Ag2Se-based thermoelectric material and preparation method thereof

Abstract

The invention discloses an Ag2Se-based thermoelectric material and a preparation method thereof, and belongs to the technical field of thermoelectric materials. The preparation method comprises the steps that Ag powder and Se powder are mixed and ground according to the molar ratio of (1.9-2.1): 1, and mixed powder is obtained; the mixed powder is subjected to cold pressing to form blocks, and prefabricated blocks are obtained; the prefabricated block is subjected to heat preservation for 20-120 minutes under the conditions that the pressure is 1-5 GPa and the temperature is 400-1000 DEG C, and an Ag2Se initial product is generated through reaction; crushing the primary product, and grinding into fine powder; and sintering the fine powder for 5-30 minutes under the conditions that the pressure is 1-5 GPa and the temperature is 300-900 DEG C, so as to obtain the composite material. The sample is prepared through high temperature and high pressure for the first time, the method is simple, operation is easy to control, the preparation period can be greatly shortened, and the energy utilization rate is increased; the electroacoustic transport performance of Ag2Se is effectively regulated and controlled by changing the pressure and the temperature, and finally the thermoelectric performance is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermoelectric materials, and in particular relates to an Ag2Se-based thermoelectric material and a preparation method thereof. Background Art

[0002] With technological advancements, a growing global population, and rapid industrialization, energy consumption is also increasing. Non-renewable fossil fuels such as coal and oil are consumed in significant quantities annually. However, during energy use, most of the energy is released as heat, resulting in energy waste. There are two approaches to solving this energy problem: increasing energy sources or reducing them. However, developing new energy sources is extremely difficult. Therefore, reducing energy consumption can improve energy efficiency and reduce energy consumption. This is where thermoelectric materials come in. Thermoelectric materials utilize thermoelectric conversion technology, which utilizes the Seebeck, Peltier, and Thomson effects to directly convert heat into electricity. P-type and N-type thermoelectric materials can be assembled into thermoelectric devices, which can achieve thermoelectric power generation and thermoelectric cooling by converting heat into electricity. During this conversion process, waste heat from industrial production, automobile exhaust, and the environment can be fully utilized and converted into higher-value electricity. Chip refrigeration equipment, refrigerators, and other devices can also be cooled using electricity. Thermoelectric devices, with their lightweight, compact size, precise temperature control, and environmentally friendly characteristics, have broad application prospects in many fields.

[0003] An important indicator for measuring the conversion efficiency of thermoelectric materials is the dimensionless thermoelectric figure of merit zT = S 2 σT / κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity. Silver selenide is a near-room-temperature thermoelectric material that exhibits excellent thermoelectric properties even at low temperatures. It is a black crystalline substance with a metallic luster. Silver selenide materials typically have two phases: the low-temperature phase β-Ag2Se and the high-temperature phase α-Ag2Se. The low-temperature phase is an orthorhombic n-type semiconductor material with low lattice thermal conductivity and high electrical conductivity, resulting in excellent thermoelectric properties.

[0004] Ag2Se is typically prepared using methods such as melting and mechanical alloying, but these methods suffer from long synthesis times, high energy consumption, and complex operations. Currently, a common approach to this problem is chemical synthesis, such as CN118234357A, which discloses a method for preparing an Ag2Se thermoelectric material. However, this method involves complex steps, requiring prolonged ultrasound treatment, filtration, and drying, and also requires plasma sintering, hindering industrial scale-up. Therefore, research is focused on effectively shortening the synthesis and preparation time of silver selenide and improving its thermoelectric properties. Summary of the Invention

[0005] To address the current challenges with Ag2Se-based thermoelectric material preparation methods, the present invention provides an Ag2Se-based thermoelectric material and its preparation method. This method synthesizes Ag powder and Se powder under high temperature and high pressure to produce a preliminary sample. The resulting sample is then ground into a powder in a mortar and pestle, and then sintered under high temperature and high pressure to form a final product. The sample preparation process is simple, easy to operate, highly efficient, and effective. The optimal thermoelectric performance conditions are determined by regulating pressure and temperature. This method utilizes the defective structure generated by high temperature and high pressure to alter the electrical and thermal parameters of Ag2Se, ultimately optimizing its thermoelectric performance.

