WO2020184762A1 - Method for manufacturing bi-te-based thermoelectric material by using microwave sintering - Google Patents

Method for manufacturing bi-te-based thermoelectric material by using microwave sintering Download PDF

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WO2020184762A1
WO2020184762A1 PCT/KR2019/003035 KR2019003035W WO2020184762A1 WO 2020184762 A1 WO2020184762 A1 WO 2020184762A1 KR 2019003035 W KR2019003035 W KR 2019003035W WO 2020184762 A1 WO2020184762 A1 WO 2020184762A1
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thermoelectric material
manufacturing
sintering
based thermoelectric
microwave
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PCT/KR2019/003035
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French (fr)
Korean (ko)
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박주현
양승호
양승진
황병진
연병훈
손경현
박정구
장봉중
이태희
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엘티메탈 주식회사
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H10N10/80—Constructional details
    • H10N10/85—Thermoelectric active materials
    • H10N10/851—Thermoelectric active materials comprising inorganic compositions
    • H10N10/853—Thermoelectric active materials comprising inorganic compositions comprising arsenic, antimony or bismuth
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H10N10/01—Manufacture or treatment
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H10N10/80—Constructional details
    • H10N10/85—Thermoelectric active materials
    • H10N10/851—Thermoelectric active materials comprising inorganic compositions
    • H10N10/852—Thermoelectric active materials comprising inorganic compositions comprising tellurium, selenium or sulfur

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  • the present invention relates to a method of manufacturing a Bi-Te-based thermoelectric material used for thermoelectric power generation, and more particularly, a microwave sintering method in a state where a predetermined load is applied to a metal ribbon formed through rapid solidification (RSP). It relates to a novel manufacturing method capable of producing a high-density Bi-Te-based sintered body in a short time by sintering by using.
  • RSP rapid solidification
  • Thermoelectric technology is a technology that directly converts thermal energy into electrical energy and electrical energy into thermal energy in a solid state, and has been applied to thermoelectric power generation that converts thermal energy into electrical energy and thermoelectric cooling that converts electrical energy into thermal energy.
  • the thermoelectric material used for such thermoelectric power generation and thermoelectric cooling improves the performance of the thermoelectric element as the thermoelectric property increases.
  • thermoelectric material is generally manufactured by melting and solidifying raw materials constituting the thermoelectric material to prepare a master alloy, followed by pressing and sintering it.
  • sintering methods such as hot press (HP) and spark plasma sintering (SPS) have been performed.
  • HP hot press
  • SPS spark plasma sintering
  • the present invention was conceived to solve the above-described problem, and adopts a microwave sintering method that can reduce the process time instead of the conventional sintering method, but carries out a pressing method that applies a predetermined load to realize high density. Therefore, it is an object of the present invention to provide a novel method for manufacturing a Bi-Te-based thermoelectric material that can realize high density in a short time.
  • Another object of the present invention is to provide a Bi-Te-based thermoelectric material manufactured by the above-described method.
  • the present invention comprises the steps of: (i) dissolving and solidifying a raw material for a thermoelectric material including a Bi raw material and a Te raw material to form a master alloy; (ii) rapidly cooling the master alloy to form a metal ribbon; (iii) grinding the metal ribbon under an inert atmosphere; (iv) compressing the pulverized product to form a preform; And (v) microwave sintering while pressing a predetermined load so that expansion of the preform is suppressed.
  • the Bi raw material and the Te raw material may be mixed in a ratio according to the stoichiometric composition of Bi 2 Te 3 ⁇ 0.2 .
  • the raw material for the thermoelectric material in step (i) may further include at least one element selected from the group consisting of Sb and Se.
  • the master alloy formed in step (i) may be an n-type Bi-Te-Se-based alloy or a p-type Bi-Sb-Te-based alloy having a purity of 4N or higher.
  • the raw material for the thermoelectric material of step (i) is more than one metal selected from the group consisting of Al, Sn, Mn, Ag, Cu, and Ga in the range of 0.001 to 1% by weight.
  • the master alloy in the step (ii), is charged into a nozzle installed in a melt spinning equipment and melted using a heating element, and then an inert gas is pressurized into the melt in the range of 0.1 to 1.0 MPa to 5 It may be to rapidly cool the melt by contacting the surface of a high-speed rotating wheel rotating at a linear speed of ⁇ 50m/s.
  • the step (iii) is pulverized the metal ribbon so that the average particle diameter (d 50 ) is 100 ⁇ m or less under at least one inert gas atmosphere selected from the group consisting of N 2 and Ar. can do.
  • microwave sintering may be performed with at least one pressing method selected from the group consisting of a pressing jig, press, pneumatic and hydraulic pressure. .
  • the load range applied to the preform in step (v) may be 5 to 20 MPa.
  • the microwave sintering in step (v) may be performed by microwave output of 1 to 5 kW for 1 to 20 minutes at a temperature of 200 to 500°C.
  • the density of the microwave sintered Bi-Te-based thermoelectric material may be 95% or more, and a power factor value at room temperature may be 25 to 35 W/m ⁇ .
  • the present invention provides a Bi-Te-based thermoelectric material manufactured by the above-described method.
  • thermoelectric materials In the present invention, microwave sintering is adopted as a sintering method of thermoelectric materials, but by carrying out a pressing method that applies a predetermined load to achieve high density, the disadvantages of the conventional hot press or discharge plasma sintering method, which are sintering methods of thermoelectric materials. Overcoming it, it is possible to manufacture high-density thermoelectric materials in a short time.
  • thermoelectric material manufactured in the present invention can exhibit comparable thermoelectric performance compared to the conventional sintered body of thermoelectric material, which requires high cost and a long time.
  • FIG. 1 is a flowchart of a manufacturing method according to an embodiment of the present invention.
  • FIG. 2 is a result of a rate of change in power factor according to temperature of Bi-Te-based thermoelectric materials prepared in Example 1 and Comparative Example 2.
  • FIG. 2 is a result of a rate of change in power factor according to temperature of Bi-Te-based thermoelectric materials prepared in Example 1 and Comparative Example 2.
  • FIG. 3 is a result of a temperature change rate according to a total time required for a sintering process of Bi-Te-based thermoelectric materials prepared in Example 1 and Comparative Example 2.
  • FIG. 3 is a result of a temperature change rate according to a total time required for a sintering process of Bi-Te-based thermoelectric materials prepared in Example 1 and Comparative Example 2.
  • thermoelectric materials are expensive and take a long time due to high-temperature sintering such as hot press or discharge plasma.
  • a microwave sintering method is adopted instead of the above-described sintering method to shorten the process time and ensure low cost, and at the same time, apply a predetermined load (press) to secure high density of the thermoelectric material. .
  • the microwave sintering method is a type of method carried out by the conventional dental ceramics sintering method, for example, by irradiating microwaves on a powder compact to promote densification of the compact by self-heating.
  • the driving force for sintering is increased, and unlike indirect heating method, since the vibration of the lattice is actively generated, the diffusion speed is increased. Accordingly, a sintered body having a dense and fine structure can be obtained within a short time.
  • the microwave sintering method as a sintering method for thermoelectric materials, it is possible to shorten a process time of 90% or more as compared with the hot press or discharge plasma sintering method used in the past.
  • the present inventors have recognized the problem that when microwave sintering is performed on a compact of a thermoelectric material, the volume of the compact is rapidly expanded due to a rapid increase in temperature due to microwaves, and the density of the sintered compact is significantly lowered.
  • microwave sintering is performed by employing a pressing method (e.g., applying a predetermined load or a load jig) capable of suppressing the volume expansion of the above-described molded body, thereby achieving a high density of 97% or more by a short sintering process.
  • a pressing method e.g., applying a predetermined load or a load jig
  • it can exhibit comparable thermoelectric performance, and a density increase effect of approximately 24% or more can be realized compared to the control group subjected to microwave sintering in a non-pressurized state.
  • the present invention is to manufacture a Bi-Te-based thermoelectric material, which is a thermoelectric material for thermoelectric power generation and cooling. Specifically, a metal ribbon is formed through a rapid solidification method (RSP) using a raw material for a Bi-Te-based thermoelectric material. This is to microwave sintering the pulverized and cold pressed compact.
  • RSP rapid solidification method
  • thermoelectric material including a Bi raw material and a Te raw material to form a master alloy
  • a master alloy including a Bi raw material and a Te raw material to form a master alloy
  • rapidly cooling the master alloy to form a metal ribbon (iii) grinding the metal ribbon in an inert atmosphere ('S30 step');
  • compressing the pulverized material to form a preform ('S40 step');
  • microwave sintering ('S50 step') while pressing a predetermined load so that expansion of the preform is suppressed.
  • FIG. 1 is a conceptual diagram showing a method of manufacturing a Bi-Te-based thermoelectric material according to the present invention in each step.
  • the manufacturing method will be described by dividing each process step with reference to FIG. 1 as follows.
  • raw materials such as Bi and Te are mixed, dissolved, and solidified according to the stoichiometric ratio of the Bi-Te thermoelectric material to form a Bi-Te-based master alloy.
  • the master alloy may be manufactured without limitation according to a conventional method known in the art.
  • step S10 (i-1) a first element; And charging a raw material having a composition including the second element into a quartz tube (Quartz) and maintaining a vacuum state ('S10-1 step'). And (i-2) the quartz tube in the vacuum state is charged into a furnace, and then stirred and dissolved at a rate of 10 to 15 times/min for 1 to 3 hours at a temperature of 650 to 700°C to form a master alloy. It may be configured including a step ('S10-2 step').
  • thermoelectric materials which are classified into n-type and p-type, are charged into a quartz tube, and then sealed for dissolution (hereinafter referred to as'S10-1 step').
  • the raw material for a thermoelectric material usable in the present invention may be composed mainly of Bi and Te, and further include Se or Sb components according to n-type and p-type.
  • the composition of the thermoelectric material may be different depending on the cooling and power generation purposes.
  • the Bi raw material and the Te raw material may be mixed in a ratio according to the stoichiometric composition of Bi 2 Te 3 ⁇ 0.2 , and preferably Bi 2 Te 3 ⁇ 0.15 .
  • the raw material for the thermoelectric material includes: (i) at least one first element selected from the group consisting of Bi and Sb; And it may be a composition comprising a raw material of a composition comprising at least one second element selected from the group consisting of Te and Se.
  • the raw material for the n-type thermoelectric material is a Bi-Te-Se-based alloy composition
  • the raw material for the p-type thermoelectric material is a Bi-Sb-Te alloy composition
  • the composition may include 10 to 15% by weight of Bi, 25 to 30% by weight of Sb, and 55 to 60% by weight of Te based on 100% by weight of the total. have.
  • a doping element powder may be added to the composition of the thermoelectric material to be manufactured.
  • the doping element is introduced to make the Bi-Te-based thermoelectric material have n-type or p-type properties
  • conventional components in the art that can be used for n-type or p-type thermoelectric materials can be used without limitation.
  • it may be one or more metals selected from the group consisting of Al, Sn, Mn, Ag, Cu, and Ga.
  • the content of the one or more metals to be doped is not particularly limited, and for example, may be in the range of 0.001 to 1% by weight based on the total weight.
  • the dopant introduced as described above replaces the lattice of Bi or Te according to the difference in thermodynamic energy of the lattice bond or the driving force of atomic diffusion through a heat treatment process performed below.
  • the size and shape of the thermoelectric material are not particularly limited, but may be in the form of a mass having a size of about 2 to 5 mm.
  • the purity of the thermoelectric material is 5N or higher.
  • thermoelectric material for thermoelectric material is charged into a quartz tube and then sealed using a vacuum pump to maintain a vacuum state.
  • step S10-2' Each of the n-type and p-type master alloys are manufactured by using a locking furnace for the quartz tube of step S10-1 (hereinafter referred to as'step S10-2').
