Thermodynamic Barrier to Nucleation for Manganese Oxide Nanoparticles Synthesized by High-Temperature Gas-to-Particle Conversion

A complementary experimental and modeling study is reported here for nucleation of manganese oxide nanoparticles in premixed stagnation flames. The current synthesis occurs at relatively high flame temperature and low precursor loading. Thermodynamic analysis based on the postulated nucleation process, Mn(g) + O-2(g) -> MnO(s), is carried out to quantify precursor supersaturation and potential impacts of the Kelvin effect on particle formation. Nucleation and growth are analyzed based on the computed temperature-time-oxygen history in the postflame region. Agreement between measured and computed flame position for the base flame and precursor doped flames indicates that the manganese methylcyclopentadienyl tricarbonyl precursor does not inhibit flame chemistry for the conditions currently studied. Particle size distributions measured by mobility particle sizing and TEM images show reasonable agreement. Moreover, the measured particle size is predicted much more closely by a nucleation-limited mechanism rather than the size predicted by coagulation-limited growth.