Nano-scale chemical inhomogeneity in surface oxide films formed on a V-and N-containing martensite stainless steel and tempering heating induced changes are investigated by a combination of synchrotron-based hard X-ra...Nano-scale chemical inhomogeneity in surface oxide films formed on a V-and N-containing martensite stainless steel and tempering heating induced changes are investigated by a combination of synchrotron-based hard X-ray Photoelectron emission spectroscopy(HAXPES)and microscopy(HAXPEEM)as well as microscopic X-ray absorption spectroscopy(μ-XAS)techniques.The results reveal the inhomogeneity in the oxide films on the micron-sized Cr_(2)N-and VN-type particles,while the inhomogeneity on the martensite matrix phase exists due to localised formation of nano-sized tempering nitride particles at 600℃.The oxide film formed on Cr_(2)N-type particles is rich in Cr_(2)O_(3) compared with that on the martensite matrix and VN-type particles.With the increase of tempering temperature,Cr_(2)O_(3) formation is faster for the oxidation of Cr in the martensite matrix than the oxidation of Cr nitride-rich particles.展开更多
Electrochemical behavior of natural chalcopyrite in electrolyte solution containing 5×10？4 mol/L ethyl xanthate, and the effect of potential on the composition and characteristics of surface film were studied by...Electrochemical behavior of natural chalcopyrite in electrolyte solution containing 5×10？4 mol/L ethyl xanthate, and the effect of potential on the composition and characteristics of surface film were studied by cyclic voltammetry （CV）, scanning electron microscopy （SEM） and electrochemical impedance spectroscopy （EIS）. The adsorption of xanthate （X？） occurred on the mineral surface at open-circuit potential （OCP）. In the potential range from -0.11 to 0.2 V, the electrochemical reaction related to the formation of the hydrophobic film of dixanthogen （X2） occurred on natural chalcopyrite surface. This surface film had high coverage and large thickness at the potential of 0 V, but it had low coverage and small thickness at the potentials of 0.1 V and 0.2 V. Electrochemical activation started to occur when the potential was higher than 0.2 V, and the film of X2 transformed to plenty of Cu（Ⅱ） and Fe（Ⅲ） oxygen-containing species which had the porous and loose characteristics.展开更多
To study different corrosion resistances and surface film types of hexagonal close-packed(HCP)pure Mg and body-centered cubic(BCC)Mg−14wt.%Li alloy in 0.1 mol/L NaCl,a series of experiments were conducted,including hy...To study different corrosion resistances and surface film types of hexagonal close-packed(HCP)pure Mg and body-centered cubic(BCC)Mg−14wt.%Li alloy in 0.1 mol/L NaCl,a series of experiments were conducted,including hydrogen evolution,mass loss,in-situ electrochemical testing combined with Raman spectroscopy and microstructural observation.The results indicate that the corrosion resistance of pure Mg is superior to that of Mg−14Li,and the protective function of the surface films on both magnesium systems is elevated within 16 h of immersion in 0.1 mol/L NaCl.An articulated,thick,and needle-like surface film containing Li2CO3 on Mg−14Li,different from the typically thin,flaky Mg(OH)2 film on pure Mg,is confirmed via scanning electron microscopy(SEM).However,both surface films can be broken down at a high anodic over-potential.Thus,different corrosion resistances of the two Mg systems are ascribed to various protective films forming on their surfaces.展开更多
The dynamic oxidation of molten Mg–Al alloy was investigated via the oxide/metal/oxide(OMO)sandwich method.The characteristics of sandwiches were explored using optical microscopy,scanning electron microscopy,X-ray e...The dynamic oxidation of molten Mg–Al alloy was investigated via the oxide/metal/oxide(OMO)sandwich method.The characteristics of sandwiches were explored using optical microscopy,scanning electron microscopy,X-ray energy dispersive spectroscopy,and X-ray diffraction analyses.The results showed the formation of porous oxide films with varying thicknesses from 0.43 to 16.7 mm.Both the measurements and calculations confirmed the literature findings that the oxidation product consists mainly of MgO and Mg Al_(2)O_(4)compounds.The increase in thickness and amount of folds formed on the oxide films implies the significant effect of aluminum in reducing the oxidation resistance of magnesium.展开更多
This paper clarifies two issues related to the prior cathodic polarisation treatment(PCPT) for the potentiodynamic polarisation test: whether PCPT can(1) remove the air-formed surface film and(2) affect the polarisati...This paper clarifies two issues related to the prior cathodic polarisation treatment(PCPT) for the potentiodynamic polarisation test: whether PCPT can(1) remove the air-formed surface film and(2) affect the polarisation test results. X-ray photoelectron spectroscopy analyses of fluoride ion-labelled samples show that PCPT cannot remove the surface film completely due to the low reaction rate. Potentiodynamic polarisation tests demonstrate that PCPT with proper operating parameters,-1.0 V SCE for 5 min with subsequent open circuit potential(OCP) stabilisation in this study, is necessary because it can improve the test reproducibility without affecting the corrosion parameters by unifying the initial surface state. However, PCPT with lower potentials, longer time or no OCP stabilisation has significant effects on the electrochemical corrosion parameters due to the hydrogen absorption under the conditions of this study.展开更多
