To address climate change and promote environmental sustainability,electrochemical energy conversion and storage systems emerge as promising alternative to fossil fuels,catering to the escalating demand for energy.Ach...To address climate change and promote environmental sustainability,electrochemical energy conversion and storage systems emerge as promising alternative to fossil fuels,catering to the escalating demand for energy.Achieving optimal energy efficiency and cost competitiveness in these systems requires the strategic design of electrocatalysts,coupled with a thorough comprehension of the underlying mechanisms and degradation behavior occurring during the electrocatalysis processes.Scanning electrochemical microscopy(SECM),an analytical technique for studying surface electrochemically,stands out as a powerful tool offering electrochemical insights.It possesses remarkable spatiotemporal resolution,enabling the visualization of the localized electrochemical activity and surface topography.This review compiles crucial research findings and recent breakthroughs in electrocatalytic processes utilizing the SECM methodology,specifically focusing on applications in electrolysis,fuel cells,and metal–oxygen batteries within the realm of energy conversion and storage systems.Commencing with an overview of each energy system,the review introduces the fundamental principles of SECM,and aiming to provide new perspectives and broadening the scope of applied research by describing the major research categories within SECM.展开更多
A high performance preoxidized poly(acrylonitrile)(O-PAN)nanofiber membrane with excellent solvent resistance,thermal stability and flexibility was fabricated by the preoxidation of electrospun PAN nanofiber membrane....A high performance preoxidized poly(acrylonitrile)(O-PAN)nanofiber membrane with excellent solvent resistance,thermal stability and flexibility was fabricated by the preoxidation of electrospun PAN nanofiber membrane.The performance of resultant O-PAN nanofiber membrane was optimized by altering the PAN concentration and preoxidation temperature.The results showed that the O-PAN nanofiber membrane which made from PAN concentration of 14%(mass)and preoxidation temperature of 250.0℃ have a more optimal comprehensive performance.In the long-term separation test of SiO2 particle(1 μm)in DMAc suspension,the permeate flux of O-PAN nanofiber membrane stabilized at 227.91 L·m^(-2)·h^(-1)(25℃,0.05 MPa)while the SiO2 rejection above 99.6%,which showed excellent solvent resistance and separation performance.In order to further explore the application of the O-PAN nanofiber membrane,the OPAN nanofiber membrane was treated with fluoride and used in oil/water separation process.The O-PAN nanofiber membrane after hydrophobic treatment showed excellent hydrophobicity and good oil/water separation performance with the permeate flux about 969.59 L·m^(-2)·h^(-1)while the separation efficiency above 96.1%.The O-PAN nanofiber membrane exhibited a potential application prospect in harsh environment separation.展开更多
Over the past half-century, plastic consumption has grown rapidly due to its versatility, low cost, and unrivaled functional properties. Among the diff erent implemented strategies for recycling waste plastics, pyroly...Over the past half-century, plastic consumption has grown rapidly due to its versatility, low cost, and unrivaled functional properties. Among the diff erent implemented strategies for recycling waste plastics, pyrolysis is deemed the most economical option. Currently, the wax obtained from the pyrolysis of waste plastics is mainly used as a feedstock to manufacture chemicals and fuels or added to asphalt for pavement construction, with no other applications of wax being reported. Herein, the thermal pyrolysis of three common waste polyolefin plastics: high-density polyethylene(HDPE), low-density polyethylene(LDPE), and polypropylene(PP), was conducted at 450 ℃. The waste plastics-derived waxes were characterized and studied for a potential new application: phase change materials(PCMs) for thermal energy storage(TES). Gas chromatography–mass spectrometry analysis showed that paraffin makes up most of the composition of HDPE and LDPE waxes, whereas PP wax contains a mixture of naphthene, isoparaffin, olefin, and paraffin. Diff erential scanning calorimetry(DSC) analysis indicated that HDPE and LDPE waxes have a peak melting temperature of 33.8 ℃ and 40.3 ℃, with a relatively high latent heat of 103.2 J/g and 88.3 J/g, respectively, whereas the PP wax was found to have almost negligible latent heat. Fourier transform infrared spectroscopy and DSC results revealed good chemical and thermal stability of HDPE and LDPE waxes after 100 cycles of thermal cycling. Performance evaluation of the waxes was also conducted using a thermal storage pad to understand their thermoregulation characteristics for TES applications.展开更多
The precursors of La0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ(LSCCF, x=0.05, 0.10, 0.15, 0.20) as the cathode materials for intermediate temperature solid oxide fuel cell (ITSOFC) were prepared by reverse titration co-precipitatio...The precursors of La0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ(LSCCF, x=0.05, 0.10, 0.15, 0.20) as the cathode materials for intermediate temperature solid oxide fuel cell (ITSOFC) were prepared by reverse titration co-precipitation method with metal-nitrates as starting materials and mixed alkali (NaOH and Na2CO3) as a precipitating agent. The formation process of LSCCF from the precursors was monitored by TG-DSC, and the crystal structure and particles morphology of the precursors which were calcined at 600, 800, 1000 ℃ for 3 h were characterized using XRD, SEM technologies. Compared with the solid state reaction of constituent oxides, when the pH value of the precipitating solution was in the range of 9.1~9.5, the LSCCF powders from the precursors caclined at 800 ℃ for 3 h had high purity, homogeneous and single perovskite phase. The electrical conductivity of the LSCCF samples sintered at 1200 ℃ for 3 h, which was measured as a function of temperatures from 100 to 800 ℃ by DC four-probe method in air, decreased with x from 0.05 to 0.20. The value of electrical conductivity was almost equal because of Ca2+, Sr2+ co-dopant resulting in the 'mix effect' while x=0.10 or 0.15. The electrical conductivity of all doped samples was higher than 100 S·cm-1 at intermediate temperatures from 500 to 800 ℃, and there was good compatibility between the LSCCF cathode and Ce0.8Sm0.2O2 electrolyte.展开更多
