JP7782765B1 - Heat absorbing material, heat spreader and heat sink - Google Patents

Abstract

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 a ratio b _e /b _i of the thermal effusivity b _e of the heat-absorbing material to the thermal effusivity b _i of the inorganic material is greater than 1 at the transition temperature of the phase-transition material.

Description

This disclosure relates to heat-absorbing materials, heat spreaders, and heat sinks. This application claims priority to Japanese Patent Application No. 2024-113337, filed July 16, 2024. The entire contents of this Japanese patent application are incorporated herein by reference.

Traditionally, 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).

For example, Japanese Patent Application Laid-Open No. 2020-193238 (Patent Document 1) discloses a heat storage body comprising 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 through a phase transition.

Japanese Patent Application Laid-Open No. 2020-193238 JP 2011-225950 A

A heat-absorbing material according to one embodiment of the present disclosure is a heat-absorbing material including an inorganic material and a phase-transition material,
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 change material is contained within the pores;
the composition of the inorganic material is different from the composition of the phase-change material;
The ratio b _e /b _i of the thermal effusivity b _e of the endothermic material to the thermal effusivity b _i of the inorganic material is greater than 1 at the transition temperature of the phase transition material.

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. 3 is a graph showing the results of measuring the temperature of each sample in the examples, where 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) prepared in the examples. FIG. 5 is an enlarged photograph of the inorganic material (porous body) according to this embodiment. FIG. 6 is a schematic diagram illustrating interconnected pores in the 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 the 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 size and window size in the inorganic material according to this embodiment and the cross-sectional area of the skeleton of the porous body. FIG. 9 is a schematic diagram of the endothermic material provided with a sheath in Experiment 4 of the example. FIG. 10 is a schematic diagram of the endothermic material provided with a sheath in Experiment 4 of the example.

The heat storage material described in Patent Document 1 uses a porous resin material as the base material, which means that it has low thermal conductivity, and there was room for improvement in the heat absorption efficiency of the heat absorption material, i.e., its thermal effusivity.

This disclosure has been made in consideration of the above circumstances and aims to provide an endothermic material with excellent thermal effusivity.

This disclosure makes it possible to provide an endothermic material with excellent thermal effusivity.

First, embodiments of the present disclosure will be listed and described.
[1] An endothermic material according to one embodiment of the present disclosure is an endothermic material including an inorganic material and a phase transition material,
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 change material is contained within the pores;
the composition of the inorganic material is different from the composition of the phase-change material;
The ratio b _e /b _i of the thermal effusivity b _e of the endothermic material to the thermal effusivity b _i of the inorganic material is greater than 1 at the transition temperature of the phase transition material.

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-change 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 greater than the specific heat of the inorganic material, but the thermal conductivity of the phase-change material is significantly lower than that of inorganic materials. As a result, the phase transition of the phase-change 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-change material, allowing it to efficiently absorb the heat of transition from the heat source. In other words, heat-absorbing materials with the characteristics described above have excellent thermal effusivity.

[2] In the endothermic material described in [1] above, the inorganic material may be a metal or an inorganic compound. This provides an endothermic material with excellent thermal conductivity from a heat source.

[3] In the endothermic material according to [2] above, the inorganic material is the inorganic compound,
The inorganic compound may be a ceramic, which provides a heat-absorbing material that is excellent in electrical insulation as well as in thermal conductivity from a heat source.

[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;
The inorganic compound may include an inorganic salt and a ceramic. By specifying it in this way, the heat absorbing material has excellent heat absorption capacity.

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

[6] In the endothermic material described in 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 will have even greater heat absorption capacity.

[7] In the endothermic material according to any one of [1] to [6] above, the average window diameter of the porous body is less than 200 μm,
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 it in this way, the heat absorbing material has high thermal effusivity and thermal conductivity and is excellent in heat absorbing efficiency.

[8] In the endothermic material described in 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.

[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 composition of the coating may be different from the composition of the inorganic material and the composition of the phase transition material, thereby providing a heat absorbing material with excellent heat absorbing efficiency and durability against repeated use.

[10] In the endothermic material described in [9] above, the coating may include an oxide coating, a passivation coating, or a chemical conversion coating. This provides an endothermic material with excellent endothermic efficiency and durability during repeated use.

