“…Spectral intensity at multiple wavelengths is usually merged into an instantaneous effective temperature, T p,eff ( t ), which provides some indication of the sensible energy of the nanoparticles within the probe volume at any instant and reduces the dimension of the input data. Most often, T p,eff is calculated by modeling the particle sizes as having some representative uniform diameter d p,eff [ 44 ] and by invoking Wien’s approximation, so that Eq. ( 1 ) may be rearranged into an explicit expression for temperature.…”
Section: Basicsmentioning
confidence: 99%
“…Not meeting this requirement does not significantly impact the accuracy of Eq. ( 2 ) [ 44 ], but it can affect some of the underlying assumptions about the distribution of nanoparticle temperatures in the probe volume as described later in this paper. Fig.…”
Section: Basicsmentioning
confidence: 99%
“…Results show excessive absorption, where the absorption efficiency required to reach the pyrometrically inferred peak temperature greatly exceeds that predicted using the Rayleigh approximation. Also shown are the values from Sipkens et al [ 60 ] when predicting the absorption efficiency using Mie theory [ 44 ], which partially resolves the excessive absorption problem. For this latter case, the height of the shaded boxes corresponds to the range of ratios observed across the experimental conditions in that study …”
Section: Basicsmentioning
confidence: 99%
“…This is particularly the case for composite materials, where the absorption and extinction cross-sections will depend on the bulk properties of the component materials as well as their distribution within the nanoparticle. Also, the laser pulse may profoundly affect the absorption and extinction cross-sections of the nanoparticle, either by altering the structure of the nanoparticle (e.g., aggregate sintering [ 62 ]) or by changing the atomic and molecular bonding within the nanoparticle (e.g., melting [ 44 , 63 ] or defect formation [ 64 ]). These changes are difficult to model or measure, and therefore, may significantly contribute to the overall uncertainty of the analysis.…”
Section: Basicsmentioning
confidence: 99%
“…We refer the reader to Ref. [ 44 ] for more information. Fitting to temperatures also requires some amount of data pre-processing, complicating uncertainty quantification, particularly when inferring information about the optical properties, which then get incorporated into computing the “data”.…”
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.
“…Spectral intensity at multiple wavelengths is usually merged into an instantaneous effective temperature, T p,eff ( t ), which provides some indication of the sensible energy of the nanoparticles within the probe volume at any instant and reduces the dimension of the input data. Most often, T p,eff is calculated by modeling the particle sizes as having some representative uniform diameter d p,eff [ 44 ] and by invoking Wien’s approximation, so that Eq. ( 1 ) may be rearranged into an explicit expression for temperature.…”
Section: Basicsmentioning
confidence: 99%
“…Not meeting this requirement does not significantly impact the accuracy of Eq. ( 2 ) [ 44 ], but it can affect some of the underlying assumptions about the distribution of nanoparticle temperatures in the probe volume as described later in this paper. Fig.…”
Section: Basicsmentioning
confidence: 99%
“…Results show excessive absorption, where the absorption efficiency required to reach the pyrometrically inferred peak temperature greatly exceeds that predicted using the Rayleigh approximation. Also shown are the values from Sipkens et al [ 60 ] when predicting the absorption efficiency using Mie theory [ 44 ], which partially resolves the excessive absorption problem. For this latter case, the height of the shaded boxes corresponds to the range of ratios observed across the experimental conditions in that study …”
Section: Basicsmentioning
confidence: 99%
“…This is particularly the case for composite materials, where the absorption and extinction cross-sections will depend on the bulk properties of the component materials as well as their distribution within the nanoparticle. Also, the laser pulse may profoundly affect the absorption and extinction cross-sections of the nanoparticle, either by altering the structure of the nanoparticle (e.g., aggregate sintering [ 62 ]) or by changing the atomic and molecular bonding within the nanoparticle (e.g., melting [ 44 , 63 ] or defect formation [ 64 ]). These changes are difficult to model or measure, and therefore, may significantly contribute to the overall uncertainty of the analysis.…”
Section: Basicsmentioning
confidence: 99%
“…We refer the reader to Ref. [ 44 ] for more information. Fitting to temperatures also requires some amount of data pre-processing, complicating uncertainty quantification, particularly when inferring information about the optical properties, which then get incorporated into computing the “data”.…”
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.
This work examines the excessive absorption and anomalous cooling phenomena reported in laserinduced incandescence measurements on metal nanoparticles by considering the effects of aggregate structure and sintering. Experimental investigations are conducted on iron and molybdenum aerosols, which have different melting points and thus respond differently to the laser pulse. Although aggregation enhances the absorption cross-section of the nanoparticles and allows for higher peak temperatures, this enhancement does not fully explain the observed excessive absorption. Furthermore, as the aggregates of refractory metals such as molybdenum cool, they may sinter through gradual grain boundary diffusion; this change in structure alters their absorption cross-section, manifesting as a rapid drop in the pyrometric temperature, which could explain the anomalous cooling reported for this metal.
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