bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effekts of Temperature and Reactant Concentration on Properties of Fine TiO2 Particles Prepared by Vapor-Phase Hydrolysis of Titanium Teiraisopropoxide
Authors: Kirkbir Fikret , Komiyama Hiroshi 
Published: March 2011

ABSTRACTSubmicrometer-size TiO2 powders were continuously produced by vapor-phase hydrolysis of titanium tetraisopropoxide, TTIP, in a tubular-flow reactor. Particle size increased with increasing inlet TTIP concentration, and with decreasing inlet water concentration and temperature. At high water concentrations, primary particles form by instantaneous chemical reactions and particle growth occur by collision and coalescence of the particles. Brownian collision and coalescence theory could predict the experimental effect of inlet TTIP concentration on particle size. The experimental deviations occurred from the theory with increasing temperature were attributed to the changing particle properties with temperature.
Sol-Gel Syntheses and Characterization of BaTi4O9 and BaTiO3-Powders
Authors: Phule Pradeep P. , Rkbud Subhash H. 
Published: March 2011

ABSTRACTSol-gel processes for the synthesis of high purity, ultrafine BaTi4O9 and BaTiO3 powders are described. Hydrolysis of an alkoxide precursor derived from barium metal and titanium (IV) isopropoxide resulted in formation of powders consisting of ultrafine (0.2 to 1.0 μm) spherical particles. These amorphous precursor powders were converted to crystalline BaTi4O9 powders (particle size 2–3 μm) by heat treatment at 1100 C. The sol-gel process for the synthesis of BaTiOj powders utilized chemical polymerization between moisture insensitive and relatively inexpensive barium acetate and titanium (IV) isopropoxide in the presence of acetic acid. The gel to ceramic conversion was achieved by firing the gels at 1000 °C to obtain high purity, stoichiometric BaTiO3 powders. The powders were sintered to obtain relatively dense (90 % relative density) ceramic bodies.
Growth and Structure of Pyrogenic Silica
Authors: Schaefer D. W. , Hurd A. J. , Christen D. K. , Spooner S. , Lin J. S. 
Published: March 2011

ABSTRACTFractal analysis is used to interpret small-angle X-ray and neutron scattering data on commercial fumed silica powders. Rough primary particles are found in high surface area powders. A model based on ballistic polymerization, sintering, and diffusion-limited aggregation is proposed to explain the observed powder structure.
Kinetics Study of the Acidic Catalyzed Polymerization of Tetraethoxysilane by 29Si NMR.
Authors: Pouxviel Jean-Claude , Boilot J. P. 
Published: March 2011

ABSTRACTTEOS has been hydrolysed under acidic condition with stoichiome-tric or excess amount of water. Evolution of the silicon species is followed by 29Si NMR. The data are analyzed at different levels of detail; first, analysis of the by products of polymerization reactions, second determination of the extents and overall rate constants of hydrolysis and condensation reactions and finally kinetics simulations of the evolution taking into account all the present silicon species. We have shown that the hydrolysis rate increases with the number of hydroxyl groups, and the reesterification reactions have a significant contribution. We also found that condensation reactions preferentially occur with loss of water between the more hydrolyzed monomers; their rates rapidly decrease with the degree of condensation. We compare the two compositions as a function of their water content and pH.
Chemical Preparation of Powders and Films for High Temperature Superconductors
Authors: Bunker B. C. , Voigt J. A. , Lamppa D. L. , Doughty D. H. , Venturini E. L. , Kwak J. F. , Ginley D. S. , Headley T. J. , Harrington M. S. , Eatough M. O. , Tissot R. G. , Hammetter W. F. 
Published: March 2011

ABSTRACTA precipitation process has been developed to prepare precursor powders which can be calcined and sintered to form high critical temperature superconductors such as YBa2Cu3O7−x. Precursor powders are prepared using a continuous precipitation system in which a solution containing highly soluble salts of the desired metal cations is rapidly and completely mixed with a solution containing precipitating anions such as hydroxide and carbonate ions. The resulting amorphous powder can be calcined to form sub-micron particles of desired superconducting phases which are useful in preparing inks for the ink-jet printing of superconducting interconnects. The powders can be redissolved in organic solvents to form solutions which can be used in spin or dip coating substrates with thin superconducting films. Finally, the powders have been used to prepare bulk ceramics which exhibit the highest reported critical currents of any chem-prep ceramics. Bulk samples prepared from chloride doped precursors exhibit large, oriented grains and extensive flux pinning.
New Structures of Preceramic Polysilazanes Synthesized by Transition Metal Catalysis
Authors: Blum Yigal D. , Schwartz Kenneth B. , Crawford Edward J. , Hamlin Richard D. 
Published: March 2011

