查看更多>>摘要：Recently great efforts have been focused on designing high-performance microwave absorbers using sus-tainable biomass resources,but there remains a lack of green and efficient fabrication methods.Herein,inspired by natural porous character of biomass waste,we demonstrated a green one-step route to con-vert waste coffee grounds into porous C/Fe hybrids,and further explored their potential applications for broadband and high-efficiency microwave absorption.In this design,the WCG-20-750(incorporated 20 wt％Fe(C5H7O2)3 catalyst and carbonized at 750 ℃)exhibited porous microstructure with the highest char yield of 55.45 wt％.Furthermore,the as-prepared C/Fe hybrids from WCG-20-750 displayed excellent microwave absorption performances.Typically,the minimum reflection loss(RLmin)reached to-52.86 dB and the widest effective absorption bandwidth(EAB)was 6.40 GHz at the thickness of 3.0 mm.This work provides an economically viable and environmentally friendly strategy to convert biomass wastes into value-added microwave absorbers,ultimately making contributions to the upcycling of renewable biomass resources and the fostering of sustainable environment.
查看更多>>摘要：In the metal-based peroxymonosulfate(PMS)activation process,the sluggish surface redox cycle of metal ions generally hampered the efficiency of PMS activation for pollutant removal.Herein,Co-doped CuWO4/BN quantum dots(CW/Co/BNQDs)photocatalysts were developed to realize Cu2+/Cu+and Co2+/Co3+dual ions redox cycles for PMS activation,which would facilitate the tetracycline(TC)removal.CW/4Co/2BNQDs could degrade 94.8％TC within 30 min in PMS/Vis system,and the apparent rate con-stant of CW/4Co/2BNQDs was 2.7 times and 1.2 times higher than those of CW and CW/4Co,respectively.The improved TC degradation performance could be attributed to the synergetic effect between BNQDs and dual redox cycles.X-ray photoelectron spectroscopy(XPS)spectra of samples before and after the reaction demonstrated that BNQDs were beneficial for accelerating the Cu2+/Cu+and Co2+/Co3+redox cycles in CW/4Co/2BNQDs,further boosting the activation of PMS in TC degradation.Experiments of dif-ferent radical scavengers revealed that the SO4-/OH/h+/1O2 reactive species participated in the PMS activation for the TC degradation process.The possible TC degradation pathway and intermediate toxic-ity were detailed investigated.In addition,CW/4Co/2BNQDs exhibited outstanding photocatalytic activity over five consecutive cycles,which illustrated that it was supposed to be a reliable PMS activator over antibiotic elimination for practical application.And this work shed new light on constructing dual redox cycles for efficient PMS activation.
查看更多>>摘要：P-type Mg3Sb2-based Zintls have attracted considerable interest in the thermoelectric(TE)field due to their environmental friendliness and low cost.However,compared to their n-type counterparts,they show relatively low TE performance,limiting their application in TE devices.In this work,we simul-taneously introduce Bi alloying at Sb sites and Ag doping at Mg sites into the Mg3Sb2 to coopera-tively optimize the electrical and thermal properties for the first time,acquiring the highest ZT value of～0.85 at 723 K and a high average ZT of 0.39 in the temperature range of 323-723 K in sample Mg2.94Ag0.06Sb1.9Bi0.1.The first-principle calculations show that the co-doping of Ag and Bi can shift the Fermi level into the valence band and narrow the band gap,resulting in the increased carrier concentration from 3.50 × 1017 cm-3 in the reference Mg3Sb0.9Bi01 to～7.88 × 1019 cm-3 in sample Mg2.94Ag0.06Sb0.9Bi0.1.As a result,a remarkable power factor of～778.9 μW m-1 K-2 at 723 K is achieved in sample Mg2.94Ag0.06Sb0.9Bi0.1.Meanwhile,a low lattice thermal conductivity of～0.48 Wm-1 K-1 at 723 K is also obtained with the help of phonon scattering at the distorted lattice,point defects,and nano-precipitates in sample Mg2.94Ag0.06Sb0.9Bi0.1.The synergistic effect of using the multi-element co-doping/-alloying to optimize electrical properties in Mg3Sb2 holds promise for further improving the TE performance of Zintl phase materials or even others.
