Multifunctional compatible stealth materials have emerged as the focal point of contemporary protection technology research and vanadium-based nanomaterials play a pivotal role in the development of advanced stealth m...Multifunctional compatible stealth materials have emerged as the focal point of contemporary protection technology research and vanadium-based nanomaterials play a pivotal role in the development of advanced stealth materials.Here,a compatible stealth aerogel is successfully synthesized by employing mixed-valence decavanadate as the vanadium oxide(VO_(x))molecular model.Ultralight{V^(Ⅳ)VV_(9)}/MXene aerogel(0.0429 g cm^(-3))exhibits exceptional radar stealth performance with a minimal reflection loss(RL_(min))of−57.74 dB(99.9998%EMW absorption)and a significantly superior radar cross section reduction value of 26.77 dB m2.The aerogel’s exceptional properties,including a low infrared(IR)emissivity(0.479)and a low thermal conductivity of(32.30 mW m^(-1)K^(-1)),are crucial for enabling compatibility with IR and thermal stealth technologies.The presence of a mixed-valence polyoxovanadate cluster leads to an increase in the Schottky barrier and enhances magnetic properties,consequently boosting interfacial polarization and contributing to magnetic losses during electromagnetic wave(EMW)absorption.Consequently,altering the number of valence electrons significantly enhances the compatible stealth capabilities.These findings contribute significantly to our comprehension of how microstructure impacts EMW absorption processes and provide a basis for further research into the development of VO_(x)-based compatible stealth materials.展开更多
The migration and transformation of hexavalent chromium(Cr(VI))in the environment are regulated by pyrite(FeS2).However,variations in pyrite crystal facets influence the adsorption behavior and electron transfer betwe...The migration and transformation of hexavalent chromium(Cr(VI))in the environment are regulated by pyrite(FeS2).However,variations in pyrite crystal facets influence the adsorption behavior and electron transfer between pyrite and Cr(VI),thereby impacting the Cr(VI)reduction performance.Herein,two naturally common facets of pyritewere synthesized hydrothermally to investigate the facet-dependent mechanisms of Cr(VI)reduction.The experimental results revealed that the{111}facet exhibited approximately 1.30–1.50 times higher efficiency in Cr(VI)reduction compared to the{100}facet.Surface analyses and electrochemical results indicated that{111}facet displayed a higher iron-sulfur oxidation level,which was affected by its superior electrochemical properties during the reaction with Cr(VI).Density functional theory(DFT)calculations demonstrated that the narrower band gap and lower work function on{111}facet were more favorable for the electron transfer between Fe(II)and Cr(VI).Furthermore,different adsorption configurations were observed on{100}and{111}surfaces due to the unique arrangements of Fe and S atoms.Specifically,O atoms in Cr_(2)O_(7)^(2−)directly bound with the S sites on{100}but the Fe sites on{111}.According to the density of states(DOS),the Fe site had better reactivity than the S site in the reaction,which appeared to be related to the fracture of S-S bonds.Additionally,the adsorption configuration of Cr_(2)O_(7)^(2−)on{111}surface showed a stronger adsorption energy and a more stable coordination mode,favoring subsequent Cr(VI)reduction process.These findings provide an in-depth analysis of facet-dependent mechanisms underlying Cr(VI)reduction behavior,offering new insights into studying environmental interactions between heavy metals and natural minerals.展开更多
Bismuth telluride-based alloys are the most widely used thermoelectric(TE)materials.Despite this,zonemelted Bi_(2)Te_(3)-based alloys suffer from poor mechanical properties,and polycrystalline materials prepared by po...Bismuth telluride-based alloys are the most widely used thermoelectric(TE)materials.Despite this,zonemelted Bi_(2)Te_(3)-based alloys suffer from poor mechanical properties,and polycrystalline materials prepared by powder metallurgy often disrupt the desired texture due to their inherent anisotropic crystal structure.In this study,we achieved a synergistic integration of nanoscale structures,highly oriented texture,and intrinsic BiTe’antisite defects in P-type Bi_(0.5)Sb_(1.5)Te_(3) bulk materials by employing layered directional sintering(LDS)on melt-spinning ribbons produced in a Bi-rich environment.The transmission electron microscopy analysis revealed regions of high-density distortions within the well-aligned nanograins,which play a crucial role in reducing lattice thermal conductivity.Ab initio simulations and Boltzmann transport equation analyses reveal that the BiTe’antisite defects generate both resonance states and additional phonon scattering channels.This full-spectrum phonon scattering coupled with high carrier mobility leads to a maximum figure of merit(ZT)of 1.54 at 375 K.Additionally,the compressive strength of the material reaches 140 MPa,which is 3.5 times higher than that of zone-melted counterparts.This work offers an efficient pathway for the facile preparation of high-performance Bi_(2)Te_(3)-based thermoelectric materials.展开更多
Proton exchange membrane fuel cell(PEMFC)is a promising clean energy source,but its performance and stability are vulnerable to the negative effects of humidity conditions.The gas diffusion substrate(GDS)plays a pivot...Proton exchange membrane fuel cell(PEMFC)is a promising clean energy source,but its performance and stability are vulnerable to the negative effects of humidity conditions.The gas diffusion substrate(GDS)plays a pivotal role in regulating the moisture and gas transport.The single pore structure of traditionally designed GDS often leads to the pathway competition between moisture and gas,which effects the efficiency of fuel cells.In this study,we report on a hierarchical fibrous paper with tunable hierarchical pores for a sustainable GDS.This design offers gas permeability under wet conditions,by separating the gas pathway from the moisture pathway,thus mitigating their pathway competition.In addition,this paper forms a multi-scale scaffold that absorbs moisture under high humidity conditions and releases it under dry conditions.It is allowed to maintain an optimal internal humidity and further enhances the humidity adaptability.Furthermore,the carbon footprint is only 15.97%,significantly lower than commercial alternatives.This feature makes it a sustainable solution to stabilize PEMFCs under diverse humidity conditions.展开更多
The conversion process of chitin,one of the abundant biomass resources on the earth,not only follows the principles of green chemistry,but also has significant value in industrial applications.However,it is a great ch...The conversion process of chitin,one of the abundant biomass resources on the earth,not only follows the principles of green chemistry,but also has significant value in industrial applications.However,it is a great challenge to directly convert insoluble and rigid structured chitin to 5-hydroxymethylfurfural(HMF).To address this issue,we developed a green conversion process combining pretreatment and catalytic system.Chitin was first pretreated by hexafluoro isopropanol(HFIP),which somewhat disrupted the hydrogen bonding network within the chitin structure.Subsequently,formic acid(FA)and silicotungstic acid(STA)synergistically catalyzed the conversion to HMF in a biphasic system of 2-methyltetrahydrofuran(2-Me-THF)/H2O,and high yields(40.2%)HMF was obtained under the optimism conditions.The product distribution was analyzed by HPLC-MS and the co-catalysis of FA with STA was evidenced.A dual-function catalytic system with both Lewis and Br?nsted acids was created,the catalytic system that significantly improved the efficiency of complex tandem catalytic reactions with chitin.Based on the experimental results,a possible pathway for chitin conversion was deduced,providing a new catalytic idea for the efficient conversion of chitin to HMF.展开更多
