Plasma Gas Flow Rate Research Articles

Ionization of Mg and Cd in an atmospheric pressure parallel plate capacitively coupled plasma

The degree of ionization for Mg and Cd vaporized into a parallel plate capacitively coupled plasma (PP-CCP) has been studied. Using electrothermal vaporization and a CCP operating at 200 W, the degree of ionization is 83% and 48% for Mg and Cd, respectively. An increase in applied power increases the degree of ionization. Changes in plasma gas flow rate, up to 1.0 l min−1, also change the degree of ionization slightly, probably due to mass transport effects and slight changes in the discharge conditions. Additions of EIE (Na as NaNO3) up to 10 times (w/w) the analyte increase the degree of ionization slightly.

Characterization of a spray torch and analysis of process parameters

Anode for a non-transferred DC plasma spray torch was designed to improve electrothermal efficiency. A theoretical calculation was made for the electrothermal efficiency in a DC plasma torch operating with argon at atmospheric pressure with power level in the range of 5.2–20 kW using energy balance equations. ANOVA for the two level factorial design was done. Plasma gas flow rate, current intensity, nozzle diameter and length were found to influence the efficiency. The efficiency was found to decrease with increase in current intensity and nozzle length and to increase with increase in nozzle diameter and gas flow rate. The overall energy balance calculations showed that the heat transfer to the plasma-forming gas decreases with increase in arc current and the same was more significant at higher flow rates. Plasma jet velocity for different flow rates, input to the torch and nozzle dimensions was calculated from the gas enthalpy. It was found that the velocity increased with increase in the power input to the torch and gas flow rate and decreased with increase in nozzle length and diameter. The current–voltage characteristics of the torch operating with argon gas were studied for different gas flow rates. The Nottingham coefficients were calculated using least – square method.

Silica Decomposition Using a Transferred Arc Process

A novel process for silica decomposition consisting of transferring a thermal arc directly to a silica anode was investigated. The effects of current (150−250 A), plasma gas flow rate (10−20 L/min of Ar), and plasma gas composition (0−2.8% H2) on the rate of decomposition were examined. The decomposition rate ranged from 0.09 to 1.8 g/min and was determined to be heat-transfer-limited, with decomposition occurring below the arc root where the anode surface attained its boiling point. The decomposition rate was independent of plasma gas flow rate, suggesting that convective heat transfer was reduced significantly by the counterflow of decomposition products (SiO(g) and O2) from the surface. Increasing the current increased the decomposition rate because heat input to the anode because of electron flow and arc radiation increased. Adding H2 to the plasma gas increased the decomposition rate because of an increase in radiative heat transfer to the anode, a reduction in the theoretical energy requirement for decomposition, and a consumption of O2 which lowered the silica boiling point. The fumed silica produced had properties typical of commercial fumed silica products.

Plasma spray processing of Al2O3/AlN composite powders

A novel method is proposed to prepare Al2O3/AlN composite powders. The composite powders were synthesized by direct nitridation of Al2O3 powders in Ar/N2 plasma. The processing characteristics were studied. The results show that the particle size of the initial materials, the nitrogen plasma gas flow rate and the power of the plasma generator are important factors that influence the phase composition of the Al2O3/AlN composite powders. Post treatment of the Al2O3/AlN composites in nitrogen atmosphere was carried out. Microstructure analysis showed that the composite powders are spheroids, with the small particle size AlN formed on the surface of the Al2O3.

Influence of plasma gas composition on analyte ionization in furnace atomization plasma emission spectrometry

F. Sun and R. E. Sturgeon, J. Anal. At. Spectrom., 1999, 14, 901 DOI: 10.1039/A900273A

Simultaneous determination of As, Hg, Se and Sb by hydride generation-microwave induced plasma atomic emission spectrometry after preconcentration in a cryogenic trap

C. Dietz, Y. Madrid, C. Cámara and P. Quevauviller, J. Anal. At. Spectrom., 1999, 14, 1349 DOI: 10.1039/A902039J

Low-pressure helium ICP-MS with a water-cooled plasma torch.

