JPH05270917A - Sic sintered compact and calcining method thereof - Google Patents

Abstract

PURPOSE:To provide a SiC sintered compact free from warpages and cracks and also cavities at the center, excellent in resistance to oxidation and spalling. CONSTITUTION:The objective SiC sintered compact having the following characteristics: (1) containing, as constituents, at least SiC and Si; (2) flexural strength: >=15kg/mm<2>; (3) porosity: <=1.0%; (4) porosity difference between the surface layer and center: <20%; and (5) difference in flexural strength between the surface layer and center: <20%. This sintered compact can be obtained by calcining through the following process: feedstock comprising SiC powder, graphite powder, organic binder and water or organic solvent is molded, and the resulting form is set upright and calcined in a vacuum or in an inert gas atmosphere containing metallic silicon at reduced pressures at 1350-2500 deg.C. This SiC sintered compact can be preferably used for ceramic tools such as the shelf boards for quick burning ovens or saggers emphasizing resistance to oxidation and spalling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SiC-based sintered body and a firing method thereof, and more specifically, Si preferably used as a shelf plate for a rapid firing furnace such as tile firing.
The present invention relates to a C-sintered body and a firing method thereof.

[0002]

2. Description of the Related Art Sintered silicon carbide (SiC) materials occupy an important industrial position due to their excellent heat resistance and fire resistance. For example, shelf plates for firing ceramics and other furnace core tubes for firing semiconductors. It is often used for. Among such SiC-based sintered bodies, Si-Si containing SiC and Si as constituent components
C sintered body is known. This Si-SiC sintered body is S
It is manufactured by adding carbon (C) fine powder and an organic binder to iC particles, molding them by casting, extrusion molding, press molding or the like, and then firing them in a Si atmosphere.

[0003]

However, in the sintered body obtained by the casting method, there is a large difference in the density and the porosity between the surface layer and the central portion, and in the extreme case, a cavity is formed in the central portion. There was a problem. In extrusion molding, for example, warpage occurs when extruding into a plate shape,
There was a problem that the base was expensive. In the case of press molding, lamination (layered peeling) is likely to occur at the time of molding, and the shape retention is low, which may cause damage during handling. If press molding can be used in the production of the Si-SiC sintered body, it is considered to be suitable for mass production and industrialization, but there are the above-mentioned problems.

Further, the inventors of the present invention have studied and found that even when a molded body is fired in a Si atmosphere, a sintered body obtained by controlling firing conditions, that is, atmosphere, firing temperature, temperature rising rate, etc. It has become clear that the characteristics are greatly affected. Therefore, it is an object of the present invention to provide a method for firing a molded body obtained by, for example, press molding and a SiC-based sintered body having excellent properties obtained by the method.

[0005]

That is, according to the present invention, Si containing at least SiC and Si as constituent components is used.
C-sintered body having a bending strength of 15 kg / mm ² or more, a porosity of 1.0% or less, and a difference in porosity between the central portion and the surface layer portion of 20% or less, and the central portion and the surface layer. Bending strength difference of 2
Provided is a SiC-based sintered body characterized by being within 0% and excellent in oxidation resistance and spalling resistance.

Further, according to the present invention, a molding raw material containing SiC powder, graphite powder, an organic binder and water or an organic solvent is used. In the firing, a firing method for a SiC-based sintered body is provided, which comprises firing at 1350 to 2500 ° C. in a metal silicon atmosphere and a reduced pressure inert gas atmosphere or vacuum. In the present invention, 0 to 50 ° C./hr between 1350 and 1500 ° C.
It is necessary to have at least one or more temperature raising process of raising the temperature at the temperature raising rate of S and maintain the temperature raising process for 2 hours or more.
It is preferable because the reaction between i and C is promoted to sufficiently produce SiC.

[0007]

The present invention specifies a firing condition such as an atmosphere, a firing temperature and a temperature rising rate, and a firing method for obtaining a SiC quality sintered body having excellent characteristics, and a SiC quality having the specific physical properties obtained by the firing method. It is a sintered body. The SiC-based sintered body having such specific physical properties has excellent oxidation resistance and spalling resistance, and is preferably used as a shelf plate for a rapid firing furnace such as tile firing. First, the molding raw material used in the present invention will be described. The molding raw material preferably contains SiC fine powder and SiC coarse powder. SiC fine powder is
Preferably, the average particle size is 1 to 10 μm, and 0.1 to
90% by weight or more of particles are distributed in a particle size range of 15 μm, and the SiC coarse powder preferably has an average particle size of 25.
90% by weight or more of the particles are distributed in a particle size range of ˜1500 μm and 20 to 2000 μm. Also,
The content ratio of SiC fine powder and SiC coarse powder is 10/90 to 90
The range of / 10 is preferable.

