JP2007103580A - Thermoelectric transducer and method of manufacturing same - Google Patents

Thermoelectric transducer and method of manufacturing same Download PDF

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JP2007103580A
JP2007103580A JP2005290099A JP2005290099A JP2007103580A JP 2007103580 A JP2007103580 A JP 2007103580A JP 2005290099 A JP2005290099 A JP 2005290099A JP 2005290099 A JP2005290099 A JP 2005290099A JP 2007103580 A JP2007103580 A JP 2007103580A
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semiconductor material
electrode
thermoelectric semiconductor
conversion element
thermoelectric
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Yasufumi Shibata
靖文 柴田
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Toyota Motor Corp
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<P>PROBLEM TO BE SOLVED: To provide a thermoelectric transducer which is not dependent upon a type of thermoelectric semiconductor material and can prevent crackings of the thermoelectric semiconductor material due to a thermal stress. <P>SOLUTION: In the thermoelectric transducer 10, a plurality of pairs of an n-type thermoelectric semiconductor material 40 and a p-type thermoelectric semiconductor material 41 are jointed to electrodes 30, 31, 32 composed of a porous metal material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は熱電変換素子及びその製造方法に関し、特に、熱電半導体材料と電極との間の熱応力を緩和可能な熱電変換素子及びその製造方法に関する。   The present invention relates to a thermoelectric conversion element and a method for manufacturing the same, and more particularly to a thermoelectric conversion element capable of relieving thermal stress between a thermoelectric semiconductor material and an electrode and a method for manufacturing the same.

ゼーベック効果を利用した熱電変換素子は、熱エネルギーを電気エネルギーに変換することが可能である。この性質を利用し、産業・民生用プロセスや移動体から排出される排熱を有効な電力に変換することができるため、熱電変換素子は、環境問題に配慮した省エネルギー技術として注目されている。   A thermoelectric conversion element using the Seebeck effect can convert heat energy into electric energy. Because this property can be used to convert exhaust heat discharged from industrial and consumer processes and mobile objects into effective power, thermoelectric conversion elements are attracting attention as energy-saving technologies that take environmental issues into consideration.

熱電変換素子に用いられる熱電半導体材料の性能は、性能指数ＺＴ＝α2σＴ／κ〔α：ゼーベック係数、σ：電気伝導度、κ：熱伝導度、Ｔ：測定温度〕で表すことができるが、高い性能指数を示す熱電半導体材料としては従来から、ビスマス・テルル系材料、シリコン・ゲルマニウム系材料、鉛・テルル系材料などを用いた熱電半導体材料が知られている。また、アルミニウムをドープした酸化亜鉛粉を成形、焼成してなる熱電半導体材料も知られている。 The performance of the thermoelectric semiconductor material used for the thermoelectric conversion element can be expressed by a figure of merit ZT = α 2 σT / κ [α: Seebeck coefficient, σ: electrical conductivity, κ: thermal conductivity, T: measurement temperature]. However, thermoelectric semiconductor materials using bismuth / tellurium-based materials, silicon / germanium-based materials, lead / tellurium-based materials, and the like have been known as thermoelectric semiconductor materials exhibiting a high performance index. A thermoelectric semiconductor material obtained by forming and baking zinc oxide powder doped with aluminum is also known.

さらに近年では、新規な熱電半導体材料としてクラスレート化合物が注目されている。   In recent years, clathrate compounds have attracted attention as a novel thermoelectric semiconductor material.

熱電半導体材料は、温度差が大きいほど発電量が大きくなるため、数ｍｍの厚さの熱電変換素子に数百度の温度差をつけて発電することが検討されている。この場合、熱電変換素子を構成している電極、熱電半導体材料及び絶縁用のセラミックス基板間の線膨張係数の差によって熱電半導体材料に熱応力が発生し、熱電半導体材料が割れてしまうことがあった。一般に、優れた熱電変換特性を呈する熱電半導体材料は脆いため、熱応力による熱電半導体材料の割れは深刻な問題であった。   Since the thermoelectric semiconductor material generates a larger amount of power as the temperature difference is larger, it has been studied to generate power with a temperature difference of several hundred degrees on a thermoelectric conversion element having a thickness of several millimeters. In this case, thermal stress is generated in the thermoelectric semiconductor material due to a difference in coefficient of linear expansion among the electrodes constituting the thermoelectric conversion element, the thermoelectric semiconductor material, and the insulating ceramic substrate, and the thermoelectric semiconductor material may be cracked. It was. In general, since thermoelectric semiconductor materials exhibiting excellent thermoelectric conversion characteristics are brittle, cracking of thermoelectric semiconductor materials due to thermal stress has been a serious problem.

