Practising for the space station 231

Furthermore, the behaviour of fluids was known to have potentially damaging effects on materials-processing techniques, biotechnology and combustion research and surface tension-driven flows also affect crystal growth, welding and flame spreading on liquids. During the IML-2 mission, the BDPU was equipped with a bewildering array of video and still cameras and sensors to carefully scrutinise the behaviour of a variety of fluids in microgravity. One of the most important experiments involved the injection of vapour bubbles into a test cell filled with an alcohol-water solution, after which alternative sides of the cell were heated and cooled.

The results seemed to confirm a theory proposed by the experiment's designer, Antonio Viviani of the Second University of Naples: the bubbles did not always move towards the warmer side of the cell as they might in most materials. ''This demonstrates for the first time that, in some fluids of high-technology interest, bubbles can go towards the colder part of the fluid or stop in the middle, due to the particular interaction between temperature and surface tension,'' he said. It was hoped that such insights could lead to new ways of manufacturing improved glasses, ceramics, composites or alloys.

Later in the mission, as his experiment run concluded on 16 July, Viviani received a round of applause from science teams at NASA's Marshall Space Flight Center -his two-year research and computer-modelling theory seemingly vindicated. ''Because of gravity, this experiment could not be done on Earth,'' he told them, ''and it could not be done in space without a good theory, a good facility, outstanding support from the science team and a great crew.'' Other BDPU investigations included a study of the movement and shape of bubbles and drops in silicone oil and one that involved a three-layer liquid solution.

The Principal Investigator for this experiment, Belgian scientist Jean-Claude Legros, was hoping to learn more about how to control fluid flows within the middle layer of a tri-layered solution of immiscibles; such research could prove beneficial for the production of faster semiconductors and purer crystalline metals. ''The rough data we received from our remote support centre in Belgium seems to match our predictions,'' Legros said on 17 July. On another occasion, Chiao monitored the boiling of a liquid refrigerant, revealing for the first time - and captured by Spacelab's video cameras - the coalescence of two large bubbles, unaffected by buoyancy.

The Japanese, meanwhile, provided their Large Isothermal Furnace (LIF) to heat materials and rapidly cool them to identify relationships between their structures, processing and physical properties. Five samples of ceramic-metallic composites and semiconductor alloys were solidified under varying temperature levels to permit ground-based scientists to refine and improve production practices on Earth. Traditionally, in order to produce lighter, stronger or more temperature-resilient materials, metallurgists combine different metals into alloys, or they may pair dissimilar materials such as metals and ceramics, with suitable physical qualities. However, the key to success is a uniform distribution of various components in the finished product.

This is not always possible, given the complications of terrestrial gravity, which causes substances with dissimilar densities to settle differently as heavier components are pulled downward. The results can diminish the uniformity of a 'new' material's structure, distort its shape and reduce the precision of the casting process needed to produce it. In the microgravity environment, however, where the impact of buoyancy and sedimentation are drastically reduced, it became possible to mix dissimilar materials in spite of great density differences between them.

Usually, LIF followed a pre-programmed heating-and-cooling cycle to process samples - reaching temperatures as high as 1,600 Celsius - while temperature and other data were constantly monitored. As each experiment run ended, helium was injected into the furnace to rapidly cool the sample before removal. The samples were housed in cartridges that the astronauts inserted into the furnace. One of them, provided by Randall German of Pennsylvania State University, examined how gravity changed heavy alloys during a process known as 'liquid phase sintering', whereby two dissimilar metals are combined using heat and pressure, but without reaching the melting point.

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