Solid-phase preparation method of MgAgSb-based thermoelectric material

Abstract

The invention provides a solid-phase preparation method of an MgAgSb-based thermoelectric material, and belongs to the technical field of thermoelectric material preparation. The solid-phase preparation method of the MgAgSb-based thermoelectric material comprises the following steps: sufficiently and uniformly mixing Mg powder, Ag powder and Sb powder, then pouring the mixed powder into a mold, and sequentially carrying out cold press molding, vacuum sealing, solid-phase reaction, grinding and sieving, spark plasma sintering pressing and annealing treatment to finally obtain the MgAgSb-based thermoelectric material. The MgAgSb-based thermoelectric material obtained through a solid-phase reaction method has good electric transport performance, impurity phases of a sample are reduced, the thermal performance stability is good, the degree of crystallinity is high, point defects are rich, and a large number of stress concentration areas exist. On the basis of maintaining high carrier mobility, a high thermoelectric figure of merit is achieved by synchronously optimizing carrier concentration and phonon scattering, and the method is easy and convenient to operate, short in consumed time and high in repeatability.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric material preparation technology, and particularly relates to a solid-phase preparation method for MgAgSb-based thermoelectric materials. Background Technology

[0002] In recent years, with the rapid development of industrial society, energy crisis and environmental pollution have become two of the most serious problems facing humanity. Regarding resource waste, traditional heat engines still provide 80% of the electricity for humanity; however, during operation, approximately 70% of the energy is wasted as heat. If this waste heat could be effectively recovered, the energy crisis would be greatly alleviated. Therefore, developing a clean and efficient energy conversion technology is particularly crucial.

[0003] Thermoelectric conversion technology, as a green energy technology, enables the direct conversion between heat and electricity, effectively recovering waste heat without generating any pollution. Thermoelectric devices, with their unique advantages of small size, light weight, no pollution, no noise, simple structure, and high reliability, have attracted widespread attention from researchers. Currently, thermoelectric devices are applied in various fields such as aerospace, power generation in remote areas, deep space exploration, and solid-state refrigeration. With the rapid advancement of modern industrialization, the demand for thermoelectric conversion technology is increasing daily.

[0004] In low-temperature environments (usually below 500K), MgAgSb-based thermoelectric materials have high thermoelectric figure of merit (ZT) and possess advantages such as intrinsic low lattice thermal conductivity, rich and non-toxic elemental content, low contact resistance, and good mechanical properties. This makes them have great application potential in fields such as low-temperature waste heat recovery and low-temperature refrigeration.

[0005] MgAgSb possesses a complex crystal structure. High-temperature γ-MgAgSb exhibits a half-Heusler (HH) structure with space group F-43m, while room-temperature α-MgAgSb is a deformed HH structure with space group I-4c2. In this crystal structure, Mg atoms occupy specific lattice positions, typically within octahedral or tetrahedral voids. Ag and Sb atoms also occupy specific sites, interacting through chemical bonds to form a stable crystal structure. This complex crystal structure and atomic arrangement result in strong scattering of phonons propagating within the crystal. The mass differences among Mg, Ag, and Sb atoms, along with the complexity of interatomic bonding, cause phonons to continuously interact with these atoms and lattice defects during propagation. This effectively reduces lattice thermal conductivity, minimizing heat conduction loss and improving thermoelectric conversion efficiency.

[0006] Existing research has explored various methods to prepare high-performance MgAgSb-based thermoelectric materials, including high-energy ball milling, high-temperature melting, and conventional ball milling, all of which have yielded preliminary results. However, this material system also faces numerous difficulties and challenges. For example, MgAgSb-based thermoelectric materials suffer from low carrier concentration, susceptibility to impurity phase formation, poor oxidation resistance, and difficulties in large-scale preparation. These issues hinder the improvement of the overall thermoelectric performance and the full realization of its practical application potential. Therefore, further in-depth research is needed to explore effective modification strategies and optimized preparation processes to promote the development of MgAgSb-based thermoelectric materials towards greater efficiency and practicality. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes a solid-state preparation method for MgAgSb-based thermoelectric materials. This method is simple to operate, has high reproducibility, and can produce large quantities of relatively pure phase samples. The MgAgSb-based thermoelectric materials prepared by this solid-state reaction method have high thermoelectric figure of merit and good application prospects.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention proposes a solid-state preparation method for MgAgSb-based thermoelectric materials, comprising the following steps:

