Solid heat storage material

Abstract

To provide a solid heat storage material containing vanadium dioxide and aluminum and enabling suppression of reduction in latent heat.SOLUTION: A solid heat storage material is a composite of vanadium dioxide and an aluminum alloy, the aluminum alloy containing at least one of silicon or copper and having a composition that does not reduce vanadium dioxide compared with pure aluminum.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a solid heat storage material composed of a composite of vanadium dioxide and an aluminum alloy. [Background technology]

[0002] In electronic devices, such as power semiconductors, the problem of heat generation due to the miniaturization of chips, etc. has become apparent. As a solution to this problem, the use of latent heat has been proposed, and it is considered important to maximize the product of thermal conductivity and latent heat in order to more efficiently suppress temperature increases due to heat generation (Non-Patent Document 1, Non-Patent Document 2).

[0003] As a specific method, the inventors have proposed a solid heat storage material that is a composite of vanadium dioxide and a high thermal conductivity substance that are tightly bonded together (Patent Document 1). Vanadium dioxide is an insulator at room temperature, but when the material is heated, it undergoes a phase transition from the insulating phase to the metallic phase near the critical temperature Tp = 67°C. Furthermore, once the material is cooled from the high-temperature state in which it has changed to the metallic phase, it returns to its original insulating phase near Tp. The latent heat of this phase transition is approximately 220 J / cc, and during the heating process, an amount of heat equivalent to the latent heat is absorbed from the outside, and during the cooling process, an amount of heat equivalent to the latent heat is released to the outside.

[0004] In addition, Patent Document 1 exemplifies, in one form, a solid heat storage material made of vanadium dioxide and pure aluminum (a substance with high thermal conductivity). Pure aluminum has a thermal conductivity of 240 W / mK and a low density, so this form of solid heat storage material has excellent thermal conductivity and can be made lightweight. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication WO 2021 / 230357 [Patent Document 2] Patent No. 6032686 [Non-patent literature]

[0006] [Non-Patent Document 1] PJ Shamberger, “Cooling capacity figure of merit for phase change materials”, J. Heat Transfer, 138 024502 ​​(2016). [Non-patent document 2] L. Shao, A. Raghavan, CH Kim et al., “Figure of merit for phase-change materials used in thermal management”, Int. J. Heat and Mass Trans., 101 764-771(2016). [Non-patent document 3] J.B. Goodenough, “The two components of the crystallographic transition in VO2”, J. Solid. State. Chem. 3, 490-500 (1971). Summary of the Invention [Problem to be solved by the invention]

[0007] However, through intensive research by the present inventors, it was found that when vanadium dioxide is combined with pure aluminum to obtain a solid heat storage material, the latent heat of the solid heat storage material is reduced due to a chemical reaction between vanadium dioxide and pure aluminum during the manufacturing process, which is an area that needs to be improved.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress a decrease in latent heat in a solid heat storage material containing vanadium dioxide and aluminum. [Means for solving the problem]

[0009] In order to solve the above problems, the following solid heat storage material is provided. [1] A composite of vanadium dioxide and aluminum alloy, The aluminum alloy contains at least one of silicon and copper, and has a composition that does not reduce vanadium dioxide compared to pure aluminum. Solid heat storage material. [2] The silicon content in the aluminum alloy is 0.5% by mass or more. The solid heat storage material described in [1] above. [3] The copper content in the aluminum alloy is 10.0% by mass or more. The solid heat storage material according to [1] or [2] above. [4] The phase transition temperature of the vanadium dioxide is adjusted by doping. The solid heat storage material according to any one of [1] to [3] above. [Effects of the Invention]

[0010] According to the solid heat storage material of the present invention, the decrease in latent heat is suppressed. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram showing the relationship between the silicon content in the sintered body (solid heat storage material) of Example 1 and the latent heat quantity of the sintered body (solid heat storage material). FIG. [Figure 2] FIG. 10 is a diagram showing the heat absorption and heat generation properties of the sintered body (solid heat storage material) of Example 3 evaluated by differential scanning calorimetry. [Figure 3] FIG. 1 is a graph showing the endothermic and exothermic properties of the sintered body of Comparative Example 1 evaluated by differential scanning calorimetry. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present inventors have discovered a new finding that, in conventional techniques (e.g., Patent Document 1), when vanadium dioxide and pure aluminum are combined to obtain a solid heat storage material, the chemical reaction during the manufacturing process that causes a decrease in latent heat is a reduction reaction of vanadium dioxide by pure aluminum during sintering. Based on this new finding, the present inventors have investigated aluminum alloys having a composition that does not reduce vanadium dioxide as much as pure aluminum, and have thereby completed the present invention.

[0013] Hereinafter, one embodiment of the solid heat storage material of the present invention will be described.

[0014] The solid heat storage material of the present invention is a composite in which vanadium dioxide (VO2) and an aluminum alloy are closely adhered to each other. Here, "dense" means that the adhesion is at least 90% of the theoretical density, more preferably at least 95%. In order to improve the adhesion, for example, a heat treatment can be carried out in advance in air. In this case, the heat treatment temperature and heat treatment time can be appropriately set taking into account the porosity, etc., and for example, the heat treatment temperature may be 240°C or higher. The density can be measured appropriately using, for example, the Archimedes method.

