A solar heat-absorbing material and its preparation method

Abstract

The present invention discloses a solar heat-absorbing material and a preparation method thereof, belonging to the technical field of preparation of heat-absorbing materials. The raw materials for preparing the heat-absorbing material in the present invention mainly include silicon carbide powder, silica sol, silane coupling agent KH550, tetramethylethylenediamine, calcium carbonate, porous graphene, and polyvinylidene fluoride. In order to avoid problems such as environmental pollution and low density of the material itself existing in the existing preparation methods, the present invention first prepares a kind of porous graphene, and then uses the porous graphene to prepare the solar heat-absorbing material, so that the adhesion between the porous graphene and the foam ceramic slurry is firm, and the solar heat-absorbing material is obtained by sintering and heat preservation. Through the above steps, not only the properties such as hardness and porosity of the solar heat-absorbing material are improved, but also the environmental pollution caused by the release of organic gases during sintering in the traditional method is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of heat-absorbing materials, and particularly to a solar heat-absorbing material and a preparation method thereof. Background Art

[0002] Due to the limited fossil energy, humans have been constantly striving to seek new alternative energy sources. As a renewable energy source that is inexhaustible and renewable, solar energy is the most likely new energy to replace fossil energy. Solar tower thermal power generation systems have attracted the attention of countries around the world because of their high concentration ratio, high thermal cycle temperature, low heat loss, simple system and high efficiency, and are currently the solar thermal power generation technologies that various countries are vigorously researching. As the core of tower-type solar thermal power generation, the heat-absorbing body material in the heat absorber plays an important role in receiving solar concentrated energy, as well as heat absorption and heat exchange, and affects the stability and efficiency of the entire thermal power generation system.

[0003] Early research on heat-absorbing body materials mainly focused on alloys, and alloy heat-absorbing bodies mainly included heat-resistant metal wire mesh braids and wrappings. However, as a heat-absorbing body material, the working temperature of alloys cannot exceed 800 °C. In order to obtain a heat-absorbing body with a higher working temperature, ceramic materials have become a research hotspot at home and abroad. Ceramic heat-absorbing bodies mainly include foam ceramics, ceramic fibers, honeycomb ceramics and other porous ceramics. Among them, foam ceramics are currently often prepared by the sol-gel method. However, this method adds organic foam materials as skeletons, which need to be removed by sintering in the last step. A large amount of gas will be generated during the oxidative decomposition of the organic foam, causing environmental pollution and stress in the ceramic green body, resulting in the damage and even collapse of the green body.

[0004] At the same time, foam ceramic materials generally have a high porosity but a small density and low strength. The prior art often solves this problem by adding sintering aids. Sintering aids can make the green body sinter at a high density. However, when adding sintering aids, a second-phase component is likely to form a glass phase at the grain boundaries of silicon nitride during the reaction. The mechanical strength of the glass phase is very low, affecting the high-temperature creep resistance of the sintered ceramic material and causing material deformation. Therefore, the sintering aids must be carefully selected during production, and different sintering aids also require fine design of the sintering process, so it is difficult to meet the requirements of modern production.

[0005] Therefore, it is necessary to find a method to improve the porosity, density and physical strength of foam ceramic materials without adding sintering aids, which is a difficult problem faced in the production of foam ceramics for solar heat-absorbing materials. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a new type of solar heat-absorbing material and a preparation method thereof, to solve the problems of low density, small strength and small porosity of the foam ceramic material in the solar heat-absorbing material.

[0007] The present invention solves the above technical problems through the following technical means:

[0008] A solar heat-absorbing material, comprising the following raw materials:

[0009] 20-30 parts by mass of silicon carbide powder, 15-24 parts by mass of silica sol with a mass fraction of 30%, 2-5 parts by mass of silane coupling agent KH550, 0.5-2 parts by mass of tetramethylethylenediamine, 1-4 parts by mass of calcium carbonate, 8-12 parts by mass of porous graphene, 0.1-1 part by mass of polyvinylidene fluoride.

