JP2007173852A - Method of manufacturing thermoelectric material - Google Patents
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Abstract
Description
本発明は、半導体等の発熱体の冷却、各種クーラー等に好適に用いることのできる熱電材料の製造方法に関する。 The present invention relates to a method for producing a thermoelectric material that can be suitably used for cooling a heating element such as a semiconductor and various coolers.
従来より、ペルチェ効果を利用した熱電素子は、電流を流すことにより一端が発熱するとともに他端が吸熱するため、冷却用の熱電素子として用いられている。 Conventionally, a thermoelectric element using the Peltier effect has been used as a thermoelectric element for cooling because one end generates heat and the other end absorbs heat when an electric current is passed.
特に、熱電モジュールとしてレーザーダイオードの温度制御、小型で構造が簡単でありフロンレスの冷却装置、冷蔵庫、恒温槽、光検出素子、半導体製造装置等の電子冷却素子、レーザーダイオードの温度調節等への幅広い利用が期待されている。 In particular, temperature control of laser diodes as thermoelectric modules, small size and simple structure, cooling devices without refrigerators, refrigerators, thermostats, photodetectors, electronic cooling elements such as semiconductor manufacturing equipment, temperature control of laser diodes, etc. Use is expected.
この室温付近で使用される冷却用熱電モジュールに使用される熱電素子用材料は、冷却特性が優れるという観点からA2B3型金属間化合物(AはBi及び/又はSb、BはTe及び/又はSe)からなる熱電素子が一般的に用いられている。 The thermoelectric element material used for the cooling thermoelectric module used near room temperature is an A2B3 type intermetallic compound (A is Bi and / or Sb, B is Te and / or Se) from the viewpoint of excellent cooling characteristics. The thermoelectric element which consists of is generally used.
さらに、熱電モジュールにはP型及びN型の熱電素子を対にしたものを複数直列に電気的接続を行い冷却モジュールとして使用される。P型の熱電素子にはBi2Te3とSb2Te3(テルル化アンチモン)との固溶体が、N型の熱電素子にはBi2Te3とBi2Se3(セレン化ビスマス)との固溶体が特に優れた性能を示すことから、このA2B3型金属間化合物(AはBi及び/又はSb、BはTe及び/又はSe)が熱電素子として広く用いられている。 Furthermore, the thermoelectric module is used as a cooling module by electrically connecting a plurality of P-type and N-type thermoelectric elements in series. A solid solution of Bi 2 Te 3 and Sb 2 Te 3 (antimony telluride) is used for the P-type thermoelectric element, and a solid solution of Bi 2 Te 3 and Bi 2 Se 3 (bismuth selenide) is used for the N-type thermoelectric element. Since A2B3 type intermetallic compounds (A is Bi and / or Sb, B is Te and / or Se) are widely used as thermoelectric elements.
このような熱電素子の作製方法としては、ブリッジマン法、引き上げ(CZ)法などによる溶製材を作製する方法があるが、溶製材は機械的特性が悪いため、近年ではBi、Te、Sb、Seからなる固溶体合金を粉砕して、ホットプレス法などによって加圧焼結法により緻密体を作製する方法が知られている。 As a method for producing such a thermoelectric element, there is a method of producing a melted material by a Bridgeman method, a pulling (CZ) method or the like, but since the melted material has poor mechanical properties, Bi, Te, Sb, A method is known in which a solid solution alloy made of Se is pulverized and a dense body is produced by a pressure sintering method such as a hot press method.
例えば、アンチモンを含有する固溶体粉末をホットプレス法等の加圧焼結を用いることによって、常圧焼結では得られない緻密な焼結体を作製し、理論密度比97%以上することで、熱電特性を顕著に改善することが提案されている(例えば、特許文献1参照)。 For example, by using a solid solution powder containing antimony using pressure sintering such as a hot press method, a dense sintered body that cannot be obtained by atmospheric pressure sintering is produced, and the theoretical density ratio is 97% or more. It has been proposed to significantly improve thermoelectric characteristics (see, for example, Patent Document 1).
このように、ホットプレス法を用いることによって溶製材に比べて機械的特性が改善されたものの、原料粉末の酸化により特性改善が阻害されているため、その改善方法が提案されている。例えば、原料粉末から酸化されやすい微粒子を除去する熱処理を施し、得られた10〜200μmの固溶体粉末を焼結させることで粒径が均一となった高い熱電性能を有する熱電材料の製造方法が開示されている(例えば、特許文献2参照)。 As described above, although the mechanical properties are improved by using the hot press method as compared with the smelted material, the improvement of the properties is hindered by the oxidation of the raw material powder, and therefore an improvement method has been proposed. For example, a method for producing a thermoelectric material having high thermoelectric performance in which the particle size is uniformed by subjecting a heat treatment to remove fine particles that are easily oxidized from a raw material powder and sintering the obtained solid solution powder of 10 to 200 μm is disclosed. (For example, refer to Patent Document 2).
また、液体急冷法を用いて固溶体合金粉末を作製し、その後に水素ガス雰囲気で還元処理を行った原料粉末を加圧焼成することによって、酸素含有量を1500ppm以下に低減せしめ、熱電材料の性能を改善することが提案されている(例えば、特許文献3参照)。 In addition, by producing a solid solution alloy powder using a liquid quenching method and then firing the raw material powder subjected to reduction treatment in a hydrogen gas atmosphere under pressure, the oxygen content is reduced to 1500 ppm or less, and the performance of the thermoelectric material Has been proposed (see, for example, Patent Document 3).
さらに、原料表面に付着した酸素を除去する方法として、Bi、Te、Se及びSb元素からなる群より選択される少なくとも2種類以上の元素を含有した熱電変換材料を仮成形し、しかる後に減圧雰囲気下でかつ焼成温度よりも低い温度で仮焼して得られた仮焼体を焼成前に水素を含む還元性雰囲気で熱処理する方法が提案されている(例えば、特許文献4参照)。 Further, as a method for removing oxygen adhering to the raw material surface, a thermoelectric conversion material containing at least two elements selected from the group consisting of Bi, Te, Se and Sb elements is temporarily formed, and then a reduced pressure atmosphere A method has been proposed in which a calcined body obtained by calcining at a temperature lower than the calcining temperature is heat-treated in a reducing atmosphere containing hydrogen before calcining (see, for example, Patent Document 4).
さらにまた、粉末に直接電圧を負加して粉体粒子間に放電プラズマを起こし、粒子表面を活性化することにより酸化物層や吸着ガスを除去しながら加圧焼結させるため、吸着ガスの悪影響を低減して熱電素子の特性ばらつきを抑えられることが示されている(例えば、特許文献5参照)。
しかしながら、特許文献2に記載の熱電材料では、微粒子を除去する熱処理を粉末で行い10〜200μmの粒子径を有するため、強度が低下するという問題があった。 However, the thermoelectric material described in Patent Document 2 has a problem that strength is lowered because the heat treatment for removing fine particles is performed with powder and has a particle diameter of 10 to 200 μm.
