bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of binder composition on debinding and sintering processes of injection molded Fe–8Ni mixed powders
Authors: Takekawa Junjiro
Published: March 2008

The debinding process of injection-molded compacts of Fe–8Ni mixed powders, containing binders of different ratios of polymers to wax, was investigated. The effect of binder compositions and debinding conditions on the sinterability of the compacts were also studied. Distortions produced in the debinding processes of the compacts were minimized for the case where a ratio of polymer to the total binder contents was 0.35. In the case of the compacts debound in air, sintered densities increased by increasing the debinding temperature up to 350 °C, then decreased sharply for higher debinding temperatures. In the compacts debound in N2, sintered densities were almost independent of the debinding temperature. The sinterability of the compacts debound in N2 was inferior to that debound in air.
Chemical vapor deposition of α – ZrP whiskers
Authors: Motojima S. , Hirano S. , Kurosawa K. , Iwanaga H.
Published: March 2008

α–ZrP whiskers have been prepared from ZrCl4 + PCl3 + H2 + Ar gas mixtures at 1050–1250 °C using the mixed metal impurity-activated chemical vapor deposition process. The growth conditions, morphology, growth mechanism, and some properties were examined. The mixed impurities of Si + Pt and Si + Pd were very effective for the ZrP whisker growth with 8–12 mm (avg. 10 mm) long whiskers being obtained at 1300 °C for 1 h. The growth direction of the whiskers having hexagonal and square cross sections were along the c-axis and a-axis, respectively. The whiskers were very stable to an 80 min immersion in a concentrated HCl solution.
Mesoscopic structure of SiC fibers by neutron and x-ray scattering
Authors: Suzuya Kentaro , Furusaka Michihiro , Watanabe Noboru , Osawa Makoto , Okamura Kiyohito , Shibata Kaoru , Kamiyama Tomoaki , Suzuki Kenji
Published: March 2008

Mesoscopic structures of SiC fibers produced from polycarbosilane by different methods were studied by diffraction and small-angle scattering of neutrons and x-rays. Microvoids of a size of 4–10 Å in diameter have been observed for the first time by neutron scattering in a medium momentum transfer range (Q = 0.1–1.0 Å−1). The size and the volume fraction of β–SiC particles were determined for fibers prepared at different heat-treatment temperatures. The results show that wide-angle neutron scattering measurements are especially useful for the study of the mesoscopic structure of multicomponent materials.
Polarized light microstructure analysis of melt-textured DyBa2Cu3O7−x ceramics
Authors: Diko P. , Ausloos M. , Cloots R.
Published: March 2008

We report the microstructure of magnetically melt-textured Dy-123 samples, as observed by polarized light metallography. The phase dimensions, morphology, orientation, nature, and distribution are outlined. Grain, twin structure pattern, and grain boundary are characterized. The relationship among cracking, secondary phases, and tetragonal-orthorhombic phase transformation is discussed. The results are obtained by observing a “not-too-well-ordered” region. This leads to definite conclusions on the relationship between crack spacing and 211 distribution, and to some confirmation of the growth mechanism and on macro- and microcrack origins. From the present observations, the effect of the oxygenation process and the quantification of the tensile stress in the materials can also be obtained.
Reaction kinetics, sintering characteristics, and ordering behavior of microwave dielectrics: Barium magnesium tantalate
Authors: Lu Chung-Hsin , Tsai Chien-Cheng
Published: March 2008

The formation process of Ba(Mg1/3Ta2/3)O3 was confirmed to be a direct reaction between constituent compounds without the presence of intermediate compounds. Isothermal analysis of reaction kinetics indicated the controlling reaction to be a three-dimensional diffusion process. Based on the Ginstling–Brounshtein model, the activation energy of the formation process was estimated to be 257 kJ/mol. A new definition of the ordering parameter for Ba(Mg1/3Ta2/3)O3 was deduced to quantitatively evaluate the ordering degree. Raising sintering temperatures resulted in an increase in the ordering degree and bulk density of Ba(Mg1/3Ta2/3)O3. Reducing the barium content in Ba(Mg1/3Ta2/3)O3 substantially resulted in improved densification and enhanced ordering structure. On the other hand, an excess barium content in specimens hindered the progress of sintering, and also induced the disordering structure.
Refinement of low-resistance Ni–Ge–Au ohmic contacts to n+ GaAs using screening and response surface experiments
Authors: Lumpkin Nancy E. , King Warren , Tansley T. L.
Published: March 2008

Multivariable screening and response surface experiments have been performed to model ohmic contact resistance (Rc) of a Ni–Ge–Au ohmic metal process for n+ GaAs-based high electron mobility transistors (HEMTs). Seven variables were examined via a fractional factorial screening experiment to rank the effects of each process variable. The results of the screening experiment indicated that the most significant variables were total Ge and Au evaporated thickness, Ge-to-Au ratio, and the post-alloy cooling time. Response surface experiments were designed around these three variables to examine the first- and second-order effects. The results enabled the development of an empirical model of ohmic contact resistance from which a new low value of 0.03 ± 0.03 Ω · mm (one-sigma) was predicted. Twenty confirmation runs on the new process indicated an average Rc of 0.06 ± 0.02 Ω · mm (one-sigma), with a range of 0.02 Ω · mm to 0.11 Ω · mm, a reduction from the previous average process value of 0.14 ± 0.07 Ω · mm (one-sigma).
Influence of alloying elements on the chemical reactivity between Si–Al–O–N ceramics and iron-based alloys
Authors: Vleugels J. , Vandeperre L. , Van Der Biest O.
Published: March 2008

