Gradient mould pressing design method of modified polyimide for aerospace environment
Through the gradient molding design of modified polyimide, the problem of insufficient insulation performance of traditional polyimide materials in extreme aerospace environments is solved, and the material's excellent insulation and deep charging resistance under high-energy radiation and temperature gradients is achieved, which improves the operating reliability of the spacecraft.
Patent Information
- Application Number
- CN202410213772.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-02-27
- Publication Date
- 2025-08-29
AI Technical Summary
Traditional polyimide materials have insufficient insulation performance in extreme aerospace environments such as high-energy radiation and temperature gradients, resulting in spacecraft failure.
The gradient molding design method of modified polyimide is adopted, and modified polyimide molding materials with excellent insulation, thermal conductivity and deep charging resistance are prepared by selecting appropriate fillers and process flows. Combined with simulation simulation technology and experimental testing, the gradient structure and performance of the material are optimized.
It improves the insulating performance and deep charging resistance of the spacecraft in extreme aerospace environments, reduces the risk of failure, and improves the comprehensive performance of the material.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a design method, in particular to a gradient molding design method of modified polyimide for aerospace environment. Background Art
[0002] As space missions evolve, the power requirements of spacecraft systems are steadily increasing. Increasing voltage, reducing current, and making systems lighter and more efficient have become increasingly important development directions. To meet the mission requirements of future spacecraft, systems are focusing on key challenges such as ultra-high voltage, high power, lightweight, high integration, long life, and high reliability. Even today, spacecraft power requirements continue to steadily increase. However, the extreme aerospace environment can cause electrification effects on spacecraft, leading to catastrophic failures and seriously threatening safe on-orbit operations. In 2007, NASA compiled data from several authoritative databases, revealing that of 326 satellite failures caused by the space environment, 54% were due to insulation failure caused by high-energy electrons induced by charging and discharging effects in materials. Therefore, the insulation properties of materials have become an essential consideration in spacecraft development.
[0003] From the perspective of comprehensive performance and engineering applications, polyimide is an insulating material that is extremely suitable for use in aerospace environments. Since the 1960s, polyimide (PI) has been widely used in the aerospace field for its excellent resistance to high and low temperatures and electrical insulation properties. In addition to its excellent insulation properties, it also has good mechanical properties. For example, the tensile strength of Kapton-type polyimide can reach more than 170 MPa. In addition, the long-term working temperature of polyimide can reach -200 to 300 ° C, and its thermal decomposition temperature is above 500 ° C. It is one of the most thermally stable varieties of polymers today. Most importantly, polyimide has high radiation resistance. It has a thermal decomposition temperature of 5×10 9 The strength retention rate after rad fast electron irradiation can reach 90%. However, in the complex aerospace environment, even if the dielectric properties of polyimide materials are relatively excellent, when they are used as insulating materials in spacecraft electrical transmission power components, they will be affected by the rapid changes and gradient distribution of high and low temperatures in space, high-energy charged particles and plasma environments. These external factors will eventually cause the polyimide insulating medium to undergo electrothermal aging, resulting in flashover, breakdown and other phenomena, further causing spacecraft failures. In order to ensure the operational reliability of aerospace electrical transmission equipment, both academia and industry hope to explore the insulation damage characteristics and failure mechanisms of polyimide in extreme aerospace environments, and to specifically regulate the comprehensive performance of polyimide composite materials through specific modification methods. Therefore, it is very necessary to focus on the failure conditions that occur when polyimide is used in aerospace, and to modify polyimide in order to reduce such problems.
[0004] In summary, in view of the insufficient insulation performance of traditional polyimide materials when operating in extreme aerospace environments such as high-energy radiation and temperature gradients in space, it is necessary to use material modification to improve the overall comprehensive performance of polyimide, provide aerospace equipment with a design scheme of modified polyimide gradient molded materials with highly targeted insulation properties, thermal properties and excellent resistance to deep charging suppression performance, and clarify the modification and regulation influence mechanism of polyimide composite materials in extreme aerospace environments, so as to further improve the operational reliability of on-orbit spacecraft. Summary of the Invention
[0005] The present invention provides a gradient molding design method for modified polyimide for aerospace environments, the purpose of which is to solve the problems described in the background art, such as the insufficient insulation performance of traditional polyimide materials when operating in extreme aerospace environments such as space high-energy radiation and temperature gradients. This method explores solutions to common problems in the molding process through multiple attempts under different formulations in the early stage. After analyzing the test results of modified polyimide molding samples, a molding preparation process based on raw material pretreatment, mixing, screening, loading into molds, sintering, pressing, machining and other processes is proposed. Subsequently, the formulation can be further improved to produce modified polyimide molding materials with the best comprehensive properties such as insulation, thermal conductivity, and resistance to deep charging in aerospace environments.
