THERMOELECTRIC CONVERSION MATERIAL, THERMOELECTRIC CONVERSION ELEMENT, AND THERMOELECTRIC CONVERSION MODULE
20230097435 · 2023-03-30
Assignee
Inventors
Cpc classification
H10N10/8556
ELECTRICITY
H10N10/855
ELECTRICITY
H10N10/857
ELECTRICITY
International classification
Abstract
There is provided a thermoelectric conversion material in which a first layer containing Mg.sub.2Si.sub.xSn.sub.1-x (here, 0<x<1) is directly joined to a second layer containing Mg.sub.2Si.sub.ySn.sub.1-y (here, 0<y<1), where x/y is set within a range of more than 1.0 and less than 2.0. There is also provided a thermoelectric conversion element including the thermoelectric conversion material and electrodes each joined to one surface and the other surface of the thermoelectric conversion material. There is also provided a thermoelectric conversion module including terminals each joined to the electrodes of the thermoelectric conversion element.
Claims
1. A thermoelectric conversion material, wherein a first layer containing Mg.sub.2Si.sub.xSn.sub.1-x (here, 0<x<1) is directly joined to a second layer containing Mg.sub.2Si.sub.ySn.sub.1-y (here, 0<y<1), and x/y is set within a range of more than 1.0 and less than 2.0.
2. The thermoelectric conversion material according to claim 1, wherein in addition to Mg.sub.2Si.sub.xSn.sub.1-x constituting the first layer and Mg.sub.2Si.sub.ySn.sub.1-y constituting the second layer, at least one or both of the first layer and the second layer contains boride, and the boride contains one or two or more metals selected from a group consisting of titanium, zirconium, and hafnium.
3. The thermoelectric conversion material according to claim 2, wherein the boride is one or two or more borides selected from a group consisting of TiB.sub.2, ZrB.sub.2, and HfB.sub.2.
4. The thermoelectric conversion material according to claim 2, wherein a total amount of the boride is set within a range of 0.5 mass % or more and 15 mass % or less.
5. The thermoelectric conversion material according to claim 1, wherein in addition to Mg.sub.2Si.sub.xSn.sub.1-x constituting the first layer and Mg.sub.2Si.sub.ySn.sub.1-y constituting the second layer, at least one or both of the first layer and the second layer contains aluminum.
6. The thermoelectric conversion material according to claim 5, wherein an amount of the aluminum is set within a range of 0.3 mass % or more and 3 mass % or less.
7. A thermoelectric conversion element comprising: the thermoelectric conversion material according to claim 1; and electrodes each joined to one surface and an other surface of the thermoelectric conversion material.
8. A thermoelectric conversion module comprising: the thermoelectric conversion element according to claim 7; and terminals each joined to the electrodes of the thermoelectric conversion element.
Description
BRIEF DESCRIPTION OF DRAWINGS
[0040]
[0041]
[0042]
DESCRIPTION OF EMBODIMENTS
[0043] Hereinafter, a thermoelectric conversion material, a thermoelectric conversion element, and a thermoelectric conversion module according to an embodiment of the present invention will be described with reference to the attached drawings. Each embodiment to be described below is specifically described for a better understanding of the gist of the invention and does not limit the present invention unless otherwise specified. In addition, in the drawings used in the following description, for convenience, a portion that is a main part may be enlarged in some cases in order to make the features of the present invention easy to understand, and the dimensional ratio or the like of each component is not always the same as an actual one.
[0044]
[0045] The thermoelectric conversion element 10 includes a thermoelectric conversion material 11 according to the present embodiment, and electrodes 18a and 18b formed on one surface 11a and the other surface 11b of the thermoelectric conversion material 11.
[0046] Further, the thermoelectric conversion module 1 includes terminals 19a and 19b each joined to the electrodes 18a and 18b of the thermoelectric conversion element 10 described above.
[0047] Since thermoelectric conversion element 10 according to the present embodiment generates a temperature difference between one surface 11a and the other surface 11b of the thermoelectric conversion material 11, it can be used as a Seebeck element that generates a potential difference between the electrode 18a and the electrode 18b.
[0048] The thermoelectric conversion element 10 can be used as a Peltier element that generates a temperature difference between one surface 11a and the other surface 11b of the thermoelectric conversion material 11, by applying a voltage between the electrode 18a side and the electrode 18b. For example, in a case of allowing an electric current to flow between the electrode 18a side and the electrode 18b, it is possible to cool or heat one surface 11a or the other surface 11b of the thermoelectric conversion material 11.
[0049] Here, nickel, silver, cobalt, tungsten, molybdenum, or the like is used in the electrodes 18a and 18b. The electrodes 18a and 18b can be formed by energized sintering, plating, electrodeposition, or the like.
[0050] The terminals 19a and 19b are formed of a metal material having excellent conductivity, for example, a plate material such as copper or aluminum. In the present embodiment, a rolled aluminum plate is used. Further, the thermoelectric conversion element 10 (the electrodes 18a and 18b) can be joined to the terminals 19a and 19b by Ag wax, Ag plating, or the like.
[0051] In addition, the thermoelectric conversion material 11 according to the present embodiment has a structure in which a first layer 14 containing Mg.sub.2Si.sub.xSn.sub.1-x (here, 0<x<1) is directly joined to a second layer 15 containing Mg.sub.2Si.sub.ySn.sub.1-y (here, 0<y<1).
