Aircraft exhaust waste heat recovery and catalytic device based on TPMS structure

Abstract

The application relates to the technical field of aviation tail gas treatment, and discloses an aviation tail gas waste heat recovery and catalysis device based on a TPMS structure, which comprises a heat exchange core body with a Gyroid type TPMS topological structure. A micro-arc oxidation ceramic layer is grown on the surface of the heat exchange core body, an SiC-cordierite composite coating with added alumina powder is deposited on the micro-arc oxidation ceramic layer, a porous alumina wash coating layer is formed on the surface of the composite coating, and the porous alumina wash coating layer is loaded with catalytic components containing platinum, palladium and cerium. By combining the Gyroid type structure with the multistage coating layer, the tail gas can be mixed in the radial direction to improve the heat transfer efficiency and avoid high back pressure; meanwhile, the thermal expansion coefficients among the coating layers are balanced by using the mixed powder to buffer the thermal stress, so that the interface peeling of the catalytic coating under the severe cold and hot alternation is prevented; and the synergistic effect of the multi-metal components improves the tail gas catalytic oxidation conversion rate and the high-temperature stability, and ensures the long-term stable operation of the device.

Description

Technical Field

[0001] This invention relates to the field of aviation exhaust gas treatment technology, specifically to an aviation exhaust gas waste heat recovery and catalytic device based on a TPMS structure. Background Technology

[0002] The aircraft auxiliary power unit (APU) is the core power source for aircraft during ground operations, emitting large amounts of high-temperature exhaust gases containing hydrocarbons and carbon monoxide. Traditional exhaust gas treatment solutions generally employ a separate structure with a heat exchanger and catalytic converter connected in series. This design not only increases the overall weight and fluid resistance of the system, but also causes drastic temperature fluctuations due to frequent start-ups and shutdowns of the APU, making it difficult for the catalytic converter to maintain a stable operating temperature. This, in turn, leads to rapid degradation of catalyst activity and waste of waste heat resources.

[0003] To reduce exhaust back pressure and improve heat exchange efficiency, the Triple-Period Minimal Surface (TPMS) structure, with its high surface area-to-volume ratio and continuous smooth channels, has attracted widespread attention in the field of heat exchange. This structure can optimize flow field distribution, enhance fluid turbulence, and eliminate local dead zones. When applying the TPMS structure to aviation exhaust gas treatment, a porous ceramic coating must be attached to its metal substrate surface to support the catalyst. However, APU exhaust gas temperatures are typically between 400°C and 650°C, accompanied by high-frequency thermal shocks from room temperature to high temperatures. The difference in thermal expansion coefficients between the metal substrate and the surface ceramic coating leads to concentrated thermal stress at the interface under harsh alternating hot and cold environments. This stress easily causes the ceramic catalytic coating to crack and peel off. Coating detachment not only directly leads to the failure of catalytic purification and heat exchange functions, but the resulting debris can also clog internal microchannels, causing a surge in exhaust back pressure and severely affecting the safe operation of the auxiliary power unit. Therefore, how to construct a treatment device that can avoid interfacial thermal stress cracking and simultaneously achieve low back pressure waste heat recovery and long-term catalytic purification in an environment of severe thermal shock and limited space is a technical problem that needs to be solved. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an aviation exhaust waste heat recovery and catalytic device based on a TPMS structure, which solves the problems of easy peeling and failure of the catalytic coating and excessively high back pressure in the internal flow channel of aviation exhaust treatment devices under severe thermal shock.

[0005] To address the above problems, the present invention provides the following technical solution:

[0006] This invention provides a waste heat recovery and catalytic device for aviation exhaust gas based on a TPMS structure, employing the following technical solution:

[0007] A waste heat recovery and catalytic device for aviation exhaust gas based on a TPMS structure includes a heat exchange core with a Gyroid-type TPMS topology. A micro-arc oxidation ceramic layer is grown in situ on the surface of the heat exchange core. A SiC-cordierite composite coating is deposited on the surface of the micro-arc oxidation ceramic layer. The SiC-cordierite composite coating is formed by depositing a mixed powder, which comprises 20% cordierite powder, 80% silicon carbide powder, and additionally 15 wt% alumina powder of the total mass of the cordierite powder and silicon carbide powder. A porous alumina wash coating is formed on the surface of the SiC-cordierite composite coating. The heat exchange core with the alumina wash coating is impregnated with a catalyst precursor solution, subjected to static adsorption, and calcined to obtain a catalytic composition containing platinum, palladium, and cerium, wherein palladium is converted into highly active palladium oxide.

[0008] By adopting the above technical solution, this device uses a Gyroid-type TPMS topology as the substrate and combines it with a multi-layer gradient coating system, achieving good results in improving heat and mass transfer efficiency and preventing coating peeling at high temperatures. The specific mechanism and reaction process are manifested in the following aspects:

[0009] The Gyroid's three-period continuous minimal curved surface structure alters the linear flow state of the fluid, generating a spatially interwoven secondary flow within the channels. Within this complex channel, the fluid boundary layer continuously breaks down and reforms, thereby enhancing the convective heat transfer between the exhaust gas and the pipe wall. Simultaneously, this curved structure provides a continuous adhesion surface for the catalytic reaction.

[0010] Considering the inconsistency in thermal expansion coefficients between the aluminum alloy substrate and the subsequent catalytic ceramic layer, this scheme utilizes a micro-arc oxidation process to construct a gradient transition. Under the combined action of an electric field and the electrolyte, the aluminum alloy surface undergoes electrochemical transformation, generating a dense alumina ceramic layer in situ. This ceramic layer, metallurgically bonded to the metal substrate, acts as the first physical barrier to alleviate thermal stress.

[0011] Building upon this, a SiC-cordierite composite layer, deposited via cold spraying, is further adhered to the aforementioned micro-arc oxide layer. Silicon carbide possesses high thermal conductivity, while cordierite has a relatively low coefficient of thermal expansion. The sprayed powder, after plastic deformation and micro / nano-scale fragmentation, forms a porous, rough surface. The density of the composite coating is enhanced by the additional addition of alumina powder as a compacting agent during the cold spraying process. The presence of this composite layer not only reduces the overall coefficient of thermal expansion of the surface but also provides mechanical anchoring sites for the outer wash coating layer.

[0012] For heterogeneous catalytic reactions, the high specific surface area provided by the porous alumina coating allows for the high dispersion of platinum, palladium, and cerium nanoparticles. When the exhaust gas passes through, carbon monoxide is catalytically oxidized to carbon dioxide, while hydrocarbons are oxidized to carbon dioxide and water. The palladium component, converted to palladium oxide through calcination, exhibits a bimetallic synergistic effect with platinum, lowering the ignition temperature of carbon monoxide and hydrocarbons. Furthermore, cerium ions undergo redox cycles between different valence states to regulate local oxygen concentration, maintaining the stability of the catalytic system under fluctuating operating conditions.

[0013] Preferably, the heat exchange core has a unit cell size of 2.5–3.0 mm and a porosity of 65%–70%; the matrix material of the heat exchange core is Al250C high-strength heat-resistant aluminum alloy powder; the surface of the heat exchange core, from the inside to the outside, includes: a 25 μm thick micro-arc oxidation Al2O3 transition layer, a 50 μm thick SiC-cordierite composite coating, a 20 μm thick γ-Al2O3 impregnation layer, and a 10 μm thick Pd-Ce catalyst layer.

[0014] By adopting the above technical solution, the unit cell size and porosity set within this range can balance the fluid resistance pressure drop and the interphase heat transfer area. Controlling the specific thickness of each coating avoids the increased thermal resistance and pore blockage problems caused by excessively thick local coatings, thereby ensuring that the catalyst layer can directly contact the main fluid.

