KR101528589B1 - Method of manufacturing thermoelectric material and thermoelectric material prepared by the method and thermoelectric generator - Google Patents

Abstract

According to one aspect of the present invention, there is provided a method of manufacturing a Pb-Te based thermoelectric material, comprising the steps of: mixing an element lead, an element tellurium and a dopant to form a Pb- ; Quenching the mixture after melting; And hot-pressing the formed body after the quenching to obtain a thermosetting body.

Description

TECHNICAL FIELD [0001] The present invention relates to a thermoelectric material manufacturing method, a thermoelectric material, and a thermoelectric generator. BACKGROUND OF THE INVENTION 1. Field of the Invention [0002]

The present invention relates to a thermoelectric material production method, a thermoelectric material and a thermoelectric generator using the same.

There is a great demand for electricity all over the world, and sustainable energy technology is receiving great attention. However, renewable energy sources such as solar, wind, and the like currently provide only a very small portion of the total electricity because of the relatively high cost. In this regard, thermal energy is valued as a potential source of low-cost, sustainable energy. However, a significant amount of energy is wasted in the form of heat. Both domestic heating processes, automotive exhaust and industrial processes result in a significant amount of unused waste heat. Due to this great potential, there is much interest in cost effective techniques for generating electricity from waste heat.

In this regard, thermoelectric materials have attracted more attention because thermoelectric materials can convert heat into electricity. The thermoelectric material is a metal or ceramic material having a function of directly converting heat into electric furnace or electric power into heat, and it is a metal or ceramic material which can be used as waste heat, waste heat of turbine generation, heat of automobile exhaust gas, combustion arrangement of city gas, Application to thermoelectric power generation or thermoelectric cooling has attracted attention. Thermoelectric power generation using thermoelectric materials is advantageous in that it is simple in structure, easy to maintain and easy to maintain, has no noise, and has a wide selection range of heat source to use, in addition to its ability to generate electricity without moving parts if only temperature difference is given. In addition, thermoelectric cooling has features and advantages that it does not require a compressor or a refrigerant because it has fewer faults, no noise, enables selective cooling of minute portions, and has high temperature response sensitivity.

On the other hand, the efficiency of the thermoelectric material can be evaluated by the performance index ZT = S ² T / ρκ where S is the Seebeck coefficient, ρ is the electrical resistance, κ is the thermal conductivity, and T is the absolute temperature. That is, the larger the figure of merit, the greater the conversion efficiency.

The larger the figure of merit of the thermoelectric material is, the greater the electric energy generated, and therefore, the thermoelectric material exhibits excellent characteristics. Therefore, from the above equations, a thermoelectric material having a large Seebeck coefficient and electrical conductivity and a small thermal conductivity is required for application as a thermoelectric material.

One of the traditional thermoelectric materials, PbTe-based alloys, has been studied for a long time, but its figure of merit remains around one in the past decades. Recently, new physical principles for improving thermoelectric performance have been proposed in PbTe alloys, but improvement of performance index is limited.

An object of the present invention is to provide a thermoelectric material manufacturing method and a thermoelectric material which can reduce processing time and cost.

Another object of the present invention is to provide a thermoelectric material manufacturing method and a thermoelectric material capable of improving the figure of merit.

According to an aspect of the present invention, there is provided a method of manufacturing a Pb-Te based thermoelectric material, comprising: forming a Pb-Te based mixture by mixing elemental lead, elemental tellurium and a dopant; Quenching the mixture after melting; And hot pressing the formed body after the quenching to obtain a thermosetting body. The present invention also provides a method of manufacturing a Pb-Te based thermoelectric material.

In one embodiment, the dopant corresponds to at least one of sodium (Na), potassium (K), and silver (Ag).

In one embodiment, the step of forming the mixture may include mixing element lead, element tellurium and a dopant such that the composition ratio of the dopant is 2 atomic%.

In one embodiment, 0.5 atomic% of the 2 atomic% dopant may be doped and 1.5 atomic% may be precipitated in the crystal grains of the Pb-Te system thermoelectric material.

In one embodiment, 1.5 atomic% of the dopant may be precipitated in a grain size of 2 nm to 4 nm in the grain of the Pb-Te-based thermoelectric material.

In one embodiment, the hot pressing may be performed without quenching the mixture and then performing the annealing process.

In one embodiment, the method may further comprise performing a soaking treatment of the mixture before the melting.

In one embodiment, the thermoelectric element has a thermoelectric performance index of at least 2.0 in a medium temperature region of 700K to 800K.

In one embodiment, the step of obtaining the thermoselectively sintered body may include a step of pulverizing the molded body into a powder form and hot-pressing.

