KR20080099632A - Method of sic micro tube with a controlled wall porosity and porous wall sic micro tube - Google Patents

Abstract

A porous polycarbosilane tube and a method for manufacturing the same is provided to control the thickness of tube wall freely due to high specific surface area of the wall and the developed pore structure and to ensure excellent high strength, heat resistance, corrosion resistance and environmental proofing property. A method for manufacturing polycarbosilane tube comprises a step for extruding polycarbosilane in a fibrous type; a step for heat-treating it in the oxidizing atmosphere and hardening from the surface of polycarbosilane to form a uncured part on the fibrous polycarbosilane central part; and a step for forming hollow by dissolving the uncured central part of the fibrous polycarbosilane with a polar solvent.

Description

Method for manufacturing silicon carbide microtubes with controlled porosity and its tubes {Method of SiC micro tube with a controlled wall porosity and porous wall SiC micro tube}

1 is an optical micrograph of a SiC microtube manufactured by the present invention.

Figure 2a is a flow chart showing a process for producing a silicon carbide microtube provided in the present invention.

Figure 2b is a photograph of the state of each step of the process for producing a silicon carbide microtube provided by the present invention.

Figure 3a is a graph recording the increase in weight with the heat treatment time during the heat treatment of the polycarbosilane fibers at 245 degrees in an atmosphere-controlled electric furnace in the second step of the present invention.

Figure 3b is the result of analyzing the distribution of oxygen concentration of polycarbosilane fiber by EDS according to the stabilization time in the stabilization step of the second step of the present invention.

3c is a polycarbosilane fiber having a diameter of 240-250 micrometers by stabilizing for a predetermined time in the stabilization step of the second step of the present invention and then eluted in a polar solvent to dissolve the unstabilized central portion to have different wall thicknesses It is an optical micrograph of the adjusted polycarbosilane tube.

Figure 3d is a scanning electron micrograph after the heat treatment and sintering at 1600 degrees after drying the polycarbosilane tube prepared in the step shown in Figure 3 above.

Figure 3e is a graph showing the thickness of the wall of the polycarbosilane tube with the stabilization time and the thickness of the wall of the silicon carbide microtube prepared by heat-treating the polycarbosilane microtube at 1600 degrees.

4A is a scanning electron micrograph of a SiC microtube prepared by stabilizing at 200 ^° C. for 30 min to determine the thickness of the tube to 60 micrometers, followed by heat treatment at 1200, 1400, 1600, 1800 ^° C. The thickness of the tube was plastic shrinkage to about 45 micrometers.

4A and 4B are scanning electron microscopes of silicon carbide microtubes prepared by heat-linking precursor microtubes having a thickness of about 60 microns in an argon atmosphere of 1200, 1400, 1600, and 1800 degrees, respectively, by cross-linking for 30 minutes. It is a photograph.

Figure 4c is a BET result of measuring the specific surface area of the SiC microtubes heat-treated at each heat treatment temperature from 1200 to 1800 degrees.

Figure 4d is a SEM image of the outer wall, inner wall, single wall of the silicon carbide microtubes prepared by heat treatment at different temperatures.

Figure 4e is a graph showing the results of measuring the distribution of nano-pores formed on the wall of the silicon carbide microtubes prepared by heat treatment at 1400 degrees.

FIG. 5 is a view schematically showing how a silicon carbide-based microtube manufactured according to the present invention is used for gas separation.

   The present invention relates to a method for providing a hollow silicon carbide microtube, and more particularly, to prepare a hollow fiber by partially curing the fiber derived from polycarbosilane to elute and remove the uncured portion. The present invention relates to a method for producing a high performance silicon carbide microtube in which the pore size and porosity of wall pores are controlled by heat treatment.

