Plasma Torch Power Research Articles

Plasma Spray of Nano Composite Ceramics Using Solution Precursors and Combustion Synthesized Nano Powders

AbstractPlasma spraying is a well-established method for depositing nanostructured ceramic coatings on structural components. Two different plasma spraying techniques - solution precursor plasma spray (SPPS) and suspension plasma spray (SPS) - have been used to produce MgO-50vol% ZrO2 composite coatings. The microstructural features of the coatings were characterized using Environmental Scanning Electron Microscopy (ESEM) and X-Ray Diffractometry (XRD). The micro hardness of the coatings was measured on cross-sectional samples. The coatings produced using the SPS process with ethanol-based suspensions at a high plasma torch power (45.5 kW) exhibited the densest microstructures with hardnesses as high as ∼1350 HV. However, the backscattered electron (BSE) ESEM characterization of these coatings revealed that the coatings obtained using the SPPS technique had superior chemical homogeneity over those obtained using the SPS technique.

Toxic wastes treatment using different configurations of plasma torches

Plasma technologies for waste treatment are rapidly emerging due to their effectiveness in destroying organic compounds, since they present a very high power density, enthalpy and chemical reactivity employed in the process. In this work, different configurations of plasma torches and their application in waste treatments are examined. The plasma discharge process was characterized by optical emission spectroscopy (OES) for obtaining some plasma parameters like temperature distribution in the plasma column. Efficiency in the waste degradation, for several experimental conditions, was also studied besides important electrical parameters normally linked to the mechanisms through which plasma discharge gains or loses energy are also presented. In addition, the principal characteristics of the plasma torch power supply are also described.

Tungsten carbide nanopowder by plasma-assisted chemical vapor synthesis from WCl6–CH4–H2 mixtures

Nanosized tungsten carbide powder was prepared by a thermal plasma process using tungsten hexachloride (WCl6) as the precursor. The reduction and carburization of the vaporized precursor by methane–hydrogen mixtures produced nanosized WC1−x powder, which sometimes contained WC and/or W2C phase. The effects of the molar ratio of reactant gases, plasma torch power, the flow rate of plasma gas, and the addition of secondary plasma gas (H2) on the product composition and grain size were investigated. The tungsten carbide powder produced by the plasma process showed particle sizes less than 20 nm. The produced powder was heated in hydrogen to fully carburize the WC1−x, and W2C phases to the WC phase as well as to remove excess carbon in the product. Finally, WC powder with particle size less than 100 nm was obtained.

Processing–microstructure relationships for plasma-sprayed yttrium aluminum garnet

Plasma-sprayed yttrium aluminum garnet (YAG) has been considered as a component in a thermal barrier coating system to reduce oxidation of the bond coat by impeding oxygen diffusion through the coating. For this application, a fully crystalline, dense YAG coating would be advantageous to maximize lifetime and minimize oxygen diffusion. The effects of nine processing variables on the porosity and percent crystallinity in plasma-sprayed YAG were determined. Two powder types were investigated to compare a commercial, off-the-shelf, fused-and-crushed powder to a specially-processed, spherical plasma-spray powder. The resultant models suggest that plasma torch power and spray distance had the largest effect on the responses. It was determined that the processing parameters that lead to a coating with low porosity produce a coating with low crystallinity and vice versa. A possible route to producing a dense, crystalline coating was explored where a dense, amorphous coating was subsequently heat treated to produce crystalline material that retained the microstructure of the as-sprayed YAG in the bulk of the coating. However, macrocracking in the system due to thermal mismatch and crystallization stresses would need to be addressed for a viable multilayer TBC.

Plasma torches and electrophysical parameters of the diaphragm discharge in water

This work is aimed at studying plasma torch formation, voltages, currents, power distribution, and resistance variation in the case of the little understood low-energy (≤10 J) diaphragm discharge initiated in water and salt solutions. Plasma torches associated with this type of discharge differ considerably from those of other discharges. Different shapes of anode and cathode torches, breakdowns between the diaphragm and one of the electrodes, and a specific form of cathode breakdown are observed. It is found that the electrical conductivity of the medium influences the parameters of the plasma formations, current pulses, dielectric strength of the medium, current pulse variation at “semibreakdowns,” etc. Based on the experimental data, it is concluded that the process of discharge initiation differs from that described in the literature.

