A nano / micro honeycomb sandwich structure Ca3Co4O9-based cermet material and its preparation method

Abstract

This invention discloses a nano / micro honeycomb sandwich structure Ca3Co4O9-based cermet material and its preparation method, belonging to the technical field of high-temperature ceramic-based thermoelectric conversion materials. The method successfully prepares Ca3Co4O9 cermet materials by impregnating a heated and molten alloy into a surface-modified porous Ca3Co4O9 ceramic matrix using atmospheric pressure infiltration or double-sided vacuum melt infiltration techniques. After surface modification of the ceramic, the Ca3Co4O9 ceramic matrix is ​​vertically placed on the alloy under atmospheric pressure or vacuum conditions. When the alloy is heated and melted, the liquid alloy phase spontaneously fills the internal pores of the ceramic or penetrates into the ceramic interior due to capillary forces. After solidification, the alloy forms a honeycomb sandwich structure combining the two, which effectively improves the material's electrical conductivity and Seebeck coefficient, thereby enhancing the material's overall performance. ZT value.

Description

Technical Field

[0001] This invention belongs to the technical field of high-temperature ceramic-based thermoelectric conversion materials, specifically relating to a nano / micro honeycomb sandwich structure Ca3Co4O9-based metal ceramic material and its preparation method. Background Technology

[0002] For hypersonic vehicles, heat management during acceleration and atmospheric breakthrough has always been a key development issue. Currently, heat conduction and dissipation are the main forms of aerodynamic heat dissipation, transferring heat from high-temperature regions to low-temperature regions and ultimately dissipating it through radiation, thereby ensuring the safety of the vehicle's internal structure, equipment, and fuel. This technology is called heat dissipation technology, and based on the diversity of structural functions, it can be divided into heat-resistant structures and multi-functional structures. Multi-functional structures refer to structures that can achieve multiple functions such as load-bearing, heat insulation, and heat protection. Common multi-functional structures include integrated load-bearing / heat-resistant structures and composite structures that meet other functions.

[0003] Oxide thermoelectric materials exhibit excellent stability at high temperatures, are simple to prepare, low in cost, non-toxic, and cause minimal environmental pollution, thus showing promising development prospects in the field of hypersonic vehicles. Among them, layered cobalt-based oxide Ca3Co4O9 is a highly anticipated thermoelectric material, possessing a large thermoelectric potential and low resistivity, along with advantages such as oxidation resistance, high-temperature resistance, low cost, and long service life. Ca3Co4O9 ceramics exhibit even better thermal stability at high temperatures, making them suitable for use in harsh environments. Despite the excellent performance of Ca3Co4O9 in many aspects, its current thermoelectric properties are still insufficient to meet the stringent requirements of hypersonic vehicles for heat dissipation technology; at present, the thermoelectric performance of this material is inadequate to meet the requirements. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a nano / micro honeycomb sandwich structure Ca3Co4O9-based metal ceramic material and its preparation method, so as to solve the problem that the performance of Ca3Co4O9 ceramics in the prior art does not meet the requirements of practical applications.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A method for preparing a nano / micro honeycomb sandwich structure Ca3Co4O9-based cermet material includes the following steps:

[0007] Step 1: Modify porous Ca3Co4O9 ceramic with a modifier solution to obtain modified porous Ca3Co4O9 ceramic, wherein the channels in the Ca3Co4O9 ceramic matrix are radial pores;

[0008] Step 2: Polish and grind the modified Ca3Co4O9 ceramic matrix to obtain polished porous Ca3Co4O9 ceramic.

[0009] Step 3: The reinforcing metal is infiltrated into the polished Ca3Co4O9 ceramic matrix by atmospheric pressure melting infiltration or double-sided vacuum melting infiltration to obtain a nano / micro honeycomb sandwich structure Ca3Co4O9-based metal ceramic material. The nano / micro honeycomb sandwich structure Ca3Co4O9-based metal ceramic material includes a matrix material and a reinforcing phase. The matrix material is Ca3Co4O9 ceramic, and the reinforcing phase fills the pores of the Ca3Co4O9 ceramic or adheres to the sidewalls of the pores of the Ca3Co4O9 ceramic.

[0010] The atmospheric pressure melting and infiltration method involves placing the polished Ca3Co4O9 ceramic and the reinforcing metal together in a heating furnace, with the lower end of the Ca3Co4O9 ceramic in contact with the upper end of the reinforcing metal, and the pores of the Ca3Co4O9 ceramic being radially perpendicular to the reinforcing metal. The heating furnace is then purged with a protective gas and heated and kept at a constant temperature to obtain a nano / micro honeycomb sandwich structure Ca3Co4O9-based metal ceramic material.

[0011] The process of the double-sided vacuum melting method is as follows: the polished porous Ca3Co4O9 ceramic and the reinforcing metal are placed together in a vacuum heating furnace, with the lower end of the Ca3Co4O9 ceramic matrix in contact with the upper end of the reinforcing metal. The pores of the Ca3Co4O9 ceramic are radially perpendicular to the reinforcing metal. After the vacuum heating furnace is purged, it is heated and kept at a certain temperature. Then the Ca3Co4O9 ceramic is flipped over, and the purging, heating and holding are repeated to obtain a nano / micro honeycomb sandwich structure Ca3Co4O9-based metal ceramic material.

