Abstract:
The present invention addresses the problem of providing a heat conversion member capable of efficiently converting light to heat. This heat conversion member is characterized in that it includes a composite material of at least one type of semiconductor and at least one type of metal material.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a heat conversion member and to a heat conversion laminate. 
       BACKGROUND ART 
       [0002]    Photovoltaic power generation systems are known that convert sunlight to heat and utilize the heat for electric power generation. In the known systems, sunlight is collected with a collector and the collected sunlight is used to heat a heating medium (such as oil, dissolved salts or molten sodium) in a container or flow channel. Provision of covering materials, thin-films and the like on the surfaces of containers or flow channels is also being studied as a way of accelerating heating of the heating medium by the collected sunlight. 
         [0003]    In NPL 1, for example, a covering material is provided on the surface of a container or flow channel, and the covering material promotes absorption of collected sunlight while minimizing heat release by heat radiation from the container or flow channel to the exterior. As another example, PTL 1 proposes a method for producing a solar heat collector comprising a first glass tube having a vacuum interior and allowing sunlight to impinge from the exterior, and a second glass tube or metal tube provided on the inner side of the first glass tube and having a selective absorbing film on the surface, the selective absorbing film being composed of a metal film that contacts with the second glass tube or metal tube and a dielectric thin-film adhering onto the metal film, wherein the metal film is formed by an electroless plating method selected from among nickel, cobalt, silver and copper plating, and the dielectric thin-film is formed by coating a film by a method of coating a solution of one kind or a mixture selected from among titanium dioxide, tantalum pentoxide and niobium pentoxide, followed by heat treatment of the film at 500° C. or higher in an oxidizing atmosphere. Also, PTL 2 proposes a coating composition for the heat-collecting surface of a solar heat collector, comprising a pigment with a high solar absorption rate that is highly permeable to infrared rays, polymethylpentene, and a solvent that dissolves polymethylpentene, while PTL 3 proposes a solar heat collecting apparatus utilizing sunlight energy, the solar heat collecting apparatus comprising a wavelength converter that absorbs at least a portion of sunlight and converts it to light of a different wavelength, and a heat accumulator that absorbs light emitted from the wavelength converter and generates heat. In addition, PTL 4 proposes a sunlight selective absorption coating having a sunlight absorbing property and low emissivity, the sunlight selective absorption coating comprising a support ( 1 ) of a metal, dielectric material or ceramic material, at least one mid-to-far-infrared ray highly-reflecting metal layer ( 2 ) accumulated on the support ( 1 ), a multilayer absorbing structure ( 3 ) composed of an alternating dielectric layer ( 5 ) and metal layer ( 6 ), accumulated on the metal reflective layer ( 2 ), and at least one anti-reflection dielectric layer ( 4 ), accumulated on the multilayer absorbing structure ( 3 ), the dielectric layers ( 5 ) of the multilayer absorbing structure ( 3 ) being either of the same or different thicknesses and/or compositions, the metal layers ( 6 ) of the multilayer absorbing structure ( 3 ) being either of the same or different thicknesses and/or compositions, the respective thicknesses of the metal layers ( 6 ) and dielectric layers ( 5 ) of the multilayer absorbing structure ( 3 ) being less than 10 nm and preferably less than 1 nm, the total thickness of the multilayer absorbing structure ( 3 ) being 5-1000 nm, wherein it is specified that the layer of the dielectric material of the sunlight selective absorption coating is accumulated by reactive sputtering including an inert gas and a reactive gas in a chamber or a part of a chamber in which the dielectric layer is to be accumulated, and the metal layer of the sunlight selective absorption coating is accumulated by DC sputtering, introducing only an inert gas into a chamber or part of a chamber in which the metal sheet is to be accumulated. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         [PTL 1] Japanese Unexamined Patent Publication No. 59-056661 
         [PTL 2] Japanese Unexamined Patent Publication No. 58-001760 
         [PTL 3] Japanese Unexamined Patent Publication No. 2010-002077 
         [PTL 4] Japanese Patent Public Inspection No. 2012-506021 
       
     
       Non Patent Literature 
       [0000]    
       
         [NPL 1] July 2002, NREL/TP-520-31267, “Review of Mid-to High-Temperature Solar Selective Absorber Materials”, C. E. Kennedy. 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0009]    At the current time, it is desirable to achieve more accelerated heating of heating media by collected sunlight and achieve more efficient light-to-heat conversion. 
