Gas phase processing of nanostructured titania particles and films: Environmentally benign methodologies.

摘要

This dissertation is a study of the gas phase synthesis using flame aerosol reactors to produce nanostructured particles and films with desired features as size, morphology, agglomeration state, crystalline phase composition and modified solid state properties. The following particles/films were produced: titania, lead titanate, Mn-Zn ferrite, Fe{dollar}sp{lcub}3+{rcub}{dollar} doped titania and nanocomposites of FeO/TiO.; On supercooling titania droplets in flames, metastable anatase was preferentially nucleated. At high flame temperatures of 1570{dollar}spcirc{dollar}C, 100% anatase spherical titania particles were obtained; at 900 {dollar}sim{dollar} 1430{dollar}spcirc{dollar}C, polyhedral shaped particles with mixtures of anatase and rutile were obtained; and at 400{dollar}spcirc{dollar}C, amorphous titania was obtained. A 3-D computer simulation was used to study the aggregration and restructuring of small clusters in flames. These small aggregates are fractal-like and comply with the fractal power law only in a statistical sense, with a decrease in fractal dimension as the clusters become smaller. A cluster-restructuring model was developed to simulate the topological evolution in a high temperature sintering process. The fractal dimension was found to increase as sintering proceeded for small clusters, in contrast to large clusters where the fractal dimension remained constant. A light scattering technique was used to capture the sintering restructuring of nanosized titania particles in flames by in situ determination of the fractal dimension change of titania agglomerates. Laser Induced Fluorescence was used to optimize flame conditions to produce perovskite structured lead titanate particles in flame reactors. Also, the flame reaction provides a novel method to synthesize Fe(III) doped titania. As the doping concentrations varied from trace to comparable to TiO{dollar}sb2{dollar}, solid state properties of titania were modified. Substitutionally doped ferric ion accelerated the anatase-rutile transformation in flames, resulting in a more compact lattice structure and generating oxygen deficiency defects, as revealed by the increased shifting and broadening of anatase peaks in the Raman spectra. Further the UV/VIS absorption spectra was observed to be shifted towards the visible. As the iron dopant increased to the amount of comparable with titanium, the as produced pseudo binary mixture of FeO/TiO had superparamagnetic characteristics indicated by Mossbauer and magnetization measurements. Flame assisted aerosol coating processes were used to deposited titania films onto stainless steel and silica substrates. Deposition mechanisms were studied and related to the film characteristics. Interesting solid state properties were observed as the film thickness diminished to nanoscales. The titania films were tested to have a good anti-corrosive characteristics and other exciting functionality having wide applications.