The local overheating issue is a serious threat to the safe operation of data centers(DCs).The chip level liquid cooling with pool boiling is expected to solve this problem.The effect of nano configuration and surface...The local overheating issue is a serious threat to the safe operation of data centers(DCs).The chip level liquid cooling with pool boiling is expected to solve this problem.The effect of nano configuration and surface wettability on the boiling characteristics of copper surfaces is studied using molecular dynamics(MD)simulation.The argon is chosen as the coolant,and the wall temperature is 300 K.The main findings and innovations are as follows.(1)Compared to the smooth surface and fin surface,the cylindrical nano cavity obtains the superior boiling performance with earlier onset of nucleate boiling(ONB),larger heat flux because of the higher heat transport rate.(2)The nano cavity with hydrophilicity can improve the response speed and heat dissipation efficiency.Compared to the contact angleθ=121°,the formation times of nucleate bubble and film boiling for theθ=0°are reduced by 90.84%and 93.57%,respectively.(3)A deeper cavity of 3.3 nm is beneficial for triggering boiling and improving the heat dissipation rate.The highest heat flux can be achieved at 21.86 x 10°W/m2,which can meet the cooling requirements of the micro devices with ultra-high heat flux(107-108 W/m2).The coupling effect of nano configuration and surface wettability is illustrated,and the essential reasons for the enhanced heat transport are revealed.The findings can guide the optimization of cooling systems and promote the practical application of phase change liquid cooling in DCs.展开更多
At present,the effects of pore throat structure on micro-scale seepage characteristics of tight gas reservoirs are less researched,and traditional numerical simulation methods are faced with a great number of challeng...At present,the effects of pore throat structure on micro-scale seepage characteristics of tight gas reservoirs are less researched,and traditional numerical simulation methods are faced with a great number of challenges in the study of micro-scale flow.In this paper,the flow pattern of tight gas was studied based on the actual temperature and pressure of tight gas reservoir and the characteristic size of reservoir pore throat,and the rationality of tight gas flow was simulated by means of lattice Boltzmann method.Then,considering the influences of micro-scale effect,slippage effect and other factors,a tight gas flow model was established on the basis of LBGK-D2Q9 model,and its calculation results were compared with the analytical solutions and the numerical solutions listed in the literature.Finally,the influential laws of pore throat structure on the micro-scale seepage characteristics of tight gas were discussed.And the following research results were obtained.First,when the pressure is in the range of 3-70 MPa and the temperature is in the range of 293.15-373.15 K,the Knudsen number(Kn)is less than 0.1 and the gas flow is in the pattern of slippage flow and weak continuous flow.And in this case,it is reasonable to adopt the LBGK-D2Q9 model to simulate tight gas flow.Second,the effect of the characteristic size of the flow channel on the Kn is much greater than that of the pressure change.When the pore-throat ratio is constant,the Kn increases slowly along the throat.And its increasing trend gets more obvious with the increase of pore-throat ratio.Third,the presence of the throat makes the non-linear distribution characteristics of the pressure in the pore throat significant,and the pressure drop mainly lies in the throat.And the higher the pore-throat ratio is,the larger the pressure drop range in the throat is.Fourth,the non-linear distribution of pressure decreases the gas flow speed significantly,thus reducing the mass flow rate in the flow channel.In conclusion,the simulation result of the model established in this paper is highly coincident with the analytical solutions and the numerical solutions calculated by DSMC and IP methods in the literature,which verifies that this proposed model is reliable.The research results reveal the importance of“connecting fracture and expanding throat”in the practical development engineering of tight gas reservoirs.展开更多
The recent advancement in the design,synthesis,and fabrication of micro/nano structured LiNixCoyMnzO2 with one-,two-,and three-dimensional morphologies was reviewed.The major goal is to highlight LiNixCoyMnzO2 materia...The recent advancement in the design,synthesis,and fabrication of micro/nano structured LiNixCoyMnzO2 with one-,two-,and three-dimensional morphologies was reviewed.The major goal is to highlight LiNixCoyMnzO2 materials,which have been utilized in lithium ion batteries with enhanced energy and power density,high energy efficiency,superior rate capability and excellent cycling stability resulting from the doping,surface coating,nanocomposites and nano-architecturing.展开更多
In order to enhance electrochemical properties of LiFePO4 （LFP） cathode materials, spherical porous nano/micro structured LFP/C cathode materials were synthesized by spray drying, followed by calcination. The result...In order to enhance electrochemical properties of LiFePO4 （LFP） cathode materials, spherical porous nano/micro structured LFP/C cathode materials were synthesized by spray drying, followed by calcination. The results show that the spherical precursors with the sizes of 0.5-5 μm can be completely converted to LFP/C when the calcination temperature is higher than 500 ℃. The LFP/C microspheres obtained at calcination temperature of 700 ℃ are composed of numerous particles with sizes of -20 nm, and have well-developed interconnected pore structure and large specific surface area of 28.77 mE/g. The specific discharge capacities of the LFP/C obtained at 700 ℃ are 162.43, 154.35 and 144.03 mA.h/g at 0.5C, 1C and 2C, respectively. Meanwhile, the capacity retentions can reach up to 100% after 50 cycles. The improved electrochemical properties of the materials are ascribed to a small Li＋ diffusion resistance and special structure of LFP/C microspheres.展开更多
