JP4192145B2 - Process for producing reaction bonded silicon carbide - Google Patents

Description

  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 reaction-bonded silicon carbide.

  Reaction bonded (or reaction sintered) silicon carbide is produced by infiltrating molten silicon into a preform composed of silicon carbide and carbon. The infiltrated molten silicon reacts with the carbon particles present in the preform to form silicon carbide, and this silicon carbide acts as a binder to bond the silicon carbide particles present in the preform, and between the silicon carbide particles. It has a fine structure in which voids existing in are filled with silicon.

  In order to produce reaction bonded silicon carbide, molten silicon is supplied to the silicon carbide / carbon preform by immersing the preform in a crucible containing molten silicon and melting through the capillary of the soaked preform. In general, silicon is supplied to the entire preform. However, in this case, a heating device for melting silicon, a crucible for containing molten silicon, and a device for supplying molten silicon from a crucible to a specimen are required, so that the manufacturing process is complicated and the manufacturing cost is low. high.

  In the case of a preform having a simple shape, there is a method in which silicon powder is laminated on the preform, and heat treatment is performed at a temperature higher than the melting temperature of silicon to allow the molten silicon to permeate the preform. In this method, when the molten silicon is formed at a temperature higher than the melting temperature, the silicon powder aggregates due to surface tension, and when the molten silicon becomes one lump, the entire area to which the molten silicon is to be supplied cannot be covered, In some cases, gravity may drop due to the weight of the aggregated mass.

  In such a conventional silicon supply method, when the molten silicon agglomerates, it is far from the intended contact point, the supply distance of the molten silicon becomes very long, and the permeation area is reduced. There is a drawback that the position of the above should be fixed at a fixed position with respect to the preform. Moreover, since molten silicon has a very large surface tension and low viscosity, it has a tendency to reduce the surface area by agglomeration, and the larger the agglomerate size, the greater the influence of gravity. Such agglomeration of molten silicon not only reduces the area through which silicon penetrates, but also localizes the penetration location to a limited area. In order to produce reaction bonded silicon carbide, it is essential to supply molten silicon. However, in the conventional method, it has been difficult to supply molten silicon uniformly throughout the preform.

An object of the present invention is to provide a method capable of producing reaction bonded silicon carbide more economically.
Another object of the present invention is to maintain the maximum penetration area by uniformly melting silicon during the production of reaction-bonded silicon carbide and preventing agglomeration of the molten silicon due to surface tension.
Still another object of the present invention is to shorten the process time by maintaining a uniform spatial distribution of molten silicon and maintaining a uniform permeation rate over the entire permeation surface.

In order to achieve the object of the present invention, a silicon supplier composed of silicon powder and a thermosetting resin as a binder is prepared, a silicon carbide / carbon preform is prepared, and a reaction sintering furnace is used. The silicon supply is brought into contact with one surface of the preform, and heated at a temperature higher than the melting temperature of silicon in a vacuum or in an inert atmosphere in order to infiltrate the molten silicon in the silicon supply into the preform. A method for producing reaction bonded silicon carbide is provided.

  In the present invention, molten silicon can be efficiently supplied regardless of the shape, size, and thickness of the reaction bonded silicon carbide, the aggregation of the molten silicon can be prevented, and the molten silicon can be supplied uniformly.

The present invention includes a step of preparing a silicon supply body having a predetermined shape composed of silicon powder and a thermosetting resin as a binder, a step of preparing a silicon carbide / carbon preform, and a reaction sintering furnace. Contacting the preform with the silicon supply, and heating at a temperature higher than the melting temperature of silicon in a vacuum or inert atmosphere to allow the molten silicon in the silicon supply to penetrate into the preform. And a process for producing reaction bonded silicon carbide comprising the steps of:

The silicon supplier is a slurry prepared by mixing 70 to 99% by weight of silicon powder having a particle size of 10 to 5000 μm and 1 to 10% by weight of thermosetting resin as a binder in a solvent, and drying the slurry. The granules are obtained, and the granules are formed into a predetermined shape and manufactured.
As the binder, a thermosetting resin having a large amount of residual carbon such as a phenol resin is used. The binder may further include 1 to 10% by weight of a thermoplastic resin such as polyvinyl butyral (PVB) to impart hot deformability to the silicon supply. When a thermoplastic resin is added together with a thermosetting resin as a binder to impart thermoplasticity to the silicon supply body, even if the permeation surface of the contacted preform is not flat, it can be brought into contact with the entire uneven permeation surface. . Furthermore, when 1 to 10% by weight of a plasticizer is added to further increase the hot deformability, the silicon supply body can be easily deformed according to the shape of the permeation surface even at a low temperature.

  As the thermosetting resin, in addition to the phenol resin, a furfuryl alcohol resin, an epoxy resin, or the like can be used. In addition to PVB, polyvinyl alcohol (PVA), polyvinyl acetate (PVAC), polymethyl methacrylate (PMMA), and the like can be used as the thermoplastic resin. As plasticizers, dibutyl phthalate (DBP), butyl benzyl phthalate (BBP), polyethylene glycol (PEG), dimethyl phthalate (di-methyl phthalate): DMP), di-octyl phthalate (DOP), glycerol, and the like can be used.

