CN118812276A - A method for preparing a carbon/carbon composite material with high thermal conductivity and high strength - Google Patents
A method for preparing a carbon/carbon composite material with high thermal conductivity and high strength Download PDFInfo
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Abstract
本发明公开了一种高导热高强度碳/碳复合材料及其制备方法，涉及碳/碳复合材料技术领域。所述方法包括将碳纤维预制体置于沉积炉中，抽真空后，将沉积炉温度升至950~1250℃，随后通入碳源气体和水蒸汽，并通入载气进行稀释和保护，沉积80~100 h后，停止加热，得到碳基复合材料；将碳基复合材料进行石墨化处理，得到高导热高强度的碳/碳复合材料。本发明以甲烷和水蒸汽为混合前驱体，可在较大的工艺参数范围内快速制备出密度均匀且致密，基体均为高织构热解碳的碳/碳复合材料，在碳/碳复合材料的低成本快速制备领域具有深远意义。
The present invention discloses a high thermal conductivity and high strength carbon/carbon composite material and a preparation method thereof, and relates to the technical field of carbon/carbon composite materials. The method comprises placing a carbon fiber preform in a deposition furnace, evacuating the vacuum, raising the temperature of the deposition furnace to 950-1250°C, then introducing a carbon source gas and water vapor, and introducing a carrier gas for dilution and protection, and after deposition for 80-100 hours, stopping heating to obtain a carbon-based composite material; graphitizing the carbon-based composite material to obtain a high thermal conductivity and high strength carbon/carbon composite material. The present invention uses methane and water vapor as mixed precursors, and can quickly prepare a carbon/carbon composite material with uniform and dense density, and the matrix is all high-texture pyrolytic carbon within a large process parameter range, which has far-reaching significance in the field of low-cost and rapid preparation of carbon/carbon composite materials.
Description
Technical Field
The invention relates to the technical field of carbon/carbon composite materials, in particular to a high-heat-conductivity high-strength carbon/carbon composite material and a preparation method thereof.
Background
The carbon/carbon composite material is widely applied to the fields of aerospace, civil extreme environments and the like due to the advantages of high specific strength, high specific modulus, thermal shock resistance, wear resistance, corrosion resistance and the like. The preparation methods of the carbon/carbon composite material mainly include a liquid-phase impregnation carbonization method and a chemical vapor infiltration method, wherein the chemical vapor infiltration method is widely used in the production of the carbon/carbon composite material as a technique which can be large-scale and has flexible designability. The properties of the carbon/carbon composite material are closely related to the matrix carbon, and the properties of the carbon/carbon composite material have large differences due to different microstructures of pyrolytic carbon. The microstructure of pyrolytic carbon can be classified into isotropy, low texture, medium texture and high texture, wherein the high texture pyrolytic carbon has the least defects and the highest density, and is more beneficial to obtain a carbon/carbon composite material with high density, high heat conduction and high strength as a matrix.
At present, raw materials for preparing high-texture pyrolytic carbon by a chemical vapor infiltration method are mainly divided into single hydrocarbons and mixed precursors. Among the single precursors, methane, ethylene, propylene, propane, etc. are mainly used, and methane has been studied intensively because of its simple molecular structure and good diffusivity. The literature 1"Chemical vapor infiltration of carbon fiber felt: optimization of densification and carbon microstructure. Carbon, 2002, 40: 2529-2545." takes methane as a precursor, and prepares the carbon/carbon composite material through an isothermal chemical vapor infiltration process, when the deposition temperature is 1095 ℃, the methane partial pressure is 9.5-11 kPa, pure high-texture pyrolytic carbon can be obtained, and when the methane partial pressure is increased or decreased, medium-texture and isotropic pyrolytic carbon can be generated. The process parameters of the pure high-texture pyrolytic carbon obtained by the method have narrow variation range, and the temperature and pressure are strictly controlled in practical application, so that the method has certain limitation. The literature 2"The influence of temperature on the texture of carbon /carbon composites infiltrated by ethylene pyrolysis. Journal of Solid Rocket Technology, 2012, 35(4): 528-531." takes ethylene as a carbon source, researches the influence of temperature on texture under the same pressure and residence time, and discovers that single high-texture pyrolytic carbon can be prepared only at 1150-1200 ℃. Propylene, propane and the like can obtain high-texture pyrolytic carbon under certain process conditions, but the process parameters are narrow in range. With the development of chemical vapor infiltration techniques, various precursors have been studied, such as xylene, ethanol, n-propanol, n-butanol, etc. The literature 3"Deposition of Pyrolytic Carbon using Ethanol as Precursor in Chemical Vapor Infiltration. Journal of Inorganic Materials. 2009, 24(5):1073-1076." uses ethanol as a precursor, nitrogen as a carrier gas, and an isothermal chemical vapor infiltration method is adopted under the conditions of 1125 ℃ and 20: 20 kPa pressure, and a carbon/carbon composite material of a pure high-texture pyrolytic carbon matrix is prepared through 114 and h, but pure ethanol deposition is easy to generate hole sealing crust, so that the density is about 1.67: 1.67 g/cm 3, and the densification effect is not ideal.
