JP2010010366A - Production process of bismuth telluride thermoelectric conversion element - Google Patents
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- 238000006243 chemical reaction Methods 0.000 title claims abstract description 68
- 229910052797 bismuth Inorganic materials 0.000 title claims abstract description 22
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 title claims abstract description 15
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 14
- XSOKHXFFCGXDJZ-UHFFFAOYSA-N telluride(2-) Chemical compound [Te-2] XSOKHXFFCGXDJZ-UHFFFAOYSA-N 0.000 title claims abstract description 14
- 239000002245 particle Substances 0.000 claims abstract description 72
- 239000000919 ceramic Substances 0.000 claims abstract description 38
- 239000003638 chemical reducing agent Substances 0.000 claims abstract description 24
- 239000006185 dispersion Substances 0.000 claims abstract description 22
- 229910052714 tellurium Inorganic materials 0.000 claims abstract description 19
- PORWMNRCUJJQNO-UHFFFAOYSA-N tellurium atom Chemical compound [Te] PORWMNRCUJJQNO-UHFFFAOYSA-N 0.000 claims abstract description 12
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims abstract description 11
- JHXKRIRFYBPWGE-UHFFFAOYSA-K bismuth chloride Chemical compound Cl[Bi](Cl)Cl JHXKRIRFYBPWGE-UHFFFAOYSA-K 0.000 claims abstract description 11
- 239000002002 slurry Substances 0.000 claims abstract description 8
- 238000005245 sintering Methods 0.000 claims abstract description 6
- OAKJQQAXSVQMHS-UHFFFAOYSA-N hydrazine group Chemical group NN OAKJQQAXSVQMHS-UHFFFAOYSA-N 0.000 claims description 14
- 238000005406 washing Methods 0.000 claims description 4
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 claims description 3
- 229910052739 hydrogen Inorganic materials 0.000 claims description 3
- 239000001257 hydrogen Substances 0.000 claims description 3
- 125000004435 hydrogen atom Chemical class [H]* 0.000 claims description 3
- 238000010438 heat treatment Methods 0.000 claims 1
- 238000002156 mixing Methods 0.000 abstract description 4
- 239000007788 liquid Substances 0.000 abstract description 3
- 238000004140 cleaning Methods 0.000 abstract 1
- 239000002244 precipitate Substances 0.000 abstract 1
- 239000000463 material Substances 0.000 description 46
- 239000010419 fine particle Substances 0.000 description 18
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 17
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 15
- 238000009826 distribution Methods 0.000 description 7
- 238000006722 reduction reaction Methods 0.000 description 7
- 239000000243 solution Substances 0.000 description 7
- 239000011246 composite particle Substances 0.000 description 6
- 230000007423 decrease Effects 0.000 description 6
- 238000000034 method Methods 0.000 description 6
- 239000000377 silicon dioxide Substances 0.000 description 6
- 238000003917 TEM image Methods 0.000 description 5
- 239000002105 nanoparticle Substances 0.000 description 5
- 239000012279 sodium borohydride Substances 0.000 description 5
- 229910000033 sodium borohydride Inorganic materials 0.000 description 5
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 4
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 4
- 239000011810 insulating material Substances 0.000 description 4
- 150000002500 ions Chemical class 0.000 description 4
- 239000002994 raw material Substances 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 239000006227 byproduct Substances 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 239000007858 starting material Substances 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- CPLXHLVBOLITMK-UHFFFAOYSA-N Magnesium oxide Chemical compound [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 238000004220 aggregation Methods 0.000 description 2
- 230000002776 aggregation Effects 0.000 description 2
- 239000000969 carrier Substances 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
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- 238000001914 filtration Methods 0.000 description 2
- 238000001027 hydrothermal synthesis Methods 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 239000011259 mixed solution Substances 0.000 description 2
- 230000000704 physical effect Effects 0.000 description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- LRHPLDYGYMQRHN-UHFFFAOYSA-N N-Butanol Chemical compound CCCCO LRHPLDYGYMQRHN-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 230000005678 Seebeck effect Effects 0.000 description 1
- 238000005411 Van der Waals force Methods 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 239000000395 magnesium oxide Substances 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 239000003002 pH adjusting agent Substances 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- PDYNJNLVKADULO-UHFFFAOYSA-N tellanylidenebismuth Chemical compound [Bi]=[Te] PDYNJNLVKADULO-UHFFFAOYSA-N 0.000 description 1
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Abstract
Description
本発明は、絶縁材料としてのセラミックスを含有するテルル化ビスマス系熱電変換素子の製造方法に関する。 The present invention relates to a method for producing a bismuth telluride thermoelectric conversion element containing ceramics as an insulating material.
