JP7773178B2 - Latent heat storage particles, heat exchange material, and method for producing latent heat storage particles - Google Patents

Description

The present invention relates to latent heat storage particles, heat exchange materials, and methods for producing latent heat storage particles.

Known methods for storing heat include sensible heat storage, which utilizes temperature changes, and latent heat storage, which utilizes the phase change of a substance. While sensible heat storage technology can store heat at high temperatures, it suffers from low heat storage density because it only utilizes the sensible heat generated by temperature changes in the substance. In contrast, latent heat storage technology utilizes the latent heat generated by the solid-liquid phase change of a phase change material (PCM), allowing for higher heat storage densities than sensible heat storage technology. Furthermore, its ability to recover, transport, and supply waste heat derived from reaction heat at a constant phase change temperature has attracted attention in the fields of solar thermal and waste heat utilization. Because PCM melts and becomes liquid during heat storage, it must be encapsulated to prevent leakage of the liquid PCM. Various methods for encapsulating PCM have been proposed.

For example, Patent Document 1 proposes latent heat storage capsules in which the surface of a latent heat storage material is coated with one, two, or three layers of metal film, and latent heat storage capsules in which a metal film is coated on a latent heat storage material using an electrolytic plating method. Patent Document 2 also proposes heat storage microcapsules and a method for manufacturing them, each having a core coated with a shell, in which the core contains at least one water-soluble latent heat storage material selected from salt hydrates and sugar alcohols, and a polymer obtained from a water-soluble monomer mixture of a water-soluble monofunctional monomer and a water-soluble polyfunctional monomer, and the shell is formed from a hydrophobic resin. This technology is a microencapsulation technology for PCM, which has a relatively low melting point.

Patent Document 3 proposes a heat storage body comprising an internal heat storage body made of a heat-storing material and an outer shell containing the internal heat storage body and made of ceramics with a relative density of 75% or more. It proposes that the internal heat storage body be made of a metal containing at least one element selected from the group consisting of Al, Mg, Sn, Zn, and Cu, or a carbonate compound, hydroxide, chloride, or composite thereof containing at least one element selected from the group consisting of K, Li, Na, Ca, and Mg, and that the outer shell (capsule) be made of at least one element selected from the group consisting of alumina, silicon nitride, and silicon carbide, or a composite containing at least one element selected from the group. The technology in Patent Document 3 encapsulates a PCM with a high melting point.

The latent heat storage capsules in Patent Document 1 have a metal coating with low heat resistance, making it difficult to maintain the metal coating at high temperatures and therefore difficult to use in high-temperature conditions. Furthermore, the heat storage microcapsules described in Patent Document 2 are likely to be difficult to use in harsh environments where high temperatures and corrosion are likely to occur. Furthermore, the heat storage material described in Patent Document 3 has an outer shell made of ceramic, which is likely to have excellent heat resistance and corrosion resistance, but is likely to be difficult to mold and process.

In view of the above-mentioned problems, the present inventors have proposed in Patent Document 4 latent heat storage microcapsules, a method for manufacturing a latent heat storage, a heat exchange material, and a catalytically functional latent heat storage material, in which the surfaces of core particles made of a metal or alloy latent heat storage material are coated with an oxide film of the constituent elements of the core particles. Furthermore, Patent Document 5 proposes a latent heat storage material, a method for manufacturing a latent heat storage, and a heat exchange material, which include a core portion and a coating layer, and which have a BET specific surface area of 10 m ² /g or more. These techniques eliminate the need for a process of separately preparing an oxide film corresponding to the core particle and the shell that contains the core particle, and then accommodating the core particle inside the shell. Furthermore, because the core particle does not expand upon transformation from a solid phase to a liquid phase, the dissolved components of the latent heat storage material remain within the space covered by the oxide film, preventing damage to the oxide film. Furthermore, the oxide film can be made chemically stable. Furthermore, according to Patent Document 5, the core material can be easily captured, and the occurrence of leakage from the core can be reduced.

