bluuebunny/crossref_metadata_2025 huggingface dataset:
Containerless solidification studies of the α–1/1 crystal approximant in Ti–Cr–Si–O alloys
Authors: Croat T. K. , Kelton K. F. , Holland-Moritz D. , Rathz T. J. , Robinson M. B.
Published: March 2008

The nucleation behavior of α(TiCrSiO), a 1/1 Fibonacci crystal approximant phase, was investigated in alloys made near the stoichiometric composition. Containerless solidification studies were made with electromagnetic radio-frequency levitation and the 105-m NASA Drop Tube. The solidification microstructures indicate that the α–Ti hexagonal solid solution was the primary crystallizing phase in these alloys, growing dendritically. The α(TiCrSiO) phase nucleated in the remaining liquid. The competition between these two phases resulted from the high oxygen concentration needed to form α(TiCrSiO), which also stabilized the hexagonal-close-packed α–Ti phase.
Fiber breakage in polymer-matrix composite during static and fatigue loading, observed by electrical resistance measurement
Authors: Wang Xiaojun , Chung D. D. L.
Published: March 2008

By measuring the electrical resistance of a continuous unidirectional carbon fiber epoxy-matrix composite along the fiber direction during loading in this direction, fiber breakage was progressively monitored in real time. Fiber breakage occurred in spurts involving 1000 or more fibers. It started at about half of the failure strain during static tensile loading and at about half of the fatigue life during tension–tension fatigue testing. Immediately before static failure, at least 35% of the fibers were broken. Immediately before fatigue failure, at least 18% of the fibers were broken. The fiber breakage was accompanied by decrease in modulus.
Formation and structure of carbon nanocage structures produced by polymer pyrolysis and electron-beam irradiation
Authors: Oku Takeo , Hirano Takanori , Suganuma Katsuaki , Nakajima Satoru
Published: March 2008

Carbon nanocapsules with SiC and Au nanoparticles were produced by thermal decomposition of polyvinyl alcohol at about 500 °C in Ar gas atmosphere. The formation mechanism of nanocapsules and a structural model for the nanocapsule/SiC interface were proposed. In addition, carbon clusters were formed at the surface of carbon nanocapsules, and carbon onions were produced by electron irradiation of amorphous carbon produced from polyvinyl alcohol. The present work indicates that the pyrolysis of polymer materials with clusters is a useful fabrication method for the mass production of carbon nanocapsules and onions at low temperatures compared to the ordinary arc discharge method.
Mechanochemically synthesized NbC cermets: Part I. Synthesis and structural development
Authors: Murphy B. R. , Courtney T. H.
Published: March 2008

The mechanochemical synthesis of NbC-based cermets is described. Nanocrystalline NbC is synthesized by room-temperature milling of Nb and graphite (or hexane) mixtures. While some structural coarsening occurs during powder consolidation to full density, a nanoscale structure is maintained. Grinding media wear occurs during milling, and milled powders contain Fe from this abrasion. This phase, homogeneously distributed in milled powders, segregates during consolidation and heat treatment, and a cermetlike microstructure results. Copper added to the powder charge yields NbC–Cu or NbC–Cu-Fe cermets. Copper-containing materials have different phase morphologies. In particular, relatively large NbC particles are dispersed in a matrix containing finer NbC and metal particles. Higher Cu-content materials also develop a pure Cu constituent on heat treatment. A companion paper, “Mechanochemically synthesized NbC cermets: Part II. Mechanical properties,” addresses aspects of the mechanical behavior of these materials.
Mechanism of grain growth in liquid-phase-sintered β–SiC
Authors: Kim Young-Wook , Mitomo Mamoru , Zhan Guo-Dong
Published: March 2008

The mechanism for grain growth of β–SiC was investigated by annealing hot-pressed β–SiC–oxynitride glass (Y–Mg–Si–Al–O–N) ceramics at 1800 °C. An observed decrease in grain growth with increasing weight fraction of liquid confirms a diffusion-controlled growth mechanism in the system. The growth of nearly spherical β–SiC grains in the annealed specimen also supports the above conclusion.
Fabrication of (Ba,Pb)TiO3-based tapes with positive temperature coefficients of resistivity by the oxidation of malleable, metal-bearing precursors (the volume identical metal oxidation process)
Authors: Allameh Seyed M. , Sandhage Kenneth H.
Published: March 2008

The feasibility of producing (Ba,Pb)TiO3-based thermistor tapes by the oxidation of malleable, metal-bearing precursors has been demonstrated. Intimate Ba–Pb–Ti–TiO2-bearing powder mixtures, produced by high-energy vibratory milling, were packed within a fugitive metal can and then compacted and formed into tapes of uniform thickness by cold drawing and rolling. The tape-shaped precursors were oxidized and converted into (Ba,Pb)TiO3-based tapes with a series of heat treatments at ≤1120 °C. With proper control of thermal treatments and chemical additions (Sb2O3 + MnO2 dopants), positive-temperature-coefficient-of-resistivity thermistors were produced that exhibited significant increases in resistivity commencing at temperatures ≥350 °C.
Three-dimensional vapor growth mechanism of carbon microcoils
Authors: Chen Xiuqin , Saito T. , Kusunoki M. , Motojima S.
Published: March 2008

Carbon microcoils were grown by the Ni-catalyzed pyrolysis of acetylene. The growth patterns and the tip morphologies of the carbon coils are examined in detail, and a growth mechanism is proposed. Basically, six thin fibers grew from a Ni catalyst grain during the initial growth stage immediately followed by the coalescence of the four fibers to form two fibers and then forming double-helixed carbon coils. A small amount of S and O, as well as C and Ni, was observed on the periphery of the cross section of the Ni catalyst grain. On the other hand, S and O were not observed in the central part. The driving force of the coiling of the straight fibers to form carbon coils is considered to be the strong anisotropy of the carbon deposition between different crystal faces.
Gas-phase nucleation during chemical vapor deposition of copper films and its effect on the resistivity of deposited films
Authors: Rauf I. A. , Siemsen R. , Grunwell M. , Egerton R. F. , Sayer M.
Published: March 2008

