KR20180087964A - METHOD FOR MANUFACTURING Bi-Te BASED THERMOELECTRIC MATERIAL WITH CONTROLLED PARTICLE SIZE AND Bi-Te BASED THERMOELECTRIC MATERIAL MANUFACTURED THEREBY - Google Patents

Abstract

The present invention relates to a method for manufacturing a Bi-Te based thermoelectric material and, more specifically, to a novel method of improving thermoelectric properties by decreasing thermal conductivity through grain size control and maintaining high Seebeck coefficient and electric conductivity by uniformly pulverizing a metal ribbon, formed through rapid solidification (RSP), into particles through planetary mill, which is high energy milling, under inert atmosphere and sintering the particles. The method comprises the following steps: (i) dissolving and coagulating a raw material for a thermoelectric material containing a Bi raw material and a Te raw material to form a parent alloy; (ii) forming a metal ribbon through rapid cooling of the parent alloy; (iii) milling the metal ribbon to an average particle size (d50) of 20 μm or less by a planetary mill under inert atmosphere; and (iv) compressing the pulverized material to form a preform and pressing and sintering the preform.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of manufacturing a Bi-Te thermoelectric material according to particle size control, and a Bi-Te thermoelectric material produced therefrom. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a method of manufacturing a Bi-Te thermoelectric material for use in thermoelectric power generation, and more particularly, to a method of manufacturing a thermoelectric material for a thermoelectric generator, which comprises a Bi-Te system metal ribbon formed through Rapid Solidification Process (RSP) A method for manufacturing a Bi-Te thermoelectric material in which thermoelectric properties are improved by uniformly pulverizing and then pressing and sintering in the form of fine particles through a milling planetary mill to secure a low thermal conductivity through particle size control, The present invention relates to a Bi-Te thermoelectric material produced.

Thermoelectric technology is a technology that directly converts heat energy into electric energy and electric energy into thermal energy in a solid state, and is applied to thermoelectric power generation for converting thermal energy into electric energy and thermoelectric cooling for converting electric energy into heat energy. The thermoelectric material used for such thermoelectric power generation and thermoelectric cooling improves the performance of the thermoelectric device as the thermoelectric property is increased. The determination of the thermoelectric performance is based on the assumption that the thermoelectric performance is determined based on the thermoelectric power V, the Seebeck coefficient?, The Peltier coefficient?, The Thomson coefficient?, The Nernst coefficient Q, the Etchinghausen coefficient P, ), The output factor (PF), the figure of merit (Z), the dimensionless figure of merit (ZT = α2σT / κ where T is the absolute temperature), thermal conductivity (κ), Lorentz number (L) ρ). In particular, the dimensionless figure of merit (ZT) is an important factor that determines the thermoelectric conversion energy efficiency. By manufacturing a thermoelectric element using a thermoelectric material having a high performance index (Z =? 2? /?), . That is, the thermoelectric material has a higher thermoelectric performance as the higher the Seebeck coefficient, the higher the electric conductivity, and the lower the thermal conductivity.

On the other hand, as the thermoelectric material is fine and the uniform particles are formed, the thermoelectric performance can be further improved. For this purpose, a thermoelectric material is generally produced in powder form through a method such as melt-spraying, simple crushing, electrolytic electrodeposition, chemical coprecipitation, or mechanical pulverization.

The molten metal spraying method is a method in which molten metal is jetted at high speed in a chamber in an atmosphere, mass production is possible, but particle size control is impossible. In addition, the simple crushing method requires a long period of time to be made into powder of a predetermined size, and particle size control is also impossible. In addition, the chemical coprecipitation method (precipitation method) is capable of producing fine powder, but has difficulty in controlling the concentration and has a disadvantage in that it is present in an agglomerated state rather than as a unit powder. The mechanical pulverization method is a method of pulverizing a spherical ball and a ball using a mechanical kinetic energy in an atmosphere controlled container, and the production speed is low, and there is a possibility that impurities are mixed with balls. In addition, there are various methods for each process such as sol-gel method.