Japanese Patent Application Publication No. 11-23172 JP 2012-140600 A JP 2012-111825 A Japanese Patent Application Laid-Open No. 2019-173017 Japanese Patent Application Laid-Open No. 2019-203128

The methods for manufacturing latent heat storage materials shown in Patent Documents 4 and 5 produce micron-order latent heat storage materials, but they are prone to supercooling when the temperature drops during the heat storage cycle, making it difficult to accurately control the heat storage temperature due to a discrepancy with the PCM's natural freezing point. The present invention was made in light of the above circumstances, and its purpose is to provide latent heat storage particles that suppress PCM leakage and maintain a stable structure even after heat treatment, and that can control solid-liquid temperature hysteresis, for example, by suppressing supercooling and accurately controlling the heat storage temperature; a heat exchange material formed from the latent heat storage particles; and a method for manufacturing the latent heat storage particles.

Aspect 1 of the present invention is
A core particle and a coating portion that coats at least a portion of the surface of the core particle,
the core particle is composed of Al or an alloy containing Al, and the core particle contains one or more elements selected from Groups 1 to 15 as a dopant, the elements being different from the Al or alloy containing Al;
The coating portion is a latent heat storage particle that is an oxide film containing Al.

Aspect 2 of the present invention is
The latent heat storage particle according to aspect 1, wherein the dopant is one or more elements selected from the group consisting of Ti, Zr, V, B, Ni, Si, Mn, Cr, Zn, P, Fe, Co, Pb, Cu, Na, and Sr.

Aspect 3 of the present invention is
In the latent heat storage particles according to aspect 1 or 2, the dopant is an element whose standard free energy of formation of an oxide at 880° C. or higher and 1230° C. or lower is higher than the standard free energy of formation of _Al 2 O ₃ .

Aspect 4 of the present invention is
In the latent heat storage particles according to any one of Aspects 1 to 3, the average particle diameter of the core particles is 10 μm or more and 200 μm or less.

Aspect 5 of the present invention is
In the latent heat storage particle according to any one of Aspects 1 to 4, the component of the coating portion is α-Al ₂ O ₃ .

Aspect 6 of the present invention is
A heat exchange material formed from the latent heat storage particles according to any one of Aspects 1 to 5.

Aspect 7 of the present invention is
Core raw material particles whose component is Al or an alloy containing Al;
providing a daughter particle whose composition is an oxide of one or more elements from Groups 1 to 15, the oxide being different from the aluminum or aluminum-containing alloy contained therein;
the core material particles and the child particles are collided with each other by an impact method in a high-speed air stream to perform hybridization in which the child particles are fixed to the surfaces of the core material particles, thereby obtaining hybridization-treated particles;
The method for producing latent heat storage particles includes: performing a chemical conversion coating treatment on the hybridization treated particles to obtain chemical conversion coated particles; and performing a heat treatment on the chemical conversion coated particles at a temperature of 880°C or higher and 1230°C or lower.

Aspect 8 of the present invention is
Aspect 7 is a method for producing latent heat storage particles according to aspect 7, wherein the chemical conversion coating treatment of the hybridization treated particles is carried out by a boehmite method.

Aspect 9 of the present invention is
In the method for producing latent heat storage particles according to aspect 7 or 8, the child particles are blended so that the ratio of the child particles to the total of the core material particles and the child particles is 0.5 mass % or more and 10 mass % or less.

Aspect 10 of the present invention is
the average particle size of the core raw material particles is 10 μm or more and 200 μm or less,
the average particle size of the child particles is 0.1 μm or more and 2 μm or less;
A method for producing latent heat storage particles according to any one of Aspects 7 to 9, wherein the ratio of (average particle size of the child particles/average particle size of the core raw material particles) is 0.001 or more and 0.2 or less.

Aspect 11 of the present invention is
In the method for producing latent heat storage particles according to any one of Aspects 7 to 10, the hybridization is carried out at a peripheral speed of 40 m/s or more and 100 m/s or less.

The present invention provides latent heat storage particles that suppress PCM leakage, are structurally stable even after heat treatment, and are capable of controlling solid-liquid phase temperature hysteresis; a heat exchange material formed from the latent heat storage particles; and a method for manufacturing the latent heat storage particles.

