Extreme cold weather seriously harms human thermoregulatory system,necessitating high-performance insulating garments to maintain body temperature.However,as the core insulating layer,advanced fibrous materials always...Extreme cold weather seriously harms human thermoregulatory system,necessitating high-performance insulating garments to maintain body temperature.However,as the core insulating layer,advanced fibrous materials always struggle to balance mechanical properties and thermal insulation,resulting in their inability to meet the demands for both washing resistance and personal protection.Herein,inspired by the natural spring-like structures of cucumber tendrils,a superelastic and washable micro/nanofibrous sponge(MNFS)based on biomimetic helical fibers is directly prepared utilizing multiple-jet electrospinning technology for high-performance thermal insulation.By regulating the conductivity of polyvinylidene fluoride solution,multiple-jet ejection and multiple-stage whipping of jets are achieved,and further control of phase separation rates enables the rapid solidification of jets to form spring-like helical fibers,which are directly entangled to assemble MNFS.The resulting MNFS exhibits superelasticity that can withstand large tensile strain(200%),1000 cyclic tensile or compression deformations,and retain good resilience even in liquid nitrogen(-196℃).Furthermore,the MNFS shows efficient thermal insulation with low thermal conductivity(24.85 mW m^(-1)K^(-1)),close to the value of dry air,and remains structural stability even after cyclic washing.This work offers new possibilities for advanced fibrous sponges in transportation,environmental,and energy applications.展开更多
Thermal protection systems are very essential for high temperature thermal conductivity measurement system to reduce the heat loss to environment at the range of 600-1800 K. A compound multi-layer insulations structur...Thermal protection systems are very essential for high temperature thermal conductivity measurement system to reduce the heat loss to environment at the range of 600-1800 K. A compound multi-layer insulations structure which composed of inner carbon fibrous materials and outer alternately arranged alumina fibrous materials and high reflectivity foils is proposed for use in high temperature cylinder thermal protection systems. A coupled conductive and radiation governing equations is presented for heat transfer analysis of the structure. The finite volume method and the discrete ordinate method are used to solve the goveming equations. The optimization structure of the compound multi-layer insulations is investigated by considering the pressure of the gas, the density of the carbon fibrous materials, the density of the alumina fibrous materials, the number of reflective foil layers and the emissivity of reflective foils. The results show that the compound structure has the best thermal insulation performance when the pressure of the gas is below 0.01 kPa, the density of carbon fibrous materials is 180 kg m^-3, the density of alumina fibrous materials is 256 kg m^-3 and the number of reflective foil layers is 39. In addition, the thermal insulation performance is much better when the emissivity of reflective foils is lower.展开更多
At present,the emerging solid-phase friction-based additive manufacturing technology,including friction rolling additive man-ufacturing(FRAM),can only manufacture simple single-pass components.In this study,multi-laye...At present,the emerging solid-phase friction-based additive manufacturing technology,including friction rolling additive man-ufacturing(FRAM),can only manufacture simple single-pass components.In this study,multi-layer multi-pass FRAM-deposited alumin-um alloy samples were successfully prepared using a non-shoulder tool head.The material flow behavior and microstructure of the over-lapped zone between adjacent layers and passes during multi-layer multi-pass FRAM deposition were studied using the hybrid 6061 and 5052 aluminum alloys.The results showed that a mechanical interlocking structure was formed between the adjacent layers and the adja-cent passes in the overlapped center area.Repeated friction and rolling of the tool head led to different degrees of lateral flow and plastic deformation of the materials in the overlapped zone,which made the recrystallization degree in the left and right edge zones of the over-lapped zone the highest,followed by the overlapped center zone and the non-overlapped zone.The tensile strength of the overlapped zone exceeded 90%of that of the single-pass deposition sample.It is proved that although there are uneven grooves on the surface of the over-lapping area during multi-layer and multi-pass deposition,they can be filled by the flow of materials during the deposition of the next lay-er,thus ensuring the dense microstructure and excellent mechanical properties of the overlapping area.The multi-layer multi-pass FRAM deposition overcomes the limitation of deposition width and lays the foundation for the future deposition of large-scale high-performance components.展开更多
In the present work,by virtue of the synergistic and independent effects of Janus structure,an asymmetric nickel-chain/multiwall carbon nanotube/polyimide(Ni/MWCNTs/PI)composite foam with absorption-dominated electrom...In the present work,by virtue of the synergistic and independent effects of Janus structure,an asymmetric nickel-chain/multiwall carbon nanotube/polyimide(Ni/MWCNTs/PI)composite foam with absorption-dominated electromagnetic interference(EMI)shielding and thermal insulation performances was successfully fabricated through an ordered casting and directional freeze-drying strategy.Water-soluble polyamic acid(PAA)was chosen to match the oriented freeze-drying method to acquire oriented pores,and the thermal imidization process from PAA to PI exactly eliminated the interface of the multilayered structure.By controlling the electro-magnetic gradient and propagation path of the incident microwaves in the MWCNT/PI and Ni/PI layers,the PI composite foam exhibited an efficient EMI SE of 55.8 dB in the X-band with extremely low reflection characteristics(R=0.22).The asymmetric conductive net-work also greatly preserved the thermal insulation properties of PI.The thermal conductivity(TC)of the Ni/MWCNT/PI composite foam was as low as 0.032 W/(m K).In addition,owing to the elimination of MWCNT/PI and Ni/PI interfaces during the thermal imidization process,the composite foam showed satisfactory compressive strength.The fabricated PI composite foam could provide reliable electromagnetic protection in complex applications and withstand high temperatures,which has great potential in cuttingedge applications such as advanced aircraft.展开更多
Due to excellent thermal insulation performance at room temperature and ultralow density,silica aero-gels are candidates for thermal insulation.However,at high temperatures,the thermal insulation prop-erty of silica a...Due to excellent thermal insulation performance at room temperature and ultralow density,silica aero-gels are candidates for thermal insulation.However,at high temperatures,the thermal insulation prop-erty of silica aerogels decreased greatly caused by transparency to heat radiation.Opacifiers introduced into silica sol can block heat radiation yet destroy the uniformity of aerogels.Herein,we designed and prepared a silica aerogel composite with oriented and layered silica fibers(SFs),SiC nanowires(SiC_(NWs)),and silica aerogels,which were prepared by papermaking,chemical vapor infiltration(CVI),and sol-gel respectively.Firstly,oriented and layered SFs made still air a wall to block heat transfer by the solid phase.Secondly,SiC_(NWs) were grown in situ on the surface of SFs evenly to weave into the network,and the network reduced the gaseous thermal conductivity by dividing cracks in SFs/SiC_(NWs)/SA.Thirdly,SiC_(NWs) weakened the heat transfer by radiation at high temperatures.Therefore,SFs/SiC_(NWs)/SA presented remarkable thermal insulation(0.017 W(m K)^(-1) at 25℃,0.0287 W(m K)^(-1) at 500℃,and 0.094 W(m K)^(-1) at 1000℃).Besides,SFs/SiC_(NWs)/SA exhibited remarkable thermal stability(no size transform after being heat treated at 1000℃ for 1800 s)and tensile strength(0.75 MPa).These integrated properties made SFs/SiC_(NWs)/SA a promising candidate for highly efficient thermal insulators.展开更多
