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At least 1,243 records · Page 69

Dust Spectroscopy and the Nature of Grains

Ground-based, air-borne and space-based, infrared spectra of a wide variety of objects have revealed prominent absorption and emission features due to large molecules and small dust grains. Analysis of this data reveals a highly diverse interstellar and circumstellar grain inventory, including both amorphous materials and highly crystalline compounds (silicates and carbon). This diversity points towards a wide range of physical and chemical birthsites as well as a complex processing of these grains in the interstellar medium. In this talk, I will review the dust inventory contrasting and comparing both the interstellar and circumstellar reservoirs. The focus will be on the processes that play a role in the lifecycle of dust in the interstellar medium.

Tielens, A. G. G. M.↗

Bringing Thunder and Lightning Indoors

Piezoelectric materials convert mechanical energy into electrical energy and electrical energy into mechanical energy. They generate electrical charges in response to mechanical stress and generate mechanical displacement and/or force when subjected to an electric current. Scientists at Langley Research Center have developed a piezoelectric device that is superior in many ways to those that used to be the only ones commercially available. It is tougher, has far greater displacement and greater mechanical load capacity for a comparative voltage operation, can be easily produced at a relatively low cost, and lends itself well to mass production. The NASA-developed piezoelectric device is also unique in that it is more efficient in extracting electrical energy from the mechanical energy that goes in. It works on a simple principle. A thin ceramic piezoelectric wafer is sandwiched between an aluminum sheet and a steel sheet and held together with LaRC-SI, an amorphous thermoplastic adhesive with special properties created by NASA at Langley. The sandwich is heated in an autoclave, and the adhesive melts. When the sandwich cools, the adhesive bonds the parts together into one piezoelectric element. While they cool, the components of the element contract at different rates, since they are made of different materials. This differential shrinkage causes the element to warp in either a convex or concave shape, depending on which way it is oriented. The shrinking of the outside metal layers places the inside piezoelectric ceramic under mechanical stress. If the element is cantilevered by clamping one side and then plucked, it reverberates like a diving board that has just ejected a diver. This way, a small amount of mechanical energy can result in a relatively long period of electrical generation. When the piezoelectric element is used for the creation of electricity, it is called Lightning. This same sandwiched piezoelectric wafer can also convert electrical energy into mechanical energy. Then, it is called Thunder. Electricity goes in, excites the element, and then, mechanical energy in the form of movement is generated.

Source record↗

Optical Spectroscopy of Stardust Samples

The Stardust spacecraft collected dust samples of the Kuiper belt comet 81P Wild-2 in aerogel and returned them to Earth January 15, 2006. Preliminary examination (PE) of the collected dust includes teams focused on mineralogy, chemical composition, isotopic measurements, organic analysis, cratering and spectroscopic properties. The main PE science goals are to provide an initial characterization of the returned samples with an emphasis on the capture process and its effects on the samples, a comparison of Stardust samples to other meteoritic materials, and the abundance of presolar materials in the Stardust samples. The science objectives of the Spectroscopy team are to obtain spectroscopic data on Stardust particles through infrared (IR), UV/Vis and Raman measurements of particles in aerogel, extracted particles, keystones, and microtome thin sections. These data will be used to answer fundamental science questions about the nature of the samples, but will also serve as preliminary mineralogical data to guide follow-on measurements that will be performed in the other preliminary examination teams. The IR characteristics of Stardust particles are measured to determine: 1) the nature of the indigenous 3.4 micron organic feature, is it detected and can it be differentiated/deconvolved from the contaminated aerogel? How does it compare to features observed in interplanetary dust particles (IDPs) and to astronomical measurements of comets and interstellar dust? 2) the shape and fine structure within the 10 micron silicate feature. Overlap with the strong Si-O stretching vibration from the aerogel complicates this analysis, but we hope to determine if the feature is dominated by amorphous silicates such as those observed in IDPs and comets and whether or not crystalline silicates (e.g. olivine, pyroxene, clays) are present, 3) the presence of secondary (alteration) phases. Deep Impact results suggest that IR observations of Stardust particles should be evaluated for the presence of hydrated materials (water bands at 3 and 6 microns) and carbonates (6.8 microns and other resonances) and 4) the detection of crystalline features in the far-IR (20-100 microns) region where crystalline silicates and other minerals have strong bands that can be used both for phase analysis and phase chemistry. It has been demonstrated that these far-IR measurements can be obtained in situ on particles in aerogel keystones.

