Generation of Particles by Reactions

Abstract

Making particles by gas phase chemical reactions is a fascinating process. It makes some of the most widely used fine particulate commodities (carbon black, pigmentary titania, optical fibers, filamentary Ni, ferrites, fumed silica, etc.) and sophisticated nanomaterials (e.g. nanosilver, biomedical carbon-coated cobalt particles selling for $200/g). At the same time, this process is responsible for generation of air pollutants (e.g. soot) with profound effects on human health and environment (climate, visibility). As a result, it attracts keen interest from various scientific fields and many sectors of applications. In the context of classic particle technology and chemical reaction engineering, the reactors employed for synthesis of these powders are most closely related to lean phase fluidization with pneumatic transport as the solids volume fraction is very low, less than 10 even at production rates of 25 t/h. The text by Friedlander provides a lucid account of the fundamentals while the book of Kodas and HampdenSmith details various processes for aerosol synthesis of materials. The history of industrial development of the above commodities has been summarized and the in-situ (laser) diagnostics for characterization of such particles have been reviewed. A summary of processes for gas-phase synthesis of materials has been given while the fundamentals for multi-scale design of such processes have been presented quantitatively. Athanassiou et al. have shown how chemical engineering facilitates gas-phase synthesis of nanoparticles. The impact of aerosol processing in heterogeneous catalysis has been brought forward by a review of nearly 500 articles with Koirala et al. highlighting the role of scalable flame aerosol technology in catalyst synthesis and Fujiwara et al. pointing out the significance of strong metal-support interactions in such catalysts. Aerosol particle technology is attractive for the assembly of devices (nanogenerators, battery and fuel cell electrodes) and most notably for highly selective chemoresistive gas sensors for breath analysis. Here a summary of the fundamental phenomena and main processes for particle synthesis by gasphase reactions is provided along with references for more detailed coverage of specific aspects.