Nucleate pool boiling on micro-pin-finned surface structure is proposed for efficiently cooling electronic compo- nents with high heat flux in microgravity, and was verified by experiments performed utilizing the drop...Nucleate pool boiling on micro-pin-finned surface structure is proposed for efficiently cooling electronic compo- nents with high heat flux in microgravity, and was verified by experiments performed utilizing the drop tower Beijing. Micro-pin-fins with tile dimensions of 50 × （30 μm2 （thickness × height） and the space of 50 μm were fabricated on the chip surface by the dry etching technique. FC-72 was used as the working fluid. Nucleate pool boiling of FC-72 on a smooth surface was also tested for comparison. Unlike much obvious deterioration of heat transfer of nucleate pool boiling on the smooth surface in microgravity, constant heater surface temperature of nucleate pool boiling for the micro-pin-finned surface was observed, even though a large coalesced bubble completely covered the surface under microgravity condition. The performance of high efficient heat transfer on micro-pin-finned surface is independent of the gravity, which stems from the sufficient supply of fresh liquid to the heater surface due to the capillary forces.展开更多
The electrochemical behavior of X70 pipeline steel in (0.5mol·L-1 Na2CO3+1 mol·L-1 NaHCO3) solution was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). X-ray photoel...The electrochemical behavior of X70 pipeline steel in (0.5mol·L-1 Na2CO3+1 mol·L-1 NaHCO3) solution was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to analyze the composition and microstructure of the surface film. The results showed that there were two anodic peaks at -600 mV and -350 mV. The surface film formed at -600 mV mainly consisted of ferrous carbonates and ferrous hydroxycarbonates. It had a small reaction resistance. It was metastable and possessed poor protective property. Numerous pits and microcracks existed on the film, which could be the active paths for the initiation of stress corrosion cracking. The surface film formed at -350 mV, mainly consisted of ferric oxides. It has high reaction resistance and offered good protection for the substrate.展开更多
In the present study,the non-isothermal early stages of surface oxidation of liquid Mg-1%Y alloy during casting were studied under UPH argon,dry air,and air mixed with protective fluorine-bearing gases.The chemistry a...In the present study,the non-isothermal early stages of surface oxidation of liquid Mg-1%Y alloy during casting were studied under UPH argon,dry air,and air mixed with protective fluorine-bearing gases.The chemistry and morphology of the surface films were characterized by SEM and EDX analyses.The results indicate a layer of smooth and tightly coherent oxidation film composed of MgO and Y_(2)O_(3) formed on the molten Mg-Y alloy surface with 40-60 nm thickness under dry air.A dendritic/cellular microstructure is clearly visible with Y-rich second phases gathered in surface of the melt and precipitated along the grain/cell boundaries under all gas conditions.Under fluorine-bearing gas mixtures,the surface film was a mixed oxide and fluoride and more even;a flat and folded morphology can be seen under SF6 with oxide as dominated phase and under 1,1,1,2-tetra-fluoroethane,a smooth and compact surface film uniformly covering the inner surface of the bubble with equal oxide and fluoride thickness,which results in a film without any major defects.MgF_(2) phase appears to be the key characteristic of a good protective film.展开更多
An ultra-sensitive and highly selective parathion methyl （PM） detection method by surface plasmon resonance （SPR） combined with molecularly imprinted films （MIF） was developed. The PM-imprinted film was prepared...An ultra-sensitive and highly selective parathion methyl （PM） detection method by surface plasmon resonance （SPR） combined with molecularly imprinted films （MIF） was developed. The PM-imprinted film was prepared by thermo initiated polymerization on the bare Au surface of an SPR sensor chip, Template PM molecules were quickly removed by an organic solution of acetonitrilelacetic acid （9：1, v/v）, causing a shift of 0.5° in SPR angle. In the concentrations range of 10^-13-10^-10 mol/L, the refractive index showed a gradual increase with higher concentrations of template PM and the changes of SPR angles were linear with the negative logarithm of PM concentrations. In the experiment, the minimum detectable concentration was 10^-13 mol/L. The selectivity of the thin PM-imprinted film against diuron, tetrachlorvinphose and fenitrothion was examined, but no observable binding was detected. The results in the experiment suggested that the MIF had the advantages of high sensitivity and selectivity.展开更多
