Photodegradation of nonylphenol ethoxylates （NPloEO） was investigated in laboratory scale under UV irradiation. The intermediate photodegradation products were analyzed by LC-ESI-MS. Three kinds of intermediate prod...Photodegradation of nonylphenol ethoxylates （NPloEO） was investigated in laboratory scale under UV irradiation. The intermediate photodegradation products were analyzed by LC-ESI-MS. Three kinds of intermediate products including aldehydic compounds, carboxylic compounds and cyclohexanyl compounds were identified. Five main degradation routes involving the oxidation of the alkyl chain and ethoxylate unit, shortening of the alkyl chain and ethoxylate unit, hydrogenation of the benzene ring were proposed.展开更多
Upconversion （UC） phosphor Tm3＋ doped YF3 nano-erystals were prepared by hydrothermal method under different conditions and characterized by Field Transmission electron microscopy （TEM）, Scanning electron microsc...Upconversion （UC） phosphor Tm3＋ doped YF3 nano-erystals were prepared by hydrothermal method under different conditions and characterized by Field Transmission electron microscopy （TEM）, Scanning electron microscopy （SEM） and X-ray diffraction （XRD）. Their UC luminescence properties were studied by fluorescence spectrophotometer with 980 nm diode laser excitation, and impact of different grain sizes and morphology on the UC luminescence intensity was discussed. The fluorescence decay lifetime was calculated by Multi-exponential function fitting method. Results show that UC emission intensity was enhanced with the reduction of grain size, and the decay lifetime is 0.60 us.展开更多
In this article, hydrothermal process is applied to synthesize nanometer InVO4. Influences of different experimental conditions （including mixing ratio of raw materials, reaction temperature, reaction time and so on...In this article, hydrothermal process is applied to synthesize nanometer InVO4. Influences of different experimental conditions （including mixing ratio of raw materials, reaction temperature, reaction time and so on） upon the synthetic products＇ purity and crystallite size are discussed to determine the best synthetic condition. The structure of nanometer InVO4 is analyzed, which helps to further understand the structure characteristics of InVO4 synthesized by applying hydrothermal process and lays foundation for further research.展开更多
The on-surface synthesis method allows the fabrication of atomically precise narrow graphene nanoribbons(GNRs),which bears great potential in electronic applications.Here,we synthesize armchair graphene nanoribbons(AG...The on-surface synthesis method allows the fabrication of atomically precise narrow graphene nanoribbons(GNRs),which bears great potential in electronic applications.Here,we synthesize armchair graphene nanoribbons(AGNRs)and chevron-type graphene nanoribbons(CGNRs)array on a vicinal Au(111112)surface using 10,10′-dibromo-9,9′-bianthracene(DBBA)and 6,12-dibromochrysene(DBCh)as precursors,respectively.This process creates spatially wellaligned GNRs,as characterized by scanning tunneling microscopy.AGNRs show strong Raman linear polarizability for application in optical modulation devices.Different from the distinct polarization of AGNRs,only weak polarization exists in CGNRs polarized Raman spectrum,which suggests that the presence of the zigzag boundary in the nanoribbon attenuates the polarization rate as an important factor affecting the polarization.We analyze the Raman activation mode of CGNRs using the peak polarization to expand the application of the polarization Raman spectroscopy in nanoarray analysis.展开更多
We report the synthesis and characterization of a Si-based ternary semiconductor Mg_(3)Si_(2)Te_(6),which exhibits a quasitwo-dimensional structure,where the trigonal Mg_(3)Si_(2)Te_(6)layers are separated by Mg ions....We report the synthesis and characterization of a Si-based ternary semiconductor Mg_(3)Si_(2)Te_(6),which exhibits a quasitwo-dimensional structure,where the trigonal Mg_(3)Si_(2)Te_(6)layers are separated by Mg ions.Ultraviolet-visible absorption spectroscopy and density functional theory calculations were performed to investigate the electronic structure.The experimentally determined direct band gap is 1.39 eV,consistent with the value of the density function theory calculations.Our results reveal that Mg_(3)Si_(2)Te_(6)is a direct gap semiconductor,which is a potential candidate for near-infrared optoelectronic devices.展开更多
A field survey was conducted to investigate the metal and arsenic contamination in soils and vegetables on four villages （Shuichuan （SCH）, Beiwan （BWA）, Dongwan （DWA） and Wufe （WFE）） located along, Baiyin, C...A field survey was conducted to investigate the metal and arsenic contamination in soils and vegetables on four villages （Shuichuan （SCH）, Beiwan （BWA）, Dongwan （DWA） and Wufe （WFE）） located along, Baiyin, China, and to evaluate the possible health risks to local population through foodchain. Results show that the most significantly contaminated soils occurred upstream at SCH where Cd, Cu and As concentrations exceeded maximum allowable concentrations for Chinese agricultural soil. Further downstream the degree of contamination semi-systematically decreased in concentrations of metal. Generally, the leafy vegetables were more heavily contaminated than non-leafy vegetables. Chinese cabbage is the most severely contaminated, the concentrations of Cd exceeded the maximum permit levels （0.05 mg/kg） by 4.5 times. Bio-accumulate factor also shows that an entry of Cd to food chain plants is the greatest potential. Furthermore, the estimated daily intake amounts of the considered toxic elements （Cd, Pb and Cu） from the vegetables grown at SCH and BWA and DWA have exceeded the recommended dietary allowance levels. Thus, the vegetables grown in three villages above, which affected by Baiyin mining and smelting have a health hazard for human consumption.展开更多
