JP4373296B2 - Raw material for thermoelectric conversion material, method for producing thermoelectric conversion material, and thermoelectric conversion material - Google Patents
Raw material for thermoelectric conversion material, method for producing thermoelectric conversion material, and thermoelectric conversion material Download PDFInfo
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- 239000000463 material Substances 0.000 title claims description 68
- 238000006243 chemical reaction Methods 0.000 title claims description 65
- 239000002994 raw material Substances 0.000 title claims description 24
- 238000004519 manufacturing process Methods 0.000 title claims description 10
- 239000000843 powder Substances 0.000 claims description 36
- 239000011812 mixed powder Substances 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 6
- 238000002156 mixing Methods 0.000 claims description 3
- 238000005245 sintering Methods 0.000 description 15
- 238000011156 evaluation Methods 0.000 description 7
- 239000002245 particle Substances 0.000 description 7
- 239000012071 phase Substances 0.000 description 7
- 229910007657 ZnSb Inorganic materials 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 5
- 238000010298 pulverizing process Methods 0.000 description 3
- 239000007790 solid phase Substances 0.000 description 3
- 238000003746 solid phase reaction Methods 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000001192 hot extrusion Methods 0.000 description 2
- 229910000765 intermetallic Inorganic materials 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 239000004570 mortar (masonry) Substances 0.000 description 2
- 238000005096 rolling process Methods 0.000 description 2
- 239000010409 thin film Substances 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000000280 densification Methods 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 238000000227 grinding Methods 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 239000011164 primary particle Substances 0.000 description 1
- 238000007712 rapid solidification Methods 0.000 description 1
- 238000010671 solid-state reaction Methods 0.000 description 1
- 238000001778 solid-state sintering Methods 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
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本発明は、Ｚｎ−Ｓｂ系焼結体からなる熱電変換材料の成形に用いる熱電変換材料用原料、およびＺｎ−Ｓｂ系焼結体からなる熱電変換材料の製造方法、ならびにＺｎ−Ｓｂ系焼結体からなる熱電変換材料に関する。 The present invention relates to a raw material for a thermoelectric conversion material used for forming a thermoelectric conversion material comprising a Zn-Sb-based sintered body, a method for producing a thermoelectric conversion material comprising a Zn-Sb-based sintered body, and Zn-Sb-based sintering. The present invention relates to a thermoelectric conversion material comprising a body.
自動車、各種プラント、ゴミ焼却設備などから発生する排熱を直接電気に変換する熱電変換技術は次代の省エネルギー技術として注目されている。そのため、さまざまな熱電変換材料が検討されている。その中でも、トータル的に大量の排熱を発生している自動車の排熱利用に関しては、２００〜３００℃において１０％程度の熱電変換効率を示す熱電変換材料が求められ、この温度領域で優れた熱電変換性能を有するＺｎ−Ｓｂ系の金属間化合物からなる熱電変換材料が検討されている。 Thermoelectric conversion technology that directly converts exhaust heat generated from automobiles, various plants, garbage incinerators, etc. into electricity has attracted attention as the next-generation energy-saving technology. Therefore, various thermoelectric conversion materials are being studied. Among them, regarding the exhaust heat utilization of automobiles that generate a large amount of exhaust heat, a thermoelectric conversion material having a thermoelectric conversion efficiency of about 10% at 200 to 300 ° C. is required, and excellent in this temperature range. Thermoelectric conversion materials made of Zn-Sb-based intermetallic compounds having thermoelectric conversion performance have been studied.
