Endothermic material, heat spreader, and heat sink

Abstract

Provided is an endothermic material comprising an inorganic material and a phase change material. The inorganic material comprises a porous body containing internal pores, the porous body having a porosity of 10-95% and an average pore diameter of 50-5000 μm. The phase change material is retained within the pores, and the inorganic material differs from the phase change material in composition. The ratio of be that denotes the thermal effusivity of the endothermic material to bi that denotes the thermal effusivity of the inorganic material, i.e., the ratio be / bi, is greater than 1 at the transition temperature of the phase change material.

Description

Heat absorbing material, heat spreader and heat sink

[0001] The present disclosure relates to a heat absorbing material, a heat spreader, and a heat sink. This application claims priority to Japanese Patent Application No. 2024-113337, filed on July 16, 2024. The entire contents of the Japanese patent application are incorporated herein by reference.

[0002] Conventionally, heat storage materials such as paraffin and sugar alcohols have been used, and the latent heat, heat absorption, and heat release due to the phase transition of these heat storage materials have been utilized. These heat storage materials store or absorb heat when they undergo a phase transition from solid to liquid, and release heat when they undergo a phase transition from liquid to solid. This heat storage, absorption, or release due to phase transition can be repeated. Heat storage bodies using such heat storage materials are used in applications such as preventing battery overheating (particularly preventing overheating during high-speed charging of EVs).

[0003] For example, Japanese Patent Laid-Open Publication No. 2020-193238 (Patent Document 1) discloses a heat storage body made of a porous resin material and a heat storage substance contained in at least some of the pores of the porous resin material, wherein the porous resin material is a high thermal conductivity resin having a thermal conductivity of more than 0.3 W / (m·K), and the heat storage substance contains a phase transition material that stores and releases heat by phase transition.

[0004] JP 2020-193238 A JP 2011-225950 A

[0005] A heat-absorbing material according to one aspect of the present disclosure is a heat-absorbing material including an inorganic material and a phase-transition material, wherein the inorganic material is a porous body having pores therein, the porosity of the porous body is 10% or more and 95% or less, the average pore diameter of the porous body is 50 μm or more and 5000 μm or less, the phase-transition material is accommodated inside the pores, the composition of the inorganic material is different from the composition of the phase-transition material, and the thermal effusivity b of the inorganic material is 0.05 μm or more. ｉ The thermal effusivity b of the heat absorbing material ｅ The ratio b ｅ / b ｉ is greater than 1 at the transition temperature of the phase-change material.

[0006] FIG. 1 is a schematic diagram showing an example of a method for producing an endothermic material according to this embodiment. FIG. 2 is a schematic diagram of an apparatus for measuring the temperature of an endothermic material according to this embodiment. FIG. 3 is a graph showing the temperature measurement results of each sample in the examples. The horizontal axis represents the heater output time (seconds), and the vertical axis represents the temperature (°C) at the temperature measurement point. FIG. 4 is a graph showing the thermal effusivity (vertical axis) of each sample (horizontal axis) produced in the examples. FIG. 5 is an enlarged photograph of an inorganic material (porous body) according to this embodiment. FIG. 6 is a schematic diagram illustrating the interconnected pores in an inorganic material according to this embodiment. FIG. 7 is a schematic diagram showing the relationship between the degree of powder mixing and molding pressure during the production of an inorganic material according to this embodiment and the window diameter in the produced inorganic material. FIG. 8 is a schematic diagram showing the relationship between the pore diameter and window diameter in an inorganic material according to this embodiment and the cross-sectional area of ​​the skeleton of a porous body. FIG. 9 is a schematic diagram of an endothermic material coated with an exterior in Experiment 4 of this embodiment. FIG. 10 is a schematic diagram of an endothermic material coated with an exterior in Experiment 4 of this embodiment.

[0007] The heat storage body described in Patent Document 1 uses a porous resin material as the base material, and therefore has low thermal conductivity, and there is room for improvement in the heat absorption efficiency of the heat absorption material, that is, the thermal effusivity.

[0008] The present disclosure has been made in view of the above circumstances, and aims to provide an endothermic material having excellent thermal effusivity.

[0009] According to the present disclosure, it is possible to provide a heat absorbing material with excellent thermal effusivity.

[0010]

[0013] First, embodiments of the present disclosure will be described. [1] A heat-absorbing material according to one aspect of the present disclosure is a heat-absorbing material comprising an inorganic material and a phase-transition material, wherein the inorganic material is a porous body having pores therein, the porosity of the porous body is 10% or more and 95% or less, the average pore size of the porous body is 50 μm or more and 5000 μm or less, the phase-transition material is accommodated inside the pores, the composition of the inorganic material is different from the composition of the phase-transition material, and the thermal effusivity b of the inorganic material is 0.05 μm. ｉ The thermal effusivity b of the heat absorbing material ｅ The ratio bｅ / b ｉ is greater than 1 at the transition temperature of the phase-change material.

[0011] Inorganic materials have high thermal conductivity and transfer heat from a heat source quickly, but tend to have low specific heats and therefore little heat absorption. On the other hand, when a phase-transition material undergoes a phase transition (e.g., melting), it absorbs heat of transition (e.g., heat of fusion) from the heat source. This heat of transition is much larger than the specific heat of the inorganic material, but the thermal conductivity of the phase-transition material is significantly lower than that of the inorganic material. As a result, the phase transition of the phase-transition material only occurs near the contact surface with the heat source, resulting in very low heat absorption efficiency. However, when these two materials are mixed, the inorganic material efficiently diffuses heat into the phase-transition material, enabling it to efficiently absorb the heat of transition from the heat source. In other words, a heat-absorbing material with the characteristics described above has excellent thermal effusivity.

[0012] [2] In the endothermic material according to the above [1], the inorganic material may be a metal or an inorganic compound. By specifying it in this way, the endothermic material has excellent thermal conductivity from a heat source.

[0013] [3] In the endothermic material according to the above [2], the inorganic material is the inorganic compound, and the inorganic compound may be a ceramic. By specifying it in this way, the endothermic material has excellent electrical insulation properties in addition to thermal conductivity from a heat source.

[0014] [4] In the endothermic material according to any one of [1] to [3] above, the phase transition material is an organic compound, an inorganic compound, or a metal, and the inorganic compound may include an inorganic salt and a ceramic. By specifying it in this way, the endothermic material has an excellent heat absorption capacity.

[0015] [5] In the endothermic material according to the above [4], the phase transition material may be paraffin, a fatty acid, an ester, an alcohol, a hydrated salt, a shape memory alloy, a metal oxide, or a metal having a transition temperature lower than that of the inorganic material. By specifying it in this way, the endothermic material has excellent heat absorption capacity.

[0016] [6] In the endothermic material according to any one of [1] to [5] above, the phase transition material may have a temperature range of −90° C. or higher and 280° C. or lower. By specifying it in this way, the endothermic material has an even greater heat absorption capacity.

[0017] [7] In the endothermic material according to any one of [1] to [6] above, the porous body may have an average window diameter of less than 200 μm, and the ratio of the average window diameter to the average pore diameter may be 0.02 or more and 0.4 or less. By specifying in this way, the endothermic material has high thermal effusivity and thermal conductivity and excellent heat absorption efficiency.

[0018] [8] In the endothermic material according to any one of [1] to [7] above, the crystal grain size in the skeleton of the porous body may be 2.0 μm or more and 50.0 μm or less. By specifying it in this way, the endothermic material has high thermal effusivity and thermal conductivity and excellent heat absorption efficiency.

