Asbestos, also known as "asbestos", refers to silicate mineral products with high tensile strength, high flexibility, chemical and thermal corrosion resistance, electrical insulation and spinnability.It is the general name of natural fibrous silicate minerals.According to its composition and internal structure, asbestos is divided into serpentine asbestos (chrysotile asbestos) and hornblende asbestos (including crocidolite, crocidolite, etc.)[4]There are 2 categories of 6 minerals (including serpentine asbestos, hornblende asbestos, actinolite asbestos, tremolite asbestos, iron asbestos, tremolite asbestos, etc.).Asbestos consists of fiber bundles, which are long and thin fibers that can be separated from each other.Asbestos has high fire resistance, electrical insulation and thermal insulation, and is an important fire prevention, insulation and thermal insulation material.However, because asbestos fibers can cause diseases such as asbestosis and pleural mesothelioma, many countries choose to completely ban the use of this dangerous substance.
On October 27, 2017, the list of carcinogens published by the International Agency for Research on Cancer of the World Health Organization (WHO) was preliminarily sorted out for reference. Asbestos (in various forms, including actinolite, amosite, tremolite, chrysotile, crocidolite, and tremolite) was included in the list of Class I carcinogens.[1]
The production and use of hornblende asbestos was banned in China in 2002 because of its strong carcinogenicity.[4]
Chinese name
asbestos
Foreign name
asbestos
harmfulness
Contaminated and carcinogenic
Features
High tensile strength, high flexibility
Application
Fire prevention, insulation and thermal insulation materials
Asbestos is also called "asbestos fiber", which is the general name of some silicate minerals that can be split into elastic fiber filaments.Chemical formula: 3MgO · 2SiOtwo·2HtwoO，It is fibrous, greenish yellow or white, white when it is split into flocs, silky luster, elastic fiber, asbestos has acid resistance, alkali resistance and heat resistance, and is also a poor conductor of heat and electricity.The longer fibers are used to make fireproof textiles, such as asbestos rope, asbestos tape, asbestos cloth, etc;The shorter fibers are used to manufacture asbestos cement products, asbestos sound insulation materials, asbestos insulation materials (asbestos magnesium carbonate insulation powder) and insulation materials for low-voltage electrical appliances.A large amount of dust produced in the process of mining and use of asbestos will cause damage to human body in many ways, and attention should be paid to strengthening protection.[2]
Discovery History
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Asbestos has been used for weaving for a long time. With high fire resistance, electrical insulation and heat insulation, asbestos is an important fire prevention, insulation and thermal insulation material.There are nearly 3000 kinds of asbestos products or products containing asbestos.It is mainly used in mechanical transmission, braking, heat preservation, fire prevention, heat insulation, corrosion prevention, sound insulation, insulation and other aspects, among which the more important ones are manufacturing sectors such as automobile, chemical industry, electrical equipment, and construction industry.
Human use of asbestos has been proved to be traceable toAncient EgyptAt that time, asbestos was used to makePharaohTheir shroud.In Finland, asbestos fibers are stillPaleolithic AgeOur pottery workshop was found.Herodotus (5th century BC), a Greek historian, once talked about the fireproof containers used to hold the skeletons of burned corpses.It is said that Charlemagne (742-814) had a white tablecloth made of asbestos. He threw the tablecloth into the fire after a banquet to surprise the guests.
In the Zhou Dynasty, China was able to make fabrics from asbestos fibers. Because they were as white as new after being stained by fire, they were called Huohuan Cloth or Huotan Cloth.Liezi's book has recorded that: "The cloth of the fire lane will be thrown into the fire, and the cloth will be colored by the fire and dirt. When the fire breaks out, it will vibrate, and it will be bright and suspicious of snow".Marco Polo once said that a "mineral substance" was used by the Tatars to make fireproof clothes.