   Ceramic-like tubular material is generally produced by extrusion through an orifice-forming extrusion die using a ceramic slurry and dry sintering. Depending on the size of the orifices and dies being extruded, tubes of various sizes can be produced, but the size of the tubes can be only up to several millimeters in diameter and is not suitable for producing micro-sized tubes. In addition, a method of manufacturing a microtube in which pores are formed by extrusion of a mixture of a polymer and a ceramic powder into a tube and then undergoing a heat treatment firing process is known in the art.

   However, the ceramic tube manufactured through this method has the nanostructure of the tube such that even if the size of the raw material particles starts from the nano size, large pores formed by the thermal decomposition volatilization of the added polymer with the growth of the particles during sintering remain. It is not easy to adjust.

   In contrast, a method is known in which a microtube is produced by extruding and pyrolyzing a preceramic polymer which is converted into ceramics by pyrolysis. A known method is a method in which a polymer resin in which carbon is added to polycarbosilane or polysiloxane is extruded through various orifices to form a tube, and then heat-treated to produce a micro tube (Paolo Colombo et al., Journal of american ceramic society). , 86 [6] 1025-27 (2003). As such, when the microtube is manufactured using the preceramic polymer, the microtube having a dense wall made of nano-sized particles can be manufactured, and the microtube having excellent mechanical strength is obtained.

   In this case, however, separate orifices must be secured in order to control the size of the wall and the hollow of the microtube, and it is difficult to control the size of the hollow and the wall thickness independently, and there is a limit to obtaining a smaller hollow microtube. there was.

   On the other hand, Masaki Sugimoto et al. (US Pat. No. 6780370) of the Japan Atomic Energy Research Institute have a micro diameter having an outer diameter of 10-20 microns by stabilizing a polycarbosilane fiber with an electron beam to locally stabilize the surface and then dissolving it in a polar solvent. The tube was prepared. The stabilization method using electron beams has the advantage that silicon carbide microtubes with excellent crystallinity can be obtained by suppressing oxygen incorporation into polycarbosilane, while the outer diameter of the fibers used is very small, around 20 micrometers, Since there is a process using an expensive electron beam curing method, it is not suitable for the manufacturing method of the hollow yarn of 100-500 micron size larger than this invention. In addition, in the above known method of manufacturing a silicon carbide tube, it is not yet known about the process of controlling the porosity of the wall of the tube.

An object of the present invention is to provide a porous polycarbosilane tube having a large specific surface area of the wall surface and a well-developed pore structure and having a freely adjustable tube wall thickness, and a method for producing a silicon carbide tube produced therefrom.

It is also an object of the present invention to provide porous polycarbosilane tubes and silicon carbide-based tubes having narrow pore distribution and small pore sizes.

   The present invention to achieve the above technical problem, the step of extruding polycarbosilane into a fibrous form; Heat-treating in an oxidizing atmosphere to form an uncured region at the center of the fibrous polycarbosilane and curing from the surface of the polycarbosilane; And dissolving the uncured central portion of the fibrous polycarbosilane with a polar solvent to form a hollow.

In the present invention, the polycarbosilane may include at least one polycarbosilane selected from the group consisting of polymethyl carbosilane, polymethylphenyl carbosilane, polyvinyl carbosilane, and polymethylsilane. In addition, the polycarbosilane may be polyaluminocarbosilane.

In the present invention, the fibrous polycarbosilane may have a diameter of 50-500 micrometers.

In addition, the curing step in the present invention may be carried out by heat treatment of the polycarbosilane at a temperature of 150-250 degrees.

In order to achieve the above technical problem, the present invention comprises the steps of extruding a mixture of polycarbosilane and a low molecular weight polymer having a molecular weight of 2000 or less; Heat-treating in an oxidizing atmosphere to form an uncured region at the center of the fibrous polycarbosilane and curing from the surface of the polycarbosilane; And dissolving the uncured central portion of the fibrous polycarbosilane with a polar solvent to form a hollow.

In order to achieve the above another technical problem, the present invention provides a method for producing a silicon carbide tube by heat-treating the polycarbosilane tube manufactured by the above-described method at 1050 degrees-2000 degrees.

