Plasma Gas Flow Rate Research Articles

Suspension Plasma Spraying of Nanostructured WC-12Co Coatings

Nanostructured WC-12% Co coatings were deposited by suspension plasma spraying of submicron feedstock powders, using an internal injection plasma torch. The liquid carrier used in this approach allows for controlled injection of much finer particles than in conventional thermal spraying, leading to thin coatings with a fine surface finish. A polyethylene-imine (PEI) dispersant was used to stabilize the colloidal suspension in an ethanol carrier. In-flight particle states were measured for a number of operating conditions of varying plasma gas flow rates, feed rates, and standoff distances and were related to the resulting microstructure, phase composition (EDS, SEM, XRD), and Vickers hardness. High in-flight particle velocities (>800 m/s) were generated, leading to dense coatings. It was observed that the coating quality was generally compromised by the high temperature and reactivity of the small particles. To compensate for this shortcoming, the suspension feed rate was adjusted, thereby varying the thermal load on the plasma. Results showed that a slightly larger agglomerate size, in conjunction with low particle jet temperatures, could somewhat limit the decomposition of WC into brittle W2C/W3C and amorphous cobalt containing binder phases.

Flow rate effect on the structure and morphology of molybdenum oxide nanoparticlesdeposited by atmospheric-pressure microplasma processing

Nanoparticles of crystalline molybdenum oxide were prepared by changing the flowrate of plasma gas (2% oxygen balanced by Ar) using an atmospheric-pressuremicroplasma technique. The morphology and crystalline structure of the nanoparticleswere characterized by field emission scanning electron microscopy (FESEM) andtransmission electron microscopy (TEM). The FESEM results revealed that theshape of the deposited nanoparticles depended on the plasma gas flow rate. TheTEM results supported the FESEM observations. The transmission electrondiffraction (TED) pattern revealed that the obtained nanoparticles changed fromMoO2 toMoO3 with the flow-rate increase, and correspondingly the nanoparticle size drastically decreased.A process mechanism is proposed from the observations of optical emission spectroscopy(OES) during the process and consumed wire surface analysis from x-ray photoelectronspectroscopy (XPS) and FESEM studies.

Design of Experiment for Optimization of Plasma-Polymerized Octafluorocyclobutane Coating on Very High Aspect Ratio Silicon Molds

As-fabricated deep reactive ion etched (DRIE) silicon mold with very high aspect ratio (>10) feature patterns is unsuitable for poly(dimethylsiloxane) (PDMS) replication because of the strong interaction between the Si surface and the replica and the corrugated mold sidewalls. The silicon mold can be conveniently passivated via plasma polymerization of octafluorocyclobutane (C4F8), which is also employed in the DRIE process itself, to enable the mold to be used repeatedly. To optimize the passivation conditions, we have undertaken a Box-Behnken experimental design on the basis of three passivation process parameters (plasma power, C4F8 flow rate, and deposition time). The measured responses were fluorinated film thickness, demolding status/success, demolding force, and fluorine/carbon ratio on the fifth replica surface. The optimal passivation process conditions were predicted to be an input power of 195 W, a C4F8 flow rate of 57 sccm, and a deposition time of 364 s; these were verified experimentally to have high accuracy. Demolding success requires medium-deposited film thickness (66-91 nm), and the thickness of the deposited films correlated strongly with deposition time. At moderate to high ranges, increased plasma power or gas flow rate promoted polymerization over reactive etching of the film. It was also found that small quantities of the fluorinated surface were transferred from the Si mold to the PDMS at each replication, entailing progressive wear of the fluorinated layer.

Electron number density measurement on a DC argon plasma jet by stark broadening of Ar I spectral line

In thermal plasma processing, input power and gas flow rate play a major role in controlling the plasma jet temperature, velocity and density. Emission spectroscopy study is an important method for plasma diagnostics. A DC atmospheric plasma spray torch was operated at different power levels and flow rates of plasma gas (argon). Electron number density of the plasma jet, the corresponding temperature and the degree of ionization were determined using stark broadening of the Ar I (430.010 nm) line, the atomic Boltzmann plot method and the Saha equation, respectively. In the present work, we have investigated the effect of input power, axial position of the plasma jet and gas flow rate on the electron number density in the plasma jet. While an increase in input power considerably increased the electron number density, gas flow rate did not show any significant effect on the same.

Assessment of the Microplasma Spraying Process for Coating Application

Among the different existing plasma spraying processes, Microplasma Spraying (MPS) is comparatively new and offers specific and unique properties. MPS is particularly characterised by a very low plasma power, low plasma gas flow rate, small spray spot and low heat input into the substrate. These properties are very advantageous for the application of coatings on small parts or with high accuracy. However, until today the MPS process has been barely studied and its potential as well as limitations are vaguely known. This paper presents results from a fundamental study of the MPS process. Sprayed materials include metallic, ceramic and cermet materials.