[0015] In one embodiment of the solid heat storage material of the present invention, other elements or inevitable impurities may be contained in addition to vanadium dioxide and aluminum alloy.

[0016] The aluminum alloy constituting the solid heat storage material of the present invention contains at least one of silicon and copper, and has a composition that does not reduce vanadium dioxide as compared with pure aluminum.

[0017] In a form in which the aluminum alloy contains silicon (but does not contain copper), the silicon content in the aluminum alloy is preferably 0.5% by mass or more. The upper limit of the silicon content in the aluminum alloy is not particularly limited, but can be, for example, 25% by mass or less. When the silicon content in the aluminum alloy is 0.5% by mass or more, the thermal conductivity is excellent, and the aluminum alloy is less likely to reduce vanadium dioxide, so that a decrease in the latent heat of the solid heat storage material (latent heat of vanadium dioxide) can be suppressed. The latent heat can be evaluated, for example, by differential scanning calorimetry.

[0018] In a form in which the aluminum alloy contains copper (but does not contain silicon), the copper content in the aluminum alloy is preferably 10.0 mass% or more. The upper limit of the copper content in the aluminum alloy is not particularly limited, but can be, for example, 53 mass% or less. When the copper content in the aluminum alloy is 10.0 mass% or more, the aluminum alloy has excellent thermal conductivity, and since the aluminum alloy does not easily reduce vanadium dioxide, a decrease in the latent heat of the solid thermal storage material can be suppressed.

[0019] In a form in which the aluminum alloy contains silicon and copper, the content of silicon in the aluminum alloy is expressed as follows, where the silicon (Si) content is α(Si) mass% and the copper (Cu) content is α(Cu) mass%: α(Cu)≧-20×α(Si)+10 α(Cu)≦-2.12×α(Si)+53 It is desirable that the α(Si) and α(Cu) are positive and satisfy the following. Even in this form, the thermal conductivity is excellent, and since the aluminum alloy does not easily reduce vanadium dioxide, the decrease in the latent heat of the solid heat storage material can be suppressed.

[0020] The aluminum alloy may contain elements other than silicon and copper or unavoidable impurities.

[0021] In one embodiment of the solid heat storage material of the present invention, the phase transition temperature of vanadium dioxide may be adjusted by doping. An example of a method for increasing the phase transition temperature of vanadium dioxide is to substitute chromium at the vanadium lattice site. On the other hand, an example of a method for decreasing the phase transition temperature of vanadium dioxide is to substitute tungsten or niobium at the vanadium lattice site (Non-Patent Document 3, Patent Document 2).

[0022] The solid heat storage material of the present invention is a composite of vanadium dioxide and an aluminum alloy, and almost no compound is formed between the two. Therefore, the solid heat storage material of the present invention may have a composition such that the aluminum alloy does not reduce vanadium dioxide at the interface between the vanadium dioxide and the aluminum alloy compared to pure aluminum, and the volume fraction of the aluminum alloy in the solid heat storage material is not particularly limited. Therefore, the volume fraction of the aluminum alloy in the solid heat storage material of the present invention can be appropriately set depending on the application. Specifically, the volume fraction of the aluminum alloy in the solid heat storage material can be, for example, in the range of 0.03 to 0.75. Within this range, the volume fraction can be appropriately determined depending on the application. However, considering the tradeoff between latent heat quantity and thermal response, for example, when prioritizing latent heat quantity, a range of 0.03 to 0.40 can be exemplified, when achieving both, a range of 0.40 to 0.60 can be exemplified, and when prioritizing thermal response, a range of 0.60 to 0.75 can be exemplified.

[0023] The thermal conductivity of the solid heat storage material of the present invention can be adjusted appropriately depending on the composition and volume fraction of the aluminum alloy, but is preferably 15 W / mK or more. The thermal conductivity can be measured by a steady-state method or a non-steady-state method depending on the shape of the sample, etc.

[0024] In the solid heat storage material of the present invention, the aluminum alloy contains at least either silicon or copper and has a composition that does not reduce vanadium dioxide as much as pure aluminum does. Therefore, according to the present invention, the decrease in latent heat caused by the composite of the aluminum alloy and vanadium dioxide is suppressed, and a lightweight solid heat storage material is realized that can effectively utilize the latent heat of vanadium dioxide and the thermal conductivity of the aluminum alloy.

[0025] The solid heat storage material (composite) of the present invention may have a particle dispersion structure obtained by mixing vanadium dioxide and aluminum alloy powders, or a layered laminate structure obtained by laminating these. Another example is a bonded body in which an aluminum alloy plate and a solid heat storage material are bonded together.

[0026] An embodiment of the method for producing a solid heat storage material of the present invention will be described.

