CN113185312A - Porous SiC ceramic with high porosity, high strength and low thermal conductivity and preparation method thereof - Google Patents
Porous SiC ceramic with high porosity, high strength and low thermal conductivity and preparation method thereof Download PDFInfo
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- 239000000919 ceramic Substances 0.000 title claims abstract description 60
- 238000002360 preparation method Methods 0.000 title claims abstract description 22
- 239000011810 insulating material Substances 0.000 claims abstract description 8
- 238000007710 freezing Methods 0.000 claims description 80
- 230000008014 freezing Effects 0.000 claims description 80
- 229920000049 Carbon (fiber) Polymers 0.000 claims description 70
- 239000004917 carbon fiber Substances 0.000 claims description 70
- CRPUJAZIXJMDBK-UHFFFAOYSA-N camphene Chemical compound C1CC2C(=C)C(C)(C)C1C2 CRPUJAZIXJMDBK-UHFFFAOYSA-N 0.000 claims description 50
- 239000002002 slurry Substances 0.000 claims description 44
- 239000002243 precursor Substances 0.000 claims description 40
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 33
- PXRCIOIWVGAZEP-UHFFFAOYSA-N Primaeres Camphenhydrat Natural products C1CC2C(O)(C)C(C)(C)C1C2 PXRCIOIWVGAZEP-UHFFFAOYSA-N 0.000 claims description 25
- XCPQUQHBVVXMRQ-UHFFFAOYSA-N alpha-Fenchene Natural products C1CC2C(=C)CC1C2(C)C XCPQUQHBVVXMRQ-UHFFFAOYSA-N 0.000 claims description 25
- 229930006739 camphene Natural products 0.000 claims description 25
- ZYPYEBYNXWUCEA-UHFFFAOYSA-N camphenilone Natural products C1CC2C(=O)C(C)(C)C1C2 ZYPYEBYNXWUCEA-UHFFFAOYSA-N 0.000 claims description 25
- 239000000843 powder Substances 0.000 claims description 21
- 238000000498 ball milling Methods 0.000 claims description 20
- 229920003257 polycarbosilane Polymers 0.000 claims description 18
- 238000003756 stirring Methods 0.000 claims description 18
- 239000002131 composite material Substances 0.000 claims description 17
- 238000010438 heat treatment Methods 0.000 claims description 14
- 239000011268 mixed slurry Substances 0.000 claims description 14
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 12
- 239000002904 solvent Substances 0.000 claims description 12
- 238000000034 method Methods 0.000 claims description 10
- 238000004108 freeze drying Methods 0.000 claims description 7
- 239000013078 crystal Substances 0.000 claims description 6
- 238000005261 decarburization Methods 0.000 claims description 6
- 239000007788 liquid Substances 0.000 claims description 6
- 238000002844 melting Methods 0.000 claims description 6
- 230000008018 melting Effects 0.000 claims description 6
- 239000002184 metal Substances 0.000 claims description 6
- 229910052751 metal Inorganic materials 0.000 claims description 6
- 238000002156 mixing Methods 0.000 claims description 6
- 230000003647 oxidation Effects 0.000 claims description 6
- 238000007254 oxidation reaction Methods 0.000 claims description 6
- 238000000197 pyrolysis Methods 0.000 claims description 6
- 238000009210 therapy by ultrasound Methods 0.000 claims description 6
- 238000009777 vacuum freeze-drying Methods 0.000 claims description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 6
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 5
- 229910052802 copper Inorganic materials 0.000 claims description 5
- 239000010949 copper Substances 0.000 claims description 5
- 239000010453 quartz Substances 0.000 claims description 5
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 5
- 239000011148 porous material Substances 0.000 abstract description 4
- 239000000835 fiber Substances 0.000 abstract description 3
- 230000006835 compression Effects 0.000 abstract description 2
- 238000007906 compression Methods 0.000 abstract description 2
- 230000007547 defect Effects 0.000 abstract description 2
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 42
- 229910010271 silicon carbide Inorganic materials 0.000 description 42
- 229910010293 ceramic material Inorganic materials 0.000 description 4
- 239000000463 material Substances 0.000 description 3
- 239000012774 insulation material Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 235000015842 Hesperis Nutrition 0.000 description 1
- 235000012633 Iberis amara Nutrition 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000002657 fibrous material Substances 0.000 description 1
- 238000005187 foaming Methods 0.000 description 1