Ｚｎ−Ｓｂ系金属間化合物としては、ＺｎＳｂ、Ｚｎ３Ｓｂ２、Ｚｎ４Ｓｂ３の３種類があるが、ＺｎＳｂおよびＺｎ４Ｓｂ３は常温安定相であり、Ｚｎ３Ｓｂ２は高温安定相である。常温安定相であるＺｎＳｂとＺｎ４Ｓｂ３を比較した場合、抵抗率およびゼーベック係数ともＺｎＳｂが大きく、下記のように定義されるパワーファクターに関してもＺｎＳｂの方が高い値を示すが、熱伝導率が２倍も大きいために、熱電性能は逆にＺｎ４Ｓｂ３の方が高い値を示す。そのため、Ｚｎ４Ｓｂ３からなる熱電変換材料が提案されている。 The ZnSb based intermetallic compound, ZnSb, there are three kinds of Zn 3 Sb 2, Zn 4 Sb 3, ZnSb and Zn 4 Sb 3 is a normal temperature stable phase, Zn 3 Sb 2 at a high temperature stable phase is there. When ZnSb and Zn 4 Sb 3 which are stable at room temperature are compared, both the resistivity and the Seebeck coefficient are large, and the power factor defined as follows shows that ZnSb has a higher value. Is twice as large, and the thermoelectric performance of Zn 4 Sb 3 is higher than that of Zn 4 Sb 3 . Therefore, a thermoelectric conversion material made of Zn 4 Sb 3 has been proposed.
たとえば特許文献１は、Ｚｎ粉末とＳｂ粉末を溶解して製造したβ−Ｚｎ４Ｓｂ３溶製材を粉砕して得られる粉末を分級して混合し、次いで加熱・加圧することにより成形してなる、粒径２０μｍ未満の微細単結晶粒を１次粒子とし、粒径２０μｍ未満の不定形粒が緊密に充填された粒径１００μｍから粒径２００μｍの多結晶粒の間を、粒径２０μｍ未満の微細単結晶粒が充填された微細構造を有する焼結体からなる熱電変換材料を提案している。この特許文献１の図１０によれば、この熱電変換材料は２００〜３００℃、すなわち４７３〜５７３Ｋにおいて０．８４〜１．２４程度の高い無次元性能指数（ＺＴ）を有することが示されている。ちなみに無次元性能指数（ＺＴ）とは、下記の式で示される性能指数（Ｚ）に温度を乗じて無次元化した値であり、Ｚが大であるほど高性能であることを示す。
Ｚ＝α２σ／κ（Ｋ−１）
この式において、α：ゼーベック係数（Ｖ／Ｋ）、σ：電気伝導度（Ｓ／ｍ）、κ：熱伝導率（Ｗ／ｍＫ）、Ｋ：絶対温度である。また、α２σの項はパワーファクターと呼ばれ、熱電変換材料の性能の目安として用いられる。
For example, Patent Document 1 is formed by classifying and mixing powder obtained by pulverizing β-Zn 4 Sb 3 ingot produced by dissolving Zn powder and Sb powder, and then heating and pressurizing to form. A fine single crystal grain having a particle size of less than 20 μm is used as a primary particle, and an amorphous particle having a particle size of less than 20 μm is intimately packed between a polycrystalline particle having a particle size of 100 μm to 200 μm and having a particle size of less than 20 μm. A thermoelectric conversion material composed of a sintered body having a fine structure filled with fine single crystal grains has been proposed. According to FIG. 10 of this patent document 1, this thermoelectric conversion material is shown to have a high dimensionless figure of merit (ZT) of about 0.84 to 1.24 at 200 to 300 ° C., that is, 473 to 573 K. Yes. Incidentally, the dimensionless figure of merit (ZT) is a value obtained by multiplying the figure of merit (Z) represented by the following formula by the temperature, and the higher the Z, the higher the performance.
Z = α 2 σ / κ (K −1 )
In this equation, α: Seebeck coefficient (V / K), σ: electrical conductivity (S / m), κ: thermal conductivity (W / mK), and K: absolute temperature. The term α 2 σ is called a power factor and is used as a measure of the performance of the thermoelectric conversion material.
