What is Metal silicon?Who will buy metal silicon?

- Jun 01, 2018 -

                                             What is Metal silicon?Who will buy metal silicon?


Chinese name:metal silicon

Chinese alias: crystalline silicon; industrial silicon; silicon powder; silicon powder; polycrystalline silicon; monocrystalline silicon; silicon optical windows; 


English name:silicon

English allas:silicon coating quality balzers; silicium; silicon, containing by weight not less than 99.99 % of silicon; SiliconpowderNmesh; Silicon Monocrystalline; SiliconchipsNmm; SiliconrandompiecesNcm; Silicon wafer orientation P-doped;

Silicon wafer orientation; Silicon powder; Siliconwaferorientation;

Siliconwafer; Silicon (low oxygen); Silicon (3 oxygen levels); Silicon chips (99.9999%); Silicon random pieces (99.5%); Silicon solution 1000 ppm

definition



Metal silicon description


"Metal silicon" (also known as industrial silicon in China) was a trade name that appeared in the mid-1960s. Its appearance is related to the rise of the semiconductor industry. 


The international practice is to classify commercial silicon into metal silicon and semiconductor silicon. 

Metal silicon is produced from quartz and coke smelted in an electric furnace. The content of main component silicon is about 98% (99.99% of Si is also contained in silicon metal), and the remaining impurities are iron, aluminum, calcium, etc. . Semiconductor silicon High-purity metal silicon used to make semiconductor devices. It is sold in polycrystalline and monocrystalline form. The former is cheap and the latter is expensive.


It is divided into various specifications because of its different uses. According to statistics, in 1985, the world consumed a total of about 500,000 tons of metal silicon, of which about 60% were used for aluminum alloys, less than 30% for organic silicon, about 3% for semiconductors, and the rest were used for Iron and steel smelting and precision ceramics.




Atomic structure


Outer nuclear electronic arrangement: 1s22s22p6 3s23p2;

Cell type: cubic diamond type;

Cell parameters: The cell parameters measured at 20°C were a = 0.543087 nm;

Color and appearance: dark gray, blue tone;


Using nanoindentation method, single crystal silicon (100) has an E of 140-150 GPa.

Conductivity: The conductivity of silicon has a great relationship with its temperature. With the increase of temperature, the conductivity increases, reaching the maximum around 1480°C, and decreases with the temperature after the temperature exceeds 1600°C[1] .




The nature of silicon

Silicon is one of the semi-metals, formerly known as "". The melting point is 1420°C and the density is 2.34 grams per cubic centimeter. Hard and brittle. 


At room temperature, it is insoluble in acid and soluble in alkali. Metal silicon is similar to germanium, lead and tin and has semiconductor properties. Silicon is extremely rich in resources in the crust, second only to oxygen, accounting for more than a quarter of the total weight of the earth's crust, in the form of silica or silicate. The purest silicon mineral is quartz or silica. 


Silicon has two allotropes: one is a dark brown amorphous powder, lively in nature, capable of burning in air; the other is a crystalline crystal (crystalline silicon). General silica and quartz are used for glass and other building materials, and high quality quartz is used for making alloys, metals and single crystals




The use of silicon,who will buy metal silicon


A large amount of silicon is used for smelting into a ferrosilicon alloy as an alloying element in the steel industry, and is used as a reducing agent in many kinds of metal smelting. Silicon is also a good component in aluminum alloys. The vast majority of cast aluminum alloys contain silicon. Silicon is a raw material for ultra-pure silicon in the electronics industry.


 Ultra-pure semiconductors made of monocrystalline silicon have the advantages of small size, light weight, high reliability, and long life. High-power transistors, rectifiers, and solar cells made of silicon single crystals doped with specific trace impurities are better than those made from single crystals of germanium. Amorphous silicon solar cells have made rapid progress and the conversion rate has reached more than 8%. Molybdenum-silicon-molybdenum rod heating element can reach a maximum temperature of 1700 °C, with resistance to aging and good oxidation resistance. 


