Hot Oxide Steel Blackening Agent
Hot oxide steel blackening agent is a highly alkaline mixture of sodium hydroxide and sodium nitrite/nitrate used at 130-145°C to form a controlled black magnetite (Fe3O4) oxide layer on steel surfaces, providing a decorative black finish with mild corrosion protection. The black oxide coating is the standard surface finish for tools, firearms, industrial machine parts, and decorative metalwork requiring a matte black appearance. The thin oxide layer maintains part dimensions and is often sealed with oil for enhanced corrosion resistance.
Technical Specifications
| pH | >14.0 (working solution) |
| appearance | White to off-white granular solid |
| coating type | Fe3O4 black magnetite |
| active content (%) | ≥98 |
| process temperature (°C) | 130-145 |
Applications
- Tool and die blackening for decoration and mild corrosion protection
- Firearm component hot black oxide finish
- Industrial machine part and fastener blackening
- Automotive engine and powertrain component blackening
- Decorative metalwork and hardware black oxide finish
Key Features
- Produces uniform dense black magnetite (Fe3O4) coating
- Zero dimensional change — coating thickness < 2 μm
- Excellent adhesion base for subsequent oil or wax sealing
- Simple process control with caustic bath titration monitoring