JP2011096717A - Nano-composite thermoelectric conversion material, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nano-composite thermoelectric conversion material which does not require material for phonon scattering particles separately and achieves uniform and fine dispersion of the phonon scattering particles. <P>SOLUTION: The nano-composite thermoelectric conversion material, in which nano-sized phonon scattering particles are dispersed in a matrix formed of thermoelectric conversion material, is characterized by that oxide as a by-product during reduction of the thermoelectric conversion material is contained as the phonon scattering particle. The manufacturing method includes: a process for depositing the thermoelectric conversion material and depositing the by-product derived from a reductant by reducing a precursor solution of the thermoelectric conversion material; and a process for alloying the thermoelectric conversion material and forming oxide of the by-product by heat treatment. Preferably, NaBH<SB>4</SB>is used as the reductant, and H<SB>3</SB>BO<SB>3</SB>is generated as the by-product in reduction, and B<SB>2</SB>O<SB>3</SB>, which is oxide of it, is dispersed as the phonon scattering particle. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a nanocomposite thermoelectric conversion material in which nano-sized phonon scattering particles are dispersed in a thermoelectric conversion material matrix, and a nanocomposite thermoelectric conversion material produced thereby.

  The thermoelectric conversion material is an energy material that performs direct conversion between thermal energy and electric energy based on two basic thermoelectric effects, the Seebeck effect and the Peltier effect.

  Thermoelectric power generation devices using thermoelectric conversion materials have a simple structure, robustness, high durability, no moving parts, easy microfabrication, no maintenance, and reliability compared to conventional power generation technology There are many advantages such as high life, long life, no noise, no pollution and low temperature waste heat can be used.

  Compared to conventional compression cooling technology, thermoelectric cooling devices using thermoelectric conversion materials do not require chlorofluorocarbon, do not cause contamination, are easily downsized, have no moving parts, and do not generate noise. is there.

  Therefore, especially in recent years, energy and environmental issues have become more serious, such as aviation / space, national defense construction, geological and meteorological observation, medical hygiene, microelectronics, etc. Is expected to be put to practical use for a wide range of applications.

As an index for evaluating the performance of the thermoelectric conversion material, a power factor P = S ² σ and a dimensionless performance index ZT = (S ² σ / κ) T are used. Here, S: Seebeck coefficient, σ: conductivity, κ: thermal conductivity, T: absolute temperature. That is, in order to obtain good thermoelectric properties, it is necessary that the Seebeck coefficient S and the electrical conductivity σ are high and the thermal conductivity κ is low.

  In order to reduce the thermal conductivity κ, it is effective to scatter phonons, one of the players in heat conduction, and a composite thermoelectric conversion material in which phonon scattering particles are dispersed in a thermoelectric conversion material matrix is proposed. Has been.

  In particular, it has been proposed to increase the phonon scattering ability by the form of phonon scattering particles.

  Patent Document 1 discloses a nanocomposite in which a core part is formed, then a shell part is formed by a hot soap method to form core / shell structure nanoparticles, and organic substances adhering to the shell part are removed, followed by compression molding. A method for producing a thermoelectric conversion material is disclosed. The manufactured nanostructure thermoelectric conversion material has a form in which a plurality of particles of a core / shell structure are continuous between shell portions, the continuous phase, that is, the shell portion constituting the matrix has electronic conductivity, and the core portion is Has phonon scattering ability.

  However, in addition to the material of the shell part that constitutes the matrix, the material of the core part that constitutes the phonon scattering particles is required, and there is a problem that the material cost increases accordingly.

  Further, it has been difficult to make uniform phonon scattering particles in the nanocomposite thermoelectric conversion material. For example, Patent Document 2 discloses that a nanocomposite thermoelectric conversion material is prepared by mixing ceramic particles and thermoelectric conversion material particles (BiSbTe series) and performing hot press sintering. In addition, the nanoparticles aggregate together due to van der Waals force and coarsen to a micro size, so that high phonon scattering ability cannot be exhibited.

JP 2007-21670 A JP-A-3-148879

  An object of the present invention is to provide a nanocomposite thermoelectric conversion material that does not require a separate material for phonon scattering particles and achieves uniform and fine dispersion of phonon scattering particles, and a method for producing the same.

