JP2023038418A - Method for producing latent heat storage material - Google Patents

Abstract

To provide a method for producing, with high productivity, an alloy-based latent heat storage material that can be used at relatively high temperatures and has excellent heat storage density and thermal conductivity.SOLUTION: The present invention provides a method for producing an alloy-based latent heat storage material that comprises a core particle composed of an Al-Si alloy coated with an aluminum oxide coat. The method includes a coat formation step for forming the aluminum oxide coat on the core particle, in which the core particle is added into water containing an antifoamer of 20 ppm or more and 5000 ppm or less. The production method can increase a charge ratio to a reaction container, leading to improved productivity.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a latent heat storage material, and more particularly to a method for producing a micro-sized latent heat storage material that can be used at relatively high temperatures and has excellent heat storage density and thermal conductivity.

As methods for storing heat, sensible heat storage using temperature change (for example, Patent Document 1) and latent heat storage using phase change of substances (for example, Patent Document 2) are known.

Of these, the sensible heat storage technology is capable of storing heat at high temperatures, but has the problem of low heat storage density because it uses only sensible heat due to temperature changes in substances. A latent heat storage technique for storing heat by utilizing the latent heat of molten salt or the like has been proposed as a method for solving such problems.

Various embodiments have been proposed as a heat storage material used in latent heat storage technology. Inventions such as a characteristic latent heat storage capsule and a method of manufacturing a latent heat storage capsule characterized by coating a latent heat storage material with a metal film by electrolytic plating are disclosed.

Further, in Patent Document 4, in a latent heat storage body composed of a core portion and a shell covering the core portion, the shell is subjected to a chemical conversion coating treatment on the core particles, and further subjected to a thermal oxidation treatment to form an oxide coating. It discloses that

JP-A-6-50681 JP-A-10-238979 JP-A-11-23172 International publication 2015/162929 pamphlet

However, in the production of the alloy-based latent heat storage microcapsules (Micro-Encapsulated Phase Change Material: hereinafter abbreviated as MEPCM) disclosed in Patent Document 4, there is a risk of severe foaming during the chemical conversion coating treatment and the reaction solution overflowing from the reaction vessel. Therefore, it was necessary to carry out the reaction with less than half the charged amount of the reactor, and the productivity was remarkably low.

The present invention has been made in view of such conventional problems, and provides a highly productive method for producing a latent heat storage material that can be used even at relatively high temperatures and has excellent heat storage density and thermal conductivity. be.

In order to achieve the above object, the inventor conducted various studies and came up with the present invention. That is, in a method for producing an alloy-based latent heat storage material in which core particles made of an Al—Si alloy are coated with an aluminum oxide coating, in the coating forming step of forming the aluminum oxide coating on the core particles, 20 ppm of an antifoaming agent is added. A method for producing an alloy-based latent heat storage material, characterized by adding core particles to water containing not less than 5000 ppm.

According to the production method of the present invention, it is possible to increase the charging ratio to the reaction vessel compared to the conventional method, and to improve the productivity of the alloy-based latent heat storage material. Thereby, it becomes possible to supply the molded body of the latent heat storage material at a lower cost.

The present invention will be described in detail below.
A combination of two or more of the individual preferred embodiments of the invention described below is also a preferred embodiment of the invention.
[Method for producing the latent heat storage material of the present invention]
The production method of the present invention is a method for producing an alloy-based latent heat storage material in which core particles made of an Al—Si alloy are coated with an aluminum oxide coating, and in the coating forming step of forming the aluminum oxide coating on the core particles, A method for producing an alloy-based latent heat storage material, characterized by adding core particles to water containing 20 ppm or more and 5000 ppm or less of an antifoaming agent.

The film forming step of the present invention is a step of forming an aluminum oxide film on the Al—Si alloy core particles by boehmite treatment, and the core particles are immersed in high-temperature water containing 20 ppm or more and 5000 ppm or less of an antifoaming agent. It is a method of forming a film on the surface.

The content of the antifoaming agent is 20 ppm or more, preferably 50 ppm or more, and more preferably 100 ppm or more. When the content of the antifoaming agent is 20 ppm or more, an effect of inhibiting foaming can be expected, but the larger the content, the greater the effect of inhibiting foaming. The upper limit of the content of the antifoaming agent is 5000 ppm or less, more preferably 2000 ppm or less, and even more preferably 1000 ppm. The larger the content of the antifoaming agent, the greater the effect of suppressing foaming. By containing the antifoaming agent within the above range, foaming is suppressed when the core particles are added, and efficient production can be achieved.