         [0010]    It is an object of the present invention to provide a heat conversion member that can efficiently convert light to heat. It is another object of the present invention to provide a heat conversion laminate comprising a heat conversion member that can efficiently convert light to heat. 
       Solution to Problem 
       [0011]    The means for achieving these objects is described by the following (1) to (8). 
         [0012]    (1) A heat conversion member comprising a composite material of one or more kinds of semiconductor and one or more kinds of metal material. 
         [0013]    (2) The heat conversion member according to (1), wherein the metal material is in the form of particles. 
         [0014]    (3) The heat conversion member according to (1) or (2), wherein the semiconductor comprises FeSi X  (X=0.5-4). 
         [0015]    (4) The heat conversion member according to (3), wherein X in FeSi X  is 2. 
         [0016]    (5) The heat conversion member according to any one of (1) to (4), which is film-shaped. 
         [0017]    (6) The heat conversion member according to (5), wherein the film shape has a thickness of 1 nm to 10 μm. 
         [0018]    (7) A heat conversion laminate having laminated at least one or more layers including at least the heat conversion member according to (5) or (6), and a metal layer. 
         [0019]    (8) A heat conversion laminate having laminated at least a metal layer, one or more layers including at least the heat conversion member according to (5) or (6), and a transparent dielectric layer, in that order. 
       Advantageous Effects of Invention 
       [0020]    According to the present invention, there is provided a heat conversion member that can efficiently convert light to heat. According to the present invention, there is further provided a heat conversion laminate comprising a heat conversion member that can efficiently convert light to heat. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0021]      FIG. 1  is a cross-sectional schematic drawing showing a heat conversion laminate  1  as one embodiment of a heat conversion laminate according to the present invention. 
           [0022]      FIG. 2  is a graph showing the results for the absorption properties of a Ag—FeSi 2  “metasemi” monolayer film. 
           [0023]      FIG. 3  is a graph showing the results for the absorption properties of a Mo—FeSi 2  “metasemi” monolayer film. 
           [0024]      FIG. 4  is a graph showing the results for the absorption properties of a Cu—FeSi 2  “metasemi” monolayer film. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     (1) Heat Conversion Member 
       [0025]    The heat conversion member of the present invention is a heat conversion member comprising a composite material of one or more kinds of semiconductor and one or more kinds of metal material. The heat conversion member of the present invention allows the absorption property for sunlight to be varied by adjusting the content (addition rate) of the one or more kinds of metal material, thereby allowing efficient conversion of light to heat with improved optical selectivity. Here, “optical selectivity” refers to dramatic change in the optical characteristics, such as reflectance at certain wavelengths or certain wavelength ranges. 
         [0026]    The one or more kinds of semiconductor in the composite material in the heat conversion member of the present invention (also referred to as “composite material”) may be of a single kind of semiconductor, or a mixture of two or more different kinds of semiconductor. 
         [0027]    The semiconductor of a composite material in the heat conversion member of the present invention is not particularly restricted, and may be FeSi X  (X=0.5-4), for example. 
         [0028]    The one or more kinds of metal material in the composite material in the heat conversion member of the present invention may also be a single kind of metal material or a mixture of two or more different kinds of metal material. 
         [0029]    The metal material in the composite material in the heat conversion member of the present invention is not particularly restricted and may be an Ag material, Mo material or Cu material, for example. 
         [0030]    The one or more kinds of metal material in the composite material in the heat conversion member of the present invention may be in any desired form, but is preferably in the form of particles. If the one or more kinds of metal material is in particle form, it may be metallic particles or metal fine particles. The particle diameter of particles of the metal material is preferably 1-100 nm. 
