Pore-size expansion of hexagonal-structured assembly of nanocrystalline titania (anatase) combined with cetyltrimethyammonium bromide (CH3(CH2)15N+(CH3)3Br−, CTAB) (named as Hex-ncTiO2/CTAB Nanoskeleton) was achieved with the aid of cosolvent organic molecules (COMs). The pore-size expanded Hex-ncTiO2/CTAB Nanoskeleton was prepared through the sol–gel reaction of titanium oxysulfate sulfuric acid hydrate (TiOSO4·xH2SO4·xH2O, TiOSAH) in an aqueous solution initiated by CTAB swollen micelles pre-prepared with the addition of COMs into aqueous CTAB micellar solutions at 60 °C (the product was named as Hex-ncTiO2/CTAB/COM Nanoskeleton). Long-chain alcohol (1-hexadecanol, C16OH), normal alkane (n-decane, C10) and benzene derivatives (benzene, Bz; 1,3,5-trimethylbenzene, TMB; 1,3,5-triethylbenzene, TEB; 1,3,5-triisopropylbenzene, TiPB) were used as COMs to evaluate the effects of COM solubilization site in CTAB micelles and COM molecular size on the pore-size expansion of the Hex-ncTiO2/CTAB/COM Nanoskeleton. We found that 1,3,5-trimethylbenzene (TMB) and 1,3,5-triethylbenzene (TEB) act as effective COMs for pore-size expansion of the Hex-ncTiO2/CTAB/COM Nanoskeleton in aqueous media. Pore sizes (average diameters) of the Hex-ncTiO2/CTAB/TMB Nanoskeleton and Hex-ncTiO2/CTAB/TEB Nanoskeleton were enlarged up to 4.2 nm and 4.3 nm, respectively, while pore size (average diameter) of the Hex-ncTiO2/CTAB Nanoskeleton prepared in the absence of any COMs was 2.9 nm. We also revealed that thermal stability of the Hex-ncTiO2/CTAB/TMB Nanoskeleton became higher than that of Hex-ncTiO2/CTAB Nanoskeleton. The hexagonally pore-structure of the Hex-ncTiO2/CTAB/TMB Nanoskeleton was retained up to 400 °C, while the hexagonally pore-structure of the Hex-ncTiO2/CTAB Nanoskeleton was kept up to 300 °C.
Research Containing: Spaceflight
Study of radiation conditions onboard the International space station by means of the Liulin-5 dosimeter
For estimating radiation risk in space flights it is necessary to determine radiation dose obtained by critical organs of a human body. For this purpose the experiments with human body models are carried out onboard spacecraft. These models represent phantoms equipped with passive and active radiation detectors which measure dose distributions at places of location of critical organs. The dosimetric Liulin-5 telescope is manufactured with using three silicon detectors for studying radiation conditions in the spherical tissue-equivalent phantom on the Russian segment of the International space station (ISS). The purpose of the experiment with Liulin-5 instrument is to study dynamics of the dose rate and particle flux in the phantom, as well as variations of radiation conditions on the ISS over long time intervals depending on a phase of the solar activity cycle, orbital parameters, and presence of solar energetic particles. The Liulin-5 dosimeter measures simultaneously the dose rate and fluxes of charged particles at three depths in the radial channel of the phantom, as well as the linear energy transfer. The paper presents the results of measurements of dose rate and particle fluxes caused by various radiation field components on the ISS during the period from June 2007 till December 2009.
In this paper, we report on the SHS reaction 3NiO + 5Al → 3NiAl + Al2O3 carried out aboard International Space Station (Flight Mission 18) with special emphasis on the effect of the composition of reaction products on the composition of coatings formed on a Ti substrate.
We show that the dynamics of large fractal colloid aggregates are well described by a combination of translational and rotational diffusion and internal elastic fluctuations, allowing both the aggregate size and internal elasticity to be determined by dynamic light scattering. The comparison of results obtained in microgravity and on Earth demonstrates that cluster growth is limited by gravity-induced restructuring. In the absence of gravity, thermal fluctuations ultimately inhibit fractal growth and set the fundamental limitation to the lowest volume fraction which will gel.
Colloidal silica gels are shown to stiffen with time, as demonstrated by both dynamic light scattering and bulk rheological measurements. Their elastic moduli increase as a power law with time, independent of particle volume fraction; however, static light scattering indicates that there are no large-scale structural changes. We propose that increases in local elasticity arising from bonding between neighboring colloidal particles can account for the strengthening of the network, while preserving network structure.
