Method for preparing uniform N-type bismuth telluride powder based on melting centrifugation method and N-type bismuth telluride powder

Abstract

The invention provides a method for preparing uniform N-type bismuth telluride powder based on a melting centrifugation method and the N-type bismuth telluride powder.The preparation method comprises the steps that raw materials of the N-type bismuth telluride powder are subjected to vacuum packaging, then smelting ingot casting and zone melting crystal pulling are conducted, and an N-type bismuth telluride crystal bar is obtained; the preparation method comprises the following steps: coarsely breaking an N-type bismuth telluride crystal bar, melting, and dripping molten liquid onto a hydrophobic membrane disc rotating at a specified rotating speed to obtain N-type bismuth telluride powder with uniform particle size. The N-type bismuth telluride powder is prepared by adopting a melting centrifugation method instead of a mechanical grinding method, so that a polymerization effect and a donor-like effect of a material can be effectively avoided, crystal defects are reduced, and the forming quality and the particle size uniformity of the material are improved; the N-type bismuth telluride powder with different particle sizes can be obtained by adjusting the melting temperature, setting the rotating speed and the like, the particle size of the powder prepared under the same condition is uniform, further screening of the particle size of the powder is not needed, the powder can be directly put into use, and the method is suitable for industrial batch production.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoelectric materials, and in particular to a method for preparing uniform N-type bismuth telluride powder based on a melt centrifugal method and the N-type bismuth telluride powder. Background Art

[0002] Bi2Te3 alloy and its solid solution are the best near-room temperature thermoelectric materials at present. They have a large Seebeck coefficient and high electrical conductivity in the low temperature range, so they are widely used in thermoelectric cooling devices. With the continuous deepening of research, the performance of N-type bismuth telluride materials prepared by hot forging and hot extrusion has gradually improved, which is basically equivalent to the single-crystal bismuth telluride materials prepared by zone melting process, and the material strength is higher, which can be used for micro thermoelectric cooling devices or high-reliability thermoelectric cooling devices.

[0003] However, the disadvantage of hot forging and hot extrusion is that bismuth telluride alloys and their solid solutions will be affected by non-basic slip during the crushing and grinding process, resulting in a large number of point defects and holes. When a large number of Bi vacancies are generated, the Bi atoms occupying the Te position will more easily diffuse back to their original lattice and interact with antisite defects, thereby generating redundant Te vacancies and a large number of electrons. That is, the reaction is the interaction of two vacancies generated by the combination of antisite defects and mechanical deformation process, which is called "donor-like effect", and the expression is as follows:

[0004]

[0005] Where e' is the generated electron, and a similar formula also applies to Sb' Te and V” S ' b The donor-like effect will deteriorate the carrier concentration of N-type bismuth telluride materials, resulting in a decrease in the room temperature Seebeck coefficient and a deviation from the optimal performance range, which fundamentally restricts the improvement of the thermoelectric performance of N-type bismuth telluride materials near room temperature, and further leads to performance mismatch between N- and P-type material components, which greatly limits the development of thermoelectric cooling devices. Once the donor-like effect occurs, the impact on the performance of bismuth telluride materials is irreversible and difficult to eliminate through subsequent heat treatment processes.

[0006] In addition, N-type bismuth telluride materials are very prone to cold alloying. Traditional processes such as jaw crushing and ball milling will cause the separated bismuth telluride powder to re-aggregate into flakes or blocks in a short period of time, and the powder particle size distribution is uneven. Repeated grinding of the formed flakes or blocks will result in a new aggregation effect, resulting in a decrease in material utilization. Multiple grinding will also result in a large distribution range of the obtained powder particle size, and different particle sizes contain different defect concentrations, which will lead to uneven site performance of N-type bismuth telluride materials.

[0007] Therefore, it is urgent to develop a new method for preparing N-type bismuth telluride powder to replace mechanical grinding, avoid the generation of polymerization effect and donor-like effect, and meet the preparation of uniform powder of N-type bismuth telluride material. Summary of the invention

[0008] The object of the present invention is to provide a method for preparing uniform N-type bismuth telluride powder based on melt centrifugation and N-type bismuth telluride powder, so as to solve the problems existing in the background technology.

