JP2973790B2 - Method for producing reaction sintered silicon carbide product - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a silicon carbide product by a reaction sintering method.

[0002]

2. Description of the Related Art A number of methods have been proposed for producing a reaction sintered silicon carbide product by impregnating a calcined body of silicon carbide and carbon with metallic silicon. In each case, the calcined body was reacted with gaseous or molten metal silicon.

[0003] However, the conventional method of obtaining a reaction sintered body using gaseous metallic silicon has a very large defect that the reaction takes a long time and it is impossible to completely react. there were. In addition, in the method of reacting carbon in the calcined body using molten metal silicon, it is presumed that the reaction is a violent exothermic reaction, but during the reaction, the surface layer portion of the calcined body slightly rises. After the reaction, the ratio of metal silicon contained in the surface layer portion becomes large, so that it is difficult to say that the surface layer state is silicon carbide. Therefore, chemical treatment of the sintered body performed after the reaction, for example, high-temperature caustic soda The metal silicon contained in the surface layer is eluted by the solution treatment, and as a result, the surface state becomes rough,
The dimensional accuracy and surface roughness in the "as-cast" state used in the terms used in this field are poor, and there is a serious defect that expensive machining is indispensable.

[0004] The present invention has been made in view of the above circumstances,
A strong outer shell of silicon carbide can be formed on the surface layer of the calcined body, so that the surface state of the calcined body after the reaction sintering can be maintained at the same state as that of the calcined body. Provided is a method for producing a reaction-sintered silicon carbide product that can omit machining after sintering.

[0005]

The present inventors have made intensive studies to achieve the above object, and as a result, have impregnated a calcined body mainly composed of silicon carbide and carbon with metallic silicon to carry out reaction calcination. In obtaining a sintered silicon carbide product, first, gaseous metallic silicon is allowed to act on the calcined body to silicify (silicon carbide) at least a portion of the carbon present in the surface layer, thereby calcining. After forming a strong silicon carbide shell on the surface layer of the body, the calcined body is supplied with molten metal silicon and reacted to obtain a reaction-sintered silicon carbide product. But clean and excellent dimensional accuracy,
It has been found that even if the surface is treated with an alkaline solution after the reaction sintering, the skin is not roughened, so that the subsequent machining can be omitted.

That is, in the production of a silicon carbide product by the reaction sintering method, the metal silicon remaining in the sintered body as an unreacted material at the time of sintering expands by about 8% when it solidifies. It is most economically advantageous to use a chemical capable of dissolving metallic silicon, such as caustic soda, to remove this. However, if the sintered body is not sufficiently bonded with silicon carbide, in this chemical treatment step, the sintered body itself collapses, or at least its surface state becomes rough.

However, in the present invention, first, a strong silicon carbide shell is formed on the surface layer by the reaction between gaseous metallic silicon and carbon on the surface layer of the calcined body. Since it is bonded sufficiently firmly by silicon carbide, it does not adversely affect the sintered body by the above chemical treatment, and as described above, by performing molten metal silicon treatment after gaseous metal silicon treatment, Since a clean product can be obtained, a good product can be obtained only by performing chemical treatment after reaction sintering. Therefore, according to the present invention, machining, which is the most difficult point in the production of ceramics, can be omitted.

Accordingly, the present invention provides a method for producing a reaction-sintered silicon carbide product by impregnating a calcined body containing silicon carbide and carbon as main components with metal silicon under reduced pressure at a temperature not lower than the melting point of metal silicon. Exposing the calcined body to an atmosphere of gaseous metallic silicon to convert at least a portion of carbon present in the surface layer into silicon carbide, and then reacting the calcined body with molten metallic silicon. To provide a method for producing a reaction sintered silicon carbide product.

Hereinafter, the present invention will be described in more detail. In the method for producing a reaction sintered silicon carbide product of the present invention, first, a calcined body mainly containing silicon carbide and carbon is produced.

In this case, a known method can be adopted as a method for producing the calcined body. For example, silicon carbide, carbon, and a binder are mixed and formed into a desired shape.
Further, a method of calcining at 600 to 1000 ° C. in an inert atmosphere can be adopted. The types, particle sizes, mixing ratios, and the like of silicon carbide, carbon, and a binder may be the same as usual.

In the present invention, it is preferable to process into the final product shape and dimensions at the stage of forming the calcined body from the viewpoint that machining after sintering is omitted. If the sintered body is obtained with good dimensional accuracy and good skin condition, and the skin is not roughened even with alkali treatment, it is finished in the final shape and dimensions at the stage of the calcined body in this way No problem.

In the present invention, the calcined body is then exposed to a gaseous metallic silicon atmosphere under reduced pressure at a temperature equal to or higher than the melting point of metallic silicon, so that at least a part of the carbon present in the surface layer is carbonized. It is siliconized to form a silicon carbide shell on the surface layer.

In this case, from the viewpoint of forming a strong surface silicon carbide shell, it is necessary that the vapor pressure of metallic silicon be high to some extent. For example, when the temperature is 1800 ° C., the vapor pressure becomes about 0.1 Torr. Therefore, it is desirable to maintain the temperature at 1600 ° C. or higher after once evacuating. If the temperature is too high, the material of the furnace will be damaged.