[0012] A further improvement of the present invention is that:

[0013] Preferably, in step 1, the modifier is any one of TEOA, SDBS, DA, KH-550 or NaOH.

[0014] Preferably, in step 1, the process of modifying the porous Ca3Co4O9 ceramic with the modifier solution is as follows: the Ca3Co4O9 ceramic matrix is ​​immersed in the modifier solution, the container is sealed, and the modification is carried out for 24 hours.

[0015] Preferably, in step 2, the polishing and grinding is performed by sequentially grinding the porous Ca3Co4O9 ceramic with sandpaper of 300 mesh, 500 mesh, 800 mesh, 1000 mesh and 2000 mesh.

[0016] Preferably, in step 3, the reinforcing metal is an Ag-Cu alloy, Ag, or Al-Cu alloy.

[0017] Preferably, in step 3, the gas washing process of the atmospheric pressure melting infiltration method is as follows: argon gas is introduced into the furnace cavity at a flow rate of 30-80 mL / min until all the air in the furnace is exhausted.

[0018] Preferably, in step 3, the heating temperature of the atmospheric pressure melting infiltration method is 1123-1273 K, and the holding time is 0.5-2 h.

[0019] Preferably, in step 3, the gas washing process in the double-sided vacuum melt impregnation method is as follows: the air in the vacuum heating furnace is extracted, and the pressure in the vacuum heating furnace is reduced to below 30 Pa; then, argon gas is introduced into the vacuum heating furnace until the pressure in the vacuum heating furnace rises to 0.5 MPa; finally, after maintaining the pressure for 10-60 min, the gas in the vacuum heating furnace is extracted again, and the above steps are repeated 2-3 times.

[0020] Preferably, the heating process of the double-sided vacuum melt infiltration method is as follows: argon gas is introduced into the vacuum heating furnace to atmospheric pressure, the furnace is heated to 1123-1273 K, the argon gas is extracted to a pressure of less than 30 Pa in the vacuum heating furnace, and the temperature is maintained for 0.5-2 h.

[0021] A nano / micro honeycomb sandwich structure Ca3Co4O9-based metal ceramic material prepared by any one of the above preparation methods includes a matrix material and a reinforcing phase. The matrix material is a porous Ca3Co4O9 ceramic, and the channels in the Ca3Co4O9 ceramic matrix are radial pores. The reinforcing phase is a metal, and the reinforcing phase fills the channels of the Ca3Co4O9 ceramic or is attached to the sidewalls of the channels of the Ca3Co4O9 ceramic.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention relates to the technical field of high-temperature ceramic-based thermoelectric conversion materials, and proposes a novel method for preparing honeycomb sandwich structured Ca3Co4O9 cermet materials. The method successfully prepares Ca3Co4O9 cermet materials by impregnating a heated molten alloy into a porous Ca3Co4O9 ceramic matrix using atmospheric pressure impregnation or double-sided vacuum melt infiltration techniques. Under atmospheric pressure impregnation or vacuum conditions, the Ca3Co4O9 ceramic matrix is ​​placed vertically on the alloy. After the alloy is heated and melted, the liquid alloy phase spontaneously fills the internal pores of the ceramic or penetrates into the ceramic interior due to capillary forces. After solidification, the alloy forms a honeycomb sandwich structure combining the two. Generally, while alloys bring high electrical conductivity, they also increase the thermal conductivity of cermets. However, this structure introduces a large number of metal / non-metal interfaces, mainly connected by covalent bonds or hydrogen bonds and van der Waals forces. The presence of these interfaces reduces phonon transport channels, effectively scattering phonons and thus reducing thermal conductivity. Furthermore, the presence of these interfaces also inhibits carrier transport, effectively increasing the Seebeck coefficient of the material without reducing electrical conductivity. This preparation method is simple and uses low-cost raw materials. The alloy is impregnated into the internal pores of a porous Ca3Co4O9 ceramic preform to prepare a Ca3Co4O9 cermet material with a honeycomb sandwich structure. This optimizes the mechanical and thermoelectric properties of the ceramic material, thereby broadening the application fields of Ca3Co4O9-based thermoelectric materials. This method can effectively prepare Ca3Co4O9-based cermet thermoelectric materials with good stability and excellent mechanical properties, enabling them to operate at high temperatures for extended periods. They are suitable for waste heat recovery in high-temperature fields such as thermal management of hypersonic aircraft, and have broad application prospects.

[0024] Furthermore, when the insulation temperature is in the range of 1073-1273 K, the porosity of the prepared ceramic matrix composite material decreases by more than 60%, leaving only about 3%, exhibiting an ideal impregnation effect. This material possesses excellent thermoelectric properties, with a maximum electrical conductivity of 38.48 S / m, a power factor of 0.30 mW / (m·K²), and a final thermoelectric figure of merit of 0.24.

