bluuebunny/crossref_metadata_2025 huggingface dataset:
A low-temperature and low-cost method to produce high-quality epitaxial anatase TiO2 thin films
Authors: Zhang Zhaoming
Published: May 2005

Epitaxial anatase TiO2 thin films were successfully grown on lattice-matched SrTiO3 (001) substrates by a novel hydrothermal method at very low temperatures (120–200 °C). This method is extremely simple and inexpensive in that the SrTiO3 substrate itself provides the source material for the TiO2 film. X-ray diffraction confirmed the high crystallinity and phase purity of the anatase films. The epitaxial relationship between the film and the substrate was determined as (001)[100]anatase // (001)[100]SrTiO3. Atomic force microscopy revealed the average size of the anatase crystallites as approximately 50 to 200 nm.
Solute concentration dependence of strength and plastic instabilities in Al-Mg alloys
Authors: Horváth Gy. , Chinh N.Q. , Lendvai J.
Published: May 2005

Characteristics of the dynamic strain aging (DSA) in the Portevin-Le Chatelier effect are experimentally investigated by dynamic indentation tests and numerically analyzed by using literature models. Experimental results obtained on Al–Mg alloys show that the occurrence and development of the plastic instabilities—serrated indentation—depend strongly on the solute content. During dynamic microindentation tests the amplitude of microhardness drops—similarly to the global hardness—and is changing as a power law function of Mg solute content with an exponent of 2/3. It has been shown that the term describing the effect of DSA in serrated flow is not proportional but rather a power expression of the local solute concentration, Cs, on the dislocation line with the exponent of 1/2. Together with this, the kinetics of solute segregation during DSA is controlled by the pipe diffusion.
Large-scale synthesis of amorphous phosphorus nitride imide nanotubes with high luminescent properties
Authors: Guo Qixun , Yang Qing , Zhu Lei , Yi Chengqi , Xie Yi
Published: May 2005

A facile solvothermal approach was successfully developed for the large-scale synthesis of amorphous phosphorus nitride imide (H3xP3N5+x) nanotubes with high luminescent properties by the reaction of 1,3,5-hexachlorotriphosphazene (P3N3Cl6) with sodium amide (NaNH2) at low temperatures. Transmission electron microscope images showed that the inner diameter of nanotubes is 120 ± 20 nm, wall thickness is 40 ± 10 nm, and length ranges from several to ten micrometers. Scanning electron microscope images revealed that the proportion of the nanotubes exceeds 90%. X-ray photoelectron spectroscopy spectra indicated that the binding energies of P2p and N1s are 133.30 and 398.40 eV, respectively, and the atomic ratio of P:N is 3:5.13. The infrared spectra of the sample are comparable to those of the reported HPN2 and HP4N7. Thermogravimetric analysis revealed that the product is very robust in a nonoxidizing atmosphere. The structure and the optical properties of the product and the annealed samples were investigated by x-ray diffraction and photoluminescence measurements, respectively.
Nucleation of the Fe3C in reaction of methane with nanocrystalline iron
Authors: Narkiewicz U. , Arabczyk W. , Konicki W. , Pattek-Janczyk A.
Published: May 2005

The carburization process of nanocrystalline iron in a flow of CH4/H2mixture under atmospheric pressure at 580 °C in a differential reactor–thermobalance was studied. The course of reaction was followed by thermogravimetry, and the phase composition of the samples carburized to different degrees was determined by x-ray diffraction (XRD) and Mössbauer spectroscopy techniques. The XRD method was also used for calculating the mean crystallite size of unconverted iron after reaction at different time intervals. An unexpected relation between the average size of iron crystallites and the degree of conversion was found. The nucleation mechanism of the nanocrystalline iron carbide in the kinetic area of the reaction, limited by the dissociative adsorption of methane, has been suggested. According to this mechanism, iron crystallites are carburized successively, from the smallest to the largest.
Mg-based bulk glassy alloys with high strength above 900 MPa and plastic strain
Authors: Yuan Guangyin , Qin Cunling , Inoue Akihisa
Published: May 2005

Bulk metallic glasses with a maximum diameter of 2.5–5 mm were formed in Mg75Cu5Ni10Gd10, Mg70Cu15Ni5Gd10, and Mg65Cu20Ni5Gd10 systems by copper mold casting. There is a clear tendency for glass-forming ability (GFA) to increase with increasing solute content. These bulk glassy alloys exhibit a large supercooled liquid region (ΔTx) of 44–64 K, indicating high thermal stability of the supercooled liquid. The Young’s modulus, fracture strength, elastic elongation limit, and plastic strain are in the range of 54–59 GPa, 854–904 MPa, 1.50–1.55%, and 0.10–0.20%, respectively. The Mg65Cu20Ni5Gd10 alloy exhibited the highest values of Young’s modulus and strength, while the largest plastic strain was obtained for the Mg75Cu5Ni10Gd10 alloy. The bulk Mg–Cu–Ni–Gd-based metallic glasses exhibited distinct enhanced corrosion resistance compared to Mg65Cu25Gd10 glassy alloy in NaCl aqueous solutions. The fabrication of the Mg-based bulk glassy alloys exhibiting a high strength level of about 900 MPa and plastic strains of ∼0.2%, in conjunction with good corrosion resistance, indicates that the Mg-based bulk glassy alloys may be used as a new generation of structural material.
Initial study of strengthening of NiAl–Cr(Mo)–Hf alloys by strong magnetic field
Authors: Ma G.J. , Wu C.W. , Zhou W.L. , Guo X.L. , Ren M.F. , Guo J.T.
Published: May 2005

