bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of metal vapor vacuum arc-implanted Cr on the electrochemical behavior of CrN-coated steels
Authors: Chang Ku-Ling , Chung Shih-Chun , Han Sheng , Hsu Jyh-Wei , Guo Xing Jian , Shih Han C.
Published: May 2005

Using cathodic arc plasma to deposit CrN on the steel has been explored and extensively studied to improve the wear and corrosion resistance of the steel structures. Metal vapor vacuum arc (MEVVA) source implantation is a novel and profitable surface-modification process coupled with the cathodic arc plasma. The effect of the MEVVA-implanted chromium on the corrosion behavior in form of Cr/steel, CrN/steel, and CrN/Cr/steel was evaluated in an aerated 0.1N HCl solution. The composition and structure of the MEVVA-implanted chromium and the cathodic arc plasma deposited CrN on steel were both examined by x-ray diffraction and transmission electron microscopy. The polarization resistance (Rp) of all samples was measured and compared with the results obtained from electrochemical impedance spectroscopy simulated by the equivalent circuit, to interpret the effect of MEVVA-implanted chromium on the corrosion mechanism of the CrN/Cr/steel. The corrosion products associated with the microstructures were analyzed by electron probe x-ray microanalyzer. The results indicated that the corrosion resistance of the CrN-coated steel was significantly enhanced by the MEVVA-implanted chromium in the CrN/Cr/steel assembly.
Hydrothermal synthesis of zirconia nanocrystals in supercritical water
Authors: Hakuta Yukiya , Ohashi Tomotugu , Hayashi Hiromichi , Arai Kunio
Published: May 2005

Zirconia nanocrystals were prepared by hydrothermal reaction of 0.05 M zirconyl nitrate and zirconyl acetate solutions at supercritical conditions of 400 °C and30 MPa for 1.8 s reaction time. Characterization of products were performed byx-ray diffraction, transmission electron microscopy, and Brunauer–Emmett–Teller measurements. The product particles were compared with zirconia particles prepared by conventional hydrothermal synthesis routes and precipitation-calcination. From the results, zirconia powders prepared in supercritical water had higher crystallinity than those obtained by other methods. Product particles with tetragonal crystal structure with a mean diameter of 6.8 nm could be formed from 0.05 M zirconyl acetate solution in the presence of 0.1 M potassium hydroxide at supercritical conditions.
Indentation strain burst phenomenon induced by grain boundaries in niobium
Authors: Wang M.G. , Ngan A.H.W.
Published: May 2005

Using depth-sensing indentation, a pop-in phenomenon induced by grain boundaries, namely, a sudden indenter displacement jump when indented near a grain boundary segment, was observed in polycrystalline niobium. This grain-boundary type of pop-in occurs at a larger force than the initial elasto-plastic pop-in, which is observed with and without a grain boundary nearby. The experimental results show that this pop-in effect has a close relationship with the misorientation across the grain boundary. The occurrence of this pop-in phenomenon is rationalized in terms of slip transmission across the grain boundary.
Nano-scale study of microstructure of Eu(DBM)3phen-doped poly(methyl methacrylate) by near-field scanning microscopy and optical properties
Authors: Liang Hao , Sun Xiaohong , Zhang Qijin , Ming Hai , Cao Jianhua , Li Zengchang , Chen Biao , Xu Jie , Zhao Hui
Published: May 2005

Eu(DBM)3phen-doped poly(methyl methacryate) (PMMA) with different doping concentration were prepared. The highest doping concentration sample (10000 ppm) was examined by near-field scanning optical microscopy (NSOM) with a resolution of 50 nm; and the result showed that there were no aggregates larger than 50 nm in the doped polymer. This result was further confirmed by optical properties of the doping material. Concentration quenching was not detected by metastable-state lifetime measurements, indicating that no aggregates existed. According to the fluorescence spectra analysis, the relative intensity ratio (R) of 5D0→7F2 to 5D0→7F1 transition was not shown to be significantly changed with the increasing of Eu3+ content. The analysis reflected that the local structure and asymmetry in the vicinity of europium ions were not changed, and that the Eu3+ ions in PMMA were homogeneously dispersed.
Fabrication and structural characterization of self-supporting electrolyte membranes for a micro solid-oxide fuel cell
Authors: Baertsch Chelsey D. , Jensen Klavs F. , Hertz Joshua L. , Tuller Harry L. , Vengallatore Srikar T. , Spearing S. Mark , Schmidt Martin A.
Published: May 2005

Micromachined fuel cells are among a class of microscale devices being explored for portable power generation. In this paper, we report processing and geometric design criteria for the fabrication of free-standing electrolyte membranes for microscale solid-oxide fuel cells. Submicron, dense, nanocrystalline yttria-stabilized zirconia (YSZ) and gadolinium-doped ceria (GDC) films were deposited onto silicon nitride membranes using electron-beam evaporation and sputter deposition. Selective silicon nitride removal leads to free-standing, square, electrolyte membranes with side dimensions as large as 1025 μm for YSZ and 525 μm for GDC, with high processing yields for YSZ. Residual stresses are tensile (+85 to +235 MPa) and compressive (–865 to -155 MPa) in as-deposited evaporated and sputtered films, respectively. Tensile evaporated films fail via brittle fracture during annealing at temperatures below 773 K; thermal limitations are dependent on the film thickness to membrane size aspect ratio. Sputtered films with compressive residual stresses show superior mechanical and thermal stability than evaporated films. Sputtered 1025-μm membranes survive annealing at 773 K, which leads to the generation of tensile stresses and brittle fracture at elevated temperatures (923 K).
Novel yttrium-stabilized zirconia polymeric precursor for the fabrication of thin films
Authors: Smith Roger M. , Zhou Xiao-Dong , Huebner Wayne , Anderson Harlan U.
Published: May 2005

