Formation of amorphous Co-Nb system by mechanical alloying(MA)in the composition range of Co_(25)Nb_(75)-Co_(70)Nb_(30) was studied by X-ray diffraction.Magnetic properties of the mechanically alloyed Co_(70)Nb_(30) p...Formation of amorphous Co-Nb system by mechanical alloying(MA)in the composition range of Co_(25)Nb_(75)-Co_(70)Nb_(30) was studied by X-ray diffraction.Magnetic properties of the mechanically alloyed Co_(70)Nb_(30) powder were measured.The variation in H_(c) curve with milling time can be explained by two-stage mechanism involved in the milling process.The results show that the amorphous powder prepared by MA is of good soft magnetic properties.展开更多
The microstructure, electrical properties, and density of Dy2O3-doped ZnO-based varistor ceramics, prepared using high-energy ball milling （HEBM） and sintered at 800℃, were investigated by increasing the cooling ra...The microstructure, electrical properties, and density of Dy2O3-doped ZnO-based varistor ceramics, prepared using high-energy ball milling （HEBM） and sintered at 800℃, were investigated by increasing the cooling rate in the order of H （slow cooling in furnace） → L （cooling in furnace） → K （cooling in air）. With the increase in cooling rate, the grain size and density decreased, the breakdown voltage （VImA/mm） increased, and the nonlinear coefficient （α） and leakage current （IL） exhibited extremum. The sample with the cooling type L showed the best properties with the breakdown voltage of 2650 V/ram, o：of 20.3, IL of 5.2 laA, and density of 5.42 g/cm^3. The barrier height （ФB）, donor concentration （Nd）, density of the interface states （Nd）, and barrier width （ω） all exhibited extremum during the alteration in cooling rate. The different relative amount of Bi-rich phase and its distribution as well as the characteristic parameters of grain boundary, resulting from the alteration of cooling rate, led to the changes in the properties of varistor ceramics.展开更多
Amorphous Nb_(62.5)Si_(37.5) and Nb_(75)Si_(25) alloys were produced from mixtures of elemental Nb and Si powders by mechanical alloying(MA).The structural changes of mechanically alloyed powders were monitored by x-r...Amorphous Nb_(62.5)Si_(37.5) and Nb_(75)Si_(25) alloys were produced from mixtures of elemental Nb and Si powders by mechanical alloying(MA).The structural changes of mechanically alloyed powders were monitored by x-ray diffraction.It was found that NbSi_(2),intermetallic compound was formed in the initial stage of MA of or Nb_(62.5)Si_(37.5) or Nb_(75)Si_(25) powders.With continued milling,the mixtures of intermetallic NbSi_(2) and elemental Nb transformed into amorphous Nb-Si alloys(Nb_(62.5)Si_(37.5) or Nb_(75)Si_(25)).The slow interdiffusion of Nb and Si and the slower diffusion of silicon atoms to niobium matrix than that of niobium atoms to silicon matrix were suggested to be responsible for the formation of intermetallic NbSi_(2).The amorphization of 3NbSi_(2)+7Nb mixtures(or NbSi_(2)+5Nb mixtures)is believed to be controlled by material transfer,which moves composition of line intermetallic NbSi2 off stoichiometry,and causes the matrix of elemental Nb deformed.展开更多
Nano-crystalline elemental iron powder was successfully formed by high-energy ball grinding.The x-ray diffraction,transmission electron microscopy and Mdssbauer spectroscopy were employed to follow the structure chang...Nano-crystalline elemental iron powder was successfully formed by high-energy ball grinding.The x-ray diffraction,transmission electron microscopy and Mdssbauer spectroscopy were employed to follow the structure changes in the process of mechanical grinding with milling time.The thermal stability of nanocrystalline iron powder was also studied by differential scanning calorimetry.The results showed that the grain size reduces drastically at the initial stage of the milling and reaches 6nm after 40h milling.The broadening of Mdssbauer spectrum is attributed to the large fraction of iron atoms existing at the interfaces for the powder milled.展开更多
Silicon carbon nitride (SiCN) nanowires, nanorods and nanotubes have gained much attention due to their excellent field emission and photoluminescence properties. These nanostructures were usually grown using catalyst...Silicon carbon nitride (SiCN) nanowires, nanorods and nanotubes have gained much attention due to their excellent field emission and photoluminescence properties. These nanostructures were usually grown using catalysts at high temperature (800–1000 °C). In this paper, synthesis of SiCN nanostructures at a temperature less than 500°C is reported. Various kinds of SiCN nanostructures were synthesized using microwave plasma chemical vapor deposition method. Gas mixtures of CH4, H2 and N2 were used as precursors and Si chips were inserted in the sample holder at symmetrical positions around the specimen as additional Si sources. Metallic gallium was used as the liquid medium in a mechanism similar to vapor-liquid-solid. Morphologies of the resultant were characterized by field emission scanning electron microscopy. Energy dispersive spectrometry and X-ray photoelectron spectroscopy were used to characterize their compositions and bonding states.展开更多
基金Supported by the National Natural science Foundation of China.
