Electrostatic charging of micro- and nano-particles for use with highly energetic applications

Electrostatically charging spherical and cylindrical conducting particles against an electrode with an applied electric field is investigated both theoretically and experimentally as a method of charging micro- and nano-particles for use with a variety of high energy and high velocity applications, which include nano-particle electrostatic space propulsion systems, materials processing, and nano-printing. Increasing the particles' charge-to-mass ratios is critical for maximizing their velocities when accelerated with applied electric fields, which requires minimizing the particles' sizes down to the micro- and nano-meter ranges for some applications. An analysis reveals that the charge-to-mass ratio is maximized with low aspect ratio particles when the maximum electric field strength, which is at the top of the particles, is held constant. Experimental results of charging titanium and aluminum spherical and cylindrical particles are presented, which suggest that under appropriate conditions, the particles are charged as predicted by theory. But that electrical contact resistance between the particles and electrode can influence the charging time. An analysis of the expected particle charging times is presented, which shows a strong dependence on the conductivity and thickness of the oxide layer coating the particles.