bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of Ion Bombardment-Induced SubSurface Compositional Modifications in Ni-Cu Alloys at Elevated Temperatures by Ion Scattering Spectroscopy
Authors: Lam N. Q. , Hoff H. A. , Wiedersich H. , Rehn L. E. 
Published: March 2011

ABSTRACTChanges in the subsurface composition of Ni-40 at.% Cu alloys during 3-keV Ne+ bombardment at temperatures between 25 and 700°C were studied by means of ion scattering spectroscopy.Both the time evolution of the composition in the surface atom layer during ion bombardment and subsurface concentration profiles after rapid specimen cooling to room temperature were measured as a function of temperature. Radiation-enhanced diffusion coefficients were derived from the effective altered-layer thicknesses obtained. A comparison of the experimental measurements with theoretical calculations based on a phenomenological model enabled the identification of processes and kinetics responsible for subsurface compositional modifications.
Boltzmann Approach to Cascade Mixing
Authors: Manning Irwin 
Published: March 2011

ABSTRACTThe Boltzmann transport equation is used to describe a beam of ions of atomic species 1 (1-atoms) bombarding a target modelled as an amorphous mixture of 2-atoms and 3-atoms. In a manner familiar in nuclear reactor theory, the method of characteristics is used to integrate the resulting transport equations. An exact expression for the migration flux J3 of 3-atoms is obtained in closed form. This expression can be evaluated in terms of a power series in a distance parameter s. For the case of slowly varying density N3 of 3-atoms, Fick's law, relating J3 to the gradient of N3, is derived from this expression; it is given by the lowest order term of the power series. J3 is shown to be proportional to the bombarding flux. Concomittantly, a closed expression for the mixing parameter in Fick 's law is obtained, which allows a calculation of this quantity for realistic interatomic potentials. A model Kinchin-Pease displacement cascade is proposed, which is expected to allow a reasonable first approximation calculation of the mixing parameter in Fick's law. It is deduced that the mixing parameter will depend sensitively on the lattice displacement energy. This dependence constitutes a physical mechanism for chemical effect in cascade mixing, as well as for fluence and temperature dependence of cascade mixing.
Aggregation and Hydrolysis Reactions of Bismuth Alkoxides
Authors: Whitmire Kenton H. , Jones Carolyn M. , Burkart Michael D. , Chris Hutchison J. , McKnight Andrew L. 
Published: March 2011

ABSTRACTNew bismuth alkoxide and oxo-alkoxide complexes have been prepared from the salt metathesis reaction of NaOR with BiCl3. When R = CH(CF3)2, the product is [Bi(μ- OR)(OR)2(THF)]2 Similar work with R = C6F5 has not yielded a simple alkoxide, but complexes of formulation NaBi3(μ3-O)(OR)8(THF), NaBi4((μ3-O)2(OR)9(THF)2, Na2Bi4(μ3- O)2(OR)10 and Bi6(μ3 -OR)(μ3 -O)4[μ3-OBi(OR)4]3 have been observed. The reaction of BiPh3 with HOC6F5, however, did produce the desired alkoxide which has been characterized as [Bi(OR)2(μ-OR)(toluene)]2 and [Bi(OR)2(μ-OR)(toluene)[2.2 toluene. The reaction of this alkoxide with NaOC6F5 led to the production of Bi6(ν3--O)2 (μ4-O)(OR)12 and NaBi3(μ3- O)(OR)8(THF)3. Reaction of BiPh3 with HOC6F5 in THF led to the formation of Bi6(μ3-OR)(μ3-O)4[μ3-OBi(OR)4]3 (THiF)2. Surprisingly the reaction of BiEt3 and HOR (R = C6F5 or Ph) displaced only one Et group to give [Et2Bi(μ-OR)]∞ which exist as infinite chain polymers with alternating Bi-O-Bi backbones. These spiral chains form chiral helices in the crystal lattice.
Preparation of BSCCO Precursors by Water Extraction Variant of Sol-Gel Process
Authors: Deptula A. , Lada W. , Olczak T. , Di Bartolomeo A. 
Published: March 2011