This article discusses the effect of temperature field on the Pulse Magneto-Oscillation(PMO) induced solidification refinement of pure aluminium to provide more information for the industrial application of the PMO so...This article discusses the effect of temperature field on the Pulse Magneto-Oscillation(PMO) induced solidification refinement of pure aluminium to provide more information for the industrial application of the PMO solidification technology.The temperature field is altered mainly by applied variable cooling conditions and pulse parameters.Experimental results show that the refinement effect in the case of full sand mould applied is weakened with the decreasing of cooling rate,however,in the alternative case,the sand mould whose sand bottom was replaced by a graphite block is favorable to the survival of equiaxed nucleus.The refinement mechanism is discussed in terms of the relationship between temperature field and the formation process of solidified structure.The formation or survival of nucleus depends on both temperature field and Joule heat produced by PMO,both low pulse frequency and high pulse current were experimentally confirmed to be effective;and PMO was demonstrated high potential in industrial application.展开更多
The effect of niobium on the formation of NbC phase and solidification structure in high carbon equivalent grey cast iron was investigated.The experimental results indicated that an increase in the niobium content is ...The effect of niobium on the formation of NbC phase and solidification structure in high carbon equivalent grey cast iron was investigated.The experimental results indicated that an increase in the niobium content is favorable to refining the graphite and eutectic cell;and the pearlite lamellar spacing is reduced.Based on the thermodynamic calculation the formation of NbC is prior to the eutectic reaction.The reduction in the pearlite lamellar spacing is mainly attributed to the decrease of eutectic temperature with the addition of niobium.Additionally,properties including hardness and wear resistance were improved after the addition of niobium.展开更多
Nanocrystalline TiO_(2) powder was prepared by sol-gel process.The structures of the as-prepared and the TiO_(2) powder heat-treated at different temperatures were studied by thermogravimetric analyzer,differential th...Nanocrystalline TiO_(2) powder was prepared by sol-gel process.The structures of the as-prepared and the TiO_(2) powder heat-treated at different temperatures were studied by thermogravimetric analyzer,differential thermal analysis,x-ray diffraction,and Raman spectra.As the powder was heat-treated at 350℃,it turned into tetragonal anatase structure.A structural transformation from anatase to rutile type occurred and the grains of the powder grew drastically when the powder was heat-treated at above 550℃.The structural transformation from anatase to rutile type completed at 750℃.The Raman spectra of TiO_(2) nanocrystalline powder were also studied.展开更多
The reaction of ZnO nanoparticles grafted with KH570 silane coupling agent was carried out in water-alcohol mixed solvent. Several characterization methods were applied to analyzing the results of surface modification...The reaction of ZnO nanoparticles grafted with KH570 silane coupling agent was carried out in water-alcohol mixed solvent. Several characterization methods were applied to analyzing the results of surface modification such as Soxhlet extraction, Fourier transform infrared spectroscopy （FT-IR）, transmission electron microscopy （TEM）, thermogravimetry （TG）, differential scanning calorimetry （DSC） and zeta potential （ζ）. The results of FT-IR and TG-DSC show that the desired reaction chains have been covalently bonded on the surface of ZnO nanoparticles. Zetasizer results reveal that the maximal absolute value of ζ of the modified ZnO particles in acetone medium was 67.0 mV, which was much higher than that of the unmodified ZnO particles. So the surface of nanosized ZnO changed from hydrophilicity to hydrophobicity and the dispersity of ZnO nanoparticles were improved simultaneously. Finally, the mechanism of graft modification was discussed.展开更多
Size-dependence of optical properties and energy relaxation in CdSe/ZnS quantum dots （QDs） were investigated by two-colour femtosecond （fs） pump-probe （400/800 nm） and picosecond time-resolved photoluminescence ...Size-dependence of optical properties and energy relaxation in CdSe/ZnS quantum dots （QDs） were investigated by two-colour femtosecond （fs） pump-probe （400/800 nm） and picosecond time-resolved photoluminescence （ps TRPL） experiments. Pump-probe measurement results show that there are two components for the excited carriers relaxation, the fast one with a time constant of several ps arises from the Auger-type recombination, which shows almost particle sizeindependence. The slow relaxation component with a time constant of several decades of ns can be clearly determined with ps TRPL spectroscopy in which the slow relaxation process shows strong particle size-dependence. The decay time constants increase from 21 to 34 ns with the decrease of particle size from 3.2 to 2.1 nm. The room-temperature decay lifetime is due to the thermal mixing of bright and dark excitons, and the size-dependence of slow relaxation process can be explained very well in terms of simple three-level model.展开更多
