bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of Titanium and Boron Containing Polymers: Potential Precursors for Advanced Ceramics
Authors: Gonsalves Kenneth E. , Kembaiyan K. T. 
Published: March 2011

AbstractTitanium containing fibers have been synthesized via the modification of organic materials. Thermal processing of these chemically modified organic fibers in reactive/inert atmospheres, has produced materials containing Ti (C,O). Materials analysis was performed using SEM-EDS, ESCA and Auger spectroscopy. Novel monomeric titanium materials were synthesized for the above mentioned modification of organic materials. Boron containing monomers and polymers were also synthesized as possible precursors for B-N-C materials.
The Mechanical Performance of Fiber Reinforced Ceramic Matrix Composites
Authors: Evans A. G. , Marshall D. B. 
Published: March 2011

AbstractThis article evaluates the current understanding of relationships between microstructure and mechanical properties in ceramics reinforced with aligned fibers. Emphasis is placed on definition of the micromechanical properties of the interface that govern the composite toughness. Issues such as the debond and sliding resistance of the interface are discussed based on micromechanics calculations and experiments conducted on both model composites and actual composites.
Effect of Thermal Expansion Mismatch on Fiber Pull-out in Glass Matrix Composites
Authors: Deshmukh U. V. , Kanei A. , Freiman S. W. , Cranmer D. C. 
Published: March 2011

AbstractSingle fiber pull-out tests can be used to directly measure the fiber-matrix interfacial shear stress in glass matrix composites. The system under investigation consisted of a soda-lime-silica glass matrix containing SiC monofilaments with a carbon-rich surface. The presence of the carbon-rich layer on the surface of these fibers makes them non-wetting to most glasses; hence the fibers are held in the matrix only by frictional forces acting at the interface. The mechanical gripping responsible for this force can be changed by manipulating the glass matrix/fiber thermal expansion coefficient mismatch. Frictional stresses (τ) and friction coefficients (μ) obtained for SiC monofilaments in a soda-lime-silica glass matrix were compared with previously obtained data on a borosilicate glass matrix (τ = 2–3 MPa, μ = 0.72 ± 0.36). For the soda-lime-silica system, τ's of 4–20 MPa and μ of 0.10 ± 0.03 were obtained. τ in the soda-lime-silica system is higher due to the larger difference in thermal expansion mismatch between the fiber and matrix. The differences in μ may be due to lubrication effects caused by water at the fiber-matrix interface.
Electrochemical Synthesis of Zirconia
Authors: Switzer Jay A. , Phillips Richard J. 
Published: March 2011

ABSTRACTZirconia powder was produced in aqueous solution from zirconyl nitrate using electrogenerated base. Both divided and undivided electrochemical cells were used. In the divided cell, hydroxide ion was discharged in the cathode compartment, and hydrated zirconia was produced. The as-produced material was weakly agglomerated, amorphous, and had a surface area of up to 316 m2/g. The surface area of the powder did not vary systematically with the electrosynthesis current density, but did depend on subsequent processing. Crystalline zirconia was produced by calcining in air at temperatures above 400°C. Tetragonal zirconia was the only phase observed until about 800°C. After calcining at 800°C the crystallite size increased to about 20nm and about 34% monoclinic zirconia was produced. When an undivided cell was used, the pH remained constant (1–1.5) throughout the electrosynthesis, and amorphous zirconia deposited on the cathode.
A Study of Solvent Effects on the Synthesis of Pure Component and Composite Ceramic Powders by Metal Alkoxide Hydrolysis
Authors: Harris Michael T. , Byers Charles H. , Brunson Ronald R. 
Published: March 2011

ABSTRACTThe production of ceramics having high density, low porosity, and fine grains requires the use of high-purity metal oxide powders that consist of particles of uniform shape, size, and composition. Metal alkoxide hydrolysis is an attractive method for the synthesis of high-purity metal oxide particles. The nature of the precipitate formed is affected by the solvent.This present study investigates the growth kinetics and characteristics of metal oxide particles (i.e., ZrO2 and TiO2) that are produced in various alcohol solvents (ethanol, 1-butanol, 2-butanol, and tert-butyl alcohol). Results are also presented for the synthesis of uniform homogeneous composite metal oxide particles (i.e., Y2O3-ZrO2 and ZrO2-TiO2) by low temperature metal alkoxide hydrolysis.
Structural Investigation of the Hydrolysis-Condensation Process of a Modified Titanium Alkoxide.
Authors: Babonneau Florence , Leaustic Anne , Livage Jacques 
Published: March 2011

