Variable emissivity material

Abstract

To provide a variable emissivity material that exhibits satisfactory variation in emissivity.SOLUTION: This variable emissivity material is a perovskite-type variable emissivity material represented by AMnO3, where A includes at least one rare earth ion selected from La, Pr, Nd, and Sm, and at least one alkaline earth metal ion selected from Ca, Sr, and Ba, the emissivity at 353 K is 0.5 or greater, and the emissivity at 203 K is 0.3 or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to variable emissivity materials.

Background Art

[0002] Conventionally, a thermal control device described in Japanese Patent No. 3221412 (Patent Document 1 below) is known. The thermal control device of Patent Document 1 uses a phase change material that has insulating properties in a high-temperature phase, metallic properties in a low-temperature phase, and a large heat radiation amount in the high-temperature phase and a small heat radiation amount in the low-temperature phase. Examples of this phase change material include perovskite oxides containing Mn.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 discloses a graph of the temperature dependence of the emissivity of La 0.825 Sr 0.175 MnO 3 However, there is a demand for developing a variable emissivity material that exhibits an even larger change in emissivity.

[0005] The present disclosure has been completed based on the above circumstances, and an object thereof is to provide a variable emissivity material in which the emissivity changes favorably.

Means for Solving the Problems

[0006] The variable emissivity material of the present disclosure is AMnO 3A perovskite-type variable emissivity material represented by wherein A includes at least one of rare earth ions of La, Pr, Nd, and Sm and at least one of alkaline earth metal ions of Ca, Sr, and Ba, and the emissivity at 353K is 0.5 or more and the emissivity at 203K is 0.3 or less.

Effect of the Invention

[0007] According to the present disclosure, a variable emissivity material with good emissivity change can be provided.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0009] [Outline of the Embodiment] (1) The variable emissivity material of the present disclosure is a perovskite-type variable emissivity material represented by AMnO 3 wherein A includes at least one of rare earth ions of La, Pr, Nd, and Sm and at least one of alkaline earth metal ions of Ca, Sr, and Ba, and the emissivity at 353K is 0.5 or more and the emissivity at 203K is 0.3 or less.

[0010] According to such a configuration, a variable emissivity material with good emissivity change can be provided.

[0011] (2) In the above (1), it is preferable that the valence of Mn is 3.21 or more and 3.27 or less.

[0012] According to such a configuration, the temperature at which the emissivity changes greatly can be suitably adjusted.

[0013] (3) The variable emissivity material of (1) above is La (1-x-y) Sr x Ca y MnO 3 represented by, and it is preferable that 0.107 ≦ x ≦ 0.138 and 0.103 ≦ y ≦ 0.132. Here, x and y are numerical values determined by elemental analysis of the variable emissivity material.

[0014] According to such a configuration, the temperature at which the emissivity changes significantly can be suitably adjusted.

[0015] (4) In (1) above, it is preferable that the difference between the emissivity at 353 K and the emissivity at 203 K is 0.4 or more.

[0016] (5) In (1) above, it is preferable that the emissivity at 353 K is 3 times or more the emissivity at 203 K.

[0017] [Details of Embodiments] Specific examples of embodiments of the present disclosure will be described with reference to FIGS. 1 and 2. Note that the present disclosure is not limited to these examples, and is intended to be indicated by the claims and to include all modifications within the meaning and scope equivalent to the claims.

[0018] The variable emissivity material of this embodiment (hereinafter simply referred to as the variable emissivity material) is a perovskite-type oxide represented by AMnO 3 Here, A includes at least one of rare earth ions such as La, Pr, Nd, and Sm and at least one of alkaline earth metal ions such as Ca, Sr, and Ba.

[0019] The variable emissivity material exhibits a phase transition in which the emissivity changes significantly with temperature change. The variable emissivity material exhibits a high emissivity at a temperature higher than the phase transition temperature and a low emissivity at a temperature lower than the phase transition temperature. Specifically, the emissivity of the variable emissivity material at 353 K is 0.5 or more, and the emissivity of the variable emissivity material at 203 K is 0.3 or less.

[0020] In order to obtain an appropriate phase transition temperature, the valence of Mn in the variable emissivity material is preferably 3.21 or more and 3.27 or less.