Although ICP mass spectrometry offers a powerful multi element analytical method, the background spectra often interfere with the determination. The detectability for halogens is not adequate because of insufficient ionization. In the present work, a low-pressure helium ICP was studied in order to overcome these problems. A plasma was sustained with a water-cooled torch at 400 800 W forward power with a maximum signal intensity at 500 W. The optimal plasma gas-flow rate and sampling depth were 40 ml min-1 and 17 mm, respectively. The signal intensities of 127I+ were much higher than those of the conventional atmospheric-pressure Ar ICP. Background species (ArN+ and Ar2+) were not observed, which may allow the determination of traces of Se (as 80Se+) as well.

Anode-boundary-layer behaviour in a transferred, high-intensity arc

The effects of the plasma's gas-flow rate on phenomena such as the negative anode fall and the heat flux to the anode in high-intensity arcs are discussed on the basis of a numerical model of the anode's boundary layer. The modelling system consists of a rotationally symmetrical argon plasma formed between the outlet of a constrictor tube and a water-cooled flat copper anode perpendicular to the axis of the plasma flow which is directed towards the anode. The arc is operated at atmospheric pressure and at a current level of 200 A. The boundary conditions for the electron temperature and the electron number density at the anode's surface are obtained by solving the electron-energy equation and the diffusion equation at the anode's surface simultaneously with all conservation equations for the calculation domain. A diffuse anode attachment is obtained for a mass flow rate exceeding 0.2 g and a constricted anode attachment is found for rates below 0.02 g . There is a (probably unstable) transition region between these flow rates. The anode boundary layer of the diffuse attachment is strongly affected by the mass-flow rate. Increasing the mass-flow rate shifts the location of the peak of the electrical potential towards the anode while its magnitude decreases and the total heat flux to the anode increases. This is a consequence of the effects of the mass-flow rate on the axial profiles of electron and heavy-particle temperatures and of the electron number density. In contrast, the anode boundary layer of the constricted attachment seems not to be affected by the mass-flow rate.

<![CDATA[<b>Physical and Mathematical Modeling of non Transferred Plasma Torches</b>]]>

The main objective of this work is to obtain temperature and velocity profiles of the plasma jet, including the electric arc region, generated by non transferred plasma torches. The profiles are obtained from a numerical solution of the conservation equations wich were used to describe the plasma flow. This modelling approach will help the development and optimization of plasma torches, saving time and reducing costs of an alternative empirical development; it could also give some insight on the phenomena occuring inside the torch. Fluid mechanics models for laminar and turbulent flows were adopted to simulate the plasma inside and outside the torch. Patankar's control volume method was chosen to solve the resulting coupled differential equations. The method is very stable and requires less computational time than higher order methods, although it can be less accurate for some applications. A computer code was developed to simulate the jet flow of a plasma torch. The results obtained from this program compared very well with published ones, corroborating the assumptionsn of the present model and the numerical method. Temperature and velocity profiles for a plasma torch with dimentions and operating conditions similar to the ones used in indusrtial applications of spraying were generated and analyzed. The plasma torch simulated had an eletric arc of 100A, plasma gas flow rate of 20 l / min, cross section of 5.2 mm and anode length of 13mm.

Plasma generation for the plasma cutting process

This study is an attempt to estimate the overall properties, viz. the thermal power and force, of an intense plasma jet produced by a plasma cutting torch, and to relate the properties of the plasma to the diameter of the nozzle of the plasma torch and the flow rate of plasma-forming gas. For cutting metallic plates using a thermal plasma, a narrow plasma jet is produced by means of a transferred electric are between an electrode in a plasma torch and the material to be cut. The power density and pressure exerted by the plasma jet on the material at the region of cut needs to be high so that a straight cut, without dress at the bottom of the plate, can be obtained. A simple theory to describe the behavior of the arc in a plasma cutting torch has been developed to predict the are radius, pressure, and arc voltage at the nozzle exit as a function of are current for a range of nozzle sizes and air flow rates. The results obtained are in good agreement with the measured values for an air plasma cutting torch nominally rated for 100-A operation. The relationships between the mass flow rate of plasma gas, plasma power, and arc force have been discussed in the light of design of plasma torches for plasma cutting.