Traditional small molecular hydrocarbons have the advantage of diffusion, but have the disadvantage of narrower process parameters in the aspect of high-texture pyrolytic carbon tissue control; the deposition rate of the macromolecules of xylene and cyclic hydrocarbon is high, but the deposition rate is difficult to control in the aspects of density uniformity and high-texture pyrolytic carbon matrix preparation. Therefore, by mixing methane with the ethanol precursor, the advantages of high diffusion coefficient of methane and high deposition speed of ethanol are combined, and the carbon/carbon composite material with good densification effect and high texture pyrolytic carbon tissue control degree can be prepared. The literature 4"Preparation of carbon/carbon composite by pyrolysis of ethanol and methane. Materials&Design, 2015, 65:174-178." and the literature 5"Preparation of high texture three-dimensional braided carbon/carbon composites by pyrolysis of ethanol and methane. Ceramics International, 2016, 42:2887-2891." use methane mixed ethanol, and a needled carbon fiber felt with the density of 0.45 g/cm 3 is used as a reinforcement, so that a carbon/carbon composite material with uniform tissue and uniform density is prepared at 1180 ℃. The prepared composite material can reach 1.80 g/cm 3 only by 85 h, and the carbon matrix is pure high-texture pyrolytic carbon, but the technological parameters are still more strict, and the introduction of ethanol increases the preparation cost.
Disclosure of Invention
Aiming at the defects in the background technology, the invention provides a high-heat-conductivity high-strength carbon/carbon composite material and a preparation method thereof. According to the invention, the diffusion deposition efficiency and texture control of the precursor in the deposition process are comprehensively considered, methane and water vapor are used as mixed precursors, the carbon/carbon composite material with uniform and compact density and high-texture pyrolytic carbon matrix can be rapidly prepared in a larger process parameter range, and the method has profound significance in the field of low-cost rapid preparation of the carbon/carbon composite material.
The first object of the invention is to provide a preparation method of a high-heat-conductivity high-strength carbon/carbon composite material, which comprises the following steps:
Placing the carbon fiber preform in a deposition furnace, vacuumizing, raising the temperature of the deposition furnace to 950-1250 ℃, then introducing carbon source gas and water vapor, introducing carrier gas for dilution and protection, and stopping heating after depositing for 80-100 hours to obtain a carbon-based composite material;
graphitizing the carbon-based composite material to obtain the carbon/carbon composite material with high heat conductivity and high strength.
Preferably, the flow rate of the carbon source gas is 100-500 mL/min, and the flow rate of the water vapor is 10-200 mL/min.
Preferably, the carbon source gas is methane or natural gas.
Preferably, the carrier gas is argon or nitrogen, and the flow rate of the carrier gas is 100-300 mL/min.
Preferably, in the deposition process, the pressure in the deposition furnace is regulated to be 10-80 mbar.
Preferably, the graphitization treatment temperature is 2000-3000 ℃ and the duration is 0.5-2 h.
Preferably, the density of the carbon fiber preform is 0.15-0.25 g/cm 3.
Preferably, the carbon fiber preform is a high thermal conductivity carbon fiber net felt preform.
A second object of the present invention is to provide a high thermal conductivity and high strength carbon/carbon composite.
