METHOD FOR PRODUCING alpha-SILICON CARBIDE PARTICLE

The present invention relates to a method for producing α-type silicon carbide particles and α-type silicon carbide particle fibers, which are excellent in oxidation resistance and heat resistance even at a high temperature of 1,000 ° C. or higher.

Silicon carbide is a material that is not easily oxidized even at a high temperature of 1,000 ° C or higher, has excellent heat resistance, has strong mechanical strength, and is chemically stable. As the ceramic sintered body, it is used as a crucible for high temperature, a member for firing, a member for heat exchanger, a mechanical seal for high temperature, a jig for semiconductor heat treatment process, and more recently, as a filter material for automobile exhaust gas. ..

In addition, hexagonal α-type silicon carbide has high thermal conductivity even at room temperature, and is used as a heat dissipation substrate, and recently, as an LED substrate and a power transistor substrate, and has high abrasion resistance. It is also used as an abrasive. On the other hand, nanoparticle silicon carbide has recently been mixed with a metal material such as aluminum or magnesium to be used as a metal composite material called MMC in a lightweight heat-dissipating substrate or the like. In addition, nanoparticle silicon carbide has been developed as an abrasive for difficult-to-cut materials such as diamond and sapphire by dispersing it in an aqueous solution or the like, and as an abrasive capable of polishing the surface more finely.

There are the following reports as a method for producing the silicon carbide nanoparticles. Patent Document 1 describes a fibrous structure made of cubic silicon carbide by putting silicon monoxide and amorphous activated carbon into a crucible and heating them to a temperature at which silicon monoxide evaporates in an inert gas atmosphere. Therefore, silicon carbide nanorods having a length of 10 to 100 μm and a diameter of 20 nm to 100 nm have been obtained. This production method is different from the production method of α-type silicon carbide, which is a hexagonal system, because the reactant is cubic silicon carbide.

Patent Document 2 describes the production of cubic silicon carbide nanowires, which comprises heating chlorosilane to a temperature range of 900 ° C. or higher and 1300 ° C. or lower in a carrier gas stream under a reduced pressure atmosphere in the range of 1 to 100 Torr. Disclose the method. This production method is also not a method for producing α-type silicon carbide, which is a hexagonal system, because the reactant is cubic silicon carbide.

Non-Patent Document 1 examines the gas phase reaction between SiO gas and CO gas in an argon atmosphere for the synthesis of silicon carbide nanofibers, and graphite powder (0.2 wt% of impurity level as a catalyst) in a graphite crucible. (Iron-containing) was put in, and a carbide powder was placed on it, and the crucible lid was used as a graphite substrate. When the reactor was degassed at 873 K for 1 hour and then held at 1,523 K for 1 to 24 hours in an argon atmosphere at 1 atm, the silicon carbide nanofibers formed on the substrate had a diameter of 10 to 100 nm and a length of 10 to 100 nm. Approximately 10 μm, this nanofiber is β-SiC with a small amount of α-SiC phase in the core and a nearly amorphous SiO in the shell.₂It consists of. Also in this production method, only a part of α-type silicon carbide having a hexagonal reaction product can be obtained.

<patcit num="1"><text>Japanese Unexamined Patent Publication No. 2004-161507</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 2004-292222</text></patcit><nplcit num="1"><text>Trans. Indian Ceram. Soc., Vol.63, No.4, Page.195-198 (2004.10)</text></nplcit>

<p> As described above, a method for producing cubic silicon carbide particles is known, but a method for producing α-type silicon carbide nanoparticles belonging to the hexagonal system with high purity is not known. An object to be solved by the present invention is to provide a method capable of producing α-type silicon carbide particles.</p>

<p> The above task was achieved by the following means (1). Listed with preferred embodiments (2)-(5). (1) A step of placing carbon fibers and / or carbon tubes and silicon monoxide, which satisfy the following conditions (a) and / or (b), in a reaction vessel apart from each other without mixing with each other. In addition, the carbon fiber and / or the carbon tube is heated to a temperature of 1,400 ° C. or higher in a heating furnace under a vacuum of 0.1 atm or lower, and the silicon monoxide is heated to 1,100 ° C. or higher. A method for producing α-type silicon carbide particles, which comprises a step of heating the carbon fiber and / or the carbon tube to a temperature lower than the heating temperature of the carbon fiber to generate α-type silicon carbide particles. , (a) The half width of the diffraction peak on the graphite (002) plane as measured by the powder X-ray diffraction method is 1 ° or less. (b) Weight loss of 10% or less when heated in the atmosphere at 600 ° C (2) Production of α-type silicon carbide particles according to (1), wherein the average outer diameter of the carbon fiber and / or carbon tube is 30 nm or more, and the ratio of the length to the diameter (aspect ratio) is 10 or more. Method, (3) Production of α-type silicon carbide particles according to (1) or (2), wherein the step of producing α-type silicon carbide particles is a step of producing α-type silicon carbide particles having whisker-shaped fibers. Method, (4) The method for producing α-type silicon carbide particles according to any one of (1) to (3), which uses silicon monoxide having an average particle size of 1 to 10 μm or more. (5) Following the step of producing α-type silicon carbide particles, the step of heating the α-type silicon carbide particles in the atmosphere of 600 ° C. or higher and 800 ° C. or lower to oxidize and remove the remaining carbon is included. The method for producing α-type silicon carbide particles according to any one of (1) to (4).</p>

