KR100188988B1 - Fabrication method of silicon nitride/silicon carbide nanocomposites from polymer and silicon compounds - Google Patents

Abstract

In the present invention, a polymer and a silicon compound are added and mixed with a known silicon nitride powder, and the carbon in the mixture is carbonized to react the carbon (C) formed with an oxide film of silicon nitride or the added silicon compound, thereby producing ultrafine silicon carbide. A method for producing evenly dispersed silicon nitride / silicon carbide ultrafine composite materials. According to the method of the present invention, a silicon nitride / silicon carbide ultrafine composite material having a low manufacturing cost and excellent dispersion characteristics of silicon carbide can be produced compared to the conventional method.

Description

Manufacturing method of silicon nitride / silicon carbide ultrafine composite material using polymer and silicon compound

The invention powder base merchant silicon nitride (Si ₃ N ₄₎ in the particle size of several tens nm to several hundreds nm and ultra fine silicon carbide (SiC) is evenly the silicon nitride / silicon carbide ultrafine dispersion composites in the grain boundaries and the mouth on the base for making and A method for producing a sintered body without the addition of silicon carbide powder.

Silicon nitride (Si ₃ N ₄ ) has excellent fracture strength, fracture toughness, and heat resistance required for structural ceramics, and is currently used in automotive engine parts such as wear-resistant materials such as cutting tools, preburn chambers, valves, and turbo charger rotors. Widely used. However, since such silicon nitride has covalent bonding properties, a compact sintered compact cannot be obtained even if it is sintered at a high temperature of 1700 ° C. or higher unless an additive (sintering aid) which promotes sintering is used. Therefore, an oxide-based sintering aid is used to promote the sintering of silicon nitride to produce a dense sintered body. However, the oxide added to promote sintering forms a glassy film at the grain boundaries, which in most cases significantly lowers the strength of the silicon nitride sintered body at 1200 ° C or higher.

As a method of suppressing the strength drop at high temperatures of silicon nitride described above, there is a method of adding and complexing silicon carbide having high heat resistance and which is not reactive with silicon nitride. Depending on the type of silicon carbide to be added, fiber reinforcement (for example, Japanese Patent No. 113893, 113113902), fiber reinforcement (for example, US Patent No. 450147, International Patent Application Publication No. 9108992, etc.), There is a particle-reinforced (for example, Japanese Patent No. 329552) composite material, and the ultrafine composite material is a composite material in which the matrix phase is reinforced by using the ultrafine particles which are one of the particle-reinforced composite materials.

Silicon nitride / silicon carbide ultrafine composite material is a material known to have excellent mechanical properties. As a production method, a mixed gas of ([Si (CH) ₃ ] ₂ NH + NH ₃ + N ₂ ) is used as a starting material at 1000 ° C. There is a method of producing by using a Si-CN amorphous powder synthesized by gas phase reaction at (Japanese Patent No. 329552) and a method of producing by depositing carbon by thermal decomposition of methane gas to silicon nitride powder. In addition, there is also a method for producing ultrafine composite material sintered bodies by directly mixing silicon nitride powder and ultrafine silicon carbide powder without using these ultrafine composite material powders.

An advantage of the method of producing amorphous powders for the production of silicon nitride / silicon carbide ultrafine composite materials by gas phase reaction is that the powder synthesized by this method is close to spherical and the chemical composition is homogeneous. However, the method of producing the silicon nitride / silicon carbide ultrafine composite material powder by the above gas phase reaction has a disadvantage of low productivity, high manufacturing cost, and difficulty in mass production, and about 40% of the amorphous powder crystallizes during sintering. Due to the weight reduction of, a compact sintered body can be obtained only by a special sintering method such as pressure sintering.

As a method of depositing carbon on silicon nitride powder also uses a vapor phase method, the manufacturing cost is high, productivity is low, and carbon deposition is limited to a place where carbon deposition sites are exposed to methane gas. In addition, this method does not supply silicon necessary for synthesizing silicon carbide, and only deposits carbon, so that there is a disadvantage in that it cannot control the amount of silicon carbide that can be included in the silicon nitride / silicon carbide sintered body.

