JPS5817146B2 - Method for manufacturing high-density silicon carbide sintered body - Google Patents

Description

Detailed Description of the Invention The present invention comprises silicon carbide (SiC) powder consisting essentially of β-type silicon carbide (hereinafter referred to as β-8iC), boron (B) or boron carbide (B4C), and carbon. The present invention relates to a method for producing a high-density silicon carbide sintered body having a density of 3.0 g/i or more (relative density of 93% or more) by sintering a mixture without pressure.

Recently, high-density silicon carbide sintered bodies have become available and are beginning to be used for high-temperature-resistant structural materials, sliding materials, etc.

Manufacturing methods include reaction sintering, hot pressing, and pressureless sintering.

Among these methods, the reaction sintering method tends to contain excess silicon (Si) and has the disadvantage of lacking chemical resistance and high temperature strength.

Further, although the hot pressing method has a density of about 100% of the theoretical density and can obtain the highest strength, it is extremely difficult to obtain a sintered body with a complicated shape.

On the other hand, the pressureless sintering method has the advantage that it is possible to obtain a molded article with a considerably complicated shape by using various molding methods, and that it can be sintered without applying pressure.

However, as a result of various studies, when using β-8iC powder,
If the oxygen content in β-8iC powder is high, the conventional method
．． It was found that there is a drawback that it can only be sintered to a density of less than OgZc11.

The conventional method, for example, Japanese Patent Application Laid-open No. 50-78609,
8iC powder with 0.3-3.0% by weight of boron and 0.1-1.
A starting material containing 0% by weight of carbon is molded and sintered.

Furthermore, in Japanese Patent Application Laid-open No. 50-78609, 1'-0,
A boron-doped powder with an oxygen content of 0.06% can be easily sintered to 98.5% of theoretical density with the addition of 0.3% carbon.

Another powder containing 0.3% oxygen can be sintered to 91% relative density with 0.9% carbon.

``Also, 0.1-1.0% by weight of carbon was found to be sufficient to provide sinterability.''

A powder that does not sinter under these conditions will not sinter even if a large amount of carbon is added.

In other words, if the β-8iC powder contains 0.3% by weight or more of oxygen and the added amount of carbon exceeds 1.0% by weight, sintering with a density of 3.0 g/ff1 or more, which is the object of the present invention, can be achieved. This means that the body cannot be obtained.

β-8iC powder tends to contain SiO2 due to the manufacturing method, and fine powder with an average particle size of 0.5 μm or less is susceptible to oxidation and the surface tends to become SiO□.

For this reason, the β-8iC powder necessarily contains about 1% by weight of oxygen at most.

The object of the present invention is to use β-8iC powder containing up to 1% by weight or less of oxygen, which was impossible with conventional methods, and to add carbon in an amount greater than the conventional 1.0% by weight. Oglcr!
It is an object of the present invention to provide a method for manufacturing a high-density silicon carbide sintered body sintered to a density higher than that (relative density 93% or higher).

As a result of various studies on the above drawbacks, the present inventors found that 0.5 to 5.0 parts by weight of boron or 0.6 to 6 parts of boron carbide was added as a sintering aid to SiC powder mainly consisting of β-8iC.
,0 parts by weight, and adding 1.5 to 5.0 parts by weight of carbon, 3.
It was found that a density of 0 g/ff1 or more (relative density of 93% or more) could be obtained.

When the oxygen content in the β-8iC powder is 0.1% by weight, the minimum amount of carbon added is 1.5 parts by weight or more, and when the oxygen content is 0.3% by weight, the amount of carbon added is 2.0 parts by weight or more. It was found that when the oxygen content is 1.0% by weight, it is necessary to add 4.0 parts by weight or more of carbon.

However, the amount of carbon added is limited to 5.0 parts by weight, and even if more than this is added, it is difficult to increase the density to 3.0 g/d or more.

That is, if more carbon is added than is necessary to reduce the amount of Si02, the carbon will interfere with sintering.

Sio2 becomes SiC through the reaction of 5i02+3C-+SiC+2CO and participates in sintering.

Stoichiometrically, it is sufficient that the amount of carbon is approximately the same amount as the amount of oxygen by weight, but in reality, extra carbon is required.

