bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface Melting of Particles: Predicting Spherule Size in Vapor-Phase Nanometer Particle Formation
Authors: Xing Y. , Rosner D. E. 
Published: April 2011

ABSTRACTThere is still no reliable method to predict the all-important size of the ‘primary’ spherules found in combustion-synthesized particulate products. Toward this end, we introduce surface melting concepts in developing a coagulation-coalescence model for nanoparticles in the low temperature regions of diffusion flames. The associated surface self-diffusivity, which controls the rate of spherule sintering at temperatures well below the equilibrium melting point, is therefore modified to include an important size effect. This formulation is used to calculate the sintering rate of two adjacent particles in a flame coagulation environment corresponding to a condensed phase volume fraction of Ca. 10−1 ppm. Predicted spherule sizes show encouraging agreement with our experimental data for ca. 10 nm diameter Al2O3 particles synthesized on the fuel side of a laminar CH4/O2 diffusion flame seeded with Al(CH3)3 (TMA)[1].
Synthesis and Characterization of Small Grain Sized Molybdenum Nitride Films
Authors: Roberson S. L. , Finello D. , Davis R. F. 
Published: April 2011

ABSTRACTPolycrystalline, small grain sized, 15 μm thick MoxN (x=1 or 2) films, void of detectable concentrations of molybdenum oxides, have been prepared on 50 μm thick nitrided Ti substrates via conversion of precursor MoO3 films in a programmed reaction with NH3. The latter films were produced via liquid spray pyrolysis of an MoCl5/methanol mixture in air at 500° C. The reaction of MoO3 films with NH3 resulted in a two-phase MoxN mixture consisting of γ-Mo2N and δ-MoN. The change in density of MoO3(ρ=4.69 g/cm3) to γ-MoN (ρ=9.50 g/cm3) and δ-MoN (ρ=9.05 g/cm3) produced grains with a calculated average size of 10 nm without losing adherence to the substrate. The composition of the MoxN films was determined by X-ray diffraction (XRD) and Auger electron spectroscopy (AES) to be ∼ 60% γ-Mo2N and 40% δ-MoN. The results of scanning electron microscopy (SEM) showed the surface morphology of the MoxN films to be highly porous.
Electrical/Dielectric Properties of Nanocrystalline Cerium Oxide
Authors: Hwang Jin-Ha , Mason Thomas O. , Garboczi Edward J. 
Published: April 2011

ABSTRACTElectrical/dielectric properties of nanocrystalline cerium oxide have been studied using impedance spectroscopy, thermopower, and DC 4-point conductivity. The combined techniques identified the effect of poor electroding on impedance spectra. Incomplete contact between the specimen and the electrode induces an additional arc in the impedance spectra. The additional high resistance feature results from the geometric constriction of current flow at the specimen/electrode interface and can be misinterpreted as a grain boundary response. The defect chemistry, nonstoichiometry, and transport properties were investigated in nanoscale ceria and compared with those of microcrystalline material.
Cluster Formation by Laser Ablation of Zeolites
Authors: Komiyama Hiroshi T. , Harano Azuchi , Okubo Tatsuya , Sadakata Masayoshi 
Published: April 2011

ABSTRACTSeveral kinds of zeolites, crystal-SiO2 (α-quartz), arnorphous-SiO2 (quartz glass and ultrafine particles) and α-Al2O3, were ablated by an Nd:YAG laser. Generated positive ions from the targets were measured by TOF-MS (time-of-flight mass spectrometry). In the TOF mass spectra of ablated zeolites, TOx (x=0–2, T = tetrahedral atom, e.g., Si, Al), T2Ox (x=1) and T3Ox (x=4,5) were observed up to m/z=170 (m = mass, z = plus charge of clusters). In the spectra due to the oc-quartz, quartz glass and an α-Al2O3 plate, smaller species, T+, TO+ and TO2+, were mainly detected. These results demonstrate that the clusters from zeolites reflect the characters of the mother structure.
Plasticity and Interfacial Dislocation Structures in Ti-Al
Authors: Parrini L. , Heinrich H. , Kostorz G. 
Published: April 2011

