JPH0426600A - Production of sic whisker - Google Patents

Abstract

PURPOSE:To produce SiC whiskers having properties including a prescribed average diameter and diameter distribution under control by regulating the particle size of powdery starting material as an Si source to a specified range in production with a solid starting material system. CONSTITUTION:A starting material mixture of starting material as an Si source with carbon is heated to a reaction temp. range in a non-oxidizing atmosphere and SiC whiskers are formed. In this method, the particle size of the starting material as an Si source is regulated to a certain range of <=250mum by classification. The particle size of the starting material affects properties of formed whiskers, especially the average diameter and diameter distribution and the average diameter is reduced by reducing the particle size. In the case of >250mum particle size, unreacted starting material remains in large quantities, segregation is caused and the yield of formation is remarkably reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing SiC whiskers useful as composite reinforcing materials, and particularly to a method for producing SiC whiskers whose average diameter size can be controlled.

[Conventional technology] Whiskers composed of acicular single crystals of SiC have excellent performance characteristics in terms of specific strength, specific modulus of elasticity, heat resistance, chemical stability, etc., and are therefore used in various plastic materials and metals. It is used as a composite reinforcement material for ceramic materials.

Composite formation using SiC whiskers is aimed at reinforcing fibers, so for example, when aiming at unidirectional composite reinforcement of a plastic base material, it is necessary to use SiC whiskers with a thin diameter and long properties that have good orientation. is suitable. However,
In composite reinforcement of ceramic materials with poor fracture toughness, whiskers dispersed within the structure have the function of stopping or suppressing the growth of cranks that occur in the ceramic body, as well as bending the direction of crack propagation and relieving stress concentration. However, in order to achieve higher toughness due to the phenomenon of absorbing energy at the tip of the crack due to the pulling action of the whiskers, it is effective to combine whiskers with large diameter types. has been confirmed. In addition, even in cases where a composite material is subjected to secondary processing such as extrusion or forging, thick and short length types are used to minimize whisker damage caused by stress during secondary processing. It is considered suitable.

As described above, the requirements for the properties of SiC whiskers are changing depending on the type of matrix to be composited, the composite purpose, etc., and in particular, the grade requirements for the average diameter are becoming stricter.

Conventionally, methods for producing SiC whiskers using a gas phase raw material system and a solid phase raw material system are known, but among these, the manufacturing method using a solid phase raw material system, which is currently considered the most industrial mass production technology (for example, , Japanese Patent Publication No. 60-44280, Japanese Patent Application Laid-Open No. 61-102416)
If the diameter of the iC whisker can be controlled and variations can be reduced, it will be possible to fully meet the above grade requirements.

In order to achieve this objective, JP-A-2-18399 discloses that a solid silicon raw material and a solid carbon raw material are heated in a non-oxidizing atmosphere in the presence of a catalyst, the temperature is raised to 1400~
A method for producing silicon carbide whiskers by maintaining and reacting at a temperature of 1600°C, characterized in that after the reaction start temperature, a temperature raising step is performed in an inert gas atmosphere, and then the silicon carbide atmosphere is switched to a hydrogen atmosphere. A method for producing whiskers has been proposed.

[Problems to be Solved by the Invention] However, in the method disclosed in JP-A-2-18399, hydrogen gas must be introduced into the high-temperature reactor, which poses a risk to business and increases costs. There is a problem.

The present invention has developed a manufacturing technology that controls the average diameter of SiC whiskers produced by classifying and adjusting the particle size of silicon source raw material powder.The purpose of this is to improve operability, economic efficiency, etc. in solid phase raw material systems. It is an object of the present invention to provide a method for manufacturing SiC whiskers that can be produced in a controlled manner to have properties with a predetermined average diameter and distribution without deterioration.

[Means to solve the problem]

A method for producing SiC whiskers according to the present invention to achieve the above object is a method of producing SiC whiskers by heating a powdered mixed raw material of a silicon source material and a carbonaceous material to a reaction temperature range in a non-oxidizing atmosphere. The structural feature is that the silicon source raw material powder is classified and adjusted to a certain particle size range in a fine region of 250 μm or less.