Magnesium and its alloys,as a promising class of materials,is popular in lightweight application and biomedical implants due to their low density and good biocompatibility.Additive manufacturing(AM)of Mg and its alloy...Magnesium and its alloys,as a promising class of materials,is popular in lightweight application and biomedical implants due to their low density and good biocompatibility.Additive manufacturing(AM)of Mg and its alloys is of growing interest in academia and industry.The domain-by-domain localized forming characteristics of AM leads to unique microstructures and performances of AM-process Mg and its alloys,which are different from those of traditionally manufactured counterparts.However,the intrinsic mechanisms still remain unclear and need to be in-depth explored.Therefore,this work aims to discuss and analyze the possible underlying mechanisms regarding defect appearance and elimination,microstructure formation and evolution,and performance improvement,based on presenting a comprehensive and systematic review on the relationship between process parameters,forming quality,microstructure characteristics and resultant performances.Lastly,some key perspectives requiring focus for further progression are highlighted to promote development of AM-processed Mg and its alloys and accelerate their industrialization.展开更多
Based on the density functional theory within the local density approximation (LDA), we studied the electronic, elastic, and dynamic properties of AgNbO<sub>3</sub> and AgTaO<sub>3</sub> compou...Based on the density functional theory within the local density approximation (LDA), we studied the electronic, elastic, and dynamic properties of AgNbO<sub>3</sub> and AgTaO<sub>3</sub> compounds under pressure. The elastic constants, optic and static dielectric constants, born effective charges, and dynamic properties of AgNbO<sub>3</sub> and AgTaO<sub>3</sub> in cubic phase were studied as pressure dependences with the ab initio method. For these compounds, we have also calculated the bulk modulus, Young’s modulus, shear modulus, Vickers hardness, Poisson’s ratio, anisotropy factor, sound velocities, and Debye temperature from the obtained elastic constants. In addition, the brittleness and ductility properties of these compounds were estimated from Poisson’s ratio and Pugh’s rule (G/B). Our calculated values also show that AgNbO<sub>3</sub> (0.37) and AgTaO<sub>3</sub> (0.39) behave as ductile materials and steer away from brittleness by increasing pressure. The calculated values of Vicker hardness for both compounds indicate that they are soft materials. The results show that band gaps, elastic constants, elastic modules, and dynamic properties for both compounds are sensitive to pressure changes. We have also made some comparisons with related experimental and theoretical data that is available in the literature.展开更多
Energy storage and conservation are receiving increased attention due to rising global energy demands.Therefore,the development of energy storage materials is crucial.Thermal energy storage(TES)systems based on phase ...Energy storage and conservation are receiving increased attention due to rising global energy demands.Therefore,the development of energy storage materials is crucial.Thermal energy storage(TES)systems based on phase change materials(PCMs)have increased in prominence over the past two decades,not only because of their outstanding heat storage capacities but also their superior thermal energy regulation capability.However,issues such as leakage and low thermal conductivity limit their applicability in a variety of settings.Carbon-based materials such as graphene and its derivatives can be utilized to surmount these obstacles.This study examines the recent advancements in graphene-based phase change composites(PCCs),where graphene-based nanostructures such as graphene,graphene oxide(GO),functionalized graphene/GO,and graphene aerogel(GA)are incorporated into PCMs to substantially enhance their shape stability and thermal conductivity that could be translated to better storage capacity,durability,and temperature response,thus boosting their attractiveness for TES systems.In addition,the applications of these graphene-based PCCs in various TES disciplines,such as energy conservation in buildings,solar utilization,and battery thermal management,are discussed and summarized.展开更多
Solar steam generation(SSG)is widely regarded as one of the most sustainable technologies for seawater desalination.However,salt fouling severely compromises the evaporation performance and lifetime of evaporators,lim...Solar steam generation(SSG)is widely regarded as one of the most sustainable technologies for seawater desalination.However,salt fouling severely compromises the evaporation performance and lifetime of evaporators,limiting their practical applications.Herein,we propose a hierarchical salt-rejection(HSR)strategy to prevent salt precipitation during long-term evaporation while maintaining a rapid evaporation rate,even in high-salinity brine.The salt diffusion process is segmented into three steps—insulation,branching diffusion,and arterial transport—that significantly enhance the salt-resistance properties of the evaporator.Moreover,the HSR strategy overcomes the tradeoff between salt resistance and evaporation rate.Consequently,a high evaporation rate of 2.84 kg m^(-2) h^(-1),stable evaporation for 7 days cyclic tests in 20 wt%NaCl solution,and continuous operation for 170 h in natural seawater under 1 sun illumination were achieved.Compared with control evaporators,the HSR evaporator exhibited a>54%enhancement in total water evaporation mass during 24 h continuous evaporation in 20 wt%salt water.Furthermore,a water collection device equipped with the HSR evaporator realized a high water purification rate(1.1 kg m^(-2) h^(-1)),highlighting its potential for agricultural applications.展开更多
