CN1755961A - Ag-Pb-Sb-Te thermoelectric materials and preparation process thereof - Google Patents

Abstract

The invention discloses an Ag-Pb-Sb-Te thermoelectric material and a preparation method thereof, which belong to the technical field of new energy materials and their preparation, and relate to a thermoelectric semiconductor compound with a high-temperature differential electric effect. The present invention adopts the method of mechanical alloying (MA) combined with spark plasma sintering (SPS) to prepare PbTe series high-performance thermoelectric materials, and the composition of the material is represented by Ag _1-X Pb _18+Y SbTe ₂₀ , where x indicates that Ag deviates from the equivalent substitution The amount, y represents the amount of Pb exceeding the metering ratio in the raw material powder. Compared with the traditional powder metallurgy process, the MA+SPS process of the present invention has the advantages of short process, high efficiency, low energy consumption, and is suitable for industrialized large-scale production, and the obtained thermoelectric material has more excellent thermoelectric properties. The dimensionless figure of merit ZT of the Ag _1－X Pb _18+Y SbTe ₂₀ thermoelectric material prepared by MA and SPS reaches 1.37 at 450℃.

Description

Ag-Pb-Sb-Te thermoelectric material and its preparation method

technical field

The invention belongs to the technical field of new energy materials and their preparation, and in particular relates to an Ag-Pb-Sb-Te thermoelectric material which is a thermoelectric semiconductor compound with a high-temperature differential electric effect and a preparation method thereof.

Background technique

Thermoelectric materials, or thermoelectric materials, refer to a type of energy that converts heat and electricity based on two basic thermoelectric effects—the Seebeck effect and the Peltier effect. Material. Compared with traditional power generation technology, thermoelectric power generation devices made of thermoelectric materials have simple structure, strong durability, no moving parts, easy miniaturization, no maintenance, good reliability, long life, no noise, no pollution, and can be used Low-temperature waste heat and other characteristics; thermoelectric refrigeration devices made of thermoelectric materials, compared with traditional compression refrigeration technology, also have the advantages of fluorine-free and pollution-free, easy to miniaturize, no moving parts, and no noise. Therefore, with the recent increasingly prominent energy problems and environmental problems, the application of thermoelectric devices is becoming more and more extensive. In the fields of aerospace, national defense construction, geological and meteorological detection, medical and health, microelectronics and other fields, as well as waste heat in petrochemical, metallurgical, and electric power industries Utilization has a broad application background.

Thermoelectric materials with the above application background use their Seebeck coefficient S, electrical conductivity σ, and thermal conductivity κ as the main performance parameters, and their power factor P=S ² σ and dimensionless figure of merit ZT=(S ² σ /κ)T is the most commonly used performance index for evaluating thermoelectric materials. Good thermoelectric materials require high Seebeck coefficient S, high electrical conductivity σ, and low thermal conductivity κ.

At present, thermoelectric materials that are more actively studied include: Bi ₂ Te ₃ (BismuthTelluride) and its solid solution alloys used in low temperature regions; SiGe alloys and Clathrate structures in high temperature regions; and other thermoelectric materials such as half-Heusler alloys, boron-rich solids, oxides, and polymers.

Among them, the application of Bi ₂ Te ₃ and its solid solution alloy is relatively mature, and its dimensionless figure of merit ZT is greater than 1. However, due to its relatively low operating temperature, this material is mainly used for electronic refrigeration. PbTe-based thermoelectric compounds are suitable for thermoelectric power generation, but their performance needs to be improved. The dimensionless figure of merit ZT of traditional bulk PbTe-based thermoelectric materials is less than 1. A recent literature (KF Hsu et al., Science, 303(2004), g18) reported that a PbTe-based compound bulk material has better thermoelectric properties than Bi ₂ Te ₃ alloys, but its preparation process is relatively special, and the detailed process is unknown . Although some research institutions are currently conducting experiments related to this material system, the obtained dimensionless figure of merit ZT is far lower than the value reported by KF Hsu et al., and the highest ZT is 1.07.

On the other hand, at present, after the compounds are synthesized by smelting, powder metallurgy processes such as pulverization and hot pressing are used to prepare thermoelectric materials. This preparation process has the disadvantages of numerous procedures, complex equipment, long production cycle, high energy consumption, long exposure time of materials at high temperature, and serious volatilization of components.