Experimental study of the heat and mass transfer in a high-frequency thermal plasma reactor

The present study reveals some of the important parameters which control the decomposition of ammonia introduced by radial injection into an induction plasma. Temperature and composition gradients of the plasma stream were evaluated with an enthalpy probe connected to a mass spectrometer. Axial and radial profiles are measured at the exit of the plasma torch to quantify the important mass and energy transfer mechanisms occurring at two levels of ammonia flow rate. Other experiments were made using the enthalpy probe at a fixed point along the centerline of the reactor, near the exit of the plasma torch. These experiments were useful in establishing: 1) the minimum radial flow rate that permits the ammonia to completely penetrated the plasma, and 2) to evaluate the maximum load of ammonia that could be decomposed by the plasma. Finally, the fixed point configuration is used in combination with a 2/sup 3/ factorial experiment design to quantitatively determine the important parameters that affected the transport properties of the plasma during the NH/sub 3/ radial injection. The controlled experimental parameters employed for the factorial were the flow rate of ammonia, the plate power, the reactor pressure, and the flow rate of the central plasma gas, while the torch exit temperature and the N/sub 2/ and NH/sub 3/ concentrations formed the studied outputs. The findings of the factorial design showed that the plasma temperature inside the decomposition zone could only be modified by means of plasma plate power and ammonia flow rate changes or adjustments. The diffusion of species during ammonia decomposition is strongly affected by the four controlled experimental parameters under study.

Spatial Characterization of Emission Intensities and Temperatures of a High Power Nitrogen Microwave-induced Plasma

The spatial characterization of a high power nitrogen microwave-induced plasma (N 2 -MIP), using an Okamoto cavity, was undertaken. The plasma operating conditions were fixed during all the experiments at a microwave frequency of 2.45 GHz, an incident power of 1.3 kW, a plasma gas flow rate of 11.0 l min -1 , a carrier gas flow rate of 1.0 l min -1 and a sample uptake rate of 1.6 ml min -1 . A Ca solution was used to measure the emission intensity distribution for both Ca atom and ion lines in the N 2 -MIP, and an Fe solution was used to determine the excitation temperature distribution of the N 2 -MIP, which was obtained by using a Boltzmann plot under the assumption of LTE. In addition, rotational temperature measurements were carried out using the N 2 + (0–0):B 2 Σ u + →X 2 Σ g + band. Because the H β line (486.13 nm) could not be excited in the N 2 -MIP, measurement of the electron number density was carried out by a method involving the Saha equation using both the emission intensity ratio (Ca II:Ca I) and the excitation temperature of the N 2 -MIP. The degree of ionization of various elements in the N 2 -MIP was also calculated. The spatial characteristics of the N 2 -MIP were compared with those of the Ar-ICP.

A direct current, plasma fluidized bed reactor: its characteristics and application in diamond synthesis

In this study, the bed temperature profile of a conical/plasma fluidized bed without a distributor was studied. The same reactor was also used for growing diamond by chemical vapour deposition. It was found that the fluidized bed quenches the plasma gas quite significantly. The bed temperature increases with both the plasma gas flow rate and the plasma input power. A lateral temperature difference from the centre of the bed to the wall exists due to heat loss through the wall. The temperature profiles obtained are suitable for controlling of bed quenching conditions in particle processing and synthesis. The conical/plasma fluidized bed with a distributor on top of the plasma was then applied to diamond synthesis from a gas phase using a distribution between the bed and the plasma. The deposition mainly occurred in the plasma tail fame. Both the scanning electron micrographs and Raman spectra show the existence of diamond on seed particle surfaces, but with a rather low nucleation density. The limitations of the d.c. plasma fluidized bed system are discussed and modifications to the reactor are recommended.

