Preparation method of TiO2-BG-SA / CEG-BNNS composite phase change heat storage material

Abstract

The invention discloses a preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material, and particularly relates to the technical field of heat storage, and the preparation method comprises the following steps: uniformly stirring and mixing phase change material powder and modified expanded graphite according to a mass ratio of (6.5-7.2): 1, and then carrying out heating mixing, vacuum drying and directional briquetting to obtain the TiO2-BG-SA / CEG-BNNS composite phase change heat storage material. The high-density composite phase change heat storage material block is obtained. The preparation method of the TiO2-BG-SA / CEG-BNNS composite phase change heat storage material provided by the invention has the beneficial effects that the modified expanded graphite not only remarkably improves the heat conduction efficiency, but also strengthens the interface stability of the material through bonding, so that the leakage of a phase change medium in the recycling process is fundamentally inhibited; the preparation method has the characteristics of high process parameter controllability and high equipment compatibility, and provides a reliable technical path for large-scale production of high-performance phase change energy storage materials.

Description

Technical Field

[0001] This invention patent relates to the technical field of heat storage, and specifically relates to a preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material. Background Art

[0002] Solar energy phase change heat storage technology stores thermal energy in a heat storage device through a phase change material (PCM), effectively alleviating the intermittency and instability of solar energy. Currently, the commonly used phase change heat storage materials include two categories: inorganic substances and organic substances. Among them, the existing patent with the application number CN202411393184.2 and the name of a preparation method of a composite phase change heat storage material discloses that a phase change material powder and modified expanded graphite are stirred and mixed evenly according to a mass ratio of 7-7.5:1, and then through heating and mixing, vacuum drying and pressing, a composite phase change heat storage material block is obtained; among them, the preparation method of the modified expanded graphite includes the following steps: (1) pretreatment; (2) mixing; (3) crushing and cooling; (4) suction filtration and drying. It has good dispersion stability and strong lipophilicity, effectively improving the thermal conductivity of the modified expanded graphite, and has excellent heat transfer performance, thermal stability and anti-leakage performance. However, the above-mentioned phase change heat storage materials have bottleneck problems such as discontinuous heat conduction network (i.e., the thermal conductivity is only 8.93 W / (m·K)), weak interfacial bonding force (i.e., the leakage rate > 1.5% after 1000 thermal cycles), and insufficient material density (i.e., leakage occurs when the density ≥ 821 kg / m³) due to their single physical adsorption modification. Summary of the Invention

[0003] The purpose of the present invention is to provide a preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material that significantly improves the heat conduction efficiency, strengthens the interfacial stability of the material, and inhibits the leakage of the phase change medium during the recycling process.

[0004] The purpose of the present invention is implemented by the following technical solution: A preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material, which includes the following steps: Stir and mix a phase change material powder and modified expanded graphite evenly according to a mass ratio of 6.5-7.2:1, and then through heating and mixing, vacuum drying and directional pressing, a high-density composite phase change heat storage material block is obtained; Among them, the preparation method of the phase change material powder includes the following steps: Stir and mix 72-75 parts of glyceryl behenate (BG), 14-15 parts of stearyl alcohol (SA), and 1.2-1.5 parts of nano-titanium dioxide by weight under water bath heating, then naturally cool to room temperature and solidify, and finally grind into a powder with a particle size of 120-160 μm, and store it sealed; The preparation method of the modified expanded graphite comprises the following steps: (1) Pretreatment process: The graphite expanded powder is dried to thoroughly remove the trace moisture adsorbed by the raw materials, and then transferred to a muffle furnace at 820 - 880 °C. It is calcined in an oxygen-rich environment with an oxygen concentration of 95 - 98% for 53 - 58 s, enabling the rapid decomposition of the graphite intercalation compound to produce a volume expansion of up to 200 - 300 times, forming expanded graphite with a three-dimensional interconnected pore structure. Its porosity ≥ 92%, and the specific surface area reaches 200 - 250 m² / g, providing an ideal carrier structure for subsequent nano-intercalation; (2) Nano-intercalation mixing: Mix the expanded graphite in step (1), an oleic acid ethanol (OAE) solution with a titanium dioxide concentration of 0.02 - 0.05 mol / L, and boron nitride nanosheets (BNNS). Through the π-π interaction between the long-chain alkyl groups of OAE molecules and the graphite surface, the directional intercalation of the nanosheets is achieved; then, under an environment with a temperature of 50 - 52 °C, magnetic-ultrasonic alternating stirring is carried out for 25 - 28 min to enable BNNS to achieve nano-scale penetration along the graphite lamellae, forming a graphite / boron nitride heterostructure. During this process, the OAE solution serves as both a dispersion medium, and its carboxylic acid groups can also form hydrogen bond binding with the graphite edge to ensure the stable anchoring of BNNS, obtaining a graphite / boron nitride material; (3) Grafting: Mix the graphite / boron nitride material in step (2), a titanium dioxide ethanol solution with a concentration of 0.15 - 0.2 mol / L, and a silane coupling agent (KH550). Then, a grafting reaction is carried out at a temperature of 55 - 58 °C for 65 - 70 min. The amino-siloxane group of KH550 undergoes a condensation reaction with the hydroxyl groups on the graphite surface, and at the same time, an Si-O-B bond is formed at the edge of BNNS to construct a three-dimensional crosslinked network. Subsequently, ultrasonic treatment is carried out for 6 - 6.5 h, which not only eliminates nano-agglomerates but also promotes the stretching and arrangement of grafted molecular chains through the cavitation effect, finally forming a dense organic-inorganic composite interface layer on the graphite surface to obtain a mixed solution; (4) Filtration and drying: The mixed solution in step (3) is filtered by suction, and then dried at 78 - 80 °C for 11 - 11.5 h to obtain the modified expanded graphite with a particle size of 50 - 75 μm.

