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Rapid and non-destructive quantification of low-Z elements (Si, Al, Mg, Na, F, and B) via external (in air) PIGE in coal samples.

Present article discusses the role of plasma parameters on the morphology of nanocrystalline powders of lanthanum hexaboride (LaB6) synthesized by arc plasma gas-phase condensation method. The nanocrystalline powders so obtained were used to fabricate pellet-shaped cathodes of 5 mm diameter and thickness of 1 mm. Moreover, thermal plasma plume was used for sintering the cathodes and achieve desired densification. Prior to fabrication of cathodes, the synthesized powders of LaB6 were characterized using X-ray diffraction, Raman spectroscopy, and transmission electron microscopy to investigate phase purity and morphological properties. Finally, an indigenously developed thermionic emission experimental set-up was used to record thermionic emission current obtained from LaB6 cathode at different temperatures. Richardson Dushman equation was used to find out the work function of the cathode under investigation.

A computational model for nucleation and growth of iron (II) oxide nanoparticle (IONP) in thermal plasma has been developed. A nondimensional form of the aerosol general dynamic equations (GDEs) along with a discrete volume sectional model assumption is used to numerically solve the coupled system of GDEs. The variation in supersaturation ratio and the mean particle diameter of IONPs with respect to temperature across the plasma reactor has been presented. The scatter plot showing the distribution of particle number density of certain size across the reactor chamber is shown. In silico molecular docking study was performed to reveal the putative interaction of the IONPs with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) virus. The results revealed significant binding affinity of IONPs with 6LZG (spike receptor-binding domain complexed with its receptor ACE2) and 5RH4 (main protease) of SARS-COV-2 by forming hydrogen and hydrophobic bonds with nearby amino acid residues. The interactions of IONPs are associated with the conformational changes in the protein which could be used to treat and control SARS-CoV-2 infection.

Novel features of arc plasma devices with thermionic and thermo-chemical cathodes and development of associated thermal plasma process reactors are investigated from device design and application point of view. Different types of plasma torches and open arcs, their fundamental differences in architecture, jet behavior, operational constraints, and evolution of interesting electromagnetic forces inside them have been probed. Investigation of instabilities in arcs through direct real-time imaging of arc path using fast photography and impact of powder loading on such instabilities are presented. Development of low power air plasma torches delivering large volume high-temperature plasma jet with long penetration depth has been investigated together with an estimation of hazardous NOx, produced from such devices during operation. Interesting attributes of various types of thermal plasma reactors including plasma spray chemical vapor deposition (CVD) reactors for thick and dense coating, reactors for generation of H-OH plasma, radio frequency (RF) thermal plasma reactors for the synthesis of nanostructures, and air plasma gasifier reactors for environment-friendly mitigation of municipal solid waste (MSW) and electronic wastes have been presented. Coke bed air plasma gasifiers are specially investigated for their important technological aspects. Experimental results are presented with simulation supports for enhanced understanding, wherever necessary.

Plasma spray deposition of Al2O3 is a well-established technique for thick ceramic coatings on various substrates to shield them from corrosion and wear. Owing to its high hardness, aluminum oxide is known to protect stainless steel substrates from wear. However, the plasma process requires optimization for desired coating thickness and adhesion strength. It is also necessary to understand the sensitivity of friction and wear resistance of the deposited coating on exposed environment for evaluation of service life. The study offers comprehensive investigation on plasma process parameters for the development of strongly adherent aluminium oxide coatings on SS 316L substrate. Impact of environment like dry air and dry nitrogen on tribological properties of the coatings was also investigated. Dense adherent coatings of alumina could be deposited on SS 316L at a plasma power of 20 kW with an intermediate bond coat of NiCrAlY to enhance the adhesion properties. The effects of stand-off distance and bond coat thickness on adhesion strength were additionally examined. Further, the coatings were characterised for phase composition, microstructure, microhardness and wear resistance potential. Reciprocating wear tests of the coatings were carried out using ball on disc reciprocating tribometer at different loading conditions (5, 10 and 15 N) at constant (5 Hz) sliding frequency. Unlike the coefficient of friction (COF), wear volume was found to increase with an increase in normal load. These adherent coatings revealed promising properties for the applications where the tribological failure of SS 316L in dry air or dry nitrogen environment is to be controlled.