Parametric study of the decomposition of NH3 for an induction plasma reactor design

The present paper reports a study of the gas mixing and chemical transformation in an induction plasma reactor under atmospheric pressure, and its dependence on the plasma operating conditions. For this purpose, the thermal dissociation of ammonia into nitrogen and hydrogen was chosen because of the relative simplicity of the reactions involved and its use in a number of studies on plasma synthesis of ultrafine nitride ceramic powders using ammonia as nitriding agent. A hot-wall reactor configuration is investigated in which ammonia is injected radially through multiple orifices into the gases at the exit nozzle of an induction plasma torch. Concentration mapping in the mixing zone was carried out, using a VG-Micromass-PC 300 D quadrupole mass spectrometer, for different plasma power levels, in the range 13–24 kW. A 3-point injection mode is used with the injection ports oriented upstream at 45° to the torch axis. This allows uniform mixing of the injected gas in the plasma jet. A systematic study of the effects of plate power and ammonia and plasma gas flow rates on the mixing and dissociation of NH3 in the reactor is reported. The results are analyzed and discussed from the viewpoint of their use for optimizing the design of induction plasma reactors, to he applied to the vapor-phase synthesis of ultrafine silicon nitride powders.

Reactive ion etching of GaN using CHF3/Ar and C2ClF5/Ar plasmas

III–V nitride semiconductors have great potential for optoelectronic and electronic devices due to their wide direct band gaps. Because GaN is chemically very stable, dry etching techniques must be established in order to fabricate devices. In this work, we report the reactive ion etching (RIE) of GaN using CHF3/Ar and C2ClF5/Ar plasmas. GaN films on (001) GaAs were grown by electron cyclotron resonance (ECR) plasma associated molecular beam epitaxy (MBE) and the films showed (0001)hex orientation along the surface normal. We used a Drytek DRIE-184 rf plasma discharge RIE system with no ECR discharge or high energy Ar ion beam. The effects of rf plasma power, pressure, and gas flow rates on the etch rate were investigated and the surface contamination due to RIE was examined by XPS. The etch rate varied between 60 and 470 Å/min. The conditions for etching were 100–500 W of rf plasma power, 60–300 mTorr of pressure, a CHF3 or C2ClF5 flow rate of 5–50 sccm and an Ar flow rate of 0–50 sccm. The highest etch rates were obtained with high rf plasma power and low pressure.

Characterization of d.c. plasma torch voltage fluctuations

The arc root fluctuations at the anode-nozzle of a d.c. plasma spray torch with a special configuration of the electrodes allowing to work with the same gas flowrate with nozzle diameters ranging from 6 to 10 mm were systematically studied. The plasma gas was Ar/H2 (25 vol % H2), the current was varied between 200 and 600 A and the plasma gas flowrate between 24 and 80 slm. After 30–60 mn working the nozzle wall started to be sufficiently eroded to have a stagnant arc spot which lived until arcing created another one. It was shown that the life time of the upstream arc spots were 30–40 % longer than the downstream ones which could play an important role in the electrode erosion. Dimensional analysis allowed to find a relationship between the nozzle diameter D, the arc current I and gas flow rate G and the mean spot lifetime which is closely connected with the difference between D and the electrical diameter of the arc column. The comparison of voltage signal and light emission at a point of the plasma jet close to the nozzle exit on its axis allowed to determine the mean electrical field within the plasma column and the mean position of the arc root. The comparison with the electrode erosion area for well defined conditions showed a good correlation with the calculated arc root position.

