查看更多>>摘要：Different types of polymer films were used in the combined in-mold decoration and microcellular injec-tion molding(IMD/MIM)process.The multiphase fluid-solid coupled heat transfer model was established to study the thermal response at the melt filling stage in the IMD/MIM process.It was found that the temperature distributed asymmetrically along the thickness direction due to the changed heat transfer coefficient of the melt on the film side.When polyethylene terephthalate(PET)films were applied,the temperature of the melt-film interface increased faster and to be higher at the end of melt filling stage in comparison with the application of polycarbonate(PC)and thermoplastic polyurethane(TPU)films.And the effects of film types on the cellular structure,forming defects and mechanical properties of IMD/MIM parts were also studied experimentally.The results showed that the film types had no obvious effect on the cells size in the transition layer and the mechanical properties of the parts.Under certain film thick-ness,the offset distance of core layer was the largest with PET film used,while the offset distance was the smallest with TPU film used.And similar results were found for the warpage of the parts.However,an exactly opposite change occurred for the thickness of film-side transition layer and the bubble marks on the surface of the parts.
查看更多>>摘要：980 high-strength steel has been widely used in marine engineering structures due to its high strength and toughness.However,it is easily affected by the harsh environmental conditions(such as the pres-ence of sulfate-reducing bacteria,SRB),leading to the risk of stress corrosion cracking(SCC).In this pa-per,the effects of SRB and its metabolites on hydrogen permeation and SCC mechanism of 980 steel in seawater solution were investigated by slow strain rate tensile test,scanning electron microscope,X-ray energy spectroscopy,Raman spectroscopy and Devanathan-Stachurski double electrolytic cell.Results demonstrated that the SCC susceptibility of 980 steel was promoted in the presence of SRB,which was related to the cultivation time of the bacteria.When SRB were cultivated for 3 d and 6 d,the SCC mech-anism was controlled by hydrogen-induced cracking(HIC);while the cultivation time extended to 11 d,the SCC of 980 steel was under the combined effect of the anodic dissolution(AD)and HIC mechanism.When cultivated for 16 d,the SCC of 980 steel was caused by the dominant AD.Both the SRB acceler-ated hydrogen permeation under cathodic depolarization process and SRB assisted AD(pitting corrosion)played an enhancing role in promoting SCC susceptibility of 980 steel.
查看更多>>摘要：As cathodes,iron-series(Fe,Co,Ni)clusters supported by carbon materials exhibit outstanding electrocat-alytic reduction activities in many electrocatalytic applications.To date,this general characteristic of iron-series clusters that should be related to the inherent attributes of these electrodes has not been fully un-derstood from the perspectives of thermodynamics and electronic structure alone.Electron transport is a necessary process in electrocatalysis,and therefore,the study of the change of the electronic state in elec-tron transport is beneficial for understanding this general characteristic of iron-series cluster catalysts.In this work,the electron transport properties,including the conductivity and transport spin-polarization at the Ni-cluster/graphene interface are carefully investigated as an example of carbon-supported iron-series electrodes.Using first-principles calculations within the framework of the nonequilibrium Green's func-tion density functional theory(NEGF-DFT),we reveal that the electronic transport states of the coupled Ni-cluster/graphene are strongly changed compared to those of their isolated Ni-cluster and graphene component.It is found that graphene dominates the overall conductivity of the interface,while the mor-phology of Ni-clusters controls the spin polarization efficiency.High spin polarization can lead to the self-excitation effect of the electrons that raises the energy of the electronic system,improves the ther-modynamics of the reduction reaction and promotes catalytic activity.Our work hints that iron-series elements(Fe,Co,Ni)based electrodes may generally show transport polarization that is likely to give rise to a high electrocatalytic reduction activity and such transport polarizability can be used as a new factor in the further exploration and design for electrocatalytic materials.
