KR20020010768A - Method of producing thermoelectric transform materials by using the twin rolling and the hot forming process - Google Patents

Abstract

PURPOSE: A method is provided to manufacture a thermoelectric semiconductor green compact having high strength and superior thermoelectric properties consecutively using hot forming such as hot forging, hot extrusion and sintering after manufacturing and pulverizing a flake shaped Bi2Te3 based thermoelectric material in which composition is uniform, and structure is fine using twin rolling. CONSTITUTION: The method for manufacturing a Bi2Te3 based thermoelectric material comprises the steps of fusing a Bi2Te3 based alloy to which n type compositions of Sb2Te3 and Bi2Se3 are added, and a Sb2Te3 based alloy to which p type composition of Bi2Te3 is added as basic materials in a furnace where a constant pressure of vacuum, or an argon or nitrogen atmosphere is maintained, and manufacturing the fused alloy into thermoelectric semiconductor flakes having homogeneous and fine structure using twin rolling, wherein CdCl2 and Sbi2 are added to the basic materials as a dopant in case of n type while Te is added to the basic materials as a dopant in case of p type; pulverizing the manufactured thermoelectric semiconductor flakes in a fine powder form; cold forming and degassing the pulverized thermoelectric semiconductor powder; and hot forming the cold green compact that is obtained from the cold forming and degassing step, wherein the cold green compact is charged into a hot forging equipment, a hot extruder or a sintering furnace so that it is preheated and press formed, extruded, or hot sintered, thereby obtaining a green compact having a high density and superior bending strength and thermoelectric performance.

Description

Method of producing thermoelectric transform materials by using the twin rolling and the hot forming process

The present invention uses twin rolling, which is part of the rapid solidification method, to prepare P-type and N-type Bi ₂ Te ₃ -based thermoelectric materials with uniform composition, fine structure, and homogeneous powder in spherical powder form, and then process The present invention relates to a method for producing P-type and N-type Bi ₂ Te ₃ -based thermoelectric molded products for mass production, which have excellent mechanical strength and also secure thermoelectric performance, by performing hot plastic working as a method.

The thermoelectric semiconductor material has a Seebeck effect in which electrons or holes are diffused to a lower temperature when there is a temperature difference across the material, and heat is generated and endothermic to both junctions when a direct current is applied to a circuit connecting dissimilar materials. When the phenomenon occurs and the direction of the current is reversed, the Peltier effect using the phenomenon that the relationship is changed with each other, and the temperature distribution is kept constant when the temperature of both ends of the material of uniform composition with a certain length is different and the DC flows in the longitudinal direction In order to achieve the endothermic or exothermic phenomena in the material, the Thomson effect is used to convert thermal energy into electrical energy or directly into thermal energy.

By using this principle, thermoelectric semiconductor materials can be used in the fields of thermoelectric power generation and thermoelectric cooling, which are future energy fields, so that various electronic devices such as infrared sensors, laser diodes and focal plate cooling of CCD devices can be used. It is applied to local cooling of IC products, and is also applied to medical and scientific thermostats, thermoelectric cooling refrigerators, air conditioners and heat exchangers.

Bi ₂ Te ₃ based thermoelectric materials, which are spotlighted as cooling thermoelectric materials due to their high performance index near room temperature, are manufactured by the conventional single crystal manufacturing method, and the unit crystals are rhombohedral. Therefore, it has strong anisotropy in electrical and thermoelectric properties, and because it breaks easily along the wall interface during processing, it has a considerable loss of materials and processing difficulties.

In addition, when the powder is manufactured in the form of powder metallurgy using the casting-grinding method, the cast product itself forms a highly heterogeneous structure, which is caused by the presence of segregation even after grinding, incorporation of impurities in the grinding media, and coarsening of the tissue. It is a cause of deterioration of thermoelectric properties and strength, and a decrease in productivity is a disadvantage.

The present invention has been made to solve the conventional problems as described above, the object of the present invention by using a twin roll method to produce and pulverize Bi ₂ Te ₃ type thermoelectric material of uniform flake shape and fine structure Then, the present invention provides a method of manufacturing a thermoelectric semiconductor molded body having high strength and excellent thermoelectric properties by using a hot plastic working method such as hot forging, hot extrusion and sintering.