Diagnostics in a High-Flow-Rate (>6 L min−1) Helium Capacitively Coupled Microwave Plasma: Aqueous versus Organic Solution

A helium capacitively coupled microwave plasma (CMP) with a high plasma gas flow rate (>6 L min−1) is described. Plasma gas flow rates above 6–8 L min−1 produce a cylindrical-shaped plasma. Diagnostic studies were performed. Electronic excitation ( Texc), rotational ( Trot), and ionization-recombination ( Tion) temperatures were determined, along with the electron number density ( ne). Texc was calculated from the slope of the Boltzmann plot with the use of Fe as the thermometric species. Values for Texc in aqueous and organic solution were 3430 and 3450 K, respectively. Trot determined with the use of both OH and N2+. With OH, Trot values were 1620 and 1660 K for aqueous and organic solutions, respectively. If no solution was introduced, a Trot value of 2350 K was determined with N2+. N2+ also gave Trot values of 1900 and 1930 K with aqueous and organic solutions, respectively. The Tion values were 6220 and 5610 K with the use Cd and Mg, respectively. The ne value was on the order of 4 × 1014 cm−3. Background spectra and limits of detection are also presented.

Effect of plasma spray processing variations on particle melting and splat spreading of hydroxylapatite and alumina

Splats of hydroxylapatite (HA) and alumina were obtained via plasma spraying using systematically varied combinations of plasma velocity and temperature, which were achieved by altering the primary plasma gas flow rate and plasma gas composition. Particle size was also varied in the case of alumina. Splat spreading was quantified via computer- aided image analysis as a function of processing variations. A comparison of the predicted splat dimensions from a model developed by Madejski with experimental observations of HA and alumina splats was performed. The model tended to underestimate the HA splat sizes, suggesting that evaporation of smaller particles occurred under the chosen experimental conditions, and to overestimate the observed alumina splat dimensions. Based on this latter result and on the surface appearance of the substrates, incomplete melting appeared to take place in all but the smaller alumina particles. Analysis of the spreading data as a function of the processing variations indicated that the particle size as well as the plasma temperature and velocity influenced the extent of particle melting. Based on these data and other considerations, a physical model was developed that described the degree of particle melting in terms of material and processing parameters. The physical model correctly predicted the relative splat spreading behavior of HA and alumina, assuming that spreading was directly linked to the extent of particle melting.

The Effect of Weld Gas Flow Rate on Al-Li Weldability

Adequate shield and plasma gas flow rate during plasma arc welding are crucial factors in achieving high quality welds. Too low a shield gas flow rate lets atmosphere enter into the arc and too high a rate wastes weld gas and may cause turbulence and entrain atmosphere. Sufficient plasma gas flow is required for keyhole welding and, as shown in this paper, can reduce hydrogen contamination in the weld. In-situ optical spectroscopy used to detect oxygen and hydrogen in the welding arc during variable polarity plasma arc (VPPA) welding of aluminum 2090 revealed that there is an easily detected critical shield gas flow rate needed to exclude atmosphere and that this critical rate can be used to automatically control gas flow rates during welding.

Computer simulation of atmospheric-pressure helium inductively coupled plasma discharges

Computer simulation was used to predict fundamental properties of pure helium inductively coupled plasmas (He ICPs) in a torch most often used in experimental studies of He ICPs. Plasma characteristics for the He ICP were compared to those of an Ar ICP formed in the same torch and to the existing experimental data. The distributions of temperature, gas velocity, power dissipation, and electric and magnetic fields were obtained as a function of active power, the number of turns (length) for the induction coil, the gap between the plasma tube and the MACOR insert, injector gas flow rate, injector tube orifice, and plasma gas flow rate. Overall, the He ICP was predicted to have a higher plasma temperature, but its axial temperature at 10–30 mm above the induction coil was lower than that of the Ar ICP. Heat dissipation was concentrated in a smaller area in the He ICP as compared to the Ar ICP. The magnetic and electric fields inside the induction coil in He plasma were approximately one order of magnitude higher than those in Ar plasma. These theoretical predictions, based on an LTE model of the plasma, also were used to interpret existing analytical results, and to devise new directions for research in He ICP spectrometry.