The method for producing silicon nitride / silicon carbide ultrafine composite materials using ultrafine silicon carbide powder as a starting material is the same as that of a conventional ceramic manufacturing process, and thus is more industrially easier than the amorphous powder or carbon deposition method described above. Ultrafine composite material sintered body can be manufactured. However, this method is difficult to produce sintered compacts having excellent mechanical properties and defects due to defects in the sintered compacts because the ultrafine silicon carbide particles, which are starting materials, are difficult to be uniformly mixed with the silicon nitride particles and are well aggregated during drying. Ultrafine powder having an average particle diameter of several tens of nm is expensive because it is manufactured by a gas phase reaction.

Accordingly, an object of the present invention is to overcome the problems of the conventional method described above, to provide a method for producing a powder for silicon nitride / silicon carbide ultrafine composite material in which the starting material is low in cost and silicon carbide is uniformly distributed in silicon nitride. will be.

Another object of the present invention is to provide a method for producing a sintered body of the silicon nitride / silicon carbide ultrafine composite material.

Other objects and advantages of the present invention will become apparent from the following detailed description of the invention.

1 is a conceptual diagram illustrating the basic principle of the present invention.

Figure 2 is a manufacturing process of the powder for silicon nitride / silicon carbide ultrafine composite material according to Example 1 of the present invention.

3 is a manufacturing process diagram of a sintered compact for silicon nitride / silicon carbide ultrafine composite material according to Example 2 of the present invention;

4 is an XRD diffraction diagram of a silicon nitride / silicon carbide ultrafine composite material sintered body (a) prepared according to Example 2 of the present invention and a silicon nitride sintered body (b) prepared by a conventional process.

Hereinafter, the present invention will be described in more detail.

First, according to the present invention, there is provided a method for producing a powder for silicon nitride / silicon carbide ultrafine composite material in which ultrafine silicon carbide is uniformly distributed in silicon nitride powder.

The method for producing a silicon nitride / silicon carbide ultrafine composite material powder according to the present invention is characterized in that a polymer is added to silicon nitride powder, and carbon produced by carbonizing the polymer reacts with an oxide film on the surface of silicon nitride.

In addition, the method for producing a powder for silicon nitride / silicon carbide ultrafine composite materials according to the present invention includes adding a polymer and a silicon compound to the silicon nitride powder, and reacting the carbon film formed by carbonizing the polymer with the oxide film on the silicon nitride surface and the silicon compound. It features.

More specifically, the method for producing the powder for silicon nitride / silicon carbide ultrafine composite material according to the present invention is

Mixing a silicon nitride powder with a polymer, optionally a silicon compound and a solvent,

Drying the mixture,

Mixing the dried mixture by a method such as a ball mill to crush the aggregates,

Heat treating the pulverized dry powder in an electric furnace to carbonize the polymer,

And continuing to increase the temperature to react the carbon formed in the carbonization step with an oxide film or silicon compound on the silicon nitride surface to produce silicon carbide on the silicon nitride surface.

Hereinafter, the manufacturing method of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1, when silicon nitride is formed on the surface by contact with air and an oxide film having a predetermined thickness is formed, further oxidation hardly proceeds at room temperature. In this case, the amount occupied by the oxide film in the silicon nitride powder may be measured by the amount of oxygen contained in the powder. For example, SN-E10, manufactured by UBE CEMENT CO., Contains 1.26% oxygen, and HM-5MF of ONODA CEMENT CO., 1.5% oxygen. Is included. Therefore, in the case of producing the silicon nitride / silicon carbide ultrafine composite material of the present invention, if the polymer is uniformly coated on the surface of the silicon nitride powder with the oxide film as described above, and heat treatment while suppressing rapid volatilization in an atmosphere in which the polymer is not oxidized However, there is a difference depending on the type of polymer, but carbonized to carbon. Subsequently, when the temperature is increased, silicon oxide, which is an oxide film of carbon and silicon nitride, reacts to generate silicon carbide on the surface of silicon nitride, thereby preparing a powder for silicon nitride / silicon carbide ultrafine composite material.

