Results from space-bound experiments unencumbered by gravity are crystallizing the wondrous possibilities of creating glass that breaks the mold in ways not thought possible on Earth. Space glass could revolutionize fiber optics and other terrestrial technologies and even serve as construction material for erecting structures on other planets.
Trailblazers on the cutting-edge of glassmaking envision extraordinarily transparent glass fibers stretching for thousands of miles across continents or super-strong glass glue made of "moon dust" that can cement walls, floors and roads on extraterrestrial worlds.
The pioneering craftsmen think they can bring seemingly pie-in-the-sky notions down to Earth.
Already, National Aeronautics and Space Administration researchers who have dabbled in making glass in the weightlessness of space have discovered their creation is endowed with some remarkable properties. For one, it has the pristine purity of an object untainted by touch because it lacks the need for a container that must hold the molten precursor of glass -- called the melts -- back on the ground.
"At high temperatures, these glass melts are very corrosive toward any known container," explained Delbert Day, Curators' Professor of Ceramic Engineering and senior research investigator in the Graduate Center for Materials Research at the University of Missouri, Rolla. Day conducted the first U.S. glass melting experiments in near-weightlessness aboard the space shuttle in 1983.
As it eats away at the confining crucible, the melt -- and thus the glass -- becomes contaminated by the dissolving particles. In contrast, in gravity-free experiments, the molten glass stayed suspended inside a hot furnace simply by the pressure of sound waves emitted by a special device called an acoustic levitator. Like a trick out of a magician's book of floating gimmicks, acoustic levitation can position and move a tiny sample -- a mere fraction of an inch (a few millimeters) across -- in mid-air. The force from the sound waves suffices to suspend, place and manipulate the test target, eliminating the necessity for containers and the danger of contamination.
"The great potential is that we will gain information from experiments in space which will let us better understand materials that we already are making on Earth so that we can make them faster, better and cheaper," predicted Day, whose credits as an inventor include thinner-than-a-human hair glass spheres that deliver high doses of cancer-shattering radiation directly to a disease-riddled organ or tissue.
With the newfound availability of space as a one-of-a-kind laboratory, the sky could be the limit in glass research, scientists told United Press International.
"We can't even comprehend what we are missing," Day marveled.
For example, his crystal ball points to glass as a major player in the future settling of other worlds, if such comes to pass.
"If and when we colonize another planet, we will need to use as much of the material on the planet as possible since we can't transport all of the materials required from Earth," Day projected.
Glass made of "moon dust" and native soils melted by solar energy could provide the construction material for floors and walls, he envisioned.
"Molten glass could be used to glue the naturally occurring rocks together in much the same way that cement is now used to glue the rocks (aggregate) together to build roads and buildings," Day added. "Might sound a little far-fetched, but everything about living on another planet will be far-fetched."
Closer to home, space glass also could have a life-altering impact, scientists proposed.
"The key to producing the highly transparent glass fibers used for optical communication, which are revolutionizing our world -- we are now rewiring the world a second time, the first was with copper wires and the second is with glass fibers -- is to develop an entirely new method for melting high purity silica glasses," Day told UPI.
"The main idea at this time is to use the information gained from experiments in space to improve our manufacture of glass made on Earth."
On Earth or beyond it, glass -- be it of the ordinary variety used in windows and bottles or of a more exotic form that facilitates optical communication -- follows a fundamental formula. The age-old recipe calls for combining such materials as sand, limestone and soda, boiling the mixture until it glows red-hot, then cooling the incandescent goop with utmost care to avoid the formation of crystals, which would ruin the desired effect.
Glass -- a solid with an amorphous internal structure -- can form only if the melt cools quickly enough to preclude the atoms from hooking up into the patterns that typify crystals.
When all goes according to plan, the result is a hard, brittle, usually clear or translucent substance that can stand up to wind, rain or sun and serve an ever-expanding range of pragmatic and cosmetic purposes.
