Ferrosilicon (FeSi) is an iron-silicon alloy with pronounced physical characteristics that depend on the silicon content (usually 45-90% Si). The following are the main physical properties:
1. Appearance
Color: Silver-grey to dark grey, depending on the silicon content and oxidation of the surface.
Form: Usually comes in lumps (10-100mm), granules (1-10mm) or powder (<1mm).
Texture: Hard, brittle and non-conductive; when destroyed, it cracks conchoidally (like a shell).
2. Density
Range: 3.5-5.2 g/cm³, decreases with increasing silicon content:
FeSi75 (~75% Si): ~3.5 g/cm³
FeSi45 (~45% Si): ~5.0 g/cm³
3. Melting point
Overall Range: 1200-1400°C (2192-2552°F).
A higher silicon content lowers the melting point:
FeSi75: ~1200°C
FeSi45: ~1400°C
4. Hardness
Mohs hardness: ~6-7 (similar to quartz).
Brittleness: Extremely brittle due to its high silicon content; unsuitable for machining.
5. Electrical conductivity
Poor conductor: Electrical conductivity decreases with increasing silicon content.
Silicon is a semiconductor and iron is a conductor; doping reduces overall conductivity.
Resistivity: ~50-100 μΩ-cm (higher than pure iron).
6. Thermal conductivity
Moderate: ~30-50 W/(m-K) at room temperature, lower than pure iron.
7. Magnetic properties
Ferromagnetic: Retains weak magnetism due to its iron content, but silicon reduces magnetic permeability.
Application: Not used in magnetic cores (unlike pure iron or silicon steel).
8. Thermal expansion
Ratio: ~11-14 ×10-⁶/K (similar to cast iron).
9. Reactivity with water
Slow reaction: Reacts with moisture/water vapor over time, releasing hydrogen gas (H₂):
FeSi+2H2O→SiO2+Fe(OH)2+H2↑
Safety Note: Dry storage is required to prevent hydrogen build-up (risk of explosion).
10. Solubility
Insoluble: In water or organic solvents.
Acid Resistance: Reacts with strong acids (e.g. HCl, H₂SO₄) to release hydrogen.