A preparation method of a thermoelectric material with CNTs grown in situ on the surface

Abstract

The present invention relates to a preparation method of a surface in-situ grown CNTs thermoelectric material, wherein the material is CNTs uniformly distributed on a thermoelectric material matrix. The present invention can solve the problem of CNTs agglomeration in the thermoelectric material matrix, can give full play to the excellent properties of CNTs, and improve the overall performance of the composite material. In addition, the method has a simple process, a short cycle, low production cost, can be mass-produced, and is helpful for the preparation of next-generation thermoelectric devices.

Description

Technical Field

[0001] The present invention belongs to the field of thermoelectric materials, and particularly relates to a preparation method for a thermoelectric material with in-situ growth of CNTs on the surface. Background Art

[0002] Thermoelectric materials are functional materials that can directly convert thermal energy and electrical energy into each other. The Seebeck effect, Peltier effect, and Thomson effect provide a theoretical basis for thermoelectric energy conversion applications. Thermoelectric devices prepared therefrom have the advantages of small size, no noise, accurate temperature control, no transmission components, and environmental friendliness, and have important applications in the fields of space exploration, waste heat recovery, military equipment, etc. At the same time, it can provide an effective way to solve environmental pollution and energy crisis.

[0003] The thermoelectric conversion efficiency is represented by the dimensionless thermoelectric figure of merit ZT, and the relationship is: ZT = σ z α / k, where α is the Seebeck coefficient, σ is the electrical conductivity, and k is the thermal conductivity. Improving the Seebeck coefficient and electrical conductivity and reducing the thermal conductivity are the keys to optimizing thermoelectric performance. Theoretical studies have shown that when the ZT value of the material reaches about 3, the conversion efficiency of the thermoelectric device prepared therefrom can be comparable to that of traditional power generation. Although various thermoelectric materials have developed greatly in recent years, and the ZT of some thermoelectric materials has exceeded 2, there is still no breakthrough of 3. Due to reasons such as device structure design and electrode preparation, the current development of thermoelectric devices is far lower than that of materials and is still at a relatively low level. In addition, some high-performance thermoelectric materials cannot be made into thermoelectric devices because the preparation of thermoelectric devices needs to meet the following requirements: (1) stable thermoelectric performance; (2) batch preparation; (3) mechanical properties meet certain requirements to meet processability.

[0004] Carbon nanotubes (CNTs) have excellent mechanical and physical properties and low density, which can not only improve the thermoelectric performance but also improve their mechanical properties, facilitating the preparation of thermoelectric devices. Ren et al. (Ren F, Wang H, Menchhofer P A, et al. Thermoelectric and mechanical properties of multi-walled carbon nanotube doped Bi 0.4 Sb 1.6 Te3 thermoelectric material[J]. Applied Physics Letters, 2013, 103(22): 221907) incorporated multi-walled carbon nanotubes into polycrystalline Bi 0.4 Sb 1.6In Te3, the flexural strength increases from 32 MPa to 90 MPa. Schmitz et al. (Schmitz A, Schmid C, de Boor J, et al. Dispersion of multi-walled carbon nanotubes in skutterudites and its effect on thermoelectric and mechanical properties [J]. Journal of Nanoscience and Nanotechnology, 2017, 17(3): 1547-1554.) prepared carbon nanotube / skutterudite-based composites through a process of grinding combined with ultrasonic treatment, indicating that adding an appropriate amount of carbon nanotubes can increase the Seebeck coefficient, carrier concentration, and phonon scattering, and reduce the thermal conductivity. In the above two literatures, it is difficult to uniformly disperse carbon nanotubes by using the grinding method, and the agglomerated carbon nanotubes will reduce the electrical conductivity and mechanical strength of the composite material. Patent (CN110218077A) prepared a calcium cobalt oxide dispersion and a carbon nanotube dispersion by a liquid-phase method, and then mixed, filtered, dried, and sintered the two to prepare a calcium cobalt oxide / carbon nanotube composite thermoelectric material to improve its performance. Since carbon nanotubes are extremely prone to entanglement and agglomeration, it is difficult to achieve uniform dispersion even when using a solution for dispersion, reducing the composite effect. Summary of the Invention

[0005] Aiming at the defects of the prior art, the technical problem to be solved by the present invention is to provide a preparation method for a thermoelectric material with CNTs grown in-situ on the surface. The method of the present invention can achieve uniform dispersion of CNTs in the matrix of the thermoelectric material, improve the thermoelectric performance and mechanical performance at the same time, has a simple process, low cost, can be mass-produced, and is helpful for the preparation of high-performance thermoelectric devices.

