Carbon black spectral features

The sizes of the cometary dust grains vary from less than a micron to probably several centimeters. Infrared observations near 10 pm show the silicate spectral features. In addition, there seems to be a black ingredient presumed to be carbon. Due to different accelerations from the solar radiation pressure, the larger particles follow the comet close in its orbit and are more concentrated to the orbital plane. They become sometimes visible in the anti-tails , narrow spikes which point towards the Sun by an effect of projection when the Earth crosses the comet s orbital plane. Non of the meteorites found so far on Earth seem to be of cometary origin. However, very fluffy micron sized interplanetary dust grains (Brownlee particles) which have been collected by high flying aircraft are possibly cometary debris. 

The data manipulation capabilities of the FTIR spectrometer can be used to quantitatively resolve the structural features which are superimposed upon the intrinsic absorption. The spectral features which exceed a baseline drawn between 1880 and 880 cm 1 in five independent preparation and measurement experiments are shown in Figure 4. The superposition of these five spectra illustrate both the reproducibility and the quantitative nature of this technique. The "resolved" spectra consist of three broad absorptions centered around 1725,1595 and 1245 cm1 and two superimposed sharp bands at 1135 and 1340 cm1. These latter peaks are characteristic of the particular type of carbon black and are presumably caused by impurities introduced in the manufacturing process. They may reflect the presence of residual sulfur compounds present in the form of sulfones or sulfonic esters in which the symmetric and antisymmetric stretching modes of the S02 vibrational modes occur in the range of 1140-1160 cm1 and 1300-1350 cm 1 [24], Note the absence of discemable bands above 1730 cm 1. This implies that these carbon blacks do not contain the lactone and cyclic anhydride functionalities observed on other carbon surfaces (see Figure 1) [17]. 

The dominant bands in the resolved spectra obey Beer s law in that the magnitude of the absorbance (defined in terms of the peak heights relative to a linear baseline drawn between 880 and 1880 cm1) is linear in both concentration and thickness (Figures 5 A B). Futhermore, when these spectra are divided by the magnitude of the intrinsic absorption at 2800 cm the resultant absorbances are independent of sample thickness and concentration as shown in Figure 6. This supports the previous conclusion that both the broad background absorption and the superimposed spectra are directly related to the chemical structure of the black. The data also demonstrate that the spectral features of carbon black can be routinely measured to within 0.005 absorbance units. This capabilitity for the quantitative measurement of the effects of various modification procedures... 

IR spectrum of the decomposition residues and the commercially available sodium carbonate are shown in Figure 15.18. The spectral features obtained for the residues around 1450 and 870 cm match exactly with the features of sodium carbonate with that reported in the literature [26]. This confirms that the residues contain sodium carbonate. The IR spectra of insoluble black particles did not show any spectral feature of C-C or C-H bonding. It is clear that the black particles were free of hydrocarbons. 

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