- 239000012510 hollow fiber Substances 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 230000003014 reinforcing effect Effects 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
- C04B35/56—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides
- C04B35/565—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on silicon carbide
- C04B35/571—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on silicon carbide obtained from Si-containing polymer precursors or organosilicon monomers
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- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
- C04B38/06—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof by burning-out added substances by burning natural expanding materials or by sublimating or melting out added substances
- C04B38/0605—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof by burning-out added substances by burning natural expanding materials or by sublimating or melting out added substances by sublimating
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Abstract
The invention discloses a porous SiC ceramic with high porosity, high strength and low thermal conductivity and a preparation method thereof. According to the preparation method, the hollow porous SiC fibers are introduced as the pore wall units, so that the compressive strength of the porous material is improved on the premise of ensuring the porous functionality and not reducing the porosity of the porous SiC, the defect that the existing porous SiC ceramic has low compression performance under high porosity is overcome, the thermal conductivity of the porous SiC ceramic is reduced to a certain extent, and the prepared porous SiC ceramic has wide application prospects in the field of aerospace heat-insulating materials.
Description
Technical Field
The invention belongs to the technical field of material preparation, and particularly relates to porous SiC ceramic with high porosity, high strength and low thermal conductivity and a preparation method thereof.
Background
The silicon carbide ceramic has the characteristics of small density, high mechanical property, good chemical stability and the like, so that the silicon carbide ceramic is widely applied to the fields of airplanes, rockets, machinery, mining industry, thermal engineering, metallurgy, individual protection and the like. At present, the application environment of the silicon carbide ceramic is relatively harsh, so higher requirements are also put forward on the preparation process of the silicon carbide ceramic. The aerospace aircraft is subjected to long-time pneumatic heating in the flying process, so that high temperature is generated due to surface friction heating, and in order to ensure the safety of an aircraft operation structure and internal instruments, high-efficiency heat insulation materials are required to prevent external heat from diffusing to the inside of the aircraft. The porous SiC ceramic material has the advantages of low density, high thermal shock resistance, high chemical stability and the like, and is an ideal light high-efficiency heat-insulating material.
The prior art for preparing porous SiC ceramics comprises the following steps: template method, gas foaming method, and freeze drying method. Lightweight, high porosity, and high strength are often the goals sought for porous ceramics, and porous ceramics made using these processes have high porosity rarely combined with high strength. Therefore, it is necessary to provide a preparation method for improving the material strength of the porous ceramic while ensuring the porosity of the porous ceramic.
In the design of the porous ceramic material, reinforcing and toughening by using a fiber material are effective ways for improving the fracture toughness of the ceramic material. The hollow fiber can not only improve the strength of the ceramic material, but also improve the specific surface area of the material to reduce the thermal conductivity. Therefore, the preparation method for exploring the porous SiC ceramic with high porosity, high strength and low thermal conductivity has wide application prospect.
Disclosure of Invention
The invention aims to provide a porous SiC ceramic with high porosity, high strength and low thermal conductivity and a preparation method thereof, and solves the problem of low compressive strength of the porous SiC ceramic with high porosity prepared by the prior art.