この問題を解決するために、Ｓｉ基熱電変換材料（線膨張係数：４ｐｐｍ／Ｋ）を線膨張係数が１０ｐｐｍ／Ｋ以下の材料からなる電極で接合した熱電変換素子が報告されている（例えば、特許文献１参照。）。
特開２００２−９４１３１号公報 In order to solve this problem, a thermoelectric conversion element in which a Si-based thermoelectric conversion material (linear expansion coefficient: 4 ppm / K) is joined with an electrode made of a material having a linear expansion coefficient of 10 ppm / K or less has been reported (for example, (See Patent Document 1).
JP 2002-94131 A

線膨張係数は物質固有の係数であるため、特許文献１の技術はＳｉ基熱電変換材料を熱電半導体材料として用いた場合にのみ有効な技術である。つまり、Ｓｉ基熱電変換材料以外の物質を用いた場合には、電極の材料を再度検討する必要がある。   Since the linear expansion coefficient is a substance-specific coefficient, the technique of Patent Document 1 is an effective technique only when an Si-based thermoelectric conversion material is used as a thermoelectric semiconductor material. That is, when a substance other than the Si-based thermoelectric conversion material is used, it is necessary to examine the electrode material again.

本発明は上記従来の問題点に鑑みてなされたものであり、熱電半導体材料の種類に依存しない、熱応力による熱電半導体材料の割れを防止可能な熱電変換素子及びその製造方法を提供することを目的とする。   The present invention has been made in view of the above-described conventional problems, and provides a thermoelectric conversion element capable of preventing cracking of a thermoelectric semiconductor material due to thermal stress, and a method for manufacturing the same, independent of the type of thermoelectric semiconductor material. Objective.

即ち、本発明は、
＜１＞ ｐ型熱電半導体材料及びｎ型熱電半導体材料の単数又は複数対を、多孔性金属材料からなる電極で接合した熱電変換素子である。 That is, the present invention
<1> A thermoelectric conversion element in which one or more pairs of a p-type thermoelectric semiconductor material and an n-type thermoelectric semiconductor material are joined by an electrode made of a porous metal material.

＜２＞ 前記熱電半導体材料の少なくとも一つが、前記電極の凹部に接触して接合した＜１＞に記載の熱電変換素子である。   <2> The thermoelectric conversion element according to <1>, wherein at least one of the thermoelectric semiconductor materials is in contact with and joined to the concave portion of the electrode.

＜３＞ 前記熱電半導体材料の少なくとも一つが、前記電極の凹部に嵌合した状態で接合した＜１＞に記載の熱電変換素子である。   <3> The thermoelectric conversion element according to <1>, in which at least one of the thermoelectric semiconductor materials is joined in a state of being fitted in the concave portion of the electrode.

＜４＞ 前記熱電半導体材料の少なくとも一つが、前記電極にめり込んだ状態で接合した＜１＞に記載の熱電変換素子である。   <4> The thermoelectric conversion element according to <1>, wherein at least one of the thermoelectric semiconductor materials is joined to the electrode while being embedded.

＜５＞ 前記多孔性金属材料が、発泡金属である＜１＞乃至＜４＞のいずれか１つに記載の熱電変換素子である。   <5> The thermoelectric conversion element according to any one of <1> to <4>, wherein the porous metal material is a foam metal.

＜６＞ 多孔性金属材料からなる電極と熱電半導体材料とを圧着して接合する工程を含む熱電変換素子の製造方法である。   <6> A method for manufacturing a thermoelectric conversion element including a step of pressure bonding and joining an electrode made of a porous metal material and a thermoelectric semiconductor material.

＜７＞ 多孔性金属材料からなる電極に凹部を形成する工程と、前記電極の凹部に熱電半導体材料を嵌合する工程と、を含む熱電変換素子の製造方法である。   <7> A method for producing a thermoelectric conversion element, comprising: a step of forming a recess in an electrode made of a porous metal material; and a step of fitting a thermoelectric semiconductor material into the recess of the electrode.

＜８＞ 前記多孔性金属材料が、発泡金属である＜６＞又は＜７＞に記載の熱電変換素子の製造方法である。   <8> The method for producing a thermoelectric conversion element according to <6> or <7>, wherein the porous metal material is a foam metal.

本発明によれば、熱電半導体材料の種類に依存しない、熱応力による熱電半導体材料の割れを防止可能な熱電変換素子及びその製造方法が提供される。   ADVANTAGE OF THE INVENTION According to this invention, the thermoelectric conversion element which can prevent the crack of the thermoelectric semiconductor material by a thermal stress independent of the kind of thermoelectric semiconductor material, and its manufacturing method are provided.

以下、本発明の熱電変換素子及びその製造方法を、図面に基づき詳細に説明する。なお、以下の実施形態においては、低温側基板及び高温側基板として窒化珪素からなるセラミックス基板を、ｐ型熱電半導体材料としてクラスレート化合物の一種であるＢａ8Ｇａ18Ｇｅ28を、ｎ型熱電半導体材料としてクラスレート化合物の一種であるＢａ8Ｇａ15Ｇｅ31を、多孔性金属材料からなる電極として銅製の発泡金属を用いた場合について説明する。また、同様の機能を有する部材には、全図面を通じて同じ符合を付与し、その説明を省略することがある。 Hereinafter, the thermoelectric conversion element of the present invention and the manufacturing method thereof will be described in detail with reference to the drawings. In the following embodiments, a ceramic substrate made of silicon nitride is used as the low-temperature side substrate and the high-temperature side substrate, Ba 8 Ga 18 Ge 28 which is a kind of clathrate compound is used as the p-type thermoelectric semiconductor material, and the n-type thermoelectric semiconductor is used. The case where Ba 8 Ga 15 Ge 31 , which is a kind of clathrate compound, is used as a material and a copper foam metal is used as an electrode made of a porous metal material will be described. In addition, members having similar functions may be given the same reference numerals throughout the drawings, and description thereof may be omitted.

