KR102088009B1 - Thermoelectric composite material and preparation method thereof - Google Patents

Abstract

The present invention provides a thermoelectric conversion composite material and a method for manufacturing the same, which can guarantee excellent thermoelectric properties of the thermoelectric conversion material by suppressing material loss or property degradation due to deterioration, oxidation, or sublimation of a thermoelectric conversion material including Te or Se. It is about. The thermoelectric conversion composite material includes an inorganic thermoelectric conversion material including Te or Se; A glass layer formed on at least a portion of the surface of the inorganic thermoelectric conversion material, the glass layer including tellurium oxide (TeOx), the glass layer having a glass transition temperature (Tg) of 300 ° C to 300 ° C and 300 ° C. It has a softening point (Ts) of C-400 degreeC.

Description

Thermoelectric conversion composite and its manufacturing method {THERMOELECTRIC COMPOSITE MATERIAL AND PREPARATION METHOD THEREOF}

The present invention provides a thermoelectric conversion composite material and a method for manufacturing the same, which can guarantee excellent thermoelectric properties of the thermoelectric conversion material by suppressing material loss or property degradation due to deterioration, oxidation, or sublimation of a thermoelectric conversion material including Te or Se. It is about.

Recently, due to resource depletion and environmental problems caused by combustion, research on thermoelectric conversion materials using waste heat as one of alternative energy is being accelerated.

The energy conversion efficiency of such thermoelectric conversion material depends on ZT, which is a figure of merit of a thermoelectric material. Here, ZT is determined according to Seebeck coefficient, electrical conductivity and thermal conductivity, and more specifically, is proportional to the square of the Seebeck coefficient and electrical conductivity and inversely proportional to the thermal conductivity. Therefore, in order to increase the energy conversion efficiency of the thermoelectric conversion element, it is necessary to develop a thermoelectric conversion material having high Seebeck coefficient or high electrical conductivity or low thermal conductivity.

On the other hand, the thermoelectric conversion material has a different temperature range mainly representing electromotive force and energy conversion efficiency for each type of specific material. For example, it is known that bismuthelulide (BiTe) -based thermoelectric conversion materials, which are widely applied in recent years, exhibit excellent thermoelectric conversion characteristics (energy conversion efficiency) at temperatures up to 300 ° C from normal temperature. In addition, since the thermoelectric module including the thermoelectric conversion material exhibits a higher output as the temperature difference between both ends is larger, the thermoelectric module including the bismuthulelide (BiTe) -based thermoelectric conversion material has a temperature close to 300 ° C at one end. It is desirable to have a low temperature as close to room temperature as possible, and the other end is preferable in view of high output.

However, in the case of a thermoelectric conversion material including Te or Se as a main element such as the bismuthlidelide (BiTe) thermoelectric conversion material, the thermoelectric conversion characteristics may be understood by volatilization or sublimation of Te / Se-based components in a temperature range of 250 ° C. or higher. It was confirmed that the degradation appears. In the presence of oxygen, when the thermoelectric conversion material containing Te or Se is exposed to a temperature of 200 ° C. or higher, surface oxidation or deterioration of the thermoelectric conversion material occurs, and corrosion and thermoelectric conversion of the thermoelectric conversion material occur. It was confirmed that the deterioration of the properties appeared.

For this reason, when the thermoelectric module including the bismuthyllidene (BiTe) -based thermoelectric conversion material is utilized at a temperature close to 300 ° C., the final output may be greatly improved. Due to volatilization / sublimation or oxidation, there is a problem in that the output of the thermoelectric module is reduced and the life is decreased.

For reference, Table 1 below shows how high temperature the thermoelectric conversion material is subjected to inside the module for each application temperature of the thermoelectric module, and is exposed to a 50-hour oxidizing atmosphere or a 100-hour sublimation atmosphere compared to the initial use of the module. After the simulation, the simulation results on how much the output density is reduced are shown.

uses
Temperature module 200 ℃ 250 ℃ 300 ℃ 350 ℃ 400 ℃ The temperature experienced by the material 170 ℃ 210 ℃ 250 ℃ 287 ℃ 323 ℃ Print
density Early 0.65
Current, 0% 0.95
46% ↑ 1.23
89% ↑ 1.46
124% ↑ 1.62
149% ↑ Unprotected
Deterioration rate > -0.1% -2.7%
(50hr oxidation atmosphere) -4.9%
(50hr oxidation atmosphere) -6.8%
(100hr sublimation atmosphere) -8.5%
(100hr sublimation atmosphere) Issue by temperature Lack of output Weak oxidation Strong oxidation
Sublimation Junction limit
Oxidation / Sublimation Kang Seung-hwa
Material deformation

Referring to Table 1, when the module utilization temperature is 300 ℃ or more, the output of the thermoelectric module can be greatly improved, the thermoelectric conversion material is exposed to a temperature of 200 ℃ or more by oxidation or sublimation, such as thermoelectric according to the utilization time It has been found that the output of the module is greatly reduced and its life is reduced.

