查看更多>>摘要：The electromagnetic wave absorption(EMWA)performance of materials is affected by their dielectric and magnetic properties.Here,ferroferric oxide@N-doped residual carbon(Fe3O4@NRC)composites were successfully fabricated by decorating NRC with Fe3O4 nanoparticles via a facile chemical co-precipitation method.The RC was obtained through acid treatment to remove the inorganic minerals in coal gasifica-tion fine slag.The structure,composition,thermal stability,morphology,and related EM parameters of the as-fabricated Fe3O4@NRC composites were thoroughly tested via analytical techniques.Notably,both the Fe3O4@NRC-2 and Fe3O4@NRC-3 composites exhibited superior EMWA capacity.When 40％mass was added,the value of minimal reflection loss(RLmin)for Fe3O4@NRC-2 was-37.4 dB,and the effective ab-sorption bandwidth(EAB,RL≤-10 dB)reached 4.16 GHz(13.84-18.00 GHz)at a thickness of 1.5 mm.Besides,the value of impedance matching was 1.00 as the RLmin was achieved.The results demonstrated that the EMWA performance of the composites could be adjusted by controlling the content of Fe3O4 nanoparticles.The magnetic/carbon composites exhibited superior EMWA performance,thus promoting the resource utilization of residual carbon in coal gasification fine slag from coal gasification.
查看更多>>摘要：Multicomponent alloys of Zr50M50,Zr50(M,Ag)50 and Zr50(M,Pd)50(M=Fe,Co,Ni,Cu)can be melt-spun to obtain amorphous ribbons.The maximum thickness for fully amorphous ribbons varies with composi-tion in the range 34-53 μm.In contrast,fully amorphous ribbons are not obtainable for binary Zr50Ni50 or ternary Zr50(Ni,Cu)50 alloys.Heating-induced crystallization occurs through:two stages of amorphous[am]→[am'+B2]→[B2+B33]for Zr50M50;and[am]→[am'+B2]→[B2+AgZr]for Zr50(M,Ag)50;and a single stage of[am]→[B2]for Zr50(M,Pd)50,while no B2 phase is formed for the binary and ternary Zr50Q50(Q=Ni or/and Cu)alloys.As-spun amorphous ribbons have good bending plasticity.Re-markably,Zr50M50 ribbons in tension show 0.22-0.28％plastic elongation and work-hardening(the yield stress is～820 MPa,the fracture stress is～1200 MPa).When cold-rolled at room temperature to 30％reduction in thickness,Zr50Ms0 ribbons show 10％increase in hardness,while retaining good bending plasticity.Cold-rolling induces precipitation of spheroidal B2 and irregular B33 particles,while deforma-tion in tension induces B2,B33 and also plate-like monoclinic precipitates.The B2 and B33 particles form by polymorphic transformation,and include a high density of internal defects.This novel deformation-induced precipitation has not been recognized for any Zr50Q50 binary or ternary alloys.The new multi-component systems are encouraging for future progress as structural amorphous alloys.
查看更多>>摘要：Recently,the anomalous photovoltaic effect of ferroelectric materials has attracted considerable atten-tion in the construction of efficient solar cells owing to the above-bandgap photovoltage of these ma-terials.In this study,we investigate the anomalous photovoltaic effect of relaxor-based ferroelectric Pb(ln1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3(PIMN-PT)ceramics with large remnant polarization and a nar-row optical bandgap.Excellent photovoltaic performance with an ultrahigh open-circuit voltage of 23 V(575 V/cm)is achieved,which is higher than the open-circuit voltages of all reported polycrystalline ma-terials with similar thickness.The phase structure,microstructure morphology,domain structure,ferro-electric and optical characteristics are analyzed,which could provide clues to the origin of the ultrahigh open-circuit voltage of PIMN-PT ceramics.The results suggest that the relaxor-based ferroelectric PIMN-PT system is a potential candidate for photovoltaic solar energy conversion devices.