In order to achieve another technical problem, the present invention is a porous tube consisting of a plurality of pores, the hollow is formed in the longitudinal direction and 50-500 nm in diameter, the pores of the tube is made of pores with a radius of less than 10nm A porous silicon carbide based tube is provided.

In addition, the present invention is a porous tube formed in the longitudinal direction and the diameter of 50-500 nm, a plurality of pores, the pores of the tube has a peak of pore volume change rate (dV _p / dr _p ) with respect to the pore radius It provides a porous silicon carbide-based tube, characterized in that present when the pore radius is 5nm or less.

In the present invention, the diameter of the microtube is determined by the rate of spinning while forming the precursor polymer while extruding the precursor polymer, which is usually 50 microns to 500 microns and preferably 150-250 microns.

The curing step in the present invention can be carried out by heating in a temperature range of 150-250 degrees for 10 minutes to 24 hours in an electric oven controlled atmosphere. Preferably, the wall thickness of the tube can be adjusted from about 20 microns to 60 microns by heat treatment at 200 degrees for 30 minutes to 2 hours.

The fiber that has undergone the curing step of the present invention is dissolved in a polar solvent, that is, toluene, xylene, acetone, or the like for 1 hour to 24 hours to dissolve the soluble component of the core portion of the fiber. At this time, it is preferable to cut the end of the fiber before dissolving so that the unstabilized core part is in direct contact with the solvent. The time for eluting on a solvent is good to be about 6 hours.

   In the present invention, the heat treatment step may be performed in an atmosphere-controlled electric furnace, in which the temperature increase rate is in the range of 1 to 20 degrees per minute in argon, vacuum, or a gas atmosphere in which argon and hydrogen are mixed, preferably 1050-2000 degrees, preferably 1200-2000 degrees. It is achieved by heat treatment in between. In particular, the heat treatment conditions in this process are important for producing a microtube having a porous wall to be obtained in the present invention. In order to obtain a porous tube, the porosity and grain size of the fiber can be controlled while controlling the time at the heat treatment temperature from 30 minutes to 4 hours. When sintering at low temperature for a short time, it is possible to obtain a fine SiOC-like microtube without porosity, and when sintering at a medium temperature for a long time, the pore size and grain size grow together to obtain a porous microtube with a reduced specific surface area. After prolonged sintering at very high temperatures, a dense microtube becomes fully crystalline. Therefore, in order to use the microtube for the purpose of hydrogen separation, the heat treatment conditions should be well controlled.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is an optical micrograph of a silicon carbide microtube manufactured by the present invention. The outer diameter of the tube shows variation due to the nonuniformity of the spinning speed of the fiber. The surface of the tube was smooth and the wall thickness of the tube between the outer diameter and the inner diameter was about 45 microns uniform.

In the present invention, first, polycarbosilanes and polyaluminocarbosilanes having a molecular weight of 2000 to 3000 were prepared. Regarding the method for producing polyaluminocarbosilane, the method described in Korean Patent 10-0684649 may be used, and a commercially available polycarbosilane may be used. The molecular weight-controlled polycarbosilane was then placed in an extruder and melted at a temperature of 200-300 degrees and spun through a 500 micron circular orifice. The diameter of the spun fibers was around 200-350 microns. The spun precursor fibers were cut to a constant length of 5 cm, aligned and placed in the alumina crucible, and then 10 minutes, 30 minutes, 1 hour or 2, respectively, at a temperature between 200 and 250 degrees in an atmosphere-controlled electric oven. Heat treatment for a time.

