bluuebunny/crossref_metadata_2025 huggingface dataset:
Combustion Synthesis of Sr-Substituted LaCo0.4Fe0.6O3 Powders
Authors: Kingsley J. J. , Chick L. A. , Coffey G. W. , McCready D. E. , Pederson L. R.
Published: March 2011

Sr-substituted perovskite LaCo0.4Fe0.6O3 is known to have excellent mixed ionic and electronic conductivity and increased O2 sorption characteristics. These perovskites are usually prepared by lengthy solid-state reactions of the component oxides at temperatures near 1150°C, and often produce inhomogeneous, multi-phase powders. Presently, it has been prepared by the calcination of combustion-derived fine mixed oxides at 850°C in 6 hrs. Combustion reactions are carried out using precursor solutions containing the corresponding metal nitrates (oxidizers) and glycine (fuel) at 250°C. The metal oxides produced by this process and subsequent calcination were characterized by XRD, TEM and BET surface area analysis.
A Raman Spectroscopic Study of the Initial Stages of Hydrolysis Oftetraethoxysilane
Authors: Barrie J. D. , Aitchison K. A.
Published: March 2011

Multichannel detection Raman spectroscopy was used to follow the hydrolysis and condensation reactions of TEOS/ethanol solutions. Effects of alkoxide concentration, catalyst concentration, watenTEOS ratios, and temperature were studied. It was found that the initial oligomeric composition of hydrolyzed solution was dependent upon the amount of water added to the solution: not only did reaction rates differ, but so to did the reaction products. Higher water concentrations resulted in formation of an oligomer which may contain a trisiloxane ring.
Theoretical and Experimental Investigations of the Growth of Silica and Titania Particles in Low Molecular Weight Alcohols
Authors: Harris Michael T. , Basaran Osman A. , Byers Charles H.
Published: March 2011

Silica and titania particles are readily synthesized by the hydrolysis of alkoxides in various alcohols. The present research studies experimentally and models the chemistry and growth kinetics of silica and titania particles in low molecular weight alcohols (methanol, ethanol, 1-propanol, 1-butanol). The theoretical model is based on solving the hydrolysis and condensation kinetic expressions and applying the method of moments to expedite the solution of the governing population balance equation.
Chemical Processing of Ferroelectric Niobates Epitaxial Films
Authors: Hirano Shin-Ichi , Yogo Toshinobu , Kikuta Koichi , Urahata Hisanobu , Isobe Yasuhide , Morishita Toshiyuki , Ogiso Koji , Ito Yasuhiro
Published: March 2011

Recent achievements in the chemical processing of ferroelectric niobates epitaxial films are reported. The molecular level designing of the precursor solution was stressed as well as the control of key processing factors. Examples are presented for LiNbO3/Ti, K(Ta,Nb)O3 and (Sr,Ba)Nb2O6 films from metal alkoxide precursors. Crystalline epitaxial films with stoichiometry could be synthesized through control of the intermediate state of starting molecules in solution. Water vapor stream was found to play an important role in crystallizing gel films to desired phases at relatively lower temperatures.
Optimization of Sol-Gel Derived PZT thin Films by the Incorporation of Excess PBO
Authors: Teowee G. , Boulton J. M. , Uhlmann D. R.
Published: March 2011

A series of PZT precursor solutions was prepared which incorporated excess PbO to give the composition Pb1+xZr0.53Ti0.47O3+x, where 0 < × < 0.3. These solutions were spin coated on platinized Si wafers and fired at elevated temperatures up to 750C for 30 mins. After crystallization into single-phase perovskite, the films were studied using XRD, optical microscopy and electrical characterization techniques (hysteresis loops and dielectric properties). It was found that the presence of excess PbO significantly improved the PZT films in terms of phase assemblage, microstructure and electrical properties. Under optimized conditions, films with dielectric constants of around 3000 can be obtained.
Application of Ethanolamine Method FOB the Preparation of Indium Oxide-Based Sols And Films
Authors: Taiahashi Yasutaia , Hayashi Hideo , Ohya Yutaka
Published: March 2011

It is found that ethanolamine method, recently developed by us, is very useful to form stable, concentrated (0.4–0.5M) indium oxide-based sols from which very uniform, transparent In2O3 and ITO films are obtained by dip-coating. Indium isopropoxide and acetate can be used as the starting materials. The optical and electrical properties of these films were examined. A transparent ITO film with the highest conductivity (3030 S/cm, after annealing at 0.05 torr-600°C for 60 min) was obtained from the acetate at 600°C. The films from the alkoxide had lower conductivities probably due to the impurities included in the alkoxide.
Structural and Electrical Properties of Mn-Co-Ni-O Thin Films Prepared by Dip-Coating Technique
Authors: Kaneko Shoji , Mazuka Naoto , Yamada Tamotsu
Published: March 2011

Mn-Co-Ni-O thin films of metal atomic ratio 3.0 : 1.9 : 1.0 were prepared on glass substrates from methanol solutions of the corresponding metal β-diketonates by dip-coating. As-prepared films were heated at 900°C for 1 h mostly after being calcined at 450°C for 5 min. The film thickness increased with increasing concentration of the solution as well as the number of lifting times. However, the effect was not apparent with the sample prepared without calcination. The prepared films were observed to crystallize into a complicated spinel phase by the heating process at 900°C for 1 h. The surface of the dense film composed of particles of about 0.2 μm diameter, was almost even. The thermal and aging responses of electric resistance showed the film to be a good material as a thermistor.
Hydrolysis-Condensation of Alkyltin-Trialkoxides
Authors: Ribot François , Banse F. , Sanchez C.
Published: March 2011

