bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on the Formation of Tin(IY) Oxygen Compounds by Sol-Gel-Process
Authors: Reuter H. , Kremser M. , Schröder D. , Jansen M. 
Published: March 2011

ABSTRACTSolutions of Sn(OR)4 and R'Sn(OR)3 with different amounts of alkali and alkaline earth metal alkoxides, MI(OR) and MII(OR)2 respectively, have been prepared. Slow evaporation of the solvent resulted in the crystallization of mixed metal alkoxide compounds. Solid state structures have been determined for two examples: K3H[Sn(O/Pr)6]2 and Na2[iPrSn(OiPr)5]·5iPrOH. Solutions as well as solids have been hydrolyzed by moisture. The thermal behaviour of the resulting amorphous powders was investigated by TG, DTA and XRD up to 1000°C in argon atmosphere. The structural evolution during the solid state step mainly depends on the nature and amount of the mono- and bivalent cations. The different influence of both parameters is described.
Electrical and Optical Properties of Sol-Gel Processed Pb(Zr,Ti)o3 Films
Authors: Ramamurthi S. D. , Swartz S. L. , Marken K. R. , Busch J. R. , Wood Battelle V. E. 
Published: March 2011

ABSTRACTLead-zirconate-titanate, Pb(Zr0.53Ti0.47)O3, films were produced by the sol-gel method from alkoxide and acetate precursors in a 2-methoxyethanol solvent system. The PZT films were deposited on platinized silicon and single-crystal SrTiO3 substrates for electrical and optical characterization, respectively. The processing parameters, especially excess PbO content and annealing conditions, were shown to have a significant effects on the properties of PZT films. Epitaxial PZT films deposited on SrTiO3 waveguided over 10 mm distances with propagation losses as low as 5.9 dB/cm at 783 nm and a linear electro-optic effect was also demonstrated.
Sol-Gel Multilayers Applied by A Meniscus Coating Process
Authors: Britten Jerald A. , Thomas Ian M. 
Published: March 2011

ABSTRACTWe describe a meniscus coating method to produce high-laser damage threshold, silica/alumina sol-gel multilayer reflectors on 30+ cm substrates for laser-fusion applications. This process involves forcing a small suspension flow through a porous applicator tube, forming a falling film on the tube. A substrate contacts this film to form a meniscus. Motion of the substrate relative to the applicator entrains a thin film on the substrate, which leaves behind a porous, optical quality film upon solvent evaporation. We develop a solution for the entrained film thickness as a function of geometry, flow and fluid properties by an analysis similar to that of the classical dip-coating problem. This solution is compared with experimental measurements. Also, preliminary results of multilayer coating experiments with a prototype coater are presented, which focus on coating uniformity and laser damage threshold (LDT).
Phase Transformations in Sol-Gel Yag Films
Authors: Hay R. S. 
Published: March 2011

ABSTRACTDiphasic yttrium-aluminum garnet (YAG) sols were gelled across TEM grids to make films. The films were heat-treated up to 300 hours between 800°C to 1150°C. Microstructure and phase evolution were observed by TEM. YAG fraction and grain size, matrix phases and grain size, nuclei/area, and film thickness were measured. Yttrium-aluminum monoclinic and transition alumina appeared at 800°C. YAG nucleated between 800°C and 950°C. Above 850°C nudeation was site-saturated. Final nuclei density averaged 0.3/μm3. Between 850°C and 1000°C YAG growth had ∼t1/2 dependence and Q ∼ 280 kJ/mole. Below 850°C nudeation was continuous and growth had ∼t0.85 dependence. Above 1000°C YAG growth had ∼t1/4 dependence and the matrix grains coarsened with ∼t1/4 dependence. Unreacted areas were more abundant in thinner films because the nuclei/area and reaction rate decreased. YAG growth was often accompanied by formation of 20 – 100 nm subgrains. Above 1100°C there was some readion to YAG by a different process.
Crystalline Thin and/or Thick Film of Perovskite-Type Oxides by Hydrothermal Electrochemical Techniques
Authors: Yoshimura Masahiro 
Published: March 2011

