The purity of the reduced silicon is mostly 98% to 99.9%, which is called metallurgical grade silicon (MG-Si). Metallurgical grade silicon, also known as industrial silicon, chemical silicon, crystalline silicon or metallic silicon, is mainly used as an additive for non-ferrous alloys, as an alloying agent for silicon steel, and as a deoxidizer for smelting special steel and non-ferrous alloys. After a series of process treatments, industrial silicon can be drawn into monocrystalline silicon for use in the electronics industry and for the production of organic silicon in the chemical industry. Therefore, it is called magic metal and has a wide range of uses. The industrial silicon produced in China was originally metallurgical silicon. The production of industrial silicon has been mainly developed since the mid-1990s. In recent years, the output and export of chemical silicon in China have grown rapidly. In recent years, from a global perspective, the main exporters of industrial silicon are China, Norway, Brazil, South Africa, etc.; the countries that import industrial silicon are mainly Japan, Western Europe, North America and some countries in Southeast Asia. Since 2000, China’s annual industrial silicon output has reached more than 400,000 tons, accounting for about one-third of the world’s total industrial silicon output. The annual export volume has exceeded 300,000 tons, and it has been exported to more than 50 countries and regions. At present, China’s industrial silicon production capacity, output and export growth rank first in the world. Most of the industrial silicon produced in China is exported, and it is the world’s largest industrial silicon exporter, except for exports to Japan, South Korea, and some countries in Southeast Asia. It also exports to some countries in North America, Western Europe and North Africa.
The purity of metallic silicon is usually expressed as the percentage of the content of the three main impurities, iron, aluminum, and calcium. If the content of iron, aluminum, and calcium are 0.4%, 0.3%, and 0.2%, it is called 432. The content of calcium in these three impurities is usually less than one thousandth, just add a “0” in front of this position. For example, the content of iron, aluminum, and calcium are respectively: 0.2%, 0.2%, and 0.03%, converted into One part per million (10-6), the content of iron, aluminum, and calcium is 2000×10-6, 2000×10-6, 300×10-6, and the unit of polysilicon impurity concentration is generally expressed by 10-6, and 1×10-6 is 6N . In the metal silicon industry, three elements are mainly concerned: iron, aluminum, and calcium. If the sum of the three elements is less than 1%, it can be called 99% metallic silicon. If the sum of the content of these three elements is less than 0.1%, it can be called 3N metallic silicon. The physical method of polysilicon is directly purified by metallic silicon. This habit, because boron and phosphorus play a key role in the production of solar cells, so boron and phosphorus must be added. Of course, carbon, oxygen, nitrogen, hydrogen and other elements also play an important role. If the sum of these elements is less than 1×10-6, it can be called 6N; if the sum of these elements is less than 10×10-6, it is called 5N. Of course, there are also questions here: Do other elements also need to be removed? In fact, it is rare to use a figure obtained by subtracting the sum of 108 elements outside of silicon by 100% to express the purity of silicon. Therefore, we can also express the content of a certain element separately. At present, with a precision of 10-6, the most common instrument for measuring element content is the inductively coupled plasma emission spectrometer (ICP-AES). If the accuracy is higher, you can use the inductively coupled plasma mass spectrometer (ICP-MS). When the impurity content is expressed by 10-6, there is a difference between the concentration calculated by weight (mass) and the one-millionth calculated by atomic density. The latter means that there are several impurity atoms per million silicon atoms. For the same material, there is a certain correspondence between one part per million calculated by weight (mass) and one part million calculated by atomic density, and its ratio is the ratio of the atomic weight of silicon atoms and impurity atoms. same. For example, the atomic weight of silicon is 28 and the atomic weight of boron is 11. If the concentration of boron is calculated by weight (mass) as 4×10-6, the corresponding value calculated by atomic density is 4×10-6x28÷11=10.2×10-6
The production scene of metal silicon and metal silicon products are shown in Figure 1 and Figure 2.