CA2764762C - Nanocomposite thermoelectric conversion material and method of producing the same - Google Patents
Nanocomposite thermoelectric conversion material and method of producing the same Download PDFInfo
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- 239000000463 material Substances 0.000 title claims abstract description 128
- 238000006243 chemical reaction Methods 0.000 title claims abstract description 116
- 239000002114 nanocomposite Substances 0.000 title claims abstract description 55
- 238000000034 method Methods 0.000 title claims abstract description 31
- 239000002245 particle Substances 0.000 claims abstract description 133
- 239000011159 matrix material Substances 0.000 claims abstract description 54
- 239000002002 slurry Substances 0.000 claims abstract description 27
- 239000002105 nanoparticle Substances 0.000 claims abstract description 18
- 239000003638 chemical reducing agent Substances 0.000 claims abstract description 16
- 239000002243 precursor Substances 0.000 claims abstract description 16
- 150000003839 salts Chemical class 0.000 claims abstract description 15
- 230000001376 precipitating effect Effects 0.000 claims abstract description 8
- 238000001914 filtration Methods 0.000 claims abstract description 6
- 238000005406 washing Methods 0.000 claims abstract description 6
- 238000005275 alloying Methods 0.000 claims abstract description 4
- 229910052787 antimony Inorganic materials 0.000 claims description 18
- 229910052759 nickel Inorganic materials 0.000 claims description 17
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 claims description 13
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 20
- 230000003247 decreasing effect Effects 0.000 description 18
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 18
- 239000000203 mixture Substances 0.000 description 14
- 229910052797 bismuth Inorganic materials 0.000 description 13
- 238000010438 heat treatment Methods 0.000 description 13
- 229910045601 alloy Inorganic materials 0.000 description 11
- 239000000956 alloy Substances 0.000 description 11
- 239000002184 metal Substances 0.000 description 11
- 229910052751 metal Inorganic materials 0.000 description 11
- 238000003917 TEM image Methods 0.000 description 8
- 238000010586 diagram Methods 0.000 description 8
- 239000000843 powder Substances 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 7
- 238000005516 engineering process Methods 0.000 description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 7
- 238000001816 cooling Methods 0.000 description 6
- 239000003708 ampul Substances 0.000 description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 5
- 229910052760 oxygen Inorganic materials 0.000 description 5
- 239000001301 oxygen Substances 0.000 description 5
- 241000252073 Anguilliformes Species 0.000 description 4
- 239000000919 ceramic Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 238000005430 electron energy loss spectroscopy Methods 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 238000013507 mapping Methods 0.000 description 4
- 238000005245 sintering Methods 0.000 description 4
- 229910018985 CoSb3 Inorganic materials 0.000 description 3
- 239000000470 constituent Substances 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 230000008018 melting Effects 0.000 description 3
- 229910052714 tellurium Inorganic materials 0.000 description 3
- 229910002908 (Bi,Sb)2(Te,Se)3 Inorganic materials 0.000 description 2
- 229910016312 BiSb Inorganic materials 0.000 description 2
- 229910005347 FeSi Inorganic materials 0.000 description 2
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 2
- 229910002665 PbTe Inorganic materials 0.000 description 2
- 229910000577 Silicon-germanium Inorganic materials 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 229910007657 ZnSb Inorganic materials 0.000 description 2
- FAPDDOBMIUGHIN-UHFFFAOYSA-K antimony trichloride Chemical compound Cl[Sb](Cl)Cl FAPDDOBMIUGHIN-UHFFFAOYSA-K 0.000 description 2
- JHXKRIRFYBPWGE-UHFFFAOYSA-K bismuth chloride Chemical compound Cl[Bi](Cl)Cl JHXKRIRFYBPWGE-UHFFFAOYSA-K 0.000 description 2
- 238000011109 contamination Methods 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 238000010335 hydrothermal treatment Methods 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 239000010453 quartz Substances 0.000 description 2
- 238000011946 reduction process Methods 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 239000012279 sodium borohydride Substances 0.000 description 2
- 229910000033 sodium borohydride Inorganic materials 0.000 description 2
- 238000002490 spark plasma sintering Methods 0.000 description 2
- OCGWQDWYSQAFTO-UHFFFAOYSA-N tellanylidenelead Chemical compound [Pb]=[Te] OCGWQDWYSQAFTO-UHFFFAOYSA-N 0.000 description 2
- 239000002918 waste heat Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910002688 Ag2Te Inorganic materials 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- 229910015400 FeC13 Inorganic materials 0.000 description 1
- JQGGAELIYHNDQS-UHFFFAOYSA-N Nic 12 Natural products CC(C=CC(=O)C)c1ccc2C3C4OC4C5(O)CC=CC(=O)C5(C)C3CCc2c1 JQGGAELIYHNDQS-UHFFFAOYSA-N 0.000 description 1
- 230000005679 Peltier effect Effects 0.000 description 1
- 230000005678 Seebeck effect Effects 0.000 description 1
- 241000519995 Stachys sylvatica Species 0.000 description 1
- 230000004520 agglutination Effects 0.000 description 1
- 229910000410 antimony oxide Inorganic materials 0.000 description 1
- KYKAJFCTULSVSH-UHFFFAOYSA-N chloro(fluoro)methane Chemical compound F[C]Cl KYKAJFCTULSVSH-UHFFFAOYSA-N 0.000 description 1
- GFHNAMRJFCEERV-UHFFFAOYSA-L cobalt chloride hexahydrate Chemical compound O.O.O.O.O.O.[Cl-].[Cl-].[Co+2] GFHNAMRJFCEERV-UHFFFAOYSA-L 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000007123 defense Effects 0.000 description 1
- 229940044631 ferric chloride hexahydrate Drugs 0.000 description 1
- NQXWGWZJXJUMQB-UHFFFAOYSA-K iron trichloride hexahydrate Chemical compound O.O.O.O.O.O.[Cl-].Cl[Fe+]Cl NQXWGWZJXJUMQB-UHFFFAOYSA-K 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000005551 mechanical alloying Methods 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000004377 microelectronic Methods 0.000 description 1
- LAIZPRYFQUWUBN-UHFFFAOYSA-L nickel chloride hexahydrate Chemical compound O.O.O.O.O.O.[Cl-].[Cl-].[Ni+2] LAIZPRYFQUWUBN-UHFFFAOYSA-L 0.000 description 1
- VTRUBDSFZJNXHI-UHFFFAOYSA-N oxoantimony Chemical compound [Sb]=O VTRUBDSFZJNXHI-UHFFFAOYSA-N 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- PORWMNRCUJJQNO-UHFFFAOYSA-N tellurium atom Chemical compound [Te] PORWMNRCUJJQNO-UHFFFAOYSA-N 0.000 description 1
- 230000005676 thermoelectric effect Effects 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/16—Making metallic powder or suspensions thereof using chemical processes
- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
- B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
- C22C1/047—Making non-ferrous alloys by powder metallurgy comprising intermetallic compounds
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C32/00—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ
- C22C32/001—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides
- C22C32/0015—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides with only single oxides as main non-metallic constituents
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
- H10N10/01—Manufacture or treatment
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
- H10N10/80—Constructional details
- H10N10/85—Thermoelectric active materials
- H10N10/851—Thermoelectric active materials comprising inorganic compositions
- H10N10/852—Thermoelectric active materials comprising inorganic compositions comprising tellurium, selenium or sulfur
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
- H10N10/80—Constructional details
- H10N10/85—Thermoelectric active materials
- H10N10/857—Thermoelectric active materials comprising compositions changing continuously or discontinuously inside the material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
- B22F2998/10—Processes characterised by the sequence of their steps
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S977/00—Nanotechnology
- Y10S977/70—Nanostructure
- Y10S977/778—Nanostructure within specified host or matrix material, e.g. nanocomposite films
- Y10S977/779—Possessing nanosized particles, powders, flakes, or clusters other than simple atomic impurity doping
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Inorganic Chemistry (AREA)
- Powder Metallurgy (AREA)
- Manufacture Of Metal Powder And Suspensions Thereof (AREA)
Abstract
A method of producing a nanocomposite thermoelectric conversion material includes preparing a solution that contains salts of a plurality of first elements constituting a thermoelectric conversion material, and a salt of a second element that has a redox potential lower than redox potentials of the first elements; precipitating the first elements, thereby producing a matrix-precursor that is a precursor of a matrix made of the thermoelectric conversion material, by adding a reducing agent to the solution; precipitating the second element in the matrix-precursor, thereby producing slurry containing the first elements and the second element, by further adding the reducing agent to the solution; and alloying the plurality of the first elements, thereby producing the matrix (70) made of the thermoelectric conversion material, and producing nano-sized phonon-scattering particles (80) including the second element, which are dispersed in the matrix (70), by filtering and washing the slurry, and then, heat-treating the slurry.
Description
NANOCOMPOSITE THERMOELECTRIC CONVERSION MATERIAL AND
METHOD OF PRODUCING THE SAME
BACKGROUND OF THE INVENTION
1. Field of the Invention 10001) The invention relates to a method of producing a nanocomposite thermoelectric conversion material in which nano-sized phonon-scattering particles are dispersed in a matrix made of a thermoelectric conversion material, and a nanocomposite thermoelectric conversion material produced using the method.
METHOD OF PRODUCING THE SAME
BACKGROUND OF THE INVENTION
1. Field of the Invention 10001) The invention relates to a method of producing a nanocomposite thermoelectric conversion material in which nano-sized phonon-scattering particles are dispersed in a matrix made of a thermoelectric conversion material, and a nanocomposite thermoelectric conversion material produced using the method.
