bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of dendrite arm spacing on the thermal conductivity of an aluminum-silicon casting alloy
Authors: Vázquez-López C. , Calderón A. , Rodríguez M. E. , Velasco E. , Cano S. , Colás R. , Valtierra S.
Published: March 2008

The photoacoustic technique and the thermal relaxation method were used to determine the thermal conductivity of some representative samples obtained from an aluminumsilicon casting alloy A319. This material was solidified with an imposed unidirectional thermal gradient to obtain samples with different microstructures characterized by the secondary dendrite arm spacing, which increases as the solidification rate decreases. It was found that the thermal conductivity of the alloy decreases with an increase in the secondary dendrite arm spacing and a decrease in the integral dendrite perimeter.
Pyrocarbon anisotropy as measured by electron diffraction and polarized light
Authors: Bourrat Xavier , Trouvat Béatrice , Limousin Guillaume , Vignoles Gérard , Doux François
Published: March 2008

This work deals with the measurement of pyrocarbon anisotropy on very thin fiber coatings used to control the interfacial behavior in carbon/carbon composites. Differentiation of the various pyrocarbons was performed through computerized image analysis of the electron diffraction patterns by measuring the azimuth opening of the carbon 002 diffraction arcs. This orientation angle decreases when the texture switches from rough to smooth laminar. The relationship with the polarized light measurement technique at a lower resolution is discussed.
Slow crack-growth behavior of alumina ceramics
Authors: Ebrahimi M. E. , Chevalier J. , Fantozzi G.
Published: March 2008

The fracture behavior of high-purity alumina ceramics with grain sizes ranging from 2 to 13 μm is studied by means of the double torsion method. Crack-propagation tests conducted in air, water, and silicon oil, for crack velocities from 10−7 to 10−2 m/s, show that slow crack growth is due to stress corrosion by water molecules. An increase of the grain size leads to enhanced crack resistance, which is indicated by a shift of the V–KI (crack velocity versus applied stress intensity factor) plot toward high values of KI. Moreover, the slope of the curve is apparently higher for coarse grain alumina. However, if the R-curve effect is substracted from the experimental results, a unique V–KItip (crack velocity versus stress intensity factor at the crack tip) law is obtained for all alumina ceramics, independently of the grain size. This means that the crack-growth mechanism (stress corrosion by water molecules) is the same and that the apparent change of the V–KI law with grain size is a direct effect of crack bridging.
Water-based Si3N4 suspensions: Part II. Effect of wet mixing/milling processes on the addition of the sintering aids
Authors: Galassi C. , Bertoni F. , Ardizzone S. , Bianchi C. L.
Published: March 2008

Three mixing processes were used to introduce lanthanum oxide and yttrium oxide in silicon nitride suspensions. X-ray photoelectron spectroscopy (XPS) analysis was used to identify the surface composition and investigate the surface coverage by the added oxides. XPS results evidenced the protective effect against hydrolysis and oxidation of the coated layer. Electroacoustic measurements showed that the milling/mixing process and solids loading contents had a great influence on the isoelectric point (IEP) and on the dispersing degree for suspensions with sintering aids. With the change of solids load content and mixing energy, the IEP of mixed powders suspensions reflected a surface behavior dominated by the additives oxides. The attrition mixing and the ultrasonication resulted in the more efficient processing routes to distribute the sintering aids on the starting Si3N4 powders, especially at high solids volume fraction.
Calculation of metastable immiscibility region in the Al2O3–SiO2system using molecular dynamics simulation
Authors: Takei Takahiro , Kameshima Yoshikazu , Yasumori Atsuo , Okada Kiyoshi
Published: March 2008

The metastable immiscibility region in the Al2O3–SiO2system was calculated by conventional thermodynamic equations using thermodynamic parameters obtained from molecular dynamics simulation. The calculated miscibility gap has a consolute temperature of around 1500 °C at the critical composition of about 20 mol% Al2O3and spreads more widely towards the Al2O3-rich composition side than the SiO2-rich side. The calculated miscibility gap in this study showed a fair agreement with that reported by Banet al.[T. Ban, S. Hayashi, A. Yasumori, and K. Okada, J. Mater. Res.11,1421 (1996)] calculated by a regular solution model, but the present calculated region is somewhat narrower in the Al2O3-rich composition side than that reported by Banet al.
Structural and physical properties of Fe2O3-doped lead vanadate glass
Authors: Mandal S. , Hazra S.
Published: March 2008

The role of Fe2O3in the structural and physical properties of ternary lead vanadium iron glass system has been studied in comparison with the binary lead vanadate glasses. X-ray diffraction, scanning electron microscopy, and differential thermal analysis show that homogeneous glasses of composition 10Fe2O3 · xV2O5 · (90 − x)PbO can be obtained for x = 50 to 80 mol%. Observation from the infrared spectroscopy shows that the basic building blocks of these glasses are same as those of crystalline V2O5, while differential thermal analysis and electrical conduction of these glasses suggest that there is a strong role of iron, both in the glass network and in the conduction mechanism for the glasses containing a low percentage of vanadium.
Effect of crystallization on microwave dielectric properties of stoichiometric cordierite glasses containing B2O3 and P2O5
Authors: Wu Jenn-Ming , Huang Hong-Lin
Published: March 2008

