A novel sintering method for preparing thermoelectric materials

Abstract

The present invention belongs to the technical field of industrial waste heat energy recycling, and particularly relates to a novel sintering method for preparing thermoelectric materials; Step 1: Prepare the sintering precursor powder of the thermoelectric material, and the powder synthesis method of the thermoelectric material is not limited; Step 2: Sinter the bulk sample by using the oscillating hot pressing process; Step 3: Perform pre-treatment before testing on the sintered bulk sample; Step 4: Perform comprehensive characterization tests on the sintered sample; The present invention synthesizes the thermoelectric bulk sample through the novel oscillating hot pressing sintering process. On the one hand, the alternating load of the oscillating hot pressing during the sintering process promotes particle rearrangement and removes the gas residue in the gaps between powder particles to reduce the porosity of the sample, which is beneficial to improving the electrical conductivity of the material; on the other hand, by applying the oscillating force, the grain size is significantly reduced, the grain boundaries are increased and strengthened, and a large number of interfaces are introduced, thereby regulating the thermal conductivity and hardness, so as to obtain a thermoelectric material with high density, high thermoelectric performance, and high machining performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of industrial waste heat energy reuse, and particularly relates to a novel sintering method for preparing thermoelectric materials. Background Art

[0002] While the energy consumption of human society continues to grow, the issues of environmental protection and sustainable energy utilization have become extremely urgent. Thermoelectric materials play a key role in new energy research due to their ability to directly convert waste heat into electrical energy. The thermoelectric conversion technology has the characteristics of environmental protection and zero emissions, and flexible size design, which can effectively improve the energy utilization efficiency. However, in such a system, the low thermoelectric conversion efficiency has become the main factor restricting its high-power power generation.

[0003] [The conversion efficiency of thermoelectric materials can be evaluated by the thermoelectric figure of merit ZT value, which can be expressed as:

[0004] ZT = α 2 δT / (κ e + κ l )

[0005] Wherein, δ, α, κ e , κ l and T are the electrical conductivity, Seebeck coefficient, carrier thermal conductivity, lattice thermal conductivity and absolute temperature respectively. Generally, high-performance thermoelectric materials should exhibit a high power factor and a low thermal conductivity.

[0006] At present, high-performance thermoelectric material systems that have been commercially applied, such as Bi 2 Te 3 , PbTe, etc., contain expensive and toxic metal elements, and their applications pose certain hazards to human health and the natural environment. The Cu-S-based thermoelectric material is a new type of thermoelectric material, which has the characteristics of low cost, low toxicity and rich reserves. Its complex crystal structure and atomic arrangement make it a green thermoelectric material with great development potential.

[0007] Currently, the stable Cu-S thermoelectric system includes Cu 2 S, Cu 1.97 S, Cu 1.96 S, Cu 2-x S. Even Cu 2 S also has the existence of intrinsic copper vacancies (its actual composition is between Cu 1.997 S - Cu 1.999 S). Cu 2-x S deviates from the normal chemical composition ratio, and atoms disappear at the copper atom lattice points, forming point defects, also called vacancies. Since the formed bonds are unsaturated, vacancies are easy to accept electrons, so they show acceptor effects and become P-type semiconductors. Cu 2-xAs the temperature increases, the structure transforms from the low-temperature phase to the high-temperature cubic phase. At this time, the crystal structure changes from an ordered state to a disordered state, and Cu ions randomly occupy positions within the rigid face-centered cubic lattice framework composed of S ions, becoming a superionic conductor. Excessive copper vacancies lead to a high carrier concentration, showing a low Seebeck coefficient and a high thermal conductivity. Therefore, the regulation of copper vacancies is mainly achieved through doping or alloying. Research has shown that doping with elements of the same main group in chalcogenide compounds can adjust the band structure and optimize the thermoelectric properties. It has been found that the doping of Te, due to the electron contribution of Te atoms in the 5p orbital, has been proven to effectively reduce the 2-x density of states (DOS) of Cu