また、熱処理後の粉末が凝集しやすく、焼結時の粉末挿入に時間がかかりまた凝集の度合いによって性能がばらつくなど量産性に劣り、得られた焼結体の強度も低いという問題があった。 In addition, the powder after heat treatment tends to agglomerate, it takes time to insert the powder during sintering, the performance varies depending on the degree of agglomeration, and there is a problem that the strength of the obtained sintered body is low. .
また、特許文献3に記載の熱電材料の製造方法では、前記特許文献2の場合と同様に熱処理後の粉末を加圧焼結しなければならない問題に加えて、特殊な設備を必要とする液体急冷法により作製するため量産性に劣り、また加圧焼結方法によっては特性が不安定で内外差が発生しやすいという問題があった。 Further, in the method for producing a thermoelectric material described in Patent Document 3, in addition to the problem that the powder after heat treatment must be pressure-sintered as in the case of Patent Document 2, a liquid that requires special equipment is used. Since it is produced by a rapid cooling method, it is inferior in mass productivity, and depending on the pressure sintering method, there are problems that characteristics are unstable and internal / external differences are likely to occur.
さらに、特許文献4に記載の熱電材料の製造方法では、短時間で原料を作製するため、原料中の酸素量の低減はできるものの、工程が多数で、且つ複雑であるとともに、また性能の向上が充分ではなかった。 Furthermore, in the method for producing a thermoelectric material described in Patent Document 4, since the raw material is produced in a short time, the amount of oxygen in the raw material can be reduced, but the number of steps is complicated and the performance is improved. Was not enough.
さらにまた、特許文献5に記載の熱電材料の製造方法では、原料粉末の粒子表面に付着した酸素を除去しながら焼結をするため、低コスト化に効果があるものの、成形体内部の酸素量を十分に低減するのは容易ではなく性能向上が困難であったり、特性が不安定で内外差が発生しやすいという問題があった。 Furthermore, in the method for producing a thermoelectric material described in Patent Document 5, since sintering is performed while removing oxygen adhering to the particle surface of the raw material powder, the amount of oxygen in the molded body is effective although it is effective in reducing the cost. However, it is not easy to sufficiently reduce the performance, and it is difficult to improve the performance, or the characteristics are unstable and an internal / external difference is likely to occur.
このように、従来の熱電素子の製造方法では、方法自体は簡便であるが十分な性能が得られないか、または高性能が得られるものの量産性が劣るものであり、量産性に優れ、且つ高性能という両特性を併せ持つ熱電焼結材を得ることが難しかった。 Thus, in the conventional method for producing a thermoelectric element, the method itself is simple but sufficient performance cannot be obtained, or high performance is obtained, but mass productivity is inferior, excellent in mass productivity, and It was difficult to obtain a thermoelectric sintered material having both the high performance characteristics.
従って、本発明は、生産性が高く高性能の熱電材料の製造方法を提供することを目的とする。 Accordingly, an object of the present invention is to provide a method for producing a thermoelectric material having high productivity and high performance.
本発明は、従来の加圧焼成法が固溶体合金粉末をカーボン焼成型に充填して焼成するため、カーボンが焼結体中に混入して特性劣化を招くという新規な知見に基づき、還元性雰囲気中で常圧焼成を行い、得られた焼結体をパルス通電等により短時間で緻密化することで、焼結体中に混入するカーボン量を顕著に抑制でき、且つ酸素量も低減できるため、微細な組織であっても高強度で優れた熱電特性を有する熱電材料を生産することを見出したものである。 The present invention is based on the novel knowledge that the conventional pressure firing method fills a solid solution alloy powder into a carbon firing mold and fires, so that carbon is mixed in the sintered body and causes deterioration of the characteristics. Because the sintered body obtained under normal pressure firing is densified in a short time by pulse energization etc., the amount of carbon mixed in the sintered body can be remarkably suppressed and the amount of oxygen can also be reduced. The present inventors have found that a thermoelectric material having high strength and excellent thermoelectric properties can be produced even in a fine structure.
本発明の熱電材料の製造方法は、Bi、Sb、Te及びSeのうち少なくとも2種を含み、平均粒径が30μm以下の合金粉末からなる成形体を作製し、該成形体を常圧で焼成して前記合金粉末の粒子同士を結合させて常圧焼結体を作製した後に、該常圧焼結体に連続通電又はパルス通電による加熱処理を行って緻密体を作製することを特徴とするものである。この方法を採用することによって、常圧焼結体中へのカーボンと酸素との混入を抑えつつ、粒成長も同時に抑えることができる。その結果、高強度で熱電性能の優れ、冷却や発電用熱電モジュールとして好適に使用できる材料を生産性の高い方法で得ることができる。 The method for producing a thermoelectric material according to the present invention is to produce a compact comprising an alloy powder containing at least two of Bi, Sb, Te and Se and having an average particle size of 30 μm or less, and firing the compact at normal pressure. Then, after the particles of the alloy powder are bonded together to produce a normal pressure sintered body, the normal pressure sintered body is subjected to heat treatment by continuous energization or pulse energization to produce a dense body. Is. By adopting this method, it is possible to simultaneously suppress grain growth while suppressing mixing of carbon and oxygen into the atmospheric pressure sintered body. As a result, it is possible to obtain a material having high strength and excellent thermoelectric performance and capable of being suitably used as a thermoelectric module for cooling or power generation by a high productivity method.
特に、前記常圧焼成における焼成温度が、前記緻密化処理の処理温度以上であることが好ましい。これにより、常圧焼結によって粒子間の物質移動を確実に生じせしめ、粒子同士の焼結を促進するとともに、緻密化温度を焼成温度よりも低くすることで粒成長を抑制し、高い強度を容易に実現することができる。 In particular, the firing temperature in the normal pressure firing is preferably equal to or higher than the treatment temperature of the densification treatment. As a result, mass transfer between the particles is surely caused by atmospheric pressure sintering, the sintering of the particles is promoted, and the densification temperature is made lower than the firing temperature, thereby suppressing the grain growth and increasing the strength. It can be easily realized.
前記緻密化処理が、パルス電流による加熱処理であることが好ましい。パルス通電による直接通電加熱を行うことによって、エネルギー効率が高く、急速加熱が可能となり、熱処理時間を短縮でき、不純物の混入を効果的に防止するとともに、部分的な過熱を防止でき、均一な温度制御を容易に行うことができる。 The densification treatment is preferably a heat treatment using a pulse current. Direct current heating by pulse energization enables high energy efficiency and rapid heating, shortens heat treatment time, effectively prevents impurities from being mixed, and prevents partial overheating, uniform temperature Control can be easily performed.