Previously, a method of suppressing oxidation, deterioration, or sublimation of a thermoelectric conversion material by adding a metal layer, a metal oxide layer, a polymer layer, a plastic layer, or an aerosol to the thermoelectric conversion material has been considered. The disadvantages of this method are that the degradation of the thermoelectric conversion characteristics due to oxidation, deterioration or sublimation is not sufficiently suppressed, or the formation process of the thermoelectric module is complicated.

Accordingly, there is a continuous demand for the development of a technology capable of more effectively suppressing material loss or property degradation due to deterioration, oxidation, or sublimation of a thermoelectric conversion material including Te or Se, thereby ensuring excellent thermoelectric properties of the thermoelectric conversion material. Has been.

Accordingly, the present invention is to suppress the loss of the material due to deterioration, oxidation or sublimation of the thermoelectric conversion material containing Te or Se, or deterioration of the properties, to ensure the excellent thermoelectric properties of the thermoelectric conversion material and its preparation To provide a way.

The present invention is an inorganic thermoelectric conversion material including Te or Se;

Is formed on at least a portion of the surface of the inorganic thermoelectric conversion material, and comprises a glass layer containing tellurium oxide (TeOx),

The glass layer provides a thermoelectric conversion composite having a glass transition temperature (Tg) of 250 ° C to 300 ° C and a softening point (Ts) of 300 ° C to 400 ° C.

The present invention also provides a method of forming a glass paste composition comprising a glass frit powder including tellurium oxide (TeOx), an organic binder, and a solvent on an inorganic thermoelectric conversion material including Te or Se;

Drying the glass paste composition applied on the inorganic thermoelectric conversion material at 70 to 250 ° C .; And

It provides a method for producing a thermoelectric conversion composite comprising the step of cooling the glass paste composition after heating at 300 ℃ or more to form a glass layer.

Hereinafter, a thermoelectric conversion composite and a method for manufacturing the same according to specific embodiments of the present invention will be described in more detail.

According to one embodiment of the invention, the inorganic thermoelectric conversion material including Te or Se;

Is formed on at least a portion of the surface of the inorganic thermoelectric conversion material, and comprises a glass layer containing tellurium oxide (TeOx),

The glass layer is provided with a thermoelectric conversion composite having a glass transition temperature (Tg) of 250 ° C to 300 ° C and a softening point (Ts) of 300 ° C to 400 ° C.

The thermoelectric conversion composite of one embodiment includes tellurium oxide (TeOx) on at least a portion of the surface of an inorganic thermoelectric conversion material including Te or Se, such as, for example, a BiTe-based thermoelectric conversion material and meets a predetermined Tg and Ts range. A glass layer is formed as a protective layer.

As a result of continuous experiments by the present inventors, the application of such a tellurium oxide (TeOx) -containing glass layer as a surface protective layer of the thermoelectric conversion material, the main operating temperature of the thermoelectric conversion material (for example, about 200 to 300 ℃ In), it was confirmed that the volatilization / sublimation, oxidation and deterioration of the Te / Se-based component can be effectively prevented and suppressed, thereby reducing the deterioration of the thermoelectric conversion characteristics. In particular, the glass layer comprises tellurium oxide (TeOx) and the glass layer is at least 250 ° C. to 300 ° C. in comparison to the main operating temperature of the thermoelectric conversion material (eg, about 200 to 300 ° C.). Having a glass transition temperature (Tg) and a softening point (Ts) of 300 ° C to 400 ° C, the surface of the thermoelectric conversion material is effectively protected at the main operating temperature, and volatilization / sublimation, oxidation and It was confirmed that deterioration can be reduced to a minimum.

In addition, as the glass layer has the above-described Tg range and Ts range, such a glass layer may be formed to have excellent bonding property on the surface of the thermoelectric conversion material including Te or Se. In particular, the Tg and Ts ranges of the glass layer are not only in the appropriate range, but also the melting point (Tm) of the corresponding thermoelectric conversion material is also in the appropriate range (for example, Tm: 500 to 800 ° C.) not so low, The said glass layer can be formed favorably at the temperature of 400 degrees C or less, or 300-400 degreeC. Therefore, in the process of forming the glass layer, it is possible to form a glass layer satisfactorily without fear that the thermoelectric conversion material including Te or Se is damaged or deformed at a high temperature.

In particular, a thermoelectric conversion material including Te or Se, such as the BiTe-based thermoelectric conversion material, may be physically modified or deformed when the heat treatment is performed at a temperature of 350 ° C. or higher, for example, 350 ° C. to 400 ° C. to degrade thermoelectric conversion characteristics. Can be. However, as the glass layer having the above-described Tg and Ts ranges is formed, the possibility of applying a high temperature of 350 ° C. or higher in the process of forming such a glass layer is reduced, so that the thermoelectric conversion material is not damaged or deformed at high temperature. The layer can be formed well.

Meanwhile, the glass layer may have a thermal expansion coefficient that satisfies the above-described Tg range, Ts range, and the like, for example, a thermoelectric conversion material including Te or Se, such as a BiTe-based thermoelectric conversion material. For example, the glass layer may be 125 * 10 ^-7 / ℃ to 150 * 10 ^-7 / ℃, or 125 * 10 ^-7 / ℃ to 140 * 10 ^-7 / at room temperature (eg, about 20 ℃) It may have a coefficient of thermal expansion (CTE) of ℃. This is a thermal expansion coefficient in a range similar to that of the thermoelectric conversion material, and as the glass layer has such a thermal expansion coefficient, problems such as the thermoelectric conversion material is warped or the glass layer is peeled off by the formation of the glass layer. While reducing, a glass layer that suppresses volatilization / sublimation, oxidation, and deterioration of the Te / Se-based component can be satisfactorily formed on the thermoelectric conversion material.