    The heat-treated fibers gradually increased oxygen concentration from the surface to the inside of the fibers depending on the heat treatment time and temperature. The longer the heat treatment time or the higher the heat treatment temperature, the greater the amount of oxygen incorporation into the polycarbosilane fiber and the deeper the diffusion depth of oxygen into the fiber. The polycarbosilane fibers stabilized by heat treatment were soaked in toluene solution and sufficiently dissolved for 1 to 6 hours. After the dissolution step was completed, the fibers were separated from the solvent and dried well to obtain a tubular polycarbosilane hollow fiber. At this time, the higher the stabilization temperature, the longer the stabilization time, the thickness of the hollow wall of the hollow fiber increased from 20 microns to 90 microns.

2A is a diagram illustrating a tube manufacturing process according to the present invention.

Referring to FIG. 2A, a polyaluminocarbosilane precursor was prepared, and the precursor was prepared by melt extrusion (range 200-300 degrees) by putting the prepared precursor into an extruder. When the prepared precursor fiber is heat treated in an atmosphere-controlled electric oven in the range of 200-300 degrees, oxygen in the atmosphere is crosslinked while reacting on the surface of the precursor fiber. As the heat treatment temperature and time increase, the crosslinked portion diffuses from the surface to the center of the fiber. When crosslinked precursor fibers are dissolved in a polar solvent such as toluene or xylene, there is a difference in the degree of crosslinking from the surface to the depth direction, which causes a difference in solubility. The central part of the fiber is easily eluted because of the low degree of reaction with oxygen, but the surface part is insoluble. With this difference in solubility, it is easy to elute the center by a few centimeters. The eluted precursor fiber is carefully separated from the solvent, and the dried and dried fibers are pyrolyzed and sintered at a high temperature of 1000 hours or more according to predetermined heat treatment conditions to form silicon carbide microtubes.

   2b summarizes such a series of processes in photographs. Fibers at each stage produced through extrusion, cutting and stabilization, elution, and heat treatment were shown.

   3a to 3e summarized the results of the experiment to understand the cross-link process of the precursor fiber according to the stabilization treatment time at a constant temperature between 200 to 300 degrees.

Figure 3a is a result of measuring the weight change of the precursor fiber five times each one at a time of heating up to 245 degrees at 10 ^o C / min and maintained at that temperature for 10 minutes, 3 minutes, 120 minutes, 360 minutes . At this time, the fiber was cut into a length of about 1cm and the amount of about 1 mg was placed in the alumina crucible and measured while flowing air at a constant speed in the TG-DT measuring apparatus. After each temperature increase and temperature increase, the weight increase curves were almost identical in the isothermal process. The weight of the precursor fiber tended to increase continuously at 245 degrees. The weight gain continued during the heat treatment up to 6 hours, but the weight gain was saturated. An increase in weight of about 9% was observed after 6 hours of heat treatment.

   Figure 3b is a diameter of the cross-section of the fiber using an EDS (Energy Dispersive X-ray Spectroscopy) coupled to a high resolution scanning electron microscope after carefully breaking the fiber after the stabilization heat treatment process of 245 degrees to expose a flat fracture surface It is a graph which records the change of oxygen content continuously by performing X-ray analysis in the linear direction. (3b-1) of FIG. 3B is a result of EDS analysis of oxygen concentration linearly along the diameter (from one outer layer to the outer outer layer) of the fracture surface of unstabilized polyaluminocarbosilane. (3b-2) is the result of EDS analysis of oxygen concentration linearly along fracture diameter after 10 minutes of stabilization. (3b-3) is the result of EDS analysis of oxygen concentration linearly along fracture diameter after 30 minutes of stabilization. (3b-4) is the result of EDS analysis of oxygen concentration linearly along fracture diameter after 1 hour stabilization. (3b-5) is the result of EDS analysis of oxygen concentration linearly along the diameter of fracture surface after 2 hours stabilization. Specifically, each sample was divided into 10 equal parts along the diameter, and once again, the specific amount of oxygen was accurately analyzed using EDS. Therefore, (1) and (10) mean both ends of the diameter, and (5) means the center.

