Plasma Gas Flow Rate Research Articles

Parameters Optimization of Plasma Hardening Process Using Genetic Algorithm and Neural Network

Plasma surface hardening process was performed to improve the performance of the AISI 1045 carbon steel. Experiments were carried out to characterize the hardening qualities. A predicting and optimizing model using genetic algorithm-back propagation neural network (GA-BP) was developed based on the experimental results. The non-linear relationship between properties of hardening layers and process parameters was established. The results show that the GA-BP predicting model is reliable since prediction results are in rather good agreement with measured results. The optimal properties of the hardened layer were deduced from GA. And through multi optimizations, the optimum comprehensive performances of the hardened layer were as follows: plasma arc current is 90 A, hardening speed is 2.2 m/min, plasma gas flow rate is 6. 0 L/min and hardening distance is 4. 3 mm. It concludes that GA-BP mode developed in this study provides a promising method for plasma hardening parameters prediction and optimization.

Understanding the Flowing Atmospheric-Pressure Afterglow (FAPA) Ambient Ionization Source through Optical Means

The advent of ambient desorption/ionization mass spectrometry (ADI-MS) has led to the development of a large number of atmospheric-pressure ionization sources. The largest group of such sources is based on electrical discharges; yet, the desorption and ionization processes that they employ remain largely uncharacterized. Here, the atmospheric-pressure glow discharge (APGD) and afterglow of a helium flowing atmospheric-pressure afterglow (FAPA) ionization source were examined by optical emission spectroscopy. Spatial emission profiles of species created in the APGD and afterglow were recorded under a variety of operating conditions, including discharge current, electrode polarity, and plasma-gas flow rate. From these studies, it was found that an appreciable amount of atmospheric H(2)O vapor, N(2), and O(2) diffuses through the hole in the plate electrode into the discharge to become a major source of reagent ions in ADI-MS analyses. Spatially resolved plasma parameters, such as OH rotational temperature (T(rot)) and electron number density (n(e)), were also measured in the APGD. Maximum values for T(rot) and n(e) were found to be ~1100 K and ~4×10(19) m(-3), respectively, and were both located at the pin cathode. In the afterglow, rotational temperatures from OH and N(2)(+) yielded drastically different values, with OH temperatures matching those obtained from infrared thermography measurements. The higher N(2)(+) temperature is believed to be caused by charge-transfer ionization of N(2) by He(2)(+). These findings are discussed in the context of previously reported ADI-MS analyses with the FAPA source.

Energy Fluctuations in a Direct Current Plasma Torch with Inter-Electrode Inserts Operated at Reduced Pressure

Direct current (dc) plasma torch with inter-electrode inserts has the merits of fixed arc length, relative high enthalpy and may show advantages in future plasma processes where stability and controllability are must-have. Energy fluctuations in the plasma may result from power supply ripple, arc length variation, and/or acoustic oscillation. Using an improved power supply with a flat waveform, the characteristics of an argon plasma energy instabilities under reduced pressure were studied by means of simultaneously monitoring the arc voltage and arc current spectrum. Dependence of the arc fluctuation behavior on the plasma generating parameters, such as the current intensity, the plasma gas flow rates and the vacuum chamber pressure were investigated and discussed. Results show that the plasma torch has a typical U-shaped voltage-ampere characteristic (VAC). The correlation between the VAC and the probability of energy distributions was studied. Through pressure measurements at the cathode cavity and the vacuum chamber, the existence of sonic flow in the inter-electrode insert channel was confirmed.

Suspension Plasma Spray and Performance Characterization of Half Cells with NiO/YSZ Anode and YSZ Electrolyte

The use of a liquid feedstock carrier in suspension plasma spray (SPS) permits injection of fine powders, providing the possibility of producing sprayed coatings that are both thin and dense and have fine microstructures. These characteristics make SPS an attractive process for depositing highly efficient electrodes and electrolytes for solid oxide fuel cell (SOFC) applications. In this study, NiO-yttria stabilized zirconia (YSZ) anode and YSZ electrolyte half cells were successfully deposited on porous Hastelloy X substrates by SPS. The NiO-YSZ anode deposition process was optimized by design of experiment. The YSZ electrolyte spray process was examined by changing one parameter at a time. The results from the design-of-experiment trials indicated that the porosity of the as-deposited coatings increased with an increase of suspension feed rate while it decreased with an increase of total plasma gas flow rate and standoff distance. The deposition rate increased with an increase of total plasma gas flow rate, suspension feed rate, and standoff distance. The microstructure examination by SEM showed that the NiO and YSZ phases were homogeneously distributed and that the YSZ phase had a lamellar structure. It was observed that the density of the YSZ electrolyte layer increased as input power of the plasma torch increased. Electrochemical characterization of the fabricated cells indicated that an open cell voltage of 0.989 V at 500 °C and a peak power of 0.610 W/cm2 at 750 °C were reached.

