JPH05279007A - Production of silicon carbide powder - Google Patents

Abstract

PURPOSE:To provide a method for production of the silicon carbide powder excellent in sintering properties produced by a more simple process than a conventional method inexpensively. CONSTITUTION:A water glass is allowed to impregnate in a cellulose material and sodium silicate is neutralized with an acidic material (mineral acid, acidic gas, etc.) and washed with water. The obtained cellulose material supporting 5-50% silica is fired at 1100 deg.-2300 deg.C in vacuum or in an inert gas atmosphere and ground to produce the powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of fine silicon carbide powder having excellent sinterability, which is useful as a raw material for sintering for producing mechanical parts and electronic parts, and as a polishing and grinding material.

[0002]

The following methods are known as methods for producing silicon carbide powder. (1) Reductive carbonization method of silica and carbon (2) Direct reaction method of metallic silicon and carbon (3) Thermal decomposition method of organosilicon compound (4) Gas phase reaction method

(1) Method for reducing carbonization of silica and carbon (Kazuo Yajima et al., "High-purity beta SiC by silica reduction method"
Powder Synthesis and Sinterability ", Silicon Carbide Ceramics, edited by Shigeyuki Soumiya et al., Uchida Lao Tsuruga, 1988. Although it is a relatively simple manufacturing method, the silicon carbide produced is coarse, so when using this as a raw material for sintering, a great deal of labor is required for crushing and classification, and the obtained powder is also sintered. It is not always suitable as a raw material.

The direct reaction method of metallic silicon and carbon of (2) is carried out by a method of reacting powdery metallic silicon with carbon, but the silicon carbide produced is coarse as in (1) and crushed or crushed. A great deal of effort is required for classification.

(3) Pyrolysis method for organosilicon compounds (
J. Less-Common Met., 68, 29-41 (1979)., Or Science, 11 (12) 79 (1981).), When decomposing low molecular compounds and when decomposing high molecular compounds. However, in either case, the raw material organosilicon compound is expensive and is not suitable for industrial production.

(4) Gas phase reaction method (High Tech Ceramic
s, 501-509 (1987). Elsevier Science Publishers,).
Is a relatively fine powder can be obtained, but the raw material cost is high, the raw material gas, particularly silicon compound gas is highly toxic, explosive and difficult to handle,
It has drawbacks such as not being suitable for mass production.

There is also known a method for obtaining silicon carbide by firing rice husk containing silica by firing it (Japanese Patent Laid-Open Nos. 64-28210 and 60-5072).
Nos. 4,248,844, 3,754,076, etc.) Silicon carbide produced by these methods also has the same problems as (1). In any of the above methods, there is a problem in producing a powder having good sinterability at low cost.

[0008]

DISCLOSURE OF THE INVENTION The present invention provides a method for producing a fine silicon carbide powder having good sinterability, which could not be achieved in the prior art, at low cost.

[0009]

The silicon carbide of the present invention comprises:
A silica material-supported cellulosic material is substantially vacuumed,
Alternatively, it can be obtained by firing at 1100 to 2300 ° C. in an inert gas atmosphere and crushing this. Further, in the method for producing silicon carbide of the present invention, the maximum temperature when firing in a substantially vacuum or inert atmosphere is 110.
It is preferably 0 to 1500 ° C.

There are no particular restrictions on the type of cellulose material used in the present invention, and various raw materials can be used. That is, natural lignocellulosic materials such as wood and wood fibers (pulp), grasses and their fibers, cotton, regenerated cellulose, cellophane and the like can be used.

In the method of the present invention, as a method for supporting silica on the cellulose material, for example, Japanese Patent Application No. 2-1
The methods disclosed in No. 11785 and Japanese Patent Application No. 2-162946 can be used. In these methods, the cellulosic material is immersed in an aqueous solution of a water-soluble silicic acid compound such as sodium silicate, carbon dioxide gas after deliquoring, or a water-soluble silicic acid compound impregnated in the cellulosic material using an aqueous solution of an acid. It is neutralized and silica (silicon dioxide) is supported inside the material.

The sodium silicate aqueous solution (water glass) is
The thing normally used industrially can be used.
Among industrial water glasses, the No. 3 sodium silicate solution is easy to handle and is particularly suitable for the purpose of the present invention. When impregnating water glass into a cellulosic material, the concentration of water glass may be an industrial solution as it is,
It can also be used after diluting it if necessary. The content of silica in the water glass affects the loading ratio of silica to be loaded on the cellulosic material (weight of silica / ratio% by weight of silica-supporting cellulosic material). That is, the higher the silica content in the water glass, the higher the silica loading rate.
The content of silica in the water glass is preferably 5 to 40%.