Keller, Lindsay P.↗

Real-Time Radiographic In-Situ Characterization Of Ply Lift In Composite Aerospace Materials

The problem of ply lifting in composite materials is a significant issue for various aerospace and military applications. A fundamental element in the prevention or mitigation of ply lift is determination of the timing of the ply lifting event during exposure of the composite material to flight conditions. The Marshall Space Flight Center s Nondestructive Evaluation Team developed a real-time radiographic technique for the detection of ply lift in carbon phenolic ablative materials in situ during live firings of subscale test motors in support of NASA s Reusable Solid Rocket Motor program, using amorphous silicon detector panels. The radiographic method has successfully detected ply lifting in seven consecutive carbon phenolic converging cones attached to solid fuel torches, providing the time of ply lift initiation in each test. Post-processing of the radiographic images improved the accuracy of timing measurements and allowed measurement of the ply lifting height as a function of time. Radiographic data correlated well with independent pressure and temperature measurements that indicate the onset of ply lift in the nozzle material.

Beshears, Ronald D.↗

The Selicate Material In Comets

Silicates in comets appear to be a mix of high-temperature crystalline enstatite and forsterite plus glassy or amorphous grains that formed at lower temperatures.

comets Hale-Bopp silicates infrared spectra↗

H2O-Rich Interstellar Grain Mantles: An Equilibrium Picture

Experiments simulating the codeposition of molecular hydrogen and water ice on interstellar grains demonstrate that amorphous water ice at 12 K can incorporate a substantial amount of H2, up to a molar ratio of H2/H2O=0.53.

molecular hydrogen↗

Fluorescent Applications to Crystallization

By covalently modifying a subpopulation, less than or equal to 1%, of a macromolecule with a fluorescent probe, the labeled material will add to a growing crystal as a microheterogeneous growth unit. Labeling procedures can be readily incorporated into the final stages of purification, and tests with model proteins have shown that labeling u to 5 percent of the protein molecules does not affect the X-ray data quality obtained . The presence of the trace fluorescent label gives a number of advantages. Since the label is covalently attached to the protein molecules, it "tracks" the protein s response to the crystallization conditions. The covalently attached probe will concentrate in the crystal relative to the solution, and under fluorescent illumination crystals show up as bright objects against a darker background. Non-protein structures, such as salt crystals, do not show up under fluorescent illumination. Crystals have the highest protein concentration and are readily observed against less bright precipitated phases, which under white light illumination may obscure the crystals. Automated image analysis to find crystals should be greatly facilitated, without having to first define crystallization drop boundaries as the protein or protein structures is all that shows up. Fluorescence intensity is a faster search parameter, whether visually or by automated methods, than looking for crystalline features. Preliminary tests, using model proteins, indicates that we can use high fluorescence intensity regions, in the absence of clear crystalline features or "hits", as a means for determining potential lead conditions. A working hypothesis is that more rapid amorphous precipitation kinetics may overwhelm and trap more slowly formed ordered assemblies, which subsequently show up as regions of brighter fluorescence intensity. Experiments are now being carried out to test this approach using a wider range, of proteins. The trace fluorescently labeled crystals will also emit with sufficient intensity to aid in the automation of crystal alignment using relatively low cost optics, further increasing throughput at synchrotrons.

Pusey, Marc L.↗

Decoding IR Spectra of Cosmic Ices and Organics in the Laboratory

Tremendous strides have been made in our understanding of interstellar material over the past twenty-five years thanks to significant developments in observational IR astronomy and dedicated laboratory experiments. Twenty-five years ago the composition of interstellar dust was largely guessed at. Today the composition of interstellar dust is reasonably well understood. In the diffuse interstellar medium (ISM) the dust population is mainly comprised of small grains of silicates and amorphous carbon. In dark molecular clouds, the birthplace of stars and planets, these cold refractory dust particles are coated with mixed molecular ices whose composition is reasonably well constrained. Lastly, the signature of carbon-rich polycyclic aromatic hydrocarbons (PAHs), shockingly large molecules by early interstellar chemistry standards, is widespread throughout the Universe. This extraordinary progress has been made possible by the close collaboration of laboratory experimentalists and theoreticians with IR astronomers using groundbased, air-borne, and orbiting telescopes.