Influence of gas flow rate on the microstructure and mechanical properties of hydroxyapatite coatings fabricated by gas tunnel type plasma spraying

Gas tunnel type plasma torch was used to spray hydroxyapatite (HA) coatings on 304 stainless steel substrate at different plasma gas (Ar) flow rates (100–170 l/min). Microstructure was observed by scanning electron microscope and phase analysis by X-ray diffraction. The mechanical properties such as hardness and abrasive wear resistance of HA coatings sprayed at different gas flow rates were investigated. The results showed that the gas flow rates affect greatly the microstructure and mechanical properties of HA coatings. Crystallinity increased and porosity decreased as the gas flow rate increased. Hardness and abrasion resistance increased as the gas flow rates increased.

Spheroidization of metal and ceramic powders in thermal plasma jet: Comparison between experimental results and theoretical estimation

For smooth and uniform feeding of powders into plasma jet, for thermal spray coating, the powder particles have to be spherical in shape since they have good flow quality. Spheroidization of micron sized metal and ceramic powders to produce flow quality powders using plasma processing is a modern concept. In the present work a theoretical estimation of the percentage of spheroidization of particles has been made from basic fluid dynamic equations. Particles of nickel and alumina of 50–60 μm were considered at different plasma gas flow rates and temperatures (input power). Particles with the same specifications were spheroidized using plasma processing. Optical micrographs showed spherical shape of processed powders. Percentage of spheroidization was measured by irregularity parameter (IP) and roundness (RN) and the same were compared with theoretical estimation. Experimentally a maximum of 87% spheroidization was obtained. Comparatively the maximum difference between theory and experiment is 7% that of the experimental value.

In-flight formation and characterization of nickel aluminide powders in a dc thermal plasma jet

The strength of some intermetallics increases with temperature instead of exhibiting a decrease: thus, they are ideally suited for high temperature applications. The formation of intermetallic compound during the spray process leads to metallurgical bonding due to the high exothermicity of the formation reaction. In this paper formation of nickel aluminide in a thermal plasma jet from ball-milled nickel–aluminium powders is reported. Commercially available nickel and aluminium powders were mixed in the appropriate amount and injected in to a thermal plasma jet produced by an atmospheric plasma torch. During in flight the formation of nickel aluminide takes place in plasma jet. Powders were collected at two different collection distances (40 and 80 cm) for three power levels (10, 15 and 20 kW), different plasma gas flow rates (15 and 20 lpm) and different powder feed rate (7 and 14 g/min). The powders are characterized using SEM, optical micrograph, TG/DTA and XRD analysis. The effect of plasma parameters on the formation have been studied and reported. The formation is better at higher power levels, low powder feed rate, low plasma gas flow rate and longer collection distances.

Application to cleaning of waste plastic surfaces using atmospheric non-thermal plasma jets

The removal of paint on the surface of waste plastics is difficult by the conventional process; in this research, a new cleaning mechanism using atmospheric plasmas was examined through optical emission spectroscopy, electron spectroscopy for chemical analysis, and scanning electron microscopy. Results indicate that an increase of pulse frequency enables for a short processing time for the removal of the paint film, signifying that the production of radicals in plasma, especially oxygen radicals, can be controlled by pulse frequency. Plasma jets were generated under the experimental conditions of an input power of 250 W to 400 W, a pulse frequency of 2 kHz to 12 kHz, and a plasma gas flow rate of 30 L/min. Examination of the intensity ratio of the reactive species, as measured by emission spectroscopy, showed that the O/N value increased with an increase in pulse frequency. Results of analysis with electron spectroscopy for chemical analysis show that nitrogen atoms and molybdenum in only the paint film decreased through plasma processing.

Application of a wall-stabilized argon plasma arc for the determination of some volatile hydride-forming elements

Volatile hydrides of As, Se, Sb and Sn, produced by a continuous manifold hydride generator, have been swept with argon and injected into the plasma of home-made direct current wall-stabilized argon plasma arc via one of its stabilizing segments. The arc burns in argon with an arc current of 20 A and a cathode-anode voltage of 40 V. Measurements were carried out using a 1 m focal length computer-controlled monochromator (Jobin Yvon 1000R) equipped with a holographic grating having 2400 grooves mm − 1 . Optimal values of the experimental variables that give the highest value of intensity ratio of line-to-background were determined. These are: plasma gas flow rate 1.0 l min − 1 , carrier gas flow rate 0.35 l min − 1 for As and Sb and 0.6 l min − 1 for Se and Sn, concentration of nitric acid used for acidification of the sample 2 M for As and Sb, 0.5 M for Se and 0.1 M for Sn and sodium borohydride concentration: 1.5% for As and Se and 2% for Sb and Sn. Chemical interference of some transition elements that affect the hydride generation process and a trial to mask their interference effect were investigated. Calibration curves were linear and limits of detection calculated on the base of 3 σ of the background were found to be as low as 3.9, 6.8, 9.8 and 13.2 ng ml − 1 for As, Se, Sb and Sn, respectively. Finally, the analytical applicability of the arc device was tested by the determination of As in four lake sediment samples, LKSD 1, LKSD 2, LKSD 3 and LKSD 4, of the Centre for Mineral and Energy Technology, Ottawa, Ontario, Canada, which have been analyzed for As using atomic absorption spectrometry (AAS). The results were in good agreement with those obtained by AAS.

