Weightless experiments to probe universality of fluid critical behavior

by on 22 August 2016in Physical Sciences No comment

Near the critical point of fluids, critical opalescence results in light attenuation, or turbidity increase, that can be used to probe the universality of critical behavior. Turbidity measurements in SF6 under weightlessness conditions on board the International Space Station are performed to appraise such behavior in terms of both temperature and density distances from the critical point. Data are obtained in a temperature range, far (1 K) from and extremely close (a few muK) to the phase transition, unattainable from previous experiments on Earth. Data are analyzed with renormalization-group matching classical-to-critical crossover models of the universal equation of state. It results that the data in the unexplored region, which is a minute deviant from the critical density value, still show adverse effects for testing the true asymptotic nature of the critical point phenomena.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/26172640

Growth of InxGa1−xSb alloy semiconductor at the International Space Station (ISS) and comparison with terrestrial experiments

by on 22 August 2016in Physical Sciences No comment

BACKGROUND: InxGa1 − xSb is an important material that has tunable properties in the infrared (IR) region and is suitable for IR-device applications. Since the quality of crystals relies on growth conditions, the growth process of alloy semiconductors can be examined better under microgravity (μG) conditions where convection is suppressed.;AIMS: To investigate the dissolution and growth process of InxGa1 − xSb alloy semiconductors via a sandwiched structure of GaSb (seed)/InSb/GaSb(feed) under normal and μG conditions.;METHODS: InxGa1 − xSb crystals were grown at the International Space Station (ISS) under μG conditions, and a similar experiment was conducted under terrestrial conditions (1G) using the vertical gradient freezing (VGF) method. The grown crystals were cut along the growth direction and its growth properties were studied. The indium composition and growth rate of grown crystals were calculated.;RESULTS: The shape of the growth interface was nearly flat under μG, whereas under 1G, it was highly concave with the initial seed interface being nearly flat and having facets at the peripheries. The quality of the μG crystals was better than that of the 1G samples, as the etch pit density was low in the μG sample. The growth rate was higher under μG compared with 1G. Moreover, the growth started at the peripheries under 1G, whereas it started throughout the seed interface under μG.;CONCLUSIONS: Kinetics played a dominant role under 1G. The suppressed convection under μG affected the dissolution and growth process of the InxGa1 − xSb alloy semiconductor.

Related URLs:
http://www.nature.com/articles/npjmgrav201511

Contribution to the benchmark for ternary mixtures: Measurement of diffusion and Soret coefficients in 1,2,3,4-tetrahydronaphthalene, isobutylbenzene, and dodecane onboard the ISS

by on 22 August 2016in Physical Sciences No comment

The paper is devoted to processing the data of DCMIX 1 space experiment. In this experiment, the Optical digital interferometry was used to measure the diffusion and Soret coefficients in the ternary mixture of 1,2,3,4-tetrahydronaphthalene, isobutylbenzene and n-dodecane at mass fractions of 0.8/0.1/0.1 and at 25 degrees C. The raw interferometric images were processed to obtain the temporal and spatial evolution of refractive indices for two laser beams of different wavelengths. The method for extracting the diffusion and thermal diffusion coefficients originally developed for optical beam deflection was extended to optical digital interferometry allowing for the spatial variation of refractive index along the diffusion path. The method was validated and applied to processing the data for Soret and diffusion steps in 5 experimental runs. The obtained results for the Soret coefficients and one of the eigenvalues of diffusion matrix showed acceptable agreement within each step. The second eigenvalue was not determined with sufficient accuracy.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/25916235

Complex Plasma Research under Microgravity Conditions: PK-3 Plus Laboratory on the International Space Station

by on 22 August 2016in Earth Science and Remote Sensing, Physical Sciences

Complex (dusty) plasmas are composed of weakly ionised gas and charged microparticles and represent the plasma state of soft matter. Due to the ”heavy” component — the microparticles — and the low density of the surrounding medium, the rarefied gas and plasma, it is necessary to perform experiments under microgravity conditions to cover a broad range of experimental parameters which are not available on ground. The investiga- tions have been performed onboard the International Space Station (ISS) with the help of the ”Plasma Crystal-3 Plus” (PK-3 Plus) laboratory. It was perfectly suited for the formation of large stable liquid and crystalline sys- tems and provided interesting insights into processes like crystallisation and melting, laning in binary mixtures, electrorheological effects due to ac electric fields and projectile interaction with a strongly coupled complex plasma cloud.

Related URLs:
http://onlinelibrary.wiley.com/store/10.1002/ctpp.201500102/asset/253_ftp.pdf;jsessionid=DEAB8F0A50B92611C7E8452240AC9A9A.f04t01?v=1&t=iqco4j6s&s=0c979d5aab3acebedef378f599c08687d05a8c9a

Experimental Observations of Cool-Flame Supported Binary- Droplet Arrays Combustion in Microgravity

by on 22 August 2016in Physical Sciences No comment

Recent droplet combustion experiments conducted on board the International Space Station (ISS) showed that large, isolated n-alkane droplets can burn quasi-steadily following radiative extinction, supported by cool-flame chemistry in the Negative Temperature Coefficient (NTC) region. In this study we report preliminary experimental results from the ongoing binary- droplet arrays experiments. For the first time, it is shown that quasi-steady combustion of cool flames can be supported by binary-droplet arrays. Under some conditions binary droplets support cool flames when a single droplet of similar size burns to completion with hot flame. The large, merged hot flame of the binary-array leads to the necessary thermal and species fields that can transition to cool flame combustion following radiative extinction, unlike the single droplet in that ambient environment. These observations may have important implications with regard to spray combustion.

