bluuebunny/crossref_metadata_2025 huggingface dataset:
Vigorous Physical Activity Increases Fracture Risk in Children Irrespective of Bone Mass: A Prospective Study of the Independent Risk Factors for Fractures in Healthy Children
Authors: Clark Emma M , Ness Andy R , Tobias Jon H
Published: March 2008

Low bone mass is a determinant of fractures in healthy children. Small studies provide limited evidence on the association between ethnicity, birth weight, family size, socioeconomic status, dietary calcium intake, or physical activity and fracture incidence. No studies have investigated whether these determinants of fracture risk act through affecting bone mass or through other mechanisms. The aim of this study was to use a population-based birth cohort to confirm which variables are determinants of fracture risk and to further study which of these risk factors act independently of bone mass. Children from the Avon Longitudinal Study of Parents and Children have been followed up from birth to 11 yr of age. Maternal self-reported data have been collected contemporaneously on early life factors, diet, puberty, and physical activity. These were linked to reported fractures between 9 and 11 yr of age. Multivariable logistic regression techniques were used to assess whether these potential determinants were independent of, or worked through, estimated volumetric BMD or estimated bone size relative to body size measured by total body DXA scan at 9.9 yr of age. A total of 2692 children had full data. One hundred ninety-three (7.2%) reported at least one fracture over the 2-yr follow-up period. Children who reported daily or more episodes of vigorous physical activity had double the fracture risk compared with those children who reported less than four episodes per week (OR, 2.06; 95% CI, 1.21–1.76). No other independent determinants of fracture risk in healthy children were found. In conclusion, reported vigorous physical activity is an independent risk factor for childhood fracture risk. However, the interrelationship between physical activity, bone mass, and childhood fracture risk suggests that the higher bone mass associated with increased physical activity does not compensate for the risk caused by increased exposure to injuries.
RNA switches regulate initiation of translation in bacteria
Authors: Marzi Stefano , Fechter Pierre , Chevalier Clément , Romby Pascale , Geissmann Thomas
Published: March 2008

A large variety of RNA-based mechanisms have been uncovered in all living organisms to regulate gene expression in response to internal and external changes, and to rapidly adapt cell growth in response to these signals. In bacteria, structural elements in the 5′ leader regions of mRNAs have direct effects on translation initiation of the downstream coding sequences. The docking and unfolding of these mRNAs on the 30S subunit are critical steps in the initiation process directly modulating and timing translation. Structural elements can also undergo conformational changes in response to environmental cues (i.e., temperature sensors) or upon binding of a variety of trans-acting factors, such as metabolites, non-coding RNAs or regulatory proteins. These RNA switches can temporally regulate translation, leading either to repression or to activation of protein synthesis.
Lipopolysaccharide: a tool and target in enterobacterial vaccine development
Authors: Nagy Gábor , Pál Tibor
Published: March 2008

Lipopolysaccharide (LPS) is an essential component of Gram-negative bacteria. While mutants exhibiting truncated LPS molecules are usually over-attenuated, alternative approaches that affect the extent or timing of LPS expression, as well as its modification may establish the optimal balance for a live vaccine strain of sufficient attenuation and retained immunogenicity. On the other hand, a specific immune response to LPS molecules in itself is capable of conferring protective immunity to certain enterobacterial pathogens. Therefore, purified LPS derivatives could be used as parenteral vaccines. This review summarizes various LPS-based vaccination strategies, as well as approaches that utilize LPS mutants as whole-cell vaccines.
Not to wake a sleeping giant: new insights into host-pathogen interactions identify new targets for vaccination against latentMycobacterium tuberculosisinfection
Authors: Lin May Young , Ottenhoff Tom H.M.
Published: March 2008

Mycobacterium tuberculosisis one of the worlds' most successful and sophisticated pathogens. It is estimated that over 2 billion people today harbour latentM. tuberculosisinfection without any clinical symptoms. As most new cases of active tuberculosis (TB) arise from this (growing) number of latently infected individuals, urgent measures to control TB reactivation are required, including post-exposure/therapeutic vaccines. The current bacille Calmette-Guérin (BCG) vaccine and all new generation TB vaccines being developed and tested are essentially designed as prophylactic vaccines. Unfortunately, these vaccines are unlikely to be effective in individuals already latently infected withM. tuberculosis. Here, we argue that detailed analysis ofM. tuberculosisgenes that are switched on predominantly during latent stage infection may lead to the identification of new antigenic targets for anti-TB strategies. We will describe essential host-pathogen interactions in TB with particular emphasis on TB latency and persistent infection. Subsequently, we will focus on novel groups of late-stage specific genes, encoded amongst others by theM. tuberculosisdormancy (dosR) regulon, and summarise recent studies describing human T-cell recognition of these dormancy antigens in relation to (latent)M. tuberculosisinfection. We will discuss the possible relevance of these new classes of antigens for vaccine development against TB.
Pre-clinical development of cell culture (Vero)-derived H5N1 pandemic vaccines
Authors: Howard M. Keith , Kistner Otfried , Barrett P. Noel
Published: March 2008