[0015] Preferably, the porous alumina coating is formed by impregnation and calcination of a carrier slurry containing boehmite sol and alumina powder. The specific preparation method of the boehmite sol is as follows: dry boehmite powder is dispersed in deionized water to prepare a suspension with a solid content of 10wt% to 15wt% by mass; the suspension is stirred in a water bath at 60 to 80°C, and dilute nitric acid with a mass concentration of 5% to 10% is added dropwise to adjust the pH value to 3.0 to 4.0. The mixture is stirred continuously for 2 to 4 hours until the suspension is transformed into a translucent sol. The translucent sol is then allowed to stand for 12 to 24 hours.

[0016] By employing the above technical solution, the addition of dilute nitric acid provides a suitable dissolution environment, causing the surface of the boehmite particles to acquire a positive charge and form a stable colloidal dispersion. Subsequently, after static aging, the colloidal particles aggregate to form a spatial network structure. This structure, upon calcination, transforms into an alumina carrier with abundant mesoporous distribution, enhancing the adhesion of the coating to the composite substrate.

[0017] Preferably, the molar ratio of platinum, palladium, and cerium in the catalytic component is 1:(8-9):(1-2).

[0018] By adopting the above technical solution, a higher proportion of palladium helps to reduce the overall material cost of precious metals. At the same time, the incorporated cerium element creates steric hindrance around the platinum-palladium particles, which can inhibit the migration and aggregation of precious metal particles in high-temperature environments, thereby maintaining a high specific surface area of ​​active sites.

[0019] Preferably, it also includes a stainless steel shell with a diffuser section, the heat exchange core is assembled with the stainless steel shell, an all-metal toothed gasket is placed at the flange sealing surface, and eight bolts are tightened in a cross sequence to 15 N·m to complete the split flange connection.

[0020] By adopting the above technical solution and using a split mechanical assembly structure, residual internal stress caused by direct welding of different metals can be avoided. The toothed gaskets allow the heat exchange core to undergo slight axial and radial displacement when subjected to the impact of high-temperature exhaust gas. This moderate displacement absorbs the thermal expansion of the system, helping to maintain the integrity of the overall structure of the device.

[0021] Preferably, the heat exchange core is prepared by a method comprising the following steps:

[0022] Selective laser melting 3D printing technology is used to print a heat exchange core with a Gyroid-type TPMS topology using high-strength heat-resistant aluminum alloy powder as raw material. The heat exchange core is then cut, sandblasted, ultrasonically cleaned and dried to obtain a cleaned heat exchange core.

[0023] The cleaned heat exchange core is placed as the anode in a micro-arc oxidation electrolytic cell for constant current oxidation treatment, and a micro-arc oxidation ceramic layer is grown in situ on the surface of the cleaned heat exchange core.

[0024] Using a supersonic cold spraying system, the mixed powder is sprayed as cold spray powder onto the surface of the micro-arc oxidation ceramic layer, causing the powder to break down and combine at the micro-nano scale, depositing to form a SiC-cordierite composite coating, thus obtaining a heat exchange core with a SiC-cordierite composite coating.

[0025] The heat exchange core with the SiC-cordierite composite coating is boiled with oxalic acid solution to remove surface impurities and improve roughness. After washing and drying, it is immersed in carrier slurry. After taking it out, excess slurry is blown away with compressed air to ensure that the channels are unobstructed. Then it is dried and calcined to form a porous alumina wash coating on the surface of the SiC-cordierite composite coating, thus obtaining a heat exchange core with a wash coating.

[0026] The heat exchange core with the wash coating is immersed in a catalyst precursor solution containing palladium chloride, platinum chloride, cerium nitrate hexahydrate and urea. After static adsorption, it is taken out and dried, and then calcined in air atmosphere to completely convert palladium into highly active palladium oxide, thus obtaining the heat exchange core.

[0027] By employing the above technical solution, the selected 3D printing technology can form complex continuous curved surfaces that are difficult to achieve with traditional machining. The subsequent oxalic acid boiling treatment, through weak acid etching, dissolves some free substances on the coating surface while simultaneously etching out micropores, thus increasing surface roughness. During the static heating process, urea in the precursor solution undergoes slow hydrolysis and releases ammonia gas, causing the pH value of the solution to rise more uniformly. This pH change guides noble metal ions to distribute into the micropores of the alumina carrier in a homogeneous precipitation manner, preventing particle agglomeration caused by excessively high local concentrations.

[0028] Preferably, during the constant current oxidation process, an aqueous sodium silicate solution with a concentration of 8-10 g / L is used as the base electrolyte; a square wave pulse mode with a pulse frequency of 300 Hz and a duty cycle of 50% is used to control the current density at 3.5-4.0 A / dm2 for constant current oxidation, and the voltage is gradually increased to 520-540 V before stopping.

[0029] By employing the above technical solution, the sodium silicate system can promote the formation of a dense amorphous oxide layer. The square wave pulse mode provides energy intermittency, preventing localized heat accumulation and microcrack propagation caused by continuous discharge. Furthermore, control of the endpoint voltage helps maintain the uniformity of the final film thickness.

[0030] Preferably, when using the supersonic cold spray system for spraying, the spraying gas of the supersonic cold spray system is controlled to be nitrogen, the spraying gas pressure is 4.5 to 5.0 MPa, and the temperature is 480 to 500°C.

[0031] By employing the above technical solution, the entire cold spraying process is maintained in a solid deposition state. Nitrogen gas, as the spraying gas, provides kinetic energy, allowing the mixed powder to impact the substrate at a temperature below its own melting point. This method avoids the oxidation phase transition phenomenon that easily occurs when silicon carbide is sprayed at high temperatures, thus preserving its original thermophysical properties.

[0032] Preferably, in the process of forming the porous alumina coating, the boiling treatment is performed for 1 hour using an oxalic acid solution with a mass concentration of 20%; after impregnation, the coating is dried at 120°C and then calcined in a muffle furnace at 500°C for 4 hours.

[0033] By employing the above technical solution, the complexing effect of oxalic acid removes impurity ions from the surface, preventing subsequent catalyst poisoning. Subsequent high-temperature calcination causes the pseudoboehmite to undergo a dehydration phase transformation, generating a stable alumina phase, thereby constructing a robust porous support framework.

[0034] Preferably, when preparing the catalyst precursor solution, an appropriate amount of hydrochloric acid is added to aid dissolution, and the mass fraction of urea in the solution is controlled to be 0.5 wt%; after impregnation and adsorption, the solution is dried at 120°C for 2 hours, and then calcined in an air atmosphere in a muffle furnace at 500-550°C for 4 hours.

[0035] By employing the above technical solution, the addition of hydrochloric acid can inhibit premature hydrolysis of metal chlorides. During high-temperature calcination in an air atmosphere, the metal chloride precursor undergoes thermal decomposition and oxidation. This process promotes the transformation of the palladium component into a highly reactive palladium oxide state, firmly fixing it within the pores of the support.

[0036] This invention provides a waste heat recovery and catalytic device for aviation exhaust gas based on a TPMS structure. It has the following beneficial effects:

[0037] 1. This invention employs a Gyroid-type TPMS topology as the framework of the heat exchange core, enabling periodic fluid separation and mixing of exhaust gas as it passes through the channels. This structure increases the contact area between the fluid and the orifice walls and enhances internal radial heat transfer. While improving heat exchange efficiency, it avoids the high back pressure problem that is easily generated by the complex channels inside traditional treatment devices, ensuring the smooth exhaust process of aero-engines.