[0052] Both Mg.sub.2Si.sub.xSn.sub.1-x constituting the first layer 14 and Mg.sub.2Si.sub.ySn.sub.1 -y constituting the second layer 15 are made of an Mg—Si—Sn material. Here, the ratio of Si to Sn is different, and x/y is set within a range of more than 1.0 and less than 2.0.
[0053] x/y is preferably in a range of 1.2 to 1.8 and more preferably in a range of 1.3 to 1.6.
[0054] Mg.sub.2Si.sub.xSn.sub.1-x constituting the first layer 14 is contained in the first layer 14 preferably in an amount of 82 mass % or more and 100 mass % or less, and more preferably 85 mass % or more and 99.7% or less.
[0055] Mg.sub.2Si.sub.ySn.sub.1-y constituting the second layer 15 is contained in the second layer 15 preferably in an amount of 82 mass % or more and 100 mass % or less, and more preferably 85 mass % or more and 99.7% or less.
[0056] Here, Mg.sub.2Si.sub.xSn.sub.1-x (here, 0<x<1) constituting the first layer 14 of the thermoelectric conversion material 11 is a material of which thermoelectric characteristics are improved in a high temperature region, for example, 300° C. or higher, as compared with Mg.sub.2Si.sub.ySn.sub.1-y (here, 0<y<1) constituting the second layer 15. On the other hand, Mg.sub.2Si.sub.ySn.sub.1-y (here, 0<y<1) constituting the second layer 15 is a material of which thermoelectric characteristics (particularly, PF) are improved in a low temperature region, for example, less than 300° C., as compared with Mg.sub.2Si.sub.xSn.sub.1-x (here, 0<x<1) constituting the first layer 14. Here, 300° C. is used as a boundary as an example. However, the first layer having good characteristics at a temperature of 300° C. or higher and the second layer having good characteristics at a temperature of less than 400° C. (that is, two materials both having good characteristics at a temperature from 300° C. to 400° C.) may be combined.
[0057] As described above, by using the thermoelectric conversion material 11 in which the first layer 14 and the second layer 15 having mutually different temperature regions where the thermoelectric characteristics are improved are directly joined, the thermoelectric characteristics of each of the first layer 14 and the second layer 15 are maximized, for example, by placing the electrode 18a side of the first layer 14 in the high temperature environment and the electrode 18b side of the second layer 15 in the low temperature environment. As a result, it is possible to significantly improve the thermoelectric power generation output and the thermoelectric power conversion efficiency (power generation efficiency) as compared with a thermoelectric conversion material made of a material having a single composition.
[0058] It is noted that the thermoelectric conversion material 11 (the first layer 14 and the second layer 15) may be a non-doped material containing no dopant, or it may include, as the dopant, one or two or more selected from the group consisting of Li, Na, K, B, Ga, In, N, P, As, Sb, Bi, Ag, Cu, and Y.
[0059] Regarding the thermoelectric conversion material 11 (the first layer 14 and the second layer 15) of the present embodiment, antimony which is a pentavalent donor is added to obtain an n-type thermoelectric conversion material having a high carrier density.
[0060] Further, in the thermoelectric conversion material 11 (the first layer 14 and the second layer 15) of the present embodiment, at least one or both of the first layer 14 and the second layer 15 contains boride, in addition to Mg.sub.2Si.sub.xSn.sub.1-x constituting the first layer 14 and Mg.sub.2Si.sub.ySn.sub.1-y constituting the second layer 15, where this boride may contain one or two or more metals selected from the group consisting of titanium, zirconium, and hafnium, which are the Group 4 elements. Examples of the above-described boride include TiB.sub.2, ZrB.sub.2, or HfB.sub.2.
[0061] Here, in the present embodiment, in a case where the boride is contained, it is preferable that the total amount of the boride is set within a range of 0.5 mass % or more and 15 mass % or less.
[0062] Further, the lower limit of the total amount of the boride is more preferably 1 mass % or more and still more preferably 1.5 mass % or more. On the other hand, the upper limit of the total amount of the boride is more preferably 12 mass % or less and still more preferably 10 mass % or less.
[0063] Alternatively, in the thermoelectric conversion material 11 (the first layer 14 and the second layer 15) of the present embodiment, at least one or both of the first layer 14 and the second layer 15 may contain aluminum, in addition to Mg.sub.2Si.sub.xSn.sub.1-x constituting the first layer 14 and Mg.sub.2Si.sub.ySn.sub.1-y constituting the second layer 15.
[0064] Here, in the present embodiment, in a case where aluminum is contained, it is preferable that the aluminum content is set within a range of 0.3 mass % or more and 3 mass % or less.
[0065] Next, a method for producing the thermoelectric conversion material 11 according to the present embodiment will be described with reference to
Massive Mg—Si—Sn Forming Step S01
[0066] First, a first massive Mg—Si—Sn which is the raw material of the first layer 14 (Mg.sub.2Si.sub.xSn.sub.1-x) of the thermoelectric conversion material 11, and a second massive Mg—Si—Sn which is the raw material of the second layer 15 (Mg.sub.2Si.sub.ySn.sub.1-y) are produced.
