An electrocaloric / joule heating porous c / c composite material, a preparation method and application thereof

Abstract

This invention belongs to the field of composite material technology, specifically relating to an electrothermal / Joule-thermal porous C / C composite material, its preparation method, and its applications. The composite material is composed of carbon fibers, an industrial carbon matrix, and a bio-carbon matrix, with the carbon fibers and bio-carbon matrix bonded together by the industrial carbon matrix. The mass percentages of the three components are: carbon fibers 10-60 wt%, bio-carbon matrix 10-50 wt%, and industrial carbon matrix 5-80 wt%. The electrothermal / Joule-thermal porous C / C composite material of this invention is rich in bio-carbon matrix, which retains the porous structure of biomass for adsorption. It also achieves near-net-shape molding at low density, resulting in low cost. It possesses excellent electrothermal properties, adsorption capacity, and mechanical strength. After being energized, it heats up rapidly, exhibits a uniform and stable thermal field, and shows no aging issues. It can be used to manufacture electrothermal elements for indoor heating and outdoor de-icing, and can also be used as a reusable adsorption element for removing odors and harmful gases.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber composite material technology, specifically relating to an electrothermal / Joule-thermal porous C / C composite material, its preparation method, and its application. Background Technology

[0002] Carbon-based materials can withstand temperatures above 2000℃, have an electrothermal efficiency of over 95%, and emit far-infrared rays that are beneficial to the human body. Therefore, carbon-based materials are widely used as heating elements in various high-temperature furnaces, while carbon fiber sheet-like electrothermal films / papers / sheets are highly favored in fields such as indoor heating and outdoor de-icing.

[0003] C / C composite materials are composed of a single carbon element, and their strength and toughness are higher than those of graphite. They also exhibit pseudoplastic fracture characteristics and are gradually replacing graphite in key components in the thermal field. Compared with commercially available carbon fiber polymer-based electrothermal films / papers / sheets, they have advantages such as non-aging, no emission of harmful gases during service, high heating temperature, and corrosion resistance.

[0004] Currently, C / C composite materials are mainly used in aircraft hot-end structural components, high-performance braking components, and thermal field structural components. They are also used as electrical contacts for pantograph sliders in high-speed railways, high-performance internal combustion engine pistons, and artificial bones. Their density is typically higher than 1.4 g / cm³. 3 Most of them are boards or blocks with a thickness greater than 5mm.

[0005] Using C / C composite materials, a cutting-edge engineering material, as electric heating elements for daily heating is not only lighter than metal heating wires, but also significantly energy-efficient and has certain health benefits. However, there are the following problems: (1) When used as a planar heating element, the cost is much higher than that of polymer-based carbon fiber electric heating film / paper / sheet, and the high density and excessive thickness lead to material waste or the need for post-processing to thin it, resulting in complicated molding; (2) When using sheet-like preforms, warping and shrinkage deformation occur during carbonization, leading to uncontrolled molding; (3) When used for filtration and adsorption, the porosity is insufficient. For example, the prior art CN202210426502.5 proposes a graphite-based electric heating material and its preparation method and electric heating equipment. The graphite-based electric heating material is composed of carbon fiber, graphene and worm-like graphite, with a density of 1.5~2.0 g / cm³. 3 It has a flexible texture and is resistant to aging, but it is expensive, dense, and has few pores. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides an electrothermal / Joule-thermal porous C / C composite material, its preparation method, and its applications. By introducing low-cost biochar with naturally occurring multi-level and multi-morphological pores into the C / C composite material, its porosity is increased and manufacturing costs are reduced. Furthermore, by leveraging the characteristics of the biochar source, the material is dried, cured, and carbonized under semi-constant volume or constant pressure conditions after molding, achieving near-net-shape forming. The main problem this invention aims to solve is developing a low-cost, low-density, high-porosity C / C composite material for everyday heating electric heating elements.

[0007] This invention is specifically achieved through the following technical solution: An electrothermal / joule-heated porous C / C composite material is a dual-carbon matrix porous composite sheet composed of carbon fibers, an industrial carbon matrix, and a bio-carbon matrix, wherein the carbon fibers and the bio-carbon matrix are bonded together by the industrial carbon matrix. The mass percentages of the three components are as follows: carbon fiber 10-60 wt%, bio-carbon matrix 10-50 wt%, and industrial carbon matrix 5-80 wt%, and the sum of the mass percentages of the three components is 100%. Carbon fiber is used to enhance the mechanical properties of the composite material. The bio-carbon matrix retains the original pore structure characteristics of the carbon source of the bio-carbon matrix. The bio-carbon matrix provides some pores. The porous bio-carbon matrix can increase the micropores used for adsorption. The industrial carbon matrix is ​​used to bond the carbon fiber and the bio-carbon matrix. In this invention, an electrothermal / Joule-thermal porous C / C composite material made from carbon fiber, industrial carbon matrix, and bio-carbon matrix is ​​provided. Carbon fiber has a large specific surface area and high electrothermal conversion efficiency. The resistivity of industrial carbon matrix is ​​lower than that of bio-carbon matrix. Therefore, industrial carbon matrix has better conductivity than bio-carbon matrix. By adjusting the ratio of the two, the resistance of the electrothermal / Joule-thermal porous C / C composite material can be adjusted.

