Patent Application
20150136195
The present application claims priority from Japanese patent applications JP 2013-239155 filed on Nov. 19, 2013 and JP 2014-184235 filed on Sep. 10, 2014, the entire contents of which are hereby incorporated by reference into this application.
The present invention relates to a thermoelectric conversion material and a thermoelectric conversion module using the thermoelectric conversion material.
In recent years, international concern on the reduction of CO2 that is thought to be a substance responsible for the global warming phenomenon increases and technological innovation for transferring from resource energy emitting a large volume of CO2 to next-generation energy including natural energy and the reutilization of thermal energy advances. As candidates for next-generation energy technologies, a technology of using natural energy such as sunlight and wind power and a technology of reutilizing a lost part of primary energy such as heat emitted by the use of resource energy and vibration are considered.
Whereas conventional resource energy is centralized energy supplied mainly by large-scale electric generating facilities, a feature of the next-generation energy is that both natural energy and reusable energy take the form of being unevenly distributed. In energy utilization today, the energy that is not utilized but exhausted accounts for as large as about 60% of primary energy and is discharged in the form of exhaust heat. Consequently, the improvement of a technology of increasing the proportion of next-generation type energy in primary energy and simultaneously reutilizing energy, in particular converting exhaust heat energy into electric power, is requested.
When the utilization of exhaust heat energy is considered, since exhaust heat is generated at various situations, an electric generating system having a high versatility in installation mode is required. As a dominant candidate technology, a thermoelectric conversion technology is named.
The core of the thermoelectric conversion technology is a thermoelectric conversion module. The thermoelectric conversion module is arranged close to a heat source and generates electricity by generating temperature difference in the module. The thermoelectric conversion module takes a structure of alternately arraying: an n-type thermoelectric conversion material of generating electromotive force from a high temperature side to a low temperature side along a temperature gradient; and a p-type thermoelectric conversion material generating electromotive force in the inverse direction to the n-type thermoelectric conversion material.
The maximum output P of a thermoelectric conversion module is decided by the product of a heat flow rate Q flowing in the module and a conversion efficiency η of a thermoelectric conversion material. The heat flow rate Q depends on a module structure suitable for a thermoelectric conversion material. Further, the conversion efficiency η depends on a non-dimensional variable ZT that is decided by the Seebeck coefficient S, the electric resistivity ρ, and the heat conductivity κ of a material. Consequently, it is necessary to improve the physical property value of a thermoelectric conversion material in order to improve the conversion efficiency.
To cope with the problem, research on many thermoelectric conversion materials has heretofore been worked on. As a thermoelectric conversion material already practically used, there is a BiTe alloy. Although the material has a high conversion efficiency, both Bi and Te are expensive, Te is highly poisonous, and hence mass production, cost reduction, and environmental load reduction are hardly attained. Consequently, a highly-efficient thermoelectric conversion material substituting for a BiTe alloy is desired. International Publications WO 2003/019681 and WO 2013/093967 describe a thermoelectric conversion material that adopts a material having a Heusler alloy type crystal structure.
A conventional Heusler alloy is less poisonous than Te but has not necessarily exhibited characteristics comparable to BiTe.
An object of the present invention is to provide: a thermoelectric conversion material that is a material comprising elements less poisonous than Te and has a Seebeck coefficient comparable to BiTe; and a thermoelectric conversion module having a thermoelectric conversion efficiency comparable to the case of using BiTe by using the thermoelectric conversion material.
An embodiment for attaining the object of the present invention is a thermoelectric conversion material that: is a full-Heusler alloy; is represented by the composition formula Fe2+σTi1+ySi1+z; and has σ, y, and z allowing the material to fall within the region surrounded by (Fe, Ti, Si)=(50, 37, 13), (50, 14, 36), (45, 30, 25), (39.5, 25, 35.5), (54, 21, 25), and (55.5, 25, 19.5) {excluding (50, 25, 25)} by at % in an Fe—Ti—Si ternary alloy phase diagram.