Thermally conductive papers with electrical insulation and mechanical robustness are essential for efficient thermal management in modern electronics.In this study,we introduced a metal ion-assisted interfacial crossl...Thermally conductive papers with electrical insulation and mechanical robustness are essential for efficient thermal management in modern electronics.In this study,we introduced a metal ion-assisted interfacial crosslinking strategy to strengthen sugarfunctionalized graphene fluoride(SGF)and cellulose nanofibers(CNF)by hydrogen bonding and metal ion crosslinking that leads to simultaneous enhancements in thermal conductivity and mechanical properties.The facile sugarassisted ball-milling exfoliation method was developed to achieve the exfoliation of graphite fluoride and hydroxyl group functionalization on the surface of graphene fluoride.Thanks to the good dispersibility of the SGF sheets in water,the flexible SGF/CNF composite papers with hydrogen bonding were prepared via vacuum-assisted filtration.We introduced hydrogen bonding and metal ion crosslinking into SGF/CNF papers to obtain densely packed composite papers.Ca^(2+)or Al^(3+)ion-crosslinked SGF/CNF papers exhibited superior thermal and mechanical properties owing to hydrogen bonding and metal ion crosslinking.SGF/CNF-Ca^(2+)and SGF/CNF-Al^(3+)papers at 50 wt%of SGF yield in-plane thermal conductivities of 72.93 and 75.02 W m^(-1) K^(-1),and tensile strengths of 121.5 and 135.7 MPa,respectively.A thermal percolation value was observed at 12.6 vol%of SGF filler content.In addition,the SGF/CNF papers exhibited electrical insulation properties.These remarkable characteristics of the metal ion-crosslinked SGF/CNF papers are attributed to the densely packed structures caused by the strong interfacial interactions from hydrogen bonding as well as metal ion-crosslinking that could promote phonon transport.High-performance metal ion-crosslinked SGF/CNF papers with these fascinating advantages offer great potential for the thermal management of flexible electronics.展开更多
BACKGROUND Elderly patients undergoing laparoscopic colorectal cancer surgery are at high risk for hypothermia-related complications.This study explores the efficacy of periop-erative composite insulation intervention...BACKGROUND Elderly patients undergoing laparoscopic colorectal cancer surgery are at high risk for hypothermia-related complications.This study explores the efficacy of periop-erative composite insulation interventions in maintaining normothermia and reducing postoperative risks in this vulnerable group.AIM To evaluate the efficacy of perioperative composite insulation in older patients undergoing colorectal cancer surgery.METHODS We selected 100 older patients who underwent laparoscopic surgery for colorectal cancer at Huzhou Central Hospital from September 2023 to April 2024.Using a random number table,patients were divided into a control group and inter-vention group of 50 patients each.After returning to the regular ward,the con-ventional group received traditional insulation intervention measures,while the intervention group received composite insulation nursing intervention.We ob-served and recorded postoperative blood pressure and heart rate changes,as well as postoperative anesthesia recovery time and incidence of complications.RESULTS The statistical results showed significant differences(P<0.05)in heart rate changes and systolic blood pressure between the two groups.There was a sig-nificant change in heart rate between the groups immediately after surgery and at 15 and 30 minutes after surgery(P<0.05).The heart rate and systolic blood pressure of the intervention group were significantly lower than those of the control group at 15 and 30 minutes after surgery(P<0.05).The rewarming time of the intervention group was shorter than that of the control group,and the overall incidence of postoperative complications was significantly lower than that of the control group(P<0.05).CONCLUSION For elderly patients undergoing laparoscopic colorectal cancer surgery,a composite insulation intervention during the perioperative period can maintain body temperature,reduce postoperative stress,and significantly reduce the incidence of hypothermia and related complications.展开更多
A multi-layer interconnection structure is a basic component of electronic devices, and printing of the multi-layer interconnection structure is the key process in printed electronics. In this work, electrohydrodynami...A multi-layer interconnection structure is a basic component of electronic devices, and printing of the multi-layer interconnection structure is the key process in printed electronics. In this work, electrohydrodynamic direct-writing （EDW） is utilized to print the conductor-insulator--conductor multi-layer ~nterconne^ction structure. Silver ink is chosen to print the conductor pattern, and a polyvinylpyrrolidone （PVP） solution is util^zed to f^bricate the insulator layer between the bottom and top conductor patterns. The influences of EDW process parameters on the line width of the printed conductor and insulator patterns are studied systematically. The obtained ~es^l~s show that the line width of the printed structure increases with the increase of the flow rate, but decreases with the increase of applied voltage and PVP content in the solution. The average resistivity values of the bottom and top silver conductor tracks are determined to be 1.34 × 10-7 Ω.m and 1.39×10-7 Ω.m, respectively. The printed PVP layer between the two conductor tracks is well insulated, which can meet the insulation requirement of the electronic devices. This study offers an alternative, fast, and cost-effective method of fabricating conductor-insulator-conductor multi-layer interconnections in the electronic industry.展开更多
This applied research seeks to explore feasible plant design for manufacturing insulation materials for construction projects using waste sheep fleece to address environmental issues related to wasted sheep wool and e...This applied research seeks to explore feasible plant design for manufacturing insulation materials for construction projects using waste sheep fleece to address environmental issues related to wasted sheep wool and enhance the gross national product. The process starts by collecting low-cost sheep fleece from farms and processed via a production line, including scouring, plucking, carding, thermal bonding, and packing. The design process involves determining an optimal location, infrastructure, staffing, machinery, environmental impact, and utilities. A final economic analysis is undertaken to estimate the product’s cost, selling price, and break-even point based on the anticipated capital and operational costs. The plant is intended to process 6778 tons of sheep wool annually. The study suggests that Mafraq Industrial City is a perfect location for the plant, and purchasing land and structures is the optimal option. The projected capital cost is 1,416,679 USD, while the anticipated operational costs amount to 3,206,275 USD. Insulation material production is estimated to be 114,756 m3 annually. The material may be manufactured into 1 m wide, 0.05 m thick sheets for 2.02 USD per square meter. Thus, for a 10-year plant, a 2.47 USD/m2 selling price breaks even in one year.展开更多
As the application scenarios of aerogels expand,higher requirements are put forward for the materials used to prepare aerogels.Due to the unique chemical structure,polytetrafluoroethylene(PTFE)has excellent properties...As the application scenarios of aerogels expand,higher requirements are put forward for the materials used to prepare aerogels.Due to the unique chemical structure,polytetrafluoroethylene(PTFE)has excellent properties such as high-temperature resistance,hydrophobicity,and chemical stability.However,the PTFE aerogels are difficult to be molded due to the weak interaction between resin particles.In this work,poly(ethylene oxide)(PEO)was selected as the carrier to assist the PTFE aerogels molding.The pure PTFE aerogels were prepared by homogeneously mixing PTFE aqueous dispersion and PEO,freeze-drying,and high-temperature sintering.When the mass fraction of PTFE and PEO were appropriate,the porosity of PTFE aerogels exceeded 90%and had a hierarchical honeycomb structure.Results showed that the PTFE aerogels not only had excellent hydrophobicity but also possessed superior acoustic insulation,mechanical strength,thermal insulation,and heat resistance properties.Specifically,the water contact angle is about 140°.The noise reduction coefficient is 0.34 and the average sound absorption coefficient is greater than 88%in the frequency range of 2000-6400 Hz.Meanwhile,the thermal conductivity in the air is about 0.045 W/(m·K),and the initial thermal decomposition temperature is 450℃.More importantly,the PTFE aerogels had excellent temperature and corrosion resistance.Even after extremely thermal and chemical treatment,they remained unchanged porous structure as well as acoustic and thermal insulation properties,which exhibits great potential for application in many harsh environments.展开更多
