Flame Synthesis of Nanoparticles - Investigation of Intermediates between Precursor Decomposition and Particle Nucleation

Flame Synthesis of Nanoparticles - Investigation of Intermediates between Precursor Decomposition and Particle Nucleation presented by Hartmut Wiggers on 2016-12-01
Authors: Hartmut Wiggers, Sebastian Kluge, Christof Schulz
Address: 900 Boylston St, Hynes, Level 2, Room 209, 02115, Boston, United States
Keywords: reactivity, nucleation and growth, nanoscale

Date: 2016-12-01 (08:45:00 - 09:15:00)


The production of inorganic nanoparticles from the gas phase is a standard method to manufacture a variety of bulk chemicals amounting to millions of tons a year. They are used industrially as reinforcements, pigments, stabilizers, catalysts or catalyst supports, flowing aids, and for multiple other applications. As gas phase processes enable for a kinetic control of nanoparticle formation, this method is basically favored for the production of metastable materials as doped nanoparticles and nanocomposites. Due to an increased understanding of size- and composition-dependent nanoparticle properties and probable applications thereof, an increasing demand in understanding synthesis steps towards the formation of specific nanoparticles with tuned properties has evolved. The principles of high temperature reactive particle formation in flames are characterized by a sequence of partly interacting rate processes in the gas flow, while the necessary energy is delivered by the exothermic combustion reaction heating the flow to high temperatures. A complete description of the precursor decomposition kinetics and the subsequent oxidation/hydrolysis reactions is rarely obtained, while the properties of the products manufactured like size, morphology, phase composition, and crystallography are decisively influenced by these parameters. Therefore, a precise understanding and control of the initial steps is required to open the ability for tuning particle properties. Within the last years, our low pressure premixed H2/O2 burner has evolved into a standard experiment for the investigation of intermediates occurring between precursor decomposition in the flame zone and particle nucleation downstream. Due to the spatial expansion of the almost one-dimensional low-pressure flame allowing for an increased time resolution, multiple experimental methods mostly based on online laser diagnostics and inline mass spectrometry enable a precise measurement of the emergence and disappearance of intermediate chemical compounds. This has extremely broadened the experimental database for the development and validation of simulations covering combustion and precursor decomposition as well as nanoparticle formation and growth. Examples will be presented for the growth processes of iron oxide and tungsten oxide nanoparticles. As flame synthesis in a low pressure premixed reactor is limited to vaporizable precursors, only a finite number of materials is accessible via this technique while spray flame synthesis of metal oxide nanoparticles covers an almost unlimited number of chemical compounds. Therefore, an outlook will be presented concerning strategies towards standardized experiments for the spray flame synthesis of nanoparticles that allow both, in-depth determination of experimentally accessible data as well as a detailed simulation of the nanoparticle production process.

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