Further, the present invention is a thermoelectric conversion material that: is a full-Heusler alloy; is represented by the composition formula Fe2+σTi1+ySn1+z; and has σ, y, and z allowing the material to fall within the region surrounded by (Fe, Ti, Sn)=(50, 37, 13), (50, 14, 36), (45, 30, 25), (39.5, 25, 35.5), (54, 21, 25), and (55.5, 25, 19.5) {excluding (50, 25, 25)} by at % in an Fe—Ti—Sn ternary alloy phase diagram.
Furthermore, the present invention is a thermoelectric conversion module having a p-type thermoelectric conversion section and an n-type thermoelectric conversion section, wherein each of the p-type thermoelectric conversion section and the n-type thermoelectric conversion section: is a full-Heusler alloy; is represented by the composition formula Fe2+σTi1+ySi1+z; and has σ, y, and z allowing the material to fall within the region surrounded by (Fe, Ti, Si)=(50, 37, 13), (50, 14, 36), (45, 30, 25), (39.5, 25, 35.5), (54, 21, 25), and (55.5, 25, 19.5) {excluding (50, 25, 25)} by at % in an Fe—Ti—Si ternary alloy phase diagram.
The present invention makes it possible to provide: a thermoelectric conversion material that is a material comprising elements less poisonous than Te and has a Seebeck coefficient comparable to BiTe; and a thermoelectric conversion module having a thermoelectric conversion efficiency comparable to the case of using BiTe by using the thermoelectric conversion material.
Other problems, configurations, and effects than described above will be obvious through the following explanations on the embodiments.
c comprise top views of a thermoelectric conversion module;
The p-type thermoelectric conversion sections 11 and the n-type thermoelectric conversion sections 12 are joined through the electrodes 13 and arrayed alternately so as to be electrically connected in series. A set formed by connecting a p-type thermoelectric conversion section 11 and an n-type thermoelectric conversion section 12 in series is called a pn element. The pn elements are installed between the substrates in the manner of vertically interposing the pn elements with the upper substrate 14 and the lower substrate 15. The module is structured so that heat may be transferred to the thermoelectric conversion sections through the upper substrate 14 and the lower substrate 15. In this way, the thermoelectric conversion sections are arrayed electrically in series and thermally in parallel.
The principle of improving the conversion performance of a thermoelectric conversion material is explained hereunder. Many material candidates substituting for a BiTe alloy have heretofore been studied and, among them, materials named as candidate materials in a low temperature region are some of full-Heusler alloys. A full-Heusler alloy having the thermoelectric conversion performance and being represented by Fe2VAl (Fe: iron, V: vanadium, and Al: aluminum) has an electron state called a pseudo gap. In order to explain how the pseudo gap is related to the thermoelectric conversion performance, the general relationship between thermoelectric conversion performance and an electron state is explained.
The performance index of a thermoelectric conversion material is defined by a non-dimensional numeral called ZT and is given by the following formula (1).
S: Seebeck coefficient, κ: heat conductivity, ρ: electric resistivity, T=room temperature (300 K)
As the Seebeck coefficient S increases or the electric resistivity ρ and the heat conductivity κ decrease, the performance index increases. The Seebeck coefficient S and the electric resistivity ρ are physical quantities decided by the electron state of a material. The Seebeck coefficient S has the relationship represented by the following formula (2).
E: binding energy, N: state density
According to formula (2), the Seebeck coefficient S is inversely proportional to the absolute value of the state density N in a Fermi level and is proportional to the energy gradient thereof. It is obvious therefore that a material having a small state density in the Fermi level and having a rapidly changing rise of the state density has a high Seebeck coefficient S.
Meanwhile, the electric resistivity ρ has the relationship represented by the following formula (3).
According to formula (3), since the electric resistivity ρ is inversely proportional to the state density N, the electric resistivity ρ is small when the Fermi level is at an energy position where the absolute value of the state density N is large.
