阅读说明：本技术 一种碲化铋热电材料及其制备方法 (Bismuth telluride thermoelectric material and preparation method thereof ) 是由 刘睿恒 任琳琳 曾小亮 孙蓉 于 2020-12-14 设计创作，主要内容包括：本发明属于热电材料技术领域,公开了一种碲化铋热电材料的制备方法,包括如下步骤：步骤一、按照N型碲化铋材料的化学式X_w/Bi_2Te_(2.7-)_wSe_(0.3)称取Bi、Te和Se单质粉末为原料,或者按照P型碲化铋材料的化学式X_w/Bi_(0.5-w)Sb_(1.5)Te_3称取Bi、Sb和Te单质粉末为原料,X为掺杂元素,w为掺杂元素X的化学计量比,范围为0≤w≤0.1；步骤二、将上述原料混合均匀后置于加装等离子发生器的球磨罐中进行高能球磨；步骤三、将球磨之后的罐体内的粉体在惰性气体下转移至烧结模具中进行烧结,烧结分两次进行,冷却后得到碲化铋热电材料。本发明首次结合等离子球磨和放电等离子烧结技术制备高性能碲化铋材料,该方法具有速度快,粉体成分可控,能耗小、适合大批量生产。(The invention belongs to the technical field of thermoelectric materials, and discloses a preparation method of a bismuth telluride thermoelectric material, which comprises the following steps: step one, according to a chemical formula X of the N-type bismuth telluride material w /Bi 2 Te 2.7‑ w Se 0.3 Weighing Bi, Te and Se simple substance powder as raw materials, or according to the chemical formula X of the P-type bismuth telluride material w /Bi 0.5‑w Sb 1.5 Te 3 Weighing Bi, Sb and Te simple substance powder as raw materials, wherein X is a doping element, w is the stoichiometric ratio of the doping element X, and the range of w is more than or equal to 0 and less than or equal to 0.1; step two, uniformly mixing the raw materials, and then placing the mixture into a ball milling tank provided with a plasma generator for high-energy ball milling; thirdly, transferring the powder in the tank body after ball milling to a sintering mold for sintering under inert gas, wherein the sintering is carried out twice, and cooling to obtain the powderA bismuth telluride thermoelectric material. The invention combines the plasma ball milling and the spark plasma sintering technology for the first time to prepare the high-performance bismuth telluride material, and the method has the advantages of high speed, controllable powder components, low energy consumption and suitability for mass production.)

1. A preparation method of a bismuth telluride thermoelectric material is characterized in that the prepared bismuth telluride thermoelectric material is of an N type or a P type, and comprises the following steps:

step one, according to a chemical formula X of the N-type bismuth telluride material_w/Bi₂Te_2.7-wSe_0.3Weighing Bi, Te and Se simple substance powder as raw materials, or according to the chemical formula X of the P-type bismuth telluride material_w/Bi_0.5-wSb_1.5Te₃Weighing Bi, Sb and Te simple substance powder as raw materials, wherein X is a doping element, w is the stoichiometric ratio of the doping element X, and the range of w is more than or equal to 0 and less than or equal to 0.1;

step two, uniformly mixing the raw materials, and then placing the mixture into a ball milling tank provided with a plasma generator for high-energy ball milling treatment;

and step three, transferring the powder in the tank body after ball milling to a sintering mold under the protection of inert gas for densification sintering, wherein the sintering is carried out twice, and cooling to obtain the bismuth telluride thermoelectric material.

2. The method for preparing a bismuth telluride thermoelectric material as In claim 1, wherein X is selected from at least one of S, I, Cl, Br, In, Sn, Ge, Pb, S, Cu and Ag.

3. The method for preparing the bismuth telluride thermoelectric material as in claim 1, wherein in the second step, the lining of the ball milling tank body additionally provided with the plasma generating device is made of polytetrafluoroethylene or hard alloy, the ball milling ball is made of hard alloy, stainless steel, zirconium oxide or tungsten carbide, and preferably made of hard alloy.

4. The method for preparing the bismuth telluride thermoelectric material as claimed in claim 1, wherein in the second step, the technological parameters of the ball milling treatment are as follows: the ball material mass ratio in the ball milling tank is (10-20): 1, ball milling is carried out in an inert atmosphere, and the ball milling time is 0.5-12 h.

