Argon Arc Plasma Research Articles

Modelling the position of analyte emission maxima in low temperature direct current arc plasma using statistical procedures

In low temperature argon arc plasma, emission spectral lines of different analytes have characteristic radial distributions with emission maxima distributed over a wide plasma region, from the arc axis toward the arc periphery. It was assumed that the occurrence of emission maxima is a result of collective action of factors that control vaporization, dissociation, excitation, ionization and analyte transport. A statistical analysis was used to reveal a correlation between these various factors and a radial position of maximum emission. A regression analysis was used both for predictive and explanatory purposes: a model was built that successfully predicted analyte spatial emission characteristics, based on their physical properties and local plasma parameters, and a relative importance of proposed predictors was estimated.

Ionization effect on arc plasma’s optical diagnosis by the measurement of the refractive index

The effect of arc plasma ionization on its temperature diagnosis by the measurement of the refractive index is discussed. The refractive index of arc plasma in two conditions is compared: 1) only the first ionization is considered and 2) both the first and second ionizations are considered. In order to facilitate plasma temperature reconstruction, two corresponding refractive index models are deduced. For the sake of making this study universal, both the monatomic and dual-atomic molecule arc plasmas are chosen as typical examples for theoretical deduction and analysis. A condition, which can be adopted to estimate whether the second ionization should be considered in temperature reconstruction, is proposed. Finally, an argon arc plasma is chosen as an example for experiment, and the experimental results match well with the theoretical analysis. This study is crucial to arc plasma's optical diagnosis, which is based on the measurement of the refractive index.

Dynamic Behavior of an Atmospheric Argon Gliding Arc Plasma

The dynamic behavior of an argon gliding arc discharge has been investigated by means of electrical diagnostics and high-speed photography. Two different arc breakdown regimes are identified: initial breakdown in the narrowest electrode gap and restrike breakdown on the electrode surface. It is also found that the anode and cathode arc roots exhibit different motion behaviors.

Diagnostics of Three-Dimensional Temperature Distribution of Ar Arc Plasma by Spectrum Tomography Technique

In this paper, a new technology which can be used to diagnose 3-D temperature distribution of argon arc plasma is proposed. Compared with current technologies, two aspects have been improved. First, a new hybrid reconstruction technique [max-entropy, least square, and flatness reconstruction technique (MLFRT)] is presented as an algorithm system, where the numerical simulation of the MLFRT has been realized. The results show that the MLFRT has good convergence, stability, and efficiency. Second, two orthographic double-wavelength light paths have been designed in the experimental setup, which can collect intensity data in real time. Based on these data, we reconstruct the emission coefficient using the MLFRT. Then, a spectral line relative intensity method was chosen to calculate the 3-D temperature distribution, where the spectral analysis of argon arc plasma was introduced. This new technology can acquire good result by just two orthographic intensity data sets. Therefore, the experimental system is simple, and the experimental cost is low. The result is beneficial to understand the working principle of argon arc plasma, improving the level of craftsmanship. It also has good application advantages over other 3-D flow field testing, such as density field, pressure field, velocity field, etc. It shows great academic and economic value.

Nanostructure and mineral composition of trabecular bone in the lateral femoral neck: Implications for bone fragility in elderly women

Despite interest in investigating age-related hip fractures, the determinants of decreased bone strength in advanced age are not clear enough. Hitherto it has been obscure how the aging process affects the femoral neck nanostructure and composition, particularly in the lateral subregion of the femoral neck, which is considered as a fracture-initiating site. The femoral bone samples used in this study were obtained at autopsy in 10 women without skeletal disease (five younger: aged 20–40 years, and five elderly: aged 73–94 years). Atomic force microscopy (AFM) was applied to explore the mineral grain size in situ in young vs. old trabecular bone samples from the lateral femoral neck. The chemical compositions of the samples were determined using inductively coupled plasma optical emission spectroscopy and direct current argon arc plasma optical emission spectrometry. Our AFM study revealed differences in trabecular bone nanostructure between young and elderly women. The mineral grain size in the trabeculae of the old women was larger than that in the young (median: 95 vs. 59 nm), with a particular bimodal distribution: 45% were small grains (similar to the young) and the rest were larger. Since chemical analyses showed that levels of calcium and phosphorus were unchanged with age, our study suggests that during aging the existing bone mineral is reorganized and forms larger aggregates. Given the mechanical disadvantage of large-grained structures (decreased material strength), the observed nanostructural differences contribute to our understanding of the increased fragility of the lateral femoral neck in aged females. Moreover, increasing data on mineral grains in natural bone is essential for advancing calcium-phosphate ceramics for bone tissue replacement.