<p> According to the present invention, α-type silicon carbide particles having excellent oxidizing properties and heat resistance could be produced with high purity (purity of 95% or more).</p>

The manufacturing method of the present invention described above will be described below. In the method for producing α-type silicon carbide particles of the present invention, carbon fibers and / or carbon tubes satisfying the following conditions (a) and / or (b) and silicon monoxide are not mixed with each other. The step of separating and placing the reaction vessel in the reaction vessel, and heating the carbon fiber and / or the carbon tube to a temperature of 1,400 ° C. or higher in a heating furnace under a vacuum of 0.1 atm or less. It is characterized by comprising a step of heating the silicon monoxide to a temperature of 1,100 ° C. or higher and lower than the heating temperature of the carbon fiber and / or the carbon tube to generate α-type silicon carbide particles. To do. Here, (a) is that the half width of the diffraction peak of the graphite (002) plane measured by the powder X-ray diffraction method is 1 ° or less, and (b) is the atmosphere at 600 ° C. The weight loss is 10% or less when heated in.

The above reaction is written in the chemical formula as follows. 2C + SiO SiC + CO

The raw material carbon fiber and / or carbon tube and silicon monoxide will be described below. As the raw material for carbon, only one of carbon fiber (carbon fiber) and carbon tube may be used, and both may be used in combination, but it is preferable to use only one of them. Hereinafter, a case where only one of them is used will be described. The carbon fibers or carbon tubes are both made of graphite, and preferably have an average outer diameter of 30 nm or more and an aspect ratio of 10 or more, which is the ratio of the length to the diameter. The carbon fiber is not hollow, and the carbon tube is hollow, and both ends may or may not be closed. Carbon nanotubes having an average outer diameter of 40 nm or more and 100 nm or less can be preferably used as a raw material for carbon.

Carbon fibers can be produced by various methods. It is obtained by carbonizing polyacrylonitrile fibers, phenol resin fibers, etc. by heating them to a high temperature in a nitrogen stream. In the present invention, carbon fibers obtained by carbonizing phenol resin fibers can be preferably used. The carbon fiber used as a raw material preferably has an average outer diameter of 50 nm or more and an average outer diameter of 50 to 1,000 nm (meaning 50 nm or more and 1,000 nm or less, and the same applies hereinafter). It is more preferably ~ 1,000 nm, and particularly preferably 100 to 500 nm. When the ratio of the length to the diameter is defined as the aspect ratio, the aspect ratio is 10 or more, preferably 10 to 1,000, and more preferably 50 to 500.

The carbon fiber or carbon nanotube used in the present invention needs to be oxidation resistant, and is required to satisfy the following conditions (a) and / or (b). In (a), the half width of the diffraction peak on the graphite (002) plane measured by the powder X-ray diffraction method is 1 ° or less. In (b), the weight loss is 10% or less when heated in the air at 600 ° C.

The condition (a) is that the half-value width of the X-ray diffraction peak on the graphite (002) plane (also simply referred to as diffraction peak in the present invention) measured by the powder X-ray diffraction method is 1 ° or less. To have. The carbon fiber or carbon nanotube having such a diffraction peak by the powder X-ray diffraction method has a graphite structure, and shows a diffraction peak on the (002) plane in the vicinity of 2θ = 24 to 25 °. When the diffraction peak of the (002) plane is sharp and its half width is 1 ° or less, it means that the crystal face of graphite is growing neatly, and the oxidation resistance at high temperature becomes strong. ..

Condition (b) is to heat the carbon fiber or carbon nanotube to be used at a constant speed up to 900 ° C in the atmosphere by a differential thermal balance (TG-DTA) manufactured by Rigaku Co., Ltd. (heating rate 20 ° C / min). ), The weight loss curve with respect to the heating time is obtained, and the weight loss at 600 ° C is 10% or less (0 to 10%). The weight loss with heating is an index of oxidation resistance, and is preferably 5% or less (0 to 5%).