As a conventional technique, Korean Patent Registration No. 10-0228464 discloses a method of melting a Bi ₂ Te ₃ -Sb ₂ Te ₃ -based material and cooling it by a rapid solidification method (atomizing method) by spraying a high-pressure nitrogen gas to form a fine, Lt; / RTI > of the thermo-changeable material powder. Korean Patent No. 10-0228463 also discloses a method of forming a Bi ₂ Te ₃ thermoelectric material into a chemically homogeneous ribbon shape by press forming by cold pressing and pressing and sintering by hot pressing, 10-0382599 discloses a method of pulverizing a PbTe-based thermoelectric material with a ball mill by cooling molten metal in a copper block. In addition, Korean Patent No. 10-0440268 discloses a method of melting a Bi ₂ Te ₃ -Sb ₂ Te ₃ -based thermoelectric material, growing it into crystals, solidifying it, and then reducing it by hydrogen reduction to form a powder. However, since the above-described conventional techniques are difficult to produce nanopowders having a uniform size and most of the manufacturing processes are performed in the air, the degree of oxidation in the thermoelectric material is lowered due to oxygen in the atmosphere, .

Disclosure of the Invention The present invention has been conceived in order to solve the above-mentioned problems, and it is an object of the present invention to provide a method for producing a metal ribbon by pulverizing a metal ribbon produced by rapid solidification (RSP) under an inert atmosphere, A Te-based thermoelectric material and a Bi-Te-based thermoelectric material produced from the same.

In order to achieve the above object, the present invention provides a method for manufacturing a thermoelectric material, comprising the steps of: (i) dissolving and coagulating a raw material for a thermoelectric material containing a Bi raw material and a Te raw material to form a parent alloy; (ii) forming a metal ribbon through rapid cooling of the parent alloy; (iii) pulverizing the metal ribbon to an average particle size (d ₅₀ ) of 20 μm or less by an planetary mill under an inert atmosphere; And (iv) compressing the pulverized material to form a preform, followed by pressure sintering.

The mother alloy ingot in the step (i) is preferably an n-type Bi-Te-Se alloy or a p-type Bi-Sb-Te alloy having a high purity of 5N or more.

The present invention also provides a Bi-Te thermoelectric material produced by the above-described method.

More specifically, the density of the Bi-Te thermoelectric material may be 95 to 99%, the thermal conductivity may be 0.65 to 1.0 W / mK, and the thermoelectric performance index ZT may be 1.0 or more.

The present invention relates to a method for producing a metal ribbon by pulverizing a metal ribbon produced by rapid solidification (RSP) in a non-oxygen-containing inert atmosphere through a planetary mill, And a high thermoelectric performance can be secured by showing a high Seebeck coefficient and electrical conductivity.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process flow chart of a manufacturing method according to an embodiment of the present invention. FIG.
Fig. 2 is a particle distribution diagram of a ground product obtained by pulverizing the metal ribbon produced in Example 1 by a planetary mill. Fig.
3 is a particle distribution diagram of the pulverized product obtained by pulverizing the metal ribbon produced in Comparative Example 1 with a mortar.
Fig. 4 shows the results of measurement of the thermal conductivity of the Bi-Te thermoelectric material produced in Example 1 and Comparative Example 1. Fig.
Fig. 5 shows the results of measurement of the thermoelectric performance index (ZT) of the Bi-Te thermoelectric material prepared in Example 1 and Comparative Example 1. Fig.

Hereinafter, the present invention will be described in detail.

Generally, ZT, which is an index of thermoelectric performance evaluation of a thermoelectric material, is measured by the following equation (1).

ZT = (POWER FACTOR x (electrical conductivity) ² / thermal conductivity) x DELTA T

For most metallic materials, as the electrical conductivity increases, the thermal conductivity increases proportionally, so the higher the thermal conductivity, the more the ZT is significantly reduced. In the field of thermoelectric materials, we are studying the control of three factors such as power factor, electric conductivity and thermal conductivity independently by the concept of nanostructure. We also manufacture thermoelectric material with controlled nano structure through rapid cooling (RSP) . As a result, the thermal conductivity and the electric conductivity can be controlled independently, and the ZT can be increased when the thermal conductivity is lowered and the electric conductivity is increased. In view of the foregoing, in the present invention, the thermal conductivity index ZT of the thermoelectric material is increased by relatively reducing the thermal conductivity of the thermoelectric material through particle size control.