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

[0007] In one aspect, the present invention provides a method for preparing an Ag2Se-based thermoelectric material, comprising the following steps:

[0008] (1) Raw material pretreatment: Under inert gas protection, Ag powder and Se powder were mixed and ground in a molar ratio of 1.9 to 2.1:1 to obtain a mixed powder;

[0009] (2) Cold pressing: cold pressing the mixed powder into blocks to obtain prefabricated blocks;

[0010] (3) High-pressure synthesis: The prefabricated block is kept at a pressure of 1 to 5 GPa and a temperature of 400 to 1000°C for 20 to 120 minutes to generate the primary product of Ag2Se;

[0011] (4) Primary product processing: crushing the Ag2Se primary product and grinding it into fine powder;

[0012] (5) High-pressure sintering: The fine powder is cold-pressed into a block, and the resulting block is sintered at a pressure of 1 to 5 GPa and a temperature of 300 to 900° C. for 5 to 30 minutes to obtain the Ag 2 Se-based thermoelectric material.

[0013] Furthermore, the mixing and grinding time in step (1) is 15 minutes to 2 hours.

[0014] Furthermore, the method of cold pressing into blocks in step (2) is: placing the mixed powder in a powder tablet press, maintaining the pressure at 2 MPa for 15 seconds, and obtaining a prefabricated block.

[0015] Furthermore, in step (3), the prefabricated blocks are loaded into a high-pressure synthesis assembly block and transferred to a six-sided top press for high-pressure synthesis;

[0016] Preferably, the prefabricated block is kept at a pressure of 1 to 3 GPa and a temperature of 700 to 1000° C. (excluding 1000° C.) for 20 to 40 minutes;

[0017] Preferably, the prefabricated block is kept at a pressure of 1 to 3 GPa and 700° C. for 20 to 40 minutes;

[0018] Preferably, the prefabricated block is kept at a pressure of 3 GPa and a temperature of 700° C. for 30 minutes.

[0019] Furthermore, in step (5), the obtained block is loaded into a high-pressure synthesis assembly block and transferred to a six-sided top press for high-pressure sintering;

[0020] Preferably, in step (5), the fine powder is sintered at a pressure of 1 to 5 GPa and a temperature of 500 to 900° C. for 5 to 30 minutes;

[0021] Preferably, in step (5), the fine powder is sintered at a pressure of 1 to 5 GPa and 500° C. for 5 to 30 minutes;

[0022] Preferably, in step (5), the fine powder is sintered at a pressure of 3 GPa and a temperature of 500 to 900° C. for 5 to 30 minutes;

[0023] Preferably, in step (5), the fine powder is sintered at a pressure of 3 GPa and a temperature of 500° C. for 10 minutes.

[0024] Furthermore, the heating rate of step (3) is 50 to 150° C. / min.

[0025] Furthermore, the heating rate of step (5) is 80 to 200° C. / min.

[0026] Furthermore, the high-pressure synthesis assembly in step (3) and step (5) comprises a pyrophyllite sealing ring, a graphite heating tube and a magnesium oxide liner. (steel cap, graphite sheet, magnesium oxide sheet, dolomite tube, boron nitride ring, molybdenum sheet)

[0027] Furthermore, in step (4), the Ag2Se primary product is crushed and then ground in a mortar for 0.5-1 h;

[0028] Preferably, the particle size of the fine powder is about 50 μm.

[0029] The present invention also provides an Ag2Se-based thermoelectric material prepared by the above preparation method.

[0030] The beneficial effects of the present invention are:

[0031] The present invention provides a preparation method for Ag2Se-based thermoelectric materials, which comprises the following steps: mixing Ag powder and Se powder according to a certain atomic ratio, cold-pressing the mixed powder into a block, and then subjecting the mixed powder to high temperature and high pressure, setting pressure and temperature conditions to obtain a primary product, and re-grinding the product into powder using a mortar; due to stress release caused by the synthesis pressure, some samples are broken; the obtained sample is re-manually ground into powder using a mortar, and then subjected to high temperature and high pressure sintering to obtain a dense and complete Ag2Se-based thermoelectric material block, wherein the chemical composition of the obtained block material is Ag. 2-x Se, where x = -0.1 to +0.1, grain size 0.5 to 5 μm, relative density ≥ 98%, electrical conductivity ≥ 2000 S·cm at 300K -1 , Seebeck coefficient absolute value ≥ 120μV·K -1 . The preparation method of the present invention has the following advantages: 1) The preparation method has a short cycle and a simple process. The present invention has a simple process, a rapid reaction time, saves costs, and is suitable for industrial production. 2) The prepared bulk material has good density. The material has high electrical conductivity and low thermal conductivity, so it has good thermoelectric properties. For the Ag2Se-based thermoelectric material synthesized by high temperature and high pressure method, the minimum thermal conductivity value is reduced to 0.6Wm -1 K -1 , which optimizes the thermoelectric performance of this material. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 X-ray diffraction patterns of Ag2Se prepared at different synthesis temperatures at 1 GPa;