[0008] Furthermore, the thickness of the dual-carbon matrix porous composite sheet is 0.1-5 mm, the width is 50-2000 mm, and the density is 0.2-1.2 g / cm³. 3 Materials outside the above range are prone to breakage, insufficient porosity, and chipping.

[0009] Furthermore, the dual-carbon matrix porous composite sheet has a thickness of 0.5-2mm, a width of 200-1000mm, and a density of 0.3-0.9g / cm³. 3 This thickness facilitates molding and provides a certain level of strength and rigidity; too thin a thickness makes molding difficult and causes breakage. This width is a suitable width determined based on specific applications such as heating for household appliances and buildings. The density is an optimal range determined by considering electrothermal properties, strength, and adsorption properties.

[0010] Furthermore, the carbon source for the industrial carbon matrix is ​​selected from one or a combination of several of resin carbon, pitch carbon, sugar carbon, and pyrolytic carbon.

[0011] Furthermore, in order to improve the adsorption capacity of industrial carbon matrix, the carbon source of industrial carbon matrix can also be foamed. The purpose of foaming is to increase the porosity after fermentation, thereby improving the adsorption capacity. The foaming treatment method is as follows: mix the carbon source of industrial carbon matrix with foaming agent and heat it at 60-220℃ for 0.5-3h to obtain porous industrial carbon matrix carbon source. The foaming agent is selected from baking soda or yeast powder.

[0012] Furthermore, to improve the conductivity of industrial carbon matrix, the carbon source of industrial carbon matrix can be modified with conductive carbon materials. The conductive carbon materials are selected from carbon nanotubes, graphene, diamond, graphite or carbon black. The modification method is to mix industrial carbon matrix with carbon materials to obtain conductive industrial carbon matrix carbon source.

[0013] Furthermore, the bio-carbon matrix is ​​selected from porous plant carbon or porous animal carbon, and the bio-carbon matrix retains the original pore structure characteristics of the bio-carbon source.

[0014] Porous plant carbon sources are derived from one or more of the roots, stems, leaves, flowers, and fruits of plants. The preferred sources are grasses rich in pores, such as wood, bamboo poles, sugarcane, rice, wheat, corn, sorghum, and cotton stalks; fruit shells such as coconut shells, walnut shells, and hazelnut shells; fruit peels such as grapefruit peels; lotus roots and lotus leaves; and fruit pits such as peach pits and jackfruit pits. Porous animal carbon sources are derived from one or more of the following biomass sources: animal bones, shells, horns, meat, internal organs, skin, hair, and feces. Preferably, porous animal bones, skins, and hair, as well as cattle and sheep horns, turtle shells, cicada molts, silkworm silk, egg membranes, and human hair are preferred.

[0015] Furthermore, the carbon source for bio-based carbon can also be selected from kitchen waste that has undergone screening and purification.

[0016] This invention also protects a method for preparing electrothermal / Joule-thermal porous C / C composite materials, comprising the following steps: S1. The carbon source of the bio-carbon matrix is ​​repeatedly crushed by cutting, chopping, smashing, squeezing, pressing and grinding to obtain bio-carbon source slurry or powder; S2, Multi-component mixing: The bio-carbon source slurry or powder from step S1 is mixed evenly with the carbon source of carbon fiber and industrial carbon matrix to obtain a mixture; here, the carbon source of industrial carbon matrix can also be replaced with porous industrial carbon matrix carbon source or conductive industrial carbon matrix carbon source. S3, Laying out the mold, leveling, and drying: Lay the mixture from step S2 into the sheet mold, level it, and then dry it under semi-constant volume or constant pressure conditions to obtain the composite material sheet preform. S4. Carbonization and shaping: The composite material sheet preform from step S3 is cured and carbonized under semi-constant volume or constant pressure conditions to obtain an electrothermal / Joule-thermal porous C / C composite material.

