Asbestos

CAS RN:1332-21-4

Other Properties

Magnesium ... which occurs naturally in asbestos ... contributes to the surface charge of the asbestos fibers.
Chemical composition
Mineral Molecular formula
Anthophyllite ((Mg,Fe)7Si8O22(OH)2)n
Actinolite (Ca2(Mg,Fe)5Si8O22(OH)2)n
Crocidolite (NaFe3(2+)Fe2(3+)Si8O22(OH)2)n
Crocidolite Physical Properties
Property Value
Color cobalt blue to lavender blue
Luster silky to dull
Mohs hardness 4.0
Specific gravity 3.2-3.3
Optical properties biaxial oblique extinction
Refractive index 1.65-1.72
Flexibility fair to good
Texture soft to harsh
Tensile MPa 1400-1600
Surface charge, mV -32
Decomposition temp, deg C 400-900
Asbestos (Greek: inextinguishable) is the common name of a number of naturally occurring, hydrated silicate minerals that possess a crystalline structure and low thermal conductivity. They are incombustible in air and separable into filaments. These minerals occur as extremely thin flexible fibers having great tensile strength and thermal stability, and they can be spun into yarn and made into textiles. There are some 3000 recorded uses of asbestos including "fireproof" textiles, paper and boards, clutch and brake linings, asbestos cement sheets and pipes, flooring and roofing products, electrical and thermal insulating materials, coatings, and heat shields.
Tensile strength of the asbestos fiber is an important and highly significant physical property. The tensile strength values for the different asbestos varieties should be considered as relative for the different variety rather than specific, since all these measured values are far less than the theoretical value of over 10,000 MPa (1.45X10+6 psi) attributable to silicate chain structures. Physical strengths of asbestos are adversely affected by elevated temperatures.
The typical tensile strengths of asbestos fibers have the order: crocidolite > chrysotile > amosite > anthophyllite > tremolite
Commercial amphiboles are harsh fibers. They are relatively stiff, brittle, and coarser in diameter than crysotile, and rodlike in appearance under the microscope. /Amphiboles/
Amphiboles have a lower water (hydroxyl) content, and their dehydrylation reaction begins between 400 and 600 deg C, depending on the amphibole type ... the products resulting from the thermal decomposition of the amphiboles are pyrosenes, magnetite, hemetaite and silica /Amphiboles/
... The amphibole asbestos fibers dehydroxylate and decompose at elevated temperatures. The presence of large quantities of iron (particularly ferrous iron) makes the decomposition or thermal analysis determinations particularly complex and very dependent on the composition of the atmosphere. ... Compared to crysotile, the amphibole fibers are relatively acid resistant. However, under boiling conditions and high acid concn the amphiboles can exhibit wt losses of approx 2-20%. ... Amphiboles fibers have a negative charge ... The magnitude of the charge exhibited by the amphiboles is substantially lower than chrysotile's. /Amphiboles/
Relative order of acid resistance is: tremolite > anthophyllite > crocidolite > amosite > chrysotile
Asbestos fibers used in most industrial applications consist of aggregates of smaller units (fibrils), which is most evident in chrysotile that exhibits an inherent, well-defined unit fiber. Diameters of fiber bundles in bulk industrial samples may be in the millimeter range in some cases; fiber bundle lengths may range from several millimeters to 10?cm or more. ... Morphological variances occur more frequently with chrysotile than amphiboles. The crystal structure of chrysotile, its higher flexibility, and interfibril adhesion (3) allow for a variety of intermediate shapes when fiber aggregates are subjected to mechanical shear. Amphibole fibers are generally more brittle and accommodate less morphological deformation during mechanical treatment.
Surface areas of 1.8-9 sq m/g have been reported for crocidolite /Crocidolite/
Structure: lamellar, fibrous asbestiform; mineral association: in crystalline schists and gneisses; origin: metamorphic, usually from olivine; veining: slip, mass fiber unoriented and interlacing; essential composition: magnesium silicate with iron; crystal structure: prismatic, lamellar to fibrous; crystal system: orthorhombic; color: gray white, brown, gray, or green; luster: viterous to pearly; Mohs hardness: 5.5-6.0; specific gravity: 2.85-3.1; cleavage: 110%; optical properties: biaxial positive extinction parallel; index of refraction: about 1.61; Seger cones fusibility: infusible or difficult to fuse; flexibility: very brittle, nonflexible; length: short; texture: harsh; acid resistance: fairly resistant to acids; spinnability: poor; specific heat: 879 J/kg deg K or 0.210 Btu/lb deg F. /Anthophyllite/
Anthophyllite Properties
Property Value
Color White orthorhombic
MF Mg7Si8O22(OH)2
Mohs hardness 5.5-6.0
Specific gravity 2.85-3.1
Optical properties Parallel extinction
Refractive index 1.578-1.652
Flexibility fair to brittle
Tensile kg/sq cm 25X10+3
Structure: reticulated long prismatic crystals & fibers; mineral association: in limestone & in crystalline schists; origin: results of contact metamorphism; veining: slip or mass fiber; essential composition: calcium, magnesium, and iron silicates, water up to 5%; crystal structure: long & thin columnar to fibrous; crystal system: monoclinic; color: green; luster: silky; Mohs hardness: about 6; specific gravity: 3.0-3.2; cleavage: 110%; optical properties: biaxial negative extinction inclined; index of refraction: 1.63 weakly pleochroic; Seger cones fusibility: fusible at 4, 1165-1190 deg C; flexibility: brittle and nonflexible; length: short to long; texture: harsh; acid resistance: relatively insol in hydrochloric acid; spinnability: poor; specific heat: 908 J/kg deg K or 0.217 Btu/lb deg F. /Actinolite/
Asbestos minerals, despite a relatively high fusion temperature, are completely decomposed at temperatures of 1000 deg C. Both the dehydroxylation temperature and decomposition temperature increase with increased magnesium oxide content among the various amphibole species. ... Most materials have a negative surface charge in aqueous systems. However, since chrysotile has a positive charge, it will attract, or be attracted to, most dispersed materials. The highly reactive surface of asbestos causes many surface reactions which are intermediate between simple absorption and a true chemical reaction. The absorption of various materials on the surface of chrysotile has a greater affinity for polar molecules (eg water, ammonia) than for non-polar molecules.
Amphiboles can ... occur in nonfibrous forms which may result because of structural disorder. The dominant cations are magnesium, ferrous, ferric, sodium, and calcium. Minor isomorphic substitutions of aluminum, titanium, potassium, and lithium also occur. Because of the wide compositional range, the amphiboles are often assigned to three generic series; ie, the anthophyllite cummingtonite series, the calcic amphiboles and the soda amphiboles. /Amphiboles/
Find more information on this substance at: Hazardous Substances Data Bank , TOXNET , PubMed