JP5175571B2 - Method for manufacturing thermoelectric conversion element - Google Patents
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- 238000004519 manufacturing process Methods 0.000 title claims description 36
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- 229910052714 tellurium Inorganic materials 0.000 description 2
- PORWMNRCUJJQNO-UHFFFAOYSA-N tellurium atom Chemical compound [Te] PORWMNRCUJJQNO-UHFFFAOYSA-N 0.000 description 2
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Description
本発明は、産業炉、自動車等の廃熱から電気エネルギーを直接取り出すことが可能な発電モジュールに用いられる酸化物熱電変換素子の製造方法に関する。 The present invention relates to a method for manufacturing an oxide thermoelectric conversion element used in a power generation module that can directly extract electrical energy from waste heat of an industrial furnace, an automobile, or the like.
従来からゼーベック効果を利用して熱電変換素子に温度差を付けて電気エネルギーを取り出す技術はよく知られている。熱電変換素子に用いられる材料としては、ビスマス・テルル系、鉛・テルル系あるいはシリコン・ゲルマニウム系などの金属系材料があるが、金属系材料は稀少元素であることや毒性の強い環境負荷物質を含むこと、高温大気中で使用する場合に酸化が生じたり成分元素の融解が生じたりすることなどの問題から、高温環境下では酸化物系材料を用いた方が好ましいとされている。このような酸化物系熱電変換素子材料としては、ＣａＣｏ系酸化物が高いゼーベック効果を有することから有望視されている（例えば、特許文献１、特許文献２参照）。
2. Description of the Related Art Conventionally, a technique for extracting electric energy by applying a temperature difference to a thermoelectric conversion element using the Seebeck effect is well known. The materials used for thermoelectric conversion elements include metallic materials such as bismuth / tellurium, lead / tellurium, or silicon / germanium. However, metallic materials are rare elements and highly toxic environmentally hazardous substances. In view of problems such as inclusion and the occurrence of oxidation or melting of component elements when used in a high-temperature atmosphere, it is preferable to use an oxide-based material in a high-temperature environment. As such oxide-based thermoelectric conversion element materials, CaCo-based oxides are considered promising because they have a high Seebeck effect (see, for example,
しかし、このＣａＣｏ系酸化物は、結晶が鱗片状であることから結晶方位に異方性があり、ａ軸及びｂ軸により構成される面（ａｂ面）方向の電気伝導度がｃ軸方向より高いために、選択的にａｂ面方向に通電するように素子を形成する必要がある。 However, this CaCo-based oxide has an anisotropy in crystal orientation because the crystals are scaly, and the electric conductivity in the plane (ab plane) direction constituted by the a-axis and b-axis is higher than that in the c-axis direction. Therefore, it is necessary to form an element so as to selectively energize in the ab plane direction.
このような場合、その製造にあたって従来は加圧焼結法が用いられていた。加圧焼結法は、ホットプレス、ホットホージングなどによって素子を焼結するときに一軸加圧して配向度を高める方法である。 In such a case, a pressure sintering method has been conventionally used in the production thereof. The pressure sintering method is a method of increasing the degree of orientation by uniaxial pressing when a device is sintered by hot pressing, hot hosing or the like.
また、異方性の問題を解決するために、酸化物系セラミック材料である原料粉末を結合剤及び可塑剤と混合した後、ドクターブレード法などでシート状に成型することで原料粉末の配向性を高める方法も提案されている（例えば、特許文献３、特許文献４参照）。その他、セラミック成型体を押出成型にて製造する方法も知られており、酸化物熱電変換素子を押出成型により作成する方法も提示されている（例えば、特許文献１、特許文献２参照）。
In order to solve the problem of anisotropy, the raw material powder, which is an oxide-based ceramic material, is mixed with a binder and a plasticizer, and then molded into a sheet shape by the doctor blade method, etc. There has also been proposed a method for enhancing the above (for example, see
上記したように、異方性のある酸化物系材料については加圧焼結法により配向度を高める方法が用いられてきたが、加圧焼結法は作製処理がバッチ式のため、素子として使用するためには焼結後のバルク体を少なくとも２軸方向に精密切断する必要があり、素子の大量生産が困難であるという問題があった。 As described above, methods for increasing the degree of orientation by the pressure sintering method have been used for anisotropic oxide-based materials. However, since the pressure sintering method is a batch process, In order to use it, it is necessary to precisely cut the bulk body after sintering in at least two axial directions, and there is a problem that mass production of elements is difficult.
また、ドクターブレード法などでシート状に成型することで原料粉末の配向性を高める方法では、シートの厚さを厚くすることが困難であるという制限があり、やはり素子化する際に２軸方向に精密切断をする必要があることから素子の大量生産が困難であるという問題があった。 In addition, the method of increasing the orientation of the raw material powder by molding into a sheet shape by the doctor blade method or the like has a limitation that it is difficult to increase the thickness of the sheet. In addition, there is a problem that it is difficult to mass-produce elements because it is necessary to perform precision cutting.
さらに、熱電変換素子材料を押出成型により製造する方法においては、現在適切な押出条件が把握できていないという問題がある。 Furthermore, in the method of manufacturing a thermoelectric conversion element material by extrusion molding, there is a problem that appropriate extrusion conditions cannot be grasped at present.
本発明は上記のような課題を解決するためになされたもので、高性能の酸化物熱電変換素子を安定して大量に製造することができる押出成型に関する方法を提供するものである。 The present invention has been made to solve the above-described problems, and provides a method related to extrusion molding capable of stably producing a high-performance oxide thermoelectric conversion element in large quantities.