The rapid spread of avian influenza (H5N1) and its transmission to humans has raised the possibility of an imminent pandemic and concerns over the ability of standard influenza vaccine production methods to supply sufficient amounts of an effective vaccine. We report here on a robust and flexible strategy which uses wild-type virus grown in a continuous cell culture (Vero) system to produce an inactivated whole virus vaccine. Candidate vaccines based on clade 1 and clade 2 influenza H5N1 strains, produced at a variety of manufacturing scales, were demonstrated to be highly immunogenic in animal models without the need for adjuvant. The vaccines induce cross-neutralising antibodies and are protective in a mouse challenge model not only against the homologous virus but against other H5N1 strains, including those from other clades. These data indicate that cell culture-grown, whole virus vaccines, based on the wild-type virus, allow the rapid high-yield production of a candidate pandemic vaccine.
Microstructural Characterization of Oxides Formed on Model Zr Alloys Using Synchrotron Radiation
Authors: Motta A. T. , Gomes da Silva M. J. , Yilmazbayhan A. , Comstock R. J. , Cai Z. , Lai B.
Published: March 2008

To understand how alloy chemistry and microstructure impact corrosion performance, oxide layers formed at different stages of corrosion on various model zirconium alloys (Zr-xFe-yCr, Zr-xCu-yMo, for various x, y) and control materials (pure Zr, Zircaloy-4) were examined to determine their structure and the connection of such structure to corrosion kinetics and oxide stability. Microbeam synchrotron radiation diffraction and fluorescence of oxide cross sections were used to determine the oxide phases present, grain size, and orientation relationships as a function of distance from the oxide-metal interface. The results show a wide variation of corrosion behavior among the alloys, in terms of the pretransition corrosion kinetics and in terms of the oxide susceptibility to breakaway corrosion. The alloys that exhibited protective behavior at 500°C also were protective during 360°C corrosion testing. The Zr-0.4Fe-0.2Cr model ternary alloy showed protective behavior and stable oxide growth throughout the test. The results of the examination of the oxide layers with microbeam X-ray diffraction show clear differences in the structure of protective and nonprotective oxides both at the oxide-metal interface and in the bulk of the oxide layer. The nonprotective oxide interfaces show a smooth transition from metal to oxide with metal diffraction peaks disappearing as the monoclinic oxide peaks appear. In contrast, the protective oxides showed a complex structure near the oxide-metal interface, showing peaks from Zr3O suboxide and a highly oriented tetragonal oxide phase with specific orientation relationships with the monoclinic oxide and the base metal. The same interfacial structures are observed through their diffraction signals in protective oxide layers formed during both 360°C and 500°C corrosion testing. These diffraction peaks showed much higher intensities in the samples from 500°C testing. The results for the various model alloys are discussed to help elucidate the role of individual alloying elements in oxide formation and the influence of oxide microstructure on the corrosion mechanism.
Simple Expressions for the Evaluation of Stresses in Sphere-Loaded Disks Under Biaxial Flexure
Authors: Fett T. , Rizzi G. , Esfehanian M. , Oberacker R.
Published: March 2008

In testing ceramic materials, sphere-loaded disk tests are of increasing importance. Three different tests including one, four, and six spheres are addressed. For the first two tests, the maximum stress in the disk center was already studied in several papers. In this note, simple analytical relations for the distribution of the tangential stress will be given. The stress distribution in the center region is, for instance, necessary for the determination of effective surface and volume as used for Weibull statistics. For special applications also, stresses across larger distances from the center are desirable. As an example, strength tests on coarse-grained alumina are mentioned briefly which need a fracture mechanics evaluation for interpretation.
Preparation of large single grains of the quasicrystalline icosahedral Al–Cu–Fe ψ phase
Authors: Lograsso T.A. , Delaney D.W.
Published: March 2008

A cyclic heat-treatment process was used to prepare single grains of the quasicrystalline icosahedral phase, ψ–Al65Cu23Fe12. Alloys of appropriate composition are melted and chill cast into copper molds. Multiple cyclic heat treatments at successively higher temperatures below 860 °C, the peritectic decomposition temperature of the quasicrystal phase, are used to enhance the growth of the ψ phase. Single grains up to 10 mm × 5 mm × 5 mm have been prepared.
Fabrication of submicrometer-grained Zn–22% Al by torsion straining
Authors: Furukawa Minoru , Horita Zenji , Nemoto Minoru , Valiev Ruslan Z. , Langdon Terence G.
Published: March 2008

The Zn–22% Al eutectoid alloy is capable of exhibiting very high superplastic elongations, in excess of 2000% in tension, when the grain size is in the range of ∼ 1–10μm. This paper describes the fabrication of a submicrometer grain size in the Zn–22% Al alloy by subjecting the samples to intense plastic straining in torsion under high pressure (∼5 GPa) at room temperature. Observations after straining revealed a heterogeneous microstructure with grain sizes in the range of ∼0.1–0.5μm. As a result of the low melting temperature of the alloy, the high internal stresses introduced by torsion straining are relaxed and the grain boundaries are close to an equilibrium configuration.
Synthesis of nanocrystalline Ni–Fe alloy powders by spray pyrolysis
Authors: Eroglu S. , Zhang S.C. , Messing G. L.
Published: March 2008

Nanocrystalline 70 wt. % Ni–30 wt.% Fe alloy powders were synthesized by spray pyrolysis from a solution of nickelcene (C2H5)2Ni and ferrocene (C2N5)2Fe dissolved in 2-methoxyethanol. The alloy powder consisted of <10 nm and 70 to 80 nm particles. Thermodynamic analysis is shown to be a useful tool for gaining insight into the thermochemistry of the spray pyrolysis process.
An investigation of the invariant reactions in the BiPbSrCaCuO system
Authors: Liu Libin , Jin Zhanpeng
Published: March 2008