[0008] Different sintering processes of thermoelectric materials will seriously affect the microstructure and thermoelectric properties of the bulk. As previously reported, Cu-S-based thermoelectric materials can be sintered by forming processes such as induction vacuum hot pressing (IHP), hot pressing (hp), spark plasma sintering (sps), room temperature high pressure sintering (RT-HPS), etc. Vacuum hot pressing sintering is the most commonly used sintering technique. It can avoid the reduction of material stability caused by the relative electromigration of highly mobile copper ions under the driving of a bias voltage during the SPS sintering process. At the same time, because it completes the sintering process in a short time, it inhibits the growth of grains and maintains the nanostructure of the precursor powder as much as possible. However, during the sintering process, the static constant pressure also has its inherent limitations. Especially in the later stage of sintering, the main mechanism of densification is grain boundary diffusion, which promotes grain growth, reduces the grain boundary energy, and degrades the thermal and mechanical properties. Hot Oscillating Pressure (hop) or oscillating pressure sintering, this new sintering technique, has great potential in the preparation of high-performance materials. Studies on ceramics, cemented carbides, and metals have shown that oscillating pressure can increase the density and densification rate, inhibit grain growth, and improve the mechanical properties of ceramics. There is currently no research on using oscillating hot pressing to prepare thermoelectric materials.

[0009] Therefore, this application proposes a new sintering method for preparing thermoelectric materials. Summary of the Invention

[0010] In order to make up for the deficiencies of the prior art and solve the technical problems existing in the background art, the present invention proposes a new sintering method for preparing thermoelectric materials.

[0011] The present invention is achieved through the following technical solutions:

[0012] A new sintering method for preparing thermoelectric materials, comprising the following steps:

[0013] Step 1: Prepare the sintering precursor powder of the thermoelectric material;

[0014] Step 2: Sinter the bulk sample using the oscillating hot pressing process;

[0015] Step 3: Conduct pre-treatment before testing on the sintered bulk sample;

[0016] Step 4: Conduct comprehensive characterization tests on the sintered sample.

[0017] Preferably, the particle size of the precursor powder obtained in Step 1 satisfies normal filling of the graphite mold.

[0018] Preferably, the specific steps in Step 2 are as follows:

[0019] A1: Put the precursor powder from Step 1 into a graphite mold with a diameter of 15 mm, and apply an axial pressure of 800 N - 1000 N on the graphite mold to pre-tighten the mold;

[0020] A2: Place the graphite mold filled with the sample powder in an oscillating hot pressing furnace filled with an argon atmosphere and close the furnace door;

[0021] A3: Based on A2, first raise the temperature to 440 °C at a rate of 10 °C / min. After reaching 440 °C, then raise the temperature to 440 - 520 °C at a rate of 3 - 7 °C / min to ensure that the heat conduction temperature of the sample powder reaches 440 - 520 °C; -1 -1

[0022] A4: At the hot pressing and holding temperature of 440 - 520 °C, apply a sinusoidal oscillating force of 50 MPa denoted as hp, and apply a sinusoidal oscillating force of 5 MPa denoted as hop under a constant axial pressure of 50 Mpa. Hold for one hour. After cooling to 440 - 520 °C, release the pressure. After the temperature drops to room temperature, take out the sample, and the powder sintering is completed.

[0023] Among them, when the sample is about to reach 440 - 520 °C, apply a pressure of 8830 N (50 Mpa) with a target pressure, an amplitude of 883 N (5 Mpa), and a pressure increase rate of 4000 N - 7000 N / min; the sample is sintered at a constant temperature of 440 - 520 °C for one hour. After the holding ends, when the furnace temperature drops to 400 - 440 °C, reduce the pressure to 883 N at a rate of 4000 N - 7000 N / min. Wait until the furnace temperature drops to room temperature, then take out the sample. The sample is a cylindrical block with a height of 8 - 11 mm and a diameter of 15 mm.

[0024] ​​Preferably, the powder in A1 is fixed and compacted by the upper and lower pressing columns in a graphite mold, and three layers of 0.1 mm graphite carbon paper are placed at the places where the powder contacts the pressing columns.

[0025] Preferably, in A2, first reduce the vacuum degree of the oscillating hot press furnace to 10 -3 or less, and introduce argon at a rate of 120 ml / min -1 to ensure that it is always under atmospheric pressure during the sintering process.