[0038] 2. This invention constructs a multi-level composite coating system consisting of a micro-arc oxidation ceramic layer, a SiC-cordierite composite coating, and an alumina coating. By growing a ceramic layer in situ on the surface of an aluminum alloy substrate to form a metallurgical bond, and by utilizing a mixture of SiC and cordierite powders with different thermal properties to harmonize the overall structure's coefficient of thermal expansion, the interfacial thermal stress caused by the severe thermal shock of high-temperature exhaust gas is buffered. This prevents the catalytic coating from mismatching and peeling off under alternating hot and cold environments, thereby improving the overall service life of the device.

[0039] 3. This invention loads a specific ratio of platinum, palladium, and cerium catalytic components onto a porous alumina coating. The palladium phase dominates the catalytic oxidation reaction under low-temperature conditions, while the added platinum component suppresses palladium sintering at high temperatures. Cerium, in conjunction with the platinum, regulates the local oxygen partial pressure and maintains the dispersion of the noble metals. This multi-component synergistic effect not only improves the conversion rate of carbon monoxide and hydrocarbons in the exhaust gas but also ensures the long-term stability of the catalytic coating under harsh high-temperature conditions. Attached Figure Description

[0040] Figure 1 This is a front view of the present invention;

[0041] Figure 2 This is a schematic cross-sectional view of the stainless steel casing of the present invention;

[0042] Figure 3The figures show the coating load and bonding performance evaluation of each group of heat exchanger core samples in this invention; wherein, Figure 3 Figure (a) shows the coating loading rate and BET specific surface area test results for each group of samples. Figure 3 (b) shows the ultrasonic shedding rate test results for each group of samples;

[0043] Figure 4 These are macroscopic thermophysical parameter test diagrams of various heat exchange core samples of the present invention at 400℃; wherein... Figure 4 Figure (a) shows the test results of bulk density and specific heat capacity of each group of samples. Figure 4 Figure (b) shows the test results of equivalent thermal conductivity and thermal diffusivity for each group of samples.

[0044] Figure 5 These are test diagrams showing the comprehensive heat transfer and hydrodynamic performance of each heat exchange device in this invention.

[0045] Figure 6 These are test diagrams showing the thermal shock resistance of various heat exchange core samples from this invention.

[0046] Figure 7 This is a graph showing the catalytic activity evaluation of each group of samples under a wide temperature range; wherein, Figure 7 Figure (a) shows the test results of the ignition temperature T50 and complete conversion temperature T90 of CO gas for each group of samples. Figure 7 Figure (b) shows the test results of the ignition temperature T50 and the complete conversion temperature T90 of HC gas for each group of samples.

[0047] Figure 8 These are macroscopic mechanical reliability assessment diagrams for each group of TPMS heat exchanger core materials in this invention; wherein, Figure 8 Figure (a) shows the compressive yield strength test results of each group of TPMS matrix specimens at room temperature (25℃) and 400℃. Figure 8 Figure (b) shows the steady-state creep rate test results of each group of TPMS matrix specimens at 400℃.

[0048] Among them, 1. Stainless steel shell; 2. Heat exchange core. Detailed Implementation

[0049] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] Preparation Examples 1-3

[0051] Preparation Example 1:

[0052] This preparation example provides a method for preparing a pseudo-boehmite sol, including the following steps:

[0053] 120 g of boehmite powder was evenly dispersed in 880 g of deionized water to prepare a suspension with a solid content of 12 wt%. Under constant temperature and vigorous stirring in a 70°C water bath, 8% dilute nitric acid was slowly added as a gel solvent to adjust the pH of the system to 3.5. The system was stirred continuously for 3 hours until the suspension turned into a translucent sol. After standing for 18 hours, the boehmite sol was obtained.

[0054] Preparation Example 2:

[0055] This preparation example provides a method for preparing a pseudo-boehmite sol, including the following steps:

[0056] 100g of boehmite powder was evenly dispersed in 900g of deionized water to prepare a suspension with a solid content of 10wt%. Under constant temperature stirring in a 60℃ water bath, 5% dilute nitric acid was added dropwise as a gel solvent to adjust the pH of the system to 3.0. Stirring was continued for 2 hours until the suspension turned into a translucent sol. The sol was then allowed to stand for 12 hours to obtain the boehmite sol.

[0057] Preparation Example 3:

[0058] This preparation example provides a method for preparing a pseudo-boehmite sol, including the following steps:

[0059] 150 g of boehmite powder was evenly dispersed in 850 g of deionized water to prepare a suspension with a solid content of 15 wt%. Under constant temperature and vigorous stirring in an 80°C water bath, 10% dilute nitric acid was slowly added as a gel solvent to adjust the pH of the system to 4.0. Stirring was continued for 4 hours until the suspension turned into a translucent sol. The sol was then allowed to stand for 24 hours to obtain the boehmite sol.

[0060] Examples 1-4:

[0061] Example 1:

[0062] This embodiment provides an aviation exhaust waste heat recovery and catalytic device based on a TPMS structure. The preparation and assembly method of this device includes the following steps:

[0063] (1) Selective laser melting (SLM) 3D printing technology was adopted, and Al250C high-strength heat-resistant aluminum alloy powder was used as raw material to print the heat exchange core 2 of Gyroid type TPMS topology. The unit cell size was set to 3.0 mm and the porosity was 70%. After molding, the core was cut from the substrate and then sandblasted, ultrasonically cleaned and dried in sequence.

[0064] (2) The cleaned heat exchange core 2 is placed in the micro-arc oxidation electrolytic cell as the anode. A sodium silicate aqueous solution with a concentration of 10 g / L is used as the basic electrolyte. A square wave pulse mode with a pulse frequency of 300 Hz and a duty cycle of 50% is used to control the current density at 4 A / dm³. 2 Constant current oxidation was performed, and the voltage was gradually increased to 540V and then stopped. A micro-arc oxidation ceramic layer with a thickness of 25μm was grown in situ on the surface of the heat exchange core 2. After being removed, it was rinsed with deionized water and dried at 100℃.

[0065] (3) Mix 20% cordierite powder and 80% silicon carbide powder evenly, and add an additional 15 wt% alumina powder as a cold spray powder. Use a supersonic cold spray system to spray the micro-arc oxidation ceramic layer surface, and control the spray gas (N2) 2） The pressure was 5.0 MPa and the temperature was 500 °C, which caused the ceramic powder to break down and combine at the micro-nano scale, and deposited a SiC-cordierite composite coating with a thickness of 50 μm on the surface.

[0066] (4) First, the heat exchange core 2 with SiC-cordierite composite coating was boiled for 1 hour with 20% oxalic acid solution to remove surface impurities and improve roughness. After washing, it was dried. The pseudo-boehmite sol obtained in Preparation Example 1 was mixed with alumina powder at a mass ratio of 1:2 and dispersed by ball milling to obtain a carrier slurry. The core was completely immersed in the carrier slurry for 5 minutes. After taking it out, the excess slurry was blown away with compressed air to ensure that the channels were unobstructed. Then it was dried at 120°C and calcined in a muffle furnace at 500°C for 4 hours to form a porous alumina coating.

[0067] (5) Add palladium chloride, platinum chloride, cerium nitrate hexahydrate and urea to deionized water and add an appropriate amount of hydrochloric acid to aid dissolution to prepare a clear catalyst precursor solution. Control the molar ratio of Pt, Pd and Ce in the solution to be about 1:9:1 and the mass fraction of urea to be 0.5wt%. Immerse the heat exchange core 2 with the washing coating in the precursor solution, let it stand at room temperature for 2 hours for adsorption, take it out, dry it at 120℃ for 2 hours, and finally calcine it in an air atmosphere in a muffle furnace at 500℃ for 4 hours to completely convert palladium into highly active PdO.