また特許文献２は、β−Ｚｎ４Ｓｂ３粉末を加圧焼結してβ−Ｚｎ４Ｓｂ３焼結体を製造する際に不可避的に発生する残留応力を低減して、クラックが存在しない機械的強度の大きなβ−Ｚｎ４Ｓｂ３焼結体とその製造方法を提案している。すなわち、所定の比率で混合したＺｎ粉末とＳｂ粉末を真空中で４００〜５００℃で固相反応させて得られるβ−Ｚｎ４Ｓｂ３とし、次いで５０〜１００ＭＰａの圧力を負荷して４５０〜５００℃で焼結緻密化処理し、処理終了後に温度が焼結温度の９５％に達する前に圧力を解法することにより、β−Ｚｎ４Ｓｂ３焼結体を得るものである。この焼結体は、室温において抵抗率：２〜３×１０−５Ωｍ、ゼーベック係数：１２０μＶ／Ｋ、熱伝導率：０．９２Ｗ／ｍＫ）の熱電特性を有することが示されている。 The Patent Document 2 is to reduce the inevitably occurring residual stress in producing the β-Zn 4 Sb 3 powder to pressure sintering the β-Zn 4 Sb 3 sintered body, not a crack is present A β-Zn 4 Sb 3 sintered body having high mechanical strength and a method for producing the same have been proposed. That is, β-Zn 4 Sb 3 obtained by subjecting Zn powder and Sb powder mixed at a predetermined ratio to a solid phase reaction in a vacuum at 400 to 500 ° C., and then applying a pressure of 50 to 100 MPa to 450 to 500 A β-Zn 4 Sb 3 sintered body is obtained by carrying out a sintering densification treatment at 0 ° C. and solving the pressure before the temperature reaches 95% of the sintering temperature after the treatment is completed. This sintered body is shown to have thermoelectric properties of resistivity: 2-3 × 10 −5 Ωm, Seebeck coefficient: 120 μV / K, thermal conductivity: 0.92 W / mK) at room temperature.
一方、Ｚｎ３Ｓｂ２は電気抵抗が小さく電気伝導性に優れているが、高温安定相であるので、常温で得られにくく、そのためＺｎ３Ｓｂ２を焼結して熱電変換材料として用いる試みはなされていない。
本発明は、高い無次元性能指数（ＺＴ）を有する熱電変換材料に用いる原料、高い無次元性能指数（ＺＴ）を有する熱電変換材料の製造方法、および高い無次元性能指数（ＺＴ）を有する熱電変換材料を提供することを目的とする。 The present invention relates to a raw material used for a thermoelectric conversion material having a high dimensionless figure of merit (ZT), a method for producing a thermoelectric conversion material having a high dimensionless figure of merit (ZT), and a thermoelectric having a high dimensionless figure of merit (ZT). The object is to provide a conversion material.
上記課題を解決するために種々研究の結果、本発明の発明者等は、ＺｎとＳｂを加熱溶解した後、急冷凝固させることにより高温安定相のＺｎ３Ｓｂ２を低温で固相焼結し、固相反応により常温安定相であるβ−Ｚｎ４Ｓｂ３が生成してＺｎ３Ｓｂ２とβ−Ｚｎ４Ｓｂ３とからなる焼結体が得られ、この焼結体がＺｎ３Ｓｂ２の優れた電気伝導性と、Ｚｎ４Ｓｂ３の高いゼーベック係数と低い熱伝導度を兼ね備えることにより、高い無次元性能指数（ＺＴ）を有することを見出した。 As a result of various studies to solve the above-mentioned problems, the inventors of the present invention solidified and sintered Zn 3 Sb 2 as a high-temperature stable phase at a low temperature by heating and dissolving Zn and Sb and then rapidly solidifying them. Then, β-Zn 4 Sb 3, which is a room temperature stable phase, is generated by a solid phase reaction to obtain a sintered body made of Zn 3 Sb 2 and β-Zn 4 Sb 3, and this sintered body is Zn 3 Sb 2. It has been found that it has a high dimensionless figure of merit (ZT) by combining the excellent electrical conductivity of the above, the high Seebeck coefficient of Zn 4 Sb 3 and the low thermal conductivity.