[0017] Furthermore, in step S1, the carbonized biocarbon can be crushed and sieved by methods such as smashing, squeezing, pressing and grinding to obtain biocarbon source powder with a specific particle size (retaining pore characteristics), so as to use biocarbon source powder to replace the carbon source of biocarbon matrix for the preparation of electrothermal / Joule thermal porous C / C composite material.

[0018] Furthermore, in step S2, when using short-cut carbon fibers, the fibers, bio-carbon source, and industrial carbon source are mixed by stirring, ball milling, and repeated rolling.

[0019] Furthermore, in step S2, when using two-dimensional fiber fabric as carbon fiber, the carbon source of the bio-carbon matrix and the carbon source of the industrial carbon matrix can be mixed evenly by stirring and ball milling, and then coated onto the surface of carbon fiber woven fabric, braided fabric or carbon felt fiber two-dimensional fabric with a thickness of less than 5 mm.

[0020] Furthermore, in step S3, the mixture laid on the mold is leveled by using a rolling or scraping method.

[0021] Furthermore, in step S4, curing-carbonization is carried out under semi-constant volume conditions that control the width and thickness, or under a pressure of 2-20 kPa perpendicular to the sheet direction.

[0022] Furthermore, in step S4, curing-carbonization is carried out under semi-constant volume conditions with controlled thickness, or under a pressure of 0.1-1 kPa perpendicular to the sheet direction.

[0023] Furthermore, in step S4, the curing conditions are: curing at 120-240℃ for 0.5-3 hours, and the carbonization conditions are: carbonization at 800-1300℃ for 2 hours.

[0024] The semi-constant volume operation involves clamping the mixture between two clamps, detachably connecting the two clamps, and then performing the curing-carbonization operation. Under semi-constant volume or constant pressure conditions, this avoids warping, wrinkling, and deformation during the curing-carbonization process. It also ensures that the electrothermal / Joule-thermal porous C / C composite material can only expand in the horizontal direction and not in the thickness direction.

[0025] This invention also protects a densified electrothermal / Joule-thermal porous C / C composite material. The electrothermal / Joule-thermal porous C / C composite material is obtained by impregnation pyrolysis or chemical vapor deposition. By employing impregnation pyrolysis or chemical vapor deposition, a carbon layer is formed on the surface of the electrothermal / Joule-thermal porous C / C composite material, and carbon material is added to the interior of the electrothermal / Joule-thermal porous C / C composite material, thereby improving the density and strength of the electrothermal / Joule-thermal porous C / C composite material. The impregnation pyrolysis method is as follows: the electrothermal / Joule-thermal porous C / C composite material is immersed in the carbon source of the industrial carbon matrix, and then taken out and subjected to pyrolysis treatment. The pyrolysis conditions are: pyrolysis at 800-1300℃ for 0.5-3h. The operation of chemical vapor deposition is as follows: using a 0.4-1.2m... 3 A gaseous carbon source is introduced at a flow rate of / h, and carbon is deposited on the surface of the electrothermal / Joule-thermal porous C / C composite material at 900-1280℃. The gaseous carbon source is selected from methane, propylene, or alcohol. The carbon obtained after high-temperature pyrolysis of the gaseous carbon source is introduced into the electrothermal / Joule-thermal porous C / C composite material by chemical vapor deposition.

[0026] The present invention also provides a method for purifying composite materials, wherein the composite materials include electrothermal / Joule-thermal porous C / C composite materials and densified electrothermal / Joule-thermal porous C / C composite materials; The purification method includes the following steps: the composite material is heat-treated at 1500-2500℃ for 1-5 hours. After purification, the ash content in the composite material is reduced, the odor is removed, and the purity is improved.

[0027] Furthermore, the electrothermal / Joule-thermal porous C / C composite material or the densified electrothermal / Joule-thermal porous C / C composite material of the present invention can be used in the following scenarios: together with insulators, connecting wires, power supplies, switches, thermostats, and fuses, it can be used to form an electric heater for indoor heating or outdoor de-icing.

[0028] Furthermore, the electrothermal / Joule-thermal porous C / C composite material or the densified electrothermal / Joule-thermal porous C / C composite material of the present invention can be used in the following scenarios: together with insulators, connecting wires, power supplies, switches, thermostats, and fuses, it can form an adsorption-type purifier that can be recycled to remove odors and harmful gases.

[0029] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses inexpensive straw, renewable bamboo poles, and kitchen waste as carbon sources for the bio-carbon matrix, which can effectively reduce the production cost of electrothermal / Joule-thermal porous C / C composite materials.

