Silicon Carbide Production — Acheson Furnace Process
title: "Silicon Carbide Production — Acheson Furnace Process" description: "How black and green silicon carbide are produced in Acheson electric resistance furnaces, and how crude SiC is processed into abrasive grit, micropowder, and sintering-grade feedstock." section: "upstream"
The Acheson Process
Silicon carbide has been made by essentially the same process since Edward Acheson's 1891 patent:
SiO₂ + 3C → SiC + 2CO↑ (at >2200°C)
High-purity quartz sand (SiO₂ ≥99%) and petroleum coke (C ≥98%) are packed around a graphite core electrode in a horizontal resistance furnace 15–40 m long. Electric current heats the core to >2200°C via resistive heating; the carbothermal reduction proceeds outward from the core over 24–72 hours.
After cooling, the furnace is excavated. The crude product forms concentric shells:
- Inner core — high-purity, well-crystallised green SiC (SiC ≥99.0%)
- Middle ring — black SiC (SiC ≥98.5%), partially oxidised outer shell
- Outer layer — unreacted or partially reacted material, recycled
Black vs Green SiC
| Property | Black SiC | Green SiC |
|---|---|---|
| SiC purity | ≥98.5% | ≥99.0% |
| Colour | Grey-black | Green |
| Fe₂O₃ max | 0.30% | 0.10% |
| Microhardness | ~2600 HV | ~2800 HV |
| Toughness | Slightly higher | Slightly lower |
| Key uses | General abrasives, refractory | Precision grinding, wire-saw slurry, semiconductor |
| Price | Lower | ~15–30% premium |
Black SiC dominates by volume (coated abrasives, refractory aggregate, foundry blast). Green SiC serves applications requiring lower Fe contamination or higher hardness.
Post-Furnace Processing
The crude SiC ingot undergoes a multi-step conversion before reaching final product form:
- Primary crushing — jaw crushers break the ingot into manageable chunks
- Acid leaching — HF + HCl treatment removes SiO₂ and Fe surface contamination
- Water washing and kiln drying — removes acid residues and moisture
- Magnetic separation — removes Fe₂O₃ particles to meet magnetic substance spec
- Size classification — determines final product form:
- Screen classification → F-grit (F14–F220) and P-grit (P12–P2500) for abrasives
- Water sedimentation → JIS micropowder (JIS240–JIS10000)
- Air classification → FEPA fine micropowder and sintering-grade feedstock
Energy and Scale
The Acheson process is energy-intensive — 6,000–8,000 kWh per tonne of SiC produced. China dominates global production (~65–70%), concentrated in provinces with low electricity costs: Xinjiang, Inner Mongolia, Ningxia, Gansu. Major domestic producers include Shandong Luxin, Henan Sicheng, and Shandong Juhuan (jhhqsic.com).
For technical grade and sintered structural SiC applications, see the Silicon Carbide products page.