bluuebunny/crossref_metadata_2025 huggingface dataset:
Sintering Process and Mechanical Properties for Oxide-Based Nanocomposites
Authors: Niihara Koichi , Nakahira Atsushi , Inoue Masahiro
Published: March 2011

Oxide-based Al2O3/SiC nanocomposites, in which the nanometer-sized nonoxide SiC particles are dispersed mainly within the matrix Al2O3 grains, were fabricated by the normal powder metallurgical methods. High resolution transmission electron microscopic observation showed that the nanometer sized SiC particles were directly bonded to the matrix Al2O3 grain without any reacting layers. The nano-sized SiC dispersions gave the significant improvement of mechanical properties such as fracture strength over 1000 MPa and no degradation of its strength up to 1000°C for Al2O3/SiC nanocomposites, was observed. The sintering process and the correlation between mechanical properties and micro/nanostructure will be discussed for this nanocomposite.
Amorphization at the Metal-Ceramic Interface in Nb – Al2O3 Composite Through Extensive Interphase Diffusion
Authors: Ray Abhijit , Samanta Shyam K.
Published: March 2011

A novel, low temperature and pressureless bonding technique has been developed to fabricate Al2O3 coated Nb composite. The nature of the interface bond has been characterized by extensive electron microscopic investigation, and a phenomenological model has been developed to explain the mechanism of bond formation. In the present technique a suspension (in distilled water) of fine Al2O3 powder (mean particle size of 0.2μm) was applied on polished and cleaned Nb blocks. The coatings were air dried and the coated metals were heat treated at 1100°C to achieve bonding between the ceramic and the metal. The process was carried out in an argon atmosphere. To reduce the oxygen impurity content in argon, the gas was passed over Mg turnings at 300°C before its entry into the bonding apparatus. Control of oxygen impurity in the bonding atmosphere in conjunction with the use of fine ceramic particles led to enhancement of interfacial diffusion. Scanning electron microscopy of the bonded specimens showed a consolidated layer in the ceramic phase close to the metal-ceramic interface. Transmission electron microscopy of the metal-ceramic interfacial region rOevealed a distribution of Al2O3 particles in an amorphous phase containing varying amount of Al, Nb, and 0. Prior treatment with Mg was to reduce the oxygen impurity content below the equlibrium oxygen partial pressure (at 1100°C) of Al2O3. This would result in loss of oxygen from the surface of the ceramic particles. Thus a region, with high concentration of 0= vacancy would form along the surfaces of the particles. As a result of excessive oxygen depletion, further continuation of this process would lead to degeneration of the crystal structure of the regions along the surfaces of the Al2O3 particles. These regions along the Al2O3 particle surfaces may then act as easy diffusion paths for Nb. Extensive diffusion of the metal into the ceramic phase along these paths would lead to the formation of an amorphous phase along the ceramic particle surfaces. Eventually, this phase will occupy the voids in between the ceramic particles, that are close to the metal-ceramic interface, and thus bond them together with the metal.
Diffusion of Carbon Monoxide in Metalorganic thin Films Derived from Titanium Alkoxide Carboxylates
Authors: Gagliardi Charles D. , Dunuwila Dilum , Chang C. K. , Berglund Kris A.
Published: March 2011

The diffusion of carbon monoxide into thin, transparent, porous film media is studied by doping the film with an iron porphyrin and spectroscopically monitoring the chemical interaction between the reduced iron porphyrin and the diffusing solute. The films are spin-cast from metal alkoxide carboxylates. Both optical absorption and resonance Raman spectroscopies have been used to study the porphyrin-doped film and the diffusion process.

The studies yield information on the effective pore size and homogeneity of the materials, and show that redox chemistry can be performed on incorporated metallo-porphyrins. This investigation also demonstrates the usefulness of porphyrin-doped films as chemical sensors, showing a sensitivity below 70 ppb to aqueous carbon monoxide.
Raman and Surface Enhanced Raman Spectroscopy of Titanium Carboxylates
Authors: Van Vlierberge-Torgerson Beatrice A. , Dunuwila Dilum , Berglund Kris A.
Published: March 2011

Porous stable metal-organic films can be processed under mild conditions by the hydrolysis of carboxylic acid and titanium isopropoxide mixtures. It is of importance to establish the structure of such materials. Raman spectroscopy is a useful technique in determining structural changes in titanium isopropoxide carboxylate solutions, but weak scattering does not allow for study of thin films unless surface enhancement is used. In an attempt to elucidate the relationship between coating solutions and the final structure of a cast film, we discuss Raman spectra of precursor solutions in a variety of conditions.
Synthesis and Characterization of Organic Dye Doped Silica Glasses
Authors: Lee Ilzoo , Covino Josephine , Seltzer Michael D.
Published: March 2011

The sol-gel process was used to incorporate organic dyes including Rhodamine 6G (Rh6G), 2-(4-pyridyl)-5-(4-phenyl) oxazole (4PyPO) and the n-methyl tosylate salt of 2-(4-pyridyl)-5-(4-methoxy phenyl)oxazole (4PyMPO-MePTS) in silica gel. Thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) analysis of the dye doped gels showed that the gel structure loses the adsorbed water molecules from room temperature to 150°C and decomposition of the dye molecules followed at the higher temperature. Absorption and emission of the dyes in the sol-gel glass matrix were also studied and compared with the results of the dyes in alcohol solution. The environments of the dye in silica were different than in alcohol solution.
The Effect of Ultrasonic Radiation on Gelation and Properties of Ormosils
Authors: Monta Kazuki , Hu Yi , Mackenzie John D.
Published: March 2011