[0005] Further, the stirring and mixing under water bath heating specifically mean that under the condition of water bath heating at a temperature of 82 - 84 °C, stirring is carried out for 8.2 - 8.8 h to make it evenly mixed, and the stirring speed is 890 - 920 r / min.

[0006] Further, the particle size of the graphite expanded powder in step (1) is 150 - 200 mesh, and the purity is 97 - 98%; the drying conditions of the graphite expanded powder are constant temperature drying at 85 - 88 °C for 13 - 14 h in a drying oven with a vacuum degree ≤ 100 Pa.

[0007] Furthermore, in step (2), the mass ratio of expanded graphite, oleic acid ethanol solution and boron nitride nanosheets is 32 - 34:60 - 62:4 - 8, where the thickness of the boron nitride nanosheets is 5 - 8 nm and the aspect ratio > 200.

[0008] Furthermore, in step (2), the magnetic - ultrasonic alternating stirring is specifically as follows: magnetic stirring and ultrasonic stirring are alternated every 5 - 8 min, where the speed of magnetic stirring is 880 - 910 r / min, and the working condition parameters of ultrasonic stirring include: ultrasonic power is 223 - 354 W, and the stirring speed is 880 - 910 r / min.

[0009] Furthermore, in step (3), the mass ratio of graphite / boron nitride material, titanium dioxide ethanol solution and silane coupling agent is 28 - 30:58 - 61:9 - 14; the conditions for ultrasonic treatment are: the frequency is 220 - 256 kHz, and the pulse duty cycle is 12 - 23%.

[0010] Furthermore, the specific conditions for heating and mixing are as follows: the uniformly mixed material is placed in an environment at 83 - 85 °C, stirred once every 50 min, and continued for 10 - 10.5 h to obtain a mixed material.

[0011] Furthermore, the stirring time for each time is 6 - 7 min, and the stirring speed is 850 - 880 r / min.

[0012] Furthermore, the vacuum drying is specifically as follows: the mixed material is placed in a vacuum drying oven, heated and dried at a temperature of 82 - 84 °C and a vacuum degree of 9500 - 11500 Pa for 15.2 - 15.8 h, and then naturally cooled to room temperature to obtain a composite phase - change heat - storage material.

[0013] Furthermore, the directional briquetting is specifically as follows: the composite phase - change heat - storage material is briquetted using a briquetting machine to obtain a composite phase - change heat - storage material block with a density of 800 - 860 kg / m 3 In this process, three - stage pressure briquetting is carried out using a briquetting machine: the first stage: pre - press for 20 - 25 s at 5.5 - 6.0 MPa, the second stage: main - press for 38 - 43 s at 9.0 - 9.5 MPa, and the third stage: keep the pressure stable for 12 - 14 s at 7.0 - 7.5 MPa.

[0014] Advantages of the present invention: 1. The present invention provides a preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material. Through the synergistic effect of nano-intercalation and grafting, a three-dimensional composite reinforcement structure is constructed; and by using the directional interpenetration of two-dimensional nanomaterials and the interfacial grafting of organic molecules, a continuous heat conduction network and cross-linked interface are formed in the graphite skeleton, effectively solving the problems of discontinuous heat conduction paths and poor wettability of phase change materials in traditional materials. The modified expanded graphite designed with the above multi-level structure not only significantly improves the heat conduction efficiency but also strengthens the interface stability of the material through bonding, fundamentally suppressing the leakage of phase change media during the recycling process.

[0015] 2. The present invention provides a preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material, achieving a breakthrough through the synergistic modification technology of BNNS directional intercalation and KH550 grafting: BNNS with an aspect ratio > 200 is intercalated into the interlayer space of EG sheets to construct a three-dimensional continuous heat conduction heterojunction, and combined with the Si-O-B / graphite bond bridging effect of KH550 to strengthen the interfacial bonding, increasing the thermal conductivity to 9.58 W / (m·K), with a 7.3% increase compared to the existing patent; meanwhile, through a three-stage pressurization process, the densification of the material is optimized, increasing the density to 860 kg / m³ (porosity ≤ 5%), and relying on chemical bonding to inhibit the leakage of phase change media under thermal cycling. After 1000 cycles of heat storage and release, the leakage rate drops to 0.5% (a 74.7% decrease compared to the existing patent). This technology uses a synergistic strategy of nano-enhancement and interfacial bonding to overcome the technical barriers of broken heat conduction paths, nano-agglomeration, and unstable physical adsorption in traditional EG modification, realizing a composite phase change heat storage material with high thermal conductivity (9.58 W / (m·K)), ultra-low leakage (≤0.5%), and long-term stability.

[0016] 3. The present invention provides a preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material, adopting a new process system combining heating mixing and three-stage pressurization molding, precisely regulating the phase transition process of the material, and realizing the uniform distribution and directional arrangement of nano-enhanced phases in the matrix; adopting an alternating stirring mode and a multi-stage pressurization process, overcoming the technical difficulties of densifying and molding high-porosity materials, and ensuring the integrity and performance consistency of the composite material structure; this preparation method has the characteristics of strong process parameter controllability and high equipment compatibility, providing a reliable technical path for large-scale production of high-performance phase change energy storage materials. Description of the Drawings

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the accompanying drawings required for use in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0018] Figure 1 Flow chart of preparing TiO2-BG-SA in Example 1 of the present invention.