[0010] (1) Mix Mg powder, Ag powder and Sb powder evenly, then pour the evenly mixed powder into a mold and cold press it into shape;

[0011] (2) Vacuum seal the cold-pressed blank;

[0012] (3) The vacuum-sealed compact undergoes a solid-phase reaction;

[0013] (4) Grind and sieve the sample after the solid-phase reaction to obtain powder;

[0014] (5) The powder is loaded into a mold and pressed into a block by spark plasma sintering;

[0015] (6) Anneal the bulk material to obtain the MgAgSb-based thermoelectric material.

[0016] In the solid-state preparation method of MgAgSb-based thermoelectric materials of this invention, the raw materials are first mixed and cold-pressed to ensure uniform powder contact, laying the foundation for subsequent solid-state reactions. Vacuum sealing isolates the raw materials from air, preventing oxidation and the formation of impurity phases, thus reducing interference with electrical transport properties. The solid-state reaction promotes full atomic diffusion, forming a complete main crystalline phase, while utilizing the difference in thermal expansion of components to construct stress concentration regions. Grinding and sieving ensure uniform powder particle size, preparing for subsequent densification. Spark plasma sintering can rapidly achieve powder densification and inhibit excessive grain growth; annealing can eliminate internal stress and optimize lattice defects. Overall, through multi-step synergy, phonon scattering is enhanced to reduce lattice thermal conductivity, and carrier concentration and mobility are simultaneously optimized, ultimately achieving a high thermoelectric figure of merit. Furthermore, the process is simple and highly repeatable.

[0017] Further, in step (1), the molar ratio of Mg powder, Ag powder and Sb powder is 1:1:0.99.

[0018] Furthermore, in step (1), the cold pressing pressure is 20 MPa and the time is 5 min; even further, in step (1), the cold pressing process includes pre-pressing, the pre-pressing pressure is 10 MPa and the time is 30 s.

[0019] Further, in step (2), the vacuum sealing is performed by loading the carbon paper-wrapped blank into a quartz tube using a vacuum pump and drawing it into a vacuum, and then sealing it by molten encapsulation using an oxyhydrogen flame.

[0020] Further, in step (3), the solid-phase reaction is carried out by heating at a rate of 2℃ / min to 300℃ and holding for 5h, and then heating at a rate of 2℃ / min to 600-700℃ and holding for 5h.

[0021] Furthermore, in step (4), the grinding time for grinding and sieving is greater than 30 minutes, and the particle size of the powder after grinding and sieving is ≤300 mesh.

[0022] Further, in step (5), the powder is pre-pressed by 10 MPa in the mold. The discharge plasma sintering includes the following steps: setting the pressure to 65 MPa, heating the powder to 400°C at a heating rate of 126°C / min, holding it at that temperature for 2 min, then cooling it down to 300°C and holding it at that temperature for 8 min, then depressurizing and cooling it to room temperature in a vacuum environment.

[0023] Furthermore, in step (5), the obtained block is a high-density block with a relative sample density ρ / ρ0 ≥ 94%, where ρ is the sample density and ρ0 is the theoretical density of the material.

[0024] Further, in step (6), the annealing process involves heating to 300°C at a heating rate of 3°C / min, holding at that temperature for 120 hours, and then cooling to room temperature.

[0025] The present invention also provides a MgAgSb-based thermoelectric material, which is prepared according to the preparation method described above.

[0026] Compared with the prior art, the present invention has the following advantages and technical effects:

[0027] (1) This invention provides a method for preparing high-performance MgAgSb-based thermoelectric materials using a solid-state reaction method. This method is simple and produces samples with stable performance. The microstructure and actual composition of the MgAgSb-based sample can be adjusted using the solid-state reaction method. The resulting MgAgSb-based thermoelectric material exhibits good electrical transport properties, reduced impurity phases, excellent thermal stability, high crystallinity, abundant point defects, and numerous stress concentration regions. While maintaining a high carrier mobility, a high thermoelectric figure of merit is achieved by simultaneously optimizing carrier concentration and phonon scattering.

