Diatomite-based shaped composite phase change material and preparation method thereof

Abstract

The invention relates to a diatomite-based shaped composite phase change material and a preparation method thereof, and the method comprises the following steps: weighing lauric acid-hexadecanol-palmitic acid LA-HD-PA and modified diatomite according to a predetermined mass ratio; drying the modified diatomite at a first constant temperature until the weight is constant, heating lauric acid-hexadecanol-palmitic acid LA-HD-PA in a solid state until the lauric acid-hexadecanol-palmitic acid LA-HD-PA is in a liquid state, and adding the lauric acid-hexadecanol-palmitic acid LA Stirring the mixture at a second temperature for a first preset time, then putting the mixture into a vacuum drying oven for vacuum drying, and after drying for a second preset time, taking out and grinding to obtain the diatomite-based shaped composite phase change material LA-HD-PA / DME.

Description

Technical Field

[0001] The present invention relates to the technical field of composite phase change materials, and particularly to a diatomite-based shaped composite phase change material and a preparation method thereof. Background Art

[0002] As a new type of thermal energy storage material, phase change materials have good thermal energy storage and regulation capabilities. When the ambient temperature rises, they absorb excess heat and change from a solid state to a liquid state, thereby reducing the temperature of the surrounding environment and preventing overheating. When the temperature drops, the stored thermal energy is released, promoting the temperature to rise. By absorbing and releasing heat, they regulate the temperature, keep the indoor temperature stable, can effectively improve energy utilization efficiency, and reduce energy consumption. However, due to the low thermal conductivity of pure phase change materials, slow heat exchange speed, possible phase separation during the phase change process, leakage during heating affecting performance, and poor stability under extreme temperature conditions, these defects limit their application scope in high-efficiency energy storage and temperature regulation. To overcome these defects, pure phase change materials often need to be combined with porous material carriers to form new composite materials. The composite materials can not only utilize the high thermal energy storage capacity of the phase change materials but also improve the thermal conductivity and mechanical strength through the support structure of the porous materials. Such composite phase change materials are called shaped phase change materials, which can ensure that the pure phase change materials do not deform or break during the phase change process. In the field of low-temperature phase change heat storage, diatomite, as a lightweight porous material, has good thermal conductivity and hygroscopicity, which helps to improve the overall phase change efficiency and heat transfer capacity of the composite material. In addition, the large number of microporous structures in diatomite can provide a larger specific surface area for the phase change material, realize the uniform distribution of the phase change material, enhance its overall stability. At the same time, the environmental protection and lightweight characteristics of diatomite can also improve the sustainability and usability of the composite material, thus achieving a more efficient energy storage and temperature regulation solution. Therefore, combining phase change materials with diatomite to form a new composite phase change material can achieve higher energy utilization efficiency, and the advantages are obvious.

[0003] The main combination methods of existing phase change materials and diatomite include: mechanical mixing, impregnation method, solution method, etc. Mechanical mixing is simple and low-cost, but there are problems such as uneven distribution of the phase change material, and possible phase separation or performance degradation after long-term use. The impregnation method can better immerse the phase change material into the pores of diatomite, improving material utilization rate, but it requires an additional drying step, increasing the process complexity. If the impregnation is not sufficient, it may lead to uneven material distribution. The solution method can achieve uniform dispersion, but it involves organic solvents, with high requirements for the environment and safety. In addition, the removal of the solvent will increase the complexity of subsequent processes.

[0004] The above information disclosed in the background art section is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0005] The present invention provides a diatomite-based shaped composite phase change material and a preparation method thereof. Using a multi-component phase change material lauric acid-hexadecanol-palmitic acid (LA-HD-PA) as the phase change medium and modified diatomite (DEM) as the carrier, a diatomite-based shaped phase change composite material (LA-HD-PA / DME) is prepared by vacuum adsorption, which can effectively improve the comprehensive performance of the material.