[11] In the endothermic material described in [9] or [10] above, the thickness of the coating may be 100 nm or more and 5000 nm or less. This provides an endothermic material with excellent endothermic efficiency and durability against repeated use.

[12] In the endothermic material according to any one of [1] to [11] above, the thermal conductivity of the endothermic material may be 1 W·m ⁻¹ K ⁻¹ or more and 360 W·m ⁻¹ K ⁻¹ or less. By specifying it in this way, the endothermic material has a high thermal effusivity and excellent heat absorption efficiency.

[13] In the heat-absorbing material described in 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 that coats the outer surface of the porous body. This specification completely prevents leakage of the phase-change material. Furthermore, if the phase-change material is flammable, the heat-absorbing material can prevent the phase-change material from igniting due to direct contact with a heat source.

[14] A heat spreader according to one aspect of the present disclosure is a heat spreader made of the heat-absorbing material described in any one of [1] to [13] above. This results in a heat spreader with excellent thermal effusivity.

[15] In the heat spreader according to the above [14], 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, thereby providing a heat spreader that can completely prevent leakage of the phase change material.

[16] A heat sink according to one aspect of the present disclosure is a heat sink made of the heat-absorbing material described in any one of [1] to [13] above. This results in a heat sink with excellent thermal effusivity.

[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.

[18] In the heat sink according to [16] above, the phase transition 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;
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 providing a heat sink that can completely prevent leakage of the phase change material.

One embodiment of the present disclosure (hereinafter referred to as "this embodiment") will be described below. However, this embodiment is not limited to this. In this specification, notations in the format "A-Z" refer to the upper and lower limits of a range (i.e., A or greater and Z or less). When no unit is specified for A and a unit is specified only for Z, the units of A and Z are the same.

<Heat-absorbing materials>
The heat-absorbing material according to this embodiment is a heat-absorbing material including an inorganic material and a phase-transition material,
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 change material is contained within the pores;
the composition of the inorganic material is different from the composition of the phase-change material;
The ratio b _e /b _i of the thermal effusivity b _e of the endothermic material to the thermal effusivity b _i of the inorganic material is greater than 1 at the transition temperature of the phase transition material.

<Inorganic materials>
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.

The above metals are not particularly limited, but examples include aluminum, copper, iron, titanium, and silver. The above metals may be elemental metals or alloys (e.g., brass, stainless steel, etc.).

The inorganic compound is not particularly limited, but examples thereof include ceramics. Examples of the ceramic 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 insulating properties of the heat-absorbing material. Furthermore, the higher the thermal conductivity of the ceramic, the easier it tends to be to increase the thermal effusivity of the inorganic material.

In this embodiment, the thermal effusivity b _i of the inorganic material may be 4.8 kJ/(m ² s ^1/2 K) or more and 42.3 kJ/(m ² s ^1/2 K) or less, or 6.4 kJ/(m ² s ^1/2 K) or more and 37.2 kJ/(m ² s ^1/2 K) or less. The thermal effusivity b _i of the inorganic material and the thermal effusivity b _o of the phase change material described later can be calculated using the following formula 1. In formula 1, λ represents thermal conductivity (W·m ⁻¹ K ⁻¹ ), ρ represents density (g/cm ³ ), and C represents 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 change material.
(Thermal effusivity) = (λ・ρ・C) ^1/2 (Formula 1)

In this embodiment, the structure of the above inorganic material is a porous structure.

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-change material described below can be increased, thereby enabling efficient heat transfer from the inorganic material to the phase-change material.

A porous material 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. Interconnectedness 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 not interconnected and is in a free state, the inorganic material is not porous. If at least a portion of the inorganic material is interconnected, the inorganic material is porous.

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

The porosity of the porous body can be calculated from the following formula A.
Porosity (%) = [1 - {M / (V × d)}] × 100 (Equation A)
M: Mass of porous body [g]
V: Volume of the external shape of the porous body [cm ³ ]
d: density of the material constituting the porous body [g/cm ³ ].

The average pore diameter of the porous body is 50 μm or more and 5,000 μm or less, and may be 50 μm or more and 4,500 μm or less. If 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 be difficult. Furthermore, if the average pore diameter exceeds 5,000 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, if the average pore diameter exceeds 5,000 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.