熱電変換材料は、熱エネルギーと電気エネルギーを相互に変換することができる材料であり、熱電冷却素子や熱電発電素子として利用される熱電変換素子を構成する材料である。この熱電変換材料はゼーベック効果を利用して熱電変換を行うものであるが、その熱電変換性能は、性能指数ＺＴと呼ばれる下式（１）で表される。
ＺＴ＝α2σＴ／κ （１）
（上式中、αはゼーベック係数を、σは電気伝導率を、κは熱伝導率を、そしてＴは測定温度を示す）
The thermoelectric conversion material is a material that can mutually convert heat energy and electric energy, and is a material that constitutes a thermoelectric conversion element used as a thermoelectric cooling element or a thermoelectric power generation element. This thermoelectric conversion material performs thermoelectric conversion using the Seebeck effect, and the thermoelectric conversion performance is represented by the following formula (1) called a figure of merit ZT.
ZT = α 2 σT / κ (1)
(Where α is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the measured temperature)
上記式（１）から明らかなように、熱電変換材料の熱電変換性能を高めるためには、用いる材料のゼーベック係数α及び電気伝導率σを大きくし、熱伝導率κを小さくすればよいことがわかる。ここで材料の熱伝導率κを小さくするために、熱電変換材料の出発原料の粒子に熱電変換材料の母材と反応しない微粒子（不活性微粒子）を添加することがある。これにより、不活性微粒子が熱電変換材料における熱伝導の主要因であるフォノンを散乱させて、熱伝導率κを低減することができる。 As is clear from the above formula (1), in order to improve the thermoelectric conversion performance of the thermoelectric conversion material, it is only necessary to increase the Seebeck coefficient α and the electric conductivity σ of the material to be used and to decrease the thermal conductivity κ. Recognize. Here, in order to reduce the thermal conductivity κ of the material, fine particles (inactive fine particles) that do not react with the base material of the thermoelectric conversion material may be added to the starting material particles of the thermoelectric conversion material. As a result, the inactive fine particles can scatter phonons, which are the main cause of heat conduction in the thermoelectric conversion material, and reduce the thermal conductivity κ.
しかしながら、従来の熱電変換材料では、不活性微粒子が偏在することによって、不活性微粒子によるフォノンの散乱効果よりも不活性微粒子の偏在による電気抵抗率等の他の物性値の悪化の影響が大きく、熱電変換材料の性能向上が妨げられている。この問題を解消するため、例えば、出発原料を微粒子とし、それに母材と反応しないセラミックス等の微粒子を均一に分散させて焼結してなる熱電変換材料が提案されている。この熱電変換材料では、出発原料と不活性微粒子の両者を微粒子とすることで、不活性微粒子が熱電変換材料の母材全体に分散し易くなり出発原料の粒子間に存在する確率が高くなるので、母材の粒子同士の結晶化を防止することができる。また粒径比がほぼ１の同等の大きさの粒子となるように出発原料と不活性微粒子とを調製するため、不活性微粒子は熱電変換材料中に偏在することなく均一に分布して存在でき、不活性微粒子の偏在による電気抵抗率等の他の物性値の悪化を抑えることができる。 However, in the conventional thermoelectric conversion material, due to the uneven distribution of the inert fine particles, the influence of deterioration of other physical properties such as the electrical resistivity due to the uneven distribution of the inert fine particles is larger than the phonon scattering effect by the inert fine particles, Improvement of the performance of thermoelectric conversion materials is hindered. In order to solve this problem, for example, a thermoelectric conversion material is proposed in which the starting material is fine particles, and fine particles such as ceramics that do not react with the base material are uniformly dispersed and sintered. In this thermoelectric conversion material, since both the starting raw material and the inert fine particles are made into fine particles, the inert fine particles are easily dispersed in the entire base material of the thermoelectric conversion material, and the probability of existing between the starting raw material particles is increased. The crystallization of the base material particles can be prevented. In addition, since the starting material and the inert fine particles are prepared so that the particle size ratio is approximately equal to 1 in size, the inert fine particles can be uniformly distributed without being unevenly distributed in the thermoelectric conversion material. Further, deterioration of other physical properties such as electrical resistivity due to uneven distribution of inert fine particles can be suppressed.
