Ceramic film and manufacturing method thereof, emitter, and thermophotovoltaic power generation device

Abstract

To provide a ceramic film for a TPV power generation device that has sufficient strength and can acquire a desirable radiation spectrum.SOLUTION: A ceramic film 20 including a pore formed on a substrate includes: a plurality of high-density regions 1 having a density that is larger than an average density of the whole ceramic film; and a plurality of low-density regions 2 having a density that is smaller than the average density of the whole ceramic film. The high-density regions 1 and the low-density regions 2 are stacked in layers. The ceramic film comprises a rare-earth element-containing oxide ceramic.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a ceramic film and a method for manufacturing the same, an emitter, and a thermophotovoltaic power generation device. [Background technology]

[0002] Thermo-Photo-Voltaic (TPV) power generation is a technology that converts thermal radiation into electricity using photovoltaic cells, and is expected to achieve high-efficiency power generation by controlling the radiation spectrum. TPV power generation has a wide range of applications because it can use a variety of heat sources, and it is attracting attention as a power generation technology with a high energy density per weight.

[0003] The basic configuration of a TPV power generation device is shown in Figure 13. The TPV power generation device 100 shown in Figure 13 converts heat generated by a combustion device or heat generated by collecting sunlight into infrared light using an emitter 101, and the emitted infrared light is incident on a photovoltaic (PV) element 102, where it is converted into electricity.

[0004] A variety of materials have been reported for the emitter 101. To increase the efficiency of thermophotovoltaic power generation, it is necessary to narrow the spectrum of infrared light emitted by the emitter 101 to a wavelength that is compatible with the photoelectric conversion element 102. Research into photonic crystals and metamaterials as emitters has progressed, but there have been issues with size, heat resistance, and cost reduction. Emitters made of ceramics have been reported as one means of solving these issues.

[0005] Patent Document 1 describes the composition R3Al5O 12 or R3Ga5O 12 The paper discloses a ceramic emitter that includes a polycrystalline body having a garnet structure (R: rare earth element), and has pores with a porosity of 20% to 40% within the polycrystalline body. The pores are connected, but include portions that are not linearly continuous. Since the pores do not include portions that are linearly continuous from the heat supply surface to the emission surface of the ceramic emitter, good wavelength selectivity can be achieved.

[0006] Furthermore, Non-Patent Documents 1 and 2 report examples of applying a ceramic film to the emitter of a TPV power generation device. Non-Patent Document 1 reports that Er 1.5 Y 1.5 AlO 12 Non-Patent Document 2 describes an emitter in which a ceramic film is formed on a MoSi2 substrate. 12 An emitter in which a ceramic film is deposited on a SiC substrate is described. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6620751 [Non-patent literature]

[0008] [Non-Patent Document 1] WJ Tobler et al., “High-performance selective Er-doped YAG emitters for thermophotovoltaics”, Applied Energy 85, 483-493 (2008) [Non-patent document 2] A. Licciulli et al., “Porous Garnet Coatings Tailoring the Emissivity of Thermostructural Materials”, Journal of Sol-Gel Science and Technology 32, 247-251 (2004) Summary of the Invention [Problem to be solved by the invention]

[0009] For example, if a ceramic film could be coated on the combustor surface of a fuel-fired TPV power generation system as an emitter, efficient heat transfer from the heat source to the emitter would be possible, and the power generation system would be expected to become more efficient. Thus, there is a need for a technology for forming emitters that can be easily combined with various types of heat sources. However, ceramic films generally have strength-related issues, such as breakage due to temperature changes and peeling from the substrate.

[0010] Furthermore, the ceramic film described in Non-Patent Document 1 is formed on a substrate, but is dense and has the problem of transmitting radiation from the substrate. The ceramic film described in Non-Patent Document 2 is porous, but it is difficult to control the porosity using the sol-gel method, and the porosity is very high at 57%. This results in a problem of a low concentration of Er ions contained in the emitter to generate wavelength-selective radiation, resulting in a low radiation intensity.

