Preparation method of zirconium oxide doped bismuth telluride-based thermoelectric material

Abstract

The invention provides a preparation method of a zirconium oxide-doped bismuth telluride-based thermoelectric material, a nano zirconium oxide material is introduced to prepare the composite bismuth telluride-based thermoelectric material, and due to the outstanding electrical properties and mechanical properties of nano zirconium oxide, the thermoelectric properties and mechanical properties of a composite product are improved by ball-milling mixing and hot extrusion preparation processes. Compared with a commercial bismuth telluride material, the bismuth telluride material is improved. By doping the nano zirconia material, more stress can be effectively borne, the matrix load is reduced, the mechanical property of the material is improved, the thermoelectric property of the material is not reduced, and the application prospect of the bismuth telluride thermoelectric material is effectively widened.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermoelectric materials, and in particular relates to a method for preparing a bismuth telluride-based thermoelectric material. Background Art

[0002] With the progress of society, environmental pollution and energy crisis are becoming increasingly serious. People are paying more and more attention to the sustainable development of society and nature, and are also paying more and more attention to the development and utilization of new environmentally friendly energy replacement materials. Thermoelectric effect is a general term for the electric effect caused by temperature difference and the reversible thermal effect caused by current, including Seebeck effect, Peltier effect and Thomson effect. Thermoelectric material is a green energy material that uses thermoelectric effect to realize the direct conversion between thermal energy and electrical energy. Thermoelectric materials have many advantages, such as small size, light weight, compact structure, no mechanical rotating parts, no pollution, no leakage, no noise, precise temperature control, fast response speed, etc. These advantages make thermoelectric materials an important type of functional materials, with broad application space and prospects in both temperature difference power generation and thermoelectric refrigeration, such as recycling of industrial waste heat, infrared sensors, portable thermoelectric refrigerators, special space power sources, etc.

[0003] At present, the bottleneck restricting the practical application of thermoelectric materials is their relatively low thermoelectric conversion efficiency. The performance figure of merit ZT of thermoelectric materials is an important indicator to measure the thermoelectric conversion efficiency. The ZT value can be expressed as ZT = α 2 σT / κ=α 2 σT / (κ L +κ e ), where α is the Seebeck coefficient of the material, σ is the electrical conductivity, and κ is the total thermal conductivity, including the lattice thermal conductivity κ L and the electronic thermal conductivity κ e , T is the absolute temperature. A good thermoelectric material should have a large Seebeck coefficient and electrical conductivity and a small thermal conductivity. These three parameters are mutually coupled and interrelated, and are all related to carrier transport and scattering. The Seebeck coefficient and electrical conductivity depend on the electronic structure of the material and the scattering of carriers, and show opposite trends with the increase of carrier concentration; while thermal conductivity is not only related to the scattering of carriers, but also affected by the chemical composition and crystal structure of the material. Therefore, how to optimize these three parameters of thermoelectric materials to achieve coordinated regulation of electrical and thermal transport properties is the key to improving the thermoelectric performance of materials.

[0004] Bismuth telluride (Bi2Te3) alloy materials are the most mature and widely used thermoelectric materials with superior performance compared to other materials. However, the hardness and mechanical stability of commercial bismuth telluride are relatively low, which limits its use in some applications that require high mechanical stability. Summary of the invention

[0005] The present invention is to solve the above problems and provides a method for improving the mechanical properties of bismuth telluride-based thermoelectric materials. Nano zirconium oxide powder is doped into bismuth telluride material, bismuth telluride powder and nano zirconium oxide powder are evenly mixed by a ball mill, a composite material is prepared by vacuum sintering, and then hot extrusion is performed, and a composite material crystal rod is prepared after annealing.

[0006] The specific technical solutions of the present invention are as follows:

[0007] In a first aspect of the present invention, a method for preparing a zirconium oxide-doped bismuth telluride-based thermoelectric material is provided, comprising the following steps:

[0008] 1) mixing three single-element raw materials of Sb, Bi and Te, and then melting them in vacuum to obtain an ingot, which is then crushed to obtain a bismuth telluride-based powder;

[0009] 2) mixing the obtained bismuth telluride powder and nano zirconium oxide powder by ball milling to obtain a mixed powder;

[0010] 3) cold pressing the mixed powder by a hydraulic press, and then vacuum sintering to obtain a bismuth telluride-based bulk material;

[0011] 4) The bismuth telluride-based block material is placed in a hot extrusion die to obtain a composite material crystal rod, which is then annealed.

[0012] The optimal conditions for the four steps are as follows:

[0013] In step (1), the molar ratio of the three single-substance raw materials Bi, Sb and Te is 0.4:1.6:3; the purity of the three single-substance raw materials Bi, Sb and Te is 99.999%.

[0014] The operation of obtaining the ingot by vacuum melting is as follows: the three elements of Bi, Sb and Te are mixed and placed in a graphite crucible, the graphite crucible is placed in a quartz tube, the quartz tube is evacuated and then packaged for vacuum melting. The vacuum melting conditions are as follows: under a vacuum degree of 0.01 Pa, the temperature is increased to 700-800°C (preferably 750°C) at a rate of 10°C / min, and the temperature is kept for at least 6 hours and then cooled to room temperature.