[0006] The purpose of the present invention can be achieved by the following formulation:
[0007] A gradient molding formula of modified polyimide for aerospace environment mainly includes YS20 polyimide molding powder, tetrapod-shaped zinc oxide whiskers, potassium hexatitanate whiskers, alkali-free glass fiber powder, and cage-type polysilsesquioxane (POSS). The procurement sources are YS20 fusible polyimide molding powder from Shanghai Plastics Research Institute Co., Ltd., tetrapod-shaped zinc oxide whiskers from Dongguan Zhangmutou Yongxin Plasticizing Additives Business Department, potassium hexatitanate whiskers from Shanghai Whisker Composite Materials Manufacturing Co., Ltd., alkali-free glass fiber powder from Nanjing Shirui Composite Materials Co., Ltd., and P815521 vinyl-POSS from Shanghai MacLean Biochemical Technology Co., Ltd.
[0008] Among them, four-needle zinc oxide whisker is a highly safe inorganic antibacterial material that does not require light. It is widely used in medical and health and industrial products, can achieve all-weather antibacterial properties, and has good application prospects in manned space projects; potassium titanate whisker was developed by the National Aeronautics and Space Administration (NASA) of the United States. It is a material with excellent thermal insulation properties, wear resistance, and impact resistance. After its surface is treated with Sb / SnO2 for conductivity, it can be used as a conductive material, or it can be composited with plastics to make conductive composite materials. It can also be used as an ion exchange material and adsorbent; graphite has the characteristics of self-lubrication, easy molding and processing, good thermal conductivity, thermal stability, and stable chemical properties. Points, widely used in the aerospace field, such as sealing materials, throat lining materials, brush materials, etc.; electron-conducting materials such as copper nanowires have the flexibility and processability of polymer materials and the conductivity of metal materials. They can be used to produce composite molded conductive materials with excellent electrical properties, flexibility and practicality, as well as composite molded heating materials with good photoelectric properties, thermal response and temperature stability; electron-capturing materials such as voltage stabilizers are mostly aromatic compounds. Their characteristics of capturing high-energy electrons and weakening electron energy reduce the impact of electrons on polymer molecular chains under strong electric fields, improve resistance to electrical treeing and short-time breakdown strength, and are non-consumable, and are used to suppress the degradation of electrical treeing in spacecraft insulation.
[0009] After multiple molding attempts under different ratios in the early stage, the following three modified polyimide molding formulas are now implemented:
[0010] Formula 1: 60% YS20 + 5% GF + 30% ZnO + 5% POSS
[0011] Formula 2: 60% YS20 + 5% GF + 30% KTiO3 + 5% POSS
[0012] Formula 3: 60% YS20 + 5% GF + 35% ZnO
[0013] The present invention also discloses a gradient molding process for preparing modified polyimides for aerospace environments, employing a micron-composite modification method among polyimide modification methods. YS20 molding powder is loaded into a mold in the required amount and molded at a set temperature and pressure. Simultaneously, the YS20 molding powder and filler are dry-mixed to obtain a moldable raw material, which is then loaded into a mold in the required amount and molded at a set temperature and pressure. Specifically, micron-sized materials such as semiconductors, inorganic particles, metals, and fibers are used as the dispersed phase and uniformly dispersed in a polyimide matrix using a corresponding preparation method, thereby forming a polyimide composite material containing micron-sized fillers. This method is referred to as micron-composite modification of polyimide. Compared to fillers of other sizes, micron-sized fillers exhibit unique size effects, macroscopic tunneling effects, and volume effects, which can have unexpected impacts on the electrical, thermal, and mechanical properties of the composite material, offering strong design potential. Research indicates that polyimide has excellent heat resistance and maintains its excellent performance even at high temperatures, making it highly suitable for the dispersion of micron-sized fillers. Compared to molecular structure modification, micron composite modification is more economical and suitable for industrial production. However, studies have shown that after micron composite modification of polyimide, the dispersion of micron-sized fillers inside it is still not ideal, and agglomeration effects will occur, which to some extent affects the further optimization and improvement of material properties. The specific molding preparation steps are as follows:
[0014] Step 1: Raw material pretreatment—Zinc oxide and YS20 were dried at 200°C for 2 h, and the zinc oxide was stirred and broken up.
[0015] Step 2: Mixing - Use a high-speed tissue blender to mix the powder at a speed of 10,000 rpm, mixing 100 grams at a time.
[0016] Step 3: Sieve - Pass the mixture through a 100-mesh sieve to remove obvious black lumps and lumps that are difficult to sieve out.
[0017] Step 4: Load into the mold - put the sifted powder into the mold, spread it evenly and then level it.
