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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

Enhanced Field Emission From The Gold- Polyaniline (Au-PANI) Nanocomposite

The gold-polyaniline nanocomposite was synthesized by electrochemical route in two steps. In the first step polyaniline film was deposited by cyclic voltammetry on the ITO coated glass substrate, and then synthesis of gold-polyaniline nanocomposite via chronoamperometry. The synthesized gold-polyaniline nanocomposite film was characterized using scanning electron microscope (SEM), X-ray diffraction (XRD), Ultra-violet spectroscopy (UV-vis) and Fourier Transform Infrared Spectrometry (FTIR). The SEM analysis shows well adherent gold nanoparticles on the surface of polyaniline nanofibers. The XRD and UV-Vis spectra indicate formation of gold nanoparticles. From the field emission studies, the value of the turn on field, corresponding to 1 nA emission current, is found to be 0.65 V/{mu}m and emission current density of 1 {mu}A/cm{sup 2} has been drawn at an applied field of 1.1 V/{mu}m. These values are observed to be superior than the reported ones. The field emission current stability investigated at 1 {mu}A over duration of more than four hours is found to be good. The observed field emission characteristics suggest the gold polyaniline nanocomposite as promising material for field emission based applications.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Effect Of EDTA On Luminescence Property Of Eu{sup +3} Doped YPO{sub 4} Nanoparticles

Nanoparticles of Eu{sup 3+} doped YPO{sub 4} have been prepared using ethylene glycol (EG). Ethylene diamine tetra acetic acid (EDTA) is used as a complexing agent. X-ray diffraction results show that the nanoparticles are crystalline in tetragonal structure. Based on William-Hall relation, the effective crystallite size and strain developed in lattice are found to be 28 nm and 0.002, respectively. With the addition of EDTA, there is a slight shift towards the lower wavelength in emission peaks. Asymmetric ratio of electric to magnetic dipole transition intensities are found to decrease with addition of EDTA. Emission intensity decreases with EDTA because of decrease of particle size as well as decrease of number of Eu{sup 3+} activators per unit volume. These materials are dispersible in water, which may have potential biological applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

Grinding Wear Behaviour of Stepped Austempered Ductile Iron as Media Material During Comminution of Iron Ore in Ball Mills

An attempt has been made to evaluate the suitability of austempered ductile iron (ADI) as media material for grinding iron ore in a ball mill. Spheroidal graphite (S.G) iron balls are austenitised at 900 deg. C for 60 minutes and given stepped austempering treatment at 280 deg. C for 30 minutes and 60 minutes followed by 380 deg. C for 60 minutes in each case. These materials are characterised by measuring hardness, analysing X-ray diffraction (X-RD), studying microstructure using optical and scanning electron microscope (SEM). Grinding wear behaviour of these materials was assessed for wear loss in wet condition at different pH value of the mineral slurry and found that the wear rate of grinding media material decreases with increase in pH of the slurry. The wear resistance of ADI balls were compared with forged En31 steel balls and found that the stepped austempered ductile iron is superior to forged En31 steel balls.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Low Temperature, Self-nucleated Growth of Indium Tin Oxide Nanostructures by Pulsed Laser Deposition in Argon

Indium tin oxide (ITO) nanostructures were successfully deposited on glass substrate by pulsed laser ablation in argon gas at 250 deg. C. Microstructural changes were observed in the argon gas pressure between 30 to 50 mTorr. The as-grown, nanostructured ITO exhibit In{sub 2}O{sub 3} bixbyite structure orientated at <111> direction. At the initial stage of growth, there was a large number of nucleation sites detected which eventually evolved into needle-like branches. The presence of spheres at the tip of these branches indicates that these nanostructured ITO were likely governed by vapor-liquid-solid (VLS) growth mechanism.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

Visible Luminescence from Au Nanoparticles Stabilized with Aromatic Thiols

Photoemission in the visible range is reported from Au nanoparticles stabilized with two different organic thiols. The efficiency and wavelength of the emissions are found to be different for the different capping agents. The size of the particles was estimated from TEM and XRD measurements. The observed luminescence may arise from interband electronic transitions between the filled 5d{sup 10} and 6(sp){sup 1} conduction band modified by a metal-ligand charge transfer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Investigation of historical metal objects using Laser Induced Breakdown Spectroscopy (LIBS) technique