[0006] The present invention provides a preparation method for a thermoelectric material with CNTs grown in-situ on the surface, including:

[0007] (1) Freeze-grind the matrix and the catalyst, load them into a corundum boat, calcine under an inert gas, and then reduce in a reducing atmosphere;

[0008] (2) Load the powder obtained in step (1) into a corundum boat, place it in a tube furnace, react in a mixed gas of methane and an inert gas, and then load it into a mold and sinter under the protection of an inert gas to obtain a thermoelectric material.

[0009] The preferred mode of the above preparation method is as follows:

[0010] In the step (1), the matrix is one or more of telluride, CoSb3, and oxide; the catalyst is one or more of iron, nickel, cobalt, gold, ruthenium, platinum nanoparticles, etc.; wherein the mass ratio of the catalyst to the matrix is 0.1:99.9 to 10:90.

[0011] The telluride is one or more of germanium telluride, lead telluride, bismuth telluride, silver telluride, etc.; the oxide is one or more of zinc oxide, strontium titanate, calcium cobalt oxide, etc.

[0012] In the step (1), the cryogenic milling time is 1 to 60 min, and the temperature is -180°C to 196°C.

[0013] The calcination under an inert gas in the step (1) is specifically as follows: the inert gas is Ar, the gas flow rate is 50 sccm to 300 sccm; the calcination time is 2.5 to 8 hours, the calcination temperature is 200°C to 500°C, and the heating rate is 5 to 10°C / min.

[0014] That is, the calcination under an inert gas protection in the step (1) is specifically as follows: the inert gas is argon, the gas flow rate is 50 sccm to 300 sccm; the heating rate is 5 to 10°C / min to the calcination temperature of 200°C to 500°C, and the calcination time is 2.5 to 8 hours.

[0015] The reduction in a reducing atmosphere in the step (1) is specifically as follows: the reduction time is 1 to 2 hours, the reduction temperature is 250°C to 700°C, the heating rate is 5 to 10°C / min, the reducing gas is hydrogen, and the gas flow rate is 20 sccm to 200 sccm.

[0016] That is, the reduction in a reducing atmosphere in the step (1) is specifically as follows: the heating rate is 5 to 10°C / min to the reduction temperature of 250°C to 700°C, the reduction time is 1 to 2 hours, the reducing gas is hydrogen, and the gas flow rate is 20 sccm to 200 sccm.

[0017] In the step (2), the volume ratio of methane to the inert gas is 1:8 to 1:1; the reaction time is 0.5 to 4 hours, the reaction temperature is 500°C to 750°C, and the heating rate is 1 to 10°C / min.

[0018] That is, in the step (2), the volume ratio of methane to the inert gas is 1:8 to 1:1; the reaction is that the heating rate is 1 to 10°C / min to the reaction temperature of 500°C to 750°C, the reaction time is 0.5 to 4 hours, and the inert gas is argon.

[0019] In step (2), the sintering is spark plasma sintering or hot pressing sintering, and the process parameters are as follows: sintering pressure is 50 - 200 MPa, sintering temperature is 500 - 1000 °C, heat preservation time is 5 - 120 min, and heating rate is 2 °C / min - 100 °C / min.

[0020] That is, in step (2), the sintering is spark plasma sintering or hot pressing sintering, and the process parameters are as follows: sintering pressure is 50 - 200 MPa, heating rate is 2 °C / min - 100 °C / min to the sintering temperature of 500 - 1000 °C, and heat preservation time is 5 - 120 min; the sintering is carried out in a mold, where the mold is a graphite mold or a stainless steel mold.