ABSTRACTThe starling acetate sols of molar compositions of Bi:Pb:Sr:Ca:Cu=I-2:O:2:l: 2, 11–2:0:2:2:3 and 111–1.6:0.4:2:2:3 were prepared by NH4OH addition at various rates, followed by evaporation. Sols were gelled by further evaporation to shard or to microspheres (diameter below 100 μm) by water extraction from the sol emulsion drops formed in 2-ethyl-l-hexanol. The gels were converted to BSCCO phases by thermal treatment. The processes were characterized by XRD and IR examinations. The influence of the sol preparation step connected with formation of polynuclear cations on the following stages of the process was examined.
Fractal Growth During Gelation
Authors: Pope Edward J. A. 
Published: March 2011

ABSTRACTSol-gel processing has emerged as an important new technology for the fabrication of a wide variety of glass, ceramic, and composite materials. In order to better understand and control the gelation process, a theoretical model has been developed which quantitatively links features of fractal growth with measurable properties of a solution during the sol-gel transition. The result of that effort is the fractal growth model of gelation (FGMG) which expresses the solution viscosity, light scattering, and refractive index changes as a funtion of time and the fractal dimension. In this paper, the application of FGMG to silica gels and multi-component system, such as titanium aluminosilicates, is presented.
Solvent Quality Effects in Sol-Gel Processing
Authors: Bailey Joseph K. 
Published: March 2011

ABSTRACTTo understand how solvent quality can be used to tailor structure in sol-gel processing of silicon alkoxides, polymerized tetramethoxysilane polymers were synthesized and fractionated to give relatively stable, narrow molecular weight dispersion samples. These polymers had molecular weights ranging from 8000 to 45,000. The solubility parameter range for these polymers is 8.9–14.5 (cal/cm3)1/2. Light scattering confirmed that this range could be used to predict solvent quality. Bulk gels prepared using good versus poor solvents demonstrated that solvent quality can be used to tailor properties of the gels, presumably by modifying the extent of interpenetration of the growing polymers.
Electronegativity-Based Computation of29Si Chemical Shifts
Authors: M Henry. , C Gerardin. , F Taulelle. 
Published: March 2011

ABSTRACTThe Partial Charge Model has been modified to take into account the detailed structure of any molecular sol-gel precursors or inorganic solid networks. Starting from these structure-dependent partial charges, the classical theory of nuclear shielding is applied to compute the electronic cloud compacity <r-3>p, the population unbalance Puand also the mean excitation energy ΔE. With these three parameters it is possible to explain the chemical shifts variations, spanning from +40 down to -140 ppm, of more than 50 precursors. Depending on the ligands, the well-known upside-down U-curves for series SiXnY4-n(n=0‥4) can be ascribed either to the population unbalance term Puor to a competition between the two other terms <r-3>pand ΔE.
Raman and Infrared Study of Metal Alkoxides During Sol-Gel Process
Authors: Poncelet O. , Robert J -C. , Guilment J. 
Published: March 2011

ABSTRACTOrganic additives are commonly used in sol-gel chemistry [1]. They can operate as stabilizers of reactive metal alkoxides [2] towards hydrolysis or as drying control chemical additives (such as dimethylformamide). These organic compounds and the by-products of sol-gel reactions can drastically modify the physical properties of final oxide materials, so that it is necessary to optimize the use of these additives. The first steps of hydrolysis of metal alkoxides stabilized by organic additives have been studied by many sophisticated analytical techniques which are difficult to use at technical level and often strongly alter the sol-gel reactions [3]. We chose to use FT-Raman and Infrared spectrocopies, which allow to remain as close as possible of the sol-gel process without altering it. The first steps of hydrolysis of group (IVb) metal alkoxides, more particularly titanium, modified by chlorides, carboxylic acids and alkanolamines have been investigated.
Production of Spherical Powders of Inorganic Compounds by Water Extraction Variant of Sol-Gel Process
Authors: DeptuLa A. , Rebandel J. , Drozda W. , Lada W. , Olczak T. 
Published: March 2011

