JP2007013000A - Thermoelectric conversion material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelectric conversion material and a thermoelectric conversion element which has increased mechanical strength while keeping the figure of merit of a Bi-Te-based thermoelectric material. <P>SOLUTION: When a Bi-Te-based thermoelectric conversion material having a uniaxial temperature gradient applied thereto is cooled upon melting and solidifying the thermoelectric conversion material, the material exhibits a specific value of X-ray diffraction intensity ratio of reflection on a specific surface perpendicular to the temperature gradient direction when measured, and thus the figure of merit can be increased. When a ratio between the full length of an element having metallic materials positioned at both end faces of the thermoelectric conversion material and the length of the thermoelectric conversion material is set at a specific value, electric resistivity ρ is reduced in the entire element, a Seebeck coefficient is remarkably increased by the interface effect between the metal material and the thermoelectric conversion material and by the metal heatsink effect to thereby increase power generation efficiency. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a Bi-Te thermoelectric conversion material and a thermoelectric conversion element used for a Peltier cooling element and a thermoelectric conversion element.

  Thermoelectric conversion elements are already used for temperature control of electronic coolers, optical communication equipment, measuring equipment, incubators, etc. If further improvements are made in the future, refrigerators that do not use CFCs and automotive air conditioners will be commercialized. It becomes possible.

  Thermoelectric conversion elements are devices that are expected to be put into practical use from the viewpoint of effective use of thermal energy, which is highly demanded in recent industries.For example, systems that convert waste heat into electrical energy, or outdoors. It can also be used for small portable power generators for easily obtaining electricity, flame sensors for gas appliances, and the like. If the performance is further improved, it will also be used for temperature control of a fuel reformer for an on-vehicle fuel cell.

  A thermoelectric conversion element can convert heat into electricity by providing a temperature gradient at both ends of P-type and N-type thermoelectric conversion materials, or conversely, voltage can be applied to the material to convert electricity into heat. The latter is well known as a Peltier element.

The thermoelectric conversion element has a configuration in which, for example, a P-type and an N-type semiconductor are PN-bonded by plating, soldering, silver brazing, or the like to form an element. In addition to high-performance chalcogen compounds such as Zn ₄ Sb ₃ , IrSb ₃ , Bi ₂ Te ₃ , and P _b Te as thermoelectric conversion materials for forming these elements, they have low thermoelectric properties but are abundant in resources Silicides such as FeSi ₂ and SiGe are known.

Conventional thermoelectric conversion elements (Peltier elements) generate thermoelectromotive force (temperature difference) using the temperature gradient (potential difference) applied to the material, and the conversion efficiency is a figure of merit for thermoelectric (electrothermal) conversion elements. (ZT = TS ² / ρκ, where T is the absolute temperature, S is the Seebeck coefficient, ρ is the electrical resistivity, and κ is the thermal conductivity). The efficiency was as low as several percent and was not sufficient. Since this conversion efficiency increases as ZT increases, a material having a performance index as high as possible is required.

  Currently, most Bi-Te-based thermoelectric materials are produced in a crystal state close to a single crystal using the Bridgeman method, the Czochralski method, and the zone melt method, or powder metallurgy by hot pressing. It is produced as a polycrystal using the method.

As a technique related to a method for manufacturing a thermoelectric conversion element, for example, Patent Document 1 describes that a powder is sintered to produce a thermoelectric conversion element, and Bi ₂ Te ₃ is used as a main material and Se and Sb are used. Although it is described that they are added, they are contained in the form of Bi ₂ Se ₃ , Sb ₂ Te ₃ or the like, respectively, and do not destroy the basic structure of Bi ₂ Te ₃ .
JP2002-33525

  The conversion efficiency of electrothermal or thermoelectric conversion elements is very low compared to about 20% of solar cells, etc., and it is only a few% at present, which is the reason for narrowing the applications of thermoelectric conversion elements or Peltier elements. This is also the reason why thermoelectric conversion elements are not widespread.