An acetate-based polymeric precursor for producing yttrium-stabilized zirconia (YSZ) was developed. The precursor was prepared under ambient conditions and contains only yttrium and zirconium cations. Dense, crack-free films were fabricated with this precursor on alumina substrates at a rate of 60 nm per deposition, producing polycrystalline YSZ at temperatures as low as 600 °C. Grain growth in thin YSZ films followed Arrhenius equation with an activation energy approximately 0.45 eV. The residual strain in YSZ films decreased with increasing annealing temperature from 600 to 900 °C.
Lossy AlN–SiC composites fabricated by spark plasma sintering
Authors: Zhang Xiang-Yu , Tan Shou-Hong , Zhang Jing-Xian , Jiang Dong-Liang , Hu Bo , Gao Chen
Published: May 2005

Dense lossy AlN–SiC composites doped with Y2O3 were fabricated by spark plasma sintering (SPS). Both the microstructure and the dielectric properties are different from those of hot-pressed samples. Microstructure analysis reveals little solid solution (AlN)x(SiC)1-x is formed. Scanning evanescent microwave microscopy images show that the materials by SPS exhibit large contrast in dielectric permittivity, whereas the hot-pressed materials show very mild fluctuation in dielectric permittivity over the samples. The results indicate that AlN–SiC composites fabricated by SPS can be treated approximately as a mechanical mixture of AlN and SiC when estimating complex permittivity of the composite in the microwave range. The complex permittivity of the composites with different SiC contents can be phenomenologically predicted by effective medium approximation.
Spherical indentation of ductile power law materials
Authors: Mulford Roberta , Asaro Robert J. , Sebring Robert J.
Published: May 2005

A procedure for extracting simple constitutive parameters from microindentationtests is described. The analysis used to interpret the indentation tests is based onthe analysis of the spherical indentation test developed by Hill et al. for power law materials. Indentation tests are supplemented by scanning interference microscopyof the residual indented surface profiles and a method is suggested for using the residual surface profiles to estimate the actual contact surface. This, in turn, allowsfor the construction of the entire stress versus strain curve.
Effect of particle size distribution on strength of precipitation-hardened alloys
Authors: Kulkarni A.J. , Krishnamurthy K. , Deshmukh S.P. , Mishra R.S.
Published: May 2005

Aging of precipitation hardened alloys results in particle coarsening, which in turn affects the strength. In this study, the effect of particle size distribution on the strength of precipitation-hardened alloys was considered. To better represent real alloys, the particle radii were distributed using the Wagner and Lifshitz and Slyozov (WLS) particle size distribution theory. The dislocation motion was simulated for a range of mean radii and the critical resolved shear stress (CRSS) was calculated in each case. Results were also obtained by simulating the dislocation motion through the same system but with the glide plane populated by equal strength particles, which represent mean radii for each of the aging times. The CRSS value with the WLS particle distribution tends to decrease for lower radii than it does for the mean radius approach. The general trend of the simulation results compares well with the analytical values obtained using the equation for particle shearing and the Orowan equation.
Influence of boron content on the microstructure of sintered Al62.5−xCu25.3Fe12.2Bx alloys (x = 0, 3, 5)
Authors: Brien V. , Khare V. , Herbst F. , Weisbecker P. , Ledeuil J-B. , de Weerd M.C. , Machizaud F. , Dubois J-M.
Published: May 2005

Microstructures and morphological features of a series of sintered quasicrystalline Al62.5−xCu25.3Fe12.2Bx alloys, with x ranging from 0 to 5 at.% were studied using x-ray diffraction, scanning electron microscopy, x-ray mapping, and electron probe microanalysis. Electron backscattering diffraction (EBSD) was also used to get information about the structures of some phases and identify the crystalline relationship in-between phases. Increasing x results in the change of the nature of extra phases. These secondary phases are all less than 1% in volume of the total matter except for the β phase at 5% of boron. Whatever the percentage of boron considered, boron seems to concentrate essentially in the parasite phases confirming doubts found in literature about the solubility of boron inside the face-centered-icosahedral Al–Cu–Fe phase. No special crystallographic relationship in between the tested phases could be spotted. EBSD is thus also confirmed as an excellent technique to get quasicrystalline grains orientations.
Multiple-frequency dynamic nanoindentation testing
Authors: Fischer-Cripps A.C.
Published: May 2005

A new method of dynamic nanoindentation testing is introduced in this paper. Conventional dynamic nanoindentation testing involves the superposition of a single frequency sinusoidal force or displacement onto the quasi-static load–displacement curve. However, the viscoelastic response of many materials depends upon the frequency of the deformation of the material. This paper describes a method whereby the storage and loss modulus of viscoelastic solids can be determined using a multi-frequency dynamic oscillatory motion mode of deformation. In this method, the applied load is modulated by a pseudo-random force signal comprising multiple frequencies. A Fourier analysis is then used to deconvolute the signal into frequency-dependent values of storage and loss modulus for the specimen material as a function of frequency. The instrument response is cancelled by the use of a reference transfer function using an equalization process. Established modeling equations can then be used to extract the modulus of elasticity and the viscosity of the specimen material.
Effect of the frequency of electromagnetic vibrations on microstructural refinement of AZ91D magnesium alloy
Authors: Mizutani Yoshiki , Kawata Jun , Miwa Kenji , Yasue Kazuo , Tamura Takuya , Sakaguchi Yasuji
Published: May 2005

