an SiC refractory having excellent compression strength as well as thermal shock resistance and high-temperature mechanical strength by adding amorphous silica in the sintering of a molded product containing powder essentially composed of silicon carbide. CONSTITUTION:Powder essentially composed of silicon carbide is incorporated with 0.1-5wt.% of amorphous silica. The silicon carbide powder may further contain a vanadium compound, a calcium compound, a bentonite compound, kaolin, etc. The molded product is baked at <=1000 deg.C and then sintered at 1300-1600C deg.. The obtained SiC refractory has the following properties. The refractory is composed of a number of crystal grains essentially composed of silicon carbide and grain boundaries and contains >=60wt.% of silicon carbide and <=15wt.% of cristobalite wherein the cristobalite is present at the grain boundary. The open pore ratio is 7-14% and the bulk specific gravity is 2.64-2.84g/cm<3>.

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 compressive strength, thermal shock resistance, mechanical strength at high temperature, erosion resistance against molten metal, and the like.

[0002]

2. Description of the Related Art Conventionally, silicon carbide (SiC) -based refractory materials have been used for firing jigs and the like because of their excellent fire resistance. For example, a shelf plate for placing a sheath, ceramics, and the like, a column for supporting the shelf plate, and the like used in a firing furnace are examples of silicon carbide refractories. In addition, a silicon carbide refractory is also used for bricks, blocks, and the like that are structural materials such as walls and floors in a firing furnace. For shelf boards, etc., thermal shock resistance, oxidation resistance,
In addition, it is important for the structural material to be strong against mechanical deformation, and for the structural material, it is important to be strong against compressive strength and erosion. It goes without saying that these SiC refractories need to have high mechanical strength at high temperatures. In addition, SiC
Quality refractories are required to be resistant to thermal shock. For example,
This is because the shelf plate is cooled from a high temperature to room temperature every time it is taken out of the firing furnace and is subjected to thermal shock, and conversely, when it is put into the firing furnace, it is also subjected to thermal shock. The high temperature means these S
It is the temperature in a firing furnace in which iC silicon carbide is used, and means, for example, 1000 ° C to 1400 ° C.

The microscopic structure of these SiC refractories is
It is composed of a large number of crystal grains and grain boundaries between the crystal grains. The crystal grain is a single crystal of silicon carbide, and the crystal grains are connected to each other by a grain boundary. Conventional SiC-based carbide is
The grain boundary contains a large amount of vitreous matter originating from the starting clay and minerals. Therefore, the SiC-based carbide has a good room-temperature strength, but has a drawback that the mechanical strength at a high temperature is low due to the vitreous nature of the grain boundaries. Further, it was difficult to obtain a refractory having a high density, and the oxidation resistance was poor.

Therefore, in recent years, the addition amount of clay minerals has been reduced as much as possible, and instead of this, a trace amount of metal oxides and SiC are added.
A manufacturing method in which the surface of the SiC powder is oxidized by kneading and shaping the powder together and firing in an oxidizing atmosphere, and the SiC crystal grains are bonded by silicon dioxide (SiO ₂ ) generated by the oxidation. Is attracting attention. It is known that the SiC refractory produced in this way has higher high temperature strength than the SiC refractory using conventional clay minerals.

Japanese Patent Application No. 4-347858 discloses a SiC refractory containing cristobalite at grain boundaries in order to improve thermal shock resistance and mechanical strength at high temperatures. The amount of cristobalite is not more than 15% by weight of SiC refractory. Cristobalite is one of the polymorphs of silicon dioxide. The polymorph of silicon dioxide is composed of Si atoms in which four oxygen atoms are arranged at the apexes of a tetrahedron.
Depending on the arrangement of O ₄ tetrahedra, cristobalite has a low temperature type that belongs to a tetragonal system and a high temperature type that belongs to a cubic system.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a SiC refractory material which is excellent not only in thermal shock resistance and mechanical strength at high temperatures but also in mechanical strength such as compressive strength. Another object of the present invention is to form cristobalite not only near the surface of the refractory but also inside the refractory in the thick refractory.

[0007]

[Means for Solving the Problems] Therefore, the present inventor
In order to improve the compressive strength, it has been found that the molded body may be made to contain amorphous silica or silicon carbide powder having an average particle size of 5 μm or less and sintered, and the present invention has been completed. According to the present invention, a SiC refractory having a large number of crystal grains substantially composed of silicon carbide and grain boundaries, wherein the SiC refractory is 60% of the SiC refractory.
It contains not less than 15% by weight of silicon carbide and not more than 15% by weight of cristobalite, the cristobalite is present at grain boundaries, the open porosity is 7 to 14%, and the bulk specific gravity is 2.
Si characterized in that it is 64-2.84 g / cm ^3.
A C-quality refractory is provided. In the present invention, the compressive strength is preferably 900 kgf / cm ² or more.