Examples of the antifoaming agent include silicone antifoaming agents, alcohol antifoaming agents, polyether antifoaming agents and the like, with silicone antifoaming agents being more preferred.

The Al—Si alloy may be an alloy composed of aluminum and silicon, and the content of silicon is preferably in the range of 4% to 40%, more preferably in the range of 10% to 30%, and more preferably 12% to 25%. Ranges are particularly preferred. Within the above range, large heat absorption and heat generation occur at the eutectic temperature of 580 ° C., so that while functioning as a heat storage material with a high heat storage amount, the volume expansion occurs when the phase changes from the solid phase to the liquid phase. Since the modulus can be kept low, the durability of the MEPCM can be increased.

In the film forming step, it is preferable to add aluminum hydroxide before adding the core particles for the purpose of preventing MEPCM from sintering and agglomerating during the thermal oxidation treatment step. The amount of aluminum hydroxide to be added is 0.5 to 25 parts by mass, preferably 1 to 20 parts by mass, per 100 parts by mass of the core particles. Aggregation can be prevented by adding 0.5 parts by mass or more, and the larger the amount added, the more likely it is to prevent aggregation during the thermal oxidation treatment process. does not change much. On the other hand, if 25 parts by mass or more is added, the amount of aluminum oxide in the alloy increases after the thermal oxidation treatment step, and the amount of heat storage decreases, so the above range is preferable.

The crystal structure of the aluminum hydroxide is not particularly limited, and examples thereof include bayerite, gibbsite, boehmite, etc. Among them, gibbsite and boehmite are preferable, since weight change is small during the thermal oxidation treatment step and defects can be reduced. , and boehmite are particularly preferred.

In the film forming step, a small amount of ammonia or the like may be added for treatment. It has been confirmed that the higher the pH value of the solution for boehmite treatment, the better the quality of the aluminum oxide film obtained. 10.0 is more preferred, and 8.5-9.5 is most preferred.

The reaction temperature in the film forming step is preferably 60° C. to 100° C., more preferably 70° C. or higher, still more preferably 80° C. or higher, and particularly preferably 90° C. or higher. The upper limit of the temperature is the boiling point of the aqueous solution, which is 100°C under normal pressure. The reaction time is preferably 0.25 to 24 hours, more preferably 0.5 to 5 hours. A higher temperature and a longer reaction time result in a better film formation, so the aluminum oxide film after the thermal oxidation treatment step is also better, and a highly durable film can be obtained.

Preferably, the production method of the present invention further includes a thermal oxidation treatment step. As a result, the aluminum oxide film formed in the film forming step is further oxidized, and MEPCM of crystalline Al ₂ O ₃ can be obtained.

The temperature of the thermal oxidation treatment process is preferably higher than the melting point of the Al--Si alloy that is the component of the core portion. An alloy with a silicon content of 25 wt % has a melting point of 580° C., and is preferably heated at a temperature higher than that (for example, 700° C. or higher). It is more preferable to treat at 800° C. or higher, still more preferably at 900° C. or higher. The reason for this is that the aluminum oxide film formed by heat treatment has a crystal structure of γ-Al ₂ O ₃ at a relatively low temperature of 800° C. or less, and is a chemically stable α-Al ₂ O ₃ crystal. This is because a structured film can be obtained at a relatively high temperature of 880° C. or higher. Although the upper limit is not particularly limited, it is preferably 1300° C. or less. When the temperature of the thermal oxidation treatment process exceeds 1300 ° C., the thickness of the aluminum oxide film increases in the ratio of the aluminum oxide film and the Al-Si alloy in MEPCM, so the ratio of the Al-Si alloy decreases. This is because the heat storage amount decreases. The heat treatment time is preferably 0.5 to 12 hours, more preferably 2 to 5 hours. By performing the above thermal oxidation treatment step, MEPCM with high repetitive stability can be obtained.

A further coating may be formed on the thermally oxidized coating obtained in the above steps to enhance strength. For example, chemical or physical treatments may be performed to form metallic and/or ceramic coatings. For example, chemical methods include sol-gel method, CVD, electroplating, electroless plating and the like, and physical methods include PVD and the like. The mechanical strength of the capsule can be enhanced by applying a metal coating and/or a ceramic coating over the capsule.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited only to these examples. Unless otherwise specified, "part" means "mass part" and "%" means "mass %".