The silicon source materials used in the present invention include silica gel,
Examples include substances containing silicon components such as silica sand, quartz powder, inorganic silicates, and organic silicon compounds, among which SiO□
It is effective to use silica gel, quartz powder, and silica sand whose main ingredients are silica gel, quartz powder, and silica sand.

As the carbon material, carbon blank, coke powder, graphite powder, powdered activated carbon, etc. can be used, but the most suitable carbon material is carbon blank. When applying carbon black, it does not matter whether it is furnace black, channel blank, acetylene black, etc., but especially DBP.
Those having an oil absorption of 100 m/100 g or more are effectively used.

As the catalyst, a metal component selected from Fe, Co, Ni, Ca, and their oxides, chlorides, carbonates, sulfates, and nitrates is used.

The silicon source material, carbonaceous material, and catalyst component are mixed uniformly in a powder state, but if the catalyst component is added and mixed to the silicon source material in advance and then mixed with the carbonaceous material, the three components will be homogeneously mixed. development will proceed smoothly. The blending of the raw material components is such that the ratio of carbonaceous material to the silicon source raw material is set in the range of 60 to 120% by weight, and the catalyst is blended in an amount equivalent to 0.03 mol or more as metal per 1 mol of Si in the silicon source raw material. It is preferable to add the catalyst to the mixed raw material. In this case, if the amount of catalyst is less than 0.03 mol as metal,
It becomes difficult to generate SiC whiskers with a diameter of 5 μm or more. However, if the amount exceeds 0.3 mol, the shape of the resulting SiC whiskers tends to deteriorate, so it is desirable to set the upper limit of the amount of catalyst to be 0.3 mol.

The main requirement of the present invention is to classify and adjust the silicon source raw material powder in the above-mentioned component system to a certain particle size range in a fine region of 250 μm or less. The upper limit of particle size of silicon source raw material powder is 2
The reason why the particle size is set to 50 μm is that if the particle size is larger than zso a-, a large amount of unreacted silicon source raw material components will remain and segregate after generation. Adjusting the classification to a certain particle size range means, for example, 150 to 250 μm, 100 to 150 μm in a fine region of 250 μm or less.
The particle size is to be aligned within a certain distribution width range, such as m, 50 to 100 ttm, and 50 μm or less. Grinding and classification can be performed using a normal micron separator or the like.

The raw material components, including the silicon source material, carbonaceous material, and a specific amount of metal catalyst, are lightly filled into a reaction vessel made of a highly heat-resistant material such as graphite, sealed, and placed in a non-oxidizing atmosphere such as nitrogen or argon. It is heated to the reaction temperature range in a heating furnace maintained at .

At this time, the conditions for the heat treatment are a temperature increase rate of 5 to 5 b/in;
, the reaction temperature is set at 1600-1900°C. More suitable conditions are a temperature increase rate of 10 to 30"C/win,
The reaction temperature is to be in the range of 1610 to 1700°C.

If the temperature increase rate is less than 5°C/sin, it will be difficult to generate large-diameter SiC whiskers, and the heating rate will be 40°C/-! If n is increased, the temperature gradient in the raw material structure increases, which tends to increase the irregular shape and variation in the shape of the generated whiskers.In addition, if the reaction temperature is less than 1600 °C, the generation of SiC whiskers is smooth. In addition, more silicon source raw materials remain, and in a high temperature range exceeding 1900° C., the shape of the whiskers increases, and at the same time, the whiskers begin to become granular and the number of shots increases.

After the reaction, unreacted carbonaceous components remaining in the reaction vessel are removed by incineration.

The SiC whiskers obtained in this way are acicular single crystals of SiC with no lattice defects and exhibit a pale greenish white color, and can have a desired shape with different average diameters, aspect ratios, etc. depending on the degree of classification adjustment of the silicon source material powder. present.