FIG. 1 is a schematic diagram illustrating the manufacturing process of latent heat storage particles. FIG. 2 is a schematic cross-sectional view of a high-speed airflow impact device. FIG. 3 is an SEM micrograph of hybridization-treated particles in the example. FIG. 4 shows SEM micrographs of hybridization-treated particles, conversion-coated particles, and a sample (latent heat storage particles) in the examples. FIG. 5 shows SEM micrographs of other hybridization-treated particles, conversion-coated particles, and a sample (latent heat storage particles) in the example. FIG. 6 shows the results of XRD measurement of hybridization-treated particles, conversion-coated particles, and a sample (latent heat storage particles) in the example. FIG. 7 shows the results of differential scanning calorimetry in the examples.

After extensive research, the inventors discovered that latent heat storage particles comprise a core particle and a coating covering at least a portion of the surface of the core particle, the core particle being composed of Al or an alloy containing Al, the core particle containing one or more elements from Groups 1 to 15 as a dopant that are different from the Al or alloy containing Al, and the coating being an oxide coating containing Al, thereby suppressing PCM leakage, resulting in latent heat storage particles that are structurally stable even after heat treatment and capable of controlling solid-liquid temperature hysteresis. Furthermore, the inventors discovered that the latent heat storage particles can be obtained by preparing child particles made of an oxide of the dopant, colliding core raw material particles with the child particles using a high-velocity airflow impact method to hybridize them, and then performing a predetermined chemical conversion coating process and heat treatment. The latent heat storage particles, heat exchange materials formed from the latent heat storage particles, and a method for manufacturing the latent heat storage particles according to this embodiment are described below.

[Latent heat storage particles]
[Core particle]
The core particle is composed of Al or an alloy containing Al. The Al-containing alloy is preferably an alloy containing Al as the main component. The "main component" refers to a proportion of Al of 50 mass% or more of the entire core particle. These metals and alloys are phase change materials (PCMs) that can utilize the latent heat of solid-liquid phase change, and have a heat of fusion of, for example, 200 J/g or more, ensuring a high amount of latent heat.

The core particle may contain, as its main component, an element (e.g., a metal element) that is more easily oxidized than the dopant described below. A preferred core particle component is Al or an alloy of Al and Si. When the core particle component is an alloy of Al and Si, the Si content is not particularly limited, and may be greater than 0% by mass and less than 100% by mass. For example, the Si amount may be in the range of 10% by mass or more and 90% by mass or less. Within this range, the Si content may also be 10% by mass or more and 25% by mass or less.

The average particle diameter of the core particles is preferably 10 μm or more and 200 μm or less. According to this embodiment, latent heat storage particles can be realized in which the core particles (PCM) have the above components and are on the micron order of size. The average particle diameter may be, for example, 100 μm or less, or even 50 μm or less. Note that the "average particle diameter" referred to in this specification is a value measured using a laser diffraction particle size distribution analyzer (e.g., HORIBA LA-920). More specifically, the volume distribution of the particle group is measured using a laser diffraction particle size distribution analyzer, and the cumulative 50% volume diameter value (D50) is considered to be the average particle diameter.

[Dopant]
The latent heat storage particles according to this embodiment contain one or more dopants from Groups 1 to 15 of the core particle, which are different from the Al or Al-containing alloy contained therein. The dopants contained in the core particle, for example, serve as heterogeneous nucleation sites during solidification of the PCM, thereby modifying the PCM constituting the core particle and changing its temperature characteristics. As a result, for example, supercooling during temperature reduction in the heat storage cycle, which occurs in conventional latent heat storage particles, can be suppressed, enabling precise control of the solid-liquid temperature hysteresis. As described above, the dopant is not limited to elements that form an alloy or compound with the components of the core raw material particle, as long as it is incorporated into the core and serves as, for example, a heterogeneous nucleation site during solidification of the PCM. The phrase "different from the Al or Al-containing alloy contained therein" refers to one or more elements from Groups 1 to 15 other than Al and Si, for example, when the core particle is composed of an Al-Si alloy.

The dopant is preferably one or more elements selected from the group consisting of Ti, Zr, V, B, Ni, Si, Mn, Cr, Zn, P, Fe, Co, Pb, Cu, Na, and Sr. From the viewpoint of further suppressing supercooling of the latent heat storage particles, one or more elements selected from the group consisting of Ti, Zr, V, B, and Ni are more preferred, with Ti being particularly preferred.