即ち、上記課題を解決する本発明の熱電変換材料用原料は、Ｚｎ粉末とＳｂ粉末をモル比で３対２の割合で配合してなる混合粉末を不活性雰囲気中で溶解し、次いで急冷凝固させて得られるＺｎ３Ｓｂ２からなることを特徴とするものである（請求項１）、または
Ｚｎ粉末とＳｂ粉末をモル比で３対２の割合で配合し、さらにＳｂ粉末を０．５〜５％添加してなる混合粉末を不活性雰囲気中で溶解し、次いで急冷凝固させて得られるＺｎ３Ｓｂ２からなることを特徴とする熱電変換材料用原料（請求項２）である。
That is, the raw material for thermoelectric conversion material of the present invention that solves the above-mentioned problems is obtained by dissolving a mixed powder composed of Zn powder and Sb powder in a molar ratio of 3 to 2 in an inert atmosphere, and then rapidly solidifying. Zn 3 Sb 2 obtained by processing (Claim 1), or Zn powder and Sb powder are blended at a molar ratio of 3 to 2, and Sb powder is further added to 0.5 A raw material for a thermoelectric conversion material comprising Zn 3 Sb 2 obtained by dissolving a mixed powder obtained by adding ˜5% in an inert atmosphere and then rapidly solidifying it by solidification (Claim 2).
また、本発明の熱電変換材料の製造方法は、上記（請求項１または２）の熱電変換材料用原料を粉末化して圧粉成形し、圧粉成形した圧粉体を２５０〜３５０℃の温度範囲で仮焼結し、仮焼結した仮焼結体を３００〜４５０℃の温度範囲で熱間押出成形すること（請求項３）を特徴とし、さらに
上記（請求項３）の熱電変換材料の製造方法において、仮焼結体を３００〜３５０℃の温度範囲で熱間押出成形すること（請求項４）を特徴とする。
Moreover, the manufacturing method of the thermoelectric conversion material of this invention pulverizes the raw material for thermoelectric conversion materials of the said (Claim 1 or 2), it compacts, and the green compact formed by compacting is the temperature of 250-350 degreeC. Characterized in that it is pre-sintered in a range, and the pre-sintered pre-sintered body is hot-extruded in a temperature range of 300 to 450 ° C. (Claim 3), In this manufacturing method, the temporary sintered body is hot-extruded in a temperature range of 300 to 350 ° C. (Claim 4).
またさらに、本発明の熱電変換材料は、Ｚｎ３Ｓｂ２とβ−Ｚｎ４Ｓｂ３とからなる焼結体で構成される熱電変換材料（請求項５）であり、
上記（請求項５）の熱電変換材料において、前記焼結体が４０〜８０％のＺｎ３Ｓｂ２と２０〜６０％のβ−Ｚｎ４Ｓｂ３とからなる焼結体であること（請求項６）を特徴とする。
また本発明の熱電変換材料は、上記（請求項５または６）の熱電変換材料において、上記（請求項１または２）の熱電変換材料用原料粉末、および上記（請求項３または４）の熱電変換材料の製造方法を用いて製造してなること（請求項７）を特徴とする。
Furthermore, the thermoelectric conversion material of the present invention is a thermoelectric conversion material (Claim 5) composed of a sintered body composed of Zn 3 Sb 2 and β-Zn 4 Sb 3 ,
In the thermoelectric conversion material of the above (Claim 5), the sintered body is a sintered body composed of 40 to 80% Zn 3 Sb 2 and 20 to 60% β-Zn 4 Sb 3 (Claim). 6).
The thermoelectric conversion material of the present invention is the thermoelectric conversion material of the above (Claim 5 or 6), the raw material powder for the thermoelectric conversion material of (Claim 1 or 2), and the thermoelectric conversion material of (Claim 3 or 4). It is manufactured using the manufacturing method of the conversion material (Claim 7).