5. The preparation method of the bismuth telluride thermoelectric material as in claim 1, wherein in the second step, the rotation speed of a ball milling tank provided with a plasma generator is 500-1500 r/min, and the electric power of the plasma generator is 0.5-3 kW.

6. The method for preparing the bismuth telluride thermoelectric material as in claim 1, wherein in the third step, the sintering is spark plasma sintering or hot-press sintering, and the process conditions of the first sintering are as follows: the vacuum degree is less than 10Pa, the heating rate is 20-100K/min, the sintering pressure is 50-65 Mpa, the pressure holding time is not less than 10 minutes, the sintering temperature is 400-520 ℃, and the preferred temperature is 450-500 ℃.

7. The preparation method of the bismuth telluride thermoelectric material as in claim 6, wherein the second sintering is to place the compact block material obtained by the first sintering in a sintering mold with a larger size again for second liquid phase plastic sintering, wherein the process conditions of the second sintering are that the vacuum degree is less than 10Pa, the heating rate is 20-100K/min, the sintering temperature is 450-500 ℃, the sintering pressure is 50-65 MPa, and the temperature and pressure holding time is 10-30 minutes.

8. A bismuth telluride thermoelectric material produced by the production method for a bismuth telluride thermoelectric material as claimed in any one of claims 1 to 7.

Technical Field

The invention belongs to the technical field of thermoelectric materials, and particularly relates to a bismuth telluride-based thermoelectric material with excellent thermoelectric performance and mechanical performance and a preparation method thereof.

Background

The thermoelectric material is a functional material that directly converts thermal energy and electric energy into each other using a Seebeck effect (Seebeck effect) and a Peltier effect (Peltier effect) of a semiconductor. The thermoelectric refrigeration technology based on the Peltier effect has the characteristics of small volume, no moving part, no noise, high precision and the like, and is widely applied to local refrigeration and temperature control of electronic elements in the fields of microelectronics, computers, aerospace and the like. In recent years, with the rapid development of the 5G industry, micro thermoelectric cooling devices have become one of the key components essential for thermal management of high-speed communication optical modules.

At present, bismuth telluride-based alloys are always the best thermoelectric conversion materials with performance near room temperature, and are the only commercial materials used for thermoelectric refrigeration devices. The bismuth telluride-based thermoelectric material has a hexagonal crystal structure and is an anisotropic layered compound, wherein the layer along the 100 crystal plane has higher mobility and is the dominant direction of thermoelectric performance. In addition, since adjacent tellurium atomic layers are bonded with weak van der waals force and are easily cleaved, mechanical strength is low, and workability of materials and reliability in use of components are greatly affected. With the development of 5G and other electronic technologies, the packaging of devices such as communication optical modules and the like is developing towards miniaturization, so that the requirements on the miniaturization, reliability and refrigeration power consumption of thermoelectric refrigeration devices are higher and higher, and how to obtain a bismuth telluride material which has good grain orientation, excellent thermoelectric performance and very good mechanical strength to meet the requirements of fine cutting processing becomes the key for improving the performance of the miniature refrigeration devices at present.

At present, three mainstream processes are available for batch synthesis of bismuth telluride materials, firstly, a region melting method is adopted to grow rod-shaped crystals, the method can realize very good crystal grain orientation, so that the thermoelectric performance along the growth direction is ensured, the maximum ZT of the N-type material grown by the region melting method reaches about 0.9, and the maximum ZT of the P-type material can reach 1.1; however, the material obtained by the process has very large crystal grains, very poor mechanical strength and easy dissociation, and the segregation of components can occur in the melt crystallization process, so that the uniformity of mass production materials is poor; and secondly, a hot extrusion method is adopted to carry out thermoplastic densification on the zone-melting crystal bar under pressure, so that the grain refinement is promoted and the grain turning is promoted to improve the texturing degree. Because the grain refinement is enhanced, the mechanical strength of the material of the process is increased, and the thermoelectric property basically keeps the level of crystals of a zone melting method; the third is a powder metallurgy method, namely, raw material powder is mixed and ball-milled mechanically alloyed or melted and spun to obtain bismuth telluride ultrafine powder, and then densification is carried out in a sintering mode. The process has better material consistency because the powder mixing uniformity is higher; the high-energy ball milling can refine the grain size to nano level, so that phonons can be strongly scattered to reduce the thermal conductivity of the material, and the mechanical strength of the material is greatly improved due to the fine-grain strengthening effect. However, in the process of preparing the ultrafine powder by high-energy ball milling, impurities are very easily introduced due to the high energy in the ball milling process, and the ultrafine powder is very easily oxidized in the transfer process, so that the optimization of the electrical property and the final thermoelectric figure of merit is difficult. Although the melting rotary-throwing process can avoid the introduction of impurities, the equipment is expensive and large-scale mass production is difficult to realize. Therefore, how to realize the ultrafine-grained and directionally arranged microstructure and the component-controllable bismuth telluride material in batch is still a key bottleneck problem.

