Heat storage material

Abstract

To provide a heat reservoir that suppresses degradation of insulation properties of coolant.SOLUTION: A heat reservoir having a spherical silica porous body including a plurality of pores in an approximately columnar shape has a phase change material contained in the pores of the spherical silica porous body and an outer shell part made of solid silica crystal that fills at least a part of the pores of the spherical silica porous body. In the spherical silica porous body, the pores have a uniform pore size and are radially arranged from the center toward the surface of the spherical silica porous body.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heat storage medium having a spherical porous silica material. [Background technology]

[0002] BACKGROUND ART Conventionally, a technology has been proposed for storing heat by maintaining a phase change substance (latent heat storage material) that absorbs and releases latent heat in response to temperature changes in a solid state (see, for example, Patent Document 1 and Non-Patent Documents 1 and 2).

[0003] Patent Document 1 discloses a hard-shelled microencapsulated latent heat transport material in which a phase-change substance is encapsulated in non-porous hollow silica particles. Non-Patent Document 1 discloses a technology for confining a phase-change substance inside the pores of mesoporous silica. Non-Patent Document 2 discloses a material in which LiOH is supported in the pores of mesoporous silica that has water vapor adsorption properties. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2015 / 025529 [Non-patent literature]

[0005] [Non-Patent Document 1] Kota Nakano and two others, "Solidification and Melting Phenomena of Erythritol in the Pores of Mesoporous Silica," Proceedings of the 2013 Thermal Engineering Conference of the Japan Society of Mechanical Engineers, G133, No. 13-55, pp. 219-220 [Non-patent document 2] Mitsuhiro Kubota, "Development of Lithium Hydroxide-Mesoporous Silica Hybrid Materials Aiming for High-Density Chemical Heat Storage," Grant-in-Aid for Scientific Research, Research Results Report, May 27, 2015 Summary of the Invention [Problem to be solved by the invention]

[0006] The technology described in Patent Document 1 had problems with the packing density and dispersibility of the capsule particles, and sufficient heat storage stability was not achieved. In the technology described in Non-Patent Document 1, leakage of erythritol as a heat storage material from pores was confirmed. In the technology described in Non-Patent Document 2, a sufficient hydration reaction (=heat release) rate was not achieved. Thus, stable heat storage was difficult even with the technologies described in Patent Document 1 and Non-Patent Documents 1 and 2.

[0007] Furthermore, in the above-mentioned technology, no consideration is given to maintaining the heat storage when the heat storage medium comes into contact with an organic solvent.

[0008] In view of the above problems, an object of the present invention is to provide a technology for improving the stability of heat storage in a technology for storing heat by holding a phase-change material in a porous silica body. [Means for solving the problem]

[0009] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following aspects.

[0010] (1) According to one aspect of the present invention, there is provided a heat storage medium having a spherical porous silica body having a plurality of substantially cylindrical pores formed therein, the heat storage medium comprising: a phase-change material contained in the pores of the spherical porous silica body; and an outer shell formed of solid silica crystals that closes at least some of the pores of the spherical porous silica body, the pores in the spherical porous silica body having a uniform pore diameter and arranged radially from the center to the surface of the spherical porous silica body.

[0011] According to this configuration, the spherical porous silica body has a shell that blocks at least a portion of the pores of the porous silica body containing the phase-change material. Because the shell is solid, even if the thermal storage body is immersed in an organic solvent such as ethanol or toluene, at least a portion of the pores are blocked, preventing the organic solvent from penetrating the pores and preventing the phase-change material from eluting. Furthermore, because the pores are radially arranged from the center to the surface, compared to the honeycomb-shaped porous silica body described in Non-Patent Document 1, one end of the pores is closed, further preventing leakage of the phase-change material. Because the pores are approximately cylindrical, the phase-change material is held in place by capillary force. Even if the phase-change material dissolves in the organic solvent, leakage to the outside is prevented. As a result, the thermal storage stability is improved.

[0012] (2) In the heat storage body of the above embodiment, the thickness of the outer shell may be 0.055 μm or more, which can further suppress elution of the phase change material when the heat storage body is immersed in an organic solvent.

[0013] (3) In the heat storage body of the above embodiment, the central pore diameter of the plurality of pores of the spherical porous silica body may be 1 nm or more and 20 nm or less. If the pore diameter of the spherical porous silica body is too small, it may be difficult to introduce the phase change material. Furthermore, since the introduction of the phase change material into the pores of the spherical porous silica body is achieved by utilizing the capillary force of the pores, if the pore diameter of the spherical porous silica body is too large, the capillary force may not work effectively and the phase change material may not be sufficiently filled. If the amount of phase change material filled is insufficient, the amount of heat stored by the heat storage body will be small. In contrast, with the heat storage body of this configuration, the central pore diameter of the pores of the spherical porous silica body is 1 nm or more and 20 nm or less, so a sufficient amount of phase change material is filled, thereby further improving the heat storage capacity of the heat storage body.

[0014] (4) In the heat storage body of the above embodiment, the plurality of pores of the spherical porous silica body may have a standard deviation of 20% or less of the median pore diameter in the pore diameter distribution curve in the range of pore diameters greater than 1 nm. In this way, the pore diameters of the spherical porous silica body are highly uniform, so that capillary forces act more uniformly, the filling rate of the phase-change material can be improved, and the heat storage capacity of the heat storage body can be further improved.

[0015] (5) In the heat storage medium of the above embodiment, the diameter of the spherical porous silica material may be 10 nm or more and 3000 nm or less. This makes it possible to improve the packing rate when a plurality of heat storage materials are packed in a container and used, and the monodispersity when a plurality of heat storage materials are dispersed in a dispersion medium.

[0016] (6) In the heat storage body of the above embodiment, the plurality of pores of the spherical porous silica body have a pore volume of 0.9 [ml / g] or more and a specific surface area per unit pore volume of 1.4 × 10 9 [m 2 / m 3 In this way, the proportion of the phase change material that effectively functions as a latent heat storage material can be increased, and the heat storage density can be increased.