[0033] Figure 2 Characterization of thermoelectric properties of Ag2Se prepared at different synthesis temperatures at 1GPa;

[0034] Figure 3 Thermoelectric properties of Ag2Se prepared at 700℃ and different synthesis pressures are characterized;

[0035] Figure 4 Ag2Se was synthesized at 1GPa and 700℃, and the thermoelectric properties of the samples were characterized by secondary sintering at 3GPa and different temperatures.

[0036] Figure 5 Ag2Se was synthesized at 1GPa and 700℃; the thermoelectric properties of the samples were characterized by secondary sintering at 500℃ and different pressures. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the following described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0038] It should be understood that the experimental operations not described in detail in the experiment are all conventional experimental operations well known to those skilled in the art.

[0039] In order to test the performance of the obtained sample, the sample after high-pressure sintering is polished and cut, and the electrical and thermal properties of the sample are tested by using a China-made Coorey CTA-3s type thermoelectric material electrical property tester and a Germany Nierstein company produced model LFA457 laser thermal conductivity instrument respectively.

[0040] Embodiment 1

[0041] A preparation method of an Ag2Se-based thermoelectric material, comprising the following steps:

[0042] 1) batching, batching Ag powder and Se powder according to a certain molar ratio. The raw materials are high-purity Se powder (purity 99.999%) and Ag powder (purity 99.99%); the molar ratio of Ag powder to Se powder is 2:1, the Ag powder is 2.8046g, and the Se powder is 1.0265g.

[0043] 2) mixing, putting the Ag powder and Se powder into an agate mortar and mixing in a glove box for 1h to fully mix. It is necessary to clean and dry the mortar in advance. After cleaning the mortar, dry it in a constant temperature box, and then place it in a vacuum glove box after oxygen treatment.

[0044] 3) cold pressing, putting the fully mixed powder into a 12mm mold, using a powder tablet machine to press the powder into a block, the oil pressure is 2MPa, maintaining for 15s and then releasing the mold, to obtain a cylindrical block.

[0045] 4) synthesis, placing the cylindrical block in an assembled cavity as shown in Figure 5 , and placing it into a six-surface press, setting the pressure to 1GPa, the synthesis temperature to 400-1000℃, and maintaining for 30min and then stopping suddenly, and reducing to room temperature in a short time. The required sample is obtained.

[0046] Figure 1X-ray diffraction patterns of Ag2Se at 1 GPa under different synthesis temperatures, it can be observed that the sample synthesized below 900℃ can be consistent with the standard card of Ag2Se, when the synthesis temperature is 1000℃, the existence of Ag peak in the sample is found, which shows that Se will volatilize in the sample during high temperature and high pressure process, in order to obtain pure phase Ag2Se, the synthesis temperature needs to be lower than 1000℃.

[0047] Figure 2 The performance results of Ag2Se at 1 GPa under different synthesis temperatures, it can be observed that the performance of the sample changes greatly by changing the synthesis temperature, with the increase of the synthesis temperature, the resistivity decreases; the thermal conductivity is basically unchanged at 0.7 Wm -1 K -1 nearby, the maximum zT value of 1 is obtained at 700℃.

[0048] Example 2

[0049] A preparation method of an Ag2Se-based thermoelectric material, comprising the following steps:

[0050] 1) batching, batching Ag powder and Se powder according to a certain molar ratio. The raw materials are high-purity Se powder (purity 99.999%) and Ag powder (purity 99.99%); the molar ratio of Ag powder to Se powder is 2:1, Ag powder 2.8046g, Se powder 1.0265g.

[0051] 2) mixing, putting the Ag powder and Se powder into an agate mortar and mixing in a glove box for 1h to fully mix. It is necessary to clean and dry the mortar in advance. After cleaning the mortar, dry it in an incubator, and then place it in a vacuum glove box after oxygen treatment.

[0052] 3) cold pressing, putting the fully mixed powder into a 12mm mold, using a powder tablet machine to press the powder into a block, the oil pressure is 2MPa, maintaining for 15s and then releasing the mold, to obtain a cylindrical block.

