WO2013141180A1 - Selective light absorption film, heat collection pipe, and solar heat electricity generation device - Google Patents

Abstract

This selective light absorption film is formed on a substrate, and has: a first stacked-layer part that is stacked on the substrate and has two or more structures wherein a metal layer and a semiconductor layer alternate in order from the substrate side; a second stacked-layer part that is stacked on the first stacked-layer part and has one or more structures wherein a dielectric layer and a semiconductor layer alternate; and a third stacked-layer part that is stacked on the second stacked-layer part and comprises a dielectric layer. This selective light absorption film has high solar energy absorptivity and has low emissivity at 400°C and above.

Description

Light selective absorption film, heat collecting tube, and solar thermal power generation device

The present invention relates to a light selective absorption film, a heat collecting tube, and a solar power generation device, and in particular, a light selective absorption film suitably formed on the surface of a heat collection tube for a solar power generation device, a heat collecting tube having the light selective absorption film, And a solar thermal power generation apparatus.

Solar thermal power generation (CSP: Concentrating Solar Power), for example, condenses sunlight with a solar reflector such as a mirror to generate heat, heats a liquid such as oil with this heat, and converts this heat into steam In this power generation system, the steam turbine is rotated to generate power. The principle of power generation is basically the same as that of traditional thermal power generation, but it is an environmentally friendly power generation system that uses solar heat instead of fuel combustion for heat generation.

CSP includes a parabolic trough type, a linear Fresnel type, a dish type, and a tower type. For example, the parabolic trough type has a raindrop-shaped curved mirror serving as a solar reflector and a pipe-shaped heat collecting tube installed near the focal point of the curved mirror, and collects sunlight with the curved mirror. This is a power generation method in which a liquid such as oil that is condensed on a heat tube and flows in the heat collection tube is heated, thereby generating electric power. Compared to a tower type solar thermal power generation, it is excellent in that it is easy to construct a large-scale facility because the solar reflector is easily arranged.

The temperature of the liquid flowing through such a heat collecting tube is 400 ° C. or higher. The surface of the heat collection tube is provided with a light selective absorption film for the purpose of efficiently absorbing solar radiation energy and reducing heat radiation from the heat collection tube to the outside.

As the light selective absorption film, for example, a film using gold, silver, or platinum for an infrared region reflection layer has been proposed (for example, see Patent Document 1). However, when gold, silver, or platinum is used for the infrared region reflection layer, a barrier layer composed of a SiO _x layer is required so as to sandwich the infrared region reflection layer.

Further, as the light selective absorption film, for example, a film having a dielectric layer and one or more chromium-based layers selected from the group consisting of chromium, chromium nitride, and chromium oxynitride has been proposed (for example, Patent Document 2). However, such a light selective absorption film is mainly used in solar water heaters, and the emissivity is not necessarily low in the wavelength range of 4 to 5 μm, which corresponds to the operating temperature of the heat collecting tube in solar thermal power generation, around 400 ° C. Absent. That is, the reflectance in the above wavelength range is not necessarily high enough, and when applied to a solar heat collection heat collection tube, heat easily escapes from the heat collection tube to the outside.

Furthermore, as a light selective absorption film, for example, a film having a TiSi layer, a TiO ₂ layer, and a SiO ₂ layer has been proposed (see, for example, Patent Document 3). However, such a light selective absorption film tends to have a large number of layers, a complicated structure, and it is necessary to precisely control the film thickness of each layer.

Further, as a light selective absorption film, for example, a film having a cermet layer of Mo and SiO ₂ has been proposed (for example, see Patent Document 4). However, since Mo is used, oxidation resistance at high temperatures is not sufficient, and it is not easy to stably form a cermet layer. Further, those having a cermet layer having a graded composition of W and Al ₂ O ₃ is proposed (e.g., see Patent Document 5). However, since a film forming method using an RF sputtering method is used in part, the film forming speed is not always fast and the productivity is not sufficient.

Japanese Unexamined Patent Publication No. 2009-198170 Japanese Unexamined Patent Publication No. 2006-214654 International Publication No. 2009/51595 International Publication No. 2002/103257 International Publication No. 2009/107157

The present invention has been made to solve the above-described problems, and an object thereof is to provide a light selective absorption film having a high solar energy absorption rate and a low emissivity at 400 ° C. or higher. Another object of the present invention is to provide a heat collecting tube having such a light selective absorption film and a solar thermal power generation apparatus.

The light selective absorption film of the present invention is a light selective absorption film formed on a base material, and is laminated on the base material, and has two or more repeating structures of a metal layer and a semiconductor layer in order from the base material side. A first laminated portion having a first laminated portion, a second laminated portion laminated on the first laminated portion, and having one or more repeating structures of a dielectric layer and a semiconductor layer, and laminated on the second laminated portion. And a third laminated portion made of a dielectric layer.

The heat collection tube of the present invention is a heat collection tube having a heat collection tube main body and a light selective absorption film formed on the outer surface of the heat collection tube main body, wherein the light selective absorption film is the light selective absorption film of the present invention described above. It is characterized by being.

The solar thermal power generation device of the present invention is a solar thermal power generation device including a heat collector having a heat collecting tube and a light collecting means for concentrating sunlight on the heat collecting tube, wherein the heat collecting tube is the above-described heat collecting tube of the present invention. It is a heat tube.