Trichlorosilane produced from silicon can be formulated into hundreds of silicone lubricants and waterproof compounds. In addition, silicon carbide can be used as an abrasive, and quartz tubes made of high-purity silicon oxide are important materials for high-purity metal smelting and lighting fixtures. Paper in the 1980s - Silicon People call silicon "the paper of the 1980s." This is because paper can only record information, and silicon can not only record information, but also process information to obtain new information. T


he world’s first electronic computer manufactured in 1945 was equipped with 18,000 electron tubes, 70,000 resistors, and 10,000 capacitors. The entire machine weighed 30 tons and occupies 170 square meters, which is equivalent to the size of 10 houses. 


Today's electronic computers, due to advances in technology and improved materials, can accommodate tens of thousands of transistors on a fingernail-size silicon wafer; they also have a series of functions such as input, output, calculation, storage, and control information. 


Microporous silica-calcium insulation microporous silica-calcium insulation is an excellent insulation material. It has the characteristics of small thermal capacity, high mechanical strength, low thermal conductivity, non-flammable, non-toxic, odorless, and can be cut and transported. It can be widely used in metallurgy, electric power, chemical industry, ships and other thermal equipment and pipelines. After testing, the energy-saving benefits are superior to those of asbestos, cement, vermiculite and cement perlite. The special silica-calcium material can be used as a catalyst carrier and is widely used in petroleum refining and automobile exhaust gas purification.




Silicon smelting process


Metal silicon smelting is a high-energy-consuming production. China's metal silicon production has a long history. With the tightening of national energy policy and the implementation of energy-saving emission reduction, as well as the promotion of new energy sources, metal silicon smelting has become a primary product and In the process, many domestic emerging energy companies have built a series of cyclical industrial chains such as metallic silicon, polysilicon, monocrystalline silicon, and solar cells, which will inevitably affect the development of the entire energy sector and the application of new energy in the next few years.


The following describes the metal silicon smelting process and process.


1. The necessity of producing silicon for chemical industry

China's production of metal silicon (silicon content is mainly 98.5%), the original mainly metallurgical silicon, chemical metal silicon (silicon content is mainly 99.85%) production is mainly from the mid-1990s has developed, China's chemical silicon The production and export volume have grown faster. 


From 1999 to 2001, China's chemical silicon exports to Japan reached 22,000 tons, 30,000 tons and 40,000 tons, respectively. 


In 2001, China’s chemical silicon exports to Japan accounted for more than 40% of Japan’s chemical silicon imports. . China has begun to join the ranks of producers and suppliers of chemical silicon, and the number of companies producing chemical silicon is increasing. As Shanghai Guangji Silicon Materials Co., Ltd. fully disclosed the carbothermic reduction smelting process in 2002, China's production capacity of silicon metal quickly increased from 100,000 tons to 1.2 million tons between 2002 and 2004. As a result, the NDRC imposed full sanctions. 


In 2006, the actual production of silicon metal fell back to 700,000 tons. In 2006, only Shanghai Guangji Silicon Material Co., Ltd. Dawu Silicon Plant successfully built Jingxin Plant of 10,000-ton metal silicon plant in the border town of Xinjiang. Other new silicon factory. Chemical silicon refers to metal silicon used in the production of silicones and polysilicon. 


From a worldwide point of view, the consumption of metallurgical silicon is greater than that of chemical silicon, but with the continuous development of science and technology, chemical silicon is used in the area of organic silicon and semiconductors to continuously expand, and is widely used in organic production. 


Silicon monomer and polymer silicone oil, silicone rubber, silicone resin building anticorrosion, waterproof agent, etc. They have unique features such as high temperature resistance, electrical insulation, radiation resistance, and waterproof. For electrical, aviation, machinery, chemical, pharmaceutical, national defense, construction and other departments. More than 95% of the electronic components used as the core of integrated circuits are made of semiconductor silicon, which is the pillar of the contemporary information industry. Optical fibers in a large number of applications in the "information superhighway" are also produced from metallic silicon. 


The consumption of chemical silicon in the United States and the European Union accounts for more than half of the total consumption of silicon metal. Chemical silicon is widely used as a high-tech field and an important basic industry, and its consumption tends to grow steadily. In the normal international market, the price per ton of chemical silicon is 300-400 dollars higher than that of metallurgical silicon. Therefore, whether it is to meet the export and domestic needs, or to improve the economic benefits of metal silicon enterprises, improve product quality, vigorously develop chemical silicon production is necessary.


