KR20020006338A - Method of producing thermoelectric transform materials by using the gas atomixation and the hot forming process - Google Patents

Abstract

PURPOSE: A method for manufacturing a Bi2Te3-based thermoelectric conversion material using a gas atomization process and a hot molding process is provided to guarantee a fine structure of a uniform single solid solution which has a uniform composition and doesn't almost have segregation, by using a gas atomization process to manufacture n-type and p-type Bi2Te3-based alloy powder which has a fine structure and is chemically uniform. CONSTITUTION: Sb2Te3 and Bi2Se3-added Bi2Te3-based alloy as an n-type composition and Bi2Te3-added Sb2Te3-based alloy as a p-type composition are used as a basic material, and are melted in a furnace which maintains a vacuum state of a predetermined pressure or an atmosphere of argon or nitrogen. The melted alloy is used to manufacture thermoelectric semiconductor powder which has a uniform structure and a fine spherical shape. The thermoelectric semiconductor powder is reduced. The reduced powder is cooling-molded and degassed. The cooling-molded material is hot-molded.

Description

Method of producing thermoelectric transform materials by using the gas atomixation and the hot forming process}

The present invention uses the gas atomization (part of rapid solidification method) to prepare uniform P-type and N-type Bi ₂ Te _3- based thermoelectric materials with uniform composition, fine structure and spherical powder form and subsequent processing 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 superior mechanical strength and thermoelectric performance compared to conventional processes by performing reduction treatment and hot plastic working.

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 at 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 direct current flows in the longitudinal direction when the temperature of both ends of the material of uniform composition with a certain length is different 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 is to produce a spherical Bi ₂ Te _{3 type} thermoelectric material of uniform composition and fine structure by using the gas spray method, and subsequently hot 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 forging, hot extrusion, and sintering.

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

FIG. 2 is a view schematically illustrating a configuration of a reducing apparatus for removing an oxide film of a thermoelectric semiconductor alloy powder manufactured in the rapid solidification gas spraying apparatus of FIG. 1;

3 is a view schematically showing the configuration of a hot forging apparatus for plastic processing the cold-formed body reduced in the reducing apparatus of FIG.

4 is a view schematically showing the configuration of a hot extrusion apparatus for plastic processing the cold-formed body reduced in the reducing apparatus of FIG.

FIG. 5 is a view schematically illustrating a configuration of a sintering furnace for plastic processing cold-formed bodies that have been reduced in the reducing apparatus of FIG. 2.

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

10: rapid solidification gas spraying device 11: alloy melting device

13: crucible 15: high frequency induction furnace

17: thermocouple 19: vacuum device

21: Orifice 23: Stopper

31: rapid solidification device 33: gas supply

35: air nozzle 37: chamber

39,51: powder collection container 47: cyclone

60: reducing device 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 Manufacturing a molten and molten alloy in a furnace where gas is maintained by using a gas spraying method to produce a uniform and fine spherical thermoelectric powder (S1);

Reducing the prepared thermoconductor powder (S2);

Cold forming and degassing the reducing 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.

In addition, 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 and 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 based thermoconductor alloy, the rapid solidification n-type of the microstructure and chemically homogeneous structure by using gas atomization as part of the rapid solidification method And p-type Bi ₂ Te ₃ -based alloy powder, to obtain a homogeneous single solid microstructure having a uniform composition and little segregation. After the alloy powder thus obtained is reduced and degassed, the n-type and p-type Bi ₂ Te ₃ system having high bending strength and comparatively excellent thermoelectric performance by using hot forming methods such as hot forging, hot extrusion and hot sintering processes. 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 gas spraying device 10 suitable for use in manufacturing the Bi ₂ Te ₃ based thermoelectric semiconductor powder according to the present invention is mainly an alloy melting device 11 and a rapid solidification disposed thereunder. Apparatus 31 is 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 molten metal. Vacuum chamber 19 which surrounds the heat generating part of the crucible 13 and the high frequency induction furnace 15, and the heat insulation furnace in the lower part of the crucible 13 so that a molten metal can fall freely outside when it opens. An orifice 21 installed in the stopper and a stopper 23 for opening and closing the orifice 21.

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 operated by opening the stopper 23 to open the orifice 21. Free fall into the chamber 37 of the rapid solidification device 31 disposed below.

The rapid solidification device 31 surrounds the gas supply 33 for supplying high pressure nitrogen gas or air into the chamber 37, the orifice 21 of the alloy melting device 11 and is supplied from the gas supply 33. The air nozzle 35 which injects the high pressure gas to the stem of the molten metal discharged through the orifice 21, and the thermoconductor powder which collides with the high pressure gas which the molten stem which passed through the orifice 21 are sprayed fall The chamber 37 and the primary powder collection container 39 for collecting the rapidly solidified alloy powder.

