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Siliceous dusts

Miners, stonecutters, and others engaged in work where siliceous dust is breathed into large quantities often develop a serious lung disease known as silicosis. [Pg.34]

Silicate dust Marine High temperature processes volcanic, rock and plant emissions, forest fires Anthropogenic... [Pg.124]

Silicon w is first isolated and described as an element in 1824 by Jdns Jacob Berzelius, a Swedish chemist. Silicon does not occur uncombined in nature, i.e.- as an element. It is found in practically aU rocks as well as in sand, clays, and soils, combined either with oxygen as silica (Si02= silicon dioxide) or with oxygen plus other elements (e.g., aliuninum, mcignesium, calcium, sodium, potassium, or iron) as silicates. Its compounds also occur in all natural waters, in the atmosphere (as siliceous dust), in many plants, and in the skeletons, tissues, and body fluids of some animals. [Pg.309]

Despite the quantitative variability of salts and silicate dust particles in the plants of Arid ecosystems, we can easily discern a trend towards the selective uptake of trace elements. The calculation of coefficient of biogeochemical uptake (Cb) shows the rates of exposure to heavy metals in biogeochemical food webs. One can see that the elements contained in the plant species of both Steppe and Desert ecosystems are in equal measure susceptible to the influence of environmental factors. The most extensively absorbed are Sr, Cu, Mo, and Zn. Their values of Cb are more than unit. The group of other elements, like Ti, Zr, and V, are poorly taken up, with their values of Cb often dropping below 0.1 (see Figures 4 and 5). [Pg.177]

The aerial parts of grasses in Savanna ecosystems exhibit a high ash content from 6 to 10%. This is partly due to the presence of minute particles of mineral dust, which are discernible under a microscope or, occasionally, even with the naked eye. The exposure to mineral dust accounts for 2-3% of the weight of dry mass of grass aerial parts. We can consider that this dust is responsible for the elevated concentrations of some minerals, like Ga, which has a low Cb value. This element contains in windblown finely dispersed clay particles. Nevertheless, even with allowance made for the silicate dust content, the total sum of ash elements in grasses of savanna ecosystems is twice as much as that of the grasses from Alpine Meadow ecosystems. [Pg.189]

Russell AE, Britten RH, Thompson LR, Bloomfield JJ The Health of Workers in Dusty Trades—II. Exposure to Siliceous Dust (Granite Industry.) US Public Health Service Bulletin No 187. Washington, DC, US Government Printing Office, 1929... [Pg.630]

Cosmic ray particles can work as a trigger of the chain of polymerization of formaldehyde adsorbed (e.g., at the surface of interstellar silicate dust). However, the triggering of the polymerization chain is a necessary but still not sufficient condition for obtaining the interstellar polymers. If the addition of any new link of the chain would require a hit of adsorbed monomer layer by another cosmic ray particle (i.e., if there is no spontaneous growth of chains after they are started by some external factor), the formation of polymers in interstellar space would be highly improbable. Therefore the spontaneous growth of polymer chains near absolute... [Pg.246]

It is now well established that surface defects and imperfections determine the chemical reactivity of solid surfaces, making defect engineering an important branch of modern solid state chemistry and physics. However, this reactivity can in turn be responsible for the toxicity of different silicate dusts. A number of interesting studies have appeared which correlate the surface properties of different silicates to their genotoxicity and potential health hazards.190 192 In particular the potential of a surface to generate and release free radicals via the... [Pg.310]

Infrared spectra of evolved stars are generally dominated by the radiation from their circumstellar shells. M stars are characterized by the 10 pm emission feature from silicate dust grains, while C stars by the 11 pm SiC band. However, some C stars have been found to show the 10 pm feature indicating the oxygen-rich property of their circumstellar dust (Willems and de Jong 1986, Little-Marenin 1986). [Pg.53]

The strict solution for the problem of the resistance to the motion of a small sphere moving through gas has been obtained by Baines et al. (1965). They considered both specular and diffuse reflection of the molecules at the surface of the sphere mass of which is large in comparison with the mean mass of gas molecules and the radius to be small compared with the mean free path of gas molecules. All these assumptions are applicable for circumstellar outflows. Fadeyev and Henning (1987) used these solutions for calculation of momentum transfer from silicate dust grains to gas molecules in cool 0-rich red giants... [Pg.179]