In order to achieve the purpose, the invention adopts the technical scheme that:
a preparation method of porous SiC ceramic with high porosity, high strength and low thermal conductivity is characterized by comprising the following steps:
step 1, ball milling carbon fibers:
selecting commercial carbon fibers, placing the commercial carbon fibers and absolute ethyl alcohol in a ball milling tank, and carrying out ball milling treatment in a roller ball mill to obtain stable mixed slurry;
step 2, prefabricating carbon fibers:
placing the mixed slurry prepared in the step 1 in a culture dish, and volatilizing absolute ethyl alcohol in the mixed slurry in the air to obtain prefabricated carbon fibers;
step 3, precursor slurry preparation:
placing camphene crystallized at room temperature into a beaker, placing the beaker into a water bath stirring pot, keeping the temperature at 60-80 deg.C to convert camphene into liquid, using as solvent, adding polycarbosilane powder and prefabricated carbon fiber, mixing to obtain precursor slurry, preparing n groups of precursor slurry with a mark T of more than or equal to 2 groups1，T2，T3，…，Tn-1，TnWherein the volume ratio of polycarbosilane powder to preformed carbon fiber in the nth group is less than that of the (n-1) th group;
step 4, heating and stirring:
stirring the precursor slurry prepared in the step (3) for 3-6h at the temperature of 60-80 ℃ to obtain uniform mixed precursor slurry;
and 5, freezing:
carrying out ultrasonic treatment on the precursor slurry obtained in the step 4 to remove air bubbles in the precursor slurry, carrying out freezing treatment, wherein directional freezing is adopted for freezing, a freezing mold is adopted for freezing, the side wall of the freezing mold is a tubular heat-insulating material, the bottom surface of the freezing mold is a heat-conducting metal, the freezing direction is vertical to the ground and upwards, n groups of the freezing molds are more than or equal to 2, and the groups are respectively marked as M1，M2，M3，…，Mn-1，MnThe cylindrical composite frozen bodies obtained after each freezing are respectively marked as F1，F2，F3，…，Fn-1，Fn；
Step 6, vacuum freeze drying:
subjecting the cylindrical composite frozen body F obtained in the step 5 tonFreeze-drying under vacuum to obtain cylindrical composite frozen body FnSublimating the solvent crystal to obtain a porous blank;
step 7, thermal oxidation curing:
curing the porous blank obtained in the step 6 in air at 180-200 ℃ for 1.5-2h to form a cross-linked three-dimensional network structure inside the porous blank so as to prevent the porous blank prepared in the step 6 from melting;
step 8, pyrolysis:
placing the cured porous blank prepared in the step 7 in a vacuum tube furnace, and pyrolyzing the porous blank for 1-2h at 1000-1600 ℃ under the protection of Ar gas to obtain carbon fiber reinforced porous SiC ceramic;
step 9, decarburization treatment:
and (3) placing the carbon fiber reinforced porous SiC ceramic prepared in the step (8) in a box-type furnace, and carrying out heat treatment at the temperature of 350-600 ℃ for 1-2h to separate the carbon fibers from the porous SiC ceramic, thereby obtaining the porous SiC ceramic with high porosity, high strength and low thermal conductivity.
Further, the diameter Dn of the commercial carbon fiber in the step 1 is 0.2-5 μm, and the length Ln is 20-100 μm.
Further, the rotating speed of the ball mill in the step 1 is 300r/min, and the ball milling time is 12h-24 h.
Further, in the step 3, 10g of camphene is taken, the total adding amount of the polycarbosilane powder and the prefabricated carbon fiber is 10-20 vol% of the adding amount of camphene, and the volume ratio of the polycarbosilane powder to the prefabricated carbon fiber is 2: 1.
Further, the directional freezing temperature in the step 5 is-40 to-20 ℃; the freezing mould is a cylindrical quartz tube with the inner diameter of 10mm and the height of 15mm, the freezing time t is more than or equal to 1h, and a cold source at the bottom is a heat-conducting copper plate.
A high porosity, high strength, low thermal conductivity porous SiC ceramic prepared by the method as described herein.
