Nanostructure Evolution: From Aggregated to Spherical SiO₂ Particles Made in Diffusion Flames

Abstract

The formation of nanostructured silica particles by oxidation of hexamethyldisiloxane (HMDSO) in co-annular diffusion flames is investigated by in-situ small-angle X-ray scattering (SAXS). This enabled the nonintrusive monitoring of the mass fractal dimension, the aggregate size, and the number of primary particles per aggregate, along with the silica volume fraction, the primary particle diameter, the geometric standard deviation, and the number density along the flame axis. Parallel to this, thermophoretic sampling (TS) of the particles and analysis by transmission electron microscopy (TEM) allowed for direct comparison of particle morphology to that obtained from the above SAXS analysis, which were compared also to the ultra-small-angle X-ray scattering (US-

Aerosol‐based technologies in nanoscale manufacturing: from functional materials to devices through core chemical engineering

“…12 Such capability allowed nonintrusive monitoring of the formation of perfectly spherical or fractal-like nanoparticles along with their temperature history in robust and flexible diffusion flames. 13 Interfacing particle mass and mobility measurements 14 led also to extraction of particle structure (fractallike dimension D f ), showing that aerosol particles hardly attain the asymptotic D f predicted by the well-known fractal simulations of Meakin, Mandelbrot and others. 15 Third, and most important for the synthesis of nanostructured materials, the understanding of how process variables affect product particle characteristics has enabled research for the synthesis of better performing materials than those available by other techniques.…”

“…Going one step further beyond particle composition 23 and structure, [12][13][14] there is a need for synthesis of nanostructured materials with engineered surfaces to take advantage of functional core properties (e.g., optic, magnetic, plasmonic, thermal or support) and avoid adverse ones (e.g., catalytic, toxic or flocculating). That way, surface-engineered nanoparticles can be readily incorporated in host matrices and devices.…”

Time-resolved structure investigation with small angle X-ray scattering using scanning techniques

“…The information about the nanometre-scale structure leads to an understanding of the basic physical principles involved in their formation and is a requirement for specific industrial applications. Similar experiments have been performed on soot nanoparticle formation of various types (Hessler 2001;Sorensen et al 2003;Gardner et al 2005;Kim et al 2006;Jossen et al 2006;Sztucki 2007;Camenzind 2008 Fig. 7 a Sketch of the diffusion flame and X-ray scattering geometry.…”

Aerobic Oxidation of Cyclohexane Catalyzed by Flame-Made Nano-Structured Co/SiO2 Materials

“…The actual Co content, measured by ICP-OES after digestion with HF, and the BET surface areas of the materials are summarized in Table 1. Flame-made silica particles from turbulent, vapor-fed flames are known to have an agglomerate size of around 10-300 nm [28], the structure of the agglomerates being very fractal (D f around 2.1) [29]. FSP-made silica-based materials usually show a type IV isotherm with a very small hysteresis loop and possess no micro-or mesoporosity as seen for Pt/SiO 2 [27] and V 2 O 5 /SiO 2 [30] catalysts.…”