なお、本発明において多孔性金属材料とは、金属の内部又は表面に多数の小さな空隙をもつ材料をいう。多孔性金属材料の具体例としては、発泡金属、金属不織布、金属箔の表面に数百μｍの凹凸を設けた材料などが挙げられる。金属箔の表面に数百μｍの凹凸を設けた材料を電極として用いる場合、凹凸を有する面が熱電半導体材料と接するように配置される。   In the present invention, the porous metal material refers to a material having a large number of small voids inside or on the surface of the metal. Specific examples of the porous metal material include a foam metal, a metal nonwoven fabric, and a material provided with unevenness of several hundreds μm on the surface of a metal foil. When using the material which provided the unevenness | corrugation of several hundred micrometers on the surface of metal foil as an electrode, it arrange | positions so that the surface which has an unevenness | corrugation may contact | connect a thermoelectric semiconductor material.

＜第一実施形態＞
図１は、本発明の熱電変換素子の第一実施形態を示す斜視図である。図１の熱電変換素子は、ｐ型熱電半導体材料及びｎ型熱電半導体材料の複数対を多孔性金属材料からなる電極で接合したものである。図１に示す熱電変換素子１０は、ｎ型熱電半導体材料４０とｐ型熱電半導体材料４１とが交互に電気的に直列になるように電極３０，３１及び３２で接続されている。 <First embodiment>
FIG. 1 is a perspective view showing a first embodiment of a thermoelectric conversion element of the present invention. The thermoelectric conversion element of FIG. 1 is obtained by joining a plurality of pairs of a p-type thermoelectric semiconductor material and an n-type thermoelectric semiconductor material with an electrode made of a porous metal material. In the thermoelectric conversion element 10 shown in FIG. 1, n-type thermoelectric semiconductor material 40 and p-type thermoelectric semiconductor material 41 are connected by electrodes 30, 31, and 32 so that they are alternately electrically in series.

また、熱電変換素子１０においては、下側の電極３１，３２と上側の電極３０とがそれぞれＡｇろうなどのろう材を用いて低温側基板２０と高温側基板２１とに接合されている。そして、熱電変換素子１０は、高温側基板２１を加熱すると共に低温側基板を所定の温度が保たれるように冷却して温度差を与えることにより発電し、不図示の正極端子と負極端子とから電気エネルギーが取り出し可能なようになっている。   Further, in the thermoelectric conversion element 10, the lower electrodes 31 and 32 and the upper electrode 30 are joined to the low temperature side substrate 20 and the high temperature side substrate 21 using a brazing material such as Ag brazing. Then, the thermoelectric conversion element 10 generates power by heating the high temperature side substrate 21 and cooling the low temperature side substrate so as to maintain a predetermined temperature to give a temperature difference, and a positive electrode terminal and a negative electrode terminal (not shown) The electric energy can be taken out from.

次に、熱電半導体材料と電極との接合形態について説明する。図２は、第一実施形態に係る熱電変換素子の電極と熱電半導体材料との接合形態を説明するための図である。ｎ型熱電半導体材料４０とｐ型熱電半導体材料４１とは、ろう材５０により電極３０，３１及び３２と接合されている。   Next, the joining form of the thermoelectric semiconductor material and the electrode will be described. FIG. 2 is a diagram for explaining a bonding configuration between the electrode of the thermoelectric conversion element according to the first embodiment and the thermoelectric semiconductor material. The n-type thermoelectric semiconductor material 40 and the p-type thermoelectric semiconductor material 41 are joined to the electrodes 30, 31 and 32 by a brazing material 50.

電極３０，３１及び３２の厚みは１００〜１５００μｍが好ましく、５００〜１０００μｍがさらに好ましい。   The thickness of the electrodes 30, 31, and 32 is preferably 100-1500 μm, and more preferably 500-1000 μm.

高熱側基板２１が加熱され低温側基板２０が冷却されることにより熱電変換素子１０が発電するが、この際、セラミックス基板（高熱側基板２１及び低温側基板２０）とクラスレート化合物（ｎ型熱電半導体材料４０及びｐ型熱電半導体材料４１）との間の線膨張係数の差により熱応力が生ずる。しかし、本実施形態においては同一組成の金属材料と比較してヤング率の低い発泡金属を電極に用いているため、該発泡金属がセラミックス基板とクラスレート化合物との間の熱応力を緩和することができる。その結果として、熱応力による熱電半導体材料の割れの防止が可能となる。   The thermoelectric conversion element 10 generates electric power by heating the high-temperature substrate 21 and cooling the low-temperature substrate 20. At this time, the ceramic substrate (the high-temperature substrate 21 and the low-temperature substrate 20) and the clathrate compound (n-type thermoelectric device). Thermal stress is caused by the difference in coefficient of linear expansion between the semiconductor material 40 and the p-type thermoelectric semiconductor material 41). However, in the present embodiment, a foam metal having a lower Young's modulus compared to a metal material having the same composition is used for the electrode, so that the foam metal relieves thermal stress between the ceramic substrate and the clathrate compound. Can do. As a result, cracking of the thermoelectric semiconductor material due to thermal stress can be prevented.

