KR102383432B1 - Mg-Si based thermoelectric material and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a thermoelectric material and a method for manufacturing the same. Since the thermoelectric material has excellent thermoelectric performance and high mechanical strength (especially, compressive strength), when applied to a thermoelectric element and/or a thermoelectric module, the thermoelectric performance is excellent. It is possible to provide a thermoelectric element and/or a thermoelectric module having a long lifespan.

Description

Mg-Si based thermoelectric material and method for manufacturing the same

The present invention relates to an Mg-Si-based thermoelectric material having improved mechanical strength (particularly, compressive strength) and a method for manufacturing the same.

Thermoelectric technology is a technology that directly converts thermal energy into electrical energy or electrical energy into thermal energy in a solid state.

An example of the thermoelectric power generation field may include a technology for converting vehicle waste heat into electrical energy. Specifically, a thermoelectric material for a vehicle is manufactured by processing a thermoelectric material into a predetermined shape, a thermoelectric module for a vehicle is manufactured by bonding the manufactured thermoelectric element for a vehicle with an electrode, and the vehicle waste heat is converted into electrical energy by applying it inside the vehicle. to convert to In this case, since pressure is applied to the bonding between the vehicle thermoelectric element and the electrode, the thermoelectric material is required to have properties that can sufficiently withstand the applied pressure.

Meanwhile, the currently commercialized thermoelectric materials can be divided into Bi-Te-based for room temperature use, Pb-Te-based and Mg-Si-based for medium temperature use, and oxide and Fe-Si-based for high temperature use. Since the Mg-Si-based thermoelectric material has good thermoelectric performance and is light and inexpensive, it is suitable for manufacturing a thermoelectric device for a vehicle that requires mass production.

However, since the Mg-Si-based thermoelectric material has low compressive strength due to its brittle nature, cracks occur in the thermoelectric element in the process of bonding to the electrode by applying pressure to the thermoelectric element made of the thermoelectric element, or repeated use There is a problem in that the lifespan of the thermoelectric module for a vehicle is reduced because the thermoelectric element cannot withstand the thermal shock applied in the process and the thermoelectric element is broken.

Republic of Korea Patent Publication No. 2013-0036638

An object of the present invention is to provide an Mg-Si-based thermoelectric material having excellent thermoelectric performance and high mechanical strength.

Another object of the present invention is to provide a method for manufacturing the Mg-Si-based thermoelectric material.

Another object of the present invention is to provide a thermoelectric device including the Mg-Si based thermoelectric material.

Another object of the present invention is to provide a thermoelectric module including the thermoelectric element.

In order to solve the above problems, the present invention includes a crystal structure consisting of crystal grains comprising a composition of Mg ₂ Si, and alloy particles in which two or more metals are bonded, wherein the alloy particles are Mg present at the interface in the crystal structure. -Si-based thermoelectric material is provided.

In addition, the present invention, a) Mg ₂ Si powder and the step of obtaining a mixture by mixing two or more kinds of metal precursor powder, b) reducing heat treatment of the mixture to the Mg ₂ Si powder is combined with two or more kinds of metal particles granules ( It provides a method for manufacturing a Mg-Si-based thermoelectric material comprising the steps of obtaining granule), and c) sintering the granules to form alloy particles in which the two or more kinds of metal particles are bonded.

Another aspect of the present invention provides a thermoelectric device including the Mg-Si-based thermoelectric material.

The present invention also provides an upper insulating substrate, a lower insulating substrate facing the upper insulating substrate, an upper electrode formed on the upper insulating substrate, a lower electrode formed on the lower insulating substrate, and the upper electrode and the lower electrode, respectively Provided is a thermoelectric module including the thermoelectric element in contact.

The Mg-Si-based thermoelectric material of the present invention has low thermal conductivity and high electrical conductivity and compressive strength because alloy particles that act as a buffer against external forces and the path of current flow exist at the interface in the crystal structure. Therefore, when a thermoelectric element and/or thermoelectric module is manufactured using the Mg-Si-based thermoelectric material of the present invention, it is possible to provide a thermoelectric element and/or thermoelectric module having excellent thermoelectric performance and a long lifespan.