         [0031]    The one or more kinds of semiconductor in the composite material in the heat conversion member of the present invention preferably contains FeSi X  (X=0.5-4) and more preferably contains FeSi 2 . 
         [0032]    The heat conversion member of the present invention may be in any desired form, such as in the form of a film shape, tube shape, sheet shape or the like, however a film shape is preferred. The thickness of a film of the heat conversion member of the present invention may be any desired thickness so long as the effect of the present invention is exhibited, however preferably a film of the heat conversion member of the present invention has a thickness of 1 nm to 10 μm, and more preferably it has a thickness of 5 nm to 100 nm. 
         [0033]    The content of the one or more kinds of metal material in the heat conversion member of the present invention may be as desired, such as 1-50 vol %, for example. 
         [0034]    The heat conversion member of the present invention may yet also contain any desired material other than a composite material of the one or more kinds of semiconductor and one or more kinds of metal materials. For example, a transparent dielectric material such as SiO 2  may be mixed in the form of particulates or fine particulates. 
         [0035]    The heat conversion member of the present invention can be obtained by any desired publicly known production method. For example, the heat conversion member of the present invention can be produced by physical vapor phase deposition (PVD), sputtering or the like. 
       (2) Heat Conversion Laminate 
       [0036]    As one feature, the heat conversion laminate of the present invention has laminated one or more layers comprising a film-like heat conversion member of the present invention, and a metal layer, and it may have a metal layer and one or more layers comprising a film-like heat conversion member of the present invention laminated in that order, or the lamination may be in the reverse order. 
         [0037]    As another feature, the heat conversion laminate of the present invention also have at least a metal layer, one or more layers comprising a film-like heat conversion member of the present invention and a transparent dielectric layer, laminated in that order. 
         [0038]    The one or more layers containing a film-like heat conversion member of the present invention in the heat conversion laminate of the present invention may be constructed as a photoabsorbing layer, and this allows the absorption property for sunlight to be varied by adjusting the content of the one or more kinds of metal material, thereby allowing efficient conversion of light to heat with improved optical selectivity. The thickness of the one or more layers comprising a film-like heat conversion member in the heat conversion laminate of the present invention may be any desired thickness so long as the effect of the present invention is exhibited, and it is preferably a thickness of 5 nm to 100 nm. The layer comprising the film-like heat conversion member in the heat conversion laminate of the present invention may be a single layer or multiple layers. The one or more layers comprising a film-like heat conversion member in the heat conversion laminate of the present invention may also include any materials other than the film-like heat conversion member. 
         [0039]    The metal layer in the heat conversion laminate of the present invention may be constructed as an infrared anti-reflection layer. The metal layer in the heat conversion laminate of the present invention is not particularly restricted, and for example, it may be a molybdenum (Mo) layer, tungsten (W) layer, silver (Ag) layer, gold (Au) layer, copper (Cu) layer or the like, and is preferably a molybdenum (Mo) layer. The thickness of the metal layer in the heat conversion laminate of the present invention may have any desired thickness so long as the effect of the present invention is exhibited, and it is preferably a thickness of 100 nm or greater. 
         [0040]    The transparent dielectric layer in the heat conversion laminate of the present invention may also be constructed as an anti-reflection layer. The transparent dielectric layer in the heat conversion laminate of the present invention is not particularly restricted, and examples include a SiO 2  layer, Al 2 O 3  layer, AlN layer or the like, with a SiO 2  layer being preferred. The thickness of the transparent dielectric layer in the heat conversion laminate of the present invention may be any desired thickness so long as the effect of the present invention is exhibited, and it is preferably a thickness of 10 nm to 500 nm. 
         [0041]    The heat conversion laminate of the present invention may also include an absorbing layer other than a heat conversion member of the present invention, as a photoabsorbing layer. 
         [0042]    The heat conversion laminate of the present invention can be obtained by any desired publicly known production method. For example, the heat conversion laminate of the present invention can be produced by physical vapor phase deposition (PVD), sputtering or the like. 