Premature failure of coated tool often results from a poor adhesion of coating-substrate and shortens the lifetime of the tool. The results of increasing the adhesion strength of thin film coatings on cutting tool ins...Premature failure of coated tool often results from a poor adhesion of coating-substrate and shortens the lifetime of the tool. The results of increasing the adhesion strength of thin film coatings on cutting tool inserts by pretreating the inserts with sandblasting technique to obtain a desirable surface morphology of the inserts are presented. A geometric model representing the ideal surface morphology is established to enhance the nucleation density and adhesion strength of coating-substrate. Thin film coating experiment is conducted on the substrates of four different sample groups. Indentation and wear tests are performed on coated inserts to evaluate the effect of sandblasting on the adhesion strength of the coatings. A theoretical analysis is provided on the formation and growth of atom clusters in terms of the contact angle and the thermodynamic barrier of a substrate to predict thin film nucleation.展开更多
The effect of annealing temperature on the formation of the PtSi phase. distribution of silicides and the surface morphologies of silicides films is investigated by XPS. AFM. It is shown that the phase sequences of t...The effect of annealing temperature on the formation of the PtSi phase. distribution of silicides and the surface morphologies of silicides films is investigated by XPS. AFM. It is shown that the phase sequences of the films change from Pt-Pt2Si-PtSi-Si to Pt+Pt2Si+PtSi-PtSi-Si or Pt+Pt2Si+PtSi-PtSi-st with an increase of annealing temperature and the reason for the formation of mixed layers is discussed.展开更多
Surface films that formed on molten AZ91D magnesium alloy in S02/air cover gases at 680 ℃ in a sealed furnace were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and ...Surface films that formed on molten AZ91D magnesium alloy in S02/air cover gases at 680 ℃ in a sealed furnace were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and Auger electron spectroscopy. It is revealed that the film formed on molten AZ91D alloy surface in cover gas with high air content can prevent the molten AZ91D alloy from oxidation and ignition. The surface film contained three elements, namely magnesium, oxygen and sulfur, and was mainly composed of MgO and MgS. The properties of the film depended on air content in the cover gas and holding time. Thermodynamic calculation showed that MgSO4 was the stable phase, and it was concluded that the formation of MgS04 was important for the formation of the protective surface film in S02/air atmospheres.展开更多
Surface acoustic wave（SAW） resonators with Pt/AlN/Si and Pt/AlN/Pt/Si configurations were fabricated by lift-off photolithography techniques. High-temperature performances of both configurations were investigated fo...Surface acoustic wave（SAW） resonators with Pt/AlN/Si and Pt/AlN/Pt/Si configurations were fabricated by lift-off photolithography techniques. High-temperature performances of both configurations were investigated for temperature sensor applications. AlN films grown on Ptcoated Si substrates exhibit a lower（002） preferred orientation than those grown on Si substrates. The center frequencies of Pt/AlN/Si and Pt/AlN/Pt/Si configurations at room temperature are 424.1 and 456.4 MHz, respectively.The SAW was limited by Pt bottom electrodes to propagate in AlN layer. The temperature coefficient of frequency（TCF） values of Pt/AlN/Si and Pt/AlN/Pt/Si configurations are-51.6 × 10^-6 and-69.2 × 10^-6℃^-1, respectively.Compared with that of Pt/AlN/Si configuration, the TCF value of Pt/AlN/Pt/Si configuration decreases by 34.1 %.AlN resonator with the Pt floating bottom electrodes provides a large, quasi-constant temperature sensitivity which is suitable for temperature sensor applications.展开更多
Pan and field experiments were conducted to investigate the effect of surface film on ammonia volatilization from water and paddy soil. The results showed that the addition of the surface film on floodwater reduced th...Pan and field experiments were conducted to investigate the effect of surface film on ammonia volatilization from water and paddy soil. The results showed that the addition of the surface film on floodwater reduced the rate of ammonia volatilization, however, the reduction of the latter varied greatly with its rates of addition. Jayaweera-Mikkelsen ammonia volatilization model with the introduction of a parameter Kf, a relative measure of the resistance of the surface film on ammonia volatilization, was used to elucidate the effectiveness of the surface film on lowering ammonia volatilization. The Kf value was calculated from the results ob-展开更多