ABSTRACTWell crystallized polycrystalline perovskite-type oxide thin and/or thick films were prepared at sufficiently low temperatures by newly developed “hydrothermal electrochemical techniques” where metals were electrochemically oxidized and reacted with some components in hydrothermal solutions. BaTiO3 films 70 to 300 nm thick were formed in Ba(OH)2 solution at 100–200°C under saturation vapor pressure on the Ti substrate and Ti deposited glass substrates. The electrical current enhanced to thicken their films. SrTiO3, BaFeO3 and LiNbO3 films were also prepared.
Mechanics of Gels
Authors: Scherer George W. 
Published: March 2011

ABSTRACTThe response of wet gels to applied stresses is discussed, with emphasis on the role of flow of the pore liquid. Even when the network of the gel is purely elastic, the gel exhibits time-dependent behavior that resembles viscoelasticity, which results from fluid flow. The permeability of the gel can be determined from measurement of this time-dependence. Fluid flow also influences the thermal expansion behavior of gels, and can cause severe stresses to develop during supercritical drying, if the autoclave is heated too rapidly.
Pore Structure Evolution of Silica Gel during Aging/ drying: Effect of Surface Tension
Authors: Deshpande Ravindra , Smith Douglas M. , Jeffrey Brinker C. 
Published: March 2011

ABSTRACTTwo-step acid/base (B2) and acid/acid (A2) catalyzed silica gels have been aged in ethanol or water baths followed by various aprotic solvents with a range of surface tensions. The physical and chemical structures of xerogels dried from these aprotic solvents were studied by a series of techniques (nitrogen adsorption, elemental analysis, TGA, SAXS)and compared to the corresponding structures of low temperature (CO2) and high temperature (ethanol) aerogels. The aprotic solvents help to isolate the effects of pore fluid surface tension during drying since they do not react with the gel surface. B2 xerogels showed a linear decrease in surface area with increasing surface tension. Pore volume and pore size followed a similar trend. Micropore analysis on A2 xerogels showed an increase in micropore volume and surface area with increase in surface tension, whereas total surface area and pore volume showed an opposite trend. Thus, by varying surface tension and aging, one is able to independently control surface area, pore volume, and pore size.
Interpretation of Aerogel Shrinkage During Drying.
Authors: Rangarajan Bharath , Lira Carl T. 
Published: March 2011

ABSTRACTA variety of silica aerogels have been prepared by the hydrolysis of TEOS, and dried using supercritical CO2. The shrinkage which occurs during the drying process is dependent on the gel formulation and the extent of aging of the gels in their pore liquor. Such aging normally results in an increased density, modulus and pore size of wet gels. Upon drying the corresponding aerogels show the opposite behavior for modulus and density, which decrease with the extent of aging. Both drying and aging shrinkage were not observed for base-catalyzed gels, and were very small for HF-catalyzed gels. The use of formamide resulted in reduced drying shrinkage and a slightly larger amount of syneresis. Drying shrinkage is associated with the presence of micropores. Shrinkage during drying has been observed using a high pressure view cell and it was found that most of the shrinkage occurred during depressurization. An explanation consistent with the above is proposed.
Tailoring of Transition Metal Alkoxides Via complexation For The Synthesis of Hybrid Organic-Inorganic Sols and Gels
Authors: Sanchez C. , In M. , Toledano P. , Griesmar P. 
Published: March 2011

ABSTRACTThe chemical control of hydrolysis-condensation reactions of transition metal alkoxides can be performed through the modification of the transition metal coordination sphere by using strong complexing ligands (SCL). Complexing organic groups can be bonded to the transition metal oxide network in two different ways, as network modifiers or network formers. Different illustrations of the role of complexing ligands on Ti(IV) and Zr(IV) alkoxides are presented. As a network modifier, SCL act as termination agents for condensation reactions allowing a control of particle growth. The complexing ligands being located at the periphery of the oxo core open many opportunities for colloid surface protection. SCL carrying organofunctional groups which exhibit non linear optical (NLO) properties have also been used as probes to study sol-gel transformations. SCL functionalized with organic polymerizable functions act as network formers. Hybrid organic-inorganic copolymers intimately interpenetrated on a nanometer size scale were synthesized from zirconium oxo polymers chemically bonded to polymeric methacrylate chains via a complexing function.
Characterization of Microporous Silica Gels Prepared from Modified Silicon Alkoxides
Authors: Fahrenholtz W. G. , Smith D. M. 
Published: March 2011

