Studies on nanoparticle synthesis via gas-to-particle conversion

In this thesis the synthesis of nanoparticles via gas-to-particle conversion was studied both experimentally and theoretically. In the experimental part, nonagglomerated silver nanoparticles were produced via evaporation-condensation. It was shown that it is possible to control the particle size and degree of agglomeration using dilution. A new one-step process for synthesis of supported metal catalyst nanoparticles was developed. The carrier was produced via thermal decomposition of a metalorganic precursor and the metal was added via evaporation-condensation. The metal was well dispersed in 1-2 nm sized particles on the surface of the agglomerated carrier particles. A simple system was also developed for depositing single nonagglomerated nanoparticles with a narrow particle size distribution. The system relied on the competition between diffusion and negative thermophoresis. Ruthenium dioxide nanorods were synthesised via decomposition of ruthenium tri- and tetroxide vapours. However, since no optimisation of the system was done, the size distribution was broad. In the modelling part of this thesis the formation of silver nanoparticles via evaporation-condensation was studied. The modelling was done using two different approaches. In the first approach the classical nucleation theory and a sectional model were used, whereas in the second approach a discrete model was used and the nucleation was described as a dimerisation process. The results showed that for the classical nucleation theory to predict the final particle properties in the various cases, very different correction factors, 1-15 000, were needed. The kinetic nucleation approach gave better agreement between the model and experimental results.