Hierarchical dendritic micro–nano structure Zn Fe_2O_4 have been prepared by electrochemical reduction and thermal oxidation method in this work. X-ray diffractometry, Raman spectra and field-emission scanning electr...Hierarchical dendritic micro–nano structure Zn Fe_2O_4 have been prepared by electrochemical reduction and thermal oxidation method in this work. X-ray diffractometry, Raman spectra and field-emission scanning electron microscopy were used to characterize the crystal structure, size and morphology. The results show that the sample(S-2) is composed of pure ZnFe_2O_4 when the molar ratio of Zn^(2+)/Fe^(2+)in the electrolyte is 0.35. Decreasing the molar ratio of Zn^(2+)/Fe^(2+), the sample(S-1) is composed of ZnFe_2O_4 and α-Fe_2O_3, whereas increasing the molar ratio of Zn^(2+)/Fe^(2+), the sample(S-3) is composed of ZnFe_2O_4 and Zn O. The lattice parameters of ZnFe_2O_4 are influenced by the molar ratio of Zn^(2+)/Fe: Zn at excess decreases the cell volume whereas Fe at excess increases the cell volume of Zn Fe_2O_4. All the samples have the dendritic structure, of which S-2 has micron-sized lush branches with nano-sized leaves. UV–Vis diffuse reflectance spectra were acquired by a spectrophotometer. The absorption edges gradually blue shift with the increase of the molar ratio of Zn^(2+)/Fe^(2+). Photocatalytic activities for water splitting were investigated under Xe light irradiation in an aqueous olution containing 0.1 mol·L^(-1)Na_2S/0.02 mol·L^(-1)Na_2SO_3 in a glass reactor. The relatively highest photocatalytic activity with 1.41 μmol·h-1· 0.02 g^(-1)was achieved by pure ZnFe_2O_4sample(S-2). The photocatalytic activity of the mixture phase of Zn Fe_2O_4 and α-Fe_2O_3(S-1) is better than ZnF e_2O_4 and ZnO(S-3).展开更多
The crystal structure evolution of the Cu-rich nano precipitates from bcc to 9R during thermal aging was studied in nuclear reactor pressure vessel （RPV） model steels. The specimens, contained higher copper and nick...The crystal structure evolution of the Cu-rich nano precipitates from bcc to 9R during thermal aging was studied in nuclear reactor pressure vessel （RPV） model steels. The specimens, contained higher copper and nickel contents than commercially available one, were heated at 890 ~C for 0.5 h and then water quenched followed by tempering at 0（50 ~C for I0 h and aging at 400 ~C for 1000 h. It was observed that bcc and 9R orthogonal structure, as well as 9R orthogonal and 9R monoclinic structure, coexist in a single Cu-rich nano precipitate. Further analyses pointed out that Cu-rich nano precipitates of bcc structure were not stable, it may preferentially transform to 9R orthogonal structure and then to 9R monoclinic structure. This results showed that the crystal structure evolution of the Cu-rich nano precipitates was complex.展开更多
In order to improve the osseointegration and antibacterial activity of titanium alloys,micro/nano-structured ceramic coatings doped with antibacterial element F were prepared by plasma electrolytic oxidation(PEO)proce...In order to improve the osseointegration and antibacterial activity of titanium alloys,micro/nano-structured ceramic coatings doped with antibacterial element F were prepared by plasma electrolytic oxidation(PEO)process on Ti6Al4V alloy in NaF electrolyte.The influence of NaF concentration(0.15-0.50 mol/L)on the PEO process,microstructure,phase composition,corrosion resistance and thickness of the coatings was investigated using scanning/transmission electron microscopy,energy dispersive spectroscopy,atomic force microscopy,X-ray diffractometer,and potentiodynamic polarization.The results demonstrated that Ti6Al4V alloy had low PEO voltage(less than 200 V)in NaF electrolyte,which decreased further as the NaF concentration increased.A micro/nano-structured coating with 10-15μm pits and 200-800 nm pores was formed in NaF electrolyte;the morphology was different from the typical pancake structure obtained with other electrolytes.The coating formed in NaF electrolyte had low surface roughness and was thin(<4μm).The NaF concentration had a small effect on the phase transition from metastable anatase phase to stable rutile phase,but greatly affected the corrosion resistance.In general,as the NaF concentration increased,the surface roughness,phase(anatase and rutile)contents,corrosion resistance,and thickness of the coating first increased and then decreased,reaching the maximum values at 0.25 mol/L NaF.展开更多
The influences of nano silica (NS) on the hydration and microstructure development of steam cured cement high volume fly ash (40 wt%, CHVFA) system were investigated. The compressive strength of mortars was tested wit...The influences of nano silica (NS) on the hydration and microstructure development of steam cured cement high volume fly ash (40 wt%, CHVFA) system were investigated. The compressive strength of mortars was tested with different NS dosage from 0 to 4%. Results show that the compressive strength is dramatically improved with the increase of NS content up to 3%, and decreases with further increase of NS content (e g, at 4%). Then X?ray diffraction (XRD), differential scanning calorimetry-thermogravimetry (DSCTG), scanning electron microscope (SEM), energy disperse spectroscopy (EDS), mercury intrusion porosimeter (MIP) and nuclear magnetic resonance (NMR) were used to analyze the mechanism. The results reveal that the addition of NS accelerates the hydration of cement and fly ash, decreases the porosity and the content of calcium hydroxide (CH) and increases the polymerization degree of C-S-H thus enhancing the compressive strength of mortars. The interfacial transition zone (ITZ) of CHVFA mortars is also significantly improved by the addition ofNS, embodying in the decrease of Ca/Si ratio and CH enrichment of ITZ.展开更多
Condensation is an important regime of heat transfer which has wide applications in different industries such as power plants,heating,ventilating and air conditioning,and refrigeration.Condensation occurs in two diffe...Condensation is an important regime of heat transfer which has wide applications in different industries such as power plants,heating,ventilating and air conditioning,and refrigeration.Condensation occurs in two different modes including filmwise (FWC) and dropwise (DWC) condensation.DWC occurring on hydrophobic and superhydrophobic surfaces has a much higher heat transfer capacity than FWC.Therefore,wide investigations have been done to produce DWC in recent years.Superhydrophobic surfaces have micro/nano structures with low surface energy.In this study,a two-step electrodeposition process is used to produce micro/nano structures on copper specimens.The surface energy of specimens is reduced by a self-assembled monolayer using ethanol and 1-octadecanethiol solution.The results show that there is an optimum condition for electrodeposition parameters.For example,a surface prepared by 2000 s step time has 5 times greater heat transfer than FWC while a surface with 4000 s step time has nearly the same heat transfer as FWC.The surfaces of the fabricated specimens are examined using XRD and SEM analyses.The SEM analyses of the surfaces show that there are some micro-structures on the surfaces and the surface porosities are reduced by increasing the second step electrodeposition time.展开更多
