JP2004119648A - p-TYPE THERMOELECTRIC CONVERSION MATERIAL AND THERMOELECTRIC CONVERSION ELEMENT USING IT - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a p-type thermoelectric conversion material that is high in output factor by using an Fe-V-Al-based compound. <P>SOLUTION: This p-type thermoelectric conversion material contains a compound having the composition expressed by Fe<SB>x</SB>Al<SB>y</SB>V<SB>100-x-y</SB>(wherein, 40≤x≤49 and 26≤y≤40). <P>COPYRIGHT: (C)2004,JPO

Description

（表１）に示すように、Ｆｅ_ｘＡｌ_ｙＶ_{１００−ｘ−ｙ}（ただし、４０≦ｘ≦４９、２６≦ｙ≦４０である）の組成で表される各実施例の熱電変換材料が出力因子の高いｐ型熱電変換材料であるのに対し、各比較例の熱電変換材料は、出力因子が低いか、もしくはｎ型熱電変換材料となってしまっている。特に、比較例１ではＦｅの組成比が大きすぎてＡｌの組成比が小さすぎることからゼーベック係数の絶対値が小さくなり、その結果低い出力因子となってしまっている。逆に、比較例２ではＦｅの組成比が小さすぎてＡｌの組成比が大きすぎることから同様にゼーベック係数の絶対値が小さくなり、その結果低い出力因子となってしまっている。また、比較例３では、Ｆｅの組成比は各実施例と同様であるがＡｌの組成比が小さすぎることにより、ゼーベック係数の絶対値は大きく高い出力因子が得られるものの、ゼーベック係数の符号が負であるｎ型熱電変換材料となってしまっている。
【００４３】
また、各実施例の中でも、実施例５ではＦｅの一部をＣｒで、実施例６ではＡｌの一部をＳｉで、また実施例７ではＦｅの一部をＮｉ、Ａｌの一部をＳｂで夫々置換しており、これによって電気抵抗率が低下して、その結果より高い出力因子が得られている。
【００４４】
【発明の効果】
以上詳述したように、本発明によれば、Ｆｅ−Ｖ−Ａｌ系の化合物を用いて出力因子の高いｐ型熱電変換材料を提供することが出来る。
【図面の簡単な説明】
【図１】本発明の実施形態に係る熱電変換素子の構造を表わす斜視図である。
【図２】本発明の実施形態に係る熱交換器を示す概略断面図である。
【図３】本発明の実施形態に係る熱電変換モジュールを示す概略断面図である。
【符号の説明】
１…熱電変換素子
２、１１…ｐ型素子
３、１２…ｎ型素子
４…電極
５…第１の端子
６…第２の端子
１０…熱電変換モジュール
１３…第１の電極
１４…第２の電極
１５…第１の絶縁性導熱板
１６…第２の絶縁性導熱板
２０…熱交換器
２１…ガス通路
２２…熱交換フィン
２３…外囲器
２４…流路
２５…導入管
２６…排出管[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a p-type thermoelectric conversion material and a thermoelectric conversion element using the same, and more particularly, to a Fe-V-Al-based p-type thermoelectric conversion material and a thermoelectric conversion element using the same.
[0002]
[Prior art]
In recent years, interest in thermoelectric conversion elements using the Peltier effect, which is a Freon-less cooling device, has been increasing due to increasing awareness of global environmental issues. In particular, the cooling of CPUs in personal computers is currently performed using heat pipe cooling fins, cooling fans, etc., but as PCs become smaller and thinner and clock frequencies increase, more aggressive cooling is performed. It is becoming necessary. For this reason, the cooling by the Peltier element has been highlighted.
[0003]
A Peltier element (thermoelectric conversion element) is generally formed by alternately connecting a p-type element including a p-type thermoelectric conversion material and an n-type element including an n-type thermoelectric conversion material in series. At present, most thermoelectric conversion materials used near room temperature use Bi-Te single crystals or polycrystals because of their high efficiency. Among these, when forming an n-type thermoelectric conversion material, Se (selenium) is generally added. In addition, a Pb-Te-based thermoelectric conversion material is used at a temperature higher than room temperature because of its high efficiency.