[0019] [9] The endothermic material according to any one of [1] to [8] above, further comprising a coating between the inorganic material and the phase-transition material, the coating having a composition different from that of the inorganic material and the phase-transition material. By specifying the coating in this way, the endothermic material has excellent endothermic efficiency and durability against repeated use.

[0020]

[10] In the endothermic material according to the above item [9], the coating may include an oxide coating, a passivation coating, or a chemical conversion coating. By specifying it in this way, the endothermic material has excellent endothermic efficiency and durability against repeated use.

[0021]

[11] In the endothermic material according to the above [9] or

[10] , the thickness of the coating may be 100 nm or more and 5000 nm or less. By specifying it in this way, the endothermic material has excellent endothermic efficiency and durability against repeated use.

[0022]

[12] In the endothermic material according to any one of [1] to

[11] above, the thermal conductivity of the endothermic material is 1 W m －１ K －１ More than 360W・m －１ K －１By specifying it in this way, the heat absorbing material has a high thermal effusivity and is excellent in heat absorbing efficiency.

[0023]

[13] In the heat-absorbing material according to any one of [1] to

[12] above, the heat-absorbing material may further include a metal film, an organic compound film, or a composite film thereof, which coats the outer surface of the porous body. This configuration completely prevents leakage of the phase-change material. Furthermore, if the phase-change material is flammable, the heat-absorbing material can be prevented from igniting due to direct contact with a heat source.

[0024]

[14] A heat spreader according to one aspect of the present disclosure is a heat spreader made of the heat absorbing material according to any one of [1] to

[13] above. This results in a heat spreader with excellent thermal effusivity.

[0025]

[15] In the heat spreader according to

[14] , the phase change material may be paraffin, a fatty acid, an ester, an alcohol, a hydrated salt, or a metal having a melting point lower than that of the inorganic material, and the heat absorbing material may further include a metal film, an organic compound film, or a composite film thereof, which coats the outer surface of the porous body. This makes it possible to provide a heat spreader that can completely prevent leakage of the phase change material.

[0026]

[16] A heat sink according to one aspect of the present disclosure is a heat sink made of the heat absorbing material according to any one of [1] to

[13] above. This results in a heat sink with excellent thermal effusivity.

[0027]

[17] In the heat sink described in

[16] above, the phase transition material may be a shape memory alloy or a metal oxide. This results in a heat sink with excellent heat absorption capacity.

[0028]

[18] In the heat sink described in

[16] above, the phase change material is paraffin, fatty acid, ester, alcohol, hydrated salt, or a metal having a transition temperature lower than that of the inorganic material, and the heat absorbing material may further include a metal film, an organic compound film, or a composite film thereof, which coats the outer surface of the porous body. This makes it possible to obtain a heat sink that can completely prevent leakage of the phase change material.

[0029] An embodiment of the present disclosure (hereinafter referred to as "this embodiment") will be described below. However, this embodiment is not limited thereto. In this specification, the notation in the form of "A to Z" means the upper and lower limits of a range (i.e., A or more and Z or less), and when no unit is specified for A and a unit is specified only for Z, the unit of A and the unit of Z are the same.

[0030] <<Heat-Endowing Material>> The heat-enduring material according to this embodiment is a heat-enduring material including an inorganic material and a phase-transition material, wherein the inorganic material is made of a porous body having pores therein, the porosity of the porous body is 10% or more and 95% or less, the average pore diameter of the porous body is 50 μm or more and 5000 μm or less, the phase-transition material is accommodated inside the pores, the composition of the inorganic material is different from the composition of the phase-transition material, and the thermal effusivity b of the inorganic material is 0.05 μm or more. ｉ The thermal effusivity b of the heat absorbing material ｅ The ratio b ｅ / b ｉ is greater than 1 at the transition temperature of the phase-change material.

[0031] <Inorganic Material> In this embodiment, the term "inorganic material" refers to a material made of a metal or an inorganic compound. The inorganic material may be a metal or an inorganic compound. In one aspect of this embodiment, the inorganic material may not contain a hydrated salt. The composition of the inorganic material is different from the composition of the phase-change material described below.

[0032] The metal is not particularly limited, but examples thereof include aluminum, copper, iron, titanium, and silver. The metal may be a simple metal or an alloy (e.g., brass, stainless steel, etc.).

[0033] The inorganic compound is not particularly limited, and examples thereof include ceramics. Examples of the ceramics include alumina, silicon carbide, and aluminum nitride. In one aspect of this embodiment, the inorganic material is the inorganic compound, and the inorganic compound may be ceramic. When the inorganic material is ceramic, it becomes easier to ensure the insulation of the heat-absorbing material. Furthermore, the higher the thermal conductivity of the ceramic, the easier it becomes to increase the thermal effusivity of the inorganic material.

[0034] In this embodiment, the thermal effusivity b of the inorganic material ｉ is 4.8 kJ / (m ２ s １／２ K) or more 42.3kJ / (m ２ s １／２ K) or less, or 6.4 kJ / (m ２ s １／２ K) or more 37.2kJ / (m ２ s １／２ The thermal effusivity b of the inorganic material may be equal to or less than K. ｉ and the thermal effusivity b of the phase change material described later. ｏ can be calculated using the following formula 1. In formula 1, λ is the thermal conductivity (W m －１ K －１ ) and ρ is the density (g / cm ３ ) and C is the specific heat (J / (g K)) of the inorganic material or the equivalent specific heat (J / (g K)) calculated from the latent heat of phase transition of the phase transition material. (Thermal effusivity) = (λ ρ C) １／２ (Formula 1)

[0035] In this embodiment, the inorganic material has a porous structure.

[0036] In one aspect of this embodiment, the inorganic material is a porous body having pores therein. The porous body can also be understood as having pores formed therein. In this embodiment, the "pores" can be understood as three-dimensional cavities formed inside the porous body. By forming the inorganic material into a porous body, the contact area with the phase-transition material described below can be increased, thereby enabling efficient heat transfer from the inorganic material to the phase-transition material.

[0037] A porous body can also be understood as having a structure in which at least a portion of the inorganic material is interconnected. This structure facilitates thermal conduction within the inorganic material, thereby enabling efficient transfer of heat from the inorganic material to the phase-change material. "Interconnected" refers to the continuity of the inorganic material between two points on the heat-absorbing material. The distance between these two points is, for example, 0.5 mm or more, and is preferably the same as the size of the heat-absorbing material. Whether an inorganic material has an interconnected structure can be determined using X-ray CT scanning or serial sectioning. If all of the inorganic material is in a free, unconnected state, the inorganic material is not porous. If at least a portion of the inorganic material is in a connected state, the inorganic material is porous.

[0038] The porosity of the porous body is 10% or more and 95% or less, and may be 10% or more and 85% or less, or may be 10% or more and 84% or less.

[0039] The porosity of the porous body can be calculated from the following formula A: Porosity (%) = [1 - {M / (V x d)}] x 100 (Formula A), where M is the mass of the porous body [g], V is the volume of the external shape of the porous body [cm ３ d: density of the material itself constituting the porous body [g / cm ３ ].

[0040] The average pore diameter of the porous body is 50 μm or more and 5000 μm or less, and may be 50 μm or more and 4500 μm or less. When the average pore diameter of the porous body is less than 50 μm, the strength of the porous body tends to decrease and shape retention tends to become difficult. Furthermore, when the average pore diameter exceeds 5000 μm, the capillary force tends to decrease. As a result, when the phase change material contained in the pores melts, the phase change material tends to leak out of the porous body. Furthermore, when the average pore diameter exceeds 5000 μm, the mechanical strength of the porous body tends to vary (the standard deviation of the strength distribution tends to increase). As a result, the strength of the endothermic material tends to vary.