1 is a view schematically showing the configuration of a rapid solidification twin roll apparatus suitable for producing n-type and p-type thermoelectric semiconductor alloy powder using the rapid solidification twin roll method according to the present invention;

FIG. 2 is a view schematically showing the configuration of a pulverizing apparatus for pulverizing the thermoelectric alloy flakes prepared in the rapid solidification twin roll apparatus of FIG. 1 in the form of fine powder;

3 is a view schematically showing the configuration of a hot forging apparatus for plastic processing a thermoelectric semiconductor alloy powder obtained as a product in the grinding apparatus of FIG.

4 is a view schematically showing the configuration of a hot extrusion device for plastic processing a thermoelectric semiconductor alloy powder obtained as a product in the grinding device of FIG.

FIG. 5 is a view schematically showing a configuration of a sintering furnace for plastic working thermoelectric semiconductor alloy powder obtained as a product in the crushing apparatus of FIG. 2.

<Explanation of symbols for the main parts of the drawings>

10: rapid solidification double roll device 11: alloy melting device

13,23: crucible 15: high frequency induction furnace

17,24: thermocouple 20: thermostat

21: Orifice 22: Resistance heating wire

30: rapid solidification device 32: twin roll

34: electric feed device 35: flake collection container

70: hot forging device 80: hot extrusion device

90: sintering furnace

In order to achieve the above object, the present invention,

n-type composition of Sb ₂ Te ₃ and Bi ₂ Se ₃ adding Bi ₂ Te ₃ based alloys, and the p-type composition of Bi ₂ Te ₃ is added Sb ₂ Te ₃ based alloys a vacuum or an argon or a nitrogen atmosphere at a predetermined pressure as the base material Melting and melting the molten alloy in the furnace in which the molten alloy is prepared by using a twin roll method to produce a uniform and fine thermal semiconductor flake (S1);

Grinding the prepared thermoconductor flakes in the form of fine powder (S2);

Cold forming and degassing the ground thermoelectric semiconductor powder (S3); And

It provides a method for producing a Bi ₂ Te ₃ system thermoelectric conversion material comprising the step (S4) of hot forming the cold-formed body obtained from the step (S3).

In the step (S1), in the case of a n-type dopant in the base material is added to CdCl ₂ and Sbi ₂ was added to the case of p-Te.

Further, in the step (S4), the cold molded body is charged into a hot forging device, a hot extrusion device or a sintering furnace, and then preheated, press-molded, extruded or hot sintered to obtain a molded product having high density, excellent bending strength and thermoelectric performance. Get

As mentioned above, according to the present invention, in the preparation of the Bi ₂ Te _{3 type} thermoconductor alloy, the rapid solidification n-type of fine and chemically homogeneous tissues using twin rolling, which is part of the rapid solidification method And p-type Bi ₂ Te ₃ -based alloy flakes to obtain a homogeneous single solid microstructure having a uniform composition and little segregation. In addition, the alloy flakes thus obtained are pulverized and degassed, and then n-type and p-type Bi ₂ Te ₃ based on high bending strength and relatively high thermoelectric performance by using hot forming methods such as hot forging, hot extrusion and hot sintering. An alloy molding is produced.

Hereinafter, a method of manufacturing a Bi ₂ Te ₃ based thermoelectric conversion material according to the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, the rapid solidification twin roll device 10 suitable for use in manufacturing Bi ₂ Te ₃ based thermoconductor flakes according to the present invention is mainly an alloy melting device 11 and a thermostat disposed below it. 20 and the rapid solidification apparatus 30 are provided.

First, the alloy melting apparatus 11 is a high frequency induction furnace that surrounds the crucible 13 to heat the crucible 13 and the crucible 13 to contain an alloy for the Bi ₂ Te _{3 type} thermoelectric semiconductor. (15), the thermocouple 17 provided in the crucible 13 for measuring the temperature of a molten metal is provided.

The thermostat 20 disposed below the crucible 13 is a crucible 23 heated by a resistance heating wire 22 to maintain the molten alloy at a constant temperature in the crucible 13 of the alloy melting apparatus 11. ) And a thermocouple 24 for temperature measurement, and an orifice 21 installed below the crucible 23 so that the molten metal can freely fall to the outside when opened.

