bluuebunny/crossref_metadata_2025_split huggingface dataset:
New Chemistry for the Sol-Gel Process: Acetone as a New Condensation Reagent
Authors: Goel Subhash C. , Chiang Michael Y. , Gibbons Patrick C. , Buhro William E. 
Published: March 2011

ABSTRACTA nonhydrolytic sol-gel process that uses acetone as the condensation reagent is described. In the new process, the hydrocarbon soluble Zn(OCEt3)2 is converted to a rigid, transparent gel and then to ZnO by an aldol-condensation-elimination sequence. The chemical pathway for the transformation has been established, and differs completely from the pathway for the conventional hydrolytic sol-gel processing of alkoxide precursors. The new, nonhydrolytic strategy may prove applicable to a variety of metal-alkoxide systems.
Electrical Properties of Crystalline and Amorphous Pb(ZrxTi1−x)O3 Thin Films Prepared by the Sol-Gel Technique
Authors: Xu Yuhuan , Cheng Chih-Hsing , Xu Ren , Mackenzie John D. 
Published: March 2011

ABSTRACTPb(ZrxTi1−x)O3 (PZT) solutions were prepared by reacting lead 2-ethylhexanoate with titanium n-propoxide and zirconium n-propoxide. Films were deposited on several kinds of metal substrate by dip-coating. Crystalline PZT films and amorphous PZT films were heat-treated for 1 hour at 650°C and at 400°C, respectively. Electrical properties including dielectric, pyroelectric and ferroelectric properties of both crystalline and amorphous PZT films were measured and compared. The amorphous PZT thin films exhibited ferroelectric-like behaviors.
Preparation of BaTiO3 and PbTiO3 thin Films on BaPb3 Substrates by the SOL-GEL Method and Their Properties
Authors: KuWabAra M. , Kuroda T. , Takahashi S. , Azuma T. 
Published: March 2011

ABSTRACTBarium titanate, lead titanate and barium-lead titanate thin films were prepared by the sol-gel method using metal alkoxides on metallic conducting BaPbO3 ceramic substrates. Thin films were deposited on the polished surfaces of the substrates by spin coating solutions containing Ba(OC2H4OCH3)2, Pb(OCOCH3)2 and Ti(O-iC3H7)4 and methoxyethanol. The gel films were then fired at appropriate temperatures to yield ceramic thin films. A 0.50 µm-thick BaTio3 film showed a dielectric constant of 280 and tan ° of 3% at 1kHz with no distinguishable peak of dielectric constant at any temperature between 20°C and 200°C. Both PbTiO3 (0.75 µm thick) and Ba0.7Pb0.3 (0.2 µm thick) films, on the other hand, showed a distinguishable peak of dielectric constant at their Curie point with a rather deformed P-E hysteresis loop at room temperature.
Growth of Oriented Tin Oxide Thin Films from an Organctin Compound by Spray Pyrolysisxf
Authors: Yag Isao , Kaneko Shoji 
Published: March 2011

ABSTRACTTin oxide films were grown from di-n-butyltin diacetate on a heated glass substrate by a pneumatic spraying system The effects of various film growth parameters. i.e solvent, solution feed rate, film thickness, and film growth rate on the microstructures of the films were studied by X-ray diffraction and scanning electron microscopy The SnO2 films of the (200) plane were grown by the optimum growth parameters
Laser Densification of Sol-Gel Derived TiO2 - Thin Films.
Authors: Arfsten N. , Lintner B. , Heming M. , Anderson O. , Otter-Mann C. R. 
Published: March 2011

ABSTRACTLaser substrate heating is discussed as an alternative for the densification of sol -gel thin films. Homogeneous films of n(550 nm) = 2.30 could be obtained, keeping the bulk substrate temperature below 80 °C.
Hydrolysis and Condensation of Modified TIN (IV) Alkoxide Compounds to form Controlled Porosity Materials
Authors: Roger Christophe , Hampden Smith M. J. , Brinker C. J. 
Published: March 2011