1 is a reference diagram for explaining the organizational structure of a Mg-Si-based thermoelectric material according to the present invention.
2 is a reference diagram for explaining a method of manufacturing a Mg-Si-based thermoelectric material according to the present invention.
3 is a perspective view illustrating a thermoelectric module according to the present invention.
4 to 7 are reference views for explaining experimental examples according to the present invention.

Hereinafter, the present invention will be described.

The present invention is characterized in that it improves the thermoelectric performance of the Mg-Si-based thermoelectric material by increasing the electrical conductivity and at the same time increases the mechanical strength (eg, compressive strength) of the Mg-Si-based thermoelectric material. As follows.

1. Mg-Si based thermoelectric material

Referring to FIG. 1 , an Mg-Si-based thermoelectric material (hereinafter, referred to as a 'thermoelectric material') of the present invention includes a crystalline structure 10 and alloy particles 20 .

The crystal structure 10 included in the thermoelectric material of the present invention is composed of crystal grains 11 including a composition of Mg ₂ Si. That is, in the crystal structure 10 of the present invention, a plurality of crystal grains 11 are combined with each other.

The alloy particles 20 included in the thermoelectric material of the present invention exist at the interface (ie, the interface between the crystal grains 11) 12 within the crystal structure 10 .

As such, when the alloy particles 20 having conductivity are present at the interface 12 in the crystal structure 10 , a path of current movement is secured, and the electrical resistance of the interface 12 and the alloy particles 20 are As the electrical resistance is connected in parallel to lower the total electrical resistance of the thermoelectric material, the present invention can increase the electrical conductivity of the thermoelectric material.

In addition, when the alloy particles 20 having a composition different from that of Mg ₂ Si are present at the interface 12 in the crystal structure 10, phonon scattering occurs and the overall thermal resistance of the thermoelectric material increases. The invention can lower the thermal conductivity of the thermoelectric material.

In addition, when the alloy particles 20 are present at the interface 12 in the crystal structure 10, the mechanical strength of the interface 12 increases, and even when an external force is applied, the alloy particles 20 serve as a cushioning material, so the present invention is It is possible to increase the mechanical strength (especially compressive strength) of the thermoelectric material.

Here, the alloy particles 20 may exist in the crystal structure 10 together with the interface 12 in the crystal structure 10 . In addition, the non-alloyed metal particles may exist alone in the crystal structure 10 (ie, the crystal grains 11 ) or the interface 12 within the crystal structure 10 during the sintering process to manufacture the thermoelectric material.

The alloy particles 20 may have a composition in which two or more types of metals are combined.

Specifically, in consideration of the electrical conductivity and mechanical strength of the thermoelectric material, the alloy particles 20 include a first metal selected from the group consisting of copper (Cu), tin (Sn) and zinc (Zn), aluminum (Al) and zirconium. (Zr) is preferably made of an alloy to which a second metal selected from the group consisting of is bonded.

More specifically, the alloy particles 20 may be formed of a composition of Cu ₃ Al or CuAl ₂ having high electrical conductivity.

The alloy particles 20 preferably have an average particle size (particle diameter) of 10 to 500 nm in consideration of electrical conductivity, thermal conductivity, and mechanical strength of the thermoelectric material.

In addition, the content of the alloy particles 20 is preferably 0.01 to 10 parts by weight based on 100 parts by weight of the crystal structure 10 .

On the other hand, the thermoelectric material of the present invention is one selected from the group consisting of bismuth (Bi), antimony (Sb), arsenic (As), phosphorus (P), tellurium (Te), selenium (Se), and aluminum (Al). It may further include more than one doping agent. Such a dopant may be present in the grains 11 including the composition of Mg ₂ Si.

2. Manufacturing method of thermoelectric material

The present invention provides a method for manufacturing the above-described thermoelectric material, which will be described in detail with reference to FIG. 2 as follows.

a) Preparation of mixtures

Mg ₂ Si powder and two or more kinds of metal precursor powders are mixed to prepare a mixture. At this time, the method of mixing the Mg ₂ Si powder and two or more kinds of metal precursor powder is not particularly limited as long as it is a method known in the art (eg, milling, v-mixer, etc.).