この目的を達成するために本発明の熱電変換素子の製造方法の第１の態様は、熱電変換素子を形成するための原料粉末を結合剤、可塑剤とともに混合した後混練して混和物とし、当該混和物を押出機を用いて所定の形状に押し出して押出成型体を作成し、その後押出成型体を乾燥した後焼結して焼結成型体とし、焼結成型体を所定の長さに切り分け、モジュール化して熱電変換素子を製造する方法において、原料粉末１００重量部に対して結合剤を３〜１５重量部、可塑剤を１０〜３５重量部混合し、かつ結合剤と可塑剤の合計が原料粉末１００重量部に対して４０重量部以下とした混和物を押し出すことによって円筒状の押出成型体を作成する際に、押出機出口での押出圧力を２〜１０ＭＰａとし、その後円筒状の押出成型体を自然乾燥して２．０〜２．５×１０ −４ Ｗ／ｍＫ ２ の出力因子（ここで、出力因子はゼーベック係数をα、抵抗率をρとするとα ２ ／ρで表される値）を有するようにすることを特徴とする。 In order to achieve this object, the first aspect of the method for producing a thermoelectric conversion element of the present invention is to mix a raw material powder for forming a thermoelectric conversion element together with a binder and a plasticizer, and then knead to obtain an admixture. The mixture is extruded into a predetermined shape using an extruder to produce an extruded molded body, and then the extruded molded body is dried and then sintered to form a sintered molded body. In the method of manufacturing the thermoelectric conversion element by cutting and modularizing, 3 to 15 parts by weight of the binder and 10 to 35 parts by weight of the plasticizer are mixed with 100 parts by weight of the raw material powder, and the total of the binder and the plasticizer When extruding a mixture of 40 parts by weight or less with respect to 100 parts by weight of the raw material powder to produce a cylindrical extrusion molded body, the extrusion pressure at the exit of the extruder is 2 to 10 MPa, and then cylindrical Naturally dry the extruded product (Here, the power factor is the Seebeck coefficient alpha, the resistivity value expressed by When ρ α 2 / ρ) 2.0~2.5 output factor × 10 -4 W / mK 2 to have a It is characterized by doing.
さらに本発明の熱電変換素子の製造方法の第２の態様は、第１の態様において、原料粉末は平均粒径が０．５〜１０μｍであることを特徴とする。 Furthermore, the 2nd aspect of the manufacturing method of the thermoelectric conversion element of this invention is the 1st aspect. WHEREIN: The raw material powder is 0.5-10 micrometers in average particle diameter, It is characterized by the above-mentioned.
また本発明の熱電変換素子の製造方法の第３の態様は、第２の態様において、原料粉末は平均粒径が２〜６μｍであることを特徴とする。 Moreover, the 3rd aspect of the manufacturing method of the thermoelectric conversion element of this invention is a 2nd aspect. WHEREIN: Raw material powder is 2-6 micrometers in average particle diameter, It is characterized by the above-mentioned.
さらに本発明の熱電変換素子の製造方法の第４の態様は、第１から第３の態様において、原料粉末は平均アスペクト比が５〜１００であることを特徴とする。 Furthermore, the 4th aspect of the manufacturing method of the thermoelectric conversion element of this invention is the 1st-3rd aspect, The raw material powder is 5-100 in average aspect ratio, It is characterized by the above-mentioned.
また本発明の熱電変換素子の製造方法の第５の態様は、第４の態様において、原料粉末は平均アスペクト比が１０〜５０であることを特徴とする。 Moreover, the 5th aspect of the manufacturing method of the thermoelectric conversion element of this invention is a 4th aspect. WHEREIN: The average aspect-ratio of raw material powder is 10-50, It is characterized by the above-mentioned.
さらに本発明の熱電変換素子の製造方法の第６の態様は、第１から第５の態様において、原料粉末がＣａ3-XＡXＣｏ4Ｏ9（ただし、ＡはＢｉ、Ｓｒ、Ｍｇ、Ｇｄ、Ｙ、Ｋ、Ｎａから選ばれた１種または２種、Ｘは０＜Ｘ≦０．６）であることを特徴とする。 Furthermore, a sixth aspect of the method for producing a thermoelectric conversion element of the present invention is the first to fifth aspects, wherein the raw material powder is Ca 3−X A X Co 4 O 9 (where A is Bi, Sr, Mg, One or two selected from Gd, Y, K, and Na, and X is 0 <X ≦ 0.6).
また本発明の熱電変換素子の製造方法の第７の態様は、第１から第６の態様において、焼結成型体の配向度が５０％以上であることを特徴とする。 A seventh aspect of the method for producing a thermoelectric conversion element of the present invention is characterized in that, in the first to sixth aspects, the degree of orientation of the sintered molded body is 50% or more.
さらに本発明の熱電変換素子の製造方法の第８の態様は、第１から第７の態様において、熱電変換素子の抵抗率が８５０℃において１２ｍΩ・ｃｍ以下であることを特徴とする。 Furthermore, an eighth aspect of the method for producing a thermoelectric conversion element of the present invention is characterized in that, in the first to seventh aspects, the resistivity of the thermoelectric conversion element is 12 mΩ · cm or less at 850 ° C.
本発明の熱電変換素子の製造方法によれば、焼結後に高い配向度を有する焼結成型体を安定して大量に製造することができ、優れた特性を示す熱電変換素子を提供することができる。 According to the method for manufacturing a thermoelectric conversion element of the present invention, a sintered compact having a high degree of orientation after sintering can be stably manufactured in large quantities, and a thermoelectric conversion element having excellent characteristics can be provided. it can.
