KR20170067457A - Bi-Sb-Te based thermoelectric powder and materials with improved thermostability and manufacturing methods thereof - Google Patents
Bi-Sb-Te based thermoelectric powder and materials with improved thermostability and manufacturing methods thereof Download PDFInfo
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Abstract
The present invention provides a thermoelectric material with improved thermal stability and a method of manufacturing the same. In particular, the present invention proposes a thermoelectric powder capable of producing thermoelectric materials with improved thermal stability. This thermoelectric powder includes a Bi-Sb-Te thermoelectric material core part; And a graphene oxide shell portion coated on the surface of the core portion.
Description
BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a thermoelectric conversion technology, and more particularly, to a technology capable of improving thermal stability of a thermoelectric material constituting a thermoelectric device. In particular, the present invention relates to a thermoelectric powder suitable for producing a thermoelectric material having improved thermal stability, a method for producing the thermoelectric powder, and a thermoelectric material produced using the thermoelectric powder.
Due to the temperature difference at both ends of the solid state material, the electrons (or holes) having a thermal dependence cause a difference in the concentration at both ends, and this is caused by an electric phenomenon, that is, a thermoelectric phenomenon. Such a thermoelectric phenomenon can be classified into a thermoelectric power generating electric energy and a thermoelectric cooling / heating which causes a temperature difference at both ends by electric power supply.
Thermoelectric materials show such a thermoelectric phenomenon, and many researches have been made because of their environmental and sustainable advantages in power generation and cooling. Particularly, there is a high interest as a technology to improve fuel efficiency and reduce CO 2 by producing electric power from industrial waste heat and automobile waste heat.
Generally, a thermoelectric device includes a p-type thermoelectric element made of a p-type thermoelectric material that moves a hole by moving a hole, and a p-type thermoelectric element made of an n-type thermoelectric element made of an n- One pair of elements may be a basic unit, and may be configured as a module type comprising a plurality of pairs of pn thermoelectric elements, electrodes above and below the pn thermoelectric element, and an insulating substrate.
The energy conversion efficiency of thermoelectric devices depends on ZT (= S 2 σTk - 1 ), which is the dimensionless performance index value of the thermoelectric material. Where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and k is the total thermal conductivity. Many thermoelectric materials have been proposed and developed so far. The thermoelectric materials are largely classified into a metal system and an oxide system, and the metal system includes a chalcogenide system, a silicide system, a clathrate system, a Half Heusler system, a skutterudite system, And so on.
Generally, the higher the temperature difference between the two materials is, the higher the efficiency and the electromotive force are formed. However, a high temperature for forming a large temperature difference causes thermoelectric material composition change through atomic physical chemical phenomena such as melting, diffusion, and sublimation, leading to degradation of the thermoelectric material , A thermoelectric element, a module as an aggregate thereof, and a thermoelectric device including the same.
This problem is called degradation due to thermal stability. In order to increase the thermal stability of thermoelectric devices, a metal thin film coating technique utilizing various vapor deposition is known. However, due to various problems such as secondary diffusion of the metal thin film, interfacial adhesion, reduction of electromotive force due to contact resistance, and the like, it is necessary to develop a new technology.
It is an object of the present invention to provide a thermoelectric material having improved thermal stability and a method of manufacturing the same.
In order to achieve the above object, the present invention proposes a thermoelectric powder that can produce a thermoelectric material having improved thermal stability.
The thermoelectric powder according to the present invention is a composite of a Bi-Sb-Te-based thermoelectric material and graphene oxide. In particular, the thermoelectric powder according to the present invention comprises a Bi-Sb-Te thermoelectric material core part; And a graphene oxide shell portion coated on the surface of the core portion.
The core portion may have an average particle size of 50 nm to 500 mu m. The shell portion may include a single layer of graphene oxide.
The thermoelectric material according to the present invention includes a sintered body of such a thermoelectric powder. Therefore, the method of manufacturing a thermoelectric material according to the present invention includes the step of sintering this thermoelectric powder.