The phases present around the (Bi, Pb)2Sr2Ca2Cu3Ox (2223) phase between 830–880 °C have been studied by x-ray diffraction (XRD) and electron probe microanalysis (EPMA) methods. The decomposition and melting temperatures of the 2223 phase in these samples have been measured by the differential thermal analysis (DTA) method. Partial substitution of Bi with Pb (Pb: Bi = 3: 22) does not change the 850 °C phase relations around 2223 phase. 2223 decomposes to liquid, Sr7Ca7Cu24O41 (7724), and Ca2CuO3 at 875 °C. The invariant reactions (degree of freedom is zero) among 2223, 7724, Ca2CuO3, CuO, Bi2Sr2CaCu2O8 (2212), and liquid were proposed to be L + 7724 + Ca2CuO3 → 2223 + 2212, L + 7724 + Ca2CuO3 → 2223 + CuO, L + 7724 → 2223 + 2212 + CuO. The reaction temperatures were estimated to be 860 °C, 860 °C, and 854 °C, respectively. An invariant reaction scheme and a tentative liquidus projection were sketched out.
Creep behavior and microstructural correlation of a particle-strengthened Nb–1Zr–0.1C alloy
Authors: Farkas D.M. , Mukherjee A.K.
Published: March 2008

The steady-state creep behavior of a particle-strengthened alloy of niobium (Nb–1Zr–0.1C) was compared with pure niobium and a Nb–1Zr alloy. The approach to a threshold stress was indicated at stress levels below 16 MPa and was supported by a statistical analysis of mean particle size. Analysis of the crept microstructure showed a classic dislocation substructure whose cell size was inversely proportional to the applied stress except at very low stresses. The smaller than predicted cell size observed at low applied stresses was attributed to the particles, preventing the dislocation cells from reaching their equilibrium dimension. Some amount of particle growth was observed which led to a reduction in creep resistance with time.
TiC/metal nacrous structures and their fracture toughness increase
Authors: Liu C.H. , Li Wen-Zhi , Li Heng-De
Published: March 2008

Multilayers of TiC and a series of metals have been fabricated by ion beam sputtering deposition to simulate nacre. The individual layer thickness varies from 1 to 10 nm, and the total thickness of the multilayers is about 1 μm. Transmission electron microscopy (TEM), low-angle x-ray diffraction (LXRD), and high-resolution electron microscopy (HREM) show their periodicity and lattice images. A particular method is devised to evaluate the relative toughness of this artificial pearlite. It is shown that the toughness of these nanocomposite materials can be tremendously improved. A maximum of toughness appears at a certain modulation. Metals with high plasticity such as Al and Cu can produce a particularly spectacular effect on increasing the toughness of these multilayers.
X-ray absorption near edge structures in cobalt oxides
Authors: Jiang T. , Ellis D. E.
Published: March 2008

Theoretical studies have been made of K-edge x-ray absorption near edge structure (XANES) of Co in CoO, Co(OH)2, CoTiO3, Co3O4, and CoAl2O4. Correlations of experimental near edge features with site symmetry, local geometry, local electronic structure, i.e., atomic configuration, charge transfer, and backscattering from neighboring atomic potentials are interpreted. The self-consistent Discrete Variational Xa Method (DV-Xα) within an embedded cluster technique has been used to generate the crystal potential. A multiple scattering (MS) approach is then used to solve for the final state wave function. The ground state DV wave functions are analyzed in terms of the projected density of states, whereas the final state MS continuum wave functions are analyzed through the concept of photoelectron trapping time.
Characteristics of conductive SrRuO3 thin films with different microstructures
Authors: Jia Q. X. , Chu F. , Adams C. D. , Wu X. D. , Hawley M. , Cho J. H. , Findikoglu A. T. , Foltyn S. R. , Smith J. L. , Mitchell T. E.
Published: March 2008

Conductive SrRuO3 thin films were epitaxially grown on (100) LaAlO3 substrates by pulsed laser deposition over a temperature range from 650 °C to 825 °C. Well-textured films exhibiting a strong orientation relationship to the underlying substrate could be obtained at a deposition temperature as low as 450 °C. The degree of crystallinity of the films improved with increasing deposition temperature as confirmed by x-ray diffraction, transmission electron microscopy, and scanning tunneling microscopy. Scanning electron microscopy revealed no particulates on the film surface. The resistivity of the SrRuO3 thin films was found to be a strong function of the crystallinity of the film and hence the substrate temperature during film deposition. A residual resistivity ratio (RRR = ρ300 K/ρ4.2 K) of more than 8 was obtained for the SrRuO3 thin films deposited under optimized processing conditions.
Spectroscopic characterization of annealed Si1−xCx films synthesized by ion implantation
Authors: Compagnini G. , Calcagno L. , Foti G. , Baratta G.
Published: March 2008

Amorphous hydrogenated silicon carbon alloys were synthesized by C2H2 ions implantation in a silicon substrate at different fluences to obtain samples with different carbon atomic concentrations (10−50 at. %). As-implanted and subsequently annealed samples were investigated by using Rutherford backscattering, infrared, and Raman spectroscopies in order to follow the crystallization process. It was found that crystallization of stoichiometric SiC phase starts at 1000 °C both in low and high containing carbon films, while at the stoichiometric composition silicon (or carbon) was found to clusterize into homonuclear islands even at lower temperatures. The analysis of the fundamental absorption edge reveals the presence of an optical energy gap of about 1.3 eV independently on the film composition in the as-implanted samples, while after the thermal process at 1000 °C it increases to 2 eV for a carbon concentration below 0.5 and up to 1.8 eV for all those samples with a carbon excess.
Formation of SrBi2Ta2O9: Part I. Synthesis and characterization of a novel “sol-gel” solution for production of ferroelectric SrBi2Ta2O9 thin films
Authors: Boyle Timothy J. , Buchheit Catherine D. , Rodriguez Mark A. , Al-Shareef Husam N. , Hernandez Bernadette A. , Scott Brian , Ziller Joseph W.
Published: March 2008

