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At least 829 records · Page 46

All sources NASA NTRS DOE OSTI

DOE OSTI2023

Synthesis and morphological characterization of linear and miktoarm star poly(solketal methacrylate)- block -polystyrene copolymers

The synthesis, molecular characterization, and morphological evaluation of AB n, (n = 2,3) miktoarm star block copolymers consisting of poly(glycerol monomethacrylate) (PGMA) and polystyrene (PS) with varying molecular weights and compositions is described. The system is known to demonstrate a remarkably high Flory-Huggins interaction parameter. The corresponding linear diblock copolymer analogues, were synthesized as well, and comparisons with regard to feature dimensions and morphologies are provided. Well-ordered nanostructures of various morphologies were formed with domain spacing as low as 7.2 nm. Different morphologies were attained by some of the topological isomers indicating that in miktoarm star block copolymers the phase boundaries were strongly shifted. Additionally, a triblock ABA analogue was studied to investigate the effect of triblock copolymer conformations. Noteworthy is that for copolymers with different macromolecular architecture leading to similar morphology; different domain spacings were obtained. The synthesis of all the samples was carried out by high-vacuum anionic polymerization techniques. Molecular characterization with Size Exclusion Chromatography (SEC) and Proton Nuclear Magnetic Resonance Spectroscopy ( 1 H NMR) confirmed well-defined copolymers obtained. The morphological characterization was accomplished by Small-Angle X-ray Scattering (SAXS). In conclusion, the observations from this study highlight the potential of incorporating macromolecular architecture in the self-assembly of strongly immiscible block copolymers to attain ultra-small nanofeatures with desired morphologies.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Nanoporous Thermosets with Percolating Pores from Block Polymers Chemically Fixed above the Order–Disorder Transition

A lamellar diblock polymer combining a cross-linkable segment with a chemically etchable segment was cross-linked above its order–disorder temperature (TODT) to kinetically trap the morphology associated with the fluctuating disordered state. After removal of the etchable block, evaluation of the resulting porous thermoset allows for an unprecedented experimental characterization of the trapped disordered phase. Through a combination of small-angle X-ray scattering, nitrogen sorption, scanning electron microscopy, and electron tomography experiments we demonstrate that the nanoporous structure exhibits a narrow pore size distribution and a high surface to volume ratio and is bicontinuous over a large sample area. Together with the processability of the polymeric starting material, the proposed system combines attractive attributes for many advanced applications. In particular, it was used to design new composite membranes for the ultrafiltration of water.

36 MATERIALS SCIENCE↗

DOE OSTI2013

Kinetics of linear domains in LiNbO{sub 3} single crystals polarized by scanning probe microscopy

Growth and decay processes of linear domains in lithium niobate single crystals fabricated utilizing scanning probe microscopy were investigated. It is found that the initial configuration of linear domains is dependent on the fabrication parameters as scan velocity and voltage. The linear domains decay at the part where the domain width is small for two different processes. A comparison of critical stable domain size between dot and linear domains was carried out. The critical linear domain width is 0.7 times as large as the critical diameter of dot domain at the same sample thickness due to their smaller surface energy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

High resolution coherent diffractive imaging with a table-top extreme ultraviolet source

We demonstrate a resolution of 45 nm with a sample size down to 3 μm × 3 μm is achieved in a short exposure time of 2 s, from the diffraction pattern generated by a table-top high harmonic source at around 30 nm. By using a narrow-bandwidth focusing mirror, the diffraction pattern's quality is improved and the required exposure time is significantly reduced. In order to obtain a high quality of the reconstructed image, the ratio of the beam size to the sample size and the curvature of the focused beam need to be considered in the reconstruction process. This new experimental scheme is very promising for imaging sub-10 nm scale objects with a table-top source based on a small inexpensive femtosecond laser system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