[0025] This invention also discloses a nano / micro honeycomb sandwich structure Ca3Co4O9-based metal ceramic material prepared by the above-described method. This ceramic material, based on thermoelectric materials, develops a multifunctional structure integrating load-bearing, heat protection, and power supply. By adding a layer of thermoelectric ceramic matrix composite material within the high-temperature resistant layer on the surface of the aircraft, it is possible to generate electrical energy using the significant temperature difference between the inside and outside, thus achieving waste heat recovery and utilization. Attached Figure Description

[0026] Figure 1 SEM images of Ag-Cu alloy / Ca3Co4O9 cermet material parallel to the infiltration direction;

[0027] Figure 2 SEM images of Ag-Cu alloy / Ca3Co4O9 cermet material perpendicular to the infiltration direction;

[0028] Figure 3 SEM-EDS line scan data of the two-phase boundary of Ag-Cu alloy / Ca3Co4O9 cermet material;

[0029] Figure 4 XRD pattern of Ag-Cu alloy / Ca3Co4O9 cermet material;

[0030] Figure 5 The interfacial contact resistance of Ag-Cu alloy / Ca3Co4O9 cermet material;

[0031] Figure 6 Infrared thermal image of Ag-Cu alloy / Ca3Co4O9 cermet material heated at 1073K;

[0032] Figure 7 The total thermal conductivity is the Ag-Cu alloy / Ca3Co4O9 cermet material of Examples 1 and 2;

[0033] Figure 8 The Seebeck coefficients of the Ag-Cu alloy / Ca3Co4O9 cermet materials in Examples 1 and 2 are shown.

[0034] Figure 9 The electrical conductivity of the Ag-Cu alloy / Ca3Co4O9 cermet materials in Examples 1 and 2;

[0035] Figure 10 The power factor of the Ag-Cu alloy / Ca3Co4O9 cermet materials in Examples 1 and 2;

[0036] Figure 11 The ZT figure of merit is given for the Ag-Cu alloy / Ca3Co4O9 cermet materials of Examples 1 and 2. Detailed Implementation

[0037] The present invention will now be described in further detail with reference to the accompanying drawings:

[0038] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0039] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0040] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0041] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0042] This experiment used porous Ca3Co4O9 ceramic as the matrix. For the preparation method and specific materials of this porous ceramic, please refer to the patent document with publication number CN 115710137 A. The analysis was conducted on analytically pure triethanolamine (TEOA, C6H). 15 NO3, Sinopharm Group), sodium dodecylbenzenesulfonate (SDBS, C 18 H 29 NaO3S, Sinopharm Group), dopamine (DA, C8H) 11 NO2, Sinopharm Group), silane coupling agent (KH-550, C9H) 23 NO3Si (Sinopharm Group) and sodium hydroxide (NaOH, Sinopharm Group) are used as modifiers, and Ag-Cu alloys (AgCu3, AgCu7.5, AgCu10, AgCu28 and AgCu55, etc.) and Ag and Al-Cu alloys (ZAICu4, ZAICu10 and ZAICu33, etc.) are used as reinforcing phases. The reinforcing metals have excellent electrical conductivity.

[0043] This invention discloses a method for preparing Ca3Co4O9-based cermet material with a nano / micro honeycomb sandwich structure, the method comprising the following steps:

[0044] Step 1: Pretreatment of ceramic matrix and reinforcing phase.

[0045] Step 1.1 Preparation of the modifier solution. The modifier is TEOA, SDBS, DA, KH-550, or NaOH, and the concentration of the modifier solution is 0.05-1 mol / L. Taking the preparation of 100 ml of 1 mol / L NaOH as an example, calculate the required amount of 0.4 g of NaOH powder, weigh it, pour it into a beaker, add distilled water, stir with a glass rod to dissolve, and fill the liquid to the level of 100 ml. After preparing the required solution, label it for later use. In this process, the wettability of the Ca3Co4O9 ceramic with the molten metal is improved by introducing the groups carried by the modifier. Specifically, DA, TEOA, and NaOH are used to provide -OH groups; SDBS is a sulfonic acid group (-SO3H); KH-550 provides an amino group to increase the polarity of the material surface, thereby increasing the wettability with the metal solution.

[0046] Step 1.2: Cut the porous Ca3Co4O9 ceramic into small cubes of 2×2×3 cm and place them in a beaker. Pour the solution prepared in step 1.1 into the beaker using a glass cup until the Ca3Co4O9 ceramic is completely submerged. Cover with plastic wrap and immerse for 24 hours for modification. Remove the modified Ca3Co4O9 ceramic and dry it in an incubator for later use.

[0047] Step 1.3: The surface roughness of the ceramic and the oxide layer of the alloy have a significant impact on the infiltration effect. Therefore, appropriate pretreatment is required for the modified Ca3Co4O9 ceramic matrix and the alloy before the experiment. The Ca3Co4O9 ceramic matrix is ​​sequentially polished with sandpaper of 300, 500, 800, 1000, and 2000 mesh until the surface is smooth. The polished sample is then polished for 10-20 minutes to ensure no obvious scratches on the surface. After polishing, it is ultrasonically washed 2-3 times in a beaker containing alcohol and then dried for later use. The alloy is sanded before the experiment and then polished to remove the oxide layer on its surface. The polishing process ensures that the wetting effect is consistent throughout the prepared cermet, resulting in a more uniform metal distribution.

