bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microstructural Studies of the Deformation of TiAl Alloys
Authors: Hall Ernest L. , Huang Shyh-Chin 
Published: March 2011

ABSTRACTThe mechanical behavior and microstructures of TiAl alloys after tensile and bend tests at room temperature and elevated temperatures were studied. The results for two-phase Ti52Al48 alloys are compared with those of single phase Ti48Al52, and the effect of adding 3 at. pct. vanadium as a substitute for Ti in these two alloys is considered. It is shown that Ti52Al48 has greater strength and ductility than Ti48Al52 at room temperature and elevated temperatures up to 871°C (1600°F). Adding vanadium increases the ductility of both binary alloys. The microstructure of the Ti52Al48 alloy deformed at room temperature contains primarily twins and 1/2<110> easy slip dislocations, whereas the similar Ti48Al52 sample exhibits superdislocations and associated pinned faulted dipoles. If these samples are deformed at 540°C (1000°F) or above, the Ti52Al48 exhibits extensive twinning, and the pinned faulted dipoles in the Ti48Al52 sample disappear. The vanadium additions do not noticeably change the deformation microstructure at room temperature. It is suggested that the strength and ductility of these alloys may be controlled by tetragonality, bonding, interstitial element, and grain size effects, which in turn are affected by the presence of second phases and by the alloy composition.
Preparation of Ti2CuAl5 by Reactive Sintering
Authors: Maeland Arnulf J , Narasimhan Dave 
Published: March 2011

ABSTRACTThe exothermic formation of intermetallic compounds from the constituent powders through reactive sintering at relatively low temperatures is a promising new process being explored for the preparation of nickel aluminides. The process is useful for synthesis of other intermetallics as well.We describe here the preparation of Ti2CuAl5 using the technique of reactive sintering. This intermetallic compound has a L12 structure which is also the structure of the very interesting Ni3Al intermetallic. Characterization of the Ti2CuAl5 phase is done by x-ray diffraction, microhardness, and microstructure.
Influence of Stoichiometry on the Strength of Nickel Beryllide
Authors: Nieh T. G. , Wadsworth J. , Liu C. T. 
Published: March 2011

ABSTRACTIt is demonstrated that the hardness of NiBe is dependant upon its stoichiometry; a minimum hardness is observed at the equiatomic composition. This behavior is similar to intermetallics that have the same crystallographic structure, e.g., NiAI and CoAl. The hardness increase for the off-stoichiometric compositions is a result of defect and anti-site defect structures, but may also, in part, be caused by interstitial oxygen. Nickel beryllides appear to have some intrinsic room temperature ductility, as evidenced by the absence of cracking near hardness indentations.
Twinning in A-15 Compounds
Authors: Khantha M. , Vitek V. , Pope D. P. 
Published: March 2011

ABSTRACTTwinning modes in topologically close-packed A-15 compounds are examined from a geometrical viewpoint. The crystallographically possible twinning modes with a shear less than a certain maximum are tabulated along with the percentage of shuffles involved for each of the modes. Based on some simple criteria, two of the most likely modes for deformation twinning are discussed in detail. The shuffle parameters usually employed to determine the percentage of lattice shuffles for a given mode have not been found to be useful in these structures because the primitive unit cell typically contains more than one formula unit. One has to examine the distribution of atoms in detail in order to determine the percentage of shuffles involved.
Articulated Rigid-Rod Polymers Containing Benzobisoxazole and Benzobisthiazole Moieties
Authors: Evers Robert C. , Dotrong My 
Published: March 2011