The dopant is preferably an element whose standard free energy of formation of oxide at 880° _C or higher and 1230°C or lower is higher than the standard free energy of formation of _Al2O3 . Such an element is preferable because during heat treatment, the child particles of the oxide, which is the raw material for the dopant, are easily reduced by Al in the core raw particle, making it easier for the dopant to be incorporated into the _core particle. The standard free energy of formation ^ΔG0 of _Al2O3 is expressed by the following formula (1) in the oxidation reaction of Al below, where T in formula (1) represents temperature (°C).
4/3Al(l)+ _O2 (g)=2/ _3Al2O3 ( _s )
ΔG ⁰ =-1126890+218.81T(J)...(1)

The content of dopant contained in the latent heat storage particles can be, for example, in the range of more than 0% by mass and not more than 5% by mass, which is less than the proportion of the added child particles.

The dopant contained in the latent heat storage particles can be confirmed by EDS analysis (energy dispersive X-ray spectroscopy) of the cross section of the latent heat storage particles. The dopant inside the core particle can exist as a compound with the components of the core particle. It is believed that by forming a compound in this way and bringing the dopant and core particle components into contact, it becomes easier to control the hysteresis temperature. If the dopant is located inside or outside the coating, it is believed that there is no effect from including the dopant and that hysteresis temperature cannot be controlled.

[Covering part]
The coating portion is an oxide film containing Al. The oxide film containing Al may be, for example, α-Al ₂ O ₃ , or α-Al ₂ O ₃ and θ-Al ₂ O ₃ .

The coating portion of the latent heat storage particles according to this embodiment may have a thickness in the range of 200 nm to 3 μm. The coating portion may be, for example, a coating layer with a thickness of 1 to 2 μm.

The coating portion of the latent heat storage particles according to this embodiment only needs to cover at least a portion of the surface of the core particle. The coverage of the surface of the core particle by the coating portion is preferably 50 area% or more. This coverage is more preferably 70 area% or more, even more preferably 80 area% or more, even more preferably 90 area% or more, and most preferably 100 area%.

(Heat exchange material formed from latent heat storage particles)
The latent heat storage particles according to the present embodiment may be used as a heat exchange material, as long as the latent heat storage particles according to the present embodiment constitute at least a part of the heat exchange material. For example, the latent heat storage particles according to the present embodiment may be dispersed and contained in a thermal matrix, or dispersed and supported in a porous material. Examples of heat exchange materials include, but are not limited to, heat storage bricks, heat storage ceramic balls, and porous ceramic filters.

[Method of manufacturing latent heat storage particles]
The method for producing latent heat storage particles according to this embodiment includes the steps of:
(i) preparing a core raw material particle whose component is Al or an alloy containing Al, and a child particle whose component is an oxide of one or more elements from Groups 1 to 15 that is different from the Al or alloy containing Al contained therein;
(ii) subjecting the core material particles and the child particles to collision in a high-speed airflow impact method to hybridization in which the child particles are fixed to the surfaces of the core material particles, thereby obtaining hybridization-treated particles;
(iii) performing a chemical conversion coating treatment on the hybridization-treated particles to obtain chemically coated particles; and (iv) performing a heat treatment on the chemically coated particles at a temperature of 880°C or higher and 1230°C or lower.

The process by which dopants are introduced into core particles using the above-mentioned manufacturing method is explained using a schematic diagram, but the manufacturing method according to this embodiment is not limited to this. Furthermore, the manufacturing method for the latent heat storage particles according to this embodiment is not limited to the method shown in the schematic diagram, and they can also be manufactured by other methods.

