Latent heat storage particles, heat exchange material, and method for producing latent heat storage particles

Abstract

Provided are a latent heat storage particle in which even a core raw material particle having a low Al concentration is encapsulated and which has a surface with a high specific surface area, a heat exchange material formed of the latent heat storage particle, and a method for producing the latent heat storage particle.SOLUTION: A latent-heat storage particle comprising: a core particle; and a coating portion covering at least a part of a surface of the core particle, wherein a component of the core particle is Al or an alloy containing Al, and wherein the coating portion contains an Al oxide and contains a metal element forming a sparingly soluble compound in an aqueous solution having a pH of 8 to 12.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to latent heat storage particles, a heat exchange material, and a method for producing latent heat storage particles. [Background technology]

[0002] Known methods for storing heat include sensible heat storage, which utilizes temperature changes, and latent heat storage, which utilizes the phase change of a material. Sensible heat storage technology can store heat at high temperatures, but it has the drawback of low heat storage density because it only utilizes the sensible heat generated by the temperature change of a material. 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, because it can recover, transport, and supply waste heat from reaction heat at a constant phase change temperature, it has attracted attention in the fields of solar thermal energy utilization and waste heat utilization. Because PCMs melt and become liquid during heat storage, they must be encapsulated to prevent leakage of the liquid PCM. Various methods for encapsulating PCMs have been proposed.

[0003] 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 coating, and latent heat storage capsules in which a metal coating is coated on a latent heat storage material by electrolytic plating. Patent Document 2 also proposes heat storage microcapsules and a method for producing the same, each having a core coated with a shell, the core containing 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 being formed from a hydrophobic resin. This technology is a microencapsulation technology for PCM, which has a relatively low melting point.

[0004] Patent Document 3 proposes a heat storage body comprising an internal heat storage body made of a heat-storing material and an outer shell made of ceramics with a relative density of 75% or more, which encloses the internal heat storage body. The internal heat storage body is made of a metal containing at least one element selected from the group consisting of Al, Mg, Sn, Zn, and Cu, or a carbonate, hydroxide, chloride, or composite thereof containing at least one element selected from the group consisting of K, Li, Na, Ca, and Mg. The outer shell (capsule) is 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 consisting of alumina, silicon nitride, and silicon carbide. The technology in Patent Document 3 encapsulates a PCM with a high melting point.

[0005] The latent heat storage capsules of Patent Document 1 have a metal coating with low heat resistance, making it difficult to maintain the metal coating at high temperatures, and are therefore thought to be difficult to use at high temperatures. Furthermore, the heat storage microcapsules described in Patent Document 2 are thought to be difficult to use in harsh environments where high temperatures and corrosion are likely to occur. Furthermore, the heat storage medium described in Patent Document 3 has an outer shell made of ceramics, and is thought to have excellent heat resistance and corrosion resistance, but is thought to be difficult to mold and process.

[0006] In view of the above problems, the present inventors have proposed in Patent Document 4 latent heat storage microcapsules, a method for producing a latent heat storage material, a heat exchange material, and a catalytically functional latent heat storage material, in which the surface of a core particle made of a metal or alloy latent heat storage material is coated with an oxide film of the constituent elements of the core particle. Also, Patent Document 5 proposes a latent heat storage material having a core part and a coating layer, and a BET specific surface area of ​​10 m 2The present publication proposes a latent heat storage material, a method for manufacturing a latent heat storage material, and a heat exchange material, each of which has a density of 1 / g or more. These technologies 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, reducing the occurrence of core leakage. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-23172 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-140600 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-111825 [Patent Document 4] Japanese Patent Application Publication No. 2019-173017 [Patent Document 5] Japanese Patent Application Publication No. 2019-203128 Summary of the Invention [Problem to be solved by the invention]

[0008] Although the methods for manufacturing latent heat storage materials disclosed in Patent Documents 4 and 5 produce micron-order latent heat storage materials, encapsulation is difficult with core raw material particles with a low Al concentration, making it difficult to realize latent heat storage particles containing alloy PCMs that do not contain Al as a main component. Furthermore, in order to use latent heat storage particles for various applications, there is a demand for latent heat storage particles with a high specific surface area. The present invention has been made in view of the above circumstances, and its object is to provide latent heat storage particles that can be encapsulated even with core raw material particles with a low Al concentration and have a high specific surface area, a heat exchange material formed from the latent heat storage particles, and a method for manufacturing the latent heat storage particles. [Means for solving the problem]

[0009] 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, The coating portion is a latent heat storage particle that has Al oxide and also contains a metal element that forms a poorly soluble compound in an aqueous solution of pH 8-12.

[0010] Aspect 2 of the present invention is In the latent heat storage particles according to aspect 1, the metal element is one or more metal elements selected from the group consisting of La, Ni, Zn, Fe, and Mg.

[0011] Aspect 3 of the present invention is In the latent heat storage particles according to aspect 1 or 2, the alloy containing Al is an alloy containing 10 mass % or more of Al.

[0012] A fourth aspect of the present invention is BET specific surface area is 10m 2 The latent heat storage particles according to any one of aspects 1 to 3, wherein the solubility is 1 / g or more.

[0013] A fifth aspect of the present invention is In the latent heat storage particles according to any one of aspects 1 to 4, the average particle size of the core particles is 10 μm or more and 200 μm or less.