The huge impact kinetic energy cannot be quickly dissipated by the energy-absorbing structure and transferred to the other vehicle through the car body structure,which will cause structural damage and threaten the liv...The huge impact kinetic energy cannot be quickly dissipated by the energy-absorbing structure and transferred to the other vehicle through the car body structure,which will cause structural damage and threaten the lives of the occupants.Therefore,it is necessary to understand the laws of energy conversion,dissipation and transfer during train collisions.This study proposes a multi-layer progressive analysis method of energy flow during train collisions,considering the characteristics of the train.In this method,the train collision system is divided into conversion,dissipation,and transfer layers from the perspective of the train,collision interface,and car body structure to analyze the energy conversion,dissipation and transfer characteristics.Taking the collision process of a rail train as an example,a train collision energy transfer path analysis model was established based on power flow theory.The results show that when the maximum mean acceleration of the vehicle meets the standard requirements,the jerk may exceed the allowable limit of the human body,and there is a risk of injury to the occupants of a secondary collision.The decay rate of the collision energy along the direction of train operation reaches 79%.As the collision progresses,the collision energy gradually converges in the structure with holes,and the structure deforms when the gathered energy is greater than the maximum energy the structure can withstand.The proposed method helps to understand the train collision energy flow law and provides theoretical support for the train crashworthiness design in the future.展开更多
The growing incidence of cyberattacks necessitates a robust and effective Intrusion Detection Systems(IDS)for enhanced network security.While conventional IDSs can be unsuitable for detecting different and emerging at...The growing incidence of cyberattacks necessitates a robust and effective Intrusion Detection Systems(IDS)for enhanced network security.While conventional IDSs can be unsuitable for detecting different and emerging attacks,there is a demand for better techniques to improve detection reliability.This study introduces a new method,the Deep Adaptive Multi-Layer Attention Network(DAMLAN),to boost the result of intrusion detection on network data.Due to its multi-scale attention mechanisms and graph features,DAMLAN aims to address both known and unknown intrusions.The real-world NSL-KDD dataset,a popular choice among IDS researchers,is used to assess the proposed model.There are 67,343 normal samples and 58,630 intrusion attacks in the training set,12,833 normal samples,and 9711 intrusion attacks in the test set.Thus,the proposed DAMLAN method is more effective than the standard models due to the consideration of patterns by the attention layers.The experimental performance of the proposed model demonstrates that it achieves 99.26%training accuracy and 90.68%testing accuracy,with precision reaching 98.54%on the training set and 96.64%on the testing set.The recall and F1 scores again support the model with training set values of 99.90%and 99.21%and testing set values of 86.65%and 91.37%.These results provide a strong basis for the claims made regarding the model’s potential to identify intrusion attacks and affirm its relatively strong overall performance,irrespective of type.Future work would employ more attempts to extend the scalability and applicability of DAMLAN for real-time use in intrusion detection systems.展开更多
Hygroscopic hydrogel is a promising evaporativecooling material for high-power passive daytime cooling with water self-regeneration.However,undesired solar and environmental heating makes it a challenge to maintain su...Hygroscopic hydrogel is a promising evaporativecooling material for high-power passive daytime cooling with water self-regeneration.However,undesired solar and environmental heating makes it a challenge to maintain sub-ambient daytime cooling.While different strategies have been developed to mitigate heat gains,they inevitably sacrifice the evaporation and water regeneration due to highly coupled thermal and vapor transport.Here,an anisotropic synergistically performed insulation-radiation-evaporation(ASPIRE)cooler is developed by leveraging a dual-alignment structure both internal and external to the hydrogel for coordinated thermal and water transport.The ASPIRE cooler achieves an impressive average sub-ambient cooling temperature of~8.2℃ and a remarkable peak cooling power of 311 W m^(-2)under direct sunlight.Further examining the cooling mechanism reveals that the ASPIRE cooler reduces the solar and environmental heat gains without comprising the evaporation.Moreover,self-sustained multi-day cooling is possible with water self-regeneration at night under both clear and cloudy days.The synergistic design provides new insights toward high-power,sustainable,and all-weather passive cooling applications.展开更多
In order to support the physical research on the EAST tokamak,a new positive ion source with designed beam energy of 120 keV was proposed to be developed.Accelerator structure is one of the key components of the ion s...In order to support the physical research on the EAST tokamak,a new positive ion source with designed beam energy of 120 keV was proposed to be developed.Accelerator structure is one of the key components of the ion source.Through the finite element analysis method,the electrostatic analyses of insulators and grid plates were carried out,the material and structure parameters of insulators were determined.The maximum electric field around each insulator is about 4 kV/mm,and the maximum electric field between grids is about 14 kV/mm,which can meet the 120 keV withstand voltage holding.The insulation system for the positive ion source accelerator with 120 keV is designed,and the connection and basic parameters of insulators and support flanges are analyzed and determined.展开更多
In practical engineering construction,multi-layered barriers containing geomembranes are extensively applied to retard the migration of pollutants.However,the associated analytical theory on pollutants diffusion still...In practical engineering construction,multi-layered barriers containing geomembranes are extensively applied to retard the migration of pollutants.However,the associated analytical theory on pollutants diffusion still needs to be further improved.In this work,general analytical solutions are derived for one-dimensional diffusion of degradable organic contaminant(DOC)in the multi-layered media containing geomembranes under a time-varying concentration boundary condition,where the variable substitution and separated variable approaches are employed.These analytical solutions with clear expressions can be used not only to study the diffusion behaviors of DOC in bottom and vertical composite barrier systems,but also to verify other complex numerical models.The proposed general analytical solutions are then fully validated via three comparative analyses,including comparisons with the experimental measurements,an existing analytical solution,and a finite-difference solution.Ultimately,the influences of different factors on the composite cutoff wall’s(CCW,which consists of two soil-bentonite layers and a geomembrane)service performance are investigated through a composite vertical barrier system as the application example.The findings obtained from this investigation can provide scientific guidance for the barrier performance evaluation and the engineering design of CCWs.This application example also exhibits the necessity and effectiveness of the developed analytical solutions.展开更多
This study focuses on the electrical properties and microstructure of polypropylene(PP)-based blends used for cable insulation in nuclear power plants(NPPs).The PP-based blend,comprising isotactic PP and propylene-bas...This study focuses on the electrical properties and microstructure of polypropylene(PP)-based blends used for cable insulation in nuclear power plants(NPPs).The PP-based blend,comprising isotactic PP and propylene-based elastomer(PBE)at concentrations ranging from 0 to 50 wt%,underwent a melt blending process and subsequent cobalt-60 gamma-ray irradiation with doses ranging from 0 to 250 kGy.Electrical conductivity,trap distribution,and alternating(AC)breakdown strength were chosen to assess the insulation performance.These results indicate that the addition of PBE significantly improves the electrical properties of PP under irradiation.For PP,the electrical conductivity increased with irradiation,whereas the trap depth and breakdown strength decreased sharply.Conversely,for the blend,these changes initially exhibit opposite trends.When the irradiation was increased to 250 kGy,the AC breakdown strength of the blend improved by more than 21%compared to that of PP.The physical and chemical structures of the samples were investigated to explore the improvement mechanisms.The results offer insights into the design of new cable-insulation materials suitable for NPPs.展开更多