<Measurement of average particle size>
Measurement was performed using a laser diffraction particle size distribution analyzer LA-950V2 manufactured by HORIBA. Specifically, the Al—Si alloy is dispersed in an aqueous solution in which 0.2% sodium pyrophosphate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) is dissolved, and the measurement is performed with a particle size distribution meter, and the cumulative 50% volume diameter was taken as the average particle size.

<Al—Si alloy>
A core particle made of an Al--Si alloy (Al-25 wt % Si) having a weight ratio of Al of 75% and a weight ratio of Si of 25% was prepared. These core particles had a diameter of less than 38 μm and an average diameter of 36.3 μm.

[Example 1]
A self-emulsifying antifoaming agent (manufactured by Shin-Etsu Chemical Co., Ltd.: KS-538) containing silicone as a main component was added to a flask with a diameter of 8.5 cm and a height of 25 cm so as to be 200 ppm with respect to water, and then water. 500 g was added. The mixture was heated using an oil bath while stirring at 150 rpm with a stirring blade. After measuring the water temperature and reaching 100° C., 5 g of aluminum hydroxide having a boehmite crystal structure (manufactured by Taimei Chemical Industry Co., Ltd.) was added and dispersed. After that, ammonia water adjusted to 1M was added, and the pH of the dispersion liquid was adjusted to be in the range of 9.0 to 9.5 when measured at room temperature.
Al--Si alloy: 50 g was added to the dispersion after pH adjustment. After the addition, the mixture was continuously stirred for 2 hours while adjusting the pH, and then cooled. After the Al—Si alloy was added, the height of the liquid surface due to the generated bubbles was recorded, and the difference between the highest value: 20 cm and the height of the liquid surface after cooling: 10.5 cm. : 9.5 cm was taken as the foam height.
After cooling, the reaction liquid was decanted to remove excess aluminum hydroxide, filtered, and dried to obtain a powdery latent heat storage material.

[Example 2]
A reaction was carried out in the same manner as in Example 1, except that 200 ppm of a self-emulsifying antifoaming agent (manufactured by Kyoeisha Chemical Co., Ltd.: Aqualen SB-630) containing polysiloxane as a main component was used as an antifoaming agent. The foam height was 10 cm.

[Example 3]
The reaction was carried out in the same manner as in Example 1, except that 200 ppm of an emulsion-type antifoaming agent (manufactured by Nisshin Chemical Laboratory Co., Ltd.: Bisfoam FSR-4) containing polysiloxane as a main component was used as the antifoaming agent. At the time, the foam height was 9.5 cm.

[Example 4]
The reaction was carried out in the same manner as in Example 1, except that 200 ppm of an emulsion-type antifoaming agent (manufactured by Nisshin Kagaku Kenkyusho Co., Ltd.: Bisfoam TDI-1) containing higher alcohol as the main component was used as the antifoaming agent. At the time, the foam height was 10 cm.

[Example 5]
The reaction was carried out in the same manner as in Example 1 except that 5 g of aluminum hydroxide (manufactured by Nippon Light Metal Co., Ltd.) having a gibbsite crystal structure was used, and the foam height was 10 cm.

[Example 6]
In Example 1, the reaction was carried out in the same manner as in Example 1, except that 1000 ppm of a self-emulsifying antifoaming agent (manufactured by Shin-Etsu Chemical Co., Ltd.: KS-538) containing silicone as a main component was used. was 8 cm.

[Example 7]
100 ppm of a self-emulsifying antifoaming agent mainly composed of silicone as an antifoaming agent (manufactured by Shin-Etsu Chemical Co., Ltd.: KS-538), a self-emulsifying antifoaming agent mainly composed of polysiloxane (manufactured by Kyoeisha Chemical: Aqualen The reaction was carried out in the same manner as in Example 1 except that SB-630) was used at 100 ppm, resulting in a foam height of 9.5 cm.

[Example 8]
As an antifoaming agent, a self-emulsifying antifoaming agent mainly composed of silicone (manufactured by Shin-Etsu Chemical Co., Ltd.: KS-538) is used at 100 ppm, and an emulsion type antifoaming agent mainly composed of higher alcohol (manufactured by Nisshin Chemical Laboratory : The foam height was 10 cm when the reaction was carried out in the same manner as in Example 1 except that 100 ppm of bisfoam TDI-1) was used.