[0048] Step 2, atmospheric pressure infiltration process of Ag-Cu alloy / Ca3Co4O9 cermet.

[0049] Step 2.1: Place the polished AgCu28 alloy raw material as the reinforcing metal into the crucible, and fix the modified Ca3Co4O9 ceramic matrix from Step 1 above the reinforcing metal. The pore diameter of the Ca3Co4O9 ceramic matrix is ​​perpendicular to the direction of the reinforcing metal, and the lower end of the Ca3Co4O9 ceramic matrix is ​​in contact with the alloy. Then, send it into the quartz tube and close the tube furnace.

[0050] Step 2.2, purge the tubular furnace: First, connect the pipeline; then, introduce argon gas into the furnace chamber at a flow rate of 30-80 ml / min for 5-10 minutes until the air in the furnace is basically exhausted.

[0051] Step 2.3: After gas washing, the tube furnace is heated to 1123-1223 K at a heating rate of 2-8 K / min; then held at this temperature for 0.5-2 h; finally, the tube furnace is allowed to cool naturally to room temperature to obtain Ca3Co4O9 cermet. The prepared sample is polished, ultrasonicated, and then dried. Samples with dimensions of 3 mm × 4 mm × 15 mm and Φ12.7 mm × 3 mm are obtained by wire cutting for testing pore structure and thermoelectric properties.

[0052] Step 3: Research on double-sided vacuum melt infiltration process technology for Ag-Cu alloy / Ca3Co4O9 cermet.

[0053] Step 3.1: Place the polished AgCu28 alloy raw material as the reinforcing metal into the crucible, and fix the modified Ca3Co4O9 ceramic matrix from Step 1 above the reinforcing metal. The pore size of the Ca3Co4O9 ceramic matrix is ​​perpendicular to the direction of the reinforcing metal, and the lower end is in contact with the alloy. Then, seal the furnace lid of the vacuum heating furnace.

[0054] Step 3.2, purge the vacuum furnace: First, extract the air from the vacuum furnace and reduce the pressure inside the vacuum furnace to below 30 Pa; then, introduce argon gas into the vacuum furnace until the pressure inside the vacuum furnace reaches about 0.5 MPa; finally, after maintaining the pressure for 10-60 minutes, extract the gas from the vacuum furnace again, and repeat the above steps 2-3 times.

[0055] Step 3.3: After gas purging, argon gas is introduced into the vacuum furnace to atmospheric pressure, and the furnace is heated to 1123-1223 K at a heating rate of 2-8 K / min. Then, the argon gas is extracted from the furnace until the pressure inside is less than 30 Pa, and the furnace is held at this temperature for 0.5-2 h. Finally, the furnace is allowed to cool naturally to room temperature to obtain Ca3Co4O9 cermet. This process removes air from the furnace and prevents metal oxidation.

[0056] Step 3.4: Fix the opposite side of the impregnated surface of the cermet from Step 3.3 onto the alloy. Then seal the furnace lid of the vacuum heating furnace; repeat steps 3.2 and 3.3 to obtain Ca3Co4O9 cermet. Grind and polish the prepared sample, sonicate it, and then dry it. Wire cutting was used to obtain samples with dimensions of 3 mm × 4 mm × 15 mm and Φ12.7 mm × 3 mm for testing pore structure and thermoelectric properties.

[0057] It should be noted that steps 2 and 3 above are parallel steps. In the above preparation process, after the reinforcing metal melts, under the action of capillary force, the liquid phase spontaneously fills the internal pores of the ceramic or penetrates into the ceramic. After the alloy solidifies, it forms a composite material combining the two. The reinforcing metal phase in the ceramic forms a honeycomb sandwich structure, and the reinforcing metal phase also penetrates into the ceramic.

[0058] The second aspect of the present invention discloses a nano / micro honeycomb sandwich structure Ca3Co4O9-based metal ceramic material prepared by the above preparation method, comprising a matrix material and a reinforcing phase; the matrix material is a porous Ca3Co4O9 ceramic with a pore size of about 2.5 μm, and the reinforcing phase is a reinforcing metal, wherein the reinforcing phase fills the pores of the Ca3Co4O9 ceramic or is attached to the sidewalls of the pores of the Ca3Co4O9 ceramic.

[0059] Step 4: Compositional study of Ca3Co4O9 cermet preparation.

[0060] In steps 2.1 and 3.1, the alloy type can be replaced with other specifications of Ag-Cu alloy, Al-Cu alloy or other suitable metal materials, and the melting temperature in steps 2.3 and 3.3 can be replaced with the temperature suitable for the alloy phase.