Ultrasound has been applied to organically modified silicates (ORMOSILs) solutions during gelation. A series of silica and polydimethylsiloxane (PDMS) composites have been prepared by the sol-gel method. Tetraethoxysilane (TEOS), PDMS, water and a HC1 catalyst were mixed and exposed to 20 kHz ultrasonic radiation under different conditions. Ultrasonic radiation made it possible to obtain wet gels in 5 to 30 min. without solvent (e.g. alcohol, and THF). And exothermic reaction was observed due to hydrolysis and polycondensation of TEO S. The reaction process was examined by liquid state 29Si NM R. Densities of obtained sono-ORMOSILs were observed to be higher than those produced by ordinary processes. Some sono-ORMOSIL samples demonstrated extremely low porosity and low specific surface areas.
Hypervalent Siliconate Materials. Synthesis and Characterization of Novel Ladder and Network Ionomers
Authors: Shea Kenneth J. , Loy Douglas A. , Small James H.
Published: March 2011

The first representatives of novel materials that contain five- and six-coordinate anionie silicon are reported. Linear (or cyclic) ionomers incorporating pentacovalent siliconate were synthesized by condensation of 1,2,4,5-tetrahydroxybenzene (THB) with alkyl and aryl trialkoxysilylanes. Network ionomers that incorporate pentacovalent siliconates were formed from THB and alkyl and aryl bistrialkoxysilanes. In addition, network ionomers with hexacoordinate silicon result from condensation of TEOS and THB. Spectroscopie evidence is presented to verify the identity of the novel structural features of these materials.
Multifunctional (Meth)Acrylate Alkoxysilanes a New Type of Reactive Compounds
Authors: Wolter H. , Glaubitt W. , Rose K.
Published: March 2011

A new class of (meth)acrylate substituted alkoxysilanes has been developed. These are synthesized by addition of the H-S- or H-Si-unit of thiosilanes (e.g. HS- (CH2)3-SiCH3(OCH32)or hydrosila-nes to one (meth) acrylate C=C bond of commercially available di-, tri-, tetra- or penta-(meth)acrylate compounds. The alkoxysilyl groups allow the formation of an inorganic Si-O-Si-network by a hydrolysis and polycondensation reaction (sol-gel process), and the (meth)acrylate groups are available for thermally or photochemical ly induced organic polymerisation. The elegant procedure for the synthesis of a wide variety of multifunctional alkoxysilanes and the preparation of optical lenses will be discussed.
Multifunctional Acrylate Alkoxysilanes for Polymeric Materials.
Authors: Rose K. , Wolter H. , Glaubitt W.
Published: March 2011

Multifunctional acrylate alkoxysilanes synthesized from commercial acrylate compounds and mercapto-substituted alkoxysilanes were used as precursors in the development of materials for various purposes. The alkoxysilyl groups are available for the construction of an inorganic backbone by the sol-gel process, and the acrylate groups for building an organic polymeric matrix by thermal or photochemical curing.

Tailoring the material properties is achieved by use of specific molecular structures and functionalities within the monomeric compounds. Linear and branched structural units influence the mechanical properties (modulus of elasticity, abrasion resistance, flexural strength). Rapidly UV-cured materials have been prepared for use as primary or secondary coatings for silica optical fibres with improved adhesion under humid conditions. Further organic modification results in polymers which can be used for manufacturing lenses of high optical quality. Preliminary attempts to draw fibres have also been successful.
Chemically Designed, UV Curable Polycarbosilane Polymers
Authors: Thorne Kevin J. , Johnson Stephen E. , Zheng Haixing , Mackenzie John D. , Hawthorne M. F
Published: March 2011

To prepare new polycarbosilane polymer precursors with high solubility and the capability of UV cross-linking, commercial polycarbosilane was modified by a chemical route. These modifications involved AlCl3 catalyzed chlorination reactions of polycarbosilane's Si-H bonds. The resultant Si-Cl bonds were substituted by a reaction with sodium acetylyde to form Si-C=CH ligands. These ligands are suitable for controlled, free radical initiated cross-linking of the polycarbosilane polymers. The increase in molecular weight should allow for increased Tg's and the retention of polymer pre-forms. In this report, the chlorination of the polycarbosilane polymer and the substitution reactions of polycarbosilane were examined with IR, 29Si and 13C NMR spectroscopy. In addition, the retention of polymer pre-forms were analyzed after UV exposure and inert atmosphere pyrolysis.
The Role of Si-H Functionality in Oxycarbide Glass Synthesis
Authors: Singh Anant K. , Pantano Carlo G.
Published: March 2011

Silicon oxycarbide gels and glasses were synthesized using various ratios of methyldimethoxysilane and TEOS. These gels and glasses were compared with those made from methyltrimethoxysilane and TEOS. The effect of the Si-H functionality in the methyldimethoxysilane was of primary interest. Hydrolysis and condensation processes were monitored using 1H and 29Si-NMR spectroscopy. The structures and the oxycarbide fractions of the glasses, obtained after heating the gels to 900°C in flowing argon, were investigated with 29si-MAS NMR. The total carbon and silicon contents of the glasses were determined using chemical analysis. The glasses covered the range of carbon concentration from ∼1 to 15%, while the silicon concentrations were constant at about 40%. The concentration of the oxycarbide species was enhanced in the glasses synthesized with the Si-H functionality in the precursor.
Reaction Sintering Mechanism of Submicrometer Silicon Powder in Nitrogen
Authors: Yasutomi Yoshiyuki , Sobue Masahisa , Kondo Jiro
Published: March 2011