On the other hand, as supported by the following examples and comparative examples, when forming a glass layer outside the above-described Tg and / or Ts range, not only it is difficult to suppress deformation of the thermoelectric conversion material at high temperature, but also thermoelectric conversion material It was also confirmed that sublimation and the like could not be suppressed properly, and the thermoelectric properties of the composite material were lowered.

Therefore, by using the above-described glass layer and the composite of one embodiment including the same, it is possible to effectively suppress the volatilization / sublimation, oxidation and deterioration of Te / Se-based components and the like from the thermoelectric conversion material at the operating temperature of the thermoelectric module. Excellent thermoelectric conversion efficiency can be ensured.

Hereinafter, the thermoelectric conversion composite and the manufacturing method thereof according to one embodiment will be described in more detail.

The thermoelectric conversion composite of one embodiment includes an inorganic thermoelectric conversion material that basically includes Te or Se. As such inorganic thermoelectric conversion materials, all previously known Te / Se-based thermoelectric conversion materials can be used without any particular limitations. For example, MnTe-based thermoelectric conversion materials, BiTe-based thermoelectric conversion materials, SbTe-based thermoelectric conversion materials, and PbTe-based materials At least one thermoelectric conversion material selected from the group consisting of a thermoelectric conversion material and a PbSe-based thermoelectric conversion material may be used. Moreover, according to the general application form of such Te / Se type thermoelectric conversion material, the said thermoelectric conversion material can be used as a sintered compact form under pressurization and / or high temperature.

However, since the inorganic thermoelectric conversion material can be used without any limitation Te / Se-based thermoelectric conversion material of the previously known type and form, further description thereof will be omitted.

Meanwhile, the composite of one embodiment includes a glass layer including tellurium oxide (TeOx) as a main component, and the glass layer is formed on part or all of the inorganic thermoelectric conversion material, for example, the surface of the sintered body. have. The tellurium oxide contained in the glass layer may be, for example, in the form of TeOx (x is 2 or less), and may be 35 to 70 wt%, or 40 to 60 wt% based on the total weight of the glass layer. It may be included in the content.

According to the formation of the glass layer including the tellurium oxide, it is possible to more effectively suppress the volatilization / sublimation, oxidation and deterioration of the Te / Se-based component in the thermoelectric conversion material to ensure excellent thermoelectric conversion characteristics. Moreover, Tg, Ts, a thermal expansion coefficient, etc. of the said glass layer can be controlled in an appropriate range, and the favorable glass layer excellent in joinability can be formed in the thermoelectric conversion material surface. In addition, as the glass layer including the tellurium oxide in an appropriate content is formed under appropriate process conditions described below, a chemical bonding / adsorption relationship may be formed between the glass layer and the thermoelectric conversion material. Accordingly, sublimation of the thermoelectric conversion material may be more effectively prevented due to surface energy stabilization.

Meanwhile, the glass layer has a Tg of 250 ° C. to 300 ° C. to more effectively prevent and suppress the volatilization / sublimation, oxidation, and deterioration of Te / Se-based components, and exhibit excellent bonding property and appropriate thermal expansion coefficient to a thermoelectric conversion material. And Ts of 300 ° C to 400 ° C or 350 ° C to 400 ° C. The Tg, Ts and thermal expansion coefficient range of the glass layer may be controlled not only by the composition of the tellurium oxide described above, but also by the composition of the remaining additional components included in the glass layer.

In one embodiment of the glass layer, the glass layer may further comprise 25 to 60% by weight, or 30 to 50% by weight of vanadium oxide (V2O5), in addition to the above tellurium oxide, BaO, 0.01 to 10% by weight of at least one oxide selected from the group consisting of Bi ₂ O ₃ , B ₂ O ₃ , SiO ₂ , ZnO, Al ₂ O ₃ , P ₂ O ₅ , PbO, WO ₃ , CaO and Na ₂ O Or, it may further comprise 0.1 to 5% by weight.

According to the composition of the glass layer, it is possible to more easily achieve the appropriate Tg, Ts and thermal expansion coefficient ranges as described above, so that the glass layer can be formed better with good bonding to the thermoelectric conversion material. At the same time, volatilization / sublimation, oxidation and deterioration of Te / Se-based components from the thermoelectric conversion material can be effectively suppressed.

In addition, the glass layer effectively suppresses volatilization / sublimation, oxidation and deterioration of the Te / Se-based components, and does not deteriorate the basic characteristics of the thermoelectric conversion material, for example, from 10 nm to 100 μm, or from 0.1 to 100. It may have a thickness of 1 μm or 1 to 50 μm.