Further, the SiC refractory has a thickness of 30 mm or more, and is 10 to 1
When a powder having a depth of 5 mm is used and the powder is analyzed by X-ray diffraction, the diffraction peak of cristobalite having 2θ of 21 ° 90 ′ with respect to the height of the diffraction peak of silicon carbide having 2θ of 34 ° 10 ′. The height ratio is 0.06 ~
It is preferably 0.6. That is, in a thick refractory, cristobalite is formed not only near the surface of the refractory but also inside the refractory.
Inside the refractory, a position deeper than the thickness of the refractory was selected to a depth of 10 to 15 mm from the surface of the refractory. Further, the content of cristobalite was defined by the diffraction peak of powder X-ray diffraction in comparison with silicon carbide.

Further, when the above powder is analyzed by X-ray diffraction, the height of the diffraction peak of cristobalite having 2θ of 21 ° 90 ′ is higher than the height of the diffraction peak of silicon carbide having 2θ of 34 ° 10 ′. More preferably, the ratio is 0.1 to 0.4. The SiC refractory may be brick-shaped or rod-shaped.

Further, according to the present invention, a molded body containing a powder substantially made of silicon carbide is provided in the range of 1300 to 160.
A method for producing a SiC-based refractory material, characterized in that the compact contains 0.1 to 5% by weight of amorphous silica. In the present invention, the average particle size of the powder is preferably 5 μm or less, more preferably 2.5 μm or less. The powder preferably contains 90% by weight or more of silicon carbide. Amorphous silica is a powder having an average particle size of 5 μm or less, and at least a part of the amorphous silica is preferably converted into cristobalite after sintering.

[0011]

In the present invention, the open porosity is 7 to 14%.
Within this range, the compressive strength is improved, the number of bubbles or pores that hinder the heat conduction at the grain boundaries is reduced, and cracks are less likely to occur.

Further, according to the present invention, the bulk specific gravity is 2.64.
Is about 2.84 g / cm ³ . The refractory material has open pores that communicate with the external space of the refractory material, and also has closed pores that are closed and do not communicate with the external space of the refractory material. The bulk specific gravity means the mass with respect to the volume of the substance portion, the open pores, and the closed pores. On the other hand, the apparent specific gravity means the mass relative to the volume of the substance portion and the closed pores, which does not include the open pores. Therefore, the apparent specific gravity becomes a value slightly smaller than the theoretical density of the composition of the refractory, but the bulk specific gravity becomes a value smaller than the apparent specific gravity. The bulk specific gravity is 2.64 g / cm ^3.
When it is smaller, the number of pores that hinder the heat conduction increases in the grain boundaries, and the mechanical strength decreases. Also, through this pore, Si
When the oxidation of C is promoted and SiO ₂ is generated by the oxidation, the refractory may be damaged due to volume expansion. On the other hand, when the bulk specific gravity exceeds 2.84 g / cm ³ , SiO ₂ is insufficient in the grain boundaries, so that the thermal shock resistance decreases. The bulk specific gravity is preferably 2.75 g / cm ³ or less.
The theoretical density of silicon carbide is 3.2 g / cm ³ .

The grain boundary contains a crystalline or vitreous component, but contains SiO ₂ . This silicon dioxide is partly cristobalite but also contains non-cristobalite silicon dioxide. These silicon dioxides are other crystalline phases or glassy. At the grain boundary, Al, Cr, M
n, Cu, V, Ca, Ba and the like may be further contained,
The flux component and the amount of the component are determined according to the application and shape of the refractory.

Further, the SiC-based refractory material is 15.0% by weight or less of the whole SiC-based refractory material, preferably 1.0 to 10%.
It contains cristobalite in a weight percentage. When sintering a SiC refractory, the surface of the SiC crystal grains is partially oxidized, and SiO ₂ is produced. This SiO ₂ contains a trace amount of metal oxide flux (calcium or vanadium oxide) in the raw material ( Reacts with the glass component) to form a strong grain boundary bonded phase. At this time, SiO generated by oxidation of SiC
₂ , part of the transition from vitreous to cristobalite,
It remains as a subphase.