PROBING THE PHYSICAL CONDITIONS OF ATOMIC GAS AT HIGH REDSHIFT

A new method is used to measure the physical conditions of the gas in damped Lyα systems (DLAs). Using high-resolution absorption spectra of a sample of 80 DLAs, we are able to measure the ratio of the upper and lower fine-structure levels of the ground state of C{sup +} and Si{sup +}. These ratios are determined solely by the physical conditions of the gas. We explore the allowed physical parameter space using a Monte Carlo Markov chain method to constrain simultaneously the temperature, neutral hydrogen density, and electron density of each DLA. The results indicate that at least 5% of all DLAs have the bulk of their gas in a dense, cold phase with typical densities of ∼100 cm{sup –3} and temperatures below 500 K. We further find that the typical pressure of DLAs in our sample is log (P/k{sub B} ) = 3.4 (K cm{sup –3}), which is comparable to the pressure of the local interstellar medium (ISM), and that the components containing the bulk of the neutral gas can be quite small with absorption sizes as small as a few parsecs. We show that the majority of the systems are consistent with having densities significantly higher than expected for a purely canonical warm neutral medium, indicating that significant quantities of dense gas (i.e., n {sub H} > 0.1 cm{sup –3}) are required to match observations. Finally, we identify eight systems with positive detections of Si II*. These systems have pressures (P/k{sub B} ) in excess of 20,000 K cm{sup –3}, which suggest that these systems tag a highly turbulent ISM in young, star-forming galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

Complex modeling for the quantification of nanoscale disorder using genetic algorithms, density functional theory and line-profile analysis

Abstract not provided

Koch, Robert J.↗

DOE OSTI2013

Preparation and Magnetic Properties of Sub-Micrometer Sized Sm-Co Powders Prepared From Nanostructured Precursor Oxides

Submicrometer-sized Sm-Co powders have been prepared by the calciothermic reduction and subsequent solid-state diffusion of a nanostructured Sm-Co-O/Co-O precursor. The Sm and Co containing precursor was prepared by an autocombustion process. X-ray diffraction identified the product as a mixture of SmCoO3 and Co-3 O-4. This powder was mixed in a 1:2 mass ratio with CaO (which served as a thermal ballast and aggregation inhibitor) and milled to reduce the particle size below 1 micrometer. Ca metal was added to the mixed powder in amounts between 2 and 6 times those required to reduce the Sm and Co oxides, and sealed in Nb tubes for heat treatment at 900 degrees C for various lengths of time. After cooling to room temperature, metallic Sm-Co particles were isolated from the undesired reaction products by a series of washing steps in acetic acid and ethyl alcohol. The Sm-Co particles were characterized by scanning electron microscopy, vibrating sample magnetometry, and x-ray diffraction. These measurements demonstrated that smaller particle sizes were associated with shorter reaction times and smaller quantities of reducing agent. The formation of hard SmCo5 was systematically associated with either long diffusion times with small amounts of reducing agent, or short diffusion times with large amounts of reducing agent.

Kelly, BG↗

DOE OSTI2016

Influence of RF excitation during pulsed laser deposition in oxygen atmosphere on the structural properties and luminescence of nanocrystalline ZnO:Al thin films

Thin ZnO:Al layers were deposited by pulsed laser deposition in vacuum and in oxygen atmosphere at gas pressures between 10 and 70 Pa and by applying radio-frequency (RF) plasma. Grazing incidence small angle x-ray scattering and grazing incidence x-ray diffraction (GIXRD) data showed that an increase in the oxygen pressure leads to an increase in the roughness, a decrease in the sample density, and changes in the size distribution of nanovoids. The nanocrystal sizes estimated from GIXRD were around 20 nm, while the sizes of the nanovoids increased from 1 to 2 nm with the oxygen pressure. The RF plasma mainly influenced the nanostructural properties and point defects dynamics. The photoluminescence consisted of three contributions, ultraviolet (UV), blue emission due to Zn vacancies, and red emission, which are related to an excess of oxygen. The RF excitation lowered the defect level related to blue emission and narrowed the UV luminescence peak, which indicates an improvement of the structural ordering. The observed influence of the deposition conditions on the film properties is discussed as a consequence of two main effects: the variation of the energy transfer from the laser plume to the growing film and changes in the growth chemistry.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2020

A new mechanism for void-cascade interaction from nondestructive depth-resolved atomic-scale measurements of ion irradiation–induced defects in Fe

The nondestructive investigation of single vacancies and vacancy clusters in ion-irradiated samples requires a depth-resolved probe with atomic sensitivity to defects. The recent development of short-pulsed positron beams provides such a probe. Here, we combine depth-resolved Doppler broadening and positron annihilation lifetime spectroscopies to identify vacancy clusters in ion-irradiated Fe and measure their density as a function of depth. Despite large concentrations of dislocations and voids in the pristine samples, positron annihilation measurements uncovered the structure of vacancy clusters and the change in their size and density with irradiation dose. When combined with transmission electron microscopy measurements, the study demonstrates an association between the increase in the density of small vacancy clusters with irradiation and a remarkable reduction in the size of large voids. This, previously unknown, mechanism for the interaction of cascade damage with voids in ion-irradiated materials is a consequence of the high porosity of the initial microstructure.