[0026] Preferably, the specific steps in step three are as follows:

[0027] B1: Cut with a diamond wire cutting machine into round slices with a height of about 2.5 mm;

[0028] B2: Roughly polish the diameter and surface samples of each round slice with 320# silicon carbide sandpaper, and grind and polish the part where each round slice sample is adhered to the graphite sheet;

[0029] B3: Then polish the samples with 320#, 800#, 1000#, and 1440 - 520# sandpaper respectively, and measure the thickness with a vernier caliper at the same time, and grind and polish them into thin slice samples with a diameter of 12.7 mm and a thickness of 2 mm;

[0030] B4: Put the thin slice samples into a polishing machine for polishing;

[0031] B5: Put the polished thin slice samples into a small beaker containing anhydrous ethanol solution, and put them into an ultrasonic cleaner for ultrasonic cleaning for 30 min;

[0032] B6: Take out the thin slice samples, wipe them clean with alcohol cotton and put them into a drying oven, and keep them at a constant temperature of 80 °C for 4 h;

[0033] B7: Repeat B1 - B6 to complete the pre - treatment work of each thin slice sample before testing.

[0034] Preferably, a layer of nylon polishing cloth is laid on the polishing machine in B4, and the nylon polishing cloth is wetted with deionized water, and diamond polishing paste with a particle size of 1.5 μm is evenly coated on the nylon polishing cloth to polish the samples.

[0035] Preferably, the specific steps of step four include:

[0036] Perform phase analysis on the thin slice samples using an X - ray diffractometer;

[0037] When testing, use Cu - Kα rays as the X - ray source, the test voltage and current of the X - ray tube are 40 kV and 30 mA, and the scanning speed is 4° / min -1 .

[0038] Preferably, it further includes:

[0039] Performing morphological analysis on the thin slice fracture sample using a scanning electron microscope;

[0040] Performing tests on the conductivity and Seebeck coefficient of the thin slice sample using a Seebeck meter, with the test temperature range being 293 - 873K and the heating rate being 5°C / min -1 , and the test is carried out under the protection of an argon gas atmosphere.

[0041] Preferably, it further includes:

[0042] Measuring the density of the thin slice sample using the Archimedes method;

[0043] Performing a thermal conductivity test on the thin slice sample using a laser thermal conductivity meter;

[0044] Measuring the surface hardness of the thin slice sample using a Vickers hardness tester.

[0045] The beneficial effects of the present invention are:

[0046] The present invention synthesizes a thermoelectric bulk sample through a novel oscillating hot - pressing sintering process. On the one hand, the alternating load of oscillating hot - pressing during the sintering process promotes particle rearrangement and removes gas residues in the gaps between powder particles, thereby reducing the porosity of the sample, which is beneficial to improving the conductivity of the material. On the other hand, by applying an oscillating force, the grain size is significantly reduced, the grain boundaries are increased and strengthened, introducing a large number of interfaces, so as to regulate the thermal conductivity and hardness, resulting in a high - density, high - thermoelectric - performance, and high - machining - performance high - performance copper - sulfur - based thermoelectric material. Moreover, this preparation method is simple, efficient, feasible, and suitable for large - scale production, and is a relatively promising commercial production preparation method for copper - sulfur - based thermoelectric materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a flowchart of the method in the present invention;

[0048] Figure 2 It is a schematic diagram of the principle of oscillating hot - pressing sintering in the present invention;

[0049] Figure 3 It is the XRD pattern and enlarged view of the hot - pressed and oscillating hot - pressed bulk samples in the present invention;

[0050] Among them, the left side is the XRD pattern, and the right side is the enlarged view of the XRD;

[0051] Figure 4 It is the microscopic morphology diagram of the fracture surface of the hot - pressed and oscillating hot - pressed samples in the present invention;

[0052] Among them, (a) is the hot - pressed diagram of Cu 2-x S, (b) is the oscillating hot - pressed diagram of Cu 2-x S, (c) is Cu2-x S 1-y Tey hot press diagram, (d) is Cu 2-x S 1-y Te y Oscillating hot press diagram;

[0053] Figure 5 This is a comparison diagram of the indentations left on the surface by the Vickers hardness test of each thin-film sample in the present invention. Detailed implementation manners

[0054] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions noted in the following embodiments are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer.

[0055] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to persons skilled in the art. The reagents or raw materials used in the present invention can be obtained through conventional channels. Unless otherwise specified, the reagents or raw materials used in the present invention are used in the conventional manner in the art or according to the product instructions. In addition, any methods and materials similar or equivalent to the recorded content can be applied to the method of the present invention. The present invention will be further described below according to the accompanying drawings of the specification and the detailed implementation manners. The preferred implementation methods and materials described in the present invention are only for demonstration purposes.