The time evolution of oxygen plasma treated polystyrene(PS)surfaces was investigated upon storing them in theair under controlled humidity conditions.The methods of water contact angle,X-ray photoelectron spectroscopy...The time evolution of oxygen plasma treated polystyrene(PS)surfaces was investigated upon storing them in theair under controlled humidity conditions.The methods of water contact angle,X-ray photoelectron spectroscopy(XPS),sumfrequency generation(SFG)vibrational spectroscopy,and atomic force microscopy(AFM)were used to infer the surfaceproperties and structure.Chemical groups containing oxygen were formed on the PS surface with the plasma treatment,demonstrated by water contact angle and XPS.The surface polarity decayed markedly on time,as assessed by steady increasein the water contact angle as a function of storage time,from zero to around 60°.The observed decay is interpreted as arisingfrom surface rearrangement processes to burying polar groups away from the uppermost layer of the surfaces,which is incontact with air.On the other hand,XPS results show that the chemical composition in the first 3 nm surface layer isunaffected by the surface aging,and the depth profile of oxygen is essentially the same with time.A possible change of PSsurface roughness was examined by AFM,and it showed that the increase of water contact angle during surface aging couldnot be attributed to surface roughness.Thus,it is concluded that surface aging is attributable to surface reorganization andthe motion of oxygen containing groups is confined within the XPS probing depth.SFG spectroscopy,which is intrinsicallyinterface-specific,was used to detect the chemical structure of PS surface at the molecular level after various aging times.The results are interpreted as follows.During the aging of the plasma treated PS surfaces,the oxygen containing groupsundergo reorientation processes toward the polymer bulk and/or parallel to the surface,while the CH_2 moiety stands up onthe PS surface.Our results indicate that the surface configuration changes do not require large length scale segmentalmotions or migration of macromolecules.Motions that are responsible for surface configuration changes could be relativelysmall rotational motions.The aging behaviors under different relative humidity conditions were shown to be similar from18% to 91%,whereas the kinetics of surface polarity decays were faster in higher relative humidity.Here,the surfacerearrangement of polystyrene films that were previously treated by oxygen plasma and aged,and was investigated in terms ofcontact angle after the water immersion.The contact angles of the water-immersed samples were found to change andapproach the initial values before the immersion asymptotically.展开更多
The activated chemisorption of N<sub>2</sub> on Ni （poly） and La film was performed on a molecular beam—surface scattering apparatus. Experimental results indicate that the initial sticking probability ...The activated chemisorption of N<sub>2</sub> on Ni （poly） and La film was performed on a molecular beam—surface scattering apparatus. Experimental results indicate that the initial sticking probability s<sub>o</sub> increases linearly from 0 to 0.03 as normal component of translational energy of the molecuar beam E<sub>n</sub> increases from 11.00 to 19.91 kcal/mol for N<sub>2</sub>/Ni system and S<sub>0</sub> from 0 to 0. 10 as E<sub>n</sub> from 10. 40 to 19.91 kcal/mol for N<sub>2</sub>/La system. The apparent activation energy △E are 6.16 kcal/mol and 5.30 kcal/mol for N<sub>2</sub>/Ni and N<sub>2</sub>/La systems respectively.展开更多
A novel method for preparing metalllzed film has been studied.The reduction process and properties of the poly(vinyl alcohol)(PVA)were probed by several analytic means.According to the etudies,a mechanism for the poly...A novel method for preparing metalllzed film has been studied.The reduction process and properties of the poly(vinyl alcohol)(PVA)were probed by several analytic means.According to the etudies,a mechanism for the polymer surface reduction metallization was proposed and proved.展开更多
The elementary beam model is modified to include the surface effects and used to analyze the deflections of nanowires under different boundary conditions. Tile results show that compared to deflections of nanowires wi...The elementary beam model is modified to include the surface effects and used to analyze the deflections of nanowires under different boundary conditions. Tile results show that compared to deflections of nanowires without consideration of surface effects, the surface effects can enlarge or reduce deflections of nanowires, and nanowire buckling occurs under certain conditions. This study might be helpful for design of nanowire-based nanoelectromechanical systems.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
We investigate the impurity effects on surfaces of a thin film topological insulator, applied by an off-resonant circular polarized light. It is found that the off-resonant driving induces a quantized total Hall condu...We investigate the impurity effects on surfaces of a thin film topological insulator, applied by an off-resonant circular polarized light. It is found that the off-resonant driving induces a quantized total Hall conductivity, when the driving strength is larger than a critical value and the Fermi level lies in the band gap, indicating that our system is converted into the topological phase. We also find that with the increasing disorder strength, the Dirac masses of top and bottom surfaces are renormalized and then fixed to half of their initial values, respectively,which will shrink the widths of the half-integer plateau of anomalous Hall conductivities.展开更多
基金supported by the Vinnova(project number 2020-03778)supported by the Swedish Research Council(Vetenskapsradet,project number 2021-04157).
