KR100795194B1 - Method for fabricating thermoelectric material by mechanical milling-mixing and thermoelectric material fabricated thereby - Google Patents

Abstract

The present invention relates to a method of manufacturing a thermoelectric material whose mechanical properties are mechanically milled to a different size and the milled thermoelectric material is controlled by a combination of mixing processes, and a thermoelectric material manufactured by the method. Preparing thermoelectric material powders having different particle characteristics, uniformly mixing powders having different particle characteristics, and sintering the mixed powder uniformly. Provided is a method of manufacturing a thermoelectric material.

Conventional general powder metallurgy method (simple mechanical milling) that does not undergo mechanical milling + mixing process by using a thermoelectric material manufacturing method according to the present invention, that is, a mechanical milling + mixing process using a thermoelectric material powder dissolved + pulverized initial raw material Compared with the thermoelectric material manufactured by the Bi ₂ Te ₃ , about 130%, PbTe has about 170% of the improved performance index has the advantage of manufacturing an improved thermoelectric material.

Thermoelectric Materials, Milling, Blending, Powders, PbTe

Description

Method for fabricating thermoelectric material by mechanical milling-mixing method and thermoelectric material thereby {Method for fabricating thermoelectric material by mechanical milling-mixing and thermoelectric material fabricated Thus}

1 is Bi ₂ Te ₃ according to a first embodiment of the present invention. It is a flowchart explaining the manufacturing method of a thermoelectric material.

FIG. 2 is a graph illustrating thermoelectric properties of Bi ₂ Te ₃ thermoelectric materials manufactured according to the first embodiment.

3 is a flowchart illustrating a method of manufacturing a PbTe thermoelectric material, which is a second embodiment according to the present invention.

4 is a graph illustrating thermoelectric properties of the PbTe thermoelectric material manufactured according to the second embodiment.

The present invention relates to a method of manufacturing a thermoelectric material by a mechanical milling-mixing process and a thermoelectric material produced thereby. More specifically, the present invention relates to a method of manufacturing a thermoelectric material whose mechanical properties are controlled by mechanical milling of different sizes and the milled thermoelectric material is controlled by a combination of mixing processes, It relates to a thermoelectric material.

In general, a thermoelectric material is an energy conversion material in which electrical energy is generated when a temperature difference is applied between both ends of a material, and conversely, a temperature difference is generated between both ends of a material when an electric energy is applied to the material.

These thermoelectric materials were found in the early 19th century after the discovery of thermoelectric phenomena, Seebeck effect, Peltier effect and Thomson effect. It is developed as a thermoelectric material and recently used as a special power supply device such as mountain wallpaper, space, military, etc. using thermoelectric power generation, and precise temperature control in semiconductor laser diode, infrared detection device, etc. It is used in optical communication laser chiller, chiller and water cooler, semiconductor temperature control device and heat exchanger.

The energy conversion efficiency of these thermoelectric materials is expressed as Z = α ² / ρκ (α: Seebeck coefficient, ρ: electrical resistivity, κ: thermal conductivity). It means that the efficiency is high.

Therefore, in order to obtain a thermoelectric material having a high performance index, it is necessary to increase the Seebeck coefficient of the material or to reduce the electrical resistivity and thermal conductivity.

However, in general, it is known that a thermoelectric material having a low electrical resistivity has a high thermal conductivity, and a thermoelectric material having a high electrical resistivity has a low thermal conductivity.

The reason for this conflicting characteristic is that Seebeck coefficient and electrical resistivity depend mainly on scattering of charge and thermal conductivity mainly on scattering of phonon. More specifically, when the scattering of charge increases in the thermoelectric material, the electrical resistivity increases, and when the scattering of the phonons constituting the thermoelectric material increases, the thermal conductivity decreases, and consequently, scattering of the charge and scattering of the lattice. This is because they have opposite effects on the performance index.

As is well known, as a material processing technique for producing a thermoelectric material having a high performance index, mainly a single crystal growth method and a powder metallurgy method (dissolution + coagulation + grinding + sintering, simple mechanical milling) are used.

However, the thermoelectric material manufactured by the single crystal growth method is a single crystal material, which is advantageous for the improvement of the electrical properties, but has a limitation in the improvement of the thermal properties.The thermoelectric material manufactured by the powder metallurgy method is a polycrystalline material, which is advantageous for the improvement of the thermal properties, It has the disadvantage of decreasing the performance index due to the electrical resistivity.

The present invention has been proposed to solve the above-described problems, in order to overcome the disadvantages of the conventional material processing technology, it is possible to efficiently simultaneously and simultaneously give a thermoelectric material by controlling the thermal / electrical properties having properties opposite to each other To provide a new method of manufacturing thermoelectric materials.

