JPS5924754B2 - Method for manufacturing silicon carbide molded body - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a silicon carbide molded body.

A conventional method for manufacturing a silicon carbide (hereinafter referred to as SiC) molded body using a reaction sintering method involves kneading and molding SiC powder, carbon powder, and an organic temporary binder (hereinafter referred to as a blow molded body), After the binder is changed into volatile matter and carbon by heating (hereinafter referred to as the secondary molded body), metallic silicon at a temperature above the melting point is infiltrated into this molded body to generate SiC. there were.

Compared to the so-called hot press method, in which mixed powders such as SiC powder and magnesia are molded using a hot press, this method has a long lifespan and allows for easier production of irregularly shaped products.
Since an organic temporary binder is used, the strength of the primary molded body and the secondary molded body before metal silicon infiltration is low, and it is impossible to perform processing with high dimensional accuracy at this stage.

Furthermore, the secondary molded product is transformed into SiC by infiltrating metallic silicon, and has a Vickers hardness of over 3200, so only diamond tools can be used for processing, which increases processing costs. There is.

The present inventors have made efforts to eliminate the need for machining the final SiC molded body, improve its strength at the stage of the secondary molded body, and make cutting processing easier and more accurate. As a result of study, we found a new method that does not have the disadvantages of the conventional methods and completed the present invention.

That is, the present invention contains 10 to 80% by weight of SiC powder, 10 to 70% by weight of carbon powder, and 0.5 to 6% of polyorganopolysilane and/or polyorganocarbosilane.
A mixture consisting of 0% by weight is molded to form a molded body, then this molded body is heated to a temperature at which thermal decomposition of polyorganopolysilane and polyorganocarbosilane occurs, and the molded body after thermal decomposition is subjected to cutting. The present invention relates to a method for manufacturing a silicon carbide molded body, which comprises straining and then impregnating molten metal silicon.

The SiC powder used in the present invention has an average particle size of 20 μm or less,
Preferably, the crystal structure is 5 μm or less, and the crystal structure may be α or β, but it is preferably rich in α-SiC structure.

Carbon powder can be used regardless of its type, and the particle shape is not limited to spherical but may be acicular. However, it is convenient to use graphite powder with an average particle size of 100 μm or less, preferably 10 μm or less.

The polyorganopolysilane is preferably one having a methyl group as an organic group, such as polymethylpolysilane, and there is no particular restriction on the molecular weight as long as it is liquid at room temperature or melts when heated. Those with low molecular weight are preferred.

This polyorganopolysilane has a main chain consisting of only Si atoms and is represented by the general formula (R is a monovalent hydrocarbon group, m is a positive integer), but the polyorganocarbosilane used similarly to this is The main chain is (Japanese Patent Application Laid-Open No. 126300/1983
(Refer to Publication No.-80500).

In the method of the present invention, the mixing ratio of SiC and carbon powder, polyorganopolysilane and/or polyorganocarbosilane is adjusted to 10 to 70%, preferably 20 to 5%.
0%, polyorganopolysilane and/or polyorganopolysilane 0.5-60%, preferably 20-50%
%, SiC is 10-80%, preferably 20-45% (
% by weight (the same applies hereinafter), good results can be obtained.

If the carbon powder is below this range, it becomes difficult for metal silicon to penetrate, and if it exceeds this range, cracks may occur in the molded body when metal silicon penetrates.

In addition, if there is too little polyorganopolysilane and/or polyorganocarbosilane, the secondary molded product will easily collapse and will be difficult to process due to lack of strength, while if it is too much, cutting tools will be severely worn out. Therefore, it is not economical, but processing is possible, so if a suitable tool is selected and limited, it may be greater than the above range.

After sufficiently kneading the mixture of the above formulation, the mixture is press-molded using a mold press or a rubber press machine to form a primary molded body, and the organopolysilane and/or polyorganocarbosilane is converted into SiC in an appropriate atmosphere. When heated until , a highly strong secondary molded body can be obtained.

In this case, the heating effect occurs at temperatures above 100°C.
If the temperature is 600°C, a sufficient effect can be obtained quickly, but
Above this temperature, the strength tends to increase as the temperature increases.

However, care must be taken as rapid heating may cause cracks in the molded product.

In this case, heating to 400° C. or higher causes an oxidation reaction due to oxygen in the surrounding air, so if necessary, the surrounding air may be replaced with an inert gas such as argon or a vacuum.