BuSn(OPri)3 and BuSn(OAmt)3 have been synthesized according to a literature procedure. Their hydrolysis have been studied by 119Sn and 1H NMR spectroscopy. The former precursor yields only a closo-type oxo-hydroxo cation of formula [(BuSn)12O14(OH)6]2+. Investigation of the hydrolysis-condensation products of BuSn(OAmt)3 reveals expanded coordinenceabout the tin atoms from 4 to 5 and 6 when H2O/Sn>l. For butyltin tri-tert-amyloxide, condensation also promotes the formation of a cluster whose structure is as yet unknown.
Sol-Gel Derived PZT Fibers
Authors: Boulton J. M. , Teowee G. , Uhlmann D. R.
Published: March 2011

Sol-gel routes were developed to prepare densified PZT fibers. The effects of the degree of hydrolysis and the addition of an organic polymer to the precursor sol on fiber forming ability were investigated. Results on the crystalline and microstructural development of gels and fibers are presented. The effects of the incorporation of excess PbO and sintering atmosphere are also discussed, particularly in relation to densification.
Sol-Gel Films With Tailored Microstructures
Authors: Logan Deborah L. , Ashley Carol S. , Jeffrey Brinker C.
Published: March 2011

The refractive index and porosity of silicate films formed by dip-coating were tailored by varying the aging time of a two-step acid- and base-catalyzed sol to control the size and structure of the polymeric species prior to coating. 29Si NMR showed that there was a 2% increase in the total number of bridging oxygens with sol age, consistent with a cluster-cluster growth mechanism. However, several percent monomer remained regardless of aging. Dip-coated films were characterized by ellipsometry before and after heating to moderate temperatures at three rates. Sol aging prior to film deposition leads to greater film porosity, consistent with the concept of aggregation of fractal clusters, but only after a heat treatment to remove the organic species associated with incompletely hydrolyzed monomers from the pores.
Modeling and Experimental Investigations of Pressure Infiltration of Sol-Gel processed 3-D Ceramic Matrix Composites
Authors: Liu Hsien-Kuang , Parvizi-Majidi Azar
Published: March 2011

A parabolic rate kinetics model has been developed and verified by experiments for the pressure infiltration of textile ceramic matrix composites using sol-gel processing with added solid particles. Darcy's law and a global permeability of the whole system were adopted in the model. The permeability of the whole system consisting of fiber preform, compaction, and filter was derived from the individual permeabilities of the fiber preform and particle compaction inside the preform which were based on the Kozeny-Carman equation. Experiments were conducted using 3-D angle interlock woven carbon fiber preforms and silica sol containing silica particles of 0.25μm and 0.5μm sizes. The total infiltration time was inversely proportional to the constant processing pressure and increased significantly with reducing the solid particle size by a factor of two. This is because the permeability of particle compaction layer is the dominant term and it is proportional to the square of particle size.
Rigidochromism as a Probe of Gelation, Aging, and Drying in SOL-GEL Derived Ormosils
Authors: Hanna Stephen D. , Dunn Bruce , Zink Jeffrey I.
Published: March 2011

The sol-gel derived ORMOSIL (organically modified silicate) composed of copolymerized tetramethylorthosilicate (TMOS), methylmethacrylate (MMA), and 3-(trimemoxysilyl)-propylmethacrylate (TMSPM) is a stable host for organic molecules. Due to the ORMOSILs utility as an optical host matrix, it is important to obtain a more detailed understanding of the changes that occur during gelation, aging and drying. A useful probe molecule for this purpose is ReCl(CO)3-2,2'-bipyridine. The emission band of this molecule shows a large blue shift as the medium is changed from fluid to rigid. In this paper the changes that occur during the gelation, aging, and drying of a sol-gel derived ORMOSIL are studied. The emission maximum shifts gradually from 615 ran in the sol to 575 nm in dried gels. The final wavelength is indicative of an environment that is not fully rigid, and suggests that the molecule is in a flexible organic site. The properties of the ORMOSIL are contrasted with those of silicate and aluminosilicate sol-gel matrices.
Monitoring of Heteropolysiloxane Thin film Properties Using Rheological and Acoustic Characterization Methods
Authors: Guizard C. , Lacan P. , Saurel J. M. , Hajoub F. , Cot L.
Published: March 2011

This paper emphasizes on the mechanical characterization of heteropolysiloxane (HPS) derived materials using rheology and acoustic microscopy methods. Dynamic rheological measurements have been performed at the sol and the gel stages with two different precursors. An organic gel-like behaviour has been brought into evidence related to the fact that several microns thick coated layers can be obtained with these materials. On the contrary acoustic analysis revealed a glass-like behaviour for the cured layers. These results confirm the interest of organic/inorganic polymers to design new materials with tailored properties.
Preparation of Aryl-Bridged Polysilsesquioxane Aerogels
Authors: Loy Douglas A. , Shea Kenneth J. , Russick Edward M.
Published: March 2011

We report the preparation of a new class of organic/inorganic hybrid aerogels from aryl-bridged polysilsesquioxanes [1]. l,4-Bis(triethoxysilyl)benzene and 4,4'-bis(triethoxysilyl)-biphenyl were sol-gel processed to form phenyl- and biphenyl-bridged polysilsesquioxane gels (Figure 1, structures 1 and 2, respectively). The gels were then dried using supercritical carbon dioxide extraction. It was discovered that aryl-bridged polysilsesquioxane aerogels are indeed formed, but with a pronounced influence on surface area from the reaction conditions used in preparing the initial gels. Specifically, high surface aerogels ( up to 1750 m2/g) are obtained from gels prepared with either acid or base catalysts. With reduced concentrations of base catalyst, however, supercritical processing afforded phenyl-bridged xerogel-like materials, The materials were characterized by nitrogen sorption surface analysis, and by transmission electron microscopy.
Characterisation of Hydrolysed Alkoxysilanes and Zirconiumalkoxides for the Development of UV-Curable Scratch Resistant Coatings
Authors: Greiwe K. , Glaubitt W. , Amberg-Schwab S. , Piana K.
Published: March 2011

The development of a new scratch resistant UV-curable coating system is described. The material can be applied to optical data discs by spin coating. The coating shows superior adhesion even without priming and good weathering performance especially on polycarbonate.