The simultaneous presence of hazardous chemicals and pathogenic microorganisms in wastewater is tremendously endangering the environment and human health. Therefore, developing a mitigation strategy for adequately degrading toxic compounds and inactivating/killing microorganisms is urgently needed to protect ecosystems. In this paper, the synergetic effects of the photocatalytic activity of TiO2 and Cu-TiO2 nanoparticles (NPs) and the oxidation processes of non-thermal atmospheric pressure plasma (NTAPP) were comprehensively investigated for both the inactivation/killing of common water contaminating bacteria (Escherichia coli (E. coli)) and the degradation of direct textile wastewater (DTW). The photocatalytic NPs were synthesized using the hydrothermal method and further characterized employing field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), ultraviolet-visible diffuse reflection spectroscopy (UV-Vis DRS) and photoluminescence (PL). Results revealed the predominant presence of the typical anatase phase for both the flower-like TiO2 and the multipod-like Cu-TiO2 structures. UV-Vis DRS and PL analyses showed that the addition of Cu dopants reduced the bandgap and increased oxygen defect vacancies of TiO2. The inactivation of E. coli in suspension and degradation of DTW were then examined upon treating the aqueous media with various plasma alone and plasma/NPs conditions (Ar plasma, Ar + O-2 plasma and Ar + N-2 plasma, Ar plasma + TiO2 NPs and Ar plasma + Cu-TiO2 NPs). Primary and secondary excited species such as OH, O, H and N-2* generated in plasma during the processes were recognized by in situ optical emission spectrometry (OES) measurements. Several other spectroscopic analyses were further employed to quantify some reactive oxygen species (ROS) such as OH, H2O2 and O-3 generated during the processes. Moreover, the changes in the pH and electrical conductivity (EC) of the solutions were also assessed. The inactivation of bacteria was examined by the colony-forming unit (CFU) method after plating the treated suspensions on agar, and the degradation of organic compounds in DTW was further validated by measuring the total organic carbon (TOC) removal efficiency. All results collectively revealed that the combinatorial plasma-photocatalysis strategy involving Cu-TiO2 NPs and argon plasma jet produced higher concentrations of ROS and proved to be a promising one-step wastewater treatment effectively killing microorganisms and degrading toxic organic compounds.

Unusually, high electro-thermal efficiency, observed under certain cooling rates of the anode boundary layer in a typical non-transferred arc argon plasma torch, is reported. The behavior is reproducible at different arc currents and gas flow rates. To understand the origin of such behavior, total arc voltage, which bears an overall signature of the internal arc dynamics, has been analyzed using tools of dynamical analysis such as frequency space behavior, phase space dynamics, correlation dimension and Lyapunov exponent under different rates of anode cooling. Simultaneous emission spectroscopic investigation of the plasma temperature at the nozzle exit and fast photographic study of the anode boundary layer have been carried out for better insight. Observed significant variation in the dominant frequency components with change in cooling rates gives concrete signature of onset on new dynamics induced by anode cooling. Vivid differences in the dynamics are brought out in phase space representations. True natures of the dynamics are obtained through the estimated values of correlation dimension and Lyapunov exponents.

Plasma temperature, density and arc dynamics have been investigated in underwater arc discharges under different anodic environments. Distinct differences in the behaviour with different anode material and rich variety of interesting dynamics have been directly revealed through fast photography and emission spectroscopic analysis. Four different anode materials of high technological relevance, namely SS304, copper, zircaloy, and P91 [ASTM387-Gr91] have been used as anode material. Instabilities in the plasma channel with alternate expansion and contraction zones, highly prominent magnetic pumping near the anode arc root, formation of strong anode jet, dynamic branching of arcs, formation of distinct shock boundaries, and coexistence of multiple anode and cathode arc roots are some of the interesting features observed. Observation of Hα line and absence of Hβ line in the emission spectra is an interesting observation. Emission lines, characteristic to chosen anode material, have been used in determining the axial plasma temperature using a modified Boltzmann plot technique, suitable for spatially unstable arc discharges and pulsating arcs. Electron density inside the plasma has been determined from the width of Stark broadened Lorentzian profile of Hα line. Typical temperatures for discharges with P91, Zr, SS304 and Cu anodes are estimated around 8159 K, 14525 K, 6151 K, and 10534 K respectively under similar operating conditions. Respective electron densities per m3 in the discharge zone are estimated to be 2.97 × 1023, 3.76 × 1023, 0.41 × 1023 and 6.21 × 1023. Estimated plasma coupling parameter finds the discharge in the regime of weakly non-ideal plasma.

