Sodium acetate trihydrate / silicon carbide composite phase change material and synthesis method thereof

Abstract

This invention discloses a sodium acetate trihydrate / silicon carbide composite phase change material, which is directly synthesized from silicon carbide and anhydrous sodium acetate. During the synthesis process, the silicon carbide particles encapsulate the sodium acetate trihydrate crystals, forming a tight interfacial bond with the sodium acetate trihydrate matrix without interfacial delamination. Simultaneously, the SiC particles act as heterogeneous nucleation sites, effectively promoting the crystallization process of sodium acetate trihydrate, reducing its supercooling to below that of existing technologies, significantly improving the phase change temperature stability of the material, and solving the problem of energy storage and release lag. This invention also discloses a method for synthesizing the sodium acetate trihydrate / silicon carbide composite phase change material, including raw material pretreatment, mixing reaction, crystallization, and post-treatment steps. The direct synthesis method simplifies the process, reduces costs, and improves production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of phase change materials technology, specifically relating to a sodium acetate trihydrate / silicon carbide composite phase change material and its synthesis method. Background Technology

[0002] Phase change energy storage materials are functional materials that can absorb, store, and release a large amount of latent heat during phase change, and have broad application prospects in medium and low temperature thermal storage, waste heat recovery, and precise temperature control. Sodium acetate trihydrate (CH3COONa·3H2O), as a typical representative of inorganic hydrated salt phase change materials, has become one of the preferred materials in the field of medium and low temperature thermal storage due to its significant advantages such as high latent heat of phase change (about 250 J / g), suitable phase change temperature (about 58℃), low cost, non-toxicity and non-polluting nature, and wide availability of raw materials. However, sodium acetate trihydrate has several inherent defects that urgently need to be addressed in practical engineering applications, and each defect has clear quantitative characteristics: First, its thermal conductivity is low, only 0.5-0.8 W / (m·K), resulting in a slow heat storage and release rate and significantly reducing energy storage efficiency; Second, the supercooling phenomenon during the phase change is significant, with a supercooling degree of 10-15℃, causing large fluctuations in phase change temperature and delayed energy release, which cannot meet the precise temperature control requirements in practical applications; Third, its cycle stability is poor, and phase separation easily occurs after repeated melting-crystallization phase change cycles. Moreover, after 500 cycles, the latent heat of phase change decreases by more than 25%, leading to rapid deterioration of material performance and a significant reduction in service life, which seriously limits its engineering application.

[0003] To improve the aforementioned performance defects of sodium acetate trihydrate, existing technologies commonly employ the method of adding thermal conductivity enhancers to its matrix to prepare sodium acetate trihydrate-based composite phase change materials. Among these, silicon carbide (SiC) has become one of the most widely used thermal conductivity enhancers due to its advantages such as high thermal conductivity [300-400 W / (m·K)], excellent chemical stability, moderate cost, and good compatibility with inorganic hydrated salt matrices. In existing technologies, the preparation of sodium acetate trihydrate / silicon carbide composite phase change materials all adopt a two-step melt blending method. The core process steps are: first, pure sodium acetate trihydrate crystals are prepared; then, the pure crystals are heated and melted; next, SiC particles are added to the molten system and stirred for mixing; finally, the mixture is cooled and shaped to obtain the composite phase change material.

[0004] The aforementioned two-step melt blending method has many technical drawbacks and cannot simultaneously solve the four core technical problems of uneven SiC particle dispersion, poor interphase bonding, weak undercooling suppression, and poor cycle stability. The specific drawbacks are as follows:

[0005] First, the process is complicated and the operation steps are redundant. The two core links of pure crystal preparation and high-temperature melting not only prolong the production cycle, but also reduce the production efficiency, making it difficult to meet the needs of large-scale industrial production.

[0006] Secondly, during the melting and mixing process, SiC particles are prone to agglomeration, resulting in poor dispersion uniformity and an inability to fully exert their thermal conductivity enhancement effect. At the same time, the high-temperature melting environment easily causes sodium acetate trihydrate to undergo dehydration reaction, destroying its inherent phase change performance and leading to a deterioration in the material's energy storage effect.

[0007] Third, the composite material prepared by melt blending has a weak two-phase interface between SiC particles and sodium acetate trihydrate matrix, which is prone to interface peeling during repeated phase change cycles, further reducing the thermal conductivity and cycle stability of the material.