[0009] The first object of the present invention is to provide: a method for preparing uniform N-type bismuth telluride powder based on a melt centrifugal method, which comprises the steps of:

[0010] The raw material of N-type bismuth telluride powder is vacuum packaged, then melted and cast into ingots, and then zone melt-pulled to obtain N-type bismuth telluride crystal rods;

[0011] The N-type bismuth telluride crystal rod is roughly broken and then melted, and the molten liquid is dropped onto a hydrophobic membrane disk rotating at a specified speed to obtain N-type bismuth telluride powder with uniform particle size.

[0012] Preferably, the raw materials include simple substances and halides of metal elements in N-type bismuth telluride powder, wherein:

[0013] The stoichiometric ratio of the substances in the single substance satisfies: bismuth: antimony: tellurium: selenium = (2-x): x: (3-y): y, 0≤x≤1, 0≤y≤1;

[0014] The halide accounts for 0.05% of the total mass of the single substance, and includes at least one of antimony halide and tellurium halide.

[0015] Preferably, during vacuum packaging, the substances in the raw materials are placed in a quartz container in order from low to high melting points.

[0016] Preferably, when melting the ingot, the vacuum-packaged raw material is placed in a rocking furnace, and the reaction conditions are: melting temperature 923-1123K, melting holding time 8h-24h, rocking angle 20°-90°.

[0017] Preferably, during zone melting and crystal pulling, the temperature of the zone melting furnace is 873-1173 K, and the moving rate of the heating zone is 1-10 mm / min.

[0018] Preferably, during coarse crushing, the output size is 0.5 mm to 10 mm.

[0019] Preferably, during melting after rough breaking, the protective atmosphere is a nitrogen atmosphere or an inert gas atmosphere.

[0020] Preferably, when the raw material is melted after being roughly crushed, the melting temperature is 900-1200K.

[0021] Preferably, the top surface of the hydrophobic membrane disk is a polyimide film, and the specified rotation speed is 5000-15000 rpm.

[0022] Another object of the present invention is to provide: an N-type bismuth telluride powder, which is prepared by the method for preparing uniform N-type bismuth telluride powder based on the melt centrifugation method as described above.

[0023] The invention has the beneficial effects of: using the melt centrifugal method instead of the mechanical grinding method to prepare the N-type bismuth telluride powder, the polymerization effect and the donor-like effect of the material can be effectively avoided, the crystal defects can be reduced, and the molding quality and particle size uniformity of the material can be improved; in addition, by adjusting the melting temperature, formulating the rotation speed and other parameters, the N-type bismuth telluride powder with different particle sizes can be obtained, the powder prepared under the same conditions has a uniform particle size, the powder particle size consistency is high, and the utilization rate is as high as more than 95%, so that the powder has better performance and uniformity, and there is no need to further screen the powder particle size, and the powder can be directly put into use, which is suitable for industrial mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a statistical diagram of powder particle size distribution of the N-type bismuth telluride powder material prepared in Example 1 of the present invention;

[0025] Figure 2 is a FE-SEM image of the N-type bismuth telluride powder material prepared in Example 1 of the present invention;

[0026] Figure 3 is a statistical diagram of powder particle size distribution of N-type bismuth telluride powder material prepared in Example 2 of the present invention;

[0027] Figure 4 is a FE-SEM image of the N-type bismuth telluride powder material prepared in Example 2 of the present invention;

[0028] Figure 5 is a statistical diagram of powder particle size distribution of N-type bismuth telluride powder material prepared in Example 2 of the present invention;

[0029] Figure 6 This is a FE-SEM image of the N-type bismuth telluride powder material prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with embodiments and drawings:

[0031] Unless otherwise defined, all professional terms used hereinafter have the same meaning as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and comparative examples, and are not intended to limit the scope of protection of the present invention. It should be particularly noted that there may be multiple names for the same organic structure, as long as the structure is within the scope of this patent, it belongs to the protection object of this patent.

[0032] Unless otherwise defined, the raw materials, reagents, etc. in the following examples can be purchased from the market or prepared according to reported methods.

[0033] This embodiment provides a method for preparing uniform N-type bismuth telluride powder based on a melt centrifugal method and the N-type bismuth telluride powder prepared by the method. The process of preparing N-type bismuth telluride powder by the method includes the following steps:

[0034] (1) The raw material of N-type bismuth telluride powder is vacuum packaged, then melted into an ingot, and then zone melt-pulled to obtain an N-type bismuth telluride crystal rod.

