CARBONACEOUS DUSTS

Combustible dusts include metal dust (e.g., aluminum, magnesium, and their commercial alloys), carbonaceous dust (e.g., carbon black, charcoal, and coal), flour, grain, wood, plastics, and chemicals. 

Compiled from the following reports of the U.S. Department of Interior, Bureau of Mines Rl 5753, The Explosibility of Agricultural Dusts Rl 6516, Explosibility of Metal Powders Rl 5971, Explosibility of Dusts Used in the Plastics Industry Rl 6597, Explosibility of Carbonaceous Dusts Rl 7132, Dust Explosibility of Chemicals, Drugs. Dyes and Pesticides and Rl 7208, Explosibility of Miscellaneous Dusts.)... 

Group F. Atmospheres containing combustible carbonaceous dusts, including carbon black, charcoal, coal, or dusts that have been sensitized by other material so that they present an explosion hazard. 

Othmer, ChemProcessEng 45(4), 165-74(1964) (A dust-explosion test app is described and exptl data are reported) 51) M. Jacobson et al, USBurMines Rl 6516(1964) (Explosibility of metal powders) 52) J. Nagy et al, USBurMines Rl 6597(1965) (Explosibility of carbonaceous dusts) 53) J.P. Gillis, InstEnvironSciAnnuTechMeet,Proc 1965,... 

The explosibility of a carbonaceous dust is governed by its fineness and its volatile content. A hazardous dust would, in general, have a fineness greater than 200 mesh and a volatility greater than 13%. A governing factor for a metal or alloy would be its fine ness and for a plastic, molecular configuration plays a part. Other factors that play important roles in the initiation and development of an explosion are composition of the dust, concentration of the dust cloud, composition of the atmosphere and the ignition source. 

The basic information on the nature of the dust has been obtained from analysis of interstellar extinction from the near-infrared to the far-ultraviolet spectral region, using ground-based telescopes and the first space-borne ultraviolet telescopes. The derived interstellar extinction curve is in most parts rather smooth and shows only one broad and strong absorption feature centered around 220 nm (cf. Fitzpatrick Massa 2007). This feature is explained by carbonaceous dust grains (Stecher Donn 1965) with a wide distribution of sizes. The true nature of the carbonaceous dust material remains still somewhat unclear, but seems to be some kind of amorphous carbon (cf. Draine 2003, 2004, for a detailed discussion). 

Already the first infrared observations of late-type giant stars have revealed that many of them are indeed surrounded by thick dust shells (Woolf Ney 1969). These were rapidly found to consist of carbonaceous dust (some kind of soot) if the stellar spectrum indicates the star to be carbon-rich, and to be silicate dust (olivine, pyroxene) if the star is oxygen-rich (Gilman 1969). Since this dust is mixed into the interstellar medium due to mass loss by stellar winds, it was then assumed that silicate and carbon particles are abundant dust components in the interstellar medium. 

As it was pointed out above, AGB stars are the most prolific suppliers of stardust into the ISM (see Fig. 2.3). An example for dust injection by an AGB star into its surroundings is shown in Fig. 2.9. Oxygen-rich dust particles, mainly silicates, are expected to form at an early stage on the AGB, namely, when C/O < 1 in the stellar wind. Once C exceeds O in the wind, carbonaceous dust can form which occurs at a later stage on the AGB (see below). 

Although there is, as yet, no convincing evidence for the interstellar/circumstel-lar presence of C60, there are suggestive data [115]. Also, the proposal has been made that C60 can serve as a useful model for carbonaceous dust, at least in the limit of spherical carbon structures [110]. Mass spectrometry played a crucial role in the discovery of C60 and related fullerenes [116] in the laboratory in 1985, and once C60 became available in powder form in 1990 [117], mass spectrometry was used extensively to characterize this molecule with ionization, protonation and fragmentation experiments [118,119]. 

The vent ratio is defined as the ratio of vent area to the volume of the vessel. Based on the maximum rate of pressure rise in a 1.2-L Hartmann bomb, for vessels up to about 30 mk the vent ratio can be selected from Table 56.7. For most carbonaceous dusts, 1 5 seems to be a safe vent ratio. 

F Carbonaceous dusts, carbon black, coal black, charcoal, coal/coke dusts (>8% total entrapped volatiles). ... 

---