[0018] Step 5: Sintering - Place the mold in a sintering furnace, set the sintering temperature to 375°C, and sinter the mixture until it becomes molten.
[0019] Step 6: Pressing - Place the mold on the hydraulic press platform, set the pressure to 950kN, hold the pressure for 30min, press the mixture until it is completely set, take out the sample and cool it to room temperature for 1h before demolding.
[0020] Step 7: Machining - Use CNC lathe to machine according to the size requirements of the drawing sample.
[0021] During the molding process of modified polyimide, problems such as black spots and white blocks on the sample surface, white smoke and white powder seepage during the molding process repeatedly occurred. After several attempts, the causes and solutions of each problem are summarized as follows:
[0022] Problem 1: Small black lumps and spots appear on the surface. This is caused by the carbonization of the glass fiber during stirring due to the increased temperature, and some raw materials contain impurities. The solution is to stir the glass fiber separately and in mixed mixtures gently, dissipate heat intermittently, and replace the raw glass fiber with a very high purity.
[0023] Problem 2: White lumps appear on the surface. The raw materials tend to clump and stick to the screen when sieving. Zinc oxide is susceptible to moisture, so it clumps after mixing. The solution is to switch to a three-dimensional mixer, gently sieve to remove obvious lumps, replace the zinc oxide raw materials, and store them in a sealed container.
[0024] Issue 3: Slight white smoke and white powder seepage occur during stirring and compacting. Due to the current lack of advanced sintering technology, the sintering temperature cannot be lowered sufficiently, and the sintering time cannot be shortened sufficiently to allow the grains to continue growing within a certain range. However, this does not affect the final preparation result, so this issue will not be addressed for now.
[0025] Based on the common problems encountered during the molding process, further optimization can be made based on the existing preparation process, including innovations in the powder mixing and stirring processes, and improvements in the powder screening and sintering processes. Traditional mixers use a two-dimensional mixing method; this innovation uses a three-dimensional mixer, where the drum rotates at various angles and internal balls evenly mix the materials. Traditional mixers can easily produce black spots due to high-temperature carbonization when mixing some materials; this innovation incorporates additional auxiliary stirring mechanisms within the mixer, allowing for the addition of auxiliary stirring materials to aid in the mixing process.
[0026] Based on the above molding process, a single molding modified polyimide material was tried. After testing the basic properties, it was found that compared with pure polyimide, the electrical conductivity of the single modified sample was improved, the thermal conductivity increased, the tensile strength decreased, the bending strength increased, and the linear expansion coefficient decreased by one order of magnitude. It can be seen that its electrical, thermal, and mechanical properties are improved compared with pure polyimide. Therefore, the concept of functional gradient material (FGM) was introduced for gradient structure molding modification. When preparing double-layer gradient molding samples, the upper layer formula was 60% YS20 + 30% ZnO + 5% POSS + 5% GF, and the lower layer formula was 90% YS20 + 5% POSS + 5% GF. After sintering once and twice respectively, there was no obvious change in the two sintered layers. In the future, we can pay attention to the changes in the physical and chemical properties of each layer after different sintering times. When preparing three-layer gradient molded samples, the process recipes for each layer can be selected based on the principle of an A-rich layer, a transition layer, and a B-rich layer. Alternatively, while maintaining the same base material, different fillers with significantly different resistivities and other properties can be added. The final formulation selected was pure YS20 for the upper layer, 60% YS20 + 30% ZnO + 5% POSS + 5% GF for the middle layer, and 90% YS20 + 5% POSS + 5% GF for the lower layer. The three-layered sample exhibits good lamination, with clear and tightly bonded interfaces between the layers. Further research is underway, focusing on the following key areas: first, replacing fillers with improved insulation and thermal conductivity, adjusting filler type and content to create a variety of formulations; second, analyzing the effects of different sintering temperatures on the material's microstructure, morphology, and properties; and third, comparing the effects of vacuum hot pressing and pressureless sintering on these properties.
[0027] When designing polyimide gradient molded structures, simulation techniques can be combined with experimental preparation and testing to achieve comprehensive cross-scale design and deep-charge optimization of modified polyimide gradient molded structures. Specifically, a novel design method for polyimide gradient molded composites, utilizing software such as Materials Studio, LAMMPS, and Marc, is proposed. This method can assist in precise experimental design and produce gradient molded composites with ideal properties. Molecular simulation is also employed in the design process. A Marc finite element mesh model is established at the macroscale to numerically simulate multiple particles within the compact, as molecular-scale material simulation is not feasible. The finite element method can be used to analyze the relative density and equivalent Mises stress distribution of the compact, while the discrete element coupling method is used to analyze the changing interparticle force chain structure and the influence of the friction coefficient. This aims to explore the compaction densification process, observing the flow patterns and relative density distribution of powder compaction at both the macroscale and the microscale. Ultimately, simulation techniques can be combined with experimental preparation and testing to achieve comprehensive cross-scale design and deep-charge optimization of modified polyimide gradient molded structures.