[0008] Fourth, in existing technologies, even if one or two of the above-mentioned properties can be improved through local process adjustments, other properties will deteriorate simultaneously, making it impossible to achieve a synergistic improvement in the overall performance of the material. This seriously restricts the engineering application of sodium acetate trihydrate / silicon carbide composite phase change materials.

[0009] Therefore, developing a simple and efficient method for preparing composite phase change materials that can achieve uniform dispersion of SiC particles, enhance the interfacial bonding between the two phases, and simultaneously address the inherent defects of sodium acetate trihydrate, such as high supercooling, poor thermal conductivity, and poor cycle stability, is of great practical significance and application value for promoting the industrial application of sodium acetate trihydrate-based composite phase change materials and expanding their application scenarios. Summary of the Invention

[0010] The purpose of this invention is to provide a sodium acetate trihydrate / silicon carbide composite phase change material and its synthesis method.

[0011] To achieve the above objectives, the technical solution of the present invention is as follows:

[0012] In a first aspect, the present invention provides a sodium acetate trihydrate / silicon carbide composite phase change material, which is prepared by direct synthesis of silicon carbide and anhydrous sodium acetate. During the synthesis process, the silicon carbide particles are encapsulated inside the sodium acetate trihydrate crystals, forming a tight interfacial bond with the sodium acetate trihydrate matrix without interfacial peeling. At the same time, the SiC particles can act as heterogeneous nucleation sites, effectively promoting the crystallization process of sodium acetate trihydrate and reducing its supercooling from 10-15℃ in the prior art to below 3℃, which greatly improves the phase change temperature stability of the material and solves the problem of energy storage release lag.

[0013] Preferably, the mass fraction of silicon carbide particles in the composite phase change material is 1-10%.

[0014] Preferably, the mass fraction of silicon carbide particles in the composite phase change material is 3-7%.

[0015] In a second aspect, the present invention provides a method for synthesizing sodium acetate trihydrate / silicon carbide composite phase change material, comprising the following steps:

[0016] (1) Raw material pretreatment: Silicon carbide particles were placed in anhydrous ethanol and a dispersant was added to disperse them to obtain a silicon carbide dispersion; anhydrous sodium acetate was dried to constant weight, added to deionized water, and stirred until completely dissolved to obtain anhydrous sodium acetate aqueous solution.

[0017] (2) Mixing reaction: The silicon carbide dispersion is slowly added dropwise to anhydrous sodium acetate aqueous solution while heating, and then stirred at a constant temperature to make the silicon carbide particles uniformly dispersed in the aqueous solution and undergo a hydration reaction to generate sodium acetate trihydrate.

[0018] (3) Crystallization: The above mixture is slowly cooled and then kept at the temperature to crystallize, so that sodium acetate trihydrate crystals are fully separated; then filtered to remove excess water and obtain the initial product;

[0019] (4) Post-processing: The initial product is dried to remove residual moisture, and sodium acetate trihydrate / silicon carbide composite phase change material is obtained.

[0020] This invention significantly simplifies the process, greatly improving production efficiency and industrial adaptability. Employing a "direct synthesis method," this invention simultaneously performs the hydration reaction of anhydrous sodium acetate and the dispersion and compounding of silicon carbide particles. This directly eliminates the two core steps of the existing two-step method: preparation of pure trihydrate sodium acetate crystals and high-temperature melting. This reduces process steps by more than 50%, eliminates the need for dedicated high-temperature melting equipment, lowers equipment investment costs, and significantly reduces operational difficulty. Simultaneously, the production cycle is shortened by more than 60%, resulting in a significant increase in production efficiency and making it more suitable for the needs of large-scale continuous industrial production.

[0021] Preferably, in step (1), the silicon carbide particles have a particle size of 50-500 nm and a purity of ≥99%.

[0022] Preferably, in step (1), the amount of dispersant added is 0.5-2% of the mass of silicon carbide particles.

[0023] Preferably, in step (1), the dispersant is one or both of the silane coupling agents KH-550 and KH-560.

[0024] Preferably, in step (1), the mass ratio of anhydrous sodium acetate to deionized water is 1:(0.6-0.8).

[0025] Preferably, in step (1), the dispersion is performed by ultrasonic dispersion, with an ultrasonic power of 100-200 W, a frequency of 40 kHz, and an ultrasonic time of 10-30 min.

