查看更多>>摘要：Bi1-xHoxVO4(0.1 ≤ x ≤ 0.9)ceramics were prepared via a solid-state reaction method,and all the ceram-ics could be well densified in the 920-980 ℃ range.The ceramics with 0.1 ≤ x＜0.4 were composed of both monoclinic scheelite(M)and tetragonal zircon(T)phases,and a single M phase could be obtained in the range of x ≥ 0.4.The measured εr decreased from 58.9(x=0.1)to 14.7(x=0.9),so do the calcu-lated values(εr(C-M)=34.3-12.1),and the main reason for εr＞εr(c-M)was the rattling of Ho3+in the dodecahedron.Two points with zero τf appeared in Bi1-xHoxVO4(0 ≤ x ≤ 1)ceramics,and the best mi-crowave dielectric properties with εr=16.6,Q × f=18,400 GHz(f=10.69 GHz),and τf=+3.29 ppm/℃ were obtained in the Bi0.2Ho0.8VO4 ceramic.The change in temperature coefficient of ionic polarizability(ταm)caused by the rattling effect of cations is the physical essence that affects τf.Therefore,the rattling effect can be used as an effective mechanism to regulate τf in low-εr materials.Furthermore,there was no chemical reaction between Bi1-xHoxVO4 and Ag electrode,which indicates potential applications in low-temperature co-fired ceramic(LTCC)technology.
查看更多>>摘要：Conductive polymer composites(CPCs)have attracted significant interest in the field of flexible electro-magnetic protection,but the challenge of balancing high electromagnetic interference shielding effec-tiveness(EMI SE)and low reflection losses still exists.Herein,thermoplastic polyurethane/silver nanorod(TPU/AgNR)composite foams have been successfully prepared using both the salt template and vacuum-assisted thermal compression methods.By varying the AgNRs content and employing a layer-by-layer bonding approach,a gradient structure with optimized impedance matching is achieved.The"absorb-reflect-reabsorb"EM attenuation mechanism of the asymmetric gradient EMI shielding in the internal structure is exploited,resulting in TPU/AgNR foam(TAF)with high EMI SE and significantly reduced EM reflection.Notably,the three-layer foams exhibit an average shielding efficacy of 35.5 dB and a reflected power coefficient(R)of 0.085 in the X-band,thereby substantially mitigating secondary EM wave reflec-tions.Furthermore,these foams demonstrate exemplary compressive resilience,with the sample main-taining excellent EMI shielding stability even after undergoing 100 compression cycles at 50％strain.Consequently,a straightforward approach is employed to fabricate materials with high EMI SE and low reflectivity,offering the potential for use in EM shielding applications of next-generation flexible elec-tronic devices.
查看更多>>摘要：The He production rate(i.e.,He/dpa)in nuclear reactors strongly affects the degradation of material prop-erties.This is an important but not yet fully understood issue.Here,the effect of He/dpa on bubble char-acteristics in Fe9Cr1.5W0.4Si ferrite-martensitic(F/M)steel was in situ studied during 400 keV Fe+and 30 keV He+dual-beam irradiation at 723 K with three ratios of 100,500,and 2500 appm He/dpa and subsequent stepwise annealing using transmission electron microscopy(TEM).He/dpa strongly affected the bubble characteristics.During irradiation,the higher the He/dpa,the smaller the size of irradiated bubbles,but the higher their density.However,He/dpa didn't affect the final saturation size of irradiated bubbles for all three cases,which was～2.2 nm.During annealing,high He/dpa caused large,immobile,dense polyhedral bubbles with a wider bubble size distribution,while low He/dpa caused small,low-mobility,and relatively low-density spherical bubbles.It was found that the higher the He/dpa ratio,the greater the swelling during irradiation and annealing,and annealing further enhanced the swelling.Moreover,the tunnel structure was first found in body-centered cubic(BCC)F/M steel during in-situ irra-diation.The current work provides valuable and potential insights for further understanding the He/dpa effects in materials serving in different nuclear reactors.