Disclosure of Invention

In order to solve the problems in the background art and overcome the respective disadvantages of the processes, the invention provides a bismuth telluride thermoelectric material and a preparation method thereof, which adopt a plasma-assisted ball milling powder preparation technology and combine a sintering densification process under a totally-enclosed system to realize a synthesis preparation technology of a component-controllable ultrafine-grained bismuth telluride material.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

the invention provides a method for preparing a high-performance bismuth telluride material in batch by combining plasma-assisted powder preparation with a totally-enclosed system sintering densification technology, which comprises the following steps:

step one, according to a chemical formula X of the N-type bismuth telluride material_w/Bi₂Te_2.7-wSe_0.3Weighing Bi, Te and Se simple substance powder as raw materials, or according to the chemical formula X of the P-type bismuth telluride material_w/Bi_0.5-wSb_1.5Te₃Weighing Bi, Sb and Te simple substance powder as raw materials, wherein X is a doping element, w is the stoichiometric ratio of the doping element X, and the range of w is more than or equal to 0 and less than or equal to 0.1;

step two, uniformly mixing the raw materials, and then placing the mixture into a ball milling tank provided with a plasma generator for high-energy ball milling treatment;

and step three, transferring the powder in the tank body after ball milling to a sintering mold under the protection of inert gas for densification sintering, wherein the sintering is carried out twice, and cooling to obtain the bismuth telluride thermoelectric material.

In the technical scheme of the invention, X is selected from at least one of S, I, Cl, Br, In, Sn, Ge, Pb, S, Cu and Ag.

In the technical scheme of the invention, in the second step, the lining of the ball milling tank body additionally provided with the plasma generating device is made of polytetrafluoroethylene or hard alloy, and the ball milling ball is made of hard alloy, stainless steel, zirconium oxide or tungsten carbide, preferably made of hard alloy.

In the technical scheme of the invention, in the second step, the technological parameters of ball milling treatment are as follows: the ball material mass ratio in the ball milling tank is (10-20): 1, ball milling is carried out in an inert atmosphere, and the ball milling time is 0.5-12 h.

In the technical scheme of the invention, in the second step, the rotating speed of a ball milling tank additionally provided with the plasma generator is 500-1500 r/min, and the electric power of the plasma generator is 0.5-3 kW.

In the technical scheme of the invention, in the third step, the sintering adopts spark plasma sintering or hot-pressing sintering, and the process conditions of the first sintering are as follows: the vacuum degree is less than 10Pa, the heating rate is 20-100K/min, the sintering pressure is 50-65 Mpa, the pressure holding time is not less than 30 minutes, the sintering temperature is 400-520 ℃, and the preferable temperature is 450-500 ℃.

In the technical scheme of the invention, the second sintering is to place the compact block material obtained by the first sintering in a sintering mold with a larger size again for secondary liquid phase plastic sintering, wherein the process conditions of the second sintering are that the vacuum degree is less than 10Pa, the heating rate is 20-100K/min, the sintering temperature is 450-500 ℃, the sintering pressure is 50-65 Mpa, and the temperature and pressure holding time is 10-30 minutes.

In another aspect, the invention also provides a bismuth telluride thermoelectric material prepared according to the method.

After the ball milling is finished, placing the ball milling tank in a glove box, loading the powder into a sintering mold under the protection of inert gas, and transferring the powder to a discharge plasma sintering furnace;

compared with the prior art, the invention has the following beneficial effects:

1. the invention combines the plasma ball milling and the spark plasma sintering technology for the first time to prepare the high-performance bismuth telluride material, and the method has the characteristics of high speed, controllable powder components, low energy consumption and suitability for mass production.