The effect of crystallization on microwave dielectric properties of cordierite glasses containing B2O3 and P2O5 additions was investigated. Two glasses containing 5 wt% B2O3/5 wt% P2O5 and 7.5 wt% B2O3/7.5 wt% P2O5 were studied. Both glasses were sintered to nearly full density at temperatures as low as 860 °C. The frequency constant and quality factor of α cordierite are, respectively, about five times and two times larger than those of glassy phase and μ cordierite. The temperature coefficients of resonant frequency are estimated to be about −13, −55, and −15 ppm/°C for glassy phase, μ cordierite, and α cordierite, respectively. As a result of the microwave dielectric properties of the individual phase, cordierite glasses containing α cordierite possess the best microwave properties.
Martensitic transformation behavior of FeMnGe alloys
Authors: Lu Xing , Qin Zuoxiang , Zhang Yansheng , Ding Bingzhe , Hu Zhuangqi
Published: March 2008

The martensitic transformation behavior of FeMnGe alloy (0–6 wt% Ge) was investigated by resistivity and dilation methods. Ge depresses the martensitic transformation of FeMn alloy. The effect of Ge on starting temperature of martensitic transformation (Ms) temperature of FeMn alloy is −12 K/wt% Ge. Comparing Ge (4s24p2) with Si (3s23p2) and Al (3S23P1), which have similar outer shells of electrons, we found that their effects on the Ms of FeMn alloy are completely different. The result suggests that the outer shell of electron is not the main factor governing the Ms temperature of FeMn alloy, although it is essential in the alloy's antiferromagnetic transition.
Microstructural evolution and mechanical properties of Si3N4–SiC (nanoparticle)–Si3N4 (whisker) composites
Authors: Koh Young-Hag , Kim Hae-Won , Kim Hyoun-Ee
Published: March 2008

The effects of SiC-nanoparticle and Si3N4-whisker additions on the microstructural evolution and mechanical properties of Si3N4 were investigated. The addition of SiC nanoparticles suppressed Si3N4 grain growth, leading to an improvement in the flexural strength. On the other hand, Si3N4 whiskers in the specimen promoted the formation of large elongated grains, which were found to be beneficial to the fracture toughness of the material. When both SiC nanoparticles and Si3N4 whiskers were added concurrently, large grains were formed in fine matrix grains. The microstructure of Si3N4 was controlled by adjusting the relative concentrations of SiC nanoparticles and the Si3N4 whiskers added. These compositional and microstructural variations of the Si3N4 had significant influence on the mechanical properties, such as strength, fracture toughness, R-curve behavior, and high-temperature strength.
Diffraction studies of cubic phase stability in undoped zirconia thin films
Authors: Moulzolf S. C. , Lad R. J.
Published: March 2008

Pure stoichiometric ZrO2 films were deposited on amorphous silica substrates by electron beam evaporation of Zr in the presence of an electron cyclotron resonance oxygen plasma. Grain size, strain, and texture were analyzed by x-ray diffraction and reflection high-energy electron diffraction. Films grown at room temperature are polycrystalline and exist in the cubic phase. Growth at elevated temperatures produces coexisting cubic and monoclinic phases and shows a maximum critical grain size of ??~10 nm for stabilization of the cubic phase. Pole figure analysis indicates a preferred cubic [200] fiber axis for room-temperature growth and dual monoclinic {111} and in-plane textures for films grown at 400 °C. Postdeposition annealing experiments confirm the existence of a critical grain size and suggest mechanisms for grain growth.
Composite ceramics with a positive temperature coefficient of electrical resistivity effect
Authors: Lisjak Darja , Drofenik Miha , Kolar Drago
Published: March 2008

Composite ceramics with compositions within the ZnO–NiO–TiO2, ZnO–MgO, and ZnO–Ln2O3(Ln = Nd, Sm) systems were found to exhibit an anomalous positive temperature coefficient of electrical resistivity (PTCR) effect. The investigations revealed, that in all cases when the PTCR effect was identified, the composite ceramics were found to be composed of phases with different electrical resistivities and linear thermal expansion coefficients. Thermal mismatch between the phases in the composites leads to a disconnection of the grains of the low resistivity constituent phase on account of the high thermal expansion of the other high resistivity constituent phase, resulting in a PTCR effect.
Characteristics of ultraviolet-assisted pulsed-laser-deposited Y2O3 thin films
Authors: Craciun V. , Lambers E. S. , Bassim N. D. , Singh R. K. , Craciun D.
Published: March 2008

The properties of thin Y2O3 films grown using an in situ ultraviolet (UV)-assisted pulsed laser deposition (PLD) technique were studied. With respect to Y2O3 films grown by conventional PLD under similar conditions but without UV illumination, the UVPLD-grown films exhibited better structural and optical properties, especially for lower substrate temperatures, from 340 to 400 °C. These layers were highly crystalline and textured along the (111) direction, and their refractive index values were similar to those of reference Y2O3 layers. They also exhibited a better stoichiometry and contained less physisorbed oxygen than the conventional PLD-grown layers.
Cathodoluminescence depth-profiling studies of GaN/AlGaN quantum-well structures
Authors: Godlewski M. , Goldys E. M. , Phillips M. R. , Langer R. , Barski A.
Published: March 2008

In this paper we evaluate the in-depth homogeneity of GaN epilayers and the influence of electric field present in strained GaN/AlGaN heterostructures and quantum wells on the yellow and “edge” emission in GaN and AlGaN. Our depth-profiling cathodoluminescence measurements show an increased accumulation of defects at the interface. Inhomogeneities in the doping level are reflected by the enhancement of the yellow emission in the interface region. The piezoelectric effect is found to strongly reduce the emission from the strained AlGaN quantum-well barriers. We also show that Ga droplets, commonly found on surfaces of samples grown in Ga-rich conditions, screen the internal electric field in a structure and thus result in a local enhancement of the edge emission intensity.
A novel form of carbon nitrides: Well-aligned carbon nitride nanotubes and their characterization
Authors: Sung S. L. , Tsai S. H. , Liu X. W. , Shih H. C.
Published: March 2008

