Paper PS-ThP15
The Optical Diagnostics of Microplasmas in Different Types of Electrolyte Solutions

Thursday, October 21, 2010, 6:00 pm, Room Southwest Exhibit Hall

The optical diagnostics of microplasmas in various electrolyte solutions are performed. This microplasma is sustained by using a DC power source with the voltage up to 600 V. The powered electrode, the electrode where the plasma is ignited, consists of a thin platinum wire 0.5 mm in diameter covered by a glass tube. The grounding electrode is a bare platinum wire of the same diameter. Both electrodes are immersed in the solution. The electrolyte solutions studied include NaCl, NaNO₃, Na₂SO₄, ZnCl₂, Zn(NO₃)₂ and ZnSO₄ with the concentration of 0.01 M ~ 2 M . Time-averaged optical emission and time-resolved intensities of the light emanating from the plasma are studied. With an applied voltage greater than 500V and the concentration below 0.02 M, there exists a bubble that stays steadily at the electrode tip for many seconds, and microplasma is ignited inside the bubble. Under this condition, the emission of H, OH, O and atomic metal emissions are observed regardless of the electrolyte type. In the high concentration conditions and low applied voltages, atomic metal emissions dominate and nearly no H, OH, and O emissions are seen. It is observed that for all electrolyte solutions studied except NaCl, there exist a hump-like continuous emission band in the optical emission spectra between 400~900 nm. The source of this continuous band is not identified yet but can potentially be a result of the thermal emission or free-bound transition. In this presentation, the implication of the optical emission to the plasma reactivity will be discussed.