KR20030085371A - Method of manufacturing reaction-bonded silicon carbide - Google Patents

Abstract

PURPOSE: Provided is a method for producing a reaction bonding silicon carbide, which supplies melted silicon effectively regardless of the form, size and thickness of the reaction bonding silicon carbide, prevents the cohesion of the melted silicon, and supplies the melted silicon uniformly. CONSTITUTION: The method comprises the steps of: preparing a silicon supplying specimen composed of a silicon powder and a thermosetting resin selected from the group consisting of a phenol resin, a furfuryl alcohol resin and an epoxy resin as a binding agent; preparing a silicon carbide/carbon filling body; contacting the silicon supplying specimen to one side of the filling body in a reaction bonding furnace; and heat treating at the temperature higher than the melting point of the silicon under vacuum or an inert atmosphere to infiltrate the melted silicon in the silicon supplying specimen into the inside of the filling body.

Description

METHODS OF MANUFACTURING REACTION-BONDED SILICON CARBIDE}

The present invention relates to a method for producing reaction-bonded silicon carbide, and more particularly, to a method for uniformly supplying molten silicon throughout the specimen when producing reaction-bonded silicon carbide.

Reaction-bonded (or sintered) silicon carbide is made by infiltrating molten silicon into a preform consisting of silicon carbide and carbon. The impregnated molten silicon is formed of silicon carbide by reaction with carbon particles present in the filler, and the silicon carbide acts as a binder to bond the silicon carbide particles present in the filler, and the voids present between the silicon carbide particles. It has a microstructure filled with silicon.

In order to manufacture reaction-bonded silicon carbide, molten silicon is supplied to the silicon carbide / carbon filler by immersing the filler in a crucible containing molten silicon, and the molten silicon is transferred to the entire filler through the capillary of the locked filler. It is common to be supplied. However, in this case, a heating apparatus for melting silicon, a crucible capable of containing molten silicon, a feeder from a crucible to a specimen, and the like are required, which makes the manufacturing process complicated and expensive.

In addition, in the case of a simple shape, there is a method in which silicon powder particles are stacked on the filler specimen and heat-treated above the melting temperature of silicon to allow molten silicon to penetrate into the specimen. In this method, the liquid silicon is formed above the melting temperature, and the silicon powder particles are agglomerated by the surface tension. When the liquid silicon is agglomerated, the silicon does not cover the entire area to be supplied, and in some cases, the agglomerated mass It is also very likely that gravity will drop due to its own weight.

In the conventional silicon supply method, when liquid silicon agglomerates, it is far from the intended contact surface, so that the transfer distance of the molten silicon becomes very long and the penetration cross-sectional area is also relatively small, and the position of the molten silicon source relative to the specimen The disadvantage is that it must be fixed at a certain position. In addition, molten silicon has a very large surface tension, has a low viscosity, tends to easily agglomerate to reduce the total surface area, and the larger the size of the aggregate, the greater the influence of gravity. This agglomeration of the molten silicon not only reduces the area of shear in which the silicon is infiltrated, but also allows the region to be infiltrated to be confined to a limited area. Although the supply of molten silicon is essential for the production of reaction-bonded silicon carbide, it is difficult to supply molten silicon uniformly throughout the specimen in conventional methods.

Accordingly, it is an object of the present invention to provide a process which can produce reaction bonded silicon carbide more economically.

In addition, another object of the present invention is to maintain the penetration area to the maximum by manufacturing the reaction bonded silicon carbide by melting the silicon uniformly and preventing the agglomeration of the molten silicon by the surface tension.

In addition, another object of the present invention is to reduce the process time by maintaining a uniform spatial distribution of molten silicon to maintain a uniform penetration rate over the entire penetration surface.

Other objects and features of the present invention will be apparent from the detailed description and the claims that follow.

1a to 1d schematically illustrate a method for producing reaction-bonded silicon carbide of the present invention,

1a shows a state in which a silicon supply specimen is in contact with a silicon carbide filler,

Figure 1b shows that the carbonized particles formed in the silicon feed specimen by the heat treatment,

Figure 1c shows that the silicon carbide network structure formed in the silicon feed specimen by heat treatment,

Figure 1d shows the final reaction bonded silicon carbide fed molten silicon

2a shows the microstructure of silicon carbide / carbon filler specimens.