また、前記緻密化処理が加圧を伴うことが好ましい。これにより、緻密化を促進し、短時間での緻密化処理を容易に実現できる。 Moreover, it is preferable that the said densification process involves pressurization. Thereby, densification is accelerated | stimulated and the densification process in a short time is easily realizable.
さらに、前記緻密化処理において、前記常圧焼結体が200℃以上の温度に曝される時間が1時間以内であることが好ましい。1時間以内で緻密化処理における加熱を短時間で終了させることで焼結体へのカーボン及び酸素の混入を低減させることができる。 Further, in the densification treatment, it is preferable that the time during which the atmospheric sintered body is exposed to a temperature of 200 ° C. or higher is within 1 hour. Mixing carbon and oxygen into the sintered body can be reduced by finishing the heating in the densification treatment within a short time within a short time.
さらにまた、前記常圧焼成における焼成温度が、300〜550℃であることが好ましい。このような焼成温度であればBi、Sb、Te及びSeのうち少なくとも2種を含む熱電材料を焼結させ、粒子間の結合を生じせしめるとともに、分解や急激な粒成長を防止することができる。 Furthermore, it is preferable that the baking temperature in the said normal pressure baking is 300-550 degreeC. With such a firing temperature, a thermoelectric material containing at least two of Bi, Sb, Te, and Se can be sintered to cause bonding between particles and to prevent decomposition and rapid grain growth. .
また、前記常圧焼成における焼成雰囲気が、還元性雰囲気であり、特に、少なくとも水素を含有するガスで構成されることが好ましい。このような還元性ガスを用いた雰囲気、特に水素雰囲気は酸素の除去に効果が大きい。 Further, the firing atmosphere in the normal pressure firing is a reducing atmosphere, and it is particularly preferable that the firing atmosphere is composed of a gas containing at least hydrogen. An atmosphere using such a reducing gas, particularly a hydrogen atmosphere, is highly effective in removing oxygen.
さらに、前記常圧焼成によって前記常圧焼結体の相対密度を60〜95%にすることが好ましい。これにより、粒子同士が結合しているため、通電処理を行うと容易に発熱することができ、更にカーボンの混入を低下できる。 Furthermore, it is preferable that the relative density of the atmospheric sintered body is 60 to 95% by the atmospheric firing. As a result, since the particles are bonded to each other, heat can be easily generated when energization processing is performed, and mixing of carbon can be further reduced.
さらにまた、前記緻密化処理によって前記緻密体の相対密度を98%以上にすることができる。これにより、抵抗率を低下せしめ、熱電特性をより高めることが可能となる。 Furthermore, the relative density of the dense body can be increased to 98% or more by the densification treatment. Thereby, the resistivity can be lowered and the thermoelectric characteristics can be further improved.
また、前記成形体を作製する成形圧力が10MPa以上であることが好ましい。 Moreover, it is preferable that the shaping | molding pressure which produces the said molded object is 10 Mpa or more.
10MPa以上にすることによって成形体の保持力を高め、製造上の取扱いを容易にするとともに、焼結を効果的に推進することができる。 By setting the pressure to 10 MPa or more, it is possible to increase the holding power of the molded body, facilitate the handling in manufacturing, and effectively promote the sintering.
本発明の熱電材料の製造方法は、Bi、Sb、Te及びSeのうち少なくとも2種を含み、平均粒径が30μm以下の合金粉末からなる成形体を作製し、該成形体を常圧で焼成して焼結体を作製した後に、該焼結体の緻密化処理を行って緻密体を作製するものであり、あらかじめ焼結体を作製し、それにパルス通電等により緻密化することで焼結体中に混入するカーボン及び酸素を顕著に抑制でき、且つ組織も微細に保つことができる。また、上記のような熱電素子を容易に製造することができる。 The method for producing a thermoelectric material according to the present invention is to produce a compact comprising an alloy powder containing at least two of Bi, Sb, Te and Se and having an average particle size of 30 μm or less, and firing the compact at normal pressure. After the sintered body is manufactured, the sintered body is densified to prepare a dense body. The sintered body is prepared in advance and then sintered by densification by pulse energization or the like. Carbon and oxygen mixed in the body can be remarkably suppressed, and the tissue can be kept fine. Moreover, the thermoelectric element as described above can be easily manufactured.
本発明の熱電材料は、Bi、Sb、Te、Seのうち少なくとも2種を含む緻密体であることが重要である。このような材料は性能指数に優れ、特に、A2B3型金属間化合物であることが好ましく、例えばAがBi及び/又はSb、BがTe及び/又はSeからなる半導体結晶であって、組成比B/Aが1.4〜1.6であることが、室温における性能指数を高めるために好ましい。 It is important that the thermoelectric material of the present invention is a dense body containing at least two of Bi, Sb, Te, and Se. Such a material has an excellent figure of merit, and is particularly preferably an A2B3 type intermetallic compound. For example, A is a semiconductor crystal composed of Bi and / or Sb, B is Te and / or Se, and a composition ratio B / A is preferably 1.4 to 1.6 in order to increase the figure of merit at room temperature.
A2B3型金属間化合物としては、Bi2Te3、Sb2Te3、Bi2Se3の少なくとも1種、或いはBi2Te3とBi2Se3の固溶体であるBi2Te3−xSex(x=0.05〜0.25)、又はBi2Te3とSb2Te3の固溶体であるBixSb2−xTe3(x=0.1〜0.6)等を例示できる。 Examples of the A2B3 type intermetallic compound include Bi 2 Te 3 , Sb 2 Te 3 , Bi 2 Se 3 , or Bi 2 Te 3-x Se x (a solid solution of Bi 2 Te 3 and Bi 2 Se 3 ). x = 0.05 to 0.25), or Bi x Sb 2−x Te 3 (x = 0.1 to 0.6) which is a solid solution of Bi 2 Te 3 and Sb 2 Te 3 can be exemplified.
また、金属間化合物を効率よく半導体化するために、不純物をドーパントとして含有することができる。例えば、原料粉末にI、Cl及びBr等のハロゲン元素を含む化合物を含有せしめることにより、N型半導体を製造することができる。例えば、AgI粉末、CuBr粉末、SbI3粉末、SbCl3粉末、SbBr3粉末、HgBr2粉末等を加えることにより、金属間化合物半導体中のキャリア濃度を調整することができ、その結果、性能指数を高めることが可能となる。上記のハロゲン元素は、効率的な半導体化の点で、0.01〜5質量%、特に0.05〜4質量%の割合で含むことが好ましい。 Moreover, in order to make an intermetallic compound into a semiconductor efficiently, an impurity can be contained as a dopant. For example, an N-type semiconductor can be produced by incorporating a compound containing a halogen element such as I, Cl and Br into the raw material powder. For example, AgI powder, CuBr powder, SbI 3 powder, SbCl 3 powder, SbBr 3 powder, by addition of HgBr 2 powder or the like, it is possible to adjust the carrier concentration in the intermetallic compound semiconductor, as a result, the performance index It becomes possible to raise. The halogen element is preferably contained in an amount of 0.01 to 5% by mass, particularly 0.05 to 4% by mass in terms of efficient semiconductorization.
