Prediction of Spherule Size in Gas Phase Nanoparticle Synthesis

摘要: Surprisingly, there is still no rational yet practical method to reliably predict absolute ‘primary’ nanospherule sizes and, hence, specific surface areas, in gas phase flame nanoparticle synthesis. The present paper summarizes our approach this important problem, using a plausible and tractable coagulation–coalescence (two-rate process) model, but with an modification the rate of coalescence. Smoluchowski equation used describe particle Brownian coagulation process (free-molecule regime), together assumption that population follows self-preserving size distribution. decisive coalescence process, driven by minimization energy coalescing nanoparticles, presumed occur via mechanism diffusion. However, curvature-dependent barrier for surface-diffusion proposed, taking into account extended ‘surface-melting’ behavior nanoparticles. This shown here have effect accelerating touching leading (at predicted onset aggregate formation) encouraging agreement available experiments. It was found rate, especially curvature-augmented diffusivity, far more sensitive than rate. As result, when cast terms characteristic times, distinct crossover generally exists, allowing determination observed spherule within larger aggregates. successfully applied several published synthesis examples vapor-derived nanosized alumina titania. Its broader implications non-isothermal reactors, including own counterflow diffusion reactor, are also briefly summarized.