KR101161675B1 - Silicon carbide hollow fiber and method for fabricating the same - Google Patents

Abstract

The present invention relates to a silicon carbide (SiC) hollow fiber and a method for producing the same, comprising the steps of: forming a mixed powder by mixing silicon carbide and a sintering aid; and dispersing and mixing the mixed powder, a polymer, and a dispersant in an organic solvent. Forming, and passing the slurry through a spinneret, followed by solvent replacement, washing, and drying to form silicon carbide-polymer hollow fiber, and heat treating the silicon carbide-polymer hollow fiber to remove polymer components. And a step in which the silicon carbide particles are partially sintered by the sintering aid, thereby making it easy to manufacture silicon carbide hollow fibers.

Description

Silicon carbide hollow fiber and its manufacturing method {SILICON CARBIDE HOLLOW FIBER AND METHOD FOR FABRICATING THE SAME}

The present invention relates to a silicon carbide (SiC) Hollow Fibers manufacturing technology, and more particularly to a technology that can be used to manufacture a silicon carbide hollow fiber reliably and simply by using a wet spinning and sintering method.

Inorganic hollow yarns have the shape of a hollow hole in the center, and have a very high membrane area per unit volume, and have excellent productivity. Therefore, when preparing the inorganic membrane module using this, it can be applied to processes such as water treatment, gas separation, liquid separation, dust filter, membrane reaction, catalyst carrier, air conditioning.

Most of the inorganic hollow yarns known to date are manufactured by the following methods. As a first method of preparing inorganic hollow fiber, a polymer and inorganic particles are well dispersed in an organic solvent, and then a polymer-inorganic hollow fiber is manufactured through a spinneret and heat treated by sintering. This method is to sinter inorganic particles, and sometimes an excess of sintering aid is added to assist the sintering. Representative inorganic hollow yarns produced by this method include Al ₂ O ₃ hollow fiber, ZrO ₂ hollow fiber, Ni hollow fiber, Ni-Fe hollow fiber, Perovskite hollow fiber, Si ₃ N ₄ hollow fiber, etc. Can be.

As a second method of manufacturing inorganic hollow fiber, a carbon or Si-C polymer precursor raw material is spun through a spinning nozzle to form a hollow fiber, and then heat-treated under specific gas atmosphere conditions. Inorganic hollow yarns produced by this method include SiC hollow fiber, Si ₃ N ₄ hollow fiber, carbon hollow fiber and the like.

Meanwhile, most of the inorganic hollow yarns produced so far are oxide hollow fibers such as Al ₂ O ₃ hollow fibers, and need to be sintered at low temperature in order to have a high porosity of about 30 to 50%, which is a prerequisite for use as an inorganic separator support. There was this. However, when the sintering temperature is low, it has a low strength due to the low density, there is a problem that easily broken in the post-treatment process such as membrane modularization and regeneration.

Therefore, there is a demand for a technology capable of producing inorganic hollow fibers having high porosity and excellent mechanical properties, that is, strength. Such inorganic hollow fiber materials may be provided with silicon carbide (SiC) and silicon nitride (Si 3 N 4) materials having high strength and low coefficient of thermal expansion.

Meanwhile, the silicon carbide hollow yarns designed to date are mainly manufactured using organic silazane polymers as raw materials.

1 is a flowchart showing a conventional silicon carbide hollow fiber manufacturing method.

Referring to FIG. 1, after the conventional silicon carbide hollow yarn is melt-spun into an organic silazane polymer containing a silane group and carbon (S110), the fiber surface is non-fusing (S120, S130) to form a hollow fiber precursor. It was prepared by pyrolysis (S140). At this time, the cost-fusion process is a silicon (R _a SiX _{4 -a} , R is a radical containing a hydrogen or an alkyl group, X is a halogen element), boron (B), phosphorus (P), a vapor containing a metal compound, etc. The process of treating in gas (S120) and the process of hydrolyzing the surface in a gas containing water or ammonia (S130) were used.

As described above, the method of manufacturing silicon carbide hollow fiber was made by using a relatively expensive organic silazane polymer as a raw material, and through a complicated process such as cost fusion process and pyrolysis process, since silicon carbide is an incombustible material, This is because it cannot be easily produced by the first inorganic hollow fiber manufacturing method described above from the powder.

