Variable emissivity material

Abstract

To provide a variable emissivity material that exhibits a large change in emissivity and offers superior hardness.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 and Sr. The variable emissivity material contains, as impurities, 30 ppm or more of Al, 20 ppm or more of Ti, 19 ppm or more of Fe, 30 ppm or more of Y, 600 ppm or more of Zr, 3 ppm or more of Nb, and 15 ppm or more of Ba.SELECTED DRAWING: None

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] Since the thermal control device as described above can be applied to equipment used in outer space, houses, automobiles, etc., there is a demand for the development of a variable emissivity material that not only shows a large change in emissivity but also has impact resistance.

[0005] The present disclosure has been completed based on the above circumstances, and an object thereof is to provide a variable emissivity material that shows a large change in emissivity and has excellent hardness.

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 and Sr, and as impurities, it contains 30 ppm or more of Al, 20 ppm or more of Ti, 19 ppm or more of Fe, 30 ppm or more of Y, 600 ppm or more of Zr, 3 ppm or more of Nb, and 15 ppm or more of Ba.

Advantages of the Invention

[0007] According to the present disclosure, a variable emissivity material that exhibits a large change in emissivity and is excellent in hardness can be provided.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Modes 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 and Sr, and as impurities, it contains 30 ppm or more of Al, 20 ppm or more of Ti, 19 ppm or more of Fe, 30 ppm or more of Y, 600 ppm or more of Zr, 3 ppm or more of Nb, and 15 ppm or more of Ba.

[0010] With such a configuration, it is possible to provide a variable emissivity material that exhibits a large change in emissivity and has excellent hardness.

[0011] (2) In the above (1), it is preferable that the average particle size D50 is 5.3 μm or less.

[0012] With such a configuration, the hardness of the variable emissivity material can be further increased.

[0013] [Details of Embodiment] Specific examples of the embodiments of the present disclosure will be described with reference to FIGS. 1 and 2. It should be noted that the present disclosure is not limited to these examples, and is intended to be represented by the claims and to include all modifications within the meaning and scope equivalent to the claims.

[0014] 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 of La, Pr, Nd, and Sm and at least one of alkaline earth metal ions of Ca, Sr, and Ba.

[0015] 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.

[0016] The variable emissivity material further contains, as impurities, 30 ppm or more of Al, 20 ppm or more of Ti, 19 ppm or more of Fe, 30 ppm or more of Y, 600 ppm or more of Zr, 3 ppm or more of Nb, and 15 ppm or more of Ba.

[0017] The average particle size D50 of the variable emissivity material is preferably 5.3 μm or less.

[0018] For example, it is preferable that the emissivity of the variable emissivity material at 353K is 0.6 or more, and the emissivity of the variable emissivity material at 203K is 0.3 or less.

[0019] 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.

[0020] [Examples] 1. Preparation of variable emissivity material According to the procedure shown in Fig. 1, La 0.775 Sr 0.115 Ca 0.110 MnO 3 The variable emissivity material represented by was prepared (manufactured). Note that the coefficients of each metal element in the above composition formula are based on the stoichiometric ratio of each metal ion during weighing.

[0021] First, 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, CaCO 3 powder, SrCO 3 powder, MnCO 3 powder, etc. Ethanol was added to the weighed raw material powders, and the slurry was obtained by pulverizing and mixing with a ball mill. The slurry was dried to obtain a mixed powder.

[0022] The above mixed powder was calcined at 600 - 1200°C for 1 - 10 hours in, for example, an air atmosphere to obtain a calcined powder (step S2).

[0023] A dispersant, a binder, and ethanol were added to the above calcined powder, pulverized and mixed 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, by uniaxially pressing the granulated powder using a mold with a diameter of 30 mm at a pressure of 150 MPa, a disk-shaped molded body was obtained.

[0024] The above molded body was subjected to a debinding (debinder) treatment by holding it at 500 to 800 °C for 2 to 10 hours in, for example, an air atmosphere (step S4).

[0025] The obtained debound molded body was fired by holding it at a predetermined firing temperature (for example, 1400 °C) for 1 to 100 hours in, for example, an air atmosphere to obtain a fired body (step S5).

[0026] The above fired body was processed, for example, by double-sided polishing into a shape having a predetermined thickness to obtain elements (samples 1 to 9) of the variable emissivity material (step S6).