The static magnetic field and the alternating electric field were simultaneously imposed on AZ91D magnesium alloy melt, and α-dendrite particles were refined by the electromagnetic vibrations. The effect of the frequency of electromagnetic vibrations on microstructural refinement was quantitatively investigated. In the frequency range from 60 to 1000 Hz, the vibration frequency near 200 Hz was the most effective for the refinement of α-dendrite particles, and α-dendrite particles were refined up to approximately 100 μm from 1800 μm at this frequency. However, the effect of refinement by the electromagnetic vibrations became weak at frequencies above 400 Hz. Although the degree of refinement of the primary particles differed with the frequency of the electromagnetic vibrations, the dendrite arm spacing was almost constant, 30–40 μm, in our experiment. Therefore, the refinement of primary α-dendrite particles is likely to be caused by collapse of dendrite arms due to the cavitation phenomenon and the stirring of the melt.
Photoelectrochemical properties of titania nanotubes
Authors: Mor Gopal K. , Shankar Karthik , Varghese Oomman K. , Grimes Craig A.
Published: May 2005

N-type nanocrystalline titania is a promising material for use in semiconductor photoelectrochemical cells and, potentially, the solar generation of hydrogen. In this study, we examined the photochemical properties of titania nanotube arrays made by anodization of a starting Ti foil in a fluoride ion containing electrolyte. The absorption properties of the titania nanotube samples were investigated using diffuse reflectance ultraviolet (UV)-visible (vis) spectroscopy, with a broadening of the absorption spectra seen as a function of material phase, nanotube diameter, and Pd sensitization. The magnitude of the anodic photocurrent obtained from the polycrystalline nanotube samples, measured under band gap UV illumination, appeared to be significantly higher than that reported for any other form of nanocrystalline titania. A maximum photoconversion efficiency (UV light exposure at 365 nm, intensity 146 mW/cm2) of 4.8% was obtained for 22 nm diameter nanotubes annealed at 500 °C and coated with a discontinuous palladium layer of 10 nm average effective thickness.
Chemical vapor deposition of ruthenium and ruthenium oxide thin films for advanced complementary metal-oxide semiconductor gate electrode applications
Authors: Papadatos Filippos , Consiglio Steve , Skordas Spyridon , Eisenbraun Eric T. , Kaloyeros Alain E. , Peck John , Thompson David , Hoover Cynthia
Published: May 2005

A low-temperature (320–480 °C) metal-organic chemical vapor deposition (MOCVD) process was developed for the growth of ruthenium and ruthenium oxide thin films. The process used bis(ethylcyclopentadienyl)ruthenium [Ru(C5H4C2H5)2] and oxygen as, respectively, the ruthenium and oxygen sources. Systematic investigations of film formation mechanisms and associated rate limiting factors that control the nucleation and growth of the Ru and RuO2 phases led to the demonstration that the MOCVD process can be smoothly and reversibly modified to form either Ru or RuO2 through simple and straightforward modifications to the processing conditions–primarily oxygen flow and substrate temperature. In particular, films grown at low oxygen flows (50 sccm) exhibited a metallic Ru phase at processing temperatures below 480 °C. In contrast, films grown at high oxygen flow (300 sccm) were metallic Ru below 400 °C. Above 400 °C, a phase transition was observed from Ru to RuOx (0 < x < 2.0) to RuO2 as the processing temperature was gradually increased to 480 °C.
Fe–Mn–Cr–Mo–(Y,Ln)–C–B (Ln = Lanthanides) bulk metallic glasses as formable amorphous steel alloys
Authors: Ponnambalam V. , Poon S. Joseph , Shiflet Gary J.
Published: May 2005

The glass formability of high-manganese amorphous steel alloys reported earlier by us has been found to improve upon additions of yttrium and lanthanide elements, enabling the formation of bulk glassy samples with diameter thicknesses reaching 7 mm by casting. Based on extensive studies using different Ln additions and systematic measurements of alloy oxygen contents, the intrinsic roles of Y/Ln in attaining good glass formability in both the high-Mn alloys and previously reported high-Cr alloys are revealed. The yield strengths of the non-ferromagnetic glassy alloys obtained are estimated to be three times those of high-strength stainless steel alloys, and high elastic moduli in the range 150–200 GPa are measured. Furthermore, in the supercooled liquid regions, the glassy rods can be bent into various configurations by hand without fracturing. The observed plastic behavior together with the measured high mechanical strengths suggests that the present Fe–based bulk metallic glasses can potentially be developed as formable non-ferromagnetic amorphous steel alloys.
Crack penetration and deflection at a bimaterial interface in a four-point bend test
Authors: Roham Sassan , Hardikar Kedar , Woytowitz Peter
Published: May 2005

The four-point bend (4PB) test is an industry standard in assessment of adhesion in thin films. Obtaining crack propagation along the desired interface plays a cardinal role in the success of this test. Crack penetration and deflection at a bimaterial interface has been extensively studied in the past. Most general results are based on asymptotic analyses involving the interface between two semi-infinite media. The results of these analyses cannot be directly used in case of the 4PB test since the boundary conditions and finite size effects in actual test specimen geometry are not accounted for. The purpose of this paper is twofold: first to develop a simple methodology to understand the preferred failure mode in a 4PB test and gain insight into the factors governing its success; second to examine the extent to which the results can be reconciled with those reported previously based on analysis of a crack in two semi-infinite media bonded together at the interface.
Extracting the mechanical properties of a viscoelastic polymeric film on a hard elastic substrate
Authors: Zhang C.Y. , Zhang Y.W. , Zeng K.Y.
Published: May 2005