[0021] The variable emissivity material may be a perovskite-type oxide represented by La (1-x-y) Sr x Ca y MnO 3 In this case, in order to obtain an appropriate phase transition temperature, it is preferable that 0.107 ≦ x ≦ 0.138 and 0.103 ≦ y ≦ 0.132.

[0022] The difference between the emissivity of the variable emissivity material at 353 K and the emissivity at 203 K is preferably 0.4 or more.

[0023] The emissivity of the variable emissivity material at 353 K is preferably 3 times or more the emissivity of the variable emissivity material at 203 K.

[0024] The variable emissivity material can be used, for example, as a heat radiating material on the high temperature side of the phase transition temperature and as a heat insulating material on the low temperature side of the phase transition temperature.

[0025] [Examples] 1. Preparation of variable emissivity material According to the procedure shown in FIG. 1, a variable emissivity material represented by La (1-x-y) Sr x Ca y MnO 3 was prepared (manufactured).

[0026] First, according to the target x and y in the composition formula La (1-x-y) Sr x Ca y MnO 3 a plurality of types of raw material powders were weighed and mixed (step S1). Here, as the plurality of types of raw material powders, oxides, carbonates, hydroxides, etc. of each metal element can be used. The plurality of types of raw material powders are, for example, La 2 O 3 powder, CaCO3 Powder, SrCO 3 Powder, MnCO 3 etc. Ethanol was added to the weighed raw material powders, and the slurry was obtained by pulverizing and mixing them with a ball mill. The slurry was dried to obtain a mixed powder.

[0027] The above-mentioned mixed powder was calcined at 600 - 1200 °C for 1 - 10 hours in an air atmosphere, for example, to obtain a calcined powder (step S2).

[0028] A dispersant, a binder, and ethanol were added to the above-mentioned calcined powder, followed by pulverizing and mixing to obtain a slurry. The obtained slurry was dried to obtain a granulated powder. By press-molding this granulated powder, a molded body with a predetermined shape was obtained (step S3). For example, a disk-shaped molded body was obtained by uniaxially pressing the granulated powder at a pressure of 150 MPa using a mold with a diameter of 30 mm.

[0029] The above-mentioned molded body was subjected to a debinding (removing the binder) treatment by holding it at 500 - 800 °C for 2 - 10 hours in an air atmosphere, for example (step S4).

[0030] The obtained molded body after debinding was fired by holding it at 900 - 1500 °C for 1 - 100 hours in an air atmosphere, for example, to obtain a fired body (step S5).

[0031] The above-mentioned fired body was processed, for example, by double-sided polishing to have a shape with a predetermined thickness, to obtain elements (samples 1 - 6) of the variable emissivity material (step S6).

[0032] 2. Test It was confirmed by XRD (X-ray Diffraction) that the obtained variable emissivity material has a perovskite-type crystal structure.

[0033] By performing elemental analysis of the variable emissivity material using XRF (X-ray Fluorescence) and XPS (X-ray Photoelectron Spectroscopy), x and y in the composition formula were determined.

[0034] The valence of Mn in the variable emissivity material was determined by XPS. Specifically, XPS measurement was performed on the cross-section exposed by breaking the element of the variable emissivity material in vacuum. Then, by performing peak fitting of the obtained XPS spectrum, the stoichiometric ratio of trivalent Mn and tetravalent Mn was calculated, and the valence (average value) of Mn was determined.

[0035] Using the obtained element of the variable emissivity material, the emissivity was measured in the temperature range of 193 to 373 K.

[0036] 3. Results Table 1 shows x and y, the valence of Mn, and the phase transition temperature calculated from the results of elemental analysis using XPS for each of Samples 1 to 6. The phase transition temperature was determined based on the temperature dependence of the emissivity.

[0037]

Table 1

[0038] From Table 1, the Mn valence increases as x and y increase. The phase transition temperature also shows a tendency to increase as x and y increase.

[0039] Figure 2 is a graph showing the temperature dependence of the emissivity of Samples 1 to 6. The phase transition temperature in Table 1 is defined as the temperature at which the emissivity changes rapidly, that is, the temperature at which the slope in Figure 2 becomes very large.