Here, let's go back to the discussion on a pseudo gap electron state. The band structure of a pseudo gap is an electron state where the state density in the vicinity of a Fermi level decreases extremely. Further, as a feature of the band structure of an Fe2VAl system alloy, it is said that the Fe2VAl system alloy behaves like a rigid band model, which means that, when the composition ratio of the chemical compound is changed, the band structure does not change largely and only the energy position of the Fermi level changes. In an Fe2VAl system alloy therefore, it is possible to control the Fermi level at an energy position allowing the state density to change steeply and the absolute value of the state density to be optimized either by changing the composition ratio of the chemical compound or by changing the composition of the chemical compound and applying electron doping or hole doping. It is possible thereby to optimize the relationship between a Seebeck coefficient and a resistivity. The electron doping or the hole doping can be controlled on the basis of a VEC (Valence Electron Concentration: valence electron number per one atom) computed from the composition ratio of a chemical compound. A VEC is defined as a value obtained by dividing the total valence electron number Z in a chemical compound by the atom number a in a unit cell. In the case of Fe2VAl for example, the valence electron numbers of the elements are Fe: 8, V: 5, and Al: 3, the atom numbers of the elements in a unit cell are Fe: 2, V: 1, and Al: 1, and hence Z is computed as Z=8×2+5×1+3×1=24. Further, a is computed as a=2+1+1 and hence VEC=6 is obtained. When the composition ratio of a chemical compound is varied, the value of a VEC increases or decreases. It is known that the increase and the decrease of a VEC are approximately equivalent to electron doping and hole doping in the aforementioned rigid band model and it is possible to change the value and the polarity of the Seebeck coefficient by the control of the VEC. Concretely, when the VEC is less than 6, it can be regarded as hole doping and hence a p-type thermoelectric conversion material is obtained. In contrast, when the VEC is not less than 6, an n-type thermoelectric conversion material is obtained. Further, it is known that each of the p-type and the n-type bears the maximum Seebeck coefficient in the vicinity of the VEC from a preceding example of continuously changing the VEC in the vicinity of 6. In this way, an Fe2VAl system alloy is a material system allowing both the p-type and the n-type to be obtained. Then by actively using an energy level generating a steep change of a state density allowing Fe2VAl to exhibit thermoelectric conversion performance by the modulation of the constituent composition and VEC control by an added element, further improvement of performance can be expected.
A heat conductivity κ can be regarded as the sum of a lattice heat conductivity κp to transfer heat through lattice vibration and an electron heat conductivity κe to transfer heat by using electrons as a medium. With regard to κe, the value increases as the electric resistivity decreases by the Wiedemann-Franz law and depends on a pseudo gap electron state. The electron heat conductivity κe can decrease by controlling a carrier density and generally, when a carrier density is smaller than 1020/cm3, κe comes to be minimum and κp comes to be dominant. Since the decrease of a carrier density simultaneously causes the increase of an electric resistivity however, from the definition of ZT, it is estimated that ZT responding to a carrier density has a maximum value by the balance between the increase of an electric resistivity and the decrease of a heat conductivity. On the other hand, it has been known from the following formula (4) that κp depends on the magnitude of a lattice. Summing up the above discussion, the heat conductivity κ can be expressed as follows.
ζ: density of material, d: particle size, Cp: specimen constant pressure specific heat, τf: time spent during heat transfer from bottom face to top face of particle
As shown in formulas (4) and (5), it is obvious that a heat conductivity κ decreases as the particle size of a specimen decreases. In this way, in a full-Heusler alloy, it is possible to dramatically improve thermoelectric conversion performance by controlling the electron state of the alloy and decreasing a specimen particle size.
In view of the above situation, the present inventors have adopted a full-Heusler alloy as a thermoelectric conversion material. The present inventors have decided to use an Fe2TiSi alloy or an Fe2TiSn alloy as the material of a p-type thermoelectric conversion section 11 and the material of an n-type thermoelectric conversion section 12 respectively. An Fe2TiSi alloy or an Fe2TiSn alloy has a high Seebeck coefficient in both the p-type and the n-type by giving appropriate composition and added element quantity.