  A single crystal of a Bi-Te thermoelectric conversion material is usually produced by cooling a molten metal with a temperature gradient and growing the c-plane of the crystal along the direction of the temperature gradient. The single crystal has the property of easily cracking along the (001) cleavage plane (c-plane).

  On the other hand, the polycrystalline body has a problem that the electrical resistivity increases due to the grain boundary scattering of the carrier and the figure of merit decreases. For this reason, when producing a module having a high figure of merit (ZT), a single crystal is used, and when giving priority to mechanical strength, a polycrystal is used.

  In general, when using Bi-Te thermoelectric conversion materials as a Peltier module in a state close to a single crystal, both the direction of the generated temperature gradient and the direction of current flow are assembled so as to be perpendicular to the c-axis of the crystal. For this reason, only the thermoelectric properties of the component perpendicular to the c-axis of the crystal have been used so far, and the thermoelectric properties of the c-axis component have hardly been used.

  In order to satisfy both the figure of merit and the mechanical strength, the composition of Bi-Te, the kind of additive, the amount added, etc. were studied, but the figure of merit at room temperature did not greatly exceed 1. The Seebeck coefficient is not sensitive to the crystal anisotropy, but the thermal conductivity is low in the direction parallel to the c-axis, and conversely the electrical resistivity is high in the direction parallel to the c-axis. The figure of merit changes greatly.

  An object of the present invention is to provide a thermoelectric conversion element comprising a thermoelectric conversion material with an improved figure of merit and a high power generation efficiency in a Bi-Te based thermoelectric conversion material.

  As a result of diligent research on the configuration that can improve the figure of merit in the Bi-Te thermoelectric conversion material, the inventors have found that the Bi-Te thermoelectric compound contains an additive element that determines the polarity of the Bi-Te compound alone or in combination. X-ray diffraction intensity ratio of (006) and (105) reflections measured on a plane perpendicular to the direction of the temperature gradient by cooling by applying a uniaxial temperature gradient during melt solidification or hot pressing of the conversion material It has been found that I (006) / I (105) shows a specific value and the figure of merit can be greatly improved.

  In addition, as a result of intensive studies on the structure of the thermoelectric conversion element with high power generation efficiency, the inventors have plated the both ends of the thermoelectric conversion material material that has been cut and polished into an ingot, and then assembled by soldering with a metal material. In the above, by making the length of the thermoelectric conversion material a specific ratio of the total length of the element, the electrical resistivity ρ of the entire element is lowered, and at the same time, the Seebeck coefficient S is the interfacial effect between the metal material and the thermoelectric conversion material and the metal It was found that the power generation efficiency can be improved dramatically by the heat sink effect.

  Furthermore, in the thermoelectric conversion element in which the metal material is arranged at both ends of the thermoelectric conversion material material, the ratio of the length of the thermoelectric conversion material and the distance between the lead wires provided in the metal material is a specific ratio, and further from the lead wire attachment position. It is possible to improve the power generation efficiency by assembling so that the distance to the end face of the metal material that is in contact with the heat sink or heat sink is equal to or greater than the distance from both end faces of the thermoelectric conversion material to the lead wire. It was found that this was possible and the present invention was completed.

That is, the present invention is a thermoelectric conversion material mainly composed of Bi ₂ Te ₃ , and the X-ray diffraction intensity ratio of (006) and (105) reflections measured on a plane perpendicular to the temperature gradient direction of the material. A thermoelectric conversion material characterized in that I (006) / I (105) is 2 to 15%.

Further, the present invention is a composite thermoelectric conversion element in which a metal material (length l _M ) is disposed at both ends of a thermoelectric conversion material (length l _B ), and the thermoelectric conversion material length and the total length of the thermoelectric conversion element (l _B + 2l _M ) ratio (l _B / (l _B + 2l _M )) is 0.03 to 0.10, and the metal end faces of the P-type and N-type thermoelectric conversion elements are arranged so as to form the same plane. It is a composite thermoelectric conversion element for power generation characterized by being solidified and lead-bonded in each plane and having an insulating coating.

