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Tellurium is A quasi-metallic element with the element symbol Te, belonging to group in the periodic table of elements, atomic number 52, atomic mass 127.6. Tellurium comes in two allotrope forms. One is a hexagonal system, with atoms arranged in a spiral shape and a silvery-white metallic luster. The other is amorphous, black powder. Tellurium has a melting point of 452ºC and a boiling point of 1390ºC. It is brittle and chemically similar to antimony. Tellurium is soluble in sulfuric acid, aqua regia, potassium cyanide, potassium hydroxide; Insoluble in water, carbon disulfide. Tellurium burns in air with a blue flame, forming tellurium dioxide. When inhaled at very low concentrations, tellurium produces an unpleasant garlic stench on the breath and in sweat and urine. Tellurium is one of seven scattered metals that are generally associated with minerals, and independent deposits are rare, as is tellurium. Dashuigou tellurium bismuth pyrite in Shimian County, Sichuan Province, China is the only primary tellurium deposit in the world so far. Tellurium is also produced in relatively small quantities, given the scarcity of resources, with the United States, Canada, Peru, China and Russia supplying relatively large quantities. Because of the huge market demand for Cdtelluride thin film solar cells, Cdtelluride is currently the most demanding and promising telluride products. Tellurium has applications in metallurgy, electronics and chemistry.
Early tellurium applications were limited. Tellurium was used as a vulcanizing agent in the production of natural rubber during World War II and did not become an element of industrial use until the late 1950s. Tellurium and its compounds are widely used in the downstream industries, including solar energy, alloy, thermoelectric refrigeration, electronics, rubber and other industries. The development of the downstream industry directly determines the demand for tellurium. Cadmium telluride thin film solar energy industry is developing rapidly and is considered as one of the most promising solar energy technologies. It is expected that with the development of cadmium telluride thin film solar energy industry, the demand for telluride will continue to grow rapidly.
Classification of tellurium applications
The main product of tellurium
The main products of tellurium include metallic tellurium, tellurium dioxide, tellurium powder and high purity tellurium.
Metallurgical industry
Tellurium accounts for 42% of the total application in the metallurgical industry, but the proportion of tellurium in the metallurgical industry is decreasing due to the rapid development of tellurium in the photovoltaic field.
Tellurium is mainly used as an alloying element in nonferrous metals and steel in the metallurgical industry. In the non-ferrous metals industry, tellurium is used to improve the machining properties of copper alloys. Adding tellurium to tin, aluminium and lead-based alloys can increase the hardness and plasticity of the alloys. Adding tellurium to lead can be used to make the jacket of electric cables, such as oil drilling pumps. Adding 0.03%-0.04% tellurium to cast iron and steel can reduce the nitrogen absorption of cast iron and steel, change the grain size of the steel, improve the strength and corrosion resistance of the steel. Adding 0.001%-0.002% tellurium to cast iron can make its surface strong and wear resistant. Tellurium has a non-negligible effect on the microstructure, crystallization process and mechanical properties of cast iron. Its whiteness tendency is the first among the elements. The tellurium-treated steel is already used in mines, automation, railways and other equipment.
Chemical industry
The chemical industry of tellurium powder used in chemicals and rubber accounts for about 21% of the total tellurium applications. In the chemical industry, tellurium and tellurium compounds are used as additives in catalysts and as dispersants in the rubber industry to improve the strength and elasticity of rubber. Tellurium plays an important role in the electrolysis of nickel. The addition of NaTeO3(75ml/L) to the electrolyte can produce an excessive nickel layer, which can eventually form an electrolytic nickel layer with strong corrosion resistance. Tellurium catalysts have been used in petroleum cracking and coal hydrogenation. Tellurium also prevents the oxidation of polymethylsiloxane. Tellurium has also been used as a toner and solid lubricant in photography and printing. In addition, bismuth telluride, a compound of tellurium, is an ideal substitute for CFC-11 and CFC-12 (short for Freon) used in human refrigeration (refrigerators, air conditioners, etc.) because of its excellent refrigeration properties.