以下、本発明の熱電変換素子の製造方法の好ましい実施の形態について図面を用いて説明する。 Hereinafter, preferred embodiments of a method for producing a thermoelectric conversion element of the present invention will be described with reference to the drawings.
図１は本発明の熱電変換素子の製造方法を説明するフロー図である。図１において、本発明の熱電変換素子の製造方法は、まず第１工程において熱電変換素子を形成するための原料粉末を準備する。 FIG. 1 is a flowchart illustrating a method for manufacturing a thermoelectric conversion element of the present invention. In FIG. 1, the manufacturing method of the thermoelectric conversion element of this invention prepares the raw material powder for forming a thermoelectric conversion element in a 1st process first.
原料粉末の平均粒径はできるだけ揃っていることが望ましいが、０．５〜１０μｍの範囲にあることが好ましい。平均粒径が０．５μｍ未満では押し出し時の圧力を適正に調整しても所望の配向度が得られず、また分散性も悪くなり後述する混和物の粘度が著しく高くなり押し出し性が悪くなるからである。一方、平均粒径が１０μｍを超えると配向の乱れが大きくなり、得られる成型体に含まれる気孔が多くなることによって熱電変換特性が低下する。 The average particle size of the raw material powder is preferably as uniform as possible, but is preferably in the range of 0.5 to 10 μm. If the average particle size is less than 0.5 μm, the desired degree of orientation cannot be obtained even if the pressure at the time of extrusion is properly adjusted, the dispersibility also deteriorates, and the viscosity of the admixture described later becomes remarkably high and the extrudability deteriorates. Because. On the other hand, when the average particle diameter exceeds 10 μm, the disorder of the orientation becomes large, and the thermoelectric conversion characteristics are deteriorated by increasing the number of pores contained in the obtained molded body.
なお、平均粒径が０．５μｍ未満の粉末や１０μｍを超える粉末が多く混在すると、粒径の小さい粉末がスクリューによる押し出しの渦の中心に集まりやすくなり、結果として成型体の中心部に気孔が残ったり、また密度の不均一によって焼結時に割れが生じたりすることからも、平均粒径は０．５〜１０μｍであることが好ましい。特に平均粒径が２〜６μｍの場合は成型体に気孔の含まれる割合が極端に低下し、また密度の均一性も高くなるのでより好ましい。 When many powders with an average particle size of less than 0.5 μm or more than 10 μm are mixed, the powder with a small particle size tends to gather at the center of the vortex of extrusion by a screw, resulting in pores in the center of the molded body. The average particle size is preferably 0.5 to 10 μm because it may remain or crack due to non-uniform density. In particular, when the average particle size is 2 to 6 μm, the proportion of pores contained in the molded body is extremely reduced, and the uniformity of density is also increased, which is more preferable.
さらに、原料粉末は平均アスペクト比が５〜１００であることが好ましい。平均アスペクト比をこの範囲に設定するのも上述した平均粒径の場合と同様であり、平均アスペクト比が５未満では押し出し時の圧力を適正に調整しても配向度の向上が望めず、一方、平均アスペクト比が１００を超えると配向の乱れが大きくなり、得られる成型体に含まれる気孔が多くなるので熱電変換特性が低下する。特に平均アスペクト比が１０〜５０の範囲が成型体の気孔の割合が少なく、密度の均一性も高くなる。 Further, the raw material powder preferably has an average aspect ratio of 5 to 100. Setting the average aspect ratio in this range is the same as in the case of the average particle diameter described above. If the average aspect ratio is less than 5, no improvement in the degree of orientation can be expected even if the pressure during extrusion is adjusted appropriately. If the average aspect ratio exceeds 100, the disorder of the orientation becomes large, and the pores contained in the resulting molded body increase, so that the thermoelectric conversion characteristics deteriorate. In particular, when the average aspect ratio is in the range of 10 to 50, the proportion of pores in the molded body is small, and the density uniformity is also high.
ところで、原料粉末はゼーベック効果の高い酸化物系材料、特にＣａＣｏ系酸化物が好ましい。ＣａＣｏ系酸化物はＣａ3Ｃｏ4Ｏ9を主体とする材料を用いるとよい。ただし、実際にはＣａサイトは数種類の元素から選ばれた１種または２種の元素で置換されていることが好ましく、具体的には、Ｃａ3-XＡXＣｏ4Ｏ9がより好ましい。ここで、ＡはＢｉ、Ｓｒ、Ｍｇ、Ｇｄ、Ｙ、Ｋ、Ｎａから選ばれた１種または２種の元素を表し、またＸは０＜Ｘ≦０．６の範囲にある。Ｘが０．６を超えると熱電変換特性が低下するという不都合があるからである。 By the way, the raw material powder is preferably an oxide-based material having a high Seebeck effect, particularly a CaCo-based oxide. As the CaCo-based oxide, a material mainly composed of Ca 3 Co 4 O 9 may be used. However, in practice, the Ca site is preferably substituted with one or two elements selected from several elements, and more specifically, Ca 3−X A X Co 4 O 9 is more preferable. Here, A represents one or two elements selected from Bi, Sr, Mg, Gd, Y, K, and Na, and X is in the range of 0 <X ≦ 0.6. This is because if X exceeds 0.6, there is a disadvantage that the thermoelectric conversion characteristics deteriorate.