The invention has the beneficial effects that:
by introducing the hollow porous SiC fiber as the pore wall unit, the compressive strength of the porous material is improved on the premise of ensuring the porous functionality and not reducing the porosity of the porous SiC, the defect that the existing porous SiC ceramic has lower compression performance under high porosity is overcome, the thermal conductivity of the porous SiC ceramic is reduced to a certain extent, and the porous SiC ceramic has wide application prospect in the field of aerospace thermal insulation materials.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention more comprehensible, the present invention is described in detail with reference to the following embodiments.
A preparation method of porous SiC ceramic with high porosity, high strength and low thermal conductivity specifically comprises the following steps:
step 1, ball milling carbon fibers:
selecting commercial carbon fibers with the diameter Dn of 0.2-5 mu m and the length Ln of 20-100 mu m, placing the commercial carbon fibers and absolute ethyl alcohol into a ball milling tank, and carrying out ball milling treatment in a roller ball mill to obtain stable mixed slurry;
step 2, prefabricating carbon fibers:
placing the mixed slurry prepared in the step 1 into a culture dish, and volatilizing absolute ethyl alcohol in the slurry in the air to obtain prefabricated carbon fibers with the length less than Ln;
step 3, precursor slurry preparation:
placing 10g of camphene crystallized at room temperature into a beaker, placing the beaker into a water bath stirring pot, keeping the temperature at 60-80 ℃ to convert camphene into liquid, using the camphene as a solvent, then adding polycarbosilane powder and prefabricated carbon fibers, wherein the total addition amount of the polycarbosilane powder and the prefabricated carbon fibers is 10-20 vol% of the camphene addition amount, the volume ratio of the polycarbosilane powder to the prefabricated carbon fibers is 2:1, mixing to obtain precursor slurry, preparing n groups of precursor slurry with the number being more than or equal to 2, and marking the precursor slurry as T1，T2，T3，…，Tn-1，TnWherein the volume ratio of polycarbosilane powder to preformed carbon fiber in the nth group is less than that of the (n-1) th group;
step 4, heating and stirring:
stirring the precursor slurry prepared in the step 3 for 3-6h at the temperature of 60-80 ℃ to obtain uniform mixed precursor slurry;
and 5, freezing:
and (4) carrying out ultrasonic treatment on the precursor slurry obtained in the step (4) to remove bubbles in the precursor slurry, and then carrying out freezing treatment, wherein directional freezing is adopted for freezing, a freezing mold is adopted for freezing, the side wall of the freezing mold is made of a tubular heat-insulating material, the bottom surface of the freezing mold is made of a heat-conducting metal, and the freezing direction is vertical to the ground and is upward. The total n of the freezing molds is more than or equal to 2 groups and respectively marked as M1，M2，M3，…，Mn-1，MnThe cylindrical composite frozen bodies obtained after each freezing are respectively marked as F1，F2，F3，…，Fn-1，Fn；
Step 6, vacuum freeze drying:
subjecting the cylindrical composite frozen body F obtained in the step 5 tonFreeze-drying under vacuum to obtain cylindrical composite frozen body FnSublimating the solvent crystal to obtain a porous blank;
step 7, thermal oxidation curing:
curing the porous blank obtained in the step 6 in air at 180-200 ℃ for 1.5-2h to form a cross-linked three-dimensional network structure inside the porous blank so as to prevent the porous blank prepared in the step 6 from melting;
step 8, pyrolysis:
placing the cured porous blank prepared in the step 7 in a vacuum tube furnace, and pyrolyzing the porous blank for 1-2h at 1000-1600 ℃ under the protection of Ar gas to obtain carbon fiber reinforced porous SiC ceramic;
step 9, decarburization treatment
And (3) placing the carbon fiber reinforced porous SiC ceramic prepared in the step (8) in a box-type furnace, and carrying out heat treatment at the temperature of 350-600 ℃ for 1-2h to separate the carbon fibers from the porous SiC ceramic, thereby obtaining the porous SiC ceramic with high porosity, high strength and low thermal conductivity.