Allamandola, Louis J.↗

Comet Mineralogy as Inferred from Infrared Spectra of Comets

For most comets, infrared (IR) spectroscopy (remote sensing) is the method through which we diagnose the mineralogy and size distribution of dust in their comae. The shape and contrast of the IR spectral features depend on the particle size: optically active minerals (absorbing of visible and near-IR solar photons) and submicron solid grains or highly porous (> 90% vacuum) grains primarily contribute to the shapes of the observed resonances. Comet mineralogies typically are determined by fitting thermal emission models of ensembles of discrete mineral grains to observed IR spectral energy distributions. The absorptivities (Q-abs) and scattering efficiencies (Q-scat) of the discrete mineral grains are computed using Mie scattering, Maxwell-Garnet mixing, Discrete Dipole Approximation, and Multi-Layered Sphere codes. These techniques when applied to crystalline minerals, specifically olivine (Mg_x, Fe_1-x)2 Si04, x>0.9, require the use of ellipsoidal shaped particles with elongated axial ratios or hollow spheres to produce the shapes of the resonances observed both from comet comae and laboratory samples. The wavelength positions of the distinct resonances from submicron-radii crystalline silicates, as well as their thermal equilibrium temperatures, constrain the crystalline olivine to have a relatively high Mg-content (x>0.9, or Fo>90). Only resonances computed for submicron Mg-rich crystalline olivine and crystalline orthopyroxene match the observed IR spectral features. However, this has led to the interpretation that micron-radii and larger crystals are absent from comet comae. Furthermore, the mass fraction of silicate crystals is dependent upon whether just the submicron portion of the size distribution is being compared or the submicron crystals compare to the aggregates of porous amorphous silicates that are computationally tractable as porous spheres. We will discuss the Deep Impact results as examples of these challenges to interpreting mid-IR spectra of short-period comets.

Wooden, Diane H.↗

Ice Chemistry Through Quiescent Dust In IC5146

IC 5146 is a nearby (200pc) dark cloud complex in Cygnus. The lack of star formation activity makes it an excellent laboratory for the study of the chemical complexity in the earliest stages of dense molecular cloud evolution. We have used the Spitzer Infrared Spectrometer (IRS) to probe dust along 10 sight-lines toward K-Giant background stars, sampling a range of visual extinction from 2-20mag. Here we present 5-20micron spectra and correlation studies of the 6.0micron water-ice band and 9.7micron silicate absorption band with Av for a sample of our Spitzer program sources. Our IC5146 Spitzer data indicate grain growth and ice formation occurs early in the history of dense cloud formation. Each sight-line observed reveals the 9.7micron amorphous silicate absorption band. The highest Av sightlines show clear detections of ices at 6.0micron (water-ice mixture), 6.85micron (processed ice) and 15.2micron (CO2). However, sight-lines in the low-to-mid Av range provide intriguing variations. We may have the first example of two objects, one with ice features and one without, seen through the same cloud sightline with similar Av approx. 6 and similar silicate band optical depths. Also, the nominally expected linear correlation of Av with silicate band depth does not appear to hold for this cloud (turnover at Av approx.10-12). Both trends imply complexities in the grain growth at one of the earliest stages of dust and ice interaction ever observed. The highest extinction source in our sample, Av=20, reveals the 6.0micron (water), 6.85micron (processed ice), 9.7micron silicate and 15.2micron CO2 ice bands. Until recently, the 6.85micron band had only been detected towards embedded protostellar objects. Two additional quiescent dust sightlines from the C2D results now also indicate the 6.85micron band (Taurus and Serpens) by Knez et al. 2005, demonstrating the role of energetic processing within pristine ices prior to the onset of star formation.

Ennico, Kimberly↗

Does Comet WILD-2 contain Gems?

It is expected that Comet Wild-2 dust should resemble anhydrous carbon-rich, chondritic porous (CP) interplanetary dust particles (IDPs) collected in the stratosphere because some CP IDPs are suspected to be from comets. The rarity of carbonaceous grains and presolar silicates, as well as the presence of high-temperature inner solar nebula minerals in the Wild-2 sample (e.g. osbornite and melilite), appear incompatible with most CP IDPs. However, it is premature to draw firm conclusions about the mineralogy of comet Wild-2 because only approx. 1% of the sample has been examined. The most abundant silicates in CP IDPs are GEMS (glass with embedded metal and sulfides). Nonsolar O isotopic compositions confirm that at least some GEMS in IDPs are presolar amorphous silicates. The presence or absence of GEMS in the Wild-2 sample is important because it addresses, (a) the relationship between CP IDPs and comets, and (b) the hypothesis that other GEMS in IDPs formed in the solar nebula. Here we show that most of the GEMSlike materials so far identified in Stardust aerogel were likely impact generated during collection. At the nanometer scale, they are compositionally and crystallographically distinct from GEMS in IDPs.