Poly(vinylidene fluoride)(PVDF)foam has received widespread attention due to its high strength,and excellent combination of flame-retardancy,antibacterial performance,and chemical stability.However,the foaming ability...Poly(vinylidene fluoride)(PVDF)foam has received widespread attention due to its high strength,and excellent combination of flame-retardancy,antibacterial performance,and chemical stability.However,the foaming ability of conventional PvDF is severely limited by its rapid crystallization kinetics and poor melt strength.Although ultra-high molecular weight PVDF(H-PVDF)theoretically offers prolonged melt elasticity favorable for foaming,the extremely high melt viscosity poses substantial processing challenges,and its foaming behavior has remained largely unexplored.To address these issues,this study proposes a novel fabrication strategy combining solvent casting with microcellular foaming to prepare H-PVDF foams.Dynamic mechanical analysis and differential scanning calorimetry reveal that extensive chain entanglements in H-PVDF impose constraints on crystallization and significantly enhance melt strength.By tuning the processing parameters,the distinctive foaming be-havior of H-PVDF under various conditions is systematically elucidated.Remarkably,a record-high expansion ratio of 55.6-fold is achieved,ac-companied by a highly uniform and fine cellular structure.The resulting H-PVDF foams exhibit a low thermal conductivity of 31.8 mW·m^(-1).K^(-1),while retaining excellent compressive strength,flame-retardancy,and hydrophobicity.These outstanding properties highlight the great potential of H-PVDF foams as the thermal insulation materials for applications in aerospace,energy infrastructure,and other extreme environments.展开更多
This study proposes a general imperfect thermal contact model to predict the thermal contact resistance at the interface among multi-layered composite structures.Based on the Green-Lindsay(GL)thermoelastic theory,semi...This study proposes a general imperfect thermal contact model to predict the thermal contact resistance at the interface among multi-layered composite structures.Based on the Green-Lindsay(GL)thermoelastic theory,semi analytical solutions of temperature increment and displacement of multi-layered composite structures are obtained by using the Laplace transform method,upon which the effects of thermal resistance coefficient,partition coefficient,thermal conductivity ratio and heat capacity ratio on the responses are studied.The results show that the generalized imperfect thermal contact model can realistically describe the imperfect thermal contact problem.Accordingly,it may degenerate into other thermal contact models by adjusting the thermal resistance coefficient and partition coefficient.展开更多
The demand for anisotropic aerogels with excellent comprehensive properties in cutting-edge fields such as aerospace is growing.Based on the above background,a novel heterocyclic para-aramid nanofiber/reduced graphene...The demand for anisotropic aerogels with excellent comprehensive properties in cutting-edge fields such as aerospace is growing.Based on the above background,a novel heterocyclic para-aramid nanofiber/reduced graphene oxide(HPAN/rGO)composite aerogel was prepared by combining electrospinning and unidirectional freeze-drying.The anisotropic HPAN/rGO composite aerogel exhibited a honeycomb morphology in the direction perpendicular to the growth of ice crystals,and a through-well structure of directed microchannels in the direction parallel to the temperature gradient.By varying the mass ratio of HPAN/rGO,a composite aerogel with an ultra-low density of 5.34-7.81 mg·cm^(-3) and an ultra-high porosity of 98%-99%was obtained.Benefiting from the anisotropic structure,the radial and axial thermal conductivities of HPAN/rGO-3 composite aerogel were 29.37 and 44.35 mW·m^(-1)·K^(-1),respectively.A combination of software simulation and experiments was used to analyze the effect of anisotropic structures on the thermal insulation properties of aerogels.Moreover,due to the intrinsic self-extinguishing properties of heterocyclic para-aramid and the protection of the graphene carbon layer,the composite aerogel also exhibits excellent flame retardancy properties,and its total heat release rate(THR)was only 5.8 kJ·g^(-1),which is far superior to many reported aerogels.Therefore,ultralight anisotropic HPAN/rGO composite aerogels with excellent high-temperature thermal insulation and flame retardancy properties have broad application prospects in complex environments such as aerospace.展开更多
As electromagnetic pollution escalates and protection demands diversify,there is an urgent requirement for versatile carbon foam materials capable of absorbing electromagnetic waves(EMWs).Furthermore,the concern about...As electromagnetic pollution escalates and protection demands diversify,there is an urgent requirement for versatile carbon foam materials capable of absorbing electromagnetic waves(EMWs).Furthermore,the concern about global warming and the depletion of petrochemical resources calls for facile and eco-friendly methods for the large-scale production of multi-functional and biodegradable carbon foams.Herein,cornstraw-derived carbon foams(CCFs)integrating EMW absorption,sound absorption,and heat insulation were prepared by a facile dual-template strategy.Benefiting from the dual-template effect of air bubbles and ice crystals,the obtained foam manifests an ultra-low density of 31 mg/cm^(3),large poros-ity of 0.85 and also super-broad absorption with an effective absorption bandwidth(EAB)of 7.18 GHz at 3.6 mm,even beyond most carbon-based composite foams.Moreover,abundant pores also endow the foam with good thermal insulation performance(as low as 0.041 W/(m K))and high sound absorp-tion coefficient(0.8 at 1250-6000 Hz),which are equivalent to commercial foams.The excellent EMW absorption performance originates from conduction loss produced by the three-dimensional(3D)inter-connected network structure and also interfacial polarization and multiple scattering induced by porous structure.Additionally,the abundant closed pores in foam prevent thermal convection and thus provide good thermal-insulation performance,yet the opening pores proffer excellent sound absorption through resonance and friction absorption.This study provides new insights into the green synthesis of multi-functional microwave absorbing foam and also supplies a new thermal-insulation material for exterior walls of buildings exposed to electromagnetic environment.展开更多
基金supported by Young Elite Scientists Sponsorship Program by China Association for Science and Technology(No.2022QNRC001)the National Natural Science Foundation of China(No.52273053)the Chenguang Program of Shanghai Education Development Foundation and Shanghai Municipal Education Commission(No.21CGA41)。
文摘Extreme cold weather seriously harms human thermoregulatory system,necessitating high-performance insulating garments to maintain body temperature.However,as the core insulating layer,advanced fibrous materials always struggle to balance mechanical properties and thermal insulation,resulting in their inability to meet the demands for both washing resistance and personal protection.Herein,inspired by the natural spring-like structures of cucumber tendrils,a superelastic and washable micro/nanofibrous sponge(MNFS)based on biomimetic helical fibers is directly prepared utilizing multiple-jet electrospinning technology for high-performance thermal insulation.By regulating the conductivity of polyvinylidene fluoride solution,multiple-jet ejection and multiple-stage whipping of jets are achieved,and further control of phase separation rates enables the rapid solidification of jets to form spring-like helical fibers,which are directly entangled to assemble MNFS.The resulting MNFS exhibits superelasticity that can withstand large tensile strain(200%),1000 cyclic tensile or compression deformations,and retain good resilience even in liquid nitrogen(-196℃).Furthermore,the MNFS shows efficient thermal insulation with low thermal conductivity(24.85 mW m^(-1)K^(-1)),close to the value of dry air,and remains structural stability even after cyclic washing.This work offers new possibilities for advanced fibrous sponges in transportation,environmental,and energy applications.