The carbonylation of amines offers a promising route for synthesizing N-substituted carbamates with high atom economy.However,conventional catalysts exhibit limited catalytic efficiency,and the underlying proton trans...The carbonylation of amines offers a promising route for synthesizing N-substituted carbamates with high atom economy.However,conventional catalysts exhibit limited catalytic efficiency,and the underlying proton transfer mechanism remains elusive.Herein,we reported a metal-free,room-temperature strategy utilizing 1,5,7-triazabicyclo[4.4.0]dec-5-ene(TBD)as a dual hydrogen bond catalyst to synergistically activate propylamine(PA)and dimethyl carbonate(DMC).This green catalytic system achieves a 10-fold acceleration in reaction rate compared to other hydrogen bonding catalysts under mild conditions.This is enabled by dual hydrogen bonding of TBD with PA and DMC,which facilitates rapid proton transfer and stabilizes tetrahedral intermediates.Theoretical calculations confirm that the dual hydrogen bond system significantly lowers activation energy compared to single hydrogen bond analogs.Furthermore,it was revealed that the hydrogen bonding network within the product is the primary factor responsible for the sluggish reaction rate.This study demonstrates the effectiveness of a dual hydrogen bond system in accelerating the carbonylation of amines and provides a green route to access carbamates.展开更多
The efficient synthesis of methanol and ethylene glycol via the chemoselective hydrogenation of ethylene carbonate（EC） is important for the sustainable utilization of CO_2 to produce commodity chemicals and fuels. I...The efficient synthesis of methanol and ethylene glycol via the chemoselective hydrogenation of ethylene carbonate（EC） is important for the sustainable utilization of CO_2 to produce commodity chemicals and fuels. In this work, a series of β-cyclodextrin-modified Cu/SiO_2 catalysts were prepared by ammonia evaporation method for the selective hydrogenation of EC to co-produce methanol and ethylene glycol. The structure and physicochemical properties of the catalysts were characterized in detail by N_2 physisorption, XRD, N_2O titration, H_2-TPR, TEM, and XPS/XAES. Compared with the unmodified 25 Cu/SiO_2 catalyst, the involvement of β-cyclodextrin in 5β-25 Cu/SiO_2 could remarkably increase the catalytic activity—excellent activity of 1178 mgEC g_（cat）^（–1） h^（–1） with 98.8%ethylene glycol selectivity, and 71.6% methanol selectivity could be achieved at 453 K. The remarkably improved recyclability was primarily attributed to the remaining proportion of Cu~＋/（Cu^0＋Cu~＋）. Furthermore, the DFT calculation results demonstrated that metallic Cu^0 dissociated adsorbed H_2, while Cu~＋ activated the carbonyl group of EC and stabilized the intermediates. This study is a facile and efficient method to prepare highly dispersed Cu catalysts—this is also an effective and stable heterogeneous catalyst system for the sustainable synthesis of ethylene glycol and methanol via indirect chemical utilization of CO_2.展开更多
Eutectic high-entropy alloys(EHEAs),combining the advantages of both eutectic alloys and high-entropy alloys(HEAs),possess good castability and superior comprehensive mechanical properties which are regarded as a revo...Eutectic high-entropy alloys(EHEAs),combining the advantages of both eutectic alloys and high-entropy alloys(HEAs),possess good castability and superior comprehensive mechanical properties which are regarded as a revolutionary material system.In this paper,a current study of EHEAs is captured comprehensively for the first time,including basic theory,microstructure and deformation behavior,and alloy design.An in-depth analysis of the formation of different microstructures of EHEAs and their mechanical properties is presented,and four methods of designing EHEAs are summarized.Due to their unique characteristics,EHEAs show great potential in materials processing engineering.Here we give a comprehensive summary of their applications in welding,surface engineering,and additive manufacturing for the first time.Among them,EHEAs in welding are divided into three sections based on different welding techniques:fusion-based welding,solid-state welding,and diffusion reaction-based welding;EHEAs in surface engineering are separated into two parts:surface modification of bulk EHEAs and EHEA coatings;EHEAs in additive manufacturing are elaborated in two parts:laser powder bed fusion(LPBF)and laser direct energy deposition(LDED).Finally,a summary is given and a future outlook is prospected.展开更多
To measure the surface stress of thin laser cladding coatings with Rayleigh waves based on the cross correlation function, this pa- per introduced the influence of cross correlation step length on the stress measureme...To measure the surface stress of thin laser cladding coatings with Rayleigh waves based on the cross correlation function, this pa- per introduced the influence of cross correlation step length on the stress measurement. Flat-shaped specimens made of laser cladding Fe314 alloy coatings were performed by static tensile tests, and Rayleigh wave signals were collected during the test process with an ultrasonic pulser and receiver instrument combined with two Rayleigh wave transducers. The difference in time of flight between two signals was de- termined based on the cross correlation function. The microstructure was observed by scanning electronic microscopy. The influence of the stress on the propagation velocity of Rayleigh waves and the relationship between the difference in time of flight and tensile stress under dif- ferent cross correlation step lengths were analyzed. The inhomogeneous deformation of the coatings affects the relationship between the dif- ference in time of flight and tensile stress; the stress measurement of the coatings is nearly constant with the increase of cross correlation step length when it attains one cycle.展开更多
Rechargeable aqueous zinc-ion batteries are recently gaining incremental attention because of low cost and material abundance,but their development is plagued by limited choices of cathode materials with satisfactory ...Rechargeable aqueous zinc-ion batteries are recently gaining incremental attention because of low cost and material abundance,but their development is plagued by limited choices of cathode materials with satisfactory cycling performance.The polyoxometalates perform formidable redox stability and able to participate in multi-electron transfer,which was well-suited for energy storage.Herein,a bicomponent polyoxometalate-derivative KNiVO(K_(2)[Ni(H_(2)O)_(6)]_(2)[V_(10)O_(28)]·_(4)H_(2)O polyoxometalates after annealing)is firstly demonstrated as a cathode material for aqueous ZIBs.The layered KV_(3)O_(8)(KVO)In the bi-component material constitutes Zn^(2+) migration and storage channels(K^(+) were substantially replaced by Zn^(2+) in the activation phase),and the three-dimensional NiV_(3)O_(8)(NiVO)part acts as skeleton to stabilize the ion channels,which assist the cell to demonstrate a high-rate capacity and specific energy of229.4 mAh/g and satisfactory cyclability(capacity retention of 99.1%after 4500 cycles at a current density of 4 A/g).These results prove the feasibility of POM as cathode materials precursor and put forward a novel pattern of the Zn^(2+)storage mechanism in the activated-KNiVO clusters,which also provide a new route for selecting or designing high-performance cathode for aqueous ZIBs and other advanced battery systems.展开更多