查看更多>>摘要：High-entropy alloys(HEAs)have attracted tremendous attention owing to their controllable mechanical properties,whereas additive manufacturing(AM)is an efficient and flexible processing route for novel materials design.However,a profound appraisal of the fundamental material physics behind the strength-ening of AM-printed HEAs upon low/intermediate-temperature annealing is essential.In this work,CoCr-FeNiMn HEAs have been prepared using laser-engineered net shaping(LENS)and subsequently annealed at different temperatures.The CoCrFeNiMn HEA annealed at intermediate-temperature(873 K)exhibits a strong strain hardening capability,resulting in ultimate strength of 725 MPa and plasticity of 22％.A ternary heterogeneous strengthening mechanism is proposed to explain this phenomenon,in which equiaxed grains,columnar grains,and σ precipitates play different roles during tensile deformation.The resultant excellent strength and ductility can be ascribed to the heterostructure-induced mismatch.The equiaxed grains provide adequate grain boundaries(GBs),which induce dislocation plugging-up and en-tanglement;the columnar grains induce the onset and arrest of the dislocations for plastic deformation;and the σ precipitates hinder the movement of slip dislocations.The results provide new insights into overcoming the strength-ductility trade-off of LENS-printed HEAs with complex geometries.
查看更多>>摘要：The magnetic refrigeration(MR)utilizing magnetocaloric effect(MCE)has been recognized as an envi-ronmentally friendly and energy efficiency technology.Here we presented the magnetic properties and MCE in Pr-doped La1-xPrxFe12B6(x=0.05-0.2)itinerant-electron metamagnetic(IEM)compounds.A small amount of Pr doping La site can greatly improve the peak values in the magnetic entropy change ΔSM(T)curves,especially under relatively low magnetic field changes(ΔH).Additionally,the peak temperature increases gradually and the magnetic hysteresis reduces gradually with increasing x.The observed MCE in present La1-xPrxFe12B6 compounds is related to its field-induced first-ordered IEM transition.The peak values of ΔSM for La1-xPrxFe12B6 compounds reach 13.4,15.4,12.5 and 13.0 J/(kg K)at Tc～58,68,72 and 89 K for x=0.05,0.10,0.15 and 0.2 under ΔH of 0-7 T,respectively.The corresponding relative cool-ing power values are 462.3,480.7,372.4 and 375.7 J/kg.The present La1-xPrxFe12B6 compounds could be good candidates for active MR application if the magnetic and thermal hysteresis can be further reduced.The present work indicates that the LaFe12B6-based material system could also exhibit promising magne-tocaloric performances.
查看更多>>摘要：We propose a method to quantitatively characterize the fine phase transition processes of Li+/Er3+∶BaTiO3(BLET)ferroelectric materials by observing fluorescence wavelength shift.A lithium and erbium co-doped barium titanate ferroelectric ceramic was fabricated and the down-conversion infrared fluorescence spec-tra of the transition 4I13/2 → 4I15/2 were measured as a function of temperature.The three structural phase transition processes,namely rhombohedral-orthorhombic,orthorhombic-tetragonal,and tetragonal-cubic transformations,determined by X-ray diffraction results are accompanied by corresponding changes in the position of the fluorescence peaks,yielding an exact consistency.This contactless,non-destructive and spatially-resolved fluorescence method provides a localized quantitative analysis for the phase tran-sition processes of BLET ceramics.As this method is based on the fluorescence peak wavelength depen-dence on the crystal environment,it may potentially be used to characterize the phase transitions in other ferroelectric materials.
查看更多>>摘要：The role of additional ternary alloying elements on the performance of stationary TiFe-based hydrogen storage alloys was investigated based on first-principles density functional theory calculations.As a ba-sic step for examinations,the site preference of each alloying element in the stoichiometric and non-stoichiometric B2 TiFe compounds was clarified considering possible anti-site defects.Based on the re-vealed site preference,the effect of various possible ternary elements on the hydrogen storage was exam-ined by focusing on the formation enthalpies of TiFeH and TiFeH2 hydrides,which were closely related to the change in the location of plateaus in the pressure-composition-temperature curve.Several physical properties such as the volume expansion due to hydride formation were also examined to provide ad-ditional criteria for selecting optimum alloying conditions in future alloying design processes.Candidate alloying elements that maximize the grain boundary embrittlement due to the solute segregation were proposed for the enhanced initial activation of TiFe-based hydrogen storage alloys.