Knowing the nitridation mechanism of Si is important to obtain near-net-shape high strength reaction bonded ceramics. In this report, comparison of nitridation mechanism of small spherical Si powder produced by plasma arc method and large faceted Si powder, is discussed on the basis of microstructural analyses by SEM and TEM. From the analyses, nitrogen diffuses through the oxide film of Si powder and forms Si3N4 under the oxide films during the initial stage of sintering. At higher temperature, the oxide film transform into fine Si3N4 grains when heated to the 1350°C. The Si3N4 has morphology of hollow shell and a size, which corresponds to that of the original Si particles.
Synthesis of Advanced Ceramics in the Systems Si-B-N and Si-B-N-C Employing Novel Precursor Compounds
Authors: Baldus H.-P. , Wagner O. , Jansen M.
Published: March 2011

The reaction of Cl3Si-NH-Si(CH3)3 with BCl3 yields the novel compounds Cl3Si-NH-BCl2 and (Cl3SiNH)2-BCl. The ammonolysis of these monomeric precursors in liquid ammonia gives rise to highly crosslinked borosilicon imides. Pyrolysis of the polymeric imides in a stream of ammonia at 1250°C yields amorphous borosilicon nitrides with formal compositions of Si3B3N7 and Si6B3Nu respectively. MAS-NMR, DTA/TG, SEM and TEM investigations reveal that the resulting materials are single phase.

The reaction of the novel precursors with primary amines yields meltable and soluble polymers suitable for producing fibers or coatings. Subsequent pyrolysis in NH3 leads also to amorphous borosilicon nitride. The physical and chemical properties of the new materials will be discussed.
Design and Synthesis of Chemical Precursors to Boron Carbide
Authors: Yang Xiaoguang , Johnson Stephen , Frederick M. , Zheng Hadcing , Thorne Kevin , Mackenzie J. D.
Published: March 2011

The design of molecular and preceramic polymer precursors to boron carbide based ceramics is described. The goal was to design nonvolatile, tractable precursors to boron carbide with high ceramic yields. Molecular precursors containing carburane cages and acetylenie groups were synthesized and converted to nonvolatile, soluble preceramic polymers. Pyrolysis of these polymers gave boron carbide based ceramics in 60–70% ceramic yield. A B4C/SiC film has been fabricated from one of the polymers and the film is uniform and crack-free.
Properties of ZrO2, Gels Prepared by Controlled Chemical Modification Method of Alkoxide
Authors: Suzuki Hisao , Saito Hajime , Hayashl Hiroaki
Published: March 2011

Polymeric ZrO2 gels were prepared by the controlled chemical modification method (CCM method) of zirconium-n-propoxide. In this method, the steric hindrance by alkoxide-acetic acid chelation could be used to control the hydrolysis and condensation reaction of the zirconium alkoxide if the amount of hydrolysis water was limited. As a result, polycondensaticn occurred uniformly in the solution, forming a linear zirconoxane polymer. When the solvent evaporated, the zirconoxane polymer crosslinked with each other and formed polymeric ZrO2, gels, which were monolithic and transparent. These polymeric gels could be re-dissolved into n-butyl alcohol with acetic acid and mechanical stirring. Heating would enhance the dissolution of the gels. Using the re-dissolved gel solution, dense thin films of ZrO2, could be obtained by dip-coating procedures without many coating operations.
Optimization of Aluminum Nitride Thermal Conduchvity VIA Controlled Powder Processing
Authors: Guiton Theresa A. , Volmering James E. , Killinger Kris K.
Published: March 2011

The emergence of aluminum nitride ceramics in electronic and structural applications has been largely due to the increased availability of high quality powders. Much of the process development has been concentrated in capturing markets within the electronics industry, mainly high thermal conductivity substrates. The thermal conductivity of A1N substrates is strongly dependent on oxygen chemistry and sintering parameters. A key source of oxygen is AlN powder impurities. In this study, powders with differing oxygen contents were formulated with various Y2O3 levels. The results indicate that the distribution of sintered oxygen is strongly correlated with the relative concentration of the powder's lattice and surface oxygen. Under the sintering parameters of the analysis, optimal thermal conductivities were achieved when Y4Al2O9 was present as the grain boundary phase. As predicted, the powders with the lowest lattice oxygen concentrations exhibited the highest thermal conductivities. Hence, depending upon the surface oxygen content, different yttria levels were required for optimal thermal conductivities, i.e., higher surface oxygen contents required higher sintering additive levels than did low surface oxygen powders.
Electrochemical Synthesis of Aluminum Nitride in Liquid Ammonia Electrolyte Solutions
Authors: Wade Travis , Park Jongman , Garza Gene , Ross Claudia B. , Smith Douglas M. , Crooks Richard M.
Published: March 2011

An electrochemical method for the preparation of high purity metal nitride ceramic precursors is described. Constant current electrolysis of an electrolyte solution containing NH3 and NH4Br at an Al electrode yields a solid mixture consisting of Al(NH3)6Br3 and [Al(NH2)(NH)]n after evaporation of excess NH3. Calcination of this mixture above 800 C in flowing NH3 results in sublimation of Al(NH3)6Br3 and conversion of the ceramic polymer precursor, [Al(NH2)(NH)]n, to pure, high surface area AlN. Here we discuss some electrochemical aspects of the polymer precursor synthesis, precursor processing parameters, and materials characterization of the AlN powder before and after sintering.
Electrochemically Prepared Polymeric Precursors for the Formation of Non-Oxide Ceramics and Coatings
Authors: Zahneisen Ralph , Rüssel Christian
Published: March 2011