しかしながら、粒径がナノオーダーである粒子は比表面積が大きいため、ファンデルワールス力等によって凝集しやすく、従って従来の方法のように熱電変換材料粒子と不活性微粒子を混合するのみでは、不活性微粒子が凝集してミクロサイズになってしまい、熱電変換材料中に不活性微粒子をナノオーダーで分散させることができない。その結果、不活性材料同士の間隔がフォノンの平均自由行程より大きくなってしまい、熱伝導率を十分に低減することができない。 However, particles with a nano-order particle size have a large specific surface area, so they tend to aggregate due to van der Waals force, etc. Therefore, just mixing thermoelectric conversion material particles and inert fine particles as in the conventional method is inactive. The fine particles are aggregated to become micro size, and the inert fine particles cannot be dispersed in the nano-order in the thermoelectric conversion material. As a result, the interval between the inert materials becomes larger than the phonon mean free path, and the thermal conductivity cannot be sufficiently reduced.
そこで本発明者は先に、セラミックス粒子を含む分散液中で熱電変換材料を構成する元素の塩を還元し、セラミックス粒子の表面に熱電変換材料の原料粒子を析出させ、加熱処理し、焼結する工程を含む、熱電変換素子の製造方法を提案した。この方法によれば、セラミックス粒子同士又は熱電変換材料粒子同士が凝集することなく、両者が均一に分散した状態の複合粒子を得ることができ、この複合粒子を焼結することにより、熱電変換材料中にセラミックス粒子が均一に分散した熱電変換素子を得ることができる。 Therefore, the present inventor first reduced the salt of the element constituting the thermoelectric conversion material in the dispersion containing the ceramic particles, precipitated the raw material particles of the thermoelectric conversion material on the surface of the ceramic particles, heat-treated, sintered The manufacturing method of the thermoelectric conversion element including the process to do was proposed. According to this method, it is possible to obtain composite particles in which both ceramic particles or thermoelectric conversion material particles are uniformly dispersed without being agglomerated, and by sintering the composite particles, the thermoelectric conversion material is obtained. A thermoelectric conversion element in which ceramic particles are uniformly dispersed can be obtained.
ところで、熱電変換材料としては各種のものが知られているが、なかでもテルル化ビスマス（Ｂｉ2Ｔｅ3)は常温用熱電変換材料として広く知られている。このテルル化ビスマスのナノ粒子の製造方法として、塩化ビスマスの溶液と、塩化テルルと還元剤を混合し、還元反応を行うことが提案されている（特許文献１参照）。 Various thermoelectric conversion materials are known, and bismuth telluride (Bi 2 Te 3 ) is widely known as a thermoelectric conversion material for room temperature. As a method for producing nanoparticles of bismuth telluride, it has been proposed to perform a reduction reaction by mixing a solution of bismuth chloride, tellurium chloride and a reducing agent (see Patent Document 1).
