JPH01215758A - Production of silicon carbide sintered form - Google Patents

Abstract

PURPOSE:To obtain the title dense sintered form improved in heat and wear resistances, by mixing, in a specific solvent, SiC powder, silicon boride powder with a mean size smaller than that of said SiC powder, and a carbonaceous additive and by drying, forming and sintering the resultant mixture. CONSTITUTION:Firstly, a mixture is prepared by mixing (A) SiC containing >=90wt.% of beta-SiC, with an average particle size of <=1mum, (B) 0.2-1.5wt.% on an elemental boron basis, of silicon boride of the formula BnSi (n is 6 or 14-24) with an average particle size smaller than that of the component A, and (C) 1-3wt.% on an elemental carbon basis, of a carbonaceous additive (e.g., phenolic resin) in a solvent soluble for said additive (e.g., acetone). Thence, this mixture is dried and formed to a desired shape, and then heated to 900-1,500 deg.C in a vacuum to remove the gases and impurities produced followed by calcination in a vacuum or inert gas atmosphere at 1,850-2,100 deg.C, thus obtaining the objective sintered form.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a silicon carbide sintered body used for heat-resistant, wear-resistant parts, etc.

[Conventional technology]

Silicon carbide sintered bodies are expected to be heat-resistant and wear-resistant materials, but because they are difficult to sinter, boron, carbon, silicon ferride, alumina, ittria, etc. are added as sintering aids. The method of firing was used.

In addition, β-B10 powder for silicon carbide sintered bodies is generally manufactured by a pulverization method with an average particle size of 0.1 to 1 μm.
B or A4O having a similar average particle size was also used as a sintering aid.

[Electricity charges that the invention attempts to solve]

However, the silicon carbide sintered body obtained by the conventional manufacturing method has a problem in that it lacks density sufficient to satisfy heat resistance or wear resistance.

In view of this state of the art, the present invention seeks to provide a method for producing a silicon carbide sintered body with excellent density.

[Means to solve the problem]

The present invention combines 810 powder with an average particle size of 1 μm or less, silicon boride powder with a smaller average particle size, and a carbonaceous additive.
This method of producing a silicon carbide sintered body is characterized by adding and mixing the carbonaceous additive in a solvent capable of dissolving it, drying, shaping, and firing.

And, β-8IC-containing particles with an average particle size of 1 μm or less
In addition to the 810 powder having a particle diameter of 810 or more, the silicon boride powder having an average particle size smaller than this is converted to elemental boron and is 0.2 to 1.
5% by weight, and the carbonaceous additive is converted to elemental carbon from 1 to 5% by weight.
3% by weight is added and mixed in a solvent capable of dissolving the carbonaceous additive, dried, molded, heated to a temperature of 900 to 1500C in a vacuum, and then heated to a temperature of 185C in a vacuum or an inert atmosphere.
A preferred embodiment of the present invention is to perform firing at a temperature of 0 to 2100C.

That is, in order to produce a dense silicon carbide sintered body, the present invention selects silicon hydride and a carbonaceous additive as sintering aids for silicon carbide, and as a sintering aid, #1. The second place is novel because the average particle size of the silicon carbide powder is smaller than that of the raw material silicon carbide powder.

Hereinafter, the raw materials used, compounding conditions, firing conditions, etc. of the present invention will be explained in detail.

As the silicon hydride, 13 nSz (n = 6 and 14 to 24) is used. B2S in this place
3 is a compound, but B148L and B 2 a 8
1 is a solid solution and has the same crystal structure even if the B/81 ratio changes between 14 and 240. Other silicon hydrides include K B and Si, but these have a low melting point of about f400r and have an adverse effect on the silicon carbide sintered body, so they cannot be used.

An example of producing fine powder of silicon hydride is as follows.

A thermal plasma is generated by heating argon gas with a high-frequency induction coil with an output of about 50%, and in this plasma there are particles with a particle size of 30 mm.
If silicon boride powder with a density of 0 mesh or less is supplied with argon gas as a carrier gas, the silicon boride powder will be vaporized, so if argon gas is then blown into the lower part of the thermal plasma as a cooling gas, the vaporized silicon boride will be is rapidly cooled to obtain ultrafine silicon uroride powder of 0.1 μm or less.

Such ultra-fine silicon boride powder has an average particle size of 1 μm.
In the following, it is preferable to add and mix 0.2 to 1.5% by weight of elemental boron into silicon carbide powder having a β-810 content of 90% or more.

This silicon boride is converted to elemental boron by 0.2 times! If it is less than 2, the effect of improving the density of the sintered body will be small;
This is because the increase in density is saturated even if it exceeds 1.5 weight tx.

As the carbonaceous additive, phenol resin, carbon black, tar pitch, etc. are used, and the amount added is preferably 1 to 3% by weight, calculated as elemental carbon, to the silicon carbide powder. This quantitative range is preferred for the same reasons as for silicon hydride.

Acetone, benzene, alcohol, etc. can be used as a solvent for dissolving the carbonaceous additive.

The silicon carbide sintered body is manufactured as follows.

In the above-mentioned solvent, β-810 with an average particle size of 1 μm or less
Silicon carbide powder having a content of 90% or more, ultrafine powder having the quantitative range described above, silicon uroride powder, and a carbonaceous additive are added and mixed. The resulting mixture is dried and shaped into the desired shape.

