KR20120011779A - Thermoelectric materials deformed by cryogenic impact and process for preparing the same - Google Patents

Abstract

PURPOSE: A thermoelectric material which is deformed with low temperature and a manufacturing method thereof are provided to improve performance of the thermoelectric material with a flat anisotropy fine structure. CONSTITUTION: A composite precursor includes thermoelectric powder(2) and powder with thermal and electrical insulation properties. The composite precursor is packed and sealed after being introduced into a metal jacket(1). A cold shock(4) is applied to the metal jacket which includes the thermoelectric powder within a supporter(5). A fine structure of the thermoelectric powder is deformed. The cold shock is performed at a temperature of approximately 0°C or less.

Description

Thermoelectric materials deformed by cryogenic impact and process for preparing the same}

Provided are a thermoelectric material deformed by low temperature impact and having an increased defect density, and a method of manufacturing the same.

Thermoelectric materials and thermoelectric devices have been studied in recent years due to the efficient solid-state cooling and power generation. In general, it is known that bulk phase thermoelectric materials do not exhibit high efficiency for energy conversion or energy transfer applications. However, with advances in nanotechnology and material fabrication techniques, quantum confined structures such as artificially produced quantum wells have made it possible to significantly increase the efficiency of converting heat into electrical energy. Recently, studies on such structures have steadily increased the figure of merit (ZT).

As a factor for measuring the performance of such a thermoelectric material, a dimensionless performance index ZT value defined by Equation 1 below is used.

&Quot; (1) "

Where S is the Seebeck coefficient (Volts / degree K), σ is the electrical conductivity (1 / W-meter), T is the absolute temperature, and κ is the thermal conductivity (Watt / meter-degree K).

The Seebeck coefficient S depends on the density of state (DOS). In reduced dimensions, for example two-dimensional quantum wells or one-dimensional nanowires, the DOS becomes higher than three-dimensional bulk material. As a result, higher DOS results in higher S and σ. If the dimension involved is smaller than the phonon wavelength, the thermal conductivity κ becomes smaller.

It is already recognized that if ZT> 1, thermoelectric materials useful in a variety of applications, such as heat recovery and space power applications, will be significantly stimulated for technology replacement in devices such as generators and heat pumps. have. In addition, reducing the size of the particles that make up the thermoelectric material will yield significantly improved efficiencies for the bulk thermoelectric equipment used so far.

The problem to be solved is to provide a thermoelectric material with a new structure.

Another problem to be solved is to provide a method of manufacturing the thermoelectric material.

Another problem to be solved is to provide a device employing the thermoelectric material.

According to one aspect, there is provided a thermoelectric material having a microstructure modified by low temperature impact.

According to another aspect, preparing a thermoelectric powder, introducing it into a metal or plastic jacket, and then packing and sealing; And deforming a microstructure of the thermoelectric material powder by applying a low temperature impact on the thermoelectric material powder-containing metal or plastic jacket.

According to another aspect, there is provided a thermoelectric element, a thermoelectric module, and a thermoelectric device including the thermoelectric material.

Deformation according to the low temperature impact on the thermoelectric material increases the defect density in the microstructure therein, and has a flat anisotropic microstructure, which improves the performance index of the thermoelectric material. This improves the efficiency of the thermoelectric element, thermoelectric module or thermoelectric device employing the thermoelectric material.

1 and 2 is a schematic diagram showing a single axis deformation and low temperature impact process according to one embodiment.
3 is a schematic diagram showing a low temperature impact process according to one embodiment.
4 is a perspective view of a thermoelectric module according to one embodiment.
5 is a schematic diagram of a thermoelectric module according to one embodiment, showing thermoelectric cooling by the Peltier effect.
6 is a schematic diagram of a thermoelectric module according to an embodiment, showing thermoelectric generation by a Seebeck effect.

Hereinafter will be described with reference to the accompanying drawings and specific embodiments. In addition, content related to starting materials, processing processes, components, and equipment that are well known to those skilled in the art are excluded so as not to cause confusion about the following description. However, the detailed description and specific embodiments described below are for the purpose of description and not limitation, unless otherwise specified.

The thermoelectric material according to one embodiment may have a microstructure deformed by low temperature impact.

When the thermoelectric material powder is impacted at a low temperature, deformation is applied to the thermoelectric material microstructure, which causes defects in the microstructure. The increase in defects in the microstructure inside the thermoelectric material will control the size of the microstructure. This can increase the position where phonon scattering occurs. As a result, the thermal conductivity of the thermoelectric material κ can be made smaller by blocking the movement of the phonon which is responsible for the heat transfer and not the carrier movement, thereby improving the performance index ZT.

