A Study on Gas Evolving Electrodes under Extreme Current Densities

ABSTRACT A Study on Gas Evolving Electrodes under Extreme Current Densities Zahra Ghorbani Electrochemical discharges or electrode effects are used in different fields such as micro-machining, nano-particle production, and surface engineering. Further development and improvement of the different applications of electrochemical discharges require a better understanding of this process. Beyond the critical voltage, an insulating gas film forms around the electrode and discharges take place through the gas film. The stability of the gas film affects the quality of the discharges. The gas film formation is therefore investigated in the present thesis. The main objective of the current project is to attain a better insight into the gas film dynamics. This goal is achieved through the following approaches: 1. The current-voltage characteristics are studied prior to the gas film formation and then compared with a model developed based on the percolation theory. 2. Since the hydrodynamic forces define the shape and thickness of the gas film, the effect of the hydrodynamic parameters on a gas film are analyzed. Based on the Pi theorem and dimensional analysis, important dimensionless parameters are derived to investigate the gas film formation. 3. Different system configurations are examined to improve the electrochemical discharge activity. Visual observations indicate that stable discharges are obtained by using a covered electrode and applying an offset pulsed voltage. Key words: Electrochemical discharges, Gas film formation time, Gas film thickness, Gas bubble evolutio