Multi-layer coated calcium oxide heat storage material and preparation method thereof

Abstract

The invention belongs to the technical field of thermochemical heat storage materials, and relates to a multilayer coated calcium oxide heat storage material and a preparation method thereof. The preparation method comprises the following steps: preparing Al2O3 coated calcium hydroxide particles; the preparation method comprises the following steps: mixing and stirring a silicon source and tetraethoxysilane, and adding an ethanol solution and cetyltrimethylammonium bromide to obtain a mixed solution; heating under a water bath condition to form sol; adding graphene oxide into the sol, and dropwise adding an alkaline solution to obtain gel; the Al2O3 coated calcium hydroxide particles are poured into the gel, and a mixed system is obtained; the mixed system is subjected to electrolysis and freeze drying, and Ca (OH) 2 / Al2O3 particles wrapped by SiO2 / graphene oxide composite aerogel are obtained; and then dipping in a PVP (Polyvinyl Pyrrolidone) solution, and carrying out heat treatment in an air atmosphere to obtain the multi-layer coated calcium oxide heat storage material. The problem that the existing SiC shell-coated calcium oxide core is easy to crack is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermochemical heat storage materials, and in particular relates to a multi-layer coated calcium oxide heat storage material and a preparation method thereof. Background Art

[0002] Thermochemical heat storage is a novel thermal energy storage technology with advantages such as high heat storage density and cross-seasonal heat storage. CaO / Ca(OH)2, due to its low cost and availability, holds broad application prospects. However, Ca(OH)2 particles have extremely poor thermal conductivity, typically 0.4-0.7 W / (mK). This slow heat transfer rate during heating results in prolonged heat storage, hindering their widespread adoption in the field.

[0003] The current solution to these problems is to improve the thermal conductivity of the material by adding activated carbon, graphite, heavy oil, and other materials. However, physical mixing is often used, which results in uneven mixing. Furthermore, Ca(OH)2 particles are easily broken during the heat storage / release cycle. Once broken, they aggregate due to gravity and intermolecular attraction, leading to material failure and the appearance of a reaction "dead zone." Therefore, there is an urgent need to develop high-strength, high-thermal-conductivity CaO / Ca(OH)2 composite heat storage materials.

[0004] One of the earliest discovered properties of SiC is its excellent hardness and wear resistance. In terms of hardness, the Mohs hardness of SiC is between 9.2 and 9.3, which is between diamond (10) and topaz (8); the Kerr hardness is 3000 kg / mm 2 In terms of high wear resistance, if the wear resistance of diamond is considered to be 10 and corundum is 9, then SiC is 9.15, and the Young's modulus of elasticity is 4x10 4 kg / mm. SiC can still maintain its inherent hardness and strength at 1000℃.

[0005] SiC also possesses excellent thermal conductivity, a low coefficient of thermal expansion, and high thermal shock resistance, making it a high-quality refractory material. SiC also has excellent thermal stability, and its coefficient of thermal expansion is nearly identical to that of Si, both at 2.9 x 10⁻⁶ K⁻. Therefore, SiC is chosen as the outer shell to minimize thermal stress at high temperatures, thus preventing extrusion deformation. However, currently, the calcium oxide core is simply encased in a SiC shell, leaving no buffer between the core and the shell. During repeated cycles of reaction, the calcium oxide / calcium hydroxide expands in volume, leading to shell rupture. Summary of the Invention

[0006] The purpose of the present invention is to provide a multi-layer coated calcium oxide heat storage material and a preparation method thereof, which solves the problem of easy shell rupture in the existing SiC shell coated calcium oxide core.

