CN115385307A - Preparation method and application of bismuth telluride micro-nano powder material - Google Patents

Abstract

The invention belongs to the technical field of thermoelectric semiconductor material preparation, and particularly relates to a preparation method of a bismuth telluride micro-nano powder material, which comprises the steps of crushing an alloy ingot of bismuth telluride into particles, placing the particles in a ball milling device, adding ethyl acetate for dry ball milling, discharging and drying, wherein the mass ratio of bismuth telluride to ethyl acetate is not less than 5:1. The bismuth telluride micro-nano powderIn the preparation method, a mode of combining smelting ingot casting and dry ball milling is adopted, and ethyl acetate is added in the ball milling process to assist dispersion, so that powder aggregation and integration blocks in the dry ball milling process are effectively avoided, the uniformity of the powder particle size is improved, the efficiency of the preparation process is high, and the energy consumption is low. Meanwhile, after the prepared bismuth telluride micro-nano powder is prepared into a bismuth telluride block, the thermoelectric property of the bismuth telluride block is obviously improved, and the thermoelectric figure of merit is obviously improvedzTIs improved.

Description

Preparation method and application of bismuth telluride micro-nano powder material

technical field

The invention belongs to the technical field of preparation of thermoelectric semiconductor materials, and in particular relates to a preparation method and application of a bismuth telluride micronano powder material.

Background technique

Thermoelectric materials can directly realize the conversion of heat and electricity, have great potential in power generation and refrigeration applications, and play an important role in solving energy and environmental problems. Now the commonly used thermoelectric materials are mainly bismuth telluride. The thermoelectric properties of thermoelectric materials are restricted by the Seebeck coefficient, electrical conductivity, and thermal conductivity, which are difficult to control independently. Since the micro-nano powder can increase the crystal interface, resulting in increased phonon scattering, effectively reducing the thermal conductivity of the material lattice, and the reduction in thermal conductivity is greater than the change in electrical properties, which can enhance the thermoelectric properties of the material.

At present, the preparation methods of micro-nano thermoelectric materials include mechanical alloying method, melt spinning method, etc. However, the equipment of the melt spinning method is expensive, and the energy consumption is high. The particle orientation is not high, so it is particularly important to develop methods with high efficiency, low energy consumption, and batch preparation of micro-nano powders. The method of smelting combined with ball milling can effectively avoid the above problems. Ball milling can be divided into wet ball milling and dry ball milling. Wet ball milling needs to use high-purity alcohol, hexane, acetone, etc. The powder is oxidized, and there are problems such as subsequent separation complexity. Dry ball milling does not need to introduce a large amount of wet milling media, and is easy to operate. However, during the dry ball milling process, the time is prolonged, and the materials are prone to agglomeration and uneven particle size distribution.

Contents of the invention

Aiming at the problems of material agglomeration and uneven particle size distribution in the dry ball milling process, the purpose of the present invention is to provide a preparation method of bismuth telluride micro-nano powder, smelting combined with ball milling to make powder, adding ethyl acetate during ball milling Ester dry ball milling avoids the agglomeration phenomenon of dry ball milling, and the particle size distribution of the obtained bismuth telluride micro-nano powder is uniform.

The present invention provides following technical scheme:

A preparation method of bismuth telluride micro-nano powder material, the alloy ingot of bismuth telluride is broken into particles, placed in a ball milling device, added with ethyl acetate for dry ball milling, discharging and drying, wherein bismuth telluride and The mass ratio of ethyl acetate is ≥5:1.

In the preparation method of the present invention, the bismuth telluride micro-nano powder is prepared by combining ingot melting and dry ball milling, and the ingot melting can improve the uniformity of alloy composition. Adding ethyl acetate during dry ball milling can effectively improve the phenomenon of powder agglomeration in dry ball milling and improve the particle size of the powder by taking advantage of the characteristics of ethyl acetate, such as high surface tension, strong permeability, and easy separation. Uniformity, and can significantly reduce the particle size of the powder.

As a preference of the method of the present invention, the crushed bismuth telluride particles have a particle size of 1-2 mm.

As a preferred method of the present invention, the alloy ingot of bismuth telluride is prepared through the following process:

Take Bi powder, Sb powder and Te powder according to the molar ratio of the nominal composition, weigh and mix them evenly, seal them in a vacuum quartz tube with a vacuum degree of less than 2 Pa, seal the tube, and then raise the temperature at a rate of 12-18°C/min Heat to 780-800°C, keep warm for 1-1.5 hours, then rock for 2-3 hours, the rocking frequency is 5-8 rpm/min, the rocking angle is 60°-65°, and then cool. Bi powder, Sb powder and Te powder with a purity of 99.99% are selected when preparing the alloy ingot.