[0041] The average pore diameter of a porous body can be determined by the following method. First, a measurement field of view is set using an SEM so that at least five pores are included, and the appearance of the porous body is photographed. Next, the size of the pores observed within the field of view is calculated as the diameter of a circle with an equal area, and the average value of the sizes of the observed pores is taken as the average pore diameter.

[0042] In one aspect of this embodiment, the porosity of the porous body may be 10% or more and 95% or less, and the average pore diameter of the porous body may be 50 μm or more and 420 μm or less. The porosity of the porous body may be 10% or more and 95% or less, and the average pore diameter of the porous body may be 50 μm or more and 400 μm or less. The porosity of the porous body may be 10% or more and 85% or less, and the average pore diameter of the porous body may be 50 μm or more and 5,000 μm or less. The porosity of the porous body may be 10% or more and 85% or less, and the average pore diameter of the porous body may be 50 μm or more and 420 μm or less. In another aspect of this embodiment, the porosity of the porous body may be 15% or more and 85% or less, and the average pore diameter of the porous body may be 50 μm or more and 400 μm or less.

[0043] In this embodiment, the average window diameter of the porous body may be less than 200 μm. In this embodiment, the continuous pores of the porous body refer to two-dimensional pores formed by the interconnection of pores in the porous body. The window diameter of the porous body refers to the diameter of an imaginary circle inscribed in the continuous pores of the porous body (FIGS. 5 to 7). The average window diameter is determined by observing the surface of the porous body and averaging 20 continuous pores. This window diameter may be determined not only by SEM observation, but also from the size of the continuous pores in a three-dimensional image of the porous body reconstructed from X-ray CT scan data or a three-dimensional image of the porous body obtained by serial sectioning.

[0044] When powder X (coarse particles) and powder Y (fine particles) are mixed, molded, and sintered, the resulting sintered body contains areas where the particles of powder X contact each other ( Figure 6 ). By subjecting this sintered body to a specific process and removing the areas of the sintered body derived from powder X, a porous body consisting of the sintered body derived from powder Y is obtained. In this case, the "areas where the particles of powder X contact each other" in Figure 6 become interconnected pores ( Figures 6 and 7 ). By thoroughly mixing powder X and powder Y and applying a moderately high pressure to the resulting mixed powder, the powders are densely dispersed without forming voids, which tends to result in a small window diameter in the resulting porous body ( Figure 7 ). This is unique to the inorganic material and its manufacturing method disclosed herein. The smaller the average window diameter, the larger the cross-sectional area per interconnected skeleton of the porous body ( Figure 8 ). As a result, the thermal resistance of the interconnected skeleton tends to be low. Therefore, the smaller the window diameter of a porous body, the higher its thermal conductivity. When the powder molding pressure is reduced within an appropriate range, the elastic-plastic deformation between the powders is reduced, reducing the contact area and therefore the window diameter. The larger the ratio of the particle sizes of Powder X and Powder Y, the more easily Powder Y (fine powder) penetrates into the gaps between Powder X (coarse powder), resulting in a smaller window diameter. On the other hand, the window diameter of a porous body manufactured by a manufacturing method in which a metal is plated, vacuum deposited, or sputtered onto a resin porous skeleton is likely to be larger than that of the inorganic material according to this embodiment. Furthermore, the window diameter of a porous body manufactured by a manufacturing method in which a metal powder paste is impregnated into a resin porous skeleton and sintered is likely to be larger than that of the inorganic material according to this embodiment. Furthermore, the window diameter of a porous body manufactured by a manufacturing method in which metal powder is sintered without being molded, commonly known as "loose powder sintering," is likely to be larger than that of the inorganic material according to this embodiment.

[0045] If the average window diameter is less than 200 μm, the thermal conductivity of the porous body is easily increased. Furthermore, if the average window diameter is less than 200 μm, the capillary force is easily increased. As a result, leakage of the phase change material contained in the pores upon melting is easily prevented. While there is no particular lower limit for the average window diameter, a larger average window diameter allows for a higher cold-forming pressure and therefore a higher mechanical strength of the molded body. As a result, handling of the molded body during manufacturing is facilitated, and manufacturing costs can be reduced. For example, if the lower limit for the average window diameter is 1 μm or more, manufacturing is facilitated. The lower limit for the average window diameter may be 5 μm or more, or 10 μm or more. In one aspect of this embodiment, the average window diameter may be 1 μm or more but less than 200 μm, 1 μm or more but 195 μm or less, 5 μm or more but 195 μm or less, 10 μm or more but 14 μm or more but 180 μm or less.

[0046] The ratio of the average window diameter to the average pore diameter (average window diameter / average pore diameter) may be 0.02 or more and 0.4 or less, or 0.04 or more and 0.29 or less. If the ratio is 0.02 or more, it is possible to prevent the strength of the molded body from being excessively reduced. If the ratio is 0.4 or less, it is easy to increase the thermal conductivity of the porous body. In one aspect of this embodiment, the average window diameter of the porous body may be less than 200 μm, and the ratio of the average window diameter to the average pore diameter may be 0.02 or more and 0.4 or less.

[0047] In this embodiment, the crystal grain size in the skeleton of the porous body may be 2.0 μm or more and 50.0 μm or less, or 2.1 μm or more and 3.5 μm or less. Here, the "skeleton of the porous body" refers to the substantial portion of the porous body. The skeleton of the porous body can also be understood to be composed of a metal or an inorganic compound. The crystal grain size can be determined, for example, by embedding the porous body in resin, mirror-polishing it, finishing it with a cross-section polisher manufactured by JEOL Ltd., and then observing it with EBSD using an FE-SEM. The area-weighted average crystal grain size can be determined by regarding grain boundaries with an inclination angle of 5° or more as crystal grain boundaries. If the crystal grain size is 2.0 μm or more, the thermal resistance due to the crystal grain boundaries can be suppressed low, making it easy to increase the thermal conductivity of the porous body. If the crystal grain size is 50.0 μm or less, it is easy to increase the mechanical strength of the porous body.

[0048] Lattice strain introduced by compacting metal powder acts as a driving force for grain boundary migration during sintering, facilitating grain growth. Therefore, using a manufacturing method that involves compacting and sintering metal powder makes it easy to achieve a crystal grain size in the skeleton of a porous body of 2.0 μm to 50.0 μm. On the other hand, when metal is plated, vacuum deposited, or sputtered onto the skeleton of a resin porous body, crystal grain growth is difficult, resulting in an excessively fine crystal grain size. Furthermore, when a metal powder paste is impregnated into the skeleton of a resin porous body and sintered, lattice strain is not introduced, making grain migration difficult, resulting in a fine crystal grain size. Furthermore, when metal powder is sintered without compacting, commonly known as "loose powder sintering," lattice strain is not introduced, making grain migration difficult, resulting in a fine crystal grain size. While increasing the sintering temperature and prolonging the sintering time can increase the crystal grain size, the manufacturing cost tends to increase.

[0049] In one aspect of this embodiment, the external shape of the inorganic material is not particularly limited, and examples thereof include a rectangular parallelepiped, a plate, a column, a cone, a cylinder, and a triangular pyramid.