On the other hand, according to another embodiment of the invention, there is provided a method of manufacturing a thermoelectric conversion composite of one embodiment described above. This manufacturing method includes forming a glass paste composition comprising glass frit powder including tellurium oxide (TeOx), an organic binder, and a solvent on an inorganic thermoelectric conversion material including Te or Se;

Drying the glass paste composition applied on the inorganic thermoelectric conversion material at 70 to 250 ° C .; And

It may include the step of forming the glass layer by cooling the glass paste composition after heating at 300 ℃ or more.

According to the manufacturing method of this other embodiment, it is possible to form a good glass layer containing tellurium oxide on the surface of the inorganic thermoelectric conversion material including Te or Se, and having an appropriate Tg and Ts, thereby providing the thermoelectric of one embodiment. The conversion composite can be easily obtained.

In the manufacturing method of this other embodiment, the inorganic thermoelectric conversion material containing Te or Se may be prepared in the form of a sintered body, according to a method for producing a thermoelectric conversion material that is well known.

Thereafter, a glass paste composition including a glass frit powder including a predetermined tellurium oxide (TeOx), an organic binder, and a solvent may be applied onto the thermoelectric conversion material.

In this case, the glass frit powder included in the paste composition may have the same or corresponding composition as that of the glass layer described above. For example, 35 to 70% by weight of tellurium oxide (TeOx), or 40 to 60 Wt%, 25 to 60 wt%, or 30 to 50 wt% of vanadium oxide (V2O5), BaO, Bi ₂ O ₃ , B ₂ O ₃ , SiO ₂ , ZnO, Al ₂ O ₃ , P ₂ O ₅ It may include 0.01 to 10% by weight, or 0.1 to 5% by weight of at least one oxide selected from the group consisting of, PbO, WO ₃ , CaO and Na ₂ O.

In addition, the glass frit powder may have a particle size of 100 nm to 10 μm, or 1 μm to 5 μm, so that a good glass layer may be formed while appropriately dispersed in the paste composition.

As the organic binder included in the paste composition, any polymer binder known to be usable in a general glass paste composition may be used. Specific examples thereof include cellulose binders such as ethyl cellulose, and poly (meth) acrylic compounds. A binder or a polyvinyl type binder etc. are mentioned.

In addition, the paste composition further includes a solvent for uniformly dissolving or dispersing the glass frit powder and the organic binder. The solvent may be an organic solvent or water having excellent solubility / dispersibility according to the type of the organic binder. The solvent can be appropriately selected and used by those skilled in the art. Specific examples of such a solvent include an alcohol solvent such as α-Terpineol or phenol, an acetate solvent such as Butyl carbitol acetate, an aromatic hydrocarbon solvent such as toluene, or an aqueous solvent such as water.

On the other hand, it is possible to obtain a glass paste composition by mixing each of the above components to have a viscosity suitable for application, the glass paste composition in consideration of such a suitable viscosity range, for example, 1 to 50% by weight of the glass frit powder, or 5 To 30% by weight, 5 to 25% by weight of the organic binder, or 5 to 20% by weight and 28 to 90% by weight of the solvent, or 55 to 85% by weight.

The glass paste composition thus obtained may be applied to a predetermined region of the surface of the thermoelectric conversion material to which the above-described glass layer is to be formed, and such a coating method is not particularly limited. For example, the glass paste composition may be applied onto the thermoelectric conversion material by, for example, supporting the thermoelectric conversion material in the glass paste composition or coating the glass paste composition directly on the thermoelectric conversion material.

Subsequently, the glass paste composition coated on the inorganic thermoelectric conversion material may be dried at 70 to 250 ° C. or 80 to 200 ° C. to remove a solvent and the like contained in the glass paste composition.

At this time, the drying method is not particularly limited, and may be performed by removing the solvent by drying for 30 seconds to 36 hours or 1 minute to 90 minutes in the above-described temperature range in consideration of the type and boiling point of the solvent.

On the other hand, after the above drying step, the glass paste composition may be proceeded to form a continuous glass layer by heating and cooling after heating at 300 ℃ or more, or 300 to 400 ℃. As already mentioned above, the glass frit powder included in the glass paste composition and the glass layer formed therefrom have a Tg and Ts range that are not too high, so that the glass frit powders are bonded to each other during heating at a temperature of 300 ° C. or higher. A continuous and flexible glass film can be formed, and then a continuous glass layer capable of preventing oxidation and sublimation on the thermoelectric conversion material during cooling can be formed well. Moreover, such a heating temperature makes it possible to form a glass layer satisfactorily without fear of damaging the thermoelectric conversion material including Te or Se at a high temperature.

Such a heating process may be performed, for example, for 1 minute to 1 hour in the above-described temperature range, may be performed in a general electric furnace or an atmosphere electric furnace well known to those skilled in the art, and may be performed under vacuum or atmospheric pressure.

On the other hand, according to another embodiment of the invention, there is provided a thermoelectric device comprising the thermoelectric conversion composite of the above-described embodiment. Such a thermoelectric device may include the thermoelectric conversion composite of the embodiment as a p-type or n-type thermoelectric material, and for this purpose, the thermoelectric conversion composite of the embodiment is further doped with an additional p-type element or n-type element. can do. However, the type or doping method of the p-type element or n-type element that can be used at this time is not particularly limited, and elements and doping methods that have been generally used to apply the thermoelectric material to p-type or n-type can be applied. .