クラスレート化合物のような熱電特性に優れた熱電半導体材料は、一般的に脆性材料であり非常に脆い材料である。熱電変換素子の発電においては、数ｍｍの厚みの素子に数百度の温度差を与えて発電することがあり、従来では熱応力緩和のために熱電半導体材料、電極並びに高温側基板及び低温側基板の線膨張係数をシビアに合わせ込む必要があった。そのため、電気伝導率及び熱伝導率に優れた銅などの材料を電極として用いることができない場合があった。このような場合には電気伝導率及び熱伝導率が銅よりも劣るその他の材料が電極として用いられるが、熱電変換素子の出力が低下する可能性があった。しかし、本発明の熱電変換素子においては、線膨張係数の合わせ込みをすることなく銅などの電気伝導率及び熱伝導率に優れた金属を、電極を構成する材料として用いることができるため、熱応力を緩和することができると共に熱電変換素子の出力を向上させることができる。   Thermoelectric semiconductor materials having excellent thermoelectric properties such as clathrate compounds are generally brittle materials and very brittle materials. In power generation of a thermoelectric conversion element, power generation may be performed by giving a temperature difference of several hundred degrees to an element having a thickness of several millimeters. Conventionally, thermoelectric semiconductor materials, electrodes, a high temperature side substrate, and a low temperature side substrate are used for thermal stress relaxation. It was necessary to adjust the linear expansion coefficient to severe. Therefore, in some cases, a material such as copper having excellent electrical conductivity and thermal conductivity cannot be used as the electrode. In such a case, other materials whose electrical conductivity and thermal conductivity are inferior to copper are used as electrodes, but the output of the thermoelectric conversion element may be reduced. However, in the thermoelectric conversion element of the present invention, a metal having excellent electrical conductivity and thermal conductivity such as copper can be used as a material constituting the electrode without adjusting the linear expansion coefficient. The stress can be relaxed and the output of the thermoelectric conversion element can be improved.

また、接合性に劣る金属材料を電極として用いると、熱電半導体材料と電極との間の剥離の問題が生ずることがある。しかし、本発明の熱電変換素子においては、接合性に優れた金属を、線膨張係数の合わせ込みをすることなく電極を構成する材料として用いることができるため、熱電半導体材料と電極との間の剥離の問題の発生を抑えることができる。   In addition, when a metal material having poor bonding properties is used as an electrode, there may be a problem of peeling between the thermoelectric semiconductor material and the electrode. However, in the thermoelectric conversion element of the present invention, a metal having excellent bondability can be used as a material constituting the electrode without adjusting the linear expansion coefficient. Occurrence of a peeling problem can be suppressed.

本実施形態の熱電変換素子においては、ｎ型熱電半導体材料としてクラスレート化合物の一種であるＢａ8Ｇａ15Ｇｅ31を、ｐ型熱電半導体材料としてクラスレート化合物の一種であるＢａ8Ｇａ18Ｇｅ28を用いたが、熱電半導体材料はこれらに限定されるものではない。 In the thermoelectric conversion element of the present embodiment, Ba 8 Ga 15 Ge 31 which is a kind of clathrate compound as an n-type thermoelectric semiconductor material, and Ba 8 Ga 18 Ge 28 which is a kind of clathrate compound as a p-type thermoelectric semiconductor material. However, the thermoelectric semiconductor material is not limited to these.

熱電半導体材料として使用可能なクラスレート化合物としては、例えば、一般式ＩＩ8（ＩＩＩ，ＩＶ）46：〔ＩＩ＝Ｂａ，Ｓｒ，アルカリ金属，アルカリ土類金属；ＩＩＩ＝Ｇａ，Ｓｉ，Ｓｎ，Ａｌ，遷移金属；ＩＶ＝Ｇｅ，Ｓｉ，Ｓｎ，遷移金属〕で表される立方晶系のクラスレート化合物が挙げられる。これらから、ｎ型熱電半導体材料、ｐ型熱電半導体材料に適宜選択して用いることができる。 Examples of the clathrate compound that can be used as the thermoelectric semiconductor material include, for example, general formula II 8 (III, IV) 46 : [II = Ba, Sr, alkali metal, alkaline earth metal; III = Ga, Si, Sn, Al , Transition metal; IV = Ge, Si, Sn, transition metal]. From these, an n-type thermoelectric semiconductor material and a p-type thermoelectric semiconductor material can be appropriately selected and used.

クラスレート化合物以外の熱電半導体材料としては、例えば、ＢｉＴｅ系、ＰｂＴｅ系、ＳｉＧｅ、ＺｎＳｂ、ＭｎＳｉ系、ＭｇＳｉ系、スクッテルダイト系、ホイスラー系の材料等が挙げられる。   Examples of thermoelectric semiconductor materials other than the clathrate compounds include BiTe-based, PbTe-based, SiGe, ZnSb, MnSi-based, MgSi-based, skutterudite-based, and Heusler-based materials.