[0014] A sixth aspect of the present invention is The latent heat storage particles according to any one of aspects 1 to 5 have a catalyst on the surface thereof.

[0015] A seventh aspect of the present invention is A heat exchange material formed from the latent heat storage particles according to any one of the first to fifth aspects.

[0016] Aspect 8 of the present invention is preparing core raw material particles whose component is Al or an alloy containing Al; performing a chemical conversion coating treatment on the core material particles using a chemical conversion coating treatment solution to obtain chemical conversion coated particles; and subjecting the chemical conversion coated particles to a heat treatment; The chemical conversion coating solution contains a salt containing a metal element that forms a poorly soluble compound in an aqueous solution of pH 8 to 12, and in the chemical conversion coating treatment, the pH of the chemical conversion coating solution is adjusted to a pH at which the metal element precipitates as a poorly soluble compound. 析出 This is a method for producing latent heat storage particles in the above range.

[0017] A ninth aspect of the present invention is Aspect 9 is a method for producing latent heat storage particles according to aspect 8, wherein the metal element is one or more metal elements selected from the group consisting of La, Ni, Zn, Fe, and Mg.

[0018] A tenth aspect of the present invention is Aspect 10 is a method for producing latent heat storage particles according to aspect 8 or 9, wherein the salt containing a metal element is a nitrate.

[0019] An eleventh aspect of the present invention is The pH 析出 is a method for producing latent heat storage particles according to any one of aspects 8 to 10, represented by the following formula (1):

[0020]

number

[0021] In equation (1), K sp is the solubility product at the reaction temperature, [M n+ ] indicates the metal ion concentration (M), and n indicates the valence.

[0022] A twelfth aspect of the present invention is The pH at which the metal element precipitates as a poorly soluble compound 析出 In the method for producing latent heat storage particles according to any one of aspects 8 to 11, the above range is a pH of 8 to 12 when the metal element is one or more metal elements selected from the group consisting of La, Ni, Zn, and Fe, and a pH of 10 to 12 when the metal element is Mg.

[0023] A thirteenth aspect of the present invention is In the method for producing latent heat storage particles according to any one of Aspects 8 to 12, the concentration of the nitrate of the metal element is 1 to 5 mM. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide latent heat storage particles in which even core raw material particles with a low Al concentration are encapsulated and have a surface with a high specific surface area, a heat exchange material formed from the latent heat storage particles, and a method for manufacturing the latent heat storage particles. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1(a) shows a schematic cross-sectional view of a conventional latent heat storage particle, and FIG. 1(b) shows a schematic cross-sectional view of a latent heat storage particle according to this embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the catalyst-supporting latent heat storage particles according to this embodiment applied to a catalyst layer. [Figure 3] FIG. 3 is a graph showing the change in pH after core material particles are added to a nitrate-containing chemical conversion coating treatment solution. [Figure 4] FIG. 4 is a diagram showing the results of SEM observation of the precursor in the example. [Figure 5] FIG. 5 shows the results of XRD measurement of precursors in the examples. [Figure 6] FIG. 6 is a diagram showing the results of SEM observation of a sample (latent heat storage particles) in an example. [Figure 7] FIG. 7 is a diagram showing the results of XRD measurement of a sample (latent heat storage particles) in an example. [Figure 8] FIG. 8 is a diagram showing the results of observing the weight change during the precursor heat treatment in the examples. [Figure 9] FIG. 9 is a diagram showing the results of measuring the specific surface area of ​​the precursor and the sample (latent heat storage particles) in the examples. [Figure 10] FIG. 10 is a diagram showing the results of SEM observation of the precursor in the example. [Figure 11] FIG. 11 is a diagram showing the results of measuring the specific surface area of ​​precursors in the examples. [Figure 12] FIG. 12 is a diagram showing the results of SEM observation of a precursor in an example. [Figure 13] FIG. 13 shows the results of XRD measurement of precursors in Examples. [Figure 14] FIG. 14 is a diagram showing the results of observation of weight changes during precursor heat treatment in the examples. [Figure 15] FIG. 15 is a diagram showing the results of SEM observation of a sample (latent heat storage particles) in an example. [Figure 16] FIG. 16 is a diagram showing the results of XRD measurement of a sample (latent heat storage particles) in an example. [Figure 17] FIG. 17 is a diagram showing the results of measuring the specific heat capacity of a sample (latent heat storage particles) in an example. DETAILED DESCRIPTION OF THE INVENTION

[0026] As a result of intensive research, the present inventors have found that, in the production of latent heat storage particles, by adding a nitrate of a specified metal element and performing a chemical conversion coating treatment with a chemical conversion coating treatment solution having a controlled pH, even core raw material particles with a reduced amount of Al, which have been difficult to encapsulate by conventional methods, can be encapsulated by forming a shell, and latent heat storage particles with a large specific surface area can be obtained. Below, the latent heat storage particles, the heat exchange material formed from the latent heat storage particles, and the method for producing the latent heat storage particles according to this embodiment will be described.

[0027] [Latent heat storage particles] [Core particle] The core particle is composed of Al or an alloy containing Al. The Al-containing alloy may or may not be mainly composed of Al. The term "main component" means that the proportion of the Al in the entire core particle is 50% by mass or more.