According to another aspect of the present invention, there is provided a thermoelectric material including: a crystal grain of a Bi-Sb-Te-based thermoelectric material; And graphene oxide located at grain boundaries of the thermoelectric material are consolidated by sintering.
The thermoelectric material having such a structure can be produced by a simple mixing and sintering of a general Bi-Sb-Te thermoelectric material powder and graphene oxide, but it is preferable to sinter the thermoelectric powder according to the present invention. In the case of sintering by simple mixing, it may be difficult to obtain a fine structure in which graphene oxide surrounds crystal grains of a Bi-Sb-Te-based thermoelectric material depending on the degree of mixing. However, This is because graphene oxide can easily and reproducibly obtain the microstructure surrounding the grains of the Bi-Sb-Te based thermoelectric material by sintering the powder having the structure in which the Sb-Te thermoelectric material core portion is surrounded by the graphen oxide shell portion.
The thermoelectric material according to the present invention may further include amorphous carbon in the grain boundaries. The amorphous carbon may be due to thermal decomposition of the graphene oxide. And may further include graphene oxide reduced to the grain boundaries. The reduced graphene oxide may be one in which the graphene oxide is partially reduced upon sintering.
The thermoelectric material according to the present invention may have a D / G peak ratio of 0.9 or more and less than 1.3 in Raman measurement.
A method of manufacturing a thermoelectric powder according to the present invention includes: preparing a Bi-Sb-Te thermoelectric material core; And forming a graphene oxide shell part on the surface of the core part.
At this time, the step of forming the graphene oxide shell part may include: preparing a graphene oxide dispersion; And mixing the thermoelectric material core portion with the graphene oxide dispersion. Further, after the mixing step, at least one of ultrasonic treatment, heating, stirring, and shaking may be further performed.
The graphene oxide dispersion is composed of graphene oxide and deionized water.
In the present invention, a bulk thermoelectric material including such a thermoelectric material, a thermoelectric element dicing the same, and a thermoelectric device such as a thermoelectric module integrated therewith are also proposed.
According to the present invention, a thermoelectric material having thermal stability can be produced by coating graphene oxide on the surface of a Bi-Sb-Te based thermoelectric material. Grabpin oxide wrapped around the Bi-Sb-Te system thermoelectric material suppresses the volatilization of the Te element from the Bi-Sb-Te system thermoelectric material and prevents or suppresses the diffusion of the material in the thermoelectric material, The heat resistance and thermal stability of the material are improved. A thermoelectric device such as a thermoelectric element or a thermoelectric module including such a thermoelectric material is excellent in thermal stability, and the degree of deterioration is relatively small even after long-term use at a high temperature.
In the present invention, graphene oxide can be coated on the surface of a Bi-Sb-Te thermoelectric material by utilizing graphene oxide having excellent adhesion without using other organic materials, and phonon scattering can be increased through graphene oxide The thermal conductivity is reduced, the performance index ZT is improved, and the thermal stability can be ensured.
As described above, the thermoelectric material according to the present invention has an effect of improving ZT and securing thermal stability.
In addition, the thermoelectric powder and the thermoelectric material manufacturing method according to the present invention are economical because they are performed by a simple solution-based method without expensive deposition processes and the like.
BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description of the invention given below, serve to further augment the technical spirit of the invention. Should not be construed as limiting.
FIG. 1 is a diagram schematically illustrating a configuration of a thermoelectric powder according to an embodiment of the present invention. Referring to FIG.
2 is a flowchart schematically showing a method of manufacturing a thermoelectric powder according to an embodiment of the present invention.
FIG. 3 is a diagram schematically showing a configuration of a thermoelectric material manufactured using a thermoelectric powder according to an embodiment of the present invention. Referring to FIG.
4 is a schematic diagram of a process for manufacturing powder of an embodiment.
5 shows XRD (X-Ray Diffractometer) analysis results of Examples of the present invention and Comparative Powders.
6 shows the results of Raman analysis for the sintered bodies of Examples and Comparative Examples.
7 is an SEM photograph of the sintered body of the embodiment.