A study of the electrical resistivity and microstructure of thin copper films deposited by low-pressure chemical vapor deposition from copper (I) hexafluoroacetylacetonate vinyltrimethylsilane (Cupra Select) was undertaken. Evidence for the nucleation of solid copper in the gas phase at substrate temperatures of about 250 °C is presented. A process to predict the effects of gas-phase nucleation and growth on the electrical resistivity of the resulting film is discussed.
Germanium segregation in the Co/SiGe/Si(001) thin film system
Authors: Goeller Peter T. , Boyanov Boyan I. , Sayers Dale E. , Nemanich Robert J. , Myers Alline F. , Steel Eric B.
Published: March 2008

Cobalt disilicide contacts to silicon–germanium alloys were formed by direct deposition of pure cobalt metal onto silicon–germanium films on Si(001) substrates. Segregation of germanium was observed during the reaction of the cobalt with the silicon–germanium alloy. The nature of the Ge segregation was studied by transmission electron microscopy, energy dispersive spectroscopy, and x-ray diffraction. In the case of cobalt films deposited onto strained silicon–germanium films, the Ge segregation was discovered to be in the form of Ge-enriched Si1−xGex regions found at the surface of the film surrounding CoSi and CoSi2 grains. In the case of cobalt films deposited onto relaxed silicon–germanium films, the Ge segregation was dependent on formation of CoSi2. In samples annealed below 800 °C, where CoSi was the dominant silicide phase, the Ge segregation was similar in form to the strained Si1−xGex case. In samples annealed above 800 °C, where CoSi2 was the dominant silicide phase, the Ge segregation was also in the form of tetrahedron-shaped, Ge-enriched, silicon–germanium precipitates, which formed at the substrate/silicon– germanium film interface and grew into the Si substrate. A possible mechanism for the formation of these precipitates is presented based on vacancy generation during the silicidation reaction coupled with an increased driving force for Ge diffusion due to silicon depletion in the alloy layer.
Study of hydrogen annealing of ultrahigh molecular weight polyethylene irradiated with high-energy protons
Authors: Wilson J. F. , Liu J. R. , Romero-Borja F. , Chu Wei-Kan
Published: March 2008

Ultrahigh molecular weight polyethylene, an important biomaterial for orthopedic implants, was irradiated with 2.6- and 3-MeV H+ ions at low doses from 5.7 × 1011 to 2.3 × 1014 ions/cm2. Fourier transform infrared spectroscopy showed that irradiation resulted in increased free radicals, carbon double bonds, and increased methyl and vinyl end groups. The free radicals resulted in poor polymer oxidative stability, as measured by increased carbonyl concentration. Hydrogen annealing after ion irradiation reacted with the free radicals generated during proton irradiation resulted in a 40–50% decrease in infrared absorption associated with carbonyl and prevented further oxidation.
Magnetophoretic deposition of nanocomposites
Authors: Katz Joseph L. , Xing Yangchuan , Cammarata R. C.
Published: March 2008

This communication reports the novel idea of using a magnetic field gradient to hold magnetic nanoparticles at desired densities in a fixed location (e.g., on an electrode surface), while metal atoms are deposited electrochemically in the interstices between them. Using it, nanocomposites consisting of γ–Fe2O3 nanoparticles (with a mean size of about 40 nm) in a copper metal matrix were reproducibly fabricated, with particle volume fractions ranging from 0.2% to 50%. These nanocomposites, ceramic magnetic particles in a conductive metal matrix, are expected to have unusual or enhanced mechanical, electrical, and magnetic properties.
Evolution of tensile residual stress in thin metal films during energetic particle deposition
Authors: Misra A. , Nastasi M.
Published: March 2008

Physical-vapor-deposited thin metal films often exhibit tensile residual stresses. We studied the stress evolution in thin Cr films and found that increasing bombardment with energetic particles (atoms or ions) at low energies leads to an increase of tensile stress to a maximum followed by a rapid decrease. Microstructural characterization by transmission electron microscopy revealed that two different microstructures are observed for the same level of tensile stress: films processed at low bombardment had columnar porosity while no porosity was observed in films processed at higher bombardment. The observed stress evolution is interpreted by considering how the mean interatomic distance (and hence the force) in the intercolumnar regions is modified by energetic particle bombardment.
Static and cyclic creep behavior of in situTiB2 particulate reinforced aluminum composite
Authors: Ma Z. Y. , Tjong S. C. , Li S. X.
Published: March 2008

Static and cyclic creep tests of Al–15 vol% TiB2in situ composite were carried out at 573–623 K. The values of apparent stress exponent and activation energy for cyclic creep of the composite were much higher than that for static creep. Furthermore, the cyclic creep rate tended to decrease with increasing percentage of unloading amount but was independent of the loading frequencies under the frequency ranges investigated. Finally, the true stress exponent of the composite was equal to 8, and the true activation energy was close to the value for the lattice self-diffusion of aluminum by incorporating a threshold stress for the analysis.
Improved densification by nano-sized sintering aids for Si3N4
Authors: Wang Liwu , Sigmund Wolfgang M. , Roy Sukumar , Aldinger Fritz
Published: March 2008