ABSTRACTSol-gel type hydrolysis and condensation has been studied extensively as a method for the control of evolution of microstructure in the formation of inorganic silicates. However, in non silicate systems, the same level of control of microstructural evolution has yet to be demonstrated. In this work, we report the synthesis of mixed ligand tin (IV) alkoxide complexes specifically designed to undergo sequential hydrolysis reactions, where, as a result, control over porosity of the final metal oxide network is expected. A series of tin (IV) alkoxide compounds modified with difunctional carboxylate ligands as templates has been prepared with internuclear tin separations that are determined by the length of the bridging carboxylate group. The first hydrolysis step consists of the removal of the alkoxide ligands to create a three-dimensional network of oxo-bridged tin carboxylate species. In the second step, the bridging groups are removed by acid hydrolysis to leave pores without creating new Sn-O-Sn bonds. The synthesis and characterization of these species and the connection between pore structure (i.e. micro- vs. meso- porosity) as a function of the dimensions of the bridging ligands will be reported.
Preparation of Low-Density Aerogels at Ambient Pressure
Authors: Smith Douglas M. , Deshpande Ravindra , Jeffrey Brinke C. 
Published: March 2011

ABSTRACTLow density aerogels have numerous unique properties which suggest a number of applications such as ultra high efficiency thermal insulation. However, the commercial viability of these materials has been limited by the high costs associated with drying at high pressures (supercritical), low stability to water vapor, and low mechanical strength. Normally, critical point drying is employed to eliminate the surface tension and hence, the capillary pressure, of the pore fluid to essentially zero. However, we show that by employing a series of aging and surface derivatization steps, the capillary pressure and gel matrix strength may be controlled such that gel shrinkage is minimal during rapid drying at ambient pressure. The properties (density, surface area, pore size, SAXS) of aerogel monoliths prepared from base catalyzed silica gels using this technique, supercritical CO2 drying, and supercritical ethanol drying are compared. An additional advantage of this approach is that the final gels are hydrophobic.
Leucite-Pollucite Glass Ceramics: A new Family of Refractory Materials with Adjustable Thermal-Expansion
Authors: Bedard R. L. , Broach R. W. , Flanigen E. M. 
Published: March 2011

ABSTRACTNovel ceramic compositions can be produced from carefully chosen, modified, and processed zeolites. The use of zeolites as precursors for leucite-pollucite glass ceramics having adjustable thermal-expansion behavior is described. The facile sintering properties of the zeolite-derived precursors allow production of these high-temperature materials at several hundred degrees below the solidus temperatures. A representative leucite-pollucite ceramic was studied by high temperature x-ray powder diffraction and synchrotron powder diffraction to determine the nature of the crystal structure and its relationship to the leucite and pollucite end members of the family.
Sintering Process and Mechanical Properties for Oxide-Based Nanocomposites
Authors: Niihara Koichi , Nakahira Atsushi , Inoue Masahiro 
Published: March 2011

ABSTRACTOxide-based Al2O3/SiC nanocomposites, in which the nanometer-sized nonoxide SiC particles are dispersed mainly within the matrix Al2O3 grains, were fabricated by the normal powder metallurgical methods. High resolution transmission electron microscopic observation showed that the nanometer sized SiC particles were directly bonded to the matrix Al2O3 grain without any reacting layers. The nano-sized SiC dispersions gave the significant improvement of mechanical properties such as fracture strength over 1000 MPa and no degradation of its strength up to 1000°C for Al2O3/SiC nanocomposites, was observed. The sintering process and the correlation between mechanical properties and micro/nanostructure will be discussed for this nanocomposite.
Amorphization at the Metal-Ceramic Interface in Nb – Al2O3 Composite Through Extensive Interphase Diffusion
Authors: Ray Abhijit , Samanta Shyam K. 
Published: March 2011

ABSTRACTA novel, low temperature and pressureless bonding technique has been developed to fabricate Al2O3 coated Nb composite. The nature of the interface bond has been characterized by extensive electron microscopic investigation, and a phenomenological model has been developed to explain the mechanism of bond formation. In the present technique a suspension (in distilled water) of fine Al2O3 powder (mean particle size of 0.2μm) was applied on polished and cleaned Nb blocks. The coatings were air dried and the coated metals were heat treated at 1100°C to achieve bonding between the ceramic and the metal. The process was carried out in an argon atmosphere. To reduce the oxygen impurity content in argon, the gas was passed over Mg turnings at 300°C before its entry into the bonding apparatus. Control of oxygen impurity in the bonding atmosphere in conjunction with the use of fine ceramic particles led to enhancement of interfacial diffusion. Scanning electron microscopy of the bonded specimens showed a consolidated layer in the ceramic phase close to the metal-ceramic interface. Transmission electron microscopy of the metal-ceramic interfacial region rOevealed a distribution of Al2O3 particles in an amorphous phase containing varying amount of Al, Nb, and 0. Prior treatment with Mg was to reduce the oxygen impurity content below the equlibrium oxygen partial pressure (at 1100°C) of Al2O3. This would result in loss of oxygen from the surface of the ceramic particles. Thus a region, with high concentration of 0= vacancy would form along the surfaces of the particles. As a result of excessive oxygen depletion, further continuation of this process would lead to degeneration of the crystal structure of the regions along the surfaces of the Al2O3 particles. These regions along the Al2O3 particle surfaces may then act as easy diffusion paths for Nb. Extensive diffusion of the metal into the ceramic phase along these paths would lead to the formation of an amorphous phase along the ceramic particle surfaces. Eventually, this phase will occupy the voids in between the ceramic particles, that are close to the metal-ceramic interface, and thus bond them together with the metal.
Diffusion of Carbon Monoxide in Metalorganic thin Films Derived from Titanium Alkoxide Carboxylates
Authors: Gagliardi Charles D. , Dunuwila Dilum , Chang C. K. , Berglund Kris A. 
Published: March 2011