[0040] From the comparison between the auxiliary line shown by the dashed line in Figure 2 and the markers, all of Samples 1 to 6 show an emissivity of 0.5 or more at 353 K and an emissivity of 0.3 or less at 203 K. Therefore, La(1-x-y) Sr x Ca y MnO 3 When constructing a variable emissivity material with [substances not translated], it has been found that when 0.107 ≤ x ≤ 0.138 and 0.103 ≤ y ≤ 0.132, a variable emissivity material showing a preferable change in emissivity can be obtained.

[0041] Also, the phase transition phenomenon in [substances not translated] is considered to be controllable in terms of the phase transition temperature by the number of d electrons of Mn, that is, the valence of Mn, because it is greatly affected by the interaction between the d electron spins of Mn. According to the above tests, when the valence of Mn is 3.21 or more and 3.27 or less, [substances not translated] is considered to show a preferable change in emissivity as a variable emissivity material. Here, the metal species of A does not have to be [substances not translated]. 3 3 (1-x-y) Sr x Ca y

[0042] Table 2 shows, for each of Samples 1 to 6, the difference between the emissivity at 353 K and the emissivity at 203 K, and the ratio of the emissivity at 353 K to the emissivity at 203 K. The difference between the emissivity at 353 K and the emissivity at 203 K is the value obtained by subtracting the emissivity at 203 K from the emissivity at 353 K. The ratio of the emissivity at 353 K to the emissivity at 203 K is the value obtained by dividing the emissivity at 353 K by the emissivity at 203 K. In Table 2, E(353K) and E(203K) represent the numerical values of the emissivity at 353 K and 203 K, respectively.

[0043]

Table 2

[0044] From Table 2, the difference between the emissivity at 353 K and the emissivity at 203 K for Samples 2 to 6 is 0.4 or more, and the change in emissivity is particularly large. Therefore, referring to Table 1, [substances not translated] (1-x-y) Sr x Ca y MnO 3 ​​​When forming a variable emissivity material, it is particularly preferable that 0.118 ≦ x ≦ 0.138 and 0.112 ≦ y ≦ 0.132. Or, AMnO 3 When forming a variable emissivity material, it is particularly preferable that the valence of Mn is 3.23 or more and 3.27 or less.

[0045] According to Table 2, the ratio of the emissivity at 353 K to the emissivity at 203 K for Samples 3 to 6 is 3 or more, and the change in emissivity is particularly large. Therefore, referring to Table 1, La (1-x-y) Sr x Ca y MnO 3 When forming a variable emissivity material, it is particularly preferable that 0.124 ≦ x ≦ 0.138 and 0.118 ≦ y ≦ 0.132. Or, AMnO 3 When forming a variable emissivity material, it is particularly preferable that the valence of Mn is 3.24 or more and 3.27 or less.

[0046] <Other Embodiments> (1) The variable emissivity material of the example was an element formed by double-side polishing a disk-shaped molded body, but the shape of the variable emissivity material does not have to be disk-shaped. For example, the variable emissivity material of the present disclosure may be in the form of powder, thin film, or the like. (2) The manufacturing method of the variable emissivity material is not limited to the method described in the example. The variable emissivity material of the present disclosure may be manufactured, for example, by vapor deposition, sputtering, PLD (Pulsed Lazer Deposition), CVD (Chemical Vapor Deposition), sol-gel method, or the like.

Claims

1. AMnO ３ A perovskite-type variable emissivity material represented by: A includes at least one of rare earth ions of La, Pr, Nd, and Sm, and at least one of alkaline earth metal ions of Ca, Sr, and Ba, A variable emissivity material having an emissivity of 0.5 or more at 353K and an emissivity of 0.3 or less at 203K.

2. 2. The variable emissivity material of claim 1, wherein the valence of Mn is 3.21 or more and 3.27 or less.

3. La （１－ｘ－ｙ） Sr ｘ Ca ｙ MnO ３ It is expressed as 2. The variable emissivity material of claim 1 , wherein 0.107≦x≦0.138 and 0.103≦y≦0.

132.

4. 2. The variable emissivity material of claim 1, wherein the difference between the emissivity at 353 K and the emissivity at 203 K is 0.4 or greater.

5. 10. The variable emissivity material of claim 1, wherein the emissivity at 353K is at least three times its emissivity at 203K.

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