Gas-phase synthesis of functional nanomaterials: Challenges to kinetics, diagnostics, and process development

Gas-phase synthesis of nanoparticles enables production of high-purity materials with well-controlled properties in continuous flow processes. It is an established technology for a couple of (mostly inorganic) commodities with more or less specific materials characteristics. However, increasing process understanding and control provides a chance for scale-up of highly specialized lab-scale technologies used for the manufacturing of unique materials to industrial scale. Nanoparticles with adjustable composition and size distributions are of interest for a wide variety of applications from coatings to electronics to functional materials, e.g., for energy conversion and storage. For the synthesis of materials with desired properties, the reaction conditions must be well controlled. Understanding the decomposition kinetics and mechanisms of vaporized precursor compounds, cluster formation, and the potential interaction with bath gases and flame chemistry is a prerequisite for a targeted synthesis of materials. The scientific challenges concerning the precursor chemistry and particle formation and the experimental and theoretical approaches to overcome them have a large overlap with those in combustion science. Kinetics experiments are carried out in shock-tube reactors with optical and mass spectrometric detection of intermediate and product species, and in flow reactors with laser-based detection of temperature and species concentration as well as molecular-beam sampling techniques. Reaction conditions such as temperature, intermediate species concentration and particle size must be determined in situ in lab-scale nanoparticle reactors and the definition of standardized experiments that allow to build-up large data bases for model development is important. The scale-up to pilot-plant-scale based on experimentally validated simulations finally helps to prove the viability of new technologies and their application on mass markets such as materials for batteries or catalysis. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.