[0006] The preparation method of the diatomite-based shaped composite phase change material includes, Step 1: Weigh lauric acid-hexadecanol-palmitic acid LA-HD-PA and modified diatomite according to a predetermined mass ratio; Step 2: Heat the modified diatomite in a constant temperature at the first temperature until it reaches a constant weight, heat the solid lauric acid-hexadecanol-palmitic acid LA-HD-PA to a liquid state and then add it to the dried modified diatomite to form a mixture; Step 3: At the second temperature, stir the mixture for the first predetermined time and then put it into a vacuum drying oven for vacuum drying. After drying for the second predetermined time, take it out and grind it to obtain the diatomite-based shaped composite phase change material LA-HD-PA / DME.

[0007] In the preparation method of the diatomite-based shaped composite phase change material, the predetermined mass ratio is that the lauric acid-hexadecanol-palmitic acid LA-HD-PA accounts for 35% - 60% of the total weight.

[0008] In the preparation method of the diatomite-based shaped composite phase change material, the diatomite is treated by roasting, pickling and alkali washing to obtain the modified diatomite.

[0009] In the preparation method of the diatomite-based shaped composite phase change material, the first temperature is 120 °C.

[0010] In the preparation method of the diatomite-based shaped composite phase change material, the second temperature is 80 °C.

[0011] In the preparation method of the diatomite-based shaped composite phase change material, the first predetermined time is 20 minutes and the second predetermined time is 2 hours.

[0012] In the preparation method of the diatomite-based shaped composite phase change material, pour the mixture into a beaker, and put the beaker containing the mixture into a vacuum drying oven for vacuum drying.

[0013] In the preparation method of the diatomite-based shaped composite phase change material, under vacuum conditions, capillary force and intermolecular force adsorb the liquid lauric acid-hexadecanol-palmitic acid LA-HD-PA in the pores of the modified diatomite.

[0014] In the preparation method of the diatomite-based shaped composite phase change material described above, the set temperature of the vacuum drying oven is 80 °C and the vacuum degree is 0.08 MP.

[0015] A diatomite-based shaped composite phase change material is made by the preparation method of the diatomite-based shaped composite phase change material described above.

[0016] Compared with the prior art, the present invention has the following advantages: The present invention can effectively reduce the interfacial tension between materials, thereby achieving more efficient mass transfer, enabling the phase change material to be more uniformly dispersed in the microporous structure of diatomite. This uniform dispersion not only improves the overall thermal conductivity and phase change efficiency of the composite material, but also avoids the phase separation phenomenon during the phase change process, ensuring the stability and consistency of performance. The vacuum environment can remove the bubbles that may be introduced during the processing, promoting the materials to combine more tightly, which helps to improve the mechanical strength and durability of the composite. The vacuum adsorption method is relatively mild during the preparation process, which helps to maintain the chemical properties and thermal characteristics of the phase change material, avoiding the degradation or failure of the material under high temperature or strong acid-base conditions. These advantages make the vacuum adsorption method more superior in the preparation of high-performance diatomite-phase change material composites and can meet more stringent application requirements. The diatomite modified by multiple steps has significant advantages after calcination, pickling, and alkali washing, including: (1) The pickling process can remove impurities and metal ions in diatomite, thereby improving its purity and enhancing its chemical stability and reactivity in applications. (2) The alkali washing treatment helps to further remove minerals and organic substances, providing more openness for the microporous structure of diatomite, which can significantly increase its specific surface area and adsorption capacity, making its performance more superior in the fields of hygroscopicity, catalysis, and filtration. (3) The diatomite after calcination, pickling, and alkali washing usually has better thermal stability and mechanical strength and can maintain good structural stability in high-temperature or high-load environments. These comprehensive advantages make the diatomite treated by multiple processes more competitive in the field of building material applications. The lauric acid-hexadecanol-palmitic acid composite phase change material has multiple significant advantages compared with traditional organic phase change materials such as n-butyl stearate, methyl stearate, or paraffin wax, including: (1) The composite phase change material adopted has a wider phase change temperature range, which can provide a more flexible thermal management solution in different application scenarios and adapt to higher temperature requirements; (2) The combination of lauric acid, hexadecanol, and palmitic acid not only improves the thermal conductivity of the material, but also enhances its thermal stability, reduces the phase separation phenomenon, and ensures the performance consistency during long-term use; (3) The composite material has a higher latent heat of phase change, which can store more thermal energy in a relatively small volume and improve the energy storage efficiency; (4) The natural sources of lauric acid and palmitic acid make this composite material superior to some synthetic organic phase change materials in terms of environmental protection and meet the requirements of sustainable development. In summary, the lauric acid-hexadecanol-palmitic acid composite phase change material shows greater potential in building, energy storage, and temperature control applications. Brief Description of the Drawings