In the synthesis of alloy nanoparticles (NPs) via arc evaporation and fast quenching, the composition of the synthesized NPs differs significantly from that of the precursor. The properties of the NPs formed following evaporation of a copper–nickel anode by a helium arc are investigated using a nucleation model coupled to the thermal and flow fields derived from a magneto-hydrodynamic simulation of the arc, and experimentally. Results are obtained for three different Cu:Ni precursor compositions, 10:90, 50:50 and 90:10 at%. The synthesized particles are spherical with different size distributions and have a higher concentration of Cu than the precursor in all three cases, in contrast to previous observations, but in accordance with the predictions of the model. Emission spectroscopic measurements of copper and nickel lines indicate that the concentration of atomic copper in the plasma region near the anode is much higher than that of the nickel, in accordance with the predictions of the model. The higher vapour pressure of copper compared to nickel, and its higher activity in the alloy precursor (anode), immersed in a self-consistent thermal and flow field maintained by the transferred arc are found to play a critical role. The thermodynamic, radiative and transport properties of the helium plasma contaminated with evaporated precursor are important in determining the thermal and flow fields.

Electron emission properties of lanthanum hexaboride are dependent on the crystal structure as well as stoichiometric ratio of boron and lanthanum. Present research deals with the influence of carbon diffusion on the stoichiometric LaB6 synthesized using arc plasma gas phase condensation process. Noncrystalline LaB6 has been synthesized using arc plasma at different plasma powers viz 2–3.4 kW. Further, an inclusion of carbonaceous species from the graphite anode with increasing plasma power and its correlation with stoichiometry has been elucidated. X-ray photo-electron spectroscopic technique has been used for the identification of surface chemistry of the synthesized powders and more effectively to infer the stoichiometry i. e. ratio of B:La in the samples synthesized with increasing plasma in put power. The influence of plasma parameters on the work function of the synthesized nanoparticles has also been elucidated using Ultraviolet Photoelectron Spectroscopy (UPS).

In the present study, we report the morphological tuning of carbonaceous nanocrystalline lanthanum hexaboride (LaB6) using an arc plasma route. It was possible to obtain different morphologies, namely: pebbles, rods and sheets, on a nano-scale by means of plasma assisted vapour phase growth and by varying the plasma current. At elevated plasma currents, as a consequence of graphite electrodes being used in the arc geometry, the synthesized product was obtained in the form of carbonaceous LaB6 having a high degree of crystallinity. Detailed morphological analysis using electron microscopy has revealed that nanorods and nanosheets of carbonaceous LaB6 can be grown by elevating the plasma currents. The field emission (FE) current was found to be enhanced from 200 μA cm−2 to 660 μA cm−2 for the hierarchical structure of nanosheets as compared to that of nanopebbles at a much reduced turn-on potential. A stable FE current is an important feature exhibited by all these LaB6 nanostructures.

High temperature synthesis process of microcrystalline and nanocrystalline (LaCe)B6 by Self-propagating High temperature Synthesis (SHS) and arc plasma gas phase condensation method respectively have been investigated in the present work. These are rapid and economically viable processes used for the synthesis of technologically important refractory hexaborides. Microcrystalline powders of (LaCe)B6 were synthesized using SHS process, starting from oxide precursors of lanthanum, cerium, and boron. The powders so obtained were used as a precursor to obtain nanocrystalline (LaCe)B6 using thermal plasma route. The thermal plasma synthesis was carried out using nitrogen and argon plasmas, respectively. In-situ plasma diagnostics was used to identify evaporated species and to determine plasma temperature during formation of nanocrystalline (LaCe)B6 using optical emission spectroscopy. Further, an effect of plasma temperature on the structural and optical properties of as synthesized nanocrystalline (LaCe)B6 was investigated using XRD analysis, Raman spectroscopy and X-ray Photoelectron spectroscopy. Thorough investigation of morphological and structural properties of synthesized nanocrystalline (LaCe)6 has been carried out using transmission electron microscopy. Finally, field effect electron emission properties of the microcrystalline and nanocrystalline product were investigated and current density, turn on field, stability of emission performance were determined.