Al-substituted barium ferrite powders were synthesized using the sol-gel auto-combustion method according to the molecular formula BaAlxFe12-xO19 （x=0, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0）. Compared with non-substituted ba...Al-substituted barium ferrite powders were synthesized using the sol-gel auto-combustion method according to the molecular formula BaAlxFe12-xO19 （x=0, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0）. Compared with non-substituted barium ferrite annealing at 1000 ℃, the vibrating sample magnetometer （VSM） measurement manifested that the optimum magnetic properties formation temperature of Al-substituted barium ferrite was 1 100 ℃. The data from X-ray diffractometer （XRD） showed that with increasing x, the lattice constants （a and c） decreased as well as the unit-cell volume Vcell. Magnetic measurement of non-substituted and Al-substituted powders annealed from 900 ℃ to 1 200 ℃ exhibited that the maximum magnetization M （10 kOe）, the remanent magnetization Mr and the coercivity Hc depended strongly on the chemical composition of powder as well as the annealing temperature. When annealing at 1 100 ℃, BaAl0.5Fe11.5O19 of high coercivity Hc （6584 Oe） was produced. Meanwhile, M （10 kOe） and Mr were 42.83 emu/g and 25.65 emu/g, respectively.展开更多
Lightweight,flexibility,and low thickness are urgent requirements for next-generation high-performance electromagnetic interference(EMI)shielding materials for catering to the demand for smart and wearable electronic ...Lightweight,flexibility,and low thickness are urgent requirements for next-generation high-performance electromagnetic interference(EMI)shielding materials for catering to the demand for smart and wearable electronic devices.Although several efforts have focused on constructing porous and flexible conductive films or aerogels,few studies have achieved a balance in terms of density,thickness,flexibility,and EMI shielding effectiveness(SE).Herein,an ultrathin,lightweight,and flexible carbon nanotube(CNT)buckypaper enhanced using MXenes(Ti3C2Tx)for high-performance EMI shielding is synthesized through a facile electrophoretic deposition process.The obtained Ti3C2Tx@CNT hybrid buckypaper exhibits an outstanding EMI SE of 60.5 dB in the X-band at 100μm.The hybrid buckypaper with an MXene content of 49.4 wt%exhibits an EMI SE of 50.4 dB in the X-band with a thickness of only 15μm,which is 105%higher than that of pristine CNT buckypaper.Furthermore,an average specific SE value of 5.7×10^(4) dB cm^(2) g^(−1) is exhibited in the 5-μm hybrid buckypaper.Thus,this assembly process proves promising for the construction of ultrathin,flexible,and high-performance EMI shielding films for application in electronic devices and wireless communications.展开更多
In this paper, TitaiJum dioxide （TiO2） rutile single crystal was irradiated by infrared femtosecond laser pulses with repetition rate of 250 kHz. For a P-polarized femtosecond laser, the periodic nanograting structu...In this paper, TitaiJum dioxide （TiO2） rutile single crystal was irradiated by infrared femtosecond laser pulses with repetition rate of 250 kHz. For a P-polarized femtosecond laser, the periodic nanograting structure on the ablation crater surface was formed . The periodicity is much less than the laser wavelength. The direction of nanograting alignment depends on the polarization laser beam. Micro-Raman spectra show that the intensity of Eg Raman vibrating mode of rutile phase increases and that of Alg Raman vibrating mode decreases apparently within the ablation crater. With the increase of irradiation time and laser average power, the Raman vibrating modes of anatase phase emerged. Rutile phase of TiO2 single crystal is partly transformed into anatase phase.展开更多
Nanostructured silver was obtained by potentiostatic electrolysis.The effects of ionized surfactant(sodium dodecanesulphonate)and the substrate(Cu and Ti)on the morphology of depositions were investigated.It is found ...Nanostructured silver was obtained by potentiostatic electrolysis.The effects of ionized surfactant(sodium dodecanesulphonate)and the substrate(Cu and Ti)on the morphology of depositions were investigated.It is found that morphologies of silver nanostructures can be simply controlled via change of the substrate.Spherical Ag nanoparticles with narrow size distribution were obtained by electrodeposition in Ag NO3-SDS aqueous solution on copper substrate.In the case of titanium substrate,silver dendrite structures were obtained.Despite of different morphologies,XRD and TEM results showed that the as-prepared samples belong to face-centered cubic silver structure with good crystallinity.The formation mechanism of different silver nanostructures was discussed.展开更多
This paper reports self-organized nanostructures observed on the surface of ZnO crystal after irradiation by a focused beam of a femtosecond Ti：sapphire laser with a repetition rate of 250kHz. For a linearly polarize...This paper reports self-organized nanostructures observed on the surface of ZnO crystal after irradiation by a focused beam of a femtosecond Ti：sapphire laser with a repetition rate of 250kHz. For a linearly polarized femtosecond laser, the periodic nanograting structure on the ablation crater surface was promoted. The period of self-organization structures is about 180 nm. The grating orientation is adjusted by the laser polarization direction. A long range Bragglike grating is formed by moving the sample at a speed of 10μm/s. For a circularly polarized laser beam, uniform spherical nanoparticles were formed as a result of Coulomb explosion during the interaction of near-infrared laser with ZnO crystal.展开更多