[0050] <Phase Change Material> In this embodiment, the term "phase change material" refers to a material that changes from one phase to another when it reaches a transition temperature. In one aspect of this embodiment, the term "phase change material" includes a material that changes from a solid to a liquid when it reaches its melting point. In one aspect of this embodiment, the phase change in the phase change material may be a phase other than melting (a transition from solid to liquid), such as a crystalline phase transition, a martensitic transformation, an order-disorder transformation, an insulator-metal phase transition, or a glass transition. The phase change temperature of the phase change material may be −90°C or higher and 280°C or lower, −90°C or higher and 170°C or lower, or −87°C or higher and 166°C or lower. In one aspect of this embodiment, the melting point of the phase change material may be −90°C or higher and 170°C or lower, or −87°C or higher and 166°C or lower. The phase change material absorbs latent heat near its transition temperature (e.g., absorbs heat of fusion near its melting point), thereby suppressing the temperature rise of the heat source. In other words, by setting the transition temperature (e.g., melting point) of the phase-change material within the above-mentioned temperature range, the heat-absorbing material can effectively absorb heat within that temperature range. The phase-change material may be an organic compound, an inorganic compound, or a metal, and the inorganic compound may include an inorganic salt (e.g., a hydrated salt) and a ceramic. In one aspect of this embodiment, the phase-change material may be paraffin, a fatty acid, an ester, an alcohol, or a hydrated salt.

[0051] The paraffin is not particularly limited, but examples thereof include octadecane, tetradecane, and tetracosane.

[0052] The fatty acid is not particularly limited, but examples thereof include metal soaps (metal salts of fatty acids), palmitic acid, stearic acid, and linoleic acid.

[0053] The ester is not particularly limited, but examples thereof include ethyl acetate, cetyl myristate, and behenyl behenate.

[0054] The alcohol is not particularly limited, but examples thereof include erythritol, sorbitol, threitol, mannitol, and xylitol.

[0055] The hydrated salt is not particularly limited, but examples thereof include calcium chloride hexahydrate, sodium sulfate decahydrate, sodium acetate trihydrate, potassium alum, and ammonium alum.

[0056] In addition to the above, the phase change material may be, for example, a metal (low melting point metal, shape memory alloy) or a ceramic (metal oxide). That is, the phase change material may be paraffin, fatty acid, ester, alcohol, hydrated salt, shape memory alloy, metal oxide, or a metal having a transition temperature lower than that of the inorganic material. Examples of "metals having a transition temperature lower than that of the inorganic material" include metals having a melting point lower than that of the inorganic material. Examples of low melting point metals include pure metals such as Sn and Bi, as well as alloys such as Sn-Pb alloy, Sn-Ag-Cu alloy, and Sn-Bi alloy. Examples of shape memory alloys include Ni-Ti alloy and Cu-Zn-Al alloy. Examples of metal oxides include vanadium dioxide (VO ２ ), and titanium pentoxide (Ti ３ O ５ ) are listed.

[0057] In this embodiment, the thermal effusivity b of the phase change material ｏ is 4.7 kJ / (m ２ s １／２ K) or more 8.2kJ / (m ２ s １／２ K) or less, or 5.1 kJ / (m ２ s １／２ K) or more 7.2kJ / (m ２ s １／２ The thermal effusivity b of the phase change material may be less than or equal to K. ｏ can be calculated using the above formula 1. In this case, the equivalent specific heat (J / (g·K)) obtained from the latent heat of phase transition of the phase transition material can be calculated using the following formula 4. In formula 4, L represents the latent heat of phase transition (J / g). Also, ΔT represents the phase transition temperature range when the phase transition is considered to occur in a "finite temperature range greater than 0". In this embodiment, ΔT is defined as 1 K. This makes it easier to compare the equivalent specific heat of phase transition materials at the phase transition point. (Equivalent specific heat) = L / ΔT (Formula 4)

[0058] In one aspect of this embodiment, a coating may be further provided between the inorganic material and the phase-change material. The composition of the coating may be different from the composition of the inorganic material and the composition of the phase-change material. The presence of the coating suppresses chemical reactions at the interface between the inorganic material and the phase-change material during high-temperature heating to produce the endothermic material or during high-temperature environments when using the endothermic material, thereby improving endothermic efficiency and repeated use durability. The coating may include, for example, an oxide coating, a passivation coating, or a chemical conversion coating.

[0059] The thickness of the coating may be, for example, 100 nm or more and 5000 nm or less. A thickness of 100 nm or more easily suppresses the chemical reaction at the interface described above. A thickness of 5000 nm or less easily reduces the interfacial thermal resistance between the inorganic material and the phase transition material. The thickness of the coating can be determined by the following method. First, a thin piece is cut out from the heat-absorbing material using focused ion beam processing (FIB processing). Then, the cut surface of the cut piece is observed using a transmission electron microscope (TEM) to determine the thickness of the coating at at least five locations. The average of the determined thicknesses of the coating is defined as the thickness of the coating. Furthermore, if the coating is thick (200 nm or more), the thickness can be determined by the following method. First, the heat-absorbing material is embedded in resin, and the surface of the heat-absorbing material is mirror-polished. Then, the surface is finished using a cross-section polisher manufactured by JEOL Ltd. The finished surface is observed using a field emission scanning electron microscope (FE-SEM) to determine the thickness of the coating at at least five locations. The average of the determined coating thicknesses is used as the coating thickness. This coating is more effective when the phase-change material is a metal. Oxide and passive coatings can be formed by exposing the inorganic material or phase-change material to an oxidizing atmosphere (e.g., air) or a solution (e.g., water). High temperatures may be maintained to accelerate the coating formation reaction. Chemical conversion coatings can be formed by immersing the inorganic material or phase-change material in a chemical conversion reaction solution.

[0060] <Thermal effusivity of heat-absorbing material> The thermal effusivity b of the inorganic material ｉ The thermal effusivity b of the heat absorbing material ｅ The ratio b ｅ / b ｉ is greater than 1 at the transition temperature (e.g., melting point) of the phase-change material. Thermal effusivity is an index of heat storage efficiency. Here, "transition temperature of a phase-change material" refers to the temperature range in which the phase-change material can change from one phase to another. "Melting point of a phase-change material" refers to the temperature range in which the phase-change material can change from solid to liquid.

[0061] In one aspect of this embodiment, the ratio b ｅ / b ｉ may be greater than 1 and less than or equal to 6.0, or greater than 1 and less than or equal to 5.5, at the transition temperature (e.g., melting point) of the phase-change material. ｅ / b ｉ may be 1.1 or more and 6.0 or less, or 1.1 or more and 5.5 or less, at the transition temperature (for example, melting point) of the phase transition material.

[0062] When the phase change material is paraffin, the melting point of the paraffin may be -30°C or higher and 80°C or lower, or may be -26°C or higher and 75°C or lower.

[0063] In this embodiment, the thermal effusivity b of the heat-absorbing material ｅ can be calculated using the following formula 2. In formula 2, λ ｅ is the thermal conductivity of the heat-absorbing material (W m －１ K －１ ), and ρ ｅ is the density of the endothermic material (g / cm ３ ) and C ｅ indicates the equivalent specific heat (J / (g·K)) of the endothermic material. ｅ can be calculated using the following formula 3. In formula 3, ε represents the porosity (%) of the inorganic material, C1 represents the specific heat (J / (g·K)) of the inorganic material, and C2 represents the equivalent specific heat (J / (g·K)) calculated from the latent heat of phase transition of the phase transition material. ｅ = (λ ｅ ・ρ ｅ ・C ｅ ) １／２ (Formula 2) C ｅ =(1-ε)・C1+ε・C2 (Formula 3)

[0064] The thermal effusivity of the heat-absorbing material is, for example, 50 kJ / (m ２ s １／２ K) or more, 30kJ / (m ２ s １／２ K) or more, 20kJ / (m ２ s １／２ K) or more, 10kJ / (m ２ s １／２ The higher the thermal effusivity, the higher the heat storage efficiency. There is no particular upper limit, but by combining an inorganic material and a phase transition material, for example, 200 kJ / (m ２ s １／２ K) Below, 180kJ / (m ２ s １／２ K) Below, 160kJ / (m ２ s １／２ K) Below, 100kJ / (m ２ s １／２ K) or less.