[0056] A new sintering method for preparing thermoelectric materials. Taking the preparation of precursor powder by mechanical alloying method as an example, it is sintered and formed by using the oscillating hot press equipment produced by Chengdu Yifeide Technology Co., Ltd. The Cu 2-x S and Cu 2-x S 1-y Te y powders are sintered into blocks by oscillating hot pressing, where 0 ≤ x ≤ 0.2 and 0 ≤ y ≤ 0.5. Due to the existence of the oscillating force during the sintering process, the powder gaps are eliminated, so as to improve the density of the material, optimize the thermal properties while improving the electrical properties, and can greatly improve the mechanical processing performance, and then use mature industrial equipment for commercial production.

[0057] As Figure 1 shown, it includes the following steps:

[0058] Step 1: Prepare the sintering precursor powder of the thermoelectric material;

[0059] Step 2: Sinter the bulk sample by using the oscillating hot pressing process;

[0060] Step 3: Perform pre-treatment before testing on the sintered bulk sample;

[0061] Step 4: Perform comprehensive characterization tests on the sintered sample.

[0062] The precursor powder in Step 1 is synthesized Cu 2-x S and Cu 2-x S 1-y Te y powder;

[0063] The specific operation process of Step 1 is as follows:

[0064] Analytical pure Cu powder (purity ≥ 99.0%, AR), S powder (purity ≥ 98.5%, AR) and Te powder (purity ≥ 99.9%, AR) are used as synthetic raw materials, and the theoretical chemical reaction equation is as follows:

[0065] 2-xCu+S==Cu 2-x S

[0066] 2-xCu+1-yS+yTe==Cu 2-x S 1-y Te y

[0067] The prepared Cu 2-x S and Cu 2-x S 1-y Te y powders are all synthesized by mechanical alloying. The volume of the vacuum ball milling tank used is about 250 ml, the mass ratio of large balls to small balls is 1:1, and the ball-to-material ratio is 20:1. To avoid oxidation of metal powders, the raw materials are weighed in a glove box, with argon as the protective gas, the ball milling speed is 215 rpm, and the time is 2 h.

[0068] The specific operation process of Step 2 is as follows:

[0069] The powder obtained by ball milling is put into a graphite mold with a diameter of 15 mm and pre-pressed into shape. Then it is put into an oscillating hot press furnace.

[0070] First, an axial pressure of 883 N is applied to the graphite mold to pre-tighten the mold, the furnace door is closed, and the vacuum degree of the oscillating hot press furnace is reduced to 10 -3 below, and argon is introduced at 120 ml / min to keep it under atmospheric pressure during the sintering process.

[0071] Then it is heated to 400 °C at a rate of 10 °C / min. After reaching 400 °C, it is further heated to 440 - 520 °C at a rate of 5 °C / min -1 to fully ensure that the actual heat conduction temperature of the sample reaches 440 - 520 °C;

[0072] When the sample is about to reach 440 - 520 °C, applying a pressure of 8830 N (50 Mpa) is recorded as hot pressing (hp). Based on hot pressing, a superimposed amplitude of 883 N (5 Mpa) is recorded as hot oscillating pressure (hop). The unified pressure increase rate is 4000 - 7000 N / min.

[0073] The sample is sintered at a constant temperature of 440 - 520 °C for one hour. After the heat preservation ends, when the furnace temperature drops to 440 - 520 °C, the pressure is reduced to 883 N at a rate of 4000 - 7000 N / min. When the furnace temperature drops to room temperature, the sample is taken out, and the powder sintering is completed; then the powder X-ray diffraction test is carried out and compared with the standard PDF diffraction card to determine that the synthesized powder is a pure phase, and then the next step is carried out.

[0074] Figure 2 It is the schematic diagram of the hot oscillating pressure sintering equipment. Different from hot pressing sintering, under the axial pressure condition of the sample, a sinusoidal oscillating force is added.

[0075] The specific operation process of step three is as follows:

[0076] After hot oscillating pressure sintering, the sample has a relatively high height and is wrapped with carbon paper on the surface. To meet the test requirements and standardize the specifications, the sintered sample needs to be processed.

[0077] First, use a diamond wire cutting machine to cut it into round slices with a height of about 2.5 mm.