The densification of Si3N4 with nano-sized sintering aids that were in situ incorporated by a combustion process was studied in comparison with that of sintering aids mixed by ball milling. The combustion process directly produces amorphous and nano-sized Y–Al oxides within the Si3N4 powder. X-ray diffraction results indicate that amorphous Y–Al oxides begin to crystallize into Y3Al5O12 at about 600 °C. Additionally the nano-sized sintering aids are more homogeneously distributed and thereby promote the formation of eutectic melts at lower temperatures during liquid-phase sintering. Therefore, the densification process of Si3N4 during liquid-phase sintering is strongly accelerated. The microstructure of as-sintered parts from combusted powder seems more dense and homogeneous.
Carbon–silica alloy material as silicon carbide precursor prepared from phenol resin and ethyl silicate
Authors: Narisawa Masaki , Yamane Kentaro , Okabe Yoshio , Okamura Kiyohito , Kurachi Yasuo
Published: March 2008

Three kinds of inorganic–organic hybrid gel sheets were prepared from the liquid mixtures of ethyl silicate and water–soluble phenol resin. The prepared transparent gel sheets were fired at various temperatures. The density of the fired sheets jumped up at 773–1023 K with disappearance of organic groups. The sheets kept the prepared shape after the 1273 K firing, and their density increased with the silica content. After the firing at 1873 K, the sheets with high carbon content (C/SiO2: 5.60, 3.52) were converted into the sheets composed of silicon carbide aggregate with excess carbon, while the sheet with low carbon content (C/SiO2: 1.43) was converted into the fragile powders.
Synthesis of nanocrystalline manganese oxide powders: Influence of hydrogen peroxide on particle characteristics
Authors: Moon Jooho , Awano Masanobu , Takagi Hiroyoshi , Fujishiro Yoshinobu
Published: March 2008

Nanocrystalline manganese oxide powders have been prepared at 25 °C by precipitation from Mn(NO3)2 aqueous solution. The presence and addition sequence of H2O2 significantly influence particle characteristics of the resulting manganese oxides, including crystal structure, particle size and morphology, and surface area, depending upon molar ratio of H2O2 with respect to Mn. The precipitation from preoxidized manganese solution by H2O2 results in flakelike-shaped amorphous hydrous manganese oxide (MnO2xH2O). In the absence of H2O2, on the other hand, amorphous Mn(OH)2 is obtained, and a part of Mn(OH)2 subsequently transforms into crystalline Mn3O4 by oxidation in air. Relative population of amorphous Mn(OH)2 decreases by dissolution when post-treated with H2O2. At Mn:H2O2 = 1:4, the well-defined 16-nm-sized nanocrystalline Mn3O4 with homogenous particle morphology is prepared. The treatment with excess H2O2, however, destroys crystalline Mn3O4 and leads to further oxidation of the aqueous manganese species. Under these conditions, a mixture of needlelike Mn2O3 and cubelike Mn3O4, including amorphous MnO2xH2O, is obtained.
Effect of oxygen partial pressure on texture development in lead zirconate titanate thin films processed from metalorganic precursors
Authors: Norton Jarrod L. , Liedl Gerald L. , Slamovich Elliott B.
Published: March 2008

Metalorganic liquid precursors were used to examine the effects of processing atmosphere on texture development in oriented Pb(Zr0.60Ti0.40)O3 thin films. After removal of organic ligands via pyrolysis, the films were heated at 25 °C/min in a 5% H2/Ar atmosphere until a switching temperature, after which the atmosphere was switched to pure oxygen. The films were heated to a maximum temperature of 650 °C with switching temperatures ranging from 450 to 600 °C. The degree of (111) orientation in the lead zirconate titanate (PZT) films increased with increasing switching temperature, resulting in highly textured (111) PZT films. These results suggest that atmosphere control plays a significant role in texture development during rapid thermal processing.
Thermochemistry of Si6–zAlzOzN8–z(z = 0 to 3.6) materials
Authors: Liang Jian-Jie , Navrotsky Alexandra , Leppert Valerie J. , Paskowitz Michael J. , Risbud Subhash H. , Ludwig Thomas , Seifert Hans J. , Aldinger Fritz , Mitomo Mamoru
Published: March 2008

Enthalpies of formation were determined for β-sialon phases (Si6–zAlzOzN8–z, z = 0.46 to 3.6) by high-temperature oxidative drop solution calorimetry using an alkali-metal borate (52 wt% LiBo2; 48 wt% NaBO2) solvent. Oxygen gas was bubbled through the melt to accelerate oxidation of the oxynitride samples during dissolution. Sialons near z = 2 appear less stable energetically than ones with higher or lower nitrogen content. A large configurational entropy contribution for sialons with z > 2 may further stabilize these materials. This larger free energy driving form may be the reason for success in pulse-activated processing of these materials. The enthalpies of formation further suggest that a greater driving form for oxynitride formation exists in batch synthesis using SiO2 rather than Al2O3.
Phase transition and the soft lattice mode of a perovskite crystal studied by Raman scattering and thermal measurements
Authors: Xia H. R. , Li L. X. , Wei J. Q. , Wang J. Y. , Yang Z. H. , Guan Q. C. , Jiang W. L.
Published: March 2008

The paraelectric–ferroelectric structural transition of potassium lithium tantalite niobate has been studied by both Raman scattering and thermal measurements. A condensed soft lattice vibrational mode at the phase transition has been analyzed. It originates from the symmetric O2/O3–Nb/Ta–O3/O2 in-plane bending of the Nb/TaO6group. The soft optical phonon mode concerns the extraordinary transverse optical phonons propagating along the [110] direction. The thermal expansion experiments show a displacive phase transition and a big thermal contraction in thecdirection of the crystal, with an average linear expansion coefficient αc= −4.52 × 10−5K−1. The phase transition temperature and enthalpy are 358 K and 0.50 J/g, respectively. Curie temperature measured by four methods is within 353 and 360 K.
Fabrication of cellular NiTi intermetallic compounds
Authors: Li Bing-Yun , Rong Li-Jian , Li Yi-Yi , Gjunter V. E.
Published: March 2008