[0007] The present invention is achieved through the following technical solutions: The present invention discloses a method for preparing a multi-layer coated calcium oxide heat storage material, comprising the following steps: S1. Evenly coating the surface of calcium hydroxide particles with Al2O3 powder, and drying to obtain Al2O3-coated calcium hydroxide particles; A silicon source and ethyl orthosilicate are mixed and stirred to obtain a mixture; the mixture is added to an ethanol solution, and hexadecyltrimethylammonium bromide is added to obtain a mixed solution; the pH of the mixed solution is adjusted to 1-5, and the mixed solution is heated in a water bath to fully hydrolyze the silicon source to form a sol; graphene oxide is added to the sol, and ultrasonically dispersed to obtain a mixed sol; an alkaline solution is added dropwise to the mixed sol, the pH is adjusted to 8-9.5, and the mixed sol is allowed to stand to obtain a gel; S2, pouring the Al2O3-coated calcium hydroxide particles into the gel, mixing and stirring uniformly to obtain a mixed system; S3, electrolyzing the mixed system to promote gel aging; then freeze-drying to prepare Ca(OH)2 / Al2O3 particles wrapped in SiO2 / graphene oxide composite aerogel; S4. Under a protective atmosphere, heat-treating the Ca(OH)2 / Al2O3 particles wrapped by the SiO2 / graphene oxide composite aerogel to obtain porous SiC and SiO2-coated CaO / Al2O3 particles; S5. The porous SiC and SiO2 coated CaO / Al2O3 particles are immersed in a PVP solution and heat treated in an air atmosphere to obtain a multi-layer coated calcium oxide heat storage material.

[0008] Furthermore, in S1, the drying is: drying at 150-250° C. for 16-48 hours; In S1, heating is performed under water bath conditions, specifically, heating at a water bath temperature of 45-60° C. for 4-8 h.

[0009] Furthermore, in S1, the silicon source is methyltriethoxysilane, dimethoxydimethylsilane or (3-aminopropyl)triethoxysilane.

[0010] Furthermore, in S1, the amount of graphene oxide added is 2.5% to 10% of the sol.

[0011] Furthermore, in S2, the mass ratio of Al2O3-coated calcium hydroxide particles to gel is 2-4:1.

[0012] Further, in S3, the mixture is electrolyzed, specifically: A positive electrode is inserted into the reaction container of the mixture, and a graphite rod is used as the negative electrode, and a voltage is applied between the positive and negative electrodes.

[0013] Furthermore, in S3, freeze drying is to freeze the material into a solid state at -10°C to -50°C, and then sublime the water into a gaseous state under vacuum to dehydrate and dry the material.

[0014] Further, in S4, heat treatment is performed at 1300° C.-1500° C. with a holding time of 1 h-5 h; In S5, heat treatment is performed at 1160-1260° C. in an air atmosphere, and the holding time is 1 h to 5 h.

[0015] The present invention also discloses a multi-layer coated calcium oxide heat storage material prepared by the preparation method. The multi-layer coated calcium oxide heat storage material is a multi-layer coated structure, specifically comprising an inner core, a composite layer sequentially coated outside the inner core, and an outer layer; The inner core is calcium oxide particles, the composite layer is a compound of calcium oxide, aluminum oxide and silicon dioxide, and the outer layer is silicon carbide.

[0016] Furthermore, the hardness of the multi-layer coated calcium oxide heat storage material is 20-50N.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention discloses a method for preparing a multi-layer coated calcium oxide heat storage material. First, Al2O3 powder is evenly coated on the surface of calcium hydroxide particles. After drying, Al2O3-coated calcium hydroxide particles are obtained. The SiC coated on the surface can improve the thermal conductivity and mechanical strength of the CaO / Ca(OH)2 heat storage particles, thereby significantly reducing the heat storage and release time of the heat storage particles and improving the cycle performance of the particles. Compared with directly adhering a silicon carbide shell to the surface of the calcium hydroxide particles by rolling, the sol-gel method can make SiO2 / graphene oxide evenly attached to the surface of the calcium hydroxide particles. By introducing a positive electrode to enhance the positive potential of the calcium hydroxide surface, the adsorption of the sol on the calcium hydroxide surface is promoted, thereby regulating the thickness of the SiO2 / graphene oxide sol shell.

[0018] Under a protective atmosphere, Ca(OH)2 / Al2O3 particles encapsulated in SiO2 / graphene oxide composite aerogels are heat-treated, causing the SiO2 and graphene oxide to react, forming a SiC shell. The SiC shell, rich in mesoporous and microporous structures, promotes the cyclic reaction of the CaO / Ca(OH)2 thermal storage material within. Subsequently, the particles are placed in an air atmosphere, where the excess SiO2 reacts with the Al2O3 and CaO near the core. PVP acts as a foaming agent, generating porous calcium feldspar near the core, providing space for the particles to expand and contract.