ABSTRACTArticulated rigid-rod polymers with 2,6-benzobisoxazole and 2,6-benzobisthiazole units in the backbone were synthesized by copolycondensation in polyphosphoric acid of 4,6-diamino-l,3-benzenediol dihydrochloride and 2,5-diamino-l,4-benzenedithiol dihydrochloride, respectively, with terephthalic acid and suitably-structured difunctional monomers. Early efforts centered on the incorporation of flexible diphenoxybenzene tructures into the polymer backbone while subsequent efforts involved the more thermooxidatively stable 3,3'-biphenyl- or 4,4'-(2,2'-bipyridyl)-structures. Under dilute reaction conditions, the copolycondensation reactions proceeded in the isotropic phase to yield polymers with inherent viscosities of less than 13dL/g (CH3 SO3 H, 25°C, 0.2g/dL). Later efforts carried out under higher concentration in the nematic state led to intrinsic viscosities as high as 20dL/g. Films which exhibited optical birefringence under crossed polars could be cast from methanesulfonic acid solutions of the polymers. Thermooxidative stability of the articulated polymers was evaluated by isothermal aging in air at 316°C and/or 371°C. Stability of the polymers was found to decrease with increased content of the flexible structures, with the loss of thermooxidative stability being more pronounced with the diphenoxybenzene structures.
The Synthesis and Characterization of Polybenzamides Containing Siloxanes.
Authors: Kumpf Robert J. , Gordon Bernard 
Published: March 2011

ABSTRACTThree different kinds of siloxane-containing polybenzamide copolymers have been prepared: a series of siloxane-containing segmented copolymers; a siloxane-poly(benzamide) random copolymer; and a poly(benzamide) - poly(dimethylsiloxane) block copolymer. The structures of these copolymers were confirmed using diffuse reflectance FTIR spectroscopy. Dilute solution viscometery showed them to be high polymers. The thermal stabilities of these copolymers were studied using thermal gravimetric analysis. Incorporation of siloxane units via a phenyl link was found to not affect the inherent thermal stability of the poly(benzamide) chain. The solution phase behavior of these copolymers in DMAC/LiCl was studied using an optical microscope fitted with cross-polars. The segmented copolymers and the block copolymer exhibited lyotropic behavior, which was influenced by the amount of siloxane and the overall molecular architecture. Solutions of the random copolymer were isotropic at all concentrations studied.
Conformational Rearrangement in the Nematic Phase of a Polymer Comprising Rigid and Flexible Sequences in Alternating Succession. Orientation-Dependent Interactions Included
Authors: Flory P. J. 
Published: March 2011

Consider a homopolymer consisting of rigid and flexible sequences in alternating succession. The prototype isThe degree of polymerization DP is very large. The oxyethylene units may occur in various disordered conformations or in the ordered one, ttt, with a statistical weight s* compared with unity for the disordered forms, collectively. Let γζ be the number of rigid sequences containing ζ rigid units, i.e., consisting of ζ rigid members joined by ζ-1 oxyethylene units in extended (ordered, ttt) conformations, the oxyethylene units flanking this sequence being otherwise conformed.
Nonlinear Elasticity of Poly (P-Phenylene Benzobisthiazole) (PBZT) Fibers
Authors: Jiang H. , Eby R.K. , Adams W. W. , Lenhert Galen 
Published: March 2011

ABSTRACTWe have developed a method which uses laser-generated ultrasound to measure the Young's modulus of fibers as a function of temperature and static tensile stress. For fibers of PBZT, measurements have been made to 580°C and 1.7 GPa. The fibers are shown to exhibit nonlinear elasticity which changes systematically with temperature, tensile stress and fiber processing conditions. They exhibit a relaxation associated with a structure change at about 300–400°C.We have also used x-ray diffraction to measure both the crystal modulus and aspects of the ultrastructure such as crystal orientation as a function of static tensile stress, crystal size and unit cell. It is shown that improved crystal orientation with increased tensile stress is one of the most important mechanisms of the nonlinear elasticity. The measurements of orientation distribution are combined with other measurements to make calculations of the crystal modulus for the assumptions of uniform stress and uniform strain. These apparent crystal moduli are considerably greater than the measured ultrasonic ones and both are less than the theoretical values. The assumptions of uniform stress and uniform strain have also been used together with the orientation distribution and other parameters to calculate the macroscopic modulus. Both results exhibit less nonlinear elasticity than that observed experimentally, indicating that there is another mechanism in addition to the crystal reorientation which contributes to the nonlinear elasticity. The x-ray measurements of unit cell as a function of temperature to 450°C show a structure change at about 300-400°C. It is consistant with an oscillation of the phenyl and bisthiazole moities around the connecting single bonds.
Direct Imaging of Compressive Failure Zones in Rigid-Rod Polymer Fibers
Authors: Martin David C. , Thomas Edwin L. 
Published: March 2011