Self-propagating high-temperature synthesis (SHS) has been successfully developed for the fabrication of cellular NiTi intermetallic compounds, which have an open cellular structure with about 60 vol% porosity and more than 95% open-porosity ratio. The SHS reactions lead to the formation of TiNi, Ti2Ni, Ni3Ti, and Ni4Ti3 intermetallics. The SHS process can be controlled by regulating the preheating temperature, which has effects on the phase amount and the shape as well as macrodistribution of pores in the products.
Fracture origins in LiNbO3 wafers due to postprocessing micro-repolarization
Authors: Nagata Hirotoshi , Ichikawa Junichiro , Sakima Mitsuru , Shima Kaori , Haga Eungi Min
Published: March 2008

In the process of developing electro-optic devices from ferroelectric z-cut LiNbO3 wafers, a repolarization throughout the wafer thickness occurs due to a localization of electric charges on the wafer. The repolarization not only generates microdomains causing light to scatter but also large defects in the crystal that become the origin of wafer fracture. The size of such defects is comparable to the wafer thickness (0.5 mm), and an anomaly in the chemical and crystalline structures can be found in them. X-ray diffractometry and x-ray photoelectron spectroscopy confirm that a chemical reduction in the defective region occurs.
Influence of reduction mechanism on the morphology of cobalt nanoparticles in a silica-gel matrix
Authors: Basumallick A. , Das G. C. , Mukherjee S.
Published: March 2008

Cobalt-chloride- and dextrose-containing silica gels were reduced in situ under nitrogen atmosphere in the temperature range of 600 to 950 °C. Analysis of kinetic data on the in situ reduction shows that, in the temperature range of 600 to 750 °C, the contracting geometry type and, in the temperature range of 800 to 950 °C, the nucleation and growth type of mechanisms remain operative. The shape and size of the reduced cobalt nanoparticles in the silica matrix was studied by examining the transmission electron micrographs of the reduced Co/SiO2 samples. The morphology of the reduced metallic particles was found to be influenced by the change in reduction mechanism.
Fracture mode of alumina/silicon carbide nanocomposites
Authors: Zimmermann André , Hoffman Mark , Rödel Jürgen
Published: March 2008

Computer simulations have been designed to elucidate the evolution of microcracking in a nanocomposite using appropriate material values for alumina and silicon carbide. These are compared to a single-phase material using elastic and thermal expansion coefficients for alumina. It is found that the region and the fracture mode where microcracking ensues are determined by the intensity and the length scale of the residual stress fields, which interact. Of specific interest are the region, fracture mode, and length of ensuing microcracks for materials with different inclusion locations (at the grain boundary or within the grain) and with different grain size to inclusion size ratios.
Orientation-dependent properties of silicon nitride with aligned reinforcing grains
Authors: Park Dong-Soo , Choi Myoung-Je , Roh Tae-Wook , Kim Hai-Doo , Han Byung-Dong
Published: March 2008

Silicon nitride with the aligned reinforcing grains was prepared by tape casting with addition of the silicon nitride whiskers and gas-pressure sintering at 2148 K. The microstructure and the mechanical properties of the sintered sample, including the fracture toughness and the three-point flexural strength, were highly anisotropic. Both the fracture toughness and the flexural strength were the highest when the crack-propagation direction was normal to the alignment direction. This result was interpreted from the laminate composite materials’ point of view. Although the large elongated grains were as long as 44.4 ± 12 μm and as wide as 5.1 ± 0.67 μm, they were not the fracture origins.
Nanoindentation and adhesion of sol-gel-derived hard coatings on polyester
Authors: Chan C. M. , Cao G. Z. , Fong H. , Sarikaya M. , Robinson T. , Nelson L.
Published: March 2008

We investigated sol-gel-derived silica-based hard coatings on modified polyester substrates. The silica network was modified by incorporating an organic component and adding transition metal oxides. These modifications resulted in tailored thermal, optical, and mechanical properties of the coatings. Various low-temperature densification techniques were studied including sol-preparation procedure, enhanced solvent evaporation, ultraviolet irradiation, and low-temperature heating (below 150 °C). Oxygen plasma etching was applied to improve the adhesion of the sol-gel coatings on the plastic surface. Nanoindentation analysis revealed that the coatings have a surface hardness up to 2.5 ± 0.27 GPa and an elastic modulus up to 13.6 ± 0.4 GPa, approximately an order of magnitude higher than that of the plastic surface.
Water-based Si3N4 suspensions: Part I. Effect of processing routes on the surface chemistry and particle interactions
Authors: Galassi C. , Bertoni F. , Ardizzone S. , Bianchi C. L.
Published: March 2008

Si3N4 powders manufactured by two different preparative routes were characterized for the solid–liquid interfacial reactivity and surface composition. Three mixing processes were tried to investigate the modifications of silicon nitride particle surface in aqueous suspensions. The surfaces of the starting powders and the dried mixed powders were investigated by x-ray photoelectron spectroscopy to determine the nature and ratios of surface groups. Electroacoustic measurements show that no change occurs in the isoelectric point for the mixed Si3N4 powders while the milling/mixing process has a great influence on the zeta potential magnitude and particle size distribution.
Ultrafine MnFe2O4 powder preparation by combusting the coprecipitate with and without Mg2+ or Zn2+ additives
Authors: Yu Hsuan-Fu , Zhong Wen-Bing
Published: March 2008