Blended elemental 90W 7Ni 3Fe (mass fraction, %) powder was mechanically alloyed in a planetary ball mill. Nano crystalline grains were obtained after 10 h milling. The nano structured powder was processed to full den...Blended elemental 90W 7Ni 3Fe (mass fraction, %) powder was mechanically alloyed in a planetary ball mill. Nano crystalline grains were obtained after 10 h milling. The nano structured powder was processed to full density by metal injection molding approach. Compacts from the optimal powder binder mixture were studied for molding and sintering behaviors. Milling significantly increases the maximum powder loading and homogeneity of the feedstock, and enhances the sintering densification process. When solid state sintered at 1 350～1 450 ℃, the alloy shows very fine grains (～3 μm), high tensile strength (>1 130 MPa) and almost no distortion. [展开更多
The Si L2,3 X-ray absorption near-edge structure (XANES) can be used to probe thelocal structure around Si and derive electronic information of the unoccupied s- andd-like partial density of states in nano-size SiO2. ...The Si L2,3 X-ray absorption near-edge structure (XANES) can be used to probe thelocal structure around Si and derive electronic information of the unoccupied s- andd-like partial density of states in nano-size SiO2. We present Si L2,3-edge for threedifferent size silicates acquired by total electron yield (TEY) at the photoemission sta-tion of Beijing Synchrotron Radiation Facility (BSRF). The Si L2,3-edge spectra areinterpreted based on ab initio full multiple-scattering (MS) calculation. The Si L2.3-edge of nano-size materials has XANES similar to that of a-quartz. The similaritiesbetween the Si L2.3-edge shapes attest to a common molecular-orbital picture of theirSi-O bonding and the same coordination state. However, a considerable broadeningof Si L2,3-edge XANES spectra as decrease of particle size is also an indicative ofpolyhedral distortions.展开更多
Nanograins are characterized by a typical grain size from 1 to 100 nm. Molecular dynamics simulations have been carried out for the nanograin sphere with the diameters from 1.45 to 10.12 nm. We study the influence of ...Nanograins are characterized by a typical grain size from 1 to 100 nm. Molecular dynamics simulations have been carried out for the nanograin sphere with the diameters from 1.45 to 10.12 nm. We study the influence of grain size on structure and diffusion properties of the nanograins. The results reveal that as the grain size is reduced, the fraction of grain surface increases significantly, and the surface width is approximately constant; the mean atomic energy of the surface increases distinctly, but that of the grain interior varies insignificantly; the diffusion coefficient is increased sharply, and the relation of the diffusion coefficient and the grain size is close to exponential relation below 10 nm.展开更多
The recent research progress of structure- and size-controlled micro/nano-energetic materials is reviewed, which properties are fundamentally different from those of their corresponding bulk materials. The development...The recent research progress of structure- and size-controlled micro/nano-energetic materials is reviewed, which properties are fundamentally different from those of their corresponding bulk materials. The development of the construction strategies for achieving zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) micro/nanostructures from energetic molecules is introduced. Also, an overview of the unique properties induced by micro/nanostructures and size effects is provided. Special emphasis is focused on the size-dependent properties that are different from those of the conventional micro-sized energetic materials, such as thermal decomposition, sensitivity, combustion and detonation, and compaction behaviors. A conclusion and our view of the future development of micro/nano-energetic materials and devices are given.展开更多
The investigation on the oxidation behaviour of Si1-xGex alloys （x=0.05, 0.15, and 0.25） is carried out. It is found for the first time that on the oxide film a germanium nano-cap with a thickness of 1.8-2.8nm and a...The investigation on the oxidation behaviour of Si1-xGex alloys （x=0.05, 0.15, and 0.25） is carried out. It is found for the first time that on the oxide film a germanium nano-cap with a thickness of 1.8-2.8nm and a few Ge nanoparticles with diameters ranging from 5.5 nm to 10 nm are formed by the low-temperatu.re laser-assisted dry oxidation of Si1-xGex substrate. A new scanning method on the decline cross-section of the multiple-layer sample is adopted to measure the layer thickness and the composition. Some new peaks in photoluminescence （PL） spectra are discovered, which could be related to the nano-cap and the nano-particles of germanium. A suitable model and several new calculating formulae with the unrestricted Hartree-Fock-Roothaan （UHFR） method and quantum confinement analysis are proposed to interpret the PL spectra and the nano-structure mechanism in the oxide.展开更多
304 austenitic stainless steel was cold rolled in the range of 20%-80%reductions and then annealed at 700-900°C for 60 sto obtain nano/ultrafine-grained（NG/UFG）structure.Transmission electron microscopy,electro...304 austenitic stainless steel was cold rolled in the range of 20%-80%reductions and then annealed at 700-900°C for 60 sto obtain nano/ultrafine-grained（NG/UFG）structure.Transmission electron microscopy,electron backscatter diffraction and X-ray diffraction were used to characterize the resulting microstructures.The results showed that with the increase of cold reduction,the content of martensite was increased.The steel performed work hardening during cold-working owing to the occurrence of strain induced martensite which nucleated in single shear bands.Further rolling broke up the lath-type martensite into dislocation-cell type martensite because of the formation of slip bands.Samples annealed at 800-960°C for 60 swere of NG/UFG structure with different percentage of nanocrystalline（60-100 nm）and ultrafine（100-500 nm）grains,submicron size（500-1000 nm）grains and micron size（〉1000 nm）grains.The value of the Gibbs free energy exhibited that the reversion mechanism of the reversion process was shear controlled by the annealing temperature.For a certain annealing time during the reversion process,austenite nucleated first on dislocation-cell type martensite and the grains grew up subsequently and eventually to be micrometer/submicrometer grains,while the nucleation of austenite on lath-type martensite occurred later resulting in nanocrystalline/ultrafine grains.The existence of the NG/UFG structure led to a higher strength and toughness during tensile test.展开更多