2. Description of the Related Art [0002] A thermoelectric conversion material is an energy material that directly converts thermal energy to electric energy, based on two basic thermoelectric effects, that is, the Seebeck effect and the Peltier effect.
[0003] A thermoelectric generation device, which uses the thermoelectric conversion material, has many advantages as compared to conventional power generation technologies. For example, the thermoelectric generation device has a simple structure, and is robust and highly durable. The thermoelectric generation device does not have a movable member. The micro-sized thermoelectric generation device is easily produced.
The thermoelectric generation device does not require maintenance. The thermoelectric generation device is highly reliable, has a long lifespan, does not cause noise, and does not cause contamination. The thermoelectric generation device uses low-temperature waste heat.
The thermoelectric generation device does not require maintenance. The thermoelectric generation device is highly reliable, has a long lifespan, does not cause noise, and does not cause contamination. The thermoelectric generation device uses low-temperature waste heat.
[0004] A thermoelectric cooling device, which uses the thermoelectric conversion material, also has advantages as compared to conventional compression cooling technologies. For example, the thermoelectric cooling device does not require chlorofluorocarbon, and does not cause contamination. The small-sized thermoelectric cooling device is easily produced. The thermoelectric cooling device does not have a movable member, and does not cause noise.
[0005] Therefore, particularly because energy-related issues and environment-related issues have recently become more serious, it is expected that the thermoelectric conversion material will be put to practical use in fields of aerospace, national defense, construction, geological observation, weather observation, medical care, hygiene, microelectronics, and the like. Also, it is expected that the thermoelectric conversion material will be used for various 1:imposes, for example, for the purpose of using waste heat in petrochemical industry, metallurgy, and electric power industry.
100061 A power factor P = S2a, and a nondimensional performance index ZT =
(S2a / T
are used as indices for evaluating the performance of the thermoelectric conversion material. In this case, S represents a Seebeck coefficient, a represents an electric conductivity, ic represents a thermal conductivity, and T represents an absolute temperature. That is, in order to obtain a good thermoelectric characteristic, the Seebeck coefficient S and the electric conductivity a need to be high, and the thermal conductivity K needs to be low.
[0007]
To scatter phonons, which conduct heat, is effective for decreasing the thermal conductivity K. Thus, a composite thermoelectric conversion material, in which particles used for scattering the phonons (hereinafter, referred to as "phonon-scattering particles") are dispersed in a matrix made of a thermoelectric conversion material, has been proposed.
[0008] Japanese Patent Application Publication No. 2000-164940 (JP-A-2000-164940) describes a technology in which particles of Ag2Te (that is a thermoelectric conversion material) are dispersed in a matrix made of a thermoelectric conversion material AgBiTe2. The phonons are scattered by the dispersed particles, and thus, the thermal conductivity ic is decreased. In a production method thereof, a mixture of a matrix material and the dispersed particles is molten; the dispersed particles are uniformly precipitated by maintaining the temperature of the mixture at a temperature equal to or higher than the melting point of the matrix material, and equal to or lower than the melting point of the dispersed particles; and then, the matrix is precipitated by cooling the mixture to a temperature equal to or lower than the melting point of the matrix. Accordingly, the dispersed particles are precipitated before the matrix is precipitated. Therefore, the dispersed particles are likely to agglutinate, and thus, the size of the dispersed particles is likely to be increased. As a result, the dispersibility of the dispersed particles is decreased, the effect of scattering the phonons is decreased, and the effect of decreasing the thermal conductivity is decreased.
[0009] Japanese Patent Application Publication No. 2000-261047 (JP-A-2000-261047) describes a technology in which ceramic particles are dispersed in a matrix made of a thermoelectric conversion material CoSb3. In this method, however, even the smallest dispersed ceramic particles are sub-micron sized particles.
Therefore, the phonons are not highly scattered, Even if the nano-sized ceramic particles were used, the nano-sized ceramic particles would be likely to agglutinate, and as a result, the dispersed particles would not be nano-sized particles.
[0010] Japanese Patent Application Publication No. 2003-73705 (JP-A-2003-73705) describes a technology in which a reducing agent is dropped into a solution containing a metal with a high reduction potential and a metal with a low reduction potential, and the metal with the high reduction potential is precipitated first, and then, the metal with the low reduction potential is precipitated. However, the publication No. 2003-73705 merely describes the fact that metals are reduced and precipitated in order of decreasing the reduction potential. The publication No.
2003-73705 does not describe a technology in which phonon-scattering particles are dispersed in a matrix made of a thermoelectric conversion material.
[0011] Japanese Patent Application Publication No. 2008-305919 (JP-A-2008-305919) describes a technology in which a solution containing salts of elements constituting a thermoelectric conversion material and a salt of a metal or an alloy is mixed with a solution containing a reducing agent. The amount of the salt of the metal or the alloy contained in the solution is excessive with respect to the amount of the metal or the alloy to be contained in the thermoelectric conversion material.
Particles including the elements constituting the thermoelectric conversion material and particles including the metal or the alloy are precipitated, and heat treatment is performed. Thus, the particles including the metal or the alloy are dispersed in the matrix made of the thermoelectric conversion material. Then, sintering is performed, and thus, the particles including the metal or the alloy are integrated with the matrix. In this method, however, the particles including the elements constituting the thermoelectric conversion material of the matrix, and the phonon-scattering particles are precipitated in a mixed state.
Therefore, it is not possible to prevent the agglutination of the precipitated phonon-scattering particles, and the increase in the size of the phonon-scattering particles.
SUMMARY OF THE INVENTION
[00121 The invention provides a nanocomposite thermoelectric conversion material in which nano-sized phonon-scattering particles are dispersed in a matrix made of a thermoelectric conversion material, and which has a greatly decreased thermal conductivity, and significantly improved thermoelectric conversion performance, and a method of producing the same.
[00131 A
first aspect of the invention relates to a method of producing a nanocomposite thermoelectric conversion material. The method includes preparing a solution that contains salts of a plurality of first elements constituting a thermoelectric conversion material, and a salt of a second element that has a redox potential lower than redox potentials of the first elements; precipitating the first elements, thereby producing a matrix-precursor that is a precursor of a matrix made of the thermoelectric conversion material, by adding a reducing agent to the solution; precipitating the second element in the matrix-precursor, thereby producing slurry containing the first elements and the second element, by further adding the reducing agent to the solution; and alloying the plurality of the first elements, thereby producing the matrix made of the thermoelectric conversion material, and producing nano-sized phonon-scattering particles including the second element, which are dispersed in the matrix, by filtering and washing the slurry, and then, heat-treating the slurry.
[0014] A
second aspect of the invention relates to a method of producing a nanocomposite thermoelectric conversion material. The method includes preparing a solution that contains salts of a plurality of first elements constituting a thermoelectric conversion material, wherein the solution contains an excessive amount of a salt of a predetermined element among the plurality of the first elements, with respect to a predetermined composition of the thermoelectric conversion material, and a redox potential of the predetermined element is not the highest among redox potentials of the plurality of the first elements; precipitating an element among the first elements, which has the redox potential higher than the redox potential of the predetermined element, by adding a reducing agent to the solution; precipitating the predetermined element, and producing slurry containing all the plurality of the first elements, by further adding the reducing agent to the solution; and producing a matrix made of the thermoelectric conversion material with the predetermined composition, and nano-sized phonon-scattering particles dispersed in the matrix, by filtering and washing the slurry, and then, heat-treating the slurry, wherein the nano-sized phonon-scattering particles include a surplus of the predetermined element with respect to the predetermined composition.
[0015] A
third aspect of the invention relates to a nanocomposite thermoelectric conversion material produced by the method according to the first aspect of the invention.
A fourth aspect of the invention relates to a nanocomposite thermoelectric conversion material produced by the method according to the second aspect of the invention.
[0016]
According to the above-described aspects, the elements constituting the thermoelectric conversion material of the matrix are precipitated first, and particles including the elements are produced. Then, the phonon-scattering particles are precipitated among the particles including the elements constituting the matrix.
Therefore, the phonon-scattering particles are not agglutinated, and the nano-size of the phonon-scattering particles is maintained. Therefore, it is possible to obtain the extremely high phonon-scattering effect. As a result, it is possible to produce the nanocomposite thermoelectric conversion material with the significantly decreased thermal conductivity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The features, advantages, and technical and industrial significance of this invention will be described in the following detailed description of example embodiments of the invention with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:
FIGS. 1A to 1E are diagrams schematically showing changes in phases due to reduction and heat treatment in a method according to a first embodiment of the invention;
FIGS. 2A to 2D are diagrams schematically showing changes in phases due to reduction and heat treatment in a method according to a second embodiment of the invention;
FIGS. 3A and 3B are diagrams relating to a nanocomposite thermoelectric conversion material produced in a first example (a matrix made of a thermoelectric conversion material: (Co, Ni) Sb3, phonon-scattering particles: Fe203), FIG.