The light selective absorption film of the present invention includes a first laminated portion having two or more repeating structures of a metal layer and a semiconductor layer in order from the substrate side, and a dielectric layer and a semiconductor laminated on the first laminated portion. A second laminated portion having at least one repeating structure with the layer, and a third laminated portion made of a dielectric layer laminated on the second laminated portion. According to such a structure, the solar radiation energy absorption rate can be increased, and the emissivity at 400 ° C. or higher can be decreased. Moreover, according to the heat collecting tube and solar thermal power generation apparatus of this invention, the power generation efficiency of solar thermal power generation can be improved by having such a light selective absorption film.

The external view which shows an example of the parabolic trough type | mold heat collector of embodiment. The top view which shows an example of the heat collecting tube of the heat collector shown in FIG. Sectional drawing of the heat collecting tube shown in FIG. The external view which shows an example of the linear Fresnel type heat collector of embodiment. Sectional drawing which shows an example of the receiver of the heat collector shown in FIG. Sectional drawing which shows an example of the light selective absorption film of embodiment FIG. 6 is a diagram showing the reflectance distribution and the absorptance distribution of the evaluation substrate of Example 1. The figure which shows the reflectance distribution of the board | substrate for evaluation of the comparative example 1. The figure which shows the reflectance distribution of the board | substrate for evaluation of the comparative example 2. The figure which shows the reflectance distribution of the board | substrate for evaluation of the comparative example 3.

Embodiments of the present invention will be described below.
FIG. 1 is an external view of a parabolic trough heat collector as an embodiment of a heat collector in a solar thermal power generation apparatus.

The parabolic trough heat collector 1 has a parabolic reflector 2 that is a parabolic reflector as a condensing means. The parabolic reflector 2 is supported by a reflector support 3. A heat collecting tube 4 is provided at the focal portion of the parabolic reflector 2 so as to extend along the focal portion. The heat collecting tube 4 is fixed to the parabolic reflecting mirror 2 and the reflecting mirror support 3 by a heat collecting tube support 5.

In such a parabolic trough heat collector 1, sunlight is condensed on the heat collecting tube 4 by the parabolic reflecting mirror 2, and the heat collecting tube 4 is heated by the condensed sunlight. A heat medium such as oil flows inside the heat collecting tube 4, and the heat medium inside the heat collecting tube 4 is heated by heating the heat collecting tube 4. Although not shown, the parabolic trough heat collector 1 is connected to a steam turbine, and power is generated by rotating the steam turbine using the heat of the heat medium.

FIG. 2 is a plan view showing an embodiment of the heat collecting tube 4 used in the parabolic trough type heat collector 1. FIG. 3 is a cross-sectional view of the heat collection tube 4 shown in FIG. The heat collection tube 4 has a heat collection tube main body 41 made of a steel tube or the like through which a heat medium flows, and a light selective absorption film 42 is provided on the outer surface thereof. A glass tube 43 is provided outside the heat collecting tube main body 41 at a predetermined interval so as to cover the heat collecting tube main body 41. Both ends of the heat collecting tube main body 41 and the glass tube 43 are fixed by the fixing brackets 44 so that a vacuum state is established therebetween.

FIG. 4 is an external view of a linear Fresnel type heat collector as another embodiment of the heat collector in the solar thermal power generation apparatus. Moreover, FIG. 5 is sectional drawing which shows the receiver of the linear Fresnel type heat collector shown in FIG.

The linear Fresnel type heat collector 6 has, for example, a plurality of parallel plate-like first reflecting mirrors 7 serving as light collecting means, and a position between them in parallel with and higher than these. The receiver 8 is disposed in The receiver 8 is fixed by, for example, a receiver support 9. The receiver 8 houses the heat collecting tube 4, a second reflecting mirror 81 as a condensing means for collecting the reflected light of the first reflecting mirror 7 on the heat collecting tube 4, and the second reflecting mirror 81. 1 has a case portion 82 opened on the reflecting mirror 7 side, and a glass plate 83 disposed in the opening portion of the case portion 82. The heat collecting tube 4 of the linear Fresnel type heat collector 6 has, for example, a heat collecting tube main body 41 made of a steel tube or the like in which a heat medium flows, and a light selective absorption film 42 is provided on the outer surface thereof.

FIG. 6 is a cross-sectional view showing an embodiment of the light selective absorption film 42. In addition, in FIG. 6, the heat collecting tube main body 41 used as a base material is shown collectively.

The light selective absorption film 42 has a first laminated portion 421, a second laminated portion 422, and a third laminated portion 423 in this order from the heat collecting tube main body 41 side. The first laminated portion 421 has two or more repeating structures of a metal layer 421a and a semiconductor layer 421b in order from the heat collecting tube main body 41 side. The second laminated portion 422 has one or more repeating structures of a dielectric layer 422a and a semiconductor layer 422b in order from the heat collecting tube main body 41 side. The third stacked unit 423 includes a dielectric layer 423a.