[0019] Figure 2 Flow chart of preparing CEG-BNNS in Example 1 of the present invention.

[0020] Figure 3 Flow chart of preparing TiO2-BG-SA / CEG-BNNS in Example 1 of the present invention.

[0021] Figure 4 Physical photos of pretreated EG and CEG-BNNS.

[0022] Figure 5 Contact diagrams of EG and CEG-BNNS flakes with water and oil respectively.

[0023] Figure 6 Fourier infrared spectra of TiO2-BG-SA, CEG-BNNS, TiO2-BG-SA / CEG-BNNS, EG and TiO2-BG-SA / EG.

[0024] Figure 7 XRD diffraction patterns of TiO2-BG-SA, CEG-BNNS, TiO2-BG-SA / CEG-BNNS, EG and TiO2-BG-SA / EG.

[0025] Figure 8 Appearance photos of composite phase change heat storage material blocks with different densities after 120 cycles of heat storage and release.

[0026] Figure 9 SEM scanning electron micrographs of TiO2-BG-SA / EG in Comparative Example 1, CEG-BNNS in Example 1, and TiO2-BG-SA / CEG-BNNS in Example 1.

[0027] Figure 10 Flow chart of heat storage / release; where (a) is the heat storage flow chart and (b) is the heat release flow chart.

[0028] Figure 11 Graphs of heat storage / release temperature changes; where (a) is the graph of heat storage temperature changes and (b) is the graph of heat release temperature changes. Detailed implementation mode

[0029] The present invention will be further described in detail through embodiments below.

[0030] Embodiment 1: A preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material, which includes the following steps: As Figure 1 shown, the preparation method of the phase change material powder (TiO2-BG-SA) includes the following steps: Mix 720 g of BG, 140 g of SA and 12 g of TiO2 under stirring in a water bath at a temperature of 82-84 °C for 8.2-8.8 h to make the mixture uniform, where the stirring speed is 890-920 r / min, then naturally cool to room temperature and solidify, and finally grind into powder with a particle size of 120-160 μm and store it sealed.

[0031] As Figure 2 shown, the preparation method of the modified expanded graphite (CEG-BNNS) includes the following steps: (1) Pretreatment process: Dry the expanded graphite powder, then transfer it to a muffle furnace at 820-880 °C, and calcine it in an oxygen-rich environment with an oxygen concentration of 95-98% for 53-58 s to form expanded graphite (EG) with a three-dimensional interconnected pore structure, whose porosity ≥92% and specific surface area reaches 200-250 m² / g; where the particle size of the expanded graphite powder is 150-200 mesh and the purity is 97-98%; the drying conditions of the expanded graphite powder are in a drying oven with a vacuum degree ≤100 Pa, and keep it at a constant temperature of 85-88 °C for 13-14 h.

[0032] (2) Nano-intercalation mixing: Mix 100 g of the expanded graphite in step (1), 190 g of an oleic acid ethanol (OAE) solution with a titanium dioxide concentration of 0.02-0.05 mol / L and 18.75 g of boron nitride nanosheets (BNNS), and then carry out magnetic-ultrasonic alternating stirring at a temperature of 50-52 °C for 25-28 min to obtain a graphite / boron nitride material; where the thickness of the boron nitride nanosheets is 5-8 nm and the aspect ratio >200; the magnetic-ultrasonic alternating stirring is specifically: the magnetic stirring and ultrasonic stirring are alternated every 5-8 min, where the speed of the magnetic stirring is 880-910 r / min, and the working condition parameters of the ultrasonic stirring include: the ultrasonic power is 223-354 W and the stirring speed is 880-910 r / min.

[0033] (3) Grafting: Mix 121 g of the graphite / boron nitride material from step (2), 256 g of a titanium dioxide ethanol solution with a concentration of 0.15 - 0.2 mol / L, and 47.5 g of a silane coupling agent (KH550). Then, conduct a grafting reaction at a temperature of 55 - 58 °C for 65 - 70 min, followed by ultrasonic treatment for 6 - 6.5 h to obtain a mixed solution. The conditions for ultrasonic treatment are as follows: the frequency is 220 - 256 kHz, and the pulse duty cycle is 12 - 23%.

[0034] (4) Filtration and drying: Filter the mixed solution from step (3), and then dry it at 78 - 80 °C for 11 - 11.5 h to obtain modified expanded graphite with a particle size of 50 - 75 μm.

[0035] As Figure 3 shown, stir and mix 52.5 g of the phase change material powder with 7.5 g of the modified expanded graphite evenly. Then, place the evenly mixed material in an environment at 83 - 85 °C, stir once every 50 min, with each stirring time being 6 - 7 min and the stirring speed being 850 - 880 r / min, for 10 - 10.5 h to obtain a mixed material. Then, place the mixed material in a vacuum drying oven and heat and dry it at a temperature of 82 - 84 °C and a vacuum degree of 9500 - 11500 Pa for 15.2 - 15.8 h, and then naturally cool it to room temperature to obtain a composite phase change heat storage material. Finally, press the composite phase change heat storage material using a tablet press to obtain a composite phase change heat storage material block (TiO2 - BG - SA / CEG - BNNS) with a density of 800 - 860 kg / m 3 . Among them, the tablet press is used for three - stage pressurized briquetting: The first stage: pre - press at 5.5 - 6.0 MPa for 20 - 25 s, the second stage: main - press at 9.0 - 9.5 MPa for 38 - 43 s, and the third stage: stabilize the pressure at 7.0 - 7.5 MPa for 12 - 14 s.