In the present work, osteoblast behavior on a hierarchical micro-/nano-structured titanium surface was investigated. A hi- erarchical hybrid micro-/nano-structured titanium surface topography was produced via Electrol...In the present work, osteoblast behavior on a hierarchical micro-/nano-structured titanium surface was investigated. A hi- erarchical hybrid micro-/nano-structured titanium surface topography was produced via Electrolytic Etching （EE）. MG-63 cells were cultured on disks for 2 h to 7 days. The osteoblast response to the hierarchical hybrid micro-/nano-structured titanium surface was evaluated through the osteoblast cell morphology, attachment and proliferation. For comparison, MG-63 cells were also cultured on Sandblasted and Acid-etched （SEA） as well as Machined （M） surfaces respectively. The results show signifi- cant differences in the adhesion rates and proliferation levels of MG-63 cells on EE, SLA, and M surfaces. Both adhesion rate and proliferation level on EE surface are higher than those on SLA and M surfaces. Therefore, we may expect that, comparing with SLA and M surfaces, bone growth on EE surface could be accelerated and bone formation could be promoted at an early stage, which could be applied in the clinical practices for immediate and early-stage loadings.展开更多
Pulse current technique was applied for the preparation of novel electroactive manganese dioxide and possible influences of different electrokinetic phenomena on material characteristics were discussed. The characteri...Pulse current technique was applied for the preparation of novel electroactive manganese dioxide and possible influences of different electrokinetic phenomena on material characteristics were discussed. The characterizations of pulse deposited sample （pcMD） were carried out by different techniques： Fourier transform infrared spectroscopy （FTIR）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）, Brunauer-Emmett-Teller （BET） method, Raman spectroscopy, and atomic force microscopy （AFM）. SEM image revealed that pulse current could improve the current distribution. This was confirmed by AFM images showing a decrease in surface roughness of pcMDs in comparison to amorphous samples, which were deposited by direct current （dcMD）. Higher distortion of MnO6 octahedral environment of dcMD was detected by FTJR and Raman spectroscopy. Cyclic voltammetric （CV） measurements showed a generally higher energy level drained from the second electron discharge of pcMD. This is mainly attributed to a higher surface area and a lower diffusion pass of electrons and protons arisen via a rather unique nanostructural arrangement of pcMD grains. Results indicate a higher surface area available for the non homogenous second electron discharge of pcMD grains.展开更多
A bulk nanostructured twinning-induced plasticity （TWIP） steel with high ductility and high strength was fabricated by cryogenic asymmetry-rolling （cryo-ASR） and subsequent recovery treatment. It was found that th...A bulk nanostructured twinning-induced plasticity （TWIP） steel with high ductility and high strength was fabricated by cryogenic asymmetry-rolling （cryo-ASR） and subsequent recovery treatment. It was found that the cryo-ASRed TWIP steels exhibit simultaneous improvements in the ductility, strength and work hardening. Typical microstructures of the cryo-ASR TWIP steel were characterized by shear bands and intensive mechanical nano-sized twins induced by cryogenic deformation. These mechanical nano-scale twins remain thermally stable during the subsequent recovery treatment. It is believed that the ductility enhancement and high work-hardening ability for the cryo-ASR TWIP steels should be mainly attributed to the high-densitv pre-existing nano-scale twins.展开更多
Nano-structured photon management is currently an interesting topic since it can enhance the optical absorption and reduce the surface reflection which will improve the performance of many kinds of optoelectronic devi...Nano-structured photon management is currently an interesting topic since it can enhance the optical absorption and reduce the surface reflection which will improve the performance of many kinds of optoelectronic devices, such as Si-based solar cells and light emitting diodes. Here, we report the fabrication of periodically nano-patterned Si structures by using polystyrene nano-sphere lithography technique. By changing the diameter of nano-spheres and the dry etching parameters, such as etching time and etching power, the morphologies of formed Si nano-structures can be well controlled as revealed by atomic force microscopy.A good broadband antireflection property has been achieved for the formed periodically nano-patterned Si structures though they have the low aspect ratio(<0.53). The reflection can be significantly reduced compared with that of flat Si substrate in a wavelength range from 400 nm to 1200 nm. The weighted mean reflection under the AM1.5 solar spectrum irradiation can be as low as 3.92% and the corresponding optical absorption is significantly improved, which indicates that the present Si periodic nano-structures can be used in Si-based thin film solar cells.展开更多
Gradient cemented carbides with nano-TiN were prepared by the common powder metallurgical procedure. The formation of gradient zone and the microstructure, properties of the alloys were investigated using scanning ele...Gradient cemented carbides with nano-TiN were prepared by the common powder metallurgical procedure. The formation of gradient zone and the microstructure, properties of the alloys were investigated using scanning electron microscope（SEM）, energy dispersive spectroscopy（EDS） and other performance testing apparatus. Moreover, the effect of nano-TiN on the gradient cemented carbide was studied. It is found that gradient zone width increases slightly with nano-TiN introduction. Both cobalt and titanium concentrations reach the maximum near the gradient border. Tungsten concentration shows fluctuation from the surface to the bulk. （Ti ,W）C phase grains are refined for nitrogen introduction. Core-rim structure has been observed under the SEM back-scattered mode. The core appears as dark due to more titanium in it and the rim with more tungsten appears as grey. In addition, the hardness and transverse rupture strength of gradient cemented carbide are enhanced with nano-TiN introduced.展开更多
基金the National Natural Science Foundation of China (No. 52406191, No. 52408123)the Science and Technology Project of Tianjin (No. 24YDTPJC00680).