[0017] (7) In the heat storage medium of the above embodiment, the phase change material may be at least one of a sugar alcohol and paraffin. Because sugar alcohol has a high heat storage density, it is possible to provide a heat storage medium with good heat storage properties. Because paraffin has a low degree of supercooling, it is possible to suppress a decrease in heat storage efficiency.

[0018] (8) In the heat storage body of the above embodiment, the shell portion may have a molecular size of raw material smaller than the pore diameter of the plurality of pores in the spherical porous silica body. In this case, the raw material molecules are likely to crosslink inside the pores of the spherical porous silica body and block the pores, thereby improving the blocking rate of the pores by the shell portion and further suppressing the elution of the phase-change material.

[0019] The present invention can be realized in various forms, for example, in the form of a method for manufacturing a heat storage body, a heat transport system using a heat storage body, or a system including the heat transport system. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 2 is an explanatory diagram conceptually showing heat storage in the heat storage body of the embodiment. [Figure 2] FIG. 1 is an explanatory diagram conceptually showing the structure of a spherical porous silica material. [Figure 3] FIG. 3 is a process diagram showing an example of a manufacturing process of the heat storage body of the embodiment. [Figure 4] FIG. 1 is an explanatory diagram conceptually showing a method for producing a spherical porous silica material. [Figure 5] 1 is an SEM image of a heat storage body according to an embodiment of the present invention. [Figure 6] 1 is an SEM image of a heat storage body of a comparative example. [Figure 7] FIG. 10 is a diagram showing the specifications of each heat storage material obtained from an SEM image. [Figure 8] FIG. 2 is a diagram showing the specifications of a heat storage body obtained by thermal analysis. [Figure 9] FIG. 10 is a diagram showing the results of a durability test. [Figure 10] FIG. 1 shows a TGA curve of a phase change material. [Figure 11] FIG. 1 is a diagram showing a DSC curve of a phase change material. [Figure 12] 1 is an SEM image of a heat storage body according to an embodiment of the present invention. [Figure 13] FIG. 2 is a diagram showing specifications obtained from SEM images of the heat storage bodies of the example and comparative example. [Figure 14] FIG. 2 is a diagram showing the specifications obtained by thermal analysis of the heat storage bodies of the examples and comparative examples. [Figure 15] FIG. 10 is a diagram showing the results of a durability test. [Figure 16] FIG. 1 is a diagram showing the main specifications of a shell source. [Figure 17] 1 is an SEM image of a heat storage body according to an embodiment of the present invention. [Figure 18]1 is an SEM image of a heat storage body of a comparative example. [Figure 19] 1 is an SEM image of a heat storage body of a comparative example. [Figure 20] FIG. 2 is a diagram showing specifications obtained from SEM images of the heat storage bodies of the example and comparative example. [Figure 21] FIG. 2 is a diagram showing the specifications obtained by thermal analysis of the heat storage bodies of the examples and comparative examples. [Figure 22] FIG. 10 is a diagram showing the results of a durability test. [Figure 23] FIG. 10 is an explanatory diagram conceptually showing the formation of an outer shell portion. DETAILED DESCRIPTION OF THE INVENTION

[0021] Fig. 1 is an explanatory diagram conceptually showing heat storage in a heat storage material 1 according to one embodiment of the present invention. In Fig. 1, a portion of the heat storage material 1 is cut away to show the internal structure. The heat storage material 1 has a spherical porous silica material 100 having a plurality of pores 10, a phase change material 200 present in the pores 10, and an outer shell 300 that closes the plurality of pores 10 of the spherical porous silica material 100.

[0022] The pores 10 of the spherical porous silica material 100 are generally cylindrical. The pores 10 have uniform diameters and are arranged radially from the center of the spherical porous silica material 100 toward the surface. In the figure, some of the pores 10 and some of the phase change material 200 are labeled with reference numerals, while other portions are not labeled. FIG. 1 conceptually illustrates the heat storage material 1, and the number of pores may be greater or less than that illustrated. Although the figure illustrates an example in which the phase change material 200 fills the entire pores 10, the phase change material 200 may be filled only in part of the pores 10. Although the figure illustrates an example in which the outer shell 300 fills all of the pores 10 of the spherical porous silica material 100, it is sufficient that the outer shell 300 fills at least a portion of the pores 10.

[0023] The phase change material 200 absorbs and releases latent heat in response to temperature changes. The heat storage unit 1 absorbs and releases heat by utilizing the phase change (solid, liquid) of the phase change material 200. Specifically, when the phase change material 200 held in the spherical porous silica 100 changes from solid phase change material 200S (upper part of FIG. 1) to liquid phase change material 200L (lower part of FIG. 1), it absorbs ambient heat near its melting point and attempts to maintain a temperature near its melting point. Conversely, when it changes from liquid phase change material 200L (lower part of FIG. 1) to solid phase change material 200S (upper part of FIG. 1), it releases heat to the ambient near its freezing point and attempts to maintain a temperature near its freezing point until it is completely solidified. In other words, the heat storage unit 1 stores heat by utilizing the absorption and release of latent heat accompanying the solidification and melting of the phase change material 200. In FIG. 1, the solid phase change material 200 is cross-hatched and designated by the reference numeral 200S, and the liquid phase change material 200 is dot-hatched and designated by the reference numeral 200L.

[0024] (1) Spherical porous silica 100 FIG. 2 is an explanatory diagram conceptually showing the configuration of a spherical porous silica material 100 of this embodiment. In FIG. 2, as in FIG. 1, a portion of the spherical porous silica material 100 is cut away to illustrate the shape and arrangement of the pores 10. The pores 10 are shown by hatching in the cross section. As shown in the figure, the spherical porous silica material 100 of this embodiment has a plurality of approximately cylindrical pores 10, which are arranged radially from the center of the spherical porous silica material 100 toward the surface. The arrangement of the pores 10 can be confirmed by observing the heat storage material 1 with a TEM (Transmission Electron Microscope). The arrangement of the pores can be confirmed more clearly by introducing a metal (e.g., platinum) into the pores of the heat storage material 1 and observing it with a TEM.