Further, the present invention is a composite thermoelectric conversion element in which a metal material (length l _M ) is disposed at both ends of a thermoelectric conversion material (length l _B ), and the thermoelectric conversion material length and the total length of the thermoelectric conversion element (l _B + 2l _M ) ratio (l _B / (l _B + 2l _M )) is 0.60 to 0.98, and the metal end faces of the P-type and N-type thermoelectric conversion elements are arranged so as to form the same plane. It is a composite thermoelectric conversion element for power generation characterized by being solidified and lead-bonded in each plane and having an insulating coating.

Further, the present invention has a lead provided at a distance (t) between lead wires on a metal material (length l _M ) disposed at both ends of a thermoelectric conversion material (length l _B ), and has a total length l. A heat sink with leads on the metal material at a position of (tl _B ) / 2 from both end faces of the thermoelectric conversion element, and the metal end faces of the P-type and N-type thermoelectric conversion elements being arranged to form the same plane Alternatively, the structure is in contact with the endothermic plate, and the distance to the metal end face (= (lt) / 2) is equal to or more than (tl _B ) / 2, and at the same time, l _B / t is 0.60 to 0.98. This is a composite thermoelectric conversion element for power generation.

  According to the present invention, a polycrystalline Bi-Te thermoelectric conversion material has sufficient strength and at the same time a material with a high figure of merit. The length of the metal and the thermoelectric conversion material is set to a predetermined ratio. By assembling the conversion element, the electrical resistivity ρ of the entire element is reduced, and at the same time, the Seebeck coefficient S is dramatically increased by the interface effect between the metal electrode and the thermoelectric conversion material and the heat sink effect of the metal, and the figure of merit Can be greatly improved.

  According to this invention, in the thermoelectric conversion element, by specifying the ratio of the length of the thermoelectric conversion material to the distance between the lead wires provided in the metal material and the distance from the lead attachment position to the end surface of the metal material, the thermoelectric conversion material The power generation efficiency can be effectively utilized and the power generation efficiency can be greatly improved.

In this invention, the Bi-Te thermoelectric conversion material is a compound in which a part of Bi atom in a Bi ₂ Te ₃ compound having a rhombohedral crystal structure is substituted with a group 5 element, or a part of Te atom is group 6 This is a material obtained by adding a group 4 element, a group 6 element, or a group 7 element alone or in combination to an element-substituted compound.

  The inventors have made a molten metal obtained by adding an additive element that determines the polarity of a Bi-Te compound alone or in combination, a temperature gradient in the molten metal and in the ingot to be 1 ° C / cm to 15 ° C / cm, and 0.1% Cooling at a cooling rate of ℃ / min ~ 5 ℃ / min, aligning the c axis of some crystal grains in the direction of the temperature gradient, greatly reducing the thermal conductivity while maintaining the mechanical strength of the material, It has been found that a material with a high figure of merit can be obtained.

Bi ₂ Te ₃ thermoelectric conversion materials originally show P-type thermoelectric properties, but Bi ₂ Te ₃ has a hole carrier concentration that is too high, so it entered the crystal to reduce the hole carrier concentration. The index of performance is enhanced by adding chalcogen elements of group 6 that sometimes emit electrons.

In an embodiment where the Bi ₂ Te ₃ thermoelectric conversion material is applied as an N-type semiconductor, the polarity is changed from positive to negative by adding a halide of a group 6 chalcogen element, a group 7 halogen element or a metal element. At the same time, the carrier index is adjusted by the added amount to improve the figure of merit.

The additive amount of additive elements and additives to the Bi ₂ Te ₃ system thermoelectric conversion material is at least one in the P type in order to make a semiconductor having the desired polarity and carrier concentration (˜10 ¹⁹ cm ⁻³ ). Is preferably added in an amount of 3 wt% or more, and if added in excess of 15 wt%, the electrical resistivity may increase due to the impurity effect, so it is preferably 15 wt% or less, particularly preferably 3 to 12 wt%. %. When adding in combination, the total addition amount is desirably 4 to 13 wt%.

  In addition, in N type, it is necessary to add at least one kind of 0.01 wt% or more, and if it exceeds 0.10 wt%, the electrical resistivity may increase due to the impurity effect. It is preferable. When adding in combination, the total addition amount is preferably 0.09 to 0.25 wt%.