Ultrafine MnFe2O4 powder with its crystallites less than 100 nm was prepared using a combustion process. The coprecipitates containing the stoichiometric amount of Mn2+ and Fe3+ to form MnFe2O4 were prepared by dissolving the required metallic nitrates in de-ionized water and adding NH4OH to adjust the pH of the solutions to 9. The collected dried precipitates were then heated up to predetermined temperatures and then quickly contacted with the acetone spray. Upon contacting with the heated precipitates, the acetone spray was ignited. The combustion of acetone caused the precipitates to form crystalline MnFe2O4 without chemical segregation. The crystallinity of MnFe2O4 powder so obtained depended on the ignition temperature of acetone spray. MnFe2O4 powder obtained at acetone ignition temperature of 773 K had higher crystallinity than that obtained at acetone ignition temperature of 523 K. The presence of a small amount of Mg2+ or Zn2+ in the composition of the coprecipitates promoted the mobility of constituent ions of the combusted powder and resulted in bigger MnFe2O4 crystallites at a lower acetone ignition temperature.
Microstructural and electrical property studies of Pb(Zr0.52Ti0.48)O3 films grown on p-InP (100) substrates by a radio-frequency magnetron-sputtering technique at low temperature
Authors: Kim T. W. , Yoon Y. S.
Published: March 2008

Pb(Zr0.52Ti0.48)O3 thin films were grown on p-InP (100) substrates by using radio-frequency magnetron-sputtering at a relatively low temperature (∼450 °C). X-ray diffraction measurements showed that the Pb(Zr0.52Ti0.48)O3 film layers grown on the InP substrates were polycrystalline, and Auger electron spectroscopy measurements indicated that the compositions of the as-grown films consisted of lead, zirconium, titanium, and oxygen. Transmission electron microscopy measurements showed that the grown Pb(Zr0.52Ti0.48)O3 was a polycrystalline layer with small domains and that the Pb(Zr0.52Ti0.48)O3/InP (100) heterointerface had no significant interdiffusion problem. Room-temperature current–voltage and capacitance–voltage (C–V) measurements clearly revealed a metal–insulator–semiconductor behavior for the Pb(Zr0.52Ti0.48)O3 insulator gates, and the interface state densities at the Pb(Zr0.52Ti0.48)O3/p-InP interfaces, as determined from the C–V measurements, were approximately low 1011 eV−1 cm−2 at an energy of about 0.6 eV below the conduction-band edge. The dielectric constant of the Pb(Zr0.52Ti0.48)O3 thin film, as determined from the C–V measurements, was as large as 907.2. These results indicate that the Pb(Zr0.52Ti0.48)O3 layers grown on p-InP (100) substrates at low temperatures hold promise for potential high-density nonvolatile memories and high-speed infrared sensors based on InP substrates.
Mechanical properties of biocompatible protein polymer thin films
Authors: Buchko Christopher J. , Slattery Margaret J. , Kozloff Kenneth M. , Martin David C.
Published: March 2008

A silklike protein with fibronectin functionality (SLPF) (ProNectin F®, Protein Polymer Technologies, Inc.) is a genetically engineered protein polymer containing structural and biofunctional segments. The mechanical properties and deformation mechanisms of electrostatically deposited SLPF thin films were examined by scratch testing, tensile testing, and nanoindentation. Scanning electron microscopy and scanned probe microscopy revealed that the macroscopic properties were a sensitive function of microstructure. The SLPF films were relatively brittle in tension, with typical elongation-to-break values of 3%. Nanoindentation data were fit to a power law relationship.
High-tensile ductility in nanocrystalline copper
Authors: Lu L. , Wang L. B. , Ding B. Z. , Lu K.
Published: March 2008

In this work we report a high-tensile ductility in a fully dense bulk nanocrystalline (nc) pure copper sample prepared by electrodeposition. A tensile ductility with an elongation to fracture of 30% was obtained in the nc Cu specimen with an average grain size of 27 nm, which is comparable to that for the coarse-grained polycrystalline Cu. An enhanced yield stress (119 MPa) and a depressed strain hardening exponent (0.22) were observed in the nc Cu sample with respect to the conventional polycrystalline Cu. The high-tensile ductility was attributed to the minimized artifacts in the nc sample, and the grain-boundary sliding deformation mechanism resulted from the numerous amount small-angle grain boundaries and the low microstrain (dislocation density).
Spatial variations in composition in high-critical-current-density Bi-2223 tapes
Authors: Holesinger T. G. , Bingert J. F. , Teplitsky M. , Li Q. , Parrella R. , Rupich M. P. , Riley G. N.
Published: March 2008

A detailed compositional analysis of high-critical-current-density (Jc) (55 and 65 kA/cm2at 77 K) (Bi,Pb)2Sr2Ca2Cu3Oy(Bi-2223) tapes was undertaken by energy dispersive spectroscopy in the transmission electron microscope. Structural features were coupled with characteristic compositions of the Bi-2223 phase. The average of all compositional measurements of the Bi-2223 phase was determined to be Bi1.88Pb0.23Sr1.96Ca1.95Cu2.98Oy. However, spatial variations in the Bi-2223 composition and differing phase equilibria were found throughout the filament structure. In particular, a considerable range of Bi-2223 compositions can be found within a single tape, and the lead content of the Bi-2223 phase is significantly depressed in the vicinity of lead-rich phases. The depletion of lead in the Bi-2223 phase around the 3221 phases may be a current-limiting microstructure in these tapes.
Fabrication of Ag/Bi2Sr2Ca1Cu2O8±x superconducting tapes by the oxidation and postoxidation (partial melt) annealing of malleable, metal-bearing precursors
Authors: Detrie Terry J. , Sandhage Kenneth H.
Published: March 2008

