Breakthrough Made in Electrical Current Conduction
After more than a decade of making almost no progress, researchers have discovered an unexpected new family of materials that lose all resistance to the flow of electricity at temperatures much higher than those previously known.
The breakthrough has far-reaching implications because the new materials can be cooled to their superconducting temperatures much more cheaply than existing metals. That, in turn, could sharply reduce the cost of medical imaging devices such as CT scanners, experimental fusion devices to harness the sun’s energy and the massive accelerators used in physics.
It could also make possible cheaper and more efficient generation and transmission of electricity, faster and more powerful computers and magnetically levitated trains that would glide smoothly over superconducting roadbeds.
Superconductivity is a phenomenon that is exhibited by only a few metals and metal alloys at very low temperatures. In contrast, even such good electrical conductors as copper and silver display some resistance. In long-distance power transmission, for example, between 10% and 25% of the electricity is converted to heat and lost.
If an electric current were produced in a ring of superconducting metal, however, it would circle the ring indefinitely.
In today’s Science magazine, physicist Paul C.W. Chu of the University of Houston reports on a material that becomes superconducting at 52.5 degrees above absolute zero (minus 366 degrees Fahrenheit), more than twice the record of 23.2 degrees (minus 419 degrees Fahrenheit) that stood from 1973 to early 1986.
Chu’s achievement is the fourth significantly increased temperature to be reported this month. Other scientists believe that much higher temperatures are now obtainable.
The discovery of the new materials has set off a scramble among scientists. More than 100 research teams around the world are already exploring the new materials, according to physicist Maw-Kuen Wu of the University of Alabama.
The potential rewards of such research are great. A 1986 analysis by Naval Research Reviews, a technical journal, predicted that the market for products incorporating superconducting components could reach $36 billion by the year 2000.
Many also believe that a Nobel Prize will go to the scientist who explains the theoretical basis of the phenomenon.
The economic significance of the new discoveries lies less in the materials themselves than in the techniques used for cooling them. Existing superconductors must be cooled by immersing them in a bath of liquid helium, which boils at 4 degrees Kelvin.
Scientists measure temperature in degrees Kelvin, named for the 19th-Century British physicist, Lord Kelvin, who developed the first accurate thermometers. Water freezes at 273 degrees Kelvin and boils at 373 degrees Kelvin. The theoretical point at which all motion of atoms ceases, absolute zero, is set at 0 degrees Kelvin or minus 460 degrees Fahrenheit.
Engineers would like to use liquid nitrogen, which boils at 77 degrees Kelvin, for cooling. It is only one-tenth as expensive as liquid helium and a given amount of liquid nitrogen is 10 times as effective as a coolant as the same amount of liquid helium, according to Roy Weinstein, dean of natural sciences at the University of Houston.
Liquid nitrogen thus provides a hundredfold gain in the practicality of industrial applications, he said.
The current research was triggered in April, 1986, when scientists at the IBM Corp.’s Zurich Research Laboratory in Switzerland reported that they had made a material that became superconducting at 30 degrees Kelvin by combining copper, oxygen, barium and lanthanum.
This result was “surprising,” Chu said in a telephone interview, because physics theory predicts that such metal oxides should become superconducting only at temperatures near absolute zero.
In December, Chu announced that he had achieved a superconducting temperature of 40.2 degrees Kelvin, 12.3 degrees lower than today’s report, by subjecting the same material to pressures of about 150,000 pounds per square inch.
In a separate press conference the same day, Robert J. Cava of the AT&T; Bell Laboratories in Murray Hill, N.J., reported a superconducting temperature of 36 degrees Kelvin. Cava substituted strontium for barium in the compound, and his material is superconducting at atmospheric pressure, about 15 pounds per square inch.
Shortly thereafter, the New China News Agency reported that researchers at the Academy of Sciences in Peking had achieved superconducting at a temperature of 48.5 degrees Kelvin.
Chu’s new discovery uses the same four elements as in his original report but in slightly different proportions. The discovery has also had an important psychological effect, according to physicist Donald W. Capone of Argonne National Laboratory near Chicago . It had been so long since superconducting temperatures increased, he said, that “people had developed a mind block against getting higher temperatures.”