According to one embodiment, the thermoelectric material powder may be used having a nano size or a micron size, for example, the nano size may have an average size of about 1nm to about 1,000nm, the micron size is about 1 It may have a size of about μm to about 1,000 μm.

Impacts on thermoelectric materials at low temperatures cause defects, such as dislocations, twins, point defects, twisted grain boundaries, or twisted lattice structures. Can be. The amount of such defects increases as the strain rate increases. The strain rate is generally slower than 0.1 inches / inch / second in cold rolling, bending, extrusion, and the like. Hand hitting a large hammer provides a strain rate of 1 inch / inch / second. Therefore, when the strain rate is increased, more defects are caused in the thermoelectric material, and as a result, more phonon scattering is generated, thereby reducing thermal conductivity.

According to one embodiment, the strain rate may, for example, range from 5 inches / inch / second or more, or 50 inches / inch / second to 2,000 inches / inch / second. As a device providing such a high strain rate, for example, a gas-driven gun or an explosive-charge-driven gun may be used. As the gas-driven gun, Hopkinson Bar Impact deformation may be used as an example. Can be mentioned.

Such impact deformation is carried out at low temperatures, and as such low temperatures, for example, a range of about 0 ° C. or less, or about −50 ° C. or less, or about −150 ° C. or less to about −270 ° C. may be used. As an example of such a low temperature, about -196 degreeC which is the temperature of liquid nitrogen can be used. Defects in the microstructure of the thermoelectric powder may be better induced in such a low temperature range, and there is a concern that crushing of the thermoelectric powder may occur at a temperature higher than room temperature.

The amount of defects in the thermoelectric material caused by such a low temperature impact can be defined as the defect density, which is defined as the "defect area / unit volume (mm ² / 1mm ³ )" as the defects generated per unit volume and the microstructure. Can be observed by direct observation. In the case of the low temperature impact deformation, it is possible to provide a defect density of at least about 2 times or more as compared with the previous, for example, to provide a defect density of about 5 times or more to about 20 times.

The thermoelectric material may be subjected to a single axis deformation before the low temperature impact deformation as described above. Such uniaxial deformation can be carried out at room temperature or at a high temperature of about 100 to about 600 ° C., and the thermoelectric material particles can be stretched in one direction by processes such as rolling, twisting, extrusion to have an anisotropic microstructure.

Due to such a single axis deformation, the thermoelectric material powder has a more linear structure. As a result, the state density becomes higher and the Seebeck coefficient S and the electric conductivity σ become higher due to the higher state density. In addition, the thermal conductivity κ becomes smaller when the included dimension is smaller than the phonon wavelength.

According to one embodiment, as the thermoelectric material, those containing at least one element selected from the group consisting of transition metals, rare earth elements, group 2 elements, group 13 elements, group 14 elements, group 15 elements, and group 16 elements may be used. Can be. For example, Si-based, Bi-Sb-Te-based, Bi-Te-Se-based, Bi-Sb-based, Mg-Si-based, Mg-Ge-based, Mg-Sn-based, Pb-Sb-Ag-Te-based, BC Selected from the group consisting of Bi-Te, Co-Sb, Pb-Te, Ge-Tb, Si-Ge, Sb-Te, Sm-Co, transition metal silicides, and combinations thereof One or more may be used, or Si, Si _1-x Ge _x (0 <x <1), Bi ₂ Te ₃ , Sb ₂ Te ₃ , Bi _x Sb _2-x Te ₃ (0 <x <2), Bi ₂ Te _x Se _3-x (0 <x <3), B ₄ C / B ₉ C, BiSb alloy, and PbTe, Mg-Si, Mg-Ge, Mg-Sn or triple systems thereof, binary One or more selected from the group consisting of binary, tertiary or quaternary scooters rudite and Pb-Sb-Ag-Te can be used.

According to one embodiment, the thermoelectric material powder may be used having a nano-size, for example may have an average size of about 1nm to about 1,000nm.

The deformation process of the thermoelectric material as described above with reference to the drawings as follows.

As shown in FIG. 1, a thermoelectric material powder 2 is prepared, introduced into the jacket 1, then packed and sealed, and a low temperature is applied to the thermoelectric material powder-containing jacket 1, 2 in the support 5. The impact 4 is applied to deform the microstructure of the thermoelectric material powder 2 to cause defects.