The molding raw material contains graphite powder, and its particle size is preferably 0.1 to 20 μm in average particle size.
Then, those having a distribution of 90% by weight or more in the particle size range of 0.05 to 30 μm are used. The graphite powder is contained in an amount of 0.5 to 25% by weight based on the total amount of the SiC fine powder and the SiC coarse powder. The SiC fine powder and coarse powder, and the graphite powder further contain an organic binder and water or an organic solvent to form a raw material for molding. As the organic binder, methyl cellulose, isoban, etc. are preferably used, and the content thereof is 0.1 to 5.0% by weight based on the total amount of the SiC fine powder and the SiC coarse powder. Further, the content of water or the organic solvent is 0.5 to 5.0% by weight based on the total amount of the SiC fine powder and the SiC coarse powder.

SiC fine powder having such a predetermined particle size, SiC
A raw material for molding which contains a predetermined amount of coarse powder and graphite powder and further contains an organic binder and water or an organic solvent is mixed, and the mixture is preferably adjusted by using a pulverizer such as a ball mill or a fret mill. When making this adjustment
It is preferable to disintegrate until 90% by weight or more of the agglomerated particles of graphite are disintegrated. The crushing degree here is 20 mm x 2
The ratio is calculated by measuring the number of agglomerated graphite particles on the press surface and the raw material after crushing with a magnifying glass when press-molding by putting an appropriate amount of raw material before crushing into a 0 mm mold. It

Next, the obtained molding raw material is molded,
Press molding is preferable as a molding method. A hydraulic press is preferable as the press molding. The hydraulic press pressure is usually 50 to 2000 kgf / cm ² . It should be noted that it is effective to subject the compact after the hydraulic pressing to rubber pressing because it increases the homogeneity of the compact and eventually the sintered compact.
When the molded body is thin, when the above-mentioned pressing is performed, the raw material is pre-molded at a pressure of 1/2 or less of the molding pressure to remove air contained in the raw material, and then molded at a predetermined molding pressure. It is preferable from the viewpoint of preventing the occurrence of lamination.

The molded product obtained by molding as described above is fired under a predetermined condition in a metallic silicon atmosphere (the metallic silicon is melted during firing and the molded body is placed in the liquid phase of metallic silicon). Thereby, a sintered body having excellent oxidation resistance and spalling resistance can be obtained.
At the time of the above firing, it is important to stand and fire the molded body to prevent warpage. Here, the term "standing" means that when the molded product is a plate-shaped molded product such as a shelf plate, it is stood in the vertical direction and fired. When the molded products are erected, the interval between the molded products is 2 mm or more, preferably 5 mm.
mm or more, and in the case of a plate-shaped molded body, 1 / of the wall thickness
It is preferable to provide an interval of 2 or more from the viewpoint of preventing adhesion between the molded products due to the seepage of Si.

Next, as the firing conditions, it is basically necessary to perform firing at 1350 to 2500 ° C. in a metal silicon atmosphere and a reduced pressure inert gas atmosphere or vacuum. Then, in order to promote the reaction between Si and C to sufficiently generate SiC, the temperature raising process of raising the temperature range of 1350 to 1500 ° C. at a heating rate of 0 to 50 ° C./hr is performed at least once or more. In addition, it is preferable that the temperature rising process is maintained for 2 hours or more. Further, as the inert gas atmosphere, considering the reactivity with SiC,
N ₂ gas atmosphere is unsuitable, and other argon (A
An atmosphere of r) gas, helium (He) gas, or the like is preferable.

A specific firing schedule will be described below. First, firing is performed under vacuum of 10 Torr or less, preferably 0.01 to 0.1 from room temperature to about 600 ° C. About 60
Firing is performed under a vacuum of 50 Torr or less, preferably 0.1 to 10 Torr or an atmosphere such as argon gas between 0 ° C and about 1000 ° C. Next, from about 1000 ° C. to the maximum temperature (between about 1600 to about 2500 ° C.), it is preferable to reduce the pressure in an argon gas atmosphere because the wettability of Si with SiC is improved.

Among the above firing steps, 1350 to 15
It is important to have a temperature increasing process of increasing the temperature between 00 ° C. at a temperature increasing rate of 0 to 50 ° C./hr at least once, and to control this temperature increasing process for 2 hours or more. ..
This is because the melting temperature of metallic Si is about 1420 ° C., which promotes the reaction between dissolved Si and C, and Si + C → SiC
Can be sufficiently performed. The SiC-based sintered body that has been fired under the above conditions does not warp or break, has no cavities in the center, and is characteristically high in strength and low in porosity. And this SiC
The quality sintered body has a difference in porosity and strength between the central portion and the surface layer portion that is smaller than a predetermined value, and is excellent in oxidation resistance and spalling resistance.