[For production]

When producing SiC whiskers using a solid raw material system, the particle size of the silicon source raw material powder influences the properties of the produced whiskers, particularly the average diameter and its distribution. This relationship shows that as the particle size decreases, the average diameter becomes thinner, and as the particle size increases, the average diameter tends to become thicker.
If it exceeds 0 μm, a large amount of unreacted silicon source material remains and segregates, which significantly reduces the production yield.

The present invention skillfully utilizes the above-mentioned technical cause-and-effect relationship, and classifies and adjusts the silicon source raw material powder to be used within a certain particle size range in a fine region of 250 μm or less, thereby controlling the average diameter and distribution of the SiC whiskers to be produced. This makes it possible to control the level.

Moreover, since the process of the present invention does not have any factors that reduce operability and economic efficiency, it is extremely useful as a technique for individually mass-producing SiC whiskers for composite reinforcing materials with desired properties mainly based on average diameter.

〔Example〕

Examples of the present invention will be described below while comparing them with comparative examples.

Examples 1 to 3, Comparative Example Particle size of silicon source material is 75 μm or less, 75 to 150 μm
Using 33.3 g of quartz powder classified into three types, 150 to 250 μm, F of straw with a particle size of 8 to 9 μm was used as a catalyst.
2g of e powder (0.06 for Silmol in quartz powder)
(equivalent to 5 moI) was added and mixed with stirring.

Next, 40 g of carbon black carbon material was added and uniformly mixed by stirring. As a carbon blank for carbonaceous materials, DB
P@oil amount 130 m/100g, iodine adsorption amount 104
A furnace blank [manufactured by Tokai Carbon ■, "5EAST 5) 1"] having a characteristic of 1.5 g/g was used.

This powder mixed raw material was lightly filled into a reaction vessel made of high-purity graphite, the top of which was coated with graphite blue, and placed in an electric resistance heating furnace maintained in a nitrogen gas atmosphere. The temperature of the furnace was raised to 1640° C. at a temperature increase rate of 10”/sin, and the temperature was maintained for 2 hours to generate a reaction.

After the heating reaction, the contents were collected from the reaction vessel and placed in a large tank for 6 minutes.
The remaining carbonaceous components were removed by heat treatment at a temperature of 00° C. by incineration.

When the obtained product was subjected to X-ray diffraction, β
Clear peaks appeared at the wavelength positions of -5iC atomic open circuits 82.15 and 154, but no diffraction lines corresponding to SiO□ or C were confirmed.

Table 1 shows the average diameter of each SiC whisker produced and its standard deviation value in comparison with the particle size range of the silicon source material.

Comparative Example The same quartz powder as in the example was used as a silicon source material, and a powder with a particle size distribution of 250 μm or less was used without finely classifying the particle size. Other than that, SiC whiskers were manufactured under the same conditions as in the example.

The average diameter and standard deviation of the obtained SiC whiskers are also shown in Table 1.

Table 1 From Table 1, according to the present invention, it was possible to produce SiC whiskers with three-grade grade properties having a distribution of average diameters with little variation depending on the use of classified and adjusted silicon source materials. It is found that in the comparative example in which the raw material particle size is not classified and adjusted, only one type of SiC whisker with a wide dispersion distribution can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, high-quality SiC whiskers having desired properties with a particularly uniform average diameter can be economically mass-produced with good operability by applying silicon source raw material powder classified to a certain particle size range. can do.

Therefore, it is possible to set up a production system that supplies a variety of composite reinforcing materials that meet the required shapes.

Applicant: Tokai Carbon Co., Ltd. Agent: Patent Attorney Masaya Takahata July 10, 1990

Claims (1)

[Claims] 1. In a method of generating SiC whiskers by heating a powder mixture of a silicon source raw material and a carbonaceous material to a reaction temperature range in a non-oxidizing atmosphere, the silicon source raw material powder is finely divided into particles of 250 μm or less. 1. A method for producing SiC whiskers, which comprises classifying and adjusting the particle size within a certain range. 2. The method for producing SiC whiskers according to claim 1, wherein the reaction temperature range is set in the range of 1600 to 1900°C.