The material is prepared from Zr(OPr)4 and 3-Methacryloxi-propyltrialkoxysilanes via sol-gel processing. Complexation of Zr(OPr)4 with methacrylic acid yields complexes which can be copolymlrized with the prehydrolyzed silane. The hydrolysis and self-condensation of the trialkoxysilanes were studied under different conditions. The consumption of water was studied by Karl-Fischer titration and the formation of oligomeric and polymeric species by GPC-measurements.
Preparation of Non-Oxide Ceramics by Pyrolysis of Organometallic Precursors
Authors: Interrante Leonard V. , Schmidt Wayde R , Marchetti Paul S. , Maciel Gary E.
Published: March 2011

Chemical processing routes to advanced ceramic materials are gaining importance as a convenient approach to control the stoichiometry, purity, microstructure and final form of the ceramic products [1]. The pyrolytic conversion of organometallic molecules and polymers is one such chemical processing route that has been widely applied in ceramic fiber technology [1,2], in coating processes [1,2], and in the sintering of bulk ceramic objects [3]. Despite these advances in practical applications, there is a continuing need in this area for a better fundamental understanding of the chemistry involved during the precursor-to-ceramic conversion process and for the development of new precursors which yield the desired ceramic(s) in high yield and purity.
Molecular Design of Carboxylic Precursors for Zirconia
Authors: Apblett Allen W. , Lei Jin , Georgeva Galina D.
Published: March 2011

Several carboxylic acid derivatives of zirconium were investigated for their potential utility as precursors for zirconia fibers and thin films. The reactions of ZrOCl2· 8H2O and ZrCl4 with succinic acid, oxalic acid, maleic acid, benzene tetracarboxylic acid, 2-hydroxyiminopropionic acid, 3-hydroxybutyric acid, and β-alanine were performed and the thermal behavior of the products was investigated by thermal gravimetric analysis. The objective was to find preceramic compounds with low pyrolysis temperatures and physical properties suitable for materials processing.
High Temperature Stability of Oxycarbide Glasses
Authors: Zhang Hanxi , Pantano Carlo G.
Published: March 2011

The stability of silicon oxycarbide glasses has been studied at temperatures up to 1500°C. The silicon oxycarbide glasses were synthesized using a sol/gel process. The pyrolysis treatment in argon influenced the structure and composition of the synthesized glasses, and in turn, their high temperature stability in oxidizing atmosphere. The oxycarbide glasses pyrolyzed at > 1000°C had lower hydrogen concentration and a more polymerized network structure, and thereby were more resistant to oxidation and crystallization at higher temperatures.
Boron Carbide Nitride Derived from Amine-Boranes
Authors: Bill Joachim , Riedel Ralf
Published: March 2011

Amine-boranes such as pyridine- or piperazine-borane can be converted into infusible polymers by thermal crosslinking at temperatures up to 420°C. Further rise of the temperature up to 1050° C in argon results in transformation of the polymers into black residues. Microstructural (TEM/EELS, ESCA) and chemical investigations indicate the presence of single phase boron carbide nitrides which exhibit a graphite-like, turbostratic structure with a homogeneous distribution of the elements B, N, and C. Subsequent annealing at 2200° C in argon gives rise to crystallization of the pyrolytic material generating the thermodynamically stable phases BN, C, and B4C.

The semiconducting properties of the X-ray amorphous boron carbide nitride synthesized at 1050°C depend on the B/N/C-ratio which can be influenced a) by the type of amine-borane-precursor and b) by the applied atmosphere (Ar or NH3) during pyrolysis.

The amine-boranes can be converted into boron carbide nitride- and BN-monoliths at 1050°C under argon or reactive gas (NH3), respectively. The monoliths are transformed into composites with 91% rel. density containing BN, C, and B4C when heated up to 2200° C.
New Routes to Group Iva Metal-Nitrides
Authors: Narula Chaitanya K.
Published: March 2011

The reactions of TiCl4 with [(CH3)3Si]2NH have been examined under several reaction conditions. One of the reaction products, (CH3)3Si(H)NTiCl3, can be crystallized in 60% yield on reacting TiCl4 with TiCl4 with [(CH3)3Si]2NH in a 1:1 molar ratio in dichloromethane at -78°C. [(CH3)3Si(H)NTi(Cl2)(NH)]2TiCl2 is the primary product on increasing the amount of TiCl4 with [(CH3)3Si]2NH to two equivalents. (CH3)3Si(H)NTiCl3 and [(CH3)3Si(H)NTi(Cl2)(NH)]2TiCl2 form titanium nitride on pyrolysis at 600°C in an ammonia atmosphere.
Single-Component Routes to Perovsktte Phase Mixed Metal Oxides
Authors: Chandlertw Clive D. , Hampden-Smitht M. J. , Brinker C. J.
Published: March 2011

Crystalline perovskite phase mixed metal oxides have been prepared at low temperatures from single-component mixed metal-organic precursors specifically designed for this purpose. Pyridine solutions of divalent metal α-hydroxycarboxylates of general empirical formula A(O2CMe2OH)2 where A = Pb, Ca, Sr, Ba; Me = methyl, react with metal alkoxide compounds such as B(OR')4, where B = Ti, Zr, Sn with the elimination of two equivalents of alcohol to form species with a fixed A:B stoichiometry of 1:1 according to the equation below.
Preparation of Titanium Carbonitride Coatings by the Sol-Gel Process
Authors: Zheng Haixing , Oka Kris , Mackenzie John D.
Published: March 2011