[0028] The Al-containing alloy is preferably an alloy containing 10% by mass or more of Al. The Al content of the Al-containing alloy may be, for example, 20% by mass or more, with the upper limit being less than 100% by mass, for example, 90% by mass or less, or even 75% by mass or less, and further 50% by mass or less.

[0029] Examples of elements other than Al in Al-containing alloys include one or more elements selected from the group consisting of Ca, Si, Bi, Mg, Sb, In, Sn, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Ag, Au, and Pb. The Al or Al-containing alloy is a phase change material (PCM) that can utilize the latent heat of solid-liquid phase change, and has a heat of fusion of, for example, 200 J / g or more, ensuring a high amount of latent heat.

[0030] One of the more preferred components of the core particle is an alloy of Al and Si. The amount of Si in the alloy of Al and Si can be 10 mass% or more and 25 mass% or less. Another more preferred component of the core particle is a Cu-Si-Al alloy. An example of a Cu-Si-Al alloy is Cu-9.6 mass% Si-40 mass% Al, where Cu is the main component. Another preferred component of the core particle is a Zn-Al alloy.

[0031] According to the manufacturing method of this embodiment, unlike conventional methods, encapsulation is possible even when the amount of Al contained in the core material particles is smaller than conventional methods. The preferable lower limit of the Al content of the core particles is determined depending on the type of Al alloy. For example, in the case of the Cu-Si-Al alloy, the Al content is preferably 30 mass% or more, and in the case of the Zn-Al alloy, the Al content should be 10 mass% or more. The minimum Al content required to be contained in the core particles can be calculated, for example, from the thickness of the Al oxide shell to be formed.

[0032] 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 that are micron-order in size, have core particles (PCM) containing the above components, and have a high specific surface area. 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.

[0033] [Covering part] The coating portion has Al oxide and also contains a metal element that forms a poorly soluble compound in an aqueous solution of pH 8 to 12. Examples of Al oxide contained in the coating portion include α-Al2O3 and θ-Al2O3. The coating portion is preferably mainly composed of α-Al2O3. The coating portion of the latent heat storage particle according to this embodiment preferably contains θ-Al2O3, which has a high specific surface area, in addition to α-Al2O3.

[0034] The metal element that forms a poorly soluble compound in an aqueous solution of pH 8 to 12 is preferably one or more metal elements selected from the group consisting of La, Ni, Zn, Fe, and Mg. The presence of the metal element in the coating portion can be confirmed and quantified by energy dispersive X-ray spectroscopy (EDS).

[0035] The coating portion of the latent heat storage particles according to this embodiment may have a thickness in the range of 500 nm to 4 μm. The coating portion may be, for example, a coating layer with a thickness of 1 to 2 μm.

[0036] The coating portion of the latent heat storage particle according to this embodiment may cover at least a portion of the surface of the core particle. The coverage of the coating portion on the surface of the core particle is preferably 50 area% or more. The 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%.

[0037] (specific surface area of ​​latent heat storage particles) The specific surface area of ​​the latent heat storage particles according to this embodiment can be expressed as a BET specific surface area. More specifically, the BET specific surface area of ​​the latent heat storage particles is 2 The BET specific surface area of ​​the latent heat storage particles is preferably 10 to 100 m 2 / g, more preferably 10m 2 / g, 20m 2 / g, 30m 2 / g, 40m 2 / g, 50m 2 / g, 60m 2 / g, 70m 2 / g, 80m2 / g, 90m 2 / g and 100m 2 The lower limit may be within a range defined by two values ​​selected from the ranges of 30 m / g. 2 / g or more, more preferably 40m 2 / g or more, most preferably 50m 2 / g or more. The upper limit is usually 90m 2 / g or less, typically 80m 2 / g or less, more typically 70m 2 / g or less, and even more typically 60m 2 / g or less.

[0038] (Heat exchange material made of 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.

[0039] (catalyst-supported latent heat storage particles) The latent heat storage particles according to this embodiment may be catalyst-supported latent heat storage particles, which have a catalyst on their surface. Supporting various catalyst particles on the surface of latent heat storage particles can provide a material that functions both as a catalyst and a heat storage medium. Conventional methods for manufacturing latent heat storage particles have difficulty increasing the specific surface area of ​​the latent heat storage particle. As shown in the schematic cross-sectional view of FIG. 1(a), it has been difficult to sufficiently support catalyst 2 on the surface of the oxide film 3 of the latent heat storage particle. However, according to the manufacturing method of this embodiment, as shown in the schematic cross-sectional view of FIG. 1(b), latent heat storage particles are obtained in which a precipitate layer 4 with a high specific surface area is formed on the surface of the oxide film 3 of the latent heat storage particle. This allows for the realization of catalyst-supported latent heat storage particles with a large amount of catalyst 2 supported on the surface of the precipitate layer 4. The catalyst-supported latent heat storage particles can be used by being packed into a catalyst layer, as shown in the schematic cross-sectional view of FIG. 2. When the catalyst-supported latent heat storage particles of this embodiment are used, the reaction heat generated by the catalyst 2 on the surface of the precipitate layer 4 of the particle can be absorbed by the core particle (PCM) 1, as shown by the black arrow in the enlarged view of Figure 2. As a result, the excessive heat generated in the center of the catalyst layer in conventional catalyst layers (the temperature curve shown by the dashed line in Figure 2) can be suppressed as shown by the temperature curve shown by the solid line in Figure 2, allowing the catalyst to be used for a long period of time without deterioration.