文摘Nano-scale chemical inhomogeneity in surface oxide films formed on a V-and N-containing martensite stainless steel and tempering heating induced changes are investigated by a combination of synchrotron-based hard X-ray Photoelectron emission spectroscopy(HAXPES)and microscopy(HAXPEEM)as well as microscopic X-ray absorption spectroscopy(μ-XAS)techniques.The results reveal the inhomogeneity in the oxide films on the micron-sized Cr_(2)N-and VN-type particles,while the inhomogeneity on the martensite matrix phase exists due to localised formation of nano-sized tempering nitride particles at 600℃.The oxide film formed on Cr_(2)N-type particles is rich in Cr_(2)O_(3) compared with that on the martensite matrix and VN-type particles.With the increase of tempering temperature,Cr_(2)O_(3) formation is faster for the oxidation of Cr in the martensite matrix than the oxidation of Cr nitride-rich particles.
基金Project (50874030) supported by the National Natural Science Foundation of ChinaProject (N090602011) supported by the Fundamental Research Funds for the Central Universities, China Project (2009AA06Z104) supported by the National High-Tech Research and Development Program of China
文摘Electrochemical behavior of natural chalcopyrite in electrolyte solution containing 5×10？4 mol/L ethyl xanthate, and the effect of potential on the composition and characteristics of surface film were studied by cyclic voltammetry （CV）, scanning electron microscopy （SEM） and electrochemical impedance spectroscopy （EIS）. The adsorption of xanthate （X？） occurred on the mineral surface at open-circuit potential （OCP）. In the potential range from -0.11 to 0.2 V, the electrochemical reaction related to the formation of the hydrophobic film of dixanthogen （X2） occurred on natural chalcopyrite surface. This surface film had high coverage and large thickness at the potential of 0 V, but it had low coverage and small thickness at the potentials of 0.1 V and 0.2 V. Electrochemical activation started to occur when the potential was higher than 0.2 V, and the film of X2 transformed to plenty of Cu（Ⅱ） and Fe（Ⅲ） oxygen-containing species which had the porous and loose characteristics.
基金Projects(51901047,51801029)supported by the National Natural Science Foundation of ChinaProjects(201911845185,xj201911845345)supported by the National College Students Innovation and Entrepreneurship Training Program,China。
文摘To study different corrosion resistances and surface film types of hexagonal close-packed(HCP)pure Mg and body-centered cubic(BCC)Mg−14wt.%Li alloy in 0.1 mol/L NaCl,a series of experiments were conducted,including hydrogen evolution,mass loss,in-situ electrochemical testing combined with Raman spectroscopy and microstructural observation.The results indicate that the corrosion resistance of pure Mg is superior to that of Mg−14Li,and the protective function of the surface films on both magnesium systems is elevated within 16 h of immersion in 0.1 mol/L NaCl.An articulated,thick,and needle-like surface film containing Li2CO3 on Mg−14Li,different from the typically thin,flaky Mg(OH)2 film on pure Mg,is confirmed via scanning electron microscopy(SEM).However,both surface films can be broken down at a high anodic over-potential.Thus,different corrosion resistances of the two Mg systems are ascribed to various protective films forming on their surfaces.
文摘The dynamic oxidation of molten Mg–Al alloy was investigated via the oxide/metal/oxide(OMO)sandwich method.The characteristics of sandwiches were explored using optical microscopy,scanning electron microscopy,X-ray energy dispersive spectroscopy,and X-ray diffraction analyses.The results showed the formation of porous oxide films with varying thicknesses from 0.43 to 16.7 mm.Both the measurements and calculations confirmed the literature findings that the oxidation product consists mainly of MgO and Mg Al_(2)O_(4)compounds.The increase in thickness and amount of folds formed on the oxide films implies the significant effect of aluminum in reducing the oxidation resistance of magnesium.
