bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical and Morphological Analysis of Sol-derived Kca2Nb3O10
Authors: Kim Steven T. , Dravid Vinayak P. , Sambasivan Sankar
Published: March 2008

The chemical and morphological properties of a sol-derived layered perovskite compound, Kca2Nb3O10 (KCN), are presented. Development of this compound is motivated by its use as an interphase fiber-coating material for ceramic matrix composites (CMC's). In such systems, this material is to be placed between the fiber and matrix to control crack propagation in the vicinity of the fiber, thereby enhancing toughness. Comparative analyses are performed between known bulk specimens of KCN and the sol-derived product using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The suitability of the sol-derived KCN for CMC applications is demonstrated through microstructure and chemical composition similar to that of the known bulk KCN samples.
Synthesis and Properties of Chemically Modified Polycarbosilane Containing Organofluoric Groups
Authors: Okuzaki Sachiko , Iwamoto Yuji , Kikuta Koichi , Hirano Shin-ichi
Published: March 2008

The chemically modified polycarbosilane (PC) containing organofluoric groups, PCOCF, was synthesized through chemical reaction of PC and fluoric alcohol. Pyrolysis of the polymer precursor occurred in three stages under 1000 °C. Weight loss due to evaporation of low molecular compounds was observed at the first stage below 300 °C, followed by the largest weight loss from 300 to 600 °C at the second stage. At this stage, side chains formed during the chemical reaction were removed. Finally, side chains such as Si–CH3 decomposed at the third stage above 600 °C. At 1000 °C, the chemical modification of PC resulted in high yield of solid product. After coating PCOCF on silicon carbide (SiC) powders, the conversion yield of pyrolyzed PCOCF was further improved due to the interaction between PCOCF and SiC powders. Coating of PCOCF on SiC powders was found to be effective in increasing the green density of uniaxially pressed bodies.
Effects of Borosilicate Glass on Densification and Properties of Borosilicate Glass + TiO2 Ceramics
Authors: Jean Jau-Ho , Lin Shih-Chun
Published: March 2008

Effects of borosilicate glass (BSG) on densification and dielectric and thermal expansion properties of a binary composite of BSG + TiO2 ceramics have been investigated. Two different phases of TiO2 including anatase and rutile are used. A much greater densification is observed with anatase because it has a much better wetting with BSG than rutile. With increasing BSG content, the densification of BSG + TiO2 increased. Activation analysis shows that the densification is controlled by viscous flow of BSG. Both dielectric constant and coefficient of thermal expansion of the binary composite of BSG + TiO2 increase with decreasing BSG content and increasing the degree of anatase-to-rutile transformation, as well.
Relations Between Coarsening and Densification and Mass Transport Path in Solid-state Sintering of Ceramics: Model Analysis
Authors: Shi J. L.
Published: March 2008

The correlations between coarsening (including grain and pore growth) and densification, and the effects of mass transport on particle coarsening and densification were discussed based on the simple particle array models and for the real particle compacts. Grain boundary motion could cause particle coarsening only under a certain particle size distribution but not densification; mass transport is reasoned to contribute to both grain growth (particle coarsening) and shrinkage for one-dimensional particle arrays. Under a certain limitation for the change of the particle size aspect ratio during sintering, very limited effects of grain grown by itself on the shrinkage of particle a rrays throughreinitiating the sintering could be found. For a real powder compact system, mass transport between the particles, which surround a pore, contributes to the particle coarsening and densification when the pore is thermodynamically unstable and only to particle coarsening when the pore is thermodynamically stable. The mass transport mechanism for both particle coarsening and densification would be the same, which cannot exclude, at least on thermodynamics, the contribution from surface diffusion in the intermediate stage of sintering.
Thermodynamics and Densification Kinetics in Solid-state Sintering of Ceramics
Authors: Shi J. L.
Published: March 2008

Based on the stability analysis of the closed pores in two dimensions which was determined mathematically with their particle coordination number and dihedral angle, the stability of those in three dimensions was determined with a spherical pore model. The model is set up by first excluding the effect of interface tension, so the pore was supposed to be spherical, and then the tensile stress arisen from the interface tension was supposed to act on this hypothesized spherical pore. On the basis of the spherical pore model, microstructure models based on pores, not grains, for the real powder compacts were first established. Densification kinetics were then determined from the models by the densification rate equations, which were derived by relating density to pore size to grain size ratio, for the intermediate and final stages of sintering. The criteria for pore shrinkage were discussed quantitatively. The derived equations can be used to simulate the relation between densification rate and density during heating with a constant rate and for the explanation of the effects of pore size distribution, agglomerates, and green density on sintering.
Effective Sintering Aids for Low-temperature Sintering of AlN Ceramics
Authors: Watari Koji , Hwang Hae J. , Toriyama Motohiro , Kanzaki Shuzo
Published: March 2008

A disappearing sintering aid was used to promote densification during the initial and middle stages of sintering and to be removed in gaseous form from the specimens during the final stage of sintering. From thermodynamic consideration such as assessment of Gibbs free energy change of formation of Al2O3 compounds including metal-oxide and evaluation of the vapor pressure of metal-oxide, Li2O is expected to become a disappearing sintering aid for AlN sintering. Doping with Li2O resulted in densification of AlN ceramics with Y2O3 and CaO additives by sintering at a firing temperature of 1600 °C. The amount of Li2O in the specimens decreased by volatilization at temperatures higher than 1300 °C, and its amount was at a level of several ppm after firing at 1600 °C for 6 h. Low-temperature densification of AlN specimens by addition of Li2O also caused the improvement of thermal conductivity and mechanical strength of sintered specimens. Present results indicate that a Li2O addition is effective for AlN sintering. Furthermore, LiYO2 was also used as a new sintering aid instead of Li2O and Y2O3, and the results of thermal conductivity and mechanical strength are shown.
Atomistic Structure of Sodium and Calcium Silicate Intergranular Films in Alumina
Authors: Litton David A. , Garofalini Stephen H.
Published: March 2008