The present invention relates to a material for a thermoelectric element of n-type (Bi, Te, Se) and p-type (Bi, Te, Sb) based Bi-Te system, preferably Rapid Solidification Process RSP) can be applied to control the uniformity of the ribbon composition. At the same time, under an inert atmosphere containing oxygen, the metal ribbon is uniformly dispersed in particulate form through a planetary mill, , It is possible to exhibit high thermoelectric performance such as reduction in thermal conductivity, high Seebeck coefficient and excellent electric conductivity through control of particle size and oxidation degree.

More specifically, in the present invention, the mother alloy is produced by melting and solidifying a raw material having a composition containing high-purity Bi and Te having a size of 2 to 5 mm in size, To 700.degree. C.) to prepare a Bi-Te ribbon for a thermoelectric element having improved compositional uniformity. After that, the thermoelectric element ribbon is pulverized into a fine powder through a planetary mill in an inert atmosphere and then subjected to pressure sintering A thermoelectric material having high density and excellent thermoelectric properties can be produced.

The Bi-Te thermoelectric material prepared through the above-described method can secure a low thermal conductivity through controlling the particle size and oxidation degree, and since it is a nano-sized amorphous powder having a uniform particle size, the composition is homogeneous, In addition to high strength properties, the thermoelectric performance is further improved.

In addition, since the target composition of the Bi ₂ Te ₃ thermoelectric parent alloy can be uniformly controlled in the present invention, uniformity can be maintained in the production of ribbons through the RSP process, and the thermal characteristics of the final product are excellent. Further, as the nanoblock is finer, the thermal conductivity decreases to show an excellent thermoelectric performance (ZT). In the present invention, the thermal characteristic is further increased as the nano-block size of the ribbon becomes finer according to the RSP process conditions.

≪ Method of producing Bi-Te thermoelectric material &

Hereinafter, a method of manufacturing a Bi-Te-based thermoelectric material according to an embodiment of the present invention will be described. However, the present invention is not limited to the following production methods, and the steps of each process may be modified or optionally mixed as required.

For example, (i) a step of dissolving and solidifying a raw material for a thermoelectric material containing a Bi raw material and a Te raw material to form a parent alloy (step S10); (ii) forming a metallic ribbon through the rapid cooling of the parent alloy (step S20); (iii) milling the metal ribbon in an inert atmosphere by planetary mill so that the average particle diameter (d ₅₀ ) is not more than 20 탆 (Step S30); And (iv) compressing the pulverized material to form a preform, followed by pressure sintering (step S40).

FIG. 1 is a conceptual diagram showing a method of manufacturing a Bi-Te thermoelectric material according to the present invention. Hereinafter, referring to FIG. 1, the manufacturing method will be described separately for each process step as follows.

(1) Dissolve and solidify raw materials constituting the Bi-Te thermoelectric material to form a parent alloy (step S10).

In this step, the Bi-based raw material and the Te-based raw material are mixed and dissolved and coagulated in accordance with the stoichiometric ratio constituting the Bi-Te-based thermoelectric material to form an n-type and / or p- Type Bi-Te alloy.

The step S10 may be performed without limitation on the mother alloy according to a conventional method known in the art.

More specifically, as a preferable example of the step S10, (i-1) a first element; And a second element, into a quartz tube and then maintaining a vacuum state (step S10-1); (I-2) The quartz tube in the vacuum state is charged into a locking furnace and stirred and melted at a temperature of 650 to 700 ° C for 1 to 3 hours at a rate of 10 to 15 times / minute to form a parent alloy (Step < RTI ID = 0.0 > S10-2) < / RTI >

First, (i-1) n-type and p-type raw materials for thermoelectric materials corresponding to respective compositions are charged into a quartz tube and sealed for dissolution (hereinafter referred to as step S10-1) .