A solid metal-bearing precursor route has been used to fabricate Ag-sheathed Bi2Sr2Ca1Cu2O8±x (2212) superconducting tapes. Intimately mixed Bi2O3–Sr–Ca–Cu-bearing powder was first synthesized by a two-stage, high-energy/low-energy mechanical alloying process. The powder was then packed into silver tubes and formed into tapes by drawing and biaxial (Turk's-head) rolling. The precursor tapes were oxidized and converted into Ag-sheathed 2212 by heat treatment at 350–860 °C in oxygen. Subsequent annealing at 897 °C, followed by slow cooling and subsolidus annealing at 850 °C, yielded 2212 grains with enhanced c-axis alignment. The resulting tapes exhibited average and maximum transport Jc (4.2 K, self-field) values of 3.2 × 104 and 6.8 × 104 A/cm2, respectively.
Preparation and magnetic properties of nanosized amorphous ternary Fe–Ni–Co alloy powders
Authors: Shafi Kurikka V. P. M. , Gedanken Aharon , Prozorov Ruslan , Revesz Adam , Lendvai Janos
Published: March 2008

Nanosized amorphous alloy powders of Fe25Ni13Co62, Fe38Ni23Co39, Fe40,Ni24,Co36, and Fe69Ni9Co22 were prepared by sonochemical decomposition of solutions of volatile organic precursors, Fe(CO)5, Ni(CO)4, and Co(NO)(CO)3 in decalin, under an argon pressure of 100 to 150 kPa at 273 K. The amorphous nature of these particles was confirmed by various techniques, such as scanning electron microscopy, transmission electron microscopy, electron microdiffraction, and x-ray diffractograms. Magnetic measurements indicated that the as-prepared amorphous Fe–Ni–Co alloy particles were superparamagnetic. The observed magnetization measured up to a field of 1.5 kG of the annealed Fe–Ni–Co samples (75–87 emu g−1) was significantly lower than that for the reported multidomain bulk particles (175 emu g−1), reflecting the ultrafine nature of our sample.
Ordered nanostructure of single-crystalline GaN nanowires in a honeycomb structure of anodic alumina
Authors: Cheng G. S. , Zhang L. D. , Chen S. H. , Li Y. , Li L. , Zhu X. G. , Zhu Y. , Fei G. T. , Mao Y. Q.
Published: March 2008

Ordered nanostructure of single-crystalline GaN nanowires in a honeycomb structure of anodic alumina was synthesized through a gas reaction of Ga2O vapor with a constant ammonia atmosphere at 1273 K in the presence of nano-sized metallic indium catalysis. Atomic force microscopy, x-ray diffraction, Raman backscattering spectroscopy, scanning electron microscopy, and transmission electron microscopy indicate that the ordered nanostructure consists of single-crystalline hexagonal wurtzite GaN nanowires in the uniform pores of anodic alumina about 20 nm in diameter and 40–50 μm in length. The growth mechanism of the ordered nanostructure is discussed. The photoluminescence spectrum of this nanostructure is also reported.
Shear-induced ordered structure in polystyrene/clay nanocomposite
Authors: Chen Guangming , Qi Zongneng , Shen Deyan
Published: March 2008

A shear-induced ordered structure in an exfoliated polystyrene (PS)/clay nanocomposite is reported. X-ray diffraction (XRD), transmission electron microscopy (TEM), and infrared dichroism techniques have been employed to investigate the shear-induced ordered structure in the exfoliated PS/clay nanocomposite. Compared with the broad amorphous peaks before extrusion, a series of sharp diffraction peaks were observed in XRD pattern for the extruded PS/clay nanocomposite pellet sample, showing that an ordered structure occurred under shear flow. TEM images confirmed directly that the origin of the ordered structure was mainly due to the planar orientation of the primary particles of silicate layers as well as local ordered microstructure of the primary particles, induced by shear flow. The infrared dichroism study indicated that the phenyl group of PS apparently oriented parallel to the film surface, whereas no obvious orientation of the aliphatic chain could be observed. Based on these investigations, a possible mechanism was deduced for the formation of the ordered structure induced by shear flow in the exfoliated PS/clay nanocomposite.
Thermal and mechanical properties of aluminum titanate–mullite composites
Authors: Huang Y. X. , Senos A. M. R. , Baptista J. L.
Published: March 2008

The thermal and mechanical properties of aluminum titanate–mullite composites prepared by a gel-coated powder processing method, namely a mullite precursor gel coating aluminum titanate particles (containing 2.5 wt% MgO), were investigated. A microstructure with both elongated and equiaxed mullite grains was observed in the composite samples. Both the mechanical strength and the thermal expansion coefficient increased with the mullite amount. The mechanical strength showed a strong dependence on the grain size of aluminum titanate with an exponent of −3. Inhibition of aluminum titanate grain growth due to the presence of the mullite phase enhanced the mechanical strength of the composites. The thermal shock resistance tended to decrease as the mullite content increased. The thermal stability of aluminum titanate was improved in the present composite system.
Stability of monoclinic and tetragonal zirconia at low oxygen partial pressure
Authors: Mommer Niels , Lee Theresa , Gardner John A.
Published: March 2008

We have found that both tetragonal and monoclinic zirconia annealed at temperaturess in the range of 1100 to 1300 °C in atmospheres of low oxygen partial pressures (down to 10−26Pa) transform slowly to an apparently cubic phase. The transformation can be reversed by increasing the oxygen partial pressure sufficiently, i.e., exposing the sample to air again. These observations were made by111In/Cd perturbed angular correlation (PAC) measurements of undoped zirconia samples. Upon annealing under various reducing atmospheres PAC spectra show a steadily increasing fraction of Cd probe atoms in a locally cubic environment with the fraction of probe atoms in tetragonal or monoclinic sites decreasing accordingly.
Silicon dioxide nanotubes prepared by anodic alumina as templates
Authors: Zhang Ming , Bando Y. , Wada K.
Published: March 2008