Example 1
A preparation method of porous SiC ceramic with high porosity, high strength and low thermal conductivity specifically comprises the following steps:
step 1, ball milling carbon fibers:
selecting commercial carbon fibers, wherein the diameter Dn is 0.2 mu m, and the length Ln is 20 mu m; putting commercial carbon fibers and absolute ethyl alcohol into a ball milling tank, and carrying out ball milling treatment in a roller ball mill for 12 hours, wherein the rotating speed of the ball mill is 300r/min, so as to obtain stable mixed slurry.
Step 2, prefabricating carbon fibers:
placing the mixed slurry prepared in the step 1 into a culture dish, and volatilizing absolute ethyl alcohol in the slurry in the air to obtain prefabricated carbon fibers with the length less than Ln;
step 3, precursor slurry preparation:
placing 10g of camphene crystallized at room temperature into a beaker, placing the beaker into a water bath stirring pot, keeping the temperature at 60 ℃ to convert camphene into liquid, taking the camphene as a solvent, then adding 0.6g of carbosilane powder and 0.4g of the prefabricated carbon fiber prepared in the step (2), and mixing to obtain precursor slurry, wherein the total adding amount of the polycarbosilane powder and the prefabricated carbon fiber is 10% of the adding amount of the camphene, and the volume ratio of the polycarbosilane powder to the prefabricated carbon fiber is 2: 1;
step 4, heating and stirring:
stirring the precursor slurry prepared in the step 3 for 3 hours at the temperature of 60 ℃ to obtain uniform mixed precursor slurry;
and 5, freezing:
carrying out ultrasonic treatment on the precursor slurry obtained in the step 4 to remove bubbles in the precursor slurry, carrying out freezing treatment, wherein directional freezing is adopted for freezing, a freezing mold is adopted for freezing, the side wall of the freezing mold is made of a tubular heat-insulating material, the bottom surface of the freezing mold is made of a heat-conducting metal, the freezing direction is vertical to the ground and upwards, n groups of the freezing molds are more than or equal to 2, and the groups are respectively marked as M1，M2，M3，…，Mn-1，MnThe cylindrical composite frozen bodies obtained after each freezing are respectively marked as F1，F2，F3，…，Fn-1，Fn(ii) a The directional freezing temperature is-20 ℃; the freezing mould is a cylindrical quartz tube with the inner diameter of 10mm and the height of 15mm, the freezing time t is 1.5h, and a bottom cold source is a heat-conducting copper plate.
Step 6, vacuum freeze drying
Subjecting the cylindrical composite frozen body F obtained in the step 5 tonFreeze-drying under vacuum to obtain cylindrical composite frozen body FnSublimating the solvent crystal to obtain a porous blank;
step 7, thermal oxidation curing
Carrying out curing treatment on the porous blank obtained in the step 6 at 180 ℃ for 1.5 in the air, so that a cross-linked three-dimensional network structure is formed in the porous blank to realize non-melting of the porous blank obtained in the step 6;
step 8, pyrolysis:
placing the cured sample prepared in the step 7 in a vacuum tube furnace, and pyrolyzing for 1h at 1000 ℃ under the protection of Ar gas to obtain carbon fiber reinforced porous SiC ceramic;
step 9, decarburization treatment:
and (3) placing the carbon fiber reinforced porous SiC ceramic prepared in the step (8) in a box type furnace, and carrying out heat treatment for 1h at the temperature of 600 ℃ to separate the carbon fibers from the porous SiC ceramic, thereby obtaining the high porosity and high strength. Porous SiC ceramics of low thermal conductivity.