It was found that after treatment under 10T magnetic field and temperature 900 °C the bending strength of NiAl–Cr(Mo)–Hf alloy is increased by about 75%. The fracture section observation shows that the specimens' ductility is enhanced by the magnetic field treatment. Electron probe microanalysis shows that after treatment of the magnetic field the Heusler phases at NiAl/Cr(Mo) grain boundaries are partially dissolved and the small Heusler phases particles at Cr(Mo) and matrix phases interfaces almost dissolved into NiAl matrix.
Measuring fracture toughness of coatings using focused-ion-beam-machined microbeams
Authors: Di Maio D. , Roberts S.G.
Published: May 2005

Measuring the toughness of brittle coatings has always been a difficult task. Coatings are often too thin to easily prepare a freestanding sample of a defined geometry to use standard toughness measuring techniques. Using standard indentation techniques gives results influenced by the effect of the substrate. A new technique for measuring the toughness of coatings is described here. A precracked micro-beam was produced using focused ion beam (FIB) machining, then imaged and loaded to fracture using a nanoindenter.
Synthesis of SiC microtube with villus-like morphology and SiC fiber
Authors: Kim Jae-Won , Lee Seoung-Soo , Jung Yeon-Gil , Choi Baig-Gyu , Jo Chang-Yong , Paik Ungyu
Published: May 2005

Silicon carbide (SiC) microtubes were synthesized and characterized via a vapor–solid (VS) reaction of carbon fiber (Csolid) and SiO(gas). The synthesis mechanisms were investigated. The precursor led complete conversion of [SiO(gas) + C(solid)] into [SiC(solid) + CO(gas)] through overall reaction under inert gas flow at and above 1350 °C. Carbon fibers with small surface area (0.7–2.0 m2 g−1) were gradually converted to SiC microtubes with large specific surface area (45–63 m2 g−1). Inner surface of SiC microtubes indicated a villus-like morphology, which consisted of submicron-sized SiC villi. The outer surface of the SiC microtubes was smooth. Inner surface morphology of SiC microtubes was dependent upon synthesizing temperature. Thickness of villus-like layer in SiC microtubes increased with increasing synthesizing temperature, showing 0.25 and 0.5 at 1350 and 1400 °C, respectively. Both VS and gas–liquid–solid (VLS) growth mechanisms were investigated in synthesis of SiC fiber as a reaction byproduct, and the reaction was governed by both growth mechanisms.
Enhanced mechanical properties in ultrafine grained 7075 Al alloy
Authors: Zhao Y.H. , Liao X.Z. , Zhu Y.T. , Valiev R.Z.
Published: May 2005

Highest strength for 7075 Al alloy was obtained by combining the equal-channel-angular pressing (ECAP) and natural aging processes. The tensile yield strength and ultimate strength of the ECAP processed and naturally aged sample were 103% and 35% higher, respectively, than those of the coarse-grained 7075 Al alloy counterpart. The enhanced strength resulted from high densities of Guinier–Preston (G-P) zones and dislocations. This study shows that severe plastic deformation has the potential to significantly enhance the mechanical properties of precipitate hardening 7000 series Al alloys.
Formation of Al2O3 during heating of an Al/TiO2 nanocomposite powder
Authors: Zhang D.L. , Ying D.Y. , Munroe P.
Published: May 2005

The solid-state reactions between Al and TiO2 that occur during heating an Al/TiO2 nanocomposite powder produced using high-energy mechanical milling have been studied using thermal analysis, x-ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) in combination with compositional microanalysis. It has been found that Al and TiO2 react in the temperature range from 650 to 800 °C, forming Al3Ti, but XRD analysis, SEM examination, and detailed TEM characterization of the powder particles heated to 800 °C show that the expected Al2O3 does not form. However, α–Al2O3 particles form during heating from 800 to 1000 °C. The possible reasons for the time gap between formation of Al3Ti and Al2O3 are discussed.
Microwave-hydrothermal synthesis and photoluminescence characteristics of zinc oxide powders
Authors: Lu Chung-Hsin , Hwang Wen-Jeng , Godbole S.V.
Published: May 2005

A microwave-hydrothermal process for the synthesis of crystalline zinc oxide powders has been developed in this study. Well-crystallized zinc oxide powders exhibiting different morphology, crystallinity, and particle size have been successfully prepared by controlling the process temperature and molarity of NH4OH in the starting solution. With increasing process temperature and NH4OH molarity during synthesis, the morphology of ZnO powders changes from flowerlike agglomeration to a well-developed rodlike shape. The band gap of ZnO powders increases with a decrease in the molarity of NH4OH during synthesis. Vacuum ultraviolet radiation (VUV) excited luminescence studies for ZnO powders reveal an excitation band at 161 nm possibly due to the absorption of O2− 2p electrons in the valence band. The VUV excitation band of ZnO powders observed at 161 nm will be useful for excitation of gas-discharged plasma display devices.
Indentation fracture toughness of amorphous steel
Authors: Hess Peter A. , Poon S. Joseph , Shiflet G.J. , Dauskardt Reinhold H.
Published: May 2005

Indentation fracture toughness experiments were performed on amorphous steel. Measured toughness values were 3.2 ± 0.3 MPa for 3-mm-thick specimens and 3.8 ± 0.3 MPa for 10-mm-thick specimens. Crack geometry was determinedto be of the “Palmqvist” or radial configuration. High indentation loads >40 N were necessary for crack formation, and indentation cracks did not form adjacent to every indent, or in a uniform pattern. Possible reasons for crack formation thresholds and geometry are discussed.
Growth and properties of Si–N–C–O nanocones and graphitic nanofibers synthesized using three-nanometer diameter iron/platinum nanoparticle-catalyst
Authors: Cui H. , Yang X. , Meyer H.M. , Baylor L.R. , Simpson M.L. , Gardner W.L. , Lowndes D.H. , An L. , Liu J.
Published: May 2005