The raw material for a thermoelectric material usable in the present invention may be a composition based on Bi and Te, and further containing Se or Sb components depending on the n-type and p-type, respectively. For example, the Bi raw material and the Te raw material may be mixed at a ratio according to the stoichiometric composition of Bi ₂ Te _{3 ± 0.2} , preferably Bi ₂ Te _{3 ± 0.15} .

According to a preferred embodiment of the present invention, the thermoelectric material raw material comprises (i) at least one first element selected from the group consisting of Bi and Sb; And at least one second element selected from the group consisting of Te and Se.

More specifically, when the raw material for the n-type thermoelectric material is a Bi-Te-Se alloy composition, it is preferable that 50 to 55% by weight of Bi, 40 to 45% by weight of Te, 3 to 4% . ≪ / RTI > When the raw material for the p-type thermoelectric material is a Bi-Sb-Te alloy, the composition may include 10 to 15% by weight of Bi, 25 to 30% by weight of Sb, and 55 to 60% have.

In the present invention, a doping element powder may be added to the composition of the thermoelectric material to be produced.

Here, since the dopant is introduced to make the Bi-Te thermoelectric material have n-type or p-type characteristics, conventional components in the field that can be used for n-type or p-type thermoelectric materials can be used without limitation have. For example, at least one metal selected from the group consisting of Al, Sn, Mn, Ag, Cu and Ga. By doping the above-mentioned metal component, it is possible to improve the electric conductivity and the anti-skew property to improve the thermoelectric performance. At this time, the content of the at least one kind of metal to be doped is not particularly limited, and may be in the range of 0.001 to 1% by weight based on the total weight.

The dopant introduced in this manner replaces Bi or Te lattice depending on the thermodynamic energy difference of the lattice coupling or the driving force of atomic diffusion through the following heat treatment process or the like.

In the present invention, the size and shape of the thermoelectric material are not particularly limited, but may be in the form of a block having a size of about 2 to 5 mm. The purity of the thermoelectric material is preferably 5 N or more.

The raw material for the thermoelectric material described above is charged into a quartz tube, sealed by using a vacuum pump, and maintained in a vacuum state.

(i-2) Each of the n-type and p-type parent alloys is manufactured by using a furnace of a quartz tube of step S10-1 (hereinafter referred to as step S10-2).

In a preferred example of step S10-2, a quartz tube sealed in a vacuum state is charged into a furnace and stirred at a temperature of about 650 to 700 DEG C for 1 to 3 hours at a rate of 10 to 15 times / And dissolves to form the parent alloy.

In order to produce ribbons using Rapid Solidification (RSP), a homogeneous master alloy of Bi ₂ -Te ₃ -based thermoelectric materials should be prepared. Accordingly, in the present invention, a Φ 30 * 100 mm parent alloy or a parent alloy having a size in the range of about Φ 20 to 30 × 100 to 150 mm can be produced.

The mother alloy ingot produced through step S10-2 may be a Bi-Te system having a high purity of 5N or more. For example, it may be an n-type Bi-Te-Se alloy or a p-type Bi-Sb-Te alloy, preferably a p-type Bi-Sb-Te alloy.

(2) The n-type and / or p-type parent alloy obtained in the step S10-2 is melt-spun to form a metal ribbon (hereinafter referred to as step S20).

In this step, the Bi-Te system alloy obtained in the previous step is subjected to rapid solidification (R.S.P.) to produce a Bi-Te system metal ribbon having a complex microstructure.

In a preferred example of step S20, the mother alloy ingot is charged into a nozzle provided in a melt spinning machine, and then the melt is completely melted using a heating body capable of continuously supplying and supplying heat, and then the melt is inert The gas is pressurized and injected so that the melt is brought into contact with the surface of the rotating high-speed rotating wheel so as to be rapidly cooled. Thereby forming a Bi-Te-based metal ribbon.