  • step S10-2 after charging the sealed quartz tube in a vacuum state into the furnace, stirring at a rate of 10 to 15 times/min for 1 to 3 hours at a temperature of about 650 to 700°C for melting And melt to form a master alloy.
  • a master alloy of a uniform Bi 2 -Te 3 thermoelectric material In order to manufacture a ribbon using the rapid solidification method (RSP), a master alloy of a uniform Bi 2 -Te 3 thermoelectric material must be manufactured. Thus, in the present invention, it is possible to manufacture a ⁇ 30 ⁇ 100 mm master alloy or a master alloy having a size range of approximately ⁇ 20 to 30 ⁇ 100 to 150 mm.
  • the master alloy ingot manufactured through the step S10-2 may be a Bi-Te-based alloy having a high purity of 5N or higher, and preferably an n-type Bi-Te-Se-based alloy or a p-type Bi-Sb-Te-based alloy. .
  • a Bi-Te-based metal ribbon having a complex microstructure is manufactured through the rapid solidification method (R.S.P) of the Bi-Te-based master alloy included in the previous step.
  • step S20 after charging the mother alloy to a nozzle installed in the melt spinning equipment, heat is supplied and completely dissolved using a heating element that can be continuously maintained to form a melt, and then inert to the melt. By pressurizing and spraying gas, the melt is brought into contact with the rotating high-speed rotating wheel for rapid cooling. Through this, a Bi-Te-based metal ribbon is formed.
  • 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 may be used.
  • a resistance heating element that generates heat by receiving current may be used, and the temperature may be controlled by an electric furnace type heater, for example, a graphite heater, for example, of the available resistance heating element.
  • the temperature range at which the heating element generates heat is not particularly limited as long as it is a range capable of completely dissolving the Bi-Te-based master alloy. For example, it is maintained in the range of 500 to 800 °C, preferably 600 to 700 °C.
  • the type or the pressurization range of the inert gas is not particularly limited, but it is preferable to pressurize injection in the range of 0.1 to 0.5 MPa using argon gas as an example.
  • the high-speed rotating wheel in contact with the melt may be a conventional wheel known in the art, for example a copper wheel (Cu wheel).
  • the rotation speed of the high-speed rotation wheel is not particularly limited, and for example, the wheel linear speed may be in the range of 5 to 50 m/s.
  • the cooling rate of the dissolved master alloy by controlling the cooling rate of the dissolved master alloy, uniform particle size control is possible, and in general, when the cooling rate is slow, nano-sized amorphous powder can be prepared, or fine particle powder can be prepared. . In addition, it can be manufactured by varying the manufacturing conditions according to the concentration and type of raw materials.
  • the master alloy that has undergone the above-described process does not become crystalline through a rapid cooling (RSP) process, but is solidified in a state in which an amorphous structure and a crystalline structure are mixed.
  • RSP rapid cooling
  • the rapid cooling rate is very fast, it is manufactured in the form of a ribbon, but when the cooling rate is adjusted, powder having a size of several hundred nanometers may be manufactured as a simple connected half-ribbon.
  • a thin Bi-Te-based thermoelectric material ribbon may be formed.
  • the length of the manufactured metal ribbon may be 5 to 15 mm
  • the width may be 0.5 to 5 mm
  • the thickness may be 10 ⁇ m or less.
  • a ribbon-like raw material having high brittleness is rapidly solidified by direct spraying of the molten mother alloy, thereby obtaining a nano-sized amorphous fine powder having a uniform particle size and shape.
  • the pulverization process of step S30 may be performed without limitation in a conventional crushing/crushing process known in the art. As an example, it can be pulverized using a ball mill method.
  • the particle diameter of the powder to be pulverized is not particularly limited, and as an example, the average particle diameter may be adjusted to 100 ⁇ m or less, preferably 10 to 100 ⁇ m.
  • the above-described crushing/crushing process is performed in an inert atmosphere.
  • the oxygen content in the pulverized powder can be reduced, thereby controlling the degree of oxidation to be low.
  • the pulverized product according to the present invention can reduce the oxygen content in the range of about 30% or more, specifically 30 to 45%, compared to the pulverized product carried out under atmospheric conditions containing oxygen, and preferably the The oxygen content in the pulverized material can be controlled to 0.03% or less.
  • the type or pressure range of the inert gas is not particularly limited, and may be, for example, nitrogen gas, argon gas, or a mixed atmosphere.
  • the Bi-Te-based powder formed through the step S30 may have an average particle diameter of 100 ⁇ m or less, and an oxygen content in the powder of 0.03% or less, preferably 0.02 to 0.03%.
  • a molded body having a predetermined shape is manufactured using the pulverized metal ribbon obtained in step S30.
  • step S40 a conventional compression or molding method known in the art may be used without limitation.
  • a molding press a cold press, or a compressor to form a nano-sized amorphous powder crushed in step S30.
  • the conditions of step S40 are not particularly limited, and can be appropriately adjusted under conventional compression conditions known in the art. For example, it is desirable to compress at 10 MPa or less.
  • thermoelectric material is manufactured by sintering the preform obtained in step S40.
  • microwave sintering is a sintering method that uses heat generated when a dipole of a material vibrates by microwaves having a high frequency of 2.45 GHz.
  • sintering using microwave output has advantages such as 10 times faster temperature rise rate and sintering time than conventional electric furnaces or gas furnaces, low power consumption, and the resulting sintered body is dense and grain growth is suppressed.
  • thermoelectric material when microwave sintering is simply performed on a preform of a thermoelectric material, it is recognized that the volume of the preform is expanded by microwaves and the density is significantly reduced. It is characterized by performing sintering. Accordingly, in the present invention, a high-density thermoelectric material of 97% or more can be manufactured through microwave sintering for 20 minutes or less, specifically 1 to 10 minutes. In fact, in the present invention, compared with the hot press or discharge plasma sintering method, which is a conventional thermoelectric material sintering method, the sintering process time can be shortened by 90% or more, and comparable density can be secured.
  • microwave sintering is performed while a method of pressing or fixing a predetermined load on the thermoelectric material preform is performed.
  • the method of pressing the preform is not particularly limited, for example, may be at least one method selected from the group consisting of a pressing jig, press, pneumatic and hydraulic pressure known in the art.
  • the pressing jig or the like plays a role of suppressing the expansion of the molded body due to rapid increase in temperature during microwave sintering.
  • the load pressurization range is not particularly limited as long as it is a range capable of effectively suppressing the expansion of the preform. For example, it may be in the range of 5 to 20 MPa, and specifically, 5 to 10 MPa is preferred.
  • the material of the pressing jig is not particularly limited, and for example, it is preferable to be made of a material that is capable of passing microwaves and does not respond to microwaves. That is, heat generated by microwave output is related to dielectric loss, and in general, dielectric loss is proportional to dielectric constant.
  • a material having a high dielectric constant such as barium titanate absorbs microwaves and is easily heated, but a material having a low dielectric constant such as alumina and zirconia is not heated because it is not sensitive to microwaves.
  • the pressing jig may be made of a material having a low dielectric constant that is not sensitive to microwaves, and for example, a jig made of Al 2 O 3 or graphite is preferable.
  • the conditions of the hot working in the S50 step are not particularly limited, for example, it may be carried out at a temperature of 200 to 500 °C for 1 to 20 minutes with a microwave output of 1 to 5 kW, specifically a temperature range of 200 to 300 °C It is preferable to perform at a microwave output of 1.5 to 2.5 kW for 5 to 10 minutes.
  • the conditions (temperature, time) of the hot working are less than 200°C or 1 minute, high-density materials cannot be obtained, and if the conditions exceed 500°C or exceed 20 minutes, the vapor pressure of Te is high. It volatilizes and becomes unsuitable for the target composition, and there is a high possibility that the thermoelectric performance index decreases.
  • Bi-Te-based thermoelectric material according to an embodiment of the present invention manufactured through the above-described manufacturing method may have a density in the range of 95 to 99%, preferably about 97% or more.
  • the degree of oxidation is adjusted so that the oxygen content in the thermoelectric material can be controlled within a predetermined range.
  • a power factor value of the Bi-Te-based thermoelectric material according to an embodiment of the present invention may be in the range of 25 to 30 W/mk 2 .
  • a power factor value is defined as in Equation 1 below, and is used as an index for evaluating the maximum power density that can be produced by a thermoelectric device according to an embodiment of the present invention.
  • thermoelectric figure of merit Z
  • ⁇ the Seebeck coefficient
  • ⁇ the electrical conductivity
  • ⁇ the thermal conductivity.
  • the product of the square of the Seebeck coefficient and the electrical conductivity is referred to as a power factor.
  • thermoelectric figure of merit which converts heat of a thermoelectric material into electricity
  • the Seebeck coefficient ( ⁇ ) must be large, and the thermal conductivity ( ⁇ ) must be small to maintain the temperature difference between both ends of the material.
  • the electrical conductivity ( ⁇ ) should be large. In general, in most thermoelectric materials, as the electrical conductivity increases, the thermal conductivity also increases. Therefore, when the power factor value is increased, it is advantageous to increase the Seebeck coefficient ( ⁇ ) rather than the electrical conductivity ( ⁇ ).
  • thermoelectric material containing Bi, Te, Sb and Se having a high purity of about 2 to 5 mm and having a high purity of 4N or more was prepared.
  • p-type in order to have a ternary system such as Bi, Te, and Sb, it was composed of 13 wt% of Bi, 28 wt% of Sb, and 59 wt% of Te.
  • the thermoelectric material was charged into a locking furnace, and then stirred and dissolved at 650 to 750°C for 2 to 4 hours at a rate of 10 times/min to prepare a ⁇ 30 ⁇ 100 mm master alloy ingot.
  • the master alloy ingot is charged into the nozzle installed in the melt spinning equipment and completely dissolved at about 700°C using a resistance heating element (a structure surrounding the nozzle as a graphite heater) to form a melt, and then 0.1 ⁇
  • a Bi-Te-based metal ribbon was formed by contacting the surface of a rotating copper wheel and cooling rapidly. At this time, the rotational speed of the copper wheel was performed at 1000 rpm.
  • the formed metal ribbon was pulverized to have an average particle diameter of 100 ⁇ m or less using a ball mill method in an argon (Ar) atmosphere.
  • the pulverized powder was prepared by cold isostatic pressing (Cold Isostatic Pressing). Combine the preform with an Al 2 O 3 pressurizing jig and apply a load of 5 MPa to 230°C using microwave sintering at a heating rate of 50°C/min. As a result of sintering while maintaining a microwave output of kW, a high density Bi-Te thermoelectric material of 97% or more was manufactured.
  • the density of the Bi-Te-based thermoelectric material prepared as described above was 78%.
  • thermoelectric material containing Bi, Te, Sb and Se having a high purity of about 2 to 5 mm and having a high purity of 4N or more was prepared.
  • p-type it was made to have a ternary system such as Bi, Te, and Sb.
  • the thermoelectric material was charged into a locking furnace, and then stirred and dissolved at 650 to 750°C for 2 to 4 hours at a rate of 10 times/min to prepare a ⁇ 30 ⁇ 100 mm master alloy ingot.
  • the master alloy ingot is charged into the nozzle installed in the melt spinning equipment and completely dissolved at about 700°C using a resistance heating element (a structure that surrounds the nozzle as a graphite heater), and then 0.1 ⁇
  • a Bi-Te-based metal ribbon was formed by contacting the surface of a rotating copper wheel and cooling rapidly. At this time, the rotational speed of the copper wheel was performed at 1000 rpm.
  • the formed metal ribbon was pulverized to have an average particle diameter of 100 ⁇ m or less using a ball mill method in an argon (Ar) atmosphere.
  • the pulverized powder was heated to about 525° C. at a rate of 7° C./min using hot press sintering, maintained for 1 hour, and sintered by maintaining a pressure of 70 MPa, thereby producing a high-density thermoelectric material of 99% or more.
