Liquid Metal Diffusion Experiment (LMD) - MIM

Objectives

The objectives of this experiment were: (1) to measure the diffusion coefficient of In metal at 185° C, (2) to investigate the "wall effect", i.e., transport differences between the bulk and wall regions of the sample, and (3) to characterize the convective contamination of diffusivity measurements on Earth via using the MIM in its three operating modes; 3a.vibration isolation, 3b.programmed g-input and 3c.deactivated.

Shuttle-Mir Missions
NASA-4

Approach
The LMD apparatus was mounted to the Microgravity Isolation Mount (MIM) with four captive screws. The MIM was used to provide several different acceleration profiles to the LMD during the running of five samples on the Mir Space Station. The MIM oven is used to heat the samples up to 185 degrees Celsius and, the samples are allowed to diffuse for 96 hours. Following sample processing, data from the LMD is transferred to the MIPS system for data storage.

Results
The raw LMD data from the three completed diffusion runs have been processed. Diffusivity values have been obtained. Accelerometer data from the MIM has been received and reviewed. The diffusivity values obtained from experiments conducted on Mir/NASA-4 are within 5% (i.e., within the experimental error) of the terrestrial experiments. No effect of the container wall on diffusive transport was detected. The acceleration disturbances measured on the MIM floater platform (during sample processing) were generally less than 10-4 g for the latched (deactivated) mode and 10-6 g for the isolating mode. Thus, buoyancy-driven convection effects were minimal in our samples.

Similarities between the self-diffusivity of Indium at 185°C between the terrestrial and space experiments was observed. At 185°C the temperature non-uniformities in the liquid indium were probably less than 0.05°C. The residual acceleration/g-jitter was typically less than 10-4 g. Therefore, convective contamination was minimal. In addition, the scatter of all diffusivity values were well within the experimental error; which is not true for the ground-based measurements. The performance of our radiation detectors and our sample containment method was well within our expectations. Hence, these components will be used for future missions. Although increased background noise from the South Atlantic Anomaly was evident in the detector data, it did not interfere with the diffusivity measurements. These results will be published shortly.

Earth Benefits
Diffusion is an important phenomena in the solidification of liquid metal alloys and pure metals. It increases the homogeneity of the liquid metal. However, buoyancy-driven convection, caused by gravitational forces, can influence diffusion. In molten metals, thermal differences cause the less dense atoms to rise and the more dense atoms to fall. This movement of molecules, buoyancy-driven convection, alters the diffusion process. In space, scientists have the unique opportunity to study diffusion in liquid metals without the effects of gravity, therefore, they can determine the true diffusion rate in different liquid metals. This information can be used to improve metal solidification processes on the ground which could ultimately lead to better automotive, airplane, and building materials.

Publications
None available at this time.

Principal Investigators
Franz Rosenberger
University of Alabama in Huntsville

Co-Investigators
R.M. Banish

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Page last updated: 07/16/1999

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