A semi-analytical approach was developed to study the creep response of a viscoelastic polymeric thin film on a hard elastic substrate under flat-ended punch indentation. This approach allows one to separate mechanical properties of the film from its substrate. To verify the approach, flat-ended punch creep indentation tests were performed to obtain the long-time viscoelastic behaviors of a polymethyl-methacrylide film overlying on an aluminum substrate. Three viscoelastic models describing the constitutive equations of the polymer film are compared in this paper. “Film-only” viscoelastic parameters were extracted by fitting with the experimental creep curves of flat-ended punch indentation. It is shown that the present approach provides an effective way to characterize the mechanical properties of a polymeric film on an elastic substrate.
Length-scale-based hardening model for ultra-small volumes
Authors: Jungk J.M. , Mook W.M. , Cordill M.J. , Chambers M.D. , Gerberich W.W. , Bahr D.F. , Moody N.R. , Hoehn J.W.
Published: May 2005

Understanding the hardening response of small volumes is necessary to completely explain the mechanical properties of thin films and nanostructures. This experimental study deals with the deformation and hardening response in gold and copper films ranging in thickness from 10 to 400 nm and silicon nanoparticles with particle diameters less than 100 nm. For very thin films of both gold and copper, it was found that hardness initially decreases from about 2.5 to 1.5 GPa with increasing penetration depth. Thereafter, an increase occurs with depths beyond about 5–10% of the film thickness. It is proposed that the observed minima are produced by two competing mechanisms. It is shown that for relatively deep penetrations, a dislocation back stress argument reasonably explains the material hardening behavior unrelated to any substrate composite effect. Then, for shallow contacts, a volume-to-surface length scale argument relating to an indentation size effect is hypothesized. A simple model based on the superposition of these two mechanisms provides a reasonable fit to the experimental nanoindentation data.
Quantitative phase transformation behavior in TiNi shape memory alloy thin films
Authors: Lai Bo-Kuai , Kahn H. , Phillips S.M. , Akase Z. , Heuer A.H.
Published: May 2005

Phase transformations in near-equiatomic TiNi shape memory alloy thin films were studied, and the phase fraction evolutions were quantitatively correlated to the stress and resistivity of the films. TiNi thin films with compositions of 50.1, 51.1, and 51.7 at.% Ti all exhibited transformation temperatures between 65 and 100 °C, low residual stresses at room temperature (RT), and high recoverable stresses, thus making them suitable for microactuators in microelectromechanical systems. Low residual stresses at RT, less than 50 MPa, can be obtained even when only a small quantity of martensite, less than 30%, is present. Phase fraction evolution during complete thermal cycles (heating and cooling) was studied using elevated temperature x-ray diffraction, combined with quantitative Rietveld analysis. R-phase always appeared in these near-equiatomic TiNi thin films during cooling but did not have a noticeable effect on the stress–temperature hysteresis curves, which mainly depend on the phase fraction evolution of martensite. On the other hand, the occurrence of R-phase determined the variation of film resistivity. Martensite, austenite, and R-phase coexisting within a single grain were observed using transmission electron microscopy.
Ca-doped lead zirconate titanate thin film capacitors on base metal nickel on copper foil
Authors: Kim Taeyun , Kingon Angus I. , Maria Jon-Paul , Croswell Robert T.
Published: May 2005

Ca-doped lead zirconate titanate (52/48) thin film capacitors were prepared on electroless nickel-coated copper foils for embedded capacitor applications. The impact of Ca doping and process parameter variations was studied. Ca addition significantly reduced the temperature coefficient of capacitance. Specifically, the temperature variation was reduced to less than 10% between 300 and 580 K through calcium addition. Optimized capacitance densities and loss tangents were 400 nF/cm2 and 0.02, respectively. Crystallization temperatures of 600 °C yielded these optimized electrical properties, while higher temperatures resulted in interfacial reactions. The influence of oxygen partial pressure during crystallization was also studied. Dielectric properties were sensitive to pO2, with optimal properties occurring in a narrow pO2 window centered about 10−3 Torr. The trends with oxygen pressure were mirrored by changes in phase assemblage. Electrical transport across the dielectric layers was not strongly dependent upon doping level. This insensitivity was attributed to a thin interfacial layer present in all samples. Interface analysis using equivalent circuit analogues showed the nature of the interface to be highly resistive (insulating), rather than semiconducting or conducting.
Nickel aluminum superalloys created by the self-propagating high-temperature synthesis of nanoparticle reactants
Authors: Hunt Emily M. , Granier John J. , Plantier Keith B. , Pantoya Michelle L.
Published: May 2005