Sodium silicate intergranular films (IGF) in contact with the [0001] basal plane of α-alumina were studied using the molecular dynamics computer simulation technique. The results were compared to previous simulations of calcium silicate and sol-gel silica IGF's in contact with alumina. An ordered, cagelike structure was observed at the interface. Sodium ions segregated to the cages at the interfaces. Calcium and hydrogen ions were also observed to segregate to the cages in the previous simulations. The modifier ions were surrounded by more oxygen ions in the cages at the interface than in the bulk of the IGF. This explains the segregation of modifiers at the interface. Interface energy decreased as the sodium content of the IGF increased. Interface energy decreased faster as a function of Na2O content than as a function of CaO content. However, interface energy decreased slower as a function of Na+ content than as a function of Ca2+content.
Initiation of Dislocation Systems in Alumina Under Single-point Scratching
Authors: Zarudi Irena , Zhang Liangchi
Published: March 2008

This paper aims to investigate the initiation and distribution of dislocations and twins in the subsurface of alumina subjected to single-point scratching and to gain a deeper understanding of the mechanisms of ductile-regime grinding of alumina. It found that there generally exist three regions of dislocation and twin systems in the scratched alumina. The first region contains five independent slip systems so that macroscopic plastic flow is possible there. In the second and third regions, not all the systems can be activated, and then microcracking in the subsurface may occur easily. The distribution of these regions varies with the grain size of alumina. In the 25 μm-grained alumina all three regions appear. Thus, in this case, microcracking is difficult to avoid. In the 1 μm-grained alumina, however, only the first region appears, indicating that the material may be scratched under a real ductile mode without microcracking. A comparison shows that theoretical predictions are in good agreement with experimental observations.
Effects of Phase Equilibrium on the Oxidation Behavior of Rare-earth-doped a-sialon ceramics
Authors: Shen Zhijian , Käll Per-Olov , Nygren Mats
Published: March 2008

A series of rare-earth-(RE-)doped α-sialons (RExSi12–4.5xAl4.5xO1.5xN16–1.5x, withx= 0.40 for RE = Nd, Sm, Yb, andx= 0.48 for RE = Y) were prepared and heat-treated in air at 1350 °C for 66–727 h (3–30 days), and the variations in composition and structure with time of the formed oxide scales and matrix materials were investigated. In the oxide scales of the Nd-, Sm-, and Y-containing samples a liquid was formed, apparently in (quasi-)equilibrium with the crystalline phases cristobalite and mullite, while only crystalline Yb2Si2O7, cristobalite, and mullite were observed in the Yb sample. Apparently, the liquid plays an important role in the oxidation process. In the depleted zone, located between the scale and the matrix, the liquid attacks the matrix phases, and a process takes place in which the originally formed phases dissolve and reprecipitate as more oxygen-rich phases. In the Nd- and Sm-doped systems, where the α-sialon phase is inherently metastable at 1350 °C, an extensive α → β-sialon transformation takes place, creating still more liquid. As a consequence, the oxidation resistance of α-sialons containing Nd and Sm is much lower than those containing Y and, in particular, Yb.
The Indentation Load-depth Curve of Ceramics
Authors: Sakai M. , Shimizu S. , Ishikawa T.
Published: March 2008

The pyramidal indentation-induced surface deformation of brittle ceramics is examined on the basis of extensive test results for indentation load (P)-depth (h) curves during loading/unloading cycle. A mechanically stiff test system is essential for obtaining P-h curves acceptable and reliable for subsequent analyses. Both the loading and unloading P-h curves are expressed by quadratic functions within experimental variations for all the indenters used (Vickers, Berkovich, and Knoop). The loading curve is then related to the Meyer hardness and the unloading curve to Young's modulus by the use of semiempirical equations which enable one to estimate these moduli from the observed loading/unloading parameters. An elastoplastic constitutive equation for indentation surface deformation is theoretically derived. This equation not only predicts well the experimental observations but also gains an important physical insight into the Meyer hardness. The Meyer hardness of brittle materials is not a measure for plasticity, but an elastic/plastic parameter which significantly depends on the geometry of indenter. The concept and experimental determination of “true” hardness as a characteristic material measure for plasticity are proposed.
The Synthesis of ZnO Acicular Particles by the Hydrothermal Discharging-gas Method
Authors: Li Wen-Jun , Shi Er-Wei , Tian Ming-Yuan , Zhong Wei-Zhuo , Yin Zhi-Wen
Published: March 2008

In this paper, a new hydrothermal method—discharging-gas method—is introduced. ZnO acicular particles with the ratio of length and diameter 16: 1 are synthesized by the hydrothermal discharging-gas method using a mixed solution of Zn(CH3COO)2 with NaNO2 as precursor at 190 °C for 1 h. The effects of reaction temperature and precursor concentration on formation of acicular particles are investigated. The results show that the main factor for formation of acicular particles prepared by the hydrothermal discharging-gas method is the extent of crystallinity of ZnO powders before releasing gas.
Hot Isostatic Pressing to Increase Thermal Conductivity of Si3N4 Ceramics
Authors: Watari Koji , Hirao Kiyoshi , Brito Manuel E. , Toriyama Motohiro , Kanzaki Shuzo
Published: March 2008