High performance aluminosilicate based cementitious materials were produced using calcined gangue as one of the major raw materials. The gangue was calcined at 500℃. The main constituent was calcined gangue, fly ash ...High performance aluminosilicate based cementitious materials were produced using calcined gangue as one of the major raw materials. The gangue was calcined at 500℃. The main constituent was calcined gangue, fly ash and slag, while alkali-silicate solutions were used as the diagenetic agent. The structure of gangue-containing aluminosilicate based cementitious materials was studied by the methods of IR, NMR and SEM. The results show that the mechanical properties are affected by the mass ratio between the gangue, slag and fly ash, the kind of activator and additional salt. For 28-day curing time, the compressive strength of the sample with a mass proportion of 2:1:1 (gangue: slag: fly ash) is 58.9 MPa, while the compressive strength of the sample containing 80wt% gangue can still be up to 52.3 MPa. The larger K^+ favors the formation of large silicate oligomers with which AI(OH)4- prefers to bind. Therefore, in Na-K compounding activator solutions more oligomers exist which result in a stronger compressive strength of aluminosilicate-based cementitious materials than in the case of Na-containing activator. The reasons for this were found through IR and NMR analysis. Glauber's salt reduces the 3-day compressive strength of the paste, but increases its 7-day and 28-day compressive strengths.展开更多
Maximum bubble pressure measurement was employed to evaluate surface tension of Sn-8Zn-3Bi- (00.15)Nd and Sn-8Zn-3Bi-(00.15)La solder melts. Wetting balance method was used to measure wetting force and wetting time on...Maximum bubble pressure measurement was employed to evaluate surface tension of Sn-8Zn-3Bi- (00.15)Nd and Sn-8Zn-3Bi-(00.15)La solder melts. Wetting balance method was used to measure wetting force and wetting time on Cu substrate of the two group solders. The experimental results show that minute amount of Nd or La addition to Sn-8Zn-3Bi solder causes significant decrease of the surface tension of the solder melts at 200240℃ and Nd addition is more effective on reduction of surface tension than that of La. Nd or La addition has the effect on enhancing the wetting force of the solder melts on Cu substrate, which results from the decrease of interfacial tension between the solder melt and Cu substrate. The wetting force reaches the maximum when 0.1% Nd is added to the base alloy. The contact angle between Sn-8Zn-3Bi base solders and Cu substrate decreases with the addition of Nd or La and the minimum of the contact angle is obtained from the solder with 0.1% Nd addition.展开更多
Niobium (Nb)-clad stainless steels(SS) produced via roll bonding are being considered for use in the bipolar plates of polymer electrolyte membrane fuel cell(PEMFC) stacks. Because the roll bonding process induces sub...Niobium (Nb)-clad stainless steels(SS) produced via roll bonding are being considered for use in the bipolar plates of polymer electrolyte membrane fuel cell(PEMFC) stacks. Because the roll bonding process induces substantial work hardening in the constituent materials, thermal annealing is used to restore ductility to the clad sheet so that it can be subsequently blanked, stamped and dimpled in forming the final plate component. Two roll bonded materials, niobium clad 340L stainless steel (Nb/340L SS) and niobium clad 434 stainless steel (Nb/434 SS) were annealed under optimized conditions prescribed by the cladding manufacturer. Comparative mechanical testing conducted on each material before and after annealing shows significant improvement in ductility in both cases. However, corresponding microstructural analyses indicate an obvious difference between the two heat treated materials. During annealing, an interlayer with thick less than 1 μm forms between the constituent layers in the Nb/340L SS, whereas no interlayer is found in the annealed Nb/434 SS material. Prior work suggests that internal defects potentially can be generated in such an interlayer during metal forming operations. Thus, Nb/434 SS may be the preferred candidate material for this application.展开更多
In order to control the size and distribution of the high conductive Fe2P in LiFePO4/Fe2P composite, two different cooling rates (Fast: 15 ℃·min-1, Slow: 2 ℃·min-1) were employed after mechanical alloying....In order to control the size and distribution of the high conductive Fe2P in LiFePO4/Fe2P composite, two different cooling rates (Fast: 15 ℃·min-1, Slow: 2 ℃·min-1) were employed after mechanical alloying. The discharge capacity of the fast cooled was 83 mAh·g-1 and the slow cooled 121 mAh·g-1. The particle size of the synthesized powder was examined by transmission electron microscopy and distribution of Fe2P was characterized using scanning electron microscopy (SEM). In addition, two-step heat treatment was carried out for better distribution of Fe2P. X-ray diffraction (XRD) and Rietveld refinement reveal that LiFePO4/Fe2P composite consists of 95.77% LiFePO4 and 4.33% of Fe2P.展开更多
The effects of Ca and Sr addition on the microstructure and creep properties of Mg-4Al-2Sn alloys were examined.Tensile tests at 25℃ and 200℃ and creep tests at 150℃ and 200℃ were carried out to estimate the room ...The effects of Ca and Sr addition on the microstructure and creep properties of Mg-4Al-2Sn alloys were examined.Tensile tests at 25℃ and 200℃ and creep tests at 150℃ and 200℃ were carried out to estimate the room temperature and high temperature mechanical properties of these alloys.The microstructure of the Mg-4Al-2Sn alloy showed dendriticα-Mg,Mg17Al12 and Mg2Sn phases.The latter two phases precipitated along the grain boundaries.The addition of Ca and Sr resulted in the formation of ternary CaMgSn and SrMgSn phases within the grain.The grain size was reduced slightly with the addition of Sr and Ca.The tensile strength was decreased by the addition of Ca and Sr at room temperature.However,the high temperature tensile strength was increased.The creep strength was improved by the addition of Ca and Sr.展开更多
