MARC REISCH

A particle widely used as a white, opaque pigment in paint--titanium dioxide--is at the heart of a new system to make self-cleaning clear window glass.

SEEING CLEARLY Water sheets off glass coated with TiO2 (left) while leaving streaks on regular glass. COURTESY OF PILKINGTON NORTH AMERICA

British glassmaker Pilkington says it is the first to make a glass that could put professional window washers out of business. All the glass needs is sun and rain to stay clean. (See a press release and video about the glass)

Now in production at the company's Ottawa, Ill., plant 80 miles southwest of Chicago, the glass should be available in new windows later this year.

Pilkington Glass's Kevin D. Sanderson, an inorganic chemist with a Ph.D. from Imperial College of Science, Technology & Medicine at London University, says the glass cleans itself by two modes. First, the TiO₂ on its surface acts as a catalyst in the presence of ultraviolet light to reduce organic dust and grime to water and carbon dioxide. Second, because TiO₂ reduces surface tension, rainwater "sheets down the surface" and washes dirt away.

Sanderson says he led a five-year effort of about 20 chemists, chemical engineers, production engineers, and physicists who are exploring new coatings technology to make the new Pilkington Activ glass.

What they came up with was "a proprietary mixture of chemical precursor materials and a proprietary chemical vapor deposition process" to lay down a 500- to 600-Å film on the surface of the glass while it is still in its molten state at about 700 ºC. The proprietary mixture flows onto the glass as a gaseous stream, reacts, and binds to the glass, forming TiO₂.

Others are working on similar technology. PPG says it will introduce a self-cleaning glass soon.

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