ABSTRACTTitanium isopropoxide was modified with acetylacetone in order to get stable photosensitive colloids via an hydrolysis-condensation process. The various steps of this process were followed by infrared, 1H and 13C NMR and X-Ray absorption (XANES and EXAFS). The latter techniques provided some interesting structural data (coordination of titanium, Ti-O and Ti-Ti distances) on the various species, from the precursor to the colloids. A structural model is proposed for each one, with a scheme of the different reactions occuring during the process.
The Optical Behavior of Organic and Organometallic Molecules in Sol-Gel Matrices
Authors: Dunn B. , Knobbe E. , McKiernan J. M. , Pouxviel J. C. , Zink J. I. 
Published: March 2011

ABSTRACTThe low temperatures involved in sol-gel processing have enabled organic and organometallic molecules to be incorporated in gel matrices. These molecules serve as optical probes to characterize gel chemistry and structure. The present paper describes the use of luminescence spectroscopy to detail matrix rigidity effects and protonation/deprotonation reactions during the sol-gel transition and subsequent aging processes. In separate experiments, the addition of a laser dye, rhodamine 6G, has enabled us to demonstrate lasing and optical gain in a silica gel.
Chemical Control of Stress in Sol-Gel Derived Titania Films and Their Pressure Dependent Optical Properties
Authors: Frydrych Wendy S. , Exarhos Gregory J. , Ferris Kim F. , Hess Nancy J. 
Published: March 2011

ABSTRACTOptical properties and durability of thin films are influenced by strain which can be evaluated from frequency shifts of the lattice phonon lines in measured Raman spectra. The response of titania samples to applied pressure is reported in this work. Anatase and rutile samples of thin films (sol-gel and sputter deposited) and bulk materials have been subjected to hydrostatic pressures approaching 100 kbar in a diamond anvil cell. Results indicate that the rutile samples exhibit similar responses to applied pressure. Anatase sol-gel films exhibit a pressure-dependent response that suggests that the sol-gel film is more compressible than the bulk material, and a pressure-induced phase transformation observed for the bulk material is inhibited in the anatase sol-gel film. The anomalous pressure response of the anatase sol-gel film may result from the film microstructure which has been shown by transmission electron microscopy to consist of spheres of crystalline TiO2 surrounded by microscopic voids.
An Electron Microscopy Study of the Alkaline Hydrolysis Products of Tetraethoxysilane
Authors: Adams Jeffrey , Baird Thomas , Braterman Paul S. , Cairns James A. , Segal David L. 
Published: March 2011

ABSTRACTThe hydrolysis of tetraethoxysilane was studied in an ethanol-water system with ammonium hydroxide catalyst. Reactions were carried out with water concentrations of 5M and 10M and ammonia concentrations up to 1.7M, and the products examined by electron optical methods. Variation of reagent concentrations lead to changes in the product morphology from small irregular particles, through roughly spherical and spherical particles to large fused particles. Within the range of particulate material the variations in size can be related to the effect of reagent concentrations by consideration of the reactions occurring. The effect on morphology of replacing ammonia with ethylamine was investigated and resembles that of the use of much higher ammonia concentrations.
Comparison of Several CU(I) and CU(II) Precursors for the Sol-Gel Preparation of HighTCSuperconducting Metal Oxides
Authors: Accibal Mariquita A. , Draxton Jonathan W. , Gabor Allen H. , Gladfelter Wayne L. , Hassler Beth Anne , Mecartney Martha L. 
Published: March 2011

ABSTRACTA comparison of the use of three different coordination compounds of copper as precursors for the sol-gel synthesis of YBa2Cu3O7-δ has been made. For yttrium, the tris(isopropoxide) was used exclusively, while the use of both Ba(O-i-Pr)2and Ba(OCH2CH2OEt)2(preparedin situfrom Ba metal) as sources for Ba were studied. After dissolving Y(O-i-pr)3, a Ba source, and the copper(I) alkoxide, [Cu(O-i-Bu)]4, hydrolysis led immediately to an orange gelatinous solid which yielded YBa2Cu3O7-δ upon firing in oxygen. Copper(II) acetate was found to give heterogeneous mixtures under our conditions and was not further studied. Copper(II) acac (acac = acetylacetonate) yielded the best results. Partially hydrolyzed solutions of Cu(acac)2, Ba(OCH2CH2OEt)2, and Y(O-i-pr)3were spin coated on SrTi03 (100) and fired under oxygen to give oriented (baxis normal to the surface) thin films of YBa2Cu3O7-δ. The onset of superconductivity for the films was 92 K, but they did not reach zero resistance until much lower temperatures.
Branching Theory in Sol-Gel Processing
Authors: Peppas Nikolaos A. , Scranton Alec B. , Tsou Andy H. , Edwards Dawn E. 
Published: March 2011