[0025] The plurality of pores 10 are arranged radially from the center of the spherical porous silica body 100 toward the surface, and one end of the pores 10 is not open, which further suppresses leakage of the phase-change material 200 compared to, for example, the honeycomb-shaped porous silica body described in Non-Patent Document 1. Furthermore, since the pores 10 are approximately cylindrical, the phase-change material 200 is held by capillary force, and even if the phase-change material dissolves in an organic solvent, leakage to the outside can be suppressed, and the phase-change material can be stably held.

[0026] The central pore diameter of the plurality of pores 10 is not particularly limited, but is preferably 1 nm or more and 20 nm or less. More preferably, it is 2 nm or more and 10 nm or less. If the diameter of the pores 10 of the spherical porous silica material 100 is too small, it may be difficult to introduce the phase change material 200. Furthermore, since the introduction of the phase change material 200 into the pores 10 of the spherical porous silica material 100 is achieved by utilizing the capillary force of the pores 10, if the diameter of the pores 10 of the spherical porous silica material 100 is too large, the capillary force may not work effectively, and the phase change material 200 may not be sufficiently filled. If the amount of the phase change material 200 filled is insufficient, the amount of heat stored by the heat storage material 1 will be small. If the central pore diameter of the pores 10 of the spherical porous silica material 100 is 1 nm or more and 20 nm or less, a sufficient amount of the phase change material 200 can be filled, thereby improving the heat storage capacity of the heat storage material 1.

[0027] The pores 10 in the spherical porous silica material 100 have a uniform pore size. Here, "uniform pore size" means that the standard deviation of the pore size distribution curve in the range of pore sizes greater than 1 nm is within 35% of the median pore diameter. The median pore diameter refers to the pore diameter at which the pore size distribution curve shows a maximum peak in the range of pore sizes greater than 1 nm. The standard deviation of the pores 10 in the spherical porous silica material 100 in the range of pore sizes greater than 1 nm is preferably within 25% of the median pore diameter, more preferably within 20%. In this way, the pore sizes of the pores 10 in the spherical porous silica material 100 are highly uniform, which allows capillary forces to act more uniformly and improves the filling rate of the phase-change material 200, resulting in a heat storage material 1 with higher heat storage capacity.

[0028] The diameter of the spherical porous silica material 100 is not particularly limited, but is preferably on the order of several hundred nanometers. The diameter of the spherical porous silica material 100 is more preferably 10 nm or more and 30,000 nm or less. This makes it possible to improve the packing rate when a plurality of heat storage materials 1 are packed into a container for use, and the monodispersity when a plurality of heat storage materials 1 are dispersed in a dispersion medium. In the spherical porous silica material 100 of this embodiment, the pores 10 have a uniform pore size and are arranged radially from the center of the spherical porous silica material 100 toward the surface, and therefore, it can also be said to be a "spherical porous silica material having highly regular pores."

[0029] The pore volume of the plurality of pores in the spherical porous silica material 100 and the specific surface area per unit pore volume are not particularly limited, but the pore volume is preferably 0.9 ml / g or more and the specific surface area per unit pore volume is preferably 1.4×10 9 [m 2 / m 3 In this way, the proportion of the phase change material 200 that effectively functions as a latent heat storage material increases, and the heat storage body 1 can have a high heat storage density.

[0030] The spherical porous silica material 100 can be synthesized by the method described in Japanese Patent No. 5480461. During synthesis, the diameter of the pores 10 can be adjusted by changing the type of surfactant. In addition, the pore size can be enlarged after synthesis by replacing the surfactant with another surfactant, introducing a swelling agent, or performing hydrothermal treatment under acidic conditions. The shape of the spherical porous silica material 100 (diameter, arrangement of multiple pores, pore diameter, pore volume), details of its effects, and manufacturing method are as described, for example, in Japanese Patent Application Nos. 2021-196743 and 2021-196745, which have already been filed by the applicant of the present application.

[0031] (2) Phase change material 200 In the heat storage body 1, a phase change material 200 is retained within the pores 10 of the spherical porous silica body 100 (FIG. 1). While the phase change material 200 is not particularly limited, sugar alcohols are preferred because they have a high heat storage density and can provide a heat storage body with good heat storage properties. Paraffin is also preferred because it has a low degree of supercooling and can suppress a decrease in heat storage efficiency. Erythritol is preferred as the sugar alcohol, and linear paraffin is preferred as the paraffin. Other examples of the phase change material 200 that can be used include sugar alcohols such as mannitol, galactitol, xylitol, sorbitol, and ribitol, inorganic salts such as inorganic phosphates, branched paraffins, and inorganic hydrates. Details of the types of phase change materials and their effects are described, for example, in Japanese Patent Application Nos. 2021-196743 and 2021-196745, previously filed by the applicant of the present application.

[0032] (3) Outer shell 300 The outer shell 300 is formed of solid silica crystals and blocks at least a portion of the multiple pores 10 of the spherical porous silica material 100. Here, "solid silica crystals" refers to so-called non-porous silica crystals that are highly dense and have substantially no pores. The fact that the outer shell 300 is solid can be confirmed by a TEM image of the heat storage body 1. In FIG. 1, a two-layer structure having a first outer shell layer 310 and a second outer shell layer 320 is shown as an example of the outer shell 300, but the outer shell may be a single layer or may have three or more layers.

[0033] The raw material for the outer shell 300 (hereinafter also referred to as the "shell source") is not particularly limited as long as it forms solid silica crystals, but it is preferable that the molecular size of the shell source be smaller than the pore diameter of the pores 10 in the spherical porous silica material 100. For example, if tetraethyl orthosilicate (hereinafter also referred to as "TEOS") is used as the raw material for the outer shell 300, its small molecular diameter makes it easy to crosslink inside the multiple pores 10 in the spherical porous silica material 100 and block the pores. The raw material for the outer shell 300 will be described in detail later.