  • Comparative Example 2 subjected to the conventional hot press sintering method took about 24 times as long as the sintering process time compared to Example 1 employing the microwave sintering method, resulting in lower productivity and additional process costs.
  • the total time required for the sintering process means not only the sintering treatment time, but also the total treatment time including the heating time and cooling time required for the sintering treatment.
  • thermoelectric material of Comparative Example 1 which was simply sintered with microwaves without applying a predetermined load, had a significantly lower density after the sintering process.
  • thermoelectric material of Example 1 of the present application increased in density after sintering, so that high density can be realized within a short time (see Table 1 above).
  • thermoelectric material of the present invention subjected to the microwave sintering process in a state where a predetermined load was applied can produce a high-density thermoelectric material in a short time compared to Comparative Example 2 subjected to the conventional hot press sintering process. It could be confirmed (see Figs. 2 to 3 below).

Abstract

The present invention relates to a method for manufacturing a Bi-Te-based thermoelectric material and, more specifically, provides a novel manufacturing method capable of manufacturing a high-density thermoelectric material within a short time by pulverizing, under an inert atmosphere, a metal ribbon having been formed by a rapid solidification process (RSP), and then microwave sintering same in a state in which a predetermined load is applied.

Description

마이크로파 소결법을 이용한 Bi-Te계 열전소재의 제조방법Manufacturing method of Bi-Te-based thermoelectric material using microwave sintering method
본 발명은 열전발전에 사용되는 Bi-Te계 열전재료의 제조방법에 관한 것으로, 보다 상세하게는 급속응고(RSP)를 통해 형성된 금속 리본을 소정의 하중을 인가한 상태에서 마이크로파 소결법(Microwave sintering)을 이용하여 소결함으로써, 고밀도의 Bi-Te계 소결체를 단시간에 제조할 수 있는 신규 제조방법에 관한 것이다. The present invention relates to a method of manufacturing a Bi-Te-based thermoelectric material used for thermoelectric power generation, and more particularly, a microwave sintering method in a state where a predetermined load is applied to a metal ribbon formed through rapid solidification (RSP). It relates to a novel manufacturing method capable of producing a high-density Bi-Te-based sintered body in a short time by sintering by using.
열전기술은 일반적으로 열에너지를 전기에너지로, 전기에너지를 열에너지로 고체 상태에서 직접 변환하는 기술로서, 열에너지를 전기에너지로 변환하는 열전발전 및 전기에너지를 열에너지로 변환하는 열전냉각 분야에 응용되고 있다. 이러한 열전발전 및 열전냉각을 위해 사용되는 열전재료는 열전특성이 증가할수록 열전소자의 성능이 향상된다. 그 열전성능을 결정하는 것은, 열기전력(V), 제벡 계수(α), 펠티어 계수(π), 톰슨 계수(τ), 네른스트 계수(Q), 에팅스하우젠 계수(P), 전기 전도율(σ), 출력 인자(PF), 성능 지수(Z), 무차원 성능지수(ZT=α2σT/κ (여기에서, T는 절대온도이다)), 열전도율(κ), 로렌츠수(L), 전기 저항율(ρ) 등의 물성이다. 특히, 무차원 성능지수(ZT)는 열전 변환 에너지 효율을 결정하는 중요한 요소로서, 성능 지수(Z=α2σ/κ)의 값이 큰 열전 재료를 사용하여 열전 소자를 제조함으로써, 냉각 및 발전의 효율을 높일 수 있게 된다. 즉, 열전재료는 제벡 계수와 전기전도도가 높을수록, 열전도도가 낮을수록, 우수한 열전성능을 가지게 된다.Thermoelectric technology is a technology that directly converts thermal energy into electrical energy and electrical energy into thermal energy in a solid state, and has been applied to thermoelectric power generation that converts thermal energy into electrical energy and thermoelectric cooling that converts electrical energy into thermal energy. The thermoelectric material used for such thermoelectric power generation and thermoelectric cooling improves the performance of the thermoelectric element as the thermoelectric property increases. The thermoelectric performance is determined by thermoelectric power (V), Seebeck coefficient (α), Peltier coefficient (π), Thompson coefficient (τ), Nernst coefficient (Q), Ettingshausen coefficient (P), and electrical conductivity (σ ), output factor (PF), figure of merit (Z), dimensionless figure of merit (ZT=α2σT/κ (where T is the absolute temperature)), thermal conductivity (κ), Lorentz number (L), electrical resistivity ( ρ), etc. In particular, the dimensionless figure of merit (ZT) is an important factor in determining the energy efficiency of thermoelectric conversion, and the efficiency of cooling and power generation by manufacturing a thermoelectric element using a thermoelectric material having a large value of the figure of merit (Z=α2σ/κ) Will be able to increase. That is, the thermoelectric material has excellent thermoelectric performance as the Seebeck coefficient and electrical conductivity are higher and the thermal conductivity is lower.
한편 열전재료는 일반적으로 열전재료를 구성하는 원료를 용해 및 응고시켜 모합금을 제조한 후, 이를 가압 성형하고 소결하여 제조된다. 종래에는 열전재료를 소결시, 핫 프레스(Hot Press, HP), 방전플라즈마(Spark Plasma Sintering, SPS) 등의 소결법을 실시하였다. 그러나 전술한 핫 프레스 (HP)나 방전플라즈마 (SPS) 등의 소결법의 경우, 초기설비 투자비용과 유지보수 비용이 높을 뿐만 아니라, 장시간의 공정시간이 요구된다는 문제점이 있었다.Meanwhile, the thermoelectric material is generally manufactured by melting and solidifying raw materials constituting the thermoelectric material to prepare a master alloy, followed by pressing and sintering it. Conventionally, when sintering a thermoelectric material, sintering methods such as hot press (HP) and spark plasma sintering (SPS) have been performed. However, in the case of a sintering method such as hot press (HP) or discharge plasma (SPS) described above, there is a problem in that the initial facility investment cost and maintenance cost are high, and a long process time is required.
본 발명은 전술한 문제점을 해결하기 위해 안출된 것으로서, 종래 소결법 대신에 공정시간 단축을 구현할 수 있는 마이크로파 소결법(Microwave sintering)을 채용하되, 고밀도를 구현하고자 소정의 하중을 인가하는 가압법을 동반 실시하여 단시간에 고밀도를 구현할 수 있는 Bi-Te계 열전재료의 신규 제조방법을 제공하는 것을 목적으로 한다. The present invention was conceived to solve the above-described problem, and adopts a microwave sintering method that can reduce the process time instead of the conventional sintering method, but carries out a pressing method that applies a predetermined load to realize high density. Therefore, it is an object of the present invention to provide a novel method for manufacturing a Bi-Te-based thermoelectric material that can realize high density in a short time.
또한, 본 발명은 전술한 방법에 의해 제조된 Bi-Te계 열전재료를 제공하는 것을 또 다른 목적으로 한다. In addition, another object of the present invention is to provide a Bi-Te-based thermoelectric material manufactured by the above-described method.
상기한 목적을 달성하기 위해, 본 발명은 (i) Bi 원료와 Te 원료를 포함하는 열전재료용 원료를 용해 및 응고시켜 모합금을 형성하는 단계; (ii) 상기 모합금을 급속냉각시켜 금속 리본을 형성하는 단계; (iii) 상기 금속리본을 비활성 분위기하에서 분쇄하는 단계; (iv) 상기 분쇄물을 압축하여 예비성형체를 형성하는 단계; 및 (v) 상기 예비성형체의 팽창이 억제되도록 소정의 하중을 가압하면서, 마이크로파 소결하는 단계를 포함하는 열전 재료의 제조방법을 제공한다.In order to achieve the above object, the present invention comprises the steps of: (i) dissolving and solidifying a raw material for a thermoelectric material including a Bi raw material and a Te raw material to form a master alloy; (ii) rapidly cooling the master alloy to form a metal ribbon; (iii) grinding the metal ribbon under an inert atmosphere; (iv) compressing the pulverized product to form a preform; And (v) microwave sintering while pressing a predetermined load so that expansion of the preform is suppressed.
본 발명의 일 구현예에 따르면, 상기 단계 (i)에서 Bi 원료와 Te 원료는, Bi2Te3±0.2의 화학양론 조성에 따른 비율로 혼합될 수 있다. According to an embodiment of the present invention, in the step (i), the Bi raw material and the Te raw material may be mixed in a ratio according to the stoichiometric composition of Bi 2 Te 3±0.2 .
본 발명의 일 구현예에 따르면, 상기 단계 (i)의 열전재료용 원료는 Sb 및 Se로 이루어진 군에서 선택되는 1종 이상의 원소를 더 포함할 수 있다.According to one embodiment of the present invention, the raw material for the thermoelectric material in step (i) may further include at least one element selected from the group consisting of Sb and Se.
본 발명의 일 구현예에 따르면, 상기 단계 (i)에서 형성된 모합금은, 4N 이상의 순도를 갖는 n형 Bi-Te-Se계 합금 또는 p형 Bi-Sb-Te계 합금일 수 있다. According to one embodiment of the present invention, the master alloy formed in step (i) may be an n-type Bi-Te-Se-based alloy or a p-type Bi-Sb-Te-based alloy having a purity of 4N or higher.
본 발명의 일 구현예에 따르면, 상기 단계 (i)의 열전재료용 원료는 Al, Sn, Mn, Ag, Cu 및 Ga로 이루어진 군에서 선택되는 1종 이상의 금속을 0.001 내지 1 중량% 범위로 더 포함할 수 있다. According to an embodiment of the present invention, the raw material for the thermoelectric material of step (i) is more than one metal selected from the group consisting of Al, Sn, Mn, Ag, Cu, and Ga in the range of 0.001 to 1% by weight. Can include.
본 발명의 일 구현예에 따르면, 상기 단계 (ii)는 모합금을 용융 방사 장비에 설치된 노즐에 장입하고 발열체를 이용하여 용융시킨 후, 상기 용융물에 불활성 가스를 0.1~1.0 MPa 범위로 가압하여 5~50m/s의 선속도로 회전하는 고속회전 휠 표면에 용융물을 접촉시켜 급냉시키는 것일 수 있다. According to an embodiment of the present invention, in the step (ii), the master alloy is charged into a nozzle installed in a melt spinning equipment and melted using a heating element, and then an inert gas is pressurized into the melt in the range of 0.1 to 1.0 MPa to 5 It may be to rapidly cool the melt by contacting the surface of a high-speed rotating wheel rotating at a linear speed of ~50m/s.
본 발명의 일 구현예에 따르면, 상기 단계 (iii)는 N2, 및 Ar로 이루어진 군에서 선택되는 적어도 1종의 비활성 가스 분위기하에서 평균입경(d50)이 100㎛ 이하가 되도록 금속리본을 분쇄할 수 있다. According to an embodiment of the present invention, the step (iii) is pulverized the metal ribbon so that the average particle diameter (d 50 ) is 100 μm or less under at least one inert gas atmosphere selected from the group consisting of N 2 and Ar. can do.
본 발명의 일 구현예에 따르면, 상기 단계 (v)는 가압 지그(Jig), 프레스, 공압 및 유압으로 구성된 군에서 선택된 적어도 1종의 가압방법을 동반하여 마이크로파(microwave) 소결을 실시할 수 있다. According to an embodiment of the present invention, in step (v), microwave sintering may be performed with at least one pressing method selected from the group consisting of a pressing jig, press, pneumatic and hydraulic pressure. .
본 발명의 일 구현예에 따르면, 상기 단계 (v)에서 예비성형체에 가압되는 하중범위는 5 내지 20 MPa일 수 있다. According to an embodiment of the present invention, the load range applied to the preform in step (v) may be 5 to 20 MPa.
본 발명의 일 구현예에 따르면, 상기 단계 (v)에서 마이크로파 소결은, 200~500℃의 온도에서 1~20분 동안 1~5 kW의 마이크로파(Microwave) 출력에 의해 실시될 수 있다. According to an embodiment of the present invention, the microwave sintering in step (v) may be performed by microwave output of 1 to 5 kW for 1 to 20 minutes at a temperature of 200 to 500°C.