基金supported by the National Natural Science Foundation of China(Grant No.51225602)
文摘Thermal protection systems are very essential for high temperature thermal conductivity measurement system to reduce the heat loss to environment at the range of 600-1800 K. A compound multi-layer insulations structure which composed of inner carbon fibrous materials and outer alternately arranged alumina fibrous materials and high reflectivity foils is proposed for use in high temperature cylinder thermal protection systems. A coupled conductive and radiation governing equations is presented for heat transfer analysis of the structure. The finite volume method and the discrete ordinate method are used to solve the goveming equations. The optimization structure of the compound multi-layer insulations is investigated by considering the pressure of the gas, the density of the carbon fibrous materials, the density of the alumina fibrous materials, the number of reflective foil layers and the emissivity of reflective foils. The results show that the compound structure has the best thermal insulation performance when the pressure of the gas is below 0.01 kPa, the density of carbon fibrous materials is 180 kg m^-3, the density of alumina fibrous materials is 256 kg m^-3 and the number of reflective foil layers is 39. In addition, the thermal insulation performance is much better when the emissivity of reflective foils is lower.
基金supported by the National Key Research and Development Program of China(No.2022YFB3404700)the National Natural Science Foundation of China(Nos.52105313 and 52275299)+2 种基金the Research and Development Program of Beijing Municipal Education Commission,China(No.KM202210005036)the Natural Science Foundation of Chongqing,China(No.CSTB2023NSCQ-MSX0701)the National Defense Basic Research Projects of China(No.JCKY2022405C002).
文摘At present,the emerging solid-phase friction-based additive manufacturing technology,including friction rolling additive man-ufacturing(FRAM),can only manufacture simple single-pass components.In this study,multi-layer multi-pass FRAM-deposited alumin-um alloy samples were successfully prepared using a non-shoulder tool head.The material flow behavior and microstructure of the over-lapped zone between adjacent layers and passes during multi-layer multi-pass FRAM deposition were studied using the hybrid 6061 and 5052 aluminum alloys.The results showed that a mechanical interlocking structure was formed between the adjacent layers and the adja-cent passes in the overlapped center area.Repeated friction and rolling of the tool head led to different degrees of lateral flow and plastic deformation of the materials in the overlapped zone,which made the recrystallization degree in the left and right edge zones of the over-lapped zone the highest,followed by the overlapped center zone and the non-overlapped zone.The tensile strength of the overlapped zone exceeded 90%of that of the single-pass deposition sample.It is proved that although there are uneven grooves on the surface of the over-lapping area during multi-layer and multi-pass deposition,they can be filled by the flow of materials during the deposition of the next lay-er,thus ensuring the dense microstructure and excellent mechanical properties of the overlapping area.The multi-layer multi-pass FRAM deposition overcomes the limitation of deposition width and lays the foundation for the future deposition of large-scale high-performance components.
基金supported by the Natural Science Foundation of Shanxi Province(Nos.20210302123015 and 20210302123035)the Opening Project of State Key Laboratory of Polymer Materials Engineering(Sichuan University)(No.sklpme2022-4-06)the Open Foundation of China-Belarus Belt and Road Joint Laboratory on Electromagnetic Environment Effect(No.ZBKF2022030301).
文摘In the present work,by virtue of the synergistic and independent effects of Janus structure,an asymmetric nickel-chain/multiwall carbon nanotube/polyimide(Ni/MWCNTs/PI)composite foam with absorption-dominated electromagnetic interference(EMI)shielding and thermal insulation performances was successfully fabricated through an ordered casting and directional freeze-drying strategy.Water-soluble polyamic acid(PAA)was chosen to match the oriented freeze-drying method to acquire oriented pores,and the thermal imidization process from PAA to PI exactly eliminated the interface of the multilayered structure.By controlling the electro-magnetic gradient and propagation path of the incident microwaves in the MWCNT/PI and Ni/PI layers,the PI composite foam exhibited an efficient EMI SE of 55.8 dB in the X-band with extremely low reflection characteristics(R=0.22).The asymmetric conductive net-work also greatly preserved the thermal insulation properties of PI.The thermal conductivity(TC)of the Ni/MWCNT/PI composite foam was as low as 0.032 W/(m K).In addition,owing to the elimination of MWCNT/PI and Ni/PI interfaces during the thermal imidization process,the composite foam showed satisfactory compressive strength.The fabricated PI composite foam could provide reliable electromagnetic protection in complex applications and withstand high temperatures,which has great potential in cuttingedge applications such as advanced aircraft.
基金supported by the National Natural Science Foun-dation of China(Grant No.U2167214).
文摘Due to excellent thermal insulation performance at room temperature and ultralow density,silica aero-gels are candidates for thermal insulation.However,at high temperatures,the thermal insulation prop-erty of silica aerogels decreased greatly caused by transparency to heat radiation.Opacifiers introduced into silica sol can block heat radiation yet destroy the uniformity of aerogels.Herein,we designed and prepared a silica aerogel composite with oriented and layered silica fibers(SFs),SiC nanowires(SiC_(NWs)),and silica aerogels,which were prepared by papermaking,chemical vapor infiltration(CVI),and sol-gel respectively.Firstly,oriented and layered SFs made still air a wall to block heat transfer by the solid phase.Secondly,SiC_(NWs) were grown in situ on the surface of SFs evenly to weave into the network,and the network reduced the gaseous thermal conductivity by dividing cracks in SFs/SiC_(NWs)/SA.Thirdly,SiC_(NWs) weakened the heat transfer by radiation at high temperatures.Therefore,SFs/SiC_(NWs)/SA presented remarkable thermal insulation(0.017 W(m K)^(-1) at 25℃,0.0287 W(m K)^(-1) at 500℃,and 0.094 W(m K)^(-1) at 1000℃).Besides,SFs/SiC_(NWs)/SA exhibited remarkable thermal stability(no size transform after being heat treated at 1000℃ for 1800 s)and tensile strength(0.75 MPa).These integrated properties made SFs/SiC_(NWs)/SA a promising candidate for highly efficient thermal insulators.
基金supported by the Basic Science Program(No.2022R1A2C2009700)through the National Research Foundation of Korea(NRF)funded by the Ministry of Science and ICTthe Basic Science Research Capacity Enhancement Project(National Research Facilities and Equipment Center)through the Korea Ba-sic Science Institute funded by the Ministry of Education(No.2019R1A6C1010047)the Industrial Strategic Technology Development Program(No.20013248)through Korea Evaluation In-stitute of Industrial Technology funded by the Ministry of Trade,Industry&Energy(MOTIE,Korea).
