Yanyang He

Hydrogen storage for carbon nanotubes synthesized by the pyrolysis method using lanthanum nickel alloy as catalyst

We have investigated the adsorption of hydrogen of multiwall carbon nanotubes synthesized by the pyrolysis method using a lanthanum nickel hydrogen storage alloy as a catalyst. The mechanism of carbon nanotubes synthesized using a La–Ni alloy catalyst is discussed. In the hydrogen atmosphere and high-temperature process of carbon nanotube preparation, the LaNi5 alloy particle may be changed into an intermetallic compound of Ni and La by the analysis of the x-ray diffraction patterns and energy-dispersive x-ray spectroscopy of the nanotubes samples using a La–Ni alloy as a catalyst. The H2 uptake capacity of the carbon nanotubes using a La–Ni alloy catalyst is about 5 wt % through to the pressure of 10 MPa. Using a La–Ni alloy as a catalyst increases the effect of chemistry adsorption in the H2 adsorption of the La–Ni alloy catalyzed carbon nanotubes. The P–C–T curve has an approximate plateau. The La–Ni alloy catalyzed carbon nanotubes have better activation for H2 uptake and larger hydrogen uptake in com...

Electron spin resonance of carbon nanotubes prepared under two kinds of inert gas ambient

The nanotubes were prepared by the dc arc-discharge method in helium and argon gas ambient under controlled pressure, and subsequently purified by oxidation in air. The room temperature electron spin resonance (ESR) spectra of purified carbon nanotubes prepared under different inert gases and their pressure were measured. The dependence of the ESR line shape, linewidth, g-value of the nanotubes on the inert gases and their pressures is found and discussed.

Structural, morphological and optical properties of C60 cluster thin films produced by thermal evaporation under argon gas

C60 cluster thin films were obtained by thermal evaporation under argon atmosphere. The surface morphology, optical absorption characteristics and structure of these films have been investigated. The ultraviolet-visible optical absorption spectrum of this C60 film is obviously different from that of the film obtained under vacuum conditions. The position and intensity of absorption peaks of the films grown in argon are modified compared with the film grown in vacuum. The bandgap energy changes from 2.02?eV to 2.24?eV. IR analyses show no evidence of chemical change. The x-ray diffraction pattern reveals the existence of a mixture of face-centred cubic and hexagonal close-packed phases. The collisions of C60 molecules and buffer gas molecules are discussed. We also found the surface particles of these C60 cluster films are larger and sharper than those of C60 films prepared in vacuum by the observation of atomic force microscopy (AFM). This may be advantageous for using C60 for electron field emission.

The preparation of carbon-coated iron nanocrystals produced from Fe2O3-containmg composite anode in arc discharge

Abstract Using an Fe2O3-containing composite anode instead of an Fe-containing composite anode in the Kratschmer-Huffman carbon arc method, carbon-coated Fe (not Fe2O3) nanocrystals are produced both in the soot on the reactor walls and in the cathode deposits. The encapsulates also contain a little iron carbide, but do not contain iron oxides, as identified by transmission electron microscopy ( TEM ) and X-ray diffraction (XRD). As compared with Ni2O3- and Co2O3-containing composite anodes, the action of the Fe2O3-containing composite anode is unique. When the Fe2O3 contents in the composite graphite rod for the carbon arc nanocrystal production are increased in the range 5-33 wt.%, the effect on the structure and diameter distribution of the iron nanocrystals is investigated. The diameter distribution of iron nanocrystals is about 1–30 nm. The effect of helium pressure in the range 80–680 torr on the yield of C60/70 in carbon soot produced from the composite graphite rod has also been examined. We present a novel result about the relationship of C60/70 yields and helium gas pressure using a composite anode differing remarkably from the result using a homogeneous graphite anode in arc discharge.

Morphology and characteristics of C60 thin films grown in argon atmosphere by thermal evaporation

The surface morphology, structure, and optical absorption characteristics of C60 thin films grown in argon atmosphere by thermal evaporation have been studied. X-ray diffraction studies reveal a mixture phase of face-centered-cubic and hexagonal-close-packed phases for this film. Infrared analyses show no evidence of chemical change. The observations of atomic force microscopy of C60 thin films grown in argon atmosphere found that surface particles are larger and sharper than that grown in vacuum, thus C60 thin films grown in argon atmosphere may be advantageous to using C60 for electron field emission. Ultraviolet-visible optical absorption spectrum of this film in the range of wavelength from 200 to 600 nm is very different than that of the film obtained under vacuum conditions. The position and intensity of absorption peaks are obviously changed compared to vacuum C60 thin film. The band gap energy of this film also changes from 2.02 to 2.24 eV compared to the film prepared under vacuum.The surface morphology, structure, and optical absorption characteristics of C60 thin films grown in argon atmosphere by thermal evaporation have been studied. X-ray diffraction studies reveal a mixture phase of face-centered-cubic and hexagonal-close-packed phases for this film. Infrared analyses show no evidence of chemical change. The observations of atomic force microscopy of C60 thin films grown in argon atmosphere found that surface particles are larger and sharper than that grown in vacuum, thus C60 thin films grown in argon atmosphere may be advantageous to using C60 for electron field emission. Ultraviolet-visible optical absorption spectrum of this film in the range of wavelength from 200 to 600 nm is very different than that of the film obtained under vacuum conditions. The position and intensity of absorption peaks are obviously changed compared to vacuum C60 thin film. The band gap energy of this film also changes from 2.02 to 2.24 eV compared to the film prepared under vacuum.

The dielectric time domain differential spectroscopy of polyethylene terephthalate

Studies of dielectric time domain differential spectroscopy in thermodynamically equilibrium state for polyethylene terephthalate (PET) film samples are reported. The experimental results show that the response function is F/sub n/=exp[-(t//spl tau//sub n/)/spl alpha/(n)] with and two typical value of /spl alpha//sub n/ are /spl alpha//sub n/=1 and /spl alpha//sub n/=1/2 in low temperature condition; the line of time domain spectroscopy split up in high temperature condition and the /spl tau//sub n/(n>1) of slow response can increase as the temperature rising. A model that free diffusion of the unequilibrium binding space charge can describe the discharge relaxation process of PET film is suggested.