JP5718671B2 - Thermoelectric conversion material and manufacturing method thereof - Google Patents
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Description
本発明は、熱と電気との相互エネルギー変換を行う熱電変換材料に関し、特に、高い熱電性能指数を有する、熱電変換材料及びその製造方法に関する。 The present invention relates to a thermoelectric conversion material that performs mutual energy conversion between heat and electricity, and particularly relates to a thermoelectric conversion material having a high thermoelectric figure of merit and a method for producing the same.
近年、システムが単純でしかも小型化が可能な熱電発電技術が、ビル、工場等で使用される化石燃料資源等から発生する未利用の廃熱エネルギーに対する回収発電技術として注目されている。しかしながら、熱電発電は一般に発電効率が悪いこともあり、さまざまな企業、研究機関で発電効率の向上のための研究開発が活発になされている。発電効率の向上には、熱電変換材料の高効率化が必須となるが、これらを実現するために、金属並みの高い電気伝導率とガラス並みの低い熱伝導率を備えた材料の開発が望まれている。 In recent years, thermoelectric power generation technology that has a simple system and can be reduced in size has attracted attention as a recovery power generation technology for unused waste heat energy generated from fossil fuel resources used in buildings, factories, and the like. However, thermoelectric power generation generally has poor power generation efficiency, and various companies and research institutions are actively researching and developing power generation efficiency. In order to improve power generation efficiency, it is essential to improve the efficiency of thermoelectric conversion materials. To achieve these, development of materials with high electrical conductivity similar to metal and low thermal conductivity comparable to glass is desired. It is rare.
熱電変換特性は、熱電性能指数Ｚ（Ｚ＝σＳ2／λ）によって評価することができる。ここで、Ｓはゼーベック係数、σは電気伝導率（抵抗率の逆数）、λは熱伝導率である。上記、熱電性能指数Ｚの値を大きくすれば、発電効率が向上するため、発電の高効率化にあたっては、ゼーベック係数Ｓ及び電気伝導率σが大きく、熱伝導率λが小さい熱電変換材料を見出すことになる。 The thermoelectric conversion characteristic can be evaluated by a thermoelectric figure of merit Z (Z = σS 2 / λ). Here, S is a Seebeck coefficient, σ is electrical conductivity (reciprocal of resistivity), and λ is thermal conductivity. When the value of the thermoelectric figure of merit Z is increased, the power generation efficiency is improved. Therefore, in increasing the efficiency of power generation, a thermoelectric conversion material having a large Seebeck coefficient S and electrical conductivity σ and a small thermal conductivity λ is found. It will be.
一般に、固体物質の熱伝導率λと電気伝導率σは、材料の密度やキャリア濃度をパラメータとして設計することが可能ではあるが、両物性はヴィーデマンフランツの法則から、互いに独立ではなく、密接に連動するため、大幅な熱電性能指数の向上が図れていないのが実情であった。このような中で、材料を焼結体にして数十ミクロンオーダーの多数の結晶粒界を導入することによって熱伝導率を小さくする試みがなされているが、キャリアも粒界で散乱を受けるため、電気伝導率が小さくなり、かつゼーベック係数の変化がわずかなため、この手法においても、熱電性能指数の大幅な向上を望むことができなかった。
特許文献１及び２には、半導体材料内部に電子とフォノンの平均自由行程と同程度あるいはそれ以下の間隔で分散した非常に微細な空孔を多数導入して多孔質化し、熱伝導率の減少やゼーベック係数を増加させた熱電変換材料が提案されている。特許文献１及び２の実施例によると、熱伝導率は低減したものの、電気伝導率もともに低下（抵抗率が大幅増加）してしまい、無次元熱電性能指数ＺＴ（Ｔ：絶対温度３００Ｋとして算出）としては、０．０１７から多孔質化により０．１５６に増加したにすぎず、実用化に向けての指標値となるＺＴ≧１にはほど遠い状況であった。
In general, the thermal conductivity λ and electrical conductivity σ of a solid substance can be designed using the material density and carrier concentration as parameters, but the two physical properties are not independent of each other from Wiedemann Franz's law. The actual situation is that the thermoelectric figure of merit has not been improved significantly. Under such circumstances, attempts have been made to reduce the thermal conductivity by introducing a large number of grain boundaries of the order of several tens of microns using a sintered body as the material, but the carriers are also scattered at the grain boundaries. Since the electric conductivity is small and the change in Seebeck coefficient is slight, even in this method, a great improvement in the thermoelectric figure of merit cannot be expected.
Patent Documents 1 and 2 introduce a large number of very fine vacancies dispersed at an interval equal to or less than the mean free path of electrons and phonons into the semiconductor material, thereby reducing the thermal conductivity. Thermoelectric conversion materials with an increased Seebeck coefficient have been proposed. According to the examples of Patent Documents 1 and 2, although the thermal conductivity is reduced, the electrical conductivity is also lowered (the resistivity is greatly increased), and the dimensionless thermoelectric figure of merit ZT (T: calculated as an absolute temperature of 300K). ) Was increased from 0.017 to 0.156 due to the porous structure, and was far from ZT ≧ 1, which is an index value for practical use.
本発明は、上記実情を鑑み、熱伝導率が低減され、電気伝導率の低下が抑制された、トータルとして熱電性能指数が向上した熱電変換材料及びその製造方法を提供することを課題とする。 In view of the above circumstances, an object of the present invention is to provide a thermoelectric conversion material having improved thermoelectric performance index as a whole, in which thermal conductivity is reduced and reduction in electrical conductivity is suppressed, and a method for manufacturing the thermoelectric conversion material.
本発明者らは、上記課題を解決すべく鋭意検討を重ねた結果、微細孔を有するアルミナ基板上に、ｐ型ビスマステルライドを成膜することにより、トータルとして熱電性能指数が大幅に向上することを見出し、本発明を完成した。
すなわち、本発明は、以下の（１）〜（１０）を提供するものである。
（１）基板の厚み方向に、独立した微細孔を有するアルミナ基板上に、ｐ型ビスマステルライドを成膜したことを特徴とする熱電変換材料。
（２）前記微細孔内を貫通する中心線が、前記アルミナ基板上に立てた法線に対し±１０°以内の角度を有する上記（１）の熱電変換材料。
（３）前記微細孔の平均直径が１０〜３０ｎｍ、深さが１００〜１０００ｎｍ、及び微細孔間の平均間隔が３０〜６０ｎｍである上記（１）又は（２）の熱電変換材料。
（４）前記ｐ型ビスマステルライドが微細孔内底部とアルミナ基板表面に存在し、かつ該微細孔内底部と該アルミナ基板表面とは絶縁性を維持する上記（１）〜（３）のいずれかの熱電変換材料。
（５）前記ｐ型ビスマステルライドの前記アルミナ基板表面における膜厚が１〜３５０ｎｍ、前記微細孔内底部における膜厚が０〜３００ｎｍである上記（４）の熱電変換材料。
（６）前記ｐ型ビスマステルライドがＢｉXＴｅ3Ｓｂ2-Xであって、０＜Ｘ≦０．６である上記（１）〜（５）のいずれかの熱電変換材料。
（７）アルミナ微細孔作製工程と、その後に行うｐ型ビスマステルライド成膜工程とを有することを特徴とする上記（１）〜（６）のいずれかの熱電変換材料の製造方法。
（８）前記アルミナ微細孔作製工程が、二段陽極酸化法による上記（７）の熱電変換材料の製造方法。
（９）前記二段陽極酸化工程の後に、さらに、エッチング処理工程を有する上記（８）の熱電変換材料の製造方法。
（１０）前記ｐ型ビスマステルライド成膜工程が、フラッシュ蒸着法による上記（７）〜（９）のいずれかの熱電変換材料の製造方法。
As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention can significantly improve the thermoelectric performance index as a whole by forming a p-type bismuth telluride film on an alumina substrate having micropores. The present invention has been completed.