Electronic and electrical industry
Infrared laser tellurium accounts for about 8% in the electronic and electrical industry. In the optoelectronics industry, involving infrared to ultraviolet spectrum of lasers, photodiodes, optical receivers and other semiconductor components ZnTe, CdTe, HgTe, HgCdTe and so on. Tellurides of lead, tin, and cadmium are sensitive to infrared radiation. PbSnTe and CdHgTe compounds are important infrared photoelectric materials. Tellurides are important raw materials for producing infrared materials. Due to the high sensitivity of SeTe and SeAs alloys per unit time, the cadmium telluride compound is the main photosensitive material used for infrared detectors in military and space systems. Cadmium telluride (CdTe) is applied in optoelectric systems for its good light absorption properties. The high purity telluride used in the military in the United States is up to 99.99999%. Using the excellent photosensitive characteristics of tellurium compounds, it has shown outstanding advantages in resource survey, satellite aerial survey, laser guidance and so on, which was vividly demonstrated in the modern American war against Iraq. Tellurium is an important photoresist element in photoplate making and laser printing and copying. It is tellurium's optoelectronic properties that are playing a key role in one of the most glamorous industries of the 21st century.
Cadmium telluride thin film solar cells
1. What are cadmium telluride thin film solar cells?
CdTe thin film solar cell CdTe thin film solar cell is short for CDTE cell, it is a kind of thin film solar cell based on the heterogeneous P-type CDTE and N-type Cd. General standard CdTe thin film solar cells are composed of five layers: back electrode, back contact layer, CdTe absorption layer, CDTE window layer and TCO layer. Current CdTe cells can be prepared by a variety of methods, including near-space sublimation, chemical water bath deposition (CBD), screen printing, sputtering, evaporation, etc. General industrialization and laboratory are using CBD method, this is because of the low cost of CBD method and the CdS generated can form a good compact bond with TCO.
2. Overview of global CdTE thin film solar cells
The global manufacturers include Canada's 5NPlus, Redlen and Lead Thin Materials. Among them, 5NPlus is the world's earliest producer of thin-film cadmium telluride for solar use in scale production. At present, it is the world's largest producer of thin-film cadmium telluride for solar use and has a large market share in this field. Its scale has grown rapidly with the growth of its main customer, First Solar, which accounts for about 75% of its sales. Redlen is one of the world's leading manufacturers of radiation detectors and medical imaging equipment. It is also one of the few companies in the world with the technology to manufacture cadmium telluride for thin-film solar applications. Due to the lack of an integrated industry chain, Redlen has a small market share in cadmium telluride products. Lead Thin Material has been developing cadmium telluride for thin-film solar use since 2006, and has passed quality certification from some customers and has the technical ability to scale up production.
3. Development status and trend of CdTe thin film solar cell industry in China
In 1980s, the research of CdTe thin film battery was started. At first, Inner Mongolia University used evaporation technology and Beijing Solar Energy Research Institute used electrodeposition technology (ED) to study and prepare CdTe thin film cells. The efficiency of the cells developed by the latter reached 5.8%. From the mid 1980s to the mid 1990s, research work basically came to a standstill with few results. In the late 1990s, Professor Feng Lianghuan from the Institute of Solar Materials and Devices of Sichuan University led the research of cadmium telluride thin film solar cells. During the Ninth Five-Year Plan period, he undertook the research project funded by the Ministry of Science and Technology: "Development of Group - compound semiconductor polycrystalline thin film solar cells". The near-space sublimation technique is used to study CdTe thin film cells, and good results have been obtained. Battery efficiency has recently surpassed 13.38 percent, making it one of the world's most advanced. During the Tenth Five-Year Plan period, CdTe film battery research was included in the national high technology research and development program "863" key projects.
After the unremitting efforts of several generations of scientists, our country is in the rapid development stage of basic laboratory research to application industrialization, and plans to set up a pilot production line with an annual output of 0.5MW. The research on CdTe thin film solar cells, from the original only a few scientific research institutions such as Inner Mongolia University, Sichuan University, Xinjiang University and other basic research in this field, to this year's Sichuan Apollo Solar Technology Development Co., LTD., the new thin film CdTe/CdS solar cell core material industrialization, a two-year period. China will build a production line with an annual output of 50 tons of cadmium telluride and 10 tons of cadmium sulfide, so that the industrialization of CdTe thin film solar cells in China will get great development and stride forward to the world's leading level.
4. Existing problems and constraints
Cdtelluride thin-film solar cells are relatively easy to make, so they are progressing faster than other thin-film solar cells. From laboratory research stage to large-scale industrial production. At present, the next step of CdTe solar cell research and development focus on how to further reduce the cost, improve the efficiency and improve the production process. At present, the market share of CdTe battery is not ideal. The reasons for its failure to rise to the mainstream of the market are as follows:
First, module and base material costs are too high, the overall CdTe solar cell materials account for 53% of the total cost, among which semiconductor materials only account for about 5.5%.
Second, tellurium is naturally in limited supply, and its total quantity is bound to be unable to cope with the large and total reliance on such photovoltaic cells for power generation.
Third, cadmium toxicity, so that people can not be assured to accept this kind of photocell.