本実施形態の熱電変換素子においては、電極３０，３１及び３２として銅製の発泡金属を用いたが、これに限定されるものではない。   In the thermoelectric conversion element of the present embodiment, copper foam metal is used as the electrodes 30, 31 and 32, but is not limited to this.

電極の素材としては銅、チタン、ニッケル及び鉄並びにこれら金属の酸化物及び合金を用いることができる。これらの材料は、クラスレート化合物と優れた接合性を示すため、熱電半導体材料としてクラスレート化合物を用いた場合に特に有効である。電極の形態としては、発泡金属、金属不織布及び表面に数百μｍの凹凸が設けられた金属箔等が挙げられるが、これらの中でも、入手の容易性から発泡金属を用いることが好ましい。   As an electrode material, copper, titanium, nickel and iron, and oxides and alloys of these metals can be used. These materials are particularly effective when a clathrate compound is used as a thermoelectric semiconductor material because they exhibit excellent bonding properties with the clathrate compound. Examples of the form of the electrode include a foam metal, a metal nonwoven fabric, and a metal foil having unevenness of several hundreds μm on the surface. Among these, it is preferable to use a foam metal because of its availability.

表面に数百μｍの凹凸が設けられた金属箔は、金属箔の一方の面にエッチング等の化学的処理又はサンドブラスト加工やブラシ加工等の物理的加工を施すことにより得ることができる。   A metal foil having unevenness of several hundreds μm on the surface can be obtained by subjecting one surface of the metal foil to chemical processing such as etching or physical processing such as sandblasting or brushing.

本発明に用いられる発泡金属の気孔率は、７０〜９０％が好ましく、８０〜９０％がさらに好ましい。なお本発明において発泡金属の気孔率とは、体積と重量とを測定し、密度（文献値）を基に算出された値をいう。   The porosity of the metal foam used in the present invention is preferably 70 to 90%, more preferably 80 to 90%. In the present invention, the porosity of the foam metal refers to a value calculated based on the density (document value) by measuring the volume and weight.

また、本実施形態の熱電変換素子においては、電極３０，３１及び３２として銅製の発泡金属を用いたが、低温側基板２０側では熱電半導体材料に対する熱応力が小さいため電極として発泡金属等の多孔性金属材料を用いなくてもよい。さらに、ｎ型熱電半導体材料４０と電極３１との接合及びｐ型熱電半導体材料４１と電極３２との接合には、半田を用いることもできる。   In the thermoelectric conversion element of the present embodiment, copper foam metal is used as the electrodes 30, 31 and 32. However, since the thermal stress on the thermoelectric semiconductor material is small on the low temperature side substrate 20, the porous metal such as foam metal is used as the electrode. The conductive metal material may not be used. Furthermore, solder can be used for joining the n-type thermoelectric semiconductor material 40 and the electrode 31 and joining the p-type thermoelectric semiconductor material 41 and the electrode 32.

＜第二実施形態＞
本発明の第二実施形態に係る熱電変換素子を、図３を用いて説明する。本実施形態は、第一実施形態に係る熱電変換素子における熱電半導体材料が電極にめり込んだ状態で接合したものである。第二実施形態に係る熱電変換素子に用いられる熱電半導体材料及び電極の具体例等は第一実施形態に係る熱電変換素子の場合と同様のものが挙げられる。 <Second embodiment>
The thermoelectric conversion element which concerns on 2nd embodiment of this invention is demonstrated using FIG. In the present embodiment, the thermoelectric semiconductor material in the thermoelectric conversion element according to the first embodiment is joined in a state of being embedded in the electrode. Specific examples of the thermoelectric semiconductor material and electrodes used in the thermoelectric conversion element according to the second embodiment include the same as those of the thermoelectric conversion element according to the first embodiment.

図３は、第二実施形態に係る熱電変換素子の電極と熱電半導体材料との接合形態を説明するための図である。ｎ型熱電半導体材料４０とｐ型熱電半導体材料４１とは、電極３０にめり込んだ状態で接合している。また、ｎ型熱電半導体材料４０と電極３１と、及びｐ型熱電半導体材料４１と電極３２と、は半田５１により接合されている。   FIG. 3 is a diagram for explaining a bonding configuration between the electrode of the thermoelectric conversion element according to the second embodiment and the thermoelectric semiconductor material. The n-type thermoelectric semiconductor material 40 and the p-type thermoelectric semiconductor material 41 are joined in a state of being embedded in the electrode 30. Further, the n-type thermoelectric semiconductor material 40 and the electrode 31, and the p-type thermoelectric semiconductor material 41 and the electrode 32 are joined by solder 51.