We have developed a simple and rapid method for the synthesis of a precursor solution used in the production of SBT powders and thin films of the layered-perovskite phase SrBi2Ta2O9 (SBT). Precursor solution preparation takes less than 30 min and involves the generation of two solutions: (a) Bi(O2CMe)3 dissolved in pyridine and (b) Ta(OCH2Me)5 added to Sr(O2CMe)2 and then solubilized by HO2CMe. After stirring separately for 10 min, these solutions are combined, stirred for an additional 10 min, and used without any further modifications. The individual solutions and ternary mixture were studied using a variety of analytical techniques. Films of the layered-perovskite phase were formed at temperatures as low as 700 °C. Ferroelectric testing of SBT films, fired at 750 °C, reveals standard hysteresis loops with no fatigue for up to 4 × 109 cycles.
Structural and dielectric properties of Bi2NbxVi−xO5.5 ceramics
Authors: Varma K. B. R. , Prasad K. V. R.
Published: March 2008

Bi2Nbx V1−xO5.5 ceramics with x ranging from 0.01 to 0.5 have been prepared. The crystal system transforms from an orthorhombic to tetragonal at x 3= 0.1 and it persists until x = 0.5. Scanning electron microscopic (SEM) investigations carried out on thermally etched Bi2NbxV1−xO5.5 ceramics confirm that the grain size decreases markedly (18 μm to 4 μm) with increasing x. The shift in the Curie temperature (725 K) toward lower temperatures, with increasing x, is established by Differential Scanning Calorimetry (DSC). The dielectric constants as well as the loss tangent (tan δ) decrease with increasing x at room temperature.
Domain structure-property relations in lead lanthanum zirconate titanate ceramics
Authors: Akbas Mehmet A. , Reaney Ian M. , Lee William E.
Published: March 2008

The domain structure and dielectric properties as a function of lanthanum concentration and Zr/Ti ratio have been investigated in rhombohedral and tetragonal lead lanthanum zirconate titanate (PLZT) ceramics. Transmission electron microscopy revealed that, with increasing lanthanum concentration and Zr/Ti ratio, the long-range-ordered domains (macrodomains) reduced in width, initially being fine scale (20 nm) striations, but eventually forming a “mottled” contrast (5 nm), characteristic of a relaxor. Relative permittivity measurements as a function of temperature revealed a correlation between broadening of the dielectric maxima and the onset of relaxor-type behavior with the appearance of the striations and mottled (relaxor) contrast, respectively.
Reactive-infiltration processing of SiC-metal and SiC-intermetallic composites
Authors: Hozer Leszek , Chiang Yet-Ming
Published: March 2008

Liquid-phase reactive infiltration is a rapid and net-shape method of synthesizing silicon carbide composites. We use reactive infiltration of carbon with Si–A1 and Si–Cu melts to prepare composites consisting of interpenetrating networks of β–SiC and a secondary phase assemblage containing ductile metal (A1–Si) or a metal silicide (Si–Cu). The mechanisms of phase formation have been characterized. It is shown that a rapid initial reaction upon infiltration forms a largely stationary SiC network, within which the secondary phase constitution evolves due to solute rejection and liquid phase diffusion processes. Both homogeneous composites and those with controlled composition gradients have been synthesized.
Fourteen-year-old aging study of the effect of thickness on methanol transport in crosslinked poly(methyl methacrylate)
Authors: Lee Sanboh
Published: March 2008

The effect of thickness on methanol transport in fourteen-year-old crosslinked poly(methyl methacrylate) was investigated. The samples studied here are from the same primary source of those used by a study made fourteen years earlier. The sample was encapsulated by a plastic bag and maintained in a desiccator at room temperature. Four thicknesses, 0.6, 1.0, 1.5, and 1.9 mm, were examined. Methanol sorption data were fit to a model in which the mass sorption is a combination of case I, case II, and anomalous sorption. The diffusion coefficient for case I transport increases with increasing thickness, but the velocity for case II transport does the opposite. The diffusion coefficient for case I transport and the velocity for case II transport exhibit the Arrhenius behavior. The activation energies for case II transport are 18.9, 16.3, 14.6, and 13.4 kcal/mole, corresponding to the thicknesses 0.6, 1.0, 1.5, and 1.9 mm, respectively. The activation energies for case I transport are 24.7, 24.2, 21.7, and 21.9 kcal/mole, corresponding to the thicknesses 0.6, 1.0, 1.5, and 1.9 mm, respectively. For thickness 1.5 mm the activation energies for case I and case II transport are 21.7 and 14.6 kcal/mole for this study and 24.9 and 17.3 kcal/mole obtained fourteen years ago.
Structural and superconducting properties of melt-grown Y–Ba–Cu–O superconductors
Authors: Gopalan R. , Rajasekharan T. , Roy T. , Rangarajan G. , Ganesan V. , Srinivasan R.
Published: March 2008