Ti(NPri2)4 has been synthesized and used as a precursor for aminolysis andpolymerization by reaction with isopropylamine. The resultant dark red solution was utilized for dip coating of silicon substrates. Firing of these coatings in N2 or Ar produced dense and crack-free titanium carbonitride coatings.
Multicomponent Ceramic Powder Generation by Spray Pyrolysis
Authors: Lyons Shirley W. , Ortega J. , Wang L. M. , Kodas T. T.
Published: March 2011

We have examined methods for controlling the morphology and microstructure of ceramic particles produced by spray pyrolysis. A variety of materials were examined including SrTiO3and BaTiO3 and the oxides of Al, Mg, Zn, Pd, V, Mo, and Bi. The morphology of the particles was influenced by using colloidal precursors in combination with molecular precursors for particle generation. Slow drying rates obtained by using high relative humidities and controlled axial temperature gradients did not influence particle morphology for the systems and conditions studied. The microstructure of Al2O3, V2O5, and PdO particles was controlled by varying the temperature to provide nanocrystalline or single-crystal particles. Evaporation and condensation of volatile species such as MoO3 and V2O5 dramatically modified particle microstructure and morphology.
An Electrochemical Study of the Au55(PPh3)12 Cl6 Cluster
Authors: Steggerda J. J. , Linden J. G. M. Van Der , Gootzen J. E. F.
Published: March 2011

Voltammetric studies of Au55(PPh3)12Cl6 (kindly provided by Prof. G. Schmid, Essen, Germany) in solutions of CH2Cl2 and THF with Pt electrodes show that the reduction of the cluster is a multistep, irreversible process. Precipitation of colloidal metal or any high molecular super-cluster is observed when stabilising. NBu+ –ions are absent and when the reduced solution is reoxidised.

The parent cluster and the precipitate were studied by X-ray powder diffraction and UV-vis spectroscopy. The origin of the diffuse lines and the low-angle diffractions will be discussed. They suggest that the Au55 particles flocculate by changing their electric charge in the electrochemical redox reactions. The floc is unstable and congulates to particles of 25 Å and larger.
Giant Palladium Clusters: Synthesis and Characterization
Authors: Moiseev Ilya I. , Vargaftik Michael N. , Zamaraev Kirill I. , Kochubey Dmitry I.
Published: March 2011

A series of palladium clusters containing from 4 to some hundred Pd atoms in the metal skeleton was prepared and characterized with structural data as well as by chemical properties including catalytic activity. An agreement between X-ray and EXAFS data was obtained for single-crystal low-molecular clusters. Giant clusters approximated as Pd56L60(OCOCH3)180 (L=Phen, Bipy) and Pd561Phen60O60X60 (X = PF6, CIO4, SO4, BF4, CF3COO)were characterized with TEM, SAXS, EXAFS, NMR, and magnetic susceptibility data. The clusters consisting of close-packed metal core and L, X ligands at its periphery could be considered as a bridge between low-molecular clusters and the particles of colloidal metals.
Shape and Size Effect on Ultrafine Metallic Particles
Authors: Kimura Keisaku
Published: March 2011

The effect of size and shape on the electronic state of ultrafine metallic particles is described with the critical review of so far proposed experimental and theoretical results. The temperature dependence of the spin susceptibility of small metal particles is presented as function of size, shape, spin-orbit interaction of the elements, and magnetic field strength. Based upon a proposed formula, the spin susceptibility of small Mg particles is precisely analyzed with the view point of shape effect. It is emphasized that the exogenous impurities have crucial effect. on the magnetic properties of small metal particles. It is clarified that the confusion in the magnetic experiments originates from the extrinsic magnetic effect. The deviation of the nature of chemical bond in small size systems from that in bulk is briefly outlined.
Sol-Gel Synthesis of Metal Oxide Clusters and Colloids
Authors: Livage J. , Sanchez C. , Toledano P.
Published: March 2011

The hydrolysis and condensation of metal alkoxides M(OR)z allows the formation of oxopolymers or oxide colloids under mild conditions in solution. The molecular design of these precursors provides a chemical control over the formation of condensed phases. This can be conveniently performed via the chemical modification of alkoxides by nucleophilic species such as carboxylates or β-diketones. Condensation can be tailored with two chemical parameters; the hydrolysis ratio which leads to more condensed species and the amount of complexation which prevents condensation. Molecular clusters or colloidal particles can be obtained instead of precipitates. Moreover, non hydrolyzable complexing organic ligands lead to the formation of hybrid materials in which organic and inorganic moities are chemically bonded. These hybrid clusters and colloids are important starting points for producing solids and films with novel physical properties.
Conversion of (R4N+)4[S4M4(SPh)16]4− Molecular Solids to Bulk Metal Sulfides
Authors: Farneth W. E. , Herron N. , Wang Y.
Published: March 2011

