KR100355348B1 - Method of manufacturing silicon nitride/silicon carbide nanocomposites - Google Patents

Abstract

The present invention relates to a method for producing silicon nitride / silicon carbide ultrafine composite materials, wherein silicon nitride powder and a sintering aid are mixed, the mixture is dried, and an organic binder, an inorganic binder, or water is used as a polymer material and a plasticizer in the dried mixture. A paste is prepared by adding and kneading, molding the paste to which the plasticizer is added, heat-treating the molded body to remove water and a part of the plasticizer, heat-treating the molded body from which the water and the plasticizer are removed, and heat-treating the molded body. It raises and consists of manufacturing a sintered compact. According to the present invention, a silicon nitride / silicon carbide ultrafine composite material having fewer complicated defects such as pores and agglomeration and having evenly dispersed ultrafine silicon carbide can be produced.

Description

Silicon nitride / silicon carbide ultra-fine composite material manufacturing method {METHOD OF MANUFACTURING SILICON NITRIDE / SILICON CARBIDE NANOCOMPOSITES}

The present invention relates to a method for producing a silicon nitride / silicon carbide ultrafine composite material, and specifically, silicon carbide powder is added to an ultrafine composite material component in which ultrafine silicon carbide is uniformly dispersed in a matrix on a matrix and in a mouth. It relates to a method of manufacturing effectively without

Silicon nitride (Si ₃ N ₄ ) has excellent fracture strength, fracture toughness, and heat resistance, and is widely used as an automotive engine component such as wear resistant materials such as cutting tools, preburn chambers, valves, and turbo charger rotors. However, silicon nitride is covalently bonded, and thus, without a sintering aid, that is, an additive that promotes sintering, a compact sintered body cannot be obtained even when sintered at a high temperature of 1700 ° C or higher. 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 boundary, 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 decrease in strength at the high temperature of the silicon nitride, there is a method of adding and complexing silicon carbide (SiC) having high heat resistance and no reaction with silicon nitride. Depending on the type of silicon carbide to be added, there are fiber reinforced (for example, JP113893, JP113902, etc.), fiber reinforced (for example, US450147, WO9108992, etc.), particle reinforced (for example, JP329552) composite materials.

As a starting material, a silicon nitride / silicon carbide ultra-fine composite material is prepared by Si-CN amorphous by gas phase reaction of a mixed gas of ([Si (CH) ₃ ] ₂ NH + NH ₃ + N ₂ ) at 1000 ° C. (JP329552), a method of manufacturing by using powder and pyrolysis of methane gas on silicon nitride powder, and a method of manufacturing carbon, and a method of manufacturing ultrafine composite material sintered body by directly mixing silicon nitride powder and ultrafine silicon carbide powder, In addition, there is an in-situ method (Patent No. 0188988) which produces a mixture of a polymer and silicon nitride by reacting carbon produced by thermal decomposition of the polymer with an oxide on a silicon nitride or silicon nitride surface.

In order to manufacture a part by the above-described method for producing a ultrafine composite material, a mixed powder obtained by mixing ultrafine silicon carbide and silicon nitride powder is made, and then molded into a shape of a part using the mixed powder and sintered to manufacture a part, or Instead of using particulate silicon carbide as a starting material, a polymer is added and heat-treated instead of silicon oxide to produce silicon carbide by the reaction of silicon oxide or a silicon compound with pyrolysis carbon, thereby preparing a mixed powder, and molding and sintering the mixed powder. . These methods use a mixed powder containing ultra fine powder in the molding process. However, the ultra fine powder has a low flowability and a large specific surface area, which is easy to aggregate because of its tendency to agglomerate with each other, and is not only difficult to mold, but also a fatal defect that causes mechanical properties in the sintered body due to aggregation of pores or ultra fine particles. In many cases, it is difficult to manufacture a component having a complicated shape.

An object of the present invention is to use a method of forming and sintering without using silicon carbide as a starting material and without using a silicon carbide mixed powder during molding to overcome the problems of the conventional method described above, The present invention provides a manufacturing process for producing a silicon nitride / silicon carbide ultra-fine composite material part having a complicated shape without defects such as aggregation.

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.

FIG. 2 is a manufacturing process diagram of Si ₃ N ₄ / SiC ultrafine composite material component by injection molding according to Example 1 of the present invention.

3 is a photograph of a silicon nitride / silicon carbide ultrafine composite material component prepared according to Example 1. FIG.

According to the present invention, there is provided a method for producing a silicon nitride / silicon carbide ultrafine composite material in which ultrafine silicon carbide is uniformly distributed on a silicon nitride matrix and has fewer defects such as pores and agglomeration.

The method for producing a silicon nitride / silicon carbide ultrafine composite material component according to the present invention uses organic or inorganic binders or water for imparting plasticity to polymers and powders for producing pyrolytic carbon without using silicon carbide ultrafine particles as starting materials. After the addition to form a molded article, it is characterized in that the carbon produced by carbonizing the polymer and the surface oxide of silicon nitride, silicon nitride or the silicon compound to be added to react.