[0061] The main process of double-sided vacuum melt infiltration technology includes several key steps: First, the reinforcing powder is made into a porous preform using methods such as freeze drying; then, metal is placed at the bottom of the porous preform and heated under vacuum conditions, allowing the metal to melt and spontaneously infiltrate into the gaps of the preform through the capillary force generated by the porous structure itself. After cooling and solidification, the same melt infiltration process is repeated on the opposite side of the infiltrated surface. During the infiltration process, factors such as the surface roughness of the material, the wettability between materials, the holding temperature, and the holding time all significantly affect the infiltration effect. This technology can prepare composite materials with large planar dimensions and complex surface shapes at low cost, making it suitable for mass production. This invention successfully combines Ag-Cu alloys with porous Ca3Co4O9 ceramics to prepare ceramic composite materials with a honeycomb sandwich structure, proposing a method to effectively improve the performance of Ca3Co4O9-based cermet materials, further broadening its application fields.

[0062] The following description, in conjunction with specific embodiments, provides further details.

[0063] Example 1: Preparation process of atmospheric pressure impregnation

[0064] Step 1: Pretreatment of ceramic matrix and reinforcing phase.

[0065] Step 1.1 Prepare a modified solution with a concentration of 1 mol / L using the modifier TEOA.

[0066] Step 1.2: Cut the porous Ca3Co4O9 ceramic wire into small cubes of 2×2×3 cm and place them in a beaker. Use a glass rod to guide the solution prepared in step 1.1 into the beaker until the Ca3Co4O9 ceramic substrate is completely submerged. Cover with plastic wrap and allow to soak for 24 hours for modification. Remove the modified Ca3Co4O9 ceramic substrate and dry it in an incubator for later use.

[0067] Step 1.3: The surface roughness of the ceramic and the oxide layer of the alloy have a significant impact on the infiltration effect. Therefore, appropriate pretreatment is required for the modified Ca3Co4O9 ceramic matrix and alloy before the experiment. The porous Ca3Co4O9 ceramic is sequentially polished with sandpaper of 300, 500, 800, 1000, and 2000 mesh until the surface is smooth. The polished sample is then polished for 15 minutes to ensure no obvious scratches on the surface. After polishing, it is ultrasonically washed three times in a beaker containing alcohol and then dried for later use. The alloy is polished with sandpaper before the experiment to remove the oxide layer on its surface before use.

[0068] Step 2: Study on atmospheric pressure infiltration process of Ag-Cu alloy / Ca3Co4O9 cermet

[0069] Step 2.1: Place the polished AgCu28 alloy raw material into the crucible, fix the modified Ca3Co4O9 ceramic matrix from Step 1 on top of the alloy, send it into the quartz tube, and close the tube furnace.

[0070] Step 2.2, purge the tubular furnace: First, connect the pipeline; then, introduce argon gas into the furnace chamber at a flow rate of 50 ml / min for 10 minutes until the air inside the furnace is basically exhausted.

[0071] Step 2.3: After gas washing, the tube furnace was heated to 1173 K at a heating rate of 5 K / min; then held at that temperature for 2 h; finally, the tube furnace was allowed to cool naturally to room temperature to obtain Ca3Co4O9 cermet. The prepared sample was polished, ultrasonicated, and then dried. Samples with dimensions of 3 mm × 4 mm × 15 mm and Φ12.7 mm × 3 mm were obtained by wire cutting for testing pore structure, thermoelectric properties, and mechanical properties.

[0072] Example 2, Preparation process of double-sided vacuum melt infiltration process

[0073] Step 1: Pretreatment of ceramic matrix and reinforcing phase.

[0074] Step 1.1 Prepare a modified solution with a concentration of 1 mol / L using the modifier TEOA.

[0075] Step 1.2: Cut the porous Ca3Co4O9 ceramic into small cubes of 2×2×3 cm and place them in a beaker. Use a glass rod to pour the solution prepared in step 1.1 into the beaker until the Ca3Co4O9 ceramic is completely submerged. Cover with plastic wrap and let it soak for 24 hours for modification. Remove the modified Ca3Co4O9 ceramic and dry it in an incubator for later use.

[0076] Step 1.3: The surface roughness of the ceramic and the oxide layer of the alloy have a significant impact on the infiltration effect. Therefore, appropriate pretreatment is required for the modified porous Ca3Co4O9 ceramic and alloy before the experiment. The porous Ca3Co4O9 ceramic was polished sequentially with sandpaper of 300, 500, 800, 1000, and 2000 mesh until the surface was smooth. The polished sample was then polished for 15 minutes to ensure no obvious scratches on the surface. After polishing, it was ultrasonically washed three times in a beaker containing alcohol and then dried for later use. The alloy was polished with sandpaper before the experiment to remove the oxide layer on its surface before use.

[0077] Step 2: Research on double-sided vacuum melt infiltration process technology for Ag-Cu alloy / Ca3Co4O9 cermet.

[0078] Step 2.1: Place the polished AgCu28 alloy raw material into the crucible, fix the modified porous Ca3Co4O9 ceramic from Step 1 on top of the alloy, and then seal the furnace lid of the vacuum heating furnace.

[0079] Step 2.2, purge the vacuum furnace: First, extract the air from the vacuum furnace and reduce the pressure inside the vacuum furnace to below 30 Pa; then, introduce argon gas into the vacuum furnace until the pressure inside the vacuum furnace reaches about 0.5 MPa; finally, after maintaining the pressure for 50 min, extract the gas from the vacuum furnace again, and repeat the above steps twice.