3A being an XRD chart, and FIG 3B being a IBM image;
FIGS. 4A to 4D are diagrams relating to a nanocomposite thermoelectric conversion material produced in a second example (a matrix made of a thermoelectric conversion material: (Bi, Sb)2Te3, phonon-scattering particles: Sb203), FIG. 4A being an XRD chart, FIG. 4B being an EELS oxygen mapping image, FIG. 4C being an TEM image showing the nanocomposite thermoelectric conversion material before heat treatment, and FIG. 4D
being an TEM image showing the nanocomposite thermoelectric conversion material after heat treatment;
FIGS. 5A to 5C are diagrams relating to the nanocomposite thermoelectric conversion materials in the first example and the second example, FIG. 5A
being a graph showing average diameters of phonon-scattering 'particles, FIG. 5B being a graph showing rates of decrease in a thermal conductivity, and FIG. 5C being a graph showing nondimensional performance indices ZT and values in related art described in a publication for comparison; and FIGS. 6A to 6D are diagrams relating to the nanocomposite thermoelectric conversion material in the second example, FIG. 6A being a graph showing a Seebeck coefficient with respect to a measured temperature and a value in related art described in a publication for comparison, FIG. 6B being a graph showing a specific resistance with respect to the measured temperature and a value in related art described in the publication for comparison, FIG 6C being a graph showing the thermal conductivity with respect to the measured temperature and a value in related art described in the publication for comparison, and FIG. 6D being a graph showing a nondimensional performance index ZT
with respect to the measured temperature and a value in related art described in the publication for comparison.
DETAILED DESCRIPTION OF EMBODIMENTS
[0018] Changes in phases in processes of producing a nanocomposite thermoelectric conversion material according to the invention will be described with reference to FIGS. lA to 1E and FIG 2A to 2D.
First embodiment [0019]
FIGS. IA to 1E schematically show processes according to a first embodiment of the invention. The description will be made on the assumption that a nanocomposite thermoelectric conversion material, in which particles made of Fe2O3 are dispersed in a matrix made of a thermoelectric conversion material (Co, Ni) Sb3, is produced. The particles made of Fe203 serve as particles used for scattering phonons (hereinafter, referred to as "phonon-scattering particles").
First step [0020] A
solution, which contains salts of a plurality of first elements Co, Ni, and Sb that constitute the thermoelectric conversion material (Co, Ni) Sb3, and a salt of a second element Fe that has a redox potential lower than redox potentials of the first elements, is prepared.
100061 A power factor P = S2a, and a nondimensional performance index ZT =
(S2a / T
are used as indices for evaluating the performance of the thermoelectric conversion material. In this case, S represents a Seebeck coefficient, a represents an electric conductivity, ic represents a thermal conductivity, and T represents an absolute temperature. That is, in order to obtain a good thermoelectric characteristic, the Seebeck coefficient S and the electric conductivity a need to be high, and the thermal conductivity K needs to be low.
[0007]
To scatter phonons, which conduct heat, is effective for decreasing the thermal conductivity K. Thus, a composite thermoelectric conversion material, in which particles used for scattering the phonons (hereinafter, referred to as "phonon-scattering particles") are dispersed in a matrix made of a thermoelectric conversion material, has been proposed.
[0008] Japanese Patent Application Publication No. 2000-164940 (JP-A-2000-164940) describes a technology in which particles of Ag2Te (that is a thermoelectric conversion material) are dispersed in a matrix made of a thermoelectric conversion material AgBiTe2. The phonons are scattered by the dispersed particles, and thus, the thermal conductivity ic is decreased. In a production method thereof, a mixture of a matrix material and the dispersed particles is molten; the dispersed particles are uniformly precipitated by maintaining the temperature of the mixture at a temperature equal to or higher than the melting point of the matrix material, and equal to or lower than the melting point of the dispersed particles; and then, the matrix is precipitated by cooling the mixture to a temperature equal to or lower than the melting point of the matrix. Accordingly, the dispersed particles are precipitated before the matrix is precipitated. Therefore, the dispersed particles are likely to agglutinate, and thus, the size of the dispersed particles is likely to be increased. As a result, the dispersibility of the dispersed particles is decreased, the effect of scattering the phonons is decreased, and the effect of decreasing the thermal conductivity is decreased.
[0009] Japanese Patent Application Publication No. 2000-261047 (JP-A-2000-261047) describes a technology in which ceramic particles are dispersed in a matrix made of a thermoelectric conversion material CoSb3. In this method, however, even the smallest dispersed ceramic particles are sub-micron sized particles.
Therefore, the phonons are not highly scattered, Even if the nano-sized ceramic particles were used, the nano-sized ceramic particles would be likely to agglutinate, and as a result, the dispersed particles would not be nano-sized particles.
[0010] Japanese Patent Application Publication No. 2003-73705 (JP-A-2003-73705) describes a technology in which a reducing agent is dropped into a solution containing a metal with a high reduction potential and a metal with a low reduction potential, and the metal with the high reduction potential is precipitated first, and then, the metal with the low reduction potential is precipitated. However, the publication No. 2003-73705 merely describes the fact that metals are reduced and precipitated in order of decreasing the reduction potential. The publication No.
2003-73705 does not describe a technology in which phonon-scattering particles are dispersed in a matrix made of a thermoelectric conversion material.
[0011] Japanese Patent Application Publication No. 2008-305919 (JP-A-2008-305919) describes a technology in which a solution containing salts of elements constituting a thermoelectric conversion material and a salt of a metal or an alloy is mixed with a solution containing a reducing agent. The amount of the salt of the metal or the alloy contained in the solution is excessive with respect to the amount of the metal or the alloy to be contained in the thermoelectric conversion material.
Particles including the elements constituting the thermoelectric conversion material and particles including the metal or the alloy are precipitated, and heat treatment is performed. Thus, the particles including the metal or the alloy are dispersed in the matrix made of the thermoelectric conversion material. Then, sintering is performed, and thus, the particles including the metal or the alloy are integrated with the matrix. In this method, however, the particles including the elements constituting the thermoelectric conversion material of the matrix, and the phonon-scattering particles are precipitated in a mixed state.
Therefore, it is not possible to prevent the agglutination of the precipitated phonon-scattering particles, and the increase in the size of the phonon-scattering particles.
SUMMARY OF THE INVENTION
[00121 The invention provides a nanocomposite thermoelectric conversion material in which nano-sized phonon-scattering particles are dispersed in a matrix made of a thermoelectric conversion material, and which has a greatly decreased thermal conductivity, and significantly improved thermoelectric conversion performance, and a method of producing the same.
[00131 A
first aspect of the invention relates to a method of producing a nanocomposite thermoelectric conversion material. The method includes preparing a solution that contains salts of a plurality of first elements constituting a thermoelectric conversion material, and a salt of a second element that has a redox potential lower than redox potentials of the first elements; precipitating the first elements, thereby producing a matrix-precursor that is a precursor of a matrix made of the thermoelectric conversion material, by adding a reducing agent to the solution; precipitating the second element in the matrix-precursor, thereby producing slurry containing the first elements and the second element, by further adding the reducing agent to the solution; and alloying the plurality of the first elements, thereby producing the matrix made of the thermoelectric conversion material, and producing nano-sized phonon-scattering particles including the second element, which are dispersed in the matrix, by filtering and washing the slurry, and then, heat-treating the slurry.
[0014] A
second aspect of the invention relates to a method of producing a nanocomposite thermoelectric conversion material. The method includes preparing a solution that contains salts of a plurality of first elements constituting a thermoelectric conversion material, wherein the solution contains an excessive amount of a salt of a predetermined element among the plurality of the first elements, with respect to a predetermined composition of the thermoelectric conversion material, and a redox potential of the predetermined element is not the highest among redox potentials of the plurality of the first elements; precipitating an element among the first elements, which has the redox potential higher than the redox potential of the predetermined element, by adding a reducing agent to the solution; precipitating the predetermined element, and producing slurry containing all the plurality of the first elements, by further adding the reducing agent to the solution; and producing a matrix made of the thermoelectric conversion material with the predetermined composition, and nano-sized phonon-scattering particles dispersed in the matrix, by filtering and washing the slurry, and then, heat-treating the slurry, wherein the nano-sized phonon-scattering particles include a surplus of the predetermined element with respect to the predetermined composition.
[0015] A
third aspect of the invention relates to a nanocomposite thermoelectric conversion material produced by the method according to the first aspect of the invention.
A fourth aspect of the invention relates to a nanocomposite thermoelectric conversion material produced by the method according to the second aspect of the invention.
[0016]
According to the above-described aspects, the elements constituting the thermoelectric conversion material of the matrix are precipitated first, and particles including the elements are produced. Then, the phonon-scattering particles are precipitated among the particles including the elements constituting the matrix.
Therefore, the phonon-scattering particles are not agglutinated, and the nano-size of the phonon-scattering particles is maintained. Therefore, it is possible to obtain the extremely high phonon-scattering effect. As a result, it is possible to produce the nanocomposite thermoelectric conversion material with the significantly decreased thermal conductivity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The features, advantages, and technical and industrial significance of this invention will be described in the following detailed description of example embodiments of the invention with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:
FIGS. 1A to 1E are diagrams schematically showing changes in phases due to reduction and heat treatment in a method according to a first embodiment of the invention;
FIGS. 2A to 2D are diagrams schematically showing changes in phases due to reduction and heat treatment in a method according to a second embodiment of the invention;
FIGS. 3A and 3B are diagrams relating to a nanocomposite thermoelectric conversion material produced in a first example (a matrix made of a thermoelectric conversion material: (Co, Ni) Sb3, phonon-scattering particles: Fe203), FIG.