2. The invention provides a synthesis and preparation technology for realizing a component-controllable ultrafine-grained bismuth telluride material by adopting a plasma-assisted ball milling powder preparation technology and combining a sintering densification process under a totally-enclosed system.

3. The invention adopts a plasma-assisted high-energy ball milling technology, and the high energy of local plasma is adopted to enable the surface of the powder to generate a high activation state, so that the ultrafine grinding can be realized under the condition of low overall ball milling energy, and the introduction of impurities is avoided; the powder is transferred, filled and sintered under the protection of inert gas, so that the exposure and oxidation of high-activity nano superfine powder in the air are avoided, and the controllability of material components and the maintenance of a nano crystal grain microstructure are realized; and then the crystal grain steering is realized by a secondary thermal deformation sintering method, the improvement of the texturing degree is promoted, the bismuth telluride material with controllable crystal grain components and high texturing degree is finally obtained, and the dual improvement of the thermoelectric property and the mechanical property is realized.

Drawings

Fig. 1 is a sectional SEM image of a bismuth telluride thermoelectric material produced in example 1 of the present invention, wherein (a) is a sectional microstructure diagram taken in a direction parallel to a sintering pressure direction, and (b) is a sectional microstructure diagram taken in a direction perpendicular to the sintering pressure direction.

Fig. 2 is a graph of ZT values of materials prepared in examples 1 to 3 and comparative examples 1 to 4, wherein (a) is a graph showing a comparison of ZT values of materials prepared in example 1, example and comparative example 1 and comparative example 3 of the present invention, and (b) is a graph showing a comparison of ZT values of materials prepared in example 2, comparative example 2 and comparative example 4.

FIG. 3 shows P-type Bi prepared in example 1 of the present invention_0.5Sb_1.5Te₃And N-type Bi prepared in example 2₂Te_2.7Se_0.3Comparison of the flexural strength properties of the materials and the materials prepared in comparative examples 3 and 4.

Detailed Description

The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, but it should be understood that the scope of the present invention is not limited by the specific embodiments.

Example 1

According to the chemical formula Bi_0.5Sb_1.5Te₃Weighing simple substance raw materials Bi, Sb and Te (the purity of each element is more than or equal to 99.99%) according to a stoichiometric ratio, putting the prepared raw materials into a stainless steel ball milling tank in a glove box filled with high-purity argon, then carrying out high-speed ball milling by a plasma ball mill, setting the rotating speed of the ball mill to be 500r/min, setting the power of a plasma generator to be 2kW, carrying out ball milling for 60 minutes, fully grinding to obtain powder, then putting a sintering mold with the diameter of 15mm into the glove box, and then transferring the powder into a vacuum discharge plasma sintering furnace for sintering by a sealing device, wherein the process conditions are that the temperature is increased to 400 ℃ at the speed of 100 ℃ per minute, the sintering pressure is kept at 50MPa, and the sintering time is 15min, obtaining a columnar block material; and then putting the columnar block into a mold with the diameter of 25mm again for sintering again, wherein the sintering temperature is 500 ℃, the pressure is 60Mpa, and the sintering time is 20 minutes.

Example 2

According to the chemical formula Bi₂Te_2.7Se_0.3Weighing simple substance raw materials Bi, Sb and Te (the purity of each element is more than or equal to 99.99%) according to a stoichiometric ratio, putting the prepared raw materials into a tungsten carbide lining ball milling tank in a glove box filled with high-purity argon, then carrying out high-speed ball milling by a plasma ball mill, wherein the rotating speed of the ball mill is 600 revolutions per minute, the power of a plasma generator is set to be 1.5kW, the ball milling time is 60 minutes, fully grinding to obtain powder, then putting into a sintering mold with the diameter of 15mm in the glove box, and then transferring into a vacuum discharge plasma sintering furnace for sintering by a sealing device, wherein the process conditions are that the temperature is increased to 400 ℃ at the speed of 100 ℃ per minute, the sintering pressure is kept at 60MPa, and the sintering time is 10 minutes to obtain a columnar block material; and then putting the columnar block into a mold with the diameter of 25mm again for sintering again, wherein the sintering temperature is 480 ℃, the pressure is 60Mpa, and the sintering time is 20 minutes.