36 MATERIALS SCIENCE↗

NASA NTRS1990

Space Station Payload Adaptation System

The development and design of a system of containers for the efficient integration of Space Station payloads is described called the Space Station Payload Adaptation System (SSPAS). The SSPAS was developed to address the incorporation of multiple payloads, the use of a small payload carrier, large numbers of samples, and on-orbit servicing. SSPAS subsystems such as the Spacelab rack are modular and designed for integration into the 'Quick Is Beautiful' (QIB) facility. The QIB is designed to provide access to space for small- and medium-sized microgravity research projects and proof-of-concept investigations. The power-distribution and heat-rejection potential of the QIB are described, and an improved experiment-apparatus container is proposed. The SSPAS rack-mounting and container concepts are concluded to make up an efficent system that can effectively exploit the R&D potential of the Space Station.

Taylor, Kenneth R.↗

NASA NTRS2000

Subsurface Science from a Penetrator

Much of what we know about the geologic history and present state of Mars is based upon interpretations of data collected from the immediate surface. Unweathered soil samples covered by dust and sand sized particles may provide clues about the role of water and the biological history of the planet. The use of drills and scoops to obtain such samples for lander-based instruments implies the development of relatively large, sophisticated platforms. Small (several kilograms), scientifically focussed penetrators can carry instruments to the subsurface and should be included in the Mars exploration strategy.

Yen, Albert S.↗

NASA NTRS2006

CFDP Performance over Weather-Dependent Ka-Band Channel

This study presents an analysis of the delay performance of the CCSDS File Delivery Protocol (CFDP) over weather-dependent Ka-band channel. The Ka-band channel condition is determined by the strength of the atmospheric noise temperature, which is weather dependent. Noise temperature data collected from the Deep Space Network (DSN) Madrid site is used to characterize the correlations between good and bad channel states in a two-state Markov model. Specifically, the probability distribution of file delivery latency using the CFDP deferred Negative Acknowledgement (NAK) mode is derived and quantified. Deep space communication scenarios with different file sizes and bit error rates (BERs) are studied and compared. Furthermore, we also examine the sensitivity of our analysis with respect to different data sampling methods. Our analysis shows that while the weather-dependent channel only results in fairly small increases in the average number of CFDP retransmissions required, the maximum number of transmissions required to complete 99 percentile, on the other hand, is significantly larger for the weather-dependent channel due to the significant correlation of poor weather states.

weather↗

NASA NTRS2006

CFDP Performance over Weather-dependent Ka-band Channel

deep space communications↗

DOE OSTI2013

EFFECTS OF SIZE AND GEOMETRY ON THE EQUIBIAXIAL FLEXURAL TEST OF FINE GRAINED NUCLEAR GRAPHITE

Reduction of specimen size is an essential requirement for neutron irradiation effect studies of materials since space in nuclear reactors for those studies are often very limited and costly. Reducing the specimen size can dramatically reduce the cost of these studies, the irradiation exposure to personnel involved in post irradiation examination and the volume of radioactive waste. In this study, 4 specimen sizes were systematically varied to examine the size effect on the equibiaxial flexure test of fine grain nuclear graphite in non-irradiated conditions at room temperature. A statistically significant sample population of 30 was used for each specimen geometry or dimension. The results showed that the round shaped samples followed weibull distribution with Weibull modulus of 25 to 35. The average strength followed the trend of the weakest link theory. The 2 sizes of square shaped samples had Weibull modulus of 29 and 40. Data from round and square samples agree with others reasonably and collectively follow the Weibull scaling theory. It is concluded that the equibiaxial flexural test using adequate population of small specimens provides useful and reliable information on the statistical strength properties for fine-grained nuclear graphite materials.