[0027] 2. Test The obtained variable emissivity material was confirmed to have a perovskite crystal structure by XRD (X-ray Diffraction).

[0028] The amount of impurities contained in the elements (samples 1 to 4) of the obtained variable emissivity material was detected by inductively coupled plasma mass spectrometry (ICP-MS).

[0029] The polished surfaces of the elements (samples 4 to 9) of the obtained variable emissivity material were photographed at a magnification of 1000 using a scanning electron microscope (SEM: Scanning Electron Microscope) to obtain SEM images (backscattered electron images). The average particle size D50 was determined from the particle sizes of a plurality of crystal particles included in the SEM images.

[0030] The emissivity of the obtained element (sample 4) of the variable emissivity material was measured in the temperature range of 193 to 373 K.

[0031] The martensite hardness of the elements (samples 1 to 9) of the obtained variable emissivity material was measured using a dynamic ultra-micro hardness tester.

[0032] 3. Results Figure 2 shows the temperature dependence of the emissivity of Sample 4. Sample 4 undergoes a phase transition at approximately 235 K, and a rapid change in emissivity is observed near the phase transition temperature. Specifically, the emissivity of Sample 4 at 353 K is 0.6 or more, and the emissivity of Sample 4 at 203 K is 0.3 or less.

[0033] Table 1 shows the amount of each impurity and the martensite hardness for each of Samples 1 to 4. Since Samples 1 to 4 are all fired at the same firing temperature (1450 °C) in Step S5, it is considered that there is no significant difference in the average particle size D50 (details will be described later).

[0034]

Table 1

[0035] Here, when it is determined that the case where the martensite hardness is 2000 N / mm 2 or more is a good result, referring to Table 1, it can be said that good results are obtained for Samples 2 to 4. Therefore, it is considered preferable that the variable emissivity material contains, as impurities, 30 ppm or more of Al, 20 ppm or more of Ti, 19 ppm or more of Fe, 30 ppm or more of Y, 600 ppm or more of Zr, 3 ppm or more of Nb, and 15 ppm or more of Ba.

[0036] In Samples 2 to 4 with a large amount of impurities, there are many elements different from the main phase La 0.775 Sr 0.115 Ca 0.110 MnO 3 existing in the element. For example, since the stress applied to the crystal is dispersed, the strain field against compression is relaxed, and as a result, it is considered that the fracture hardness is improved.

[0037] Table 2 shows the firing temperature, the average particle size D50, and the martensite hardness for each of Samples 4 to 9. The amount of impurities in Samples 5 to 9 is the same as that of Sample 4.

[0038]

Table 2

[0039] It was found from Table 2 that the average particle size D50 of the variable emissivity material tended to increase as the firing temperature was increased. That is, it was shown that the average particle size D50 of the variable emissivity material can be controlled by the firing temperature.

[0040] Figure 3 is a graph plotting the martensite hardness against the average particle size D50 of the variable emissivity material based on the results of Table 2. From Figure 3, in the region where the average particle size D50 of the variable emissivity material is 5.3 μm or less, it was found that the martensite hardness tended to improve as the average particle size D50 decreased. Therefore, in order to increase the hardness of the variable emissivity material, in addition to the above-described conditions of the impurity amount, it can be said that it is particularly preferable that the average particle size D50 of the variable emissivity material be 5.3 μm or less.

[0041] <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 a vapor deposition method, a sputtering method, a PLD (Pulsed Lazer Deposition) method, a CVD (Chemical Vapor Deposition) method, a sol-gel method, or the like. (3) In the example, the variable emissivity material was La 0.775 Sr 0.115 Ca 0.110 MnO 3 However, for the variable emissivity material AMnO3 of the present disclosure, the metal species of A does not have to be La 0.775 Sr 0.115 Ca 0.110 and may not be. (4) The temperature dependence of the emissivity of the variable emissivity material shown in FIG. 3 is an example, and the emissivity values, phase transition temperatures, etc. of the variable emissivity material of the present disclosure at each temperature may be different from those shown in FIG. 3.

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 and Sr, A variable emissivity material containing, as impurities, 30 ppm or more of Al, 20 ppm or more of Ti, 19 ppm or more of Fe, 30 ppm or more of Y, 600 ppm or more of Zr, 3 ppm or more of Nb, and 15 ppm or more of Ba.

2. 2. The variable emissivity material of claim 1, having an average particle size D50 of 5.3 μm or less.

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