KR101831150B1 - Apparatus and method for fabricating thermoelectric materials using cold deformation - Google Patents
Apparatus and method for fabricating thermoelectric materials using cold deformation Download PDFInfo
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- KR101831150B1 KR101831150B1 KR1020150159168A KR20150159168A KR101831150B1 KR 101831150 B1 KR101831150 B1 KR 101831150B1 KR 1020150159168 A KR1020150159168 A KR 1020150159168A KR 20150159168 A KR20150159168 A KR 20150159168A KR 101831150 B1 KR101831150 B1 KR 101831150B1
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Abstract
The present invention relates to an apparatus and a method for manufacturing a thermoelectric material using cold deformation capable of improving the reproducibility of thermoelectric properties and selectively controlling the carrier concentration of the thermoelectric material, A method of manufacturing a thermoelectric material includes: preparing a thermoelectric material mass by melting and cooling the thermoelectric material; Performing cold deformation to apply pressure to the thermoelectric material mass to increase the carrier concentration in the thermoelectric material mass; And thermo-extruding the thermoelectric material having undergone cold-deforming to produce a thermoelectric material.
Description
The present invention relates to an apparatus and a method for manufacturing a thermoelectric material using cold deformation, and more particularly, to a thermoelectric material manufacturing apparatus using cold deformation capable of selectively controlling a carrier concentration of a thermoelectric material, And methods.
The thermoelectric module utilizes the Peltier effect or the Seebeck effect of a thermoelectric element and is used as a cooling device utilizing a Peltier effect in which one end generates heat and the other end absorbs heat when electricity is applied to the thermoelectric element And when the temperature difference is applied to both ends of the thermoelectric element, it can be used as a power generation device utilizing the Seebeck effect in which an electromotive force is generated.
The performance of the thermoelectric module is directly determined by the thermoelectric properties of the thermoelectric material as well as the structure of the module (figure of merit). The temperature at which the thermoelectric performance index is optimized differs for each thermoelectric material, and bismuth-tellurium (Be-Ti) type alloy is known to exhibit the best thermoelectric performance index at room temperature.
On the other hand, the thermoelectric material is usually produced by hot extrusion of the thermoelectric powder. Such a thermoelectric material manufacturing method has an advantage in that the crystal orientation can be controlled through extrusion, thereby improving the thermoelectric performance, and is excellent in productivity and processability. On the other hand, the use of a powder form, that is, a thermoelectric powder, has a high possibility that the thermoelectric powder is oxidized during the manufacturing process, and the physical properties of the thermoelectric material are likely to change due to the incorporation of foreign materials. Further, it is difficult to precisely control the carrier concentration of the thermoelectric material, and there is a problem of causing air pollution by using a powdery material.
Another method of producing a thermoelectric material is to produce a thermoelectric material in the form of a single crystal. Specifically, a method of melting a thermoelectric material to produce an ingot of a single crystal and using it as a thermoelectric material. However, the single crystal thermoelectric material has a high probability of cracking during processing and module assembly, which causes the defect rate to increase. In addition, the zone melting method is generally used in the production of a single crystal. The ingot formed by the joining method has a compositional deviation, which cuts the upper part and the lower part, .
Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made to solve the above problems, and an object of the present invention is to provide an apparatus and a method for manufacturing a thermoelectric material using cold deformation capable of improving the reproducibility of thermoelectric properties and selectively controlling the carrier concentration of the thermoelectric material. There is a purpose.
According to another aspect of the present invention, there is provided a method of manufacturing a thermoelectric material using cold deformation, the method comprising: melting and cooling a thermoelectric material to produce a thermoelectric material mass; Performing cold deformation to apply pressure to the thermoelectric material mass to increase the carrier concentration in the thermoelectric material mass; And thermo-extruding the thermoelectric material having undergone cold-deforming to produce a thermoelectric material.
The cold deformation is performed at least once, and as the number of times of cold deformation increases, the carrier concentration in the thermoelectric material ingot increases.
The cold deformation is performed at least once. As the number of cold deformations increases, the shear modulus, thermal conductivity, and carrier density of the thermoelectric material mass change, and based on the shear coefficient, thermal conductivity, The thermoelectric performance index can be calculated and the number of cold deformations indicating the maximum thermoelectric performance index can be specified.
(expression)
(Z: thermoelectric performance index,?: Seebeck coefficient,?: Electrical resistivity,?: Thermal conductivity)
And thermally treating the thermoelectric material that is hot extruded to prevent oxidation of the thermoelectric material.
The thermoelectric material may be a Bi-Te, Sb-Te, Pb-Te, Pb-Se, Si-Ge, In-Co, Bi-Te- -Sb system, or a mixture thereof, and the thermoelectric material is one of electrically n-type, p-type, and intrinsic type.