3A being an XRD chart, and FIG 3B being a IBM image;
FIGS. 4A to 4D are diagrams relating to a nanocomposite thermoelectric conversion material produced in a second example (a matrix made of a thermoelectric conversion material: (Bi, Sb)2Te3, phonon-scattering particles: Sb203), FIG. 4A being an XRD chart, FIG. 4B being an EELS oxygen mapping image, FIG. 4C being an TEM image showing the nanocomposite thermoelectric conversion material before heat treatment, and FIG. 4D
being an TEM image showing the nanocomposite thermoelectric conversion material after heat treatment;
FIGS. 5A to 5C are diagrams relating to the nanocomposite thermoelectric conversion materials in the first example and the second example, FIG. 5A
being a graph showing average diameters of phonon-scattering 'particles, FIG. 5B being a graph showing rates of decrease in a thermal conductivity, and FIG. 5C being a graph showing nondimensional performance indices ZT and values in related art described in a publication for comparison; and FIGS. 6A to 6D are diagrams relating to the nanocomposite thermoelectric conversion material in the second example, FIG. 6A being a graph showing a Seebeck coefficient with respect to a measured temperature and a value in related art described in a publication for comparison, FIG. 6B being a graph showing a specific resistance with respect to the measured temperature and a value in related art described in the publication for comparison, FIG 6C being a graph showing the thermal conductivity with respect to the measured temperature and a value in related art described in the publication for comparison, and FIG. 6D being a graph showing a nondimensional performance index ZT
with respect to the measured temperature and a value in related art described in the publication for comparison.
DETAILED DESCRIPTION OF EMBODIMENTS
[0018] Changes in phases in processes of producing a nanocomposite thermoelectric conversion material according to the invention will be described with reference to FIGS. lA to 1E and FIG 2A to 2D.
First embodiment [0019]
FIGS. IA to 1E schematically show processes according to a first embodiment of the invention. The description will be made on the assumption that a nanocomposite thermoelectric conversion material, in which particles made of Fe2O3 are dispersed in a matrix made of a thermoelectric conversion material (Co, Ni) Sb3, is produced. The particles made of Fe203 serve as particles used for scattering phonons (hereinafter, referred to as "phonon-scattering particles").
First step [0020] A
solution, which contains salts of a plurality of first elements Co, Ni, and Sb that constitute the thermoelectric conversion material (Co, Ni) Sb3, and a salt of a second element Fe that has a redox potential lower than redox potentials of the first elements, is prepared.
[00211 The redox potentials of the elements in decreasing order are as follows.
The redox potential of Sb is 0.16V. The redox potential of Ni is ¨0.25 V. The redox potential of Co is ¨0.27V. The redox potential of Fe is ¨0.44V.
Second step [00221 The first elements are precipitated, and thus, a matrix-precursor, which is a precursor of the matrix made of the thermoelectric conversion material, is produced, by adding a reducing agent to the above-described solution. In this reduction process, the elements are precipitated in order of decreasing the redox potential. More specifically, first, an element 10 (Sb) with the highest redox potential among the first elements is precipitated as particles in the solution. Thus, the particles including the element 10 (i.e., Sb particles) are dispersed in the solution (FIG. 1A).
[0023] Next, elements 20 (Ni) and 30 (Co) among the first elements are precipitated in order of decreasing the redox potential. Thus, a matrix-precursor 40, which is an aggregate of the particles including the elements 10, 20, and 30 (i.e., the Sb particles, Ni particles, and Co particles), is produced (FIG 1B).
[0024] Gaps between the particles in the matrix-precursor 40 are filled with the solution containing a second element 50 (Fe). Thus, the particles are dispersed in the entire solution.
Third step [00251 The second element 50 (Fe) is precipitated in the matrix-precursor 40, and thus, slurry 60 containing the first elements and the second element is produced, by further adding the above-described reducing agent to the solution in which the particles are dispersed as shown in FIG IC. More specifically, the particles including the second element 50 are mixture of Fe and Fe0H. FIG. ID shows the slurry 60 in a different manner. As shown in FIG. 1D, the slurry 60 includes a base including the first element 10 (Sb) with the highest redox potential among the first elements constituting the thermoelectric conversion material, and the particles including the rest of the first elements, that is, the first elements 20 and 30 (Ni and Co), and the particles including the second element 50 (Fe). The particles including the first elements 20 and 30 and the particles including the second element 50 are dispersed in the base.
Fourth step [0026]
Next, the plurality of first elements 10, 20, and 30 (Sb, Ni, and Co) are alloyed, and thus, a matrix 70 including the thermoelectric conversion material (Co, Ni) Sb3 is produced, and nano-sized phonon-scattering particles 80 including the second element 50, which are dispersed in the matrix 70, are produced, by filtering and washing the slurry 60, and then, heat-treating the slurry 60. Fe or Fe0H of the particles including the second element 50 is oxidized, and thus, the phonon-scattering particles 80 made of iron oxide Fe203 are produced. That is, the phonon-scattering particles 80 are made of oxide of the second element 50.
[0027]
As described above, the particles including the second element 50 are precipitated in the gaps in the matrix-precursor 40. Therefore, each of the precipitated particles including the second element 50 is restrained by the matrix-precursor 40, and thus, the particles including the second element 50 are not agglutinated.
Accordingly, the size of the particles including the second element 50 remains the same as the nano-size of the particles including the second element 50 when precipitated from the solution.
[0028]
Thus, a nanocomposite thermoelectric conversion material 100, in which the nano-sized phonon-scattering particles 80 are dispersed in the matrix 70 including thermoelectric conversion material, is produced.
[0029]
Examples of the nanocomposite thermoelectric conversion material, which are appropriately produced by the method according to the first embodiment of the invention, include (Bi, Sb)2 (Te, Se)3-based nanocomposite thermoelectric conversion materials, PbTe-based nanocomposite thermoelectric conversion materials, CoSb3-based nanocomposite thermoelectric conversion materials, SiGe-based nanocomposite thermoelectric conversion materials, ZnSb-based nanocomposite thermoelectric conversion materials, FeSi-based nanocomposite thermoelectric conversion materials, and BiSb-based nanocomposite thermoelectric conversion materials.
Second embodiment [0030] FIGS.
2A to 2D schematically show processes according to a second embodiment of the invention. The description will be made on the assumption that a nanocomposite thermoelectric conversion material, in which particles made of Sb203 are dispersed in a matrix made of a thermoelectric conversion material (Bi, Sb)2Te3, is 5 produced. The particles made of Sb203 serve as phonon-scattering particles.
First step [0031] A
solution, which contains salts of a plurality of first elements Bi, Sb, and Te that constitute the thermoelectric conversion material (Bi, Sb)2Te3, is prepared.
The solution contains an excessive amount of the salt of a predetermined element (Sb) 10 among the plurality of the first elements, with respect to a predetermined composition of the thermoelectric conversion material, and the redox potential of the predetermined element (Sb) is not the highest among the redox potentials of the first elements (Te has the highest redox potential).
[0032] In this case, the redox potentials of the elements in decreasing order are as follows. The redox potential of Te is 0.53V. The redox potential of Sb is 0.16 V.
The redox potential of Bi is 0.16V. In another example of this embodiment, the solution may contain an excessive amount of Bi, instead of containing an excessive amount of Sb.
Second step [0033] The element among the first elements, which has the redox potential higher than the redox potential of the predetermined element, is precipitated by adding a reducing agent to the above-described solution. More specifically, first, the element 11 (Te) with the highest redox potential among the first elements is precipitated as particles in the solution. Thus, the particles including the element 11 (i.e., Te particles) are dispersed in the solution (FIG. 2A).
Third step [0034] The predetermined element 51 (Sb) is precipitated by further adding the above-described reducing agent to the solution in which the particles are dispersed. In the assumed case, the predetermined element 51 is Sb. However, Bi, which has the redox potential equal to the redox potential of Sb, is simultaneously precipitated to produce particles including the element 21 (i.e., Bi particles).
Thus, slurry 60 containing all the plurality of the first elements Te, Bi, and Sb is produced as shown in FIG. 2B. FIG. 2C shows the slurry 60 in a different manner. As shown in FIG.
2C, the slurry 60 includes a base including the element 11 (Te) with the highest redox potential among the first elements constituting the thermoelectric conversion material, and the particles including the rest of the first elements, that is, the particles including the first elements 21 and 51 (Bi and Sb). The particles including the first elements 21 and 51 are dispersed in the base.
Fourth step [00351 Next, a matrix 70 including the thermoelectric conversion material with a predetermined composition (Bi, Sb)2Te3 is produced due to alloying, and nano-sized phonon-scattering particles 80 dispersed in the matrix 70 are produced, by filtering and washing the slurry 60, and then, heat-treating the slimy 60.
The nano-sized phonon-scattering particles 80 include a surplus of the predetermined element 51 with respect to the predetermined composition. At this time, part of the predetermined element 51 is incorporated into the predetermined composition to produce the matrix 70 including the thermoelectric conversion material. During the heat treatment, the surplus of the predetermined clement 51 is oxidized, and thus, particles made of oxide of the predetermined element Si (i.e., particles made of antimony oxide Sb203), which serve as phonon-scattering particles 80, are produced. That is, the phonon-scattering particles 80 are made of oxide of the predetermined element 51.
[00361 Thus, the predetermined element 51 is precipitated in the matrix 70.
Therefore, each of the precipitated particles including the predetermined element 51 is restrained by the matrix 70, and thus, the particles including the predetermined element 51 are not agglutinated. Accordingly, the size of the particles including the predetermined element 51 remains the same as the nano-size of the particles including the predetermined element 51 when precipitated from the solution.