Interim Results from the Capillary Flow Experiment Aboard ISS: The Moving Contact Line Boundary Condition
This paper highlight the in-flight operations of the Capillary Flow Experiment Contact Line experiments (2 each) performed aboard the International Space Station (ISS) during the period between Increment 9 ad 13 (8/2004-9/2006). The CFE-CL vessels are simple fluid interface experiments that probe the uncertain impact of the boundary condition at the contact line – the region where liquid, gas, and solid meet. This region controls perhaps the most significant static and dynamic characteristics of the large length scale capillary phenomena critical to most multiphase fluid management systems aboard spacecraft. Difference in fluid behavior of nearly identical statics interfaces to nearly identical disturbances are attributed to differences in fluid physics in the vicinity of the contact line. The CFE-CL experiments are conducted on five occasions by ISS Astronauts M. Fincke, W. McArthur, and J. Williams. The number of tests performed including additional science experiments is made possible by various centrifuge techniques employed by the astronauts permitting the re-use of the once-wetted container. Several of these ‘extra science’ experiments are briefly described herein. Intermittent real-time video and audio downlink, continuous communication with the ground crews at NASA JSC, MSGFC and GRC, and the clear and entreating commentary of the crew made the conduct of the tests on ISS an enjoyable, laboratory-like experience for the science on the ground. The flight tapes from the onboard cameras have been results to Earth (name flight) and are expected to be digitized, reduced and made publically available in the near future. A concurrent blind numerical analysis is underway to predict the experiments result using a generally accepted CFD-tool with specific contact line boundary conditions.
This paper serves as a first presentation of quantitative data reduced from the Capillary Flow Contact Line Experiments recently completed aboard the International Space Station during Expeditions 9-16, 8/2004-11/2007. The simple fluid interface experiments probe the uncertain impact of the boundary condition at the contact line—the region where liquid, gas, and solid meet. This region controls perhaps the most significant static and dynamic characteristics of the large length scale capillary phenomena critical to most multiphase fluids management systems aboard spacecraft. Differences in fluid behavior of nearly identical static interfaces to nearly identical perturbations are attributed primarily to differences in fluid physics in the vicinity of the contact line. Free and pinned contact lines, large and small contact angles, and linear and nonlinear perturbations are tested for a variety of perturba- tion types (i.e. axial, slosh, and other modes) to right circular cylinders. The video and digi- tized datasets are to be made publicly available for model benchmarking. In parallel with the experimental effort, blind numerical predictions of the dynamic interface response to the experimentally applied input perturbations are offered as a demonstration of current capa- bilities to predict such phenomena. The agreement and lack of agreement between the experiments and numerics is our best guide to improve and/or verify current analytical methods to predict such phenomena critical to spacecraft fluid systems design.
Everybody is familiar with the action of gravity on a fluid where density gradients are present due to heating or compositional difference. Due to buoyancy, the denser portions sink to the bottom of the container, pushing away the lighter ones. As a result, convection sets in, transporting heat and mass. In weightlessness conditions, this driving force is absent but inertia exists as the tendency of a body to resist acceleration. When a container filled with liquid is subjected to high frequency vibrations, the fluid is not able to react due to inertia and this may create a flow. If the density is uniform, then the fluid moves as a solid body. However, when density gradient is present, also inertia will not be uniform, resulting in convective motion. Obviously, there is analogy between gravity-induced and inertia-driven convection, as a result of the Einstein equivalence principle, although the second one is almost unknown. What would be the impact of vibration on dispersion by molecular diffusion and heat transfer without buoyancy?
We investigate the phase behavior of mixtures of colloids and polymers near their critical point in a microgravity environment. Astronauts onboard the International Space Station (ISS) are using photography to record the rate of phase separation of six samples near the liquid-gas critical point. These photographs are taken both by an automated photograpy system (based on EarthKAM hardware and software) and manually by the astronuats who have setup the experiment. We have obtained high-quality photographs of processes that are not observable on Earth, since both sedimentation and convection are negligible onboard the International Space Station. Interestingly, we observe that gravity does not affect the onset of phase separation in colloid-polymer mixtures near the liquid-gas critical point: samples which phase separate on earth also do so onboard the ISS. However, the rates at which this phase separation occurs is affected by several orders of magnitude by gravity, suggesting future avenues for exploration. The understanding of this system is important for both practical earth-bound applications, as well as the development of products and materials that are stable and function over long periods of time in a low-gravity environment. Thus, our results may assist the long-term spaceflight required for proposed exploration missions to the moon and to Mars.
Variation of absorbed doses onboard of ISS Russian Service Module as measured with passive detectors
Cosmic radiation represents possible risk for the astronauts. For estimation of the radiation onboard the spacecraft in space flights, it is necessary to obtain the data on dose distribution in real space flight conditions. This contribution deals with the study of absorbed dose and dose equivalent due to space radiation in different compartments of the International Space Station (ISS) using passive detectors. Luminescent detectors (LD) and CR-39 plastic nuclear track detectors (PNTD) were exposed onboard of Russian Service Module on ISS from August 2004 to October 2005 (425 days); they were placed at SPD boxes and positioned at 6 various locations inside the Russian Service Module. LD were used to measure absorbed doses, particularly from low-LET particles and photons, PNTDs were used to measure the spectra of linear energy transfer (LET), absorbed dose, and dose equivalents from particles with LET∞H2O >5 keV/μm. Results from both types of detectors (LD and PNTD) were then combined together to obtain total values of absorbed doses and dose equivalents. Distribution of absorbed doses and dose equivalents measured with passive detectors, as well as LET spectra of registered particle fluxes, are presented as the function of position of SPD boxes (shielding thickness). Also the influence of position of detectors inside the SPD boxes (top and bottom wall) will be discussed. The dose characteristics depend on the location inside the Service Module; their variation has been observed to be up to factor of almost 2.