The thermoelectric element may include a thermoelectric element formed by processing and molding the p-type or n-type thermoelectric conversion composite in a sintered state, and may include an insulating substrate and an electrode. The coupling structure of the thermoelectric element, the insulating substrate and the electrode may be in accordance with the structure of a conventional thermoelectric element.

In addition, a sapphire substrate, a silicon substrate, a Pyrex substrate, a quartz substrate, or the like may be used as the insulating substrate, and an electrode containing any metal or a conductive metal compound may be used as the electrode.

As the above-mentioned thermoelectric element includes the thermoelectric conversion composite of one embodiment, even when used for a long time at the operating temperature, it is possible to express and maintain excellent thermoelectric conversion performance, and in various fields and applications, it is preferable as a thermoelectric cooling system or a thermoelectric power generation system. Can be applied.

According to the present invention, a thermoelectric conversion composite material capable of effectively suppressing the loss or property loss due to deterioration, oxidation or sublimation of a thermoelectric conversion material including Te or Se, and ensuring excellent thermoelectric properties of the thermoelectric conversion material, and Methods for their preparation may be provided.

FIG. 1 is a photograph of a portion of an n-type thermoelectric conversion composite formed in Example 2 and photographed by electron microscope photographing the boundary of each layer included therein.
FIG. 2 is a photograph showing an EDX elemental analysis result by expanding the region shown in FIG. 1. FIG.
FIG. 3 is a photograph illustrating an edge of the thermoelectric conversion composite of Example 2 not polished in FIG. 1.
4 is a photograph of the surface of the thermoelectric conversion composite of Comparative Example 4 observed with an optical microscope.
5 is a photograph showing a state in which the thermoelectric conversion composite of Comparative Example 4 is deformed after exposure to high temperature during the glass layer forming process.
Figure 6 is a photograph showing a comparison of the sublimation test results of Example 1 and Comparative Example 1.
7 is a photograph showing comparison of the sublimation test results of Comparative Examples 1 and 3. FIG.
8 is a graph showing the results of measuring the Seebeck coefficient of Comparative Example 1 (before / after the sublimation test), Comparative Example 3 (after the sublimation test) and Example 3 (after the sublimation test).
9 is a graph showing the results of measuring the Seebeck coefficient of Comparative Example 2 (before / after the sublimation test), Comparative Example 4 (after the sublimation test) and Example 2 (after the sublimation test).

The invention is explained in more detail in the following examples. However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited by the following examples.

Example 1 Preparation of p-BiTe-based Thermoelectric Conversion Materials and Thermoelectric Conversion Composites

1) Preparation of p-BiTe Thermoelectric Conversion Material

Bi, Sb, Te, Pb shot is weighed to the composition ratio (molar ratio) of Bi 0.5, Sb 1.5, Te 3.0 and Pb 0.01, the mixture is placed in a quartz tube and vacuum sealed to make an ampoule, and then the ampoule is placed in a tube furnace. And melt at a temperature of 800 ° C. The melt synthesized ingot was jetted at 650 ° C. and rapidly cooled with cold water, and then ground and classified to about 50 μm. The powder thus classified was pressurized to 50 MPa and pressure sintered by spark plasma sintering at a temperature of 475 ° C. for 2 minutes. The sintered p-type BiTe-based thermoelectric material was processed into a 2.5 mm x 2.5 mm x 12 mm square pillar.

2) Preparation of Glass Paste Composition

Glass frit powder containing TeO ₂ , V ₂ O ₅ and ZnO in a weight ratio of 55: 44: 1 and having a particle diameter of 4 μm, mineral spirit (D80; organic binder) and α-Terpineol in a volume ratio of 9: 1 The mixed solution was mixed at a weight ratio of 1: 1. The glass paste composition was formed by vibrating for 72 hours at 3000 rpm through the Voltex.

3) Preparation of thermoelectric conversion composite with glass layer

10 g of the glass paste composition formed in 2) and 30 ml of α-Terpineol were mixed, and then dispersed through Voltex for 1 hour. The p-type BiTe-based thermoelectric material formed in 1), which was processed in the form of a square column, was deeped in the dispersion and dried in an electric furnace at 200 ° C. for 1 hour and 30 minutes. A total of three coating and drying processes were carried out to coat all sides of the square pillar. Or, to check the difference between the coated surface and the general surface, only a part of the thermoelectric material was deepened to perform coating and drying. After three coating and drying processes, the specimens were put in an electric furnace, heated at 380 ° C. for 30 minutes, and then naturally cooled.

Example 2: Preparation of n-BiTe-based Thermoelectric Conversion Materials and Thermoelectric Conversion Composites

1) Preparation of n-BiTe Thermoelectric Conversion Material

Bi, Sn, Te shot was weighed according to the composition ratio (molar ratio) of Bi 2, Sn 0.5, Te 2.5, the mixture was put in a quartz tube and vacuum-sealed to form an ampoule, and the ampoule was subjected to a solid phase reaction in an electric furnace at 450 ° C. . The solid ingot thus synthesized was naturally cooled, and then ground and classified to about 50 µm. The powder thus classified was pressurized to 50 MPa and pressure sintered by spark plasma sintering at a temperature of 450 ° C. for 5 minutes. The sintered n-type BiTe-based thermoelectric material was processed into a 2.5 mm x 2.5 mm x 12 mm square pillar.