[0028] (2) The present invention can synthesize samples with high carrier mobility at a lower reaction temperature through solid-state reaction method, and simultaneously optimize carrier concentration and reduce lattice thermal conductivity to obtain a higher thermoelectric figure of merit.

[0029] (3) The present invention can change the microstructure of the material by solid-state reaction at 600°C and above to obtain a richer microstructure and enhance the scattering of phonons.

[0030] (4) The method of the present invention is simple to operate, short in time and highly repeatable. Attached Figure Description

[0031] The accompanying drawings, which constitute a part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0032] Figure 1 The XRD pattern of the solid reaction powder obtained after solid-phase reaction at 600℃ in step (3) of Example 1;

[0033] Figure 2 SEM image of the MgAgSb-based thermoelectric material obtained in Example 1;

[0034] Figure 3 The XRD patterns of MgAgSb-based thermoelectric materials obtained at different solid-phase reaction temperatures in Examples 1-2 and Comparative Examples 1-2 are shown.

[0035] Figure 4The thermal properties of MgAgSb-based thermoelectric materials obtained at different solid-state reaction temperatures in Examples 1-2 and Comparative Examples 1-2 are shown in the figure, where (a) is the total thermal conductivity, (b) is the electronic thermal conductivity, and (c) is the lattice thermal conductivity.

[0036] Figure 5 The electrical properties and ZT values ​​of the MgAgSb-based thermoelectric materials obtained at different solid-state reaction temperatures in Examples 1-2 and Comparative Examples 1-2 are shown in the figure. (a) represents electrical conductivity, (b) represents power factor, (c) represents Seebeck coefficient, and (d) represents ZT value.

[0037] Figure 6 The thermal properties of the MgAgSb-based thermoelectric material obtained in Comparative Example 3 are shown in the figure, where (a) is the power factor, (b) is the total thermal conductivity, and (c) is the ZT value.

[0038] Figure 7 The thermal performance diagram of the MgAgSb-based thermoelectric material obtained in Comparative Example 4 is shown, where (a) is the power factor, (b) is the total thermal conductivity, and (c) is the ZT value.

[0039] Figure 8 The figure shows the thermal properties of the MgAgSb-based thermoelectric material obtained in Comparative Example 4, where (a) is the power factor, (b) is the total thermal conductivity, and (c) is the ZT value. Detailed Implementation

[0040] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0041] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0042] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0043] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0044] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0045] This invention provides a solid-state preparation method for MgAgSb-based thermoelectric materials, comprising the following steps:

[0046] (1) Mix Mg powder, Ag powder and Sb powder evenly, then pour the evenly mixed powder into a mold and cold press it into shape;

[0047] (2) Vacuum seal the cold-pressed blank;

[0048] (3) The vacuum-sealed compact undergoes a solid-phase reaction;

[0049] (4) Grind and sieve the sample after the solid-phase reaction to obtain powder;

[0050] (5) The powder is loaded into a mold and pressed into a block using spark plasma sintering (SPS);

[0051] (6) Anneal the bulk material to obtain MgAgSb-based thermoelectric material.

[0052] In step (1) of the preferred embodiment of the present invention, the molar ratio of Mg powder, Ag powder and Sb powder is 1:1:0.99.

[0053] In this invention, the molar ratio of Sb is slightly lower than the theoretical value (1:1:0.99 instead of 1:1:1) to actively form Sb vacancy defects (instead of excess Sb precipitation forming a second phase). If Sb is in excess, unreacted Sb will exist in the grain boundary in elemental form, becoming a trap for electrical transport (scattering carriers) and a pathway for thermal conduction (increasing electronic thermal conductivity); while Sb vacancies can serve as beneficial defects (instead of impurities), both avoiding the formation of a second phase and laying the foundation for subsequent carrier regulation, corresponding to "reduction of impurity phase". At the same time, Sb vacancies and the low-temperature sintering in step (3) (avoiding defect annihilation) can retain a large number of point defects (vacancies, substitution atoms), achieving optimization of carrier concentration.

