bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTAn 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTStructural 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

ABSTRACTGas 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

ABSTRACTA 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

ABSTRACTAll 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

ABSTRACTA 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

ABSTRACTWe 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

ABSTRACTThe 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

ABSTRACTNanocrystalline 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

ABSTRACTWe 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

ABSTRACTPowders 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

ABSTRACTAn 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

ABSTRACTThe 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

SUMMARYA 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

ABSTRACTFinite 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

ABSTRACTThe 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

ABSTRACTMoSi2 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

ABSTRACTIn 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

ABSTRACTFilms 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

ABSTRACTHigh-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

ABSTRACTIn 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

ABSTRACTTo 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

ABSTRACTSingle 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.