That is, the present invention provides the following (1) to (10).
(1) A thermoelectric conversion material in which a p-type bismuth telluride film is formed on an alumina substrate having independent micropores in the thickness direction of the substrate.
(2) The thermoelectric conversion material according to (1), wherein a center line penetrating through the fine holes has an angle of ± 10 ° or less with respect to a normal line standing on the alumina substrate.
(3) The thermoelectric conversion material according to (1) or (2) above, wherein the average diameter of the micropores is 10 to 30 nm, the depth is 100 to 1000 nm, and the average interval between the micropores is 30 to 60 nm.
(4) Any of the above (1) to (3), wherein the p-type bismuth telluride is present on the inner bottom portion of the micropore and the surface of the alumina substrate, and the inner bottom portion of the micropore and the surface of the alumina substrate maintain insulation. Thermoelectric conversion material.
(5) The thermoelectric conversion material according to (4) above, wherein the p-type bismuth telluride has a thickness of 1 to 350 nm on the surface of the alumina substrate and a thickness of 0 to 300 nm at the bottom of the fine hole.
(6) The thermoelectric conversion material according to any one of (1) to (5), wherein the p-type bismuth telluride is Bi X Te 3 Sb 2-X and 0 <X ≦ 0.6.
(7) The method for producing a thermoelectric conversion material according to any one of the above (1) to (6), comprising an alumina micropore preparation step and a p-type bismuth telluride film formation step performed thereafter.
(8) The method for producing a thermoelectric conversion material according to the above (7), wherein the alumina micropore preparation step is a two-step anodizing method.
(9) The method for producing a thermoelectric conversion material according to (8), further comprising an etching treatment step after the two-step anodizing step.
(10) The method for producing a thermoelectric conversion material according to any one of (7) to (9), wherein the p-type bismuth telluride film forming step is performed by a flash vapor deposition method.
本発明によれば、熱伝導率が低減され、電気伝導率の低下が抑制された、トータルとして熱電性能指数が向上した熱電変換材料が得られ、従来の熱電変換材料と比べ、高い変換効率を実現することができる。 According to the present invention, it is possible to obtain a thermoelectric conversion material having an improved thermoelectric performance index as a whole, in which the thermal conductivity is reduced and the decrease in electrical conductivity is suppressed, and a high conversion efficiency is obtained compared to a conventional thermoelectric conversion material. Can be realized.
［熱電変換材料］
本発明の熱電変換材料は、基板の厚み方向に、独立した微細孔を有するアルミナ基板上に、ｐ型ビスマステルライドを成膜したことを特徴とする。ここで、独立した微細孔とは、個々の微細孔が隣接する他の微細孔と物理的に繋がることなく、適度の間隔を保ち、分布している態様を意味する。パーコレーション理論により、独立していない微細孔を有する多孔質体の電気伝導率は極めて低いことが知られている。
[Thermoelectric conversion material]
The thermoelectric conversion material of the present invention is characterized in that a p-type bismuth telluride film is formed on an alumina substrate having independent micropores in the thickness direction of the substrate. Here, the independent micropores mean a mode in which individual micropores are distributed without being physically connected to other adjacent micropores. From the percolation theory, it is known that the electrical conductivity of a porous body having micropores that are not independent is extremely low.
（アルミナ基板）
本発明で使用されるアルミナ基板は、アルミニウム（Ａｌ）又はその合金を基体とし、陽極酸化を行うことで形成することができる。アルミニウム合金としては、アルミニウムと合金が形成できかつ微細孔を有する多孔質の酸化皮膜を形成できるものであれば、特に制限なく使用することができる。例えば、アルミニウムに微量の他の金属を添加したアルミニウム−銅合金、アルミニウム−シリコン合金が挙げられる。
(Alumina substrate)
The alumina substrate used in the present invention can be formed by performing anodization using aluminum (Al) or an alloy thereof as a base. Any aluminum alloy can be used without particular limitation as long as it can form an alloy with aluminum and can form a porous oxide film having fine pores. For example, an aluminum-copper alloy or an aluminum-silicon alloy obtained by adding a trace amount of another metal to aluminum can be used.
本発明の熱電変換材料のアルミナ基板を図により説明する。図１は、本発明の熱電変換材料におけるｐ型ビスマステルライドを設けるアルミナ基板の断面を模式的に示した図である。図１において、アルミナ基板１は、アルミニウム基体２、アルミナの多孔質膜３、微細孔４で構成される。図に示すとおり、アルミニウム基体２の上には、陽極酸化により形成されたアルミナの多孔質膜３が存在し、多孔質膜３はアルミナ基板１の厚み方向に多数の独立した微細孔４を有している。 The alumina substrate of the thermoelectric conversion material of the present invention will be described with reference to the drawings. FIG. 1 is a view schematically showing a cross section of an alumina substrate provided with p-type bismuth telluride in the thermoelectric conversion material of the present invention. In FIG. 1, an alumina substrate 1 includes an aluminum substrate 2, an alumina porous film 3, and micropores 4. As shown in the figure, an alumina porous film 3 formed by anodic oxidation exists on an aluminum substrate 2, and the porous film 3 has a number of independent micropores 4 in the thickness direction of the alumina substrate 1. doing.
アルミナ基板１の微細孔４の平均直径は、好ましくは１０〜３０ｎｍ、より好ましくは
１５〜２５ｎｍである。平均直径が１０ｎｍ以上であると、蒸着後も独立した微細孔が維持されやすいので好ましく、３０ｎｍ以下であると、熱変換材料の機械的強度が確保でき、電気特性も維持されるため好ましい。尚、微細孔４の平均直径は、測定倍率１０万倍でのＳＥＭ写真（アルミナ基板微細孔表面）から、視野内に存在する独立した微細孔４の個々の孔径の最大径、最小径を読み取り単純平均し、次いで、測定を全数にわたり行い、最後に再度単純平均することにより算出している。
微細孔４の深さは、好ましくは１００〜１０００ｎｍ、より好ましくは５００〜１０００ｎｍである。深さが１００ｎｍ以上であると、独立した微細孔が維持されるという観点から好ましい。１０００ｎｍ以下であると乾燥時の強い表面張力構造が壊れることなくアルミナ生成プロセスが容易であるので好ましい。
また、微細孔４の配列する平均間隔（隣接する孔と孔との中心間距離）は、好ましくは３０〜６０ｎｍであり、より好ましくは５０〜６０ｎｍである。平均間隔が３０ｎｍ以上であると、電子の平均自由行程より長くなり、電子の散乱因子となりにくくなるため、電気伝導率の低下が抑制され好ましい。６０ｎｍ以下であると、フォノンの平均自由行程より短くなり、フォノンの散乱因子となりやすくなるため、熱伝導率が低減でき好ましい。微細孔４の個数は、平均間隔を３０〜６０ｎｍとした場合、１ｍｍ2当たり２．８×１０8〜１１×１０8個程度となる。
The average diameter of the fine holes 4 of the alumina substrate 1 is preferably 10 to 30 nm, more preferably 15 to 25 nm. When the average diameter is 10 nm or more, it is preferable because independent micropores are easily maintained even after vapor deposition, and when the average diameter is 30 nm or less, the mechanical strength of the heat conversion material can be secured and the electrical characteristics are also maintained. The average diameter of the micropores 4 is read from the SEM photograph (alumina substrate micropore surface) at a measurement magnification of 100,000 times with the maximum and minimum diameters of the individual micropores 4 existing in the field of view. It is calculated by simple averaging, then measuring over all, and finally simple averaging again.