[0054] In step (1) of the preferred embodiment of the present invention, the pressure of cold pressing is 20 MPa and the time is 5 min; in addition, in step (1), pre-pressing is also included before cold pressing, the pressure of pre-pressing is 10 MPa and the time is 30 s.

[0055] In step (2) of the preferred embodiment of the present invention, vacuum sealing involves loading a carbon paper-wrapped compact into a quartz tube using a vacuum pump, drawing the tube to a vacuum level, and then sealing it using an oxyhydrogen flame. Vacuum sealing can reduce oxidation impurities, which may act as carrier traps and scatter carriers.

[0056] In step (3) of the preferred embodiment of the present invention, the solid-phase reaction is carried out by heating at a rate of 2℃ / min to 300℃ and holding for 5h, and then heating at a rate of 2℃ / min to 600-700℃ and holding for 5h.

[0057] The solid-state reaction of this invention adopts a low-temperature pre-calcination followed by high-temperature sintering. The low-temperature stage achieves the initial diffusion of Mg / Ag / Sb, avoiding compositional segregation caused by excessively rapid local reactions at high temperatures. The high-temperature stage promotes full atomic migration, forming a complete MgAgSb main crystalline phase and reducing lattice distortion.

[0058] In step (4) of the preferred embodiment of the present invention, the grinding time for grinding and sieving is greater than 30 minutes, and the particle size of the powder after grinding and sieving is ≤300 mesh.

[0059] In step (5) of the preferred embodiment of the present invention, the powder is pre-pressed by a pressure of 10 MPa and the discharge plasma sintering includes the following steps: the pressure is set to 65 MPa, the powder is heated to 400°C at a heating rate of 126°C / min, held for 2 min, then cooled to 300°C and held for 8 min, and then the pressure is released and cooled to room temperature in a vacuum environment.

[0060] In the SPS process of this invention, the Joule heat generated by the pulsed current is concentrated at the powder contact point, which can rapidly densify at 400°C (far below the melting temperature) and avoid excessive grain growth; the subsequent "cooling down to 300°C and holding for 8 minutes" can release the sintering internal stress, reduce porosity (porosity will cause thermal conductivity fluctuations), and make the crystal structure more regular.

[0061] In step (5) of the preferred embodiment of the present invention, the obtained block is a high-density block with a relative sample density ρ / ρ0 ≥ 94%, where ρ is the sample density and ρ0 is the theoretical density of the material.

[0062] In step (6) of the preferred embodiment of the present invention, the annealing process involves heating to 300°C at a heating rate of 3°C / min, holding at that temperature for 120 hours, and then cooling to room temperature.

[0063] In the annealing process of this invention, slow heating avoids grain boundary cracking caused by thermal shock, and long-term heat preservation allows lattice defects (such as dislocations) to rearrange, making the crystal structure more ordered (improving crystallinity); at the same time, it eliminates the residual internal stress of SPS and the high-temperature phase generated in the early stage, reduces the performance degradation of the material due to uneven thermal expansion during temperature cycling, thereby improving the thermal stability of the material.

[0064] This invention also provides a MgAgSb-based thermoelectric material, prepared according to a specific method.

[0065] In the MgAgSb-based thermoelectric materials prepared by solid-state reaction at 600℃ and above in the embodiments of this invention, the MgAgSb phase is dominant, and Sb, Ag3Sb impurity phases and MgAg phase are also present in the sample. The electrical performance parameters increase sharply with increasing synthesis temperature, and the power factor (PF) is ~2.3 μW m. -1 K -2 Thermoelectric figure of merit (ZT) ~0.9.

[0066] The Mg powder, Ag powder, and Sb powder used in the embodiments of the present invention have a particle size of less than 200 mesh and a purity of ≥99.9%.

[0067] In this invention, room temperature refers to "25±2℃".