[0019] The present invention discloses a multi-layered calcium oxide heat storage material, comprising an inner core, a composite layer sequentially coated around the inner core, and an outer layer. The inner core comprises calcium oxide particles, the composite layer comprises a composite of calcium oxide, aluminum oxide, and silicon dioxide, and the outer layer comprises silicon carbide. The porous structure of the central composite layer prevents the inner core from expanding during repeated cycles due to the porous, loose material in the middle, which acts as a buffer. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The chemical reaction process of the present invention; Figure 2 This is a layer structure diagram of the multi-layer coated calcium oxide heat storage material prepared by the present invention; Figure 3 This is a physical picture of the multi-layer coated calcium oxide heat storage material prepared by the present invention; Figure 4 The present invention is a flow chart of a method for preparing a multi-layer coated calcium oxide heat storage material.

[0021] Among them, 1. inner core; 2. composite layer; 3. outer layer. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clear, the following is a further detailed description with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. That is, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments.

[0023] The detailed description of the embodiment of the present invention provided in the following figures is not intended to limit the scope of the claimed invention, but merely represents a selected embodiment of the present invention. All other embodiments derived by those skilled in the art based on the figures and embodiments of the present invention without inventive effort shall fall within the scope of protection of the present invention.

[0024] It should be noted that the terms "comprises", "includes" or any other variations are intended to cover non-exclusive inclusion, so that a process, element, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to the process, element, method, article or apparatus.

[0025] like Figure 4 As shown, the present invention discloses a method for preparing a multi-layer coated calcium oxide heat storage material, comprising the following steps: S1. Evenly coating the surface of calcium hydroxide particles with Al2O3 powder, and drying to obtain Al2O3-coated calcium hydroxide particles; A silicon source and ethyl orthosilicate are mixed and stirred to obtain a mixture; the mixture is added to an ethanol solution, and hexadecyltrimethylammonium bromide is added to obtain a mixed solution; the pH of the mixed solution is adjusted to 1-5, and the mixed solution is heated in a water bath to fully hydrolyze the silicon source to form a sol; graphene oxide is added to the sol, and ultrasonically dispersed to obtain a mixed sol; an alkaline solution is added dropwise to the mixed sol, the pH is adjusted to 8-9.5, and the mixed sol is allowed to stand to obtain a gel; S2, pouring the Al2O3-coated calcium hydroxide particles into the gel, mixing and stirring uniformly to obtain a mixed system; S3, electrolyzing the mixed system to promote gel aging; then freeze-drying to prepare Ca(OH)2 / Al2O3 particles wrapped in SiO2 / graphene oxide composite aerogel; S4. Under a protective atmosphere, heat-treating the Ca(OH)2 / Al2O3 particles wrapped by the SiO2 / graphene oxide composite aerogel to obtain porous SiC and SiO2-coated CaO / Al2O3 particles; S5. The porous SiC and SiO2 coated CaO / Al2O3 particles are immersed in a PVP solution and heat treated in an air atmosphere to obtain a multi-layer coated calcium oxide heat storage material.

[0026] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0027] Example 1 like Figure 1 As shown, the present invention provides a method for preparing a multi-layer coated calcium oxide heat storage material, comprising the following steps: (1) Take 200g of calcium hydroxide powder (200 mesh), adjust the ball rolling machine speed, add appropriate amount of deionized water, and prepare calcium hydroxide particles with a particle size of about 3mm. After forming into balls, evenly coat the surface of the balls with a layer of Al2O3 powder, place them in a 200℃ oven and dry them for 24h to increase their hardness, thereby obtaining Al2O3-coated calcium hydroxide particles.

[0028] Among them, the thickness of Al2O3 is about 0.2mm.

[0029] (2) Preparation of gel First, methyltriethoxysilane (MTES) and tetraethyl orthosilicate (TEOS) were mixed in a molar ratio of 9:1 and stirred for 1 h.