The present invention uses 89 to 98 parts by weight of β-8iC powder with a maximum particle size of 10 pm, an average particle size of 0.5 μm or less, 0.5 to 5.0 parts by weight of boron of 30 p, m or less, or 0.6 to 0.6 to boron carbide.
6.0 parts by weight of carbon powder with a diameter of 10 μm or less at 1.5 to 5.
An amount of organic compound equivalent to producing 0 parts by weight or 1.5 to 5.0 parts by weight of carbon powder is blended, and a solvent is added, mixed and molded, and further in a nitrogen atmosphere or an inert atmosphere in a vacuum. The above molded product is baked at a temperature of 1900 to 2300°C in a
% or more).

In the present invention, β-8iC powder is 100% β-8
It is preferable to use iC powder, but S as an impurity
Up to 1% by weight of oxygen present in the form of i02, 5% by weight
Anisometric α-form silicon carbide up to, essentially β-8i, necessarily containing up to 2% by weight of other impurities such as free silicon iron, aluminum, magnesium, calcium, etc.
It is also possible to use silicon carbide powder made of C.

These β-8iC powders have a maximum particle size of 10 μm, an average particle size of 0.5 μm or less, and an average particle size of 0.5 μm or less.
If it exceeds 3.0 g/cr#J, it is difficult to achieve high density during sintering.

Further, if the maximum particle size exceeds 10 μm, defects will occur in the high-density silicon carbide sintered body and the strength will decrease.

In addition, the particle size of boron and boron carbide is 30 μm or less, preferably 10 μm or less, and if it exceeds 30 μm, (Bi'/
It is difficult to increase the density beyond i.

The particle size of the carbon powder is 10 μm or less, and if it exceeds 10 μm, it is difficult to achieve a high density of 3.0 g/i or more, as described above.

Further, the organic compounds used in the present invention include phenol formaldehyde resin, cresol formaldehyde resin, furan resin, which generates carbon at high temperatures and has a particularly high carbonization rate.
Polyphenylene resin, tar, pitch, etc. are suitable.

Further, the solvent may be any solvent suitable for dispersing silicon carbide powder and other additives, and water and organic solvents are used.

Additionally, water contains surfactants and pH pH to facilitate dispersion.
A regulator or the like may be added.

Further, when a non-water-soluble organic compound is used as a carbon additive, an organic solvent necessary to dissolve the organic compound, such as acetone, methyl ethyl ketone, methanol, isopropyl alcohol, toluene, xylene, etc., is used.

The amount of boron or boron carbide added is β-8iC powder 89-9
To 8 parts by weight, 0.5 to 5.0 parts by weight of boron and 0.6 to 6.0 parts by weight of boron carbide are added, and the optimum amount is 1.0 parts by weight for boron and 1 part by weight for boron carbide. .28 parts by weight.

If the amount added is less than 0.5 parts by weight for boron or less than 0.6 parts by weight for boron carbide, mixing tends to be insufficient and it is difficult to achieve a high density of <3.0 g/i or more. .0 parts by weight or 6.0 in boron carbide
If the weight exceeds 3.0. ! ? It is difficult to achieve higher density than /i.

Carbon powder is 1.5 to 5.0 parts by weight or 1.5 to 5.0 parts by weight
If an amount of organic compound is added equivalent to producing parts by weight of carbon powder, and outside this range, 3.0 g/cIf
It is difficult to increase the density of 1 or more.

Note that the amount of carbon powder required generally depends on the oxygen content in the starting silicon carbide powder.

The carbon powder is preferably added by adding and mixing an organic compound together with a solvent.

If molding is to be carried out by a casting method, it is preferable to use carbon black.

Also suitable is a method of adding and mixing an aqueous solution of carboxymethylcellulose, methylcellulose, gum arabic, avicel, gelatin, starch, alginate, stearate, polyvinyl alcohol, etc. as an excipient.

Molding is usually carried out by a known method, and sintering must be carried out in vacuum, in a nitrogen atmosphere, or in an inert atmosphere such as argon or helium at a temperature of 1900 to 2300°C.

If the sintering temperature is less than 1900°C, the sintering progresses slowly.3.
It is difficult to increase the density to 0g/cr/1 or more, and 2300
If the temperature exceeds ℃, the crystals will grow and become coarse, as described in 3.
(It is difficult to increase the density to 1/cIft or higher.

The present invention will be explained below with reference to Examples.

Example 1 Silica powder with a purity of 99.5% and coke powder with a carbon content of 99.0% were processed at 1900°C. Maximum particle size 2 μm, average particle size 0.25 pm, Si02 content 0.3 weight %(
β-8iC containing 0.16% by weight of oxygen), 1.0% by weight or less of α-8iC, and 1.0% by weight or less of other impurities
96.0 parts by weight of powder, 1.0 parts by weight of boron powder of 1 μm or less, novolak type phenolic resin (Mitsubishi Gas Chemical, -■
6 parts by weight (3 parts by weight as carbon content) of SM-P 107A (trade name, manufactured by Manufacturer Co., Ltd.) were blended, 100 parts by weight of acetone was added in an outer layer, mixed for 30 minutes in a ball mill, and then dried at 80° C. for 2 hours.