In this paper we report on the mechanism of the solid state conversion of a series of IINI precursors of general formula (R4N+)4[S4M4(SPh)16]4− (R=Me, Et; M=Cd, Zn) to the bulk metal sulfide structure. This family of cluster compounds was first reported by Dance et al [1]. On heating these solids in vacuum or inert atmosphere, we find that they convert to the corresponding extended metal sulfide lattice in two discrete reaction steps. The overall reaction appears to be general, but there are interesting differences in the rates and mechanistic details as R and M are varied. The first step, ˜200°C, can be characterized as a nucleophilic substitution or elimination initiated by the attack of a fragment of the anion cluster on the tetra-alkyl ammonium counterion. The intermediate solid produced in this step has been isolated and recrystallized. It consists of charge neutral M10S16Ph12 clusters that retain the cluster size present in the starting material but appear to aggregate to varying degrees in the solid or solution.
Preparation, Structure and Properties of Novel Bimetallic Au/Pd Colloids
Authors: Baddeley Christopher J. , Jefferson David A. , Lambert Richard M. , Ormerod R. Mark , Rayment Trevor , Schmid Günter , Walker Andrew P.
Published: March 2011

Ligand-stabilized bimetallic Au/Pd colloids may be prepared from 180–200Å Au colloids which can be covered by Pd shells of varying thickness. They can be isolated as solid materials without agglomeration. HREM observations indicate a narrow particle size distribution and reveal a well-defined Au(core)/Pd(shell) structure. This is convincingly confirmed by EXAFS data. Thermal treatment leads to Au/Pd alloy formation at ≥ 500 K, as evidenced by the appearance of characteristic Au-Pd distances in the EXAFS.
Platinum Clusters with Phosphide Ligands: Synthesis and Characterization
Authors: Moiseev Ilya I. , Kozitsyna N. Yu. , Kochubey D. I. , Zamaraev K. I.
Published: March 2011

Reduction of triphenylphosphine-containing Pt(II) complexes with H2, HCOOH and Na-amalgam was studied to compare the results with those for similar reductions of analogous Pd(II) complexes. Clusters of compositions [Pt(PPh2)]n, n=6–10, have been found to be the products of the reduction reactions under consideration.
Interdiffusion Between Mo and TiAl
Authors: Zhang Min-Xian , Hsieh Ker-Chang , Chang Y. Austin
Published: March 2011

Diffusion couple experiments were carried out for Mo/γ-TiAl at 900, 1000 and 1100°C for periods of time ranging from 121 to 553 hrs. Using the Boltzmann-Matano analysis, the two diagonal interdiffusion coefficients for the two phases formed in these couples were obtained assuming the cross diagonal terms to be negligible. These two phases are δ-(Mo, Ti)3Al and β-(Mo,Al)Ti. The three intrinsic diffusion coefficients were also obtained using the Darken-type relationships between the interdiffusion and intrinsic diffusion coefficients. The calculated interdiffusion coefficients from the three intrinsic diffusion coefficients are in reasonable accord with those obtained directly from the Boltzmann-Matano analysis.
Microstructural Effects On Fatigue-Crack Growth Behavior In γ-TiAl/β-TiNb Intermetallic Composites
Authors: Rao K. T. Venkateswara , Ritchie R. O.
Published: March 2011

Cyclic crack-propagation behavior is examined in a series of γ-TiAl intermetallic alloys reinforced with pancake-shaped, ductile β-TiNb particles as a function of microstructure and specimen orientation. In contrast to results under monotonic loading, TiNb reinforcements are found to be far less effective in impeding crack extension under cyclic loading due to their susceptibility to premature fatigue failure, and consequently to the diminished role of shielding from crack-bridging mechanisms. Modest improvements in fatigue-crack growth resistance are observed in TiAl/TiNb composites compared to monolithic γ-TiAl, provided the particle faces are oriented perpendicular to the crack plane; however, properties are compromised in orientations where the particle edges are stacked normal to the crack plane. Microstructural effects on cyclic crack growth are less prominent in the composites, with crack-growth rates exhibiting a strong dependence on the applied ΔK level; measured exponents for the da/dN-ΔK relationship range between 10 and 20, and are found to decrease with increasing ductile phase content, yet are independent of particle thickness.
Fracture Toughness of NiAlIn-SituEutectic Composites.
Authors: Heredia F. E. , Valencia J. J.
Published: March 2011

Mechanical tests were performed on directionally solidified (DS) NiAlin-situeutectic composites in order to evaluate the effect of ductile reinforcements on the fracture resistance of the B2 ordered intermetallic compound NiAl. Reinforcements consisted of i) Mo fibers, ii) Cr fibers, and iii) Cr(Mo) solid solution plates. Near stoichiometric NiAl ingots were prepared by induction melting as reference material to compare with the eutectic composites. Resistance curves were obtained for the NiAl/Mo fibrous eutectic alloy as well as for the NiAl/Cr(Mo) layered material. The initiation fracture toughness of the DS NiAl/Mo and NiAl/Cr(Mo) eutectic composites is larger than that of the stoichiometric NiAl, with the layered material. producing the better properties. The mechanisms for such increase in fracture toughness are discussed.
Effect of Ductile Phase Reinforcement Morphology on Toughening of MoSi2
Authors: Alman D. E. , Stoloff N. S.
Published: March 2011

Niobium was added to MoSi2 in the form of particles, random short fibers and continuous aligned fibers. It was found that the morphology of Nb played a role in the toughening that occurred (as measured by the area under load displacement curves from room temperature three point bend tests and the examination of fracture surfaces). The Nb particles did not toughen MoSi2. The random short fibers appeared to toughen MoSi2 via crack deflection along the fiber matrix interface. Aligned fibers imparted the greatest toughness improvements, as toughening resulted from fiber deformation. However, larger diameter fibers displayed a greater ability to toughen MoSi2 than smaller diameter fibers. This was attributed to the constraint resulting from the interfacial layer between the MoSi2 matrix and the Nb fiber. Maximum toughness occurs when the fiber is able to separate from the matrix and freely deform.
Plasticity Enhancement of MoSi2 at Elevated Temperatures Through the Addition of TiC
Authors: Chang H. , Kung H. , Gibala R.
Published: March 2011

