KR20200002435A - METHOD FOR MANUFACTURING Bi-Sb-Te BASED THERMOELECTRIC MATERIAL WITH CONTROLLED GRAIN SIZE AND THERMOELECTRIC MATERIAL MANUFACTURED THEREBY - Google Patents

Abstract

The present invention relates to a method for manufacturing a Bi-Sb-Te-based thermoelectric material and a thermoelectric material manufactured thereby. The method for manufacturing a Bi-Sb-Te-based thermoelectric material comprises the following steps of: (a) heat-treating a Bi-Sb-Te-based thermoelectric powder through electric conduction heating; and (b) manufacturing a Bi-Sb-Te-based thermoelectric material sintered body by sintering the powder heat-treated in the step (a) by spark plasma sintering (SPS). According to the present invention, it is possible to control a grain size of a thermoelectric material by performing heat treatment of heating a thermoelectric powder through electric conduction heating before manufacturing a thermoelectric material through sintering, thereby manufacturing a thermoelectric material with an optimized grain size to have not only excellent figure of merit (ZT) but also improved mechanical properties compared to a conventional thermoelectric material.

Description

Method for manufacturing Bi-Sb-Te-based thermoelectric material with controlled grain size and thermoelectric material manufactured by the same

The present invention relates to a method of manufacturing a thermoelectric material and a thermoelectric material produced thereby, and more particularly, to manufacturing a Bi-Sb-Te-based thermoelectric material including a process for controlling grains of a thermoelectric material finally manufactured. To a method and a thermoelectric material produced thereby.

A thermoelectric material is a new alternative energy material that converts thermal energy due to temperature gradient into electrical energy, and inversely, direct current is applied to one end of the material, where endothermic heat is generated and heat is converted to thermal energy.

The above-mentioned energy conversion phenomenon is called thermoelectric phenomenon, and the Seebeck effect of converting thermal energy into electrical energy is used for thermoelectric generation, and the peltier effect of converting electrical energy into thermal energy is thermoelectric refrigeration. It is used for.

The thermoelectric power generation has the advantage that there is little noise and can easily convert heat and electricity mutually, unlike a conventional power generation device. In addition, the thermoelectric cooling is environmentally friendly because it does not use a refrigerant as in the conventional apparatus, and since there is no mechanical driving unit, there is no noise and vibration and selective cooling of the local part is possible. Therefore, its use is gradually being extended to the home appliance industry, such as high-power laser diodes, measuring equipment, medical equipment, and small refrigerators.

In order for thermoelectric materials to be widely used, the thermal / electric conversion efficiency of materials must be high. Generally, the conversion efficiency of thermoelectric materials is evaluated by a figure of merit (ZT).

로 나타내며, 높은 변환효율을 나타내기 위해서는 높은 Seebeck 계수(α)와 낮은 전기비저항(ρ) 및 낮은 열전도도(κ)가 동시에 요구된다. 이들 물성들은 재료내부의 전하(carrier)와 격자진동(phonon)의 거동에 의존하는 물질상수로서, 서로 종속적인 관계를 가지고 있다. 이러한 물성들의 상호의존적인 관계는 열전재료의 연구가 진행된 이래 성능지수를 높이는데 큰 장애요소로 작용하여 왔으며, 이를 극복하기 위한 여러 연구가 활발히 진행되고 있다.The performance index of thermoelectric materials

In order to exhibit high conversion efficiency, high Seebeck coefficient (α), low electrical resistivity (ρ), and low thermal conductivity (κ) are simultaneously required. These properties are material constants that depend on the behavior of carriers and lattice vibrations within the material and have a mutually dependent relationship. The interdependent relationship of these properties has been a major obstacle to improving the performance index since the study of thermoelectric materials, and various studies to overcome them have been actively conducted.

The performance index is divided into alloys having excellent performance indexes according to the operating temperature.Bi-Te-based in the room temperature range (below 200 ℃) and TAGS (tellurium-antimony-germanium-silver) in the mid-temperature zone (200 ~ 400 ℃) Si-Ge-based materials are used in the high-temperature regions 500-1000.