The time required for this heating varies widely depending on the temperature, but for example, at 500° C., about 3 hours is sufficient, and the molded product reaches a certain weight.

This secondary molded body can be processed into a complicated shape using a general purpose tool such as a cutting tool made of high-speed steel, carbide, or ceramic, a GO grindstone, a hacksaw, or a diamond tool.

By infiltrating the processed secondary molded body with molten silicon metal using a conventional method, a dense SiC molded body with highly accurate dimensions that does not require any or very little finishing processing can be obtained. This makes it possible to easily obtain a molded body with a complex shape and high dimensional accuracy, which was difficult to produce using conventional methods.

The specific gravity of the secondary molded product varies from 1.75 to 1.75 depending on its composition.
Although the range is 2.00, the specific gravity of the completed SiC molded body is approximately 3.05 to 3.15.

As mentioned above, in conventional technology, SiC is manufactured and then subjected to cutting, which results in (1) only simple shapes being possible; (2) only diamond tools can be used, resulting in high machining costs (generally for precision parts). Processing costs account for most of the cost of ceramic products for industrial use).

(3) The secondary molded product has low strength and is extremely difficult to process, making it impossible to obtain high precision, so processing at this stage is rarely performed. However, in the present invention,
These problems have been eliminated, and (1) products with complex shapes can be manufactured, (2) machining can be performed using general-purpose tools, and (3) sword roe can be performed with high precision in the secondary molded state. (4) The proportion of manufacturing processing costs can be significantly reduced compared to conventional methods.

You will get great benefits such as:

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

Example l α-3iC (#3000), graphite powder (average particle size 2 μm
), polymethylpolysilane (viscosity 430 centistokes at 25°C, average molecular weight 1400) was mixed in a weight percent ratio of 71.22.7, and the mixture was mixed with 5 saws x 5 CTL x 1 ( The molded product was molded into a plate shape of m in size, and further molded under pressure of 2t/i using a rubber press to obtain a primary molded product.

This primary molded body was heated in a furnace at 10'mmHg and 1000
The temperature was increased and heated at a rate of 'C/3 hours.

Next, after the metal silicon in the crucible placed directly below this secondary molded body in the same furnace is melted, argon gas is introduced into the furnace to set the pressure to IO-2mrILHg, and the temperature is set at 160°
The molded body was heated to C and one end of the molded body was immersed in molten metal silicon to allow the metal silicon to penetrate thereinto, thereby producing a SiC plate material.

The specific gravity of the board is 3. It was IO. The speed of sound in this plate is
Table 1 shows the results of simultaneous measurements with comparative samples of commercially available products made by the reaction sintering method and the hot press method.

Example 2 α-8iC (#3000), graphite powder (average particle size 5 μm
), polyethylpolysilane (viscosity at 25°C 430 centistokes, average molecular weight 1400) hexane in weight percent 32, 30, 18, 20, respectively.
After kneading thoroughly, 5CIrL×5cTLxlC was formed under a pressure of 350 kg/i using a mold press.
It was molded into a 1rL plate shape.

This primary molded body was heated at 10% per hour in an argon atmosphere.
It was heated to 500°C at a temperature increase rate of 0°C.

This secondary molded body was processed into a dumbbell-shaped specimen for physical property testing using a GC amorphous grindstone, and one end of the specimen was melted and held in an argon atmosphere at 1500°C and brought into contact with silicon metal.
As for the molded product, a test piece for physical property testing with sufficient accuracy was obtained without any finishing processing.

The specific gravity of this product was 3.05. For comparison, a kneaded product of the above composition in which polysilane was replaced with the same amount of methylcellulose and hexane was replaced with pure water was prepared using a mold press at 350°C.
kg/ffl and molded at 500°C in an argon atmosphere.
It was completely impossible to process with the GO special type grindstone.

Example 3 α-8iC (#3000), graphite powder (average particle size 2 μm
), polymethylpolysilane (viscosity at 25°C: 1700 centistokes, average molecular weight 3800), polycarbosilane (n is a positive integer) consisting of a chain of (n is a positive integer)
The viscosity at 5° C. is 130 centistokes, the average molecular weight is 500), and the weight percent of hexane is 56.
28.3.3.10, and after thorough kneading, using a rubber press, the diameter was 10 iMJ at a pressure of 41/d.
It was molded into a rod shape with a length of 100 mm and heated at a rate of 300°C per hour in an argon atmosphere.
Heated to ℃.