Next, this molded body is heated to a temperature of 900 to 1500C in a vacuum. This means heating under reduced pressure to fully accelerate the decomposition of the carbonaceous additive in the compact, remove the gases and impurities formed, and promote the formation of carbon particles needed as sintering aids. It is something.

Finally, it is fired at a temperature of 1850 to 2100 G in vacuum or an inert gas atmosphere such as argon to obtain a dense silicon carbide sintered body. If the firing temperature is less than 1850C, the sintering reaction will be slow and the density of the sintered body will not increase, resulting in 2too
ct-, grain growth will occur in the sintered body, and even if the density increases, the sintered body will not be of good quality, and the manufacturing cost will also increase.

When using B2S3i as a sintering aid, liquid phase sintering is involved, so the firing temperature is 1850-2000.
The range of C is preferable, and when Bnsl (n=14 to 24) is used, the firing temperature is more preferably 1900 to 2050C.

Furthermore, it is better to perform the firing in an inert gas such as argon gas than in a vacuum, since the density of the resulting sintered body is approximately 3.
%, so in actual operation, argon gas is introduced into the furnace at 150 QC, and after 1850 to 2100 QC.
It is preferable to employ a method of firing with C.

〔Example〕

Examples of the present invention are shown below.

First, a method for synthesizing silicon boride layer fine particles used in the present invention using thermal plasma will be described. Thermal plasma outputs argon gas (flow rate 7 QA/l1ln) at 5V! N
obtained by heating with a high-frequency induction coil. 5A with argon gas as carrier gas in the powder supply device
The silicon boride powder having a particle size of 300 mesh or less is fed into the thermal plasma at a rate of about 19/min and heated and vaporized. The obtained high-temperature plasma containing silicon borobide is rapidly cooled by blowing argon gas into the lower part of the plasma at about 50 p/min to obtain silicon boride layer fine particles.

The obtained silicon boride layer fine particles are recovered by a recovery device.

The ultrafine particles synthesized in this example had an average particle size of 0.02
/in B, 4S process and B24S process, B6Si and B248i with an average particle size of 0.4 μm by ball mill grinding were selected as silicon boride powders to be used for comparison.

Next, a method for manufacturing the sintered body will be described.

The average particle size of the silicon carbide raw material powder used is 0.5 μm.
The average particle size of silicon boride, which is a sintering aid, is 0.4μ for B6Sz and B24St fine particles obtained by ball mill grinding.
■, B synthesized by thermal plasma, 481 and 8248
1 ultrafine particle is approximately 0.02 μm. Phenol resin was used as the carbonaceous additive, and acetone was used as the solvent to dissolve it.

These were blended in the ratio shown in Table 1, mixed in a ball mill, dried, and pressed to a diameter of 60 mm and a thickness of 511 mm.
Form it into a disk shape of 1.5 mm and press it using a hydrostatic press.
Molding was carried out at a pressure of rx2, heated to 1500C at a rate of 5CI in a vacuum atmosphere, then held at 1500t:' for 50 minutes while introducing argon gas. Sinter at a temperature of 2100C. The sintering time was kept constant at 30 minutes at all temperatures. The density of the obtained β-810 sintered body and the raw material blending ratio 1. Table 1 shows the relationship between firing conditions.

Next, FIG. 1 shows the influence of the amount of boron added on the density of the silicon carbide sintered body. In the WJ1 diagram, the carbon addition was 2%, the firing conditions were 2000C, 30 minutes, in an argon atmosphere, and the silicon carbide powder used was β-8 with an average particle size of 0.3 μm.
iO, silicon hydride has a particle size of 0.02μs OB2481
Ultrafine particles.

Figure 2 also shows 82 a 8 with an average particle size of 0.02 μm.
1. Add 0.5% of ultrafine particles and incubate at 200 °C in argon gas.
The influence of the amount of carbon added on the density of a silicon carbide sintered body when fired at 0C for 50 minutes is shown.

Figure 3 is a diagram showing the influence of firing temperature on the density of the sintered body, and the amount of carbon added is 2% by weight. .4
μm 86Si is used as a sintering aid. From the results shown in Figures 1 to 3 above, the amount of boron added is 0.2 to 1.
．． It can be seen that a carbon addition amount of 1 to 3 times iX of 5% by weight is effective in promoting sintering. Regarding the firing temperature, B6S1
When t- was used, sintering already started to occur at 1850C, which is considered to be due to the B6S1t-based and subsequent liquid phase sintering. No liquid phase appears in B24S1,
The effect of promoting sintering at a temperature of 1900 to 2100C was confirmed.

〔Effect of the invention〕

The present invention provides a method for producing a dense β-SiC sintered body, which has great industrial utility as a method for producing a heat-resistant and wear-resistant silicon carbide sintered body. In particular, by using ultrafine particles as a sintering aid, the sintering temperature can be lowered to about tsac without causing a significant increase in cost, which has great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a chart showing the effect of silicon boride addition on the density of β-810 sintered body, FIG. 2 is a chart showing the effect of carbon addition amount, and FIG. 3 is a chart showing the effect of firing temperature.

Claims (1)

[Claims] SiC powder with an average particle size of 1 μm or less, silicon boride powder with a smaller average particle size and a carbonaceous additive are added and mixed in a solvent that can dissolve the carbonaceous additive, and after drying and molding, A method for producing a silicon carbide sintered body, which comprises firing.