Bi-Te-based thermoelectric material, which is a material having a high performance index at room temperature, is typically Bi ₂ Te _{3 and} is manufactured in p-type or n-type by adding Sb or Se.

As described above, most of the related arts are related to the development of new materials and compositions for improving the performance index of thermoelectric materials, and there is virtually no attempt to improve thermoelectric performance by controlling grain sizes of thermoelectric materials.

Korea Patent Registration No. 10-1114252 (Registration Date: 2012. 02. 02.) Korea Patent Registration No. 10-1104677 (Registration Date: 2012. 01. 04.) Japanese Patent Laid-Open No. 2004-342893 (published: 2004. 12. 02.)

The technical problem to be solved by the present invention is a thermoelectric material manufacturing method capable of producing a thermoelectric material having improved mechanical properties and excellent thermoelectric index (ZT) by including a process that can control the grain size of the thermoelectric material and It is to provide a thermoelectric material produced thereby.

In order to achieve the above technical problem, the present invention comprises the steps of (a) heat-treating the Bi-Sb-Te-based thermoelectric powder through energization heating; And (b) sintering the powder heat-treated in step (a) by spark plasma sintering (SPS) to produce a Bi-Sb-Te-based thermoelectric material sintered body. We propose a method of manufacturing the material.

In addition, the Bi-Sb-Te-based thermoelectric powder in step (a) proposes a method of manufacturing a Bi-Sb-Te-based thermoelectric material, characterized in that the Bi _0.5 Sb _1.5 Te ₂ .

In addition, the Bi-Sb-Te-based thermoelectric powder of the Bi-Sb-Te-based thermoelectric material in a vacuum atmosphere in the step (a) and maintained for 30 to 90 minutes at a temperature of 400 ~ 550 ℃ characterized in that We propose a manufacturing method.

In addition, in step (a), the Bi-Sb-Te-based thermoelectric powder is energized and heated at a heating rate of 10 ° C./min under a vacuum atmosphere of 10 ⁻³ torr and maintained at 470 ° C. for 60 minutes. We propose a method of manufacturing Sb-Te-based thermoelectric materials.

In addition, the step (b) proposes a method for producing a Bi-Sb-Te-based thermoelectric material, characterized in that the discharge plasma sintering at a temperature of 350 ~ 550 ℃ and a pressure of 30 ~ 80 MPa.

In another aspect of the present invention, the present invention proposes a thermoelectric material manufactured by the above method.

According to the method of manufacturing a thermoelectric material according to the present invention, it is possible to control the grain size of the thermoelectric material by performing a heat treatment for heating the thermoelectric powder through energizing heating before manufacturing the thermoelectric material through sintering, and accordingly the existing thermoelectric material Compared with ZT, the thermoelectric material with the optimized grain size can be manufactured to have improved mechanical properties.

1 (a) to 1 (c) are scanning electron microscope (SEM) photographs showing fracture surfaces of the sintered bodies prepared in Comparative Examples, Examples 2 and 5, respectively.
2 (a) to 2 (c) are graphs comparing Seebeck coefficient, electrical conductivity, and power factor of the thermoelectric material sintered bodies manufactured in Comparative Examples and Examples 1 to 5, respectively.
Figure 3 is a graph comparing the thermal conductivity of the thermoelectric material sintered body prepared in Comparative Examples and Examples 1 to 5.
Figure 4 is a graph comparing the thermoelectric performance index (ZT) of the thermoelectric material sintered body prepared in Comparative Examples and Examples 1 to 5.

In describing the present invention, when it is determined that detailed descriptions of related known functions or configurations may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

Embodiments according to the concept of the present invention can be variously modified and can have various forms, and specific embodiments will be illustrated in the drawings and described in detail in the present specification or application. However, this is not intended to limit the embodiments in accordance with the concept of the present invention to a particular disclosed form, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. As used herein, the terms "comprise" or "having" are intended to indicate that there is a feature, number, step, action, component, part, or combination thereof that is described, and that one or more other features or numbers are present. It should be understood that it does not exclude in advance the possibility of the presence or addition of steps, actions, components, parts or combinations thereof.

