bluuebunny/crossref_metadata_2025_split huggingface dataset:
Viscoelastic Probes of Suspension Structure
Authors: Zukoski C. F. , Goodwin J. W. , Hughes R. W. , Partridge S. J. 
Published: March 2011

ABSTRACTThe use of the high frequency elastic modulus, G∞, to probe particle interactions in weakly agglomerated, concentrated suspensions is discussed. We show that a model based on pair interaction potentials and a statistical description of pair spatial distribution yields accurate prediction of the volume fraction dependence of G∞. The use of statistical treatments of particle distributions as predicted from particle interaction potentials is found to provide insight on how surface chemistry affects the uniformity of powder compacts.
Saxs Study of Silica Sols and Gels
Authors: Orcel Gerard , Gould Robert W. , Hench Larry L. 
Published: March 2011

ABSTRACTSmall angle X-ray scattering was used to characterize the structure of sols and gels in the TMOS-MeOH-H2O-CHONH2 system. The scattering curves were analyzed in both the Porod and Guinier regions. A fractal analysis shows that the structure evolves with time and temperature from a linear type polymer to a more highly branched polymer and then towards a “particle”. However, these structural units disappear when the temperature increases above a critical value.
Growth and Structure of Fractally Rough Silica Colloids
Authors: Keefer K. D. 
Published: March 2011

ABSTRACTSmall-angle x-ray scattering measurements on partially hydrolyzed silicon tetraethoxide solutions indicate the formation of colloidal particles which have fractal structures or fractally rough surfaces. The structures and growth kinetics are consistent with chemically limited nucleation and growth of the particles from slowly generated reactive silanol species. Two dimensional computer simulations of nucleation and random growth of clusters from partially hydrolyzed monomers generate the same range of non-fractal, fractally rough and fractal clusters observed in the experiment.
Fractal Aspects of Surface Science - An Interim Report
Authors: Avnir David 
Published: March 2011

ABSTRACTThe activity in our laboratory and in collaboration with other laboratories in applying fractal geometry for the characterization of irregular surfaces and materials and for the analysis of molecular interactions with such objects are summarized in this report. Most of the studies were performed on the xerogel of silica. Various theories and experimental techniques have been employed for this purpose. They include adsorption studies, computerized image analyses in one (boundary lines), two (textures) and three (proteins) dimensions; non-radiative, Förster-type, one step electronic energy transfer (EET); small angle X-ray scattering; and analysis of chemical reactivity of fractal objects. The relation between porosity and fractal dimension has been studied by EET, by the photophysics of adsorbed pyrene and by monolayer adsorption studies. A direct method for the determination of adsorption conformations has been developed. Limitations of the fractal approach have been identified and outlined.
Structural Observations of Porous Silica Gels
Authors: Shafer M. W. , Castano V. , Krakow W. , Figat R. A. , Ruben G. C. 
Published: March 2011

ABSTRACTSilica gels were prepared by two methods; from the alkoxides under conditions where moderate degrees of crosslinking are expected and from LUDOX - alkaline silicate sols from which the alkali was subsequently removed. By selective thermal treatment from 300 to 850°C, pore diameters (excluding micropores) in the range 35Å to 400Å are seen. The pore size increased with temperature while the surface area and total porosity remained essentially constant. Extensive high resolution TEM analyses showed both colloid and polymeric structures with particle sizes between 60Å and 250Å which decreased on heating. An intra particle structure, presumably micropores of 10Å to 30Å is also seen. By using a shadow cast Pt-C replica technique, stereoimages show the particles to have a filamentry type structure.
The Role of Chemical Additives in Sol-Gel Processing
Authors: Hench L. L. , Orcel G. , Nogues J. L. 
Published: March 2011

ABSTRACTThe effect of various concentrations of formamide with and without acid catalysis on TMOS derived silica sol and gel structures and physical properties is described using a quantitative structural model. The model is based upon 29Si NMR, SAXS, Raman and FTIR spectroscopy, and an acid solubility test. Changes in chemical reactions during drying due to formamide are presented using FTIR, DSC and TGA data.
Applications of Molecular Dynamics Simulations to Sol-Gel Processing
Authors: Carofalini S. H. , Melman H. 
Published: March 2011