ABSTRACTThe alloy Ti-48.6Al-l.9Cr-l.9Nb-IB with an equiaxed γ microstructure, obtained by heat treatment at 1200°C for 4 h, and with a lamellar mi ero structure, obtained by heat treatment at 1380°C for 1 h, is characterized by compression tests and transmission electron microscopy. A lower activity of superdislocations and a more frequent pinning of ordinary dislocations are detected in the lamellar Ti-Al specimens in comparison with the non-lamellar ones during deformation at room temperature. The activity of superdislocations and the pinning of ordinary dislocations are responsible for the differences in yield stress and brittleness between lamellar and non-lamellar Ti-Al. A very high density of ordinary interfacial dislocations is found in the lamellar structure. These influence the activity of superdislocations and the pinning of ordinary dislocations. At high temperature a change in the deformation mechanism occurs. Above the brittle-to-ductile transition, the material is remarkably softer and the mechanical properties are insensitive to the presence of the lamellar interfaces.
Static and Dynamic Strain Aging in Two-Phase γ-Titanium Aluminides
Authors: Christoph U. , Appel F. , Wagner R. 
Published: April 2011

ABSTRACTDeformation of two-phase titanium aluminides exhibits discontinuous yielding and a negative strain rate sensitivity over the temperature range 450–750 K. These phenomena are usually associated with the Portevin-LeChatelier effect which is due to the dynamic interaction of diffusing defects with the dislocations. The resulting glide resistance was investigated by static strain aging. The experiments involve the prestraining of samples followed by aging under a relaxing load for certain periods of time. Reloading of the samples resulted in distinct yield points. The investigations were performed on two-phase γ-titanium aluminides having different compositions and microstructures which are currently being considered for technical applications. Accordingly, dislocation locking occurs with fast kinetics which is characterized by a low activation energy. The experimental results will be discussed with respect to the nature of the diffusional mechanism and possible implication on the mechanical properties of the materials.
Strength, Thermal Defects, and Solid Solution Hardening in Nickel-Containing B2 Iron Aluminides
Authors: Schneibel J. H. , Munroe P. R. , PIKE L. M. 
Published: April 2011

ABSTRACTNickel-containing ternary iron aluminides with an aluminum concentration of 45 at. % were investigated with respect to room temperature strength, equilibrium vacancy concentration, and the kinetics of vacancy removal. As compared to binary iron aluminides with the same Al concentration, nickel additions reduce the thermal equilibrium vacancy concentration at 1273 K, whereas they increase this concentration at 973 K. Furthermore, at low temperatures such as 673 K, nickel additions increase dramatically the time needed to reach vacancy equilibrium. During prolonged annealing at 673 K, the density of <001> dislocations in Fe-45Al-3Ni (at. %) increased by an order of magnitude. This suggests that dislocations act as sinks for vacancies. At the same time, the number density of small (20–50 nm) voids decreased, indicating that they were not stable in the absence of substantial vacancy supersaturations. Our findings show also that the solid solution strengthening of iron aluminides due to Ni is much weaker than previously thought.
Preparation, Deformation and Fracture of Stoichiometric NiAl Single Crystals
Authors: Löser W. , Köthe A. , Vaerst G. , Güth A. 
Published: April 2011

ABSTRACTA modified Bridgman method involving vacuum treatment prior to the growth process was developed for preparation of high-accuracy stoichiometric NiAl crystals. Single crystals with stoichiometry deviations < 0.2 wt.% Ni characterized by residual resistance ratios R298K/R4.2K > 4 have been prepared. An improved gravimetric analysis ensured the best accuracy among the various wet chemical analysis methods tested and a total error less than 0.1 at.% for Ni determination in NiAl. The stoichiometric NiAl single crystals exhibit high compressive strain in <123> crystallographic axis of the order of 20 % in the as-grown state and 40 % after annealing 1 h at 1073 K. The critical resolved shear stress was reduced from 104 MPa to 45 MPa by annealing. In 3-point bend tests tensile strains to failure up to 10 % have been achieved. Microscopic oxide inclusions near the sample surface were identified as the cause of crack initiation in bent samples.
Atomistic Simulations of Ti Additions to NiAl
Authors: Bozzolo Guillermo , Noebe Ronald D. , Garg Anita , Ferrante John , Amador Carlos 
Published: April 2011

ABSTRACTThe development of more efficient engines and power plants for future supersonic transports depend on the advancement of new high-temperature materials with temperature capabilities exceeding those of Ni-based superalloys. Having theoretical modelling techniques to aid in the design of these alloys would greatly facilitate this development. The present paper discusses a successful attempt to correlate theoretical predictions of alloy properties with experimental confirmation for ternary NiAl-Ti alloys. The B.F.S. (Bozzolo- Ferrante-Smith) method for alloys is used to predict the solubility limit and site preference energies for Ti additions of 1 to 25 at. % to NiAl. The results show the solubility limit to be around 5 % Ti, above which the formation of Heusler precipitates is favored. These results were confirmed by transmission electron microscopy performed on a series of NiAl-Ti alloys.
Investigation of Superplastic Behavior of NiAI and Ni3Al Duplex Alloy
Authors: Zhenyun Liu , Dongliang Lin , Lin T. L. , Yuefeng Gu , Aidang Shan 
Published: April 2011