According to the manufacturing method of the ultrafine composite material powder of the present invention as shown in Fig. 2, first, commercially available silicon nitride powder is mixed with a water-soluble polymer and a silicon compound by a general wet mixing method such as a ball mill or an attention mill. do. At this time, when the polymer used is in the solid state or liquid state, but the viscosity is high enough to sufficiently wet the silicon nitride powder, by adding a solvent capable of dissolving the polymer to lower the viscosity of the aqueous polymer solution so that the silicon nitride powder wet well. . The aggregate of silicon nitride powder is broken and mixed until the primary particles are completely wetted. The mixed mixture is dried for 6 hours at a temperature at which the polymer does not oxidize, that is, 70 to 100 ° C. The dried mixture is dry mixed by a dry ball mill or the like to pulverize the aggregates produced during drying. The powder of the pulverized dry mixture is placed in an alumina boat or an alumina crucible and heat treated at 300 ° C. to 1000 ° C. for 24 hours in a vacuum or nitrogen gas or argon gas atmosphere in an electric furnace to control the atmosphere, thereby carbonizing the polymer. The carbon is continuously raised at 1300 ° C to 1500 ° C for 4 hours to react with an oxide film or silicon compound on the silicon nitride surface to produce silicon carbide on the silicon nitride surface. Through the simple conventional ceramic manufacturing process as described above, the powder for silicon nitride / silicon carbide ultrafine composite material can be produced.

Further, according to another aspect of the present invention, there is provided a method for producing a compact silicon nitride / silicon carbide ultrafine composite material sintered body by sintering the powder for silicon nitride / silicon carbide ultrafine composite material prepared as described above.

The method for producing a silicon nitride / silicon carbide ultrafine composite material sintered body according to the present invention is characterized in that a polymer and a sintering aid are added to silicon nitride powder, and carbon produced by carbonizing the polymer is reacted with an oxide film on the surface of silicon nitride.

In addition, the method for producing a silicon nitride / silicon carbide ultrafine composite material sintered body according to the present invention includes adding a polymer, a sintering aid, and a silicon compound to silicon nitride powder, and reacting carbon produced by carbonizing the polymer with an oxide film and a silicon compound on the silicon nitride surface. It is characterized by.

More specifically, the method for producing the silicon nitride / silicon carbide ultrafine composite material sintered body according to the present invention

Adding a polymer, a sintering aid and optionally a silicon compound and a solvent to the silicon nitride powder and mixing the same;

Drying the mixture,

Mixing the dried mixture by a method such as a ball mill to crush the aggregates,

Heat treating the pulverized dry powder in an electric furnace to carbonize the polymer,

Continuously increasing the temperature to react the carbon formed in the carbonization step with an oxide film or silicon compound on the silicon nitride surface to produce silicon carbide on the silicon nitride surface,

Forming a granule through the sieve through the powder of silicon carbide,

Molding the granules into a predetermined form to produce a molded article,

The molded body is sintered to form a silicon nitride / silicon carbide ultrafine composite material sintered body.

According to the method for producing the silicon nitride / silicon carbide ultrafine composite material sintered body according to the present invention, as shown in FIG. 3, the content of the sintering aid for promoting the densification of the polymer, additionally the sintered body, and optionally silicon carbide in silicon nitride as a starting material Using a silicon compound and a solvent for controlling the above, substantially the same process as the manufacturing process of the powder for the ultrafine composite material described above, and further, the silicon carbide powder is granulated through a sieving The granulated powder is molded into a predetermined form by a press or a hydrostatic molding method. The molded article thus formed is sintered at 1700 ° C. to 2000 ° C. for 4 hours in an electric furnace, and cooled to prepare a compact silicon nitride / silicon carbide ultrafine composite material sintered body.

The polymers and silicon compounds used in the present invention are less expensive than the ultrafine silicon carbide powder [For example, the price of ultrafine silicon carbide powder T-1 of Sumitomo Chemical Company is $ 1,000 / Compared to kg, polyvinyl alcohol, a polymer of TOKYO KASEI, is $ 20 / kg and silicon oxide of SIGMA CHEMICAL CO. is $ 26.4 / kg].

Examples of suitable polymers for use in the present invention include polyethylene glycol, polybutadiene, polypropylene, polyvinyl alcohol, polyethylene, polystyrene, polyvinyl acetate, phenol resins.

Further examples of silicon compounds suitable for use in the present invention include silicon oxide, silica sol, silica gel, silicon hydroxide and silicon carbonate.

In the preparation of the silicon nitride / silicon carbide ultrafine composite material powder, the polymer is added, for example, in an amount of 3% to 30% by weight of PEG, relative to silicon nitride.

In addition, the silicon compound for controlling the content of the silicon carbide described above is preferably added in an amount of 1% by weight to 20% by weight with respect to silicon nitride, and an organic solvent such as water or an alcohol is used as the solvent. It is preferred to add in an amount of 100% by volume to 200% by volume relative to the silicon nitride powder.