[0030] 2. The preparation method of the electrothermal / Joule-thermal porous C / C composite material of the present invention adopts the simultaneous carbonization of the carbon source of the biological carbon matrix and the carbon source of the industrial carbon matrix, thereby reducing the energy consumption of heat treatment, shortening the process cycle, and thus reducing the production cost.

[0031] 3. The preparation method of the electrothermal / Joule-thermal porous C / C composite material of the present invention adopts porous bio-carbon modification combined with semi-constant volume or surface micro-pressure carbonization technology to ensure that the obtained sheet retains low density and high porosity while achieving near-net-shape molding.

[0032] 4. The electrothermal / Joule-thermal porous C / C composite material obtained by this invention has certain strength and rigidity, and can be post-processed by carving, such as carving into handicrafts.

[0033] 5. The present invention can also process the carbon source of the industrial carbon matrix to improve the conductivity or adsorption capacity of the industrial carbon matrix, and then modify the carbon source of the industrial carbon matrix according to the application requirements of the electrothermal / Joule thermal porous C / C composite material.

[0034] 6. This invention can also densify the obtained electrothermal / Joule-thermal porous C / C composite material by using impregnation pyrolysis or chemical vapor deposition to increase its density and strength. Testing shows that after densification, the density of the electrothermal / Joule-thermal porous C / C composite material can be increased from 0.2-0.6 g / cm³. 3 Increased to 1.2g / cm 3 .

[0035] 7. The present invention can also purify the obtained electrothermal / joule-thermal porous C / C composite material or the densified electrothermal / joule-thermal porous C / C composite material to reduce odor and ash content, and further improve the adsorption performance and electrical and thermal conductivity of the composite material. Attached Figure Description

[0036] Figure 1 This is a photograph of the electrothermal / Joule-thermal porous C / C composite material of Embodiment 1 of the present invention; Figure 2 This is a microstructure diagram of the electrothermal / Joule-thermal porous C / C composite material of Embodiment 1 of the present invention; Figure 3 The figure shows the tensile stress-strain curve of the electrothermal / Joule-heated porous C / C composite material in Embodiment 1 of the present invention; the inset is a photograph of the specimen being tested in a tensile testing machine. Figure 4 This is an electrothermal curve of the electrothermal / Joule-thermal porous C / C composite material of Embodiment 2 of the present invention; Figure 5These are microscopic morphology images of the electrothermal / Joule-thermal porous C / C composite materials of Examples 1 and 3 of the present invention; wherein, (a) is a microscopic morphology image of the sample of Example 1, and (b) is a microscopic morphology image of the sample of Example 3. Figure 6 The images show the microstructure of the electrothermal / Joule-thermal porous C / C composite materials of Examples 1 and 4 of the present invention; wherein, (a) is the microstructure of the sample of Example 1 and (b) is the microstructure of the sample of Example 4. Detailed Implementation

[0037] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0038] Unless otherwise specified, the experimental and detection methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0039] This invention provides an electrothermal / Joule-heated porous C / C composite material and its preparation method. By using inexpensive straw, renewable bamboo poles, and kitchen waste as carbon sources for the bio-carbon matrix, the production cost is reduced from the perspective of raw materials. Furthermore, carbonizing the bio-carbon matrix can yield porous plant carbon or porous animal carbon, resulting in an electrothermal / Joule-heated porous C / C composite material with high porosity, which can be used for filtration and adsorption.

[0040] This invention mixes carbon sources from biological carbon matrix and industrial carbon matrix and then performs simultaneous carbonization, which reduces the high energy consumption caused by multiple heat treatments and shortens the process cycle, thereby further reducing costs from the perspective of optimizing the manufacturing process.

[0041] The electrothermal / Joule-thermal porous C / C composite material obtained by the method of this invention has a low density, ranging from 0.2 to 1.2 g / cm³. 3 The preparation process mainly adopts semi-constant volume or surface micro-pressure carbonization technology, which not only avoids product warping and wrinkling problems, but also obtains low-density products.