The depth of the fine holes 4 is preferably 100 to 1000 nm, more preferably 500 to 1000 nm. A depth of 100 nm or more is preferable from the viewpoint of maintaining independent micropores. The thickness of 1000 nm or less is preferable because the strong surface tension structure at the time of drying is not broken and the alumina production process is easy.
Moreover, the average interval (distance between the centers of adjacent holes) in which the micropores 4 are arranged is preferably 30 to 60 nm, and more preferably 50 to 60 nm. When the average interval is 30 nm or more, it becomes longer than the mean free path of electrons, and it becomes difficult to become an electron scattering factor. If it is 60 nm or less, it becomes shorter than the mean free path of phonons and tends to be a phonon scattering factor, which is preferable because the thermal conductivity can be reduced. The number of the fine holes 4 is about 2.8 × 10 8 to 11 × 10 8 per 1 mm 2 when the average interval is 30 to 60 nm.
微細孔内を基板の厚み方向に貫通する中心線５とアルミナ基板１上に立てた法線６とのなす角度７は、好ましくは±１０°以内、より好ましくは±５°以内である。法線６とのなす角度７が±１０°以内であると、ｐ型ビスマステルライドを成膜した時、微細孔内部の壁面にｐ型ビスマステルライドが付着しにくくなるため、好ましい。尚、前記微細孔内を基板の厚み方向に貫通する中心線５とアルミナ基板１上に立てた法線６とのなす角度７は、測定倍率８万倍でのＳＥＭ写真（アルミナ基板断面）を用い測定した。
さらに、図２に示すように、微細孔４は、ｐ型ビスマステルライドを成膜した時に、微細孔内部の壁部に付着しない形状、例えば、アルミナ基板１の深さ方向に、逆テーパー形状（ａ）、ビア樽形状（ｂ）、又は一部壁部に付着しても、アルミナ基板１の表面との絶縁性が維持されるような、折曲部が存在する形状（ｃ）等でも使用することができる。ここで、貫通する中心線５は、微細孔上部の中心と底部の中心を結んだものである。
The angle 7 formed by the center line 5 penetrating through the fine hole in the thickness direction of the substrate and the normal 6 standing on the alumina substrate 1 is preferably within ± 10 °, more preferably within ± 5 °. It is preferable that the angle 7 formed with the normal line 6 is within ± 10 °, because when p-type bismuth telluride is formed, it is difficult for the p-type bismuth telluride to adhere to the wall surface inside the micropores. The angle 7 formed between the center line 5 penetrating the fine hole in the thickness direction of the substrate and the normal 6 standing on the alumina substrate 1 is an SEM photograph (alumina substrate cross section) at a measurement magnification of 80,000 times. Used and measured.
Further, as shown in FIG. 2, the micropore 4 has a shape that does not adhere to the wall inside the micropore when the p-type bismuth telluride is deposited, for example, a reverse taper shape (in the depth direction of the alumina substrate 1). a), via barrel shape (b), or a shape (c) in which a bent portion exists so that insulation with the surface of the alumina substrate 1 is maintained even if it is attached to a part of the wall portion. can do. Here, the penetrating center line 5 connects the center of the top and bottom of the fine hole.
上記のアルミナ基板１に、ｐ型ビスマステルライドをフラッシュ蒸着法等により成膜することにより、本発明の熱電変換材料を得ることができる。 The thermoelectric conversion material of the present invention can be obtained by forming a film of p-type bismuth telluride on the above-mentioned alumina substrate 1 by flash vapor deposition or the like.
（ｐ型ビスマステルライド）
本発明の熱電変換材料（ｐ型：キャリアが正孔、ゼーベック係数が正値）において、成膜されたｐ型ビスマステルライドは、通常アルミナ基板１の表面と微細孔４の底部に存在するが、微細孔４の底部には微細孔４の直径及び形状によっては殆ど存在しないこともある。また、微細孔４の底部とアルミナ基板１の表面との絶縁性は、熱伝導率の低減効果が低くなることを防ぐために、常に維持されている。
前記ｐ型ビスマステルライドの、前記アルミナ基板表面における膜厚は、好ましくは、１〜３５０ｎｍであり、より好ましくは１０〜３００ｎｍ、更に好ましくは５０〜２５０ｎｍである。アルミナ基板表面の膜厚が１ｎｍ以上であると底面と連続した膜にならずに多孔質膜構造の薄膜を形成できる観点から好ましい。３５０ｎｍ以下であると、材料コスト削減及び成膜時間短縮の点で好ましい。
また、前記微細孔４の底部の、前記ｐ型ビスマステルライドの膜厚は、好ましくは３００ｎｍ以下であり、より好ましくは１００ｎｍ以下である。微細孔４の底部のｐ型ビスマステルライドの膜厚が３００ｎｍ以下であると、微細孔構造が維持され好ましい。
本発明の熱変換材料に使用されているｐ型ビスマステルライドは、ＢｉXＴｅ3Ｓｂ2-Xが好ましいが、この場合、Ｘは、好ましくは０＜Ｘ≦０．６であり、より好ましくは０．４＜Ｘ≦０．６である。Ｘが０より大きく０．６以下であるとゼーベック係数と電気伝導率が大きくなり、ｐ型熱電変換材料としての特性が維持されるので好ましい。
(P-type bismuth telluride)
In the thermoelectric conversion material of the present invention (p-type: carriers are holes, and the Seebeck coefficient is positive), the formed p-type bismuth telluride is usually present on the surface of the alumina substrate 1 and the bottom of the micropores 4, Depending on the diameter and shape of the micropore 4, there may be almost no bottom at the bottom of the micropore 4. Further, the insulation between the bottom of the fine holes 4 and the surface of the alumina substrate 1 is always maintained in order to prevent the effect of reducing the thermal conductivity from being lowered.
The film thickness of the p-type bismuth telluride on the surface of the alumina substrate is preferably 1 to 350 nm, more preferably 10 to 300 nm, and still more preferably 50 to 250 nm. A film thickness of 1 nm or more on the surface of the alumina substrate is preferable from the viewpoint that a thin film having a porous film structure can be formed without forming a film continuous with the bottom surface. A thickness of 350 nm or less is preferable from the viewpoint of reducing material costs and film formation time.
