Preparation technology of metal silicon

Metal silicon can also be referred to as metallurgical silicon, coarse silicon, or industrial silicon. In terms of crystal structure, metal silicon is also in a polycrystalline state, with a purity of about 98%~99%. It is mainly used as an additive for steel and other silicon products, with a small amount (about 2%) of metallic silicon further purified to prepare solar grade and semiconductor grade polycrystalline silicon The raw material of metallic silicon, quartz sand, is a form of SiO. In order to improve the purity of metal silicon and reduce production costs, there are generally certain purity requirements for the raw material of metal silicon - quartz ore, and not all quartz sand can be used as the raw material for silicon materials The preparation of metallic silicon generally uses an electric arc furnace, with raw materials consisting of quartz sand and coke or charcoal with a purity of around 98% to 99%. At around 2000 ℃, a reduction reaction can generate metallic silicon, with the main reaction formula being

SiO23C -- SiC2C0 (3.8)

2SiCSiO2--3Si2C0 (3.9)

From equations (3.8) and (3.9), it can be seen that in addition to generating silicon, a large amount of harmful CO gas is also produced, which neutralizes oxygen in the air and further generates a large amount of CO2, becoming a harmful gas that pollutes the environment, As shown in the following equation:

2C002--2C02 (3.10)

Figure 3.3 shows a schematic diagram of the preparation of metallic silicon. From the figure, it can be seen that carbon electrodes are generally used to generate an arc, which generates molten silicon at high temperatures. After being collected, it is metallic silicon. At the same time, slag is generated at the bottom of the furnace, and CO2 overflows on the surface The preparation of metal silicon is relatively energy-efficient and can also cause air pollution. Therefore, how to reduce energy consumption and how to reduce CO2 emissions are currently the focus of research. In addition, in selecting quartz raw materials, how to minimize B and P impurities is also a noteworthy issue