At the end of the Eastern Han Dynasty, the world was in turmoil and the four barbarians were disturbed. People in the Central Plains had not seen Huo Huanbu for a long time, so people questioned Huo Huanbu everywhere, including the burning of single clothes in Liang and Ji. Some people thought it was absurd.In the Three Kingdoms Period, Wang Su wrote a book called "On the Sacred Evidence", which said, "In the past, there was a country called You Shi Li, the Han family called You Ya, and there were Huo Huanbu and jade cutting knives in Yunliang and Hebei, which were not believed because they were born." At that time, the representative who suspected Huo Huanbu was Cao Pi, the Emperor of Wei Wen.Ge Hong's "Bao Puzi · On Immortals" said: "Emperor Wei Wen, after looking at and hearing everything, said that there was no jade cutting knife, no cloth of Huohuan, and the book" Dianlun ". According to this statement, the two things came to an end before the deadline. The emperor sighed and suddenly destroyed the theory." Ganbao's "Soushen" also said: "In the Han Dynasty, the Western Regions used to offer this cloth (referring to Huohuan cloth), which was unique in the middle;At the beginning of Wei Dynasty, people doubted that there was no such thing.Emperor Wen thought that the fire was cold and there was no life in it. He wrote Dianlun, which showed that it was not the case.When the Ming Emperor was appointed, the imperial edict Sangong said: 'The ancient emperor wrote the "Dianlun", an immortal aphorism, which was published outside the temple gate and the Imperial College, and combined with the stone scriptures to show the afterlife forever.'It was the Western Regions who sent people to offer the Huohuan cloth cassock, so they published this theory, and the world laughed. "The two records are slightly different. The former said that Emperor Wei Wendi's Dianlun claimed that there was no Huo Huanbu less than a year ago, and the Western Regions came to offer Huo Huanbu, so he sighed and "destroyed the theory of Si suddenly";The latter said that after Cao Pi's death, his son, Emperor Wei Ming, published Dianlun at the gate of the ancestral temple and the Imperial College. After the Western Regions came to offer Huo Huanbu, he ordered that the words denying Huo Huanbu be published, but the world still laughed at him.Baopuzi's Inner Chapter and Soushen's Records are not official history, but collections of folk legends. Although there are historical shadows, they cannot be read as historical facts.The Records of the Three Kingdoms records the offering of fire and Huanbu in the Western Regions, which can be regarded as a true record of historical events.
In February (the third year of the reign of Emperor Jingchu), the Western Regions presented Huo Huanbu again, and called the Grand General and the First Lieutenant to take a test to show Bailiao.(Records of the Three Kingdoms · Wei Shu · San Shao Di Ji)
In France, Emperor Napoleon was very interested in asbestos and encouraged experiments in Italy.The oldest asbestos mines were found in Crete (Greece), Cyprus, Greece, India and Egypt.In the 18th century, 20 asbestos mines were recorded in Europe, the largest of which was in Reichenstein, Germany（Reichenstein）。In the American continent, Pennsylvania started quarrying asbestos in the late 17th century.
After 1860, industrial mining developed, which was driven by the textile industry in Italy and England, and also because of the discovery of large asbestos deposits in South Africa, North America and Russia.
Around 1900, the amount of asbestos mined worldwide was about 300000 tons per year.Asbestos mining has been developing continuously since the industrial era. In 1975, about 5 million tons of asbestos was mined. Since then, the health risks caused by inhalation of asbestos dust have been widely spread. The amount of asbestos used has gradually declined to about 3 million tons by 1998.
Before July 1, 2002, asbestos was widely used on ships.Because of its harm to human beings and the environment, the International Maritime Organization (IMO) adopted the SOLAS 2000 Amendment in the form of MSC.99 (73), requiring that on July 1, 2002 and after, all ships, except for the watertight joints and linings, specific blades and insulation devices under high temperature, are not allowed to use new equipment containing asbestos materialsEquipment and materials are used for shipment.
On June 5, 2009, the International Maritime Organization (IMO) adopted Resolution MSC.282 (86) - Amendment to SOLAS Convention in the form of a resolution.The use of asbestos on ships was further revised, requiring that all ships should be prohibited from installing new materials containing asbestos from January 1, 2011.In this regard, the China Classification Society (CCS) has issued Circular No. 30 (General No. 30), which requires the drawing review and inspection departments to conduct drawing review and inspection in accordance with the requirements of the new Reg, II-1/3-5.2.
According to the Hong Kong International Convention on Safe and Environmentally Sound Shipbreaking 2009 (hereinafter referred to as the "Hong Kong Convention", to come into force) adopted by IMO on May 15, 2009, asbestos is listed in Appendix 1 "Control of Hazardous Substances", which clearly requires that all ships should be prohibited from installing new materials containing asbestos (see CCS2010 Circular No. 11 General No. 11).
As far as the text of the convention is concerned, the classification society is not required to detect whether the products contain asbestos, but the shipyard must issue an asbestos free declaration, which may also be required by the shipyard to issue a corresponding asbestos free declaration.In order to facilitate shipowners, shipyards and marine product manufacturers to implement the requirements of the above conventions and circulars, and more conveniently and reliably select asbestos free marine products,CCS2011 Circular No. 38 has formulated relevant regulations to provide voluntary asbestos free certification services for marine products and conduct third-party compliance verification on whether the marine products contain asbestos components, so as to meet the requirements of the SOLAS Convention revised by MSC.282 (86) that ships are prohibited from installing new asbestos containing materials.Enterprises can entrust relevant testing departments or third-party testing organizations such as SGS to conduct asbestos free assessment.
classification method
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The types of asbestos mainly include:
(1) Serpentine asbestos.Also called serpentine asbestos or chrysotile asbestos.It is widely distributed in nature. Generally, the so-called asbestos refers to serpentine asbestos.It is the fibrous crystal of serpentine, accounting for 95% of the total output of asbestos.The chemical formula is 3MgO · 2SiOtwo·2HtwoO，Theoretical content MgO 43.46%, SiOtwo43.50%、HtwoO13.04%。Before decomposition, it is green, yellow, gray, white and has silk or pearl luster. After decomposition, it is gray white. The fiber length is generally 1~20cm, and the maximum length can be more than 200cm.