In one embodiment, the dopant comprises sodium, and the step of obtaining the thermoselected body may include the step of precipitating the sodium.

In one embodiment, at the step at which the precipitated sodium, the sodium may be deposited to at least one of the NaTe, Na ₂ Te.

In one embodiment, the NaTe, Na ₂ Te may be precipitated to a size of 2nm to 4nm.

In one embodiment, the thermoselective element may have a plurality of crystal grains having an average size of 3 mu m to 4 mu m.

According to another aspect of the present invention, there is provided a Pb-Te-based thermoelectric material composed of Pb-X-Te doped with a dopant X, And a Pb-Te-based thermoelectric material including a precipitate having a size of 2 nm to 4 nm and including the dopant in the plurality of crystal grains.

In one embodiment, the dopant may be at least one of sodium (Na), potassium (K), and silver (Ag).

In one embodiment, the size of the plurality of grains may be on the order of 3 mu m to 4 mu m in average.

In one embodiment, the Pb-Te-based thermoelectric material may have a composition of Pb _{0 .98- d} X _{0 .02 + d} Te (-0.001 <d <0.001).

In one embodiment, the dopant may be a sodium, and at least one precipitation phase NaTe, Na ₂ Te of the precipitate containing the sodium.

According to still another aspect of the present invention, a thermoelectric generator including the Pb-Te-based thermoelectric material may be provided.

According to the embodiment of the present invention, the Pb-Te-based thermoelectric material can be manufactured through a simple new method such as melting / quenching / hot pressing without annealing, thereby greatly reducing the processing time and cost, The performance index can be greatly improved.

1 is an SEM image showing a grain size of a thermoelectric material according to Examples 1 to 3, wherein FIG. 1A is an SEM image of a thermoelectric material according to Example 1, FIG. 1B is Example 2, and FIG.
Fig. 2 is an enlarged view of Fig.
3 is a view showing XRD patterns of the thermoelectric materials according to Examples 1 to 3 at room temperature.
Fig. 4 shows the Vickers hardness characteristics of the thermoelectric materials according to Examples 1 to 3. Fig.
5 is a graph showing the temperature dependence of the thermal conductivity and the lattice thermal conductivity of the thermoelectric material according to Examples 1 to 3.
6 is a graph showing the temperature dependence of the power factor of the thermoelectric material according to Examples 1 to 3;
7 is a graph showing the temperature dependence of the electrical resistance of the thermoelectric material according to Examples 1 to 3;
8 is a graph showing the temperature dependence of the Seebeck coefficient of the thermoelectric material according to Examples 1 to 3;
9 is a graph showing the temperature dependence of the figure of merit (ZT) of the thermoelectric material according to Examples 1 to 3.
Figure 10 shows the highest performance index of the reported Na-doped PbTe (Nature 473 (2011) 66) and the highest performance index of the reported bulk thermoelectric material (Nature 489 (2012) 414) As shown in FIG.
11 is a TEM image for comparing the sodium precipitation size of the thermoelectric materials according to Examples 1 to 3. Fig. Fig. 11A is a TEM image of Example 1, Fig. 11B is Example 2, and Fig. 11C is Example 3.
12 is an enlarged view of Fig.
13 is a graph showing the size of precipitated sodium of the thermoelectric material according to Examples 1 to 3. Fig. 13A is a graph of Example 1, FIG. 13B is Example 2, and FIG. 13C is a graph of Example 3. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the description of technical constructions and principles well known in the art will be omitted. Even if these explanations are omitted, the typical configuration of the present invention can be easily understood by a person skilled in the art through the following description.

The present invention relates to a method of manufacturing a Pb-Te based thermoelectric material and a method of manufacturing a thermoelectric material by melting, quenching, and hot pressing without annealing, and a thermoelectric material manufactured by the method.

The composition of the thermoelectric material according to one embodiment of the present invention is Pb _{0 .98 - d} Na _{0 .02 + d} Te (-0.001 <d <0.001). In one embodiment, the thermoelectric material may include crystal grains having a size of 3 to 4 占 퐉 and precipitates having a size of 2 nm to 4 nm in the crystal grains. According to one embodiment, in the thermoelectric material, Na serves as a dopant, and in addition to Na, k and Ag may be used as the dopant. Experiments have shown that the addition of Na in the range of 0.02 ± 0.001, as shown in Table 1, results in less change in the thermoelectric performance index and stability. Each of the three methods tested by the present inventors will be described as follows.