[0004]
However, Se, Pb (lead), and Te (tellurium) used in these thermoelectric conversion elements are toxic and harmful to the human body, and are not preferable from the viewpoint of global environmental problems. For this reason, harmless alternatives to Bi-Te and Pb-Te materials have been studied.
[0005]
One of the harmless thermoelectric conversion materials replacing the Bi-Te system is an Fe-V-Al system material. For example, an Fe ₂ VAl alloy in which 1/3 of Fe (iron) in the composition of Fe ₃ Al is replaced with V (vanadium) has an L2 ₁ type crystal structure (a Heusler structure, a crystal structure represented by X ₂ YZ). (Intermetallic compounds), exhibiting semiconductor-like electric conduction behavior, and exhibiting a high Seebeck coefficient at room temperature comparable to that of Bi-Te-based materials.
[0006]
Further, the thermoelectric conversion material preferably has a high power factor P (P = α ² / ρ, α is a Seebeck coefficient, and ρ is an electrical resistivity), but is one of Al (aluminum) in the Fe ₂ VAl alloy. The power factor P of a compound in which a part is replaced with Si (silicon) reaches 5.4 × 10 ⁻³ W / mK ² at room temperature, and is comparable to 4 to 5 × 10 ⁻³ W / mK ² of a Bi—Te-based material. (See, for example, Non-Patent Document 1).
[0007]
These Fe-V-Al-based thermoelectric conversion materials having high Seebeck coefficient and output factor are all n-type, and only p-type has a Seebeck coefficient of +80 μV / K or less (for example, See Non-Patent Document 2.).
[0008]
[Non-patent document 1]
Kato Hideaki, and four others, "the effect of Si-substitution on the thermoelectric properties of Heusler-type _Fe 2 VAl alloy", the Japan Institute of Metals Magazine, Institute of the Japan Institute of Metals, 2001, Vol. 65, No. 7, p. 652-656
[0009]
[Non-patent document 2]
Y. Nishino, H .; Kato, and M.S. Kato, "Effect of off-stoichiometry on the transport properties of the Heusler-type Fe2VAL compound, 63, 1st, 3rd, 1991, Physics Review, 63, 1991
[0010]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to provide a p-type thermoelectric conversion material having a high output factor using an Fe-V-Al-based compound.
[0011]
[Means for Solving the Problems]
The present _invention, p-type, characterized by containing a compound having a composition expressed in _{Fe x Al y V 100-x} -y ( provided that 40 ≦ x ≦ 49,26 ≦ y ≦ 40) A thermoelectric conversion material is provided.
[0012]
In the present invention, the compound may have a Heusler structure as a main phase.
[0013]
In the present invention, part of Fe is at least one selected from the group consisting of Ti, Cr, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ag, Hf, Ta, W, Y, and a rare earth element. It may be replaced.
[0014]
In the present invention, a part of Al may be substituted with at least one selected from the group consisting of C, N, Si, P, S, Mg, Ga, Ge, Sn, Sb, In, and Bi.
[0015]
Further, the present invention provides a thermoelectric conversion element in which a p-type element including a p-type thermoelectric conversion material and an n-type element including an n-type thermoelectric conversion material are alternately connected in series. A thermoelectric conversion element characterized by using a material is provided.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
The present inventors have in ternary Fe-V-Al, the result of the examination of thermoelectric performance by producing a number of alloys, Se, without using a Pb and _{Te, Fe x Al y V 100} -x- _y (where 40 ≦ x ≦ 49, 26 ≦ y ≦ 40) A p-type thermoelectric conversion material having excellent performance in a compound having a composition represented by y has been found, and the present invention has been achieved. By forming a thermoelectric conversion material having such a composition, a high Seebeck coefficient exceeding about 90 μV / K can be obtained. In the present invention, it is considered that the valence electron concentration decreases due to the high Al content, and a p-type thermoelectric conversion material having a high Seebeck coefficient can be obtained.
