The Dunhuang–Golmud railway passes through different deserts in arid areas,especially drifting-sand desert and sandy-gravel Gobi.The near-surface wind environment and wind-sand transport process vary due to different...The Dunhuang–Golmud railway passes through different deserts in arid areas,especially drifting-sand desert and sandy-gravel Gobi.The near-surface wind environment and wind-sand transport process vary due to different external factors,such as topography,vegetation,and regional climate,resulting in evident spatial differences in surface erosion and deposition.Consequently,the measures for preventing wind-sand hazards will differ.However,the mechanism and control theory of sand damage remain poorly understood.In this study,we used meteorological observation,three-dimensional(3D)laser scanning,and grain-size analysis to compare and evaluate the spatial distribution of wind conditions,sand erosion and deposition patterns,and grain composition in the drifting-sand desert and sandy-gravel Gobi along the Dunhuang–Golmud railway in China.Results show that the annual mean wind speed,the frequency of sand-driving wind,and the drift potential of sandy-gravel Gobi are higher than those of drifting-sand desert,indicating a greater wind strength in the sandy-gravel Gobi,which exhibits spatial heterogeneity in wind conditions.The major sediment components in sandy-gravel Gobi are very fine sand,fine sand,and medium sand,and that in drifting-sand desert are very fine sand and fine sand.We found that the sediment in the sandy-gravel Gobi is coarser than that in the drifting-sand desert based on mean grain size and sediment component.The spatial distributions of sand erosion and deposition in the sandy-gravel Gobi and drifting-sand desert are consistent,with sand deposition mainly on the west side of the railway and sand erosion on the east side of the railway.The area of sand deposition in the drifting-sand desert accounts for 75.83%of the total area,with a mean deposition thickness of 0.032 m;while the area of sand deposition in the sandy-gravel Gobi accounts for 65.31%of the total area,with a mean deposition thickness of 0.028 m,indicating greater deposition amounts in the drifting-sand desert due to the presence of more fine sediment components.However,the sand deposition is more concentrated with a greater thickness on the embankment and track in the sandy-gravel Gobi and is dispersed with a uniform thickness in the drifting-sand desert.The sand deposition on the track of the sandy-gravel Gobi mainly comes from the east side of the railway.The results of this study are helpful in developing the preventive measures and determining appropriate selection and layout measures for sand control.展开更多
As a simulation of surface solidification of materials,quasi-two dimensional dendritic deposition of ammonium chloride(NH_4Cl)crystals from an aqueous solution film with free surface by vapourization was investigated ...As a simulation of surface solidification of materials,quasi-two dimensional dendritic deposition of ammonium chloride(NH_4Cl)crystals from an aqueous solution film with free surface by vapourization was investigated by the in- situ observation technique.The depositing morphologies of NH_4Cl crystals are faceted and of growth laws differing from the three-dimensional case.Under low supersaturation,faceted dendrites formed,whereas the anisotropy in growth kinetics decreases with the increase of supersaturation.When vapourizing rate(supersaturation)is not very low, oscillations of growth rate.tip-radius and second arm spacing of the dendrites were observed.It is suggested that this dynamic phenomenon is attributed to the correlation between the convection-transfer effect induced by the surface tension gradient of solution film.and the driving force for deposition.展开更多
To aim at prototype parts fabricated with fused deposition modeling （FDM） process, the problems how to improve and enhance their surface micro-precision are studied. The producing mechanism of surface roughness is e...To aim at prototype parts fabricated with fused deposition modeling （FDM） process, the problems how to improve and enhance their surface micro-precision are studied. The producing mechanism of surface roughness is explained with three aspects concretely including the principle error of rapid prototyping （RP） process, the inherent characteristics of FDM process, and some mi- cro-scratches on the surface of the extruded fiber. Based on the micro-characters of section shape of the FDM prototype, a physical model reflecting the outer shape characters is abstracted. With the physical simplified and deduced, the evaluating equations of surface roughness are acquired. According to the FDM sample parts with special design for experimental measurement, the real surface roughness values of different inclined planes are obtained. And the measuring values of surface roughness are compared with the calculation values. Furthermore, the causes of surface roughness deviation between measuring values and calculation values are respectively analyzed and studied. With the references of analytic conclusions, the measuring values of the experimental part surface are revised, and the revised values nearly accord with the calculation values. Based on the influencing principles of FDM process parameters and special post processing of FDM prototype parts, some concrete measures are proposed to reduce the surface roughness of FDM parts, and the applying effects are better.展开更多
Superhydrophilic surfaces were fabricated on copper substrates by an electrochemical deposition and sintering process. Superhydrophobic surfaces were prepared by constructing micro/nano-structure on copper substrates ...Superhydrophilic surfaces were fabricated on copper substrates by an electrochemical deposition and sintering process. Superhydrophobic surfaces were prepared by constructing micro/nano-structure on copper substrates through an electrochemical deposition method. Conversion from superhydrophobic to superhydrophilic was obtained via a suitable sintering process. After reduction sintering, the contact angle of the superhydrophilic surfaces changed from 155° to 0°. The scanning electron microscope （SEM） images show that the morphology of superhydrophobic and superhydrophilic surfaces looks like corals and cells respectively. The chemical composition and crystal structure of these surfaces were examined using energy dispersive spectrometry （EDS） and X-ray diffraction （XRD）. The results show that the main components on superhydrophobic surfaces are Cu, Cu2O and CuO, while the superhydrophilic surfaces are composed of Cu merely. The crystal structure is more inerratic and the grain size becomes bigger after the sintering. The interracial strength of the superhydrophilic surfaces was investigated, showing that the interfacial strength between superhydrophilic layer and copper substrate is considerably high.展开更多