[0030] Take 1 g of the above mixture, add 20 g of ethanol aqueous solution and 0.4 g of cetyltrimethylammonium bromide (CTAB) to obtain a mixed solution; then add 0.1 M hydrochloric acid solution to the mixed solution to adjust the pH to 3.0, and incubate in a water bath at 45°C for 8 hours to fully hydrolyze the silicon source and form a sol.

[0031] 2.5 g of graphene oxide was added to 100 g of the sol and ultrasonicated for 30 min to fully mix it with the silica sol to obtain a mixed sol; Subsequently, 1 M ammonia solution was added dropwise to the mixed sol while stirring to adjust the pH to 9.0. The container was sealed and allowed to stand at room temperature for 20 minutes to allow gelation to obtain a gel.

[0032] (3) Subsequently, 20 g of the Al2O3-coated calcium hydroxide particles prepared in step (1) were poured into 10 g of the gel prepared in step (2), and the mixture was gently stirred to uniformly mix the Al2O3-coated calcium hydroxide particles and the gel; (4) Then, a positive electrode is inserted into the beaker, and a graphite rod is used to replace the negative electrode. A certain voltage is applied between the positive and negative electrodes; the mixture prepared in step (3) is electrolyzed for 1 hour to promote gel aging.

[0033] It is then frozen into a solid state at -10°C, and then the water is sublimated into a gaseous state under vacuum, and the material is dehydrated and dried to prepare Ca(OH)2 / Al2O3 particles wrapped in SiO2 / graphene oxide composite aerogel.

[0034] (5) The SiO2 / graphene oxide composite aerogel-coated Ca(OH)2 / Al2O3 particles obtained in step (4) were placed in an alumina crucible and placed in a tubular high-temperature furnace, where nitrogen was introduced for 30 minutes. The crucible was then heat treated at 1300°C to 1500°C (at a heating rate of 5°C / min) for 1 hour. After the reaction was complete, the sample was removed to obtain porous SiC and SiO2-coated CaO / Al2O3 particles.

[0035] (6) The porous SiC-coated CaO / Al2O3 particles obtained in step (5) were immersed in a PVP solution (K15 saturated solution) for 30 min to allow the solution to penetrate the particles. The particles were placed in an alumina crucible and placed in a tubular high-temperature furnace for heat treatment at 1200°C (heating rate of 5°C / min) in an air atmosphere for 1 h. After the reaction was completed, the sample was removed to obtain a multi-layer coated calcium oxide heat storage material.

[0036] The heat storage experiment proceeded as follows: 1g of the prepared heat storage material was placed in a porcelain boat and heated in a tube furnace. The material was then cooled to room temperature and weighed. The decomposition efficiency of the heat storage medium was calculated. The results showed that after 30 minutes, the decomposition efficiency of the heat storage medium generated at 500°C, 550°C, and 600°C reached 85%, 87%, and 91%, respectively. These efficiency rates were higher than the rated heat storage rates of pure Ca(OH)2 at 500°C, 550°C, and 600°C (51%, 55%, and 60%). After ten cycles, the hardness of the heat storage material reached 20N, significantly higher than that of pure Ca(OH)2 (after crushing).

[0037] Example 2 The present invention provides a method for preparing a multi-layer coated calcium oxide heat storage material, comprising the following steps: (1) Take 200g of calcium hydroxide powder (200 mesh), adjust the ball rolling machine speed, add appropriate amount of deionized water, and prepare calcium hydroxide particles with a particle size of about 3mm. After forming into balls, evenly coat the surface of the balls with a layer of Al2O3 powder, place them in a 150℃ oven and dry them for 48h to increase their hardness, thereby obtaining Al2O3-coated calcium hydroxide particles.

[0038] Among them, the thickness of Al2O3 is about 0.2mm.

[0039] (2) Preparation of gel First, dimethoxydimethylsilane and tetraethyl orthosilicate (TEOS) were mixed in a molar ratio of 9:1 and stirred for 1 hour to obtain a mixture.

[0040] Take 1 g of the above mixture, add 20 g of ethanol aqueous solution and 0.4 g of hexadecyltrimethylammonium bromide (CTAB) to obtain a mixed solution; then add 0.1 M hydrochloric acid solution to the mixed solution to adjust the pH to 5, and incubate in a water bath at 60°C for 4 hours to fully hydrolyze the silicon source to form a sol.