Conversion efficiency of soft X-ray from 0.35μm pulse laser-irradiated aluminium planar target at laser intensities 10^13- 10^15 W/cm^2 on the Xingguang-Ⅱ facility （laser energy 5 - 90 J, focal spot - Φ 200μm ful...Conversion efficiency of soft X-ray from 0.35μm pulse laser-irradiated aluminium planar target at laser intensities 10^13- 10^15 W/cm^2 on the Xingguang-Ⅱ facility （laser energy 5 - 90 J, focal spot - Φ 200μm full width of half maximun （FWHM） 400 - 800 ps） was measured. A simple model was given to explain soft X-ray conversion efficiency. In this model, because of the heat conduction from the laser-heated spot, the conversion was very small at lower irradiance limit, while at higher limit it was bounded by the energy lost in blow off plasma. Consequently, at the laser intensity around 2×10^14 W/cm^2 , the X-ray conversion efficiency reaches a maximum.展开更多
The thermal behavior, miscibility, crystallite conformation and thermal stability ofcrosslinked(CL-) PVA/PVP blends were studied by DSC and TG methods, respectively. DSCresults showed that in the blend, the crystallin...The thermal behavior, miscibility, crystallite conformation and thermal stability ofcrosslinked(CL-) PVA/PVP blends were studied by DSC and TG methods, respectively. DSCresults showed that in the blend, the crystallinity,T_m and T_c of PVA were obviously lower thanthose of pure PVA; the crystal growth changed from three dimensional to two dimensional andonly a single T_g was detected. These facts demonstrated that this crystalline and amorphousblend have good miscibility. TG curves showed that providing the quantity of K_2S_2O_8 added ismore than 3 wt%,in the blends PVA will form a stable CL-network, whose thermal degradationtemperature was near to that of PVP. But crosslinking reaction will not take place for PVP. Theprocesses of thermal degradation of CL-blends are based on combining both the thermaldegradation of PVP and that of PVA crosslinked with corresponding quantity of K_2S_2O_8 CL-agent, respectively. The UV measurements showed that 75 wt% of PVP may be remained in CL-blend hydrogelscrosslinked by adding (3--5 wt% )K_2S_2O_8. This is mainly due to the stable CL-network formed and the good compatibility and properentanglement between the composites in the CL-blends.展开更多
Microstructure and magnetic properties of Nd8.5Fe77.1B6.4Co4Zr3Nb0.5V0.5 nanocomposite ribbons were investigated. A fine and uniform grain with 30 nm in average size was achieved for the ribbons annealed at 710 ℃ for...Microstructure and magnetic properties of Nd8.5Fe77.1B6.4Co4Zr3Nb0.5V0.5 nanocomposite ribbons were investigated. A fine and uniform grain with 30 nm in average size was achieved for the ribbons annealed at 710 ℃ for 4 min, which enhanced the interaction coupling between grains and improved the magnetic properties. The results of three-dimensional atom probe (3DAP) revealed that V-enriched intergranular phase existed at the grain boundaries, suppressing the grain growth during crystallization process. The remanence and coercivity for annealed ribbons reached to 80 emu·g-1 and 567 kA·m-1, respectively.展开更多
The damage on the atomic bonding and electronic state in a SiO_x（1.4-2.3 nm）/c-Si（150 μm） interface has been investigated.This occurred in the process of depositing indium tin oxide（ITO） film onto the silicon s...The damage on the atomic bonding and electronic state in a SiO_x（1.4-2.3 nm）/c-Si（150 μm） interface has been investigated.This occurred in the process of depositing indium tin oxide（ITO） film onto the silicon substrate by magnetron sputtering.We observe that this damage is caused by energetic particles produced in the plasma（atoms,ions,and UV light）.The passivation quality and the variation on interface states of the SiO_x/c-Si system were mainly studied by using effective minority carrier lifetime（τ_（eff）） measurement as a potential evaluation.The results showed that the samples＇ τ_（eff）was reduced by more than 90%after ITO formation,declined from 107 μs to 5 μs.Following vacuum annealing at 200 ℃,the τ_（eff） can be restored to 30 μs.The components of Si to O bonding states at the SiO_x/c-Si interface were analyzed by x-ray photoelectron spectroscopy（XPS） coupled with depth profiling.The amorphous phase of the SiO_x layer and the ＂atomistic interleaving structure＂ at the SiO_x/c-Si interface was observed by a transmission electron microscope（TEM）.The chemical configuration of the Si-O fraction within the intermediate region is the main reason for inducing the variation of Si dangling bonds（or interface states） and effective minority carrier lifetime.After an appropriate annealing,the reduction of the Si dangling bonds between SiO_x and near the c-Si surface is helpful to improve the passivation effect.展开更多
文摘Photodegradation of nonylphenol ethoxylates （NPloEO） was investigated in laboratory scale under UV irradiation. The intermediate photodegradation products were analyzed by LC-ESI-MS. Three kinds of intermediate products including aldehydic compounds, carboxylic compounds and cyclohexanyl compounds were identified. Five main degradation routes involving the oxidation of the alkyl chain and ethoxylate unit, shortening of the alkyl chain and ethoxylate unit, hydrogenation of the benzene ring were proposed.