[0034] (4) Manufacturing method FIG. 3 is a process diagram showing an example of a manufacturing process for the heat storage body 1 of the embodiment. First, spherical porous silica into which a phase-change material has been introduced and a shell source liquid are prepared (step P102). For example, a 100% TEOS liquid is prepared as the shell source liquid. Next, the prepared spherical porous silica is added to the shell source liquid, and the mixture is stirred and maintained at a predetermined temperature for a predetermined time (step P104). For example, the mixture is maintained at room temperature for 24 hours. Step P104 forms a first outer shell layer 310 on the surface of the spherical porous silica 100 (FIG. 1).

[0035] The liquid 1 produced in step P104 is filtered, and the particles on which the first outer shell layer 310 has been formed are taken out and dried to obtain the particles 1 (step P106). For example, the particles are dried at 45° C. for 24 hours.

[0036] Next, the particles 1 are immersed in an aqueous solution and hydrated to obtain liquid 2 (step P108). For example, the particles 1 are immersed in an ethylene glycol (EG) aqueous solution and left at room temperature for 24 hours. The ethylene glycol aqueous solution has, for example, an ethylene glycol:water ratio of 1:1 by weight. The hydration treatment can increase the proportion of silanol groups on the surface of the particles 1.

[0037] The liquid 2 produced in step P108 is filtered, and the particles are taken out and dried to obtain particles 2 (step P110). For example, the particles are dried at 45° C. for 24 hours. Note that step P108 (hydration treatment) and step P110 do not necessarily have to be performed.

[0038] The particles 2 obtained in step P110 are added to a shell source liquid and maintained at a predetermined temperature for a predetermined time while stirring (step P112). As in step P104, a 100% TEOS liquid is used as the shell source liquid, and the liquid is maintained at room temperature for 24 hours. In step P112, a second outer shell layer 320 is formed on the first outer shell layer 310 (FIG. 1). Steps P104 and P112 are also referred to as the "outer shell layer formation step."

[0039] The liquid 3 produced in step P112 is filtered, and the particles on which the first outer shell layer 310 and the second outer shell layer 320 have been formed are taken out and dried to obtain particles 3 (step P106). For example, the particles are dried at 45°C for 24 hours. The particles 3 correspond to the heat storage body 1 of the embodiment.

[0040] The spherical porous silica material doped with a phase-change material prepared in step P102 may be prepared in advance or may be prepared in step P102. The spherical porous silica material doped with a phase-change material can be synthesized by mixing a predetermined amount of spherical porous silica material 100 with a predetermined amount of liquid phase-change material 200L that has been melted by heating above its melting point. The liquid phase-change material 200L is introduced into and retained in the pores 10 of the spherical porous silica material 100 by capillary force. Furthermore, the pore diameter of the spherical porous silica material 100 into which the phase-change material is doped can be enlarged, for example, by subjecting the base spherical porous silica material to a treatment.

[0041] The heat storage body 1 of this embodiment has an outer shell 300 that blocks at least a portion of the pores 10 of the spherical porous silica body 100 having the phase change material 200 in the pores 10, and the outer shell 300 is solid. Therefore, even if the heat storage body 1 is immersed in an organic solvent such as ethanol or toluene, since at least a portion of the pores are blocked, the organic solvent can be prevented from penetrating into the pores, and the elution of the phase change material can be prevented. As a result, the stability of heat storage can be improved.

[0042] Because the multiple pores are arranged radially from the center toward the surface of the spherical porous silica body, one end of the pores is not open, which can further suppress leakage of the phase-change material compared to, for example, the honeycomb-shaped porous silica body described in Non-Patent Document 1. Because the pores are approximately cylindrical, the phase-change material is held by capillary force. Even if the phase-change material dissolves in an organic solvent, leakage to the outside can be suppressed, improving the stability of the retention. Furthermore, because the pores are approximately cylindrical, the phase-change material is held by capillary force, which can suppress elution of the phase-change material during the formation of the outer shell compared to, for example, the technology described in Patent Document 1.

[0043] The heat storage material 1 of this embodiment has a spherical porous silica material 100 with highly ordered pores 10. Silica has a higher thermal conductivity than a phase-change material, and heat is easily transferred from the spherical porous silica material 100 to the phase-change material. Because the spherical porous silica material 100 has highly ordered pores 10, the phase-change material can be introduced uniformly, improving the thermal conductivity from the silica to the phase-change material. As a result, the degree of supercooling of the phase-change material can be reduced, and the decrease in the heat storage capacity can be suppressed.

[0044] The heat storage body 1 of this embodiment can be used, for example, to regulate the temperature of clothing, building materials, and automotive components. For example, in an electric vehicle, the heat storage body 1 can be used to cool the battery by filling it around the battery pack. When using the heat storage body 1 in this way, there is a possibility that the heat storage body 1 may come into contact with an organic solvent due to, for example, a leakage of oil used in the vehicle. Even in such a case, as described above, the elution of the phase change material can be suppressed, and therefore the stability of heat storage can be maintained. [Example]

[0045] The present invention will be explained in more detail with reference to Examples 1 to 3 and Comparative Examples 1 to 3, but the present invention is not limited to the following Examples. The Examples and Comparative Example are all heat storage bodies in which the pores of spherical porous silica having approximately the same shape (particle diameter, pore diameter, pore volume, etc.) are filled with the same type of phase change material. The Examples and Comparative Example differ from each other in the presence or absence of an outer shell, the number of layers of the outer shell, the thickness of the outer shell, and the raw material (shell source) of the outer shell. In Examples 1 to 3 and Comparative Examples 1 to 3, normal paraffin (RT90HC, Rubitherm) was used as the phase change material.

[0046] <Sample manufacturing method> Fig. 4 is an explanatory diagram conceptually showing a method for producing a spherical porous silica material 100 used in Examples 1 to 3 and Comparative Examples 1 to 3. Like Fig. 1, Fig. 4 shows the internal structure of a spherical porous silica material with a portion cut away.