In a pseudo gap structure to decide the thermoelectric conversion characteristic of a full-Heusler alloy, a specific band structure called a flat band exists. It is estimated that the flat band mostly decides a thermoelectric conversion material. By controlling a flat band in an appropriate state therefore, it is possible to propose a novel thermoelectric conversion material having an improved thermoelectric conversion characteristic.
As shown in
The calculated values of Seebeck coefficients estimated from such band structures are shown in
Further, it is found through the studies by the present inventors that the maximum value of a Seebeck coefficient increases by a modulation method from the stoichiometric composition to a non-stoichiometric composition in an Fe—Ti—Si Heusler alloy and hence that is explained. Furthermore, it is found through the studies by the present inventors that practically sufficient performance is obtained by the modulation from the stoichiometric composition to a non-stoichiometric composition in an Fe—Ti—Si Heusler alloy and hence that is also explained together. The plots of the variations of the Seebeck coefficients to the modulation quantities from the stoichiometric composition to non-stoichiometric compositions in an Fe—Ti—Si Heusler alloy are shown in
By observing the relationship between an Si increment and a Seebeck coefficient shown in
Further, by observing the relationship between a Ti increment and a Seebeck coefficient shown in
Further, the characteristic is particularly good in the range surrounded by the straight lines connecting the 6 points of (Fe, Ti, Si)=(39.5, 25, 35.5), (47.5, 27.5, 25), (50, 17, 33), (50, 35, 15), (52.8, 25, 22.2), and (52.2, 22.8, 25) in atm % on the ternary alloy phase diagram. Furthermore, the region of better characteristics than the stoichiometric composition is the region surrounded by the straight lines connecting the following 6 points of (Fe, Ti, Si)=(41, 25, 34), (49.2, 25.8, 25), (50, 23, 27), (50, 32.6, 17.4), 51, 25, 24), and (51, 24, 25). It is found that an Fe—Ti—Si system alloy that is a novel material formed by synthesizing an alloy in the range shown in
A definitional formula of a VEC is introduced from a composition formula of an Fe—Ti—Si Heusler alloy in order to define the quantity of a replaced element causing an appropriate VEC variation in VEC control. Firstly, the composition formula of the Fe—Ti—Si Heusler alloy is set at Fe2+σ(Ti1−xMx)1+y(Si1−wNw)1+z. The VEC=[8(2+σ)+{4(1−x)+(valence electron number of M)x}(1+y)+{4(1−w)+(valence electron number of N)w}(1+z)]/4, σ={(at % of Fe in the region of FIG. 6)−50}/25, y={(at % of Ti in the region of FIG. 6)−25}/25, and z={(at % of Si in the region of FIG. 6)−25}/25 are obtained and, when the variation of a VEC is defined as ΔVEC, the ΔVEC=VEC−(VEC center value of each mother alloy composition) is obtained.
The |ΔVEC| is preferably in the range of 0.001≦|ΔVEC|≦0.09 and a thermoelectric conversion material of a large Seebeck coefficient can be obtained.
A maximum value is obtained in both the cases of a p-type and an n-type by adding at least any one of Nb, V, Al, Ta, Cr, Mo, W, Hf, Ge, Ga, In, P, B, Bi, and Zr as each of M and N so that a ΔVEC may be at most not more than ±0.2 (−0.2≦ΔVEC≦0.2). Here, the VEC center value of each mother alloy composition means the VEC value obtained when x and w are 0 and 0 respectively. From the VEC dependency of the Seebeck coefficient indicated in each of
Here, in the case of adding at least any one of Nb, V, Ta, Cr, Mo, W, Hf, Ge, Ga, In, P, B, Bi, and Zr as an added material for adjusting the quantity of total electrons too, a characteristic similar to
In the present embodiment, in the alloy composition range suggested by the first principle computation shown in
The configuration example of a thermoelectric conversion module 10 manufactured in accordance with the aforementioned principle is explained hereunder. Here, an Fe2TiSiSn system alloy is used as the material of a p-type thermoelectric conversion section 11 and an n-type thermoelectric conversion section 12. Ta is used as the material of an electrode 13 and AlN is used as the material of an upper substrate 14 and a lower substrate 15. As the material of a skeleton, any material is acceptable as long as it is a material having a high heat conductivity and a high strength. Steel is used here.