8 is an SEM photograph of a comparative sintered body.
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. It is provided to let you know. It should be noted that the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention and are not intended to represent all of the technical ideas of the present invention so that various equivalents And variations are possible.
FIG. 1 is a diagram schematically illustrating a configuration of a thermoelectric powder according to an embodiment of the present invention. Referring to FIG.
1, a
The
Bi-Sb-Te-based thermoelectric materials are p-type thermoelectric materials by substituting Sb for Bi-Te-based thermoelectric materials. Representative materials are represented by the formula Bi x Sb 2 - x Te 3 (where x is 0 < x < 2). In order to adjust the temperature band at which the maximum ZT appears, the composition of any one of Bi, Sb and Te can be changed.
The Bi-Sb-Te-based thermoelectric material may further include at least one of Pb, Cu, and Se in addition to Bi, Sb, and Te which are the main elements. These additional elements may be contained in a total amount of 5 wt% or less. If the content exceeds 5 wt%, the carrier concentration increases and the performance index ZT can be reduced. However, the Bi-Sb-Te-based thermoelectric material used in the present invention is not limited thereto, and can be applied to all the composition ranges corresponding to known Bi-Sb-Te-based thermoelectric materials.
On the other hand, the shape of the
In one example, the
As described above, the
On the other hand, the
The
The
As described above, the
In the
The
Graphite is a structure in which planes of carbon are arranged like honeycomb hexagonal nets, and one layer of this graphite is called graphene. Graphene has a very high physical and chemical stability with a thickness of 0.35 nm. Graphene oxide is a state in which the hexagonal ring structure of carbon is partially destroyed in the form of oxygen attached to a carbon layer such as a thin atomic layer of paper. The defects generated during the separation process have lower electrical characteristics and mechanical strength than graphene. There are various functional groups on the surface, which are well dispersed in water and have a high negative charge on the surface. Various researches have been carried out to utilize graphene oxide to ceramic / metal / polymer bases so far, but the effect of improving the properties of thermoelectric materials has yet to be specified / implemented.
At present, chemical peeling method is widely used as a method of manufacturing graphene. The chemical stripping method is a method utilizing the oxidation-reduction characteristics of graphite. First, graphite oxide is produced by oxidizing graphite with strong acid and oxidizing agent. Since graphite oxide is hydrophilic, it is easy for water molecules to be inserted between the surface and the surface, and when it comes into contact with water, water molecules permeate between the surface and the surface due to the strong hydrophilic nature of the graphite oxide. As a result, the interplanar spacing is increased, and it can be easily peeled off by stirring for a long time or using an ultrasonic mill. The exfoliated graphite oxide is graphene oxide. In the present invention, such graphene oxide is used.
The Bi-Sb-Te thermoelectric material is a thermoelectric material suitable for use in a low-temperature region of 300 ° C or lower. In the case of Bi-Sb-Te based thermoelectric materials, it is difficult to control the bulk manufacturing process and thus reproducibility is poor, which has been a major obstacle to commercialization. Te has a high volatility at high temperature and is easy to volatilize during material synthesis / sintering and thermoelectric power generation application, and thus has a great effect in lowering the thermoelectric performance of the thermoelectric device.
In the present invention, graphene oxide is coated on the surface of a Bi-Sb-Te thermoelectric material core portion to enhance safety, thereby suppressing the formation of uneven Te vacancy. Therefore, a Bi-Sb-Te-based thermoelectric material having good physical property reproducibility can be produced.
As described above, the thermoelectric material powder according to the present invention is a high-efficiency p-type thermoelectric material capable of improving thermal stability and controlling thermoelectric performance by providing a graphene oxide coating layer as compared with a material in a conventional Bi-Sb- Material. Specifically, graphene oxide suppresses the volatilization of Te element and prevents or suppresses diffusion in the material, thereby improving the thermal stability and increasing the lattice scattering, thereby decreasing the thermal conductivity and increasing the thermoelectric performance of the material itself.
