This fine, white powder is so common that it can be purchased on eBay for home concoctions of soap, lip colour or ceramic glazes. Few buyers know that the pigment originates as a colourful crystalline mineral found in ore in large quantities in Australia, Canada, India, Norway, South Africa, Ukraine and the United States. Most titanium dioxide (T102) is produced from ruby-coloured, blue or yellow-brown minerals such as rutile or anatase through a process of oxidation (combining the ground minerals with oxygen).
These minerals resemble gems, and are so highly light refractive that small quantities found inside other gemstones add value to the stones. The "star" in star sapphires, for instance, are needle-like flaws of rutile. But rutile or anatase crystals, cut and worn as jewellery, would not withstand the wear and tear given the minerals' softness (6 on the MOHs scale). Instead, this highly refractive property of rutile has found industrial and commercial uses as protective sunscreens, coatings on eye glasses and photovoltaic solar cells.
Pigment from titanium dioxide generates up to 95 per cent of the world's demand for it. Titanium dioxide produced from the titanium found in ilmenite must be leached using sulphuric acid, an expensive and environmentally unfriendly product. The largest producers of titanium dioxide, therefore, use a chloride process effective for removing pigment from the more available rutile and anatase minerals.
First, the dry ore is fed into a chlorinator together with petroleum coke and chlorine to make titanium chloride. Next, burning the titanium chloride with oxygen and a combustible gas, oxidises it. Then, seeding this mixture with crystals forms solids that are filtered from the gas and milled as powder. Treatment of the final product is important for brightness, opacity and reflective qualities.
Titanium dioxide as a pigment is found in house paint, artist's oils, cosmetics, rubber, plastics, textiles, paper, pills, tattoo inks and skimmed milk. Manufactured as a nano particle (a particle created on the molecular scale), titanium dioxide can be found as an antimicrobial in coatings for its oxidising effects. These titanium dioxide nano particles are also used in antifogging products because the small nanometre-sized particles become transparent and allow water to sheet instead of bead. Similar uses are found in the cosmetics industry. The solar cell industry is also testing nano particle titanium dioxide for its semiconducting abilities. In 2007, scientists found another use for this substance: cleaving genes without the use of enzymes.
Several health concerns have hobbyists as well as users of cosmetics and sunscreen worried. According to Ceramics Today, titanium dioxide as a powder is an upper airways irritant and occupational exposure can occur for anyone mining ore or preparing titanium dioxide for storage or use. Those working in areas of high use should wear a respirator. Also, the International Agency for Research on Cancer, part of the World Health Organization, has concluded that there is "sufficient evidence that titanium dioxide is carcinogenic in experimental animals."
Scientists have found that nano particles of titanium dioxide cause proinflammatory responses in the MIMIC high-speed assay system developed by the U.S. Department of Defense for testing vaccines.
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- "ACS Nano":Exposure to Titanium Dioxide Nanomaterials Provokes Inflammation of an in Vitro Human Immune Construct;Brian C. Schanen, et al.; Sept. 2009
- International Agency for Research on Cancer: Search on IARC Monographs; Titanium Dioxide; Working Group
- "Ceramics Today":Titanium Dioxide; Edouard Bastarache M.D.
- "Science Daily":Titanium Dioxide -- It Slices, It Dices ...; Apr. 2007
- Amethyst Galleries: The Mineral Ilmenite