The cold deformation is performed by preparing a compressor having an upper plate and a lower plate and pressing the upper surface of the thermoelectric material mass with a certain pressure with the upper plate in a state in which the thermoelectric material mass is provided on the lower plate of the compressor You can proceed.
An apparatus for manufacturing a thermoelectric material using cold deformation according to the present invention includes: a thermoelectric material block manufacturing apparatus for producing a thermoelectric material block by melting and cooling a thermoelectric material; A compressor which performs cold deformation more than once to apply pressure to a mass of thermoelectric material to change a Seebeck coefficient, a thermal conductivity and an electric resistance value of the thermoelectric material mass; A hot extruder for hot extruding a cold deformed thermoelectric material to produce a thermoelectric material; And a heat treatment apparatus for heat-treating the hot extruded thermoelectric material.
A thermoelectric performance index calculating device for calculating the thermoelectric performance index using the following equation based on the Seebeck coefficient, the thermal conductivity and the electric resistance value depending on the number of cold deformations and for specifying the number of cold deformations indicating the maximum thermoelectric performance index; As shown in FIG.
(expression)
(Z: thermoelectric performance index,?: Seebeck coefficient,?: Electrical resistivity,?: Thermal conductivity)
The apparatus and method for manufacturing thermoelectric materials using cold deformation according to the present invention have the following effects.
It is possible to selectively control the carrier concentration of the thermoelectric material through the cold deformation and to produce the thermoelectric material having the optimum thermoelectric performance index. In addition, since the thermoelectric material is manufactured using the thermoelectric material mass other than the powder thermoelectric material, the possibility of oxidation of the thermoelectric material and contamination of the foreign material, which is a problem of the powdery manufacturing method, can be minimized.
1 is a flowchart illustrating a method of manufacturing a thermoelectric material using cold deformation according to an embodiment of the present invention.
2 is a block diagram of an apparatus for manufacturing thermoelectric materials using cold deformation according to an embodiment of the present invention.
Fig. 3 shows experimental results showing changes in thermoelectric properties of a thermoelectric material mass according to the number of cold deformation.
FIG. 4 is a graph showing the change in thermoelectric properties of the thermoelectric material according to the heat treatment.
The present invention provides a thermoelectric material manufacturing method capable of solving the problems of a conventional single crystal manufacturing method and a powder type manufacturing method in manufacturing a thermoelectric material. The single crystal manufacturing method refers to a method in which an ingot of a single crystal is produced by melting a thermoelectric material and is used as a thermoelectric material, and the powder type manufacturing method means a method of thermoelectrically producing a thermoelectric material by hot extrusion of a thermoelectric powder.
The present invention proposes a technique of manufacturing a thermoelectric material mass, cold-deforming a thermoelectric material mass, and hot extruding a cold-deformed thermoelectric material to produce a thermoelectric material. In the present invention, the term " thermoelectric material mass " means that the thermoelectric material is produced by melting and solidifying, and may be an ingot itself or an ingot divided into several portions. For ease of cold deformation, And the like.
The mass of the thermoelectric material is produced by melting and solidifying a thermoelectric material. Since the object to be hot-pressed is a mass of thermoelectric material (or a group thereof), the possibility of oxidation of the thermoelectric material and contamination of foreign materials, which is a problem of the conventional powder- . In addition, by using a mass of thermoelectric material other than the powder phase, it is possible to take an excellent electrical characteristic, which is an advantage of the single crystal manufacturing method, and the crystal orientation of the thermoelectric material can be controlled by applying the hot extrusion method unlike the single crystal manufacturing method.
The method of manufacturing a thermoelectric material using the cold deformation according to the present invention is characterized by being able to selectively control the carrier concentration of the thermoelectric material through cold deformation, in addition to the advantages over the single crystal manufacturing method and the powder type manufacturing method as described above.
The cold deformation induces a defect in the thermoelectric material mass by applying pressure to the thermoelectric material mass at room temperature or in a cold state. When a physical deformation occurs due to a pressure applied to the thermoelectric material mass, vacancies, dislocations, and the like are increased. The increase in defects in the crystal means that the number of electrons or holes that can be moved increases, and the carrier concentration in the crystal increases in other words.
The present invention can control the carrier concentration of the thermoelectric material through such cold deformation. In detail, the carrier concentration of the thermoelectric material can be selectively controlled by controlling the number of times of cold deformation and the pressure applied during cold deformation.
Hereinafter, a method of manufacturing a thermoelectric material using cold deformation according to an embodiment of the present invention will be described in detail with reference to the drawings.
Referring to FIG. 1, first, a thermoelectric material mass is manufactured (S101).