ABSTRACTThe molecular dynamics computer simulation technique has been used to study silicic acid and pyrosilicic acid molecules (H4 SiO4 and H6 Si 2 O7, respectively). The structure of the simulated molecules are compared to those found by molecular orbital calculations as well as structures inferred from silicate hydrates. The potentials used to simulate the molecules were also used in simulations of bulk silicates and compared with experimental data. Results indicate good correlation.
Si-O-N Ceramics From Organosilicon Polymers
Authors: Yu Yuan-Fu , Mah Tai-Il 
Published: March 2011

ABSTRACTThe preparation of new, hybrid pre-ceramic organosilicon polymers are described. These hybrid polymers were prepared by reactions of polysilazanes and polysiloxanes. Ceramic materials containing Si-O-N were obtained with high yields (∼ 80%) by pyrolyzing these new polymers at low temperatures (< 800°C). A wide range of chemical compositions and properties can be obtained by using different ratios of polysilazanes and polysiloxanes. Microstructural characterization and densification studies of these ceramic materials are presented.
The Accurate Determination of Bulk Glasses and Glass Film Compositions by Inductively Coupled Plasma-Atomic Emission Spectronmtry
Authors: Kometani T. Y. 
Published: March 2011

ABSTRACTA sequential inductivly coupled plasma-atomnic emission spectrrnetric (ICP-AES) method has been dewvloped for the cnmplete quantitative analyses of silicate glasses. B, P, Ge, and Si have been determined with 2%precisicn and accuracy in bulk glass and glass films on Si wafer substrates. Two chemical sample processing steps, dissdution in hydrofluoric acid at roam temperature and fusion in a sodium carbonate flux, were equally effective for deconposing samples without loss of volatile components. Rapid analysis for controlling glass film composition during IC process devlopment wer provided by the ICP-AES maethod. Where accurate film w~ghts were not obtainable, coatpositions wee established by complete analyses of all glass components except cxygen. The sum of the weights of components converted to their cides served as the sample weight for calculation purposes.
Physico-Chemical Characterization of Alumina Sols Prepared From Aluminum Alcoxides
Authors: Olson William L. 
Published: March 2011

ABSTRACTAlumina sols derived from aluminum sec-butoxide (Yoldas) were characterized. The distribution of the polymer sizes within the sol, determined by gel filtration chromatography (GFC), was found to be dramatically affected by small changes in the chemical processing or preparative procedure. Aging the sol at room temperature for two weeks produced no significant change in the GFC elution curves of the alumina sol. Sols with a “milky” appearance were found to exhibit a wider distribution of polymers by GFC than transparent sols. Rotary evaporation of the sol followed by redissolution of the residue was found to change the polymer size distribution described by the gel filtration elution curves. These observations coupled with 27Al NMR spectroscopy and viscometry measurements were used to elucidate the effects of process conditions and aging on the molecular structure of the sol.
Raman Spectroscopic Studies of Titanium Alkoxides Using UV Excitation
Authors: Payne Mark J. , Berglund Kris A. 
Published: March 2011

ABSTRACTThe use of Raman spectroscopy can be greatly hindered by the presence of fluorescing impurities. Even at low concentrations, fluorescence can completely obscure the Raman signal. In the current study, Raman spectra were recorded for various titanium alkoxides (ethoxide, isopropoxide, isobutoxide) as a function of concentration and laser excitation wavelength. It has been shown that fluorescence can be avoided by using uv-excitation (363.8 nm). In addition, titanium alkoxides exhibit a preresonance Raman enhancement as the excitation wavelength appreaches the UV. This result is confirmed by a uv-visible absorption spectrum of the isopropoxide.
Precipitation Kinetics of the Titanium Isopropoxide Hydrolysis Reaction
Authors: Hartel R. W. , Berglund K. A. 
Published: March 2011