The chemical interaction between two β′–O′ Si–Al–O–N ceramics and a number of iron-based alloys is studied by means of static interaction couple experiments at 1100 and 1200 °C. The onset temperature of reaction of Si3N4 with pure iron was found to be at 1095 °C, which is in good agreement with a calculated temperature of 1033 °C. During the interaction, silicon and nitrogen from the ceramic dissolve and diffuse into the iron alloy, whereas the remaining aluminum and oxygen form Al2O3 particles. The interaction between ceramic and iron alloy is reaction controlled. In the initial stage of the interaction, the dissociation rate of the ceramic is the rate-controlling step. After the ceramic/metal interface is isolated from the furnace atmosphere, the nitrogen solution rate into the iron alloy becomes rate controlling. The influence of alloying elements on the reactivity could be related to their effect on the nitrogen solubility in the iron alloy. Ni, Si, and C decrease the nitrogen solubility and decrease the reactivity with the sialon ceramic. Cr and Mo have the opposite effect. The thickness of the interaction layer on the ceramic side of the interaction couple was found to be a function of the calculated nitrogen solubility in the iron alloy at 1 atm nitrogen pressure, making it possible to predict the relative chemical reactivity of a number of iron-based alloys with the same sialon ceramic.
Effect of silicon additions on characteristics of carbon fiber reinforced aluminum composites during thermal exposure
Authors: Cheng Hui-Ming , Zhou Ben-Lian , Kitahara Akira , Akiyama Shigeru , Kobayashi Kazuo
Published: March 2008

The effects of Si additions on the behavior of high modulus carbon fiber reinforced aluminum matrix (CF/Al) composites during thermal exposure at 773 K for different times have been investigated. The composites were fabricated via hybridization with a small volume fraction of SiC particles using a pressure-casting process. The change of longitudinal tensile strength, the strength degradation of carbon fibers, and the microstructural observations on the interfaces of CF/pure Al composites and CF/Al-Si composites after thermal exposure undoubtedly indicate that the alloying element Si in an aluminum matrix can effectively prohibit the interfacial reactions at the fiber/aluminum interface and has positive effects on the characteristics of CF/Al composites.
Effect of mechanical damage on thermal conduction of plasma-sprayed coatings
Authors: Wei Lanhua , Pajares Antonia , Lawn Brian R.
Published: March 2008

A thermal wave methodology for monitoring the thermal conduction of ceramic coatings with accumulating mechanical damage is described. Tests are conducted on a model alumina coating containing laminar defect intralayers. Controlled subsurface damage introduced with a spherical indenter is observed using a presectioned specimen. Microcrack damage accumulates progressively with increasing contact load and number of cycles. Associated changes in thermal diffusivity, specifically in the through-thickness direction, are imaged and quantified point-by-point using laser-generated thermal waves. The effective thermal resistance of the coating increases with crack density, up to the point of failure.
Process optimization for the fabrication of Tl2Ba2Ca2Cu3O10 thin films
Authors: Holstein W. L. , Parisi L. A.
Published: March 2008

A process has been developed for the fabrication of nearly single phase superconducting Tl2Ba2Ca2Cu3O10 thin films on (100) LaAlO3 substrates with a superconducting transition temperature Tc of 120 K and low microwave surface resistance at temperatures up to 110 K. Amorphous BaCaCuO precursor films were first deposited by rf magnetron sputtering and then thallinated at elevated temperatures. The double TlO layer phases (Tl2Ba2Ca2Cu3O10 + Tl2Ba2CaCu2O8) formed preferentially over the single TlO layer phases (TlBa2Ca2Cu3O9 + TlBa2CaCu2O7) at high Tl2O partial pressures. Thin films containing Tl2Ba2Ca2Cu3O10 and a small amount of CuO were prepared from Cu-rich precursor films (Cu/Ba > 1.7), while lower Cu content led to the formation of Tl2Ba2CaCu2O8 as a secondary phase. Tl2Ba2Ca2Cu3O10 film epitaxy was enhanced by carrying out the thallination in reduced oxygen partial pressures of 0.01–0.05 atm. Following the thallination step, the Tl2Ba2Ca2Cu3O10 thin films had a superconducting transition temperature Tc of only 106 ± 4 K. An additional 62 h anneal at 800 °C or an 8 h anneal at 850 °C in a Tl2O/O2 atmosphere increased the Tc to 120 K. The increase in Tc was accompanied by a decrease in the c-axis lattice constant, an enhancement in the long-range order in the c-direction, and the formation of a small amount of Tl2Ba2CaCu2O8 as a secondary phase. Minimization of surface resistance at high temperature (95–110 K) requires that the fraction of Tl2Ba2CaCu2O8 secondary phase in the films be kept low. Process routes are also described for the formation of nearly single phase TlBa2Ca2Cu3O9 and TlBa2CaCu2O7 thin films and the formation of a new ordered intergrowth phase, Tl4Ba4Ca3Cu5O18, which consists of alternating Tl2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10 layers.
Texture and chemical composition analyses on the Hg0.66Pb0.33Ba2Ca2Cu3Oy superconductor using the sealed quartz tube technique
Authors: Chow J.C.L. , Fung P.C.W. , Shao H.M. , Lam C.C.
Published: March 2008

