ELECTROSTATIC ATOMIZATION OF VISCOUS LIQUIDS AND CERAMIC SUSPENSIONS
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The research carried out in this thesis describes the processing of liquids and ceramic suspensions, having a viscosity >100mPa s, using electrostatic atomization, mainly in the stable cone-jet mode. Electrostatic atomization, also called electrospraying, refers to a process where a liquid or a suspension is made to flow through a needle. The liquid or suspension is subjected to a high voltage maintained between the needle and a ground electrode. Two major physical properties, namely electrical conductivity and viscosity, affect electrostatic atornization in the stable cone-jet mode and the investigations described in this thesis focussed on the latter. Firstly, a set of liquid mixtures were prepared using distilled water and glycerol. The dc electrical conductivity of these mixtures were kept constant and the viscosity was varied. The mixtures were subjected to electrostatic atornization and in each case the mode of atornization, the cone/jet characteristics and relic sizes were studied as a function of viscosity. The effect of applied voltage on the conejet mode electrostatic atornization of glycerol having a viscosity of 1338mPa s was also investigated. Secondly, the possibilities of electrostatically atomizing ceramic suspensions were studied in detail. Several alumina suspensions were used including one containing a high volume fraction of solids (20 vol. % - the highest filler loading attempted to date using any jet-based processing route). Applied voltage - flow rate - atornization mode maps were constructed for this suspension incorporating even pico-flow rate regimes. This is a new input into the aerosol science and engineering literature. This section also highlights the importance of controlling the applied voltage and flow rate as these parameters affect the jet diameter and relic/droplet size generated. The effect of the geometry of the ground electrode used for electrostatic atornization was also investigated.In particular, the use of a point-like ground electrode was studied for the very first time. The third and most innovative facet of this research was the discovery of ceramic electrostatic atornization printing (CEAP) and the use of electrostatic atornization to produce ceramic foams. In CEAP a point-like ground electrode is used to focus the spray which was printed as characters, collection of characters and single tracks. This investigation was extended to explore the printing of multiple tracks produced with the aid of several needles and ground electrodes which worked simultaneously. A ring shaped ground electrode was used to electrospray ceramic droplets onto a polyurethane template and this paved the way for the development of a new method to prepare open-cell ceramic foams with a very high porosity. This method was extended to prepare ceramic structures and complex components.
AuthorsJayasinghe, Suwan Nalin
- Theses