The electrochemical preparation of polymeric precursors and the subsequent formation of non-oxide powders, ceramics and coatings is described. The metals were anodically dissolved in an electrolyte consisting of a primary organic amine, acetonitrile as a solvent, and a tetraalkylammonium salt. This procedure led to the formation of polymeric precursor solutions. Removal of the excess organic compounds resulted in the formation of polymeric amorphous solids. Pyrolysis was carried out at temperatures in the range of 750 to 1100°C. In an atmosphere of ammonia, metal nitrides were formed, while calcination under nitrogen or argon led to carbonitrides or to carbides, depending on temperature and the metal used. Up to now, this route has been applied to Al, Ti, Zr, Cr, Ta, Mg, Ca and Y, and it is suppossed, that this route is applicable to the formation of many metal carbides and nearly all metal nitrides relevant for materials science.
Xps Study of the Nitridation Process of A Polytitanocarbosilane into Si-Ti-N-O Ceramics
Authors: Granozzi G. , Glisenti A. , Bertoncello R. , Soraru G. D.
Published: March 2011

The nitridation process of a polytitanocarbosilane, leading to the formation of a Si-Ti-N-O ceramics, has been investigated mainly by means of X-ray photoelectron spectroscopy (XPS). Ti2p spectra collected on samples fired at various stages of the transformation process clearly shown that Ti-N bonds of TiOxNy mixed units start to form at 500 °C. By increasing the firing temperature, the Ti2p peak shifts toward values typical of titanium nitride ceramics, so indicating the progressive nitrogen enrichment of the mixed units up to the formation of a TiN phase.
Structural and Thermal Investigations on Barium, Copper and Yttrium Mocvd Precursors
Authors: Gleizes Alain , Medus Dominique , Sans-Lenain Sandrine
Published: March 2011

Structural and thermal results concerning four barium tetramethylheptane-dionates, Ba(thd)2(H2)(CH3OH)3.CH3OH, amorphous Ba(thd)2, [Ba(thd)2]4, and Ba(thd)2(H2O)2(CH3OH)2, a methoxo bridged dimer of copper tetramethylheptane-dionate, [Cu(μ-OCH3)(thd)]2, and two yttrium tetramethylheptanedionates are presented and discussed.
Effect of Dopants in Vapor Phase Synthesis of Titania Powders
Authors: Kamal Akhtar M. , Pratsinis S. E. , Mastrangelo S. V. R.
Published: March 2011

Gas phase synthesis of titania from titanium tetrachloride (Ticl4) oxidation in the presence of dopants (SiCl4 and POCl3) was systematically investigated in an aerosol reactor as a function of temperature (1300–1700 K) and dopant concentration (0–15 mole % of TiCl4). The particle morphology was dramatically altered in the presence of dopants from polyhedral to spherical. Energy dispersive analysis indicated that the powders were homogeneous and that the dopants were not segregated at the surface or at the grain boundaries. Lattice parameter measurements from X-ray diffraction indicated that the dopant oxide was present in solid solution in titania. While titania synthesized in the absence of dopants was ∼80% anatase, the introduction of Si4+ and P5+ resulted in greater than 98 % anatase. The effects of foreign ions on titania phase composition, aggregate size and gas phase coalescence are explained by the creation of oxygen vacancies and reduction/enhancement of the titania sintering rates.
Preparation of Metal-Cluster-Ormosil Nanocomposites
Authors: Li Chia-Yen , Tseng Justine Y. , Lechner Cornelia , Mackenzie John D.
Published: March 2011

A series of metal-cluster-organically modified silicate, or Ormosil, nanocomposites were prepared by the sol-gel method. Each of the metals (Ag, Au, Cu, and Pt), was incorporated individually into the Ormosil matrices at various weight percents by reduction of the appropriate metal salt. The preparation for these metal-cluster doped-Ormosils is described. Ormosil proved to be an ideal matrix material, offering excellent transparency and good cracking resistance. The presence of the metal clusters inside the Ormosil matrices was detected by transmission electron microscope and verified by X-ray diffraction. Optical absorption. measurements of these nanocomposites are also presented.
Electronic Properties of Compact and Diluted Metal-Clusters by Impedance Spectroscopy
Authors: Simon U. , Schmid G. , Schön G.
Published: March 2011

All presently published electrical and optical measurements on concentrated ligand stabilized Au55-cluster samples reveal an inter-cluster tunnel-conductivity and indicate the influence of a “quantum-size-effect” (QSE) [1],[2]. However these data do not show any initials for the separation of inter- and possible intracluster effects. In the present Raper electronic intra-cluster Properties such as the electrical “conductivity” of 1nm chemical auantum dots, their relaxation frequencies and the relevant activation enthalpies as well as the respective Properties of pairs of Au55-clusters have been investigated in comparison to diluted clusters and interpreted by means of Impedance Spectroscopy. Furthermore a method to determine the number and the density of states (DOS) in the metal-core from the measuring data by means of very simple quantum-size assumptions is presented, which is compatible with both the SIMIT[3] and the existing cluster models.
Absorption Spectrum and Chemical Reactions of Colloidal Cadmium in Aqueous Solution
Authors: Gutiérrez M. , Henglein A.
Published: March 2011

A radiolysis method is described to prepare isolated cadmium particles in aqueous solution. The spectrum of these particles (narrow band at 260nm) agrees with the spectrum calculated from the optical data of cadmium. Clusters of particles absorb at longer wavelengths. Redox reactions of the particles with methyl viologen, nitrous oxide and carbon tetrachloride were also investigated. It is shown that the absorption spectrum of the particles changes during these reactions as de-clustering takes place.
Tight-Binding Calculation of the Electronic Structure of Semiconductor Nanocrystals
Authors: Lippens P. E. , Lannoo M.
Published: March 2011

We show that an empirical tight-binding approximation can be used for the determination of some electronic properties of semiconductor nanocrystals. Two different calculations based on this approximation are presented. The first calculation concerns the band-gap energy and the second one the density of states. The results are given for different II-VI compounds and compared to available experimental data.
Spectroscopy of Semiconductor Nano-Crystals at High Pressure
Authors: Schroeder John , Silvestri Markus R. , Zhao Xue-Shu , Persans Peter D. , Hwang Lih-Wen
Published: March 2011