ABSTRACTThe precipitation product of the titanium isopropoxide (TiPT) hydrolysis reaction was followed using photon correlation spectroscopy. This technique followed the mean size of the precipitate as the reaction progressed, as well as giving an indication of the number of particles being produced. From this analysis, the induction time for the onset of nucleation, nucleation rate (or the rate of particle production) and mean growth rate were correlated with reactant concentrations. In the concentration ranges studied, it was found that the induction time was a very strong inverse function of the reactant concentrations. Both nucleation rate and average growth rate were found to increase very rapidly as reactant concentration increased, with the TiPT concentration being more important. This reaction was also followed using absorbance spectrophotometry in the 500 to 320 nm range. After mixing of the reactants, an absorbance peak was seen between 330 and 335 nm, depending on the conditions. This peak increased slowly during the induction period and then increased rapidly after the onset of nucleation due to the increasing turbidity.
New Magnetic Materials Produced By The Sol-Gel Process: A Possibility Of Producing Exotic Devices
Authors: Kordas G. 
Published: March 2011

ABSTRACTFerromagnetic resonance (FMR) spectra of an iron-oxide thin film with a thickness of 70 A were recorded between 100 and 410 K at 9.5 GHz after heat treatment at about 500 °C in hydrogen atmosphere. The FMR-signal of this film consisted of two components (A and B) when the film plane was oriented parallel to the external fieTp The intensity of these components is not proportional toT3/2 in the range from 100 to 410 K. The line width of the A-component is determined by inhomogeneities in the magnetic structure. The line width of the B-component may be influenced by the spin-spin relaxation mechanism and skin effect. The temperature behavior of the resonance field of the A- and B-components was tentatively attributed to variation of the local fields with the temperature of measurements.
Non-Conventional Route To Glass-Ceramics For Electronic Packaging
Authors: Gensse C. , Chowdhry U. 
Published: March 2011

ABSTRACTThis paper describes a non-conventional route to formation of dense glass-ceramics at relatively low temperatures. Organometallic precursors were used to synthesize powders with controlled purity and stoichiometry in the MgO/Al2 O3 /SiO2 system. These amorphous powders sintered by viscous flow to form a dense glass below 1000°C. Further heating resulted in the formation of very fine grained glass-ceramics. Beta-quartz, cordierite, and cordierite-mullite glass-ceramics were obtained with attractive properties for electronic packaging.
Synthesis, Structure And Applications Of TiO2 Gels
Authors: Livage J. 
Published: March 2011

ABSTRACTTiO2 gels are usually obtained through hydrolysis of titanium alkoxides. Chemical additives can however react with the precursor at a molecular level and therefore modify the hydrolysis-condensation reactions. Several examples will be described :acetic acid, acetylacetone or Cr(acac)3 The whole solgel process is followed all the way from the precursors to the gel and each step is characterized by spectroscopic experiments (Infra-red, N.M.R, E.S.R.). Some electronic properties of TiO2 gels are then described. Chemical additives allow an optimization of the sol-gel process according to each specific applications : electrochromic display devices, photoanodes or photochemical reactions.
Characterization Of Sol-Gel Derived Tantalum Oxide Films
Authors: Silverman L. A. , Teowee G. , Uhlmann D. R. 
Published: March 2011

ABSTRACTWe have studied the densification and dielectric properties of sol-gel derived tantalum oxide thin films as the insulators in MIS capacitors. Hydrolysis of tantalum ethoxide is extremely rapid and goes to completion in ethanol. Condensation is also rapid, and goes to completion in toluene Multiple layers were applied by spin-coating up to thicknesses of 3000 Å before cracking of the coating during drying ensued. Densification occurs from room temperature to 450 C, with the original film thickness decreasing by about half in one hour at 450 C. No additional densification occurs upon heating to 750 C. The dielectric constant decreases from unfired samples to those fired at 450 C, and then increases on firing from 600 to 750 C. The value of the dielectric constant at 1 MHz for samples fired at 750 C for one hour is 20, similar to that of anodically grown Ta2O5. Leakage currents as low as 2 × 10−7 amp cm−2 have been measured for applied fields of 200,000 V cm−1.
Thermal. Acoustical and Structural Properties of Silica Aerogels
Authors: Fricke J. , Reichenauer G. 
Published: March 2011

ABSTRACTSilica aerogels either in monolithic or in granular form provide excellent thermal insulation and thus may be used as superinsulating spacer in all kinds of window systems. Highly porous aerogels also are exciting acoustic materials with sound velocities in the order of 100 m/s and acoustic impedances between 104and 105kg/(m2·s). Silica aerogels produced from TMOS seem to consist of massive primary particles (ø ≅ 1 nm, ρ ≅ 2000 kg/m3) which form secondary particles (ø ≅ 5 to 6 nm, ρ ≅800 kg/in3) displaying fractal properties (D≅ 2). The further buildup creates the highly porous low-density structure which is responsible for the special thermal, acoustical and optical properties of aerogels. Above about 100 nm, transparent aerogels should be homogeneous.
Synthesis of Metal Sulfide Powders From Organometallics
Authors: Johnson Curtis E. , Hickey Deborah K. , Harris Daniel C. 
Published: March 2011