查看更多>>摘要：Many non-precious metal-based catalysts with high intrinsic activity for catalytic reactions are prone to structural degradation in practical application,which leads to poor stability.In this work,we propose c-CoSe2/o-CoSe2 as the oxygen electrode of lithium-oxygen batteries(LOBs)to improve its cycle stability.The heterogeneous interface inside c-CoSe2/o-CoSe2 leads to an increase in the covalence bonds between Co and Se ions,which greatly enhances the robustness of the crystal lattice,thereby improving the sta-bility of the catalyst.In addition,the strong interaction between the mixed phases is favorable for ad-justing the electron density around the active sites and boosting oxygen electrode kinetics.Moreover,the epitaxial growth of o-CoSe2 on c-CoSe2 will cause abundant heterogeneous interfaces and slight lattice distortion along the interfaces,thereby providing sufficient catalytic reaction sites.The DFT calculation results show that the optimized adsorption of intermediates at the heterogeneous interface plays an im-portant role in boosting oxygen electrode reactions and improving the electrochemical performance of LOBs.The experimental results show that LOBs with the c-CoSe2/o-CoSe2 electrodes exhibit outstanding performance,including large specific capacity of about 23,878 mA h g-1,high coulombic efficiency of up to 93.66％,and excellent stability of over 176 cycles(1410 h).
查看更多>>摘要：Although perovskite solar cells(PSCs)have achieved a high power conversion efficiency(PCE)within a short period of development,the high-temperature sintering of the constituent electron-selective layers(ESLs)impedes the commercialization.In this report,we demonstrate the effectiveness of an intense-pulsed-light(IPL)treatment for the rapid and damage-free sintering of amorphous-SnO2 ESLs for use in PSCs.The IPL treatment of amorphous-SnO2 substantially reduced the amount of surface hydroxyl groups,modified the surface energy,and enabled the growth of a low-stress perovskite layer with large grain sizes,all of which enhanced the photovoltaic properties and led to the proper alignment of band structures for efficient PSCs.Through comprehensive optimization of the IPL conditions,a PCE of 17.68％was achieved from the MAPbI3 planar PSC based on an amorphous-SnO2 IPL treated for a few tens of seconds,which was significantly increased compared with a PCE(7.06％)of nontreated SnO2 based coun-terpart.In addition,the PCE of the IPL-treated SnO2 based PSC is comparable to the best PCE(18.16％)of PSCs fabricated with SnO2 ESL annealed for three hours at 185℃.Because of its ultrafast sintering time and tendency to not damage SnO2 ESLs,the new IPL process is expected to open new opportunities for the commercialization of PSCs.
查看更多>>摘要：Owing to the unique features,such as mechanically robust,low-toxic,high stability,and high thermo-electric performance,CoSb3-based skutterudite materials are among art-of-the state thermoelectric can-didates.In this work,we develop a facile in-situ method for the growth of well-crystallinity(Ag,Sn)co-doped CoSb3 thin films.This preparation method can efficiently control the dopant concentration and distribution in the thin films.Both the density functional theory calculation and the experimental results suggest that Sn and Ag dopants trend to enter the lattice and preferentially fill interstitial sites.Addi-tionally,band structure calculation results suggest that the Fermi level moves into the conduction bands due to co-doping and eventually induces the increased electrical conductivity,which agrees with the optimization of carrier concentration.Moreover,an increase in the density of state after co-doping is re-sponsible for the increased Seebeck coefficient.As a result,the power factors of(Ag,Sn)co-doped CoSb3 thin films are greatly enhanced,and the maximum power factor achieves over 0.3 mW m-1 K-2 at 623 K,which is almost two times than that of the un-doped CoSb3 film.Multiple microstructures,including Sb vacancies and Ag/Sn interstitial atoms as point defects,and a high density of lattice distortions coupled with nano-sized Ag-rich grains,lead to all scale phonon scatterings.As a result,a reduced thermal con-ductivity of～0.28 W m-1 K-1 and a maximum ZT of～0.52 at 623 K are obtained from(Ag,Sn)co-doped CoSb3 thin films.This study indicates our facile in-situ growth can be used to develop high-performance dual doped CoSb3 thins.
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