Observing the conditions during the gas-phase synthesis of nanoparticles: Challenges to chemical kinetics and laser diagnostics

C. Schulz
University of Duisburg-Essen, DE

Keywords: nanoparticles

Summary:

The synthesis of nanoparticles in high-temperature gas-phase systems, such as flames, plasmas, and wall-heated reactors allows to generate high purity materials with well-controlled properties in continuous flow situations that provide a chance for scale-up to industrial scale. Nanoparticles with well-controlled composition and narrow 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, however, the reaction conditions must be well controlled and the underlying processes understood. The decomposition kinetics of vaporized metal organic compounds, the ignition properties of the mixture of these materials with oxidizing environments as well as the reaction mechanisms of the decomposition, cluster formation and the potential interaction with flame chemistry is a prerequisite for a targeted synthesis of materials. Kinetics experiments are carried out in shock tube reactors with optical and mass spectrometric detection of intermediate and product species, in flow reactors with laser-based detection of temperature and species concentration as well as in particle-generating systems connected to molecular-beam particle mass spectrometers. At the same time, reaction conditions such as temperature, intermediate species concentration and particle size must be measured in lab-scale nanoparticle reactors as well as in pilot-plant-scale reactors to provide input and validation data for numerical simulation. In this presentation these aspects will be introduced based on four systems, iron-penta-carbonyl-based synthesis of iron-oxide particles [1], the decomposition and reaction of Ga-based metal organic compounds [2], the formation of particles with tuned stoichiometry [3-4] of as well as the ignition, reaction and particle formation from silicon-based precursors for the synthesis of silicon dioxide particles [5]. Detailed mechanisms are derived from these measurements that than can be used for the simulation of reactive flows that then also allow to transfer the knowledge gained from small-scale laboratory experiments to the design of production plants that can be used to generate significant amounts of nanomaterials with well-defined properties [6].