Iron Oxide Black

Iron Oxide Black

Iron oxide black is an important inorganic black pigment, chemically composed ofMagnetite (Fe₃O₄)OrIron Oxide (II,III)Exceptional magnetic properties, coloring strength, and stability; widely used in coatings, building materials, and magnetic materials fields.

1. Basic Features

• Chemical FormulaFe₃O₄ (FeO·Fe₂O₃, containing Fe²⁺ and Fe³⁺).

• ColorPure black, with a hint of blue or brown tone (depending on particle size and purity).

• Stability：

• Thermal resistanceStable below 180°C, high-temperature oxidation becomesIron Oxide Red (Fe₂O₃)。

• LightfastnessSuperior quality, colorfast.

• Acid and alkali resistanceResistant to weak acids and alkalis; soluble in strong acids (e.g., HCl).

• ConductivityMagnetized (main component of natural magnetite).

• Form FactorFine powder, particle size typically 0.1~1 μm.

2. Preparation Method

(1) Chemical Co-precipitation Method (Main Production Process)

• Reactive Principle：

  $${\text{Fe}}^{2+}+2{\text{Fe}}^{3+}+8{\text{OH}}^{-}\to {\text{Fe}}_3{\text{O}}_4\downarrow +4{\text{H}}_2\text{O}$$

• Step：

1. Mix ferrous sulfate (FeSO₄) and FeCl₃ in a 1:2 molar ratio.

2. Add alkali (NaOH) to adjust the pH to 9-11, and use nitrogen gas to protect against the oxidation of Fe²⁺.

3. Nanometer-sized Fe₃O₄ obtained through sedimentation, washing, drying, and calcination (200~400°C).

(2) High-Temperature Oxidation Method

• Iron or ferrous oxide (FeO) heated under controlled oxygen pressure:

  $$6\text{FeO}+{\text{O}}_2\to 2{\text{Fe}}_3{\text{O}}_4$$

(3) Pure Natural Magnetite

• Magnetite (main component Fe₃O₄) crushing, magnetic separation, and purification; however, it contains a high level of impurities and has a darker color.

3. Main Applications

(1) Paints & Inks

• Architectural PaintExterior black tones, floor paint.

• Corrosion-Resistant PaintFor metal undercoat (magnetic adhesion enhancement for better adhesion).

• InkPrinting Inks, Toner (for laser printers).

(2) Construction Materials

• Colored cement, asphalt pavements, artificial stone.

(3) Plastic & Rubber

• Cable sheath, automotive tires (UV-resistant).

(4) Magnetic Materials

• Magnetic recording media (tapes, disks), magnetic fluids, and absorbent materials.

(5) Miscellaneous

• Cosmetics (eyebrow pencils, eyeliner), Pharmaceuticals (magnetic targeted drug carriers).

4. Categories & Models

Common International Models：

• PBk11Color Black 11 (International Code)

• C.I. 77499Chemical Index Number

5. Comparison with Other Black Pigments

Advantages of Iron Oxide Black：
✅ Non-toxic and environmentally friendly, suitable for food contact materials (such as toys, cosmetics).
✅ Magnetic, suitable for special function materials (such as microwave absorbing coatings).
✅ Better weather resistance than carbon black (less prone to grayish discoloration).

Limitations：
⛔ Oxidizes to Fe₂O₃ (turns red) at high temperatures.
✖ Blackness is not as good as carbon black (mixing required for high blackness).

6. Important Notes

• Temperature ControlProcessing temperature should not exceed 180°C (for plastic injection molding, a low-temperature process is required).

• Acidic environmentAvoid strong acids (such as pH < 2) to prevent dissolution.

• StorageSealed and moisture-proof, to prevent oxidation and caking.

• Magnetic ApplicationsNano Fe₃O₄ requires anti-agglomeration (dispersant can be added).

Summary

Iron oxide black is a versatile black pigment with coloring power, magnetic properties, and environmental friendliness, suitable for paints, building materials, and high-tech fields. For higher blackness, mix with carbon black; for high-temperature resistance, choose chromium oxide black. Specific selection should consider temperature resistance, electrical conductivity requirements, and cost!