Each of the thermoelectric conversion sections can be manufactured by a sintering method with a hot press. The weights of the powder of elements to be the material are adjusted and then the material is fed into a carbon die and sintered so that the element composition ratio of the alloy may meet a design.
In the case of manufacturing an Fe2TiVSi system alloy for example, the powder of the elements Fe, Ti, V, and Si is weighed so that the element composition ratio may meet the design and is fed into a carbon die. For example, it is possible to prepare a material so as to satisfy, in Fe2+σ(Ti1−xMx)1+y(Si1−wNw)1+z, Fe:Ti:V:Si=1.98:0.855:0.095:1.07 (σ=−0.02, x=0.1, y=−0.05, z=0.07, and w=0). Successively, the material is reacted and sintered at 800° C. for 5,000 seconds for example. Further, it is also possible to apply heating treatment at 600° C. for 2 days for example in order to improve the regularity of the crystal structure of the sintered body finished by the reaction and sintering. In the present composition, by mixing V as an additive material, it is attempted to improve the performance of a thermoelectric conversion material and stabilize the crystal structure. The pellets thus manufactured are processed into the aforementioned sizes and mounted on the thermoelectric conversion module 10.
Although Fe2+σ(Ti1−xMx)1+y(Si1−wNw)1+z is adopted as the material of the p-type thermoelectric conversion section 11 in the aforementioned configuration example, the material is not limited to the example and Fe2NbAl, FeS2, or the like can be used for example. The material of the upper substrate 14 and the lower substrate 15 may also be GaN. The material of the electrode 13 may also be Cu or Au.
Although the material composition of the n-type thermoelectric conversion section 12 is Fe1.98Ti0.855V0.095Si1.07 in the aforementioned configuration example, the composition is not limited to the composition and may be any composition as long as it is an alloy composition having the characteristic shown in
In order to know the full picture of the appropriate composition range, materials of some compositions are synthesized on the basis of
From the results shown in
Further, when at least any one of Nb, V, Ta, Cr, Mo, W, Hf, Ge, Ga, In, P, B, Bi, and Zr is added as an additive material, it is desirable to configure the material so that the sum of the composition ratios of the additive materials may be smaller than the composition ratio of Ti. The reason is that, if the composition ratio of the additive material is larger, it deviates from the range as an Fe2TiSiSn system alloy explained in
In this way, a thermoelectric conversion module 10 according to Embodiment 1 is formed by using a full-Heusler alloy as the material for each of a p-type thermoelectric conversion section 11 and an n-type thermoelectric conversion section 12 and the material of the n-type thermoelectric conversion section 12 is a full-Heusler alloy of an Fe2TiSi system, an Fe2TiSn system, or an Fe2TiSiSn system. It is thereby possible to provide a less poisonous thermoelectric conversion module having a high thermoelectric conversion efficiency.
The thermoelectric conversion performance of a thermoelectric conversion module is influenced also by the flow rate Q of the heat flowing into the module besides the conversion efficiency η of a thermoelectric conversion material. Since the heat flow rate Q is a variable influenced by the structure (particularly the sizes of the sections) of a thermoelectric conversion module, it is important to design an optimum module structure in response to the characteristic of a selected thermoelectric conversion material. In Embodiment 2 according to the present invention therefore, the optimization of the sizes of sections of a thermoelectric conversion module 10 is examined on the premise of employing a thermoelectric conversion material explained in Embodiment 1. The other configuration of the thermoelectric conversion module 10 is the same as Embodiment 1.
The horizontal axis in
As shown in
As shown in
The horizontal axis in
As shown in
Further,
The (pattern a) can be interpreted as a maximum output is obtained in response to the value of L and hence it is obvious that the results nearly similar to
The (pattern b) can be interpreted as, if the value of L does not change, the output of a pn element increases and reaches a maximum value as the value of L/An1/2 shifts from a smaller value toward a larger value, namely as both Ap and An shift from smaller values toward larger values and after that the output of the pn element decreases as the value of L/An1/2 increases, namely as both Ap and An decrease.