本発明の熱電変換材料用原料は、従来高温安定相であるため常温で得られにくく、電気伝導性に優れているが熱電変換材料用原料として用いられてなかったＺｎ３Ｓｂ２を、常温でも安定して保持することができ、熱電変換材料用原料とすることができる。また、本発明の熱電変換材料は、一定比率で配合したＺｎとＳｎを加熱溶解した後に急冷凝固して得られる本発明の熱電変換材料用Ｚｎ３Ｓｂ２を粉末化して圧粉して焼結し、焼結の際に固相反応によりＺｎ３Ｓｂ２中にβ−Ｚｎ４Ｓｂ３を生成させることによる、Ｚｎ３Ｓｂ２とβ−Ｚｎ４Ｓｂ３とからなる焼結体で構成される。この焼結体はＺｎ３Ｓｂ２の優れた電気伝導性と、Ｚｎ４Ｓｂ３の高いゼーベック係数と低い熱伝導度を兼ね備えており、１．２５〜１．４０の高い無次元性能指数（ＺＴ）を有している。そのため、本発明の熱電変換材料は高い熱電変換性能を有する熱電変換材料として、極めて好適に適用することができる。 The raw material for thermoelectric conversion material of the present invention is Zn 3 Sb 2 which has not been used as a raw material for thermoelectric conversion material, although it is difficult to obtain at normal temperature because it is a high-temperature stable phase and has not been used as a raw material for thermoelectric conversion material. It can be stably held and can be used as a raw material for a thermoelectric conversion material. Further, the thermoelectric conversion material of the present invention is prepared by powderizing and compacting and sintering Zn 3 Sb 2 for thermoelectric conversion material of the present invention obtained by rapidly solidifying Zn and Sn blended at a constant ratio after heating and melting. and, due to the fact that to produce a β-Zn 4 Sb 3 in Zn 3 Sb 2 by solid state reaction during sintering, and a sintered body consisting of Zn 3 Sb 2 and the β-Zn 4 Sb 3 Metropolitan . This sintered body combines the excellent electrical conductivity of Zn 3 Sb 2 with the high Seebeck coefficient and low thermal conductivity of Zn 4 Sb 3 , and a high dimensionless figure of merit (ZT) of 1.25 to 1.40. )have. Therefore, the thermoelectric conversion material of the present invention can be very suitably applied as a thermoelectric conversion material having high thermoelectric conversion performance.
以下、本発明を詳細に説明する。本発明の熱電変換材料はＺｎ３Ｓｂ２を粉末化して圧粉し焼結して得られるが、上記のように、本発明の熱電変換材料に用いる原材料であるＺｎ３Ｓｂ２は高温安定相であるので、安定な溶融状態から急冷凝固させることにより固相状態でも安定なＺｎ３Ｓｂ２を生成させることができる。すなわち、Ｚｎ粉末とＳｂ粉末をモル比で３対２の比率で配合した混合粉をＡｒなどの不活性雰囲気中で６００℃以上に加熱して溶解させた後、単ロール法を用いて急冷凝固させてリボン状のＺｎ３Ｓｂ２からなる原材料を得る。このようにして得られるリボン状のＺｎ３Ｓｂ２をボールミルなどを用いて微粉砕し、篩分けして粒度を揃えることが好ましい。このようにして得られるＺｎ３Ｓｂ２粉末を金型に入れ５〜１０Ｇｐａの圧力を負荷して加圧し、圧粉体に成形する。次いで圧粉成形体をＡｒなどの不活性雰囲気中で液相が生じない２５０〜３５０℃に加熱して固相焼結する。このように低温で固相焼結させることにより、Ｚｎ３Ｓｂ２中に均一なβ−Ｚｎ４Ｓｂ３が生成する。このβ−Ｚｎ４Ｓｂ３の生成量を調整して、高い無次元性能指数（ＺＴ）を有する仮焼結体を得る。その後仮焼結体を３００〜４５０℃の温度、好ましくは３００〜３５０℃の温度で熱間押出成形して最終形状に成形するとともに本焼結を行い、高強度の熱電変換材料とする。低温における固相焼結を行わず、Ｚｎ３Ｓｂ２粉末を直接熱間押出成形して最終形状に成形すると、均一なβ−Ｚｎ４Ｓｂ３が生成せず、高い無次元性能指数（ＺＴ）が得られない。 