[0017] By reading the following detailed description of the preferred embodiments, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The accompanying drawings of the specification are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts. Moreover, throughout the drawings, the same reference numerals are used to represent the same components.

[0018] In the drawings: Figure 1 is a schematic diagram of the preparation process of the composite phase change material of the present invention; Figure 2 is a schematic diagram of the appearance of the sample of the present invention with the mass fraction of LA-HD-PA / DME being 35% - 60%; Figure 3 is a schematic diagram of the adsorption effect test of the present invention using LA-HD-PA samples with a mass content of 35 - 55%, Figure 3 in which (a) is a schematic diagram of the adsorption effect test before the heat treatment of the acid-washed diatomite, Figure 3 in which (b) is a schematic diagram of the adsorption effect test after the heat treatment of the acid-washed diatomite; Figure 4 is a schematic diagram of the leakage rate test of the present invention using LA-HD-PA samples with a mass content of 35 - 55%, Figure 4 in which (a) is a schematic diagram of the leakage rate test before the heat treatment of the acid-washed + alkali-washed diatomite, Figure 4 in which (b) is a schematic diagram of the leakage rate test after the heat treatment of the acid-washed + alkali-washed diatomite; Figure 5 is the FT-IR diagram of LA-HD-PA, DME, and LA-HD-PA / DME of the present invention, where FT-IR is Fourier Transform Infrared Spectrometer, Figure 5 in which (a) is the FT-IR diagram of LA-HD-PA, Figure 5 in which (b) is the FT-IR diagram of DME, Figure 5 in which (c) is the FT-IR diagram of LA-HD-PA / DME; Figure 6 is the DSC diagram of LA-HD-PA / DME of the present invention, where DSC is Differential Scanning Calorimeter; Figure 7 is the TG diagram of DME and LA-HD-PA / DME of the present invention, where TG is Thermogravimetric Analyzer; Figure 8 is the scanning electron microscope diagram of LA-HD-PA / DME of the present invention; Figure 9 These are the DSC diagrams of LA-HD-PA / DME of the present invention before the hot and cold cycle, and after 100, 200, and 300 times of the hot and cold cycle.

[0019] The present invention will be further explained below in conjunction with the accompanying drawings and embodiments. Specific Embodiments

[0020] Specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although specific embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present invention can be more thoroughly understood and the scope of the present invention can be fully conveyed to those skilled in the art.

[0021] It should be noted that in the description of the specification and claims, certain terms are used to refer to specific components. Those skilled in the art should understand that technicians may use different terms to refer to the same component. The specification and claims do not use the difference in terms as a way to distinguish components, but use the difference in the functions of components as the criterion for distinction. For example, the terms "comprising" or "including" mentioned throughout the specification and claims are open-ended terms and should be interpreted as "including but not limited to". The subsequent description of the specification is for the purpose of implementing the preferred embodiments of the present invention, but the description is based on the general principles of the specification and is not used to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the scope defined by the appended claims.

[0022] For the convenience of understanding the embodiments of the present invention, the following will further explain with specific embodiments as examples in conjunction with the accompanying drawings, and each accompanying drawing does not constitute a limitation to the embodiments of the present invention.