[0078] Then, use 320# silicon carbide sandpaper to roughly polish the diameter and surface of each round slice, and grind and polish the part where each round slice sample is adhered to the graphite sheet.

[0079] Then, use 320#, 800#, 1000#, and 1440 - 520# sandpaper to polish the sample respectively. At the same time, measure the thickness with a vernier caliper and grind and polish it into a thin slice sample with a diameter of 12.7 mm and a thickness of 2 mm.

[0080] Take out one of them for polishing. On the polishing machine, lay a layer of nylon polishing cloth, then wet the polishing cloth with deionized water, evenly apply diamond polishing paste with a particle size of 1.5 microns on it, and polish the sample.

[0081] Finally, put all the thin slice samples into a small beaker containing anhydrous ethanol solution, put it into an ultrasonic cleaner, and ultrasonically clean it at a low power for 30 min. Take out the thin slice samples, wipe them clean with alcohol cotton, put them in a drying oven, and dry them at a constant temperature of 80 °C for 4 h; perform the pre-test treatment work for each thin slice sample in the same operation sequence.

[0082] The specific operation process of Step 4 is as follows:

[0083] (1) Use an X-ray diffractometer (SmartLab, Rigaku Corporation, Japan) to perform phase analysis on the thin-film samples. The test uses Cu-Kα rays as the X-ray source, the test voltage and current of the X-ray tube are 40 kV and 30 mA, and the scanning speed is 4° / min.

[0084] Figure 3 Comparison chart of the diffraction results of the bulk before and after oscillatory hot pressing. The spectrogram shows:

[0085] Cu 2-x After CuS has undergone two sintering processes, the diffraction peaks of all samples are consistent with the standard card of the rhombohedral CuS phase (PDF#23-0962), and no second phase is found within the detection accuracy limit of XRD, indicating that the phase structure of the sample is a single CuS. 2-x S. 2-x S.

[0086] However, the diffraction peaks of CuS prepared by two different sintering methods are shifted towards smaller angles compared to the standard card (PDF#23-0962). This indicates that the volatilization of S during the sintering process has led to lattice expansion. And for CuS doped with Te element, 2-x after being sintered by hot pressing and oscillatory hot pressing sintering processes, the phase composition of the Cu2-xS 2- x S 1-y Te y Te bulk does not change due to the sintering process. However, in addition to the main phase being consistent with the standard card CuS (PDF#23-0962), a second phase is also generated, and the second phase matches the standard card CuS (PDF99-0028) phase, indicating that the doping of Te element promotes the volatilization of S, thereby generating a copper-rich phase CuS. After Te doping of S vacancies, the diffraction peak further shifts towards smaller angles. This indicates that Te element enters the lattice. Since the radius of Te atom is 1-y Te y greater than that of S atom, during the process of adding larger-radius Te atoms to the lattice arrangement, the original lattice expands, and the diffraction peak of the sample shifts along the smaller angle. 2-x S 1-y Te y In addition to the main phase being consistent with the standard card CuS (PDF#23-0962), a second phase is also generated, and the second phase matches the standard card CuS (PDF99-0028) phase, indicating that the doping of Te element promotes the volatilization of S, thereby generating a copper-rich phase CuS. After Te doping of S vacancies, the diffraction peak further shifts towards smaller angles. This indicates that Te element enters the lattice. Since the radius of Te atom is 2-x S (PDF#23-0962), a second phase is also generated, and the second phase matches the standard card CuS (PDF99-0028) phase, indicating that the doping of Te element promotes the volatilization of S, thereby generating a copper-rich phase CuS. After Te doping of S vacancies, the diffraction peak further shifts towards smaller angles. This indicates that Te element enters the lattice. Since the radius of Te atom is 2 S (PDF99-0028) phase, indicating that the doping of Te element promotes the volatilization of S, thereby generating a copper-rich phase CuS. After Te doping of S vacancies, the diffraction peak further shifts towards smaller angles. This indicates that Te element enters the lattice. Since the radius of Te atom is 2 S. S vacancies after Te doping, the diffraction peak further shifts towards smaller angles. This indicates that Te element enters the lattice. Since the radius of Te atom is greater than that of S atom, during the process of adding larger-radius Te atoms to the lattice arrangement, the original lattice expands, and the diffraction peak of the sample shifts along the smaller angle.