Influence of pressure distribution on flow field temperature reconstruction

This research proposes an issue that has previously been omitted in flow field temperature reconstruction by optical computerized tomography (OCT). To prove that it is not reasonable to always assume an isobaric process occurs when OCT is adopted to obtain the temperature distributions of flow fields, a propane-air flame and an argon arc plasma are chosen as two practical examples for experiment. In addition, the measurement of the refractive index is achieved by moiré deflection tomography. The results indicate that the influence of pressure distribution on temperature reconstruction is a universal phenomenon for various flow fields. Hence, the condition that can be introduced to estimate when an isobaric process can no longer be assumed is presented. In addition, an equation is offered to describe the temperature reconstruction imprecision that is caused by using the supposed pressure instead of the practical pressure.

Absorption characteristic of arc plasma in the infrared region**Project supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 10804052), the Postgraduate Innovation Foundation of Jiangsu Province and the Key Postgraduate Planting Plan of Nanjing University of Science and Technology, China.

In this paper, argon arc plasma is chosen as an example to study the absorption characteristics of arc plasma in the infrared region. Firstly, the phase and the attenuation constants are deduced for the given temperature, pressure and probe wavelength regions. Based on those constants, the dependence of the attenuation constant on the temperature and pressure in the vicinity of a certain probe wavelength is found. Then, theoretical analysis and discussion are conducted. Maximal absorption occurs at the position where the contributions of neutral particles and electrons come to a balance in a physical point of view, which may provide some measures to take for decreasing or controlling the plasma absorption of electromagnetic waves.

A model for arc plasma's optical diagnosis by the measurement of the refractive index

A model, which introduces the ionization degree of plasma, is deduced to reconstruct the temperature and electron number density distributions for arc plasmas via the measurement of the refractive index. The rationality, applicability and superiority of the model are analyzed and discussed theoretically. To experimentally verify whether the model is rational and feasible, an argon arc plasma is chosen as a practical example for experiment, while the measurement of the refractive index is achieved by moiré deflection tomography with the probe wavelength 635 nm. The distribution and imprecision of the reconstructed temperature results indicate that the model is reasonable, feasible and dependable. Besides, the factors which may cause the imprecision of the reconstructed temperature are also analyzed and proposed.

A uniform description of the gas and plasma flow fields' refractive index

In this paper, a definition called the equivalent particle number density is introduced to describe and unify the refractive indexes of the gas and plasma flow fields. As a result, the uniform refractive index model can be described by three independent parameters—the specific composition, the probe wavelength and the equivalent particle number density. To verify whether the uniform description is feasible, the argon gas and argon arc plasma flow fields are chosen as two practical examples for experiment, while the refractive index measurements are achieved by moiré deflection tomography with the probe wavelength 635 nm. The distribution and the order of magnitude of the equivalent particle number density which is reconstructed via the new model, match well with the theoretically estimated results. This agreement implies that the uniform description is reasonable and effective.