ABSTRACTFurther capability of silazane dehydrocoupling polymerization catalyzed by ruthenium carbonyl (20–200 ppm) is demonstrated in a series of reactions. Ammonia and monomethylamine are used as reactants to bridge oligomers and polymers containing Si-H bonds to provide higher molecular weight polymers with higher latent reactivity and to increase the ceramic yields and the nitrogen-to-carbon ratio in the final ceramic compositions. New types of tractable polymers containing cyclomers having [MeSiHNH] units with molecular weights over 2000 d are formed. Various polymeric properties (e.g., viscosities, softening and melting points) and ceramic yields up to 80–85 wt% are obtained by controlling the catalytic reaction conditions.
Studies of the Hydrolysis and Polymerization of Silicon Alkoxides in Basic Alcohol Solutions
Authors: Bogush G. H. , Dickstein G. L. , Lee P. , K.C.  , Zukoski C. F. 
Published: March 2011

ABSTRACTWe report here an experimental technqiue based on changes in reaction medium volume which we have used to observe the kinetics of hydolysis and polymerization of TEOS in aqueous ethanol solutions containing NH3. Our results show that there are three distinct reaction regions. By combining these results with determinations of change in reaction medium conductivity and average particle size, we are able to link the short and long time regions to TEOS hydrolysis and particle growth respectively. The intermediate reaction time region is not associated with hydrolysis, loss of ionic species due to condensation or to particle growth.
Silicon Carbide Via the Hydrolysis-Condensation Process of Dimethyldiethoxysilane/Tetraethoxysilane Copolymers.
Authors: Chen K. C. , Thorne K. J. , Chemseddine A. , Babonneau Florence , Mackenzie J. D. 
Published: March 2011

ABSTRACTTransparent monolithic pieces of gel have been prepared from the hydrolysis of a mixture of dimethyldiethoxysilane (DEDMS) and tetraethoxysilane (TEOS). The characterization of this gel has been done by infrared and shows that a copolymerization between the two precursors has occurred during the hydrolysis-condensation process. Pyrolysis of this gel lead to the formation of β-SiC at 1550°C. The characterization of the pyrolysing process has been investigated. The Si-CH3 bonds are broken during the heat treatment, leading to a mixture of silica and carbon. The formation of β-SiC is therefore due to a carbothermal reduction of this silica matrix.
Physical and Structural Evolution of Sol-Gel Derived TiO2-SiO2 Glasses
Authors: CHENG Yeu-Chyi , Hench Larry L. 
Published: March 2011

ABSTRACTA method for producing large TiO2-SiO2 gel-glass monoliths using the sol-gel method has been developed. The gel-glasses are prepared by a pre-hydrolysis method using tetramethylorthosilicate and titanium isopropoxide as precursors. The microhardness, specific surface area and pore radius of the gel-glasses do not change significantly below 600°C. Above 600°C, these properties increase rapidly with densification temperature. At lower TiO2concentration, the glasses obtained by heating to 900°C for 15 hours were not crystallized, while for 15 wt % TiO2 glass, anatase precipitated.
Luminescent Oxide Gels
Authors: Newsham Mark D. , Cerreta Michael K. , Berglund Kris A. , Nocera Daniel G. 
Published: March 2011

ABSTRACTLuminescent oxide gels were prepared by hydrolysis of silicon alkoxides in solutions containing the luminescent hexanuclear molybdenum cluster Mo6Cl12. The resulting gel exhibited emission and lifetime behavior characteristic of Mo6Cl12 thereby indicating that the excited-state properties of the metal cluster species are not significantly perturbed by the gel environment.
Preparation of YBa2Cu3O7-δ Superconductor by Sol-Gel Method and Fiber Drawing
Authors: Kozuka H. , Umeda T. , Jin J. S. , Sakka S. 
Published: March 2011

ABSTRACTSuperconducting YBa2Cu3O7-δ, ceramic pieces and fibers were prepared through a sol-gel route from ametal acetate aqueous solution of controlled pH. Concentrating the starting solution by evaporating the solvent provided a transparent viscous sol, from which gel fibers could be drawn. Further concentrating of the viscous solution led to formation of gel pieces. Conversion of gel fibers and pieces to superconductors were investigated in terms of precipitating crystalline species and electrical conductivities.
Formation and Characterization of Inorganic Membranes from Zeolite-Silica Microcomposites
Authors: Bein Thomas , Brown Kelly , Enzel Patricia , Jeffrey Brinker C. 
Published: March 2011