[00371 Thus, a nanocomposite thermoelectric conversion material 100, in which the nano-sized phonon-scattering particles 80 are dispersed in the matrix 70 including the thermoelectric conversion material, is produced.
[0038]
Examples of the nanocomposite thermoelectric conversion material, which are appropriately produced by the method according to the second embodiment of the invention, include (Bi, Sb)2 (Te, Se)3-based nanocomposite thermoelectric conversion materials, PbTe-based nanocomposite thermoelectric conversion materials, CoSb3-based nanocomposite thermoelectric conversion materials, SiGe-based nanocomposite thermoelectric conversion materials, ZnSb-based nanocomposite thermoelectric conversion materials, FeSi-based nanocomposite thermoelectric conversion materials, and BiSb-based nanocomposite thermoelectric conversion materials.
Examples First example [0039]
The nanocomposite thermoelectric conversion material, in which 10 vol % of Fe203 particles were dispersed in the matrix made of the thermoelectric conversion material (Co, Ni) Sb3, was produced according to a procedure described below on a condition described below, using the method according to the first embodiment of the invention. The Fe203 particles served as phonon-scattering particles.
Preparation of a source material solution [0040] A
source material solution was prepared by dissolving source materials described below, in 100 nil of ethanol.
[0041] The source materials for the matrix were 2.75 g of antimony chloride (SbC13), 0.9 g of cobalt chloride hexahydrate (CoC12=61-120), and 0.057 g of nickel chloride hexahydrate (NiC12=6F120). The source material for the dispersed particles was 0.335 g of ferric chloride hexahydrate (FeC13=6H20).
Reduction [0042] A solution, which was produced by dissolving 2.4 g of NaBH4, which served as a reducing agent, in 100 ml of ethanol, was dropped into the above-described source material solution. Ethanol slurry containing =nano particles precipitated by reduction was filtered and washed using a solution produced by mixing 500 ml of water and 300 ml of ethanol, and further, the shiny was filtered and washed using 300 ml of ethanol.
Heat treatment Then, the slurry was placed in a hermetically-sealed autoclave device, and the alloy matrix was produced by performing hydrothermal treatment at 240 C for 48 hours. Then, drying was performed in an N2 gas flow atmosphere, and powder was collected. At this time, approximately 2.0 g of powder was collected.
Sintering [0044]
Spark plasma sintering (SPS) was performed on the collected powder at 500 C. Thus, the nanocomposite thermoelectric conversion material, in which vol % of Fe203 particles were dispersed in the matrix made of the thermoelectric conversion material (Co, Ni) Sb3, was produced. The Fe203 particles served as the phonon-scattering particles.
Observation of constituent phases [0045]
The produced powder was analyzed and observed by XRD analysis and TEM observation. FIG 3A shows an XRD chart, and FIG 3l3 shows a TEM image.
As shown in the XRD chart, diffraction peaks of (Co, Ni) Sb3 (indicated by rhombus marks in FIG. 3A) and diffraction peaks of Fe203 (indicated by circles in FIG.
3A) were clearly observed. Thus, it was confirmed that the nanocomposite thermoelectric conversion material included both of the phase of (Co, Ni) Sb3 and the phase of Fe203.
Also, the dispersed Fe203 particles with the average diameter of 19 nm were observed in the TEM image.
Performance [0046]
Table 1 shows the measured Seebeck coefficient, the measured specific resistance, the measured thermal conductivity, and the measured nondimensional performance index ZT at 400 C. Further, for the purpose of comparison, Table 1 shows - values that are considered to be best values obtained in a thermoelectric conversion material (Co, Ni) Sb3 with a single phase, in which there is no phonon-scattering particle, in a conventional example. The values are described, in a publication (*1). It is evident from Table 1 that the thermal conductivity of the nanocomposite thermoelectric conversion material according to the invention is 0.7 (W/m/K) that is one-fifth of the thermal conductivity of the thermoelectric conversion material in the conventional example. Also, it is evident from Table 1 that the nondimensional performance index ZT of the nanocomposite thermoelectric conversion material according to the invention is 1.33 that is more than 2.5 times the nondimensional performance index ZT of the thermoelectric conversion material in the conventional example, and thus, the nondimensional performance index ZT of the nanocomposite thermoelectric conversion material according to the invention is significantly improved.
Table 1 Seebeck Specific Thermal ZT
coefficient resistance conductivity ( V/K) (1-1-Qm) (W/rn/K) First example -204 30 0.7 1.33 Conventional -200 15 3.5 0.5 example(*1) [0047] The cited related art is described in the publication (*1) "Katsuyarna S., Watanabe M., Kuroki M. et al, Journal of Applied Physics, volume 93, Issue 5, pp2758-2764 (2003)". In a production method described in the publication, (1) Co, Ni, Sb are sealed in quartz, heated and molten, and mixed to produce an alloy; (2) the alloy is subjected to mechanical alloying, that is, the alloy is fractured; and (3) sintering is performed using a hot press.
Second example [0048] The nanocomposite thermoelectric conversion material, in which 10 vol % of Sb203 particles were dispersed in the matrix made of the thermoelectric conversion material (Bi, Sb)2Te3, was produced according to a procedure described below on a condition described below, using the method according to the second embodiment of the invention. The Sb203 particles served as phonon-scattering particles.
Preparation of a source material solution [00419] A source material solution was prepared by dissolving source materials described below, in 100 ml of ethanol. The source materials for the matrix were 0.4 g of bismuth chloride (BiC13), and 2.56 g of tellurium chloride (TeC14). The source material used for producing the matrix and the dispersed particles was 1.5 g of antimony chloride (SbC13).
Reduction [0050] A
solution, which was produced by dissolving 2.4 g of NaBH4, which served as a reducing agent, in 100 ml of ethanol, was dropped into the above-described source material solution. Ethanol slurry containing nano particles precipitated by reduction was filtered and washed using a solution produced by mixing 500 ml of water and 300 ml of ethanol, and further, the slurry was filtered and washed using 300 ml of ethanol.
10 Heat treatment [0051]
Then, the slurry was placed in a hermetically-sealed autoclave device, and the alloy matrix was produced by performing hydrothermal treatment at 240 C for 48 hours. Then, drying was performed in an N2 gas flow atmosphere, and powder was collected. At this time, approximately 2.0 g of powder was collected.
The redox potential of Sb is 0.16V. The redox potential of Ni is ¨0.25 V. The redox potential of Co is ¨0.27V. The redox potential of Fe is ¨0.44V.
Second step [00221 The first elements are precipitated, and thus, a matrix-precursor, which is a precursor of the matrix made of the thermoelectric conversion material, is produced, by adding a reducing agent to the above-described solution. In this reduction process, the elements are precipitated in order of decreasing the redox potential. More specifically, first, an element 10 (Sb) with the highest redox potential among the first elements is precipitated as particles in the solution. Thus, the particles including the element 10 (i.e., Sb particles) are dispersed in the solution (FIG. 1A).
[0023] Next, elements 20 (Ni) and 30 (Co) among the first elements are precipitated in order of decreasing the redox potential. Thus, a matrix-precursor 40, which is an aggregate of the particles including the elements 10, 20, and 30 (i.e., the Sb particles, Ni particles, and Co particles), is produced (FIG 1B).
[0024] Gaps between the particles in the matrix-precursor 40 are filled with the solution containing a second element 50 (Fe). Thus, the particles are dispersed in the entire solution.
Third step [00251 The second element 50 (Fe) is precipitated in the matrix-precursor 40, and thus, slurry 60 containing the first elements and the second element is produced, by further adding the above-described reducing agent to the solution in which the particles are dispersed as shown in FIG IC. More specifically, the particles including the second element 50 are mixture of Fe and Fe0H. FIG. ID shows the slurry 60 in a different manner. As shown in FIG. 1D, the slurry 60 includes a base including the first element 10 (Sb) with the highest redox potential among the first elements constituting the thermoelectric conversion material, and the particles including the rest of the first elements, that is, the first elements 20 and 30 (Ni and Co), and the particles including the second element 50 (Fe). The particles including the first elements 20 and 30 and the particles including the second element 50 are dispersed in the base.
Fourth step [0026]
Next, the plurality of first elements 10, 20, and 30 (Sb, Ni, and Co) are alloyed, and thus, a matrix 70 including the thermoelectric conversion material (Co, Ni) Sb3 is produced, and nano-sized phonon-scattering particles 80 including the second element 50, which are dispersed in the matrix 70, are produced, by filtering and washing the slurry 60, and then, heat-treating the slurry 60. Fe or Fe0H of the particles including the second element 50 is oxidized, and thus, the phonon-scattering particles 80 made of iron oxide Fe203 are produced. That is, the phonon-scattering particles 80 are made of oxide of the second element 50.
[0027]
As described above, the particles including the second element 50 are precipitated in the gaps in the matrix-precursor 40. Therefore, each of the precipitated particles including the second element 50 is restrained by the matrix-precursor 40, and thus, the particles including the second element 50 are not agglutinated.
Accordingly, the size of the particles including the second element 50 remains the same as the nano-size of the particles including the second element 50 when precipitated from the solution.
[0028]
Thus, a nanocomposite thermoelectric conversion material 100, in which the nano-sized phonon-scattering particles 80 are dispersed in the matrix 70 including thermoelectric conversion material, is produced.