[0041] 10 g of graphene oxide was added to 100 g of the sol and ultrasonicated for 30 min to fully mix it with the silica sol to obtain a mixed sol; Subsequently, 1M ammonia solution was added dropwise to the mixed sol while stirring, and the pH was adjusted to 9.5. The container was sealed and allowed to stand at room temperature for 20 minutes to gel, thereby obtaining a gel.

[0042] (3) Subsequently, 40 g of the Al2O3-coated calcium hydroxide particles prepared in step (1) were poured into 10 g of the gel prepared in step (2), and the mixture was gently stirred to uniformly mix the Al2O3-coated calcium hydroxide particles and the gel; (4) Then, a positive electrode is inserted into the beaker, and a graphite rod is used to replace the negative electrode. A certain voltage is applied between the positive and negative electrodes; the mixture prepared in step (3) is electrolyzed for 1 hour to promote gel aging.

[0043] It is then frozen into a solid state at -50°C, and then the water is sublimated into a gaseous state under vacuum, and the material is dehydrated and dried to prepare Ca(OH)2 / Al2O3 particles wrapped in SiO2 / graphene oxide composite aerogel.

[0044] (5) The SiO2 / graphene oxide composite aerogel-coated Ca(OH)2 / Al2O3 particles obtained in step (4) were placed in an alumina crucible and placed in a tubular high-temperature furnace, where nitrogen was introduced for 30 minutes. The crucible was then heat treated at 1300°C to 1500°C (at a heating rate of 5°C / min) for 1 hour. After the reaction was complete, the sample was removed to obtain porous SiC and SiO2-coated CaO / Al2O3 particles.

[0045] (6) The porous SiC-coated CaO / Al2O3 particles obtained in step (5) were immersed in a PVP solution (K15 saturated solution) for 30 min to allow the solution to penetrate the particles. The particles were placed in an alumina crucible and placed in a tubular high-temperature furnace for heat treatment at 1160°C (heating rate of 5°C / min) in an air atmosphere for 5 h. After the reaction was completed, the sample was removed to obtain a multi-layer coated calcium oxide heat storage material.

[0046] The heat storage experiment proceeded as follows: 1g of the prepared heat storage material was placed in a porcelain boat and heated in a tube furnace. The material was then cooled to room temperature and weighed. The decomposition efficiency of the heat storage medium was then calculated. The results showed that after 30 minutes, the decomposition efficiency of the heat storage medium generated at 500°C, 550°C, and 600°C reached 86%, 90%, and 92%, respectively. These efficiency rates were higher than the rated heat storage rates of pure Ca(OH)2 at 500°C, 550°C, and 600°C (51%, 55%, and 60%). After ten cycles, the hardness of the heat storage material reached 30N, significantly higher than that of pure Ca(OH)2 (after crushing).

[0047] Example 3 The present invention provides a method for preparing a multi-layer coated calcium oxide heat storage material, comprising the following steps: (1) Take 200g of calcium hydroxide powder (200 mesh), adjust the ball rolling machine speed, add appropriate amount of deionized water, and prepare calcium hydroxide particles with a particle size of about 3mm. After forming into balls, evenly coat the surface of the balls with a layer of Al2O3 powder, place them in a 250℃ oven and dry them for 16h to increase their hardness, thereby obtaining Al2O3-coated calcium hydroxide particles.

[0048] Among them, the thickness of Al2O3 is about 0.3mm.

[0049] (2) Preparation of gel First, (3-aminopropyl)triethoxysilane and tetraethyl orthosilicate (TEOS) were mixed in a molar ratio of 9:1 and stirred for 1 hour to obtain a mixture.

[0050] Take 1 g of the above mixture, add 20 g of ethanol aqueous solution and 0.4 g of cetyltrimethylammonium bromide (CTAB) to obtain a mixed solution; then add 0.1 M hydrochloric acid solution to the mixed solution to adjust the pH to 1, and incubate in a water bath at 60°C for 4 hours to fully hydrolyze the silicon source and form a sol.