The surface morphology of buffer layer yttrium-stabilized zirconia （YSZ） of YBa2CuaO7-σ （YBCO） high temperature superconducting films relies on a series of controllable experimental parameters. In this work, we f...The surface morphology of buffer layer yttrium-stabilized zirconia （YSZ） of YBa2CuaO7-σ （YBCO） high temperature superconducting films relies on a series of controllable experimental parameters. In this work, we focus on the influence of pulsed laser frequency and target crystalline type on surface morphology of YSZ films deposited by pulsed laser deposition （PLD） on rolling assisted biaxially textured substrate tapes. Usually two kinds of particles are observed in the YSZ layer： randomly distributed ones on the whole film and self-assembled ones along grain boundaries. SEM images are used to prove that particles can be partly removed when choosing dense targets of single crystalline. Lower frequency of pulsed laser also contributes to a smoother film surface. TEM images are used to view the crystalline structure of thin film. Thus we can obtain a basic understanding of how to prepare a particle-free YSZ buffer layer for YBCO in optimized conditions using PLD. The YBCO layer with nice structure and critical current density of around 5 MA/cm2 can be reached on smooth YSZ samples.展开更多
Carbon deposition on nickel powders in methane involves three stages in different reaction temperature ranges. Temperature programing oxidation test and Raman spectrum results indicated the formation of complex and or...Carbon deposition on nickel powders in methane involves three stages in different reaction temperature ranges. Temperature programing oxidation test and Raman spectrum results indicated the formation of complex and ordered carbon structures at high deposition temperatures. The values of I（D）/I（G） of the deposited carbon reached 1.86, 1.30, and 1.22 in the first, second, and third stages, respectively. The structure of carbon in the second stage was similar to that in the third stage. Carbon deposited in the first stage rarely contained homogeneous pyrolytic deposit layers. A kinetic model was developed to analyze the carbon deposition behavior in the first stage. The rate-determining step of the first stage is supposed to be interfacial reaction. Based on the investigation of carbon deposition kinetics on nickel powders from different resources, carbon deposition rate is suggested to have a linear relation with the square of specific surface area of nickel particles.展开更多
Porous polypropylene hollow fiber(PPHF) membranes are widely used in liquid purification. However, the hydrophobicity of polypropylene(PP) has limited its applications in water treatment. Herein, we demonstrate that, ...Porous polypropylene hollow fiber(PPHF) membranes are widely used in liquid purification. However, the hydrophobicity of polypropylene(PP) has limited its applications in water treatment. Herein, we demonstrate that, for the first time, atomic layer deposition(ALD) is an effective strategy to conveniently upgrade the filtration performances of PPHF membranes. The chemical and morphological changes of the deposited PPHF membranes are characterized by spectral, compositional, microscopic characterizations and protein adsorption measurements. Al_2O_3 is distributed along the cross section of the PP hollow fibers, with decreasing concentration from the outer surface to the inner surface. The pore size of the outer surface can be easily turned by altering the ALD cycles. Interestingly, the hollow fibers become much more ductile after deposition as their elongation at break is increased more than six times after deposition with 100 cycles. The deposited membranes show simultaneously enhanced water permeance and retention after deposition with moderate ALD cycle numbers.For instance, after 50 ALD cycles a 17% increase in water permeance and one-fold increase in BSA rejection are observed. Moreover, the PP membranes exhibit improved fouling-resistance after ALD deposition.展开更多
Atomic-layer-deposited（ALD） aluminum oxide（Al2O3） has demonstrated an excellent surface passivation for crystalline silicon（c-Si） surfaces, as well as for highly boron-doped c-Si surfaces. In this paper, water-b...Atomic-layer-deposited（ALD） aluminum oxide（Al2O3） has demonstrated an excellent surface passivation for crystalline silicon（c-Si） surfaces, as well as for highly boron-doped c-Si surfaces. In this paper, water-based thermal atomic layer deposition of Al2O3 films are fabricated for c-Si surface passivation. The influence of deposition conditions on the passivation quality is investigated. The results show that the excellent passivation on n-type c-Si can be achieved at a low thermal budget of 250℃ given a gas pressure of 0.15 Torr. The thickness-dependence of surface passivation indicates that the effective minority carrier lifetime increases drastically when the thickness of Al2O3 is larger than 10 nm. The influence of thermal post annealing treatments is also studied. Comparable carrier lifetime is achieved when Al2O3 sample is annealed for 15 min in forming gas in a temperature range from 400℃ to 450℃. In addition, the passivation quality can be further improved when a thin PECVD-SiNx cap layer is prepared on Al2O3, and an effective minority carrier lifetime of2.8 ms and implied Voc of 721 mV are obtained. In addition, several novel methods are proposed to restrain blistering.展开更多
The cation exchange and the chemical weathering are two important processes for sedi-ments to buffer the acidification of surface water. In this paper, for sediments these two processeshave been studied. The relations...The cation exchange and the chemical weathering are two important processes for sedi-ments to buffer the acidification of surface water. In this paper, for sediments these two processeshave been studied. The relationship between BFC of sediments and ANC of the surface waters andthe weathering characteristics of sediments were discussed. The buffering effect and mechanism of sedi-ments against acidic deposition have also been studied. The results show that BFC of sediments arepositively correlative to ANC of the surface waters. the chemical weathering rate of sediments can beexpressed as R=k×[H￣ +]￣m.展开更多
