Email：star15@alloyssi.com
news
As an indispensable basic material in the huge system of modern industry, silicon metal is widely used in many key fields such as metallurgy, semiconductors and silicones. From helping to improve the performance of steel to becoming a core raw material for chip manufacturing, the quality and yield of silicon metal directly affects the development of many downstream industries. In this article, we will analyze the refining process of silicon metal (industrial silicon) and unravel the mysteries of production from raw material to finished product.
Silicon metal, also known as industrial silicon or crystalline silicon, is a form of silicon monomers with important industrial value in the chemical field. Due to its wide range of applications in industrial production, these different designations are widely used in the industry.
Silicon metal is classified mainly on the basis of the content of three main impurities: iron, aluminum and calcium. This classification is reflected by specific numbers, for example, the “553” grade of silicon metal represents 5% iron, 5% aluminum, and 3% calcium, while “3303” means 3% iron, 3% aluminum, and 0.3% calcium. The industry has been able to achieve this through clear numbering rules. Through this clear numbering rule, the industry can quickly determine the impurity situation and quality level of silicon metal.
Silicon metal has a wide range of downstream applications, and the proportion varies in different fields. Among them, 30.28% is used for the production of polysilicon, which serves the semiconductor and solar energy industries; 26.82% is refined into metallurgical-grade silicon, which is used for the manufacture of aluminum alloys; and 38.03% is further refined through the hydrometallurgical process into chemical-grade silicon, which is used for the production of silicone rubber and silane. Different applications require different purity and impurity content of silicon metal, which determines the differences in the refining process.
Silica, as the core raw material for silicon metal production, is subject to strict compositional standards. Industrial production requires that the SiO2 content of silica must be ≥ 99%, while Fe2O3 ≤ 0.15%, Al2O3 < 0.2%, CaO < 0.1%, and the total impurities should preferably be < 0.6%. Excessive impurity content will directly affect the smelting process, increase energy consumption and even reduce the quality of silicon metal.
In addition to its chemical composition, the physical properties of silica are equally critical. It needs to be highly resistant to heat and should minimize cracking when subjected to thermal phase changes when added to the furnace. The higher the onset temperature for intense disruption, the better, to ensure stability in the high temperature environment of the furnace. In addition, the reducibility of SiO2 is an important characteristic that determines whether silica can be successfully reduced to silicon metal.
The quality of silica raw materials varies, and so do their uses. High-quality quartz sand, due to its purity and quality, is usually used directly in the production of high-grade quartz glass products, and can even be processed into gem-quality crystals and tourmalines, etc., whereas silica with slightly lower grades, but with larger reserves, better mining conditions, and lower cost of electricity in the surrounding area, is more suitable for the production of silicon metal.
Carbonaceous reductants commonly used in the smelting process of silicon metal include charcoal, petroleum coke and coal. These reducing agents react with silica at high temperatures to reduce silicon from silica.
Not all carbonaceous materials are suitable for use as reducing agents, and production has strict performance requirements. Generally speaking, the reductant needs to be characterized by high fixed carbon, low ash, moderate volatile matter, low moisture, high resistivity, high reactivity and certain mechanical strength. Only by meeting these requirements can we ensure the effective reduction of silica in the smelting process, and at the same time, reduce the introduction of impurities, so as to reduce the burden of the subsequent decontamination process.
The smelting of silicon metal mainly adopts the electric furnace method, i.e. the carbothermal method. The core principle is that in an electric arc furnace, silica (SiO2) reacts chemically with a carbonaceous reducing agent. Under high temperature conditions, SiO2 reacts with carbon (C) to form silicon (Si) and carbon monoxide (CO), with the chemical equation: SiO2 + 2C → Si + 2CO. This process requires precise control of the temperature and reaction conditions in order to realize the efficient reduction of silicon.
Dosing and mixing are the basic stages of smelting. They need to be accurately matched to the chemical composition and particle size of the silica and carbonaceous reductant to ensure the uniformity and stability of the charge in terms of composition and physical properties. Only uniform charge can realize stable and efficient reaction in the electric furnace.
The charging process is strictly sequential and the charge is loaded into the furnace in a specific way. With the gradual lowering of the electrodes, the power supply is started and the current is gradually increased according to the reaction process. This stage requires the operator to pay close attention to all parameters to ensure that the feeding process is smooth and that the reaction is not affected by abnormalities in the current.
Stewing and refining is the key to the whole smelting process. By precisely adjusting the voltage, current and other parameters of the electric furnace, the temperature inside the furnace is maintained in a suitable range to ensure that SiO2 is fully reduced to silicon metal. At the same time, some impurities can be effectively removed during the process, which improves the initial quality of silicon metal.
The silicon metal obtained from smelting contains certain impurities, which need to be further refined and purified. A common method is to treat volatile silicon compounds through distillation to separate out the impurities, thus significantly improving the purity of silicon to meet the needs of different applications.
Purified silicon after impurity separation is cast into solid forms such as ingots, blocks or pellets. Afterwards, it is crushed, ground and processed according to the application requirements of different industries to make silicon metal products that meet the specifications.
After molding and processing, the finished silicon metal products will be packaged according to product characteristics and customer requirements. After packaging, these products will be distributed to various industries such as electronics, metallurgy, chemicals, etc., and put into different production processes.
Silicon metal production is typically a high-energy industry, with an average electricity consumption of 13,000kwh per ton of silicon. In electric arc furnaces, reaction temperatures of up to 1800°C are required to ensure that the reduction of silica and carbon takes place smoothly. This makes silicon metal production very dependent on electricity resources, and production is usually carried out in areas with sufficient electricity resources.
Various measures have been taken to reduce energy consumption. It selects high-quality silica source ores and carbonaceous reductants with high activity and low ash content to improve the reaction efficiency from the raw material side; adopts advanced thermoelectric furnaces to optimize the performance of the equipment; and further reduces energy consumption by optimizing the process operation to reduce problems such as hot stops and uneven fabrics, so as to achieve energy saving and reduction in energy consumption.
The impurity content of silica raw materials has a significant impact on production. When producing high-quality industrial silica, Fe2O3 is less than 15%, Al2O3 is less than 20%, CaO is less than 15%; if producing super high-quality industrial silica, the control standard of these oxides is more strict. The high content of impurities will lead to sticky material surface of the furnace mouth, poor permeability, increasing heat loss and power consumption.
The thermal stability and explosion resistance of silica are equally important. If the thermal stability of silica is poor, easy to rupture after heating, surface flaking, will seriously affect the permeability of the furnace, resulting in the upper part of the furnace charge bonding, heat can not be effectively transferred, and ultimately, the power consumption increased significantly. In addition, the silica particle size should be strictly controlled at 50 - 120mm, too small or too large a particle size will have a negative impact on the production.
With the continuous progress of industrial technology, silicon metal refining technology will also develop in the direction of energy saving, high efficiency and high purity. In the future, the industry will face challenges such as reducing energy consumption and improving product purity, and there are also opportunities such as technological innovation and opening up new application areas. Through continuous technological research and development and process optimization, the silicon metal industry will surely provide more solid support for modern industrial development.
Copyright Notice © Anyang Jinsheng Metallurgical Materials Co., Ltd. All rights reserved. Site Index Product Index
.jpg)