Cone-shaped nanostructures of mixed composition (nanocones) and largely graphitic nanofibers were synthesized on silicon substrates using iron/platinum alloy nanoparticles as the catalyst in a direct-current plasma enhanced chemical vapor deposition reactor. The catalyst nanoparticles were monodisperse in size with an average diameter of 3 (±1) nm. The nanocones were produced on laterally widely dispersed catalyst particles and were oriented perpendicular to the substrate surface with an amorphous internal structure. The nanocones were produced by gas phase mixing and deposition of plasma-sputtered silicon, nitrogen, carbon, and oxygen species on a central backbone nucleated by the Fe–Pt catalyst particle. Field emission measurements showed that a very high turn-on electric field was required for electron emission from the nanocones. In contrast, the graphitic nanofibers that were produced when silicon sputtering and redeposition were minimized had the “stacked-cup” structure, and well-defined voids could be observed within nanofibers nucleated from larger catalyst particles.
Preparation of stable magnetorheological fluids based on extremely bimodal iron–magnetite suspensions
Authors: López-López M.T. , de Vicente J. , Bossis G. , González-Caballero F. , Durán J.D.G.
Published: May 2005

The high magneto-viscous response of magnetorheological fluids (MRFs) comes from the large size (≈1 μm) of the magnetic particles dispersed in the carrier liquid. Unfortunately, in the absence of a magnetic field, this large size constitutes the origin of some problems facing the technological applications of MRFs. These problems are (i) the instability of the suspensions caused by the fast settling of the high density magnetic particles used, and (ii) the poor redispersibility due to an irreversible aggregation. In this work, we used an electromagnetic induction method to study the stability of MRFs containing micron-sized iron particles dispersed in ferrofluids composed by oleate-covered magnetite nanoparticles dispersed in kerosene. Interestingly, we demonstrated that the sedimentation rate in iron/ferrofluid suspensions can be significantly lower than in iron/kerosene MRFs.
Sintering mechanisms of attrition milled titanium nano powder
Authors: Panigrahi B.B. , Godkhindi M.M. , Das K. , Mukunda P.G. , Dabhade V.V. , Ramakrishnan P.
Published: May 2005

Detailed sintering studies have been carried out on attrition milled nanocrystalline titanium powder through isothermal dilatometry over a temperature range of 300–1250 °C along with microstructural and x-ray diffraction studies. The sintering behavior of attrition milled nanocrystalline titanium appears to be characterized by: (i) very low activation energies, (ii) high shrinkage anisotropy, (iii) very rapid grain growth in the beta range, and (iv) two kinds of densification processes, namely, intra-agglomerate and inter-agglomerate. Analysis of the kinetic data through sintering diagram approach indicates the operation of particle sliding and grain boundary rotation, type of mechanism in addition to the grain-boundary diffusion, and lattice diffusion as the dominant mass transport mechanisms.
Low-temperature processable inherently photosensitive polyimide gate dielectric for organic thin-film transistors: Synthesis, characterization, and application to transistors
Authors: Pyo Seungmoon , Son Hyunsam , Yi Mi Hye
Published: May 2005

Low-temperature processable inherently photosensitive polyimide was prepared from a dianhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, and aromatic diamines, 4,4′-diamino-3,3′dimethyl-diphenylmethane, through a polycondensation reaction, followed by a chemical imidization method. The photosensitive polyimide cured at 180 °C is used as a gate dielectric to fabricate flexible organic thin-film transistors with pentacene as an active semiconductor on polyethersulfone substrate. With the inherently photosensitive polyimide, the access to the gate electrode could be created easily without complicated and expensive lithographic techniques. A field effect carrier mobility of 0.007 cm2/V s was obtained for the pentacene organic thin-film transistors (OTFTs) with the photo-patterned polyimide as a gate dielectric. More detailed analysis for the pentacene OTFTs will be given with electrical properties of the thin polyimide film. Low-temperature processability and patternability of the polyimide give us more freedom to choose plastic substrates in OTFTs and facilitate the realization of low-cost organic electronics.
Thermodynamic assessment of the MgO–Al2O3–SiO2 system
Authors: Mao Huahai , Fabrichnaya Olga , Selleby Malin , Sundman Bo
Published: May 2005

Thermodynamic properties of the phases in the MgO–Al2O3–SiO2 system were assessed, resulting in a set of self-consistent thermodynamic data. The two ternary compounds, cordierite and sapphirine, were optimized from subsolidus reactions. The liquid phase was described by the ionic two-sublattice model with a new species AlO2−1, yielding the formula (Al+3,Mg+2)P(AlO2−1,O−2,SiO4−4,SiO20)Q. Projection of the liquidus surface was calculated. Various isothermal and isoplethal sections were compared with the experimental data.
Investigation on the kinetics of devitrification of GeS2-based glasses
Authors: Liu Xiaobo , Shen Shaoxiong , Jha Animesh
Published: May 2005