Hereinafter, the present invention will be described in detail.

According to the present invention, a method for manufacturing a Bi-Sb-Te-based thermoelectric material having a controlled grain size includes: (a) heat treating a Bi-Sb-Te-based thermoelectric powder through energizing heating; And (b) sintering the powder heat-treated in step (a) by spark plasma sintering (SPS) to produce a Bi-Sb-Te-based thermoelectric material sintered body.

The step (a) is performed in order to control the size of the thermoelectric material grains in the sintered body prior to manufacturing the sintered body directly from the Bi-Sb-Te-based thermoelectric powder using spark plasma sintering (SPS). In this step, the Sb-Te-based thermoelectric powder is energized and heated in a vacuum atmosphere and maintained at a predetermined temperature for a predetermined time.

For example, after filling the Bi-Sb-Te-based thermoelectric powder in the mold, a pair of electrodes in contact with both ends of the filled thermoelectric powder layer and a power supply device capable of supplying a pulse current to the pair of electrodes According to this step by applying a voltage between the pair of electrodes in a vacuum atmosphere to generate electricity in the thermoelectric powder layer by heating the thermoelectric powder layer by Joule heat and maintaining for 30 to 90 minutes at a temperature of 400 ~ 550 ℃ Heat treatment takes place.

As the heat treatment temperature and heat treatment time made in this step increase, the grain size in the thermoelectric material sintered body obtained by step (b) to be described later increases, so that it is possible to control the grain size of the thermoelectric material by performing this step, Accordingly, it is possible to manufacture a thermoelectric material having a grain size optimized to have excellent ZT and improved mechanical properties compared to the existing thermoelectric material.

Meanwhile, the Bi-Sb-Te-based thermoelectric powder may further include at least one of Pb, Cu, and Se in addition to Bi, Sb, and Te as main elements, but is not limited thereto. It may be a powder selected from all composition ranges corresponding to the material, and may be preferably made of Bi _0.5 Sb _1.5 Te ₂ .

For reference, the Bi-Sb-Te-based thermoelectric powder may be manufactured by a milling method, a rapid solidification method, etc., and in the case of the milling method, a casting material including bismuth (Bi), antimony (Sb), and tellurium (Te) May be prepared by milling or milling each element of bismuth (Bi), antimony (Sb) and tellurium (Te). In addition, the rapid solidification method may be gas atomizing (Gas Atomizing) and the like, bismuth (Bi), antimony (Sb) and tellurium (Te) in a carbon crucible, and then in a high-frequency in argon (Ar) gas atmosphere By melting through induction heating and injecting the molten metal through an orifice, argon (Ar) gas may be used to produce an alloy for manufacturing thermoelectric materials including bismuth (Bi), antimony (Sb), and tellurium (Te).

Next, in step (b), the powder heat-treated in the previous step is sintered by spark plasma sintering (SPS) to prepare a Bi-Sb-Te-based thermoelectric material sintered body.

Production of the sintered body in this step is performed by spark plasma sintering (Spark Plasma Sintering, SPS) of the pressure sintering method, preferably discharge plasma sintering at a temperature of 350 ~ 550 ℃ and a pressure of 30 ~ 80 MPa. .

As a specific example of this step, a thermoelectric material manufacturing process made of Bi-Sb-Te based alloy through discharge plasma sintering will be described below.

The discharge plasma sintering process is a process in which a powder is filled into a mold, mounted in a vacuum chamber of a discharge plasma sintering apparatus, and sintered to a desired size by applying pressure and a direct current pulse to the powder. Due to the above instantaneous high energy, the surface of the alloy powder is melted and the powder is sintered without oxidation, thereby effectively controlling the growth of the powder particles and thus sintering in a short time to maintain the microstructure.

In order to manufacture a Bi-Sb-Te alloy thermoelectric material sintered body through a discharge plasma sintering process, a cylindrical mold having a diameter of 15 to 25 φ and a thickness of 5 to 7 mm was prepared, and then the Bi-Sb-Te based system was manufactured. The thermoelectric powder is filled, the mold is mounted in a chamber of the discharge plasma sintering apparatus, and a DC pulse is applied using a pulsed DC generator while pressurizing after decompression.