さらに、P型半導体を製造する場合には、キャリア濃度調整のためにTeを含有することができ、N型半導体と同様に、性能指数を高めることができる。 Further, when a P-type semiconductor is manufactured, Te can be contained for adjusting the carrier concentration, and the figure of merit can be increased like the N-type semiconductor.
本発明によれば、上記のような組成の緻密体が、熱電性能を高め、冷却デバイスとして好適に用いる上で重要である。 According to the present invention, a dense body having the above composition is important for improving thermoelectric performance and being suitably used as a cooling device.
また、本発明の熱電材料を構成する緻密体の平均粒径が30μm以下であることが必要である。粒径を小さくすることによって強度を高めることができ、熱電モジュールの熱電素子として用いた場合に、熱電モジュールの信頼性を高める効果がある。 Moreover, it is necessary that the average particle diameter of the dense body constituting the thermoelectric material of the present invention is 30 μm or less. The strength can be increased by reducing the particle size, and when used as a thermoelectric element of a thermoelectric module, there is an effect of improving the reliability of the thermoelectric module.
また、粒径を小さくすることによって熱伝導率が低下し、熱電材料の性能指数を高めることができる。このような効果をさらに高めるため、緻密体の平均粒径を特に15μm以下、更には10μm以下、より好適には8μm以下にすることが好ましい。 Further, by reducing the particle size, the thermal conductivity is lowered, and the figure of merit of the thermoelectric material can be increased. In order to further enhance such an effect, the average particle size of the dense body is preferably 15 μm or less, more preferably 10 μm or less, and even more preferably 8 μm or less.
上記緻密体の平均粒径の下限値は、特に制限されるものではないが、小さすぎると製造に用いる原料粉末を細かくすることが必要となるが、爆発性や取扱いが難しくなるため、平均粒径の下限値は実質的に1μm、特に3μm、更には5μmであることが好ましい。 The lower limit of the average particle size of the dense body is not particularly limited, but if it is too small, it is necessary to make the raw material powder used for production fine, but the explosiveness and handling become difficult, so the average particle size It is preferable that the lower limit of the diameter is substantially 1 μm, particularly 3 μm, more preferably 5 μm.
なお、性能指数Zとは、ゼーベック係数をS、抵抗率をρ、熱伝導率をkとしたとき、Z=S2/ρkで定義されるもので、熱電素子を冷却素子あるいは発電素子として用いる場合の効率を示すものである。 The figure of merit Z is defined as Z = S 2 / ρk, where the Seebeck coefficient is S, the resistivity is ρ, and the thermal conductivity is k, and the thermoelectric element is used as a cooling element or a power generation element. Shows the efficiency of the case.
本発明の熱電材料は、カーボン含有量が0.3質量%以下であることが重要である。 It is important that the thermoelectric material of the present invention has a carbon content of 0.3% by mass or less.
カーボンは導電性粒子であるため、半導体中に混入すると電荷を粒子周辺に発生させ、キャリアの散乱を招くため、緻密体に含まれるカーボン量は0.3質量%以下であることが熱電性能を高めるために重要である。特に、性能指数で3×10−3/Kの高い熱電材料を得るため、0.25質量%以下、更には0.2質量%以下であることが好ましい。 Since carbon is a conductive particle, when it is mixed in a semiconductor, it generates electric charges around the particle and causes carrier scattering. Therefore, the amount of carbon contained in the dense body is 0.3% by mass or less. Is important to enhance. In particular, in order to obtain a thermoelectric material having a high figure of merit of 3 × 10 −3 / K, it is preferably 0.25% by mass or less, more preferably 0.2% by mass or less.
また、酸素含有量は、絶縁層を形成して比抵抗を増大する働きがあるため、0.3質量%以下であることが性能指数を高めるために重要である。特に、性能指数で3×10−3/Kの高い熱電材料を得るため、0.25質量%以下、更には0.2質量%以下であることが好ましい。 In addition, since the oxygen content serves to increase the specific resistance by forming an insulating layer, it is important for the performance index to be 0.3% by mass or less. In particular, in order to obtain a thermoelectric material having a high figure of merit of 3 × 10 −3 / K, it is preferably 0.25% by mass or less, more preferably 0.2% by mass or less.
カーボン含有量、酸素含有量は少なければ少ないほど好ましいが、これらの含有量の少ない緻密体を作製するのは容易ではなく、或いは高コストとなるため、カーボン、酸素の含有量の下限値は、0.01質量%又は0.001質量%が良いが、熱電特性の低下が抑制され、製造しやすく、且つ低コストで製造する点で0.1質量%でも十分である。 The smaller the carbon content and the lower the oxygen content, the better, but it is not easy to produce a dense body with a small content, or the cost is high, so the lower limit of the carbon and oxygen content is Although 0.01% by mass or 0.001% by mass is preferable, 0.1% by mass is sufficient in that the deterioration of thermoelectric properties is suppressed, the manufacturing is easy, and the manufacturing cost is low.
本発明の緻密体は、98%以上、特に98.5%以上、更には99%以上の相対密度を有することが好ましい。このように相対密度を高めることにより、電気的特性、即ち抵抗率を低減することができ、その結果、熱電素子としての性能を一層高める効果がある。 The dense body of the present invention preferably has a relative density of 98% or more, particularly 98.5% or more, and more preferably 99% or more. By increasing the relative density in this manner, electrical characteristics, that is, resistivity can be reduced, and as a result, there is an effect of further improving the performance as a thermoelectric element.
このような構成の熱電材料は、下記に示すような焼結法によって得ることが出来、性能指数が高いため、熱電モジュールとして用いたときの冷却性能に優れ、冷却や加熱用の熱電モジュールに使用する熱電素子として好適に用いることが出来る。 The thermoelectric material with such a structure can be obtained by the sintering method as shown below, and has a high figure of merit, so it has excellent cooling performance when used as a thermoelectric module and is used for thermoelectric modules for cooling and heating. It can be suitably used as a thermoelectric element.
なお、本発明の熱電材料は、P型及びN型の熱電素子を組合せて形成される熱電モジュールにおいて、少なくとも一方の型の熱電素子に応用することができる。 The thermoelectric material of the present invention can be applied to at least one type of thermoelectric element in a thermoelectric module formed by combining P-type and N-type thermoelectric elements.
即ち、P型熱電素子又はN型熱電素子の一方にのみ本発明の熱電材料を用いることが可能であり、更には両方に用いることも可能である。 That is, the thermoelectric material of the present invention can be used for only one of the P-type thermoelectric element and the N-type thermoelectric element, and can also be used for both.