In order to achieve the above object, the nanocomposite thermoelectric conversion material of the present invention is a nanocomposite thermoelectric conversion material in which nano-sized phonon scattering particles are dispersed in a matrix composed of a thermoelectric conversion material.
The by-product oxide at the time of reduction production of the thermoelectric conversion material is included as the phonon scattering particles.

In order to achieve the above object, the method for producing a nanocomposite thermoelectric conversion material of the present invention produces a nanocomposite thermoelectric conversion material in which nano-sized phonon scattering particles are dispersed in a matrix composed of the thermoelectric conversion material. In the method
Reducing the precursor solution of the thermoelectric conversion material to precipitate the thermoelectric conversion material and depositing a by-product derived from a reducing agent; and heat treatment to alloy the thermoelectric conversion material and to form the by-product. The manufacturing method of the nanocomposite thermoelectric conversion material characterized by including the process of forming the oxide of a thing.

  When the thermoelectric conversion material precursor is reduced to produce thermoelectric conversion material particles, thermoelectric conversion material particles are generated when the reducing agent reacts with ions of the thermoelectric conversion material precursor, and the by-product is the thermoelectric conversion material. Precipitates near the particles. Therefore, the by-product is uniformly and finely dispersed, and the oxide of the double product is also uniformly and finely dispersed. Therefore, by using the by-product oxide as phonon scattering particles, a nanocomposite thermoelectric conversion material with good dispersibility can be obtained, and the thermal conductivity can be effectively reduced. Furthermore, since a material for phonon scattering particles is not required separately, the material cost can be reduced.

FIG. 1 is a schematic diagram showing a state of (1) during reductive precipitation and (2) bulking by sintering of a by-product of a reduction reaction constituting the phonon scattering particles of the present invention. FIG. 2 is an example of an EDX chart of the nanocomposite thermoelectric conversion material of the present invention after heat treatment. Bi, Sb, Te peaks of thermoelectric conversion materials (Bi, Sb) ₂ Te ₃ constituting the matrix, and oxide B ₂ O ₃ (boron oxide) B of by-product H ₃ B 0 ₃ (boric acid), A peak of O is clearly recognized. Note that the peak of Cu is due to the sample holder made of Cu. FIG. 3 is a TEM image of the nanocomposite thermoelectric conversion material of the present invention after sintering. In the figure, (1) and (2) are photographs of the same sample with the same magnification, taken from different fields of view. In any case, the B ₂ O ₃ particles are observed as white spots, and the particle size is 5 nm or less. FIG. 4 is a graph showing the characteristic values of the nanocomposite thermoelectric conversion material produced in the example in comparison with the conventional values.

  FIG. 1 schematically shows a state of (1) during reduction precipitation and (2) bulkization by sintering of the by-products of the reduction reaction constituting the phonon scattering particles of the present invention.

  In the present invention, a double product that is inevitably generated when a thermoelectric conversion material is generated by reduction is used as a precursor of phonon scattering particles.

  As shown in FIG. 1 (1), in the state where the precursor of the thermoelectric conversion material (salt of the constituent element of the thermoelectric conversion material) is reduced, the nanoparticle 12 ′ of the thermoelectric conversion material constituent element as the main product, It is the state of the slurry 10 ′ in which the by-product nanoparticles 14 ′ derived from the reducing agent uniformly deposited in the vicinity of the flocculated material. This slurry is filtered and washed in a purification process to remove unnecessary substances. Next, the aggregate of the thermoelectric conversion material constituting element nanoparticles 12 ′ is alloyed by heat treatment to form the matrix 12, and at the same time, the oxide particles 14 of the by-product nanoparticles 14 ′ are formed. This is sintered to form a bulk body 10 of the nanocomposite thermoelectric conversion material. This is the state shown in FIG.