查看更多>>摘要：In history,semiconductor-metal-semiconductor transistor(SMST)was proposed for frequency improve-ment.However,a general fabrication method is still missing due to the unsolved technological problem of deposition of a general crystalline semiconductor on metal,and a thinner metal base is also difficult to be fabricated with high quality.Recently,due to the atomic thickness of graphene,the concept of semiconductor-graphene-semiconductor transistor(SGST)has emerged which leads to the renaissance of SMST,however the experimental study is in its infancy.In this letter,SMST and SGST are fabricated using Si membrane transfer.It is found the common base current gain can be improved from about 0.5％in a Si-Au-Si transistor to about 1％in a Si-Gr-Ge one,and to above 10％in a Si-Gr-Si one,which is attributed to both the ultra-thin thickness and the quantum capacitance effect of graphene.
查看更多>>摘要：LaMgAl11O19(LMA),characterized by high melting point,low density and thermal conductivity as well as good infrared emissivity,is regarded as a potential candidate for the thermal protection of hyper-sonic vehicles.Nevertheless,the unsatisfied phase stability at high temperature results in declining of the emissivity below 6 μm,which limits the extensive applications of LaMgAl11O19.In order to overcome this obstacle,three dense bulk high-entropy ceramics,(La0.2Nd0.2Gd0.2Sm0.2Pr0.2)MgAl11O19(HE LMA-1),(La0.2Nd0.2Gd0.2Sm0.2Dy0.2)Mg Al11O19(HE LMA-2)and La(Mg0.2Fe0.2Co0.2Ni0.2Zn0.2)Al11O19(HE LMA-3),were designed and successfully prepared through solid state reaction at 1700℃for 4 h in one step.XRD analyses show that the phase compositions of HE LMA-1,HE LMA-2 and HE LMA-3 are single-phase solid solutions with the relative density of 95.61％,95.49％and 94.31％,respectively.Heat treatment experiments demonstrate that the phase composition of HE LMA-1 remains a single phase after high-temperature heating,while second phase appears in other two samples.The stability of HE LMA-1 is attributed to small average size difference δ(～4％)of constitute elements.Intriguingly,the average emissivity of HE LMA-1 in the range of 3-6 μm reaches 0.9,which is significantly higher than that of LMA and other two HE LMA samples.The emissivity of all samples remains above 0.95 from 6 to 10 μm.In the far infrared region(10-14 μm),although the emissivity of these specimens decreases slightly,it still exceeds 0.85.The UV-Vis absorption spectra indicate that the formation of many discrete impurity energy levels with small intervals in HE LMA-1 promotes the f electrons to transit between adjacent impurity energy levels and conduction band,which enhances the infrared emission of HE LMA-1 below 6 μm.In a word,with improved phase stability and thermal emissivity in infrared range,high-entropy REMgAl11O19,especially(La0.2Nd0.2Gd0.2Sm0.2Pr0.2)MgAl11O19(HE LMA-1),is a promising candidate in thermal protection coatings of hypersonic vehicles.
查看更多>>摘要：Aluminum-based composite abradable seal coatings are pivotal to improving the efficiency of aero en-gines or gas turbines.However,the adhesive transfer frequently occurs between metallic blade tips and aluminum-based composite coatings,resulting in engine vibration and even jam.Many past studies had tried to solve this problem by reducing coating hardness,improving lubrication,or strengthening blade tips,but all had failed.In this paper,we proposed a novel epoxy-based composite abradable seal coat-ing,eliminating adhesive transfer by changing metal-to-metal scraping pair to metal-to-polymer scraping pair.The coating was developed via a hierarchical structure design.Large spherical pores were uniformly distributed in the continuous epoxy matrix with fine graphite dispersion.By adding 20 vol.％graphite and 50 vol.％hollow microspheres,a self-lubricating epoxy-based coating of 0.26 friction coefficient with thermal conductivity of 0.28 W/(m.K),coating HR15Y hardness at 54.8,and bonding strength at 18.7 MPa can be reached.When the metallic blades scrape the epoxy-based composite coating,no adhesive trans-fer occurs.Besides,a smooth scraped surface is formed by pseudoplastic deformation.This epoxy-based composite abradable seal coating opens a new way to improve the efficiency and reliable operations of air engine compressors.