[0010] The porous graphene comprises the following raw materials: 4-8 parts by mass of 10mg / mL graphene oxide aqueous solution, 10-20 parts by mass of 3mol / L potassium hydroxide solution, 10-20 parts by mass of 5wt% hydrochloric acid solution.

[0011] A preparation method of a solar heat-absorbing material prepared by the present invention comprises the following steps:

[0012] (1) Weigh silicon carbide powder, silane coupling agent KH550 and silica sol, stir and mix them evenly in water, put them into a ball mill and ball mill at a speed of 30r / min for 45min to obtain a suspension slurry;

[0013] (2) Add tetramethylethylenediamine and calcium carbonate to the obtained suspension slurry, place it under a stirrer to stir and foam. After foaming is completed, add polyvinylidene fluoride to the slurry, and continuously stir to make polyvinylidene fluoride disperse evenly in the slurry to obtain a foam slurry;

[0014] (3) Immerse the porous graphene in the foam slurry and then fish it out to obtain a gel. Then dry the obtained gel under vacuum conditions, dry-press the dried powder into a shape, then sinter and keep warm to obtain a sintered body. Finally, anneal the sintered body at 1500°C for 20h to obtain the solar heat-absorbing material.

[0015] Further, in step (3) of the solar heat-absorbing material, the conditions for vacuum drying are -30°C and a vacuum degree of 8Pa, and the vacuum degree for heat preservation of the sintered powder is 1.0-10Pa.

[0016] Further, in step (3) of the solar heat-absorbing material, the pressure for dry pressing is 30-50MPa.

[0017] Further, in step (3) of the solar heat-absorbing material, the sintering temperature is 1700°C, sinter for 4h and then keep warm for 4h.

[0018] Further, the preparation method of the porous graphene is as follows:

[0019] (1) After ultrasonic treatment of the graphene oxide aqueous solution, it is loaded into a reaction kettle and reacted for 14 - 18 h, then washed 3 times with deionized water, soaked in a potassium hydroxide solution for 22 - 26 h, the hydrogel is fished out and vacuum dried at 110 - 130 °C for 20 - 28 h to obtain the dried initial product;

[0020] (2) After the dried initial product is protected by introducing nitrogen, it is heated to 800 °C and reacted at 800 °C for 1 h. After taking it out and washing it with deionized water until the pH is 7 - 8, it is then put into a 5 wt% hydrochloric acid solution and stirred for 2 h. After the reaction is completed, it is filtered by suction and washed with water until neutral, and vacuum dried at 120 °C for 24 h to obtain porous graphene.

[0021] Furthermore, in the preparation step (1) of the porous graphene, the reaction temperature in the reaction kettle is 170 - 190 °C. Preferably, the optimal reaction temperature is 180 °C.

[0022] Furthermore, in the preparation step (2) of the porous graphene, the heating rate to 800 °C is 10 - 12 °C / min. Preferably, the optimal heating rate is 10 °C / min.

[0023] Furthermore, in the preparation steps of the porous graphene, the vacuum degree of vacuum drying is 8 - 10 Pa.

[0024] The present invention prepares a solar heat-absorbing material in the form of a foam ceramic material. During the preparation process, since no sintering aid is added, problems such as low density, small strength, and few porosity of the foam ceramic material will occur. Therefore, it is necessary to support the raw materials during the preparation process to prevent the collapse caused by the escape of gas during the sintering process, which leads to the destruction of pores.

[0025] Disperse silicon carbide powder and silane coupling agent KH550 in silica sol to prepare silicon carbide foam ceramic slurry. Add tetramethylethylenediamine and polyvinylidene fluoride to the ceramic slurry for dispersion and foaming. When the foaming ceramic slurry is injected into porous graphene, during the preparation of the previously prepared porous graphene, potassium hydroxide etches graphene oxide while activating it, and at the same time destroys the stacking between the layers of graphene oxide. This weakened stacking forms a macroscopically visible three-dimensional structure, increasing the content of mesopores and generating a large number of micropores in graphene oxide. When the slurry submerges the porous graphene, tetramethylethylenediamine can bond polyvinylidene fluoride to the porous graphene and complex the foam ceramic slurry at the other end, making it supported by the porous graphene to form a gel material with numerous and firm pores. Subsequently, through vacuum drying, the water is directly sublimated and evaporated, avoiding the destruction of pores caused by the expansion when the water in the gel turns from liquid to gas, and even the formation of open pores, resulting in uneven pore sizes. Finally, sintering makes the gel further become loose and porous, and heat preservation forms a foam ceramic material. The foam structure of the ceramic can increase the specific surface area of the ceramic, promote heat transfer, and the inner-layer porous graphene can absorb heat at high temperatures, dissipate heat by flowing, enhancing the heat transfer performance of the heat-absorbing ceramic and improving the high-temperature strength and thermal shock resistance of the heat-absorbing ceramic.

