An Al-3Ti-0.2C-1RE grain refiner was prepared by in-situ reaction method.The microstructure was investigated by optical microscopy(OM),scanning electron microscopy(SEM) equipped with energy-dispersive spectrometry(EDS...An Al-3Ti-0.2C-1RE grain refiner was prepared by in-situ reaction method.The microstructure was investigated by optical microscopy(OM),scanning electron microscopy(SEM) equipped with energy-dispersive spectrometry(EDS) and X-ray diffraction(XRD).The results show that the Al-3Ti-0.2C-1RE grain refiner is composed of α-Al,TiAl3,TiC and Ti2 Al20 Ce phases.Compared with Al-3Ti-0.2C refiner,the morphology of TiAl3 phase is changed and Ti2 Al20 Ce phases form with the addition of RE.Accordingly,the refining performance is improved.The phase forming process of the refiner is as follows: Blocky Ti2 Al20 Ce and fine blocky TiAl3 form in the melt at the initial stage of reaction,then the fine blocky TiAl3 gradually disappears,and the blocky Ti2 Al20 Ce grows bigger with the increase of holding time.The predominant mechanism to synthesize TiC particles is the reaction between high concentration of solute Ti atoms and graphite particles.展开更多
The dynamics of oxidation of cobalt nanoparticles were directly revealed by in situ environmental transmission electron microscopy.Firstly,cobalt nanoparticles were oxidized to polycrystalline cobalt monoxide,then to ...The dynamics of oxidation of cobalt nanoparticles were directly revealed by in situ environmental transmission electron microscopy.Firstly,cobalt nanoparticles were oxidized to polycrystalline cobalt monoxide,then to polycrystalline tricobalt tetroxide,in the presence of oxygen with a low partial pressure.Numerous cavities(or voids) were formed during the oxidation,owing to the Kirkendall effect.Analysis of the oxides growth suggested that the oxidation of cobalt nanoparticles followed a parabolic rate law,which was consistent with diffusion-limited kinetics.In situ transmission electron microscopy allowed potential atomic oxidation pathways to be considered.The outward diffusion of cobalt atoms inside the oxide layer controlled the oxidation,and formed the hollow structure.Irradiation by the electron beam,which destroyed the sealing effect of graphite layer coated on the cobalt surface and resulted in fast oxidation rate,played an important role in activating and promoting the oxidations.These findings further our understanding on the microscopic kinetics of metal nanocrystal oxidation and knowledge of energetic electrons promoting oxidation reaction.展开更多
As lanthanide-doped sodium yttrium flouride(NaYF_4)nanoparticles have great potential inbiomedical applications,their biosafety is important and has attracted significant attention.In the present work,three different ...As lanthanide-doped sodium yttrium flouride(NaYF_4)nanoparticles have great potential inbiomedical applications,their biosafety is important and has attracted significant attention.In the present work,three different sized NaYF_4:Eu^(3+)nanoparticles have been prepared.Liver BRL 3 A cell was used as a cell model to evaluate their biological effects.Cell viability and apoptosis assays were used to confirm the cytotoxicity induced by NaYF_4:Eu^(3+)NPs.Apart from the elevated malondialdehyde(MDA),the decrease of superoxide dismutase(SOD),glutathione peroxidase(GSH-PX)and catalase(CAT)activity indicated reactive oxygen species(ROS)generation,which were associated with oxidative damage.The decrease of mitochondrial membrane potential(MMP)value demonstrated the occurrence of mitochondria damage.Then,release of cytochrome c from mitochondria and activation of caspase-3 confirmed that NaYF_4:Eu^(3+)NPs induced apoptosis was mitochondria damage-dependent.展开更多
Particulate pollution has raised serious concerns regarding its potential impacts on human health in developing countries. However, much less attention has been paid to the threat of haze particles to machinery and in...Particulate pollution has raised serious concerns regarding its potential impacts on human health in developing countries. However, much less attention has been paid to the threat of haze particles to machinery and industry. By employing a state-of-the-art in situ scanning electron microscope compression testing technique, we demonstrate that iron-rich and fly ash haze particles, which account for nearly 70% of the total micron-sized spherical haze particles, are strong enough to generate abrasive damage to most engineering alloys, and therefore can generate significant scratch damage to moving contacting surfaces in high precision machineries. Our finding calls for preventive measures to protect against haze related threat.展开更多
基金Project(51174177)supported by the National Natural Science Foundation of China
文摘An Al-3Ti-0.2C-1RE grain refiner was prepared by in-situ reaction method.The microstructure was investigated by optical microscopy(OM),scanning electron microscopy(SEM) equipped with energy-dispersive spectrometry(EDS) and X-ray diffraction(XRD).The results show that the Al-3Ti-0.2C-1RE grain refiner is composed of α-Al,TiAl3,TiC and Ti2 Al20 Ce phases.Compared with Al-3Ti-0.2C refiner,the morphology of TiAl3 phase is changed and Ti2 Al20 Ce phases form with the addition of RE.Accordingly,the refining performance is improved.The phase forming process of the refiner is as follows: Blocky Ti2 Al20 Ce and fine blocky TiAl3 form in the melt at the initial stage of reaction,then the fine blocky TiAl3 gradually disappears,and the blocky Ti2 Al20 Ce grows bigger with the increase of holding time.The predominant mechanism to synthesize TiC particles is the reaction between high concentration of solute Ti atoms and graphite particles.