In order to lower the raw materials cost and develop a novel cathode materials for intermediate temperature solid oxide fuel cell(ITSOFC), using mixed rare earth replacing the expensive pure La2O3 as the raw materials...In order to lower the raw materials cost and develop a novel cathode materials for intermediate temperature solid oxide fuel cell(ITSOFC), using mixed rare earth replacing the expensive pure La2O3 as the raw materials, the powders of Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ (Ln=the mixed rare earth, x=0.05, 0.10, 0.15) for the applications as the cathode materials were prepared by microwave sintering process. The crystal structure and the particles morphology of the obtained powders were characterized by XRD and SEM, the electrical conductivity of all samples sintered at 1200 ℃ for 3 h was also measured as the function of the temperature from 100 to 800 ℃ by DC four-probe method in air. The experimental results show that due to the influence of mixed rare earth the powders of Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ synthesized at 1200 ℃ for 0.5 h with the mean particle size of 1~20 μm was of perovskite and cubic fluorite phase as well a little SrO phase, the electrical conductivity of the samples decreases with the adding Ca2+ content, and are all higher than 100 S·cm-1 from 500 to 700 ℃ when x≤0.10. Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ. Can meet the demand of the electrical properties for the cathode materials in ITSOFC.展开更多
The microstructure and mechanical properties of friction stir welded 2. 5 mm 7050-T7451 aluminum alloy natural aging 72 h and 17 520 h were investigated, respectively. The uniaxial tensile test showed that yield stren...The microstructure and mechanical properties of friction stir welded 2. 5 mm 7050-T7451 aluminum alloy natural aging 72 h and 17 520 h were investigated, respectively. The uniaxial tensile test showed that yield strength, tensile strength and elongation of the joints 17 520 h natural aging were about 20%, 12% and 24% higher than those joints natural aging 72 h. Hardness profile of natural aging 17 520 h joint witnessed significant enhancement in nugget zone, compared with 72 h natural aging. Differential scanning calorimetry ( DSC ) and transmission electron microscopy (TEM) test revealed that more Guinier-Preston zone, η' and 71 phase emerged in nugget zone as natural aging duration increased, high density of dislocation located within grain boundary in nugget zone of joints natural aging 72 h. It is concluded that natural aging was feasible to enhalwe strength and plasticity of FSW joints simultaneously.展开更多
It is pointed out that the quantum mechanical Hamiltonian of two L-C circuits with mutual-inductance is equivalent to a pair of harmonic oscillators with a kinetic coupling term.We then diagonalize the Hamiltonian.It ...It is pointed out that the quantum mechanical Hamiltonian of two L-C circuits with mutual-inductance is equivalent to a pair of harmonic oscillators with a kinetic coupling term.We then diagonalize the Hamiltonian.It is shown that instantaneously switching on the external sources may result in a two-mode squeezed state of the system,which actually arises from the effect of mutual-inductance.The quantum fluctuation for the case of l_(1)c_(1)=l_(2)c_(2 ) is analysed and it is found that the current fluctuation in the circuits increases with the increment of the mutual-inductance.展开更多
Thermomechanical treatments were carried out to improve the properties of AZ31B joints prepared by gas tungsten arc welding. The microstructures of the joints were studied by optical microscopy and scanning electron m...Thermomechanical treatments were carried out to improve the properties of AZ31B joints prepared by gas tungsten arc welding. The microstructures of the joints were studied by optical microscopy and scanning electron microscopy with energy-dispersive spectrometry. Tensile tests and hardness tests were performed to investigate the effects of thermomechanical treatments on the mechanical properties of the joints. It is found that the thermomechanical-treated joints show superior mechanical properties against the as-welded joints, and their ultimate tensile strength can reach more than 92% of the base material. This mainly attributes to the formation of fine equiaxed grains in the fusion zone. ARer thermomechanical treatments the dendrites are transformed to fine spherical grains, and the dendritic segregation can be effectively eliminated.展开更多
We propose a new two-fold integration transformation in p-q phase space∫∫_(-∞)~∞ (dqdq/π) e^(2i(p-x)(q-y))f(p,q)2≡G(x,y),which possesses some well-behaved transformation properties.We apply this transformation t...We propose a new two-fold integration transformation in p-q phase space∫∫_(-∞)~∞ (dqdq/π) e^(2i(p-x)(q-y))f(p,q)2≡G(x,y),which possesses some well-behaved transformation properties.We apply this transformation to the Weyl ordering ofoperators,especially those Q-P ordered and P-Q ordered operators.展开更多
基金supported by a characterization platform for advanced materials funded by the Korea Research Institute of Standards and Science(KRISS-2023-GP2023-0014)the KRISS(Korea Research Institute of Standards and Science)MPI Lab.program。
文摘To address climate change and promote environmental sustainability,electrochemical energy conversion and storage systems emerge as promising alternative to fossil fuels,catering to the escalating demand for energy.Achieving optimal energy efficiency and cost competitiveness in these systems requires the strategic design of electrocatalysts,coupled with a thorough comprehension of the underlying mechanisms and degradation behavior occurring during the electrocatalysis processes.Scanning electrochemical microscopy(SECM),an analytical technique for studying surface electrochemically,stands out as a powerful tool offering electrochemical insights.It possesses remarkable spatiotemporal resolution,enabling the visualization of the localized electrochemical activity and surface topography.This review compiles crucial research findings and recent breakthroughs in electrocatalytic processes utilizing the SECM methodology,specifically focusing on applications in electrolysis,fuel cells,and metal–oxygen batteries within the realm of energy conversion and storage systems.Commencing with an overview of each energy system,the review introduces the fundamental principles of SECM,and aiming to provide new perspectives and broadening the scope of applied research by describing the major research categories within SECM.