Chi, M.↗

Composite Electrolytes for Lithium Batteries: Ionic Liquids in APTES Crosslinked Polymers

Solvent free polymer electrolytes were made consisting of Li(+) and pyrrolidinium salts of trifluoromethanesulfonimide added to a series of hyperbranched poly(ethylene oxide)s (PEO). The polymers were connected by triazine linkages and crosslinked by a sol-gel process to provide mechanical strength. The connecting PEO groups were varied to help understand the effects of polymer structure on electrolyte conductivity in the presence of ionic liquids. Polymers were also made that contain poly(dimethylsiloxane) groups, which provide increased flexibility without interacting with lithium ions. When large amounts of ionic liquid are added, there is little dependence of conductivity on the polymer structure. However, when smaller amounts of ionic liquid are added, the inherent conductivity of the polymer becomes a factor. These electrolytes are more conductive than those made with high molecular weight PEO imbibed with ionic liquids at ambient temperatures, due to the amorphous nature of the polymer.

Tigelaar, Dean M.↗

Stress Rupture Testing and Analysis of the NASA WSTF-JPL Carbon Overwrapped Pressure Vessels

Carbon composite overwrapped pressure vessels (COPVs) are widely used in applications from spacecraft to life support. COPV technology provides a pressurized media storage advantage over amorphous technology with weight savings on the order of 30 percent. The National Aeronautics and Space Administration (NASA) has been supporting the development of this technology since the early 1970's with an interest in safe application of these components to reduce mass to orbit. NASA White Sands Test Facility (WSTF) has been testing components in support of this objective since the 1980s and has been involved in test development and analysis to address affects of impact, propellant and cryogenic fluids exposure on Kevlar and carbon epoxy. The focus of this paper is to present results of a recent joint WSTF-Jet Propulsion Laboratories (JPL) effort to assess safe life of these components. The WSTF-JPL test articles consisted of an aluminum liner and a carbon fiber overwrap in an industry standard epoxy resin system. The vessels were specifically designed with one plus-minus helical wrap and one hoop wrap over the helical and they measured 4.23 x 11.4 in. long. 120 test articles were manufactured in August of 1998 of one lot fiber and resin and the 110 test articles were delivered to WSTF for test. Ten of the 120 test articles were burst tested at the manufacturer to establish the delivered fiber stress. Figure 1 shows a test article in a pre burst condition and with a hoop fiber failure (no leak of pressurized media) and post burst (failure of liner and loss of pressurized media).

Greene, Nathanael↗

Measurement of Damage Profiles from Solar Wind Implantation

NASA's Genesis Mission launched from Cape Canaveral in August of 2001 with the goal of collecting solar wind in ultra-pure materials. The samples were returned to Earth more than three years later for subsequent analysis. Although the solar wind is comprised primarily of protons, it also contains ionized species representing the entire periodic table. The Genesis mission took advantage of the natural momentum of these ionized species to implant themselves in specialized collectors including single crystal Si and SiC. The collectors trapped the solar wind species of interest and sustained significant damage to the surface crystal structure as a result of the ion bombardment. In this work, spectroscopic ellipsometry has been used to evaluate the extent of this damage in Si and SiC samples. These results and models are compared for artificially implanted samples and pristine non-flight material. In addition, the flown samples had accumulated a thin film of molecular contamination as a result of outgassing in flight, and we demonstrate that this layer can be differentiated from the material damage. In addition to collecting bulk solar wind samples (continuous exposure), the Genesis mission actually returned silicon exposed to four different solar wind regimes: bulk, high speed, low speed, and coronal mass ejections. Each of these solar wind regimes varies in energy, but may vary in composition as well. While determining the composition is a primary goal of the mission, we are also interested in the variation in depth and extent of the damage layer as a function of solar wind regime. Here, we examine flight Si from the bulk solar wind regime and compare the results to both pristine and artificially implanted Si. Finally, there were four samples which were mounted in an electrostatic "concentrator" designed to reject a large fraction (>85%) of incoming protons while enhancing the concentration of ions mass 4-28 amu by a factor of at least 20. Two of these samples were single crystal 6H silicon carbide. (The others were polycrystalline CVD diamond and amorphous carbon that were not examined in the work.) The ion damaged SiC samples from the concentrator were studied in comparison to the flight Si from the bulk array to understand differences in the extent of the damage.