[0028] The above simulation and experimental processes incorporate research on the modification and regulation of polyimide gradient molded materials. When designing material modifications, a comprehensive modification and regulation approach is implemented, focusing on radiation-resistant charging modification, supplemented by anti-corona modification, anti-proton oxygen modification, and high thermal conductivity modification. The electric field distortion generated by high-energy electrons is studied through experimental and simulation methods. However, temperature can have a significant impact on the polyimide dielectric, such as affecting the material's conductivity distribution, which in turn triggers new charging characteristics. Therefore, it is necessary to conduct deep charging characteristics research on modified polyimide molded materials under temperature gradients. Simultaneously, considering deep charging characteristics analysis, the performance of polyimide is regulated to adapt it to the extreme environment of space. Insulation is then rationally configured in space based on the dielectric performance requirements of different parts of the gradient molded material. Therefore, the impact of particle radiation on electric field distortion should be considered, and the superposition of electric field distortion caused by high-energy particles should be considered to avoid triggering new insulation problems.
[0029] Finally, the comprehensive performance of polyimide gradient molding materials was evaluated, mainly including two categories: interface charge regulation based on surface treatment, structural optimization and composite gradient electric field regulation. There are three ways to regulate the interface charge based on surface treatment, all of which can provide ideas for the geometric structure design of molded materials, but the applicability of surface coatings for new gradient materials needs further exploration. The first way is uniform coating regulation, which has the function of promoting charge dissipation, but its effect on electric field regulation is still limited; the second way is surface gradient coating regulation, which can only achieve single gradient regulation, and the effect of the presence of particles on interface insulation is not clear; the third way is fluorinated coating regulation, which effectively regulates the interface charge, but based on the existing fluorination technology, the method of introducing fluorinated groups is relatively random and the stability is not high. There are two ways to optimize the structure and regulate the composite gradient electric field, neither of which comprehensively considers the influence of nanocomponents and the role of surface coatings. It is necessary to carry out integrated design of composite gradient of surface coating and geometric structure. The first method is to regulate the bulk gradient insulation. The gradient distribution of material components places high demands on the molding process, and the effect of changes in the filler ratio on the overall mechanical properties of the molded material also requires further analysis. The second method is to regulate the bulk insulation of low bulk conductivity. Whether the method of nano-doping to improve bulk conductivity is applicable to gradient molded materials based on the polyimide system remains to be verified. In addition, in order to meet the development needs of spacecraft, polyimide needs to be composite-modified to improve its thermal conductivity. Currently, a preparation method that adds high thermal conductivity fillers to the polyimide matrix is commonly used to obtain polyimide composite materials with high thermal conductivity coefficients. Commonly used high thermal conductivity fillers include carbon nanotubes, graphene, boron nitride, etc. Therefore, the present invention will focus on the structural optimization of gradient materials, and the comprehensive performance of molded composite materials can be synergistically regulated through the polyimide gradient structure.
[0030] Beneficial effects
[0031] (1) Establish a gradient compression cross-scale model to study deep charging characteristics
[0032] A cross-scale simulation model of polyimide gradient molded materials was established to analyze interlayer interface effects and their influencing factors. The deep charging characteristics of the molded materials were studied and optimized, and an optimization scheme for suppressing deep charging of polyimide gradient molded materials in aerospace environments was proposed.
[0033] (2) Innovate and improve the process flow of gradient molding materials
[0034] Improve the hierarchical scheme of modified polyimide gradient molding, analyze the role of traditional and new fillers and their content in composite materials, select the best process suitable for the current sample preparation formula, and form complete formula sample preparation specifications and process preparation specifications.
[0035] (3) Analyze the influence of the interlayer interface and propose a performance optimization solution for gradient molded materials
[0036] The mechanical behavior and electrical properties of the interface between the layers of the gradient molded material are studied, and its electrical, thermal, mechanical and other physical and chemical properties are verified and evaluated. Finally, the formula of the modified polyimide gradient molded material with the best comprehensive performance is determined. BRIEF DESCRIPTION OF THE DRAWINGS
[0037] Figure 1 Schematic diagram of the raw material pretreatment steps in the molding process;
[0038] Figure 2 Schematic diagram of the mixing steps in the molding process;
[0039] Figure 3 Schematic diagram of the screening step in the molding process;
[0040] Figure 4 This is a schematic diagram of the steps of inserting the mold in the molding process;
[0041] Figure 5 Schematic diagram of the sintering step in the molding process;
[0042] Figure 6 Schematic diagram of the pressing steps in the molding process;
[0043] Figure 7 Schematic diagram of the machining steps in the molding process;
[0044] Figure 8 This is a schematic diagram of the innovative three-dimensional mixer;
[0045] Figure 9 Schematic diagram of double-layer and triple-layer gradient molding samples;
[0046] Figure 10 Schematic diagram of cross-scale simulation and interface impact analysis;
[0047] Figure 11It is a schematic diagram of the molded gradient level scheme;
[0048] Figure 12 Schematic diagram of the comprehensive performance of polyimide gradient molding materials. DETAILED DESCRIPTION
[0049] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.