[0087] (2) Use a scanning electron microscope (JSM-7001F, JEOL Ltd., Japan) to perform morphology analysis on the thin-film samples.

[0088] Figure 4 (a-d) are samples of Cu 2-x S and Cu 2-x S 1-y Te y Hot pressing and oscillating hot pressing diagrams of the cross-section:

[0089] From Figure 4 (a-b), it can be seen that during the sintering process, after introducing the oscillating axial force, Cu 2-x S shows a dense structure, but the pores are significantly reduced, the grain size is significantly decreased, and grain boundaries begin to appear at the fracture surface; indicating that the oscillating pressure has the advantage of promoting particle rearrangement and removing the gas residue in the gaps between powder particles to reduce the porosity of the sample.

[0090] Figure 4 (c-d) are Cu 2-x S 1-y Te y SEM diagrams of the fracture surface before and after oscillation. From Figure 4 (c-d), it can be seen that after introducing the oscillating axial force, Cu 2-x S 1-y Te y shows a more dense structure, the pores are significantly reduced, the grain size is significantly decreased to within 3 μm, and the grain boundaries are significantly increased; indicating that under the action of the oscillating pressure, the atomic diffusion energy after doping with Te can be further reduced, and the pinning effect of the Te element is more obvious.

[0091] (3) Test the performance data with a Seebeck tester and a laser thermal conductivity meter.

[0092] Table 1 shows several implementation examples of the thermoelectric material prepared by oscillating sintering of the present invention

[0093]

[0094]

[0095] From Figure 5 as shown, whether after hot pressing or oscillating hot pressing, the hardness of the Cu 2-x S sample is significantly lower than that of the Cu 2-x S 1-y Te y sample after doping with the Te element. This is because Te atoms enter the lattice interior, softening the lattice. After introducing the oscillating force during the sintering of Cu 2- x S, the hardness of the sample is increased by 20%. 2-x S 1-y Te yAfter oscillating hot-press sintering, the hardness of the sample also increased by 28.4%. This is because the presence of the oscillating force during sintering refined the grains, increased the dislocation grain boundaries, and improved the mechanical properties of the material.

[0096] It can be seen from this that the new oscillating hot-press process effectively improves the Vickers hardness of the bulk sample, provides ideas for the subsequent improvement of the thermoelectric and mechanical properties of the Cu-S system, and is beneficial to the preparation of thermoelectric devices with high mechanical properties and stable durability in the Cu-S system.

[0097] The technical effects are as follows:

[0098] (1) For the samples sintered by oscillating hot-press, while significantly improving the material density to enhance the electrical properties of the material, it also refined the grains, increased the grain boundaries, reduced the thermal properties of the material, and comprehensively improved the thermoelectric properties of the material. Cu 2-x After doping with S and Te elements, the Cu 2-x S 1-y Te y bulk materials, the power factors of the materials increased by 14.3% and 8.6% respectively, the average thermal diffusion coefficients decreased by 28.5% and 18.8% respectively, and finally the average ZT values increased by 10.4% and 30% respectively.

[0099] (2) The mechanical properties of the surfaces of the hot-pressed and oscillating hot-pressed polished samples show that after introducing a sinusoidal oscillating force of 50±5 MPa during sintering, the Cu 2-x After doping with S and the doped Cu 2-x S 1-y Te y bulk materials had their hardness increased by 20% and 28.4% respectively.

[0100] (3) Using mechanical alloying to prepare powders has a simple process and high production efficiency, can carry out batch preparation of high-performance copper-sulfur-based thermoelectric materials, and enables rapid commercial production and application.

[0101] (4) Using oscillating hot-press sintering, the sintering temperature is low and the sintering time is short, thus retaining a large number of grain boundaries between the sample grains, avoiding grain boundary reactions caused by high-temperature sintering, and using the retained grain boundaries to scatter the phonon of heat conduction to reduce the thermal conductivity.

[0102] In summary, through the combination of mechanical alloying and oscillating hot-press sintering, the present invention tests the intrinsic and doped samples, and obtains samples with high density, high machining strength, high conductivity, and high power factor. More importantly, it can reversely regulate the thermal conductivity through the oscillating pressure, so as to effectively curb the deterioration of the thermal conductivity while significantly improving the electrical properties of the samples, and further coordinately regulate the thermoelectric properties of the samples.