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 equivalent 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.

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 5000 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.

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 (Figures 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.

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 packed 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 materials and manufacturing methods of these inorganic materials 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.

When the average window diameter is less than 200 μm, the thermal conductivity of the porous body is easily increased. Furthermore, when 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 during melting is more 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 higher mechanical strength of the molded body. As a result, handling of the molded body during manufacturing is easier and manufacturing costs can be reduced. For example, a lower limit of the average window diameter of 1 μm or more facilitates manufacturing. The lower limit of 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.

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. A ratio of 0.02 or more can prevent the strength of the molded body from becoming excessively low. A ratio of 0.4 or less can easily 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.

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, "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 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 FE-SEM using EBSD. The area-weighted average crystal grain size can be calculated by regarding grain boundaries with an inclination angle of 5° or more as crystal grain boundaries. A crystal grain size of 2.0 μm or more can reduce the thermal resistance due to the crystal grain boundaries, thereby increasing the thermal conductivity of the porous body. A crystal grain size of 50.0 μm or less can increase the mechanical strength of the porous body.

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 compacts and sinters metal powder makes it easy to achieve a grain size of 2.0 μm or more and 50.0 μm or less in the porous body skeleton. On the other hand, methods that involve plating, vacuum deposition, or sputtering metal onto a resin porous body skeleton tend to result in excessively fine grain size because grain growth is difficult. Furthermore, methods that involve impregnating a resin porous body skeleton with a metal powder paste and sintering the skeleton tend to result in fine grain size because lattice strain is not introduced and grain migration is difficult. Furthermore, methods that involve sintering metal powder without compacting, commonly known as "loose powder sintering," also tend to result in fine grain size because lattice strain is not introduced and grain migration is difficult. While it is possible to increase the grain size by increasing the sintering temperature and prolonging the sintering time, this tends to increase manufacturing costs.

In one aspect of this embodiment, the external shape of the inorganic material is not particularly limited, and examples include rectangular parallelepiped, plate-like, columnar, conical, cylindrical, triangular pyramidal, etc.

<Phase transition materials>
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 other than melting (a transition from solid to liquid), and may be, for example, 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 the transition temperature (e.g., absorbs heat of fusion near the 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.

The above-mentioned paraffins are not particularly limited, but examples include octadecane, tetradecane, tetracosane, etc.

The above fatty acids are not particularly limited, but examples include metal soaps (metal salts of fatty acids), palmitic acid, stearic acid, linoleic acid, etc.

The above esters are not particularly limited, but examples include ethyl acetate, cetyl myristate, behenyl behenate, etc.

The above alcohols are not particularly limited, but examples include erythritol, sorbitol, threitol, mannitol, xylitol, etc.

The above-mentioned hydrated salts are not particularly limited, but examples include calcium chloride hexahydrate, sodium sulfate decahydrate, sodium acetate trihydrate, potassium alum, ammonium alum, etc.

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 with a transition temperature lower than that of the inorganic material. Examples of "metals with a transition temperature lower than that of the inorganic material" include metals with 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 trititanium pentoxide (Ti ₃ O ₅ ).

In this embodiment, the thermal effusivity b _o of the phase change material may be 4.7 kJ/(m ² s ^1/2 K) or more and 8.2 kJ/(m ² s ^1/2 K) or less, or 5.1 kJ/(m ² s ^1/2 K) or more and 7.2 kJ/(m ² s ^1/2 K) or less. The thermal effusivity b _o of the phase change material can be calculated using the above formula 1. In this case, the equivalent specific heat (J/(g·K)) calculated from the latent heat of phase transition of the phase change material can be calculated using the following formula 4. In formula 4, L represents the latent heat of phase transition (J/g). 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 heats of phase change materials at their phase transition points.
(Equivalent specific heat) = L / ΔT (Equation 4)

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 this 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.

The thickness of the coating may be, for example, between 100 nm and 5000 nm. A thickness of 100 nm or greater tends to suppress the chemical reaction at the interface described above. A thickness of 5000 nm or less tends to reduce the interfacial thermal resistance between the inorganic material and the phase-change material. The thickness of the coating can be determined using the following method. First, a thin piece is cut out of 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 used as the thickness of the coating. Furthermore, if the coating is thick (200 nm or greater), it can be determined using 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.

