Gas-phase manufacturing of nanoparticles: Molecular dynamics and mesoscale simulations

Particle technology is used routinely for gas-phase (aerosol) manufacturing of carbon black, fumed SiO₂, pigmentary TiO₂, filamentary Ni, and ZnO for rubber vulcanization as well as for advanced materials (e.g., photocatalysts, nanofluids, and biomaterials) with a number of functionalities and high-performance applications. Aerosol processes offer distinct advantages in large-scale synthesis (tons/h) of such nanostructured commodities and facilitate particle handling and the formation of materials of high purity (e.g., optical fibers) with unique morphology. Furthermore, they allow more rigorous process design than in liquid-phase production of particles. Such nanostructures consist of clusters of primary particles (PPs) that are formed by chemical reactions, condensation/evaporation, or surface growth and grow further by sintering and coagulation. Depending on process conditions and particle residence time, coagulation and sintering (or partial coalescence) result in either aggregates (PPs held together by strong chemical bonds) which are attractive in catalysis, lightguide preforms, and electronics and/or agglomerates (PPs held together by rather weak, physical forces) that are attractive in nanocomposites, pigments, and liquid suspensions. This article gives an overview of recent advances in aerosol particle formation, crystalline structure, and process design optimization, highlighting the effect of dynamically evolving agglomerate structure on product characteristics.