Oxygen concentration (molar ratio) from (1) to (10) in (3b-2) is 18.65 (1), 16.67 (2), 12.52 (3), 10.78 (4), 8.87 (5), 8.12 (6) , 8.33 (7), 10.77 (8), 15.19 (9), 18.36 (10).

Oxygen concentration (molar ratio) from (1) to (10) in (3b-3) is 20.06 (1), 16.94 (2), 12.13 (3), 10.91 (4), 10.41 (5), 9.30 (6) , 11.51 (7), 10.42 (8), 19.62 (9), 21.27 (10).

Oxygen concentrations (molar ratios) from (1) to (10) in (3b-4) are 17.88 (1), 16.44 (2), 14.52 (3), 11.95 (4), 11.40 (5), 12.63 (6) , 13.04 (7), 15.14 (8), 16.70 (9), 18.93 (10).

Oxygen concentration (molar ratio) from (1) to (10) in (3b-5) is 18.64 (1), 18.04 (2), 15.10 (3), 12.49 (4), 10.33 (5), 9.81 (6) , 12.09 (7), 14.80 (8), 16.74 (9), 18.11 (10).

Precursor fibers spun from the extruder showed a constant level of oxygen concentration from the surface to the center and back to the opposite surface direction, showing almost symmetrical oxygen concentration. As the stabilization heat treatment time increased, the oxygen concentration in the surface portion increased symmetrically, and after about 2 hours, the oxygen concentration in the central portion of the fiber also increased to about 15% or more.

It can be easily understood that the crosslinking caused by the increase of the oxygen crosslinking of the polycarbosilane fiber is diffused, so that the concentration of oxygen is increased and thus the weight of the precursor fiber is increased. When the heat treatment was performed for about 6 hours or more, the cross link was saturated, and the oxygen concentration was kept constant regardless of the inside and outside of the surface of the fiber.

The precursor fibers crosslinked by oxygen crosslinking showed a difference in solubility in polar solvents due to the difference in oxygen concentration. Figure 3c is an optical micrograph of the precursor tube formed after the cross-linked precursor fiber for 10 minutes, 30 minutes, 60 minutes, 120 minutes in toluene solvent dissolved for 6 hours and then separated from the solvent and dried. FIG. 3D is a scanning electron micrograph of the obtained ceramic-ized silicon carbide microtube after heat-treating and sintering the precursor tube thus prepared under an argon atmosphere at 1600 ° C. for 1 hour. Figure 3e is a graph showing the stabilization time of the thickness of the wall of the tube after forming the precursor tube and the thickness of the tube of the tube subjected to the pyrolysis sintering process at 1600 degrees. The thickness of the walls of the precursor fibers prepared by crosslinking for 10 minutes was about 50 microns, which greatly contracted to about 30 microns after the fiber was sintered. Pyrolysis and sintering of the precursor fiber with 30 minutes of crosslinking from about 60 microns to 40 microns, and the precursor fiber with one hour of crosslinking from about 70 microns to 48 microns for 2 hours. Through the wall thickness was shown to shrink. As such, the thickness of the wall of the microtube shrinks through the high temperature pyrolysis and sintering process because of the following two processes. That is, when polycarbosilane is generated from SiOCH compound at a temperature of 1000 degrees or less, gas generation such as H2, CH4, CH2 occurs from around 600 degrees, and thermal decomposition gradually occurs to form b-SiC nanocrystals and undergo a sintering process of 1200 degrees. About 5-10 nm of b-SiC particles are in the form of dense fine particles dispersed on the amorphous matrix of SiOC and have about 30% shrinkage. At a temperature of 1200 ° C. or higher, thermal decomposition reaction occurs while SiO and CO 2 gases are generated in SiOC, which is an amorphous phase, and b-SiC particles are further grown to grow to about 50 nm at 1600 ° C. At this time, due to the growth of the crystal grains and the partial decomposition of the amorphous phase, the size of the pores and the growth of grains are accompanied by the increase of the sintering temperature.