[0050] The gradient molding design method of modified polyimide for aerospace environment includes the following steps:
[0051] Step 1: Polyimide gradient molding cross-scale design and deep charging characteristics research
[0052] ① Cross-scale simulation and interface impact analysis of the model during gradient molding
[0053] This project not only achieves gradient structural distribution in space, but also exhibits gradient changes in properties such as conductivity at vertical height. When simulating gradient models across scales, cell-type and interface-type gradient models can be established in MS at the molecular scale, and grid-type gradient models can be established in Marc at the macroscopic scale to simulate real molded materials. Based on this, the interface conditions of gradient molded materials are analyzed, and the structure and composition of the interlayer interfaces of each gradient model are analyzed to explore the factors that significantly change the interface morphology and performance. After establishing gradient models of cell-type and interface-type MS models and grid-type Marc models, the interface structure and composition, the main influencing factors of interface performance, etc. are clarified to guide the design of composite molded models with conductivity gradient distribution and subsequent preparation processes.
[0054] ② Research and optimization design of deep charging characteristics of polyimide gradient molding materials
[0055] When studying deep-charge characteristics, the gradient molded material is used as the model basis, and the effects of local reinforcement and double-layer shielding are analyzed to optimize the shielding design. The effects of groove structure and embedded structure are analyzed to optimize the structure design, thereby effectively reducing the electric field distortion at the triple junction. When optimizing the anti-deep charging design, the gradient molded material is used as the model basis, and a high-energy electron deposition model is established and the discharge process of the deposited electrons is simulated. This will clarify the optimization direction of basic characteristics such as shielding material, shielding thickness, dielectric temperature, and baffle parameters, and guide the development of an optimization plan for suppressing deep charging with polyimide gradient molded materials in aerospace environments.
[0056] Step 2: Process innovation and improvement of polyimide gradient molding
[0057] ① Gradient molding level solution
[0058] The next steps are mainly divided into two categories: traditional solutions and new solutions. Traditional solutions include adding fillers with greatly different properties such as conductivity and adding the same fillers at different contents. New solutions include adding electron-conducting materials such as copper nanowires and electron-capturing materials such as voltage stabilizers. Among them, four-needle zinc oxide whiskers are a highly safe inorganic antibacterial material that does not require light. They are widely used in medical and health care and industrial products. They can achieve all-weather antibacterial properties and have good application prospects in manned space projects. Potassium titanate whiskers were developed by NASA and are a material with excellent thermal insulation, wear resistance, and impact resistance. After the surface is treated with Sb / SnO2 for conductivity, it can be used as a conductive material, or compounded with plastics to make conductive composite materials. It can also be used as an ion exchange material and adsorbent. Graphite has the characteristics of self-lubricating properties, easy molding and processing, good thermal conductivity, thermal stability, and stable chemical properties. It is widely used in the aerospace field, such as sealing materials, throat lining materials, brush materials, etc.; electron-conducting materials such as copper nanowires have the flexibility and processability of polymer materials and the conductivity of metal materials, and can be used to produce composite molded conductive materials with excellent electrical properties, flexibility and practicality, as well as composite molded heating materials with good photoelectric properties, thermal response capabilities and temperature stability; electron-capturing materials such as voltage stabilizers are mostly aromatic compounds, and their characteristics of capturing high-energy electrons and weakening electron energy reduce the impact of electrons on polymer molecular chains under strong electric fields, thereby improving resistance to electrical treeing and short-time breakdown strength, and are non-consumable, and are used to suppress the degradation of electrical treeing in spacecraft insulation.
[0059] ② Gradient molding process selection
[0060] The molding process selection for different types of materials is also different. Therefore, the process route suitable for modified polyimide gradient molded composite materials should be selected after multiple attempts. The main considerations include layered stacking or layer-by-layer molding method, sample size (thickness of each layer), vacuum hot pressing sintering or normal pressure sintering, pressing pressure and time, sintering temperature and time, etc. The final process also needs to be adjusted in detail according to the sample test results.