As a method of impregnating the water glass into the cellulose material, any method such as dipping, spraying or mixing can be used. In this case, when the dipping method is used, it is necessary to remove excess water glass by deliquoring after dipping. The method of removing liquid is not particularly limited, and a commonly used method such as centrifugation or pressing can be used. The time for impregnating the water glass into the cellulosic material is not particularly limited, but it is necessary to take the time necessary for the water glass to sufficiently penetrate into the cellulosic material. This time depends on the cellulosic material to be soaked. For example, when 1 to 10 denier rayon is immersed in No. 3 water glass, a suitable immersion time is about 6 hours. The temperature for impregnating the cellulosic material with water glass is not particularly limited, but generally room temperature is suitable. Applying an external force such as stirring during the impregnation or applying a pressure to the liquid during the immersion may be effective for prompt and uniform impregnation.

To neutralize the alkali of the water glass in the cellulosic material impregnated with water glass, it is contacted with an acidic substance. As the acidic substance, a method of immersing in a solution of a mineral acid such as sulfuric acid or hydrochloric acid, spraying these solutions, or a method of exposing to an acidic gas such as carbon dioxide can be used. When using mineral acids, it is necessary to choose a concentration such that the cellulosic material is not damaged excessively. The same caution is required when using a gas such as hydrogen chloride, which has a strong power to damage cellulose, as the acidic gas. When a mineral acid is used for neutralization, if the acid concentration is too low, the water glass may not be neutralized and may be eluted from the cellulosic material. In the case of sulfuric acid, a suitable concentration is about 0.05 to 2 N.
The neutralized cellulosic material is washed with water in order to wash away the sodium salts produced simultaneously with the silica.

Through the above steps, silica is supported on the cellulosic material. The loading rate of silica is related to the amount of silicon carbide produced after firing. The silica support rate suitable for the purpose of the present invention is 5 to 50%, and the particularly preferred range is 10 to 40.
%. If the supporting rate of silica is too low, silicon carbide will not be sufficiently generated by firing, and if it is too high, the silica content will remain unreacted after firing, which is not preferable.

The cellulosic material on which silica is supported by the method of the present invention is a mixture of silica and an organic substance as a carbon source in an extremely fine state, and is ideal as a raw material for producing silicon carbide. That is, when silicon carbide is produced using this material as a raw material, silicon carbide can be produced at a lower temperature than conventional methods. Further, because of this, it becomes possible to suppress the growth of crystals, and it becomes possible to produce powder having excellent properties as a raw material for sintering.

The washed cellulosic material is dried and calcined in a vacuum or an inert atmosphere. When firing is performed, it is possible to raise the temperature to the maximum temperature in one firing, but since a considerable amount of tar-like substances are generated from the cellulosic material, it is customary to perform preliminary firing up to about 1000 ° C. is there.

A nitrogen stream is suitable as the atmosphere for the preliminary firing. The rate of temperature rise is from room temperature to 500 ° C.
50 to 20 ° C at 50 ° C / hr up to 500 to 1000 ° C
It is desirable to raise the temperature at 0 ° C./hr in order to increase the carbonization yield of the cellulosic material. Maximum temperature is 800-1000
C. is suitable, and the maximum temperature may be maintained for an appropriate time, but the retention time may be omitted.

The main firing is carried out in vacuum or in an inert atmosphere. Argon, helium and the like are suitable as the inert atmosphere. The temperature rising rate during the main firing is 100
~ 2000 ° C / hr is preferred. Maximum temperature is 1000
~ 2000 ° C is preferred, and 1100-1500 ° C is particularly preferred. The maximum temperature holding time is not necessarily provided, but a holding time of 0.1 to 64 hr may be provided, and a holding time of 0.5 to 5 hr is preferably set. There is no particular limitation on the cooling rate.

The material that has been fired is crushed. As a pulverization method, a method used for producing ordinary ceramic powder such as a ball mill can be used. According to the method of the present invention, it is possible to pulverize into a fine powder having excellent sintering characteristics with a remarkably shorter time than before and less energy.

When carbon remains in the material after firing, a step of firing carbon in the air before or after pulverization to remove carbon may be provided. Further, in the later sintering step, when it is necessary to add carbon as an auxiliary agent, it is also possible to intentionally leave a proper amount of carbon and perform firing by adjusting the amount of silica supported on the raw material cellulose material. is there. If you want to remove impurities such as metals and silica that remain in the material after firing, wash with an acid such as hydrofluoric acid or an alkaline aqueous solution before or after crushing as usual. Things are also done.