ABSTRACTThe complex sequence of the hydrolysis/polymerization reaction of certain types of alkoxysilanes is modelled using a novel approach based on the branching theory. Network formation is described, resulting from the reaction of multifunctional oligomers. Expressions are derived for the critical silane conversion at the gel point, the molecular weight, and changes in the sol and gel fractions as a function of time.
Chemical Precursors to Zinc Sulfide: ZnS Whisker Synthesis
Authors: Guiton Theresa A. , Czekaj Corinna L. , Rau Melinda S. , Geoffroy Gregory L. , Pantano Carlo G. 
Published: March 2011

ABSTRACTA variety of reactions employing organometallic precursors have been explored for the synthesis of ZnS. One of the most successful routes involves the reaction of [EtZn(SButS)]5 with H2S at ambient or sub-ambient temperature to yield a precipitate which is subsequently heated under flowing H2S at 500°C to yield a mixture of sub-micron particles and single-crystal ZnS whiskers. Transmission electron micrographs of the [EtZn(SBut)]5 products indicate that the ZnS morphology is critically dependent upon the rate of H2S reaction. Corresponding x-ray/ electron diffraction, electron microscopy, elemental analysis, NMR and infrared spectroscopies have been conducted. A summary of the chemical methods, product characterization results, and proposed synthesis mechanisms will be presented.The authors gratefully acknowledge the Office of Naval Research for the support of this research under Contract N0014–86-K-0191.
The Effect of Trioxane in HF-Catalyzed Sol-Gel Reactions of Tetraethoxysilane
Authors: Dorain Paul B. , Rafalko Joseph J. , Feeney James E. , Forbes Charles E. , Carney Raymond V. , Che Tessie M. 
Published: March 2011

ABSTRACTPorous silica glasses have been prepared using an HF-catalyzed tetraethoxysilane(TEOS)-ethanol-water formulation. The optical and physical properties of these glasses, which find use as host matrices for optical organic dyes, can be further improved with the addition of 1,3,5-trioxane to the sol-gel chemical system. In order to understand the effect of trioxane, the time-dependent concentrations of the species involved in TEOS hydrolysis and condensation have been followed by Raman, FT-IR, and NMR spectroscopie methods in both HF-catalyzed TEOS-ethanol-water systems with and without trioxane.
Silicon-29 Nuclear Magnetic Resonance Spectroscopy of Silicon Ethoxide and Titanium Ethoxide Sols: Resonance Assignments and Solution Stability
Authors: Boulos E. N. , Carduner K. R. , Carter R. O. , Best M. F. 
Published: March 2011

ABSTRACTSilicon-29 NMR spectroscopy has been widely applied to characterize the development of molecular complexity of silicon alkoxide sols. In the present study, the progression of molecular complexity of partially hydro-lyzed/condensed tetraethoxysilane (TEOS) sols with increasing H2O/TEOS ratio is demonstrated by the study of a carefully prepared set of solutions. Intriguing trends in the 29si NMR spectra of increasingly hydro-lyzed sols are discussed. In an set of samples, TEOS is replaced in part by tetraethoxytitane, Ti(OEt)4 (TEOT). The effects on the 29Si NMR spectrum due to the presence of TEOT are presented and interpreted in terms of changes in the distribution of siloxane monomers and oligomers in solution. Preliminary data on the stability of these solutions with time are reported.
An Analytical and Experimental Study of Plasma Spraying of Alumina
Authors: Varacalle D. J. 
Published: March 2011

ABSTRACTAs part of an investigation of the dynamics that occur in the plume of a typical thermal spray torch, an analytical and experimental study of the plasma spraying of alumina is being performed; preliminary results are reported here. Numerical models of the physical processes in the torch column and plume were used to determine the temperature and flow fields. Computer simulations of particle injection (15, 34, and 53 μm alumina particles) are also presented. The alumina experiments were conducted at a 35 kW power level using a 100 scfh argon and 15 scfh hydrogen gas mixture for two alumina powders. The quality of the coatings is discussed with respect to porosity, sample metallography, and microhardness.
Oxide-Diamond Composite Coating Via Sol-Gel Method
Authors: Nazeri-Eshghi Azar , Mackenzie J. D. , Yang J.-M. 
Published: March 2011