Well-aligned carbon nitride nanotubes were prepared with a porous alumina membrane as a template when using electron cyclotron resonance (ECR) plasma in a mixture of C2H2 and N2 as the precursor with an applied negative bias to the graphite sample holder. The hollow structure and good alignment of the nanotubes were verified by field-emission scanning electron microscopy. Carbon nitride nanotubes were transparent when viewed by transmission electron microscopy, which showed that the nanotubes were hollow with a diameter of about 250 nm and a length of about 50–80 μm. The amorphous nature of the nanotubes was confirmed by the absence of crystalline phases arising from selected-area diffraction patterns. Both Auger electron microscopy and x-ray photoelectron spectroscopy spectra indicated that these nanotubes are composed of nitrogen and carbon. The total N/C ratio is 0.72, which is considerably higher than other forms of carbon nitrides. No free-carbon phase was observed in the amorphous carbon nitride nanotubes. The absorption bands between 1250 and 1750 cm−1 in Fourier transform infrared spectroscopy provided direct evidence for nitrogen atoms, effectively incorporated within the amorphous carbon network. Such growth of well-aligned carbon nitride nanotubes can be controlled by tuning the ECR plasma conditions and the applied negative voltage to the alumina template.
High-temperature stability of epitaxial, non-isostructural Mo/NbN superlattices
Authors: Engström C. , Madan A. , Birch J. , Nastasi M. , Hultman L. , Barnett S. A.
Published: March 2008

The effect of 1000 °C vacuum annealing on the structure and hardness of epitaxial Mo/NbN superlattice thin films was studied. The intensity of superlattice satellite peaks, measured by x-ray diffraction, decreased during annealing while new peaks corresponding to a MoNbN ternary phase appeared. The results are consistent with the Mo–Nb–N phase diagram, which shows no mutual solubility between Mo, NbN, and MoNbN. Even after 3-h anneals and a loss of most of the superlattice peak intensity, the room-temperature hardness was the same as for as-deposited superlattices. The retained hardness suggests that a residual nanocomposite structure is retained even after the formation of the ternary structure.
Yttria-based nano-sized powders: A new class of fractal materials obtained by combustion synthesis
Authors: Fagherazzi Giuliano , Polizzi Stefano , Bettinelli Marco , Speghini Adolfo
Published: March 2008

Small-angle x-ray scattering (SAXS) technique has been used to investigate nano-sized powders of Y2O3, Y1.8Er0.2O3, and Y1.8Nd0.2O3, obtained by means of combustion synthesis. The results show that the powders have a mass-fractal behavior, with fractal dimension, Df, in the 1.7–1.8 range, and average particle sizes in the 20–30-nm range. These results are supported by transmission electron microscope observations. Moreover, from SAXS data, it has been possible to establish a narrow particle size polydispersity, as well as the presence of particle-diffuse or “fuzzy” interfaces. These results show, for the first time, the fractal behavior of materials prepared by combustion synthesis and are in agreement with a recently developed model. The nanostructural features are discussed within the framework of the peculiar optical properties of the doped luminescent materials.
Growth mechanism of YBa2Cu3O7–δthin films and precipitates on planar and vicinal SrTiO3substrates
Authors: Kim J. , Chrisey D. B. , Horwitz J. S. , Miller M. M. , Gilmore C. M.
Published: March 2008

Effects of the vicinal angle, film thickness, and temperature on the growth modes, microstructures, and electrical properties of YBa2Cu3O7–δon SrTiO3were studied. Island growth transition between the initial nucleation and the later coalescence stages was observed with film thickness on a planar SrTiO3, while no islands were observed at the later stage due to the step-flow mode. As the growth temperature increased,a-axis precipitates were transformed toc-axis precipitates (islands), while no islands formed on vicinal SrTiO3. The supercurrent critical temperature was strongly related to the substrate vicinal angle due to the step-flow mode.
Phase growth and microstructure modifications induced by annealing in highly textured superconducting Bi-2212 thin rods
Authors: Mora M. , Martínez E. , Díez J. C. , Angurel L. A. , Fuente G. F. de la
Published: March 2008

Bi-2212 cylindrical rods were obtained using a laser-induced directional solidification system. Although as-grown Bi-2212 samples are well textured, they do not exhibit superconducting behavior and, as a result, need further heat treatments. The modifications taking place during annealing were analyzed in the present work, in particular with respect to the evolution of the microstructure with the annealing time and the phase content. Diffusion processes in which the Bi-2212 phase grows along the thickness of the platelets take place during annealing. The presented results show that the physical properties of these samples improve during the initial approximately 60 h of annealing and that they remain constant thereafter.
Epitaxial growth of gadolinium oxide on roll-textured nickel using a solution growth technique
Authors: Morrell Jonathan S. , Xue Ziling B. , Specht Eliot D. , Goyal Amit , Martin Patrick M. , Lee Dominic F. , Feenstra R. , Verebelyi D. T. , Christen D. K. , Chirayil Thomas G. , Paranthaman Mariappan , Vallet Catherine E. , Beach David B.
Published: March 2008

