Asbestos

ASBESTOS

Asbestos is a naturally occurring mineral derived from a Greek word which means incombustibal or unquenchable. Asbestos mineral originates in rock form. It is a hydrated mineral and hence has some quantity of silicate. This is a fibrous mineral utilised in industries. Generally, asbestos fibers are long, thin, strong, fireproof, flexible, and resistant to the action of many chemical. In some mines, the fibers are exceedingly long and flexible, making asbestos excellent for weaving into fire and heat resistant cloth.
Based on its chemical,physical and commercial properties asbestos is classified into mainly 2 types and are as follows-
1. Serpentine
2. Amphibole

1. Serpentine Serpentine is olive green color and smooth or scaly appearance is the basis of the name from the Latin serpentinus, meaning serpent rock group has one type,
a.Chrysotile Chrysotile is obtained from serpentine rocks having the chemical formula Mg3Si2O5(OH)4 . Chrysotile is a curly shaped and white in colour, it looks greenish when present in mass. It is more flexible compared to other types of asbestos, also very silky and fine with greater strength. It forms in metamorphic rock, i.e, rock that has been altered by intense heat and pressure.

2. Amphibole The amphiboles represent the majority of the double-chained inosilicates. They are common rock forming minerals and are present in most metamorphic and many igneous rocks. The complex possibilities of formulas lead to a lot of variety in the amphibole group, a. Amosite b. Crocidolite c. Tremolite d. Actinolite e. Anthophyllite
a. Amosite Amosite is a long fibre having the chemical formula Fe7Si8O22(OH)2. It has very high resistance power towards acids since it contains rich quantity of iron. Amosite is brown in colour with needle like structure.It is also known as Grunerite, It forms as fibrous, columnar or massive aggregates of crystals. The Mohs hardness is 5 to 6 and the specific gravity is 3.4 to 3.5.
b. Crocidolite Crocidolite is having the chemical formula Na2Fe2+3Fe3+2Si8O22(OH)22 Normally it is blue in colourwith fibrous structure.It is also known as Riebeckite, Its Mohs hardness is 5.0–6.0, and its specific gravity is 3.0–3.4.
c. Tremolite Tremolite is a long fibre with silky white in colour. Tremolite is a calcium, magnesium, and silicate material with chemical formula Ca2(Mg,Fe)5Si8O22(OH)2. Tremolite forms by metamorphism of sediments rich in dolomite and quartz. It has a hardness on Mohs scale of 5 to 6.
d. Actinolite Actinolite is a magnesium and iron rich mineral having the chemical formula Ca2(Mg,Fe)5Si8O22(OH)2 Its Mohs Hardness is 5.5 – 6 and the Specific Gravity is approximately 2.9 - 3.3.
e. Anthophyllite Anthophyllite is silicate rich mineral and it is represented by the chemical formula Mg7Si8O22(OH)2. Anthophyllite is a component of some metamorphic and metasomatic rocks. Since its shape is like clove and the word is taken from italic language. Hardness is 5.5 - 6. Specific Gravity is approximately 2.9 - 3.4.

Occurence and Geological Deposits Asbestos originates mainly from different forms of rocks such as peridolite, pyroxenite and dunite which comes under the olivine types of rocks.Its deposits are natural, underground concentrations of the fibrous mineral and are found all over the Earth. In its natural state, asbestos occurs in two-thirds of the rocks located in the earth's crust. Asbestos fibers are formed by the gradual growth of mineral crystals in cracks, or veins, found in soft rock formations. The crystals grow across the vein, and the width of the vein determines the resulting asbestos fiber length.When these fibers are released into the air through mining or natural erosion, wind can carry the fibers great distances.Asbestos occurrence can be mainly seen in countries like Canada, China, USA, Bazil, India and South Africa etc,.. but the main contributer is Canada and China which contributes more than 50 % of the total asbestos.Mainly chrysotile is available in Quebec part of Canada.Asbestos deposit in India is found in states like Rajasthan, Andhra Pradesh, Karnataka and Tamil Nadu. Amphibole is the major deposit in india.

Properties of Asbestos
1. Asbestos is the mineral with highest tensile strength.
2. It has very high capacity for heat resistance.
3. Asbestos is having good chemical resistance towards acids and as well as alkali.
4. It has good resistance with friction on high pressures since the hardness of it is more.
5. It is a good insulating material for electrical resistance.
6. It also has good acoustical property.

Applications/uses of Asbestos Crysotile are used in construction of the buildings, mainly it is being used in USA. Amosite is used as fire retardant in thermal insulation products. Asbestos is also has application in tiles industries. Also used as spinning fiber. Tremolitea are used as filters for the removal of fine particulates from chemicals, liquids and wine. Asbestos is having great absorbing capacity for cement and when admixed in suitable proportion in water it forms a first class construction material of high resistance. Asbestos is having great application in braking system of cars, trains, cranes, transmission systems and in clutch systems as well. It has wide variety of applications in electrical industries as cable wraps, panels, conduits, fuse and switch gear etc,. Being a high insulating material it is used in many industries for the insulation of pipes, boilers, furnaces, and hot water tanks etc,. In tiles industries as vinyl floor tiles, In fire blankets and in fire proofing clothes. And also in decorating purpose as textured paint.

QUESTION and ANSWERS
1. What are the different types of asbestos?
Ans: Asbestos has 2 types a).Serpentine b) Amphibole
2. What are the uses of Asbestos?
Ans: Asbestos is having great application in braking system of cars, trains, cranes, transmission systems and in clutch systems as well. It has wide variety of applications in electrical industries as cable wraps, panels, conduits, fuse and switch gear etc, In fire blankets and in fire proofing clothes.
3. Mention properties of asbestos?
Ans: Asbestos is the mineral with highest tensile strength. It has very high capacity for heat resistance.
4. Write the chemical formula for amosite and crocidolite?
Ans: Amosite Fe7Si8O22(OH)2 Crocidolite Na2Fe2+3Fe3+2Si8O22(OH)22

References : 1.www.wikipedia.com 2.www.galleries.com 3. R.K.Sinha

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