[0017]
In the thermoelectric conversion material according to the embodiment of the present invention having the composition formula _{Fe x Al y V 100-x} -y, the content x of Fe (iron) has a range of about 49 atomic% or less than about 40 atomic% Is preferred. When the iron content is less than about 40 atomic%, the Seebeck coefficient is significantly deteriorated, and when the iron content is more than about 49 atomic%, the material may be an n-type thermoelectric conversion material.
[0018]
_Further, in the thermoelectric conversion material according to the embodiment of the present invention having the composition formula _{Fe x Al y V 100-x} -y, Al content y of (aluminum) is about 40 atomic% or less than about 26 atomic% It is preferable to set the range. If the aluminum content is less than about 26 atomic%, the material may be an n-type thermoelectric conversion material. If the aluminum content is more than about 40 atomic%, the Seebeck coefficient may be deteriorated.
[0019]
In the embodiment of the present invention, it is particularly preferable that the thermoelectric conversion material has a Heusler structure as a main phase. By using a Heusler structure as a main phase, a high Seebeck coefficient can be obtained. Here, the main phase refers to a phase having the largest volume occupancy among the crystalline phase and the amorphous phase constituting the thermoelectric conversion material. The proportion of the main phase is preferably at least about 50% by volume, more preferably at least about 70% by volume, most preferably at least about 90% by volume.
[0020]
Fe _x Al _y In the thermoelectric conversion material according to the embodiment of the present invention having the composition formula of V _100-x-y, a portion of Fe (iron), Ti, Cr, Co, Ni, Cu, Zn, Zr , Nb, Mo, Ag, Hf, Ta, W, Y and at least one selected from the group consisting of rare earth elements. Since the electronic structure and the carrier concentration are optimized by such substitution, the Seebeck coefficient can be increased, the electric resistivity can be reduced, and the output factor can be increased. However, the substitution of such an element is preferably about 20 atomic% or less based on the total amount of iron and the substitution element. Excessive substitution exceeding about 20 atomic% may cause a decrease in the output factor due to a decrease in the Seebeck coefficient. In addition, as an element that replaces part of iron, Ti, Cr, Ni, Zr, Nb, Mo, Ta, W, and the like are particularly preferable from the viewpoint of optimization of carrier concentration and raw material cost.
[0021]
_Further, Fe _x Al in the thermoelectric conversion material according to the embodiment of the present invention having a _{y V 100-x-y} composition formula, a part of Al (aluminum), C, N, Si, P, S, Mg , Ga, Ge, Sn, Sb, In, and Bi. Since the electronic structure and the carrier concentration are optimized by such substitution, the Seebeck coefficient can be increased, the electric resistivity can be reduced, the output factor can be increased, and the thermal conductivity can be reduced. However, the substitution of such elements is preferably not more than about 20 atomic% with respect to the total amount of aluminum and the substitution elements. Excessive substitution exceeding about 20 atomic% may cause a decrease in the output factor due to a decrease in the Seebeck coefficient. In addition, Sn, Sb, In, Bi, and the like are particularly preferable as the element that substitutes for part of aluminum because the effect of reducing the thermal conductivity is high.
[0022]
The thermoelectric conversion material according to the embodiment of the present invention can be manufactured, for example, by the following method.
[0023]
First, an alloy containing a predetermined amount of each element is prepared by arc melting, high frequency melting, or the like. In producing the alloy, a liquid quenching method such as a single roll method, a twin roll method, a rotating disk method, a gas atomizing method, or a method utilizing a solid phase reaction such as a mechanical alloying method may be employed. Methods such as the liquid quenching method and the mechanical alloying method are advantageous in that the crystal phase constituting the alloy is refined and the solid solution region of the element in the crystal phase is expanded. Therefore, it is effective in reducing the thermal conductivity, increasing the Seebeck coefficient, and the like.