[0029]
Examples of the nanocomposite thermoelectric conversion material, which are appropriately produced by the method according to the first embodiment of the invention, include (Bi, Sb)2 (Te, Se)3-based nanocomposite thermoelectric conversion materials, PbTe-based nanocomposite thermoelectric conversion materials, CoSb3-based nanocomposite thermoelectric conversion materials, SiGe-based nanocomposite thermoelectric conversion materials, ZnSb-based nanocomposite thermoelectric conversion materials, FeSi-based nanocomposite thermoelectric conversion materials, and BiSb-based nanocomposite thermoelectric conversion materials.
Second embodiment [0030] FIGS.
2A to 2D schematically show processes according to a second embodiment of the invention. The description will be made on the assumption that a nanocomposite thermoelectric conversion material, in which particles made of Sb203 are dispersed in a matrix made of a thermoelectric conversion material (Bi, Sb)2Te3, is 5 produced. The particles made of Sb203 serve as phonon-scattering particles.
First step [0031] A
solution, which contains salts of a plurality of first elements Bi, Sb, and Te that constitute the thermoelectric conversion material (Bi, Sb)2Te3, is prepared.
The solution contains an excessive amount of the salt of a predetermined element (Sb) 10 among the plurality of the first elements, with respect to a predetermined composition of the thermoelectric conversion material, and the redox potential of the predetermined element (Sb) is not the highest among the redox potentials of the first elements (Te has the highest redox potential).
[0032] In this case, the redox potentials of the elements in decreasing order are as follows. The redox potential of Te is 0.53V. The redox potential of Sb is 0.16 V.
The redox potential of Bi is 0.16V. In another example of this embodiment, the solution may contain an excessive amount of Bi, instead of containing an excessive amount of Sb.
Second step [0033] The element among the first elements, which has the redox potential higher than the redox potential of the predetermined element, is precipitated by adding a reducing agent to the above-described solution. More specifically, first, the element 11 (Te) with the highest redox potential among the first elements is precipitated as particles in the solution. Thus, the particles including the element 11 (i.e., Te particles) are dispersed in the solution (FIG. 2A).
Third step [0034] The predetermined element 51 (Sb) is precipitated by further adding the above-described reducing agent to the solution in which the particles are dispersed. In the assumed case, the predetermined element 51 is Sb. However, Bi, which has the redox potential equal to the redox potential of Sb, is simultaneously precipitated to produce particles including the element 21 (i.e., Bi particles).
Thus, slurry 60 containing all the plurality of the first elements Te, Bi, and Sb is produced as shown in FIG. 2B. FIG. 2C shows the slurry 60 in a different manner. As shown in FIG.
2C, the slurry 60 includes a base including the element 11 (Te) with the highest redox potential among the first elements constituting the thermoelectric conversion material, and the particles including the rest of the first elements, that is, the particles including the first elements 21 and 51 (Bi and Sb). The particles including the first elements 21 and 51 are dispersed in the base.
Fourth step [00351 Next, a matrix 70 including the thermoelectric conversion material with a predetermined composition (Bi, Sb)2Te3 is produced due to alloying, and nano-sized phonon-scattering particles 80 dispersed in the matrix 70 are produced, by filtering and washing the slurry 60, and then, heat-treating the slimy 60.
The nano-sized phonon-scattering particles 80 include a surplus of the predetermined element 51 with respect to the predetermined composition. At this time, part of the predetermined element 51 is incorporated into the predetermined composition to produce the matrix 70 including the thermoelectric conversion material. During the heat treatment, the surplus of the predetermined clement 51 is oxidized, and thus, particles made of oxide of the predetermined element Si (i.e., particles made of antimony oxide Sb203), which serve as phonon-scattering particles 80, are produced. That is, the phonon-scattering particles 80 are made of oxide of the predetermined element 51.
[00361 Thus, the predetermined element 51 is precipitated in the matrix 70.
Therefore, each of the precipitated particles including the predetermined element 51 is restrained by the matrix 70, and thus, the particles including the predetermined element 51 are not agglutinated. Accordingly, the size of the particles including the predetermined element 51 remains the same as the nano-size of the particles including the predetermined element 51 when precipitated from the solution.
[00371 Thus, a nanocomposite thermoelectric conversion material 100, in which the nano-sized phonon-scattering particles 80 are dispersed in the matrix 70 including the thermoelectric conversion material, is produced.
[0038]
Examples of the nanocomposite thermoelectric conversion material, which are appropriately produced by the method according to the second embodiment of the invention, include (Bi, Sb)2 (Te, Se)3-based nanocomposite thermoelectric conversion materials, PbTe-based nanocomposite thermoelectric conversion materials, CoSb3-based nanocomposite thermoelectric conversion materials, SiGe-based nanocomposite thermoelectric conversion materials, ZnSb-based nanocomposite thermoelectric conversion materials, FeSi-based nanocomposite thermoelectric conversion materials, and BiSb-based nanocomposite thermoelectric conversion materials.
Examples First example [0039]
The nanocomposite thermoelectric conversion material, in which 10 vol % of Fe203 particles were dispersed in the matrix made of the thermoelectric conversion material (Co, Ni) Sb3, was produced according to a procedure described below on a condition described below, using the method according to the first embodiment of the invention. The Fe203 particles served as phonon-scattering particles.
Preparation of a source material solution [0040] A
source material solution was prepared by dissolving source materials described below, in 100 nil of ethanol.
[0041] The source materials for the matrix were 2.75 g of antimony chloride (SbC13), 0.9 g of cobalt chloride hexahydrate (CoC12=61-120), and 0.057 g of nickel chloride hexahydrate (NiC12=6F120). The source material for the dispersed particles was 0.335 g of ferric chloride hexahydrate (FeC13=6H20).
Reduction [0042] A solution, which was produced by dissolving 2.4 g of NaBH4, which served as a reducing agent, in 100 ml of ethanol, was dropped into the above-described source material solution. Ethanol slurry containing =nano particles precipitated by reduction was filtered and washed using a solution produced by mixing 500 ml of water and 300 ml of ethanol, and further, the shiny was filtered and washed using 300 ml of ethanol.
Heat treatment Then, the slurry was placed in a hermetically-sealed autoclave device, and the alloy matrix was produced by performing hydrothermal treatment at 240 C for 48 hours. Then, drying was performed in an N2 gas flow atmosphere, and powder was collected. At this time, approximately 2.0 g of powder was collected.
Sintering [0044]
Spark plasma sintering (SPS) was performed on the collected powder at 500 C. Thus, the nanocomposite thermoelectric conversion material, in which vol % of Fe203 particles were dispersed in the matrix made of the thermoelectric conversion material (Co, Ni) Sb3, was produced. The Fe203 particles served as the phonon-scattering particles.
Observation of constituent phases [0045]
The produced powder was analyzed and observed by XRD analysis and TEM observation. FIG 3A shows an XRD chart, and FIG 3l3 shows a TEM image.
As shown in the XRD chart, diffraction peaks of (Co, Ni) Sb3 (indicated by rhombus marks in FIG. 3A) and diffraction peaks of Fe203 (indicated by circles in FIG.
3A) were clearly observed. Thus, it was confirmed that the nanocomposite thermoelectric conversion material included both of the phase of (Co, Ni) Sb3 and the phase of Fe203.
Also, the dispersed Fe203 particles with the average diameter of 19 nm were observed in the TEM image.
Performance [0046]
Table 1 shows the measured Seebeck coefficient, the measured specific resistance, the measured thermal conductivity, and the measured nondimensional performance index ZT at 400 C. Further, for the purpose of comparison, Table 1 shows - values that are considered to be best values obtained in a thermoelectric conversion material (Co, Ni) Sb3 with a single phase, in which there is no phonon-scattering particle, in a conventional example. The values are described, in a publication (*1). It is evident from Table 1 that the thermal conductivity of the nanocomposite thermoelectric conversion material according to the invention is 0.7 (W/m/K) that is one-fifth of the thermal conductivity of the thermoelectric conversion material in the conventional example. Also, it is evident from Table 1 that the nondimensional performance index ZT of the nanocomposite thermoelectric conversion material according to the invention is 1.33 that is more than 2.5 times the nondimensional performance index ZT of the thermoelectric conversion material in the conventional example, and thus, the nondimensional performance index ZT of the nanocomposite thermoelectric conversion material according to the invention is significantly improved.
Table 1 Seebeck Specific Thermal ZT
coefficient resistance conductivity ( V/K) (1-1-Qm) (W/rn/K) First example -204 30 0.7 1.33 Conventional -200 15 3.5 0.5 example(*1) [0047] The cited related art is described in the publication (*1) "Katsuyarna S., Watanabe M., Kuroki M. et al, Journal of Applied Physics, volume 93, Issue 5, pp2758-2764 (2003)". In a production method described in the publication, (1) Co, Ni, Sb are sealed in quartz, heated and molten, and mixed to produce an alloy; (2) the alloy is subjected to mechanical alloying, that is, the alloy is fractured; and (3) sintering is performed using a hot press.
Second example [0048] The nanocomposite thermoelectric conversion material, in which 10 vol % of Sb203 particles were dispersed in the matrix made of the thermoelectric conversion material (Bi, Sb)2Te3, was produced according to a procedure described below on a condition described below, using the method according to the second embodiment of the invention. The Sb203 particles served as phonon-scattering particles.