ABSTRACTOrganometallic reagents have been examined for the low-temperature preparation of metal sulfide powders which are desired as precursors to optical ceramics. The general approach is typified by the reaction of diethylzinc with hydrogen sulfide in toluene solution at room temperature. Electron microscopy shows that the white ZnS product consists of aggregates of ≤ 0.1 μm particles. The product is further characterized as predominantly cubic zinc sulfide (X-ray diffraction) which contains some residual hydrocarbon. Various organozinc reagents and experimental procedures have been tried in order to optimize the reaction. The reaction has also been extended to organometallic complexes of Al and Mg, and also to a ternary system, ZnAl2 S4
Precipitation of Monodisperse Ceramic Particles; Theoretical Models
Authors: Calvert Paul 
Published: March 2011

ABSTRACTMonodisperse ceramic powders with sizes in the range of 0.1-μm have been prepared by a number of groups. Generally a dilute solution of a metal compound is hydrolysed to produce amorphous, spherical particles which may be crystallized by subsequent heat treatments. Emulsion polymerization can produce similarly monodisperse latices if the polymerization conditions are carefully controlled. This paper discusses models of the precipitation process which are based on crystallization from aqueous solutions but are believed to be more generally applicable. From simulations it is concluded that monodisperse particles are a most unlikely outcome of a batch precipitation process. Surface active compounds could play an important role in controlling particle size. Inhomogenous mixing during the early stages of reaction should also be important.
Direct Process Metal Alkoxides as Ceramic Precursors
Authors: Ayen R. J. , Burk J. H. 
Published: March 2011

ABSTRACTMetal alkoxides have great promise as oxide ceramic precursors. Direct manufacture from the metal and the alcohol permits the production of high purity materials and of those alkoxides which cannot be easily obtained by other routes. Examples which are of great interest to ceramics are the alkoxides of silicon, aluminum, magnesium and yttrium.Currently, only tetraethyl silicate is produced in large volumes by the direct route, employing a catalytic continuously fed process, yielding a distilled product. The reactivity of silicon, aluminum, magnesium and yttrium is governed by the metal surface state and activation and varies with different catalysts and alcohol chain length and branching.The major use of tetraethyl silicate is in partially hydrolyzed form as binder for precision casting molds and zinc-rich primer coatings. Judicious choice of alkoxide ligands allows the manufacture of soluble or liquid Si, Al, Mg, and Y derivatives. These are especially suitable for molecular doping and mixing in the manufacture of yttriastabilized zirconia, mullite, spinel, cordierite and other oxide ceramic precursors.
An Equation for Melting and Freezing Transition Rates
Authors: Bucksbaum Philip H. , Thompson Michael O. 
Published: March 2011

AbstractStatistical thermodynamics is used to derive the reaction rate for melting and freezing by considering an atomically sharp interface with or without an activated intermediate state. The resulting predictions differ substantially from those of the classical kinetic rate theory at large deviations from equilibrium. The model may be appropriate for the analysis of pulsed laser melting experiments where large deviations are expected.
Phase Selection During Pulsed Laser Annealing of Fe-V Alloys
Authors: Perepezko J. H. , Follstaedt D. M. , Peercy P. S. 
Published: March 2011

