The criteria for judging high-quality silicon metal are based on "high silicon content, low impurities, and stable physical properties." Key indicators and standard requirements are as follows:
| Indicator Type | Core Indicators | High-Quality Requirements (by Level) | Impact of exceeding standards |
| Key Content Indicators | Silicon (Si) Content | Electronic Grade ≥99.9%, Chemical Grade ≥99.5%, High-End Industrial Grade ≥99.0% | Lower content results in lower alloying/reaction efficiency and substandard product performance. |
| Hazardous Impurity Index | Sulfur (S) Content | ≤0.03% (Electronic Grade ≤0.01%) | Causes hot brittleness in steel/aluminum alloys and reduces photovoltaic cell conversion efficiency. |
| Hazardous Impurity Indicators | Phosphorus (P) Content | ≤0.04% (Electronic Grade ≤0.01%) | Causes metal brittleness and reduces low-temperature impact toughness |
| Limiting Impurity Indicators | Iron (Fe) / Aluminum (Al) / Calcium (Ca) Content | Electronic Grade ≤0.01%/0.01%/0.005%; Chemical Grade ≤0.3%/0.3%/0.05% | Forms brittle phases, affecting material strength and processing performance. |
| Physical Properties | Ash Content | ≤0.5% (Electronic Grade ≤0.1%) | Increases metallurgical slag production, reduces smelting efficiency. |
| Physical property indicators | Moisture content | ≤0.3% | Causes porosity in castings and fluctuations in the reaction system |
| Physical Properties | Size Distribution | Large (5-50mm, ≥90%) | Uneven particle size affects the uniformity of feeding; excessively fine particles are prone to oxidation. |
| Physical property indicators | Volatile content | ≤0.5% | Reflects the maturity of the production process; excessively high levels can lead to fluctuations in composition. |
Criteria and Applicable Scenarios for Different Grades of High-Quality Silicon metal
(1) Chemical-grade silicon metal (Si≥99.5%): Mid-to-high-end application grade
Composition: Si≥99.5%, S≤0.03%, P≤0.03%, Fe/Al/Ca≤0.3%/0.3%/0.05%, Ash ≤0.3%;
Physical properties: Moisture ≤0.3%, Volatile matter ≤0.5%, size 10-50mm;
Applicable scenarios: Organosilicon synthesis, silane coupling agent production, silicon conversion rate exceeding 90%, 5%-8% higher than industrial grade;
Typical applications: Organosilicon plants use chemical-grade silicon metal, methylchlorosilane monomer purity ≥99.2%, by-product reduction 3%-5%.
(2) Industrial High-End Silicon metal (Si≥99.0%): General High-Quality Grade
Composition: Si≥99.0%, S≤0.05%, P≤0.04%, Fe/Al/Ca≤0.5%/0.5%/0.1%, Ash ≤0.5%;
Physical Properties: Moisture ≤0.3%, Volatile Matter ≤0.5%, Size 5-50mm;
Suitable Applications: High-end aluminum alloys, precision casting, high-end refractory materials; increases tensile strength of aluminum alloys by 15%-20%;
Typical Application: When using this grade of silicon metal in automotive die-cast aluminum alloys (A356), the porosity defect rate of castings decreases from 1.2% to 0.3%.
Practical Judgment Methods for High-Quality Silicon metal
Composition Detection
Detection Tools: Direct-reading spectrometer (rapid detection) or ICP-MS (precise detection, suitable for electronic grade);
Detection Items: Si, S, P, Fe, Al, and Ca must be tested. For electronic grade, trace impurities such as Na and K must also be tested;
Judgment Criteria: According to the corresponding grade index limits, exceeding the limit for any single impurity indicates non-high quality.
Physical Property Detection
Ash Content Detection: Take 50g of sample and burn it to constant weight. If the ash content exceeds the limit, it is unqualified;
Moisture Content Detection: Drying and weighing method (drying at 105℃ for 2 hours). If the moisture content is >0.3%, it must be dried before use;
Size Detection: Sieve using a standard sieve. If the proportion of 5-50mm particles is <90%, the size is unqualified, affecting the uniformity of feeding.
Appearance and Process Traceability Judgment
Appearance: High-quality silicon metal is a uniform silver-gray block with no obvious oxide layer on the surface (the oxide layer will reduce the reactivity) and no impurity agglomeration;
Process Traceability: Prioritize products made with high-purity quartz sand (SiO₂≥99.5%) and green electricity smelting, as impurity control is more stable.
Common Quality Problems and Avoidance Points
(1) Risk of Excessive Impurities
Hazards: Excessive S/P leads to hot/cold brittleness of metal; excessive Fe/Al/Ca forms brittle inclusions;
Avoidance: Require suppliers to provide SGS/Intertek test reports during procurement, and conduct random sampling and re-inspection of core impurities for each batch.
(2) Moisture and Oxidation Problems
Hazards: Excessive moisture leads to porosity in castings and abnormal chemical reactions; the oxide layer (SiO₂) reduces reactivity;
Avoidance: Store in a dry and ventilated environment (humidity ≤60%), in sealed packaging, with a storage period not exceeding 6 months, and use as soon as possible after opening.
(3) Problem of uneven size
Hazards: Overly fine particles (<5mm) are easily oxidized and burned, while overly coarse particles (>80mm) do not dissolve completely;
Avoidance: The size distribution should be 5-50mm. Overly coarse particles need to be crushed and screened before use.