第二実施形態に係る熱電変換素子は、多孔性金属材料である発泡金属からなる電極３０と熱電半導体材料（ｎ型熱電半導体材料４０及びｐ型熱電半導体材料４１）とを圧着して接合する工程を経て製造できる。圧着して接合する場合、加熱して電極と熱電半導体材料とを拡散接合してもよい。拡散接合を実施可能な装置としては、例えば、電気炉等が挙げられる。拡散接合の処理条件は、電極及び熱電半導体材料の組み合わせにより適宜決定される。   The thermoelectric conversion element according to the second embodiment is a process in which an electrode 30 made of foam metal, which is a porous metal material, and a thermoelectric semiconductor material (n-type thermoelectric semiconductor material 40 and p-type thermoelectric semiconductor material 41) are bonded by pressure bonding. Can be manufactured through. When bonding by pressure bonding, the electrode and the thermoelectric semiconductor material may be diffusion bonded by heating. An apparatus that can perform diffusion bonding includes, for example, an electric furnace. The processing conditions for diffusion bonding are appropriately determined depending on the combination of the electrode and the thermoelectric semiconductor material.

発泡金属は軟らかいため、圧力をかけることで熱電半導体材料を発泡金属にめり込ませることができる。そのため、高さばらつきのある熱電半導体材料を用いたとしてもこのばらつきを隠蔽することが可能となり、熱電変換素子の高さばらつきを減少させることができる。   Since the foam metal is soft, the thermoelectric semiconductor material can be embedded in the foam metal by applying pressure. Therefore, even if a thermoelectric semiconductor material having a variation in height is used, this variation can be concealed, and the variation in height of the thermoelectric conversion element can be reduced.

第二実施形態に係る熱電変換素子においては、ｎ型熱電半導体材料４０と電極３１と、及びｐ型熱電半導体材料４１と電極３２と、を半田５１により接合したが、熱電半導体材料が電極にめり込んだ状態で接合していてもよい。   In the thermoelectric conversion element according to the second embodiment, the n-type thermoelectric semiconductor material 40 and the electrode 31, and the p-type thermoelectric semiconductor material 41 and the electrode 32 are joined by the solder 51. However, the thermoelectric semiconductor material is embedded in the electrode. You may join in the state.

また、第二実施形態に係る熱電変換素子は、ｎ型熱電半導体材料４０又はｐ型熱電半導体材料４１が電極３０に設けられた凹部に嵌合した状態で接合する態様であってもよい。この態様は、例えば、あらかじめ電極３０にｎ型熱電半導体材料４０及びｐ型熱電半導体材料４１と嵌合可能な凹部を設けておき（凹部を形成する工程）、該凹部にｎ型熱電半導体材料４０及びｐ型熱電半導体材料４１を嵌合する（熱電半導体材料を嵌合する工程）ことにより実施可能である。熱電半導体材料を電極に嵌合する際、熱電半導体材料と電極とを拡散接合してもよい。該凹部はエッチング等の化学的処理により形成可能である。
なお、第二実施形態に係る熱電変換素子においては、熱電半導体材料が電極の凹部に接触して接合していればよく、熱電半導体材料が電極の凹部に嵌合した状態で接合した態様又は電極にめり込んだ状態で接合した態様に限られない。 In addition, the thermoelectric conversion element according to the second embodiment may be an embodiment in which the n-type thermoelectric semiconductor material 40 or the p-type thermoelectric semiconductor material 41 is joined in a state of being fitted in a recess provided in the electrode 30. In this embodiment, for example, a recess that can be fitted with the n-type thermoelectric semiconductor material 40 and the p-type thermoelectric semiconductor material 41 is provided in advance in the electrode 30 (step of forming the recess), and the n-type thermoelectric semiconductor material 40 is formed in the recess. And p-type thermoelectric semiconductor material 41 is fitted (step of fitting thermoelectric semiconductor material). When the thermoelectric semiconductor material is fitted to the electrode, the thermoelectric semiconductor material and the electrode may be diffusion bonded. The recess can be formed by chemical treatment such as etching.
In addition, in the thermoelectric conversion element which concerns on 2nd embodiment, the thermoelectric semiconductor material should just be contacting and joined to the recessed part of an electrode, and the aspect or electrode which joined the thermoelectric semiconductor material in the state fitted to the recessed part of the electrode It is not restricted to the aspect joined in the state where it was embedded.

以上、ｐ型熱電半導体材料及びｎ型熱電半導体材料を複数対備えた本発明の熱電変換素子について説明したが、本発明はｐ型熱電半導体材料及びｎ型熱電半導体材料を一対（単数対）備えた熱電変換素子に対しても適応可能である。   The thermoelectric conversion element according to the present invention including a plurality of pairs of p-type thermoelectric semiconductor materials and n-type thermoelectric semiconductor materials has been described above, but the present invention includes a pair (single pair) of p-type thermoelectric semiconductor materials and n-type thermoelectric semiconductor materials. It can also be applied to thermoelectric conversion elements.

以下、本発明の熱電変換素子及びその製造方法について、実施例に基づきさらに詳細に説明するが、本発明は下記実施例により限定されるものではない。   Hereinafter, although the thermoelectric conversion element of this invention and its manufacturing method are demonstrated in detail based on an Example, this invention is not limited by the following Example.

