JP2013014493A - Carbon-silicon carbide composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon-silicon carbide composite material having excellent processability and high strength.SOLUTION: The carbon-silicon carbide composite material has a structure in which carbon particles are mutually joined through a silicon carbide layer, wherein bending strength is 50 MPa or more, and a Shore hardness is HSD 50 or less.

Description

  The present invention relates to a carbon-silicon carbide composite material in which carbon and silicon carbide are combined.

  Various studies have been made on carbon-silicon carbide composite materials in which carbon and silicon carbide are combined.

  For example, Patent Document 1 discloses a method for producing a carbon-silicon carbide composite material by mixing finely divided silicon carbide particles and carbon particles and sintering them into a desired shape at high temperature and pressure. .

  Patent Document 2 discloses a method for producing a carbon-silicon carbide composite by melt-impregnating silicon into a carbon fiber compact that has been pressure-molded.

  Since the carbon-silicon carbide composite material contains silicon carbide, there is a problem that the hardness is high and it is difficult to process into a desired shape. If the hardness is lowered in order to improve the workability, there arises a problem that the mechanical strength such as bending strength is lowered.

  Therefore, good workability and high strength are contradictory properties, and it has been difficult to obtain a carbon-silicon carbide composite material having excellent workability and high strength.

  In Patent Document 3, a carbon-silicon carbide composite material is obtained by sintering carbon particles having a silicon carbide coating layer in which silicon carbide is formed on the surface of carbon particles by reacting carbon of the substrate with a silicon component. A method of manufacturing is disclosed. However, no carbon-silicon carbide composite material having excellent workability and high strength is disclosed or suggested.

JP 2004-339048 A JP 2006-290670 A JP 2011-51866 A

  An object of the present invention is to provide a carbon-silicon carbide composite material having excellent processability and high strength.

  The carbon-silicon carbide composite material of the present invention is a carbon-silicon carbide composite material having a structure in which carbon particles are bonded via a silicon carbide layer, and has a bending strength of 50 MPa or more and a Shore hardness of HSD 50 or less. It is characterized by that.

  In the carbon-silicon carbide composite material of the present invention, the proportion of the silicon carbide layer is preferably in the range of 20 to 70% by weight.

The bulk density is preferably 1.90 g / cm ³ or more.

  The thickness of the silicon carbide layer is preferably in the range of 100 nm to 20 μm.

  The carbon-silicon carbide composite material of the present invention is preferably obtained by sintering carbon particles having a silicon carbide coating layer.

  The average particle diameter of the carbon particles having the silicon carbide coating layer is preferably in the range of 50 nm to 500 μm.

  The thickness of the silicon carbide coating layer is preferably in the range of 50 nm to 10 μm.

  According to the present invention, a carbon-silicon carbide composite material having excellent workability and high strength can be obtained.

1 is a schematic cross-sectional view showing a carbon-silicon carbide composite material in an embodiment according to the present invention. FIG. 3 is a schematic cross-sectional view showing carbon particles having a silicon carbide coating layer. Typical sectional drawing which shows the arrangement | positioning state in the crucible for manufacturing the carbon particle which has a silicon carbide coating layer in the Example according to this invention. The figure which shows the X-ray-diffraction pattern of the raw material 1 used for Example 1 according to this invention. The figure which shows the X-ray-diffraction pattern of the raw material 2 used for Example 2 according to this invention. The figure which shows the X-ray-diffraction pattern of the raw material 3 used for Example 3 according to this invention. The figure which shows the X-ray-diffraction pattern of the raw material 4 used for the comparative example 1. FIG. The figure which shows the X-ray-diffraction pattern of the raw material 5 used for the comparative example 2. FIG.