ABSTRACTFibers of rigid-rod polymers are comparatively weak in compression with deformation occurring by strain localization into kink bands. Here, we present an ultrastructural study of the deformation processes accompanying kink formation in fibers of poly(paraphenylene benzobisthiazole) (PBZT) and poly(paraphenylene benzobisoxazole) (PBZO). Lateral packing between chains is maintained after shear deformation. The local strain is heterogeneous and has been analyzed in detail. Observation of sharp, high angle tilt boundaries confirms a deformation mechanism which involves kinking of individual polymer chains. A model of the micromechanisms involved in kinking is proposed.
Structural Transformations in Crystalline Oligomers of Polyparaphenylene
Authors: Baker Kenneth N. , Knachel Howard C. , Fratini Albert V. , Adams W. Wade 
Published: March 2011

ABSTRACTWe report the room and low temperature crystal structures of the unsubstituted pquinquephenyl (PQP) and p-sexiphenyl (PSP), and substituted 22,45 -diphenyl-pquinquephenyl (DPQP), 22,65-diphenyl-p-septiphenyl (DPSP), and 1,2,4-triphenylbenzene (TPB) polyparaphenylene oligomers. The unsubstituted oligomers exhibit a solid state transition when cooled from room temperature to 110K, as indicated by a change in crystallographic space group. No transition is observed for the substituted oligomers other than the usual thermal contraction of the unit cell. The transition observed for the unsubstituted oligomers is interpreted in terms of a conformational change from an “averaged” planar structure to a static non-planar one. Comparisons of room temperature and low temperature crystal data are presented.
Nonlinear Optical Properties of Rigid Rod Polymers and Model Compounds
Authors: Prasad Paras N. 
Published: March 2011

ABSTRACTPicosecond and femtosecond degenerate four-wave mixing have been used to measure third-order nonlinear optical susceptibility of several rigid-rod polymers and model compounds. A significant X(3) with femtosecond response was observed. The effects of processing conditions and structural variations on X(3) were studied. Four-wave mixing studies can also be conveniently used to generate ultrasonic phonons of well defined wave length and propagation direction. From this result one can investigate mechanical properties of polymers. Using this technique both the longitudinal and shear components of the elastic moduli for a uniaxially oriented rigid-rod polymer, poly-p-phenylene bis benzooxazole (PBO), were determined.
Rigid Rod Polymers for Nlo Applications: An Overview and Evaluation
Authors: Druy Mark A. , Domash Lawrence H. 
Published: March 2011

ABSTRACTNonlinear optics (NLO) is increasingly important for a variety of military and commercial needs ranging from new types of laser weapons to fiber optic communications networks, to optical computing applications. Rapid advances in optical phase conjugation, optical switching, and logic have demonstrated the enormous potential for practical applications with concurrent fast-paced materials development. A new class of organic materials called rigid rod (also known as ordered polymers) have the excellent intrinsic properties and tailorability to meet the requirements of a wide range of nonlinear optical devices. This manuscript provides a multidisciplinary effort to target key applications and material and processing requirements for ordered polymers. This manuscript provides the framework for the applications development required for the rapidly growing field of NLO devices from ordered polymeric materials.
Electrically Conductive Molecular Composites Based Upon Ppbt and Metallophthalocyanines: Processing, Microstructure, and Electrochemistry
Authors: Depra P. A. , Giesler J. M. , Marks T. J. , Carr S. H. 
Published: March 2011