[0067] In the present embodiment, each of the magnesium powder, the silicon powder, the tin powder, and the dopant is weighed and mixed, as necessary. For example, a pentavalent material such as antimony or bismuth is mixed as a dopant in a case of forming an n-type thermoelectric conversion material, and a material such as lithium or silver is mixed as a dopant in a case of forming a p-type thermoelectric conversion material. It is noted that non-doped magnesium silicide may be used without adding a dopant.
[0068] Then, this mixed powder is introduced into, for example, an alumina crucible, heated to a range of 700° C. or higher and 900° C. or lower, and then cooled and solidified. As a result, a first massive magnesium silicide as a raw material of the first layer 14 (Mg.sub.2Si.sub.xSn.sub.1-x) and a second massive magnesium silicide as a raw material of the second layer 15 (Mg.sub.2Si.sub.ySn.sub.1-y) are obtained.
[0069] Since a small amount of magnesium sublimates during heating, it is preferable to add a large amount of magnesium, for example, about 1 at % to 3 at % with respect to the stoichiometric composition of Mg:Si+Sn=2:1 at the time of weighing the raw material.
Pulverization Step S02
[0070] Next, the obtained first massive Mg—Si—Sn and second massive Mg—Si—Sn are pulverized with a pulverizer to form a first Mg—Si—Sn powder and a second Mg—Si—Sn powder.
[0071] In this pulverization step S02, it is preferable that the average particle diameters of the first Mg—Si—Sn powder and the second Mg—Si—Sn powder are set within a range of 1 μm or more and 100 μm or less.
[0072] It is noted that regarding the first Mg—Si—Sn powder and the second Mg—Si—Sn powder, to which a dopant has been added, the dopant is uniformly present in the first Mg—Si—Sn powder and the second Mg—Si—Sn powder.
Sintering Raw Material Powder Forming Step S03
[0073] Next, the obtained first Mg—Si—Sn powder and second Mg—Si—Sn powder are mixed, as necessary, with a boride powder containing one or two or more metals selected from the group consisting of titanium, zirconium, and hafnium, or an aluminum powder, to obtain a first sintering raw material powder Q1 and a second sintering raw material powder Q2.
Sintering Step S04
[0074] Next, the first sintering raw material powder Q1 and the second sintering raw material powder Q2 obtained as described above are heated while being pressurized, to obtain a sintered body.
[0075] Here, in the present embodiment, in the sintering step S04, a sintering device (an energized sintering device 100) shown in
[0076] The sintering device (the energized sintering device 100) shown in
[0077] In the sintering step S04, first, the carbon mold 103 of the energized sintering device 100 shown in
[0078] The inside of the carbon mold 103 is covered with, for example, a graphite sheet or a carbon sheet. Then, using the power supply device 106, a direct current is allowed to pass between the pairing electrode parts 105a and 105b to allow a current to flow through the first sintering raw material powder Q1 and the second sintering raw material powder Q2, thereby raising the temperature by self-heating. Further, among the pairing electrode parts 105a and 105b, the moving electrode part 105a is moved toward the first sintering raw material powder Q1 and the second sintering raw material powder Q2, and then the first sintering raw material powder Q1 and the second sintering raw material powder Q2 are pressurized between the moving electrode part 105a and the fixing electrode parts 105b with a predetermined pressure. In addition, the heater 109 is heated.
[0079] As a result, the first sintering raw material powder Q1 and the second sintering raw material powder Q2 are sintered as one body by the self-heating of the first sintering raw material powder Q1 and the second sintering raw material powder Q2 and the heat from the heater 109 and by the pressurization, and at the same time, the sintered body of the first sintering raw material powder Q1 is joined to the sintered body of the second sintering raw material powder Q2.
[0080] In the present embodiment, the sintering conditions in the sintering step S04 are such that the sintering temperatures of the first sintering raw material powder Q1 and the second sintering raw material powder Q2 are set within a range of 600° C. or higher and 800° C. or lower, and the holding time at this sintering temperatures is set to 10 minutes or less. Further, the pressurization load is set within a range of 20 MPa or more and 50 MPa or less.
[0081] Further, the atmosphere inside the pressure-resistant housing 101 may be an inert atmosphere such as an argon atmosphere or a vacuum atmosphere. In of case of a vacuum atmosphere, the pressure may be 5 Pa or less.
[0082] Here, in a case where the sintering temperatures of the first sintering raw material powder Q1 and the second sintering raw material powder Q2 are less than 600° C., the oxide film formed on the surface of the powder of each of the first sintering raw material powder Q1 and the second sintering raw material powder Q2 cannot be sufficiently removed, the surface oxide film of the raw material powder itself remains at the crystal grain boundary, and the binding between the raw material powders is insufficient, which results in a low density of the sintered body. For these reasons, there is a risk that the electric resistance of the obtained thermoelectric conversion material increases. In addition, there is a risk that the mechanical strength of the element may be low due to insufficient binding.
[0083] On the other hand, in a case where the sintering temperatures of the first sintering raw material powder Q1 and the second sintering raw material powder Q2 are more than 800° C., there is a risk that the decomposition of Mg—Si—Sn progresses in a short time, a part of Sn and Mg melts and leaks to the outside, causing composition deviation, and the electric resistance increases, and at the same time, the Seebeck coefficient decreases.