[0065] If the thermal conductivity of the heat-absorbing material is high, the heat of the heat source can be easily accumulated in the heat-absorbing material and transferred to other components, which makes it easier to prevent excessive temperature rise of the heat source. In this application, the higher the thermal conductivity, the better. The thermal conductivity of the heat-absorbing material is, for example, 1 W m －１ K －１ Above, 3W・m －１ K －１ Above, 8W・m －１ K －１ Above, 12W・m －１ K －１ When the accumulated heat is reused, if the thermal conductivity is excessively high, the accumulated heat is likely to dissipate, which tends to hinder the reuse of the heat. In this case, the thermal conductivity of the heat-absorbing material is, for example, 360 W m －１ K －１ Below, 90W・m －１ K －１ Below, 80W・m －１ K －１ Below, 70W・m －１ K －１ It may be the following:

[0066] In one aspect of this embodiment, the thermal conductivity of the heat-absorbing material is 1 W m －１ K －１ More than 360W・m－１ K －１ It may be less than 3 W m －１ K －１ More than 90W・m －１ K －１ It may be less than 8 W·m －１ K －１ More than 80W・m －１ K －１ It may be less than 12 W m －１ K －１ More than 70W・m －１ K －１ It may be the following:

[0067] In one aspect of the present embodiment, the inorganic material is a porous body having pores therein, and the phase change material is contained within the pores. In this case, the phase change material may be contained within at least some of the pores of the porous body, or may be contained within all of the pores.

[0068] In another aspect of this embodiment, in order to achieve a high thermal effusivity, the phase change material may be densely packed in the pores of the porous body.

[0069] In another aspect of this embodiment, the heat-absorbing material may further include a metal film, an organic compound film, or a composite film thereof, which coats the outer surface of the porous body, thereby preventing leakage of the phase-change material.

[0070] The metal constituting the metal film is not particularly limited, and examples thereof include aluminum, copper, iron, titanium, and silver. The metal constituting the metal film may be a simple metal or an alloy (e.g., brass, stainless steel, etc.). Examples of the metal film include a metal foil or a metal plate. In this embodiment, for convenience, plate-shaped metals are also considered to be "metal films." The metal plate may be a welded, brazed, or soldered container, or may be a seamless container such as a thin-plate molded can. A metal container can increase the mechanical strength of the heat-absorbing material. The thickness of the metal film is not particularly limited, and may be, for example, 10 μm or more and 500 μm or less.

[0071] Examples of organic compound films include films made of polyethylene, nylon, or polyethylene terephthalate, and resin coatings made of epoxy resin or silicone resin. Organic compound films can reduce the weight of the heat-absorbing material. The thickness of the organic compound film is not particularly limited, but may be, for example, 10 μm or more and 500 μm or less.

[0072] In another aspect of this embodiment, the composite film may be a composite film made of an organic compound and a metal. Examples of the composite film include a resin-aluminum laminate film containing aluminum as an intermediate. These films may further include an adhesive layer, which can be applied to the heat-absorbing material at low cost by, for example, heat bonding. The thickness of the composite film is not particularly limited, but may be, for example, 10 μm or more and 500 μm or less.

[0073] <Heat Spreader> The heat spreader according to this embodiment is a heat spreader made of the heat absorbing material. In the heat spreader, the phase transition material is paraffin, a fatty acid, an ester, an alcohol, a hydrated salt, or a metal having a melting point lower than that of the inorganic material. The heat absorbing material may further include a metal film, an organic compound film, or a composite film thereof, which coats the outer surface of the porous body. The shape of the heat spreader is not particularly limited, and any known shape may be adopted.

[0074] <Heat Sink> The heat sink according to this embodiment is a heat sink made of the heat-absorbing material. In one aspect of this embodiment, the phase-change material in the heat sink may be a shape-memory alloy or a metal oxide. In another aspect of this embodiment, the phase-change material in the heat sink may be paraffin, a fatty acid, an ester, an alcohol, a hydrated salt, or a metal with a transition temperature lower than the transition temperature of the inorganic material, and the heat-absorbing material may further include a metal film, an organic compound film, or a composite film thereof that coats the outer surface of the porous body. The shape of the heat sink is not particularly limited, and any known shape may be adopted. The heat sink may be a heat dissipation fin.

[0075] <<Method for Producing Endothermic Material (1)>> A first method for producing an endothermic material according to this embodiment includes the steps of: preparing a porous inorganic material; and accommodating a phase transition material in the pores of the porous material.

[0076] (Step of Preparing Porous Inorganic Material) The porous inorganic material may be produced from metal powder and sodium chloride powder, for example, by the following procedure. First, the metal powder and sodium chloride powder are mixed in a predetermined ratio to obtain a mixed powder. Next, the mixed powder is added to a graphite mold and preformed using a hand press. Thereafter, a molded body is obtained by using a vacuum press at a predetermined temperature and pressure (e.g., 570°C, 30 MPa). The obtained molded body is transferred to a water tank containing water to remove the sodium chloride from the molded body, thereby obtaining a porous body. In one aspect of this embodiment, ceramic powder may be used instead of the metal powder.

[0077] The mixing ratio of the metal powder and the sodium chloride powder may be changed depending on the desired porosity of the porous body.

[0078] The particle size of the metal powder is not particularly limited, and may be 1 μm or more and 200 μm or less, or 2 μm or more and 180 μm or less.

[0079] The particle size of the sodium chloride powder may be varied depending on the average pore size of the desired porous body. For example, the particle size of the sodium chloride powder may be 50 μm or more and 5000 μm or less, or 50 μm or more and 4500 μm or less. In one aspect of this embodiment, the sodium chloride powder may be classified by sieving before being mixed with the metal powder.

[0080] (Step of Filling the Pores of the Porous Body with a Phase-Change Material) The method for filling the pores of the porous body with a phase-change material is not particularly limited, but for example, the porous body may be immersed in a liquid phase-change material. The porous inorganic material allows the phase-change material to penetrate into the porous body by capillary action.

[0081] When the phase-change material is a solid at room temperature, the porous body may be immersed in the phase-change material in a liquid state at a temperature at least 5° C. higher than the melting point of the phase-change material.

[0082] (Other Steps) The method for producing the endothermic material may further include other steps in addition to the two steps described above, such as a step of coating the outer surface of the porous body containing the phase transition material with a metal film.

[0083] <<Method for Producing Endothermic Material (2)>> A second method for producing an endothermic material according to this embodiment includes the steps of: mixing a raw powder of an inorganic material and a raw powder of a phase transition material to obtain a mixed powder; and molding and sintering the mixed powder to obtain an endothermic material.

[0084] (Step of Obtaining Mixed Powder) In this step, the raw powder of the inorganic material and the raw powder of the phase change material are mixed to obtain the mixed powder. The mixing ratio of the raw powder of the inorganic material and the raw powder of the phase change material may be changed depending on the porosity of the desired porous body.

[0085] Examples of the inorganic raw material powder include metal powder, ceramic powder, etc. The particle size of the inorganic raw material powder is not particularly limited and may be 1 μm or more and 200 μm or less, or 2 μm or more and 180 μm or less.

[0086] Examples of the raw powder of the phase change material include metal powder (low melting point metal, shape memory alloy), ceramic powder, and hydrated salt powder. The particle size of the raw powder of the phase change material can be changed depending on the average pore diameter of the target porous body. For example, the particle size of the raw powder of the phase change material may be 50 μm or more and 5000 μm or less, or 50 μm or more and 4500 μm or less. In one aspect of this embodiment, the raw powder of the phase change material may be classified by sieving before being mixed with the raw powder of the inorganic material.