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

In one aspect of this embodiment, the ratio b _e /b _i may be greater than 1 and less than 6.0, or greater than 1 and less than 5.5, at the transition temperature (e.g., melting point) of the phase-change material. In another aspect of this embodiment, the ratio b _e /b _i may be greater than 1.1 and less than 6.0, or greater than 1.1 and less than 5.5, at the transition temperature (e.g., melting point) of the phase-change material.

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

In this embodiment, the thermal effusivity b _e of the heat-absorbing material can be calculated by the following formula 2. In formula 2, λ _e represents the thermal conductivity (W·m ⁻¹ K ⁻¹ ) of the heat-absorbing material, ρ _e represents the density (g/cm ³ ) of the heat-absorbing material, and C _e represents the equivalent specific heat (J/(g·K)) of the heat-absorbing material. The equivalent specific heat C _e of the heat-absorbing material can be calculated by 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.
b _e = (λ _e・ρ _e・C _e ) ^1/2 (Formula 2)
C _e = (1-ε)・C1+ε・C2 (Formula 3)

The thermal effusivity of the heat-absorbing material is, for example, 50 kJ/(m ² s ^1/2 K) or more, 30 kJ/(m ² s ^1/2 K) or more, 20 kJ/(m ² s ^1/2 K) or more, or 10 kJ/(m ² s ^1/2 K) or more. The higher the thermal effusivity, the higher the heat storage efficiency. There is no particular upper limit, but depending on the combination of inorganic material and phase transition material, it is possible to achieve, for example, 200 kJ/(m ² s ^1/2 K) or less, 180 kJ/(m ² s ^1/2 K) or less, 160 kJ/(m ² s ^1/2 K) or less, or 100 kJ/(m ² s ^1/2 K) or less.

When the thermal conductivity of a heat-absorbing material is high, heat from the heat source can be easily accumulated in the heat-absorbing material and transferred to other components, making it easier to prevent excessive temperature rise in the heat source. In this application, the higher the thermal conductivity, the more preferable. The thermal conductivity of the heat-absorbing material may be, for example, 1 W·m ^- 1K ^-1 or more, 3 W·m ^- 1K- ¹ or more, 8 W·m ^- 1K ^-1 or more, or 12 W·m ^- 1K ^-1 or more. When reusing accumulated heat, excessively high thermal conductivity makes the accumulated heat more likely to dissipate, which tends to hinder heat reuse. In this case, the thermal conductivity of the heat-absorbing material may be, for example, 360 W·m ^- 1K ^-1 or less, 90 W·m ^- 1K ^{-1 or} less, 80 W·m ^- 1K-1 or less, or 70 W·m ^- 1K ^-1 or less.

In one aspect of this embodiment, the thermal conductivity of the heat-absorbing material may be 1 W·m ⁻¹ K ⁻¹ or more and 360 W·m ⁻¹ K ⁻¹ or less, 3 W·m ⁻¹ K ⁻¹ or more and 90 W·m ⁻¹ K ⁻¹ or less, 8 W·m ⁻¹ K ⁻¹ or more and 80 W·m ⁻¹ K ⁻¹ or less, or 12 W·m ⁻¹ K ⁻¹ or more and 70 W·m ⁻¹ K ⁻¹ or less.

<Structure of heat-absorbing material>
In one aspect of this embodiment, the inorganic material is a porous body having pores therein, and the phase change material is contained within the pores, and 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.

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

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 that coats the outer surface of the porous body. By coating the outer surface of the porous body with a metal film, an organic compound film, or a composite film thereof, leakage of the phase-change material can be prevented.

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 single metal or an alloy (e.g., brass, stainless steel, etc.). Examples of the metal film include metal foil or metal plate. Note that in this embodiment, for convenience, plate-shaped metal will also be treated as a "metal film." The metal plate may be a welded, brazed, or soldered container, or 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.

Examples of organic compound films include films made of polyethylene, nylon, or polyethylene terephthalate, or 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.