YBa2Cu3O7 (123) samples with varying Y2BaCuO5 (211) concentrations (0 mol%, 20 mol%, 28 mol%, and 50 mol%) were synthesized by the melt-growth process. Microstructural characterizations were done using x-ray diffraction (XRD), optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). It was found that 123 platelet width, crack width between the platelets, and 211 particle size decreased systematically with increasing 211 concentration. TEM study showed that there is a critical radius of curvature (rc ≤ 0.2 μm-0.3 μm) of the 123/211 interface where defects/contrasts of strain field start to appear, and these defects are believed to be responsible for pinning the magnetic flux. Microhardness measurements showed that Vickers hardness (VHN) increases with increasing 211 content. Critical current density (Jc) values obtained from magnetization measurements using a SQUID magnetometer were found to increase in melt-grown samples by the addition of 211 content.
High resolution transmission electron microscopy study of interface structures and growth defects in epitaxial Bi2Sr2Can−1CunO4+2n + δ films on SrTiO3 and LaAlO3
Authors: Zakharov N. D. , Hesse D. , Auge J. , Roskos H. G. , Kurz H. , Hoffschulz H. , Dreβen J. , Stahl H. , Güntherodt G.
Published: March 2008

The defect structure of epitaxial, c-oriented Bi2Sr2Can−1CunO4+2n+δ (BSCCO) thin films grown by dc-sputtering and layer-by-layer MBE on SrTiO3 and LaAlO3 single crystal substrates was investigated by high-resolution transmission electron microscopy (HRTEM). Particular emphasis was put on the structure of the film/substrate interface. The films grown by dc-sputtering show a rather perfect structure involving a regular stacking of the unit cells. In spite of this regularity, there are many defects, such as twins, chemical stacking faults, and precipitates, as well as interfacial dislocations accommodating the film/substrate lattice misfit. The MBE-grown films contain twins and interfacial dislocations, but most prominent are precipitates of various size and rather high number density. Composition and structure of the precipitates were analyzed. Interfacial dislocations were found to be located in the films at a distance of up to 3 nm from the film/substrate interface. The experiments showed that the quality of the film/substrate interface in MBE-grown films is considerably higher with respect to smoothness, sharpness, and regularity, if the layer-by-layer MBE process starts with a Sr–O layer instead of a Bi–O layer. This observation is in correspondence to the observed interface structure of the dc-sputtered films, where the first film layer was a Sr–O layer, not a Bi–O layer, in spite of the films being sputtered from a composite target. A structure model of the Bi2Sr2Can−1CunO4+2n+δ/(100)SrTiO3 interface is proposed. The prolonged MBE process was shown to imply a chemical interaction between the SrTiO3 substrate and the growing film, resulting in the formation of Sr-rich phases in the near-interface substrate regions.
Control of meandering grain boundary configurations in YBa2Cu3Oy bicrystal thin films based on deposition rate
Authors: Zhang X. F. , Miller D. J. , Talvacchio J.
Published: March 2008

Changing the film deposition rate is shown to be one way to influence the meandering configurations of grain boundaries (GB's) formed in YBa2Cu3Oy (YBCO) bicrystal thin films. The magnitude and wavelength of the meander in YBCO films deposited at two different rates have been characterized by transmission electron microscopy (TEM) and statistically quantified. It has been found that the meander becomes more uniform and considerably less rough in films deposited at lower rates compared to that observed in films deposited at higher rates. A mechanism for the formation of the meandering GB is proposed based on heterogeneous nucleation and three-dimensional (3D) island growth together with overgrowth of the YBCO films across the substrate grain boundary. The different island sizes and tendency for overgrowth induced by changing the film deposition rate are believed to play important roles in controlling the meandering GB configuration. The possible effects of meandering configurations on transport properties are discussed.
Preparation of EuO films by sol-gel technique
Authors: Yi Guanghua , Batalla E.
Published: March 2008

EuO thin films with the cubic NaCl structure were fabricated by a sol-gel technique. The composition and crystal structure of the films were investigated as a function of firing temperature. The preparation of the stock solution and the coating and firing of the films are described. The firing of the gel film and the reduction of the Eu2O3 phase are also discussed.
Microstructure and magnetic properties in percolating (Ni–Fe)x(SiO2)1–x granular films
Authors: Xu Y. , Yan X.
Published: March 2008

We studied composition, structure, microstructure, and magnetic properties of percolating (Ni–Fe)x(SiO2)1−x granular thin films. We found that the magnetic susceptibility increases and the coercivity decreases when increasing x toward xt, the critical metallic volume fraction for the metal-insulator transition, and the susceptibility decreases and the coercivity increases when increasing annealing temperature for x just below xt. Comparison of the microstructure and the magnetic properties suggests that the enhanced magnetic susceptibility for x just below xt is probably associated with the labyrinthine structure of the granular magnetic particles where there is an enhanced surface-to-volume ratio of the magnetic particles.
Mechanical properties and oxidation resistivity of carbon fiber/ceramic composites prepared from borosiloxane
Authors: Hoshii Shinsuke , Kojima Akira , Otani Sugio
Published: March 2008

Diphenylborosiloxane (PBS), an organometallic compound with Si–O–B bonds, was compounded with carbon fiber (CF) to form CF/ceramic composite. Three types of PBS with different molar ratios (Si/B) in the materials were used. On the PBS obtained, specific gravity, Si content, molecular weight, melting point, and infrared absorption spectrum were measured. On the basis of these results, structures of PBS were examined, which clarified that the PBS thus synthesized consisted of several components with different molecular weights. Mechanical properties and oxidation resistivity of the CF/ceramic composites obtained differed with the Si/B ratios of PBS. Mechanical strength of the CF/ceramic composites increased with increase of Si content of PBS. It was also found that, when PBS with high boron content was used, compact vitreous film consisting mainly of B2O3 was formed over the composite. Due to the formation of this film, oxidation resistivity of the composite was improved.
Chemical vapor deposition synthesis and characterization of co-deposited silicon–nitrogen–boron materials
Authors: Essafti A. , Gómez-Aleixandre C. , Fierro J. L. G. , Fernández M. , Albella J. M.
Published: March 2008