[0084] Therefore, in the present embodiment, the sintering temperature in the sintering step S04 is set within a range of 600° C. or higher and 800° C. or lower.
[0085] The lower limit of the sintering temperature in the sintering step S04 is preferably 650° C. or higher. On the other hand, the upper limit of the sintering temperature in the sintering step S04 is preferably 770° C. or lower and more preferably 740° C. or lower.
[0086] Further, in a case where the holding time at the sintering temperature exceeds 10 minutes, there is a risk that the decomposition of Mg—Si—Sn proceeds, the composition deviates, the electric resistance increases, and at the same time, the Seebeck coefficient decreases. Further, there is a risk that particles become coarse, and the thermal conductivity increase. Therefore, in the present embodiment, the holding time at the sintering temperature in the sintering step S04 is set to 10 minutes or less.
[0087] The upper limit of the holding time at the sintering temperature in the sintering step S04 is preferably 5 minutes or less and more preferably 3 minutes or less.
[0088] Further, in a case where the pressurization load in the sintering step S04 is less than 20 MPa, there is a risk that the density does not increase, and the electric resistance of the thermoelectric conversion material increase. In addition, there is a risk that the mechanical strength of the element may not increase.
[0089] On the other hand, in a case where the pressurization load in the sintering step S04 exceeds 50 MPa, there is a risk that force applied to the carbon jig is large, and thus the jig is cracked.
[0090] Therefore, in the present embodiment, the pressurization load in the sintering step S04 is set within a range of 20 MPa or more and 50 MPa or less.
[0091] The lower limit of the pressurization load in the sintering step S04 is preferably 23 MPa or more and more preferably 25 MPa or more. On the other hand, the upper limit of the pressurization load in the sintering step S04 is preferably 45 MPa or less and more preferably 40 MPa or less.
[0092] By each of the above steps, the thermoelectric conversion material 11 according to the present embodiment is produced.
[0093] According to the thermoelectric conversion material 11 according to the present embodiment having such a configuration as described above, by using a thermoelectric conversion material 11 in which the first layer 14 and the second layer 15, having mutually different temperature regions where the thermoelectric characteristics are improved, are directly joined and integrated, the thermoelectric characteristics of the first layer 14 and the second layer 15 are maximized by placing one surface of first layer 14 the high temperature environment and another surface of the second layer 15 in the low temperature environment. As a result, it is possible to significantly improve the thermoelectric power generation output and the thermoelectric power conversion efficiency (power generation efficiency) as compared with a thermoelectric conversion material made of a material having a single composition.
[0094] In addition, in thermoelectric conversion material 11 of the present embodiment, a first layer 14 containing Mg.sub.2Si.sub.xSn.sub.1-x (here, 0<x<1) is directly joined to a second layer 15 containing Mg.sub.2Si.sub.ySn.sub.1-y (here, 0<y<1), where x/y is set within a range of more than 1.0 and less than 2.0. As a result, both the first layer 14 and the second layer 15 are formed of a material system, and the electric resistance and the coefficient of thermal expansion are extremely close to each other. For this reason, it is possible to suppress a decrease in electric resistance, and it is possible to sufficiently improve the power generation efficiency. In addition, the difference in the coefficient of thermal expansion is small, the occurrence of cracking due to the temperature difference can be suppressed, and the stable use is possible.
[0095] Further, in the present embodiment, in a case where at least one or both of the first layer 14 and the second layer 15 contain a boride containing one or two or more metals selected from the group consisting of titanium, zirconium, and hafnium, in addition to Mg.sub.2Si.sub.xSn.sub.1-x constituting the first layer 14 and Mg.sub.2Si.sub.ySn.sub.1-y constituting the second layer 15 are made of an Mg—Si—Sn material, the boride aggregates at the crystal grain boundary of Mg—Si—Sn to improve the electrical conductivity, and it is possible to further improve the power factor (PF), which is one of the indicators of the thermoelectric characteristics, as well as the dimensionless figure of merit (ZT).
[0096] Further, since the boride contains one or two or more kinds of metals selected from the group consisting of titanium, zirconium, and hafnium, it is possible to suppress the oxidation of magnesium and improve the oxidation resistance.
[0097] Further, since the above-described boride is relatively hard, it is possible to improve the mechanical strength of the thermoelectric conversion material 11.
[0098] Here, in a case where the boride is one or two or more borides selected from the group consisting of TiB.sub.2, ZrB.sub.2, and HfB.sub.2, it is possible to reliably improve the thermoelectric characteristics, oxidation resistance, and mechanical strength of the thermoelectric conversion material 11.
[0099] Further, in a case where the total amount of the boride is set within a range of 0.5 mass % or more and 15 mass % or less, it is possible to sufficiently improve the thermoelectric characteristics, oxidation resistance, and mechanical strength of the thermoelectric conversion material 11.
[0100] Further, in the present embodiment, in a case where at least one or both of the first layer 14 and the second layer 15 contain aluminum, in addition to Mg.sub.2Si.sub.xSn.sub.1-x constituting the first layer 14 and Mg.sub.2Si.sub.ySn.sub.1-y constituting the second layer 15 are made of an Mg—Si—Sn material, aluminum can suppress the infiltration of oxygen in the atmosphere into the inside of thermoelectric conversion material 11, and the oxidation resistance in a case of being used under high temperature conditions can be reliably improved.