[0053] 4) synthesis, placing the cylindrical block in the assembly cavity as shown in Figure 5 , and placing it into a six-surface press, setting the temperature to 700℃ and the pressure to 1-5GPa, maintaining for 30min and then stopping suddenly, and reducing to room temperature in a short time. It is found that the synthesized samples under different pressures at 700℃ have cracks, which do not meet the test standards, so suitable samples are selected for testing.

[0054] Figure 3The results show the changes in thermoelectric properties at different synthesis pressures at 700°C. It can be observed that the resistivity increases with increasing pressure, which is due to the decrease in carrier concentration at higher synthesis pressures. The performance of the samples does not change significantly between 1 and 3 GPa. Ag2Se synthesized at 3 GPa achieves the highest ZT value of 1, indicating that the optimal synthesis conditions are 3 GPa and 700°C.

[0055] Example 3

[0056] A method for preparing an Ag2Se-based thermoelectric material comprises the following steps:

[0057] 1) Mixing Ag powder and Se powder according to a specific molar ratio. The raw materials used are high-purity Se powder (purity: 99.999%) and Ag powder (purity: 99.99%); the molar ratio of Ag powder to Se powder is 2:1, with 2.8046g of Ag powder and 1.0265g of Se powder.

[0058] 2) Mixing: Place Ag and Se powders in an agate mortar and mix thoroughly in a glove box for 1 hour. Clean and dry the mortar beforehand. After cleaning, dry the mortar in a constant temperature oven. Deoxygenate the dried mortar and place it in a vacuum glove box.

[0059] 3) Cold pressing: Place the thoroughly mixed powder in a 12 mm die and press the powder into blocks using a powder tablet press with an oil pressure of 2 MPa. Hold for 15 seconds and then withdraw the die to obtain a cylindrical block.

[0060] 4) Synthesis: Place the cylindrical block in the Figure 5 The assembly cavity shown is placed in a six-sided top press, the pressure is set to 3 GPa, the synthesis temperature is 700 ° C, and it is kept for 30 minutes and then stopped suddenly, and cooled to room temperature in a short time.

[0061] 5) High-pressure sintering. The obtained sample is ground into a powder in a mortar and pestle, the resulting fine powder is cold-pressed, and the resulting block is then sintered at high temperature and high pressure. The sintering pressure is fixed at 3 GPa, the sintering temperature is 300-900°C, and the sintering time is 10 minutes. After high-pressure sintering, a complete and well-dense block of thermoelectric material is obtained, which meets the thermoelectric test standards and has no cracks found under an optical microscope.

[0062] Figure 4 The thermoelectric performance of samples synthesized at 3 GPa and 700°C and sintered at different temperatures at 3 GPa is shown in the figure. At 300°C, the sample is less dense, resulting in poor electrical conductivity and low thermal conductivity. The thermoelectric performance of samples sintered at 500-900°C shows little difference, so we selected 500°C as the optimal sintering temperature.

[0063] Example 4

[0064] A method for preparing an Ag2Se-based thermoelectric material comprises the following steps:

[0065] 1) Mixing Ag powder and Se powder according to a specific molar ratio. The raw materials used are high-purity Se powder (purity: 99.999%) and Ag powder (purity: 99.99%); the molar ratio of Ag powder to Se powder is 2:1, with 2.8046g of Ag powder and 1.0265g of Se powder.

[0066] 2) Mixing: Place Ag and Se powders in an agate mortar and mix thoroughly in a glove box for 1 hour. Clean and dry the mortar beforehand. After cleaning, dry the mortar in a constant temperature oven. Deoxygenate the dried mortar and place it in a vacuum glove box.

[0067] 3) Cold pressing: Place the thoroughly mixed powder in a 12 mm die and press the powder into blocks using a powder tablet press with an oil pressure of 2 MPa. Hold for 15 seconds and then withdraw the die to obtain a cylindrical block.

[0068] 4) Synthesis: Place the cylindrical block in the Figure 5 The assembled chamber shown was placed in a six-sided press, set to 700°C and a pressure of 1-5 GPa. The press was maintained for 30 minutes before being abruptly stopped and cooled to room temperature over a short period of time. Cracks were observed in some samples synthesized at 700°C and different pressures, indicating they did not meet the test criteria. Suitable samples were selected for testing.

