The microstructure of soot at larger (~1 s) residence times within a propane-air diffusion flame is here investigated by Transmission Electron Microscopy. Three classes of nanoparticles are observed. The first of them is recognised as the well-known class of primary particles (20-50 nm) that usually are reported to be the sub-units constituting the chain-like and fractal soot aggregates. The other two categories of carbon nanoparticles here evidenced are distinguished in sub-primary graphitical particles (6-9 nm) and elementary particles, (less than 5 nm). Sub-primaries appear to be graphite-like, ellipsoidal in shape and clustered together to form small chains of less than ten units. Elementary particles appear to be constituted by very regularly sized transparent shells (~ 4 nm) of amorphous carbon and by inner graphitic nuclei (~0.5-2 nm). Elementary particles are often observed to be closely packed together and to fill all the available space between graphitic layers and larger particles. Aggregation of sub-primary with primary particles is also observed to occur. Vesicle-like structures of external dimension about 15 nm with a shell about 5 nm thick, and short tubular structures of length 5-10 nm and diameter 0.5-1 nm are episodically individuated in TEM micrographs. Major result can be summarised in the evidence of a strongly polydispersed agglomeration mechanism occurring under three different scales of particle size. Implications of such a result, in terms of coagulation times for each of the observed nanoparticle typology are also discussed.
Electron microscopy evidence of aggregation under three different size scales for soot nanoparticles in flame
di Stasio S
2001
Abstract
The microstructure of soot at larger (~1 s) residence times within a propane-air diffusion flame is here investigated by Transmission Electron Microscopy. Three classes of nanoparticles are observed. The first of them is recognised as the well-known class of primary particles (20-50 nm) that usually are reported to be the sub-units constituting the chain-like and fractal soot aggregates. The other two categories of carbon nanoparticles here evidenced are distinguished in sub-primary graphitical particles (6-9 nm) and elementary particles, (less than 5 nm). Sub-primaries appear to be graphite-like, ellipsoidal in shape and clustered together to form small chains of less than ten units. Elementary particles appear to be constituted by very regularly sized transparent shells (~ 4 nm) of amorphous carbon and by inner graphitic nuclei (~0.5-2 nm). Elementary particles are often observed to be closely packed together and to fill all the available space between graphitic layers and larger particles. Aggregation of sub-primary with primary particles is also observed to occur. Vesicle-like structures of external dimension about 15 nm with a shell about 5 nm thick, and short tubular structures of length 5-10 nm and diameter 0.5-1 nm are episodically individuated in TEM micrographs. Major result can be summarised in the evidence of a strongly polydispersed agglomeration mechanism occurring under three different scales of particle size. Implications of such a result, in terms of coagulation times for each of the observed nanoparticle typology are also discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