More specifically, the silicon nitride / silicon carbide ultrafine composite material manufacturing method according to the present invention is mixed with silicon nitride powder and a sintering aid, and the mixture is dried, the organic binder, inorganic binder as a polymer material and a plasticizer to the dried mixture Or by adding water and kneading to prepare a paste, molding the paste to which plasticizer is added, and heat-treating the molded body to remove water and a part of the plasticizer, heat-treating the molded body from which the water and the plasticizer are removed, and heat-treated the molded body It comprises the step of producing a sintered body by raising the temperature.

As the starting material, a silicon compound may be additionally used in addition to the silicon nitride. The silicon compound not only functions to generate silicon carbide by reacting with carbon, but also forms a liquid phase with the added sintering aid to promote densification of the molded body.

The heat treatment of the molded body from which the water and the plasticizer is partially removed causes the polymer to be carbonized to produce carbon, and the produced carbon reacts with silicon nitride or a silicon compound according to the following reaction formula to produce silicon carbide.

Si ₃ N ₄ + 3C = 3SiC + 2N ₂

SiO ₂ + 3C = SiC + 2CO

Therefore, silicon nitride / silicon carbide ultrafine composites do not use silicon carbide as starting material and evenly distribute ultrafine silicon carbide on silicon nitride matrix and have less defects such as pores and agglomeration without using silicon carbide mixed powder during molding. Is formed.

In addition, after the heat treatment of the molded body from which the water and the plasticizer are partially removed, the step of cold pressing the molded body may be added before sintering.

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

Referring to FIG. 1, silicon nitride is in contact with air to form an oxide film (SiO ₂ ), and when an oxide film having a predetermined thickness is formed, further oxidation is hardly performed at room temperature. The amount occupied by the oxide film in the silicon nitride powder can be measured by the amount of oxygen contained in the powder. For example, UBE CEMENT CO. SN-E10 produced by the company contains 1.26% oxygen, and ONODA CEMENT CO. HM-5MF contains 1.5% oxygen. In this way, the polymer is uniformly coated on the surface of the silicon nitride powder with the oxide film, and a plasticizer is added to give the fluidity of the powder, followed by molding and heat treatment while suppressing rapid volatilization in an atmosphere where the polymer is not oxidized. However, when carbonized, carbon is formed on the silicon nitride particle surface, and when the temperature is continuously raised, carbon and silicon nitride oxide film or silicon nitride react to form silicon carbide on the silicon nitride surface, and the sintered compact is continued as shown in FIG. A silicon nitride / silicon carbide ultrafine composite having a uniform distribution of ultrafine silicon carbide on a silicon nitride matrix is prepared as shown on the right.

According to the manufacturing method of the ultrafine composite material component of the present invention as shown in FIG. 2, first, commercial wet mixing such as a ball mill or an attrition mill is added by adding a commercially available silicon nitride powder and a sintering aid to promote sintering. The mixture is mixed by the method and dried to form a mixed powder. In the dry mixed powder, an organic binder or an inorganic binder and water are added and kneaded to give a fluidity of a polymer for producing pyrolytic carbon, a powder required for molding, and kneaded to form a paste. The kneaded paste is used to mold a complex shaped part by a molding method such as injection molding or extrusion molding. The molded body is heated to 350 ° C. in a nitrogen atmosphere to remove water and binder added for molding. Subsequently, heat treatment is performed at 1000 to 1400 ° C. to form a compact in which silicon carbide fine particles are uniformly distributed, and the temperature is further increased to produce a compact sintered compact. If necessary, the molded body in which silicon carbide is produced may be cold press-molded before sintering to increase the molding density.

As the sintering aid for sintering promotion, it is preferable to add 1-4% by weight of alumina (Al ₂ O ₃ ), 3-8% by weight of yttria (Y ₂ O ₃ ), and 1-3% by weight of magnesia (MgO). Do.

As the polymer for producing the pyrolytic carbon, polystyrene, phenol resin, polybutadiene, polypropylene, or the like is preferably used.

Examples of the organic binder include polyethylene glycol, vinyl acetate, hydroxypropylmethylcellulose, methylcellulose, methylethylcellulose, and the like. It is preferable to add, and clay etc. are preferable as an inorganic binder.

When removing the water and binder added for the above molding, it is preferable that the temperature increase rate is set to 5 to 15 ° C / hour depending on the thickness of the molded body.

As for the pressure of the said cold press molding, 200-400 MPa is preferable.

In the production of the sintered body, the sintering of the molded body is preferably performed for 2 to 4 hours at 1900 to 2100 ℃.