[0021] In step (2), the sintering is carried out under an inert gas, where the inert gas is argon.

[0022] A surface in-situ growth CNTs thermoelectric material prepared by the method of the present invention.

[0023] The present invention provides an application of the surface in-situ growth CNTs thermoelectric material in the fields of space exploration, waste heat recovery or military equipment.

[0024] Beneficial effects

[0025] (1) The material prepared by the present invention has excellent thermoelectric performance;

[0026] (2) The thermoelectric material prepared by the present invention has excellent mechanical properties;

[0027] (3) The preparation process of the present invention is simple, the process parameters are easy to control, and industrial production can be realized. Description of the Drawings

[0028] Figure 1 It is a scanning electron microscope picture of the final obtained thermoelectric material powder in Example 1;

[0029] Figure 2 It is a transmission electron microscope picture of the final powder obtained in Example 1;

[0030] Figure 3 It is a hardness diagram of the samples with different contents of grown carbon nanotubes obtained in Examples 1, 2, and 3;

[0031] Figure 4 It is a figure of the thermoelectric figure of merit (ZT) of the samples with different contents of grown carbon nanotubes obtained in Examples 1, 2, and 3;

[0032] Figure 5 It is a Raman spectrum diagram of the powder obtained in Example 4;

[0033] Figure 6ZT diagram of the obtained skutterudite composite carbon nanotube bulk sample for Example 4. Detailed implementation mode

[0034] 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. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0035] Example 1

[0036] (1) Weigh 0.99 g of ZnO and 0.01 g of nano nickel particles, that is, the catalyst: matrix mass ratio = 1:99, and freeze-grind for 30 minutes at a temperature of -196 °C;

[0037] (2) Load the obtained powder into a corundum crucible and place it in a tubular furnace, and calcine it in an argon atmosphere for 3 hours, where the calcination temperature is 400 °C, the heating rate is 10 °C / minute, and the gas flow rate of argon is 150 sccm;

[0038] (3) Reduce the powder obtained in step (2) in a hydrogen atmosphere for 1 hour, where the reduction temperature is 550 °C, the heating rate is 5 °C / minute, and the gas flow rate of hydrogen is 150 sccm;

[0039] (4) In-situ grow carbon nanotubes on the powder obtained in step (3) in a mixed atmosphere of methane and argon; where the flow rates of methane and argon are 20 sccm and 120 sccm respectively; the growth temperature is 650 °C, the heating rate is 5 °C / minute, and the growth time is 30 min;

[0040] (5) Load the powder obtained in step (4) into a graphite mold, and the process parameters for spark plasma sintering under argon protection are: sintering pressure 80 MPa, sintering temperature 900 °C, holding time 10 min, heating rate 100 °C / min, and test the thermoelectric properties of the obtained bulk, and the results are as Figure 3 shown by the curve of 1 wt% CNTs;

[0041] (6) Polish both sides of the bulk obtained in step (5), and use a Vickers hardness tester to test its microhardness. The parameters for microhardness testing are: load 0.5 Kgf, holding time 10 s, and the hardness value of the obtained sample is as Figure 3 shown by the corresponding value of 1.0 wt% CNTs in

[0042] Example 2

[0043] (1) Weigh 0.98 g of ZnO and 0.02 g of nano-nickel particles, i.e., the catalyst:matrix mass ratio = 1:98, and perform cryogenic milling for 30 minutes at a temperature of -196 °C;

[0044] (2) Load the obtained powder into a corundum crucible and place it in a tube furnace, and calcine it in an argon atmosphere for 3 hours, where the calcination temperature is 400 °C, the heating rate is 10 °C / minute, and the gas flow rate of argon is 150 sccm;

[0045] (3) Reduce the powder obtained in step (2) in a hydrogen atmosphere for 1 hour, where the reduction temperature is 550 °C, the heating rate is 5 °C / minute, and the gas flow rate of hydrogen is 150 sccm;