[0061] a. When choosing layered stacking or layer-by-layer molding, the base material and filler are both micron-sized powders. When stacked vertically, the upper layer powder easily penetrates into the lower layer, resulting in a blurred interface between layers. When molding layer by layer, there is no obvious appearance change after multiple sintering layers. The differentiation of the mixing formula of each layer is controlled to produce a clear interface between layers. Therefore, the layer-by-layer molding method is selected.
[0062] b. When selecting the sample size, there are no specific requirements for the length and width of the sample cross section; instead, the thickness of each layer should be the primary focus. For a single-layer molded polyimide sample, a thickness of 4-5mm is sufficient to ensure sample integrity and facilitate subsequent testing of mechanical properties, impact strength, and other performance. Therefore, based on actual spacecraft requirements, considering the total thickness limit of the insulation baffle and the minimum thickness requirement for each layer, a three-layer, 3mm thick layer was temporarily selected for this gradient sample, for a total thickness of 9mm.
[0063] c. When choosing between vacuum hot pressing sintering or normal pressure sintering, vacuum hot pressing sintering is performed first and then pressed. The entire sample is in a molten state before pressing, and the upper layer with higher density is easy to penetrate into the lower layer with lower density, affecting the interface state; normal pressure sintering is performed first and then sintered, which effectively avoids the infiltration problem, and normal pressure is easier to achieve than vacuum environment, so normal pressure sintering is selected.
[0064] d. When selecting the pressing pressure and time, lower pressure or shorter pressing time during sample preparation will result in poor powder compatibility and loose bonding in the sample preparation, affecting the test results of subsequent performance. After multiple attempts, the selected pressing pressure was about 500kg / cm^2 and the pressing time was at least 30 minutes.
[0065] e. When selecting the sintering temperature and time, if the temperature is too high or the sintering time is too long, it will affect the sample organization, morphology and performance, such as overall deformation of the sample, exceeding the melting point of a certain raw material and causing changes in the composition. After many attempts, the sintering temperature of about 370°C and the time of 2 hours are selected as the best (suitable for the current sample size).
[0066] In addition, attention should also be paid to the final heat treatment step. During machining, the sample groove is prone to deformation under stress, and the corresponding gradient can be flexibly changed with the height of the sample.
[0067] Step 3: Study on the interface characteristics of polyimide gradient molding materials
[0068] When studying the interfacial properties of polyimide gradient molded materials, the conditions that create the interface are first explored. Once the interface is created, the effects of large charge accumulation and strong deep charging are analyzed. This facilitates observation of interface strength and allows for probe or tomographic observation of the interface. Interface-specific research methods are employed to analyze the interface and the role of dopants in interfacial properties, such as improving interfacial compatibility, to better guide the comprehensive performance and verification evaluation of gradient molded materials. When analyzing the accumulation of large charges, simulation and experimentation are combined to consider increasing the number of layers to offset interfacial effects. This can be addressed through improved process flow and formulation.
[0069] When analyzing interface properties, the key lies in interface strength and toughness. Using interlayer bonding strength as an assessment metric, mechanical parameters such as interfacial shear strength, flexural strength, tensile strength, and impact toughness are analyzed to optimize the design of gradient structural materials. At the same time, attention is paid to the electrical properties of the interface. Space charge measurements using the PEA method are used to determine the dielectric space charge characteristics. The electric field distribution and space charge transport characteristics of the insulating interface are analyzed to summarize charge control methods and suppression mechanisms. Using this as a support, the comprehensive performance of interlayer interfaces can be studied, focusing on properties such as interfacial energy / interfacial strength, interlayer morphology, electrical conductivity, thermal expansion coefficient, and bonding strength. The influence of factors such as molding temperature and speed, molding pressure, friction coefficient, mold shape and size, and filler aspect ratio are also explored. The parameter ranges can be adjusted accordingly, providing feedback to guide the design of gradient structural materials.
[0070] Step 4: Comprehensive performance assessment of polyimide gradient molding materials
[0071] The comprehensive performance of polyimide gradient molded materials mainly includes electron radiation, high-energy electron beam impact, material outgassing, partial discharge, surface flashover, mechanical properties, thermal properties, and deep charging suppression. Electron radiation performance is used to measure the amount of electron radiation within the system measurement area; high-energy electron beam impact performance is used to measure the micro-region composition and morphology of the material when the radiation and electrons are excited; material outgassing performance is used to measure the outgassing level and gas composition; partial discharge performance is used to measure the ability of localized discharge in the insulator; surface flashover performance is used to measure the ability of penetrating discharge to occur along the insulation surface; mechanical properties mainly measure tensile strength, flexural strength, and linear expansion coefficient; thermal properties mainly measure thermal conductivity; deep charging suppression performance is used to measure the suppression mechanism of high-energy electron deep charging experiments. Through the comprehensive assessment and evaluation of the above properties, the goal is to find the modified polyimide gradient molded material with the best comprehensive performance or its process and formulation rules.