After the treatment with the gaseous metallic silicon in this way, molten metallic silicon is supplied to the calcined body and reacted. As this step, known methods and conditions can be adopted, and reaction sintering can be performed at 1450 ° C. or higher. As a method of supplying and impregnating molten silicon into the calcined body, see FIG. As shown, the molten metal silicon is supplied through a fibrous body composed of an aggregate of a large number of filaments,
A method of impregnation is preferably employed. That is, in FIG.
Is a calcined body, 2 is a crucible containing molten metal silicon, 3
Is a fibrous body in which a number of filaments are bundled. One end of the fibrous body 3 is in contact with (in some cases, integrated with) the calcined body 1, and the other end of the fibrous body 3 is molten metal. By immersing in the silicon, the molten metal silicon can be supplied and impregnated to the calcined body 1 easily and reliably, and at this time, the amount of excess metallic silicon adhering to the outside of the calcined body 1 can be reduced. This makes the post-processing process easier. In addition, it is preferable to use carbon fiber, silicon carbide fiber, or the like having a diameter of 100 μm or less, particularly 50 μm or less, for the filament constituting the fibrous body 3, and use a plurality of fibrous bodies 3 having a diameter of 0.1 to 1 mm. Is preferred. In the drawing, reference numeral 4 denotes a support stand, 5 denotes a spacer made of carbon or silicon carbide, 6 denotes a crucible base which is disposed so as to be movable up and down, and 7 denotes a hanger for hanging and fixing the fibrous body. .

After the calcined body is impregnated with the molten metal silicon and subjected to reaction sintering as described above, post-treatment such as alkali washing can be performed according to a conventional method. Since there is no machining, machining can be omitted.

The sintered body after the reaction sintering needs to be sufficiently firmly bonded by silicon carbide from the viewpoint of more reliably preventing surface roughness due to alkali treatment or the like. The density of the sintered silicon carbide product is preferably at least 3.0 g / cm ³ , particularly preferably at least 3.03 g / cm ³ .

[0017]

According to the present invention, the as-cast skin is clean,
Good dimensional accuracy, no roughening by alkali treatment,
It is possible to easily and reliably manufacture a reaction sintered silicon carbide product which can omit machining after reaction sintering.

[0018]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples.

The following raw materials: Silicon carbide fine powder (average particle size: 5 μm) 55 parts by weight Graphite powder 27 parts by weight Toluene is added to 18 parts by weight of silicone varnish KR-280 (as solid content), and the mixture is mixed well by a ball mill. Was removed to obtain a granular mixture, which was subjected to a pressure of 1500 kg / cm ² using a mold press to obtain an outer diameter of 20 kg / cm ^2.
A ring having a diameter of 0 mm, an inner diameter of 150 mm, and a height of 30 mm was produced. This was heated to 800 ° C. in a nitrogen stream over about 24 hours, and kept at that temperature for 4 hours to obtain a calcined body. This was subjected to step processing to obtain the shape of the final product shown in FIG.

Next, as shown in FIG. 1, three calcined bodies 1 each having a ring-shaped step are placed via a spacer 5 in a vacuum vessel having a heating means and an exhaust means. One end of the carbon fiber body 3 is connected, the other end of the fiber body 3 is fixed above the crucible 2 containing metal silicon, and the vessel is heated and heated while keeping the inside of the vessel at 10 ⁻² Torr or less. The temperature was higher than the melting point of silicon, that is, 1800 ° C. in this case. This state is continued for about 1 hour, and after the surface layer of the calcined body 1 is brought into contact with the vapor of metallic silicon to siliconize the surface layer, the temperature is lowered to 1550 ° C., and the crucible 2 is raised to raise the carbon content. The tip of the fibrous body 3 was brought into contact with the molten metal silicon. Thereby, the molten metal in the crucible 2 was supplied to the calcined body 1 through the carbon fiber body 3, and the reaction proceeded. afterwards,
The crucible 2 where the reaction was completed was lowered, and the supply of the molten metal was stopped.

Since the thus obtained sintered body mainly had metallic silicon adhered thereto in a blown state, it was immersed in an aqueous solution of caustic soda at 80 ° C. to dissolve and remove the metallic silicon. Washed well. When observing the ring that became the product, the back of the cutting edge formed when processing the calcined body was clearly left, and the surface condition was smooth and the corner of the step was firm, Did not need to be applied.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of an apparatus used for carrying out a manufacturing method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Calcination body 2 Crucible 3 Fiber body

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C04B 35/56

Claims (1)

(57) [Claims] 1. A method for producing a reaction-sintered silicon carbide product by impregnating a calcined body mainly composed of silicon carbide and carbon with metallic silicon, wherein the calcined material is heated at a temperature not lower than the melting point of metallic silicon. Exposing the body to an atmosphere of gaseous metal silicon to convert at least a portion of carbon present in the surface layer into silicon carbide, and then reacting the calcined body with molten metal silicon. A method for producing a sintered silicon carbide product.