At this time, in order to remove the oxidizing gas existing in the chamber can be reduced to less than 10 ^-3 torr, DC pulse can be applied in the range of 0.1 ~ 2000A.

Subsequently, the uniaxial compression of the thermoelectric material powder filled in the mold is carried out at a pressure of 30 to 80 MPa by using a punch at the top and the bottom thereof. If it is difficult to manufacture and exceeds 80 MPa because cracks may occur in the sintered body after the sintering process is completed.

In addition, with respect to the sintering temperature and the sintering time, the sintering may be performed at 350 to 550 ° C. for 10 to 1800 seconds at a heating rate of 35 to 45 ° C./min, which is sintered at the surface of the powder particles at a temperature lower than 350 ° C. This is because the unsintered portion is generated because the strength of the sintered compact is low, and the sintered compact is crumbly, and at a temperature higher than 550 ° C., it is difficult to produce a healthy sample by Te melting.

The sintered body manufactured through discharge plasma sintering as described above has fine grains by increasing density and suppressing grain growth, thereby improving thermoelectric performance by excellent mechanical properties such as hardness and reducing thermal conductivity by phonon scattering.

According to the Bi-Sb-Te-based thermoelectric material manufacturing method according to the present invention, before the thermoelectric material is manufactured by sintering, the grain size of the thermoelectric material is controlled by performing a heat treatment to heat the thermoelectric powder through energizing heating. It is possible to manufacture a thermoelectric material having a grain size optimized to have an excellent mechanical index (ZT) as well as improved mechanical properties compared to conventional thermoelectric materials.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Embodiments according to the present disclosure may be modified in many different forms, and the scope of the present disclosure is not to be construed as limited to the embodiments described below. The embodiments of the present specification are provided to more fully describe the present specification to those skilled in the art.

<Example 1>

1. Thermoelectric powder design

In this technology, Bi ₂ Te ₃ -based thermoelectric materials exhibiting excellent thermoelectric performance at room temperature were used, and the composition was selected as P-type Bi _0.5 Sb _1.5 Te ₃ .

2. Thermopowder Manufacturing

Prior to powder production, the Bi, Sb, and Te elements with a purity of 99.99% (4N) were measured and loaded into carbon crucibles, and then melted with a P-type Bi _0.5 Sb _1.5 Te ₃ (hereinafter referred to as thermal starch powder) composition using a high frequency induction furnace. An alloy was prepared and a powder was prepared using the prepared alloy.

3. Heat treatment by energizing heating

In the vacuum atmosphere (10 ^-3 torr) was heated to 450 ℃ at a heating rate of 10 ℃ / min and then subjected to a heat treatment process through the energized heating maintained for 60 minutes.

4. Fabrication of Thermoelectric Sintered Body by Discharge Plasma Sintering

The discharge plasma sintering method can perform sintering in a short time and is characterized by using thermal, mechanical and electronic energy as the sintering driving force. In addition, the surface diffusion phenomenon between the particles due to the ON-OFF vs. the current pulse conduction effect is the dominant process, and the reactivity rapid heating sintering effect or the electric field diffusion effect promotes the densification rate and suppresses the growth of the microstructure of the powder. The advantage is that it can be kept intact. In this embodiment, a sintered body was manufactured using a discharge plasma sintering process having such an advantage.

In order to prepare the sintered body, 45 g of the powder prepared before the cylindrical mold having an outer diameter of 75 mm, an inner diameter of 25 mm and a height of 60 mm was charged, and then the charged powder was fixed to the upper and lower portions by using a graphite punch. Sintering was carried out in a vacuum atmosphere (10 ^-3 torr), the temperature was heated to 400 ℃ at a heating rate of 50 ℃ / min with 50 MPa pressure and maintained for 10 minutes for sufficient sintering. Finally, a cylindrical sintered body having a diameter of 25 mm and a thickness of about 12 mm was prepared.