Liquid metal Lead-Lithium (PbLi) flow channels in Indian LLCB (lead lithium cooled ceramic breeder) Test Blanket Module consist of a sequence of parallel channels which are fed from a common inlet header. Thin radial-toroidal vertical plates known as partition plates at the central plane perpendicular to the applied magnetic field are primarily envisaged to enhance the mechanical strength of high aspect ratio electrically coupled parallel poloidal channels. In that case the partition plates are acting as an internal Hartmann wall and they have significant effects on velocity profile, pressure drop and heat transfer characteristics at ITER relevant applied magnetic field (B0 = 4 T). Three dimensional numerical simulation is performed in a model of full scale LLCB variant to study the effects of these partition plates on various flow field variables. Axial velocity near the thin partition wall and side wall jet structures are found to get significantly. Magneto-hydraulic pressure drop and redistribution of flow rates due to the presence of partition plates are assessed by comparing the results with no partition wall. Thermofluid simulation is carried out to obtain the temperature distribution of various structures for a given heat load profile based on neutronic estimation. The effects of buoyancy force on thermofluid flow profile in channels with high temperature gradient are also presented.

Numerical simulation of 3D MHD flow in a full scale variant of India propose Lead-Lithium cooled Ceramic Breeder (LLCB) Test Blanket Module(TBM) for ITER program has been carried out at high Hartmann number (Ha=17,845). The model geometry takes into account the integrated First wall (FW) which is provisioned with internal helium cooling channels for dual cooling purpose. The MHD effects on steady state velocity profile, modification of wall electric potential distribution due to electrical coupling of parallel channels has been analysed. Flow rate distribution in electrically coupled parallel channels has been obtained for a fixed PbLi flow rate in the common inlet header. Steady state thermofluid analysis has been performed using user defined heat density data obtained from neutronic estimation in similar variant. Prediction of thermal hot spots in various structural walls and sharing of heat load by coupled PbLi and First wall helium cooling circuit is presented.

Looking at the increasing scope of plasma processing of materials surface, here we present the development and diagnostics of a microwave assisted Electron Cyclotron Resonance (ECR) plasma system suitable for surface modification of polymers. Prior to the surface-treatment, a detailed diagnostic mapping of the plasma parameters throughout the reactor chamber was carried out by using single and double Langmuir probe measurements in Ar plasma. Conventional analysis of I-V curves as well as the elucidation form of the Electron Energy Distribution Function (EEDF) has become the source of calibration of plasma parameters in the reaction chamber. The high energy tail in the EEDF of electron temperature is seen to extend beyond 60 eV, at much larger distances from the ECR zone. This proves the suitability of the rector for plasma processing, since the electron energy is much beyond the threshold energy of bond breaking in most of the polymers. Nylon 6 is used as a representative candidate for surface processing in the presence of Ar, H

Assuming a seven species model of nitrogen plasma, thermodynamic and transport properties are calculated under thermal equilibrium and non-equilibrium conditions. Species densities, mass densities, specific heat, enthalpy, viscosity, thermal conductivity, collision frequency, and electrical conductivity are studied as a function of temperature, pressure, and different degrees of thermal and chemical non-equilibrium. Effect of both electrons and ions are considered in the shielding for charged–charged interactions under shield coulomb potential and obtained results are found to be in excellent agreement with experimentally obtained results, especially at higher temperatures. Accounting up to third ionized states, results are presented with temperatures ranging from 300 to 50,000 K, the ratio of electron temperature (Te) to the heavy particle temperature (Th) ranging from 1 to 20 and the pressure ranging from 0.1 to 7 atmospheres. Under atmospheric pressure, results obtained for thermodynamic equilibrium (Te = Th) are compared with number of published results under similar conditions. Computed properties under different degrees of chemical non-equilibrium are also discussed.

Measurements of temperature patterns in an inductively coupled plasma (ICP) have been carried out experimentally. Plasma torch was operated at different RF powers in the range of 3–14 kW at near atmospheric pressure and over a wide range of sheath gas flow rate (3–25 lpm). Measurements were made at five different axial positions in ICP torch. The chordal intensities were converted into a radial intensity profile by Abel Inversion technique. Typical radial temperature profile shows an off-axis temperature peak, which shifts toward the wall as the power increases. Temperatures in the range of 6000–14,000 K were recorded by this method. The temperature profiles in the plasma reactor were simulated using computational fluid dynamics (CFD). A good agreement was found between the CFD predictions of the flow and temperature pattern with those published in the literature as well as the temperature profiles measured in the present work. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3647–3664, 2014

Multi-component diffusion coefficients are calculated for a seven species model of nitrogen plasma under thermal non-equilibrium following the first order perturbation technique of Chapman and Enskog. Binary, thermal, thermal ambipolar, general and general ambipolar diffusion coefficients are presented over electron temperatures ranging from 300 to 50,000 K and thermal non-equilibrium parameter (Te/Th) ranging from 1 to 5. Considering large volume of data, binary, general and general ambipolar diffusion coefficients are presented only for atmospheric pressure. Thermal and thermal ambipolar diffusion coefficients are presented for pressures ranging from 0.1 to 2 atm. The results are compared with published experimental and theoretical data. Necessary electronic levels, associated transition data and collision integrals are collected from recent literature. Details of behaviour of each of the coefficients are presented.