基金supported by the Science and Technology Plans of Tianjin(18PTSYJC00170)the Young Elite Scientists Sponsorship Program by China Association for Science and Technology(YESS20160168)The Analytical&Testing Center of Tiangong University was appreciated.
文摘A high performance preoxidized poly(acrylonitrile)(O-PAN)nanofiber membrane with excellent solvent resistance,thermal stability and flexibility was fabricated by the preoxidation of electrospun PAN nanofiber membrane.The performance of resultant O-PAN nanofiber membrane was optimized by altering the PAN concentration and preoxidation temperature.The results showed that the O-PAN nanofiber membrane which made from PAN concentration of 14%(mass)and preoxidation temperature of 250.0℃ have a more optimal comprehensive performance.In the long-term separation test of SiO2 particle(1 μm)in DMAc suspension,the permeate flux of O-PAN nanofiber membrane stabilized at 227.91 L·m^(-2)·h^(-1)(25℃,0.05 MPa)while the SiO2 rejection above 99.6%,which showed excellent solvent resistance and separation performance.In order to further explore the application of the O-PAN nanofiber membrane,the OPAN nanofiber membrane was treated with fluoride and used in oil/water separation process.The O-PAN nanofiber membrane after hydrophobic treatment showed excellent hydrophobicity and good oil/water separation performance with the permeate flux about 969.59 L·m^(-2)·h^(-1)while the separation efficiency above 96.1%.The O-PAN nanofiber membrane exhibited a potential application prospect in harsh environment separation.
基金financial support from Individual Research Grant (Grant reference No.: A20E7c0109) of the Agency for Science,Technology and Research of Singapore (A*STAR)。
文摘Over the past half-century, plastic consumption has grown rapidly due to its versatility, low cost, and unrivaled functional properties. Among the diff erent implemented strategies for recycling waste plastics, pyrolysis is deemed the most economical option. Currently, the wax obtained from the pyrolysis of waste plastics is mainly used as a feedstock to manufacture chemicals and fuels or added to asphalt for pavement construction, with no other applications of wax being reported. Herein, the thermal pyrolysis of three common waste polyolefin plastics: high-density polyethylene(HDPE), low-density polyethylene(LDPE), and polypropylene(PP), was conducted at 450 ℃. The waste plastics-derived waxes were characterized and studied for a potential new application: phase change materials(PCMs) for thermal energy storage(TES). Gas chromatography–mass spectrometry analysis showed that paraffin makes up most of the composition of HDPE and LDPE waxes, whereas PP wax contains a mixture of naphthene, isoparaffin, olefin, and paraffin. Diff erential scanning calorimetry(DSC) analysis indicated that HDPE and LDPE waxes have a peak melting temperature of 33.8 ℃ and 40.3 ℃, with a relatively high latent heat of 103.2 J/g and 88.3 J/g, respectively, whereas the PP wax was found to have almost negligible latent heat. Fourier transform infrared spectroscopy and DSC results revealed good chemical and thermal stability of HDPE and LDPE waxes after 100 cycles of thermal cycling. Performance evaluation of the waxes was also conducted using a thermal storage pad to understand their thermoregulation characteristics for TES applications.
