JPS6121200B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for dismantling and dispersing a SiC or Si ₃ N ₄ produced whisker cake. Whiskers, which are composed of pure frame single crystals of SiC and Si ₃ N ₄ , have extremely high strength and elastic modulus, as well as heat resistance and chemical stability unique to the material, so they have long been used for composite reinforcement of metals or plastics. Although it is attracting attention as a material, it is not yet on track for practical use. One of the main technical reasons for this is that it is extremely difficult to break up the whiskers that are produced into a state that allows them to be homogeneously dispersed in the matrix material. That is, SiC whiskers or Si ₃ N ₄ whiskers are produced by mixing SiO ₂ -containing powder with a carbonaceous material such as carbon black and an appropriate generation space forming material, filling a reaction vessel, and heating the mixture for 1400 min in an inert atmosphere or nitrogen stream. It is produced by a heating reaction in the temperature range of ~2000℃, and the resulting product has a nodular cake-like structure in which dense short fibrous whiskers are intertwined in no direction. The cake cannot be broken up by simple stirring or other means. Furthermore, if rapid stirring or long-term stirring is applied, although some degree of disassembly is possible, damage such as breakage and broken clumps occurs in the whiskers, making it difficult to obtain a high-performance composite material. As a result of repeated studies on technology to dismantle and disperse the cake without damaging the whiskers, the inventors found that once the generated whisker cake is compressed and then stirred, it can be done within an extremely short time without causing any damage to the whiskers. We confirmed the surprising fact that uniform dispersion can be obtained. The present invention has been made based on the above-mentioned knowledge, and has a constitutional feature that, after compressing the generated whisker cake of SiC or Si ₃ N ₄ , it is stirred as it is or in water. The resulting whisker cake can be compressed using a mold pressurization method in which the nodule cake is filled into a mold and pressurized.
Alternatively, it may be carried out by a method such as a roll pressure method in which the material is passed between rolls having a narrow gap. If the produced whisker cake is in the form of a large lump, either put it in a stirring device and stir it for a few seconds to make it smaller, or add water to the stirring device and stir it to make it smaller, then dehydrate it and use it for the compression process. This is convenient for smooth processing. The degree of compression varies depending on the texture of the resulting whisker cake, particularly its bulk density, and whether or not the above-mentioned particle size reduction treatment has been carried out, but it is generally desirable to carry out the compression until the volume shrinks by 1/5 to 1/50. If the volumetric shrinkage is less than 1/5, sufficient decomposition and dispersion will not be achieved, whereas high compression exceeding 1/50 is unnecessary, and depending on the cake quality, high compression of 500 kg/cm ² or more may be required. Since pressure is required, this is not preferred in practice. The flattened whisker pieces after compression are stirred as they are or in water. As the stirring device, appropriate equipment such as an impeller type stirrer such as a propeller type or a turbine type, a stirring mixer such as a kneader, or a floating stirrer using air may be used. In addition, in the case of underwater stirring, water whose weight is 50 to 100 times the weight of the whisker pieces to be treated is used. When stirring is started, the whisker pieces disintegrate almost instantaneously and are completely dispersed within a stirring time of about a few seconds. The reason why such remarkable rapid disintegration and dispersion can be achieved has not yet been fully elucidated, but the compression process in the first stage separates the physical adhesion between the whiskers that make up the resulting cake, releasing the entanglement. It is presumed that the conditions enable smooth disassembly and dispersion with short agitation. Therefore, the whiskers are not damaged during the stirring process. When stirring in water, whiskers uniformly dispersed in water are separated and then dried. The whiskers thus disintegrated and dispersed are in the form of a homogeneous powder that does not contain any particulate matter, and are converted into properties that ensure rapid and smooth mixing and dispersion in various matrix materials. As described above, according to the present invention, SiC or
The generated whisker cake of Si ₃ N ₄ can be dismantled and dispersed without damaging the whiskers through an extremely simple processing process, thus facilitating smooth homogeneous dispersion into matrix materials, which has traditionally been a bottleneck in compounding. Because of this, it makes a significant contribution to industry. Example 1 Fine silica gel powder (200 mesh or less) containing 7.0% by weight of CoCl ₂ based on Si content was used as a silicon source material, and this was used as a carbon material with a DBP oil absorption of 130 ml/100 g,
IISAF- which has the characteristic of iodine adsorption amount of 104mg/g
110 parts by weight of Hs class furnace carbon black (manufactured by Tokai Carbon Co., Ltd., "SEAST 5H") and 90 parts by weight of NaCl as a generation space forming material were uniformly mixed. The mixed raw materials were filled into a reaction vessel made of high-purity graphite, a graphite lid was attached to the top of the reaction vessel, the vessel was transferred to an Acheson type electric furnace, and the surrounding area was covered with coke grain packing. Electricity was applied to the furnace to raise the temperature, and heat treatment was performed at 1600° C. for 4 hours while maintaining the inside of the furnace in a non-oxidizing atmosphere. After the heat treatment, the contents were taken out from the reaction vessel without being disassembled and heat treated in the atmosphere at a temperature of 700°C to burn off the remaining carbonaceous components. The resulting product is an algae-like nodular cake in which pure SiC whiskers are intertwined nondirectionally, and the constituent SiC
The whisker has a diameter of 0.2 to 0.5 μm and a length of 100 μm.
~200μm β type single crystal, cake properties are true specific gravity
3.17g/cm ³ , bulk density 0.04g/cm ³ , average porosity 98.7%
It was hot. The nodule-shaped produced SiC whiskers were placed in a mold and pressurized to form flat compressed whisker pieces having different volume shrinkage ratios. Next, each compressed whisker piece was placed in a propeller type stirrer and stirred for about 1 second at a rotational speed of 11,000 rpm (dry stirring). Separately, the whisker pieces were put into a propeller-type stirrer together with 50 times their weight of water and stirred (rotation speed 8000 rpm.
The mixture was stirred for about 5 seconds), water was removed separately, and then dried (wet stirring). The results of observing the properties of the SiC whiskers disassembled and dispersed in this way are shown in the table, comparing them with the degree of compression (volume compression ratio) of the generated whisker cake.