ｐ型熱電半導体材料４１としてクラスレート化合物の一種であるＢａ8Ｇａ18Ｇｅ28を、ｎ型熱電半導体材料４０としてクラスレート化合物の一種であるＢａ8Ｇａ15Ｇｅ31を用い、図４に示す熱電変換素子を作製して発泡金属を電極に用いた場合の効果を確認した。 The p-type thermoelectric semiconductor material 41 is Ba 8 Ga 18 Ge 28 which is a kind of clathrate compound, and the n-type thermoelectric semiconductor material 40 is Ba 8 Ga 15 Ge 31 which is a kind of clathrate compound. The effect at the time of producing a conversion element and using a metal foam for an electrode was confirmed.

＜熱電半導体材料の製造＞
原材料として、Ｂａ、Ｇａ及びＧｅを用いて、これらをＢａ8Ｇａ18Ｇｅ28及びＢａ8Ｇａ15Ｇｅ31の仕込み組成となるように秤量し、アルゴン雰囲気下でアーク溶解を行うことによりＢａ8Ｇａ18Ｇｅ28及びＢａ8Ｇａ15Ｇｅ31を得た。 <Manufacture of thermoelectric semiconductor materials>
Ba, Ga, and Ge are used as raw materials, and these are weighed so as to have a charged composition of Ba 8 Ga 18 Ge 28 and Ba 8 Ga 15 Ge 31 , and arc melting is performed in an argon atmosphere to perform Ba 8 Ga. 18 Ge 28 and Ba 8 Ga 15 Ge 31 were obtained.

得られたＢａ8Ｇａ18Ｇｅ28及びＢａ8Ｇａ15Ｇｅ31を乳鉢で粉砕後、放電プラズマ焼結装置で焼結して熱電半導体材料を得た。得られた熱電半導体材料を４ｍｍ×４ｍｍ×４ｍｍに切断して測定試料に供した。 The obtained Ba 8 Ga 18 Ge 28 and Ba 8 Ga 15 Ge 31 were pulverized in a mortar and then sintered in a discharge plasma sintering apparatus to obtain a thermoelectric semiconductor material. The obtained thermoelectric semiconductor material was cut into 4 mm × 4 mm × 4 mm and used as a measurement sample.

得られた測定試料と電極とを拡散接合して図４に示す熱電変換素子を得た。電極としては、銅箔（気孔率０％）及び気孔率が５０％、７０％、８０％、９０％又は９５％の銅製の発泡金属を用いた。拡散接合には電気炉を用い、拡散接合の条件は、圧力２０ＭＰａ、温度７００℃、接合時間６０分とした。なお、電極の厚みは１０００μｍとした。   The obtained measurement sample and the electrode were diffusion bonded to obtain the thermoelectric conversion element shown in FIG. As the electrodes, copper foil (porosity 0%) and copper foam metal having a porosity of 50%, 70%, 80%, 90% or 95% were used. An electric furnace was used for diffusion bonding, and the conditions for diffusion bonding were a pressure of 20 MPa, a temperature of 700 ° C., and a bonding time of 60 minutes. The electrode thickness was 1000 μm.

＜高さばらつきの検討＞
図４に示す熱電変換素子を１０個作製し、各素子の高さ（図４参照）をマイクロメータで測定した。１０個の熱電変換素子のうち、一番高い熱電変換素子の高さと一番低い熱電変換素子の高さとの差を高さばらつきとした。図５に高さばらつきと気孔率との関係を示す。なお、電極として銅箔を用いた場合の高さばらつきは１００μｍであった。電極に銅箔を用いた場合と比較して、発泡金属を電極として用いた熱電変換素子の高さばらつきは小さいことがわかる。 <Examination of height variation>
Ten thermoelectric conversion elements shown in FIG. 4 were produced, and the height of each element (see FIG. 4) was measured with a micrometer. Among the ten thermoelectric conversion elements, the difference between the height of the highest thermoelectric conversion element and the height of the lowest thermoelectric conversion element was defined as height variation. FIG. 5 shows the relationship between the height variation and the porosity. In addition, the height dispersion | variation at the time of using copper foil as an electrode was 100 micrometers. It can be seen that the variation in height of thermoelectric conversion elements using foam metal as an electrode is small compared to the case where copper foil is used for the electrode.

＜線膨張係数の検討＞
図６に線膨張係数と気孔率との関係を示す。銅箔の線膨張係数は１９×１０-6／℃であった。なお、Ｂａ8Ｇａ18Ｇｅ28及びＢａ8Ｇａ15Ｇｅ31の線膨張係数は、約１４×１０-6／℃である。また、熱電変換素子作製中のクラスレート化合物の割れの発生の数を数えたところ、電極として銅箔を用いた場合１０個（全数）、気孔率５０％の電極を用いた場合１個、気孔率７０％の電極を用いた場合０個、気孔率８０％の電極を用いた場合０個、気孔率９０％の電極を用いた場合０個、気孔率９５％の電極を用いた場合０個の割れが発生した。 <Examination of linear expansion coefficient>
FIG. 6 shows the relationship between the linear expansion coefficient and the porosity. The linear expansion coefficient of the copper foil was 19 × 10 −6 / ° C. The linear expansion coefficients of Ba 8 Ga 18 Ge 28 and Ba 8 Ga 15 Ge 31 are about 14 × 10 −6 / ° C. Further, when the number of occurrences of cracking of the clathrate compound during the production of the thermoelectric conversion element was counted, it was 10 when the copper foil was used as the electrode (total number), and 1 when the electrode having a porosity of 50% was used. 0 when 70% porosity is used, 0 when 80% porosity is used, 0 when 90% porosity is used, 0 when 95% porosity is used Cracking occurred.