The moisture-conserving effect of straw mulch-based no-tillage(SMNT)is expected to increase fertile spikes and grain yield in environments with rainfall less than 200 mm.However,the mechanisms under-lying the positive...The moisture-conserving effect of straw mulch-based no-tillage(SMNT)is expected to increase fertile spikes and grain yield in environments with rainfall less than 200 mm.However,the mechanisms under-lying the positive effect of SMNT on wheat tillering are not fully elucidated.A split-plot experiment was designed to investigate the combined effects of SMNT and cultivars on tillering of dryland wheat grown under both dry and favorable climates.Application of SMNT to a cultivar with 1-2 tillers exploited both tillering and kernel-number plasticity,increasing the mean grain yield by 20.5%.This increase was attrib-uted primarily to an increased first-tiller emergence rate resulting from increased N uptake,leaf N con-tent,and N remobilization from tillers to their grain.The second and third tillers,as transient sinks,contributed to the tiller survival rate,which depends on tiller leaf number.The increased total N uptake by SMNT also increased the dry mass yield of tillers and the C:N ratio,reducing the asymmetric compe-tition between main stem and tillers.Owing to these beneficial effects,reduced mitogen-activated pro-tein kinase(MAPK)and abscisic acid signals were observed under SMNT,whereas indole-3-acetic acid(IAA)signals and genes involved in DNA replication and mismatch repair were increased.These signals activated three critical transcription factors(the calmodulin-binding transcription activator,GRAS domain,and cysteine-2/histidine-2 family)and further increased rapid drought response and tiller main-tenance after stem extension.Phenylpropanoid biosynthesis,sphingolipid biosynthesis,and galactose metabolism were most relevant to increased tillering under SMNT because of their critical role in drought response and lignin biosynthesis.Our results suggest that straw mulch-based no-tillage activates rapid drought response and improved wheat tillering by coordinating root N uptake,N remobilization,and asymmetric competition between main stem and tillers.展开更多
A non-phosgene route for the synthesis of hexamethylene-1,6-diisocyanate(HDI) was developed via catalytic decomposition of hexamethylene-1,6-dicarbamate(HDC) over Zn–Co bi-metallic supported ZSM-5 catalyst.The cataly...A non-phosgene route for the synthesis of hexamethylene-1,6-diisocyanate(HDI) was developed via catalytic decomposition of hexamethylene-1,6-dicarbamate(HDC) over Zn–Co bi-metallic supported ZSM-5 catalyst.The catalyst was characterized by FTIR and XRD analyses. Three solvents dioctyl sebacate(DOS), dibutyl sebacate(DBS) and 1-butyl-3-methylimidazolium tetrafluoroborate(BMIMBF_4) were investigated and compared; DOS gave better performance. The catalytic performances for thermal decomposition of HDC to HDI using DOS as solvent were then investigated, and the results showed that, under the optimized reaction conditions, i.e.,10 wt%concentration of HDC in DOS, 250 °C temperature, 60 min reaction time, 83.8% yield of HDI had been achieved over Zn–Co/ZSM-5. Decomposition of the intermediate hexamethylene-1-carbamate-6-isocyanate(HMI) over Zn–Co/ZSM-5 in DOS solvent was further studied and the results indicated that yield of HDI from HMI reached to 69.6%(98.6% HDI selectively) at 270 °C, which further increased the yield of the total HDI(HDI_(tol)) to as high as 95.0%. Recycling of catalyst showed that HDI and HMI yield slightly decreased, and by-product yield increased after the catalyst was reused for 4 times. At last possible reaction mechanism was proposed.展开更多
Large-scale patterns of species richness have gained much attention in recent years; however, the factors that drive high species richness are still controversial in local regions, especially in highly diversified mon...Large-scale patterns of species richness have gained much attention in recent years; however, the factors that drive high species richness are still controversial in local regions, especially in highly diversified montane regions. The Qinghai-Tibetan Plateau （QTP） and the surrounding mountains are biodiversity hot spots due to a high number of endemic montane species. Here, we explored the fac- tors underlying this high level of diversity by studying the relationship between species richness and environmental variables. The richness patterns of 758 resident bird species were summarized at the scale of 1°× 1° grid cell at different taxonomic levels （order, family, genus, and species） and in differ- ent taxonomic groups （Passeriformes, Galliformes, Falconiformes, and Columbiformes）. These rich- ness patterns were subsequently analyzed against habitat heterogeneity （topographical heterogen- eity and land cover）, temperature amplitude （annual temperature, annual precipitation, precipitation seasonality, and temperature seasonality） and a vegetation index （net primary productivity）. Our re- sults showed that the highest richness was found in the southeastern part of the QTP, the eastern Himalayas. The lowest richness was observed in the central plateau of the QTP. Topographical het- erogeneity and temperature amplitude are the primary factors that explain overall patterns of species richness in the QTP, although the specific effect of each environmental variable varies between the different taxonomic groups depending on their own evolutionary histories and ecological require- ments. High species richness in the southeastern QTP is mostly due to highly diversified habitat types and temperature zones along elevation gradients, whereas the low species richness in the cen- tral plateau of the QTP may be due to environmental and energetic constraints, as the central plateau is harsh environment.展开更多
The separation of ethylene glycol(EG)and 1,2-butanediol(1,2-BDO)azeotrope in the synthesis process of EG via coal and biomass is becoming of increasing commercial and environmental importance.Selective adsorption is d...The separation of ethylene glycol(EG)and 1,2-butanediol(1,2-BDO)azeotrope in the synthesis process of EG via coal and biomass is becoming of increasing commercial and environmental importance.Selective adsorption is deemed as the most promising methods because of energy saving and environment favorable.In this paper,NaY zeolite was used to separate 1,2-BDO from EG,and its adsorption properties was then investigated.The isotherms of EG and 1,2-BDO in vapor and liquid phases from 298 to 328 K indicated that they fitted Langmuir model quite well,and the NaY zeolite absorbent favored EG more than 1,2-BDO.The Grand Canonical Monte Carlo(GCMC)and molecular dynamics(MD)simulation techniques were conducted to investigate the competition adsorption and diffusion characteristics in different adsorption regions.It was observed that EG and 1,2-BDO molecules all have the most probable locations of the center of the 12-membered ring near the Na cations.The diffusivities of EG are lower than those of 1,2-BDO at the same adsorption concentration.At last,the breakthrough curves of the binary mixture regressed from the empirical Dose–Response model in fixed-bed column showed that the adsorption selectivity of EG could reach to as high as 2.43,verified that the NaY zeolite could effectively separate EG from 1,2-BDO.This work is also helpful for further separation of other dihydric alcohol mixtures from coal and biomass fermentation.展开更多
Microstructure and mechanical properties of the heat affected zone(HAZ)in multi-pass gas metal arc(GMA)welded Al Zn Mg Cu alloy plates were investigated,based upon which the mechanical anisotropy and fracture mechanis...Microstructure and mechanical properties of the heat affected zone(HAZ)in multi-pass gas metal arc(GMA)welded Al Zn Mg Cu alloy plates were investigated,based upon which the mechanical anisotropy and fracture mechanism were analyzed.The microstructure and composition were analyzed by scanning electron microscope(SEM)and energy dispersive spectroscope(EDS).X-ray diffractometer(XRD),transmission electron microscope(TEM)and selective area electron diffraction(SAED)were used to analyze the phase composition.The distribution of microhardness was identified as gradual transition and tensile strength had a tendency to decrease first and then increase.The distribution of nano-sizedη(MgZn2)particles in theα(Al)matrix and Al2MgCu phase determined the tensile performances along the thickness direction and led to the formation of ductile/brittle composite fracture in the HAZ.The continuous distribution of Al2MgCu phase in the strip intergranular precipitates gave birth to premature cracks and the brittle fracture region.The precipitated particles coarsening also led to the deterioration of mechanical properties.展开更多