Monolithic MoSi2 and MoSi2-TiC particulate composites with 10 vol % and 15 vol % TiC were tested in compression between 950°C and 1200°C. The MoSi2-TiC composites can be deformed plastically at lower temperatures than MoSi2 can before brittle fracture occurs. The composites exhibit much lower strain hardening rates and attain zero strain hardening rate at much lower strains than monolithic MoSi2. The differences between the composites and monolithic MoSi2 in plasticity and in strain hardening behavior is attributed to efficient dislocation generation into the matrix from sources at the MoSi2-TiC interfaces.
In-Situ Growth of SiC in MoSi2 by Melt Processing
Authors: Tilly Daniel J. , Löfvander J. P. A. , Levi C. G.
Published: March 2011

The growth of SiC during solidification of Mo-Si-C melts was investigated to explore the potential for developing in-situ refractory reinforcements for MoSi2 matrices. Volume fractions of up to 20% were readily incorporated by arc melting. Primary β-SiC grows as equiaxed particles, plates and hopper crystals, whereas secondary SiC grows with ribbon, thin flake or whisker morphologies. The dominant facets of both primary and secondary SiC are of the (111) and {002) type, which are also characteristic of the equilibrium crystal shape. There is a clear orientation relationship between the phases wherein the close packed planes and directions of the C11b and B3 structures are parallel.
Mechanics of Interfacial Failure during Thin-Slice Fiber Pushout Tests
Authors: Koss D. A. , Kallas M. N. , Hellmann J. R.
Published: March 2011

Interfacial failure along the fiber-matrix interface during fiber push-out tests is examined for conditions where (1) a “thin-slice” specimen geometry is used and (2) matrix plasticity is necessary for large scale fiber displacement. The influence of both test geometry and the combination of thermally and mechanically induced stresses on the potential failure process is discussed. Experimental results are presented which illustrate a range of interfacial failure processes as a consequence of different combinations of specimen geometries, thermally induced residual stresses, and mechanically applied stresses. It is concluded that mode I crack opening and growth induced by specimen bending can be a major contributor to the interfacial failure process. Accurate quantitative measurements of interfacial shear properties must therefore rely on test configurations in which specimen bending is eliminated.
Evaluation of A Ti-22ai-23nb “Orthorhombic” Alloy for use as the Matrix in A High Temperature Ti-Based Composite
Authors: Graves J. A. , Smith P. R. , Rhodes C. G.
Published: March 2011

The production of titanium aluminide intermetallic compound foil represents a significant manufacturing challenge. Cold rolling, which imparts excellent thickness uniformity and surface finish characteristics that are of benefit in composite fabrication, is especially difficult with these alloys. However, recent modifications in Ti aluminide alloy compositions and advances in thermomechanical processing have made it possible to produce foil of thickness less than 100 μm, having the microstructure and mechanical property characteristics required for composite fabrication and improved performance. This paper describes the properties of a new Ti aluminide alloy, of nominal composition Ti-22AI-23Nb (at.%), comprising a three phase microstructure of α2 (Ti3Al), an ordered orthorhombic phase (Ti2AINb) and an ordered beta phase. The discussion emphasizes the processing of this alloy through cold rolling to foil, and the associated microstructures and mechanical property characteristics that are relevant to the use of this foil to form a composite matrix.
Statistical Analysis of the Properties of Advanced Fibers Designed for Titanium Alloy and Intermetallic Reinforcement
Authors: Porter John R.
Published: March 2011

The mechanical properties of new ceramic reinforcing fibers need to be well characterized before their incorporation into composite materials. Critical fiber properties include strength and Weibull modulus, both off the spool and after matrix extraction, bundle strength, modulus and creep resistance. Important composite properties include thermochemical stability, interface debond energy and interfacial sliding resistance. Tailoring these interfacial properties invariably involves the use of a fiber coating that can, in turn, influence fiber properties. Methods of measuring strength related properties are addressed and the results of a computer simulation to assess the quality of measured data using statistical methods are presented. The simulation was developed to determine the errors associated with a strength/Weibull modulus determination based on a limited number of samples. Finally, an assessment of the effect of mixing of high and low quality fiber on bundle strength and composite properties is made.
Fiber Push-Out Testing of Intermetallic Matrix Composites at Elevated Temperatures
Authors: Eldridge Jeffrey I.
Published: March 2011

A newly developed apparatus for performing fiber push-out testing at elevated temperatures has been applied towards testing fiber-reinforced intermetallic and metal matrix composites. This new capability shows the effects of the relief of residual stresses and increased matrix ductility with increasing temperature on fiber debonding and sliding behavior.
Use of Shock Waves to Measure Adhesion at Interfaces
Authors: Nutt Gerald L. , King Wayne E.
Published: March 2011

The central problem in the study of composite materials is the adhesive strength of the electronic bond between reinforcement and matrix. We have introduced a unique method of measuring the interface bond strength of a wide variety of engineering interfaces (e.g. metal/ceramic, semiconductor/metal, metal/polymer). Specimens are composed of a relatively thin overlayer on a thick substrate. The specimens are shocked using a magnetic hammer which accelerates a thin metal flyer onto the substrate. The shock, upon reflection at the free surface, is incident on the bonded interface as a tensile wave, spalling the overlayer. The method is unique in using free surface velocity measurements to determine the interface stress at the instant of separation. The debonding process is sufficiently rapid (on the order of 1.0 ns) that debonding occurs by the simultaneous breaking of atomic bonds, rather than by propagation of cracks nucleating at stress concentrations near existing flaws.
Strength and Toughness of Be12Nb, Be17 Nb2 and Two-Phase Be12Nb-Be17Nb2
Authors: Bruemmer Stephen M. , Arey Bruce W. , Henager Charles H.
Published: March 2011