[0024]
The produced alloy may be subjected to a heat treatment as needed. By this heat treatment, the alloy can be made into a single phase, the crystal grain size can be controlled, and the thermoelectric properties can be further improved.
[0025]
The steps of melting, liquid quenching, mechanical alloying, and heat treatment as described above are preferably performed in an inert atmosphere such as Ar from the viewpoint of preventing the oxidation of the alloy.
[0026]
Next, the alloy is pulverized by a ball mill, a brown mill, a stamp mill, or the like to obtain an alloy powder, and the alloy powder is integrally formed by a sintering method, a hot press method, an SPS method, or the like. The integral molding is preferably performed in an inert atmosphere such as Ar from the viewpoint of preventing the oxidation of the alloy. Next, the obtained molded body is processed into a desired size, whereby a p-type element including the p-type thermoelectric conversion material according to the embodiment of the present invention is obtained. The shape and dimensions of the molded body can be appropriately selected according to the purpose of use and the like. For example, it can have a cylindrical shape with an outer diameter of about 0.5 to 10 mmφ and a thickness of about 1 to 30 mm, or a rectangular parallelepiped shape of about 0.5 to 10 mm × 0.5 to 10 mm × 1 to 30 mm.
[0027]
Using the thermoelectric conversion material thus obtained, a thermoelectric conversion element according to an embodiment of the present invention can be manufactured. FIG. 1 shows a perspective view of one example.
[0028]
The thermoelectric conversion element 1 shown in FIG. 1 is one in which a p-type element 2 and an n-type element 3 are alternately connected in series by an electrode 4. When this thermoelectric conversion element 1 is used as a Peltier element, one of the surfaces on which the electrodes 4 are formed is applied with a voltage between the first terminal 5 and the second terminal 6 so that one of the surfaces has a high temperature side. The other surface is on the low temperature side, and the low temperature surface can be cooled by contacting the heating element. When the thermoelectric conversion element 1 is used as a Seebeck element, one of the surfaces on which the electrodes 4 are formed is brought into contact with a high-temperature substance or the like, and the other is brought into contact with a low-temperature substance or the like. By doing so, power can be extracted from between the first terminal 5 and the second terminal 6.
[0029]
Further, a thermoelectric conversion module (Seebeck element) can be formed using the thermoelectric conversion material according to the embodiment of the present invention, and a heat exchanger using the same can be manufactured. FIG. 2 is a schematic sectional view of such a heat exchanger, and FIG. 3 is a schematic sectional view of a thermoelectric conversion module portion in the heat exchanger.
[0030]
The heat exchanger 20 of FIG. 2 has a high temperature side and a low temperature side as described later, and has a configuration in which the thermoelectric conversion module 10 is incorporated so as to be in contact with the high temperature side and the low temperature side.
[0031]
This heat exchanger 20 has a gas passage 21 in the center, and a number of heat exchange fins 22 are installed around the gas passage 21. The thermoelectric conversion module 10 is provided in contact with the heat exchange fins 22. The thermoelectric conversion module 10 is surrounded by the envelope 23 together with the heat exchange fins 22, and a space between the envelope 23 and the thermoelectric conversion module 10 for cooling, such as water, from the introduction pipe 25 to the discharge pipe 26. It becomes a flow path 24 for the substance.
[0032]
In the heat exchanger 20, high-temperature exhaust gas from, for example, a refuse incinerator is introduced into the gas passage 21, while cooling water is introduced into the flow path 24 through an introduction pipe 25. The heat of the high-temperature gas is removed by the heat exchange fins 22 and heats the water flowing in the flow path 24. As a result, the water is taken out from the discharge pipe 26 as warm water. At this time, the surface of the thermoelectric conversion module 10 on the side of the flow path 24 is on the low temperature side due to the water flowing in the flow path 24, and the surface on the side of the gas flow path 21 is on the high temperature side due to the high temperature exhaust gas flowing in the gas passage 21. It becomes. Therefore, electric power corresponding to the temperature difference is extracted from the thermoelectric conversion module 10 by the Seebeck effect.