上記方法では、還元剤として水素化ホウ素ナトリウムが用いられているが、この水素化ホウ素ナトリウムを用いてセラミックス粒子を含む分散液中で塩化ビスマスと塩化テルルを還元すると、図１に示すように、ＢｉやＴｅのナノ粒子１はセラミックス粒子２の表面上で析出するものの、一部のナノ粒子１はセラミックス粒子２の表面上以外で析出し、セラミックス粒子同士が凝集してしまう箇所がある割合で発生し、十分な特性を達成できないという問題がある。このように還元剤として水素化ホウ素ナトリウムを用いた場合に、ＢｉやＴｅのナノ粒子がセラミックス粒子の表面上以外で析出するのは、水素化ホウ素ナトリウムの還元力が塩化ビスマスや塩化テルルに対して強すぎるためであると考えられる。すなわち、還元力が強いため、自由表面で核生成が可能となるため、セラミックス粒子表面以外でも容易にＢｉやＴｅが析出してしまうからである。 In the above method, sodium borohydride is used as the reducing agent. When this sodium borohydride is used to reduce bismuth chloride and tellurium chloride in a dispersion containing ceramic particles, as shown in FIG. Bi and Te nanoparticles 1 are deposited on the surface of the ceramic particles 2, but some nanoparticles 1 are deposited on the surface other than the surface of the ceramic particles 2 and the ceramic particles are aggregated at a certain ratio. There is a problem in that sufficient characteristics cannot be achieved. Thus, when sodium borohydride is used as the reducing agent, Bi and Te nanoparticles are precipitated on the surface of the ceramic particles except for the reducing power of sodium borohydride against bismuth chloride and tellurium chloride. This is probably because it is too strong. That is, since the reducing power is strong, nucleation is possible on the free surface, and Bi and Te are easily deposited on the surface other than the ceramic particle surface.
本願発明は上記問題を解決し、セラミックス粒子のスラリーを用いて、優れた性能指数を有するテルル化ビスマス系熱電変換素子を製造する方法を提供することを目的とする。 This invention solves the said problem, and it aims at providing the method of manufacturing the bismuth telluride type thermoelectric conversion element which has the outstanding performance index using the slurry of ceramic particle | grains.
上記問題点を解決するために本発明によれば、セラミックス粒子のスラリーと、塩化ビスマス及び塩化テルルとを混合して分散液を調製した後、この分散液中に還元剤を加えてセラミックス粒子上でＢｉ及びＴｅを還元析出させ、洗浄、加熱処理し、次いで焼結する工程を含む、テルル化ビスマス系熱電変換素子の製造方法において、前記還元剤として常温での還元電位が０〜−０．５Ｖである還元剤を用いている。この還元剤としては、好ましくはヒドラジン、水素、又はシュウ酸塩、より好ましくはヒドラジンを用いる。 In order to solve the above problems, according to the present invention, a slurry of ceramic particles, bismuth chloride and tellurium chloride are mixed to prepare a dispersion, and then a reducing agent is added to the dispersion to In the method for producing a bismuth telluride-based thermoelectric conversion element comprising steps of reducing and precipitating Bi and Te, washing, heat-treating, and then sintering, the reduction potential at room temperature is 0 to −0. A reducing agent that is 5V is used. As this reducing agent, preferably hydrazine, hydrogen, or oxalate, more preferably hydrazine is used.
還元剤として常温での還元電位が０〜−０．５Ｖである還元剤を用いることにより、セラミックス粒子を含むスラリー中において、分散させたセラミックス粒子上でＢｉ及びＴｅを析出させることができ、セラミックス粒子の凝集を防ぐことができる。 By using a reducing agent having a reduction potential of 0 to −0.5 V at room temperature as a reducing agent, Bi and Te can be deposited on the dispersed ceramic particles in a slurry containing ceramic particles. Aggregation of particles can be prevented.
まず、性能指数ＺＴと熱電変換材料の組織構成との関係について、図２を参照しながら詳細に説明する。図２に示すように、熱電変換材料の組織寸法が、フォノンの平均自由行程の長さを起点にこれよりも小さくなるにつれて、熱電変換材料の熱伝導率κは徐々に減少する。したがって、組織寸法がフォノンの平均自由行程よりも小さくなるように設計すると、性能指数ＺＴが向上する。 First, the relationship between the figure of merit ZT and the structure of the thermoelectric conversion material will be described in detail with reference to FIG. As shown in FIG. 2, the thermal conductivity κ of the thermoelectric conversion material gradually decreases as the structure size of the thermoelectric conversion material becomes smaller starting from the length of the phonon mean free path. Therefore, the figure of merit ZT is improved when the structure size is designed to be smaller than the mean free path of phonons.