次に、本発明の熱電材料の製造方法について説明する。まず、熱電材料の原料粉末を準備する。用いる原料粉末は、溶製法等により上述したBi、Sb、Te、Seのうち少なくとも2種を含む組成のインゴットを作製し、粒子径の大きい市販粉末を分級しても良いが、例えば比較的安価で粒子径の不揃いな市販粉末を所望の組成に調合し、有機溶媒を加えて粉砕することで、本発明で使用する粉末を容易に得ることができる。 Next, the manufacturing method of the thermoelectric material of this invention is demonstrated. First, raw material powder of a thermoelectric material is prepared. The raw material powder to be used may be an ingot having a composition containing at least two of Bi, Sb, Te, and Se described above by a melting method, etc., and a commercially available powder having a large particle diameter may be classified. The powder used in the present invention can be easily obtained by preparing a commercially available powder having a non-uniform particle size in a desired composition, adding an organic solvent and pulverizing.
原料粉末の粉砕には、振動ミル、バレルミル又は回転ボールミルで窒化珪素製ボールを使用することが好ましい。粉砕に用いる容器としては、例えばポリエチレン製等の樹脂ポット又は樹脂の内張りを有するセラミックポットを用い、ボールとして窒化珪素製ボールを使用することで粉砕時に混入する不純物量を500ppm以下、特に100ppm以下、更には50ppm以下にまで削減することも可能で、不純物混入による特性低下を防ぎ、更に優れた熱電特性の実現が容易になる。 For pulverizing the raw material powder, it is preferable to use silicon nitride balls in a vibration mill, barrel mill or rotating ball mill. As a container used for pulverization, for example, using a resin pot made of polyethylene or a ceramic pot having a resin lining, the amount of impurities mixed during pulverization by using a silicon nitride ball as a ball is 500 ppm or less, particularly 100 ppm or less, Further, it can be reduced to 50 ppm or less, preventing deterioration of characteristics due to mixing of impurities and facilitating the realization of superior thermoelectric characteristics.
粉砕に用いる有機溶媒としては、メタノール、エタノール、イソプロパノール、ブタノール、ヘキサンのうち少なくとも1種で良いが、これらの中でも、粉砕効率及びコストの面で、イソプロパノールが好適である。 The organic solvent used for pulverization may be at least one of methanol, ethanol, isopropanol, butanol, and hexane. Among these, isopropanol is preferable in terms of pulverization efficiency and cost.
粉砕して得られた原料粉末の平均粒径は、30μm以下にすることが重要である。このような原料粉末を用いることにより、焼結工程及び緻密化工程を経て得られる緻密体の平均粒径を30μm以下にすることができる。さらに、常圧焼成時における焼結性を高めるため、原料粉末の平均粒径は、特に15μm以下、更には10μm以下、より好適には8μm以下であるのが良い。 It is important that the average particle size of the raw material powder obtained by pulverization is 30 μm or less. By using such raw material powder, the average particle diameter of the dense body obtained through the sintering step and the densification step can be reduced to 30 μm or less. Furthermore, in order to enhance the sinterability during normal pressure firing, the average particle diameter of the raw material powder is particularly preferably 15 μm or less, more preferably 10 μm or less, and more preferably 8 μm or less.
本発明によれば、上記の原料粉末を用いて成形を行って成形体を作製することが重要である。焼成前に予め成形体を作製するのは、形状が保持されているため、製造時の取扱いが容易で、不良品の発生を抑制し、また焼成前の酸素混入を防止する効果がある。 According to the present invention, it is important to produce a molded body by molding using the above raw material powder. Producing a molded body in advance before firing is easy to handle at the time of manufacture because the shape is maintained, and has the effect of suppressing the occurrence of defective products and preventing oxygen contamination before firing.
成形時の成形圧力は、10MPa以上、特に20MPa以上、さらには30MPa以上が良い。これにより、成形体の保持力を高め、製造上の取扱いを容易にするとともに、容易に生密度を高めることができるため、焼結を効果的に推進することができる。 The molding pressure at the time of molding is preferably 10 MPa or more, particularly 20 MPa or more, and more preferably 30 MPa or more. Thereby, while holding power of a molded object can be raised, handling in manufacture can be made easy, and a green density can be raised easily, sintering can be promoted effectively.
成形体の相対密度が50〜90%になるように成形することが好ましい。成形体の理論密度の下限値はハンドリング時に形状が保たれるため、50%、特に60%、更には70%、上限値は常圧焼成時に酸素が効率よく除去されるため、90%、特に85%、更には80%が好ましい。 It is preferable to mold so that the relative density of the molded body is 50 to 90%. The lower limit value of the theoretical density of the molded body is 50%, particularly 60%, and further 70% because the shape is maintained during handling, and the upper limit value is 90% because oxygen is efficiently removed during normal pressure firing. 85%, more preferably 80% is preferable.
成形方法は、公知の技術であるプレス成形、押出し成形、鋳込み成形、テープ成形、冷間静水圧成形(CIP)等いかなる成形法でも可能であるが、量産性に優れ、理論密度比が一定になりやすいプレス成形またはCIPが好ましい。 The molding method can be any molding method such as press molding, extrusion molding, casting molding, tape molding, cold isostatic pressing (CIP), which is a well-known technique, but it has excellent mass productivity and a constant theoretical density ratio. Press molding or CIP, which is easy to become, is preferable.
本発明によれば、得られた成形体を常圧で焼成(常圧焼成)することが重要である。このように、カーボン型に挿入する前にあらかじめ常圧焼成で成形体を焼結させておくことで、緻密化処理時にカーボンや酸素が焼結体中に混入するのを防ぐことができる。 According to the present invention, it is important to fire the obtained molded body at normal pressure (normal pressure firing). As described above, by pre-sintering the molded body by normal-pressure firing before insertion into the carbon mold, it is possible to prevent carbon and oxygen from being mixed into the sintered body during the densification treatment.
常圧焼成で得られた常圧焼結体は、平均粒径を30μm以下でカーボン含有量及び酸素含有量を0.3質量%以下にしておくことが好ましい。また、常圧焼結体の相対密度を60%以上、好ましくは70%以上、より好ましくは80%以上にすることが通電パルス焼結中のカーボン、酸素の不純物混入を防ぐ上で重要である。なお、理論密度の上限値は、成形体の理論密度及び常圧焼成の温度によるが、常圧焼成では緻密化が十分ではないため、上限値は95%である。不純物混入を防止しつつ、特性の優れた熱電材料を容易に製造するためには80〜90%が好適である。 The normal pressure sintered body obtained by normal pressure firing preferably has an average particle size of 30 μm or less and a carbon content and oxygen content of 0.3 mass% or less. In addition, it is important to prevent the contamination of carbon and oxygen during energization pulse sintering by setting the relative density of the atmospheric sintered body to 60% or more, preferably 70% or more, more preferably 80% or more. . The upper limit of the theoretical density depends on the theoretical density of the compact and the temperature of normal pressure firing, but the upper limit is 95% because densification is not sufficient in normal pressure firing. In order to easily manufacture a thermoelectric material having excellent characteristics while preventing impurities from being mixed, 80 to 90% is preferable.
