Iron Oxide Yellow

Iron Oxide Yellow

Iron oxide yellow is a commonly used inorganic yellow pigment, chemically composed of hydrated iron(III) oxide (FeO(OH)·nH₂O) or hydroxide of iron(III), featuring excellent weather resistance, lightfastness, and chemical stability. It is widely used in paints, construction materials, plastics, papermaking, and other fields.

1. Basic Features

Chemical Formula: FeOOH (Hydroxide of Iron) or Fe₂O₃·H₂O (Hydrated Iron Oxide).

Color: From bright yellow to amber yellow, the specific hue depends on the particle size and crystal form.

Stability:

UV and alkali resistant, but may dissolve in strong acids.

Poor heat resistance (starts to dehydrate and transform into iron oxide red Fe₂O₃ above 180°C).

Not soluble in water, ethanol, and other solvents; non-toxic and environmentally friendly.

Form: Fine powder, usually in needle-like or spherical granules.

2. Preparation Method

(1) Wet Precipitation Method (commonly used)

Ferrous sulfate (FeSO₄) reacts with alkali (NaOH), and upon oxidation with air, it produces FeOOH.

FeSO4+2NaOH+O2→2FeOOH+Na2SO4+H2OFeSO4+2NaOH+O2→2FeOOH+Na2SO4+H2O

Adjustable pH, temperature, and oxidation rate for color depth control.

(2) The Penniman-Zoph Process (Continuous Oxidation Method)

Iron shavings + nitric acid catalytic oxidation, suitable for mass production.

(3) Purification of Natural Minerals

Magnetite (Goethite, α-FeOOH) grinding and purification available, but with lower purity and darker color.

3. Main Applications

Construction Industry:

Color concrete, cement bricks, road coatings, exterior wall putty, etc.

Paints & Coatings:

Outdoor Paint (UV-resistant), Anti-rust Paint, Road Marking Paint.

Plastic & Rubber:

Yellow dye for PVC, PE, and rubber products.

Paper & Ink:

For packaging paper, decorative paper, and printing inks.

Cosmetics:

Iron oxide yellow meeting food-grade standards is suitable for eyeshadows, foundations, etc. (requires high purity).

4. Categories & Models

By hue: Lemon yellow, medium yellow, deep yellow, etc. (depending on particle size and crystal type).

By purity:

Industrial grade (90-95%), Pigment grade (96%+), Food grade (99%+, low heavy metals).

International Pigment Index: PY42 (Pigment Yellow 42).

Common Models:

China Standard: 313, 920

BASF: Sicotan® Yellow

Lanxess: Bayferrox® 3910

5. Comparison with Iron Oxide Red

Natural Iron Oxide Yellow (FeOOH), Iron Oxide Red (Fe₂O₃)

Chemical Formula: FeOOH, Fe₂O₃

Yellow, Brownish Red

Temperature resistance: ~180°C; Decomposition: ~1200°C; Stability

Alkali and Acid Resistance - Acid-resistant, moderately alkali-resistant, alkali-resistant

Primary Applications: Paints, Plastics, Building Materials; Ceramics, Magnetic Materials

6. Cautionary Notes

Temperature Sensitive: Turns red and dehydrates at high temperatures (→ Fe₂O₃); avoid use in high-temperature processing materials.

Dispersibility: Must be well dispersed in plastic or paint to prevent lumps.

Storage: Seal to prevent moisture, avoid contact with strong acids.

Iron oxide yellow is an ideal choice for replacing toxic pigments like cadmium yellow and chrome yellow due to its environmental friendliness, low cost, and excellent weather resistance.