According to such a light selective absorption film 42, the first laminated portion 421 having two or more repeating structures of the metal layer 421a and the semiconductor layer 421b, and one or more repeating structures of the dielectric layer 422a and the semiconductor layer 422b. By including the second stacked portion 422 and the third stacked portion 423 having the dielectric layer 423a, the solar energy absorption rate can be increased, and the emissivity at 400 ° C. or higher can be decreased. Therefore, by applying to the one where the temperature of the heat collecting tube 4 is 400 ° C. or higher, such as the parabolic trough type heat collector 1 and the linear Fresnel type heat collector 6 described above, the power generation efficiency of the solar thermal power generation apparatus having these is improved. It can be improved effectively.

In addition, since the constituent material of each layer is relatively simple, for example, it can be easily and stably formed as compared with a material having a cermet layer. Furthermore, the basic constituent elements of the semiconductor layer and the dielectric layer can be the same kind of element, and according to such a structure, the number of targets used can be reduced, for example, in the case of manufacturing by sputtering. Can be improved. Hereinafter, each lamination part is explained.

The first stacked portion 421 mainly has a role of improving wavelength selectivity. That is, it mainly has a function of absorbing light in the visible region and near infrared region and reflecting light in the infrared region. The number of repeating structures is at least 2 or more from the viewpoint of wavelength selectivity, that is, the reflectance is close to 0% in the visible region and the near infrared region, while the reflectance is rapidly increased from the near infrared region to the infrared region. is there. The number of repeating structures is preferably larger from the viewpoint of improving the wavelength selectivity. However, if the number is increased, the number of films increases, so that productivity is lowered and heat resistance is likely to be lowered. Therefore, the number of repeating structures is preferably 2 to 10, more preferably 2 to 8, and further preferably 2 to 6.

Here, the number of repetitive structures is counted assuming that the combination of the metal layer 421a and the semiconductor layer 421b is 1. That is, when the number of repeating structures is 2, the structure is “metal layer 421a / semiconductor layer 421b / metal layer 421a / semiconductor layer 421b”.

The metal layer 421a mainly has a role of improving wavelength selectivity. The metal layer 421a is not necessarily limited as long as it is made of a metal material and has wavelength selectivity, that is, absorbs light in the visible region and near infrared region and reflects light in the infrared region. Is selected from Ag, Al, Au, Cr, Cu, Fe, Hf, In, La, Mo, Ni, Pd, Pt, Rh, Sn, Ta, Ti, Zr, or W, or one of these elements What consists of the alloy containing the above element is preferable. Among these, from the viewpoints of heat resistance, chemical stability, adhesion to the heat collecting tube main body 41 as a base material, availability, etc., those made of Cr alone or a Cr alloy are more preferable, and particularly from Cr alone. Is preferred.

Note that the constituent elements of the plurality of metal layers 421a may be the same as or different from each other, but may be the same because, for example, the number of targets used in the case of manufacturing by a sputtering method can be reduced. preferable.

The physical thickness of the metal layer 421a is preferably 60 to 200 nm for the metal layer 421a first laminated on the heat collecting tube body 41, and 5 to 10 nm for the other metal layers 421a. When there are a plurality of other metal layers 421a, the physical film thicknesses may be the same or different. When the physical film thickness of the metal layer 421a is within the above range, sufficient wavelength selectivity can be obtained and productivity can be improved. The physical film thickness of the metal layer 421a first laminated on the heat collecting tube body 41 is more preferably 65 to 200 nm, further preferably 70 to 130 nm, and the physical film thickness of the other metal layer 421a is more preferably 6 to 9 nm.

The semiconductor layer 421b has a role of improving wavelength selectivity by the metal layer 421a. The semiconductor layer 421b is made of a semiconductor material and is not necessarily limited as long as the wavelength selectivity by the metal layer 421a can be improved. However, the semiconductor layer 421b is at least one selected from Si or Ge alone or these elements. It is preferable to consist of a compound containing an element. Among these, those made of Si alone or Si compounds are more preferred, and those made of Si alone are particularly preferred. According to what consists of Si simple substance, while being excellent in heat resistance, a high absorption factor is obtained as an absorption layer in a visible region, and a low emissivity is obtained as a transparent layer in an infrared region.

Note that the constituent elements of the plurality of semiconductor layers 421b may be the same as or different from each other, but may be the same because, for example, the number of targets used in the case of manufacturing by a sputtering method can be reduced. preferable.

The physical film thickness of the semiconductor layer 421b is preferably 5 to 20 nm. Note that the physical film thickness of the semiconductor layer 421b may be the same as or different from each other, but it is preferable that both be in the above range. When the physical film thickness of the semiconductor layer 421b is within the above range, the wavelength selectivity by the metal layer 421a can be effectively improved. As for the physical film thickness of the semiconductor layer 421b, the physical film thickness of the semiconductor layer 421b closest to the heat collecting tube main body 41 is more preferably 7 to 18 nm, and the physical film thickness of the other semiconductor layer 421b is 9 to 15 nm. It is more preferable that

In the first stacked portion 421, a dielectric layer (not shown) can be provided in addition to the metal layer 421a and the semiconductor layer 421b from the viewpoint of improving heat resistance. By providing the dielectric layer, the heat resistance can be improved without affecting the optical characteristics. The dielectric layer can be provided without particular limitation as long as it is between the metal layer 421a and the semiconductor layer 421b, and may be provided only between a part or all of them. Hereinafter, such a dielectric layer is referred to as an interlayer dielectric layer.