查看更多>>摘要：Here we report a new one-step thermal polycondensation process to form crinkly graphitic carbon nitride nanosheets(CGCNNs)via supramolecular preorganization,using a mixture of urea and melamine as the starting material.Systematical studies reveal that the newly developed CGCNNs significantly strengthen the optical absorption,widen the bandgap,and increase the Hall mobility and carrier density compared to that of its bulk counterpart,regardless of the similar chemical composition and structure.As a result,the photocatalytic hydrogen production rate is improved by 7 times.Moreover,Na doping of CGCNNs can further promote its photocatalytic activity,leading to an excellent photocatalytic hydrogen production rate of 250.9 μmol h-1,which is approximately 10.5 times higher than its bulk counterpart.Moreover,an impressive apparent quantum efficiency of 19.12％is achieved at 420 nm.This study provides a facile strategy for the design of efficient low-cost carbon-nitride-based photocatalysts for solar fuel production.
查看更多>>摘要：Facile strategy enabling the fabrication of carbon dots(CDs)with favorable performance useful for various applications is highly desirable.Here,we report the fabrication of highly fluorescent carbon dots(CDs)towards sensitive metal ion detection,brightly fluorescent printing pattern,as well as green flame retar-dants for synthetic polymeric materials.CDs are synthesized by solvothermal treatment of polypropylene carbonate(PPC)with ethylenediamine,and the quantum yield of CDs could increase from 30％to 86％by further adding trace of citric acid.The abundant functional groups on the surface of CDs allow CDs well incorporated into polymers to form CD-loaded polystyrene(PS)microspheres,which are employed to construct fluorescent supraballs via triphase microfluidic technique and used as"inks"for uniform fluorescent patterns.Interestingly,the resultant CDs show good flame retardancy for highly flammable polymeric foams and fibers.The CDs surpass previously reported flame-retardant additives,to show ex-cellent combustion resistance that the addition of 20 wt％CDs causes 75％decrease in the peak of heat release rate(P-HRR)for polyurethane(PU)foams.Significantly,a molecular dynamics simulation pro-cess for PU/CDs combustion is constructed.This work may spur the preparation and application of high-performance carbon-based nanomaterials.
查看更多>>摘要：Perovskite functional ceramics have been widely applied for thermal protection owing to their unique physical properties.However,formation of oxygen vacancies under external stimuli usually limits their performance in practical applications.Therefore,the mechanism of the effect of oxygen vacancy on the layer structure of perovskite La0.9Sr0.1TiO3+δ was investigated by experiments and first-principles simula-tions.The experimental results showed that the lattice distortion occurred in oxygen-deficient environ-ment to give a longer c-axis,along with a significant adjustment in the modes of A/B-O bond vibration,resulting in lower reflectivity.Advanced transmission electron microscopy studies revealed that oxygen vacancies induced localized atomic rearrangements via[TiO6]layer movements to adapt to the lattice distortion.This eventually restructured a part of the layer interfaces by expanding the overlapping pro-jection of atoms in the c-axial direction.The specific transformation process was described as a com-pendious process,while geometric phase analysis effectively clarified how oxygen vacancies can inhibit reflectivity on the layer structure.Thus,this study provides effective approaches for researching the ef-fects of oxygen vacancy on the physical properties of orthorhombic layer perovskite structures,which may facilitate the development of perovskite-based functional devices.
查看更多>>摘要：This work investigated the dependence of deformation mechanisms and mechanical properties on cold rolling reductions of the metastable TB8 titanium alloy.Results shown that the crystal orientation of the matrix changes with the increasing level of reduction,leading to the activation of complex deformation mechanisms in the matrix.When the rolling reduction is 10％,the deformation mechanisms are dom-inated by dislocations and{332}<113>deformation twins.As the reductions increase to 20％-50％,the secondary deformation twinning(SDT)is triggered in primary deformation twins besides the primary kink band is activated.Meanwhile,the secondary kink bands and{332}<113>twins have be observed in the primary kink bands.When the reduction reaches to 60％,the deformation mechanisms are dominated by dislocations and deformation twins.Furthermore,the matrix refined by crisscrossing among the twins,kink bands and other deformation mechanisms during cold rolling,which shortens the dislocation mean free path and then affects the strength and shape of the alloy.The dynamic Hall-Petch effect and the interaction between multi-scale deformed structures control the work hardening behavior of the alloy.
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