[0087] (Step of Obtaining an Endothermic Material) In this step, the mixed powder is molded and sintered to obtain an endothermic material. For example, the mixed powder obtained in the previous step is placed in a graphite mold and preformed using a hand press. Then, a molded body is obtained using a vacuum press at a predetermined temperature and pressure (e.g., 570°C, 30 MPa). The obtained molded body is sintered by holding it at a predetermined temperature and time (e.g., 800°C, 2 hours). The endothermic material can be obtained by the above steps. At this time, either the raw powder of the inorganic material or the raw powder of the phase transition material may melt and become liquid.

[0088] <<Other Manufacturing Methods for Endothermic Material>> In another aspect of this embodiment, the endothermic material may be manufactured by a manufacturing method including a step of preparing a porous phase-change material and placing an inorganic material inside the pores. In this case, the pores of the phase-change material are open pores, and the inorganic material placed therein may have a connected structure. In other words, the inorganic material also becomes porous. To place the inorganic material in the pores of the phase-change material, for example, the inorganic material may be melted and spontaneously infiltrated by capillary force.

[0089] The above description includes the following additional features: (Additional Note 1) A heat-absorbing material including an inorganic material and a phase-transition material, wherein the inorganic material is a porous body having pores therein, the phase-transition material is contained within the pores, and the thermal effusivity b of the inorganic material is ｉ The thermal effusivity b of the heat-absorbing material ｅ The ratio b ｅ / b ｉ is greater than 1 at the melting point of the phase transition material. (Appendix 2) The endothermic material according to Appendix 1, wherein the inorganic material is a metal. (Appendix 3) The endothermic material according to Appendix 1 or Appendix 2, wherein the phase transition material is paraffin, a fatty acid, an ester, an alcohol, or a hydrated salt. (Appendix 4) The endothermic material according to any one of Appendix 1 to Appendix 3, wherein the melting point of the phase transition material is -90°C or higher and 170°C or lower. (Appendix 5) The endothermic material according to any one of Appendix 1 to Appendix 4, wherein the porosity of the porous body is 10% or higher and 85% or lower, and the average pore diameter of the porous body is 50 μm or higher and 5,000 μm or lower. (Appendix 6) The endothermic material according to any one of Appendix 1 to Appendix 5, further comprising a metal film coating the outer surface of the porous body.

[0090] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0091] <Experiment 1> <Preparation of Endothermic Material> (1. Classification of Sodium Chloride Powder) Sodium chloride powder (manufactured by Naikai Salt Industry Co., Ltd., product name: Nakulfor-UM-45) was classified by passing it through a sieve of up to 75 μm.

[0092] (2. Weighing and Mixing of Raw Powders) 9.7 g (hereinafter referred to as "Powder A") and 4.9 g (hereinafter referred to as "Powder B") of pure aluminum powder (manufactured by Toyo Aluminum K.K., product name: TAP-10C) were weighed out. In addition, 11.7 g (hereinafter referred to as "Powder C") of the above sodium chloride powder after classification was weighed out.

[0093] The above-mentioned powders A and C were placed in a glass container and mixed for 5 minutes in a ball mill under the following conditions: (Ball mill conditions) Rotation speed: 120 rpm

[0094] (3. Preparation of Molded Body) The powder B was placed in a graphite mold of 30 mm × 30 mm × 20 mm and preformed by hand pressing at 5 MPa. The mixed powder was then pulverized in a ball mill and placed in the graphite mold, and preformed again by hand pressing.

[0095] Spark plasma sintering was carried out at 570° C. for 8 minutes while applying a pressure of 30 MPa to obtain a compact.

[0096] (4. Cleaning and desalination of molded body) The molded body was placed in a water tank containing 5 L of tap water and allowed to stand for 8 hours. Next, the molded body was removed from the water tank and brought into contact with a hot plate heated to 200°C to remove residual sodium chloride powder. The molded body was then cleaned in an ultrasonic cleaner for 10 minutes and dried to obtain a porous body (inorganic material) measuring 30 mm x 30 mm x 12 mm (10 mm was a porous body portion with a porosity of 60%, and 2 mm was a bulk portion (metal film)).

[0097] (5. Impregnation of Phase Change Material) The porous body and 10 g of paraffin C (Hayashi Pure Chemical Industries, Ltd., product name: Paraffin (48-50) (for research and experiment use)) (melting point: 48-50°C) were placed in a stainless steel container. The stainless steel container was placed in a vacuum furnace. The temperature inside the vacuum furnace was set to 70°C and heated for 1 hour, thereby impregnating the porous body with molten paraffin C (see Figure 1), and an endothermic material (Sample 7) was obtained.

[0098] (6. Preparation of Other Heat-Endorse Materials) When preparing a porous body using a metal other than aluminum or ceramic (metal oxide) as the inorganic material, the following metal powders or ceramic powders were used instead of pure aluminum powder: Copper powder: manufactured by Kojundo Chemical Laboratory Co., Ltd. Iron powder: manufactured by Kojundo Chemical Laboratory Co., Ltd. Titanium powder: manufactured by Kojundo Chemical Laboratory Co., Ltd. Silver powder: manufactured by Kojundo Chemical Laboratory Co., Ltd. Aluminum oxide powder: manufactured by Kojundo Chemical Laboratory Co., Ltd.

[0099] Furthermore, when producing porous bodies with different porosities, the mixing ratio of powder A and powder C was changed to achieve the porosity shown in Table 3. When producing porous bodies with different average pore diameters, sodium chloride powder was classified using a stainless steel sieve to achieve the average pore diameter shown in Table 3. The thermal conductivity, density, specific heat, and thermal effusivity of each metal and ceramic are shown in Table 1.

[0100]

[0101] When a phase change material other than paraffin C was used, the following paraffins, esters, metal oxides, shape memory alloys, or low-melting-point metals were used. The thermal conductivity, density, heat of fusion, and thermal effusivity of each phase change material are shown in Table 2. Paraffin A: Manufactured by Tokyo Chemical Industry Co., Ltd., product name: tetradecane Paraffin B: Manufactured by Tokyo Chemical Industry Co., Ltd., product name: octadecane Ester D: Manufactured by NOF Corporation, product name: WEP-5 VO ２ : Manufactured by High Pure Chemical Laboratory Co., Ltd., Product name: Smartec HS 70 NiTi: In-house product obtained by arc melting and crushing Bi: Manufactured by High Pure Chemical Laboratory Co., Ltd., Product name: BIE06GB

[0102]

[0103] As described above, endothermic materials Samples 2 to 8 and Samples 10 to 21 were prepared. An aluminum block (30 mm x 30 mm x 12 mmt) was used as Sample 1. Sample 9 was prepared by filling an aluminum container (30 mm x 30 mm x 12 mmt) with paraffin C (manufactured by Hayashi Pure Chemical Industries, Ltd., product name: Paraffin (48-50) (for research and experiment use)) (for research and experiment use, melting point: 48-50°C, 9.5 g).

[0104] <Evaluation of Endothermic Materials> The endothermic materials were evaluated using the following method. A sample was placed in contact with an aluminum plate measuring 30 mm x 70 mm x 2 mm thick and firmly attached with a pressure plate (see Figure 2). The aluminum plate was heated with a rubber heater (8 W), and the temperature at a point 5 mm from the end of the sample (temperature measurement point) was monitored with a K-type thermocouple. The monitoring results for Samples 1, 7, and 9 are shown in Figure 3.