[0011] As described above, when forming a film of a ceramic emitter to match the shape of a heat source, there are problems such as strength issues and difficulty in controlling the porosity, making it difficult to obtain a desirable radiation spectrum.

[0012] An object of the present disclosure is to provide a ceramic film that has sufficient strength and is capable of obtaining a desirable radiation spectrum, a method for manufacturing the same, an emitter, and a thermophotovoltaic power generation device. [Means for solving the problem]

[0013] A ceramic film according to one embodiment is a ceramic film having pores formed on a substrate, and includes a plurality of high-density regions having a density higher than the average density of the entire ceramic film, and a plurality of low-density regions having a density lower than the average density of the entire ceramic film.

[0014] In one embodiment of the method for producing a ceramic film, the ceramic film is formed on a substrate by plasma-assisted aerosol deposition.

[0015] An emitter according to one embodiment comprises the ceramic film formed on a heat source, and converts heat from the heat source into infrared rays.

[0016] A thermophotovoltaic power generation device according to one embodiment comprises an emitter that converts heat from a heat source into infrared rays, and a photoelectric conversion cell that converts the infrared rays emitted from the emitter into electric power, wherein the emitter is made of the ceramic film described above formed on the heat source. [Effects of the Invention]

[0017] According to the embodiments, it is possible to provide a ceramic film that has sufficient strength and is capable of obtaining a desirable radiation spectrum, a method for manufacturing the same, an emitter, and a thermophotovoltaic power generation device. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic diagram showing the configuration of a thermophotovoltaic power generation device according to an embodiment. [Figure 2] 1A and 1B are diagrams illustrating an example of the structure of a ceramic film according to an embodiment. [Figure 3] 10A and 10B are diagrams illustrating another example of the structure of the ceramic film according to the embodiment. [Figure 4] 10A and 10B are diagrams illustrating another example of the structure of the ceramic film according to the embodiment. [Figure 5] 1 is a schematic diagram illustrating a method for manufacturing a ceramic film according to an embodiment using a plasma-assisted aerosol deposition apparatus. [Figure 6] 1 is a schematic diagram illustrating a method for manufacturing a ceramic film according to an embodiment using a plasma-assisted aerosol deposition apparatus. [Figure 7] 1 shows an external photograph of a ceramic film deposition heater when an Er3Ga5O12 ceramic film is deposited on a silicon nitride heater (during film deposition), and an external photograph of the ceramic film deposition heater when heated (during heating), according to Example 1. [Figure 8]FIG. 1 is a diagram showing an emissivity spectrum obtained by FT-IR measurement of thermal radiation from the Er3Ga5O12 ceramic film formed on the ceramic film-forming heater of Example 1. [Figure 9] 10 is an SEM image showing a cross section of an Er3Ga5O12 ceramic film formed on an Inconel substrate according to Example 2. [Figure 10] 10 is an enlarged image of the vicinity of the center in the thickness direction of the ceramic film in FIG. [Figure 11] This is an enlarged image of Figure 10. [Figure 12] 10 is an enlarged image of the surface of the ceramic film in FIG. 9. [Figure 13] This is an enlarged image of the vicinity of the substrate interface of the ceramic film in FIG. [Figure 14] 1 is a schematic diagram showing the basic configuration of a thermophotovoltaic power generation device. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are designated by the same reference numerals, and for clarity of explanation, duplicate explanations will be omitted as necessary.

[0020] The present embodiment relates to a ceramic film used in a wavelength-selective emitter of a thermophotovoltaic (TPV) power generation device. Fig. 1 is a schematic diagram showing a configuration example of a TPV power generation device 100 according to the embodiment. As shown in Fig. 1, the TPV power generation device 100 according to the embodiment includes an emitter 101A and a photoelectric conversion element 102. The emitter 101A converts heat from a heat source into thermal radiation (infrared rays).

[0021] The heat source is, for example, a combustion device that mixes fuel and air and burns them to generate heat, and its mechanism and structure are not limited. Liquid fuel or gas can be used as the fuel. The heat source may also be structured to supply oxygen or the like instead of air. The converted infrared rays are emitted from the surface of the emitter 101A.