AbstractPulsed laser melting of the low-temperature σ (tetragonal, D8b) phase has been used to generate a liquid undercooled with respect to the melting point of the higher-temperature, equilibrium α (bcc) solid solution in equiatomic Fe-V alloys. From calculations based on reported thermodynamic data and equilibrium transformation temperatures, the metastable melting point of the σ phase is about 1720 K for an Fe-50 at.% V alloy, which is 54 K below the melting temperature of the α phase. During rapid heating of well-annealed σ-phase material with a 30 ns laser pulse to above melt threshold, the σ → α reaction is suppressed, so that the melt zone is undercooled by ∼ 54 K with respect to the equilibrium α phase. The α phase nucleates from the undercooled molten surface layer and is retained during the subsequent rapid cooling (∼ 1010K/s) because of the relatively sluggish α → σ transformation. X-ray diffraction (Read camera) and TEM identified the α phase in the near-surface after melting σ with incident laser energies (1.0–1.41 J/cm2) which are well above the melt threshold as determined by changes in reflectivity (∼ 0.7 J/cm2). The α phase nucleated from the undercooled liquid within ∼ 20 ns.
Crystallization of Indium Implanted Amorphous Silicon
Authors: Nygren E. , Williams J. S. , Pogany A. , Elliman R. G. , Olson G. L. , McCallum J. C. 
Published: March 2011

AbstractThe annealing behavior of In+-implanted amorphous Si layers is reviewed. Particular attention is given to the amorphous to polycrystalline transformation for peak In concentrations > 0.5 atomic percent. New data concerning the transformation rate, associated In transport and microstructure are presented and phase transformation mechanisms are discussed.
Ion Irradiation Induced Metastable Phase Formation in the Al-Zr System
Authors: Lilienfeld David A. , Mayer J. W. 
Published: March 2011

AbstractThe Al-Zr system was investigated in an effort to form quasicrystals. While no quasicrystals were found, a metastable phase previously formed only by annealing of a metastable solid solution was observed. This phase was formed by thermal annealing or by elevated temperature ion irradiations of thin film specimens. This work is the first observation of ion irradiation induced formation of this metastable phase.
Precipitation of Kr In Ni at Room Temperature
Authors: Birtcher R. C. , Liu A. S. 
Published: March 2011

AbstractThe fluence dependence of Kr precipitation in Ni at room temperature has been studied with the aid of Transmission Electron Microscopy. As in other metals, the Kr precipitates in small cavities. Electron diffraction demonstrates that the Kr precipitates are solid, fcc crystals aligned with each other and the Ni lattice. The trends are similar to those observed for Kr precipitation in Al at room temperature. The average Kr lattice parameter, determined from the electron diffraction, increases with increasing Kr fluence from 0.515 nm to an asymptotic value of 0.545 nm. The asymptotic limit is due to the melting of the larger Kr precipitates. The mismatch between the Kr and Ni lattices is as large as 55%. Diffuse electron scattering was observed from large, liquid Kr precipitaes. This occurs for Kr fluences above 5.1020 Kr+ m-2 in Ni and above 2.5.1020 Kr+ m-2 in Al. At room temperature, the largest solid Kr precipitate observed in dark field images was 8.3 nm in diameter compared to 4.7 nm in Al. The larger precipitates are liquid or gas. The solid Kr metals at the same lattice parameter in both Ni and Al suggesting that the melting is thermodynamic in nature and independent of the host material.
Precipitation of Krypton in an Amorphous Ti-Cr Alloyc.
Authors: Allen W. , Birtcher R. C. 
Published: March 2011

AbstractResults of a TEM investigation of the microstructural changes produced by the room temperature implantation of energetic Kr+ ions into a glassy Ti-Cr thin film are reported. As in other metals, the Kr precipitates as solid crystallites. The precipitation of crystalline Kr is accompanied by ultrafine crystallization of the metal host around each Kr crystal. With increasing fluence, the Kr precipitates grow to a critical size at which they melt, and the adjacent fine metal crystals disappear. A new TEM imaging technique is described briefly which utilizes the small angle electron scattering fine structure and which in principle is capable of revealing all fine particles simultaneously.
Solid Phase Epitaxial Regrowth of Implanted III-V Materials and Alloys
Authors: Licoppe Christian , Nissim Yves. I. , Meriadec Christelle , Henoc Pierre , D'Anterroches Cecile 
Published: March 2011

AbstractThe amorphous-crystalline (with residual defects) transition is studied in several III-V binary semiconductors and a ternary alloy. Regrowth shows the same behaviour in all cases. The growth kinetics are thermally activated and the activation energies have been measured using time resolved reflectivity measurements. Correlation with vacancy migration characteristic energy is discussed. In the particular case of GaAs, high resolution electron micrograph of the growth front are displayed. They show a rough microscopic structures together with larger scale smooth deformations, attributed to diffusion instabilities.