Development of a flame based process for controllable synthesis of ceramic nanoparticles

A novel flame-based process, termed combustion aerosol synthesis, for production of ceramic oxide nanoparticles with controlled characteristics was developed. The effect of process parameters on the synthesis and final properties of the nanoparticles such as the morphology, size and crystallinity was investigated. The combustion aerosol process was found to produce particles by two distinctly different mechanisms, which produced different morphologies of nanoparticles. Either of the particle formation mechanisms could be selectively activated by controlling the process variables thereby providing a good control of the final particle characteristics. The important process variables that affected the nanoparticles produced were found to be the flame temperature, the size of the droplet of the atomized precursor solution, the precursor type and its concentration. High temperatures led to precursor vaporization and were shown to produce agglomerated fractal-like particles, similar to those typically obtained from vapor based nanoparticle generation processes. Low temperature operation on the other hand produced unagglomerated spherical nanoparticles in a process similar to spray pyrolysis. By changing the droplets sizes, it was shown that unagglomerated spherical nanoparticles having a mean size of 60 nm could be produced. In addition, an alternate method for the control of the final particle sizes using hydrocarbon solvent mixtures to induce droplet fragmentation was successfully demonstrated. ^ The effect of the precursor type on the final particle morphology was also investigated. Inorganic precursors were controllably used to produce particles of either spherical or shell-like morphology. Organometallic precursors, on the other hand, were used to produce particles ranging from spherical, to shell-like, to agglomerated fractal-like morphology by controlling the precursor solution composition. Particles composed of yttria/zirconia and alumina/zirconia mixed oxides were synthesized using both inorganic and organic precursors. Sintering studies were conducted on pairs of similarly sized zirconia and yttria/zirconia nanoparticles in an aerosol stream. Comparison of the experimental data with calculations indicated that the classical two-sphere model could be used to predict the trends in the sintering behavior of nanoparticles as small as 40 nm. Finally the potential utilization of nanoparticles of controlled morphology and composition in making composite membranes for use in proton exchange membrane fuel cells was investigated.