Mineral fibers Asbestos Fibrous materials

Asbestos It is not the name of a distinct mineral species but is a commercial term applied to fibrous varieties of several silicate minerals such as amosite and crocido-lite. These extremely fine fibers are useful as fillers and/or reinforcements in plastics. Property performances include withstanding wear and high temperatures, chemical resistance, and strengths with high modulus of elasticity. When not properly handled or used, like other fibrous materials, they can be hazardous. 

The most common, and certainly the most familiar, inorganic fibers are the mineral fibers known as asbestos. Several minerals have been mined as asbestos (Fig. 1.1 A, C see chapter 2 for a detailed discussion of the asbestos minerals). These minerals are widespread in nature, but mining is economical only when they occur as continuous fibrous aggregates (veins) crosscutting rock masses. The veins are made up of hairlike fibers in parallel array that, on close inspection, appear bent (Fig. I.IB). Not surprisingly, a mineralogical term, asbestiform, has been used to describe this subset of inorganic materials. 

In Chapter 2 we introduce some basic concepts from mineralogy and materials sicence before describing several mineral and synthetic fibrous inorganic materials. In Chapter 3 we outline the physiology of the human lung, cellular biology and the diseases associated with asbestos exposure—the pertinent information for discussions of the health effects of asbestos and other inorganic fibers. 

Asbestos refers to a group of impure magnesium silicate minerals. As you can see, asbestos is a fibrous material. When inhaled, these fibers are highly toxic and carcinogenic. 

Asbestos was a widely used, mineral-based material that is resistant to heat and corrosive chemicals. Typically, asbestos appears as a whitish, fibrous material that may release fibers that range in texture from coarse to silky however, the airborne fibers that can cause health damage may be too small to see with the naked eye. 

The structural variety of the compounds that form fibers is as diverse as their chemistries. From glasses (fiberglass), and partially crystalline materials (carbon), to special three-dimensional arrays, including polymers, the small, elongate solids may have aspect ratios up to 5000. From our research and compilation (Appendices 1, 2) we noted many mineral and synthetic compounds that have structures characterized by basic linear units. Amphi-boles, the major mineral group mined as asbestos, are characterized as doublechain structures. Many of the minerals in Appendix 1 are polymorphic (di-or trimorphs), and where one member of a mineral series has been described as fibrous the others in the same series are likely to be able to grow as fibers as well. Probably all compounds with similar structures and compositions, mineral or synthetic, can form fibers, even though they are not presently listed. It is also clear that fibrous formation is not confined to compounds with linear structural units indeed the variety of crystalline structure patterns is remarkably diverse. 

The Fibrous Minerals. The fibrous minerals contain very long silicate ions in the form of tetrahedra condensed into a chain, as shown in Figure 31-6. These crystals can be cleaved readily in directions parallel to the silicate chains, but not in the directions which cut the chains. Accordingly crystals of these minerals show the extraordinary property of being easily unravelled into fibers. The principal minerals of this sort, tremolite, C.a.jMg..Si 022(0H)2, and chrysotile, Mg6Si40u(0H)p/H20, are called asbestos. Deposits of these minerals are found, especially in South Africa, in layers several inches thick. These minerals are shredded into fibers, which are then spun or felted into asbestos yarn, fabric, and board for use for thermal insulation and as si heat-resistant structural material. 

I. Physical and Chemical Properties. Asbestos is a generic term for a variety of hydrated silicate minerals (see Table 4.7.1), which are characterized by their fibrous structure [6-8]. Although there are six different asbestos minerals and several have found use in cell separators, chrysotile predominates as a chlorine cell diaphragm material. Chrysotile fibers consist of bundles of parallel fibrils. These fibrils are hollow needles with an outer diameter of about 30nm and an inner diameter of 4nm, and consist of... 

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