Hereinafter, the present invention will be described in detail. The thermoelectric conversion material of the present invention is obtained by pulverizing, compacting and sintering Zn 3 Sb 2. As described above, Zn 3 Sb 2 which is a raw material used for the thermoelectric conversion material of the present invention is a high-temperature stable phase. Therefore, stable Zn 3 Sb 2 can be generated even in the solid phase by rapid solidification from a stable molten state. That is, a mixed powder in which Zn powder and Sb powder are mixed at a molar ratio of 3 to 2 is dissolved by heating to 600 ° C. or higher in an inert atmosphere such as Ar, and then rapidly solidified using a single roll method. Thus, a raw material made of ribbon-like Zn 3 Sb 2 is obtained. The ribbon-like Zn 3 Sb 2 thus obtained is preferably finely pulverized using a ball mill or the like and sieved to make the particle sizes uniform. The Zn 3 Sb 2 powder thus obtained is placed in a mold and pressed under a pressure of 5 to 10 Gpa to form a green compact. Next, the green compact is heated to 250 to 350 ° C. in a liquid phase in an inert atmosphere such as Ar and solid phase sintered. By thus solid-phase sintering at a low temperature, uniform β-Zn 4 Sb 3 is produced in Zn 3 Sb 2 . By adjusting the amount of β-Zn 4 Sb 3 produced, a temporary sintered body having a high dimensionless figure of merit (ZT) is obtained. Thereafter, the temporary sintered body is hot-extruded at a temperature of 300 to 450 ° C., preferably 300 to 350 ° C., and formed into a final shape and subjected to main sintering to obtain a high-strength thermoelectric conversion material. When solid-state sintering at low temperature is not performed and the Zn 3 Sb 2 powder is directly hot-extruded and formed into a final shape, uniform β-Zn 4 Sb 3 is not generated, and a high dimensionless figure of merit (ZT) Cannot be obtained.
このようにして得られる本発明の熱電変換材料は、Ｚｎ３Ｓｂ２とβ−Ｚｎ４Ｓｂ３とからなる焼結体で構成されるが、特に４０〜８０％のＺｎ３Ｓｂ２と２０〜６０％のβ−Ｚｎ４Ｓｂ３とからなる組成比の焼結体で構成されている場合に高い無次元性能指数（ＺＴ）が発現する。焼結体中のＺｎ３Ｓｂ２の含有量が４０％未満であるある場合はβ−Ｚｎ４Ｓｂ３の増加にともなって電気抵抗率が高い値になり、８０％を超えるとゼーベック係数が低い値となり、好ましくない。焼結体中のＺｎ３Ｓｂ２とβ−Ｚｎ４Ｓｂ３の組成比は、仮焼結温度およびで熱間押出温度（本焼結温度）で制御することができる。すなわち、これらの焼結温度が低い場合はＺｎ３Ｓｂ２含有量が多くなり、焼結温度が高い場合はβ−Ｚｎ４Ｓｂ３含有量が多くなる。また、Ｚｎ粉とＳｂ粉をモル比で３対２の比率で配合した混合粉にさらに微調整しながらＳｂ粉末を０．５〜５％追加配合すると、β−Ｚｎ４Ｓｂ３含有量が増加する温度が高温側に移動するので、β−Ｚｎ４Ｓｂ３含有量が増加する温度以下のより高温で焼結してもβ−Ｚｎ４Ｓｂ３生成が抑制され、安定した組成比が得られやすくなるので好ましい。なお、Ｚｎ３Ｓｂ２とβ−Ｚｎ４Ｓｂ３の組成比はＸ線回折法を用いて測定することができる。さらに、本発明の熱電変換材料に用いる原材料粉末であるＺｎ粉末およびＳｂ粉末の純度は、熱電変換性能上および経済上の見地からそれぞれ９９〜９９．９９％程度の純度のものを用いることが好ましく、９９〜９９．９％程度の純度のものを用いることよりが好ましい。９９．９９％を超える純度のものを用いても熱電変換性能は向上しないか、むしろ熱電変換性能は劣化する。また、高純度材は極めて高価であるので、経済的にも有利でなくなる。９９％未満の程度のものを用いた場合は、高い無次元性能指数（ＺＴ）が得られない。 