[0015] In step (2), the mass fraction of the nano zirconium oxide powder in the mixed powder is 0.2% to 1.0%, and the mixed powder is placed in a ball mill. The ball milling process is: rotation speed 500r / min, ball milling time 5 to 20min.

[0016] In step (3), the cold pressing conditions are: axial pressure of 1000-2000 kN (preferably 1500 kN), and pressure holding for 3-10 minutes; vacuum sintering conditions are: vacuum degree less than 1 MPa, and heat preservation at a temperature of 500-600° C. (preferably 550° C.) for 8-15 hours.

[0017] In step (4), the hot extrusion temperature is set to 300-400°C (preferably 350°C), a pressure of 100-200 MPa (preferably 150 MPa) is applied in the extrusion direction, and the annealing temperature is set to 300-400°C (preferably 350°C) for 10 hours.

[0018] In a second aspect, the present invention provides a zirconium oxide-doped bismuth telluride-based thermoelectric material prepared by the above method.

[0019] In a specific embodiment of the present invention, the performance of crystal rods prepared from mixed powders with nano zirconium oxide powder mass fractions of 0.2%, 0.5%, and 1.0% was compared with that of crystal rods prepared from pure bismuth telluride-based powders. The results show that the hardness of the zirconium oxide-containing crystal rods is significantly better than that of the crystal rods prepared from pure bismuth telluride-based powders, and the hardness increases with the increase of zirconium oxide content. In terms of thermoelectric performance, there is no difference in the electrical conductivity between the nano zirconium oxide-doped mixed material crystal rods and the pure bismuth telluride-based crystal rods; the Seebeck coefficient α increases with the increase of zirconium oxide content, but the ZT value is the best when 0.2% zirconium oxide is doped.

[0020] Functions and Effects of the Invention

[0021] This application aims at the thermoelectric and mechanical performance limitations that restrict the current commercial bismuth telluride thermoelectric materials from being applied and promoted on a larger scale. The composite bismuth telluride-based thermoelectric materials are prepared by introducing nano zirconium oxide materials. Due to the outstanding electrical and mechanical properties of nano zirconium oxide, the mechanical properties of the composite product are improved compared with the commercial bismuth telluride materials through ball milling and hot extrusion preparation processes, while the thermoelectric performance of the materials will not be reduced. This application scheme has a great role in promoting the expansion of the current application scope of bismuth telluride materials.

[0022] The present invention can effectively bear more stress, reduce the matrix load, and improve the mechanical properties of the material by incorporating nano zirconium oxide materials without reducing the thermoelectric properties of the material, thereby effectively broadening the application prospects of bismuth telluride thermoelectric materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure is a process flow chart for preparing bismuth telluride-based thermoelectric materials of the present invention.

[0024] Figure 2 The indentation hardness comparison of the crystal rods of Examples 1 to 3 and the comparative example is shown.

[0025] Figure 3 The conductivity σ of the crystal rods of Examples 1 to 3 is compared with that of the comparative example.

[0026] Figure 4 Comparison of the Seebeck coefficient α of the crystal rods of Examples 1 to 3 and the comparative example.

[0027] Figure 5 Comparison of thermoelectric figures of merit ZT of Examples 1 to 3 and the comparative example crystal rod. DETAILED DESCRIPTION

[0028] The present invention is described in detail below in conjunction with the embodiments and the accompanying drawings. However, the following embodiments should not be considered as limiting the scope of the present invention.

[0029] Example 1

[0030] Preparation method of zirconia-doped bismuth telluride-based thermoelectric material Figure 1 , the specific steps are as follows:

[0031] (1) According to the molar ratio of Bi, Sb and Te of 0.4:1.6:3, 3000g of pure tellurium, bismuth and antimony element particles were weighed as matrix materials and loaded into a quartz tube, and vacuumed until the pressure in the tube was less than 2Pa and sealed. Then the quartz tube was placed in a tubular heating furnace, the temperature was set to 750℃, and the temperature was increased to 750℃ at a rate of 10℃ / min under a vacuum of 0.01Pa, and the temperature was kept at 750℃ for at least 6h, and then cooled outside the furnace. The high-temperature synthesized material was mechanically crushed for 3min, and bismuth telluride powder was obtained after screening.

[0032] (2) After mixing bismuth telluride powder and nano zirconium oxide powder, ball milling is performed at 500 revolutions per minute for 5 to 20 minutes to obtain a composite bismuth telluride powder material doped with 0.2% nano zirconium oxide.

[0033] (3) The obtained composite powder material is cold pressed into a blank by a hydraulic press, and then vacuum sintered for 8 to 15 hours. Vacuum sintering parameters: temperature 550°C, heat preservation for 8 to 15 hours.

[0034] (4) The sintered billet was placed in a hot extrusion die, and the die was placed in a heater together with the die. The temperature of the heater was set to 350°C. A pressure of 15 MPa was applied in the extrusion direction to extrude a rod with a diameter of 30 cm in the pressure direction. The extruded rod was kept at 350°C for 10 hours and then annealed.