[0080] Step 2.3: After gas washing, argon gas is introduced into the vacuum heating furnace to atmospheric pressure, and the vacuum heating furnace is heated to 1173 K at a heating rate of 5 K / min. Then, the argon gas in the vacuum heating furnace is extracted until the pressure in the vacuum heating furnace is less than 30 Pa, and the temperature is maintained for 0.5 h. Finally, after the vacuum heating furnace is naturally cooled to room temperature, Ca3Co4O9 cermet is obtained.

[0081] Step 2.4: Fix the opposite side of the impregnated surface of the cermet from Step 2.3 onto the alloy. Then seal the furnace lid of the vacuum heating furnace; repeat steps 2.2 and 2.3 to obtain Ca3Co4O9 cermet. Grind and polish the prepared sample, sonicate it, and then dry it. Wire cutting was used to obtain samples with dimensions of 3 mm × 4 mm × 15 mm and Φ12.7 mm × 3 mm for testing pore structure, thermoelectric properties, and mechanical properties.

[0082] This embodiment successfully filled the internal channels of a porous Ca3Co4O9 ceramic matrix with Ag-Cu alloy using a double-sided vacuum melt infiltration technique (see...). Figure 1 and Figure 2 In the SEM-EDS line scan, Ag can be observed precipitating from the alloy and filling the channels, while Cu is uniformly distributed in the ceramic matrix. During this process, Cu reacts with calcium cobaltate, thus easily penetrating the ceramic matrix and precipitating from the alloy. Ag, however, does not react with Ca3Co4O9 and therefore directly fills the through-holes. This combination of metal and ceramic matrix forms a honeycomb sandwich structure (see...). Figure 3 This effectively improves the performance of composite materials.

[0083] (2) In the Ag-Cu alloy / Ca3Co4O9 ceramic composite material prepared by double-sided vacuum melt infiltration technology, in addition to the Ca3Co4O9 ceramic phase with monoclinic structure, diffraction peaks of Co3O4, CuO and Ag were also found (see Figure 4 The presence of CuO is related to the reaction of Ca3Co4O9 ceramics, producing CuO and Co3O4. Ag exists in elemental form. Figure 3 The line scan results suggest that during the infiltration process, Cu reacts to form CuO, which enters the ceramic matrix, while Ag precipitates and fills the pores. This structure allows the material to overcome the melting point limitation of Ag-Cu alloys, making it suitable for higher-temperature applications.

[0084] (3) At the boundary between the impregnated and unimpregnated areas at the impregnation front, the interfacial contact resistance was measured using the room temperature scanning voltage probe method. The results showed a significant jump in resistance at the impregnation front. The calculated interfacial resistivity was 10.8 KΩ•cm (see...). Figure 5 This result indicates that the infiltration process has a significant impact on the interfacial resistance characteristics, which may be related to the interfacial structure and charge transport mechanism between the metal and ceramic matrices.

[0085] (4) The thermal conductivity of Ca3Co4O9-based cermet materials prepared by atmospheric pressure infiltration and vacuum-double-sided melt infiltration techniques decreased with increasing test temperature, a phenomenon similar to that of porous Ca3Co4O9 ceramics. At 1073 K, the thermal conductivity of the vacuum-double-sided melt-infiltrated sample reached 1.545 W / (m·K), while that of the atmospheric pressure infiltration sample reached 1.21 W / (m·K). Furthermore, due to the better effect of vacuum-double-sided melt infiltration and more complete metal filling, coupled with the higher thermal conductivity of the alloy, the thermal conductivity of the prepared composite material increased. Further infrared thermal analysis of the vacuum-double-sided melt-infiltrated sample showed that, under a fixed heat source heating condition at 1073 K, the temperature difference between the upper and lower ends of the sample remained relatively large within 20 seconds, indicating that the material exhibits good thermal insulation performance in high-temperature environments. Furthermore, the sample exhibited an excellent Seebeck coefficient, reaching 281.36 μV / K at a test temperature of 1073 K, while the conductivity also increased to 38.48 S / cm. In contrast, the Seebeck coefficient of the atmospheric pressure impregnated sample was 213.47 μV / K, and the conductivity was 31.41 S / cm. The introduction of the alloy phase did not significantly improve the conductivity of the ceramic matrix, which is attributed to the presence of interfacial resistance. Calculations showed that their power factors reached 0.14 mW / (m·K²) and 0.30 mW / (m·K²), respectively. Ultimately, the vacuum-double-sided melt-impregnated sample exhibited higher... ZT The value reached 0.24, indicating that this material has good application potential in thermoelectric conversion (see...). Figures 6-11 ).

[0086] Example 3

[0087] Step 1: Pretreatment of ceramic matrix and reinforcing phase.

[0088] Step 1.1 Prepare a modified solution with a concentration of 1 mol / L using the modifier TEOA.