A third object of the present invention is to provide the use of a high thermal conductivity and high strength carbon/carbon composite in extreme environments.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a high-heat-conductivity high-strength carbon/carbon composite material and a preparation method thereof, the invention takes steam modified methane as a precursor, the characteristics of small molecular weight and easier diffusion of water are utilized to enable the water to be mixed with methane to enter the preform, so that the crusting problem generated in the pyrolytic carbon deposition process is effectively solved. At the deposition temperature, methane is cleaved to form six-membered rings and other cyclic structures (five-, seven-, eight-, etc.) which partially form larger hydrocarbon molecules. When methane is cracked, the bond formation and bond breaking of a carbon structure are frequent, and when the concentration of methane is smaller and the reaction time is shorter, smaller and flat carbon atom clusters are easy to form, so that graphene sheets are formed by combination; when the concentration of methane is too high and the reaction time is long, distorted carbon clusters are easy to form, and finally medium-low texture pyrolytic carbon is formed.
According to the method, an oxidizing atmosphere is introduced, and carbon atoms which are not bonded at the edge of the carbocycle are oxidized and consumed during methane pyrolysis, so that the forming speed of the carbocycle is reduced, the defect of the carbocycle is reduced, and further the graphene sheet layer with smaller initial size and relatively flat morphology is formed and adsorbed on the surface of the carbon fiber for growth. In addition, in the process of stacking graphene sheets to form high-texture pyrolytic carbon, carbocycles tend to be adsorbed on defective graphene sheet sites with high energy and grow large, and if defects are more, carbon ring adsorption sites correspondingly increase, a large number of graphene sheets are staggered, so that more defects are generated, and the regular graphene sheets are not generated. Therefore, oxygen atoms with proper concentration can oxidize carbon atoms at defect sites when graphene sheets are stacked and grown, so that the carbon atoms are formed into six-membered rings through re-bonding, and the formation of defects in the graphene sheets is reduced.
According to the invention, by introducing oxygen atoms, the speed of methane cracking into rings is reduced, so that the reaction is easier to control. The proper amount of oxygen atoms can also reduce the defects of graphene sheets, so that the deposition process and the organization structure of pyrolytic carbon are more controllable. In the oxygen-containing gas, the proportion of oxygen content of water vapor is maximum, the cost is lowest, other elements are not additionally introduced, and the molecular weight is small and the diffusion is easy.
According to the preparation method disclosed by the invention, the water vapor modified methane is used as a precursor, so that the tissue structure, defects and preparation speed of the prepared pyrolytic carbon are effectively controlled, the temperature range of the obtained high-texture pyrolytic carbon matrix can reach 300 ℃, and the pressure range can reach 70 mbar. In addition, by adjusting the technological parameters, the densification time of the carbon/carbon composite material can be shortened to 80 h, the XY heat conduction coefficient can reach 328.05W/m/K, the Z heat conduction coefficient can reach 132.55W/m/K, and the bending strength can reach 157 MPa after high-temperature graphitization.
Drawings
FIG. 1 is a polarized tissue structure of the carbon/carbon composite material provided in example 2;
FIG. 2 is a polarized tissue structure of the carbon/carbon composite material provided in example 3;
fig. 3 is a polarized tissue structure of the carbon/carbon composite material provided in comparative example 1.
Detailed Description
In order that those skilled in the art will better understand the technical solution of the present invention, the present invention will be further described with reference to the specific examples and the accompanying drawings, but the examples are not intended to be limiting.
The invention is mainly based on the prior art, and ethanol and ethylene are used as precursors independently to prepare the carbon/carbon composite material with uniform structure and high texture pyrolytic carbon matrix under certain process conditions. In addition, the precursor formed by mixing ethanol and methane is used as a carbon source to prepare the high-texture pyrolytic carbon, so that the adjustable range of the technological parameters is wider, and the fact that methane is the main carbon source substance in the deposition process and the ethanol mainly plays a role in adjustment is indicated. Previous studies and experience have shown that ethanol first decomposes to form ethylene and water during pyrolysis, but that the process parameters of ethanol and methane are simpler and more controllable than those of ethylene and methane, indicating that water molecules are important components in the deposition of highly textured pyrolytic carbon, wherein the presence of oxygen can significantly improve the deposition efficiency of the carbon source gas and the texture of the pyrolytic carbon produced. Therefore, the diffusion deposition efficiency, the texture control and the practical value of the precursor in the deposition process are comprehensively considered, the methane and the water vapor are used as the mixed precursor, the carbon/carbon composite material with uniform and compact density and high texture pyrolytic carbon matrix can be rapidly prepared in a larger process parameter range, and the method has profound significance in the field of low-cost rapid preparation of the carbon/carbon composite material.