Nanophase alumina is synthesized in an atmospheric pressure radio frequency (RF) plasma reactor through melting, evaporation, and vapor phase nucleation technique. A specially designed high-pressure RF plasma reactor fitted with an indigenously built RF plasma torch converts commercially available micrometer size alumina chunks into spherical nanophase alumina in a single step under ambient quenching conditions without use of any additional quenching gas. Obtained powder contains mixed phases of α and δ -alumina as revealed by X-ray diffraction studies. Transmission Electron Microscopy analyses exhibit very small particle size (peak at 15 nm), narrow size distribution (half width ~ 24 nm), zero agglomeration, and good crystallinity. Obtained particle characteristics together with the high purity owing to inherent electrode-less feature of the RF discharge are suitable for important technological applications including fabrication of high-power ceramic laser gain media like Y3Al5O12 (YAG) from composites of Al2O3 and Y2O3. Characteristics of the synthesized alumina are compared with that of nanoalumina synthesized in atmospheric arcs.

Wide ranges of technological applications involve arc plasma devices as the primary plasma source for processing work. Recent findings exhibit the existence of appreciable thermal non-equilibrium in these so-called thermal plasma devices. Commercially available magnetohydrodynamic codes are not capable of handling such systems due to unavailability of non-equilibrium thermodynamic and transport property data and self-consistent models. A recipe for obtaining mechanical design of arc plasma devices from numerical simulation incorporating two-temperature thermal non-equilibrium model is presented in this article with reference to the plasma of the mixture of molecular gases like nitrogen and oxygen. Such systems are technologically important as they correspond to the plasma devices operating with air, oxygen plasma torches in cutting industries and plasma devices using nitrogen as shielding gas. Temperature field, associated fluid dynamics and electrical characteristics of a plasma torch are computed in a systematic manner to evaluate the performance of a conceived design using a two-fluid CFD model coupled with a two-temperature thermodynamic and transport property code. Important effects of different nozzle designs and plasma gases obtained from the formalism are discussed. Non-equilibrium thermodynamic properties are computed using modified two-temperature Saha equations and transport properties are computed using standard Chapman–Enskog approach.

The synthesis of nanocrystalline Nd2O3 through an inductively coupled radiofrequency thermal plasma route is reported. Unlike in conventional synthesis processes, plasma-synthesized nanoparticles are directly obtained in a stable hexagonal crystal structure with a faceted morphology. The synthesized nanoparticles are highly uniform with an average size around 20 nm. The nanoparticles are characterized in terms of phase formation, crystallinity, morphology, size distribution, nature of chemical bonds and post-synthesis environmental effects using standard characterization techniques. X-ray diffraction, transmission electron microscopy, and scanning electron microscopy are used for structural and morphological studies. The thermo-gravimetric technique, using a differential scanning calorimeter, is used to investigate the purity of phase. Fourier transform infrared spectroscopy is used to investigate the nature of existing bonds. The optical response of the nanoparticles is investigated through the electronic transition of Nd(3+) ions in its crystalline structure via UV-visible spectroscopy. The presence of defect states and corresponding activation energies in the nanocrystalline Nd2O3 compared to those of the precursors are studied using thermoluminescence.

The stability of dc non-transferred arc plasma jets and their internal structures is investigated through fast photography, emission spectroscopy, and arc dynamics under different operating conditions. A novel method to explore structures inside extremely intense hot plasma jet is conceived and applied for the first time to investigate arc plasma jets. The study revealed distinct interesting structures and their evolution inside the plasma jet, apparently not reported earlier. The associated fundamental mechanisms are identified from direct experimental evidences. Respective steady state jet characteristics with and without air entrainment are obtained from computational fluid dynamic simulation. Arc root motion, air entrainment, and interaction between electromagnetic and fluid dynamic body forces are found to result in a variety of interesting dynamics and structures inside the plasma jet under different operating conditions. Observed behaviors are notably different in argon, nitrogen, and air plasma. While no unusual structures are found over a range of lower flow rates, interesting structures evolve at higher flow rates. Statistical behavior of these structures is found to have a significant dependence on the gas flow rate and torch power. Apart from air entrainment in the downstream, observed isolated temperature islands inside the jet in the upstream have potential to affect particle trajectory, physical processes, and process chemistry in a significant manner.