[0068] (6) The prepared heat exchange core 2 is assembled with the 304L stainless steel shell 1 with the diffuser section. An all-metal toothed gasket is placed at the flange sealing surface. Eight bolts are tightened in a cross sequence to 15 N·m to complete the split flange connection and obtain the aviation exhaust waste heat recovery and catalytic device based on the TPMS structure. After final molding, the surface of the heat exchange core 2 includes, from the inside to the outside: a 25 μm thick micro-arc oxidation Al2O3 transition layer, a 50 μm thick SiC-cordierite composite coating, a 20 μm thick γ-Al2O3 impregnation layer, and a 10 μm thick Pd-Ce catalyst layer.

[0069] Example 2:

[0070] This embodiment provides an aviation exhaust waste heat recovery and catalytic device based on a TPMS structure. The preparation and assembly method of this device includes the following steps:

[0071] (1) Selective laser melting (SLM) 3D printing technology was adopted, and Al250C high-strength heat-resistant aluminum alloy powder was used as raw material to print the heat exchange core 2 of Gyroid type TPMS topology. The unit cell size was set to 2.5 mm and the porosity was 65%. After molding, the core was cut from the substrate and then sandblasted, ultrasonically cleaned and dried in sequence.

[0072] (2) is exactly the same as step (2) in Example 1.

[0073] (3) is exactly the same as step (3) in Example 1.

[0074] (4) is exactly the same as step (4) in Example 1.

[0075] (5) is exactly the same as step (5) in Example 1.

[0076] (6) is exactly the same as step (6) in Example 1.

[0077] Example 3:

[0078] This embodiment provides an aviation exhaust waste heat recovery and catalytic device based on a TPMS structure. The preparation and assembly method of this device includes the following steps:

[0079] (1) is exactly the same as step (1) in Example 1.

[0080] (2) The cleaned heat exchange core 2 is placed in a micro-arc oxidation electrolytic cell as the anode, and an aqueous sodium silicate solution with a concentration of 8 g / L is used as the basic electrolyte. The current density is controlled at 3.5 A / dm³. 2 Constant current oxidation was performed, and the voltage was gradually increased to 520V and then stopped. A micro-arc oxidation ceramic layer with a thickness of 20μm was grown in situ on the surface of the heat exchange core 2. After removal, it was rinsed and dried.

[0081] (3) Prepare the same cold spray powder as in Example 1, and spray it on the surface of the micro-arc oxidation layer using a cold spray system. Control the spray gas pressure to be 4.5 MPa and the temperature to be 480 °C to deposit a SiC-cordierite composite coating with a thickness of 45 μm.

[0082] (4) is exactly the same as step (4) in Example 1.

[0083] (5) is exactly the same as step (5) in Example 1.

[0084] (6) is exactly the same as step (6) in Example 1.

[0085] Example 4:

[0086] This embodiment provides an aviation exhaust waste heat recovery and catalytic device based on a TPMS structure. The preparation and assembly method of this device includes the following steps:

[0087] (1) is exactly the same as step (1) in Example 1.

[0088] (2) is exactly the same as step (2) in Example 1.

[0089] (3) is exactly the same as step (3) in Example 1.

[0090] (4) First, boil the sample with 20% oxalic acid solution for 1 hour; mix the pseudo-boehmite sol obtained in Example 3 with alumina powder at a mass ratio of 1:2.5 to prepare a carrier slurry; immerse the core for 5 minutes, blow out the pores, dry it at 120°C, and calcine it in a muffle furnace at 500°C for 4 hours to form a porous alumina coating.

[0091] (5) Add palladium chloride, platinum chloride, cerium nitrate hexahydrate and urea to deionized water, and control the molar ratio of Pt, Pd and Ce in the solution to be 1:8:2, and the mass fraction of urea to be 0.5wt%; after impregnation and adsorption, dry at 120℃ for 2 hours, and finally calcine in an air atmosphere in a muffle furnace at 550℃ for 4 hours to completely convert Pd into highly active PdO.

[0092] (6) is exactly the same as step (6) in Example 1.

[0093] Comparative Examples 1-5:

[0094] Comparative Example 1:

[0095] Compared with Example 1, the difference is that in step (1), the heat exchange core 2 of the Gyroid type TPMS topology is replaced with the heat exchange core 2 of the traditional honeycomb straight-through structure with the same external dimensions and porosity, while the rest are the same.

[0096] Comparative Example 2:

[0097] Compared with Example 1, the difference is that the micro-arc oxidation treatment in step (2) is omitted, and the cold spraying treatment in step (3) is performed directly on the bare surface of the cleaned heat exchange core 2. The rest are the same.

[0098] Comparative Example 3:

[0099] Compared with Example 1, the difference is that the SiC-cordierite composite coating cold spraying treatment in step (3) is omitted, and the coating impregnation in step (4) is performed directly on the surface of the micro-arc oxidation ceramic layer. The rest are the same.

[0100] Comparative Example 4:

[0101] Compared with Example 1, the difference is that in step (5), only palladium chloride is added when preparing the catalyst precursor solution, and platinum chloride and cerium nitrate hexahydrate are not added, while the rest are the same.

[0102] Comparative Example 5:

[0103] Compared with Example 1, the difference is that in step (1), the high-strength heat-resistant aluminum alloy powder is replaced with conventional AlSi. 10 Mg aluminum alloy powder, all others are the same.

[0104] Test Examples 1-6:

[0105] Test Example 1:

[0106] Coating specific surface area and coating load test

[0107] Intermediate samples from Examples 1 to 4 and Comparative Examples 1 and 3 that had completed the washing and baking process but had not yet been impregnated with the noble metal catalyst precursor solution were selected as test objects.

[0108] The mass of the bare substrate and the overall heat exchange core 2 after coating calcination were weighed using an analytical balance. The actual load percentage of the coating on the heat exchange core 2 per unit mass was calculated by dividing the difference between the two by the mass of the bare substrate.

[0109] The coated sample was completely immersed in a glass container filled with deionized water and placed in an ultrasonic cleaner. It was continuously ultrasonically vibrated for 35 minutes at a frequency of 40 kHz and a room temperature water bath. After vibration, the sample was removed and the residual moisture in the pores was blown away with a high-pressure air gun. Then it was placed in a 120°C forced-air drying oven to dry for 4 hours until constant weight. The percentage of coating mass loss caused by ultrasonic vibration was weighed and calculated.

[0110] Approximately 0.8 g of alumina coating powder was scraped from the microchannels of each sample in the same batch using a stainless steel scraper and placed into the standard degassing tube of a fully automated specific surface area and pore size analyzer. The powder was continuously heated and degassed at 200°C in a vacuum environment for 4.5 hours to remove surface-adsorbed impurities and moisture. Subsequently, standard nitrogen adsorption and desorption isotherm tests were performed at liquid nitrogen temperature. The specific surface area was calculated based on the multi-point BET equation, and the total pore volume was determined using the BJH model.