本発明によれば、常圧焼成後の状態が、粉末を単に成形して各粒子が独立した状態ではなく、少なくとも粒子同士が結合し、粒子間のネックが成長した焼結体になっていることが重要である。原料粉末を単に加圧した成形体は気孔率が大きいため、カーボンや酸素が混入しやすい。特に、常圧焼成後の試料の粒子がそれぞれ独立した粉末の状態であると、電流を通電した際に粒子間にプラズマ放電が発生し、粒子表面の酸素除去には効果があるものの、焼結体中にカーボンが混入して本発明の熱電材料を得るのが困難となるが、本発明の常圧焼結体のように、粒子同士が焼結した焼結体の場合には、プラズマ放電が発生せず、カーボンの混入を効果的に抑制することができる。 According to the present invention, the state after firing at atmospheric pressure is not a state in which the powder is simply formed and each particle is independent, but is a sintered body in which at least the particles are bonded and the neck between the particles is grown. This is very important. Since a molded body obtained by simply pressurizing the raw material powder has a large porosity, carbon and oxygen are easily mixed therein. In particular, if the particles of the sample after firing at normal pressure are in an independent powder state, a plasma discharge occurs between the particles when current is applied, which is effective for removing oxygen from the surface of the particles. It is difficult to obtain the thermoelectric material of the present invention by mixing carbon in the body, but in the case of a sintered body in which particles are sintered like the atmospheric pressure sintered body of the present invention, plasma discharge Does not occur, and mixing of carbon can be effectively suppressed.
本発明の常圧焼成の雰囲気としては、還元性雰囲気が好ましく、成形体中に含まれる不純物酸素を効率良く除去することができ、熱電特性改善に有効である。特に、水素を含有する還元性雰囲気を用いるのが良い。そのときの水素濃度は10%以上あれば良いが、酸素を効率良く除去するため、特に30%以上、更には50%以上、より好適には70%以上であることが望ましい。 The atmosphere for normal pressure firing of the present invention is preferably a reducing atmosphere, which can efficiently remove impurity oxygen contained in the molded body, which is effective in improving thermoelectric characteristics. In particular, a reducing atmosphere containing hydrogen is preferably used. The hydrogen concentration at that time may be 10% or more, but in order to efficiently remove oxygen, it is particularly preferably 30% or more, more preferably 50% or more, and more preferably 70% or more.
本発明の常圧焼成の焼成温度は、組成によっても変動するが300〜550℃、特に350〜525℃、更には385〜500℃、より好適には400〜500℃が、粒子間のネック成長を助長して焼結させ、分解や急激な粒成長を防止して高強度を容易に実現し、効率的な酸素除去を行う点で好ましい。 The firing temperature of the normal pressure firing of the present invention varies depending on the composition, but is 300 to 550 ° C., particularly 350 to 525 ° C., more preferably 385 to 500 ° C., more preferably 400 to 500 ° C., and neck growth between particles. It is preferable in that it is sintered by promoting the above, preventing decomposition and rapid grain growth, easily realizing high strength, and efficiently removing oxygen.
また、本発明における常圧とは、通常のステンレス製あるいは石英管による低コストの炉心管で耐え切れる圧力のことをさし、0.05〜0.2MPa程度、特に0.5〜0.15MPaを示すものである。 The normal pressure in the present invention means a pressure that can be withstood by a low-cost core tube made of ordinary stainless steel or quartz tube, and is about 0.05 to 0.2 MPa, particularly 0.5 to 0.15 MPa. Is shown.
次に、常圧焼結体に対して緻密化処理を施して緻密体を作製することが重要である。緻密化処理には、直接通電過熱法、ホットプレス法(HP)、ガス圧焼結法(GPS)、熱間等方加圧焼結法(HIP)のうち少なくとも1種を用いることができる。これらの中でも、直接通電加熱を行うことによって、エネルギー効率が高く、急速加熱が可能となり、熱処理時間を短縮でき、不純物の混入を効果的に防止することができ、微細組織による高強度、高性能熱電材料を実現するため、直接通電加熱法を用いることが好ましい。 Next, it is important to produce a dense body by subjecting the atmospheric pressure sintered body to a densification treatment. For the densification treatment, at least one of a direct current heating method, a hot press method (HP), a gas pressure sintering method (GPS), and a hot isostatic pressing method (HIP) can be used. Among these, by direct current heating, energy efficiency is high, rapid heating is possible, heat treatment time can be shortened, contamination of impurities can be effectively prevented, and high strength and high performance due to fine structure In order to realize a thermoelectric material, it is preferable to use a direct current heating method.
さらに、直接通電過熱における通電方法が、パルス電流を用いたパルス通電法であることが好ましい。パルス通電法を用いることによって、部分的な過熱を防止でき、均一な温度制御を容易に行い、均一な組成分布を有する緻密体を容易に得ることができる。 Furthermore, the energization method in direct energization overheating is preferably a pulse energization method using a pulse current. By using the pulse current method, partial overheating can be prevented, uniform temperature control can be easily performed, and a dense body having a uniform composition distribution can be easily obtained.
また、緻密化処理において、加熱と同時に加圧することが好ましい。加圧によって緻密化が促進され、更に短時間で緻密化を達成することが容易となる。 In the densification treatment, it is preferable to pressurize simultaneously with heating. Densification is promoted by pressurization, and it becomes easier to achieve densification in a shorter time.
本発明の緻密化処理と類似の方法として、ホットプレス法が挙げられる。即ち、ホットプレスでは、原料粉末をダイスに装填し、原料粉末ごとダイスを加熱させるため、ダイスから酸素、カーボンが飛散して焼結体内に混入しやすい。 As a method similar to the densification treatment of the present invention, there is a hot press method. That is, in the hot press, raw material powder is loaded into a die and the die is heated together with the raw material powder, so that oxygen and carbon are scattered from the die and easily mixed into the sintered body.
これに対して、本発明では、カーボンダイスに常圧焼結体を装填して加熱するため、緻密化処理中の酸素混入やカーボンダイスからのカーボン汚染を抑制することができる。 On the other hand, in the present invention, since the atmospheric pressure sintered body is charged into the carbon die and heated, oxygen contamination during the densification treatment and carbon contamination from the carbon die can be suppressed.
