JPH05221799A - Modification treatment of sic whisker - Google Patents

Abstract

PURPOSE:To provide a modification treatment method for efficiently increasing the diameter of SiC whiskers by sublimation recrystallization while inhibiting the formation of sintered grains as a by-product. CONSTITUTION:A blend of 100 pts.wt. SiC whiskers based on beta-crystals and having 0.3-1.5mum diameter and 10-100mum length with 1-50 pts.wt. short carbon fibers is well dispersed and mixed and this mixture is heated to 1,700-2,200 deg.C in an Ar atmosphere. The SiC whiskers preferably have <=0.14 deg. half-width of (111) diffraction line at <=20% alpha proportion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a Si whisker which is heat-treated to convert it into a thick diameter having a diameter of 2 μm or more.
The present invention relates to a method for modifying C whiskers.

[0002]

2. Description of the Related Art Whiskers composed of SiC needle-like single crystals exhibit excellent properties such as specific strength, specific elastic modulus, heat resistance, and chemical stability. , Is used as a composite reinforcing material for plastics materials. Among these, composite strengthening of ceramic materials, which are particularly poor in fracture toughness, has recently been regarded as an important development issue, and various research proposals have been made.

The compounding of whiskers with ceramics stops or suppresses the growth of cracks generated in the ceramic body by the whiskers dispersed inside the structure, and bends the direction of progress of the cracks (crack deflection) to relieve stress concentration. Alternatively, it is carried out in order to improve the fracture toughness through a mechanism of absorbing the energy at the crack tip by the action of pulling out the whiskers. It has been clarified that it is effective to increase the toughness of the ceramic material by this mechanism, especially by compounding with thick whiskers having a large diameter.

Further, since whiskers have a fine needle-like fiber form, when they are inhaled into the respiratory system of the human body, they are likely to remain in the lungs, causing a risk of respiratory disorders. There is. It has been reported that this hazard risk has a strong relationship with the diameter of the whiskers, and that the risk is particularly great when the diameter is less than 2 μm.

In order to deal with such a situation, the present applicant has developed and has already proposed a technique for manufacturing a thick type SiC whisker having a diameter of more than 2 μm (Japanese Patent Laid-Open No. 3-3719).
No. 8, JP-A-3-141200).

[0006]

The above-mentioned prior art utilizes a reforming mechanism in which SiC whiskers undergo sublimation recrystallization and become thicker by being subjected to heat treatment under a certain condition, which is relatively simple. 2μ diameter with efficient heat treatment
A thick SiC whisker having a diameter of m or more can be obtained. However, during the heating process, the SiC whiskers that are in contact with each other sinter at the contact site, and
The phenomenon of intervening as iC particles is likely to occur. If such sintered particles are present in the composite structure with ceramics, they act as fracture initiation points and reduce strength and fracture toughness. Therefore, it is necessary to separate and remove them by a complicated secondary treatment.

The present invention is a technique for improving the prior art (Japanese Patent Laid-Open No. 3-37198) in order to solve the above-mentioned problems and for suppressing the sintering particle formation phenomenon of SiC whiskers at the stage of heat treatment. It was the clarification of that that led to the development. Therefore, an object of the present invention is to provide a modification treatment method for efficiently increasing the diameter of SiC whiskers by sublimation recrystallization while suppressing by-production of sintered particles.

[0008]

A method for modifying a SiC whisker according to the present invention to achieve the above object is as follows.
100 parts by weight of β crystal type SiC whiskers having an aspect property of 0.3 to 1.5 μm in diameter and 10 to 100 μm in length were mixed with carbon fibers at a ratio of 1 to 50 parts by weight and sufficiently dispersed and mixed. 1700-2200 in a non-oxidizing atmosphere
The constitutional feature is to perform heat treatment at a temperature of ° C.