The optical and vibrational properties of small CdSe and CdS particles embedded in a glass matrix and as a colloid have been studied as a function of pressure up to 90 kbar using Raman scattering and photoluminescence techniques. We will discuss the use of high pressure optical spectroscopy techniques, where the sample is contained in a diamond anvil.cell with optical access, to study the nature of the electronic states in semiconductor nanocrystals. Raman scattering is employed to establish the enhanced pressure stability of the wurtzite phase in the II-VI nanocrystalline composites. Photolurninescence is used to study the energies of electronic states. The wurtzite to rocksalt phase transition behavior in the nanocrystallite systems is quite different from that in the bulk material. This different behavior is attributed to a large number of defects (vacancies) in the nanocrystallite system. This work demonstrates that the main defects in the CdS glass composites are cadmium vacancies; while in CdSe Selenium vacancies exist in the conduction band. The pressure dependence of the Huang-Rhys parameter, characteristic for the strength of the electron-phonon coupling, will also be discussed for the nanocrystalline samples versus the bulk material.
Relaxation and Grain Growth Behavior of Nanocrystalline Iron
Authors: Holzer J. C. , Birringer R. , Eckert J. , Krill C.E. , Johnson W.L.
Published: March 2011

Nanocrystalline Fe has been prepared by inert gas condensation and ball milling. The kinetics of relaxation and grain growth are investigated by differential scanning calorimetry. The development of the microstructure is monitored by x-ray powder diffraction and transmission electron microscopy. Emphasis is placed on the differences observed for samples prepared by the two different techniques. We find that the kinetics of relaxation and grain growth are very sensitive to the sample preparation method. Samples with the same initial average grain size, as determined by the peak broadening in x-ray diffraction, show very different recovery behavior. The differences are discussed in terms of the estimated grain boundary energies and the initial grain size distribution obtained by the two preparation techniques.
EXAFS Studies on Nanocrystalline Materials with Doped Grain Boundaries
Authors: Boscherini F. , Haubold T. , Pascarelli S. , Mobilio S. , Gleiter H.
Published: March 2011

We present an EXAFS study of the local environment of Co dopant atoms in nanocrystalline Cu. Due to the low solubility of Co atoms in bulk Cu, these measurements yield information on the local atomic structure of grain boundaries in nanocrystalline Cu. Previous EXAFS studies on pure nanocrystalline metals have indicated an atomic arrangement in the grain boundary component exhibiting a broad distribution of interatomic spacings which differs from the atomic structure of the crystalline or glassy state. In the present investigation a significantly reduced coordination number around Co is found; also, the first shell bond length varies with dopant concentration from that typical of Co substitutional impurities in Cu to that of bulk Co. These results suggest that Co atoms substitute Cu atoms both in the disordered grain boundaries and in the lattice of the Cucrystallites and/or form Co-precipitates.
Nanosize Silicon and Gallium Arsenide Particles Left After Stopping Dissolution in Molten Glass
Authors: Liu Li-Chi , Risbud Subhash H.
Published: March 2011

Powders of pure silicon and gallium arsenide were reacted with molten silicate glass of a composition used in our prior work on CdS and CdTe quantum dots in glass [1–4]. After the Si or GaAs agglomerated particles had reacted with the melt for an hour, the material was solidified to obtain a gray-black glass. Ground powders of this glass were again mixed with additional base glass powders to dilute the concentration of the semiconductor, remelted, and cast into glass. Samples of silicon-in-glass showing green photoluminescence peaked at 530 nm were obtained. The GaAs-in-glass samples show absorption features in the optical spectra which suggest the possibility of quantum confinement.
Preparation of Quantum-Size Semiconductor-Doped Ormosils and their Optical Properties
Authors: Li Chia-Yen , Wilson Matthew , Haegel Nancy , Mackenzie John. D. , Knobbe Edward T. , Porter Cindy , Reeves Roger
Published: March 2011

An Organically-modified silicate (Ormosil) which contains 28 wt% polydimethylsiloxane and 72 wt% silica has been used as a matrix to fabricate CdS-doped glassy nanocomposites by using the sol-gel method. Samples were prepared both in bulk and film forms. High semiconductor concentrations, up to 20 wt% CdS could be obtained and the semiconductor microcrystallites were formed at temperatures much lower than that of the purely inorganic glass matrix. Preparation methods of these CdS-doped Ormosils are described. Optical behaviors of these nanocomposites under normal and intense photon influx were studied.
Nanostructures of the Product Sequence in the Decomposition of Mixed Rare Earth Hydroxycarbonate Colloidal Particles
Authors: kang Z. C. , Mckelvy M. J. , Eyring L.
Published: March 2011

The decomposition of colloidal spheres of mixed rare earth hydroxycarbonate to the oxide has been studied by three methods. a) The spheres are treated in a thermal analysis apparatus up to 1100°C and afterward successive reruns were made and specimens cooled rapidly at temperatures where intermediate or final products are formed. X-ray diffraction patterns and HREM studies were made of each sample thus produced. b) The spheres were heated to 450°C in the specimen chamber of a mass spectrometer and the gaseous decomposition products were monitored continuously. c) The colloidal spheres were introduced into the electron microscope and the decomposition followed at high resolution as evolution to the oxide was induced by the electron beam. The results are compared and contrasted.
Highly dispersed metal-clusters and -colloids for the preparation of active liquid-phase hydrogenation-catalysts
Authors: Bönnemann Helmut , Brijoux Werner , Brinkmann Rainer , Dinjus Eckard , Fretzen Rainer , Joußen Thomas , Korall Barbara
Published: March 2011