Example 3

According to the chemical formula Cu_0.002Bi_0.498Sb_1.5Te₃Weighing simple substance raw materials Cu, Bi, Sb and Te (the purity of each element is more than or equal to 99.99%) according to a stoichiometric ratio, putting the prepared raw materials into a zirconia lining ball milling tank in a glove box filled with high-purity argon, then carrying out high-speed ball milling by a plasma ball mill at the rotating speed of 800 r/min, setting the power of a plasma generator to be 0.5kW and the ball milling time to be 90 minutes, fully grinding to obtain powder, then putting the powder into a sintering mold with the diameter of 10mm in the glove box, and then transferring the powder into a vacuum discharge plasma sintering furnace for sintering by a sealing device, wherein the process conditions are that the temperature is increased to 450 ℃ at the speed of 100 ℃ per minute, the sintering pressure is kept at 50MPa, and the sintering time is 10 minutes. And then putting the columnar block into a mold with the diameter of 25mm again for sintering again, wherein the sintering temperature is 500 ℃, the pressure is 60Mpa, and the sintering time is 20 minutes.

Comparative example 1

According to the chemical formula Bi_0.5Sb_1.5Te₃Weighing simple substance raw materials Bi, Sb and Te (the purity of each element is more than or equal to 99.99%) according to the stoichiometric ratio, sealing the prepared raw materials in quartz tubes with unequal diameters of 50mm/30mm in vacuum, then placing a coarse quartz tube in a vacuum hot extrusion furnace at the temperature of 520 ℃, setting the temperature of a switching part of the quartz tube at 450 ℃, simultaneously pressing the materials into the quartz tube with the diameter of 30mm from the quartz tube with the diameter of 50mm by adopting air pressure, finally extruding the materials into a crystal bar, and finally obtaining the columnar hot extrusion crystal material at the extrusion moving speed of 5 cm/h.

Comparative example 2

According to the chemical formula Bi₂Te_2.7Se_0.3Weighing simple substance raw materials Bi, Sb and Te (the purity of each element is more than or equal to 99.99%) according to a stoichiometric ratio, putting the prepared raw materials into a stainless steel ball milling tank in a glove box filled with high-purity argon, then adopting a planetary ball mill, wherein the rotating speed of the ball mill is 1000 r/min, the ball milling time is 60 minutes, fully grinding to obtain powder, then sintering in a vacuum discharge plasma sintering furnace, and carrying out the sintering under the process conditions that the temperature is increased to the sintering temperature of 420 ℃ at the speed of 100 ℃ per minute, the sintering pressure is kept at 60MPa, the sintering time is 20 minutes, and then cooling at the speed of 60 ℃ per minute to obtain the columnar block material.

Comparative example 3

According to the chemical formula Bi_0.5Sb_1.5Te₃Weighing simple substance raw materials Bi, Sb and Te (the purity of each element is more than or equal to 99.99%) according to the stoichiometric ratio, sealing the prepared raw materials in a quartz tube in vacuum, melting and solidifying the raw materials in a zone melting mode, wherein the temperature of a melting zone is 520 ℃, the width of the melting zone is 3cm, and the moving speed of the quartz tube is 3cm/h, so that the columnar zone-melting crystal material is finally obtained.

Comparative example 4

According to the chemical formula Bi₂Te_2.7Se_0.3Weighing simple substance raw materials Bi, Se and Te (the purity of each element is more than or equal to 99.99%) according to the stoichiometric ratio, vacuum sealing the prepared raw materials in quartz tubes with unequal diameters of 50mm/30mm, and then carrying out vacuum sealing on the quartz tubesAnd (3) placing the coarse quartz tube in a vacuum hot extrusion furnace at the temperature of 520 ℃, setting the temperature of the joint of the quartz tube at 450 ℃, simultaneously pressing the material into a quartz tube with the diameter of 50mm in an air pressure mode, extruding the material into a crystal bar, and finally obtaining the columnar hot extrusion crystal material, wherein the extrusion moving speed is 5 cm/h.