[0047] The spherical porous silica used in Examples 1 to 3 and Comparative Examples 1 to 3 was obtained by enlarging the pore diameter of a base spherical porous silica 100A (hereinafter also referred to as a base spherical porous silica) by treating it with reference to JP-A Nos. 2011-111332 and 2007-45701.

[0048] The base spherical porous silica 100A (top panel of Figure 4) was synthesized by the same method as described in Japanese Patent No. 5,480,461, except that the surfactant used was changed from hexadecyltrimethylammonium chloride (C16Cl) to octadecyltrimethylammonium chloride (C18Cl). The surfactant 12A remaining in the pores 10A of the spherical porous silica 100A is C18Cl. The central pore diameter of the pores in the spherical porous silica 100A is 2.0 nm.

[0049] 2.26 g of swelling agent 14 (trimethylbenzene, TMB), 30 cc of ethanol, and 30 cc of pure water were mixed / dispersed in 1.0 g of spherical porous silica 100A, and the mixture was kept at 100°C for three days. Swelling agent 14 penetrated the hydrophobic parts of surfactant 12A, resulting in spherical porous silica 100B with an expanded pore size of 5.5 nm. The synthesized spherical porous silica 100B was calcined at 550°C for 8 hours to remove surfactant 12A and swelling agent 14, yielding spherical porous silica 100.

[0050] A predetermined amount of liquid phase change material (linear paraffin) that had been melted by heating above its melting point was mixed with a predetermined amount of spherical porous silica 100, thereby introducing the phase change material into the pores 10 of the spherical porous silica 100.

[0051] First, a method for manufacturing the heat storage body of Example 2 will be described with reference to FIG. Spherical porous silica containing normal paraffin as a phase-change material and a liquid shell source (100% TEOS) were prepared (step P102), and the prepared spherical porous silica was added to the liquid shell source and kept at room temperature for 24 hours while stirring (step P104). This resulted in the formation of a first outer shell layer on the surface of the spherical porous silica (Figure 1).

[0052] The liquid 1 produced in step P104 was filtered, and the particles on which the first outer shell layer had been formed were taken out and dried at 45° C. for 24 hours to obtain particles 1 (step P106).

[0053] Next, particle 1 was immersed in an ethylene glycol (EG) aqueous solution and left at room temperature for 24 hours (hydration treatment), to obtain liquid 2 (step P108). The ethylene glycol aqueous solution had an ethylene glycol:water ratio of 1:1 by weight. Liquid 2 produced in step P108 was filtered to remove the particles, which were then dried at 45°C for 24 hours to obtain particle 2 (step P110). Particle 2 had an increased proportion of silanol groups on the surface of the first outer shell layer.

[0054] The particles 2 obtained in step P110 were added to a liquid of the shell source (100% TEOS) and kept at room temperature for 24 hours while stirring (step P112). This resulted in the formation of a second shell layer on the first shell layer (Figure 1). The liquid 3 produced in step P112 was filtered, and the particles with the first and second shell layers formed were taken out and dried at 45°C for 24 hours to obtain the heat storage material of Example 2 (step P106).

[0055] The heat storage body of Example 3 was obtained by sequentially performing all steps except steps P108 and P110 of the manufacturing process for the heat storage body of Example 1. That is, like the heat storage body of Example 2, the heat storage body of Example 3 also has an outer shell part with a two-layer structure (first outer shell layer and second outer shell layer).

[0056] The heat storage bodies of Example 1 and Comparative Examples 2 and 3 were obtained by sequentially carrying out steps P102, P104, and P106 in the heat storage body manufacturing process shown in Figure 3. That is, the heat storage bodies of Example 1 and Comparative Examples 2 and 3 are heat storage bodies in which one layer of outer shell portion is formed on the surface of a spherical porous silica body. That is, these heat storage bodies have only a first outer shell layer as the outer shell portion. Example 1 and Comparative Examples 2 and 3 differ from each other in the raw materials (shell sources) of the outer shell portion, which are 100% TEOS, TEOS / ethanol, and perhydropolysilazane (hereinafter also referred to as PHPS), respectively. The heat storage body of Comparative Example 1 is a heat storage body without an outer shell portion.

[0057] <Comparison of outer shell thickness> The difference in durability of the heat storage body due to differences in the thickness of the outer shell will be explained using the above-mentioned Examples 1 and 2 and Comparative Example 1. Here, durability is evaluated using the change in the packing rate of the phase change material and the change in the proportion of effective heat storage material when immersed in an organic solvent.

[0058] FIG. 5 is a scanning electron microscope (SEM) image of the heat storage bodies of Examples 1 and 2. FIG. 6 is an SEM image of the heat storage body of Comparative Example 1. FIG. 7 is a diagram showing the specifications of each heat storage body obtained from the SEM image. FIG. 7 shows the average particle diameter and thickness of the outer shell of the heat storage body. The average particle diameter was determined by measuring the diameters of 200 particles using the SEM image and taking the arithmetic mean. Assuming that the outer shell of the heat storage body of Examples 1 and 2 has a uniform thickness, the thickness of the outer shell was calculated using the average particle diameter of each heat storage body as follows. Since Comparative Example 1 is a spherical porous silica body without an outer shell, the average particle diameter of Comparative Example 1 was subtracted from the average particle diameter of Examples 1 and 2, and the result divided by 2 was used as the thickness of the outer shell of each of Examples 1 and 2.

[0059] As shown in Fig. 7, the heat storage body of Example 1 has a shell thickness of 0.55 µm. The heat storage body of Example 2 has a shell thickness of 0.11 µm, which is thicker than the heat storage body of Example 1. The heat storage body of Comparative Example 1 does not have an outer shell.