Therefore, there is a need for a method that can produce silicon carbide hollow fibers more simply and reliably by using silicon carbide powder as a raw material and through wet spinning and sintering methods.

SUMMARY OF THE INVENTION An object of the present invention is to provide a composition for producing silicon carbide hollow fiber which can produce a hollow fiber in silicon carbide which can be used as a microfiltration membrane or a membrane support by simply heat treating a polymer-silicon hollow fiber made from silicon carbide powder as a raw material. .

Another object of the present invention is to provide a method for producing silicon carbide hollow fiber more simply by using a wet spinning and sintering method using the composition.

Silicon carbide hollow fiber manufacturing composition according to an embodiment of the present invention for achieving the one object is 45 to 60% by weight of silicon carbide, 1 to 6% by weight of sintering aid, 6 to 17% by weight of polymer, dispersant 0.1 to 4 It is characterized by comprising a weight percent and the residual organic solvent.

At this time, the sintering aid is used as a sintering aid is selected from Y ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , Mullite (3Al ₂ O ₃ -2SiO ₂ ) and CaCO ₃ alone or in combination of two or more Can be.

Silicon carbide hollow fiber manufacturing method according to an embodiment of the present invention for achieving the above another object comprises the steps of: (a) preparing a slurry composition comprising a silicon carbide, a sintering aid, a polymer, a dispersant and an organic solvent; (b) wet spinning the composition using a spinneret; (c) washing and drying the resultant of step (b) to obtain a polymer-silicon carbide hollow fiber; And (d) heat-treating the polymer-silicon hollow fiber to remove the polymer and partially sinter the silicon carbide particles.

In this case, the heat treatment process may be made in air, it may be carried out at a temperature of 1000 ~ 1800 ℃.

The method for manufacturing silicon carbide hollow fiber according to the present invention is cheaper than the case of spinning and heat-treating an existing organic silazane polymer by using a wet spinning and sintering method and a sintering aid that enables silicon carbide sintering at low temperature. And there is an advantage that can be simply manufactured silicon carbide hollow fiber.

In addition, in the case of the silicon carbide hollow fiber manufactured by the manufacturing method according to the present invention, there is an advantage in the inorganic membrane manufacturing and regeneration process using a silicon carbide hollow fiber as a support through excellent thermal, mechanical, chemical properties.

In addition, the silicon carbide hollow fiber manufactured according to the present invention has a low coefficient of thermal expansion to prevent breakage of the layers due to thermal shock when introducing an intermediate layer and a separation layer when preparing an inorganic separator using silicon carbide hollow fiber as a support. There is an advantage. In particular, the effect is expected to be excellent when introducing a zeolite separation layer shrinking with increasing temperature.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, and only the embodiments make the disclosure of the present invention complete, and those skilled in the art to which the present invention pertains. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

Hereinafter, the silicon carbide hollow fiber manufacturing method according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Silicon Carbide Hollow fiber  Composition for Preparation

The composition for manufacturing silicon carbide hollow fiber according to the present invention includes silicon carbide, a sintering aid, a polymer, a dispersant, and an organic solvent to enable the production of hollow silicon carbide by wet spinning and sintering methods.

Silicon Carbide

Silicon carbide (SiC) is a raw material for producing silicon carbide hollow fiber according to the present invention.

Such silicon carbide is in the form of a powder, and the average particle diameter is preferably 0.1 to 10 mu m. If the average particle diameter is less than 0.1㎛, there are problems that the pores of the silicon carbide hollow yarn to be used as the microfiltration membrane or the separator support are too small and difficult to disperse uniformly, and when the average particle diameter exceeds 10㎛, the silicon carbide hollow yarn There are problems of pore size becoming too large and problems of low strength. That is, the silicon carbide powder should be adopted by selecting the particle size according to the pore structure of the silicon carbide hollow yarn to be desired.