基金the National Science and Technology Major Project of China(No.2016ZX05016-004)the National Natural Science Foundation of China(Nos.51801218 and 51571200)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA13040500)。
文摘This paper clarifies two issues related to the prior cathodic polarisation treatment(PCPT) for the potentiodynamic polarisation test: whether PCPT can(1) remove the air-formed surface film and(2) affect the polarisation test results. X-ray photoelectron spectroscopy analyses of fluoride ion-labelled samples show that PCPT cannot remove the surface film completely due to the low reaction rate. Potentiodynamic polarisation tests demonstrate that PCPT with proper operating parameters,-1.0 V SCE for 5 min with subsequent open circuit potential(OCP) stabilisation in this study, is necessary because it can improve the test reproducibility without affecting the corrosion parameters by unifying the initial surface state. However, PCPT with lower potentials, longer time or no OCP stabilisation has significant effects on the electrochemical corrosion parameters due to the hydrogen absorption under the conditions of this study.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50806057 and 10972225, and the Key Laboratory of Mierogravity/CAS for experiments utilizing the drop tower Beijing.
文摘Nucleate pool boiling on micro-pin-finned surface structure is proposed for efficiently cooling electronic compo- nents with high heat flux in microgravity, and was verified by experiments performed utilizing the drop tower Beijing. Micro-pin-fins with tile dimensions of 50 × （30 μm2 （thickness × height） and the space of 50 μm were fabricated on the chip surface by the dry etching technique. FC-72 was used as the working fluid. Nucleate pool boiling of FC-72 on a smooth surface was also tested for comparison. Unlike much obvious deterioration of heat transfer of nucleate pool boiling on the smooth surface in microgravity, constant heater surface temperature of nucleate pool boiling for the micro-pin-finned surface was observed, even though a large coalesced bubble completely covered the surface under microgravity condition. The performance of high efficient heat transfer on micro-pin-finned surface is independent of the gravity, which stems from the sufficient supply of fresh liquid to the heater surface due to the capillary forces.
基金Supported by State Key Basic Research Plan (G19990650).
文摘The electrochemical behavior of X70 pipeline steel in (0.5mol·L-1 Na2CO3+1 mol·L-1 NaHCO3) solution was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to analyze the composition and microstructure of the surface film. The results showed that there were two anodic peaks at -600 mV and -350 mV. The surface film formed at -600 mV mainly consisted of ferrous carbonates and ferrous hydroxycarbonates. It had a small reaction resistance. It was metastable and possessed poor protective property. Numerous pits and microcracks existed on the film, which could be the active paths for the initiation of stress corrosion cracking. The surface film formed at -350 mV, mainly consisted of ferric oxides. It has high reaction resistance and offered good protection for the substrate.
文摘In the present study,the non-isothermal early stages of surface oxidation of liquid Mg-1%Y alloy during casting were studied under UPH argon,dry air,and air mixed with protective fluorine-bearing gases.The chemistry and morphology of the surface films were characterized by SEM and EDX analyses.The results indicate a layer of smooth and tightly coherent oxidation film composed of MgO and Y_(2)O_(3) formed on the molten Mg-Y alloy surface with 40-60 nm thickness under dry air.A dendritic/cellular microstructure is clearly visible with Y-rich second phases gathered in surface of the melt and precipitated along the grain/cell boundaries under all gas conditions.Under fluorine-bearing gas mixtures,the surface film was a mixed oxide and fluoride and more even;a flat and folded morphology can be seen under SF6 with oxide as dominated phase and under 1,1,1,2-tetra-fluoroethane,a smooth and compact surface film uniformly covering the inner surface of the bubble with equal oxide and fluoride thickness,which results in a film without any major defects.MgF_(2) phase appears to be the key characteristic of a good protective film.
基金supported by the National Natural Science Foundation of China (No.20771015)the National ‘‘111’’ Project of China’s Higher Education (No.B07012)
文摘An ultra-sensitive and highly selective parathion methyl （PM） detection method by surface plasmon resonance （SPR） combined with molecularly imprinted films （MIF） was developed. The PM-imprinted film was prepared by thermo initiated polymerization on the bare Au surface of an SPR sensor chip, Template PM molecules were quickly removed by an organic solution of acetonitrilelacetic acid （9：1, v/v）, causing a shift of 0.5° in SPR angle. In the concentrations range of 10^-13-10^-10 mol/L, the refractive index showed a gradual increase with higher concentrations of template PM and the changes of SPR angles were linear with the negative logarithm of PM concentrations. In the experiment, the minimum detectable concentration was 10^-13 mol/L. The selectivity of the thin PM-imprinted film against diuron, tetrachlorvinphose and fenitrothion was examined, but no observable binding was detected. The results in the experiment suggested that the MIF had the advantages of high sensitivity and selectivity.