ABSTRACTSmall crystals of zeolites (500–1000 nm) with two- and three-dimensional channel systems (faujasite and ZSM-5 structures) were embedded in amorphous thin films derived from TEOS hydrolyzed in alcoholic solution. Scanning electron microscopy studies show that the zeolites can be quite evenly dispersed in the membrane, resulting in single layers of zeolite crystals protruding out of the amorphous matrix. In situ FT-IR studies with a series of probe molecules revealed that in most membranes the zeolites were 100% accessible from the gas phase. The membranes excluded molecules which are larger than the pore openings of the zeolite embedded in the composite.
Chemical Durability of Sio2-Tio2-Zro2, Glass Films Made from Alkoxide Solutions
Authors: Beier W. , Frischat G. H. 
Published: March 2011

ABSTRACTWater, ethanol, and hydrochloric acid containing solutions of silicon ethoxide, titanium butoxide, and zirconium pro-poxide have been developed which show a constant viscosity for some days. The influence of formamide additions on the viscosity behavior was studied too.Glass slides have been dip coated in the solutions, dried in ethanol containing atmosphere, and baked at 300 ° C. Multilayered films were obtained by repeating this procedure. After a final baking at 500 ° C, crack-free transparent SiO2-TiO2-ZrO2 glassy films have been obtained. Compared to the substrate, the films of thicknesses below 500 nm were very stable against hot NaOH solution. The stability of the coatings was analyzed by detection of the remaining TiO2 and ZrO2 in the films after the attack. This was done by a x-ray fluorescence (XFA) technique.
Synthesis and Characterization of Vanadium Oxide Gels from Alkoxy-Vanadate Precursors
Authors: Sanchez C. , Nabavi M. , Taulelle F. 
Published: March 2011

ABSTRACTVanadium oxide gels are synthesized through vanadium oxo-alkoxide hydrolysis condensation processes. Different precursors and hydrolysis conditions lead to different sorts of gels. V0(0Amt)3hydrolyzed with a large excess of water results in red jammy gels with a layered structure. They exhibit electronic and ionic behavior comparable to vanadium pentoxide gels from inorganic precursors. Hydrolysis of VO(OPrn)3in an alcoholic medium, leads to orange transparent monolithic gels. They have a highly branched polymeric structure. Controlled hydrolysis of vanadium oxo-alkoxide precursors has the further advantage of giving good adherent thin films.
Maya Blue: How the Mayas Could Have Made the Pigment
Authors: Torres Luis M. 
Published: March 2011

AbstractFor over 50 years Maya Blue has been an unsolved problem in the manufacture of ancient pigments. It can be reproduced with several procedures using palygorskite, indigo and heat; however we do not know how the Mayans made this pigment. Interpretation of ethnohistoric data allows us to deduce that Prehispanic, and even Spanish Colonial, procedures for manufacturing indigo may produce Maya blue if clay is added during the process.We present ethnohistoric and archaeological evidence to support this hypothesis and following the proposed procedures, Maya Blue is reproduced in the laboratory. Microscopic examination and chemical microscopy are applied to the synthetic Maya Blue to characterize and compare it with original Mayan samples.
Linear Free Energy Relationships in Glass Corrosion
Authors: Abrajano Teofilo A. , Bates John K. , Bohlke J. K. 
Published: March 2011

AbstractVarious theoretical models that have been proposed to correlate glass durability to their composition for a wide variety of silicate, borosilicate, and aluminosilicate glasses are examined. Comparisons are made between the predictions of these models and those of an empirical formulation extracted from existing data in the present work. The empirical approach provides independent confirmation of the relative accuracy of the silica release rate predictions of the different theoretical models in static leaching systems. Extensions of the empirical approach used in this work are discussed.
Dielectric Heating Sensitizers for Processing of Polymers
Authors: Thorsrud Agmund K. 
Published: March 2011

ABSTRACTMicrowave heating has for years been successfully used for some polymer applications, especially in preheating or continous vulcanization of rubber and also for crosslinking of thermosets. It may therefore seem surprising to find how little woork has been reported on the use of dielectric heating of thermoplastic resins. Certainly a major reason is that very few thermoplastics have dielectric properties making them respond to high frequency electromagnetic fields, or their response is inadequate for practical applications.Many processes could benefit from the many advantages of dielectric heating if the most suitable polymer could be made to absorb such energy. Therefore a study was undertaken to find additives which in small amounts could render virtually all polymers, especially the thermoplastic ones, responsive to microwave or radio frequency electromagnetic energy without significantly changing processing and physical properties.A series of such sensitizers was developed. Some of these are now commercially available as white, fine particle size, freeflowing powders and others are colorless liquids. Their use will depend on polymer type and application, but their common objective is to substantially increase the material's loss factor.Selected tests with difficult to process ultrahigh molecular weight polyethylene (UHWPE) and polyphenylene sulfide (PPS) proved that the sensitizers in low concentration will allow dielectric heating of unresponsive polymers with potential for important advantages in cost and quality.
Interactions of Silicate Glasses with Aqueous Environments Under Conditions of Prolonged Contact and Flow
Authors: Barkatt A A. , Saad E. E. , Adiga R. B. , Sousanpour W. , Barkatt A L. , Feng X. , O'keefe J. A. , Alterescu S. 
Published: March 2011