ABSTRACTThe superplastic behavior of a NiAI and Ni3Al duplex alloy was investigated. It was found that the alloy exhibits superplastic behavior over a narrow temperature range, from 975 °C to 1025°C at the strain rate of 1.52 × 10-4 s-1. A maximum tensile elongation of 149% was obtained at 1000°C with the strain rate sensitivity up to 0.375. The superplastic deformation of the duplex alloy can be approximately described by an empirical equation of the form: ε = Ao2.67 exp(-303,000 / RT). Optical microstructure and TEM observation show that the superplastic behavior mechanism of the investigated alloy is a process of continuous recovery and recrystallization during deformation.
An Analysis of The Slip of Screw Dislocations in Ll2 Alloys
Authors: Veyssière Patrick , Lem  
Published: April 2011

ABSTRACTThe annihilation of dislocations by cross-slip is studied by numerical simulation of infinitely long dissociated screw dislocations, allowed to move in an elastically anisotropie crystal. The external load is along [123] and cross-slip is permitted both on the octahedral and on the cube plane. The latter, together with cube slip, is thermally activated. Anisotropie elasticity modifies the properties of cross-slip significantly. Under the conditions of the simulations, the processes of APB jumps (APBJs) and repeated APB jumps (RAPBJs) can be largely promoted by interactions with other dislocations, while it is much less likely to occur at an isolated dislocation submitted to the same applied stress. The encounter of dislocations of opposite signs produces dipoles which may or may not tend to annihilate by cross-slip. APB tubes may form upon annihilation under certain circumstances again largely controlled by elastic anisotropy.
Phase Relation and Microstructure of NbCr2 Laves Intermetallics in Ternary Nb-Cr-X Alloy Systems
Authors: Yoshida M. , Takasugi T. 
Published: April 2011

ABSTRACTThe isothermal phase diagrams of ternary alloy systems Nb-Cr-V and Nb-Cr-Mo are determined by metallography, X-ray diffraction (XRD) and transmission electron microscopy (TEM) equipped with energy dispersive X-ray (EDX). In two alloy systems, the C15 NbCr2 Laves phases are equilibrated directly with bcc solid solution without forming any intermediate phases. Relatively large amount of ternary elements V and Mo are soluble in the C15 NbCr2 Laves phases. It is shown that the C15 Laves phases extend along directions so that V occupies Cr site while Mo occupies Nb site. Also, characteristic structure containing micro twins and stacking faults is observed in the C15 Laves phase alloyed with Mo. Bcc phase has a wider solid solution range in the X(=V and Mo)-rich side than the Nb-rich and Cr-rich sides. A variety of duplex microstructures are observed depending on alloy system and alloy composition.
Modification of Interfacial Properties of Polymer Blends with Diblock Copolymer
Authors: Kim S. , Han C. C. 
Published: April 2011

ABSTRACTThe effect of diblock copolymer on the phase-separation process of polymer blends has been investigated by using light scattering and optical microscopic observations. To quench the system into the two phase region, a shear-jump technique is employed instead of the conventional temperature-jump technique. The samples studied are blends of low-molecular-weight polystyrene and polybutadiene with and without added styrene-butadiene block copolymer as a compatibilizer. It was observed that the addition of diblock copolymers could accelerate the phase separation kinetics depending on the shear history. As the concentration of diblock copolymer increases, the distribution of domain sizes becomes narrower and the growth rate slows down. The extent of slowing-down depends on the molecular weight and concentration of the copolymer. The time dependence of domain growth is clearly observed with optical microscopy.
Analysis of Gold Hoard from Late Roman/Early Byzantine Period Found in Jordan
Authors: Williams W.S. , Flanagan J. W. 
Published: April 2011