查看更多>>摘要：Spark erosion is a convenient,flexible,and low-cost method to quickly produce fine powders of met-als,alloys,and semiconductors in size ranging from nearly a hundred micrometers to submicrometer by repetitive spark discharges.Due to the complexity of the powder-forming journey,normally accompanied by high temperature,high pressure,decomposition,diffusion and rapid quenching caused by discharge plasma,the mechanisms of powder formation and possible contaminant infiltration are still controversial,posing a significant challenge to control particle size and chemical composition of the powder produced by this method.In this study,Fe-based amorphous powders in different particle-size distributions with high sphericity were fabricated by spark erosion under different discharge-energy conditions.The max-imum particle size of the resultant powders can be correlated with discharge parameters,crater depth,and crater radius,respectively.A multi-ring-breakup model is proposed to reveal the particle-size dis-tribution of the powder formed from the electrode melt under a single-pulse discharge.Furthermore,a dielectric-element infiltration model is provided to quantitatively evaluate the infiltration mass ratio of the contaminant elements,stemming from the decomposed products of dielectric liquid,in the resultant powder with different particle sizes.The models verified through the experimental data are significant for the development of high-performance fine Fe-based amorphous powder with controlled particle size and chemical composition.
查看更多>>摘要：Cold spray,as a solid-state additive manufacturing process,has been attracting increasing attention from both scientific and industrial communities.However,cold-sprayed deposits generally have unfavorable mechanical properties in their as-fabricated state compared to conventionally manufactured and fusion-based additive-manufactured counterparts due to the inherent microstructural defects in the deposits(e.g.,porosity and incomplete interparticle bonding).This downside reduces its competitiveness and lim-its its wide applications as an additive manufacturing process.In the past years,many strengthening technologies have been developed or introduced to adjust the microstructure and improve the mechanical properties of cold-sprayed deposits.The term"strengthening"in this work specifically refers to improving the mechanical strength,particularly the tensile strength of the cold-sprayed bulk deposits.According to the stage that the strengthening technologies are used in the cold spray process,they can be classified into three categories:pre-process(e.g.,powder heat treatment),in-process(e.g.,powder heating,in-situ micro-forging,laser-assisted cold spray),and post-process(e.g.,post heat treatment,hot isostatic pressing,hot rolling,friction stir processing).Therefore,a comprehensive review of these strengthening technolo-gies is conducted to illuminate the possible correlations between the strengthening mechanisms and the resultant deposit microstructures and mechanical properties.This review paper aims to help researchers and engineers well understand the different strengthening methods and provide guidance for the cold spray community to develop new strengthening strategies for future high-quality mass production.
查看更多>>摘要：Gradient microstructure modification is a cost-efficient strategy for high strength without compromising ductility,which is urgently needed in the fundamental science of engineering materials.In this study,heterogeneous structures of AZ61 alloy bars with anisotropic gradients(with different grain size distribu-tions from the surface to the center)were observed to exhibit strong strength-ductility synergies under different deformation temperatures.The results reveal that the grain refinement process under medium-low temperature deformation conditions(≤ 350 ℃)consists of four transition stages along the radial direction,i.e.,twin activations and deformation band formations,dislocation cells and pile-ups,ultra-fine sub-grains,and randomly orientated quasi-micron grains.Different deformation temperatures have a great influence on twin activations and deformation band formations,and the high temperature can easily provoke the initiation of non-basal slip.The deformation bands were determined as a primary nucleation site due to their highly unstable dislocation hindrance ability.Analysis in combination with the Radial forging(RF)deformation process,the differences of dynamic precipitates can be attributed to microstructural difference and solubility limit of Al at different temperatures.By summarizing the ten-sile test results,the sample forged at 350 ℃ exhibited the best strength-ductility synergy,exhibiting the highest elongation(EL)of 23.2％with a 251 MPa yield strength(YS)and 394 MPa ultimate tensile strength(UTS)in center region,and combined with the highest strength value of 256 MPa YS and 420 MPa UTS in the center region,while the EL was slightly degraded to 19.8％.
查看更多>>摘要：Piezoelectric materials with unique properties are hugely appealing for high sensitivity sensors and ultra-sonic transducers.Here,Pb(Ni1/3Nb2/3)O3-Pb(Yb1/2Nb1/2)O3-PbTiO3 piezoelectric system was designed and investigated in detail.The optimized piezoelectric response(d33=826 pC/N,d33*=1017 pm/V)together with good temperature stability and negligible performance degradation up to 106 cycles was achieved in 0.58PNN-0.10PYN-0.32PT composition.Rayleigh analysis revealed the amplification of intrinsic and ex-trinsic contributions in MPB region due to more spontaneous polarization orientations and an increase in chemical disorder of system after the introduction of PYN.The origin of high piezoelectric response was investigated through the combination of scanning electron microscopy and piezoresponse force mi-croscopy.The diversity of B-site cations was shown to enhance local structural heterogeneity,weaken long-range ferroelectric ordered domains,and lower free energy barrier via the formation of nanodomain configuration that promoted polarization rotation,thereby improving piezoelectric properties of the ma-terial.Therefore,it is suggested that increasing the diversity of B-site cations is an effective strategy for achieving outstanding piezoelectric performance.