A comparison of the activities of conventionally precipitated metals on charcoal, deposited organometallic clusters and metal colloids for liquid-phase hydrogenation has been made under standard conditions in order to assess the effect of particle size. The strong SMSI-effect known for TiO2-supports was simulated on charcoal by doping the surface with small amounts of Ti(0) and subsequent oxygenation.
Residual Stresses and Resulting Damage Within Fibers Intersecting A Free Surface
Authors: Galbraith J. M. , Kallas M. N. , Koss D. A. , Hellmann J. R.
Published: March 2011

Finite element as well as indentation fracture mechanics modeling have been used to analyze the evolution of fiber damage that was observed at the ends of fibers intersecting a free surface in sapphire-reinforced TiAl matrix composites. Experimental observations indicate that, under certain conditions, surface cracks introduced during cutting will propagate along the fiber axis due to thermally-induced residual stresses. Finite element computations predict that significant thermally-induced residual tensile stresses exist near the ends of sapphire fibers which are embedded within TiAl-based matrices and are oriented normal to a free surface. Crack growth behavior induced by microhardness indentations is used to experimentally verify the FEM predictions. The results indicate that a biaxial tensile residual stress state exists near the fiber ends due to a thermal expansion mismatch. The magnitude of the residual stresses are a sensitive function of interfacial bond strength and elastic/plastic properties of the interfacial region and may be sufficient to propagate pre-existing cracks.
Mechanical Properties and Deformation Mechanisms of an A12O3 Fiber-Reinforced Nial Matrix Composite
Authors: Jeng S. M. , Yang J.-M. , Amato R. A.
Published: March 2011

The mechanical behavior of a continuous Al2O3 fiber-reinforced NiAl matrix composite was investigated. The interfacial mechanical properties were measured at room temperature using a fiber pushout test. Tensile test was conducted at room and elevated temperatures. Four-point bending creep test was also conducted at 700 °C. The key microstructural parameters controlling the mechanical behavior and fracture processes were identified. The effect of fiber surface coating on the interfacial properties and mechanical behavior of the composite was also studied.
A Perspective on MoSi2 Based Composites
Authors: Petrovic J. J. , Vasudevan A. K.
Published: March 2011

MoSi2 based composites represent an important new class of “high temperature structural silicides”, with significant potential for elevated temperature structural applications in the range of 1200–1600 °C in oxidizing and aggressive environments. The properties of MoSi2 which make it an attractive matrix for high temperature composites are described and the developmental history of these materials traced. Latest results on elevated temperature creep resistance, low temperature fracture toughness, and composite oxidation behavior are summarized. Important avenues for future MoSi2 based composite development are suggested.
The Effect of Second Phase Properties on the Compression Creep Behavior of MoSi2 Composites
Authors: Ghosh A. K. , Basu A. , Kung H.
Published: March 2011

In an effort to enhance the toughness and creep strength of MoSi2, the role of various metallic and ceramic reinforcements is being examined. In this work, the effects of an oxide, a carbide and a nitride reinforcement on the compression creep behavior of MoSi2 are explored. Variations in the deformability of reinforcements and their relative strength and flaw population appear to influence the creep strength of the composites. Refinements in grain size also improve crack tolerance of the composite during deformation at 1200°C.
Synthesis and Properties of Mo/MoSix Microlaminates Using Ion Beam Assisted Deposition
Authors: Mashayekhi A. , Parfitt L. , Kalnas C. , Jones J. W. , Was G. S. , Hoffman D. W.
Published: March 2011

Films of Mo, MoSix and Mo/MoSix (1.22<x<1.35) multilayers were formed by physical vapor deposition (PVD) and ion beam assisted deposition (IBAD) onto (100) Si, glass and graphite substrates. Ion to atom arrival rate (R) ratios for IBAD varied from 0.01 to 0.1 and film thicknesses varied from 200 to 1100 nm. The Si/Mo ratio decreased with increasing R ratio. The oxygen content of Mo films was greater than silicide films, but both decreased substantially with increasing R ratio. Ar incorporation increased with increasing R ratio to a maximum of 1 at% in Mo and 5 at% in MoSi1.22. Mo films exhibit a strong (110) fiber texture at low R ratios. At the highest R ratio, a tilting of the (110) fiber texture by 15° occurs, along with the development of a distinct azimuthal texture indicative of planar channeling of the ion beam along (110) planes. The microstructure of the multilayer consists of small Mo grains and an amorphous silicide. Average film stress in Mo films increases from tension to a maximum value of 0.63 GPa and becomes compressive with increasing normalized energy. The stress in the MoSix films decreases with increasing normalized energy and saturates at a compressive stress of -0.24 GPa at 25 eV/atom. Indentation fracture experiments using a Vickers indenter with a 300 g load show a fracture behavior that is consistent with a residual stress effect for the IBAD monolithic MoSix and microlaminate, but which is influenced by additional factors in the PVD microlaminate.
An Overview of Potential Titanium Aluminide Composites in Aerospace Applications
Authors: Larsen James M. , Revelos William C. , Gambone Mary L.
Published: March 2011

High-temperature, light-weight materials represent enabling technology in the continued evolution of high-performance aerospace vehicles and propulsion systems being pursued by the U.S. Air Force. In this regard, titanium aluminide matrix composites appear to offer unique advantages in terms of a variety of weightspecific properties at high temperatures. However, a key requirement for eventual structural use of these materials is a balance of mechanical properties that can be suitably exploited by aircraft and engine designers without compromising reliability. An overview of the current capability of titanium aluminide composites is presented, with an effort to assess the balance of properties offered by this class of materials. Emphasis is given to life-limiting cyclic and monotonic properties and the roles of high-temperature, time-dependent deformation and environmental effects. An attempt is made to assess the limitations of currently available titanium aluminide composites with respect to application needs and to suggest avenues for improvements in key properties.
Internal Stresses in TiAl Based Lamellar Composites
Authors: Hazzledine P. M. , Kad B. K. , Fraser H. L. , Dimiduk D. M.
Published: March 2011