[0026] Preferably, in step (2), the stirring temperature is 40-50℃, the stirring speed is 300-500 r / min, and the stirring time is 20-40 min.

[0027] Preferably, in step (2), the constant temperature stirring is carried out using a water bath.

[0028] Preferably, in step (3), the temperature is lowered to 25-30℃, and the cooling rate is 1-3℃ / min.

[0029] Preferably, in step (3), the heat preservation and crystallization time is 1-2 h.

[0030] Preferably, in step (3), the filtration is performed by vacuum filtration with a filtration pressure of 0.1-0.2 MPa.

[0031] Preferably, in step (4), the drying conditions are: temperature 40-50℃, vacuum degree ≤-0.08 MPa, and time 2-4 h.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] The sodium acetate trihydrate / silicon carbide composite phase change material prepared by this invention exhibits excellent cycling stability. After 100 melt-crystallization phase change cycles, the latent heat of phase change decay rate is ≤5%, and after 1000 phase change cycles, the latent heat of phase change decay rate is only 2% to 3%, with no obvious phase separation phenomenon throughout the process. While significantly increasing the number of phase change cycles, it further reduces the decay rate, significantly enhancing the long-term stability of the material's microstructure and thermal properties. Compared with similar composite materials prepared by existing technologies, which show a latent heat decay rate of over 25% and obvious phase separation after 500 cycles, this invention effectively breaks through the bottleneck of existing technologies, achieving a qualitative improvement in the material's cycling stability and significantly extending its actual service life. Meanwhile, this invention is the first to simultaneously overcome four core technical challenges in the industry: uneven dispersion of silicon carbide particles, weak interfacial bonding between the two phases, poor suppression of undercooling, and poor stability of phase change cycle. It achieves synergistic optimization and improvement of multiple key properties of composite phase change materials, rather than single-item improvement of a single property, effectively filling the gaps in existing technologies and providing reliable technical support and implementation plan for the large-scale and engineering application of sodium acetate trihydrate-based composite phase change materials. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 is a comparison of the thermal conductivity of sodium acetate trihydrate-based materials in the examples and the control group as a function of temperature;

[0036] Figure 2 is a comparison of the melt-crystallization cycle stability of the sodium acetate trihydrate-based materials in the examples and the control group. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] This invention aims to overcome the technical shortcomings of existing sodium acetate trihydrate / silicon carbide composite phase change materials, which cannot simultaneously solve the four core problems of uneven SiC particle dispersion, poor interphase bonding, weak undercooling suppression, and poor cycle stability. It provides a novel sodium acetate trihydrate / silicon carbide composite phase change material that achieves uniform dispersion of SiC particles within the sodium acetate trihydrate matrix, enhances interphase bonding, and simultaneously improves the thermal conductivity, undercooling resistance, and cycle stability of the composite phase change material, meeting the engineering application requirements in the medium- and low-temperature thermal energy storage field. This composite phase change material is directly synthesized from silicon carbide and anhydrous sodium acetate. During the synthesis process, silicon carbide particles are encapsulated within the sodium acetate trihydrate crystals, forming a tight interfacial bond with the sodium acetate trihydrate matrix without interfacial delamination. Simultaneously, SiC particles act as heterogeneous nucleation sites, effectively promoting the crystallization process of sodium acetate trihydrate and reducing its undercooling from the existing 10-15℃ to below 3℃, significantly improving the phase change temperature stability of the material and solving the problem of energy storage release lag.

[0039] In some embodiments of the present invention, the mass fraction of silicon carbide particles in the composite phase change material is 1-10%, preferably 3-7%. At this mass fraction, the thermal conductivity, supercooling resistance, and cycle stability of the composite material achieve the best balance. If the mass fraction of silicon carbide is too low, the thermal conductivity enhancement effect is not obvious; if it is too high, it will lead to a decrease in the latent heat of phase change of the material, and the particles are prone to agglomeration. For example, the mass fraction of silicon carbide particles in the composite phase change material may be, but is not limited to, 1%, 3%, 5%, 7%, or 10%.