[0026] Beneficial effects:

[0027] (1) In the present invention, porous graphene is used as the skeleton material of the gel, avoiding the use of organic foam plastics as the gel skeleton in the traditional process. The gel adheres to the porous graphene, improving the porosity of the heat-absorbing material while increasing the density of the material and enhancing the physical strength of the heat-absorbing material.

[0028] (2) By adding porous graphene, while improving the thermal conductivity of the foam ceramic product, it avoids environmental pollution caused by sintering materials and improves the product performance. Specific embodiments

[0029] The present invention will be described in detail below in conjunction with embodiments:

[0030] The present invention provides a solar heat-absorbing material and its preparation method. However, before preparing the recycled artificial board, porous graphene needs to be prepared first. The specific preparation steps of the porous graphene prepared in the present invention are as follows:

[0031] Example 1: Preparation of porous graphene I

[0032] (1) Ultrasonically treat 6 g of an aqueous graphene oxide solution with a concentration of 10 mg / mL for 1 h at a power of 180 W, put it into a reaction kettle, react for 16 h under the condition of 180 °C, wash it 3 times with deionized water, then soak it in 15 g of 3 mol / L potassium hydroxide solution at room temperature for 24 h, fish it out and vacuum dry it at 120 °C and 8 Pa for 24 h to obtain the dried primary product;

[0033] (2) Put the dried primary product into a tubular furnace, introduce nitrogen, evacuate the air for protection, heat it to 800 °C at a rate of 10 °C / min, and react at 800 °C for 1 h. Take it out, wash it with deionized water until the pH reaches 7.5, then put it into 15 g of 5 wt% hydrochloric acid solution and stir for 2 h. After the reaction, filter it by suction and wash it with water until it is neutral, and vacuum dry it at 120 °C and 8 Pa for 24 h to obtain porous graphene.

[0034] Example 2: Preparation of Porous Graphene II

[0035] (1) Ultrasonically treat 4 g of an aqueous graphene oxide solution with a concentration of 10 mg / mL for 0.5 h at a power of 180 W, put it into a reaction kettle, react for 14 h under the condition of 180 °C, wash it 3 times with deionized water, then soak it in 10 g of 3 mol / L potassium hydroxide solution at room temperature for 22 h, fish it out and vacuum dry it at 110 °C and 8 Pa for 20 h to obtain the dried primary product;

[0036] (2) Put the dried primary product into a tubular furnace, introduce nitrogen, evacuate the air for protection, heat it to 800 °C at a rate of 10 °C / min, and react at 800 °C for 1 h. Take it out, wash it with deionized water until the pH reaches 7, then put it into 10 g of 5 wt% hydrochloric acid solution and stir for 1 h. After the reaction, filter it by suction and wash it with water until it is neutral, and vacuum dry it at 115 °C and 8 Pa for 24 h to obtain porous graphene.

[0037] Example 3: Preparation of Porous Graphene III

[0038] (1) Ultrasonically treat 8 g of an aqueous graphene oxide solution with a concentration of 10 mg / mL for 1.5 h at a power of 180 W, put it into a reaction kettle, react for 18 h under the condition of 180 °C, wash it 3 times with deionized water, then soak it in 20 g of 3 mol / L potassium hydroxide solution at room temperature for 26 h, fish it out and vacuum dry it at 130 °C and 8 Pa for 28 h to obtain the dried primary product;

[0039] (2) Put the dried initial product into a tubular furnace, introduce nitrogen, evacuate the air for protection, heat it to 800 °C at a rate of 10 °C / min, and react at 800 °C for 1 h. After taking it out and washing it with deionized water until the pH reaches 8, then put it into 20 g of 5 wt% hydrochloric acid solution and stir for 3 h. After the reaction is completed, filter it by suction and wash it with water until it is neutral, and dry it under vacuum at 125 °C and 8 Pa for 24 h to obtain porous graphene.

