By Tyler Irving
Posted February 2011
A plasma discharge from an electrode made of aluminum covered with carbon nanotubes. The gas is mostly argon, but the reddish hue indicates the presence of water vapour. New fluorescent bulbs based on this technology could eliminate the presence of toxic mercury vapour.
Environmentalists have good reason to be conflicted about fluorescent light bulbs. True, they are more efficient and longer-lasting than the incandescent variety, but they also contain mercury, a well-known neurotoxin. Now, an accidental discovery at McGill University has led to a new breed of bulb that replaces the mercury with plain old water.
Fluorescent bulbs use electrodes to excite plasmas (vapours made of charged particles) producing light. Many substances can form plasmas, including water. However, water interacts with the complex mix of metals that make up the electrodes, causing them to become brittle and break. Mercury, by contrast, is inert toward most electrodes. Another problem with current electrodes is that they can’t be made very big, due to their need to operate at high temperature. This, in turn, constrains the bulb geometry.
Sylvain Coulombe and his team were working on new electrodes, made of carbon nanotubes grown on various metal surfaces, for an unrelated application. In one experiment, the nanotubes became contaminated with water. To their surprise, the water didn’t degrade the electrodes, and actually improved their ability to emit electrons. “That was a total surprise to us,” says Coulombe. “There’s some very complex physics behind this thing, but we know that it works now.”
Coulombe and his team have already constructed a new bulb using the carbon electrodes and water vapour. Because his team can grow the nanotubes on almost any shape of substrate, Coulombe believes they could open the door to new geometries for fluorescent bulbs. “Instead of linear tubes, we could build panels, a wall, a ceiling,” he says. And how long before carbon nanotube-water bulbs are on the market? “I would hope within five years, but it all depends on the support that we receive from the big players.”
Photo Credit: Sylvain Coulombe
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