   By the way, in the case of polyalumino carbosilane in which a small amount of aluminum is added to the present polycarbosilane, the growth rate of the crystal grains is a little faster and the densification rate is also slightly increased, so that a relatively high strength fiber can be produced. By controlling the heat treatment conditions by using a process of newly forming and densifying pores at high temperature, silicon carbide microtubes in which the nanoporosity of the tube wall is controlled are obtained.

The accompanying phenomenon in the overall heat treatment process as shown above is shown in Figure 3f conceptually.

4A and 4B are scanning electron microscopes of silicon carbide microtubes prepared by heat-linking precursor microtubes having a thickness of about 60 microns in an argon atmosphere of 1200, 1400, 1600, and 1800 degrees, respectively, by cross-linking for 30 minutes. 4a is a low magnification and 4b is a high magnification electron micrograph. Since there is a variation in the outer diameter of the precursor fiber that occurs during the spinning of the fiber, it was difficult to quantify the shrinkage of the outer diameter and the thickness of the wall of the tube, which may be observed as the sintering temperature increases. However, the thickness of the wall of the precursor tube, which was about 60 microns, sintered and contracted to around 40-45 microns, respectively.

On the other hand, the thickness of the wall of the tube was not significantly different according to the sintering temperature. As shown in FIG. 4 b, the fibers heat-treated at 1200 degrees were very dense and no pores could be observed by scanning electron microscopy. The fiber heat-treated at 1400 ° C had a slight grain growth and nanopores were formed between these nanoparticles, and at 1600 ° C, the pore size and grain growth were remarkable. The nanoporous sintered body was changed. It is thought that if the nanostructure of the wall of the microtube is well controlled, the pores of the wall can be used as a membrane for hydrogen separation.

     Figure 4c is a graph showing the change in the specific surface area of the microtube by the nitrogen-substituted BET method using the temperature as a variable in the sintering heat treatment temperature. At 1200 degrees, it showed a low specific surface area of 2.64 m2 / g, and the 1400 degrees microtube showed a large specific surface area of 35.14 m2 / g as a consistent result, as shown by scanning electron microscopy. It decreased to m2 / g, and further decreased to 7.18 m2 / g at 1800 degrees.

In order to examine whether the change of specific surface area is regarded as the change of surface nanostructure or the change of nanostructure inside microtube, the nanostructure of the surface of the fiber heat-treated at each temperature is compared and observed. It was.

Figure 4d is a scanning electron micrograph showing the microstructure of the outer wall, inner wall and the inside of the tube treated at 1200, 1400, 1600, 1800 degrees. As shown in the photograph, the specimen treated at 1200 degrees showed a dense structure in the inner wall, outer wall, and wall of the tube. At 1400 degrees, the shape of the tube is slightly different, and the inner, outer walls, and portions of the walls have a slight grain growth and nanopores are formed. On the other hand, at 1600 degrees, the nanopores were well connected, and the nanocrystals showed well developed structures in both the inner and outer walls and walls of the tube, and at 1800 degrees, except for a whisker-shaped deposit formed on the inner wall of the tube during heat treatment. Porosity was shown.

In order to observe the porosity of the tube more closely, the amount of sample of the tube was sufficiently prepared, and the porosity of the tube was examined again using another type of BET apparatus. In the case of the test specimen of 1200 degrees, it was difficult to obtain the measurement result, because it was difficult to obtain a reproducible result because the specific surface area was low because of perfect densities.

Table 1 summarizes the BET measurement results of specimens heat-treated at 1400, 1600, and 1800 degrees, except for the 1200 degree specimens. First, the average pore diameter was 6.2 nm, 6.1 nm, and 5.9 nm. However, the total pore volume was 6.2710 ^-2 cm ³ / g, 5.29 ■ 10 ^-3 cm ³ / g, and 2.17 ■ 10 ^-3 cm ³ / g. 4 measured with BET equipment). The specific surface areas were 41.37, 3.49 and 1.47 m ² / g.