본 발명의 일 구현예에 따르면, 마이크로파 소결된 Bi-Te계 열전재료의 밀도는 95% 이상이며, 상온에서의 파워 팩터(Power factor)값은 25~35 W/mΩ일 수 있다. According to an embodiment of the present invention, the density of the microwave sintered Bi-Te-based thermoelectric material may be 95% or more, and a power factor value at room temperature may be 25 to 35 W/mΩ.
또한, 본 발명은 전술한 방법에 의해 제조된 Bi-Te계 열전재료를 제공한다. In addition, the present invention provides a Bi-Te-based thermoelectric material manufactured by the above-described method.
본 발명에서는 열전재료의 소결법으로서 마이크로파 소결법(Microwave sintering)을 채용하되, 고밀도를 구현하고자 소정의 하중을 인가하는 가압법을 동반 실시함으로써, 종래 열전재료의 소결법인 핫프레스 또는 방전플라즈마 소결법의 단점을 극복하여 단시간에 고밀도의 열전재료를 제조할 수 있다. In the present invention, microwave sintering is adopted as a sintering method of thermoelectric materials, but by carrying out a pressing method that applies a predetermined load to achieve high density, the disadvantages of the conventional hot press or discharge plasma sintering method, which are sintering methods of thermoelectric materials. Overcoming it, it is possible to manufacture high-density thermoelectric materials in a short time.
또한 본 발명에서 제조된 열전재료는, 높은 비용과 장시간이 소요되는 종래 열전재료 소결체와 비교하여 대등한 열전성능을 발휘할 수 있다. In addition, the thermoelectric material manufactured in the present invention can exhibit comparable thermoelectric performance compared to the conventional sintered body of thermoelectric material, which requires high cost and a long time.
본 발명에 따른 효과는 이상에서 예시된 내용에 의해 제한되지 않으며, 보다 다양한 효과들이 본 명세서 내에 포함되어 있다.The effects according to the present invention are not limited by the contents exemplified above, and more various effects are included in the present specification.
도 1은 본 발명의 일 실시형태에 따른 제조방법의 공정 순서도이다.1 is a flowchart of a manufacturing method according to an embodiment of the present invention.
도 2는 실시예 1 및 비교예 2에서 제조된 Bi-Te계 열전재료의 온도에 따른 파워 팩터(power factor) 변화율 결과이다. FIG. 2 is a result of a rate of change in power factor according to temperature of Bi-Te-based thermoelectric materials prepared in Example 1 and Comparative Example 2. FIG.
도 3은 실시예 1 및 비교예 2에서 제조된 Bi-Te계 열전재료의 소결공정 총 소요시간에 따른 온도 변화율 결과이다.3 is a result of a temperature change rate according to a total time required for a sintering process of Bi-Te-based thermoelectric materials prepared in Example 1 and Comparative Example 2. FIG.
이하, 본 발명을 상세히 설명한다. Hereinafter, the present invention will be described in detail.
종래 열전재료는 핫프레스나 방전플라즈마 등의 고온 소결법을 실시함에 따라 고비용과 장시간이 소요되는 문제가 초래된다. Conventional thermoelectric materials are expensive and take a long time due to high-temperature sintering such as hot press or discharge plasma.
본 발명에서는 전술한 소결법 대신에 마이크로파 소결법(Microwave sintering)을 채용하여 공정시간 단축과 저비용을 확보함과 동시에, 소정의 하중을 인가(가압)하는 방식을 동반 실시하여 열전재료의 고밀도를 확보하고자 한다. In the present invention, a microwave sintering method is adopted instead of the above-described sintering method to shorten the process time and ensure low cost, and at the same time, apply a predetermined load (press) to secure high density of the thermoelectric material. .
구체적으로, 마이크로파 소결법은 종래 치과용 세라믹스 소결법으로 실시되는 방법의 일종으로서, 예컨대 분말 성형체에 마이크로파(micro wave)를 조사하여 자체 발열에 의해 해당 성형체의 치밀화를 촉진시키는 방법이다. 50℃/min 이상의 급승온에 의해 입자성장이 최소화되므로 소결 구동력이 커지고, 간접가열 방식과 달리 격자의 진동이 활발하게 일어나기 때문에 확산속도가 빨라진다. 이에 따라 단시간 내에 치밀하고 미세한 조직의 소결체를 얻을 수 있다. 특히, 본 발명에서는 마이크로파 소결법을 열전재료의 소결법으로 채택함으로써, 기존 사용되는 핫 프레스 또는 방전플라즈마 소결법과 비교하였을 때 90% 이상의 공정시간을 단축시킬 수 있다.Specifically, the microwave sintering method is a type of method carried out by the conventional dental ceramics sintering method, for example, by irradiating microwaves on a powder compact to promote densification of the compact by self-heating. As particle growth is minimized by a rapid increase in temperature of 50°C/min or more, the driving force for sintering is increased, and unlike indirect heating method, since the vibration of the lattice is actively generated, the diffusion speed is increased. Accordingly, a sintered body having a dense and fine structure can be obtained within a short time. In particular, in the present invention, by adopting the microwave sintering method as a sintering method for thermoelectric materials, it is possible to shorten a process time of 90% or more as compared with the hot press or discharge plasma sintering method used in the past.
한편, 본 발명자들은 열전재료의 성형체에 마이크로파 소결을 단순 실시할 경우, 마이크로파에 의한 급승온에 의해 성형체의 부피 팽창이 급속도로 발생하여 오히려 소결체의 밀도가 현저히 저하되는 문제를 인식하였다. On the other hand, the present inventors have recognized the problem that when microwave sintering is performed on a compact of a thermoelectric material, the volume of the compact is rapidly expanded due to a rapid increase in temperature due to microwaves, and the density of the sintered compact is significantly lowered.
이에 따라, 본 발명에서는 전술한 성형체의 부피 팽창을 억제할 수 있는 가압 방식(예, 소정의 하중을 인가 또는 하중 지그)을 채용하여 마이크로파 소결을 실시함으로써, 단시간의 소결 공정에 의해 97% 이상의 고밀도를 확보할 수 있다. 특히, 장시간과 고비용이 소요되는 종래 소결법이 실시된 소결체와 비교하여 대등한 열전 성능을 나타낼 수 있으며, 비(非)가압 상태에서 마이크로파 소결을 실시한 대조군보다 대략 24% 이상의 밀도 상승 효과를 구현할 수 있다. Accordingly, in the present invention, microwave sintering is performed by employing a pressing method (e.g., applying a predetermined load or a load jig) capable of suppressing the volume expansion of the above-described molded body, thereby achieving a high density of 97% or more by a short sintering process. Can be secured. In particular, compared to a sintered body subjected to a conventional sintering method, which takes a long time and high cost, it can exhibit comparable thermoelectric performance, and a density increase effect of approximately 24% or more can be realized compared to the control group subjected to microwave sintering in a non-pressurized state. .
<Bi-Te계 열전재료의 제조방법><Method of manufacturing Bi-Te thermoelectric material>
이하, 본 발명의 일 실시형태에 따른 Bi-Te계 열전재료의 제조방법에 대해 설명한다. 그러나 하기 제조방법에 의해서만 한정되는 것은 아니며, 필요에 따라 각 공정의 단계가 변형되거나 또는 선택적으로 혼용되어 수행될 수 있다. Hereinafter, a method of manufacturing a Bi-Te-based thermoelectric material according to an embodiment of the present invention will be described. However, it is not limited only by the following manufacturing method, and the steps of each process may be modified or selectively mixed and performed as necessary.
본 발명은 열전 발전 및 냉각용 열전소재인 Bi-Te계 열전재료를 제조하는 것으로서, 구체적으로 Bi-Te계 열전재료용 원료를 이용하여 급속응고법(RSP)을 통해 금속리본을 형성한 후, 이를 분쇄하여 냉각 압착한 성형체를 마이크로파 소결하는 것이다. The present invention is to manufacture a Bi-Te-based thermoelectric material, which is a thermoelectric material for thermoelectric power generation and cooling. Specifically, a metal ribbon is formed through a rapid solidification method (RSP) using a raw material for a Bi-Te-based thermoelectric material. This is to microwave sintering the pulverized and cold pressed compact.
상기 제조방법의 바람직한 일 실시예를 들면, (i) Bi 원료와 Te 원료를 포함하는 열전재료용 원료를 용해 및 응고시켜 모합금을 형성하는 단계('S10 단계'); (ii) 상기 모합금을 급속냉각시켜 금속 리본을 형성하는 단계('S20 단계'); (iii) 상기 금속리본을 비활성 분위기하에서 분쇄하는 단계('S30 단계'); (iv) 상기 분쇄물을 압축하여 예비성형체를 형성하는 단계('S40 단계'); 및 (v) 상기 예비성형체의 팽창이 억제되도록 소정의 하중을 가압하면서, 마이크로파 소결하는 단계('S50 단계')를 포함하여 구성될 수 있다. In a preferred embodiment of the manufacturing method, (i) dissolving and solidifying a raw material for a thermoelectric material including a Bi raw material and a Te raw material to form a master alloy ('S10 step'); (ii) rapidly cooling the master alloy to form a metal ribbon ('S20 step'); (iii) grinding the metal ribbon in an inert atmosphere ('S30 step'); (iv) compressing the pulverized material to form a preform ('S40 step'); And (v) microwave sintering ('S50 step') while pressing a predetermined load so that expansion of the preform is suppressed.
한편 도 1은 본 발명에 따른 Bi-Te계 열전재료의 제조방법을 각 단계별로 도시한 개념도이다. 이하, 도 1을 참고하여 상기 제조방법을 각 공정 단계별로 나누어 설명하면 다음과 같다.Meanwhile, FIG. 1 is a conceptual diagram showing a method of manufacturing a Bi-Te-based thermoelectric material according to the present invention in each step. Hereinafter, the manufacturing method will be described by dividing each process step with reference to FIG. 1 as follows.
(i) 모합금 형성 단계('S10 단계')(i) master alloy formation step ('S10 step')
본 단계는 Bi-Te 열전재료를 구성하는 화학양론적 비율에 맞게 Bi, Te 등의 원료를 혼합하고 용해, 응고시켜 Bi-Te계 모합금을 형성하는 단계이다.In this step, raw materials such as Bi and Te are mixed, dissolved, and solidified according to the stoichiometric ratio of the Bi-Te thermoelectric material to form a Bi-Te-based master alloy.
상기 S10 단계에서는, 당 분야에 알려진 통상적인 방법에 따라 모합금을 제한 없이 제조할 수 있다. In the step S10, the master alloy may be manufactured without limitation according to a conventional method known in the art.
보다 구체적으로, 상기 S10 단계의 바람직한 일례를 들면, (i-1) 제1원소; 및 제2원소를 포함하는 조성의 원료를 석영관(Quartz)에 장입한 후, 진공상태를 유지하는 단계('S10-1 단계'); 및 (i-2) 상기 진공상태의 석영관을 퍼니스(Locking furnace)에 장입한 후 650~700℃의 온도에서 1~3시간 동안 10~15회/분 속도로 교반 및 용해시켜 모합금을 형성하는 단계('S10-2 단계')를 포함하여 구성될 수 있다. More specifically, for a preferred example of the step S10, (i-1) a first element; And charging a raw material having a composition including the second element into a quartz tube (Quartz) and maintaining a vacuum state ('S10-1 step'). And (i-2) the quartz tube in the vacuum state is charged into a furnace, and then stirred and dissolved at a rate of 10 to 15 times/min for 1 to 3 hours at a temperature of 650 to 700°C to form a master alloy. It may be configured including a step ('S10-2 step').