基金This project is Supported by National Science Foundation of China (No.59475090)National Science Foundation of USA (No.DDM-93-9669)
文摘Premature failure of coated tool often results from a poor adhesion of coating-substrate and shortens the lifetime of the tool. The results of increasing the adhesion strength of thin film coatings on cutting tool inserts by pretreating the inserts with sandblasting technique to obtain a desirable surface morphology of the inserts are presented. A geometric model representing the ideal surface morphology is established to enhance the nucleation density and adhesion strength of coating-substrate. Thin film coating experiment is conducted on the substrates of four different sample groups. Indentation and wear tests are performed on coated inserts to evaluate the effect of sandblasting on the adhesion strength of the coatings. A theoretical analysis is provided on the formation and growth of atom clusters in terms of the contact angle and the thermodynamic barrier of a substrate to predict thin film nucleation.
文摘The effect of annealing temperature on the formation of the PtSi phase. distribution of silicides and the surface morphologies of silicides films is investigated by XPS. AFM. It is shown that the phase sequences of the films change from Pt-Pt2Si-PtSi-Si to Pt+Pt2Si+PtSi-PtSi-Si or Pt+Pt2Si+PtSi-PtSi-st with an increase of annealing temperature and the reason for the formation of mixed layers is discussed.
基金supported by the Specialized Research Fund for the Doctoral Program of Higher Education under Grant No.20090002110029the High Technology Research and Development Program of China under Grant No.2009AA03Z114the MOST(Ministry of Science and Technology)of China under Grant No.2010DFA72760
文摘Surface films that formed on molten AZ91D magnesium alloy in S02/air cover gases at 680 ℃ in a sealed furnace were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and Auger electron spectroscopy. It is revealed that the film formed on molten AZ91D alloy surface in cover gas with high air content can prevent the molten AZ91D alloy from oxidation and ignition. The surface film contained three elements, namely magnesium, oxygen and sulfur, and was mainly composed of MgO and MgS. The properties of the film depended on air content in the cover gas and holding time. Thermodynamic calculation showed that MgSO4 was the stable phase, and it was concluded that the formation of MgS04 was important for the formation of the protective surface film in S02/air atmospheres.
基金financially supported by the National Nature Science Foundation of China (No. 61223002)Sichuan Youth Science and Technology Innovation Research Team Funding (No. 2011JTD0006)
文摘Surface acoustic wave（SAW） resonators with Pt/AlN/Si and Pt/AlN/Pt/Si configurations were fabricated by lift-off photolithography techniques. High-temperature performances of both configurations were investigated for temperature sensor applications. AlN films grown on Ptcoated Si substrates exhibit a lower（002） preferred orientation than those grown on Si substrates. The center frequencies of Pt/AlN/Si and Pt/AlN/Pt/Si configurations at room temperature are 424.1 and 456.4 MHz, respectively.The SAW was limited by Pt bottom electrodes to propagate in AlN layer. The temperature coefficient of frequency（TCF） values of Pt/AlN/Si and Pt/AlN/Pt/Si configurations are-51.6 × 10^-6 and-69.2 × 10^-6℃^-1, respectively.Compared with that of Pt/AlN/Si configuration, the TCF value of Pt/AlN/Pt/Si configuration decreases by 34.1 %.AlN resonator with the Pt floating bottom electrodes provides a large, quasi-constant temperature sensitivity which is suitable for temperature sensor applications.
文摘Pan and field experiments were conducted to investigate the effect of surface film on ammonia volatilization from water and paddy soil. The results showed that the addition of the surface film on floodwater reduced the rate of ammonia volatilization, however, the reduction of the latter varied greatly with its rates of addition. Jayaweera-Mikkelsen ammonia volatilization model with the introduction of a parameter Kf, a relative measure of the resistance of the surface film on ammonia volatilization, was used to elucidate the effectiveness of the surface film on lowering ammonia volatilization. The Kf value was calculated from the results ob-
基金This work was funded in part by NSF(DMR-0084301)Eastman Kodak Company.