拡散接合は高温高圧下で実施されるため、熱電半導体材料には熱電変換素子の発電時と同様な熱応力がかかる。電極に銅箔を用いた場合と比較して、発泡金属を電極として用いた熱電変換素子の割れの発生が減少した。   Since diffusion bonding is performed under high temperature and high pressure, the thermoelectric semiconductor material is subjected to thermal stress similar to that during power generation of the thermoelectric conversion element. Compared with the case where copper foil was used for the electrode, the occurrence of cracks in the thermoelectric conversion element using the foam metal as the electrode was reduced.

本発明の熱電変換素子の第一実施形態を示す斜視図である。It is a perspective view which shows 1st embodiment of the thermoelectric conversion element of this invention. 第一実施形態に係る熱電変換素子の電極と熱電半導体材料との接合形態を説明するための図である。It is a figure for demonstrating the joining form of the electrode of the thermoelectric conversion element which concerns on 1st embodiment, and a thermoelectric-semiconductor material. 第二実施形態に係る熱電変換素子の電極と熱電半導体材料との接合形態を説明するための図である。It is a figure for demonstrating the joining form of the electrode of the thermoelectric conversion element which concerns on 2nd embodiment, and a thermoelectric-semiconductor material. 実施例に供された熱電変換素子の構造を説明するための図である。It is a figure for demonstrating the structure of the thermoelectric conversion element provided to the Example. 熱電変換素子の高さばらつきと電極の気孔率との関係を示す図である。It is a figure which shows the relationship between the height variation of a thermoelectric conversion element, and the porosity of an electrode. 電極の線膨張係数と電極の気孔率との関係を示す図である。It is a figure which shows the relationship between the linear expansion coefficient of an electrode, and the porosity of an electrode.

符号の説明Explanation of symbols

１０ 熱電変換素子
２０ 低温側基板
２１ 高温側基板
３０，３１，３２ 電極
４０ ｎ型熱電半導体材料
４１ ｐ型熱電半導体材料
５０ ろう材
５１ 半田 DESCRIPTION OF SYMBOLS 10 Thermoelectric conversion element 20 Low temperature side substrate 21 High temperature side substrate 30, 31, 32 Electrode 40 N-type thermoelectric semiconductor material 41 P-type thermoelectric semiconductor material 50 Brazing material 51 Solder

Claims (8)

ｐ型熱電半導体材料及びｎ型熱電半導体材料の単数又は複数対を、多孔性金属材料からなる電極で接合した熱電変換素子。   A thermoelectric conversion element in which one or a plurality of pairs of a p-type thermoelectric semiconductor material and an n-type thermoelectric semiconductor material are joined by an electrode made of a porous metal material. 前記熱電半導体材料の少なくとも一つが、前記電極の凹部に接触して接合した請求項１に記載の熱電変換素子。   The thermoelectric conversion element according to claim 1, wherein at least one of the thermoelectric semiconductor materials is in contact with and joined to the concave portion of the electrode. 前記熱電半導体材料の少なくとも一つが、前記電極の凹部に嵌合した状態で接合した請求項１に記載の熱電変換素子。   The thermoelectric conversion element according to claim 1, wherein at least one of the thermoelectric semiconductor materials is joined in a state of being fitted in the recess of the electrode. 前記熱電半導体材料の少なくとも一つが、前記電極にめり込んだ状態で接合した請求項１に記載の熱電変換素子。   The thermoelectric conversion element according to claim 1, wherein at least one of the thermoelectric semiconductor materials is bonded to the electrode while being embedded. 前記多孔性金属材料が、発泡金属である請求項１乃至４のいずれか１項に記載の熱電変換素子。   The thermoelectric conversion element according to claim 1, wherein the porous metal material is a foam metal. 多孔性金属材料からなる電極と熱電半導体材料とを圧着して接合する工程を含む熱電変換素子の製造方法。   A method for manufacturing a thermoelectric conversion element, comprising a step of pressing and joining an electrode made of a porous metal material and a thermoelectric semiconductor material. 多孔性金属材料からなる電極に凹部を形成する工程と、前記電極の凹部に熱電半導体材料を嵌合する工程と、を含む熱電変換素子の製造方法。   A method for manufacturing a thermoelectric conversion element, comprising: forming a recess in an electrode made of a porous metal material; and fitting a thermoelectric semiconductor material into the recess of the electrode. 前記多孔性金属材料が、発泡金属である請求項６又は７に記載の熱電変換素子の製造方法。   The method for manufacturing a thermoelectric conversion element according to claim 6 or 7, wherein the porous metal material is a foam metal.
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