次に第２工程として、原料粉末、結合剤及び可塑剤を混合する。これらの混合には例えば羽付きの高速ミキサーを使用して行う。混合割合は原料粉末１００重量部に対して結合剤を３〜１５重量部、可塑剤を１０〜３５重量部の割合で行うとよい。結合剤の割合が３重量部未満では、押出成型体の強度が低く、連続的な成型が困難であり、結合剤の割合が１５重量部を超えると焼結時に結合剤は揮散するが、その結果として焼結後に気孔が生じ密度が低下することから熱電変換素子の特性が低下するためである。 Next, as a second step, the raw material powder, the binder and the plasticizer are mixed. For example, a high-speed mixer with wings is used for mixing. The mixing ratio may be 3 to 15 parts by weight of the binder and 10 to 35 parts by weight of the plasticizer with respect to 100 parts by weight of the raw material powder. When the proportion of the binder is less than 3 parts by weight, the strength of the extruded molded body is low and continuous molding is difficult. When the proportion of the binder exceeds 15 parts by weight, the binder is volatilized during sintering. As a result, pores are formed after sintering, and the density is lowered, so that the characteristics of the thermoelectric conversion element are lowered.
また、可塑剤の割合が１０重量部未満では、後述する混和物の可塑性が不十分となり、成型体にクラックが発生し、可塑剤の割合が３５重量部を超えるとやはり焼結後気孔が生じ密度が低下することから熱電変換素子の特性が低下するためである。 Further, if the plasticizer ratio is less than 10 parts by weight, the plasticity of the mixture described later becomes insufficient, cracks occur in the molded product, and if the plasticizer ratio exceeds 35 parts by weight, pores after sintering are also generated. This is because the characteristics of the thermoelectric conversion element are lowered because the density is lowered.
基本的には製造の効率化を考慮すると焼結時には結合剤も可塑剤も速やかに分解、揮散することが望まれることから結合剤も可塑剤もできるだけ少ない方がよいが、焼結後の成型体の密度を高く維持し、成型体の形状維持や寸法安定性を図るためには所定の量が必要であることから、これらの点を考慮して結合剤及び可塑剤の割合を決定すればよい。 Basically, considering the efficiency of production, it is desirable that both the binder and the plasticizer be quickly decomposed and volatilized during sintering, so it is better to have as few binder and plasticizer as possible. A predetermined amount is required to maintain a high density of the body and to maintain the shape and dimensional stability of the molded body, so if the ratio of the binder and the plasticizer is determined in consideration of these points Good.
なお、結合剤と可塑剤の合計が原料粉末１００重量部に対して４０重量部以下であると製造効率及び熱電変換特性の双方の観点から極めて優れた熱電変換素子を製造することができる。４０重量部を超えると上記したような結合剤や可塑剤が多く含まれた場合と同様な不都合が生じるからである。 In addition, when the total of the binder and the plasticizer is 40 parts by weight or less with respect to 100 parts by weight of the raw material powder, an extremely excellent thermoelectric conversion element can be manufactured from the viewpoint of both production efficiency and thermoelectric conversion characteristics. This is because when it exceeds 40 parts by weight, the same inconvenience as in the case where many binders and plasticizers as described above are contained occurs.
ここで、結合剤としては、例えばヒドロキシアルキルセルロース、ポリビニルブチラール、アクリル樹脂のようなセラミックスの成型に用いられる既知の物質が使用できる。また、可塑剤は後述するように真空押し出しを行うことから揮発性の高い（蒸気圧の高い）物質の使用は避けるべきであり、基本的には水が好ましい。水を使用する場合は例えばグリセリンなどの保水力のある非水可塑剤を添加することで、押し出し後の乾燥を速やかにし、押出成型体のクラックの発生を抑制する効果が得られる。 Here, as the binder, for example, known substances used for molding ceramics such as hydroxyalkyl cellulose, polyvinyl butyral, and acrylic resin can be used. Moreover, since the plasticizer is vacuum-extruded as described later, the use of a highly volatile (high vapor pressure) substance should be avoided, and water is basically preferable. In the case of using water, for example, by adding a non-aqueous plasticizer having water retention ability such as glycerin, it is possible to quickly dry after extrusion and to suppress the occurrence of cracks in the extruded product.
次いで、第３工程として、第２工程で混合した原料粉末、結合剤及び可塑剤に混練を施し混和物を作成する。そして、第４工程として、押出機に第３工程で作成した混和物を送り込み、所定の押出圧力にて混和物を円筒状に押し出して押出成型体を作成する。この押出圧力は混和物の硬さにも影響されるが、主として押出機のスクリューの回転数を調整することにより押出機の出口において２〜１０ＭＰａの範囲になるようにする。押出圧力が２ＭＰａ未満では十分な熱電変換特性を有するだけの成型体の配向度が得られず、一方１０ＭＰａを超えると押出時の高い圧力が出口において一気に開放されるので、それに伴い圧縮された成型体の外径も増加し、寸法の安定性が損なわれるとともに配向も乱れることから熱電変換特性が低下するためである。 Next, as the third step, the raw material powder, the binder and the plasticizer mixed in the second step are kneaded to create an admixture. And as a 4th process, the mixture created at the 3rd process is sent into an extruder, and a mixture is extruded cylindrically with predetermined extrusion pressure, and an extrusion molding object is created. Although this extrusion pressure is also influenced by the hardness of the mixture, the extrusion pressure is mainly adjusted by adjusting the number of revolutions of the screw of the extruder so that it is in the range of 2 to 10 MPa at the outlet of the extruder. If the extrusion pressure is less than 2 MPa, the degree of orientation of the molded body having sufficient thermoelectric conversion characteristics cannot be obtained. This is because the outer diameter of the body also increases, the dimensional stability is impaired, and the orientation is disturbed, resulting in a decrease in thermoelectric conversion characteristics.
なお、押出速度は特に限定しないが、遅すぎると生産効率が低下し、また速すぎると押出成型体が蛇行したりひびが生じたりすることがあるので、０．５〜５ｍ／ｍｉｎ程度が望ましい。 The extrusion speed is not particularly limited, but if it is too slow, the production efficiency is lowered, and if it is too fast, the extruded molded product may meander or crack, so about 0.5 to 5 m / min is desirable. .