For this reason, this patent has invented a new thermoelectric material and its preparation method. The thermoelectric material belongs to the Ag-Pb-Sb-Te series compound, and its dimensionless figure of merit ZT is as high as 1.37. The thermoelectric material can be synthesized by mechanical alloying (Mechanical Alloying MA) to synthesize its compound powder, and then sintered into a bulk material at a lower temperature by using a spark plasma sintering (Spark Plasma Sintering SPS) process.

Contents of the invention

The object of the present invention is to provide a kind of Ag-Pb-Sb-Te thermoelectric material which is thermoelectric semiconductor compound with high temperature differential electric effect and its preparation method. It is characterized in that: Ag-Pb-Sb-Te thermoelectric material with PbTe as matrix is prepared by adopting mechanical alloying and spark plasma sintering technology. Page: 2 The so-called mechanical alloying is a process in which metal powders are directly combined into intermetallic compounds or alloys through the energy generated by the collision in the process of high-energy ball milling. Compared with the traditional smelting process, it has the characteristics of synthesis temperature close to room temperature, simple equipment, low cost, and suitable for large-scale production, and the obtained alloy has fine grains, which can increase the phonon concentration without significantly reducing the electrical conductivity. Grain boundary scattering reduces the thermal conductivity of the material, resulting in better thermoelectric performance.

The so-called discharge plasma sintering is in a vacuum environment, through the upper and lower graphite pressure heads, while pressurizing the sintered body, a pulsed direct current is used to generate a discharge plasma, so that the particles inside the sintered body generate Joule heat and activate the surface. Therefore, the sintering process can be completed in a very short time. It has the characteristics of low sintering temperature, short sintering cycle, high production efficiency, and the sintered body grains are not easy to grow.

The material composition is represented by Ag _1-X Pb _18+Y SbTe ₂₀ . This compound has the same rock-salt structure as PbTe. Under the condition of keeping the original structure of PbTe unchanged, equal amounts of Ag and Sb replace the position of Pb: x represents the amount of its deviation from equivalent substitution, and y represents the amount exceeding the stoichiometric ratio Pb content, in order to adjust its electrical and thermoelectric properties, to obtain materials with high thermoelectric properties.

The specific process of preparation includes:

1) According to the Ag _1-X Pb _18+Y SbTe ₂₀ chemical formula, use Ag, Pb, Sb and Te elemental powders as raw materials, mix according to the values of X and Y, put them into a ball mill tank, and add a tank volume of 0.1 % of ethanol, the function of ethanol is to prevent the powder from adhering to the tank wall and affecting the subsequent ball milling effect;

2) After pre-evacuation and high-purity argon gas used as a protective gas for ball milling, install the ball mill tank on a planetary ball mill for dry ball milling. In the stainless steel ball mill tank, use 10mm diameter stainless steel balls at a speed of 300-600 rpm, and the milling time is 3-8 hours. The specific ball milling time and speed are determined by the ball mill used and the specific conditions of the tank and balls;

3) Take out the ball mill powder, put it into a Φ20mm graphite mold, compact it with a graphite pressure head, install it in an SPS machine, and sinter it under a vacuum condition of <6Pa. SPS heating rate is 50°C/min, maximum holding temperature is 300-500°C, SPS pressure is 50Mpa, after holding for 1-10 minutes, the sintering furnace cools down to room temperature;

4) After the sample is taken out, the surface of the sample is polished with a sandpaper mill, and then the phase identification and microstructure analysis are carried out, and the thermoelectric performance test is carried out.

The X value is 0-0.6, and the Y value is 1-5.

The beneficial effect of the present invention is that the Ag-Pb-Sb-Te thermoelectric material prepared by adopting the technology combined with mechanical alloying and spark plasma sintering (abbreviated as MA+SPS technology) has its outstanding advantages: (1) the process flow is short , high efficiency, suitable for large-scale industrial production; (2) does not need high-temperature melting and long-time hot pressing, and consumes less energy; (3) reduces the volatilization of harmful elements, and the preparation process has less impact on the environment; (4) The obtained material has finer crystal grains and more excellent thermoelectric properties.

Description of drawings

Fig. 1 X-ray diffraction pattern of Ag _1-X Pb _18+Y SbTe ₂₀ (x=0.2, y=4) compound powder and its SPS sintered body (sintering temperature=400°C) synthesized by mechanical alloying.

Figure 2(a)(b) Scanning electron microscope (SEM) and transmission electron microscope (TEM) of Ag _1-X Pb _18+Y SbTe ₂₀ (x=0.2, y=4) compound bulk samples sintered by SPS at 400℃ photo.