[0033]
As shown in FIG. 3, the thermoelectric conversion module 10 in the heat exchanger shown in FIG. 2 includes a plurality of p-type elements 11 having a p-type thermoelectric conversion material and a plurality of n-type elements having an n-type thermoelectric conversion material. 12 are alternately arranged, and the first electrode 13 and the second electrode 14 are connected so that the adjacent p-type element 11 and n-type element 12 are all arranged in series. Specifically, the first electrode 13 connects the adjacent p-type element 11 and n-type element 12 on the upper surface in the figure, and the second electrode 14 connects the adjacent p-type element 11 on the lower surface in the figure. The element 11 and the n-type element 12 are connected, and the first electrode 13 and the second electrode 14 are arranged so as to be alternated. Also, a first insulating heat conducting plate 15 and a second insulating material are provided on the upper surface in the figure where the first electrode 13 is formed and on the lower surface in the figure where the second electrode 14 is formed, respectively. A heat guide plate 16 is provided.
[0034]
In the thermoelectric conversion module 10 of FIG. 3, the first insulating heat conducting plate 15 side is set to the low temperature side (L) of FIG. 2, and the second insulating heat conducting plate 16 is set to the high temperature side (H) of FIG. When a temperature difference is given, a potential difference occurs between the first electrode 13 and the second electrode 14. When a load is connected to the terminals (not shown) of the array of the electrodes 13 and 14 and the plurality of p-type elements 11 and n-type elements 12, power can be extracted.
[0035]
In the thermoelectric conversion element 1 of FIG. 1 or the thermoelectric conversion module 10 of FIG. 3, the thermoelectric conversion material according to the embodiment of the present invention can be used as a material for a p-type element. When the p-type thermoelectric conversion material according to the embodiment of the present invention is used, a thermoelectric conversion element having a small difference in coefficient of thermal expansion by using a conventional Fe-V-Al-based material or the like as the n-type thermoelectric conversion material. Can be formed.
[0036]
Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited thereto.
(Example 1)
Predetermined amounts of Fe, V, and Al raw materials were weighed, and an alloy was prepared by arc melting. Then, after pulverizing to a particle diameter of 45 μm or less using a ball mill, hot pressing was performed at 950 ° C. for 1 hour to obtain a molded body having an outer diameter of 10 mmφ and a thickness of 2 mm. When the formed phase in the molded product was examined by X-ray diffraction, it was confirmed that the phase having a Heusler-type crystal structure was the main phase. Specifically, 95% or more of the total volume was composed of a phase having a Heusler-type crystal structure.
[0037]
The obtained molded body was cut out into a needle shape of 4 × 1 × 0.5 mm, and an electromotive force was measured by applying a temperature difference of 3 ° C. (300 K and 303 K) to both ends of the molded body to obtain a Seebeck coefficient α. However, it was +111 μV / K.
[0038]
The electrical resistivity ρ of the needle-shaped cutout was measured by a four-terminal method and found to be 0.44 Ωcm at 300K. It was determined power factor P at 300K These results were ^{2.8 × 10 -3 W / mK 2} .
[0039]
The results obtained are shown in Table 1 together with the composition of the alloy.
(Examples 2 to 7)
The raw materials were blended according to the compositions shown in (Table 1), and alloys of Examples 2 to 7 were produced in the same manner as in Example 1. Next, after being pulverized in a ball mill in the same manner as in Example 1, a hot pressed body was formed to obtain a thermoelectric conversion material of each Example. When the formed phases in the molded body were examined by X-ray diffraction, it was confirmed that a phase having a Heusler-type crystal structure was present as a main phase in each case. Specifically, in each case, 90% or more of the total volume was composed of a phase having a Heusler-type crystal structure.
[0040]
Further, the Seebeck coefficient α, the electrical resistivity ρ, and the output factor P were determined in the same manner as in Example 1. The values are shown in (Table 1).