[0042] Electrothermal / Joule-thermal porous C / C composite materials are prepared according to the following steps: S1. Preparation of bio-carbon source slurry / powder: Prepare a bio-carbon matrix carbon source rich in pores, such as grass, wood, bamboo poles, straw, animal bones, skin, and horns. Repeatedly crush it by cutting, chopping, smashing, squeezing, pressing, and grinding to obtain a slurry or powder with a scale of microns or millimeters. This facilitates subsequent mixing with other components and ensures that the porous structure of the bio-carbon matrix carbon source is not completely destroyed, thus obtaining a bio-carbon source slurry or powder. S2, Multi-component hybrid: The bio-carbon source slurry or powder is mixed evenly with short-cut carbon fibers of 5-20mm in length and industrial carbon matrix carbon source, and the mixture is prepared by stirring, ball milling or repeated rolling. S3, Laying out the mold, leveling, and drying: The mixture is laid in a mold, leveled by rolling or scraping, and then the thickness is limited by a cover plate or micro-pressure is applied. Then it is dried under semi-constant volume or constant pressure conditions to obtain composite material sheet preforms. S4, Carbonization and Shaping: The composite sheet preform, along with the die and cover plate, is cured and carbonized in an inert atmosphere heat treatment furnace to obtain an electrothermal / Joule-thermal porous C / C composite material.

[0043] It should be noted that in step S1, commercially available bio-carbon, whether fully or partially carbonized, can be used to replace the carbon source of the industrial carbon matrix. The bio-carbon source powder with a specific particle size that retains the pore characteristics can be obtained by crushing, squeezing, pressing, and grinding the bio-carbon through crushing, squeezing, pressing, and grinding. In step S2, when the carbon fiber used is a two-dimensional fabric of carbon cloth or thin carbon felt, the preparation method is adjusted to mix the carbon source of the bio-carbon matrix and the carbon source of the industrial carbon matrix evenly by stirring and ball milling, and then brushing it onto the surface of the fabric. By foaming the carbon source of the industrial carbon matrix in step S2 with a foaming agent, a porous industrial carbon matrix carbon source is obtained, thereby increasing the porosity of the carbon source of the industrial carbon matrix. By modifying the carbon source of the industrial carbon matrix in step S2 by adding carbon nanotubes, graphene, diamond, graphite, and carbon black, a conductive industrial carbon matrix carbon source is obtained, thereby improving the conductivity of the industrial carbon matrix. In steps S3 and S4, the use of semi-constant volume or constant pressure methods can control the thickness of the electrothermal / Joule-thermal porous C / C composite material, prevent sheet warping and shrinkage, and avoid defects such as the formation of pores. This is a necessary technical means for near-net-shape forming, and at the same time, it can keep the electrothermal / Joule-thermal porous C / C composite material with low density and high porosity. In step S4, after obtaining the electrothermal / Joule-thermal porous C / C composite material, the mechanical and electrothermal properties of the electrothermal / Joule-thermal porous C / C composite material or the densified electrothermal / Joule-thermal porous C / C composite material can be further densified by impregnation pyrolysis or chemical vapor deposition, or by high-temperature purification treatment.

[0044] The electrothermal / joule-thermal porous C / C composite material or the densified electrothermal / joule-thermal porous C / C composite material obtained by this invention can be made into an electric heating element with curved, locally protruding, concave, or hollow features according to actual application.

[0045] The electrothermal / Joule-thermal porous C / C composite material provided by this invention has advantages such as high electrothermal conversion efficiency, emission of infrared heat rays beneficial to the human body, non-aging, non-toxic, high heating temperature, and corrosion resistance. In addition, it is low in cost, lightweight, and has good adsorption capacity. It not only heats up quickly and has a stable temperature, but also has a certain strength and rigidity. It can be used in electric heaters for indoor heating and outdoor de-icing, and can also be used as a recyclable adsorbent material. When used as an adsorbent material, after adsorption reaches saturation, it desorbs by heating itself to 150~350℃ through electrothermal heating, thereby realizing the recycling of the adsorbent material. It can be made into an adsorption-type purifier that removes odors and harmful gases such as formaldehyde, such as carbon sculpture handicrafts.

[0046] The technical solution of the present invention will be specifically described below through embodiments, as follows: Example 1 A method for preparing an electrothermal / Joule-thermal porous C / C composite material, wherein the mass percentages of the three components are: carbon fiber 60wt%, bio-carbon matrix 20wt%, and industrial carbon matrix 20wt%, comprising the following steps: S1. The bamboo poles are crushed by cutting and grinding to obtain bamboo powder of 100-200 mesh; S2. The bamboo powder from step S1 is mixed evenly with short-cut carbon fibers with a length of 10mm and phenolic resin powder of 100-200 mesh to obtain a mixture. S3. The mixture from step S2 is laid in a steel concave mold with a depth of 1 mm, a width of 50 mm, and a length of 100 mm. It is then leveled with a scraper. A steel plate weighing 0.12 kg is placed on top of the mold and dried at 80°C for 10 hours to obtain a composite material sheet preform. S4. The composite material sheet blank from step S3, together with the steel mold, cover plate, and 2kg weight on the cover plate, is first cured at 200℃ for 0.5h, then carbonized at 900℃ for 2h in a nitrogen atmosphere. After cooling to room temperature, it is taken out and the burrs and flash on the edges are polished or trimmed to obtain the electrothermal / Joule-thermal porous C / C composite material.