Further, the film thickness of the p-type bismuth telluride at the bottom of the fine hole 4 is preferably 300 nm or less, and more preferably 100 nm or less. When the film thickness of the p-type bismuth telluride at the bottom of the micropore 4 is 300 nm or less, the micropore structure is maintained, which is preferable.
The p-type bismuth telluride used in the heat conversion material of the present invention is preferably Bi X Te 3 Sb 2-X . In this case, X is preferably 0 <X ≦ 0.6, more preferably 0.4 <X ≦ 0.6. It is preferable that X is greater than 0 and less than or equal to 0.6 because the Seebeck coefficient and electrical conductivity are increased, and the characteristics as a p-type thermoelectric conversion material are maintained.
本発明のｐ型熱電変換材料は、単独で、好ましくはｎ型熱電変換材料（ｎ型：キャリアが電子、ゼーベック係数が負値）と一対にし、使用することができる。例えば、複数対を、電気的には電極を介して直列に、熱的にはセラミックス等の絶縁体を介して並列に接続して、熱電変換素子として、発電用及び冷却用として使用することができる。 The p-type thermoelectric conversion material of the present invention can be used alone, preferably paired with an n-type thermoelectric conversion material (n-type: carrier is electron, Seebeck coefficient is negative value). For example, a plurality of pairs may be electrically connected in series via electrodes, and thermally connected in parallel via an insulator such as ceramics, and used as thermoelectric conversion elements for power generation and cooling. it can.
［熱電変換材料の製造方法］
本発明の熱電変換材料の製造方法は、アルミナ微細孔作製工程と、その後に行うｐ型ビスマステルライド成膜工程とを有することを特徴とする。さらに詳述すると、（１）アルミナ微細孔作製工程は、例えば、アルミニウム基体表面の自然酸化膜を除去する電解処理工程、多孔質膜（Ａｌ2Ｏ3）を形成する陽極酸化工程（一段陽極酸化）、形成した多孔質膜を除去し、再度、陽極酸化工程（二段陽極酸化）により多孔質膜を形成する工程、さらに、その後、アルミナ基板の孔の拡張、表面の平滑化を行うエッチング処理工程を含むことが好ましい。また、（２）ｐ型ビスマステルライド成膜工程は、例えば、アルミナ基板を真空装置内に設置、排気し、真空に保持されたアルミナ基板にフラッシュ蒸着を行う工程を含むことが好ましい。
[Method for producing thermoelectric conversion material]
The manufacturing method of the thermoelectric conversion material of this invention has an alumina micropore preparation process, and the p-type bismuth telluride film-forming process performed after that. More specifically, (1) the alumina micropore preparation process includes, for example, an electrolytic treatment process for removing a natural oxide film on the surface of an aluminum substrate, an anodization process for forming a porous film (Al 2 O 3 ) (one-step anodization) ), Removing the formed porous film, forming a porous film again by anodizing (two-stage anodizing), and then performing an etching process to expand the pores of the alumina substrate and smooth the surface It is preferable to include a process. In addition, the (2) p-type bismuth telluride film forming step preferably includes, for example, a step in which an alumina substrate is placed in a vacuum apparatus, evacuated, and flash deposition is performed on the alumina substrate held in a vacuum.
（１）アルミナ微細孔作製工程
（１）−１ 電解処理工程
陽極酸化する金属は、金属酸化物の成長等に影響を与えるおそれがあるため、前処理をすることが好ましい。本発明で使用されるアルミニウム金属のように、自然酸化膜が容易に形成されてしまうおそれのある金属に関しては、必要に応じて、自然酸化膜を除去する。
まず、本発明で使用したアルミニウム基体の表面の自然酸化膜は、一例として、過塩素酸とエチルアルコールの混合溶液で電解処理することにより除去することが好ましい。
（１）−２ 陽極酸化工程１
本発明で使用されるアルミナ基板は、アルミニウム又はその合金を基体とし、電解液の濃度、温度及び電解時間を制御しつつ、２０〜３０Ｖで陽極酸化することにより製造され、微細孔の孔径及び深さが制御される。
(1) Alumina micropore preparation step (1) -1 Electrolytic treatment step Since the metal to be anodized may affect the growth of the metal oxide and the like, pretreatment is preferably performed. As for the metal that can easily form a natural oxide film, such as the aluminum metal used in the present invention, the natural oxide film is removed as necessary.
First, as an example, the natural oxide film on the surface of the aluminum substrate used in the present invention is preferably removed by electrolytic treatment with a mixed solution of perchloric acid and ethyl alcohol.
(1) -2 Anodizing step 1
The alumina substrate used in the present invention is manufactured by anodizing at 20 to 30 V using aluminum or an alloy thereof as a base and controlling the concentration, temperature and electrolysis time of the electrolytic solution. Is controlled.
ここで、一例として、本発明で適用した陽極酸化法について説明する。本発明で適用した陽極酸化は、陽極酸化すべく金属アルミニウムを陽極に、対極となる陰極に、例えば、カーボン材からなる電極を配置し、これらを電解液に浸漬し、外部電源を接続し、電気（通常は直流電流）を流すことにより行う。 Here, as an example, the anodizing method applied in the present invention will be described. The anodic oxidation applied in the present invention is performed by anodizing metal aluminum as an anode and an anode made of a carbon material, for example, by immersing them in an electrolytic solution, and connecting an external power source. This is done by passing electricity (usually direct current).
次に、定電流条件で陽極酸化した場合の、酸化皮膜の成長メカニズムは以下のように考えられる。
生成する酸化皮膜の厚さは、成長開始時は電解時間に比例し直線的に増加するが、生成する酸化皮膜の電気抵抗が、厚さ方向に必ずしも一定とはならないため、酸化皮膜の成長とともにその両端にかかる電圧が飽和傾向を示す。この時の、酸化皮膜の膜厚、電位を、アルミニウム金属を陽極酸化する時の、限界膜厚、限界高電位と呼ぶ。この限界高電位はアルミニウム金属の陽極酸化速度と陽極溶解速度とのバランスにより決まるため、電解液の種類、濃度等により異なり、一般に硫酸では２０Ｖ、シュウ酸では４０Ｖ程度の電位で行われる。
また、構造的に見た場合、酸化皮膜はバリヤー皮膜とポーラス皮膜からなり、バリヤー皮膜は、緻密で孔がなく、電流が高電場のもとで絶縁性の酸化物の中を流れ、厚く成長するが、ポーラス皮膜は、最初にできたバリヤー皮膜が高電場による作用と、電解液の溶解作用を受けて、局部的に孔を形成することにより、多孔質膜となる。
Next, the growth mechanism of the oxide film when anodized under constant current conditions is considered as follows.
The thickness of the generated oxide film increases linearly in proportion to the electrolysis time at the start of growth, but the electrical resistance of the generated oxide film is not always constant in the thickness direction. The voltage applied to both ends shows a saturation tendency. The film thickness and potential of the oxide film at this time are called the limit film thickness and the limit high potential when anodizing aluminum metal. Since this critical high potential is determined by the balance between the anodic oxidation rate and the anodic dissolution rate of aluminum metal, it varies depending on the type and concentration of the electrolytic solution, and is generally 20 V for sulfuric acid and 40 V for oxalic acid.