[0068] The specific methods and principles of performance testing in this invention are as follows: The method for testing the thermal properties of materials uses the formula k (thermal conductivity) = DdC. p The calculation yielded the result. Where D represents the thermal diffusivity of the sample, d represents the density of the sample, and C... p This represents the specific heat of the sample. The sample density was measured by the water displacement method; the thermal diffusivity was measured using a Netzsch LFA467 laser thermal conductivity meter (temperature range: -100~500℃) and an LFA467 HT (temperature range: room temperature~1200℃). The thermal diffusivity was directly measured using the laser scattering method. After the laser emits a laser beam, an infrared detector can detect the change in temperature at the other end of the sample over time. Under heat-insulated conditions, the thermal diffusivity D of the sample can be expressed by the formula... The calculation yields the result, where l is the thickness of the sample being measured, and t... 1 / 2 It is the time required for the back of the sample to rise by 1 / 2.

[0069] The electrical performance testing method in this invention is performed using a CTA-3 (room temperature - 1000℃) instrument manufactured by Beijing Kerui Co., Ltd. The instrument's working principle is as follows: when the furnace temperature rises to the set temperature, the temperature difference heater in the bottom support rod begins to heat to the set temperature, creating a temperature difference. Temperature and voltage are measured using two thermocouple probes, with temperatures T1 and T2 obtained from the upper and lower probes, and voltages U1 and U2, respectively. The Seebeck coefficient can then be calculated using the formula... Calculations show that the upper and lower electrodes and the upper and lower probes together form a four-probe method for resistivity testing. Therefore, the conductivity of the sample can be expressed by the formula... The values ​​are calculated to be ρ, L, A, R, I, and V, where ρ is resistivity, L is length, A is cross-sectional area, R is resistance, I is current, and V is voltage.

[0070] The technical solution of the present invention will be further illustrated by the following embodiments.

[0071] Example 1

[0072] A solid-state preparation method for MgAgSb-based thermoelectric materials includes the following steps:

[0073] (1) Weigh and mix Mg powder, Ag powder and Sb powder in a molar ratio of 1:1:0.99. Then pour the mixed powder into a mold, pre-press it at 10MPa for 30s, and then cold-press it at 20MPa for 5min.

[0074] (2) The cold-pressed blank wrapped with carbon paper is placed into a quartz tube and evacuated to a vacuum. It is then melted and sealed with an oxyhydrogen flame to obtain a vacuum-sealed quartz tube containing the blank.

[0075] (3) The vacuum-sealed quartz tube is placed in a muffle furnace for solid-phase reaction. The solid-phase reaction is carried out by heating at a rate of 2℃ / min to 300℃ and holding for 5h, and then heating at a rate of 2℃ / min to 600℃ and holding for 5h.

[0076] (4) Take out the quartz tube containing the sample after the solid-phase reaction, and take out the sample. Grind it in an agate mortar for more than 30 minutes so that all the powder passes through a 300-mesh sieve to obtain uniform powder.

[0077] (5) After the uniform powder is placed into the graphite mold, it is pre-pressed by a pressure of 10MPa and pressed into a block by spark plasma sintering. Specifically, the pressure is adjusted to 65MPa, the powder is heated to 400℃ at a heating rate of 126℃ / min, held for 2min, then cooled to 300℃ and held for 8min, then the pressure is released and the powder is naturally cooled to room temperature in a vacuum environment.

[0078] (6) The block is placed in a box furnace and heated to 300°C at a heating rate of 3°C / min. The temperature is kept constant for 120 hours and then naturally cooled to room temperature to obtain MgAgSb-based thermoelectric material.

[0079] Example 2

[0080] Same as Example 1, except that in step (3), the solid-phase reaction is heated to 300°C at a rate of 2°C / min and held for 5 hours, and then heated to 700°C at a rate of 2°C / min and held for 5 hours.

[0081] Comparative Example 1

[0082] Same as Example 1, except that in step (3), the solid-phase reaction is heated to 300°C at a rate of 2°C / min and held for 5 hours, and then heated to 400°C at a rate of 2°C / min and held for 5 hours.

[0083] Comparative Example 2

[0084] Same as Example 1, except that in step (3), the solid-phase reaction is heated to 300°C at a rate of 2°C / min and held for 5 hours, and then heated to 500°C at a rate of 2°C / min and held for 5 hours.

