Green Silicon Carbide for Opacifier Application‑SiC Purity
Minimum control requirement: SiC ≥98.5% by weight. Preferred specification: SiC ≥99.0% for more stable infrared opacifying performance, especially for high‑temperature working conditions.
Key Impurity Limits for Opacifier Grade
| Item | Maximum Limit | Risk Description |
|---|---|---|
| Ferric Oxide (Fe₂O₃) | ≤0.15% | Causes red spots under high temperature, accelerates oxidation and damages insulation boards |
| Free Carbon (F.C) | ≤0.30% | Burns out above 500℃, creates voids and reduces opacifying effect |
| Free Silica (SiO₂) | ≤0.70% | High‑temperature phase transition impairs board strength and thermal conductivity |
Notes
- If SiC content is below 98.5%, higher impurity content will reduce infrared extinction efficiency. Impurity phases tend to react at high temperature, resulting in spots, shrinkage and increased thermal conductivity of insulation boards. It is not recommended for opacifier use.
- Regular‑grade green silicon carbide for grinding can reach 99‑99.5% SiC. Ultra‑fine powder (commonly D50 1‑5 μm for opacifiers) is harder to purify; 98.5% is the general industry minimum threshold.
- Black silicon carbide normally reaches only 97‑98.2% SiC, which fails to meet the purity requirement for opacifiers. Substitution by black silicon carbide is not recommended.