It is preferable to add alumina (Al ₂ O ₃ ) and yttria (Y ₂ O ₃ ) by 4% by weight and 6% by weight, respectively, as the sintering aid for producing the sintered body.

Ball milling during mixing of the starting material and mixing of the dried mixture is preferably carried out for 6 to 24 hours using silicon nitride balls or the like.

In the production of the sintered compact, the sintering of the compact is preferably performed at 1700 to 2000 ° C. for 2 to 4 hours.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

100 g of silicon nitride powder (UBE E-10), 300 cc of 5% PVA aqueous solution and 150 cc of silicon nitride ball were put into a polyethylene container and wet mixed for 24 hours. The mixed slurry was placed in a beaker and completely dried at 80 ° C. The dried mixture was placed in a polyethylene container and dry mixed for 4 hours using silicon nitride balls. The dry mixed powder was put into an alumina boat and placed in an atmosphere-controlled tube furnace, heated at 350 ° C. for 24 hours while flowing nitrogen gas, and then heated up to 1400 ° C. for 4 hours, cooled, and silicon nitride A powder for silicon nitride / silicon carbide ultrafine composite materials was prepared in which ultrafine silicon carbide powder was uniformly distributed on the surface of the powder.

Example 2

100 g of silicon nitride powder (UBE E-10) in a polyethylene container, 300 cc of 5% PVA aqueous solution as polymer, 4 g of alumina (Al ₂ O ₃ ) as a sintering aid and 6 g of itrira (Y ₂ O ₃ ), and silicon nitride 150 cc of the ball was added and wet mixed for 24 hours. The mixed slurry was placed in a beaker and completely dried at 80 ° C. The dried mixture was placed in a polyethylene container and dry mixed for 4 hours using silicon nitride balls. The dry mixed powder was put into an alumina boat, placed in a tube furnace for controlling the atmosphere, heated to 350 ° C. for 24 hours while flowing nitrogen gas, and subsequently heated to 1400 ° C. for 4 hours, cooled, and A powder for silicon nitride / silicon carbide ultrafine composite materials, in which fine silicon carbide powder and silicon nitride powder were evenly mixed, was prepared. The powder thus obtained was sieved through a 150-neck sieve to obtain granular form. The granular powder was put into a mold and pressed to form a disk having a diameter of 15 mm and a height of 10 mm, and cold-statically molded. The cold hydrostatically formed molded body was heated to 1900 ° C. in a nitrogen gas atmosphere of 10 atm in an electric furnace using a graphite heating element, held for 4 hours, and cooled to prepare a silicon nitride / silicon carbide ultrafine composite material sintered body. The sintered density of the obtained silicon nitride / silicon carbide ultrafine composite material sintered body was 99%, and it was confirmed using an X-ray diffraction analyzer that silicon carbide was produced.

4 is an X-ray diffraction diagram of a silicon nitride / silicon carbide ultrafine composite material sintered body prepared according to Example 2 of the present invention, through which silicon carbide, which was not added as a starting material by the manufacturing method of the present invention, is contained in the sintered body You can see that it was created.

The method for producing powders and sintered compacts for silicon nitride / silicon carbide ultrafine composite materials using the polymer of the present invention uses relatively inexpensive polymers and silicon compounds in place of expensive ultrafine silicon carbide, which is more expensive than conventional methods. Low, simple manufacturing process, suitable for industrial scale production, ultra-fine silicon carbide particles can be uniformly dispersed on the silicon nitride surface to improve the properties of the material.

Claims (4)

A method for producing a silicon nitride / silicon carbide ultrafine composite material powder, comprising adding a polymer to silicon nitride powder and reacting carbon produced by carbonizing the polymer with an oxide film on a silicon nitride surface. A method for producing a powder for silicon nitride / silicon carbide ultrafine composite materials, comprising adding a polymer and a silicon compound to a silicon nitride powder, and reacting the carbon produced by carbonizing the polymer with an oxide film on the silicon nitride surface and the silicon compound. A method of producing a silicon nitride / silicon carbide ultrafine composite material sintered body, wherein a polymer and a sintering aid are added to silicon nitride powder, and carbon is produced by carbonizing the polymer to react with an oxide film on the surface of silicon nitride. A method for producing a silicon nitride / silicon carbide ultrafine composite material sintered body, comprising adding a polymer, a sintering aid, and a silicon compound to silicon nitride powder, and reacting the carbon produced by carbonizing the polymer with an oxide film on the silicon nitride surface and a silicon compound.

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