Therefore, the carbon fiber or carbon tube needs to have oxidation resistance at a high temperature for producing silicon carbide by satisfying at least one of the condition (a) and the condition (b).

Further, the amount of metal element impurities (for example, iron, nickel, cobalt, etc.) contained in the carbon fiber or the carbon (nano) tube is preferably 1% or less.

The silicon monoxide powder to be reacted with the carbon fiber or the carbon (nano) tube is not particularly specified in the average particle size, but is preferably 10 μm or less, and more preferably 1 to 10 μm. The metal element impurities of silicon monoxide (for example, iron, nickel, cobalt, etc.) are also preferably 1% or less.

When reacting carbon fiber or carbon nanotubes with silicon monoxide powder, for example, in a so-called tubular furnace in which an alumina tube of 80φ x 800 mm is placed in a tubular heater of 100φ x 500 mm (100φ indicates an inner diameter of 100 mm). .. The tubular heater is preferably one that can be controlled in three zones, but one zone control is also acceptable. On the other hand, the alumina tube preferably has a purity of 99% or more and is dense. The carbon material is placed in a tubular furnace alumina tube, and the position is set at a position where the carbon material is 1,400 ° C or higher. Further, the silicon monoxide material is placed in a tubular furnace alumina tube, and the position is set so that the silicon monoxide material has a temperature of 1,100 ° C. or higher and is lower than the heating temperature of the carbon material. The two materials are set apart without mixing, but at a position where the temperature of the carbon material is higher than the temperature of the silicon monoxide material. For example, if the carbon material is 1,400 ° C, set the position where the silicon monoxide material is 1,200 ° C. Alternatively, the structure should be such that the temperature distribution of the tube furnace can be set, or the set temperature of the heater should be determined. Next, the tube furnace is evacuated to 0.1 atm or less. It is preferable to increase the degree of vacuum in order to reduce and densify the defects of the silicon carbide obtained by the reaction.

Silicon monoxide begins to sublimate at about 1,000 ° C and finishes sublimating at about 1,200 ° C, depending on the degree of vacuum. The higher the degree of vacuum, the lower the sublimation temperature, but if the temperature is too low, the activity of the carbon fibers or carbon nanotubes decreases, so that the sublimated silicon monoxide gas does not react with the carbon fibers or carbon nanotubes. Therefore, the range of the degree of vacuum is preferably 1 to 1,000 Pa.

When the heater is heated, as described above, silicon monoxide begins to sublimate at about 1,000 ° C and finishes sublimating at about 1,200 ° C, depending on the degree of vacuum. The sublimated silicon monoxide gas diffuses in the tube furnace and reacts with carbon fibers or carbon nanotubes heated to 1,400 ° C or higher to form α-type silicon carbide. At temperatures above 1,400 ° C, α-type silicon carbide is preferentially produced over β-type silicon carbide, but below 1,400 ° C, β-type silicon carbide is preferentially produced. It is preferable to heat the carbon fibers or carbon nanotubes to 1,400 ° C or higher and 1,800 ° C or lower. Silicon monoxide is preferably heated to about 1,000 ° C. or higher and about 1,200 ° C. or lower, although it depends on the degree of vacuum. Further, the position where the carbon fiber or the carbon nanotube is set is preferably set on the vacuum exhaust side rather than the silicon monoxide. This is because the sublimated silicon monoxide gas easily diffuses to the vacuum exhaust side and easily reacts with carbon fibers or carbon nanotubes near the exhaust side. In addition, the annealing effect reduces densification and crystal defects.

(Example 1) Inner diameter 100φ Length 500mm In a tubular cantal heater that can control 3 zones, an outer diameter 80φ x inner diameter 70φ length 700mm high-purity alumina tube (purity 99.9%, trade name: SSA-S, manufactured by Kyocera Corporation) is placed in the heater. It was set so that the central axis and the central axis of the tube were almost the same. The cantal heater was heated to 1,500 ° C. without putting anything in the alumina tube in advance, and the temperature distribution in the length direction inside the tube was measured. It was confirmed in advance that the center position of the length of the alumina tube was heated to approximately 1,400 ° C, and the position 100 mm away from the center was heated to approximately 1,200 ° C. Next, 10 g of silicon monoxide having an average particle diameter of 5 μm was set to a length of 20 mm in a semi-arc-shaped 60φ high-purity alumina container having a length of 150 mm. In another high-purity alumina container, an alumina partition plate is provided, and 5 g of carbon nanotubes with an average outer diameter of 80 nm (inner diameter of 20 nm) and an average length of 20 μm (aspect ratio of 250) are placed at a position 100 mm away from the setting position of silicon monoxide. Was set.