The first aspect of the invention provides a method for preparing a high-heat-conductivity high-strength carbon/carbon composite material, which comprises the following steps:
Placing the carbon fiber preform in a deposition furnace, vacuumizing, raising the temperature of the deposition furnace to 950-1250 ℃, then introducing carbon source gas and water vapor, introducing carrier gas for dilution and protection, and stopping heating after depositing for 80-100 hours to obtain a carbon-based composite material;
graphitizing the carbon-based composite material to obtain the carbon/carbon composite material with high heat conductivity and high strength.
Wherein the flow rate of the carbon source gas is 100-500 mL/min, and the flow rate of the water vapor is 10-200 mL/min.
The carbon source gas is methane or natural gas.
The carrier gas is argon or nitrogen, and the flow rate of the carrier gas is 100-300 mL/min.
In the deposition process, the pressure in the deposition furnace is regulated to be 10-80 mbar.
The graphitization treatment temperature is 2000-3000 ℃ and the duration is 0.5-2 h.
The density of the carbon fiber preform is 0.15-0.25 g/cm 3.
The carbon fiber preform is a high-heat-conductivity carbon fiber net felt preform.
In one embodiment, a method for preparing a high thermal conductivity and high strength carbon/carbon composite material is provided, comprising:
Step 1: and injecting water into the storage, placing the storage in a constant-temperature water bath, and adjusting the temperature of the water bath to 50-80 ℃.
Step 2: and (3) placing the carbon fiber preform with the density of 0.15-0.25 g/cm 3 into a deposition furnace, vacuumizing the deposition furnace, removing air in the deposition furnace and a storage, and stopping after the pressure in the furnace reaches 2 mbar.
Step 3: and (3) raising the temperature of the deposition furnace to 950-1250 ℃, then introducing methane with the flow rate of 100-500 mL/min and the flow rate of water vapor of 10-200 mL/min, introducing carrier gas for dilution and protection, wherein the flow rate of the carrier gas is 100-300 mL/min, and regulating the pressure in the deposition furnace to be 10-80 mbar by regulating a vacuum pump controller.
Step 4: after depositing for 80-100 h, closing the deposition furnace and the water bath kettle to heat, and closing methane, water vapor and carrier gas.
Step 5: after cooling to room temperature, the vacuum pump is turned off, carrier gas is introduced to atmospheric pressure, and the carbon/carbon composite material is taken out.
Step 6: and (3) placing the carbon/carbon composite material prepared in the step (5) in a high-temperature graphitization furnace for heat treatment for 0.5-2 h at the temperature of 2000-3000 ℃, and obtaining the carbon/carbon composite material with high heat conductivity and high strength after the heat treatment is finished.
The water in the step 2 is tap water.
And 3, the methane in the step is natural gas.
The carrier gas in the step 3 is any one of argon and nitrogen.
The water in the storage is obtained by the evaporation equipment and then is introduced into the deposition furnace.
The second aspect of the present invention provides a high thermal conductivity and high strength carbon/carbon composite.
A third aspect of the invention provides the use of a high thermal conductivity high strength carbon/carbon composite in an extreme environment.
It should be noted that, the experimental methods adopted in the invention are all conventional methods unless otherwise specified; the reagents and materials employed, unless otherwise specified, are commercially available.
The carbon fiber preform employed in the following examples is a high thermal conductivity carbon fiber web felt preform, wherein,
The preparation process of the high-heat-conductivity carbon fiber net felt preform is as follows:
step 1; loading the high-heat-conductivity carbon fibers into a creel, and cutting off the high-heat-conductivity carbon fibers by a fiber cutting machine, wherein the length of the high-heat-conductivity carbon fibers is about 50 mm;
Step 2: soaking the cut high-heat-conductivity carbon fibers in a sulfuric acid solution for 10-120 min, and then taking out and airing the cut high-heat-conductivity carbon fibers to loosen the cut high-heat-conductivity carbon fibers, so that carding is facilitated;
Step 3: placing the treated high-heat-conductivity carbon fibers on a carding machine, carrying out loose carding, carding the fibers into a monofilament state from a state of thousands of fibers to form high-heat-conductivity carbon fiber embryo cloth;
step 4: and (3) performing pressing and needling on the carded high-heat-conductivity carbon fiber embryo cloth to form a high-heat-conductivity carbon fiber net embryo felt preform, wherein the density of the high-heat-conductivity carbon fiber net embryo felt preform is regulated to be 0.15-0.25 g/cm 3 through pressing.
