Soot-particle core-shell and fractal structures from small-angle X-ray scattering measurements in a flame

Distinguishing Gas-Phase and Nanoparticle Contributions to Small-Angle X-ray Scattering in Reacting Aerosol Flows

“…43 The Thomson scattering length (or classical Thomson electron radius) 44 is given by r 0 = e 2 /mc 2 , 45 where e is the charge of an electron (1.602177 × 10 −19 C); m is the mass of an electron (9.1093836 × 10 −28 g); and c is the speed of light (2.9979246 × 10 10 cm/s), such that r 0 = 2.81794 × 10 −13 cm. The square of the Thomson scattering length gives the differential Thomson cross section for a free electron, 42 that is, r 0 2 = 7.94079 × 10 −26 cm 2 . The molecular form factor in eq 1 can be approximated according to the method proposed by Debye, 42,46,47 that is…”

“…The square of the Thomson scattering length gives the differential Thomson cross section for a free electron, 42 that is, r 0 2 = 7.94079 × 10 −26 cm 2 . The molecular form factor in eq 1 can be approximated according to the method proposed by Debye, 42,46,47 that is…”

“…SAXS measurements in a flame involve passing a beam of collimated, monochromatic hard or tender X-ray photons through the flame and measuring the photons scattered by the particles and gas-phase species as a function of scattering angle on a position-sensitive detector placed several meters downstream of the flame. The angular distribution of the scattered photons provides information about the particle size distribution, morphology, and internal structure. ,, …”

The Identity and Chemistry of C7H7 Radicals Observed during Soot Formation

“…The particles they identified as incipient were sampled at the beginning of the luminous zone, indicating that the particles were likely partially aged, perhaps explaining the larger hydrocarbon masses observed. Faccinetto et al similarly sampled particles at the beginning of the luminous zone, and Jacobson et al sampled particles from flame regions where soot was mature enough to produce a signal from laser-induced incandescence (LII), a technique that lacks sensitivity to incipient particles . The cumulative body of theoretical and experimental work performed to date thus strongly indicates that thermodynamically driven nucleation is unlikely to occur at atmospheric pressure.…”

“…Thermodynamically driven mechanisms require species to have low enough volatility that they can nucleate at soot-inception temperatures (900–1700 K ,− ), and multiple studies have demonstrated that such a phase transition would require species that are larger ,− than typically observed − under soot-inception conditions at atmospheric and lower pressures. A few studies, on the other hand, have demonstrated polycyclic aromatic hydrocarbon (PAH) species large enough to explain inception via nucleation; − these studies, however, appear to be influenced by soot-aging effects.…”