文摘The local overheating issue is a serious threat to the safe operation of data centers(DCs).The chip level liquid cooling with pool boiling is expected to solve this problem.The effect of nano configuration and surface wettability on the boiling characteristics of copper surfaces is studied using molecular dynamics(MD)simulation.The argon is chosen as the coolant,and the wall temperature is 300 K.The main findings and innovations are as follows.(1)Compared to the smooth surface and fin surface,the cylindrical nano cavity obtains the superior boiling performance with earlier onset of nucleate boiling(ONB),larger heat flux because of the higher heat transport rate.(2)The nano cavity with hydrophilicity can improve the response speed and heat dissipation efficiency.Compared to the contact angleθ=121°,the formation times of nucleate bubble and film boiling for theθ=0°are reduced by 90.84%and 93.57%,respectively.(3)A deeper cavity of 3.3 nm is beneficial for triggering boiling and improving the heat dissipation rate.The highest heat flux can be achieved at 21.86 x 10°W/m2,which can meet the cooling requirements of the micro devices with ultra-high heat flux(107-108 W/m2).The coupling effect of nano configuration and surface wettability is illustrated,and the essential reasons for the enhanced heat transport are revealed.The findings can guide the optimization of cooling systems and promote the practical application of phase change liquid cooling in DCs.
基金Project supported by the Key Program of National Natural Science Foundation of China“Fundamental study on tight gas reservoir formation drying and tight gas seepage capacity improvement”(No.:51534006).
文摘At present,the effects of pore throat structure on micro-scale seepage characteristics of tight gas reservoirs are less researched,and traditional numerical simulation methods are faced with a great number of challenges in the study of micro-scale flow.In this paper,the flow pattern of tight gas was studied based on the actual temperature and pressure of tight gas reservoir and the characteristic size of reservoir pore throat,and the rationality of tight gas flow was simulated by means of lattice Boltzmann method.Then,considering the influences of micro-scale effect,slippage effect and other factors,a tight gas flow model was established on the basis of LBGK-D2Q9 model,and its calculation results were compared with the analytical solutions and the numerical solutions listed in the literature.Finally,the influential laws of pore throat structure on the micro-scale seepage characteristics of tight gas were discussed.And the following research results were obtained.First,when the pressure is in the range of 3-70 MPa and the temperature is in the range of 293.15-373.15 K,the Knudsen number(Kn)is less than 0.1 and the gas flow is in the pattern of slippage flow and weak continuous flow.And in this case,it is reasonable to adopt the LBGK-D2Q9 model to simulate tight gas flow.Second,the effect of the characteristic size of the flow channel on the Kn is much greater than that of the pressure change.When the pore-throat ratio is constant,the Kn increases slowly along the throat.And its increasing trend gets more obvious with the increase of pore-throat ratio.Third,the presence of the throat makes the non-linear distribution characteristics of the pressure in the pore throat significant,and the pressure drop mainly lies in the throat.And the higher the pore-throat ratio is,the larger the pressure drop range in the throat is.Fourth,the non-linear distribution of pressure decreases the gas flow speed significantly,thus reducing the mass flow rate in the flow channel.In conclusion,the simulation result of the model established in this paper is highly coincident with the analytical solutions and the numerical solutions calculated by DSMC and IP methods in the literature,which verifies that this proposed model is reliable.The research results reveal the importance of“connecting fracture and expanding throat”in the practical development engineering of tight gas reservoirs.
基金Projects(51134007,21003161,21250110060) supported by the National Natural Science Foundation of ChinaProject(11MX10) supported by Central South University Annual Mittal-Founded Innovation ProjectProject(2011ssxt086) supported by Fundamental Research Funds for the Central Universities,China
文摘The recent advancement in the design,synthesis,and fabrication of micro/nano structured LiNixCoyMnzO2 with one-,two-,and three-dimensional morphologies was reviewed.The major goal is to highlight LiNixCoyMnzO2 materials,which have been utilized in lithium ion batteries with enhanced energy and power density,high energy efficiency,superior rate capability and excellent cycling stability resulting from the doping,surface coating,nanocomposites and nano-architecturing.
基金Project(2013AA050901)supported by the National High-tech Research and Development Program of China
文摘In order to enhance electrochemical properties of LiFePO4 （LFP） cathode materials, spherical porous nano/micro structured LFP/C cathode materials were synthesized by spray drying, followed by calcination. The results show that the spherical precursors with the sizes of 0.5-5 μm can be completely converted to LFP/C when the calcination temperature is higher than 500 ℃. The LFP/C microspheres obtained at calcination temperature of 700 ℃ are composed of numerous particles with sizes of -20 nm, and have well-developed interconnected pore structure and large specific surface area of 28.77 mE/g. The specific discharge capacities of the LFP/C obtained at 700 ℃ are 162.43, 154.35 and 144.03 mA.h/g at 0.5C, 1C and 2C, respectively. Meanwhile, the capacity retentions can reach up to 100% after 50 cycles. The improved electrochemical properties of the materials are ascribed to a small Li＋ diffusion resistance and special structure of LFP/C microspheres.