Advancements in nanotechnology for material processing via combustion synthesis have spurred the development of superalloys that provide improved protective properties. Nanoscale reactant particles offer unique thermal properties and increased homogeneity that improve the microstructural features and macroscopic properties of the synthesized product. In this study nanoscale molybdenum trioxide (MoO3) particles were added to micron scale nickel (Ni) and aluminum (Al). The goal was to incorporate a nanoscale additive within the reactant matrix that would produce a superalloy by generating excessively high heating rates and creating controlled quantities of Al2O3 (a strengthening agent) within the microstructure of the alloy. Ignition and flame propagation were examined using a CO2 laser and imaging diagnostics that include a copper-vapor laser coupled with a high-speed camera. Product microstructure was examined using micro-x-ray diffraction analysis and scanning electron microscopy. Abrasion testing was performed to evaluate the wear resistance properties of the superalloy. Results show that adding MoO3 increases the flame temperature, results in greater ignition sensitivity, produces a more homogeneous microstructure, and increases the overall wear resistance of the product.
Hydrogen storage properties of mechanically alloyedMg–8 mol% LaNi0.5 composite
Authors: Li Qian , Lin Qin , Chou Kuo-Chih , Jiang Li-Jun , Zhan Feng
Published: May 2005

A new nano-ternary Mg–8 mol% LaNi0.5 was prepared by melted and subsequent mechanical alloying technique for hydrogen storage. It was found from our experiments that, this kind of alloy had superior hydriding/dehydriding characteristics in comparison with conventional materials for hydrogen storage. It possessed large hydrogen capacity at a lower temperature, which could absorb 4.55–7.01 mass% H under 3 MPa hydrogen pressure and desorb 4.40–6.90 mass% H under 0.0133 MPa in 600 s above 423 K without any activation requirement drawn from our pressure-composition isotherm and kinetic experiments. Through the x-ray diffraction and transmission electron microscopy experiments, we further found that these superior characteristics could be attributed to the multiphase structure and a catalytic effect of LaH3 and Mg2Ni that were formed in the material preparation of mechanical alloying process. Finally, based on these data the relationships between equilibrium pressure of hydrogen and temperature were obtained, they were lgp(0.1 MPa) = −3985/T + 7.188(553 K ⩽ T ⩽ 573K) for hydriding and lgp(0.1 MPa) = −3804/T + 6.770 (553 K ⩽ T ⩽ 573 K) for dehydriding.
Modeling austenite–ferrite transformation in low carbon steel using the cellular automaton method
Authors: Lan Y.J. , Li D.Z. , Li Y.Y.
Published: May 2005

Austenite–ferrite transformation at different isothermal temperatures in low carbon steel was investigated by a two-dimensional cellular automaton approach, which provides a simple solution for the difficult moving boundary problem that governs the ferrite grain growth. In this paper, a classical model for ferrite nucleation at austenite grain boundaries is adopted, and the kinetics of ferrite grain growth is numerically resolved by coupling carbon diffusion process in austenite and austenite–ferrite (γ–α) interface dynamics. The simulated morphology of ferrite grains shows that the γ–α interface is stable. In this cellular automaton model, the γ–α interface mobility and carbon diffusion rate at austenite grain boundaries are assumed to be higher than those in austenite grain interiors. This has influence on the morphology of ferrite grains. Finally, the modeled ferrite transformation kinetics at different isothermal temperatures is compared with the experiments in the literature and the grid size effects of simulated results are investigated by changing the cell length of cellular automaton model in a set of calculations.
Combustion synthesis method for synthesis of aluminum nitride powder using aluminum containers (II)
Authors: Lin Chun-Nan , Chung Shyan-Lung
Published: May 2005

A combustion synthesis method was developed for synthesis of AlN powder. Al powder and small amounts of urea were thoroughly mixed and placed in aluminum containers. A layer of AlN powder was placed on the top of the reactant powdersand in between the reactant powders and the container walls. The combustion reaction was ignited by heating the top surface of the powder stack and the aluminum container was converted completely to AlN during combustion reaction. High product yields (∼99.5%) were obtained under N2 pressures of 0.3–0.5 MPa. The product as synthesized is porous and loose and can be easily ground. A quenching technique was developed and formation of the various types of product morphology was investigated. Effects of several process parameters on the product yield were also studied. These results were reported and discussed.
Water-vapor-induced transformation of two-dimensional vanadyl hydrogen phosphate hemihydrate, VOHPO4·0.5H2O, to one-dimensional tetrahydrate, VOHPO4·4H2O
Authors: Dasgupta Soumen , Agarwal Monika , Datta Arunabha
Published: May 2005

The catalytically important, two-dimensional vanadyl hydrogen phosphate hemihydrate, VOHPO4·0.5H2O phase was transformed to the one-dimensional vanadyl hydrogen phosphate tetrahydrate, VOHPO4·4H2O for the first time by mild treatment with water vapor. It was also observed that for three samples of VOHPO4·0.5H2O prepared under different conditions, the rate of transformation to the tetrahydrate was markedly affected by morphology and crystallinity. The tetrahydrate phase could also be re-transformed to the hemihydrate by applying high vacuum or by heating at 120 °C, but this was accompanied by significant loss in crystallinity.
Transmission electron microscopy investigation of tubular and capsular needlelike crystals of C60 produced by the liquid–liquid interfacial precipitation method
Authors: Miyazawa Kun’ichi , Suga Tadatomo
Published: May 2005

Tubular and capsular needlelike crystals of C60 with a few hundreds nanometers to about one micrometer in diameter were discovered among the precipitates prepared by the liquid–liquid interfacial precipitation method. Addition of a small amount of (η2–C60)Pt(PPh3)2 to the toluene solution of C60 produced various morphologies of hollow C60 crystals. This paper gives the first report on the formation of structures we named “C60 nanotubes.”
In situ synthesis of nanocrystalline BaTiO3 particle–polymer hybrid
Authors: Yogo Toshinobu , Yamamoto Tomoe , Sakamoto Wataru , Hirano Shin-ichi
Published: May 2005

