| Bimetallic nanoparticles with core-and-shell structures are being considered as new and promising catalysts with enhanced catalytic activity, better stability, and higher resistance to contaminants for fuel cells and other applications. This dissertation reports the experimental and modeling studies on synthesis of nanoparticles by spray pyrolysis process. Spray pyrolysis is a versatile technique for production of inorganic materials of a wide range of composition, size, and morphology. It typically consists of several steps including precursor preparation, precursor atomization, droplet evaporation, droplet precipitation, droplet drying, droplet coagulation, thermolysis, and sintering. The main objective of this research is to investigate and understand the fundamental properties of nanoparticles as a function of synthesis process parameters, especially the process conditions leading to the formation of bimetallic ruthenium (Ru) and nickel (Ni) nanoparticles with core-and-shell structures.;Ruthenium chloride and nickel chloride solution mixtures were used to synthesize the corresponding bimetallic Ru-Ni nanoparticles with core-and-shell structures by spray pyrolysis. It was found out that the Ru/Ni atomic ratio in the precursor and the pyrolysis temperature are the two most important process parameters affecting core-and-shell formation in the Ru-Ni nanoparticles. The precursor concentration also has a significant effect on the average diameter (<100 nm) of the bimetallic nanoparticles. Smooth Ru-Ni core-and-shell nanoparticles were obtained when the Ru/Ni atomic ratio was maintained between 3:1 and 5:1 at pyrolysis temperatures of 600°C to 800°C. It was also found that as the Ru/Ni atomic ratio in the precursor increased, the temperature required for core-and-shell formation could be lowered.;Synthesis of carbon supported nanoparticles was studied in this work to explore the application as electro-catalysts in proton exchange membrane fuel cells. Binary Ru-Ni nanoparticles were deposited on a carbon nanolayer that has an average particle diameter of 50 nm. The core-and-shell nanoparticles covered with carbon layer are thermally stable at temperatures up to 800°C. Ni-C carbon nanotubes and nanowires were obtained.;Effect of ammonium nitrate on the particle size reduction was studied for silver, ruthenium and nickel nanoparticles. Ammonium nitrate was added to the aqueous precursor solution and was subjected to pyrolysis in the reactor at high temperatures. The ammonia gas generated from ammonium nitrate decomposition was very effective in reducing the aerosol droplet size and resulted in about twenty times the reduction of the average diameter of the final particles. (Abstract shortened by UMI.). |