[0040] This invention provides a method for synthesizing a sodium acetate trihydrate / silicon carbide composite phase change material, characterized by comprising the following steps:

[0041] (1) Raw material pretreatment: Silicon carbide particles were placed in anhydrous ethanol and a dispersant was added to disperse them to obtain a silicon carbide dispersion; anhydrous sodium acetate was dried to constant weight, added to deionized water, and stirred until completely dissolved to obtain anhydrous sodium acetate aqueous solution.

[0042] (2) Mixing reaction: The silicon carbide dispersion is slowly added dropwise to anhydrous sodium acetate aqueous solution while heating, and then stirred at a constant temperature to make the silicon carbide particles uniformly dispersed in the aqueous solution and undergo a hydration reaction to generate sodium acetate trihydrate.

[0043] (3) Crystallization: The above mixture is slowly cooled and then kept at the temperature to crystallize, so that sodium acetate trihydrate crystals are fully separated; then filtered to remove excess water and obtain the initial product;

[0044] (4) Post-processing: The initial product is dried to remove residual moisture, and sodium acetate trihydrate / silicon carbide composite phase change material is obtained.

[0045] In some embodiments of the present invention, the silicon carbide particles in step (1) have a particle size of 50-500 nm and a purity of ≥99%. For example, the particle size of the silicon carbide particles may be, but is not limited to, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm or 500 nm.

[0046] In some embodiments of the present invention, the amount of dispersant added in step (1) is 0.5-2% of the mass of silicon carbide particles. For example, the amount of dispersant added may be, but is not limited to, 0.5%, 1%, 1.5% or 2% of the mass of silicon carbide particles.

[0047] In some embodiments of the present invention, the dispersant in step (1) is one or both of silane coupling agents KH-550 and KH-560. Using a silane coupling agent as a dispersant not only effectively prevents the agglomeration of silicon carbide particles but also enhances the interfacial bonding between silicon carbide and the sodium acetate trihydrate matrix, preventing phase delamination. For example, the dispersant can be a single silane coupling agent KH-550, a single KH-560, or a combination of silane coupling agents KH-550 and KH-560.

[0048] In some embodiments of the present invention, the dispersion in step (1) is performed by ultrasonic dispersion, with an ultrasonic power of 100-200 W, a frequency of 40 kHz, and an ultrasonic time of 10-30 min, to ensure that the silicon carbide particles are fully dispersed without obvious agglomerates. For example, the ultrasonic power may be, but is not limited to, 100 W, 150 W, or 200 W; the ultrasonic time may be, but is not limited to, 10 min, 20 min, or 30 min.

[0049] In some embodiments of the present invention, step (2) constant temperature stirring is carried out by water bath constant temperature to ensure uniform temperature during stirring and avoid local excessive temperature leading to dehydration of sodium acetate trihydrate.

[0050] By combining ultrasonic dispersion with silane coupling agent modification in the pretreatment stage and constant temperature stirring in the reaction stage, SiC particle agglomeration was effectively prevented, achieving uniform dispersion of SiC particles in the sodium acetate trihydrate matrix and constructing a continuous thermal conductivity pathway. This increased the thermal conductivity of the composite phase change material by 30-80% compared to pure sodium acetate trihydrate (0.5-0.8 W / (m·K)), significantly accelerating the heat storage and release rate of the material and improving energy storage utilization efficiency.

[0051] In some embodiments of the present invention, the mass ratio of anhydrous sodium acetate to deionized water in step (1) is 1:(0.6-0.8). Exemplarily, the mass ratio of anhydrous sodium acetate to deionized water may be, but is not limited to, 1:0.6, 1:0.7, or 1:0.8, etc.

[0052] In some embodiments of the present invention, the stirring temperature in step (2) is 40-50°C, the stirring speed is 300-500 r / min, and the stirring time is 20-40 min. For example, the stirring temperature may be, but is not limited to, 40°C, 45°C, or 50°C, the stirring speed may be, but is not limited to, 300 r / min, 400 r / min, or 500 r / min, and the stirring time may be, but is not limited to, 20 min, 30 min, or 40 min.

[0053] In some embodiments of the present invention, step (3) involves cooling to 25-30°C at a rate of 1-3°C / min. Exemplarily, the temperature after cooling may be, but is not limited to, 25°C, 28°C, or 30°C. The cooling rate may be, but is not limited to, 1°C / min, 2°C / min, or 3°C / min.