[0022]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 1 100 g of rayon having 1.5 denier and 3 mm length was immersed in 2 liter of No. 3 sodium silicate aqueous solution (water glass) for 3 hours. The rayon after the immersion was suction-filtered on a Buchner funnel and centrifugally drained at 1500 G (gravitational acceleration) to remove excess water glass. The rayon impregnated with water glass was placed in a pressure-resistant container having a volume of 5 liters, carbon dioxide gas was supplied to maintain the pressure in the container at 1 kg / cm ² (gauge), and the container was left standing for 1 hour. This was taken out of the container, defibrated in water using a mixer, and washed with a large amount of water. The silica loading rate of the silica-supported rayon (900
℃ calcined ash content / supported fiber weight x 100%) is 20%
Met.

The rayon supporting silica was dried and prebaked in an electric furnace in a nitrogen stream. Room temperature to 500 ° C
Up to 20 ° C / hr, up to 500-1000 ° C is 1
It was carried out at 00 ° C / hr. No holding at 1000 ° C,
Immediately, it was naturally cooled. The firing yield of the preliminary firing was 45%. The pre-fired sample was main-fired in an electric furnace in an argon stream. Firing from room temperature to 1200 ° C 1000
The temperature was raised at 1,000 ° C./hr, the temperature was kept at 1,200 ° C. for 1 hour, and then cooled to room temperature at 1,000 ° C./hr. The firing yield of the main firing is
It was 73%.

The calcined sample was calcined in air at 800 ° C. for 40 minutes to remove carbon and ground in a mortar made of silicon nitride. B. of this sample E. T. The specific surface area by the method is 25
It was m ² / g. As a result of analyzing this sample by X-ray diffraction and infrared absorption spectroscopy, it was confirmed that beta-type silicon carbide was produced. No silica was detected. Observation with a transmission electron microscope revealed that the particle size of this powder was 40 to 100 nanometers.

To 98 parts of this sample, one part each of boron (amorphous type) and carbon (carbon black) were added, acetone was added, and the mixture was wet-mixed for 5 hours with a nylon ball mill. This sample was put into a mold and the diameter was 13.2 m under hydrostatic pressure.
It was molded into a cylinder having a height of m and a height of 5.00 mm. The density of the molded body was 2.11 g / cm ³ . The compact was calcined in an argon stream at 2050 ° C. for 30 minutes, resulting in a density of 2.97 g / cm ³ . As a result of observing the fracture surface of the sintered body with a scanning electron microscope (SEM), it was observed that the sintered body had almost no pores and that the sintering proceeded to a high degree.

Example 2 Softwood bleached kraft pulp was used as a lignocellulosic material, and a silicon carbide powder and a sintered body were prepared in the same manner as in Example 1. The specific surface area of the powder is 19.6 m ² /
g, the density of the sintered body was 2.83 g / cm ³ .

Comparative Example 1 Silica powder (manufactured by Wako Pure Chemical Industries, 200 mesh) and carbon powder (coke, 200 mesh) were dry-mixed in a ball mill and placed in a carbon crucible in the same manner as in Example 1 in an argon stream 1200. Baking for 1 hour at ℃. The fired sample is X
As a result of line diffraction analysis, only silica was present,
Silicon carbide was not formed.

Comparative Example 2 A mixed powder of silica and carbon prepared in the same manner as in Comparative Example 1 was used.
Firing was performed at 1700 ° C. for 1 hour in an argon stream. Analysis by X-ray diffraction confirmed the formation of silicon carbide. This sample was ground in a silicon nitride mortar in the same manner as in Example 1 and the specific surface area was measured. As a result, it was 0.05 m ² / g. When this sample was molded and sintered in the same manner as in Example 1, the density after sintering was 1.69 g / cm ³ . It was confirmed by SEM observation that the sintering had hardly progressed.

Comparative Example 3 Commercially available silicon carbide powder for sintering (beta type, average particle size 0.4 micron) was molded and sintered in the same manner as in Example 1. The density of the sintered body was 2.74 g / cm ³ .

[0031]

According to the method of the present invention, a silicon carbide powder having good sinterability can be manufactured at a low cost with a simpler manufacturing process than the conventional method.

Claims (1)

[Claims] 1. A cellulosic material supporting silica,
1100 in a substantially vacuum or inert gas atmosphere
A method for producing a silicon carbide powder, which comprises calcination at ˜2300 ° C. and crushing this.