The silicon carbide is preferably included in the content of 45 to 60% by weight of the total weight of the composition. If the silicon carbide is added in less than 45% by weight in the composition, there is a problem that the silicon carbide hollow fiber produced due to the content of silicon carbide is too low, on the contrary, if the content exceeds 60% by weight, the wetness of the composition is excessive due to the excessive viscosity of the composition There is a problem.

Sintering aid

The sintering aid applied to the present invention serves to provide a bonding force and mass transfer path between silicon carbide particles during the sintering process. A sintering aid to be applied to the present invention, _{Y 2 O 3, Al 2 O} 3, SiO 2, mullite _{(3Al 2 O 3 -2SiO 2)} , can be present, such as CaCO _3, alone or in combination of two or more kinds thereof Can be used.

As the sintering aid, more preferably, it can be proposed to use a mixed sintering aid in which mullite and CaCO 3 are mixed in a weight ratio of 5: 1. This substance of Si and C to the addition of CaCO ₃ is naturally react with the SiO ₂ layer formed on the Al ₂ O ₃ and SiO _2, and silicon carbide powder having a surface layer of the mullite to form a glass phase and enhance the binding force, constituting the SiC This is because it acts as a passage, and the excess mullite can produce silicon carbide hollow fiber having a low coefficient of thermal expansion even when a sintering aid is added due to the low coefficient of thermal expansion.

The sintering aid is preferably included in the content of 1 to 6% by weight of the total weight of the composition. If the content of the sintering aid is less than 1% by weight, there is a problem that the strength of the silicon carbide hollow fiber produced due to the amount of the sintering aid is too small, on the contrary, when the content of the sintering aid exceeds 6% by weight, the silicon carbide hollow fiber is used as a microfiltration membrane or a membrane support. Porosity of 35 to 50% will not be secured.

It is advantageous in terms of uniformity that the sintering aid is mixed with the silicon carbide powder in advance. The mixing process of the sintering aid and the silicon carbide is preferably using a dry vibration mill, the dry vibration mill may be performed for 1 to 24 hours at a rate of 200 ~ 900 cycles / min using a ceramic ball. If the dry vibration mill process is less than 200 cycles / min, less than 1 hour, it is difficult to obtain a uniform mixed powder, whereas if it is 900 cycles / min, more than 24 hours, excessive energy consumption occurs.

Polymer

The polymer applied in the present invention serves to determine the shape retention and microstructure of the silicon carbide hollow yarn. Such polymers may include polysulfone polymers, polyethersulfone polymers, polyacrylonitrile polymers, cellulose acetate polymers, polyvinylidene fluoride polymers, polyimide polymers, and the like. Or it can mix and use 2 or more types.

The polymer is preferably included in the content of 6 to 17% by weight of the total weight of the composition. When the content of the polymer is less than 6% by weight, wet spinning is difficult to maintain the shape of the hollow fiber is difficult, and when it exceeds 17% by weight, the viscosity of the composition is excessive, there is a problem that the wet spinning is not made well.

Dispersant

The dispersant applied in the present invention serves to improve dispersion of silicon carbide particles and to control the viscosity of the composition in preparing the composition. The dispersant applied to the present invention may be appropriately selected according to the type of the organic solvent and the polymer, and more preferably, in the case of using polysulfone as a polymer and N-methyl-2pyrrolidone (NMP) as the organic solvent, Polyvinylpyrrolidone (PVP), polyethylene glycol (PEG) and the like can be presented, these can be used alone or in combination of two or more.

The dispersant is preferably included in an amount of 0.1 to 4% by weight of the total weight of the composition. When the content of the dispersing agent is less than 0.1% by weight, the dispersion of the silicon carbide powder is low, it can not be uniformly wet spinning, while if the content of more than 4% by weight, the viscosity of the composition is too high to wet spinning well There is this.

Organic solvent

The organic solvent applied to the present invention plays a role of dispersing the polymer and the dispersant and at the same time serves as a dispersion medium of the silicon carbide and the sintering aid.

Organic solvents to be applied to the present invention are appropriately selected according to the type of polymer, dimethylformamide, N-methyl-2pyrrolidone, dimethylamide, dimethylacetamide, dimethyl sulfoxide, 1,4-dioxane, ethylene glycol Monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether and the like can be given, and these can be used alone or in combination of two or more thereof.