Different oxygen and nitrogen containing functional groups were created on the surface of the multiwalled carbon nanotubes. The multi-walled carbon nanotubes were treated in ultrasonic bath with sulfuric or nitric aci...Different oxygen and nitrogen containing functional groups were created on the surface of the multiwalled carbon nanotubes. The multi-walled carbon nanotubes were treated in ultrasonic bath with sulfuric or nitric acid. Furthermore the surface texture was modified by increase of the roughness. In particular after treatment with the oxidizing nitric acid, in comparison to the H2SO4 or ultra-sonic treated samples,craters and edges are dominating the surface structures. Manganese oxide was deposited on the multiwalled carbon nanotubes by precipitation mechanism. Various manganese oxides are formed during the deposition process. The samples were characterized by elemental analysis, microscopy, thermal analysis,Raman spectroscopy, and by the zeta potential as well as X-ray diffraction measurements. It was shown that the deposited manganese oxides are stabilized rather by surface texture of the multi-walled carbon nanotubes than by created functional groups.展开更多
In the paper, the effect of temper temperature on microstructures and wear resistance of surfacing deposits of Ferro-base with Cr-W-MO alloy were investigated. The results show that the secondary hardening can be obta...In the paper, the effect of temper temperature on microstructures and wear resistance of surfacing deposits of Ferro-base with Cr-W-MO alloy were investigated. The results show that the secondary hardening can be obtained when the surfacing deposits is tempered. Temper temperature is lower than 400 ℃, the hardness of surfacing deposits of Ferro-base with Cr-W-MO alloy has little change, when it exceeded 600 ℃, the hardness decreases obviously, the surfacing deposits tempering at 560 ℃ for 2 h has excellent wear resistance. As a result, the microstructure of surfacing deposits is in relation to its wear resistance.展开更多
Gravity modelling was carried out along five profiles that traverse the Eastern Cape Province of South Africa in order to determine the depositional surface and isochore thickness of the Ecca sediments.Gravity models ...Gravity modelling was carried out along five profiles that traverse the Eastern Cape Province of South Africa in order to determine the depositional surface and isochore thickness of the Ecca sediments.Gravity models of the subsurface rock density reveal that the Ecca Group has a maximum vertical thickness of about 3215 ± 160 m.The maximum depositional surface（elevation）above sea level for the Ecca sediments is about 500 m,whilst the depth below sea level reaches about10000 m.Correlation of the isochore thickness maps with the depositional surfaces shows that the sediments in the basement highs were subsided,deformed,eroded and deposited in the basement lows.The basement highs served as the source area（s） for the sediments in the basement lows,thus basement highs are characterized with thin sediment cover whilst the lows have thick sediment cover.展开更多
During heteroepitaxial overlayer growth multiple crystal domains nucleated on a substrate surface compete with each other in such a manner that a domain covered by neighboring ones stops growing.The number density of ...During heteroepitaxial overlayer growth multiple crystal domains nucleated on a substrate surface compete with each other in such a manner that a domain covered by neighboring ones stops growing.The number density of active domains ρ decreases as the height h increases.A simple scaling argument leads to a scaling law of ρ~ h^（-γ） with a coarsening exponent γ=d/z,where d is the dimension of the substrate surface and z the dynamic exponent of a growth front.This scaling relation is confirmed by performing kinetic Monte Carlo simulations of the ballistic deposition model on a two-dimensional（d=2） surface,even when an isolated deposited particle diffuses on a crystal surface.展开更多
The unique columnar structure endows thermal barrier coatings(TBCs)prepared by plasma spray-physical vapor deposition(PS-PVD)with high thermal insulation and long lifetime.However,the coating delamination failure resu...The unique columnar structure endows thermal barrier coatings(TBCs)prepared by plasma spray-physical vapor deposition(PS-PVD)with high thermal insulation and long lifetime.However,the coating delamination failure resulting from an intra-column fracture(within a column rather than between columns)is a bottleneck in the solid dust particle impact environment for aero-engine.To clarify the intra-column fracture mechanism,a basic layer deposition model is developed to explore a heterogeneous weak-to-strong layered structure formed by a local transient in-situ deposit temperature.During the PS-PVD,an in-situ deposit surface is continuously updated due to constantly being covered by vapor condensation,showing a transient temperature,which means that the in-situ deposit surface temperature rises sharply in short period of 0.2 s of depositing a thin layer during a single pass.Meanwhile,the increasing temperature of the in-situ deposit surface results in an experimentally observed heterogeneous weak-to-strong structure,showing a continuous transition from a porous weak structure at the bottom region to a dense strong structure at the top region.This structure easily makes the intra-column fracture at the porous weak region.The results shed light on improving TBC lifetime by restraining the intra-column fracture.展开更多
CeO2 film plays an essential role in nucleation and growth of YBa2 Cu3 O（7-x）（YBCO） films. In this work,the dependence of superconducting properties of YBCO on CeO2 films with different thicknesses was investigate...CeO2 film plays an essential role in nucleation and growth of YBa2 Cu3 O（7-x）（YBCO） films. In this work,the dependence of superconducting properties of YBCO on CeO2 films with different thicknesses was investigated,in order to achieve fabrication of high-performance YBCO coated conductors in industrial scale. The crystalline structure and morphology of CeO2 films with thickness ranging from 21 to 563 nm were systematically characterized by means of X-ray diffraction（XRD）, atomic force microscope（AFM） and reflection high-energy electron diffraction（RHEED）. Additional focus was addressed on evolution of the surface quality of CeO2 films with thickness increasing. The results show that at the optimal thickness of 221 nm, CeO2 film exhibits sharp in-plane and out-of-plane texture with full width of half maximum（FWHM） values of 5.9° and 1.8°, respectively, and smooth surface with a mean root-mean-square（RMS） roughness value as low as 0.6 nm. Combing RHEED and transmission electron microscope（TEM） cross-sectional analysis, it is found that nucleation and growth of CeO2 films at early stage remain in island growth mode with rougher surface,while further increasing the thickness beyond the optimal thickness leads to weak surface quality, consequently resulting in degradation of superconductor layers deposited subsequently. Eventually, a critical current density（Jc） as high as 4.6×10-6 A·cm-（-2）（77 K, self-field） is achieved on a YBCO film on a thickness-modulated CeO2/MgO/Y2 O3/Al2 O3/C276 architecture, demonstrating the advantages of CeO2 films as buffer layer in high-throughput manufacture of coated conductors.展开更多
