In Situ Determination of Droplet and Nanoparticle Size Distributions in Spray Flame Synthesis by Wide-Angle Light Scattering (WALS)

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.

Characterization of Fractal Structures by Spray Flame Synthesis Using X-ray Scattering

“…However, only measurement techniques based on electron microscopy or light/X-ray scattering provide the necessary information [ 17 ]. Here, wide-angle light scattering (WALS) has shown great potential to analyze the shape and size of aggregates in the micrometer range [ 18 ].…”

Combustion, Chemistry, and Carbon Neutrality

“…Species detected, e.g., by LIF, include Fe, FeO, SiO, AlO, TiO, and others . Laser methods can be difficult to apply in dense media with spray and particle clouds, but techniques such as LII, LIBS, and line-of-sight attenuation can be valuable for analyzing the process development and/or materials properties in situ . ,,,, Further diagnostic approaches include tomographic imaging with multiple simultaneous emission measurements, wide-angle light scattering for in situ determination of droplet and particle size distributions, and mass spectrometry to probe the particle growth. , To improve the understanding of flame synthesis reaction systems further, specific aspects have been investigated in depth, for example by studying atomization, droplet formation, and droplet–gas phase interactions, or by modeling the dynamics of SiO 2 nanoparticle synthesis using Reynolds-averaged Navier–Stokes (RANS) or large eddy simulation (LES). , …”

Flame Synthesis of Carbon and Metal-Oxide Nanoparticles: Flame Types, Effects of Combustion Parameters on Properties and Measurement Methods

“…Yang et al [ 159 ] observed the isolated titania particles in the high-temperature region, and a sintering equation was developed based on the light scattering data. Simon et al investigated the size distribution of TiO 2 nanoparticles using a wide-angle light scattering method with pulsed light at 532 nm, which could also identify the presence of morphological fraction [ 170 ]. The formation of silica particles in co-annular diffusion flame was investigated by Adrian et al [ 160 ] using an in situ small-angle X-ray scattering (SAXS) technique, with the ability to monitor the mass fractal dimension, aggregate size, and the number of primary particles per aggregate.…”