When the Mg ₂ Si powder (x) and two or more kinds of metal precursor powder (y) are mixed, the mixing ratio (x:y) is 1:0.0001 to 1:0.1 in consideration of the thermoelectric performance and mechanical strength of the thermoelectric material. It is preferable that it is a weight ratio.

In addition, the metal precursor powder is two kinds selected from the group consisting of copper acetate powder, zinc acetate powder, aluminum acetate powder, zirconium acetate powder, and tin acetate powder in consideration of the thermoelectric performance and mechanical strength of the thermoelectric material, and the manufacturing efficiency of the thermoelectric material. more preferably.

b) preparation of granules

The mixture is subjected to reduction heat treatment to prepare granules in which two or more kinds of metal particles are bonded to Mg ₂ Si powder. That is, two or more kinds of metal precursor powders are each reduced to metal particles (specifically, acetate is removed from metal acetate powder) to prepare granules in which two or more kinds of metal particles are bonded to the surface of Mg ₂ Si powder. .

The reduction heat treatment of the mixture is preferably made in a temperature range of 150 to 400 ℃ so that two or more kinds of metal particles can be uniformly dispersed and bonded to the surface of the Mg ₂ Si powder. As the reduction heat treatment is performed within the above temperature range, two or more kinds of metal particles are uniformly dispersed and bonded to the surface of the Mg ₂ Si powder to further increase the mechanical strength (especially compressive strength) of the thermoelectric material.

In addition, the reduction heat treatment of the mixture is preferably performed in the presence of a mixed gas in which hydrogen and an inert gas are mixed so that the reduction of two or more kinds of metal precursor powders can be made well. In this case, the inert gas may be at least one selected from the group consisting of helium, argon and nitrogen.

c) sintering

The granules are put into a mold and sintered to form alloy particles in which two or more kinds of metal particles are combined.

The method for sintering the granules is not particularly limited as long as it is a method known in the art, but may include hot press or spark plasma sintering. At this time, the conditions for sintering are not particularly limited, but considering the density of the sintered body, it is preferable to appropriately control the temperature, time, and pressure. Specifically, the hot press may be sintered under a pressure of 30 to 80 MPa at 550 to 850 ° C for 30 minutes to 2 hours, and the discharge plasma sintering is performed at 500 to 800 ° C. for 2 to 20 minutes at a pressure of 20 to 40 MPa. Sintering may proceed under

3. Thermoelectric element

The present invention provides a thermoelectric device including the thermoelectric material. Specifically, the present invention provides a thermoelectric element manufactured in a predetermined shape (eg, a rectangular parallelepiped) through the process of cutting and/or processing the above-described thermoelectric material.

The thermoelectric element may be a p-type thermoelectric element or an n-type thermoelectric element.

Such a thermoelectric element may be applied to a thermoelectric cooling system capable of exhibiting a cooling effect by application of current as it is modularized by being coupled to an electrode, or a thermoelectric power generation system capable of exhibiting a power generation effect by a temperature difference.

4. Thermoelectric module

The present invention provides a thermoelectric module including the thermoelectric element, which will be described in detail with reference to FIG. 3 as follows.

The thermoelectric module of the present invention includes an upper insulating substrate 100 , a lower insulating substrate 200 , an upper electrode 300 , a lower electrode 400 , and a thermoelectric element 500 .

The upper insulating substrate 100 included in the thermoelectric module of the present invention and the lower insulating substrate 200 spaced apart from the upper insulating substrate 100 and facing each other by a predetermined distance are the places where the electrodes 300 and 400 are formed. The material constituting the insulating substrates 100 and 200 is not particularly limited, but may include gallium arsenide (GaAs), sapphire, silicon, Pyrex, and quartz.

The upper electrode 300 and the lower electrode 400 included in the thermoelectric module of the present invention may be formed through a process of patterning the upper insulating substrate 100 and the lower insulating substrate 200, respectively. Although the method of patterning is not specifically limited here, Lift-off, vapor deposition, photolithography, etc. are mentioned. The material constituting the upper electrode 300 and the lower electrode 400 is not particularly limited, but may include aluminum, nickel, gold, titanium, and the like.