Chemical solution epitaxy was used to deposit an epitaxial film of Gd2O3 on roll-textured nickel. A 2-methoxyethanol solution of gadolinium methoxyethoxide was used for spin-coating and dip-coating. Films were crystallized using a heat treatment at 1160 °C for 1 h in 4% H2/96% Ar. Single-layer films were approximately 600 Å in thickness, and thicker films could be produced using multiple coatings. θ/2θ x-ray diffractograms revealed only (0041) reflections, indicating a high degree of out-of-plane texture. A pole-figure about the Gd2O3 (222) reflection indicated a single in-plane epitaxy. Scanning electron microscopy showed that the films were smooth, continuous, and free of pin holes. Atomic force microscopy revealed an average surface roughness of 53 Å. Electron diffraction indicated that the misalignment of the majority of the grains in the plane was less than 10°. High-current (0.4 MA/cm2) Yba2Cu3O7–δ films were grown on roll-textured nickel substrates using Gd2O3 as the base layer in a three-layer buffer structure.
A solvothermal route to wurtzite ZnSe nanoparticles
Authors: Zhan J. H. , Yang X. G. , Zhang W. X. , Wang D. W. , Xie Y. , Qian Y. T.
Published: March 2008

Zinc powder reacts with equivalent elemental selenium in solvent ethylenediamine at 120 °C for 6 h to form a complex, which is converted to ZnSe nanoparticles by pyrolysis or protonization. X-ray diffraction results suggest that the as-formed products have wurtzite structure. Transmission electron microscopy observation show that particles with spherical and laminar morphology were produced by pyrolysis and protonization, respectively. The formation of ZnSe nanoparticles is also investigated by infrared and thermal analysis.
Contact damage in porcelain/Pd-alloy bilayers
Authors: Zhao Hong , Hu Xiaozhi , Bush Mark B. , Lawn Brian R.
Published: March 2008

An analysis is made of contact damage in brittle coatings on metal substrates, using a case study of a dental porcelain coating of thickness between 0.1 and 1 mm fused onto a Pd alloy base, with spherical indenter of radii 2.38 and 3.98 mm. At large coating thicknesses (>300 μm), the first damage takes the form of surface-initiated transverse cone cracks outside the contact. At small coating thicknesses (<300 μm), the first damage occurs as yield in the substrate, with attendant formation of subsurface transverse median cracks in the coating. At high loads and thin coatings, both forms of transverse cracking occur, along with subsequent delamination of the ceramic/metal interface, signalling impending failure. Conditions for avoiding such transverse cracking are considered in terms of minimum coating thicknesses and maximum sustainable contact loads. General implications concerning the design of brittle coating systems for optimum damage resistance are considered, with special reference to dental crowns.
Preparation of nanocomposites containing iron and nickel–zinc ferrite
Authors: Pal M. , Das D. , Chintalapudi S. N. , Chakravorty D.
Published: March 2008

Composites consisting of nanometer-sized nickel–zinc ferrite and α-iron were prepared by subjecting micrometer-sized ferrite particles to a reduction treatment in the presence of α–Fe2O3. The materials were characterized by x-ray diffraction, electron microscopy, Mossbauer spectroscopy, and magnetization measurements. A wide range of saturation magnetization and coercivity can be obtained by changing the reduction schedule. The reduction process appears to break down the particle size of the precursor powder of nickel–zinc ferrite.
Uniaxial compression experiments on lead zirconate titanate 95/5-2Nb ceramic: Evidence for an orientation-dependent, “maximum compressive stress” criterion for onset of the ferroelectric to antiferroelectric polymorphic transformation
Authors: Zeuch D. H. , Montgomery S. T. , Holcomb D. J.
Published: March 2008

Recently we showed that, under nonhydrostatic loading, the FR1 →AO polymorphic transformation of unpoled lead zirconate titanate 95/5-2Nb (PNZT) ceramic began when the maximum compressive stress equaled the hydrostatic pressure at which the transformation otherwise occurred. More recently we showed that this criterion seemed not to apply to poled ceramic. However, unpoled ceramic is isotropic whereas poled ceramic is not. If we further assume that the transformation depends on both the stress magnitude and its orientation relative to PNZT's structure, these disparate results can be resolved. This modified hypothesis makes two predictions for transformation of unpoled ceramic under uniaxial compression: (i) it will begin when the compressive stress equals the hydrostatic pressure for transformation, and (ii) steadily increasing stress will be required to drive it to completion. Here we present experimental results that confirm these predictions. We then revisit our earlier results for poled and unpoled PNZT. The new hypothesis quantifies the observed effect of shear stress on the mean stress for onset of the transformation of unpoled ceramic and explains previously reported kinetic effects.
Effect of SiO2 and Y2O3 additives on the anisotropic grain growth of dense mullite
Authors: Huang T. , Rahaman M. N. , Mah T-I , Parthasarathay T. A.
Published: March 2008

Mullite powder with a nearly stoichiometric composition was doped with 1.5–5 wt% SiO2 or 0.5–1.0 wt% Y2O3 and hot pressed at 1525–1550 °C to produce almost fully dense materials. The effect of the additives on the grain growth of the dense systems was investigated during subsequent annealing at temperatures above that of the eutectic (∼1590 °C) for the SiO2–Al2O3 system. The average length and width of the grains were measured by image analysis of polished and etched sections. At 1750 °C, anisotropic grain growth was relatively rapid, leading to the formation of rodlike grains. Compared to the undoped mullite, the addition of SiO2 and Y2O3 produced a small reduction in the grain growth kinetics. Transmission electron microscopy revealed that the glassy second phase was concentrated at the three-grain junctions or distributed inhomogeneously at the grain boundaries. For the materials annealed at 1750 °C, the indentation fracture toughness at room temperature increased from 2.0 to 2.5 MPa m1/2 for the undoped mullite to values as high as 4.0–4.5 MPa m1/2 for the doped mullite. The implications of the data for enhancing the fracture toughness of mullite by the in situ development of a microstructure of elongated grains are considered.
Residual stresses in polycrystalline Cu/Cr multilayered thin films
Authors: Misra A. , Kung H. , Mitchell T. E. , Nastasi M.
Published: March 2008