Highly anisotropic Si3N4 ceramics were successfully fabricated by tape-casting of raw α–Si3N4 powders with β–Si3N4 single-crystal particles as seed particles and Y2O3 as an effective sintering aid, followed by hot isostatic pressing at a temperature of 2773 K for 2 h under a nitrogen gas pressure of 200 MPa. The microstructure consists of very large elongated grains (diameter ~10 μm; length of ~200 μm), highly oriented in the tape-casting direction. The thermal conductivity along this direction reaches 155 W m-1K-1 at room temperature, but varies significantly between room temperature and 1273 K. This thermal conductivity is closely related to (1) formation of extremely large elongated β–Si3N4 grains with a reduced amount of crystal defects due to the high-temperature firing and to (2) orientation of β–Si3N4 grains due to addition of seed particles and to tape-casting.
Control of Cobalt Nanoparticle Size by the Germ-growth Method in Inverse Micelle System: Size-dependent Magnetic Properties
Authors: Lin X. M. , Sorensen C. M. , Klabunde K. J. , Hajipanayis G. C.
Published: March 2008

Control of Co particle size was archived by a germ-growth method during inverse micelle synthesis. Magnetic coercivity and blocking were both a function of the particle size, which ranged from 38 to 88 Å. Interparticle dipolar interaction was proven to be important in order to interpret the magnetic properties for large-size particles.
Characterization of Nanocrystalline γ–Fe2O3Prepared by Wet Chemical Method
Authors: Ennas G. , Marongiu G. , Musinu A. , Falqui A. , Ballirano P. , Caminiti R.
Published: March 2008

Homogeneous maghemite (γ–Fe2O3) nanoparticles with an average crystal size around 5 nm were synthesized by successive hydrolysis, oxidation, and dehydration of tetrapyridino-ferrous chloride. Morphological, thermal, and structural properties were investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and x-ray diffraction (XRD) techniques. Rietveld refinement indicated a cubic cell. The superstructure reflections, related to the ordering of cation lattice vacancies, were not detected in the diffraction pattern. Kinetics of the solid-state phase transition of nanocrystalline maghemite to hematite (α–Fe2O3), investigated by energy dispersive x-ray diffraction (EDXRD), indicates that direct transformation from nanocrystalline maghemite to microcrystalline hematite takes place during isothermal treatment at 385 °C. This temperature is lower than that observed both for microcrystalline maghemite and for nanocrystalline maghemite supported on silica.
Deposition of Epitaxial Titanium Carbide Films on MgO(001) and 6H–SiC(0001) by Coevaporation of Ti and C60
Authors: Norin Lars , Lu Jun , Jansson Ulf , Malm Jan-Olle
Published: March 2008

Epitaxial films of TiC1-x (0.15 < x < 0.50) were deposited on MgO(001) and 6H–SiC(0001) at 250 and 400 °C by coevaporation of C60 and Ti. Films deposited on MgO(001) were single-crystalline down to deposition temperatures of at least 250 °C as determined by x-`ray diffraction (XRD), low energy electron diffraction (LEED), and transmission electron microscopy (TEM). Films deposited on 6H–SiC(0001) were also epitaxial at 250 °C, but TEM showed a columnar microstructure due to the occurrence of twinned domains in the [111] growth direction normal to the substrate.
Interface Characterization of AlN/TiN/MgO(001) Prepared by Molecular Beam Epitaxy
Authors: Ma X. L. , Shibata N. , Ikuhara Y.
Published: March 2008

The AlN/TiN/MgO(001) interfaces, prepared by molecular beam epitaxy, have been characterized by cross-sectional high-resolution electron microscopy (HREM). The thin TiN buffer layer, with the thickness of 40 nm, is epitaxially grown on the MgO(001) substrate. Owing to the same structure-type as well as the small mismatch of their lattice parameters, the growth is governed by the parallel orientation relationship of (001)TiN||(001)MgO, (010)TiN||(010)MgO, and (111)TiN||(111)MgO. Two kinds of processes of the hexagonal AlN epitaxial growth on the as-received TiN(001), differed by the (0001)AlN plane parallel to, and the (1012) plane approximately parallel to the MgO substrate surface, respectively, are identified, and within them, several cases are classified which are based on the consideration of crystallographic symmetry. Theoretical calculations based on the geometrical model that was recently proposed and applied to a number of epitaxial systems have been carried out to rationalize these observations.
Sol-gel Processing and Characterization of Alkaline Earth and Rare-earth Fluoride Thin Films
Authors: Tada Munehiro , Fujihara Shinobu , Kimura Toshio
Published: March 2008

Alkaline earth and rare-earth fluoride thin films were prepared on silica glass substrates by a sol-gel process using trifluoroacetic acid (TFA) as a fluorine source. Homogeneous solutions were obtained by stirring a mixture of alkaline earth or rare-earth metal acetates, TFA and H2O, dissolved in isopropanol. The solutions were spin-coated and heated at 300–800 °C. The fluoride thin films were obtained by heat treatment around 400 °C in air. The crystallization behavior, the surface morphology, and the optical properties of the films depended on the heating temperature as well as the chemical species of the metal ions.
Characterization and Optical Investigation of Diamondlike Carbon Prepared by Electron Cyclotron Resonance Plasma
Authors: He Xiao-Ming , Lee S-T. , Bello I. , Cheung A. C. , Li W. Z. , Chiu D. S. , Lam Y. W. , Lee C. S. , Leung K. M. , Zhou X. T.
Published: March 2008