(Comparative Examples 1 to 3)
The raw materials were blended according to the compositions shown in (Table 1), and alloys of Comparative Examples 1 to 3 were produced in the same manner as in Example 1. Next, after being pulverized in a ball mill in the same manner as in Example 1, a hot pressed body was formed to obtain a thermoelectric conversion material of each comparative example. When the formed phases in the molded body were examined by X-ray diffraction, it was confirmed that a phase having a Heusler-type crystal structure was present as a main phase in each case. Specifically, in each case, 80% or more of the total volume was composed of a phase having a Heusler crystal structure.
[0041]
Further, the Seebeck coefficient α, the electrical resistivity ρ, and the output factor P were determined in the same manner as in Example 1. The values are shown in (Table 1).
[0042]
[Table 1]

As shown in (Table _{1), Fe x Al y V} 100-x-y ( however, 40 ≦ x ≦ 49,26 ≦ y ≦ 40 at a) thermoelectric conversion material of each example represented by the composition of While the p-type thermoelectric conversion material having a high output factor, the thermoelectric conversion material of each comparative example has a low output factor or is an n-type thermoelectric conversion material. In particular, in Comparative Example 1, since the composition ratio of Fe was too large and the composition ratio of Al was too small, the absolute value of the Seebeck coefficient was small, resulting in a low output factor. Conversely, in Comparative Example 2, since the composition ratio of Fe is too small and the composition ratio of Al is too large, the absolute value of the Seebeck coefficient similarly becomes small, resulting in a low output factor. Further, in Comparative Example 3, although the composition ratio of Fe was the same as that of each example, the absolute value of the Seebeck coefficient was large and a high output factor was obtained because the composition ratio of Al was too small. This is a negative n-type thermoelectric conversion material.
[0043]
In each of the examples, part of Fe is Cr in Example 5, part of Al is Si in Example 6, part of Fe is Ni, and part of Al is Sb in Example 7. Respectively, thereby lowering the electrical resistivity, resulting in a higher power factor.
[0044]
【The invention's effect】
As described in detail above, according to the present invention, a p-type thermoelectric conversion material having a high output factor can be provided using an Fe-V-Al-based compound.
[Brief description of the drawings]
FIG. 1 is a perspective view illustrating a structure of a thermoelectric conversion element according to an embodiment of the present invention.
FIG. 2 is a schematic sectional view showing a heat exchanger according to an embodiment of the present invention.
FIG. 3 is a schematic sectional view showing a thermoelectric conversion module according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Thermoelectric conversion element 2, 11 ... p-type element 3, 12 ... n-type element 4 ... electrode 5 ... 1st terminal 6 ... 2nd terminal 10 ... thermoelectric conversion module 13 ... 1st electrode 14 ... 2nd Electrode 15: first insulating heat conducting plate 16: second insulating heat conducting plate 20: heat exchanger 21 ... gas passage 22 ... heat exchange fins 23 ... envelope 24 ... flow path 25 ... introduction pipe 26 ... discharge pipe

Claims (5)

_{Fe x Al y V 100-x} -y ( however, 40 ≦ x ≦ 49,26 ≦ y ≦ 40 at a) p-type thermoelectric conversion material characterized by containing a compound having a composition represented by. The p-type thermoelectric conversion material according to claim 1, wherein the compound has a Heusler structure as a main phase. Part of the Fe is substituted with at least one selected from the group consisting of Ti, Cr, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ag, Hf, Ta, W, Y and rare earth elements. The p-type thermoelectric conversion material according to claim 1 or 2, wherein: A part of the Al is substituted with at least one selected from the group consisting of C, N, Si, P, S, Mg, Ga, Ge, Sn, Sb, In and Bi. 3. The p-type thermoelectric conversion material according to 1 or 2. 5. The thermoelectric conversion element in which a p-type element including a p-type thermoelectric conversion material and an n-type element including an n-type thermoelectric conversion material are alternately connected in series, wherein the p-type thermoelectric conversion material is any one of claims 1 to 4. A thermoelectric conversion element characterized by using the thermoelectric conversion material described in (1).

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