That is, an object of the present invention is to provide a method for producing a polycrystalline thermoelectric material capable of simultaneously controlling electrical resistivity and thermal conductivity.

To this end, in the present invention, two types of thermoelectric material powders having different thermal / electrical properties are prepared by mechanical milling of the thermoelectric material powders which have been melted, solidified and pulverized, and then the two powders are uniformly mixed at a predetermined ratio. An object of the present invention is to provide a method for producing a desired thermoelectric material by molding and sintering the obtained mixed powder.

The thermoelectric material manufacturing method according to the first embodiment of the present invention comprises the steps of (1) preparing a Bi ₂ Te ₃ system raw powder through melting, coagulation and pulverization, and (2) different mechanical milling times for the raw powder. Preparing a first powder and a second powder (the mechanical milling time for the first powder is less than the mechanical milling time for the second powder), and (3) the first and Uniformly mixing the second powder; and (4) molding and sintering the powder mixed in the step (3).

In the first embodiment according to the present invention, the ratio of the particle size of the first powder and the particle size of the second powder is 4: 1.

In the first embodiment according to the present invention, the mixing ratio in the step (3) is characterized in that the second powder is 20 ~ 80wt% with respect to the first powder.

The thermoelectric material manufacturing method according to the second embodiment of the present invention comprises the steps of (1) preparing a PbTe-based raw powder through melting, coagulation, and pulverization; and (2) a first powder by varying the mechanical milling time for the raw powder. And preparing a second powder (the mechanical milling time for the first powder is less than the mechanical milling time for the second powder), and (3) the first and second powders produced by the mechanical milling. Uniform mixing and (4) forming and sintering the powder mixed in the step (3).

In a second embodiment according to the present invention, the ratio of the particle size of the first powder and the particle size of the second powder is 7: 1.

In the second embodiment according to the present invention, the mixing ratio in the step (3) is characterized in that the second powder is 20 ~ 80wt% with respect to the first powder.

Finally, the present invention is characterized by the thermoelectric material produced in the manufacturing method of the first or second embodiment.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 and 2 are flow charts illustrating a method of manufacturing a Bi ₂ Te ₃ thermoelectric material, which is a first embodiment of the present invention, and a graph of a figure of merit of the thermoelectric material thus manufactured, and FIGS. 3 and 4 A flowchart illustrating a method of manufacturing PbTe thermoelectric material, which is a second embodiment, and a figure of merit graph of the thermoelectric material thus manufactured are shown.

Hereinafter, a first preferred embodiment of the present invention will be described with reference to FIGS. 1 and 2.

First Example

1 is a flowchart illustrating a method for manufacturing a Bi ₂ Te ₃ thermoelectric material proposed by the present invention.

The method for producing Bi ₂ Te ₃ thermoelectric material proposed in the present invention is largely divided into (1) raw material powder production step, (2) mechanical milling step, (3) mechanical milling powder, (4) Forming and sintering the mixed powder.

Hereinafter, each step will be described in detail.

Raw material powder manufacturing

The raw material powder manufacturing step is a process of preparing Bi ₂ Te ₃ powder of a predetermined size by dissolving, coagulating and pulverizing the powder of Bi and Te.

More specifically, in the present invention, the powder or bulk containing Bi and Ti components is weighed in a Bi ₂ Te ₃ composition and vacuum-melted in a vacuum furnace of 10 ^-5 torr to produce an alloy ingot, followed by alumina. It was ground using a mortar to prepare Bi ₂ Te ₃ starting powder having an average particle diameter of 200 μm.

Mechanical milling

The mechanical milling step is a process of manufacturing thermoelectric material powders of different sizes by varying the mechanical milling time with respect to Bi ₂ Te ₃ starting powder having an average particle diameter of 200 μm manufactured by the raw material powder manufacturing step.

More specifically, in the present invention, Bi ₂ Te ₃ powder prepared in the raw material powder manufacturing step was mechanically milled using a rotary ball mill.

Mechanical milling uses a stainless steel mill container with an internal diameter of 70 mm and a length of 100 mm and a stainless steel ball with a diameter of 6 mm. The ball loading is 50% of the volume of the mill container and the loading ratio of the balls and powder is 50: 1. Was carried out.

Mechanical milling was performed for 24 hours and 100 hours to prepare two kinds of Bi ₂ Te ₃ thermoelectric powders having different particle characteristics. In this case, the average particle size when mechanical milling was performed for 24 hours was 4 μm, and the average particle size when mechanical milling was performed for 100 hours was 1 μm.

In the present invention, the difference in the mechanical milling time is merely exemplary, and when the difference between the average particle size by the short time mechanical milling and the average particle size by the long time mechanical milling is 2: 1 or more, the mechanical proposed by the present invention It is desirable to see the characteristics according to the difference in milling time.