Analysis of metal objects is a necessary step for establishing an appropriate conservation treatment of an object or to follow up the application's result of the suggested treatments. The main considerations on selecting a method that can be used in investigation and analysis of metal objects are based on the diagnostic power, representative sampling, reproducibility, destructive nature/invasiveness of analysis and accessibility to the appropriate instrument. This study aims at evaluating the usefulness of the use of Laser Induced Breakdown Spectroscopy (LIBS) Technique for analysis of historical metal objects. In this study various historical metal objects collected from different museums and excavations in Egypt were investigated using (LIBS) technique. For evaluating usefulness of the suggested analytical protocol of this technique, the same investigated metal objects were investigated by other methods such as Scanning Electron Microscope with energy-dispersive x-ray analyzer (SEM-EDX) and X-ray Diffraction (XRD). This study confirms that Laser Induced Breakdown Spectroscopy (LIBS) Technique is considered very useful technique that can be used safely for investigating historical metal objects. LIBS analysis can quickly provide information on the qualitative and semi-quantitative elemental content of different metal objects and their characterization and classification. It is practically non-destructive technique with the critical advantage of being applicable in situ, thereby avoiding sampling and sample preparations. It is can be dependable, satisfactory and effective method for low cost study of archaeological and historical metals. But we have to take into consideration that the corrosion of metal leads to material alteration and possible loss of certain metals in the form of soluble salts. Certain corrosion products are known to leach out of the object and therefore, their low content does not necessarily reflect the composition of the metal at the time of the object manufacture. Another point should be taken into consideration that the heterogeneity of a metal alloy object that often result from poor mixing of the different metal alloy composition.There is a necessity to carry out further research to investigate and determine the most appropriate and effective approaches and methods for conservation of these metal objects.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Anisotropic charge density wave in layered 1 T - TiS e 2

We present a three-dimensional study on the anisotropy of the charge density wave (CDW) in 1T-TiSe 2 , by means of in situ atomically resolved electron microscopy at cryogenic temperatures in both reciprocal and real spaces. Using coherent nanoelectron diffraction, we observed short-range coherence of the in-plane CDW component while the long-range coherence of out-of-plane CDW component remains intact. An in-plane CDW coherence length of ~10 nm and an out-of-plane CDW coherence length of 17.5 nm, as a lower bound, were determined. The electron modulation was observed using electron energy-loss spectroscopy and verified by an orbital-projected density of states. Our integrated approach reveals anisotropic CDW domains at the nanoscale, and illustrates electron modulation-induced symmetry breaking of a two-dimensional material in three dimensions, offering an opportunity to study the effect of reduced dimensionality in strongly correlated systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Chemical and mechanical stability of sodium sulfate activated slag after exposure to elevated temperature

The chemical and mechanical stability of slag activated with two different concentrations of sodium sulfate (Na{sub 2}SO{sub 4}) after exposure to elevated temperatures ranging from 200 to 800 Degree-Sign C with an increment of 200 Degree-Sign C has been examined. Compressive strengths and pH of the hardened pastes before and after the exposure were determined. The various decomposition phases formed were identified using X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. The results indicated that Na{sub 2}SO{sub 4} activated slag has a better resistance to the degradation caused by exposure to elevated temperature up to 600 Degree-Sign C than Portland cement system as its relative strengths are superior. The finer slag and higher Na{sub 2}SO{sub 4} concentration gave better temperature resistance. Whilst the pH of the hardened pastes decreased with an increase in temperature, it still maintained a sufficiently high pH for the protection of reinforcing bar against corrosion.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Substrate orientation effects on the nucleation and growth of the M{sub n+1}AX{sub n} phase Ti{sub 2}AlC

The M{sub n+1}AX{sub n} (MAX) phases are ternary compounds comprising alternating layers of a transition metal carbide or nitride and a third ''A-group'' element. The effect of substrate orientation on the growth of Ti{sub 2}AlC MAX phase films was investigated by studying pulsed cathodic arc deposited samples grown on sapphire cut along the (0001), (1010), and (1102) crystallographic planes. Characterization of these samples was by x-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy. On the (1010) substrate, tilted (1018) growth of Ti{sub 2}AlC was found, such that the TiC octahedra of the MAX phase structure have the same orientation as a spontaneously formed epitaxial TiC sublayer, preserving the typical TiC-Ti{sub 2}AlC epitaxial relationship and confirming the importance of this relationship in determining MAX phase film orientation. An additional component of Ti{sub 2}AlC with tilted fiber texture was observed in this sample; tilted fiber texture, or axiotaxy, has not previously been seen in MAX phase films.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Electron back scattered diffraction characterization of Sm(CoFeCuZr){sub z} magnets