[0105] 3, it was found that the endothermic material (Sample 7) composed of an inorganic material and a phase transition material suppressed temperature rise near the melting point of paraffin C (approximately 50°C to 55°C). In other words, it was found that Sample 7 has a higher endothermic effect and can suppress temperature rise more effectively than Sample 1 (which is composed of only the inorganic material) and Sample 9 (which is composed of only the phase transition material).

[0106] In addition, each parameter is measured by the following method, and the thermal effusivity b of the endothermic material is calculated based on the above formulas 2 and 3. ｅ The ratio b ｅ / b ｉ The results are shown in Table 3 and Figure 4. (Method of measuring each parameter) Thermal conductivity λ of the endothermic material ｅ : Measured by the laser flash method. Density ρ of the endothermic material ｅ : Calculated by determining the mass and volume of the heat-absorbing material. Porosity ε of inorganic porous body: Calculated based on the above formula A. Specific heat C1 of inorganic material: Measured using a differential scanning calorimeter. Heat of fusion C2 of phase transition material: Measured using a differential scanning calorimeter.

[0107]

[0108] From the results in Table 3 and Figure 4, it was found that the heat-absorbing material composed of an inorganic material and a phase-transition material has a higher thermal effusivity than the inorganic material and the phase-transition material, and is therefore superior as a heat-absorbing material.

[0109] <Experiment 2> <Preparation of Endothermic Material> Endothermic materials of Samples 31 to 34 and Samples 47 to 52 in Tables 4-1 and 4-2 were prepared in the same manner as in <Preparation of Endothermic Material> in Experiment 1.

[0110] The endothermic materials of Samples 35 and 36 in Tables 4-1 and 4-2 were prepared as follows. First, aluminum powder and nitinol powder were placed in a glass container and mixed in a ball mill at 120 rpm for 5 minutes to obtain a mixture. The composition of the nitinol powder was 50 atomic % Ni and 50 atomic % Ti, and the average particle size was 110 μm. The transition temperature of the nitinol powder was 70°C. The resulting mixture was sintered using the same process as in Experiment 1 (3. Preparation of a Molded Body). However, the step of adding powder B in Experiment 1 (3. Preparation of a Molded Body) was omitted.

[0111] The endothermic materials of Samples 37 and 38 in Tables 4-1 and 4-2 were prepared as follows. First, copper powder and nitinol powder were placed in a glass container and mixed in a ball mill at 120 rpm for 5 minutes to obtain a mixture. The composition of the nitinol powder was 50 atomic % Ni and 50 atomic % Ti, and the average particle size was 110 μm. The transition temperature of the nitinol powder was 70°C. The resulting mixture was sintered using the same process as in Experiment 1 (3. Preparation of a Compact). However, the step corresponding to adding powder B in Experiment 1 (3. Preparation of a Compact) was omitted, and the spark plasma sintering temperature was changed to 700°C.

[0112] The endothermic materials of Samples 39 to 42 in Tables 4-1 and 4-2 were produced as follows. A porous body (inorganic material) was obtained in the same manner as in Experiment 1, except that copper powder or silver powder was used as the raw material and the spark plasma sintering temperature was set to 700°C. Next, the obtained porous body and bismuth were placed in a stainless steel container and heated in a vacuum furnace at 280°C for 1 hour, thereby impregnating the porous body with the molten bismuth and producing an endothermic material.

[0113] The endothermic materials of Samples 43 and 44 in Tables 4-1 and 4-2 were prepared as follows. First, copper powder and vanadium dioxide powder were placed in a glass container and mixed in a ball mill at 120 rpm for 5 minutes to obtain a mixture. The phase transition point of vanadium dioxide powder is 70°C. The obtained mixture was sintered using the same process as in (3. Preparation of a compact) of Experiment 1. However, the step corresponding to adding powder B in (3. Preparation of a compact) of Experiment 1 was omitted, and the spark plasma sintering temperature was changed to 700°C.

[0114] The endothermic materials of Samples 45 and 46 in Tables 4-1 and 4-2 were prepared as follows. First, alumina powder and PMMA (polymethyl methacrylate) powder were mixed, and a small amount of ethanol was added and further mixed to obtain a mixture. The resulting mixture was placed in a 30 mm x 30 mm x 20 mm steel die and subjected to uniaxial compaction at a pressure of 5 MPa, followed by CIP compaction at a pressure of 100 MPa to produce a compact. The resulting compact was fired at 1350°C for 3 hours to remove the PMMA, yielding a porous alumina body. The material was then impregnated with paraffin C using the same method as in Experiment 1 (5. Impregnation of Phase Change Material).

[0115] <Evaluation of Endothermic Material> The endothermic material was evaluated using the same method as in Experiment 1. The results are shown in Tables 4-1 and 4-2.

[0116] Furthermore, the heat absorbing performance of each heat absorbing material was evaluated using the following method. Using the same test equipment as in Experiment 1 (see Figure 2), the temperatures of the heat absorbing material and the bulk inorganic material alone were monitored. If the temperature of the heat absorbing material 50 seconds after it reached its transition temperature was lower than that of the bulk inorganic material alone, it was judged as good, and if it was the same temperature or higher, it was judged as bad. The results are shown in Table 4-2.

[0117]

[0118]

[0119] From the results of Tables 4-1 and 4-2, the endothermic materials of Samples 31 to 49, Sample 51, and Sample 52 have a thermal effusivity ratio b ｅ / b ｉIt was confirmed that the heat absorption performance was good, being larger than 1 at the transition temperature of the phase transition material.

[0120] <Experiment 3> <Preparation of Endothermic Materials> Endothermic materials Samples 38a to 38e and Samples 36a to 36c in Tables 5-1 to 5-3 were prepared by the same methods as Sample 38 and Sample 36 in Experiment 2, respectively. However, some of the raw material powders used had an oxide film formed on them by the pretreatment method described in Table 5-1 or Table 5-2. The thickness of the oxide film was measured by the above-mentioned FIB thin section processing and TEM observation, or FE-SEM observation.

[0121] <Evaluation of Endothermic Material> The endothermic material was evaluated using the same method as in Experiment 1. The results are shown in Tables 5-1 to 5-3.

[0122] Furthermore, the repeated endothermic performance of each endothermic material was evaluated using the following method. Two identical endothermic materials were prepared, and one was placed in a thermal shock tester and subjected to 100 repeated endothermic cycles, each held at 0°C and 100°C for one hour. Using the same test equipment as in Experiment 1 (see Figure 2), the temperatures of the endothermic material that had undergone 0 repeated endothermic cycles and the endothermic material that had undergone 100 repeated endothermic cycles were monitored. The temperatures 50 seconds after each endothermic material reached its transition temperature were compared, and the endothermic material that had undergone 100 repeated endothermic cycles was evaluated as good if its temperature did not exceed 3 K above the temperature of the endothermic material that had undergone 0 repeated endothermic cycles, and as poor if its temperature exceeded 3 K. The results are shown in Table 5-3.

[0123]

[0124]

[0125]

[0126] From the results in Table 5-3, when an oxide film (film) was present and its thickness was 100 nm or more and 5000 nm or less, the repeated heat absorption performance was good.

[0127] <Experiment 4> <Preparation of Endothermic Material> Endothermic materials Samples 47a to 47d in Tables 6-1 and 6-2 were prepared by the same method as Sample 47 in Experiment 2. Note that the endothermic materials Samples 47b to 47d were provided with an exterior coating (a metal film, an organic compound film, or a composite film that covers the outer surface) shown in Table 6-2 (FIGS. 9 and 10).

[0128] <Evaluation of Endothermic Material> The endothermic material was evaluated using the same method as in Experiment 1. The results are shown in Tables 6-1 and 6-2.