[0036] Among them, the physical photos of the pretreated expanded graphite (EG) and the modified expanded graphite (CEG - BNNS) can be seen in Figure 4 , and the dispersibility of CEG - BNNS is better than that of the pretreated EG. In addition, conduct a wettability study on the pretreated EG and CEG - BNNS. By compressing EG and CEG - BNNS into thin slices with a diameter of 10 mm and a height of 1 mm respectively under a pressure of 7.0 MPa, and then measuring the contact angles of the EG and CEG - BNNS thin slices with water and oil (OA). As Figure 5 shown, from Figure 5 (a) and Figure 5 (b), it can be seen that the contact angle of EG with water is 61°, while the contact angle of CEG - BNNS with water is 128°, indicating that the hydrophobicity of CEG - BNNS has been improved. In addition, fromFigure 5 (c) and Figure 5 As can be seen from (d), the contact angle between EG and OA is 55°, while the contact angle between CEG-BNNS and OA is about 2°. This indicates that the lipophilicity of CEG-BNNS has been significantly improved. Obviously, the hydrophobicity and lipophilicity of CEG-BNNS have been significantly enhanced, reducing the phase separation phenomenon of the PCM after synthesis. In this example, after the nano-intercalation and grafting process of EG, the original worm-like microstructure is destroyed, the lamellar structure is broken, the particles tend to be micronized, and its dispersibility is improved, making it easier to disperse in organic solvents.

[0037] Example 2: A preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material, which includes the following steps: The preparation method of the phase change material powder (TiO2-BG-SA) includes the following steps: Mix 552 BG, 105 g SA and 10.4 g TiO2 under stirring in a water bath at a temperature of 82 - 84 °C for 8.2 - 8.8 h to make it evenly mixed, where the stirring speed is 890 - 920 r / min, then naturally cool to room temperature and solidify, and finally grind it into a powder with a particle size of 120 - 160 μm, and store it sealed.

[0038] The preparation method of the modified expanded graphite (CEG-BNNS) includes the following steps: (1) Pretreatment process: Dry the expanded graphite powder, and then transfer it to a muffle furnace at 820 - 880 °C for roasting for 53 - 58 s in an oxygen-rich environment with an oxygen concentration of 95 - 98% to form expanded graphite (EG) with a three-dimensional interconnected pore structure, whose porosity ≥ 92% and specific surface area reaches 200 - 250 m² / g; among them, the particle size of the expanded graphite powder is 150 - 200 mesh and the purity is 97 - 98%; the drying condition of the expanded graphite powder is to keep it dry at a constant temperature of 85 - 88 °C for 13 - 14 h in a drying oven with a vacuum degree ≤ 100 Pa.

[0039] (2) Nano-intercalation mixing: Mix 33 g of the expanded graphite in step (1), 62 g of an oleic acid ethanol (OAE) solution with a titanium dioxide concentration of 0.02 - 0.05 mol / L, and 4.2 g of boron nitride nanosheets (BNNS), and then carry out magnetic-ultrasonic alternating stirring for 25 - 28 min in an environment at a temperature of 50 - 52 °C to obtain a graphite / boron nitride material; among them, the thickness of the boron nitride nanosheets is 5 - 8 nm and the aspect ratio > 200; the magnetic-ultrasonic alternating stirring is specifically: the magnetic stirring and ultrasonic stirring are carried out alternately every 5 - 88 min, where the speed of the magnetic stirring is 880 - 910 r / min, and the working condition parameters of the ultrasonic stirring include: the ultrasonic power is 223 - 354 W and the stirring speed is 880 - 910 r / min.

[0040] (3)Grafting: Mix 28 g of graphite / boron nitride material from step (2), 60 g of titanium dioxide ethanol solution with a concentration of 0.15 - 0.2 mol / L, and 10 g of silane coupling agent (KH550). Then, conduct a grafting reaction at a temperature of 55 - 58 °C for 65 - 70 min, and subsequently perform ultrasonic treatment for 6 - 6.5 h to obtain a mixed solution. The conditions for ultrasonic treatment are: the frequency is 220 - 256 kHz, and the pulse duty cycle is 12 - 23%.

[0041] (4)Filtration and drying: Filter the mixed solution in step (3), and then dry it at 78 - 80 °C for 11 - 11.5 h to obtain modified expanded graphite with a particle size of 50 - 75 μm.

[0042] Stir and mix 325 g of phase change material powder with 50 g of modified expanded graphite evenly. Then, place the evenly mixed material in an environment at 83 - 85 °C, stir once every 50 min, with each stirring time being 6 - 7 min and the stirring speed being 850 - 880 r / min, for 10 - 10.5 h to obtain a mixed material. Then, place the mixed material in a vacuum drying oven, heat and dry it at a temperature of 82 - 84 °C and a vacuum degree of 9500 - 11500 Pa for 15.2 - 15.8 h, and then naturally cool it to room temperature to obtain a composite phase change heat storage material. Finally, press the composite phase change heat storage material using a tableting machine to obtain a composite phase change heat storage material block (TiO2 - BG - SA / CEG - BNNS) with a density of 800 - 860 kg / m 3 In this process, three - stage pressure pressing is carried out using a tableting machine: The first stage: pre - press at 5.5 - 6.0 MPa for 20 - 25 s, the second stage: main - press at 9.0 - 9.5 MPa for 38 - 43 s, and the third stage: stabilize the pressure at 7.0 - 7.5 MPa for 12 - 14 s.