According to the present invention, the graphene oxide coated on the surface of the Bi-Sb-Te based thermoelectric material part can prevent or suppress the volatilization of the main elements constituting the Bi-Sb-Te based thermoelectric material, Thermal stability of the thermoelectric powder and the thermoelectric material sintered therewith can be ensured.
Particularly, in the present invention, graphene oxide is used instead of graphene. When the graphene is complexed, the dispersion characteristics are deteriorated and the mechanical strength is lowered. In addition, graphene has a low surface charge and tends to self-aggregate due to van der Waals forces, and exhibits very low solubility in any solvent, which has been a significant obstacle to practical application and academic research. As is the case with compounding with other materials, it is common to use a graphene surface modified with a surfactant or block copolymer when applying graphene to a thermoelectric material.
In contrast, graphene oxide is well dispersed in water and does not aggregate. In the present invention, the use of such graphene oxide does not require the use of a surfactant or the like.
2 is a flowchart schematically showing a method of manufacturing a thermoelectric powder according to an embodiment of the present invention.
As shown in FIG. 2, the thermoelectric powder manufacturing method according to the present invention includes a material synthesis step (S10), a powder formation step (S20), and a graphene oxide coating step (S30).
The material synthesis step (S10) is a step of synthesizing, for example, a Bi-Sb-Te-based material, and a conventional Bi-Sb-Te-based material synthesis method may be employed. For example, the material synthesis step S10 includes a step of mixing a raw material for forming a Bi-Sb-Te-based material and a step of synthesizing a Bi-Sb-Te-based compound by heat-treating the mixed raw material .
In the material synthesis step S10, the heat treatment may be performed using an ampoule method, an arc melting method, a solid state reaction (SSR), a metal flux method, a Bridgeman method ) Method, an optical floating zone method, a vapor transport method, and a mechanical alloying method.
Particularly, in the present invention, such a heat treatment step may be performed by an SSR method in which the mixture is put into an electric furnace and heated at a predetermined temperature for a predetermined time. Even thermoelectric materials of the same composition may have different thermoelectric performances depending on the reaction method between the raw materials. In the case of Bi-Sb-Te system, the raw materials are reacted by other methods such as SSR method rather than melting method The thermoelectric performance of the manufactured material can be further improved.
For example, in the material synthesis step (S10), the raw material mixture powder is hand-pressed to prepare a green body, which is then charged into a chamber, held in vacuum up to 10 -2 torr with a rotary pump, . At this time, heating can be performed in an Ar atmosphere.
The powder forming step (S20) is a step of forming a Bi-Sb-Te-based compound formed in step S10 in powder form. As described above, when the Bi-Sb-Te based compound is formed into a powder form, it has a high surface area, so that coating of graphene oxide on the Bi-Sb-Te based material can be more successfully performed in step S30. Further, when the Bi-Sb-Te-based composite is formed into a powder form, the sintered density can be further increased. Preferably, in the step S20, the particle size may be 50 nm to 500 mu m. More specifically, in step S20, a material having a grain size of 10 占 퐉 can be produced with a grain size of 26 占 퐉 or less.
The steps S10 and S20 correspond to the step of preparing the thermoelectric material core portion of the Bi-Sb-Te thermoelectric powder.
The coating step S30 is a step of coating a Bi-Sb-Te-based material formed in powder form with graphene oxide. For example, in the coating step S30, the Bi-Sb-Te based powder is mixed with a solution in which graphene oxide is dispersed, and at least one of ultrasonic treatment, heating, stirring, and shaking Processing may be carried out in a manner.
In the present invention, graphene oxide, which is low in graphene value and easy to utilize / apply, is used. As mentioned above, graphene oxide can be used after concentration adjustment by purchasing a product obtained by chemical peeling of graphite oxide and dispersing it in deionized water.
The Hummers method is well known as a method of obtaining graphite oxide from graphite. In this method, to form oxidized graphite, NaNO 3 , H 2 SO 4 , and KMnO 4 are used to break graphite intergranular bonds and to attach functional groups such as -OH and -COOH. This process will be described in more detail as follows.