Residual stresses in sputter-deposited Cu/Cr multilayers and Cu and Cr single-layered polycrystalline thin films were evaluated by the substrate curvature method. The stresses in the multilayers were found to be tensile and to increase in magnitude with increasing layer thickness (h) to a peak value of ∼1 GPa for h = 50 nm. For h > 50 nm, the residual stress decreased with increasing h but remained tensile. The same trends were observed in single-layered Cu and Cr thin films, except that the maximum stress in Cu films is 1 order of magnitude lower than that in Cr. Transmission electron microscopy was used to study the microstructural evolution as a function of layer thickness. The evolution of tensile growth stresses in Cr films is explained by island coalescence and subsequent growth with increasing thickness. Estimates of the Cr film yield strength indicated that, for h ≥ 50 nm, the residual stress may be limited by the yield strength. Substrate curvature measurements on bilayer films of different thicknesses were used to demonstrate that a non-negligible contribution to the total stress in the multilayers arises from the interface stress.
Nanoscale Mechanical Properties of Polymer Composites: Changes in Elastic Modulus and Measurement of Ion Penetration Depth Due to α-radiation
Authors: Chien Allen T. , Felter Tom , LeMay James D. , Balooch Mehdi
Published: March 2008

The local mechanical properties of silica-reinforced silicone composites were investigated using a modified atomic force microscopy technique. Elastic modulus measurements (1.5 ± 0.1 MPa) are consistent with bulk measurements (1.9 MPa), and changes in the modulus at the surface of the composite samples (E = 1.5 to 3.5 MPa) were observed as a result of α-irradiation (dose = 1.7 × 1010 to 2.0 × 1012 α/cm2). The sensitivity of the technique was demonstrated by a detectable change in modulus at even the small dose of 1.7 × 1010 α/cm2. The penetration depth of the α-particles into the material, estimated to be 22 ± 2 μm from the sample edge, was determined by cross-section depth profiling; and modeling of the ion penetration depth using transport of ions in matter codes (24.4 ± 0.4 μm) closely matched experimental observations.
Microwave-assisted Al-substituted Tobermorite Synthesis
Authors: Miyake Michihiro , Niiya Shigeto , Matsuda Motohide
Published: March 2008

The effect of microwave heating on the hydrothermal synthesis of Al-substituted tobermorite and the removal characteristics of resulting materials were examined and compared with the effect of conventional heating. The microwave heating reduced the crystallization time of Al-substituted tobermorite—i.e., Al-substituted tobermorite was synthesized within 80 min at around 140 °C—and produced smaller crystallites than the conventional heating. The minute crystallites were found to promote the removal characteristics for Cs+ ions in short reaction time.
Nanophase Fe Alloys Consolidated to Full Density from Mechanically Milled Powders
Authors: He L. , Allard L. F. , Breder K. , Ma E.
Published: March 2008

Nanophase elemental Fe powders prepared by mechanical milling were sinter forged to full density with an average grain size in the nanophase range (below 100 nm). If Cu additions are introduced during milling to form supersaturated solid solutions (Fe85Cu15 and Fe60Cu40), grain sizes can be easily controlled to below 50 nm after consolidation. For Fe–Cu, it was observed that atomic level alloying between the two elements during milling was very helpful for obtaining a homogeneous microstructure and nanocrystalline grain/domain sizes in the consolidated product. The advantages of using sinter forging (upset die forging), as well as the role of the Cu addition, in the retention of nanocrystalline grain sizes are discussed. The consolidated Fe alloys exhibit very high strength under compression, further demonstrating that low populations of flaws and nanophase grain structures were attained in the consolidated products.
Aligned Diamond Nanowhiskers
Authors: Baik Eun-Song , Baik Young-Joon , Jeon Dongryul
Published: March 2008

We investigated the formation of nanowhiskers by means of air plasma dry etching using diamond films of two different kinds: as-grown diamond films and films with molybdenum (Mo) deposits. As for the as-grown diamond films, nanowhiskers were found to form preferentially at grain boundaries of diamond crystals. Auger depth profile analysis of the etched films revealed a progressive enrichment by Mo toward the whisker tip, resulting from accidental sputtering of Mo substrate holder. With dry etching of diamond films with preformed Mo deposits, well-aligned whiskers 100 nm in diameter were found to form uniformly over the entire film surface with a population density of 30/μm2. From these findings, it follows that Mo deposits serve as micromasks for the formation of the nanowhiskers. It was also confirmed that these whiskers showed excellent field-emission behavior.
Nanocrystalline Tungsten Oxide Thin Film: Preparation, Microstructure, and Photochromic Behavior
Authors: Sun Mu , Xu Ning , Cao Y. W. , Yao J. N. , Wang E. G.
Published: March 2008

