Metals and Alloys
TEMPUS
Everything floats in weightlessness, but making things float where you want them to float is a challenge. Germany is meeting that with TEMPUS, an electromagnetic levitation furnace that will melt samples without them touching the walls, thus rendering nearly perfect samples.
Large
Isothermal Furnace
The Large Isothermal Furnace developed by Ishikawajima-Harima Heavy Industries Co., Ltd., for the National Space Development Agency of Japan (NASDA). Japan's National Space Development Agency will be making its third flight in space. LIF heats and cools an entire sample, hence the name iso (same) thermal (temperature). Six experiments are to be conducted using the LIF. They are:
- Liquid Phase Sintering (LPS-2) :This process is used by industry to form very hard, dense solids, which are used in anything from cutting tools, to car transmission gears to radiation shields! The materials are made by fusing (sintering) metal or ceramic powders. Liquid phase sintering uses a special liquid, made from the material itself, to suspend the powders for fusing. However, gravity affects the dispersal of the powders suspended in the liquid, and causes the resulting solid to be less uniform. This experiment is designed to better understand this process and develop techniques that can be used to lower costs of production, and create even better solids using LPS.
The history of physics has been marked by measurements of constants, numbers - like the speed of light in a vacuum or the value of pi - that anchor equations so we can get useful answers from other values that vary. Despite centuries of experience in mixing, molding, and casting metals, we still don't have several constants - called diffusion coefficients - for mixing certian sets of metals. In samples large enough to measure the diffusion, gravity can disturb the answer the results. Five LIF experiments will pursue these constants:
- Measurement of Diffusion Coefficient by Shear Cell Method will test a new approach to measuring how fast metals diffuse into each other (much like a scent traveling from one end of a room to another). The shear cell does just what its name suggests: after the experiment has run a set period of time, the sample cartridge is rotated so a portion is sheared away from the main body, thus preventing further diffusion as the sample is cooled.
- Diffusion of Liquid Metals and Alloys will look at how metals of almost the same atomic mass - two isotopes of tin - diffuse into each other.
- Diffusion in Liquid Lead-Tin-Telluride, a potential material for infrared detectors, to measure its dependence on temperature,
- Impurity Diffusion in Ionic Melts will electrolyze salts of potassium chloride and lithium chloride in somewhat the same manner as basic chemistry experiments that electrolyze water.
- Diffusion Processed in Molten Semiconductors (DPIMS) also uses shear cells that rotate samples into position to face each other so diffusive mixing can start, then apart to end the process. Samples on one side contain pure germanium; those on the other side have germanium with traces (doping) of gallium, silicon, and arsenic. Measuring the samples after the mission will help us understand how materials mix as solid-state electronics are built up.
Coarsening
in Solid-Liquid Mixtures (CSLM)
Coarsening is a process that can severely degrade the strength of an alloy-product such as a turbine blade in an aircraft engine. When you make an alloy, consisting of two or more different metals, as the alloy cools, the two metals generally have different freezing points. One metal can begin to solidify before the other. In the cooling process, the first metal to solidify can begin as very small particles, but coarsen, or grow into fewer larger particles before the second metal in the alloy cools. Alloys with a few larger particles tend to be weaker than alloys with many small particles. The pictures at left show coarsening over a four hour period for a laboratory sample.
The speed and mechanisms of coarsening are not well understood. Furthermore, in 1-g, the heavier metal can sink to the bottom, further confusing the ability to study the process. Scientists at Lewis Research Center will be studing this phenomenon during the MSL-1 mission.