[0022] The photoelectric conversion element 102 converts the infrared rays emitted from the emitter 101A into electric power. The photoelectric conversion element 102 is sensitive to light in a specific wavelength band, and has a wavelength band of light that can be photoelectrically converted. Therefore, it is desirable that the wavelength band of the infrared rays emitted from the emitter 101A coincides with the region in which the photoelectric conversion element 102 has high sensitivity. The photoelectric conversion element 102 is made of a silicon semiconductor, a compound semiconductor, or the like. The electric power generated by the photoelectric conversion element 102 is collected via wiring (not shown).

[0023] Emitter 101A is a wavelength-selective heat radiator that covers the surface of the heat source. Emitter 101A selectively emits light of a specific wavelength range to which photoelectric conversion element 102 is highly sensitive. If emitter 101A is made of a material that selectively emits light of a specific wavelength range to which photoelectric conversion element 102 is highly sensitive, the power generation efficiency of TPV power generation device 100 can be improved.

[0024] As a material for the emitter 101A, for example, a ceramic film 20 shown in FIG. 2 is used. FIG. 2 is a diagram showing an example of the structure of the ceramic film 20 according to the embodiment. This ceramic film 20 is formed on a substrate (not shown) and has pores. In this example, the ceramic film 20 is formed on a heat source as the substrate.

[0025] 2, the ceramic film 20 has, within a film of the same composition, a plurality of high-density regions 1 having a density higher than the average density of the entire ceramic film 20, and a plurality of low-density regions 2 having a density lower than the average density of the entire ceramic film 20. In other words, the porosity of the high-density regions 1 is lower than the average porosity of the entire ceramic film 20, and the porosity of the low-density regions 2 is higher than the average porosity of the entire ceramic film 20.

[0026] It is necessary that there be a plurality of high-density regions 1 and a plurality of low-density regions 2, but there are no restrictions on the distribution state or the size of each region. The size of the particles that form the ceramic film 20 is generally about 0.1 μm to 5 μm. Because the high-density regions 1 and the low-density regions 2 are made up of particle aggregates, it is desirable that the size of each region be several μm or more.

[0027] The thickness of the ceramic film 20 is not particularly limited, and can be, for example, 30 μm or more and 1 mm or less. The upper limit of the size of each region is smaller than the thickness of the ceramic film 20.

[0028] By providing a layer (low-density region 2) in the ceramic film 20 with a porosity greater than the average porosity, the low-density region 2 acts as a stress relief layer, even if thermal expansion and contraction occur during heating and cooling, and it is possible to prevent peeling or damage to the ceramic film 20. In order for the low-density region 2 to function as a stress relief layer, it is desirable that the thickness of the low-density region 2 be several μm or more. However, if the size of the low-density region 2 becomes too large, the mechanical strength of that part will deteriorate, so it is desirable that the size be 20 μm or less, preferably 10 μm or less.

[0029] Furthermore, it is desirable that the particle size of the ceramic in the low-density region 2 is 1 μm or less. The reason for this is that, although regions with high porosity generally have low mechanical strength, by forming said region with ceramic particles with a particle size of 1 μm or less and high surface energy, it is possible to maintain strength.

[0030] The average porosity of the ceramic film 20 is preferably 20% or more. Thermal radiation from a heat source irradiating the ceramic film 20 is scattered by the pores, reducing the amount of thermal radiation that penetrates the ceramic film. On the other hand, the infrared rays emitted from the ceramic film 20 have sufficient radiation intensity at their peak wavelengths. As a result, wavelength-selective thermal radiation by the ceramic film 20 is achieved.

[0031] Furthermore, it is desirable that the average porosity of the ceramic film 20 be 40% or less. The reason for this is that as the porosity of the ceramic film 20 increases, the ion concentration for generating wavelength-selective radiation decreases, and the radiation intensity of the peak wavelength of infrared rays decreases.