Example 1:
Step 1: water was poured into the reservoir and placed in a thermostatic water bath, the temperature of which was adjusted to 50 ℃.
Step 2: the carbon fiber preform with the density of 0.15 g/cm 3 is placed into a deposition furnace, the deposition furnace is vacuumized, air in the deposition furnace and a storage is removed, and the furnace pressure is stopped after reaching 2 mbar.
Step 3: and (3) heating the deposition furnace to 900 ℃, then introducing methane with the flow rate of 100 mL/min and the flow rate of water vapor of 10 mL/min, introducing carrier gas for dilution and protection, wherein the flow rate of the carrier gas is 100 mL/min, and regulating the pressure in the deposition furnace to 10 mbar by regulating a vacuum pump controller.
Step 4: after deposition of 100 h, the deposition furnace and water bath heating were turned off, and methane, steam, and carrier gas were turned off.
Step 5: after cooling to room temperature, the vacuum pump is turned off, carrier gas is introduced to atmospheric pressure, and the carbon/carbon composite material is taken out.
Step 6: and (3) placing the carbon/carbon composite material prepared in the step (5) in a high-temperature graphitization furnace for heat treatment at the temperature of 2000 ℃ for 0.5: 0.5 h, and obtaining the carbon/carbon composite material with high heat conductivity and high strength after the heat treatment is finished.
Example 2:
Step 1: water was poured into the reservoir and placed in a thermostatic water bath, the temperature of which was adjusted to 60 ℃.
Step 2: the carbon fiber preform with the density of 0.2 g/cm 3 is placed into a deposition furnace, the deposition furnace is vacuumized, air in the deposition furnace and a storage is removed, and the furnace pressure is stopped after reaching 2 mbar.
Step 3: and (3) heating the deposition furnace to 1100 ℃, then introducing methane with the flow rate of 200 mL/min and the flow rate of water vapor of 100 mL/min, introducing carrier gas for dilution and protection, wherein the flow rate of the carrier gas is 200 mL/min, and regulating the pressure in the deposition furnace to 30 mbar by regulating a vacuum pump controller.
Step 4: after depositing for 80-100 h, closing the deposition furnace and the water bath kettle to heat, and closing methane, water vapor and carrier gas.
Step 5: after cooling to room temperature, the vacuum pump is turned off, carrier gas is introduced to atmospheric pressure, and the carbon/carbon composite material is taken out.
Step 6: and (3) placing the carbon/carbon composite material prepared in the step (5) in a high-temperature graphitization furnace for heat treatment at a temperature of 0.5 h and a temperature of 3000 ℃, and obtaining the carbon/carbon composite material with high heat conductivity and high strength after the heat treatment is finished.
The polarized light tissue structure of the carbon/carbon composite material prepared in example 2 is shown in fig. 1, and it can be seen that the pyrolytic carbon has high optical activity, irregular cross extinction, and extinction angle of about 20.3 degrees, and is typical high-texture pyrolytic carbon. The density of the carbon/carbon composite material prepared in the embodiment is about 1.95 g/cm 3, the aperture ratio is about 0.8%, the XY heat conduction coefficient can reach 328.05W/m/K, the Z heat conduction coefficient can reach 132.55W/m/K, and the bending strength can reach 157 MPa.
Example 3:
step 1: water was poured into the reservoir and placed in a thermostatic water bath, the temperature of which was adjusted to 80 ℃.
Step 2: and (3) placing the high-heat-conductivity carbon fiber felt preform with the density of 0.25 g/cm 3 into a deposition furnace, vacuumizing the deposition furnace, removing air in the deposition furnace and a storage, and stopping after the pressure in the furnace reaches 2 mbar.
Step 3: and (3) heating the deposition furnace to 1100 ℃, then introducing methane with the flow rate of 300 mL/min and the flow rate of water vapor of 150 mL/min, introducing carrier gas for dilution and protection, wherein the flow rate of the carrier gas is 300 mL/min, and regulating the pressure in the deposition furnace to 70 mbar by regulating a vacuum pump controller.