[0035] In this step, the raw materials of N-type bismuth telluride powder include the simple substance and halide of the metal element in the N-type bismuth telluride powder, wherein: the simple substance of the metal element includes bismuth, antimony, tellurium and selenium, and the stoichiometric ratio satisfies bismuth: antimony: tellurium: selenium = (2-x): x: (3-y): y, 0≤x≤1, 0≤y≤1; the halide of the metal element includes at least one of antimony halide and tellurium halide, such as SbI3, TeI4, etc., and the halide of the metal element is used as a dopant, and its mass accounts for 0.05% of the total mass of the simple substance of the metal element.

[0036] The above-mentioned bismuth, antimony, tellurium and selenium are all selected from single substances with a purity of not less than 99.99% to ensure the purity and molding quality of the product.

[0037] During vacuum packaging, a quartz container (such as a quartz tube) is used to hold the raw materials. When holding the raw materials, the materials in the raw materials are placed in the quartz container in order from low to high melting points, so that the liquid-solid interface remains basically unchanged or moves very slowly during smelting, thereby reducing the segregation coefficient and component supercooling phenomenon, ensuring the microscopic uniformity of the grown crystal ingot, and improving the quality of product molding; after the filling is completed, the vacuum packaging is carried out using a hydrogen-oxygen flame to 10 -6 Torr.

[0038] When melting the ingot, the above-mentioned quartz container containing the raw materials and after vacuum packaging is placed in a swing furnace for melting to prepare an N-type bismuth telluride alloy ingot; the melting point of the N-type bismuth telluride material is 823-873K, so the melting temperature can be controlled at 923-1123K, the melting and holding time can be controlled at 8h-24h, and the swing angle can be controlled at 20°-90° to ensure that the material in the quartz container is fully melted and has good fluidity, and the raw materials are mixed and fully reacted.

[0039] During zone melting and crystal pulling, the quartz tube containing the N-type bismuth telluride alloy ingot is placed in a zone melting furnace to melt the crystal and obtain an N-type bismuth telluride crystal rod. In order to improve the quality of crystal pulling, the temperature of the zone melting furnace should be controlled at 873-1173K, and the moving rate of the heating zone should be controlled at 1-10mm / min.

[0040] (2) The N-type bismuth telluride crystal rod is roughly broken and then melted, and the molten liquid is dripped onto a hydrophobic membrane disk rotating at a specified speed to obtain N-type bismuth telluride powder with uniform particle size.

[0041] For coarse crushing, a jaw crusher or mechanical ball milling can be used. If a jaw crusher is used, the N-type bismuth telluride crystal rod is first divided into blocks of 5 to 60 mm, and then added to the jaw crusher, and the discharge size is set to 1 to 10 mm; if mechanical grinding is used, the speed of the ball mill is set to 290 rpm, the ball-to-material ratio is 1:1 to 1:10, the ball milling time is 2 to 10 minutes, and the discharge size is 0.5 to 10 mm.

[0042] After rough crushing, the crushed materials are added to a sealed heating furnace, the heating furnace is evacuated to below 100Pa, and nitrogen or rare gas is introduced, and the vacuum and gasification are repeated three times for washing, and finally nitrogen or rare gas is filled into the heating furnace as a protective atmosphere to prevent oxidation of the material. The heating furnace used in this embodiment is a prior art, and has a dripping hole at the bottom, and a flow valve can also be set at the dripping hole. The molten liquid in the furnace drips directly through the dripping hole onto the hydrophobic membrane disk below, collides with the hydrophobic membrane disk rotating at a specified speed, and is centrifugally dispersed, avoiding the occurrence of donor-like effect and polymerization effect.

[0043] During melting, the temperature in the heating furnace is controlled at 900-1200K, which exceeds the melting point of the N-type bismuth telluride material to ensure the fluidity of the molten droplet.

[0044] The hydrophobic membrane disk used in this embodiment has a polyimide film on its top surface and a specified rotation speed of 5000 to 15000 rpm. The polyimide film can increase the contact angle of the N-type bismuth telluride droplets, reduce the wettability, and facilitate the centrifugal splashing of the N-type bismuth telluride droplets. In addition, the polyimide film is resistant to high temperatures, does not react with the N-type bismuth telluride droplets, and can reduce the agglomeration of bismuth telluride.