(2) Amphibole asbestos.It includes crocidolite, amosite, tremolite asbestos, actinolite asbestos and other species.Its content of iron and sodium is much higher than that of serpentine asbestos. It has good acid resistance and corrosion resistance, and has many special uses.
(3) Pyrophyllite asbestos.It is the aluminosilicate of iron and calcium. The fiber length is short, mostly 0.5~1cm. The fiber has good splitting property, but poor bending resistance.
(4) Bischofite asbestos.Fibrous variety of brucite, with chemical composition of Mg (OH)two, good alkali resistance, but poor acid resistance.
Serpentine asbestos
Serpentine asbestos
Also called chrysotile asbestos or chrysotile asbestos（chrysotile）The main components are silicon dioxide, magnesium oxide and crystal water, and its molecular formula is Mgsix[(OH)fourSitwoOfive]two。Wherein, MgO 43.0%, SiOtwo44.1%、HtwoO 12.9%。
Serpentine asbestos is white or gray, translucent;Hardness: 2.0~2.5, density: 2.49~2.53g/cmthree, axial tensile strength: 3000Mpa, non-magnetic, non-conductive, fire-resistant, alkali resistant, tough and soft fiber, with silk luster and good spinnability.The asbestos produced in the world is mainly serpentine asbestos, accounting for about 95% of the world's asbestos production.
Asbestos tailings, namely serpentine, is composed of serpentine mineral (3MgO · 2SiOtwo·2HtwoO) The theoretical composition of rocks with main composition is: MgO: 43%;SiOtwo：44.1%；HtwoO：12.9%。When mixed with proper amount of dolomite (CaCOthree·MgCOthree）After combined calcination, periclase as the main mineral can be generatedthreeS、CtwoS is the magnesium calcium refractory of the combination.
Iron asbestos: (MgFe)seven[SifourOeleven]two(OH)two， MgO：15.31%；SiOtwo：54.33%[3]
The hornblende asbestos is distinguished by the amount of sodium, calcium, magnesium and iron.It should be noted that serpentine and hornblende minerals can have either fibrous structure or non fibrous structure. Only serpentine and hornblende with fibrous structure are called asbestos.
Category of asbestos
S/N
Chinese name
English name
CAS No
one
Chrysotile asbestos
Chrysotile
12001-29-5
two
Iron asbestos
Amosite
12172-73-5
three
Crocidolite
Crocidolite
12001-28-4
four
Chrysotile asbestos
Anthophyllite asbestos
77536-67-5
five
Actinic asbestos
Actinolite asbestos
77536-66-4
six
Tremolite asbestos
Tremolite asbestos
77536-68-6
Physical and chemical properties
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Different kinds of asbestos have different physical, mechanical and chemical properties.The length of asbestos fiber is generally 3~50 mm, and some are longer.The longest asbestos fiber found in China is 2.18 meters, which is the longest in the world at present.
physical property
Asbestos fibers have high axial tensile strength, sometimes up to 374 × 10fourkg/mtwoHowever, it is not resistant to crease, and the tensile strength decreases significantly after several creases.The structural water content of asbestos fiber is 10~15%, with more 14%.When heated to 600~700 ℃ (10 ℃/min temperature rise), the structural water of asbestos fiber will precipitate, and the fiber structure will be damaged and brittle. After rubbing, it will easily become powder, and the color will change.The thermal conductivity of asbestos fiber is 0.104~0.260 kcal/(m · ℃ · h), and its conductivity is also very low. It is a good thermal and electrical insulation material.Asbestos fibers have good heat resistance. Generally, the weight loss is less when heated at 300 ℃ for 2 hours. If heated at 1700 ℃ for 2 hours, the weight loss of chrysotile fibers is more than that of other types of asbestos fibers.
Serpentine asbestos is an hydrous silicate mineral of magnesium, belonging to monoclinic layered structure.The original structure is dark green, light green, light yellow, earthy yellow, gray white, white and other colors, translucent, fibrous in appearance, with silk like luster.Serpentine asbestos fiber has good splitting, flexibility, strength, heat resistance and insulation, with specific gravity of 2.49~2.53, specific heat of 0.266, and surface specific resistance of 8.2 × 10seven～1.2×10tenΩ, volume specific resistance 1.9 × 10eight～4.79×10nineΩ·cm。
chemical property
Serpentine asbestos has good alkali resistance, almost free from alkali corrosion, but poor acid resistance. Very weak organic acids can separate magnesium oxide from asbestos, reducing the strength of asbestos fibers.