Here, the heating element is not particularly limited as long as it can continuously supply and maintain heat, and a conventional resistance heating element known in the art can be used. For example, a resistor A heating element can be used. For example, the temperature of the resistance heating body can be controlled by using an electric furnace type heater such as a graphite heater.

The temperature range at which the resistance heating element generates heat is not particularly limited as long as it can completely dissolve the Bi-Te alloy. For example, it is maintained in the range of 500 to 800 ° C, preferably 650 to 700 ° C. The surface resistance of the resistance heating body may be adjusted depending on its thickness and type, and may be adjusted within a range of 0.1 to 100 ohm (ohm), for example.

Also, the type and pressure range of the inert gas are not particularly limited, but it is preferable to pressurize the inert gas to 0.1 to 0.5 MPa using argon gas or the like.

In step S20, the high-speed rotary wheel in contact with the melt may use a conventional wheel known in the art, such as a copper wheel. Here, the rotation speed of the high-speed rotation wheel is not particularly limited, and may be, for example, 500 to 2,000 rpm, and the wheel line speed may range from 5 m / s to 40 m / s. When the above-mentioned conditions are satisfied, the melt contacting the surface of the wheel is rapidly cooled, and at the same time, an alloy ribbon having a thin thickness and a fine structure can be formed.

In the present invention, by controlling the cooling rate of the molten parent alloy, it is possible to control the uniform particle size, and in general, when the cooling rate is slow, nano-sized amorphous powder can be produced, or fine particle powder can be produced . In addition, the production conditions can be varied depending on the concentration and kind of the raw material.

The parent alloy, which has undergone the above-described processes, is not crystallized through the rapid cooling (RSP) process, but is solidified while the amorphous structure and the crystalline structure are mixed. In this case, if the rapid cooling rate is very fast, it is produced in the form of a ribbon. However, if the cooling rate is controlled, the powder having a size of several hundred nanometers can be also produced as a simple connected semi-ribbon.

A thin Bi-Te thermoelectric material ribbon is formed through the rapid cooling of step S20 described above. In one example, the length of the produced metal ribbon is 5 to 15 mm and the width may be 0.5 to 5 mm.

(3) The metallic ribbon is pulverized through an oil-based ball mill under an inert atmosphere (hereinafter referred to as step S30).

In step S30, the high-brittle ribbon-like material rapidly solidified by direct injection of the molten parent alloy is crushed using a planetary mill, which is a type of high-energy milling, to produce nano-sized An amorphous fine powder is obtained.

Processes commonly used in conventional grinding processes include mortar and ball milling. The induction is a manual grinding apparatus for finely pulverizing solids, which is easy to handle and inexpensive, while it is difficult to control the particle size of the pulverized powder and it is difficult to improve the grinding efficiency.

In addition, the ball mill is a principle in which after the object to be ground and the ball are put in, the ceramic ball inside falls by the rotation of the cylinder with respect to the central axis to crush the object to be ground. Generally, as the rotation speed (rpm) of the ball mill increases, the crushing efficiency increases. However, if the rotation speed of the ball exceeds a predetermined speed, the centrifugal force acting on the ceramic ball becomes equal to the centrifugal force. There is a limit in improving the grinding efficiency.

In contrast, the planetary mill is a type of high-energy milling that maximizes the rotation of the ceramic ball inside through the rotation of two different rotating shafts by allowing the vessel to revolve and rotate at different rotational axes Thereby maximizing the grinding efficiency of the object to be ground. As a result, a fine and uniform powder can be obtained in a short time.

In one embodiment of the step S30, a metallic ribbon and a ball are put into a container for conducting a magnetic field, and oil milling is performed.

At this time, the balls may be any of ceramic balls well known in the art, and examples thereof include zirconia balls, STS ball, and SKD-11 ball. Also, the size of the balls may be 1 to 5, but is not limited thereto, and can be appropriately adjusted in consideration of the size and amount of the object to be ground.

Also, the weight ratio of the metal ribbon and the ball may be 5 to 15: 1, and preferably 7 to 12: 1.