In permanent magnets based on the Sm{sub 2}Co{sub 17} phase, the high coercivity depends on the presence of a complex microstructure, consisting of a Sm{sub 2}(Co,Fe){sub 17} cell phase, a cell boundary phase Sm(Co,Cu){sub 5}, and a Zr-rich platelet or lamellae phase. The aim of this work is to use electron back scatter diffraction (EBSD) in order to identify the different phases present in the isotropic magnets produced from cast alloys with the composition of Sm(Co{sub bal}Fe{sub 0.2}Cu{sub 0.1}Zr{sub x}){sub 8}, where x = 0, 0.02, or 0.06, and correlate them with the different phases observed in scanning electron microscopy (SEM) images. Due to the combination of careful surface preparation and high resolution microscopy, it was possible to observe the cellular structure characteristic of the 2:17 magnets in the SEM images. Until now, only transmission electron microscopy (TEM) had been used. Composition maps, energy dispersive spectroscopy (EDS), and EBSD measurements were used for doing the phase identification.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Coherent growth of GaGdN layers with high Gd concentration on GaN(0001)

We report on the coherent growth of GaGdN with high Gd concentration on a GaN template using radio-frequency plasma-assisted molecular beam epitaxy under elevated growth conditions. X-ray diffraction and cross-sectional transmission electron microscopy observations revealed that at a growth temperature of 700 {sup Degree-Sign }C or below, GaGdN layers are coherently grown on the GaN templates without segregation of the secondary phases. As the GdN mole fraction x was increased to 0.08, the c-axis lattice parameter in Ga{sub 1-x}Gd{sub x}N increased linearly. Increasing the growth temperature to 750 {sup Degree-Sign }C causes lattice relaxation in GaGdN. All GaGdN samples exhibited photoluminescence emissions near the band-edge, a blue luminescence band emission, and a green luminescence band emission. The origin of the green luminescence band emission is discussed in relation to the compressive strain existing in the GaGdN layers coherently grown on GaN.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Hydration mechanisms of ternary Portland cements containing limestone powder and fly ash

The effect of minor additions of limestone powder on the properties of fly ash blended cements was investigated in this study using isothermal calorimetry, thermogravimetry (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques, and pore solution analysis. The presence of limestone powder led to the formation of hemi- and monocarbonate and to a stabilisation of ettringite compared to the limestone-free cements, where a part of the ettringite converted to monosulphate. Thus, the presence of 5% of limestone led to an increase of the volume of the hydrates, as visible in the increase in chemical shrinkage, and an increase in compressive strength. This effect was amplified for the fly ash/limestone blended cements due to the additional alumina provided by the fly ash reaction.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Influence of high power impulse magnetron sputtering plasma ionization on the microstructure of TiN thin films

HIPIMS (High Power Impulse Magnetron Sputtering) discharge is a new PVD technology for the deposition of high-quality thin films. The deposition flux contains a high degree of metal ionization and nitrogen dissociation. The microstructure of HIPIMS-deposited nitride films is denser compared to conventional sputter technologies. However, the mechanisms acting on the microstructure, texture and properties have not been discussed in detail so far. In this study, the growth of TiN by HIPIMS of Ti in mixed Ar and N{sub 2} atmosphere has been investigated. Varying degrees of metal ionization and nitrogen dissociation were produced by increasing the peak discharge current (I{sub d}) from 5 to 30 A. The average power was maintained constant by adjusting the frequency. Mass spectrometry measurements of the deposition flux revealed a high content of ionized film-forming species, such as Ti{sup 1+}, Ti{sup 2+} and atomic nitrogen N{sup 1+}. Ti{sup 1+} ions with energies up to 50 eV were detected during the pulse with reducing energy in the pulse-off times. Langmuir probe measurements showed that the peak plasma density during the pulse was 3 x 10{sup 16} m{sup -3}. Plasma density, and ion flux ratios of N{sup 1+}: N{sub 2}{sup 1+} and Ti{sup 1+}: Ti{sup 0} increased linearly with peak current. The ratios exceeded 1 at 30 A. TiN films deposited by HIPIMS were analyzed by X-ray diffraction, and transmission electron microscopy. At high I{sub d}, N{sup 1+}: N{sub 2}{sup 1+} > 1 and Ti{sup 1+}: Ti{sup 0} > 1 were produced; a strong 002 texture was present and column boundaries in the films were atomically tight. As I{sub d} reduced and N{sup 1+}: N{sub 2}{sup 1+} and Ti{sup 1+}: Ti{sup 0} dropped below 1, the film texture switched to strong 111 with a dense structure. At very low I{sub d}, porosity between columns developed. The effects of the significant activation of the deposition flux observed in the HIPIMS discharge on the film texture, microstructure, morphology and properties are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Nanoindentation Studies Of Hard Nanocomposite Ti-B-N Thin Films