The utilization of CO2 as raw material for chemical synthesis has the potential for substantial economic and green benefits. Thermal decomposition of hexamethylene-1,6-dicarbamate （HDC） is a promising approach for i...The utilization of CO2 as raw material for chemical synthesis has the potential for substantial economic and green benefits. Thermal decomposition of hexamethylene-1,6-dicarbamate （HDC） is a promising approach for indirect utilization of CO2 to produce hexamethylene-1,6-diisocyanate （HDI）. In this work, a green route was developed for the synthesis of HD1 by thermal decomposition of HDC over Co3O4/ZSM-5 catalyst, using chlorobenzene as low boiling point solvent. Different metal oxide supported catalysts were prepared by incipient wetness impregnation （IWI）, PEG-additive （PEG） and deposition precipitation with ammonia evaporation （DP） methods. Their catalytic performances for the thermal decomposition of HDC were tested. The catalyst screening results showed that Co3O4/ZSM-525 catalysts prepared by different methods showed different performances in the order of Co3O4/ZSM-5 25（PEG） 〉 Co3O4/ZSM-525（IWI） 〉 Co3O4/ZSM-525（DP）. The physicochemical properties of Co3O4/ZSM- 52s catalyst were characterized by XRD, FTIR, N2 adsorption-desorption measurements, NH3-TPD and XPS. The superior catalytic performance of Co3O4/ZSM-52S（PEG） catalyst was attributed to its relative surface content of Co3 ＋, surface lattice oxygen content and total acidity. Under the optimized reaction conditions： 6.5% HDC concentration in chlorobenzene, 1 wt% Co3O4/ZSM-525（PEG） catalyst, 250℃ temperature, 2.5 h time, 800 ml.min 1 nitrogen flow rate and 1.0 MPa pressure, the HDC conversion and HDI yield could reach 100% and 92.8% respectively. The Co3O4/ZSM-525（PEG） catalyst could be facilely separated from the reaction mixture, and reused without degradation in catalytic performance. Furthermore, a possible reaction mechanism was proposed based on the physicochemical properties of the Co3O4/ZSM-5 25 catalysts.展开更多
In this study,nanosheet g-C_(3)N_(4)-H_(2) was prepared by thermal exfoliation of bulk g-C_(3)N_(4) under hydrogen.A series of Ru/g-C_(3)N_(4)-H_(2) catalysts with Ru species supported on the nanosheet g-C_(3)N_(4)-H_...In this study,nanosheet g-C_(3)N_(4)-H_(2) was prepared by thermal exfoliation of bulk g-C_(3)N_(4) under hydrogen.A series of Ru/g-C_(3)N_(4)-H_(2) catalysts with Ru species supported on the nanosheet g-C_(3)N_(4)-H_(2) were synthesized via ultrasonic assisted impregnation-deposition method.Ultrafine Ru nanoparticles(<2 nm)were highly dispersed on nanosheet g-C_(3)N_(4)-H_(2).Strong interaction due to Ru-Nx coordination facilitated the uniform distribution of Ru species.Meanwhile,the involvement of surface basicity derived from abundant nitrogen sites was favourable for enhancing the selective hydrogenation performance of bi-benzene ring,i.e.,almost complete 4,40-diaminodiphenylmethane(MDA)conversion and>99%4,40-diaminodicyclohexylmethane selectivity,corresponding to a reaction activity of 35.7 mol_(MDA) mol_(Ru)^(-1) h^(-1).Moreover,the reaction activity of catalyst in the fifth run was 36.5 mol_(MDA) mol_(Ru)^(-1) h^(-1),which was comparable with that of the fresh one.The computational results showed that g-C_(3)N_(4) as support was favorable for adsorption and dissociation of H_(2) molecules.Moreover,the substrate scope can be successfully expanded to a variety of other aromatic diamines.Therefore,this work provides an efficient and green catalyst system for selective hydrogenation of aromatic diamines.展开更多
In the present work,Fe–Mn–Al–C powder mixtures were manufactured by elemental powders with different ball milling time,and the porous high-Mn and high-Al steel was fabricated by powder sintering.The results indicat...In the present work,Fe–Mn–Al–C powder mixtures were manufactured by elemental powders with different ball milling time,and the porous high-Mn and high-Al steel was fabricated by powder sintering.The results indicated that the powder size significantly decreased,and the morphology of the Fe powder tended to be increasingly flat as the milling time increased.However,the prolonged milling duration had limited impact on the phase transition of the powder mixture.The main phases of all the samples sintered at 640℃ were α-Fe,α-Mn and Al,and a small amount of Fe2Al5 and Al8Mn5.When the sintering temperature increased to 1200℃,the phase composition was mainly comprised of γ-Fe and α-Fe.The weight loss fraction of the sintered sample decreased with milling time,i.e.,8.3wt% after 20 h milling compared to15.3wt% for 10 h.The Mn depletion region(MDR) for the 10,15,and 20 h milled samples was about 780,600,and 370 μm,respectively.The total porosity of samples sintered at 640℃ decreased from ~46.6vol% for the 10 h milled powder to ~44.2vol% for 20 h milled powder.After sintering at 1200℃,the total porosity of sintered samples prepared by 10 and 20 h milled powder was ~58.3vol% and ~51.3vol%,respectively.The compressive strength and ductility of the 1200℃ sintered porous steel increased as the milling time increased.展开更多
Sn/ENIG has recently been used in flexible interconnects to form a more stable micron-sized metallurgical joint,due to high power capability which causes solder joints to heat up to 200℃.However,Cu_(6)Sn_(5)which is ...Sn/ENIG has recently been used in flexible interconnects to form a more stable micron-sized metallurgical joint,due to high power capability which causes solder joints to heat up to 200℃.However,Cu_(6)Sn_(5)which is critical for a microelectronic interconnection,will go through a phase transition at temperatures between 186 and 189℃.This research conducted an in-situ TEM study of a micro Cu/ENIG/Sn solder joint under isothermal aging test and proposed a model to illustrate the mechanism of the microstructural evolution.The results showed that part of the Sn solder reacted with Cu diffused from the electrode to formη´-Cu_(6)Sn_(5)during the ultrasonic bonding process,while the rest of Sn was left and enriched in a region in the solder joint.But the enriched Sn quickly diffused to both sides when the temperature reached 100℃,reacting with the ENIG coating and Cu to form(Ni_(x)Cu_(1-x))_(3)Sn_(4),AuSn_(4),and Cu_(6)Sn_(5)IMCs.After entering the heat preservation process,the diffusion of Cu from the electrode to the joint became more intense,resulting in the formation of Cu_(3)Sn.The scallop-type Cu_(6)Sn_(5)and the seahorse-type Cu_(3)Sn constituted a typical two-layered structure in the solder joint.Most importantly,the transition betweenηandη’was captured near the phase transition temperature for Cu_(6)Sn_(5)during both the heating and cooling process,which was accompanied by a volume shifting,and the transition process was further studied.This research is expected to serve as a reference for the service of micro Cu/ENIG/Sn solder joints in the electronic industry.展开更多
基金supported by the Natural Science Foundation of Hunan Province(No.2024JJ5419)the Hunan Provincial Key Research and Development Plan Project in 2024(No.2024JK2074)+1 种基金the Natural Science Foundation of Changsha(No.2023-197)the Open project of the Key Laboratory of digital flavor research of Hunan China Tobacco Industry Co.,Ltd(No.202143000834024).
