The properties of asbestos fibers such as dimensions, thickness, strength, and related features are discussed in this article.

The ultra-fine thickness of individual asbestos fibers affect its properties, utility, and hazardous nature as explained here.

This article series describes the physical properties of asbestos including its mechanical, chemical, electrical and related properties both in pure asbestos form and when asbestos is mixed with other materials like cement or rubber. As the author points out, while this is a lenghty article, there is far more detailed information about asbestos properties, chemistry, etc.

Properties of Asbestos Fibers

Figure 2.2. View showing parallel fiber structure of asbestos vein, (Courtesy Johns-Manville-Corp.) [Click to enlarge any image]

Asbestos is generally as dense as the rock in which it occurs but it forms masses of fibers. Specific gravity of the fibers range from 2.5 for chrysotile to 3.3 for the other types.

The fibrous structure of asbestos is as important to its industrial value as its mineral nature. Asbestos can be subdivided into fibers so fine that only the electron microscope will reveal them. The finest fibers are found in chrysotile. Its basic single fiber is a smooth cylinder approximately A in diameter (0.00000071 in.) .

In comparison, a human hair might have a diameter of 0.00158 in. Because of the fine structure of the asbestos, approximately 850,000 1,400,000 fibrils are found in a linear inch of chrysotile ; however, only 630 human hairs can packed into a linear inch.

Table 2.2 below includes information comparing chrysotile asbestos fibers with other common fibers.

[You will observe that asbestos fibers are among the smallest diameter materials known - Ed.]

TABLE 2.2 COMPARISON OF DIAMETERS OF VARIOUS FIBERS WITH ASBESTOS *

* Can. Mining and Met. Bull. (April, 1951).

Asbestos fibers have an extremely large surface area value which is a very important property.

TABLE 2.3. COMPARISON OF THE SURFACE AREA OF VARIOUS Asbestos Fibers *
Surface Area by N2 Adsorption Type of Fiber

* Can Mining and Met. Bull. (April, 1951) .

The surface area determination of chrysotile depends upon the type of measuring apparatus used. For example, if measurement of the degree of the opening of the fiber bundles is desired, then an air permeability method is quite satisfactory. However, if it is -desired to measure all the available pore space between the fibers, it is necessary to resort to a method employing gas absorption techniques.

The specific surface areas reported by nitrogen absorption show an extreme range of values which is caused by the method of opening the fiber bundles. These values range from 4 to 12 m²/g when carefully opened by hand, or from 30 to 50 m²/g when special mechanical equipment and chemical dispersing agents are used.

Observations made with the electron microscope suggest that fibers of chrysotile may be hollow. The fiber of hornblende types is rather thicker and more solid than chrysotile, consequently it is also less pliable and ductile. The subject of structure of fibers has been of considerable controversy by different basic investigators.

Low angle x-ray scattering techniques have shown that chrysotile fibrils are hexagonally close packed and parallel to each other, having crosssectional diameters varying from 180A to 300A (1 Angstrom unit equals .0000001 mm) while the amphibole fibers are many times larger in cross section.

With regard to physical characteristics of fibers, one of the investigators, Dr. F. L. Pundsack, states: "Although the empirical composition of chrysotile is 3MgO2SiO₂.2H₂0, the true unit cell composition is best represented as Mg₁₂(OH)₁₆S₈O₂₀.

This cell has dimensions of a = 5.3A, b = 9.2A and c = 14.6A where the "a" direction is the fiber axis. The calculated density of this unit is 2.56 g/cc, a value in close agreement with experimentally determined density values for chrysotile asbestos.

The exact manner in which the unit cells of asbestos are stacked together to build up a single fiber of chrysotile is not known, but from various lines of experimental evidence it can be estimated that stacking in the "b" direction probably does not exceed a width of about 1,000A.

Stacking in the "c" direction probably is limited to a thickness of not more than 200A, whereas stacking in the "a" direction may extend to a length of many millions of Angstrom units. Because of the nature of the x-ray diffraction pattern of chrysotile it is generally accepted that a single fiber of chrysotile does not exist as a flat lathlike structure, but instead the fiber must be distorted in some way.

Efforts to account for this distortion have ranged from depicting the single fiber as a slightly curved lath all the way to viewing it as a completely curved structure which forms a hollow tube. Recent evideice seems to mitigate against a simple hollow tube structure, but as yet no com- pletely satisfactory structure has been evolved."

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Citations & References

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