[0089] Step 1.2: Cut the porous Ca3Co4O9 ceramic wire into small cubes of 2×2×3 cm and place them in a beaker. Pour the solution prepared in step 1.1 into the beaker using a glass cup until the Ca3Co4O9 ceramic substrate is completely submerged. Cover with plastic wrap and allow to soak for 24 hours for modification. Remove the modified Ca3Co4O9 ceramic substrate and dry it in an incubator for later use.

[0090] Step 1.3: The surface roughness of the ceramic and the oxide layer of the alloy have a significant impact on the infiltration effect. Therefore, appropriate pretreatment is required for the modified Ca3Co4O9 ceramic matrix and alloy before the experiment. The porous Ca3Co4O9 ceramic is sequentially polished with sandpaper of 300, 500, 800, 1000, and 2000 mesh until the surface is smooth. The polished sample is then polished for 15 minutes to ensure no obvious scratches on the surface. After polishing, it is ultrasonically washed three times in a beaker containing alcohol and then dried for later use. The alloy is polished with sandpaper before the experiment to remove the oxide layer on its surface before use.

[0091] Step 2: Study on atmospheric pressure infiltration process of Ag-Cu alloy / Ca3Co4O9 cermet

[0092] Step 2.1: Place the polished AgCu28 alloy raw material into the crucible, fix the modified Ca3Co4O9 ceramic matrix from Step 1 on top of the alloy, send it into the quartz tube, and close the tube furnace.

[0093] Step 2.2, purge the tubular furnace: First, connect the pipeline; then, introduce argon gas into the furnace chamber at a flow rate of 50 ml / min for 5-10 minutes until the air inside the furnace is basically purged.

[0094] Step 2.3: After gas washing, the tube furnace was heated to 1173 K at a heating rate of 5 K / min; then held at this temperature for 2 h; finally, the tube furnace was allowed to cool naturally to room temperature to obtain Ca3Co4O9 cermet. The prepared sample was polished, ultrasonicated, and then dried. Samples with dimensions of 3 mm × 4 mm × 15 mm and Φ12.7 mm × 3 mm were obtained by wire cutting for testing the pore structure and thermoelectric properties.

[0095] Step 3: Research on double-sided vacuum melt infiltration process technology for Ag-Cu alloy / Ca3Co4O9 cermet.

[0096] Step 3.1: Place the polished AgCu28 alloy raw material into the crucible, fix the modified Ca3Co4O9 ceramic matrix from Step 1 on top of the alloy, and then seal the furnace lid of the vacuum heating furnace.

[0097] Step 3.2, purge the vacuum furnace: First, extract the air from the vacuum furnace and reduce the pressure inside the vacuum furnace to below 30 Pa; then, introduce argon gas into the vacuum furnace until the pressure inside the vacuum furnace reaches about 0.5 MPa; finally, after maintaining the pressure for 50 min, extract the gas from the vacuum furnace again, and repeat the above steps twice.

[0098] Step 3.3: After gas washing, argon gas is introduced into the vacuum heating furnace to atmospheric pressure, and the vacuum heating furnace is heated to 1173 K at a heating rate of 2-8 K / min. Then, the argon gas in the vacuum heating furnace is extracted until the pressure in the vacuum heating furnace is less than 30 Pa, and the temperature is maintained for 0.5 h. Finally, after the vacuum heating furnace is naturally cooled to room temperature, Ca3Co4O9 cermet is obtained.

[0099] Step 3.4: Fix the opposite side of the impregnated surface of the cermet from Step 3.3 onto the alloy. Then seal the furnace lid of the vacuum heating furnace; repeat steps 3.2 and 3.3 to obtain Ca3Co4O9 cermet. Grind and polish the prepared sample, sonicate it, and then dry it. Wire cutting was used to obtain samples with dimensions of 3 mm × 4 mm × 15 mm and Φ12.7 mm × 3 mm for testing pore structure and thermoelectric properties.

[0100] In other embodiments, the modifier can be replaced with SDBS, DA, KH-550 or NaOH, relative to Example 2.

[0101] In other embodiments, relative to Embodiment 1, the heating temperature during the atmospheric pressure melting and infiltration process can be 1150 K, 1200 K, 1250 K or 1273 K, and the corresponding holding time can be 2 h, 1.5 h, 1 h or 0.5 h.

[0102] In other embodiments, relative to Embodiment 2, the heating temperature of the vacuum melt infiltration process in the double-sided vacuum melt infiltration process can be 1150 K, 1200 K, 1250 K or 1273 K, and the corresponding holding time can be 2 h, 1.5 h, 1 h or 0.5 h.

[0103] In other embodiments, the reinforcing metal can be replaced with Ag or an Al-Cu alloy.