A Novel Method of Synthesizing Spherical Nano-structured Composite Particles of Aluminum Nitride using Transferred Type DC Arc Plasma

Aluminum nitride (AlN) composite particles consisting of nano-particles dispersed on the surface of spherical micro-particles are one of the materials necessary for developing solid insulating materials with high thermal conductivity. This paper describes a novel method of synthesizing AlN composite particles using transferred type DC nitrogen arc plasma. The shape of the synthesized particles, the diameter of micro-particles and the volume fraction of micro-particles in the synthesized composite particles were controlled simply by varying the travelling time of the raw AlN angular particles in the arc plasma. The travelling time was controlled by varying the plasma length and the plasma gas flow rate. The diameter of the nano-particles in the synthesized composite particles was controlled simply by varying the travelling time of the raw AlN particles in the arc plasma, and varying the temperature and the vapor density in the nano-particle synthesis space. The temperature and the vapor density were controlled by varying the flow rate of reacting/quenching ammonia gas. The AlN content in the synthesized composite particles was higher than 99%.

A new ion source design for inductively coupled plasma mass spectrometry (ICP-MS)

Based on the static high sensitivity inductively coupled plasma (SHIP) introduced by Buscher et al. (W. Buscher, A. Klostermeier, C. Engelhard, S. Evers, M. Sperling, J. Anal. At. Spectrom., 2005, 20, 308-314), a new torch design for ICP mass spectrometry was developed. The SHIP-torch, including the external air cooling system, was modified in order to allow its application as an ion source in a conventional ICP mass spectrometer. While the torch geometry was adjusted for its use in connection with the sampling interface, the principal shape of the torch remained the same as in the recently developed SHIP-OES-system. The plasma discharge was operated at 0.65 kW rf power with a total plasma gas flow rate of 1.95 L min−1 and the mass spectrum was investigated. A standard pneumatic nebuliser was used as sample introduction system and the ion signals of a multi elemental standard solution were measured for different sample carrier gas flow rates from 0.2 to 1.4 L min−1. Limits of detection were obtained for a number of elements. These results were compared to those achieved with the conventional ICP-MS setting.

Miniature atmospheric pressure glow discharge torch (APGD-t) for local biomedical applications

Abstract The operating parameters of a miniature atmospheric pressure glow discharge torch (APGD-t) are optimized for the production of excited atomic oxygen, and the effect of the plasma jet on endothelial cells grown in Petri dishes is studied. We first demonstrate the importance of accounting for the effect of the voltage probe used to measure the electrical parameters of the torch on its ignition and operation characteristics. When operated with a main plasma gas flow rate of 1 SLM He and a power level of ~1 W, the torch shows an optimum in the production of excited atomic oxygen for a O2 flow of ~3.5 SCCM injected downstream from the plasma-forming region through a capillary electrode (i.e., 0.35 v/v % O2/He). It is shown that endothelial cells are detached from the Petri dishes surface under the action of the optimized plasma jet and that this effect does not originate from heating and fluid shearing effects. It is postulated that the cell detachment is caused solely by plasma-induced biochemical processes taking place at the cell-substrate interface.

Comparison Between Two Sample Emulsification Procedures for the Determination of Mo, Cr, V and Ti in Diesel and Fuel Oil by ICP OES Along with Factorial Design

Inductively coupled plasma optical emission spectrometry (ICP OES) was used to determine Mo, Cr, V and Ti, in diesel and in used fuel oil. Samples were introduced into the ICP as emulsions to reduce interferences and allow the use of inorganic standards for quantification. A comparative study between one Triton X-100 emulsion and one detergentless emulsion was made. A 23 factorial design was applied to elucidate and establish the relationship between three experimental variables: presence of HNO3, amount of diesel fuel oil (between 5 and 25%) and the presence or O2 into the Ar plasma gas flow rate. Results indicated that best performance were achieved using 10% sample (w/w) together with concentrated HNO3 (0.5 mL) and using O2 as auxiliary gas (0.047 L min−1). The use of O2 minimized both carbon deposits at the injector tip and plasma background. The addition of HNO3 resulted in good correlation between inorganic standards used for calibration, and metallo-organic standards used for sample enrichment. Analyte enriched diesel and SRM 1634b were analyzed using the optimized conditions. Recoveries from 90.1 to 106.5% were achieved, with better results for detergent emulsions which enabled limits of detection at the ng g−1 range for Mo, Cr, V and Ti and at smaller background.