As a preference of the method of the present invention, the mass ratio of bismuth telluride to ethyl acetate is 5-10:1. The amount of ethyl acetate introduced should not be too much, nor too little, too little will not achieve the dispersing effect, and agglomeration is still prone to occur, and too much will cause complicated separation, and the material is easy to be polluted, which will affect the material performance.

As a preference of the method of the present invention, the ball-to-material ratio of the ball milling balls to the bismuth telluride is 2-3:1.

As preferred method of the present invention,

The size of the grinding ball is 0.6~1.2mm;

And/or the ball milling speed is 350-500rpm/min;

And/or the single-cycle grinding time is 30-40 minutes, and the grinding time is 1-2 hours. Preferably, grinding is performed for at least two weeks in a single-cycle grinding time, and more preferably, the intermediate interval is about 10 to 20 minutes.

As a preferred method of the method of the present invention, the method of drying the materials is as follows: after spreading the materials, they are ventilated and dried at room temperature, and then heated to 40-50°C for drying. Ethyl acetate dispersant has a slightly fruity smell, low boiling point, and easy separation: put the discharged material on a sieve to separate the grinding balls and powder, then spread the powder and dry it at the vent for 10-20 minutes, then blow Dry in an air oven for 20-30 minutes.

A bismuth telluride micronano powder material obtained by the above preparation method. The obtained bismuth telluride micronano powder has uniform particle size distribution, small particle size, no agglomeration, and no pollution.

A method for improving the thermoelectric performance of a bismuth telluride block, the bismuth telluride block is obtained by vacuum hot-pressing sintering of the above-mentioned bismuth telluride micro-nano powder material. The zT value of the prepared bismuth telluride block at room temperature is improved.

As a preference of the present invention, the pressure of vacuum hot-press sintering is 70-100 MPa, the sintering temperature is 420-500° C., and the hot-press sintering time is 60-120 min.

The beneficial effects of the present invention are as follows:

In the preparation method of the bismuth telluride micro-nano powder of the present invention, the method of combining smelting ingot and dry ball milling is adopted, and ethyl acetate is used to assist dispersion during the ball milling process, which effectively avoids powder formation during the dry ball milling process. Aggregation into blocks improves the uniformity of the particle size of the powder, and the preparation process has high efficiency and low energy consumption. At the same time, after the prepared bismuth telluride micro-nano powder is prepared into a bismuth telluride block, the thermoelectric performance of the obtained bismuth telluride block is obviously improved, and the thermoelectric figure of merit zT is improved.

Description of drawings

FIG. 1 is an SEM image of the bismuth telluride micro-nano powder prepared in Example 1.

2 is a particle size distribution diagram of the bismuth telluride micro-nano powder prepared in Example 1.

3 is a particle size distribution diagram of the bismuth telluride micro-nano powder prepared in Comparative Example 1.

4 is a particle size distribution diagram of bismuth telluride micro-nano powder prepared in Comparative Example 2.

Detailed ways

The specific embodiments of the present invention will be further described below.

Unless otherwise specified, the raw materials used in the present invention can be purchased from the market or commonly used in the field. If not specified, the methods in the following examples are all conventional methods in the field.

The present invention provides an embodiment of a preparation method of bismuth telluride micro-nano powder material, specifically, the bismuth telluride alloy ingot is broken into particles, placed in a ball milling device such as a ball milling tank, and ethyl acetate is added Dry ball milling, discharging and drying, wherein the mass ratio of bismuth telluride to ethyl acetate is ≥5:1.

In some embodiments provided by the present invention, the preparation process of the bismuth telluride alloy ingot is as follows: take Bi powder, Sb powder and Te powder according to the molar ratio of the nominal composition, weigh and mix them evenly, and seal them in a vacuum less than 2Pa In the vacuum quartz tube inside, seal the tube, then raise the temperature to 780-800°C at a rate of 12-18°C/min, keep it warm for 1-1.5h, then swing for 2-3h, the swing frequency is 5-8rpm/min, and the swing angle 60°～65°, then cool down.

Preferably, the chemical formula of the alloy ingot is Bi _0.5 Sb _1.5 Te ₃ , and it is prepared by using Bi powder, Sb powder and Te powder with a purity of 99.99%.

In some embodiments provided by the present invention, the particle size of the crushed bismuth telluride particles is 1-2 mm.

In some embodiments provided by the present invention, the mass ratio of bismuth telluride to ethyl acetate is 5-10:1, preferably such as 5:1, 6:1, 7:1, 8:1, 9:1, 10:1.

In some embodiments provided by the present invention, the ball-to-material ratio of the balls used in the ball mill to the bismuth telluride is 2-3:1. During ball milling, the feeding sequence is: weigh the crushed bismuth telluride particles into the ball mill tank according to a certain ball-to-material ratio. parameter.