[0040] Comparative Example 1: Preparation of Porous Graphene

[0041] This comparative example is compared with the porous graphene prepared in Example 1. The difference is only that potassium hydroxide solution is not used in this comparative example, and the remaining steps and raw materials used are the same as those in Example 1. The specific steps (1) are as follows:

[0042] (1) Ultrasonically treat 6 g of graphene oxide aqueous solution with a concentration of 10 mg / mL at a power of 180 W for 1 h, load it into a reaction kettle, react at 180 °C for 16 h, then wash it 3 times with deionized water to obtain a hydrogel. Scoop out the hydrogel and dry it under vacuum at 120 °C and 8 Pa for 24 h to obtain the dried initial product.

[0043] Comparative Example 2: Preparation of Porous Graphene

[0044] This comparative example is compared with the porous graphene prepared in Example 1. The difference is only that hydrochloric acid solution is not used in this comparative example, and the remaining steps and raw materials used are the same as those in Example 1. The specific steps (2) are as follows:

[0045] (2) Put the dried initial product into a tubular furnace, introduce nitrogen, evacuate the air for protection, heat it to 800 °C at a rate of 10 °C / min, and react at 800 °C for 1 h. After taking it out and washing it with deionized water until the pH reaches 7.5, then filter it by suction and dry it under vacuum at 120 °C and 8 Pa for 24 h to obtain porous graphene.

[0046] Comparative Example 3: Preparation of Porous Graphene

[0047] This comparative example is compared with the porous graphene prepared in Example 1. The difference is only in step (2) of this comparative example, and the remaining steps and raw materials used are the same as those in Example 1. The specific steps (2) are as follows:

[0048] (2) Wash the dried initial product with deionized water until the pH reaches 7.5, then put it into 15 g of 5 wt% hydrochloric acid solution and stir for 2 h. After the reaction is completed, filter it by suction and wash it with water until it is neutral, and dry it under vacuum at 120 °C and 8 Pa for 24 h to obtain porous graphene.

[0049] The raw materials of the solar heat-absorbing material prepared by the present invention are weighed according to the data in Table 2, and the specific ratios are shown in Table 1 below:

[0050] Table 1: Preparation of solar heat-absorbing material (unit: g)

[0051]

[0052] Weigh the raw materials according to Table 2 to prepare the solar heat-absorbing material. Among them, the porous graphene used in Examples 4-6 and Comparative Example 6 is prepared in Example 1.

[0053] Example 4: Preparation of solar heat-absorbing material I

[0054] (1) Weigh silicon carbide powder, silane coupling agent KH550 and silica sol in 20 g of water, stir and mix evenly, put it into a ball mill, and ball mill at a speed of 30 r / min for 45 min to obtain a suspension slurry;

[0055] (2) Add tetramethylethylenediamine and calcium carbonate to the obtained suspension slurry, place it under a stirrer and stir to foam at 180 r / min. After the foaming is completed, add polyvinylidene fluoride to the slurry, and continuously stir to make the polyvinylidene fluoride evenly dispersed in the slurry to obtain a foam slurry;

[0056] (3) Fully immerse the porous graphene in the foam slurry and then fish it out to obtain a gel. Then, dry the obtained gel under vacuum at -30 °C and a vacuum degree of 8 Pa. The dried powder is placed in a steel film and dry-pressed into shape at a pressure of 40 MPa. Then, sinter at 1700 °C for 4 h and keep it warm at a vacuum degree of 5.5 Pa for 4 h to obtain a sintered body. Finally, anneal the sintered body in a muffle furnace at 1500 °C for 20 h to prepare the solar heat-absorbing material.