Nanocrystalline BaTiO3 particle–polymer hybrid was synthesized by polymerization and hydrolysis of [2-(methacryloxy)ethoxy]triisopropoxytitanium (MEPT) and barium alkoxide. The precursor for hybrid was synthesized from prepolymerized MEPT and barium alkokide, which was then hydrolyzed to form BaTiO3 particle–polymer hybrids below 100 °C. BaTiO3 particles increased in crystallinity when the amount of water for hydrolysis increased. The nanocrystalline particles were identified to be BaTiO3 by electron diffraction. Nanometer-sized BaTiO3 particle–polymer hybrid was shaped to a film with a dielectric constant of 8.2 at 10 kHz. A suspension consisting of the hybrid and silicone oil responded to a direct-current field, exhibiting a typical electrorheological behavior.
Evaluation of microstructure and superplasticity in friction stir processed 5083 Al alloy
Authors: Charit I. , Mishra R.S.
Published: May 2005

Friction stir processing (FSP) has been developed as a potential grain refinement technique. In the current study, a commercial 5083 Al alloy was friction stir processed with three combinations of FSP parameters. Fine-grained microstructures with average grain sizes of 3.5–8.5 μm were obtained. Tensile tests revealed that the maximum ductility of 590 was achieved at a strain rate of 3 × 10−3 s−1 and 530 °C in the 6.5-μm grain size FSP material, whereas for the material with 8.5-μm grain size, maximum ductility of 575 was achieved at a strain rate of 3 × 10−4 s−1 and490 °C. The deformation mechanisms for both the materials were grain boundary sliding (m ∼0.5) However, the 3.5-μm grain size material showed maximum ductility of 315 at 10−2 s−1 and 430 °C. The flow mechanism was solute-drag dislocation glide (m ∼0.33) This study indicated that establishing a processing window is crucial for obtaining optimized microstructure for optimum superplasticity.
Material characteristics and capacitive properties of aluminum anodic oxides formed in various electrolytes
Authors: Chang Jeng-Kuei , Liao Chi-Min , Chen Chih-Hsiung , Tsai Wen-Ta
Published: May 2005

The microstructure and composition of aluminum oxide films, formed by a two-step anodization process in various electrolytes at 100 V then subject to an intermediate heat treatment (500 °C, 2 min), were investigated. The anodization electrolytes used included ammonium adipate electrolyte, phosphoric acid electrolyte, ammonium dihydrogen phosphate electrolyte, and their mixtures. The cross-section morphologies, crystal structure, and chemical composition of aluminum anodic oxides were examined by transmission electron microscopy. X-ray photoelectron spectroscopy was carried out to study the surface chemical state of the anodic films. The corresponding capacitances and retention voltages of these oxide films were also explored. The results indicated that amorphous-to-crystalline transformation of the oxide, primarily in films formed in ammonium adipate electrolyte, was induced by the heat treatment. Electron diffraction analyses further revealed the oxide films consisted of two distinct zones, which included an inner amorphous layer and an outer layer containing crystalline γ′-Al2O3. This study found that the phosphorous species in either the primary or the re-anodization electrolytes had a potential to cause changes of Al and O distributions within the oxides. The oxide film primarily anodized in ammonium adipate and re-anodized in phosphoric acid had the highest capacitance due to its high degree of crystallinity and thinness compared to oxides formed in other electrolytes. The presence of phosphorus, from the primary anodization electrolytes, in the oxides could inhibit the formation of crystalline γ′-Al2O3 and, consequently, decrease the capacitances of the anodic films. At the same time, the retention voltage and hydration resistance of these oxide films were improved.
Wet chemical synthesis and luminescence properties of erbium-doped nanocrystalline yttrium oxide
Authors: Vetrone Fiorenzo , Boyer John-Christopher , Capobianco John A. , Speghini Adolfo , Bettinelli Marco
Published: May 2005

The luminescence properties of nanocrystalline Y2O3:Er3+ prepared via wet chemical synthesis were investigated. A broadening of both the reflectance spectrum and 77 K luminescence spectrum (λexc = 488 nm) was observed in the nanocrystalline material compared to bulk Y2O3:Er3+. The spectral broadening was attributed to the presence of Er3+ ions on the surface of the particle, which experienced different crystal fields than the ions buried in the core of the particle. Upconversion was observed in both the bulk and nanocrystal material following excitation with 650-nm or 800-nm radiation. Following excitation with 800-nm radiation, an enhancement of the red (4F9/2 → 4I15/2) upconverted emission was observed and occurred as a result of the (4I9/2, 4I11/2) → (4I13/2, 4F9/2) ion-pair process that directly populated the 4F9/2 state. The magnitude of the red enhancement in the nanocrystalline material prepared via wet chemical synthesis was less than that of the identically doped bulk sample and less still than Y2O3:Er3+ nanocrystals prepared via a combustion synthesis technique. An explanation is proposed to account for the drastic difference in the red upconverted luminescence intensity.
Synthesis and properties of nanocrystalline ceria powders
Authors: Basu S. , Devi P. Sujatha , Maiti H.S.
Published: May 2005

