Experimental and modeling studies on laser-driven aerosol synthesis and processing of nanoparticles
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In this dissertation, a CO 2 laser-driven photothermal reactor for production of nanoparticles was studied using both experiments and computer simulations. A novel technology to produce light emitting silicon nanoparticles in macroscopic quantities by gas phase laser-driven pyrolysis of silane has been developed. Due to many important potential applications of light emitting silicon nanoparticles, the synthesis and surface passivation of these particles has been extensively studied. Preparation of macroscopic quantities by the methods described here opens the door to chemical studies of free silicon nanoparticles that could previously be carried out only on porous silicon wafers, as well as to potential commercial applications of silicon nanoparticles. Magnetic nanoparticles are considered as ideal systems for fundamental research in several areas including superparamagnetism, magnetic dipolar interactions, and magnetoresistance. In our lab, iron and nickel nanoparticles with controlled size have been produced using the laser-driven aerosol synthesis reactor. Iron nanoparticles are prepared directly from commercially available iron carbonyl. However, to produce nickel nanoparticles, nickel carbonyl was generated in situ from activated nickel powder and CO at room temperature so that we never maintain any inventory of this highly toxic compound. By varying with the reaction parameters, we can control average particle size, typically from 5 to 50 nm in diameter. Results of magnetization measurements for small iron and nickel nanoparticles are also presented. Furthermore, we present a detailed 3D model of the laser-driven reactor system used in our laboratory to produce nanoparticles of silicon and other materials. This model includes detailed descriptions of the fluid flow, heat and mass transfer, and chemical reactions leading to silane decomposition in the gas phase. So far, eight chemical reactions and eight chemical species have been successfully incorporated in the reacting flow CFD simulation. The 3D CFD model was also used to simulate temperature and velocity fields during nickel production. From the detailed 3D CFD models, temperature and velocity profiles along the axis of the reactor have been extracted and coupled with the 1D aerosol dynamics model. Primary particle size, concentration and size distribution can be obtained from this simple model.