The interlayer dielectric layer is not necessarily limited as long as it is made of a dielectric material, but one kind selected from Al, Ce, Hf, In, La, Nb, Sb, Si, Sn, Ta, Ti, Zn, and Zr An oxide of the above elements or a composite oxide containing one or more elements selected from these elements is preferable. As such, for example, Al ₂ O ₃ , CeO ₂ , HfO ₂ , In ₂ O ₃ , La ₂ O ₃ , Nb ₂ O ₅ , Sb ₂ O ₅ , SiO ₂ , SnO ₂ , Ta ₂ O ₅ , TiO ₂ , ZnO, ZrO _{2 and the} like.

Among these, an oxide of Si or Ge, or a composite oxide containing one or more elements selected from Si and Ge is preferable, and an oxide of Si or a composite oxide containing Si is particularly preferable. Are more preferable, and those made of an oxide of Si are more preferable.

When there are a plurality of interlayer dielectric layers, the constituent elements of the interlayer dielectric layer may be the same or different from each other. For example, the number of targets used in the case of manufacturing by sputtering can be reduced. Therefore, they are preferably identical to each other. From the same viewpoint, the constituent elements other than oxygen of the interlayer dielectric layer are preferably the same as the constituent elements of the semiconductor layer 421b of the first stacked portion 421.

The physical film thickness of the interlayer dielectric layer is preferably 1 to 30 nm. When there are a plurality of interlayer dielectric layers, the physical thicknesses of the interlayer dielectric layers may be the same or different from each other, but it is preferable that both are within the above range. When the physical film thickness of the interlayer dielectric layer is within the above range, the heat resistance can be effectively improved. The physical film thickness of the interlayer dielectric layer is more preferably 2 to 20 nm, and further preferably 3 to 10 nm.

The second stacked unit 422 and the third stacked unit 423 have a role of improving wavelength selectivity by optical interference.

The second stacked portion 422 has one or more repeating structures of a dielectric layer 422a and a semiconductor layer 422b. From the viewpoint of improving wavelength selectivity, the number of repeating structures in the second stacked unit 422 is at least one. The number of repeating structures is preferably larger from the viewpoint of improving the wavelength selectivity. However, if the number is increased, the number of films increases, so that productivity is lowered and heat resistance is likely to be lowered. Therefore, the number of repeating structures is preferably 1 to 10, more preferably 1 to 6, and further preferably 1 to 4.

The number of repetitive structures here is also counted as 1 for the combination of the dielectric layer 422a and the semiconductor layer 422b. That is, when the number of repeating structures is 1, the structure is “dielectric layer 422a / semiconductor layer 422b”.

The dielectric layer 422a has a function of improving wavelength selectivity by optical interference together with the semiconductor layer 422b. The dielectric layer 422a is not necessarily limited as long as it is made of a dielectric material, but is selected from Al, Ce, Ge, Hf, In, La, Nb, Sb, Si, Sn, Ta, Ti, Zn, and Zr. An oxide of one or more elements or a composite oxide containing one or more elements selected from these elements is preferable.

Among these, an oxide of Si or Ge, or a composite oxide containing one or more elements selected from Si and Ge is preferable, and an oxide of Si or a composite oxide containing Si is more preferable. In particular, those made of an oxide of Si are preferable. According to the material composed of an oxide of Si, in particular, it has excellent heat resistance and physicochemical stability, and as a low refractive index substance, a high absorption rate can be obtained by optical interference.

In the case where there are a plurality of dielectric layers 422a, the constituent elements of the dielectric layer 422a may be the same or different from each other, but the number of targets used when manufacturing by sputtering, for example, can be reduced. Therefore, they are preferably identical to each other. From the same viewpoint, the constituent elements other than oxygen of the dielectric layer 422a are preferably the same as the constituent elements of the semiconductor layer 421b of the first stacked portion 421.

The physical film thickness of the dielectric layer 422a is preferably 10 to 30 nm. When there are a plurality of dielectric layers 422a, the physical thicknesses of the dielectric layers 422a may be the same or different from each other, but it is preferable that both are within the above range. When the physical thickness of the dielectric layer 422a is within the above range, the wavelength selectivity can be effectively improved. The physical film thickness of the dielectric layer 422a is more preferably 15 to 25 nm.

The semiconductor layer 422b has a function of improving wavelength selectivity by optical interference together with the dielectric layer 422a. The semiconductor layer 422b is not necessarily limited as long as it is made of a semiconductor material, but is preferably made of Si or Ge alone or a compound containing one or more elements selected from these elements. Among these, those made of Si alone or Si compounds are more preferred, and those made of Si alone are particularly preferred. According to what consists of Si simple substance, while being excellent in heat resistance, a high absorption factor is obtained as an absorption layer in a visible region, and a low emissivity is obtained as a transparent layer in an infrared region.