먼저, (i-1) n형과 p형으로 구분되어 각각의 조성에 맞는 열전재료용 원료를 석영관에 장입한 후 용해를 위해 실링(Sealing)한다(이하 'S10-1 단계'라 함).First, (i-1) the raw materials for thermoelectric materials, which are classified into n-type and p-type, are charged into a quartz tube, and then sealed for dissolution (hereinafter referred to as'S10-1 step'). .
본 발명에서 사용 가능한 열전재료용 원료는, Bi 및 Te를 주재로 하고, 여기에 n형과 p형에 따라 각각 Se 또는 Sb 성분을 추가로 포함하는 조성일 수 있다. 이러한 열전 재료의 조성은 냉각 및 발전 용도에 따라 상이할 수 있다. 일례로, 상기 Bi 원료와 Te 원료는, Bi2Te3±0.2의 화학양론 조성에 따른 비율로 혼합될 수 있으며, 바람직하게는 Bi2Te3±0.15일 수 있다. The raw material for a thermoelectric material usable in the present invention may be composed mainly of Bi and Te, and further include Se or Sb components according to n-type and p-type. The composition of the thermoelectric material may be different depending on the cooling and power generation purposes. For example, the Bi raw material and the Te raw material may be mixed in a ratio according to the stoichiometric composition of Bi 2 Te 3±0.2 , and preferably Bi 2 Te 3±0.15 .
본 발명의 바람직한 일례에 따르면, 상기 열전재료용 원료는, (i) Bi 및 Sb로 구성된 군에서 선택되는 1종 이상의 제1원소; 및 Te 및 Se로 구성된 군에서 선택되는 1종 이상의 제2원소를 포함하는 조성의 원료를 포함하는 조성일 수 있다. According to a preferred embodiment of the present invention, the raw material for the thermoelectric material includes: (i) at least one first element selected from the group consisting of Bi and Sb; And it may be a composition comprising a raw material of a composition comprising at least one second element selected from the group consisting of Te and Se.
보다 구체적으로, 상기 n형 열전재료용 원료가 Bi-Te-Se계 합금 조성일 경우, 전체 100 중량%를 기준으로 Bi 50~55 중량%, Te 40~45 중량%, 및 Se 3~4 중량%를 포함하는 조성일 수 있다. 또한 p형 열전재료용 원료가 Bi-Sb-Te계 합금 조성일 경우, 전체 100 중량%를 기준으로 Bi 10~15 중량%, Sb 25~30 중량%, Te 55~60 중량%를 포함하는 조성일 수 있다. More specifically, when the raw material for the n-type thermoelectric material is a Bi-Te-Se-based alloy composition, Bi 50 to 55 wt%, Te 40 to 45 wt%, and Se 3 to 4 wt% based on 100 wt% It may be a composition containing. In addition, when the raw material for the p-type thermoelectric material is a Bi-Sb-Te alloy composition, the composition may include 10 to 15% by weight of Bi, 25 to 30% by weight of Sb, and 55 to 60% by weight of Te based on 100% by weight of the total. have.
본 발명에서는 제조하고자 하는 열전재료의 조성에, 도핑원소 분말을 첨가할 수 있다. In the present invention, a doping element powder may be added to the composition of the thermoelectric material to be manufactured.
도핑 원소(dopant)는 Bi-Te계 열전재료가 n형 또는 p형 특성을 갖도록 하기 위해 도입된 것이므로, n형 또는 p형 열전 재료에 사용될 수 있는 당 분야의 통상적인 성분을 제한 없이 사용할 수 있다. 일례로 Al, Sn, Mn, Ag, Cu 및 Ga로 이루어진 군에서 선택되는 1종 이상의 금속일 수 있다. 전술한 금속 성분을 도핑함으로써, 전기전도도나 제벡 특성을 높여 열전 성능을 향상시킬 수 있다. 이때 도핑되는 상기 1종 이상의 금속 함량은 특별히 한정되지 않으며, 일례로 전체 중량 대비 0.001~1 중량% 범위일 수 있다. Since the doping element (dopant) is introduced to make the Bi-Te-based thermoelectric material have n-type or p-type properties, conventional components in the art that can be used for n-type or p-type thermoelectric materials can be used without limitation. . For example, it may be one or more metals selected from the group consisting of Al, Sn, Mn, Ag, Cu, and Ga. By doping the above-described metal component, it is possible to improve the thermoelectric performance by increasing electrical conductivity or Seebeck characteristics. At this time, the content of the one or more metals to be doped is not particularly limited, and for example, may be in the range of 0.001 to 1% by weight based on the total weight.
상기와 같이 도입되는 도펀트는, 하기 실시되는 열처리 공정 등을 통해 격자 결합의 열역학적 에너지 차이 또는 원자확산의 구동력 등에 따라 Bi 또는 Te의 격자(lattice)를 치환하게 된다.The dopant introduced as described above replaces the lattice of Bi or Te according to the difference in thermodynamic energy of the lattice bond or the driving force of atomic diffusion through a heat treatment process performed below.
본 발명에서, 열전재료의 크기와 형태는 특별히 한정되지 않으나, 약 2 내지 5mm 크기의 괴상 형태일 수 있다. 또한 상기 열전재료의 순도는 5N 이상의 고순도인 것이 바람직하다. In the present invention, the size and shape of the thermoelectric material are not particularly limited, but may be in the form of a mass having a size of about 2 to 5 mm. In addition, it is preferable that the purity of the thermoelectric material is 5N or higher.
전술한 열전재료용 원료를 석영관(Quartz)에 장입한 후 진공펌프를 이용하여 실링(Sealing)한 후 진공상태를 유지하도록 한다. The above-described raw material for thermoelectric material is charged into a quartz tube and then sealed using a vacuum pump to maintain a vacuum state.
(i-2) 상기 S10-1 단계의 석영관을 퍼니스(Locking Furnace)를 이용하여 각각의 n형 및 p형 모합금을 제조한다(이하 'S10-2 단계'라 함).(i-2) Each of the n-type and p-type master alloys are manufactured by using a locking furnace for the quartz tube of step S10-1 (hereinafter referred to as'step S10-2').
상기 S10-2 단계의 바람직한 일례를 들면, 진공상태에서 실링된 석영관을 퍼니스에 장입한 후 용해를 위해 약 650~700℃ 온도에서 1~3시간 동안, 10~15회/분의 속도로 교반하고 용해시켜 모합금을 형성한다. For a preferred example of the step S10-2, after charging the sealed quartz tube in a vacuum state into the furnace, stirring at a rate of 10 to 15 times/min for 1 to 3 hours at a temperature of about 650 to 700°C for melting And melt to form a master alloy.
급속응고법(R.S.P)을 이용하여 리본(Ribbon)을 제조하기 위해서는, 균일한 Bi2-Te3계 열전재료의 모합금을 제조하여야 한다. 이에, 본 발명에서는 Φ 30 × 100㎜ 모합금이나 대략 Φ 20~30 ×100~150㎜ 크기 범위의 모합금을 제조할 수 있다.In order to manufacture a ribbon using the rapid solidification method (RSP), a master alloy of a uniform Bi 2 -Te 3 thermoelectric material must be manufactured. Thus, in the present invention, it is possible to manufacture a Φ 30 × 100 mm master alloy or a master alloy having a size range of approximately Φ 20 to 30 × 100 to 150 mm.
상기 S10-2 단계를 통해 제조된 모합금 잉곳은 5N 이상의 고순도를 갖는 Bi-Te계일 수 있으며, 바람직하게는 n형 Bi-Te-Se계 합금 또는 p형 Bi-Sb-Te계 합금일 수 있다.The master alloy ingot manufactured through the step S10-2 may be a Bi-Te-based alloy having a high purity of 5N or higher, and preferably an n-type Bi-Te-Se-based alloy or a p-type Bi-Sb-Te-based alloy. .
(ii) 금속리본 형성단계 ('S20 단계')(ii) Metal ribbon formation step ('S20 step')
본 단계에서는 이전 단계에서 수록된 Bi-Te계 모합금을 급속응고법(R.S.P)을 통해 복합 미세구조를 갖는 Bi-Te계 금속리본을 제조한다.In this step, a Bi-Te-based metal ribbon having a complex microstructure is manufactured through the rapid solidification method (R.S.P) of the Bi-Te-based master alloy included in the previous step.
상기 S20 단계의 바람직한 일례를 들면, 상기 모합금 이곳을 용융 방사 장비에 설치된 노즐에 장입한 후 열을 공급하고 지속적으로 유지할 수 있는 발열체를 이용하여 완전히 용해시켜 용융물을 형성하고, 이후 상기 용융물에 불활성 가스를 가압하고 분사시켜, 회전하는 고속회전 휠(wheel) 표면에 용융물을 접촉시켜 급속냉각시키는 것이다. 이를 통해 Bi-Te계 금속 리본이 형성된다. For a preferred example of the step S20, after charging the mother alloy to a nozzle installed in the melt spinning equipment, heat is supplied and completely dissolved using a heating element that can be continuously maintained to form a melt, and then inert to the melt. By pressurizing and spraying gas, the melt is brought into contact with the rotating high-speed rotating wheel for rapid cooling. Through this, a Bi-Te-based metal ribbon is formed.
여기서, 상기 발열체는 열을 지속적으로 공급하고 유지시킬 수 있다면 특별히 한정되지 않으며, 당 분야에 알려진 통상적인 저항 발열체를 사용할 수 있다. 일례로, 전류를 공급받아 발열하는 저항 발열체를 사용할 수 있으며 사용 가능한 저항 발열체의 예를 들면, 전기로 타입의 히터, 예컨대 그래파이트(Graphite) 히터로 온도를 제어할 수 있다.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 may be used. For example, a resistance heating element that generates heat by receiving current may be used, and the temperature may be controlled by an electric furnace type heater, for example, a graphite heater, for example, of the available resistance heating element.
이때 발열체가 발열하는 온도 범위는 Bi-Te계 모합금을 완전히 용해시킬 수 있는 범위이기만 하면 특별히 한정되지 않는다. 일례로 500~800℃, 바람직하게는 600~700℃ 범위로 유지하는 것이다.At this time, the temperature range at which the heating element generates heat is not particularly limited as long as it is a range capable of completely dissolving the Bi-Te-based master alloy. For example, it is maintained in the range of 500 to 800 ℃, preferably 600 to 700 ℃.
또한 비활성 가스의 종류나 가압 범위 역시 특별히 한정되지 않으나, 일례로 아르곤 가스 등을 이용하여 0.1~0.5 MPa 범위로 가압 분사시키는 것이 바람직하다.In addition, the type or the pressurization range of the inert gas is not particularly limited, but it is preferable to pressurize injection in the range of 0.1 to 0.5 MPa using argon gas as an example.
상기 S20 단계에서, 상기 용융물과 접촉하는 고속회전 휠은 당 분야에 알려진 통상적인 휠을 사용할 수 있으며, 일례로 구리 휠(Cu wheel) 등이 있다. 여기서 고속회전 휠의 회전 속도는 특별히 한정되지 않으며, 일례로 휠 선속도는 5~50m/s 범위일 수 있다. 전술한 조건을 만족할 경우 휠의 표면과 접촉하는 용융물이 급속 냉각됨과 동시에 두께가 얇고 미세구조를 갖는 합금 리본이 형성될 수 있다.In the step S20, the high-speed rotating wheel in contact with the melt may be a conventional wheel known in the art, for example a copper wheel (Cu wheel). Here, the rotation speed of the high-speed rotation wheel is not particularly limited, and for example, the wheel linear speed may be in the range of 5 to 50 m/s. When the above-described conditions are satisfied, the molten material in contact with the surface of the wheel is rapidly cooled, and an alloy ribbon having a thin thickness and a microstructure may be formed.