Nanocrystalline CeO2 powder was synthesized by a citrate-nitrate autoignition process and characterized by thermal analysis, x-ray diffraction, and impedance spectroscopy measurements. Nanocrystalline (20–40 nm) ceria powder with fluorite structure had formed in situ during the citrate-nitrate autoignition process. The powder prepared could be sintered to density more than 98% of theoretical density at 1450 °C. The nanocrystalline CeO2 exhibited an increase in conductivity in Ar and H2 than air above 600 °C, suggesting a possible electronic contribution to the conductivity at low oxygen partial pressures. Impedance measurements on the sintered samples unequivocally established the potential of this process in developing phase pure ceria compositions.
Raman spectroscopy studies on the thermal stability of TiN, CrN, TiAlN coatings and nanolayered TiN/CrN, TiAlN/CrN multilayer coatings
Authors: Barshilia Harish C. , Rajam K.S.
Published: May 2005

About 1.5-μm-thick single-layer TiN, CrN, TiAlN coatings and nanolayered TiN/CrN, TiAlN/CrN multilayer coatings were deposited on silicon (111) substrates using a reactive direct current magnetron sputtering process. Structural characterization of the coatings was done using x-ray diffraction (XRD) and micro-Raman spectroscopy. All the coatings exhibited NaCl B1 structure in the XRD data. Raman spectroscopy data of as-deposited coatings exhibited two broad bands centered at 230–250 and 540–630 cm-1. These bands have been assigned to acoustical and optical phonon modes, respectively. Thermal stability of the coatings was studied by heating the coatings in air in a resistive furnace for 30 min in the temperature range 400–900 °C. Structural changes as a result of heating were characterized using Raman spectroscopy and XRD. Raman data showed that TiN, CrN, TiN/CrN, TiAlN, and TiAlN/CrN coatings started to oxidize at 500, 600, 750, 800, and 900 °C, respectively. To isolate the oxidation-induced spectral changes as a result of heating of the coatings in air, samples were also annealed in vacuum at 800 °C under similar conditions. The Raman data of vacuum-annealed coatings showed no phase transformation, and intensity of the optical phonon mode increased and shifted to lower frequencies. The origin of these spectral changes is discussed in terms of defect structure of the coatings. Our results indicate that the thermal stability of nanolayered multilayer coatings is superior to the single-layer coatings.
Dose-window dependence on Si crystal orientation in separation by implanted oxygen substrate formation
Authors: Iikawa H. , Nakao M. , Izumi K.
Published: May 2005

Separation by implemented oxygen (SIMOX)(111) substrates have been formed by oxygen-ion (16O+) implantation into Si(111), showing that a so-called “dose-window” at 16O+-implantation into Si differs from Si(100) to Si(111). In SIMOX(100), an oxygen dose of 4 × 1017/cm2 into Si(100) is widely recognized as the dose-window when the acceleration energy is 180 keV. For the first time, our work shows that an oxygen dose of 5 × 1017/cm2 into Si(111) is the dose-window for the formation of SIMOX(111) substrates when the acceleration energy is 180 keV. The difference between dose-windows is caused by anisotropy of the crystal orientation during growth of the faceted buried SiO2. We also numerically analyzed the data at different oxidation velocities for each facet of the polyhedral SiO2 islands. Numerical analysis results show good agreement with the experimental data.
Analysis of creep behavior of SiC/Al metal matrix composites based on a generalized shear-lag model
Authors: Ryu Ho J. , Chung Kyung H. , Cha Seung I. , Hong Soon H.
Published: May 2005

The creep behaviors of 20 vol% SiCw/2124Al, extruded with different ratios, and SiCp/2124Al, reinforced with 10–30 vol% SiC particles, were investigated to clarify the effects of aspect ratio, alignment, and volume fraction of reinforcement on creep deformation. The effective stresses on the matrix of SiC/Al composites are calculated based on the generalized shear-lag model. The minimum creep rates of SiCw/2124Al extruded with different ratios and SiCp/2124Al reinforced with different volume fractions of SiC particles are found to be similar under a same effective stress on matrix, which is calculated by the generalized shear-lag model. The subgrain sizes in matrices of crept SiC/Al composites are dependent on the effective stress on matrix but not on the applied stress on the composite. It is suggested that the role of SiC reinforcements is to increase the creep resistance of SiC/Al composite by reducing the effective stress on matrix.
Effect of elastic surface deformation on the relation between hardness and yield strength
Authors: Vandeperre L.J. , Giuliani F. , Clegg W.J.
Published: May 2005

The use of an analytical approach to determine the relation between hardness and yield strength for materials with a high ratio of yield strength to Young's modulus is re-examined. It is shown that predictions using the analogy of the spherical cavity fail to reproduce experimental and finite element results because the surface deflection that occurs during loading is not taken into account. A modification is proposed to allow this. This gives a greatly improved prediction of the relationship between the hardness and yield strength of a material. It also enables the effect of the indenter shape on the measured hardness to be incorporated and explains why in some very hard materials, indentation is observed to be completely elastic.
Dislocation–grain boundary interactions in martensitic steel observed through in situ nanoindentation in a transmission electron microscope
Authors: Ohmura T. , Minor A.M. , Stach E.A. , Morris J.W.
Published: May 2005

Dislocation–interface interactions in Fe–0.4 wt% C tempered martensitic steel were studied through in situ nanoindentation in a transmission electron microscope (TEM). Two types of boundaries were imaged in the dislocated martensitic structure: a low-angle (probable) lath boundary and a coherent, high-angle (probable) block boundary. In the case of a low-angle grain boundary, the dislocations induced by the indenter piled up against the boundary. As the indenter penetrated further, a critical stress appeared to have been reached, and a high density of dislocations was suddenly emitted on the far side of the grain boundary into the adjacent grain. In the case of the high-angle grain boundary, the numerous dislocations that were produced by the indentation were simply absorbed into the boundary, with no indication of pileup or the transmission of strain. This surprising observation is interpreted on the basis of the crystallography of the block boundary.
(Fe,Co,Ni)–B–Si–Nb Bulk Glassy Alloy With Super-High Strength and Some Ductility [Article Retracted]
Authors: Shen Baolong , Inoue Akihisa
Published: May 2005