[0072] The present invention first introduces the concept of functional gradient material (FGM) to carry out gradient structure molding modification, and by constructing a non-uniform distribution structure of polyimide material, regulates the electrical conductivity, further improves the characteristics of deep charging suppression, radiation charging resistance, corona resistance and atomic oxygen erosion resistance, so as to better adapt to the space environment, and aims to improve insulation, optimize thermal conductivity and control internal electric field and other properties. Secondly, the present invention carries out targeted design regulation and improvement on the insulation performance of polyimide in terms of insulation improvement, and carries out composite modification on polyimide in terms of thermal conductivity optimization to improve its thermal conductivity, which is achieved by a preparation method of adding high thermal conductivity fillers to the polyimide matrix, and at the same time realizes volume gradient regulation in terms of controlling the internal electric field, fully suppressing charge accumulation and deep charging. Ultimately, the problems that the current gradient molding materials still face, such as high surface energy, difficulty in preparation, easy agglomeration, and poor long-term stability of the dispersed system, are solved, and a gradient molding method for modifying polyimide is proposed.
[0073] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions merely illustrate the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.
Claims
1. A gradient molding design method for modified polyimide for aerospace environments, including cross-scale design and deep charging characteristics of polyimide gradient molding, process innovation and improvement methods for polyimide gradient molding, interface characteristics research and comprehensive performance assessment of polyimide gradient molding materials, characterized by: By using material modification to improve the overall performance of polyimide, a design scheme for modified polyimide gradient molded materials with highly targeted insulation, thermal and deep charging suppression properties is provided for aerospace equipment. The modification and regulation mechanism of polyimide composite materials in extreme aerospace environments is clarified to further improve the operational reliability of on-orbit spacecraft.
2. The gradient molding design method of modified polyimide for aerospace environment according to claim 1, characterized by: When designing the polyimide gradient molded structure, the most mature lamination method is used to prepare the gradient material. Considering the large difference in density and melting point between the raw materials and each layer, the simultaneous molding of each layer after stacking will produce a fuzzy interlayer interface, and the accumulation of interfacial charge will aggravate the impact. After the composite pressed compact is sintered, the layer-by-layer molding method is given priority.
3. The gradient molding design method of modified polyimide for aerospace environment according to claim 1, characterized by: When studying the modification and regulation of polyimide gradient molded materials, radiation-resistant charging modification and regulation is the main direction to be considered in the modification design of polyimide gradient molded materials for high-voltage and high-power electrical transmission in spacecraft. Effects such as corona discharge, atomic oxygen corrosion, and thermal decomposition of materials caused by extreme temperatures in space will also affect its charging effect; temperature gradients will affect the conductivity distribution, thereby triggering new charging characteristics. At present, it is necessary to carry out deep charging characteristics research of composite materials under temperature gradients.
4. The gradient molding design method of modified polyimide for aerospace environment according to claim 1, characterized by: When evaluating the comprehensive performance of polyimide gradient molded materials, it was found that polyimide's high and low temperature resistance and thermal stability are very ideal, but its heat dissipation performance is poor. Therefore, to meet the development needs of spacecraft, polyimide needs to be composite modified to improve its thermal conductivity. At the same time, the control of interfacial charge based on surface treatment provides ideas for the geometric structure design of molded materials and further explores its applicability as a surface coating for new gradient materials. Optimize the structure and regulate the composite gradient electric field, comprehensively consider the influence of nanocomponents and the effect of surface coating, and carry out integrated design of surface coating and geometric structure composite gradient.
5. The gradient molding design method of modified polyimide for aerospace environment according to claim 1, characterized by: When studying the deep charging characteristics, the suppression of deep charging is taken into consideration, the electron migration mechanism and the modification direction of radiation-resistant charging polyimide are clarified, the performance of polyimide is regulated to adapt it to the extreme environment of space, and according to the requirements of dielectric properties of different parts of gradient molded materials, insulation is rationally configured in space. Focusing on the research of polyimide gradient molded materials and high-energy particle charging, it has a strong guiding significance for subsequent related research.
6. The gradient molding design method of modified polyimide for aerospace environment according to claim 2, characterized by: By using a variety of simulation software, a design concept for a new type of polyimide gradient molded composite material was proposed. The flow law and relative density distribution of powder pressing were observed from the macro and micro scales, and a gradient molded composite material with ideal performance was produced. This can assist in precise experimental design and use molecular simulation methods for modified design.