[0045] The present invention utilizes a melt centrifugal method instead of a mechanical grinding method to prepare N-type bismuth telluride powder, which can effectively avoid the occurrence of a polymerization effect and a donor-like effect in the material, reduce crystal defects, and improve the material molding quality and particle size uniformity. In addition, N-type bismuth telluride powders with different particle sizes can be obtained by adjusting the melting temperature, formulating parameters such as a rotation speed, and the like. The powders prepared under the same conditions have a uniform particle size, a high consistency in the powder particle size, and a utilization rate of more than 95%. The powders have more excellent performance and uniformity, and can be directly put into use without further screening the powder particle size, and are suitable for industrial mass production.

[0046] Some specific embodiments are listed below.

[0047] Embodiment 1:

[0048] S1. Raw material weighing:

[0049] Take out high-purity bismuth blocks (≥99.99%), antimony blocks (≥99.99%), tellurium blocks (≥99.99%), selenium particles (≥99.99%), and SbI3 compounds (≥99.9%) from the vacuum cabinet or glove box;

[0050] Weigh the metal element in a stoichiometric ratio of bismuth: antimony: tellurium: selenium = 1.9:0.1:2.7:0.3, and add SbI3 accounting for 0.05% of the total weight of the metal element;

[0051] The raw materials were placed into the quartz tube in order of melting point from low to high, and vacuum-sealed with hydrogen-oxygen flame until 10 -6 Torr.

[0052] S2. Melting ingot:

[0053] The above-mentioned quartz tube containing raw materials and vacuum packaging is placed in a swing furnace for melting, the melting temperature is 1073K, the insulation time is 8h, the swing angle is 20-90°, and after melting, it is cooled to room temperature with the furnace to obtain the N-type bismuth telluride alloy ingot with the above-mentioned stoichiometric ratio.

[0054] S3, zone melting and crystal pulling:

[0055] A quartz tube containing an N-type bismuth telluride alloy ingot is placed in a zone melting furnace, and is pulled and grown at a speed of 1 mm / min at a zone melting temperature of 1153 K to form an N-type bismuth telluride crystal rod with a diameter of 30 mm.

[0056] S4, block coarse crushing:

[0057] The N-type bismuth telluride crystal rod is crushed into fragments with a size of 1 mm to 10 mm using a jaw crusher or mechanical crushing method, and the crushing time does not exceed 30 seconds.

[0058] S5. Atmosphere cleaning:

[0059] Add the crushed materials into a sealed heating furnace, evacuate the heating furnace to below 100Pa, then introduce nitrogen or rare gas, repeat the evacuation and filling three times for washing, and finally fill the heating furnace with nitrogen or rare gas as a protective atmosphere.

[0060] S6, melting centrifugation:

[0061] Turn on the heating switch of the heating furnace to raise the temperature of the heating furnace to 1200K, adjust the rotation speed of the hydrophobic membrane disk to 6000rpm, melt the N-type bismuth telluride material and drip it on the hydrophobic membrane disk, and the material is thrown out by high-speed centrifugal action and drips into the collection container outside the hydrophobic membrane disk. After cooling in the furnace, spherical N-type bismuth telluride powder with good particle size uniformity is obtained.

[0062] The particle size distribution statistics of powders are as follows: Figure 1 As shown, the FE-SEM image of the powder is as follows Figure 2 shown.

[0063] Embodiment 2:

[0064] The difference from Example 1 is that, during melt centrifugation, the temperature of the heating furnace is controlled at 1100K, the rotation speed of the hydrophobic membrane disk is 10000rpm, and the cooling method is changed to circulating water cooling, so as to obtain spherical N-type bismuth telluride powder with good particle size uniformity.

[0065] The particle size distribution statistics of powders are as follows: Figure 3 As shown, the FE-SEM image of the powder is as follows Figure 4 shown.

[0066] Comparative Example 1:

[0067] The difference from Example 1 is that, in Comparative Example 1, the following operations are performed after the block is roughly broken:

[0068] In a glove box filled with argon gas and with oxygen and water contents less than 10 ppm, N-type bismuth telluride material fragments with a size of 1 mm to 10 mm obtained by jaw crushing or mechanical crushing, as well as corundum balls and stainless steel grinding balls are placed in a grinding jar at a ball-to-material ratio of 10:1.

[0069] The mouth of the grinding jar is sealed by a vacuum sealing ring, a gasket, a bolt, etc. to keep an argon atmosphere inside the grinding jar, and the jar is loaded into a high-energy ball mill or a planetary ball mill. The speed of the high-energy ball mill or the planetary ball mill is set to 570 rpm, and the ball milling time is forward rotation for 6 hours and reverse rotation for 6 hours to obtain N-type bismuth telluride powder.