Mechanical Milled  Mix of powder

The mixing of the mechanically milled powder may be performed by mechanically milling the powder for a long time using two kinds of Bi ₂ Te ₃ powders prepared to have different particle characteristics (ie, powder having a small particle size). The mixing ratio of 20 to 80wt.% Is a process of uniformly mixing. Powder mixing in this process was carried out for about 30 minutes using a "turbular shaker".

Forming and sintering

In the step of forming and sintering the mixed powder, the mixed powder is molded at a molding pressure of 1t / cm2 using a die, and then, at 1,500 ° C at a pressure of 1t / cm2 in an arcon atmosphere using a "hot press". Time was sintered under pressure.

2 shows a change in the performance index of the thermoelectric material according to the mixing ratio of the mechanically milled powder (small particle size powder) of the sintered body of the mixed powder.

As can be seen in Figure 2, the sintered body produced through the mixing process of the powder having different sizes show a higher performance index than the sintered body produced by the general powder metallurgy process (ie, simple mechanical milling) without the mixing process It can be seen that.

As can be seen in Figure 2, the performance index of the sintered body manufactured through the mechanical milling + mixing process increases as the mixing ratio of the mechanically milled powder (small particle size powder) increases for a long time. In particular, when the mixing ratio of the mechanically milled powder for a long time is 40wt.%, It can be seen that the performance index decreases after showing the maximum value. In particular, when the mechanically milled powder is mixed 40wt.% By the mechanical milling + mixing method, it can be seen that the performance index is increased by about 130% than when not mixed.

Thus, using powders dissolved and pulverized as an initial raw material, Bi ₂ Te ₃ powders having different thermal / electrical properties were prepared by mechanical milling, and then mixed powders were prepared to form mixed powders, followed by molding and sintering. In the powder metallurgy process (simple mechanical milling), Bi ₂ Te ₃ thermoelectric materials having a higher performance index were prepared.

Hereinafter, a second preferred embodiment of the present invention will be described with reference to FIGS. 3 and 4.

2nd Example

3 is a flowchart illustrating a method of manufacturing a PbTe thermoelectric material proposed by the present invention.

The method for producing a PbTe thermoelectric material proposed in the present invention is a step of mixing (1) a raw material powder manufacturing step, (2) a mechanical milling step, (3) a mechanical milling powder, as in the first embodiment, (4) forming and sintering the mixed powder.

Hereinafter, each step will be described in detail.

Raw material powder manufacturing

The raw material powder manufacturing step is a process of preparing PbTe powder having a predetermined size by dissolving, coagulating and pulverizing the powder of Pb and Te.

More specifically, in the present invention, an alloy ingot is prepared by weighing a powder or bulk containing Pb and Te components in a PbTe composition and vacuum melting in a vacuum furnace of 10 ^-5 torr, followed by grinding to obtain an average particle diameter of 300 µm. PbTe initial powder was prepared.

Mechanical milling

The mechanical milling step is a process of preparing thermoelectric material powders of different sizes by varying the mechanical milling time with respect to the PbTe initial powder having an average particle diameter of 300 μm manufactured by the raw material powder manufacturing step.

More specifically, in the present invention, the PbTe powder prepared in the raw material powder manufacturing step was mechanically milled using a rotary ball mill.

Mechanical milling uses a stainless steel mill with an internal diameter of 70 mm and a length of 100 mm and a stainless steel ball with a diameter of 6 mm. The ball loading is 50% of the volume of the mill container and the loading ratio of the balls and powder is 50: 1. Was carried out.

Mechanical milling was performed for 6 hours and 50 hours to prepare two kinds of powders each having a particle size of 75 to 200 μm and a particle size of 1 to 10 μm.

That is, the average particle size when the mechanical milling for 6 hours was 75 ~ 200㎛, the average particle size 1 ~ 10㎛ when mechanical milling for 50 hours.

In the present invention, the difference in the mechanical milling time is merely exemplary, and when the difference between the average particle size by the short time mechanical milling and the average particle size by the long time mechanical milling is 7: 1 or more, it is proposed in the present invention. It is desirable to see the characteristics according to the difference in the mechanical milling time.

Mechanical Milled  Mix of powder

In the mixing step of the mechanical milling powder, two kinds of powders each prepared to have different particle characteristics by the mechanical milling process, that is, powders having a particle size of 75 to 200 μm (short-term mechanical milling powder) and Two kinds of powders having a particle size of 1 to 10 μm (mechanical milled powder for a long time) were used, and uniformly mixed so that the mixing ratio of the powder having a particle size of 1 to 10 μm was 20 to 80 wt.%. The mixing process was carried out for about 30 minutes using a turbular shaker as in Example 1.