To form graphite from graphite, graphite can be pretreated with a strong acid such as H 2 SO 4 and then oxidized with an oxidizing agent such as KMnO 4 . When H 2 SO 4 with further addition of the NaNO 3 HNO 3 is generated and HNO 3 is also helps to not only serves to act as an oxidizer to help the graphite oxide to remove the impurities contained in graphite. The mixture of graphite and NaNO 3 , H 2 SO 4 , and KMnO 4 is added with deionized water to form an aqueous solution, and H 2 O 2 is added to the graphite.
This aqueous graphite oxide solution is subjected to ultrasonic treatment to peel off the graphite oxide layer to obtain a solution in which graphene oxide is dispersed. This solution is diluted to an appropriate concentration, and a thermoelectric material powder such as the Bi-Sb-Te thermoelectric material powder prepared through steps S10 and S20 is mixed and subjected to ultrasonic treatment to form the graphene oxide coating step (S30) of the present invention Can be performed. After the ultrasonic treatment, a subsequent treatment for generally obtaining the powder can be performed in the order of washing and drying the precipitate.
Graphene oxide is easily adsorbed on the surface of a metallic thermoelectric material such as a Bi-Sb-Te thermoelectric material powder due to the functional group (-OH, -COO-, -CO) of the graphene surface. Therefore, there is no need to use a surfactant in comparison with the conventional methods using graphene directly. Even if a solution in which graphene oxide is dispersed for use in the production of the thermoelectric powder of the present invention is made of only graphene oxide and deionized water, Easy to operate, economical and other variables to control are reduced, and the process is simple and reproducible.
When graphene oxide is physically dispersed in deionized water, adsorption between graphene oxide and graphene oxide is not well induced. Therefore, graphene oxide can be coated as a single layer on the surface of the Bi-Sb-Te thermoelectric material powder.
The surface of the material can be coated 100% so that the remaining dispersion can be used to coat the surface of other materials. It is advantageous for mass synthesis if the concentration can be maintained to enable continuous coating.
As described above, the thermoelectric powder manufacturing method according to the present invention is economical because it is performed by a simple solution-based method without expensive deposition processes and the like.
The thermoelectric material according to the present invention can be manufactured by using the thermoelectric powder according to the present invention produced by the above-described method. In particular, the thermoelectric material according to the present invention can be obtained by sintering the thermoelectric powder according to the present invention. For example, the method of manufacturing a thermoelectric material according to the present invention may further include a step of sintering the powders coated in steps S 10 to
Therefore, the
This sintering step is a step of sintering the Bi-Sb-Te-based powder coated with graphene oxide. Here, the sintering step may be performed by a hot press (HP) method, a spark plasma sintering (SPS) method, or extrusion.
In the case of the thermoelectric material according to the present invention, when sintered by this pressure sintering method, a high sintering density and thermoelectric performance improving effect can be easily obtained. However, the present invention is not necessarily limited to this sintering method, and the sintering step may be performed in various other ways such as HPHT (High Pressure High Temperature) and HPT (High Pressure Torsion).
The sintering step may be performed in a vacuum state or while flowing an inert gas such as Ar, He, or N 2 containing a part of hydrogen or not containing hydrogen or maintaining the atmosphere.
P-type and n-type thermoelectric elements can be obtained if the bulk thermoelectric material obtained by the pressure sintering is formed by a cutting method or the like and made into a desired size sintered body from the beginning. A module can be manufactured by integrating such thermoelectric elements together with electrodes on a substrate. As the substrate, alumina, DBC (direct bonded copper), sapphire, silicon, Pyrex, quartz substrate, or the like can be used. The material of the electrode may be selected from copper, aluminum, nickel, gold, titanium, and the like, and the size of the electrode may be variously selected. The electrode may be patterned by any known patterning method without limitation. For example, a lift-off semiconductor process, a deposition method, a photolithography process, or the like may be used.