ABSTRACTThe diffusion of carbon monoxide into thin, transparent, porous film media is studied by doping the film with an iron porphyrin and spectroscopically monitoring the chemical interaction between the reduced iron porphyrin and the diffusing solute. The films are spin-cast from metal alkoxide carboxylates. Both optical absorption and resonance Raman spectroscopies have been used to study the porphyrin-doped film and the diffusion process.The studies yield information on the effective pore size and homogeneity of the materials, and show that redox chemistry can be performed on incorporated metallo-porphyrins. This investigation also demonstrates the usefulness of porphyrin-doped films as chemical sensors, showing a sensitivity below 70 ppb to aqueous carbon monoxide.
Raman and Surface Enhanced Raman Spectroscopy of Titanium Carboxylates
Authors: Van Vlierberge-Torgerson Beatrice A. , Dunuwila Dilum , Berglund Kris A. 
Published: March 2011

ABSTRACTPorous stable metal-organic films can be processed under mild conditions by the hydrolysis of carboxylic acid and titanium isopropoxide mixtures. It is of importance to establish the structure of such materials. Raman spectroscopy is a useful technique in determining structural changes in titanium isopropoxide carboxylate solutions, but weak scattering does not allow for study of thin films unless surface enhancement is used. In an attempt to elucidate the relationship between coating solutions and the final structure of a cast film, we discuss Raman spectra of precursor solutions in a variety of conditions.
Synthesis and Characterization of Organic Dye Doped Silica Glasses
Authors: Lee Ilzoo , Covino Josephine , Seltzer Michael D. 
Published: March 2011

ABSTRACTThe sol-gel process was used to incorporate organic dyes including Rhodamine 6G (Rh6G), 2-(4-pyridyl)-5-(4-phenyl) oxazole (4PyPO) and the n-methyl tosylate salt of 2-(4-pyridyl)-5-(4-methoxy phenyl)oxazole (4PyMPO-MePTS) in silica gel. Thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) analysis of the dye doped gels showed that the gel structure loses the adsorbed water molecules from room temperature to 150°C and decomposition of the dye molecules followed at the higher temperature. Absorption and emission of the dyes in the sol-gel glass matrix were also studied and compared with the results of the dyes in alcohol solution. The environments of the dye in silica were different than in alcohol solution.
The Effect of Ultrasonic Radiation on Gelation and Properties of Ormosils
Authors: Monta Kazuki , Hu Yi , Mackenzie John D. 
Published: March 2011

ABSTRACTUltrasound has been applied to organically modified silicates (ORMOSILs) solutions during gelation. A series of silica and polydimethylsiloxane (PDMS) composites have been prepared by the sol-gel method. Tetraethoxysilane (TEOS), PDMS, water and a HC1 catalyst were mixed and exposed to 20 kHz ultrasonic radiation under different conditions. Ultrasonic radiation made it possible to obtain wet gels in 5 to 30 min. without solvent (e.g. alcohol, and THF). And exothermic reaction was observed due to hydrolysis and polycondensation of TEO S. The reaction process was examined by liquid state 29Si NM R. Densities of obtained sono-ORMOSILs were observed to be higher than those produced by ordinary processes. Some sono-ORMOSIL samples demonstrated extremely low porosity and low specific surface areas.
Hypervalent Siliconate Materials. Synthesis and Characterization of Novel Ladder and Network Ionomers
Authors: Shea Kenneth J. , Loy Douglas A. , Small James H. 
Published: March 2011