Study of the Kinetics of Droplets Size Evolution and the Mechanisms of Solid Particles Creation in an Atmospheric Plasma Jet, Using a Laser Beam Diffraction Technique

AbstractThe kinetics of droplets size evolution in an atmospheric plasma jet in which a precursor is injected in liquid phase through a nebulizer to deposit thin films is studied using laser diffraction. In the absence of plasma, droplets reach the substrate (at 75 mm from the nebulizer), but when a pure helium discharge is ignited all the droplets transform into gaseous phase before reaching the substrate. Theoretical and experimental analysis of the system show that the size of these droplets evolve due to evaporation in the plasma and depends upon the plasma gas composition and gas flow rate. Other possible mechanisms like particle charging have been found to play a minor role in the droplet size evolution. In high energy pure helium plasmas when the droplets interact with plasma, small size SiOx particles (1 µm maximum diameter compared to droplet of size up to 70 µm) are formed. Increasing the power dissipated in the discharge increases the number of particles formed but not their size suggesting that nucleation depends on the density of active plasma species. The particle size however depends on the time of residence and precursor concentration in the high energy zone, hence particle size growth depends upon the local concentration and transport of the precursor species.magnified image

Influence of nozzle orifice diameter in keyhole plasma arc welding

Keyhole welding with the plasma arc welding process occurs when the engineered nozzle and the plasma gas flowrate impart the arc pressure and heat distribution necessary for the formation of a keyhole weld pool. Experimental investigations were conducted to determine the influence of nozzle orifice diameter on weld width and weld stability for a range of substrate thicknesses in Ti-6Al-4V. The experimental results are compared with a semianalytical heat flow model. Both the experimental results and the semianalytical model show that the nozzle orifice diameter can significantly influence the top width and penetration for a given parameter set, particularly in relatively thin substrates.

Effect of suspension plasma spraying process parameters on YSZ coating microstructure and permeability

Suspension plasma spraying (SPS) is a modification of plasma spray processes that uses small feedstock powders suspended in a liquid to rapidly produce fully sintered, thin ceramic coatings with good microstructural control and no need for post-deposition heat treatments. This technique has been proposed as a potential next generation manufacturing method to fabricate metal supported solid oxide fuel cells (SOFC). This study produced SPS YSZ layers and characterized the effect of torch power and particle velocity on coating physical properties that are relevant to SOFC electrolyte performance such as density and permeability. The highest density (> 95% dense), lowest permeability coatings were produced from conditions with large plasma gas flow rates and small nozzles; however, these conditions resulted in low deposition efficiency. Coatings produced from conditions with slightly lower plasma gas flow rates and small nozzles were also fairly dense (93% dense) and had fairly low permeabilities, but had 70% higher deposition efficiency compared to the densest coatings.

Determination of OH Radicals in an Atmospheric Pressure Helium Microwave Plasma Jet

A recent study has reported the observation of the OH radicals in the far downstream of an atmospheric argon microwave plasma jet. The far downstream is referred to as the location where the ratio of the distance from the jet orifice to the length of the jet column is greater than three. In this paper, we report that this phenomenon also exists in a similar plasma jet that is 2.5 mm long, operated in helium gas. A detailed characterization of the helium microwave plasma jet was carried out by using UV-pulsed cavity ringdown spectroscopy and optical emission spectroscopy. The absolute number densities of the OH radicals were measured along the plasma jet column from the jet orifice to the far downstream, and the OH concentrations vary from 9.64 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> near the jet orifice to 7.32 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> molecules/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> in the far downstream (16 mm away from the jet orifice, corresponding to a distance ratio of 6.4). The dependence of the OH concentration on plasma power and gas flow rate at different locations along the jet axis is characterized, and the result suggests that the OH concentration increases with an increase in plasma power and gas flow rate in the downstream.