The thermoelectric mass can be produced by melting and cooling the thermoelectric material. Specifically, after a crucible or a quartz tube charged with a thermoelectric material having a specific composition is mounted in a melting furnace, the melted thermoelectric material is melted by heating the melting furnace, and then the melted thermoelectric material is cooled A thermoelectric mass can be produced.
The thermoelectric material may be at least one selected from the group consisting of Bi-Te, Sb-Te, Pb-Te, Pb-Se, Si-Ge, In-Co, Bi- Co-Sb system binary or ternary system thermoelectric materials can be used alone or in combination. In addition, selenium (Se) or antimony (Sb) is added to the thermoelectric material so that the thermoelectric material can be electrically divided into n type or p type. In one embodiment, selenium (Se) is added to a Bi-Te system to form an n-type thermoelectric material, or antimony (Sb) is added to a Bi-Te system to form a p-type thermoelectric material. The mass of the thermoelectric material may have any one of intrinsic, n-type, and p-type electrical characteristics depending on the composition of the thermoelectric material.
Further, the thermoelectric material mass can be produced in a hexahedral shape, and in this case, the thermoelectric material mass can be produced using a hexagonal crucible or a tube. The reason why the mass of the thermoelectric material is formed in a hexahedron shape is to apply a uniform pressure to the thermoelectric material mass during the cold deformation described later.
In a state in which the thermoelectric material mass is prepared, the cold deformation process for the thermoelectric material mass is performed (S102). Specifically, after attaching the thermoelectric material mass to the compressor, pressure is applied to the thermoelectric material mass to induce the physical deformation of the thermoelectric material mass. In one embodiment, a compressor having an upper plate and a lower plate is prepared, and the upper surface of the thermoelectric material mass is pressed to the upper plate at a constant pressure in a state in which a hexagonal thermoelectric material mass is provided on the lower plate of the compressor have. Crystal defects such as vacancy and dislocation are increased in the mass of the thermoelectric material due to the pressure applied to the mass of thermoelectric material and the carrier concentration is increased as the defect is increased in the crystal. Is increased. The cold deformation increases the number of electrons in the n-type thermoelectric material mass, increases the number of holes in the p-type thermoelectric material mass, and increases the number of electrons or holes in the mass of the true thermoelectric material . The pressure applied to the thermoelectric material mass during the cold deformation may be varied depending on the size of the thermoelectric material mass and the type of thermoelectric material, and in one embodiment, a pressure of 100 to 2000 MPa may be applied.
The increase in the carrier concentration due to the cold deformation is supported by the experimental example described later. According to the experimental example of the present invention, the carrier concentration increases as the number of cold deformation increases. Here, one cold deformation refers to a case where the thermoelectric material mass is pressurized once at a constant pressure.
On the other hand, according to the execution of the cold deformation, the carrier concentration increase phenomenon as described above occurs, as well as a change in the Seebeck coefficient and the thermal conductivity. That is, changes in the overall thermoelectric properties such as the carrier concentration, the Seebeck coefficient and the thermal conductivity are caused by the cold deformation.
The Seebeck coefficient and the thermal conductivity are also supported by the experimental examples described below. In the case of the Seebeck coefficient, the Seebeck coefficient tends to decrease as the number of cold deformations increases, and the thermal conductivity tends to increase as the number of cold deformations increases .
On the other hand, as the thermoelectric performance index is a function of the Seebeck coefficient, the thermal conductivity and the electric resistance (see the formula below), the thermoelectric performance index can be calculated based on the Seebeck coefficient, the thermal conductivity and the electric resistance value according to the number of cold deformations , The optimum number of cold deformations can be determined through the Seebeck coefficient, the thermal conductivity, and the electrical resistance value corresponding to the maximum value of the thermoelectric performance index. In other words, the thermoelectric material having the optimum thermoelectric performance index can be manufactured by performing the specific number of times of the cold-deforming process.
(expression)
(Z: thermoelectric performance index,?: Seebeck coefficient,?: Electrical resistivity,?: Thermal conductivity)
When the cold deformation process for the thermoelectric material mass is completed, a hot extrusion process for the thermoelectric material after the cold deformation is performed (S103). Specifically, a thermoelectric material having undergone cold deformation is charged into an extruder, and the thermoelectric material is produced by hot extrusion at a temperature of 300 to 550 占 폚. As described in the Background of the Invention, there is an advantage that the crystal orientation of the thermoelectric material for producing the thermoelectric material can be controlled through hot extrusion.
When the thermoelectric material manufactured through the hot extrusion process is subjected to heat treatment for preventing oxidation, the method for manufacturing thermoelectric material using the cold deformation according to an embodiment of the present invention is completed (S104). The heat treatment of the thermoelectric material can be carried out at a temperature of 270 to 400 캜 for 10 to 40 hours in a vacuum or an inert gas atmosphere.