The thermoelectric element 500 included in the thermoelectric module of the present invention is made of the above-described thermoelectric material, and the p-type thermoelectric element 501 and the n-type thermoelectric element which are in mutual contact with the upper electrode 300 and the lower electrode 400, respectively. (502).

Since the thermoelectric module of the present invention includes the thermoelectric element 500 made of a thermoelectric material having excellent thermoelectric performance and high mechanical strength, it can exhibit excellent performance and efficiency while exhibiting a long lifespan.

Hereinafter, the present invention will be described in detail through examples. However, the following examples only illustrate the present invention, and the present invention is not limited by the following examples.

[Example 1]

100 g of Mg ₂ Si powder, 4.38 g of copper acetate powder, and 0.62 g of aluminum acetate powder were put into a container, and a mixture was prepared using SPEX Mill.

Next, the mixture was subjected to reduction heat treatment at 350° C. for 2 hours in the presence of a mixed gas (95% by volume of N ₂ + 5% by volume of H ₂ ) to prepare granules.

Then, the granules are put into a mold and hot pressed under vacuum (10 ^-2 torr or less) at 750° C. under a 40 MPa pressure condition to combine copper and aluminum alloy particles at the interface within the Mg ₂ Si crystal structure. A thermoelectric material in which (composition: Cu ₃ Al, average particle size: 50 nm) exists was prepared.

[Example 2]

The same procedure as in Example 1 was performed except that the granules were put into a mold and hot pressed at 750 ° C., and copper and aluminum were bonded to the interface in the Mg ₂ Si crystal structure (composition: CuAl ₂ ) , average particle size: 50 nm) was prepared.

[Comparative Example 1]

100 g of Mg ₂ Si powder was put into a mold and hot-pressed under vacuum (10 ^-2 torr or less) at 370° C. under 70 MPa pressure to prepare a thermoelectric material.

[Comparative Example 2]

97 g of Mg ₂ Si powder and 3 g of copper acetate powder were placed in a container, and a mixture was prepared using SPEX Mill.

Next, the mixture was subjected to reduction heat treatment at 350 for 2 hours in the presence of a mixed gas (95% by volume of N ₂ + 5% by volume of H ₂ ) to prepare granules.

Then, the granules are put into a mold and hot pressed under vacuum (10 ^-2 torr or less) under a pressure condition of 750 to 70 MPa to form copper particles (average particle size: 50 nm) at the interface within the Mg ₂ Si crystal structure. ) in the presence of a thermoelectric material was prepared.

[Comparative Example 3]

A thermoelectric material having aluminum particles (average particle size: 50 nm) present at the interface within the Mg ₂ Si crystal structure was prepared in the same manner as in Comparative Example 2, except that aluminum acetate powder was applied instead of copper acetate powder.

[Comparative Example 4]

A thermoelectric material in which tin particles (average particle size: 50 nm) exist at the interface within the Mg ₂ Si crystal structure was prepared in the same manner as in Comparative Example 2 except that tin acetate powder was applied instead of copper acetate powder.

[Experimental Example 1] Thermoelectric performance evaluation

The performance of each of the thermoelectric materials prepared in Examples and Comparative Examples was evaluated as follows according to temperature, and the results are shown in FIGS. 4 and 5 .

1. Electrical conductivity ( δ ): It was measured by the four point method.

2. Seebeck coefficient ( S ): It was measured using Ulvac ZEM-3 equipment.

3, thermal conductivity (κ): was measured by LFA (Laser Flash Analysis).

4. Dimensionless figure of merit (ZT): It was calculated by applying Equation 1 below.

[Equation 1]

(S: Seebeck coefficient, δ : Electrical conductivity, κ: thermal conductivity, T: absolute temperature)

5. Output factor (PF): It was calculated by applying Equation 2 below.

[Equation 2]

4 and 5 , it can be seen that the thermoelectric material according to the present invention has excellent thermoelectric performance.

