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You Really Can Catch Lightning in a Bottle

5 May 2009 (All day)
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April Benson/MRI

Flash point. Very thin sheets of industrial glass could make more powerful electrical capacitors.

Here's something that sounds preposterous but as it turns out, it's actually true. Take a very thinly drawn piece of industrial glass, and you can use it to store and release a surprising amount of electricity, a group of materials scientists has found. When sandwiched between two metal plates as part of a device called a capacitor, the glass slivers could provide large bursts of energy for devices such as heart defibrillators, and they could even help power the next generation of electric vehicles.

Usually a rectangular plate of material, capacitors are essential to electronics because they can perform tasks that batteries can't. Each contains a material called a dielectric, which can store electrical energy and then release it in a large burst. Capacitors are much faster than batteries at charging and releasing electricity, which makes them ideal for providing the pulses of power required by camera flashes and diesel engine starters. They can also endure millions of cycles of charging and discharging, compared to mere thousands of cycles for conventional rechargeable batteries.

To meet the power demands of modern devices, researchers have been looking for materials that can store more and more electricity. That's where the use of industrial glass comes in. Industrial glass is stronger and more durable than the glass in household windowpanes and mirrors, and it's more resistant to repeated chemical reactions. Materials scientists at Pennsylvania State University, University Park, have now found that an extremely thin piece of the industrial glass called barium boroaluminosilicate--which is used in flat-panel TV displays--can hold more than twice as much electrical charge as polypropylene, which is currently the most common material for high-energy capacitors.

Reporting online this week in Materials Letters, the researchers say they used samples of the glass about 50 micrometers thick, or about half the diameter of a human hair, which they etched in acid until the samples eroded to a thickness of only 10 to 20 micrometers. Then they hooked the samples to two electrodes and applied an increasing voltage to test the material's breakdown strength: its ability to withstand electrical energy. When the material reached this breakdown limit--at about 22,000 volts--the stored energy was released in what resembles "a lightning bolt conducting through air," says co-author Nicholas Smith.

The ability of the glass to hold so much charge renders it "of prime interest to people who make capacitors and other energy storage devices," Smith says. He adds that the low cost of the material adds to its attractiveness, because researchers have been looking mainly at materials, such as specialty polymers and nanocomposites, that tend to be more expensive.

This could be a breakthrough, says chemical engineer Richard Wool of the University of Delaware, Newark. Wool, who specializes in the chemistry of glass, says the ability of the material to combine high energy storage and high breakdown strength, as well as its low cost, gives it an advantage over currently used materials.

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