[0129] Furthermore, the leak resistance of each endothermic material was evaluated using the following method. First, the mass of each endothermic material was measured. The temperature of the endothermic material was monitored using the same test equipment as in Experiment 1 (see Figure 2). 50 seconds after the endothermic material reached its transition temperature, it was cooled to room temperature. The mass of the endothermic material was measured again, and a ratio of 99% or more compared to the mass before the temperature increase was evaluated as good, and a ratio of less than 99% was evaluated as poor. The results are shown in Table 6-2.

[0130]

[0131]

[0132] From the results in Table 6-2, the endothermic material including the sheath had good leak-proof performance.

[0133] <Experiment 5> <Preparation of Endothermic Material> Endothermic materials of Samples 51a and 51b in Tables 7-1 and 7-2 were prepared by the same method as Sample 51 in Experiment 2. The endothermic material of Sample 51b had a larger average pore diameter.

[0134] <Evaluation of Endothermic Material> The endothermic material was evaluated using the same method as in Experiment 1. The results are shown in Tables 7-1 and 7-2.

[0135] Furthermore, the mechanical strength of each endothermic material was evaluated by the following method. First, a compression tool consisting of two parallel surfaces was attached to an autograph and pressure was applied to the endothermic material to obtain a load-displacement diagram. This test was repeated 10 times to determine the average value and standard deviation. A coefficient of variation (standard deviation / average value) of 5% or less was evaluated as good, and a coefficient of variation of more than 5% was evaluated as poor. The results are shown in Table 7-1.

[0136]

[0137]

[0138] From the results in Table 7-2, when the average pore diameter was 5000 μm or less, the mechanical strength was good.

[0139] <Experiment 6> <Preparation of Endothermic Materials> The endothermic materials of Samples 53a to 53d, and Samples 54a and 54b in Tables 8-1 and 8-2 were prepared by the same method as Samples 53 and 54 in Experiment 2, respectively. However, some of the endothermic materials were prepared with the following changes. Sample 53a: Prepared by changing the spark plasma sintering pressure to 15 MPa. Sample 53c: Prepared by changing the spark plasma sintering temperature and time to 520°C and 5 minutes, respectively. Sample 53d: A metal porous body made of aluminum with a three-dimensional network structure was manufactured using the method described in JP 2011-225950 A (Patent Document 2) and used as an inorganic material. The metal porous body had a porosity of 95% (metallic content 5%), a pore diameter of 0.55 mm, and an aluminum purity of 99.9% by mass. Sample 54b: Aluminum powder was poured into a mold and heated at 655°C for 2 hours in a hydrogen atmosphere without cold compacting. This sintered body was used as an inorganic material. This is a porous body obtained by the so-called "loose powder sintering" manufacturing method.

[0140] <Evaluation of Endothermic Material> The endothermic material was evaluated using the same method as in Experiment 1. The results are shown in Tables 8-1 and 8-2.

[0141]

[0142]

[0143] The following was found from Tables 8-1 and 8-2. The average window diameter of sample 53a was smaller than that of sample 53b. This was because the pressure of spark plasma sintering was low. As a result, the cross-sectional area of ​​each interconnected porous skeleton relatively increased, and the thermal conductivity of the heat-absorbing material increased.

[0144] The grain size of sample 53b was larger than that of sample 53c. This was due to the higher temperature and longer duration of spark plasma sintering. As a result, the thermal resistance due to the grain boundaries in the interconnected porous skeleton was reduced, and the thermal conductivity of the heat-absorbing material was increased.

[0145] The thermal conductivity of the endothermic materials of Samples 53a to 53c was higher than that of Sample 53d. This is because the crystal grain size of the former porous body was larger and the average window diameter was smaller. As a result, the thermal effusivity ratio b of the endothermic materials of Samples 53a to 53c was ｅ / b ｉ was high, indicating good endothermic performance.

[0146] The thermal conductivity of the endothermic material of sample 54a was higher than that of sample 54b. This is because the average window diameter of the former porous body was smaller and the ratio of average window diameter to average pore diameter was smaller. As a result, the thermal effusivity ratio b of the endothermic material of sample 54a was ｅ / b ｉ was high, indicating good endothermic performance.

[0147] Although the embodiments and examples of the present invention have been described above, it is intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways.

[0148] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the embodiments and examples described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

Claims

1. A heat-absorbing material comprising an inorganic material and a phase-transition material, wherein the inorganic material is a porous body having pores therein, the porosity of the porous body is 10% or more and 95% or less, the average pore diameter of the porous body is 50 μm or more and 5000 μm or less, the phase-transition material is accommodated inside the pores, the composition of the inorganic material is different from the composition of the phase-transition material, and the thermal effusivity b of the inorganic material is ｉ The thermal effusivity b of the heat-absorbing material ｅ The ratio b ｅ / b ｉ is greater than 1 at the transition temperature of the phase-change material.

2. The heat-absorbing material according to claim 1, wherein the inorganic material is a metal or an inorganic compound.

3. The heat absorbing material according to claim 2, wherein the inorganic material is an inorganic compound, and the inorganic compound is a ceramic.

4. The heat-absorbing material according to any one of claims 1 to 3, wherein the phase-change material is an organic compound, an inorganic compound, or a metal, and the inorganic compound includes an inorganic salt and a ceramic.

5. The heat-absorbing material of claim 4, wherein the phase-change material is paraffin, a fatty acid, an ester, an alcohol, a hydrated salt, a shape-memory alloy, a metal oxide, or a metal with a transition temperature lower than the transition temperature of the inorganic material.

6. The endothermic material according to any one of claims 1 to 5, wherein the phase transition temperature of the phase transition material is -90°C or higher and 280°C or lower.

7. The heat absorbing material according to any one of claims 1 to 6, wherein the porous body has an average window diameter of less than 200 μm, and the ratio of the average window diameter to the average pore diameter is 0.02 or more and 0.4 or less.

8. The heat absorbing material according to any one of claims 1 to 7, wherein the crystal grain size in the skeleton of the porous body is 2.0 μm or more and 50.0 μm or less.

9. The heat absorbing material according to any one of claims 1 to 8, further comprising a coating between the inorganic material and the phase change material, the composition of the coating being different from the composition of the inorganic material and the composition of the phase change material.

10. The heat absorbing material according to claim 9, wherein the coating comprises an oxide coating, a passivation coating, or a chemical conversion coating.

11. The heat absorbing material according to claim 9 or 10, wherein the thickness of the coating is 100 nm or more and 5000 nm or less.

12. The thermal conductivity of the heat-absorbing material is 1 W m －１ K －１ More than 360W・m －１ K －１ The heat-absorbing material according to any one of claims 1 to 11, wherein:

13. The heat-absorbing material according to any one of claims 1 to 12, further comprising a metal film, an organic compound film, or a composite film thereof that coats the outer surface of the porous body.

14. A heat spreader made of the heat absorbing material according to any one of claims 1 to 13.

15. The heat spreader according to claim 14, wherein the phase change material is paraffin, a fatty acid, an ester, an alcohol, a hydrated salt, or a metal having a melting point lower than that of the inorganic material, and the heat absorbing material further includes a metal film, an organic compound film, or a composite film thereof, which coats the outer surface of the porous body.

16. A heat sink made of the heat absorbing material according to any one of claims 1 to 13.

17. The heat sink of claim 16, wherein the phase change material is a shape memory alloy or a metal oxide.

18. The heat sink according to claim 16, wherein the phase change material is paraffin, a fatty acid, an ester, an alcohol, a hydrated salt, or a metal having a transition temperature lower than that of the inorganic material, and the heat absorbing material further includes a metal film, an organic compound film, or a composite film thereof that coats the outer surface of the porous body.

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