The thermoelectric cooling module may be a general cooling device such as a non-refrigerant refrigerator or an air conditioner, a CPU cooler, a laser diode cooling device, a CCD A micro cooling system such as a cooling element, a high output transistor cooling element, and an IR sensor cooling element, an air conditioner, a waste heat generation system, and the like, but is not limited thereto. The construction and the manufacturing method of the thermoelectric cooling system are well known in the art, and a detailed description thereof will be omitted herein.
During the production of the thermoelectric material through the sintering of the thermoelectric powder, graphene oxide prevents the material from moving, thereby ensuring thermal stability during manufacture. When a thermoelectric element, a thermoelectric module or a thermoelectric device using a sintered thermoelectric material is used, graphene oxide prevents oxidation, prevents volatilization, and changes the composition of the thermoelectric element, thereby ensuring thermal stability during use.
FIG. 3 is a diagram schematically showing a configuration of a thermoelectric material produced by sintering a thermoelectric powder according to an embodiment of the present invention, which is a schematic representation of a microstructure in a cross section of a sintered body.
3, the
Here, the crystal grain (A) of the Bi-Sb-Te-based thermoelectric material is a crystal grain containing a Bi-Sb-Te-based thermoelectric material, and a matrix may be formed in a form in which a plurality of the crystal grains are adjacent to each other. The graphene oxide (B) can be located at the grain boundary of the grain (A) of the Bi-Sb-Te-based thermoelectric material, that is, at grain boundaries.
The grain A of the Bi-Sb-Te-based thermoelectric material can be formed into various sizes and shapes. For example, the size of the grain (A) of the Bi-Sb-Te-based thermoelectric material may be several tens of nanometers to several hundreds of micrometers. Further, the size of the grain A of the Bi-Sb-Te-based thermoelectric material may be, for example, 1 to 500 mu m. The grain (A) of the Bi-Sb-Te-based thermoelectric material may be formed into various shapes such as a spherical shape, an acicular shape, a plate shape and the like depending on synthesis conditions and the like.
Particularly, in the
The graphene oxide (B) in the
Meanwhile, the graphene oxide included in the grain boundaries in the thermoelectric material according to an embodiment of the present invention may exist in the form of a film or may exist in the form of agglomerated particles.
As described above, the thermoelectric material according to the present invention is a structure in which grains of a Bi-Sb-Te-based thermoelectric material and graphene oxide located in a grain boundary of the Bi-Sb-Te-based thermoelectric material are consolidated.
The thermoelectric material having such a structure can be produced by sintering the thermoelectric powder according to the present invention as described above, or by mixing and sintering Bi-Sb-Te thermoelectric material powder and graphene oxide. In the case of using the thermoelectric powder according to the present invention, it is possible to uniformly coat graphene oxide with respect to a large surface area of the Bi-Sb-Te thermoelectric material core portion, so that the Bi-Sb-Te thermoelectric material powder and graphene oxide are mixed Sb-Te-based thermoelectric material core in the sintering process, compared to the sintering of the sintered Bi-Sb-Te based thermoelectric material, and the graphen oxide is uniformly distributed in the grain boundaries of the Bi- It is easy.
As mentioned above, ZT is related to the Seebeck coefficient, electrical conductivity, and thermal conductivity. The high ZT means that the energy conversion efficiency of the thermoelectric material is high. To increase the figure of merit, it is necessary to increase the power factor or decrease the thermal conductivity. In particular, among the functions that influence the performance index of the thermoelectric material, since the Seebeck coefficient and the electric conductivity depend mainly on the charge scattering and the thermal conductivity depends mainly on the lattice scattering, it is necessary to control the characteristics through control of the microstructure have.
In the present invention, it is possible to improve the figure of merit (ZT) by minimizing the scattering of charges in the thermoelectric material and increasing the lattice scattering constituting the thermoelectric material to induce the reduction of the thermal conductivity.
The thermoelectric material according to the present invention can constitute a thermoelectric device. Such a thermoelectric device can secure the thermal stability and can maintain the efficiency without deterioration even when it is used for a long time at a high temperature.
Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. It should be understood, however, that the embodiments of the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.