[0043] Example 3: A preparation method of a TiO2 - BG - SA / CEG - BNNS composite phase change heat storage material, which includes the following steps: The preparation method of the phase change material powder (TiO2 - BG - SA) includes the following steps: Mix 547 g of BG, 113 g of SA, and 11 g of TiO2 under water - bath heating at a temperature of 82 - 84 °C, stir for 8.2 - 8.8 h to make them evenly mixed, with the stirring speed being 890 - 920 r / min. Then, naturally cool it to room temperature and solidify, and finally grind it into powder with a particle size of 120 - 160 μm and store it sealed.

[0044] The preparation method of the modified expanded graphite (CEG - BNNS) includes the following steps: (1) Pretreatment process: The expanded graphite powder is dried and then transferred to a muffle furnace at 820 - 880 °C for roasting in an oxygen-rich environment with an oxygen concentration of 95 - 98% for 53 - 58 s to form expanded graphite (EG) with a three-dimensional interconnected pore structure, having a porosity ≥ 92% and a specific surface area of 200 - 250 m² / g; the particle size of the expanded graphite powder is 150 - 200 mesh and the purity is 97 - 98%; the drying conditions of the expanded graphite powder are in an oven with a vacuum degree ≤ 100 Pa, and constant temperature drying is carried out at 85 - 88 °C for 13 - 14 h.

[0045] (2) Nano-intercalation mixing: 29 g of the expanded graphite from step (1), 56 g of an oleic acid ethanol (OAE) solution with a titanium dioxide concentration of 0.02 - 0.05 mol / L, and 6 g of boron nitride nanosheets (BNNS) are mixed, and then magnetic-ultrasonic alternating stirring is carried out for 25 - 28 min in an environment at a temperature of 50 - 52 °C to obtain a graphite / boron nitride material; the thickness of the boron nitride nanosheets is 5 - 8 nm and the aspect ratio > 200; the magnetic-ultrasonic alternating stirring is specifically: magnetic stirring and ultrasonic stirring are alternated every 5 - 8 min, where the speed of magnetic stirring is 880 - 910 r / min, and the working condition parameters of ultrasonic stirring include: ultrasonic power is 223 - 354 W, and the stirring speed is 880 - 910 r / min.

[0046] (3) Grafting: 29 g of the graphite / boron nitride material from step (2), 63 g of a titanium dioxide ethanol solution with a concentration of 0.15 - 0.2 mol / L, and 11 g of a silane coupling agent (KH550) are mixed, and then a grafting reaction is carried out at a temperature of 55 - 58 °C for 65 - 70 min, and then ultrasonic treatment is carried out for 6 - 6.5 h to obtain a mixed solution; the conditions of ultrasonic treatment are: frequency is 220 - 256 kHz, and the pulse duty cycle is 12 - 23%.

[0047] (4) Filtration and drying: The mixed solution in step (3) is filtered by suction and then dried at 78 - 80 °C for 11 - 11.5 h to obtain modified expanded graphite with a particle size of 50 - 75 μm.

[0048] Mix 358 g of phase change material powder with 53 g of modified expanded graphite evenly. Then, place the evenly mixed material in an environment of 83 - 85 °C, stir once every 50 min, with each stirring time being 6 - 7 min and the stirring speed being 850 - 880 r / min, for 10 - 10.5 h to obtain a mixed material. Then, place the mixed material in a vacuum drying oven and heat and dry it at a temperature of 82 - 84 °C and a vacuum degree of 9500 - 11500 Pa for 15.2 - 15.8 h, and then naturally cool it to room temperature to obtain a composite phase change heat storage material. Finally, press the composite phase change heat storage material using a tablet press to obtain a composite phase change heat storage material block (TiO2 - BG - SA / CEG - BNNS) with a density of 800 - 860 kg / m 3 During the tablet pressing of the composite phase change heat storage material block, three - stage pressure pressing is carried out: The first stage: pre - press for 20 - 25 s at 5.5 - 6.0 MPa, the second stage: main - press for 38 - 43 s at 9.0 - 9.5 MPa, and the third stage: keep the pressure stable for 12 - 14 s at 7.0 - 7.5 MPa.

[0049] Comparative Example 1: The overall method is the same as that of Example 1. The difference is that only step (1) pretreatment is carried out, and the pretreated expanded graphite obtained in step (1) is directly mixed with the phase change material powder.

[0050] Comparative Example 2: A composite phase change heat storage material block prepared by the preparation method of a composite phase change heat storage material disclosed in an existing patent (application number: CN202411393184.2).

[0051] Experiment 1: Fourier transform infrared spectroscopy tests were respectively carried out on TiO2 - BG - SA, CEG - BNNS, TiO2 - BG - SA / CEG - BNNS, EG, and TiO2 - BG - SA / EG, and the results are as Figure 6 shown. The peaks at 2915 cm -1 and 2846 cm -1 represent the stretching vibrations of - CH3 and - CH2 functional groups. In the range of 3000 cm -1 and 2750 cm -1 is the absorption band of O - H stretching vibration, which usually overlaps with the absorption band of fatty acid C - H stretching vibration. The peak at 1696 cm -1 is the characteristic absorption peak of C = O stretching vibration. The peak at 1472 cm -1 is the - CH2 bending peak. The peak at 1295 cm -1 is the bending peak of C - H and C - C. The peaks at 934 cm -1 and 723 cm -1The peaks at [specific positions] correspond to rocking vibration and bending respectively, which are characteristic of fatty chains. TiO2-BG-SA / EG shows absorption peaks with the same characteristics at 2915 cm -1 、2846 cm -1 、1696 cm -1 、1472 cm -1 、1295 cm -1 、934 cm -1 and 723 cm -1 There are no new absorption peaks, indicating that TiO2-BG-SA / EG in Comparative Example 1 is only physically combined and no chemical reaction has occurred.