From a structural point of view, the oxide film consists of a barrier film and a porous film. The barrier film is dense and has no pores, and the current flows through the insulating oxide under a high electric field and grows thick. However, the porous film is formed into a porous film by locally forming pores when the barrier film formed first receives the action of a high electric field and the dissolving action of the electrolytic solution.
本発明で使用したアルミニウム酸化皮膜の成長のメカニズムは必ずしも明確ではないが、以下のように考えられる。まず、陽極酸化の初期には酸化物の均一溶解を伴って、バリヤー皮膜の厚さが増大する。次に、皮膜の成長とともに酸化物の局所的溶解が起こり、無数の微細孔が発生する。さらに、初期に発生した微細孔の一部が芽孔により成長し、残りの大部分の微細孔は成長を停止する。定常状態では六角セル構造が完成し、多孔質陽極酸化皮膜が成長していく。
また、細孔底部に素地金属と接して存在する半円球状のバリアー層には、アノード電場がかかり、これにより、Ａｌ3+イオンが素地金属バリアー層を横切り孔底部に向かって移動する。孔底部に到達したＡｌ3+イオンは、直接溶液中を移動する。Ｏ2-に関しては、逆に孔底部から素地金属表面部へ移動する。バリアー層と素地金属界面に到達したＯ2-イオンはＡｌ3+と反応して新しい酸化物を形成する。これらにより、初期にできた芽孔は深さ方向に進行し、柱状構造の多孔質体となる。
The growth mechanism of the aluminum oxide film used in the present invention is not necessarily clear, but is considered as follows. First, at the initial stage of anodic oxidation, the thickness of the barrier film increases with uniform dissolution of the oxide. Next, as the film grows, local dissolution of the oxide occurs, and innumerable micropores are generated. Furthermore, a part of the micropores generated in the initial stage grows by the bud, and the remaining most micropores stop growing. In the steady state, the hexagonal cell structure is completed and the porous anodic oxide film grows.
In addition, an anode electric field is applied to the hemispherical barrier layer existing in contact with the base metal at the bottom of the pores, whereby Al 3+ ions move across the base metal barrier layer toward the bottom of the holes. Al 3+ ions that have reached the bottom of the hole move directly in the solution. On the other hand, O 2− moves from the bottom of the hole to the surface of the base metal. O 2− ions that reach the interface between the barrier layer and the base metal react with Al 3+ to form a new oxide. As a result, the initial buds proceed in the depth direction and become a columnar porous body.
本発明に使用した多孔質膜の細孔の数、孔径は、陽極酸化条件により変化する。アノード電位を高くすると、孔径は増大し、細孔の数は減少する。よって、陽極酸化の電位、電流条件により、細孔数及び孔径を適宜制御することができる。 The number of pores and the pore diameter of the porous membrane used in the present invention vary depending on the anodizing conditions. Increasing the anode potential increases the pore size and decreases the number of pores. Therefore, the number of pores and the pore diameter can be appropriately controlled according to the potential of anodic oxidation and current conditions.
本発明に適用した陽極酸化では、使用するアルミナ基板の細孔の平均直径を１０〜３０ｎｍに制御する観点から、例えば、硫酸を電解液とし、陽極酸化電圧を２０Ｖとした場合、電解液の濃度を好ましくは０．２〜５質量％、より好ましくは０．２〜０．５質量％とし、一段目の陽極酸化を行うことが好ましい。 In the anodic oxidation applied to the present invention, from the viewpoint of controlling the average diameter of the pores of the alumina substrate used to 10 to 30 nm, for example, when sulfuric acid is used as the electrolytic solution and the anodic oxidation voltage is 20 V, the concentration of the electrolytic solution Is preferably 0.2 to 5% by mass, more preferably 0.2 to 0.5% by mass, and the first-stage anodic oxidation is preferably performed.
（１）−３ 陽極酸化工程２（二段陽極酸化）
上記により得られた多孔質膜は、そのまま使用できるが、得られた多孔質膜を除去して、再度新たな多孔質膜を形成させ、すなわち陽極酸化を二回行う（二段陽極酸化）ことにより、より孔径の揃った、内壁の凸部が少ない多孔質膜を形成できる。
本発明における、二段陽極酸化法は以下の工程（ａ）〜（ｃ）を順次行う方法である。
（ａ）硫酸等の酸性溶液中での陽極酸化（一段目）により多孔質膜を形成する工程。
（ｂ）形成した多孔質膜を、リン酸とクロム酸の混合溶液等で除去する工程（アルミニウム素地金属表面部に孔の底部に対応したパターンを形成）。
（ｃ）（ａ）と同様、硫酸等の酸性溶液中で陽極酸化（二段目）により多孔質膜を形成する工程。
すなわち、本発明の熱電変換材料の製造においては、一度、陽極酸化して得られた多孔質膜をリン酸とクロム酸の混合溶液等で剥離し、素地金属表面部に孔の底部に対応したパターンを形成させる。次に、このパターン上に二段目の陽極酸化を行う。このようにして、予め孔のパターンを形成した素地表面に、陽極酸化を行うことにより、一段目に比べ、より孔径の揃った、内壁の凸部が少ない多孔質膜を形成できるので好ましい。
(1) -3 Anodizing step 2 (two-stage anodizing)
The porous film obtained as described above can be used as it is, but the obtained porous film is removed and a new porous film is formed again, that is, anodization is performed twice (two-stage anodization). As a result, a porous film with a more uniform pore diameter and fewer convex portions on the inner wall can be formed.
In the present invention, the two-stage anodic oxidation method is a method of sequentially performing the following steps (a) to (c).
(A) A step of forming a porous film by anodic oxidation (first stage) in an acidic solution such as sulfuric acid.
(B) A step of removing the formed porous film with a mixed solution of phosphoric acid and chromic acid (a pattern corresponding to the bottom of the hole is formed on the surface of the aluminum base metal).
(C) A step of forming a porous film by anodic oxidation (second stage) in an acidic solution such as sulfuric acid as in (a).
That is, in the production of the thermoelectric conversion material of the present invention, the porous film obtained by anodic oxidation once was peeled off with a mixed solution of phosphoric acid and chromic acid, etc., and the base metal surface portion corresponded to the bottom of the hole. A pattern is formed. Next, second-stage anodic oxidation is performed on this pattern. In this way, it is preferable to perform anodization on the surface of the substrate on which the hole pattern has been formed in advance, so that a porous film having a more uniform hole diameter and fewer inner wall projections can be formed compared to the first stage.
（１）−４ エッチング処理工程
さらに、アルミナ基板の孔の拡張、表面の平滑化をするために、リン酸等の酸性溶液を使用して、エッチング処理を行うことが好ましい。このエッチング処理は、アルミナ基板そのものを溶解することにより成形するものであるので、所定の形状を得るために、細かい条件出しを行う必要がある。
(1) -4 Etching treatment step Further, in order to expand the pores of the alumina substrate and smooth the surface, it is preferable to perform an etching treatment using an acidic solution such as phosphoric acid. Since this etching process is performed by melting the alumina substrate itself, it is necessary to perform fine conditions in order to obtain a predetermined shape.