In another aspect of this embodiment, the composite film may be a composite film made of an organic compound and a metal. Examples of composite films include resin-aluminum laminate films 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.

<Heat spreader>
The heat spreader according to this embodiment is a heat spreader made of the above-described heat-absorbing material. In the heat spreader, 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. 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 may be any known shape.

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 having 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, which 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.

<Method for producing endothermic material (1)>
The first method for producing the endothermic material according to this embodiment is
A step of preparing a porous inorganic material;
and placing a phase change material inside the pores of the porous body.

(Step of preparing a porous inorganic material)
The porous inorganic material may be manufactured 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.

The mixing ratio of the above-mentioned metal powder and sodium chloride powder can be changed depending on the porosity of the desired porous body.

The particle size of the above 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.

The particle size of the sodium chloride powder may be varied depending on the average pore diameter 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 sieved to classify it before being mixed with the metal powder.

(Step of containing a phase change material inside the pores of the porous body)
The method for filling the pores of the porous body with the phase change material is not particularly limited, but for example, the porous body may be immersed in the liquid phase change material, which allows the phase change material to permeate the porous body by capillary action.

If 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.

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

<Method for producing endothermic material (2)>
The second method for producing the endothermic material according to this embodiment is as follows:
mixing a raw powder of an inorganic material and a raw powder of a phase change material to obtain a mixed powder;
and a step of molding and sintering the mixed powder to obtain an endothermic material.

(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 a mixed powder. The mixing ratio of the raw powder of the inorganic material and the raw powder of the phase change material can be changed depending on the porosity of the desired porous body.

Examples of inorganic raw material powders include metal powders and ceramic powders. The particle size of the inorganic raw material powders 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.

Examples of raw powders of phase change materials include metal powders (low-melting-point metals, shape-memory alloys), ceramic powders, and hydrated salt powders. The particle size of the raw powders of phase change materials can be varied depending on the average pore size of the desired porous body. For example, the particle size of the raw powders of phase change materials 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 powders of phase change materials may be sieved and classified before being mixed with the raw powders of inorganic materials.

(Step of obtaining endothermic material)
In this process, the mixed powder is molded and sintered to obtain an endothermic material. For example, the mixed powder obtained in the previous process is placed in a graphite mold and preformed using a hand press. A vacuum press is then used to obtain a molded body at a predetermined temperature and pressure (e.g., 570°C, 30 MPa). The resulting molded body is then sintered at a predetermined temperature and time (e.g., 800°C, 2 hours). The endothermic material can be obtained through these processes. 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.

<Other manufacturing methods for endothermic materials>
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 of the porous phase-change material. In this case, the pores of the phase-change material are open pores, and the inorganic material placed therein may have a interconnected structure. In other words, the inorganic material also becomes porous. For example, one method for placing the inorganic material in the pores of the phase-change material is to melt the inorganic material and allow it to spontaneously infiltrate due to capillary force.

The above description includes the following additional features.
(Appendix 1)
A heat-absorbing material comprising an inorganic material and a phase-transition material,
the inorganic material is a porous body having pores therein,
the phase change material is contained within the pores;
An endothermic material, wherein a ratio b _e /b _i of the thermal effusivity b _e of the endothermic material to the thermal effusivity b _i of the inorganic material is greater than 1 at the melting point of the phase change material.
(Appendix 2)
2. The heat-absorbing material according to claim 1, wherein the inorganic material is a metal.
(Appendix 3)
3. The endothermic material of claim 1 or claim 2, wherein the phase change material is a paraffin, a fatty acid, an ester, an alcohol, or a hydrated salt.
(Appendix 4)
4. The endothermic material according to claim 1, wherein the melting point of the phase transition material is −90° C. or higher and 170° C. or lower.
(Appendix 5)
The porosity of the porous body is 10% or more and 85% or less,
5. The endothermic material according to claim 1, wherein the porous body has an average pore diameter of 50 μm or more and 5,000 μm or less.
(Appendix 6)
6. The heat absorbing material according to claim 1, further comprising a metal film covering an outer surface of the porous body.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

<Experiment 1>
<Preparation of heat-absorbing material>
1. Classification of Sodium Chloride Powder
Sodium chloride powder (manufactured by Naikai Salt Industry Co., Ltd., product name: Nakulfor-UM-45) was classified through a sieve of up to 75 μm.