When the thermoelectric material powder 2 is packed in the jacket 1 as described above, the porosity and the void space may be reduced to increase the performance index ZT. Therefore, high strength packing can be performed.

As the material of the jacket 1 in which the thermoelectric material powder 2 is packed, metal or plastic may be used, and as the metal, copper, stainless steel, high temperature alloy, or the like may be used. The shape of the jacket 1 can be formed in a predetermined shape and size, for example, it can be formed in the form of a tube. This shape allows the thermoelectric material powder to be anisotropically stretched or deformed.

The low temperature impact on the jacket 1 is at a high strain rate, for example at least about 5 inches / inch / second, or in the range of about 50 inches / inch / second to about 2,000 inches / inch / second, This increases the amount of nanoscale defects occurring in the thermoelectric material.

Defects generated in the low temperature impact increases the phonon scattering, thereby reducing the thermal conductivity, it can increase the performance index ZT.

In the low temperature impact, the low temperature may be used, for example, in the range of about 0 ° C. or less, or about −50 ° C. or less, or about −150 ° C. or less to about −270 ° C., and in such a range, suitable types of defects may be used as thermoelectric materials. Triggered within. Liquid nitrogen may be used to obtain the low temperature.

The low temperature may be formed by configuring the chamber 6 in the region to which the impact is applied, as shown in FIG.

The low temperature shock 4 is carried out in the chamber 6, by impacting the jacket 1 at a high strain rate on the support 5 using a tool such as a hammer on the support 5. . Such a low temperature shock 4 can be repeated once or twice or more as shown in FIG. That is, in a single impact process, a single impact is applied to the jacket 1, and in a repeated impact process, the homogenized shock is applied to the jacket (1) by changing the position of the jacket 1 in the chamber following the single impact, and then hitting it again. To 1).

In the process before the low temperature impact is applied, the preheat treatment may be performed to achieve a crystal orientation with a higher figure of merit ZT value. Such preheating increases the temperature of the thermoelectric material by applying heat to the jacket through simple heating, laser heating, flame heating, furnace heating and the like.

Before the low temperature impact process and the preliminary heat treatment process, a single axis deformation may be applied to the jacket 1. As shown in Fig. 2 or 3, such a single-axis deformation can be performed at room temperature or at a high temperature of 100 to 600 ° C, and thermoelectric by processes such as rolling, twisting and extrusion using a mechanism 3 such as a roller. The material particles are stretched in one direction to allow for a planarized anisotropic microstructure.

Due to such a single-axis deformation, the structure of the thermoelectric material powder has a flattened linear structure. As a result, the state density becomes higher and the Seebeck coefficient S and the electric conductivity σ become higher due to the higher state density. In addition, the thermal conductivity κ becomes smaller when the included dimension is smaller than the phonon wavelength.

Information relating to such a single axis deformation is disclosed in WO 2010/018976 and incorporated herein.

The single axis deformation, preheat treatment and low temperature impact processes as described above may proceed sequentially in a series of processes. That is, although it is possible to perform in a separate process, it is possible to advance simultaneously with a series of processes and to improve manufacturing efficiency.

The kind of thermoelectric material used in the manufacturing process is as described above.

According to another aspect of the present invention, a thermoelectric element including the thermoelectric material is provided.

The thermoelectric element is, for example, mixed with a thermoelectric material having a defect as described above by a mechanical or chemical method, and then partially reduced heat treatment, or after a post-process such as quenching after melting, and then sintered under pressure to bulk-type thermoelectric The device can be manufactured. The sintering may be performed by a spark plasma sintering (SPS) method. The spark plasma sintering method enables rapid sintering at a relatively low temperature as compared with the conventional sintering method, so that the initial structure of the thermoelectric semiconductor particles and the nanosheets is not exposed to high temperature during the sintering process to preserve the characteristics of the initial raw material. In addition, the spark plasma sintering method may remove a surface oxide layer in real time to manufacture a thermoelectric device having high strength and uniform characteristics.

The thermoelectric element may be formed in a predetermined shape, for example, a rectangular parallelepiped by a cutting process or the like, and applied to the thermoelectric module. The thermoelectric element may be a p-type or n-type thermoelectric element. The thermoelectric element may be combined with an electrode to exhibit a cooling effect by applying an electric current, or to generate a power generation effect by a temperature difference between the elements.

According to another aspect of the invention,

A first electrode;

A second electrode disposed to face the first electrode; And

There is provided a thermoelectric module including the thermoelectric element disposed between the first electrode and the second electrode.