文摘Formation of amorphous Co-Nb system by mechanical alloying(MA)in the composition range of Co_(25)Nb_(75)-Co_(70)Nb_(30) was studied by X-ray diffraction.Magnetic properties of the mechanically alloyed Co_(70)Nb_(30) powder were measured.The variation in H_(c) curve with milling time can be explained by two-stage mechanism involved in the milling process.The results show that the amorphous powder prepared by MA is of good soft magnetic properties.
基金This work is financially supported by the National Natural Science Foundation of China (No. 50471045)Shanghai Nano-technology Promotion Center (No. 0452nm026).
文摘The microstructure, electrical properties, and density of Dy2O3-doped ZnO-based varistor ceramics, prepared using high-energy ball milling （HEBM） and sintered at 800℃, were investigated by increasing the cooling rate in the order of H （slow cooling in furnace） → L （cooling in furnace） → K （cooling in air）. With the increase in cooling rate, the grain size and density decreased, the breakdown voltage （VImA/mm） increased, and the nonlinear coefficient （α） and leakage current （IL） exhibited extremum. The sample with the cooling type L showed the best properties with the breakdown voltage of 2650 V/ram, o：of 20.3, IL of 5.2 laA, and density of 5.42 g/cm^3. The barrier height （ФB）, donor concentration （Nd）, density of the interface states （Nd）, and barrier width （ω） all exhibited extremum during the alteration in cooling rate. The different relative amount of Bi-rich phase and its distribution as well as the characteristic parameters of grain boundary, resulting from the alteration of cooling rate, led to the changes in the properties of varistor ceramics.
基金Supported by the National Natural Science Foundation of Cliina.
文摘Amorphous Nb_(62.5)Si_(37.5) and Nb_(75)Si_(25) alloys were produced from mixtures of elemental Nb and Si powders by mechanical alloying(MA).The structural changes of mechanically alloyed powders were monitored by x-ray diffraction.It was found that NbSi_(2),intermetallic compound was formed in the initial stage of MA of or Nb_(62.5)Si_(37.5) or Nb_(75)Si_(25) powders.With continued milling,the mixtures of intermetallic NbSi_(2) and elemental Nb transformed into amorphous Nb-Si alloys(Nb_(62.5)Si_(37.5) or Nb_(75)Si_(25)).The slow interdiffusion of Nb and Si and the slower diffusion of silicon atoms to niobium matrix than that of niobium atoms to silicon matrix were suggested to be responsible for the formation of intermetallic NbSi_(2).The amorphization of 3NbSi_(2)+7Nb mixtures(or NbSi_(2)+5Nb mixtures)is believed to be controlled by material transfer,which moves composition of line intermetallic NbSi2 off stoichiometry,and causes the matrix of elemental Nb deformed.
基金Supported by the National Natural Science Foundation of China。
文摘Nano-crystalline elemental iron powder was successfully formed by high-energy ball grinding.The x-ray diffraction,transmission electron microscopy and Mdssbauer spectroscopy were employed to follow the structure changes in the process of mechanical grinding with milling time.The thermal stability of nanocrystalline iron powder was also studied by differential scanning calorimetry.The results showed that the grain size reduces drastically at the initial stage of the milling and reaches 6nm after 40h milling.The broadening of Mdssbauer spectrum is attributed to the large fraction of iron atoms existing at the interfaces for the powder milled.
基金Supported by the National Natural Science Foundation of China (Grant No. 60606004)
文摘Silicon carbon nitride (SiCN) nanowires, nanorods and nanotubes have gained much attention due to their excellent field emission and photoluminescence properties. These nanostructures were usually grown using catalysts at high temperature (800–1000 °C). In this paper, synthesis of SiCN nanostructures at a temperature less than 500°C is reported. Various kinds of SiCN nanostructures were synthesized using microwave plasma chemical vapor deposition method. Gas mixtures of CH4, H2 and N2 were used as precursors and Si chips were inserted in the sample holder at symmetrical positions around the specimen as additional Si sources. Metallic gallium was used as the liquid medium in a mechanism similar to vapor-liquid-solid. Morphologies of the resultant were characterized by field emission scanning electron microscopy. Energy dispersive spectrometry and X-ray photoelectron spectroscopy were used to characterize their compositions and bonding states.