Forming and sintering

In the step of forming and sintering the mixed powder, the mixed powder is molded at a molding pressure of 1t / cm2 by using a die and then hot pressing at 750 ° C for 1 hour at a pressure of 1t / cm2 in an irgon atmosphere. Pressurized and sintered.

Figure 4 shows the change in the performance index of the thermoelectric material according to the mixing ratio of the powder (powder with a small particle size) of the mechanically milled powder of the mixed powder for a long time.

As can be seen in Figure 4, it can be seen that the sintered body manufactured through the mixing process shows a higher performance index than the sintered body manufactured by the general powder metallurgy process (simple mechanical milling) without the mixing process.

The performance index of the sintered body manufactured through the mechanical milling + mixing process increases as the mixing ratio of the mechanically milled powder (small particle size powder) increases for a long time and shows a maximum value at 40 wt.% And then decreases.

In particular, when the mechanical milling powder (powder having a small particle size) is mixed 40wt.% By a mechanical milling + mixing process, it can be seen that the performance index is increased by about 170% compared to the case where the mixing process is not performed.

Thus, using powders dissolved and pulverized as an initial raw material, PbTe powders having different thermal / electrical properties were prepared by mechanical milling, and then mixed with each other to prepare mixed powders, followed by molding and sintering. In the case of (simple mechanical milling), a PbTe thermoelectric material having a higher performance index was manufactured.

As can be seen from the first and second embodiments described above, when a material having a low electrical resistivity (powder having a small particle size) is added to a material having a high electrical resistivity (a powder having a large particle size) and mixed, The electrical resistivity depends on the electrical resistivity value of a material with a high electrical resistivity when the amount of the substance having a low electrical resistivity is small. However, when the amount of the substance having a low electrical resistivity is more than a certain amount, the electrical resistivity of the whole mixed material becomes the electrical resistivity. It can be seen that it depends on the electrical resistivity value of the low material.

Therefore, by using this characteristic of the electrical resistivity, which is one of the functions that influence the performance index of the thermoelectric material, it is possible to control the electrical resistivity and thermal conductivity independently, thereby achieving low electrical resistivity and low thermal conductivity at the same time. Thermoelectric materials with better performance indices will be obtained.

Embodiments of the present invention described above are only specific examples of the technical idea of the present invention, and processing conditions such as pressure, temperature, time, particle size, etc. in the manufacturing process may be selectively modified by those skilled in the art.

In particular, the present invention has a core technical feature in that it forms and sinters thermoelectric material powders milled in different sizes, and thus all thermoelectrics undergoing the mechanical milling process proposed by the present invention to produce thermoelectric materials. It is to be understood that all methods of making materials belong to the invention within the scope of the claims set out below.

As described above, in the present invention, by using a manufacturing method in which thermoelectric material powders having different sizes are mixed at a predetermined ratio, and then molded and sintered, a relatively high performance index is compared with conventional thermoelectric materials made of powder of the same size. A thermoelectric material having a was obtained.

When the thermoelectric material having a high performance index manufactured according to the present invention is used in an electronic device or the like, a cooling effect can be obtained more efficiently than in the conventional case.

Claims (7)

(1) preparing a Bi ₂ Te _3- based powder by melting, solidifying and pulverizing; (2) manufacturing a first powder and a second powder by varying the mechanical milling time for the raw material powder (the mechanical milling time for the first powder is less than the mechanical milling time for the second powder); (3) uniformly mixing the first and second powders produced by the mechanical milling, (4) A method of manufacturing a thermoelectric material, comprising forming and sintering the powder mixed in the step (3). The method of claim 1, The ratio of the particle size of the first powder and the particle size of the second powder is 4: 1, characterized in that. The method according to claim 1 or 2, The mixing ratio in the step (3) is the thermoelectric material manufacturing method, characterized in that the second powder is 20 ~ 80wt% with respect to the first powder. (1) preparing a PbTe raw material powder through melting, coagulation and grinding; (2) manufacturing a first powder and a second powder by varying the mechanical milling time for the raw material powder (the mechanical milling time for the first powder is less than the mechanical milling time for the second powder); (3) uniformly mixing the first and second powders produced by the mechanical milling, (4) A method of manufacturing a thermoelectric material, comprising forming and sintering the powder mixed in the step (3). The method of claim 4, wherein The ratio of the particle size of the first powder and the particle size of the second powder is 7: 1, characterized in that the thermoelectric material. The method according to claim 4 or 5, The mixing ratio in the step (3) is the thermoelectric material manufacturing method, characterized in that the second powder is 20 ~ 80wt% with respect to the first powder. A thermoelectric material manufactured by the thermoelectric material manufacturing method of claim 1.

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