  FIG. 1 is a schematic cross-sectional view showing a carbon-silicon carbide composite material according to an embodiment of the present invention. As shown in FIG. 1, the carbon-silicon carbide composite material 1 of the present invention has a silicon carbide layer 3 around the carbon particles 2, and the carbon particles 2 are bonded together via the silicon carbide layer 3. It has the structure. The silicon carbide layer 3 is provided in the carbon-silicon carbide composite material 1 continuously in a three-dimensional network. The silicon carbide layer 3 provided around the carbon particles 2 is continuously formed with a uniform thickness.

  Furthermore, since the carbon-silicon carbide composite material of the present invention has a structure in which the carbon particles 2 are joined to each other via the silicon carbide layer 3, the carbon-silicon carbide composite material has a high bending strength and a low Shore hardness. Can do. As described above, generally, as the bending strength increases, the Shore hardness also increases. However, in the carbon-silicon carbide composite material of the present invention, high bending strength and low Shore hardness can coexist.

  The carbon-silicon carbide composite material of the present invention has a bending strength of 50 MPa or more and a Shore hardness of HSD 50 or less. By having such bending strength and Shore hardness, a carbon-silicon carbide composite material having high strength and excellent workability can be obtained.

  In the present invention, the bending strength is 50 MPa or more. When the bending strength is less than 50 MPa, the mechanical strength of the carbon-silicon carbide composite becomes insufficient. The bending strength is preferably in the range of 50 to 300 MPa, more preferably in the range of 60 to 250 MPa.

  The carbon-silicon carbide composite material of the present invention has a Shore hardness of HSD 50 or less. If the Shore hardness exceeds 50, good processability cannot be obtained. The shore hardness is preferably in the range of HSD 20-50, more preferably in the range of HSD 25-45.

  Since the carbon-silicon carbide composite material of the present invention has the above-described bending strength and shore hardness, it is excellent in workability and is less likely to be cracked after processing. Therefore, it can be set as the structural material excellent in workability and intensity | strength.

  In addition, since the carbon-silicon carbide composite material of the present invention has a structure in which carbon particles are bonded to each other via a silicon carbide layer, a newly appearing surface by cutting or the like is almost uniform. There is no great variation in physical properties. For this reason, even if processed, there is almost no difference in performance on the surface.

  In the carbon-silicon carbide composite material of the present invention, the ratio of the silicon carbide layer is preferably in the range of 20 to 70% by weight. When the proportion of the silicon carbide layer is less than 20% by weight, the strength of the silicon carbide layer may be weakened, and the strength as a material may be reduced.

  On the other hand, when the ratio of the silicon carbide layer exceeds 70% by weight, the ratio of the carbon itself is too small, so that the characteristics of the carbon are hardly exhibited.

  The proportion of the silicon carbide layer is more preferably in the range of 25 to 65% by weight, particularly preferably in the range of 30 to 55% by weight.

The bulk density of the carbon-silicon carbide composite material of the present invention is preferably 1.90 g / cm ³ or more. If the bulk density is less than 1.90 g / cm ³ , the structure does not become relatively dense and the strength may be reduced.

The bulk density is more preferably in the range of 1.95~2.80g / cm ^3, particularly preferably from 2.05~2.70g / cm ^3.

  In the carbon-silicon carbide composite material of the present invention, the silicon carbide layer preferably has a thickness in the range of 100 nm to 20 μm.

  If the thickness of the silicon carbide layer is too thin, the strength of the silicon carbide layer may be reduced.

  If the thickness of the silicon carbide layer is too thick, it may be difficult to develop good characteristics of carbon.

  The carbon-silicon carbide composite material of the present invention is preferably obtained by sintering carbon particles having a silicon carbide coating layer. By sintering using carbon particles having a silicon carbide coating layer, a carbon-silicon carbide composite material having a uniform silicon carbide layer around the carbon particles can be obtained. For this reason, a carbon-silicon carbide composite material having excellent workability and high strength can be easily produced.

  FIG. 2 is a schematic cross-sectional view showing carbon particles having a silicon carbide coating layer. As shown in FIG. 2, the silicon carbide-coated carbon particles 12 have a silicon carbide coating layer 11 on the surface of the carbon particles 10.