[0101] Further, in a case where the amount of aluminum is set within a range of 0.3 mass % or more and 3 mass % or less, the oxidation resistance in a case of being used under high temperature conditions can be reliably improved. Aluminum may be added at the same time as the dopant at the time of producing the raw material particles of Mg.sub.2Si.sub.xSn.sub.1-x and Mg.sub.2Si.sub.ySn.sub.1-y. Further, a boride and aluminum may be added at the same time.
[0102] Further, in the thermoelectric conversion element 10 and the thermoelectric conversion module 1 according to the present embodiment, since a thermoelectric conversion material 11 in which the first layer 14 and the second layer 15 having mutually different temperature regions where the thermoelectric characteristics are improved are directly joined, the thermoelectric characteristics of the first layer 14 and the second layer 15 are maximized by, for example, placing one surface (the side opposite to the joining interface) of first layer 14 the high temperature environment and another surface (the side opposite to the joining interface) of the second layer 15 in the low temperature environment, and thus it is possible to significantly improve the thermoelectric power generation output and the thermoelectric power conversion efficiency (power generation efficiency) as compared with a thermoelectric conversion device using the thermoelectric conversion material made of a material having a single composition.
[0103] Although the embodiment of the present invention has been described above, the present invention is not limited thereto and can be appropriately modified without departing from the technical idea of the invention.
[0104] For example, in the present embodiment, although the description has been made such that a thermoelectric conversion module having a structure as shown in
[0105] Further, in the present embodiment, although the description has been made such that the sintering is carried out using the sintering device (the energized sintering device 100) shown in
Examples
[0106] Hereinafter, the results of experiments carried out to confirm the effect of the present invention will be described.
Example 1
[0107] Each of Mg having a purity of 99.9 mass % (particle diameter: 180 μm, manufactured by Kojundo Chemical Lab. Co., Ltd.), Si having a purity of 99.99 mass % (particle diameter: 300 μm, manufactured by Kojundo Chemical Lab. Co., Ltd.), Sn having a purity of 99.99 mass % (particle diameter: 63 μm, manufactured by Kojundo Chemical Lab. Co., Ltd.), and Sb having a purity of 99.9 mass % (particle diameter: 300 μm, manufactured by Kojundo Chemical Lab. Co., Ltd.) was weighed. These powders were mixed in a mortar, placed in an alumina crucible, and heated at 750° C. for 2 hours in Ar with 5% H.sub.2. Considering the deviation from the stoichiometric composition of Mg:Si+Sn=2:1 due to the sublimation of Mg, Mg was mixed to be more by 1 at % more. As a result, the massive Mg—Si—Sn having the compositions shown in Experimental Examples 1 to 18 in Tables 1 and 2 was obtained.
[0108] Next, this massive Mg—Si—Sn was coarsely pulverized with a jaw pulverizer, further pulverized finely with a ball mill, and classified using a sieve shaker to obtain an Mg—Si—Sn powder having an average particle diameter of 30 μm.
[0109] An aluminum powder (purity: 99.99 mass %, particle diameter: 45 μm) and a boride powder (TiB.sub.2) (purity: 99.9 mass %, average particle diameter: 3 μm) were prepared as raw materials.
[0110] Next, the Mg—Si—Sn powder, the aluminum powder, and the boride powder were mixed in the formulations shown in Experimental Examples 1 to 18 in Tables 1 and 2 to obtain a raw material powder (the Mg—Si—Sn powder is treated as a remainder). It is noted that as will be described below in Experimental Example 14, the aluminum powder may be added at the time of producing the massive Mg—Si—Sn.
[0111] These raw material powders were packed in a carbon mold of which the inner side was covered with a carbon sheet, set in the sintering device (the energized sintering device 100) shown in
[0112] Heating was carried out to 500° C. under the sintering conditions of vacuum (vacuum degree: 2 Pa or less before the start of sintering), a pressurization pressure of 40 MPa, and a temperature elevation rate of 40° C./min. The heating was further carried out at a temperature elevation rate of 30° C./min, and the temperature was held at 700° C. for 5 minutes.
[0113] First, as Experimental Example, a single-layer thermoelectric conversion material was produced using the single Mg—Si—Sn powder.
[0114] Regarding the thermoelectric conversion material obtained as described above, the power factor PF and the dimensionless figure of merit ZT at various temperatures were evaluated. The evaluation results are shown in Table 1 and Table 2.
[0115] It is noted that, for example, the description of Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb)+0.06 wt % Al in Experimental Example 13 of Table 1 indicates that a massive Mg—Si—Sn obtained by adding an Sb dopant of a proportion of 0.5 at % to Mg—Si—Sn of Mg:Si:Sn=2:0.5:0.5 is pulverized, and 0.06 wt % of Al is added thereto at the time of sintering to obtain a thermoelectric conversion material. Similarly, the description of Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb, 0.1 at % Al) in Experimental Example 14 indicates it is a thermoelectric conversion material obtained by adding Sb of a proportion of 0.5 at % and Al of 0.1 at % to Mg—Si—Sn of Mg:Si:Sn=2:0.5:0.5 to obtain a massive Mg—Si—Sn and then pulverizing and sintering the obtained massive Mg—Si—Sn.