ABSTRACTA method of preparation of spherical powders (with particle diameters <100µm) of metal oxidcs, their homegeneous mixtures or compounds, composites and metals has been elaborated. Depending on the nature of cations, the starting solutions were prepared by extraction of anions with Primene JMT from salt solutions, by addition of dopants to the sols or by complexing with acetic acid or/and ammonia. The sols or broths were then emulsified in 2-ethyl-l-hexanol containing SPAN 80. Drops of the emulsion were solidified by extraction of water with the solvent. The process was carried out continuously in a laboratory and/or in a pilot plant.
The Fast Sol-Gel Synthetic Route to Supported Glass Films: Synthetic Features, Scope, Applications and Mechanistic Studies
Authors: Haruvy Y. , Webber S. E. 
Published: March 2011

ABSTRACTThe fast sol-gel synthetic route to glass films is facilitated by a solvent-free reaction of trialkoxysilane monomers at 60–80°C and near-stoichiometric water-to-siloxane ratios. The viscous polymer formed within several minutes is spin-cast onto a support (typical thickness 10–25µm), cured within a few hours at 60–70°C or 10–40 min. under an intense electric field at room temperature, and can be characterized on the same day. Multi-layered glass-film assemblies of varying indices of refraction and a total thickness up to 80µm are prepared by the same fast process with slight modifications.Guest molecules such as laser dyes for 2D lasers and chromophores for second-harmonic-generation are incorporated into these glass films at high concentrations by direct addition to the reaction mixture. Their absorbance and fluorescence spectra are typical of monomeric chromophores up to concentrations of ∼10-2M. Crystallites that may appear at higher concentrations exhibit unusual polymorphism. The smoothness of such films enables surface anchoring of iso-environment photoactive molecules and investigation of their photophysics.29Si-NMR studies of the hydrolysis pattern in our acid-catalyzed fast sol-gel reaction prove that uniform hydrolysis of the monomer, necessary for a single-phase polymerization, is attained only when the hydrolysis is fast enough to become kinetically controlled, e.g. at elevated temperature or at high acid-concentration. Our reaction pattern and the data of others can be interpreted in terms of a single mechanism of hydrolysis in which two different rate-determining-steps can prevail, depending predominantly on the reactivity of the alkoxysilane and the ratio of the acid-catalyst to the (apparently-inert) proton-binding solvent.
Chemical Processing and Properties of Nanocrystalline BaTiO3
Authors: Xu Z. , Chae H. K. , Frey M. H. , Payne D. A. 
Published: March 2011

ABSTRACTBarium titanate (BaTiO3) thin layers were prepared by sol-gel processing. Details are reported for the synthesis route from methoxyethoxide precursors. Partially hydrolyzed solutions were spin-cast onto metallized silicon substrates, and a multilayering technique was used to develop sub-micron structures. Information is reported on the thermal processing conditions used and the development of structure. Crystallization started at 600°C and was fully developed by 700°C. The room temperature structure was cubic, and the grain size was 25–50 nm. Details are reported for the dielectric properties. Ferroelectricity was not observed. Dielectric constant (200–300) increased with increasing grain size, and was stable with respect to temperature, field and frequency. The properties are attractive for potential integrated capacitor applications.
Microstructural Variations in Sol-Gel Processed Lithium Niobate thin Films
Authors: Joshi Vikram , Goo Grace K. , Mecartney Martha L. 
Published: March 2011