When the crystallinity of this carbon nanotube was evaluated by an X-ray diffractometer manufactured by Rigaku Co., Ltd., it showed a (002) plane diffraction peak of graphite at 2θ = 24 to 25 °, and its half width was 0.5 °. Next, the alumina container was set in the tubular furnace alumina tube, and the center of the carbon nanotube was set so as to be in the center of the alumina tube. The tube furnace was evacuated to 50 Pa and then heated to 1,500 ° C. As a result, the heating temperature of the carbon nanotubes became about 1,400 ° C, and the heating temperature of silicon monoxide finally became about 1,200 ° C.

When heated to around 1,200 ° C on the way, the degree of vacuum decreased to about 500 Pa because the silicon monoxide powder sublimated and gasified. After that, when the carbon nanotubes were heated to 1,500 ° C, the degree of vacuum decreased to about 100 Pa. When the temperature was kept constant for about 5 hours in a stable state and then lowered to room temperature, silicon monoxide was almost sublimated, and 0.5 g of white residue remained. In addition, the carbon nanotubes remained black and were partially glossy. 5 g of the reacted black sample was collected.

When the sample was observed with a scanning electron microscope, approximately hexagonal plate-shaped silicon carbide particles having an average particle size of about 3 μm were formed, and whisker-shaped fibers were grown on the outer peripheral portion. When this was measured with an X-ray diffractometer, it became 95% αSiC, and 5% of the graphite peak remained. The outer diameter of the fiber was about 50 nm, and the length was about 5 μm. Figure 1 shows an electrophotographic micrograph of the generated silicon carbide particles. When the impurities of the silicon carbide particles were analyzed by glow discharge mass spectrometry, metal impurities such as iron were contained in an amount of 10 ppm or less, and aluminum was contained in an amount of 50 ppm.

(Example 2) The tubular cantal heater and alumina tube used in Example 1 were used to change the heating conditions. Next, 10 g of silicon monoxide having an average particle diameter of 5 μm was set to a length of 20 mm in a semi-arc-shaped 60φ high-purity alumina container having a length of 150 mm. In another high-purity alumina container, an alumina partition plate is provided, and carbon nanofibers with an average outer diameter of 40 nm (inner diameter 20 nm) and an average length of 4 μm (aspect ratio 100) are placed at a position 100 mm away from the setting position of silicon monoxide. I set 5g.

This carbon nanofiber was measured by the thermogravimetric analyzer manufactured by Rigaku Co., Ltd. by raising the temperature to 900 ° C in the atmosphere at a constant velocity (heating rate 20 ° C / min) and measuring the amount of weight loss. The weight loss at 600 ° C was 5%.

Next, the high-purity alumina container was set in the tubular furnace alumina tube, and the center of the carbon fiber was set so as to be in the center of the alumina tube. The tube furnace was evacuated to 50 Pa and then heated to 1,600 ° C. As a result, the heating temperature of carbon fiber became approximately 1,450 ° C, and the heating temperature of silicon monoxide became approximately 1,250 ° C. When heated to around 1,200 ° C on the way, the degree of vacuum dropped to about 500 Pa because the silicon monoxide powder sublimated and gasified. After that, when heated to 1,600 ° C, the degree of vacuum decreased to 100 Pa. When the temperature was lowered to room temperature after holding for about 5 hours in a stable place, silicon monoxide was almost sublimated, and 1.0 g of white residue remained. In addition, the carbon nanofibers remained black and were partially glossy. 5 g of the reacted black sample was collected.

When the sample was observed with a scanning electron microscope, approximately hexagonal plate-shaped silicon carbide particles having an average particle size of about 4 μm were formed, and whisker-shaped fibers were grown on the outer peripheral portion. The outer diameter of the fiber was about 40 nm, and the length was about 5 μm. When this was measured with an X-ray diffractometer, it became 95% αSiC, and 5% of the graphite peak remained. When the impurities of the silicon carbide nanoparticles were analyzed by glow discharge mass spectrometry, the impurities of metals such as iron were 20 ppm and that of aluminum was 80 ppm.

(Comparative example 1) The tubular cantal heater and alumina tube used in Example 1 were used and operated under the same heating conditions as in Example 1.

In a semi-arc-shaped 60φ high-purity alumina container with a length of 150 mm, 10 g of silicon monoxide having an average particle diameter of 5 μm was set to a length of 20 mm. In another high-purity alumina container, an alumina partition plate is provided, and a carbon tube with an average outer diameter of 40 nm (inner diameter 20 nm) and an average length of 4 μm (aspect ratio 100) is placed at a position 100 mm away from the setting position of silicon monoxide. I set it.