[0051] 5 g of graphene oxide was added to 100 g of the sol and ultrasonicated for 30 min to fully mix it with the silica sol to obtain a mixed sol; Subsequently, 1M ammonia solution was added dropwise to the mixed sol while stirring, and the pH was adjusted to 8. The container was sealed and allowed to stand at room temperature for 20 minutes to gel, thereby obtaining a gel.

[0052] (3) Subsequently, 30 g of the Al2O3-coated calcium hydroxide particles prepared in step (1) were poured into 10 g of the gel prepared in step (2), and the mixture was gently stirred to uniformly mix the Al2O3-coated calcium hydroxide particles and the gel; (4) Then, a positive electrode is inserted into the beaker, and a graphite rod is used to replace the negative electrode. A certain voltage is applied between the positive and negative electrodes; the mixture prepared in step (3) is electrolyzed for 1 hour to promote gel aging.

[0053] It is then frozen into a solid state at -30°C, and then the water is sublimated into a gaseous state under vacuum, and the material is dehydrated and dried to prepare Ca(OH)2 / Al2O3 particles wrapped in SiO2 / graphene oxide composite aerogel.

[0054] (5) The SiO2 / graphene oxide composite aerogel-coated Ca(OH)2 / Al2O3 particles obtained in step (4) were placed in an alumina crucible and placed in a tubular high-temperature furnace, where nitrogen was introduced for 30 minutes. The crucible was then heat treated at 1300°C to 1500°C (at a heating rate of 5°C / min) for 1 hour. After the reaction was complete, the sample was removed to obtain porous SiC and SiO2-coated CaO / Al2O3 particles.

[0055] (6) The porous SiC-coated CaO / Al2O3 particles obtained in step (5) were immersed in a PVP solution (K15 saturated solution) for 30 min to allow the solution to penetrate the particles. The particles were placed in an alumina crucible and placed in a tubular high-temperature furnace for heat treatment at 1260°C (heating rate of 5°C / min) in an air atmosphere for 1 h. After the reaction was completed, the sample was removed to obtain a multi-layer coated calcium oxide heat storage material.

[0056] The heat storage experiment proceeded as follows: 1g of the prepared heat storage material was placed in a porcelain boat and heated in a tube furnace. The material was then cooled to room temperature and weighed. The decomposition efficiency of the heat storage medium was calculated. The results showed that after 30 minutes, the decomposition efficiency of the heat storage medium generated at 500°C, 550°C, and 600°C reached 88%, 92%, and 94%, respectively. These efficiency rates were higher than the rated heat storage rates of pure Ca(OH)2 at 500°C, 550°C, and 600°C (51%, 55%, and 60%). After ten cycles, the heat storage material had a hardness of 50N, significantly higher than that of pure Ca(OH)2 (after crushing).

[0057] like Figure 1 As shown, compared with directly adhering the silicon carbide shell on the surface of calcium hydroxide particles by rolling, the present invention adopts the sol-gel method to make SiO2 / graphene oxide evenly adhere to the surface of calcium hydroxide particles, and by introducing the positive electrode to enhance the positive potential of the calcium hydroxide surface, promote the adsorption of the sol on the calcium hydroxide surface, thereby regulating the thickness of the SiO2 / graphene oxide sol shell.

[0058] High-temperature calcination causes SiO2 and graphene oxide to react as follows: SiO2(S) + 3C(S) = SiC(S) + 2CO(g). The resulting SiC shell has a rich mesoporous and microporous structure, which is conducive to promoting the cyclic reaction of the CaO / Ca(OH)2 thermal storage material inside.

[0059] Subsequently, the particles are placed in an air atmosphere, and the excess SiO2 reacts with the Al2O3 and CaO near the core. At this time, PVP acts as a foaming agent, causing porous calcium feldspar to form near the core, providing space for the expansion and contraction of the particles.

[0060] The core-shell structure interface of the multilayer coated calcium oxide heat storage material prepared by the present invention is as follows Figure 3 shown.