[0032] Furthermore, if the porosity of the ceramic is 40% or more, the pores are connected to form linear spaces, allowing the thermal radiation from the heat source to pass through. This impairs the wavelength selectivity of the emitter 101. Furthermore, if the porosity of the ceramic is 40% or more, the mechanical strength decreases, making it unsuitable for use as the emitter 101 of the TPV power generation device 100. Therefore, in order to suppress unnecessary thermal radiation from the heat source and obtain the radiation intensity of the desired peak wavelength, the porosity is preferably between 20% and 40%.

[0033] As shown in Figure 2, it is desirable that the high density region 1 and the low density region 2 are layered one on top of the other. In the example shown in Figure 2, the high density region 1 and the low density region 2 of a certain thickness are alternately layered one on top of the other. The interface between each layer does not have to be smooth. For example, as shown in Figure 3, the interface between the high density region 1 and the low density region 2 may be wavy.

[0034] Alternatively, one region may be contained within the layer of the other region, as shown in Fig. 4. In the example shown in Fig. 4, a high-density region 1 and a low-density region 2 are layered one on top of the other, and the high-density region 1 contains a plurality of low-density regions 2 with elliptical cross sections and different sizes in the layer, and the low-density region 2 contains a plurality of high-density regions 1 with elliptical cross sections and different sizes in the layer.

[0035] The composition of the ceramic film 20 is not particularly limited. Since the ceramic film 20 is intended for use as the photoelectric conversion element 102 of the TPV power generation device 100, it is desirable that the ceramic film 20 be made of an oxide ceramic containing a rare earth element. More preferably, the composition of the ceramic film 20 is R3Ga5O 12 or R3Al5O 12 (R: rare earth element).

[0036] Next, a method for manufacturing a ceramic film 20 according to an embodiment will be described with reference to Figures 5 and 6. The method for manufacturing the ceramic film 20 is not particularly limited, but a film formation method using a plasma-assisted aerosol deposition method is preferred. Figures 5 and 6 are schematic diagrams illustrating a method for manufacturing a ceramic film according to an embodiment using a plasma-assisted aerosol deposition apparatus 200.

[0037] Plasma-assisted aerosol deposition is a method of forming a film by aerosol deposition (AD) with the assistance of plasma energy. Here, "aerosol" refers to fine particles of solid or liquid suspended in a gas. The "AD" is a film formation method in which an aerosol containing raw material powder is generated and sprayed from a nozzle toward a substrate to deposit the powder.

[0038] Fig. 5 shows a portion of the configuration of a plasma-assisted aerosol deposition apparatus 200. As shown in Fig. 5, the plasma-assisted aerosol deposition apparatus 200 includes a nozzle 3 and a radio frequency (RF) coil 4. A ceramic powder aerosol 5 is generated by blowing gas into a container (not shown) that contains ceramic powder having the same composition as the ceramic film 20 to be formed. The ceramic powder aerosol 5 is sprayed from the nozzle 3 equipped with the RF coil 4.

[0039] The RF coil 4 is a part of the plasma generator. The ceramic powder aerosol 5 is introduced into the RF coil 4 and converted into plasma, becoming a plasma-passing aerosol 6. The plasma-passing aerosol 6 collides with a substrate 7 placed in a decompressed chamber (not shown), and a ceramic film 20 is formed on the substrate 7 at room temperature.

[0040] The gas that carries the ceramic powder aerosol 5 and the plasma-passing aerosol 6 is not limited, but may be, for example, Ar or He. The nozzle 3 may have any shape, such as a circular outlet. A stage (not shown) on which the substrate 7 is placed is moved so that the center of the outlet of the nozzle 3 scans over the substrate 7, thereby forming a ceramic film 20 over the entire surface of the substrate 7. The substrate 7 may be fixed and a movable nozzle 3 may be used, or both the substrate 7 and the nozzle 3 may be movable.

[0041] The average porosity of the ceramic film 20 can be controlled by various deposition parameters (gas flow rate, chamber pressure, plasma power, stage movement speed, etc.). In addition, the low-porosity region (high-density region 1) and high-porosity region (low-density region 2) in the ceramic film 20 can be obtained, for example, by changing the deposition parameters during deposition.

