Papers by Keyword: Arc-Discharge

Abstract: The carbon material was synthesized by the plasma-arc method at the buffer gas pressure of 3 Torr. The material has physical properties different from the properties of the material synthesized at pressure of 25 Torr and higher. The low pressure of buffer gas leads to formation of materials consisting of carbon nanoparticles with average size lower than 10nm. The nanoparticles have form of carbon globules, which consist of the graphite-like structure. This structure is the composition of the stacked, twisted and closed nanofragments of graphene. The dominating interlayer distance in the structure is 0.4 nm. The dominating size of crystallinity La is 2.7nm. The graphite-like structure allows to enhance the electrical conductivity in compare with the material synthesized at buffer gas pressure of 25 Torr and higher. Nevertheless the conductivity of the material is significantly lower than the conductivity of pure graphite because of the contact resistance arising from the presence of the outer layer of amorphous carbon on some globules and the presence of the globules of fully amorphous carbon.

Abstract: This paper reports a brief outlook of carbon nanotubes (CNT) history, synthesis methods as well as natural carbon sources such as camphor powder, turpentine, eucalyptus, palm, neem, coconut, castor, olive, corn, sesame oil, palm olein, waste cooking palm oil and waste chicken fat.

Abstract: BiFeO₃ coated ferromagnetic Fe nanocapsules is synthesized by arc-discharging method. Typical HRTEM images show that the nanocapsules form in a core-shell structure. X-ray photoelectron spectrum (XPS) and X-ray diffraction (XRD) reveal that the core is ferromagnetic Fe, while the shell is BiFeO₃/Bi₂Fe₄O₉.The reflection loss R of less than -10 dB was obtained for the whole frequency within the 2-18GHz range by choosing an appropriate layer thickness between 1.0mm and 7.0mm. An optimal reflection loss of -21.5 dB was reached at 10.6 GHz with an absorber thickness of 2.0mm. It is worth noticing that the BiFeO₃ coated Fe nanocapsules have two absorption peaks below -10 dB at each thickness layer ranging from 4.0nm to 7.0nm, which means the composites nanocapsules absorber simultaneously are able to absorb microwaves in different band of several GHz.

Abstract: B4C/C coated Co nanocapsules were prepared by arc-discharging a Co-B amorphous alloy. The structure, morphology and surface composition as well as magnetic properties were investigated by X-Ray diffraction, High Resolution Transmission Electron Microscopy and XPS photoelectron spectrum as well as Vibrating Sample Magnetometer, respectively. The results show the as-prepared nanoparticles form in a core¬¬¬-shell structure with the size of nanoparticles in range of 20-100nm, the thickness of the shell is about 3-10nm. The core is Co grains, while the shell is B4C/C compound. That B4C coated Co nanoparticles form in a core¬¬¬-shell structure ascribed to Co as catalysts accelerating reaction between B with C ionize in the arc-discharge course. This structure can prevent Co nanoparticles from oxidation and agglomeration. A saturation magnetization of Ms=75.6 Am2/kg and a coercive force of Hc=20.1 kA/m are achieved for as-prepared nanocapsules by VSM. For as–prepared nanocapsules, the saturation magnetization is reduced and coercive force of is enhanced while Comparing with Co block. The increase coercive force for as-prepared nanoparticles can be mainly ascribed to size of particles diminished and the domain-wall depinned in the multi-domain particles.

Abstract: Al₂O₃ coated polyhedral Fe nanocapsules were prepared by arc-discharging a Fe-Al(8at%Al) alloy. High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy, and network analyzer were employed to investigate the microstructures, compositions and electromagnetic properties (2-18GHz). The reflection loss R(dB) of the nanocapsules reaches to -50.5dB at 7.9GHz with a 3mm thickness, and EM absorption properties(RL<-20dB) in the 5.2~16.1GHz range with thickness range of 1.67-4.7mm. The excellent Microwave-absorption properties of as-prepared nanocapsules are ascribed to shape anisotropy and core/shell structure.