Asbestos rope
Amphibole asbestos belongs to monoclinic structure.The color is generally dark, the proportion is large, and it has high acid resistance, alkali resistance, chemical stability, and corrosion resistance.In particular, blue asbestos has good filtration performance, and has important characteristics of preventing chemical poisons and purifying the air polluted by radioactive substances.The difference between serpentine asbestos and amphibole asbestos is that when the asbestos is ground in a mortar, the serpentine asbestos becomes a confused felt, and the fibers are not easy to separate, and the amphibole asbestos is easy to separate into many small fibers after grinding.The asbestos without iron is white, and the asbestos with iron is blue in different colors.Fibrous aggregate has silk luster, and the fiber luster after splitting is dim.
Asbestos is a collection of fine tubular fibers arranged in parallel with each other, which can be split into very fine asbestos fibers with a diameter of less than 0.1 microns.After complete splitting and loosening, it is difficult to observe with the naked eye, so it is a good bacterial filter material.
Asbestos with a fiber length of more than 8 mm can be mixed with 20~25% cotton yarn to make fireproof textile materials. Shorter fibers can be used to make asbestos plywood, asbestos board, insulating materials, etc.Blue asbestos has unique performance of preventing chemical poisons and purifying radioactive particles from polluting the air. It is used to make various high-efficient filters. The filter efficiency of asbestos paper made with it reaches 99.9%.
Asbestos fibers perpendicular to the crack are called transverse fibers, which are generally less than 30cm long. Serpentine asbestos is mostly produced in this form. Asbestos fibers extending parallel to the crack direction are called longitudinal fibers, which can be more than 1m long. Blue asbestos is mostly longitudinal fibers.Other asbestos has both fibers.
Origin reserves
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According to USGS statistics, the world's proven asbestos reserves are 200 million tons, mainly distributed in Russia, China, Canada, Kazakhstan, Brazil, South Africa and Zimbabwe, especially in the Ural region of Russia and Quebec region of Canada, accounting for about 50% of the world's total reserves.Its asbestos production and reserves in Canada rank first in the world.
Asbestos deposits occur in ultrabasic rocks or metamorphic dolomite.Asbestos occurs in rock fissures several millimeters or centimeters wide to form cotton veins, and ore bodies are composed of clustered cotton veins.Serpentine asbestos is widely distributed, accounting for 95% of the total output of asbestos.It is mainly formed in the contact zone between intrusion and dolomite or dolomitic limestone, and in the network fissure of serpentinite formed by metamorphism of ultrabasic rock.Amphibole asbestos is mostly formed by hydrothermal replacement of iron bearing siliceous rocks with sodium and magnesium under dynamic metamorphic conditions.The largest chrysotile deposit is located in the Ural Mountains of the Russian Federation.
Mining and processing
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worldwide
asbestos
In 2003, the total amount of asbestos produced in the world was about 2060000 tons, 70000 tons less than that in 2002.Russia's output ranks first in the world, followed by China, Kazakhstan, Canada, Brazil and Zimbabwe.The total output of the above countries accounts for 95% of the world's total output.
Although the decrease of asbestos production in 2003 was not significant, the prospect of asbestos production is not very bright. Some countries have taken legislative action to completely or partially ban the use of asbestos.For example, Uruguay has passed legislation to prohibit the production and import of asbestos products, and New Zealand has also banned the import of asbestos raw ores.
The asbestos produced in the world is mainly serpentine asbestos, accounting for about 95% of the world's asbestos production.The second is tremolite asbestos, which is mined in India and other countries, but its production is limited.The production of commercially exploited crocidolite and crocidolite has ended in South Africa, and the exploitation of amphibole asbestos has not been carried out for a long time in many countries.China also announced in July 2002 that it would ban the production, import and use of amphibole asbestos.
China scope
China's asbestos production began in the early 1950s, and production and consumption accelerated with the development of the national economy.After 1996, due to environmental protection and other reasons, as well as the impact of Russian asbestos imports, China produced 337000 tons of asbestos in 2003. In fact, China's demand for asbestos has not weakened, but its imports have increased significantly.
According to statistics, at present, there are about 31 large and medium-sized asbestos mines and processing enterprises that can basically operate normally in China, of which the enterprises with a production capacity of more than 30000 tons include Mangya Serpentine Asbestos Mine in Qinghai (with an annual output of 80000 tons), Bazhou Asbestos Mine in Xinjiang (with an annual output of 40000 tons), and Ruoqiang Asbestos Mine in Xinjiang (with an annual output of 30000 tons);There are Sichuan Xinkang, Sichuan asbestos mine, Qinghai Qilian, Gansu Mingsha asbestos mine with an annual output of more than 20000 tons.In 2003, the actual annual production capacity of asbestos in China reached 450000 tons, while the actual output was about 330000 tons.China produces less long fiber asbestos and more medium and short fiber asbestos.
Inspection standard
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China's chrysotile asbestos standard system is established by reference to the standards of the world's advanced countries and in combination with its own actual national conditions.Not only detailed inspection methods and judgment methods are specified, but also detailed inspection equipment parameters are determined.
In 1961, China promulgated the asbestos industry standard - Jianbiao 54-61 Chrysotile Asbestos, which was formulated by the Nonmetallic Mineral Research Institute of the Ministry of Construction and Engineering with reference to the standards of the former Soviet Union.