Step 4: after deposition 85 h, the deposition furnace and water bath heating are turned off, and methane, water vapor and carrier gas are turned off.
Step 5: after cooling to room temperature, the vacuum pump is turned off, carrier gas is introduced to atmospheric pressure, and the carbon/carbon composite material is taken out.
Step 6: and (3) placing the carbon/carbon composite material prepared in the step (5) in a high-temperature graphitization furnace for heat treatment for 0.5-2 h, wherein the temperature is 2500 ℃, and obtaining the carbon/carbon composite material with high heat conductivity and high strength after the heat treatment is finished.
The polarized light tissue structure of the carbon/carbon composite material prepared in example 3 is shown in fig. 2, and it can be seen that the pyrolytic carbon has high optical activity, irregular cross extinction, and extinction angle of about 19.8 degrees, and is typical of high-texture pyrolytic carbon. The density of the carbon/carbon composite material prepared in the embodiment is about 1.89 g/cm 3, the aperture ratio is about 1.7%, the XY heat conduction coefficient can reach 165.76W/m/K, the Z heat conduction coefficient can reach 60.74W/m/K, and the bending strength is about 136 MPa.
Comparative example 1
Step 1: and (3) placing the high-heat-conductivity carbon fiber felt preform with the density of 0.2 g/cm 3 into a deposition furnace, vacuumizing the deposition furnace, removing air in the deposition furnace, and stopping after the pressure in the furnace reaches 2 mbar.
Step 2: the temperature of the deposition furnace is increased to 1250 ℃, then methane is introduced, the flow rate is 300 mL/min, the carrier gas is introduced for dilution and protection, the flow rate of the carrier gas is 200 mL/min, and the pressure in the deposition furnace is 80 mbar by adjusting a vacuum pump controller.
Step 3: after deposition of 100h, the deposition furnace heating was turned off and methane and carrier gas were turned off.
Step 4: after cooling to room temperature, the vacuum pump is turned off, carrier gas is introduced to atmospheric pressure, and the carbon/carbon composite material is taken out.
Step 5: and (3) placing the carbon/carbon composite material prepared in the step (4) in a high-temperature graphitization furnace for heat treatment at a temperature of 2h ℃ and obtaining the carbon/carbon composite material with high heat conductivity and high strength after the heat treatment is finished.
The polarized light tissue structure of the carbon/carbon composite material prepared in comparative example 1 is shown in fig. 3, and it can be seen that the pyrolytic carbon has a general optical activity, has more annular cracks, is regular in cross extinction, has a extinction angle of about 13.5 degrees, and is typical of medium-texture pyrolytic carbon. The density of the product prepared in this comparative example was about 1.83 g/cm 3, the aperture ratio was about 2.7%, the XY heat conduction coefficient was 132.36W/m/K, the Z heat conduction coefficient was 51.31W/m/K, and the bending strength was about 108 MPa. And (3) methane is cracked at the deposition temperature to form a six-membered ring and other ring structure (five-membered ring, seven-membered ring, eight-membered ring and the like) so as to form graphene sheets which are adsorbed on carbon fibers for growth. Because no steam is introduced and no oxygen atoms exist, carbon atoms which are not bonded at the edge can not be timely oxidized and removed when methane is cracked to form a six-membered ring and other ring structures, and are combined with other carbon ring structures, so that more defects are generated. In addition, as the growth speed is too high and defects are more and difficult to eliminate, larger pores are generated between two adjacent pyrolytic carbon grains, so that the orientation and the tissue structure of a pyrolytic carbon matrix are reduced, and finally, the density of the prepared carbon/carbon composite material is reduced and the aperture ratio is improved. It can be seen from examples and comparative examples that the introduction of water vapor with a proper content can significantly improve the order of the pyrolytic carbon matrix and reduce defects, thereby improving the thermal conductivity and flexural strength of the prepared carbon/carbon composite material. The invention comprehensively considers the preparation cost, process control and practical value, takes the steam modified methane as the precursor, can effectively control the organization structure, defects and preparation speed of the prepared pyrolytic carbon, and improves the temperature range and pressure range required by obtaining the high-texture pyrolytic carbon matrix.
The present invention describes preferred embodiments and effects thereof. Additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (10)
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