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TRENDS | IN DEVELOPMENT / KATHLEEN WIEGNER

An All-Plastic Battery That's Full of Positives

December 09, 1996|KATHLEEN WIEGNER | Kathleen Wiegner, a freelance writer specializing in science and technology, can be reached via e-mail at kkwrite@aol.com

If the words "charge" and "plastic" make you think of credit cards, think again. Researchers at Johns Hopkins University have developed an all-plastic battery that is rechargeable, lightweight and can be molded into almost any size and shape.

Unlike nickel-cadmium rechargeables, these plastic batteries contain no heavy metals, which are a problem to dispose of. They also contain no liquids, which can leak and pose safety hazards.

All batteries consist of three main components: the positive electrode; the negative electrode; and the electrolyte, conductive material between the electrodes, such as the liquid in a car battery. Although other researchers have used plastic for one of the components, the Hopkins scientists in Baltimore are among the first to create a practical battery in which both of the electrodes and the electrolyte are made of plastic.

The positive and negative electrodes (the anode and the cathode) are made of thin, foil-like plastic sheets. The electrolyte is a film of polymer gel sandwiched between the electrodes. This thin, flat design could allow battery users to cut a cell to fit a particular space. The battery, whose development was funded by the Air Force, was designed for military and space applications, but it could eventually be suitable for small consumer products such as hearing aids and wristwatches.

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Cold Bugs: The U.S., the world's largest grain producer and exporter, stores billions of bushels of grain for as long as three years before it is processed and consumed. But stored grain is subject to insect infestations and damage from molds and mycotoxins, and such problems result in $500 million a year in losses. Insect control is typically accomplished with two chemical fumigants, methyl bromide and phosphine. Beginning in 2001, methyl bromide will be banned to avoid damage to the ozone layer. One alternative to pesticides, called chilled aeration, literally "chills out" bugs by reducing the temperature of stored grains to a level that inhibits insect growth. When wheat in 45,000-bushel-capacity steel grain bins is cooled to below 60 degrees Fahrenheit, insects cannot breed. Chilled aeration has been used in Europe for some time, but recently researchers at Purdue University in Indiana improved the technology by using variable-speed blower drives to reduce total energy consumption. Trials, sponsored by the Electric Power research Institute in Palo Alto show that grains can be chilled to a protective level in an average of 220 hours. Because of the grain's insulating properties, it will then stay cool for four to six weeks. Cooling also reduces humidity and thus prevents mold.

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