On bullet trains, a clean view on every journey

Cars of the future will likely not come equipped with windshield wipers thanks to researchers affiliated with Central Japan Railway Co. (JR Tokai).

Researchers there developed a self-cleaning glass using niobium that cuts down on the need to wash windows, thereby saving on water and soap.

For now, the process is being introduced only for Shinkansen trains.

Niobia nanosheet technology uses the photocatalytic properties of niobium to clean glass windows by exposing the wet surface to sunlight.

A niobia nanosheet is 0.7 nanometer thick. A nanometer is one-billionth of a meter. It would take 100,000 nanosheets to equal the thickness of a standard sheet of copy paper.

Several layers of the niobia nanosheet are used to form a membrane to cover glass. When ultraviolet rays hit the glass, water spreads over the membrane surface. The photocatalytic properties of niobium pick up any dirt on the membrane and wash it away.

Self-cleaning glass is not a new concept. The most representative example until now has used titanium oxide.

However, because membranes made of titanium oxide are fused on a glass surface at relatively low temperatures of about 150 degrees, the attachment of the membrane to the glass surface is weak and not suited for windows cleaned with scrub brushes. Moreover, because of the uneven surface of the membrane, dirt particles are more likely to adhere to the surface.

Akira Fujishima, a world-renowned photocatalysis researcher, studied the possibility of using photocatalysis to keep the windows of Shinkansen trains clean.

Fujishima heads JR Tokai's research lab on functional materials.

His lab developed a method for soaking glass in a solution containing sheets of titanium oxide and fusing the membrane that forms on the glass surface at high temperatures between 450 and 600 degrees.

The process produces a smooth surface more resistant to dirt. The surface can also withstand scrubbing. One problem, however, is that sodium in the glass melts at the high temperatures used to fuse the membrane and that in turn reduces the photocatalysis of the titanium oxide.

One solution to the problem was to insert a layer of silicon oxide between the glass and membrane, but that doubled production costs.

That is when the research lab turned to niobium, which has been used in the production of superconductive magnets.

Researchers confirmed that photocatalysis of niobium is not affected even if sodium melts into the membrane. The cost problem was also solved because there was no need to insert the silicon layer.

JR Tokai officials hope the research can be applied to windows used in automobiles.

Masayuki Matsumoto, JR Tokai president, predicted windshield wipers would become obsolete once the niobium sheet technology becomes available for cars.

Another JR Tokai official said the amount of soap used to wash windows could be reduced drastically if rainwater was used to perform the same function on cars with self-cleaning glass installed.

JR Tokai officials said the company plans to install the niobium membrane glass windows in the first-class cars of its N700 series of Shinkansen trains within the next several years. (IHT/Asahi: April 29,2008)