A nanocrystalline tungsten oxide photochromic thin film was prepared by colloid chemistry method. The microstructure, phase transition involved in the solution process, photochromic behavior, and mechanism of the film were investigated by means of transmission electron microscope, x-ray diffraction, ultraviolet-visible absorption spectra, and x-ray photoelectron spectra. It was found that the particle size and crystallinity of the thin film could be easily controlled by adjusting the concentration of oxalic acid in the colloid solution of tungsten oxide hydrate. With the increase of the oxalic acid concentration, the size of nanoparticles in the film decreased sharply, and meanwhile, a blue shift of the absorption peaks caused by the quantum size effect was observed accordingly. With the increase of the pH in the solution, tungsten oxide hydrate was gradually transformed into an oxided 12-tungstate with Keggin structure, which led to the change of photochromic property of the films. The photochromism of the film is believed to be due to the electron transfer between the different valence states of tungsten ions located in adjacent sites.
Electrical Conductivity of Discontinuous Filament–reinforced Unidirectional Composites
Authors: Ting Jyh-Ming , Chen Kuo-Wei
Published: March 2008

The electrical conductivity of discontinuous filament–reinforced unidirectional composites was investigated. The discontinuous reinforcement used was copper filament, and the matrix materials included solder and epoxy. It was found that the composite conductivity increases with filament length and eventually becomes a constant. Such behavior is described by introducing an interface impedance and the principle of rule of mixture. It was found both experimentally and theoretically that there exists a critical filament length that must be exceeded so the composites will exhibit conductivity as composites having continuous reinforcing filaments.
Preparation and Nonstoichiometric Property of wide Compositional Fe(III)-doped TiO2 (anatase)
Authors: Uekawa N. , Kurashima Y. , Kakegawa K. , Sasaki Y.
Published: March 2008

Fe(III)-doped TiO2 (anatase) was prepared by the oxidation of FexTiS2. Two calcination methods were used to oxidize FexTiS2. In the first, sulfide was calcined in air at a given temperature for 2 h. In the second method, the sulfide was heated in air at a finite heating rate (2.5 K/min) and then held at a constant temperature for 2 h. Fe(III) ions completely dissolved into TiO2 (anatase), forming Fe(III)-doped TiO2 (anatase), in the composition range of 0 ⩽ Fe/Ti ⩽ 0.3 (mole ratio). The properties of the obtained oxide depended on the oxidation method of FexTiS2. The electronic property and the valence stage of the Fe(III)-doped TiO2 (anatase) were examined. The activation energy of electronic conduction decreased with an increase of the doped amount of Fe(III) ions. The x-ray photoelectron spectroscopy result showed that the electron density on the Ti ion in the Fe(III)-doped TiO2 (anatase) was decreased by the Fe(III) doping.
Densification of Al2O3 Powder Using Spark Plasma Sintering
Authors: Wang S. W. , Chen L. D. , Hirai T.
Published: March 2008

Al2O3 powders with four different particle sizes were densified using a spark plasma sintering (SPS) apparatus under three different sintering conditions: holding time, heating rate, and mechanical pressure. The Al2O3 powder compact sintered at a higher heating rate produced a sample with a higher density and a fine-grained microstructure, while abnormal grain growth and a lower density resulted when a lower heating rate was applied, though the sintering temperature and holding time were the same in both cases. This revealed that rapid sintering by SPS was effective for promoting the densification of the powder. However, the powder with a coarse particle size was hard to sinter at a higher heating rate. Microstructural observation revealed that the edge part was denser than the inside of the sample when the holding time was short. Increasing the holding time made it possible for the inside to be sintered almost as dense as the edge part. Mechanical pressure was found to enhance densification of the Al2O3 powder. On the basis of these results, the SPS process is discussed.
Structural Properties of Strontium Vanadate Glasses
Authors: Sen S. , Ghosh A.
Published: March 2008

Structural studies of the strontium vanadate glasses of compositionsxV2O5–(100 −x)SrO are reported. X-ray diffractograms, density, and oxygen molar volume, etc., of the glasses show that single-phase and homogeneous glasses were obtained in the composition domainx= 50 to 90 mol%. The network structure for the glass compositions with 90 and 80 mol% V2O5is built up of the VO5polyhedra, while the other glass compositions consist of the VO4polyhedra. Density and glass transition temperature are observed to decrease with an increase in the V2O5content. The magnetic susceptibility of the glasses shows an increase of concentration of the reduced V4+ion with the increase of vanadium oxide content in the compositions. The well-resolved electron spin resonance structure observed for the glass composition with 50 mol% V2O5gradually becomes poor and reduces to a single component line, which has been attributed to the increase of the hopping rate of charge carriers with the increase of the V2O5content in the compositions.
Controlled Planar Interface Synthesis by Ultrahigh Vacuum Diffusion Bonding/deposition
Authors: Kim M. J. , Carpenter R. W. , Cox M. J. , Xu J.
Published: March 2008

An ultrahigh vacuum (UHV) diffusion bonding/deposition instrument was designed and constructed, which can produce homophase and heterophase planar interfaces from a wide array of materials. The interfaces are synthesizedin situby diffusion bonding of two substrates with or without various interfacial layers, at temperatures up to about 1500 °C. Substrate surfaces can be heat treated, ion-beam sputter cleaned, and chemically characterizedin situby Auger electron spectroscopy prior to deposition and/or bonding. Bicrystals can be synthesized by bonding two single-crystal substrates at a specified orientation. Interfacial layers can be deposited by electron beam evaporation and/or sputter deposition in any layered or alloyed combination on the substrates before bonding. The instrument can accommodate cylindrical and/or wafer type specimens whose sizes are sufficient for fracture mechanical testing to measure interface bond strength. A variety of planar interfaces of metals, semiconductors, and ceramics were synthesized. Examples of bonded stainless steel/Ti/stainless steel, Si/Si, and sapphire/sapphire interfaces are presented.
A Transmission Electron Microscope Study of Hardness Indentations in MoSi2
Authors: Boldt P. H. , Weatherly G. C. , Embury J. D.
Published: March 2008