A vectorization analysis technique for crystal growth and microstructure development in single-crystal weld was developed in our previous work. Based on the vectorization method, crystal growth and stray grain distrib...A vectorization analysis technique for crystal growth and microstructure development in single-crystal weld was developed in our previous work. Based on the vectorization method, crystal growth and stray grain distribution in laser surface remelting of single crystal superalloy CMSX-4 were investigated in com- bination of simulations with experimental observations. The energy distribution of laser was taken into consideration in this research. The experimental results demonstrate that the simulation model applies well in the prediction of dendrite growth direction. Moreover, the prediction of stray grain distribution works well except for the region of dendrites growing along the [100] direction.展开更多
This paper focuses on an analysis of the surface texture formed during precision machining of tungsten carbide. The work material was fabricated using direct laser deposition （DLD） technology. The experiment include...This paper focuses on an analysis of the surface texture formed during precision machining of tungsten carbide. The work material was fabricated using direct laser deposition （DLD） technology. The experiment included precision milling of tungsten carbide samples with a monolithic torus cubic boron nitride tool and grinding with diamond and alumina cup wheels. An optical surface profiler was applied to the measurements of surface textures and roughness profiles. In addition, the micro-geometry of the milling cutter was measured with the appli- cation of an optical device. The surface roughness height was also estimated with the application of a model, which included kinematic-geometric parameters and minimum uncut chip thickness. The research revealed the occurrence of micro-grooves on the machined surface. The surface roughness height calculated on the basis of the traditional kinematic-geometric model was incompatible with the measurements. However, better agreement between the theoretical and experimental values was observed for the minimum uncut chip thickness model.展开更多
High wear resistance,low cytotoxicity and excellent antibacterial properties are the basis for osseointegration of implant materials.Polyetheretherketone(PEEK)has been considered as a potential implant material due to...High wear resistance,low cytotoxicity and excellent antibacterial properties are the basis for osseointegration of implant materials.Polyetheretherketone(PEEK)has been considered as a potential implant material due to its excellent biocompatibility,natural radiolucency and mechanical properties.In this work,to improve the wear resistance,cytotoxicity and antibacterial properties of PEEK,carbon fiber(CFR)and Black Phosphorus(BP)were used to synergistically modify PEEK by two methods,deposition of BP coating on CFR-PEEK and BP/CFR-PEEK coating on Ti6Al4V(TC4)through electrostatic spraying.After CFR and BP synergistically modified PEEK,the friction coefficient of BP coating on CFR-PEEK and BP/CFR-PEEK coating were 0.14±0.01 and 0.09±0.02,respectively.The wear volume of BP coating on CFR-PEEK(30.54±1.32)was higher than that of BP/CFR-PEEK coating(9.46±1.32),which indicated that BP/CFR-PEEK coating showed high wear resistance.The difference in wear resistance may be caused by the fact that BP was not easily oxidized in BP/CFR-PEEK coating.In addition,BP coating on CFR-PEEK and BP/CFR-PEEK coating showed no obvious cytotoxicity to L929 cell and presented excellent antibacterial efficiency(up to 94.5%±2.8%and 96.0%±3.8%,respectively)against Staphylococcus aureus(S.aureus).It was concluded that BP/CFR-PEEK coating exhibited high wear resistance,low cytotoxicity and excellent antibacterial properties against S.aureus,which might provide a foundation for osseointegration of implants.展开更多
An empirical simulation method to simulate the possible position of shallow rainfall-induced landslides in China has been developed.This study shows that such a simulation may be operated in real-time to highlight tho...An empirical simulation method to simulate the possible position of shallow rainfall-induced landslides in China has been developed.This study shows that such a simulation may be operated in real-time to highlight those areas that are highly prone to rainfall-induced landslides on the basis of the landslide susceptibility index and the rainfall intensity-duration(I-D) thresholds.First,the study on landslide susceptibility in China is introduced.The entire territory has been classified into five categories,among which high-susceptibility regions(Zone 4-'High' and 5-'Very high') account for 4.15%of the total extension of China.Second,rainfall is considered as an external triggering factor that may induce landslide initiation.Real-time satellite-based TMPA3B42 products may provide real rainfall spatial and temporal patterns,which may be used to derive rainfall duration time and intensity.By using a historical record of 60 significant past landslides,the rainfall I-D equation has been calibrated.The rainfall duration time that may trigger a landslide has resulted between 3 hours and 45 hours.The combination of these two aspects can be exploited to simulate the spatiotemporal distribution of rainfall-induced landslide hazards when rainfall events exceed the rainfall I-D thresholds,where the susceptibility category is 'high' or 'very high'.This study shows a useful tool to be part of a systematic landslide simulation methodology,potentially providing useful information for a theoretical basis and practical guide for landslide prediction and mitigation throughout China.展开更多
基金This research was supported by the National Natural Science Foundation of China(42171083,41871016)the Natural Science Foundation of Gansu Province,China(22JR5RA066).