Example 2
A preparation method of porous SiC ceramic with high porosity, high strength and low thermal conductivity specifically comprises the following steps:
step 1, ball milling carbon fibers:
selecting commercial carbon fibers, wherein the diameter Dn is 5 mu m, and the length Ln is 100 mu m; putting commercial carbon fiber and absolute ethyl alcohol into a ball milling tank, and carrying out ball milling treatment in a roller ball mill for 24 hours, wherein the rotating speed of the ball mill is 300r/min, so as to obtain stable mixed slurry;
step 2, prefabricating carbon fibers:
placing the mixed slurry prepared in the step 1 into a culture dish, and volatilizing absolute ethyl alcohol in the slurry in the air to obtain prefabricated carbon fibers with the length less than Ln;
step 3, precursor slurry preparation:
placing 10g of camphene crystallized at room temperature into a beaker, placing the beaker into a water bath stirring pot, keeping the temperature at 80 ℃, converting camphene into liquid, using the camphene as a solvent, then adding 0.865g of carbosilane powder and 0.635g of the prefabricated carbon fiber prepared in the step 2, and mixing to obtain precursor slurry, wherein the total adding amount of the polycarbosilane powder and the prefabricated carbon fiber is 15 vol% of the adding amount of the camphene, and the volume ratio of the polycarbosilane powder to the prefabricated carbon fiber is 2: 1;
step 4, heating and stirring:
stirring the precursor slurry prepared in the step 3 at 80 ℃ for 6 hours to obtain uniform mixed precursor slurry;
and 5, freezing:
carrying out ultrasonic treatment on the precursor slurry obtained in the step 4 to remove bubbles in the precursor slurry, carrying out freezing treatment, wherein directional freezing is adopted for freezing, a freezing mold is adopted for freezing, the side wall of the freezing mold is made of a tubular heat-insulating material, the bottom surface of the freezing mold is made of a heat-conducting metal, the freezing direction is vertical to the ground and upwards, n groups of the freezing molds are more than or equal to 2, and the groups are respectively marked as M1，M2，M3，…，Mn-1，MnThe cylindrical composite frozen bodies obtained after each freezing are respectively marked as F1，F2，F3，…，Fn-1，Fn(ii) a The directional freezing temperature is-40 ℃; the freezing mould is a cylindrical quartz tube with the inner diameter of 10mm and the height of 15mm, the freezing time t is 1h, and a cold source at the bottom is a heat-conducting copper plate;
step 6, vacuum freeze drying:
subjecting the cylindrical composite frozen body F obtained in the step 5 tonFreeze-drying under vacuum to obtain cylindrical composite frozen body FnSublimating the solvent crystal to obtain a porous blank;
step 7, thermal oxidation curing:
curing the porous blank obtained in the step 6 in air at 200 ℃ for 2h to form a cross-linked three-dimensional network structure inside the porous blank so as to prevent the porous blank obtained in the step 6 from melting;
step 8, pyrolysis:
placing the cured porous blank prepared in the step 7 in a vacuum tube furnace, and pyrolyzing for 2h at 1600 ℃ under the protection of Ar gas to obtain carbon fiber reinforced porous SiC ceramic;
step 9, decarburization treatment:
and (3) placing the carbon fiber reinforced porous SiC ceramic prepared in the step (8) in a box-type furnace, and carrying out heat treatment for 2h at 450 ℃ to separate the carbon fibers from the porous SiC ceramic, thereby obtaining the high porosity and high strength. Porous SiC ceramics of low thermal conductivity.