文摘Upconversion （UC） phosphor Tm3＋ doped YF3 nano-erystals were prepared by hydrothermal method under different conditions and characterized by Field Transmission electron microscopy （TEM）, Scanning electron microscopy （SEM） and X-ray diffraction （XRD）. Their UC luminescence properties were studied by fluorescence spectrophotometer with 980 nm diode laser excitation, and impact of different grain sizes and morphology on the UC luminescence intensity was discussed. The fluorescence decay lifetime was calculated by Multi-exponential function fitting method. Results show that UC emission intensity was enhanced with the reduction of grain size, and the decay lifetime is 0.60 us.
文摘In this article, hydrothermal process is applied to synthesize nanometer InVO4. Influences of different experimental conditions （including mixing ratio of raw materials, reaction temperature, reaction time and so on） upon the synthetic products＇ purity and crystallite size are discussed to determine the best synthetic condition. The structure of nanometer InVO4 is analyzed, which helps to further understand the structure characteristics of InVO4 synthesized by applying hydrothermal process and lays foundation for further research.
基金Project supported by the National Natural Science Foundation of China(Grant No.61901200)the Yunnan Fundamental Research Projects(Grant Nos.2019FD041,202101AU070043,202101AV070008+2 种基金202101AW070010)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.NXDB30010000)the Dongguan Innovation Research Team Program。
文摘The on-surface synthesis method allows the fabrication of atomically precise narrow graphene nanoribbons(GNRs),which bears great potential in electronic applications.Here,we synthesize armchair graphene nanoribbons(AGNRs)and chevron-type graphene nanoribbons(CGNRs)array on a vicinal Au(111112)surface using 10,10′-dibromo-9,9′-bianthracene(DBBA)and 6,12-dibromochrysene(DBCh)as precursors,respectively.This process creates spatially wellaligned GNRs,as characterized by scanning tunneling microscopy.AGNRs show strong Raman linear polarizability for application in optical modulation devices.Different from the distinct polarization of AGNRs,only weak polarization exists in CGNRs polarized Raman spectrum,which suggests that the presence of the zigzag boundary in the nanoribbon attenuates the polarization rate as an important factor affecting the polarization.We analyze the Raman activation mode of CGNRs using the peak polarization to expand the application of the polarization Raman spectroscopy in nanoarray analysis.
基金the National Natural Science Foundation of China(Grant Nos.12174454,11904414,11904416,and 12104427)the Guangdong Basic and Applied Basic Research Foundation,China(Grant No.2021B1515120015)+1 种基金the Guangzhou Basic and Applied Basic Research Foundation(Grant No.202201011123)the National Key Research and Development Program of China(Grant No.2019YFA0705702).
文摘We report the synthesis and characterization of a Si-based ternary semiconductor Mg_(3)Si_(2)Te_(6),which exhibits a quasitwo-dimensional structure,where the trigonal Mg_(3)Si_(2)Te_(6)layers are separated by Mg ions.Ultraviolet-visible absorption spectroscopy and density functional theory calculations were performed to investigate the electronic structure.The experimentally determined direct band gap is 1.39 eV,consistent with the value of the density function theory calculations.Our results reveal that Mg_(3)Si_(2)Te_(6)is a direct gap semiconductor,which is a potential candidate for near-infrared optoelectronic devices.
基金The Special Science Fund of Northwest University for Nationalities and the Natural Science Foundation ofGansu Province
文摘A field survey was conducted to investigate the metal and arsenic contamination in soils and vegetables on four villages （Shuichuan （SCH）, Beiwan （BWA）, Dongwan （DWA） and Wufe （WFE）） located along, Baiyin, China, and to evaluate the possible health risks to local population through foodchain. Results show that the most significantly contaminated soils occurred upstream at SCH where Cd, Cu and As concentrations exceeded maximum allowable concentrations for Chinese agricultural soil. Further downstream the degree of contamination semi-systematically decreased in concentrations of metal. Generally, the leafy vegetables were more heavily contaminated than non-leafy vegetables. Chinese cabbage is the most severely contaminated, the concentrations of Cd exceeded the maximum permit levels （0.05 mg/kg） by 4.5 times. Bio-accumulate factor also shows that an entry of Cd to food chain plants is the greatest potential. Furthermore, the estimated daily intake amounts of the considered toxic elements （Cd, Pb and Cu） from the vegetables grown at SCH and BWA and DWA have exceeded the recommended dietary allowance levels. Thus, the vegetables grown in three villages above, which affected by Baiyin mining and smelting have a health hazard for human consumption.