  The silicon carbide-coated carbon particles 12 as shown in FIG. 2 can be produced by, for example, reacting a carbon component 10 with a silicon component to carbonize the surface carbon to form silicon carbide. The method of converting into silicon carbide by reacting carbon of the base material with the silicon component as a reaction source in this way is called CVR method. For example, in patent document 3, the carbon particle which has a silicon carbide coating layer as shown in FIG. 2 is manufactured using such a CVR method. You may form the carbon-silicon carbide composite material of this invention using the carbon particle which has the silicon carbide coating layer manufactured using the method disclosed by patent document 3. FIG.

  In the CVR method, for example, a silicon carbide coating layer can be formed on the surface of the carbon particles by reacting the surface of the carbon particles with SiO gas in an atmosphere at a temperature of 1400 ° C. to 1600 ° C. and a pressure of 1 to 150 Pa. .

  The average particle size of the carbon particles having the silicon carbide coating layer is preferably in the range of 50 nm to 500 μm, more preferably in the range of 1 μm to 250 μm, and particularly preferably in the range of 5 μm to 100 μm.

  If the average particle size is too small, there is a possibility that carbon particles having a sufficient silicon carbide layer may not be obtained. Therefore, the strength of the silicon carbide layer is reduced, and the strength of the carbon-silicon carbide composite material cannot be obtained.

  If the average particle size is too large, a sufficient density cannot be obtained during sintering, and the strength of the fired carbon-silicon carbide composite material may decrease.

  The thickness of the silicon carbide coating layer is preferably in the range of 50 nm to 10 μm, more preferably in the range of 200 nm to 10 μm, and particularly preferably in the range of 500 nm to 5 μm. If the thickness of the silicon carbide coating layer is too thin, the bonding strength between the carbon particles and the carbon particles may be reduced, and the strength of the entire material may be reduced. If the thickness of the silicon carbide coating layer is too thick, There is a possibility that a dense carbon-silicon carbide composite material having a high relative density cannot be obtained.

  FIG. 3 is a schematic cross-sectional view showing an arrangement state in a crucible for producing carbon particles having a silicon carbide coating layer by a CVR method. As shown in FIG. 3, a carbon sheet 22 is disposed in a graphite crucible 21, and an SiO powder 23 is disposed thereon as an SiO source. A carbon felt 24 is disposed on the SiO powder 23, and carbon particles 25 are disposed on the carbon felt 24. A carbon felt 26 is disposed on the carbon particles 25, and a carbon sheet 27 is disposed thereon.

  Instead of the graphite crucible 21, an alumina crucible may be used.

  The graphite crucible 21 arranged as shown in FIG. 3 is placed in a firing furnace, the inside of the firing furnace is evacuated and heated to heat and exhaust the interior of the graphite crucible 21 to a predetermined temperature and a predetermined pressure. To do.

  By evacuating the graphite crucible 21 to a predetermined pressure and heating it to a predetermined temperature, SiO gas is generated from the SiO powder, and this SiO gas reacts with the surface of the carbon particles, so that the surfaces of the carbon particles are carbonized. Carbon particles having a silicon carbide coating layer can be produced by conversion to silicon and the CVR method.

  The carbon particles having a silicon carbide coating layer in the present invention are not limited to those produced by the CVR method, and may be produced by other methods. For example, the silicon carbide layer may be produced by forming it on the surface of the carbon particles by a vapor phase method, a liquid phase method, a mechanical mixing method, or a combination thereof. For example, by adding carbon particles to a slurry of silicon carbide particles, the silicon carbide particles may be attached to the surface of the carbon particles to form a silicon carbide layer.

  Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to the following examples.