In addition, the composition for producing silicon carbide hollow fiber according to the present invention may further include an additive, the additive may be an antifoaming agent for removing bubbles in the composition. Antifoaming agent may be used octanol, cyclohexanol, ethylene glycol, nonionic antifoaming agent, silicone antifoaming agent and the like, preferably added in an amount of 1 part by weight or less based on 100 parts by weight of the composition. The addition of antifoaming agents helps to uniformly prepare polymer-silicon carbide hollow fibers in wet spinning by removing bubbles from the composition.

Silicon Carbide Hollow fiber  Manufacturing method

Figure 2 is a flow chart showing a method for producing silicon carbide hollow fiber according to the present invention using the wet spinning and sintering method.

Referring to Figure 2, the illustrated silicon carbide hollow fiber manufacturing method comprises a composition preparation step (S210), wet spinning step (S220), washing and drying step (S230) and sintering step (S240).

The composition preparing step (S210) is a step of preparing a composition in which a mixed powder, a polymer, and a dispersant of silicon carbide (SiC) and a sintering aid are dispersed in an organic solvent. The composition is a composition for producing silicon carbide hollow fiber comprising 45 to 60% by weight of silicon carbide, 1 to 6% by weight of sintering aid, 6 to 17% by weight of polymer, 0.1 to 4% by weight of dispersant and residual organic solvent. This can be

The composition may be mixed and dispersed by using a wet ball mill, and may further enhance dispersibility by using a rod mill.

The composition is prepared by dispersing and mixing the mixed powder of the silicon carbide and the sintering aid, polymer, and dispersant in an organic solvent in a slurry form, preferably using a ball mill, and the ball mill process using a ceramic ball. It is preferable to perform 4 to 168 hours at 100-400 rpm speed, and it is preferable that the obtained composition slurry was degassed for 4 to 24 hours at 30-80 degreeC. When the ball mill rotation speed is less than 100rpm, the ceramic ball is not easy to move from the bottom of the ball mill to the top, and when the ball mill rotation speed is 400rpm, because the ceramic ball rotates with the slurry, it is not possible to prepare a well dispersed composition slurry. In addition, when the mixed composition slurry is not subjected to a degassing process, bubbles are present in the composition slurry, thereby causing hollow fibers to burst in the wet spinning step.

Next, in the wet spinning step (S220), the composition slurry composed of the silicon carbide, the sintering aid, the polymer, the dispersant, and the organic solvent is wet-spun using a triple spinning nozzle. Three diameters that determine the outer and inner holes of the spinning nozzle should be selected in consideration of the inner diameter and the outer diameter of the desired silicon carbide hollow yarn, and the composition slurry is introduced into the outer hole of the triple spinning nozzle by a gear pump. The rotation speed of the gear pump is preferably 5-18 rpm. In addition, water should be introduced into the inner hole of the triple spinning nozzle by the LC pump, and the water inflow rate is 8-20 ml / min, and the inlet pressure is preferably 1-6 MPa.

Next, the hollow fiber-type slurry discharged through the triple spinning nozzle is dropped into the washing tank filled with water. The distance between the triple nozzle inlet and the bath water surface can be between 0 and 100 cm, and the organic solvent in the hollow fiber slurry spun by the water introduced into the triple nozzle internal hole and the water contained in the bath is exchanged for water. The polymer-silicon carbide hollow yarn is allowed to form.

Here, the polymer-silicon carbide hollow yarn may be wound with a spinning wheel by passing through a separate washing tank, and the polymer-silicon carbide hollow yarn wound on the spinning wheel may be subjected to another washing step (S230). Separate washing process of the polymer-silicon carbide hollow yarn wound on the spinning wheel is preferably carried out at 30 ~ 100 ℃ for 6 to 168 hours. In addition, the polymer-silicon carbide hollow fiber is preferably dried at 80 ~ 120 ℃ (S230) for 12 to 48 hours to completely remove the solvent-substituted water, the polymer-silicon hollow fiber is completed by the end of the drying step.

In addition, the wet spinning step (S220) and the washing and drying step (S230) may be performed by any method well known in the production of inorganic hollow fiber including silicon carbide.