次に、第５工程として、押出成型体に乾燥を施す。この乾燥においては成型体にクラックが生じないようにすることを考慮して自然乾燥させることが好ましい。その後、第６工程として、酸素雰囲気中において所定時間焼結を行い、焼結成型体を作成する。 Next, as a fifth step, the extruded molded body is dried. In this drying, it is preferable to naturally dry in consideration of preventing cracks in the molded body. Thereafter, as a sixth step, sintering is performed for a predetermined time in an oxygen atmosphere to produce a sintered compact.
そして、第７工程として、焼結成型体を所定の長さに切り分けた後、第８工程として、アルミナ基板に電極を付設してこの電極に焼結成型体を配置、接合してモジュール化し熱電変換素子を製造する。 Then, as a seventh step, after the sintered molded body is cut into a predetermined length, as an eighth step, an electrode is attached to the alumina substrate, and the sintered molded body is arranged and joined to this electrode to form a modular thermoelectric device. A conversion element is manufactured.
このようにして製造した熱電変換素子は、高い配向度を有していることから優れた熱電変換特性を示し、高い熱電変換効率を示すようになる。 Since the thermoelectric conversion element manufactured in this way has a high degree of orientation, it exhibits excellent thermoelectric conversion characteristics and high thermoelectric conversion efficiency.
なお、焼結成型体の配向度は高いほど好ましいが、少なくとも５０％は必要である。５０％未満では実用上十分な熱電変換特性を有するとは言い難いためである。 The higher the degree of orientation of the sintered molded body, the better, but at least 50% is necessary. If it is less than 50%, it is difficult to say that the thermoelectric conversion characteristics are practically sufficient.
ここで、本発明における配向度は次のように定義される。即ち、配向度（Ｑ’）は押出成型体を押出方向に垂直に切断し、その断面に対してＸ線回折を行った場合に、特定の結晶面（ＨＫＬ）（例えば（００６）、（００８）、（００１０）等）からのＸ線回折強度の総和と測定されたすべての結晶面（ｈｋｌ）からのＸ線回折強度の総和に対する比率を指標として表したもので、以下の式により算出される。 Here, the degree of orientation in the present invention is defined as follows. That is, the degree of orientation (Q ′) is determined by cutting an extruded product perpendicularly to the extrusion direction and performing X-ray diffraction on the cross section, and a specific crystal plane (HKL) (for example, (006), (008) ), (0010), etc.) and the ratio of the total X-ray diffraction intensity from all measured crystal planes (hkl) to the total X-ray diffraction intensity as an index. The
ここで、ΣＩ（ｈｋｌ）は押出成型体におけるすべての結晶面（ｈｋｌ）からのＸ線回折強度の総和であり、Σ’Ｉ（ＨＫＬ）は押出成型体における特定の結晶面（ＨＫＬ）からのＸ線回折強度の総和である。またΣＩ０（ｈｋｌ）及びΣ’Ｉ０（ＨＫＬ）は、それぞれ押出成型体と同一組成の同一化合物であり、かつ無配向のものについて測定されたすべての結晶面（ｈｋｌ）からのＸ線回折強度の総和、及び特定の結晶面（ＨＫＬ）からのＸ線回折強度の総和である。数１の式に示す配向度Ｑ’の値は、無配向の場合には０％、Ｘ線回折測定における回折面に平行な特定の結晶面（ＨＫＬ）が存在しない場合には１００％となる。
Here, ΣI (hkl) is the sum of X-ray diffraction intensities from all crystal planes (hkl) in the extruded product, and Σ′I (HKL) is from a specific crystal plane (HKL) in the extruded product. This is the sum of the X-ray diffraction intensities. Also, ΣI 0 (hkl) and Σ′I 0 (HKL) are X-ray diffractions from all crystal planes (hkl), which are the same compounds of the same composition as the extrusion-molded product and measured for non-oriented ones. The sum of the intensities and the sum of the X-ray diffraction intensities from a specific crystal plane (HKL). The value of the degree of orientation Q ′ shown in the
また、本発明の製造方法を用いた熱電変換素子の抵抗率は８５０℃において１２ｍΩ・ｃｍ以下であることが好ましい。熱電変換特性を評価する指標としてゼーベック係数があるが、ゼーベック係数は材料によって決定されるために同じ材料ならばほぼ同等のゼーベック係数を示すことになる。従って、同一材料における熱電変換特性の違いを比較するには抵抗率を評価するとよい。例えば本発明に用いるＣａＣｏ系酸化物の場合、鱗片状の結晶の配向が揃うほど（配向度が高くなるほど）抵抗が下がることから、抵抗率が小さければ熱電変換特性が向上し、大きければ熱電変換特性が低下することになる。ここで抵抗率が１２ｍΩ・ｃｍを超えると抵抗が大きくなりすぎ、実用に耐え得るような熱電変換素子を得ることが困難になるからである。 Moreover, it is preferable that the resistivity of the thermoelectric conversion element using the manufacturing method of this invention is 12 mohm * cm or less at 850 degreeC. There is a Seebeck coefficient as an index for evaluating the thermoelectric conversion characteristics. Since the Seebeck coefficient is determined depending on the material, the Seebeck coefficient is almost the same for the same material. Therefore, the resistivity should be evaluated to compare the difference in thermoelectric conversion characteristics of the same material. For example, in the case of the CaCo-based oxide used in the present invention, the resistance decreases as the scale-like crystals are aligned (the higher the degree of orientation), the lower the resistivity, the better the thermoelectric conversion characteristics; The characteristics will deteriorate. This is because if the resistivity exceeds 12 mΩ · cm, the resistance becomes too high, and it becomes difficult to obtain a thermoelectric conversion element that can withstand practical use.