基金supported by the National Natural Science Foundation of China(11227403,11327901,51472215,51222202)the National Basic Research Program of China(2014CB932500,2015CB921004)+1 种基金Cyrus Tang Center for Sensor Materials and Applicationsthe resources of the Center of Electron Microscopy of Zhejiang University(ZJU)
文摘The dynamics of oxidation of cobalt nanoparticles were directly revealed by in situ environmental transmission electron microscopy.Firstly,cobalt nanoparticles were oxidized to polycrystalline cobalt monoxide,then to polycrystalline tricobalt tetroxide,in the presence of oxygen with a low partial pressure.Numerous cavities(or voids) were formed during the oxidation,owing to the Kirkendall effect.Analysis of the oxides growth suggested that the oxidation of cobalt nanoparticles followed a parabolic rate law,which was consistent with diffusion-limited kinetics.In situ transmission electron microscopy allowed potential atomic oxidation pathways to be considered.The outward diffusion of cobalt atoms inside the oxide layer controlled the oxidation,and formed the hollow structure.Irradiation by the electron beam,which destroyed the sealing effect of graphite layer coated on the cobalt surface and resulted in fast oxidation rate,played an important role in activating and promoting the oxidations.These findings further our understanding on the microscopic kinetics of metal nanocrystal oxidation and knowledge of energetic electrons promoting oxidation reaction.
基金the Natural Science Foundation of China(21271059,31470961,21603051,21601046, 31500812)Science and Technology Research Project of Higher Education Institutions in Hebei Province(QN2015230,QN2015132)+1 种基金the Natural Science Foundation of Hebei Province(B2015201097,B2016201169)the Science and Technology Support Program of Baoding(15ZF055)
文摘As lanthanide-doped sodium yttrium flouride(NaYF_4)nanoparticles have great potential inbiomedical applications,their biosafety is important and has attracted significant attention.In the present work,three different sized NaYF_4:Eu^(3+)nanoparticles have been prepared.Liver BRL 3 A cell was used as a cell model to evaluate their biological effects.Cell viability and apoptosis assays were used to confirm the cytotoxicity induced by NaYF_4:Eu^(3+)NPs.Apart from the elevated malondialdehyde(MDA),the decrease of superoxide dismutase(SOD),glutathione peroxidase(GSH-PX)and catalase(CAT)activity indicated reactive oxygen species(ROS)generation,which were associated with oxidative damage.The decrease of mitochondrial membrane potential(MMP)value demonstrated the occurrence of mitochondria damage.Then,release of cytochrome c from mitochondria and activation of caspase-3 confirmed that NaYF_4:Eu^(3+)NPs induced apoptosis was mitochondria damage-dependent.
基金supported by the National Natural Science Foundation of China(Grant Nos.5123100551471128 and 51321003)+3 种基金the National Basic Research Program of China("973"Project)(Grant No.2012CB619402)the"111"Project of China(Grant No.B06025)W.Z.Han was supported by the Youth Thousand Talents Plan and the Young Talent Support Plan of XJTU.J.L.support by the NSF DMR-1120901 and DMR-1410636
文摘Particulate pollution has raised serious concerns regarding its potential impacts on human health in developing countries. However, much less attention has been paid to the threat of haze particles to machinery and industry. By employing a state-of-the-art in situ scanning electron microscope compression testing technique, we demonstrate that iron-rich and fly ash haze particles, which account for nearly 70% of the total micron-sized spherical haze particles, are strong enough to generate abrasive damage to most engineering alloys, and therefore can generate significant scratch damage to moving contacting surfaces in high precision machineries. Our finding calls for preventive measures to protect against haze related threat.