In the crucible 13 heated by the high-frequency induction path 15, the Bi ₂ Te ₃ -based thermoconductor alloy molten metal melted in a vacuum or gas atmosphere is used to orifice 21 installed in the crucible 23 of the thermostat 20. Through this, free fall into the pair roll 32 of the rapid solidification device 30 disposed thereunder.

Rapid solidification device 30 is an electric motor (not shown) for rotating the pair of rolls 32 at high speed, an electric feeder 34 for reciprocating the thermostat 20, and a pair of rolls to collect the solidified alloy flakes. (32) It is provided with a flake collection container 35 disposed below.

Using the rapid solidification twin roll device 10 configured as described above will be briefly described a process for producing a fine and uniform Bi ₂ Te ₃ system thermoelectric alloy powder.

n-type composition of Sb ₂ Te ₃ and Bi ₂ Se ₃ adding Bi ₂ Te ₃ based alloys, and the p-type composition of Bi ₂ Te ₃ is added n-type as the dopant if necessary to take the Sb ₂ Te ₃ based alloys as the base material In the case of p-type, the alloy to which CdCl ₂ and Sbi ₂ are added and Te is added is about 600 to 800 ° C. in a vacuum of 10 ⁻² to 10 ⁻⁵ torr or a high frequency induction furnace 15 in which an argon or nitrogen atmosphere is maintained. It melts at the temperature of and pours it into the crucible 23 of the heating furnace 20. At this time, the molten metal is maintained for about 30 minutes after melting to stabilize and stabilize the reaction.

When the molten metal is poured into the crucible 23 of the heating furnace 20, the molten metal flows in the direction of the twin roll 32 through an orifice 21 having a diameter of 2 to 6 mm, and at this time, the twin roll 32 rotating at 100 to 1,000 rpm. Crushing between them takes the form of flakes, causing rapid solidification. At this time, the size and rapid solidification effect of the flakes change depending on the spacing (0 to 5 mm) of the rotating twin roll 32 and the diameter of the orifice 21.

The solidified alloy flake is collected in the flake collecting container (35).

FIG. 2 is a view schematically illustrating a configuration of a pulverizing apparatus for pulverizing the thermoelectric alloy flakes manufactured in the rapid solidification twin roll apparatus of FIG. 1 in the form of fine powder.

Referring to FIG. 2, the grinding device 40 includes an alumina container 41, and inside the container 41, an alumina ball 42 capable of finely grinding a quick solidified thermoelectric semiconductor flake is provided with a flake 43. It is charged together. The alumina container 41 is designed to be rotated on the rotating table 45 which is rotated by the rotary motor 44, and is equipped with a nozzle 46 for supplying a vacuum or atmosphere gas.

The Bi ₂ Te ₃ -based thermoconductor alloy powder obtained as a product in the crusher 40 shown in FIG. 2 is cold molded by applying a pressure of about 100 tons using a known cold forming press (not shown) for easy handling. Make it.

The cold formed body formed into a billet in the cold forming apparatus is plastically processed using the hot forging apparatus 70, the hot extrusion apparatus 80, or the sintering furnace 90.

3 is a view schematically showing the configuration of a hot forging apparatus for plastic processing a thermoelectric semiconductor alloy powder obtained as a product in the crushing apparatus of FIG.

Referring to FIG. 3, the hot forging device 70 includes a molding die 71, a die heating device 72, a pressurizing device 73, a main body 74, an upper punch 75, a support rod 76, and a billet. The preheater 77 and the controller 78 are provided.

The cold formed body is charged into the forming die 71 of the hot forging device 70 after degassing, and then preheated together with the forming die 71 within a temperature range of about 350 to 500 ° C., and then the upper punch 75 is lowered. Press molding within the temperature range to produce a high-strength molded body having a density of 99% or more. The bending strength of the molded article thus obtained is 50 to 80 MPa, and is relatively excellent as thermoelectric performance Z = 2.7 to 3.0 x 10 ^-3 / K.

FIG. 4 is a view schematically showing the configuration of a hot extrusion apparatus for plastic processing a thermoelectric semiconductor alloy powder obtained as a product in the crushing apparatus of FIG. 2.

As shown in FIG. 4, the hot extrusion device 80 includes a pressurization device 81, a container 82, and a container heating device 83, a die 84, a ram 85, a cylinder 86, and a main support. 87, a billet preheating furnace 88, and the like.