Diamondlike carbon (DLC) films have been prepared on radio-frequency (rf) biased substrates maintained at low temperature (∼60 °C) using electron cyclotron resonance CH4 –Ar plasma. The structures of the resultant films were characterized by Fourier transform infrared (FTIR), Raman, and ultraviolet/visible (UV/VIS) spectrometry. The studies revealed that the deposited structures were DLC films with sp3/sp2 bond hybridization, extremely high hardness (>3000 kgf/mm2), and high electrical resistivity (up to 1014 Ω cm). The DLC films deposited on colorless (transparent) polymer plastics were examined to determine visible light transparencies and optical bandgaps. The results indicate that electron cyclotron resonance (ECR) plasma processing with low negative rf bias, low deposition temperature, and suitable CH4/Ar gas composition can form optically visible light transparent and hard protective DLC films on polymer plastic surfaces.
The Effect of Heat Treatment on the Corrosion Behavior of Amorphous Mg–Ni–Nd Alloys
Authors: Kam C. H. , Li Y. , Ng S. C. , Wee A. , Pan J. S. , Jones H.
Published: March 2008

The effect of heat treatment on the corrosion behavior of seven amorphous melt-spun Mg–Ni–Nd alloys containing 10–20 at.% Ni and 5–15 at.% Nd has been studied. Hydrogen evolution testing was used to determine the dissolution rate of the heat-treated specimens immersed in a 3% NaCl solution saturated with Mg(OH)2. The dissolution rates of the partially crystallized specimens were found to be lower than those of the untreated specimens, while the fully crystallized specimens exhibited marked deterioration of corrosion resistance. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies on the heat-treated specimens revealed precipitation of Mg3Nd, Mg12Nd, and Mg2Ni phases during the crystallization. TEM results show that the partially crystallized structure consists of uniform dispersion of either Mg3Nd or Mg2Ni in the amorphous matrix. In contrast, multiple phases precipitate in the fully crystallized specimen.
Crystalline Morphologies of Polychloroprene Thin Films as Revealed by Transmission Electron Microscopy Observation
Authors: Shimizu Toshiki , Tsuji Masaki , Kohjiya Shinzo
Published: March 2008

Thin films of polychloroprene (CR; Neoprene-W) were made by casting its solution (2.0 wt%) in benzene onto the water surface, and some of them were stretched by a desired amount of strain (ε) in their “molten” state. The specimens thus prepared were then crystallized and examined by transmission electron microscopy. Morphological observations in bright- and dark-field imaging modes and selected-area electron diffraction analysis revealed directly that filamentous entities observed in the bright-field image are the edge-on lamellar crystals. It was, therefore, confirmed that the morphological results obtained from the thin specimens of CR without any electron staining are basically in accord with those reported so far for the OsO4-stained thin films of CR.
Effect of Temperature and Vapor-phase Encapsulation on Particle Growth and Morphology
Authors: Ehrman Sheryl H. , Aquino-Class Maria I. , Zachariah Michael R.
Published: March 2008

The effect of in situ vapor phase salt-encapsulation on particle size and morphology was systematically investigated in a sodium co-flow/furnace reactor. The temperature of the furnace was varied, and the primary particle size and degree of agglomeration of the resulting silicon and germanium particles were determined from transmission electron micrograph images of particles sampled in situ. Particle size increased with increasing temperature, a trend expected from our understanding of particle formation in a high-temperature process in the absence of an encapsulant. Germanium, which coalesces faster than silicon, formed larger particles than silicon at the same temperatures, also in agreement with observations of particle growth in more traditional aerosol processes. At the highest temperatures, unagglomerated particles were formed, while at low temperatures, agglomerated particles were formed, with agglomerate shape following the shape of the salt coating.
Effects of thermal annealing on the dielectric properties of Pb(Zn1/3Nb2/3)O3-based ceramics
Authors: Xia Feng , Yao Xi
Published: March 2008

Pb(Zn1/3Nb2/3)O3-based ceramics were thermally annealed at 700–900 °C for 4 h. Both the relative dielectric constant and dissipation factor in the vicinity of transition temperature were increased when the specimens were thermally annealed at 700–900 °C, but the diffusion factor was decreased. After thermal annealing, the maximum dielectric constant Km was increased from about 11,000 to 26,000. These phenomena can be related to the domain wall motion and the elimination of internal stress.
Synthesis of large-size β–Si3N4 crystals
Authors: Furuya K. , Matsuo K. , Munakata F. , Akimune Y. , Ye J. , Yamamoto Y. , Ishikawa I.
Published: March 2008

Large-sized β–Si3N4 crystals up to 10 mm in length and 0.3 mm in diameter with low impurity concentration are successfully grown from silicon melt in a nitrogen atmosphere. By controlling the concentration of impurities in the silicon melt, a new kind of β–Si3N4 crystal, that is, a transparent coloring one with an absorption edge around a wavelength of 520 nm, is obtained.
Texture analysis and microstructural features in YBa2Cu3O6+x zone-partial-melted samples with Y2BaCuO5 additions
Authors: Cabré R. , Martínez E. , Gavaldá Jna. , Solé R. , Massons J. , Rillo C. , Aguiló M. , Díaz F.
Published: March 2008

Rod-shaped samples of YBa2Cu3O6+x (Y123) with different contents of Y2BaCuO5 (Y211) are textured by the partial-zone melting method in order to produce single-domain specimens. The microstructure and magnetic properties of the samples are analyzed as a function of the Y211 initial addition. Y211 precipitates are more homogeneously distributed and smaller, and the superconducting properties of the sample also improve, so when the initial content of Y211 increases, Jc values are high. Texture analysis is carried out by the x-ray pole figure technique.
Effects of inorganic components on the mechanical properties of inorganic-organic hybrids synthesized from metal alkoxides and polydimethylsiloxane
Authors: Yamada Noriko , Yoshinaga Ikuko , Katayama Shingo
Published: March 2008