Si–N–B films have been deposited by LPCVD from SiH4/B2H6/NH3 gas mixtures. The influence of the temperature and the composition of the gas mixture on the deposition process and film properties has been investigated. At 1000 °C, for the highest ammonia flow rate (SiH4 :B2H6 : NH3, 10 : 25 : 500), a mixture of turbostratic boron nitride and silicon nitride was deposited. For decreasing ammonia flow rates the Si–N–B ternary system was formed (1260 cm−1 band in the infrared spectra), which co-exists with the unstable turbostratic boron nitride structure. Finally, for a low NH3 flow rate of 100 sccm, stable amorphous films are obtained. On the other hand, at 800 °C, stable films with a high content in the ternary Si–N–B compound were obtained for a wide range of ammonia concentrations (100–500 sccm). At this temperature (800 °C), the composition of the films, as measured by Auger and photoelectron spectroscopies, strongly depends on the [SiH4]/[B2H6] ratio in the gas mixture. The improvement in the mechanical and chemical properties of the samples has been associated with the increase in the content of Si–N bonds in the Si–N–B films.
Microstructural observation of the ZrC/ZrO2 interface formed by oxidation of ZrC
Authors: Shimada Shiro , Inagaki Michio , Suzuki Mikio
Published: March 2008

The oxidation of ZrC single crystals having (100) faces was performed at a temperature of 600 °C at an oxygen pressure of 2.6 kPa. A polished cross section of oxide scale was observed by backscattered electron imaging (BEI) in a scanning electron microscope (SEM). The oxide scale was observed to consist of two subscales, zones 1 and 2; zone 1 is adjacent to the ZrC. The thickness of zone 1 was kept constant (about 2 μm), independent of oxidation time. The interfacial microstructure between ZrC and cubic ZrO2 (c-ZrO2) phase in zone 1 was observed by high resolution transmission electron microscopy, by using an extremely thin foil of an oxidized crystal. The c-ZrO2 crystallites of 2 to 10 nm in size showing the (111), (200), and (220) lattice fringes were aggregated and distributed in an area about 10 to 20 nm away from the interface, with an amorphous layer observed adjacent to the ZrC. Electron dispersive x-ray analysis (EDX) indicated that carbon is concentrated at the interface; a decreasing oxygen concentration gradient in the oxide phase and away from the interface in the ZrC suggests the formation of oxygen-deficient ZrO2–x and oxycarbide on the respective sides of the interface. A black coating layer appeared, resulting from detachment or dissolution of zone 2, when a crystal oxidized for 1 h was treated in a HF solution. The layer was shown by the Raman spectrum to be amorphous carbon.
Synthesis of cubic diamond in the graphite-magnesium carbonate and graphite-K2Mg(CO3)2 systems at high pressure of 9–10 GPa region
Authors: Taniguchi T. , Dobson D. , Jones A. P. , Rabe R. , Milledge H. J.
Published: March 2008

Cubic diamond was synthesized with two systems, (1) graphite with pure magnesium carbonate (magnesite) and (2) graphite with mixed potassium and magnesium carbonate at pressures and temperatures above 9.5 GPa, 1600 °C and 9 GPa, 1650 °C, respectively. At these conditions (1) the pure magnesite is solid, whereas (2) the mixed carbonate exists as a melt. In this pressure range, graphite seems to be partially transformed into hexagonal diamond. Measured carbon isotope δ13C values for all the materials suggest that the origin of the carbon source to form cubic diamond was the initial graphite powder, and not the carbonates.
Influences of oxygen partial pressure on YBCO grain growth by a zone melting method
Authors: Yao X. , Sumida M. , Shiohara Y.
Published: March 2008

This study investigates the influences of Y–Ba–Cu–O compounds solidification under different oxygen partial pressures by a zone melting method. In the Y–Ba–Cu–O system, P(O2) ranged from 0.02 to 1 atm, and the following reaction occurred during heating: YBa2Cu3O6−δ (Y123) → Y2BaCuO5 (Y211) + L. With an increase of oxygen partial pressure or decrease of pulling rate, the morphology of the solidified interface changed from mushy to equiaxed, cellular, and planar. The continuous Y123 grains were readily obtained under high oxygen partial pressure. Based on the constitutional supercooling theory and combining the result of the yttrium solubility limit for different oxygen partial pressures, the influences of oxygen partial pressure on Y123 morphological evolution were clarified.
Synthesis of submicrometer-grained-ultrahigh-carbon steel containing 10% aluminum by ball-milling of powders
Authors: Taleff Eric M. , Nagao Mamoru , Ashida Yoshio , Sherby Oleg D.
Published: March 2008

An ultrahigh-carbon (1.25 wt.%) steel alloy containing 10 wt.% aluminum (UHCS–10Al) was processed by a powder metallurgy technique. Gas-atomized powders were subjected to ball-milling in an attritor in order to obtain a submicrometer grain size. Powder material was consolidated by both hot isostatic pressing (HIP) and by hot isopressure extrusion (HIE). Bulk material with submicrometer grain sizes was produced from attrited powders. The chemical composition and microstructure of this material are characterized at each processing step, from atomization through consolidation. Tensile tests show that a high strength results from the submicrometer grain size produced in the bulk material.
Thermodynamic stability of binary oxides in contact with silicon
Authors: Hubbard K. J. , Schlom D. G.
Published: March 2008