查看更多>>摘要：Photocatalytic CO2 reduction provides a promising strategy for the alleviation of greenhouse effect and energy shortage problem.Metal single atom modification is an effective method to improve the CO2 re-duction performance of covalent organic framework(COF)photocatalysts,while the intrinsic mechanism is not revealed in depth.Herein,a Pt-COF photocatalytic system was constructed by embedding Pt sin-gle atom in TFPT-TMT-COF(TFPT:1,3,5-tris(4-formylphenyl)-triazine,TMT:2,4,6-trimethyl-1,3,5-triazine).Based on density functional theory(DFT)calculation,the geometric structure and electronic property of Pt-COF were investigated,and the CO2 adsorption and reduction reaction process on Pt-COF were simu-lated.The results show that the Pt atom can be steadily anchored in COF via the formation of Pt-N and Pt-C bonds.Moreover,there is strong electronic interaction between Pt and COF.The incorporation of Pt atom benefits the CO2 reduction activity of COF from multiple aspects:(ⅰ)reducing the band gap and improving light absorption;(ⅱ)enhancing CO2 adsorption and activating the CO2 molecule;(ⅲ)decreas-ing the energy barrier in the hydrogenation step of CO2→COOH,thus facilitating CO2 conversion to CO;(ⅳ)inhibiting the hydrogenation of CO,thereby increasing the selectivity of CO.This work brings a novel insight into the excellent CO2 reduction performance of Pt modified COF,and provides useful references for the design of single atom photocatalysts.
查看更多>>摘要：Additive manufacturing technology based on laser powder bed fusion(LPBF)offers a novel approach for fabricating bulk metallic glass(BMG)products without restriction in size and geometry.Nevertheless,the BMGs prepared by LPBF usually suffered from less plasticity and poorer fracture toughness as compared to their cast counterparts due to partial crystallization in heat-affected zones(HAZs).Since crystalliza-tion in HAZs is hard to avoid completely in LPBF BMGs,it is desirable to design a suitable alloy system,in which only ductile crystalline phase,instead of brittle intermetallics,is formed in HAZs.This unique structure could effectively increase the toughness/plasticity of the LPBF BMGs.To achieve this goal,a qua-ternary BMG system with a composition of Zr47.5Ct45.5Al5Co2 is adopted and subjected to LPBF.It is found that nearly a single phase of B2-ZrCu is precipitated in HAZs,while a fully amorphous phase is formed in molten pools(MPs).This B2 phase reinforced BMG composite exhibits excellent mechanical properties with enhanced plasticity and toughness.Furthermore,it is easy to modulate the mechanical properties by altering the amount of the B2 phase via adjusting the laser energy input.Finally,the best combination of strength,plasticity,and notch toughness is obtained in the BMG composite containing 27.4％B2 phase and 72.6％amorphous phase,which exhibits yield strength(σs)of 1423 MPa,plastic strain(εp)of 4.65％,and notch toughness(Kq)of 53.9 MPa m1/2.Furthermore,a notable strain-hardening is also observed.The improvement of plasticity/toughness and appearance of strain-hardening behavior are mainly due to the martensite phase transformation from the B2 phase to the Cm phase during plastic deformation(i.e.,the phase transformation-induced plasticity effect).The current work provides a guide for making advanced BMGs and BMG composites by additive manufacturing.
查看更多>>摘要：To improve the surface integrity and high cycle fatigue property of Ti6Al4V ELI alloy,the electric pulse has been introduced into the ultrasonic surface rolling process(USRP),which is called electric pulse-assisted ultrasonic surface rolling process(EUSRP).With the help of"electroplasticity"of the electric pulse,the thickness of the surface gradient deformation layer was about three times of the USRP specimens by adjusting the pulse current level.However,the surface hardness decreases due to the continuous effect of the pulse current and the"skin effect"during treatment.It is worth noting that the higher the ap-plied pulse current,the more severe the softening.This paradox causes the fatigue performance of EUSRP specimens lower than that of USRP specimens.To break this paradox,the EUSRP treatment is followed by a USRP treatment.The EUSRP-2(with a pulse current of 200 A)+USRP specimens exhibit excellent surface hardness,a gradient deformation layer thickness of about 400 pm,low surface roughness and high compressive residual compressive stress.Besides,the hardening mechanisms of the different surface strengthening specimens have been quantitatively analyzed in combination with microstructure analysis.The fatigue life of Ti6Al4V ELI alloy can be improved by about 25 times at 780 MPa using the EUSRP-2+USRP treatment,the main reason for the highest fatigue life is the deepest surface gradient layer and the deepest crack initiation site.The fatigue limit of the EUSRP-2+USRP specimens is not the highest because too much surface hardening causes compressive residual stress relaxation during cycling and the beneficial effect of compressive residual stress is eliminated.
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