  When the thermoelectric conversion material precursor is reduced to produce thermoelectric conversion material particles, thermoelectric conversion material particles are generated when the reducing agent reacts with ions of the thermoelectric conversion material precursor, and the by-product is the thermoelectric conversion material. Precipitates near the particles. Therefore, the by-product is uniformly and finely dispersed, and the oxide of the double product is also uniformly and finely dispersed. Therefore, by using the by-product oxide as phonon scattering particles, a nanocomposite thermoelectric conversion material with good dispersibility can be obtained, and the thermal conductivity can be effectively reduced. Furthermore, since a material for phonon scattering particles is not required separately, the material cost can be reduced.

  In the conventional technique, the by-product is removed by washing after the reduction reaction, but in the present invention, a specific substance of the by-product is left without being removed in the washing step. Therefore, the amount of the cleaning medium (usually water) is adjusted in consideration of the solubility of the by-product to be left in the cleaning medium. The specific substance among the by-products is an oxide suitable as phonon scattering particles by the following heat treatment.

  In the heat treatment, a mixture of the constituent elements of the thermoelectric conversion material deposited by the reduction reaction is alloyed to form thermoelectric conversion material particles having a predetermined composition, and at the same time, the by-product left during the cleaning is oxidized to phonon scattering particles. Form. That is, in this state, it is nanocomposite particles of matrix particles of thermoelectric conversion material and phonon scattering particles made of by-product oxide, and the state of the material is powder.

  Finally, the nanocomposite particle powder is molded and sintered to obtain a bulk body of the nanocomposite thermoelectric conversion material of the present invention.

  As a matrix thermoelectric conversion material to which the present invention is applied, the following can be typically used.

(Bi, Sb) ₂ (Te, Se) ₃ . (Bi, Sn) ₂ Te ₃ . PbTe system, SiGe system, CoSb system, Zn ₄ Sb ₃ system.
However, it is not necessary to limit to the above.

  Typically, the following can be used as the reducing agent of the present invention.

NaBH ₄ , LiAlH ₄ , LiBH ₄ , Ni (BH ₄ ) ₂ , Zn (BH ₄ ) ₂ .
However, it is not necessary to limit to the above.

  Typical examples of the oxide of the reducing agent include the following.

_{B 2 O 3, Al 2 O} 3, Ni or NiOx, Zn or ZnOx.
However, it is not necessary to limit to the above.

  Hereinafter, the present invention will be described in more detail with reference to examples.

In accordance with the present invention, a nanocomposite thermoelectric conversion material was prepared according to the following procedure and conditions. This nanocomposite thermoelectric conversion material has a structure in which B ₂ O ₃ nanoparticles are uniformly dispersed as phonon scattering particles in a matrix of (Bi, Sb) ₂ Te ₃ thermoelectric conversion material.

<Preparation of precursor solution of thermoelectric conversion material>
In 100 ml of ethanol, 0.4 g of bismuth chloride BiCl ₃ , 1.2 g of antimony chloride SbCl _3, 1.2 g of tellurium TeCl chloride as a salt of the constituent elements Bi, Sb, Te of the thermoelectric conversion material (Bi, Sb) ₂ Te ₃ constituting the matrix ₄ 2.56 g was added and dissolved to prepare a precursor solution.

<Reduction treatment>
NaBH ₄ 2.4 as a reducing agent was added and dissolved in 100 ml of ethanol, and this was dropped into the precursor solution to perform a reduction treatment. This reduction reaction is represented by the following formula.

BiCl ₃ (SbCl ₃ , TeCl ₄ ) + NaBH ₄ + H ₂ 0
→ Bi (Sb, Te) + NaCl + H ₃ BO ₃ + H ₂ ↑
Main product: Bi (Sb, Te)
By-products: NaCl, H ₃ BO ₃ , H ₂
Of the by-product, H ₂ escapes as gas and is removed.

<Filter washing process>
The ethanol slurry containing the nanoparticles obtained by the reduction was filtered and washed with a solution of 50 ml of water and 100 ml of ethanol.

By putting the reducing organism Bi (Sb, Te) + NaCl + H ₃ BO ₃ into water, the by-product NaCl and the excess of H ₃ BO ₃ are removed by filtration in a state dissolved in water. A certain nanocomposite particle Bi (Sb, Te) and a necessary amount of the by-product nanoparticle H ₃ BO ₃ are recovered.