[0061] like Figure 2 As shown, the multi-layer coated calcium oxide heat storage material is a multi-layer coated structure, specifically comprising an inner core 1, a composite layer 2 and an outer layer 3 sequentially coated outside the inner core; The inner core 1 is calcium oxide particles, the composite layer 2 is a composite of calcium oxide, aluminum oxide and silicon dioxide, and the outer layer 3 is silicon carbide.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a multi-layer coated calcium oxide heat storage material, characterized in that: The following processes are included: S1. Evenly coating the surface of calcium hydroxide particles with Al2O3 powder, and drying to obtain Al2O3-coated calcium hydroxide particles; A silicon source and ethyl orthosilicate are mixed and stirred to obtain a mixture; the mixture is added to an ethanol solution, and hexadecyltrimethylammonium bromide is added to obtain a mixed solution; the pH of the mixed solution is adjusted to 1-5, and the mixed solution is heated in a water bath to fully hydrolyze the silicon source to form a sol; graphene oxide is added to the sol, and ultrasonically dispersed to obtain a mixed sol; an alkaline solution is added dropwise to the mixed sol, the pH is adjusted to 8-9.5, and the mixed sol is allowed to stand to obtain a gel; S2, pouring the Al2O3-coated calcium hydroxide particles into the gel, mixing and stirring uniformly to obtain a mixed system; S3, electrolyzing the mixed system to promote gel aging; then freeze-drying to prepare Ca(OH)2 / Al2O3 particles wrapped in SiO2 / graphene oxide composite aerogel; S4. Under a protective atmosphere, heat-treating the Ca(OH)2 / Al2O3 particles wrapped by the SiO2 / graphene oxide composite aerogel to obtain porous SiC and SiO2-coated CaO / Al2O3 particles; S5. The porous SiC and SiO2 coated CaO / Al2O3 particles are immersed in a PVP solution and heat treated in an air atmosphere to obtain a multi-layer coated calcium oxide heat storage material.

2. The method for preparing a multi-layer coated calcium oxide heat storage material according to claim 1, characterized in that: In S1, the drying is: drying at 150-250°C for 16-48h; In S1, heating is performed under water bath conditions, specifically, heating at a water bath temperature of 45-60° C. for 4-8 h.

3. The method for preparing a multi-layer coated calcium oxide heat storage material according to claim 1, characterized in that: In S1, the silicon source is methyltriethoxysilane, dimethoxydimethylsilane or (3-aminopropyl)triethoxysilane.

4. The method for preparing a multi-layer coated calcium oxide heat storage material according to claim 1, characterized in that: In S1, the addition amount of graphene oxide is 2.5%~10% of the sol.

5. The method for preparing a multi-layer coated calcium oxide heat storage material according to claim 1, characterized in that: In S2, the mass ratio of Al2O3-coated calcium hydroxide particles to gel is 2-4:

1.

6. The method for preparing a multi-layer coated calcium oxide heat storage material according to claim 1, characterized in that: In S3, the mixture is electrolyzed, specifically: A positive electrode is inserted into the reaction container of the mixture, and a graphite rod is used as the negative electrode, and a voltage is applied between the positive and negative electrodes.

7. The method for preparing a multi-layer coated calcium oxide heat storage material according to claim 1, characterized in that: In S3, freeze drying is to freeze the material into a solid state at -10°C to -50°C, and then sublime the water into a gaseous state under vacuum to dehydrate and dry the material.

8. The method for preparing a multi-layer coated calcium oxide heat storage material according to claim 1, characterized in that: In S4, heat treatment is performed at 1300°C-1500°C with a holding time of 1h-5h; In S5, heat treatment is performed at 1160-1260° C. in an air atmosphere, and the holding time is 1 h to 5 h.

9. A multi-layer coated calcium oxide heat storage material prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The multi-layer coated calcium oxide heat storage material is a multi-layer coated structure, specifically comprising an inner core (1), a composite layer (2) and an outer layer (3) sequentially coated outside the inner core; The inner core (1) is calcium oxide particles, the composite layer (2) is a composite of calcium oxide, aluminum oxide and silicon dioxide, and the outer layer (3) is silicon carbide.

10. The multi-layer coated calcium oxide heat storage material according to claim 9, characterized in that: The hardness of the multi-layer coated calcium oxide heat storage material is 20-50N.

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