Laser-induced incandescence for non-soot nanoparticles: recent trends and current challenges

Abstract

Laser-induced incandescence (LII) is a widely used combustion diagnostic for in situ measurements of soot primary particle sizes and volume fractions in flames, exhaust gases, and the atmosphere. Increasingly, however, it is applied to characterize engineered nanomaterials, driven by the increasing industrial relevance of these materials and the fundamental scientific insights that may be obtained from these measurements. This review describes the state of the art as well as open research challenges and new opportunities that arise from LII measurements on non-soot nanoparticles. An overview of the basic LII model, along with statistical techniques for inferring quantities-of-interest and associated uncertainties is provided, with a review of the application of LII to various classes of materials, including elemental particles, oxide and nitride materials, and non-soot carbonaceous materials, and core–shell particles. The paper concludes with a discussion of combined and complementary diagnostics, and an outlook of future research.

Combustion, Chemistry, and Carbon Neutrality

“…The exothermic combustion reactions can be used as a source of heat, and the reactive environment can contribute to forming nonequilibrium products. Technologies, analyses of process conditions, characterization of material properties, and current and emerging applications have been described in a number of recent review and perspective articles. − While syntheses can be performed entirely in the solid state or in solution, , the focus here will be on the formation of solid (nano)­materials from the gas phase in different burner and reactor configurations. − As one strategy, precursor solutions may be introduced into a flame as spray or aerosol, where evaporation occurs and desired nanoparticles may form in the reactive gaseous environment. − Process diagnostics is challenging under such multiphase conditions with time-dependent nanometer-sized particle growth and can build on techniques used in combustion (Section ), including laser methods and mass spectrometry. − The analysis of the flame conditions must be complemented with in-depth characterization of the formed material to establish process–structure–function correlations. Nanostructures from such processes can be as different as particles, fibers, sheets, films, porous materials, and composites .…”

“…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). , …”

Simultaneous Inversion of Particle Size Distribution, Thermal Accommodation Coefficient, and Temperature of In-Flame Soot Aggregates Using Laser-Induced Incandescence

“…LII-based particle sizing involves exposing soot particles to nanosecond pulsed lasers, elevating them to incandescent temperatures (~3000 K), and generating LII signals [ 9 , 10 ]. Over the past two decades, LII technology has witnessed notable advancements [ 11 , 12 ]. Initially designed for pointwise (0D) or line-wise (1D) measurements, it has evolved to facilitate 2D imaging of planar LII (PLII) signals and even 3D volumetric LII (VLII) signal reconstruction [ 13 , 14 , 15 ].…”

Spectroscopic Properties of Semiconductor Nanoparticles near the Solid-to-Liquid Phase Transition

“…Optical diagnostics based on elastic light scattering, , line-of-sight absorption, and laser-induced incandescence (LII) − are routinely used to measure the particle size, phase, and concentration distribution in situ in order to gain insight into the nanoparticle synthesis process. All of these diagnostics require robust spectroscopic models that connect the optical data with properties of interest, e.g., size, volume fraction, and phase.…”