2b shows the microstructure of the silicon carbide sintered body after reaction bonding.

*** Explanation of symbols for the main parts of the drawing ***

10: Silicon supply specimen 20: Silicon carbide / carbon filler

11: Silicon Particle 12: Binder

21: silicon carbide particles 22: carbon particles

In the present invention, the silicon feed specimen composed of silicon powder and thermosetting resin is brought into contact with and heat treated with the silicon carbide specimen to be reacted, and the molten silicon is supplied while the molten silicon is most efficiently supplied regardless of the shape, size, and thickness of the reaction bonded silicon carbide. Prevents agglomeration and enables a uniform supply of molten silicon.

Specifically, the present invention is to prepare a silicon supply specimen of a certain type consisting of a thermosetting resin as a silicon powder and a binder, to prepare a silicon carbide / carbon filler, the silicon supply specimen on one side of the filler in a reaction furnace Contacting and heat treatment at the melting temperature of the silicon in a vacuum or inert atmosphere to infiltrate the molten silicon in the silicon feed specimen into the filler body provides a method for producing a reaction-bonded silicon carbide.

The silicon feed specimen was prepared by mixing 70-99 wt% of silicon powder of 10-5000 μm and 1-10 wt% of thermosetting resin as a binder in a solvent to prepare a slurry, drying the slurry to obtain granules, and preparing the granules in a predetermined form. It is manufactured by molding.

As the binder, a thermosetting resin having a high residual carbon (residual carbon content) such as a phenol resin is used. The binder may further comprise 1 to 10% by weight of a thermoplastic resin such as polyvinyl butyral (PVB) to impart hot deformation of the specimen. Adding a thermoplastic resin together with a thermosetting resin as a binder to impart thermoplasticity to the silicon feed specimen can make it possible to contact the entire curved surface even if the penetration surface, which is the interface contacting the reactive bonding filler, has a curved surface. In addition, by adding a plasticizer of 1 to 10% by weight in order to increase the hot deformation more, it is possible to easily deform the feed specimen according to the shape of the penetration surface even at low temperatures.

In addition to phenol resin, furfural alcohol resin and epoxy resin may be used as the thermosetting resin. In addition to polyvinyl butyral (PVB), polyvinyl alcohol (PVA) and PVAc may be used as the thermoplastic resin. (polyvinyl acetate), polymethyl methacrylate (PMMA), etc. may be used, and plasticizers include di-butyl phthalate (DBP), benzyl-butyl phthalate (BPB), polyethylene glycol (PEG), di-methyl phthalate (DMP), and DOP. (di-octyl phthalate), glycerol and the like can be used.

In the silicon feed specimen, the binder forms a mesh structure, and reacts with silicon at the initial stage of the reaction bond to form a silicon carbide mesh structure, which prevents the agglomeration of molten silicon into a single mass. .

Specimens for supplying molten silicon can be controlled in the temperature range between room temperature and 120 ℃ by controlling the strength of the supply specimen, the treatment for hot deformation is ideally 60 ~ 120 ℃. When the silicon fraction is formed by increasing the fraction of silicon in the silicon feed specimen, almost no shrinkage occurs during heating by the network of silicon powder, so the entire initial contact area of the silicon feed specimen that is in contact with the silicon carbide filler specimen acts as the penetration area of the molten silicon. do.

Silicon feed specimens may be used as necessary, fully bonded to reactive bonded silicon carbide fillers using commercially available adhesives.

Reaction-bonded silicon carbide components as the molten silicon penetrates into the reaction-bonded silicon carbide filler when it is heated above the melting temperature of silicon, for example, in the range of 1410-1550 ° C, in the surface contact state of the silicon-supplied specimen and the reaction-bonded silicon carbide filler It will be prepared.

On the other hand, the silicon powder of the silicon feed specimen is generally larger in particle than the silicon carbide powder of the reaction bond filler. In the present invention, by increasing the particle size difference between the silicon powder and the silicon carbide powder as large as possible, the penetration rate of the molten silicon is increased, thereby greatly reducing the reaction time. In the present invention, the size ratio of silicon powder and silicon carbide powder is 5: 1 to 25: 1.