Pb-substituted Hg-based superconductor of Hg0.66Pb0.33Ba2Ca2Cu3Oy has been fabricated using the sealed quartz tube technique. R- and x-ray diffraction pattern (XDP) measurements show that the specimen has a Tc of 135 K and contains mainly the Hg-1223 phase. Scanning electron microscopy/energy dispersive x-ray analysis (SEM/EDX) and transmission electron microscopy/energy dispersive x-ray analysis (TEM/EDX) were employed to study the texture and chemical composition of the specimen. It is found that the specimen contains round-shaped grains with a mixture of Hg-1223, BaCuO2, and Ca0.85CuO2 phases, square-shaped grains with a formula of PbBa2O3, small single crystals with single Hg-1223 phase, and crystal-like layers with a mixture of Hg-1223 and BaCuO2 phase. We consider that though the doping of Pb can benefit the stabilization of the Hg-1223 phase, it introduces other impurity phases and textures in the specimen at the same time.
Effect of Ag-particulate addition on processing, microstructure, and properties of MgO-whisker-reinforced bulk BPSCCO high-Tc superconductor composites
Authors: Yuan Y. S. , Wong M. S. , Wang S. S.
Published: March 2008

In associated papers [Y. S. Yuan, M. S. Wong, and S. S. Wang, J. Mater. Res. 11, 8–17 (1996); J. Mater. Res. (1996, in press)] it has been shown that weak thermo-mechanical properties of a bulk monolithic high-Tc superconductor (HTS) can be improved by introducing strong ceramic whiskers into the HTS ceramic materials. In this paper, we report a further study of incorporating Ag particulates, (Ag)p, in a bulk monolithic BPSCCO and in the MgO-whisker reinforced BPSCCO composite. Effects of the (Ag)p addition on processing, microstructure, and superconducting and mechanical properties of the bulk monolithic BPSCCO and the (MgO)w/BPSCCO composite are investigated. The results indicate that the highly ductile Ag particulates promote densification of the BPSCCO matrix phase in the composite during hot pressing. The microstructure of the HTS composite with the (Ag)p addition is similar to that in the HTS material without the (Ag)p. The (MgO)w/BPSCCO composite with 10% (by weight) Ag particulates has been shown to possess excellent superconducting properties. The (Ag)p addition to both the monolithic BPSCCO and the (MgO)w/BPSCCO is found to increase appreciably their fracture toughnesses, but has little effects on mechanical strengths of the materials. Quantitative relationships have been established among solid-state processing variables, HTS phase developments, microstructures, and superconducting and mechanical properties of the (Ag)p/BPSCCO and the (MgO)w/(Ag)p/BPSCCO HTS composites.
Faceting, dislocation network structure, and various scales of heterogeneity in a YBa2Cu3O7−δ low-angle [001] tilt boundary
Authors: Tsu I-Fei , Babcock S. E. , Kaiser D.L.
Published: March 2008

The grain boundary topography and grain boundary dislocation network structure of a 6° [001] bicrystal of YBa2Cu3O7−δ were studied using diffraction-contrast transmission electron microscopy (TEM). Saw-tooth-shaped arrays of facets composed of facets with lengths of a few tens of nanometers were observed in each of two widely separated sections of the boundary. The facet planes were {110}, {310}, and {221}. Further subfaceting of the (130) facets into a smaller-scale (a few nanometers) saw-tooth configuration of (010) and (110) facets produced a hierarchy of facets in at least one boundary section. The dislocation content observed in each type of facet agreed well with Frank's formula. However, the dislocations within individual facets frequently were inhomogeneously distributed, contrasting the picture of evenly spaced dislocations that is derived for boundaries of infinite extent. Certain types of dislocations repeatedly were grouped near the facet centers and ends. Well-separated partial dislocations frequently were observed near the facet midsections, but not near the facet junctions. Extended (∼30 nm) strain contrast was observed at all of the facet junctions formed by facets with dimensions on the order of tens of nanometers. This long-range strain may be due to the finite extent of the individual facets. These results all suggest that structural inhomogeneities occur on various length scales ranging from macroscopic to just a few nanometers. Such structural heterogeneity is consistent with the electrical heterogeneity that is indicated for many YBa2Cu3O7−δ grain boundaries.
Synthesis of metastable tetragonal (t′) zirconia-calcia solid solution by pyrolysis of organic precursors and coprecipitation route
Authors: Yashima Masatomo , Kakihana Masato , Ishii Koutaroh , Ikuma Yasuro , Yoshimura Masahiro
Published: March 2008

Three kinds of chemical processes, citrate gel process, acetate gel process, and coprecipitation route, have been applied to the synthesis of homogeneous metastable tetragonal (t′) and cubic solid solutions of ZrO2−X mol% CaO (X = 4–20). From a Raman scattering study, the citrate gel process based on the gelation of the aqueous solution of citric acid containing Zr and Ca ions was found to produce compositionally homogeneous samples in comparison with the other two methods. The axial ratio c/a decreases with increasing concentration of CaO and becomes unity around 8–10 mol% CaO composition.
Calculation of metastable immiscibility region in the Al2O3–SiO2 system
Authors: Ban Takayuki , Hayashi Shigeo , Yasumori Atsuo , Okada Kiyoshi
Published: March 2008

Metastable liquid-liquid immiscibility region in the Al2O3–SiO2 system was calculated by a regular solution model using three sets of liquidus data from the stable phase diagrams reported. These calculations indicated that the immiscibility region was richer in Al2O3 composition than those reported before. A miscibility gap calculated using the liquidus data reported by Klug et al. [F. J. Klug, S. Prochazka, and R. H. Doremus, J. Am. Ceram. Soc. 70, 750 (1987)] (model A) ranged from 2.6 to 71 mol % Al2O3 at around 1000 °C, which was the most compatible result with the idea that metastable pseudotetragonal mullite crystallized at around 1000 °C became Al2O3-rich composition due to the immiscibility phase separation before mullitization among three sets of liquidus data.
Diffraction analysis of nonuniform stresses in surface layers: Application to cracked TiN coatings chemically vapor deposited on Mo
Authors: Sloof W.G. , Kooi B. J. , Delhez R. , de Keijser Th. H. , Mittemeijer E. J.
Published: March 2008