Transmission electron microscopy and electron diffraction were used to study hardness indentations made at room temperature in ⟨001⟩-oriented single crystals of MoSi2. Two families of slip systems, {110}⟨001⟩ and {101}⟨010⟩, were identified. The first system formed ⟨001⟩ dislocation loops by prismatic punching beneath the indenter, while the second system led to large rotations of the crystal lattice beneath the indenter. The lattice rotations were used to estimate the density of dislocations stored in this volume. The results demonstrate that the hardness response of MoSi2 can be explained by the expanding cavity model with most of the plastic accommodation occurring immediately beneath the indenter.
Reversible bending of Si3N4 nanowire
Authors: Zhang Yingjiu , Wang Nanlin , He Rongrui , Zhang Qi , Zhu Jing , Yan Yunjie
Published: March 2008

A reversible bending phenomenon of Si3N4 nanowires on the conductive carbon–formalin microgrid under an illumination of electron beam was observed using a transmission electron microscope. The nanowires exhibit high flexibility. The bending deflection is approximately proportional to the square of the current density (J) of the electron beam. The bending strength of Si3N4 nanowire is much higher than that of bulk Si3N4 materials. The force that bent the nanowires may be an electrostatic force.
Interfacial adhesion and toughness of nanostructured diamond coatings
Authors: Toprani Neeta , Catledge Shane A. , Vohra Yogesh K. , Thompson Raymond
Published: March 2008

Microwave plasma chemical vapor deposition was used to deposit ultrasmooth nanostructured diamond films (roughness of 14 nm) on a titanium alloy (Ti–6Al–4V) by employing a feedgas mixture containing a high methane fraction (15% by volume) in nitrogen and hydrogen. Of particular interest in this study is the exceptional adhesion of the 4-μm-thick diamond coatings to the metal substrates as observed by indentation testing up to 150 kg load with a 1/8-in.-diameter tungsten carbide ball. No film delamination was observed up to 150 kg indentation load for each of 5 samples grown under the same processing conditions. Scanning electron microscopy of the film surrounding the indentations revealed circumferential microcracking beginning at loads ranging from 60 kg to as high as 150 kg. The strain to cause film microcracking was estimated from calculations of indentation surface areas to be as high as 1.9 ± 0.2%, which represents a significant improvement in toughness over other ceramic coatings.
Analysis of grain orientation and intergrain properties by micro-Raman spectroscopy in YBa2Cu3O7−x thin films
Authors: Martínez O. , Jiménez J. , Chambonnet D. , Belouet C.
Published: March 2008

Superconducting YBa2Cu3O7−x (YBCO) thin films grown by pulser-laser-assisted deposition were studied by micro-Raman spectroscopy. This technique was used to estimate the epitaxial quality of the films in terms of the presence of c-axis- and a-axis-oriented areas. The advantage of micro-Raman spectroscopy is its high lateral resolution, and this was used to study the homogeneity of the films at submicrometric level. Local structural changes from a large number of intergrain regions were revealed by changes of the Raman parameters. For example, the aggregation of a-axis-oriented grains formed needle-shaped macrograins. Micro-Raman measurements suggest that these grains were seeded at large-angle grain boundaries in c-axis-oriented areas.
The microstructure of continuously processed Yba2Cu3Oy coated conductors with underlying CeO2 and ion-beam-assisted yttria-stabilized zirconia buffer layers
Authors: Holesinger T. G. , Foltyn S. R. , Arendt P. N. , Kung H. , Jia Q. X. , Dickerson R. M. , Dowden P. C. , DePaula R. F. , Groves J. R. , Coulter J. Y.
Published: March 2008

The microstructural development of YBa2Cu3Oy (Y-123) coated conductors based on the ion-beam-assisted deposition (IBAD) of yttria-stabilized zirconia (YSZ) to produce a biaxially textured template is presented. The architecture of the conductors was Y-123/CeO2/IBAD YSZ/Inconel 625. A continuous and passivating Cr2O3 layer forms between the YSZ layer and the Inconel substrate. CeO2 and Y-123 are closely lattice-matched, and misfit strain is accommodated at the YSZ/CeO2 interface. Localized reactions between the Y-123 film and the CeO2 buffer layer result in the formation of BaCeO3, YCuO2, and CuO. The positive volume change that occurs from the interfacial reaction may act as a kinetic barrier that limits the extent of the reaction. Excess copper and yttrium generated by the interfacial reaction appear to diffuse along grain boundaries and intercalate into Y-123 grains as single layers of the Y-247, Y-248, or Y-224 phases. The interfacial reactions do not preclude the attainment of high critical currents (Ic) and current densities (Jc) in these films nor do they affect to any appreciable extent the nucleation and alignment of the Y-123 film.
Copper–lithium ion exchange in LiNbO3
Authors: Caccavale F. , Sada C. , Segato F. , Bogomolova L. D. , Krasil'nikova N. A. , Korkishko Yu. N. , Fedorov V. A. , Morozova T. V.
Published: March 2008

Copper-doped LiNbO3 waveguides were prepared by Cu–Li ion-exchange process. Compositional, structural, and optical analyses were performed by secondary ion mass spectrometry, x-ray diffraction, and m-line spectroscopy, respectively. The chemical state of Cu2+ ions was studied by electron paramagnetic resonance, and the results were correlated with structural modification of the LiNbO3 matrix. Copper incorporation in the crystal took place under different regimes, and it induced a lattice rearrangement with the formation of new crystalline phases. Cu2+ ions were surrounded by tetragonally compressed octahedra with rhombic distortions. Cu:LiNbO3 optical waveguides were formed supporting two optical modes.
Surface texture and structure of ZnO films synthesized by off-axis sputtering deposition
Authors: Zhu Shen , Su C-H. , Lehoczky S. L. , George M. A. , Lowndes D. H.
Published: March 2008

