查看更多>>摘要：With the increased electromagnetic wave(EMW)threat to military and human health,the develop-ment of EMW-absorbing materials is crucial.Metal-organic framework derivatives containing magnetic nanoparticles and a carbon matrix are potential candidates for designing efficient EMW-absorbing mate-rials.Herein,a zeolitic imidazolate framework-67(ZIF-67)-embedded three-dimensional melamine foam is pyrolyzed to afford carbon foam-based nitrogen-doped carbon nanotube composites,named 3D foam-like CoO/Co/N-CNTs.Magnetic CoO/Co particles are confined in the dielectric carbon nanotube skeleton.The carbon nanotubes provide considerable conductive loss,while CoO/Co magnetic particles are con-ducive to providing magnetic loss and adjusting impedance matching.Moreover,the numerous defect structures introduced by heteroatomic doping(nitrogen)cause dipole polarization and simultaneously adjust impedance matching.Meanwhile,the unique porous nanotube structure promotes multiple re-flections and scattering of EMWs,further optimizing impedance matching.CoO/Co/N-CNTs composites exhibit a minimum reflection loss of-52.3 dB at a matching thickness of 2.0 mm,while the correspond-ing effective absorption bandwidth is 5.28 GHz at a matching thickness of 2.2 mm.This study reports a novel approach to fabricating a lightweight high-performance EMW-absorbing material.
查看更多>>摘要：Tetrahedrite,an Earth-abundant natural mineral,has attracted extensive research interest because of its excellent thermoelectric performance.Herein,tetrahedrite samples comprising Cu-poor Cu12Sb4S13 and Cu-rich Cu14Sb4S13 phases have been synthesized using a colloidal method,in which the ratio of two phases is manipulated by controlling the synthesis temperature to improve the thermoelectric perfor-mance.It is found that an ultralow total thermal conductivity of～0.3 W m-1 K-1 at 723 K is realized in the sample with a Cu-rich phase fraction of～50％,which can be attributed to maximized phonon scattering by phase boundaries.As a result,combined with a decent power factor,this sample obtains an optimal zT of 1.15,which is about 85％higher than that of the sample with a Cu-rich phase fraction of～64％and comparable to zT values of other eco-friendly,abundant Cu-based thermoelectric materials.This work demonstrates an effective synthesis-temperature-dependent phase composition manipulation strategy toward enhanced thermoelectric performance in tetrahedrites.
查看更多>>摘要：Lattice engineering and distortion have been considered one kind of effective strategies for discovering advanced materials.The instinct chemical flexibility of high-entropy oxides(HEOs)motivates/accelerates to tailor the target properties through phase transformations and lattice distortion.Here,a hybrid knowledge-assisted data-driven machine learning(ML)strategy is utilized to discover the A2B2O7-type HEOs with low thermal conductivity(κ)through 17 rare-earth(RE=Sc,Y,La-Lu)solutes optimized A-site.A designing routine integrating the ML and high throughput first principles has been proposed to predict the key physical parameter(KPPs)correlated to the targeted K of advanced HEOs.Among the smart-designed 6188(5RE0.2)2Zr2O7 HEOs,the best candidates are addressed and validated by the princi-ples of severe lattice distortion and local phase transformation,which effectively reduce K by the strong multi-phonon scattering and weak interatomic interactions.Particularly,(Sc0.2Y0.2La0.2Ce0.2Pr0.2)2Zr2O7 with predicted κ below 1.59 Wm-1 K-1 is selected to be verified,which matches well with the ex-perimental κ=1.69 Wm1 K-1 at 300 K and could be further decreased to 0.14 Wm-1 K-1 at 1473 K.Moreover,the coupling effects of lattice vibrations and charges on heat transfer are revealed by the cross-validations of various models,indicating that the weak bonds with low electronegativity and few bond-ing charge density and the lattice distortion(r)identified by cation radius ratio(rA/rB)should be the KPPs to decrease K efficiently.This work supports an intelligent designing strategy with limited atomic and electronic KPPs to accelerate the development of advanced multi-component HEOs with proper-ties/performance at multi-scales.