In 1987, China formulated standards such as GB8071-1987 Chrysotile Asbestos and GB6646-1986 Test Method for Chrysotile Asbestos.
In 1998, Xianyang Research and Design Institute of Non metallic Mines initiated a project to revise the national standard for asbestos GB8071-1987.In the revision, the definition of terms was added, the product code was modified, the product grading was canceled, the specific surface area item reflecting the fiber looseness was changed to the looseness measurement item, the inspection was divided into type inspection and factory inspection, the operability of the standard was increased, the inspection time and cost were saved, and the more rigorous inspection rules were stipulated to reasonably allocate the inspection risk,A more advanced and perfect asbestos standard system has been formed.
test method
There are many testing methods for asbestos. Due to different environments where asbestos occurs, different evaluation purposes, and different methods selected, no one test can solve all problems.Only by combining them can the effectiveness and accuracy of detection be guaranteed.According to the asbestos detection practice and referring to the relevant standards at home and abroad, the combination of XRD and PLM instruments is mainly used as the technical method for asbestos detection in industrial products.
The testing principle of X-ray diffractometer (XRD) is that each mineral has its specific X-ray diffraction data and pattern, and the intensity of its diffraction peak is proportional to its content, so as to judge whether a certain asbestos mineral is contained in the sample and determine its content.The method can identify asbestos species and conduct quantitative analysis;Polarization microscope (PLM) is mainly used to identify asbestos minerals by observing mineral crystal morphology, refractive index, interference color, dispersion, ductility, color, polychrome, cleavage, contour, protrusion, rough surface, Beck line and other characteristics;XRD can detect asbestos minerals, but it is impossible to confirm whether their morphology is fibrous. Therefore, PLM should be used for confirmation and combined analysis by these two devices.
Inspection process
Sampling - storage - pretreatment - determination
Common standards
standard
Standard No
Determination of Asbestos Content in Products
GB/T 23263-2009
Technical Requirements for Environmental Labeling Products Asbestos free Building Products
HJ/T206-2005
Detection of Asbestos and Chrysotile by X-ray Diffraction
NIOSH 9000
Determination of Asbestos by Polarizing Microscope
NIOSH 9002
Total Dust Weight Method Total Asbestos Dust in Workplace
NIOSH 0500-1994
Air quality - Bulk materials - Part 1: Ozone and qualitative determination of asbestos in commercial bulk materials
ISO 22262-1：2012
The Chinese asbestos standard system includes nine national asbestos standards:
standard
Standard No
Chrysotile Asbestos
GB/T 8071-2008
Sampling and Sample Preparation Method for Chrysotile Asbestos
GB 8072-1987
Wet Method for Determining the Dissolution of Chrysotile Asbestos
GB 8073-1987
Dry classification method for chrysotile asbestos
GB 6646.1-1986
Wet classification method for chrysotile asbestos fiber length
GB 6646.2-1986
Rapid wet classification method for chrysotile asbestos fiber length
GB 6646.3-1986
Determination of specific surface area of chrysotile asbestos
GB 6646.4-1986
Determination of Chrysotile Asbestos Sand and Undissociated Asbestos Content
GB 6646.5-1986
Determination of Moisture in Chrysotile Asbestos
GB 6646.6-1986
The above standards include one product standard, one sampling and sample preparation standard and nine test method standards (two test methods are specified in Appendix A and Appendix B of GB 8071-2001).
Other main asbestos product standards include:
Other main asbestos product standards include
standard
Standard No
Release time
Health Protection Zone Standard for Asbestos Products Factory
GB18077-00
2005-1-28
Hygienic standard for asbestos fiber in the air of workplace
GB16241-96
2005-1-28
Asbestos cement corrugated tile and its ridge tile
GB/T9772-96
2005-1-28
Asbestos Rubber Sheet
GB/T3985-95
2005-1-28
Specific application
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95% of the asbestos used in the world is chrysotile asbestos, whose fibers can be split into very fine primary fibers, with excellent spinning performance.Blue asbestos and iron asbestos account for less than 5% of the total asbestos consumption and are mainly used for shipbuilding.Amphibole asbestos is a kind of asbestos similar to talc, commonly used as "industrial talc".