Electrochemical testing of suspension plasma sprayed solid oxide fuel cell electrolytes

Electrochemical performance of metal-supported plasma sprayed (PS) solid oxide fuel cells (SOFCs) was tested for three nominal electrolyte thicknesses and three electrolyte fabrication conditions to determine the effects of electrolyte thickness and microstructure on open circuit voltage (OCV) and series resistance ( R s). The measured OCV values were approximately 90% of the Nernst voltages, and electrolyte area specific resistances below 0.1 Ω cm 2 were obtained at 750 °C for electrolyte thicknesses below 20 μm. Least-squares fitting was used to estimate the contributions to R s of the YSZ bulk material, its microstructure, and the contact resistance between the current collectors and the cells. It was found that the 96% dense electrolyte layers produced from high plasma gas flow rate conditions had the lowest permeation rates, the highest OCV values, and the smallest electrolyte-related voltage losses. Optimal electrolyte thicknesses were determined for each electrolyte microstructure that would result in the lowest combination of OCV loss and voltage loss due to series resistance for operating voltages of 0.8 V and 0.7 V.

切断用酸素プラズマトーチの電極現象の実験的考察

An experimental study of a torch for oxygen plasma arc cutting (PAC) was conducted. We made a nozzle equipped with a window and a port for measurement. We observed the hafnium (Hf) electrode during working, using a color high-speed video camera through the window. The color image consists of three images assign red (R), green (G) and blue (B). Each image is taken by different image sensors having different wavelength sensitivity. We estimated the temperature on the surface of the Hf electrode assuming the black body radiation of the surface. And the port of the nozzle is connected to a pressure sensor to measure the pressure in the nozzle. We could estimate the real-time flow rate of plasma gas from the difference between the pressure in the nozzle and the pressure of supply.Using the special nozzle for observation, we investigated the arc phenomena of PAC using an Hf electrode, during arc-start and arc-shut-off.

Prediction of Weld Bead Geometry in Plasma Arc Welding using Factorial Design Approach

The effect of various process parameters like welding current, torch height, welding speed and plasma gas flow rate on front melting width, back melting width and weld reinforcement of plasma arc welding on aluminum alloy is investigated by using factorial design approach. Variable polarity plasma arc welding is used for welding aluminum alloy. Trail experiments are conducted and the limits of the input process parameters are decided. Two levels and four input process parameters are chosen and experiments are conducted as per typical design matrix considering full factorial design. Total sixteen experiments are conducted and output responses are measured. The coefficients are calculated by using regression analysis and the mathematical models are constructed. By using the mathematical models the main and interaction effect of various process parameters on weld quality is studied.

Dielectric barrier discharge-plasma induced vaporization and its application to the determination of mercury by atomic fluorescence spectrometry

This paper describes a low-temperature dielectric barrier discharge (DBD)-plasma induced vaporization technique using mercury as a model analyte. The evaporation and atomization of dissolved mercury species in the sample solution can be achieved rapidly in one step, allowing mercury to be directly detected by atomic fluorescence spectrometry. The DBD plasma was generated concentrically in-between two quartz tube (outer tube: i.d. 5 mm and o.d. 6 mm, inner tube: i.d. 2 mm and o.d. 3 mm). A copper electrode was embedded inside the inner quartz tube and sample solution was applied onto the outer surface of the inner tube. The effects of operating parameters such as plasma power, plasma gas identity, plasma gas flow rate and interferences from concomitant elements have been investigated. The difference in the sensitivities of Hg(2+), methylmercury (MeHg) and ethylmercury (EtHg) was found to be negligible in the presence of formic acid (≥1% v/v). The analytical performance of the present technique was evaluated under optimized conditions. The limits of detection were calculated to be 0.02 ng mL(-1) for Hg(2+), MeHg and EtHg, and repeatability was 6.2%, 4.9% and 4.3% RSD (n = 11) for 1 ng mL(-1) of Hg(2+), MeHg and EtHg, respectively. This provides a simple mercury detection method for small-volume samples with an absolute limit of detection at femtogram level. The accuracy of the system was verified by the determination of mercury in reference materials including freeze-dried urine ZK020-2, simulated water matrix reference material GBW(E) 080392 and tuna fish GBW10029, and the concentration of mercury determined by the present method agreed well with the reference values.