Preparation of a source material solution [00419] A source material solution was prepared by dissolving source materials described below, in 100 ml of ethanol. The source materials for the matrix were 0.4 g of bismuth chloride (BiC13), and 2.56 g of tellurium chloride (TeC14). The source material used for producing the matrix and the dispersed particles was 1.5 g of antimony chloride (SbC13).
Reduction [0050] A
solution, which was produced by dissolving 2.4 g of NaBH4, which served as a reducing agent, in 100 ml of ethanol, was dropped into the above-described source material solution. Ethanol slurry containing nano particles precipitated by reduction was filtered and washed using a solution produced by mixing 500 ml of water and 300 ml of ethanol, and further, the slurry was filtered and washed using 300 ml of ethanol.
10 Heat treatment [0051]
Then, the slurry was placed in a hermetically-sealed autoclave device, and the alloy matrix was produced by performing hydrothermal treatment at 240 C for 48 hours. Then, drying was performed in an N2 gas flow atmosphere, and powder was collected. At this time, approximately 2.0 g of powder was collected.
15 Sintering [0052]
Spark plasma sintering (SPS) was performed on the collected powder at 360 C. Thus, the nanocomposite thermoelectric conversion material, in which vol % of Sb203 particles were dispersed in the matrix made of the thermoelectric conversion material (Bi, Sb)2Te3, was produced. The Sb203 particles served as the phonon-scattering particles.
Observation of constituent phases [0053]
The produced powder was analyzed and observed by XRD analysis, EELS oxygen mapping, and TEM observation. FIG. 4A shows an XRD chart, and FIG.
4B shows an EELS oxygen mapping image. FIG. 4C shows a TEM image before heat treatment, and FIG. 4D shows a TEM image after heat treatment. As shown in the XRD
chart, diffraction peaks of (Bi, Sb)2Te3 (that are not marked in FIG. 4A) and diffraction peaks of Sb203 (indicated by rhombus marks in FIG 4A) were clearly observed.
Thus, it was confirmed that the nanocomposite thermoelectric conversion material included both of the phase of (Bi, Sb)2Te3 and the phase of Sb203. In the EELS oxygen mapping image, oxygen, which was contained only in Sb203, was observed as white spots.
The average particle diameter was 10 nm in the TEM image before heat treatment (FIG. 4C), and the average particle diameter was 7 rim in the TEM image after heat treatment (FIG
4D). Thus, it was evident that the size of the particles was decreased after heat treatment. Thus, the phonon-scattering efficiency is fiuther improved, and the thermal conductivity is further decreased.
[0054]
FIGS. 5A to 5C are diagrams relating to the nanocomposite thermoelectric conversion materials in the first example and the second example. FIG.
5A shows average diameters of phonon-scattering particles, FIG. 5B shows rates of decrease in the thermal conductivity, and FIG. 5C shows nondimensional performance indices ZT. For the purpose of comparison, FIG. 5C also shows the ZT values that are considered to be the best values in the conventional example. The values are described in the above-described publication (*1). In FIG 5A to 5C, I, II, and III in the abscissa axis indicate samples described below.
Samples [0055] In FIG. 5A to 5C, I indicates the nanocomposite thermoelectric conversion material in the first example, which included the matrix made of (Co, Ni) Sb3, and the dispersed particles made of Fe203 (10 vol %). II indicates the nanocomposite thermoelectric conversion material in the second example, which included the matrix made of (Bi, Sb) Te3, and the dispersed particles made of Sb203 (10 vol %).
ifi indicates the nanocomposite thermoelectric conversion material in a comparative example, which included the matrix made of (Bi, Sb) Te3 and the dispersed particles made of Te (10 vol %). The nanocompositc thermoelectric conversion material in the comparative example was the same as the nanocomposite thermoelectric conversion material in the second example, except that the amount of Te was excessive with respect to the predetermined composition, instead of the amount of Sb. "*1" indicates the thermoelectric conversion material (Co, Ni) Sb3 with a single phase in the conventional example (described in the publication *1).
[0056]
As shown in FIG 5A, the average diameter of the dispersed particles in the first example indicated by I was 19 nm, and the average diameter of the dispersed particles in the second example indicated by II was 7 nm. Thus, the size of the dispersed particles was significantly decreased. In the comparative example indicated by III, the excessive amount of Te with respect to the predetermined composition was used, and the particles including Te were dispersed as the phonon-scattering particles.
Te has the highest redox potential among the constituent elements Bi, Sb, and Te. In this case, because Te was precipitated first during the reduction process, the particles including Te agglutinated and the size of the particles was increased.
Therefore, the average diameter of the particles was 53nm, which was much larger than the average diameters in the first example indicated by I and the second example indicated by II. As a result, in the comparative example, the phonon-scattering effect was small.
As shown in FIG. 5B, the rate of decrease in the thermal conductivity in the comparative example indicated by III with respect to the conventional example was 48 %, which was low, while the rate of decrease in the thermal conductivity in the first example indicated by I
with respect to the conventional example was 74 %, and the rate of decrease in the thermal conductivity in the second example indicated by II with respect to the conventional example was 80 %.
[0057] As shown in FIG. 5C, the nondimensional performance index ZT
in the first example indicated by I (the average diameter: 19nm) was 1.33, and the nondimensional performance index ZT in the second example indicated by II (the average diameter: 7 nm) was 2.2, while the nondimensional performance index ZT
in the conventional example indicated by "*1" was approximately 0.4 to 0.7. Thus, the nondimensional performance index ZT in the first example and the nondimensional performance index ZT in the second example were significantly improved. The nondimensional performance index ZT in the comparative example indicated by III (the average diameter: 53 nm) was slightly higher than the nondimensional performance index ZT of the thermoelectric conversion material that did not include the phonon-scattering particles in the conventional example. However, the nondimensional performance index ZT in the comparative example was lower than the nondimensional performance index ZT in the first example indicated by I and the nondimensional performance index ZT in the second example indicated by II.
(0058]
FIGS. 6A to 6D are diagrams relating to the nanocomposite thermoelectric conversion material in the second example. FIG 6A is the graph showing the Seebeck coefficient with respect to measured temperature. FIG 6B
is the graph showing the specific resistance with respect to the measured temperature. FIG
6C is the graph showing the thermal conductivity with respect to the measured temperature. FIG 6D is the graph showing the nondimensional performance index ZT
with respect to the measured temperature. For the purpose of comparison, FIGS.
6A to 6D also show values in related art described in a publication (*2).
[0059]
As shown in FIG. 6C, the thermal conductivity was substantially constant, and approximately 0.3 W/m/K, which was extremely low, in the range of the measured temperatures, regardless of the measured temperature, while the thermal conductivity in the related art was 1.57 W/m/K. Accordingly, as shown in FIG 6D, the nondimensional performance index ZT was 2.2 to 1.8, which was extremely high, while the nondimensional performance index ZT in the related art was 0.8. As the specific resistance shown in FIG. 6B was slightly increased due to the increase in the measured temperature, the nondimensional performance index ZT was slightly decreased (from 2.2 to 1.8).
[0060] The cited related art (*2) is described in "P.M.Rowe, CRC Handbook, p213-214 (Production method), and p227-235 (Material performance)". In a production method described in the publication, (1) a polycrystal with a stoichiometric composition is placed in a quartz ampule; (2) the ampule is moved to pass through a heater; (3) the polycrystal is molten in the ampule when the ampule passes through the heater, and the melt is solidified to a solid after the ampule passes through the heater. As a result, a single crystal is produced.
[0061]
According to the invention, it is possible to provide the nanocomposite thermoelectric conversion material in which the nano-sized phonon-scattering particles are dispersed in the matrix made of the thermoelectric conversion material, and which has the greatly decreased thermal conductivity, and the significantly improved thermoelectric conversion performance, and the method of producing the same.
Spark plasma sintering (SPS) was performed on the collected powder at 360 C. Thus, the nanocomposite thermoelectric conversion material, in which vol % of Sb203 particles were dispersed in the matrix made of the thermoelectric conversion material (Bi, Sb)2Te3, was produced. The Sb203 particles served as the phonon-scattering particles.
Observation of constituent phases [0053]
The produced powder was analyzed and observed by XRD analysis, EELS oxygen mapping, and TEM observation. FIG. 4A shows an XRD chart, and FIG.
4B shows an EELS oxygen mapping image. FIG. 4C shows a TEM image before heat treatment, and FIG. 4D shows a TEM image after heat treatment. As shown in the XRD
chart, diffraction peaks of (Bi, Sb)2Te3 (that are not marked in FIG. 4A) and diffraction peaks of Sb203 (indicated by rhombus marks in FIG 4A) were clearly observed.
Thus, it was confirmed that the nanocomposite thermoelectric conversion material included both of the phase of (Bi, Sb)2Te3 and the phase of Sb203. In the EELS oxygen mapping image, oxygen, which was contained only in Sb203, was observed as white spots.
The average particle diameter was 10 nm in the TEM image before heat treatment (FIG. 4C), and the average particle diameter was 7 rim in the TEM image after heat treatment (FIG
4D). Thus, it was evident that the size of the particles was decreased after heat treatment. Thus, the phonon-scattering efficiency is fiuther improved, and the thermal conductivity is further decreased.
[0054]
FIGS. 5A to 5C are diagrams relating to the nanocomposite thermoelectric conversion materials in the first example and the second example. FIG.
5A shows average diameters of phonon-scattering particles, FIG. 5B shows rates of decrease in the thermal conductivity, and FIG. 5C shows nondimensional performance indices ZT. For the purpose of comparison, FIG. 5C also shows the ZT values that are considered to be the best values in the conventional example. The values are described in the above-described publication (*1). In FIG 5A to 5C, I, II, and III in the abscissa axis indicate samples described below.