In the step S30, a preferable example of the conditions of the planetary ball milling can be carried out at a rotation speed of 100 to 500 rpm for 10 to 120 minutes. When the planetary ball milling is carried out under the above-mentioned conditions, the particle size of the pulverized product can be controlled to be low to ensure uniform fine particles

In the present invention, in order to control the oxidation degree of the metal ribbon, the aforementioned planetary ball milling step can be carried out under an inert atmosphere. By performing the pulverization under such a condition that oxygen is not contained, the oxygen content in the pulverized powder can be reduced and the degree of oxidation can be controlled to be low. For example, in the present invention, it is possible to reduce the oxygen content of about 30% or more, specifically 30 to 45%, and preferably the oxygen content in the pulverized product to 0.03 % Or less.

At this time, the type and pressure range of the inert gas are not particularly limited. For example, nitrogen gas, argon gas, or mixed atmosphere thereof may be used.

The particle size of the ground Bi-Te powder through the planetary mill process of the step S30 described above is 1/9 to 1/10 of the particle diameter of the powder ground by the existing ball mill or mortar Level. For example, the average particle diameter (d ₅₀ ) of the Bi-Te-based powder may be 20 탆 or less, and preferably in the range of 1 to 15 탆.

After step (4), the preform is produced through a compression process of the pulverized product of the metal ribbon obtained in step S30, and then a high-density thermoelectric material is produced through pressure sintering (hereinafter referred to as step S40).

In this step S40, a molded body having a predetermined shape is manufactured to secure a high density in the pressure sintering process.

For this, the nano-sized amorphous powder form crushed in step S30 is compressed. At this time, a conventional method known in the art can be used for the compression process. For example, it is preferable to use a molding press or a compressor. The compression conditions are not particularly limited and can be suitably adjusted under ordinary compression conditions known in the art. For example, compression at 10 MPa or less is preferable.

Thereafter, the preform thus obtained is press-sintered to produce a high-density thermoelectric material.

Non-limiting examples of pressure sintering methods that can be used in the present invention include hot press forming methods such as Hot Press (HP) or Spark Plasma Sintering (SPS).

Here, the temperature of the hot working is not particularly limited, but it is preferable that the hot working is performed at a temperature in the range of 400 to 500 占 폚 and a pressure of 40 to 60 MPa for 3 to 10 minutes. When the conditions (temperature, time, pressure) at the time of hot working are 400 ° C., 3 minutes or less than 40 MPa, a high-density material can not be obtained. When the condition exceeds 500 ° C. or the time exceeds 10 minutes, The vapor pressure of Te is high and volatilized, which makes it unsuitable for the intended composition, and thus the thermoelectric performance index is likely to be lowered. Also, if the pressure exceeds 60 MPa, it may lead to danger of the applied mold and equipment.

The Bi-Te thermoelectric material of the present invention produced through the above-described production method has a density of 95 to 99%, preferably 97% or more. In addition, the particle size can be controlled by securing fine particles having an average particle diameter (d ₅₀ ) of about 1/10 as compared with the control group (Comparative Example 1) pulverized with mortar. The thermal conductivity is also in the range of 0.65 to 1.0 W / mK. In addition, the thermoelectric performance index ZT can be about 1.0 or more in the case of the P type, and is preferably in the range of about 1.0 to 1.2. This is due to the fact that the nanoblocks of the ribbons produced in the rapid solidification process (RSP) process are fine, and then the particle size and oxidation degree are controlled when milled by a planetary mill under an inert atmosphere, It seems to be improved.

Hereinafter, the present invention will be described concretely with reference to Examples. However, the following Examples and Experimental Examples are merely illustrative of one form of the present invention, and the scope of the present invention is not limited by the following Examples and Experimental Examples .