[0116] The electric resistance value R and the Seebeck coefficient S were measured by ZEM-3 manufactured by ADVANCE RIKO, Inc. The measurement of the electric resistance value R and the Seebeck coefficient S was carried out at 25° C., 50° C., 100° C., 200° C., 300° C., 400° C., and 450° C.
[0117] The power factor (PF) was determined according to Expression (1).
PF=S.sup.2/R . . . (1)
[0118] Here, S: Seebeck coefficient (V/K), R: electric resistance value (Ω.Math.m)
[0119] The thermal conductivity K was obtained from, thermal diffusivity×density×specific heat capacity. The thermal diffusivity was measured using a thermal constant measuring device (TC-7000 type manufactured by ADVANCE RIKO, Inc.), the density was measured using the Archimedes method, and the specific heat was measured using a differential scanning calorimeter (DSC-7 type, manufactured by PerkinElmer, Inc.). The measurement was carried out at 25° C., 50° C., 100° C., 200° C., 300° C., 400° C., and 450° C.
[0120] The dimensionless figure of merit (ZT) was determined according to Expression (2).
ZT=S.sup.2σT/κ . . . (2)
[0121] (Here, T=absolute temperature (K), κ=thermal conductivity (W/(m×K))
TABLE-US-00001 TABLE 1 Composition (concentration ZT of dopant in terms of at %) 25° C. 50° C. 100° C. 200° C. 300° C. 400° C. 450° C. Example 1 Mg.sub.2Si.sub.0.3Sn.sub.0.7 (0.5 at % Sb) 0.09 0.11 0.15 0.23 0.31 0.32 — Example 2 Mg.sub.2Si.sub.0.35Sn.sub.0.65 (0.5 at % Sb) 0.24 0.24 0.32 0.44 0.51 0.47 0.44 Example 3 Mg.sub.2Si.sub.0.4Sn.sub.0.6 (0.5 at % Sb) 0.20 0.22 0.30 0.51 0.60 0.54 0.51 Example 4 Mg.sub.2Si.sub.0.4Sn.sub.0.6 (1.0 at % Sb) 0.21 0.23 0.30 0.52 0.59 0.53 0.51 Example 5 Mg.sub.2Si.sub.0.45Sn.sub.0.65 (0.5 at % Sb) 0.17 0.23 0.26 0.42 0.51 0.48 0.48 Example 6 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) 0.18 0.21 0.28 0.47 0.62 0.66 0.66 Example 7 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (non) 0.03 0.04 0.06 0.09 0.08 0.06 0.06 Example 8 Mg.sub.2Si.sub.0.35Sn.sub.0.65 (0.5 at % Sb) + 0.21 0.25 0.32 0.43 0.48 0.41 0.38 3 wt % TiB.sub.2 Example 9 Mg.sub.2Si.sub.0.35Sn.sub.0.65 (0.5 at % Sb) + 0.17 0.19 0.25 0.30 0.34 0.35 0.32 7 wt % TiB.sub.2 Example 10 Mg.sub.2Si.sub.0.4Sn.sub.0.6 (0.5 at % Sb) + 0.20 0.22 0.30 0.42 0.51 0.48 0.44 3 wt % TiB.sub.2 Example 11 Mg.sub.2Si.sub.0.4Sn.sub.0.6 (0.5 at % Sb) + 0.18 0.20 0.27 0.4.3 0.51 0.48 0.44 7 wt % TiB.sub.2 Example 12 Mg.sub.2Si.sub.0.4Sn.sub.0.6 (0.5 at % Sb) + 0.23 0.25 0.32 0.50 0.61 0.59 0.59 0.3 wt % Al Example 13 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) + 0.18 0.21 0.27 0.47 0.62 0.63 0.68 0.06 wt % Al Example 14 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb, 0.19 0.22 0.29 0.46 0.60 0.62 0.65 0.1 at % Al) Example 15 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) + 0.17 0.21 0.30 0.49 0.64 0.64 0.67 0.32 wt % Al Example 16 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) + 0.17 0.19 0.26 0.43 0.57 0.64 0.64 1.0 wt % Al Example 17 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) + 0.19 0.20 0.28 0.47 0.65 0.69 0.70 0.3 wt % Al + 3 wt % TiB.sub.2 Example 18 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) + 0.17 0.19 0.28 0.46 0.61 0.66 0.71 0.3 wt % Al + 7 wt % TiB.sub.2
TABLE-US-00002 TABLE 2 Composition (concentration PF of dopant in terms of at %) 25° C. 50° C. 100° C. 200° C. 300° C. 400° C. 450° C. Example 1 Mg.sub.2Si.sub.0.3Sn.sub.0.7 (0.5 at % Sb) 0.765 0.883 0.951 1.119 1.209 1.229 — Example 2 Mg.sub.2Si.sub.0.35Sn.sub.0.65 (0.5 at % Sb) 1.933 1.871 1.988 2.023 1.911 1.633 1.472 Example 3 Mg.sub.2Si.sub.0.4Sn.sub.0.6 (0.5 at % Sb) 1.686 1.676 1.798 1.885 1.846 1.657 1.486 Example 4 Mg.sub.2Si.sub.0.4Sn.sub.0.6 (1.0 at % Sb) 1.760 1.732 1.802 1.923 1.812 1.604 1.484 Example 5 Mg.sub.2Si.sub.0.45Sn.sub.0.65 (0.5 at % Sb) 1.368 1.435 1.568 1.729 1.765 1.628 1.523 Example 6 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) 1.155 1.250 1.400 1.709 1.817 1.821 1.744 Example 7 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (non) 0.211 0.241 0.299 0.313 0.219 0.176 0.161 Example 8 Mg.sub.2Si.sub.0.35Sn.sub.0.65 (0.5 at % Sb) + 2.027 2.003 2.096 2.136 1.972 1.628 1.418 3 wt % TiB.sub.2 Example 9 Mg.sub.2Si.sub.0.35Sn.sub.0.65 (0.5 at % Sb) + 1.811 1.816 1.936 2.020 1.901 1.661 1.452 7 wt % TiB.sub.2 Example 10 Mg.sub.2Si.sub.0.4Sn.sub.0.6 (0.5 at % Sb) + 1.779 1.743 1.907 