（２）ｐ型ビスマステルライド成膜工程
本発明においては、前記（１）アルミナ微細孔作製工程の後に、ｐ型ビスマステルライドをアルミナ基板へ成膜することが好ましい。ここで、成膜方法としては、微細孔内底部とアルミナ基板表面との絶縁性を維持できる成膜方法であれば、特に限定されないが、フラッシュ蒸着法が好ましく用いられる。
(2) p-type bismuth telluride film-forming process In the present invention, it is preferable to form the p-type bismuth telluride film on the alumina substrate after the (1) alumina micropore forming process. Here, the film forming method is not particularly limited as long as it is a film forming method capable of maintaining the insulation between the bottom of the fine hole and the surface of the alumina substrate, but a flash vapor deposition method is preferably used.
（フラッシュ蒸着法による成膜）
フラッシュ蒸着法とは、粒子状にした蒸発材料を、例えば、材料の沸点以上に予め加熱したるつぼ、又はボート型ヒータに、連続的に少量ずつ供給して、瞬間的に材料を蒸発させる蒸着法である。このようなプロセスで蒸着すると、瞬時に材料が蒸発するため、特に蒸気圧の異なる２種類以上の元素からなる合金を蒸着する場合、蒸発材料である蒸発源をヒータ上に固定し、加熱蒸着する蒸着法に比べ、組成比をより一定に保つことができる。また、材料の飛散、未蒸発物の残留等がなく、材料を効率良く利用でき、製造コスト的にも好ましい。また、フラッシュ蒸着法では、蒸着時の材料の直進性が高く、微細孔内の壁面に材料が蒸着されにくくなるためより好ましい。
(Film deposition by flash evaporation)
The flash vapor deposition method is a vapor deposition method that instantaneously evaporates the material by supplying the vaporized material in a particulate form continuously, for example, to a crucible or a boat-type heater preheated to the boiling point or more of the material. It is. When vapor deposition is performed in such a process, the material evaporates instantaneously. Therefore, particularly when depositing an alloy composed of two or more elements having different vapor pressures, an evaporation source as an evaporation material is fixed on the heater, and heat vapor deposition is performed. Compared to the vapor deposition method, the composition ratio can be kept more constant. In addition, there is no scattering of material, residue of non-evaporated material, etc., and the material can be used efficiently, which is preferable in terms of manufacturing cost. In addition, the flash vapor deposition method is more preferable because the straightness of the material at the time of vapor deposition is high and the material is hardly vapor deposited on the wall surface in the micropore.
フラッシュ蒸着法に使用できる装置の例を説明する。図５は、実施例１（２）で使用されたフラッシュ蒸着装置の概略図である。図５において、９はフラッシュ蒸着装置、１０は真空チャンバー、１１は蒸着材料、１２はヒータである。
真空チャンバー１０において、蒸着材料１１を加熱蒸発させるヒータ１２として、例えば、ボート型を有したヒータ１２を使用するが、ボート材料としては、通常、モリブデン、タンタル、ニオブ等に代表される高融点金属が使用され、蒸着材料１１の融点、沸点等の物性に合わせ、適宜選択される。アルミナ基板１３は、通常ヒータ１２に対向する位置に設置する。
また、フラッシュ蒸着装置９にはフラッシュ蒸着の特徴の一つである、蒸発材料１１を連続的に少量ずつ供給する機構を備えている。具体的には、例えば、フラッシュ蒸着装置９の上部に、電磁フィーダ１４を設け、電磁フィーダ１４から蒸発材料１１の粒子を漏斗１５へ供給し、所定量の蒸着材料１１が漏斗１５を介して連続的にヒータ１２上に落下するように設計されている。
An example of an apparatus that can be used for flash vapor deposition will be described. FIG. 5 is a schematic view of the flash vapor deposition apparatus used in Example 1 (2). In FIG. 5, 9 is a flash vapor deposition apparatus, 10 is a vacuum chamber, 11 is a vapor deposition material, and 12 is a heater.
In the vacuum chamber 10, for example, a heater 12 having a boat shape is used as the heater 12 for heating and evaporating the vapor deposition material 11, and the boat material is usually a high melting point metal typified by molybdenum, tantalum, niobium or the like. Is appropriately selected in accordance with physical properties such as the melting point and boiling point of the vapor deposition material 11. The alumina substrate 13 is usually installed at a position facing the heater 12.
Further, the flash vapor deposition device 9 is provided with a mechanism for continuously supplying the evaporation material 11 in small amounts, which is one of the features of flash vapor deposition. Specifically, for example, an electromagnetic feeder 14 is provided on the upper part of the flash vapor deposition apparatus 9, and particles of the evaporation material 11 are supplied from the electromagnetic feeder 14 to the funnel 15, and a predetermined amount of the evaporation material 11 continues through the funnel 15. In particular, it is designed to fall on the heater 12.
実際の蒸着は、以下のようにして行われる。フラッシュ蒸着装置９の真空排気口１３より排気をし、所定の真空度まで到達させ一定時間保持した後、ヒータ１２を加熱させる。
基板温度に関しては、膜物性の設計等によるが、通常、アルミナ基板１３を所定温度まで加熱し、一定時間保持した後、蒸着材料１１をヒータ１２上に落下させることで、蒸着を開始する。蒸発材料１１が瞬時に蒸発して、対向するアルミナ基板１３に付着し、蒸着が行われる。
蒸着終了後、ヒータ１２への電流供給を停止し、基板温度を所定温度以下まで冷却し、真空チャンバー１０を開放することでフラッシュ蒸着工程が完了する。
Actual vapor deposition is performed as follows. After exhausting from the vacuum exhaust port 13 of the flash vapor deposition apparatus 9 to reach a predetermined degree of vacuum and holding for a certain period of time, the heater 12 is heated.
Although the substrate temperature depends on the design of film properties and the like, usually, after the alumina substrate 13 is heated to a predetermined temperature and held for a certain time, the vapor deposition material 11 is dropped on the heater 12 to start vapor deposition. The evaporation material 11 instantly evaporates and adheres to the opposing alumina substrate 13, and vapor deposition is performed.
After the deposition is completed, the current supply to the heater 12 is stopped, the substrate temperature is cooled to a predetermined temperature or lower, and the vacuum chamber 10 is opened to complete the flash deposition process.
次に、本発明を実施例によりさらに詳細に説明するが、本発明は、これらの例によってなんら限定されるものではない。 EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
実施例、比較例で作製した熱電変換材料の熱電性能評価は、以下の方法で、熱伝導率、ゼーベック係数及び電気伝導率を算出することにより行った。
（ａ）熱伝導率
パルス秒加熱サーモリフレクタンス法（ピコ秒サーモリフレクタンス装置、型番：ＰｉｃｏＴＲ、株式会社ピコサーム製）により、パルスレーザで試料表面を瞬間的に加熱し、熱拡散に伴う試料表面の温度変化を測定し、膜の膜厚方向の熱伝導率を算出した。
（ｂ）ゼーベック係数
作製した試料の一端を加熱して、試料の両端に生じる温度差をクロメル−アルメル熱電対を使用し測定し、熱電対設置位置に隣接した電極から熱起電力を測定した。具体的には、温度差と起電力を測定する試料の両端間距離を１５ｍｍとし、一端を２０℃に保ち、他端を２５℃から３０℃まで１℃刻みで加熱し、その際の熱起電力を測定して、傾きからゼーベック係数を算出した。
（ｃ）電気伝導率
作製した試料の両端から定電流を供給し、デジタルボルトメーター（デジタルボルトメーター、型番：Ｍｏｄｅｌ７５５５、横河電機株式会社製）で試料の両端の電位を測定することにより、試料の抵抗値を算出し、試料のサイズ（縦×横×厚さ）を考慮して電気伝導率を算出した。
The thermoelectric performance evaluation of the thermoelectric conversion material produced by the Example and the comparative example was performed by calculating a thermal conductivity, a Seebeck coefficient, and an electrical conductivity with the following method.