基金the National High-Tech Development Plan (2006AA05Z417)the Natural Science Foundation of Lia-oning Province (20062145)the Education department of Liaoning Province (05L073)
文摘The precursors of La0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ(LSCCF, x=0.05, 0.10, 0.15, 0.20) as the cathode materials for intermediate temperature solid oxide fuel cell (ITSOFC) were prepared by reverse titration co-precipitation method with metal-nitrates as starting materials and mixed alkali (NaOH and Na2CO3) as a precipitating agent. The formation process of LSCCF from the precursors was monitored by TG-DSC, and the crystal structure and particles morphology of the precursors which were calcined at 600, 800, 1000 ℃ for 3 h were characterized using XRD, SEM technologies. Compared with the solid state reaction of constituent oxides, when the pH value of the precipitating solution was in the range of 9.1~9.5, the LSCCF powders from the precursors caclined at 800 ℃ for 3 h had high purity, homogeneous and single perovskite phase. The electrical conductivity of the LSCCF samples sintered at 1200 ℃ for 3 h, which was measured as a function of temperatures from 100 to 800 ℃ by DC four-probe method in air, decreased with x from 0.05 to 0.20. The value of electrical conductivity was almost equal because of Ca2+, Sr2+ co-dopant resulting in the 'mix effect' while x=0.10 or 0.15. The electrical conductivity of all doped samples was higher than 100 S·cm-1 at intermediate temperatures from 500 to 800 ℃, and there was good compatibility between the LSCCF cathode and Ce0.8Sm0.2O2 electrolyte.
基金supported by Scientific Research Program Funded by Shaanxi Provincial Education Department(Program No.22JK0479)Research Start-up Project of Xi’an University of Technology(Grant No.101-256082204)+5 种基金International Science and Technology Cooperation Program of Shaanxi Province(No.2023-GHZD-50)Project of Science and Technology Shaanxi Province(No.2023-JC-YB-412)Project of Science and Technology Shaanxi Province(No.2023-JC-QN-0573)Projects of Major Innovation Platforms for Scientific and Technological and Local Transformation of Scientific and Technological Achievements of Xi’an(No.20GXSF0003)Projects of Major Scientific and Technological Achievements Local Transformation of Xi’an(No.2022JHZDZH-0039)Higher Education Institution Discipline Innovation and Intelligence Base of Shaanxi Provincial(No.S2021-ZC-GXYZ-0011).
文摘Magnesium and its alloys,as a promising class of materials,is popular in lightweight application and biomedical implants due to their low density and good biocompatibility.Additive manufacturing(AM)of Mg and its alloys is of growing interest in academia and industry.The domain-by-domain localized forming characteristics of AM leads to unique microstructures and performances of AM-process Mg and its alloys,which are different from those of traditionally manufactured counterparts.However,the intrinsic mechanisms still remain unclear and need to be in-depth explored.Therefore,this work aims to discuss and analyze the possible underlying mechanisms regarding defect appearance and elimination,microstructure formation and evolution,and performance improvement,based on presenting a comprehensive and systematic review on the relationship between process parameters,forming quality,microstructure characteristics and resultant performances.Lastly,some key perspectives requiring focus for further progression are highlighted to promote development of AM-processed Mg and its alloys and accelerate their industrialization.
文摘Based on the density functional theory within the local density approximation (LDA), we studied the electronic, elastic, and dynamic properties of AgNbO<sub>3</sub> and AgTaO<sub>3</sub> compounds under pressure. The elastic constants, optic and static dielectric constants, born effective charges, and dynamic properties of AgNbO<sub>3</sub> and AgTaO<sub>3</sub> in cubic phase were studied as pressure dependences with the ab initio method. For these compounds, we have also calculated the bulk modulus, Young’s modulus, shear modulus, Vickers hardness, Poisson’s ratio, anisotropy factor, sound velocities, and Debye temperature from the obtained elastic constants. In addition, the brittleness and ductility properties of these compounds were estimated from Poisson’s ratio and Pugh’s rule (G/B). Our calculated values also show that AgNbO<sub>3</sub> (0.37) and AgTaO<sub>3</sub> (0.39) behave as ductile materials and steer away from brittleness by increasing pressure. The calculated values of Vicker hardness for both compounds indicate that they are soft materials. The results show that band gaps, elastic constants, elastic modules, and dynamic properties for both compounds are sensitive to pressure changes. We have also made some comparisons with related experimental and theoretical data that is available in the literature.
基金the support from Grant No.2022VBA0023 funded by the Chinese Academy of Sciences President's International Fellowship Initiative.
文摘Energy storage and conservation are receiving increased attention due to rising global energy demands.Therefore,the development of energy storage materials is crucial.Thermal energy storage(TES)systems based on phase change materials(PCMs)have increased in prominence over the past two decades,not only because of their outstanding heat storage capacities but also their superior thermal energy regulation capability.However,issues such as leakage and low thermal conductivity limit their applicability in a variety of settings.Carbon-based materials such as graphene and its derivatives can be utilized to surmount these obstacles.This study examines the recent advancements in graphene-based phase change composites(PCCs),where graphene-based nanostructures such as graphene,graphene oxide(GO),functionalized graphene/GO,and graphene aerogel(GA)are incorporated into PCMs to substantially enhance their shape stability and thermal conductivity that could be translated to better storage capacity,durability,and temperature response,thus boosting their attractiveness for TES systems.In addition,the applications of these graphene-based PCCs in various TES disciplines,such as energy conservation in buildings,solar utilization,and battery thermal management,are discussed and summarized.
基金support provided by the Shenzhen-Hong Kong Science and Technology Innovation Cooperation Zone Shenzhen Park Project(HZQB-KCZYB-2020030)the Research Grants Council of Hong Kong(Project No:AoE/M-402/20.)+1 种基金the Open Project of Yunnan Precious Metals Laboratory Co.,Ltd(YPML-2023050248)the Hong Kong Innovation and Technology Commission via the Hong Kong Branch of National Precious Metals Material Engineering Research Center.