[0052] The XRD diffraction patterns of TiO2-BG-SA, CEG-BNNS, TiO2-BG-SA / CEG-BNNS, EG, and TiO2-BG-SA / EG are as shown in Figure 7 It can be seen that the strong diffraction peaks of TiO2-BG-SA correspond one by one to those of TiO2-BG-SA / CEG-BNNS in Example 1. Since the addition amount of CEG-BNNS in TiO2-BG-SA / CEG-BNNS is small, the diffraction peaks of CEG-BNNS in TiO2-BG-SA / CEG-BNNS are not obvious. The strong diffraction peaks of TiO2-BG-SA / EG in Comparative Example 1 correspond one by one to those of TiO2-BG-SA / CEG-BNNS and EG in Example 1, and no new diffraction peaks are found, indicating that TiO2-BG-SA / CEG-BNNS in Example 1 is only physically combined, further verifying that no chemical reaction has occurred.

[0053] Experiment 2: Thermal stability tests were carried out on 9 composite phase change heat storage material blocks with different densities prepared in Example 1 (the specific densities are shown in Table 1). That is, the 9 composite phase change heat storage material blocks with different densities prepared in Example 1 were respectively placed in a water bath and heated from 25 to 90 °C. When the temperature reached 90 °C, the water bath was controlled to cool down. After setting the water bath program, 120 automatic cycles of heat storage and heat release were carried out, and then photos were taken of them to obtain the appearance photos of the 9 composite phase change heat storage material blocks with different densities, as shown in Figure 8 shown.

[0054] Table 1 Density values of composite phase change heat storage material blocks

[0055] It can be seen from Figure 8 that the density ranges from 875 kg / m 3 to 920 kg / m 3Cracks appeared in the composite phase change heat storage material blocks within the range, and the degree of cracking showed an increasing trend with the increase of the block density. This is because when the briquette density is relatively low, the bonding force between the materials is weak, and there is a micro-gap accommodation space for the thermal expansion and contraction during the solid-liquid conversion of the PCM, so it is not easy to leak. When the briquette density exceeds 860 kg / m 3 , leakage occurred in the composite phase change heat material blocks, and the cracking became more and more serious with the increase of density. This is because when the briquette density is too high, the pore structure of CEG-BNNS is severely damaged, the accommodation space is reduced, TiO2-BG-SA is extruded, and cracking occurs due to overload at the same time. When the briquette density is 800 g / m 3 to 860 kg / m 3 , the composite phase change heat storage material blocks basically did not change. Therefore, the composite phase change heat storage material blocks with a density of 800 - 860 kg / m 3 formed by briquetting have excellent thermal stability and anti-leakage performance.

[0056] Experiment 3: The composite phase change heat storage material blocks prepared in Example 1 and Comparative Example 1 were tested by differential scanning calorimetry (DSC). The temperature parameter range of the DSC equipment was set to 25 - 90 °C, and the results are shown in Table 2. It can be seen from Table 2 that the thermal conductivity of TiO2-BG-SA / CEG-BNNS prepared in Example 1 reached 9.58 W / (m∙K), which is 35.5 times that of TiO2-BG-SA / EG prepared in Comparative Example 1. Obviously, the composite phase change heat storage material blocks prepared in Example 1 of the present invention have better heat transfer performance. The thermal diffusivity of TiO2-BG-SA / CEG-BNNS prepared in Example 1 is 36.8 times that of TiO2-BG-SA / EG prepared in Comparative Example 1, and the heat storage coefficient of TiO2-BG-SA / CEG-BNNS prepared in Example 1 is 6.4 times that of TiO2-BG-SA / EG prepared in Comparative Example 1, indicating that the thermal stability of the composite phase change heat storage material blocks prepared in Example 1 of the present invention has been significantly improved.

[0057] Table 2 Comprehensive thermal coefficients of TiO2-BG-SA / EG and TiO2-BG-SA / CEG-BNNS

[0058] Experiment 4: The microstructures of TiO2-BG-SA / EG in Comparative Example 1, CEG-BNNS in Example 1, and TiO2-BG-SA / CEG-BNNS in Example 1 were observed by scanning electron microscopy (SEM), and the results are shown in Figure 9 , where Figure 9(a) is the SEM image of TiO2-BG-SA / EG, Figure 9 (b) is the SEM image of CEG-BNNS, Figure 9 (c) is the SEM image of TiO2-BG-SA / CEG-BNNS. It can be seen from Figure 9 (a) that the SEM of the TiO2-BG-SA / EG composite shows that the unmodified expanded graphite (EG) has a typical worm-like porous structure (pore size 50 - 200 μm). The phase change material (TiO2-BG-SA) locally aggregates at the pore entrances of EG. The TiO2 particles are micron-sized aggregates, and there are obvious voids at the interface, verifying the weak binding between EG and the phase change matrix. It can be seen from Figure 9 (b) that the modified CEG-BNNS presents a micronized structure with broken lamellae (50 - 75 μm). BNNS is intercalated along the graphite crystal plane (interlayer spacing 1.5 - 2.2 nm), and the surface is covered with a nano-island-like organic coating layer formed by KH550 (thickness 10 - 15 nm), and its rough surface is directly related to the super-lipophilic property. It can be seen from Figure 9 (c) that the TiO2-BG-SA / CEG-BNNS composite shows that CEG-BNNS is uniformly dispersed in the phase change matrix. BG-SA fills into the nano-scale pores (20 - 50 nm) through capillary action. The TiO2 particles are embedded in the pore walls to form a confined structure, and there are no cracks or voids at the interface. This multi-scale structural evolution reveals the synergistic mechanism of constructing a heterogeneous thermal conduction network through BNNS intercalation of modified graphite, strengthening the interfacial bonding by KH550 grafting, and inducing nano-crystallization of the phase change material by TiO2, ultimately achieving a performance breakthrough with a thermal conductivity of 9.58 W / (m·K), a contact angle <5°, and a leakage rate ≤0.5%.