[0085] Comparative Example 3

[0086] Same as Example 1, except that in step (3), the solid-phase reaction is carried out at a heating rate of 5℃ / min to 900℃ and held at that temperature for 5h, specifically:

[0087] (1) Weigh and mix Mg powder, Ag powder and Sb powder in a molar ratio of 1:1:0.99. Then pour the mixed powder into a mold, pre-press it at 10MPa for 30s, and then cold-press it at 20MPa for 5min.

[0088] (2) The cold-pressed blank wrapped with carbon paper is placed into a quartz tube and evacuated to a vacuum. It is then melted and sealed with an oxyhydrogen flame to obtain a vacuum-sealed quartz tube containing the blank.

[0089] (3) The vacuum-sealed quartz tube is placed in a muffle furnace for solid-phase reaction. The solid-phase reaction is carried out at a heating rate of 5℃ / min to 900℃ and held for 5h.

[0090] (4) Take out the quartz tube containing the sample after the solid-phase reaction, and take out the sample. Grind it in an agate mortar for more than 30 minutes so that all the powder passes through a 300-mesh sieve to obtain uniform powder.

[0091] (5) After the uniform powder is placed into the graphite mold, it is pre-pressed by a pressure of 10MPa and pressed into a block by spark plasma sintering. Specifically, the pressure is adjusted to 65MPa, the powder is heated to 400℃ at a heating rate of 126℃ / min, held for 2min, then cooled to 300℃ and held for 8min, then the pressure is released and the powder is naturally cooled to room temperature in a vacuum environment.

[0092] (6) The block is placed in a box furnace and heated to 300°C at a heating rate of 3°C / min. The temperature is kept constant for 120 hours and then naturally cooled to room temperature to obtain MgAgSb-based thermoelectric material.

[0093] Comparative Example 4

[0094] Same as Example 1, except that step (6) annealing is omitted. Specifically:

[0095] (1) Weigh and mix Mg powder, Ag powder and Sb powder in a molar ratio of 1:1:0.99. Then pour the mixed powder into a mold, pre-press it at 10MPa for 30s, and then cold-press it at 20MPa for 5min.

[0096] (2) The cold-pressed blank wrapped with carbon paper is placed into a quartz tube and evacuated to a vacuum. It is then melted and sealed with an oxyhydrogen flame to obtain a vacuum-sealed quartz tube containing the blank.

[0097] (3) The vacuum-sealed quartz tube is placed in a muffle furnace for solid-phase reaction. The solid-phase reaction is carried out by heating at a rate of 2℃ / min to 300℃ and holding for 5h, and then heating at a rate of 2℃ / min to 600℃ and holding for 5h.

[0098] (4) Take out the quartz tube containing the sample after the solid-phase reaction, and take out the sample. Grind it in an agate mortar for more than 30 minutes so that all the powder passes through a 300-mesh sieve to obtain uniform powder.

[0099] (5) After the uniform powder is placed into the graphite mold, it is pre-pressed by a pressure of 10 MPa and pressed into a block by spark plasma sintering. Specifically, the pressure is adjusted to 65 MPa, the powder is heated to 400°C at a heating rate of 126°C / min, held for 2 min, then cooled to 300°C and held for 8 min, then the pressure is released and the powder is naturally cooled to room temperature in a vacuum environment to obtain MgAgSb-based thermoelectric material.

[0100] Comparative Example 5

[0101] Same as Example 1, except that in step (1), Mg powder, Ag powder, and Sb powder are weighed and mixed evenly in a molar ratio of 1:1:1, and in step (3), the solid-phase reaction is carried out at a heating rate of 2℃ / min to 900℃ and held for 5h. The specific steps are as follows:

[0102] (1) Weigh Mg powder, Ag powder and Sb powder in a molar ratio of 1:1:1 and mix them evenly. Then pour the evenly mixed powder into a mold, pre-press it at 10MPa for 30s, and then cold-press it at 20MPa for 5min.

[0103] (2) The cold-pressed blank wrapped with carbon paper is placed into a quartz tube and evacuated to a vacuum. It is then melted and sealed with an oxyhydrogen flame to obtain a vacuum-sealed quartz tube containing the blank.