一方、熱電変換材料の組織寸法がフォノンの平均自由行程を起点にこれより小さくなっても、熱電変換材料の電気伝導率σは減少せず、概ねキャリアの平均自由行程以下の粒径となった場合に減少する。このように、熱伝導率κが減少し始める熱電変換材料の組織寸法と、電気伝導率σが減少し始める熱電変換材料の組織寸法とが異なることを利用し、電気伝導性の減少率よりも熱伝導率κの減少率が大きい熱電変換材料の組織寸法となるように、熱電変換材料の組織寸法をキャリアの平均自由行程以上フォノンの平均自由行程以下とすることで、上記式（１）で表される性能指数ＺＴをよりいっそう高めることができる。 On the other hand, even if the structure size of the thermoelectric conversion material is smaller than the average free path of phonons, the electrical conductivity σ of the thermoelectric conversion material does not decrease, and the particle size is generally less than the average free path of carriers. Decrease in case. Thus, using the fact that the structural dimension of the thermoelectric conversion material where the thermal conductivity κ begins to decrease and the structural dimension of the thermoelectric conversion material where the electrical conductivity σ begins to decrease are different from each other, By making the structure dimension of the thermoelectric conversion material not less than the average free path of the carrier and not more than the average free path of the phonon so that the structure dimension of the thermoelectric conversion material has a large reduction rate of the thermal conductivity κ, The expressed figure of merit ZT can be further increased.
ここで、熱電変換材料の組織寸法を規定するのは、熱電変換材料中に分散される絶縁材料であるセラミックス粒子の粒径、又はセラミックス粒子同士の分散間隔である。そこで、本発明では、セラミックス粒子同士の分散間隔を、上記効果が得られるように制御する。 Here, the size of the thermoelectric conversion material is defined by the particle size of ceramic particles, which is an insulating material dispersed in the thermoelectric conversion material, or the dispersion interval between the ceramic particles. Therefore, in the present invention, the dispersion interval between the ceramic particles is controlled so as to obtain the above effect.
本発明において、まずセラミックス粒子のスラリーと塩化ビスマス及び塩化テルルを含む溶液を調製する。 In the present invention, first, a slurry containing ceramic particle slurry and bismuth chloride and tellurium chloride is prepared.
セラミックス粒子としては、アルミナ、ジルコニア、チタニア、マグネシア、シリカ等の一般に用いられている材料を用いることができる。これらの中でも、熱伝導率の低さの観点から、シリカ、ジルコニア、チタニアを用いることが好ましい。また、用いるセラミックス粒子の種類は単一種であっても、二種以上を併用してもよい。セラミックス粒子の比抵抗は１０００μΩｍよりも大きいことが好ましく、１０6μΩｍ以上であることがより好ましく、１０10μΩｍ以上であることが更に好ましい。比抵抗が１０００μΩｍ以下の場合には、熱伝導が高いためＺＴ向上の妨げとなる場合がある。 As the ceramic particles, generally used materials such as alumina, zirconia, titania, magnesia, silica and the like can be used. Of these, silica, zirconia, and titania are preferably used from the viewpoint of low thermal conductivity. Moreover, the kind of ceramic particle to be used may be a single kind or a combination of two or more kinds. The specific resistance of the ceramic particles is preferably larger than 1000 μΩm, more preferably 10 6 μΩm or more, still more preferably 10 10 μΩm or more. When the specific resistance is 1000 μΩm or less, the heat conduction is high, which may hinder the improvement of ZT.
セラミックス粒子の平均粒子径は、フォノンの平均自由行程以下であり、具体的には１〜１００ｎｍであることが好ましく、１０〜１００ｎｍであることがさらに好ましい。このような粒径を有する微粒子を用いると、形成される熱電変換素子中に分散されるセラミックス粒子同士の間隔が、セラミックス粒子のフォノンの平均自由行程以下となり、熱電変換素子中でフォノンの散乱が充分に起こるため、熱電変換素子の熱伝導率κが減少し、性能指数ＺＴが向上する。 The average particle diameter of the ceramic particles is equal to or less than the average free path of phonons, specifically, preferably 1 to 100 nm, and more preferably 10 to 100 nm. When fine particles having such a particle size are used, the distance between the ceramic particles dispersed in the formed thermoelectric conversion element is less than the mean free path of phonons of the ceramic particles, and phonon scattering occurs in the thermoelectric conversion element. Since it occurs sufficiently, the thermal conductivity κ of the thermoelectric conversion element is reduced, and the figure of merit ZT is improved.