ABSTRACTThirty-four gold solidi coins and two pairs of gold/jewel earrings were discovered at an archaeological site in Jordan, Tell Nimrin. The coins have stamped images of six late Roman/early Byzantine emperors who reigned from 346 AD to 518 AD. These objects were analyzed by X-ray radiography, SEM/EDS and density measurements to find the gold content for comparison with other coins ofthat period to support their authenticity and to see whether debasement of coinage had occurred. The average surface gold content was found by EDS to be 98.1 wt %--typical of the period--but the bulk content calculated from density values was 1 to 3 wt % lower. The reason offered is that when a molten gold-copper or gold-silver alloy solidifies, the region in contact with the blank coin mold freezes first and is gold-enriched. Small “silvery” specks were observed on the obverse (”heads”) side of several coins and found by EDS to be Os-Ir-Ru alloys, which come from placer mining and indicate that the gold also came from placer mining.
Long-Distance Obsidian Trade in Indonesia
Authors: Tykot Robert H. , Chia Stephen 
Published: April 2011

ABSTRACTLong-distance trade in obsidian from sources in the southwest Pacific has been well-documented for the Lapita culture complex, beginning about 1600 BC. Analyses of obsidian artifacts from recent excavations at Bukit Tengkorak in southeastern Sabah (Borneo, Malaysia) indicate the use of obsidian from multiple sources in Melanesia as early as the 5th millennium BC. The archaeological presence of obsidian, up to more than 3500 km from its source, is the surviving evidence of what was almost certainly the longest Neolithic trade route in the world. In addition, these results indicate that long-distance trade networks existed in Indonesia at least 2500 years prior to the Lapita culture, and strengthen hypotheses of its origins in southeast Asia.
The Alteration and Natural Consolidation Effects of a Ceramic Vessel in Archaeological Excavation From San Lorenzo Tenochtitlán, Veracruz, Mexico
Authors: Guevara M.E. , Lopez M. , Cruz-Lara A. , Cyphers A. , Gama J.E. 
Published: April 2011

ABSTRACTA study of a ceramic vessel from San Lorenzo Tenochtitlán, Veracruz, México (Early Formative 1550–900 b.C.) was developed using three selected analytical methods: Petrographic thin section, X-ray Diffraction and Scanning Electron Microscopy. The results suggested, that the soil weathering processes on the ceramic vessel generated phenomenons, such as an increase in porosity, a decrease in bulk-density and loss in structural stability.On the other hand, the presence of amorphous materials (SiO2, FeO3) in the soil, interacted with the ceramic giving it a natural consolidation. The consequences of our study are discussed in detail.
Socioeconomic Implications of Prehistoric Textile Production in the Eastern Woodlands
Authors: Jakes K.A. , Ericksen A.G. 
Published: April 2011

ABSTRACTQuantitative measures of time and effort as well as assessment of the knowledge base required in each level of textile manufacture (i.e., plant collecting, fiber processing, yarn and fabric formation) result in cost estimates that indicate differences between simply structured materials and complexly structured elaborate materials. These measures were applied to two textiles from a Wilbanks phase (A.D. 950 to 1440) [1] burial of a high status individual from Mound C at Etowah, Georgia [2]. Socioeconomic implications inferred from the resulting analyses include the proposal of craft specialization in the production of complex textiles and of the significance of these complex textiles to Mississippian chiefdoms.
An Organic Colorant used in Painted Ancient Maya Architectural Sculpture at Nakbe, Peten, Guatemala
Authors: Hansen Eric F. , Wallert Arie , Derrick Michele 
Published: April 2011

ABSTRACTThe ancient Lowland Maya are generally considered to have used a limited number of inorganic colorants in their polychrome reliefs due to the lack or inaccessibility of mineral resources, especially during the Late Preclassic period (300 B.C. – 300 A.D.). A notable exception is the manufacture of a blue pigment from indigo and specific types of clay, known as Maya blue, from the Classic Period (300 – 900 A.D.) through Colonial times. Another exception is a recently analyzed cream (or reddish-yellow) colored paint found on exceptionally large architectural polychrome stuccoed sculpture dating to the early Late Preclassic at the site of Nakbe, Petén, Guatemala. The cream paint layer exhibits a dramatic peach-colored fluorescence upon exposure to ultraviolet light. An organic material, extracted with organic solvents from the acid hydrolyzed lime-based plaster surface, was characterized by means of visible light microspectroscopy, FT-IR microspectroscopy and three-dimensional fluorescence spectroscopy. Analysis of the spectra obtained from the cream colorant and comparison with spectra of reference organic materials suggests that anthraquinone derivatives may be responsible for the color, and that these compounds are similar to some of those present in organic red dyes. The cream paint was applied as a single layer with good hiding power overlying the stucco ground. The cream paint is of the same thickness (averaging 15 microns) as the only other paint present on the sculpture, a red paint pigmented with red iron oxide. The presence of organic colorants on exposed architectural features raises particular preservation problems in relation to the increased possibility and rate of deterioration due to environmental exposure of this type of organic colorant in comparison with most inorganic colorants.
Atomic Oxygen Treatment Technique for Removal of Smoke Damage From Paintings
Authors: Rutledge S.K. , Banks B.A. 
Published: April 2011