To install this on a lathe, use a carbide K-20 bit to machine the sides and center it, then drill a 5II diameter hole in the center to create a highly accurate secondary molded body. Manufactured pipes.

This was carried out in Example 2. Therefore, silicon was infiltrated and the specific gravity was 3.
．． A 00 SiC pipe was made, and its dimensional accuracy was almost the same as that of the secondary molded product.

In addition, when a simultaneous comparison was made under the same conditions with the same amounts of methylcellulose replacing polysilane and polycarbosilane in the above crosstalk composition and pure water replacing hexane, the strength was insufficient and it was impossible to install on a lathe.

Example 4 A mixture with the same composition as in Example 1 was prepared using a mold press.
50kg/cr? Molded with a pressure of L and 3t with a rubber press.
The secondary molded body was pressed at a pressure of /ffl and heated to 500'C in a vacuum of lo'' mmHg at the same temperature increase rate as in Example 1, and then cut into 8 mm x 60 mm.
After shaping into the shape of X5@771, molten metal silicon was infiltrated in a vacuum of No"miHg to generate SiC, and a test piece A for measuring physical properties was prepared.

It should be noted that no dimensional difference was observed in the test pieces prepared by cutting, even after infiltration with metallic silicon, as measured with calipers.

Separately, a mixture with the same composition was molded in the same way using a mold press and a rubber press to create a test specimen B that was not cut. Test piece C was created under the same conditions.

Note that this test piece C could not be cut when it was a secondary molded product.

The physical property values measured for each test piece A, B, and C are shown in Table-H.

Measured at 43 test points for each test, bending strength is span 4Qm
Measured at m, elastic modulus is based on resonance vibration method.

Example 5 Polymethylpolycarbosilane (viscosity 440 centistokes at 25°C, average molecular weight 1500) was produced from the same chain of α-8iC and graphite powder as in Example 1.
were mixed at a ratio of 56.24.20% by weight, and 1 ton/d
Formed into a plate-like body of 8CrfL x 8 sieves x 4 pieces at a forming pressure of
This was further pressed at a pressure of 4 tons/d using a rubber press to form a primary molded product.

This primary molded body was heated to 500°C over 1.5 hours in a vacuum furnace maintained at a vacuum level of 10″?f17WHg, maintained at the same temperature for 1 hour, cooled to room temperature, and then heated in a vacuum furnace. I took it outside.

A bending strength test piece of 35 mm x 8 mm x 4 mm was cut out from this secondary molded body, and the remaining part was processed using a carbide cutting tool and a GC grindstone to a multi-stage length of 5 cIrL.
, a cylindrical body with a diameter of 3CrfL was created.

These test pieces and cylindrical bodies were infiltrated with molten metal silicon under the same conditions as in Example 1 to form silicon carbide molded bodies, and the specific gravity of each was measured.
6, and the latter was 3.05.

The bending strength of these specimens was measured at room temperature, 500°C, 800°C, and 1200°C, and all were within the range of 5.6 to 6.7 tons/d, and the temperature change in bending strength was It was hardly recognized.

Example 6 Polymethylcarbosilane (viscosity 420 at 25°C
centistokes, with an average molecular weight of 1400) and the same α-8iC and graphite powder as in Example 5 at 30.50%
, 20% by weight, and a primary molded body was prepared under the same conditions as in Example 5.

This was then heated to 800°C over 2 hours in an argon gas atmosphere, maintained at the same temperature for 1 hour, cooled to room temperature, taken out of the furnace, and cut into test pieces in the same manner as in Example 5. Then, a silicon carbide molded body was obtained by infiltrating the molded body with molten metal silicon.

Their specific gravity was in the range of 3.05 to 3.12, and their bending strength was in the range of 5.6 to 6.2 tons/d.

Claims (1)

[Claims] 1 Silicon carbide powder 10-80% by weight, carbon powder 10-80% by weight
A mixture of 70% by weight and 0.5 to 60% by weight of polyorganopolysilane and/or polyorganocarbosilane is molded into a molded body, and this molded body is then subjected to thermal decomposition of polyorganopolysilane and polyorganocarbosilane. 1. A method for producing a silicon carbide molded body, which comprises heating the molded body to a temperature at which it occurs, cutting the pyrolyzed molded body, and then impregnating the molded body with molten metal silicon.