<Example 2>

A sintered body was manufactured according to the same process as in Example 1 except that the heat treatment was performed at 470 ° C.

<Example 3>

A sintered compact was manufactured according to the same process as in Example 1 except that the heat treatment was performed at 500 ° C.

<Example 4>

A sintered body was manufactured according to the same process as in Example 1 except that the heat treatment was performed at 530 ° C. through energization.

Example 5

A sintered body was manufactured according to the same process as in Example 1 except that the heat treatment was performed at 550 ° C.

Comparative Example

A sintered body was manufactured according to the same process as in Example 1 except that the heat treatment was not performed by energizing heating.

Experimental Example

1 (a) to 1 (c) are scanning electron microscope (SEM) photographs showing fracture surfaces of the sintered bodies prepared in Comparative Examples, Examples 2 and 5, respectively. It can be seen that the grain size of the sintered body increases with the heat treatment time, and it was confirmed that the grains of the sintered body were controlled by energizing pressurized heat treatment.

2 (a) to 2 (c) are graphs comparing Seebeck coefficient, electrical conductivity and power factor of the thermoelectric material sintered bodies manufactured in Comparative Examples and Examples 1 to 5, respectively. The Seebeck coefficient of the sintered body subjected to the energizing heat treatment was increased compared to the Seebeck coefficient of the conventional thermoelectric sintered body, and the sintered body of Example 1, which was heat treated at 450 ° C., was the highest at 217.3 ㎶ / K.

In addition, the electrical conductivity was higher in the sintered body subjected to the conduction heat treatment than the conventional thermoelectric sintered body, and the concentration of electrons serving as a carrier in the P-type was increased by the conduction heat treatment. The sintered body heat-treated at 530 ° C was the highest at 1021.56 / mm. As a result of comparing the power factor derived based on the two results, it was confirmed that the heat treatment at 530 ℃ has the best value.

Figure 3 shows the thermal conductivity of the thermoelectric material sintered body prepared in Comparative Examples and Examples 1 to 5. The thermal conductivity tended to decrease and increase with the heat treatment temperature compared with the conventional thermoelectric sintered body.

As shown in FIG. 4, the ZT value was calculated based on the previous results. As a result, ZT of the thermoelectric sintered through the energizing heat treatment was increased, which is interpreted as a result of the high output factor and the low thermal conductivity. Finally, when the heat treatment at 470 ℃ has the best ZT value 1.098, it was confirmed that 46% better than before.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention belongs may be embodied in other specific forms without changing the technical spirit or essential features of the present invention. You will understand that. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Claims (6)

(a) heat-treating the Bi-Sb-Te-based thermoelectric powder by energizing heating in a vacuum atmosphere; And
(b) sintering the powder heat-treated in step (a) by spark plasma sintering (SPS) to produce a Bi-Sb-Te-based thermoelectric material sintered body, the Bi-Sb-Te-based thermoelectrics including Method of manufacturing the material. The method of claim 1,
In the step (a), the Bi-Sb-Te-based thermoelectric powder is Bi _0.5 Sb _1.5 Te ₂ , characterized in that the manufacturing method of Bi-Sb-Te-based thermoelectric material. The method of claim 1,
Bi-Sb-Te-based thermoelectric powder in the step (a) is energized and heated in a vacuum atmosphere to maintain for 30 to 90 minutes at a temperature of 400 ~ 550 ℃ Bi-Sb-Te based thermoelectric material manufacturing method . The method of claim 1,
In step (a), the Bi-Sb-Te-based thermoelectric powder is energized and heated at a heating rate of 10 ° C./min under a vacuum atmosphere of 10 ⁻³ torr and maintained at 470 ° C. for 60 minutes. Te-based thermoelectric material manufacturing method. The method of claim 1,
Discharging plasma sintering at a temperature of 350 ~ 550 ℃ and a pressure of 30 ~ 80 MPa in the step (b) Bi-Sb-Te-based thermoelectric material manufacturing method. Bi-Sb-Te type thermoelectric material manufactured by the method of any one of Claims 1-5.

Images