Additive elements, the Group 4 element, Si, Ge, Sn, As P _b, 6 group elements, S, Se, As Te, 7 group elements, Br, these various elements when I is preferably added in combination Or a compound with a main component element may be used.

  In general, since the operating temperature range of the Peltier element or thermoelectric conversion element varies depending on the application, a material exhibiting a high figure of merit (ZT) in the required temperature range is required. Therefore, the main component of the Bi—Te thermoelectric conversion material is appropriately selected according to the application. For example, when using at a low temperature, the P type contains more Bi than Sb, and when used near room temperature, the Bi is selected to be less than Sb.

  When manufacturing a thermoelectric conversion material by melt solidification, if the cooling rate exceeds 5 ° C / min, the Seebeck coefficient will decrease and the figure of merit will decrease, but even if the cooling rate is less than 0.1 ° C / min, The Seebeck coefficient decreases and the figure of merit decreases. Therefore, the cooling rate is preferably 0.1 ° C / min to 5 ° C / min.

  In addition, when the temperature gradient in the molten metal and ingot exceeds 15 ° C / cm, the thermal conductivity increases at the same time as the c-plane is almost aligned along the temperature gradient direction. Grows too much, the crystal grain size exceeds 3 mm, and the mechanical strength of the polycrystal decreases. Conversely, when the temperature gradient in the molten metal and ingot is less than 1 ° C / cm, it becomes an almost isotropic polycrystal and the crystal grain size is less than 0.2 mm, increasing the electrical resistivity of the ingot and improving the performance. The index drops. Therefore, the temperature gradient is preferably 1 ° C./cm to 15 ° C./cm, and the average crystal grain size of the ingot is preferably 0.2 to 3 mm.

  This thermoelectric conversion material is a polycrystal, and the X-ray diffraction intensity ratio I (006) / I (105) of (006) and (105) reflection measured on a plane perpendicular to the direction of the temperature gradient is 2 to 15% is preferred. That is, since this thermoelectric conversion material uses a component in the c-axis direction having a very low thermal conductivity, a significant decrease in the thermal conductivity of the entire material can be expected, so that the figure of merit can be greatly improved.

  As a method for producing a polycrystal from a molten metal, it may be produced by either the Bridgeman method or the zone melt method, but in order to obtain a polycrystal, the temperature gradient in the molten metal is 1 ° C./cm to 15 ° C. The ingot crystal grain size must be 3 mm or less as described above.

  A large amount of additive elements and additives are segregated or precipitated in the crystal grain boundaries of the ingot cooled at a high speed, and they are not very dispersed in the crystal grains, but the crystal structure of the ingot cooled at a low speed. Has a large crystal grain size, and the additive elements and additives are considerably dispersed in the crystal grains.

  When the additive element is appropriately dispersed in the crystal grains, the thermal conductivity due to the phonon is lowered, and the additive element is ionized to release carriers, so that the electrical resistivity tends to be lowered. Further, when the additive element is segregated, the opposite tendency is exhibited. Therefore, if the additive element is controlled so as to be in an appropriate dispersed state, an increase in electrical resistivity can be suppressed even if some crystal grains are oriented in the c-axis direction, so that the figure of merit can be increased. become.

When this thermoelectric conversion material is produced at an appropriate cooling rate, the additive element can be appropriately dispersed in the crystal grains. However, the optimum cooling rate varies greatly depending on the size of the ingot, the crystal grain size of the ingot, the composition of the material, and the additive elements. Therefore, a suitable cooling condition may be selected according to the ingot production conditions. The cooling of the ingot may be any temperature as long as the Bi ₂ Te ₃ compound is dissolved, but the melting and cooling atmosphere is preferably a vacuum or an inert gas atmosphere.

  This thermoelectric conversion material has the same manufacturing concept not only in the above-described melt solidification but also in the production by a known powder metallurgy method. When a powder having a required particle size is produced by a hot press, a uniaxial temperature is produced. By sintering with a gradient and aligning the c-axis of some crystal grains in the direction of the temperature gradient, the above-described mechanism greatly reduces the thermal conductivity, and a material with a high figure of merit can be obtained.