Variations of residual stresses in layers on substrates can occur in directions parallel and perpendicular to the surface as a result of compositional inhomogeneity and/or porosity or cracks. Diffraction methods to evaluate such stress variations are presented. Comparison of the experimental value for the stress with a calculated value of the “diffraction-averaged stress,” on the basis of a model for the local stresses, proved to be a useful method of stress analysis. It is shown that a direct evaluation of occurring stress-depth profiles is less practical. The method of stress analysis proposed, is applied to chemically vapor deposited TiN coatings on Mo substrates. In these coatings a large tensile stress parallel to the surface develops during cooling from the deposition temperature, due to difference in thermal shrink between coating and substrate. As a result of the cooling-induced stress, cracking of the coating occurs. The mesh width of the crack pattern allows determination of the fracture-surface energy and the fracture toughness of the coating material. Conceiving the cracked coatings as assemblies of freestanding columns, and assuming full elastic accommodation of the thermal mismatch at the column/substrate interface, the stress variations in the coating are calculated. On this basis the diffraction-averaged stress and the depth profile of the laterally averaged stress can be predicted accurately for the cracked TiN layers.
Competitive gas-solid reactions realized by ball milling of Zr in ammonia gas
Authors: Chen Ying , Williams Jim S.
Published: March 2008

Competitive gas-solid reactions have been observed during high-energy ball milling of zirconium metal powder under an ammonia atmosphere at room temperature. The milling processes were investigated by monitoring pressure changes and subsequently analyzing milled powders with x-ray diffraction, thermal analysis, and elemental composition analysis. It is shown that during an early stage of milling, while the pressure is decreasing, a hydridation reaction predominates and leads to the formation of ZrH2 phase. During further milling the pressure increases again, and corresponds to a nitridation reaction between ZrH2 and available nitrogen (either excess NH3 or incorporated nitrogen in the powder) to form ZrN. Hydrogen gas is liberated and complete conversion to ZrN occurs after prolonged milling. The above reaction sequence was confirmed by the nitridation reaction of ZrH2 ball milled in NH3 atmosphere.
Impression creep behavior of SiC particle-MoSi2 composites
Authors: Butt Darryl P. , Korzekwa David A. , Maloy Stuart A. , Kung H. , Petrovic John J.
Published: March 2008

Using a cylindrical indenter (or punch), the impression creep behavior of MoSi2-SiC composites containing 0–40% SiC by volume, was characterized at 1000–1200 °C, 258–362 MPa punch pressure. Through finite element modeling, an equation that depends on the material stress exponent was derived that converts the stress distribution beneath the punch to an effective compressive stress. Using this relationship, direct comparisons were made between impression and compressive creep studies. Under certain conditions, compressive creep and impression creep measurements yield comparable results after correcting for effective stresses and strain rates beneath the punch. However, rate-controlling mechanisms may be quite different under the two stressing conditions, in which case impression creep data should not be used to predict compressive creep behavior. The addition of SiC affects the impression creep behavior of MoSi2 in a complex manner by pinning grain boundaries during pressing, thus leading to smaller MoSi2 grains and by obstructing or altering both dislocation motion and grain boundary sliding.
Crack-face fiber bridging: Finite element analysis, analytical model, and experimental result
Authors: Cao Jian-Wu , Sakai Mototsugu
Published: March 2008

Prior to considering crack-face bridging, the stress/strain-field ahead of the crack tip in the compact tension (CT) geometry is numerically assessed by means of finite element method (FEM). The stress field along the crack line which has a decreasing profile of tensile stresses from the crack tip converts to monotonically increasing compressive stresses toward the back face of the CT specimen via a rotational center. Based on these stress-field analyses, a novel crack-face bridging model for fiber-reinforced brittle matrix composites is presented. The application of the model to the experimental result of a 2D-C/C composite enables one to estimate the crack-face fiber bridging stresses and their distribution profile.
Nondestructive magneto-optical imaging analysis of superconducting (Bi, Pb)2Sr2Ca2Cu3Ox composites
Authors: Turchinskaya M. , Kaiser D. L. , Shapiro A. J. , Riley G. N. , Christopherson C.
Published: March 2008

The superconducting filaments in (Bi, Pb)2Sr2Ca2Cu3Ox/Ag composite tapes have been imaged directly through the outer silver sheath of an unpolished tape by means of a magneto-optical imaging technique. The images reveal the morphology and alignment of the uppermost layer of filaments located as much as 112 μm below the unpolished tape surface, the depths of these filaments, and the homogeneity of the magnetic flux distribution within these filaments. These results demonstrate that the magneto-optical technique is a valuable nondestructive tool for analyzing (Bi, Pb)2Sr2Ca2Cu3Ox composite tapes.
Fabrication of silicon carbide nanoceramics
Authors: Mitomo Mamoru , Kim Young-Wook , Hirotsuru Hideki
Published: March 2008

Ultrafine silicon carbide powder with an average particle size of 90 nm was densified by hot-processing with the addition of Al2O3, Y2O3, and CaO at 1750 °C. Silicon carbide nanoceramics with an average grain size of 110 nm were prepared by liquid phase sintering at low temperature. The materials showed superplastic deformation at a strain rate of 5.0 × 10-4/s at 1700 °C, which is the lowest temperature published. The microstructure and deformation behavior of materials from a submicrometer powder were also investigated as a reference.
Transmission electron study of heteroepitaxial growth in the BiSrCaCuO system
Authors: Chaiken A. , Wall M. A. , Howell R. H. , Bozovic I. , Eckstein J. N. , Virshup G. F.
Published: March 2008