FIG. 1 is a schematic diagram illustrating the manufacturing process of latent heat storage particles 10A in which Ti is introduced as a dopant 21 into core particles 22 (mainly composed of Al). Please note that in FIG. 1 , the components, such as the child particles, are depicted differently from their actual sizes and amounts for easier understanding. In manufacturing latent heat storage particles, core raw material particles and child particles for dopant insertion are first prepared as raw material particles. As shown in FIG. 1( a), a high-velocity airflow impact method is used to collide child particles (TiO ₂ particles) 9A with core raw material particles 8, resulting in hybridization-treated particles 25 in which child particles (TiO ₂ particles) 9A are fixed to the surfaces of core raw material particles 8, as shown in FIG. 1( b). Next, the hybridization-treated particles 25 are subjected to a chemical conversion coating treatment to obtain chemically coated particles 26 in which a chemical conversion coating 24 is formed on the surfaces of core raw material particles 8, as shown in FIG. 1( c). The chemical conversion-coated particles 26 are then heat-treated. Figure 1(d) is a diagram showing a particle at an early stage of heat treatment, and the dashed line portion is an enlarged cross-sectional schematic diagram of a portion of the particle near its surface. As shown in this enlarged cross-sectional schematic diagram in Figure 1(d), during heat treatment, it is believed that the _TiO2 component of the child particles (TiO2 particles) _9A present on the surface of the core raw particle 8 is reduced by the Al component constituting the core raw particle 8, and the resulting Ti is incorporated into the core raw particle. As a result, as shown in Figure 1(e), it is believed that latent heat storage particles 10A are obtained in which Ti is present as a dopant 21 within the core particle 22 and is coated with an α- _Al2O3 film, which is an oxide film ₂₃ of the Al component of the core particle. Each step is described in detail below.

(i) Preparation of Raw Material Particles As raw material particles, core raw material particles and child particles for dopant insertion are prepared. The core raw material particles may be prepared to correspond to the core particles of the desired latent heat storage particles, for example, particles having an average particle diameter of 10 μm or more and 200 μm or less. The average particle diameter may be, for example, 100 μm or less, or even 50 μm or less. Furthermore, it is preferable that the average particle diameter of the child particles is 0.1 μm or more and 2 μm or less, and the ratio (average particle diameter of child particles/average particle diameter of core raw material particles) is 0.001 or more and 0.2 or less. The average particle diameter of the child particles may be 1.0 μm or less, or even 0.4 μm or less. The components of the core raw material particles are the same as those of the core particles of the latent heat storage particles, and are as described above for the components of the core particles of the latent heat storage particles.

The component of the child particles is an oxide of one or more elements from Groups 1 to 15 that is different from the Al or Al-containing alloy contained therein. Preferred elements constituting the oxide are as described above for the dopant of the latent heat storage particles, and the component of the child particles is preferably an oxide of one or more elements selected from the group consisting of Ti, Zr, V, B, Ni, Si, Mn, Cr, Zn, P, Fe, Co, Pb, Cu, Na, and Sr. More preferably, the component is an oxide of one or more elements selected from the group consisting of Ti, Zr, V, B, and Ni, and in particular, a Ti oxide such as _TiO2 is preferred.

The blending ratio of core raw material particles to child particles fed into the device can be set such that the ratio of child particles to (core raw material particles + child particles) is in the range of 0.5% by mass or more and 10% by mass or less. This ratio is preferably 1.0% by mass or more. Furthermore, from the perspective of facilitating the chemical conversion coating process described below, this ratio is preferably 8% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less. For example, this ratio is preferably in the range of 1.0% by mass or more and 5% by mass or less.

(ii) Hybridization of Core Raw Particles and Daughter Particles by High-Velocity Air Impact Method In this embodiment, core raw particles and daughter particles for forming coating portions are used, and the daughter particles are mechanically struck against the surfaces of the core raw particles by high-velocity air impact method. A dry mechanical method is used to obtain hybridized particles in which the daughter particles are adhered to the surfaces of the core raw particles. The "adhesion" mentioned above includes physical adhesion due to changes in the shape of the daughter particles, as well as adhesion due to a chemical reaction between the core raw particles and the daughter particles. The degree of adhesion of the daughter particles is not limited, as long as at least a portion of the surface of the core particle is coated.

The following describes an embodiment of the high-velocity airflow impact method used in the manufacturing method according to this embodiment, using the high-velocity airflow impact device shown in Figure 2, but the present invention is not limited to this embodiment.

Figure 2 is a schematic cross-sectional view of a high-velocity airflow impact device 100 for performing hybridization using the high-velocity airflow impact method. The high-velocity airflow impact device 100 is equipped with a raw material particle inlet 1, a high-speed rotating rotor 2, blades 3, a stator 4, a circulation circuit 5, a discharge valve 6, and a discharge port 7.