Using tabulated thermodynamic data, a comprehensive investigation of the thermo-dynamic stability of binary oxides in contact with silicon at 1000 K was conducted. Reactions between silicon and each binary oxide at 1000 K, including those involving ternary phases, were considered. Sufficient data exist to conclude that all binary oxides except the following are thermodynamically unstable in contact with silicon at 1000 K: Li2O, most of the alkaline earth oxides (BeO, MgO, CaO, and SrO), the column IIIB oxides (Sc2O3, Y2O3, and Re2O3, where Re is a rare earth), ThO2, UO2, ZrO2, HfO2, and Al2O3. Of these remaining oxides, sufficient data exist to conclude that BeO, MgO, and ZrO2 are thermodynamically stable in contact with silicon at 1000 K. Our results are consistent with reported investigations of silicon/binary oxide interfaces and identify candidate materials for future investigations.
Thermal plasma treatment of titanium carbide powders: Part II. In-flight formation of carbon-site vacancies and subsequent nitridation in titanium carbide powders during induction plasma treatment
Authors: Ishigaki Takamasa , Moriyoshi Yusuke , Watanabe Takayuki , Kanzawa Atsushi
Published: March 2008

The in-flight modification of titanium carbide powders was carried out in radio-frequency (rf) inductively coupled plasmas. The powders were partially melted and evaporated, and then subjected to modifications in morphology, size, and chemical composition. Both the Ar–H2and Ar–N2plasma treatments induced the formation of carbon-site vacancies in titanium carbide. The mixing of NH3to Ar–H2plasma at the plasma tail, and the Ar–N2plasma treatment resulted in the partial substitution of carbon by nitrogen. The variation in physical and chemical modification was discussed compared with the predictions by the thermochemical analysis, and the numerically obtained heat transfer of our preceding paper.
Microstructure and strain in electrodeposited Cu/Ni multilayers
Authors: van Heerden David , Zolotoyabko Emil , Shechtman Dan
Published: March 2008

Electrodeposited Cu/Ni multilayers with different modulation lengths Λ = 4–18 nm were examined by means of x-ray diffraction and transmission electron microscopy. Preferred orientations of [111], [110], and [001]-types, as determined from relative x-ray diffraction peak intensities, were seen in the multilayers. By means of computer simulations of the measured x-ray diffraction spectra, several parameters of the multilayers, such as Λ-values and fluctuations ΔΛ, as well as lattice strain, were determined. Multilayers having large Λ were found to be fully relaxed due to interfacial dislocation formation. In short Λ [001]-texture multilayers partial strain relaxation occurs, probably due to the incorporation of Cu into the Ni layers. Both of the processes lead to the diffuse Cu/Ni interfaces. Short wavelength multilayers with a [111]-preferred orientation were almost fully strained. The importance of the [111]-texture in the improvement of mechanical strength of Cu/Ni multilayers resulting from its enhanced ability for stain accommodation is discussed.
Melting process of nanometer-sized In particles embedded in an Al matrix synthesized by ball milling
Authors: Sheng H. W. , Xu J. , Yu L. G. , Sun X. K. , Hu Z. Q. , Lu K.
Published: March 2008

Dispersions of nanometer-sized In particles embedded in an Al matrix (10 wt. % In) have been synthesized by ball milling of a mixture of Al and In powders. The as-milled product was characterized by using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectrometer (EDX), transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HREM), respectively. It was found that In and Al are pure components immiscible with each other, with nanometer-sized In particles dispersively embedded in the Al matrix. The melting behavior of In particles was investigated by means of differential scanning calorimeter (DSC). The calorimetric measurements indicate that both the melting point and the melting enthalpy of the In nanoparticles decrease with increasing milling time, or refinement of the In particles. Compared to its bulk melting temperature, a melting point depression of 13.4 K was observed when the mean grain size of In is 15 nm, and the melting point depression of In nanoparticles is proportional to the reciprocal of the mean grain size. The melting enthalpy depression was interpreted according to the two-state concept for the nanoparticles. Melting of the interface was deduced to be an exothermal process due to its large excess energy/volume.
Hydrothermal growth and characterization of NaLa(WO4)2 crystals
Authors: Byrappa K. , Jain Amita
Published: March 2008

The growth of NaLa(WO4)2 crystals has been carried out by the hydrothermal method at fairly low P-T conditions. The crystal morphology has been studied with respect to the growth parameters. The crystals obtained were characterized by various techniques such as x-ray diffraction (XRD), differential thermal analysis (DTA), and infrared (IR) spectroscopy.
Principle of dynamic decompression and cooling for materials processing
Authors: Apfel Robert E. , Qiu Ning
Published: March 2008

When a melt seeded with droplets of a volatile liquid is rapidly decompressed, the droplets explosively vaporize, taking their latent heat of vaporization from the melt and, therefore, homogeneously cooling and expanding it. The possibility of using this dynamic decompression and cooling (DDC) technique for producing an amorphous metallic foam is theoretically investigated. To test the premises of this theoretical model, preliminary experiments with an organic melt (p-terphenyl) seeded with water drops were performed. Results of these experiments demonstrate the potential of this novel approach to materials processing.
A new method for hardness determination from depth sensing indentation tests
Authors: Gubicza J. , Juhász A. , Lendvai J.
Published: March 2008