Bend strength, compression strength, and fracture toughness of niobium beryllide intermetallic compounds have been assessed at temperatures from ambient to 1200°C. Hot-isostatically-pressed (HIP) Be12Nb showed significantly improved lowand high-temperature mechanical properties over vacuum-hot-pressed (VHP) material. Strengths at 20°C were 250 MPa in bending and 2750 MPa in compression with a fracture toughness of ∼4 Mpa√m, much higher than previously measured for this compound. High-temperature (≥ 1000°C) mechanical properties were also improved with bend strengths of 250 MPa at 1200°C as compared to only 70 to 100 MPa for the VHP material. However, severe pest embrittlement was detected in the HIP material at temperatures between 650 and 1000°C.
Evaluation of an Scs-6/Ti-22al-23nb “Orthorhombic” Composite
Authors: Smith P. R. , Graves J. A. , Rhodes C. G.
Published: March 2011

study was undertaken to examine the attributes of utilizing a high niobiumcontaining titanium aluminide (orthorhombic) composition, specifically Ti-22AI-23Nb (a%), for use as a matrix for a continuously reinforced metal matrix composite. Both unreinforced “neat” panels and 35v% 4-ply unidirectional ([0]4) SiC (SCS-6) panels were fabricated by HIP'ing using a foil / fiber / foil approach. The microstructure of these panels were examined via optical, scanning electron and transmission electron microscopy. Reaction zone kinetics including both the primary reaction product and any beta-depleted zone growth were determined at 982°C. Analytical electron microscopy was employed to identify fiber / matrix interfacial compounds as well as local phases and their associated chemistries. Preliminary mechanical properties were obtained which included: longitudinal and transverse tensile, matrix thermal stability, thermal fatigue, thermal mechanical fatigue and transverse composite creep. The results were compared with panels fabricated from the baseline matrix composition, Ti-24AI-11 Nb.
Fracture and Fatigue Behavior in Nb3Al+ Nb Intermetallic Composites
Authors: Murugesh L. , Venkateswara K. T. , DeJonghe L. C. , Ritchie R. O.
Published: March 2011

Model high-melting point Nb3Al + Nb intermetallic composites have been fabricated in situ by vacuum hot pressing and reaction sintering elemental powders mixed in the ratio Nb + 7wt. % Al. In both cases, microstructures feature islands of ductile Nb solid solution (∼20 vol. %) in a brittle Nb3Al intermetallic matrix. Thermal treatment for 24 h at 1800°C results in a lamellar microstructure containing a uniform and fine distribution of filamentary Nb in a Nb3Al matrix following the massive peritectic transformation. In this paper, the fatigue and fracture resistance of these two microstructures are examined and compared to pure Nb3Al and Nb. Preliminary results suggest that the Nb phase can provide significant toughening to Nb3Al via crack bridging, plastic stretching and interfacial debonding mechanisms. Measured plane-strain fracture toughness values for the as hot-pressed and fully-aged microstructures are ∼6–8 Mpa√m compared to √fm for pure Nb3Al. However, under cyclic loading, the composites tend to show a strong dependence on applied stress-intensity level; fatigue thresholds range between 2–3 Mpa√m.
Laminate Orientation and Thickness Effects on An Scs-6/Ti-24ai-11 Nb Composite Under Thermal Fatigue
Authors: Revelos William C. , Roman Itzhak
Published: March 2011

A SiC/Ti-24AI-11 Nb (at. %) composite (30–35 vol. %) was thermally cycled in air and an inert environment between 150 °C and 815 °C for various cycle counts. Various hold times at maximum temperature were employed to determine timedependent effects on composite integrity. Laminate orientations investigated included: [0]4, [0]8, [90]4, [90]8 and [0/90]2S. Acoustic emission produced during thermal fatigue of selected specimens was employed to monitor damage progression. Post-cycling room temperature tension tests as well as optical and scanning electron microscopy were used to document damage, which was particularly acute when hold times at temperature were employed on tests performed in air. The roles of the environment, composite thickness, and off-axis fibers during thermal fatigue on the composite strength and integrity are discussed.
Interdiffusion and Phase Relations in Ti-Aluminide/NB/Ti-Aluminide Composite Structures
Authors: Ma Z. , Dayananda M. A. , Allen L. H.
Published: March 2011

We have studied interdiffusion and phase relations in two titanium aluminide/Nb/titanium aluminide composite structures at 1100 °C using solid state diffusion approach. The composite structures were prepared with two practical intermetallic alloys, γ (Ti-48Al-2Nb-0.3Ta, in at.%) alloy and super-α2 (Ti-25Al-10Nb-3V-1Mo, in at.%) alloy, and pure Nb sheet by diffusion bonding technique. The interfacial microstructures evolved during thermal diffusion annealing were characterized using optical microscopy, SEM, TEM and X-ray diffraction. The effect of Nb on the phase stabilities of two intermetallic alloys and the phase relations among different phases formed in the diffusion zone due to interdiffusion were analyzed in terms of rules of diffusion paths on the basis of the observed diffusion structures and experimental diffusion paths.
Growth of and Critical Current Density of TL2BA2CACU2O8 Superconducting Single Crystals
Authors: Duan H. M. , Kaplan T. S. , Dlugosch B. , Hermann A. M.
Published: March 2011