文摘The Dunhuang–Golmud railway passes through different deserts in arid areas,especially drifting-sand desert and sandy-gravel Gobi.The near-surface wind environment and wind-sand transport process vary due to different external factors,such as topography,vegetation,and regional climate,resulting in evident spatial differences in surface erosion and deposition.Consequently,the measures for preventing wind-sand hazards will differ.However,the mechanism and control theory of sand damage remain poorly understood.In this study,we used meteorological observation,three-dimensional(3D)laser scanning,and grain-size analysis to compare and evaluate the spatial distribution of wind conditions,sand erosion and deposition patterns,and grain composition in the drifting-sand desert and sandy-gravel Gobi along the Dunhuang–Golmud railway in China.Results show that the annual mean wind speed,the frequency of sand-driving wind,and the drift potential of sandy-gravel Gobi are higher than those of drifting-sand desert,indicating a greater wind strength in the sandy-gravel Gobi,which exhibits spatial heterogeneity in wind conditions.The major sediment components in sandy-gravel Gobi are very fine sand,fine sand,and medium sand,and that in drifting-sand desert are very fine sand and fine sand.We found that the sediment in the sandy-gravel Gobi is coarser than that in the drifting-sand desert based on mean grain size and sediment component.The spatial distributions of sand erosion and deposition in the sandy-gravel Gobi and drifting-sand desert are consistent,with sand deposition mainly on the west side of the railway and sand erosion on the east side of the railway.The area of sand deposition in the drifting-sand desert accounts for 75.83%of the total area,with a mean deposition thickness of 0.032 m;while the area of sand deposition in the sandy-gravel Gobi accounts for 65.31%of the total area,with a mean deposition thickness of 0.028 m,indicating greater deposition amounts in the drifting-sand desert due to the presence of more fine sediment components.However,the sand deposition is more concentrated with a greater thickness on the embankment and track in the sandy-gravel Gobi and is dispersed with a uniform thickness in the drifting-sand desert.The sand deposition on the track of the sandy-gravel Gobi mainly comes from the east side of the railway.The results of this study are helpful in developing the preventive measures and determining appropriate selection and layout measures for sand control.
文摘As a simulation of surface solidification of materials,quasi-two dimensional dendritic deposition of ammonium chloride(NH_4Cl)crystals from an aqueous solution film with free surface by vapourization was investigated by the in- situ observation technique.The depositing morphologies of NH_4Cl crystals are faceted and of growth laws differing from the three-dimensional case.Under low supersaturation,faceted dendrites formed,whereas the anisotropy in growth kinetics decreases with the increase of supersaturation.When vapourizing rate(supersaturation)is not very low, oscillations of growth rate.tip-radius and second arm spacing of the dendrites were observed.It is suggested that this dynamic phenomenon is attributed to the correlation between the convection-transfer effect induced by the surface tension gradient of solution film.and the driving force for deposition.
基金This project is supported by National Natural Science Foundation of China (No. 50575139)
文摘To aim at prototype parts fabricated with fused deposition modeling （FDM） process, the problems how to improve and enhance their surface micro-precision are studied. The producing mechanism of surface roughness is explained with three aspects concretely including the principle error of rapid prototyping （RP） process, the inherent characteristics of FDM process, and some mi- cro-scratches on the surface of the extruded fiber. Based on the micro-characters of section shape of the FDM prototype, a physical model reflecting the outer shape characters is abstracted. With the physical simplified and deduced, the evaluating equations of surface roughness are acquired. According to the FDM sample parts with special design for experimental measurement, the real surface roughness values of different inclined planes are obtained. And the measuring values of surface roughness are compared with the calculation values. Furthermore, the causes of surface roughness deviation between measuring values and calculation values are respectively analyzed and studied. With the references of analytic conclusions, the measuring values of the experimental part surface are revised, and the revised values nearly accord with the calculation values. Based on the influencing principles of FDM process parameters and special post processing of FDM prototype parts, some concrete measures are proposed to reduce the surface roughness of FDM parts, and the applying effects are better.
基金Supported by the National Natural Science Foundation of China(51275180)the Fundamental Research Funds for the Central Universities(2013ZM0003)the Doctorate Dissertation Funds of Guangdong Province(sybzzxm 201213)
文摘Superhydrophilic surfaces were fabricated on copper substrates by an electrochemical deposition and sintering process. Superhydrophobic surfaces were prepared by constructing micro/nano-structure on copper substrates through an electrochemical deposition method. Conversion from superhydrophobic to superhydrophilic was obtained via a suitable sintering process. After reduction sintering, the contact angle of the superhydrophilic surfaces changed from 155° to 0°. The scanning electron microscope （SEM） images show that the morphology of superhydrophobic and superhydrophilic surfaces looks like corals and cells respectively. The chemical composition and crystal structure of these surfaces were examined using energy dispersive spectrometry （EDS） and X-ray diffraction （XRD）. The results show that the main components on superhydrophobic surfaces are Cu, Cu2O and CuO, while the superhydrophilic surfaces are composed of Cu merely. The crystal structure is more inerratic and the grain size becomes bigger after the sintering. The interracial strength of the superhydrophilic surfaces was investigated, showing that the interfacial strength between superhydrophilic layer and copper substrate is considerably high.