[0023] As Figures 1 to 9 shown, the preparation method of the diatomite-based shaped composite phase change material includes the following steps: Step 1: Weigh lauric acid-hexadecanol-palmitic acid LA-HD-PA and modified diatomite according to a predetermined mass ratio; Step 2: Place the modified diatomite in a constant temperature drying at a first temperature until a constant weight is reached, heat lauric acid-hexadecanol-palmitic acid LA-HD-PA from solid state to liquid state and then add it to the dried modified diatomite to form a mixture; Step 3: At a second temperature, stir the mixture for a first predetermined time and then place it in a vacuum drying oven for vacuum drying. After drying for a second predetermined time, take it out and grind it to obtain the diatomite-based shaped composite phase change material LA-HD-PA / DME.

[0024] In a preferred embodiment of the preparation method of the diatomite-based shaped composite phase change material, the predetermined mass ratio of lauric acid-hexadecanol-palmitic acid LA-HD-PA accounts for 35% to 60% of the total weight parts.

[0025] In a preferred embodiment of the preparation method of the diatomite-based shaped composite phase change material, the diatomite is treated by roasting, pickling and alkali washing to obtain modified diatomite.

[0026] In a preferred embodiment of the preparation method of the diatomite-based shaped composite phase change material, the first temperature is 120 °C.

[0027] In a preferred embodiment of the preparation method of the diatomite-based shaped composite phase change material, the second temperature is 80 °C.

[0028] In a preferred embodiment of the preparation method of the diatomite-based shaped composite phase change material, the first predetermined time is 20 minutes and the second predetermined time is 2 hours.

[0029] In a preferred embodiment of the preparation method of the diatomite-based shaped composite phase change material, the mixture is poured into a beaker, and the beaker containing the mixture is placed in a vacuum drying oven for vacuum drying.

[0030] In a preferred embodiment of the preparation method of the diatomite-based shaped composite phase change material, under vacuum conditions, capillary force and intermolecular force adsorb liquid lauric acid-hexadecanol-palmitic acid LA-HD-PA in the pores of the modified diatomite.

[0031] In a preferred embodiment of the preparation method of the diatomite-based shaped composite phase change material, the vacuum drying oven is set at a temperature of 80 °C and a vacuum degree of 0.08 MP.

[0032] A diatomite-based shaped composite phase change material is made by the preparation method of the diatomite-based shaped composite phase change material.

[0033] In one embodiment, the diffusion-permeation ring method was used to compare the leakage conditions of the prepared LA-HD-PA / DME composite phase change material, and its adsorption efficiency was judged accordingly. Then, infrared spectroscopy, differential scanning calorimetry, thermogravimetry, scanning electron microscopy, thermal cycling test and other methods were used to systematically study its thermal properties and microstructural characteristics, further confirming its advantages.

[0034] Preparation and maximum adsorption capacity determination of LA-HD-PA / DME Preparation method of LA-HD-PA / DME. The diatomite-based shaped composite phase change material (LA-HD-PA / DME) is prepared by the vacuum adsorption method. The vacuum adsorption method indirectly increases the absorption amount of the phase change material by the porous adsorption material under the action of the pressure difference under vacuum conditions. The specific experimental operation process is as Figure 1 . Weigh LA-HD-PA and modified diatomite accurately according to the predetermined mass ratio. Subsequently, put the modified diatomite into an electrothermal isothermal electric blast drying oven at 120 °C and dry it to a constant weight. Heat the weighed solid LA-HD-PA to a liquid state and then slowly add it to the dried and modified diatomite. Stir at 80 °C for 20 minutes, then pour the mixture into a beaker, and put the beaker containing the mixture into a vacuum drying oven for subsequent treatment. The temperature of the vacuum drying oven is set at 80 °C and the vacuum degree is 0.08 MP. Take it out and grind it after drying for 2 h, and the LA-HD-PA / DME shaped composite phase change material is prepared.

[0035] Adsorption effect test of LA-HD-PA / DME In order to evaluate the adsorption efficiency of the prepared samples, the diffusion-exudation circle method was adopted, and the analysis was carried out by observing its leakage rate and the size of the exudation circle. The following are the detailed operation steps: (1) First, draw a circle with a diameter of 30 mm with the center of the filter paper as the center. Then evenly disperse about 0.2 g of the sample inside the circle.