[0042] It is also possible to form high-density regions 1 and low-density regions 2 by moving a stage on which the substrate 7 is placed and scanning the substrate 7 with the center of the nozzle 3's outlet. FIG. 6 shows a nozzle center trajectory 8 on the substrate 7. In the example shown in FIG. 6, the stage moves so that the nozzle 3 moves from the upper left of the substrate 7 in the +X direction, then moves a predetermined number of steps in the -Y direction at the right end of the substrate 7, turns around, and moves in the -X direction. By repeating this process, the nozzle center trajectory 8 shown in FIG. 6 is obtained.

[0043] The aerosol 6 that passes through the plasma part and is sprayed from the nozzle 3 usually has a diameter of 10 mm or more, but the plasma intensity and particle concentration in the aerosol 6 that passes through the plasma part have a spatial distribution. Therefore, the ceramic film 20 that first adheres to the substrate 7 has areas with high and low density.

[0044] As the aerosol 6 passing through the plasma part moves and deposits sequentially in this state where there are high and low density areas, high and low density areas also occur in the thickness direction of the ceramic film 20. Furthermore, as shown by the nozzle center trajectory 8 in Figure 6, during film formation, the nozzle 3 moves in steps in the -Y direction by moving the substrate 7. The distance of this step movement in the -Y direction is sufficiently smaller than the size of the aerosol 6 passing through the plasma part that is sprayed onto the substrate 7. This makes it possible to create an even more uniform distribution of high and low porosity areas.

[0045] Thus, according to the embodiment, a film formation method using plasma-assisted aerosol deposition can easily form regions (high-density region 1) and regions (low-density region 2) with a low porosity relative to the average porosity in a ceramic film 20 of the same composition.

[0046] A specific embodiment of the emitter 101 of the TPV power generation device 100 will now be described. Example 1 In Example 1, ErGaO was synthesized by solid-state reaction of ErO powder and GaO powder, and then pulverized in a ball mill. 12 The powder was used as a raw material and the average particle size of the raw material powder was 0.7 μm. The deposition conditions were Ar gas flow rate of 20 L / min, plasma power of 2 kW, chamber pressure of 105 Pa, stage movement speed in the X direction of 10 mm / sec, and stage movement step in the Y direction of 1 mm.

[0047] The stage was repeatedly moved to form Er3Ga5O films with thicknesses of 40 μm and 160 μm. 12 Figure 7 shows a photograph of the appearance of the ceramic heater when a 40 μm-thick ErGG ceramic film was formed on the silicon nitride heater (at the time of film formation) and a photograph of the appearance of the ceramic heater when heated to approximately 1000°C (at the time of heating).

[0048] The ErGG ceramics film showed no cracks or peeling even after heating. A 160 μm thick ErGG ceramics film was also formed on a silicon nitride heater in the same way and its appearance was observed after heating, but almost no difference in appearance was observed.

[0049] Figure 8 shows the emissivity spectrum obtained by FT-IR measurement of the thermal radiation from the ErGG ceramics film formed on the silicon nitride heater in Example 1. Figure 8 shows the emissivity spectrum measured when the surface temperature of the ErGG ceramics film was heated to approximately 1000°C using the silicon nitride heater. As shown in Figure 8, wavelength-selective thermal radiation can be confirmed for both the 40 μm and 160 μm thick ErGG ceramics films.

[0050] The ErGG ceramic film was selected as an emitter compatible with GaSb photoelectric conversion elements. The bandgap wavelength of GaSb is 1.7 μm, and the manufactured ErGG ceramic film exhibits wavelength selectivity suited to that wavelength. The ErGG ceramic film with a thickness of 160 μm exhibits higher wavelength selectivity than the one with a thickness of 40 μm.

[0051] Example 2 An ErGG ceramic film was formed on an Inconel alloy substrate as a base material under the same film-forming conditions as in Example 1, and the cross section was processed by ion polishing. The results of SEM observation are shown in Figures 9 to 11. Figure 9 is a low-magnification SEM image. In Figure 9, it can be seen that there are high-density regions 1, which are bright contrast areas, and low-density regions 2, which are dark contrast areas, on the Inconel alloy substrate 11.