ABSTRACTOrganically modified silica gels were prepared from mixtures of TEOS and methyl-substituted silicon alkoxides. The pore structure of dried gels was investigated in order to determine the effect of the organic additions on gel structure. For base catalyzed gels, surface area, pore volume, and skeletal density all showed dramatic decreases at high methyl contents. The surface area dropped by nearly three orders of magnitude, from over 800 m2/g for normal silica gels to less than 1 m2/g for gels containing over 60 mole percent modified alkoxide. The pore structure of acid catalyzed gels showed less dependence on composition. The nature of the surface of both acid and base catalyzed gels varied with modified alkoxide content. Higher organic contents produced materials that were more hydrophobic. In addition, the mechanical strength of acid catalyzed gels dropped in direct proportion to methyl content.
Processing of SiC-Based Fibres from Polycarbosilane
Authors: Kalyvas Vasilios , Ko J. C. , East G. C. , Mcintyre J. E. , Rand B. , Riley F. L. 
Published: March 2011

ABSTRACTA commercial polycarbosilane, thermolysis product of polysilastyrene, was spun into fibres. The self-curing character of the polymer permitted both oxidative and thermal curing of the precursor fibres. Pyrolysis of the latter produced ceramic fibres in high yields, which were fully characterised. Optimum tensile strength was attained after heat treatment at 1100°C. Oxidative reactions and crystallisation caused strength degradation above this temperature.
Alkynyl Substituted Carboranes as Precursors to Boron Carbide Thin Films, Fibers and Composites
Authors: Johnson Stephen E. , Yang Xiaoguang , Hawthorne M. F. , Thorne Kevin J. , Zheng Haixing , Mackenzie John D. 
Published: March 2011

ABSTRACTThe use of alkynyl substituted derivatives of o-carborane as precursors to boron containing ceramics is described. These compounds undergo a thermally or photochemically induced polymerization to afford cross linked polyakynyl-o-carborane derivatives. The increase in molecular weight should allow for increased Tg's and the retention of modelled polymer preforms. In this report, these modification reactions are described. In addition, the retention of molded polymer preforms were analyzed after UV exposure and inert atmosphere pyrolysis.
Polymer Precursors for Aluminum Nitride Ceramics
Authors: Jensen James A. 
Published: March 2011

ABSTRACTThe aluminum imine complexes [RCH=NAlR'2]2 undergo thermal condensation polymerization to yield alazane [poly(alkylaminoalane)] polymers. The aluminum imine complexes are prepared in quantitative yield by reduction of nitriles, such as acetonitrile and benzonitrile, with alkylaluminum hydride reagents. These alazane polymers are thermoplastic, soluble in aprotic solvents, and display low moisture and oxygen sensitivity. The alazanes convert to aluminum nitride ceramics in non-oxidizing atmospheres above 500°C.
Computation, Visualization, and Chemistry of Electric Field-Enhanced Production of Ceramic Precursor Powders
Authors: Harris Michael T. , Sisson Warren G. , Basaran Osman A. 
Published: March 2011

ABSTRACTThe stability of a liquid emanating from a nozzle is profoundly affected by an electric field. This electric-field induced instability is used here to form ceramic precursor powders having well-controlled particle-size distribution and morphology. Moreover, a hybrid boundary element/finite element method is used to determine the shapes and stability of a drop hanging from a nozzle. The efficiency of two different electrode configurations is considered: in one configuration, the nozzle is attached to the top plate of a parallel-plate capacitor and in the other, the nozzle is surrounded by a concentric cylindrical electrode. The computational results show that such pendant drops lose stability at turning points with respect to field strength. The experimental and computational results reported here are of importance not only in the development of electrodispersion apparatus, but in fields as diverse as capillarity and separations.
Synthesis of Barium Titanate by a Basic pH Pechini Process
Authors: Kumar Suresh , Messing Gary L. 
Published: March 2011

ABSTRACTBarium titanate powders and thin films have been processed by the conventional acid pH Pechini process and a modified basic pH Pechini process. Higher pH of the starting solution resulted in significantly finer grains in the sintered thin films. It is proposed that the microstructure refinement is due to the precipitates, formed only in the basic pH solution and resin.
Formation of Highly Dispersed Metal Carbides, M2C (M=Mo, W) via Chemical Reduction Methods
Authors: Zeng Dongshui , Hampden-Smith M.J. , Datye A. 
Published: March 2011

