Generation and Characterization of Micron and Sub-micron Sized Particulate using Electrothermal Plasma Source SIRENS
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Date
2003-07-07
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Abstract
The Surface Interaction Research Experiment at North Carolina State (SIRENS) is an electrothermal plasma facility which was recently used to generate particulate for the enhancement and modification of surfaces. The modification of fabrics by surface coating or particle implantation was a specific goal of the work. The SIRENS facility generates a low temperature, high density plasma using an exchangeable liner. The plasma expands from a 4mm diameter capillary into a 180mm diameter expansion cell inside a larger vacuum chamber where collection substrates and diagnostics can be used to collect particulate and analyze the plasma. A variety of conductive and nonconductive materials were used as both sources and substrates. Important for the surface modification applications is to analyze the particulate for composition and size from scanning electron microscope (SEM) images with particle counting software. Also important for the goal of eventually linking the plasma to the particulate generated is to characterize the plasma as it expands into the collection chamber. Therefore, the plasma density and temperature were measured using optical emission spectroscopy at distances 7, 32, 47, and 68cm from the source exit.
Shots were performed at similar input energies, approximately 5.7±0.14kJ. Particulate was collected using aluminum, copper, mixed aluminum/copper, Lexan, and Teflon liners. The aluminum, copper, and mixed materials all produced significant amounts of particulate that was visible with an SEM on both metal and fabric substrates. The Lexan and Teflon liners produced particulate that was only visible on fabric substrates. Washing tests showed that some particulate remained on woven fabrics after repeated washings.
The SEM images were recorded and analyzed to determine the number and size of the particulate on a substrate. Based on observations of the countable particulate, the particles were approximated as spheres and sized by the diameter determined from the measured area. Particle size ranged in diameter from approximately 0.1µm to 3.5µm, with the average size falling at or slightly below 1µm in diameter.
Important observations of aluminum particulate was that much melting occurred so that long streaks of solidified molten material were observed on the metal substrates. The size of the aluminum particles also showed a generally increasing trend with increasing distance from the source. The copper particles did not show the increasing trend and were, on average, smaller at each location. The mixed materials test returned particles composed of both metals, and with average diameters between those of pure aluminum and copper. The Lexan and Teflon particulate on fabric was too difficult to count and size; however one sample exposed to Teflon was more hydrophobic than an unexposed sample of the same fabric.
The plasma was also analyzed for temperature and density using optical emission spectroscopy. The results obtained experimentally were also compared to estimations of the plasma parameters based on the electrical and mass difference measurements of the discharge. Using the relative line method to construct Boltzmann plots, the temperatures of aluminum, copper, and Lexan plasmas were determined to be 0.5±0.125eV from the neutral copper lines. This temperature remained constant over the length of the discharge. The electron densities were determined from both Stark broadening of the H-alpha line and the neutral copper lines. The densities were found to be in the range of 10²²-10²⁴ m⁻³, with a more distinct decreasing trend with distance using the densities from the hydrogen line broadening. The parameter estimates from the discharge characteristics returned higher temperatures and lower densities. The estimates are useful for confirming the neutral-dominated and LTE assumptions about the plasma.
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Keywords
NE, TECS, electrothermal plasma
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Degree
MS
Discipline
Nuclear Engineering