[0111] Table 1 Test data of coating loading rate, adhesion and porosity characteristics of each group of samples

[0112] Example 1 12.38 0.86 148.25 0.421 Example 2 11.64 1.12 146.91 0.418 Example 3 12.07 1.35 150.13 0.435 Example 4 14.52 1.78 135.68 0.384 Comparative Example 1 8.15 2.41 147.52 0.412 Comparative Example 3 10.61 4.67 145.24 0.407

[0113] According to Table 1 and Figure 3 The test results show that the overall topological structure design and the roughness of the underlying interface have a fundamental impact on the macroscopic loading behavior of the active cleaning coating. Observing the data differences between the examples and Comparative Example 1 reveals that the loading rate of the test group using the Gyroid-type TPMS structure remained above 11.6%, while the traditional through-cell structure under the same process conditions only reached 8.15%. This data difference stems from the fact that the curved surface structure of TPMS provides a much larger geometric specific surface area than through-cells in the same volume. The three-dimensional interlaced continuous curved surface provides ample space for slurry adhesion, which can accommodate more catalytically active components within the limited space of aviation exhaust pipe layout. Different sol concentration ratios exhibit specific regulatory effects on the mesopore formation law. In Example 4, increasing the proportion of alumina powder in the ratio increased the loading rate to 14.52%, but the measured specific surface area decreased to 135.68 m². 2 / g, because the excess precursor clogs some of the micron-sized pores during the calcination shrinkage process, resulting in a reduction in total pore volume.

[0114] The physical feedback of the micro-interface bonding state under harsh mechanical vibration was quantified through the shedding rate data. After a cavitation peeling test lasting 35 minutes, the shedding rate of the example groups was generally controlled within the range of less than 1.8%, confirming that the prepared pseudo-boehmite sol has good bonding and molding performance. As a control group with the SiC-cordierite composite coating peeled off, the shedding rate of Comparative Example 3 increased sharply to 4.67%. The reduced surface roughness and the lack of a thermal stress buffer layer directly led to the inability to release the internal stress of the coating after calcination, and the initiation of microcracks exacerbated the blocky peeling trend under ultrasonic conditions. The mechanical anchoring and stress relief capabilities constructed by the multilayer composite process improve the interfacial bonding stability of the coating, improve the interfacial bonding state between the pure ceramic coating and the metal substrate, and at the same time, the high specific surface area provides sufficient gas-solid contact area for the catalytic reaction.

[0115] Test Example 2:

[0116] Test specimens were cut from the finished samples of Examples 1 to 4, Comparative Example 1 and Comparative Example 5 using a wire cutting device. The specimens were then processed into standard cylindrical thin slices with a diameter of 12.7 mm and a thickness of 3.0 mm using a grinding machine. The actual dimensions of each specimen were measured using a vernier caliper and a micrometer to calculate its volume.

[0117] The standard sample that has been processed was weighed using an analytical balance. Based on the actual volume data that has been measured, the macroscopic bulk density of the porous structure sample with coating was calculated.

[0118] The prepared samples were placed sequentially into the sample crucible of the differential scanning calorimeter (DSC) and heated from room temperature to 450°C at a heating rate of 10°C / min under an argon protective atmosphere. The heat flow curve during the heating process was recorded, and the specific heat capacity data at the 400°C temperature point was extracted.

[0119] The macroscopic equivalent thermal diffusivity of the sample was tested using a laser flare thermal conductivity meter. The sample was placed in the test chamber and heated to a stable temperature of 400°C. A transient thermal pulse was emitted to the lower surface of the sample through a bottom laser source. The temperature response of the upper surface over time was recorded using an infrared detector, and the thermal diffusivity at 400°C was obtained by fitting the data.

[0120] The macroscopic equivalent thermal conductivity of the sample under the test condition of 400℃ is calculated by multiplying the three physical quantities of bulk density, specific heat capacity and thermal diffusivity of the same sample.

[0121] Table 2 shows the test data of macroscopic thermophysical parameters of each group of samples at 400℃.

[0122] Example 1 0.942 0.915 14.21 12.24 Example 2 1.087 0.908 13.84 13.66 Example 3 0.925 0.922 14.55 12.41 Example 4 0.981 0.911 13.92 12.44 Comparative Example 1 0.938 0.916 9.87 8.48 Comparative Example 5 0.914 0.884 15.63 12.63

[0123] Summary: Based on Table 2 and Figure 4 The test results show that the macroscopic equivalent thermal conductivity of the porous structure is constrained by both the topological geometry of the solid skeleton and the inherent physical properties of the matrix material. Observing the data from Example 1 and Comparative Example 1 reveals that, under the same order of magnitude of overall porosity and surface coating preparation process, the sample using the Gyroid-type TPMS structure achieved a radial equivalent thermal conductivity of 12.24 W / (m·K), exceeding the 8.48 W / (m·K) of the traditional honeycomb through-hole structure. This difference in thermal performance stems from the lack of a continuous, interconnected metallic heat transfer medium in the transverse cross-section of the traditional honeycomb channels. The parallel thin-walled structure causes significant thermal resistance due to the large air layers encountered during radial diffusion. The minimal surface features of the TPMS structure construct a non-directional heat transfer network in three-dimensional space. The originally unidirectional heat flow can find the shortest heat dissipation path within the interlaced skeleton, reducing the problem of localized thermal stress concentration.

[0124] Slight variations in pore characteristics directly altered the cross-sectional area of ​​the heat transfer channels. In Example 2, the initial porosity of the structure was compressed to 65%, and the macroscopic bulk density of the test sample increased to 1.087 g / cm³. 3 The increased proportion of the metallic matrix led to an overall equivalent thermal conductivity of 13.66 W / (m·K). This parameter sensitivity indicates that in the engineering design of actual exhaust sections, porosity can be adjusted to balance heat transfer and pressure bearing capacity in areas with uneven temperature gradient distribution. The doping of matrix alloying elements at the deep lattice level interfered with phonon heat transfer. Comparative Example 5 used conventional AlSi... 10 The Mg alloy exhibited a slightly higher thermal diffusivity than the Sc and Zr-containing alloys in the tests. The nanoscale Al3(Sc,Zr) reinforcing phases precipitated at the grain boundaries by scandium and zirconium elements, while improving high-temperature strength, inevitably increased the scattering cross-section of the lattice for thermally conductive phonons. Although the intrinsic thermal conductivity of the Sc and Zr-containing alloys was reduced, they ensured that the structure did not creep and collapse under the impact of high-temperature APU exhaust gas; and the slight thermal conduction loss at the matrix material level was compensated for by the heat transfer area gain brought about by the TPMS topology. The ceramic composite layer and the wash coating layer attached to the skeleton surface played a role in stabilizing the heat capacity within the system. The specific heat capacity data of each group of samples were concentrated around 0.91 J / (g·K), and the coating layer enabled the overall heat exchange device to maintain its heat buffering capacity under high-temperature transient conditions.

[0125] Test Example 3:

[0126] The complete aviation exhaust waste heat recovery and catalytic device of Examples 1 to 4 and Comparative Example 1, which have been coated and loaded with catalyst, were selected as test objects. The device was wrapped with aluminum silicate refractory fiber insulation cotton and assembled and sealed in a standard stainless steel hot air tunnel test pipe with matching inner diameter.

[0127] A high-power electric heater and a Roots blower were installed at the inlet of the test pipeline. The inlet gas temperature under stable operating conditions was set to 500℃. The mass flow rate of the simulated exhaust gas mixed with air was fixed at 0.05kg / s by a mass flow controller, so that the gas was constantly introduced into the heat exchange device.

[0128] A circulating water cooling jacket is fitted outside the test section of the heat exchange device to simulate an external cold source. The inlet temperature of the cooling water is controlled to be constant at 25°C. K-type thermocouple probes arranged at both ends of the pipeline are used to read the temperature drop data of the gas before and after passing through the core in real time.

[0129] Record the cooling water flow rate and inlet / outlet water temperature difference after the system reaches thermal equilibrium to calculate the total heat transfer. Divide the total heat transfer by the actual outer volume of the heat exchange core 2 and the logarithmic mean temperature difference to deduce the volumetric heat transfer coefficient of each group of samples.