【table】

[Table] The SiC whisker powder after treatment had good dispersibility and did not become entangled again due to packaging or other general handling. When the Si ₃ N ₄ whisker cake produced by carrying out the SiC whisker production reaction in a nitrogen stream was subjected to the same disassembly and dispersion treatment, the same results as above were obtained. Comparative Example The SiC whisker cake produced in Example 1 was directly subjected to dry and wet stirring treatments without being compressed. The stirrer, rotation speed, amount of water added during wet stirring, etc. were all the same as in Example 1. As a result, in dry stirring, the whisker cake nodules turned into weed-like nodules with a diameter of about 1 to 3 mm after 1 minute of agitation, but these nodules were made up of entangled whiskers. The stirring time was further extended to 5 to 10 minutes, but the small lumps were hardly touched.
Cutting damage was observed on the whiskers. In addition, in wet stirring, when the stirring time was extended to about 5 minutes, disassembly progressed considerably, but nearly half of the particles remained suspended in the water as small lumps. Although a tendency for the number of floating small lumps to decrease was observed after 20 minutes of stirring time, when they were dehydrated and dried and observed, it was found that the whiskers had a length of 20 μm or less and were damaged by cutting. Example 2 A large SiC whisker cake produced under the same conditions as in Example 1 was directly placed in a propeller type stirrer and stirred for about 1 second at a rotational speed of 11,000 rpm. By this stirring operation, the whisker cake was granulated into small lumps of about 2 to 5 mm. The obtained small lump was continuously passed between narrow-gap rolls twice to be compressed to a volume shrinkage ratio of 1/15 to 1/20. Next, the compressed pieces were placed in a propeller-type stirrer and stirred for 1 second at a rotational speed of 11,000 rpm, whereupon they were instantly disintegrated and dispersed and converted into a homogeneous powder. The powder has a diameter of 0.2 to 0.5 μm and a length of 100 μm, the same as when it was generated.
It was composed of individual SiC whiskers with a diameter of ~200 μm, and no damage was observed during the processing process. Example 3 A large cake with a structure in which Si ₃ N ₄ whiskers with a diameter of 0.5 to 2 μm and a length of 20 to 40 μm are densely intertwined is placed in a propeller-type stirrer, and water with a weight equivalent to 90 times the weight is poured into the cake. was added and then stirred in water for about 5 seconds. After stirring, the whiskers were suspended in the water as small particles of about 1 to 3 mm. After putting the floating particles in a cloth bag and squeezing it lightly to dehydrate it, it is passed through narrow gap rolls twice to reduce the volume shrinkage ratio to 1/15 to 1/20.
compressed into. Then, the compressed pieces were placed in a propeller-type stirrer with 50 times the weight of water and wet-stirred for 5 seconds at a rotational speed of 800 rpm. The compressed pieces were disintegrated immediately after stirring, and were completely homogeneously dispersed at the end of stirring. After drying the water separately, the powder is made into individual particles with good dispersibility without cutting breakage etc.
It was Si ₃ N ₄ whiskers.

Claims (1)

[Claims] 1. A method for dismantling and dispersing a whisker cake, which comprises compressing a whisker cake produced from SiC or Si ₃ N ₄ and then stirring it as it is or in water. 2. The method for dismantling and dispersing a whisker cake according to claim 1, in which the large lump-shaped whisker cake produced is stirred as it is, or is stirred and dehydrated in water to be made into small particles and then compressed. 3. The method for dismantling and dispersing a whisker cake according to claims 1 and 2, wherein the compression is performed until the volume shrinks by 1/5 to 1/50.