特に、通電加熱による緻密化処理を行うと、ホットプレスでは焼結できない低い温度で緻密化を行うことができ、また、昇温速度も100℃/分といった高速の昇温が可能であり、短時間処理ができる。従って、低温・短時間処理と密度の高い焼結体の処理により、不純物を抑制した高性能の熱電材料を容易に得ることができる。 In particular, when the densification process is performed by energization heating, the densification can be performed at a low temperature that cannot be sintered by a hot press, and the heating rate can be increased at a high rate of 100 ° C./min. Time processing is possible. Therefore, a high-performance thermoelectric material in which impurities are suppressed can be easily obtained by low-temperature, short-time treatment and high-density sintered body treatment.
また、パルス通電による加熱と加圧とを同時に行う方法と類似の方法としてパルス通電焼結(PECS)法がある。この方法は、放電プラズマ焼結(SPS)法又はプラズマ活性焼結(PAS)法とも呼ばれる焼結方法で、粉末あるいは成形体をカーボンダイスなど抵抗が小さいジグに入れ、上下をカーボン製のパンチで挟みパンチを介してパルス状の大電流の印加しながら試料を直接加熱し焼結させる方法である。 Further, there is a pulse current sintering (PECS) method as a method similar to the method of simultaneously performing heating and pressurization by pulse current. This method is a sintering method also called a spark plasma sintering (SPS) method or a plasma activated sintering (PAS) method, in which a powder or a molded product is placed in a jig having a low resistance such as a carbon die, and the upper and lower sides are formed by a carbon punch. This is a method in which a sample is directly heated and sintered while applying a pulsed large current through a pinch punch.
このように、原料粉末に直接パルス通電焼結を行うPECS法では、粉末粒子同士が結合せず接触しているのみであるため、原料粉末や成形体にパルス通電を開始すると、焼成初期に放電プラズマが発生し、原料粉末を装填しているカーボン型からカーボンが焼結体中へ混入しやすい。 In this way, in the PECS method in which pulse current sintering is directly performed on the raw material powder, the powder particles are not in contact with each other but are in contact with each other. Plasma is generated, and carbon is easily mixed into the sintered body from the carbon mold loaded with the raw material powder.
これに対して、本発明では、常圧焼結体に連続通電又はパルス通電による直接通電を行うため放電プラズマは発生せず、焼結体の内部を電気が直接流れ、ジュール熱による加熱が効率良く起こり、直接通電過熱による短時間の緻密化処理によって粒子の成長を抑え、更にカーボン、酸素の不純物混入を抑えることが可能となる。即ち、本発明により、常圧焼成のみでは得られない緻密体が得られ、しかも優れた熱電特性を示すばかりではなく、微細な組織による機械特性向上と短時間処理による生産性向上を図ることもでき、さらに、パルス電流を用いる場合、温度の制御が容易となり、局所過熱による組成バラツキを効果的に防止できる。 On the other hand, in the present invention, since direct-current energization is performed on the atmospheric sintered body by continuous energization or pulse energization, no discharge plasma is generated, electricity flows directly inside the sintered body, and heating by Joule heat is efficient. It often occurs, and it becomes possible to suppress the growth of particles by the densification process for a short time by direct current overheating, and to further suppress the mixing of impurities of carbon and oxygen. That is, according to the present invention, a dense body that cannot be obtained only by atmospheric firing is obtained, and not only exhibits excellent thermoelectric properties, but also improves mechanical properties by a fine structure and productivity by short-time processing. In addition, when a pulse current is used, temperature control is facilitated, and compositional variation due to local overheating can be effectively prevented.
本発明における緻密化処理において、常圧焼結体が200℃以上に加熱される時間が1時間以内、特に45分以内、更に30分以内が望ましい。このような加熱条件としては、例えば500℃まで10分で昇温させ、保持時間を10分、冷却時間を5分で行うなどの条件で行えば良い。パルス通電焼結の雰囲気は不活性雰囲気でも真空中でも良いが、アルゴン雰囲気が低コスト及び試料の変質を抑える上で望ましい。 In the densification treatment in the present invention, the time during which the atmospheric pressure sintered body is heated to 200 ° C. or higher is preferably within 1 hour, particularly within 45 minutes, and further within 30 minutes. As such heating conditions, for example, the temperature may be raised to 500 ° C. in 10 minutes, the holding time is 10 minutes, and the cooling time is 5 minutes. The atmosphere of pulse electric current sintering may be an inert atmosphere or a vacuum, but an argon atmosphere is desirable in terms of low cost and suppressing sample alteration.
この緻密化処理の処理温度は、上記の常圧焼成の焼成温度以下であることが好ましい。緻密化温度を焼成温度よりも低くすることで粒成長を抑制し、高い強度を容易に実現することができるためである。 The treatment temperature of this densification treatment is preferably not more than the firing temperature of the above-mentioned normal pressure firing. This is because by making the densification temperature lower than the firing temperature, grain growth can be suppressed and high strength can be easily realized.
上記の常圧焼成体に対して本発明の緻密化処理を施すことによって、相対密度が98%以上、特に98.5%以上、更には99%以上の緻密体が得られる。このように相対密度を高めることにより、熱電性能に優れた熱電材料を得ることができる。 By subjecting the above-mentioned normal-pressure fired body to the densification treatment of the present invention, a dense body having a relative density of 98% or more, particularly 98.5% or more, and further 99% or more is obtained. By increasing the relative density in this way, a thermoelectric material having excellent thermoelectric performance can be obtained.
このような熱電材料の製造方法により、カーボンおよび酸素の混入を抑え、微細組織からなる高強度、高性能な熱電材料を実現することが出来る。 By such a method for producing a thermoelectric material, mixing of carbon and oxygen can be suppressed, and a high-strength, high-performance thermoelectric material having a fine structure can be realized.
原料粉末として、純度99.99%以上のBi、Sb、Te、Seの原料を用いて、N型はBi2Te2.85Se0.15組成にSbI3粉末を0.06質量%添加した混合粉末を、P型としてBi0.5Sb1.5Te3組成混合粉末をそれぞれ石英管にアルゴン封入し、ロッキング炉にて800〜1000℃で12時間攪拌溶解させ、冷却後取り出しそれぞれ合金インゴットを得た。 Using raw materials of Bi, Sb, Te, Se with a purity of 99.99% or more as raw material powder, N type added 0.06% by mass of SbI 3 powder to Bi 2 Te 2.85 Se 0.15 composition The mixed powder is P-type, and Bi 0.5 Sb 1.5 Te 3 composition mixed powder is sealed in argon in each quartz tube, stirred and dissolved in a rocking furnace at 800-1000 ° C. for 12 hours, taken out after cooling, and each alloy ingot Got.
合金はそれぞれグローブボックス内で300μm以下になるまでスタンプミルにて粗粉砕し、更に振動ミルにて溶媒をIPAとし、窒化珪素製ボールを用いて表1に示す粉砕時間で粉砕し、得られたスラリーを取り出して、乾燥後、40メッシュにて篩通した。 Each alloy was roughly pulverized in a glove box with a stamp mill until it became 300 μm or less, further pulverized with a vibration mill using IPA as a solvent and pulverizing times shown in Table 1 using silicon nitride balls. The slurry was taken out, dried, and sieved with 40 mesh.