[0130] The static pressure measuring holes before and after the heat exchanger are connected to the micro differential pressure transmitter through the pressure tapping pipe. The pressure drop fluctuation data is continuously recorded for 15 minutes at the set flow rate, and the time average value is taken as the irreversible flow pressure drop of the fluid passing through the device.

[0131] Table 3. Test data of heat transfer and hydrodynamic performance of each heat exchange device.

[0132] Example 1 500.0 284.32 0.05 452.18 12.45 Example 2 500.0 261.74 0.05 518.63 15.82 Example 3 500.0 289.15 0.05 435.91 11.93 Example 4 500.0 278.47 0.05 467.24 13.11 Comparative Example 1 500.0 365.81 0.05 214.56 4.28

[0133] Summary: Based on Table 3 and Figure 5 The test results show that the flow state of the fluid within the complex channels directly determines the balance between macroscopic heat transfer efficiency and energy loss. Under test conditions where the inlet wind speed and heat flux boundary are completely consistent, Comparative Example 1, using a traditional honeycomb straight-through structure, exhibits an extremely low fluid pressure drop, measured at only 4.28 kPa. This low resistance in fluid dynamics leads to a reduction in heat transfer performance, with its volumetric heat transfer coefficient remaining at 214.56 kW / (m²). 3 The low K level resulted in an outlet temperature of 365.81°C after the gas passed through the core. A stable laminar boundary layer inevitably formed inside the through-hole. After heat exchange with the fluid near the pipe wall, the high-temperature exhaust gas in the center of the channel directly penetrated the device due to the lack of lateral disturbance, causing significant heat loss. Introducing a Gyroid-type TPMS structure altered the topological constraints of the flow field, increasing the volumetric heat transfer coefficient of Example 1 to 452.18 kW / (m²). 3 This performance enhancement stems from the continuous shearing action exerted on the fluid by the three-dimensional continuous surface. The airflow continuously separates, eddies, and reconverges within the interlaced three-dimensional channels, halting the thickening process of the thermal boundary layer. High-temperature gas in the core region is guided to the cooler solid wall surface, transferring heat energy to the interior of the framework through heat and mass exchange.

[0134] The increase in pressure drop is an unavoidable physical byproduct of enhanced heat transfer. In Example 1, the pressure drop increased to 12.45 kPa, which is within the reasonable threshold of the allowable back pressure for aviation exhaust pipes. This resistance loss was compensated for by improving heat recovery efficiency. Reducing the geometric unit cell and decreasing porosity drastically amplifies the flow resistance effect. In Example 2, the unit cell size was reduced to 2.5 mm and the porosity was reduced to 65%. The narrow channel accelerated the airflow compression, causing the pressure drop to increase sharply to 15.82 kPa. Although this resulted in a power gain of 518.63 kW / (m²), the pressure drop was significantly reduced. 3The limiting heat transfer coefficient (·K) is considered, but in practical engineering configurations, the potential impact of excessively high exhaust back pressure on the upstream turbine's work efficiency is taken into account. Fine-tuning the surface coating thickness also intervenes in the flow cross-sectional area at the micrometer scale. In Example 4, the increased coating load caused a slight decrease in the hydraulic diameter of the channel, leading to a simultaneous increase in fluid resistance and the heat transfer coefficient. Comparison of data from different groups confirms that the topology parameter combination in this scheme eliminates the thermodynamic dead zone while limiting the pressure loss caused by turbulent dissipation to an acceptable range for engineering applications.

[0135] Test Example 4:

[0136] The complete heat exchange core 2 samples of Examples 1 to 4, which have completed all coating preparation and catalyst loading processes, as well as Comparative Examples 2 and 3, were selected as the objects of thermal shock performance testing.

[0137] All test samples were placed in a vacuum drying oven at 120°C and baked for 2 hours to remove adsorbed free moisture from the pores. After being removed and cooled to room temperature, the initial total mass of each sample was measured using an analytical balance. Combined with the known reference mass of the bare substrate of each sample before coating preparation, the initial net mass of the coating attached to the substrate before testing was calculated.

[0138] Place the weighed sample on a trolley with a high-temperature resistant stainless steel mesh frame, and quickly push it into a box-type resistance furnace that has been preheated to 600°C for 15 minutes to ensure that the sample reaches thermal equilibrium from the surface to the interior.

[0139] Open the furnace door and quickly transfer the sample from the mesh rack to a constant temperature water bath maintained at 25°C, where it will be completely immersed. The sample will then be rapidly cooled by water for 5 minutes. After one cooling cycle, remove the sample and use a high-pressure air gun to blow away any remaining moisture from the surface and pores. The sample will then be pushed back into the high-temperature furnace for the next cycle.

[0140] Repeat the above alternating heating and water cooling operation until a total of 100 complete thermal shock cycles are completed. Collect the coating debris scattered at the bottom of the water tank during the test to help evaluate the overall failure mode. After all cycles, the sample is dried again under the drying conditions in step 2 and the final total mass is weighed. The coating mass loss rate caused by thermal shock alternation is calculated using the mass difference before and after.

[0141] Table 4. Test data on the mass evolution of heat exchange core samples before and after thermal shock cycling.

[0142] Example 1 18.4526 14.1205 4.3321 18.3975 1.27 Example 2 19.3241 14.8872 4.4369 19.2618 1.40 Example 3 18.0152 13.9148 4.1004 17.9545 1.48 Example 4 20.1478 15.0234 5.1244 20.0381 2.14 Comparative Example 2 17.8459 14.0512 3.7947 16.7118 29.89 Comparative Example 3 18.1563 14.2115 3.9448 17.4098 18.92

[0143] Summary: Based on Table 4 and Figure 6Data shows that the cyclic thermal load induced by the rapid thrust change of aero-engines during takeoff and landing places high demands on the bonding strength of the inorganic coating on the surface of the heat exchange channel. The measured mass deviation results clearly demonstrate the thermal shock resistance of the interface structure design. After completing hundreds of high-temperature span quench cycles, the mass loss rate of the surface coating in Examples 1 to 4 remained below 2.2%, confirming the excellent structural stability of the overall multilayer interface. This physical stability against thermal stress peeling stems from the gradient stress transfer structure formed within the composite coating system. Test data shows that the thermal shock resistance of the examples with the micro-arc oxidation ceramic layer is superior to the comparative example, indicating that the structure has a good anchoring effect. Comparative example 2, without the micro-arc oxidation treatment, experienced coating peeling during thermal shock, with up to 29.89% of the coating detaching and cracking during the cycle. The difference in thermal expansion coefficient between the high intrinsic thermal expansion coefficient of the aluminum alloy substrate and the attached silicate and alumina ceramics results in significant interfacial shear stress due to the inconsistent volume deformation during the instantaneous water quenching. The untreated smooth metal surface cannot withstand this normal tensile stress, leading to interlayer fracture. The ceramic film constructed in situ on the substrate by the micro-arc oxidation process not only facilitates the underlying bonding at the metallurgical level, but also provides deep mechanical interlocking sites for the subsequent cold-sprayed powder through the dense discharge micropore structure on the film surface. This disperses and transfers the stress concentrated at the interface to the three-dimensional rough morphology. Data from Comparative Example 3 further validates the role of the buffer coating in the system; the sample without the deposited cold-sprayed thermal insulation layer ultimately recorded a mass loss of 18.92%. The cordierite and silicon carbide composite has a low coefficient of linear expansion and a slow thermal conductivity response, acting as a thermal barrier before the high-temperature gas contacts the underlying metal, reducing the peak temperature gradient transferred to the substrate. In the event of rapid cooling, this thermal barrier limits the transient shrinkage of the metal substrate, alleviating the problem of severe misalignment and delamination between the active cleaning coating and the substrate, and completely preserving the porous medium carrying the core catalyst on the surface of the reaction channel.