Hereinafter, the manufacturing method and features of the present invention with reference to the drawings in more detail.

Granules are prepared by mixing a silicon powder and a thermosetting resin such as a phenolic resin having a large residual carbon amount, and by using the same, forming a granule into a required size and shape to produce a silicon feed specimen. The silicon feed specimen is brought into contact with the desired position of the silicon carbide / carbon filler to be reacted as shown in FIG. 1A. In FIG. 1A, the upper portion shows a silicon supply specimen 10, and the lower portion shows a silicon carbide / carbon filler 20. In FIG. The silicon feed specimen is composed of silicon particles 11 and thermosetting resins 12, and the filler is composed of silicon carbide particles 21 and carbon particles 22.

In the next step, heat treatment is carried out in a vacuum or inert atmosphere in a reaction furnace with at least one side of the silicon feed specimen and the silicon carbide / carbon filler in contact. During the heat treatment, the thermosetting resin is pyrolyzed at about 400 to 500 ° C., leaving residual carbon 23 in the silicon feed specimen as shown in FIG. 1B. As the heat treatment temperature is further increased, the residual carbon is calcined, and then subjected to local densification to reach the melting temperature of silicon to react with some of the molten silicon particles to form a silicon carbide network structure (see 13 in FIG. 1C).

This mesh structure connects the molten silicon in the silicon supply specimen as a whole and prevents the molten silicon from agglomerating or skewing to one side, so that the molten silicon is evenly supplied to the shear surface 15 in contact with the filler and the silicon supply specimen. It plays a role. As a result, molten silicon in the silicon feed specimen is uniformly infiltrated into the silicon carbide filler. The silicon feed specimen finally leaves only the silicon carbide network 13 as shown in FIG. 1C. Inside the silicon carbide filler, the molten silicon penetrated from the silicon feed specimen reacts with the carbon particles to form new silicon carbide particles 25, and the infiltrated molten silicon is also interposed between the already existing silicon carbide 21 particles. Fill the voids 24.

On the other hand, since the silicon carbide network 13 is very low in strength it can be easily separated from the reaction bonding specimens, it is possible to obtain a reaction-bonded silicon carbide specimen 20 as shown in Figure 1d by a simple process.

As described above, when the reaction-bonded silicon carbide is manufactured using the silicon supply specimen of the present invention, the reaction of carbon and silicon powder obtained from the binder in the silicon supply specimen is exothermic, which leads to uniform melting of silicon. By preventing aggregation of the molten silicon due to the surface tension, the area where the molten silicon penetrates into the silicon carbide filler can be maintained to the maximum.

In addition, a uniform spatial distribution of molten silicon can be maintained to maintain a uniform penetration rate over the entire penetration surface, thus minimizing the overall penetration time, that is, the process time. In addition, there is no need for an independent molten silicon feeder, which saves on process equipment and kiln furniture costs.

Example

Silicon carbide / carbon filler by mixing 1 ~ 10 ㎛ size silicon carbide and 10 ~ 30 nm size carbon black as raw material powder to contain 0 ~ 30% by volume carbon black, and adding phenol resin as binder Was prepared.

Molten silicon feed specimens were prepared using a silicon powder of 70-2000 μm and a phenolic resin binder.

First, 1 to 15% by weight of phenolic resin and 0 to 15% of DBP (di-butyl phthalate) were dissolved in an alcohol capable of dissolving phenolic resin. Silicon slurry was added to this solution to prepare a slurry. After the addition of the silicon powder, it is preferable to mix uniformly and to separate the agglomerates by vigorous stirring, milling or ultrasonication. When the prepared slurry is added to distilled water heated to about 50-80 ° C., drastic solvent replacement occurs, and the dropped slurry is solidified as it is. Separation and drying can give the required granules.

In another method, dry mixing the desired amount of silicon powder and phenolic resin and then dry milling for 1 to 8 hours in a ball mill can obtain granules of a relatively uniform mixed state. However, the most ideal mixed state can be obtained from the granules by the former wet mixing method.