When the crystallinity of this carbon nanotube was evaluated by an X-ray diffractometer manufactured by Rigaku, it showed a (002) plane diffraction peak of graphite at 2θ = 24 to 25 °, and its half width was 2 °.

Next, the alumina container was set in the tubular furnace alumina tube, and the center of the carbon nanotube was set so as to be in the center of the alumina tube.

When evacuation and heating were performed in the same manner as in Example 1, the change in the degree of vacuum was the same as in Example 1. As in Example 1, when the mixture was kept stable for about 5 hours and the temperature was lowered to room temperature, silicon monoxide was almost sublimated, and 0.5 g of white residue remained. In addition, the carbon nanotubes remained black and were partially glossy. 5 g of the reacted black sample was collected.

When the sample was observed with a scanning electron microscope, almost polygonal silicon carbide particles having an average particle size of about 5 μm were generated. When this was measured with an X-ray diffractometer, it became 85% βSiC, and the graphite peak remained at 15%.

(Comparative example 2) The tubular cantal heater and alumina tube used in Example 2 were used and operated under the same heating conditions as in Example 2.

Next, in a semi-arc-shaped 60φ high-purity alumina container with a length of 150 mm, 10 g of silicon monoxide having an average particle diameter of 5 μm is set to a length of 20 mm. An alumina partition plate was provided in the same alumina container, and 5 g of carbon fiber having an average outer diameter of 40 nm (inner diameter of 20 nm) and an average length of 4 μm (aspect ratio of 100) was set at a position 100 mm away from the setting position of silicon monoxide.

This carbon fiber was measured by a differential thermal balance manufactured by Rigaku Co., Ltd. by raising the temperature to 900 ° C in the atmosphere at a constant speed (heating rate 20 ° C / min) and measuring the amount of weight loss. The weight loss at C was 20%.

When evacuation and heating were performed in the same manner as in Example 2, the change in the degree of vacuum was the same as in Example 2. When it was kept stable for about 5 hours and the temperature was lowered to room temperature, silicon monoxide was almost sublimated, and 1.0 g of white residue remained. In addition, the carbon nanofibers remained black and were partially glossy. 5 g of the reacted black sample was collected.

When the sample was observed with a scanning electron microscope, it reacted with approximately hexagonal plate-shaped silicon carbide having an average particle size of about 4 μm, and whisker-shaped fibers were grown on the outer periphery. When this was measured with an X-ray diffractometer, it became 90% βSiC, and 10% of the graphite peak remained.

(Comparative example 3) The tubular cantal heater and alumina tube used in Example 1 were used and operated under the same heating conditions as in Example 1. Next, in a semi-arc-shaped 60φ high-purity alumina container with a length of 150 mm, 10 g of silicon monoxide having an average particle diameter of 5 μm is set to a length of 20 mm. An alumina partition plate was provided in the same alumina container, and 5 g of carbon nanotubes having an average outer diameter of 80 nm (inner diameter of 20 nm) and an average length of 20 μm (aspect ratio of 250) were set at a position 100 mm away from the setting position of silicon monoxide.

When the crystallinity of this carbon tube was evaluated by a Rigaku X-ray diffractometer, the half width of the diffraction peak on the graphite (002) plane at 2θ = 24 to 25 ° was 0.5. Next, the alumina container is set in the tubular furnace alumina tube, and the center of the silicon monoxide is set so as to be in the center of the alumina tube. Evacuate the tube furnace to 50 Pa and then raise the temperature to 1,500 ° C. As a result, the temperature of the carbon nanotubes becomes approximately 1,200 ° C when heated, and the temperature of silicon monoxide becomes approximately 1,400 ° C. The degree of vacuum drops to about 500 Pa up to around 1,200 ° C, because the silicon monoxide powder sublimates and gasifies. After that, the degree of vacuum dropped to 1,500 ° C, and when it was stable, it was held for about 5 hours and the temperature was lowered to room temperature. Silicon monoxide was almost sublimated, leaving 2.0 g of white residue. It was. In addition, the carbon nanotubes remained black and were partially glossy. 5 g of the reacted black sample was collected.

When the sample was observed with a scanning electron microscope, almost polygonal silicon carbide particles having an average particle diameter of about 3 μm were generated as shown in FIG. When this was measured with an X-ray diffractometer, it became 95% βSiC, and 5% of the graphite peak remained.

<figref num="1">It is an electron micrograph which shows an example of the crystal structure of the generated silicon carbide particle.</figref>