Films of Bi2Sr2CaCu2O8 and Bi2Sr2CuO6 have been grown using Atomic-Layer-by-Layer Molecular Beam Epitaxy (ALL-MBE) on lattice-matched substrates. These materials have been combined with layers of closely related metastable compounds like Bi2Sr2Ca7Cu8O20 (2278) and rare-earth-doped compounds like Bi2Sr2DyxCa1–xCu2O8 (Dy: 2212) to form heterostructures with unique superconducting properties, including superconductor/insulator multilayers and tunnel junctions. Transmission electron microscopy (TEM) has been used to study the morphology and microstructure of these heterostructures. These TEM studies shed light on the physical properties of the films, and give insight into the growth mode of highly anisotropic solids like Bi2Sr2CaCu2O8.
Thermal expansion behavior of bulk Bi-based (2223) superconductors
Authors: Bellosi A. , Celotti G. , Landi E. , Tampieri A.
Published: March 2008

The thermal expansion coefficient of Bi-based 2223 and 2212 ceramics has been measured using dilatometric apparatus. Different typologies of bulk superconducting samples have been tested, in particular (2223) phase fully dense hot-pressed samples both parallel and perpendicular to the direction of applied pressure, pressureless sintered samples, and finally hot-pressed (2212) phase specimen, in order to gather information on the contribution of secondary phase to thermal expansion behavior. From the observed α (thermal expansion coefficient) values, accounting for the sample orientation degree, it was possible to distinguish the contributions along the basic crystallographic directions and to determine the following for (2223) phase: αa = 12.2 × 10-6 °C-1, and αc = 20.8 × 10-6 °C-1 for temperatures 200–600 °C. Theoretical α values were then calculated for the different samples and successfully compared with the measured ones. As regards (2212) phase, thermal expansion coefficient was evaluated for the oriented sample, and a value for random one extrapolated; the results are very similar to that of (2223), but lower with respect to previously reported data in air atmosphere.
Can carbon-implanted silicon be applied as wide-bandgap emitter?
Authors: Oostra D. J. , Politiek J. , Bulle-Lieuwma C. W. T. , Vandenhoudt D. E. W. , Zalm P. C.
Published: March 2008

We examine the formation of Si1-xCx (x = 0.04–0.2) by means of CFy (y = 0,1,3) implantation in p-type Si, for application as a wide-bandgap emitter in a Si heterojunc-tion bipolar transistor. Upon implantation with 2.5 × 1016 CF+/cm2 at 45 keV, and subsequently with 2.5 × 1016 C+/cm2 at 30 keV, an amorphous top layer is formed. Annealing at temperatures up to 900 °C leads to a layer consisting of nanocrystalline material. High resolution transmission electron microscopy and secondary ion mass spectrometry show that a well-defined nanocrystalline/crystalline interface is created at an anneal temperature of 550 °C. At higher temperatures lattice defects start to develop. Preliminary attempts to dope the material via phosphorus or arsenic implantation indicate that temperatures of at least 900 °C are required to activate a fraction of the implanted dopants. This, however, adversely affects the adlayer/substrate interface.
A comparison of the sintering characteristics of ball-milled and attritor-milled W–Ni–Fe heavy alloy
Authors: Öveçoğlu M. L. , Özkal B. , Suryanarayana C.
Published: March 2008

Blended elemental W–7 wt.%Ni–3 wt. %Fe powders were mechanically alloyed in a planetary ball mill and a heavy duty attritor. The structural and morphological characteristics of the as-milled powders were characterized by x-ray diffraction and electron microscopy techniques. A ternary solid solution of Fe and Ni in W formed in both the cases; the amount of Ni and Fe dissolved is higher in the attritor-milled powder than in the ball-milled powder. Morphologically, the W-rich particles in the attritor-milled powders were spheroidal, smaller in size, and showed a narrower size distribution than in the ball-milled condition. These differences led to increased density in the attritor-milled powder compact and significant differences in chemical composition of the matrix region and W-rich grains. Transmission electron microscopy investigations of the matrix region in the compacts revealed the presence of Fe2W precipitates uniformly distributed in an Ni(Fe, W) matrix.
High-resolution electron microscopy of Al–Ni–Fe decagonal quasicrystal
Authors: Hiraga Kenji , Yubuta Kunio , Park Ki-Tae
Published: March 2008

The structure of a stable decagonal quasicrystal with 0.4 nm periodicity, formed in a conventionally solidified alloy with composition Al71.6Ni23.7Fe4.7, was investigated by high-resolution electron microscopy. It was found that this decagonal phase is one of the best-ordered quasicrystals, without any detectable linear phason strain and with only weak random phason strain. The structure is interpreted as an aperiodic tiling of decagonal atom columns with a diameter of about 1.2 nm. The atomic arrangements in special local regions are discussed on the basis of computer simulations.
Synthesis, morphology, and formation mechanism of mullite particles produced by ultrasonic spray pyrolysis
Authors: Janaćković Dj. , Jokanović V. , Kostić-Gvozdenović Lj. , Živković Lj. , Uskoković D.
Published: March 2008