In some embodiments provided by the present invention, the size of the balls is 0.6-1.2 mm; the rotational speed of the ball mill is 350-500 rpm/min; the single-cycle grinding time is 30-40 minutes, and the grinding time is 1-2 hours. Preferably, there is an interval between two single-cycle grinding operations, and the interval is 10-20 minutes, preferably 10 minutes.

In some embodiments provided by the present invention, the method of drying the material is: spreading the material, ventilating and drying at room temperature, and then heating to 40-50° C. for drying. Preferably, the wind speed of ventilation drying at room temperature is 2-3 m/s, the drying time is 10-20 min, and the heating drying time is 10-20 min.

Some embodiments provided by the present invention are bismuth telluride micro-nano powder materials obtained by the above-mentioned preparation method.

The present invention provides an embodiment of a method for improving the thermoelectric performance of a bismuth telluride block, specifically, the bismuth telluride block is obtained by vacuum hot-pressing sintering of the bismuth telluride micro-nano powder material obtained above.

In some embodiments provided by the present invention, the pressure of vacuum hot-press sintering is 70-100 MPa, the sintering temperature is 420-500° C., and the hot-press sintering time is 60-120 min.

Example 1

(1) Ingredients smelting/material preparation:

The Bi powder, Sb powder and Te powder with a purity of 99.99% are composed into the stoichiometric ratio of Bi _0.5 Sb _1.5 Te ₃ according to the name, weighed and mixed evenly, sealed in a vacuum quartz tube with a vacuum degree of less than 2 Pa, and used oxygen The alkyne flame seals the quartz tube, then raises the temperature to 780°C at a rate of 15°C/min, and then keeps it warm for 1h, then swings for 2h, the swing frequency is 5rpm/min, and the swing angle is 60°. It is condensed by furnace cooling. Obtain bismuth telluride alloy ingot;

(2) Broken particles:

The obtained alloy ingot is crushed in a jaw crusher, and the material of the jaw plate is manganese steel to obtain coarse particles with a particle size of 1 to 2 mm;

(3) Dry ball milling:

Put the coarse material particles into the ball milling tank, the ball milling tank is equipped with stainless steel grinding balls with a diameter of 1mm, the mass ratio of balls to materials is 1:1, add ethyl acetate to the coarse material particles, the mass ratio of ethyl acetate to coarse material particles 1:5, at a speed of 400rpm/min, a duty ratio of 1:1, continuous grinding for 2 cycles of 1h under a single-cycle grinding for 30min;

(4) Ethyl acetate separation:

After the ball milling is finished, the material is discharged, and the resulting material is placed on an 850um sieve to separate the grinding ball and the powder, and then the separated powder is placed in the vent for preliminary drying for 10 minutes, and the ventilation rate is 2m/s, and then put into the Dry in an oven at 50°C for 10 minutes to completely remove ethyl acetate, and obtain bismuth telluride micro-nano powder with uniform particle size distribution.

The SEM image of the prepared bismuth telluride micro-nano powder is shown in FIG. 1 , and the particle size distribution graph is shown in FIG. 2 . It can be seen from the figure that the obtained bismuth telluride micro-nano powder has no aggregation and agglomeration, and the particle size distribution is uniform in the micro-nano range, wherein D(50) is about 1.2 μm, and D(100) is about 13.6 μm.

Example 2

(1) batching smelting/material preparation: same as embodiment 1;

(2) crushing and grinding: same as embodiment 1;

The obtained alloy ingot is crushed in a jaw crusher, and the material of the jaw plate is manganese steel to obtain a coarse material with a particle size of 1 to 2 mm;

(3) Dry ball milling:

Put the coarse material particles into the ball milling tank, the ball milling tank is equipped with stainless steel grinding balls with a diameter of 1mm, the mass ratio of balls to materials is 1:1, add ethyl acetate to the coarse material particles, the mass ratio of ethyl acetate to coarse material particles 1:10, at a speed of 400rpm/min, a duty ratio of 1:1, continuous grinding for 2 cycles of 80 minutes under a single-cycle grinding of 40 minutes;

(4) Separation of dispersant: same as Example 1.

The obtained bismuth telluride micro-nano powder has no aggregation and agglomeration, and the particle size distribution is uniform in the micro-nano range, wherein D(50) is about 1.02 μm, and D(100) is about 12.8 μm.

Example 3

The difference from Example 1 is that in the dry ball milling process of step (3), the interval between two single-cycle milling is 10 minutes.

The obtained bismuth telluride micro-nano powder has no aggregation and agglomeration, and the particle size distribution is uniform in the micro-nano range, wherein D(50) is about 1.1 μm, and D(100) is about 13.2 μm.