[Experimental Example 2] Compressive strength evaluation

The compressive strength of each of the thermoelectric materials prepared in Examples and Comparative Examples was evaluated using a RB 301 UNITECH-M (Universal Testing Machine) device, and the results are shown in Table 1 below. When measuring the compressive strength, the size of the thermoelectric material specimen was 1 mm in width. The length was 1 mm and the height was 2 mm.

division Compressive strength (㎫) Example 1 720.08 Example 2 678.48 Comparative Example 1 601.77 Comparative Example 2 623.46

Referring to Table 1, the compressive strength of the thermoelectric material of the present invention in which alloy particles are present at the interface in the crystalline structure is the compressive strength of the thermoelectric material in which metal particles are present alone or in which metal particles are not present at the interface in the crystalline structure. It can be seen that higher than

[Experimental Example 3] Confirmation of crystal structure

The fracture surface of the thermoelectric material was analyzed with a scanning electron microscope (SEM) and an X-ray spectrometer (EDS) to confirm whether alloy particles were present in the crystal structure of the thermoelectric material prepared in Examples 1 and 2, respectively. The results are shown in FIGS. 6 and 7 .

6 is an analysis of the thermoelectric material manufactured in Example 1, and FIG. 7 is an analysis of the thermoelectric material manufactured in Example 2, and it can be seen that alloy particles are present in the crystal structure.

10: crystal structure
11: grain
12: interface
20: alloy particles
100: upper insulating substrate
200: lower insulating substrate
300: upper electrode
400: lower electrode
500: thermoelectric element
501: p-type thermoelectric element
502: n-type thermoelectric element

Claims (15)

Mg ₂ A crystal structure consisting of crystal grains containing a composition of Si; and
Including alloy particles in which two or more metals are bonded,
The alloy particles are present at the interface in the crystal structure,
The alloy particles are made of a composition of Cu ₃ Al or CuAl ₂ , Mg-Si-based thermoelectric material. delete delete The method according to claim 1,
The alloy particles have an average particle size (D ₅₀ ) of 10 to 500 nm Mg-Si-based thermoelectric material. The method according to claim 1,
The content of the alloy particles is 0.01 to 10 parts by weight based on 100 parts by weight of the crystal structure Mg-Si-based thermoelectric material. The method according to claim 1,
Bismuth (Bi), antimony (Sb), arsenic (As), phosphorus (P), tellurium (Te), selenium (Se), and further comprising at least one doping agent selected from the group consisting of aluminum (Al) Mg-Si based thermoelectric material. a) mixing Mg ₂ Si powder, copper (Cu) precursor powder, and aluminum (Al) precursor powder to obtain a mixture;
b) reducing and heat-treating the mixture to obtain granules in which copper (Cu) particles and aluminum (Al) particles are bonded to the Mg ₂ Si powder; and
c) sintering the granules to form alloy particles in which copper (Cu) and aluminum (Al) are combined,
The alloy particles are made of a composition of Cu ₃ Al or CuAl ₂ , Mg-Si-based thermoelectric material manufacturing method. 8. The method of claim 7,
The copper (Cu) precursor powder of step a) includes copper acetate powder, and the aluminum (Al) precursor powder includes aluminum acetate powder, Mg-Si-based thermoelectric material manufacturing method. 8. The method of claim 7,
The reduction heat treatment of step b) is a method of manufacturing a Mg-Si-based thermoelectric material that is made in a temperature range of 150 to 400 ℃. 8. The method of claim 7,
The method for producing a Mg-Si-based thermoelectric material wherein the reduction heat treatment in step b) is performed in the presence of a mixed gas in which hydrogen and an inert gas are mixed. 11. The method of claim 10,
The inert gas is at least one selected from the group consisting of helium, argon and nitrogen. 8. The method of claim 7,
The sintering in step c) is a discharge plasma sintering performed under a pressure of 20 to 40 MPa at 500 to 800° C. for 2 to 20 minutes. 8. The method of claim 7,
The sintering of step c) is a method of manufacturing a Mg-Si-based thermoelectric material that is a hot press sintering performed under a pressure of 30 to 80 MPa at 550 to 850 ° C. for 30 minutes to 2 hours. A thermoelectric element comprising the Mg-Si-based thermoelectric material of any one of claims 1 and 4 to 6 . upper insulating substrate;
a lower insulating substrate facing the upper insulating substrate;
an upper electrode formed on the upper insulating substrate;
a lower electrode formed on the lower insulating substrate; and
A thermoelectric module comprising the thermoelectric element of claim 14 in contact with the upper electrode and the lower electrode, respectively.

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