Three-in-One Furnace Readied for Possible Space Flight
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Three-in-one furnace readied
for possible space flight
for possible space flight
U.S., Hungary participate in joint
March 23, 1999: Scientists in the United States soon will be able to resume experiments with a three-in-one Hungarian materials furnace that could lead to improved designs for turbine blades and advanced lasers for true holographic projection systems.
In a few weeks, scientists from NASA's Marshall Space Flight Center will travel to the University of Miskolc in Hungary to train on an enhanced version of the Universal Multi-Zone Crystallizator in preparation for its transfer to NASA/Marshall in August. An important step in the furnace's future was taken in December when NASA listed the UMC, along with many other facilities, in a research announcement.
Right: Looking like a gem, this crystal of zinc selenide was made by physical vaport transport in the UMC. It grew from the tip of a glass ampoule, shown above, which was at the cooler end of the furnace. The view below shows the large end of the sample after removal from the ampoule. Credit: NASA.
That listing became possible because of political events almost a decade old.
The University of Miskolc had a deal with the USSR to put the UMC aboard the planned NIKA-T satellite," explained Dr. Dale Watring, the deputy chief of the Microgravity Science and Applications Division in the Space Sciences Laboratory at Marshall Space Flight Center. "Then the Soviet Union collapsed in 1990 and the university's funding and flight opportunity were lost."
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But through the first International Conference on Solidification and Gravity, held in Hungary in 1991, the UMC came to the attention of NASA through Dr. Sandor Lehozcky, then chief of the Crystal Growth and Solidification Branch at NASA/Marshall, Dr. Ching-Hua Su, a scientist in the branch, and Dr. Martin Glicksman of Rensselaer Polytechnic Institute in Troy, N.Y. They work in the field of alloy and metal formation in microgravity.
Left: Norbert Babcsan and Dr. Peter Makk of the University of Miskolc prepare the Universal Multizone Crystallizator for an experiment. Links to 704x575-pixel, 153K JPG. Credit: NASA/Marshall.
Lehozcky and Glicksman worked out an agreement with Dr. Pal Barczy and Dr. Andras Roosz of the University of Miskolc whereby NASA would house the UMC and provide funding for Hungarian scientists to work with it in the United States.
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"It came to our laboratory in 1993 and we tested it for three years," Watring continued. "We proved it could be used for semiconductor growth."
What made the UMC attractive is that while it uses basic furnace techniques demonstrated on furnaces built by the United States and other nations, it has an unprecedented degree of precision. And it features three different processing techniques in one apparatus.
Left: A bullet-shaped creystal of zinc telluride, also grown by physical vapor transport in the UMC. Credit: NASA.
At a simple level, the manufacture of some advanced materials is like making a loaf of bread. The ingredients have to be mixed just right and then baked at the right temperature for a set period of time.
Precise heating and cooling is provided by a series of 25 heaters, each 1 cm long and controllable to 0.1 deg. C at temperatures up to 1,500 deg. C. The series of heaters eliminates the need to move the sample through a hot zone (or to move a single large heater down the length of the specimen). This lets the UMC operate on about half as much power as a conventional furnace would use.
An added benefit of moving the hot zone, rather than the furnace or sample, is the elimination of vibrations that can damage crystals as the samples resolidify.
The heater array allows the furnace to operate in several different methods, Watring explained: gradient freeze, physical vapor transport, and traveling solvent zone, and float zone.
Different samples require different methods. Gradient freeze, for example, allows a scientist to control the heaters so the hot zone is followed by a cold zone just below the specimen's melting point. Physical vapor transport will vaporize a sample at one of an ampoule and let it condense on a relatively cold spot at the other end, somewhat like frost condensing on a car windshield.
Right: The elements of an ampoule flown on the U.S. Microgravity Laboratory-2 mission are similar to those used in the UMC. The layers of glass shielding and metal support are needed to protect both sample and furnace. Credit: NASA.
"The UMC is more flexible for physical vapor transport growth," said Su who has used the furnace in physical vapor transport experiments growing zinc-selenide crystals. "This work is very complicated to do with 3- and 5-zone furnaces."
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In his experiments, Su wanted the temperature to be even across the length of an ampoule, and then taper to below vapor saturation at the tip where the evaporated materials were to condense and crystallize. Achieving that in a furnace with just a few heating zones is complicated, even if the furnace moves.
"Another advantage of UMC is space," Su pointed out. "Since neither the heater nor the sample is moving, the furnace will occupy much less space than the traditional translation furnace. On a space station, space is a very precious resource."
In addition, the UMC accommodates specimens up to 5 cm in diameter and 30 cm long (about 2x6 in.), larger than handled in Space Shuttle-borne experiments.
"We can do experiments with a number of interesting combinations of materials," Watring explained, "like certain types of electronics with germanium, and zinc-selenide for blue lasers." Blue lasers could transmit larger volumes of data than conventional red or infrared lasers, and thus would be valuable in data storage and optical computers. They could also be used in holographic projections, complementing the red and green already available.
Right :Dendrites are revealed when an alloy is cut open and lightly etched with acid. Dendrites are treelike structures that crystals form as they grow. Understanding how dendrites grow and are shaped, and how they interlock to form a strong alloy will be studied with the precision control that the UMC offers. Credit; University of Mislokc.
The UMC is also valuable for research of the formation of metal matrix composites in which metal alloys are imbedded with fibers or ceramics, somewhat like glass fibers in plastic resin to make fiberglass. It can also produce large single-crystal shapes.
"You can use this furnace to look at different processing technologies that you could apply in industry," Watring said. One example is high-temperature turbine blades for advanced jet engines. If the blades can be made to withstand temperatures 5 to 10 deg. higher than they can now handle, the efficiency of jet engines would be increased.
After three years of research at NASA/Marshall, the UMC was returned to Hungary to be rebuilt to fit into the Materials Science Research Facility that NASA/Marshall is developing for the International Space Station.
"We're ready to go back and get it," Watring said. Whether it flies on the ISS will be decided later.
"It depends on the proposals that scientists submit," he explained. "It's decided competitively. That's how every microgravity furnace has flown in the past."
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