ABSTRACTThe first representatives of novel materials that contain five- and six-coordinate anionie silicon are reported. Linear (or cyclic) ionomers incorporating pentacovalent siliconate were synthesized by condensation of 1,2,4,5-tetrahydroxybenzene (THB) with alkyl and aryl trialkoxysilylanes. Network ionomers that incorporate pentacovalent siliconates were formed from THB and alkyl and aryl bistrialkoxysilanes. In addition, network ionomers with hexacoordinate silicon result from condensation of TEOS and THB. Spectroscopie evidence is presented to verify the identity of the novel structural features of these materials.
Multifunctional (Meth)Acrylate Alkoxysilanes a New Type of Reactive Compounds
Authors: Wolter H. , Glaubitt W. , Rose K. 
Published: March 2011

ABSTRACTA new class of (meth)acrylate substituted alkoxysilanes has been developed. These are synthesized by addition of the H-S- or H-Si-unit of thiosilanes (e.g. HS- (CH2)3-SiCH3(OCH32)or hydrosila-nes to one (meth) acrylate C=C bond of commercially available di-, tri-, tetra- or penta-(meth)acrylate compounds. The alkoxysilyl groups allow the formation of an inorganic Si-O-Si-network by a hydrolysis and polycondensation reaction (sol-gel process), and the (meth)acrylate groups are available for thermally or photochemical ly induced organic polymerisation. The elegant procedure for the synthesis of a wide variety of multifunctional alkoxysilanes and the preparation of optical lenses will be discussed.
Multifunctional Acrylate Alkoxysilanes for Polymeric Materials.
Authors: Rose K. , Wolter H. , Glaubitt W. 
Published: March 2011

ABSTRACTMultifunctional acrylate alkoxysilanes synthesized from commercial acrylate compounds and mercapto-substituted alkoxysilanes were used as precursors in the development of materials for various purposes. The alkoxysilyl groups are available for the construction of an inorganic backbone by the sol-gel process, and the acrylate groups for building an organic polymeric matrix by thermal or photochemical curing.Tailoring the material properties is achieved by use of specific molecular structures and functionalities within the monomeric compounds. Linear and branched structural units influence the mechanical properties (modulus of elasticity, abrasion resistance, flexural strength). Rapidly UV-cured materials have been prepared for use as primary or secondary coatings for silica optical fibres with improved adhesion under humid conditions. Further organic modification results in polymers which can be used for manufacturing lenses of high optical quality. Preliminary attempts to draw fibres have also been successful.
Chemically Designed, UV Curable Polycarbosilane Polymers
Authors: Thorne Kevin J. , Johnson Stephen E. , Zheng Haixing , Mackenzie John D. , Hawthorne M. F 
Published: March 2011

ABSTRACTTo prepare new polycarbosilane polymer precursors with high solubility and the capability of UV cross-linking, commercial polycarbosilane was modified by a chemical route. These modifications involved AlCl3 catalyzed chlorination reactions of polycarbosilane's Si-H bonds. The resultant Si-Cl bonds were substituted by a reaction with sodium acetylyde to form Si-C=CH ligands. These ligands are suitable for controlled, free radical initiated cross-linking of the polycarbosilane polymers. The increase in molecular weight should allow for increased Tg's and the retention of polymer pre-forms. In this report, the chlorination of the polycarbosilane polymer and the substitution reactions of polycarbosilane were examined with IR, 29Si and 13C NMR spectroscopy. In addition, the retention of polymer pre-forms were analyzed after UV exposure and inert atmosphere pyrolysis.
The Role of Si-H Functionality in Oxycarbide Glass Synthesis
Authors: Singh Anant K. , Pantano Carlo G. 
Published: March 2011

ABSTRACTSilicon oxycarbide gels and glasses were synthesized using various ratios of methyldimethoxysilane and TEOS. These gels and glasses were compared with those made from methyltrimethoxysilane and TEOS. The effect of the Si-H functionality in the methyldimethoxysilane was of primary interest. Hydrolysis and condensation processes were monitored using 1H and 29Si-NMR spectroscopy. The structures and the oxycarbide fractions of the glasses, obtained after heating the gels to 900°C in flowing argon, were investigated with 29si-MAS NMR. The total carbon and silicon contents of the glasses were determined using chemical analysis. The glasses covered the range of carbon concentration from ∼1 to 15%, while the silicon concentrations were constant at about 40%. The concentration of the oxycarbide species was enhanced in the glasses synthesized with the Si-H functionality in the precursor.
Reaction Sintering Mechanism of Submicrometer Silicon Powder in Nitrogen
Authors: Yasutomi Yoshiyuki , Sobue Masahisa , Kondo Jiro 
Published: March 2011