2. Chemical silicon production raw materials In chemical silicon production, raw materials are a prerequisite for good operations. Quartz rock is used as a raw material for producing chemical silicon, and low-ash carbonaceous material is used as a reducing agent. The raw material for the production of chemical silicon by the electric furnace method is mainly silica and carbon raw materials. 


The carbon raw materials are mainly petroleum coke, with high-quality anthracite or charcoal, or they can be blended to increase the specific resistance of the charge. The raw materials are required to have the necessary purity and good reaction capability in order to achieve the product specifications; the reducing agents have different reaction capacities so that they can fully react with quartz stones; the charge materials have different compositions and have different particle sizes. In order to achieve a good influence on the furnace charge furnace through proper cooperation.


2.1, silicon oxide minerals The process of smelting metallic silicon is a slag-free process. Chemical silicon smelting is more rigorous in the selection of silica. Not only the impurity content is small, but also high mechanical strength, sufficient thermal stability, and appropriate particle size composition are required. 


Silica is best used for chemical silicon smelting. The natural form of silica exists either as an independent quartz mineral or as a rock-silica or silica-like sandstone that is almost entirely made up of silica. 


The chemically-produced silicon contains impurities and stickies in the silica minerals, and some of them are reduced during the smelting process, and some are reduced, and some enter the product silicon in the form of compounds or generate slag. This not only increases energy consumption, reduces product quality, but also causes difficulties in the smelting process. Therefore, the chemical composition of silica-containing minerals used for chemical silicon smelting is demanding. SiO2 is required to be greater than 99%, Fe2O3 is less than 0.15%, Al2O3 is not more than 0.2%, CaO is not more than 0.1%, and the sum of impurities is not more than 0.6%. The silica used must be washed and the surface cleaned before smelting.


Silica into the furnace requires a certain size. The particle size of silica is an important process factor for smelting. The suitable silica particle size is influenced by various factors such as silica type, electric furnace, capacity, operating conditions, and the type and particle size of the reducing agent, and should be determined according to the specific smelting conditions. Under normal circumstances, the 6300KVA three-phase electric furnace (built in 1983 Dawu Silicon Plant) requires three-phase electric furnace with silica particle size of 8-100mm and 3200KVA. The required silica particle size is 8-80mm, and the proportion of intermediate granularity is larger. 


When the particle size is too large, because it can not adapt to the sticking material and reaction speed of the crucible furnace, the unreacted silica easily enters into the liquid silicon, resulting in an increase in the amount of slag, difficulties in production, reduced recovery of silicon, increased energy consumption, and even the furnace The bottom rises, affecting normal production. If the particle size is too small, the contact surface of the reducing agent can be increased, which is favorable for the reduction reaction. However, the gas produced in the reaction process cannot be smoothly discharged, which in turn slows down the reaction rate. Particle size is too small. Impurities brought in will increase, affecting product quality. Silica which is generally less than 5mm in production should not be used.


2.2 Carbonaceous Reducing Agents The main reducing agents used in chemical silicon smelting are petroleum coke, bituminous coal and charcoal. In order to increase the resistivity of the charge and increase the chemical activity, there are also gas coke, silica coke, blue carbon, semi-coke, low-temperature coke, and wood blocks. In the chemical composition of the carbonaceous reducing agent, the fixed carbon, ash, volatile matter and moisture should be mainly considered. 


Generally, the fixed carbon is required to be high, and the total amount of reducing agent required is reduced, so that the impurities brought in by the ash are less, the amount of slag is reduced correspondingly, the power consumption is reduced, and the impurity content in the chemical silicon is reduced. 


The carbonaceous reducing agent has a large resistivity and a high porosity. The charge resistance of the charge depends mainly on the carbonaceous reducing agent. The carbonaceous reducing agent has a high resistivity, a good chemical activity, and a high silicon recovery rate.

Petroleum coke is the lowest ash content of reducing agent used in the production of metal silicon, containing 0.17-0.6% ash, 90-95% of fixed carbon, volatile matter is not more than 3.5%-13%. Chemical silicon smelting uses petroleum coke as a reducing agent because of its low ash content, which helps improve product quality. However, because petroleum coke has small resistivity and poor reactivity, it is easy to graphitize at high temperatures, and when the amount is too large, it leads to poor control of the furnace conditions, resulting in non-sintered charge, severe stabbing, high power consumption, and difficulty in production.