We studied the devitrification kinetics for the binary (80GeS2–20Ga2S3, mol%) and ternary (77GeS2–15Ga2S3–6CsI, mol%) glass compositions using the differential thermal analysis (DTA) technique. The overall activation energies for devitrification for these two types of glasses were determined by using the Kissinger method and the Johnson–Mehl–Avrami equation from the DTA data. The t-t-t curves were calculated using the activation energy for devitrification for each composition derived from the DTA experiments. The experimental evidences have shown that the incorporation of SnS2 and Sb2S3 in a ternary-based GeS2 glass slows down the overall devitrification rate significantly, which is confirmed by the reduction in the overall area under the crystallization exotherm.
Preparation and absorption properties of polystyrene/Ag/TiO2 multiple coated colloids
Authors: Zhang J.H. , Wang S.Z. , Liu J.B. , Wang Z.L. , Ming N.B.
Published: May 2005

We demonstrated a facile route based on the use of acetone and polyvinylpyrrolidone (PVP) to prepare polystyrene (PS)/Ag/TiO2 multilayered colloids with controllable shell thickness. In this route, PVP absorbed directly onto PS colloid surface, and the Ag seed shell composed of Ag nanoparticles was synthesized directly under the PVP shell by swelling the surface layer of the PS core. Because the PVP shell increased the affinity of the Ag shell to TiO2, the hydrolyzed titania particles could deposit directly onto the core to form the outer TiO2 shell. A seed growth technique and the controllable hydrolysis reaction of tetra-n-butyl titanate were developed to grow the shell thickness of Ag and TiO2, respectively. Studies of the absorption properties indicate that the optical properties of these multilayered composite colloids can be modified by changing the coating species and shell thickness.
Piezoelectric effect in epitaxial PbZr1−xTixO3 thin films near morphotropic phase boundary region
Authors: Kim Yong Kwan , Kim Sang Sub , Lee Bongki , Shin Hyunjung , Baik Sunggi
Published: May 2005

The relationship between crystal structure and piezo-response was investigated in epitaxially grown PbZr1−xTixO3 (PZT) thin films on Pt(001)/MgO(001) with a thin PbTiO3 interlayer. Insertion of the interlayer resulted in significant relaxation ofthe strain that could be developed in the course of deposition of the PZT films, consequently leading us to single out only the effect of composition. Composition of the morphotropic phase boundary (MPB), at which tetragonal and rhombohedral phases are mixed with the same volume fraction, was found to be ∼0.55 in Ti/(Zr + Ti) ratio in our films, which is close to the value for bulk polycrystalline PZT (∼0.50). The piezoelectric response peaks were two times higher in the MPB regime than in the single phase regime due to structural instability caused by the coexistence of two phases. The results indicate that epitaxial PZT films having the MPB composition are advantageous over those of other compositions for nano-storage devices based on scanning force microscopy.
Phase selection in precursor-derived yttrium aluminum garnet and related Al2O3–Y2O3 compositions
Authors: Gandhi Ashutosh S. , Levi Carlos G.
Published: May 2005

Al2O3–Y2O3 powders were synthesized in the range of 25–55% Y2O3 by reverse coprecipitation of nitrate solutions. All starting powders were amorphous and formed primary yttrium aluminum garnet (YAG) upon crystallization. X-ray diffraction detected only garnet in compositions of 30–40% Y2O3 after heat treatment at 1250 °C. Compositions of 45–55% Y2O3 established a metastable YAG + Y4Al2O9 microstructure. The YAG phase field was metastably extended away from its stoichiometry, as indicated by a systematic increase in lattice parameter with Y2O3 content. Although some Al2O3 enrichment was achieved, YAG appears to tolerate greater off-stoichiometry on the Y2O3-rich side. Possible defect structures accommodating the solubility extension were examined. Phase selection results indicate that compositional inhomogeneity is not the only reason behind the appearance of hexagonal YAlO3, which is frequently reported during YAG synthesis.
Natural rutile-derived titanate nanofibers prepared by direct hydrothermal processing
Authors: Suzuki Yoshikazu , Pavasupree Sorapong , Yoshikawa Susumu , Kawahata Ryoji
Published: May 2005

Long titanate nanofibers (typically 10–500 μm in length and 20–50 nm in diameter) were successfully prepared in high yield by the direct hydrothermal processing using natural rutile as a starting material. Fourier transform infrared spectroscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, electron diffraction, and x-ray diffraction demonstrated that the as-synthesized nanofibers presumably consisted of sodium hydrogen trititanate [(Na,H)2Ti3O7,e.g., Na0.4H1.6Ti3O7] including some hexatitanate-type defects [(Na,H)2Ti6O13]. A partial topotactic condensation model explained their nanostructure well. Although the as-synthesized fibers are defective, they can be cured by a post-heat-treatment in air. The direct hydrothermal treatment for natural rutile will be a promising low-cost process for one-dimensional nanomaterials, which can act not only as a reaction step but also as a purification step.
Topology of charge density and elastic anisotropy of Ti3SiC2polymorphs
Authors: Yu R. , Zhang X.F. , He L.L. , Ye H.Q.
Published: May 2005

Using an all-electron, full potential first-principles method, we have investigated the topology of charge density and elastic anisotropy of Ti3SiC2polymorphs comparatively. By analyzing the charge density topology, it was found that the Ti–Si bonds are weaker in β than in α, resulting in a destabilizing effect and lower Young’s modulus in directions betweenaandcaxes for β. On the other hand, the Si–C bonds (absent in α) are formed in β in thecdirection. The formation of the Si–C bonds not only mitigates the destabilizing effect of the weaker Ti–Si bonds, but also results in larger Young’s modulus in thecdirection. In contrast to the high elastic anisotrophy, the elastic anisotropy of Ti3SiC2is very low.
Anisotropic elastic properties of nanocrystalline nickel thin films
Authors: Hurley D.C. , Geiss R.H. , Kopycinska-Müller M. , Müller J. , Read D.T. , Wright J.E. , Jennett N.M. , Maxwell A.S.
Published: May 2005