2.026 1.973 1.751 1.563 3 wt % TiB.sub.2 Example 11 Mg.sub.2Si.sub.0.4Sn.sub.0.6 (0.5 at % Sb) + 1.743 1.766 1.911 2.032 1.987 1.774 1.566 7 wt % TiB.sub.2 Example 12 Mg.sub.2Si.sub.0.4Sn.sub.0.6 (0.5 at % Sb) + 1.822 1.758 1.874 1.982 1.970 1.821 1.702 0.3 wt % Al Example 13 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) + 1.080 1.194 1.351 1.643 1.775 1.833 1.895 0.06 wt % Al Example 14 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb, 1.293 1.368 1.483 1.727 1.821 1.837 1.808 0.1 at % Al) Example 15 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) + 1.119 1.212 1.398 1.685 1.818 1.879 1.883 0.32 wt % Al Example 16 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) + 1.170 1.239 1.427 1.705 1.823 1.923 1.855 1.0 wt % Al Example 17 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) + 1.273 1.262 1.464 1.783 1.978 1.991 1.940 0.3 wt % Al + 3 wt % TiB.sub.2 Example 18 Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) + 1.195 1.236 1.494 1.818 1.994 2.038 2.045 0.3 wt % Al + 7 wt % TiB.sub.2
[0122] As shown in Tables 1 and 2, it can be confirmed, from Experimental Examples 1 to 7 in which the proportion of silicon and tin and the dopant concentration are changed, that the temperature range in which the thermoelectric characteristics are good differs depending on the composition. Further, in Experimental Examples 8 to 11 which contain a boride containing one or two or more metals selected from the group consisting of titanium, zirconium, and hafnium, it is confirmed that the power factor (PF) and the dimensionless figure of merit (ZT) are excellent in a relatively low temperature range. Further, in Experimental Examples 12 to 16 which contain aluminum, and Experimental Examples 17 and 18 which contain a boride and aluminum, it is confirmed that the power factor (PF) and the dimensionless figure of merit (ZT) are excellent in a relatively high temperature range.
Example 2
[0123] With reference to the evaluations in Table 1 and Table 2, Two kinds of Mg—Si—Sn powders were selected as a composition of the thermoelectric conversion material having good characteristics on the high temperature side for the first layer, and a composition having good characteristics on the low temperature side for the second layer.
[0124] These raw material powders were packed in a carbon mold of which the inside was covered with a carbon sheet and set in the sintering device (the energized sintering device 100) shown in
[0125] It is noted that heating was carried out to 500° C. under the sintering conditions of vacuum (2 Pa), a pressurization pressure of 40 MPa, and a temperature elevation rate of 40° C./min. The heating was further carried out at a temperature elevation rate of 30° C./min, and the temperature was held at 700° C. for 5 minutes.
[0126] For example, a thermoelectric conversion material having the composition of Experimental Example 6 for the first layer and the composition of Experimental Example 3 for the second layer was prepared and used as Present Invention Example 1.
[0127] Further, a thermoelectric conversion material having the compositions for the first layer and the second layer shown in Table 3 was obtained.
[0128] The power generation characteristics were measured as follows. A sample of 6 mm×6 mm×10 mm, in which the first layer was directly joined to the second layer and integrated, a heating block (the high temperature side), a heat flux block (the low temperature side, a chiller set at 35° C. was used), two Ag electrode plates, and two AlN plates were prepared, and they were arranged from the bottom, in the following order; the heat flux block, the AlN plate, the Ag electrode, the sample, the Ag electrode, the AlN plate, and the heating block. A terminal for measuring voltage and a terminal for measuring current were each attached to the Ag electrode plates at the upper and lower ends. The device used for the voltage/current measurement is a 6242 DC voltage current source/monitor manufactured by ADC Corporation.
[0129] The heating block and the heat flow block were held with a constant load of 200 N with the sample being sandwiched, and the temperature of the heating block on the high temperature side was set to 55° C., 100° C., 205° C., 300° C., and 395° C. The temperature differences (ΔT) were each 20° C., 66° C., 170° C., 260° C., and 355° C.