(2. Weighing and mixing raw material 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.

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

(3. Preparation of molded body)
The powder B was placed in a graphite mold measuring 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.

Spark plasma sintering was performed at 570°C for 8 minutes under a pressure of 30 MPa to obtain a green body.

(4. Cleaning and desalting 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 placed on a hot plate heated to 200 ° C. to remove the remaining sodium chloride powder. The molded body was then washed in an ultrasonic cleaner for 10 minutes and dried to obtain a porous body (inorganic material) measuring 30 mm × 30 mm × 12 mm (10 mm = porous body portion with a porosity of 60%, 2 mm = bulk portion (metal film)).

5. Impregnation of Phase Change Material
The porous body and 10 g of paraffin C (manufactured by 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.

(6. Preparation of other endothermic materials)
When a porous body was prepared using a metal other than aluminum or ceramic (metal oxide) as the inorganic material, the following metal powder or ceramic powder was used instead of pure aluminum powder.
Copper powder: Manufactured by High Pure Chemical Laboratory Co., Ltd. Iron powder: Manufactured by High Pure Chemical Laboratory Co., Ltd. Titanium powder: Manufactured by High Pure Chemical Laboratory Co., Ltd. Silver powder: Manufactured by High Pure Chemical Laboratory Co., Ltd. Aluminum oxide powder: Manufactured by High Pure Chemical Laboratory Co., Ltd.

When producing porous bodies with varying porosity, the mixing ratio of powder A and powder C was changed to achieve the porosity shown in Table 3. When producing porous bodies with varying 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.

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
_VO2 : High Purity Chemical Laboratory Co., Ltd., product name: Smartec HS 70
NiTi: In-house product obtained by arc melting and crushing Bi: Manufactured by High Purity Chemical Laboratory Co., Ltd., product name: BIE06GB

From the above, endothermic materials Samples 2 to 8 and Samples 10 to 21 were prepared. Sample 1 was an aluminum block (30 mm x 30 mm x 12 mm thick). Sample 9 was prepared by filling an aluminum container (30 mm x 30 mm x 12 mm thick) with paraffin C (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).

<Evaluation of heat-absorbing 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.

The results in Figure 3 show that the endothermic material (Sample 7) composed of an inorganic material and a phase transition material suppresses temperature rise near the melting point of paraffin C (approximately 50°C to 55°C). In other words, Sample 7 has a stronger endothermic effect and is able to suppress temperature rise than samples composed of only the inorganic material (Sample 1) and only the phase transition material (Sample 9).

Furthermore, the various parameters were measured using the following methods, and the thermal effusivity b _e of the endothermic material was calculated based on the above formulas 2 and 3. The ratio b _e /b _i was also calculated. The results are shown in Table 3 and Figure 4.
(Method of measuring each parameter)
Thermal conductivity λ _e of heat-absorbing material: Measured by the laser flash method.
Density ρ _e of endothermic material: Calculated by determining the mass and volume of the endothermic material.
Porosity ε of inorganic porous body: Calculated based on the above formula A.
Specific heat capacity C1 of inorganic material: Measured by a differential scanning calorimeter.
Heat of fusion of phase change material C2: Measured by differential scanning calorimetry.

The results in Table 3 and Figure 4 show that endothermic materials composed of inorganic materials and phase change materials have a higher thermal effusivity than the above inorganic materials and the above phase change materials, making them superior as endothermic materials.

<Experiment 2>
<Preparation of heat-absorbing material>
The 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 Experiment 1 <Preparation of Endothermic Material>.

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, with an average particle size of 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.

The endothermic materials for 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, with an average particle size of 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 corresponding to adding powder B in Experiment 1 (3. Preparation of a molded body) was omitted, and the spark plasma sintering temperature was changed to 700°C.

The endothermic materials of Samples 39 to 42 in Tables 4-1 and 4-2 were prepared 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 molten bismuth and obtaining an endothermic material.

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 resulting mixture was sintered using the same process as in Experiment 1 (3. Preparation of a molded body). However, the step corresponding to adding powder B in Experiment 1 (3. Preparation of a molded body) was omitted, and the spark plasma sintering temperature was changed to 700°C.