본 발명에서는, 용해된 모합금의 냉각속도를 조절함으로써, 균일 입도 제어가 가능하며, 일반적으로 냉각속도가 느린 경우 나노 크기의 비결정성 분말을 제조할 수 있으며, 또는 미립자 분말의 제조가 가능하게 된다. 또한, 원료의 농도와 종류에 따라 제조 조건을 달리하여 제조할 수 있다.In the present invention, by controlling the cooling rate of the dissolved master alloy, uniform particle size control is possible, and in general, when the cooling rate is slow, nano-sized amorphous powder can be prepared, or fine particle powder can be prepared. . In addition, it can be manufactured by varying the manufacturing conditions according to the concentration and type of raw materials.
전술한 공정을 거친 모합금은 급속냉각(RSP) 공정을 통해 결정질이 되는 것이 아니라 비결정성 조직과 결정성 조직이 혼재(婚材)된 상태로 응고되게 된다. 이때, 급속냉각 속도가 매우 빠른 경우에는 리본 형태로 제조가 되지만, 냉각속도를 조절하면 수백 나노미터 크기를 가지는 분말이 단순 연결된 반리본 상으로도 제조할 수도 있다. The master alloy that has undergone the above-described process does not become crystalline through a rapid cooling (RSP) process, but is solidified in a state in which an amorphous structure and a crystalline structure are mixed. At this time, if the rapid cooling rate is very fast, it is manufactured in the form of a ribbon, but when the cooling rate is adjusted, powder having a size of several hundred nanometers may be manufactured as a simple connected half-ribbon.
전술한 S20 단계의 급속냉각을 통해 두께가 얇은 Bi-Te계 열전재료 리본이 형성될 수 있다. 일례로, 제조된 금속리본의 길이는 5 내지 15mm이며, 폭은 0.5 내지 5mm이며, 두께가 10 ㎛ 이하일 수 있다. Through the rapid cooling in step S20 described above, a thin Bi-Te-based thermoelectric material ribbon may be formed. For example, the length of the manufactured metal ribbon may be 5 to 15 mm, the width may be 0.5 to 5 mm, and the thickness may be 10 μm or less.
(iii) 금속리본의 파쇄/분쇄 단계 ('S30 단계')(iii) Metal ribbon crushing/crushing step ('S30 step')
본 단계에서는, 용해된 모합금의 직접 분사에 의해 급속 응고되어 취성이 높은 리본상 원료를 파쇄하여 균일한 입도와 형상을 가지는 나노 크기의 비결정성 미세분말을 수득한다. In this step, a ribbon-like raw material having high brittleness is rapidly solidified by direct spraying of the molten mother alloy, thereby obtaining a nano-sized amorphous fine powder having a uniform particle size and shape.
상기 S30 단계의 분쇄공정은 당 분야에 알려진 통상적인 파쇄/분쇄 공정을 제한 없이 실시할 수 있다. 일례로, 볼밀법을 이용하여 분쇄할 수 있다. 이때 분쇄되는 분말의 입경은 특별히 제한되지 않으며, 일례로 평균입경이 100 ㎛ 이하, 바람직하게는 10 내지 100㎛ 범위로 조절할 수 있다. The pulverization process of step S30 may be performed without limitation in a conventional crushing/crushing process known in the art. As an example, it can be pulverized using a ball mill method. At this time, the particle diameter of the powder to be pulverized is not particularly limited, and as an example, the average particle diameter may be adjusted to 100 μm or less, preferably 10 to 100 μm.
본 발명에서는 금속리본의 산화도 제어를 위해서, 전술한 파쇄/분쇄 공정을 비활성 분위기하에서 실시하게 된다. 이와 같이 산소가 비포함된 조건에서 분쇄를 실시함에 따라, 분쇄된 분말 내 산소 함량을 감소시켜 산화도를 낮게 제어할 수 있다. 일례로, 본 발명에 따른 분쇄물은, 산소가 포함된 대기 조건하에서 실시된 분쇄물에 비해, 대략 30% 이상, 구체적으로 30~45% 범위로 산소 함량을 감소시킬 수 있으며, 바람직하게는 당해 분쇄물 내 산소 함량을 0.03% 이하로 제어할 수 있다. In the present invention, in order to control the oxidation degree of the metal ribbon, the above-described crushing/crushing process is performed in an inert atmosphere. As the pulverization is performed under the condition that oxygen is not included as described above, the oxygen content in the pulverized powder can be reduced, thereby controlling the degree of oxidation to be low. As an example, the pulverized product according to the present invention can reduce the oxygen content in the range of about 30% or more, specifically 30 to 45%, compared to the pulverized product carried out under atmospheric conditions containing oxygen, and preferably the The oxygen content in the pulverized material can be controlled to 0.03% or less.
이때 비활성 가스의 종류나 압력 범위 역시 특별히 한정되지 않으며, 일례로 질소 가스, 아르곤 가스 또는 이들이 혼합된 분위기일 수 있다. At this time, the type or pressure range of the inert gas is not particularly limited, and may be, for example, nitrogen gas, argon gas, or a mixed atmosphere.
또한 상기 S30 단계를 거쳐 형성된 Bi-Te계 분말은 평균 입경이 100 ㎛ 이하 범위일 수 있으며, 분말 내 산소 함량이 0.03 % 이하, 바람직하게는 0.02 ~ 0.03% 범위일 수 있다. In addition, the Bi-Te-based powder formed through the step S30 may have an average particle diameter of 100 μm or less, and an oxygen content in the powder of 0.03% or less, preferably 0.02 to 0.03%.
(iv) 예비성형체 형성 단계 ('S40 단계')(iv) Preform formation step ('S40 step')
본 단계에서는 소결공정에서의 고밀도를 확보하고자, 상기 S30 단계에서 얻은 금속리본의 분쇄물을 이용하여 일정 형상의 성형체를 제조한다.In this step, in order to secure high density in the sintering process, a molded body having a predetermined shape is manufactured using the pulverized metal ribbon obtained in step S30.
상기 S40 단계는 당 분야에 알려진 통상의 압축이나 성형 방법을 제한 없이 사용할 수 있다. 일례로, 상기 S30 단계에서 파쇄된 나노 크기의 비결정성 분말 형태를 성형 프레스, 냉간 프레스 또는 압축기를 이용하는 것이 바람직하다. 또한 S40 단계의 조건은 특별히 제한되지 않으며, 당 분야에 알려진 통상적인 압축 조건하에서 적절히 조절할 수 있다. 일례로 10 MPa 이하에서 압축하는 것이 바람직하다.In the step S40, a conventional compression or molding method known in the art may be used without limitation. For example, it is preferable to use a molding press, a cold press, or a compressor to form a nano-sized amorphous powder crushed in step S30. In addition, the conditions of step S40 are not particularly limited, and can be appropriately adjusted under conventional compression conditions known in the art. For example, it is desirable to compress at 10 MPa or less.
(v) 마이크로파 소결단계 ('S50 단계')(v) Microwave sintering step ('S50 step')
본 단계에서는 상기 S40 단계에서 얻은 예비 성형체를 소결을 통해 고밀도의 열전 재료를 제조한다.In this step, a high-density thermoelectric material is manufactured by sintering the preform obtained in step S40.
종래에는 핫 프레스(Hot Press, HP), 방전플라즈마(Spark Plasma Sintering, SPS) 등의 고비용과 장시간이 요구되는 고온 가압 성형법을 실시한 것에 비해, 본 발명에서는 마이크로파 소결(Microwave sintering)법으로 변경하여 저비용 및 공정시간 단축을 도모하고자 한다. Compared to the conventional hot press (HP) and discharge plasma (Spark Plasma Sintering, SPS), etc. that require high cost and long time, in the present invention, it is changed to the microwave sintering method to reduce the cost. And reduction of processing time.
구체적으로, 마이크로파 소결은 물질의 쌍극자(dipole)가 2.45 GHz의 높은 진동수를 가지는 마이크로파에 의해 진동하면서 발생하는 열을 이용하는 소결법이다. 이와 같이 마이크로파 출력을 이용한 소결은, 종래 전기로나 가스로에 비해 승온 속도와 소결 시간이 10배 이상 빠르고, 전력소모가 적을 뿐만 아니라 제조된 소결체가 치밀하고 입자성장이 억제되는 등의 장점이 있다. Specifically, microwave sintering is a sintering method that uses heat generated when a dipole of a material vibrates by microwaves having a high frequency of 2.45 GHz. As described above, sintering using microwave output has advantages such as 10 times faster temperature rise rate and sintering time than conventional electric furnaces or gas furnaces, low power consumption, and the resulting sintered body is dense and grain growth is suppressed.
특히, 본 발명에서는 열전재료의 예비성형체에 마이크로파 소결(Microwave sintering)을 단순 실시할 경우, 오히려 마이크로파에 의해 예비성형체의 부피가 팽창하여 밀도가 현저히 저하된다는 것을 인식하여, 소정의 하중을 인가하면서 마이크로파 소결을 실시하는 것을 특징으로 한다. 이에 따라, 본 발명에서는 20분 이하, 구체적으로 1~10분 정도의 마이크로파 소결 실시를 통해 97% 이상의 고밀도 열전재료를 제조할 수 있다. 실제로 본 발명에서는 종래 열전재료의 소결법인 핫 프레스 또는 방전플라즈마 소결법과 비교하였을 때 소결 공정시간을 90% 이상 단축하면서, 대등한 밀도를 확보할 수 있다.In particular, in the present invention, when microwave sintering is simply performed on a preform of a thermoelectric material, it is recognized that the volume of the preform is expanded by microwaves and the density is significantly reduced. It is characterized by performing sintering. Accordingly, in the present invention, a high-density thermoelectric material of 97% or more can be manufactured through microwave sintering for 20 minutes or less, specifically 1 to 10 minutes. In fact, in the present invention, compared with the hot press or discharge plasma sintering method, which is a conventional thermoelectric material sintering method, the sintering process time can be shortened by 90% or more, and comparable density can be secured.
상기 S40 단계의 구체적인 일례를 들면, 열전재료 예비성형체에 소정의 하중을 가압하거나 고정하는 방식을 실시하면서, 마이크로파 소결을 실시한다.As a specific example of the step S40, microwave sintering is performed while a method of pressing or fixing a predetermined load on the thermoelectric material preform is performed.
이때, 예비 성형체를 가압하는 방식은 특별히 한정되지 않으며, 일례로 당 분야에 공지된 가압 지그(jig), 프레스, 공압 및 유압으로 이루어진 군에서 선택되는 적어도 1종의 방법일 수 있다. 가압 지그(Jig) 등은 마이크로파 소결시 급격한 승온에 의한 성형체의 팽창을 억제하는 역할을 한다. 또한 상기 하중 가압 범위는 예비성형체의 팽창을 효과적으로 억제할 수 있는 범위라면, 특별히 제한되지 않는다. 일례로는, 5~20 MPa 범위일 수 있으며, 구체적으로 5 내지 10 MPa이 바람직하다. At this time, the method of pressing the preform is not particularly limited, for example, may be at least one method selected from the group consisting of a pressing jig, press, pneumatic and hydraulic pressure known in the art. The pressing jig or the like plays a role of suppressing the expansion of the molded body due to rapid increase in temperature during microwave sintering. Further, the load pressurization range is not particularly limited as long as it is a range capable of effectively suppressing the expansion of the preform. For example, it may be in the range of 5 to 20 MPa, and specifically, 5 to 10 MPa is preferred.