ABSTRACTStudies of the corrosion process of silicate and boro-silicate glasses under a broad range of contact times, surface-to-volume ratios and leachant compositions indicate that dissolution of such glasses in aqueous media can be interpreted in terms of activity of dissolving amorphous silica. This activity is modified by the presence of elements such as Al, Mg and Fe. The effects of these elements, when initially present in the glass or in the leachant, and, in general, the effects of glass composition on the course of the corrosion process can be viewed in terms of the formation of a surface layer on the leached glass. The type, composition and structure of this layer, which are determined by glass composition, control the dissolution behavior of the glass.
Revised Eh-pH Diagrams (25 C, One Bar) for Uranium and Transuranic Elements: Application to Radioactive Waste Studies
Authors: Brookins D. G. 
Published: March 2011

ABSTRACTEh-pH diagrams are useful for comparing the probable geochemical behavior of many elements including U and the transuranics Np, Pu, Am. Revised Eh-pH diagrams have been constructed for U, Np, Pu and Am at 25 C, 1 bar conditions. These diagrams, based on new and revised thermodynamic data, include aqueous and solid species in the generic system M-C-O-H. The species M(OH)− is considered herein, although it's existence has not been verified.Aqueous U(VI) species are dominated by below pH 5 and by carbonate complexes at higher pH. U(IV) species include important fields of UO2, and U(OH)4. If Si is present, USiO4 may be important. U3O8, occurs between the U(IV) and U(VI) species.Np(IV) solid species are problematic. NpO2 covers a wide range of Eh-pH, but its precursors, NpO. (OH)2 and Np(OH)4 cover more restrictive Eh-pH ranges with more important. This increases potential for radionuclide migration. Np(V, VI) carbonate complexes are important only at high Eh.Pu(IV) species are dominated by PuO2, but Pu(OH)4 does not occupy as much Eh-pH space, being replaced in large part by . With carbonate present, Pu(III) species also replace part of the Pu(OH)4 field, and Pu2 (CO3)3 becomes important. Pu(VI) carbonate complexess occur only at high Eh.Am(III) species dominate Eh-pH space in the system Am-C-O-H, with Am2 (CO3)3 a major phase. Under carbonate-poor conditions, Am(OH) 3 is important. AmO2 occurs at high Eh, pH, and at high Eh and very high pH.The importance of the M(OH)4 precursors to MO2 species is the enhanced possibility of radionuclide migration from buried spent fuel rods, even under reducing condtions.
Induced Obsidian Hydration Experiments: An Investigation in Relative Dating
Authors: Tremaine Kim J. , Fredrickson David A. 
Published: March 2011

ABSTRACTInduced obsidian hydration experiments have been conducted over the last six months at Sonoma State University. Our initial focus has been to assess the influence of experimental conditions on hydration development within a thermally controlled pressure reaction vessel. Although an ultimate goal is to calculate source-specific rates for local obsidians, given current uncertainties regarding the ability to reliably express hydration widths as calendar years, a more immediate goal is to develop a means to compare hydration rim measurements of samples from one obsidian source relative to another so that archaeological assemblages containing obsidians from two or more sources can be placed into a time series. Induced hydration experiments are expected to provide data that illustrate the relationship between hydration measurements of different obsidians with temporal equivalency. Results and implications of initial experiments are discussed.
Chemical Interactions in Ceramic and Carbon-Carbon Composites
Authors: Luthra Krishan L. 
Published: March 2011

ABSTRACTThe useful lives of many ceramic composites are influenced, if not controlled, by chemical interactions between various constituents and the gas environment. Thermochemical calculations are extremely valuable in evaluating these concerns. Examples of many possible concerns are presented. The usefulness of a thermochemical approach is demonstrated by a somewhat detailed discussion of the oxidation protection of carbon-carbon composites. This includes discussion of the various possible rate limiting steps and the detrimental effects of CO gas formed as a result of carbon oxidation.
Effects of Rapid Thermal Processing on SiO2/GaAs Interfaces
Authors: Tokuda Yutaka , Katayama Masayuki , Ando Nobuo , Kitagawa Akio , Usami Akira , Inoue Yajiro , Takematsu Hideo , Wada Takao 
Published: March 2011