Electron Density and Temperature Measurement by Stark Broadening in a Cold Argon Arc-Plasma Jet at Atmospheric Pressure

Determination of both the electron density and temperature simultaneously in a cold argon arc-plasma jet by analyzing the Stark broadening of two different emission lines is presented. This method is based on the fact that the Stark broadening of different lines has a different dependence on the electron density and temperature. Therefore, a comparison of two or more line broadenings allows us to diagnose the electron density and temperature simultaneously. In this study we used the first two Balmer series hydrogen lines Hα and Hβ for their large broadening width. For this purpose, a small amount of hydrogen was introduced into the discharge gas. The results of the Gigosos–Cardenoso computational model, considering more relevant processes for the hydrogen Balmer lines, is used to process the experimental data. With this method, we obtained reliable electron density and temperature, 1.88 × 1015 cm−3 and 13000 K, respectively. Possible sources of error were also analyzed.

Quasi-neutrality and local thermodynamical equilibrium in atmospheric presure arc discharges

The atmospheric pressure Tungsten Inert Gas (TIG) arc plasma in argon is studied combining results from emission spectroscopy temperature maps with composition data and transport parameters available from literature. Two arc currents are considered and maps are obtained for the Debye number, the number of particle in the Debye sphere, which shows values of the order of 10 or less in the core region of these arcs. This low number puts into serious question the plasma quasi-neutrality. It is striking that this circumstance occurs where Local Thermodynamical Equilibrium (LTE) is usually assumed in these discharges. It is shown that TIG arcs violate the quasi-neutrality requirements and, as such, these discharges are called 'plasma' quite improperly. Differently from previously published works, the starting point of the discussion is the experimental two-dimensional temperature maps.

An efficient and inexpensive method for the production of multi-wall carbon nano tubes by the thermal plasma route

An extended argon arc plasma reactor has been utilised for efficiently producing multi-walled carbon nano tubes (MWCNT) with an inexpensive raw material such as the calcined petroleum coke. In this investigation, CPC powder was dry mixed with 2.5 wt %, Ni catalyst in a ball mill and the resulting homogeneous raw material mixture was heat treated in a graphite crucible in a vacuum argon arc plasma reactor for the duration of 30 minutes. It was noted that carbon nano tubes (CNTs) were deposited on a relatively cooler portion of the plasma reactor, with a yield of 15 wt %, with respect to the total weight of the charge. The extensive characterization of the carbon nano-tubes was carried out through micro-Raman, X-ray diffraction and transmission electron microscopy techniques. The XRD studies on the CNTs, produced by the above method showed 100% peak at d002 value of 3.39 A and other peaks of 4-H graphite. The d- band and g- band reflections observed in the Raman spectrum of CNTs also showed graphite as a major and cubic diamond as a minor phase. The TEM studies on the plasma processed and purified CNTs, showed aspect ratio of 15 to 16 and an average diameter of 3.4 nm.

Modelling Study on the Plasma Flow and Heat Transfer in a Laminar Arc Plasma Torch Operating at Atmospheric and Reduced Pressure

A modelling study is performed to investigate the characteristics of both plasma flow and heat transfer of a laminar non-transferred arc argon plasma torch operated at atmospheric and reduced pressure. It is found that the calculated flow fields and temperature distributions are quite similar for both cases at a chamber pressure of 1.0 atm and 0.1 atm. A fully developed flow regime could be achieved in the arc constrictor-tube between the cathode and the anode of the plasma torch at 1.0 atm for all the flow rates covered in this study. However the flow field could not reach the fully developed regime at 0.1 atm with a higher flow rate. The arc-root is always attached to the torch anode surface near the upstream end of the anode, i.e. the abruptly expanded part of the torch channel, which is in consistence with experimental observation. The surrounding gas would be entrained from the torch exit into the torch interior due to a comparatively large inner diameter of the anode channel compared to that of the arc constrictor-tube.