The configuration of the thermoelectric conversion element will be described below. As shown in FIG. 1, when assembled composite thermoelectric conversion element 1 of the required length l thermoelectric conversion material required length at both ends of the 2 l _{M M} / B / _M disposing the metal material 3, 3 of the _B, The power factor P (= S ² / ρ) of the element can be obtained by using the ratio x of the length _{B to} the total length l as a function of x = l _B / l.

When this thermoelectric conversion element is handled as an electric circuit or a thermal circuit, the electric resistivity ρ of the element is expressed by the following equation (1).
ρ = 1 / l ・ (2ρ _M l _M + ρ _B l _B ) (1)

Here, ρ _M and ρ _B are electrical resistivity of the metal and the thermoelectric conversion material. Further, if b = ρ _M / ρ _B , the following equation (2) is obtained.
ρ = ρ _B {x + b (1-x)} (2)

Here, if the thermal conductivity of the metal and the thermoelectric conversion material is κ _M and κ _B , and the temperature difference generated in each material when a certain temperature difference is applied to this element is ΔT _M and ΔT _B , the following (3) It becomes an expression.

Here, c = κ _M / κ _B. Therefore, the temperature difference of the entire element is expressed by equation (4).
ΔT = 2ΔT _M + ΔT _B (4)

Voltage generated at that time, when the Seebeck coefficients of the metal and the thermoelectric conversion material and S _M and S _B, the equation (5).
ΔV = 2ΔT _M S _M + ΔT _B S _B (5)

  Therefore, the Seebeck coefficient S of the entire thermoelectric conversion element is expressed by the following equation (6).

Here, a = S _M / S _B. The power factor P of the thermoelectric conversion element is obtained from the equation (7). Here, P _B = S _B ² / ρ _B. The power factor P / P _B of the thermoelectric conversion element is always greater than 1 and increases at a certain optimum x when P _B > P _M.

  When the electrical resistivity of the metal M constituting the element is low, the thermal conductivity is high, the Seebeck coefficient of the thermoelectric conversion material B is high, and the thermal conductivity is low, the power factor is the most at a given x. growing. Although it does not prescribe | regulate especially as a thermoelectric conversion material, the power factor of an element becomes larger when the material with a high figure of merit is used.

In the case of a combination of the Bi ₂ Te ₃ thermoelectric conversion material of the present invention and a metal with Cu, x = l _B / l (where l is the total length of the element) is maximized in the range of 0.03 to 0.10. The maximum power factor P _{max at} that time exceeds about 100 (mW / K ² m), and reaches about ten times as much as that of the Bi ₂ Te ₃ series thermoelectric conversion material.

  The composite thermoelectric conversion element with x = 0.03 to 0.10 with improved power factor in this way has a structure that sacrifices the thermal conductivity, so it is a place where temperature difference is constantly applied, that is, between the primary cooling water and seawater. It can be used for generators that use temperature differences. This is because even if heat is transferred through the element, the heat source has a large heat capacity, so that the temperature difference applied to the sandwiched thermoelectric conversion material hardly changes. Moreover, since the power factor is large, there is an advantage that a large current and a large output can be obtained with a small temperature difference. Moreover, since the usage-amount of thermoelectric conversion material can be decreased, it is effective also in cost reduction.

As a method of assembling such a thermoelectric conversion element, it is not simply a conventional method of assembling P-type and N-type thermoelectric conversion elements, but assembling so that the ratio of the length of the thermoelectric conversion material and the metal is a predetermined ratio. The present invention proposes a method in which the P-type thermoelectric conversion element 1 _P and the N-type thermoelectric conversion element 1 _N are alternately embedded in a highly insulating liquid resin, and then the resin 6 is dried and solidified to be integrated.