         [0043]    The heat conversion laminate of the present invention will now be explained in greater detail with reference to  FIG. 1 . Incidentally, the heat conversion laminate of the present invention is not limited to the embodiment of the present invention shown in  FIG. 1 , such as is within the scope of the object and gist of the present invention. 
         [0044]      FIG. 1  is a drawing showing a heat conversion laminate  1  as one embodiment of a heat conversion laminate according to an embodiment of the present invention. The heat conversion laminate  1  according to an embodiment of the present invention is formed from a transparent dielectric layer  11 , a layer comprising a heat conversion member (photoabsorbing layer)  12 , and a metal layer  13 . Also, the layer comprising a heat conversion member (photoabsorbing layer)  12  comprises metal fine particles  121  and a semiconductor  122 . As shown in  FIG. 1 , the metal fine particles  121  are dispersed within the semiconductor  122 . 
       EXAMPLES 
       [0045]    Examples will now be provided for a more concrete explanation of the present invention. The present invention is not limited to these examples, however, provided that the object and gist of the present invention are maintained. 
       &lt;Evaluation of Absorption Properties of Heat Conversion Member&gt; 
       [0046]    The absorption properties of heat conversion members were evaluated using Examples 1 to 3 and Comparative Example 1. 
       Example 1 
       [0047]    The absorption properties of a heat conversion member of the present invention were evaluated using an Ag—FeSi 2  “metasemi” monolayer film. The term “metasemi” means “metal+semiconductor”. 
       [Method of Forming Ag—FeSi 2  Metasemi Monolayer Film] 
       [0048]    On a quartz substrate at room temperature, FeSi 2  and Ag (silver) were simultaneously sputtered to form a film. Following film formation, annealing was performed for 1 hour in a vacuum furnace at a temperature of no higher than 800° C. Two Ag—FeSi 2  metasemi samples with different Ag (silver) addition rates (4.0 vol %, 8.6 vol %) were prepared. 
         [0049]    The optical constants (refractive index n, extinction coefficient k) of the Ag—FeSi 2  metasemi were calculated for the obtained sample from the measurement data with a spectroscopic ellipsometer and the reflectance property and transmittance property measured with a spectrophotometer. 
         [0050]    The calculated multilayer film approximation based on the optical constants (n, k) for Ag—FeSi 2  metasemi was used to calculate the absorption rate of the Ag—FeSi 2  metasemi monolayer film (corresponding to a film thickness of 30 nm).  FIG. 2  shows the results for the absorption properties of a Ag—FeSi 2  metasemi monolayer film. 
       Example 2 
       [0051]    The absorption properties of a heat conversion member of the present invention were evaluated using a Mo—FeSi 2  metasemi monolayer film. 
       [Method of Forming Mo—FeSi 2  Metasemi Monolayer Film] 
       [0052]    On a quartz substrate heated to a temperature no higher than 700° C., FeSi 2  and Mo (molybdenum) were simultaneously sputtered to form a film. Two Mo—FeSi 2  metasemi samples with different Mo (molybdenum) addition rates (4.2 vol %, 9.4 vol %) were prepared. 
         [0053]    The optical constants (refractive index n, extinction coefficient k) of the Mo—FeSi 2  metasemi were calculated for the obtained sample from the measurement data with a spectroscopic ellipsometer and the reflectance property and transmittance property measured with a spectrophotometer. 
         [0054]    The calculated multilayer film approximation based on the optical constants (n, k) for Mo—FeSi 2  metasemi was used to calculate the absorption rate of the Mo—FeSi 2  metasemi monolayer film (corresponding to a film thickness of 30 nm).  FIG. 3  shows the results for the absorption properties of a Mo—FeSi 2  metasemi monolayer film. 
       Example 3 
       [0055]    The absorption properties of a heat conversion member of the present invention were evaluated using an Cu—FeSi 2  metasemi monolayer film. 
       [Method of Forming Cu—FeSi 2  Metasemi Monolayer Film] 
       [0056]    On a quartz substrate heated to a temperature no higher than 700° C., FeSi 2  and Cu (copper) were simultaneously sputtered to form a film. A Cu—FeSi 2  metasemi sample with a Cu (copper) addition rate of 8.1 vol % was prepared. 