[0047] Example 2 A method for preparing a densified electrothermal / Joule-thermal porous C / C composite material, wherein the mass percentages of the three components are: carbon fiber 45wt%, bio-carbon matrix 25wt%, and industrial carbon matrix 30wt%, comprising the following steps: S1. Wood chips, sawdust, and ash are crushed by grinding to obtain 50-300 mesh wood charcoal powder. S2. The charcoal powder from step S1 is mixed evenly with the aqueous solution of yeast powder and sugar by ball milling to obtain a suspension mixture. S3. The suspension mixture from step S2 is evenly coated onto the cut carbon fiber mesh fabric with a thickness of 0.2 mm, and then clamped in a graphite mold with a thickness of 0.3 mm for semi-constant volume determination. The mold is open parallel to the fabric surface and dried at 100°C for 24 hours to obtain the composite material sheet preform. S4. The composite material sheet preform from step S3, along with the graphite mold it contained, is first cured at 200℃ for 0.5h, then carbonized at 900℃ for 2h in a nitrogen atmosphere. After cooling to room temperature, it is removed and then... 3 Methane gas was introduced at a flow rate of / h, and pyrolytic carbon was deposited at 1050℃ to densify the gas to 0.5 g / cm³. 3 After removal, the adhered deposits are polished and repaired to obtain the densified electrothermal / joule-thermal porous C / C composite material.

[0048] Example 3 A method for preparing an electrothermal / Joule-thermal porous C / C composite material is the same as the preparation steps in Example 1, except that the industrial carbon matrix is ​​foamed, and includes the following steps: S1. The bamboo poles are crushed by cutting and grinding to obtain bamboo powder of 100-200 mesh; S2. Foaming treatment of 100-200 mesh phenolic resin powder is carried out by mixing phenolic resin powder with foaming agent sodium bicarbonate and heating at 150°C for 2 hours to obtain porous phenolic resin powder. The bamboo powder from step S1 is mixed evenly with short-cut carbon fibers with a length of 10 mm and porous phenolic resin powder of 100-200 mesh to obtain a mixture. S3. The mixture from step S2 is laid in a steel concave mold with a depth of 1 mm, a width of 50 mm, and a length of 100 mm. It is then leveled with a scraper. A steel plate weighing 0.12 kg is placed on top of the mold and dried at 80°C for 10 hours to obtain a composite material sheet preform. S4. The composite material sheet blank from step S3, together with the steel mold, cover plate, and 2kg weight on the cover plate, is first cured at 200℃ for 0.5h, then carbonized at 900℃ for 2h in a nitrogen atmosphere. After cooling to room temperature, it is taken out and the burrs and flash on the edges are polished or trimmed to obtain the electrothermal / Joule-thermal porous C / C composite material.

[0049] Example 4 A method for preparing a densified electrothermal / Joule-thermal porous C / C composite material is the same as that in Example 1, except that the obtained electrothermal / Joule-thermal porous C / C composite material is densified by an impregnation pyrolysis method, including the following steps: S1. The bamboo poles are crushed by cutting and grinding to obtain bamboo powder of 100-200 mesh; S2. The bamboo powder from step S1 is mixed evenly with short-cut carbon fibers with a length of 10mm and phenolic resin powder of 100-200 mesh to obtain a mixture. S3. The mixture from step S2 is laid in a steel concave mold with a depth of 1 mm, a width of 50 mm, and a length of 100 mm. It is then leveled with a scraper. A steel plate weighing 0.12 kg is placed on top of the mold and dried at 80°C for 10 hours to obtain a composite material sheet preform. S4. The composite material sheet blank from step S3, together with the steel mold, cover plate, and 2kg load block on the cover plate, is first cured at 200℃ for 0.5h, then carbonized at 900℃ for 2h in a nitrogen atmosphere. After cooling to room temperature, it is taken out and the burrs and flash on the edges are polished or trimmed to obtain the electrothermal / Joule thermal porous C / C composite material. S5. Immerse the electrothermal / Joule-thermal porous C / C composite material from step S4 in a phenolic resin solution, then remove it and treat it with pyrolysis at 900°C for 2 hours to obtain the densified electrothermal / Joule-thermal porous C / C composite material.