[0060] Figure 8 shows the specifications of the heat storage material obtained by thermal analysis. Figure 8 shows the changes in the phase-change material filling rate, heat storage density, and effective heat storage material ratio before and after immersion in an organic solvent to evaluate the durability of the heat storage material. The phase-change material present in the pores of the spherical porous silica is divided into effective heat storage material and ineffective heat storage material. Effective heat storage material generates latent heat through melting and solidification (described in detail later). Therefore, since a large amount of effective heat storage material is desirable for a heat storage material, the durability test focuses on the change in the effective heat storage material ratio. For the durability test, 0.1 g of the heat storage material was added to 10 ml of toluene (liquid) as an organic solvent and kept at 60 °C for 3 hours while stirring. The particles were then filtered and dried at 45 °C for 24 hours for evaluation.

[0061] FIG. 9 shows the results of the durability test. As shown in FIGS. 8 and 9, in the heat storage body of Comparative Example 1, almost no effective heat storage material remained after immersion in toluene. In contrast, in the heat storage body of Example 1, although the amount of effective heat storage material decreased after immersion in toluene, more than half remained. Furthermore, in the heat storage body of Example 2, the filling rate of the effective heat storage material did not change even after immersion. In other words, it can be said that the formation of an outer shell portion in the heat storage body suppressed the elution of the effective heat storage material. Furthermore, by thickening the outer shell portion, the elution of the effective heat storage material could be further suppressed. In the heat storage body of Example 2, as described above, the outer shell layer formation step was performed twice (FIG. 3: steps P104 and P112), which is thought to have improved the density of the outer shell portion. The heat storage bodies of Examples 1 and 2 were able to suppress the elution of the effective heat storage material when immersed in an organic solvent.

[0062] The filling ratio represents the proportion of the total pore volume occupied by the introduced phase change material (hereinafter also referred to as "PCM"), and can be estimated by simultaneous thermogravimetry and differential thermal analysis (TG-DTA). In this example, the measurements were performed using a simultaneous thermogravimetry and differential thermal analysis instrument, Thermoplus TG-8120 (manufactured by RIGAKU).

[0063] 10 is a diagram showing a TGA (Thermogravimetric analysis) curve of the phase-change material. The weight loss at 150 to 700°C was taken as the organic fraction derived from the PCM, and the filling rate of the PCM in the pores was calculated. Specifically, this was calculated using the following (Equation 1).

[0064] Filling rate [vol%] = organic fraction / PCM density / pore volume × 100 … (Equation 1)

[0065] The PCM density of the PCM held in the porous silica body in the heat storage body can be measured, for example, by the following method: The PCM gas evaporated by heating the heat storage body can be analyzed by gas chromatography mass spectrometry (GC / MS) to calculate the PCM density.

[0066] In the examples and comparative examples, spherical porous silica materials of approximately the same shape were used, and the pore volume was 1.30 to 1.80 [ml / g]. The pore volume [ml / g] was estimated from the measured nitrogen adsorption isotherm using a BET (Brunauer, Emmett, and Teller) plot.

[0067] Figure 11 shows DSC curves of phase-change materials. Figure 11(a) shows a typical differential scanning calorimetry (DSC) curve for erythritol, and Figure 11(b) shows a typical DSC curve for normal paraffin. As shown in the figure, the difference between the endothermic peak and the exothermic peak represents the degree of supercooling. Also, as shown in the figure, the peak area of ​​the endothermic curve (shown hatched in the figure) corresponds to the amount of heat storage.

[0068] The effective heat storage material ratio represents the ratio of PCM that can generate latent heat by melting / solidifying out of the total PCM occupying the pores, and can be estimated by differential scanning calorimetry (DSC) (latent heat storage density [J / g]). In this example, differential scanning calorimetry was performed using a DSC Q1000 differential scanning calorimeter (manufactured by TA Instruments) at a temperature range of -20°C to 150°C and a heating / cooling rate of 10°C / min. Meanwhile, the ineffective heat storage material is the total PCM minus the effective heat storage material.

[0069] The effective heat storage material can be calculated using the following (Equation 2) and (Equation 3). Effective heat storage material [vol%] = apparent latent heat / PCM latent heat × 100 … (Equation 2) Apparent latent heat = heat storage amount / PCM density / pore volume ... (Equation 3)

[0070] <Effects of hydration treatment> Here, the effect of carrying out the hydration treatment (FIG. 3: step P108) in the method for manufacturing a heat storage body having a shell part with a two-layer structure will be described with reference to FIGS.

[0071] Fig. 12 is an SEM image of the heat storage bodies of Examples 2 and 3. Fig. 13 is a diagram showing specifications obtained from the SEM images of the heat storage bodies of Examples 2 and 3 and Comparative Example 1. Fig. 13 shows the average particle diameter and shell thickness of the heat storage body, as in Fig. 7, and the average particle diameter and shell thickness were calculated in the same manner as in Fig. 7.

[0072] As described above, the heat storage body of Example 2 is manufactured by carrying out all the steps shown in Fig. 3 and is subjected to hydration treatment. The heat storage body of Example 3 is manufactured by carrying out all the steps of the heat storage body manufacturing process of Example 2 in order except for steps P108 and P110 and is not subjected to hydration treatment.

[0073] As shown in FIG. 13, the thickness of the outer shell of the heat storage body of Example 2 was 0.11 μm, and the thickness of the outer shell of the heat storage body of Example 3 was 0.08 μm. The thickness of the outer shell could be increased by performing a hydration treatment. In the method for manufacturing a heat storage body, if a hydration treatment is performed after forming the first outer shell layer, the proportion of silanol groups on the surface of the first outer shell layer increases, making it easier to form the second outer shell layer and increasing the thickness of the outer shell. Note that the thickness of the outer shell of the heat storage body of Example 3 is thicker than the outer shell thickness of the heat storage body of Example 1 (0.055 μm in FIG. 7), and it can be said that the second outer shell layer is formed. In other words, although the second outer shell layer can be formed without performing a hydration treatment, the thickness of the outer shell can be increased by performing a hydration treatment.

[0074] 14 is a diagram showing the specifications obtained by thermal analysis of the heat storage bodies of Examples 2 and 3 and Comparative Example 1. Fig. 14 shows the results of the same durability evaluation (toluene immersion) as in Fig. 8.