本発明の方法により得られる熱電変換素子において、ビスマス及びテルル粒子に対するセラミックス粒子の混合比は５〜４０ｖｏｌ％であることが好ましい。この分散液の溶媒は、上記塩化ビスマス、塩化テルル及びセラミックス粒子を分散できるものであれば特に制限されないが、アルコール、特にエタノールを用いることが好適である。また必要に応じてｐＨ調整材を添加してもよい。ｐＨ調整材は、スラリー中で粒子等が凝集するのを抑制するために用いられ、公知のものを適宜適用することができ、例えば、塩酸、酢酸、硝酸、アンモニア水、水酸化ナトリウムなどを用いることができる。 In the thermoelectric conversion element obtained by the method of the present invention, the mixing ratio of the ceramic particles to the bismuth and tellurium particles is preferably 5 to 40 vol%. The solvent of the dispersion is not particularly limited as long as it can disperse the bismuth chloride, tellurium chloride, and ceramic particles, but alcohol, particularly ethanol, is preferably used. Moreover, you may add a pH adjuster as needed. The pH adjusting material is used to suppress aggregation of particles and the like in the slurry, and a known material can be appropriately applied. For example, hydrochloric acid, acetic acid, nitric acid, aqueous ammonia, sodium hydroxide, etc. are used. be able to.
この分散液のｐＨとしては、３〜６又は８〜１１に調製することが好ましく、４〜６又は８〜１０であることがより好ましい。 As pH of this dispersion liquid, it is preferable to adjust to 3-6 or 8-11, and it is more preferable that it is 4-6 or 8-10.
こうして分散液を調製した後、還元剤を含む溶液にこの分散液を滴下する。還元剤としては、常温での還元電位が０〜−０．５Ｖである還元剤、好ましくはヒドラジン、水素、又はシュウ酸塩、より好ましくはヒドラジンを用いる。 After preparing a dispersion in this way, this dispersion is dropped into a solution containing a reducing agent. As the reducing agent, a reducing agent having a reduction potential at room temperature of 0 to −0.5 V, preferably hydrazine, hydrogen, or oxalate, more preferably hydrazine is used.
塩化ビスマス及び塩化テルルを含む分散液中には熱電変換材料の原料イオンであるＢｉイオン及びＴｅイオンが存在する。従って、還元剤を含む溶液と混合されると、これらのイオンは還元され、Ｂｉ粒子及びＴｅ粒子が析出することになる。本願発明においては、この還元剤として常温での還元電位が０〜−０．５Ｖである還元剤を用いているため、セラミックス粒子上以外で還元されることなく、Ｂｉ粒子及びＴｅ粒子のほぼすべてがセラミックス粒子上で析出することになる。 In the dispersion containing bismuth chloride and tellurium chloride, Bi ions and Te ions, which are raw material ions of the thermoelectric conversion material, are present. Therefore, when mixed with a solution containing a reducing agent, these ions are reduced, and Bi particles and Te particles are precipitated. In the present invention, since a reducing agent having a reduction potential of 0 to −0.5 V at room temperature is used as the reducing agent, almost all Bi particles and Te particles are not reduced except on the ceramic particles. Will be deposited on the ceramic particles.
この還元において、Ｂｉ粒子やＴｅ粒子の他に、副生物、例えばＮａＣｌやＮａＢＯ3が生成する。この副生物を除去するために、濾過を行うことが好ましい。さらに、濾過後、アルコールや水を加えて、副生物を洗い流すことが好適である。 In this reduction, by-products such as NaCl and NaBO 3 are generated in addition to Bi particles and Te particles. Filtration is preferably performed to remove this by-product. Furthermore, after filtration, it is preferable to add alcohol or water to wash away by-products.