That is, the obtained SiC-based sintered body is SiC
A SiC-based sintered body containing at least Si and Si as constituent components, having a bending strength of 15 kg / mm ² or more and a porosity of 1.0.
% Or less, the difference in porosity between the central portion and the surface layer portion is within 20%, the difference in bending strength between the central portion and the surface layer portion is within 20%, and excellent in oxidation resistance and spalling resistance. Is. If the porosity of the SiC sintered body exceeds 1.0%, or if the difference in porosity between the central portion and the surface layer portion exceeds 20%, strength, oxidation resistance, and spalling resistance are low. Become.

[0016]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to these examples. (Evaluation method of spalling resistance (ΔT)) 70 of sintered body
%, An alumina brick having a wall thickness of 10 mm was loaded and pulled out from a furnace having a constant temperature T ₂ into the atmosphere (temperature T ₁ ), and ΔT (= T ₂ −T ₁ ) at which a crack was generated was measured. (Evaluation Method of Oxidation Resistance) The sintered body was measured at 1150 ° C.
It was placed in a gas of hr and H ₂ O + O ₂ and the amount of increase (△
W) was measured.

(Examples 1 to 6 and Comparative Examples 1 and 2) SiC in which the average particle size, particle size distribution and content are changed as shown in Table 1.
Fine powder, SiC coarse powder, and graphite powder were mixed with an organic binder (methyl cellulose) and water or an organic solvent in a proportion shown in Table 1 by external distribution to obtain a raw material for molding. next,
These molding raw materials were crushed using a ball mill so that the graphite agglomerated particles had a crushing degree as shown in Table 1. The ball mill used was a monoball having a surface coated with plastics at 1100 rpm. Next, the crushed molding raw material was introduced into a mold and molded under a pressure of Table 1 using a hydraulic press to obtain plate-shaped molded bodies of various thicknesses shown in Table 1.

[0018]

[Table 1]

Next, of this plate-shaped molded body, 200 ×
Those of 30 × 10 (thickness) (mm) were fired under the conditions shown in Table 2 to obtain a SiC-based sintered body. Table 2 shows the porosity and bending strength of the obtained SiC-based sintered body. The surface layer portion was measured as a portion 3 mm from the surface, and the central portion was measured as a portion 3 mm to 7 mm from the surface. Further, the spalling resistance (ΔT) and the oxidation resistance (ΔW) of the SiC sintered body were evaluated. The results are shown in Table 2. As shown in Table 2, the sintered bodies of Examples 1 to 6 have smaller porosity than the sintered bodies of Comparative Examples 1 and 2,
Moreover, it can be seen that the difference is small and the bending strength is large. It was also found that ΔT was large, but ΔW was small, and the spalling resistance and oxidation resistance were excellent.

[0020]

[Table 2]

[0021]

As described above, according to the present invention, the firing conditions such as the atmosphere, the firing temperature, and the heating rate are specified, so that there is no warp or break, there is no nest in the center, and the oxidation resistance is high. Further, a SiC-based sintered body having excellent spalling resistance can be obtained. The obtained SiC-based sintered body is preferable for shelf boards for rapid firing furnaces that place importance on oxidation resistance and spalling resistance, kiln tools such as saggers and pods, and particularly for tile firing shelf boards using a roller hearth kiln. Can be used.

Claims (4)

[Claims] 1. A SiC-based sintered body containing SiC and Si as at least constituents, and having a bending strength of 15 kg / mm ^2.
As described above, the porosity is 1.0% or less, the difference in porosity between the central portion and the surface layer portion is within 20%, the bending strength difference between the central portion and the surface layer portion is within 20%, and the oxidation resistance and A SiC-based sintered body having excellent spalling resistance. 2. A molding raw material containing a SiC powder, a graphite powder, an organic binder and water or an organic solvent is used. After molding the molding raw material, the molding obtained is erected and fired. 1350 to 250 in a metal silicon atmosphere and in a reduced pressure inert gas atmosphere or vacuum
A method for firing a SiC-based sintered body, which comprises firing at 0 ° C. 3. Between 1350 and 1500 ° C., 0-50
The firing method according to claim 2, further comprising at least one heating step for heating at a heating rate of ° C / hr and maintaining the heating step for 2 hours or more. 4. The firing method according to claim 2, wherein the molding is performed by press molding.