[ Example  One]

A thermoelectric material containing Bi, Te, and Sb having a mass of about 2 to 5 mm and a high purity of 5 N or more was prepared. In the case of p-type, 13 wt% of Bi, 28 wt% of Sb, and 59 wt% of Te were used. The thermoelectric material was charged into a quartz tube and then sealed using a vacuum pump. The quartz tube was charged into a locking furnace and stirred and melted at about 700 ° C for 2 hours at a rate of 10 times / min to prepare a Φ 30 * 100 mm parent alloy ingot. Thereafter, the mother alloy ingot was charged into a nozzle provided in a melt-spinning apparatus, and completely melted at a temperature of about 700 ° C using a resistance heating body (a structure wrapping the nozzle as a graphite heater) to form a melt. A Te-based metal ribbon (length: 10 mm, width: 2 mm) was formed by contacting with the surface of a rotating copper wheel by rapid cooling. At this time, the rotation speed of the copper wheel was 1000 rpm.

Then, to control the particle size, the formed metal ribbon was put into a planetary mill apparatus under an argon (Ar) atmosphere, and then pulverized at a rotation speed of 300 rpm for 30 minutes. The size of the zirconia balls used was 5Φ, and the weight ratio between the metal ribbon and the balls was 10: 1. At this time, the oxygen content of about 30% or more could be controlled to be lower than that when pulverized under atmospheric conditions. The pulverized powder was maintained at about 485 ° C for 3 minutes by using spark plasma sintering (SPS), and a high density Bi-Te p-type material having a relative density of 99% or more was produced at a pressure of 50 MPa.

[ Comparative Example  One]

A thermoelectric material containing Bi, Te and Sb having a mass of about 2 to 5 mm and a high purity of 5 N or more was prepared. In the case of p-type, 13 wt% of Bi, 28 wt% of Sb, and 59 wt% of Te were used. The thermoelectric material was charged into a quartz tube and then sealed using a vacuum pump. The quartz tube was charged into a locking furnace and stirred and melted at about 700 ° C for 2 hours at a rate of 10 times / min to prepare a Φ 30 * 100 mm parent alloy ingot. Thereafter, the mother alloy ingot was charged into a nozzle provided in the melt spinning apparatus, and completely melted using a resistance heating body (a structure wrapping the nozzle as a graphite heater) to form a melt, and then the inert gas was injected into the melt at 0.2 MPa for injection , A Bi-Te-based metal ribbon (length: 10 mm, width: 2 mm) was formed by rapid cooling in contact with a rotating copper wheel surface. At this time, the rotation speed of the copper wheel was 1000 rpm.

Subsequently, the formed metal ribbon was pulverized for 30 minutes using a mortar in an Ar atmosphere. The pulverized powder was maintained at about 485 ° C for 3 minutes by spark plasma sintering (SPS), and the thermoelectric material was produced at a pressure of 50 MPa.

[ Experimental Example  1. According to the grinding process Bi - Te system  Evaluation of physical properties of thermoelectric material]

A planetary mill and a mortar pulverization process were performed using the metal ribbon formed in Example 1, and the particle size distribution of the pulverized product was evaluated as follows.

The length of the metal ribbon before the milling process was 10 mm and the width was 2 mm. The particle size distribution of the milled product obtained by performing the planetary ball milling and induction milling is shown in FIGS. 2 to 3, respectively.

Experimental results show that the Example 1, the average particle diameter (d ₅₀₎ For showed the 6.03 ㎛, the case of Comparative Example 1, crushed with a mortar (mortar) average particle size (d ₅₀₎ crushed by a planetary ball mill (planetary mill) Lt; / RTI > As a result, it was confirmed that the granulated product of Example 1 pulverized by the planetary ball mill had an average particle size of about 1/9 to 1/10 as compared with the pulverized product of Comparative Example 1 (see Tables 1 and 2 below).

Planetary Mill Unit (탆) Particle size 1 time Episode 2 3rd time Average Standard Deviation d (10) 1.67 1.56 1.48 1.57 0.10 d (50) 7.20 5.86 5.02 6.03 1.10 d (90) 31.91 19.02 18.01 22.98 7.75

Mortar Unit (탆) Particle size 1 time Episode 2 3rd time Average Standard Deviation d (10) 22.984 23.494 23.239 23.24 0.25 d (50) 48.929 51.563 50.246 50.25 1.32 d (90) 87.792 102.787 95.29 95.29 7.50

[ Experimental Example  2. Bi - Te system  Evaluation of physical properties of thermoelectric material]

The physical properties of the Bi-Te thermoelectric material prepared in Example 1 and Comparative Example 1 are as follows.