Production Example 1: Production and pulverization of p-BST
Bi, Sb, and Te, which are raw materials in powder form, are weighed in a total amount of 25g at atomic ratios of 0.5, 1.5, and 3.0, pelletized at room temperature pressing, placed in a quartz tube, and vacuum sealed. The airtight tube is heated in a box furnace in a box furnace at 800 for 5 hours and then quenched at 650 to obtain a gray yield (ingot). This is crushed by a hand mill to obtain a p-type BST powder (hereinafter referred to as p-BST).
Production Example 2: Control of GO dispersion concentration
The concentration of commercially available graphene oxide (hereinafter referred to as GO) dispersion (~ 80% monolayer / deionized water) is diluted 1/20.
Example 1: Surface adsorption rate 100% GO @ p-BST Synthesis and sintering
4 is a schematic diagram of a process for manufacturing powder of an embodiment.
As shown in Fig. 4, (a) 60 ml of the diluted solution of Preparation Example 2 was added to a vial, and (b) 13 g of the product of Preparation Example 1 was added. (c) After 5 minutes of ultrasonication, GO is coated on the p-BST surface (using a sonicator for general cleaning). When the GO is not coated, the color of the solution is transparent. When the remaining GO is dispersed, the solution becomes brown.
Thereafter, the precipitate obtained through centrifugation (3000 rpm, 5 min) is washed once with deionized water and then dried in an oven at 70 캜 for one day. The powder obtained by crushing the obtained product with a hand mill is Example 1P (hereinafter referred to as GO @ p-BST).
Powder of Example 1P was placed in a graphite mold and sintered at SPS (50 MPa, 450 캜 for 5 minutes) to form a 12.7Φ sintered body. This sintered body is the example 1S.
Comparative Example 1: p-BST powder and sintered body
The powder formed under the same conditions as in Production Example 1 in which the GO coating was not carried out in Example 1 is referred to as 2P and the sintered product is referred to as 2S.
Evaluation Example 1: Comparison between Examples and Comparative Examples of Powder XRD
Fig. 5 shows XRD analysis results of Examples of the present invention and Comparative Powders.
Example Powder 1P and Comparative Powder 2P were prepared as Bi 0 . 5 Sb 1 . 5 Te 3 and the diffraction peak coincide. Therefore, it can be confirmed that there is no denaturation of p-BST in the GO treatment.
Evaluation Example 2: Sublimation test (300 DEG C)
The sintered bodies of Examples and Comparative Examples were formed into a hexagonal column having a surface area of about 1 to 2 cm 2 , and after the initial mass was measured, the resultant was placed in a quartz tube and vacuum-tight. After maintaining the temperature at 300 ° C for 100 hours, the mass of the sintered body was measured to determine the mass change, and the sublimation rates with and without graphene oxide were compared. Table 1 summarizes the results.
Thus, as a result of the sublimation test, the mass change after the GO treatment becomes small. As a result, it was confirmed that the sublimation speed was slowed down by 20%.
Evaluation Example 3: Evaluation of thermoelectric property
The sintered bodies of Examples and Comparative Examples were processed to suitable sizes, and thermal conductivity was measured by laser flash analysis. The electrical conductivities and whiteness coefficients of the samples were measured at predetermined temperature intervals using a ZEM-3 (Ulvac-Riko, Inc) The power factor (PF) and the figure of merit (ZT) were measured and the results were summarized in Table 2.
As can be seen from Table 2, the decrease in the electrical conductivity of the GO-added Example 1S versus the Comparative Example 2S appears. This is because GO having a very high resistivity exists at the grain boundaries of BST. The main cause of this decrease in electrical conductivity is a reduction in the output factor by about 5%. On the other hand, the thermal conductivity decreases at the same time. It can be confirmed that the lattice thermal conductivity itself is reduced by about 9% as compared with that due to the reduction of the electric conductivity. This is the result of inducing lattice scattering and lowering the thermal conductivity by interfering with the free movement. That is, by using the GO coating layer, a lattice heat transfer blocking structure can be formed in a bulk-phase thermoelectric material having a thickness of several micrometers to several centimeters. Therefore, it can be confirmed that the performance index indicating the efficiency of the thermoelectric material is maintained within the error range even after utilizing the GO.
