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Abstract: Mullite and mullite-zirconia composites were prepared in twin step through low power transferred arc plasma (TAP) torch melting followed by mechanical mixing. The mixture was based on 3:2 mole ratios of alumina and silica; alumina and zircon were ball milled and melted for 3min in a transferred arc plasma torch at 3 kW input power with 10 lpm of argon flow rate. The phase and microstructure formation of the melted samples was investigated by XRD and SEM respectively. The crystalline behavior of the mullite and mullite–zirconia composite was evaluated by differential thermal analysis. The obtained results clearly showed that the complete mullization was achieved only in alumina–silica system and partial mullization occurred in alumina–zircon system due to the inadequate plasma torch input power. [Copyright &y& Elsevier]

Abstract: The excitation temperature and electron number density of the atmospheric pressure D.C. argon plasma jet during spheroidization of nickel have been measured at 5mm from the nozzle exit by optical emission spectroscopic technique. Emission spectra of the argon plasma, argon plasma with carrier gas and carrier gas with nickel powder were recorded in 400–450nm wavelength interval. The effect of carrier gas and powder loading on the excitation temperature and electron number density of the plasma jet were determined using atomic Boltzmann plot method and stark broadening of the Ar I (430.010nm) line respectively. The experiment was done at 6.5, 7.9, 11.4 and 12.1kW input power levels. Argon was used as plasma gas and also carrier gas. Nickel powders in the size ranging from 40 to 100μm were processed. On introduction of carrier gas and nickel powder loading, the excitation temperature and electron density of the jet were found to decrease. From the results, the degree of ionization of the plasma jet was calculated by using the measured excitation temperature and electron density values. The spheroidzed nickel powder was characterized by SEM, optical photographs and XRD. [Copyright &y& Elsevier]

Abstract: In the present work, hydroxyapatite (Ca10(PO4)6(OH)2) was prepared from bovine bones with calcination method (up to 850°C).The calcinated hydroxyapatite was powdered (30–40μm) using a mechanical grinder; the particles were highly irregular in shape with sharp edges, angular, rounded, circular, dentric, porous and fragmented morphologies. The irregular shaped calcinated hydroxyapatite was plasma processed to produce spherical powders for thermal spray coating applications. More over; calcium phosphate silicate glass ceramics was produced by plasma melting of ball milled hydroxyapatite–borosilicate glass (50wt.%) mixture. The samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD) and energy dispersive X-ray analysis (EDX). The morphology was determined using scanning electron (SEM) and optical microscopy (OM). The microhardness, density and porosity measurements for the synthesized samples were made. [Copyright &y& Elsevier]

Abstract: In this paper, the results of plasma spheroidization of iron powders using a DC non-transferred plasma spray torch are presented. The morphology of the processed powders was characterized through scanning electron microscopy (SEM) and optical microscopy (OM). The percentages of spheroidized powders were calculated by the shape factors such as the Irregularity Parameter (IP) and Roundness (RN). A maximum of 83% of spheroidization can be achieved. The spheroidization results are compared with the theoretical estimation and they are found to be in good agreement. The phase composition of the spheroidized powder was analyzed by XRD. The effect of plasma jet temperature and plasma gas flow rate on spheroidization is discussed. At low plasma gas flow rates and at high plasma jet temperatures, the percentage of spheroidization is high. [Copyright &y& Elsevier]

Abstract: In this paper, aluminium macro powders in the size range between 300 and 500μm are processed by thermal plasma processing. A 40kW DC non-transferred DC plasma spray torch was used to get the macro powders. The morphology and the size of the powders are discussed and the results are reported. The powders produced are doughnut shaped. The size ranges between 300 and 500μm. The macro particle size is estimated theoretically and found to be in good agreement with experimental results. The error percentage between theoretical estimation and experimental result is about 25%. The pressure inside the particle is estimated. The pressure gradient develops the indentation on the powder surface which seems to be doughnut. [Copyright &y& Elsevier]

Abstract: 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 50–60μm 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. [Copyright &y& Elsevier]

Abstract: 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 63μm 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. [Copyright &y& Elsevier]