次に、実施例として原料粉末にＣａ2.7Ｂｉ0.3Ｃｏ4Ｏ9を用い、本発明の熱電変換素子の製造方法について押出圧力及びその他のパラメータを変化させて作製した焼結成型体の配向度や抵抗率を比較例とともに示す。
＜実施例１＞
平均粒径５．０μｍ、平均アスペクト比３０の原料粉末１００重量部に対して結合剤１０重量部、可塑剤２５重量部（結合剤＋可塑剤３５重量部）を混合し、押出圧力５．０ＭＰａで押し出した後乾燥、焼結して焼結成型体を作製した。作製した焼結成型体の配向度は６０％、抵抗率は８５０℃で１０．３ｍΩ・ｃｍ、ゼーベック係数は８５０℃で１６０μＶ／Ｋであった。
＜実施例２＞
平均粒径５．０μｍ、平均アスペクト比３０の原料粉末１００重量部に対して結合剤１０重量部、可塑剤２５重量部（結合剤＋可塑剤３５重量部）を混合し、押出圧力２．２ＭＰａで押し出した後乾燥、焼結して焼結成型体を作製した。作製した焼結成型体の配向度は５０％、抵抗率は８５０℃で１１．２ｍΩ・ｃｍ、ゼーベック係数は８５０℃で１６５μＶ／Ｋであった。
＜実施例３＞
平均粒径５．０μｍ、平均アスペクト比３０の原料粉末１００重量部に対して結合剤１０重量部、可塑剤２５重量部（結合剤＋可塑剤３５重量部）を混合し、押出圧力９．０ＭＰａで押し出した後乾燥、焼結して焼結成型体を作製した。作製した焼結成型体の配向度は５９％、抵抗率は８５０℃で１０．２ｍΩ・ｃｍ、ゼーベック係数は８５０℃で１６０μＶ／Ｋであった。
＜実施例４＞
平均粒径８．５μｍ、平均アスペクト比６０の原料粉末１００重量部に対して結合剤１０重量部、可塑剤２５重量部（結合剤＋可塑剤３５重量部）を混合し、押出圧力５．０ＭＰａで押し出した後乾燥、焼結して焼結成型体を作製した。作製した焼結成型体の配向度は５０％、抵抗率は８５０℃で１１．５ｍΩ・ｃｍ、ゼーベック係数は８５０℃で１５５μＶ／Ｋであった。
＜実施例５＞
平均粒径１．３μｍ、平均アスペクト比２０の原料粉末１００重量部に対して結合剤１０重量部、可塑剤２５重量部（結合剤＋可塑剤３５重量部）を混合し、押出圧力９．５ＭＰａで押し出した後乾燥、焼結して焼結成型体を作製した。作製した焼結成型体の配向度は５５％、抵抗率は８５０℃で１０．８ｍΩ・ｃｍ、ゼーベック係数は８５０℃で１６０μＶ／Ｋであった。
＜比較例１＞
平均粒径１．３μｍ、平均アスペクト比２０の原料粉末１００重量部に対して結合剤１０重量部、可塑剤２５重量部（結合剤＋可塑剤３５重量部）を混合し、押出圧力１．０ＭＰａで押し出した後乾燥、焼結して焼結成型体を作製した。作製した焼結成型体の配向度は４０％、抵抗率は８５０℃で１３．２ｍΩ・ｃｍ、ゼーベック係数は８５０℃で１６０μＶ／Ｋであった。
＜比較例２＞
平均粒径１．３μｍ、平均アスペクト比２０の原料粉末１００重量部に対して結合剤１０重量部、可塑剤２５重量部（結合剤＋可塑剤３５重量部）を混合し、押出圧力１２．０ＭＰａで押し出した後乾燥、焼結して焼結成型体を作製した。作製した焼結成型体の配向度は３８％、抵抗率は８５０℃で１３．５ｍΩ・ｃｍ、ゼーベック係数は８５０℃で１６０μＶ／Ｋであった。
＜比較例３＞
平均粒径２．０μｍ、平均アスペクト比３の原料粉末１００重量部に対して結合剤１０重量部、可塑剤２５重量部（結合剤＋可塑剤３５重量部）を混合し、押出圧力３．５ＭＰａで押し出した後乾燥、焼結して焼結成型体を作製した。作製した焼結成型体の配向度は１５％、抵抗率は８５０℃で２３．６ｍΩ・ｃｍ、ゼーベック係数は８５０℃で１６０μＶ／Ｋであった。
＜比較例４＞
平均粒径０．３μｍ、平均アスペクト比６０の原料粉末１００重量部に対して結合剤１０重量部、可塑剤２５重量部（結合剤＋可塑剤３５重量部）を混合し、押出圧力を１５〜２０ＭＰａの間で変化させて押し出した。しかし連続的な押し出しをすることが不可能で押出成型体を作製することができなかった。
＜比較例５＞
平均粒径０．３μｍ、平均アスペクト比６０の原料粉末１００重量部に対して結合剤２０重量部、可塑剤４０重量部（結合剤＋可塑剤６０重量部）を混合し、押出圧力５．０ＭＰａで押し出した後乾燥、焼結して焼結成型体を作製した。作製した焼結成型体の配向度は５５％、抵抗率は８５０℃で１６．３ｍΩ・ｃｍ、ゼーベック係数は８５０℃で１６５μＶ／Ｋであった。
＜比較例６＞
平均粒径２０．０μｍ、平均アスペクト比２０の原料粉末１００重量部に対して結合剤１０重量部、可塑剤２５重量部（結合剤＋可塑剤３５重量部）を混合し、押出圧力２．５ＭＰａで押し出した後乾燥、焼結して焼結成型体を作製した。作製した焼結成型体の配向度は１０％、抵抗率は８５０℃で３０．０ｍΩ・ｃｍ、ゼーベック係数は８５０℃で１５５μＶ／Ｋであった。
＜比較例７＞
平均粒径１．３μｍ、平均アスペクト比１２０の原料粉末１００重量部に対して結合剤１０重量部、可塑剤２５重量部（結合剤＋可塑剤３５重量部）を混合し、押出圧力８．５ＭＰａで押し出した後乾燥、焼結して焼結成型体を作製した。作製した焼結成型体の配向度は４０％、抵抗率は８５０℃で１５．５ｍΩ・ｃｍ、ゼーベック係数は８５０℃で１６０μＶ／Ｋであった。
Next, as an example, the orientation degree of the sintered compact produced by using Ca 2.7 Bi 0.3 Co 4 O 9 as the raw material powder and changing the extrusion pressure and other parameters in the method for producing the thermoelectric conversion element of the present invention The resistivity is shown together with a comparative example.