Submicrometer spherical particles of mullite powder were synthesized by ultrasonic spray pyrolysis of emulsion and solutions, using tetra-ethyl-orthosilicate (TEOS) or silicic-acid and Al(NO3)3 · 9H2O as initial compounds. Crystallization of mullite phase was determined by differential thermal (DT), thermogravimetric (TG), infrared (IR), and x-ray analyses. The synthesis of mullite from TEOS emulsion occurs by crystallization of γ–Al2O3 (or Al, Si-spinel) from the amorphous phase and its subsequent reaction with amorphous SiO2, as well as by crystallization of pseudotetragonal mullite below 1000 °C and its subsequent phase transformation into orthorhombic mullite. In the powders produced from silicic acid solutions, synthesis of mullite occurs only by crystallization of γ–Al2O3 between 900 and 1000 °C and its further reaction with amorphous SiO2 between 1100 and 1200 °C. Particle formation mechanism depended directly on the initial emulsion or solution preparation, i.e., on the phase separation in the emulsion and on the silicic-acid crosslinking conditions.
Origin of dislocation loops in α-silicon nitride
Authors: Wang Chong-Min , Pan Xiao-Qing , Rühle Manfred
Published: March 2008

Dislocation loops and stacking fault formation mechanism in α–Si3N4have been studied by annealing α–Si3N4powders at 1500 °C and 1750 °C. Thermally activated vacancies and the structural vacancies generated with replacement of nitrogen by oxygen have been tentatively suggested to be two sources of vacancies in α–Si3N4. From the point of view of mechanism, incorporation of these vacancies is believed to lie at the building-up stage of α–Si3N4lattice. As a result of the vacancies agglomeration, dislocation loops and stacking faults seem to be a distinctively structural feature of α–Si3N4fabricated by different routes [chemical vapor deposition (CVD), silicon nitridation, silica carbothermal reduction, and imide decomposition]. A general discussion has been extended to the historical controversy over the oxygen and vacancy stabilization of α–Si3N4lattice arisen from the fact that the observed unit cell dimension of α–Si3N4has a wide variation, and also to some related phenomena in processing of Si3N4.
A new insight on alkaline hydrolysis of calcium aluminate cement concrete: Part I. Fundamentals
Authors: Goñi S. , Andrade C. , Sagrera J. L. , Hernández M. S. , Alonso C.
Published: March 2008

In this work a hypothesis to explain the alkaline hydrolysis degradation process of calcium aluminate cement concrete (CACC) is presented. The hypothesis is based on x-ray diffraction (XRD) data of some samples taken from real Spanish CACC structures. The identification from XRD data of a hydrated alkaline aluminate could serve as a guide to differentiate both processes of normal carbonation and alkaline hydrolysis.
Examination of the material properties and performance of thin-diamond film cutting tool inserts produced by arc-jet and hot filament chemical vapor deposition
Authors: Olson James M. , Dawes Michael J.
Published: March 2008

Thin diamond film coated WC-Co cutting tool inserts were produced using arc-jet and hot-filament chemical vapor deposition. The diamond films were characterized using SEM, XRD, and Raman spectroscopy to examine crystal structure, fracture mode, thickness, crystalline orientation, diamond quality, and residual stress. The performance of the tools was evaluated by comparing the wear resistance of the materials to brazed polycrystalline diamond-tipped cutting tool inserts (PCD) while machining A390 aluminum (18% silicon). Results from the experiments carried out in this study suggest that the wear resistance of the thin diamond films is primarily related to the grain boundary strength, crystal orientation, and the density of microdefects in the diamond film.
Ion beam amorphization of muscovite mica
Authors: Templier C. , Desage F. , Desoyer J. C. , Hishmeh G. , Cartz L. , Donnelly S. E. , Vishnyakov V. , Birtcher R. C.
Published: March 2008

The microstructure of a muscovite mica exposed to a rare gas ion beam has been studied by transmission electron microscopy. The investigation of damage without implantation was carried out using argon and helium ions of sufficient energy to traverse the 100–150 nm mica specimens. For 340 keV Ar++ irradiation, amorphization of mica occurred at a fluence as low as 3.5 × 1014 ions · cm−2, which corresponds to 0.29 dpa. Muscovite can be amorphized using 80 keV helium ions, but this requires a much higher fluence and damage production of 4.6 × 10−6 ions · cm−2 and 0.60 dpa, respectively. Since helium irradiation results principally in ionization energy loss, it indicates that amorphization of muscovite results mainly from nuclear interactions. Complete amorphization of muscovite mica is found to take place for all ions at approximately the same amount of nuclear energy transfer to energetic primary knock-on atoms, assuming a recoil energy greater than 500 eV. This suggests that amorphization occurs directly in dense displacement cascades. A significant amount of helium, 100 ppm, can be implanted into muscovite mica without destroying the crystal structure.
The formation and stability of 80 K phase in the BiPbSrCaCuO system
Authors: Zhu W. , Kuo C.K. , Nicholson P.S.
Published: March 2008

The formation of Pb-doped 80 K phase from nitrate precursors was studied in the Bi1.84Pb0.34Sr1.91Ca2.00Cu3.04O10.05 system. Sr(Pb, Bi)O3, Ca5Bi14O26, CuO, and CaO were found to be the intermediate compounds reacting to produce 80 K phase between 600 and 820 °C. Synthesis was complete at 800 °C for 24 h. 110 K phase formed at the expense of 80 K phase at temperatures above 820 °C. Partial melting was detected and 80 K and 110 K phases were unstable in the presence of liquid phase. They decomposed to 2201, Cu2O, and (Ca, Sr, Cu) complex oxides. The melting and decomposition were accompanied by oxygen loss.
Structural relation between a 2D fivefold quasicrystal and crystalline approximants in an Al–Co–Ni–Tb alloy
Authors: Li X. Z. , Hiraga K.
Published: March 2008