Inorganic-organic hybrids (M–O–PDMS hybrids) have been synthesized from silanolterminated polydimethylsiloxane (PDMS) and inorganic sources of Al(O–sec–C4H9)3, Ti(OC2H5)4, and Ta(OC2H5)5. The molar ratio of M(OR)n/PDMS and the inorganic component derived from the different metal alkoxides were found to influence the structure and mechanical properties of the hybrids. Differential scanning calorimetry (DSC) measurements showed that the interaction between the inorganic component and PDMS increased in the order Al–O–PDMS < Ta–O–PDMS < Ti–O–PDMS hybrid. The stress-strain experiments revealed that the mechanical properties of the M–O–PDMS hybrids differed by the inorganic component, reflecting the network structure and strength of the interaction between the inorganic component and PDMS.
High-resolution x-ray diffraction study of In0.25Ga0.75Sb/InAs superlattice
Authors: Vigliante A. , Homma H. , Zborowski J. T. , Golding T. D. , Moss S. C.
Published: March 2008

An In0.25Ga0.75Sb/InAs strained-layer superlattice, grown by molecular-beam epitaxy (MBE) on a GaSb[001] substrate, has been characterized by four-circle x-ray diffractometry. This system, proposed by Maliot and Smith for ir detection application, is challenging because of the two group V species and the likelihood of cross-incorporation of the different elements during growth, leading possibly to interdiffusion and thus, to a more diffuse interface. High-resolution x-ray diffraction (XRD) profiles were obtained about several reciprocal lattice points in order to extract a reliable set of structural parameters. The profiles were then successfully modeled by computer simulation. The presence of many sharp higher-order satellite reflections in the XRD profiles is a measure of the high quality of the superlattices. The normal and lateral structural coherence was also measured and will be discussed.
Synthesis of Fe-rich Fe–Al nanocrystalline solid solutions using ball milling
Authors: Jiang H. G. , Hu H. M. , Lavernia E. J.
Published: March 2008

The synthesis of nanocrystalline Fe, Fe–4 wt% Al, and Fe–10 wt% Al solid solutions by SPEX ball milling has been studied. The microstructural evolution during ball milling, as well as subsequent heat treatment, has been characterized. The results demonstrate that ball milling promotes the formation of αFe–4 wt% Al and αFe–10 wt% Al solid solutions by reducing the activation energy of these alloys and generating thermal energy during this process. For Fe–10 wt% Al powders milled for various time intervals up to approximately 20 min, the FeAl intermetallic compound is formed. For alloys annealed at temperatures ranging from 600 to 1000 °C, the addition of 10 wt% Al to Fe significantly enhances the thermal stability of the nanocrystalline Fe–Al alloys. Interestingly, the addition of Al within the range of 4–10 wt% seems to have little effect on the thermal stability of these alloys annealed under the same conditions. Also, the thermal stability improves for alloys milled in air as opposed to those processed using Ar.
Prediction of new additives for galvanizing process by the properties of their constituent chemical elements
Authors: Jin HongMei , Li Yi , Wu Ping
Published: March 2008

Chemical element properties are generally classified in six groups: size, atomic number, electrochemical factor, valence-electron, cohesive energy, and angular valence-orbital. It is well known that some bulk properties of materials, like electrical conductivity and heat capacity of metals, may be interpreted in principle based on their constituent chemical element properties. In this study, effects of additives in galvanizing have been correlated to the chemical element properties of the additives. By screening all chemical elements (in the periodic table of elements) with this model, new additives, like Ca, Sc, Ge, Sr, and Y, have been predicted to reduce the steel weight loss in galvanizing. This model may also help to design new alloys as additives.
A new method for the production of a molybdenum-zirconia cermet
Authors: Lukaniuk Coral M. , Schwartz Lorne D. , Etsell Thomas H.
Published: March 2008

A novel method was studied for producing a ceramic-metal matrix composite (cermet) of Mo metal and zirconia powder. The first step was to precipitate dissolved molybdenum from solution onto activated zirconia powder. The molybdenum plated out on the zirconia as molybdenum hydroxide. Next, the coated powders were heated in a tube furnace under hydrogen gas to reduce the molybdenum hydroxide to metallic molybdenum. Finally, the powders were pressed and sintered into cermet pellets. The Mo coatings were 1.5 to 4.2 μm thick and very uniform, enabling the particles to be sintered together. The sintered pellets had superb electrical conductivity (less than 1 ohm of resistance).
The effects of nonhydrostatic compression and applied electric field on the electromechanical behavior of poled lead zirconate titanate 95/5–2Nb ceramic during the ferroelectric to antiferroelectric polymorphic transformation
Authors: Zeuch D. H. , Montgomery S. T. , Holcomb D. J.
Published: March 2008

We conducted hydrostatic compression and constant-stress-difference experiments, with and without an applied electric field, on poled, niobium-doped lead zirconate titanate ceramic. The objective was to quantify the effects of nonhydrostatic stress and electric field bias on electromechanical behavior of the ceramic during the ferroelectric, rhombohedral → antiferroelectric, orthorhombic phase transformation. Increasing stress difference (shear stress) decreases the mean stress at which the transformation occurs. Increasing shear stress also retards the rate of transformation, causing reductions in both the rate of charge release and peak voltage attained during depoling. Application of the electric field bias slightly increases the transformation pressure for poled ceramic. Previously, we showed that under nonhydrostatic stress, the transformation took place in unpoled ceramic when the maximum compressive stress equalled the hydrostatic pressure at which the transformation would otherwise occur. This simple stress criterion does not apply to poled ceramic. However, poled material has a preferred crystallographic orientation and mechanical anisotropy, whereas unpoled ceramic is isotropic. We present a qualitative model for the transformation under nonhydrostatic stress-related to that anisotropy, which resolves these seemingly disparate observations.
Synthesis of anorthite by the Pechini process and structural investigation of the hexagonal phase
Authors: Hong Seong-Hyeon , Young J. Francis , Yu Ping , Kirkpatrick R. James
Published: March 2008