[0036] (2) Place the prepared sample in a constant temperature drying oven at 60 °C, take it out after heating for 1 hour.

[0037] (3) After the sample is cooled to room temperature, weigh it, and calculate the leakage rate of the sample according to the weighing result.

[0038] Influence of different PCM mass fractions on the adsorption amount When the mass ratio of the phase change material to the adsorption material is too large, it will cause the adsorption material to be in a supersaturated state, and it will also cause the leakage of the phase change material, making it difficult to be applied in actual engineering. Therefore, under the requirement of a certain leakage rate, it is very necessary to conduct an experiment on the adsorption amount of the phase change material by the encapsulating material.

[0039] Experimental method Table 1 shows the designed ratios of each group of materials. According to the total mass of the sample being 10 g, the mass fraction ratios of LA-HD-PA are 35%, 40%, 45%, 50%, 55%, and 60% respectively, that is, m PCM :m DMEWeigh LA-HD-PA and modified diatomite in ratios of 35:65, 40:60, 45:55, 50:50, 60:40, etc., and prepare the LA-HD-PA / DME shaped composite phase change material according to the preparation method in 4.1.1. Observe and analyze the appearance of the prepared samples, mainly analyzing the saturation degree of the mass fraction of LA-HD-PA on the adsorption capacity of diatomite. It is necessary to ensure that the modified diatomite can achieve the maximum adsorption capacity for LA-HD-PA and maintain a low leakage rate. Moreover, the prepared LA-HD-PA / DME shaped composite phase change material should have high heat storage performance, that is, a high latent heat value.

[0040] Table 4.1 Design ratios of each group of materials Analysis of experimental results The appearance of the sample is as Figure 2 shown. Observation Figure 2 shows that when the mass fraction of LA-HD-PA / DME is 35% - 60%, the samples are in powder, powder-solid, and small solid states. As the mass fraction of LA-HD-PA / DME increases, the samples gradually change from fine powder to small granular solid states; when the mass fraction of LA-HD-PA / DME reaches 60%, the samples show significant dispersion and coagulate into fine solid particles. At this time, it can be clearly observed that the phase change material tightly covers the surface of diatomite. The samples with a mass fraction of LA-HD-PA / DME of 35% - 60% have no obvious leakage at room temperature. The following experiments will test the adsorption effect of the shaped phase change material, aiming to screen out the shaped composite phase change material with a low leakage rate and strong adsorption capacity of the modified diatomite. At the same time, compare the maximum adsorption capacity of diatomite treated only by pickling and treated by pickling plus alkali washing for the phase change material to evaluate the improvement effect of the "pickling + alkali washing" modification process on the adsorption performance compared with pickling alone.

[0041] Preparation of LA-HD-PA / DME with pickled diatomite and determination of leakage rate Use LA-HD-PA samples with a mass content of 35 - 55% to test the adsorption effect. The results are as Figure 3 . From Figure 3It can be seen that when the content of LA-HD-PA is 35%, there is no seepage ring on the heat-treated filter paper, and only a small amount of the phase change material oozes out. For the sample with an LA-HD-PA addition of 40%, the color of the filter paper surface becomes a little darker, but the exudate still does not ooze outside the ring. When the mass ratio of LA-HD-PA reaches 45% and 50%, it can be observed that the exudation amount of LA-HD-PA on the filter paper is significantly deeper, but it still does not ooze outside the test ring. The increase in the mass ratio of LA-HD-PA makes the color of the exudation circle of the sample darker and more phase change material oozes out; when the mass ratio of LA-HD-PA reaches 55%, it can be observed that the exudation amount of the phase change material LA-HD-PA on the filter paper is significantly more than the previous one and clearly oozes out of the test ring, indicating that the adsorption of the modified diatomite on the phase change material has reached a supersaturated state and cannot continue to absorb, resulting in the easy leakage of the phase change material. Under the pickled diatomite, the leakage rate percentage of LA-HD-PA / DME is shown in Table 2.

