Dusting materials

Except for siUca and natural abrasives containing free siUca, the abrasive materials used today are classified by NIOSH as nuisance dust materials and have relatively high permissable dust levels (55). The OSHA TWA allowable total dust level for aluminum oxide, siUcon carbide, boron carbide, ceria, and other nuisance dusts is 10 mg/m. SiUca, in contrast, is quite toxic as a respkable dust for cristobaUte [14464-46-1] and tridymite [15468-32-3] the allowable TWA level drops to 0.05 mg/m and the TWA for quartz [14808-60-7] is set at 0.1 mg/m. Any abrasive that contains free siUca in excess of 1% should be treated as a potential health hazard if it is in the form of respkable dust. Dust masks are requked for those exposed to such materials (see Industrial hygene). 

H. J. Grabke, Thermodynamics, Mechanisms and Kinetics of Metal Dusting, Materials and Corrosion, 49 303-308 (1998). 

Suppression of firedamp and coal dust explosions, in high humidity coal mines, by stone dusting is affected by humidity. Agglomeration of moisture content of the dusting material influenced its effectiveness as explosion suppressor. Salt dusts become ineffective above 80% relative humidity because they dissolve (Ref 7)... 

Except for silica and natural abrasives containing free silica, the abrasive materials used today are classified by NlOSH as nuisance dust materials and have relatively high permissible dust levels. 

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). 

Figure 2.3 Dust production and gas mass return rate by different stellar types in solar masses per year and kpc-2 in the galaxy at the solar cycle. Stars produce mainly silicate or carbon dust only in some cases is a different kind of dust material formed, probably iron or some iron alloy (peculiar dust). Many additional dust components with much smaller abundance are formed in most cases (Data from Tielens 1999 Zhukovska el al. 2008). Abbreviations of stellar types AGB = asymptotic giant branch stars of spectral types M, S, or C OB = massive stars of spectral types O and B on or close to the main sequence RGB = massive stars on the red giant branch LBV = luminous blue variables WCL = Wolf-Rayet stars from the lower temperature range Novae = mass ejecta from novae SN = mass ejecta from supemovae.

Dust particles in the ISM are subject to a number of destruction processes (Draine Salpeter 1979), e.g. sputtering of dust particles by energetic ions in hot(T > 5 x 105 K) supernova bubbles, evaporation of dust grains in high-velocity grain-grain collisions behind shock waves, or photo-sputtering of dust due to irradiation by hard ultraviolet photons. Such processes return part of the dust material... 

Gail (2002, 2004) has set up a series of large-scale simulations predicting the abundances of minerals formed in the early Solar System as based on assumptions on the input dust materials from the interstellar medium (ISM), and condensation,... 

Discrete dipole approximation. For particles with complex shape and/or complex composition, presently the only viable method for calculating optical properties is the discrete dipole approximation (DDA). This decomposes a grain in a very big number of cubes that are ascribed the polarizability a according to the dielectric function of the dust material at the mid-point of a cube. The mutual polarization of the cubes by the external field and the induced dipoles of all other dipoles is calculated from a linear equations system and the absorption and scattering efficiencies are derived from this. The method is computationally demanding. The theoretical background and the application of the method are described in Draine (1988) and Draine Flatau (1994). 

Data for almost all dust materials of interest for protoplanetary disks and for more general astrophysical applications have been determined by laboratory work. Tables for e or for n and k can be obtained from the Jena-St. Petersburg database.2... 

Hashimoto A., Kumazawa M., and Onuma N. (1979) Evaporation metamorphism of primitive dust material in the early solar nebula. Earth Planet. Sci. Lett. 43, 13-21. 

The participating laboratories had to apply moisture corrections according to the procedure recommended by the SM T programme, as well as corrections for extraction recoveries using a trimethyllead-spiked urban dust material provided along with the reference material. 

Grignard reagent and the mixture was shaken in the ultrasonic bath for a further 5 min. The hexane layer was removed from above by means of a 200 iL pipette. A small amount of anhydrous Na2S04 was placed within the pipette tip to dry the extract. This 25 pL of the final extract was injected into a GC-AAS system. The extraction recovery of trimethyllead in road dust was verified by spiking road dust material at a level of 4 pg kg . The range of recovery was from 66.5% to 91.3% for four replicates [mean of (77.6 9.5)%]. 

Dust material Godbert- Greenwald ignition temperatures Mini- mum explo- sion con- centra- tion g/m Mini- mum igni- tion energy mJ Maximum explosion pressure bar Maximum rate of pressure rise bar/s Maximum Oj concentration to prevent ignition % v/v... 

The second situation is that in which the dust particles are not chemically inert. They release irritant substances (acidic, alkaline or neutral) that are responsible for true irritant (i.e. chemically induced) contact dermatitis. When dust material is suspended in distilled water, the pH of the supernatant can be very alkaline, as mentioned in some reports (Lachapelle et al. 1984). Examples of dust materials producing alkaline solutions include anhydrite (pH 11.2), sewage sludge (pH 11) and trona (pH 10.5). Dried... 

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