Experimental Analysis on the Variable Polarity Plasma Arc Pressure

Arc pressure is one of the key factors for variable polarity plasma arc(VPPA) and welding pool formation. In this paper, VPPA pressure is measured by pressure transducer and U-tube barometer methods, and advantages and disadvantages of the two methods are compared. The effects of welding parameters, including with straight polarity(SP) current, reverse polarity(RP) current, time ratio of SP to RP, plasma gas flow rate, on VPPA pressure are investigated by using an orthogonal design. The experimental results indicate that the influencing degree of the welding parameters are in the order of plasma gas flow rate, SP current, time ratio of SP to RP, RP current. These results are important to researches of VPPA welding process and its mechanism. The physics behavior of VPPA is taken into account when the above influence mechanisms are analyzed. Firstly, according to the mechanism of the cooling compression to the arc, the compression to VPPA is enhanced with the increase of plasma gas flow, so the VPPA pressure would increase obviously. Secondly, although the temperature of VPPA is as a function of the welding current, the radius of VPPA is also enhanced. So the effects of SP current on VPPA pressure are inferior to the effects of plasma gas flow. Thirdly, VPPA pressure increases as a function of time ratio of SP to RP because the frequency of welding current influences the arc pressure to the some degree; Finally, the RP intervals are farther less than the SP intervals, so the influence to the pressure is minimal.

Double-arc and Its Control Procedures in Variable Polarity Plasma Arc

It's considered that the electric potential gradient would raise,and it is apt to generate double-arc if inappropriate welding parameters are selected,all these two results are affected by three compressive effects:mechanical compression,heat compression,magnetic compression.Compared with positive polarity time,reverse polarity time in aluminum alloy variable polarity plasma arc welding(VPPAW) is easier to generate double-arc.The reasonable matching of welding current with plasma gas flow rate,orifice diameter with electrode neck-in,and the power source structure of VPPAW are the main factors that influence the double-arc of VPPA.By improving welding force configurations and controls,joining-up MOSFET tubes in main circuit of dimensional arc power supply which can be controlled with the switch of MOSFET tubes,the formation of double-arc is avoided.Furthermore,by reasonably selecting the welding parameters,the double-arc phenomenon in aluminum alloy VPPAW is solved,thus obtaining desirable welding quality.

OH number densities and plasma jet behavior in atmospheric microwave plasma jets operating with different plasma gases (Ar, Ar/N2, and Ar/O2)

OH radical number density in multiple atmospheric pressure microwave plasma jets is measured using UV cavity ringdown spectroscopy of the OH (A–X) (0–0) band at 308 nm. The plasma cavity was excited by a 2.45 GHz microwave plasma source and plasma jets of 2–12 mm long were generated by using three different plasma gases, argon (Ar), Ar/N2, and Ar/O2. Comparative characterization of the plasma jets in terms of plasma shape, stability, gas temperature, emission intensities of OH, NO, and N2, and absolute number density of the OH radical was carried out under different plasma gas flow rates and powers at various locations along the plasma jet axis. With three different operating gases, the presence of OH radicals in all of the plasma jets extended to the far downstream. As compared to the argon plasma jets, the plasma jets formed with Ar/N2 and Ar/O2 are more diffuse and less stable. Plasma gas temperatures along the jet axis were measured to be in the range of 470–800 K for all of the jets formed in the different gas mixtures. In each plasma jet, OH number density decreases along the jet axis from the highest OH density in the vicinity of the jet tip to the lowest in the far downstream. OH density ranges from 1.3 × 1012 to 1.1 × 1016, 4.1 × 1013 to 3.9 × 1015, and 7.0 × 1012 to 4.6 × 1016 molecule/cm3 in the Ar, Ar/N2, and Ar/O2 plasma jets, respectively. The OH density dependence on plasma power and gas flow rate in the three plasma jets is also investigated.

The role of torch instabilities in the suspension plasma spraying process

In spite of the fact that plasma spraying is a commonly used technique for coating elaboration, it remains important to follow in time the characteristics of the arc jet delivered by the plasma torch. Arc voltage and heat loss measurement could be used, together with the control parameters such as arc current and plasma gas flow rate, to investigate the global behavior of the torch in association with a simple analytical model. It is shown that the specific enthalpy and the isentropic coefficient of the plasma gas have a strong influence on the jet velocity, this latter being also significantly modified by the drift of the torch performance. This work is completed by the analysis of the plasma jet instabilities that are responsible for the discrepancy in particle thermal histories. The rear part of the torch is involved in self sustained oscillations, so that the torch shows the characteristics of a Helmholtz resonator, giving rise to periodic variations of the torch voltage, higher in amplitude than the commonly admitted restrike mode. It is also evoked, that the generated acoustic waves are interacting with the solvent vaporization.