  The binder reacts with silicon in the silicon supply body at the initial stage of reaction bonding to form a silicon carbide network structure, and this silicon carbide network structure can prevent the molten silicon from agglomerating into one lump.

A silicon supply body can adjust the intensity | strength of a supply body by shape | molding in the temperature range of normal temperature-120 degreeC, and 60-120 degreeC is preferable for the shaping | molding process for a hot deformation. Molding with a high silicon proportion in the silicon supply causes little shrinkage during heating due to the silicon powder network, so that the entire initial contact area of the silicon supply contacting the silicon carbide / carbon preform is made of molten silicon. Acts as an infiltration area.
If necessary, the silicon supplier can be used by completely bonding to the silicon carbide / carbon preform with a conventional adhesive.

  When the silicon supplier and the silicon carbide / carbon preform are in surface contact with each other and heated at a temperature higher than the melting temperature of silicon, for example, in the range of 1410 to 1550 ° C., the molten silicon penetrates the silicon carbide / carbon preform. However, reaction bonded silicon carbide is produced.

  The silicon powder of the silicon donor has larger particles than the silicon carbide powder of the silicon carbide / carbon preform. In the present invention, by increasing the particle size difference between the silicon powder and the silicon carbide powder as much as possible, the penetration rate of molten silicon is increased, thereby greatly reducing the reaction time. In the present invention, the size ratio of the silicon powder to the silicon carbide powder is preferably 5: 1 to 25: 1.

Hereinafter, the manufacturing method and features of the present invention will be described more specifically with reference to the drawings.
A granule is produced by mixing a silicon powder and a thermosetting resin having a high residual carbon ratio such as a phenol resin, and the granule is formed into a required size and shape to produce a silicon supply body. The silicon supplier is brought into contact with the desired position of the silicon carbide / carbon preform to be reactively bonded as shown in FIG. In FIG. 1 (a), the upper part shows the silicon supply body 10, and the lower part shows the silicon carbide / carbon preform 20. The silicon supplier is composed of silicon particles 11 and a thermosetting resin 12, and the silicon carbide / carbon preform is composed of silicon carbide particles 21 and carbon particles 22.

  Next, heat treatment is performed in a reaction sintering furnace in a vacuum or in an inert atmosphere in a state where at least one surface of the silicon supplier and the silicon carbide / carbon preform is in contact. The thermosetting resin is thermally decomposed at about 400 to 500 ° C. during the heat treatment process, so that the carbon particles 23 remain in the silicon supply body as shown in FIG. When the heat treatment temperature is further increased, the residual carbon undergoes local densification while firing, and when it reaches the melting temperature of silicon, it reacts with the molten silicon particles to form a silicon carbide network structure (FIG. 1 (c)). 13).

This network structure connects the molten silicon in the silicon supply body as a whole, preventing the molten silicon from agglomerating into one lump or being biased to one side, while the preform and silicon supply are It serves to ensure that molten silicon is uniformly supplied to the contact shearing surface 15. Thereby, the molten silicon in the silicon supply body uniformly penetrates into the silicon carbide / carbon preform. As shown in FIG. 1 (c), the silicon supplier finally leaves only the silicon carbide network 13. Inside the silicon carbide / carbon preform, the molten silicon that has penetrated from the silicon supplier reacts with the carbon particles to form new silicon carbide particles 25, and the penetrated molten silicon is already present in the silicon carbide particles 21. The gap 24 between them is filled.
On the other hand, since the silicon carbide network structure has very low strength, it can be easily separated from the reaction bonded body, and reaction bonded silicon carbide can be obtained by simple processing as shown in FIG.

  Thus, when reaction-bonded silicon carbide is produced using a silicon supplier, the reaction between the carbon obtained from the binder and the silicon powder in the silicon supplier is an exothermic reaction, thereby inducing uniform melting of silicon. And agglomeration of molten silicon due to surface tension can be prevented. Therefore, the area where molten silicon penetrates into the silicon carbide / carbon preform can be maintained to the maximum.

  Also, a uniform spatial distribution of molten silicon can be maintained to maintain a uniform penetration rate across the entire penetration surface, thus minimizing the overall penetration time, i.e. process time. In addition, since no additional molten silicon supply device is required, the processing equipment and kiln furniture costs can be reduced.

  Using silicon carbide having a size of 1 to 10 μm and carbon black having a size of 10 to 40 nm as a raw material powder, mixing so as to contain 0 to 30% by volume of carbon black, adding a phenol resin as a binder, A silicon carbide / carbon preform was produced.

The silicon supplier was manufactured using silicon powder having a particle size of 70 to 2000 μm and a phenol resin binder.
First, 1 to 15% by weight of phenol resin and 0 to 15% by weight of DBP were dissolved in alcohol capable of dissolving phenol resin based on the weight of the raw material powder. Silicon powder was added to this solution to prepare a slurry. After the silicon powder is added, the mixture is uniformly mixed by vigorous stirring, milling or ultrasonic treatment to separate the aggregates. When the prepared slurry is dropped into distilled water heated to about 50 to 80 ° C., rapid solvent replacement occurs, and the dropped slurry changes to a solidified state. After minimizing residual solvent in the granules by continuous stirring, the dropped granules are separated from the solution and dried to obtain the required granules.