[0075] FIG. 15 shows the results of the durability test. As shown in FIGS. 14 and 15, in the heat storage body of Comparative Example 1, almost no effective heat storage material remained after immersion in toluene. In contrast, in the heat storage body of Example 3, although the effective heat storage material decreased after immersion in toluene, more than half remained. Furthermore, in the heat storage body of Example 2, the filling rate of the effective heat storage material did not change even after immersion in toluene. That is, in the manufacturing method of a heat storage body having a multi-layered outer shell, by performing a hydration treatment while forming the outer shell layers, the thickness of the outer shell can be increased, and elution of the heat storage material after immersion in an organic solvent can be further suppressed. Furthermore, the heat storage body of Example 3 has a two-layered outer shell with a thickness of 0.08 μm, which is thicker than the heat storage body of Example 1 (FIG. 7: single-layered outer shell, thickness 0.055 μm), but the proportion of effective heat storage material after immersion in an organic solvent is the same as that of the heat storage body of Example 1. From this result, it is considered that the density of the outer shell was low in the heat storage body of Example 3. That is, in the manufacturing method of a heat storage body having an outer shell with a multi-layer structure, the density of the outer shell can be improved by performing a hydration treatment.

[0076] <Comparison of shell sources> Here, TEOS and PHPS are used as the raw materials (shell source) for the outer shell portion, and the difference in durability of the heat storage body due to the difference in shell source will be explained with reference to FIGS. FIG. 16 is a diagram showing the main specifications of the shell source. As shown in the figure, in the heat storage bodies of Examples 1 to 3, a 100% TEOS liquid is used as the shell source. In the heat storage body of Comparative Example 2, ethanol is used as the solvent, and a TEOS solution with a 1:1 weight ratio of TEOS to ethanol is used as the shell source. In the heat storage body of Comparative Example 3, a PHPS solution is used as the shell source. Here, Durazane 2200 (manufactured by Merck) and Durazane 2800 (manufactured by Merck) were mixed in a weight ratio of 1:1 as the PHPS. The solvent for Durazane 2200 and Durazane 2800 is dibutyl ether (hereinafter also referred to as DBE). The PHPS concentration of Durazane 2200 is 20%, and the PHPS concentration of Durazane 2800 is 15%. Durazane 2200 does not contain a catalyst and has a slow curing speed, while Durazane 2800 contains an amine-based catalyst and has a very fast curing speed. Figure 16 also lists xylene as the solvent for PHPS. In other examples, other PHPS such as Durazane 2600 (manufactured by Merck) may be used. Durazane 2600 uses xylene as the solvent, has a PHPS concentration of 15%, contains an amine-based catalyst, and has a fast curing speed.

[0077] Fig. 17 is an SEM image of the heat storage body of Example 1. Fig. 18 is an SEM image of the heat storage bodies of Comparative Examples 1 and 2. Fig. 19 is an SEM image of the heat storage body of Comparative Example 3. Fig. 20 is a diagram showing specifications obtained from the SEM images of the heat storage bodies of Example 1 and Comparative Examples 1 to 3. Fig. 20 shows the average particle diameter and shell thickness of the heat storage body, as in Fig. 7, and the average particle diameter and shell thickness are calculated in the same manner as in Fig. 7.

[0078] As described above, Example 1 and Comparative Examples 2 and 3 were manufactured by sequentially performing step P102 to step P106 of the manufacturing process shown in Fig. 3, and the outer shell portion had a single-layer structure. As shown in Fig. 20, the shell source of the outer shell portion of the heat storage body of Example 1 was 100% TEOS, the shell source of the outer shell portion of the heat storage body of Comparative Example 2 was TEOS / ethanol (weight ratio 1:1), and the shell source of the outer shell portion of the heat storage body of Comparative Example 3 was PHPS. The heat storage bodies of Comparative Examples 2 and 3 had thinner outer shell portions than the heat storage body of Example 1.

[0079] 21 is a diagram showing specifications obtained by thermal analysis of the heat storage bodies of Example 1 and Comparative Examples 1 to 3. Fig. 21 shows the results of the same durability evaluation (toluene immersion) as in Fig. 8.

[0080] Fig. 22 shows the results of the durability test. As shown in Figs. 21 and 22, in the heat storage body of Comparative Example 1 (without an outer shell), almost no effective heat storage material remains after toluene immersion (after the durability test). In the heat storage body of Comparative Example 2, even before toluene immersion, the filling rate of the effective heat storage material is about half that of Comparative Example 1, and the filling rate of the effective heat storage material is low. Since the shell source of the heat storage body of Comparative Example 2 contains ethanol, it is thought that the proportion of effective heat storage material decreases due to the interaction between ethanol and the phase change material when the outer shell is formed. And, in the heat storage body of Comparative Example 2, almost no effective heat storage material remains after toluene immersion, similar to the heat storage body of Comparative Example 1.

[0081] Although the heat storage body of Comparative Example 3 had a lower phase-change material filling rate than the heat storage body of Comparative Example 1 (without an outer shell) before toluene immersion, the filling rate of the effective heat storage material was not as low as that of the heat storage body of Comparative Example 2. Therefore, it is believed that there was almost no effect of the interaction between the phase-change material and PHPS / DBE during shell formation. In the heat storage body of Comparative Example 3, after toluene immersion, more effective heat storage material remained than in the heat storage bodies of Comparative Examples 1 and 2. However, compared to Example 1, the filling rate of the effective heat storage material was lower. It is believed that the effective heat storage material was eluted and partially inactivated by toluene immersion. In other words, when 100% TEOS is used as the shell source, the density of the outer shell can be improved compared to when PHPS is used as the shell source, and elution of the effective heat storage material can be more effectively suppressed. When the outer shell is incompletely dense (has many defects), the organic solvent penetrates into the pores of the spherical porous silica and dissolves the phase-change material, which then flows out.