[0042] As can be seen from Table 2, when the mass ratio of PCM reaches 35%, 40%, 45%, 50% and 55%, the corresponding leakage rates are 4%, 6%, 10.5%, 16% and 23% respectively. With the increase in the content of the pickled PCM in the shaped composite phase change material, the corresponding leakage rate increases. When the PCM content is 35%, the leakage rate is only 4% (<5%), which can be applied to building materials. When the PCM content is 50% and 55%, the leakage rates are 16% and 23%, and the leakage situation is relatively serious.

[0043] Table 2 Experiment on the adsorption effect of pickled LA-HD-PA / DME It can be seen from Figure 4 that when the content of LA-HD-PA is 40%, there is no seepage ring on the heat-treated filter paper. When the addition of LA-HD-PA is 45%, there is no seepage ring on the heat-treated filter paper, and only a small amount of the phase change material oozes out and is dispersed within the ring. When the mass ratio of LA-HD-PA reaches 50%, it can be seen that the color of the filter paper surface appears darker and the phase change material oozing out is more full within the ring, but does not exceed the test ring. When the mass ratio of LA-HD-PA reaches 55%, it can be observed that the exudation amount of the phase change material LA-HD-PA on the filter paper is significantly more than the previous one, the filter paper color is darker, and it clearly oozes out of the test ring, indicating that the adsorption of the modified diatomite on the phase change material has reached a supersaturated state and cannot continue to absorb, resulting in the easy leakage of the phase change material. Under the "pickling + alkali washing" diatomite, the leakage rate percentage of LA-HD-PA / DME is shown in Table 3.

[0044] As can be seen from Table 3, when the mass ratio of LA-HD-PA reaches 35%, 40%, 45%, 50% and 55%, the corresponding leakage rates are 0%, 1.5%, 4.5%, 9.5% and 12% respectively. As the content of LA-HD-PA in the shaped composite phase change material increases, the corresponding leakage rate increases. When the content of LA-HD-PA is 45%, the leakage rate is only 4.5% (<5%), which can be applied to building materials. When the content of LA-HD-PA is 55%, the leakage rate is 12%, and the leakage situation is relatively serious. However, for the same content of phase change material in LA-HD-PA / DME treated by pickling, the LA-HD-PA / DME treated by "pickling + alkali washing" has a significantly lower leakage rate than that treated by pickling. Because with the increase of the content of LA-HD-PA, the heat storage capacity also increases, and the heat storage performance is also better than that of LA-HD-PA / DME treated only by pickling. Therefore, in the subsequent experiments, the ratio with 45% content of LA-HD-PA in LA-HD-PA / DME was selected.

[0045] Table 3 Adsorption effect experiment of PCM / DME treated by "pickling + alkali washing" Performance characterization and analysis of LA-HD-PA / DME Analysis of the structural characteristics of LA-HD-PA / DME The infrared spectra of LA-HD-PA, DME and LA-HD-PA / DME with 45% content of shaped phase change material were tested by FT-IR, and the parameters such as the position, number and shape of the absorption peaks in the spectra were analyzed to judge whether a chemical reaction occurred after the combination of LA-HD-PA and DME. Draw according to the test results Figure 5 . The stretching vibration absorption peaks of the O-H bond of water molecules and the Si-O-H bond of diatomite appear at 3448 cm -1 of diatomite, corresponding to the bending vibration peak of O-H appearing at 1636 cm -1 , and the characteristic absorption peak at 1084 cm -1 is the stretching vibration absorption peak of cyclic Si-O-Si. The stronger absorption peaks appearing at 792 cm -1 and 471 cm -1 are all caused by the bending vibration absorption peak of Si-O. All the characteristic peaks appearing in LA-HD-PA / DME are consistent with the spectra of LA-HD-PA and DME, only the position and transmittance of the absorption peaks change slightly, and no new characteristic peaks are generated. Similarly, at 2360 cm -1The characteristic absorption peak that appears is the absorption peak of carbon dioxide. This is because carbon dioxide was irradiated during the experiment, which has no impact on this experiment. It proves that the eutectic between LA-HD-PA and DME is only the result of simple pore capillary force and molecular force, and no chemical reaction occurs.