[0046] (4) In-situ grow carbon nanotubes on the powder obtained in step (3) in a mixed atmosphere of methane and argon; where the flow rates of methane and argon are 20 sccm and 120 sccm respectively; the growth temperature is 650 °C, the heating rate is 5 °C / minute, and the growth time is 30 min;

[0047] (5) Load the powder obtained in step (4) into a graphite mold, and perform spark plasma sintering under argon protection. The sintering process parameters are: sintering pressure 80 MPa, sintering temperature 900 °C, holding time 10 min, heating rate 100 °C / min, and test the thermoelectric properties of the obtained bulk, and the results are as Figure 3 shown in Curve 2 wt% CNTs;

[0048] (6) Polish both sides of the bulk obtained in step (5), and use a Vickers hardness tester to test its microhardness. The parameters for microhardness measurement are: load 0.5 Kgf, holding time 10 s, and the obtained hardness value is as Figure 3 shown in the corresponding value of 2.0 wt% CNTs.

[0049] Example 3

[0050] (1) Weigh 0.98 g of ZnO and 0.02 g of nano-nickel particles, i.e., the catalyst:matrix mass ratio = 2:98, and perform cryogenic milling for 30 minutes at a temperature of -196 °C;

[0051] (2) Load the obtained powder into a corundum crucible and place it in a tube furnace, and calcine it in an argon atmosphere for 3 hours, where the calcination temperature is 400 °C, the heating rate is 10 °C / minute, and the gas flow rate of argon is 150 sccm;

[0052] (3) Reduce the powder obtained in step (2) in a hydrogen atmosphere for 1 hour, where the reduction temperature is 550 °C, the heating rate is 5 °C / minute, and the gas flow rate of hydrogen is 150 sccm;

[0053] (4) The powder obtained in step (3) is used to in-situ grow carbon nanotubes in a mixed atmosphere of methane and argon; wherein the flow rates of methane and argon are 0 sccm and 140 sccm respectively; the growth temperature is 650 °C, the heating rate is 5 °C / minute, and the growth time is 30 min;

[0054] (5) The powder obtained in step (4) is loaded into a graphite mold and sintered by spark plasma sintering under argon protection. The sintering process parameters are: sintering pressure 80 MPa, sintering temperature 900 °C, holding time 10 min, heating rate 100 °C / min. The thermoelectric properties of the obtained bulk are tested, and the results are as Figure 3 shown by the curve of 0 wt% CNTs.

[0055] (6) The bulk obtained in step (5) is polished on both sides, and its microhardness is tested using a Vickers hardness tester. The parameters for microhardness measurement are: load 0.5 Kgf, holding time 10 s. The hardness value of the obtained sample is as Figure 3 shown by the corresponding value of 0 wt% CNTs in it.

[0056] As Figure 1 shown is the scanning electron microscope image of the powder obtained in step (4) of Example 1. It can be seen from the figure that carbon nanotubes are successfully synthesized, and the carbon nanotubes are uniformly distributed in the zinc oxide matrix.

[0057] As Figure 2 shown is the transmission electron microscope image of the powder obtained in step (4) of Example 1. It can be seen from the figure that the prepared carbon nanotubes are multi-walled carbon nanotubes and grow in a tip-growth mode.

[0058] As Figure 3 shown is the microhardness map of the bulk obtained in step (6) of Examples 1, 2, and 3. It can be seen from the figure that the in-situ grown carbon nanotube zinc oxide composite material has excellent mechanical properties. The hardness value of the sample with 2 wt% CNTs grown is nearly twice that of the sample without CNTs grown.

[0059] As Figure 4 shown is the thermoelectric figure of merit (ZT) of the bulk obtained in step (5) of Examples 1, 2, and 3. It can be seen from the figure that after introducing carbon nanotubes by in-situ growth, the ZT value of zinc oxide is significantly improved.