[0057] Example 5: Preparation of solar heat-absorbing material II

[0058] (1) Weigh silicon carbide powder, silane coupling agent KH550 and silica sol in 20 g of water, stir and mix evenly, put it into a ball mill, and ball mill at a speed of 25 r / min for 45 min to obtain a suspension slurry;

[0059] (2) Add tetramethylethylenediamine and calcium carbonate to the obtained suspension slurry, place it under a stirrer and stir to foam at 180 r / min. After the foaming is completed, add polyvinylidene fluoride to the slurry, and continuously stir to make the polyvinylidene fluoride evenly dispersed in the slurry to obtain a foam slurry;

[0060] (3) The porous graphene is fully immersed in the foam slurry and then fished out to obtain a gel. Then, the obtained gel is dried under vacuum at -30°C and a vacuum degree of 8 Pa. The dried powder is placed in a steel film and dry-pressed into a shape under a pressure of 50 MPa. Then, it is sintered at 1700°C for 4 h and then kept at a temperature for 4 h under a vacuum degree of 1.0 Pa to obtain a sintered body. Finally, the sintered body is annealed in a muffle furnace at 1500°C for 20 h to prepare a solar heat-absorbing material.

[0061] Example 6: Preparation of Solar Heat-Absorbing Material III

[0062] (1) Weigh silicon carbide powder, silane coupling agent KH550, and silica sol according to Table 1, stir and mix them evenly in 20 g of water, and put them into a ball mill to ball mill for 45 min at a rotation speed of 30 r / min to obtain a suspension slurry.

[0063] (2) Add tetramethylethylenediamine and calcium carbonate to the obtained suspension slurry, place it in a stirrer and stir to foam at 180 r / min. After the foaming is completed, add polyvinylidene fluoride to the slurry and continuously stir to make the polyvinylidene fluoride disperse evenly in the slurry to obtain a foam slurry.

[0064] (3) The porous graphene is fully immersed in the foam slurry and then fished out to obtain a gel. Then, the obtained gel is dried under vacuum at -30°C and a vacuum degree of 8 Pa. The dried powder is placed in a steel film and dry-pressed into a shape under a pressure of 30 MPa. Then, it is sintered at 1700°C for 4 h and then kept at a temperature for 4 h under a vacuum degree of 10 Pa to obtain a sintered body. Finally, the sintered body is annealed in a muffle furnace at 1500°C for 20 h to prepare a solar heat-absorbing material.

[0065] Comparative Example 4: Preparation of Solar Heat-Absorbing Material

[0066] This comparative example is compared with the solar heat-absorbing material prepared in Example 1. The difference is only that porous graphene is not used in step (3) of this comparative example, and the remaining steps and raw materials used are the same as those in Example 1. The specific step (3) is as follows:

[0067] (3) The foam slurry is dried under vacuum at -30°C and a vacuum degree of 8 Pa. The dried powder is placed in a steel film and dry-pressed into a shape under a pressure of 40 MPa. Then, it is sintered at 1700°C for 4 h and then kept at a temperature for 4 h under a vacuum degree of 5.5 Pa to obtain a sintered body. Finally, the sintered body is annealed in a muffle furnace at 1500°C for 20 h to prepare a solar heat-absorbing material.

[0068] Comparative Example 5: Preparation of Solar Heat-Absorbing Material

[0069] This comparative example is compared with the solar heat-absorbing material prepared in Example 1. The difference is only that tetramethylethylenediamine and polyvinylidene fluoride are not used in step (2) of this comparative example, and the remaining steps and raw materials used are the same as those in Example 1. The specific step (2) is as follows:

[0070] (2) Add calcium carbonate to the prepared suspension slurry, place it in a blender and stir to foam at 180 r / min. After foaming is completed, foam slurry is obtained in the slurry.

[0071] Experiment 1. Performance test of the foam ceramic heat-absorbing material;

[0072] 1. Preparation method:

[0073] Experimental group: In experimental group 1, the preparation method of Example 4 is used to prepare the solar heat-absorbing material, and the porous graphene is prepared in Example 1;

[0074] Control group: In control groups 1-3, the preparation method of the solar thermal material in Example 4 is used for preparation, but the porous graphene is respectively selected from the porous graphene prepared in comparative examples 1-3;

[0075] In control groups 4-5, the preparation method of the solar heat-absorbing material in comparative examples 4-5 is used for preparation, and the porous graphene is all prepared in Example 1.