查看更多>>摘要：Optimizing the local surface plasmon resonance(LSPR)effect of non-noble metals through alloying has been crucial for improving its practical application in the field of photocatalysis.Rare studies capture the detail that the change in the electronic structure of metal elements caused by alloying affects plasma carrier concentration and the local surface plasmon resonance effect.Herein,NiCuCoFe medium-entropy alloys(MEAs)nanoclusters were designed and used to modify the Bi3O4Br/CNNs Z-scheme heterojunc-tion.The cocktail effect of MEAs causes the 3d-orbital hybridization of various metal elements,which promotes the release of charge carriers.The higher the carrier concentration,the stronger the LSPR effect of MEAs.In addition,the mechanism of three typical working pathways of the LSPR effect to improve the photocatalytic performance of heterojunction is discussed.And compared with those of Bi3O4Br,CNNs,and Bi3O4Br/CNNs,the rate constant of MEAs-Bi3O4Br/CNNs was 3.26,11.16,and 3.17 times higher during the degradation of norfloxacin,respectively.This study provides a new strategy for understanding the mechanism of LSPR and the rational design of plasmonic coupling architectures for enhanced photocatalysis.
查看更多>>摘要：High-entropy alloys(HEAs)are a new type of multi-principal metal materials that exhibit excellent me-chanical properties.However,the strength-ductility balance in the HEAs remains a challenge that needs to be addressed.The amorphous/crystalline(A/C)structure is a new design strategy to achieve high strength and excellent ductility of the HEAs.Here,the influences of amorphous layer spacing,indenter velocity,and indenter radius on the mechanical properties and microstructure evolution of the A/C dual-phase CoCrFeMnNi HEAs under nanoindentation were investigated by molecular dynamics(MD)simula-tion.The results indicate that the plastic deformation mechanism of the monocrystalline HEAs is mainly dominated by the nucleation and slip of dislocations,while the plastic deformation mechanism of the dual-phase HEAs is mainly dominated by the interaction between dislocations and amorphous phases.The results show that the average indentation force of the dual-phase HEAs increases with the increase of the amorphous layer spacing.The amorphous layer in the HEAs can hinder the expansion of disloca-tions,limiting them to the crystalline matrix between the two amorphous layers.The results also indicate that Young's modulus of the HEAs increases with the increase of the indentation velocity and indentation radius.However,the hardness of HEAs is positively correlated with the indenter velocity,and negatively correlated with the indenter radius.It should be noted that the critical indentation depth and critical in-dentation force for the plastic deformation of the dual-phase HEAs decrease with the increase of indenter velocity,which is opposite to that of the single-phase crystalline HEAs.
查看更多>>摘要：Multi-functional smart textiles are receiving a lot of attention for their tremendous application devel-opment in the fields of personal thermal management,artificial muscle,electronic skin,and human-machine interaction.For the complex use of many different smart textiles,designing a multifunctional textile that integrates personal thermal management,smart sensing,and flexible actuating is still a great challenge.Here,we decorated MXene on elastic fabrics by simple dip-coating and asymmetric Ecoflex encapsulation protocol to obtain electrical/optical dual-energy-driven wearable heaters with highly re-sponsive actuating and strain-sensing performance.The MXene fabric-based heaters(MFHs)have high efficiency of Joule heating(Steady state temperature of 116.7 ℃ at 12 V)and photothermal conversion performance(180.3 ℃ in 60 s under the near infrared lamp irradiation,up to 57.5 ℃ under 600 W m-2 simulated solar irradiation).Benefiting from high electrical/optical dual-energy conversion efficiency,MFH has a fast photothermal driving effect(bending angle up to 360° in 5 s)due to the different curvature of thermal expansion on both sides of the fabric.Interestingly,MFH has the capability to monitor human strain(such as muscle and joint movements).Based on the above excellent performance,we finally be-lieve that the MFHs have broad application prospects in the fields of all-weather body heat management,health monitoring,thermal health care,and thermal robotics.