The method of manufacturing the thermoelectric material using the cold deformation according to an embodiment of the present invention has been described above. As shown in FIG. 2, the apparatus for manufacturing a thermoelectric material according to the present invention may be constructed in various forms. In one embodiment, the thermoelectric material for producing a thermoelectric material mass by melting and cooling the thermoelectric material A lump producing device (210), a compressor (220) for performing cold deformation to apply pressure to the thermoelectric material mass at least one time to change a deblocking coefficient, a thermal conductivity and an electric resistance value of the thermoelectric material mass, a cold extruded thermoelectric material A
Further, based on the Seebeck coefficient, the thermal conductivity and the electric resistance value according to the number of cold deformations, the thermoelectric performance index is calculated using the following equation, and the thermoelectric performance index to specify the number of cold deformations indicating the maximum thermoelectric performance index An
(expression)
(Z: thermoelectric performance index,?: Seebeck coefficient,?: Electrical resistivity,?: Thermal conductivity)
Hereinafter, the present invention will be described in more detail with reference to experimental examples.
<Experimental Example 1>
n-type 90Bi 2 Te 3 -10Bi 2 Se 3 A thermoelectric material was prepared by hot-extruding a thermoelectric material mass by melt-coagulation method, then cold-deforming at a pressure of 400 MPa, (Refer to 'A' in FIG. 3), the thermal conductivity (see 'C' in FIG. 3) and the electrical resistance value (see D in FIG. 3) were measured and the measured Seebeck coefficient, thermal conductivity and electrical resistance And the thermoelectric performance index (refer to 'B' in FIG. 3) was calculated.
Referring to FIG. 3, the electric resistance value tends to decrease as the number of cold deformations increases (see 'D' in FIG. 3). The decrease of the electrical resistance value means that the carrier concentration in the thermoelectric material is increased. As the number of the cold deformations increases, the number of electrons increases as the thermoelectric material mass of Experimental Example 1 is n type. The increase in the carrier concentration with an increase in the number of cold deformations means that crystal defects such as vacancy and dislocation are increased in the thermoelectric material mass due to physical deformation of the thermoelectric material mass due to cold deformation Inferred. On the other hand, as the number of cold deformations increases, the Seebeck coefficient decreases and the thermal conductivity tends to increase (see 'A' and 'C' in FIG. 3).
As a result of calculating the thermoelectric performance index (refer to 'B' in FIG. 3) using the measured Seebeck coefficient, thermal conductivity and electrical resistance value, it was confirmed that the thermoelectric performance index there was.
The electrical resistance of the thermoelectric material, that is, the carrier concentration, is one of the various thermoelectric properties of thermoelectric materials. In order to produce a thermoelectric material having an optimum thermoelectric performance index, an optimal number of cold deformations must be performed considering both the Seebeck coefficient and the thermal conductivity .
<Experimental Example 2>
The thermoelectric material prepared in Experimental Example 1 was subjected to heat treatment at a temperature of 300 ° C for 30 hours. Then, the shear modulus, thermal conductivity and electrical resistance were measured in the same manner as in Experimental Example 1, and the measured shear coefficient, thermal conductivity and electrical resistance And the thermoelectric performance index was calculated using the values.
Referring to FIG. 4, it can be seen that the thermoelectric properties, that is, the Seebeck coefficient, the thermal conductivity, the electrical resistance, and the thermoelectric performance index are improved in comparison with the thermoelectric material before the heat treatment.
210: thermoelectric material ingot manufacturing apparatus 220: compressor
230: Hot extruder 240: Heat treatment apparatus
250: Thermoelectric performance index calculating device
Claims (9)
Performing cold deformation to apply pressure to the thermoelectric material mass to increase the carrier concentration in the thermoelectric material mass; And
And thermo-extruding the thermoelectric material subjected to the cold deformation to produce a thermoelectric material,
The cold deformation is performed at least once, and as the number of cold deformation increases, the Seebeck coefficient, thermal conductivity and carrier concentration of the thermoelectric material mass change,
Wherein the thermoelectric performance index is calculated using the following equation based on the Seebeck coefficient, the thermal conductivity and the electrical resistance value according to the number of cold deformations, and the number of cold deformations indicating the maximum thermoelectric performance index is specified A method for manufacturing a thermoelectric material using the same.
(expression)
(Z: thermoelectric performance index,?: Seebeck coefficient,?: Electrical resistivity,?: Thermal conductivity)
And the upper surface of the thermoelectric material mass is pressed to the upper plate at a constant pressure in a state in which the thermoelectric material mass is provided on the lower plate of the compressor is prepared by preparing a compressor having the upper plate and the lower plate, Method of manufacturing thermoelectric material using strain.
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