文摘Solar steam generation(SSG)is widely regarded as one of the most sustainable technologies for seawater desalination.However,salt fouling severely compromises the evaporation performance and lifetime of evaporators,limiting their practical applications.Herein,we propose a hierarchical salt-rejection(HSR)strategy to prevent salt precipitation during long-term evaporation while maintaining a rapid evaporation rate,even in high-salinity brine.The salt diffusion process is segmented into three steps—insulation,branching diffusion,and arterial transport—that significantly enhance the salt-resistance properties of the evaporator.Moreover,the HSR strategy overcomes the tradeoff between salt resistance and evaporation rate.Consequently,a high evaporation rate of 2.84 kg m^(-2) h^(-1),stable evaporation for 7 days cyclic tests in 20 wt%NaCl solution,and continuous operation for 170 h in natural seawater under 1 sun illumination were achieved.Compared with control evaporators,the HSR evaporator exhibited a>54%enhancement in total water evaporation mass during 24 h continuous evaporation in 20 wt%salt water.Furthermore,a water collection device equipped with the HSR evaporator realized a high water purification rate(1.1 kg m^(-2) h^(-1)),highlighting its potential for agricultural applications.
基金supported by President Foundation of Chinese Academy of Sciences and National Natural Science Foundation of China under Grant Nos. 10775097 and 10874174
基金This work was supported by the National High-Tech Research and Development Program of China (No.2003AA332020), the Nation-al Natural Science Foundation of China (No.50474002) and the Key Project of the Ministry of Education of China (No.104231).
文摘High performance aluminosilicate based cementitious materials were produced using calcined gangue as one of the major raw materials. The gangue was calcined at 500℃. The main constituent was calcined gangue, fly ash and slag, while alkali-silicate solutions were used as the diagenetic agent. The structure of gangue-containing aluminosilicate based cementitious materials was studied by the methods of IR, NMR and SEM. The results show that the mechanical properties are affected by the mass ratio between the gangue, slag and fly ash, the kind of activator and additional salt. For 28-day curing time, the compressive strength of the sample with a mass proportion of 2:1:1 (gangue: slag: fly ash) is 58.9 MPa, while the compressive strength of the sample containing 80wt% gangue can still be up to 52.3 MPa. The larger K^+ favors the formation of large silicate oligomers with which AI(OH)4- prefers to bind. Therefore, in Na-K compounding activator solutions more oligomers exist which result in a stronger compressive strength of aluminosilicate-based cementitious materials than in the case of Na-containing activator. The reasons for this were found through IR and NMR analysis. Glauber's salt reduces the 3-day compressive strength of the paste, but increases its 7-day and 28-day compressive strengths.
文摘Maximum bubble pressure measurement was employed to evaluate surface tension of Sn-8Zn-3Bi- (00.15)Nd and Sn-8Zn-3Bi-(00.15)La solder melts. Wetting balance method was used to measure wetting force and wetting time on Cu substrate of the two group solders. The experimental results show that minute amount of Nd or La addition to Sn-8Zn-3Bi solder causes significant decrease of the surface tension of the solder melts at 200240℃ and Nd addition is more effective on reduction of surface tension than that of La. Nd or La addition has the effect on enhancing the wetting force of the solder melts on Cu substrate, which results from the decrease of interfacial tension between the solder melt and Cu substrate. The wetting force reaches the maximum when 0.1% Nd is added to the base alloy. The contact angle between Sn-8Zn-3Bi base solders and Cu substrate decreases with the addition of Nd or La and the minimum of the contact angle is obtained from the solder with 0.1% Nd addition.
基金supported by 2008 research fund by TP,Ulsan,Korea
文摘Niobium (Nb)-clad stainless steels(SS) produced via roll bonding are being considered for use in the bipolar plates of polymer electrolyte membrane fuel cell(PEMFC) stacks. Because the roll bonding process induces substantial work hardening in the constituent materials, thermal annealing is used to restore ductility to the clad sheet so that it can be subsequently blanked, stamped and dimpled in forming the final plate component. Two roll bonded materials, niobium clad 340L stainless steel (Nb/340L SS) and niobium clad 434 stainless steel (Nb/434 SS) were annealed under optimized conditions prescribed by the cladding manufacturer. Comparative mechanical testing conducted on each material before and after annealing shows significant improvement in ductility in both cases. However, corresponding microstructural analyses indicate an obvious difference between the two heat treated materials. During annealing, an interlayer with thick less than 1 μm forms between the constituent layers in the Nb/340L SS, whereas no interlayer is found in the annealed Nb/434 SS material. Prior work suggests that internal defects potentially can be generated in such an interlayer during metal forming operations. Thus, Nb/434 SS may be the preferred candidate material for this application.
文摘In order to control the size and distribution of the high conductive Fe2P in LiFePO4/Fe2P composite, two different cooling rates (Fast: 15 ℃·min-1, Slow: 2 ℃·min-1) were employed after mechanical alloying. The discharge capacity of the fast cooled was 83 mAh·g-1 and the slow cooled 121 mAh·g-1. The particle size of the synthesized powder was examined by transmission electron microscopy and distribution of Fe2P was characterized using scanning electron microscopy (SEM). In addition, two-step heat treatment was carried out for better distribution of Fe2P. X-ray diffraction (XRD) and Rietveld refinement reveal that LiFePO4/Fe2P composite consists of 95.77% LiFePO4 and 4.33% of Fe2P.