Note that when there are a plurality of semiconductor layers 422b, the constituent elements of the semiconductor layer 422b may be the same as or different from each other, but for example, the number of targets used when manufacturing by a sputtering method can be reduced. It is preferable that they are the same. From the same viewpoint, the constituent elements of the semiconductor layer 422b are the same as the constituent elements other than oxygen of the constituent element of the semiconductor layer 421b of the first stacked unit 421 and the dielectric layer 422a of the second stacked unit 422. It is preferable.

The physical film thickness of the semiconductor layer 422b is preferably 2 to 9 nm. Note that when there are a plurality of semiconductor layers 422b, the physical film thicknesses of the semiconductor layers 422b may be the same or different from each other, but it is preferable that both be within the above range. When the physical film thickness of the semiconductor layer 422b is within the above range, the wavelength selectivity can be effectively improved. The physical film thickness of the semiconductor layer 422b is more preferably 3 to 7 nm.

The third stacked unit 423 includes a dielectric layer 423a. The dielectric layer 423a has a function of improving wavelength selectivity by optical interference together with the dielectric layer 422a and the semiconductor layer 422b of the second stacked portion 422, and also has an antireflection function. The dielectric layer 423a is not necessarily limited as long as it is made of a dielectric material, but is selected from Al, Ce, Ge, Hf, In, La, Nb, Sb, Si, Sn, Ta, Ti, Zn, and Zr. An oxide of one or more elements or a composite oxide containing one or more elements selected from these elements is preferable.

Among these, an oxide of Si or Ge, or a composite oxide containing one or more elements selected from Si and Ge is preferable, and an oxide of Si or a composite oxide containing Si is more preferable. In particular, those made of an oxide of Si are preferable. According to the silicon oxide, it has excellent heat resistance and physicochemical stability, and as a low-refractive index substance, it has a good antireflection function in the visible region due to optical interference, resulting in a high absorption rate. Is obtained.

Note that the constituent elements other than oxygen in the dielectric layer 423a can reduce the number of targets used in the case where the dielectric layer 423a is manufactured, for example, by sputtering. Therefore, the constituent elements of the semiconductor layer 421b of the first stacked unit 421 and the second stacked unit It is preferable that the constituent elements other than oxygen of the dielectric layer 422a of 422 and the constituent elements of the semiconductor layer 422b of the second stacked portion 422 be the same.

The physical film thickness of the dielectric layer 423a is preferably 40 to 150 nm from the viewpoint of effectively obtaining the above functions. The physical film thickness of the dielectric layer 423a is more preferably 50 to 130 nm, and further preferably 60 to 110 nm.

In the light selective absorption film 42, the constituent elements of all the semiconductor layers are the same as each other, the constituent elements of all the dielectric layers are the same as each other, and the constituent elements of the semiconductor layer and the oxygen other than the oxygen of the dielectric layer The constituent elements are preferably the same as each other. According to such a thing, when forming by sputtering method, for example, it is sufficient to use only two kinds of targets, that is, a target for forming a metal layer and a target for forming a semiconductor layer and a dielectric layer. , Especially productivity can be improved.

Here, examples of the semiconductor layer include the semiconductor layer 421b of the first stacked unit 421 and the semiconductor layer 422b of the second stacked unit 422. Examples of the dielectric layer include an interlayer dielectric layer and a second stacked unit 422. And the dielectric layer 423a of the third stacked portion 423.

The physical film thickness of the light selective absorption film 42, that is, the total physical film thickness of all the layers is preferably 200 to 300 nm. By making the physical film thickness of the light selective absorption film 42 within the above range, the solar energy absorption rate can be increased, and the emissivity at 400 ° C. or higher can be decreased. Moreover, it can be excellent in heat resistance and productivity.

According to such a light selective absorption film 42, for example, the reflectance is preferably 6% or less, and more preferably 3% or less over the entire wavelength range of 400 to 900 nm. Further, for example, the reflectance is preferably 70% or more over the entire wavelength range of 20000 to 25000 nm, more preferably 80% or more, and particularly preferably 90% or more. Further, such a light selective absorption film 42 is preferable because, for example, the solar radiation energy absorption rate α can be 0.9 or more and the emissivity ε can be 0.2 or less.

Such a light selective absorption film 42 can be suitably formed by a dry method such as sputtering, electron beam evaporation, or vacuum evaporation. Among these, the sputtering method is preferable. In the case of the sputtering method, from the viewpoint of productivity, for example, it is preferable to use only two types of targets, that is, a target for forming a metal layer and a target for forming a semiconductor layer and a dielectric layer.

Here, examples of the metal layer include the metal layer 421a of the first stacked portion 421.

Examples of the target used for forming the metal layer include Ag, Al, Au, Cr, Cu, Fe, Hf, In, La, Mo, Ni, Pd, Pt, Rh, Sn, Ta, Ti, Zr, or Examples thereof include a metal target made of W or an alloy containing one or more elements selected from these elements. Among these, from the viewpoints of heat resistance, chemical stability of the metal layer to be formed, adhesion to the heat collecting tube main body 41 as a base material, easy availability of the target, etc., from Cr alone or Cr alloy. The metal target which becomes is more preferable, and the metal target which consists of Cr simple substance is especially preferable. The metal layer can be formed by sputtering using such a metal target in a non-oxidizing atmosphere such as an argon gas atmosphere.