[0059] Experiment 5: The composite phase change heat storage material blocks prepared in Example 1, Comparative Example 1 and Comparative Example 2 were respectively placed in a water bath and heated from 20 to 80 °C. When the temperature reached 80 °C, the water bath was controlled to cool down. After setting the water bath program, 0, 200, 400, 600, 800 and 1000 cycles of heat storage and release were carried out. Then, DSC tests were respectively carried out on the material blocks after the above heat storage and release. The specific test results are shown in Table 3-5. It can be seen from Table 3-5 that after 1000 cycles of heat storage and release, the melting temperature of TiO2-BG-SA / EG decreased by 2.86 °C. The melting temperature of TiO2-BG-SA / CEG-BNNS after 1000 cycles only decreased by 0.41 °C, the melting latent heat only decreased by 1.57 J / g, the solidification temperature only decreased by 0.11 °C, and the solidification latent heat only decreased by 1.9 J / g. Compared with TiO2-BG-SA / EG, after 1000 cycles of heat storage and release, the phase change temperature and phase change latent heat of TiO2-BG-SA / CEG-BNNS hardly changed, showing good thermal stability. Moreover, the cyclic leakage rate of TiO2-BG-SA / CEG-BNNS after 1000 cycles of heat storage and release decreased to 0.5%. Compared with the cyclic leakage rate of 1.9% of MgO-PGSA-SFA / CEG, the decrease in the cyclic leakage rate of TiO2-BG-SA / CEG-BNNS of the present invention was 74.7%.

[0060] Table 3 Thermal properties of TiO2-BG-SA / CEG-BNNS prepared in Example 1 at different cycle numbers

[0061] Table 4 Thermal properties of TiO2-BG-SA / EG prepared in Comparative Example 1 at different cycle numbers

[0062] Table 5 Thermal properties of MgO-PGSA-SFA / CEG prepared in Comparative Example 2 at different cycle numbers

[0063] Experiment 6: To verify the heat storage / release performance of TiO2-BG-SA / CEG-BNNS prepared in Experimental Example 1 and TiO2-BG-SA / EG prepared in Comparative Example 1 during actual application, Guangzhou Jia New Materials Co., Ltd. in China was entrusted to carry out heat storage / release tests according to the requirements of the two PCM production processes. The specific heat storage / release process is as follows Figure 10As shown in the figure. It mainly includes a plate - type phase - change energy - storage device, a water - supply system, and a temperature - acquisition system. Among them, the water - supply system mainly includes an atmospheric - pressure hot - water boiler, a variable - frequency circulating pump, and PPR pipelines. During the experiment, high - temperature water and low - temperature water flow into the energy - storage device respectively for heat - storage experiments and heat - release experiments. Signals are collected through thermal resistors and temperature - acquisition instruments to observe the temperature - change process of the fluid and the plate - type phase - change unit. The test instruments used in the experiment are as follows: (1) Atmospheric - pressure hot - water boiler. It provides a cold source and a heat source for the energy - storage device in the experimental test system. (2) Ultrasonic heat meter. It is set at the inlet of the energy - storage device and can measure in a small flow - rate range. (3) Temperature - acquisition instrument. It is controlled by a micro - processor and can cooperate with various thermal resistors and thermocouples. (4) Circulating pump. It cooperates with a manual regulating valve and can adjust the inlet flow rate according to the experimental requirements. Experimental preparation: Start the boiler, maintain the water temperature in the hot - water storage tank at the initial temperature, and adjust the flowmeter to the required flow rate for the experiment. Experimental start: Heat the water in the boiler to the required inlet temperature, start the variable - frequency pump, and the HTF flows into the hot - water storage tank from the inlet through the pipeline, then flows out from the outlet and returns to the boiler through the pipeline. There is an opening of 50mm×50mm on the top end - cover of the hot - water storage tank to facilitate the extraction of the thermal - resistor wiring. The temperature - inspection instrument is connected to the wiring led out from the tank, and the experimental data is recorded through a computer. Experimental end: Turn off the power of the variable - frequency pump and the boiler, and save the experimental data. Among them, during the experiment, it is consistent with the simulation boundary conditions. During the heat - storage process, the initial temperature of the water inside the heat - storage device is maintained at 30°C, the inlet temperature is 65°C, and the inlet velocity is 0.16m / s. Before the experiment starts, the phase - change unit is placed in the heat - storage device. When the internal temperature of the phase - change unit reaches the initial set temperature, the experiment starts. When the temperature of each layer of the phase - change unit reaches 65°C, the heat - storage experiment ends. When conducting the heat - release experiment, first heat each heat - storage unit to an internal temperature of 65°C, and conduct heat - release under the inlet - boundary conditions of 0.16m / s and 30°C. When the internal temperature of the heat - storage unit reaches 30°C, the experiment ends. During the heat - storage / heat - release process, to avoid experimental errors, the average value of the internal - temperature changes of the four phase - change units is processed, and the thermal - performance changes of TiO2 - BG - SA / CEG - BNNS and TiO2 - BG - SA / EG during the actual application process are analyzed. The temperature - change curves are as follows Figure 11 As shown in the figure. Among them, during the heat - storage process, the heat - storage completion time of TiO2 - BG - SA / CEG - BNNS is 5600s, and the heat - storage completion time of TiO2 - BG - SA / EG is 7400s. During the heat - release process, the time for TiO2 - BG - SA / CEG - BNNS to reach the inlet temperature is 5200s, and the heat - release completion time of TiO2 - BG - SA / EG is 11800s. Through the experiment, it is verified that TiO2 - BG - SA / CEG - BNNS shows a faster thermal - response rate and excellent heat - transfer performance in practical applications.

