TiO₂ Surface Treatment: What It Is and Why It Matters
⚡ Surface treatment is the invisible layer separating commodity TiO₂ from premium TiO₂.
🔹 Inorganic coating (silica, alumina, zirconia) — 2-8% of particle weight, determines weatherability and chemical resistance.
🔹 Organic coating (polyols, siloxanes, amines) — 0.2-1.0%, determines dispersion ease in specific resin systems.
🔹 A 4% dense silica coating extends exterior durability from ~2 years to over 10 years in architectural coatings.
What Is TiO₂ Surface Treatment?
Surface treatment deposits inorganic oxide layers (SiO₂, Al₂O₃, ZrO₂) onto TiO₂ particles, followed by an optional organic layer. The bare TiO₂ surface is photocatalytic — UV light generates reactive species that degrade surrounding organic binder, causing chalking, yellowing, and coating failure within 12-18 months.
Four functions: photocatalytic suppression (90-95% with dense silica), dispersion assistance, chemical stability, and timing control during milling.
The Two Layers
Inorganic Layer
🔬 Dense Silica
pH 9.0-10.5, 80-95°C, 2-4h. Continuous, non-porous. Suppresses photoactivity by 90-95%. Grades $2,400-2,700/MT FOB China.
🔬 Porous Silica
Sponge-like layer. 60-70% suppression. Better initial dispersion. Grades $2,100-2,400/MT.
Alumina coating improves dispersion via electrostatic repulsion. Most rutile grades carry silica inner + alumina outer ("dual coating") — industry standard for architectural paint.
Zirconia coating for chemical resistance, adds ~$200-400/MT.
Organic Layer
| Treatment | Best For | Effect |
|---|---|---|
| Polyols | Solvent paints, alkyds | Improves wetting, reduces viscosity |
| Siloxanes | PE, PP, engineering plastics | Reduces moisture, non-polar compatibility |
| Alkanolamines | Waterborne paints | Stability in high-pH systems |
| None | Masterbatch (w/dispersant) | Needs higher dispersant or longer milling |
📌 In PE masterbatch, switching from siloxane to polyol treatment increased dispersion time 8→14 min and reduced max loading 72%→64%. This is detailed on our product pages.
COA Decoding Guide
Clue 1: TiO₂ content. Uncoated rutile = 96-97%. Per ISO 591-1 data on our rutile pages, every point below this indicates coating level.
Clues 2-4: Specific gravity (pure = 4.23, coated = 3.9-4.1), residue on ignition (5-8% = heavy coating, <2% = none), pH (alumina = 7.0-8.5, silica = 6.0-7.0).
Application Recommendations
Exterior paint: Dense silica-coated rutile at 92-93% TiO₂. L* 94.5 with coating beats L* 96.0 uncoated within 6 months.
Plastics: Siloxane-treated for polyolefins; heat-stabilized with 0.3%+ organic for engineering plastics >220°C.
Paper: Anatase with alumina coating, 1-2% Al₂O₃.
Automotive: Chloride-process rutile with dense silica + matched organic. $2,600-3,200/MT FOB China.