<Example 1>
10 parts by weight of a binder and 25 parts by weight of a plasticizer (binder + 35 parts by weight of a plasticizer) are mixed with 100 parts by weight of a raw material powder having an average particle size of 5.0 μm and an average aspect ratio of 30, and an extrusion pressure of 5.0 MPa. After extruding, drying and sintering were performed to produce a sintered molded body. The produced sintered compact had an orientation degree of 60%, a resistivity of 10.3 mΩ · cm at 850 ° C., and a Seebeck coefficient of 160 μV / K at 850 ° C.
<Example 2>
10 parts by weight of binder and 25 parts by weight of plasticizer (binder + 35 parts by weight of plasticizer) are mixed with 100 parts by weight of raw material powder having an average particle size of 5.0 μm and an average aspect ratio of 30, and an extrusion pressure of 2.2 MPa. After extruding, drying and sintering were performed to produce a sintered molded body. The produced sintered compact had an orientation degree of 50%, a resistivity of 11.2 mΩ · cm at 850 ° C., and a Seebeck coefficient of 165 μV / K at 850 ° C.
<Example 3>
10 parts by weight of a binder and 25 parts by weight of a plasticizer (binder + 35 parts by weight of a plasticizer) are mixed with 100 parts by weight of a raw material powder having an average particle size of 5.0 μm and an average aspect ratio of 30, and an extrusion pressure of 9.0 MPa. After extruding, drying and sintering were performed to produce a sintered molded body. The produced sintered compact had an orientation degree of 59%, a resistivity of 10.2 mΩ · cm at 850 ° C., and a Seebeck coefficient of 160 μV / K at 850 ° C.
<Example 4>
10 parts by weight of a binder and 25 parts by weight of a plasticizer (binder + 35 parts by weight of a plasticizer) are mixed with 100 parts by weight of a raw material powder having an average particle size of 8.5 μm and an average aspect ratio of 60, and an extrusion pressure of 5.0 MPa. After extruding, drying and sintering were performed to produce a sintered molded body. The produced sintered compact had an orientation degree of 50%, a resistivity of 11.5 mΩ · cm at 850 ° C., and a Seebeck coefficient of 155 μV / K at 850 ° C.
<Example 5>
10 parts by weight of a binder and 25 parts by weight of a plasticizer (binder + 35 parts by weight of a plasticizer) are mixed with 100 parts by weight of a raw material powder having an average particle size of 1.3 μm and an average aspect ratio of 20, and an extrusion pressure of 9.5 MPa. After extruding, drying and sintering were performed to produce a sintered molded body. The produced sintered compact had an orientation degree of 55%, a resistivity of 10.8 mΩ · cm at 850 ° C., and a Seebeck coefficient of 160 μV / K at 850 ° C.
<Comparative Example 1>
10 parts by weight of binder and 25 parts by weight of plasticizer (binder + 35 parts by weight of plasticizer) are mixed with 100 parts by weight of raw material powder having an average particle size of 1.3 μm and an average aspect ratio of 20, and an extrusion pressure of 1.0 MPa. After extruding, drying and sintering were performed to produce a sintered molded body. The produced sintered compact had an orientation degree of 40%, a resistivity of 13.2 mΩ · cm at 850 ° C., and a Seebeck coefficient of 160 μV / K at 850 ° C.
<Comparative example 2>
10 parts by weight of a binder and 25 parts by weight of a plasticizer (binder + 35 parts by weight of a plasticizer) are mixed with 100 parts by weight of a raw material powder having an average particle size of 1.3 μm and an average aspect ratio of 20, and an extrusion pressure of 12.0 MPa. After extruding, drying and sintering were performed to produce a sintered molded body. The produced sintered compact had an orientation degree of 38%, a resistivity of 13.5 mΩ · cm at 850 ° C., and a Seebeck coefficient of 160 μV / K at 850 ° C.
<Comparative Example 3>
10 parts by weight of a binder and 25 parts by weight of a plasticizer (binder + 35 parts by weight of a plasticizer) are mixed with 100 parts by weight of a raw material powder having an average particle size of 2.0 μm and an average aspect ratio of 3, and an extrusion pressure of 3.5 MPa. After extruding, drying and sintering were performed to produce a sintered molded body. The produced sintered compact had an orientation degree of 15%, a resistivity of 23.6 mΩ · cm at 850 ° C., and a Seebeck coefficient of 160 μV / K at 850 ° C.