Since this cristobalite has a large difference in thermal expansion between room temperature and use temperature (1000 to 1600 ° C.), microcracks are likely to occur at grain boundaries due to repeated heating and cooling, and the microcracks are gradually connected to form SiC. The quality refractory itself is destroyed, and for example, a shelf plate is cracked. Therefore, it is preferable to control the total amount of cristobalite to the above value. The SiC refractory preferably contains 60% by weight or more of silicon carbide, and more preferably 70 to 85% by weight of silicon carbide. Silicon dioxide is
It is preferable to contain 1.0 to 10.0% by weight, and
It is more preferable to contain 8% by weight. CaO is 0.
It is preferable that the content of V ₂ O ₅ be 0.05 to 1.0% by weight, and that of V ₂ O ₅ be 0.05 to 1.0% by weight.
₂ O ₃ is preferably contained in an amount of 0.01 to 0.15% by weight.

According to the method for producing a SiC refractory, a molded body containing a powder substantially composed of silicon carbide is used for 1300
Sinter at ~ 1600 ° C. The powder preferably contains 90% by weight or more of silicon carbide. Therefore, it may contain usual impurities. The powder may include, for example, particles having a particle size of 3 mm, and at the same time, particles having a particle size of 1 μm may be contained.

At this time, when the molded body contains 0.1 to 5% by weight of amorphous silica or silicon carbide powder having an average particle diameter of 5 μm or less is used, the open porosity and the bulk density are within the above range. A certain SiC refractory is obtained. The microscopic structure of amorphous silica is such that a large number of SiO ₄ tetrahedra are randomly arranged while sharing oxygen atoms with each other. At least a part of the amorphous silica is converted into cristobalite after sintering, and the cristobalite is often present in the grain boundary of the refractory. The molded body may contain a vanadium compound, a calcium compound, bentonite, kaolin, etc. in addition to the silicon carbide powder. Molded body to 100
Temporarily calcined at a temperature of 0 ° C or lower, then 1300 to 1
Sinter at 600 ° C. When the sintering temperature is less than 1300 ° C, the thermal shock resistance is poor. On the other hand, if the sintering temperature exceeds 1600 ° C, the mechanical strength will decrease.

[0018]

EXAMPLES Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. (Examples 1 to 8) Particle size is 6 mesh or less (particle size is 283
It is 0 μm or less. Bentonite was added to the silicon carbide powder of 1). Based on the total amount of silicon carbide and bentonite,
Amorphous silica in the amount shown in Table 2 and 0.02% by weight
CaCO ₃ with 0.45 wt% V ₂ O ₅ and 6 wt%
Of water and then kneading. The compositions of Examples 1 to 4 and Reference Example are shown in the following table. The numbers are% by weight.

[0019]

[Table 1] The composition of Example 1 and the reference example is a composition for JIS normal type bricks, and the compositions of Examples 2 to 4 are compositions of refractory materials used in the firing furnace, such as columns and shelf bars.

This mixture is mixed with 230 × 114 after sintering.
It was formed into a rectangular parallelepiped shape so as to have a size of × 65 mm (thickness), and then dried to sufficiently remove water. This molded body was heated to 800 ° C. and held for a certain period of time to perform primary firing, then further heated to 1450 ° C. and held for 10 hours to sinter to obtain a SiC refractory material. Also, this S
Open porosity (%), apparent specific gravity (ρ _a , g / c) of iC refractory
m ³ ) and bulk specific gravity (ρ _b , g / cm ³ ) are JIS R 26
It measured by the underwater method according to 14-76. First, the sample was sufficiently dried, and then the dry weight (W ₁ ) was weighed. Then, the sample was boiled in water, water was completely penetrated into the open pores, and the weight of water (W ₂ ) was measured in water. Finally,
A sample in which water has completely penetrated into open pores is
The saturated water weight (W ₃ ) was weighed.

Ρ _a = W ₁ / (W ₁ −W ₂ ) ρ _b = W ₁ / (W ₃ −W ₂ ) Open porosity (%) = (W ₃ −W ₁ ) / (W ₃ −W ₂ ) ×
100 Compressive strength (kgf / cm ² ) was measured according to JIS R 2615-76. As the sample, a cube having a side of about 60 mm was used. The open porosity (%), apparent specific gravity (g / cm ³ ), bulk specific gravity (g / cm ³ ) and compressive strength (kgf / cm ² ) are summarized in Table 2.