[0070] The particle size distribution statistics of powders are as follows: Figure 5 As shown, the FE-SEM image of the powder is as follows Figure 6 shown.

[0071] Depend on Figure 1 It is known that the particle size of the N-type bismuth telluride powder prepared in Example 1 is mostly distributed in the range of 30 μm to 70 μm, and D50 is 46.75 ± 0.54 μm. Figure 2 It is known that the N-type bismuth telluride powder prepared in Example 1 is spherical and has a uniform particle size;

[0072] Depend on Figure 3 It can be seen that the particle size of the N-type bismuth telluride powder prepared in Example 2 is mostly distributed in the range of 0 μm to 10 μm. It can be seen that lowering the melting temperature, increasing the centrifugal speed, and accelerating the cooling will all lead to a decrease in the powder particle size, but Figure 4 It shows that the prepared powder is still spherical, with D7.23±0.14μm, and the powder particle size uniformity is good.

[0073] Depend on Figure 5 It is known that the particle size distribution of the powders obtained by mechanical ball milling varies greatly, and is distributed in the particle size range of 0μm to 80μm. In addition, the particle size morphology of the powders obtained by mechanical ball milling varies greatly, with the coexistence of extremely fine powder and coarse particles, and the overall shape is irregular, which is very unfavorable for the subsequent preparation of polycrystalline N-type bismuth telluride crystal rods. In addition, the donor-like effect produced by mechanical grinding is unavoidable, which will lead to the degradation of the subsequent crystal rod performance.

[0074] The above are preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing uniform N-type bismuth telluride powder based on melt centrifugation, characterized in that: Includes steps: The raw material of N-type bismuth telluride powder is vacuum packaged, then melted into an ingot, and then zone melt-pulled to obtain an N-type bismuth telluride crystal rod; The N-type bismuth telluride crystal rod is roughly broken and then melted, and the molten liquid is dropped onto a hydrophobic membrane disk rotating at a specified speed to obtain N-type bismuth telluride powder with uniform particle size.

2. The method for preparing uniform N-type bismuth telluride powder based on melt centrifugation according to claim 1, characterized in that: The raw materials include simple substance and halide of metal elements in N-type bismuth telluride powder, wherein: The stoichiometric ratio of the substances in the single substance satisfies: bismuth: antimony: tellurium: selenium = (2-x): x: (3-y): y, 0≤x≤1, 0≤y≤1; The halide accounts for 0.05% of the total mass of the single substance, and includes at least one of antimony halide and tellurium halide.

3. The method for preparing uniform N-type bismuth telluride powder based on melt centrifugation method according to claim 1 or 2, characterized in that: During vacuum packaging, the materials in the raw materials are placed in a quartz container in order of melting points from low to high.

4. The method for preparing uniform N-type bismuth telluride powder based on melt centrifugation according to claim 1, characterized in that: When melting the ingot, the vacuum-packed raw materials are placed in a rocking furnace, and the reaction conditions are: melting temperature 923-1123K, melting holding time 8h-24h, rocking angle 20°-90°.

5. The method for preparing uniform N-type bismuth telluride powder based on melt centrifugation according to claim 1, characterized in that: During zone melting and crystal pulling, the temperature of the zone melting furnace is 873-1173K, and the moving rate of the heating zone is 1-10mm / min.

6. The method for preparing uniform N-type bismuth telluride powder based on melt centrifugation according to claim 1, characterized in that: During coarse crushing, the output size is 0.5mm~10mm.

7. The method for preparing uniform N-type bismuth telluride powder based on melt centrifugation according to claim 1, characterized in that: During melting after rough breaking, the protective atmosphere is nitrogen atmosphere or inert gas atmosphere.

8. The method for preparing uniform N-type bismuth telluride powder based on melt centrifugation according to claim 1, characterized in that: When melted after rough crushing, the melting temperature is 900~1200K.

9. The method for preparing uniform N-type bismuth telluride powder based on melt centrifugation according to claim 1, characterized in that: The top surface of the hydrophobic membrane disk is a polyimide film, and the specified rotation speed is 5000-15000 rpm.

10. An N-type bismuth telluride powder, characterized in that: The powder is prepared by the method for preparing uniform N-type bismuth telluride powder based on melt centrifugation as described in any one of claims 1 to 9.

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