2) Preparation of Glass Paste Composition

Glass frit powder containing TeO ₂ , V ₂ O ₅ and ZnO in a weight ratio of 55: 44: 1 and having a particle diameter of 4 μm, mineral spirit (D80; organic binder) and α-Terpineol in a volume ratio of 9: 1 The mixed solution was mixed at a weight ratio of 1: 1. The glass paste composition was formed by vibrating for 72 hours at 3000 rpm through the Voltex.

3) Preparation of thermoelectric conversion composite with glass layer

10 g of the glass paste composition formed in 2) and 30 ml of α-Terpineol were mixed, and then dispersed through Voltex for 1 hour. The n-type BiTe-based thermoelectric material formed in 1), which was processed in the form of a square column, was deeped in the dispersion and dried in an electric furnace at 200 ° C. for 1 hour and 30 minutes. A total of three coating and drying processes were carried out to coat all sides of the square pillar. Or, to check the difference between the coated surface and the general surface, only a part of the thermoelectric material was deepened to perform coating and drying. After three coating and drying processes, the specimens were put in an electric furnace, heated at 380 ° C. for 30 minutes, and then naturally cooled.

Comparative Example 1: Preparation of p-BiTe Thermoelectric Conversion Material

The p-BiTe based thermoelectric conversion material formed in 1) of Example 1 was set as Comparative Example 1 without forming a glass layer.

Comparative Example 2: Preparation of n-BiTe Thermoelectric Conversion Material

The n-type BiTe-based thermoelectric conversion material formed in 1) of Example 2 was used as Comparative Example 2 without forming a glass layer.

Comparative Example 3: Preparation of p-BiTe Thermoelectric Conversion Material and Thermoelectric Conversion Composite

In Example 1, the composition and preparation of the glass paste composition were varied as follows. That is, TeO ₂ , V ₂ O ₅ and ZnO are contained in a weight ratio of 20:70:10, and glass frit powder having a particle diameter of 4 μm is used, and mineral spirit (D80; organic binder) and α-Terpineol are 9: 1. The solution mixed with the volume ratio of was mixed with the weight ratio of 1: 1. The glass paste composition was formed by vibrating for 72 hours at 3000 rpm through the Voltex.

A thermoelectric conversion composite of Comparative Example 3 was prepared in the same manner as in Example 1 except for the composition and formation of the glass paste composition.

Comparative Example 4: Preparation of n-BiTe Thermoelectric Conversion Material and Thermoelectric Conversion Composite

In Example 2, the composition and preparation of the glass paste composition were varied as follows. That is, TeO ₂ , V ₂ O ₅ and ZnO are contained in a weight ratio of 20:70:10, and glass frit powder having a particle diameter of 4 μm is used, and mineral spirit (D80; organic binder) and α-Terpineol are 9: 1. The solution mixed with the volume ratio of was mixed with the weight ratio of 1: 1. The glass paste composition was formed by vibrating for 72 hours at 3000 rpm through the Voltex.

A thermoelectric conversion composite of Comparative Example 4 was prepared in the same manner as in Example 2 except for the composition and formation of the glass paste composition.

Test Example 1 Measurement of Tg, Ts, and Thermal Expansion Coefficient of the Glass Layer

In the thermoelectric conversion composites of Examples 1, 2, Comparative Examples 3, and 4 in which the glass layers were formed, the Tg, Ts, and thermal expansion coefficients of the glass layers formed on the thermoelectric conversion materials, respectively, were measured by the following method. For reference, the properties of the glass layer were measured with respect to the workpiece of the glass frit powder for forming the same, and the properties of the finally formed glass layer were defined in the same manner as the properties measured with respect to the workpiece of the glass frit powder.

First, Tg cold pressed the glass frit powder to 1.2 inches in diameter and 1 cm in height, and then processed the size of 2.5 mm x 2.5 mm x 9.5 mm. The CTE of the workpiece was measured using a dilatometer, and the relationship / graph of the CTE for each temperature was derived from these measurement results (see the example in Figure 1 below), and Tg and Ts were measured from the results.

For reference, the CTE is the ratio of the length of the original length to the changed length, and the unit is (µm / m / ° C, that is, X10 ^-6 ° C ^{- 1} ), and the value is measured differently for each temperature. In addition, the Tg of the glass layer may be measured as the temperature of the inflection point (the inflection point of the second derivative value) in which the slope of the CTE for each temperature rises sharply, and Ts is the steep decrease of the slope of the CTE after Tg. Can be measured in parts by the temperature of the inflection point (additional inflection point of the second derivative; see Figure 1 below).

[Figure 1]

The measurement results are collectively shown in Table 2 below.