[0040] [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 core raw material particles whose component is Al or an alloy containing Al; (ii) performing a chemical conversion coating treatment on the core material particles using a chemical conversion coating treatment solution to obtain chemical conversion coated particles; and (iii) subjecting the chemical conversion coated particles to a heat treatment, The chemical conversion coating solution contains a salt containing a metal element that forms a poorly soluble compound in an aqueous solution of pH 8 to 12, and in the chemical conversion coating treatment, the pH of the chemical conversion coating solution is adjusted to a pH at which the metal element precipitates as a poorly soluble compound. 析出 The above range is set as follows. Each step will be described in detail below.

[0041] (i) Preparation of raw material particles As the raw material particles, core raw material particles whose component is Al or an alloy containing Al are prepared. The core raw material particles correspond to the core particles of the desired latent heat storage particles, and for example, particles having an average particle diameter of 10 μm or more and 200 μm or less are prepared. The average particle diameter may be, for example, 100 μm or less, or even 50 μm or less. The components of the core raw material particles are as described above for the core particles of the latent heat storage particles.

[0042] (ii) Chemical conversion coating In the method for producing latent heat storage particles according to this embodiment, (I) Contains a salt containing a metal element that forms a poorly soluble compound in an aqueous solution of pH 8 to 12, and (II) The pH is a pH at which the metal element precipitates as a poorly soluble compound (pH 析出 The core material particles are subjected to a chemical conversion coating treatment using a chemical conversion coating treatment solution within the above range to obtain chemical conversion coated particles.

[0043] In this embodiment, the chemical conversion coating solution contains a salt containing the metal element. In the chemical conversion coating solution, the salt containing the metal element can dissociate into a metal ion, which is a cation moiety, and an anion moiety such as an acetate ion. The salt containing the metal element can be one or more selected from the group consisting of nitrates, sulfates, phosphates, and acetates. Nitrates are preferred.

[0044] Below, we will explain how to control the pH of a chemical conversion coating treatment solution containing nitrate when nitrate is used as the salt containing a metal element in the chemical conversion coating treatment process, but the manufacturing method of this embodiment can also be applied when a salt other than nitrate is used.

[0045] From the results of the Examples described below, it is speculated that the addition of nitrates to the chemical conversion coating solution and the control of pH result in the following: First, the inventors added core raw material particles to a chemical conversion coating solution containing La nitrate, Ni nitrate, Zn nitrate, Fe nitrate, Mg nitrate, or Ca nitrate as the nitrate, and examined the change in pH after the core raw material particles were added. The results are shown in Figure 3. When pure water was used, the pH of the solution did not increase after the raw material was added, remaining at pH 4.7. However, when a chemical conversion coating solution containing dissolved nitrates was used, as is clear from Figure 3, the pH rose sharply to about 8.3 in most cases (only La rose to pH 6.5), followed by a gradual decrease in pH.

[0046] As mentioned above, the pH rose sharply when core raw material particles were added to the nitrate aqueous solution. This suggests that the nitrate ions generated by the addition of nitrate acted as an oxidizing agent, promoting the dissolution of Al, resulting in the rise in pH, as shown in the following reaction formula: Al+3(NO3) - →Al(NO3)3+3e - (Because it is in aqueous solution, Al(NO3)3 → Al 3+ +3(NO3) - ) 2H2O+2e - →2OH - (pH increase) + H2

[0047] It is believed that the increase in pH causes the metal ions in the aqueous solution that constituted the nitrates to precipitate as sparingly soluble fine hydroxides, and these fine hydroxides act as nuclei near the surfaces of the core raw material particles, promoting the formation of precipitates on the surfaces of the core raw material particles, increasing the amount of precipitates, and resulting in the formation of a precipitate layer with a large specific surface area. Therefore, the pH of the chemical conversion coating solution in this embodiment is set to a range equal to or higher than the pH at which the metal elements that constitute the nitrates precipitate as sparingly soluble compounds such as hydroxides, as described above.

[0048] The pH for forming, for example, hydroxide as a poorly soluble compound of the metal element that becomes the nucleus of the precipitate is pH that satisfies the following formula (1):析出 The above range is preferable.

[0049]

number

[0050] In equation (1), K sp is the solubility product at the reaction temperature, [M n+ ] indicates the metal ion concentration (M), and n indicates the valence.

[0051] The pH of the chemical conversion coating solution for forming hydroxides of metal elements that become the nuclei of the deposits can be calculated as follows: First, the condition at which metal hydroxides start to deposit is expressed by the following formula (2): Further modifying the formula (2), the relationship in the following formula (3) is obtained, and the pH at which hydroxides start to deposit is 析出 is expressed as in the above formula (1).

[0052] K sp =[M n+ ][OH - ] n (2) In equation (2), K sp : solubility product at reaction temperature, [M n+ ]: metal ion concentration (M), n: valence.

[0053]

number

[0054] In equation (3), K sp : solubility product at reaction temperature, [M n+ ]: metal ion concentration (M), n: valence.

[0055] Therefore, the pH of the chemical conversion coating solution for forming the hydroxide of the metal element is set to a pH at which the metal element precipitates as a poorly soluble compound. 析出 The above range applies.