Glassy [(Fe0.8Co0.1Ni0.1)0.75B0.2Si0.05]96Nb4 alloy rods with glass transition temperature of 835 K, followed by a large supercooled liquid region of 55 K were produced in the diameter range up to 2 mm by copper mold casting. The glassy alloy rods exhibit super-high true fracture strength of 4225 MPa combined with elastic strain of 0.02 and true plastic strain of 0.005. The super-high strength alloy simultaneously exhibits high magnetization of 1.1 T, low coercivity of 3 A/m, and high permeability of 1.8 × 104 at 1 kHz. The success of synthesizing a super-high strength Fe-based bulk glassy alloy with some compressive plastic strain and good soft magnetic properties is encouraging for future development of Fe-based bulk glassy alloys as new engineering and functional materials.
Fine-Grain Processing by Equal Channel Angular Extrusion of Rapidly Quenched Bulk Mg–Y–Zn Alloy
Authors: Watanabe Hiroyuki , Somekawa Hidetoshi , Higashi Kenji
Published: May 2005

The fine-grain processing of ingot metallurgy (IM) Mg–Y–Zn alloy, WZ73, was investigated. The alloy was initially produced by casting into a copper mold at a cooling rate of ∼50 K/s. The rapidly quenched bulk material was processed by means of equal channel angular extrusion (ECAE). The ECAE-processed material had equiaxed grains of 5.1 μm in size, and fine second-phase particles of Mg12YZn were dispersed in the grain boundaries. The Vickers hardness of the ECAE-processed material was 78. The dispersion of the second-phase particles, solid solution strengthening, and grain refinement contributed to the material’s hardness. The structure remained virtually unchanged, at least up to 673 K because the Mg12YZn phase served to pin the grain boundaries. The microstructure of IM WZ73 alloy, which is a suitable starting material for ECAE, was also considered.
Surface Morphology Anisotropy and Stress Distribution Uniformity in Annealed Cu–W Films
Authors: Wang Y. , Li X.-H , Chen Y.-H , Xu K.-W , Fan D.W.
Published: May 2005

Copper-tungsten films were deposited on Si and Al2O3 substrates by magnetron sputtering and then in situ annealed in vacuum chamber at different temperatures. X-ray diffraction (XRD), scanning electron microscopy (SEM), and the polarization phase shift technique were used to characterize the microstructure, surface morphology, and residual stress of Cu–W films. The results indicated that there are two successive but distinctive stages of phase transition with the change of annealing temperatures. The evolution of surface morphology of Cu–W thin films shows a significant effect on the distribution of in-plane stresses. A strategy of integrating discrete wavelet transform and fractal geometry concepts was developed to analyze the anisotropy of surface structure of Cu–W thin films. The correlation between the anisotropy of surface morphology and the stress distribution of thin films was constructed. It is found that the stress distribution of the thin films is sensitive to the variations of the anisotropy of the surface structure with annealing temperature. The variation in the uniformity of in-plane stress distribution with the evolution of surface structure of thin films is independent of the choice of substrate materials.
High-Temperature Dielectric Properties of Goethite From 400 to 3000 MHz
Authors: Pickles C.A. , Mouris J. , Hutcheon R.M.
Published: May 2005

The dielectric properties of goethite and, in particular, the changes during the topotactic conversion of goethite to hematite were studied from room temperature to about 800 °C in the frequency range of 400 to 3000 MHz using the cavity perturbation technique. The complex permittivity, that is, both the real and the imaginary or absorptive parts (έ and ἕ), were measured under various heating regimens. In addition, thermogravimetric analysis (TGA) was performed to characterize the transformation of goethite to hematite. The Debye relaxation formalism was applied to the processes occurring both during and after the main dehydroxylation reaction to calculate the relaxation times. The Arrhenius equation for thermally activated relaxation times was used to determine the activation energies. Both the real and the absorptive parts of the permittivity exhibited a significant peak during the main part of the goethite to hematite decomposition reaction. Above the transformation, there was another, less dramatic, thermally activated increase in the permittivity values. The increase in the permittivities during the goethite to hematite transformation was attributed to the formation of quasi-free migrating radicals, for example, hydroxyl ions, oxygen ions, or hydrogen atoms, during the dehydroxylation of goethite. The derivative thermogravimetric analysis (DTGA) curve was found to be directly related to the transient values of the real and the imaginary permittivities. Higher heating rates resulted in an accelerated rate of dehydroxylation and therefore higher values of the transient permittivities. In the temperature range of 400 °C to 500 °C (i.e., just above the dehydroxylation peak), the real permittivity exhibited a varying frequency dependence, which suggested that changes were occurring in the newly formed, highly defected hematite structure, which is referred to as hydrohematite. During the reaction there were multiple relaxation processes and thus the Debye relationship could not be applied. However, at temperatures above about 500 °C, the structure stabilized, the Debye relationship was more closely followed, and the relaxation times could be determined as a function of temperature. The activation energy for the relaxation process above 500 °C was determined to be 0.47 kJ/mol.