"While glass is one of the oldest materials made by man (it is thought to have been created by the Phoenicians around 3000 B.C.), we are still discovering new uses and new glasses all the time," Day pointed out. For example, he continued, there are "fibers for optical communication, oven (thermal shock) proof chemical ware and dishes, new glass which barely changes dimensions when heated/cooled that is now used in the Hubble Space Telescope (which couldn't explore the universe without those glass lenses), glass microspheres for treating patients with cancer, et cetera."
Most of the familiar types of glass blend silica obtained from beds of fine sand or from pulverized sandstone, an alkali to lower the melting point, usually a form of soda or, for finer glass, potash, lime as a stabilizer and cullet, or waste glass, to help the mixture melt.
Scientists with sights set on more exotic applications, however, strive to break out of the traditional mold.
If, as the initial results indicate and Day is convinced, glass melted in zero gravity resists crystallization, then setting up shop in space -- either as a full-force factory or even as an occasional testing ground -- could forever transform glassmaking, scientists said.
"Glasses have a wide use in our everyday life, and their use would be even greater if we were able to prevent formation of crystals," noted Tihana Fuss, a doctoral candidate from Zagreb, Croatia, who works with Day's group. "It appears that melting glass in space does exactly that."
Taking gravity out of glassmaking could have a two-fold benefit, scientists speculated.
"This would not only mean that we would be able to improve properties of present commercially used glasses, but also that we could make new types of glasses," Fuss told UPI.
Particularly intriguing to space researchers -- and of exceptional potential value to the fiber optics industry -- is an exotic glass made of metal called ZBLAN, an appellation derived from the chemical names of its components. The blend of fluorine and the metals zirconium, barium, lanthanum, aluminum and sodium (Zr, Ba, La, Al, Na) is 100 times more sheer than silica-based glass.
"A fluoride fiber would be so transparent, light shone into one end, say, in New York City, could be seen at the other end as far away as Paris," Day remarked. "With silicon glass fibers, the light signal degrades along the way."
To their dismay, scientists found fluoride fibers are difficult to produce on Earth, where the melts tend to crystallize before glass can form. But space-based processing promises to offer tips on overcoming this obstacle, researchers said.
In fact, tests conducted in a KC-135, a workhorse four-engine jet aircraft that provides short bursts of near-zero gravity interspersed with periods of high gravity, showed thin fibers of the exotic glass are clearer when made in near-weightlessness than back on the gravity-saddled ground, noted Dennis Tucker, a physicist in the Space Sciences Laboratory of NASA's Marshall Space Flight Center in Huntsville, Ala.
ZBLAN glass fibers carry enormous commercial potential -- to the tune of $2.5 billion a year by some estimates -- for advanced communications, medical and manufacturing technologies using lasers. The biggest payoff could be in optical fiber communications where glass threads carry millions of telephone conversations and video and computer data. Telecommunications companies are investing heavily in optical fiber systems, including a "glass necklace" that will encircle the world, replacing transoceanic cables and eventually entering neighborhood communications.
Day points to one crucial missing link that remains: comparison of glasses processed in space and on Earth. He hopes to fill in the blank, and confirm his theory of the superiority of space-based glassmaking, with the next set of experiments -- aboard the International Space Station.
"We will measure the number and size of crystals in the glass (produced in space) and compare those numbers with identical glass samples processed on Earth," Day explained. "These data should confirm that glass formation is improved in space."
Although the Feb. 1 disintegration of the space shuttle Columbia and the ensuing uncertainty about the future of the shuttle program have played havoc with time schedules, Day and company hope to be conducting their space tests within three years.
The realization of practical applications for space-based glass research is still several years away, scientists cautioned.
"It depends obviously on funding to perform the basic research, then interest from private companies who see a benefit from producing glass in space for use on Earth," said Tucker, who is working with a private company on the design of an automated fiber producing facility that uses robotics to perform human functions.
The plan is to launch the facility into low-Earth orbit and deploy it to produce miles of glass fiber, including ZBLAN, then have it land by parachute and repeat the cycle, Tucker said.
Day hopes eventually to bring the lessons learned from space down to Earth.
"(My) ultimate goal," he said, "is to gain knowledge which will improve our life on Earth and which might contribute to our effort and plans to explore the universe."