Asbestos fibers can be woven into yarn, thread, rope, cloth, packing, etc., and used as materials or linings for transmission, heat insulation, heat insulation, insulation and other parts. In buildings, they are mainly used to make asbestos boards, asbestos paper fireproof boards, insulation pipes and kiln mats, as well as insulation, heat protection, insulation, sound insulation and other materials.Asbestos fiber can be mixed with cement to make asbestos cement products such as asbestos cement tile, board, roof board, asbestos pipe, etc.Asbestos and asphalt can be mixed to make asbestos asphalt products, such as asbestos asphalt board, cloth (asphalt felt), paper, brick, liquid asbestos paint, putty for embedding cement pavement and expansion cracks, etc., which can be used as waterproof, thermal insulation, insulation, acid and alkali resistant materials for high-grade buildings and materials for traffic engineering.In national defense, asbestos is bonded with phenolic, polypropylene and other plastics, which can be made into rocket anti ablation materials, aircraft wings, fuel tanks, rocket tail nozzle tubes and torpedo high-speed launchers, sound insulation and heat insulation materials in ships, automobiles, aircraft, tanks and ships, and sealing materials for liquid rocket engine connectors after asbestos and various rubbers are mixed and pressed.Asbestos and phenolic resin laminates can be used as thermal protection materials for missile heads.Blue asbestos can also be used as lining plate, separator or filter for chemical and atomic radiation prevention, acid resistant packing, rubber plate, etc.
Because of its soft fiber, asbestos has the characteristics of insulation, heat insulation, sound insulation, high temperature resistance, acid and alkali resistance, corrosion resistance and wear resistance, and has a considerable number of uses in commercial, public utilities and industrial facilities, such as fire-resistant asbestos textiles, water pipes, insulating boards and other asbestos cement products, as well as various thermal insulation materials, which are widely used in buildings, electrical appliances, cars, household goods, etc.
spin
After mechanical treatment, asbestos fibers with longer fiber length and more water content can be directly processed on textile machinery to make pure asbestos products.Or a part of cotton fiber or other organic fiber is mixed into the asbestos fiber to make a blended asbestos product.Because most asbestos fibers are short, brittle and hard, easy to break, and easy to pollute the air by machining.In order to improve the spinning process and prevent pollution, wet spinning is adopted. First, asbestos film tape is made, then twisted into yarn, and then processed into various asbestos products.Asbestos yarn can be made into various ropes through rope making machining.It can also be woven into asbestos cloth to sew asbestos clothing, asbestos boots, asbestos gloves and other labor protection articles.
Architecture
Asbestos cement products are common, such as asbestos cement pipes, asbestos cement tiles, asbestos cement boards and various asbestos composite boards.The asbestos consumption of such products accounts for more than 75% of the total asbestos consumption. With the development of the coating industry, various colored asbestos tiles, colored asbestos boards, etc. will provide better materials for the construction industry.Asbestos board is used for heat insulation and sound insulation of buildings.For the production of asbestos cement products, needle shaped cotton with hard structure is generally selected, and the grade requirements are not very high. Grade 4-5 cotton can meet the use requirements.
The asbestos used in asbestos cement products is mainly chrysotile asbestos, sometimes mixed with appropriate amount of crocidolite and iron asbestos. The cement used is mainly Portland cement. If about 40% of Portland cement is replaced by ground quartz sand, the products need to be autoclaved and cured.The weight ratio of asbestos to cement ranges from 10 ∶ 90 to 20 ∶ 80.
The production methods of asbestos cement products include rotary screen copying method, Maniani molding method, extrusion method, injection method and dry method.
① Circular net copying method（Hatschek process）It is the most commonly used method.The process is that the asbestos cement slurry is diluted with water to form a suspension of a certain concentration, filtered and dehydrated by a round screen cylinder and transferred to an endless woolen cloth to form a thin material layer, and then through vacuum dehydration and pressure compaction, the thin material layer is glued into a blank with a certain thickness for processing various products, such as corrugated tiles, flat plates and pipes.
② Maniani molding（Magnani process）It is to directly flow the thick asbestos cement slurry or asbestos cement suspension into the felt of the forming machine for vacuum dehydration and pressure compaction to make asbestos cement corrugated tiles or pressure pipes.Asbestos cement products manufactured by Maniani molding method, extrusion method, injection method or dry method have lower utilization rate of asbestos than those produced by rotary screen method.
Asbestos cement products have high bending and tensile strength and can be made into thin-walled products;It also has many advantages such as corrosion resistance, impermeability, good frost resistance and heat resistance, and easy machining.Its main disadvantage is low impact strength.
Asbestos fiber in asphalt can increase the softening temperature of asphalt and reduce its brittleness at low temperature.Asbestos asphalt products include thin asbestos asphalt board, asbestos asphalt cloth (asbestos asphalt felt), asbestos asphalt paper, asbestos asphalt brick, liquid asbestos paint, soft embedded cement pavement and expansion putty, etc., which are used as waterproof, heat preservation, moisture-proof, embedded, insulation, alkali resistance and other materials of buildings.
Industry
Asbestos insulation board
① Asbestos thermal insulation products: asbestos is often used to make insulation layer on the boiler outer wall and pipe, which can improve the thermal efficiency of the boiler and reduce the heat loss.Insulating steam equipment can reduce workshop temperature, and reduce accidents in flammable and explosive departments such as petroleum refining.Asbestos insulation is adopted for refrigeration equipment, which can improve the refrigeration effect.The heat insulation of the boiler room used for vehicles such as cars and ships will not increase the temperature of the compartment or cabin.In order to make full use of short fiber asbestos and low-quality asbestos to reduce costs, the following insulation materials are made of asbestos and other materials and used in relevant equipment.For example, magnesium carbonate asbestos powder, diatomite asbestos mud, calcium carbonate asbestos powder, clay asbestos powder, etc. are relatively inexpensive asbestos insulation materials.A more advanced asbestos insulation material - foam asbestos has been developed in China. This product has low thermal conductivity, good thermal insulation performance, significant energy-saving effect, and is easy to load and unload.