文摘Multifunctional compatible stealth materials have emerged as the focal point of contemporary protection technology research and vanadium-based nanomaterials play a pivotal role in the development of advanced stealth materials.Here,a compatible stealth aerogel is successfully synthesized by employing mixed-valence decavanadate as the vanadium oxide(VO_(x))molecular model.Ultralight{V^(Ⅳ)VV_(9)}/MXene aerogel(0.0429 g cm^(-3))exhibits exceptional radar stealth performance with a minimal reflection loss(RL_(min))of−57.74 dB(99.9998%EMW absorption)and a significantly superior radar cross section reduction value of 26.77 dB m2.The aerogel’s exceptional properties,including a low infrared(IR)emissivity(0.479)and a low thermal conductivity of(32.30 mW m^(-1)K^(-1)),are crucial for enabling compatibility with IR and thermal stealth technologies.The presence of a mixed-valence polyoxovanadate cluster leads to an increase in the Schottky barrier and enhances magnetic properties,consequently boosting interfacial polarization and contributing to magnetic losses during electromagnetic wave(EMW)absorption.Consequently,altering the number of valence electrons significantly enhances the compatible stealth capabilities.These findings contribute significantly to our comprehension of how microstructure impacts EMW absorption processes and provide a basis for further research into the development of VO_(x)-based compatible stealth materials.
基金supported by the National Natural Science Foundation of China(No.42277256)the Natural Science Foundation of Hunan Province(No.2022JJ30710)+1 种基金Hunan Province Environmental Protection Research Program(No.HBKT-2021014)Guangdong Province Dabaoshan Mining Co.Ltd Technology Program(Semi-industrial test of 200T/time low-grade copper ore bio-heap leaching).
文摘The migration and transformation of hexavalent chromium(Cr(VI))in the environment are regulated by pyrite(FeS2).However,variations in pyrite crystal facets influence the adsorption behavior and electron transfer between pyrite and Cr(VI),thereby impacting the Cr(VI)reduction performance.Herein,two naturally common facets of pyritewere synthesized hydrothermally to investigate the facet-dependent mechanisms of Cr(VI)reduction.The experimental results revealed that the{111}facet exhibited approximately 1.30–1.50 times higher efficiency in Cr(VI)reduction compared to the{100}facet.Surface analyses and electrochemical results indicated that{111}facet displayed a higher iron-sulfur oxidation level,which was affected by its superior electrochemical properties during the reaction with Cr(VI).Density functional theory(DFT)calculations demonstrated that the narrower band gap and lower work function on{111}facet were more favorable for the electron transfer between Fe(II)and Cr(VI).Furthermore,different adsorption configurations were observed on{100}and{111}surfaces due to the unique arrangements of Fe and S atoms.Specifically,O atoms in Cr_(2)O_(7)^(2−)directly bound with the S sites on{100}but the Fe sites on{111}.According to the density of states(DOS),the Fe site had better reactivity than the S site in the reaction,which appeared to be related to the fracture of S-S bonds.Additionally,the adsorption configuration of Cr_(2)O_(7)^(2−)on{111}surface showed a stronger adsorption energy and a more stable coordination mode,favoring subsequent Cr(VI)reduction process.These findings provide an in-depth analysis of facet-dependent mechanisms underlying Cr(VI)reduction behavior,offering new insights into studying environmental interactions between heavy metals and natural minerals.
基金financially supported by the National Natural Science Foundation of China(No.51874111).
文摘Bismuth telluride-based alloys are the most widely used thermoelectric(TE)materials.Despite this,zonemelted Bi_(2)Te_(3)-based alloys suffer from poor mechanical properties,and polycrystalline materials prepared by powder metallurgy often disrupt the desired texture due to their inherent anisotropic crystal structure.In this study,we achieved a synergistic integration of nanoscale structures,highly oriented texture,and intrinsic BiTe’antisite defects in P-type Bi_(0.5)Sb_(1.5)Te_(3) bulk materials by employing layered directional sintering(LDS)on melt-spinning ribbons produced in a Bi-rich environment.The transmission electron microscopy analysis revealed regions of high-density distortions within the well-aligned nanograins,which play a crucial role in reducing lattice thermal conductivity.Ab initio simulations and Boltzmann transport equation analyses reveal that the BiTe’antisite defects generate both resonance states and additional phonon scattering channels.This full-spectrum phonon scattering coupled with high carrier mobility leads to a maximum figure of merit(ZT)of 1.54 at 375 K.Additionally,the compressive strength of the material reaches 140 MPa,which is 3.5 times higher than that of zone-melted counterparts.This work offers an efficient pathway for the facile preparation of high-performance Bi_(2)Te_(3)-based thermoelectric materials.
基金supported by the National Natural Science Foundation of China(Nos.U23A6005,22208112,and 32171721)the National Natural Science Foundation of China(No.22308109)+2 种基金Guangdong Basic and Applied Basic Research Foundation(No.2024A1515010678)the Fundamental Research Funds for the Central Universities(SCUT:2023ZYGXZR045)the State Key Laboratory of Pulp&Paper Engineering(Nos.2023ZD01,2023C02).
文摘Proton exchange membrane fuel cell(PEMFC)is a promising clean energy source,but its performance and stability are vulnerable to the negative effects of humidity conditions.The gas diffusion substrate(GDS)plays a pivotal role in regulating the moisture and gas transport.The single pore structure of traditionally designed GDS often leads to the pathway competition between moisture and gas,which effects the efficiency of fuel cells.In this study,we report on a hierarchical fibrous paper with tunable hierarchical pores for a sustainable GDS.This design offers gas permeability under wet conditions,by separating the gas pathway from the moisture pathway,thus mitigating their pathway competition.In addition,this paper forms a multi-scale scaffold that absorbs moisture under high humidity conditions and releases it under dry conditions.It is allowed to maintain an optimal internal humidity and further enhances the humidity adaptability.Furthermore,the carbon footprint is only 15.97%,significantly lower than commercial alternatives.This feature makes it a sustainable solution to stabilize PEMFCs under diverse humidity conditions.
基金Supported by the National Natural Science Foundation of China(No.42076126)the Shandong Key R&D Plan+2 种基金Major Scientific and Technological Innovation Project(No.2022CXGC020413)the Natural Science Foundation of Shandong Province(Nos.ZR2020MD072,ZR2021QD014)the Liaoning Provincial Natural Science Foundation:Joint Open Fund of the State Key Laboratory for the Creation and Development of New Pesticides(No.2022-KF-25-03)。
文摘The conversion process of chitin,one of the abundant biomass resources on the earth,not only follows the principles of green chemistry,but also has significant value in industrial applications.However,it is a great challenge to directly convert insoluble and rigid structured chitin to 5-hydroxymethylfurfural(HMF).To address this issue,we developed a green conversion process combining pretreatment and catalytic system.Chitin was first pretreated by hexafluoro isopropanol(HFIP),which somewhat disrupted the hydrogen bonding network within the chitin structure.Subsequently,formic acid(FA)and silicotungstic acid(STA)synergistically catalyzed the conversion to HMF in a biphasic system of 2-methyltetrahydrofuran(2-Me-THF)/H2O,and high yields(40.2%)HMF was obtained under the optimism conditions.The product distribution was analyzed by HPLC-MS and the co-catalysis of FA with STA was evidenced.A dual-function catalytic system with both Lewis and Br?nsted acids was created,the catalytic system that significantly improved the efficiency of complex tandem catalytic reactions with chitin.Based on the experimental results,a possible pathway for chitin conversion was deduced,providing a new catalytic idea for the efficient conversion of chitin to HMF.