Examples of the target used for forming the semiconductor layer and the dielectric layer include a target from a simple substance of Si or Ge, or a compound containing one or more elements selected from these elements. Among these, a target made of Si alone or a Si compound is more preferred, and a target made of Si alone is particularly preferred.

The semiconductor layer is preferably formed by sputtering using such a target in a non-oxidizing atmosphere such as an argon gas atmosphere. The dielectric layer is preferably formed by sputtering using such a target in an oxidizing atmosphere containing, for example, argon gas and oxygen.

As described above, the embodiments of the light selective absorption film, the heat collecting tube, and the solar thermal power generation device have been described, but the solar thermal power generation device is not necessarily limited to one using a parabolic trough type heat collector or a linear Fresnel type heat collector, As long as the above-described light selective absorption film is applied, other types of solar power generation apparatuses may be used. Further, as the light selective absorption film, those used for the heat collecting tube of the solar thermal power generation device can be cited as typical ones. If it exists, it may be used for other purposes.

Hereinafter, embodiments of the present invention will be specifically described with reference to examples.

Example 1
First, a stainless steel (JIS standard SUS321) substrate whose surface was polished so that the arithmetic average surface roughness Ra was about 0.4 μm was prepared. The dimensions of the stainless steel substrate were 50 mm long × 50 mm wide × 5 mm thick.

On this stainless steel substrate, a light selective absorption film 42 having a laminated structure as shown in FIG. 6 was formed by sputtering to obtain an evaluation substrate. The light selective absorption film 42 is formed in order of a Cr layer (a metal layer 421a of the first stacked unit 421, a physical film thickness of 106.25 nm) / Si layer (a semiconductor layer of the first stacked unit 421) from the stainless steel substrate side. 421b, physical film thickness 10.78 nm) / Cr layer (metal layer 421a of the first laminated part 421, physical film thickness 7.49 nm) / Si layer (semiconductor layer 421b of the first laminated part 421, physical film thickness 12) .86 nm) / SiO ₂ layer (dielectric layer 422a of second stacked portion 422, physical film thickness 19.77 nm) / Si layer (semiconductor layer 422b of second stacked portion 422, physical film thickness 5.75 nm) / The SiO ₂ layer (dielectric layer 423a of the third stacked portion 423, physical film thickness 79.15 nm) was used.

As the sputtering apparatus, a DC magnetron sputtering apparatus (manufactured by Nippon Vacuum Optics) was used. A commercially available Cr target (purity: 99.99%) is used for forming the Cr layer, and a commercially available Si target (purity: 99.999%) is used for forming the Si layer and the SiO ₂ layer. did.

In forming the Cr layer and the Si layer, argon gas was used in the film forming atmosphere. The sputtering pressure was 1 × 10 ⁻¹ Pa, and the film formation temperature (substrate temperature) was room temperature. Moreover, in order to stabilize discharge, MF power (manufactured by AE) was used as a power source, and power was periodically applied. The frequency at this time was 100 kHz.

In forming the SiO ₂ layer, a mixed gas of argon gas and oxygen gas was used as the film forming atmosphere. The mixing ratio of argon gas and oxygen gas was 70:30 in volume%. The sputtering pressure was 2 × 10 ⁻¹ Pa, and the film formation temperature (substrate temperature) was room temperature. Moreover, in order to stabilize discharge, MF power (manufactured by AE) was used as a power source, and power was periodically applied. The frequency at this time was 100 kHz.

The solar energy absorption rate α and the emissivity ε at 450 ° C. were determined for the evaluation substrate thus obtained. The solar radiation energy absorption rate α was obtained from AM1.5 (ASTM G173-03 Reference Spectra) and the measured reflectance of the evaluation substrate. The emissivity ε at 450 ° C. was obtained from Planck's formula. As a result, the solar radiation energy absorption rate α was 0.90 (design value: 0.91), and the emissivity ε was 0.16 (design value: 0.09).

FIG. 7 shows the reflectance distribution and the absorptance distribution of the evaluation substrate. The reflectance distribution and the absorptance distribution indicate actual measurement values and design values (simulation results). In addition, the standard spectrum of ASTM G173-03 and the black body radiation spectrum at 450 ° C. are also shown.

As is clear from FIG. 7, according to the evaluation substrate having a predetermined configuration, the transmittance can be lowered in a wavelength region (visible region and near infrared region) lower than the wavelength region of the 450 ° C. blackbody radiation spectrum. It can be seen that the transmittance can be increased in the wavelength region (infrared region) of the black body radiation spectrum at 450 ° C., and that the transmittance can rise sufficiently from the near infrared region to the infrared region. Moreover, according to the evaluation substrate having a predetermined configuration, it is recognized that an actual measurement value close to the design value can be obtained.

In this evaluation substrate, in the wavelength range of 400 to 900 nm, the maximum reflectivity at 900 nm is 5.5% (design value: 3.0%), and the average over the entire wavelength range of 400 to 900 nm. The reflectance is actually measured: 1.2% (design value: 0.8%). The average reflectance in the entire wavelength range of 2000 to 20000 nm is actually measured: 91% (design value: 93%).