Here, the amount of water is estimated from the solubility of H ₃ BO ₃ in water (5.7 g / 100 g of water), and needs to be adjusted to some extent according to the actual cleaning conditions. In this example, the volume was 50 ml as described above.

<Heat treatment process>
Place in a sealed autoclave and hydrothermally heat at 240 ° C. for 48 hours to alloy main composite nanocomposite particles Bi (Sb, Te) to form a matrix of thermoelectric conversion material (Bi, Sb) ₂ Te ₃ In parallel, phonon scattering particles of B ₂ O ₃ are formed from nanoparticles H ₃ BO ₃ which are by-products.

<Drying process>
The obtained mixed powder was recovered by drying in an N 2 gas flow atmosphere. At this time, about 2 g of powder was recovered.

<Sintering process>
SPS sintering was performed at 360 ° C. to obtain a bulk body of (Bi, Sb) ₂ Te ₃ / B ₂ O ₃ nanocomposite thermoelectric conversion material.

FIG. 2 shows an EDX chart of the obtained bulk body. Bi, Sb, Te peaks of thermoelectric conversion materials (Bi, Sb) ₂ Te ₃ constituting the matrix, and oxide B ₂ O ₃ (boron oxide) B of by-product H ₃ B 0 ₃ (boric acid), A peak of O is clearly recognized. Note that the peak of Cu is due to the sample holder made of Cu.

FIG. 3 shows a TEM image of the obtained bulk body, in which (1) and (2) are photographs of the same sample with the same magnification, taken from different fields of view. In any case, the B ₂ O ₃ particles are observed as white spots and have a particle size of 5 nm or less.

<Evaluation of thermoelectric conversion characteristics>
The characteristics of the bulk material of the present invention were compared with those of conventional materials described in the literature. The results are shown in FIG. The source of the conventional material is Journal of Crystal Growth 277 (2005) 258-263.
1. Measurement of thermal conductivity It was measured by a steady-state thermal conductivity evaluation method and a flash method (unsteady method) (flash method thermal conductivity measuring device manufactured by Netch Co., Ltd.).
2. Output factor Measure the Seebeck coefficient and specific resistance using ULVAC-RIKO ZE. The Seebeck coefficient was a three-point fitting of ΔV / ΔT. The specific resistance was measured by the 4-terminal method.
As a result of the characteristic evaluation, when comparing the present invention with the prior art, the Seebeck coefficient is almost the same, and the non-resistance is slightly larger in the present invention, but the thermal conductivity of the present invention is significantly lower than in the prior art I understand.

  According to the present invention, there is provided a nanocomposite thermoelectric conversion material that does not require a separate material for phonon scattering particles and achieves uniform and fine dispersion of phonon scattering particles, and a method for producing the same.

10 'Slurry 12' Nanoparticles of constituent elements of thermoelectric conversion materials as main products 14 'Nanoparticles of by-products derived from the reducing agent uniformly deposited 10 Nanocomposite thermoelectric conversion materials 12 Matrix made of thermoelectric conversion materials 14 Byproducts Phonon scattering particles composed of oxides

Claims (3)

In a method for producing a nanocomposite thermoelectric conversion material in which nano-sized phonon scattering particles are dispersed in a matrix made of a thermoelectric conversion material,
Reducing the precursor solution of the thermoelectric conversion material to precipitate the thermoelectric conversion material and depositing a by-product derived from a reducing agent; and heat treatment to alloy the thermoelectric conversion material and to form the by-product. The manufacturing method of the nanocomposite thermoelectric conversion material characterized by including the process of forming the oxide of a thing. 2. The method according to claim 1, wherein NaBH ₄ is used as the reducing agent, H ₃ BO ₃ is generated as a by-product during the reduction, and B ₂ O ₃ as an oxide is dispersed as the phonon scattering particles. A method for producing a nanocomposite thermoelectric conversion material. In a nanocomposite thermoelectric conversion material in which nano-sized phonon scattering particles are dispersed in a matrix made of a thermoelectric conversion material,
A nanocomposite thermoelectric conversion material comprising, as the phonon scattering particles, an oxide of a by-product during reduction of the thermoelectric conversion material.