Metallurgical silicon is classified into different grades depending on the degree of purity, which determines its application in various industries. Here is a detailed classification:
1. Metallurgical Silicon (MG-Si)
Purity: 97%-99% silicon
Main impurities:
Iron (Fe): ≤ 0.5%
Aluminum (Al): ≤ 0.5%
Calcium (Ca): ≤ 0.3%
Main areas of application:
Aluminum alloys (e.g., automotive parts, aerospace components).
Productionof silicon steel (for electrical transformers).
Raw materials for ferrosilicon alloys (used in steel production).
Production: Produced by carbothermic reduction in electric arc furnaces.
2. Chemical Grade Of Silicon
Purity: ≥99% silicon
Main impurities:
Fe: ≤ 0,4%
Al: ≤ 0,4%
Ca: ≤ 0.1%
Main areas of application:
Raw materials for the production of silicones (sealants, lubricants, resins).
Polysilicon production (through purification processes such as the Siemens method).
Refining: Further processing to remove impurities for use in the chemical industry and solar energy.
3. Electronic Grade Silicon (EG-Si)
Purity: ≥99,9999% (6N+ purity)
Key impurities:
Boron (B), Phosphorus (P): < 1 ppb (parts per billion).
Heavy metals (e.g. Cu, Ni): < 0.1 ppb.
Main areas of application:
Semiconductor wafers for integrated circuits (ICs) and microchips.
Photovoltaic (PV) cells for solar panels.
Production:
It is produced from polysilicon using processes such as the Czochralski (CZ) method or the float zone (FZ) method.
Ultra-high purification is required (e.g., zone refining, chemical vapor deposition).
4. Solar Grade Silicon (SoG-Si)
Purity: 99.9999% (6N) to 99.99999% (7N).
An intermediate option between chemical and electronic classes.
Application:
It is mainly used in solar photovoltaic cells.
Cost-Effective: Less stringent purity requirements compared to electronic grade, which reduces production costs.
Key Notes
Polysilicon vs. Metallurgical Silicon:
Polysilicon (>99.9999% Si) is made from chemical-grade silicon and serves as a precursor for EG-Si and SoG-Si.
Influence of impurities:
Even trace impurities (e.g., Fe, Al) degrade the electrical characteristics of semiconductors.
Purer grades require advanced refining technologies (e.g., distillation, gas-phase refining).