Microwave plasma synthesis of Co and SiC-coated Co nanopowders

This work describes the use of microwave plasma synthesis technique to prepare cobalt nanopowders. The effects of flow rate of plasma gas and carrier gas to the average particle size were studied. Modification of the microwave plasma unit can be used to produce Co nanopowders with SiC coating. The Co and SiC-coated Co nanopowders were characterized by means of transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS) and X-ray diffraction (XRD).

Spheroidization of metal and ceramic powders in thermal plasma jet

In the present investigation, a theoretical estimation of the percentage of spheroidization of particles has been made from basic fluid dynamic equations. Particles of different sizes were considered at different plasma gas flow rates and temperatures (input power). Particle inflight residence and melting times were calculated and using them, percentage of spheroidization was estimated. Spheroidization was found to be strongly dependent on particle size and plasma jet temperature.

Neural computation analysis of alumina–titania wear resistance coating

Abstract Pin-on-disc tests were performed on alumina–13 wt.% titania coatings obtained under several APS conditions. Friction coefficient data were analysed using artificial neural network. This permitted to predict parameter ranges for which good wear resistance is possible when varying each of the process parameters individually with respect to a reference condition. In this case, results suggest that large parameter ranges did not permit to obtain a significant friction coefficient variation which was mainly between 0.51 and 0.61. In addition, injection parameters and total plasma gas flow rate were the control factors.

Anode attachment stability and anode heat transfer for high-intensity arcs with lateral gas flow

This study determined the motion of an anode attachment and the heat flux to the anode for a configuration in which the arc axis is perpendicular to the anode surface with the plasma gas flowing along the arc axis, and with lateral injection of different gases parallel to the anode surface. The arc is stabilized by a constrictor except for a gap of 10 mm, the arc currents are 75 and 100 A, the plasma gas flow rate is 5 slm of argon, and the lateral gas flow rate is 0 to 25 slm, with argon, nitrogen, or helium gas that is injected laterally. High-speed videography and calorimetric measurements of the anode cooling water temperature increase are used to characterize the anode attachment. Results show that different modes of anode attachment exist, including a steady deflected anode root, a randomly fluctuating attachment, and a periodically fluctuating attachment. When the anode spot appears, the lateral gas produces an arc voltage increase. The total anode heat transfer changes with different lateral gas flow rates and for different attachments modes. This effect probably occurs because lateral gas flow causes a convective heat loss from the arc to the chamber walls.

Heating Efficiency of Twin Torch Plasma Arc

The twin torch plasma arc has a higher temperature arc column. For that reason, it can generate high temperature and treat non-conducting material, even though it is a non-transfer type. Therefore, the twin torch plasma arc is a more effective device for treatment of hazardous waste. However, the arc mode is not easy to control in the twin torch plasma arc. In this paper, a twin torch plasma arc with a rated current of 40 to 100 A is described such as arc mode, voltage as function of current and length, heating efficiency, and running cost for hazardous waste. The high temperature region of the twin torch plasma arc is larger than that of a conventional single plasma torch. The plasma arc length can be changed as a function of the plasma gas flow rate. The arc voltage is also variable as a function of the current and plasma gas flow rate. The temperature of twin torch plasma was measured to be about 10000 K near the cathode and anode, and 8900 K at the center point between the electrodes at 100 A. The neutral bar received heat power of the amount of 280-500 W, and the fraction of the total power transferred to the neutral bar is 12-18%.

New torch design for inductively coupled plasma optical emission spectrometry with minimised gas consumption

A new torch design for inductively coupled plasma optical emission spectrometry was developed. The torch was made of one quartz tube with a ball-shaped excitation zone. Under optimised working conditions of the 27.12 MHz Ar plasma with 1.1 kW RF power, the total argon gas flow could be reduced to only 0.6 L min−1 with external air cooling integrated in the fastening of the torch. Fundamental studies of selected element emissions, emission profiles, the effect of auxiliary plasma and sample carrier gas flow rates were carried out. The attainable excitation and rotational temperatures in the new torch were determined at different sample carrier gas flow rates. For 1.1 kW RF power and total gas flows between 50–800 mL min−1 they were found to be in the order of 6000–10 000 K for the excitation temperatures and 3700–4100 K for the rotational temperatures. The new torch was coupled with an ultrasonic nebuliser and detection limits between 0.03–2.9 μg L−1 could be determined for the elements Ba, Li, Mg, Ca, Cd, K and Al. The new torch delivered promising results that raise hopes of having a new generation of torches allowing low argon consumption.