Synthesis of Silicon Nanoparticles and Nanowires by a Nontransferred Arc Plasma System

Silicon nanomaterials were synthesized from solid silicon powder in microsize using a nontransferred arc plasma system. Synthesized silicon nanomaterials were sphere or wire in morphology according to the input power of arc plasma, the flow rate of plasma forming gas, and the collecting position of product. The product was spherical nanoparticles at a high input power for complete evaporation, while it was nanowires at a relatively low input power. The mean diameter of synthesized silicon nanoparticles was increased from 20.52 nm to 40.01 nm by increasing the input power from 9 kW to 13 kW. On the other hand, the diameter of silicon nanowires was controllable by changing the flow rate of plasma forming gas. The mean diameter of silicon nanowires was increased from 16.69 nm to 23.03 nm by decreasing the plasma forming gas flow rate from 15 L/min to 12 L/min

Crystallization of Amorphous Silicon Thin Film by Using a Thermal Plasma Jet

Author's versionAmorphous silicon (a-Si) films deposited on glass substrates were crystallized using a thermal plasma jet and the treated films are analyzed to find the relationship between plasma characteristics and crystallization process conditions. The crystallization process conditions were found to have different optimal operating regimes depending on the nozzle geometry. Numerical analysis of the thermal plasma jets showed that the different operating regimes for crystallization were caused by modifications of the plasma characteristics by the nozzle geometry. It is revealed that a stepped-divergent nozzle is more efficient for the thermal plasma annealing process than the conventional cylindrical one due to the broadened high-temperature region and the lowered axial velocity in the plasma jet.Ministry of Knowledge Economy, Regional Innovation Center for Ecvironmental Technology of Thermal Plasma at Inha Universit

Comparative study of two- and three-dimensional modeling on arc discharge phenomena inside a thermal plasma torch with hollow electrodes

A comparative study between two- and three-dimensional (2D and 3D) modeling is carried out on arc discharge phenomena inside a thermal plasma torch with hollow electrodes, in order to evaluate the effects of arc root configuration characterized by either 2D annular or 3D highly localized attachment on the electrode surface. For this purpose, a more precise 3D transient model has been developed by taking account of 3D arc current distribution and arc root rotation. The 3D simulation results apparently reveal that the 3D arc root attachment brings about the inherent 3D and turbulence nature of plasma fields inside the torch. It is also found that the constricted arc column near the vortex chamber plays an important role in heating and acceleration of injected arc gases by concentrating arc currents on the axis of the hollow electrodes. The inherent 3D nature of arc discharge is well preserved inside the cathode region, while these 3D features slowly diminish behind the vortex chamber where the turbulent flow begins to be developed in the anode region. Based on the present simulation results, it is noted that the mixing effects of the strong turbulent flow on the heat and mass transfer are mainly responsible for the gradual relaxation of the 3D structures of plasma fields into the 2D axisymmetric ones that eventually appear in the anode region near the torch exit. From a detailed comparison of the 3D results with the 2D ones, the arc root configuration seems to have a significant effect on the heat transfer to the electrode surfaces interacting with the turbulent plasma flow. That is, in the 2D simulation based on an axisymmetric stationary model, the turbulence phenomena are fairly underestimated and the amount of heat transferred to the cold anode wall is calculated to be smaller than that obtained in the 3D simulation. For the validation of the numerical simulations, calculated plasma temperatures and axial velocities are compared with experimentally measured ones, and the 3D simulation turns out to be more accurate than the 2D simulation as a result of a relatively precise description of the turbulent phenomena inside the torch using a more realistic model of arc root attachment. Finally, it is suggested that the 3D transient formulation is indeed required for describing the real arc discharge phenomena inside the torch, while the 2D stationary approach is sometimes useful for getting practical information about the time-averaged plasma characteristics outside the torch because of its simplicity and rapidness in computation.Ministry of Science and Technology in Kore

Numerical Computation on the Generation of CH3 and H Radicals by the Thermal Plasma Decomposition of Hydrocarbons

A two-dimensional numerical analysis on the thermal decomposition of methane (CH4) by Ar/H2 thermal plasmas has been carried out using a FLUENT code to nd out the effects of thermal plasma fields on the production rates of CH3 and H radicals during the CH4 decomposition process in a dc arc-jet diamond CVD. In the numerical analysis, the partial di erential equations describing conservations of mass, momentum, and energy as well as mass of individual chemical species are taken into account along with the K-epsilon turbulence model. The numerical calculations are performed in the following consecutive procedure. In the first step, the thermal plasma fields inside a reaction chamber are calculated from the inlet boundary conditions without considering chemical reactions. Uniform profiles of the plasma temperature and velocity at the torch exit are assumed as the inlet boundary conditions in this step. Next in the second calculation step, the chemical kinetic equations, involving 13 species and 25 reactions, are solved in the environment of the calculated two-dimensional plasma fields to give the concentration fields of all chemical species generated in the CH4 decomposition process. The calculated results show that the developed plasma elds inside the reaction chamber strongly depend on the reaction chamber geometry, and significantly affect the concentration fields and generation rates of the decomposed radicals, such as CH3 and H.Supported by the Korea Institute of Science and Technology Evaluation and Planning (KISTEP) in Kore

High Purity Synthesis of Carbon Nanotubes by Methane Decomposition Using an Arc-Jet Plasma

Author's versionHigh purity carbon nanotubes are synthesized by methane decomposition using an arc-jet plasma of high temperature (5000-20000 K). Since the arc-jet plasma process is continuous and easily scalable, it is a promising technique for the large-scale commercial production of carbon nanotubes. In this experimental work, the arc-jet plasma is generated by a dc non-transferred plasma torch, in which a mixture of argon and hydrogen is used as a plasma forming gas and nickel powder as a metal precursor. Morphology, crystallization degree and purity of the carbon nanotubes in the soot produced under various processing conditions are evaluated by using scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and thermogravimetric analysis. From the results of these material analyses, we have found that multi-walled carbon nanotubes of high purity were produced in the optimal operating condition. In addition, the thermal plasma characteristics for the carbon nanotubes growth are discussed from numerical simulation result of the arc-jet plasma

Effects of Anode Nozzle Geometry on Ambient Air Entrainment into Thermal Plasma Jets Generated by Non-Transferred Plasma Torch

The geometrical effects of anode nozzle in a non-transferred plasma torch on air entrainment are examined by measurements of plasma composition using a quadruple mass spectrometry. In addition, the radial and axial distributions of plasma enthalpy, temperature and velocity are measured by using an enthalpy probe method. Two types of anode nozzle geometry, i.e., cylindrical and stepped nozzles, are employed for the torch in this experiment. As a result of gas composition measurements, the new stepped nozzle turns out to produce a thermal plasma jet having lower air contents in it compared with the conventional cylindrical nozzle. The plasma jet produced by the stepped nozzle exhibits higher enthalpy and temperature, especially around the core of the plasma flame due to less intrusion of ambient air. Furthermore, the axial velocity distribution with a slowly changing variation is observed in the stepped nozzle case because of the plasma flow less disturbed by air entrainment. From these experimental results of thermal plasma characteristics and nozzle geometry effects on air entrainment, high quality of coating products are expected in plasma spraying by using the stepped nozzle due to higher plasma enthalpy and temperature, and lower velocity drop along the plasma jet