Stoichiometric CaAl2Si2O8 gels prepared by the Pechini process crystallize to triclinic anorthite via an intermediate, previously unknown pseudohexagonal phase. Hydrothermal treatment of this pseudohexagonal phase at 350 °C transforms it to hexagonal anorthite. These combined processes produce the hexagonal phase via a low-temperature, chemical route in contrast to the conventional high-temperature melting and crystallization method. Powder x-ray diffraction data and nuclear magnetic resonance (NMR) spectra of the hexagonal anorthite agree well with the published structure. They indicate a high degree of tetrahedral Si/Al ordering within the layers, but long-range disorder in the average structure due to (001) stacking faults present between the layers.
Properties of BaBi2Ta2O9 thin films prepared by chemical solution deposition technique for dynamic random-access memory applications
Authors: Foschini C. R. , Joshi P. C. , Varela J. A. , Desu S. B.
Published: March 2008

We report on the properties of BaBi2Ta2O9 (BBT) thin films for dynamic random-access memory (DRAM) and integrated capacitor applications. Crystalline BBT thin films were successfully fabricated by the chemical solution deposition technique on Pt-coated Si substrates at a low annealing temperature of 650 °C. The films were characterized in terms of structural, dielectric, and insulating properties. The electrical measurements were conducted on Pt/BBT/Pt capacitors. The typical measured small signal dielectric constant and dissipation factor, at 100 kHz, were 282 and 0.023, respectively, for films annealed at 700 °C for 60 min. The leakage current density of the films was lower than 10−9 A/cm2 at an applied electric field of 300 kV/cm. A large storage density of 38.4 fC/μm2 was obtained at an applied electric field of 200 kV/cm. The high dielectric constant, low dielectric loss and low leakage current density suggest the suitability of BBT thin films as dielectric layer for DRAM and integrated capacitor applications.
Si3N4–SiC–Y2O3 ceramics derived from yttrium-modified block copolymer of perhydropolysilazane and hydroxy-polycarbosilane
Authors: Iwamoto Yuji , Kikuta Ko-ichi , Hirano Shin-ichi
Published: March 2008

A polymeric precursor for the Si3N4–SiC–Y2O3 ceramic system was synthesized by block copolymerization of perhydropolysilazane (PHPS) with hydroxy-polycarbosilane (PCS-OH), followed by chemical modification with yttrium methoxide. Fully dense Si3N4–SiC–Y2O3 ceramics were successfully synthesized by pyrolysis of the polymeric precursor at 1000 °C, followed by hot pressing at 1800 °C in N2. The resulting ceramics revealed that β–SiC particles were dispersed in a size range of about 10–600 nm, and a large amount of β–SiC submicron particles were segregated at the β–Si3N4 matrix grain boundaries. It was found that the yttrium-modified block copolymer of PHPS and PCS-OH yielded unique binary ceramics composed of β–SiC–Y2O3 and β–SiC nanoparticle-dispersed Si3N4–Y2O3.
Synthesis of amorphous boron nitride from the molecular precursor ammonia-monochloroborane
Authors: Ketchum Douglas R. , DeGraffenreid Allison L. , Niedenzu Philipp M. , Shore Sheldon G.
Published: March 2008

Ammonia-monochloroborane, NH3BH2Cl, has been synthesized from the reaction of ammonia-borane with HCl in Et2O. Decomposition of the solid under NH3 to 600 °C produced amorphous BN in 97% yield. The 11B magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectrum of the amorphous BN is indicative of boron in the same environment as in hexagonal BN. Subsequent pyrolysis of the amorphous BN to 1000 °C produced turbostratic BN. Pyrolysis of NH3BH2Cl under vacuum to 1100 °C led to the formation of turbostratic BN as confirmed by x-ray diffraction (XRD) analysis. Gas evolution during this pyrolysis confirmed that the precursor loses H2 and HCl.
Fabrication of undoped near-monophase Ba2Ti9O20 via rapid thermal processing
Authors: Lin Wen-yi , Speyer Robert F.
Published: March 2008

Rapid thermal processing of BaTiO3 and TiO2 pressed powders at 500 °C/min to 1250 °C for 2 h in an infrared furnace resulted in a mixture of Ba2Ti9O20, BaTi4O9, and TiO2. Further heat treatment at 1390 °C led to 96 vol% phase-pure Ba2Ti9O20 from an initial mixture devoid of any dopant. Heat treatment at rates decreasing to 5 °C/min facilitated agglomeration of TiO2. This, in turn, increased the diffusion distance required for reaction of BaTi4O9 and TiO2 to form Ba2Ti9O20.
Face-centered-cubic titanium: An artifact in titanium/aluminum multilayers
Authors: Bonevich J. , van Heerden D. , Josell D.
Published: March 2008

The present investigation is the first comprehensive comparative study of x-ray diffraction (XRD) and transmission electron microscopy (TEM) results to address the important issue of fcc Ti formation in nanoscale multilayers. Ti/Al multilayers with 7.2 and 5.2 nm composition modulation wavelengths were studied by reflection and transmission XRD as well as transmission electron diffraction (ED), high-resolution TEM, and energy-filtered TEM. Previous reports have claimed deposition of fcc Ti in multilayer systems. Our results demonstrate that the Ti in Ti/Al multilayers deposits in the hcp form and that fcc Ti is merely an artifact of producing specimens for cross-sectional TEM.
Iron oxide films of a spinel structure from thermal decomposition of metal ion citrate complex
Authors: Uekawa Naofumi , Kaneko Katsumi
Published: March 2008