こうして得られた、表面にＢｉ粒子及びＴｅ粒子が析出したセラミックス粒子の分散液を加熱処理し、好ましくは水熱処理し、乾燥させ、得られた凝集体を、必要に応じて洗浄・乾燥した後、一般的な焼結法により、例えばＳＰＳ焼結することにより、テルル化ビスマスの連続相中にセラミックス粒子が分散して分散相を構成する熱電変換素子が得られる。 After the thus obtained ceramic particle dispersion having Bi particles and Te particles deposited on its surface is heat-treated, preferably hydrothermally treated and dried, and the resulting aggregate is washed and dried as necessary. A thermoelectric conversion element in which a ceramic particle is dispersed in a continuous phase of bismuth telluride to form a dispersed phase is obtained by, for example, SPS sintering by a general sintering method.
本発明の熱電変換材料の製造方法は、ナノオーダーでの組織寸法（絶縁材料の粒径や絶縁材料同士の分散間隔）の制御を可能とするものである。すなわち、表面にＢｉ粒子及びＴｅ粒子が析出したセラミックス粒子の凝集体を調製することにより、熱電変換素子の組織寸法（セラミックス同士の分散間隔）が、フォノンの平均自由行程以下、好ましくはキャリアの平均自由行程以上フォノンの平均自由行程以下となり、熱電変換素子中のフォノンの散乱が充分に起こり、熱伝導率κを減少させることができる。この結果、式（１）で表される性能指数ＺＴが大きい熱電変換素子となる。このように、本発明の熱電変換素子の製造方法によれば、高い性能指数ＺＴを示す優れた熱電変換素子であって、従来では作製困難であった性能指数ＺＴが２を上回るような熱電変換素子を得ることもできる。 The method for producing a thermoelectric conversion material of the present invention enables control of the nano-sized structure dimensions (particle size of insulating material and dispersion interval between insulating materials). That is, by preparing an aggregate of ceramic particles having Bi particles and Te particles deposited on the surface, the structure size of the thermoelectric conversion element (dispersion interval between ceramics) is less than the mean free path of phonons, preferably the average of carriers The free path is equal to or more than the average free path of the phonons, the phonons are sufficiently scattered in the thermoelectric conversion element, and the thermal conductivity κ can be reduced. As a result, a thermoelectric conversion element having a large figure of merit ZT represented by the formula (1) is obtained. Thus, according to the method for manufacturing a thermoelectric conversion element of the present invention, an excellent thermoelectric conversion element exhibiting a high figure of merit ZT, which has a figure of merit ZT exceeding 2 that has been difficult to produce in the past. An element can also be obtained.
実施例１
塩化ビスマス２．０ｇ及び塩化テルル１．６９８ｇをエタノール１００ｍＬに加え、溶解させた後、この溶液に平均粒径２５ｎｍのシリカ粒子０．２３ｇを加え、分散液を調製した。この分散液に、ヒドラジン５．５ｇをエタノール１００ｍＬに加えて調製した還元剤溶液を加えた。次いで、エタノールと水の混合溶液で洗浄することによって不純物を除去し、２４０℃にて２４時間水熱合成を行い、シリカ粒子上でＢｉ2Ｔｅ3を形成した。こうして得られた複合粒子を充填し、３８０〜５００℃でＳＰＳ焼結を行い、テルル化ビスマス系熱電変換素子を得た。この素子のＴＥＭ像を図３に示す。得られた熱電変換素子においては、ほぼ全ての領域において、シリカ粒子上にＢｉ、Ｔｅ粒子が析出していた。
Example 1
After adding 2.0 g of bismuth chloride and 1.698 g of tellurium chloride to 100 mL of ethanol and dissolving it, 0.23 g of silica particles having an average particle diameter of 25 nm were added to this solution to prepare a dispersion. A reducing agent solution prepared by adding 5.5 g of hydrazine to 100 mL of ethanol was added to this dispersion. Next, impurities were removed by washing with a mixed solution of ethanol and water, and hydrothermal synthesis was performed at 240 ° C. for 24 hours to form Bi 2 Te 3 on silica particles. The composite particles thus obtained were filled and SPS sintered at 380 to 500 ° C. to obtain a bismuth telluride-based thermoelectric conversion element. A TEM image of this element is shown in FIG. In the obtained thermoelectric conversion element, Bi and Te particles were deposited on the silica particles in almost all regions.