The elastic properties of a nickel film approximately 800 nm thick were measured with nanoindentation, microtensile testing, atomic force acoustic microscopy (AFAM), and surface acoustic wave (SAW) spectroscopy. Values for the indentation modulus (220–223 GPa) and Young’s modulus (177–204 GPa) were lower than predicted for randomly oriented polycrystalline nickel. The observed behavior was attributed to grain-boundary effects in the nanocrystalline film. In addition, the different measurement results were not self-consistent when interpreted assuming elastic isotropy. Agreement was improved by adopting a transversely isotropic model corresponding to the film’s 〈111〉 preferred orientation and reducing the elastic moduli by 10–15%. The SAW spectroscopy results indicated that the film density was 1–2% lower than expected for bulk nickel, consistent with models for nanocrystalline materials. Similar reductions in modulus and density were observed for two additional films approximately 200 and 50 nm thick using AFAM and SAW spectroscopy. These results illustrate how complementary methods can provide a more complete picture of film properties.
Spontaneous room temperature extrusion of Pb nano-whiskers from leaded brass surfaces
Authors: Sun Z.M. , Barsoum M.W.
Published: May 2005

We report that lightly abrading the surface of a commercial leaded brass results in the room temperature spontaneous growth of Pb whiskers and hillocks. The aspect ratios and submicron diameters of the whiskers that form render them easily dispersible in the atmosphere, with potentially serious health effects, especially for people that deal with leaded brass on a daily basis.
Liquid mediated growth and the bimodal microstructure of YBa2Cu3O7−δ films made by the ex situ conversion of physical vapor deposited BaF2 precursors
Authors: Holesinger T.G. , Arendt P.N. , Feenstra R. , Gapud A.A. , Specht E.D. , Feldmann D.M. , Larbalestier D.C.
Published: May 2005

YBa2Cu3Oy (YBCO) films produced by the ex situ conversion of BaF2-based precursors deposited by physical vapor deposition on ion-beam assisted deposited (IBAD) yttrium-stabilized zirconia (YSZ) and rolling-assisted biaxially textured substrates (RABiTS) templates are characterized by a bi-axially aligned, laminar grain structure that results from the anisotropic growth characteristics of the YBCO phase and its precipitation from a transient liquid phase during the conversion process. A bimodal microstructure characterizes these films and is defined by large, well-formed YBCO grains with Y2O3 precipitates in the bottom region of the film and small YBCO grains with a high density of stacking faults in the upper half. Ba2Cu3Oy or Ba–O–F/CuO second phase layers were often found between large YBCO grains in the bottom half of the films. YBCO grain sizes exceeded 50 μm within the plane of the film in some cases. Conversely, discrete secondary phases of Y2Cu2O5, Y2O3, and Ba2Cu3Oy/Ba–O–F could be found among the much smaller YBCO grains in the top portion of the bimodal structure. The dividing line of the bimodal structure was generally at one half of the film thickness, although exceptions to this trend were found. The highest critical current densities (Jc) and best film alignments for a given film thickness were found in samples where the layers of Ba2Cu3Oy or Ba–O–F were minimized or eliminated from the films. Samples quenched after partial conversion show the segregation of CuO to the top region of the film and the lateral growth of large YBCO grains from a precursor mix of Y2Cu2O5 and Ba–O–F. The data demonstrate that transient liquid phases are part of the conversion process of BaF2-based YBCO films. The control of both CuO segregation and the amount of liquid phases generated during the initial stages of phase formation is needed for optimizing the ex situ conversion process for high-Jc coated conductors.
Combustion synthesis of metal carbides: Part I. Model development
Authors: Locci A.M. , Cincotti A. , Delogu F. , Orrù R. , Cao G.
Published: May 2005

The definition of a rigorous theoretical framework for the appropriate physico-chemical description of self-propagating high-temperature synthesis (SHS) processes represents the main goal of this work which is presented in two sequential articles. In this article, a novel mathematical model to simulate SHS processes is proposed. By adopting a heterogeneous approach for the description of mass transfer phenomena, the model is based on appropriate mass and energy conservation equations for each phase present during the system evolution. In particular, it takes microstructural evolution into account using suitable population balances and properly evaluating the differentdriving forces from the relevant phase diagram. The occurrence of phase transitionsis treated on the basis of the so-called enthalpy approach, while a conventional nucleation-and-growth mechanistic scenario is adopted to describe quantitatively the formation of reaction products. The proposed mathematical model may be applied to the case of combustion synthesis processes involving a low melting point reactant and a refractory one, as for the synthesis of transition metal carbides from pure metal and graphite. Thus, the model can be profitably used to gain a deeper insight into the microscopic elementary phenomena involved in combustion synthesis processes through a suitable combination of experimental and modeling investigations, as it may be seen in Part II of this work [J. Mater. Res. 20, 1269 (2005)].
Synthesis of gold nanocrystals in concurrently polymerizing organic–inorganic hybrid films
Authors: Epifani Mauro , Carlino Elvio , Furlanetto Davide , Giannini Cinzia , Imperatori Patrizia
Published: May 2005