ABSTRACTLiNbO3 thin films were deposited by dip coating Li-Nb alkoxide solutions onto silicate glass substrates and single crystal sapphire substrates. Microstructural characterization using transmission electron microscopy (TEM) showed significant differences in film microstructures dependent on the initial solution chemistry. Fully crystalline films could be obtained after heat treatments at 400°C in air. The grain size and porosity were dependent on the amount of water of hydrolysis in the alkoxide sol. The higher the water content, the larger the grain size and porosity. Crystallization studies of nucleation and growth of LiNbO3 for films heat treated from 300–600°C indicated that higher temperatures or long soak times generated large facetted grain structures. Single crystalline films were obtained on (0001) sapphire substrates.
The Growth of Single Crystal-Like and Polycrystal KNbO3 Films Via Sol-Gel Process
Authors: Cheng Chih-Hsing , Xu Yuhuan , Mackenzie John D. , Zhang Jie , Eyring LeRoy 
Published: March 2011

ABSTRACTTransparent and uniform thin films of crystalline KNbO3 were synthesized on different substrates such as SrTiO3, ZrO2, MgO and Pt by the dip-coating method using a double alkoxides solution. The film was epitaxially crystallized at the temperature around 750°C for 3 hours in air on SrTiO3 single crystal substrate. The structure of the films has been studied with X-ray and electron diffraction, and transmission electron microscopy.Different molar ratios of 2-ethylhexanoic acid (2EHA) to alkoxides were applied to control the hydrolysis rate of the sol-gel solution. Dense films were obtained after modification of the alkoxides solution.
Synthesis of Cuprate Based High-Tc Superconductors by Polymerized Complex Method
Authors: Kakihana Masato , Yoshimura Masahiro , Mazaki Hiromasa , Yasuoka Hiroshi , BöRj Esson Lars 
Published: March 2011

ABSTRACTWe report on a novel precursor technique to produce highly pure and homogeneous cuprate based high-Tc superconductors based on the formation of a polymer metal complex in which various metal ions in desired stoichiometric ratio can be uniformly dispersed. Application of the polymerized complex method is demonstrated on the ceramic synthesis of polycrystalline compounds viz. YBa2Cu3Oy, YBa2Cu4Oy, Bi1.6Pb0.4Sr2Ca2Cu3Oy and Bi2Sr2Ca0.8Cu2Oy. The superconducting properties were studied with complex magnetic susceptibility measurements which exhibited sharp superconducting transitions without any indication of two-phase character. The materials fabricated by this method showed improved properties compared to those for ceramic samples of previously reported synthesis procedures.
Corrosion Resistant ZrO2 Sol-Gel Coating on Stainless Steel
Authors: Atik M. , Aegerter M. A. 
Published: March 2011

ABSTRACTCorrosion resistant Sol-Gel ZrO2, coatings deposited by dip coating technique on 316 L stainless steel sheets have been fabricated utilizing sonocatalysed precursors sols prepared from zirconium alkoxide Zr(OC3H7)4, isopropanol, glacial acetic acid and water. Their composition varied between 0,025 to 0,9 mol/1 ZrO2. The coatings have been characterized by X-ray diffraction, IR optical reflection, ellipsometry and scanning electron microscopy. When densified under a slow heat treatment thin coatings exhibit outstanding corrosion resistance as no weight change has been observed after 24 h chemical attack in H2SO4 aqueous solution at 81°C and 10 h oxidation treatment in air at 800°C. Thick films as well as films densified under rapid heat treatments tend to crack and are less corrosion resistant.
Pore Size and Surface Texture Modification of Silica Via Trialkylsilylation
Authors: Hua Duen-Wu , Smith Douglas M. 
Published: March 2011