Aligned slicon dioxide nanotubes with diameters of 30–40 nm synthesized by the sol-gel template method are presented. This process involves the growth of nanotubes from ordered nanochannel-array pores in anodic alumina. For a silica sol aged at room temperature and dipped for 1 min, nanowires were formed in a shorter period of aging time (2 days); nanotubes connecting with solid nanofibers were obtained in a longer aging time (30 days). The formation of nanotubes depends strongly on the temperature of the sol. For a short dipping time (<1 min), bamboolike nanofibers were prepared when the sol was at high temperature (50 °C); however, perfect nanotubes with the sharp wall were synthetized for the lower sol temperature (5 °C). The lower sol temperature is, the smoother the inside wall of nanotubes is. It is proved that viscosity plays an important role on the morphology of nanotubes.
Stable nanocrystalline zirconia sols prepared by a novel method: Alcohol thermal synthesis
Authors: Zhao Junping , Fan Wenhao , Wu Dong , Sun Yuhan
Published: March 2008

Nanocrystalline zirconia sols with a metastable cubic phase were synthesized from diglycol-modified zirconium n-propoxide via a novel method, alcohol thermal synthesis. The chemical bonding of diglycol with zirconium was found to be important in obtaining stable nanocrystalline zirconia sols. Sols produced in this way were translucent with the primary particles of 4-nm crystallites, and the corresponding gel was shown to be mesoporous with a pore size from 2.5 to 3.8 nm and Brunauer—Emmett—Teller surface areas between 130 and 266 m2 g−1. This indicates that alcohol thermal synthesis shares the advantages of both the sol-gel process and hydrothermal synthesis.
Molecular orbital calculations of chemical bonding states of solute elements in amorphous silicon nitride ceramics
Authors: Matsunaga Katsuyuki , Iwamoto Yuji , Matsubara Hideaki
Published: March 2008

We performed ab initio Hartree–Fock molecular orbital calculations of solute elements in amorphous silicon nitride (Si–N) ceramics. To investigate effects of solute elements, X, such as boron, carbon, aluminum, silicon, and phosphorus, on stabilization of the Si–N network, we used model clusters representing local atomic structures in the Si–N network, and the solute elements were substituted for nitrogen. Bonding characteristics around the solute elements were analyzed, and bond energies of Si–X were also calculated using model clusters. It was found that, among these solute elements in amorphous Si–N, the Si–C bond is able to make the Si–N network more stable due to its high covalency.
Optimization of heating schedules in pyrolytic binder removal from ceramic moldings
Authors: Song J. H. , Evans J. R. G. , Edirisinghe M. J. , Twizell E. H.
Published: March 2008

A model that finds the maximum permissible heating rate for pyrolysis of ceramic moldings is extended to produce multi-segment temperature–time profiles to minimize the binder removal time. The degradation of the polymer and the diffusion of degradation products in solution to the free surface in a cylinder containing 50 vol% alumina and polyalphamethylstyrene is considered. The theory has previously been validated experimentally for fixed heating rates for cylindrical and flat plate geometries and for overpressure debinding. The extended model, presented here, calculates the vapor pressure of monomer over solution and modifies the heating rate to keep this just below ambient pressure. In this way, the temperature follows the maximum allowable rate at each stage to prevent boiling and hence the incidence of defects.
Roughness development in electrodeposited ultrathin cobalt and nickel layers
Authors: Renner Robert F. , Liddell KNona C.
Published: March 2008

For both Co and Ni, a series of electrodeposited films of varying thickness (2–10 nm) was grown under otherwise identical conditions using potentiostatic control. The substrates were pieces of Si wafer onto which a Cu basal layer had been thermally evaporated. Contact mode atomic force microscopy was used to measure both the root-mean-square peak height (nm) and the areal peak density (μm−2) of each film. Root-mean-square (rms) peak heights for Co initially increase with film thickness and then plateau at a layer thickness of 3 nm. For Ni, the rms peak heights increase almost linearly for layer thicknesses less than 11 nm, reaching a value of 6 nm. Peak density shows the opposite trend, decreasing with layer thickness before reaching an approximately constant value for both metals at a film thickness of 4 nm. The atomic force microscopy data indicate that Ni and Co have different deposition mechanisms. A Co film initially nucleates rapidly; then the nucleation phase is followed by multinuclear, multilayer growth. Ni deposits also have initial rapid nucleation, but the dominant growth mode is primarily vertical, with increasing peak heights but no change in peak density. Increased peak density is linearly correlated with decreased peak height for the thinnest films in both systems.
Chemical deterioration of Al film prepared on CF4 plasma-etched LiNbO3 surface
Authors: Nagata Hirotoshi , Miyama Yasuyuki , Mitsugi Naoki , Shima Kaori
Published: March 2008

The fabrication process of an Al thin-film optical polarizer on LiNbO3 waveguides after CF4 plasma dry etching of a previously deposited SiO2 buffer layer was investigated. The problem in this process is a precipitation of compounds containing C, O, F, and Li on the etched LiNbO3 surface and a chemical deterioration of the Al caused by a reaction with these precipitates. Most notably, the growth of amorphous phase in addition to the crystalline Al metal grains and a partial oxidization of Al were found at the interface using transmission electron microscopy and x-ray photoelectron spectroscopy.
Deposition of crystal polythiophene thin films by KrF excimer laser ablation
Authors: Lu Y. F. , Ren Z. M. , Mai Z. H. , Chong T. C. , Ng S. C. , Miao P. , Cheong B. A. , Chow S. K. , Liew T. Y. F.
Published: March 2008