Example 3
A preparation method of porous SiC ceramic with high porosity, high strength and low thermal conductivity specifically comprises the following steps:
step 1, ball milling carbon fibers:
selecting commercial carbon fibers, wherein the diameter Dn is 2 mu m, the length Ln is 50 mu m, placing the fibers and absolute ethyl alcohol into a ball milling tank, and carrying out ball milling treatment for 22 hours in a roller ball mill at the rotating speed of 300r/min to obtain stable mixed slurry;
step 2, prefabricating carbon fibers:
placing the mixed slurry prepared in the step 1 into a culture dish, and volatilizing absolute ethyl alcohol in the slurry in the air to obtain prefabricated carbon fibers with the length less than Ln;
step 3, preparing precursor slurry
Taking 10g of camphene crystallized at room temperature, placing the camphene in a beaker, placing the beaker in a water bath stirring pot, keeping the temperature at 70 ℃ to convert the camphene into liquid, taking the camphene as a solvent, then adding 1.154g of carbosilane powder and 0.836g of prefabricated carbon fiber prepared in the step 2, and mixing to obtain precursor slurry, wherein the total adding amount of the polycarbosilane powder and the prefabricated carbon fiber is 20 vol% of the adding amount of the camphene, and the volume ratio of the polycarbosilane powder to the prefabricated carbon fiber is 2: 1;
step 4, heating and stirring:
stirring the precursor slurry prepared in the step 3 for 4 hours at 70 ℃ to obtain uniform mixed precursor slurry;
and 5, freezing:
performing ultrasonic treatment on the precursor slurry obtained in the step 4 to remove air bubbles in the precursor slurry, performing freezing treatment, wherein directional freezing is adopted for freezing, a freezing mold is adopted for freezing, the side wall of the freezing mold is a tubular heat-insulating material,the bottom surface is made of heat-conducting metal, the freezing direction is vertical to the ground surface, and the total n of freezing molds is more than or equal to 2 groups, which are respectively marked as M1，M2，M3，…，Mn-1，MnThe frozen bodies obtained after each freezing are respectively marked as F1，F2，F3，…，Fn-1，Fn(ii) a The directional freezing temperature is-30 ℃; the freezing mould is a cylindrical quartz tube with the inner diameter of 10mm and the height of 15mm, and the freezing time t is 1 h; the bottom cold source is a heat-conducting copper plate;
step 6, vacuum freeze drying:
subjecting the cylindrical composite frozen body F obtained in the step 5 tonFreeze-drying under vacuum to obtain cylindrical composite frozen body FnSublimating the solvent crystal to obtain a porous blank;
step 7, thermal oxidation curing:
carrying out curing treatment on the porous blank obtained in the step 6 in air at 190 ℃ for 1.6h to form a cross-linked three-dimensional network structure in the porous blank so as to prevent the porous blank prepared in the step 6 from melting;
step 8, pyrolysis:
placing the cured porous blank prepared in the step 7 in a vacuum tube furnace, and pyrolyzing at 1500 ℃ for 1.5h under the protection of Ar gas to obtain carbon fiber reinforced porous SiC ceramic;
step 9, decarburization treatment:
and (3) placing the carbon fiber reinforced porous SiC ceramic prepared in the step (8) in a box type furnace, and carrying out heat treatment at 350 ℃ for 1.5h to separate the carbon fibers from the porous SiC ceramic, thereby obtaining the high porosity and high strength. Porous SiC ceramics of low thermal conductivity.
While specific embodiments of the invention have been described above, it will be appreciated by those skilled in the art that this is by way of example only, and that the scope of the invention is defined by the appended claims. Various changes and modifications to these embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention, and these changes and modifications are within the scope of the invention.