ABSTRACTA new reduction method for the preparation of the molybdenum halides MoCl3(THF)3 and MoCl4(THF)2 in high yield and with high purity directly from MoCl5 is described. The preparation of pure starting materials is crucial to the success of the subsequent chemical reduction. Reduction of MoCl3(THF)3, MoCl4(THF)2 or WCl4 in THF with LiBEt3H at room temperature did not.result in formation of Mo and W as anticipated but instead resulted in formation of nanophase M2CM = Mo and W binary metal carbides. These species were characterized by SEM, TEM, energy dispersive spectroscopy, electron diffraction, elemental analysis, thermogravimetric analysis and X-ray diffraction techniques. These techniques showed the black solids were crystalline and comprised 1–2 nm sized crystallites Which could be grown by heating to higher temperatures (450 – 500°C). The solids isolated from these experiments could be redispersed in THF to form colloidal black solutions.
Formation of Highly Dispersed Rhodium Particles by Chemical and Photochemical Reduction
Authors: Duan Zhibang , Hampden-Smith M.J. , Datye A. , Nigrey P.J. , Quintana C. , Sylwester A.P. 
Published: March 2011

ABSTRACTNanometer-sized metal particles have been prepared by chemical and photochemical reduction of homogeneous solutions of metal-organic rhodium(I) compounds. Reduction of [(COD)RhCl]2 with LiBEt3H in THF resulted in the formation of solutions containing crystalline, mono-dispersed Rh particles with average sizes of 2–4nm as determined by TEM and SAXS. The species [(COD)RhH]4 was isolated during the formation of the Rh colloids but was found not to be an intermediate in the reduction of Rh(I) to Rh(0). The catalytic activity of these highly dispersed metals towards pyrene hydrogenation has been investigated. Photochemical reduction of [(ethylene)2Rh(OEt)]2 at room temperature also resulted in formation of Rh as shown by TEM, EDS, ED and X-ray diffraction.
Cobalt Clusters on a Giant Graphite Lattice
Authors: Xhie J. , Sattler K. , Ge M. , Venkateswaran N. 
Published: March 2011

ABSTRACTUsing a scanning tunneling microscope in UHV we have observed anomalous superstructures on highly oriented pyrolytic graphite. We found such structures on three different samples, with hexagonal symmetry in each case but with different lattice constants of 1.7 nm, 3.8 nm and 6.6 nm. These giant lattices can be explained by assuming that the top layer of graphite is slightly rotated. This produces a hexagonal modulation of the electron state density in the first layer. Lattice points in the giant lattice are characterized by high local density of states at the Fermi level. We find that adsorbed cobalt particles occupy the top sites of the giant lattice.
Electronic Structure of Pd doped InP
Authors: Khowash P. K. 
Published: March 2011

ABSTRACTThe electronic structure of metal impurities in III-V semiconductors are interesting because of their ability to create deep centers. We use a spin unrestricted self-consistent local density theory in a cluster model to calculate the charge distributions, one electron energy spectra and the density of states for pure InP and Pd doped InP, substituted at the In site. The pure semiconductor gap is calculated to be 1.44 eV in excellent agreement with the experimental value of 1.41 eV. A small magnetic moment of 0.561μB appears on the Pd site. The impurity introduces a levels of t2 character at 0.01 and 0.04 eV above the valence band edge.
Use of Calixarene Host Molecules to Stabilize Quantum-confined Cadmium Sulfide Formation
Authors: Chandler Robin R. , Coffer Jeffery L. , Gutsche C. David , Alam Iftikhar , Yang Hong , Pinizzotto Russell F. 
Published: March 2011

ABSTRACTWe describe here the use of calixarenes, methylene (-CH2-) linked phenolic macrocyclic molecules, to stabilize the formation of quantum-confined (Q-) CdS clusters. Specifically, we focus on the use of an amino-derivatized calixarene, para-[(dimethylamino)- methyl]calix[6]arene, to stabilize Q-CdS clusters which have been characterized by High Resolution TEM (HREM), as well as absorption and emission spectroscopies. Under typical preparative conditions, an average particle diameter of 36 Å is obtained. HREM, in combination with Selected Area Diffraction (SAD), confirms the structure of the clusters as zinc blende CdS. Spectroscopic studies using absorption and emission methods indicate that both particle size and cluster photophysics are sensitive to the ratio of CdS to calixarene.
Minimum Grain Size in Nanocrystalline Metal Powders
Authors: Eckert J. , Abe Y. R. , Fu Z. , Johnson W. L. 
Published: March 2011

