Coming In Out Of The Cold
To date, the most practical conductor of electricity--copper wire--works well, but is far from perfect. Electrons flowing through the wire waste energy as they bump into copper atoms--like runners on a rough track, tripping over rocks and dirt.
Superconductivity itself is not a new phenomenon. In 1911, a Dutch physicist discovered that when certain metals are cooled to extremely frigid temperatures (-460 Fahrenheit; -Celsius), they become superconductors. Although the development was scientifically exciting, the need for severely low temperatures ruled out any practical use.
For the next 75 years, scientists sought--without much success--to achieve superconductivity at higher temperatures. Then, in 1986, two scientists at the IBM Zurich Research Laboratory created a ceramic material that--when cooled to 35 Kelvin (-397 F; -238 C)-- conducts electricity with absolutely no resistance.
Physicists were exuberant. The discovery stimulated other researchers to work with and refine the ceramic, leading to ever more dramatic leaps in temperature. In March 1987, thousands of scientists gathered in New York at a meeting that came to be known as "the Woodstock of physics'' to hear their colleagues sing the praises of the new material. Not only does the ceramic have zero resistance, but it also acts as a perfect "magnetic mirror,'' as demonstrated by the levitating magnet trick (known as the Meissner effect). In other words, a magnet placed near a superconductor will "see'' its mirror image and, because like poles repel, the magnet and superconductor move away from each other.
Scientific engineers say superconductivity at higher temperatures could be the discovery of the century if they can figure out how to fashion the brittle materials into more practical forms. They dare to dream of potential applications: cheap, efficient transmission of electrical power; magnetically levitated trains; faster, practical electric cars; and advanced super-computers.
But the superconductive world of tomorrow was not even a dream in the high school classroom of today until Paul Grant, a scientist working on superconductivity research at IBM's Almaden Research Center in San Jose, decided to show his 13-year-old daughter what he was doing at the lab. He was surprised by her reaction to a demonstration of the Meissner effect. "She is normally a very calm and phlegmatic kid, but she got very excited,'' Grant says.
Her enthusiasm led him to wonder if high school students would be interested in trying to synthesize a superconductor of their own, and if they were, whether they would succeed without the sophisticated equipment that research scientists take for granted.
Curious, he proposed the idea to Pribyl, whom he had met one year earlier. The teacher jumped at the opportunity to add the hot topic to his curriculum.
In one brief meeting, Grant explained to Pribyl the process of making a superconductor. It was a relatively simple procedure involving the firing and cooling of chemicals at carefully controlled temperatures. The chemicals--yttrium oxide, barium carbonate, and copper oxide--were cheap and easy to obtain. The heat source--the school's jewelry kiln-- was close at hand.
After a few brief discussions, Pribyl let his students get to work. "I told them the chemicals that they needed and the formula,'' the teacher says. "And then I asked them to calculate how many grams each of yttrium oxide, barium carbonate, and copper oxide they would need to make the ceramic compound.''
After working with paper and pencil, the team weighed out the chemical ingredients and ground them with an ordinary mortar and pestle.
To get the materials to react, the mixture had to be fired at 1,697 F (925 C). Students took turns nursing the kiln for the 12 hours required to make the mixture into a superconductor. "Our jewelry kiln doesn't have a sophisticated, automated program to take care of the process like they do at IBM, so we had to turn the thermostat dial manually, monitoring temperature and oxygen pressure in shifts,'' recalls Pribyl.
The next day, students found that the mixture had melted. They recalibrated the furnace and tried again. This time, working with a freshly ground sample, the material didn't melt. Then, they reground the material to a fine powder and squeezed it into a pellet using a "pill press'' borrowed from IBM.
Grant suggested one more heating and cooling step called annealing to fuse the tiny grains of the superconductor. This strengthens the ceramic material and improves its ability to conduct electricity.
After another 12-hour stint at the kiln, it was time to test the results. Because materials only become superconducting at very cold temperatures, the students needed to cool the superconductor to about -320 F (-208 C). This can be accomplished by bathing the pellet in liquid nitrogen. Pribyl had obtained a few cups of the subarctic coolant from a local dermatologist who uses it to "freeze'' warts. After cooling the superconductor, the students released a rare earth magnet--a hardware store magnet's magnetic field wouldn't be strong enough to support its own weight--over the surface of the disk. If it was a genuine superconductor, it would repel the magnet, causing it to hover in midair. Unfortunately, theirs fell.
So did the spirits of Pribyl's students--but not for long. After determining that the barium carbonate they used was only 80 percent pure, they borrowed the necessary amount of 99.9 percent pure BaCO from the local junior college, and they started all over.
The third time was the charm. The magnet levitated, and Pribyl and his students were finally flying high.
Since that first success, other high school teachers across the country and around the world have duplicated the Gilroy experiment, according to Grant. And in the last two years, superconductivity has become a lecture topic at workshops and conferences in science education.
Grant emphasizes that the experience does more than turn students on to superconductivity. It teaches young people to keep trying, even when there is no guarantee of success. Tenacity is a crucial part of being a scientist, Grant says, and yet most science teachers don't teach students that.
"I think when you teach a subject like chemistry, physics, or mathematics, you should spend some time teaching about the personalities of the men and women who made the great discoveries,'' he says. "They were always stumbling around and making mistakes. They were pretty unsure of themselves most of the time. The problem with science education is that everything works all the time. That's the way the curricula are adjusted, and that's the way the experiments are designed. I'm not an expert on science teaching, but if it is anything like it was when I was in high school, it can be intimidating.''
Once a positive experience such as making a superconductor piques the curiosity of students, science educators hope that students will stay interested in science. Pribyl, who repeats the superconductivity experiment each year with a fresh batch of scientific sleuths, has been delighted to watch many of his students become involved in researching different aspects of superconductivity in great depth for science fair projects.
Pribyl's students aren't the only ones spending more time in the lab. Each summer since 1987, the teacher has been invited by IBM to work on a research project at the Almaden center. "It's the best of all possible worlds,'' he exclaims. "I dabble in research, but I can go back to high school.'' Although the IBM staff treats him well, they have not tried to lure him away from the teaching profession. They believe that teachers with his creativity and dedication are valuable in the classroom where they will influence young, potential scientists. "If we could,'' Grant says, "we'd make 20,000 clones of that guy.''
For a free copy of Synthesize Your Own Superconductor, with detailed instructions, send a stamped, selfaddressed envelope to David Pribyl, Science Department, Gilroy High School, Gilroy, CA 95020.