(Example 2)
Similarly to Example 1, a light selective absorption film 42 having a laminated structure as shown in FIG. 6 was formed on a stainless steel substrate by a sputtering method to obtain an evaluation substrate. The light selective absorption film 42 is composed of a Cr layer (a metal layer 421a of the first laminated portion 421, a physical film thickness of 104.62 nm) / SiO ₂ layer (a dielectric layer, a physical film not shown) in order from the stainless steel substrate side. (Thickness 5.00 nm) / Si layer (semiconductor layer 421b of first stacked portion 421, physical film thickness 10.42 nm) / SiO ₂ layer (dielectric layer not shown, physical film thickness 5.00 nm) / Cr layer (first film) Metal layer 421a of one laminated portion 421, physical film thickness 6.03 nm) / SiO ₂ layer (dielectric layer not shown, physical film thickness 5.00 nm) / Si layer (semiconductor layer 421b of first laminated portion 421), (Physical film thickness 8.03 nm) / SiO ₂ layer (dielectric layer 422a of second laminated portion 422, physical film thickness 19.27 nm) / Si layer (semiconductor layer 422b of second laminated portion 422, physical film thickness 3 .97nm) / SiO Layer (dielectric layer in the third multilayer portion 423 423a, a physical thickness 73.96Nm) was set to be.

For film formation, the same sputtering apparatus and target as used in Example 1 were used. The film forming conditions for each layer were the same as described in Example 1. The evaluation substrate thus obtained was evaluated in the same manner as in Example 1. As a result, the solar radiation energy absorption rate α was 0.90 (design value: 0.91), and the emissivity ε was 0.11 (design value: 0.08).

Even with the evaluation substrate having the configuration of Example 2, the transmittance can be lowered in the wavelength region (visible region and near infrared region) lower than the wavelength region of the black body radiation spectrum at 450 ° C., and the black body radiation at 450 ° C. can be achieved. It was confirmed that the transmittance can be increased in the spectral wavelength region (infrared region) and that the transmittance can be sufficiently increased from the near infrared region to the infrared region. In addition, according to the evaluation substrate having a predetermined configuration, it was confirmed that an actual measurement value close to the design value was obtained.

In the evaluation substrate of Example 2, in the wavelength range of 400 to 900 nm, the maximum reflectivity at 900 nm was 2.5% (design value: 2.4%), and the wavelength range of 400 to 900 nm. The average reflectance in the whole is actually measured: 1.3% (design value: 0.8%). Further, the average reflectance in the entire wavelength range of 2000 to 20000 nm is an actual measurement value: 92% (design value: 91%).

(Comparative Example 1)
As the light selective absorption film, an evaluation substrate provided with an alternating layered structure of Cr layers and SiO ₂ layers and having no Si layer was provided. That is, the light selective absorption film is, in order from the stainless steel substrate side, Cr layer (physical film thickness 91.79 nm) / SiO ₂ layer (physical film thickness 88.69 nm) / Cr layer (physical film thickness 5.92 nm) / SiO 2. _Two layers (physical film thickness 77.22 nm) were used. The light selective absorption film is such that the optical characteristics can be obtained as close as possible to the light selective absorption film of Example 1 was adjusting the thickness of each layer of the Cr layer and the SiO ₂ layer.

FIG. 8 shows the reflectance distribution of the evaluation substrate of Comparative Example 1. FIG. 8 also shows the reflectance distribution of the evaluation substrate of Example 1 for comparison. As is clear from FIG. 8, in the case of the evaluation substrate of Comparative Example 1 that does not have a Si layer, the reflectance in the visible region is partially higher than that of the evaluation substrate of Example 1 that has a Si layer. On the other hand, it turns out that the reflectance in an infrared region becomes low. The evaluation substrate of Comparative Example 1 has a maximum reflectance of 3.3% at 440 nm in the wavelength region of 400 to 900 nm.

(Comparative Example 2)
Lamination basically similar to the evaluation substrate of Example 1 except that the number of repeating structures of the Cr layer and the Si layer of the light selective absorption film (corresponding to the number of repeating structures in the first laminated portion) is 1. An evaluation substrate having a structure was obtained. That is, the light selective absorption film is, in order from the stainless steel substrate side, Cr layer (physical film thickness 128.35 nm) / Si layer (physical film thickness 17.14 nm) / SiO ₂ layer (physical film thickness 22.61 nm) / Si. Layer (physical film thickness 6.41 nm) / SiO ₂ layer (physical film thickness 82.19 nm). The light selective absorption film is such that the optical characteristics can be obtained as close as possible to the light selective absorption film of Example 1, Cr layer, Si layer, and to adjust the thickness of each layer of the SiO ₂ layer.

FIG. 9 shows the reflectance distribution of the evaluation substrate of Comparative Example 2. FIG. 9 also shows the reflectance distribution of the evaluation substrate of Example 1 for comparison. As is clear from FIG. 9, the evaluation substrate of Comparative Example 2 in which the number of repeating structures of the Cr layer and the Si layer is 1, compared with the evaluation substrate of Example 1 in which the number of repeating structures is 2. Thus, it can be seen that the reflectance in the visible range is generally high. Note that the evaluation substrate of Comparative Example 2 has a maximum reflectance of 5.9% at 440 nm in the wavelength region of 400 to 900 nm.