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), ₂ g of alumina (Al ₂ O ₃ ) as a sintering aid, ₆ g of itrira (Y ₂ O ₃ ), and 150 cc of silicon nitride ball and alcohol were wet mixed in a polyethylene container. . The mixed slurry was placed in a beaker and completely dried at 80 ° C. 5 wt% phenol resin, 40 vol% polyethyleneglycol, 10 vol% vinyl acetate, and 2 vol% wax were added to the mixed powder to form a paste by kneading. The pressure kneaded paste was made into pellets having a diameter of 3 mm and a length of 5 mm and used as a raw material for injection molding. The injection molding machine was used to form a complex combustion chamber with a diameter of 40 mm and a height of 35 mm with an oval hole in the center. The molded body was heated to 350 ° C. and heated for 2 hours while being heated to 5 ° C. while flowing nitrogen gas, and then heated to 1400 ° C. for 4 hours, and then heated to 2000 ° C. for 2 hours, and cooled. From 1400 ° C to 1800 ° C, the pressure of nitrogen gas was 20 atm, and at higher temperatures, 60 atm. The sintered density of the obtained complex combustion chamber was 99%, and it was confirmed using an X-ray diffractometer that silicon carbide was produced.

Example 2.

100 g of silicon nitride powder (UBE E-10), ₂ g of alumina (Al ₂ O ₃ ), 6 g of itrira (Y ₂ O ₃ ), 1 g of magnesia (MgO), 150 cc of silicon nitride and alcohol And wet mixing for 24 hours. The mixed slurry was placed in a beaker and completely dried at 80 ° C. Phenol resin was added by mixing 10% by weight of phenol resin, 45% by volume of polyethylene glycol, 10% by volume of vinyl acetate, and 2% by volume of wax to kneaded under pressure and kneading. The pressure kneaded paste was made into pellets having a diameter of 3 mm and a length of 5 mm and used as a raw material for injection molding. The injection molding machine was used to form a complex combustion chamber with a diameter of 40 mm and a height of 35 mm with an oval hole in the center. The molded body was heated to 350 ° C. and heated for 2 hours while being heated to 5 ° C. while flowing nitrogen gas, and then heated to 1400 ° C. for 4 hours, and then heated to 2100 ° C. for 2 hours and cooled. From 1400 ° C to 1800 ° C, the pressure of nitrogen gas was 20 atm, and at higher temperatures, 60 atm. The sintered density of the obtained complex combustion chamber was 99%, and it was confirmed using an X-ray diffractometer that silicon carbide was produced.

3 is a combustion chamber made of a silicon nitride / silicon carbide ultrafine composite material prepared according to Example 1 of the present invention.

In the manufacturing process of the silicon nitride / silicon carbide ultrafine composite material component of the present invention, inexpensive polymer is used in place of ultrafine silicon carbide, and ultrafine silicon carbide In order to produce the sintered body, the manufacturing cost is lower than the manufacturing method of forming and sintering using ultra-fine silicon carbide powder, the manufacturing process is simple, and no pores or agglomeration can be produced.

Claims (15)

Silicon nitride powder and 3 to 15% by weight of the sintering aid is mixed, Drying the mixture, 3-10 wt% of any one polymer selected from polystyrene, phenol resin, polybutadiene or polypropylene and the organic binder and inorganic binder as a plasticizer in the dried mixture. Or by adding water in the range of 3 to 25% by weight and kneading to prepare a paste, Molding the paste to which plasticizer is added, The molded body is heated to 350 ° C. in a nitrogen atmosphere to remove water and some of the plasticizer, Heat-treating the molded body from which water and a part of the plasticizer was removed in a range of 1000 to 1400 ° C., Method of manufacturing a silicon nitride / silicon carbide ultrafine composite material comprising the step of increasing the temperature of the heat-treated molded body by producing a sintered body by gas pressure sintering applying nitrogen gas of 20 to 3000 atm in the temperature range of 1900 ~ 2100 ℃ . The method of manufacturing a silicon nitride / silicon carbide ultrafine composite material according to claim 1, further comprising a silicon compound in addition to the silicon nitride as a starting material. The method of manufacturing a silicon nitride / silicon carbide ultrafine composite material according to claim 1, wherein the molding is performed by injection molding, extrusion molding, or press molding. The method of claim 1, further comprising the step of cold press molding the molded body after heat-treating the molded body from which water and a part of the plasticizer has been removed before sintering the silicon nitride / silicon carbide ultrafine composite material manufacturing method. The method of claim 4, wherein the cold press forming is performed under a pressure of 200 to 400 MPa. delete delete delete delete delete The method of claim 1, wherein the sintering is performed for 2 to 4 hours. The method of claim 1, wherein as the sintering aid, 1 to 4% by weight of alumina (Al ₂ O ₃ ), 3 to 8% by weight of yttria (Y ₂ O ₃ ) or 1 to 3% by weight of magnesia (MgO) is used. Silicon nitride / silicon carbide ultrafine composite material manufacturing method. delete According to claim 1, wherein the organic binder is polyethylene glycol (vinyl glycol), vinyl acetate (vinyl acetate), hydroxypropylmethyl cellulose (hydroxypropylmethylcellulose), methyl cellulose (methylcellulose) or methyl ethyl cellulose Silicon nitride / silicon carbide ultrafine composite material manufacturing method using (methylethylcellulose). The method of claim 1, wherein the inorganic binder uses clay.