Testing and characterization

FIG. 1 is a SEM image of a bismuth telluride thermoelectric material prepared in example 1, wherein (a) is a sectional micro-structural view parallel to a sintering pressure direction, and (b) is a sectional micro-structural view perpendicular to the sintering pressure direction, and it can be seen from FIG. 1 that flaky grains are arranged substantially in the pressure perpendicular direction due to the pressure-promoted grain turning, and have good orientation.

FIG. 2 shows P-type Bi prepared in example 1 of the present invention_0.5Sb_1.5N-type Te prepared in example 2₃Bi₂Te_2.7Se_0.3Materials and Cu prepared in example 3_0.002Bi_0.498Sb_1.5Te₃ZT values of the materials and the materials prepared in comparative examples 1 to 4 were compared in an analysis chart, the ZT values were determined by measuring the electrical conductivity σ, Zeebeck coefficient α and thermal conductivity κ of examples 1 to 3 and comparative examples 1 to 4, respectively, and then passing ZT ═ σ α²Calculating to obtain the result of the/kappa; it can be seen that the performance merit values of the N-type and P-type bismuth telluride-based thermoelectric materials can be greatly improved by adopting the novel plasma ball milling combined with the spark plasma sintering process.

FIG. 3 shows P-type Bi prepared in example 1 of the present invention_0.5Sb_1.5Te₃And N-type Bi prepared in example 2₂Te_2.7Se_0.3The bending strength performance of the material and the material prepared by the comparative example 3 and the comparative example 4 are compared, the mechanical bending strength is tested by adopting a three-point bending method, the bending strength of the material prepared by the example 1, the example 2, the comparative example 3 and the comparative example 4 is 81Mpa, 65Mpa, 48Mpa and 24Mpa respectively, and the mechanical bending strength of the N-type and P-type bismuth telluride-based thermoelectric materials can be greatly improved by adopting the novel plasma ball mill and sintering process.

The invention selects the plasma-assisted ball milling process to perform mechanical alloying synthesis of the bismuth telluride powder, and has the comprehensive advantages of uniform mixing, accurate and controllable components, nanometer superfine powder and the like. Specifically, the bismuth telluride high-purity raw material glove box is placed into a ball milling tank provided with a plasma generator, then high-energy ball milling is carried out in a sealing mode, the plasma generator can discharge to generate plasma in the ball milling process, so that the surface of powder is in a high-activity state, the powder is beneficial to thinning and mutual diffusion reaction, and the effect of rapid mechanical alloying is achieved; meanwhile, in the state of plasma-assisted activation, the ball-milling tank achieves high reaction energy by increasing the rotating speed and the collision mechanical energy in disorder, so that the loss of the ball-milling tank and the grinding balls is greatly reduced, the introduction of impurity elements is reduced, and the method is very suitable for component control during mass production and is also suitable for small-batch compound synthesis. In addition, the invention also combines a Spark Plasma Sintering (SPS) process to sinter the superfine powder, in particular to a novel powder metallurgy sintering technology which transfers the powder after the plasma-assisted ball milling to a sintering mould under the protection of full inert gas, utilizes upper and lower electrode pressure heads to electrify current for discharge heating, applies pressing pressure to the sintered powder, and prepares a high-performance material after the superfine powder is subjected to thermal plastic discharge deformation and densification.

Therefore, the invention combines the advantages of plasma ball milling technology and rapid sintering densification of discharge plasma for the first time to prepare the room-temperature bismuth telluride bulk thermoelectric material with high thermoelectric performance and high mechanical strength. The method is also applicable to the synthesis of other thermoelectric materials such as skutterudite, half heusler, lead telluride, germanium telluride and the like.

Finally, the invention is described by the above embodiments, but the invention is not limited to the above process steps, i.e. the invention is not meant to be implemented only by relying on the above process steps. It will be apparent to those skilled in the art that any modification of the present invention, equivalent substitutions of selected materials and additions of auxiliary components, selection of specific modes and the like, which are within the scope and disclosure of the present invention, are contemplated by the present invention.

The above disclosure is only one specific embodiment of the present invention, which is provided for the purpose of illustrating the technical solutions of the present invention and not for limiting the same, and it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the technical solutions of the present invention, and all of which are intended to be covered by the claims of the present invention.