[0076] 2. Specific experimental method:

[0077] (1) Determination of thermal shock resistance: Thermal shock resistance reflects the ability of a material to withstand rapid temperature changes without being damaged, and it is one of the most critical parameters determining the service life of the material. Place the solar heat-absorbing ceramic material prepared in the present invention and the solar heat-absorbing ceramic material in the comparative example in a high-temperature resistance furnace, heat the solar heat-absorbing ceramic material to 1200 °C, keep it warm for 15 minutes, take it out, cool it in the air for 2 minutes, and then put it into water below 30 °C and cool it for 3 minutes. Check whether the test material will crack, break or be damaged under such a rapid cooling state, and test its compressive strength;

[0078] (2) The thermal conductivity is measured using a thermal constant analyzer.

[0079] Before the test, ensure that there are no visible cracks or other defects on the surface of all specimens that may affect the test results; the above experiments are repeated three times and the average value is taken. The specific results are shown in Table 2:

[0080] Table 2

[0081]

[0082] It can be obtained from Table 2 that:

[0083] 1. The solar heat-absorbing ceramic material prepared in Experimental Group 1 has uniform pores, good thermal conductivity, good mechanical strength, and good thermal shock resistance. In the solar heat-absorbing material of Control Group 1, the porous graphene was not etched, the porosity was 88.1%, the compressive strength after thermal shock was 0.61 MPa, the impact strength was 72.16 MPa, the flexural strength was 98.3 MPa, and the thermal conductivity was 83.8 W / (m·k). In the solar heat-absorbing material of Control Group 2, the porous graphene in the solar heat-absorbing material failed to separate the potassium hydroxide in the porous graphene. After thermal shock, the compressive strength was 0.64 MPa, the impact strength was 73.41 MPa, the flexural strength was 98.8 MPa, and the thermal conductivity was 86.7 W / (m·k). It can be seen that the porous graphene added in Experimental Group 1 can make the chemical structure of the material easier to carry out subsequent modification reactions, thereby improving the performance.

[0084] 2. The solar heat-absorbing material of Control Group 4 had a compressive strength of 0.58 MPa, a porosity of 78.4%, an impact strength of 58.32 MPa, a flexural strength reduction of 78.1 MPa, and a thermal conductivity of 62.5 W / (m·k) after thermal shock. The reason is that no porous graphene was added as the skeleton support of the gel, and the gas expanded and overflowed after the gel was sintered, resulting in the destruction of the pores. The porosity of the solar heat-absorbing material of Control Group 5 was 93.7%, the compressive strength after thermal shock was 0.65 MPa, the impact strength was 75.54 MPa, the flexural strength was 99.2 MPa, and the thermal conductivity was 87.4 W / (m·k). The reason is that no tetramethylethylenediamine and polyvinylidene fluoride were added to bond the foam ceramic and the porous graphene, and the ceramic material was easily desorbed during sintering. The gel inside the skeleton material would fill the pores, reducing the porosity, and the ceramic material was unevenly distributed. Therefore, the solar heat-absorbing material prepared by the present invention has good porosity, few open pores, high material density, and strong physical compressive ability.

[0085] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention. The technologies, shapes, and structures not described in detail in the present invention are all well-known technologies.