文摘The time evolution of oxygen plasma treated polystyrene(PS)surfaces was investigated upon storing them in theair under controlled humidity conditions.The methods of water contact angle,X-ray photoelectron spectroscopy(XPS),sumfrequency generation(SFG)vibrational spectroscopy,and atomic force microscopy(AFM)were used to infer the surfaceproperties and structure.Chemical groups containing oxygen were formed on the PS surface with the plasma treatment,demonstrated by water contact angle and XPS.The surface polarity decayed markedly on time,as assessed by steady increasein the water contact angle as a function of storage time,from zero to around 60°.The observed decay is interpreted as arisingfrom surface rearrangement processes to burying polar groups away from the uppermost layer of the surfaces,which is incontact with air.On the other hand,XPS results show that the chemical composition in the first 3 nm surface layer isunaffected by the surface aging,and the depth profile of oxygen is essentially the same with time.A possible change of PSsurface roughness was examined by AFM,and it showed that the increase of water contact angle during surface aging couldnot be attributed to surface roughness.Thus,it is concluded that surface aging is attributable to surface reorganization andthe motion of oxygen containing groups is confined within the XPS probing depth.SFG spectroscopy,which is intrinsicallyinterface-specific,was used to detect the chemical structure of PS surface at the molecular level after various aging times.The results are interpreted as follows.During the aging of the plasma treated PS surfaces,the oxygen containing groupsundergo reorientation processes toward the polymer bulk and/or parallel to the surface,while the CH_2 moiety stands up onthe PS surface.Our results indicate that the surface configuration changes do not require large length scale segmentalmotions or migration of macromolecules.Motions that are responsible for surface configuration changes could be relativelysmall rotational motions.The aging behaviors under different relative humidity conditions were shown to be similar from18% to 91%,whereas the kinetics of surface polarity decays were faster in higher relative humidity.Here,the surfacerearrangement of polystyrene films that were previously treated by oxygen plasma and aged,and was investigated in terms ofcontact angle after the water immersion.The contact angles of the water-immersed samples were found to change andapproach the initial values before the immersion asymptotically.
基金Project supportec by the National Natural Science Foundation of China
文摘The activated chemisorption of N<sub>2</sub> on Ni （poly） and La film was performed on a molecular beam—surface scattering apparatus. Experimental results indicate that the initial sticking probability s<sub>o</sub> increases linearly from 0 to 0.03 as normal component of translational energy of the molecuar beam E<sub>n</sub> increases from 11.00 to 19.91 kcal/mol for N<sub>2</sub>/Ni system and S<sub>0</sub> from 0 to 0. 10 as E<sub>n</sub> from 10. 40 to 19.91 kcal/mol for N<sub>2</sub>/La system. The apparent activation energy △E are 6.16 kcal/mol and 5.30 kcal/mol for N<sub>2</sub>/Ni and N<sub>2</sub>/La systems respectively.
基金The project surported by State"863"PlanNational Natural science fund.
文摘A novel method for preparing metalllzed film has been studied.The reduction process and properties of the poly(vinyl alcohol)(PVA)were probed by several analytic means.According to the etudies,a mechanism for the polymer surface reduction metallization was proposed and proved.
基金Supported by the National Natural Science Foundation of China under Grant No 10702014, the New Century Excellent Talent Project of the Ministry of Education of China under Grant No NCET-10-0271, the Program for Changjiang Scholars and Innovative Research Team in University （PCSIRT）, the Fundamental Research Funds for the Central Universities under Grant Nos N100503002 and N100703001, the Research Fund for the Doctoral Program of Higher Education under Grant No 20070145076.
文摘The elementary beam model is modified to include the surface effects and used to analyze the deflections of nanowires under different boundary conditions. Tile results show that compared to deflections of nanowires without consideration of surface effects, the surface effects can enlarge or reduce deflections of nanowires, and nanowire buckling occurs under certain conditions. This study might be helpful for design of nanowire-based nanoelectromechanical systems.
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Supported by the National Key R&D Program of China under Grant No 2017YFA0303203the National Natural Science Foundation of China under Grant Nos 11574217 and 11474149
文摘We investigate the impurity effects on surfaces of a thin film topological insulator, applied by an off-resonant circular polarized light. It is found that the off-resonant driving induces a quantized total Hall conductivity, when the driving strength is larger than a critical value and the Fermi level lies in the band gap, indicating that our system is converted into the topological phase. We also find that with the increasing disorder strength, the Dirac masses of top and bottom surfaces are renormalized and then fixed to half of their initial values, respectively,which will shrink the widths of the half-integer plateau of anomalous Hall conductivities.