得られた粉末の粒度分布はレーザー回折法で求め、平均粒径を求めた。 The particle size distribution of the obtained powder was determined by a laser diffraction method, and the average particle size was determined.
上記の粉末を、一部は表1に示す圧力で直径20mmの金型に厚さ15mmになるようにプレス成形した。成形体の寸法と重量を測定して密度を算出し、理論密度で除して成形体の相対密度を算出した。 A part of the above powder was press-molded to a thickness of 15 mm in a 20 mm diameter mold at the pressure shown in Table 1. The density was calculated by measuring the size and weight of the molded body, and the relative density of the molded body was calculated by dividing by the theoretical density.
次いで、上記成形体を表1の条件で常圧焼成を行った。得られた常圧焼結体の相対密度を、アルキメデス法により比重を測定し、理論密度から相対密度を算出した。なお、成形体と常圧焼結体との密度差を「変化」として表1に記載した。 Next, the compact was fired at normal pressure under the conditions shown in Table 1. The relative density of the obtained normal pressure sintered body was measured by the Archimedes method, and the relative density was calculated from the theoretical density. The density difference between the molded body and the normal pressure sintered body is shown in Table 1 as “change”.
得られた常圧焼結体を表1に示す方法及び条件で緻密化処理を施した。なお、200℃以上の温度に曝される時間を「加熱」として表1に示した。 The obtained normal pressure sintered body was subjected to densification treatment by the method and conditions shown in Table 1. Table 1 shows the time of exposure to a temperature of 200 ° C. or higher as “heating”.
なお、試料No.19〜23は原料粉末又は成形体をホットプレス法により焼成したものであり、試料No.25及び26は、粉末又は成形体をPECS法で焼成したものである。 Sample No. Nos. 19 to 23 are obtained by firing a raw material powder or a molded body by a hot press method. Nos. 25 and 26 are powders or molded bodies fired by the PECS method.
得られた緻密体の相対密度は、アルキメデス法により比重を測定し、理論密度から相対密度を算出した。 The relative density of the obtained dense body was measured by the Archimedes method, and the relative density was calculated from the theoretical density.
また、緻密体は焼結時の加圧方向に対して垂直な方向に対して熱伝導率、ゼーベック係数及び抵抗率を測定するために、それぞれ測定試料を作製した。熱伝導率測定には、直径10mm、厚み1mmの円板試料を、ゼーベック係数、抵抗率測定には縦4mm、横4mm、長さ15mmの角柱試料を作製した。 Moreover, in order to measure a heat conductivity, a Seebeck coefficient, and a resistivity with respect to the direction perpendicular | vertical with respect to the pressurization direction at the time of a compact, the measurement sample was produced, respectively. For thermal conductivity measurement, a disk sample having a diameter of 10 mm and a thickness of 1 mm was prepared, and for the Seebeck coefficient and resistivity measurement, a prism sample having a length of 4 mm, a width of 4 mm, and a length of 15 mm was prepared.
熱伝導率はレーザーフラッシュ法により、ゼーベック係数、比抵抗は真空理工社製熱電能評価装置により、それぞれ20℃の条件下で測定した。 The thermal conductivity was measured by a laser flash method, the Seebeck coefficient, and the specific resistance were each measured at 20 ° C. by a thermoelectricity evaluation apparatus manufactured by Vacuum Riko Co., Ltd.
また、熱電性能指数Zは、式Z=S2/ρk(Sはゼーベック係数、ρは抵抗率、kは熱伝導率である)により算出した。 The thermoelectric figure of merit Z was calculated by the formula Z = S 2 / ρk (S is Seebeck coefficient, ρ is resistivity, and k is thermal conductivity).
また、熱伝導率を測定した試料の表面を鏡面加工後、化学エッチングして、粒子径が確認できる倍率で数枚SEM写真を撮影し、その写真から粒子200〜300個の粒子を用いてインターセプト法にて平均粒径を算出した。さらにゼーベック係数、比抵抗を測定した試料を粉砕し、堀場製作所製OXYGEN/NITROGEN ANALYZER(酸素窒素分析計)及びCARBON ANALYZER(炭素分析計)を用いて酸素含有量(O量)及び炭素含有量(C量)を測定した。加えて、直径10mm試料の片面を鏡面研磨し、2軸曲げ試験にて強度を測定した。結果を表1、2に示す。
本発明の試料No.4〜7、9〜18及び24は、強度が11MPa以上、熱電性能指数が3.12×10−3/K以上であった。 Sample No. of the present invention. 4-7, 9-18, and 24 had a strength of 11 MPa or more and a thermoelectric figure of merit of 3.12 × 10 −3 / K or more.
一方、原料粉末の平均粒径が30μmを越える本発明の範囲外の試料No.1〜3は、緻密体の平均粒径が30μmを超え、強度が1MPa以下と非常に小さかった。 On the other hand, sample Nos. Out of the scope of the present invention in which the average particle diameter of the raw material powder exceeds 30 μm. 1 to 3, the average particle size of the dense body exceeded 30 μm, and the strength was as small as 1 MPa or less.
また、成形を行わない本発明の範囲外の試料No.8は、緻密体中のカーボン含有量及び酸素含有量がいずれも0.3質量%を超え、その結果、熱電性能指数が2.66×10−3/K以下と低かった。 In addition, the sample no. In No. 8, the carbon content and oxygen content in the dense body both exceeded 0.3 mass%, and as a result, the thermoelectric performance index was as low as 2.66 × 10 −3 / K or less.
さらに、ホットプレスを行った本発明の範囲外の試料No.19〜23は、カーボンの含有量が0.3質量%を越え、強度が9MPa以下、熱電性能指数が3.10×10−3/K以下であった。 Furthermore, sample No. 5 outside the scope of the present invention was subjected to hot pressing. In 19-23, the carbon content exceeded 0.3 mass%, the strength was 9 MPa or less, and the thermoelectric figure of merit was 3.10 × 10 −3 / K or less.
さらにまた、PECS法を用いた本発明の範囲外の試料No.25〜26は、カーボン含有量又は酸素含有量が0.3質量%を越え、熱電性能指数が2.91×10−3/K以下であった。 Furthermore, sample Nos. Outside the scope of the present invention using the PECS method. In Nos. 25 to 26, the carbon content or oxygen content exceeded 0.3% by mass, and the thermoelectric figure of merit was 2.91 × 10 −3 / K or less.
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KR20200002435A (en) * | 2018-06-29 | 2020-01-08 | 공주대학교 산학협력단 | METHOD FOR MANUFACTURING Bi-Sb-Te BASED THERMOELECTRIC MATERIAL WITH CONTROLLED GRAIN SIZE AND THERMOELECTRIC MATERIAL MANUFACTURED THEREBY |
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