Applications of Asbestos Fibers

A Crude asbestos 1 hand selected, unshredded contains staple fibers 1.90 cm and longer 

3 spinning fibers for asbestos fabric, clothing, asbestos cement pressure pipes 

5 long board fibers for asbestos board and packaging, seals, floor tiles, roofing 

6 board fibers for asbestos cement boards, roofing 

7 short fibers for floor covering, asbestos paper, frictional linings, asbestos cement plates, roofing 

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The fractional breakdown of the recent world production of the various fiber types shows that the industrial applications of asbestos fibers have now shifted almost exclusively to chrysotile. Two types of amphiboles, commonly designated as amosite and crocidolite are still being used, but their combined production is currently less than 2% of die total world production. The odier three amphibole varieties, anthophyllite, actinolite, and tremolite, have no significant industrial applications presently, This... 

From the beginning of this century, the demand for asbestos fibers grew in a spectacular fashion for numerous applications, in particular for thermal insulation in steam engines and technologies (4). Moreover, the development of the Hatschek machine in 1900 for the continuous fabrication of sheets from an asbestos—cement composite opened an important field of industrial application for asbestos fibers. 

Wodd War II supported the growth of asbestos fiber production for military applications, typically in thermal insulation and fire protection. Such applications were later extended into residential or industrial constmctions for several decades foUowing the war. 

During the late 1960s and 1970s, the finding of health problems associated with heavy exposure to airborne asbestos fibers led to a strong reduction (or ban) in the use of asbestos fibers for thermal insulation. In most of the current applications, asbestos fibers are contained within a matrix, typically cement or organic resins. 

Finally, the combined reinforcing effect and high absorption capacity of asbestos fibers have been exploited in a variety of appHcations to increase dimensional stabiHty, typically in vinyl or asphalt tiles and asphalt toad surfacing. Figure 9 summarizes, as of 1984, the various classes of application for asbestos fibers in combination with other materials. The diagram shows that in recent years, most industrial appHcations have evolved towards composite materials where the fibers are bonded within an organic or inorganic matrix. 

The use of flax fibers in car disc brakes as a replacement of asbestos fibers is another example of an application of this type of material [7]. 

The mam characteristic properties of asbestos fibers that can be exploited in industrial applications arc their thermal, electrical, and sound insulation nonflammability matrix leinfoicement (cement, plastic, and resins) adsorption capacity (filtration, liquid sterilization) wear and friction properties (friction materials) and chemical inertia (except in acids). These properties have led to several main classes of industrial products or applications fire protection and heat or sound insulation,... 

Stober and McClellan 1997 Stober et al. 1994), a direct application of these models to the kinetics of asbestos fibers in humans has not been reported. 

Application of either PCM or TEM methods to the determination of asbestos fibers in biological or environmental media (air or water) requires that the fibers be separated from interfering material and collected on appropriate supports. Methods for preparing biological and environmental samples for microscopy are described below. 

The classification of asbestos fibers is carried out on the basis of type and deposits, important classification criteria are also, however, fiber length, degree of decomposition and fiber texture. This leads to a grouping according to industrial application (Table 5.2-, i). 

The high electrical resistivity of asbestos fibers is well-known, and has been widely exploited in electrical insulation applications. In general, the resistivity of chrysotile is lower than that of the amphiboles, particularly in high humidity environments (because of the availability of soluble ions). For example, the electrical resistivity of chrysotile decreases from 1 to 2100 MQ/cm in a dry environment to values of 0.01 to 0.4 MQ/cm at 91% relative humidity. Amphiboles, on the other hand, exhibit resistivity between 8,000 and 900,000 MQ/cm... 

The evolution in the world production of asbestos fibers since 1950 is illustrated in Table 5 (5) after a peak near 1980, production leveled off after 1985 at 4.2 4.3 x 106 t. Changes in the production of the two main producers, Canada and the former USSR, over the same period are also illustrated. These figures show a substantial decrease in the Canadian production with a concomitant increase in the former USSR production. During recent years, several other countries, namely Brazil, Zimbabwe, and China, have substantially increased their production of chrysotile. Most of China s production, as well as the limited production of many other countries, is used in local industrial applications. South Africa is the only country where the three main types of asbestos are produced (chrysotile, crocidolite, and amosite), and the only significant producer of amphibole fibers. 

Finally, other properties of asbestos fibers may be evaluated depending on the envisaged application. Typically, the grits and spicule content, the magnetic susceptibility (magnetic rating), the content in soluble chlorides, and the humidity level may be of a particular interest in specific applications. 

A discussion of applications of whiskers, short fibers, microtubes and nanotubes must start with a discussion of asbestos fibers. The blanket ban in the United States on all forms of asbestos was lifted by the Environmentai Protection Agency in 1991, but the legal climate is still complex. This holds true not only for asbestos and its composites [3] but also for all other needle-like fibers such as siiicon carbide whiskers and its composites when the whisker diameters are as low as <3 pm [57-58]. Pertinent governmental regulations [3] [57-58] need to be considered in the iarge-scale production, use or disposal of short needle-like fibers. 

Triboadhesive enrichment or beneficiation can be used successfully in two types of applications size classification of powdered materials and the separation of mineral particles from impurities. In the first category we may mention the classification of powders such as quartz, barite, magnetite, hematite, pyrite, feldspar, coal, asbestos, graphite, periclase (crystalline magnesium oxide), pegmatite, and iron ore. As an illustration of an application in the second category we may mention the separation of asbestos fiber ( falling product) from mineral dust that adheres to the drum surface ( retained product) [327]. 

Inhalation of the very thin and short asbestos fibers is dangerous due to their carcinogenic properties. Much effort is necessary for health protection of the operating crew. Some governments restricted the application of asbestos. Starting at the end of the 1980s, noncarcinogenic fibers have been developed by different... 

CFR 61 Subpart M, revised by 55 FR 48414, November 20, 1990 1 Regulations contain standards for the removal and disposal of asbestos-fiber-containing material. Applicable for remedial actions involving the removal and disposal of asbestos-fiber- containing material. 4... 

Applications of PVA The largest application of PVA fibers is in paper and non-woven fabrics, where a fraction of water-soluble fiber is often used as a binder. Further applications are in twines, ropes, fabrics (tatami mats), and tarpatdins. Gel-spun , very strong, PVA fibers have become an important replacement for asbestos in cement reinforcement. 

Controlled retardation could be of special benefit to the application of phosphate fibers. In this application of phosphates there is always a compromise between a fiber that is functionally strong and refractory, and one that is harmless because it degrades and is absorbed under conditions in which it serves no useful function. Perhaps a fiber of chrysotile asbestos containing weak links, subject to degradation, under conditions where safety was of paramount interest, could be ideal. See Chapter 5 For details. 

Although Dr. Hinkebein s concept was promoted as an application of phosphate fibers, it should be useful with other fibers. It is believed that, with some additional research, a very satisfactory replacement for asbestos -cement pipe can... 

Loose asbestos fibers, or formulations containing asbestos fibers for spray coatings, have been widely used in the building industry for fire protection and heat or sound insulation. Such applications used mainly chrysotile or amosite but, because of health concerns, this practice has been discontinued. 

The textile fibers have a limited range of application. They may be used with hot or cold water, steam, oils and ammonia up to a maximum temperature of 100°C (212°F). Asbestos fiber is more versatile, can be used as compression packing material with hot water, super-heated steam, hot oils and gases up to 310°C (590°F). 

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