<Sample preparation process>

Example 1. Melting, quenching and hot pressing (QH)

Samples were prepared by hot pressing followed by melting and quenching. Elemental lead (Pb, 3N, Alfa Aesar), elemental tellurium (Te, 4N, Alfa Aesar) and elemental sodium (Na, 99.95%, Alfa Aesar) were used as starting materials. The weight of these elements was adjusted to stoichiometric proportions, and the masses of Pb, Te and Na were 9.8120 g, 6.1658 g and 0.0222 g, respectively. The total mass of all particles was 16 g. All raw particles were mixed into a carbon-coated quartz tube under an Ar-filled glove box. The tube was evacuated at about 10 ^-4 torr and sealed. The tube was soaked at 1023-1123 K for about 1.5-2.5 hours and then heated to 1223-1323 K for 5.5-6.5 hours for melting and then quenched in cold water. The resulting ingot was pulverized into a powder form and then hot-pressed at 90-110 MPa for 0.8-1.2 hours.

In one embodiment, the soaking may be performed prior to the melting process for stable reaction of Na with low boiling point, so that Na may react with other elements and then participate in the reaction during the melting process.

Example 2. Melting, Annealing and Hot Pressing (AH)

Samples were prepared by melting and annealing followed by hot pressing. Elemental lead (Pb, 3N, Alfa Aesar), elemental tellurium (Te, 4N, Alfa Aesar) and elemental sodium (Na, 99.95%, Alfa Aesar) were used as starting materials. The weight of these elements was adjusted at a stoichiometric ratio, and the masses of Pb, Te and Na were 9.8120 g, 6.1658 g and 0.0222 g, respectively. The total mass of all particles was 16 g. All raw particles were mixed into a carbon-coated quartz tube under an Ar-filled glove box. The tube was introduced at about 10 ^-4 torr and sealed. The tube was soaked at 1023 to 1123 K for about 1.5 to 2.5 hours, then heated to 1223 to 1323 K for 5.5 to 6.5 hours for melting, then slowly cooled to 923 to 1123 K for 46 to 50 hours. The resultant ingot was pulverized into a powder form and hot-pressed at 90-110 MPa for 0.8-1.2 hours.

Example 3. Melting, quenching, annealing and hot pressing (QAH)

Samples were prepared by melting, quenching and annealing followed by hot pressing. Elemental lead (Pb, 3N, Alfa Aesar), elemental tellurium (Te, 4N, Alfa Aesar) and elemental sodium (Na, 99.95%, Alfa Aesar) were used as starting materials. The weight of these elements was adjusted at a stoichiometric ratio, and the masses of Pb, Te and Na were 9.8120 g, 6.1658 g and 0.0222 g, respectively. The total mass of all particles was 16 g. All raw particles were mixed into a carbon-coated quartz tube under an Ar-filled glove box. The tube was introduced at about 10 ^-4 torr and sealed. The tube was soaked at 1023 to 1123 K for about 1.5 to 2.5 hours, then heated to 1223 to 1323 K for 5.5 to 6.5 hours for melting, and then quenched in cold water. Subsequently, annealing was performed at 923 to 1123 K for 46 to 50 hours. The resultant ingot was pulverized into a powder form and hot-pressed at 90-110 MPa for 0.8-1.2 hours.

In the above three synthesis methods, the total mass of each sample after hot pressing was about 4.5-5.5 g. After hot-pressing, the length of the sample was about 0.95 to 1.05 cm, the width was about 0.95 to 1.05 cm, and the thickness was about 6 to 8 mm.

We have synthesized Na-doped PbTe alloys in the three different ways and measured / compared their properties.

Example 2 is a method by melting, quenching and hot pressing (QH), Example 2 is a method by melting, annealing and hot pressing (AH), Example 3 is a method by melting, quenching, annealing and hot pressing ). It is confirmed that Embodiment 1 is advantageous in that the process time and cost can be reduced because the annealing process is not performed as compared with Embodiments 2 and 3, and other advantages are also shown.

1 and 2 are SEM images showing the grain sizes of the thermoelectric materials according to the respective embodiments. 1 and 2, the size of the crystal grains of Example 1 (FIGS. 1A and 2A) is larger than the size of the crystal grains of Example 2 (FIGS. 1B and 2B) and Example 3 (FIGS. 1C and 2C) Small things can be seen. The average grain size of each of Example 1, Example 2, and Example 3 was 3.7 袖 m, 100 袖 m and 8 袖 m. The small grain size contributes to the effective scattering of phonons and produces a small lattice thermal conductivity. Figures 1 and 2 were obtained by JSM-6701F SEM

FIG. 3 is a graph showing XRD patterns at room temperature of Examples 1 to 3, wherein the crystal structure of each example was determined by powder X-ray diffraction (XRD) by Cu Ka radiation at room temperature using a Rigaku powder x- ). Referring to FIG. 3, it can be seen that the Pb-Te based thermoelectric materials according to Examples 1 to 3 include Pb and Te.