7. The gradient molding design method of modified polyimide for aerospace environment according to claim 3, characterized by: Radiation-resistant charging modification and regulation, corona resistance modification and regulation, anti-proton oxygen modification and regulation, and high thermal conductivity modification and regulation are taken as the main modification directions for insulation optimization of polyimide gradient molded materials in complex aerospace environments. Aiming at the deep charging effect, the electric field distortion generated by high-energy electrons is studied through experimental and simulation methods, and the internal thermal simulation of the material and the deep charging characteristics under temperature gradient are studied to conduct comprehensive modification and regulation.
8. The gradient molding design method of modified polyimide for aerospace environment according to claim 4, characterized by: Interface charge regulation based on surface treatment adopts coating regulation, surface gradient coating regulation and fluorination coating regulation methods. Structural optimization and composite gradient electric field regulation adopt bulk gradient insulation regulation and low bulk conductivity bulk insulation regulation methods. In addition, high thermal conductivity fillers are added to the polyimide matrix to obtain a polyimide composite material with high thermal conductivity.
9. A gradient molding design method for modified polyimide for aerospace environments, comprising the gradient molding research approach for modified polyimide for aerospace environments as described in claim 1, characterized by: A comprehensive design approach encompasses three key aspects: material simulation design, gradient molding modification, and deep-charge suppression. The goal is to develop a polyimide gradient molding material with ideal performance, thereby improving the reliability of spacecraft and satellites. The comprehensive design of the gradient molding material includes the following steps: The molding process of the polyimide modified material includes the following steps: Step 1: Raw material pretreatment: ZnO and YS20 were dried at 200°C for 2 h, and the ZnO was stirred and dispersed; Step 2: Mixing - Use a high-speed tissue blender to mix the powder at a speed of 10,000 rpm, mixing 100 grams of material at a time; Step 3: Sieve - Pass the mixture through a 100-mesh sieve to remove obvious black lumps and lumps that are difficult to sieve out; Step 4: Loading into the mold - Load the sifted powder into the mold, spread it evenly and flatten it; Step 5: Sintering - Place the mold in a sintering furnace, set the sintering temperature to 375°C, and sinter the mixture until it becomes molten; Step 6: Pressing - Place the mold on the hydraulic press platform, set the pressure to 950kN, hold the pressure for 30 minutes, press the mixture until it is completely formed, take out the sample and cool it to room temperature for 1 hour before demolding; Step 7: Machining - Use CNC lathe to machine according to the size requirements of the drawing sample. The gradient molding design method of the modified polyimide comprises the following steps: Step 1: Study the cross-scale design and deep charging characteristics of polyimide gradient molding. After establishing the gradient models of cell-type and interface-type MS models and grid-type Marc models, clarify the interface structure and composition, the main influencing factors of interface performance, etc., and guide the design of the composite gradient molding model with conductivity gradient distribution and the subsequent preparation process; study the deep charging characteristics and optimize the anti-deep charging design, and guide the proposal of the optimization plan for inhibiting deep charging of polyimide gradient molding materials in aerospace environment. Step 2: Process innovation and improvement methods for polyimide gradient molding. The schemes are mainly divided into two categories: traditional schemes and new schemes. Traditional schemes include adding fillers with large differences in properties such as conductivity and adding the same fillers at different contents. New schemes include adding electron-conducting materials such as copper nanowires and adding electron-trapping materials such as voltage stabilizers. The molding process selection for different types of materials is also different. Therefore, the process route suitable for modified polyimide gradient molded composite materials should be selected after multiple attempts. The main considerations include layered stacking or layer-by-layer molding method, sample size (thickness of each layer), vacuum hot pressing sintering or normal pressure sintering, pressing pressure and time, sintering temperature and time, etc. The final process also needs to be adjusted in detail according to the test results of the sample. Step 3: Study the interface properties of polyimide gradient molded materials. Determine the idea of studying the interface properties of polyimide gradient molded materials, analyze mechanical parameters such as interface shear strength, pay attention to the electrical properties of the interface, analyze the electric field distribution and spatial charge transport characteristics of the insulating interface, and use this as a support to study the comprehensive performance of the interlayer interface. At the same time, explore the influence of factors such as molding temperature and speed, molding pressure, etc., and adjust the range of each parameter accordingly to provide feedback to guide the design of gradient structure materials. Step 4: Comprehensive performance assessment of polyimide gradient molded materials. The comprehensive performance of polyimide gradient molded materials mainly includes electron radiation, high-energy electron beam impact, material outgassing, partial discharge, surface flashover, mechanical properties, thermal properties and deep charging suppression. Through comprehensive assessment and evaluation of the above properties, the aim is to find the modified polyimide gradient molded material with the best comprehensive performance and its process or formulation rules. The goal of this invention is to obtain a modified polyimide molded material that meets the requirements for spacecraft insulation in aerospace environments. The key problem to be solved is the cross-scale analysis and deep charging optimization design of modified gradient molded materials with optimal comprehensive performance.