(A) Thermal conductivity The sample surface is instantaneously heated with a pulsed laser by the pulsed second heating thermoreflectance method (picosecond thermoreflectance device, model number: PicoTR, manufactured by Picotherm Co., Ltd.) Was measured, and the thermal conductivity in the film thickness direction of the film was calculated.
(B) Seebeck coefficient One end of the prepared sample was heated, a temperature difference generated between both ends of the sample was measured using a chromel-alumel thermocouple, and a thermoelectromotive force was measured from an electrode adjacent to the thermocouple installation position. Specifically, the distance between both ends of the sample for measuring the temperature difference and the electromotive force is 15 mm, one end is kept at 20 ° C., and the other end is heated from 25 ° C. to 30 ° C. in 1 ° C. increments. The power was measured and the Seebeck coefficient was calculated from the slope.
(C) Electrical conductivity A constant current is supplied from both ends of the prepared sample, and the potential of both ends of the sample is measured with a digital voltmeter (digital voltmeter, model number: Model 7555, manufactured by Yokogawa Electric Corporation). The electrical conductivity was calculated in consideration of the sample size (length × width × thickness).
実施例１
（１）アルミナ基板の作製
微細孔を有するアルミナ多孔質膜を、二段陽極酸化法で形成し、アルミナ基板１を作製した。
まず、アルミニウム基体２（１０×１００×０．５ｍｍ、純度９９．９％；株式会社ニラコ製）をアセトンで洗浄し、６０質量％の過塩素酸とエチルアルコールを１：４（体積比）の割合で混合した溶液を２０℃に加温し、１０Ｖの直流電圧を５分間印加し、アルミニウム基体２の表面の自然酸化膜を除去した。次に、２０℃の０．３質量％の硫酸溶液中で、２０Ｖの直流電圧を２時間印加し、一段目の陽極酸化を行い、アルミナの多孔質膜を形成させた。
さらに、二段陽極酸化を行うために、６質量％のリン酸と１．８質量％のクロム酸の水溶液を６０℃に加温し、１４時間浸漬することにより、一段目の陽極酸化で形成したアルミナ多孔質膜を完全に除去した。除去後のアルミニウム基体２の素地面には、アルミニウムが陽極酸化反応で侵食されたことを示す、孔の底部に対応したパターンが形成されている。
再び、アルミニウム基体２を２０℃の０．３質量％の硫酸溶液中で、２０Ｖの直流電圧を５分間印加し、二段目の陽極酸化を行い、アルミナの多孔質膜３を形成させた。最後に、３０℃の６質量％のリン酸の水溶液中で１５分間エッチング処理し、アルミナの多孔質膜３の孔の拡張、表面の平滑化を行い、アルミナ基板１を作製した。作製したアルミナ基板１の微細孔４の平均直径は２０ｎｍ、平均間隔は５０ｎｍ、深さは１０００ｎｍであった。
Example 1
(1) Production of Alumina Substrate An alumina porous film having fine pores was formed by a two-step anodic oxidation method, and an alumina substrate 1 was produced.
First, the aluminum substrate 2 (10 × 100 × 0.5 mm, purity 99.9%; manufactured by Niraco Co., Ltd.) was washed with acetone, and 60% by mass of perchloric acid and ethyl alcohol was 1: 4 (volume ratio). The solution mixed at a rate was heated to 20 ° C. and a DC voltage of 10 V was applied for 5 minutes to remove the natural oxide film on the surface of the aluminum substrate 2. Next, a DC voltage of 20 V was applied for 2 hours in a 0.3 mass% sulfuric acid solution at 20 ° C., and the first stage of anodic oxidation was performed to form an alumina porous film.
Furthermore, in order to perform two-stage anodic oxidation, an aqueous solution of 6% by mass phosphoric acid and 1.8% by mass chromic acid is heated to 60 ° C. and immersed for 14 hours to form the first-stage anodic oxidation. The alumina porous membrane thus obtained was completely removed. A pattern corresponding to the bottom of the hole is formed on the ground surface of the aluminum substrate 2 after the removal, indicating that aluminum has been eroded by the anodic oxidation reaction.
Again, the aluminum substrate 2 was applied with a DC voltage of 20 V in a 0.3% by mass sulfuric acid solution at 20 ° C. for 5 minutes to perform second-stage anodic oxidation, thereby forming an alumina porous film 3. Finally, etching was performed in an aqueous solution of 6% by mass phosphoric acid at 30 ° C. for 15 minutes to expand the pores of the alumina porous film 3 and smooth the surface, whereby the alumina substrate 1 was produced. The average diameter of the fine holes 4 of the produced alumina substrate 1 was 20 nm, the average interval was 50 nm, and the depth was 1000 nm.
（２）ｐ型ビスマステルライドの成膜
熱電変換素材料は、前記（１）で作製したアルミナ基板１を使用し、フラッシュ蒸着法でｐ型ビスマステルライドを成膜することにより作製した。
図５に示したフラッシュ蒸着装置９の真空チャンバー１０において、蒸着材料１１を加熱蒸発させるヒータ１２としてボート型のタングステンヒータを使用し、ヒータ１２に対向する位置（２０ｃｍ）に（１）で作製したアルミナ基板１を配置した。
次いで、フラッシュ蒸着装置９の真空排気口１６より排気をし、１．４×１０-3Ｐａの真空度まで到達させ、真空度を安定させた後、８５Ａの電流をタングステンヒータ１２に供給し、加熱させた。基板温度に関しては、２００℃で一定時間保持した。蒸着材料１１であるＢｉ0.4Ｔｅ3Ｓｂ1.6合金をボート上に連続的に少量ずつ落下させ、平均蒸着速度
０．１７（ｎｍ／秒）、蒸着時間６００（秒）で成膜を行い、熱電変換材料を作製した。
図３は本発明の実施例１で得られた熱電変換材料の微細孔を示すＳＥＭ写真であり、（ａ）は表面、（ｂ）は断面である。図３（ａ）に示すように、Ｂｉ0.4Ｔｅ3Ｓｂ1.6合金が成膜されたアルミナの多孔質膜の表面は独立した微細孔になっていることがわかる。また、図３（ｂ）に示すように、微細孔の断面は、基板の厚み方向にやや傾きを有している場合があるが、各微細孔内を貫通する中心線が、アルミナ基板上に立てた法線に対し、±１０°内に十分収まっていることがわかる。成膜したＢｉ0.4Ｔｅ3Ｓｂ1.6のアルミナ基板表面の膜厚は１００ｎｍ、微細孔の底部の膜厚は０ｎｍであった。熱電性能評価結果を表１に示す。
(2) Film formation of p-type bismuth telluride The thermoelectric conversion element material was prepared by forming a film of p-type bismuth telluride by the flash vapor deposition method using the alumina substrate 1 prepared in the above (1).