基金supported by the National Natural Science Foundation of China (No.50734008 and No.50574056)
文摘This article discusses the effect of temperature field on the Pulse Magneto-Oscillation(PMO) induced solidification refinement of pure aluminium to provide more information for the industrial application of the PMO solidification technology.The temperature field is altered mainly by applied variable cooling conditions and pulse parameters.Experimental results show that the refinement effect in the case of full sand mould applied is weakened with the decreasing of cooling rate,however,in the alternative case,the sand mould whose sand bottom was replaced by a graphite block is favorable to the survival of equiaxed nucleus.The refinement mechanism is discussed in terms of the relationship between temperature field and the formation process of solidified structure.The formation or survival of nucleus depends on both temperature field and Joule heat produced by PMO,both low pulse frequency and high pulse current were experimentally confirmed to be effective;and PMO was demonstrated high potential in industrial application.
基金supported by CITIC-CBMM R&D project (No.036)Graduate Innovation Fund of Shanghai University (No.SHUCX 102233)
文摘The effect of niobium on the formation of NbC phase and solidification structure in high carbon equivalent grey cast iron was investigated.The experimental results indicated that an increase in the niobium content is favorable to refining the graphite and eutectic cell;and the pearlite lamellar spacing is reduced.Based on the thermodynamic calculation the formation of NbC is prior to the eutectic reaction.The reduction in the pearlite lamellar spacing is mainly attributed to the decrease of eutectic temperature with the addition of niobium.Additionally,properties including hardness and wear resistance were improved after the addition of niobium.
基金Supported by the Natural Science Foundation of Guangdong Province of China under Grant No.930222"211"Science Foundation of Zhongshan University.
文摘Nanocrystalline TiO_(2) powder was prepared by sol-gel process.The structures of the as-prepared and the TiO_(2) powder heat-treated at different temperatures were studied by thermogravimetric analyzer,differential thermal analysis,x-ray diffraction,and Raman spectra.As the powder was heat-treated at 350℃,it turned into tetragonal anatase structure.A structural transformation from anatase to rutile type occurred and the grains of the powder grew drastically when the powder was heat-treated at above 550℃.The structural transformation from anatase to rutile type completed at 750℃.The Raman spectra of TiO_(2) nanocrystalline powder were also studied.
基金the Foundation of National Key Technologies R&D Program-Shanghai World Exposition Special Project (Grant No.04DZ05803)the Special Project of Shanghai Nano-technology (Grant No.05nm05011)
文摘The reaction of ZnO nanoparticles grafted with KH570 silane coupling agent was carried out in water-alcohol mixed solvent. Several characterization methods were applied to analyzing the results of surface modification such as Soxhlet extraction, Fourier transform infrared spectroscopy （FT-IR）, transmission electron microscopy （TEM）, thermogravimetry （TG）, differential scanning calorimetry （DSC） and zeta potential （ζ）. The results of FT-IR and TG-DSC show that the desired reaction chains have been covalently bonded on the surface of ZnO nanoparticles. Zetasizer results reveal that the maximal absolute value of ζ of the modified ZnO particles in acetone medium was 67.0 mV, which was much higher than that of the unmodified ZnO particles. So the surface of nanosized ZnO changed from hydrophilicity to hydrophobicity and the dispersity of ZnO nanoparticles were improved simultaneously. Finally, the mechanism of graft modification was discussed.
基金Project supported by the National Natural Science Foundation of China (Grant No 10774099)Science and Technology Commission of Shanghai Municipal (Grant No 06PJ14042)+1 种基金Shanghai Municipal Education Commission (Grant No 06AZ089)the Shanghai Leading Academic Discipline Program (T0104)
文摘Size-dependence of optical properties and energy relaxation in CdSe/ZnS quantum dots （QDs） were investigated by two-colour femtosecond （fs） pump-probe （400/800 nm） and picosecond time-resolved photoluminescence （ps TRPL） experiments. Pump-probe measurement results show that there are two components for the excited carriers relaxation, the fast one with a time constant of several ps arises from the Auger-type recombination, which shows almost particle sizeindependence. The slow relaxation component with a time constant of several decades of ns can be clearly determined with ps TRPL spectroscopy in which the slow relaxation process shows strong particle size-dependence. The decay time constants increase from 21 to 34 ns with the decrease of particle size from 3.2 to 2.1 nm. The room-temperature decay lifetime is due to the thermal mixing of bright and dark excitons, and the size-dependence of slow relaxation process can be explained very well in terms of simple three-level model.
