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Monday, July 14, 1997, 7 a.m. CDT
07.14.97
 
STATUS REPORT : STS-94-21s
 
 
STS-94 Mission Science Report # 21s
 
 

Studies of material and combustion science dominated the Microgravity Science Laboratory -1 investigations in Columbia’s Spacelab during the past 24 hours.

In one area of materials research, the crew conducted an experiment to study a process that can severely degrade the strength of alloy products, such as turbine blades in aircraft engines. The Coarsening in Solid-Liquid Mixtures experiment, led by Dr. Peter Voorhees of Northwestern University in Chicago, Ill., is providing insight into processes which can cause metals to weaken or fail.

The different metals that comprise alloys often have different freezing points. One metal can begin to solidify before the others, forming small particles in the mixture. As the solidification process continues, the mixture begins to coarsen -- the small particles shrink by losing atoms to larger particles. This results in a lack of uniform particle distribution that may lead to defects in materials and products. “We are looking at how the particle sizes change over time,” said investigator Mark Assel of NASA’s Lewis Research Center in Cleveland, Ohio.

Exactly how coarsening occurs is still not well understood. On Earth, gravity causes the heavier liquid metal to sink to the bottom of the mixture, making it difficult to study the coarsening process. By studying it in space, the design and control of metals processing on Earth could be improved.

During the experiment, a cartridge of lead-tin samples is loaded into a compact, electric oven in the Middeck Glovebox. The oven heats the samples to form solid-liquid mixtures. Hundreds of thousands of solid particles are dispersed in these small samples. Then, the samples are quenched, rapidly freezing the high-temperature particle structure. “We are collecting time and temperature data in flight,” said Assel. “We won’t know for sure until we’re able to look at the samples, but we believe the runs were successful, and we expect to get a lot of good science.”

Sunday, crew members from both the red and blue shifts conducted runs of the Structure of Flame Balls at Low Lewis-number experiment, called SOFBALL. The study examines the burning processes of very weak fuel-air mixtures in near-zero gravity. Payload Specialist Dr. Greg Linteris conducted a run of the experiment Sunday morning and Mission Specialist Dr. Janice Voss conducted another run late Sunday night.

For the first, a mixture of hydrogen, oxygen and carbon dioxide was used. It was a repeat of a test that was conducted during the abbreviated STS-83 mission in April. The gas mixture resulted in four balls of flame. “This run gave us some very interesting results,” explained project scientist Dr. Karen Weiland of Lewis Research Center. “Of the four flame balls, only two burned for the duration of the experiment -- 500 seconds. The other two used up the fuel in that area and extinguished. This is different than what we observed during STS-83.”

During the second run, the hydrogen-air mixture was ignited and two flame balls developed. According to principal investigator Dr. Paul Ronney of the University of Southern California in Los Angeles, the experiment is going very well and the science team is very pleased with the results of the investigation so far.

At the beginning of his shift Sunday afternoon, Payload Specialist Dr. Roger Crouch performed a scheduled changeout of the Space Acceleration Measurement System’s hard drive, and last night, Voss performed a disk changeout in the Quasi-Steady Acceleration Measurement system. The two systems detect and record the tiny disturbances in the near- zero gravity environment of the Spacelab. Science teams rely on the information, downlinked in near-real-time, to determine the effect of the disturbances on experiments. There are four acceleration measurement systems operating aboard Columbia.

Around midnight, Crouch performed a sample exchange in the Large Isothermal Furnace, initiating a run of the Liquid Phase Sintering experiment, which is led by Dr. Randall German of Pennsylvania State University in University Park, Penn.

In industry, the liquid phase sintering process is used to form very hard and dense solids -- which, in turn, are used to manufacture products such as cutting tools, car transmission gears and radiation shields. Liquid phase sintering consists of causing particles of mixed metals to bond and form a strong material. During the experiment, compressed powders of tungsten, nickel, iron and tungsten, nickel and copper are heated. The nickel, iron and copper melt but the tungsten does not, resulting in solid-liquid mixtures. Researchers are studying these mixtures to learn more about the sintering process, specifically how the particles of the mixtures bond. On Earth, settling of constituents in the mixture during sintering tends to result in a distorted material.

This research is fundamental to powder metallurgy. Investigators hope to better understand this process and develop techniques that can be used to lower costs of production and create even better sintered materials.

Later, Mission Specialist Dr. Donald Thomas began the fifth and final run of the Diffusion of Liquid Metals study, led by Dr. Toshio Itami of Hokkaido University in Sapporo, Japan. The investigation is aimed at determining the diffusion coefficient of liquid tin in relation to temperature, a very significant measurement for describing the diffusion process by which liquid metals mix without stirring.

In the TEMPUS levitating, processing of a sample of iron, nickel and chromium was initiated Sunday. The Alloy Undercooling Experiment, led by Dr. Merton Flemings of the Massachusetts Institute of Technology in Cambridge, Mass., is measuring how fast melted steel mixtures solidify. During the study, a spherical sample will be positioned in the facility, melted and then cooled. Results of this research may improve steel strip casting and welding processes.

Early this morning, Thomas exchanged the sample in the furnace to begin another run of a study to gather fundamental measurements of an undercooled sample of cobalt-palladium. Undercooling is when a liquid remains fluid when cooled below its normal freezing point. During the experiment, an electromagnetic pulse is used to squeeze, then release the sample being levitated in the facility. Instruments record the oscillations, or movement, of the sample. “This is a new technique,” explained researcher Bob Hyers of the Massachusetts Institute of Technology in Cambridge, Mass. “Using this technique we can determine the surface tension and viscosity, or resistance to flow, of the sample.” This is the first time the viscosity of a cobalt-palladium alloy has ever been measured. And although the surface tension measurements of some of the TEMPUS samples are already known, for others this new technique is pinpointing that figure for the first time.

The TEMPUS studies are providing researchers with fundamental measurements necessary for modeling industrial materials systems needed to manufacture new and better products. “The studies are going remarkably well,” said Flemings. “They have done everything we hoped they’d do.”

Today, the Columbia crew is scheduled to perform another run of the Coarsening of Solid Liquid Mixtures experiment and Linteris will conduct another run of the flame ball experiment in the Combustion Module.

The next scheduled Public Affairs status report will be issued at approximately 6 a.m., July 15.

 

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