The endothermic materials for 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 mold and uniaxially pressed at a pressure of 5 MPa, followed by CIP pressing 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. It was then impregnated with paraffin C using the same method as in Experiment 1 (5. Impregnation of Phase Change Material).

<Evaluation of heat-absorbing materials>
The endothermic material was evaluated using the same method as in Experiment 1. The results are shown in Tables 4-1 and 4-2.

The endothermic performance of each endothermic material was also evaluated using the following method. Using the same test equipment as in Experiment 1 (see Figure 2), the temperatures of the endothermic material and the bulk inorganic material alone were monitored. If the temperature of the endothermic 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.

The results in Tables 4-1 and 4-2 confirm that the endothermic materials of Samples 31 to 49, Sample 51, and Sample 52 have a thermal effusivity ratio b _e /b _i greater than 1 at the transition temperature of the phase transition material, and have good endothermic performance.

<Experiment 3>
<Preparation of heat-absorbing material>
The endothermic materials of 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 oxide films formed thereon by the pretreatment methods described in Tables 5-1 or 5-2. The thickness of the oxide films was measured by the above-mentioned FIB thin section processing and TEM observation, or FE-SEM observation.

<Evaluation of heat-absorbing materials>
The endothermic material was evaluated using the same method as in Experiment 1. The results are shown in Tables 5-1 to 5-3.

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, with temperatures held at 0°C and 100°C for one hour each. 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 it exceeded that temperature. The results are shown in Table 5-3.

The results in Table 5-3 show that when an oxide film (coating) was present and its thickness was 100 nm or more and 5000 nm or less, the repeated heat absorption performance was good.

<Experiment 4>
<Preparation of heat-absorbing material>
The endothermic materials of Samples 47a to 47d in Tables 6-1 and 6-2 were prepared by the same method as Sample 47 in Experiment 2. The endothermic materials of 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).

<Evaluation of heat-absorbing materials>
The endothermic material was evaluated using the same method as in Experiment 1. The results are shown in Tables 6-1 and 6-2.

The leak resistance of each endothermic material was also 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.

The results in Table 6-2 show that the endothermic material, including the outer casing, had good leak resistance.

<Experiment 5>
<Preparation of heat-absorbing material>
The endothermic materials of Samples 51a and 51b in Tables 7-1 and 7-2 were prepared in the same manner as Sample 51 in Experiment 2. The endothermic material of Sample 51b had a larger average pore diameter.

<Evaluation of heat-absorbing materials>
The endothermic material was evaluated using the same method as in Experiment 1. The results are shown in Tables 7-1 and 7-2.

The mechanical strength of each endothermic material was also evaluated using the following method. First, a compression tool consisting of two parallel surfaces was attached to the 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 rated as good, and a coefficient of variation of more than 5% was rated as poor. The results are shown in Table 7-1.

The results in Table 7-2 show that when the average pore diameter was 5000 μm or less, the mechanical strength was good.

<Experiment 6>
<Preparation of heat-absorbing material>
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 methods as Samples 53 and 54 in Experiment 2. However, some of the endothermic materials were prepared with the following changes.
Sample 53a: Produced by changing the pressure of spark plasma sintering to 15 MPa.
Sample 53c: The temperature and time of spark plasma sintering were changed to 520°C and 5 minutes, respectively.
Sample 53d: A porous aluminum body having a three-dimensional network structure was produced as an inorganic material by the method described in JP 2011-225950 A. The porous aluminum body had a porosity of 95% (metallic content of 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.

<Evaluation of heat-absorbing materials>
The endothermic material was evaluated using the same method as in Experiment 1. The results are shown in Tables 8-1 and 8-2.

The following was learned 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 spark plasma sintering pressure was lower. As a result, the cross-sectional area per interconnected porous skeleton increased relatively, resulting in a higher thermal conductivity of the heat-absorbing material.

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.

The thermal conductivity of the endothermic materials of Samples 53a to 53c was higher than that of Sample 53d. This was because the crystal grain size of the former porous body was coarser and the average window diameter was smaller. As a result, the thermal effusivity ratio b _e /b _i of the endothermic materials of Samples 53a to 53c was higher, indicating good endothermic performance.