4 shows an example of a thermoelectric module employing the thermoelectric element. As shown in FIG. 4, the upper and lower electrodes 12 and 22 are patterned and formed on the upper insulating substrate 11 and the lower insulating substrate 21. The upper electrode 12 and the lower electrode are formed. The p-type thermoelectric element 15 and the n-type thermoelectric element 16 are in contact with each other at (22). These electrodes 12 and 22 are connected to the outside of the thermoelectric element by the lead electrodes 24.

As the insulating substrates 11 and 21, gallium arsenide (GaAs), sapphire, silicon, pyrex, quartz substrates and the like can be used. Materials of the electrodes 12 and 22 may be variously selected, such as aluminum, nickel, gold, titanium, and the like, and various sizes may be selected. As the method for patterning these electrodes 12 and 22, a conventionally known patterning method can be used without limitation, and for example, a lift-off semiconductor process, a deposition method, a photolithography method, or the like can be used.

As another example of the thermoelectric module, as illustrated in FIGS. 5 and 6, a thermoelectric module including a first electrode, a second electrode, and the above-mentioned thermoelectric element interposed between the first electrode and the second electrode may be used as an example. Can be mentioned. The thermoelectric module may further include an insulating substrate on which at least one of the first electrode and the second electrode is disposed, as shown in FIG. 4. As such an insulating substrate, the insulating substrate described above can be used.

As shown in FIG. 5, in one embodiment of the thermoelectric module, the first electrode and the second electrode may be electrically connected to a power supply. When a DC voltage is applied from the outside, the holes of the p-type thermoelectric element and the electrons of the n-type thermoelectric element move to generate heat and endothermic at both ends of the thermoelectric element.

As shown in FIG. 6, in one embodiment of the thermoelectric module, at least one of the first electrode and the second electrode may be exposed to a heat source. When heat is supplied by an external heat source, electrons and holes move, and current flows in the thermoelectric element, thereby generating power.

In one embodiment of the thermoelectric module, the p-type thermoelectric element and n-type thermoelectric element may be alternately arranged, at least one of the p-type thermoelectric element and n-type thermoelectric element is the nanosheet-containing thermoelectric material It may include.

According to an embodiment of the present invention, a thermoelectric device including a thermoelectric source and the thermoelectric module is provided, wherein the thermoelectric module absorbs heat from the thermal source and includes the coating layer-containing thermoelectric material, the first electrode, and the second electrode. The second electrode is disposed to face the first electrode. One of the first electrode and the second electrode may contact the thermoelectric material.

An embodiment of the thermoelectric device may further include a power supply source electrically connected to the first electrode and the second electrode. One embodiment of the thermoelectric device may further include an electrical element electrically connected to one of the first electrode and the second electrode.

The thermoelectric material, the thermoelectric element, the thermoelectric module and the thermoelectric device may be, for example, a thermoelectric cooling system, a thermoelectric power generation system, and the thermoelectric cooling system may include a micro cooling system, a general purpose cooling device, an air conditioner, a waste heat generation system, and the like. However, the present invention is not limited thereto. The construction and manufacturing method of the thermoelectric cooling system are well known in the art, and thus detailed description thereof is omitted.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1

Bi _0.5 Sb _1.5 Te ₃ thermoelectric powders having an average size of about 25 μm were filled into copper jackets having a diameter of 0.375 inches, and both ends were sealed by swaging with smaller diameter dies. The jacket diameter was reduced to 0.08 inches by swaging the thermoelectric material-containing copper jacket using a series of swaging dies.

Using a Hopkinson Bar impact device, the jacket was then impacted at a strain rate of 2,000 inches / inch / sec to cause defects in the thermoelectric powder.

Defect density of the thermoelectric material prepared as described above was in the microstructure observation shock-treated about 125mm ² / 1mm ³ to 700mm ² / 1mm ³ by about six times.

The Seebeck coefficient of the thermoelectric material prepared as described above was measured by the 4-terminal method and showed a value of S = + 199 μV / K at 300K.

The electrical conductivity of the thermoelectric material prepared as described above was measured by the 4-terminal method and showed a value of σ = 1.034X10 ⁵ μV / K at 300K.

The thermal conductivity of the thermoelectric material prepared as described above was measured by the 3-omega method and showed a value of k = 0.824W / mK at 300K. In contrast, the thermal conductivity measured by performing the Bi _0.5 Sb _1.5 Te ₃ thermoelectric material powder by using only a hot press process without using a low temperature impact or a single axial deformation showed a value of k = 1.100 W / mK at 300K.