Wood charcoal has high specific resistance and reactivity, and less impurity content. It is an ideal reductant for smelting industrial chemical silicon, but charcoal made from different woods and different methods has very different properties. The ash content of the peeled charcoal is usually lower than that of the ash content of the charcoal with skin by one half to one third. The bark has a great influence on the content of ash in the charcoal. The main component of charcoal is carbon with low ash content, generally less than 10%. The resistivity is large and the chemical activity is good. Many years of production practice have proved that charcoal is an important carbonaceous raw material that meets the needs of smelting chemical silicon, but the source of charcoal is limited and it is no longer possible to use charcoal reducing agents.


From overseas, the vast majority of countries no longer use charcoal. Many domestic manufacturers have also done a lot of work in seeking and using charcoal substitutes. Practice has proved that, among various carbonaceous reducing agents, bituminous coal is another ideal reducing agent besides charcoal, in terms of reaction capacity and specific resistance.

Bituminous coal is characterized by high resistance and strong reaction capability. Low-ash bituminous coal is obtained by washing. Ash content of up to 3%, Fe2O3 content of 0.2-0.3%, Al2O3 content of less than 1%. China's reducing agent bituminous coal ash content is more than 3%, while the foreign reducing agent bituminous coal ash content of more than 1%, the Soviet Union used the chemical method selected bituminous coal, iron oxide content can be less than 0.1% of the clean coal. The patents for the smelting process of bituminous coal and charcoal are jointly owned by Shanghai Guangji Silicon Materials Co., Ltd. and Ordos Power Smelting Co., Ltd. The role of the block is to increase the resistance of the material layer, and the amount of the volume has an effect on the furnace condition. 


The use of wood blocks is too large, the material layer is loose, the condition of the furnace is deteriorated, and the power consumption is increased. Because the ignition point and carbon content of the wood block are low, the actual reducing agent is minimal.

The impurities in the carbon feedstock are mainly ash and all consist of oxides. In chemical production, oxides in the ash are also reduced, which consumes both electrical energy and carbon, and the reduced impurities are still mixed in the silicon fluid, reducing the strength of the silicon. In the production practice, every 1% of ash content in the charge will consume 100-120 degrees of electrical energy. Therefore, the lower the ash content in the carbon raw material, the better.


2.3 Electrode Electrodes are one of the major consumable materials in the production of chemical silicon. Electrodes for chemical silicon smelting generally use graphite electrodes and carbon electrodes. Currently, graphite electrodes are mainly used in China.

In silicon smelting furnaces, the electrodes are the heart and are an important part of the conductive system. The electric current is generated by an electrode input into the furnace for chemical silicon smelting. Requirements for the electrode material: 

(1) Good electrical conductivity and low electrical resistivity to reduce power loss. 

(2) The melting point should be high, the coefficient of thermal expansion should be small, and it should not be easily deformed; 

(3) There is sufficient mechanical strength at high temperatures and the impurity content is low. Graphite electrodes have low ash content, good electrical conductivity, heat resistance and corrosion resistance and are the best choice for chemical silicon smelting.


3. Smelting process of silicon for chemical industry

The chemical silicon process includes charge preparation, electric furnace smelting, silicon refining and casting, and crushing by removing slag inclusions. Prior to the preparation of the charge, all raw materials must be treated as necessary. Silica is crushed in a jaw crusher to a block size of no more than 100mm. 


Sieves smaller than 5mm are screened out and rinsed clean with water. Because the lumps in the furnace melt in the upper part of the furnace, the gas permeability of the charge is reduced, making the production process difficult. Petroleum coke has a high conductivity, and it must be broken to a block size of no more than 10mm, and the amount of petroleum coke powder must be controlled. Because it burns directly on the mouth of the furnace, it can cause insufficient reductant.

In the production of silicon for chemical use, bituminous coal can completely replace charcoal, such as Hunan Zhuzhou refined bituminous coal, fixed carbon up to 77.19%, volatile matter divided into 19.4%, ash content 3.41%, Fe2O3 content 0.22%, Al2O3 content 0.99%, CaO content 0.17% . Through the production practice, the use of such bituminous coal for smelting chemical silicon is feasible.

Wood blocks and wood chips for the production of chemical silicon are machined using cutting machines and wood chippers. Carbonaceous charge


metal silicon

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