Related URLs:
https://www.researchgate.net/publication/277710856_Experimental_Observations_of_Cool-Flame_Supported_Binary-Droplet_Arrays_Combustion_in_Microgravity

Analysis of a resonance liquid bridge oscillation on board of the International Space Station

by on 22 August 2016in Physical Sciences No comment

We study the singular event which took place when conducting an experiment with a liquid bridge aboard the International Space Station. The liquid bridge vibrated unexpectedly for several tens of seconds with an oscillation amplitude larger than 15% of its radius. At first glance, the analysis of the mass force measured by the accelerometer during the oscillation did not show any significant perturbation. However, our study reveals the existence of two small-amplitude vibrations of the experimental setup with practically the resonance frequency of the first lateral mode. These vibrations occurred a few tens of seconds before the liquid bridge oscillation reached its maximum amplitude, produced a mass force with a magnitude of the order of 10−5g. The numerical integration of the non-linear Navier–Stokes equations reproduces remarkably well the free surface oscillations measured in the experiments. It allows us to reconstruct the three-dimensional liquid bridge motion which took place in the experiment. The present study illustrates the sensitivity of liquid bridges in a microgravity environment, where tiny perturbations may produce significant vibrations which survive over long periods of time.

Related URLs:
https://www.researchgate.net/publication/295847814_Analysis_of_a_resonance_liquid_bridge_oscillation_on_board_of_the_International_Space_Station

Sodium chloride crystallization from thin liquid sheets, thick layers, and sessile drops in microgravity

by on 22 August 2016in Physical Sciences No comment

Crystallization from aqueous sodium chloride solutions as thin liquid sheets, 0.2–0.7 mm thick, with two free surfaces supported by a wire frame, thick liquid layers, 4–6 mm thick, with two free surfaces supported by metal frame, and hemispherical sessile drops, 20–32 mm diameter, supported by a flat polycarbonate surface or an initially flat gelatin film, were carried out under microgravity on the International Space Station (ISS). Different crystal morphologies resulted based on the fluid geometry: tabular hoppers, hopper cubes, circular [111]-oriented crystals, and dendrites. The addition of polyethylene glycol (PEG-3350) inhibited the hopper growth resulting in flat-faced surfaces. In sessile drops, 1–4 mm tabular hopper crystals formed on the free surface and moved to the fixed contact line at the support (polycarbonate or gelatin) self-assembling into a shell. Ring formation created by sessile drop evaporation to dryness was observed but with crystals 100 times larger than particles in terrestrially formed coffee rings. No hopper pyramids formed. By choosing solution geometries offered by microgravity, we found it was possible to selectively grow crystals of preferred morphologies.

Related URLs:
http://www.sciencedirect.com/science/article/pii/S0022024815004911

Characterization of sodium chloride crystals grown in microgravity

by on 22 August 2016in Physical Sciences No comment

NaCl crystals grown by the evaporation of an aqueous salt solution in microgravity on the International Space Station (ISS) were characterized and compared to salt crystals grown on earth. NaCl crystallized as thin wafers in a supersaturated film of 200–700 μm thickness and 50 mm diameter, or as hopper cubes in 10 mm diameter supersaturated spheres. Neutron diffraction shows no change in crystal structure and in cell parameters compared to earth-grown crystals. However, the morphology can be different, frequently showing circular, disk-like shapes of single crystals with 〈1 1 1〉 perpendicular to the disks, an unusual morphology for salt crystals. In contrast to the growth on earth the lateral faces of the microgravity tabular hopper crystals are symmetrical because they are free floating during the crystallization process. Hopper cubes were produced without the need to suspend the growing crystals by an ongoing stirring. “Fleur de Sel” is shown as an example of two-dimensional growth of salt on earth and compared to the space grown crystals. It is shown that in microgravity conditions brine fluid inclusions form within the salt crystals.

Related URLs:
http://www.sciencedirect.com/science/article/pii/S0022024811003575

Correction of the equilibrium temperature caused by slight evaporation of water in protein crystal growth cells during long-term space experiments at International Space Station

by on 22 August 2016in Biology & Biotechnology, Physical Sciences

The normal growth rates of the {110} faces of tetragonal hen egg-white lysozyme crystals, R, were measured as a function of the supersaturation sigma parameter using a reflection type interferometer under muG at the International Space Station (NanoStep Project). Since water slightly evaporated from in situ observation cells during a long-term space station experiment for several months, equilibrium temperature T(e) changed, and the actual sigma, however, significantly increased mainly due to the increase in salt concentration C(s). To correct sigma, the actual C(s) and protein concentration C(p), which correctly represent the measured T(e) value in space, were first calculated. Second, a new solubility curve with the corrected C(s) was plotted. Finally, the revised sigma was obtained from the new solubility curve. This correction method successfully revealed that the 2.8% water was evaporated from the solution, leading to 2.8% increase in the C(s) and C(p) of the solution.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/26329200

Contribution to the benchmark for ternary mixtures: Measurement of diffusion and Soret coefficients of ternary system tetrahydronaphtalene-isobutylbenzene-n-dodecane with mass fractions 80-10-10 at 25 degrees C

by on 22 August 2016in Physical Sciences No comment

This paper provides the molecular diffusion and Soret coefficients of the ternary system 1,2,3,4-tetrahydronaphtalene, isobutylbenzene, n -dodecane system at mass fractions 0.8-0.1-0.1 and temperature 25 ( degrees )C for implementation into the benchmark presented in this topical issue. The Soret coefficients are determined by digital interferometry using the data of DSC-DCMIX microgravity experiment. The method used takes into account the influence of the thermal field on the Soret separations and the selection of the image processing techniques results in reproducible Soret coefficients.The diffusion coefficients are obtained by the Open Ended Capillary technique The fitting of the data collected through a set of two complementary experimental runs allows retrieving the four Fickian diffusion coefficients.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/25916231