As shown in
Although the aforementioned tendency is the same whatever the value of L is, the optimum value of L/An1/2 varies in response to the value of L and the value of L/An1/2 allowing an output close to the maximum value to be obtained in any of the values of L has not been found.
Further, by the results shown in
Considering
In Embodiment 2, on the premise of adopting a thermoelectric conversion material explained in Embodiment 1, the optimum dimensions of a thermoelectric conversion module 10 have heretofore been examined on the basis of various computation results. As a result, optimum values have been found on the dimensions of the sections. It is possible to optimize the efficiency of a thermoelectric conversion module 10 by adopting a thermoelectric conversion material explained in Embodiment 1 and a module structure explained in Embodiment 2 in combination.
A thermoelectric conversion material according to Embodiment 3 of the present invention is explained in reference to
As stated earlier, in the case of a thermoelectric conversion material of a Heusler alloy system, when a composition is modulated so as to adjust a VEC (total valence electron number per unit lattice), the carrier concentration of the thermoelectric conversion material is modulated and hence the thermoelectric conversion characteristic can be controlled. The case where a band structure is not changed by VEC adjustment and only a carrier concentration can be modulated however is limited only in the range where a VEC adjustment quantity is small. Consequently, a composition design taking a band structure into consideration is required in order to obtain an optimum value of a thermoelectric conversion characteristic in the range where a VEC adjustment quantity is large. In a Heusler alloy Fe2+σ(Ti1−xMx)1+y(Si1−wNw)1+z, particularly in the case of M=V and N═Al, a composition design taking the change of a band structure into consideration is carried out by using the first principle computation and an optimum value in the composition range is obtained. Since it is assumed that a band structure varies largely by M atom replacement but the band structure changes slightly by N atom replacement, numerical computation is carried out only on M replacement. The reason why a band structure varies by M atom replacement is that the main factor to decide the band structure of the alloy is estimated to be the bond of an Fe atom and a Ti atom.
(A) to (c) of
From (d) to (f) of
More concretely, a ΔVEC is in the range of −0.09≦ΔVEC(σ, w, x, y, z)≦−0.01 or 0.001≦ΔVEC(σ, w, x, y, z)≦0.09. Here, the range where x and w exceed 0.5 comes to be a composition largely deviating from Fe2TiSi and hence is excluded.
Through the above discussion, in a thermoelectric conversion material of Fe2+σ(Ti1−xMx)1+y(Si1−wNw)1+z, it is desirable that the thermoelectric conversion material has x and w allowing |ΔVEC|≦0.2 to be satisfied under the conditions of
VEC=[8(2+σ)+{4(1−x)+(valence electron number of M)x}(1+y)+{4(1−w)+(valence electron number of N)w}(1+z)]/4,
and
The |ΔVEC| is preferably in the range of 0.001≦|ΔEC|≦0.09.
Each of the elements M and N can be at least any one of Nb, V, Al, Ta, Cr, Mo, W, Hf, Ge, Ga, In, P, B, Bi, and Zr and further on this occasion, when a VEC (σ, w, x, y, z) and a ΔVEC are defined by a valence electron concentration VEC(σ, w, x, y, z)={8*(2+σ)+(4*(1−x)+Z(M)*x)*(1+y)+(4*(1−w)+Z(N)*w)*(1+z)}/4 (Z(M), Z(N)=valence electron number of the outermost shell in an atom of the element M or N), (VEC center value)=VEC(σ, 0, 0, y, z)={8*(2+σ)+(4*(1+y)+4*(1+z)}/4, and ΔVEC(σ, w, x, y, z)=VEC(σ, w, x, y, z)−(VEC center value), it is desirable that: the elements M and N are V and Al respectively; and ΔVEC(σw, x, y, z)={x*(1+y)−w*(1+z)}/4, −0.09≦ΔVEC(σ, w, x, y, z)≦−0.01, 0.001≦ΔVEC(σ, w, x, y, z)≦0.09, 0≦x<0.5, 0≦w<0.5, and σ+x+w=0(here, x=w=0 is excluded) are satisfied. More appropriate ranges of ΔVEC are −0.09≦ΔVEC(σ, w, x, y, z)≦−0.01 and 0.001≦ΔVEC(σ, w, x, y, z)≦0.09.