Morphology and structure of ZnO films deposited on (0001) sapphire and glass substrates by off-axis sputtering were investigated at various temperatures and pressures. All films show highly textured structures on glass substrates and epitaxial growth on sapphire substrates. The full width at half-maximum of theta rocking curves for epitaxial films is less than 0.5°. In textured films, it rises to several degrees. The trend of surface textures in films grown at low pressures is similar to those grown at high temperatures. A morphology transition from large well-defined hexagonal grains to flat surface was observed at a pressure of 50 mtorr and temperature of 550 °C. The experiment results are explained by the transport behavior of depositing species.
Microstructure and dielectric properties of (Ba,Sr)TiO3 thin film produced by the polymeric precursor method
Authors: Pontes F. M. , Araujo E. B. , Leite E. R. , Eiras J. A. , Longo E. , Varela J. A. , Pereira-da-Silva M. A.
Published: March 2008

BaxSr1−xTiO3 (x 4 0.6) (BST) thin films were successfully prepared on a Pt(111)/TiO2/SiO2/Si(100) substrate by spin coating, using the polymeric precursor method. BST films with a perovskite single phase were obtained after heat treatment at 700 °C. The multilayer BST thin films had a granular structure with a grain size of approximately 60 nm. A 480-nm-thick film was obtained by carrying out five cycles of the spin-coating/heating process. Scanning electron microscopy and atomic force microscopy analyses showed that the thin films had a smooth, dense, crack-free surface with low surface roughness (3.6 nm). At room temperature and at a frequency of 100 kHz, the dielectric constant and the dissipation factor were, respectively, 748 and 0.042. The high dielectric constant value was due to the high microstructural quality and chemical homogeneity of the thin films obtained by the polymeric precursor method.
Measurement of the loss tangent of low-density polyethylene with a nanoindentation technique
Authors: Loubet J. L. , Oliver W. C. , Lucas B. N.
Published: March 2008

This paper describes experimental measurements of the linear viscoelastic behavior of the surface of low-density (LD) polyethylene in contact with a pyramidal Berkovich diamond indenter. The experiments were carried out at two different temperatures, 15.9 and 27.2 °C, between frequencies of 0.1 and 800 Hz. Using the shift of the loss tangent between the two temperatures at frequencies lower than 20 Hz and an Arrhenius equation, an activation energy of 105 ± 2 kJ/mol was obtained. This value is in good agreement with the bulk value of the a relaxation of LD polyethylene reported in the literature.
The P–h2 relationship in indentation
Authors: Malzbender J. , de With G. , den Toonder J.
Published: March 2008

In this paper we derive an analytical expression for the indentation load–depth relation during loading in an indentation experiment, namely . The advantage over previously used expressions is that no additional empirical constants are necessary. A comparison between the new expression and results from finite element calculations shows excellent agreement.
Effects of boron doping for the structural evolution of vapor-grown carbon fibers studied by Raman spectroscopy
Authors: Nishimura K. , Kim Y. A. , Matushita T. , Hayashi T. , Endo M. , Dresselhaus M. S.
Published: March 2008

The structural deviation of boron-doped vapor-grown carbon fibers (VGCFs) with diameters around 10 μm relative to their undoped counterparts was investigated by polarized microprobe Raman spectroscopy and field-omission scanning electron microscopy as a function of heat-treatment temperature (HTT). Boron doping induces the formation of dislocation loops in the surface, which combine into larger loops with increasing HTT. The depolarization ratio, Dp, of the E2g2 mode for VGCFs increases gradually with increasing HTT, and finally approaches the value of highly oriented pyrolytic graphite, which is consistent with the asymmetric shape of the peak at ∼2725 cm−1 in the second-order Raman spectra. On the other hand, the Dp ratios of the E2g2 mode for boron-doped VGCFs show no deviations up to an HTT of 2100 °C, as compared to that of VGCFs, and decrease with increasing HTT, whereas the Dp ratios of the D peak show a maximum value at 2100 °C, and decrease gradually with increasing HTT. Consistent with these Raman results, boron atoms in the graphite lattice introduce a decreased d002 spacing (accelerating graphitization), but also hinder two-dimensional structural development and increase the amount of disorder. This is done by introducing tilt boundaries and vacancies, which make the Dp ratio of the E2g2 mode lower than the value for polycrystalline graphite, even though the fibers are heat treated at 2800 °C.
Melt-textured YBaCuO with High Trapped Fields up to 1.3 T at 77 K
Authors: Walter H. , Delamare M. P. , Bringmann B. , Leenders A. , Freyhardt H. C.
Published: March 2008

CeO2-doped YBaCuO monoliths synthesized with a top-seeded melt growth process in a conventional box furnace exhibited values of trapped magnetic field of up to 1.33 T at 77 K. To our knowledge, this is the highest value of trapped field reported for a melt-textured YBaCuO monolith. A suitable temperature profile and the use of high-density Y2BaCuO5 substrates led to reproducible single-domain crack-free samples investigated by optical and scanning electron microscopy and trapped field measurements. The zero-field-cooled levitation forces at 77 K of standard samples amounted to 70–83 N. A transport critical current density of up to 1.3 × 105 A/cm2 in self field at 77 K was obtained.