Large single crystals of Tl2Ba2CaCu2O8 superconductors were grown by a two step self-flux process. Crystals are plate-like. The in-plane crystal sizes are as large as 5mmX5mm and the thickness range from 0.01mm to 0.8mm. The critical currents were extracted from I-V curves measured at different temperatures. jc was about 2.4×104 A/cm2 at liquid nitrogen temperature.
Enhancement of Flux Pinning Force by Ion Beam Irradiation of Epitaxial Ba2Cu3O7-δ Films
Authors: Siegal M. P. , Phillips Julia M. , van Dover R. B. , Gyorgy E. M. , White A. E. , Marshall J. H.
Published: March 2011

Epitaxial Ba2YCu3O7-δ (BYCO) films grown by the ex situ BaF2 process are comparable to single crystals both in crystalline integrity (RBS/ion channeling χmin < 3%) and the value and temperature dependence of the critical current (Jc) in an applied magnetic field in the BYCO (001) direction of Ha = 0.9T. With the appropriate dose of either 2 MeV H+ or 135Xe+, we are able to enhance Jc by a factor of 2 in H = 0.9T with little effect on Tc. The ability to change Jc by such a large factor in these films is a prerequisite for isolation and study of the induced defects and study their properties.
In-Situ Preparation of Y-Ba-Cu-O Thin Films Using Mass-Spectrometer Rate Control and Atomic Oxygen
Authors: Ohlsén H. , Ottosson M. , Hudner J. , ÖStling M. , Stolt L. , Nordblad P. , Villegrer J. -C. , Moriceau H. , Weiss F. , Thomas O.
Published: March 2011

Thin films of YBCO were prepared using a mass-spectrometer controlled coevapora-tion/MBE process with atomic oxygen. Under the conditions of low pressure, necessary for mass-spectrometer rate control, it is shown that an atomic oxygen beam source can be utilized in order to grow high quality thin films of YBCO as well as multi-layer structures involving YBCO and Y2O3. Values of Tc = 88.5 K and Jc = 6–106 A/cm2 at 77 K were determined for a strip with a width of 10 μm of YBCO deposited on a LaAlO3 substrate. Film structure is analyzed by XRD and rocking curve measurements. Magnetic characterization of films and multi-layer structures are reported.
Low-Field Dc Josephson Magnetization of Layered Superconductors
Authors: Wang Hsang-Jue , Tai Ming-Fong
Published: March 2011

Temperature dependences of DC magnetization with low magnetic applied field (< 160 G) have been studied on layered superconductors. Two-step behavior below Tc are seen in most of the bulk samples, when the field is smaller than a few tens of Gauss. A grain-cluster model which taking both inter- and intragrain regions into consideration as two components of the present system is used to interpret the observed phenomena. The intergranular component is conjectured as coming from Josephson tunneling supercurrent between grains. A two-critical-states model including the surface-critical-state is extracted to outline the transition behavior of the shielding currents. The two-step phenomenon of the “bulk” magnetization is well explained with appropriate selections of the coupling strength and phase for the intergrains and of those critical current densities for the intragrains.
Target Surface Modification and Particulates on YBa2Cu3O7−x Thin Film by Pulsed Laser Deposition
Authors: Suh Jeong Dae , Sung Gun Yong , Kang Kwang Yong
Published: March 2011

The modifications of the laser ablated target surface morphology and the particulates on YBa2Cu3O7−x (YBCO) thin films have been investigated. As the number of laser pulse per site increases, the ablated target surface changes to conical structures. After the texturing of the target surface, the ablated surface morphology changed identically, independent of the initial surface roughness of the polished targets. The YBCO thin films deposited using the stationary target have an almost particulate-free surface. However, in the case of the YBCO films deposited using the rotating target, there is a considerable increase in the density of particulates on the film surface.
Superoonductivity in the R3CaBa3Cu7Oy System with R = Lanthanide
Authors: Kao H. -C. I. , Wang J. L. , Huang R. J. , Wang C. M. , Wu M. K.
Published: March 2011

A series of samples with a nominal composition of R3CaBa3Cu7Oy (abbreviated as R3137), where R = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm, was prepared by a similar process as for an 80-K superconductor, La3CaBa3Cu7Oy. Most of the R3137 (except for R = Ce, Tb) had a tetragonal triple-perovskite phase like La3137 identified from the XRD patterns, and they were superconducting except Pr3137. For R3+ radius larger than Dy3+ (0.908 Å), a single phase R3137 was observed, and their Tc(zero)' probably related to the rCu-o distance in the copper-oxygen layer, was spread from 85 to 76 K with a maximum for the Eu3137. Oxygen stoichiometry of these R3137 was slightly decreased with decreasing lanthanide radii. The hole concentration, (Cu-O), was found between 0.47 and 0.38/unit cell. For Smaller R3+ ions, residual resistivity was found in the superconducting samples due to the existence of second phase. From the structural study of La3137, it was known that part of the lanthanide ions had to be fitted into the bigger Ba-site. Because ionic radii of the heavy lanthanides (R3+ < Ho3+ = 0.894 Å) were too small to be located at the Ba-site, it was rather difficult to prepare these single phase R3137.
Crystal Growth Modified by Pulsed Laser Irradiation on Growing Surface in Ba-Y-Cu-O Film Preparation by Laser Ablation
Authors: Morimoto Akiharu , Mizukami Shigeru , Shimizu Tatsuo , Mlnamikawa Toshiharu , Yonezawa Yasuto , Segawa Kazuhito , Otsubo Shigeru
Published: March 2011

Ba2YCu3Ox superconducting films were prepared by Nd:YAG laser ablation, equipped with a second (ArF excimer) laser for irradiation onto the growing film surface. The irradiation onto the film during the deposition were delayed for various delay times against the ablation of Ba2YCu3Ox target. The experiment showed that the second laser irradiation within several tens us around the ablation event induces a change of the crystal orientation. This result suggests that the crystal growth for the laser ablation is determined mainly around this time scale.