Discharges in liquids: applications for nanomaterial synthesis
Ahmad Hamdan
King Abdullah University of Science and Technology (KAUST) Saudi Arabia
abstract:
In this seminar, our recent experimental work on discharges in dielectric liquids will be presented. Several physical phenomena, such as pre-breakdown, discharge ignition, discharge-channel opening, and shock wave emission, occur within the time interval extending from the application of an electric field to the liquid until its breakdown (t < 200 ns). The breakdown is followed by the formation of an oscillating gas bubble in the gap. This latter was experimentally studied by high-speed imaging techniques and by modeling to estimate the pressure in the plasma at t ~0. We demonstrate that each discharge creates simultaneously one impact at the anode and one at the cathode, and that the diameter of the impact can be controlled by the charge injected. At this stage, the energy dissipation due to each physical phenomenon is estimated. In the case of discharges in liquid heptane with platinum-aluminum electrodes, we found that the energy dissipated in the plasma channel is more than 90% of the total injected energy. Note that the energy distribution between the physical phenomena is very sensitive to the experimental conditions, such as the electrodes’ nature and liquid’s properties.
Discharges in liquids were used for the synthesis of nanomaterial. Depending on the electrode nature and liquid composition, different families of nanomaterial were synthesized via electrode erosion and liquid dissociation / polymerization. For instance, using platinum electrodes and heptane liquid, we successfully synthesized nanocomposite material: nanoparticles of Pt embedded in a matrix of hydrogenated carbon. In the case of discharges in liquid nitrogen with lead (Pb) electrodes, a new crystallographic phase of 2D-nanostructures has been synthesized.
In order to further increase the efficiency of discharges in liquid, we developed techniques based on the discharge in bi-phasic media. The first technique is the injection of gaseous bubbles in the liquid, which facilitates the breakdown due to the low density of the gas compared to that of the liquid. The second technique is the use of mixture of two dielectric liquids with different dielectric permittivity. We will show that the control of the interface position of the two liquids with respect to the anode tip will improve the discharge characteristics. We will also show, in particular, that discharge at the interface of water- hexamethyldisilazane can be applied to the synthesis of hydrogenated SiOC nanoparticles, with production rate up to 10 mg/minute.
Web site of Dr. Hamdan.