Fig. 4 shows the hardness characteristics of each of the above Examples, which was measured by the hardness by a ZHV u-S Vickers hardness tester. Referring to FIG. 4, it can be seen that the hardness value of Example 1 is larger than that of Examples 2 and 3.

5 to 9 show the temperature dependence of the thermal conductivity and the lattice thermal conductivity (FIG. 5), the temperature dependence of the power factor (FIG. 6), the temperature dependency of the electrical resistance (FIG. 7), and the temperature dependence of the Seebeck coefficient ) And the temperature dependence of the figure of merit (ZT) (Fig. 9). Electrical resistivity and Seebeck coefficients were measured simultaneously using a ULVAC ZEM-3 instrument in a helium atmosphere. As a result of calculating the figure of merit from the results shown in FIGS. 5 to 8, referring to FIG. 9, it can be seen that Example 1 has a higher figure of merit than the other Examples 2 and 3 in the middle temperature region (700K to 800K) Able to know.

Figure 10 shows the highest performance index of the reported Na-doped PbTe (Nature 473 (2011) 66) and the highest performance index of the reported bulk thermoelectric material (Nature 489 (2012) 414) FIG. Referring to FIG. 10, it can be seen that the performance index is higher in the medium temperature region (700K to 800K) than other reported data.

11 to 12 are TEM images for comparing the sodium precipitation size of the thermoelectric material according to each of the above embodiments. 11 to 12, it can be seen that the sodium precipitation size of Example 1 (Figs. 11A and 12A) is smaller than that of Example 2 (Figs. 11B and 12B) and Example 3 (Figs. 11C and 12C) .

13 is a graph showing the size of sodium precipitated according to each example. Referring to FIG. 13, the sodium precipitation size according to Example 1 (FIG. 13A) had the smallest precipitate size from 2 nm to 4 nm. The precipitation phase size is related to the thermal conductivity. The smaller the size of the precipitation phase, the lower the thermal conductivity and the higher the thermoelectric performance index can be obtained. Therefore, Example 1 having a small precipitation phase size can have a higher thermoelectric performance index than Examples 2 and 3.

 Therefore, in the first to third embodiments, the greatest figure of merit is obtained according to the first embodiment of the present invention. The average figure of merit of Example 1 was about 2.0 or more at 773K, which is about 46% higher than the performance index ZT = 1.4 (Na-doped PbTe alloy) reported so far. Which is also a higher value than the performance index reported in the bulk thermoelectric materials in the limited measurement temperature range of the present invention.

Such a higher figure of merit appears to be due primarily to the scattering of phonons of various spectra due to the distribution of nanoparticles within the matrix at various sizes, resulting in lower thermal conductivity. In addition, heat conduction in solids is mediated by phonons. Phonons are quantized lattice vibrations of solids. However, the movement of such phonons changes according to the microstructure of the solid. If there is a nano-sized precipitate with a small grain size or other composition within the grain, the motion of the phonon is disturbed and consequently the thermal conductivity is reduced. According to the present invention, a thermoelectric material is produced by melting, quenching, and hot pressing processes unlike the prior art. By this manufacturing process, it was confirmed that the finally formed thermoelectric material has various sizes of crystal grains and the distribution of nanoparticles in the crystal grains, which shows that the thermal conductivity is decreased and the figure of merit is improved. For example, there are small crystal grains of 100 to 10 nm, large crystal grains of several tens of microns, and nanometer-sized nanoparticles are distributed in the crystal grains. The stability of this higher figure of merit has been proven several times over. The Vickers hardness value of Example 1 by the QH method was also the largest among the three methods. Thus, the inventive QH method has concluded that it is the optimal method for synthesizing Na-doped PbTe alloys with greater performance index and good mechanical properties.

A feature of the present invention is that a new synthesis technique called the QH method and a Pb _{0 .98} Na _{0 .02} Te alloy with a figure of merit of 2.0 or higher are obtained. The main advantages of the QH synthesis method are the advantages of a simple synthesis process, shortening the synthesis time, and mass production.

Although Na-doped PbTe alloys have been studied by other researchers, high performance indices such as the present invention and / or such a structure have not been reported, and the thermoelectric materials proposed by the present invention for melting, The synthesis technique of presses is a new method that has never been used.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. That is, the embodiment can be variously modified and modified within the scope of the following claims, and these are also within the scope of the present invention. Accordingly, the invention is limited only by the claims and the equivalents thereof.