Shih, Chunghao↗

DOE OSTI2018

Effect of Rare Earth Ionic Radii on Structural, Electric, Magnetic and Thermoelectric Properties of REMnO{sub 3} (RE = Dy, Gd, Eu and Sm) Manganites

In this communication, we present a systematic investigation on structural, electric, magnetic and thermoelectric power properties of REMnO{sub 3} (RE = Dy, Gd, Eu and Sm) manganites which were prepared using solid-state reaction route. The samples exhibit orthorhombic crystal structure with Pbnm space group. Rietveld analysis of x-ray diffraction (XRD) data shows that the unit cell volume increases with increase in ionic radii of the rare earth ion, r{sub RE}. The particle size was calculated from the scanning electron microscope (SEM) images. The estimated particle size is observed to decrease with increasing ionic radii of the rare earth ions. All samples exhibit insulating behaviour and display immeasurably high resistivity at low temperatures. Magnetization studies indicate that the samples display a transition in the low temperature region. Magnetization data also reveals that antiferromagnetic behaviour is observed for all samples. Thermoelectric power results show that large thermoelectric power is seen for these manganites. Thermoelectric power of high-temperature region was successfully analysed using small polaron hopping (SPH) model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Damage Tolerance Assessment of Laser Clad Repairs of Coarse Grain Ti-6Al-4V

Background: Laser cladding offers a promising approach to repairing aviation components, with the ability to restore the geometric shape and the static and fatigue strength. Objective: The damage tolerance of a coarse grain Ti-6Al-4 V material is assessed via three sets of samples: (i) baseline, (ii) laser clad repaired, and (iii) laser cladding followed by heat treatment. Method: The specimens were subjected to fatigue loading using a marker band technique, in which cracks initiated from pre-defined laser slots and the small crack growth rates were measured by quantitative fractography. Additional characterization was performed on these samples, including hardness measurements, microstructure analysis, and multimodal residual stress analyses. Results: The region of the specimen undergoing laser cladding exhibited higher hardness values and a compressive residual stress, based on the slitting method. The samples subjected to heat treatment after cladding displayed negligible differences in grain size and minimal residual stress relaxation. Conclusions: The results demonstrated significant variability, with data demonstrating that cracks in the laser clad region (exhibiting the largest compressive residual stress) grew faster than cracks in the substrate region of the sample or in the baseline cases. Finally, these counterintuitive results are rationalized with additional analyses from synchrotron-based energy dispersive X-ray diffraction and high energy X-ray diffraction, demonstrating significant spatial variability in the residual elastic strains in the millimeter-sized prior β grains within the material.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Effect of post annealing on microstructure and mechanical properties in Ni-free N-containing ODS steel

The precipitation behaviour of Y2O3 and MnO nanoparticles after isothermal treatment, in a Ni-free N-containing oxide dispersion strengthened (ODS) steel was studied by wide-angle X-ray scattering (WAXS), ultra-small-angle and small-angle X-ray scattering (USAXS/SAXS), small angle neutron scattering (SANS) and scanning transmission electron microscopy (STEM). Mechanical properties were investigated via tensile and micro-hardness testing. Additional precipitation occurred during annealing, in addition to the precipitates formed during sintering. The highest volume distribution of Y2O3, with average size of 6 nm, was determined by alloy contrast variation (ACV) analysis of SAXS and SANS for the sample annealed at 800 °C; this sample shows the highest hardness and ultimate tensile strength. Above that temperature, coarsening of both matrix and precipitates and depletion of nitrogen from matrix degraded the mechanical properties. The very fine nanoparticles and thermally induced dissolution of nitrogen influenced mechanical properties.

alloy contrast variation (ACV)↗

DOE OSTI2017

Quantitative Analysis of the Morphology of {101} and {001} Faceted Anatase TiO 2 Nanocrystals and Its Implication on Photocatalytic Activity

The atomistic structure and morphology (shape and size) of nanomaterials have strong influences on their physical and chemical properties. However, many characterization techniques focus exclusively on one length-scale regime or another when developing quantitative morphology/structural models. In this article, we demonstrate that powder X-ray diffraction and neutron pair distribution function (PDF) can be used to obtain accurate average morphology and atomistic structure of {001} and {101} faceted anatase TiO 2 nanocrystals based on differential evolution refinements using Debye scattering equation calculations. It is also demonstrated that the morphology polydispersity of TiO 2 nanocrystals can be effectively obtained from the diffraction data via a numerical refinement routine. The morphology refinement results are in good agreement with those from transmission electron microscopy and the modeling of small angle neutron scattering data. This method is successfully used to quantify the facet-specified photocatalytic hydrogen evolution activity of anatase TiO 2 nanocrystals with different {001} to {101} ratios. It is found that the sample with an intermediate amount of both {001} and {101} facets shows the best photocatalytic hydrogen evolution reaction (HER) activity. It is expected that the simultaneous structure and morphology refinement technique can be generally used to study the relationship between morphology and functionality of nanomaterials.

36 MATERIALS SCIENCE↗