Gold nanocrystals were formed and grown in simultaneously polymerizing hybrid organic–inorganic films. For the preparation of Au containing films, tetraethyl orthosilicate and methacryloxypropyltrimethoxysilane were separately hydrolyzed and the resulting sols were mixed, followed by the addition of a photoinitiator and a NaAuCl4 solution in methanol. The resulting solutions were spin-coated onto glass-substrates, and the so-formed films were irradiated with a solar simulator at powers ranging from 200 to 800 W. The irradiation resulted in simultaneous polymerization of the films and formation of gold nanoparticles. The irradiated films were characterized by x-ray diffraction measurements, ultraviolet–visible optical absorption spectroscopy and transmission electron microscopy studies. After irradiation at 800 W, the transmission electron microscopy experiments showed the presence of homogeneously distributed Au nanoparticles with a size distribution ranging from 2 to 12 nm. The interpretation of the results indicates that the Au particle growth depends on the matrix polymerization rate; enhancing the rate by increasing the irradiation power or the photoinitiator concentration results in smaller particle domains. This result is explained referring to influence of the polymerization rate on the diffusion of gold species through the host.
Excellent creep properties of Mg–Zn–Cu–Gd-based alloy strengthened by quasicrystals and Laves phases
Authors: Yuan Guangyin , Kato Hidemi , Amiya Kenji , Inoue Akihisa
Published: May 2005

A new type of Mg–Zn–Cu–Gd-based alloy strengthened by quasicrystal and Laves phase was developed. This alloy exhibits much better creep properties compared to AE42(Mg–4 wt% Al–2 wt% rare-earth) alloy, which is the benchmark creep-resistant magnesium die-casting alloy under the compressive creep condition of 180 °C and80 MPa. The new alloy also exhibits high room-temperature mechanical properties close to that of AZ91 alloy. The good mechanical properties are attributed to the special microstructure; the thermally stable icosahedral quasicrystals phase (i-phase) and Laves phase distributed along the grain boundary as a hard skeleton, and some fine β′1 precipitates distributed homogenously on the matrix. The dislocation morphology after the creep test was studied, and the strengthening mechanism was proposed.
Oxygen transport studies in nanocrystalline ceria films
Authors: Saraf Laxmikant , Wang C.M. , Shutthanandan V. , Zhang Y. , Marina Olga , Baer D.R. , Thevuthasan S. , Nachimuthu P. , Lindle D.W.
Published: May 2005

Oxygen uptake and conductivity were measured by nuclear-reaction analysis and alternating current impedance technique at the intermediate temperature range on sol-gel grown nanocrystalline ceria films with average grain-sizes 7 nm and 38 nm synthesized at 723 and 1173 K, respectively. Higher oxygen uptake and lower ionic conductivity were observed in ceria films with ∼7-nm grain size. High permeation-assisted oxygen diffusion in nanocrystallites combined with oxygen trapping in the disordered region contributed to higher oxygen uptake. However, the lower ionic conductivity in the film resulted from the absence of long-range lattice ordering and inactive grain-boundary/surface oxygen vacancy sites due to oxygenation. The relationship between oxygen uptake and conductivity in ceria is discussed in details by considering grain-size dependent defect density, related surface area, and enhanced oxygen mobility.
Preparation of a transparent and flexible self-standing film of layered titania/isostearate nanocomposite
Authors: Matsumoto Taki , Iyi Nobuo , Kaneko Yoshiro , Kitamura Kenji , Masaki Satoru , Imai Tomohito , Sugimoto Wataru , Takasu Yoshio , Murakami Yasushi
Published: May 2005

A titania-based self-standing film with high transparency and flexibility was successfully prepared via a sol-gel process, in which a titanium tetraisopropoxide/isostearate complex (precursor), n-hexylammonium isostearate (catalyst), and o-xylene (solvent) were used. The sol obtained by the sol-gel reaction was floated on a water surface to form an unsupported film. This film was composed of a titania/isostearate nanocomposite with ordered layer structure. The basal spacings of the nanocomposites depended on the chain length of the carboxylate modifier.
Colloidal processing, surface characterization, and sintering of nano ZrO2 powders
Authors: Duran Cihangir , Jia Yu , Hotta Yuji , Sato Kimiyasu , Watari Koji
Published: May 2005

Colloidally stable suspensions are required to fabricate dense samples with uniform microstructure by colloidal processing methods, which necessitate dispersion of ceramic powders in a liquid medium. Aqueous nano ZrO2 suspensions were prepared using polyethylenimine (PEI) as a dispersant. PEI adsorption on nano ZrO2 surfaces was promoted with increasing initial PEI content and suspension pH. Isoelectric point was shifted from pH 7 at 0 wt% PEI to pH 10.4 at 3 wt% PEI. Stable suspensions had mean particle sizes in the range of 100 to 150 nm and sedimentation rates less than0.4 mm/h, as compared to 2–5.5 μm and 10–50 mm/h for unstable suspensions. Samples with 98% relative density were fabricated after sintering at 1300 °C for 4 h from colloidally stable suspensions.
Evolution of the microstructure, residual stresses, and mechanical properties of W–Si–N coatings after thermal annealing
Authors: Cavaleiro A. , Marques A.P. , Fernandes J.V. , Carvalho N.J.M. , De Hosson J.Th.
Published: May 2005

W–Si–N films were deposited by reactive sputtering in a Ar + N2 atmosphere from a W target encrusted with different number of Si pieces and followed by a thermal annealing at increasing temperatures up to 900 °C. Three iron-based substrates with different thermal expansion coefficients, in the range of 1.5 × 10−6 to 18 × 10−6 K−1 were used. The chemical composition, structure, residual stress, hardness (H), and Young’s modulus (E) were evaluated after all the annealing steps. The as-deposited film with low N and Si contents was crystalline whereas the one with higher contents was amorphous. After thermal annealing at 900 °C the amorphous film crystallized as body-centered cubic α–W. The crystalline as-deposited film presented the same phase even after annealing. There were no significant changes in the properties of both films up to 800 °C annealing. However, at 900 °C, a strong decrease and increase in the hardness were observed for the crystalline and amorphous films, respectively. It was possible to find a good correlation between the residual stress and the hardness of the films. In several cases, particularly for the amorphous coating, H/E higher than 0.1 was reached, which envisages good tribological behavior. The two methods (curvature and x-ray diffraction) used for calculation of the residual stress of the coatings showed fairly good agreement in the results.
Effect of cold rolling on the indentation deformation of AA6061 aluminum alloy
Authors: Yang Fuqian , Du Wenwen , Okazaki Kenji
Published: May 2005