[0082] FIG. 23 is an explanatory diagram conceptually illustrating the formation of the outer shell portion. FIG. 23(a) shows an example in which the shell source is TEOS, and FIG. 23(b) shows an example in which the shell source is PHPS. In FIG. 23, the shell source TEOS is denoted by the symbol 300t, and the shell source PHPS is denoted by the symbol 300p. The pore diameters of the pores 10 in the spherical porous silica material 100 shown in FIG. 23(a) and FIG. 23(b) are the same. TEOS has a small molecular diameter, so it can crosslink within the pores 10 and block the pores, as shown in the figure. PHPS has a large molecular diameter, so it can crosslink the upper part of the pores 10 and block the pores. As shown in FIG. 23(a), if the shell source TEOS can crosslink within the pores and block the pores, the crosslinking distance is shortened, forming a highly dense outer shell portion. This makes it possible to suppress the penetration of organic solvents and further suppress the elution of the phase-change material. Therefore, it is preferable that the molecular diameter of the shell source of the outer shell portion is smaller than the pore diameter of the spherical porous silica body. On the other hand, if the shell source PHPS, whose molecular diameter is equal to or larger than the pore diameter of the spherical porous silica body, bridges the upper part of the pore 10 and blocks the pore, as shown in Figure 23(b), the crosslinking distance will be longer and the density will be lower. Furthermore, if elemental analysis of the outer shell portion of the heat storage body is performed and, for example, nitrogen atoms (N) remain in the outer shell, it can be inferred that the shell source is PHPS and the molecular diameter can be estimated.

[0083] As described above, the heat storage body of the embodiment has an outer shell formed of solid silica crystals, compared to the heat storage body of Comparative Example 1, and therefore, the dissolution of effective heat storage material when immersed in an organic solvent can be suppressed, thereby improving the durability of the heat storage body.

[0084] Furthermore, the heat storage material of the example has a shell thickness of 0.55 μm or more, which is sufficient to further suppress the elution of effective heat storage material, compared to the heat storage materials of comparative examples 2 and 3. The pores have high regularity and the central pore diameter of the pores is 1 nm or more and 20 nm or less, so a sufficient heat storage density and heat storage capacity can be obtained.

[0085] The present invention has been described above based on embodiments and examples, but the above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit and scope of the claims, and the present invention includes equivalents thereof. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

[0086] The present invention can also be realized as the following application examples. [Application example 1] A heat storage medium having a spherical porous silica body having a plurality of substantially cylindrical pores formed therein, a phase-change material contained in the plurality of pores of the spherical porous silica material; an outer shell portion formed of solid silica crystals and closing at least a part of the plurality of pores of the spherical porous silica material; In the spherical porous silica material, the plurality of pores have a uniform pore diameter and are arranged radially from the center of the spherical porous silica material toward the surface thereof; Heat storage body. [Application example 2] The heat storage material according to Application Example 1, The thickness of the outer shell is 0.055 μm or more. Heat storage body. [Application example 3] The heat storage material according to Application Example 1 or Application Example 2, the central pore diameter of the plurality of pores in the spherical porous silica material is 1 nm or more and 20 nm or less; Heat storage body. [Application example 4] The heat storage material according to any one of Application Examples 1 to 3, The plurality of pores of the spherical porous silica material are The standard deviation of the pore size distribution curve in the range of pore sizes greater than 1 nm is within 20% of the central pore diameter. Heat storage body. [Application example 5] The heat storage material according to any one of Application Examples 1 to 4, The diameter of the spherical porous silica is 10 nm or more and 3000 nm or less. Heat storage body. [Application Example 6] The heat storage material according to any one of Application Examples 1 to 5, The plurality of pores of the spherical porous silica material are The pore volume is 0.9 [ml / g] or more, and the specific surface area per unit pore volume is 1.4 × 10 9 [m 2 / m 3 ] is less than or equal to Heat storage body. [Application Example 7] The heat storage material according to any one of Application Examples 1 to 6, the phase change material is at least one of a sugar alcohol and a paraffin; Heat storage body. [Application Example 8] The heat storage material according to any one of Application Examples 1 to 6, the shell portion is made of a raw material having a molecular size smaller than the pore size of the spherical porous silica material; Heat storage body. [Explanation of symbols]

[0087] 1...Heat storage body 10, 10A, 10B...pores 12, 12A...Surfactants 100, 100A, 100B...Spherical porous silica 200, 200L, 200S...phase change materials 300...Outer shell 310...First outer layer 320...Second outer shell layer

Claims

1. A heat storage medium having a spherical porous silica body having a plurality of substantially cylindrical pores formed therein, a phase-change material contained in the plurality of pores of the spherical porous silica material; an outer shell portion formed of solid silica crystals and closing at least a part of the plurality of pores of the spherical porous silica material; In the spherical porous silica material, the plurality of pores have a uniform pore diameter and are arranged radially from the center of the spherical porous silica material toward the surface thereof; Heat storage body.

2. The heat storage body according to claim 1, The thickness of the outer shell is 0.055 μm or more. Heat storage body.

3. The heat storage body according to claim 1, the central pore diameter of the plurality of pores in the spherical porous silica material is 1 nm or more and 20 nm or less; Heat storage body.

4. The heat storage body according to claim 1, The plurality of pores of the spherical porous silica material are The standard deviation of the pore size distribution curve in the range of pore sizes greater than 1 nm is within 20% of the central pore diameter; Heat storage body.

5. The heat storage body according to claim 1, The diameter of the spherical porous silica material is 10 nm or more and 3000 nm or less. Heat storage body.

6. The heat storage body according to claim 1, The plurality of pores of the spherical porous silica material are The pore volume is 0.9 [ml / g] or more, and the specific surface area per unit pore volume is 1.4 × 10 9 [m 2 / m 3 ]or less, Heat storage body.

7. The heat storage body according to claim 1, the phase change material is at least one of a sugar alcohol and a paraffin; Heat storage body.

8. The heat storage body according to any one of claims 1 to 7, the shell portion is made of a raw material having a molecular size smaller than the pore diameters of the plurality of pores of the spherical porous silica material; Heat storage body.

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