基金financially supported by the National Key R&D Program of China(2023YFC3905400)the Clean Combustion and Low-carbon Utilization of Coal,Strategic Priority Research Program of the Chinese Academy of Sciences,Grant No.XDA 29000000.
文摘The carbonylation of amines offers a promising route for synthesizing N-substituted carbamates with high atom economy.However,conventional catalysts exhibit limited catalytic efficiency,and the underlying proton transfer mechanism remains elusive.Herein,we reported a metal-free,room-temperature strategy utilizing 1,5,7-triazabicyclo[4.4.0]dec-5-ene(TBD)as a dual hydrogen bond catalyst to synergistically activate propylamine(PA)and dimethyl carbonate(DMC).This green catalytic system achieves a 10-fold acceleration in reaction rate compared to other hydrogen bonding catalysts under mild conditions.This is enabled by dual hydrogen bonding of TBD with PA and DMC,which facilitates rapid proton transfer and stabilizes tetrahedral intermediates.Theoretical calculations confirm that the dual hydrogen bond system significantly lowers activation energy compared to single hydrogen bond analogs.Furthermore,it was revealed that the hydrogen bonding network within the product is the primary factor responsible for the sluggish reaction rate.This study demonstrates the effectiveness of a dual hydrogen bond system in accelerating the carbonylation of amines and provides a green route to access carbamates.
文摘The efficient synthesis of methanol and ethylene glycol via the chemoselective hydrogenation of ethylene carbonate（EC） is important for the sustainable utilization of CO_2 to produce commodity chemicals and fuels. In this work, a series of β-cyclodextrin-modified Cu/SiO_2 catalysts were prepared by ammonia evaporation method for the selective hydrogenation of EC to co-produce methanol and ethylene glycol. The structure and physicochemical properties of the catalysts were characterized in detail by N_2 physisorption, XRD, N_2O titration, H_2-TPR, TEM, and XPS/XAES. Compared with the unmodified 25 Cu/SiO_2 catalyst, the involvement of β-cyclodextrin in 5β-25 Cu/SiO_2 could remarkably increase the catalytic activity—excellent activity of 1178 mgEC g_（cat）^（–1） h^（–1） with 98.8%ethylene glycol selectivity, and 71.6% methanol selectivity could be achieved at 453 K. The remarkably improved recyclability was primarily attributed to the remaining proportion of Cu~＋/（Cu^0＋Cu~＋）. Furthermore, the DFT calculation results demonstrated that metallic Cu^0 dissociated adsorbed H_2, while Cu~＋ activated the carbonyl group of EC and stabilized the intermediates. This study is a facile and efficient method to prepare highly dispersed Cu catalysts—this is also an effective and stable heterogeneous catalyst system for the sustainable synthesis of ethylene glycol and methanol via indirect chemical utilization of CO_2.
基金supported by the National Natural Science Foun-dation of China(Grant Nos.52205348 and 52275321)the Natural Science Foundation of Shandong Province(Grant Nos.ZR2023JQ021 and ZR2022QE087).
文摘Eutectic high-entropy alloys(EHEAs),combining the advantages of both eutectic alloys and high-entropy alloys(HEAs),possess good castability and superior comprehensive mechanical properties which are regarded as a revolutionary material system.In this paper,a current study of EHEAs is captured comprehensively for the first time,including basic theory,microstructure and deformation behavior,and alloy design.An in-depth analysis of the formation of different microstructures of EHEAs and their mechanical properties is presented,and four methods of designing EHEAs are summarized.Due to their unique characteristics,EHEAs show great potential in materials processing engineering.Here we give a comprehensive summary of their applications in welding,surface engineering,and additive manufacturing for the first time.Among them,EHEAs in welding are divided into three sections based on different welding techniques:fusion-based welding,solid-state welding,and diffusion reaction-based welding;EHEAs in surface engineering are separated into two parts:surface modification of bulk EHEAs and EHEA coatings;EHEAs in additive manufacturing are elaborated in two parts:laser powder bed fusion(LPBF)and laser direct energy deposition(LDED).Finally,a summary is given and a future outlook is prospected.
文摘To measure the surface stress of thin laser cladding coatings with Rayleigh waves based on the cross correlation function, this pa- per introduced the influence of cross correlation step length on the stress measurement. Flat-shaped specimens made of laser cladding Fe314 alloy coatings were performed by static tensile tests, and Rayleigh wave signals were collected during the test process with an ultrasonic pulser and receiver instrument combined with two Rayleigh wave transducers. The difference in time of flight between two signals was de- termined based on the cross correlation function. The microstructure was observed by scanning electronic microscopy. The influence of the stress on the propagation velocity of Rayleigh waves and the relationship between the difference in time of flight and tensile stress under dif- ferent cross correlation step lengths were analyzed. The inhomogeneous deformation of the coatings affects the relationship between the dif- ference in time of flight and tensile stress; the stress measurement of the coatings is nearly constant with the increase of cross correlation step length when it attains one cycle.
基金supported by the Natural Science Foundation of Hunan Province(No.2020JJ4684)the Fundamental Research Funds for the Central Universities of Central South University(No.2021zzts0522)the Recruitment Program of Global Youth Experts。
文摘Rechargeable aqueous zinc-ion batteries are recently gaining incremental attention because of low cost and material abundance,but their development is plagued by limited choices of cathode materials with satisfactory cycling performance.The polyoxometalates perform formidable redox stability and able to participate in multi-electron transfer,which was well-suited for energy storage.Herein,a bicomponent polyoxometalate-derivative KNiVO(K_(2)[Ni(H_(2)O)_(6)]_(2)[V_(10)O_(28)]·_(4)H_(2)O polyoxometalates after annealing)is firstly demonstrated as a cathode material for aqueous ZIBs.The layered KV_(3)O_(8)(KVO)In the bi-component material constitutes Zn^(2+) migration and storage channels(K^(+) were substantially replaced by Zn^(2+) in the activation phase),and the three-dimensional NiV_(3)O_(8)(NiVO)part acts as skeleton to stabilize the ion channels,which assist the cell to demonstrate a high-rate capacity and specific energy of229.4 mAh/g and satisfactory cyclability(capacity retention of 99.1%after 4500 cycles at a current density of 4 A/g).These results prove the feasibility of POM as cathode materials precursor and put forward a novel pattern of the Zn^(2+)storage mechanism in the activated-KNiVO clusters,which also provide a new route for selecting or designing high-performance cathode for aqueous ZIBs and other advanced battery systems.