1) Measurement of Seebeck coefficient and electrical conductivity: Measured according to JIS K 7194 using ZEM-3 (manufactured by Ulvac-Riko). The power factor was calculated by using the measured Seebeck coefficient (S) and electrical conductivity (σ).

Equation 2 Power factor = (Seebeck coefficient) ² x Electrical Conductivity

2) Measurement of thermal conductivity: Specific heat capacity measurement and thermal conductivity were calculated by laser flash method in accordance with JIS R 1611 and JIS R 1650-3. More specifically, after cutting into a disk having a diameter of 10 mm x 1 mm and measuring the thermal diffusivity (D), specific heat (Cp) and density (d) by a laser flash method, the thermal conductivity is measured Respectively.

[Equation 3]? = DCpd

The results of the measured thermal conductivities are shown in FIG.

3) Dimensional Thermoelectric Performance Index (ZT): The dimensionless thermoelectric performance index (ZT) was measured using the measured power factor, electrical conductivity and thermal conductivity. The results are shown in FIG.

ZT = (POWER FACTOR x (electrical conductivity) ² / thermal conductivity) x DELTA T

As a result, it was found that the Bi-Te-based thermoelectric material of the present invention ground through a planetary mill has low thermoconductivity through particle size control and has excellent thermoelectric performance index.

Claims (12)

(i) dissolving and coagulating a raw material for a thermoelectric material including a Bi raw material and a Te raw material to form a parent alloy;
(ii) forming a metal ribbon through rapid cooling of the parent alloy;
(iii) pulverizing the metal ribbon to an average particle size (d ₅₀ ) of 20 μm or less by an planetary mill under an inert atmosphere; And
(iv) compressing the pulverized material to form a preform, followed by pressure sintering
Based thermoelectric material. The method according to claim 1,
Wherein the Bi raw material and the Te raw material in the step (i) are mixed at a ratio according to a stoichiometric composition of Bi ₂ Te _{3 ± 0.2} . The method according to claim 1,
Wherein the raw material for thermoelectric material of step (i) further comprises at least one element selected from the group consisting of Sb and Se. The method of claim 3,
Wherein the mother alloy formed in step (i) is an n-type Bi-Te-Se alloy or p-type Bi-Sb-Te alloy having a purity of 5N or higher. The method according to claim 1,
In the step (ii), the mother alloy is charged into a nozzle provided in the melt spinning apparatus and melted using a heating element, and then inert gas is pressurized in the range of 0.1 to 0.5 MPa to rotate at a linear velocity of 5 to 40 m / Wherein the molten metal is brought into contact with the surface of the high-speed rotating wheel to rapidly quench the thermoelectric material. The method according to claim 1,
Wherein the metal ribbon produced in the step (ii) has a length of 5 to 15 mm and a width of 0.5 to 5 mm. The method according to claim 1,
Wherein the step (iii) is a step of milling the metal ribbon and the ball in a co-
The size of the balls is 1 to 5,
Wherein the weight ratio of the metal ribbon and the ball is 5 to 15: 1. The method according to claim 1,
Wherein the step (iii) comprises grinding the metal ribbon for 10 to 120 minutes at a rotating speed of 100 to 500 rpm in an atmosphere of argon (Ar). The method according to claim 1,
Wherein the step (iv) comprises subjecting the preform to pressure sintering through a hot press or a discharge plasma (SPS). The method according to claim 1,
Wherein the step (iv) is carried out at a temperature of 400 to 500 ° C and a pressure of 40 to 60 MPa for 3 to 30 minutes. The density of the pressure-sintered Bi-Te thermoelectric material is 95 to 99%
The thermal conductivity is 0.65 to 1.0 W / mK,
Wherein the thermoelectric performance index (ZT) of the Bi-Te thermoelectric material is 1.0 or more. A Bi-Te thermoelectric material produced by the method of any one of claims 1 to 11.

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