Thermodynamic and transport properties are computed for a 17 species model of nitrogen-oxygen plasma under different degrees of thermal non-equilibrium, pressures and volume ratios of component gases. In the computation electron temperatures range from 300 to 45,000 K, mole fractions range from 0.8 to 0.2, pressures range from 0.1 atmosphere to 5 atmospheres, and thermal nonequilibrium parameters (Te/Th) range from 1 to 20. It is assumed that all the electrons follow a temperature Te and the rest of the species in the plasma follow a temperature Th. Compositions are calculated using the two temperature Saha equation derived by van de Sanden et al. Updated energy level data from National Institute of Standards and Technology (NIST) and recently compiled collision integrals by Capitelli et al., have been used to obtain thermodynamic and transport properties. In the local thermodynamic equilibrium (LTE) regime, the results are compared with published data and an overall good agreement is observed.

A two-temperature, axi-symmetric, chemical non-equilibrium model has been developed for an oxygen-plasma cutting torch in two dimensions to obtain distributions of different plasma quantities inside the torch. Apart from mass, momentum and potential conservation equations, separate energy balance equations are considered for electrons and heavy particles. The κ–e model has been used to account for turbulence. Non-equilibrium properties required for fluid dynamic simulations are obtained from a non-equilibrium property code that includes chemical non-equilibrium. The results show distributions of temperature, velocity, pressure, potential, current density and different species densities inside the plasma torch for an arc current of 200 A. Plasma pressure inside the torch varies from several atmospheres to near-atmospheric pressure. It has been observed that the electron and the heavy particle temperatures differ less near the axis of the torch and appreciably near the wall. Interesting features, observed for other investigated quantities, found consistent with the recent experimental observations are discussed.

Synthesis of yttrium oxide nanoparticles in a specially designed radio frequency thermal plasma reactor is reported. Good crystallinity, narrow size distribution, low defect state concentration, high purity, good production rate, single-step synthesis, and simultaneous formation of nanocrystalline monoclinic and cubic phases are some of the interesting features observed. Synthesized particles are characterized through X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, thermo-luminescence (TL), and Brunauer–Emmett–Teller surface area analysis. Polymorphism of the nanocrystalline yttria is addressed in detail. Synthesis mechanism is explored through in-situ emission spectroscopy. Post-synthesis environmental effects and possible methods to eliminate the undesired phases are probed. Defect states are investigated through the study of TL spectra.

The growth process of nanoparticles and nanowires of AlN by thermal-plasma-assisted gas phase condensation reaction has been investigated by optical emission spectroscopy. The concentrations of the reacting precursors in the plasma have been correlated to the crystalline phases of nanoparticles of AlN found from X-ray diffraction analysis. The size and morphology of the nanoparticles have been studied by transmission electron microscope investigations of as-synthesized powder at a set of reactor parameters, which included arc current, reactor pressure, and standoffs of the arc column. An attempt has been made to correlate the growth of AlN to that of the precursor density present in the plasma reaction zone

Currently, research on accelerator driven subcritical systems (ADSS) is gaining significance due to their high safety levels and extremely attractive potential in terms of both thorium utilization and nuclear waste transmutation. While high energy and high current proton beams are being built worldwide, intensive efforts are being undertaken in parallel towards the development of complex lead bismuth eutectic target systems. The major focus is directed towards understanding of the material compatibility and detailed thermohydraulic simulation of the liquid metal flow. The requisite heat flux is being deposited using innovative and easily controllable heat sources. This paper presents an experimental and simulation study to explore the potential of using dc arc plasma torches as a tailored heat source for thermohydraulic simulation of proton beam–target interaction in such systems.

Investigations using in situ precursor spectroscopy during the growth of nanoparticles of iron oxide by thermal plasma induced gas phase condensation method have been shown to be useful for correlating the size of nanoparticles with existing plasma parameters. The relative abundance of ionized Fe species inside the plasma plume is seen to directly establish the relation between particle size, arc current, arc length, and ambient pressure of the reacting oxygen gas. The argon plasma from a transferred arc reactor is made to impinge on the anode that is allowed to vaporize and react with oxygen. The spectral line profiles of both Ar and Fe along the plasma column during the synthesis of nanoparticles have been proved to be useful in understanding the growth mechanism. Band intensities of FeO molecular states indicated the inverse relation with particle sizes that have been correlated to the two competitive processes in which energy is released, namely: 1) one involving the radiative transition and 2) the other that of the growth by coagulation. Atomic Boltzmann plots are used for estimating the temperatures of the zones, whereas particle sizes have been inferred using transmission electron microscopic measurements