In the high-velocity airflow impact method, core raw material particles 8, which are powder, and child particles 9, which are fine powder, are first supplied to the impact chamber through the sample inlet 1. As the rotor 2 rotates, the core raw material particles 8 and child particles 9 in the impact chamber are scattered while rotating at high speed within the chamber, during which the child particles 9 collide with the surfaces of the core raw material particles 8. Some of the raw material particles enter one connection port of the circulation circuit 5 connected to the collision chamber and circulate, before being introduced back into the collision chamber through the other connection port. This circulation circuit 5 allows repeated collisions between the core raw material particles 8 and child particles 9. By continuing this rotational collision for a certain period of time, the child particles 9 adhere to the surfaces of the core raw material particles 8, and the child particles 9 are further deformed to form latent heat storage particles 10. During the collision between the core raw material particles 8 and the child particles 9, the inlet path to the outlet 7 is closed by the discharge valve 6, but after a certain time, the resulting latent heat storage particles 10 are discharged from the outlet 7 to the outside of the device through the inlet path to the outlet 7, which is opened by moving the discharge valve 6. Although not shown, a cooling water passage may be provided to prevent the inside of the collision chamber from becoming too hot, and the collision process may be carried out while cooling by flowing cooling water.

The peripheral speed of the rotor 2 in the above-mentioned device can be, for example, in the range of 40 m/s or more and 100 m/s or less. The processing time depends on the processing amount, but can be, for example, in the range of 1 to 20 minutes. The processing temperature can be, for example, in the range of room temperature to 70°C, or even in the range of room temperature to 50°C. The pressure and atmosphere of the collision chamber are not particularly limited. The atmosphere of the collision chamber can be, for example, an inert gas atmosphere such as an Ar atmosphere.

(iii) Chemical Conversion Coating The hybridization-treated particles are subjected to a chemical conversion coating treatment. This results in chemically coated particles having a chemical conversion coating on their surfaces that contains the constituent elements of the core raw material particles. The chemical conversion coating treatment is not limited to any particular method, as long as it oxidizes the surface of Al or an Al alloy to form a dense Al oxide or Al hydroxide coating. Examples of chemical conversion coating methods include the boehmite method, phosphate chromate treatment, chromate chromate treatment, and zinc phosphate treatment. The boehmite method is preferred.

The boehmite method is a treatment defined in "JIS H 0201:1998 Terminology for Aluminum Surface Treatment," in which a coating is formed on the surface of aluminum in high-temperature distilled water or a weak alkaline aqueous solution. It has been confirmed that the higher the pH value of the boehmite treatment solution, the better the quality of the resulting Al oxide coating. It is particularly preferable to set the pH value in the range of 6.0 or higher but less than 9.0, more preferably 7.0 to 8.5, and most preferably 8. The core particles can be treated with boehmite treatment at a temperature of 80°C to 100°C for 0.25 to 3 hours. Treatment is preferably performed while stirring.

(iv) Heat treatment (calcination)
The chemically coated particles are heat-treated. This oxidizes the chemical conversion coating of the chemically coated particles, forming an oxide coating as the coating portion. The heat treatment temperature can be, for example, higher than the melting point of the metal (including alloy) that constitutes the core raw particle, for example, heating at 700°C or higher and 1300°C or lower. The aluminum oxide film formed by the heat treatment takes the γ-Al ₂ O ₃ crystal form at relatively low temperatures of approximately 800°C or lower, while a chemically stable α-Al ₂ O ₃ film is obtained at relatively high temperatures of approximately 880°C or higher. For example, to obtain a chemically stable α-Al ₂ O ₃ film, the heat treatment temperature is preferably 880°C or higher and 1230°C or lower. The heat treatment temperature is more preferably 900°C or higher and 1230°C or lower.

The atmosphere for the heat treatment is not particularly limited. Examples include air, or supplying oxygen gas to a heat treatment furnace to create an oxygen atmosphere. The temperature inside the furnace is increased using a heater, and once the sample temperature reaches a predetermined temperature, heat treatment (oxidation treatment) is carried out for, for example, 1 to 5 hours to obtain heat-treated latent heat storage particles. Heat treatment can be carried out, for example, by filling a crucible with the chemically coated particles, placing the crucible on top of a thermocouple attached to the tip of an insertion rod, and setting it in a heat treatment furnace equipped with a heater.