基金Supported by the ITER Project of the Ministry of Science and Technology of China under Grant No 2011GB113004the Shanghai Commission of Science and Technology under Grant No 11DZ1100402the Youth Fund of the National Natural Science Foundation of China under Grant No 11204174
文摘The surface morphology of buffer layer yttrium-stabilized zirconia （YSZ） of YBa2CuaO7-σ （YBCO） high temperature superconducting films relies on a series of controllable experimental parameters. In this work, we focus on the influence of pulsed laser frequency and target crystalline type on surface morphology of YSZ films deposited by pulsed laser deposition （PLD） on rolling assisted biaxially textured substrate tapes. Usually two kinds of particles are observed in the YSZ layer： randomly distributed ones on the whole film and self-assembled ones along grain boundaries. SEM images are used to prove that particles can be partly removed when choosing dense targets of single crystalline. Lower frequency of pulsed laser also contributes to a smoother film surface. TEM images are used to view the crystalline structure of thin film. Thus we can obtain a basic understanding of how to prepare a particle-free YSZ buffer layer for YBCO in optimized conditions using PLD. The YBCO layer with nice structure and critical current density of around 5 MA/cm2 can be reached on smooth YSZ samples.
基金financially supported by the National Program on Key Basic Research Project of China (973 Program, No. 2012CB215405)the National Natural Science Foundation of China (No. 51174022)
文摘Carbon deposition on nickel powders in methane involves three stages in different reaction temperature ranges. Temperature programing oxidation test and Raman spectrum results indicated the formation of complex and ordered carbon structures at high deposition temperatures. The values of I（D）/I（G） of the deposited carbon reached 1.86, 1.30, and 1.22 in the first, second, and third stages, respectively. The structure of carbon in the second stage was similar to that in the third stage. Carbon deposited in the first stage rarely contained homogeneous pyrolytic deposit layers. A kinetic model was developed to analyze the carbon deposition behavior in the first stage. The rate-determining step of the first stage is supposed to be interfacial reaction. Based on the investigation of carbon deposition kinetics on nickel powders from different resources, carbon deposition rate is suggested to have a linear relation with the square of specific surface area of nickel particles.
基金Supported by the National Basic Research Program of China(2015CB655301)the Natural Science Foundation of Jiangsu Province(BK20150063)+1 种基金the Program of Excellent Innovation Teams of Jiangsu Higher Education Institutionsthe Project of Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘Porous polypropylene hollow fiber(PPHF) membranes are widely used in liquid purification. However, the hydrophobicity of polypropylene(PP) has limited its applications in water treatment. Herein, we demonstrate that, for the first time, atomic layer deposition(ALD) is an effective strategy to conveniently upgrade the filtration performances of PPHF membranes. The chemical and morphological changes of the deposited PPHF membranes are characterized by spectral, compositional, microscopic characterizations and protein adsorption measurements. Al_2O_3 is distributed along the cross section of the PP hollow fibers, with decreasing concentration from the outer surface to the inner surface. The pore size of the outer surface can be easily turned by altering the ALD cycles. Interestingly, the hollow fibers become much more ductile after deposition as their elongation at break is increased more than six times after deposition with 100 cycles. The deposited membranes show simultaneously enhanced water permeance and retention after deposition with moderate ALD cycle numbers.For instance, after 50 ALD cycles a 17% increase in water permeance and one-fold increase in BSA rejection are observed. Moreover, the PP membranes exhibit improved fouling-resistance after ALD deposition.
基金Project supported by the Beijing Municipal Science and Technology Commission,China(Grant No.Z151100003515003)the National Natural Science Foundation of China(Grant Nos.110751402347,61274134,51402064,61274059,and 51602340)+3 种基金the University of Science and Technology Beijing(USTB)Start-up Program,China(Grant No.06105033)the Beijing Municipal Innovation and Research Base,China(Grant No.Z161100005016095)the Fundamental Research Funds for the Central Universities,China(Grant Nos.FRF-UM-15-032 and 06400071)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2015387)
文摘Atomic-layer-deposited（ALD） aluminum oxide（Al2O3） has demonstrated an excellent surface passivation for crystalline silicon（c-Si） surfaces, as well as for highly boron-doped c-Si surfaces. In this paper, water-based thermal atomic layer deposition of Al2O3 films are fabricated for c-Si surface passivation. The influence of deposition conditions on the passivation quality is investigated. The results show that the excellent passivation on n-type c-Si can be achieved at a low thermal budget of 250℃ given a gas pressure of 0.15 Torr. The thickness-dependence of surface passivation indicates that the effective minority carrier lifetime increases drastically when the thickness of Al2O3 is larger than 10 nm. The influence of thermal post annealing treatments is also studied. Comparable carrier lifetime is achieved when Al2O3 sample is annealed for 15 min in forming gas in a temperature range from 400℃ to 450℃. In addition, the passivation quality can be further improved when a thin PECVD-SiNx cap layer is prepared on Al2O3, and an effective minority carrier lifetime of2.8 ms and implied Voc of 721 mV are obtained. In addition, several novel methods are proposed to restrain blistering.
文摘The cation exchange and the chemical weathering are two important processes for sedi-ments to buffer the acidification of surface water. In this paper, for sediments these two processeshave been studied. The relationship between BFC of sediments and ANC of the surface waters andthe weathering characteristics of sediments were discussed. The buffering effect and mechanism of sedi-ments against acidic deposition have also been studied. The results show that BFC of sediments arepositively correlative to ANC of the surface waters. the chemical weathering rate of sediments can beexpressed as R=k×[H￣ +]￣m.