基金Project supported by the Science Foundation of Shanghai Municipal Commission of Science and Technology （Grant No.0452nm049）
文摘Al-substituted barium ferrite powders were synthesized using the sol-gel auto-combustion method according to the molecular formula BaAlxFe12-xO19 （x=0, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0）. Compared with non-substituted barium ferrite annealing at 1000 ℃, the vibrating sample magnetometer （VSM） measurement manifested that the optimum magnetic properties formation temperature of Al-substituted barium ferrite was 1 100 ℃. The data from X-ray diffractometer （XRD） showed that with increasing x, the lattice constants （a and c） decreased as well as the unit-cell volume Vcell. Magnetic measurement of non-substituted and Al-substituted powders annealed from 900 ℃ to 1 200 ℃ exhibited that the maximum magnetization M （10 kOe）, the remanent magnetization Mr and the coercivity Hc depended strongly on the chemical composition of powder as well as the annealing temperature. When annealing at 1 100 ℃, BaAl0.5Fe11.5O19 of high coercivity Hc （6584 Oe） was produced. Meanwhile, M （10 kOe） and Mr were 42.83 emu/g and 25.65 emu/g, respectively.
基金National Natural Science Foundation of China(Grant Nos.52072415,52072306 and 51772335)the Science and Technology Program of Guangzhou(201904010450)Science Foundation of the National Key Laboratory of Science and Technology on Advanced Composites in Special Environments(6142905192509).
文摘Lightweight,flexibility,and low thickness are urgent requirements for next-generation high-performance electromagnetic interference(EMI)shielding materials for catering to the demand for smart and wearable electronic devices.Although several efforts have focused on constructing porous and flexible conductive films or aerogels,few studies have achieved a balance in terms of density,thickness,flexibility,and EMI shielding effectiveness(SE).Herein,an ultrathin,lightweight,and flexible carbon nanotube(CNT)buckypaper enhanced using MXenes(Ti3C2Tx)for high-performance EMI shielding is synthesized through a facile electrophoretic deposition process.The obtained Ti3C2Tx@CNT hybrid buckypaper exhibits an outstanding EMI SE of 60.5 dB in the X-band at 100μm.The hybrid buckypaper with an MXene content of 49.4 wt%exhibits an EMI SE of 50.4 dB in the X-band with a thickness of only 15μm,which is 105%higher than that of pristine CNT buckypaper.Furthermore,an average specific SE value of 5.7×10^(4) dB cm^(2) g^(−1) is exhibited in the 5-μm hybrid buckypaper.Thus,this assembly process proves promising for the construction of ultrathin,flexible,and high-performance EMI shielding films for application in electronic devices and wireless communications.
基金Project supported by Shanghai Leading Academic Discipline Project, China （Grant No T0104）, the Shanghai Nano-technology Promotion Center and Science ＆ Technology of Shanghai Municipality, China （Grant No 0652nm005）, Science Foundation of Shanghai Municipal Commission Education and Science and Technology Commission of Shanghai Municipal, China （Grant No 06PJ14042）.
文摘In this paper, TitaiJum dioxide （TiO2） rutile single crystal was irradiated by infrared femtosecond laser pulses with repetition rate of 250 kHz. For a P-polarized femtosecond laser, the periodic nanograting structure on the ablation crater surface was formed . The periodicity is much less than the laser wavelength. The direction of nanograting alignment depends on the polarization laser beam. Micro-Raman spectra show that the intensity of Eg Raman vibrating mode of rutile phase increases and that of Alg Raman vibrating mode decreases apparently within the ablation crater. With the increase of irradiation time and laser average power, the Raman vibrating modes of anatase phase emerged. Rutile phase of TiO2 single crystal is partly transformed into anatase phase.
基金supported by the National Foundations of China-Australia Special Fund for Scientific and Technological Cooperation(grant No.20711120186)the Natural Science Foundations of China(grant No.20873184)+2 种基金the Natural Science Foundations of Guangdong Province(grant No.8151027501000095)the Science and Technology plan Projects of Guangdong Province(grant No.2008B010600040)the Instrumental Technique Research Foundation of Instrumental Analysis and Research Center,Sun Yat-sen University(grant No.2009006)
文摘Nanostructured silver was obtained by potentiostatic electrolysis.The effects of ionized surfactant(sodium dodecanesulphonate)and the substrate(Cu and Ti)on the morphology of depositions were investigated.It is found that morphologies of silver nanostructures can be simply controlled via change of the substrate.Spherical Ag nanoparticles with narrow size distribution were obtained by electrodeposition in Ag NO3-SDS aqueous solution on copper substrate.In the case of titanium substrate,silver dendrite structures were obtained.Despite of different morphologies,XRD and TEM results showed that the as-prepared samples belong to face-centered cubic silver structure with good crystallinity.The formation mechanism of different silver nanostructures was discussed.
