Know "asbestos"

Asbestos, also known as "asbestos," is a commercial term referring to silicate mineral products that have high tensile strength, high flexibility, resistance to chemical and thermal attack, electrical insulation, and spinnability. It is a general term for natural fibrous silicate minerals. There are 6 types of minerals under the jurisdiction of 2 categories (serpentine asbestos, amphibole asbestos, asbestos asbestos, amosite asbestos, amosite, tremolite asbestos, etc.). Asbestos is composed of fiber bundles, which in turn are composed of long, fine fibers that can be separated from each other. Asbestos has high fire resistance, electrical insulation and thermal insulation and is an important fire protection, insulation and insulation material.

Asbestos has been used for weaving for a long time. China’s Zhou Dynasty has been able to use asbestos fiber as a fabric. After being contaminated, it is burned and white as new. Therefore, it is known as a fire-stained cloth or a flaming cloth. At present, there are nearly 3,000 kinds of asbestos products or products containing asbestos, which are mainly used for mechanical transmission, braking and heat preservation, fire prevention, heat insulation, anti-corrosion, sound insulation, and insulation. The most important ones are automobiles, chemical industry, electrical equipment and construction. Industry and other manufacturing sectors. Since asbestos fibers can cause asbestos lung, pleural mesothelioma and other diseases, many countries have chosen a total ban on the use of such dangerous substances, and other countries are examining the risk of asbestos.

classification

There are many types of asbestos, which can be divided into serpentine asbestos and amphibole asbestos, depending on their mineral composition and chemical composition. Serpentine asbestos, also known as chrysotile, is the most abundant type of asbestos and has good spinnability. Amphibole asbestos can be further divided into blue asbestos, tremolite asbestos, and asbestos asbestos, with less production than serpentine asbestos.

Serpentine Asbestos (Serpentine)

Also known as fiber serpentine asbestos [1], or chrysotile, the main components are silica, magnesia, and crystal water, and its molecular formula is Mg6[(OH)4Si2O5]2. Serpentine asbestos is white or gray, translucent; no magnetic, non-conductive, fire-resistant, alkali-resistant, fiber tough and soft, with silky luster and good spinnability. At present, asbestos produced in the world is mainly serpentine asbestos, accounting for about 95% of the world's asbestos production.

Amphibole

Including crocidolite (also known as blue asbestos or purple asbestos), amosite, anthophyllite, tremolite, and actinolite. Asbestos asbestos varieties are distinguished by their different amounts of sodium, calcium, magnesium and iron. It should be noted that serpentine and hornblende minerals may have two types of fibrous structure or non-fibrous structure. Serpentine and hornblende with fiber structure are called asbestos.

nature

Different types of asbestos also have different physical and chemical properties and chemical properties. Asbestos fiber length is generally 3 ~ 50 mm, but also longer. China has found that the longest asbestos fiber is 2.18 meters, which is the longest in the world.

Physical properties

Asbestos fiber has a high axial tensile strength, sometimes up to 374×10^4 kg/m2, but it is not resistant to wrinkling, and the tensile strength decreases significantly after several times of folding. The structural water content of asbestos fibers is 10 to 15%, which is more than 14%. When heated to 600 to 700°C (temperature rise of 10°C/min), the structural water of the asbestos fiber is folded out, and the fiber structure is destroyed and becomes brittle. After being kneaded, it becomes powder and the color changes.

When the thermal conductivity of asbestos fiber is 0.104 to 0.260 kcal/m·degree·, the electrical conductivity is also low and it is a good insulating material for heat and electricity. Asbestos fiber has good heat resistance, generally less than 300°C for 2 hours. The weight loss is less. If it is heated above 1700°C for 2 hours, the weight loss of asbestos fiber is more, and the weight loss of other kinds of asbestos fiber is more. less.

Serpentine asbestos is an hydrated silicate mineral of magnesium and is a monoclinic lamellar structure. The original structure is dark green, light green, light yellow, yellow, gray, white and other colors, translucent, the appearance of fibrous, with silky luster. The serpentine asbestos fibers have better splitting properties, flexibility, strength, heat resistance and insulation, the specific gravity is 2.49-2.53, the specific heat is 0.266, and the surface specific resistance is 8.2×10^7～1.2×10^ 10Ω, volume resistivity is 1.9×10^8 to 4.79×10^9Ω·cm.

Chemical properties

Serpentine asbestos has good alkali resistance, and is almost free from alkali corrosion, but its acid resistance is poor. A weak organic acid can precipitate magnesium oxide in asbestos and reduce the strength of asbestos fibers.

Amphibolite asbestos is a monoclinic structure. The color is generally deeper, the specific gravity is larger, it has higher acid resistance, alkali resistance and chemical stability, and the corrosion resistance is also better. In particular, blue asbestos has good filtration performance and has important properties such as prevention of chemical poisons and purification of air contaminated by radioactive substances. The difference between serpentine asbestos and amphibole asbestos is: Asbestos is ground in a mortar, and serpentine asbestos is made into a chaotic felt. Fibers are not easy to separate. Amphibole asbestos is easily divided into many small fibers after grinding. Iron-free asbestos are white, and iron-containing asbestos are blue in different shades. The fibrous aggregates were shiny and the fiber gloss after dividing was dull.

Asbestos is a collection of fine tubular fibers aligned parallel to each other that can be broken into very fine asbestos fibers, with diameters as small as 0.1 microns or less. After being completely split and opened, it is difficult to observe with the naked eye and is therefore a good bacterial filter material.

Asbestos with a fiber length of more than 8 mm mixed with 20-25% of the cotton yarn can be made into a fireproof textile material, and shorter fibers can be used to make an asbestos cemented cloth, an asbestos board, and an insulating material. Blue Asbestos has a unique anti-chemical toxicant and the ability to purify radioactive particles to contaminate the air. It is used to make a variety of high-efficiency filters, and the asbestos paper made with it has a filtration efficiency of 99.9%.

The vertical asbestos fibers of asbestos are called transverse fibers, generally less than 30 cm in length. Serpentine asbestos is mostly produced in this form. Asbestos fibers with extended parallel crack directions are called longitudinal fibers and their length can be up to 1 meter or more. Asbestos is mostly vertical fiber. There are other asbestos fibers.