文摘Different oxygen and nitrogen containing functional groups were created on the surface of the multiwalled carbon nanotubes. The multi-walled carbon nanotubes were treated in ultrasonic bath with sulfuric or nitric acid. Furthermore the surface texture was modified by increase of the roughness. In particular after treatment with the oxidizing nitric acid, in comparison to the H2SO4 or ultra-sonic treated samples,craters and edges are dominating the surface structures. Manganese oxide was deposited on the multiwalled carbon nanotubes by precipitation mechanism. Various manganese oxides are formed during the deposition process. The samples were characterized by elemental analysis, microscopy, thermal analysis,Raman spectroscopy, and by the zeta potential as well as X-ray diffraction measurements. It was shown that the deposited manganese oxides are stabilized rather by surface texture of the multi-walled carbon nanotubes than by created functional groups.
文摘In the paper, the effect of temper temperature on microstructures and wear resistance of surfacing deposits of Ferro-base with Cr-W-MO alloy were investigated. The results show that the secondary hardening can be obtained when the surfacing deposits is tempered. Temper temperature is lower than 400 ℃, the hardness of surfacing deposits of Ferro-base with Cr-W-MO alloy has little change, when it exceeded 600 ℃, the hardness decreases obviously, the surfacing deposits tempering at 560 ℃ for 2 h has excellent wear resistance. As a result, the microstructure of surfacing deposits is in relation to its wear resistance.
基金the National Research Foundation(NRF)(Grant UID:101980)Govan Mbeki Research and Development Centre(GMRDC),University of Fort Hare for financial support
文摘Gravity modelling was carried out along five profiles that traverse the Eastern Cape Province of South Africa in order to determine the depositional surface and isochore thickness of the Ecca sediments.Gravity models of the subsurface rock density reveal that the Ecca Group has a maximum vertical thickness of about 3215 ± 160 m.The maximum depositional surface（elevation）above sea level for the Ecca sediments is about 500 m,whilst the depth below sea level reaches about10000 m.Correlation of the isochore thickness maps with the depositional surfaces shows that the sediments in the basement highs were subsided,deformed,eroded and deposited in the basement lows.The basement highs served as the source area（s） for the sediments in the basement lows,thus basement highs are characterized with thin sediment cover whilst the lows have thick sediment cover.
文摘During heteroepitaxial overlayer growth multiple crystal domains nucleated on a substrate surface compete with each other in such a manner that a domain covered by neighboring ones stops growing.The number density of active domains ρ decreases as the height h increases.A simple scaling argument leads to a scaling law of ρ~ h^（-γ） with a coarsening exponent γ=d/z,where d is the dimension of the substrate surface and z the dynamic exponent of a growth front.This scaling relation is confirmed by performing kinetic Monte Carlo simulations of the ballistic deposition model on a two-dimensional（d=2） surface,even when an isolated deposited particle diffuses on a crystal surface.
基金supported by the National Natural Science Foundation of China (No.51901175)the China Postdoctoral Science Foundation Funded Project (No.2020T130499)the National Program for Support of Top-notch Young Professionals.
文摘The unique columnar structure endows thermal barrier coatings(TBCs)prepared by plasma spray-physical vapor deposition(PS-PVD)with high thermal insulation and long lifetime.However,the coating delamination failure resulting from an intra-column fracture(within a column rather than between columns)is a bottleneck in the solid dust particle impact environment for aero-engine.To clarify the intra-column fracture mechanism,a basic layer deposition model is developed to explore a heterogeneous weak-to-strong layered structure formed by a local transient in-situ deposit temperature.During the PS-PVD,an in-situ deposit surface is continuously updated due to constantly being covered by vapor condensation,showing a transient temperature,which means that the in-situ deposit surface temperature rises sharply in short period of 0.2 s of depositing a thin layer during a single pass.Meanwhile,the increasing temperature of the in-situ deposit surface results in an experimentally observed heterogeneous weak-to-strong structure,showing a continuous transition from a porous weak structure at the bottom region to a dense strong structure at the top region.This structure easily makes the intra-column fracture at the porous weak region.The results shed light on improving TBC lifetime by restraining the intra-column fracture.
基金financially supported by the International Thermonuclear Experimental Reactor (ITER) Project from Ministry of Science and Technology of China (No.2011GB113004)the National High Technology Research and Development Program of China(No.2014AA032402)+1 种基金the Shanghai Commission of Science and Technology (Nos.11DZ1100402 and 13DZ0500100)the Natural Science Foundation of China(Nos.11204174 and 51372150)
文摘CeO2 film plays an essential role in nucleation and growth of YBa2 Cu3 O（7-x）（YBCO） films. In this work,the dependence of superconducting properties of YBCO on CeO2 films with different thicknesses was investigated,in order to achieve fabrication of high-performance YBCO coated conductors in industrial scale. The crystalline structure and morphology of CeO2 films with thickness ranging from 21 to 563 nm were systematically characterized by means of X-ray diffraction（XRD）, atomic force microscope（AFM） and reflection high-energy electron diffraction（RHEED）. Additional focus was addressed on evolution of the surface quality of CeO2 films with thickness increasing. The results show that at the optimal thickness of 221 nm, CeO2 film exhibits sharp in-plane and out-of-plane texture with full width of half maximum（FWHM） values of 5.9° and 1.8°, respectively, and smooth surface with a mean root-mean-square（RMS） roughness value as low as 0.6 nm. Combing RHEED and transmission electron microscope（TEM） cross-sectional analysis, it is found that nucleation and growth of CeO2 films at early stage remain in island growth mode with rougher surface,while further increasing the thickness beyond the optimal thickness leads to weak surface quality, consequently resulting in degradation of superconductor layers deposited subsequently. Eventually, a critical current density（Jc） as high as 4.6×10-6 A·cm-（-2）（77 K, self-field） is achieved on a YBCO film on a thickness-modulated CeO2/MgO/Y2 O3/Al2 O3/C276 architecture, demonstrating the advantages of CeO2 films as buffer layer in high-throughput manufacture of coated conductors.