The thermoelectric conversion material of the present invention thus obtained is composed of a sintered body composed of Zn 3 Sb 2 and β-Zn 4 Sb 3, and in particular 40 to 80% Zn 3 Sb 2 and 20 to 20%. A high dimensionless figure of merit (ZT) is exhibited when it is composed of a sintered body having a composition ratio of 60% β-Zn 4 Sb 3 . When the content of Zn 3 Sb 2 in the sintered body is less than 40%, the electrical resistivity increases as β-Zn 4 Sb 3 increases, and when it exceeds 80%, the Seebeck coefficient is low. Value, which is not preferable. The composition ratio of Zn 3 Sb 2 and β-Zn 4 Sb 3 in the sintered body can be controlled by the preliminary sintering temperature and the hot extrusion temperature (main sintering temperature). That is, when these sintering temperatures are low, the Zn 3 Sb 2 content increases, and when the sintering temperature is high, the β-Zn 4 Sb 3 content increases. In addition, when Sb powder is added in an additional amount of 0.5 to 5% while finely adjusting to a mixed powder in which Zn powder and Sb powder are mixed at a molar ratio of 3 to 2, the content of β-Zn 4 Sb 3 increases. Therefore, even if sintering is performed at a higher temperature below the temperature at which the content of β-Zn 4 Sb 3 increases, β-Zn 4 Sb 3 formation is suppressed, and a stable composition ratio is obtained. Since it becomes easy, it is preferable. Note that the composition ratio of Zn 3 Sb 2 and β-Zn 4 Sb 3 can be measured using an X-ray diffraction method. Furthermore, the purity of the Zn powder and Sb powder, which are raw material powders used in the thermoelectric conversion material of the present invention, is preferably about 99 to 99.99% from the viewpoint of thermoelectric conversion performance and economy. It is preferable to use one having a purity of about 99 to 99.9%. Even if a material having a purity exceeding 99.99% is used, the thermoelectric conversion performance does not improve, or rather, the thermoelectric conversion performance deteriorates. Moreover, since a high purity material is very expensive, it is not economically advantageous. When a material having a degree of less than 99% is used, a high dimensionless figure of merit (ZT) cannot be obtained.
以下、実施例を示して本発明をさらに詳細に説明する。
［原料粉末の作成］
表１に示す純度のＺｎ粉末およびＳｂ粉末を表１に示す割合で配合して混合し、６１０℃に加熱して溶解した後、単ロール法を用いて急冷凝固させてリボン状のＺｎ３Ｓｂ２薄膜からなる原材料を得た。このリボン状のＺｎ３Ｓｂ２薄膜を自動乳鉢に装填して磨り潰して微粉化し、熱電特性評価用の供試材作成に用いる原材料粉末とした（試料番号１〜１０、１２）。比較のため、Ｚｎ粉末およびＳｂ粉末を表１に示す割合で配合して混合し、６１０℃に加熱して溶解した後、徐冷して得られたインゴットを粉砕し、次いで自動乳鉢に装填して磨り潰して微粉化し、比較用の熱電特性評価用のβ−Ｚｎ４Ｓｂ３のみからなる供試材作成に用いる原材料粉末とした（試料番号１１）。
Hereinafter, the present invention will be described in more detail with reference to examples.