[0104] (3) The vacuum-sealed quartz tube is placed in a muffle furnace for solid-phase reaction. The solid-phase reaction is carried out at a heating rate of 2℃ / min to 900℃ and held for 5h.

[0105] (4) Take out the quartz tube containing the sample after the solid-phase reaction, and take out the sample. Grind it in an agate mortar for more than 30 minutes so that all the powder passes through a 300-mesh sieve to obtain uniform powder.

[0106] (5) After the uniform powder is placed into the graphite mold, it is pre-pressed by a pressure of 10MPa and pressed into a block by spark plasma sintering. Specifically, the pressure is adjusted to 65MPa, the powder is heated to 400℃ at a heating rate of 126℃ / min, held for 2min, then cooled to 300℃ and held for 8min, then the pressure is released and the powder is naturally cooled to room temperature in a vacuum environment.

[0107] (6) The block is placed in a box furnace and heated to 300°C at a heating rate of 3°C / min. The temperature is kept constant for 120 hours and then naturally cooled to room temperature to obtain MgAgSb-based thermoelectric material.

[0108] Performance testing

[0109] In step (3) of Example 1, the solid-phase reaction powder (MgAgSb) obtained after solid-phase reaction at 600℃ 0.99 The XRD pattern of the powder is shown in the figure. Figure 1 As can be seen, the XRD diffraction peaks of the product obtained in Example 1 are basically consistent with the diffraction peaks of the MgAgSb standard card, indicating that the MgAgSb phase with a specific crystal structure was successfully synthesized, while containing Ag3Sb impurity phase and Sb second phase.

[0110] SEM image of the MgAgSb-based thermoelectric material obtained in Example 1 is shown below. Figure 2As can be seen, the synthesized MgAgSb exhibits a layered structure.

[0111] The XRD patterns of MgAgSb-based thermoelectric materials obtained at different solid-state reaction temperatures in Examples 1-2 and Comparative Examples 1-2 are shown below. Figure 3 It can be seen that the MgAgSb phase is dominant, and the sample also contains Sb, Ag3Sb impurity phases and MgAg phase.

[0112] The thermal properties of MgAgSb-based thermoelectric materials obtained at different solid-state reaction temperatures in Examples 1-2 and Comparative Examples 1-2 are shown in the figure. Figure 4 In the figure, (a) represents the total thermal conductivity, (b) represents the electronic thermal conductivity, and (c) represents the lattice thermal conductivity. As can be seen from the figure, the total thermal conductivity of the sample decreases with increasing solid-state reaction temperature, the electronic thermal conductivity decreases first and then increases, while the lattice thermal conductivity gradually decreases with increasing solid-state reaction temperature.

[0113] The electrical properties and ZT values ​​of the MgAgSb-based thermoelectric materials obtained at different solid-state reaction temperatures in Examples 1-2 and Comparative Examples 1-2 are shown in the figure. Figure 5 Where (a) is electrical conductivity, (b) is power factor, (c) is Seebeck coefficient, and (d) is ZT value. As can be seen from the figure, the electrical conductivity of the samples first decreases and then increases with increasing solid-state reaction temperature, while the Seebeck coefficient increases with increasing solid-state reaction temperature. At 500℃, 600℃, and 700℃, the Seebeck coefficients of the three samples are not significantly different. The power factor, however, generally shows an increasing trend, and at 600℃ and 700℃, the power factors of the samples are basically similar. Finally, from... Figure 5 As can be seen from (d), the ZT value of the sample increases with the increase of solid-phase reaction temperature, and the maximum ZT value at 600℃ and 700℃ is basically the same.

[0114] Comparative Example 3 differs from Example 1 only in that, in step (3), the solid-phase reaction is carried out at a heating rate of 5°C / min to 900°C and held at that temperature for 5 hours. Its main performance is shown in the figure below. Figure 6 As shown in the figure, (a) is the power factor, (b) is the total thermal conductivity, and (c) is the ZT value. It can be seen from the figure that compared to Example 1 ( Figure 4 , Figure 5 When the solid-phase reaction temperature is 900℃, the power factor, total thermal conductivity and ZT value of the sample of Comparative Example 3 are basically the same as those of Example 1, but the synthesis temperature is 300℃ lower, which helps to save energy.