From theoretical considerations it was concluded in the 1960s that carbon (graphite) or silicate dust can condense in carbon-rich or oxygen-rich1 cool stars and that this dust can be driven out from the stars by radiation pressure (Hoyle ... [Pg.29]

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. [Pg.30]

With improved possibilities for infrared spectroscopy, broad extinction bands around 9.7 pm and 18 pm have been detected, which were ascribed to the stretching (Woolf Ney 1969) and bending (Treffers Cohen 1974) modes in the SiC>4 tetrahedron forming the building block of silicates, because they correspond to known absorption bands seen in all terrestrial silicates. These bands are also seen in the emission from dust shells around O-rich stars. This gave the first observational hints on the mineralogy of the silicate dust. The smooth, structureless nature of the bands indicated that the silicates in the ISM and in circumstellar dust shells are amorphous. [Pg.30]

Figure 2.2 A GEMS particle found in an IDP, consisting of a glassy matrix with silicate-like composition and embedded nanometer-sized inclusions of iron metal and iron sulfide (dark patches). Some of them are possibly interstellar silicate dust grains. (From NASA http //stardust.jpl.nasa.gov/science/sci2.html.)... Figure 2.2 A GEMS particle found in an IDP, consisting of a glassy matrix with silicate-like composition and embedded nanometer-sized inclusions of iron metal and iron sulfide (dark patches). Some of them are possibly interstellar silicate dust grains. (From NASA http //stardust.jpl.nasa.gov/science/sci2.html.)...
Laboratory studies of presolar dust grains also show that dust is formed in the mass ejected after an SN explosion, as will also be discussed in Section 2.2. Observations show that the ejected mass shells occasionally do form dust some time after the SN explosions (e.g. Bianchi Schneider 2007), but generally the efficiency of dust production seems to be rather low (Bianchi Schneider 2007 Zhukovska et al. 2008). Other important sources of stardust are red supergiants (mostly silicate dust). Most of the dust from red supergiants, however, is not expected to survive the shock wave from the subsequent SN explosion of the star (Zhukovska et al. 2008). Some dust is also formed by novae (Amari et al. 2001b), Wolf-Rayet stars (WRs, Crowther 2007), and luminous blue variables (LBVs, Voors et al. 2000), but the dust quantities formed by these are very small. Stardust - i.e. dust that is formed in stellar outflows or ejecta - in the interstellar medium is dominated by dust from AGB stars. [Pg.37]

Figure 5.5 Winds in the solar nebula might be one of the possible processes responsible for the mixing of hot and cold components found in both meteorites and comets. Meteorites contain calcium-aluminum-rich inclusions (CAIs, formed at about 2000 K) and chondrules (formed at about 1650K), which may have been created near the proto-Sun and then blown (gray arrows) several astronomical units away, into the region of the asteroids between Mars and Jupiter, where they were embedded in a matrix of temperature-sensitive, carbon-based cold components. The hot component in comets, tiny grains of annealed silicate dust (olivine) is vaporized at about 1600 K, suggesting that it never reached the innermost region of the disk before it was transported (white arrows) out beyond the orbit of Pluto, where it was mixed with ices and some unheated silicate dust ( cold components). Vigorous convection in the accretion disk may have contributed to the transport of many materials and has been dramatically confirmed by the Stardust mission (Nuth 2001). Figure 5.5 Winds in the solar nebula might be one of the possible processes responsible for the mixing of hot and cold components found in both meteorites and comets. Meteorites contain calcium-aluminum-rich inclusions (CAIs, formed at about 2000 K) and chondrules (formed at about 1650K), which may have been created near the proto-Sun and then blown (gray arrows) several astronomical units away, into the region of the asteroids between Mars and Jupiter, where they were embedded in a matrix of temperature-sensitive, carbon-based cold components. The hot component in comets, tiny grains of annealed silicate dust (olivine) is vaporized at about 1600 K, suggesting that it never reached the innermost region of the disk before it was transported (white arrows) out beyond the orbit of Pluto, where it was mixed with ices and some unheated silicate dust ( cold components). Vigorous convection in the accretion disk may have contributed to the transport of many materials and has been dramatically confirmed by the Stardust mission (Nuth 2001).
The spectral profiles of solid-state resonances from small particles depends on both the shape and the size of the particles. This is particular true for the strong mid-infrared Si-0 stretching and O-Si-O bending modes, characteristic of circumstellar silicate dust. In the dielectric spectrum, the stretching mode is roughly centered on 10 pm, while the bending mode is centered on 18 pm. Both resonances are very broad and strongly dependent on the structure of the molecules in which the SiO ... [Pg.200]