[0069] 5) High-pressure sintering. The obtained sample was re-ground into a powder in a mortar, the resulting fine powder was cold-pressed, and the resulting block was then sintered at high temperature and high pressure. The sintering temperature was fixed at 500°C, the sintering pressure was 1-5 GPa, and the sintering time was 10 minutes. After high-pressure sintering, a complete, well-dense block of thermoelectric material was obtained, meeting thermoelectric test standards, and no cracks were found under an optical microscope.

[0070] Figure 5 The thermoelectric performance diagram of samples sintered under different pressures with synthesis conditions of 3GPa and 700℃ and sintering conditions of 500℃ shows that the sample under 3GPa obtains the overall best power factor and the lowest thermal conductivity, resulting in an excellent zT value of 1.2, so 3GPa is the optimal sintering pressure.

[0071] In summary, the preparation method of Ag2Se-based thermoelectric materials in this application is based on the optimal high-pressure synthesis conditions of 3GPa and 700℃, and the optimal high-pressure sintering conditions of 3GPa and 500℃ for the synthesized samples. max =1.2.

[0072] The above description is merely an embodiment of the present invention, and common knowledge such as the specific materials and properties in the scheme are not described in detail here. It should be pointed out that the description of the above embodiment is only used to help understand the core concept of the present invention. For those skilled in the art, several variations and improvements can be made without departing from the present invention. According to the concept of the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for preparing an Ag2Se-based thermoelectric material, characterized in that: The following steps are involved: (1) Raw material pretreatment: Under inert gas protection, Ag powder and Se powder were mixed and ground in a molar ratio of 1.9 to 2.1:1 to obtain a mixed powder; (2) Cold pressing: cold pressing the mixed powder into blocks to obtain prefabricated blocks; (3) High-pressure synthesis: The prefabricated block is kept at a pressure of 1 to 5 GPa and a temperature of 400 to 1000°C for 20 to 120 minutes to generate the primary product of Ag2Se; (4) Primary product processing: crushing the Ag2Se primary product and grinding it into fine powder; (5) High-pressure sintering: The fine powder is cold-pressed into a block, and the resulting block is sintered at a pressure of 1 to 5 GPa and a temperature of 300 to 900° C. for 5 to 30 minutes to obtain the Ag 2 Se-based thermoelectric material.

2. The preparation method according to claim 1, characterized in that The mixing and grinding time in step (1) is 15 minutes to 2 hours.

3. The preparation method according to claim 1, characterized in that The method of cold pressing into blocks in step (2) is as follows: placing the mixed powder in a powder tablet press, maintaining the pressure at 2 MPa for 15 seconds, and obtaining a prefabricated block.

4. The preparation method according to claim 1, characterized in that In step (3), the prefabricated blocks are loaded into a high-pressure synthesis assembly block and transferred to a six-sided top press for high-pressure synthesis; Preferably, the prefabricated block is kept at a pressure of 1 to 3 GPa and a temperature of 700 to 1000° C. (excluding 1000° C.) for 20 to 40 minutes; Preferably, the prefabricated block is kept at a pressure of 1 to 3 GPa and 700° C. for 20 to 40 minutes; Preferably, the prefabricated block is kept at a pressure of 3 GPa and a temperature of 700° C. for 30 minutes.

5. The preparation method according to claim 1, characterized in that In step (5), the obtained block is loaded into a high-pressure synthesis assembly block and transferred to a six-sided top press for high-pressure sintering; Preferably, in step (5), the fine powder is sintered at a pressure of 1 to 5 GPa and a temperature of 500 to 900° C. for 5 to 30 minutes; Preferably, in step (5), the fine powder is sintered at a pressure of 1 to 5 GPa and 500° C. for 5 to 30 minutes; Preferably, in step (5), the fine powder is sintered at a pressure of 3 GPa and a temperature of 500 to 900° C. for 5 to 30 minutes; Preferably, in step (5), the fine powder is sintered at a pressure of 3 GPa and a temperature of 500° C. for 10 minutes.

6. The preparation method according to claim 1, characterized in that The heating rate of step (3) is 50 to 150° C. / min.

7. The preparation method according to claim 1, characterized in that The heating rate of step (5) is 80-200°C / min.

8. The preparation method according to claim 4 or 5, characterized in that The high pressure synthesis assembly block in step (3) and step (5) comprises a pyrophyllite sealing ring, a graphite heating tube and a magnesium oxide liner.

9. The preparation method according to claim 1, characterized in that In step (4), the Ag2Se primary product is crushed and then ground in a mortar for 0.5-1 h.

10. The Ag2Se-based thermoelectric material prepared by the preparation method according to any one of claims 1 to 9.

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