Spectroscopic temperature measurements in direct current arc plasma jets used in thermal spray processing of materials

An experimental study was conducted to determine the plasma temperature hel d and its parametric variation with respect to plasma operating conditions using emission spectroscopy. The focus of our study was the direct current (DC) are plasma systems used in thermal spray processing of ceramic materia ls. A commercial plasma system (Metco 9M series) was operated with mixtures of argon and hydrogen in the power input range from 12 to 36 kW, Temperatu re measurements were based on the detection of emission line intensities fr om Ar-I neutral species, Spatially resolved measurements were obtained of t he plasma temperatures in axisymmetric plasma jets using Abet deconvolution , The variation of plasma axial and radial temperature distributions was me asured as a function of the plasma input power, the total gas how rate, and the binary gas composition of argon and hydrogen, Time-averaged plasma gas temperatures were found to increase with increasing plasma input power, in creasing hydrogen content of the plasma gas, and decreasing total gas flow rate, Plasma temperatures decrease progressively with increasing distance f rom the nozzle exit, The peak temperatures near the nozzle exit are in the range of 12,500 to 14,000 K, The radial temperature profiles show an approx imately self-similar decay in the near field of these plasma jets, It was a lso determined from time resolved intensity measurements that there are sig nificant fluctuations in the argon emission intensity with increasing hydro gen fraction in the mixture, These fluctuations with a typical frequency of 5.2 kHz are attributed to the are root instabilities observed before, Fina lly, the measured plasma temperature field is empirically correlated in ter ms of radial and axial coordinates, plasma electrical input power, plasma e fficiency, and gas composition, These temperature data can be used to valid ate numerical simulations as well as in choosing locations where different materials can be introduced into the plasma jets. This is particularly impo rtant for "nanostructured" materials, which loose their structure upon melt ing as a result of being exposed to high plasma temperatures.