Here, multiplication is expressed by “no mark”, “x”, “*”, etc. in the present specification but they are the same.
As stated above, a thermoelectric conversion material can be manufactured in accordance with a design guide by using a sintering method with a hot press. The weight of element powder to be a material is adjusted so that the element composition ratio of an alloy may be as designed and then the powder is fed into a carbon die and sintered.
In the case of manufacturing an Fe2TiVSi system alloy for example, the powder of the elements Fe, Ti, V, and Si is weighed so that the element composition ratio may satisfy the above composition formula and is fed into a carbon die. For example, it is possible to prepare a material of Fe2+σ(Ti1−xMx)1+y(Si1−wNw)1+z so as to be Fe1.98(Ti1−xVx)0.95(Si1−yAly)1.07 (X=0.15, 0≦y≦0.23). Successively, the material is reacted and sintered at 800° C. for 5,000 seconds for example. Further, it is also possible to apply heating treatment at 600° C. for 2 days for example in order to improve the regularity of the crystal structure of a sintered body finished by the reaction and sintering. In the present composition, by mixing V as an additive material, it is attempted to improve the performance of a thermoelectric conversion material and stabilize the crystal structure. The pellets thus manufactured are processed into the aforementioned sizes and the thermoelectric conversion material is obtained.
In order to know the full picture of an appropriate composition range, materials of some compositions are synthesized on the basis of the above design guide. The relationship between a Seebeck coefficient and a ΔVEC in the alloys is shown in
A thermoelectric conversion material according to the present invention is not necessarily manufactured by the method in the present embodiment and can be manufactured appropriately also by a casting method such as an arc melting method. Further, a thermoelectric conversion material can be manufactured appropriately also by a method of being alloyed by arc melting, being pulverized thereafter, and obtaining a sintered body by hot press or spark plasma sintering. Otherwise, a thermoelectric conversion material can be manufactured appropriately also by a method of manufacturing alloy powder by mechanical alloying when the alloy is manufactured and obtaining a sintered body by hot press or spark plasma sintering. Moreover, an intended alloy can be manufactured also by a thin piece obtained by rapidly cooling the material after it is melted. Moreover, a thermoelectric conversion material can be manufactured appropriately also by a method of powderizing a thin piece obtained by rapidly cooling the material after it is melted and obtaining a sintered body by hot press or spark plasma sintering. Otherwise, a method of obtaining powder by heating raw material powder adjusted to a given composition by thermal plasma and successively rapidly cooling the powder can be adopted appropriately. Then a thermoelectric conversion material can be manufactured appropriately also by a method of obtaining a sintered body by hot press or spark plasma sintering by using the powder obtained by the thermal plasma.
A thermoelectric conversion material explained in Embodiment 3 is applied to a thermoelectric conversion module according to Embodiment 1 and a less poisonous thermoelectric conversion module having a high thermoelectric conversion efficiency can be provided. Further, a thermoelectric conversion material explained in Embodiment 3 is applied to a module structure explained in Embodiment 2 and the efficiency of the thermoelectric conversion module can be optimized.
Here, the present invention is not limited to the aforementioned embodiments and includes various modified examples. For example, the aforementioned embodiments are explained in detail for better understanding of the present invention and the present invention is not necessarily limited to the embodiments having the explained whole configuration. Further, a part of the configuration of an embodiment can also be replaced with the configuration of another embodiment and the configuration of an embodiment can be added to the configuration of another embodiment. Furthermore, a part of the configuration of an embodiment can be added to, deleted from, or replaced with another configuration.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-239155 | Nov 2013 | JP | national |
| 2014-184235 | Sep 2014 | JP | national |