The degassed cold formed body is molded to a theoretical density of 99% or more in the die 84 and the container 82 preheated to the same temperature within a temperature range of about 350 to 500 ° C. using the hot extrusion device 80. The thus obtained molded product forms a uniform and fine single solid solution when the microstructure observed by the scanning electron microscope and the X-ray analysis are examined. The bending strength of the molded body is 60 to 90 MPa, and is relatively excellent as the thermoelectric performance Z = 2.7 to 3.0 x 10 ^-3 / K.

FIG. 5 is a view schematically showing a configuration of a sintering furnace for plastic working thermoelectric semiconductor alloy powder obtained as a product in the crushing apparatus of FIG. 2.

As shown in FIG. 5, the sintering furnace 90 includes a controller 91, a vacuum pump 92, an atmosphere gas supply device 92, a mold 93, and a liner 94 capable of maintaining a constant temperature and atmosphere. ), A pressurizing device (95) consisting of an upper and a lower ram, a heating device (96), and an insulating portion (97).

The degassed cold formed body is hot sintered in a sintering furnace 90 at a temperature of about 400 to 550 ° C. in a vacuum or nitrogen gas atmosphere. The bending strength of the thus obtained sintered compact exhibits 30 to 35 MPa and is relatively excellent in thermoelectric performance Z = 2.5 to 3.5 × 10 ⁻³ / K.

As mentioned above, according to the present invention, in the preparation of the Bi ₂ Te ₃ based thermoconductor alloy, the structure is fine and chemically homogeneous by using twin rolling and a suitable grinding device which are part of the rapid solidification method. By preparing fast solidified n-type and p-type Bi ₂ Te ₃ alloy powders, it was possible to secure a homogeneous single solid solution with uniform composition and almost no segregation.

Also, after degassing the alloy powder thus obtained, n-type and p-type Bi ₂ Te ₃ based alloy moldings having high bending strength and comparatively excellent thermoelectric performance by using hot forming methods such as hot forging, hot extrusion and hot sintering processes. In addition, the productivity was also improved by about 2 times or more compared with the conventional method.

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. It will be appreciated.

Claims (5)

n-type composition of Sb ₂ Te ₃ and Bi ₂ Se ₃ adding Bi ₂ Te ₃ based alloys, and the p-type composition of Bi ₂ Te ₃ is added Sb ₂ Te ₃ based alloys a vacuum or an argon or a nitrogen atmosphere at a predetermined pressure as the base material Melting and melting the molten alloy in the furnace in which the molten alloy is prepared by using a twin roll method to produce a uniform and fine thermal semiconductor flake (S1); Grinding the prepared thermoconductor flakes in the form of fine powder (S2); Cold forming and degassing the ground thermoelectric semiconductor powder (S3); And It provides a method for producing a Bi ₂ Te ₃ system thermoelectric conversion material comprising the step (S4) of hot forming the cold-formed body obtained from the step (S3). The method of claim 1, wherein said step (S1) in the base case of the n-type as a dopant to the material CdCl ₂ and Sbi ₂ was added and Bi ₂ Te ₃ based thermoelectric further comprising a step of adding the case of a p-type Te a Method of manufacturing the conversion material. The method of claim 1, wherein in the step (S4), the cold molded body is charged into a molding die of a hot forging apparatus, and then preheated and pressed to form a density of 99% or more, a bending strength of 50 to 80 MPa, and Z = 2.7 to 3.0 × A method for producing a Bi ₂ Te ₃ based thermoelectric conversion material, characterized in that a high strength molded body having a thermoelectric performance of 10 ⁻³ / K is produced. The method of claim 1, wherein in the step (S4), the cold molded product is charged into a hot extrusion apparatus, preheated and extruded to obtain a density of 99% or more, a bending strength of 60 to 90 MPa, and Z = 2.7 to 3.0 × 10 ^-3. A method for producing a Bi ₂ Te ₃ -based thermoelectric material, comprising producing a single solid solution having a thermoelectric performance of / K. The sintered compact according to claim 1, wherein in the step S4, the cold molded body is charged into a sintering furnace and hot-sintered to exhibit a bending strength of 30 to 35 MPa and a thermoelectric performance of Z = 2.5 to 3.5 x 10 ^-3 / K. Method for producing a Bi ₂ Te ₃ system thermoelectric conversion material, characterized in that for producing.