Next, in the sintering step (S240) by sintering the polymer-silicon carbide hollow fiber, to produce silicon carbide hollow fiber.

At this time, the sintering step (S240) is made in an air atmosphere. In addition, the sintering step is performed for 1 to 48 hours at a temperature of 1000 ~ 1800 ℃, the exact heat treatment temperature and time is determined by the particle size of the selected silicon carbide powder and the type and amount of the selected sintering aid.

Unlike the silicon carbide hollow fiber manufactured by conventional pyrolysis, the silicon carbide hollow fiber produced by the manufacturing method according to the present invention is manufactured by sintering from silicon carbide powder as a raw material, and thus has a relatively low cost and high reliability. .

In addition, the silicon carbide hollow fiber manufactured by the manufacturing method according to the present invention has a low coefficient of thermal expansion, and thus, the intermediate layer and the separation layer of the intermediate layer due to thermal shock during the introduction of the separation layer using the prepared silicon carbide hollow fiber as a support. Fracture can be suppressed and the reliability of the separator can be enhanced.

Example

Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

Details not described herein are omitted because they can be inferred technically by those skilled in the art to which the present invention pertains.

Example  One

(1) production of compositions

950 g of silicon carbide powder having an average particle size of 0.65 μm, mullite 50 g, and 10 g of CaCO ₃ were manufactured through a dry vibration mill process for 4 hours at a rate of 500 cycles / min to prepare a mixed powder composed of silicon carbide and a sintering aid. At this time, mullite and CaCO ₃ are used as a sintering aid.

700 g of the above silicon carbide and sintering aid mixed powder, 100 g of polysulfone, 30 g of polyvinylpyrrolidone (PVP), 400 g of N-methyl-2-pyrrolidone (NMP) in 2000 ml volume of polypropylene Into the (PP) and using a 400g zirconia (ZrO ₂ ) ball ball mill at room temperature for 150 hours at 150rpm mixed and dispersed to prepare a composition slurry. The prepared composition slurry was degassed at 50 ° C. and atmospheric pressure for 12 hours to finally prepare a composition for wet spinning.

(2) wet spinning, washing and drying

The resultant composition slurry was passed through a triple nozzle having a diameter of 1.4-0.8-0.55 mm, and then dropped in a water washing bath to carry out solvent replacement. At this time, the composition slurry was introduced into the outer hole of the triple nozzle, the inlet speed was controlled by the gear pump, the rotation speed of the gear pump was 12rpm and the inlet pressure was 3 atm. In addition, water was introduced into the inner hole of the triple nozzle by using an LC pump. The inflow rate was 14 ml / min and the pressure was 5 MPa. The wash bath was filled with water and the temperature was room temperature. The distance between the triple nozzle inlet and the bath water surface was 15 cm. Thereafter, the obtained polysulfone-silicon carbide hollow yarn was washed with water at room temperature for 48 hours and dried at 100 ° C. for 24 hours to finally prepare polysulfone-silicon carbide hollow fiber.

3a shows a polysulfone-silicon carbide hollow fiber photograph, and FIG. 3b shows a scanning electron micrograph of the entire cross section of polysulfone-silicon carbide hollow yarn, and a polysulfone-silicon hollow hollow prepared in FIG. 3c. A high magnification scanning electron micrograph of the internal surface of the yarn was shown.

(3) heat treatment

The obtained polysulfone-silicon carbide hollow fiber was heat-treated at 1400 ° C. for 4 hours to remove the polysulfone polymer, and a partially sintered silicon carbide hollow fiber was prepared by the sintering aid. The temperature increase rate during the heat treatment was 4 ℃ / min and the cooling rate was 4 ℃ / min.

4A shows a photomicrograph of the silicon carbide hollow fiber prepared in FIG. 4B, and a scanning electron micrograph of the entire cross section of the silicon carbide hollow fiber is illustrated in FIG. 4B, and a photo of the inner surface of the silicon carbide hollow fiber manufactured in FIG. 4C is illustrated. .

As shown in Table 1, the silicon carbide hollow fiber produced by the present invention is expected to have a low coefficient of thermal expansion and a corresponding strength as compared with Al ₂ O ₃ , ZrO ₂ hollow fiber.