Influence of plasma-MIG welding parameters on aluminum weld porosity by orthogonal test

The plasma-MIG welding torch was developed. 5A06 aluminum alloys with V-grooves were welded in a single pass in the plasma-MIG welding process and the joints were examined by X-ray diffractometry analysis and mechanical tests. The orthogonal experimental design was used to study the influence of plasma-MIG welding parameters on the aluminum weld porosity. The mixed orthogonal matrix L 16(4 4×2 3) and analysis of variance (ANOVA) technique were employed to optimize the welding parameters. The experimental results indicate that the effect of plasma gas flow rate is dominant, the secondary factors are MIG welding voltage, welding speed, wire feed rate and plasma current in turn. Confirmation experiments were conducted under optimum conditions and there was almost no porosity in the welded joints, thus good mechanical performance joints were obtained.

Characterization of suspension plasma-sprayed solid oxide fuel cell electrodes

Suspension plasma spray is a promising technique that uses fine particles dispersed in a liquid as feedstock material instead of dry powder as in conventional plasma spraying and has been implemented here to produce layers with appropriate morphologies and microstructures for SOFC applications. This study uses a pressurized gas delivery system to feed the slurry through a homemade two-fluid atomizing nozzle to a conventional plasma torch. The electrodes consist of porous NiO–YSZ as anode and lanthanum nickelate as cathode. The anode and respectively the cathode were deposited onto dense or porous ferritic steel substrates in order to be characterized and optimized. The cell components were examined by scanning electron microscopy (SEM), X-ray diffraction and leakage test. This paper aims at studying the influence of the suspension characteristics (surface tension and viscosity were selected as main parameters), the conditions of injection (nozzle design, gas to liquid ratio, injection angle have been identified as major parameters), the plasma conditions (plasma gas nature and flow rates, spray distance are of major importance) and finally the kinematics on the crystalline phases, the chemical composition (distribution of NiO particles into the layer), the thickness and roughness, the pore ratio and the gas permeability. Then the optimized electrodes have been deposited onto ferritic substrate to perform Open Circuit Voltage and impedance tests at a temperature around 800 °C. This work demonstrated the feasibility for the fabrication of electrodes with interesting performance using suspension plasma spraying technique.

Synthesis of Yttria‐Stabilized Zirconia Nanopowders by a Thermal Plasma Process

A thermal plasma process was used to synthesize nanosized zirconia and yttria‐stabilized zirconia powders. This paper presents a new method on the synthesis of nanosized zirconia and yttria‐stabilized zirconia powders from the carbonates (zirconium carbonate and/or yttrium carbonate). The products from this process using zirconium carbonate were mixtures of monoclinic and tetragonal phases of zirconia. The amount of the tetragonal phase in the mixture increased as the plasma torch power or plasma gas flow rate increased. This is attributed to the formation of metastable tetragonal phase by rapid quenching. With the addition of yttria precursor, two combinations of zirconia phases were formed depending on the yttria contents. Pure tetragonal phase was obtained at 3.8 mol% yttria, while a mixture of tetragonal and cubic phases was produced at 7.7 mol% yttria. The yttria‐doped tetragonal phase was stable at high temperatures without the tetragonal–monoclinic phase transition. The grain size of each phase, the particle size, and the BET are also discussed in this paper.

Identification of a Novel Selenium-containing Compound, Selenoneine, as the Predominant Chemical Form of Organic Selenium in the Blood of Bluefin Tuna

A novel selenium-containing compound having a selenium atom in the imidazole ring, 2-selenyl-N(alpha),N(alpha),N(alpha)-trimethyl-L-histidine, 3-(2-hydroseleno-1H-imidazol-5-yl)-2-(trimethylammonio)propanoate, was identified from the blood and other tissues of the bluefin tuna, Thunnus orientalis. The selenium-containing compound was purified from the tuna blood in several chromatographic steps. High resolution mass spectrometry and nuclear magnetic resonance spectroscopy showed that the exact mass of the [M+H](+) ion of the compound was 533.0562 and the molecular formula was C(18)H(29)N(6)O(4)Se(2). Its gross structure was assigned as the oxidized dimeric form of an ergothioneine selenium analog in which the sulfur of ergothioneine is replaced by selenium. Therefore, we named this novel selenium-containing compound "selenoneine." By speciation analysis of organic selenium compounds using liquid chromatography inductively coupled plasma mass spectrometry, selenoneine was found widely distributed in various tissues of the tuna, with the highest concentration in blood; mackerel blood contained similar levels. Selenoneine was measurable at 2-4 orders of magnitude lower concentration in a limited set of tissues from squid, tilapia, pig, and chicken. Quantitatively, selenoneine is the predominant form of organic selenium in tuna tissues.