[0050] Example 5 A method for preparing an electrothermal / Joule-thermal porous C / C composite material, wherein the mass percentages of the three components are: carbon fiber 45wt%, bio-carbon matrix 50wt%, and industrial carbon matrix 5wt%, comprising the following steps: S1. Using kitchen waste that has been screened and purified as the carbon source for the biocarbon matrix, a biocarbon source slurry is obtained. S2. The bio-carbon source slurry from step S1 is mixed evenly with short-cut carbon fibers (5 mm in length), pitch, and carbon nanotubes to obtain a mixture. S3. The mixture from step S2 is laid in a steel concave mold with a depth of 1 mm, a width of 50 mm, and a length of 100 mm. It is then leveled with a scraper. A steel plate weighing 0.12 kg is placed on top of the mold and dried at 80°C for 10 hours to obtain a composite material sheet preform. S4. The composite material sheet blank from step S3, together with the steel mold, cover plate, and 2kg load on the cover plate, is first cured at 120℃ for 3 hours, then carbonized at 1300℃ for 2 hours in a nitrogen atmosphere. After cooling to room temperature, it is taken out and the burrs and flash on the edges are polished or trimmed to obtain the electrothermal / Joule-thermal porous C / C composite material.

[0051] Example 6 A method for preparing an electrothermal / Joule-thermal porous C / C composite material, wherein the mass percentages of the three components are: 10wt% carbon fiber, 50wt% bio-carbon matrix, and 40wt% industrial carbon matrix, comprising the following steps: S1. Using animal bones as a carbon source, the bones are crushed by cutting, chopping, and grinding to obtain bone meal of 100-200 mesh. S2. The bone powder from step S1 is mixed evenly with short-cut carbon fibers with a length of 20mm and asphalt to obtain a mixture. S3. The mixture from step S2 is laid in a steel concave mold with a depth of 1 mm, a width of 50 mm, and a length of 100 mm. It is then leveled with a scraper. A steel plate weighing 0.12 kg is placed on top of the mold and dried at 80°C for 10 hours to obtain a composite material sheet preform. S4. The composite material sheet blank from step S3, together with the steel mold, cover plate, and 2kg load block on the cover plate, is first cured at 240℃ for 0.5h, then carbonized at 800℃ for 2h in a nitrogen atmosphere. After cooling to room temperature, it is taken out and the burrs and flash on the edges are polished or trimmed to obtain the electrothermal / Joule-heated porous C / C composite material. S5. The electrothermal / joule-thermal porous C / C composite material was heat-treated at 2000℃ for 3 hours to obtain the purified electrothermal / joule-thermal porous C / C composite material.

[0052] Examples 1-6 of this invention all yielded composite materials with excellent thermal conductivity and adsorption properties. The composite materials from Examples 1-4 are used as examples for further research; the specific research methods and results are shown below: The method for determining the apparent porosity of carbon materials is based on GB / T 24529-2009. Figure 1 This is a photograph of the electrothermal / Joule-thermal porous C / C composite material of Embodiment 1 of the present invention. The sheet is 1 mm thick, 50 mm wide, and 100 mm long, with a density of 0.3-0.4 g / cm³. 3 The porosity measured by the drainage method was 75%, and the high porosity is conducive to adsorption.

[0053] Figure 2 This is a microstructure image of the electrothermal / Joule-thermal porous C / C composite material of Example 1 of the present invention. Figure 2The porous bamboo charcoal and carbon fiber are clearly visible being bonded together by resin carbon, while the material contains a large number of unfilled pores.

[0054] Figure 3 The figure shows the tensile stress-strain curve of the electrothermal / Joule-heated porous C / C composite material in Example 1 of the present invention. The inset is a photograph of the sample being tested in a tensile testing machine. The tensile strength of the composite material is higher than 20 MPa, and it can be subjected to subsequent processing such as engraving and hollowing.

[0055] Figure 4 The electrothermal curves of the electrothermal / Joule-heating porous C / C composite material in Embodiment 2 of the present invention are shown under different voltages. It can be seen that under different voltage conditions, the heating element has reached a stable heating temperature after 100s of power-on. The peak temperature fluctuation during 50 power-on and power-off cycles is less than ±5℃. The composite material has the advantages of fast heating and stable thermal field.

[0056] The above embodiments demonstrate that the electrothermal / Joule-thermal porous C / C composite material of the present invention has the characteristics of low cost, fast heating, stable thermal field, low density, and high porosity, and the corresponding preparation method can achieve near-net-shape molding.

[0057] Figure 5 In the figure, (a) is a morphology diagram of the electrothermal / Joule-thermal porous C / C composite material of Example 1, and (b) is a morphology diagram of the electrothermal / Joule-thermal porous C / C composite material of Example 3. Compared with Example 1, Example 3 has undergone foaming treatment. The results show that after foaming treatment, the number of pores is significantly increased, which improves the adsorption capacity of the composite material.