基金Project supported by the Shanghai Leading Academic Discipline Project (Grant No T0104)the Shanghai Nano-technology Promotion Center and Science & Technology of Shanghai Municipality (Grant No 0652nm005)Innovation Fund of Shanghai University,China
文摘This paper reports self-organized nanostructures observed on the surface of ZnO crystal after irradiation by a focused beam of a femtosecond Ti：sapphire laser with a repetition rate of 250kHz. For a linearly polarized femtosecond laser, the periodic nanograting structure on the ablation crater surface was promoted. The period of self-organization structures is about 180 nm. The grating orientation is adjusted by the laser polarization direction. A long range Bragglike grating is formed by moving the sample at a speed of 10μm/s. For a circularly polarized laser beam, uniform spherical nanoparticles were formed as a result of Coulomb explosion during the interaction of near-infrared laser with ZnO crystal.
基金Project suppoted by Shanghai Leading Academic Discipline Foundation （Grant No. T0104）, and Science Foundation of Shanghai Mtmicipal Commission of Education （Grant No. 214680）
文摘Conversion efficiency of soft X-ray from 0.35μm pulse laser-irradiated aluminium planar target at laser intensities 10^13- 10^15 W/cm^2 on the Xingguang-Ⅱ facility （laser energy 5 - 90 J, focal spot - Φ 200μm full width of half maximun （FWHM） 400 - 800 ps） was measured. A simple model was given to explain soft X-ray conversion efficiency. In this model, because of the heat conduction from the laser-heated spot, the conversion was very small at lower irradiance limit, while at higher limit it was bounded by the energy lost in blow off plasma. Consequently, at the laser intensity around 2×10^14 W/cm^2 , the X-ray conversion efficiency reaches a maximum.
文摘The thermal behavior, miscibility, crystallite conformation and thermal stability ofcrosslinked(CL-) PVA/PVP blends were studied by DSC and TG methods, respectively. DSCresults showed that in the blend, the crystallinity,T_m and T_c of PVA were obviously lower thanthose of pure PVA; the crystal growth changed from three dimensional to two dimensional andonly a single T_g was detected. These facts demonstrated that this crystalline and amorphousblend have good miscibility. TG curves showed that providing the quantity of K_2S_2O_8 added ismore than 3 wt%,in the blends PVA will form a stable CL-network, whose thermal degradationtemperature was near to that of PVP. But crosslinking reaction will not take place for PVP. Theprocesses of thermal degradation of CL-blends are based on combining both the thermaldegradation of PVP and that of PVA crosslinked with corresponding quantity of K_2S_2O_8 CL-agent, respectively. The UV measurements showed that 75 wt% of PVP may be remained in CL-blend hydrogelscrosslinked by adding (3--5 wt% )K_2S_2O_8. This is mainly due to the stable CL-network formed and the good compatibility and properentanglement between the composites in the CL-blends.
基金the National Advanced Technology Research and Development Committee of China (2002AA302602-2) Shanghai Municipal Development Foundation of Science and Technology (0552nm049)+1 种基金Shanghai institute of Technolo-gy (YJ-2006-16)Project (P1502) Supported by Shanghai Leading Academic Discipline
文摘Microstructure and magnetic properties of Nd8.5Fe77.1B6.4Co4Zr3Nb0.5V0.5 nanocomposite ribbons were investigated. A fine and uniform grain with 30 nm in average size was achieved for the ribbons annealed at 710 ℃ for 4 min, which enhanced the interaction coupling between grains and improved the magnetic properties. The results of three-dimensional atom probe (3DAP) revealed that V-enriched intergranular phase existed at the grain boundaries, suppressing the grain growth during crystallization process. The remanence and coercivity for annealed ribbons reached to 80 emu·g-1 and 567 kA·m-1, respectively.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61274067,60876045,and 61674099)the Research and Development Foundation of SHU-SOENs PV Joint Laboratory,China(Grant No.SS-E0700601)
文摘The damage on the atomic bonding and electronic state in a SiO_x（1.4-2.3 nm）/c-Si（150 μm） interface has been investigated.This occurred in the process of depositing indium tin oxide（ITO） film onto the silicon substrate by magnetron sputtering.We observe that this damage is caused by energetic particles produced in the plasma（atoms,ions,and UV light）.The passivation quality and the variation on interface states of the SiO_x/c-Si system were mainly studied by using effective minority carrier lifetime（τ_（eff）） measurement as a potential evaluation.The results showed that the samples＇ τ_（eff）was reduced by more than 90%after ITO formation,declined from 107 μs to 5 μs.Following vacuum annealing at 200 ℃,the τ_（eff） can be restored to 30 μs.The components of Si to O bonding states at the SiO_x/c-Si interface were analyzed by x-ray photoelectron spectroscopy（XPS） coupled with depth profiling.The amorphous phase of the SiO_x layer and the ＂atomistic interleaving structure＂ at the SiO_x/c-Si interface was observed by a transmission electron microscope（TEM）.The chemical configuration of the Si-O fraction within the intermediate region is the main reason for inducing the variation of Si dangling bonds（or interface states） and effective minority carrier lifetime.After an appropriate annealing,the reduction of the Si dangling bonds between SiO_x and near the c-Si surface is helpful to improve the passivation effect.