Simulation of the atomic and ionic densities in the ionization layer of a plasma arc with a binary cathode

A physical model was developed to study the behaviour of the cathode material evaporated from a thoriated tungsten cathode of an atmospheric-pressure argon plasma arc. The densities of tungsten and thorium atoms and ions in the ionization layer were obtained, and the influence of the different physical processes on the evaporated cathode material was established. It was found that almost all of the neutral atoms evaporated from the cathode are ionized near the beginning of the ionization layer, i.e. near the boundary between the sheath and the ionization layer. Thorium ions are concentrated in a 4 µm region near the beginning of this layer, while tungsten ions are found in a region of 9 µm. The contribution of the electric force to the velocity of ions is the dominant contribution only near the beginning of the ionization layer. At a distance from the interface between the sheath and the ionization layer greater than 3.8 µm in the case of thorium ions, and greater than 5 µm in the case of tungsten ions, the contributions of the density gradient forces and the frictional forces are more important than the electric force contribution.

Applicability of moiré deflection tomography for diagnosing arc plasmas

The argon arc plasma whose central temperature, 1.90x10(4) K, is used as a practical example for an experiment to research the applicability of moiré deflection tomography in arc plasma flow-field diagnosis. The experimental result indicates that moiré deflection of the measured argon arc plasma is very small, even smaller than that of a common flame with the maximal temperature of nearly 1.80x10(3) K. The refractive-index gradient in moiré deflection tomography mainly contributes to the temperature gradient in essence when the probe wavelength and pressure are certain in plasma diagnosis. The applicable temperature ranges of moiré deflection tomography in the argon arc plasma diagnosis are given with the probe wavelength 532 nm at 1 atm in certain measuring error requirements. In a word, the applicable temperature range of moiré deflection tomography for arc plasma diagnosis is intimately related to the probe wavelength and the practical measuring requirements.

S0502-3-3 アーク電極を用いた溶融塩電解法(機能性流体工学の先端融合化(3))

Molten salt electrolysis, which is free from carbon dioxide emissions, is often used. Although no carbon dioxide emissions are expected, huge amounts of CO_2 are generated in actual molten salt electrolysis because graphite electrodes are used as anodes. We are developing a CO_2-free process using arc electrodes. Alumina (Al_2O_3) with cryolite (Na_3AlF_6) and aluminum fluoride (AlF_3) are melted and electrolysis reaction is realized in a graphite crucible by argon plasma arc. Production of aluminum is confirmed although its current efficient is not so high.

Dependence of Arc Plasma Dispersion Capability on its Temperature

The relationship between the dispersion capability and the temperature of argon arc plasma at 1 atm is deduced in view of the plasma's refractive index equation. The results indicate that argon arc plasma has a normal dispersion and its dispersion capability is nonlinear to the plasma's temperature in a wide range of temperature and wavelength region. According to the results of numerical calculation, the preferred optical methods are believed to be suitable for the diagnosis of argon arc plasma in different temperature regions.

Heat flux characteristics in an atmospheric double arc argon plasma jet

In this study, the axial evolution of heat flux excited by a double arc argon plasma jet impinging on a flat plate is determined, while the nonstationary behavior of the heat flux is investigated by combined means of the fast Fourier transform, Wigner distribution, and short-time Fourier transform. Two frequency groups (<1 and 2–10 kHz) are identified in both the Fourier spectrum and the time-frequency distributions, which suggest that the nature of fluctuations in the heat flux is strongly associated with the dynamic behavior of the plasma arc and the engulfment of ambient air into different plasma jet regions.

Evolution of Cathodic Arc Roots in a Large-Scale Magnetically Rotating Arc Plasma

The behavior of the cathode arc root is one of the most fundamental phenomena associated with arc discharges. The formation of isolated multiple cathodic roots and the transition from discrete spots to a diffuse cathodic attachment in an argon arc plasma at 1 atm have been observed with short exposure time ICCD imaging in our attempt to generate a uniform large-area plasma, using magnetically rotating arc plasma.

Investigation of a Novel Large Area Dispersed Arc Plasma Source With Time-Resolved ICCD Imaging

Unsaturated time-resolved end-on images of argon arc plasma at 1 atm were captured by an intensified charge-coupled device equipped with a narrowband interference filter to evidence the homogeneity of the arc plasma dispersed by increasing the axial magnetic field. A relatively uniform diffuse current sheet was identified established between the concentric electrodes of our specified experimental geometry.