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Fact sheet number: FS-2003-09-117-MSFC
Release date:
09/03


Viscous Liquid Foam- Bulk Metallic Glass (Foam)


Experiment Name: Viscous Liquid Foam- Bulk Metallic Glass (Foam)

Mission: To be delivered on Progress 14P; experiment to be conducted during International Space Station Expedition 8 and/or Expedition 9

Experiment Location: Maintenance Work Area in Destiny Laboratory Module

Investigators: Dr. William (Bill) Johnson, and Chris Veazey, both of California Institute of Technology, Pasadena, Calif., and Dr. William Kaukler, NASA Marshall Space Flight Center, Huntsville, Ala.

Project Manager: Jim Kennedy, NASA Marshall Space Flight Center, Huntsville, Ala.


Overview

In the 1980s, scientists discovered a new family of glasses: bulk metallic glasses. NASA-funded researcher Dr. Bill Johnson and his team at the California Institute of Technology (Caltech) in Pasadena, Calif., built on this original discovery and combined five elements to make an alloy that could be stiffer and thus have more applications. Their research included experiments on the ground and during two Space Shuttle flights in the 1990s. Precise conditions for forming bulk metallic glasses -- including many elusive properties -- were identified during these flight missions.

What makes bulk metallic glass different from other metals and glasses? Conventional metallic materials have a crystalline structure consisting of single crystal grains of varying sizes that fit together to form the metal's microstructure. To create these metal alloys, materials are heated so that they combine. As they are cooled, crystals form and arrange themselves together to make the structure of the solid metal.

On the other hand, to form bulk metallic glasses, the alloy is undercooled - cooled below the temperature at which it would normally form a solid. At around 650 degrees Fahrenheit, the liquid cools rapidly and solidifies from a molten form to create the solid. Unlike normal metals, it changes into the solid without forming crystals. This solid, non-crystalline structure makes bulk metallic glasses much stronger than their metal counterparts - by factors of 2 or 3 - and tougher than ceramics.

This experiment continues the Caltech team's pioneering work on these novel materials and uses them to examine foaming, viscosity and bubble formation.

Understanding viscosity and foaming will help scientists understand industrially important materials such as paints, emulsions, polymer melts and even foams used to produce pharmaceutical, food and cosmetic products.

Viscosity - the "stiffness" of fluids - is determined by complex interactions between atoms that make up a material. It is very hard to model and calculate the viscosity of complex materials. Viscosity is a critical parameter for creating foams - materials that may flow through a tube, but also are thick enough to be shaped and molded.

Experiment Operations

Much of the hardware used for this investigation is already available on the International Space Station. To heat samples, astronauts will use a battery-operated soldering iron that is part of their on-orbit tool kit.

The experiment will be conducted inside the Space Station Maintenance Work Area -- a portable workbench with a tabletop that measures 36 inches by 25 inches. When not in use, it is folded and stored inside a drawer.

The Maintenance Work Area can be used throughout the Station. An astronaut unfolds it and clamps it to a slotted mechanism similar to seat tracks found in cars or airplanes. The tracks are located on the sides of most of the floor-to-ceiling racks inside the Station. Gloveports on the sides and ends of the workbench's plastic cover and a front flap that unzips allow crew members to use the soldering iron or other tools at the same time. e operator unable to see the work piece. In the Maintenance Work Area, this problem will be avoided by using the vacuum.

Johnson's team will prepare three small, 0.5-gram samples of bulk metallic glass on Earth. The samples will be injected with a gas so that when they are heated, they will foam. The samples will be contained in copper ampoules, containers that are evacuated and sealed by welding. The ampoules are 2.5 centimeters long by 0.6 centimeters in diameter.

The ampoules will fit into brass sleeves that slide over the soldering iron. Astronauts will use the tip of the soldering iron to heat the ampoule and the enclosed samples. The three samples will be heated for 30 minutes, 15 minutes and 7.5 minutes, respectively. The samples will foam, increasing in volume as they are heated. When cooled, they will retain this foam shape because the viscosity will increase during cooling until it is a solid.

For this experiment, scientists are mainly interested in studying viscosity - a property of fluids that causes them to resist flowing because of the internal friction created as the atoms move against each other. Structurally bulk metallic glasses are liquids with very high viscosity, and investigators have designed these samples and the processing technique to form stiff foams having thick cell walls. This is the first microgravity study of foaming in a liquid alloy that is undercooled.

Investigators have designed the processing technique to take advantage of the stability, or longevity, offered by the high viscosity when heated above the glass transition temperature. Foaming a conventional metal alloy is limited by its very low viscosity above the melting temperature. By analogy, bulk metallic glass foam captures bubbles like honey while conventional alloy foam captures bubbles like froth above soapy water. This makes bulk metallic glasses ideal for studying foaming and bubble behavior.

In microgravity, bubbles don't rise, liquid doesn't sink, and surface tension dominates. The advantage of microgravity is significant for metal foam, where the density difference between gas and liquid is very large.

Producing a bulk metallic glass foam in space that is strong enough to retain its structure on return to Earth will allow for a comprehensive study to be made of the parameters which affect bubble size, wall thickness and other foam characteristics. Investigators will compare the morphology of bulk metallic foam made in space to that made in Earth gravity to determine differences in wall thickness, bubble size distribution and shape effects.

Benefits

Bulk metallic glasses are a relatively new material with enormous potential. Solid foams are the best materials to make large, stiff structures due to their high strength to weight ratio. Foaming also considerably reduces the thermal conductivity of the metal alloy. Even bulk metallic glasses have significant thermal conductivity that engineers wish to reduce.

The more investigators characterize how and why these materials form, the more they can develop specific formulas for use in various applications - from sports equipment to military hardware to spacecraft. Better measurements of viscosity and a better understanding of foaming will help investigators improve a variety of materials used for everything from medical to industrial processing.

More Information

More information on this experiment and other Space Station experiments is available at:

http://www.spaceresearch.nasa.gov/

http://www.scipoc.msfc.nasa.gov/

http://www.spaceflight.nasa.gov/

http://www.microgravity.nasa.gov/


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