基金financial support from the Sichuan Province Science and Technology Support Program (2021YJ0504,2021YFYZ0002)National Key Research and Development Program of China (2016YFD0300406)+1 种基金Special Fund for Agro-scientific Research in the Public Interest (20150312705)the Crops Breeding Project in Sichuan Province (2016NYZ0051,22ZDZX0018)
文摘The moisture-conserving effect of straw mulch-based no-tillage(SMNT)is expected to increase fertile spikes and grain yield in environments with rainfall less than 200 mm.However,the mechanisms under-lying the positive effect of SMNT on wheat tillering are not fully elucidated.A split-plot experiment was designed to investigate the combined effects of SMNT and cultivars on tillering of dryland wheat grown under both dry and favorable climates.Application of SMNT to a cultivar with 1-2 tillers exploited both tillering and kernel-number plasticity,increasing the mean grain yield by 20.5%.This increase was attrib-uted primarily to an increased first-tiller emergence rate resulting from increased N uptake,leaf N con-tent,and N remobilization from tillers to their grain.The second and third tillers,as transient sinks,contributed to the tiller survival rate,which depends on tiller leaf number.The increased total N uptake by SMNT also increased the dry mass yield of tillers and the C:N ratio,reducing the asymmetric compe-tition between main stem and tillers.Owing to these beneficial effects,reduced mitogen-activated pro-tein kinase(MAPK)and abscisic acid signals were observed under SMNT,whereas indole-3-acetic acid(IAA)signals and genes involved in DNA replication and mismatch repair were increased.These signals activated three critical transcription factors(the calmodulin-binding transcription activator,GRAS domain,and cysteine-2/histidine-2 family)and further increased rapid drought response and tiller main-tenance after stem extension.Phenylpropanoid biosynthesis,sphingolipid biosynthesis,and galactose metabolism were most relevant to increased tillering under SMNT because of their critical role in drought response and lignin biosynthesis.Our results suggest that straw mulch-based no-tillage activates rapid drought response and improved wheat tillering by coordinating root N uptake,N remobilization,and asymmetric competition between main stem and tillers.
基金Supported by the National Natural Science Foundation of China(21476244,21406245)Transformational Technologies for Clean Energy and Demonstration,Strategic Priority Research Program of the Chinese Academy of Sciences,(XDA 21030600)the Youth Innovation Promotion Association CAS(2016046)
文摘A non-phosgene route for the synthesis of hexamethylene-1,6-diisocyanate(HDI) was developed via catalytic decomposition of hexamethylene-1,6-dicarbamate(HDC) over Zn–Co bi-metallic supported ZSM-5 catalyst.The catalyst was characterized by FTIR and XRD analyses. Three solvents dioctyl sebacate(DOS), dibutyl sebacate(DBS) and 1-butyl-3-methylimidazolium tetrafluoroborate(BMIMBF_4) were investigated and compared; DOS gave better performance. The catalytic performances for thermal decomposition of HDC to HDI using DOS as solvent were then investigated, and the results showed that, under the optimized reaction conditions, i.e.,10 wt%concentration of HDC in DOS, 250 °C temperature, 60 min reaction time, 83.8% yield of HDI had been achieved over Zn–Co/ZSM-5. Decomposition of the intermediate hexamethylene-1-carbamate-6-isocyanate(HMI) over Zn–Co/ZSM-5 in DOS solvent was further studied and the results indicated that yield of HDI from HMI reached to 69.6%(98.6% HDI selectively) at 270 °C, which further increased the yield of the total HDI(HDI_(tol)) to as high as 95.0%. Recycling of catalyst showed that HDI and HMI yield slightly decreased, and by-product yield increased after the catalyst was reused for 4 times. At last possible reaction mechanism was proposed.
基金This study was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences （XDA05080703 and XDB13020300）, the State Key Program of National Science Foundation of China （31330073 31471990）, the Knowledge Innovation Program of the Chinese Academy of Sciences （KSCX2-EW-Z-5）, the Chinese Science Database （XXH12504-1-12） and Science and Technology Foundation Project （2014FY210200）.
文摘Large-scale patterns of species richness have gained much attention in recent years; however, the factors that drive high species richness are still controversial in local regions, especially in highly diversified montane regions. The Qinghai-Tibetan Plateau （QTP） and the surrounding mountains are biodiversity hot spots due to a high number of endemic montane species. Here, we explored the fac- tors underlying this high level of diversity by studying the relationship between species richness and environmental variables. The richness patterns of 758 resident bird species were summarized at the scale of 1°× 1° grid cell at different taxonomic levels （order, family, genus, and species） and in differ- ent taxonomic groups （Passeriformes, Galliformes, Falconiformes, and Columbiformes）. These rich- ness patterns were subsequently analyzed against habitat heterogeneity （topographical heterogen- eity and land cover）, temperature amplitude （annual temperature, annual precipitation, precipitation seasonality, and temperature seasonality） and a vegetation index （net primary productivity）. Our re- sults showed that the highest richness was found in the southeastern part of the QTP, the eastern Himalayas. The lowest richness was observed in the central plateau of the QTP. Topographical het- erogeneity and temperature amplitude are the primary factors that explain overall patterns of species richness in the QTP, although the specific effect of each environmental variable varies between the different taxonomic groups depending on their own evolutionary histories and ecological require- ments. High species richness in the southeastern QTP is mostly due to highly diversified habitat types and temperature zones along elevation gradients, whereas the low species richness in the cen- tral plateau of the QTP may be due to environmental and energetic constraints, as the central plateau is harsh environment.
基金the National Natural Science Foundation of China(21576272)“Transformational Technologies for Clean Energy and Demonstration”Strategic Priority Research Program of Chinese Academy of Sciences,Grant No.XDA 21030600,Science and Technology Service Network Initiative,Chinese Academy of Sciences(KFJ-STS-QYZD-138).
文摘The separation of ethylene glycol(EG)and 1,2-butanediol(1,2-BDO)azeotrope in the synthesis process of EG via coal and biomass is becoming of increasing commercial and environmental importance.Selective adsorption is deemed as the most promising methods because of energy saving and environment favorable.In this paper,NaY zeolite was used to separate 1,2-BDO from EG,and its adsorption properties was then investigated.The isotherms of EG and 1,2-BDO in vapor and liquid phases from 298 to 328 K indicated that they fitted Langmuir model quite well,and the NaY zeolite absorbent favored EG more than 1,2-BDO.The Grand Canonical Monte Carlo(GCMC)and molecular dynamics(MD)simulation techniques were conducted to investigate the competition adsorption and diffusion characteristics in different adsorption regions.It was observed that EG and 1,2-BDO molecules all have the most probable locations of the center of the 12-membered ring near the Na cations.The diffusivities of EG are lower than those of 1,2-BDO at the same adsorption concentration.At last,the breakthrough curves of the binary mixture regressed from the empirical Dose–Response model in fixed-bed column showed that the adsorption selectivity of EG could reach to as high as 2.43,verified that the NaY zeolite could effectively separate EG from 1,2-BDO.This work is also helpful for further separation of other dihydric alcohol mixtures from coal and biomass fermentation.
基金Project(51905126) supported by the National Natural Science Foundation of ChinaProject(2018M641822) supported by the China Postdoctoral Science Foundation-General ProgramProject(HIT.NSRIF.201703) supported by the Natural Scientific Research Innovation Foundation in HIT,China
文摘Microstructure and mechanical properties of the heat affected zone(HAZ)in multi-pass gas metal arc(GMA)welded Al Zn Mg Cu alloy plates were investigated,based upon which the mechanical anisotropy and fracture mechanism were analyzed.The microstructure and composition were analyzed by scanning electron microscope(SEM)and energy dispersive spectroscope(EDS).X-ray diffractometer(XRD),transmission electron microscope(TEM)and selective area electron diffraction(SAED)were used to analyze the phase composition.The distribution of microhardness was identified as gradual transition and tensile strength had a tendency to decrease first and then increase.The distribution of nano-sizedη(MgZn2)particles in theα(Al)matrix and Al2MgCu phase determined the tensile performances along the thickness direction and led to the formation of ductile/brittle composite fracture in the HAZ.The continuous distribution of Al2MgCu phase in the strip intergranular precipitates gave birth to premature cracks and the brittle fracture region.The precipitated particles coarsening also led to the deterioration of mechanical properties.
