The systematic control of crystal growth in microgravity gives insight into the physical laws by which matter organizes itself. The Binary Colloidal Alloy Test - 5: Seeded Growth (BCAT-5- SeededGrowth) experiment studies how the “rules” for the crystallization of microscopic particles (known as colloids) suspended in liquid change when seed particles are present. These experiments are anticipated to have application to the development of new smart materials.Principal Investigator(s)
ZIN Technologies Incorporated, Cleveland, OH, United States
National Aeronautics and Space Administration (NASA)Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)ISS Expedition Duration:
March 2009 - October 2013
19/20,21/22,25/26,27/28,29/30,31/32,33/34,35/36Previous ISS Missions
The predecessors to BCAT-5, which are BCAT-3 and BCAT-4 are in operation on the ISS.
The Binary Colloidal Alloy Test - 5 (BCAT-5) hardware supports four investigations. Samples 1 - 5, the Binary Colloidal Alloy Test - 5: Phase Separation (BCAT-5-PhaseSep) will study collapse (phase separation rates that impact product shelf-life). In microgravity the physics of collapse is not masked by being reduced to a simple top and bottom phase as it is on Earth. Samples 6 - 8, Binary Colloidal Alloy Test - 5: Compete (BCAT-5-Compete) will study the competition between phase separation and crystallization, which is important in the manufacture of plastics and other materials. Sample 9, Binary Colloidal Alloy Test - 5: Seeded Growth (BCAT-5-SeededGrowth) will study the properties of concentrated systems of small particles when 99.8 percent are identical 0.36 diameter micron spheres and 0.2 percent are 4.14 microns in diameter (11.5X larger); these seed particles may cause heterogeneous crystal growth. Sample 10, Binary Colloidal Alloy Test - 5: Three-Dimensional Melt (BCAT-5-3D-Melt) will look at the mechanisms of crystal formation and 3-dimensional melting using colloidal particles that change size with temperature.
For the SeededGrowth Sample (9), plans are to experimentally explore the theoretical prediction that the use of seed particles can be used as a way to control the size of crystallites. The control of crystallite size is important in many industrial processes. By introducing the right size and concentration of 'nano-dirt', we use this experiment to record the effect of large (11.5X) spherical seed particles on crystallization. Small nuclei grow on the seed and as they grow, the presence of a larger curved substrate makes it difficult to maintain an unstrained structure. At some stage, the precritical nuclei break away from the surface, and the critical nucleus is only formed in the bulk. The seed particles are identical to the smaller PMMA spheres, including the thin polymeric steric layer attached to the particle surfaces.
BCAT-5-SeededGrowth will ultimately impact our understanding of the strength and thermal conductivity of materials by providing insight into the effects of polydisperity and the presence of larger “seed” particles in dense suspensions of particles.Earth Applications
Generally, colloidal nucleation experiments seek an understanding of the most fundamental liquid/solid transition. The relative uniformity in size of particles may impact the rise of order out of disorder. Though direct applications of that understanding do not yet drive the research, growth of ordered colloidal phases has attracted interest in a number of areas, e.g. ceramics, composites, optical filters and photonic bandgap materials.
The BCAT-5 experiment consists of ten small samples of colloidal particles. The ten BCAT-5 samples are contained within a small case the size of a school textbook. The experiment requires a crewmember to set up on a handrail/seat track configuration, ISS Laptop and utilize EarthKAM software to take digital photographs of Samples 1 - 8 at close range using the onboard Kodak DCS760 or Nikon D2Xs camera. Camera Control Files for running the EarthKAM software can be uploaded from Earth to control the photography intervals (how many photographs per hour) and spans (run for how many days) once it is running. Samples 9 - 10 (and possibly some of sample 6 - 8), which may form crystals, require manual photographs (at least initially) be taken by a crewmember. The pictures are down-linked to investigators on the ground for analysis.Operational Protocols
A crewmember sets up the video camera and BCAT-5 hardware (Slow Growth Sample Module, Kodak DCS760 or Nikon D2Xs camera, pen-light source, flash and SSC Laptop with EarthKAM software) on a seat track setup to document the BCAT-5 operations as performed on-board the ISS. The crewmember homogenizes (mixes) the sample(s) and takes the first photographs manually. This helps them optimize the setup and shows that the samples were initially fully homogenized when publishing results later. The EarthKAM software automates the rest of the photography session over a period of a few days to a few weeks. The crewmember performs a daily status check once a day (when time is available) to assure proper alignment and focus. At the completion of the run, the crewmember tears down and stows all hardware.
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Cacciuto A, Auer S, Frenkel D. Onset of heterogeneous crystal nucleation in colloidal suspensions. Nature. 2004; 428: 404-406.