基金Supported by the State Key Laboratory of Urban Water Resource and Environment,Harbin Institute of Technology(2015DX07)
文摘Hierarchical dendritic micro–nano structure Zn Fe_2O_4 have been prepared by electrochemical reduction and thermal oxidation method in this work. X-ray diffractometry, Raman spectra and field-emission scanning electron microscopy were used to characterize the crystal structure, size and morphology. The results show that the sample(S-2) is composed of pure ZnFe_2O_4 when the molar ratio of Zn^(2+)/Fe^(2+)in the electrolyte is 0.35. Decreasing the molar ratio of Zn^(2+)/Fe^(2+), the sample(S-1) is composed of ZnFe_2O_4 and α-Fe_2O_3, whereas increasing the molar ratio of Zn^(2+)/Fe^(2+), the sample(S-3) is composed of ZnFe_2O_4 and Zn O. The lattice parameters of ZnFe_2O_4 are influenced by the molar ratio of Zn^(2+)/Fe: Zn at excess decreases the cell volume whereas Fe at excess increases the cell volume of Zn Fe_2O_4. All the samples have the dendritic structure, of which S-2 has micron-sized lush branches with nano-sized leaves. UV–Vis diffuse reflectance spectra were acquired by a spectrophotometer. The absorption edges gradually blue shift with the increase of the molar ratio of Zn^(2+)/Fe^(2+). Photocatalytic activities for water splitting were investigated under Xe light irradiation in an aqueous olution containing 0.1 mol·L^(-1)Na_2S/0.02 mol·L^(-1)Na_2SO_3 in a glass reactor. The relatively highest photocatalytic activity with 1.41 μmol·h-1· 0.02 g^(-1)was achieved by pure ZnFe_2O_4sample(S-2). The photocatalytic activity of the mixture phase of Zn Fe_2O_4 and α-Fe_2O_3(S-1) is better than ZnF e_2O_4 and ZnO(S-3).
基金financially supported by the National Basic Research Program of China(No.2011CB610503)National Natural Science Foundation of China(No.50931003)Ministry of Major Subject of Shanghai(No.S30107)
文摘The crystal structure evolution of the Cu-rich nano precipitates from bcc to 9R during thermal aging was studied in nuclear reactor pressure vessel （RPV） model steels. The specimens, contained higher copper and nickel contents than commercially available one, were heated at 890 ~C for 0.5 h and then water quenched followed by tempering at 0（50 ~C for I0 h and aging at 400 ~C for 1000 h. It was observed that bcc and 9R orthogonal structure, as well as 9R orthogonal and 9R monoclinic structure, coexist in a single Cu-rich nano precipitate. Further analyses pointed out that Cu-rich nano precipitates of bcc structure were not stable, it may preferentially transform to 9R orthogonal structure and then to 9R monoclinic structure. This results showed that the crystal structure evolution of the Cu-rich nano precipitates was complex.
文摘In order to improve the osseointegration and antibacterial activity of titanium alloys,micro/nano-structured ceramic coatings doped with antibacterial element F were prepared by plasma electrolytic oxidation(PEO)process on Ti6Al4V alloy in NaF electrolyte.The influence of NaF concentration(0.15-0.50 mol/L)on the PEO process,microstructure,phase composition,corrosion resistance and thickness of the coatings was investigated using scanning/transmission electron microscopy,energy dispersive spectroscopy,atomic force microscopy,X-ray diffractometer,and potentiodynamic polarization.The results demonstrated that Ti6Al4V alloy had low PEO voltage(less than 200 V)in NaF electrolyte,which decreased further as the NaF concentration increased.A micro/nano-structured coating with 10-15μm pits and 200-800 nm pores was formed in NaF electrolyte;the morphology was different from the typical pancake structure obtained with other electrolytes.The coating formed in NaF electrolyte had low surface roughness and was thin(<4μm).The NaF concentration had a small effect on the phase transition from metastable anatase phase to stable rutile phase,but greatly affected the corrosion resistance.In general,as the NaF concentration increased,the surface roughness,phase(anatase and rutile)contents,corrosion resistance,and thickness of the coating first increased and then decreased,reaching the maximum values at 0.25 mol/L NaF.
基金Funded by the “13th Five-Year” National Science and Technology Support Program of China(No.2016YFC0701003–05)the Science and Technology Support Program of Hubei Province(No.2015BAA084)the National Natural Science Foundation of China(No.51378408)
文摘The influences of nano silica (NS) on the hydration and microstructure development of steam cured cement high volume fly ash (40 wt%, CHVFA) system were investigated. The compressive strength of mortars was tested with different NS dosage from 0 to 4%. Results show that the compressive strength is dramatically improved with the increase of NS content up to 3%, and decreases with further increase of NS content (e g, at 4%). Then X?ray diffraction (XRD), differential scanning calorimetry-thermogravimetry (DSCTG), scanning electron microscope (SEM), energy disperse spectroscopy (EDS), mercury intrusion porosimeter (MIP) and nuclear magnetic resonance (NMR) were used to analyze the mechanism. The results reveal that the addition of NS accelerates the hydration of cement and fly ash, decreases the porosity and the content of calcium hydroxide (CH) and increases the polymerization degree of C-S-H thus enhancing the compressive strength of mortars. The interfacial transition zone (ITZ) of CHVFA mortars is also significantly improved by the addition ofNS, embodying in the decrease of Ca/Si ratio and CH enrichment of ITZ.