McNamara, K. M.↗

Nanoscale Subsurface Imaging of Nanocomposites via Resonant Difference-Frequency Atomic Force Ultrasonic Microscopy

A scanning probe microscope methodology, called resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM), has been developed. The method employs an ultrasonic wave launched from the bottom of a sample while the cantilever of an atomic force microscope engages the sample top surface. The cantilever is driven at a frequency differing from the ultrasonic frequency by one of the contact resonance frequencies of the cantilever. The nonlinear mixing of the oscillating cantilever and the ultrasonic wave at the sample surface generates difference-frequency oscillations at the cantilever contact resonance. The resonance-enhanced difference-frequency signals are used to create amplitude and phase-generated images of nanoscale near-surface and subsurface features. RDF-AFUM phase images of LaRC-CP2 polyimide polymer containing embedded nanostructures are presented. A RDF-AFUM micrograph of a 12.7 micrometer thick film of LaRC-CP2 containing a monolayer of gold nanoparticles embedded 7 micrometers below the specimen surface reveals the occurrence of contiguous amorphous and crystalline phases within the bulk of the polymer and a preferential growth of the crystalline phase in the vicinity of the gold nanoparticles. A RDF-AFUM micrograph of LaRC-CP2 film containing randomly dispersed carbon nanotubes reveals the growth of an interphase region at certain nanotube-polymer interfaces.

Cantrell, Sean A.↗

Novel Nanotube Manufacturing Streamlines Production

Nanotubes have novel qualities that make them uniquely qualified for a plethora of uses, including applications in electronics, optics, and other scientific and industrial fields. The NASA process for creating these nanostructures involves using helium arc welding to vaporize an amorphous carbon rod and then form nanotubes by depositing the vapor onto a water-cooled carbon cathode, which then yields bundles, or ropes, of single-walled nanotubes at a rate of 2 grams per hour using a single setup. This eliminates costs associated with the use of metal catalysts, including the cost of product purification, resulting in a relatively inexpensive, high-quality, very pure end product. While managing to be less expensive, safer, and simpler, the process also increases the quality of the nanotubes. Goddard's Innovative Partnerships Program (IPP) Office promoted the technology, and in 2005, Boise-based Idaho Space Materials Inc. (ISM) was formed and applied for a nonexclusive license for the single-walled carbon nanotube (SWCNT) manufacturing technology. ISM commercialized its products, and the inexpensive, robust nanotubes are now in the hands of the scientists who will create the next generation of composite polymers, metals, and ceramics that will impact the way we live. In fact, researchers are examining ways for these newfound materials to be used in the manufacture of transistors and fuel cells, large screen televisions, ultra-sensitive sensors, high-resolution atomic force microscopy probes, supercapacitors, transparent conducting films, drug carriers, catalysts, and advanced composite materials, to name just a few of the myriad technologies to benefit.

Source record↗

Process to produce silicon carbide fibers using a controlled concentration of boron oxide vapor

A process for producing polycrystalline silicon carbide includes heating an amorphous ceramic fiber that contains silicon and carbon in an environment containing boron oxide vapor. The boron oxide vapor is produced in situ by the reaction of a boron containing material such as boron carbide and an oxidizing agent such as carbon dioxide, and the amount of boron oxide vapor can be controlled by varying the amount and rate of addition of the oxidizing agent.

Barnard, Thomas Duncan↗

Stable metallization for diamond and other materials

An adherent and metallurgically stable metallization system for diamond is presented. The big improvement in metallurgical stability is attributed to the use of a ternary, amorphous Ti--Si--N diffusion barrier. No diffusion between the layers and no delamination of the metallization was observed after annealing the schemes at 400.degree. C. for 100 hours and at 900.degree. C. for 30 minutes. Thermal cycling experiments in air from -65 to 155.degree. C. and adhesion tests were performed. Various embodiments are disclosed.

Bachli, Andreas↗