[Comparative Example 1]
The reaction was carried out in the same manner as in Example 1, except that the silicone-based antifoaming agent was not added. reached.

[Comparative Example 2]
In Example 1, the reaction was carried out in the same manner as in Example 1, except that 10 ppm of a self-emulsifying antifoaming agent (manufactured by Shin-Etsu Chemical Co., Ltd.: KS-538) containing silicone as a main component was used. exceeded 15 cm and reached the upper surface of the reaction vessel.

[Example 9]
In a 3 L reaction vessel, in the same manner as in Example 1, a silicone-based self-emulsifying antifoaming agent (manufactured by Shin-Etsu Chemical Co., Ltd.: KS-538) was added to 200 ppm with respect to water, Then, 2.4 kg of water was added. The mixture was heated using an oil bath while being stirred at 150 rpm with a stirring blade, and when the water temperature reached 80°C, 24 g of aluminum hydroxide having a boehmite crystal structure (manufactured by Taimei Chemical Industry Co., Ltd.) was added and dispersed. After that, ammonia water adjusted to 1M was added, and the pH of the dispersion liquid was adjusted to be in the range of 9.0 to 9.5 when measured at room temperature.
Al--Si alloy: 240 g was added to the dispersion after pH adjustment. After the addition, the water temperature was raised to 100, and the mixture was stirred for 2 hours while adjusting the pH, and then cooled.
After cooling, the reaction liquid was decanted to remove excess aluminum hydroxide, filtered, and dried to obtain a powdery latent heat storage material.
The reaction liquid did not overflow from the reaction vessel.

[Comparative Example 3]
A reaction was carried out in the same manner as in Example 9 except that no antifoaming agent was used, but after the Al--Si alloy was added, the reaction was interrupted because the generated bubbles overflowed from the reaction vessel. Therefore, the coating forming process could not be completed.

<Measurement of heat storage amount>
The heat storage amount was measured by TG-DSC (SDT650 manufactured by TA Instruments). The powdery latent heat storage material obtained in each example was placed in an alumina sample pan, and oxidized at a rate of temperature increase of 10°C/min under air flow of 200ml/min, firing conditions of 1150°C for 3h. and designated as MEPCM. After that, without cooling to room temperature, the temperature was again raised to 700 ° C. at a temperature increase rate of 10 ° C./min under nitrogen flow of 20 ml / min, and the heat storage amount (latent heat amount / heat absorption amount) was measured (1 second time). Thereafter, the temperature was lowered at a rate of 5° C./min until the temperature reached 100° C. or less, and the amount of heat release (latent heat amount/calorific value) was measured (first time). Again, the temperature was raised to 700° C. at a rate of temperature increase of 10° C./min, and the heat storage amount (latent heat amount/heat absorption amount) was measured (second time). After that, the temperature was lowered at a cooling rate of 5°C/min until the temperature reached 100°C or lower, and the amount of heat release (latent heat amount/calorific value) was measured. (2nd time). The results are shown in the table.

From these results, it was confirmed that the latent heat storage materials obtained by the reactions of Examples 1 to 6 and 9 function repeatedly as heat storage bodies.

Claims (6)

A method for producing an alloy-based latent heat storage material in which core particles made of an Al—Si alloy are coated with an aluminum oxide coating,
A method for producing an alloy-based latent heat storage material, wherein the core particles are added to water containing 20 ppm or more and 5000 ppm or less of an antifoaming agent in the film forming step of forming the aluminum oxide film on the core particles. 2. The production method according to claim 1, wherein the core particles are added when the temperature of the water is 70[deg.] C. or higher. 3. The manufacturing method according to claim 1, wherein the film forming step is performed at pH 8 or higher. 4. The production method according to any one of claims 1 to 3, wherein the antifoaming agent is an antifoaming agent containing silicone or siloxane as a main component. 4. The production method according to any one of claims 1 to 3, wherein the antifoaming agent is a high alcohol-based antifoaming agent. 6. The manufacturing method according to any one of claims 1 to 5, characterized in that after the film forming step, the substrate is baked at a temperature of 900°C or higher and 1300°C or lower.