ABSTRACTKnowing the nitridation mechanism of Si is important to obtain near-net-shape high strength reaction bonded ceramics. In this report, comparison of nitridation mechanism of small spherical Si powder produced by plasma arc method and large faceted Si powder, is discussed on the basis of microstructural analyses by SEM and TEM. From the analyses, nitrogen diffuses through the oxide film of Si powder and forms Si3N4 under the oxide films during the initial stage of sintering. At higher temperature, the oxide film transform into fine Si3N4 grains when heated to the 1350°C. The Si3N4 has morphology of hollow shell and a size, which corresponds to that of the original Si particles.
Synthesis of Advanced Ceramics in the Systems Si-B-N and Si-B-N-C Employing Novel Precursor Compounds
Authors: Baldus H.-P. , Wagner O. , Jansen M. 
Published: March 2011

ABSTRACTThe reaction of Cl3Si-NH-Si(CH3)3 with BCl3 yields the novel compounds Cl3Si-NH-BCl2 and (Cl3SiNH)2-BCl. The ammonolysis of these monomeric precursors in liquid ammonia gives rise to highly crosslinked borosilicon imides. Pyrolysis of the polymeric imides in a stream of ammonia at 1250°C yields amorphous borosilicon nitrides with formal compositions of Si3B3N7 and Si6B3Nu respectively. MAS-NMR, DTA/TG, SEM and TEM investigations reveal that the resulting materials are single phase.The reaction of the novel precursors with primary amines yields meltable and soluble polymers suitable for producing fibers or coatings. Subsequent pyrolysis in NH3 leads also to amorphous borosilicon nitride. The physical and chemical properties of the new materials will be discussed.
Design and Synthesis of Chemical Precursors to Boron Carbide
Authors: Yang Xiaoguang , Johnson Stephen , Frederick M. , Zheng Hadcing , Thorne Kevin , Mackenzie J. D. 
Published: March 2011

ABSTRACTThe design of molecular and preceramic polymer precursors to boron carbide based ceramics is described. The goal was to design nonvolatile, tractable precursors to boron carbide with high ceramic yields. Molecular precursors containing carburane cages and acetylenie groups were synthesized and converted to nonvolatile, soluble preceramic polymers. Pyrolysis of these polymers gave boron carbide based ceramics in 60–70% ceramic yield. A B4C/SiC film has been fabricated from one of the polymers and the film is uniform and crack-free.
Properties of ZrO2, Gels Prepared by Controlled Chemical Modification Method of Alkoxide
Authors: Suzuki Hisao , Saito Hajime , Hayashl Hiroaki 
Published: March 2011

ABSTRACTPolymeric ZrO2 gels were prepared by the controlled chemical modification method (CCM method) of zirconium-n-propoxide. In this method, the steric hindrance by alkoxide-acetic acid chelation could be used to control the hydrolysis and condensation reaction of the zirconium alkoxide if the amount of hydrolysis water was limited. As a result, polycondensaticn occurred uniformly in the solution, forming a linear zirconoxane polymer. When the solvent evaporated, the zirconoxane polymer crosslinked with each other and formed polymeric ZrO2, gels, which were monolithic and transparent. These polymeric gels could be re-dissolved into n-butyl alcohol with acetic acid and mechanical stirring. Heating would enhance the dissolution of the gels. Using the re-dissolved gel solution, dense thin films of ZrO2, could be obtained by dip-coating procedures without many coating operations.
Optimization of Aluminum Nitride Thermal Conduchvity VIA Controlled Powder Processing
Authors: Guiton Theresa A. , Volmering James E. , Killinger Kris K. 
Published: March 2011

ABSTRACTThe emergence of aluminum nitride ceramics in electronic and structural applications has been largely due to the increased availability of high quality powders. Much of the process development has been concentrated in capturing markets within the electronics industry, mainly high thermal conductivity substrates. The thermal conductivity of A1N substrates is strongly dependent on oxygen chemistry and sintering parameters. A key source of oxygen is AlN powder impurities. In this study, powders with differing oxygen contents were formulated with various Y2O3 levels. The results indicate that the distribution of sintered oxygen is strongly correlated with the relative concentration of the powder's lattice and surface oxygen. Under the sintering parameters of the analysis, optimal thermal conductivities were achieved when Y4Al2O9 was present as the grain boundary phase. As predicted, the powders with the lowest lattice oxygen concentrations exhibited the highest thermal conductivities. Hence, depending upon the surface oxygen content, different yttria levels were required for optimal thermal conductivities, i.e., higher surface oxygen contents required higher sintering additive levels than did low surface oxygen powders.