A two-dimensional quasicrystal with fivefold symmetry and two large-unit-cell crystalline approximants in an Al–Co–Ni–Tb alloy, which were observed in previous studies, are suggested to be composed of the same kind of atom cluster. Some characteristics of the atom cluster can be deduced from a high-resolution electron microscopy image of the Al–Co–Ni–Tb quasicrystal when the image is associated with a fivefold aperiodic tiling. By using the cut-and-projection method, a quasiperiodic tiling generated by an irrational projection is proposed as an ideal quasilattice of the Al–Co–Ni–Tb quasicrystal; in the meantime, periodic tilings generated by a rational projection present the lattices of the crystalline approximants.
The effect of Hf and Ti additions on microstructure and properties of Cr2Nb–Nb in situ composites
Authors: Bewlay B.P. , Jackson M. R.
Published: March 2008

The present paper describes the effect of Hf and Ti additions on the microstructures and mechanical properties of two-phase composites based on the Cr2Nb–Nb eutectic. The microstructures of directionally solidified in situ composites containing 50–70% by volume of the Laves phase Cr2Nb which was modified with Hf (7.5–9.2%) and Ti (16.5–26%) are described. Partitioning of Hf and Ti between the two phases is discussed using microprobe and EDS results. The tensile properties at 1100 and 1200 °C are described and compared with those of an analogous niobium silicide-based composite. The Cr2(Nb)–(Nb) composite tensile yield strengths at 1200 °C were increased over that of monolithic Cr2Nb to ∼130 MPa. However, at 1200 °C the yield strengths of the silicide-based composites were approximately twice those of the Cr2(Nb)–(Nb) composites.
Effect of BaSnO3 on the microwave dielectric properties of Ba2Ti9O20
Authors: Yoon Ki Hyun , Kim Jae Beom , Kim Woo Sup , Kim Eung Soo
Published: March 2008

The effect of BaSnO3 on the phase formation and the dielectric properties of Ba2Ti9O20 was investigated as a function of the amount of BaSnO3 in the temperature range of 20 °C to 80 °C at 7 GHz. In the reaction of 2BaCO3 + 9TiO2 → Ba2Ti9O20 + 2CO2↑, the batch with the addition of BaSnO3 enhanced the reactivity compared to the batch with the addition of SnO2. The enhancement of reactivity caused single phase Ba2Ti9O20 to form effectively with less amounts of BaSnO3. As the amount of BaSnO3 increased up to 0.03 mol, the unloaded Q increased due to an increase of the Ba2Ti9O20 phase; for further addition of BaSnO3 over 0.3 mol, the unloaded Q decreased due to the increase of rutile and BaTi4O9 phases. The dielectric constant increased with increasing BaSnO3. As single phase Ba2Ti9O20 was present in the specimen, the Q·ƒ0 value, the dielectric constant, and the TCF were approximately 37,900, 38.7, and 1.7 ppm/°C, respectively.
Electrical breakdown of the positive temperature coefficient of resistivity barium titanate ceramics
Authors: Kim Duk-Hee , Um Woo-Sik , Kim Ho-Gi
Published: March 2008

Positive temperature coefficient of resistivity barium titanate ceramic is a semiconductor at room temperature, so it is self-heated under certain applied voltage, and then changes into an insulator. The electrical breakdown has been investigated with the resistance-temperature characteristics of the three samples which have different compositions. The grain size effect on the breakdown voltage also is discussed. As the applied voltage increased, the electrical breakdown was initiated when the specimen interior was heated above the temperature corresponding to the maximum resistance on the resistance-temperature curves by joule heat.
Preparation of Al2O3/Mo nanocomposite powder via chemical route and spray drying
Authors: Lo Ming-Hung , Cheng Feng-Huei , Wei Wen-Cheng J.
Published: March 2008

A route to prepare nanometer-sized Mo particulates in Al2O3 was attempted by a combination of solution reactions in molecular scale and forcing precipitation by a spray-drying technique. MoO3 was first dissolved in ammonia water and then added in the slurry with high purity, submicrometer Al2O3 powder. Mixed suspension was spray-dried, and then the dried granules were reduced by hydrogen gas and further hot-pressing to a bulky composite at various temperatures. Dissolution of Mo oxide, adsorption reactions on the alumina surface, and surface potential of alumina particles in homogeneous ammonia suspension were studied. Characterization of the granules, including compactability, flowing properties, surface morphology, grain growth of Mo and Al2O3, and mixing homogeneity, were examined. Homogeneity of the spray-dried granules was determined by the calculation of mixing index and the observation of the microstructure of the sintered body. The existence of intergranular, intragranular, and nanosized Mo particulates within Al2O3 grains was observed by transmission electron microscopy (TEM). All the evidence revealed that homogeneous composites with nanometer-sized Mo had been successfully prepared by this attempt with the proposed chemical roue and following the spray-drying process.
Reply to the comments of O. Jørgensen et al.
Authors: Bagchi A. , Evans A.G.
Published: March 2008

Large scale yielding (LSY), in general, has a profound influence on the fracture toughness of metal/dielectric interfaces. For thin metal film/dielectric systems exhibiting “weak” bonding, small-scale yielding (SSY) prevails due to local plastic dissipation intrinsic to crack growth and the high yield strength of metal thin films. For systems involving low yield strength materials and strong interfaces, a more detailed LSY methodology needs to be developed.
Effect of Cleft Palate Repair on the Susceptibility to Contraction-Induced Injury of Single Permeabilized Muscle Fibers from Congenitally-Clefted Goat Palates
Authors: Rader Erik P. , Cederna Paul S. , McClellan William T. , Caterson Stephanie A. , Panter Kip E. , Yu Deborah , Buchman Steven R. , Larkin Lisa M. , Faulkner John A. , Weinzweig Jeffrey
Published: March 2008

Objective:

Despite cleft palate repair, velopharyngeal competence is not achieved in ∼15% of patients, often necessitating secondary surgical correction. Velopharyngeal competence postrepair may require the conversion of levator veli palatini muscle fibers from injury-susceptible type 2 fibers to injury-resistant type 1 fibers. As an initial step to determining the validity of this theory, we tested the hypothesis that, in most cases, repair induces the transformation to type 1 fibers, thus diminishing susceptibility to injury.