Claims (19)

A method for manufacturing a Pb-Te thermoelectric material,
Elemental lead, elemental tellurium and a dopant to form a Pb-Te-based mixture;
Quenching the mixture after melting; And
Hot-pressing the formed body after quenching to obtain a thermosetting body,
Wherein the melting, quenching, and hot pressing are continuously performed. The method according to claim 1,
Wherein the dopant is at least one of sodium (Na), potassium (K), and silver (Ag). A method for manufacturing a Pb-Te thermoelectric material,
Elemental lead, elemental tellurium and a dopant to form a Pb-Te-based mixture;
Quenching the mixture after melting; And
Hot-pressing the formed body after quenching to obtain a thermosetting body,
The dopant is at least one of sodium (Na), potassium (K) and silver (Ag)
Wherein forming the mixture comprises:
And a step of mixing element lead, element tellurium and a dopant so that the composition ratio of the dopant is 2 atomic%. The method of claim 3,
Wherein 0.5 at% of the 2 at% dopant is doped and 1.5 at% is precipitated in the crystal grains of the Pb-Te based thermoelectric material. 5. The method of claim 4,
Wherein 1.5 at% of the dopant is precipitated in a grain size of 2 nm to 4 nm in the grain of the Pb-Te-based thermoelectric material. delete A method for manufacturing a Pb-Te thermoelectric material,
Elemental lead, elemental tellurium and a dopant to form a Pb-Te-based mixture;
Quenching the mixture after melting; And
Hot-pressing the formed body after quenching to obtain a thermosetting body,
The dopant is at least one of sodium (Na), potassium (K) and silver (Ag)
Further comprising the step of subjecting the mixture to a soaking treatment before the melting. A method for manufacturing a Pb-Te thermoelectric material,
Elemental lead, elemental tellurium and a dopant to form a Pb-Te-based mixture;
Quenching the mixture after melting; And
Hot-pressing the formed body after quenching to obtain a thermosetting body,
The dopant is at least one of sodium (Na), potassium (K) and silver (Ag)
Wherein the thermoelectric sintered body has a thermoelectric performance index of at least 2.0 in a middle temperature region of 700K to 800K. 3. The method of claim 2,
The step of obtaining the thermo-
And pulverizing the shaped body into a powder form and hot-pressing the Pb-Te based thermoelectric material. A method for manufacturing a Pb-Te thermoelectric material,
Elemental lead, elemental tellurium and a dopant to form a Pb-Te-based mixture;
Quenching the mixture after melting; And
Hot-pressing the formed body after quenching to obtain a thermosetting body,
The dopant is at least one of sodium (Na), potassium (K) and silver (Ag)
Wherein the dopant comprises sodium,
The step of obtaining the thermo-
Wherein the sodium is precipitated. 11. The method of claim 10,
In the step in which the sodium is precipitated,
Pb-Te based thermoelectric material production method is the precipitation of the sodium being at least one NaTe, Na ₂ Te. 12. The method of claim 11,
The NaTe, Na ₂ Te is 2nm to method Pb-Te based thermoelectric material which precipitated to a size of 4nm. A method for manufacturing a Pb-Te thermoelectric material,
Elemental lead, elemental tellurium and a dopant to form a Pb-Te-based mixture;
Quenching the mixture after melting; And
Hot-pressing the formed body after quenching to obtain a thermosetting body,
The dopant is at least one of sodium (Na), potassium (K) and silver (Ag)
Wherein the thermoelectric sintered body includes a plurality of crystal grains having an average size of 3 mu m to 4 mu m. A Pb-Te-based thermoelectric material composed of Pb-X-Te doped with a dopant X,
A plurality of crystal grains; And
And a precipitate having a size of 2 nm to 4 nm and containing the dopant in the plurality of crystal grains. 15. The method of claim 14,
Wherein the dopant is at least one of sodium (Na), potassium (K), and silver (Ag). 16. The method of claim 15,
Wherein the plurality of crystal grains have an average size of 3 탆 to 4 탆. 15. The method of claim 14,
The Pb-Te-based thermoelectric material has a composition of Pb _{0 .98- d} X _{0 .02 + d} Te (-0.001 <d <0.001). 15. The method of claim 14,
Wherein the dopant is sodium,
Precipitated phase NaTe, Na ₂ Te, at least one of Pb-Te based thermoelectric material of the of the sodium containing the precipitate. A thermoelectric generator comprising the Pb-Te thermoelectric material according to any one of claims 14 to 18.

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