The indentation behavior of cold-rolled AA6061 Al alloy was investigated. Following the approach suggested by Tabor, indentation stress–indentation strain curves were constructed and analyzed. The indentation stress required to create the same indentation strain increases with an increase in the reduction of thickness, suggesting a strong effect of plastic deformation history on the deformation behavior of materials. Through the dislocation dynamics, the evolution of the dislocations underneath the indentation was correlated with the plastic deformation history and the indentation load. The plastic energy dissipated in indentation was then calculated and found to be proportional to the 3/2 power of the indentation load and the 3/4 power of the average dislocation density underneath the indentation. The ratio of the dissipated plastic energy to the total energy in the indentation was demonstrated to be a function of the deformation state in materials, independent of the indentation load.
Influence of tetracycline in the hepatic and renal development of rat's offspring
Authors: Machado Ana Lourdes da Silva , Brandão Adriana Aigotti Haberbeck , Silva Cláudia Maria de Oliveira Monteiro da , Rocha Rosilene Fernandes da
Published: May 2005

This study aimed on evaluating the possible effects of tetracycline administered to rats on the tenth day of pregnancy, on kidney and liver development of their offspring. The liver showed vacuolization, necrosis, inflammation and sinusoidal dilatations, more evident in the newborn. Mitosis, early increase of Kupffer cells population and hipertrophy of hepatocytes with greater synthesis of glycogen were present on the tenth and twentieth days of life. The kidney showed slight tubular vacuolizations and necrosis, more proeminent in the newborn, as well as signs of tubular regeneration on the tenth and twentieth days. These results suggested that the organs studied went through several transitory morphological changes during development but presented signs of regeneration along the first days of life.
Morphological aspects of the propagation in Heliconia velloziana L. Emygd. (Zingiberales: Heliconiaceae)
Authors: Simão Daniela G. , Scatena Vera L.
Published: May 2005

Morphology of seed and vegetative propagation was studied toHeliconia velloziana L. Emygd. (Heliconiaceae), a rhizomatous herb with a large aerial part. Seeds took about four months to germinate, probably due to the undifferentiated embryo and hard endocarp. Seedlings had two first foliar structures as scale leaves and the primary root developed, but the adventitious roots were more conspicuous. Vegetative propagation by rhizomes was faster than the sexual one. The roots developed after one month, while young shoots started developing after four to six weeks; young aerial shoots presented a variable number of cataphylls and two protophylls.
Impacts of the construction of the Port of Suape on phytoplankton in the Ipojuca River estuary (Pernambuco-Brazil)
Authors: Koening Maria Luise , Leça Enide Eskinazi , Neumann-Leitão Sigrid , Macêdo Silvio José de
Published: May 2005

In order to address the impact on phytoplankton, sampling was conducted monthly at 4 fixed stations, from April/86 to March/87 at diurnal low and high tide using a plankton net (65 mum mesh size) and a 1 L Van Dorn bottle. Among the 133 taxa identified, marine littoral euryhaline species were most common, outranking Gyrosigma balticum (Ehrenberg) Rabenhorst, Nitzschia sigma (Kützing) Wm. Smith, Licmophora abbreviata Agardh, Climacosphenia moniligera Ehrenberg, Surirella febigerii Lewis, Terpsinoe musica Ehrenberg and Cylindrotheca closterium (Ehrenberg) Reiman and Lewis. The port construction caused significant changes to the phytoplankton community with a strong influence of marine species (mainly dinoflagellate) because of the opening of the reef near the river mouth in 1983. The shallow depth and hydrodynamic brought many littoral species to the water columm. The community was composed by marine euryhaline and limnetic organisms, influenced by the salinity, rain and tide. Species diversity was high (> 3 bits.cel-1) owing to the high environmental heterogeneity (marine, freshwater and benthic interactions). After the port implantation, a strong decrease occurred in phytoplankton density owing to high loads of suspended matter. Lowest values (121,00 cells.l-1) were registered during rainy season. During dry season, when light intensity was higher, phytoplankton presented highest density ( 1,789,000 cells.l-1).
Spectral Reflectance as a Covariate for Estimating Pasture Productivity and Composition
Authors: Tarr Alison B. , Moore Kenneth J. , Dixon Philip M.
Published: May 2005

Pasturelands are inherently variable. It is this variability that makes sampling as well as characterizing an entire pasture difficult. Measurement of plant canopy reflectance with a ground‐based radiometer offers an indirect, rapid, and noninvasive characterization of pasture productivity and composition. The objectives of this study were (i) to determine the relationships between easily collected canopy reflectance data and pasture biomass and species composition and (ii) to determine if the use of pasture reflectance data as a covariate improved mapping accuracy of biomass, percentage of grass cover, and percentage of legume cover across three sampling schemes in a central Iowa pasture. Reflectance values for wavebands most highly correlated with biomass, percentage of grass cover, and percentage of legume cover were used as covariates. Cokriging was compared with kriging as a method for estimating these parameters for unsampled sites. The use of canopy reflectance as a covariate improved prediction of grass and legume percentage of cover in all three sampling schemes studied. The prediction of above‐ground biomass was not as consistent given that improvement with cokriging was observed with only one of the sampling schemes because of the low amount of spatial continuity of biomass values. An overall improvement in root mean square error (RMSE) for predicting values for unsampled sites was observed when cokriging was implemented. Use of rapid and indirect methods for quantifying pasture variability could provide useful and convenient information for more accurate characterization of time consuming parameters, such as pasture composition.
Identification of Essentially Derived Varieties Obtained from Biparental Crosses of Homozygous Lines: II. Morphological Distances and Heterosis in Comparison with Simple Sequence Repeat and Amplified Fragment Length Polymorphism Data in Maize
Authors: Heckenberger M. , Bohn M. , Klein D. , Melchinger A. E.
Published: May 2005