In the in situ lamellar γ-TiAl based composites, very large elastic stresses (≈ 1GPa) would be generated at coherent interfaces between close packed planes for three reasons: the tetragonality of TiAl, the larger atomic spacing in α2-Ti3Al than in γ and the differences between thermal expansion coefficients in α2 and γ. These stresses appear to be partially relaxed by the creation of van der Merwe dislocations, diffusion across α2/γ interfaces and cracking along interfaces. Measurements of lattice parameters by Convergent Beam Electron Diffraction (CBED) reveal stresses of the order of 100MPa. The presence of these stresses and the very specific form of the resulting stress tensor are used to discuss the hard/soft mode deformation of TiAl composites.
Intermetallic/Metallic Polyphase In-Situ Composites
Authors: Johnson D. R. , Joslin S. M. , Oliver B. F. , Noebe R. D. , Whittenberger J. D.
Published: March 2011

To evaluate various in-situ reinforcement schemes, a computer controlled containerless directional solidification system has been used to produce NiAl-based polyphase composites containing up to two intermetallic phases and at least one ductile phase. Systems evaluated include Ni-Al-Cr, Ni-Al-Mo, Ni-Al-V ternary systems that form NiAl/α-refractory metal eutectics and a three phase eutectic in the Ni-Al-Cr-Nb system. Initial screening of these in-situcomposites has included morphological characterization, four point bend testing, temperature dependent yield strength evaluation and compressive creep testing. Occasional growth defects termed “banding” currently interrupt the continuity of these composite structures and limit the attainment of optimum properties. However, both the creep strength and toughness of NiAl were improved by in-situreinforcement.
Growth of YSZ and Y2O3 Films on SI(100) by Solid State Epitaxy
Authors: Wecker J. , Matthee TH. , Behner H. , Friedl G. , Samwer K.
Published: March 2011

Single crystalline YSZ and Y2O3 thin films are grown on Si(100) by e-beam evaporation. The amorphous S1O2 surface layer is removed in-situ by initially growing at low oxygen partial pressures in the case of YSZ or by first evaporating metallic Y for the growth of Y2O3. Epitaxy occurs by a solid state reaction after the SiO2 has been reduced by metallic Zr or Y. For Si/YSZ/Y2O3 the growth is cube on cube while in the case of Si/Y2O3/YSZ the oxide layers grow twinned in (110) orientation. XPS analysis and AES depth profiles reveal the reoxidation of the Si during further growth. Critical temperatures of 90 K and high current densities of 3.2×106 A/cm2 are measured on 150 nm thick YBCO films on SOS/YSZ/Y2O3 proving the excellent quality of the YBCO and the underlying buffer layers.
Structural and Magnetic Properties of RBa2Cu2NbO8(R = La, Pr, Nd)
Authors: Radousky H. B. , C. O'Brien J. , Bennahmias M. , Klavins P. , Smith C. A. , Link J. M. , Goodwin T. J. , Shelton R. N.
Published: March 2011

PrBa2Cu2NbO8(PrBCNO) is an insulating analog to the YB2CU3O7(YBCO) system, which is interesting as a thin film buffer layer in YBCO/PrBCNO/YBCO tunnel junctions as well as a potential high Tcsuperconductor if proper doping could be achieved. PrBCNO has a similar structure to PrBCO, with NbO2planes replacing the CuO chains. Single phase polycrystalline samples of RBCNO have been synthesized with R = La, Pr and Nd. Attempts to synthesize this structure with the smaller ions Y and Gd have been unsuccessful. The PrBCNO samples show a signature in the magnetization of a magnetic ordering at 12 K. No such magnetic phase transition is observed down to 2 K in the NdBCNO material.
Effect of O2 Partial Pressure on Post Annealed Ba2YCU3O7-δ Thin Films
Authors: PhUlips Julia M. , Siegal M. P. , Hou S. Y. , Tiefel T. H. , Marshall J. H.
Published: March 2011

Epitaxial films of Ba2YCu3O7-δ (BYCO) as thin as 250 å A and with Jc's approaching those of the best in situ grown films can be formed by co-evaporating BaF2, Y, and Cu followed by a two-stage anneal. These results extend the work on films > 2000 Å thick by R. Feenstra et al. [J. Appl. Phys. 69, 6569 (1991)]. High quality films of these thicknesses become possible if low oxygen partial pressure [p(O2) = 4.3 Torr] is used during the high temperature portion cf the anneal (Ta). The BYCO melt line is the upper limit for Ta. The use of low p(O2) shifts the window for stable BYCO film growth to lower temperature, which allows the formation of smooth films with greater microstructural disorder than is found in films grown in p(O2) = 740 Torr at higher Ta. The best films annealed in p(O2)=4.3 Torr have Jc values a factor of four higher than do comparable films annealed in P2=740 Torr. The relationship between the T required to grow films with the strongest pinning force and p(O2) is log independent of growth method (in situ or situ) over a range of five orders of magnitude of P(O2).
Thermoelectric and Thermomagnetic Effects in High-Temperature Superconductors
Authors: Huebener R. P. , Ri H. -C. , Gross R. , Kober F.
Published: March 2011