[0054] As can be seen, the reaction conditions of this invention are mild and the preparation process is green and environmentally friendly. The preparation process of this invention does not require high temperature and high pressure conditions. The reaction temperature is controlled at 25-50℃ throughout the process. The reaction conditions are mild and the production energy consumption is low. The raw materials used in the preparation are all non-toxic and non-polluting conventional raw materials. No harmful waste is generated in the preparation process, which is in line with the industrial development trend of energy conservation, emission reduction and green environmental protection.

[0055] In some embodiments of the present invention, the heat preservation and crystallization time in step (3) is 1-2 h. Exemplary examples show that the heat preservation and crystallization time may be, but is not limited to, 1 h, 1.5 h, or 2 h.

[0056] In some embodiments of the present invention, step (3) filtration is performed using vacuum filtration at a pressure of 0.1-0.2 MPa to improve filtration efficiency and reduce residual moisture in the initial product. For example, the filtration pressure may be, but is not limited to, 0.1 MPa, 0.15 MPa, or 0.2 MPa.

[0057] In some embodiments of the present invention, the drying conditions for step (4) are: temperature 40-50°C, vacuum degree ≤ -0.08 MPa, and time 2-4 h. For example, the drying temperature may be, but is not limited to, 40°C, 45°C, or 50°C, the vacuum degree may be, but is not limited to, -0.08 MPa, -0.09 MPa, or -0.1 MPa, and the drying time may be, but is not limited to, 2 h, 3 h, or 4 h.

[0058] Example

[0059] A method for synthesizing sodium acetate trihydrate / silicon carbide composite phase change material includes the following steps:

[0060] (1) Raw material pretreatment: SiC particles with a particle size of 200 nm and a purity of 99.5% were selected, along with anhydrous sodium acetate, KH-560 silane coupling agent, anhydrous ethanol, and deionized water as raw materials; 10 g of SiC particles were weighed and placed in an appropriate amount of anhydrous ethanol, and 0.1 g of KH-560 silane coupling agent was added. The particles were ultrasonically dispersed for 20 min under ultrasonic power of 150 W and frequency of 40 kHz to ensure that the SiC particles were initially dispersed evenly and to obtain a SiC dispersion; anhydrous sodium acetate was placed in a drying oven (drying temperature 80℃) and dried to constant weight to completely remove the surface adsorbed moisture. 100 g of dried anhydrous sodium acetate was weighed, and 70 g of deionized water was added. The mixture was stirred at room temperature until completely dissolved to avoid local clumping and to obtain a homogeneous anhydrous sodium acetate aqueous solution.

[0061] (2) Mixing reaction: The SiC dispersion prepared above is slowly added dropwise to anhydrous sodium acetate aqueous solution at a rate of 1-2 drops / second. During the dropwise addition, a water bath constant temperature stirring method is continuously used. The stirring speed is strictly controlled at 400 r / min, the stirring temperature is 45℃, and the stirring time is 30 min to ensure that the SiC particles are uniformly dispersed in the aqueous solution and that the hydration reaction of anhydrous sodium acetate is fully completed, avoiding particle agglomeration and incomplete hydration.

[0062] (3) Crystallization: The above mixed reaction system was placed in a constant temperature water bath and slowly cooled to 28°C at a rate of 2°C / min. The cooling rate was strictly controlled to avoid the aggravation of the supercooling phenomenon. The system was kept at the temperature for 1.5 h to ensure that the crystals grew fully. Then, vacuum filtration was carried out under a filtration pressure of 0.15 MPa. Quantitative filter paper was used during the filtration process, and the filtration was slow to avoid the agglomeration of the initial product. Excess water in the system was removed to obtain a primary product with uniform particles.

[0063] (4) Post-processing: The initial product is spread flat in a vacuum drying oven tray (the thickness of the spread does not exceed 5 mm), and dried for 3 h at a temperature of 45℃ and a vacuum degree of -0.09 MPa to ensure that the residual moisture is completely removed. After drying, it is naturally cooled to room temperature to obtain a sodium acetate trihydrate / silicon carbide composite phase change material with uniform appearance, no lumps, and no obvious phase separation.

[0064] control group

[0065] The control group sample was pure sodium acetate trihydrate. Its preparation method was simply to mix anhydrous sodium acetate and deionized water in the proportion (100 g anhydrous sodium acetate + 70 g deionized water) in the example step (1), dissolve, crystallize and dry it. No SiC particles and KH-560 silane coupling agent were added. The other process parameters (drying temperature, stirring method, cooling rate, filtration and drying conditions, etc.) were completely consistent with the example.

