Autumn School on Materials Science and Electron Microscopy 2007

"Microscopy - advanced tools for tomorrow's materials"

Berlin, October 8th - October 11th, 2007

Quantitative HRTEM of carbonaceous aerosol particles

M. Pawlyta, S. Duber

Faculty of Earth Sciences,University of Silesia, 60, Bedzinska St., 44-200, Sosnowiec, Poland

Carbonaceous substances are important component of the atmospheric aerosols because of considerable influence the climate by altering the radiation balance and possible health effects. In atmospheric aerosols there is a continuum of carbonaceous particles [1]. At one end is the thermally refractory and strongly light absorbing near-elemental carbon (EC or soot) and at the other extreme are thermally reactive and colorless organic substances (OC). Soot particles are can be readily recognized under the transmission electron microscope by their special morphology [2]. The structure inside the aerosol soot primary particles (Fig. 1) is complex and similar to those of diesel soot [3-6] and carbon black (an industrial carbon material with widespread applications such as its use as a reinforcing agent in rubber, pigment in plastics and an electrically conductive or UV stabilizing agent in plastics) [7]. The soot particles consist of the 'basic structural units' (BSU). In these substructures 4-5 or more graphene layers are stacked together. The distances between the layers in the BSUs are larger than 0.335 nm, expected for pure graphite, and the graphene sheets are also shifted against each other [2,8]. Quantitative characterization of the microstructure could be performed by measuring BSU parameters, including the average distance of the interlayer spacing (d002), the stacking layer length (La) and the layer thickness (Lc) from the 002 lattice fringe images [9]. Some applications of this approach were tested earlier in the field of carbon characterization, in relation with environment problems, earth or universe sciences, or industrial carbon materials. Even though that the transmission electron microscope is too labor-intensive for routine investigations of atmospheric aerosol samples, it is of considerable value in testing and verifying other methods. Figure 2 demonstrates effects of heat treatment on the carbon black structure. Quantitative results obtained by HRTEM are compared with values obtained by Raman spectroscopy (Fig. 3), very promising tool for the quantification of graphite-like carbon and soot in aerosol filter samples. References [1] Pöschl, U. Angew. Chem. Int. Ed Engl., 2005, 44 (46):7520-40.

[2] Oberlin, A. In: Thrower PA, editor, Chemistry and physics of carbon, vol. 22, New York: Marcel Dekker,

1989, pp. 1–143.

[3] Kittleson, D.B., Journal of Aerosol Science, 1998, 29: 575-588.

[4] Clague, A.D.H., Donnet, J.B., Wang, T.K., Peng, J.C.M., Carbon, 1999, 37: 1553-1565.

[5] Manzello, S.L., Choi, M.Y., International Journal of Heat and Mass Transfer, 2002, 45(5): 1109-1116.

[6] Luo, C.H., Lee, W.M.G., Lai, Y.C., Wen, C.Y., Liaw, J.J., Atmospheric Environment, 2005, 39: 3565-3572.

[7] Hess, W. M., Herd, C.R., 1993. In: Donnet, J.B., Bansal, R.C., Wang, M.J. (Eds.), Carbon Black. Dekker,

New York, 89-173.

[8] Jäger C., Henning Th., Schlögl R., Spillecke O., Journal of Non-Crystalline Solids, 1999, 258: 161 – 179.

[9] Rouzaud, J.N., Clinard, C., Fuel Processing Technology, 2002, 77-78: 229-235.

Fig. 1. An aerosol soot primary particle consists of the concentrically arranged 'basic structural units'. Four graphene layers stacked together inside the BSU .

Fig. 2. Nanostructure of the untreated (left) and heated at 2700oC (right) primary particle (carbon black Printex 25, manufactured by Degussa).

Fig. 3. Raman spectra of carbon black (Printex 25) for different treatment.