The core performance and application boundaries of silicon metal (Si≥98%) are determined by its purity. Iron (Fe), aluminum (Al), and calcium (Ca) are the main impurities, and their content directly affects the deoxidation efficiency, alloying effect, and downstream product quality of metallic silicon. Precise control of impurity content is crucial to ensuring suitability for high-end applications.
Basic Characteristics and Standard Limits of Fe, Al, and Ca Impurities in Silicon Metal
| Grade | Fe content limit | Al content limit | Ca content limit | Total impurities content | Core application scenarios |
| 553# | ≤0.5% | ≤0.4% | ≤0.3% | ≤1.3% | Common aluminum alloys, steelmaking deoxidation |
| 441# | ≤0.4% | ≤0.4% | ≤0.1% | ≤0.9% | High-end aluminum alloys, precision casting |
| 3303# | ≤0.3% | ≤0.3% | ≤0.03% | ≤0.63% | Photovoltaic polysilicon, semiconductors |
| 2202# (Premium Grade) | ≤0.2% | ≤0.2% | ≤0.02% | ≤0.42% | Electronic-grade silicon materials, special alloys |
Note: Fe and Al easily form hard and brittle compounds (such as AlSi₃ and FeSi₂), while Ca readily reacts with oxygen and sulfur to form low-melting-point inclusions. All three impurities reduce the purity and performance stability of metallic silicon with increasing content.
Quantitative impact on performance and applications
Impact of iron
Mechanical properties:
High iron content may reduce the mechanical strength and hardness of silicon metal and make it easy to deform.
Oxidation reaction:
Iron is easily oxidized in silicon metal to form iron oxide, which affects the reduction of silicon and reduces the deoxidation effect.
Melting point effect:
The presence of iron may reduce the melting point of silicon metal and affect its behavior during the smelting process.
Impact of aluminum
Smelting performance:
Aluminum will react with silicon to form aluminum silicide, which affects the reduction ability and chemical stability of silicon metal.
Oxidation reaction:
Aluminum is also easy to oxidize and may form aluminum oxide at high temperature, affecting the purity and reduction performance of silicon metal.
Impact of calcium
Reducing agent activity:
Calcium can improve the reduction performance of silicon metal and improve its reduction ability to oxides.
Solid solubility:
The solid solubility of calcium in silicon metal is limited. If it exceeds a certain limit, it may form a solid phase, affecting the purity and lattice structure of silicon.
Impurity Content Limits for Core Application Scenarios
| Application Scenario | Fe≤ | Al≤ | Ca≤ | Recommended brand |
| Common aluminum alloys, steelmaking deoxidation | 0.5% | 0.5% | 0.3% | 553# |
| High-end aluminum alloys, precision casting | 0.4% | 0.4% | 0.1% | 441# |
| Photovoltaic polysilicon, semiconductors | 0.3% | 0.3% | 0.03% | 3303# |
| Electronic-grade organosilicon, special alloys | 0.2% | 0.2% | 0.02% | 2202# |
Overall, the impact of these impurities on silicon metal depends on their content and specific application scenarios. In industrial production, the composition of silicon metal is usually strictly controlled and adjusted to ensure that it meets specific technical requirements and application needs.