[0022]

[Table 2]

The cristobalite content of this SiC refractory was measured by a powder X-ray diffraction method. In order to obtain a sample for analysis from the center, first 230 × 114 × 65 m
The refractory material of m was divided into two pieces having a size of 115 × 114 × 65 mm. Next, as shown in FIG. 1, a rectangular parallelepiped 11 having a surface 10a and a divided surface 10b on its surface was cut from the divided sintered body 10. This rectangular parallelepiped was divided into 6 layers each having a thickness of 5 mm. Each layer was ground into a powder by using a tungsten carbide frisch.

This powder was analyzed by X-ray diffraction. As an automatic recording X-ray diffractometer, RINT10 manufactured by Rigaku Denki Co., Ltd.
Using 00, continuous measurement was performed with 2θ as the measurement axis. X-rays are Cu-, which has a wavelength of 1.3418 angstroms.
Kα rays were used and Cu-Kβ rays were removed using a monochromator. The applied voltage to the X-ray tube was 40 kV and the tube current was 20 mA. As conditions for the slit system of the X-ray diffractometer, the divergence slit was set to 1 °, the scattering slit was set to 1 °, and the light receiving slit was set to 0.15 mm. The conditions of the goniometer were set such that the diffraction angle 2θ was in the range of 15 to 50 °, the sampling angle was 0.020 °, and the scan speed was 2.0 ° / min.

A peak at 2θ of 34 ° 10 ′ was used as a reference peak of silicon carbide, and a peak at 2θ of 21 ° 90 ′ was used as a reference peak of cristobalite. The heights of both reference peaks were measured, and the height of the reference peak of cristobalite when the reference peak of silicon carbide was set to 1 was obtained.
The ratio of the cristobalite standard peak to the silicon carbide standard peak is summarized in Table 3.

[0026]

[Table 3] From Tables 2 and 3, it can be seen that by adding amorphous silica, cristobalite is contained even in the interior of the refractory and the compressive strength is improved to 900 kgf / cm ² or more.

[0027]

The SiC refractory material of the present invention is excellent not only in thermal shock resistance and mechanical strength at high temperatures but also in compressive strength.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a method for obtaining a sample by a powder X-ray diffraction method in Examples and Comparative Examples.

Claims (10)

[Claims] 1. A SiC refractory having a large number of crystal grains substantially composed of silicon carbide and a grain boundary, the SiC refractory being different from the SiC refractory with respect to the SiC refractory.
It contains 60% by weight or more of silicon carbide and 15% by weight or less of cristobalite, the cristobalite exists in the grain boundary, the open porosity is 7 to 14%, and the bulk specific gravity is 2.64 to.
2.84 g / cm ³ SiC-based refractory material. 2. The SiC refractory material according to claim 1, which has a compressive strength of 900 kgf / cm ² or more. 3. The SiC refractory material has a thickness of 30 mm or more, and a portion having a depth of 10 to 15 mm from the surface of the SiC refractory material is used as a powder, and the powder is analyzed by X-ray diffraction. Then, the ratio of the height of the diffraction peak of cristobalite having 2θ of 21 ° 90 ′ to the height of the diffraction peak of silicon carbide having 2θ of 34 ° 10 ′ is 0.06 to 0.6. The SiC refractory according to claim 1 or 2. 4. When the powder is analyzed by X-ray diffraction, 2
The ratio of the height of the diffraction peak of cristobalite having 2θ of 21 ° 90 ′ to the height of the diffraction peak of silicon carbide having θ of 34 ° 10 ′ is 0.1 to 0.4. The SiC refractory material according to claim 3. 5. The SiC refractory material according to claim 1, wherein the refractory material has a brick shape or a rod shape. 6. A method for producing a SiC refractory material, which comprises sintering a compact containing a powder consisting essentially of silicon carbide at 1300 to 1600 ° C., wherein the compact is 0.1 to 5% by weight. A method for producing a SiC-based refractory material, which comprises amorphous silica. 7. The method for producing a SiC refractory material according to claim 6, wherein the powder has an average particle diameter of 5 μm or less. 8. The method for producing a SiC refractory material according to claim 7, wherein the powder has an average particle diameter of 2.5 μm or less. 9. The method for producing a SiC refractory material according to claim 6, 7 or 8, wherein the powder contains 90% by weight or more of silicon carbide. 10. The amorphous silica is a powder having an average particle diameter of 5 μm or less, and at least a part of the amorphous silica is converted into cristobalite after sintering, according to any one of claims 6 to 9. Si described
Method for manufacturing C-type refractory material.