ABSTRACTSurface modification of silica via silylation is often undertaken to change surface chemistry and hence, adsorption characteristics but little attention is paid to its use for pore morphology modification, the subject of this work. Modification of two silica samples was conducted by trimethylsilylation. The degree of silylation/ surface coverage was monitored by TGA and elemental analysis. Pore structure was studied by nitrogen adsorption and condensation, and small angle x-ray scattering (SAXS). Previously, we demonstrated that surface area, surface texture, pore size distribution, and total pore volume are indeed changed in a controlled fashion due to silylation of mesoporous silicas. Generally, the mean pore size is smaller, the pore size distribution is narrower, and the pore surface is smoother after silylation. However, questions remain concerning the effect of small-scale surface roughness and the fractional surface coverage on the effective pore size. This study concentrates on the silylation of smaller pore material (r < 40 Å). Significant pore size distribution narrowing and smoothing of the pore surface with increasing surface coverage was noted.
Polynuclear Titanium Oxoalkoxides: Molecular Building Blocks for New Materials?
Authors: Chen Y. W. , Klemperer W. G. , Park C. W. 
Published: March 2011

ABSTRACTThe [Ti7O4](OEt)20 molecule, Et = C2H5, is very reactive toward ethanol, and its [Ti7O4] metal oxide core structure is largely decomposed in <10 minutes. The [Ti16O16](OEt232 molecule, however, has a [Ti16O16] core structure which is relatively stable toward alcoholysis, and solid state 17O MAS NMR experiments using selective 17O labeling techniques show that this core structure is preserved in good yield during sol-gel polymerization.
Preparation and Physical Properties of V2 O5 Aerogels
Authors: Hirashima Hiroshi , Sudoh Kazumi 
Published: March 2011

ABSTRACTMonolithic aerogels and aerogel coatings of hydrated V2O5 containing 0 to 10 mol% GeO2 were prepared from metal alkoxides by hydrolysis and autoclave drying. The bulk aerogels of high porosity, more than 90 %, were obtained. On the other hand, the porosity of the aerogel coatings, about 50 nm in thickness, was about 50 %. The aerogels consisted of micro fibrils, less than 20 nm in diameter. Diffraction peaks of crystalline vanadium oxides were not observed for the as-dried aerogels. Dynamic microhardness of the bulk aerogels was very low, but increased with addition of GeO2· Dc electrical conductivity of the bulk aerogels was lower than that of the bulk xerogels by one order of magnitude, and was isotropie. The aerogels were surface fractal with Ds ≅ 2.7.
Macro-Defect-Free Cement: A Novel Organoceramic Composite
Authors: Francis Young J. , Berg M. 
Published: March 2011

ABSTRACTMacro-defect-free cement is a composite material made by processing a hydraulic cement with a water-soluble polymer under high shear roll-milling. This paper examines the principles of processing and the development of microstructure that results in a material with ceramic-like properties. The nature of the chemical interaction between the cement and the polymer is also considered in some detail.
Formation of Highly Dispersed Metals on Functionalized Silica Supports
Authors: Rousseau Francois , Duan Z. , Hampden-Smtth M. J. , Datye A. 
Published: March 2011

ABSTRACTThe hydrolysis of H2N(CH2)2NH(CH2)3Si(oMe)3 with a stoichiometric amount of water results in loss of the -OMe groups after two days and formation of a mixture of species mainly with empirical formula, [H2N(CH2)2NH(CH2)3Si(O)3]. The reaction of representative examples of metal salts, e.g. Cu(NO1.5)2, and metal-organic compounds, [(NBD)RhCl]2, with the amino-group of the amine functionalized polysiloxanes [H2N(CH2)2NH(CH2)3Si(O)1.5] has been demonstrated. These species undergo thermal decomposition in air, typically at 200°C, with complete loss of the organic supporting ligands. On heating to 450°C in O2, sintering occurs to form large, ∼1μm, sized silica particles which contain highly dispersed, ∼4nm sized metal-containing particles. The surface areas range from 228 to 583 m2/g. After reduction, the rhodium species is active towards catalytic hydrogenation of pyrene.
Energy Transfer Between Eu2+, Eu3+ and Rh6G in Silica, Zirconia and Alumina Gels
Authors: Nie W. , Dunn B. , Sanchez B. , Griesmar P. 
Published: March 2011