ABSTRACTMechanically strong, environmentally stable, and electrically conductive polymeric films and fibers can be fabricated by processing (dry-jet, wet-spinning) solutions of PPBT and metallophthalocyanine molecular metal precursors, followed by chemical or electrochemical oxidation. X-ray diffraction, and resonance Raman measurements on (PPBT)-[Ni(Pc)I]x fibers indicate a microstructure consisting of small Ni(Pc)I crystallites imbedded in a PPBT matrix. Cyclic voltammetry and controlled potential coulometry indicate that PPBT/NiPc films can be reversibly doped.
New Approaches to the Synthesis of Ladder Polymers: Copolymers of Aniline and Thiophene
Authors: Polis David W. , Dalton Larry R. , Vachon David J. 
Published: March 2011

ABSTRACTWe would like to report the synthesis of new third order nonlinear optical materials formed from reaction of dibromothiophenes with p-phenylenediamines under Ullmann condensation conditions. Initial measurements of the third harmonic NLO susceptibilities (X3~= 4 × 10−10 esu ), high laser damage thresholds ( 4 GW/cm2 ), and low absorptions have provided promising materials for device applications. Composite films in poly(vinylalcohol), poly(methylmethacrylate). or poly(carbonate) also gave significant X3 values in less than 10 percent w/w concentrations.
Polymeric Electrolytes and Polyelectrolytes: Salt Concentration and Domain Effects on Conductivity
Authors: Ratner Mark A. , Druger Stephen D. , Nitzan A. 
Published: March 2011

AbstractSolvent-free polymer electrolytes and polyelectrolytes are usually studied at quite high ionic concentrations, (into the range above 1M). Under these conditions, correlation effects arising from ion-polymer and ion-ion interactions are expected to be important in the mechanism of conductivity. We sketch some specific ionic effects, separating those actittg on the mobility from those effecting carrier concentration. Mobility effects include reduction of the fluidity due to the effective cross-linking by cations, screening of applied fields due to high ionic concentrations, frictional drag due to counterion motion, and in some polymer hosts, lowered local availability of cation solvation sites due to reduction of the number of coordinating basic oxygens. Reduction of the carrier density from its stoichipmetric value can be discussed in terms of a generalized ion-pairing model. Though the concentrations usually studied are so high that Debye-Huckel theory is invalid and the stoichiometric average cation-anion separation is smaller than the Bjerrum length (a situation in which ordinary electrolyte theory considers all ions paired), nevertheless consideration in terms of contact ion pairs, solvent separated ion pairs and mean stoichiometric separation can be used to compute the effective concentration of carriers. Estimates based on an electrostatic continuum, cavity model for the binding energy of a pair describe the reduction of effective carrier number observed in poly (propylene oxide) materials.
Intrinsic Fast Oxygen Ionic Conductivity in the Gd2(ZrxTil−.)2O7, and Y2 (ZrxTil−x,)2O7, Pyrochlore Systems
Authors: Moon P.K. , Tuller H.L. 
Published: March 2011

AbstractThe pyrochlore solid solution Gd2(Zrx Til−x)2O7, was found to be an attractive system for investigating the relationship between composition, structural disorder and ionic conductivity. Both cation and anion order parameters were found to decrease systematically with increasing substitution of Zr for Ti leading ultimately to intrinsic fast oxygen ion conductivity in the solid solution. The degree of intrinsic disorder was determined quantitatively from doping experiments and was found to be equal to l.0×lO39 exp(-O.24±0.03eV/kT)cm−6sfor x = 0.3 and substantially larger for higher values of x. Oxygen vacancy mobilities, on the other hand, were found to be relatively independent of x with values of μv, = 0.15exp(-0.78 ± 0.02 eV/kT)cm2V−1s−1. These, and more recent results, on Y2 (ZrxTil−x)2O7, are discussed in the context of the similarities between the pyrochlore and fluorite phases.
Composite Polyphase Electrochemical Cell Components
Authors: Crouch-Baker S. , Huggins R. A. 
Published: March 2011

