Chromite Sand: Properties and Applications
1. Key Properties of Chromite Sand
Chromite sand (FeCr₂O₄) is a naturally occurring mineral with excellent refractory and thermal properties, making it ideal for demanding industrial applications.
| Property | Value/Description | Significance |
|---|---|---|
| Chemical Composition | FeCr₂O₄ (Cr₂O₃: 40-50%, FeO: 20-30%) | High chromium content provides stability at high temperatures. |
| Melting Point | ~2150°C | Suitable for high-temperature casting (steel, stainless steel, Ni alloys). |
| Density | 4.0–4.8 g/cm³ | Heavier than silica sand, reduces metal penetration in molds. |
| Thermal Conductivity | High (~3–5 W/m·K) | Promotes rapid cooling, improving casting microstructure. |
| Thermal Expansion | Low (~7 × 10⁻⁶/°C) | Minimizes mold cracking and casting defects. |
| Neutral pH | 7–8 (chemically inert) | Does not react with acidic/basic binders or molten metals. |
| Hardness (Mohs) | 5.5–6.0 | Resists abrasion, extends mold life. |
2. Major Applications of Chromite Sand
(A) Foundry & Metal Casting (Primary Use)
Mold & Core Sand
Used in steel, stainless steel, and high-alloy castings to prevent sand burn-on and metal penetration.
Replaces silica sand (SiO₂) where SiO₂ reacts with molten metals (e.g., Fe + SiO₂ → FeO + SiO gas).
Chill Applications
High thermal conductivity helps rapid solidification, reducing grain size and improving mechanical properties.
Facing Sand
Applied as a protective layer in contact with molten metal to enhance surface finish.
(B) Refractory Industry
Lining for Ladles & Furnaces
Used in steelmaking (e.g., electric arc furnaces, ladles) due to high slag resistance.
Gunning & Patching Mixes
Repairs damaged refractory linings in high-temperature environments.
(C) Other Industrial Uses
Welding Electrode Coating (stabilizes arc).
Heavy Concrete Aggregate (radiation shielding).
Catalyst Support (chemical processing).
4. Important Considerations
Health & Safety
Contains Cr⁶+ (hexavalent chromium), a potential carcinogen—requires PPE (respirators, gloves).
Grain Size Selection
AFS 40–70 (finer for precision casting, coarser for large castings).
Binder Compatibility
Works with phenolic, furan, and inorganic binders but may require adjustments.
Recycling
Can be reused after magnetic separation to remove metal particles.