The present invention will be explained in more detail below using examples. The present invention is not limited to the following examples, and appropriate modifications can be made within the scope of the above-mentioned and below-mentioned aims, and all such modifications are within the technical scope of the present invention.

In this example, core raw material particles of an Al alloy (Al-25 mass%Si) containing 25% Si by mass and having an average particle size of 20 to 37 μm, and child particles of _TiO2 having an average particle size of 0.5 μm were prepared, and the ratio of the child particles to the total of the core raw material particles and child particles was 1%, 3%, or 5% by mass, as shown in Table 1. Then, using a high-speed airflow impact device manufactured by Nara Machinery Works, Ltd., a process was carried out in which the child particles were collided with the core raw material particles by the high-speed airflow impact method under the conditions of the peripheral velocity and treatment time shown in Table 1, to obtain hybridization-treated particles.

Next, the hybridization-treated particles were placed in a beaker containing distilled water, and the distilled water was heated to 100°C on a hot plate. The surfaces of the hybridization-treated particles were treated with boehmite for 3 hours while stirring with a stirring rod, yielding chemically coated particles.

The chemically coated particles were then loaded into a crucible, which was then placed on top of a thermocouple attached to the tip of an insertion rod and placed in a heat treatment furnace equipped with a heater. In this heat treatment furnace, the temperature of the chemically coated particles was gradually increased in the air or in an oxygen atmosphere formed by supplying oxygen gas through a gas inlet of the heat treatment furnace and guiding exhaust gas to the outside through a gas outlet. Once the temperature of the chemically coated particles reached 1000°C, they were subjected to heat treatment (oxidation treatment) for 3 hours, yielding samples with an α- _Al2O3 film formed on the surface of the chemically coated _particles .

(SEM observation)
The appearance of the hybridization-treated particles in Examples 1 to 3 was observed with an SEM (JEOL, JSM-7001FA) and EDS analysis was also performed to confirm the effect of differences in the compounding ratio of the daughter particles on the degree of adhesion of the daughter particles during hybridization. The results are shown in Figure 3. The bottom part of Figure 3 shows the results of the EDS analysis, with the presence of Ti indicated in gray. Figure 3 shows that although the amount of adhered daughter particles (the proportion occupied by the gray area) differed depending on the compounding ratio of the daughter particles, the daughter particles were almost uniformly adhered to the surface of the core raw material particle at all compounding ratios.

Next, SEM observations were performed on the hybridization-treated particles, chemically coated particles, and sample (latent heat storage particles, heat treatment: air) obtained in the production of the samples (latent heat storage particles) of Examples 1 and 2. The results are shown in Figure 4 for Example 1 (child particle blend ratio: 1 mass%) and Figure 5 for Example 2 (child particle blend ratio: 3 mass%). Figures 4 and 5 confirm that all chemically coated particles have a petal-like structure characteristic of the boehmite shell. Furthermore, all samples maintained their spherical shape without PCM leakage, even after heat treatment at or above the melting point of Al-25 mass% Si, confirming that microencapsulation was achieved.

(XRD measurement)
XRD measurements were performed under the following conditions on the hybridization-treated particles produced in Example 1 (the blending ratio of daughter particles was 1% by mass), the chemical conversion coated particles obtained by chemically coating the hybridization-treated particles, and the sample obtained by heat treating the chemical conversion coated particles (latent heat storage particles, heat treatment: air). The results are shown in Figure 6. As can be seen from Figure 6, the main peaks of the hybridization-treated particles and the chemical conversion coated particles were Al and Si, while the main peaks of the sample (latent heat storage particles) were Al, Si, and α-Al ₂ O ₃ , and even the very small amount of added TiO ₂ or Ti derived from the TiO ₂ was not detected.
(Measurement conditions)
X-ray diffractometer: X-ray diffractometer XRD Rigaku MiniFlex600 X-ray source: Cu ray Detector: High-speed one-dimensional detector D/teX Ultra2
Tube voltage: 40 kV
・Tube current: 15mA
Scan speed: 1.0°/min
Step: 0.01°