[0046] Thermophysical Property Analysis of LA-HD-PA / DME It can be seen from Figure 6 that for the LA-HD-PA / DME shaped phase change material, the phase change temperature is 23.05 °C, the phase change peak temperature is 25.88 °C, and the latent heat of phase change is 70.5 J / g respectively. There is a large endothermic peak and a small endothermic peak (negligible compared to the large endothermic peak) on the DSC curve. From this, it can be known that the shaped phase change material mainly undergoes liquid-solid phase change during the temperature increase process and shows stable performance in heat storage. At the same time, the DSC curve only shows a single exothermic curve, indicating that there is only one crystallization phenomenon in the LA-HD-PA / DME shaped phase change material. The modified diatomite has no influence on the phase change performance of LA-HD-PA and is an ideal carrier material.

[0047] Thermal Stability Analysis of LA-HD-PA / DME A thermogravimetric analyzer was used to analyze the heat resistance of the modified diatomite and the LA-HD-PA / DME shaped phase change material. The test results are as Figure 7 . Figure 7 are the TG curves of the modified diatomite and the shaped phase change material LA-HD-PA / DME. The mass loss rate of the modified diatomite is 0% during the temperature increase from 30 °C to 400 °C. The experiment proves that the modified diatomite has high heat resistance. There is a weight loss peak in the range of 30 - 400 °C for LA-HD-PA / DME. It starts to lose weight at 126.64 °C, and when it rises to 364 °C, the weight of the crystal does not change at all, indicating that it has completed the weight loss. The weight loss of the LA-HD-PA / DME shaped phase change material with a weight percentage of 46.96% is mainly due to the cracking of LA-HD-PA under high temperature conditions. As the temperature increases, the entire phase change material is decomposed, and only the modified diatomite remains. The heat resistance of the modified diatomite results in no mass loss. At the same time, the weight loss rate of the LA-HD-PA / DME curve in the figure is close to the mass fraction of the phase change material LA-HD-PA (the content of the phase change material shaped by diatomite is 45%). Due to the mixing of trace impurities during the experiment, the weight loss will be 1.96% more than that of the LA-HD-PA / DME content. The influence of impurities can be ignored, which is consistent with the experimental ratio results. This shaped phase change material has good high temperature resistance below 120 °C. Therefore, the LA-HD-PA / DM shaped phase change material is completely suitable for the construction field.

[0048] Microscopic Morphology Analysis of LA-HD-PA / DME Figure 8 It can be seen that the phase change material is uniformly filled in the pores of diatomite. The surface of the composite is smooth and tightly wound together, indicating that the diatomite binary carrier effectively adsorbs the phase change material and prevents its melting and leakage. From Figure 8 it can be seen that the phase change material LA-HD-PA in the LA-HD-PA / DME material is in the process of phase change. The surface becomes relatively smooth and uniformly covers the entire surface.

[0049] Thermal Cycle Stability Analysis of LA-HD-PA / DME In actual engineering, the phase change material adsorbed by modified diatomite must continuously undergo the cycle process of "melting due to heat absorption and crystallization due to heat release". Thermal cycle stability is an important indicator for judging the durability of the shape-stabilized phase change material. Accelerated thermal cycle experiments were carried out on the LA-HD-PA / DME shape-stabilized phase change material for 100, 200, and 300 times. The results are shown in Table 4 and Figure 9 . From Figure 9 and Table 4, it can be seen that after 100, 200, and 300 times of accelerated heating and cooling cycle experiments on the LA-HD-PA / DME shape-stabilized phase change material, the phase change temperature, the phase change peak temperature, and the phase change latent heat are not much different from the phase change temperature of LA-HD-PA before the cycle. The phase change temperature of the 300th cycle is only 0.93 °C different from the phase change temperature of LA-HD-PA before the cycle, and the phase change peak temperature and the maximum latent heat are respectively 0.24 °C and 6.43 J / g different. After the heating and cooling cycle test, as the number of cycles increases, the measured multi-cycle samples all show a single endothermic peak, indicating that under the heating and cooling cycle test, the phase change temperature and latent heat do not fluctuate greatly. This shows that the shape-stabilized phase change material LA-HD-PA / DME has good thermal cycle stability.