[0056] The present inventors have investigated the pH of metal elements such as La, Ni, Zn, Fe, Ca, and Mg. 析出 That is, the pH at which the hydroxide of each metal begins to precipitate was calculated from the above theoretical formula. The results are shown in Table 1. It can be said that the pH of the chemical conversion coating treatment solution should be equal to or higher than the values ​​in Table 1 below.

[0057] [Table 1]

[0058] On the other hand, the pH of the chemical conversion coating solution should be within a pH range that does not cause excessive dissolution of the Al contained in the core raw material particles. In other words, the pH is preferably within a range of approximately pH 6 to 12, depending on the temperature, so that Al does not dissolve excessively, and as described above, the pH is within a range that causes precipitation of the metal hydroxide, which is a poorly soluble compound. For example, when the temperature of the chemical conversion coating solution is within a range of 70°C to 100°C, as described below, the highest pH value is calculated to be 12.8 at the lowest temperature of 70°C. Considering the upper limit of the pH that does not cause excessive dissolution of Al, the upper limit of the pH of the chemical conversion coating solution is preferably 12. The pH range above which a metal element precipitates as a poorly soluble compound varies depending on the metal element, and when the metal element is one or more metal elements selected from the group consisting of La, Ni, Zn, and Fe, the pH of the chemical conversion coating solution is preferably 8 to 12, and when the metal element is Mg, the pH of the chemical conversion coating solution is preferably 10 to 12. To adjust the pH, ammonia, potassium hydroxide, sodium hydroxide, or other hydroxides can be used as a pH adjuster.

[0059] The metal elements constituting the nitrate used may correspond to the metal elements contained in the coating portion of the latent heat storage particles, and are preferably one or more metal elements selected from the group consisting of La, Ni, Zn, Fe and Mg.

[0060] The concentration of the metal element nitrate contained in the chemical conversion coating treatment solution is preferably 1 to 5 mM (millimolar).The temperature of the chemical conversion coating treatment solution is preferably maintained at 70 to 100°C.

[0061] The coating portion of the precursor obtained by the chemical conversion coating treatment may have a laminated structure in which, for example, amorphous dense boehmite (AlOOH) is formed on the surface of the core particle, acicular boehmite (acicular AlOOH) is formed on the surface of this dense boehmite (AlOOH), and further, a precipitate layer containing metal elements derived from metal nitrates and having a high specific surface area is formed on the acicular boehmite.

[0062] (iii) Heat treatment (calcination) The chemically coated particles are heat-treated. This oxidizes the chemical conversion coating of the chemically coated particles, forming a layer containing Al oxide as the coating. The heat treatment temperature can be, for example, higher than the melting point of the metal (including alloy) that constitutes the core raw particle, such as heating to 700°C or higher. The aluminum oxide film formed by the heat treatment takes the γ-Al2O3 crystal form at relatively low temperatures, generally below 800°C, while a chemically stable α-Al2O3 film is obtained at relatively high temperatures, generally above 880°C. For example, to obtain a chemically stable α-Al2O3 film, the heat treatment temperature is preferably 880°C or higher. When the core particle is, for example, an Al-Si alloy, the heat treatment can be performed at a temperature between 900°C and 1230°C.

[0063] The heat treatment atmosphere is preferably air or an oxygen atmosphere created by supplying oxygen gas to a heat treatment furnace. The temperature inside the furnace is increased using a heater, and once the sample temperature reaches a predetermined temperature, heat treatment (oxidation treatment) is performed for, for example, 1 to 5 hours to obtain heat-treated latent heat storage particles. The heat treatment method can be, for example, by filling the chemical conversion coated particles into a crucible, 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. [Example]

[0064] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples, and can be practiced with appropriate modifications within the scope of the above-mentioned and below-mentioned aims, and all such modifications are included in the technical scope of the present invention.

[0065] [Example 1] In Example 1, core raw material particles made of an Al-Si alloy (Al-25 mass% Si) were used, and a chemical conversion coating treatment was performed using a chemical conversion coating treatment solution containing various metal nitrates, followed by a heat treatment to prepare a sample. The details are as follows. [Sample preparation] Core raw material particles were prepared from an Al-Si alloy with a Si content of 25 mass% (Al-25mass%Si). The average particle size of the core raw material particles was measured using a laser diffraction particle size distribution analyzer (HORIBA LA-920) and found to be 20 to 38 μm.

[0066] Next, a chemical conversion coating solution was prepared. More specifically, pure water and one of La nitrate, Ni nitrate, Zn nitrate, Fe nitrate, Ca nitrate, and Mg nitrate were added to a beaker so that each concentration was 3 mM, and a 1 M ammonia solution was added to adjust the pH to about 8 to prepare a 300 mL aqueous solution. For comparison, a beaker was also charged with 300 mL of pure water, and a 1 M ammonia solution was added to adjust the pH to about 8 to prepare another aqueous solution.

[0067] A beaker containing the chemical conversion coating solution was placed on a hot plate stirrer and heated to 100°C. 10 g of the core raw material particles (Al-25 mass% Si) were added to the chemical conversion coating solution, which was then stirred at 400 rpm for 3 hours to form a precursor. During the treatment, the pH of the chemical conversion coating solution was maintained at approximately 8 by adding 1 M aqueous ammonia solution dropwise.