Recent studies have shown that use of direct current arc plasma jet is a promising technique for bulk generation of nanostructures. This paper presents a dynamical study on such systems during the synthesis and attempts to correlate the role of inherent arc fluctuations on the properties of nanostructures produced. Different fluctuations detected during the process of nanosynthesis have been characterized in terms of behavior in real time, phase space, frequency space, fractal dimension, Lyapunov exponent of evolution and diagnosed to be chaotic. For the first time, it has been shown that size of nanoparticles are strongly related to the Lyapunov exponent of inherent voltage fluctuations realized during the synthesis. Interesting features of such dependences under different process conditions have been brought out. Since chaotic systems are controllable, the study brings out the possibility of development of new size control strategies for nanosynthesis.

Fluctuations in atmospheric pressure arc plasma devices play important role in plasma processing applications. A full knowledge and control over such fluctuations can effectively lengthen lifetime and drastically improve performance and reliability. Dynamical analyses of associated experimental fluctuating signals established existence of chaotic dynamics in such devices. However, the origin of such fluctuations remained unexplained so far and no theoretical investigation is carried out to explore underlying physics behind such phenomena. This work addresses development of a general theory for such fluctuations in atmospheric pressure arc plasma devices in terms of various nondimensional parameters using basic governing equations and presents the result of application of the theory to various important experiments reported in literature. Various aspects of dynamic behavior have been investigated through the study of coefficients appearing in the nonlinear amplitude equation. It has been shown that the theory supports arc current and gas flow rate as the major externally available controlling parameters in agreement with experiment. Theory exhibits period doubling route to chaos under variation of control parameter as observed experimentally. System includes catastrophic behavior for some operating range. The whole work is divided into two parts. This paper presents part I: development of theory for such fluctuations using basic equations of the dynamics and study of system behavior.

The results of an application of the developed nonlinear theory for atmospheric pressure arc plasma instability to various experiments are presented in this paper. Most of the important experiments on atmospheric pressure arc plasma instability reported in literature are addressed. In all cases, a good match has been observed between experiment and theory. General nature of the theory to explain observed instability features is brought out in this paper.

Understanding of the basic nature of arc root fluctuation is still one of the unsolved problems in thermal arc plasma physics. It has direct impact on myriads of thermal plasma applications being implemented at present. Recently, chaotic nature of arc root behavior has been reported through the analysis of voltages, acoustic and optical signals which are generated from a hollow copper electrode arc plasma torch. In this paper we present details of computations involved in the estimation process of various dynamic properties and show how they reflect chaotic behavior of arc root in the system.

Particle feeding is used in the most important applications of radio frequency (r.f.) thermal plasmas like synthesis of nanoparticles and particle spheroidization. The study reports an in-situ investigation of radial distribution of temperature in such devices using yttrium ion emission lines under different rates of particle loading during synthesis of yttria nanoparticles. A number of interesting facts about the response of r.f. plasma to the rate of particle loading, hitherto unknown, are revealed. Observed phenomena are supported with experimental data from fast photographic experiments and actual synthesis results. The use of the Abel inversion technique together with simultaneous multi-track acquisition of emission spectra from different spatial locations using a CCD based spectrometer allowed us to extract accurate distribution of temperature inside the plasma in the presence of inherent instabilities. The temperature profiles of this type of plasma have been measured possibly for the first time while particles are being fed into the plasma. Observed changes in the temperature profiles as the particle feed rate increases are very significant. Reaction forces resulting from particle evaporation, and increased skin depth owing to the decrease in electrical conductivity in the edge region are proposed as the two different mechanisms to account for the observed changes in the temperature profile as the powder feed rate is increased. Quantitative analyses supporting the proposed mechanisms are presented.

A detailed investigation on the neutral-neutral and neutral-ion collision integrals is reported for Y2O3-Ar plasma, an important system of functional material with unique properties having a wide range of processing applications. The calculated integrals are indispensible pre-requisite for the estimation of transport properties needed in CFD modelling of associated plasma processes. Polarizability plays an important role in determining the integral values. Ambiguity in selecting appropriate polarizability data available in the literature and calculating effective number of electrons in the ionized species contributing to the polarizability are addressed. The integrals are evaluated using Lennard-Jones like phenomenological potential up to (l,s) = (4,4). Used interaction potential is suitable for both neutral-neutral and neutral-ion interactions. For atom-parent ion interactions, contribution coming from the inelastic resonant charge transfer process has been accounted properly together with that coming fr...