基金supported by a grant from the Metals Bank by the Ministry of Knowledge Economy and a grant-in-aid for the National Core Research Center Program (No.R15-2006-022-02001-0)
文摘The effects of Ca and Sr addition on the microstructure and creep properties of Mg-4Al-2Sn alloys were examined.Tensile tests at 25℃ and 200℃ and creep tests at 150℃ and 200℃ were carried out to estimate the room temperature and high temperature mechanical properties of these alloys.The microstructure of the Mg-4Al-2Sn alloy showed dendriticα-Mg,Mg17Al12 and Mg2Sn phases.The latter two phases precipitated along the grain boundaries.The addition of Ca and Sr resulted in the formation of ternary CaMgSn and SrMgSn phases within the grain.The grain size was reduced slightly with the addition of Sr and Ca.The tensile strength was decreased by the addition of Ca and Sr at room temperature.However,the high temperature tensile strength was increased.The creep strength was improved by the addition of Ca and Sr.
基金Project supported by the National High-Tech Development Plan of China (2001AA51580) the Sweden-Asia Partnership Program (DNR6964)+1 种基金the Natural Science Foundation of Liaoning Province (20062145) the Education Department of Liaoning Province (05L073)
文摘In order to lower the raw materials cost and develop a novel cathode materials for intermediate temperature solid oxide fuel cell(ITSOFC), using mixed rare earth replacing the expensive pure La2O3 as the raw materials, the powders of Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ (Ln=the mixed rare earth, x=0.05, 0.10, 0.15) for the applications as the cathode materials were prepared by microwave sintering process. The crystal structure and the particles morphology of the obtained powders were characterized by XRD and SEM, the electrical conductivity of all samples sintered at 1200 ℃ for 3 h was also measured as the function of the temperature from 100 to 800 ℃ by DC four-probe method in air. The experimental results show that due to the influence of mixed rare earth the powders of Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ synthesized at 1200 ℃ for 0.5 h with the mean particle size of 1~20 μm was of perovskite and cubic fluorite phase as well a little SrO phase, the electrical conductivity of the samples decreases with the adding Ca2+ content, and are all higher than 100 S·cm-1 from 500 to 700 ℃ when x≤0.10. Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ. Can meet the demand of the electrical properties for the cathode materials in ITSOFC.
文摘The microstructure and mechanical properties of friction stir welded 2. 5 mm 7050-T7451 aluminum alloy natural aging 72 h and 17 520 h were investigated, respectively. The uniaxial tensile test showed that yield strength, tensile strength and elongation of the joints 17 520 h natural aging were about 20%, 12% and 24% higher than those joints natural aging 72 h. Hardness profile of natural aging 17 520 h joint witnessed significant enhancement in nugget zone, compared with 72 h natural aging. Differential scanning calorimetry ( DSC ) and transmission electron microscopy (TEM) test revealed that more Guinier-Preston zone, η' and 71 phase emerged in nugget zone as natural aging duration increased, high density of dislocation located within grain boundary in nugget zone of joints natural aging 72 h. It is concluded that natural aging was feasible to enhalwe strength and plasticity of FSW joints simultaneously.
基金Supported by the National Natural Science Foundation of China under Grant No.19574045。
文摘It is pointed out that the quantum mechanical Hamiltonian of two L-C circuits with mutual-inductance is equivalent to a pair of harmonic oscillators with a kinetic coupling term.We then diagonalize the Hamiltonian.It is shown that instantaneously switching on the external sources may result in a two-mode squeezed state of the system,which actually arises from the effect of mutual-inductance.The quantum fluctuation for the case of l_(1)c_(1)=l_(2)c_(2 ) is analysed and it is found that the current fluctuation in the circuits increases with the increment of the mutual-inductance.
基金financially supported by the Natural Science Foundation of Jiangsu Province(No.BK2009354)
文摘Thermomechanical treatments were carried out to improve the properties of AZ31B joints prepared by gas tungsten arc welding. The microstructures of the joints were studied by optical microscopy and scanning electron microscopy with energy-dispersive spectrometry. Tensile tests and hardness tests were performed to investigate the effects of thermomechanical treatments on the mechanical properties of the joints. It is found that the thermomechanical-treated joints show superior mechanical properties against the as-welded joints, and their ultimate tensile strength can reach more than 92% of the base material. This mainly attributes to the formation of fine equiaxed grains in the fusion zone. ARer thermomechanical treatments the dendrites are transformed to fine spherical grains, and the dendritic segregation can be effectively eliminated.
基金National Natural Science Foundation of China under Grant Nos.10775097 and 10874174
文摘We propose a new two-fold integration transformation in p-q phase space∫∫_(-∞)~∞ (dqdq/π) e^(2i(p-x)(q-y))f(p,q)2≡G(x,y),which possesses some well-behaved transformation properties.We apply this transformation to the Weyl ordering ofoperators,especially those Q-P ordered and P-Q ordered operators.