Evaluation Example 4: Raman spectroscopy
6 shows the results of Raman analysis of Examples and Comparative Examples. Raman analysis was performed using a Renishaw spectrometer (wavelength 514.5 nm).
Referring to FIG. 6, no D and G peaks were observed in Comparative Example 2S, and D and G peaks were formed in Example 1S due to graphene oxide. 1590cm -1 near the G peak will result from the E 2g mode vibration of the carbon sp 2 bond, D peak in the vicinity of 1350cm -1 is shown as sp 3 bonding of carbon is present. That is, in the present invention, a structure such as graphene oxide or a carbon-based material derived from graphene oxide, such as amorphous carbon or reduced graphene oxide, may be present in the thermoelectric material even after a high heat treatment such as sintering.
Table 3 is an average Raman measurement of Example 1S. D / G ratios were observed between 0.9 and less than 1.3. Therefore, depending on the sintering temperature, graphene oxide may be present in a weakly reduced atmosphere.
Evaluation Example 5: SEM measurement of Examples and Comparative Examples
FIG. 7 is a photograph of the fracture surface of Example 1S observed by SEM, and FIG. 8 is a photograph of the fracture surface of Comparative Example 2S observed by SEM. 7 and 8, a portion of the GO coating layer curled away from the surface is observed in the case of FIG. This is the result of observing the physically peeled GO coating layer during the fracturing process.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but many variations and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims. It will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the appended claims.
10: thermoelectric powder
20: core part
30: Shell part
Claims (16)
And a graphene oxide shell portion coated on the surface of the core portion.
Wherein the graphen oxide located in the grain boundary of the thermoelectric material is consolidated by sintering.
And forming a graphene oxide shell part on the surface of the core part.
Preparing a graphene oxide dispersion; And
And mixing the thermoelectric material core portion with the graphene oxide dispersion.
Bi-Sb-Te based material and preparing it in powder form,
Wherein forming the graphene oxide shell portion comprises:
Preparing a graphene oxide dispersion;
Mixing the thermoelectric material core portion with the graphene oxide dispersion;
Ultrasonic treatment and / or stirring; And
And washing and then drying the thermally conductive powder.
And sintering the thermoelectric powder.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20190080436A (en) * | 2017-12-28 | 2019-07-08 | 한국세라믹기술원 | A preparation method of composite thermoelectric material using spray drying and composite thermoelectric material prepared therefrom |
| WO2019231018A1 (en) * | 2018-05-31 | 2019-12-05 | 공주대학교 산학협력단 | Method for manufacturing bi-sb-te-based thermoelectric material containing carbon nanotube, and thermoelectric material manufactured using same |
| US10714669B2 (en) | 2017-09-26 | 2020-07-14 | Hyundai Motor Company | Thermoelectric material and method for preparing the same |
| WO2022032333A1 (en) * | 2020-08-10 | 2022-02-17 | The University Of Wollongong | Thermoelectric material |
-
2015
- 2015-12-08 KR KR1020150174159A patent/KR20170067457A/en not_active Application Discontinuation
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10714669B2 (en) | 2017-09-26 | 2020-07-14 | Hyundai Motor Company | Thermoelectric material and method for preparing the same |
| KR20190080436A (en) * | 2017-12-28 | 2019-07-08 | 한국세라믹기술원 | A preparation method of composite thermoelectric material using spray drying and composite thermoelectric material prepared therefrom |
| WO2019231018A1 (en) * | 2018-05-31 | 2019-12-05 | 공주대학교 산학협력단 | Method for manufacturing bi-sb-te-based thermoelectric material containing carbon nanotube, and thermoelectric material manufactured using same |
| WO2022032333A1 (en) * | 2020-08-10 | 2022-02-17 | The University Of Wollongong | Thermoelectric material |
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