Iron oxide films were prepared by the polymer precursor method with alkaline metal (Li, Na, and K) ion doping. Alkaline metal ions were used to regulate the thermal decomposition process of the cation-citrate complex, that is, the precursor of the film. The spinel iron oxide films were obtained by firing the precursor with the alkaline ion doping [Na/Fe (atomic ratio) ≧ 0.2 and K/Fe (atomic ratio) ≧ 0.2] at 773 K for 5 min in air. The formation mechanism of the spinel iron oxide films was investigated by differential thermal analysis (DTA) and x-ray photoelectron spectroscopy (XPS) measurements. Formation of the carbon-iron oxide complex was observed, and this reduction atmosphere induced the formation of the spinel iron oxide films. This method gave the spinel iron oxide films of which nanostructures are controlled.
Low-temperature chemical vapor deposition of tantalum nitride from tantalum pentabromide for integrated circuitry copper metallization applications
Authors: Chen Xiaomeng , Peterson Gregory G. , Goldberg Cindy , Nuesca Gerry , Frisch Harry L. , Kaloyeros Alain E. , Arkles Barry , Sullivan John
Published: March 2008

A low-temperature (>450 °C) thermal chemical vapor deposition (CVD) process was developed for the growth of TaNxfrom the reaction of tantalum pentabromide, ammonia, and hydrogen. Studies of process reaction kinetics yielded two sequential rate-controlling steps, with an activation energy of 0.45 eV for the kinetically limited reaction regime. Additionally, a systematic design of experiments approach examined the effects of key process parameters, namely, substrate temperature, source temperature, and hydrogen and ammonia flows, on film properties. A wide CVD process window was established for nitrogen-rich amorphous TaNxwith contamination below 1 at.%. Film conformality was higher than 95% in nominally 0.30 μm, 4.5: 1 aspect ratio, trench structures.
The effects of capping barrier layers on the compositional and structural variations of integrated Pb(Zr, Ti)O3 ferroelectric capacitor having the dimension 3 × 3 μm2
Authors: Hwang Cheol Seong , Shin Ju Cheol , Lee Jae Bin , Park Jae-hoo , Cho Young Jin , Kim Hyeong Joon , Lee Sang Yung , Park Soon Oh
Published: March 2008

Structure and composition of the ferroelectric Pb(Zr, Ti)O3 layers in a capacitor of the ferroelectric random-access memory (FeRAM) device having a density of 64 k were investigated by transmission electron microscopy (TEM) together with the energy-dispersive spectroscopy (EDS) technique. The 250 nm thick PZT layer derived by the sol-gel route showed a 2–3% Pb-deficient, 3–4% Ti-deficient, and 5–7% Zr-excess composition at the top electrode interface compared to the bulk composition when they were as-fabricated. The local compositional nonuniformity became more critical as the integration process proceeded, which seriously degraded the ferroelectric hysteresis and the device yield. The major cause of the compositional variation was the outward diffusion of Pb through the capping barrier TiO2 layer during annealing at 650 °C. The AlN capping barrier layer was also not effective in suppressing the diffusion of Pb. However, the Al2O3/TiO2 double capping layer was very effective in suppressing the outward diffusion of Pb, and excellent ferroelectric characteristic was expected.
Preparation and enhanced photocatalytic oxidation activity of surface-modified CdS nanoparticles with high photostability
Authors: Han M. Y. , Huang W. , Quek C. H. , Gan L. M. , Chew C. H. , Xu G. Q. , Ng S. C.
Published: March 2008

Highly photostable CdS nanoparticles modified with an alkyl group were prepared by an improved microemulsion technique using hexanethiol as cosurfactant. The surface-modified CdS nanoparticles catalyzed the photo-oxidation of 4-chlorophenol via continuously bubbling oxygen under uv light. The photocatalytic oxidation activity of the CdS nanoparticles was enhanced due to the formation of their compact CdS cores with strong chemical surface modification by heat treatment.
The phase separation mechanism of CaO–B2O3–P2O5 in an electric field
Authors: Liu W. , Gu X. M. , Liang K. M. , Chen H. , Zheng Y. K. , Gu S. R.
Published: March 2008

The effects of an electric field on phase separation in CBP (CaOB2O3P2O5) have been studied. It was discovered that an electric field can inhibit the process of phase separation in CBP glasses. If the electric field strength is increased, the inhibiting effect will increase, too. The mechanism of phase separation in an electric field has been discussed in light of the ir spectrum of CBP glasses.
High-resolution electron microscopy investigations of stacking faults in Y1Ba2Cu3O7−δ metalorganic chemical vapor deposited thin films
Authors: Grigis Ch. , Schamm S. , Dorignac D.
Published: March 2008

New structural planar defects in Ba-deficient Y1Ba2Cu3O7−δ (YBCO) (1:1.6:3) thin films grown on NdGaO3 and SrTiO3 substrates by metalorganic chemical vapor deposition have been observed by means of high-resolution electron microscopy. The defects are associated with perturbations of the YBCO “1:2:3” stacking sequences along the c direction, which give rise to structural variants with locally “2:5:7,” “3:4:7,” or “4:6:10” cationic stoichiometries. The defects can be consistently interpreted as CuO–YO–CuO/CuO conversions or YO/BaO (BaO/YO) interconversions in the (a,b) planes and extending over a few nanometers along the c axis. Structural models based on image matching with simulations are proposed for two particular cases. It is thought that these structural imperfections can be effective sites of flux pinning.
A model for the texture development of high-Tc superconductors under an elevated magnetic field
Authors: Ferreira P. J. , Liu H. B. , Sande J. B. Vander
Published: March 2008