여기서, 가압 지그의 소재는 특별히 제한되지 않으며, 일례로 마이크로파가 통과할 수 있으면서, 마이크로파에 감응하지 않는 물질로 구성되는 것이 바람직하다. 즉, 마이크로파 출력에 의해 발생하는 열은 유전 손실과 관계되는 것으로, 일반적으로 유전손실은 유전율에 비례한다. 티탄산바륨과 같은 고유전율을 가지는 물질의 경우 마이크로파를 흡수하여 쉽게 가열되지만 알루미나, 지르코니아와 같이 저유전율을 가지는 물질은 마이크로파에 대해 비감응하여 가열되지 않는다. 이에 따라, 가압 지그는 마이크로파에 감응하지 않는 저유전율 물질로 이루어진 것을 사용할 수 있으며, 일례로 Al2O3 또는 그래파이트(Graphite)로 제조된 지그(Jig)가 바람직하다.Here, the material of the pressing jig is not particularly limited, and for example, it is preferable to be made of a material that is capable of passing microwaves and does not respond to microwaves. That is, heat generated by microwave output is related to dielectric loss, and in general, dielectric loss is proportional to dielectric constant. A material having a high dielectric constant such as barium titanate absorbs microwaves and is easily heated, but a material having a low dielectric constant such as alumina and zirconia is not heated because it is not sensitive to microwaves. Accordingly, the pressing jig may be made of a material having a low dielectric constant that is not sensitive to microwaves, and for example, a jig made of Al 2 O 3 or graphite is preferable.
상기 S50 단계에서 열간가공의 조건은 특별히 제한되지 않으며, 일례로 200~500℃의 온도에서 1~20분 동안 1~5 kW의 마이크로파 출력으로 실시될 수 있으며, 구체적으로 200~300℃의 온도 범위에서 5~10분 동안 1.5~2.5 kW의 마이크로파 출력으로 실시하는 것이 바람직하다. 이때, 상기 열간가공의 조건(온도, 시간)이 200℃ 또는 1분 미만일 경우에는 고밀도의 소재를 얻을 수 없으며, 상기 조건이 500℃를 초과하거나 또는 20분을 초과할 경우, Te의 증기압이 높아 휘발되어 목적 조성에 적합하지 않게 되며, 이로 인해 열전성능 지수가 저하될 가능성이 높다.The conditions of the hot working in the S50 step are not particularly limited, for example, it may be carried out at a temperature of 200 to 500 °C for 1 to 20 minutes with a microwave output of 1 to 5 kW, specifically a temperature range of 200 to 300 °C It is preferable to perform at a microwave output of 1.5 to 2.5 kW for 5 to 10 minutes. At this time, if the conditions (temperature, time) of the hot working are less than 200°C or 1 minute, high-density materials cannot be obtained, and if the conditions exceed 500°C or exceed 20 minutes, the vapor pressure of Te is high. It volatilizes and becomes unsuitable for the target composition, and there is a high possibility that the thermoelectric performance index decreases.
전술한 제조방법을 통해 제조된 본 발명의 일 실시예에 따른 Bi-Te계 열전재료는 밀도가 95~99% 범위, 바람직하게는 약 97% 이상일 수 있다. 또한 비활성 가스 분위기 하에서 분쇄공정을 수행하였으므로, 산화도가 조절되어 당해 열전재료 내 산소 함량을 소정 범위 이하로 제어할 수 있다. Bi-Te-based thermoelectric material according to an embodiment of the present invention manufactured through the above-described manufacturing method may have a density in the range of 95 to 99%, preferably about 97% or more. In addition, since the pulverization process is performed in an inert gas atmosphere, the degree of oxidation is adjusted so that the oxygen content in the thermoelectric material can be controlled within a predetermined range.
또한 본 발명의 일 실시예에 따른 Bi-Te계 열전재료의 파워 팩터(Power factor)값은 25~30 W/mk2 범위일 수 있다. In addition, a power factor value of the Bi-Te-based thermoelectric material according to an embodiment of the present invention may be in the range of 25 to 30 W/mk 2 .
본 명세서에서 파워 팩터(power factor) 값은, 하기 수학식 1과 같이 정의되며, 본 발명의 일 실시예에 따른 열전 소자가 생산 가능한 최대 전력 밀도를 평가하는 지수로 사용된다.In the present specification, a power factor value is defined as in Equation 1 below, and is used as an index for evaluating the maximum power density that can be produced by a thermoelectric device according to an embodiment of the present invention.
[수학식 1] Power factor = (제백계수)2 × 전기전도도[Equation 1] Power factor = (Zebaek coefficient) 2 × electrical conductivity
구체적으로, 열전소재의 열을 전기로 변환하는 성능은 열전 성능 지수(Z, figure of merit)를 이용하여 나타내며, Z=(α2σ/κ)로 정의된다. 여기서, α는 제벡계수(Seebeck coefficient), σ는 전기전도도, κ는 열전도도를 나타내며, 이때 제벡계수의 제곱과 전기전도도의 곱을 파워 팩터(Power factor)라 한다. Specifically, the ability of a thermoelectric material to convert heat into electricity is expressed using a thermoelectric figure of merit (Z), and is defined as Z=(α 2 σ/κ). Here, α is the Seebeck coefficient, σ is the electrical conductivity, and κ is the thermal conductivity. In this case, the product of the square of the Seebeck coefficient and the electrical conductivity is referred to as a power factor.
열전소재의 열을 전기로 변환하는 열전 성능 지수 (Z)를 증가시키기 위해서는, 제벡계수 (α)가 커야 하며, 재료의 양단의 온도차를 유지하기 위해 열전도도 (κ)는 작아야 되고, 전류에 의한 Joule열의 발생을 최소화하기 위하여 전기전도도 (σ)는 커야 한다. 일반적으로 대부분의 열전소재는 전기전도도가 증가하면 열전도도 역시 증가하기 때문에, 파워 팩터(Power factor) 값을 높일 경우, 전기전도도 (σ) 보다 제벡계수 (α)를 높이는 것이 유리하다.In order to increase the thermoelectric figure of merit (Z), which converts heat of a thermoelectric material into electricity, the Seebeck coefficient (α) must be large, and the thermal conductivity (κ) must be small to maintain the temperature difference between both ends of the material. In order to minimize Joule heat generation, the electrical conductivity (σ) should be large. In general, in most thermoelectric materials, as the electrical conductivity increases, the thermal conductivity also increases. Therefore, when the power factor value is increased, it is advantageous to increase the Seebeck coefficient (α) rather than the electrical conductivity (σ).
[실시예 1] Bi-Te계 p-type 열전소재 제조[Example 1] Bi-Te-based p-type thermoelectric material manufacturing
약 2~5mm의 괴상형태이며, 4N 이상의 고순도를 갖는 Bi, Te, Sb 및 Se를 함유하는 열전재료를 준비하였다. p형의 경우, Bi, Te, Sb 등의 3원계를 갖도록 하기 위해서, Bi 13 wt%, Sb 28 wt%, Te 59 wt%으로 구성하였다. 해당 열전재료를 석영관(Quartz)를 Locking Furnace에 장입한 후 650~750℃에서 2~4시간, 10회/min 속도로 교반 및 용해하여 Φ 30 × 100㎜ 모합금 잉곳을 제조하였다. 이후 모합금 잉곳을 용융방사장비에 설치된 노즐에 장입하여 저항 발열체(그라파이트 히터로서 노즐을 감싸는 구조)를 이용하여 약 700℃ 온도로 완전히 용해시켜 용융물을 형성한 후, 상기 용융물에 불활성 가스를 0.1~0.5 MPa로 가압하여 분사시킴으로써, 회전하는 구리 휠(Cu wheel) 표면에 접촉하여 급속 냉각됨에 따라 Bi-Te계 금속 리본을 형성하였다. 이때 구리 휠의 회전 속도는 1000 rpm으로 진행하였다.A thermoelectric material containing Bi, Te, Sb and Se having a high purity of about 2 to 5 mm and having a high purity of 4N or more was prepared. In the case of p-type, in order to have a ternary system such as Bi, Te, and Sb, it was composed of 13 wt% of Bi, 28 wt% of Sb, and 59 wt% of Te. The thermoelectric material was charged into a locking furnace, and then stirred and dissolved at 650 to 750°C for 2 to 4 hours at a rate of 10 times/min to prepare a Φ 30 × 100 mm master alloy ingot. After that, the master alloy ingot is charged into the nozzle installed in the melt spinning equipment and completely dissolved at about 700°C using a resistance heating element (a structure surrounding the nozzle as a graphite heater) to form a melt, and then 0.1~ By pressing and spraying at 0.5 MPa, a Bi-Te-based metal ribbon was formed by contacting the surface of a rotating copper wheel and cooling rapidly. At this time, the rotational speed of the copper wheel was performed at 1000 rpm.
이어서, 형성된 금속리본을 아르곤(Ar) 분위기 하에서 볼밀법을 이용하여 평균입경이 100㎛ 이하가 되도록 분쇄하였다. 상기 분쇄된 분말을 냉간 등방압 가압법(Cold Isostatic Pressing)으로 성형체를 제조하였다. 예비성형체를 Al2O3 가압 지그(Jig)에 결합하여 5MPa의 하중을 인가한 상태에서 Microwave 소결을 이용하여 230℃까지 50℃/min의 승온속도로 승온한 후 5분 정도를 유지하고, 1.5 kW의 마이크로파(Microwave) 출력을 유지하여 소결한 결과, 97% 이상의 고밀도 Bi-Te계 열전재료를 제조하였다.Subsequently, the formed metal ribbon was pulverized to have an average particle diameter of 100 μm or less using a ball mill method in an argon (Ar) atmosphere. The pulverized powder was prepared by cold isostatic pressing (Cold Isostatic Pressing). Combine the preform with an Al 2 O 3 pressurizing jig and apply a load of 5 MPa to 230°C using microwave sintering at a heating rate of 50°C/min. As a result of sintering while maintaining a microwave output of kW, a high density Bi-Te thermoelectric material of 97% or more was manufactured.
[비교예 1] Bi-Te계 p-type 열전소재 제조[Comparative Example 1] Bi-Te p-type thermoelectric material manufacturing
예비성형체에 하중을 인가하지 않고, 마이크로파(Microwave) 소결을 이용하여 230℃까지 50℃/min의 승온속도로 승온한 후 5분간 유지하고, 1.5kW의 마이크로파(Microwave) 출력을 유지하여 소결한 것을 제외하고는, 상기 실시예 1과 동일한 방법을 실시하여 비교예 1의 Bi-Te계 열전 재료를 제조하였다. The maintaining, without applying a load to the preform, microwave (Microwave) After the temperature was raised at a heating rate of 50 ℃ / min up to 230 ℃ using a sintered for 5 min and, sintering to maintain the microwave (Microwave) output of 1.5kW Except for, the Bi-Te-based thermoelectric material of Comparative Example 1 was manufactured by performing the same method as in Example 1.
상기와 같이 제조된 Bi-Te계 열전 재료의 밀도는 78%이었다.The density of the Bi-Te-based thermoelectric material prepared as described above was 78%.
[비교예 2] Bi-Te계 p-type 열전소재 제조[Comparative Example 2] Bi-Te p-type thermoelectric material manufacturing
약 2~5mm의 괴상형태이며, 4N 이상의 고순도를 갖는 Bi, Te, Sb 및 Se를 함유하는 열전재료를 준비하였다. p형의 경우, Bi, Te, Sb 등의 3원계를 갖도록 하였다. 해당 열전재료를 석영관(Quartz)를 Locking Furnace에 장입한 후 650~750℃에서 2~4시간, 10회/min 속도로 교반 및 용해하여 Φ 30 × 100㎜ 모합금 잉곳을 제조하였다. 이후 모합금 잉곳을 용융 방사 장비에 설치된 노즐에 장입하여 저항 발열체(그라파이트 히터로서 노즐을 감싸는 구조)를 이용하여 약 700℃ 온도로 완전히 용해시켜 용융물을 형성한 후, 상기 용융물에 불활성 가스를 0.1~0.5 MPa로 가압하여 분사시킴으로써, 회전하는 구리 휠(Cu wheel) 표면에 접촉하여 급속 냉각됨에 따라 Bi-Te계 금속 리본을 형성하였다. 이때 구리 휠의 회전 속도는 1000 rpm으로 진행하였다.A thermoelectric material containing Bi, Te, Sb and Se having a high purity of about 2 to 5 mm and having a high purity of 4N or more was prepared. In the case of p-type, it was made to have a ternary system such as Bi, Te, and Sb. The thermoelectric material was charged into a locking furnace, and then stirred and dissolved at 650 to 750°C for 2 to 4 hours at a rate of 10 times/min to prepare a Φ 30 × 100 mm master alloy ingot. Thereafter, the master alloy ingot is charged into the nozzle installed in the melt spinning equipment and completely dissolved at about 700°C using a resistance heating element (a structure that surrounds the nozzle as a graphite heater), and then 0.1~ By pressing and spraying at 0.5 MPa, a Bi-Te-based metal ribbon was formed by contacting the surface of a rotating copper wheel and cooling rapidly. At this time, the rotational speed of the copper wheel was performed at 1000 rpm.