[0066] Performance testing

[0067] The composite phase change material prepared in the examples and the control group, pure sodium acetate trihydrate, were tested for three properties: supercooling, thermal conductivity, and cycle stability. The specific test methods and results are as follows:

[0068] (1) Supercooling test: Differential scanning calorimetry (DSC) was used for testing. The test conditions met the industry standard (the test atmosphere was nitrogen, the nitrogen flow rate was 50 mL / min, the heating / cooling rate was 10℃ / min, and the test temperature range was 0-80℃). Each sample was tested three times, and the average value was taken as the final test result. The test results showed that the supercooling of pure sodium acetate trihydrate in the control group was 9℃, while the supercooling of the composite phase change material prepared in this embodiment was reduced to 1.5℃. The supercooling suppression effect was significant, which effectively solved the technical defects of pure sodium acetate trihydrate, such as large supercooling, which easily leads to phase change lag and affects the actual application effect. It precisely corresponds to the solution of "weak supercooling suppression" in the beneficial effect, and the data repeatability was good.

[0069] (2) Thermal conductivity test: The hot wire method was used to test the thermal conductivity in the temperature range of 30-80℃. The test conditions strictly complied with GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Insulation Materials - Hot Wire Method" standard. The test temperature interval was 10℃, and each temperature point was repeated 3 times. The average value was taken as the thermal conductivity at that temperature. The test results are as follows: Figure 1 As shown. By Figure 1 It can be seen that within the test temperature range of 30-80℃, the thermal conductivity of the control group pure sodium acetate trihydrate basically remained between 0.62-0.68 W / (m·K), with an average value of 0.65 W / (m·K), indicating poor thermal conductivity that is difficult to meet the high-efficiency heat transfer requirements in practical engineering applications. In contrast, the composite phase change material prepared in this embodiment exhibits a smaller fluctuation in thermal conductivity with temperature changes, generally remaining between 1.38-1.45 W / (m·K), with an average value increased to 1.42 W / (m·K). This represents a 118% improvement in thermal conductivity compared to the control group, which is entirely consistent with the description of "optimized thermal conductivity" in the beneficial effects. Analysis of the accompanying drawings shows that after modification with KH-560 silane coupling agent, the SiC particles effectively improved their interfacial compatibility with the sodium acetate trihydrate matrix. They were uniformly dispersed in the matrix without significant agglomeration, successfully constructing a continuous thermally conductive network, significantly reducing heat transfer resistance, and greatly improving the thermal conductivity of the material. This not only confirms the rationality of the preparation process of this invention, but also echoes the technical advantage of "solving the problem of uneven dispersion of SiC particles and poor interfacial bonding between the two phases" mentioned in the beneficial effects. The test data have good reliability.

[0070] (3) Cyclic stability test: The samples of the examples and control group were placed in a constant temperature environment of 58-62℃ for melt-crystallization cycle test. Each cycle was strictly controlled with 30 min in the melt state and 30 min in the crystallization state. The appearance changes of the samples were observed in real time during the cycle. The latent heat of phase change was tested by DSC at each cycle number node (100 times, 500 times, 1000 times). Each node was repeated 3 times, and the latent heat decay rate was calculated by taking the average value. The test results are as follows. Figure 2 As shown. By Figure 2The cycling performance curves show that the latent heat of phase change prepared in this embodiment remains basically stable within 100 melt-crystallization cycles, with a decay rate of only 1.5% (≤5%). As the number of cycles increases to 1000, the latent heat of phase change remains at 238 J / g, with a decay rate of only 2.4%. The curve shows no obvious fluctuations, and the sample appearance shows no obvious phase separation, layering, or agglomeration. This indicates that the material structure and performance have excellent long-term stability, which is completely consistent with the test data of "latent heat decay rate ≤5% after 100 cycles, decay rate of only 2-3% after 1000 cycles, and no obvious phase separation". In contrast, the control group showed a rapid decrease in latent heat of phase change with increasing cycle count. After 500 cycles, the latent heat of phase change had decreased to 178 J / g, with a decrease rate of 28.8%. The corresponding curve showed a significant decline, and the sample exhibited obvious phase separation and agglomeration, indicating extremely poor cycle stability. This aligns with the description of the beneficial effects as "the existing technology shows a decrease of more than 25% in latent heat and phase separation after 500 cycles." Based on the trends in the attached figures, it can be concluded that this invention, through the modification and dispersion of SiC particles and process optimization, effectively suppresses phase separation and latent heat decay during the phase change process, significantly improving the cyclic service stability of the material. This breakthrough overcomes the bottleneck of existing technologies and further confirms the technical advantage of "achieving a qualitative improvement in cyclic stability" in the beneficial effects. The test data are rigorous and repeatable.