ABSTRACTUse of micron-size particles of synthetic diamond in oxide matrices prepared by sol-gel processing is explored. Alumina and borosilicate-diamond composite coatings are deposited on soda-lime microscope glass and fused silica substrates using dipping technique and thermophoresis. By varying the thermal gradient between the substrate and the solution, the quality of the films and the concentration of the particles can be controlled.
Experiences with Sol-Gel Bonded High Porosity Alumina Fiber Materials for Filter Applications
Authors: Handrick Karin E. , Mohlratzer August , Ostertag Rolf , Sporn Dieter , Schmidt Helmut 
Published: March 2011

ABSTRACTHigh porous alumina fiber structures appear promising for hot gas filtration in particular for diesel particulate traps. For this purpose, however, a method is required for manufacturing of stable shapes resistant to the blow-out by the gas flow. The sol-gel-process was expected to be the best suited method for fiber bonding to provide the required stability.The main tasks of the development-work were a uniform isotropie fiber-distribution, the adaptation of the sol-gel-process to the application, and the deliberate synthesis of the gel-derived alumina bonding phase.The appropriate fibrous structure was obtained by a repeated filtration of sol/fiber suspensions. The properties of the ceramic binder were adapted by concentrating the sol and/or adding aluminas or aluminium hydroxides.Testing of prototypes with optimized structures has shown, however, that the stability of the structure decreased after thermal load. The thermal fatigue of x-A12O3 is assumed to be responsible for this failure.
The Influence of Alkali Metal Hydroxides on Silica Condensation Rates: The Role of Ion Pairing
Authors: McCormick A. V. , Bell A. T. , Radke C. J. 
Published: March 2011

ABSTRACTThe condensation kinetics and the role of Ion pairing are investigated for silicate anions in alkaline solutions. Selective, and non-selective inversion recovery experiments are performed using the Si NMR spectrum of alkali metal silicate solutions. In this way the rates of condensation of silicate monomers is studied as a function of the nature of the base. These rates exhibit maxima with increasing cation size. The maxima are interpreted in terms of the concentration and activity of ion pair intermediates of the Si exchange reaction.Interactions between alkali metal cations and larger silicate anions in silicate solutions are investigated using NMR spectroscopy of the cations. The chemical shift and the resonance llnewidths are used to estimate the concentration of cation-silicate ion pairs. The concentration of pairs involving large anions increases with increasing cation size. Thus it is expected that condensation kinetics are influenced by the size of the silicate fragment.
Optical Characterization of Silica Aerogel
Authors: Hrubesh Lawrence W. , Alviso Cynthia T. 
Published: March 2011

ABSTRACTTwo optical methods are described for mapping the local variations of refractive index within monoliths of porous silica aerogel. One is an interferometrie measurement that produces “iso-index” fringes in a two dimensional image; an orthogonal view gives the third dimension information. The other method uses the deflection of a He-Ne laser beam to map the gradient index within a sample. The quantification of the measurements is described and the accuracy of the results is discussed.
Rheological Monitoring of Gelation Kinetics of Siuca Sols
Authors: Khan S. A. , Rabinovich E. M. , Prud'homme R. K. , Sammon M. J. , Kopylov N. J. 
Published: March 2011

ABSTRACTDynamic oscillatory measurements at low strains are used to monitor the gelation kinetics of particulate aqueous sols composed of alkoxide-derived silica powders. The dynamic storage modulus is sensitive to the sizes of the growing clusters below the gel point. A transition in the modulus is observed and large normal forces are measured at the gel point. These tests do not disrupt gel structure (in contrast to shear viscosity measurements) and therefore the measurement process does not alter the gelation kinetics. To facilitate gelation of sols composed of low-surface area silica particulates, silica powders doped with F ions were added to the undoped powder in various concentrations (10, 15 and 20 wt.%). These additions allowed a change in gelation time from 80 min. (for 10% of the F containing powder) to 17 min. (for 20%).
Polymetallic Alkoxides - Precursors for Ceramics
Authors: Mehrotra Ram C. 
Published: March 2011