Fig. 3 The relationship between resistivity and temperature of Ag _1-X Pb _18+Y SbTe ₂₀ compound SPS sintered samples with different compositions.

Fig. 4 The relationship between Seebeck coefficient and temperature of Ag _1-X Pb _18+Y SbTe ₂₀ compound SPS sintered samples with different compositions.

Fig. 5 The relationship between power factor and temperature of Ag _1-X Pb _18+Y SbTe ₂₀ compound SPS sintered samples with different compositions.

Fig. 6 The relationship between the dimensionless figure of merit ZT and the temperature of the SPS sintered material corresponding to the composition with the highest power factor (Ag _0.8 Pb ₂₂ SbTe ₂₀ ).

Detailed ways

The invention relates to an Ag-Pb-Sb-Te thermoelectric material and a preparation method thereof. The thermoelectric material adopts the process of mechanical alloying and spark plasma sintering to prepare the Ag-Pb-Sb-Te thermoelectric material with PbTe as the matrix. The material composition is represented by Ag _1-X Pb _18+Y SbTe ₂₀ . This compound has the same rock-salt structure as PbTe. Under the condition of keeping the original structure of PbTe unchanged, the same amount of Ag, Sb replaces the position of Pb: x represents the amount of Ag deviation from the equivalent substitution, and y represents the amount exceeding the stoichiometric ratio The Pb content is used to adjust its electrical and thermoelectric properties to obtain a material with high thermoelectric properties. The X value is 0-0.6, and the Y value is 1-5.

The concrete technological process of preparing above-mentioned material comprises:

1) According to the Ag _1-X Pb _18+Y SbTe ₂₀ chemical formula, use Ag, Pb, Sb and Te elemental powders as raw materials, mix according to the values of X and Y, put them into a ball mill tank, and add a tank volume of 0.1 % of ethanol, the effect of ethanol is to prevent the powder from adhering to the tank wall and affecting the subsequent ball milling effect.

2) After pre-evacuation and high-purity argon gas used as a protective gas for ball milling, install the ball mill tank on a planetary ball mill for dry ball milling. The present invention adopts the QM-2 type planetary ball mill produced by Nanjing University Instrument Factory, a 250mL stainless steel ball mill jar and 10mm diameter stainless steel balls. When the rotating speed of 300 rpm is adopted, the required ball milling time is 5 hours.

3) Take out the ball mill powder, put it into a Φ20mm graphite mold, compact it with a graphite pressure head, install it in an SPS machine, and sinter it under a vacuum condition of <6Pa. SPS heating rate is 50°C/min, maximum holding temperature is 300-500°C, SPS pressure is 50Mpa, after holding for 1-10 minutes, the furnace is cooled to room temperature.

4) After the sample is taken out, the surface of the sample is polished with a sandpaper mill, and then the phase identification and microstructure analysis are carried out, and the thermoelectric performance test is carried out.

Examples are given below for description.

Example 1

Using silver (Ag) powder, antimony (Sb) powder, lead (Pb) powder, and tellurium (Te) powder as raw materials, weigh a total of 20g of powder according to the metering ratio of Ag _0.8 Pb ₂₂ SbTe ₂₀ , and put it into a stainless steel ball mill In a tank (volume 250mL), add stainless steel grinding balls with a diameter of 10mm (the weight ratio of grinding balls to powder is 18:1). The ball mill tank was filled with Ar as a protective gas, and Ag _0.8 Pb ₂₂ SbTe was prepared by mechanical alloying (MA) in a planetary ball mill (QM-2, Nanjing University Instrument Factory) for 5 hours (rotational speed: 300r/min). ₂₀ compound powders. As shown in Figure 1(a), after the above MA treatment, the obtained powder becomes a single phase with a cubic structure, and each diffraction peak can be calibrated according to the PbTe phase. The obtained powder was sintered at a pressure of 50 MPa and kept at 400° C. for 2 minutes, and its relative density was above 98% (see the SEM photo shown in FIG. 2 ). As shown in Figure 1(b), its phase structure is basically the same as that of the SPS powder before sintering, without any change. Figure 2 shows the SEM photo and TEM photo of the SPS sintered body composed of Ag _0.8 Pb ₂₂ SbTe _2.0 , which shows that the Ag _0.8 Pb ₂₂ SbTe ₂₀ compound thermoelectric material prepared by MA and SPS has high density and fine grain (average grain size The grain is about 1m) and relatively uniform.