Claims (6)
1. A preparation method of porous SiC ceramic with high porosity, high strength and low thermal conductivity is characterized by comprising the following steps:
step 1, ball milling carbon fibers:
selecting commercial carbon fibers, placing the commercial carbon fibers and absolute ethyl alcohol in a ball milling tank, and carrying out ball milling treatment in a roller ball mill to obtain stable mixed slurry;
step 2, prefabricating carbon fibers:
placing the mixed slurry prepared in the step 1 in a culture dish, and volatilizing absolute ethyl alcohol in the mixed slurry in the air to obtain prefabricated carbon fibers;
step 3, precursor slurry preparation:
placing camphene crystallized at room temperature into a beaker, placing the beaker into a water bath stirring pot, keeping the temperature at 60-80 deg.C to convert camphene into liquid, using as solvent, adding polycarbosilane powder and prefabricated carbon fiber, mixing to obtain precursor slurry, preparing n groups of precursor slurry with a mark T of more than or equal to 2 groups1，T2，T3，…，Tn-1，TnWherein the volume ratio of polycarbosilane powder to preformed carbon fiber in the nth group is less than that of the (n-1) th group;
step 4, heating and stirring:
stirring the precursor slurry prepared in the step (3) for 3-6h at the temperature of 60-80 ℃ to obtain uniform mixed precursor slurry;
and 5, freezing:
carrying out ultrasonic treatment on the precursor slurry obtained in the step 4 to remove air bubbles in the precursor slurry, carrying out freezing treatment, wherein directional freezing is adopted for freezing, a freezing mold is adopted for freezing, the side wall of the freezing mold is a tubular heat-insulating material, the bottom surface of the freezing mold is a heat-conducting metal, the freezing direction is vertical to the ground and upwards, n groups of the freezing molds are more than or equal to 2, and the groups are respectively marked as M1，M2，M3，…，Mn-1，MnThe cylindrical composite frozen bodies obtained after each freezing are respectively marked as F1，F2，F3，…，Fn-1，Fn；
Step 6, vacuum freeze drying:
subjecting the cylindrical composite frozen body F obtained in the step 5 tonFreeze-drying under vacuum to obtain cylindrical composite frozen body FnSublimating the solvent crystal to obtain a porous blank;
step 7, thermal oxidation curing:
curing the porous blank obtained in the step 6 in air at 180-200 ℃ for 1.5-2h to form a cross-linked three-dimensional network structure inside the porous blank so as to prevent the porous blank prepared in the step 6 from melting;
step 8, pyrolysis:
placing the cured porous blank prepared in the step 7 in a vacuum tube furnace, and pyrolyzing the porous blank for 1-2h at 1000-1600 ℃ under the protection of Ar gas to obtain carbon fiber reinforced porous SiC ceramic;
step 9, decarburization treatment:
and (3) placing the carbon fiber reinforced porous SiC ceramic prepared in the step (8) in a box-type furnace, and carrying out heat treatment at the temperature of 350-600 ℃ for 1-2h to separate the carbon fibers from the porous SiC ceramic, thereby obtaining the porous SiC ceramic with high porosity, high strength and low thermal conductivity.
2. The method for preparing the porous SiC ceramic with high porosity, high strength and low thermal conductivity according to claim 1, wherein the diameter Dn of the commercial carbon fiber in step 1 is 0.2-5 μm, and the length Ln is 20-100 μm.
3. The method for preparing the porous SiC ceramic with high porosity, high strength and low thermal conductivity according to claim 1, wherein the rotation speed of the ball mill in the step 1 is 300r/min, and the ball milling time is 12h-24 h.
4. The method for preparing the porous SiC ceramic with high porosity, high strength and low thermal conductivity according to claim 1, wherein 10g of camphene is taken in step 3, the total adding amount of polycarbosilane powder and prefabricated carbon fiber is 10-20 vol% of the adding amount of camphene, and the volume ratio of polycarbosilane powder to prefabricated carbon fiber is 2: 1.
5. The method for preparing the porous SiC ceramic with high porosity, high strength and low thermal conductivity according to claim 1, wherein the directional freezing temperature in the step 5 is-40 to-20 ℃; the freezing mould is a cylindrical quartz tube with the inner diameter of 10mm and the height of 15mm, the freezing time t is more than or equal to 1h, and a cold source at the bottom is a heat-conducting copper plate.
6. A porous SiC ceramic with high porosity, high strength and low thermal conductivity, which is characterized in that the porous SiC ceramic with high porosity, high strength and low thermal conductivity is prepared by adopting the preparation method of the porous SiC ceramic with high porosity, high strength and low thermal conductivity as claimed in any one of claims 1 to 5.
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