[0058] Figure 6 In the figures, (a) is a morphology diagram of the electrothermal / Joule-thermal porous C / C composite material of Example 1, and (b) is a morphology diagram of the densified electrothermal / Joule-thermal porous C / C composite material of Example 4. Compared with Example 1, Example 4 also carried out a densification treatment on the electrothermal / Joule-thermal porous C / C composite material by impregnation pyrolysis method. The results showed that after the densification treatment, the density of carbon material in the electrothermal / Joule-thermal porous C / C composite material increased significantly.

[0059] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, it is intended to include any modifications and variations that fall within the scope of the claims and their equivalents.

Claims

1. An electrocaloric / joule heating porous C / C composite, characterized in that, The electrothermal / Joule-heated porous C / C composite material is a porous composite sheet composed of carbon fiber, industrial carbon matrix, and bio-carbon matrix. The carbon fiber and bio-carbon matrix are bonded together by the industrial carbon matrix. The bio-carbon matrix is ​​selected from porous plant carbon or porous animal carbon, and retains the original pore structure of the bio-carbon source. The mass percentages of the three components are as follows: carbon fiber 10-60 wt%, bio-carbon matrix 10-50 wt%, and industrial carbon matrix 5-80 wt%, and the sum of the mass percentages of the three components is 100%. The industrial carbon matrix is ​​selected from one or a combination of resin carbon, pitch carbon, and sugar carbon; The electrocaloric / Joule heating porous C / C composite has a thickness of 0.1-5 mm and a density of 0.2-1.2 g / cm 3 ; The preparation method of electrothermal / Joule-heated porous C / C composite material includes the following steps: crushing the carbon source of the bio-carbon matrix to obtain a bio-carbon source slurry or powder with a scale of micrometer or millimeter; mixing the bio-carbon source slurry or powder with carbon fiber and industrial carbon matrix carbon sources uniformly to obtain a mixture; laying the mixture in a mold, leveling it, and drying it under semi-constant volume or constant pressure conditions to obtain a composite material sheet preform; and curing and carbonizing the composite material sheet preform under semi-constant volume or constant pressure conditions to obtain the electrothermal / Joule-heated porous C / C composite material.

2. The electrocaloric / joule heating porous C / C composite of claim 1, wherein, The electrocaloric / Joule heating porous C / C composite has a thickness of 0.5-2 mm and a density of 0.3-0.9 g / cm 3 .

3. The electrocaloric / Joule heating porous C / C composite of claim 1, wherein, The carbon source of the industrial carbon matrix is ​​also subjected to foaming treatment. The foaming treatment method is as follows: the carbon source of the industrial carbon matrix is ​​mixed with a foaming agent and heated at 60-220℃ for 0.5-3h to obtain a porous industrial carbon matrix carbon source. The foaming agent is selected from baking soda or yeast powder.

4. The electrocaloric / Joule heating porous C / C composite of claim 1, wherein, The carbon source of the industrial carbon matrix is ​​further modified by mixing the industrial carbon matrix with conductive carbon material to obtain a conductive industrial carbon matrix carbon source.

5. A densified electrocaloric / joule heating porous C / C composite material, characterized in that, The electrothermal / Joule-thermal porous C / C composite material described in claim 1 is subjected to an impregnation pyrolysis method or a chemical vapor deposition method to obtain a densified electrothermal / Joule-thermal porous C / C composite material. The impregnation pyrolysis method is as follows: the electrothermal / Joule-thermal porous C / C composite material is immersed in the carbon source of the industrial carbon matrix, and then taken out and subjected to pyrolysis treatment. The pyrolysis conditions are: pyrolysis at 800-1300℃ for 0.5-3h. The operation of chemical vapor deposition is as follows: using a 0.4-1.2m... 3 A gaseous carbon source is introduced at a flow rate of / h, and carbon is deposited on the surface of the electrothermal / Joule-thermal porous C / C composite material at 900-1280℃.

6. A method of purifying a composite material, characterized by, The composite material is the electrothermal / Joule-thermal porous C / C composite material of claim 1 or the densified electrothermal / Joule-thermal porous C / C composite material of claim 5; The purification method includes the following steps: heat-treating the composite material at 1500-2500℃ for 1-5 hours.

7. The application of the electrothermal / joule-thermal porous C / C composite material of claim 1 or the densified electrothermal / joule-thermal porous C / C composite material of claim 5 in the preparation of electric heaters or adsorbent materials.

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