[0068] After the chemical conversion coating process, the chemically coated product (precursor) was collected and loaded into an Al2O3 dish. The precursor was then heated from room temperature to 1000°C at a rate of 10°C / min in a muffle furnace (HPM-2N, AS ONE Corporation) in an air atmosphere, and held at 1000°C for 3 hours to obtain samples (latent heat storage particles). Hereinafter, samples prepared using a chemical conversion coating solution containing La nitrate, Ni nitrate, Zn nitrate, Fe nitrate, Ca nitrate, or Mg nitrate will be referred to as the "La sample," "Ni sample," "Zn sample," "Fe sample," "Ca sample," or "Mg sample," respectively. Samples prepared using a chemical conversion coating solution without these nitrates will be referred to as the "NA sample."

[0069] [Sample Evaluation] The properties of the precursor (chemically treated coating material) and the sample (latent heat storage particles) obtained by the above steps were analyzed as follows.

[0070] (Surface properties of precursor (chemical conversion coating treated material)) The surface condition of the latent heat storage material was observed using an SEM (JEOL, JSM-7001FA). The results are shown in Figure 4. Hereinafter, the metal elements shown in the figures are those added as nitrates, and "NA" indicates a sample obtained by chemical coating treatment using only pH-adjusted pure water. As is clear from Figure 4, the surface properties of the obtained latent heat storage material particles were roughly divided into two groups: Group A, in which many needle-shaped or columnar precipitates were deposited on the surface, and Group B, in which such precipitates were hardly observed. The shape of the precipitates in Group A differed depending on the metal element of the added metal nitrate.

[0071] (XRD measurement of precursor (chemical conversion coating treated material)) XRD measurements of the precursors (chemically treated materials) were performed under the following conditions. The results are shown in Figure 5. Figure 5 indicates that the precursors in Group A, which had a large amount of precipitates on their surfaces, exhibited not only Al and Si but also prominent peaks for AlO(OH) and Al(OH)3. In contrast, the precursors in Group B, which had almost no precipitates, exhibited only peaks for Al and Si. Based on the SEM observations in Figure 4 and the XRD measurements, it can be concluded that in Group A, the La and Fe samples precipitated acicular AlO(OH) crystals, while the Ni sample precipitated columnar Al(OH)3 crystals. Furthermore, the Zn sample precipitated a mixture of acicular AlO(OH) crystals and columnar Al(OH)3 crystals. These results suggest that the structure of the resulting Al2O3 precursor can be controlled by the type of metal nitrate.

[0072] (Measurement conditions) X-ray diffractometer: X-ray diffractometer XRD Rigaku MiniFlex600 X-ray source: Cu line Detector: High-speed one-dimensional detector D / teX Ultra2 Tube voltage: 40kV ·Tube current: 15mA Scan speed: 18.0° / min Step: 0.02°

[0073] (Surface properties of sample (latent heat storage material particles)) The surface condition of the samples (latent heat storage particles) was observed using an SEM (JEOL, JSM-7001FA). The results are shown in Figure 6. Figure 6 shows that the samples in Group A maintained their capsule shape even after heat treatment (calcination). The surface precipitates of the samples in Group A also maintained their shape after heat treatment (calcination). On the other hand, for the samples in Group B, the Mg and NA samples maintained their capsule shape after heat treatment (calcination), but the Ca sample showed damage to almost all of its particles.

[0074] (XRD measurement of sample (latent heat storage material particles)) XRD measurements of the samples (latent heat storage particles) were performed under the same conditions as those of the precursor (chemically treated material). The results are shown in Figure 7. As can be seen from Figure 7, in samples from Group A, in which a large amount of precipitates were confirmed on the surface, peaks for θ-Al2O3 were observed in addition to Al, Si, and α-Al2O3. On the other hand, in samples from Group B, in which few precipitates were confirmed, peaks for Al, Si, and α-Al2O3 were mainly observed. Comparing these, it can be seen that in samples from Group A, in which a large amount of precipitates were confirmed on the surface, peaks for θ-Al2O3, which has a high specific surface area, were detected.

[0075] The present inventors confirmed that approximately 0.5 to 1 mol % of metal elements were detected in the quantitative EDS analysis.

[0076] (Weight change during heat treatment of precursor / measurement of latent heat of sample) The weight change of the precursor was observed during heat treatment, in which the temperature was raised to 1000°C and held at 1000°C for 3 hours. The results are shown in Figure 8. The latent heat of the heat-treated sample was also calculated. The results are shown in Table 2. Figure 8 shows that in the heating process up to approximately 550°C (step [1]), weight loss was observed, likely due to dehydration of the coating and precipitates (AlO(OH), Al(OH)3) formed during the chemical conversion coating process. In the heating process from approximately 550°C to the final temperature of 1000°C (step [2]), volume expansion caused cracks, leading to leakage of the core material. However, the leaked core material oxidized during the heat treatment, self-repairing the leaked area, resulting in a weight increase due to oxidation. In the holding stage at 1000°C (step [3]), the weight stabilized due to the cessation of oxidation.

[0077] [Table 2]

[0078] Furthermore, Group A showed a greater degree of weight increase or decrease than Group B. From this, it is believed that the formation of the film is promoted by the formation of a large amount of precipitates and an increase in film thickness in Group A. From these facts, it can be said that in the present invention, by performing a chemical coating treatment with an aqueous solution containing a nitrate of a specified metal element and with a controlled pH, it is possible to form a shell and encapsulate even core raw material particles that are difficult to encapsulate with a chemical coating treatment using pure water (boehmite treatment).