After drying, the mixture was crushed for 15 minutes using a crusher, 10 parts by weight of a 6% by weight aqueous polyvinyl alcohol solution was added as an excipient, mixed for another 15 minutes, and passed through a 42-mesh sieve to obtain a molded powder.

Next, the molded powder is molded at a pressure of 1000 kg/CIF ¥ to obtain a molded product with an outer diameter of 50 mm and a height of 10 mm.

This molded body was cured to 250°C at a rate of 30°C/hour, and further heated to 2000°C at a rate of 500°C/hour in a vacuum of 0.04 Torr, and sintered for 45 minutes.

The result was 3.14 g/cI with a linear shrinkage of 18%! The density of (
A high-density silicon carbide sintered body with a relative density of 97.8% was obtained.

Example 2 Using β-8iC powders obtained by the same method as in Example 1 and having different Si02 contents as shown in Table 1, the amount of carbon added was changed and the following steps were performed in the same manner as in Example 1 to obtain high-density powders. A carbon silicon sintered body was obtained.

The results are shown in Table 1.

Example 3 95 parts by weight of β-8iC powder obtained by the same method as in Example 1, 2 parts by weight of boron carbide powder of 1μ or less, and 3 parts by weight of carbon black were mixed, and 0 parts by weight of sodium silicate was added to the outer layer.
．． 1 part by weight and 60 parts by weight of distilled water were mixed in a ball mill for 30 minutes, then poured into a calcined plaster mold to form a cylinder with an outer diameter of 501nTIL1 an inner diameter of 4011t7IL1 and a length of 50mm, dried, and sintered at 2050°C for 45 minutes in an argon gas atmosphere. did.

As a result, a high-density silicon carbide sintered body having a density of 3.10 g/cd was obtained.

Comparative Example 1 β-8iC powders obtained by the same method as in Example 1 and having different SiO□ contents as shown in Table 2 were molded and sintered through the same steps as in Example 1.

However, the amount of carbon added was 1 part by weight in all cases.

The results are shown in Table 2.

Comparative Example 2 Abrasive α-8iC powder (=1
! 10,000) in the same formulation as in Example 1 and through the same steps to obtain a sintered body.

The resulting density was 2.41g/cI! (Relative density 75.1
%)Met.

Example 4 The amount of carbon at the time of blending was 1 and 1.5° and 2.2 parts by weight, respectively.
．． A silicon carbide sintered body was obtained in the same manner as in Example 1, except that samples Nos. 5, 3, 4, and 5 were used.

FIG. 1 shows the relationship between the amount of carbon added and the relative density and bending strength of the obtained silicon carbide sintered body.

Furthermore, the relationship between relative density and bending strength determined from the above data is shown in FIG.

Figure 1 shows that the relative density and bending strength show a maximum value at a carbon content of 2.5% by weight, and Figure 2 shows that the bending strength is almost proportional to the relative density. .

This value of bending strength is comparable to that of a sintered body produced by the conventional non-pressure sintering method.

According to the invention, β-8iC with an oxygen content of up to 1% by weight
When sintering powder using boron or boron carbide and carbon as a sintering aid, 3. O,! A high-density silicon carbide sintered body having sufficient mechanical strength and sintered to a density of li'/cIIt or higher (relative density of 93% or higher) can be easily produced.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the amount of carbon added, relative density and bending strength, and FIG. 2 is a graph showing the relationship between relative density and bending strength.

Claims (1)

[Claims] 1 Maximum particle size: 10 μm 1: 89 to 98 parts by weight of β-type silicon carbide with an average particle size of 0.5 μm or less, 0.5 parts by weight of boron with an average particle size of 30 μm or less
~5.0 parts by weight or 0.6 to 6.0 parts by weight of boron carbide,
1.5 to 5.0 parts by weight of carbon powder of 10 μm or less or an organic compound in an amount equivalent to producing 1.5 to 5.0 parts by weight of carbon powder, then a solvent is added and mixed,
The above molded product was molded and fired at a temperature of 1900 to 2300°C in vacuum, nitrogen atmosphere, or inert atmosphere to yield 3.0 g/cr! ! or higher density (relative density 93%)
1. A method for producing a high-density silicon carbide sintered body, characterized by sintering the above).