Silicate dust in both the diffuse ISM as well as in dense protostellar envelopes has been observed to exhibit a nearly constant band profile dominated by small particles (Bouwman et al. 2001 Kemper et al. 2005). In sharp contrast, silicate bands observed in emission from protoplanetary disks exhibit a wide range of silicate band profiles, indicating a dominant presence of dust particles larger than the Rayleigh limit (Bouwman et al. 2001 van Boekel et al. 2005 Kessler-Silacci et al. 2006). The interpretation of this observation is that the characteristic size of the dust particles has grown either by a move to a shallower dust size distribution, or by the removal of smaller particles (cf. Fig. 7.1). Either way, the inference usually made is that small particles have been removed by a coagulation process not occuring in the ISM. [Pg.201]

The earliest detailed studies of silicate dust in protoplanetary disks targeted those brightest in the mid-infrared, where high quality spectra could be obtained even by severely flux-limited observations. Cohen Wittebom (1985) reported the earliest detection of crystalline silicate emission from the environment of young stars and interpreted it as evidence for dust having been transformed from its pristine state in the interstellar medium to the material known to be contained in the comets and perhaps primitive meteorites. Interestingly, this observation and explanation pre-dated the evidence that young stars are surrounded by disks and not by spherical envelopes. [Pg.235]

Fine crystalline silicates dust jn the interstellar medium... [Pg.251]

What fraction of the primitive (silicate) dust left over from the early Solar System can be unprocessed, i.e. ISM-like Is there evidence for a crystallinity-age correlation in the chondritic matrices ... [Pg.258]

Ghio AJ, Crumbliss AE. 1992. Surface complexation of Fe by silica and silicate dusts increases in vitro oxidant generation but diminishes in vitro cytotoxicity. Durham, NC Duke University Medical Center, Division of Allergy, Critical Care, and Respiratory Medicine, Department of Medicine. [Pg.268]

Little-Marenin I. R. (1986) Carbon stars with silicate dust in their circumstellar shells. Astrophys. J. 307, L15-L19. [Pg.40]

Marker D. E. and Desch S. L. (2002) Annealing of silicate dust by nebular shocks at 10 AU. Astrophys. J. 565, L109-L112. [Pg.194]

Molster F. J., Waters L. B. F. M., and Tielens A. G. G. M. (2002a) Crystalline silicate dust around evolved stars II. [Pg.680]

C., and Chihara H. (2002b) Crystalline silicate dust around evolved stars III. A correlations study of crystalline silicate features. Astron. Astrophys. 382, 241-255. [Pg.680]

The 10 p.m feature of chondritic IDPs has been compared with the 10 p.m feature of astronomical silicates. No particular IDP IR class consistently matches the —10 p.m feature of solar system comets or silicate dust in the interstellar medium (Sandford and Walker, 1985). However, the —10 p.m features of CP IDPs composed mostly of GEMS and submicrometer enstatite and forsterite crystals generally resemble those of comets and late-stage Herbig Ae/Be stars in support of the hypothesis that some CP IDPs are of cometary origin (Figure 10). [Pg.694]

Addition of silicate dust (e.g. brick dust) and graphite. Such mixtures do not bum uniformly and leave a considerable residue. [Pg.617]


See other pages where Siliceous dusts is mentioned: [Pg.752]    [Pg.296]    [Pg.320]    [Pg.17]    [Pg.33]    [Pg.34]    [Pg.37]    [Pg.38]    [Pg.151]    [Pg.175]    [Pg.177]    [Pg.224]    [Pg.233]    [Pg.240]    [Pg.249]    [Pg.345]    [Pg.94]    [Pg.76]    [Pg.288]    [Pg.701]   
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