[0079] (BET measurement of sample) The specific surface areas of the precursors and samples obtained using each metal element were measured by the BET method. More specifically, they were calculated by the multi-point BET method using measurement points in the range of 0.05 < (p / p0) < 0.30. The results are shown in Table 3 and graphed in Figure 9.

[0080] [Table 3]

[0081] Table 2 and Figure 9 show that the precursors (before heat treatment) and samples (after heat treatment) in Group A had specific surface areas approximately 6.5 to 17.4 times larger than those in Group B. Among the samples, the La sample had the highest specific surface area, approximately 17.4 times that of the Na sample. Furthermore, the La and Fe samples showed a large decrease in specific surface area due to heat treatment, with the specific surface area of ​​the samples (after heat treatment) being approximately 43 to 49% of that of the precursors (before heat treatment). On the other hand, the Ni sample showed a small decrease in specific surface area due to heat treatment, with the specific surface area of ​​the samples (after heat treatment) being approximately 81% of that of the precursors (before heat treatment). [Example 2] In Example 2, samples were prepared by changing the pH of the chemical conversion coating solution in the example using magnesium nitrate, which hardly formed a deposit layer in Example 1, to examine the effect of pH on the formation of a deposit layer. Details are as follows.

[0082] [Sample preparation] A chemical conversion coating treatment was carried out in the same manner as in Example 1, except that the concentration of magnesium nitrate was set to 3 mM and the pH of the chemical conversion coating treatment solution was maintained at 9.5 or 10 by dropwise addition of an aqueous NaOH solution, to obtain a precursor. The precursor was recovered and dried overnight, and then heat-treated to obtain a sample (latent heat storage particles after heat treatment).

[0083] [Sample Evaluation] The precursor (chemical conversion coated product) obtained through the above steps was subjected to SEM observation and BET measurement in the same manner as in Example 1.

[0084] (SEM observation of precursor) Figure 10 shows the results of SEM observation of the precursor. As is clear from Figure 10, when the pH was adjusted to 9.5, small precipitates were observed, and the number of precipitates was greater than when the pH was 8 as in Example 1. On the other hand, by increasing the pH to 10, the amount of precipitates increased dramatically, resulting in a precursor covered with numerous precipitates. That is, although Mg was a metal element in Group B that hardly precipitated in Example 1, increasing the pH of the chemical conversion coating solution enabled the formation of a precipitate layer on the precursor. These results confirmed that increasing the pH leads to the formation of poorly soluble metal hydroxides, which act as crystal nuclei and promote the formation of a precipitate layer.

[0085] (BET measurement of precursor) Figure 11 shows the results of BET analysis of the specific surface areas of NA and Mg samples prepared using chemical conversion coating solutions with different pH values. Figure 11 shows that the specific surface area of ​​the Mg sample increased significantly when the pH of the chemical conversion coating solution was increased from 8 to 10. Furthermore, the Mg sample had a higher specific surface area than the NA sample, and the specific surface area of ​​the sample obtained by heat-treating the precursor tended to decrease significantly. This result, combined with the results shown in Figure 10, indicates that the pH at which hydroxides of metal elements contained in the chemical conversion coating solution precipitate contributes significantly to the increase in the specific surface area of ​​the precursor. Furthermore, although the specific surface area decreased slightly as the acicular and columnar precipitates of the precursor became a layer containing alumina during heat treatment, the example of a precursor with a large specific surface area (Mg sample, pH 10) maintained a high specific surface area even after heat treatment, enabling the production of latent heat storage particles with a high specific surface area, which is effective for, for example, supporting catalysts.

[0086] The following can be said from Examples 1 and 2. When the pH was adjusted to 8, the pH in Table 1 was 析出 In the case of La, Ni, Zn, and Fe, whose pH is 8 or less, a precipitate layer was obtained as shown in Example 1 described later. 析出 On the other hand, when the pH was adjusted to 10, the precipitate layer of Mg was not obtained, including Mg that did not form a precipitate layer when the pH was adjusted to 8. 析出 A precipitate layer was obtained for all of La, Ni, Zn, Fe, and Mg, whose pH values ​​are less than 10. As is clear from these results, to obtain a precipitate layer of AlOOH or Al(OH)3, it is necessary to adjust the pH of the chemical conversion coating solution depending on the type of metal element so that the hydroxide of the added metal M precipitates.

[0087] [Example 3] In Example 3, latent heat storage particles were produced using core material particles having a smaller amount of Al than in Example 1, and the surface properties and the like were evaluated.

[0088] [Sample preparation] A Cu alloy (Cu-9.6Si-40Al) containing 9.6% by mass of Si and 40% by mass of Al was used as the core raw material particles, and a chemical conversion coating treatment solution containing 3 mM and 5 mM Ni nitrate was used as the nitrate salt. Except for this, a chemical conversion coating treatment was carried out in the same manner as in Example 1 to obtain a precursor, which was then recovered and dried overnight, and then further heat-treated to obtain a sample (latent heat storage particles after heat treatment).

[0089] [Sample Evaluation] The precursor (chemical conversion coating treated product) and the sample (latent heat storage particles) obtained by the above steps were subjected to SEM observation and XRD measurement, and the weight change during the heat treatment was measured in the same manner as in Example 1. In addition, the specific heat of the sample (latent heat storage particles) was measured as follows.