ABSTRACTBeginning with the work of Dislich, metal alkoxides have been increasingly used for the preparation of oxide-ceramics by the ‘sol-gel’ process. In spite of higher initial cost of alkoxides, their main advantages are (i)homoge-neous mixing at molecular level in the initial solution; (ii)ease of hydrolysis; and (iii) lower sintering temperatures.Although the formation of new chemical bonds between different alkoxides employed in the starting mixed solution has been envisaged, the actual isolation of a large variety of polymetallic alkoxides in our laboratories has given an entirely new turn to the expectations (e.g., preparation of spinel from magnesium bis-tetraalkoxyaluminates) from this process. Some such possibilities are being presented for synthesis of novel ceramic materials.Reactions of polymetallic alkoxides with water, alcohols andβ-diketones would be discussed to throw light on their hydrolysis process in the presence of other alcohols and chelating ligands.
Techniques for Archaeothermometry
Authors: Palmiter Terese V. , Johnson Paul F. 
Published: March 2011

AbstractThis paper describes methods which have been used for the retrospective estimation of the firing temperatures of ancient ceramics, ranked by the reviewers in order of applicability from those considered least effective to the most successful. The techniques discussed include those that correlate color, physical, elastic and electronic properties, thermoluminescence sensitivity, morphology, mineralogy, and thermal behavior with temperature.
Glass Hydration Mechanisms with Application to Obsidian Hydration Dating
Authors: White William B. 
Published: March 2011

AbstractChemical analysis of typical obsidians place them with a group of silica- and alumina-rich glasses constructed of a three dimensional framework of silica and alumina tetrahedra with nearly all tetrahedra sharing corners. Raman and infrared spectra of unweathered obsidians confirm the high degree of polymerization as well as some additional structural disorder. Analysis of dissolution rates of various glasses shows obsidian to be among the most stable, comparable to the most durable synthetic glasses. Surface layers on glasses can be chemically characterized by depth-profiling techniques such as SIMS and SIPS that give depth-concentration profiles for individual elements. Hydration rinds on glasses can be structurally characterized by infrared spectroscopy which shows both hydration and re-polymerization as the rinds age. Because obsidians are already completely polymerized glasses, their hydration rinds are mainly a result of hydrolysis and alkali exchange.
Protective Coatings for Stained Glass
Authors: Colby Mary W. , Yuen Ting J. , Mackenzie J. D. 
Published: March 2011

AbstractThe protection of glass against water-initiated chemical corrosion is a significant problem. Presently, organic polymers and inorganically modified polymers are being used to protect art glass. However, the service life and durability of these coatings are not entirely satisfactory. Oxide coatings would offer much greater resistance to water penetration. Water permeability through a polymer coating is some ten orders of magnitude larger than that through an oxide coating. This, coupled with a higher scratch resistance, makes oxide coatings promising candidates for the protection of stained glass. Methods to deposit an oxide on glass at relatively low temperatures include sol-gel processing and vapor deposition. This paper compares the performance of different oxide and non-oxide coatings and presents methods for the deposition of oxide coatings at low temperatures.
Ancient Marble Sculpture: Geochemical Characterization of Surficial Weathering Products
Authors: Margolis Stanley V. , Preusser Frank , Showers W.J. 
Published: March 2011

AbstractQuantitative scientific determination of the authenticity and age of marble sculpture is an important goal of geo-archaeologists and conservation scientists. Geochemical and petrographic techniques are used here to investigate rock weathering and mineral alterations responsible for the “patina” and alteration layers on marble sculpture. We present oxygen and carbon isotopic, scanning electron microscopic and electron microprobe analyses of both fresh marble and weathering crusts materials from cores taken from Cycladic and Archaic Greek sculptures and from ancient quarries, to evaluate these techniques as indicators of antiquity.Calcitic marbles exhibit an altered weathering crust of variable thickness, where calcite has been recrystallized and interpenetrated with inclusions of iron oxide, clay minerals, gypsum and other authigenic minerals. The thickness and composition of these crusts varies with soil and water chemistry as well as marble density, texture and age.Microprobe analyses indicate trace element gradients from fresh to weathered calcite. Carbon and oxygen isotopes can differentiate between insitu alteration and precipitated carbonate. Dolomitic marbles can exhibit calcitic surficial layers formed by dedolomitization, which can be confirmed by isotopic and microprobe analyses.Analyses of known forgeries, ancient quarry samples and artificially weathered marbles have further documented our criteria and show that the majority of diagnostic geochemical and mineralogical features seen on ancient Greek sculptures cannot be accurately duplicated by artificial means.