Titanium boron nitride (Ti-B-N) films were deposited by reactive magnetron sputtering using single Titanium diboride (TiB{sub 2}) target in different Ar-N{sub 2} gas mixtures. The influence of N{sub 2}:Ar ratio on the microstructure and mechanical properties of the deposited films have been investigated. Atomic force microscopy analysis indicated the grain size decreases with incorporation of nitrogen in the films. Nanoindentation studies have shown the hardness decreases with nitrogen incorporation.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Effects of Au layer thickness and number of bilayers on the properties of Au/ZnO multilayers

Multilayered films of Au/ZnO were prepared by physical vapor deposition. Varying the Au thickness, t{sub Au}, and the number of bilayers, n, allowed us to investigate the role of these parameters on the sample structural and electronic properties. X-ray diffraction, X-ray absorption spectroscopy, grazing incidence small angle X-ray scattering and transmission electron microscopy experiments, have been combined to UV-visible and infrared spectroscopy to characterize the multilayers in the as-prepared state and after annealing. In the as-prepared state, the strong Au and ZnO lattice interaction leads to ZnO epitaxy on Au. Gold appears either as continuous layers or in form of nanoparticles. ZnO experiences a structural transformation from wurztite to rock salt monitored by the Au morphology. Annealing at 500 deg. C destroys the lattice matching. The electronic and optical properties of the systems are understood in line with the Au morphology and ZnO structural state.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Photochemical preparation of CdS hollow microspheres at room temperature and their use in visible-light photocatalysis

CdS hollow microspheres have been successfully prepared by a photochemical preparation technology at room temperature, using polystyrene latex particles as templates, CdSO{sub 4} as cadmium source and Na{sub 2}S{sub 2}O{sub 3} as both sulphur source and photo-initiator. The process involved the deposition of CdS nanoparticles on the surface of polystyrene latex particles under the irradiation of an 8 W UV lamp and the subsequent removal of the latex particles by dispersing in dichloromethane. Photochemical reactions at the sphere/solution interface should be responsible for the formation of hollow spheres. The as-prepared products were characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. Such hollow spheres could be used in photocatalysis and showed high photocatalytic activities in photodegradation of methyl blue (MB) in the presence of H{sub 2}O{sub 2}. The method is green, simple, universal and can be extended to prepare other sulphide and oxide hollow spheres. -- Graphical abstract: Taking polystyrene spheres dispersed in a precursor solution as templates, CdS hollow microspheres composed of nanoparticles were successfully prepared via a new photochemical route at room temperature. Display Omitted Research highlights: {yields} Photochemical method was first employed to prepare hollow microspheres. {yields} CdS hollow spheres were first prepared at room temperature using latex spheres. {yields} The polystyrene spheres used as templates were not modified with special groups. {yields}The CdS hollow microspheres showed high visible-light photocatalytic activities.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2010

Phase transformations induced by high electronic excitation in ion-irradiated Gd{sub 2}(Zr{sub x}Ti{sub 1-x}){sub 2}O{sub 7} pyrochlores

The pyrochlore oxides (A{sub 2}B{sub 2}O{sub 7}) exhibit a remarkable range of structural, physical, and magnetic properties related to their various chemical compositions. This article reports the phase transformations induced by high electronic excitation in pyrochlores of the Gd{sub 2}(Zr{sub x}Ti{sub 1-x}){sub 2}O{sub 7} family irradiated with swift ions. The structural changes, investigated by using several analytical techniques (x-ray diffraction, Raman spectroscopy, and transmission electron microscopy), strongly depend on the chemical composition. The high electronic excitation along the ion trajectory results in the amorphization of ion tracks for Gd{sub 2}Ti{sub 2}O{sub 7} and Gd{sub 2}TiZrO{sub 7}, whereas a defective fluorite structure is formed in Gd{sub 2}Zr{sub 2}O{sub 7}. Moreover, the results underline the existence of an electronic stopping power threshold of 6 keV/nm for amorphizable compounds and 10 keV/nm for Gd{sub 2}Zr{sub 2}O{sub 7}, below which phase transformations do not occur. Finally, the study of the thermal recovery of irradiated pyrochlores provides the recrystallization temperature for amorphized samples and reveals differences in the recovery process which are related to the chemical composition.

36 MATERIALS SCIENCE↗