The SiC whiskers used as the processing raw material of the present invention may be produced by any method without being affected by the production history. Therefore, for example, a method of reacting a decomposable silicon compound such as SiCl ₄ , SiHCl ₃ , (CH) ₃ Si with a carbonaceous material component such as CH ₄ , CCl ₄ or C ₃ H ₈ in a gas phase reaction, a solid state containing SiO _2. The SiC whiskers produced by a method of mixing the silicon source raw material and the carbon powder, or a method of heating and reacting a substance containing the above components in a complex manner such as rice husk charcoal are used.

However, SiC whiskers having an aspect property of 0.3 to 1.5 μm in diameter and 10 to 100 μm in length are selected and used as raw materials. The reason for this is that the SiC whiskers having the aspect characteristics in the above range most significantly exhibit the diameter effect by sublimation recrystallization.
In addition, the crystal system of the SiC whiskers needs to be selected mainly from the β crystal type, and if this requirement is not satisfied, the desired diameter thickening modification of 2 μm or more cannot be performed. In addition,
Being mainly β-crystal type means that the crystal system of the SiC whiskers is all β-type or β-type is dominant even if α / β mixed type is used, but especially high β-ratio with low stacking fault density. The smaller the particle content, the larger the diameter. The most suitable crystal property of SiC whisker is that α degree according to the following formula is
In the case of 20 or less, the full width at half maximum of the (111) diffraction line is 0.14 deg or less. α degree = (H ₁ × 2 / H ₂ ) × 100 However, in the above formula, H ₁ is the diffraction intensity at 2θ about 33.5 deg when CuKα is used as the radiation source in the powder X-ray diffraction method, and H ₂ is about 2θ. This is the diffraction intensity appearing at 35.6 deg.

The carbon fibers to be mixed with the SiC whiskers to be treated are not limited in kind and characteristics, and various types such as polyacrylonitrile type, rayon type and pitch type can be used. However, for the purpose of uniformly mixing with the SiC whiskers, the fiber form is preferably a thin fiber diameter and a short fiber shape. Specifically, it is preferable to use a chopped product obtained by cutting a carbon fiber tow having a diameter of 20 μm or less into a length of about 5 mm.

The blending amount of carbon fiber is set within a range of 1 to 50 parts by weight with respect to 100 parts by weight of SiC whiskers. If the blending ratio of carbon fibers is less than 1 part by weight, the effect of suppressing the formation of sintered particles in the SiC whiskers becomes insufficient, while if it exceeds 50 parts by weight, the diameter of the SiC whiskers becomes thicker at a heating temperature of less than 2000 ° C. If the temperature is 2000 ° C or higher, the granulation progresses and the aspect properties cannot be retained.
The SiC whiskers and the carbon fibers are mixed by mechanical means so that both components are sufficiently dispersed and mixed, but mixing means that destroys the whisker properties in the mixing process must be avoided. A preferable dispersive mixing is to wet mix SiC whiskers and short carbon fibers with water or an appropriate organic solvent by a mechanical stirrer, and then subject them to dispersion treatment using ultrasonic vibration or the like.

The mixture of SiC whiskers and carbon fibers is heat-treated in the temperature range of 1700 to 2200 ° C. under a non-oxidizing atmosphere such as N ₂ gas, Ar gas or vacuum. If the heating temperature at this time is less than 1700 ° C, it takes a long time to thicken the SiC whiskers to a diameter of 2 μm or more, and if the heating temperature exceeds 2200 ° C, the SiC whiskers are converted into granular substances and SiC. Vaporization becomes more intense, resulting in a decrease in weight and a decrease in yield.

[0014]

When SiC whiskers are heated in an inert atmosphere, the diameter increases through sublimation and recrystallization, but this phenomenon mainly starts sublimation from stacking faults, and sublimated atoms are the surface of the whiskers with few defects. It is presumed that recrystallization occurs in the part to increase the diameter. At this stage, Si
When C whiskers are in contact with each other, a sintering phenomenon occurs at a contact site through a process of neck formation and growth, and sintered particles by a plurality of whiskers are mixed.