② Asbestos rubber products: mainly used for sealing and gasket of various equipment.The main varieties include: oil immersed asbestos packing, oil immersed asbestos graphite packing, other asbestos packing, asbestos rubber plate, oil resistant plate, etc.The largest production is ordinary asbestos rubber sheet (high, medium and low pressure) and oil resistant sheet, which are generally made of chrysotile asbestos. Different grades are selected according to different brands.
③ Asbestos brake products: it is indispensable for any transmission machinery and vehicles, because asbestos has high mechanical strength, heat resistance and good friction performance.
·Brake products: brake band, brake pad or brake band, brake pad.There are three types of domestic brake bands: one is asbestos woven brake bands, which are divided into resin and oil immersed ones, and are mostly used in mining machinery and tractors;The second is rubber asbestos brake band;The third is asbestos fiber rubber brake band, which is mostly used for braking light machinery.The domestic brake pads are mainly made of asbestos as reinforcement, phenolic resin as adhesive, filler as friction property modifier, and film molded ternary composite materials, which are mainly used for truck braking.In addition, there are also synthetic train brake shoes, drilling rig brake shoes, etc.
·Transmission products: mainly used for power transmission of various motor vehicles and construction machinery.The main products are clutch plates and damping plates of various specifications.The main composition of asbestos clutch is similar to that of brake pad.Asbestos brake materials do not have high requirements for asbestos. As long as the asbestos fiber is fully loosened, Grade 5 and 6 asbestos can meet the product performance requirements.
④ Asbestos electrical materials: various electrical insulation materials are made of asbestos fiber and phenolic resin.On the electrician, make the base plate of high-voltage equipment, high-voltage switch handle, telephone headset handle and military equipment, as well as distribution board, distribution board, instrument panel, etc.On the paper machine, the selected asbestos is used to make insulating asbestos paper with a thickness of less than 0.2mm, which is an insulating material used in the motor coil.When chrysotile asbestos is used to manufacture electrical insulation materials, the existing form of iron contained in fibers must be fully noted.If this kind of iron is dispersed in the fiber with magnetite fines, the insulation of its products will be significantly reduced, and even cannot be used as electrical products.Therefore, such impurities must be removed through special treatment before they can be used to manufacture electrical insulation products.Laiyuan Asbestos Mine is a carbonate type asbestos deposit with low iron content and excellent insulation performance, which is most suitable for manufacturing asbestos electrical materials.
Type of asbestos products
Main types of asbestos products
Asbestos textile
Plywood woven of fireproof cloth, fireproof clothing, brake belt, gasket, packing and electrical insulating tape
Asbestos cement products
Asbestos cement tile roof, wallboard, decorative board, electrical insulation board, drainage pipe, ventilation box, pressure bearing building parts
Asbestos board
Asbestos cardboard, asbestos filter
Asbestos insulation
Pure asbestos insulation material, mixed asbestos insulation material
World asbestos consumption is declining, especially in Western Europe.In 1975, the world asbestos production reached 5.09 million tons, only 1.93 million tons in 1999, and only 2.13 million tons in 2002.Western European countries have partially or completely banned asbestos products.In another part of the world, there is a strong demand for cheap and durable asbestos products, especially for asbestos cement (A/C) products, such as asbestos cement boards for construction, asbestos cement pipes for water transportation, etc.
Asbestos consumption in the United States is decreasing year by year, and the demand for asbestos is mainly from Canada. The consumption of asbestos in the United States dropped to 6000 tons in 2003.The consumption fields mainly include commercial building roof materials, coating composite materials, friction materials, sealing gasket materials, and insulation materials.
domestic market
In China, the consumption of asbestos products is the largest, accounting for 70%~80% of the total consumption;Secondly, friction materials account for 8%~12%;Sealing materials account for 6%~8%;Textile products and other uses account for about 9%.
China's asbestos export volume is small. In 2003, it was 3472 tons, mainly exported to North Korea (1234 tons), Thailand (1539 tons), Malaysia (513 tons), and Japan (48 tons), amounting to 1556200 dollars.
Previously, China mainly imported some long fiber asbestos to make up for the shortage of domestic long fiber asbestos.After 1991, ordinary asbestos poured into Russia in large quantities, and the import volume rose sharply. In 2003 alone, in addition to 1366 tons of long fiber asbestos, worth more than 960000 US dollars, 142111 tons of ordinary asbestos were imported in the same period, worth 24.31 million US dollars.