The thermal conductivity of the endothermic material of sample 54a was higher than that of sample 54b. This was due to the smaller average window diameter of the porous body of the former and the smaller ratio of average window diameter to average pore diameter. As a result, the thermal effusivity ratio b _e /b _i of the endothermic material of sample 54a was higher, indicating good endothermic performance.

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

The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is indicated 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 (21)

A heat-absorbing material comprising an inorganic material and a phase-transition material,
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 change material is contained within the pores;
the composition of the inorganic material is different from the composition of the phase-change material;
a ratio b _e / _{b i of} the thermal effusivity b _e of the endothermic material to the thermal effusivity b i of the inorganic material is greater than 1 at the transition temperature of the phase-transition material;
a coating is further provided between the inorganic material and the phase-change material;
the composition of the coating is different from the composition of the inorganic material and the composition of the phase-change material;
The coating is an endothermic material, and includes an oxide coating, a passivation coating, or a chemical conversion coating . A heat-absorbing material comprising an inorganic material and a phase-transition material,
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 change material is contained within the pores;
the composition of the inorganic material is different from the composition of the phase-change 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 of the phase-change material,
The endothermic material, wherein the phase change material is a shape memory alloy, a metal oxide, or a metal with a transition temperature lower than the transition temperature of the inorganic material. The heat-absorbing material according to claim 1 or 2 , wherein the inorganic material is a metal or an inorganic compound. the inorganic material is the inorganic compound,
The heat-absorbing material according to claim 3 , wherein the inorganic compound is a ceramic. the phase-change material is an organic compound, an inorganic compound, or a metal;
The heat-absorbing material of claim 1 , wherein the inorganic compound comprises an inorganic salt and a ceramic. The heat-absorbing material of claim 1 , wherein the phase change material is a paraffin, a fatty acid, an ester, an alcohol, or a hydrated salt . The heat-absorbing material according to claim 1 or 2 , wherein the phase transition temperature of the phase transition material is −90° C. or higher and 280° C. or lower. The porous body has an average window diameter of less than 200 μm,
3. The heat absorbing material according to claim 1 , wherein a ratio of the average window diameter to the average pore diameter is 0.02 or more and 0.4 or less. The heat absorbing material according to claim 1 or 2 , wherein the crystal grain size in the skeleton of the porous body is 2.0 μm or more and 50.0 μm or less. a coating is further provided between the inorganic material and the phase-change material;
The heat-absorbing material of claim 2 , wherein the composition of the coating is different from the composition of the inorganic material and the composition of the phase-change material. The heat-absorbing material according to claim 10 , wherein the coating comprises an oxide coating, a passivation coating, or a conversion coating. The heat absorbing material according to claim 1 or claim 10 , wherein the thickness of the coating is 100 nm or more and 5000 nm or less. 3. The heat absorbing material according to claim 1, wherein the heat absorbing material has a thermal conductivity of 1 W·m ⁻¹ K ⁻¹ or more and 360 W·m ⁻¹ K ⁻¹ or less. 3. The heat absorbing material according to claim 1 , further comprising a metal film, an organic compound film, or a composite film thereof that coats the outer surface of the porous body. A heat spreader made of the heat absorbing material according to claim 1 or 2 . A heat spreader made of the heat absorbing material according to claim 1,
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;
The heat spreader , wherein the heat absorbing material further includes a metal film, an organic compound film, or a composite film thereof that covers the outer surface of the porous body. A heat spreader made of the heat absorbing material according to claim 2,
the phase-transition material is a metal having a melting point lower than that of the inorganic material;
The heat spreader, wherein the heat absorbing material further includes a metal film, an organic compound film, or a composite film thereof that covers the outer surface of the porous body. A heat sink made of the heat absorbing material according to claim 1 or 2 . 20. The heat sink of claim 18 , wherein the phase change material is a shape memory alloy or a metal oxide. A heat sink made of the heat absorbing material of claim 1,
the phase change material is a 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;
The heat sink , wherein 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. A heat sink made of the heat absorbing material according to claim 2,
the phase-change material is a metal having a transition temperature lower than the transition temperature of the inorganic material;
The heat sink, wherein 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.