[0060] Example 4

[0061] (1) Weigh 1.5 g of Yb 0.35 Co4Sb 12 powder and 0.075 g of nano-nickel particles, that is, the mass ratio of the matrix catalyst is 20:1, and freeze-grind for 20 minutes;

[0062] (2) Load the obtained powder into a corundum crucible and place it in a tubular furnace. Calcinate it for 4.5 hours in an argon atmosphere, where the calcination temperature is 400 °C, the heating rate is 5 °C / minute, and the argon flow rate is 200 sccm;

[0063] (3) Reduce the powder obtained in step (2) for 2 hours in a hydrogen atmosphere, where the reduction temperature is 600 °C, the heating rate is 5 °C / minute, and the hydrogen flow rate is 120 sccm;

[0064] (4) In-situ grow carbon nanotubes on the powder obtained in step (3) in a mixed atmosphere of methane and argon; where the flow rates of methane and argon are 60 sccm and 60 sccm respectively; the growth temperature is 670 °C, the heating rate is 3 °C / minute, and the growth time is 60 min;

[0065] (5) Load the powder obtained in step (4) into a graphite mold and perform spark plasma sintering under argon protection. The sintering process parameters are: sintering pressure 50 MPa, sintering temperature 650 °C, holding time 5 min, heating rate 80 °C / min

[0066] As Figure 5 shown is the Raman spectrum of the powder obtained in step (4) of Example 4. It can be seen from the figure that obvious D peak and G peak are observed, indicating that carbon nanotubes have been successfully grown in the powder.

[0067] As Figure 6 shown is the thermoelectric figure of merit (ZT) of the bulk obtained in step (5) of Example 4. It can be seen from the figure that the obtained composite sample has excellent thermoelectric performance.

Claims

1. A preparation method of a thermoelectric material with CNTs grown in-situ on the surface, comprising: (1) Freeze-grinding a substrate and a catalyst, calcining under an inert gas, and then reducing in a reducing atmosphere; Wherein the substrate is one or more of tellurides, CoSb3, and oxides; wherein the mass ratio of the catalyst to the substrate = 0.1:99.9 to 10:90; (2) Reacting the powder obtained in step (1) in a mixed gas of methane and an inert gas, and sintering under an inert gas to obtain a thermoelectric material.

2. The preparation method according to claim 1, wherein In step (1), the catalyst is one or more of iron, nickel, cobalt, gold, ruthenium, and platinum nanoparticles.

3. The preparation method according to claim 2, wherein The telluride is one or more of germanium telluride, lead telluride, bismuth telluride, and silver telluride; the oxide is one or more of zinc oxide, strontium titanate, and calcium cobalt oxide.

4. The preparation method according to claim 1, characterized in that, In step (1), the freeze-grinding time is 1 to 60 minutes, and the temperature is -180°C to 196°C.

5. The preparation method according to claim 1, characterized in that, The calcining under an inert gas in step (1) specifically is: the inert gas is Ar, the gas flow rate is 50 sccm to 300 sccm; the calcining time is 2.5 to 8 hours, the calcining temperature is 200°C to 500°C, and the heating rate is 5 to 10°C / minute.

6. According to the preparation method described in claim 1, characterized in that, The reduction in a reducing atmosphere in step (1) specifically is: the reduction time is 1 to 2 hours, the reduction temperature is 250°C to 700°C, the heating rate is 5 to 10°C / minute, the reducing gas is hydrogen, and the gas flow rate is 20 sccm to 200 sccm.

7. According to the preparation method described in claim 1, characterized in that, In step (2), the volume ratio of methane to the inert gas is 1:8 to 1:1; the reaction time is 0.5 to 4 hours, the reaction temperature is 500°C to 750°C, and the heating rate is 1 to 10°C / minute.

8. According to the preparation method described in claim 1, characterized in that, The sintering in step (2) is spark plasma sintering or hot pressing sintering, and its process parameters are: the sintering pressure is 50 to 200 MPa, the sintering temperature is 500 to 1000°C, the holding time is 5 to 120 minutes, and the heating rate is 2°C / min to 100°C / minute.

9. A thermoelectric material with CNTs grown in-situ on the surface prepared by the method according to claim 1.

10. An application of the thermoelectric material with CNTs grown in-situ on the surface according to claim 9 in the fields of space exploration, waste heat recovery, or military equipment.

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