Specific price
The price of asbestos in the international market was originally published monthly by the British Industrial Minerals Monthly. Compared with the price of British Industrial Minerals published in May 2001 and the price of Canadian chrysotile asbestos published in the British Mineral PriceWatch in March 2004, it can be seen that the price of asbestos has remained stable for a long time.
Due to the decreasing trend of asbestos use in western countries and the problems of asbestos environmental protection, the trading volume of the asbestos raw ore market will be limited to some extent in the future, and the price will fluctuate slightly on the basis of the MineralPriceWatch. However, the price of asbestos products will remain very strong.
The asbestos imported by China mainly comes from Russia, and it is mainly common asbestos. The price level has been maintained at about 171 US dollars per ton. In 2004, the price of asbestos in the international market did not change, but Russia, relying on its position as the main source country of Chinese asbestos imports, increased the price of asbestos per ton by 5 US dollars to 176 US dollars.
Classification of asbestos sales: according to British industrial minerals, it is formulated with reference to Canadian standards. From the third group to the seventh group of chrysotile asbestos, it is priced separately. South Africa chrysotile asbestos is divided into five, six and seven groups, and South Africa crocidolite is delivered as long, medium and short fibers.
Possible hazards
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Asbestos fiber can causeAsbestosis、Pleural mesotheliomaMany countries have chosen to completely ban the use of such dangerous substances, while other countries are examining the risk of asbestos.Therefore, the use of asbestos nets in chemical laboratories of junior and senior high schools in China is still very worrying.
asbestos pollution
About 95% of the asbestos used in the world is chrysotile asbestos, whose fibers can be split into very fine primary fibers. About 10 grams of asbestos fibers are released into the environment for every ton of asbestos consumed in industry.One kilogram of asbestos contains about 1 million fibers.The diameter of the primary fiber is generally 0.5 μ m, and the length is less than 5 μ m. It can be suspended in the atmosphere and water for weeks and months, causing continuous pollution.Research shows that asbestos related diseases are common in a variety of industrial occupations.Such as asbestos mining, processing and use of asbestos or asbestos containing materials in various industries (construction, ship and automobile repair, metallurgy, textile, mechanical and electrical engineering, chemistry, agriculture, etc.).
The United States Environmental Protection Agency has restricted the use of some asbestos products, such as the 1972 regulations prohibiting the spraying of refractory coatings containing asbestos fibers.
During 1980-2003 in Germany, asbestos related occupational diseases caused 12000 deaths.Asbestos kills 2000 people in France every year.The United States reported nearly 20000 cases of asbestos deposition between 1990 and 1999.
In 1998, the World Health Organization reiterated the carcinogenic effect of chrysotile asbestos, especially the risk of mesothelioma, and continued to call for the use of this asbestos substitute.Most EU member states have banned the use of this kind of asbestos (all member states must ban the use of all asbestos by 2005).
At present, there is no quality standard for indoor air asbestos concentration in any country.The standard for asbestos in water in the United States is 0.05 microgram/liter, and the maximum allowable amount of asbestos in the atmosphere in Connecticut and New York is 30 fiber grams/cubic meter (30 day average) and 27 fiber grams/cubic meter, respectively.
China: The threshold limit value of chrysotile asbestos in the air of the workshop is 2 fibers/cubic meter.
carcinogenicity
Asbestos itself is harmless. Its greatest harm comes from its dust. When these fine dust are inhaled into the human body, it will adhere to and deposit in the lungs, causing lung diseases. Asbestos has been recognized as a carcinogen by the International Cancer Research Center.
On the other hand, extremely small asbestos dust flies into the air, and after being inhaled into human lungs, it is easy to induce lung diseases such as lung cancer after a 20-40 year incubation period.This is the problem of asbestos pollution that has received different degrees of attention in countries around the world.In Europe, it is predicted that 500000 people will die of lung cancer caused by asbestos pollution by 2020.In Japan, it is predicted that 100000 people will die by 2040.
Exposure (long-term inhalation) to a certain amount of asbestos fibers or fibrils can cause the following diseases:
(1) Lung cancer, stomach cancer;
(2) Mesothelial carcinoma - pleural or peritoneal carcinoma;
(3) Asbestosis - scarring of the lungs due to fibrosis of tissues in the lungs (asbestos lung);
(4) Symptoms of asbestos related diseases often have a long incubation period, which may occur after about 10 to 40 years of exposure to asbestos (lung cancer usually lasts 15-20 years, mesothelioma 20-40 years).
The production and use of hornblende asbestos was banned in China in 2002 because of its strong carcinogenicity.Chrysotile asbestos is less carcinogenic than hornblende asbestos.In order to protect the occupational health of workers, China has promulgated the Occupational Exposure Limits for Hazardous Agents in the Workplace - Part 1: Chemical Hazardous Agents (GBZ2.1-2019), which stipulates the occupational exposure limits for asbestos. If the occupational exposure limits are met, the occupational health of most workers can be effectively protected.[4]