[0050] Table 4 Thermal Physical Properties of LA-HD-PA / DME before and after 100, 200, and 300 Heating and Cooling Cycles It can be seen that (1) by comparing the heat treatment leakage of the composite phase change material, it is found that the maximum adsorption amount of the traditional acid-washed diatomite for the vacuum-adsorbed composite phase change material LA-HD-PA is 35% when the leakage rate is less than 5%, while the maximum adsorption amount of the "acid-washed + alkali-washed" diatomite in the present invention for the vacuum-adsorbed composite phase change material LA-HD-PA is 45% when the leakage rate is less than 5%. Alkali-washing operation on the basis of acid-washed diatomite can increase the pores of diatomite and greatly improve the adsorption amount of diatomite for the composite phase change material.

[0051] (2) The SEM and FT-IR were used to analyze the microstructure and chemical structure of LA-HD-PA / DME, confirming that LA-HD-PA and DME are combined through intermolecular physical interactions during the composite process without any chemical reactions occurring. The diatomite uniformly adsorbs LA-HD-PA / DME in the pores through intermolecular forces and pore capillary forces.

[0052] (3) The DSC was used to analyze the thermophysical properties of LA-HD-PA / DME. Its phase change temperature is 23.05 °C, the peak temperature is 25.88 °C, and the latent heat is 70.53 J / g, indicating that the formulated shaped composite phase change material is suitable for the construction field and exhibits good heat storage capacity. The TG experiment analysis further confirmed that LA-HD-PA / DME has good thermal stability. In addition, 300 accelerated thermal cycle experiments on LA-HD-PA / DME proved that LA-HD-PA / DME has good thermal cycle stability and great application potential in the construction field.

[0053] Although the embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above specific embodiments and application fields. The above specific embodiments are merely illustrative and guiding, rather than restrictive. Those of ordinary skill in the art can also make many forms under the inspiration of this specification and without departing from the scope protected by the claims of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a diatomite-based shaped composite phase change material, characterized in that: The method comprises the following steps: Step 1: Weigh lauric acid-hexadecyl alcohol-palmitic acid LA-HD-PA and modified diatomaceous earth according to a predetermined mass ratio; Step 2: placing the modified diatomaceous earth in a first temperature constant temperature and drying it to a constant weight, heating the lauric acid-hexadecyl alcohol-palmitic acid LA-HD-PA solid to a liquid state and then adding it to the dried modified diatomaceous earth to form a mixture; Step 3: at a second temperature, stir the mixture for a first predetermined time, then put it into a vacuum drying oven for vacuum drying, and take it out and grind it after drying for a second predetermined time to obtain a diatomite-based shaped composite phase change material LA-HD-PA / DME.

2. The method for preparing the diatomite-based shaped composite phase change material according to claim 1, characterized in that: Preferably, the diatomaceous earth is subjected to calcination, acid washing and alkali washing to obtain modified diatomaceous earth.

3. The method for preparing the diatomite-based shaped composite phase change material according to claim 1, characterized in that: The mixture was poured into a beaker, and the beaker containing the mixture was placed in a vacuum drying oven for vacuum drying.

4. The method for preparing the diatomite-based shaped composite phase change material according to claim 1, characterized in that: The vacuum drying oven was set at a temperature of 80°C and a vacuum degree of 0.08 MPa.

5. A diatomite-based shaped composite phase change material, characterized in that: The diatomite-based shaped composite phase change material is prepared by the preparation method of any one of claims 1 to 4.

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