In the mixed state of high-temperature superconductors the dominant part of the Seebeck and Nernst effect is due to the thermal diffusion of quasiparticles and vortices, respectively. Our understanding of the Seebeck effect is based on the two-fluid counterflow model of Ginzburg and its extension to the mixed state with the presence of vortices. From the Nernst effect the transport entropy of the vortices is obtained. We summarize the recent thermoelectric and thermomagnetic experiments, paying also attention to the role of the Magnus force (Hall effect) and to the thermal fluctuation effects near TC.
YBa2Cu3O7 Thin Films on Polycrystalline Diamond Films with Buffer Layers
Authors: Cui G. , Beetz C. P. , Lincoln B. A. , Kirlin P. S.
Published: March 2011

The deposition of in-situ YBa2CU3O7-δ Superconducting films on polycrystalline diamond thin films has been demonstrated for the first time. Three different composite buffer layer systems have been explored for this purpose: (1) Diamond/Zr/YSZ/YBCO, (2) Diamond/Si3N4/YSZ/YBCO, and (3) Diamond/SiO2/YSZ/YBCO. The Zr was deposited by dc sputtering on the diamond films at 450 to 820 °C. The YSZ was deposited by reactive on-axis rf sputtering at 680 to 750 °C. The Si3N4 and SiO2 were also deposited by on-axis rf sputtering at 400 to 700 °C. YBCO films were grown on the buffer layers by off-axis rf sputtering at substrate temperatures between 690 °C and 750 °C. In all cases, the as-deposited YBCO films were superconducting above 77 K. This demonstration enables the fabrication of low heat capacity, fast response time bolometric IR detectors and paves the way for the use of HTSC on diamond for interconnect layers in multichip modules.
Vortex Dynamics and Dissipation in High Temperature Superconductors — from DC to Microwave Frequencies
Authors: Yeh N.-C. , Jiang W. , Reed D. S. , Kriplani U. , Holtzberg F. , Gupta A. , Kussmaul A.
Published: March 2011

A second-order vortex-solid melting transition in twinned Y-Ba-Cu-O single crystals is manifested by two independent types of electrical transport measurements: the electric field (E) versus current density (J) isotherms, and the ac resistivity (ρ) vs current frequency (ω) isotherms. Universal static and dynamic exponents (ν ≈ 2/3 and Ζ ≈ 3, respectively) are found for magnetic fields ranging from 1 to 90 kOe, frequencies ranging from 0 to 2 MHz, magnetic directions parallel and perpendicular to the crystal c-axis, as well as samples with and without proton irradiations. At microwave frequencies, we find that the vortex dissipation in Nd-Ce-Cu-O epitaxial films is consistent with the viscous motion of individual vortices, due to the break down of the critical scaling theory in the high frequency limit.
The Effect of Er2BaCuo5 Additions on the Microstructure and Magnetic Properties of Zone Melt Textured YBa2Cu3O6+x Wires
Authors: Balkin D. , Varanasi C. , McGinn P.
Published: March 2011

YBa2Cu3O6+x (Y-123) wires with Er2BaCuO5 (Er-211) and Y2BaCuO5 (Y-211) additions were vertically zone melted using a single element resistive furnace. The microstructure and magnetic Jc of wire segments taken from different sections of well textured wires were analyzed and compared. In both Er-211 and Y-211 doped wires the 123 plate width and the magnetic Jc decreased with increasing 211 additions. Microstructural analysis on the Er-211 doped wires confirms that Er-211 dissolves in the melt and results in the formation of a YzEr(1-z)Ba2Cu3O6+x superconducting phase upon solidification which shows improved magnetic properties over Y-211 doped wires.
A Study of Parameters that Influence Growth and Stability of the (Bi1−xPbx)2Sr2Ca2Cu3Oy Phase
Authors: Luo J. S. , Merchant N. , Maroni V. A. , Gruen D. M. , Tani B. S. , Carter W. L. , Riley G. N. , Sandhage K.H.
Published: March 2011

The growth and stability of the (Bi1-xPbx)2Sr2Ca2Cu3Oy (Bi-2223) phase contained in silver-sheathed wires has been investigated by a combination of x-ray diffraction, scanning electron microscopy, energy dispersive x-ray analysis, and transmission electron microscopy. Silver tubes loaded with Bi-2223 precursor powders were processed into filaments using established metallurgical techniques. The filaments were then heat-treated at selected temperatures (800 to 845°C) for a range of times (10 to 6000 min) in a 7.5% oxygen atmosphere. From these studies it has been possible to investigate the time-temperature-oxygen pressure domains wherein Bi2Sr2CaCu2O8 (Bi-2212) + second phases transform to Bi-2223. Fractional conversion (Bi-2212 --> Bi-2223) versus time data show good conformance to the kinetic model for a diffusion-controlled reaction at the interface between thin sheets and a fine powder or a fluid. Quenching experiments also reveal that the Bi-2223 phase is stable in a limited temperature interval between 810 and 830°C.
Metal Organic Deposition of Ybco from Neo-Decanoates
Authors: Manfredotti C. , Fizzotti F. , Boero M. , Rellecati P. , Mauro L. , Volpe P. , Andreone D.
Published: March 2011

Bulk YBCO samples have been prepared for the first time by using Metal-Organic Deposition (MOD) technique.

Solutions of Y, Ba and Cu neodecanoates have been used in order to obtain directly YBCO powders (not exactly, but approximately stoichiometric) after a back-up and a pyrolysis step at 500°C. The powders have been successively pressed and subjected to two annealing steps in order to built up the YBCO structure, to increase grain dimensions and to adjust oxygen stoichiometry. The samples, which are disk-shaped, 1 mm thick and 1 cm wide, display a sharp superconducting transition at 93 K and possess a relatively large critical current.

Diffraction patterns indicate a strong degree of orientation of (a,b) planes along the surface. The superconducting gap has been measured by SIS' tunneling with Nb and by investigation on SS' Andreev reflection.