[0130] The temperature of the heating block was set to a predetermined temperature, and the open-circuit voltage was measured when the temperatures of the heating block and the heat flux block were stable. Next, a reverse current is allowed to flow, and the current value (the maximum current, the short-circuit current) at which the voltage becomes zero is measured using a direct voltage/current source/monitor. The maximum output was determined from the open-circuit voltage and the maximum current at each temperature, and further, it was replaced with the maximum output per unit area.
[0131] Table 4 shows the power generation characteristics of the sample in which a first layer containing 14 Mg.sub.2Si.sub.xSn.sub.1-x (here, 0<x<1) is directly joined to a second layer 15 containing Mg.sub.2Si.sub.ySn.sub.1-y (here, 0<y<1).
TABLE-US-00003 TABLE 3 Thermoelectric conversion material First layer Second layer x/y Present Invention Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) Mg.sub.2Si.sub.0.4Sn.sub.0.6 (0.5 at % Sb) 1.25 Example 1 Example 6 Example 3 Present Invention Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) Mg.sub.2Si.sub.0.35Sn.sub.0.65 (0.5 at % Sb) 1.43 Example 2 Example 6 Example 2 Present Invention Mg.sub.2Si.sub.0.55Sn.sub.0.45 (0.5 at % Sb) Mg.sub.2Si.sub.0.32Sn.sub.0.68 (0.5 at % Sb) 1.72 Example 3 Present Invention Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) + Mg.sub.2Si.sub.0.4Sn.sub.0.6 (0.5 at % Sb) + 1.25 Example 4 3 wt % TiB.sub.2 3 wt % TiB.sub.2 Example 10 Present Invention Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) + Mg.sub.2Si.sub.0.4Sn.sub.0.6 (05 at % Sb) + 1.25 Example 5 0.3 wt % Al + 3 wt % TiB.sub.2 0.3 wt % Al + 3 wt % TiB.sub.2 Example 17 Comparative Mg.sub.2Si.sub.0.4Sn.sub.0.6 (0.5 at % Sb) Mg.sub.2Si.sub.0.5Sn.sub.0.5 (0.5 at % Sb) 0.8 Example 1 Example 3 Example 6 Comparative Mg.sub.2Si.sub.0.6Sn.sub.0.4 (0.5 at % Sb) Mg.sub.2Si.sub.0.3Sn.sub.0.7 (0.5 at % Sb) 2 Example 2 Example 1
TABLE-US-00004 TABLE 4 Evaluation of thermoelectric power generation characteristics Evaluation item 20° C. 66° C. 170° C. 260° C. 355° C. Present Invention Open-circuit 6.94 20.30 52.49 82.74 110.84 Example 1 voltage(mV) Maximum 0.35 3.32 27.32 80.36 170.50 output (mW/cm.sup.2) Present Invention Open-circuit 7.39 21.28 54.16 82.87 119.75 Example 2 voltage (mV) Maximum 0.40 3.67 29.32 83.19 187.37 output (mW/cm.sup.2) Present Invention Open-circuit 6.53 19.01 50.38 77.21 103.59 Example 3 voltage (mV) Maximum 0.30 3.00 23.72 74.40 166.80 output (mW/cm.sup.2) Present Invention Open-circuit 7.05 20.38 56.27 81.50 107.43 Example 4 voltage (mV) Maximum 0.37 3.52 29.37 85.89 186.41 output (mW/cm.sup.2) Present Invention Open-circuit 7.41 21.68 55.54 85.60 112.30 Example 5 voltage (mV) Maximum 0.42 3.97 31.85 91.06 204.86 output (mW/cm.sup.2) Comparative Open-circuit 6.18 17.75 48.60 74.63 99.47 Example 1 voltage (mV) Maximum 0.28 2.79 22.85 70.55 162.20 output (mW/cm.sup.2) Comparative Open-circuit 9.98 26.48 58.74 76.44 91.87 Example 2 voltage Maximum 0.16 1.75 14.46 48.48 111.66 output (mW/cm.sup.2)
[0132] As shown in Tables 3 and 4, it can be confirmed that Present Invention Examples 1 to 5, in which a first layer containing Mg.sub.2Si.sub.xSn.sub.1-x (here, 0<x<1) is directly joined to a second layer containing Mg.sub.2Si.sub.ySn.sub.1-y (here, 0<y<1), where x/y is set within a range of more than 1.0 and less than 2.0, have excellent power generation characteristics as compared with Comparative Examples 21 and 22 in which x/y is set to outside a range of more than 1.0 and less than 2.0.
[0133] In particular, it can be confirmed that in a case where x/y is less than 1, the characteristics are decreased as a whole since a material having excellent characteristics in the high temperature region is used on the low temperature side, and a material having excellent characteristics in the low temperature region is used on the high temperature side. Further, it can be confirmed that in a case where x/y is 2 or more, the thermoelectric characteristics are decreased as a whole since the characteristics of the second layer (the low temperature side) are decreased.
[0134] From the results of the above examples, it was confirmed that according to the Present Invention Examples, it is possible to provide a thermoelectric conversion material, a thermoelectric conversion element, and a thermoelectric conversion module.
Reference Signs List
[0135] 1 Thermoelectric conversion module
[0136] 10 Thermoelectric conversion element
[0137] 11 Thermoelectric conversion material
[0138] 14 First layer
[0139] 15 Second layer
[0140] 18a, 18b Electrode
[0141] 19a, 19b Terminal