[Production of carbon particles having a silicon carbide coating layer]
Using the graphite crucible 21 shown in FIG. 3, the SiO powder 23 and the carbon particles 25 are placed in the graphite crucible 21 as described above, and the CVR method is performed under the raw material charge and reaction conditions shown in Table 1. Thus, carbon particles having a silicon carbide layer (hereinafter referred to as “silicon carbide-coated carbon particles”) were produced. As the SiO powder, SiO granules having an average particle diameter of 2 to 6 μm were used. As the carbon particles, spherical graphite particles having an average particle diameter of 20 μm were used.

  “Vac.” In the atmosphere of the reaction conditions shown in Table 1 means a reduced pressure atmosphere, and specifically indicates that the pressure was reduced to 30 Pa or less using a vacuum pump. “Ar” means an argon atmosphere. Further, “C amount” and “SiO amount” in the raw material charging amount indicate the C mol amount of the graphite particles and the Si mol amount in the SiO powder.

  Under the conditions shown in Table 1, silicon carbide-coated carbon particles of raw materials 1 to 5 were obtained.

  As for the average particle diameter of the silicon carbide-coated carbon particles, all of the raw materials 1 to 5 were 20 μm.

  Moreover, the thickness of the silicon carbide coating layer in the silicon carbide coated carbon particles was 600 nm for the raw material 1, 1.5 μm for the raw material 2, 2.5 μm for the raw material 3, 150 nm for the raw material 4, and 7 μm for the raw material 5.

  4 to 8 are diagrams showing X-ray diffraction patterns of the raw materials 1 to 5 obtained as described above. 4 shows the raw material 1, FIG. 5 shows the raw material 2, FIG. 6 shows the raw material 3, FIG. 7 shows the raw material 4, and FIG. In addition, the vertical axis | shaft in each figure shows peak intensity and is an arbitrary unit.

  “SiC coating amount” shown in Table 1 indicates the coating ratio of the silicon carbide coating layer in the silicon carbide-coated carbon particles. The SiC coating amount is a value obtained from an X-ray diffraction calibration curve.

[Production of carbon-silicon carbide composite]
Using the silicon carbide-coated carbon particles of the raw materials 1 to 5, a carbon-silicon carbide composite material was produced as follows.

A carbon-silicon carbide composite material was manufactured by pressure-sintering silicon carbide-coated carbon particles using a high-current discharge bonding apparatus (“SPS-1050” manufactured by Sumitomo Coal Industry Co., Ltd.). By using this apparatus, sintering can be performed by spark plasma sintering (pulse current sintering). In the discharge plasma sintering, in addition to direct heating by electric current, a current impact by pulse energization is generated, and powder can be sintered at a temperature lower than usual.

  Here, sintering was performed by maintaining heating at a temperature of 2000 ° C. for 5 minutes while being pressurized to 30 MPa.

  A sintered body was manufactured using the raw material 1 in Example 1, the raw material 2 in Example 2, the raw material 3 in Example 3, the raw material 4 in Comparative Example 1, and the raw material 5 in Comparative Example 2.

  Comparative Example 3 is a mixed powder obtained by mixing original carbon particles and silicon carbide powder (average particle diameter 600 nm) without using silicon carbide-coated carbon particles so that the silicon carbide content is 55% by weight. Using this, a sintered body was produced.

  About the obtained sintered compact, bulk density, bending strength, and Shore hardness were measured as follows.

  In addition, as shown in FIG. 1, the obtained sintered body has a structure in which carbon particles are bonded via a silicon carbide layer. The thickness of the silicon carbide layer is 1200 nm in Example 1. Example 2 was 3.0 μm, Example 3 was 5.0 μm, Comparative Example 1 was 300 nm, and Comparative Example 2 was 14 μm.

  In Comparative Example 3, the structure as shown in FIG. 1 was not recognized, and a three-dimensional network-like continuous silicon carbide layer was not observed.

[Measurement of bulk density]
The bulk density was measured by the Archimedes method. Specifically, it measured based on JIS A1509-3.