In addition, the value of Vp was also about 100 times and 400 times larger than those of 1600 and 1800 degrees, respectively (measured by Delcoa BET equipment). The rp representing the size of the pore diameter showing the highest frequency was 1.88 nm, 2.14 nm, and 4.1 nm at 1400 degrees, respectively.

FIG. 4E is a graph of pore diameter change rate showing the pore size of silicon carbide microtubes subjected to sintering heat treatment at 1400 degrees as a variable. All are composed of pores of less than 10 nm, the pores of 1-3 nm can be seen that most of the pores.

On the other hand, as a result of measuring the change of crystal phase and crystal size accompanying the sintering heat treatment process through XRD, the 1200-degree sintering heat treated specimens were almost amorphous but some b-SiC diffraction peaks were observed. Therefore, it was confirmed that the relative strengths of the main peaks of b-SiC such as the (111) peaks 220 and 311 were increased.

On the other hand, although the above description relates to the extrusion of polycarbosilane into a fibrous form, in the present invention, a polymer having a lower temperature such as polystyrene, for example, a polymer having a molecular weight of 2000 or less, is mixed with polycarbosilane and extruded into a fibrous form to produce a polymer at a lower temperature. It may be decomposed to form pores inside the tube.

According to the present invention, it is possible to easily produce a silicon carbide microtube having a controlled porosity that cannot be produced by conventional methods. In particular, the porosity of the tube wall can be produced in a well-controlled form so that the pore size can be adjusted to fit the size of the gas to be separated without additional membrane membranes, as shown in FIG. It can be used for separation of hydrogen gas.

In addition, the present invention can provide a high-strength micro-tube, excellent heat resistance, corrosion resistance, environmental resistance, etc. can have a variety of applications.

Claims (9)

Extruding the polycarbosilane into a fibrous form; Heat-treating in an oxidizing atmosphere to form an uncured region at the center of the fibrous polycarbosilane and curing from the surface of the polycarbosilane; And Method for producing a polycarbosilane tube comprising the step of dissolving the uncured central portion of the fibrous polycarbosilane with a polar solvent to form a hollow. The method of claim 1, The polycarbosilane is a method for producing a polycarbosilane tube, characterized in that the polycarbosilane comprises at least one selected from the group consisting of polymethyl carbosilane, polymethylphenyl carbosilane, polyvinyl carbosilane and polymethylsilane. The method of claim 1, The polycarbosilane is a method for producing a polycarbosilane tube, characterized in that the polyaluminocarbosilane. The method of claim 1, Wherein said fibrous polycarbosilane has a diameter of 50-500 micrometers. The method of claim 1, The curing step is a method for producing a polycarbosilane tube, characterized in that the heat treatment of the polycarbosilane at a temperature of 150-250 degrees. Extruding into a fibrous mixture a polycarbosilane and a low molecular weight polymer having a molecular weight of 2000 or less; Heat-treating in an oxidizing atmosphere to form an uncured region at the center of the fibrous polycarbosilane and curing from the surface of the polycarbosilane; And Method for producing a polycarbosilane tube comprising the step of dissolving the uncured central portion of the fibrous polycarbosilane with a polar solvent to form a hollow. A method for producing a silicon carbide tube by heat-treating the polycarbosilane tube according to any one of claims 1 to 6 at 1050 degrees-2000 degrees. A porous tube having a hollow in the longitudinal direction and having a diameter of 50-500 nm and consisting of a plurality of pores, wherein the pores of the tube have pores having a radius of 10 nm or less. A porous tube having a hollow in the longitudinal direction and having a diameter of 50-500 nm and consisting of a plurality of pores, wherein the pore of the tube has a pore radius of 5 nm with a peak of pore volume change rate (dV _p / dr _p ) with respect to the pore radius. Porous silicon carbide-based tube, characterized in that when present.

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