ABSTRACTNanocrystalline metal powders can be synthesized by mechanical attrition in a highenergy ball mill. A general relation determining the grain size of these materials is inferred. The ultimate grain size of nanocrystalline metals (typically 6 − 22 nm) is governed by the competition between the severe plastic deformation introduced during ball milling and the recovery behavior of the material. The lower bound grain size achievable by mechanical attrition is given by the minimum distance between two dislocations in a pile-up within a grain for all pure metals. Foar binary alloys the ultimate grain size depends on the composition of the material. Varying the composition changes the grain size reversibly. This can be explained by introducing solid solution hardening effects in the general relation for the lower bound grain size in pure metals. Thus, the proposed model for the ultimate grain size achievable by ball milling seems to be. applicable to all metals and alloys subjected to heavy mechanical deformation. However, reversible grain size changes are not restricted to mechanical attrition, but have also been observed for nanocrystalline Pd-H solid solutions produced by hydriding at constant pressure. Solid solutions prepared at different compositions, i.e. samples with different compositions, exhibit different grain sizes. Cycling between different temperatures/compositions changes the grain size reversibly. This cannot be explained by a model based on plastic deformation as in the case of ball-milled metal powders. The results are compared with data for ball-milled powders and samples prepared by inert gas condensation. The grain size changes are discussed with respect to the compositional changes and the grain boundary energy of the material.
The Effect of Fatigue Loading on the Interfacial Shear Properties of SCS-6/Ti-Based MMCS
Authors: Kantzos Pete , Eldridge J. , Koss D. A. , Ghosn L. J. 
Published: March 2011

ABSTRACTFractographic analysis of SCS-6/Ti-24Al-11 Nb(a/o) (Ti-24-11 hereafter) and SCS-6/Ti-1 5V- 3Cr-3Al-3Sn(w/o) (Ti-15-3 hereafter) composites subjected to fatigue crack growth conditions indicates that the interface is prone to wear damage as a result of fiber/matrix sliding. In this study, the effect of fatigue loading on the integrity of the Interface was studied by using fiber pushout testing to compare the interfacial shear strength of composite specimens in the asreceived condition with specimens that were previously subjected to fatigue loading. Fatigue loading was also simulated by pushing fibers back and forth (multiple reverse pushouts). It was concluded that interfacial sliding during fatigue loading results in interfacial damage and degradation of the interfacial shear strength. Tensile testing of extracted fibers exposed to fatigue-induced interfacial damage was also performed to determine the effect of interface damage on the fiber strength. Interfacial damage also resulted in decreased fiber strength of the SCS-6 fiber. Fracture and wear of the outer carbon coatings on the SCS-6 fiber is the main contributing factor in the deterioration of these interfaces.
Mechanical evaluation of FP alumina reinforced NiAl Composites
Authors: Anton D. L. , Shah D. M. 
Published: March 2011

ABSTRACTNiAl is well known for its low density, superb oxidation resistance and low ductile to brittle transition temperature. It is equally renowned for its low room temperature fracture strength and poor high temperature creep strength. A compositing approach has been used to introduce chopped and aligned FP Al2O3 into a matrix of fine grain NiAl via a powder metallurgical approach. This resulted in composites with approximately 40 vol. per cent undamaged alumina reinforcement. Fiber orientation effects on strength have also been characterized. Room temperature tests resulted in yield strength increases of 425% for chopped FP reinforcements and 800% for aligned composites. Elevated temperature tests conducted at 1200°C were even more dramatic in their strength increment with 200% and 3600% increases respectively. Fractographic results show matrix ductility, fiber-matrix decohesion and minimal fiber pull-out.
Characterization of Fiber/Matrix Interfaces by Transmission Electron Microscopy in Titanium Aluminide/Sic Composites
Authors: Rhodes Cecil G. 
Published: March 2011

ABSTRACTThis paper presents examples of the use of transmission electron microscopy to characterize matrix/reinforcement interaction in titanium aluminide matrix composites reinforced with continuous SCS-6 type SiC. As a result of the high temperature required for consolidating this type composite, reaction products form in the interface. Using diffraction and x-ray energy dispersive spectroscopy techniques, reaction products in Ti3Al and Ti2AINb alloy matrix composites have been identified. TiC1 –xand Ti5Si3compounds are common in these composites, with AlTi3C also present depending on consolidation temperature and matrix composition. Residual stress calculations indicate that these reaction products may be subject to cracking during cooling from consolidationtemperatures.