[Measurement of bending strength]
The three-point bending strength of the sintered body was measured. The obtained sintered body was processed to a thickness of about 2 mm × width of about 3 mm × length of about 20 mm to obtain a sample piece. Using this sample piece, the bending strength at break was measured at a load speed of 0.1 mm / sec using a desktop small general-purpose tester (manufactured by Shimadzu Corporation, “EZ-Test Type L”).

[Measurement of Shore hardness]
About the obtained sintered compact, Shore hardness was measured using hardness tester Shore type D type (Nakai Seiki Seisakusho make, model number 20309). Five points were measured for one test piece, and the average value of three points excluding the maximum value and the minimum value of the measured values was defined as Shore hardness.

  The measurement results are shown in Table 2.

  In Examples 1 to 3 using the raw materials 1 to 3, a carbon-silicon carbide composite material having a bending strength of 50 MPa or more and a Shore hardness of HSD 50 or less could be obtained.

  In Comparative Example 1, the Shore hardness was HSD50 or less, but the bending strength was less than 50 MPa. In Comparative Example 2, the Shore hardness was higher than HSD50.

  In Comparative Example 3, the carbon particles could not be sintered well and was a brittle carbon-silicon carbide composite material, so that a test piece could not be prepared and measurement was impossible.

  Further, as a reference example, a sintered body was produced under the conditions disclosed in the example of Patent Document 3. Specifically, when a sintered body was produced by applying pressure to 40 MPa at a temperature of 2000 ° C. for 20 minutes, the Shore hardness was HSD59, which was higher than 50.

  Therefore, it can be seen that the Shore hardness in the carbon-silicon carbide composite material of the present invention can be controlled to HSD 50 or less by shortening the sintering time, for example.

[Evaluation of workability]
About the carbon-silicon carbide composite material of Examples 1-3 and Comparative Examples 1-2, workability was evaluated as follows.

  Holes having a thread width of 0.5 mm were formed in the obtained carbon-silicon carbide composite material. In Examples 1 to 3, it was possible to form the screw thread without cracking using a cutting tool, and when the screw was screwed into the screw hole, the screw could be repeatedly screwed without cracking the screw thread. On the other hand, in Comparative Example 1, the thread is cracked, the workability is poor and lacks practicality, and when the screw is screwed into the formed screw hole, the thread is further broken. The strength was weak and lacked practicality. Moreover, in comparative example 2, since it was too hard, it was not able to process with the said general cutting tool.

DESCRIPTION OF SYMBOLS 1 ... Carbon-silicon carbide composite material 2 ... Carbon particle 3 ... Silicon carbide layer 10 ... Carbon particle 11 ... Silicon carbide coating layer 12 ... Silicon carbide coated carbon particle 21 ... Graphite crucible 22 ... Carbon sheet 23 ... SiO powder 24 ... Carbon Felt 25 ... carbon particle 26 ... carbon felt 27 ... carbon sheet

Claims (7)

A carbon-silicon carbide composite material having a structure in which carbon particles are bonded together via a silicon carbide layer,
A carbon-silicon carbide composite material having a bending strength of 50 MPa or more and a Shore hardness of HSD 50 or less.   The carbon-silicon carbide composite material according to claim 1, wherein a ratio of the silicon carbide layer is in a range of 20 to 70% by weight. The carbon-silicon carbide composite material according to claim 1, wherein the bulk density is 1.90 g / cm ³ or more.   The carbon-silicon carbide composite material according to any one of claims 1 to 3, wherein a thickness of the silicon carbide layer is in a range of 100 nm to 20 µm.   The carbon-silicon carbide composite material according to any one of claims 1 to 4, wherein the carbon-silicon carbide composite material is obtained by sintering carbon particles having a silicon carbide coating layer.   The carbon-silicon carbide composite material according to claim 5, wherein an average particle diameter of the carbon particles having the silicon carbide coating layer is in a range of 50 nm to 500 µm.   The carbon-silicon carbide composite material according to claim 5 or 6, wherein a thickness of the silicon carbide coating layer is in a range of 50 nm to 10 µm.

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