[0027] An example of a method for producing a solid heat storage material of the present invention is a method including a step of mixing aluminum alloy and vanadium dioxide powders having the desired composition described above and sintering them (direct sintering). By using such a production method, a vanadium dioxide composite material (composite) in which the aluminum alloy is uniformly dispersed can be obtained. Furthermore, by having the aluminum alloy composition described above, the reduction reaction of vanadium dioxide by the aluminum alloy during sintering is suppressed, thereby suppressing a decrease in the latent heat of the solid heat storage material (composite).

[0028] Aluminum alloy powder having a desired composition can be obtained by, for example, atomization. Vanadium dioxide powder can be synthesized by, for example, solid-state reaction or chemical synthesis.

[0029] The sintering of the aluminum alloy and vanadium dioxide powder is preferably carried out by a pressure sintering method using, for example, a hot press, and in this case, a dense solid heat storage material can be obtained.

[0030] The sintering temperature is preferably lower than the melting temperature of the aluminum alloy, in which case the aluminum alloy does not dissolve from the composite, making the process easier. Specifically, the sintering temperature can be set appropriately taking into account the composition and volume fraction of the aluminum alloy, and can be, for example, in the range of 500°C to 550°C. Note that when the aluminum alloy melts during sintering, the aluminum alloy can be appropriately impregnated into the composite by applying pressure using isostatic pressure sintering or the like.

[0031] Furthermore, since the sintering behavior of doped vanadium dioxide is not significantly different from that of undoped vanadium dioxide, a solid heat storage material can also be obtained from doped vanadium dioxide under the same conditions as the above-mentioned method.

[0032] Furthermore, the method for manufacturing a solid heat storage material of the present invention can include conditions and steps for forming a form having the above-mentioned particle dispersion structure or layered laminate structure, or a form of a bonded body in which an aluminum alloy plate material and a solid heat storage material are bonded.

[0033] The solid heat storage material of the present invention is not limited to the above-described embodiments. [Example]

[0034] The present invention will be described below with reference to examples, but the solid heat storage material of the present invention is not limited to the following examples in any way.

[0035] Example 1 Atomized aluminum alloy powder and vanadium dioxide powder having the composition shown in Table 1 were mixed in a volume ratio of 1:1, and pressure sintered in a vacuum at 550°C for 30 minutes (pressure: 30 MPa) to obtain a sintered body (solid heat storage material). The latent heat of the sintered body is also shown in Table 1. The latent heat was measured by differential scanning calorimetry.

[0036] [Table 1]

[0037] Aluminum alloys with a silicon content of 0.5% by mass or more in the sintered body exhibited a latent heat of approximately 30 J / g. Since the vanadium dioxide content in the sintered body was 63% by mass and the latent heat of vanadium dioxide was approximately 50 J / g, it was confirmed that there was almost no reduction in latent heat. Furthermore, as shown in Figure 1, when an effective element such as silicon was alloyed, the effect was linear with the amount added, and it was confirmed that the reduction in latent heat due to aluminum was restored.

[0038] <Example 2> Atomized powder of an aluminum alloy having the composition shown in Table 2 and vanadium dioxide powder were mixed in a volume ratio of 1:1, and sintered under the same conditions as in Example 1. The latent heat of the sintered body is also shown in Table 2.

[0039] [Table 2]

[0040] It can be seen that the latent heat increases with increasing copper content in the aluminum alloy. The rate of increase is proportional to the copper content, as with silicon in Example 1. From the data, the relationship between latent heat and copper content is latent heat [J / g] = 1.23 x copper content [wt%] + 17, so it was confirmed that a copper content of 10 wt% or more is required to achieve a latent heat of approximately 30 J / g for the sintered body.

[0041] Example 3 Chromium-doped vanadium dioxide powder (transition temperature 120°C) and aluminum alloy powder containing 7% by mass of Si were mixed in a volume ratio of 1:1, and pressure sintered in a vacuum at 525°C for 30 minutes. The endothermic and exothermic properties of the sintered body were evaluated by differential scanning calorimetry. The results are shown in Figure 2. There was no significant difference in the transition temperature compared to the raw material powder, and the amount of latent heat was also equivalent to that of the raw material powder.

[0042] <Comparative Example 1> Chromium-doped vanadium dioxide (transition temperature 120°C) was mixed with aluminum powder in a volume ratio of 1:1, and pressure sintered in a vacuum at 550°C for 30 minutes. The endothermic and exothermic properties of the sintered body were evaluated by differential scanning calorimetry. The results are shown in Figure 3. Compared to the raw material powder, the transition temperature was lower and the endothermic / exothermic behavior was broad, making the properties unsuitable for temperature control.

Claims

1. It is a composite of vanadium dioxide and aluminum alloy, The aluminum alloy contains at least one of silicon and copper, and has a composition that does not reduce vanadium dioxide compared to pure aluminum. Solid heat storage material.

2. The silicon content in the aluminum alloy is 0.5% by mass or more. The solid heat storage material of claim 1.

3. The copper content in the aluminum alloy is 10.0% by mass or more. The solid heat storage material of claim 1.

4. The phase transition temperature of the vanadium dioxide is adjusted by doping. The solid heat storage material of claim 1.

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