In addition to genetic distances (GDs) based on molecular markers, morphological traits and heterosis have been proposed as possible tools to assess the genetic conformity between putative essentially derived varieties (EDVs) and their initial varieties (IVs). However, for maize (Zea mays L.) and other crops, no consensus has been reached regarding methods and thresholds for identification of EDVs, mainly because reliable benchmark data are lacking. The objectives of this study were to (i) evaluate the power of morphological traits and heterosis to discriminate between homozygous progenies derived from F2, BC1, and BC2 populations (BC = backcross), (ii) compare the findings to published data based on simple sequence repeats (SSRs) and amplified fragment length polymorphisms (AFLPs), and (iii) draw conclusions about the usefulness of the various criteria for identification of EDVs. Morphological distances (MDs) based on 25 traits and midparent heterosis (MPH) for 12 traits were observed for a total of 58 European maize inbred lines comprising 38 triplets. A triplet consisted of one homozygous line derived from a F2, BC1, or BC2 population and both parental inbreds. In addition, all inbreds were genotyped with 100 uniformly distributed SSR markers and 20 AFLP primer combinations in companion studies for calculation of GDs. Correlations between the coancestry coefficient, GDs, MDs, and MPH were significant and high for the majority of traits. However, thresholds for EDVs to discriminate between F2– and BC1–derived, or BC1– and BC2–derived progenies using only MDs or heterosis yielded considerably higher values for Type I (α) and Type II (1 − β) errors than observed with GDs based on SSRs and AFLPs. Consequently, morphological traits and heterosis are less suited for identification of EDVs in maize than molecular markers.
Hard Wheat Milling and Bread Baking Traits Affected by the Seed‐Specific Overexpression of Puroindolines
Authors: Hogg A. C. , Beecher B. , Martin J. M. , Meyer F. , Talbert L. , Lanning S. , Giroux M. J.
Published: May 2005

Grain texture affects many milling characteristics and end‐use qualities in wheat (Triticum aestivum L.) such as milling yield, flour particle size, and starch damage. In wheat, grain texture is controlled primarily by the two genes puroindoline a (pina) and puroindoline b (pinb) that reside at the Hardness (Ha) locus. Variation in puroindoline activity and abundance is known to influence a variety of milling and baking traits, and the reconstitution of flour with puroindoline A protein (PINA) has been shown to positively affect loaf volume and crumb grain. To investigate which milling and baking traits are affected by the addition of puroindolines in vivo, we transformed the hard red spring wheat cultivar Hi‐Line, with genetic constructs driving the expression of pina‐D1a, pinb‐D1a, or both pina‐D1a and pinb‐D1a Transgenic lines exhibited decreased grain hardness and increased puroindoline content. Selected T3 lines were grown in replicated field trials under dry and irrigated conditions. Harvested grain was then milled and baked. Lines transformed with the puroindolines exhibited decreased total flour yields and increased break flour yields, yielding flour with lower protein and ash content. Decreases in loaf volume, mixograph absorption, and crumb grain scores were also observed in transgenic lines having high puroindoline expression. Decreased loaf volume was also observed in whole wheat bakes of transgenic soft wheats vs. normal hard wheat, indicating a direct effect of puroindolines on loaf volume. Puroindoline content did not affect dough mixing times. These results demonstrate that the puroindolines can be used to profoundly influence a variety of milling and bread baking traits in wheat.
Responses to Divergent Phenotypic Selection for Fiber Traits in Timothy
Authors: Claessens Annie , Michaud Réal , Bélanger Gilles , Mather Diane E.
Published: May 2005

Selection based on fiber traits may make it possible to improve forage digestibility while maintaining plant biomass. Our objectives were to evaluate the effects of divergent phenotypic selection for fiber traits on timothy (Phleum pratense L.) digestibility, plant biomass, fiber component concentrations and their ratios, and to identify selection criteria that have effective and stable effects on timothy digestibility without affecting plant biomass. Fourteen populations derived by intercrossing plants selected for high or low values of neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and cellulose (CEL) concentrations, and for ADL/HEM, ADL/CEL, and ADL/(HEM+CEL) ratios were evaluated in a field experiment. Direct responses for the selected traits were significant for the NDF, CEL, ADL/HEM, ADL/CEL, and ADL/(HEM+CEL) populations. Indirect responses for in vitro true digestibility (IVTD) and in vitro NDF digestibility (IVNDFD) were greatest for the ratios involving ADL. The ADL/CEL selection resulted in the most stable responses across years for IVTD and IVNDFD. Averaged over 2 yr, the IVTD and IVNDFD of the low ADL/CEL population were 27 g kg−1 DM and 33 g kg−1 NDF greater than those of the high ADL/CEL population. Furthermore, the low ADL/CEL population maintained its HEM and CEL concentrations and its plant biomass. Phenotypic selection based on ADL/CEL could be used to improve timothy DM digestibility without reducing plant biomass.