[0144] Test Example 5:

[0145] Cut pieces of heat exchange core 2 from Examples 1 to 4 and Comparative Example 4 with complete catalyst layers were taken as test evaluation objects. After tightly wrapping their periphery with quartz wool, they were pushed into the isothermal section of the fixed-bed quartz tube reactor of the catalytic activity evaluation system.

[0146] A standard test gas simulating aircraft engine exhaust gas was prepared by mixing the gas with a gas mixing system and a multi-channel mass flow meter. A volume concentration of 1500 ppm CO, 500 ppm propylene (as a characterizer of hydrocarbons HC), and 10% oxygen was continuously introduced into the reaction tube. The remaining volume was filled with high-purity nitrogen as a balance gas. The total inlet flow rate was adjusted to maintain the space velocity of the reaction gas stream at 40,000 h⁻¹. -1 .

[0147] The external temperature-controlled heating furnace of the reactor is started. The control system heats the gas from ambient room temperature to 450°C at a heating rate of 5°C / min, so that the temperature of the test gas flow is continuously increased as it passes through the porous catalyst bed.

[0148] A Fourier transform infrared multi-component gas analyzer is connected in series on the outlet pipe of the quartz tube reactor to continuously monitor and acquire data on the concentrations of CO and propylene in the outflow gas.

[0149] The catalytic conversion rate of pollutants at different temperature points is calculated by comparing the real-time concentrations of inlet and outlet gases. The ignition temperature (T50) corresponding to a conversion rate of 50% and the complete conversion temperature (T90) corresponding to a conversion rate of 90% are extracted and recorded from the conversion rate and temperature curves.

[0150] Table 5. Conversion temperature test data of CO and HC gases for each group of catalytic samples.

[0151] Example 1 142.3 178.6 161.4 192.5 Example 2 138.7 174.2 157.8 188.1 Example 3 145.1 180.9 163.5 195.4 Example 4 140.5 176.3 159.2 190.8 Comparative Example 4 198.6 245.3 216.7 262.1

[0152] Summary: Based on Table 5 and Figure 7 The test results showed that the reduction in catalyst activation energy depended on the overlap of electron orbitals in multi-component active centers and the efficient migration of lattice oxygen. Comparative Example 4, using only a single noble metal palladium system, exhibited poor catalytic reaction kinetics in low-temperature exhaust gas, with high ignition temperatures for CO and HC, at 198.6℃ and 216.7℃, respectively. This high ignition threshold led to the direct emission of unburned harmful components in the exhaust gas before sufficient thermodynamic conditions were met during cold starts or low-load operation of the aero-assisted power unit. Introducing platinum into the catalytic system and forming a bimetallic alloy produced a spillover effect, reducing the CO ignition temperature in Example 1 to 142.3℃. This improvement in low-temperature activity was due to the lattice intersolubility of Pt and Pd atoms, causing a shift in the position of the active centers. This weakened the strong adsorption and poisoning effect of CO molecules on the noble metal active sites, and the released active sites made it easier for gaseous oxygen molecules to dissociate into highly reactive oxygen free radicals.

[0153] Relying solely on bimetallic synergy to maintain the oxidation reaction is susceptible to catalytic stability issues under transient conditions of drastic gas concentration fluctuations. However, CeO2 particles generated from the pyrolysis of cerium nitrate provide a dynamic lattice oxygen reserve. Data shows that Example 2, by adjusting the micropore size and heat transfer state, controlled the HC conversion temperature T90 to 188.1℃, a decrease compared to 262.1℃ in Comparative Example 4. Within the micron-scale coating interface, the highly dispersed CeO2, due to the reversible CeO2 within its cubic fluorite structure... 3＋ With Ce 4＋Valence state transitions enable the absorption or release of lattice oxygen. When local oxygen deficiency occurs in the reaction gas flow, the oxygen storage material CeO2 can transfer oxygen atoms within its structure to the vicinity of the Pt / Pd active particles, maintaining the oxygen concentration required for the catalytic oxidation reaction. This oxygen supply capability, combined with the locally high mass transfer rate induced by the TPMS curved surface structure, enhances the anti-poisoning ability of the heat exchange core 2 surface. Under conditions of sulfide interference and carbon particle deposition from incomplete combustion, the oxygen migration pathway at the bottom of the system can still maintain a stable exhaust gas purification effect thanks to its low-temperature activation characteristics.

[0154] Test Example 6:

[0155] To eliminate the interference of the surface coating on the actual mechanical response of the substrate material, bare 3D printed TPMS substrates from the same batch of Examples 1 to 4 and Comparative Example 5 that were not subjected to surface micro-arc oxidation and coating loading were taken as test objects. They were uniformly processed into standard cubic compression test blocks with an outer dimension of 15mm×15mm×15mm using a slow wire EDM machine, and the surface was polished to ensure parallelism.

[0156] The first set of test blocks was placed in the center of the pressure plate of a universal testing machine at room temperature (25°C) with a pressure of 10... -3 s -1 An initial strain rate was applied to apply a uniaxial compressive load, and the stress value at which the material underwent 0.2% plastic deformation was recorded as the room temperature compressive yield strength.

[0157] The second group of specimens of the same specifications were placed in a high-temperature universal testing machine with an ambient heating furnace. The temperature was raised to 400℃ at a rate of 5℃ / min and kept at a constant temperature for 30 minutes to eliminate the internal temperature gradient. Then, a high-temperature compression test was performed at the same strain rate to obtain the high-temperature yield strength at 400℃. The yield strength retention rate was obtained by dividing it by the room temperature strength of the corresponding group.

[0158] A new test block was loaded into a high-temperature electronic creep endurance test chamber. The test chamber was heated and stabilized at 400°C. A constant initial compressive stress of 50 MPa was instantaneously applied along the force axis of the sample to simulate the back pressure and thermal expansion coupled stress during the exhaust gas emission of an aircraft APU.

[0159] The axial deformation displacement was continuously monitored and recorded over a period of 100 hours using high-temperature extensometers mounted on both sides of the indenter. The initial transient creep stage was eliminated, and the slope of the deformation change over time in the steady-state creep stage (second stage) was extracted to calculate the steady-state creep rate of each group of samples.

[0160] Table 6. High-temperature mechanical and creep resistance test data of each group of TPMS matrix specimens.

[0161] Example 1 428.5 243.6 56.8 4.15 Example 2 441.2 251.8 57.0 3.82 Example 3 435.7 239.1 54.9 4.47 Example 4 430.4 245.9 57.1 4.03 Comparative Example 5 374.8 68.3 18.2 86.24

[0162] Summary: Based on Table 6 and Figure 8 The test results show that the structural strength of conventional lightweight aluminum alloys decreases at high temperatures approaching half their melting point, which is particularly pronounced in the data feedback of Comparative Example 5. This group used conventional AlSi... 10 Mg alloys can maintain a yield strength of 374.8 MPa at room temperature, but when the ambient temperature rises to 400℃, their load-bearing capacity drops to only 68.3 MPa, with a yield strength retention rate of only 18.2%. Simultaneously, their steady-state creep rate increases to 86.24 × 10⁻⁶. -3 This softening in materials science stems from severe Ostwald ripening of the internal silicon precipitates under high-temperature conditions, where the coarsened particles lose their ability to impede dislocation movement. When this state of material is applied to a thin-walled TPMS structure with 70% porosity, the long-term aerodynamic scouring and thermal stress from aircraft exhaust cause the collapse of the micropores, ultimately leading to the entire device losing its fluid permeability.