[0052] Figure 10 is an enlarged image of the vicinity of the center in the thickness direction of the ceramic film in Figure 9. Figure 10 shows that the film is made up of layers of high density regions 1 and low density regions 2. The thickness of each layer is approximately 4 μm to 10 μm.

[0053] Figure 11 is an enlarged image of Figure 10. It can be seen that the low-density region 2 is made up of particles with a diameter of 1 μm or less, while the high-density region 1 is made up of particles with a diameter exceeding 1 μm, due to the progress of particle sintering. It is believed that these structures were obtained by depositing the film using the plasma-assisted aerosol deposition device 200 while moving the substrate relative to the nozzle 3. Furthermore, the porosity was calculated by image analysis of the SEM image in Figure 11, and was found to be 40%.

[0054] Figure 12 is an enlarged image of the vicinity of the surface of the ceramic film in Figure 9. Also, Figure 13 is an enlarged image of the vicinity of the substrate interface of the ceramic film in Figure 9. The porosities calculated by image analysis of these SEM images were 38% and 33%, respectively.

[0055] As described above, it has been confirmed that the ceramic film 20 including the high-density region 1 and the low-density region 2 according to the embodiment has wavelength-selective thermal emission suitable for the emitter 101 of the TPV power generation device 100, and also has excellent heat resistance. Furthermore, SEM observation has confirmed that the ceramic film 20 including the high-density region 1 and the low-density region 2 according to the embodiment can be obtained by a plasma-assisted aerosol deposition method. It can be considered that the high heat resistance of the ceramic film 20 according to the embodiment is due to the presence of the low-density region 2 in the film.

[0056] As described above, according to the embodiment, it is possible to provide an emitter for TPV power generation that has excellent wavelength selectivity and is made of a ceramic film that does not peel off or break from the substrate even when subjected to heating and cooling cycles. Also, it is possible to provide a method for manufacturing an emitter made of the ceramic film.

[0057] The present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the invention. [Explanation of symbols]

[0058] 1 High density area 2 Low density area 3 nozzles 4 RF coils 5. Ceramic powder aerosol 6. Aerosol passing through the plasma section 7 Base material 8 Nozzle center trajectory 9 particles 10 vacancies 20 Ceramic membrane 100 TPV power generation equipment 101 Emitter 101A Emitter 102 Photoelectric conversion element 200 Plasma-assisted aerosol deposition device

Claims

1. A ceramic film having pores formed on a heat source, which converts heat from the heat source into infrared light, a plurality of high-density regions having a density higher than the average density of the entire ceramic film; a plurality of low-density regions having a density lower than the average density of the entire ceramic film; Including, The high density regions and the low density regions are alternately layered. Ceramic membrane.

2. The insulating film includes at least one of a low-density portion provided in a part of the high-density region and a high-density portion provided in a part of the low-density region, The ceramic film according to claim 1.

3. the ceramic film is made of an oxide ceramic containing a rare earth element; The ceramic film according to claim 1 or 2.

4. The ceramic film has a composition of R ３ Ga ５ O １２ or R ３ Al ５ O １２ (R: rare earth element), The ceramic film according to claim 3.

5. The particle size of the ceramic particles in the low-density region is 1 μm or less. The ceramic film according to claim 1 or 2.

6. The ceramic film according to claim 1 or 2 is formed on a heat source by a plasma-assisted aerosol deposition method. Method for manufacturing ceramic membranes.

7. the heat source is moved relative to a nozzle that ejects an aerosol containing raw material powder, and the ceramic film is formed on the heat source. The method for producing a ceramic film according to claim 6.

8. The ceramic film according to claim 1 or 2 is formed on a heat source and converts heat from the heat source into infrared rays. Emitter.

9. an emitter that converts heat from a heat source into infrared light; a photoelectric conversion cell that converts the infrared rays emitted from the emitter into electric power, The emitter is made of the ceramic film according to claim 1 or 2 formed on the heat source. Thermophotovoltaic power generation device.

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