Abstract: Influence of arc discharge to the contact strip of carbon-carbon composites was orthogonally studied on the HST-100 tribo-tester under electric current, which simulated working conditions of the pantograph-wire system used in electric railway. The regression equation between specific wear rate and arc discharge were obtained and analyzed through the non-linear regression and orthogonal design. The results of the experiments show that a power function between specific wear rate and arc discharge was obtained. Microstructure and phase composition were observed and analyzed by scanning electron microscope(SEM), energy dispersive X-ray spectrum(EDS) and temperature sensor. The results revealed that the arc discharge dissipation seriously affects tribological characteristics of the carboncarbon composites. The temperature of some local contact points beyond their melting point with the electric arc heat effect, and give rise to the desposite carbon and friber carbon were vaporazated, which form the lubrication film on the wear surface, and with the augmant of the arc discharge, the area of lubrication film of carbon was decrease. Therefore, the main wear form of the arc erosion of the carbon-carbon composites is evaporate erosion and material transfer.

Abstract: A new type of antiferromagnetic CoAl2O4 coated ferromagnetic Co solid solution is synthesized by arc-discharging. Typical HRTEM images show that the nanocapsules form in a core-shell structure. The size of the nanocapsules is in range of 10-90 nm and the thickness of the shell is about 3-10 nm. X-ray photoelectron spectrum (XPS) and X-ray diffraction (XRD) reveal that the core consists of Co solid solution, while the shell is CoAl2O4. The magnetic field and temperature dependence of magnetizations confirm that the Co solid solution nanocapsules are basically in the ferromagnetic state below Curie temperature. In addition, the antiferromagnetic order occurs with Neél temperature TN of about 5 K. The saturation magnetization of Ms = 76.1 Am2/kg and the coercive force of Hc= 23.28 kA/m are achieved at room temperature for the Co solid solution nanocapsules.

Abstract: Friction and wear tests of stainless steel rubbing against copper-impregnated metalized carbon with electric current were carried on the pin-on-disc tester. The result indicates that arc discharge occurs in the process of experiments, and the intensity of arc discharge of interface increases with increasing of electric current and sliding velocity. As increasing of the arc discharge intensity, friction coefficient shows a tendency of slightly increase. While the rate of copper-impregnated metalized carbon material increase significantly with the increase of arc discharge intensity. Through observing the worn surface morphology of pin samples, it is found that the abrasive wear is dominant at small arc discharge due to worn particles and arc ablation craters, but arc erosion and oxidation wear are the main wear mechanisms in condition of large arc discharge due to arc discharge and its producing high temperature. The materials transfer of contact couple occurs in the process of friction and wear.

Abstract: The growth mechanism of Onion-like fullerenes (OLFs) synthesized by arc discharge in liquid benzene was discussed. HRTEM was employed to characterize the morphologies and microstructures of the products. Results showed that the typical OLFs were highly crystallized with uniform diameter of 10-30nm. The growth of OLFs depended on the appropriate temperature gradient and quenching zone provided by the bubbles. The aromatic debris could act as graphite fragments composed of hexagonal carbon rings. The reducing of dangling bonds on the edges of graphite fragments would lower the energy of the system, resulting in formation of a close-caged structure at suitable temperature gradient by the auto-curling of graphite fragments. Based on the impact of the innermost core shape, such as C60 shape, quasi-spherical or polyhedral hollow concentric OLFs was formed. Adding ferrocene, ferrocene directly influenced the morphology and yield of OLFs.

Abstract: Geometry of electrodes, distance between them, work atmosphere and ambient temperature are the important factors, which determine quantity and variety of structures synthesized via arc discharge. Usually, electrodes of different cross-section are placed away from each other, allowing a large vapor stream directed into the reactor inside to be obtained. Generally, the anode is thinner than the cathode; it heats up to a high temperature, sublimates and supplies the carbon vapor required for nanoparticle synthesis. In contrast to this commonly used approach, when electrode dimensions are appropriately chosen and electrodes placed closely together, temperature interaction between them becomes considerable, discharge area constrains and hot electrodes can be used as heaters for the evaporation of materials of high melting point.