[0064] The above are the preferred embodiments of the present invention. For those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material, characterized in that, It includes the following steps: stirring and mixing the phase change material powder and the modified expanded graphite evenly according to a mass ratio of 6.5 - 7.2:1, and then obtaining a high-density composite phase change heat storage material block through heating and mixing, vacuum drying and directional pressing; Among them, the preparation method of the phase change material powder includes the following steps: stirring and mixing 72 - 75 parts of glyceryl behenate, 14 - 15 parts of stearyl alcohol and 1.2 - 1.5 parts of nano-titanium dioxide by weight fraction under water bath heating, then naturally cooling to room temperature and solidifying, and finally grinding into powder with a particle size of 120 - 160 μm, and storing it sealed; The preparation method of the modified expanded graphite includes the following steps: (1) Pretreatment process: drying the expanded graphite powder, and then transferring it to a muffle furnace at 820 - 880 °C for roasting for 53 - 58 s in an oxygen-rich environment with an oxygen concentration of 95 - 98% to form expanded graphite; (2) Nano-intercalation mixing: mixing the expanded graphite in step (1), an oleic acid ethanol solution with a titanium dioxide concentration of 0.02 - 0.05 mol / L and boron nitride nanosheets; then carrying out magnetic-ultrasonic alternating stirring for 25 - 28 min at a temperature of 50 - 52 °C to obtain a graphite / boron nitride material; (3) Grafting: mixing the graphite / boron nitride material in step (2), a titanium dioxide ethanol solution with a concentration of 0.15 - 0.2 mol / L and a silane coupling agent, then carrying out a grafting reaction at a temperature of 55 - 58 °C for 65 - 70 min, and then carrying out ultrasonic treatment for 6 - 6.5 h to obtain a mixed solution; (4) Filtration and drying: filtering the mixed solution in step (3), and then drying it at 78 - 80 °C for 11 - 11.5 h to obtain the modified expanded graphite with a particle size of 50 - 75 μm.

2. The preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material according to claim 1, characterized in that, Stirring and mixing under water bath heating is specifically carried out under the condition of water bath heating at a temperature of 82 - 84 °C for 8.2 - 8.8 h to make it mix evenly, where the stirring speed is 890 - 920 r / min.

3. The preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material according to claim 1, characterized in that, In step (1), the particle size of the expanded graphite powder is 150 - 200 mesh, and the purity is 97 - 98%; the drying condition of the expanded graphite powder is to keep it dry at 85 - 88 °C for 13 - 14 h in a drying oven with a vacuum degree ≤ 100 Pa.

4. The preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material according to claim 1, wherein, In step (2), the mass ratio of the expanded graphite, the oleic acid ethanol solution and the boron nitride nanosheets is 32 - 34:60 - 62:4 - 8, where the thickness of the boron nitride nanosheets is 5 - 8 nm and the aspect ratio > 200.

5. The preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material according to claim 1, characterized in that, In step (2), the magnetic-ultrasonic alternating stirring is specifically: magnetic stirring and ultrasonic stirring are alternated every 5 - 8 min, where the speed of magnetic stirring is 880 - 910 r / min, and the working condition parameters of ultrasonic stirring include: ultrasonic power is 223 - 354 W, and the stirring speed is 880 - 910 r / min.

6. The preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material according to claim 1, characterized in that, In step (3), the mass ratio of the graphite / boron nitride material, titanium dioxide ethanol solution and silane coupling agent is 28 - 30:58 - 61:9 - 14; the conditions for ultrasonic treatment are: the frequency is 220 - 256 kHz, and the pulse duty cycle is 12 - 23%.

7. The preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material according to claim 1, characterized in that, The specific conditions for the heating and mixing are as follows: the uniformly mixed material is placed in an environment at 83 - 85 °C, stirred once every 50 min, and continued for 10 - 10.5 h to obtain a mixed material.

8. The preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material according to claim 7, characterized in that, The stirring time for each time is 6 - 7 min, and the stirring speed is 850 - 880 r / min.

9. The preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material according to claim 7, characterized in that, The specific vacuum drying is as follows: the mixed material is placed in a vacuum drying oven, heated and dried at a temperature of 82 - 84 °C and a vacuum degree of 9500 - 11500 Pa for 15.2 - 15.8 h, and then naturally cooled to room temperature to obtain a composite phase change heat storage material.

10. The preparation method of a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material according to claim 9, characterized in that, The specific method for the directional pressing block is as follows: the composite phase change heat storage material is pressed into a block by a tablet press to obtain a composite phase change heat storage material block with a density of 800-860 kg / m 3 . Among them, the tablet press is used for three-stage pressure pressing: the first stage: pre-press for 20-25 s at 5.5-6.0 MPa; the second stage: main press for 38-43 s at 9.0-9.5 MPa; the third stage: keep the pressure stable for 12-14 s at 7.0-7.5 MPa.

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