CdTe solar cell as a large-scale production and application of photovoltaic devices, the problem of environmental pollution is not negligible. The toxic element cadmium (Cd) pollution to the environment and the harm to the health of operators is not negligible. We can't get clean energy and at the same time create new hazards to the human body and the living environment. Effectively disposing of discarded and broken CdTe components is not technically difficult. But cadmium is a highly toxic heavy metal, and so are its compounds.
The main effects of cadmium: first, the dust containing Cd through the respiratory tract caused harm to humans and other animals; The second is the ecological pollution caused by the discharge of production waste water. Therefore, Cd and Te from broken glass sheets should be removed and recycled, damaged and discarded components should be properly disposed of, and waste water and wastes discharged during production should be treated according to environmental protection standards. At present, all countries are committed to solving the factors that restrict the development of CdTe thin film solar cells. We believe that the above problems will be solved one by one, so that cadmium telluride thin film cells will become one of the new energy components of the future society.
other
Tellurium can also be used as a colorant for glass and ceramics. It can be added to produce different colors of glass and ceramics. It can also give silver ware, lead and brass a fine, permanent black coating. Tellurium can be added to make the glaze pink.
Compared with ordinary silicate glass, tellurium glass has the characteristics of high refractive index, low deformation temperature, high density and infrared transparency.
The glass containing certain amount of germanium, sulfur and tellurium has good chemical properties, high mechanical strength, good heat resistance (softening point 385ºC) and shock resistance in the infrared region.
The infrared transparency of tellurium glass is helpful for its applications in infrared optics, such as infrared Windows.
The good photosensitivity indicates that it can be used for vidicon applications. The low softening temperature makes it possible to make vacuum enclosed semiconductor component materials.
Tellurium compounds have obvious antitumor effects and inhibit the proliferation of leukemia cells.
In addition, it can be used in insecticides, fungicides, for the production of radioactive isotopes, and can be used to treat hair loss, syphilis and other diseases. Tellurium and its compounds were found to be less toxic than selenium, with water-soluble tellurium salts and tellurite being the most toxic and elemental tellurium the least toxic. For tellurium, the United Nations, the United States and a number of countries and organizations have proposed health standard exposure thresholds.
Trace element with cryptotoxicity
Tellurium is a non-essential trace element with latent toxicity. Inhaling tellurium powders and vapors can cause sweating disorders, resulting in feelings of lethargy and vomiting, and weeks of bad breath, tellurium poisoning's tellurium symptoms. Tellurium poisoning is characterized by a stench of sweat, urine, and breath. The maximum allowable concentration of tellurium in the air of the operation area is 0.1 to 0.05mg/m³. Compounds Almost all tellurium compounds are toxic. Industrial tellurium compounds include oxides, sulfides, telluric and tellurite acids, and halides.
The metabolism of tellurium in the human body
Sodium tellurite is readily absorbed by the gastrointestinal tract of mammals and is excreted mainly in the feces. Other tellurite compounds are absorbed by the skin, digestive tract or respiratory tract and excreted from breath, sweat, urine and feces. Tellurium dioxide and tellurium salts are first reduced to elemental tellurium in the body, partly to dimethyl tellurium and diethyl tellurium in urine, feces and exhalation, and partly to dissolved tellurium in urine and bile. After absorption, tellurium can be combined with plasma protein and distributed throughout the body. The content of tellurium is relatively high in the kidney and blood. The content of tellurium in the blood of normal people is 0.05%-0.16%, and the concentration of tellurium in urine and bile is twice of that in the blood. The absorption of tellurium in the organs peaks at the end of 24 hours, and then rapidly declines, with more than 80% excreted in urine and feces within a few days. Tellurium is slowly excreted after a few days because more than 95% of tellurium is bound to proteins in tissues. Tellurium accumulates primarily in the kidneys, especially the renal cortex, followed by the liver, spleen, heart, lungs, and brain.
Acute toxicity
Overall, tellurium is less toxic than selenium. Acute toxicity in animals mainly damages digestive system, central nervous system, cardiovascular system and respiratory system. Localized pneumonia and hemolytic anemia are typical features of tellurium acute toxicity, often accompanied by hematuria.
Chronic toxicity
Chronic poisoning in animals is characterized by indigestion, growth arrest, emaciation, depilation, garlic odor on the breath, and lethargy.
Intake standard
The susceptibility of people to tellurium varies greatly. Some people take 0.5mgTeO2 orally to cause garlic odor on breath, while others take 90mg tellurium orally. Tellurium concentration in air that does not cause garlic odor is 0.01-0.02 mg/m3, and symptoms will disappear on their own after discontact.
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