Thin films of polythiophene, a kind of polyheterocyclic compound with hydrogen function groups, were deposited by KrF excimer laser ablation of a compressed solid target in a vacuum chamber. The laser pulse fluence was approximately selected at 2 J/cm2 with a pulse duration of 25 ns. The structural, topographic, and electronic properties of the deposited thin films were analyzed by atomic force microscope, x-ray diffraction, and Raman and infrared spectroscopy measurements. Deposited thin films were observed to have good crystal properties and to be composed of crystalline cubes with a uniform size of 0.1 μm. The electronic structure of the deposited thin films should be different from the target materials, resulting from the laser irradiation effects. The influence of the deposition temperature on the structural and electronic properties of the deposited thin films was studied.
Preparation and characterization of Ni(OH)2 nanoparticles coated with dialkyldithiophosphate
Authors: Zhang Junyan , Yang Shengrong , Xue Qunji
Published: March 2008

Ni(OH)2 nanoparticles modified with di-n-hexadecyldithiophosphate (DDP) were prepared by a chemical surface modification method. The structure of the nanocluster was investigated using infrared spectroscopy, x-ray photoelectron spectroscopy, x-ray diffraction, transmission electron microscopy, and 31P nuclear magnetic resonance spectroscopy. The thermal stability of DDP coating on the Ni(OH)2 nanoparticles was compared to that of pyridinium di-n-hexadecyldithiophosphate (PyDDP) using thermogravimetric analysis. It was found that coated Ni(OH)2 nanoparticles had an average diameter of about 5 nm. Surface modification with DDP prevented water adsorption and effectively improved the dispersive capacity and antioxidative stability of Ni(OH)2 nanoparticles. The thermal stability of DDP coatings on the surface of nano-Ni(OH)2 particles was higher than that of PyDDP coatings because of the chemical interaction between PyDDP and Ni(OH)2 during the coating process.
Behavior of carbon nanotubes under high pressure and high temperature
Authors: Tang D. S. , Chen L. C. , Wang L. J. , Sun L. F. , Liu Z. Q. , Wang G. , Zhou W. Y. , Xie S. S.
Published: March 2008

The structural changes of carbon nanotubes induced by high pressure and high temperature were investigated by means of x-ray diffraction, Raman scattering, scanning electron microscopy, and transmission electron microscopy. It is shown that, with increasing pressure and temperature, the lattice constant d002 of tubes shortens, and then tubes collapse into tapelike ones; at the same time the C–C bonds at high curvature break, which lead the tapelike tubes to break into graphite sheets as diamond crystallization centers. Compared with graphite, the diamond particles from carbon nanotubes have many defects as the trace of tubes.
Effects of bonding structure on the properties of plasma immersion ion processed diamondlike carbon films
Authors: He X. M. , Walter K. C. , Nastasi M.
Published: March 2008

Hydrogenated diamondlike carbon (a-C:H DLC) films were prepared on different substrates by using C2H2–Ar plasma immersion ion processing (PIIP), and their bonding structure was modified by changing deposition parameters of the chamber pressure and the gas composition. The influence of the bonding structure on the properties of the DLC films was investigated by using ion-beam analysis techniques and Raman, infrared, and ultraviolet/visible spectroscopies and by analyzing the measured properties. The increases in density, hardness, and refractive index were found to correlate with the increase of the sp3-bonded structure and the concurrent decrease of both the C–H bonds and the average size of sp2-bonded domains in the films. An optimal combination of optical and mechanical properties was highly dependent on the hydrogen status existing in DLC films that can be adjusted by means of modulation of the synthesis parameters. The prepared DLC films exhibited desirable properties, which included a hardness above 28 GPa, a density above 2.3 g cm−3, a refractive index above 1.94, and band gap energies in the range of 1.8–1.85 eV.
Raman characterization of Li(Al1-xCox)O2
Authors: Chen G. , Hao W. , Shi Y. , Wu Y. , Perkowitz S.
Published: March 2008

For the first time, we measured Raman spectra from Li(Al1-xCox)O2 (x = 0.5 to 0.9), a new cathode material for lithium batteries. Whereas LiCoO2 sintered at 400 °C develops a spinel structure, Li(Al1-xCox)O2 sintered at 380 °C is amorphous, as shown by its single broad Raman band. Li(Al1-xCox)O2 sintered at 700 or 900 °C shows Raman peaks independent of x that coincide with those from LiCoO2, indicating that Li(Al1-xCox)O2 has the α–NaFeO2 structure (space group R3m). Traces of the impurity phase Co3O4 appear in samples treated at 900 °C but not at 700 °C. The Raman peak widths exceed those in LiCoO2, suggesting that replacement of Co by Al increases disorder among the Li ions.
Magnetic moment and atomic volume in supersaturated Fe–Cu solid solutions: Ab initiocalculations compared with experiments
Authors: Zhang Wenqing , Ma E.
Published: March 2008

The properties of nonequilibrium face-centered-cubic (fcc) and body-centered-cubic (bcc) Fe–Cu alloys were studied using the first-principles full-potential linearized augmented plane wave method within the generalized gradient approximation. The ab initio calculation results are compared quantitatively with the magnetic moment and atomic volume observed for mechanically alloyed FexCu100–x (x = 0 to 100) supersaturated bcc and fcc solid solutions. The calculations show that Cu alloying leads to a small enhancement of the magnetic moment of bcc Fe. The fcc Fe moment, on the other hand, experiences a more pronounced increase into a high-spin state upon alloying with Cu. It reaches approximately the same value as that in the bcc alloys for all Cu concentrations where fcc solutions are obtained in experiments, corroborating previous ab initio calculations using different methods. The magnetic moment increases are accompanied by an atomic volume expansion. Both the calculated moment and volume behavior are in good agreement with those measured for fcc and bcc Fe–Cu solutions. The magnetovolume expansion upon magnetic interaction between the alloyed Fe and Cu, rather than the positive heat of mixing, constitutes the primary reason for the atomic volume increase observed.