Example 2

Using silver (Ag) powder, antimony (Sb) powder, lead (Pb) powder and tellurium (Te) powder as raw materials, according to the metering ratio of Ag _0.8 Pb ₂₁ SbTe ₂₀ , Ag _0.8 Pb ₂₂ SbTe ₂₀ , Ag _0.8 Pb ₂₃ SbTe ₂₀ A total of 20 g of powder was weighed separately to prepare three groups of samples with different Pb contents. Powder synthesis and SPS sintering conditions are the same as in Example 1. Figures 3 and 4 compare the resistivity () and Seebeck coefficient (S) versus temperature for SPS sintered samples of three compositions of Ag1 _- XPb18 _{+YSbTe20 compounds} . Compared with the other two compositions, Ag _0.8 Pb ₂₂ SbTe ₂₀ has the lowest resistivity, and the absolute value of its Seebeck coefficient is between the two. Figure 5 is the relationship between the power factor (S ² /) and temperature calculated using the data in Figures 3 and 4. As shown in the figure, the power factor of the composition of Ag _0.8 Pb ₂₂ SbTe ₂₀ is the highest, reaching 1766W/mK at 650K. Figure 6 is the relationship between the dimensionless figure of merit ZT of the composition (Ag _0.8 Pb ₂₂ SbTe ₂₀ ) and temperature. At the highest test temperature (673K) ZT reaches 1.37.

Example 3

Using silver (Ag) powder, antimony (Sb) powder, lead (Pb) powder and tellurium (Te) powder as raw materials, according to the measurement of Ag _0.8 Pb ₂₂ SbTe ₂₀ , Ag _0.8 Pb ₂₂ SbTe ₂₀ and Ag _0.8 Pb ₂₂ SbTe ₂₀ A total of 20 g of powder was weighed separately to prepare three groups of samples with different Ag contents. Powder synthesis and SPS sintering conditions are the same as in Example 1. The room temperature resistivities of samples with silver contents of 0.4, 0.6 and 0.8 are 0.125m, 0.185m, 0.175×10 ^-3 m, respectively. The resistivities of the two samples with Ag contents of 0.4 and 0.6 are too high, and the samples with Ag contents of about 0.8 have much lower resistivities than the other two compositions. Therefore, its comprehensive thermoelectric performance is high, and the dimensionless figure of merit ZT is as high as 1.37.

Claims (3)

1. Ag-Pb-Sb-Te thermoelectric material is characterized in that: adopting the prepared of mechanical alloying and discharge plasma sintering to go out with PbTe is the Ag-Pb-Sb-Te thermoelectric material of matrix, and this material is formed with Ag _1-XPb _18+YSbTe ₂₀Expression, this compound has the rock salt structure identical with PbTe, keeping under the constant condition of PbTe original structure, the Ag of equivalent, Sb replaces the position of Pb: represent that with x Ag departs from the amount that equivalent replaces, represent to surpass the Pb content that measures ratio with y, adjust its electricity and thermoelectricity capability, obtain having the material of high thermoelectricity capability with this.

2. the preparation method of an Ag-Pb-Sb-Te thermoelectric material, it is characterized in that: the specific embodiment of preparation comprises:

1) according to Ag _1-XPb _18+YSbTe ₂₀Chemical formula, with Ag, Pb, Sb and Te simple substance powder are raw material, and according to X, the value of Y batching is put into ball grinder, and adds the ethanol of tank volume 0.1% in jar, and the effect of ethanol is to prevent that powder from adhering to the follow-up ball milling effect of influence on tank skin;

2), after feeding is used for the high-purity argon gas of ball milling protective gas, ball grinder is installed in planetary ball mill carries out dry ball milling through forvacuum, in stainless steel jar mill, with the stainless steel abrading-ball of 10mm diameter, adopt 300～600 rev/mins rotating speed, the ball milling time is 3～8 hours;

3) take out the ball milling powder, pack in the graphite jig of Φ 20mm, after the compacting of graphite pressure head, be installed in the SPS machine, carry out sintering under the vacuum condition of pressure＜6Pa, the SPS programming rate is 50 ℃/min, the highest holding temperature is 300-500 ℃, SPS pressure is 50Mpa, is incubated after 1～10 minute, and sintering furnace is cooled to room temperature;

4) take out sample after, after with sand paper sample surfaces being polished, carry out the thing identification of phases and microstructure analysis, and carry out the thermoelectricity capability test.

3. according to claim 1 or 2 any one described Ag-Pb-Sb-Te thermoelectric material, it is characterized in that: described X value is 0.2～0.6, and the Y value is 1～5.

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