文摘Condensation is an important regime of heat transfer which has wide applications in different industries such as power plants,heating,ventilating and air conditioning,and refrigeration.Condensation occurs in two different modes including filmwise (FWC) and dropwise (DWC) condensation.DWC occurring on hydrophobic and superhydrophobic surfaces has a much higher heat transfer capacity than FWC.Therefore,wide investigations have been done to produce DWC in recent years.Superhydrophobic surfaces have micro/nano structures with low surface energy.In this study,a two-step electrodeposition process is used to produce micro/nano structures on copper specimens.The surface energy of specimens is reduced by a self-assembled monolayer using ethanol and 1-octadecanethiol solution.The results show that there is an optimum condition for electrodeposition parameters.For example,a surface prepared by 2000 s step time has 5 times greater heat transfer than FWC while a surface with 4000 s step time has nearly the same heat transfer as FWC.The surfaces of the fabricated specimens are examined using XRD and SEM analyses.The SEM analyses of the surfaces show that there are some micro-structures on the surfaces and the surface porosities are reduced by increasing the second step electrodeposition time.
文摘Blended elemental 90W 7Ni 3Fe (mass fraction, %) powder was mechanically alloyed in a planetary ball mill. Nano crystalline grains were obtained after 10 h milling. The nano structured powder was processed to full density by metal injection molding approach. Compacts from the optimal powder binder mixture were studied for molding and sintering behaviors. Milling significantly increases the maximum powder loading and homogeneity of the feedstock, and enhances the sintering densification process. When solid state sintered at 1 350～1 450 ℃, the alloy shows very fine grains (～3 μm), high tensile strength (>1 130 MPa) and almost no distortion. [
基金supported by 100-Tatlent Research Program of The Chinese Academy of Sciencesthe Natinal Natural Science Foundation of China(NSFC)for financial support(Grant No.10074063)The Chinese Academy of Sciences(No.KJ952-S1-418)
文摘The Si L2,3 X-ray absorption near-edge structure (XANES) can be used to probe thelocal structure around Si and derive electronic information of the unoccupied s- andd-like partial density of states in nano-size SiO2. We present Si L2,3-edge for threedifferent size silicates acquired by total electron yield (TEY) at the photoemission sta-tion of Beijing Synchrotron Radiation Facility (BSRF). The Si L2,3-edge spectra areinterpreted based on ab initio full multiple-scattering (MS) calculation. The Si L2.3-edge of nano-size materials has XANES similar to that of a-quartz. The similaritiesbetween the Si L2.3-edge shapes attest to a common molecular-orbital picture of theirSi-O bonding and the same coordination state. However, a considerable broadeningof Si L2,3-edge XANES spectra as decrease of particle size is also an indicative ofpolyhedral distortions.
基金supported by the National Naturl Science Foundation of China(No.10172088)the Potdoctoral Saience Foundation of China
文摘Nanograins are characterized by a typical grain size from 1 to 100 nm. Molecular dynamics simulations have been carried out for the nanograin sphere with the diameters from 1.45 to 10.12 nm. We study the influence of grain size on structure and diffusion properties of the nanograins. The results reveal that as the grain size is reduced, the fraction of grain surface increases significantly, and the surface width is approximately constant; the mean atomic energy of the surface increases distinctly, but that of the grain interior varies insignificantly; the diffusion coefficient is increased sharply, and the relation of the diffusion coefficient and the grain size is close to exponential relation below 10 nm.
基金Sponsored by National Natural Science Foundation of China (21231002,21276026,21271023,21173021,91022006,11202193,11172276,and 11072225)the 111 Project ( B07012)+1 种基金the Program of Cooperation of the Beijing Education Commission ( 20091739006)Specialized Research Fund for the Doctoral Program of Higher Education ( 20101101110031)
文摘The recent research progress of structure- and size-controlled micro/nano-energetic materials is reviewed, which properties are fundamentally different from those of their corresponding bulk materials. The development of the construction strategies for achieving zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) micro/nanostructures from energetic molecules is introduced. Also, an overview of the unique properties induced by micro/nanostructures and size effects is provided. Special emphasis is focused on the size-dependent properties that are different from those of the conventional micro-sized energetic materials, such as thermal decomposition, sensitivity, combustion and detonation, and compaction behaviors. A conclusion and our view of the future development of micro/nano-energetic materials and devices are given.
基金Project supported by the Natural Science Foundation of Guizhou Province, China （Grant No 3067（2004））.
文摘The investigation on the oxidation behaviour of Si1-xGex alloys （x=0.05, 0.15, and 0.25） is carried out. It is found for the first time that on the oxide film a germanium nano-cap with a thickness of 1.8-2.8nm and a few Ge nanoparticles with diameters ranging from 5.5 nm to 10 nm are formed by the low-temperatu.re laser-assisted dry oxidation of Si1-xGex substrate. A new scanning method on the decline cross-section of the multiple-layer sample is adopted to measure the layer thickness and the composition. Some new peaks in photoluminescence （PL） spectra are discovered, which could be related to the nano-cap and the nano-particles of germanium. A suitable model and several new calculating formulae with the unrestricted Hartree-Fock-Roothaan （UHFR） method and quantum confinement analysis are proposed to interpret the PL spectra and the nano-structure mechanism in the oxide.
基金supported by the National Natural Science Foundation of China(Grant No.51474031)
文摘304 austenitic stainless steel was cold rolled in the range of 20%-80%reductions and then annealed at 700-900°C for 60 sto obtain nano/ultrafine-grained（NG/UFG）structure.Transmission electron microscopy,electron backscatter diffraction and X-ray diffraction were used to characterize the resulting microstructures.The results showed that with the increase of cold reduction,the content of martensite was increased.The steel performed work hardening during cold-working owing to the occurrence of strain induced martensite which nucleated in single shear bands.Further rolling broke up the lath-type martensite into dislocation-cell type martensite because of the formation of slip bands.Samples annealed at 800-960°C for 60 swere of NG/UFG structure with different percentage of nanocrystalline（60-100 nm）and ultrafine（100-500 nm）grains,submicron size（500-1000 nm）grains and micron size（〉1000 nm）grains.The value of the Gibbs free energy exhibited that the reversion mechanism of the reversion process was shear controlled by the annealing temperature.For a certain annealing time during the reversion process,austenite nucleated first on dislocation-cell type martensite and the grains grew up subsequently and eventually to be micrometer/submicrometer grains,while the nucleation of austenite on lath-type martensite occurred later resulting in nanocrystalline/ultrafine grains.The existence of the NG/UFG structure led to a higher strength and toughness during tensile test.