[0163] Optimization of the matrix alloy composition suppressed this high-temperature failure phenomenon, and the high-temperature mechanical data of the example group established a solid structural safety margin. The high-strength heat-resistant aluminum alloy used in Example 1 retained a yield strength of 243.6 MPa at 400°C, and its creep rate was reduced to 4.15 × 10⁻⁶. -3 The extremely low level of % / h. During the rapid solidification process of laser selective melting and subsequent heating, scandium and zirconium elements precipitated a large number of nanoscale Al3(Sc,Zr) coherent precipitates with L12 lattice structure at grain boundaries and within the aluminum matrix. These nanoparticles exhibit thermodynamic stability and are difficult to dissolve or coarsen at 400°C. They are anchored at grain boundaries, generating a strong Zener pinning effect, closing the high-temperature sliding and dislocation climbing channels at grain boundaries. Although there were slight fluctuations in porosity parameters in Examples 2 to 4, which changed the cross-sectional area of ​​the macroscopic test surface and caused a small displacement in the strength data, the overall yield retention rate remained stable at around 55% to 58%. The heat transfer advantage of the macroscopic structural topology design is the premise for its practical application in the exhaust pipe. It is maintained by the pressure-bearing base provided by the pressure-bearing capacity provided by the underlying alloy reinforcement effect, ensuring that the three-dimensional curved thin wall does not undergo irreversible geometric distortion when facing the high-temperature turbine exhaust gas impact at the level of hundreds of hours.

Claims

1. A waste heat recovery and catalytic device for aviation exhaust gas based on TPMS structure, characterized in that, It includes a heat exchange core (2), which has a Gyroid-type TPMS topology; A micro-arc oxide ceramic layer is grown in situ on the surface of the heat exchange core (2); The surface of the micro-arc oxidation ceramic layer is deposited with a SiC-cordierite composite coating, which is formed by the deposition of mixed powder. The mixed powder contains 20% cordierite powder and 80% silicon carbide powder by mass, and additionally adds 15 wt% alumina powder of the total mass of the cordierite powder and the silicon carbide powder. The surface of the SiC-cordierite composite coating forms a porous alumina coating. The heat exchange core (2) with the alumina coating is impregnated with a catalyst precursor solution, subjected to static adsorption and calcination, and has a catalytic composition containing platinum, palladium and cerium, and the palladium is converted into highly active palladium oxide. The heat exchange core (2) has a unit cell size of 2.5–3.0 mm and a porosity of 65%–70%. The base material of the heat exchange core (2) is Al250C high-strength heat-resistant aluminum alloy powder; The surface of the heat exchange core (2) includes, from the inside to the outside, the following components: A 25μm thick micro-arc oxidation Al2O3 transition layer, a 50μm thick SiC-cordierite composite coating, a 20μm thick γ-Al2O3 impregnation layer, and a 10μm thick Pd-Ce catalyst layer.

2. The aviation exhaust waste heat recovery and catalytic device based on TPMS structure according to claim 1, characterized in that, The porous alumina coating is formed by impregnation and calcination of a carrier slurry containing pseudoboehmite sol and alumina powder. The specific preparation method of the pseudoboehmite sol is as follows: The dry powder of boehmite was dispersed in deionized water to prepare a suspension with a solid content of 10wt% to 15wt%. The suspension was kept at a constant temperature of 60-80°C in a water bath with stirring. Dilute nitric acid with a mass concentration of 5%-10% was added dropwise to adjust the pH value to 3.0-4.

0. The mixture was stirred continuously for 2-4 hours until the suspension was transformed into a translucent sol. The translucent sol was then allowed to stand for 12-24 hours.

3. The aviation exhaust waste heat recovery and catalytic device based on TPMS structure according to claim 1, characterized in that, In the catalytic components, the molar ratio of platinum, palladium, and cerium is 1:(8-9):(1-2).

4. The aviation exhaust waste heat recovery and catalytic device based on TPMS structure according to claim 1, characterized in that, It also includes a stainless steel shell (1) with a diffuser section. The heat exchange core (2) is assembled with the stainless steel shell (1). An all-metal toothed gasket is placed at the flange sealing surface and eight bolts are tightened in a cross sequence to 15 N·m to complete the split flange connection.

5. The aviation exhaust waste heat recovery and catalytic device based on TPMS structure according to claim 1, characterized in that, The heat exchange core (2) is prepared by a method comprising the following steps: Selective laser melting 3D printing technology was adopted, and high-strength heat-resistant aluminum alloy powder was used as raw material to print a heat exchange core (2) with a Gyroid type TPMS topology. The heat exchange core (2) was then cut, sandblasted, ultrasonically cleaned and dried to obtain a cleaned heat exchange core (2). The cleaned heat exchange core (2) is placed in a micro-arc oxidation electrolytic cell as an anode for constant current oxidation treatment, and a micro-arc oxidation ceramic layer is grown in situ on the surface of the cleaned heat exchange core (2). The mixed powder was sprayed onto the surface of the micro-arc oxidation ceramic layer using a supersonic cold spraying system, causing the powder to break down and combine at the micro-nano scale, depositing a SiC-cordierite composite coating to obtain a heat exchange core (2) with a SiC-cordierite composite coating. The heat exchange core (2) with SiC-cordierite composite coating was boiled with oxalic acid solution to remove surface impurities and improve roughness. After washing and drying, it was immersed in carrier slurry. After taking it out, the excess slurry was blown away with compressed air to ensure that the channels were unobstructed. Then it was dried and calcined to form a porous alumina wash coating on the surface of SiC-cordierite composite coating, thus obtaining the heat exchange core (2) with the wash coating. The heat exchange core (2) with the washing coating is immersed in a catalyst precursor solution containing palladium chloride, platinum chloride, cerium nitrate hexahydrate and urea. After static adsorption, it is taken out and dried, and then calcined in air atmosphere to completely convert palladium into highly active palladium oxide, thus obtaining the heat exchange core (2).

6. The aviation exhaust waste heat recovery and catalytic device based on TPMS structure according to claim 5, characterized in that, During the constant current oxidation process, an aqueous solution of sodium silicate with a concentration of 8–10 g / L was used as the base electrolyte. A square wave pulse mode with a pulse frequency of 300Hz and a duty cycle of 50% is used to control the current density at 3.5–4.0 A / dm². 2 Constant current oxidation is performed, and the voltage is gradually increased to 520-540V before stopping.

7. The aviation exhaust waste heat recovery and catalytic device based on TPMS structure according to claim 5, characterized in that, When using the supersonic cold spray system for spraying, the spraying gas of the supersonic cold spray system is controlled to be nitrogen, the spraying gas pressure is 4.5 to 5.0 MPa, and the temperature is 480 to 500°C.

8. The aviation exhaust waste heat recovery and catalytic device based on TPMS structure according to claim 5, characterized in that, During the formation of the porous alumina coating, a boiling treatment with a 20% oxalic acid solution was performed for 1 hour. The impregnated material is dried at 120°C and then calcined in a muffle furnace at 500°C for 4 hours.

9. The aviation exhaust waste heat recovery and catalytic device based on TPMS structure according to claim 5, characterized in that, When preparing the catalyst precursor solution, an appropriate amount of hydrochloric acid is added to aid dissolution, and the mass fraction of urea in the solution is controlled to be 0.5 wt%. After impregnation and adsorption, the product is dried at 120°C for 2 hours, and then calcined in an air atmosphere in a muffle furnace at 500-550°C for 4 hours.

Images