ABSTRACTSoot deposits that can accumulate on surfaces of a painting during a fire can be difficult to clean from some types of paintings without damaging the underlying paint layers. A non-contact technique has been developed which can remove the soot by allowing a gas containing atomic oxygen to flow over the surface and chemically react with the soot to form carbon monoxide and carbon dioxide. The reaction is limited to the surface, so the underlying paint is not touched. The process can be controlled so that the cleaning can be stopped once the paint surface is reached. This paper describes the smoke exposure and cleaning of untreated canvas, acrylic gesso, and sections of an oil painting using this technique. The samples were characterized by optical microscopy and reflectance spectroscopy.
Electron Microscopy Studies of the High Temperature Oxidation Behavior of NiAl
Authors: Yang J. C. , Schumann E. , Levin I. , Muellejans H. , Ruhle M. 
Published: April 2011

ABSTRACTThe transient oxidation stage of single crystal (001)NiAl was investigated using scanning electron microscopy, transmission electron microscopy, electron diffraction, high resolution electron microscopy and electron energy loss spectroscopy (EELS). (001)NiAl was oxidized in air at 950°C in order to produce transient forms of alumina on the surface. After oxidation, an oxide scale with plate-like surface morphology formed. We found that the main transient alumina polymorph is γ-Al2O3. The platelets which formed on the surface of the oxide are most likely α-A12O3, not θ-Al2O3. Randomly-oriented α-Al2O3grains were observed at the oxide/metal interface. The NiAl/γ-Al2O3interfaces were examined with EELS. From the changes observed in the electron energy loss spectra, the interfacial terminating plane is determined. Lattice matching arguments are given to explain why these terminating planes are energetically favorable.
STM Study of a Defect-Related Si(001)-c(4×4) Surface
Authors: Yoshimura Masamichi , Ueda Kazuyuki 
Published: April 2011

ABSTRACTWe demonstrate scanning tunneling microscopy studies of a Si(001)-c(4×4) structure which consists of a considerable number of dimer vacancies (missing dimers). Two different preparation methods are examined; one is hydrogen desorption and another is a special annealing and cooling process without hydrogen. The STM images reveal that atomic structure of the c(4×4) prepared without hydrogen is quite different from that prepared with hydrogen and is well described by the missing dimer model. A moiré-like pattern is observed on the c(4×4) surface prepared by hydrogen with an increase in the tip-sample distance, which suggests that the atoms lying in the subsurface should be considered for the precise description of the c(4×4) structure.
The Effect of Strain Relaxation Mechanisms on the Electrical Properties of Epitaxial CaF2/Si(111) Heterostructures
Authors: Schowalter L. J. , Kim B. M. , Thundat T. G. , Ventrice Carl A. , LaBella V. P. 
Published: April 2011

ABSTRACTA new technique for growth of exactly two monolayers of CaF2 on Si(111) substrates is demonstrated. This technique takes advantage of the tendency of CaF2 to form thick islands at Si step edges on vicinal substrates once a two-monolayer thick wetting layer is deposited. A comparison of I-V characteristics for epitaxial CaF2 layers grown on on-axis versus off-axis substrates demonstrates the advantages of this technique. In addition, preliminary results for electron tunneling through the CaF2 structure is shown using the ballistic electron emission microscopy (BEEM) technique.
Quantitative Eels Profiling of Planar Faults in CaTiO3 Perovskite Approaching Atomic Resolution: A Comparison With Z-Contrast Imaging
Authors: Gu Hui , Čeh Miran 
Published: April 2011

ABSTRACTUsing EELS profiling, CaO planar faults of 1.36 nm spacing in CaTiO3 are resolved. Effective probe size was measured as 1.3 nm by quantitative analysis of EELS profiles, which is remarkably larger than 0.5 nm resolution for Z-contrast in similar conditions. Delocalization in EELS is the origin for this discrepancy, and strong elastic scattering near zone axis plays an important role in the quantification of profiles. Suitable spectrum subtraction successfully separates ELNES signal from the fault in one atomic distance with rock-salt structure. ELNES profiles for different local structures are also achieved. These examples demonstrate that EELS analysis can be performed reliably approaching atomic level, beyond the limit of probe size.