After resin 6 has hardened, P-type thermoelectric conversion element 1 _P and N-type thermoelectric conversion element 1 _N are connected in series with lead wire 5 as shown in FIG. 2A, and then a thin insulating film with good thermal conductivity Since the sealing property of the module is improved, liquids with different temperatures do not mix through the module when used for power generation, and at the same time, the waterproofness and corrosion resistance of the module are improved. Moreover, by hardening with resin, there exists an advantage which the mechanical strength of the assembled thermoelectric conversion element also improves remarkably.

For example, as the resin to be used, a mixture of an epoxy resin and a curing agent is suitable. As further illustrated the individual thermoelectric conversion elements in Figure 2B, all the thermoelectric conversion elements 1 _P in the staggered structure, 1 _N to improve the energy absorbing efficiency per unit area by increasing the percentage of the total modules Is possible.

On the other hand, the ratio x of the total length l of l _B is the composite thermoelectric conversion element from 0.60 to 0.98, than the calculated value by the interfacial effect Seebeck coefficient S is the (6) between the metal electrodes and the thermoelectric conversion material There is a phenomenon that dramatically increases, and as a result, the figure of merit significantly increases. The increase rate of the Seebeck coefficient is considered to change depending on the joining method of the thermoelectric conversion material and the metal, but the interface effect is particularly large when the metal has low electrical resistivity and high thermal conductivity.

  When a Bi-Te thermoelectric conversion material and Cu are combined, the Seebeck coefficient is improved by about 30% at x = 0.98 for both P-type and N-type, reaching an absolute value of about 260 μV / K. This corresponds to a 1.7-fold increase in the figure of merit ZT. Since the metal to be used needs to be a material excellent in corrosion resistance, a simple metal or an alloy of noble metals such as Cu, Ag and Au is preferable. Although it does not prescribe | regulate especially as a thermoelectric conversion material, the performance index of an element improves when the above-mentioned thermoelectric conversion material with a high performance index is used.

In a thermoelectric conversion element using the interface effect, this x = l _B / l
When is less than 0.60, the thermal conductivity of the entire device is high, and the figure of merit is low. However, if x exceeds 0.98, the electrical resistivity of the entire device increases, and the figure of merit is almost the same as the figure of merit of the thermoelectric conversion material itself, so x is most preferably 0.60 to 0.98.

As a method for assembling such a thermoelectric conversion element, the distance between the lead wires 4 and 4 (t) and the length of the thermoelectric conversion material (l _B ) Ratio (l _B / t) to a predetermined ratio (x) as described above, specific positions of the metal materials 3 and 3 of the P-type and N-type thermoelectric conversion elements 1 (see FIG. 3A) ), The lead wire 4 is soldered, the P-type and N-type thermoelectric conversion elements 1 are connected in series, and then a method of attaching the heat radiating plate 7 and the heat absorbing plate 8 by the same method as before is proposed.

  The metal from the mounting position of the lead wire to the heat sink and the end face of the metal in contact with the heat sink plays the role of a heat sink of the thermoelectric conversion element, and has an effect of increasing the Seebeck coefficient due to the interface effect.

The length ((lt) / 2) from the lead wire attachment position to the metal end face in contact with the heat dissipation / heat absorption plate is the distance from the lead wire attachment position to the end face of the thermoelectric conversion material ((tl _B ) / 2 ) Or more.

The increase in Seebeck coefficient was not seen with conventional modules.
This is because the distance between ((tl _B ) / 2) and ((lt) / 2) is too short. Further, in order to improve the mechanical strength, a liquid resin may be poured into the gap between the thermoelectric conversion elements as shown in FIG. 3B so as to be integrated with the thermoelectric conversion element and the heat radiating plate or the heat absorbing plate.

  When joining the thermoelectric material and the metal material, if the joining metal does not dissolve or react with the thermoelectric material or metal, either Ni or the like is plated and soldered, or Bi or Bi-Sb alloy is used. It may be melted and used as a bonding material. If the plating film thickness or the thickness of the bonding metal is reduced, there is no significant effect on the characteristics by either method.

Example 1
Examples of the thermoelectric conversion material and the manufacturing method thereof will be described. Table 1 shows various combinations of main components and additive elements used to produce N-type and P-type Bi-Te thermoelectric conversion materials.