Differential Scanning Calorimetry (DSC)
Using the samples heat-treated in air and oxygen atmospheres in Examples 1 to 3, a differential scanning calorimeter (Mettler Toledo, model number: 823e) was used. Using an alumina pan, differential scanning calorimetry was performed during temperature drop (heat dissipation side) under an Ar atmosphere at a temperature drop rate of 5 K/min from 800°C to 400°C, and a DSC curve was obtained. The results are shown in Figure 7 and Table 2. As can be seen from Figure 7 and Table 2, the exothermic peaks of the samples produced with _TiO2 added were all shifted to higher temperatures than the samples produced without _TiO2 . This suggests that the resulting latent heat storage particles suppressed the supercooling that occurred during heat dissipation in conventional latent heat storage particles.

From the above results, it is possible to incorporate Ti into the core particles using a very small amount of _TiO2 by the method according to this embodiment, and furthermore, the very small amount of Ti incorporated into the core particles, which is difficult to confirm by XRD measurement, acts as a dopant and can modify the properties of the latent heat storage particles. This makes it possible to precisely control the hysteresis of the solid-liquid phase temperature, for example, by increasing the freezing point of the latent heat storage particles and suppressing supercooling.

REFERENCE SIGNS LIST 1 Raw material particle inlet 2 Rotor 3 Blades 4 Stator 5 Circulation circuit 6 Discharge valve 7 Discharge port 8 Core raw material particle 9, 9A Child particle 10, 10A Latent heat storage particle 21 Dopant 22 Core particle 23 Oxide film 24 Chemical conversion coating 25 Hybridization treated particle 26 Chemical conversion coated particle 100 High-speed airflow impact device

Claims (10)

A core particle and a coating portion that coats at least a portion of the surface of the core particle,
the core particle is composed of Al or an alloy containing Al, and the core particle contains one or more elements selected from Groups 1 to 15 as a dopant, which are different from the Al or alloy containing Al contained therein, and the dopant is an element whose standard free energy of formation of an oxide at 880°C or higher and 1230°C or lower is higher than the standard free energy of formation of _{Al2O3 ;}
The latent heat storage particles, wherein the coating portion is an oxide film containing Al. The latent heat storage particles according to claim 1, wherein the dopant is one or more elements selected from the group consisting of Ti, Zr, V, B, Ni, Si, Mn, Cr, Zn, P, Fe, Co, Pb, Cu, Na, and Sr. 3. The latent heat storage particles according to claim 1 , wherein the average particle diameter of the core particles is 10 μm or more and 200 μm or less. 4. The latent heat storage particle according to claim 1 , wherein the coating portion is made of α-Al ₂ O ₃ . A heat exchange material formed from the latent heat storage particles according to any one of claims 1 to 4 . Core raw material particles whose component is Al or an alloy containing Al;
providing a daughter particle whose composition is an oxide of one or more elements from Groups 1 to 15, the oxide being different from the aluminum or aluminum-containing alloy contained therein;
the core material particles and the child particles are collided with each other by an impact method in a high-speed air stream to perform hybridization in which the child particles are fixed to the surfaces of the core material particles, thereby obtaining hybridization-treated particles;
a chemical conversion coating treatment of the hybridization-treated particles to obtain chemical conversion-treated particles; and a heat treatment of the chemical conversion-treated particles at a temperature of 880°C or higher and 1230°C or lower. The method for producing latent heat storage particles according to claim 6 , wherein the chemical conversion coating treatment of the hybridization treated particles is carried out by a boehmite method. The method for producing latent heat storage particles according to claim 6 or 7 , wherein the child particles are blended so that the ratio of the child particles to the total of the core raw material particles and the child particles is 0.5 mass % or more and 10 mass % or less. the average particle size of the core raw material particles is 10 μm or more and 200 μm or less,
The average particle size of the child particles is 0.1 μm or more and 2 μm or less,
The method for producing latent heat storage particles according to any one of claims 6 to 8 , wherein the ratio of (average particle size of child particles/average particle size of core raw material particles) is 0.001 or more and 0.2 or less. The method for producing latent heat storage particles according to any one of claims 6 to 9 , wherein the hybridization is carried out at a peripheral speed of 40 m/s or more and 100 m/s or less.