[Table 1]

matter Coefficient of Thermal Expansion (x 10 ^-6 / ℃) Flexural Strength (MPa) Al ₂ O ₃ 7.2 275-700 ZrO ₂ 10.5 800-1500 SiC 4.4 100-820

Although the above has been described with reference to one embodiment of the present invention, various changes and modifications can be made at the level of those skilled in the art. Such changes and modifications may belong to the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention will be determined by the claims described below.

1 is a flow chart showing a conventional silicon carbide hollow fiber manufacturing method using a cost-fusion and pyrolysis method.

Figure 2 is a flow chart showing a method for producing silicon carbide hollow fiber according to the present invention using the wet spinning and sintering method.

Figure 3a is a polysulfone-silicon carbide hollow fiber picture prepared according to the present invention.

Figure 3b is a scanning electron micrograph of the overall cross-section of the polysulfone-silicon carbide hollow yarn prepared according to the present invention.

Figure 3c is a high magnification scanning electron micrograph of the outer cross section of the polysulfone-silicon carbide hollow yarn prepared according to the present invention.

Figure 4a is a silicon carbide hollow fiber picture prepared according to the present invention.

Figure 4b is a scanning electron micrograph of the entire cross section of the silicon carbide hollow fiber prepared according to the present invention.

Figure 4c is a photograph of the outer cross section of the silicon carbide hollow yarn prepared according to the present invention.

Claims (12)

45 to 60% by weight of silicon carbide; 1 to 6% by weight of a mixed sintering aid so that the weight ratio of mullite and CaCO ₃ is 5: 1; 6 to 17% by weight of a polymeric binder including at least one selected from polysulfone, polyethersulfone, polyacrylonitrile, cellulose acetate, polyvinylidene fluoride and polyimide; 0.1-4% by weight of nonionic polymer dispersant; And A silicon carbide hollow fiber manufacturing composition comprising 20 to 50% by weight of an organic solvent. delete delete delete The method of claim 1, The organic solvent is dimethylformamide, N-methyl-2pyrrolidone, dimethylamide, dimethylacetamide, dimethyl sulfoxide, 1,4-dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol A composition for producing silicon carbide hollow fiber, which is selected from dimethyl ether, diethylene glycol diethyl ether, and diethylene glycol dibutyl ether. The method of claim 1, An antifoaming agent for removing air bubbles of the composition, 0.001 to 1 part by weight based on 100 parts by weight of the composition further comprises a silicon carbide hollow fiber manufacturing composition. (a) silicon carbide, the ratio by weight of mullite and CaCO ₃ 5: the sintering aid mixture to be 1, poly sulfone, polyether sulfone, polyacrylonitrile, cellulose acetate, polyvinylidene fluoride-based, polyimide Preparing a composition comprising a polymer binder , a nonionic polymer dispersant, and an organic solvent including at least one selected from the group consisting of a medi-based; (b) wet spinning the composition using a spinneret; (c) washing and drying the resultant of step (b) to form polymer-silicon carbide hollow fibers; (d) sintering the polymer-silicon carbide hollow fiber to form silicon carbide hollow fiber; and a method for manufacturing silicon carbide hollow fiber. The method of claim 7, wherein The step (d) is silicon carbide hollow fiber manufacturing method characterized in that proceeds in the temperature range of 1000 ℃ ~ 1800 ℃. 9. The method of claim 8, The step (d) is silicon carbide hollow fiber manufacturing method characterized in that for 1 to 48 hours. The method of claim 7, wherein The step (d) is silicon carbide hollow fiber manufacturing method, characterized in that made in the air atmosphere. 8. The method of claim 7, The composition comprises 45 to 60% by weight of silicon carbide, 1 to 6% by weight of sintering aid, 6 to 17% by weight of polymer binder, 0.1 to 4% by weight of water-soluble polymer dispersant and 20 to 50% by weight of organic solvent. Silicon carbide hollow fiber manufacturing method. Silicon carbide hollow fiber comprising a sintering aid mixed so that the weight ratio of silicon carbide, mullite and CaCO ₃ is 5: 1 .

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