<Comparative example 4>
10 parts by weight of a binder and 25 parts by weight of a plasticizer (binder + 35 parts by weight of a plasticizer) are mixed with 100 parts by weight of a raw material powder having an average particle size of 0.3 μm and an average aspect ratio of 60, and an extrusion pressure of 15 to Extrusion was performed by changing the pressure between 20 MPa. However, it was impossible to continuously extrude and an extruded product could not be produced.
<Comparative Example 5>
20 parts by weight of a binder and 40 parts by weight of a plasticizer (binder + 60 parts by weight of a plasticizer) are mixed with 100 parts by weight of a raw material powder having an average particle size of 0.3 μm and an average aspect ratio of 60, and an extrusion pressure of 5.0 MPa. After extruding, drying and sintering were performed to produce a sintered molded body. The produced sintered compact had an orientation degree of 55%, a resistivity of 16.3 mΩ · cm at 850 ° C., and a Seebeck coefficient of 165 μV / K at 850 ° C.
<Comparative Example 6>
10 parts by weight of a binder and 25 parts by weight of a plasticizer (binder + 35 parts by weight of a plasticizer) are mixed with 100 parts by weight of a raw material powder having an average particle size of 20.0 μm and an average aspect ratio of 20, and an extrusion pressure of 2.5 MPa. After extruding, drying and sintering were performed to produce a sintered molded body. The degree of orientation of the produced sintered compact was 10%, the resistivity was 30.0 mΩ · cm at 850 ° C., and the Seebeck coefficient was 155 μV / K at 850 ° C.
<Comparative Example 7>
10 parts by weight of a binder and 25 parts by weight of a plasticizer (binder + 35 parts by weight of a plasticizer) are mixed with 100 parts by weight of a raw material powder having an average particle size of 1.3 μm and an average aspect ratio of 120, and an extrusion pressure of 8.5 MPa. After extruding, drying and sintering were performed to produce a sintered molded body. The produced sintered compact had an orientation degree of 40%, a resistivity of 15.5 mΩ · cm at 850 ° C., and a Seebeck coefficient of 160 μV / K at 850 ° C.
以上の各実施例及び各比較例をまとめて表１として示す。 The above Examples and Comparative Examples are collectively shown in Table 1.
上記表１の結果から、本発明の製造方法を用いて作製した焼結成型体はいずれも配向度が５０％以上で、かつ抵抗率も１２ｍΩ・ｃｍ以下の良好な特性を示した。 From the results of Table 1 above, all of the sintered compacts produced using the production method of the present invention exhibited good characteristics with an orientation degree of 50% or more and a resistivity of 12 mΩ · cm or less.
一方、比較例１については押出圧力が低いために十分な配向度が得られなかった。また比較例２については押出圧力が高すぎて押出機の出口で圧力が開放されることにより外径が安定せず、その結果配向度も低い値であった。 On the other hand, in Comparative Example 1, a sufficient degree of orientation was not obtained because the extrusion pressure was low. In Comparative Example 2, the extrusion pressure was too high and the pressure was released at the outlet of the extruder, so that the outer diameter was not stable. As a result, the degree of orientation was also low.
さらに、比較例３については原料粉末のアスペクト比が小さいために極めて低い配向度しか得られず、その結果抵抗率が極めて高い値であった。 Further, in Comparative Example 3, since the aspect ratio of the raw material powder was small, only a very low degree of orientation was obtained, and as a result, the resistivity was a very high value.
比較例４については平均粒径が小さいために分散状態が悪く、押し出しても押出成型体が得られなかった。また、比較例５については比較例４に対して結合剤と可塑剤を増量してみたが、押出は可能であったものの焼結成型体に含まれる気孔が多く、抵抗率も高かった。 In Comparative Example 4, since the average particle size was small, the dispersion state was poor, and an extruded product was not obtained even if extruded. In Comparative Example 5, the amount of binder and plasticizer was increased compared to Comparative Example 4, but although extrusion was possible, there were many pores contained in the sintered molded body and the resistivity was high.
比較例６については平均粒径が大きいために大きな粒子が押し出し時の混和物の流れを阻害することから極めて低い配向度となり、その結果極めて高い抵抗率となった。 In Comparative Example 6, since the average particle size was large, the large particles hindered the flow of the admixture during extrusion, so the degree of orientation was extremely low, and as a result, the resistivity was extremely high.
比較例７については平均アスペクト比が非常に大きく、また結晶の厚みが小さいため押出機のスクリューでの混練で粒子が破壊されたものと考えられ、焼結成型体の中心部分により細かい粒子が確認され、また気孔も多く見られた。その結果配向度も低く、抵抗率も高かった。 In Comparative Example 7, the average aspect ratio is very large and the crystal thickness is small, so it is considered that the particles were destroyed by kneading with the screw of the extruder, and fine particles were confirmed in the central part of the sintered compact. There were also many pores. As a result, the degree of orientation was low and the resistivity was high.
なお、ゼーベック係数は用いる材料によって決定されるので実施例、比較例とも１６０μＶ／Ｋ前後で大きな違いは見られなかった。 In addition, since the Seebeck coefficient is determined by the material to be used, no significant difference was observed between about 160 μV / K in the examples and comparative examples.
以上のように本発明の製造方法を用いれば、配向度が高く、抵抗率の低い焼結成型体を得ることができ、ひいては優れた熱電変換特性を有する熱電変換素子を量産化することが可能である。 As described above, by using the production method of the present invention, a sintered molded body having a high degree of orientation and a low resistivity can be obtained, and thus thermoelectric conversion elements having excellent thermoelectric conversion characteristics can be mass-produced. It is.
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