Asbestos ore showing parallel fiber structure - Rosato (C) InspectApediaChemical Properties of Asbestos
Chemical characteristics of Asbestos: solubility, effects of heat, acid resistance, + thermal insulation, emissivity

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Chemical properties of asbestos: this article describes the chemical properties of asbestos in various forms, such as asbestos solubility, the affect of acids on asbestos, the effects of heat on asbestos, and related properties.

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.

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Chemical Properties of Asbestos

One of the more important theories concerning formation of asbestos recognizes that the primary rock formation out of'which asbestos mother rock emerged is of volcanic origin. In Canada and other important asbestos areas, this green colored mother rock is principally olivine, classified chemically as magnesium silicate.

The pH of asbestos is generally listed as 9 to 10. When asbestos is acid washed or subjected to other chemicals, it can be made to behave tisfctôrily with acid curing poly mers or resin systems

The chemical feature common to all asbestos is that they are hydrated silicates The degree of hydration varies from approximately one per cent in some types to as much as approximately 14 per cent in most kinds of chiysotile It generally accepted that asbestos is a metamorphic product derived from certain types of silica-bearing minerals.

Effects of Chemicals on Asbestos

Published data showing the effect of chemicals on asbestos are given inTable 2.9 below. it is reported that room temperature tests were conducted for periods of 24, 192, 360, and 528 hr. * ASTM (D577-52, Method D39, Section 10) tensile grab test.

Inasmuch as most of the fibers reached maximum solubility after 528 hr, only this period was reported.

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Per Cent Loss in Weight, Refluxing Two Hours, 25% Acid or Caustic

Table of Solubility of Different Forms of Asbestos - Rosato Table 2.9

* Badollet, M. S., "Asbestos, A Mineral of Unparalleled Properties," Can. Mining and Met. Bull. (1951).

Effects of Heat on Asbestos

When asbestos is exposed to heat, it loses water of crystallization. At approximately 800°F, hornblende asbestos generally loses the greatest part of its combined water while serpentine loses only approximately 15 per cent. Hornblende asbestos becomes extremely brittle at 750°F.

In the case of serpentine asbestos, flexibility remains. Table 2.10 below gives the percentages of loss in weight versus temperatures up to 1,800°F. Test specimens were predried to remove surface water and weighed; After heat exposure for two hours, the asbestos was cooled at room temperature in a desiccator prior to reweighing. If asbestos were cooled in the open room, moisture from the air would be absorbed and weights would differ.

When asbestos fibers are dehydrated, they change in such properties as mechanical strength. Water content in asbestos includes hygroscopic moisture adhering to the asbestos sur- face and the chemically combined water of crystallization.

The content of hygroscopic moisture in asbestos has no rela tionship to its chemical composition. It is directly related to such an environmental condition, as degree of relative humidity in the air. Removal of this moisture can be accom- pushed by subjecting asbestos to a temperature of approxi35 mately 212°F. At a relative humidity of approximately 40 per cent, moisture pickup in asbestos after equilibrium is reported to be approximately 1 per cent; at 70 per cent relative humidity, the total pickup is 1.5 per cent; at 95 per cent relative humidity, the total pickup is 2.5 per cent.

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Table of Effects of Temperature on Loss in Weight of Asbestos Fibers by Tyhpe of Asbestos - Rosato Table 2.10

* Can. Mining and Met. Bull. (1951).
! Iron changing in weight caused by oxidation.

The Acid Resistance of Asbestos: Acid Washed Asbestos Fiber

The acid resistance of asbestos is important in a number of such different applications as corrosion resistant plastic, cement equipment, and filters. In some applications, it is desirable to remove all metallic and foreign matter. Mechanical devices as well as chemical, cleaning or washing processes are used.

With regard to the chemical process, the general proce- dure is to immerse asbestos in a boiling solution of 15 to 25 per cent hydrochloric acid. One to two hour immersion is generally sufficient. After the acid washing, the asbestos is subjected to water rinsing. The water will remove all free chlorine and neutralize the fiber. This process generally produces a loss of approximately 10 per cent, by weight, of . the original asbestos. Loss in weight is due to removal of the metallic and foreign matter.

The acid washed fibers are dried in order to make them useful in such other processes as treatment with plastic or rubber resins.


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