Comparative example 1

The difference from Example 1 is that no ethyl acetate was added during the preparation process, and the particle size distribution diagram of the obtained powder is shown in FIG. 3 .

It can be seen from Fig. 2 that the particle size distribution uniformity of the prepared bismuth telluride micro-nano powder is reduced, and aggregation and agglomeration appear, wherein D(50) is about 7 μm, and D(100) is about 63 μm.

Comparative example 2

The difference from Example 1 is that ethyl acetate is replaced by alcohol in the preparation process, and the particle size distribution diagram of the powder is shown in FIG. 4 .

It can be seen from the figure that the obtained bismuth telluride micro-nano powder is agglomerated, wherein D(50) is about 5.1 μm, and D(100) is about 20 μm.

Put the bismuth telluride micro-nano powder (three parallel samples) prepared in the above-mentioned examples and comparative examples into a mold, keep it at a pressure of 100 MPa and a sintering temperature of 500°C for 100 minutes to obtain a bismuth telluride block, test and calculate The zT value of the bismuth telluride bulk at room temperature 298K, the results are shown in Table 1 below.

Table 1 Thermoelectric figure of merit results of bismuth telluride bulk

It can be seen from the above table that when no ethyl acetate and other dispersing agents are added during the dry ball milling process, as shown in Comparative Example 1, due to agglomeration, large particle size and uneven distribution, the obtained telluride The thermoelectric figure of merit of the bismuth block is 0.917 (mean value), and the zT value of the block fluctuates greatly. And after introducing ethyl acetate, as shown in embodiment 1 and embodiment 2, zT value is promoted, and the fluctuation of zT value reduces, and when single-cycle grinding is separated for a period of time, as shown in embodiment 3, the zT value Volatility is further reduced. When ethanol is used instead of ethyl acetate, as shown in Comparative Example 2, the zT value is slightly improved compared with Comparative Example 1, but the volatility is still large, and the effect is lower than that of ethyl acetate. This may be because ethanol is more volatile, and its permeability is not as good as that of ethyl acetate, which indicates that the ball milling medium used in wet ball milling is more likely to provide a dispersion effect, and it will be used in dry ball milling. The ideal effect cannot be achieved when using it.

Claims (10)

1. A preparation method of a bismuth telluride micro-nano powder material is characterized by crushing an alloy ingot of bismuth telluride into particles, placing the particles in a ball milling device, adding ethyl acetate for dry ball milling, discharging and drying, wherein the mass ratio of bismuth telluride to ethyl acetate is not less than 5:1.

2. The method for preparing the bismuth telluride micro-nano powder material as claimed in claim 1, wherein the particle size of the crushed bismuth telluride particles is 1-2 mm.

3. The preparation method of the bismuth telluride micro-nano powder material according to claim 1 or 2, wherein the bismuth telluride alloy ingot is prepared by the following steps:

weighing Bi powder, sb powder and Te powder according to the molar ratio of nominal composition, weighing and uniformly mixing, sealing in a vacuum quartz tube with the vacuum degree of less than 2Pa, sealing the tube, heating to 780-800 ℃ at the speed of 12-18 ℃/min, preserving the temperature for 1-1.5 h, swinging for 2-3 h at the swinging frequency of 5-8 rpm/min at the swinging angle of 60-65 ℃, and then cooling.

4. The preparation method of the bismuth telluride micro-nano powder material as claimed in claim 1, wherein the mass ratio of bismuth telluride to ethyl acetate is 5-10.

5. The preparation method of the bismuth telluride micro-nano powder material as claimed in claim 1, wherein the ball-to-material ratio of the grinding balls used for ball milling to the bismuth telluride is 2-3:1.

6. The method for preparing the bismuth telluride micro-nano powder material as claimed in claim 5,

the size of the grinding ball is 0.6-1.2 mm;

and/or the ball milling rotating speed is 350-500 rpm/min;

and/or the single-cycle grinding time is 30-40 min, and the grinding time is 1-2 h.

7. The preparation method of the bismuth telluride micro-nano powder material as claimed in claim 1, wherein the manner of drying the material is as follows: spreading the materials, ventilating and drying at room temperature, and heating to 40-50 ℃ for drying.

8. The bismuth telluride micro-nano powder material obtained by the preparation method of any one of claims 1 to 7.

9. The method for improving the thermoelectric performance of the bismuth telluride bulk is characterized in that the bismuth telluride bulk is obtained by vacuum hot-pressing sintering of the bismuth telluride micro-nano powder material as claimed in claim 8.

10. The method for improving the thermoelectric property of the bismuth telluride bulk according to claim 9, wherein the pressure of the vacuum hot-pressing sintering is 70-100 MPa, the sintering temperature is 420-500 ℃, and the hot-pressing sintering time is 60-120 min.

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