A theoretical model is proposed to explain the degree of texture achieved in high-Tc superconductors during melt-processing under an elevated magnetic field. The degree of grain alignment is quantified through a factor F which is defined as ranging from 0 (random alignment) to 1 (completely oriented). Intermediate values of F clearly characterize intermediate states of alignment in which there is still some tendency for the grains to align their c axes with the magnetic field. The model suggests that the enhancement in texture is primarily obtained through grain rotation during the early stages of grain growth from the liquid. At the later stages of growth, grains interact with each other, which hinders the phenomena of magnetic-field–induced grain alignment.
Structural, electrical, and optical property studies of indium-doped Hg0.8Cd0.2Te/Cd0.96Zn0.04Te heterostructures
Authors: Han M. S. , Kang T. W. , Kim T. W.
Published: March 2008

Transmission electron microsopy (TEM), Hall effect, and Fourier transform infrared (FTIR) transmission measurements were performed to investigate the structural, electrical, and optical properties of indium-doped Hg0.8Cd0.2Te epitaxial layers grown on Cd0.96Zn0.04Te (211) B substrates by molecular-beam epitaxy. The TEM measurements showed that high-quality Hg0.8Cd0.2Te epitaxial layers with interfacial abruptnesses were grown on the Cd0.96Zn0.04Te substrates. The Van der Pauw Hall effect measurements on typical indium-doped Hg0.8Cd0.2Te/Cd0.96Zn0.04Te heterostructures with a doping concentration of 6 × 1016 cm−3 at 10 K in a magnetic field of 0.5 T yielded a carrier density and a mobility of 2.2 × 1016 cm−3 and 40,000 cm2/V s, respectively. The FTIR spectra showed that the absorption edges of the indium-doped Hg0.8Cd0.2Te/Cd0.96Zn0.04Te heterostructures shifted to a shorter wavelength range than those of the undoped samples, which was caused by the Burstein–Moss effect. The FTIR spectra also showed that the transmittance intensities of the indium-doped Hg0.8Cd0.2Te/Cd0.96Zn0.04Te heterostructures increased compared with those of the undoped heterostructures, which is due to the compensation of the Hg vacancy defects by the indium atoms. These results indicate that the indium-doped Hg0.8Cd0.2Te epitaxial layers were high-quality n-type layers and that p-HgxCd1−xTe epilayers can be grown on indium-doped Hg0.8Cd0.2Te/Cd0.96Zn0.04Te heterostructures for the fabrication of HgxCd1−xTe photoconductors and photodiodes.
Photovoltaic spectroscopic study of GaN epilayers and InGaN quantum well structures
Authors: Liu W. , Li M. F. , Teo K. L. , Akutsu Nakao , Matsumoto Koh
Published: March 2008

Room-temperature photovoltaic spectroscopy was applied to study undoped GaN, n-type GaN, and InGaN quantum well structures. Clear exciton absorption was observed in the photovoltaic spectra of the undoped GaN, and polarization measurements were made to identify the exciton absorption. For the n-type GaN sample, instead of the exciton absorption we observed only bulk absorption edge, which may be due to the free carrier screening effect. For the InGaN quantum well structures, the photovoltaic spectra showed relatively complicated line shape due to the overlap of the signals from different layers. By changing the reference phase of the lock-in amplifier, we were able to suppress some of the signals and thus identify the origin of the corresponding signal.
Ordered γ-brass structures coexisting with the decagonal quasicrystal in a Ga46Fe23Cu23Si8 alloy
Authors: Ge S. P. , Kuo K. H.
Published: March 2008

In a moderately rapidly solidified Ga46Fe23Cu23Si8 alloy, a face-centered-cubic (fcc) superstructure (a = 1.78 nm) and a hexagonal superstructure (ahex = 2.18 nm and chex = 0.77 nm), based on the same body-centered-cubic (bcc) γ-brass structure (a = 0.89 nm), were found—by means of micro-area electron diffraction—to coexist with the decagonal quasicrystal. The fcc superstructure is probably similar to one of the F-centered-γ-brass structure and has a parallel orientation relationship with the bcc fundamental structure. The hexagonal superstructure has its (001) parallel to the (111) of the bcc γ-brass structure and its chex = abcc[111]/2, and their lattice correspondence relationship has been derived. Electron diffraction evidence is presented to show that these two superstructures are possibly crystalline approximants of the decagonal quasicrystal.
Evolution of martensitic transformation in Cu–Al–Ni shape memory alloys during low-temperature aging
Authors: Recarte V. , Pérez-Sáez R. B. , Nó M. L. , Juan J. San
Published: March 2008

The effect of thermal aging at 473 K on martensitic transformation characteristics have been studied in the Cu–Al–Ni shape memory alloys. An increase of martensitic transformation temperatures as a result of aging has been observed. Furthermore, the martensitic transformation shows an evolution with aging time from a single β3 ⇒ β′3 structural transformation to a β3 ⇒ γ′3 + β′3 transformation. Using internal friction and thermoelectric power measurements, as well as specific thermal treatments, it has been determined that the mechanism responsible for this evolution is an increase in the degree of order, thus rejecting the participation of a γ1 precipitation process. Finally, the increase of order at the next nearest neighbors has been established as the main factor responsible of the evolution of the martensitic transformation characteristics.