Samples [0055] In FIG. 5A to 5C, I indicates the nanocomposite thermoelectric conversion material in the first example, which included the matrix made of (Co, Ni) Sb3, and the dispersed particles made of Fe203 (10 vol %). II indicates the nanocomposite thermoelectric conversion material in the second example, which included the matrix made of (Bi, Sb) Te3, and the dispersed particles made of Sb203 (10 vol %).
ifi indicates the nanocomposite thermoelectric conversion material in a comparative example, which included the matrix made of (Bi, Sb) Te3 and the dispersed particles made of Te (10 vol %). The nanocompositc thermoelectric conversion material in the comparative example was the same as the nanocomposite thermoelectric conversion material in the second example, except that the amount of Te was excessive with respect to the predetermined composition, instead of the amount of Sb. "*1" indicates the thermoelectric conversion material (Co, Ni) Sb3 with a single phase in the conventional example (described in the publication *1).
[0056]
As shown in FIG 5A, the average diameter of the dispersed particles in the first example indicated by I was 19 nm, and the average diameter of the dispersed particles in the second example indicated by II was 7 nm. Thus, the size of the dispersed particles was significantly decreased. In the comparative example indicated by III, the excessive amount of Te with respect to the predetermined composition was used, and the particles including Te were dispersed as the phonon-scattering particles.
Te has the highest redox potential among the constituent elements Bi, Sb, and Te. In this case, because Te was precipitated first during the reduction process, the particles including Te agglutinated and the size of the particles was increased.
Therefore, the average diameter of the particles was 53nm, which was much larger than the average diameters in the first example indicated by I and the second example indicated by II. As a result, in the comparative example, the phonon-scattering effect was small.
As shown in FIG. 5B, the rate of decrease in the thermal conductivity in the comparative example indicated by III with respect to the conventional example was 48 %, which was low, while the rate of decrease in the thermal conductivity in the first example indicated by I
with respect to the conventional example was 74 %, and the rate of decrease in the thermal conductivity in the second example indicated by II with respect to the conventional example was 80 %.
[0057] As shown in FIG. 5C, the nondimensional performance index ZT
in the first example indicated by I (the average diameter: 19nm) was 1.33, and the nondimensional performance index ZT in the second example indicated by II (the average diameter: 7 nm) was 2.2, while the nondimensional performance index ZT
in the conventional example indicated by "*1" was approximately 0.4 to 0.7. Thus, the nondimensional performance index ZT in the first example and the nondimensional performance index ZT in the second example were significantly improved. The nondimensional performance index ZT in the comparative example indicated by III (the average diameter: 53 nm) was slightly higher than the nondimensional performance index ZT of the thermoelectric conversion material that did not include the phonon-scattering particles in the conventional example. However, the nondimensional performance index ZT in the comparative example was lower than the nondimensional performance index ZT in the first example indicated by I and the nondimensional performance index ZT in the second example indicated by II.
(0058]
FIGS. 6A to 6D are diagrams relating to the nanocomposite thermoelectric conversion material in the second example. FIG 6A is the graph showing the Seebeck coefficient with respect to measured temperature. FIG 6B
is the graph showing the specific resistance with respect to the measured temperature. FIG
6C is the graph showing the thermal conductivity with respect to the measured temperature. FIG 6D is the graph showing the nondimensional performance index ZT
with respect to the measured temperature. For the purpose of comparison, FIGS.
6A to 6D also show values in related art described in a publication (*2).
[0059]
As shown in FIG. 6C, the thermal conductivity was substantially constant, and approximately 0.3 W/m/K, which was extremely low, in the range of the measured temperatures, regardless of the measured temperature, while the thermal conductivity in the related art was 1.57 W/m/K. Accordingly, as shown in FIG 6D, the nondimensional performance index ZT was 2.2 to 1.8, which was extremely high, while the nondimensional performance index ZT in the related art was 0.8. As the specific resistance shown in FIG. 6B was slightly increased due to the increase in the measured temperature, the nondimensional performance index ZT was slightly decreased (from 2.2 to 1.8).
[0060] The cited related art (*2) is described in "P.M.Rowe, CRC Handbook, p213-214 (Production method), and p227-235 (Material performance)". In a production method described in the publication, (1) a polycrystal with a stoichiometric composition is placed in a quartz ampule; (2) the ampule is moved to pass through a heater; (3) the polycrystal is molten in the ampule when the ampule passes through the heater, and the melt is solidified to a solid after the ampule passes through the heater. As a result, a single crystal is produced.
[0061]
According to the invention, it is possible to provide the nanocomposite thermoelectric conversion material in which the nano-sized phonon-scattering particles are dispersed in the matrix made of the thermoelectric conversion material, and which has the greatly decreased thermal conductivity, and the significantly improved thermoelectric conversion performance, and the method of producing the same.
Claims (5)
1. A method of producing a nanocomposite thermoelectric conversion material, comprising:
preparing a solution that contains salts of a plurality of first elements constituting a thermoelectric conversion material, and a salt of a second element that has a redox potential lower than redox potentials of the first elements;
precipitating the first elements, thereby producing a matrix-precursor that is a precursor of a matrix made of the thermoelectric conversion material, by adding a reducing agent to the solution;
precipitating the second element in the matrix-precursor, thereby producing slurry containing the first elements and the second element, by further adding the reducing agent to the solution; and alloying the plurality of the first elements, thereby producing the matrix made of the thermoelectric conversion material, and producing nano-sized phonon-scattering particles including the second element, which are dispersed in the matrix, by filtering and washing the slurry, and then, heat-treating the slurry.
preparing a solution that contains salts of a plurality of first elements constituting a thermoelectric conversion material, and a salt of a second element that has a redox potential lower than redox potentials of the first elements;
precipitating the first elements, thereby producing a matrix-precursor that is a precursor of a matrix made of the thermoelectric conversion material, by adding a reducing agent to the solution;
precipitating the second element in the matrix-precursor, thereby producing slurry containing the first elements and the second element, by further adding the reducing agent to the solution; and alloying the plurality of the first elements, thereby producing the matrix made of the thermoelectric conversion material, and producing nano-sized phonon-scattering particles including the second element, which are dispersed in the matrix, by filtering and washing the slurry, and then, heat-treating the slurry.
2. The method according to claim 1, wherein the slurry includes a base including an element with the highest redox potential among the first elements, and particles including a rest of the first elements and particles including the second element; and the particles including the rest of the first elements and the particles including the second element are dispersed in the base.
3. The method according to claim 1 or 2, wherein the first elements are Sb, Ni, and Co, the second element is Fe, and the thermoelectric conversion material is (Co, Ni) Sb3.
4. The method according to any one of claims 1 to 3, wherein the phonon-scattering particles are made of oxide of the second element.
5. The method according to claim 4, wherein the phonon-scattering particles are made of Fe2O3.
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| PCT/IB2010/001533 WO2010146459A2 (en) | 2009-06-18 | 2010-06-18 | Nanocomposite thermoelectric conversion material and method of producing the same |
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| JP2012146928A (en) * | 2011-01-14 | 2012-08-02 | Toyota Motor Corp | Method for manufacturing nanocomposite thermoelectric conversion material |
| US20130330225A1 (en) * | 2012-06-07 | 2013-12-12 | Toyota Motor Engineering & Manufacturing North America, Inc. | Production method for nanocomposite thermoelectric conversion material |
| JP5714660B2 (en) * | 2013-07-11 | 2015-05-07 | トヨタ自動車株式会社 | Method for producing nanocomposite thermoelectric conversion material |
| JP6249426B2 (en) * | 2013-09-09 | 2017-12-20 | エルジー・ケム・リミテッド | Thermoelectric material |
| EP3026719B1 (en) | 2013-09-09 | 2019-06-26 | LG Chem, Ltd. | Thermoelectric materials and their manufacturing method |
| JP6365951B2 (en) | 2013-09-09 | 2018-08-01 | エルジー・ケム・リミテッド | Thermoelectric material manufacturing method |
| JP6460352B2 (en) | 2013-09-09 | 2019-01-30 | エルジー・ケム・リミテッド | Thermoelectric material |
| CN103981468B (en) * | 2014-05-26 | 2016-05-18 | 中国科学院上海硅酸盐研究所 | A kind of strong mechanical performance skutterudite-base thermoelectrical composite material and preparation method thereof |
| US10396263B2 (en) | 2014-12-16 | 2019-08-27 | Lg Chem, Ltd. | Thermoelectric powder and thermoelectric material prepared using the same |
| CN114744223B (en) * | 2022-05-06 | 2024-01-26 | 湖北理工学院 | Iron-chromium redox flow battery electrode material and preparation method thereof |
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| JP4803282B2 (en) | 2011-10-26 |
| CN102458726A (en) | 2012-05-16 |
| WO2010146459A3 (en) | 2011-06-03 |
| WO2010146459A2 (en) | 2010-12-23 |
| CA2764762A1 (en) | 2010-12-23 |
| US8828277B2 (en) | 2014-09-09 |
| EP2442930B1 (en) | 2015-09-09 |
| EP2442930A2 (en) | 2012-04-25 |
| JP2011003741A (en) | 2011-01-06 |
| CN102458726B (en) | 2013-10-09 |
| US20120085977A1 (en) | 2012-04-12 |
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