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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Electrostatic atomization of viscous liquids and suspensions

Author: JAYASINGHE, Suwan

Year: 2003

Supervisor(s): Mohan Edirisinghe

The research carried out in this thesis describes the processing of liquids and ceramic suspensions, having a viscosity >1000mPa s, using electrostatic atomization, mainly in the stable cone-jet mode.

In electrostatic atomization, also called electrospraying a liquid or a suspension is made to flow through a needle and subjected to a high voltage set between the needle and a ground electrode. Two major physical properties, namely liquid conductivity and viscosity, affect electrostatic atomization and the investigations described in this thesis focused on the latter.

Firstly, a set of liquid mixtures were prepared using distilled water and glycerol. The dc conductivity of these mixtures were kept constant and the viscosity was varied. The mixtures were subjected to electrostatic atomization and in each case the mode of atomization, the cone/jet characteristics and relic sizes were studied as a function of viscosity. The effect of applied voltage on the electrostatic atomization of liquid mixtures was also investigated.

The second part of the research was concerned with the electrostatic atomization of an alumina suspension containing 21 vol.% of solids (highest filler level attempted to date using any jet based processing route). The applied voltage - flow rate - atomization mode map was constructed for this suspension incorporating peco-flow rate regimes. The effect of electrode configuration used for electrostatic atomization was also investigated.

The third and most innovative facet of research led to the discovery of ceramic - electrostatic atomization printing. Here a point-like ground electrode was used to print ceramic suspension droplets produced by electrostatic atomization including the printing of multiple tracks produced with the aid of several needles which worked simultaneously. In addition the ground electrode was changed to a ring shape to develop a new method to prepare open-cell ceramic foams with a very high porosity.