The supply passage 41 communicating with the injection nozzle 35 from the nitrogen gas supply 33 controls the pressure of nitrogen or air supplied from the solenoid valve 43 and the gas supply 33 for supplying and blocking nitrogen gas. Pressure regulator 45 for the purpose is installed. The size of the chamber 37 is determined in consideration of the flight distance of the alloy powder solidified so that the alloy powder is sufficiently cooled during rapid solidification. A gas outlet 49 for exhausting gas generated in the cyclone 47 is provided at a side wall of the cyclone 47 disposed at an outer side of the chamber 37, and a cyclone 47 is disposed below the cyclone 47. The secondary powder collection container 51 which collects the powder conveyed from the primary powder collection container 39 is provided. A viewing window 55 is provided on the side wall of the upper portion of the chamber 37 so that the alloy powder solidified in the chamber 37 can be sprayed by nitrogen gas to observe the outside of the chamber 37.

The process of manufacturing a fine and uniform Bi ₂ Te ₃ based thermoelectric alloy powder using a rapid solidification gas spraying device 10 configured as described above will be briefly described.

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. Melt to a temperature of and pour it into the warmer. At this time, the molten metal is maintained for about 30 minutes after melting to stabilize and stabilize the reaction.

When the maintenance of the molten alloy in the heating furnace is completed, the molten metal flows in the direction of the chamber 37 through the orifice 21 having a diameter of 2 to 6 mm opened by the action of the stopper 23, and at this time, the air nozzle 35 It is pulverized by high-speed nitrogen gas or air injected at a high pressure of 1.4 MPa, and the molten stem which changes according to the diameter of the orifice 21 collides with the gas to form a fine liquid powder, and while flying inside the chamber 37, It solidifies into a powder.

The solidified alloy powders are collected in the cyclone 47. Collected alloy powders are classified using a mechanical classifier to classify them by particle size. In this way a spherical powder is obtained in which the tissue is fine and a complete solid solution.

FIG. 2 is a view schematically illustrating a configuration of a reducing apparatus for removing an oxide film of a thermoelectric semiconductor alloy powder manufactured in the rapid solidification gas spraying apparatus of FIG. 1.

Referring to FIG. 2, the reducing device 60 includes a reducing gas supply device 61, and includes a preheating zone 62, a uniform heating zone 63, a post-heating zone 64, and an atmosphere cooling in which heat reduction is performed therein. Zone 65 is provided. Moreover, the main controller 67 provided with the temperature and gas amount adjusting device 66 is provided. The residual reducing gas is completely burned in the combustion apparatus 68 for safety, and the heating part is protected and warmed by the upper switch 69.

The surface of the Bi ₂ Te ₃ based thermoelectric alloy alloy powder obtained as a product in the rapid solidification gas spraying device 10 shown in FIG. 1 is surrounded by an oxide film. And deterioration of mechanical properties. Therefore, the reduction is performed by using the reduction device 60 shown in FIG.

To this end, the alloy powder is charged into the preheating zone 62 of the reducing device 60, sealed, and then vacuumed or nitrogen or argon gas is removed to remove the atmosphere, and hydrogen or carbon gas is continuously supplied to provide a uniform cost. While passing through the heat zone 63 and the post-heating zone 64, a reduction treatment is performed within a temperature range of about 200 to 400 ° C. and cooled in the atmosphere cooling zone 65.

Rapidly solidified n-type and p-type Bi ₂ Te ₃ -based alloy powders reduced in the reducing apparatus 60 shown in FIG. 2 are about 100 tons using a cold forming press (not shown) known for easy handling. Pressurized to cold forming.

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.

FIG. 3 is a view schematically illustrating a configuration of a hot forging apparatus for plastic processing a cold formed body reduced in the reducing apparatus of FIG. 2.

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 illustrating a configuration of a hot extrusion apparatus for plastic processing cold-formed bodies that have been reduced in the reducing 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, 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 molded article thus obtained 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 illustrating a configuration of a sintering furnace for plastic processing cold-formed bodies that have been reduced in the reducing 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 rapid solidification n-type of the microstructure and chemically homogeneous structure by using gas atomization as part of the rapid solidification method And by producing a p-type Bi ₂ Te ₃ alloy powder, it was possible to secure a microstructure of a homogeneous single solid solution having a uniform composition and little segregation.

After the alloy powder thus obtained is reduced and degassed, the n-type and p-type Bi ₂ Te ₃ system having high bending strength and comparatively excellent thermoelectric performance by using hot forming methods such as hot forging, hot extrusion and hot sintering processes. An alloy molded body could be produced, and in addition, the productivity was improved by about 2 times or more compared with the existing 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 Manufacturing a molten and molten alloy in a furnace where gas is maintained by using a gas spraying method to produce a uniform and fine spherical thermoelectric powder (S1); Reducing the prepared thermoconductor powder (S2); Cold forming and degassing the reducing powder (S3); And A method of manufacturing a Bi ₂ Te ₃ -based thermoelectric conversion material comprising the step (S4) of hot forming the cold formed product obtained in 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.