文摘Thermally conductive papers with electrical insulation and mechanical robustness are essential for efficient thermal management in modern electronics.In this study,we introduced a metal ion-assisted interfacial crosslinking strategy to strengthen sugarfunctionalized graphene fluoride(SGF)and cellulose nanofibers(CNF)by hydrogen bonding and metal ion crosslinking that leads to simultaneous enhancements in thermal conductivity and mechanical properties.The facile sugarassisted ball-milling exfoliation method was developed to achieve the exfoliation of graphite fluoride and hydroxyl group functionalization on the surface of graphene fluoride.Thanks to the good dispersibility of the SGF sheets in water,the flexible SGF/CNF composite papers with hydrogen bonding were prepared via vacuum-assisted filtration.We introduced hydrogen bonding and metal ion crosslinking into SGF/CNF papers to obtain densely packed composite papers.Ca^(2+)or Al^(3+)ion-crosslinked SGF/CNF papers exhibited superior thermal and mechanical properties owing to hydrogen bonding and metal ion crosslinking.SGF/CNF-Ca^(2+)and SGF/CNF-Al^(3+)papers at 50 wt%of SGF yield in-plane thermal conductivities of 72.93 and 75.02 W m^(-1) K^(-1),and tensile strengths of 121.5 and 135.7 MPa,respectively.A thermal percolation value was observed at 12.6 vol%of SGF filler content.In addition,the SGF/CNF papers exhibited electrical insulation properties.These remarkable characteristics of the metal ion-crosslinked SGF/CNF papers are attributed to the densely packed structures caused by the strong interfacial interactions from hydrogen bonding as well as metal ion-crosslinking that could promote phonon transport.High-performance metal ion-crosslinked SGF/CNF papers with these fascinating advantages offer great potential for the thermal management of flexible electronics.
文摘BACKGROUND Elderly patients undergoing laparoscopic colorectal cancer surgery are at high risk for hypothermia-related complications.This study explores the efficacy of periop-erative composite insulation interventions in maintaining normothermia and reducing postoperative risks in this vulnerable group.AIM To evaluate the efficacy of perioperative composite insulation in older patients undergoing colorectal cancer surgery.METHODS We selected 100 older patients who underwent laparoscopic surgery for colorectal cancer at Huzhou Central Hospital from September 2023 to April 2024.Using a random number table,patients were divided into a control group and inter-vention group of 50 patients each.After returning to the regular ward,the con-ventional group received traditional insulation intervention measures,while the intervention group received composite insulation nursing intervention.We ob-served and recorded postoperative blood pressure and heart rate changes,as well as postoperative anesthesia recovery time and incidence of complications.RESULTS The statistical results showed significant differences(P<0.05)in heart rate changes and systolic blood pressure between the two groups.There was a sig-nificant change in heart rate between the groups immediately after surgery and at 15 and 30 minutes after surgery(P<0.05).The heart rate and systolic blood pressure of the intervention group were significantly lower than those of the control group at 15 and 30 minutes after surgery(P<0.05).The rewarming time of the intervention group was shorter than that of the control group,and the overall incidence of postoperative complications was significantly lower than that of the control group(P<0.05).CONCLUSION For elderly patients undergoing laparoscopic colorectal cancer surgery,a composite insulation intervention during the perioperative period can maintain body temperature,reduce postoperative stress,and significantly reduce the incidence of hypothermia and related complications.
基金supported by the Key Program of the National Natural Science Foundation of China(Grant No.51035002)the National Natural Science Foundation of China(Grant No.51305373)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20120121120035)
文摘A multi-layer interconnection structure is a basic component of electronic devices, and printing of the multi-layer interconnection structure is the key process in printed electronics. In this work, electrohydrodynamic direct-writing （EDW） is utilized to print the conductor-insulator--conductor multi-layer ~nterconne^ction structure. Silver ink is chosen to print the conductor pattern, and a polyvinylpyrrolidone （PVP） solution is util^zed to f^bricate the insulator layer between the bottom and top conductor patterns. The influences of EDW process parameters on the line width of the printed conductor and insulator patterns are studied systematically. The obtained ~es^l~s show that the line width of the printed structure increases with the increase of the flow rate, but decreases with the increase of applied voltage and PVP content in the solution. The average resistivity values of the bottom and top silver conductor tracks are determined to be 1.34 × 10-7 Ω.m and 1.39×10-7 Ω.m, respectively. The printed PVP layer between the two conductor tracks is well insulated, which can meet the insulation requirement of the electronic devices. This study offers an alternative, fast, and cost-effective method of fabricating conductor-insulator-conductor multi-layer interconnections in the electronic industry.
文摘This applied research seeks to explore feasible plant design for manufacturing insulation materials for construction projects using waste sheep fleece to address environmental issues related to wasted sheep wool and enhance the gross national product. The process starts by collecting low-cost sheep fleece from farms and processed via a production line, including scouring, plucking, carding, thermal bonding, and packing. The design process involves determining an optimal location, infrastructure, staffing, machinery, environmental impact, and utilities. A final economic analysis is undertaken to estimate the product’s cost, selling price, and break-even point based on the anticipated capital and operational costs. The plant is intended to process 6778 tons of sheep wool annually. The study suggests that Mafraq Industrial City is a perfect location for the plant, and purchasing land and structures is the optimal option. The projected capital cost is 1,416,679 USD, while the anticipated operational costs amount to 3,206,275 USD. Insulation material production is estimated to be 114,756 m3 annually. The material may be manufactured into 1 m wide, 0.05 m thick sheets for 2.02 USD per square meter. Thus, for a 10-year plant, a 2.47 USD/m2 selling price breaks even in one year.
基金supported by the National Natural Science Foundation of China(No.52233003)the Department of Sichuan Province(No.2022JDJQ0023)。
文摘As the application scenarios of aerogels expand,higher requirements are put forward for the materials used to prepare aerogels.Due to the unique chemical structure,polytetrafluoroethylene(PTFE)has excellent properties such as high-temperature resistance,hydrophobicity,and chemical stability.However,the PTFE aerogels are difficult to be molded due to the weak interaction between resin particles.In this work,poly(ethylene oxide)(PEO)was selected as the carrier to assist the PTFE aerogels molding.The pure PTFE aerogels were prepared by homogeneously mixing PTFE aqueous dispersion and PEO,freeze-drying,and high-temperature sintering.When the mass fraction of PTFE and PEO were appropriate,the porosity of PTFE aerogels exceeded 90%and had a hierarchical honeycomb structure.Results showed that the PTFE aerogels not only had excellent hydrophobicity but also possessed superior acoustic insulation,mechanical strength,thermal insulation,and heat resistance properties.Specifically,the water contact angle is about 140°.The noise reduction coefficient is 0.34 and the average sound absorption coefficient is greater than 88%in the frequency range of 2000-6400 Hz.Meanwhile,the thermal conductivity in the air is about 0.045 W/(m·K),and the initial thermal decomposition temperature is 450℃.More importantly,the PTFE aerogels had excellent temperature and corrosion resistance.Even after extremely thermal and chemical treatment,they remained unchanged porous structure as well as acoustic and thermal insulation properties,which exhibits great potential for application in many harsh environments.