이후 형성된 금속리본을 아르곤(Ar) 분위기 하에서 볼밀법을 이용하여 평균입경이 100 ㎛ 이하가 되도록 분쇄하였다. 상기 분쇄된 분말을 핫 프레스 소결을 이용하여 약 525℃까지 7℃/min의 승온속도로 승온 후 1시간 유지, 70 MPa 압력을 유지하여 소결한 결과 99% 이상의 고밀도 열전재료를 제조하였다.Then, the formed metal ribbon was pulverized to have an average particle diameter of 100 μm or less using a ball mill method in an argon (Ar) atmosphere. The pulverized powder was heated to about 525° C. at a rate of 7° C./min using hot press sintering, maintained for 1 hour, and sintered by maintaining a pressure of 70 MPa, thereby producing a high-density thermoelectric material of 99% or more.
[실험예 1] 열전소재 밀도평가[Experimental Example 1] Thermoelectric material density evaluation
실시예 1 및 비교예 1~2에서 제조된 각 열전재료에 대하여 소결 전/후의 밀도를 측정하였으며, 그 결과를 하기 표 1에 기재하였다. 이때 밀도측정법은 아르키메데스법으로 측정하였다. Densities before/after sintering were measured for each thermoelectric material prepared in Example 1 and Comparative Examples 1 to 2, and the results are shown in Table 1 below. At this time, the density measurement method was measured by the Archimedes method.
밀도(g/cm3)Density (g/cm 3 ) 소결공정총 소요시간(분)Total time required for the sintering process (minutes)
구분division 소결 전Before sintering 소결 후After sintering
실시예 1Example 1 6.36(93%)6.36 (93%) 6.59(97%)6.59 (97%) 2020
비교예 1Comparative Example 1 6.37(93%)6.37 (93%) 5.31(78%)5.31 (78%) 2020
비교예 2Comparative Example 2 -- 6.84(99%)6.84 (99%) 480480
실험 결과, 종래 핫프레스 소결법을 실시한 비교예 2는 마이크로파 소결법을 채용한 실시예 1에 비해, 대략 24배 정도의 소결공정 시간이 소요되어 생산성 저하 및 공정비용 추가 등이 초래되는 것을 확인할 수 있었다. 여기서, 소결공정의 총 소요시간은, 소결 처리시간 뿐만 아니라 당해 소결처리에 필요한 승온시간과 냉각시간을 포함하는 전체 처리시간을 의미한다. As a result of the experiment, it was confirmed that Comparative Example 2 subjected to the conventional hot press sintering method took about 24 times as long as the sintering process time compared to Example 1 employing the microwave sintering method, resulting in lower productivity and additional process costs. Here, the total time required for the sintering process means not only the sintering treatment time, but also the total treatment time including the heating time and cooling time required for the sintering treatment.
또한 소정의 하중 인가 없이, 마이크로파로 단순 소결된 비교예 1의 열전재료는 오히려 소결공정 이후 밀도가 현저히 저하되는 것을 알 수 있었다. In addition, it was found that the thermoelectric material of Comparative Example 1, which was simply sintered with microwaves without applying a predetermined load, had a significantly lower density after the sintering process.
이에 비해, 본원 실시예 1의 열전재료는 소결 이후 밀도가 증가하여 단시간 내에 고밀도 구현이 가능하다는 것을 확인할 수 있었다(상기 표 1 참조).In contrast, it was confirmed that the thermoelectric material of Example 1 of the present application increased in density after sintering, so that high density can be realized within a short time (see Table 1 above).
[실험예 2] 출력 변화율 평가[Experimental Example 2] Evaluation of output change rate
실시예 1 및 비교예 2에서 제조된 Bi-Te계 열전재료를 이용하여 하기와 같이 물성을 측정하였으며, 그 결과를 하기 도 2 및 3에 각각 나타내었다. Physical properties were measured as follows using the Bi-Te-based thermoelectric material prepared in Example 1 and Comparative Example 2, and the results are shown in FIGS. 2 and 3, respectively.
제백계수 및 전기전도도 측정: JISK 7194에 준거하여, ZEM-3 (Ulvac-Riko社 제조)를 이용하여 측정하였다. 측정된 제벡계수(S)와 전기전도도(σ)를 이용하여 Power factor를 계산하였다.Measurement of Seebeck coefficient and electrical conductivity: According to JISK 7194, it was measured using ZEM-3 (manufactured by Ulvac-Riko). The power factor was calculated using the measured Seebeck coefficient (S) and electrical conductivity (σ).
[수학식 1] Power factor = (제백계수)2 × 전기전도도[Equation 1] Power factor = (Zebaek coefficient) 2 × electrical conductivity
실험 결과, 소정의 하중을 가한 상태에서 마이크로파 소결 공정을 거친 본 발명의 Bi-Te계 열전재료는, 종래 핫프레스 소결공정을 거친 비교예 2에 비해 단시간에 고밀도의 열전재료를 제조할 수 있음을 확인할 수 있었다(하기 도 2~3 참조). As a result of the experiment, it was found that the Bi-Te-based thermoelectric material of the present invention subjected to the microwave sintering process in a state where a predetermined load was applied can produce a high-density thermoelectric material in a short time compared to Comparative Example 2 subjected to the conventional hot press sintering process. It could be confirmed (see Figs. 2 to 3 below).

Claims (9)

  1. (i) Bi 원료와 Te 원료를 포함하는 열전재료용 원료를 용해 및 응고시켜 모합금을 형성하는 단계;(i) dissolving and solidifying a raw material for a thermoelectric material including a Bi raw material and a Te raw material to form a master alloy;
    (ii) 상기 모합금을 급속냉각시켜 금속 리본을 형성하는 단계;(ii) rapidly cooling the master alloy to form a metal ribbon;
    (iii) 상기 금속리본을 비활성 분위기하에서 분쇄하는 단계; (iii) grinding the metal ribbon under an inert atmosphere;
    (iv) 상기 분쇄물을 압축하여 예비성형체를 형성하는 단계; 및 (iv) compressing the pulverized product to form a preform; And
    (v) 상기 예비성형체의 팽창이 억제되도록 소정의 하중을 가압하면서, 마이크로파 소결하는 단계; (v) microwave sintering while pressing a predetermined load so that expansion of the preform is suppressed;
    를 포함하는 Bi-Te계 열전재료의 제조방법.Method for producing a Bi-Te-based thermoelectric material comprising a.
  2. 제1항에 있어서, The method of claim 1,
    상기 단계 (i)의 열전재료용 원료는 Sb 및 Se로 이루어진 군에서 선택되는 1종 이상의 원소를 더 포함하는 Bi-Te계 열전재료의 제조방법. The raw material for the thermoelectric material of step (i) further comprises at least one element selected from the group consisting of Sb and Se.
  3. 제1항에 있어서,The method of claim 1,
    상기 단계 (i)의 열전재료용 원료는 Al, Sn, Mn, Ag, Cu 및 Ga로 이루어진 군에서 선택되는 1종 이상의 금속을 0.001 내지 1 중량% 범위로 더 포함하는 Bi-Te계 열전재료의 제조방법.The raw material for the thermoelectric material in step (i) is a Bi-Te-based thermoelectric material further comprising at least one metal selected from the group consisting of Al, Sn, Mn, Ag, Cu, and Ga in the range of 0.001 to 1% by weight. Manufacturing method.
  4. 제1항에 있어서,The method of claim 1,
    상기 단계 (ii)는 모합금을 용융 방사 장비에 설치된 노즐에 장입하고 발열체를 이용하여 용융시킨 후, 상기 용융물에 불활성 가스를 0.1~1.0 MPa 범위로 가압하여 5~50m/s의 선속도로 회전하는 고속회전 휠 표면에 용융물을 접촉시켜 급냉시키는 것을 특징으로 하는 Bi-Te계 열전재료의 제조방법.In the step (ii), the master alloy is charged into a nozzle installed in the melt spinning equipment and melted using a heating element, and then an inert gas is pressurized in the melt in the range of 0.1 to 1.0 MPa and rotated at a linear speed of 5 to 50 m/s. A method of manufacturing a Bi-Te-based thermoelectric material, characterized in that the melt is brought into contact with the surface of the high-speed rotating wheel to rapidly cool.
  5. 제1항에 있어서,The method of claim 1,
    상기 단계 (v)는 가압 지그(Jig), 프레스, 공압 및 유압으로 구성된 군에서 선택된 적어도 1종의 가압방법을 동반하여 마이크로파(microwave) 소결을 실시하는 Bi-Te계 열전재료의 제조방법.The step (v) is a method of manufacturing a Bi-Te-based thermoelectric material in which microwave sintering is performed with at least one pressing method selected from the group consisting of a press jig, press, pneumatic and hydraulic pressure.
  6. 제1항에 있어서,The method of claim 1,
    상기 단계 (v)에서 예비성형체에 가압되는 하중범위는 5 내지 20 MPa인 Bi-Te계 열전재료의 제조방법. The method of manufacturing a Bi-Te-based thermoelectric material having a load range of 5 to 20 MPa applied to the preform in step (v).
  7. 제1항에 있어서,The method of claim 1,
    상기 단계 (v)에서 마이크로파 소결은, 200~500℃의 온도에서 1~20분 동안 1~5 kW의 마이크로파(Microwave) 출력에 의해 실시되는 Bi-Te계 열전재료의 제조방법.The microwave sintering in step (v) is a method of manufacturing a Bi-Te-based thermoelectric material performed by microwave output of 1 to 5 kW for 1 to 20 minutes at a temperature of 200 to 500°C.
  8. 제1항에 있어서, The method of claim 1,
    마이크로파 소결된 Bi-Te계 열전재료의 밀도는 95% 이상이며, The density of the microwave sintered Bi-Te thermoelectric material is over 95%,
    상온 Power factor가 25~35 W/mΩ인 Bi-Te계 열전재료의 제조방법.A method of manufacturing Bi-Te-based thermoelectric materials with a room temperature power factor of 25~35 W/mΩ.
  9. 제1항 내지 제8항 중 어느 한 항의 방법에 의해 제조된 Bi-Te계 열전재료.A Bi-Te-based thermoelectric material manufactured by the method of any one of claims 1 to 8.
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Citations (5)

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KR20180060265A (en) * 2016-11-28 2018-06-07 희성금속 주식회사 METHOD FOR MANUFACTURING Bi-Te BASED THERMOELECTRIC MATERIAL CONTROLLED OXIDATION AND Bi-Te BASED THERMOELECTRIC MATERIAL MANUFACTURED THEREBY

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JP2002173375A (en) * 2000-12-04 2002-06-21 R & D Inst Of Metals & Composites For Future Industries Piezoelectric ceramic sintered by utilizing microwave and hot press, method of producing the same and piezoelectric actuator using the piezoelectric ceramic
JP2002232024A (en) * 2001-01-30 2002-08-16 Kyocera Corp Method for manufacturing thermoelectric element
WO2015046732A1 (en) * 2013-09-24 2015-04-02 엘지전자 주식회사 Method of manufacturing anisotropic hot-deformed magnet using hot-deformation process and hot-deformed magnet manufactured thereby
KR101719928B1 (en) * 2015-12-23 2017-03-27 한국세라믹기술원 MANUFACTURING METHOD OF Bi-Te BASED CERAMICS
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