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A specially-designed plasma chamber was constructed to study the operating characteristics of a dc plasma transferred arc struck between a fluid convective cathode and a water-cooled anode. The plasmagen gas consisted of pure argon and arc lengths as high as 7 cm were studied. / The arc voltage increased markedly with arc length and with an increase in the inlet velocity of the argon flow past the cathode tip, and much less with an increase in current. The effect of the gas velocity was minor at low velocities (1 to 3 m/s) but became important at higher velocities (20 to 60 m/s). / Arc length and gas velocity were again the major factors in the distribution of the arc energy. For long arcs and at high gas velocities, the energy emitted by the arc to the wall of the chamber was dominant, while for short arcs the energy absorbed by the water-cooled anode was greater. In all cases, the fraction of the input energy absorbed by the water-cooled cathode, or leaving the system as sensible heat in the exit gas was small. At the anode, the major contribution was from electron recombination, with convection heat transfer from the plasma somewhat less. Direct radiation from the plasma to the anode surface was very small. The recombination of the electron stream occurred on a very small area of the anode ((TURN) 5 mm in diameter). In spite of the energetic water cooling, appreciable vaporization took place on that area. / Appropriate instrumentation permitted the measurement of the stagnation-pressure and pressure distribution on the anode, and that of total heat flux and radiative heat transfer. From the latter, it was estimated that the plasma temperature just above the anode was in the range 10,000 - 12,000 K. / Preliminary experiments with an anode consisting of molten copper showed that the arc root was no longer fixed, but moved around continuously. The arc was otherwise quite stable, and its operating characteristics differed little from those reported for solid anodes, in spite of the greater extent of metal vaporization.

The basic characteristics of a transferred arc argon plasma were determined. A cathode assembly suitable for transferring the electric arc to a molten metal bath or to a cooled anode was designed and constructed to produce the plasma in open air. It included provision for the injection of secondary gas into the arc column. / The measured electrical characteristics indicated that the sustained voltage depended strongly on the arc length and much less on current. The inlet gas velocity past the cathode tip was determined to be an important operating parameter, rather than the volumetric gas flowrate. / The measurement of the axial and radial profiles of temperature was effected with (+OR-) 8% accuracy by a novel diagnostic technique based on the determination of the variations in the outputs of a two-wavelength pyrometer that views a small section of the plasma, as the latter is swept rapidly by a blocking element. Temperatures up to 18,500 K were observed on the axis of the plasma column. / A sweeping microprobe was used to measure the axial and radial profiles of velocity. Velocities up to 190 m/s were recorded. The presence of a relatively colder flow surrounding the plasma column was detected. Mass and energy balances performed by taking this flow into account agreed with the measured input rates.

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The thermal plasma production of fumed silica in a transferred arc consists of the decomposition of quartz to SiO (g) and oxygen followed by an oxidizing quench back to SiO2. The particles formed have diameters of the order of 10 to 20 nm and are linked in a three dimensional branched chain aggregate. Previous work by Addona and Munz (1999) demonstrated the technical feasibility of producing fumed silica using this method, but was unable to demonstrate the special rheological properties of the powder. The most important characteristic of fumed silica is the presence of hydroxyls on the surface of the particles, in the form of isolated hydroxyl groups, hydrogen-bonded hydroxyl groups and siloxane groups. / In the present work, we studied the changes in the powder quality by varying the quench conditions used for the production of the powder and by agglomerating the obtained particles. The fumed silica was agglomerated by conveying in a length of tubing with sharp bends. The powder was characterized using BET, Viscosity tests, FT-IR, TEM, SEM and XRD. The product was compared to both a commercial product (Aerosil 200) and the material previously produced by Addona. Tests were done before and after the agglomeration experiments. / The experimental results showed that the agglomeration had no effect on the powder's rheological properties. We concluded that the smaller viscosity values obtained for the plasma produced fumed silica were due to the lack of the free hydroxyl groups from the surface of the particles.