[0115] Comparative Example 4 differs from Example 1 only in that step (6) annealing is omitted. Its main performance is shown in the figure below. Figure 7As shown in the figure, (a) is the power factor, (b) is the total thermal conductivity, and (c) is the ZT value. It can be seen from the figure that the power factor of the unannealed sample is significantly lower than that of Example 1, and the total thermal conductivity is much higher than that of Example 1, which ultimately results in a maximum ZT value of only about 0.43.

[0116] Comparative Example 5 differs from Example 1 only in that, in step (1), Mg powder, Ag powder, and Sb powder are weighed and mixed evenly in a molar ratio of 1:1:1. In step (3), the solid-phase reaction is carried out at a heating rate of 2℃ / min to 900℃ and held for 5 hours. Its main properties are as follows: Figure 8 As shown in the figure, (a) represents the power factor, (b) represents the total thermal conductivity, and (c) represents the ZT value. It can be seen from the figure that the maximum power factor of the sample is approximately 1600 μW / m². -1 K -2 It is about 30% lower than that of Example 1, and the total thermal conductivity is basically the same as that of Example 1. Due to the lower power factor, its maximum ZT value is about 0.6.

[0117] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A solid-phase preparation method for a MgAgSb-based thermoelectric material, characterized in that, Includes the following steps: (1) Mix Mg powder, Ag powder and Sb powder evenly, then pour the evenly mixed powder into a mold and cold press it into shape; (2) Vacuum seal the cold-pressed blank; (3) The vacuum-sealed compact undergoes a solid-phase reaction; (4) Grind and sieve the sample after the solid-phase reaction to obtain powder; (5) The powder is loaded into a mold and pressed into a block by spark plasma sintering; (6) Anneal the bulk material to obtain the MgAgSb-based thermoelectric material.

2. The solid-state preparation method of the MgAgSb-based thermoelectric material according to claim 1, characterized in that, In step (1), the molar ratio of Mg powder, Ag powder and Sb powder is 1:1:0.

99.

3. The solid-state preparation method of the MgAgSb-based thermoelectric material according to claim 1, characterized in that, In step (1), the pressure of cold pressing is 20 MPa and the time is 5 min.

4. The solid-state preparation method of the MgAgSb-based thermoelectric material according to claim 3, characterized in that, In step (1), the cold pressing process includes pre-pressing, where the pressure is 10 MPa and the time is 30 s.

5. The solid-state preparation method of the MgAgSb-based thermoelectric material according to claim 1, characterized in that, In step (2), the vacuum sealing is achieved by using a vacuum pump to load the carbon paper-wrapped blank into a quartz tube and evacuate it to a vacuum, and then using an oxyhydrogen flame to melt and seal it.

6. The solid-state preparation method of the MgAgSb-based thermoelectric material according to claim 1, characterized in that, In step (3), the solid-phase reaction is carried out by heating at a rate of 2℃ / min to 300℃ and holding for 5h, and then heating at a rate of 2℃ / min to 600-700℃ and holding for 5h.

7. The solid-state preparation method of the MgAgSb-based thermoelectric material according to claim 1, characterized in that, In step (4), the grinding time for grinding and sieving is greater than 30 minutes, and the particle size of the powder after grinding and sieving is ≤300 mesh.

8. The solid-state preparation method of the MgAgSb-based thermoelectric material according to claim 1, characterized in that, In step (5), the powder is pre-pressed by 10 MPa in the mold. The discharge plasma sintering includes the following steps: setting the pressure to 65 MPa, heating the powder to 400°C at a heating rate of 126°C / min, holding it at that temperature for 2 min, then cooling it down to 300°C and holding it at that temperature for 8 min, then depressurizing and cooling it to room temperature in a vacuum environment.

9. The solid-state preparation method of the MgAgSb-based thermoelectric material according to claim 1, characterized in that, In step (6), the annealing process involves heating to 300°C at a heating rate of 3°C / min, holding at that temperature for 120 hours, and then cooling.

10. A MgAgSb-based thermoelectric material, characterized in that, It is prepared according to any one of claims 1-9.

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