(Comparative Example 3)
An evaluation substrate having a layered structure similar to that of the evaluation substrate of Example 1 was basically provided except that a repeating structure of SiO ₂ layer and Si layer (corresponding to the second layered portion) was not provided. That is, the light selective absorption film is, in order from the stainless steel substrate side, Cr layer (physical film thickness 143.32 nm) / Si layer (physical film thickness 17.5 nm) / Cr layer (physical film thickness 9.16 nm) / Si layer. (Physical film thickness 14.34 nm) / SiO ₂ layer (physical film thickness 81.42 nm). The light selective absorption film is such that the optical characteristics can be obtained as close as possible to the light selective absorption film of Example 1, Cr layer, Si layer, and to adjust the thickness of each layer of the SiO ₂ layer.

FIG. 10 shows the reflectance distribution of the evaluation substrate of Comparative Example 3. FIG. 10 also shows the reflectance distribution of the evaluation substrate of Example 1 for comparison. As is clear from FIG. 10, in the case of the evaluation substrate of Comparative Example 3 in which the repeated structure of the SiO ₂ layer and the Si layer was not provided, the visible region was larger than that of the evaluation substrate of Example 1 in which the repeated structure was provided. It can be seen that the reflectance at is significantly increased. Note that the evaluation substrate of Comparative Example 3 has a maximum reflectance of 13.0% at 900 nm in the wavelength region of 400 to 900 nm.

Although the present invention has been described in detail above, these are merely examples, and the present invention can be implemented in other modes, and various modifications can be made without departing from the spirit of the present invention.
This application is based on a Japanese patent application (Japanese Patent Application No. 2012-068037) filed on Mar. 23, 2012, which is incorporated by reference in its entirety.

DESCRIPTION OF SYMBOLS 1 ... Parabolic trough type collector, 2 ... Parabolic reflector, 3 ... Reflector support body, 4 ... Heat collecting tube, 6 ... Linear Fresnel type collector, 7 ... First reflector, 8 ... Receiver, 9 DESCRIPTION OF SYMBOLS ... Receiver support body, 41 ... Heat collecting tube body, 42 ... Light selective absorption film, 43 ... Glass tube, 44 ... Fixing bracket, 81 ... Second reflector, 82 ... Case part, 83 ... Glass plate, 421 ... First 1 layered part, 421a ... metal layer of the first layered part, 421b ... semiconductor layer of the first layered part, 422 ... second layered part, 422a ... dielectric layer of the second layered part, 422b ... first Semiconductor layer of two stacked portions, 423 ... third stacked portion, 423a ... dielectric layer of third stacked portion

Claims (7)

A light selective absorption film formed on a substrate,
A first laminated part that is laminated on the base material and has two or more repeating structures of a metal layer and a semiconductor layer in order from the base material side;
A second laminated portion laminated on the first laminated portion and having at least one repeating structure of a dielectric layer and a semiconductor layer;
And a third laminated portion made of a dielectric layer laminated on the second laminated portion. The first laminated portion has a physical film thickness of 60 to 200 nm of the metal layer first laminated on the substrate among the metal layers, and the physical film thicknesses of the other metal layers are the same or different from each other. Within the range of 5 to 10 nm, the physical film thickness of the semiconductor layers is the same or different from each other, and within the range of 5 to 20 nm,
In the second stacked portion, the physical thicknesses of the dielectric layers are the same or different from each other within a range of 10 to 30 nm, and the physical thicknesses of the semiconductor layers are the same or different from each other within a range of 2 to 9 nm.
2. The light selective absorption film according to claim 1, wherein the third laminated portion has a physical film thickness of the dielectric layer in a range of 40 to 150 nm. The light selective absorption film according to claim 1 or 2, wherein the entire physical film thickness of the light selective absorption film is 200 to 300 nm. The metal layers of the first stacked portion are the same or different from each other, and Ag, Al, Au, Cu, Fe, Hf, In, La, Mo, Ni, Pd, Pt, Rh, Sn, Ta, Ti, Zr or W, or an alloy containing one or more elements selected from these elements,
The semiconductor layer of the first stacked portion and the semiconductor layer of the second stacked portion are the same or different from each other, and include Si or Ge alone, or a compound containing one or more elements selected from these elements Consists of
The dielectric layer of the second stacked portion and the dielectric layer of the third stacked portion are the same or different from each other, and one or more elements selected from Si or Ge oxide or Si and Ge The light selective absorption film according to any one of claims 1 to 3, comprising a complex oxide containing: The constituent elements of all the semiconductor layers in the light selective absorption film are the same as each other, the constituent elements of all the dielectric layers in the light selective absorption film are the same as each other, and the constituent elements of the semiconductor layer and the dielectric 5. The light selective absorption film according to claim 4, wherein the constituent elements other than oxygen in the layer are the same. A heat collecting tube having a heat collecting tube main body and a light selective absorption film formed on the outer surface of the heat collecting tube main body,
The heat collecting tube according to any one of claims 1 to 5, wherein the light selective absorption film is the light selective absorption film according to any one of claims 1 to 5. A solar power generator comprising a heat collector having a heat collecting tube and a light collecting means for collecting sunlight on the heat collecting tube,
The solar heat power generator according to claim 6, wherein the heat collection tube is a heat collection tube according to claim 6.

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