[0104] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a Ca3Co4O9-based cermet material with a nano / micro honeycomb sandwich structure, characterized in that, Includes the following steps: Step 1: Modify porous Ca3Co4O9 ceramic with a modifier solution to obtain a modified Ca3Co4O9 ceramic matrix, wherein the channels in the Ca3Co4O9 ceramic matrix are radial pores; Step 2: Polish and grind the modified Ca3Co4O9 ceramic matrix to obtain polished porous Ca3Co4O9 ceramic. Step 3: The reinforcing metal is infiltrated into the polished Ca3Co4O9 ceramic matrix by atmospheric pressure melting infiltration or double-sided vacuum melting infiltration to obtain a nano / micro honeycomb sandwich structure Ca3Co4O9-based metal ceramic material. The nano / micro honeycomb sandwich structure Ca3Co4O9-based metal ceramic material includes a matrix material and a reinforcing phase. The matrix material is porous Ca3Co4O9 ceramic, and the reinforcing phase is infiltrated into the pores of the Ca3Co4O9 ceramic or attached to the sidewalls of the pores of the Ca3Co4O9 ceramic. The atmospheric pressure melting infiltration method involves placing the polished porous Ca3Co4O9 ceramic and the reinforcing metal together in a heating furnace, with the lower end of the porous Ca3Co4O9 ceramic in contact with the upper end of the reinforcing metal. The pores of the Ca3Co4O9 ceramic are radially perpendicular to the reinforcing metal. The heating furnace is then purged with a protective gas and heated and kept at a constant temperature to obtain a nano / micro honeycomb sandwich structure Ca3Co4O9-based metal ceramic material. The process of the double-sided vacuum melting method is as follows: the polished Ca3Co4O9 ceramic matrix and the reinforcing metal are placed together in a vacuum heating furnace, with the lower end of the Ca3Co4O9 ceramic matrix in contact with the upper end of the reinforcing metal. The pores of the Ca3Co4O9 ceramic are radially perpendicular to the reinforcing metal. After the vacuum heating furnace is purged, it is heated and kept at a certain temperature. Then the Ca3Co4O9 ceramic is flipped over, and the purging, heating and holding are repeated to obtain a nano / micro honeycomb sandwich structure Ca3Co4O9-based metal ceramic material.

2. The method for preparing a nano / micro honeycomb sandwich structure Ca3Co4O9-based cermet material according to claim 1, characterized in that, In step 1, the modifier is any one of TEOA, SDBS, DA, KH-550 or NaOH.

3. The method for preparing a nano / micro honeycomb sandwich structure Ca3Co4O9-based cermet material according to claim 1, characterized in that, In step 1, the process of modifying the Ca3Co4O9 ceramic matrix with the modifier solution is as follows: the Ca3Co4O9 ceramic is immersed in the modifier solution, the container is sealed, and the modification is carried out for 24 hours.

4. The method for preparing a nano / micro honeycomb sandwich structure Ca3Co4O9-based cermet material according to claim 1, characterized in that, In step 2, the polishing and grinding are performed by sequentially grinding the Ca3Co4O9 ceramic with sandpaper of 300 grit, 500 grit, 800 grit, 1000 grit and 2000 grit.

5. The method for preparing a nano / micro honeycomb sandwich structure Ca3Co4O9-based cermet material according to claim 1, characterized in that, In step 3, the reinforcing metal is an Ag-Cu alloy, Ag, or Al-Cu alloy.

6. The method for preparing a nano / micro honeycomb sandwich structure Ca3Co4O9-based cermet material according to claim 1, characterized in that, In step 3, the gas washing process of the atmospheric pressure melting infiltration method is as follows: argon gas is introduced into the furnace cavity at a flow rate of 30-80 mL / min until all the air in the furnace is exhausted.

7. The method for preparing a nano / micro honeycomb sandwich structure Ca3Co4O9-based cermet material according to claim 1, characterized in that, In step 3, the heating temperature of the atmospheric pressure melting infiltration method is 1123-1273 K, and the holding time is 0.5-2 h.

8. The method for preparing a nano / micro honeycomb sandwich structure Ca3Co4O9-based cermet material according to claim 1, characterized in that, In step 3, the gas washing process in the double-sided vacuum melt impregnation method is as follows: the air in the vacuum heating furnace is extracted and the pressure in the vacuum heating furnace is reduced to below 30 Pa; then, argon gas is introduced into the vacuum heating furnace until the pressure in the vacuum heating furnace rises to 0.5 MPa; finally, after maintaining the pressure for 10-60 min, the gas in the vacuum heating furnace is extracted again, and the above steps 2-3 are repeated.

9. The method for preparing a nano / micro honeycomb sandwich structure Ca3Co4O9-based cermet material according to claim 1, characterized in that, The heating process of the double-sided vacuum melt infiltration method is as follows: argon gas is introduced into the vacuum heating furnace to atmospheric pressure, the furnace is heated to 1123-1273 K, the argon gas is extracted to a pressure of less than 30 Pa in the vacuum heating furnace, and the temperature is maintained for 0.5-2 h.

10. A nano / micro honeycomb sandwich structure Ca3Co4O9-based cermet material prepared by the preparation method according to any one of claims 1-9, characterized in that, It includes a matrix material and a reinforcing phase. The matrix material is a porous Ca3Co4O9 ceramic, and the channels in the Ca3Co4O9 ceramic matrix are radial pores. The reinforcing phase is a metal, and the reinforcing phase fills the channels in the Ca3Co4O9 ceramic or penetrates into the interior of the ceramic matrix.

Images