基金Supported by the National Natural Science Foundation of China(Grant No.52172409)Postdoctoral Innovation Talents Support Program(Grant No.BX20240298)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.2682024GF023)Heilongjiang Province Postdoctoral Foundation Project(Grant No.LBH-Z23041).
文摘The huge impact kinetic energy cannot be quickly dissipated by the energy-absorbing structure and transferred to the other vehicle through the car body structure,which will cause structural damage and threaten the lives of the occupants.Therefore,it is necessary to understand the laws of energy conversion,dissipation and transfer during train collisions.This study proposes a multi-layer progressive analysis method of energy flow during train collisions,considering the characteristics of the train.In this method,the train collision system is divided into conversion,dissipation,and transfer layers from the perspective of the train,collision interface,and car body structure to analyze the energy conversion,dissipation and transfer characteristics.Taking the collision process of a rail train as an example,a train collision energy transfer path analysis model was established based on power flow theory.The results show that when the maximum mean acceleration of the vehicle meets the standard requirements,the jerk may exceed the allowable limit of the human body,and there is a risk of injury to the occupants of a secondary collision.The decay rate of the collision energy along the direction of train operation reaches 79%.As the collision progresses,the collision energy gradually converges in the structure with holes,and the structure deforms when the gathered energy is greater than the maximum energy the structure can withstand.The proposed method helps to understand the train collision energy flow law and provides theoretical support for the train crashworthiness design in the future.
基金Nourah bint Abdulrahman University for funding this project through the Researchers Supporting Project(PNURSP2025R319)Riyadh,Saudi Arabia and Prince Sultan University for covering the article processing charges(APC)associated with this publication.Special acknowledgement to Automated Systems&Soft Computing Lab(ASSCL),Prince Sultan University,Riyadh,Saudi Arabia.
文摘The growing incidence of cyberattacks necessitates a robust and effective Intrusion Detection Systems(IDS)for enhanced network security.While conventional IDSs can be unsuitable for detecting different and emerging attacks,there is a demand for better techniques to improve detection reliability.This study introduces a new method,the Deep Adaptive Multi-Layer Attention Network(DAMLAN),to boost the result of intrusion detection on network data.Due to its multi-scale attention mechanisms and graph features,DAMLAN aims to address both known and unknown intrusions.The real-world NSL-KDD dataset,a popular choice among IDS researchers,is used to assess the proposed model.There are 67,343 normal samples and 58,630 intrusion attacks in the training set,12,833 normal samples,and 9711 intrusion attacks in the test set.Thus,the proposed DAMLAN method is more effective than the standard models due to the consideration of patterns by the attention layers.The experimental performance of the proposed model demonstrates that it achieves 99.26%training accuracy and 90.68%testing accuracy,with precision reaching 98.54%on the training set and 96.64%on the testing set.The recall and F1 scores again support the model with training set values of 99.90%and 99.21%and testing set values of 86.65%and 91.37%.These results provide a strong basis for the claims made regarding the model’s potential to identify intrusion attacks and affirm its relatively strong overall performance,irrespective of type.Future work would employ more attempts to extend the scalability and applicability of DAMLAN for real-time use in intrusion detection systems.
基金financially supported by the Young Scientists Fund of National Natural Science Foundation of China(Grant No.52303106)Research Grants Council of Hong Kong SAR(16200720)+3 种基金Environment and Conservation Fund of Hong Kong SAR(Project No.21/2022)Research Institute of Sports Science and Technology(Project No.P0043535)Research Institute of Advanced Manufacturing(Project No.P0046125)the start-up fund for new recruits of Poly U(Project No.P0038855 and P0038858)。
文摘Hygroscopic hydrogel is a promising evaporativecooling material for high-power passive daytime cooling with water self-regeneration.However,undesired solar and environmental heating makes it a challenge to maintain sub-ambient daytime cooling.While different strategies have been developed to mitigate heat gains,they inevitably sacrifice the evaporation and water regeneration due to highly coupled thermal and vapor transport.Here,an anisotropic synergistically performed insulation-radiation-evaporation(ASPIRE)cooler is developed by leveraging a dual-alignment structure both internal and external to the hydrogel for coordinated thermal and water transport.The ASPIRE cooler achieves an impressive average sub-ambient cooling temperature of~8.2℃ and a remarkable peak cooling power of 311 W m^(-2)under direct sunlight.Further examining the cooling mechanism reveals that the ASPIRE cooler reduces the solar and environmental heat gains without comprising the evaporation.Moreover,self-sustained multi-day cooling is possible with water self-regeneration at night under both clear and cloudy days.The synergistic design provides new insights toward high-power,sustainable,and all-weather passive cooling applications.
基金supported by National Natural Science Foundation of China(No.11975261)。
文摘In order to support the physical research on the EAST tokamak,a new positive ion source with designed beam energy of 120 keV was proposed to be developed.Accelerator structure is one of the key components of the ion source.Through the finite element analysis method,the electrostatic analyses of insulators and grid plates were carried out,the material and structure parameters of insulators were determined.The maximum electric field around each insulator is about 4 kV/mm,and the maximum electric field between grids is about 14 kV/mm,which can meet the 120 keV withstand voltage holding.The insulation system for the positive ion source accelerator with 120 keV is designed,and the connection and basic parameters of insulators and support flanges are analyzed and determined.
基金Project(2023YFC3707800)supported by the National Key Research and Development Program of China。
文摘In practical engineering construction,multi-layered barriers containing geomembranes are extensively applied to retard the migration of pollutants.However,the associated analytical theory on pollutants diffusion still needs to be further improved.In this work,general analytical solutions are derived for one-dimensional diffusion of degradable organic contaminant(DOC)in the multi-layered media containing geomembranes under a time-varying concentration boundary condition,where the variable substitution and separated variable approaches are employed.These analytical solutions with clear expressions can be used not only to study the diffusion behaviors of DOC in bottom and vertical composite barrier systems,but also to verify other complex numerical models.The proposed general analytical solutions are then fully validated via three comparative analyses,including comparisons with the experimental measurements,an existing analytical solution,and a finite-difference solution.Ultimately,the influences of different factors on the composite cutoff wall’s(CCW,which consists of two soil-bentonite layers and a geomembrane)service performance are investigated through a composite vertical barrier system as the application example.The findings obtained from this investigation can provide scientific guidance for the barrier performance evaluation and the engineering design of CCWs.This application example also exhibits the necessity and effectiveness of the developed analytical solutions.
基金supported by the National Natural Science Foundation of China(No.52077151)the State Key Laboratory of Electrical Insulation and Power Equipment(No.EIPE23208)the Key Laboratory of Engineering Dielectrics and Its Application,Ministry of Education(No.KFM202203).
文摘This study focuses on the electrical properties and microstructure of polypropylene(PP)-based blends used for cable insulation in nuclear power plants(NPPs).The PP-based blend,comprising isotactic PP and propylene-based elastomer(PBE)at concentrations ranging from 0 to 50 wt%,underwent a melt blending process and subsequent cobalt-60 gamma-ray irradiation with doses ranging from 0 to 250 kGy.Electrical conductivity,trap distribution,and alternating(AC)breakdown strength were chosen to assess the insulation performance.These results indicate that the addition of PBE significantly improves the electrical properties of PP under irradiation.For PP,the electrical conductivity increased with irradiation,whereas the trap depth and breakdown strength decreased sharply.Conversely,for the blend,these changes initially exhibit opposite trends.When the irradiation was increased to 250 kGy,the AC breakdown strength of the blend improved by more than 21%compared to that of PP.The physical and chemical structures of the samples were investigated to explore the improvement mechanisms.The results offer insights into the design of new cable-insulation materials suitable for NPPs.