[0103] Matters not described in the present invention apply to the prior art.

Claims

1. A novel sintering method for preparing thermoelectric materials, characterized in that: The following steps are involved: Step 1: preparing sintering precursor powder of thermoelectric material; Step 2: Sintering the bulk sample using an oscillating hot pressing process; Step 3: Pre-test treatment of the sintered block sample; Step 4: Conduct comprehensive characterization tests on the sintered samples; The precursor powder in step 1 is the synthesized Cu 2-x S and Cu 2-x S 1-y Te y Powder, and the particle size of the precursor powder meets the normal filling graphite mold; The specific steps in step 2 are as follows: A1: Place the precursor powder in step 1 into a graphite mold with a diameter of 15 mm, and apply an axial pressure of 800N-1000N on the graphite mold to pre-tighten the mold; A2: Place the graphite mold containing the sample powder in an oscillating hot press furnace filled with argon atmosphere and close the furnace door; A3: Based on A2, firstly -1 The temperature was raised to 400°C at a rate of 3-7°C min -1 Raise to 440-520℃ to ensure that the heat conduction temperature of the sample powder reaches 440-520℃; A4: At a hot pressing and holding temperature of 440-520℃, apply a pressure of 50MPa, recorded as hp, and apply a sinusoidal oscillation force of 5MPa under a constant axial pressure of 50MPa, recorded as hop. Keep the temperature for one hour, and after the temperature drops to 400-440℃, remove the pressure. After the temperature drops to room temperature, take out the sample, and the powder sintering is completed; The powder in A1 is fixed and compacted by the upper and lower pressure pins in the graphite mold, and three layers of 0.1 mm graphite carbon paper are placed where the powder contacts the pressure pins; In A2, first reduce the vacuum degree of the oscillating hot press furnace to 10 -3 Below, and 120mlmin -1 Argon is introduced at a rate to ensure that the sintering process is always at atmospheric pressure.

2. A novel sintering method for preparing thermoelectric materials according to claim 1, characterized in that: The specific steps in step three are as follows: B1: Cutting is performed using a diamond wire cutting machine and is cut into discs with a height of about 2.5 mm; B2: Use 320# silicon carbide sandpaper to roughly grind the diameter and surface samples of each disc, and grind off the part of each disc sample that is adhered to the graphite sheet; B3: Grind the sample with 320#, 800#, 1000#, and 1440-520# sandpaper respectively, and measure the thickness with a vernier caliper, and grind and polish it into a thin slice sample with a diameter of 12.7mm and a thickness of 2mm; B4: Put the thin slice sample into the grinding and polishing machine for polishing; B5: Place the polished thin slice sample into a small beaker containing anhydrous ethanol solution and then into an ultrasonic cleaning machine for 30 minutes; B6: Take out the thin slice sample, wipe it clean with alcohol cotton and put it in a drying oven, and dry it at a constant temperature of 80℃ for 4 hours; B7: Repeat B1-B6 to complete the processing work before testing each thin film sample.

3. A novel sintering method for preparing thermoelectric materials according to claim 2, characterized in that: A layer of nylon polishing cloth is laid on the grinding and polishing machine in B4, and the nylon polishing cloth is wetted with deionized water, and diamond polishing paste with a particle size of 1.5 um is evenly coated on the nylon polishing cloth to achieve polishing of the sample.

4. A novel sintering method for preparing thermoelectric materials according to claim 1, characterized in that: The specific steps of step 4 include: X-ray diffractometer was used to analyze the phase of thin-section samples; Used in testing The X-ray source is X-ray tube, the test voltage and current are 40kV, 30mA, and the scanning speed is 4°min -1 .

5. A novel sintering method for preparing thermoelectric materials according to claim 4, characterized in that: Also includes: The morphology of thin-section fracture samples was analyzed using scanning electron microscopy; The conductivity and Seebeck coefficient of the thin film samples were tested using a Seebeck instrument. The test temperature range was 293-873K and the heating rate was 5℃min -1 , the test was carried out under argon atmosphere protection.

6. A novel sintering method for preparing thermoelectric materials according to claim 1, characterized in that: Also includes: The density of thin slice samples was measured using the Archimedes method; The thermal conductivity of the thin-film samples was tested using a laser thermal conductivity meter; The surface hardness of the thin sample was measured using a Vickers hardness tester.

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