Titanium Dioxide
Properties
| State | Solid at room temperature |
| Color | White |
| Solubility | Insoluble in water; slightly soluble in concentrated acids |
| Melting Point | 1843 °C |
| Boiling Point | 2972 °C |
About Titanium Dioxide
Titanium dioxide is the white pigment that beat lead — between 1920 and 1970 it displaced toxic lead carbonate (white lead) and lead sulfate from house paint, and global production is now around 9 million tonnes per year, making it the highest-volume specialty inorganic pigment on Earth. The reason TiO2 dominates is optical: its rutile-form refractive index of 2.7 is the second-highest of any common solid (only diamond and a few ZnS polymorphs beat it), so it scatters visible light more efficiently than any practical alternative. A coat of TiO2-pigmented paint hides the substrate at typical loadings of 15-25% by weight; trying to do the same with kaolin or calcium carbonate would need a film three to five times thicker. TiO2 has three crystal polymorphs — rutile (the thermodynamically stable, high-refractive-index form used in pigments), anatase (the metastable form that is the standard photocatalyst), and brookite (rare, mostly mineralogical). Anatase TiO2 illuminated above its 3.2 eV bandgap with UV light generates electron-hole pairs that produce •OH radicals from adsorbed water — that's the mechanism behind self-cleaning Pilkington Activ glass, photocatalytic concrete that breaks down NOx in city air, and the original Honda-Fujishima water-splitting experiment of 1972. Sunscreen-grade TiO2 is the rutile form coated with silica or alumina to suppress photocatalysis (you don't want radicals on skin) and milled to 50-200 nm for visible-transparency.
Where you'll encounter it
If you've ever painted a white wall, eaten a powdered-sugar donut, brushed your teeth, or slathered on a mineral sunscreen, you've used TiO2. The white you see in toothpaste, fondant frosting, sour cream, and the inside of a yogurt cup is rutile or anatase TiO2 at a few weight percent — the EU banned E171 from food in 2022 over inhalation-pathway concerns about nano-fraction particles, but the US FDA still permits it under 1% by weight. Mineral sunscreens use the rutile form coated with a passivating SiO2 or Al2O3 shell because uncoated anatase generates free radicals on skin under sun. Walk past a building with self-cleaning windows (Pilkington Activ, SunClean from PPG) and the thin TiO2 coating on the outer glass surface is doing UV-driven photocatalytic breakdown of organic film plus rain-driven sheeting — water spreads as a sheet rather than beading on the superhydrophilic TiO2 surface and rinses the loosened dirt off.
Common Uses
- Highest-volume white pigment in architectural paints, plastics, and printing inks at 9 Mt/year
- UV-blocking active ingredient in mineral sunscreens (rutile form, silica/alumina-coated)
- Anatase photocatalyst in self-cleaning Pilkington Activ glass and NOx-degrading urban concrete
- Electron transport layer in dye-sensitized and early-generation perovskite solar cells
- E171 food whitener in candy, frosting, and dairy (banned in EU 2022, permitted in US under 1%)
Safety Information
GHS: H351 (suspected of causing cancer) for the inhalable dust fraction following IARC Group 2B classification (possibly carcinogenic to humans by inhalation, based on rat lung overload studies). OSHA PEL 15 mg/m3 total dust, 5 mg/m3 respirable. Bulk pigment grade is non-hazardous for skin contact and ingestion at consumer exposure levels. Nanoparticle TiO2 (sub-100 nm) is under heavier regulatory scrutiny — the EU REACH dossier was updated in 2020 and food use was banned in 2022 specifically over GI-tract uptake of the nanofraction. Operators in pigment plants wear N95 respirators when handling dry powder; wet milling and slurry handling avoid inhalation entirely.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.