Asbestiform Fibers Nonoccupational Health Risks (1984) / Chapter Skim
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2 Asbestiform Fibers: Historical Background, Terminology, and Physicochemical Properties
2 Asbestiform Fibers: Historical Background, Terminology, and Physicochemical Properties
Pages 25-47
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From page 25... ...
As used in this report, the term asbestiform fibers includes fibers that possess great strength and flexibility, durability, a surface structure relatively free of defects, and several other properties described later. Commercial quality asbestos is an example of an asbestiform fiber.
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From page 26... ...
Roughly translated, it states: Multiple application, miraculous asbestos ointment for juvenile "tines" (head-fungus?
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From page 27... ...
The end members are identified by the hyphenated names, e.g., cu~mnington~te, which contains seven atoms of magnesium per chemical formula, and grunerite, which contains seven atoms of iron. Although asbestiform tremolite and actinolite occur In nature, large commercially mined deposits are rare.
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From page 28... ...
ASBESTIFORM HABIT refers to the unusual crystallization habit of a mineral when the crystals are thin, hairlike fibers. Historically, the definition of the asbestiform habit was based primarily on appearance, and the properties were only implied.
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From page 29... ...
and (110) planes, parallel with the c-axis ~ yielding acicular fragments.
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From page 30... ...
Asbestos is composed of distinct fibers with unique properties, whereas most fibrous quartz breaks into odd shaped fragments unrelated to its apparent fibrous appearance. The proper use of mineralogical nomenclature for fibrous materials, particularly asbestos, and problems that have arisen from improper usage have been discussed in several reports (Campbell et al., 1977; Lange r et al., 1979; Zoltai, 1978~.
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From page 31... ...
PHYSICAL PROPERTIES OF ASBESTIFORM FIBERS A complete listing of the physical properties of asbestiform fibers would be very extensive. However, their common properties, as compared with nonasbestiform crystals of the same minerals, comprise a relatively short list: · f iberlike morphology and dimensions enhanced strength and flexibility ~ lame tar-dependent strength · increased physical ant chemical durability · improved surface structure (i.e., relatively free of defects)
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From page 32... ...
Although acicular crystals and acicular fragments may also display a high aspect ratio, that ratio is almost always small compared to that of asbestos, since nonasbestiform crystals are more brittle and break more readily across the longitudinal axis. Comminution of asbestos, especially the amphibole varieties, may also produce some fragments with length-to-width ratios very similar to those observed for acicular crystals and fragments, but these are usually only a small proportion of the total mineral mass and would still be expected to possess the properties of asbestiform fibers.
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From page 33... ...
For example, asbestiform fibers are much more difficult to grins to a powder in a mortar than are the corresponding nona~bestiform cryseale. Furthermore, high quality amphibole asbestos does not possess prismatic cleavage planes.
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(See Figure 2-5. ~ Defect-Eree Surface Structure Many asbestos fibers have the shiny luster and high reflectivity indicative of a surface structure that is relatively free of defects.
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However, the conditions of growth great ly inf luence the properties of asbestos, whisker, and glass fibers. A strong surface structure with relatively few defects can develop only when the crystal grows in only one direction.
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From page 36... ...
In laboratories, whiskers are grown experimentally by creating various types of physical and chemical conditions that promote unidirectional growth (Wagner, 1970~. Because the physical quality of the fibers depends on the growth conditions, f iber properties will vary as the growth conditions vary.
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From page 37... ...
, which contribute to both the structural integrity and positive surface charge of the fiber, are leached from the fiber (Jaurand et el., 1979; Langer et al., 1972~. This leaching process apparently causes fragmentation of chrysotile and its faster disappearance from the lung in comparison to amphibole types of asbestos (Morris _ al., 1967)
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From page 38... ...
Flexibility and Tensile Strength The relatively high flexibility of the asbestiform fibers enables them to bend without breaking and may facilitate their passage through the respiratory tract. Like asbestos fibers, fine-diameter glass fibers do not tend to break across their axes and are often as strong as asbestos.
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From page 39... ...
have shown regional differences in surface charge on amphibole fibers. The charge characteristics of fibers also vary according to their size.
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From page 40... ...
Asbestiform fibers, including asbestos fibers, are mineral fibers that are characterized by a specific set of interdependent physical properties, including fiberlike shape, enhanced strength and flexibility, increased durability, strong and defect-free surface structure, and the dependence of these properties on conditions of growth. The fiber properties that have been considered for possible association with deleterious health effects are respirability (i.e., fibers <3 pm diameters, size and aspect ratio, durability, fiesibility and tensile strength, chemical composition, surface area, and surface charge.
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From page 42... ...
Where studies are conducted to determine the effects of natural fibers, characterization should ~ include such parameters as surface and internal fiber strength (discussed in I Appendix C) , surface charge, and density of surface defects.
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1978. me effect of fibre size on the in vitro biological activity of three types of amphibole asbestos.
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1972. Chemical characterization of uncoated asbestos fibers from the lungs of asbestos workers by electron microprobe analysis.
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From page 45... ...
1981. Hesotheliomas in rats following inoculation with acid-leached chrysotile asbestos and other mineral fibers.
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1980. Surface charge heterogeneity in amphibole cleavage fragments and amphibole asbestos fibers.
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From page 47... ...
1983. Cytotoxicity of 8 short-fiber chrysotile asbestos for human alveolar macrophages: Preliminary observations.
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