[Creation of raw material powder]
Zn powder and Sb powder having the purity shown in Table 1 are blended and mixed in the proportions shown in Table 1, and dissolved by heating to 610 ° C., and then rapidly solidified using a single roll method to form ribbon-like Zn 3 Sb. A raw material consisting of two thin films was obtained. This ribbon-like Zn 3 Sb 2 thin film was loaded into an automatic mortar, ground and pulverized, and used as raw material powders used for preparing test materials for thermoelectric property evaluation (sample numbers 1 to 10 and 12). For comparison, Zn powder and Sb powder were blended in the proportions shown in Table 1, mixed and heated to 610 ° C. to dissolve, and then the ingot obtained by gradual cooling was pulverized and then loaded into an automatic mortar. By grinding and pulverizing, a raw material powder used for preparing a test material consisting only of β-Zn 4 Sb 3 for thermoelectric property evaluation for comparison was obtained (sample number 11).
［熱電特性評価用供試材の作成］
このようにして得られた原材料粉末を、表１に示す条件で加圧して圧粉成形体を作成し、次いで表１に示す条件で加熱して仮焼結体を得た。次いで表１に示す条件で熱間押出成形して２０ｍｍ×３ｍｍ×３ｍｍの熱電特性評価用供試材を得た（試料番号１〜１１）。比較のため、原材料粉末を圧粉して仮焼結することなく、直接熱間押出成形した同寸法の熱電特性評価用供試材（試料番号１２）も作成した。これらの各供試材のＺｎ３Ｓｂ２とβ−Ｚｎ４Ｓｂ３の組成比は、Ｘ線回折法を用いて測定した。
[Create test material for thermoelectric property evaluation]
The raw material powder thus obtained was pressed under the conditions shown in Table 1 to prepare a green compact, and then heated under the conditions shown in Table 1 to obtain a temporary sintered body. Next, hot extrusion molding was performed under the conditions shown in Table 1 to obtain test materials for thermoelectric property evaluation of 20 mm × 3 mm × 3 mm (sample numbers 1 to 11). For comparison, a test material for thermoelectric property evaluation (sample No. 12) of the same size directly hot-extruded without pressing the raw material powder and pre-sintering was also prepared. The composition ratio of Zn 3 Sb 2 and β-Zn 4 Sb 3 in each of these test materials was measured using an X-ray diffraction method.
［熱電特性評価］
上記のようにして作成した表１示す試料番号１〜１２の供試材の熱電特性を、表２に示す各項目について２６０℃の下で測定し評価した。結果を表２に示す。
[Thermoelectric property evaluation]
The thermoelectric properties of the test materials of sample numbers 1 to 12 shown in Table 1 prepared as described above were measured and evaluated at 260 ° C. for each item shown in Table 2. The results are shown in Table 2.
表２に示すように、本発明の熱電特性評価用供試材の２６０℃における無次元性能指数（ＺＴ）は１．２５〜１．４０であり、極めて高い値を示している。 As shown in Table 2, the dimensionless figure of merit (ZT) at 260 ° C. of the test material for thermoelectric property evaluation of the present invention is 1.25 to 1.40, indicating a very high value.
本発明の熱電変換材料はＺｎ３Ｓｂ２の優れた電気伝導性と、Ｚｎ４Ｓｂ３の高いゼーベック係数と低い熱伝導度を兼ね備えており、１．２５〜１．４０の高い無次元性能指数（ＺＴ）を有している。そのため、本発明の熱電変換材料は高い熱電変換性能を有する安価な熱電変換材料として、好適に適用することができる。 The thermoelectric conversion material of the present invention combines the excellent electrical conductivity of Zn 3 Sb 2 with the high Seebeck coefficient and low thermal conductivity of Zn 4 Sb 3 , and a high dimensionless performance index of 1.25 to 1.40. (ZT). Therefore, the thermoelectric conversion material of the present invention can be suitably applied as an inexpensive thermoelectric conversion material having high thermoelectric conversion performance.
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