查看更多>>摘要：Pitting is a common type of localized corrosion in passive alloys that can cause rapid failure of material or equipment.In the case of stainless steels,non-metallic inclusions have been identified as the most susceptible sites for pitting,and have therefore garnered significant attention.This review critically ex-amines the issue of how inclusions induce pitting,with a particular focus on three mechanisms:sponta-neous dissolution of inclusions,active dissolution of Cr-depleted regions,and propagation of microcracks at the inclusion-matrix interface.While researchers have made significant strides in understanding these mechanisms over the past few decades,many gaps and controversies remain.Details such as the ini-tial driving force of inclusion dissolution and factors affecting Cr-depleted regions require further study.Moreover,some old concepts and methods need to be revised to arrive at more credible conclusions.This review aims to delve deeply into these important issues and provide inspiration for future research.
查看更多>>摘要：The fabrication of ultrafine-grained microstructures(grain size below 1 μm)in titanium alloys is beneficial for improving their mechanical properties at room temperature and medium tempera-tures(400-550 ℃).However,a long-standing challenge involves the low-cost manufacturing of bulk ultrafine-grained titanium alloys.In this work,we developed a facile strategy through martensite de-composition at thermal-mechanical coupling conditions,to fabricate an equiaxed microstructure in a Ti6Al4Mo4Zr1W0.2Si model alloy with an average α grain size of 315±62 nm.The formation of the ultrafine-grained microstructure was because the lattice strain stored in the martensitic initial mi-crostructure enhanced the nucleation rate of dynamic recrystallization,meanwhile,the pinning role of martensite decomposition products β and(Ti,Zr)5Si3 phases suppressed grain coarsening at high tem-peratures.Compared to conventional(α+β)alloys,the tensile strength of this alloy improved by 20％-30％at both room temperature and 550 ℃,without decreasing its ductility.In situ SEM observations revealed that the ultrafine-grained microstructure would not only suppress dislocation motions but also contribute to the homogenous deformation in the matrix of the material,therefore,it resulted in higher mechanical performance.The research results may be of great significance to the development of next-generation aviation titanium alloys.
查看更多>>摘要：Efficient electrocatalytic rupture of energy-rich molecules(H2 and O2)is a green approach for gener-ating clean energy for modern societies.In this context,porphyry-type molecular electrocatalysts act intelligently toward oxygen reduction reaction(ORR),a fundamental process in fuel cells,due to their redox-rich chemistry,which involves core metal ions and macrocyclic ligands.The concerned scientific community has tried many times to correlate the ORR intermediates with their formation kinetics and simplify the associated multi H+/e-stages during the ORR process,constructing several volcano plots be-tween catalytic Tafel data,turnover frequencies,and overpotentials for many electrocatalysts.Despite the fact that many review articles on molecular electrocatalysts for ORR have been published,understanding the strategic implications and molecular catalyst intelligence towards homogenous ORR has been poorly explored.This review examined the relationships between volcano plots of current vs.thermodynamic parameters and the Sabatier principle in order to explain the intelligence of molecular electrocatalysts and approaches for their creation,as well as the difficulties and potential prospects of molecular electro-catalysts.These facts distinguish this review from previously published articles and will pique the scien-tific community's interest in avoiding trial-and-error procedures for catalyst creation while also allowing for more exact evaluations of the molecular catalyst's performance.
查看更多>>摘要：Considering the challenge of aerodynamic heating,the development of high-performance insulating ce-ramic materials with lightweight and low thermal conductivity is crucially important for aerospace vehi-cles to achieve flight at high speed for a long time.In this work,macro-porous silicon oxycarbide(SiOC)ceramics with directional pores(DP-SiOC)(mean pore size of 88.1 μm)were prepared using polysiloxane precursors via freeze casting and photocrosslinking,followed by pyrolysis.The DP-SiOC samples were lightweight(density～0.135 g cm-3)with a porosity of 90.4％,which showed good shapability through the molding of polysiloxane precursors.The DP-SiOC samples also exhibited an ultra-low thermal con-ductivity of 0.048 W(m K)-1 at room temperature,which can also withstand heat treatment at 1200 ℃ for 1 h.In addition,scaffolds with triply periodic minimal surfaces(TPMS)were fabricated using digital light processing(DLP)printing,which was further filled with polysiloxane precursors for increasing the strength of DP-SiOC.The TPMS scaffolds filled with macro-porous SiOC ceramics(TPMS-DP-SiOC)showed good integration between TPMS and macro-pore structures,which had a porosity～75％and high specific strength of 9.73 × 103 Nm kg-1.The thermal conductivity of TPMS-DP-SiOC samples was 0.255 W(m K)-1 at room temperature.The biomimetic TPMS-DP-SiOC ceramics developed in this study are likely used for thermal protection systems.