Calorimetric measurements have been carried out in air to measure the heat flux delivered by an impinging plasma jet on a substrate placed perpendicular to the jet axis. The total heat flux delivered to the substrate has been resolved spatially using both Gaussian and exponential profiles with the profile constants determined from inversion of experimental data. It has been observed that the exponential profile gives a slightly better match with the experimental results compared to a Gaussian profile, which is more commonly used to represent concentrated energy flux beams such as plasma, electron or laser beams. Simultaneously, the conservation equations of mass, momentum and energy for the same plasma plume have been numerically solved to compute the stagnation heat flux profiles with conduction, convection, diffusion and radiation as the basic transport processes. An isothermal homogeneous, cylindrical, plasma column approximation has been applied in a modified form to take into account the energy lost due to radiation. The results from the simulation are compared with the experimental results. The degree of validity of the simplifying assumptions made in the analysis and their contribution to the discrepancy between the theory and the experiment are discussed.

Chaotic systems are now frequently encountered in almost all branches of sciences. Dimension of such systems provides an important measure for easy characterization of dynamics of the systems. Conventional algorithms for computing dimension of such systems in higher dimensional state space face an unavoidable problem of enormous storage requirement. Here we present an algorithm, which uses a simple but very powerful technique and faces no problem in computing dimension in higher dimensional state space. The unique indexing technique of hypercubes, used in this algorithm, provides a clever means to drastically reduce the requirement of storage. It is shown that theoretically this algorithm faces no problem in computing capacity dimension in any dimension of the embedding state space as far as the actual dimension of the attractor is finite. Unlike the existing algorithms, memory requirement offered by this algorithm depends only on the actual dimension of the attractor and has no explicit dependence on the number of data points considered.

In free burning as well as in stabilized arc columns, the inherent movement of arc root results in fluctuation in arc voltage. A full knowledge and control over the arc root dynamics can effectively lengthen the life time, drastically improve performance and reliability in arc plasma devices. In this paper, we experimentally investigate the fluctuating voltage signals generated from an atmospheric pressure arc discharge produced in a hollow electrode plasma torch. For the first time, analysis of these signals reveal them to exhibit chaotic behavior. The present analysis is supported with real time behavior, phase portraits, power spectra and Lyapunov exponents. Dependence of system behavior on various control parameters is also investigated. This approach is interesting in the sense that it can lead to better understanding of physics for future researches on arc plasma jets and related devices.

Experimental investigation of cathode erosion in atmospheric pressure hafnium-electrode plasma torches is reported under different plasma environments along with the results of numerical simulation. Air, nitrogen and oxygen are the plasma gases considered. Distinct differences in the erosion features in different plasmas are brought out. Cathode images exhibiting a degree of erosion and measured erosion rates are presented in detail as a function of time of arc operation and arc current. Physical erosion rates are determined using high precision balance. The changes in the surface microstructures are investigated through scanning electron microscopy (SEM). Evolution of cathode chemistry is determined using energy dispersive x-ray spectroscopy (EDX). Numerical simulation with proper consideration of the plasma effects is performed for all the plasma gases. The important role of electromagnetic body forces in shaping the flow field and the distribution of pressure in the region is explored. It is shown that the mutual interaction between fluid dynamic and electromagnetic body forces may self-consistently evolve a situation of an extremely low cathode erosion rate.

Summary form only given. There is increasing evidences of deviations from thermal and chemical equilibrium in highly constricted arcs. Although, equilibrium models of such arcs inside cutting torches have been studied, non-equilibrium models including the region above the work-piece are rare. In this paper, we present a two-temperature chemical non-equilibrium model of an oxygen cutting-torch to find the distribution of velocity, temperature, current, potential and pressure over a work-piece. We consider the plasma to consist of two sub-gases: one made of electrons and the other made of all other heavy particles including ions, atoms and molecules. While all the electrons have a temperature Te, all other heavy particles follow a different temperature Th for the same location. Together with mass continuity and momentum equations, separate energy conservation equations are solved for electrons and heavy particles. Apart from electromagnetic body force terms in the momentum equations and joule heating terms in the energy equation, additional energy exchange terms are introduced in the energy equations to account for transfer of energy from one sub-gas to the other. A dedicated property routine that includes chemical as well as temperature non-equilibrium is used to supply properties required for fluid dynamic simulations. Results are presented for different arc currents and geometries. Boundary conditions, appropriate for the model, are discussed.