According to the present invention, the object to be treated is a mixture of SiC whiskers and carbon fibers homogeneously dispersed, the intervening carbon fibers reduce the degree of contact between the SiC whiskers, and at the same time the carbon fibers are entangled to form a mixed structure. In addition, an appropriate void that is effective for increasing the diameter of the SiC whiskers is formed. These effects, in combination with the selection of the properties of the target SiC whisker, the blending ratio of the specified carbon fiber and the heat treatment condition, effectively suppress the generation of sintered particles and increase the diameter of the SiC whisker smoothly. It works effectively to reveal.

[0016]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples.

Examples 1 to 3 and Comparative Examples 1 to 2 have a diameter of 1.0 μm, a length of 50 μ and an aspect ratio of 0.5, and a (111) diffraction line having a half-value width of 0.1375 deg. This SiC whisker [Tokai Bourbon Co., Ltd., "Tokai Whisker TWS-400"]
Pitch-based carbon fiber chops having an average diameter of 13 μm and an average length of 3 mm relative to parts by weight [manufactured by Dainippon Ink and Chemicals, Inc.,
"Donacarb S-231"] was compounded in the range of 0.5 to 60 parts by weight.

The mixture was placed in a juicer mixer together with ethanol, stirred and mixed for 2 minutes, and further ultrasonically vibrated to sufficiently disperse the mixture. Then, the mixture obtained by filtration and drying was filled in a graphite crucible and heat-treated at a temperature of 1900 ° C. in an electric furnace maintained in an Ar gas atmosphere. The average diameter of the SiC whiskers after the heat treatment and the content of the SiC sintered particles (diameter 5 mm or more) mixed as a by-product were measured, and the results are shown in Table 1 in comparison with the blending amount of carbon fiber.

[0019]

[Table 1]

From the results shown in Table 1, it was confirmed that according to the examples of the present invention, the diameter of each SiC whisker was increased to 2 μm or more, and the content of the sintered particles was effectively suppressed. Be done. On the other hand, in Comparative Example 1 in which the carbon fiber content is less than 1 part by weight, the diameter effect is high, but the content of the sintered particles is also increased, and the carbon fiber content in the comparative example exceeds 50 parts by weight. It can be seen that in No. 2, sintered particles are not produced as a by-product, but the diameter cannot be expected to increase.

Examples 4 to 5 and Comparative Examples 3 to 4 A mixture of SiC whiskers and carbon fibers having the same composition as in Example 3 was packed in a graphite crucible and placed in an electric furnace maintained in an Ar gas atmosphere, and the mixture was heated at 1600 to 2300 ° C. The heating temperature was changed within the range to perform the heat treatment. SiC heat treated at each temperature stage
Measure and observe the average diameter of whiskers and the situation of shape change,
The results are shown in Table 2 in comparison with the applied heating temperature.

[0022]

[Table 2]

From the results shown in Table 2, the heating temperature was 1700 to 2200 ° C.
In the examples within the range of 1, the diameter effect of normal SiC whiskers can be obtained, but at 1600 ° C., the diameter of the SiC whiskers does not increase, and at 2300 ° C., the granularity of the SiC whiskers progresses and the aspect properties do not remain. ..

[0024]

As described above, according to the method of the present invention, by subjecting the SiC whisker to be treated to a simple heat treatment step in which a predetermined amount of carbon fibers are uniformly mixed, a by-product of sintered particles is produced. The diameter can be modified to a diameter of 2 μm or more while suppressing the above. Therefore, it is extremely useful as a means for obtaining SiC whiskers for a composite reinforcing material for the purpose of improving the toughness of various ceramic materials.

Claims (2)

[Claims] 1. Diameter 0.3 to 1.5 μm, length 10 to 100 μm
100 parts by weight of the β crystal type SiC whiskers having an aspect property of 1 to 50 parts by weight of carbon fibers were mixed and sufficiently dispersed and mixed, and the mixture was heated at 1700 to 2200 ° C. in a non-oxidizing atmosphere. A method for modifying a SiC whisker, which comprises performing a heat treatment at a temperature. 2. A SiC whisker mainly composed of β crystal is formed by α
The method for modifying a SiC whisker according to claim 1, wherein the half width of the (111) diffraction line is 0.14 deg or less at a temperature of 20 or less.