Example 1 Example 2 Comparative Example 3 Comparative Example 4 Tg (℃) 253 253 332 287 Ts (℃) 313 313 409 409 CTE (/ ℃) 13.5X10 ^-6 13.5X10 ^-6 15.0X10 ^-6 15.0X10 ^-6

Referring to Table 2, the Tg of the glass layers formed in Examples 1 and 2 was found to be in the range of 250 ℃ to 300 ℃, Ts 300 ℃ to 400 ℃. In comparison, the glass layers formed in Comparative Examples 3 and 4 were found to have higher Tg or Ts. In addition, the glass layers formed in Examples 1 and 2 were found to have a coefficient of thermal expansion (CTE) in the range of 125 * 10-7 / ℃ to 150 * 10-7 / ℃.

Test Example 2: Confirmation of Good Formation of Glass Layer

A portion of the surface of the n-type thermoelectric conversion composite, which was formed in Example 2 and coated with a glass layer, was polished. 1 is a result of observing a part of the polished glass film-material boundary through an electron microscope (SEM). FIG. 2 shows the results of elemental analysis through EDX by expanding the region shown in FIG. 1.

1 and 2, it can be seen that the surface on which the glass layer is formed is different from the surface without the glass layer. On darker shaded surfaces, vanadium is detected in the glass layer, with a relatively high oxygen ratio. However, on the bright surface on the right where the glass layer is not detected, the detection amount of bismuth due to the thermoelectric conversion material is high. Thus, it was confirmed that the glass layer continuously well covered the surface of the thermoelectric conversion material, and that the glass layer was formed satisfactorily.

3 is a result of observing the edge of the thermoelectric conversion composite of Example 2 not polished. Referring to this, it can be seen that a uniform glass film having a thickness of 30 μm was continuously formed through the process of Example 2.

Also in Example 1, the uniform and favorable formation of the glass layer was confirmed by the same method as mentioned above.

On the other hand, Figure 4 shows the results of observing the surface of the thermoelectric conversion composite material having a glass layer with a relatively high Tg or Ts as in Comparative Example 4 with an optical microscope. Referring to FIG. 4, it can be seen that a thermoelectric conversion material is observed between the black surfaces on which the glass layer is formed (silver white). As a result, when a glass layer having an excessively high Tg or Ts is formed, the glass layer may not be softened at a temperature of 400 ° C. or lower, which may be maintained without deformation, and thus the glass layer may be uniform. Difficulties in the protection of thermoelectric conversion materials by formation have been identified. In addition, when the temperature is increased to 500 ° C. (Ts or more) for softening the glass layer (forming and processing the glass layer), the thermoelectric conversion composite is bent as shown in FIG.

In Comparative Example 3, the same method as described above was confirmed, and as in Comparative Example 4, it was confirmed that the glass layer was not formed satisfactorily, and the temperature was increased above the softening point for processing the thermoelectric conversion composite or forming the glass layer. In this case, physical deformation of the thermoelectric conversion composite was confirmed.

Test Example 3 Sublimation Test Results of Thermoelectric Composites (Materials)

After vacuum sealing each thermoelectric conversion composite material (or thermoelectric conversion material) of Examples 1 to 2 and Comparative Examples 1 to 4, the glass tube containing each material was placed in an electric furnace and heated at 300 ° C. for 100 hours, and the opposite side of the glass tube was The sublimation gas was taken out of the electric furnace so that the sublimed gas from each material was captured on the opposite side of the relatively cold glass tube, which allowed the sublimation to continue.

6 shows the results of the sublimation test for each material of Example 1 and Comparative Example 1 in a photograph. The upper result of FIG. 6 shows the result of the sublimation test for the comparative example 1, and silver-white sublimation solid was confirmed on the opposite side of the glass tube as the glass layer was not formed. As a result, in Comparative Example 1, it was confirmed that sublimation of the thermoelectric conversion material occurred. In comparison, the bottom result of FIG. 6 shows the result of the sublimation test for Example 1, and as the glass layer is formed, sublimation of the thermoelectric conversion material is suppressed, and in Example 1, the thermoelectric conversion material is prevented by the glass layer. It was confirmed that sublimation and the like were suppressed.

7 is a photograph showing the sublimation test results for the material of Comparative Example 3 with a glass layer having a high Tg and Ts, the upper photo is the result for Comparative Example 3, the lower photo is the result of Comparative Example 1 for comparison It is shown together. Referring to FIG. 7, in both Comparative Examples 1 and 3, silver-white sublimation solids were found on the opposite side of the glass tube. Through this, it was confirmed that not only Comparative Example 1 but also Comparative Example 3 did not properly suppress sublimation of the thermoelectric conversion material.

Test Example 4 Evaluation of Thermoelectric Conversion Characteristics

The Seebeck coefficient (S) of the thermoelectric conversion composite (material) specimens prepared in Examples 1 and 2 and Comparative Examples 1 to 4 was measured according to temperature changes, and is shown in FIGS. 8 and 9. For Comparative Examples 1 and 2, the Seebeck coefficient was measured before and after the sublimation test, respectively, in order to confirm the difference in Seebeck coefficient according to the sublimation. For Examples 1, 2, Comparative Examples 3 and 4, after the sublimation test Seebeck coefficient was measured.

This Seebeck coefficient was measured in a temperature range of 0 to 200 ° C. using a measuring instrument Linseis LSR-3 and applying a differential voltage / temperature technique.