  After mixing elements and compounds in a predetermined ratio in this way, vacuum sealing in a 12 mm diameter quartz tube and melting at high frequency (purity of raw material used is 99.99% or more), melting the material, cooling rate and sample The sample for measurement was cut from the center of a cylindrical ingot produced by changing the temperature gradient of the part, and the thermoelectric conversion characteristics were measured at 25 ° C. The preparation conditions of these samples are shown in Table 2, and the measurement results of thermoelectric conversion characteristics are shown in Table 3.

  After mixing and kneading using the same raw material powder before melting, it is vacuum sealed in a hot press container and ingot by cylindrical sintering produced by changing the cooling rate and the temperature gradient of the sample part by the hot press method In this case, the same characteristics as those obtained by the above-mentioned melt-solidification were obtained.

  In addition, the pass / fail criterion of the figure of merit was 1.30, and more than this was accepted. Samples No. 2, No. 5 and No. 9 were processed into a shape of 5 × 5 × 25 mm and the bending strength was measured with a span of 15 mm in order to examine the mechanical strength. The results are shown in Table 4.

Example 2
For the assembly of thermoelectric conversion elements, the P type uses the No. 3 material in Table 3, the N type uses the No. 7 material, and is cut into a 2 x 2 mm ² shape. Cut to length shown in 5. Moreover, Cu and Ag used as electrode materials were also processed into the length dimensions shown in the table. After plating Ni on both ends of the thermoelectric conversion material, Cu and Ag were joined with eutectic solder to produce P-type and N-type thermoelectric conversion elements. Table 5 shows the results of measuring the thermoelectric characteristics of the produced thermoelectric conversion elements at 25 ° C. The Seebeck coefficient was measured by giving a temperature difference to both ends of the element.

  Next, a module was fabricated by alternately arranging 18 P-type and N-type thermoelectric conversion elements as shown in FIG. 2A. Instead of the two water tank partition plates, this module can be installed, water at a temperature of 30 ° C and 80 ° C can be placed in each tank, the temperature difference of 50 ° C applied to the module, and the generated voltage and current can be measured and taken out. The output power was calculated. The results are shown in Table 6. As a pass / fail judgment, an output power of 0.9 (W) or more was regarded as acceptable.

Here, the relative length x = l _B / l ignoring the plating and solder thickness
Was calculated. The output power W is not a ^{W = V 2 / R (W} ), were calculated using the formula W = V ² / 4R retrieval possible output power (W).

Example 3
In order to investigate the effect of increasing the Seebeck coefficient by the combination, a thermoelectric conversion element was assembled. For type P, use the material of No. 3 in Table 3, and for type N, use the material of No. 7 in Table 3, cut into a 2 x 2 mm ² shape, and then the length dimensions shown in Table 7 Disconnected. Also, Cu and Ag used as electrodes were processed similarly.

  The thermoelectric conversion material was plated with Ni and then joined with Cu or Ag by eutectic solder to produce a thermoelectric conversion element. Table 7 shows the results of measuring the thermoelectric characteristics of the produced thermoelectric conversion elements at 25 ° C. The Seebeck coefficient was measured by giving a temperature difference to both ends of the element. As a pass / fail judgment, a performance index of ZT1.5 or higher was accepted.

Example 4
In order to investigate the heat sink effect of the metal electrode of the thermoelectric conversion element, a P-type and N-type combined thermoelectric conversion element of x = l _B /l=0.38 was produced with the length dimensions shown in Table 8, and as shown in FIG. The relationship between the connection position and the figure of merit was investigated by changing the connection position of the lead wires.

25 ° C by changing the ratio (lt) / (tl _B ) between the distance (lt) / 2 from the metal end face to the lead wire connection position and the distance (tl _B ) / 2 from the end face of the thermoelectric conversion material to the lead wire connection position Table 8 shows the results of the thermoelectric properties measured at 1. The Seebeck coefficient was measured by giving a temperature difference to both ends of the element.

  As shown in Tables 3 and 4, it can be seen that the samples prepared with a small temperature gradient have improved mechanical strength.