查看更多>>摘要：Carbon fiber reinforced silicon carbide matrix composites(C/SiC)have emerged as key materials for ther-mal protection systems owing to their high strength-to-weight ratio,high-temperature durability,resis-tance to oxidation,and outstanding reliability.However,manufacturing defects deteriorate the mechani-cal response of these composites under extreme thermal-force coupling conditions,prompting significant research attention.This study demonstrates a customized in situ loading device compatible with syn-chrotron radiation facilities,enabling high spatial and temporal resolution recording of internal material damage evolution and failure behavior under thermal-force coupling conditions.Infrared thermal radia-tion units in a confocal configuration were used to create ultra-high-temperature environments,offering advantages of compactness,rapid heating,and versatility.In situ tensile tests were conducted on C/SiC samples in a nitrogen atmosphere at both room temperature and 1200 ℃.The high-resolution image data demonstrate various failure phenomena,such as matrix cracking and pore linkage.Image-based fi-nite element simulations indicate that the temperature-dependent variation of the failure mechanism is attributable to thermal residual stresses and defect-induced stress concentrations.This work seamlessly integrates extreme mechanical testing methods with in situ observation techniques,providing a compre-hensive solution for accurately quantifying crack initiation,pore connection,and failure behavior of C/SiC composites.
查看更多>>摘要：In this work,the A356/AZ91D bimetal composites were prepared by ultrasonic vibration-assisted lost foam compound casting,and the effects of ultrasonic powers on interfacial microstructures and mechan-ical properties of the Al/Mg interfaces were investigated.Results revealed that the Al/Mg bimetal com-posites without ultrasonic vibration treatment(UVT)were heterogeneous,and the Al/Mg interface was composed of Al-Mg intermetallic compounds(IMCs,i.e.,Al3Mg2 and Al12Mg17)area and Al-Mg eutec-tic structures(δ-Mg+Al12Mg17)area.The Mg2Si particles were gathered at the IMCs area and an oxide film that mainly composed of Al2O3 was existed between the IMCs area and eutectic structures area.With UVT,the oxide film was eliminated and the gathered Mg2Si particles were refined and dispersed by the acoustic cavitation effect,and part of the Al3Mg2 and Al-Mg eutectic structures were transformed into the Al12Mg17 due to the promoted solute interdiffusion,which improved the homogeneity of the Al/Mg interfaces.Besides,the grains of the Al/Mg interface with UVT under ultrasonic power of 75 W were significantly refined.The thickness of Al/Mg interface was increased with the increase of the ul-trasonic power.Due to the excessive heat induced by UVT under the further increased ultrasonic power,the cooling rates and the degree of supercooling were reduced,resulting in the coarsening of interfacial grains.The microhardness of the Al/Mg interfaces was increased and got more uniform by UVT.The shear strengths of the Al/Mg bimetal composites with UVT were enhanced to 61.4 MPa from 32.4 MPa,with an increase of 89.5％compared with that of the Al/Mg bimetal without UVT.This could be ascribed to the removal of the oxide film,the refinement of the interfacial grains and the dispersed and refined Mg2Si particles achieved by UVT,which hindered the crack propagation during deformation.
查看更多>>摘要：Microwaves are often used in communication engineering,including in microwave relays as well as mul-tichannel,mobile,and satellite communications.To meet the demand for a"small,light,thin,and precise"modern electronic machine,developing highly tunable microwave materials to manufacture miniaturized microwave devices has become a top priority.Ferroelectric materials are excellent microwave materi-als,showing outstanding dielectric properties and tunability.Introducing low dielectric loss oxides in the construction of vertical self-assembly nanocomposites(VSNs)effectively improves their tunability and reduces dielectric loss.However,the optimal doping content of simple VSN films limits further improve-ment of tunability.Herein,we propose a strategy-gradient VSN to achieve combined improvement in tunability and dielectric constant by designing a sputtering and pulsed laser co-deposition.The resulting VSN composite film has a dielectric constant of 428.08,a dielectric loss of 0.0212,and a tunability of 78.69％.Our results contribute to the development of filters and have broad application prospects in the microwave industry.
NETL
NSTL
万方数据