[0090] (SEM observation and XRD measurement of precursor) Figure 12 shows the SEM observation results of the precursor. Figure 12 indicates that a columnar precipitate layer was formed by using an aqueous solution containing metal nitrate (Ni nitrate), while a dense precipitate layer was formed by using an aqueous solution with a high concentration of metal nitrate. Figure 13 also shows the XRD measurement results of the precursor. Figure 13 shows that a significant Al(OH)3 peak was detected in the sample formed using metal nitrate (Ni nitrate). Figure 13 and Figure 12 indicate that an Al(OH)3 film was formed as the precipitate layer in the sample formed using Ni nitrate, while a dense Al(OH)3 film was formed in the sample with a high Ni nitrate concentration. Furthermore, even when particles with a low Al content of 40 mass% were used as core raw material particles, a columnar Al(OH)3 film was confirmed to be formed, similar to when the Al-25 mass% Si core raw material particles with an Al content of approximately 75 mass% in Example 1 were treated with a chemical conversion coating treatment solution containing Ni nitrate.

[0091] (Weight change when precursor is heat treated) Figure 14 shows the weight change when the precursor was heat-treated. As can be seen from Figure 14, the NA sample showed the smallest weight loss up to 500°C and the smallest weight gain thereafter. In contrast, the Ni sample prepared using Ni nitrate (3 mM) showed the largest weight gain due to oxidation. From these results, it can be seen that the weight loss of the sample formed using Ni nitrate, which is thought to be due to the dehydration of the coating and precipitates (AlO(OH), Al(OH)3) formed during the chemical coating process, was overwhelmingly greater than that of the NA sample, and it is thought that more Al from the core raw material particles was consumed in the formation of the coating and precipitate layer than in the NA sample.

[0092] (SEM observation and XRD measurement of sample (latent heat storage material particles)) Figure 15 shows the results of SEM observation of the sample (latent heat storage particles after heat treatment). Figure 15 shows that the surface of the NA sample had an uneven shape covered with ellipsoidal particles of approximately 0.3 μm. On the other hand, the Ni sample was covered with a columnar structure derived from Al(OH)3, and some smooth surfaces were also observed. Figure 16 also shows the results of XRD measurement of the sample (latent heat storage particles). Figure 16 shows that the CuAl2 and AlCu peaks were significantly smaller in the Ni sample. Furthermore, a peak for η-Cu3.17Si was detected in the Ni sample. These results suggest that the alloy composition of the core particles in the sample (after calcination) changed due to the dissolution of Al from the alloy during the chemical coating treatment (boehmite treatment).

[0093] (Specific heat measurement of sample (latent heat storage particles)) The specific heat of each sample was measured using a simultaneous thermogravimetry / differential thermal analyzer (NETZHSCH, product number: STA 449 F3 Jupiter). The results are shown in Figure 17. As can be seen from Figure 17, the Ni (5 mM) sample showed a significant increase in specific heat between 700 and 800°C during both heating and cooling. From these results, it is believed that a phase change occurred in the Ni sample between 700 and 800°C. During temperature rise: CpΔT = 186.2 (J / g) at 700-800°C When temperature falls: CpΔT=177.7(J / g) at 700-800℃

[0094] As is clear from the above examples, in the method for producing latent heat storage particles, the present invention adds metal nitrate to the chemical conversion coating solution during the step of chemically coating core raw material particles and controls the pH of the chemical conversion coating solution. This allows for the formation of a porous layer suitable for supporting a catalyst on the surface of a dense Al oxide coating in contact with the core raw material particles (PCM). Furthermore, by applying the method according to this embodiment, it is possible to promote the dissolution and shell formation of Al from the core raw material particles (PCM). This allows for the production of PCM microcapsules with low Al concentration alloys as PCMs (core raw material particles), which was difficult to achieve using conventional methods. This makes it possible to produce PCM microcapsules with melting points below 380°C or above 700°C, which was not possible with conventional PCM microcapsules primarily composed of Al. [Explanation of symbols]

[0095] 1. Core particles (PCM) 2. Catalyst 3 Oxide film 4 Precipitate layer 5 Catalyst layer 6 Refrigerant

Claims

1. It comprises a core particle and a coating portion that covers at least a part of the surface of the core particle, The core particles are composed of Al or an alloy containing Al. The coating portion comprises latent heat storage particles, which include a single layer of precipitate containing Al oxide and a metal element that forms sparingly soluble compounds in an aqueous solution with a pH of 8 to 12.

2. The latent heat storage particle according to claim 1, wherein the metal element is one or more metal elements selected from the group consisting of La, Ni, Zn, Fe, and Mg.

3. The latent heat storage particle according to claim 1 or 2, wherein the alloy containing Al is an alloy containing 10% by mass or more of Al.

4. The latent heat storage particle according to any one of claims 1 to 3, wherein the precipitate layer is a porous layer.

5. The latent heat storage particle according to any one of claims 1 to 4, wherein the coverage rate of the coating portion on the surface of the core particle is 50 area % or more.

6. The latent heat storage particle according to any one of claims 1 to 5, wherein the average particle diameter of the core particles is 10 μm or more and 200 μm or less.

7. Latent heat storage particles according to any one of claims 1 to 6, wherein a catalyst is provided on the surface.

8. A heat exchange material formed of latent heat storage particles according to any one of claims 1 to 6.

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