Nonthermal Plasma Synthesis Of Nanoparticles And Double Probe Diagnostic

Abstract

Nanoparticles are tiny particles that range in size from 1 to 100 nanometers. Their large surface area-to-volume ratio allows them to interact with their surroundings in unique ways. Nonthermal plasmas are particularly attractive sources for nanoparticle synthesis. In these plasmas, energetic plasma electrons decompose molecular gaseous precursors, producing radicals, which lead to the nucleation and growth of nanoparticles. This thesis investigates the feasibility of double probe measured in nonthermal dusty plasma and the mechanism of particle trapping and heating in nonthermal plasma synthesis of nanoparticles. This thesis also studies ICP synthesized size-tunable y-Al2O3 nanocrystals and reducing iron oxide particles by a MW hydrogen plasma. Double probes are utilized to diagnose the plasma properties of an argon:silane plasma containing nanoparticles. We demonstrate good stability of current-voltage characteristics over several minutes of operation. In addition, we developed a zero-dimensional global model to investigate the effect of the presence of nanoparticles on the plasma properties. Critical processes were investigated in nonthermal plasma synthesis of nanoparticles. We present experimental and computational evidence that, during their growth in the plasma, sub-10 nm silicon particles become temporarily confined in an electrostatic trap in radio-frequency excited plasmas until they grow to a size at which the increasing drag force imparted by the flowing gas entrains the particles, carrying them out of the trap. Furthermore, a nanoparticle heating model was used to study the temperature increase of a particle exposed to a plasma by exothermic surface reactions. y-Al2O3 is widely used as a catalyst and catalytic support due to its high specific surface area and porosity. We report a single-step synthesis of size-controlled and monodisperse, facetted y-Al2O3 nanocrystals in an inductively coupled nonthermal plasma reactor using trimethylaluminum and oxygen as precursors. Nanocrystal size tuning was achieved by varying the total reactor pressure yielding particles as small 3.5 nm, below the predicted thermodynamic stability limit for y-Al2O3. CO2 emissions from the steel production account for 8% of the global anthropogenic CO2 emissions and are a key challenge towards achieving a carbon-neutral future. We report an electrified process for reducing iron ore particles using atmospheric pressure hydrogen plasma powered by microwave energy. Iron ore particles were reduced steadily on a mesh exposed to the plasma. Moreover, in-flight iron ore reduction was achieved using the atmospheric pressure hydrogen microwave plasma, which is more than 100 times faster than the previously reported flash in-flight iron ore reduction by a thermal hydrogen technique.