[0035] Example 2

[0036] The preparation method is the same as that of Example 1, except that the mass fraction of the doped nano zirconium oxide powder is 0.5%.

[0037] Example 3

[0038] The preparation method is the same as that of Example 1, except that the mass fraction of the doped nano zirconium oxide powder is 1.0%.

[0039] Comparative Example 1

[0040] The preparation method is the same as that of Example 1, except that the nano zirconium oxide powder is not doped.

[0041] The crystal rods prepared in Examples 1 to 3 and Comparative Example 1 were tested under the same test conditions for electrical conductivity σ, Seebeck coefficient α, thermoelectric figure of merit ZT and hardness. The results are as follows:

[0042] Figure 2 The hardness of the crystal rods of Examples 1 to 3 is compared with that of the comparative example. The doping of zirconium oxide increases the hardness of the composite bismuth telluride powder material and is dependent on the doping amount. The higher the doping amount, the greater the hardness of the crystal rod.

[0043] Figure 3 The conductivity σ of the crystal rods of Examples 1 to 3 and the comparative example is shown. The doping of zirconium oxide causes the conductivity of the composite bismuth telluride powder material to decrease slightly. When the zirconium oxide doping amount is 0.2%, there is no difference in the conductivity σ of the two types of crystal rods. As the zirconium oxide content increases, the conductivity of the rod decreases slightly, but the degree of decrease is not obvious.

[0044] Figure 4 The comparison of Seebeck coefficients α of the crystal rods of Examples 1 to 3 and the comparative example is shown. The doping of zirconium oxide increases the conductivity of the composite bismuth telluride powder material. The Seebeck coefficient of the crystal rod doped with 0.5% zirconium oxide is the best, followed by the crystal rod doped with 1.0% zirconium oxide, and the third is the crystal rod doped with 0.2% zirconium oxide.

[0045] Figure 5 The thermoelectric figure of merit ZT of the crystal rods of Examples 1 to 3 and the comparative example is compared. The doping of zirconium oxide increases the thermoelectric figure of merit ZT of the composite bismuth telluride powder material. The crystal rod of Example 1 with the lowest doping amount has the best ZT, followed by the crystal rods of Example 2 and Example 3 with doping amounts of 0.5% and 1.0%, respectively. However, as the temperature rises, the ZT values ​​of the crystal rods of Example 2 and Example 3 gradually approach and become the same.

[0046] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for preparing a zirconium oxide-doped bismuth telluride-based thermoelectric material, characterized in that: The steps include: 1) mixing three single-element raw materials of Sb, Bi and Te, melting them in vacuum to obtain an ingot, and then crushing them to obtain bismuth telluride-based powder; 2) mixing the obtained bismuth telluride powder and nano zirconium oxide powder by ball milling to obtain a mixed powder; wherein the mass fraction of the nano zirconium oxide powder is 0.2% to 1.0%; 3) cold pressing the mixed powder by a hydraulic press, and then vacuum sintering to obtain a bismuth telluride-based bulk material; 4) The bismuth telluride-based block material is placed in a hot extrusion die to obtain a composite material crystal rod, which is then annealed.

2. The method for preparing bismuth telluride-based thermoelectric material according to claim 1, characterized in that: in, In step (1), the molar ratio of the three single-substance raw materials Bi, Sb and Te is 0.4:1.6:3; the purity of the three single-substance raw materials Bi, Sb and Te is 99.999%.

3. The method for preparing bismuth telluride-based thermoelectric material according to claim 1, characterized in that: in, The operation of obtaining the ingot by vacuum melting is as follows: the three elements Bi, Sb and Te are mixed and placed in a graphite crucible, the graphite crucible is placed in a quartz tube, the quartz tube is evacuated and packaged for vacuum melting, and the vacuum melting conditions are as follows: under a vacuum degree of 0.01Pa, the temperature is increased to 700-800℃ at a rate of 10℃ / min, and the mixture is kept warm for at least 6h and then cooled to room temperature.

4. The method for preparing bismuth telluride-based thermoelectric material according to claim 1, characterized in that: in, In step (2), the ball milling speed is 500 rpm and the mixing time is 5 to 20 min.

5. The method for preparing bismuth telluride-based thermoelectric material according to claim 1, characterized in that: in, In step (3), the cold pressing conditions are as follows: axial pressure of 1000 to 2000 kN, holding pressure for 3 to 10 minutes; The vacuum sintering conditions are as follows: the vacuum degree is less than 1 MPa, and the temperature is kept at 500-600°C for 8-15 hours.

6. The method for preparing bismuth telluride-based thermoelectric material according to claim 1, characterized in that: in, In step (4), the hot extrusion conditions are as follows: the temperature is set at 300-400°C, a pressure of 100-200 MPa is applied in the extrusion direction, and the annealing temperature is set at 300-400°C for 10 hours.

7. A bismuth telluride-based thermoelectric material, characterized in that: The method is prepared by any one of claims 1 to 6.

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