Influence of metal powder shape on drag coefficient in a spray jet

In plasma spraying, particle shape, size, distribution and density are the important factors to be considered in order to ensure high spray efficiency and better coating properties. In the present work, nickel, iron and aluminium irregular powders in the size range from 50 to 63 μm were spheroidized using thermal plasma processing. The spheroidization experiments have been carried out at different gas flow rates and plasma torch power levels. The sphericity was analyzed using shape factor. Drag coefficients of the powders were estimated using Reynolds number and sphericity of the powders in plasma. For irregular particles, the drag coefficient is higher than that of the spherical because of its large area of contact with plasma. The temperature dependent on drag coefficient is also discussed. Increasing temperature increases the drag coefficient of the powder particles injected in to the plasma jet. Increasing plasma jet temperature changes the density and viscosity of the plasma which affects the particle’s drag coefficient in the plasma. The results are reported and discussed.

Chemical vapor synthesis (CVS) of tungsten nanopowder in a thermal plasma reactor

Abstract Nanosized tungsten powder was synthesized by a thermal plasma process using ammonium paratungstate (APT) as the precursor. The injected precursor was vaporized in the plasma flame and the subsequent reduction of the vaporized precursor produced nanosized tungsten powder. The effects of H 2 concentration, plasma torch power, and the flow rate of plasma gas on the product properties were investigated and particle size was determined. From the results, nanosized tungsten powder of particle size less than 50 nm was obtained by the thermal plasma process.

Solution Precursor Plasma Spray of Nickel-Yittia Stabilized Zirconia Anodes for Solid Oxide Fuel Cell Application

In conventional plasma spray of SOFC components, the large NiO and YSZ particles used, about 50-150 microns for high porosity coating, reduce the density of three-phase sites for electrode reaction. In this article, the SPPS process was used to synthesize and deposit Ni-YSZ anodes. The results show that several process parameters have significant effects on the microstructure and phase composition of the deposited material. The deposits were composed of tower-like, irregularly shaped agglomerates and smooth surface deposits. The sizes of the agglomerates increase with the decrease of the plasma-torch power and most are not completely molten during the impact. After heat treatment to reduce the NiO present in the as deposited coatings, the coatings were found to contain spherical YSZ particles about 0.5 μm in diameter distributed in a continuous Ni matrix, which is verified by both SEM observation and electrical resistance measurement. The coatings have 30-50% porosity.

Thermal Plasma Synthesis of BaFe12O19 (BaM) Films

Barium Ferrite (BaFe12O19) films have been successfully deposited on high silica glass substrates using an inductively coupled plasma source. Precursor of the metals used was a barium acetate and ferric nitrate solution of controlled concentration which was injected into the hot region of the plasma using a nebulizer. Variables studied included molar ratio of precursor liquid, substrate to plasma distance, plasma torch power, and oxygen concentration in plasma and carrier gas. Films were characterized for microstructure, composition and magnetic properties using scanning and transmission electron microscopy with energy dispersive spectroscopy, X-ray diffraction, and vibrating sample magnetrometry. Results indicate that barium ferrite forms under certain conditions of oxygen content in the plasma and substrate temperature above 800°C. Magnetic properties indicate that there is some degree of preferred orientation of the barium ferrite crystals on the substrate, and coercivity and magnetization correspond to that of a hard magnetic material.

Plasma spray coating of fly ash pre-mixed with aluminium powder deposited on metal substrates

Plasma spray technology has the advantage of being able to process low-grade-ore minerals to produce value-added products, and also to deposit ceramics, metals and a combination of these, generating homogenous coatings with the desired microstructure on a range of substrate. The present work deals with the development of a ceramic composite coating on metal substrates using fly ash (the thermal power plant waste) pre-mixed with Al powder. Mixtures of fly ash with 5 and 15 wt.% Al powder were plasma sprayed onto copper and stainless steel substrates at various plasma torch power levels ranging from 10 to 20 kW DC. The coatings produced were characterised by X-ray diffraction, optical and electron microscopic studies and measurement of interface adherence strength. A maximum strength of 52 MN m −2 was recorded with a copper substrate. It is found that the coating quality and properties are improved with higher aluminium content in the feed material and are affected by the operating power level of the plasma.

99/01398 Thermal pyrolysis of used tires: the effect of plasma torch power and plasma gases : Chang, J. S. et al. Prog. Plasma Process. Mater., 1997, Proc. Int. Therm. Plasma Processes Conf. 4th, 1996, (Pub. 1997), 403–410. Edited by Fauchais, P., Bengell House, New York

99/01398 Thermal pyrolysis of used tires: the effect of plasma torch power and plasma gases : Chang, J. S. et al. Prog. Plasma Process. Mater., 1997, Proc. Int. Therm. Plasma Processes Conf. 4th, 1996, (Pub. 1997), 403–410. Edited by Fauchais, P., Bengell House, New York