基金supported by the National Natural Science Foundation of China(No.52175341)Shandong Provincial Natural Science Foundation(No.ZR2022JQ24)+2 种基金Funding Project of Jinan City's New Twenty Items for Colleges and Universities(No.202333038)Excellent Young Team Project of Central Universities(No.2023QNTD002)Qingdao Key Technology Research and Industrialization Demonstration Project(No.24-1-2-qljh-10-gx).
文摘Poly(vinylidene fluoride)(PVDF)foam has received widespread attention due to its high strength,and excellent combination of flame-retardancy,antibacterial performance,and chemical stability.However,the foaming ability of conventional PvDF is severely limited by its rapid crystallization kinetics and poor melt strength.Although ultra-high molecular weight PVDF(H-PVDF)theoretically offers prolonged melt elasticity favorable for foaming,the extremely high melt viscosity poses substantial processing challenges,and its foaming behavior has remained largely unexplored.To address these issues,this study proposes a novel fabrication strategy combining solvent casting with microcellular foaming to prepare H-PVDF foams.Dynamic mechanical analysis and differential scanning calorimetry reveal that extensive chain entanglements in H-PVDF impose constraints on crystallization and significantly enhance melt strength.By tuning the processing parameters,the distinctive foaming be-havior of H-PVDF under various conditions is systematically elucidated.Remarkably,a record-high expansion ratio of 55.6-fold is achieved,ac-companied by a highly uniform and fine cellular structure.The resulting H-PVDF foams exhibit a low thermal conductivity of 31.8 mW·m^(-1).K^(-1),while retaining excellent compressive strength,flame-retardancy,and hydrophobicity.These outstanding properties highlight the great potential of H-PVDF foams as the thermal insulation materials for applications in aerospace,energy infrastructure,and other extreme environments.
基金Projects(42477162,52108347,52178371,52168046,52178321,52308383)supported by the National Natural Science Foundation of ChinaProjects(2023C03143,2022C01099,2024C01219,2022C03151)supported by the Zhejiang Key Research and Development Plan,China+6 种基金Project(LQ22E080010)supported by the Exploring Youth Project of Zhejiang Natural Science Foundation,ChinaProject(LR21E080005)supported by the Outstanding Youth Project of Natural Science Foundation of Zhejiang Province,ChinaProject(2022M712964)supported by the Postdoctoral Science Foundation of ChinaProject(2023AFB008)supported by the Natural Science Foundation of Hubei Province for Youth,ChinaProject(202203)supported by Engineering Research Centre of Rock-Soil Drilling&Excavation and Protection,Ministry of Education,ChinaProject(202305-2)supported by the Science and Technology Project of Zhejiang Provincial Communication Department,ChinaProject(2021K256)supported by the Construction Research Founds of Department of Housing and Urban-Rural Development of Zhejiang Province,China。
文摘This study proposes a general imperfect thermal contact model to predict the thermal contact resistance at the interface among multi-layered composite structures.Based on the Green-Lindsay(GL)thermoelastic theory,semi analytical solutions of temperature increment and displacement of multi-layered composite structures are obtained by using the Laplace transform method,upon which the effects of thermal resistance coefficient,partition coefficient,thermal conductivity ratio and heat capacity ratio on the responses are studied.The results show that the generalized imperfect thermal contact model can realistically describe the imperfect thermal contact problem.Accordingly,it may degenerate into other thermal contact models by adjusting the thermal resistance coefficient and partition coefficient.
基金supported by the National Key R&D Program of China(No.2021YFB3700103).
文摘The demand for anisotropic aerogels with excellent comprehensive properties in cutting-edge fields such as aerospace is growing.Based on the above background,a novel heterocyclic para-aramid nanofiber/reduced graphene oxide(HPAN/rGO)composite aerogel was prepared by combining electrospinning and unidirectional freeze-drying.The anisotropic HPAN/rGO composite aerogel exhibited a honeycomb morphology in the direction perpendicular to the growth of ice crystals,and a through-well structure of directed microchannels in the direction parallel to the temperature gradient.By varying the mass ratio of HPAN/rGO,a composite aerogel with an ultra-low density of 5.34-7.81 mg·cm^(-3) and an ultra-high porosity of 98%-99%was obtained.Benefiting from the anisotropic structure,the radial and axial thermal conductivities of HPAN/rGO-3 composite aerogel were 29.37 and 44.35 mW·m^(-1)·K^(-1),respectively.A combination of software simulation and experiments was used to analyze the effect of anisotropic structures on the thermal insulation properties of aerogels.Moreover,due to the intrinsic self-extinguishing properties of heterocyclic para-aramid and the protection of the graphene carbon layer,the composite aerogel also exhibits excellent flame retardancy properties,and its total heat release rate(THR)was only 5.8 kJ·g^(-1),which is far superior to many reported aerogels.Therefore,ultralight anisotropic HPAN/rGO composite aerogels with excellent high-temperature thermal insulation and flame retardancy properties have broad application prospects in complex environments such as aerospace.
基金financially supported by the National Science Foundation of China(Nos.52362024,22004106,51872238 and 21806129)the Fundamental Research Funds for the Central Universities(Nos.3102018zy045 and 3102019AX11)+1 种基金the Shaanxi Excellent Young Talents Support Program for Universities(No.202120006)the Key Laboratory of Icing and Anti/Deicing of CARDC(IADL20220401).
文摘As electromagnetic pollution escalates and protection demands diversify,there is an urgent requirement for versatile carbon foam materials capable of absorbing electromagnetic waves(EMWs).Furthermore,the concern about global warming and the depletion of petrochemical resources calls for facile and eco-friendly methods for the large-scale production of multi-functional and biodegradable carbon foams.Herein,cornstraw-derived carbon foams(CCFs)integrating EMW absorption,sound absorption,and heat insulation were prepared by a facile dual-template strategy.Benefiting from the dual-template effect of air bubbles and ice crystals,the obtained foam manifests an ultra-low density of 31 mg/cm^(3),large poros-ity of 0.85 and also super-broad absorption with an effective absorption bandwidth(EAB)of 7.18 GHz at 3.6 mm,even beyond most carbon-based composite foams.Moreover,abundant pores also endow the foam with good thermal insulation performance(as low as 0.041 W/(m K))and high sound absorp-tion coefficient(0.8 at 1250-6000 Hz),which are equivalent to commercial foams.The excellent EMW absorption performance originates from conduction loss produced by the three-dimensional(3D)inter-connected network structure and also interfacial polarization and multiple scattering induced by porous structure.Additionally,the abundant closed pores in foam prevent thermal convection and thus provide good thermal-insulation performance,yet the opening pores proffer excellent sound absorption through resonance and friction absorption.This study provides new insights into the green synthesis of multi-functional microwave absorbing foam and also supplies a new thermal-insulation material for exterior walls of buildings exposed to electromagnetic environment.