The prepared granules were subjected to a pressure of 5 to 400 MPa at a temperature between 120 ° C. and a molten silicon feed specimen.

In a reaction bond furnace, the same size molten silicon feed specimens were brought into surface contact with a 50 mm × 50 mm sized reactive silicon carbide filler specimen containing 0 to 30.3% by volume of carbon black, and then, in a vacuum atmosphere, 1410 Heat treatment was performed in the range of ˜1460 ° C. to infiltrate the molten silicon into the silicon carbide filler to obtain reaction bonded silicon carbide.

Table 1 shows the molding density and sintered density of the reaction-bonded silicon carbide according to the present embodiment.

Molding Density and Sintering Density of Reaction Bonded Silicon Carbide Powder composition (vol%) Molding density (%) Sintered Density (%) SiC Carbon black 100 0 53.9 96.7 91.6 8.4 57.0 97.0 83.8 16.2 58.2 97.4 76.6 23.4 60.3 97.5 69.7 30.3 62.8 97.8

2A and 2B show the microstructure of the silicon carbide / carbon filler specimen having a carbon black content of 30.3% by volume (FIG. 2A) and the microstructure of the silicon carbide sintered body after reaction bonding (FIG. 2B).

According to the present invention, unlike in the prior art, in the production of reaction-bonded silicon carbide, a heating device for melting silicon, a crucible capable of containing molten silicon, a feeder from a crucible to a specimen, and the like are necessary for producing reaction-bonded silicon carbide. Most of the equipment is not required, and only a reaction sintering furnace capable of heating up to the temperature at which the silicon is melted can be produced so that reaction-bonded silicon carbide can be produced very economically.

In addition, according to the present invention, since the reaction between the silicon powder present in the silicon feed specimen and the carbon obtained from the binder is an exothermic reaction, it is possible to induce uniform melting of the silicon. In addition, the silicon carbide mesh structure formed in the silicon supply specimen prevents agglomeration of molten silicon due to surface tension, thereby maintaining the maximum penetration area of molten silicon and maintaining a uniform spatial distribution of molten silicon. By maintaining a uniform penetration rate over the penetration surface, it is possible to minimize the overall penetration time, that is, the process time.

Claims (10)

Prepare a silicon feed specimen of a certain type consisting of a thermosetting resin selected from silicon powder and a phenol resin, furfuryl alcohol resin, epoxy resin as a binder, Prepare a silicon carbide / carbon filler, Contacting the silicon supply specimen to one surface of the filler in a reaction furnace, Heat treatment above the melting temperature of silicon in a vacuum or inert atmosphere to infiltrate the molten silicon in the silicon feed specimen into the charge body. Reaction-bonded silicon carbide production method. The method of claim 1, wherein the silicon feed specimen is a slurry by mixing 70 to 99% by weight of silicon powder and 1 to 10% by weight of the thermosetting resin as a binder in a solvent, Drying the slurry to obtain granules, Produced by molding the granules into a predetermined form Reaction-bonded silicon carbide production method. The method of claim 2, wherein the silicon powder has a size of 10 to 5000 μm. The method of claim 2, wherein the molding temperature ranges from room temperature to 120 ° C. The method of claim 2, wherein the binder further comprises 1-10% by weight of a thermoplastic resin selected from polyvinyl butyral (PVB), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), and polymethyl methacrylate (PMMA). Manufacturing method. The method of claim 2, wherein the binder is further selected from di-butyl phthalate (DBP), benzyl-butyl phthalate (BBP), polyethylene glycol (PEG), di-methyl phthalate (DMP), di-octyl phthalate (DOP), and glycerol. Reaction-bonded silicon carbide production method comprising 1 to 10% by weight of the selected plasticizer. The method of claim 5, wherein the forming temperature is in the range of 60-120 ° C. 7. The method of claim 1, wherein the silicon carbide mesh structure is formed by reacting the silicon particles with the binder inside the silicon supply specimen by heat treatment. The method of claim 1, wherein the heat treatment temperature is in the range of 1410 ~ 1550 ℃. The method of claim 1, wherein the ratio of the size of the silicon powder and the silicon carbide powder is in the range of 5: 1 to 25: 1.