In the vacuum chamber 10 of the flash vapor deposition apparatus 9 shown in FIG. 5, a boat type tungsten heater was used as the heater 12 for heating and evaporating the vapor deposition material 11, and it was fabricated at (1) at a position (20 cm) facing the heater 12. An alumina substrate 1 was disposed.
Next, after exhausting from the vacuum exhaust port 16 of the flash vapor deposition apparatus 9 to reach a vacuum degree of 1.4 × 10 −3 Pa and stabilizing the vacuum degree, a current of 85 A is supplied to the tungsten heater 12, Heated. Regarding the substrate temperature, it was held at 200 ° C. for a certain period of time. Bi 0.4 Te 3 Sb 1.6 alloy, which is the deposition material 11, is continuously dropped onto the boat in small portions, and film formation is performed at an average deposition rate of 0.17 (nm / second) and a deposition time of 600 (second), and thermoelectric conversion is performed. The material was made.
FIG. 3 is a SEM photograph showing micropores of the thermoelectric conversion material obtained in Example 1 of the present invention, where (a) is the surface and (b) is the cross section. As shown in FIG. 3 (a), it can be seen that the surface of the porous alumina film on which the Bi 0.4 Te 3 Sb 1.6 alloy is formed has independent micropores. In addition, as shown in FIG. 3B, the cross section of the micro hole may have a slight inclination in the thickness direction of the substrate, but the center line penetrating each micro hole is on the alumina substrate. It can be seen that it is well within ± 10 ° with respect to the raised normal. The film thickness of the Bi 0.4 Te 3 Sb 1.6 film formed on the surface of the alumina substrate was 100 nm, and the film thickness at the bottom of the micropores was 0 nm. Table 1 shows the results of thermoelectric performance evaluation.
比較例１
微細孔がないアルミナ基板上に、Ｂｉ0.4Ｔｅ3Ｓｂ1.6合金をフラッシュ蒸着して、熱電変換材料を作製した。熱電性能評価結果を表１に示す。
Comparative Example 1
A Bi 0.4 Te 3 Sb 1.6 alloy was flash-deposited on an alumina substrate having no micropores to produce a thermoelectric conversion material. Table 1 shows the results of thermoelectric performance evaluation.
比較例２
微細孔が独立していないＢｉ0.4Ｔｅ3Ｓｂ1.6薄膜については、Ｂｉ0.4Ｔｅ3Ｓｂ1.6原料をナノサイズに粉砕した粒子を塗布することで成膜した。
図４は比較例２で用いた熱電変換材料の細孔を示すＳＥＭ写真であり、（ａ）は表面、（ｂ）は断面である。図４（ａ）に示すように、アルミナの多孔質膜の表面の細孔は、独立していない態様であることがわかる。また、図４（ｂ）に示すように、微細孔の断面も独立していない構造であることがわかる。熱電性能評価結果を表１に示す。
Comparative Example 2
The Bi 0.4 Te 3 Sb 1.6 thin film, in which the micropores are not independent, was formed by applying particles obtained by pulverizing Bi 0.4 Te 3 Sb 1.6 raw material into nano-size.
4 is an SEM photograph showing pores of the thermoelectric conversion material used in Comparative Example 2, wherein (a) is a surface and (b) is a cross section. As shown in FIG. 4A, it can be seen that the pores on the surface of the porous alumina film are not independent. In addition, as shown in FIG. 4B, it can be seen that the structure of the micropores is not independent. Table 1 shows the results of thermoelectric performance evaluation.
実施例１では、熱伝導率が大幅に低下し、電気伝導率の減少が抑制され、かつゼーベック係数はバルクの物性値（Ｂｉ0.4Ｔｅ3Ｓｂ1.6のバルクの物性値：２２０μＶ／Ｋ）にほぼ維持された。このため、無次元熱電性能指数ＺＴは１．８７となり、実用の目安となる指標値１をはるかに越えた値が得られた。
一方、微細孔が形成されていない薄膜のみのアルミナ基板を使用した比較例１では、無次元熱電性能指数ＺＴは１．０５であり、微細孔が独立していないアルミナ基板を使用した比較例２では、ＺＴは０．１６であった。
In Example 1, the thermal conductivity is significantly reduced, the decrease in electrical conductivity is suppressed, and the Seebeck coefficient is almost equal to the bulk physical property value (Bi 0.4 Te 3 Sb 1.6 bulk physical property value: 220 μV / K). Maintained. For this reason, the dimensionless thermoelectric figure of merit ZT was 1.87, and a value far exceeding the index value 1 which is a practical standard was obtained.
On the other hand, in Comparative Example 1 using only a thin-film alumina substrate in which no micropores are formed, the dimensionless thermoelectric figure of merit ZT is 1.05, and Comparative Example 2 using an alumina substrate in which micropores are not independent. Then, ZT was 0.16.
本発明の熱電変換材料は、熱と電気の相互エネルギー変換を行う熱電変換素子にして、モジュールに組み込み、利用される。具体的には、高効率な熱電変換材料であるので、工場や廃棄物燃焼炉、セメント燃焼炉等の各種燃焼炉からの排熱、自動車の燃焼ガス排熱及び電子機器の排熱を電気に変換する用途への適用が考えられる。 The thermoelectric conversion material of the present invention is incorporated into a module as a thermoelectric conversion element that performs mutual energy conversion between heat and electricity. Specifically, because it is a highly efficient thermoelectric conversion material, the heat from various combustion furnaces such as factories, waste combustion furnaces, cement combustion furnaces, automobile combustion gas exhaust heat, and electronic equipment exhaust heat are converted into electricity. Application to the purpose of conversion is conceivable.
１：アルミナ基板
２：アルミニウム基体
３：多孔質膜
４：微細孔
５：微細孔内を貫通する中心線
６：アルミナ基板上に立てた法線
７：微細孔内を貫通する中心線と法線のなす角度
８：アルミナ基板に対して平行に引いた仮想線
９：フラッシュ蒸着装置
１０：真空チャンバー
１１：蒸着材料
１２：ヒータ
１３：アルミナ基板
１４：電磁フィーダ
１５：漏斗
１６：真空排気口
1: Alumina substrate 2: Aluminum substrate 3: Porous film 4: Fine hole 5: Center line penetrating through the fine hole 6: Normal line standing on the alumina substrate 7: Center line and normal line penetrating through the fine hole 8: Virtual line drawn parallel to the alumina substrate 9: Flash vapor deposition apparatus 10: Vacuum chamber 11: Vapor deposition material 12: Heater 13: Alumina substrate 14: Electromagnetic feeder 15: Funnel 16: Vacuum exhaust port
Claims (8)
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| JP2011033980A JP5718671B2 (en) | 2011-02-18 | 2011-02-18 | Thermoelectric conversion material and manufacturing method thereof |
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| Application Number | Priority Date | Filing Date | Title |
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| JP2011033980A JP5718671B2 (en) | 2011-02-18 | 2011-02-18 | Thermoelectric conversion material and manufacturing method thereof |
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