Definitions

bioclean

Self-cleaning glass

Self-cleaning glass is a specific type of glass with surface which keeps itself free of dirt and grime through natural processes.

The first self-cleaning glass was based on thin film titanium dioxide coating. The glass cleans itself in two stages. The "photocatalytic" stage of the process breaks down the organic dirt on the glass using ultraviolet light in sunlight (even on overcast days) and makes the glass hydrophilic (normally glass is hydrophobic). During the following "hydrophilic" stage rain washes away the dirt, leaving almost no streaks, because hydrophilic glass spreads the water evenly over its surface..

Titanium dioxide is a material of choice because it is characterized by high photocalytic properties, chemical stability and low price. Its anatase phase is most photocalytic. What is more, under the UV irradiation its surface structure changes to generate OH groups, making it superhydrophilic.

It is speculated that other possible application areas are computer monitors and PDA screens, where fingerprints are undesirable.

Titanium dioxide–based glass cannot decompose thick non-transparent deposits, such as paint or silicone, waterstop fingerprints or bleeding after weathering, or stucco dust produced during construction.

Another approach to self-cleaning glass is suggested basing on the hydrophobic "lotus effect".

Since 2001 the TC24 "Coatings on Glass" committee International Commission on Glass has been trying to set up test methods for evaluation of photocatalytic self-cleaning coatings on glass.

Brands

  • The Pilkington Activ brand by Pilkington is claimed by the company to be the first self-cleaning glass. It uses the 15 nm thick transparent coating of microcrystalline titanium dioxide. The coating is applied by chemical vapor deposition
  • The SunClean brand by PPG Industries also uses the coating of titanium dioxide applied by a patented process.
  • Neat Glass by Cardinal Glass Industries has the <10nm titanium dioxide layer applied by magnetron sputtering
  • SGG Aquaclean (1st generation, hydrophylic only, 2002) and Bioclean (2nd generation, both photoctive and hydrophilic, 2003) by Saint-Gobain. The Bioclean coating is applied by chemical vapor deposition.

See also

  • ETFE films, transparent polymer films described as self-cleaning

References

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