查看更多>>摘要：The combination of high efficiency and environmental stability is vital to promote the commercial appli-cations of microwave absorption(MA)materials,yet remains challenging in the absence of facile routes.Here,we put forward a graphene-reinforced construct approach for one-pot synthesis of 3D intercon-nected magnetic-dielectric frameworks via pre-functionalization and subsequent assembly.Multiple in-teractions among discrete precursors are capable of manipulating the confined growth and interfacial self-assembly.Significant enhancements in MA properties are triggered in a straightforward manner us-ing ultralow feeding fractions of graphene oxide nanosheet.The minimum reflection loss is up to-60.1 dB(99.9999％wave absorption)and the effective absorption bandwidth reaches 5.9 GHz(almost covering the Ku band).Remarkably,based on the optimization by ultralow concentrations of graphene,the as-prepared nanoarchitecture simultaneously integrates strong absorption,broad bandwidth,and low matching thick-ness.The embedded graphene nanosheets serve as high-speed electron transmission channels and hollow resonance cavities,facilitating multimode attenuations and impedance-matching characteristics.Mean-while,the graphene-reinforced framework suppresses the corrosion of magnetic components,whose cor-rosion rate reduces by an order of magnitude.This study provides a simple procedure to boost magnetic-dielectric absorbers for comprehensive MA performances and enhanced corrosion resistance.
查看更多>>摘要：Mg3Sb2-based thermoelectric materials have been the focus of widespread investigations as promising candidates for the harvesting of waste heat.Interface stability and service performance are key points for the commercial applications of these materials.We utilized Mg4.3Sb3Ni as a barrier layer to improve the thermal stability of Mg3Sb2-based devices.However,its intrinsic high resistivity contributed nega-tively to the desired performance of the device.In this work,we investigated two other Mg-Sb-Ni ternary phases,MgSbNi and MgSbNi2,as new barrier layer materials to connect with Mg3.2Sb2Y0.05.The results show that the efficiency of the Mg1.2SbNi/Mg3.2Sb2Y0.05/Mg1.2SbNi joint is increased by 33％ relative to the higher Mg-content barriers due to lower resistivity.The system exhibited good interfacial compatibility and showed little change with aging at 673 K for 20 days.
查看更多>>摘要：In recent years,sodium-ion batteries(SIBs)have emerged as a promising technology for energy storage systems(ESSs)because of the abundance and affordability of sodium.Recently,metal selenides have been studied as promising high-performance conversion-type anode materials in SIBs.Among them,nickel se-lenide(NiSe2)has received considerable attention due to its high theoretical capacity of 495 mAh g-1 and conductivity.However,it still suffers from poor cycling stability because of the low electrochemical reactivity,large volume expansion,and structural instability during cycles.To address these challenges,NiSe2 nanoparticles encapsulated in N-doped graphitic carbon fibers(NiSe2@NGCF)were synthesized by using ZIF-8 as a template.NiSe2@NGCF showed a high discharge capacity of 558.3 mAh g-1 with a fading rate of 0.14％per cycle after 200 cycles at 0.5 A g-1 in 0.01-3.0 V.At a very high current density of 5 A g-1,the capacity still displayed excellent long-term cycle life with a discharge capacity of 406.1 mAh g-1 with a fading rate of 0.016％per cycle after 3000 cycles.The mechanism of the excellent electrochem-ical performance of NiSe2@NGCF was thoroughly investigated by ex-situ XRD,TEM,and SEM analyses.Furthermore,NiSe2@NGCF//Na3V2(PO4)3 full-cell also delivered an excellent reversible capacity of 378.7 mAh g-1 at 0.1 A g-1 after 50 cycles,demonstrating its potential for practical application in SIBs.
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