基金National Natural Science Foundation of China(21476244 and 21406245)Youth Innovation Promotion Association CAS
文摘The utilization of CO2 as raw material for chemical synthesis has the potential for substantial economic and green benefits. Thermal decomposition of hexamethylene-1,6-dicarbamate （HDC） is a promising approach for indirect utilization of CO2 to produce hexamethylene-1,6-diisocyanate （HDI）. In this work, a green route was developed for the synthesis of HD1 by thermal decomposition of HDC over Co3O4/ZSM-5 catalyst, using chlorobenzene as low boiling point solvent. Different metal oxide supported catalysts were prepared by incipient wetness impregnation （IWI）, PEG-additive （PEG） and deposition precipitation with ammonia evaporation （DP） methods. Their catalytic performances for the thermal decomposition of HDC were tested. The catalyst screening results showed that Co3O4/ZSM-525 catalysts prepared by different methods showed different performances in the order of Co3O4/ZSM-5 25（PEG） 〉 Co3O4/ZSM-525（IWI） 〉 Co3O4/ZSM-525（DP）. The physicochemical properties of Co3O4/ZSM- 52s catalyst were characterized by XRD, FTIR, N2 adsorption-desorption measurements, NH3-TPD and XPS. The superior catalytic performance of Co3O4/ZSM-52S（PEG） catalyst was attributed to its relative surface content of Co3 ＋, surface lattice oxygen content and total acidity. Under the optimized reaction conditions： 6.5% HDC concentration in chlorobenzene, 1 wt% Co3O4/ZSM-525（PEG） catalyst, 250℃ temperature, 2.5 h time, 800 ml.min 1 nitrogen flow rate and 1.0 MPa pressure, the HDC conversion and HDI yield could reach 100% and 92.8% respectively. The Co3O4/ZSM-525（PEG） catalyst could be facilely separated from the reaction mixture, and reused without degradation in catalytic performance. Furthermore, a possible reaction mechanism was proposed based on the physicochemical properties of the Co3O4/ZSM-5 25 catalysts.
基金financially supported by the National Nature Science Foundation of China(21576272)“Transformational Technologies for Clean Energy and Demonstration”,Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA 21030600)Science and Technology Service Network Initiative,Chinese Academy of Sciences(KFJ-STS-QYZD-138).
文摘In this study,nanosheet g-C_(3)N_(4)-H_(2) was prepared by thermal exfoliation of bulk g-C_(3)N_(4) under hydrogen.A series of Ru/g-C_(3)N_(4)-H_(2) catalysts with Ru species supported on the nanosheet g-C_(3)N_(4)-H_(2) were synthesized via ultrasonic assisted impregnation-deposition method.Ultrafine Ru nanoparticles(<2 nm)were highly dispersed on nanosheet g-C_(3)N_(4)-H_(2).Strong interaction due to Ru-Nx coordination facilitated the uniform distribution of Ru species.Meanwhile,the involvement of surface basicity derived from abundant nitrogen sites was favourable for enhancing the selective hydrogenation performance of bi-benzene ring,i.e.,almost complete 4,40-diaminodiphenylmethane(MDA)conversion and>99%4,40-diaminodicyclohexylmethane selectivity,corresponding to a reaction activity of 35.7 mol_(MDA) mol_(Ru)^(-1) h^(-1).Moreover,the reaction activity of catalyst in the fifth run was 36.5 mol_(MDA) mol_(Ru)^(-1) h^(-1),which was comparable with that of the fresh one.The computational results showed that g-C_(3)N_(4) as support was favorable for adsorption and dissociation of H_(2) molecules.Moreover,the substrate scope can be successfully expanded to a variety of other aromatic diamines.Therefore,this work provides an efficient and green catalyst system for selective hydrogenation of aromatic diamines.
基金financially supported by the National Key R&D Program of China(No.2021YFB3802300)the National Natural Science Foundation of China(No.51804239)Guangdong Major Project of Basic and Applied Basic Research,China(No.2021B0301030001)。
文摘In the present work,Fe–Mn–Al–C powder mixtures were manufactured by elemental powders with different ball milling time,and the porous high-Mn and high-Al steel was fabricated by powder sintering.The results indicated that the powder size significantly decreased,and the morphology of the Fe powder tended to be increasingly flat as the milling time increased.However,the prolonged milling duration had limited impact on the phase transition of the powder mixture.The main phases of all the samples sintered at 640℃ were α-Fe,α-Mn and Al,and a small amount of Fe2Al5 and Al8Mn5.When the sintering temperature increased to 1200℃,the phase composition was mainly comprised of γ-Fe and α-Fe.The weight loss fraction of the sintered sample decreased with milling time,i.e.,8.3wt% after 20 h milling compared to15.3wt% for 10 h.The Mn depletion region(MDR) for the 10,15,and 20 h milled samples was about 780,600,and 370 μm,respectively.The total porosity of samples sintered at 640℃ decreased from ~46.6vol% for the 10 h milled powder to ~44.2vol% for 20 h milled powder.After sintering at 1200℃,the total porosity of sintered samples prepared by 10 and 20 h milled powder was ~58.3vol% and ~51.3vol%,respectively.The compressive strength and ductility of the 1200℃ sintered porous steel increased as the milling time increased.
基金supported by the opening fund of National Key Research and Development Program of China(No.2020YFE0205300)Key Laboratory of Science and Technology on Silicon Devices,Chinese Academy of Sciences(No.KLSDTJJ2022-5)+1 种基金Chongqing Natural Science Foundation of China(No.cstc2021jcyj-msxmX1002)the Fundamental Research Funds for the Central Universities(No.AUGA5710051221).
文摘Sn/ENIG has recently been used in flexible interconnects to form a more stable micron-sized metallurgical joint,due to high power capability which causes solder joints to heat up to 200℃.However,Cu_(6)Sn_(5)which is critical for a microelectronic interconnection,will go through a phase transition at temperatures between 186 and 189℃.This research conducted an in-situ TEM study of a micro Cu/ENIG/Sn solder joint under isothermal aging test and proposed a model to illustrate the mechanism of the microstructural evolution.The results showed that part of the Sn solder reacted with Cu diffused from the electrode to formη´-Cu_(6)Sn_(5)during the ultrasonic bonding process,while the rest of Sn was left and enriched in a region in the solder joint.But the enriched Sn quickly diffused to both sides when the temperature reached 100℃,reacting with the ENIG coating and Cu to form(Ni_(x)Cu_(1-x))_(3)Sn_(4),AuSn_(4),and Cu_(6)Sn_(5)IMCs.After entering the heat preservation process,the diffusion of Cu from the electrode to the joint became more intense,resulting in the formation of Cu_(3)Sn.The scallop-type Cu_(6)Sn_(5)and the seahorse-type Cu_(3)Sn constituted a typical two-layered structure in the solder joint.Most importantly,the transition betweenηandη’was captured near the phase transition temperature for Cu_(6)Sn_(5)during both the heating and cooling process,which was accompanied by a volume shifting,and the transition process was further studied.This research is expected to serve as a reference for the service of micro Cu/ENIG/Sn solder joints in the electronic industry.