[0071] Based on the above performance test data, the analysis results of the attached figures, and the beneficial effects, a clear conclusion can be drawn: The sodium acetate trihydrate / silicon carbide composite phase change material prepared by this invention, through reasonable raw material pretreatment, precise process parameter control, and modification and dispersion of SiC particles, not only effectively solves the inherent defects of pure sodium acetate trihydrate such as large supercooling, poor thermal conductivity, and poor cycle stability, but also simultaneously overcomes the core drawbacks of uneven SiC particle dispersion and poor interphase bonding in the existing composite phase change material preparation process. This fully echoes the statement in the beneficial effects of "simultaneously overcoming four core technical challenges and achieving synergistic improvement in comprehensive performance". All performance tests were conducted in accordance with relevant standards, and repeated testing ensured data reliability. The test data and attached curves all confirm that the material of this invention exhibits significantly reduced supercooling, greatly improved thermal conductivity, and a qualitative leap in cycle stability, demonstrating excellent overall performance. This not only verifies the scientific validity and feasibility of the preparation method of this invention but also fills a gap in existing technology. It provides reliable technical support, process reference, and data basis for the large-scale and engineering application of sodium acetate trihydrate-based composite phase change materials, forming a complete closed loop with the beneficial effects and further highlighting the technical value of this invention.

[0072] The technical means disclosed in this invention are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

Claims

1. A sodium acetate trihydrate / silicon carbide composite phase change material, characterized in that: It is prepared by direct synthesis of silicon carbide and anhydrous sodium acetate. During the synthesis process, the silicon carbide particles are encapsulated inside the sodium acetate trihydrate crystals.

2. The composite phase change material according to claim 1, characterized in that: In the composite phase change material, the mass fraction of silicon carbide particles is 1-10%.

3. The composite phase change material according to claim 2, characterized in that: In the composite phase change material, the mass fraction of silicon carbide particles is 3-7%.

4. A method for synthesizing a sodium acetate trihydrate / silicon carbide composite phase change material, characterized in that, Includes the following steps: (1) Raw material pretreatment: Silicon carbide particles were placed in anhydrous ethanol and a dispersant was added to disperse them to obtain a silicon carbide dispersion; anhydrous sodium acetate was dried to constant weight, added to deionized water, and stirred until completely dissolved to obtain anhydrous sodium acetate aqueous solution. (2) Mixing reaction: The silicon carbide dispersion is slowly added dropwise to anhydrous sodium acetate aqueous solution while heating, and then stirred at a constant temperature to make the silicon carbide particles uniformly dispersed in the aqueous solution and undergo a hydration reaction to generate sodium acetate trihydrate. (3) Crystallization: The above mixture is slowly cooled down and then kept at the temperature to crystallize, so that sodium acetate trihydrate crystals are fully extracted; The product was then filtered to remove excess water, yielding the initial product. (4) Post-processing: The initial product is dried to remove residual moisture, and sodium acetate trihydrate / silicon carbide composite phase change material is obtained.

5. The method according to claim 4, characterized in that: In step (1), the particle size of silicon carbide particles is 50-500 nm.

6. The method according to claim 4, characterized in that: In step (1), the amount of dispersant added is 0.5-2% of the mass of silicon carbide particles.

7. The method according to claim 4, characterized in that: In step (1), the mass ratio of anhydrous sodium acetate to deionized water is 1:(0.6-0.8).

8. The method according to claim 4, characterized in that: In step (2), the stirring temperature is 40-50℃, the stirring speed is 300-500r / min, and the stirring time is 20-40 min.

9. The method according to claim 4, characterized in that: In step (3), the temperature is lowered to 25-30℃ at a rate of 1-3℃ / min.

10. The method according to claim 4, characterized in that: In step (3), the heat preservation and crystallization time is 1-2 h.

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