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Superconducting Ceramic （陶瓷）

　　An underground revolution begins this winter. With the flip （轻击） of a switch, 30,000 homes in one part of Detroit will soon become the first in the country to receive electricity transmitted by ice-cold high-performance cables. Other American cities are expected to follow Detroit's example in the years ahead, which could conserve enormous amounts of power.

　　The new electrical cables at the Frisbie power station in Detroit are revolutionary because they are made of superconductors. A superconductor is a material that transmits electricity with little or no resistance. Resistance is the degree to which a substance resists electric current. All common electrical conductors have a certain amount of electrical resistance. They convert at least some of the electrical energy passing through them into waste heat. Superconductors don't. No one understands how superconductivity works. It just does.

　　Making superconductors isn't easy. A superconducting material has to be cooled to an extremely low temperature to lose its resistance. The first superconductors, made more than 50 years ago, had to be cooled to -263 degrees Celsius before they lost their resistance. Newer superconducting materials lose their resistance at -143 degrees Celsius.

　　The superconductors cable installed at the Frisbie station is made of a ceramic material that contains copper, oxygen, bismuth （鉍）, strontium （锶）, and calcium （钙）. A ceramic is a hard, strong compound, made from clay or minerals. The superconducting ceramic has been fashioned into a tape that is wrapped lengthwise around a long tube filled with liquid nitrogen. Liquid nitrogen is supercold and lowers the temperature of the ceramic tape to the point where it conveys electricity with zero resistance.

　　The United States loses an enormous amount of electricity each year to resistance. Because cooled superconductors have no resistance, they waste much less power. Other cities are watching the Frisbie experiment in the hope that they might switch to superconducting cable and conserve power, too.

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