Rutile vs Anatase — Physical and Optical Differences
Rutile and anatase are TiO2's two main crystal forms. Different optics, different durability, different applications.
Titanium dioxide exists in three crystal forms: rutile, anatase, and brookite. Brookite is rare and not commercially significant. Rutile and anatase are both widely produced as white pigments, with distinct physical and optical properties that govern their application fit.
Refractive index: - Rutile: 2.75 (one of the highest of all white pigments) - Anatase: 2.50 The higher refractive index of rutile translates to greater light scattering at the pigment-binder interface, which means higher hiding power per kg in opaque coatings and plastics.
Color undertone: - Rutile typically has a slightly warmer, yellower undertone - Anatase has a bluer, brighter undertone
This is why anatase is often preferred for white papers, white inks, and certain cosmetic applications where the "absolute white" or slightly-blue-cast appearance is preferred.
Crystal hardness: - Rutile Mohs hardness 6.0–6.5 - Anatase Mohs hardness 5.5–6.0
The 0.5-point difference makes anatase noticeably less abrasive on grinding equipment, paper calender rolls, and rubber Banbury mixer rotors.
Photocatalytic activity: - Anatase is significantly more photocatalytic — under UV light, it generates reactive oxygen species that can oxidize organic compounds - Rutile is much less photocatalytic - This is the key practical difference: rutile is stable in outdoor coatings; anatase causes chalking and binder degradation - The high photocatalytic activity of anatase enables specialty applications: self-cleaning surfaces, air purification, antimicrobial coatings (in nano form)
Density: - Rutile: 4.23 g/cm³ - Anatase: 3.89 g/cm³
Rutile is slightly denser, which translates to slightly higher pigment cost per unit volume.
Thermal stability: - Rutile is the thermodynamically stable form at all temperatures - Anatase converts to rutile irreversibly at 700–800°C - Both forms are stable at typical plastic processing temperatures (up to ~300°C)
Application matrix: | Application | Crystal preference | |---|---| | Architectural coatings (interior) | Rutile (anatase ok in matte/flat economy) | | Architectural coatings (exterior) | Rutile only — anatase chalks | | Industrial coatings | Rutile | | Automotive coatings | Rutile | | PVC outdoor profile | Rutile | | Plastic masterbatch (most) | Rutile | | Printing inks | Either (rutile for opacity, anatase for brightness) | | White paper (decor) | Rutile (high loading) or anatase (moderate loading) | | Fiber delustering | Anatase (soft crystal) | | Rubber white compound | Anatase (Banbury wear) | | Cosmetic sunscreen (nano) | Rutile (anatase is photocatalytic) | | Photocatalytic / self-cleaning | Anatase (intentional photocatalysis) |
For most coating and plastic buyers, default to rutile. Use anatase intentionally where its specific properties (soft crystal, blue undertone, photocatalysis) are valuable.