Plasma data processing, velocity measurements, and nano-sized titanium powder production by plasma quench techniques

Fourier transform techniques are used to perform the Abel inversion. Noisy and asymmetric data are filtered in the frequency domain and symmetrized by phase correction methods which have been developed in Fourier spectroscopy. A procedure which allows the degree of asymmetry to be distinguished from random noise is described. The procedure is illustrated with a Gaussian distribution which is noisy and asymmetric and with optical emission data taken in a plasma jet in a side-on configuration. The Fourier transform procedure is computationally efficient and it can filter the noise, determine the degree of cylindrical asymmetry, and perform the Abel inversion simultaneously.; The optical emission intensity in a low-swirl transient argon plasma jet at atmospheric pressure has been analyzed to determine plasma gas velocities along the center axis in a region from 0 to 10 mm from the jet exit. An abrupt decrease at about 4 mm from the jet exit is observed under all gas-flow and current conditions. Measurements on a second low-swirl jet with somewhat different anode-cathode geometry did not show such a transition in this spatial region and indicate that the results are very dependent on torch geometry.; Nano-sized titanium particles were synthesized by feeding titanium tetrachloride (TiCl{dollar}sb4{dollar}) into an argon-hydrogen plasma system which consisted of a D.C. plasma torch and a convergent-divergent supersonic reactor. The theory of convergent-divergent nozzles is briefly described and is used to predict the temperature inside the reactor from the measurements of the temperature distribution in the exhausting low pressure chamber. The free energy minimization technique is used to determine the mole fraction of the components in the plasma system. The hot plasma mixture undergoes an approximate adiabatic isentropic expansion in the reactor and the energy in the mixture, or its enthalpy, is converted to unidirectional velocity and hence the gas temperature is quenched very quickly. Results show that the system can achieve a temperature quench rate of greater than {dollar}10sp8{dollar} K/sec and produce particles of {dollar}sim{dollar}5 nm diameter with an approximately uniform size distribution.