A New Class of Glass

Michael Wargo. "These tools can do something as remarkable as changing the way we see the universe, or they can be used for practical purposes that improve life on Earth," explains Wargo, who is the Enterprise Scientist for materials science in NASA's Office of Biological and Physical Research in Washington.

Designer Glass
Today, glass is used in everything from windows to bifocals to lasers: products too numerous to count. And scientists funded by NASA continue to add to the list by looking for ways to make customized, "designer" glass to meet a variety of high-tech needs. For example a new product called, REAl(tm) Glass, short for Rare Earth Aluminum oxide -- may show up in your doctor's office or be used to make your next car.

"Most surgical lasers now use expensive single crystals like sapphires," explains Dr. Richard (Rick) Weber, a NASA-funded researcher who heads up the Glass Products Division at Containerless Research Inc., the small company that invented and produces the glass in Evanston, Ill.

"These crystals are not only expensive to make, but also limit the range of operating wavelengths to very narrow bands of energy. REAl Glass will potentially give surgeons more choices -- letting them tailor the laser emissions, selecting the ones that work best for the specific type of surgery."

The glass may also improve other common products and speed up computer communications. It can be used in high-power lasers that cut metal to make cars or other products. And designers can mold and shape the glass to make devices needed for next-generation optical communications equipment -- including small, low-cost glass components needed to create powerful broadband Internet connections.

It Only Looks Like Magic
Like the first types of glass invented centuries ago, scientists make this glass by mixing materials, melting them, and cooling them to form a solid. But the remarkable difference is that this glass was first produced while suspended or levitated in a unique NASA facility -- the Electrostatic Levitator at NASA's Marshall Space Flight Center in Huntsville, Ala.

Inside the levitator, it looks like magic when molten, glowing glass floats in mid-air with no visible means of support. Actually, glass is suspended inside a chamber by static electricity generated by six electrodes. A laser beam heats the glass until it melts. Scientists, like Weber, measure the physical properties of the glass without interference of a container that would contaminate it.

"Levitating the materials allows you to learn how to create new types of glasses that are hard to devise any other way," Weber says. "Containers often contaminate glass samples, so if you can melt the ingredients without a container, you can study the material and its properties in their most pristine form. Once you get the recipe right, you can learn how to make the new glass in a more traditional way, like melting it in a container and pouring it into a mold."

Hitting the Ball Farther, Catching the Sun
What type of glass can help you hit a golf or tennis ball farther or catch pieces of the Sun? Bulk metallic glasses. Though scientists first discovered metallic glasses in the late 1950s, they learned to make them in bulk form only about ten years ago.

In 1993, NASA-funded researcher Dr. Bill Johnson and his team at the California Institute of Technology (Caltech) in Pasadena combined five elements to make an alloy that formed metallic glass when conventionally cast into bulk ingots -- a bulk metallic glass. The material is stronger and stiffer than its crystalline counterparts and is under development for numerous engineering applications.

Their research included experiments on the ground and during two Space Shuttle flights in the 1990s. The precise conditions for forming bulk metallic glasses -- particularly several elusive properties of the molten liquids -- were identified and measured during these flight experiments using containerless processing in microgravity.

Today, industry is using bulk metallic glasses to make tennis racquets, baseball bats and golf clubs. Other applications are under development including medical components, military hardware and cases for electronic devices, such as cell phones and computers.

Bulk metallic glass tiles also are being used aboard NASA's Genesis spacecraft to collect material from the solar wind -- the stream of charged particles ejected from the Sun. Genesis is scheduled to return to Earth in September 2004 with samples of the first solar wind particles locked inside coffee-lid sized detectors including one made of bulk metallic glass.

Glass Bones
For windows, glass made primarily of melted sand or silica is just fine. But glass can be made from many other combinations of elements tailored for use inside the human body. For example, there are "bioactive glasses" that can be used to aid in the repair of human bones. These glasses eventually dissolve when their work is done.

Sometimes, the opposite is desired: a glass that won't dissolve until it reaches a specific destination in the human body. NASA-funded investigator Dr. Delbert Day, the Curators' Professor Emeritus of Ceramic Engineering at the University of Missouri-Rolla, has developed glasses that are so insoluble in the body that they are being used to treat cancer by delivering high doses of radiation directly to a tumor site.

Working with NASA for more than 20 years, Day and his colleagues have conducted Space Shuttle experiments that indicate higher quality glass can be made in space. Like Weber, Day levitated the samples, but he used sound waves. In the low-gravity, or microgravity, environment inside the Space Shuttle, Day wasn't fighting the force of Earth's gravity.

He was able to suspend much larger samples than he would have been able to levitate on Earth. The glass he produced in space without a container was much higher quality than Day had predicted, and he was able to learn more about its properties by producing it in space.

"At high temperatures," says Day, "these glass melts are very corrosive toward any known container." As the melt attacks and dissolves the crucible, the melt -- and thus the glass -- becomes contaminated."

Space Glass
Like Day, other researchers want to learn what space can teach us about making glass. Working in microgravity removes some problems like convection -- fluid motion that causes a disturbance inside the sample as it is heated. Researchers can take what they learn about glassmaking in space and use the information to make all kinds of new glasses on Earth.

Weber says making glass in space also is important for NASA's exploration missions. "Glass is a basic engineering material, and the materials you need to make glass are located on the Moon and other places," Weber says. "These materials can be liquefied and made into glass, but you have to know how to do it. The Space Station is a good test bed for learning how to make glass in space."