The Coarsening in Solid-Liquid Mixtures (CSLM) experiment is a materials science space flight experiment whose purpose is to investigate the kinetics of competitive particle growth within a liquid matrix. During coarsening, small particles shrink by losing atoms to larger particles, causing the larger particles to grow. In this experiment solid particles of tin will grow (coarsen) within a liquid lead-tin eutectic matrix. By conducting this experiment in a microgravity environment, a greater range of solid volume fractions can be studied, and the effects of convection present in terrestrial experiments will be negligible. The flight hardware consists of two separable pieces of equipment, the sample processing unit (SPU) and the electronic control unit (ECU).

Research Description

CSLM-2 samples are processed inside the Sample Processing Unit (SPU), which has a large, cylindrical sample chamber. After a sample is completed, pressurized water is pumped into the chamber to quench the sample, cooling it for removal. This system can quench the sample from 185C (the temperature required to initiate coarsening in tin-lead (Sn-Pb) samples) to 120C in only 6 seconds.

The Electronics Control Unit (ECU) provides power and the software that controls all stages of processing. Parameters and status are displayed on the ECU's LCD screen. The ECU controls the temperature inside the SPU sample chamber and monitors and records the sample's temperature. The quenching stage can be initiated automatically or controlled manually by the crew. A base plate attaches the SPU and ECU to the Microgravity Science Glovebox (MSG) work volume floor.

Operational Requirements

CSLM-2 will be conducted inside the sealed MSG work volume. The crew must load and initiate each run. Quenching can be initiated manually. Data captured by the ECU is transferred to the MSG laptop for storage and downloading to the ground-based researchers. The samples are a mixture consisting of Sn (tin)-rich particles in a Pb-Sn liquid, a mixture that has a low sintering temperature and a high coarsening rate, making it perfect for studying Ostwald ripening.

Space Applications

In any mixture that contains particles of different sizes, the large particles tend to grow while the smaller particles shrink in a process called coarsening. Tiny oil droplets coalescing into a large blob are one illustration, but the process occurs in solids as well. Coarsening occurs on Earth during the processing of any metal alloy and thus the coarsening process affects products from dental fillings to turbine blades. Since the properties of an alloy are linked to the size of the particles within the solid, coarsening can be used to strengthen materials. This is the case with the majority of aluminum alloys used commercially today. Conversely, if the coarsening process proceeds too long the material can weaken. This occurs in jet turbine blades and is one of the reasons why turbine blades must be replaced after a certain number of hours of service. Thus developing accurate models of the coarsening process is central to creating a wide range of new materials from those used in automobiles to those used in space applications. Solid-liquid systems are ideal systems to study this coarsening process. However, gravity can induce particle sedimentation and thus hamper the studies of coarsening in these mixtures on Earth. The microgravity environment of the Space Station allows scientists to study the process of coarsening with reduced interference from the sedimentation that occurs on Earth.

Earth Applications

On Earth, materials that contain pores created and trapped during solidification degrade properties and cause a distinct weakening in the overall structure of the cast product. Determining what causes these problems will lead to the development of improved manufacturing processes for materials.

Previous Missions

CSLM-1, a precursor to CSLM-2, was conducted on STS-83 and STS-94. CSLM-2 was conducted during ISS Increment 7

CSLM-2 operated 5 SPU's on ISS during Increment 16 in December 2007.  CSLM-2 operated 3 SPU's on ISS during Increment 17 in April 2008.

Future Missions

The CSLM-2 SPU's that were operated on the ISS during Increment 16 and Increment 17 have been returned to earth on the Shuttle.  The CSLM-2 Principal Investigator is currently analyzing the samples from the SPU's returned.