基金financially supported by the National Natural Science Foundation of China (NSFC) under grant Nos. 51401210 and 51271186the National High Technology Research and Development Program (863 Program) of China under grant No. 2014AA041701
文摘A vectorization analysis technique for crystal growth and microstructure development in single-crystal weld was developed in our previous work. Based on the vectorization method, crystal growth and stray grain distribution in laser surface remelting of single crystal superalloy CMSX-4 were investigated in com- bination of simulations with experimental observations. The energy distribution of laser was taken into consideration in this research. The experimental results demonstrate that the simulation model applies well in the prediction of dendrite growth direction. Moreover, the prediction of stray grain distribution works well except for the region of dendrites growing along the [100] direction.
文摘This paper focuses on an analysis of the surface texture formed during precision machining of tungsten carbide. The work material was fabricated using direct laser deposition （DLD） technology. The experiment included precision milling of tungsten carbide samples with a monolithic torus cubic boron nitride tool and grinding with diamond and alumina cup wheels. An optical surface profiler was applied to the measurements of surface textures and roughness profiles. In addition, the micro-geometry of the milling cutter was measured with the appli- cation of an optical device. The surface roughness height was also estimated with the application of a model, which included kinematic-geometric parameters and minimum uncut chip thickness. The research revealed the occurrence of micro-grooves on the machined surface. The surface roughness height calculated on the basis of the traditional kinematic-geometric model was incompatible with the measurements. However, better agreement between the theoretical and experimental values was observed for the minimum uncut chip thickness model.
文摘High wear resistance,low cytotoxicity and excellent antibacterial properties are the basis for osseointegration of implant materials.Polyetheretherketone(PEEK)has been considered as a potential implant material due to its excellent biocompatibility,natural radiolucency and mechanical properties.In this work,to improve the wear resistance,cytotoxicity and antibacterial properties of PEEK,carbon fiber(CFR)and Black Phosphorus(BP)were used to synergistically modify PEEK by two methods,deposition of BP coating on CFR-PEEK and BP/CFR-PEEK coating on Ti6Al4V(TC4)through electrostatic spraying.After CFR and BP synergistically modified PEEK,the friction coefficient of BP coating on CFR-PEEK and BP/CFR-PEEK coating were 0.14±0.01 and 0.09±0.02,respectively.The wear volume of BP coating on CFR-PEEK(30.54±1.32)was higher than that of BP/CFR-PEEK coating(9.46±1.32),which indicated that BP/CFR-PEEK coating showed high wear resistance.The difference in wear resistance may be caused by the fact that BP was not easily oxidized in BP/CFR-PEEK coating.In addition,BP coating on CFR-PEEK and BP/CFR-PEEK coating showed no obvious cytotoxicity to L929 cell and presented excellent antibacterial efficiency(up to 94.5%±2.8%and 96.0%±3.8%,respectively)against Staphylococcus aureus(S.aureus).It was concluded that BP/CFR-PEEK coating exhibited high wear resistance,low cytotoxicity and excellent antibacterial properties against S.aureus,which might provide a foundation for osseointegration of implants.
基金supported by the National Natural Science Foundation of China(Grant No.41501458)China Postdoctoral Science Foundation Funded Project(Grant No.2016M592860)+4 种基金National Basic Research Program of China(Grant No.2013CB733204)Key Laboratory of Mining Spatial Information Technology of NASMG(Grant Nos. KLM201309)Science Program of Shanghai Normal University(Grant No. SK201525)the Shanghai Gaofeng & Gaoyuan Project for University Academic Program Development(Grant Nos.2013LASW-A09 & SKHL1310)the Center of Spatial Information Science and Sustainable Development Applications,Tongji University,Shanghai,China
文摘An empirical simulation method to simulate the possible position of shallow rainfall-induced landslides in China has been developed.This study shows that such a simulation may be operated in real-time to highlight those areas that are highly prone to rainfall-induced landslides on the basis of the landslide susceptibility index and the rainfall intensity-duration(I-D) thresholds.First,the study on landslide susceptibility in China is introduced.The entire territory has been classified into five categories,among which high-susceptibility regions(Zone 4-'High' and 5-'Very high') account for 4.15%of the total extension of China.Second,rainfall is considered as an external triggering factor that may induce landslide initiation.Real-time satellite-based TMPA3B42 products may provide real rainfall spatial and temporal patterns,which may be used to derive rainfall duration time and intensity.By using a historical record of 60 significant past landslides,the rainfall I-D equation has been calibrated.The rainfall duration time that may trigger a landslide has resulted between 3 hours and 45 hours.The combination of these two aspects can be exploited to simulate the spatiotemporal distribution of rainfall-induced landslide hazards when rainfall events exceed the rainfall I-D thresholds,where the susceptibility category is 'high' or 'very high'.This study shows a useful tool to be part of a systematic landslide simulation methodology,potentially providing useful information for a theoretical basis and practical guide for landslide prediction and mitigation throughout China.