As a result, the performance index ZT of the thermoelectric material exhibited a value of about 1.47, indicating that an improvement of approximately 50% was achieved compared to the ZT value of 0.95 to 1.05, which is represented by the ideal thermoelectric alloy.

Jacket ...... 1
Thermoelectric powder ..... 2
Roller ...... 3
Shocker ..... 4
Support ...... 5
Chamber ....... 6
Gate ..... 7

Claims (22)

Thermoelectric material having a microstructure deformed by low temperature impact. The method of claim 1,
And the low temperature impact has a strain rate of at least about 5 inches / inch / second. The method of claim 1,
And the low temperature impact ranges from about 50 inches / inch / second to about 2,000 inches / inch / second. The method of claim 1,
A thermoelectric material having a defect density of at least about 2 times after a low temperature shock as compared to before a low temperature shock. The method of claim 1,
Thermoelectric material having a defect density of at least about five times after a low temperature impact as compared to before a low temperature impact. The method of claim 1,
And the microstructure is anisotropically stretched and planarized microstructure. The method of claim 1,
And the low temperature impact is performed at a temperature of about 0 ° C. or less. The method of claim 1,
And wherein the low temperature impact is carried out at a temperature of about −50 ° C. or less. The method of claim 1,
And the low temperature impact is carried out at a temperature of about -100 ° C or lower. The method of claim 1,
The thermoelectric material includes at least one element selected from the group consisting of transition metals, rare earth elements, group 2 elements, group 13 elements, group 14 elements, group 15 elements, and group 16 elements. The method of claim 1,
The thermoelectric material is Si-based, Bi-Sb-Te-based, Bi-Te-Se-based, Bi-Sb-based, Mg-Si-based, Mg-Ge-based, Mg-Sn-based, Pb-Sb-Ag-Te-based, From the group consisting of BC type, Bi-Te type, Co-Sb type, Pb-Te type, Ge-Tb type, Si-Ge type, Sb-Te type, Sm-Co type, transition metal silicide type and combinations thereof One or more selected thermoelectric material. The method of claim 1,
The thermoelectric material is Si, Si _1-x Ge _x (0 <x <1), Bi ₂ Te ₃ , Sb ₂ Te ₃ , Bi _x Sb _2-x Te ₃ (0 <x <2), Bi ₂ Te _x Se _3-x (0 <x <3), B ₄ C / B ₉ C, BiSb alloys, and PbTe, Mg-Si, Mg-Ge, Mg-Sn or triple systems thereof, binary, The thermoelectric material of at least one selected from the group consisting of tertiary or quaternary scooters rudite and Pb-Sb-Ag-Te. The method of claim 1,
Thermoelectric material with a figure of merit increase of about 20% or more after low-temperature shock compared to before low-temperature shock. The method of claim 1,
Thermoelectric material with a figure of merit increase of about 30% or more after low-temperature shock, compared to before low-temperature shock. Preparing a composite precursor comprising a thermoelectric powder and a thermally and electrically insulating material powder, introducing the same into a metal jacket, and then packing and sealing; And
Deforming a microstructure of the thermoelectric material powder by applying a low temperature impact to the thermoelectric material powder-containing metal jacket;
Method for producing a thermoelectric material comprising a. 16. The method of claim 15,
Wherein the low temperature impact is carried out at a temperature of about 0 ° C. or less. 16. The method of claim 15,
Before the low-temperature impact process by applying a single-axis deformation to the metal jacket containing the thermoelectric material powder to reduce the diameter and length of the metal jacket to obtain a rod-shaped metal jacket; manufacturing a thermoelectric material further comprising Way. The method of claim 17,
Wherein said monoaxial deformation is carried out at room temperature or at a high temperature of from about 100 to about 600 ° C. The method of claim 17,
And a preliminary heat treatment process between the low temperature impact process and the single axis deformation process. A thermoelectric element comprising the thermoelectric material according to claim 1. A first electrode;
A second electrode disposed to face the first electrode; And
A thermoelectric module comprising; a thermoelectric element according to claim 20 disposed between the first electrode and the second electrode. Heat source; And
A thermoelectric device according to claim 20, which absorbs heat from the heat source;
A first electrode disposed to contact the thermoelectric component; And
A thermoelectric module disposed to face the first electrode and contacting the thermoelectric element;
Thermoelectric device having a.

Images