Abstract
The investigation of droplet and nanoparticle formation in spray flame synthesis requires sophisticated measurement techniques, as often both are present simultaneously. Here, wide-angle light scattering (WALS) was applied to determine droplet and nanoparticle size distributions in spray flames from a standardized liquid-fed burner setup. Solvents of pure ethanol and a mixture of ethanol and titanium isopropoxide, incepting nanoparticle synthesis, were investigated. A novel method for the evaluation of scattering data from droplets between 2 µm and 50 µm was successfully implemented. Applying this, we could reveal the development of a bimodal droplet size distribution for the solvent/precursor system, probably induced by droplet micro-explosions. To determine nanoparticle size distributions, an appropriate filter and the averaging of single-shot data were applied to ensure scattering from a significant amount of nanoparticles homogeneously distributed in the measurement volume. From the multivariate analysis of the scattering data, the presence of spherical particles and fractal aggregates was derived, which was confirmed by analysis of transmission electron microscopy images. Monte Carlo simulations allowed determining the distribution parameters for both morphological fractions in three heights above the burner. The results showed relatively wide size distributions, especially for the spherical fraction, and indicated an ongoing sintering, from fractal to spherical particles.
Highlights
During recent decades, gas phase processes have developed into a commonly used technique for the synthesis of functionalized nanoparticles from a wide variety of materials and compounds [1,2,3,4,5]
We demonstrate the applicability of this method for superimposed scattering data from droplets and nanoparticles in an EtOH/titanium isopropoxide (TTIP) spray flame and present the first results from nanoparticle sizing for both spheres and fractals
EtOH spray flame, derived from the novel maxima-based method in comparison to those derived from the residual-based method of our previous work [23]
Summary
Gas phase processes have developed into a commonly used technique for the synthesis of functionalized nanoparticles from a wide variety of materials and compounds [1,2,3,4,5]. The economical production of high-purity product particles in a wide range of different materials and morphologies, and with defined functionality, is feasible [1,3]. In this process, non-volatile precursor materials are dissolved in a suitable solvent and atomized in a flame, initiating droplet evaporation, thermal decomposition of the precursor, and chemical formation of the desired particle material. A comprehensive investigation of the underlying processes of FSP is crucial for successful industrial scale-up, and this is systematically carried out within the framework of the priority program on ‘Nanoparticle Synthesis in Spray Flames: Spray-Syn: Measurement, Simulation, Processes’ (SPP1980) of the German Research Foundation (DFG), using a well-defined and standardized FSP burner setup, the SpraySyn burner [2,7,8]
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