First, referring to FIG. 8 related to Examples 1, Comparative Examples 1, and 3, which are p-type thermoelectric conversion composites (materials), the composite of Example 1 is further compared with Comparative Example 1, which is a thermoelectric conversion material without sublimation. It was confirmed to exhibit an excellent Seebeck coefficient. On the contrary, in the case of Comparative Example 1, it was confirmed that the Seebeck coefficient was further lowered due to the sublimation of the thermoelectric conversion material after the sublimation test. In addition, in Comparative Example 3, it was confirmed that the poor Seebeck coefficient according to Comparative Example 1 after the sublimation test was obtained because the sublimation of the thermoelectric conversion material was not properly suppressed because the characteristics of the glass layer were out of an appropriate range. From this, in Example 1, it was confirmed that sublimation of a thermoelectric conversion material, etc. can be suppressed and the outstanding thermoelectric conversion performance can be expressed.

In addition, referring to Fig. 9 related to Example 2, Comparative Examples 2 and 4, which are n-type thermoelectric conversion composites (materials), the composite of Example 2 is superior to Comparative Example 2, which is a thermoelectric conversion material without sublimation. It was confirmed that the Seebeck coefficient was shown. On the contrary, in the case of Comparative Example 2, it was confirmed that the absolute value of the Seebeck coefficient is lowered due to the sublimation of the thermoelectric conversion material after the sublimation test. In addition, in Comparative Example 4, the glass layer was out of an appropriate range and sublimation of the thermoelectric conversion material was not properly suppressed, and it was confirmed that the absolute Seebeck coefficient absolute value according to Comparative Example 2 after the sublimation test was shown. From this, in Example 2, it was confirmed that sublimation of a thermoelectric conversion material, etc. can be suppressed and the outstanding thermoelectric conversion performance can be expressed.

Claims (15)

Inorganic thermoelectric conversion materials including Te or Se;
Is formed on at least a portion of the surface of the inorganic thermoelectric conversion material, and comprises a glass layer containing tellurium oxide (TeOx),
The glass layer has a glass transition temperature (Tg) of 250 ° C to 300 ° C and a softening point (Ts) of 300 ° C to 400 ° C and comprises 35 to 70% by weight of tellurium oxide (TeOx).
The thermoelectric conversion material of claim 1, wherein the inorganic thermoelectric conversion material is at least one thermoelectric material selected from the group consisting of an MnTe-based thermoelectric conversion material, a BiTe-based thermoelectric conversion material, an SbTe-based thermoelectric conversion material, a PbTe-based thermoelectric conversion material, and a PbSe-based thermoelectric conversion material. A thermoelectric conversion composite comprising a sintered body of a conversion material.
The thermoelectric conversion composite of claim 1, wherein the glass layer has a coefficient of thermal expansion (CTE) of 125 * 10 ^-7 / ° C to 150 * 10 ^-7 / ° C.
The thermoelectric conversion composite of claim 1, wherein the glass layer further comprises 25 to 60 wt% of vanadium oxide (V 2 O 5).
The group of claim 4, wherein the glass layer is formed of BaO, Bi ₂ O ₃ , B ₂ O ₃ , SiO ₂ , ZnO, Al ₂ O ₃ , P ₂ O ₅ , PbO, WO ₃ , CaO and Na ₂ O. Thermoelectric conversion composite further comprising 0.01 to 10% by weight of at least one oxide selected from.
The thermoelectric conversion composite of claim 1, wherein the glass layer has a thickness of 10 nm to 100 μm.
Forming a glass paste composition comprising a glass frit powder including tellurium oxide (TeOx), an organic binder, and a solvent on an inorganic thermoelectric conversion material including Te or Se;
Drying the glass paste composition applied on the inorganic thermoelectric conversion material at 70 to 250 ° C .; And
Heating and cooling the glass paste composition at 300 ° C. or higher to form a glass layer,
The glass frit powder comprises 35 to 70% by weight of tellurium oxide (TeOx).
delete The method of claim 7, wherein the glass frit powder further comprises 25 to 60 wt% of vanadium oxide (V 2 O 5).
The method of claim 9, wherein the glass frit powder is composed of BaO, Bi ₂ O ₃ , B ₂ O ₃ , SiO ₂ , ZnO, Al ₂ O ₃ , P ₂ O ₅ , PbO, WO ₃ , CaO and Na ₂ O Method for producing a thermoelectric conversion composite further comprises 0.01 to 10% by weight of at least one oxide selected from the group.
The method of claim 7, wherein the glass frit powder has a particle diameter of 100 nm to 10 μm.
The method of claim 7, wherein the organic binder comprises a cellulose binder, a poly (meth) acrylic binder, or a polyvinyl binder.
The method of claim 7, wherein the solvent comprises an alcohol solvent, an acetate solvent, an aromatic hydrocarbon solvent, or an aqueous solvent.
The method of claim 7, wherein the glass paste composition comprises 1 to 50% by weight of glass frit powder, 5 to 25% by weight of an organic binder and 28 to 90% by weight of a solvent.
A thermoelectric element comprising the thermoelectric conversion composite according to any one of claims 1 to 6.

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