Claims

1. A solar heat-absorbing material, characterized in that, The solar heat-absorbing material comprises the following raw materials: 20-30 parts by mass of silicon carbide powder, 15-24 parts by mass of silica sol with a mass fraction of 30%, 2-5 parts by mass of silane coupling agent KH550, 0.5-2 parts by mass of tetramethylethylenediamine, 1-4 parts by mass of calcium carbonate, 8-12 parts by mass of porous graphene, 0.1-1 part by mass of polyvinylidene fluoride. The preparation method of the solar heat-absorbing material comprises the following steps: (1) Weigh silicon carbide powder, silane coupling agent KH550 and silica sol, stir and mix them evenly in water, put them into a ball mill and ball mill at a speed of 30 r / min for 45 min to obtain a suspension slurry; (2) Add tetramethylethylenediamine and calcium carbonate to the obtained suspension slurry, stir and foam. After foaming is completed, add polyvinylidene fluoride to the slurry, and continuously stir to make polyvinylidene fluoride evenly dispersed in the slurry to obtain a foam slurry; (3) Immerse the porous graphene in the foam slurry and then fish it out to obtain a gel. Then dry the obtained gel under vacuum conditions. Dry-press the dried powder into a shape, then sinter and keep warm to obtain a sintered body. Finally, anneal the sintered body at 1500 °C for 20 h to obtain the solar heat-absorbing material.

2. The solar heat-absorbing material according to claim 1, wherein The porous graphene comprises the following raw materials: 4-8 parts by mass of 10 mg / mL graphene oxide aqueous solution, 10-20 parts by mass of 3 mol / L potassium hydroxide solution, 10-20 parts by mass of 5 wt% hydrochloric acid solution.

3. The preparation method of a solar heat-absorbing material according to claim 1, characterized in that, The preparation method of the solar heat-absorbing material comprises the following steps: (1) Weigh silicon carbide powder, silane coupling agent KH550 and silica sol, stir and mix them evenly in water, put them into a ball mill and ball mill at a speed of 30 r / min for 45 min to obtain a suspension slurry; (2) Add tetramethylethylenediamine and calcium carbonate to the obtained suspension slurry, stir and foam. After foaming is completed, add polyvinylidene fluoride to the slurry, and continuously stir to make polyvinylidene fluoride evenly dispersed in the slurry to obtain a foam slurry; (3) Immerse the porous graphene in the foam slurry and then fish it out to obtain a gel. Then dry the obtained gel under vacuum conditions. Dry-press the dried powder into a shape, then sinter and keep warm to obtain a sintered body. Finally, anneal the sintered body at 1500 °C for 20 h to obtain the solar heat-absorbing material.

4. The preparation method of a solar heat-absorbing material according to claim 3, characterized in that, In step (3) of the solar heat-absorbing material, the conditions for vacuum drying are -30 °C and a vacuum degree of 8 Pa, and the vacuum degree for heat preservation of the sintered powder is 1.0-10 Pa.

5. The preparation method of a solar heat-absorbing material according to claim 3, characterized in that, In step (3) of the solar heat-absorbing material, the pressure for dry pressing is 30-50 MPa.

6. The preparation method of a solar heat-absorbing material according to claim 3, characterized in that, In step (3) of the solar heat-absorbing material, the sintering temperature is 1700 °C, sinter for 4 h and then keep warm for 4 h.

7. The preparation method of a solar heat-absorbing material according to claim 3, characterized in that, The preparation method of the porous graphene is as follows: (1) After ultrasonic treatment of the graphene oxide aqueous solution, put it into a reaction kettle, react for 14-18 h, wash it 3 times with deionized water, soak it in the potassium hydroxide solution for 22-26 h, fish it out and vacuum dry it at 110-130 °C for 20-28 h to obtain a dried primary product; (2)After drying the initial product, introduce nitrogen and heat it up to 800 °C, and react at 800 °C for 1 h. Take it out, wash it with deionized water until the pH reaches 7 - 8, then put it into the hydrochloric acid solution and stir for 2 h. After the reaction is completed, filter it by suction and wash it with water until neutral, and dry it under vacuum at 120 °C for 24 h to obtain porous graphene.

8. The preparation method of a solar heat-absorbing material according to claim 7, characterized in that, In the preparation method of the porous graphene, the reaction temperature in the reaction kettle in step (1) is 170 - 190 °C.

9. The preparation method of a solar heat-absorbing material according to claim 7, wherein In the preparation method of the porous graphene, the heating rate to 800 °C in step (2) is: 10 - 12 °C / min.

10. The preparation method of a solar heat-absorbing material according to claim 7, characterized in that, In the preparation method of the porous graphene, the vacuum degree of the vacuum drying used in step (1) and step (2) is both 8 - 10 Pa.

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