比較例１
塩化ビスマス１．５ｇ及び塩化テルル１．６９８ｇをエタノール１００ｍＬに加え、溶解させた後、この溶液に平均粒径２５ｎｍのシリカ粒子０．２３ｇを加え、分散液を調製した。この分散液に、水素化ホウ素ナトリウム１．８ｇをエタノール１００ｍＬに加えて調製した還元剤溶液を加えた。次いで、エタノールと水の混合溶液で洗浄することによって不純物を除去し、２４０℃にて２４時間水熱合成を行い、シリカ粒子上でＢｉ2Ｔｅ3を形成した。こうして得られた複合粒子を充填し、３８０〜５００℃でＳＰＳ焼結を行い、テルル化ビスマス系熱電変換素子を得た。この素子のＴＥＭ像を図４に示す。得られた熱電変換素子においては、複合粒子が形成しているものの、一部領域においてシリカ同士が凝集していることが確認された。
Comparative Example 1
After 1.5 g of bismuth chloride and 1.698 g of tellurium chloride were added to 100 mL of ethanol and dissolved, 0.23 g of silica particles having an average particle diameter of 25 nm were added to this solution to prepare a dispersion. To this dispersion, a reducing agent solution prepared by adding 1.8 g of sodium borohydride to 100 mL of ethanol was added. Next, impurities were removed by washing with a mixed solution of ethanol and water, and hydrothermal synthesis was performed at 240 ° C. for 24 hours to form Bi 2 Te 3 on silica particles. The composite particles thus obtained were filled and SPS sintered at 380 to 500 ° C. to obtain a bismuth telluride-based thermoelectric conversion element. A TEM image of this element is shown in FIG. In the obtained thermoelectric conversion element, although composite particles were formed, it was confirmed that silica was aggregated in a partial region.
ここで得られた熱電変換素子中のシリカの粒径分布をＴＥＭ像から算出し、結果を図５に示す。使用したシリカ（Ｉ）の平均粒径は２５ｎｍであったのに対し、実施例１（II）では粒径分布はわずかに右にシフトし、平均粒径は３０ｎｍと一部凝集していることがわかる。さらに比較例１（III）では粒径分布は大きく右にシフトし、平均粒径は７０ｎｍとかなり凝集していることがわかる。 The particle size distribution of the silica in the thermoelectric conversion element obtained here was calculated from the TEM image, and the result is shown in FIG. The average particle size of the silica (I) used was 25 nm, whereas in Example 1 (II), the particle size distribution was slightly shifted to the right and the average particle size was partially aggregated to 30 nm. I understand. Further, in Comparative Example 1 (III), it can be seen that the particle size distribution is greatly shifted to the right, and the average particle size is considerably aggregated to 70 nm.
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| JP2011243729A (en) * | 2010-05-18 | 2011-12-01 | Toyota Motor Corp | Manufacturing method of anisotropic thermoelectric conversion nanoparticle, and manufacturing method of anisotropic thermoelectric conversion sintered body using the same |
| JP2011249749A (en) * | 2010-05-24 | 2011-12-08 | Korea Inst Of Machinery & Materials | Thermoelectric material and composite material containing the same as raw material, and method for manufacturing the same |
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| JP2011249749A (en) * | 2010-05-24 | 2011-12-08 | Korea Inst Of Machinery & Materials | Thermoelectric material and composite material containing the same as raw material, and method for manufacturing the same |
| US20120025130A1 (en) * | 2010-07-27 | 2012-02-02 | Toyota Motor Engineering & Manufacturing North America, Inc. | HIGH-Ph SYNTHESIS OF NANOCOMPOSITE THERMOELECTRIC MATERIAL |
| US8535554B2 (en) * | 2010-07-27 | 2013-09-17 | Toyota Motor Engineering & Manufacturing North America, Inc. | High-Ph synthesis of nanocomposite thermoelectric material |
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| JP2017014578A (en) * | 2015-07-01 | 2017-01-19 | トヨタ自動車株式会社 | METHOD FOR PRODUCING ALLOY PARTICLES INCLUDING Bi AND Te |
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