ABSTRACTThe sol-gel process provides new opportunities for the synthesis of photonic materials. Sol-gel chemistry is mainly based on inorganic polymerization reactions performed in solution at lower temperatures than conventional chemical methods. Homogeneous doping by mixing components at a molecular level and synthesis of mixed organic-inorganic materials can then be performed. Luminescent properties of dyes inside silica, aluminosilicates or transition metal oxide based gels have been studied extensively. Much less work has been devoted to the study of energy transfer (ET) inside sol-gel matrices. Sol-gel materials provide the opportunity to investigate dye-dye ET, as well as dye-ion ET. This communication presents an optical study of a variety of sol-gel matrices (SiO2, Al2O3, ZrO2 based gels) codoped with rhodamine 6G(Rh6G) and europium. Different types of ET are observed among Rh6G, Eu3+ and Eu2+. The Eu2+/Eu3+ ratio is found to be strongly dependent on the host matrices. The reduction of Eu3+ t· Eu2+ in dried gels may relate to the presence of Rh6G.
Dense Xerogel Matrices and Films for Optical Memory
Authors: Chaput F. , Boilot J. P. , Devreux F. , Canva M. , Georges P. , Brun A. 
Published: March 2011

ABSTRACTOptically clear gels doped with organic molecules are prepared in the zirconia-silica system by hydrolysis of metal alkoxides in a wet atmosphere. After drying, dense xerogels are obtained which exhibit a closed porosity. By using the same route, organic-inorganic hybrid xerogels are also produced as films.The molecule-matrix interactions are evaluated from the absorption recovery times of the S0→S1 transition for triphenylmethane dyes. Concerning doped xerogels with other organic molecules having polar groups, the application of the strong polarized electric field of an ultrashort optical pulse allows to locally create a birefringence with a memory effect. This type of sample could be used for optical storage and treatment of information.
Polymer-Derived Silicon Carbide Fibers with Improved Thermomechanical Stability
Authors: Toreki W. , Batich C. D. , Sacks M. D. , Saleem M. , Choi G. J. 
Published: March 2011

ABSTRACTContinuous silicon carbide fibers (”UF fibers”) with low oxygen content (∼2 wt%) were prepared by dry spinning of high molecular weight polycarbosilane solutions and subsequent pyrolysis of the polymer fibers. Room temperature mechanical properties were similar to those of commercially-available Nicalon™ fibers, as average tensile strengths as high as 3 GPa were obtained for some batches with fiber diameters in the range ∼10–15 μm Furthermore, UF fibers showed significantly better thermomechanical stability compared to Nicalon™, as indicated by lower weight losses, lower specific surface areas, and improved strength retention after heat treatment at temperatures up to 1700°C. UF fibers were also characterized by elemental analysis, X-ray diffraction, and scanning Auger microprobe. Strategies were suggested for achieving further improvements in thermomechanical stability.
Syntheses, Structures and Properties of Polycarbosilanes Formed Directly by Polymerization of Alkenylsilanes
Authors: Masnovi John , Bu Xin Y. , Beyene Kassahun , Heimann Paula , Kacik Terrence , Harry Andrist A. , Hurwitz Frances I. 
Published: March 2011

ABSTRACTVinylsilane polymerizes to form predominantly a carbosilane polymer using dimethyltitanocene catalyst. This is in contrast to alkylsilanes, which afford polysilanes under the same conditions. The mechanism of polymerization of alkenylsilanes has been shown to be fundamentally different from that for the polymerization of alkylsilanes. The silyl substituent apparently activates a double bond to participate in a number of polymerization processes in this system, particularly hydrosilation. Isotopie labeling indicates the involvement of silametallocyclic intermediates, accompanied by extensive nuclear rearrangement. Polymers and copolymers derived from alkenylsilanes have relatively high char yields even for conditions which afford low molecular weight distributions. Formation of crystalline β-SiC is optimum for a copolymer of an alkylsilane and an alkenylsilane having a silane/carbosilane backbone ratio of 85/15 and a C/Si ratio of 1.3/1.