As another method, a desired amount of silicon powder and a phenol resin are mixed in a dry state, and then dry milling is performed in a ball mill for 1 to 8 hours to obtain granules in a relatively uniform mixed state. be able to. However, the most preferred mixing state can be obtained from the granules by the former wet mixing method.
A silicon supply body was produced by applying a pressure of 5 to 400 MPa to the produced granules in a temperature range of room temperature to 120 ° C.

  In a reaction sintering furnace, a 50 mm × 50 mm reaction bonded silicon carbide / carbon preform containing 0-30.3% by volume of carbon black was brought into surface contact with a silicon supply of the same size and then vacuumed. Heat treatment was performed in the range of 1410 to 1460 ° C. under an atmosphere, and molten silicon was permeated into the silicon carbide / carbon preform to obtain reaction bonded silicon carbide.

Table 1 shows the molding density and sintering density of the reaction bonded silicon carbide according to this example.
FIGS. 2 (a) and 2 (b) show the microstructure (FIG. 2 (a)) of silicon carbide / carbon preform with a carbon black content of 30.3% by volume and sintered silicon carbide after reaction bonding. The microstructure of the body (FIG. 2 (b)) is shown.

As described above, according to the present invention, conventionally, for producing reaction-bonded silicon carbide, such as a heating device for melting silicon, a crucible for containing molten silicon, and a feeding device from a furnace to a preform, etc. The reaction-bonded silicon carbide can be produced economically because only the reaction sintering furnace capable of heating the silicon to the melting temperature is required without requiring most of the equipment required for the process.
According to the present invention, since the reaction between the silicon powder present in the silicon supply body and the carbon obtained from the binder is an exothermic reaction, silicon can be uniformly melted. Furthermore, since the silicon carbide network structure formed in the silicon supply body can prevent the molten silicon from aggregating due to the surface tension, the permeation area of the molten silicon can be maintained to the maximum. In addition, since the uniform spatial distribution of molten silicon can be maintained and a uniform penetration rate can be maintained across the entire penetration surface, the overall penetration time, ie, process time, can be minimized.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the manufacturing method of the reaction bond silicon | silicone based on this invention schematically, (a) is a figure which shows the state which contacted the silicon supply body and the silicon carbide / carbon preform, (b) is heat processing. The figure which shows that the carbonized particle was formed in the silicon supply body by (c) is a figure which shows that a silicon carbide network structure is formed in a silicon supply body by heat processing, (d) is a molten silicon supply Showing the final reaction bonded silicon carbide formed (A) is a photograph showing the microstructure of the silicon carbide / carbon preform, and (b) is a photograph showing the microstructure of the silicon carbide sintered body after reaction bonding.

Claims (10)

Providing a silicon supplier having a predetermined shape including silicon powder and any one thermosetting resin selected from a phenol resin, a furfuryl alcohol resin, and an epoxy resin as a binder;
Providing a silicon carbide / carbon preform,
Contacting the silicon supply with one side of the preform in a reaction sintering furnace;
Heat-treating at a temperature higher than the melting temperature of silicon under vacuum or inert atmosphere in order to infiltrate the molten silicon in the silicon supply body into the preform;
A process for producing reaction bonded silicon carbide comprising:   The silicon supplier is prepared by mixing 70 to 99% by weight of silicon powder and 1 to 10% by weight of thermosetting resin as a binder in a solvent to prepare a slurry, drying the slurry to obtain granules, The method for producing reaction-bonded silicon carbide according to claim 1, wherein the granules are produced by molding the granules into a predetermined shape.   The method for producing reaction-bonded silicon carbide according to claim 2, wherein the silicon powder has a size of 10 to 5000 μm.   The method for producing reaction-bonded silicon carbide according to claim 2, wherein the molding temperature is in the range of room temperature to 120 ° C.   The method for producing reaction-bonded silicon carbide according to claim 2, wherein the binder contains 1 to 10% by weight of any one thermoplastic resin selected from polyvinyl butyral, polyvinyl alcohol, polyvinyl acetate, and polymethyl methacrylate. .   The reaction according to claim 2, wherein the binder comprises 1 to 10% by weight of a plasticizer selected from dibutyl phthalate, butyl benzyl phthalate, polyethylene glycol, dimethyl phthalate, dioctyl phthalate and glycerol. A method for producing bonded silicon carbide.   The method for producing reaction-bonded silicon carbide according to claim 5 or 6, wherein the molding temperature is in the range of 60 to 120 ° C.   The method for producing reaction-bonded silicon carbide according to claim 1, wherein silicon particles and a binder are reacted inside the silicon supply body to form a silicon carbide network structure by heat treatment.   The method for producing reaction-bonded silicon carbide according to claim 1, wherein the heat treatment temperature is in a range of 1410 to 1550 ° C.   The method for producing reaction-bonded silicon carbide according to claim 1, wherein a size ratio of the silicon powder to the silicon carbide powder is in a range of 5: 1 to 25: 1.