In the case of the combination of Bi ₂ Te ₃ based thermoelectric conversion material and Cu according to the present invention, the power factor is increased, and because of the structure at the expense of thermal conductivity, the location where temperature difference is constantly applied, for example, nuclear power generation It can be used for a generator that uses the temperature difference between cooling water and seawater. Moreover, a figure of merit can be dramatically increased by attaching a lead wire in the middle of the metal at both ends of the thermoelectric conversion material and utilizing the metal heat sink effect.

FIG. 1 is an explanatory perspective view of a composite thermoelectric conversion element. 2A and 2B are a plan view and a side view illustrating an arrangement example of P-type and N-type thermoelectric conversion elements. FIG. 2A shows a configuration in which elements are arranged in parallel, and FIG. 2B shows a configuration in which elements are arranged in a staggered manner. FIG. 3A is a perspective explanatory view of a composite thermoelectric conversion element, and FIG. 3B is an explanatory view showing an assembly configuration example of P-type and N-type thermoelectric conversion elements.

Explanation of symbols

1 Composite thermoelectric transducer
1 _P P type thermoelectric transducer
1 _N N-type thermoelectric transducer
2 Thermoelectric conversion materials
3 Metal material
4,5 Lead wire
6 Resin
7 Heat sink
8 Endothermic plate

Claims (7)

A thermoelectric conversion material mainly composed of Bi ₂ Te ₃ and measured in a plane perpendicular to the temperature gradient direction of the material (006) and (105) reflection X-ray diffraction intensity ratio I (006) / I A thermoelectric conversion material having (105) of 2 to 15%. 2. The thermoelectric conversion material according to claim 1, which is a thermoelectric conversion material cooled by applying a uniaxial temperature gradient after melting, and is a polycrystal having an average crystal grain size of 0.1 to 3 mm. 2. The thermoelectric conversion material according to claim 1, which is a thermoelectric conversion material obtained by sintering material powder with a uniaxial temperature gradient, and is a polycrystal having an average crystal grain size of 0.1 to 3 mm. It is a composite thermoelectric conversion element in which metal materials (length l _M ) are arranged at both ends of the thermoelectric conversion material (length l _B ), and the ratio of the thermoelectric conversion material length to the total length of the thermoelectric conversion element (l _B + 2l _M ) (l _B / (l _B + 2l _M )) is 0.03 to 0.10, and the metal end faces of the P-type and N-type thermoelectric conversion elements are arranged so as to form the same plane, and are integrally solidified. A combined thermoelectric conversion element for power generation, which is lead-bonded within and has an insulating coating. It is a composite thermoelectric conversion element in which metal materials (length l _M ) are arranged at both ends of the thermoelectric conversion material (length l _B ), and the ratio of the thermoelectric conversion material length to the total length of the thermoelectric conversion element (l _B + 2l _M ) (l _B / (l _B + 2l _M )) is 0.60 to 0.98, and the metal end faces of the P-type and N-type thermoelectric conversion elements are arranged so as to form the same plane, and are integrally solidified. A combined thermoelectric conversion element for power generation, which is lead-bonded within and has an insulating coating. From the both end faces of the composite thermoelectric conversion element with the total length l, having leads provided at the distance (t) between the leads in the metal material (length l _M ) arranged at both ends of the thermoelectric conversion material (length l _B ) (tl _B ) / 2 lead is placed on the metal material, and the metal end faces of the P-type and N-type thermoelectric conversion elements are arranged so as to form the same plane, and are in contact with the heat sink or the heat sink. The composite thermoelectric power generation with a distance (= (lt) / 2) equal to or greater than (tl _B ) / 2 and at the same time l _B / t is 0.60 to 0.98. Conversion element. The thermoelectric conversion material was measured on a plane perpendicular to the direction of the temperature gradient of the material mainly composed of Bi ₂ Te ₃ (006) and (105) X-ray diffraction intensity ratio I (006) / I (105) of reflection. 7. The composite thermoelectric conversion element for power generation according to claim 4, wherein is 2 to 15%.

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