Interventions:

Single permeabilized levator veli palatini muscle fibers were obtained from normal palates and nonrepaired congenitally-clefted palates of young (2 months old) and adult (14 to 15 months old) goats and from repaired palates of adult goats (8 months old). Repair was done at 2 months of age using a modified von Langenbeck technique.

Main Outcome Measures:

Fiber type was determined by contractile properties and susceptibility to injury was assessed by force deficit, the decrease in maximum force following a lengthening contraction protocol expressed as a percentage of initial force.

Results:

For normal palates and cleft palates of young goats, the majority of the fibers were type 2 with force deficits of ∼40%. Following repair, 80% of the fibers were type 1 with force deficits of 20% ± 2%; these deficits were 45% of those for nonrepaired cleft palates of adult goats (p < .0001).

Conclusion:

The decrease in the percentage of type 2 fibers and susceptibility to injury may be important for the development of a functional levator veli palatini muscle postrepair.
Prevalence of Abnormalities in Dental Structure, Position, and Eruption Pattern in a Population of Unilateral and Bilateral Cleft Lip and Palate Patients
Authors: Tortora Chiara , Meazzini Maria C. , Garattini Giovanna , Brusati Roberto
Published: March 2008

Objective:

To evaluate the dental characteristics of patients subjected to a protocol that included early secondary gingivoalveoloplasty (ESGAP).

Design:

Panoramic radiographs of 87 patients with unilateral cleft lip and palate (UCLP) and 29 with bilateral cleft lip and palate (BCLP) were evaluated. Missing and supernumerary teeth were also quantified on the cleft and noncleft side and in the maxilla and mandible. Crown and root malformations and tooth rotations were quantified. A subsample in permanent dentition was extrapolated to analyze canine eruption patterns.

Results:

A total of 48.8% of the UCLP patients presented with missing permanent lateral incisors in the cleft area and 6.1% contralaterally. A total of 4.9% presented with missing second maxillary premolars on the cleft site and 1.2% contralaterally. A total of 7.3% presented with supernumerary lateral incisors, and 45% of the BCLP cleft sites presented with missing lateral incisors, while 25% of the cleft sites presented second maxillary premolars agenesis. Five percent of the cleft sites presented with supernumerary lateral incisors. Evaluation of the subsample in permanent dentition showed that 15.5% had a canine retention and 4.4% of the canines had to be surgically exposed. A significant association was observed between canine inclination and retention but not with absence of the lateral incisor.

Conclusions:

The frequency of dental anomalies in this sample was similar to other cleft populations. As surgical trauma has been suggested to damage forming teeth, the results of this study indicated that ESGAP has no detrimental influence on subsequent dental development.
Multiple Testing for SNP-SNP Interactions
Authors: Boulesteix Anne-Laure , Strobl Carolin , Weidinger Stefan , Wichmann H.-Erich , Wagenpfeil Stefan
Published: March 2008

Most genetic diseases are complex, i.e. associated to combinations of SNPs rather than individual SNPs. In the last few years, this topic has often been addressed in terms of SNP-SNP interaction patterns given as expressions linked by logical operators. Methods for multiple testing in high-dimensional settings can be applied when many SNPs are considered simultaneously. However, another less well-known multiple testing problem arises within a fixed subset of SNPs when the logic expression is chosen optimally. In this article, we propose a general asymptotic approach for deriving the distribution of the maximally selected chi-square statistic in various situations. We show how this result can be used for testing logic expressions - in particular SNP-SNP interaction patterns - while controlling for multiple comparisons. Simulations show that our method provides multiple testing adjustments when the logic expression is chosen such as to maximize the statistic. Its benefit is demonstrated through an application to a real dataset from a large population-based study considering allergy and asthma in KORA. An implementation of our method is available from the Comprehensive R Archive Network (CRAN) as R package 'SNPmaxsel'.
Why Liberals Should Enthusiastically Support Social Security Personal Accounts
Authors: Magin Konstantin
Published: March 2008

A new, Black-Scholes measure of pension risk suggests that private accounts are a win-win, according to Konstantin Magin.
New Directions in Copyright Law and Economics
Authors: Ramello Giovanni B. , Silva Francesco
Published: March 2008

The making of the information/knowledge society has driven a flourishing body of literature on the law and economics of copyright. This paper introduces the articles collected in the following symposium, produced by a number of scholars participating in the lively worldwide community devoted to the study of the economic role of copyright law in light of current technological change. The aim of these writings as a whole is to broaden the analytical perspective and stimulate further research, thanks to a wide selection of topics related to behavioral analysis, competition policy, insurance, cultural economics and other fields.
Rapid Determination of Intact Sardine Fat by NIRS Using Surface Interactance Fibre Probe
Authors: Uddin Musleh , Turza Sandor , Okazaki Emiko
Published: March 2008

A near-infrared spectrometer equipped with surface interactance optical fiber probe (400-1100 nm) was used to determine the fat content in intact sardine Sardinops melanostictus which is considered one of the important fish species of world aquaculture as well as human food source. The fat contents were 2.6425.52 % and fish weight ranges were between 45.23g and 133.76g. Partial least square regression was used to develop predictive equations for fat where two models (with and without multiplicative scatter correction known as MSC) showed relatively good performances with regression coefficients higher than 0.9 and errors below 1% on a fresh weight basis. Results showed that NIR interactance was a suitable non-destructive screening method for fat content in intact small pelagic fish like sardine.