A new semiempirical formula is developed for the hardness determination of the materials from depth sensing indentation tests. The indentation works measured both during loading and unloading periods are used in the evaluation. The values of the Meyer hardness calculated in this way agree well with those obtained by conventional optical observation, where this latter is possible. While the new hardness formula characterizes well the behavior of the conventional hardness number even for the ideally elastic material, the mean contact pressure generally used in hardness determination differs significantly from the conventional hardness number when the ideally elastic limiting case is being approached.
Study of growth kinetics in melt-textured YBa2Cu3O7−x
Authors: Athur Srinath P. , Selvamanickam V. , Balachandran U. , Salama K.
Published: March 2008

Directional solidification has been shown to be a successful way of achieving high current densities in bulk YBCO. The lack of understanding of the growth kinetics, however, makes it difficult to fabricate longer samples and reduce the processing times. To study the growth kinetics, quenching experiments of undoped YBa2Cu3O7−x (Y-123) and Y-123 doped with Pt and Nd from above the peritectic temperature with different holding times, t, were conducted. The results of these experiments indicate that the average 211 particle size varies at t1/3. Growth rate experiments were also conducted on these samples to determine the maximum growth rate for plane front solidification, Rmax. This quantity was measured for undoped and doped Y-123, and it was found that the addition of Pt did not increase Rmax while the addition of Nd doubled the growth rate. Using the coarsening results together with the growth rate experiments, the diffusivity of Y in liquid and the 211-liquid interfacial energy for undoped and doped Y-123 were calculated.
A transmission electron microscopy study of the crystallinity and secondary phase formation in melt-processed YBa2Cu3O7−δ
Authors: Yan Y. , Cardwell D. A. , Campbell A. M. , Stobbs W. M.
Published: March 2008

The microstructure of large grain melt-processed YBa2Cu3O7−δ containing 10 molar% excess Y2BaCuO5 prepared and oxygenated under atmospheric pressure has been investigated by transmission electron microscopy (TEM) and optical microscopy. These materials always contain parallel structural and microscopic platelet-like features in the crystallographic a-b plane of a few microns spacing which have been variously described as grain boundaries or microcracks. We have observed such features, which clearly influence the flow of current in melt-processed YBCO, to consist of copper deficient, impurity phase material which can be either amorphous or crystalline in nature. A variety of defects have been observed by high-resolution electron microscopy (HREM) in the vicinity of these platelet boundaries, including double and triple CuO layer stacking faults, which may constitute effective flux pinning sites.
Photoelectron spectroscopy study of amorphous silicon-carbon alloys deposited by plasma-enhanced chemical vapor deposition
Authors: Cicala G. , Bruno G. , Capezzuto P. , Favia P.
Published: March 2008

X-ray photoelectron spectroscopy (XPS) coupled with Fourier transform infrared (FTIR) and optical transmission spectroscopy (OTS) has been used for the characterization of silicon-carbon alloys (a-Si1−xCx: H, F) deposited via plasma, by varying the CH4 amount in SiF4–CH4–H2 feeding mixture. XPS measurements have shown that carbon-rich a-Si1−xCx: H, F alloys include large amounts of fluorine (>11 at. %), which make the films susceptible to the air oxidation. In addition, the effect of the alloying partner carbon on the valence band (VB) and on the VB edge position of amorphous silicon is also described.
Wet forming, sintering behavior, and dielectric properties of BaTi0.8Zr0.2O3
Authors: Hirata Yoshihiro , Kawazoe Takahiro
Published: March 2008

Density, grain size, lattice parameter, and dielectric properties were measured on BaTi0.8Zr0.2O3 sintered at 1100–1600 °C. The hydrothermally prepared BaTi0.8Zr0.2O3 particles of 128 nm diameter were consolidated by filtration of 2-methoxyethanol suspensions and subsequently compressed by isostatic pressing under a pressure of 294 MPa to form a uniform microstructure of high density (52% of the theoretical density). These green compacts were sintered to a relative density of above 99% in the temperature range from 1350 to 1600 °C where rapid grain growth to above 30 μm occurred. Increase of sintering temperature was accompanied by the increase of lattice parameter and dielectric constant of BaTi0.8Zr0.2O3 at room temperature. The sintered BaTi0.8Zr0.2O3 showed a diffuse phase transition from paraelectric (higher temperature) to ferroelectric state (lower temperature) at 32 °C.
Effect of defect structure on gas sensitivity of LaCrO3
Authors: Huang Rong-Fong , Howng Wei-Yean
Published: March 2008

The isopropyl alcohol gas sensitivity of LaCrO3 at 250 °C is found to depend on the amount of TiO2 content and cation stoichiometric ratio of the sample. The gas sensitivity enhancement is related to the defect structure and electrical conduction behavior of p-type, donor-doped semiconductive oxides. The high resistivity coupled with the increasing point defects by the donor dopants are responsible for the high gas sensitivity of TiO2 doped LaCrO3. It is believed that the positively charged ionic-type defects created by dopants act as trapping sites to adsorb oxygen.
Effects of the metal workpiece properties on the residual stresses in silicon nitride-metal brazed joints
Authors: Yvon Pascal J. , Marty Benoit , Peteves Stathis D.
Published: March 2008

Modelling, but more importantly, measurements of residual stresses are needed to guide the design and development of high integrity ceramic/metal joints. This study evaluates the influence of the metal workpiece on the residual stress state present in the ceramic part of the joint. Si3N4 was directly bonded via the active metal brazing route to several metals Cu, Mo, W, Ta, Nb, Zr, Ti, and AISI 316, selected to cover an extended range of thermomechanical properties. The residual strains in the joints were measured using an x-ray diffraction technique. The results indicate that the maximum residual stresses scale with the thermal mismatch for metals with low coefficients of thermal expansion. The experimental results are compared with analytical calculations of the residual stresses.