         [0057]    The optical constants (refractive index n, extinction coefficient k) of the Cu—FeSi 2  metasemi were calculated for the obtained sample from the measurement data with a spectroscopic ellipsometer and the reflectance property and transmittance property measured with a spectrophotometer. 
         [0058]    The calculated multilayer film approximation based on the optical constants (n, k) for Cu—FeSi 2  metasemi was used to calculate the absorption rate of the Cu—FeSi 2  metasemi monolayer film (corresponding to a film thickness of 30 nm).  FIG. 4  shows the results for the absorption properties of a Cu—FeSi 2  metasemi monolayer film. 
       Comparative Example 1 
       [0059]    The absorption properties of a FeSi 2  monolayer film were evaluated. 
       [Method of Forming FeSi 2  Monolayer Film] 
       [0060]    On a quartz substrate heated to a temperature no higher than 700° C., FeSi 2  was sputtered to form a film. A FeSi 2  sample was fabricated. 
         [0061]    The optical constants (refractive index n, extinction coefficient k) of the FeSi 2  were calculated for the obtained sample from the measurement data with a spectroscopic ellipsometer and the reflectance property and transmittance property measured with a spectrophotometer. 
         [0062]    The calculated multilayer film approximation based on the optical constants (n, k) for FeSi 2  was used to calculate the absorption rate of the FeSi 2  monolayer film (corresponding to a film thickness of 30 nm).  FIG. 2  to  FIG. 4  show the results for the absorption properties of a FeSi 2  monolayer film. 
       &lt;Evaluation Results&gt; 
       [0063]    Referring to  FIG. 2 , it is seen that the absorption property curve shifts toward the long wavelength end as the amount of Ag (silver) addition increases (0 vol %→4.0 vol %→8.6 vol %). Thus, since the sunlight absorption property of the Ag—FeSi 2  metasemi monolayer film can be varied by adjusting the Ag (silver) material content (amount of addition), it is possible to increase the optical selectivity and accomplish efficient conversion of light to heat. 
         [0064]    Referring to  FIG. 3 , it is seen that the absorption property curve shifts toward the long wavelength end as the amount of Mo (molybdenum) addition increases (0 vol %→4.2 vol %→9.4 vol %). Thus, since the sunlight absorption property of the Mo—FeSi 2  metasemi monolayer film can be varied by adjusting the Mo (molybdenum) material content (amount of addition), it is possible to increase the optical selectivity and accomplish efficient conversion of light to heat. 
         [0065]    Referring to  FIG. 4 , it is seen that the absorption property curve shifts toward the long wavelength end as the amount of Cu (copper) addition increases (0 vol %→8.1 vol %). Thus, since the sunlight absorption property of the Cu—FeSi 2  metasemi monolayer film can be varied by adjusting the Cu (copper) material content (amount of addition), it is possible to increase the optical selectivity and accomplish efficient conversion of light to heat. Thus, the absorption property curve can be shifted toward the long wavelength end compared to a FeSi 2  monolayer film, as shown in  FIGS. 2 to 4 , and optical selectivity is maintained even after shifting. It is therefore possible to use the heat conversion member of the present invention in place of a FeSi 2  monolayer film. In this case, the heat conversion member of the present invention may be laminated on a metal layer as an infrared ray-reflective layer, and a transparent dielectric layer may be additionally formed as an anti-reflection layer. 
       Example 4 
       [0066]    The properties of a laminate of the present invention were evaluated. 
         [0067]    The properties of a laminate prepared by laminating a metal layer, a metasemi layer (photoabsorbing layer) and a transparent dielectric layer in that order were evaluated by calculating the absorption rate using multilayer film approximation, in the same manner, and a shift in properties toward the long wavelength end was confirmed, similar to a monolayer film. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  Heat conversion laminate 
           11  Transparent dielectric layer 
           12  Layer comprising heat conversion member (photoabsorbing layer) 
           13  Metal layer 
           121  Metal fine particles 
           122  Semiconductor