ABSTRACTEffects of rapid thermal processing (RTP) on SiO2/GaAs interfaces have been investigated with Auger electron spectroscopy and X-ray photoelectron spectroscopy. SiO2 films of 100, 175, 200 and 1250 nm thickness have been deposited on liquid encapsulated Czochralski-grown (100) n-type GaAs wafers by the RF sputtering method. RTP has been performed at 800°C for 6 s. For comparison, conventional furnace processing (CFP) has also been performed at 800°C for 20 min for 200-nm-thick SiO2/GaAs. The Ga is observed on the outer SiO2 surface for RTP samples as well as CFP samples. This indicates that the outdiffusion of Ga occurs after only 6 s at 800°C even through 1250-nm-thick SiO2 films. The depth profile of Ga reveals the pile-up of Ga on the outer SiO2 surface for both RTP and CFP samples. The amount of Ga on the outer surface gradually increases in the thickness range 1250 to 175 nm. The As is also observed on the outer surface. The amount of Ga and As on the outer surface rapidly increases at 100 nm thickness. Electron traps in RTP samples have been studied with deep-level transient spectroscopy. Different electron traps are produced in GaAs by RTP between 100-nm- and 200-nm-thick SiO2/GaAs. It is thought that the production of different traps by RTP is related to the amount of Ga and As loss through SiO2 films from GaAs.
He+ Implanted Stripe Optical Waveguides in LiNbo3
Authors: Weiss B. L. , Reed G. T. 
Published: March 2011

ABSTRACTIn this paper the fabrication process and characteristics of waveguides produced by He+ implantation in Y-cut X- and Z-propagating LiNbO3 are presented It is shown that low propagation losses, down to 1dB cm−1 at λ = 633μm can be obtained for TM modes only in Y-cut X-propagation samples whilst Y-cut Z propagating samples support both TE and TM modes with relatively low losses.
Stable Solid-Phase Ohmic Contacts to n-GaAs with Diffusion Barriers
Authors: Kolawa E. , Nieh C. W. , Flick W. , Molarius J. , Nicolet M-A. 
Published: March 2011

ABSTRACTContacts to GaAs substrates with n-type epilayers formed by GaAs/Ni/Ge/WN/Au, GaAs/Ni/Ge/Ni/WN/Au and GaAs/Ge/ Ni/WN/Au systems were investigated. Ohmic contacts in these systems were formed by a solid-phase reaction between Ni/Ge and GaAs. Interfacial reaction and electrical properties of these contacts are characterized by backscattering spectrometry, transmission electron microscopy and contact resistivity measurements. Resistivities in the 10−δ Ω cm range are achieved.
Ion Implanted Strip Optical Waveguides in GaAs/GaAl as MQW Material
Authors: Weiss B. L. , Wismayer A. C. 
Published: March 2011

ABSTRACTThis paper is the first report of the use of Si+ implantation into GaAs/GaAlAs MQW material to form optical waveguides operating at a wavelength of 1.15μm. Lateral confinement is achieved by mixing of the MQW material which is produced by the implantation of Si+ and subsequent annealing at 750°C. The properties of these waveguides are compared with those of chemically etched rib waveguides and are shown to have reasonably low losses.
Static Leaching of Actinides and Fission Products from Fully Radioactive Waste Glass of Hllw Generated in Tokai Reprocessing Plant
Authors: Miyahara K. , Ashida T. , Yusa Y. , Sasaki N. , Tsunoda N. 
Published: March 2011

ABSTRACTFully radioactive waste glass of HLLW generated in Tokai Reprocessing Plant was produced by using a small Joule-heated ceramic melter at the Chemical Processing Facility (CPF), Tokai Works, PNC, Japan. Static leach tests using the glass were carried out in doubly distilled water for a period of up to three months at 30°C and 90 °C. Gamma spectrometry was performed to measure 134Cs, 137Cs and 60Co in the leachates. After the chemical separation of Cs isotopes in the leachates, it was newly possible to measure 125Sb, 144Ce, 154Eu and 155Eu. Alpha spectrometry was performed to measure 239Pu+240Pu, 241Am and 244Cm in the leachates. Adsorption of the actinides on the wall of the leach vessel was recognized in all cases. Leaching behavior of the measured radionuclides were evaluated by considering mass balance of the radionuclides which were leached.