文摘In the present work, osteoblast behavior on a hierarchical micro-/nano-structured titanium surface was investigated. A hi- erarchical hybrid micro-/nano-structured titanium surface topography was produced via Electrolytic Etching （EE）. MG-63 cells were cultured on disks for 2 h to 7 days. The osteoblast response to the hierarchical hybrid micro-/nano-structured titanium surface was evaluated through the osteoblast cell morphology, attachment and proliferation. For comparison, MG-63 cells were also cultured on Sandblasted and Acid-etched （SEA） as well as Machined （M） surfaces respectively. The results show signifi- cant differences in the adhesion rates and proliferation levels of MG-63 cells on EE, SLA, and M surfaces. Both adhesion rate and proliferation level on EE surface are higher than those on SLA and M surfaces. Therefore, we may expect that, comparing with SLA and M surfaces, bone growth on EE surface could be accelerated and bone formation could be promoted at an early stage, which could be applied in the clinical practices for immediate and early-stage loadings.
文摘Pulse current technique was applied for the preparation of novel electroactive manganese dioxide and possible influences of different electrokinetic phenomena on material characteristics were discussed. The characterizations of pulse deposited sample （pcMD） were carried out by different techniques： Fourier transform infrared spectroscopy （FTIR）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）, Brunauer-Emmett-Teller （BET） method, Raman spectroscopy, and atomic force microscopy （AFM）. SEM image revealed that pulse current could improve the current distribution. This was confirmed by AFM images showing a decrease in surface roughness of pcMDs in comparison to amorphous samples, which were deposited by direct current （dcMD）. Higher distortion of MnO6 octahedral environment of dcMD was detected by FTJR and Raman spectroscopy. Cyclic voltammetric （CV） measurements showed a generally higher energy level drained from the second electron discharge of pcMD. This is mainly attributed to a higher surface area and a lower diffusion pass of electrons and protons arisen via a rather unique nanostructural arrangement of pcMD grains. Results indicate a higher surface area available for the non homogenous second electron discharge of pcMD grains.
基金financially supported by the Jiangxi Provincial Science and Technology Department(No.20151BDH80082)the China National Major Science and Technology Project(No.2014ZX07214-002)the financial support from China Postdoctoral Science Foundation(No.2015M581608)
文摘A bulk nanostructured twinning-induced plasticity （TWIP） steel with high ductility and high strength was fabricated by cryogenic asymmetry-rolling （cryo-ASR） and subsequent recovery treatment. It was found that the cryo-ASRed TWIP steels exhibit simultaneous improvements in the ductility, strength and work hardening. Typical microstructures of the cryo-ASR TWIP steel were characterized by shear bands and intensive mechanical nano-sized twins induced by cryogenic deformation. These mechanical nano-scale twins remain thermally stable during the subsequent recovery treatment. It is believed that the ductility enhancement and high work-hardening ability for the cryo-ASR TWIP steels should be mainly attributed to the high-densitv pre-existing nano-scale twins.
基金supported by NSFC(Nos.61036001and 11274155)"973"pro ject(2013CB632101)NSF of Jiangsu Province(BK2010010)and PAPD
文摘Nano-structured photon management is currently an interesting topic since it can enhance the optical absorption and reduce the surface reflection which will improve the performance of many kinds of optoelectronic devices, such as Si-based solar cells and light emitting diodes. Here, we report the fabrication of periodically nano-patterned Si structures by using polystyrene nano-sphere lithography technique. By changing the diameter of nano-spheres and the dry etching parameters, such as etching time and etching power, the morphologies of formed Si nano-structures can be well controlled as revealed by atomic force microscopy.A good broadband antireflection property has been achieved for the formed periodically nano-patterned Si structures though they have the low aspect ratio(<0.53). The reflection can be significantly reduced compared with that of flat Si substrate in a wavelength range from 400 nm to 1200 nm. The weighted mean reflection under the AM1.5 solar spectrum irradiation can be as low as 3.92% and the corresponding optical absorption is significantly improved, which indicates that the present Si periodic nano-structures can be used in Si-based thin film solar cells.
基金Funded by Research Funds for the Central Universities(No.2011SCU11038)Chengdu Science and Technology Project(Nos.10GGZD080GX-268 and 11DXYB096JH-027)
文摘Gradient cemented carbides with nano-TiN were prepared by the common powder metallurgical procedure. The formation of gradient zone and the microstructure, properties of the alloys were investigated using scanning electron microscope（SEM）, energy dispersive spectroscopy（EDS） and other performance testing apparatus. Moreover, the effect of nano-TiN on the gradient cemented carbide was studied. It is found that gradient zone width increases slightly with nano-TiN introduction. Both cobalt and titanium concentrations reach the maximum near the gradient border. Tungsten concentration shows fluctuation from the surface to the bulk. （Ti ,W）C phase grains are refined for nitrogen introduction. Core-rim structure has been observed under the SEM back-scattered mode. The core appears as dark due to more titanium in it and the rim with more tungsten appears as grey. In addition, the hardness and transverse rupture strength of gradient cemented carbide are enhanced with nano-TiN introduced.