AbstractA number of composite polyphase electrode systems employing the mixed-conducting matrix principle have been proposed in this laboratory as alternatives to single lithium alloy systems for use as negative electrodes in both room and intermediate temperature lithium-based cells. Further, a composite hydroxide ion conducting electrolyte has been considered for use at intermediate temperatures which utilises liquid lithium hydroxide formed in situ and contained within a lithium aluminium oxide ceramic matrix.Both these, and other, composite electrochemical cell component systems serve to overcome certain disadvantages found in simpler, non-composite designs. In order to operate effectively, the electrode and electrolyte systems described here must satisfy certain thermodynamic, kinetic and mechanical criteria. In this work, these criteria are discussed, using, among others, the examples given above, with particular emphasis on the thermodynamic phase stability conditions which must be satisfied by a viable composite electrode or electrolyte system.
Spectroscopic Studies of Fast Ionic Conducting Halogenoborate Glasses
Authors: Massot M. , Haro E. , Oueslati M. , Balkanski M. 
Published: March 2011

AbstractLithium borate glasses B2O3-Li2O-LinX with n=l, X=F, Cl or I are fast ionic conductors. In the perspective of their use as an electrolyte in solid state micro-batteries, spectroscopic investigations of their structure were performed by using experimental techniques sensitive to the local ordering as Raman scattering and F.T.I.R. spectroscopy. In the light of these results, we find that binary and ternary systems (“doped glasses”) with same O/B ratio do not exhibit identical boron-oxygen network. The observed modifications are attributed to interactions between the network and the anions of the doping salt. In addition, the type of the anion plays an important role in the observed effects. We propose here a possible interpretation for the variation of conductivity reported on halide glasses.
Determination of Transport Properties for Solid Ionic Conductors
Authors: Pollard Richard , Comte Thierry 
Published: March 2011

AbstractA mathematical model has been developed that describes multicomponent transport in solid electrolytes that contain either three or four independent species. The treatment includes homogeneous reactions, short-time transients, and the effects of a co-continuous inert phase. Application of the model to low-frequency AC impedance experiments shows that accurate information on reaction stoichiometries and the nature of the mobile species is needed for proper interpretation of transference numbers and diffusion coefficients. A set of consistency checks for the impedance data is identified that helps distinguish between dilute and concentrated solid ionic conductors and between systems that should be regarded as four-species electrolytes rather than binary electrolytes.
Single-Ion Conducting Polymer Electrolytes: Synthesis and Characterization
Authors: Doan Kate E. , Ganapathiappan S. , Chen Kaimin , Ratner M.A. , Shriver D.F. 
Published: March 2011

AbstractTwo classes of alkali metal single-ion conducting polymer electrolytes have been characterized and their conductivities examined. Both polymers are sodium ion conductors. The first class is based upon a tetra(alkoxy)-aluminate counterion incorporated into a polyether network, and the second has a sulfonate counterion covalently bonded to a phosphazene backbone. The temperature dependent and concentration dependent conductivities of these polymers are contrasted. Phosphazene polymers that are anion conductors are also discussed.
Intercalation Compounds: Covalent and Ionic Approach
Authors: Hagenmuller Paul 
Published: March 2011

AbstractIn contrast with amphoteric graphite layer type oxides or chalcogenides play generally the role of acceptors in intercalation reactions. Due to the more ionic character of the M-0 bonds the structural evolution of the oxides may usually be explained on hand of electrostatic considerations, or in terms of cation oxido-reduction. On contrary for the more covalent chalcogenides occupancy of energy levels in the band structure by the transferred electrons constitute a determining factor, influencing strongly not only the structural changes but also the physical properties. Similar bonding considerations account for the strong tendency of the oxides to undergo 2D → 3D transformations.
Characterization of Ionically Conductive Chalcogenide Glasses
Authors: Kennedy John H. 
Published: March 2011

AbstractThe synthesis methods and chemical properties of conducting chalcogenide glasses are reviewed with special emphasis on SiS2 -based glasses. Structural information obtained from DSC, FT-IR, and solid state NMR is discussed, as well as electrochemical properties, and the use of ionically conductive glasses in battery applications.
Raman Scatteringl And Infrared Absorption in Lithium Intercalated MoS2
Authors: Sekine T. , Julien C. , Jouanne M. , Weber M. , Balkanski M. 
Published: March 2011

AbstractRaman scattering and IR absorption were studied in Li-intercalated MoS2 at room temperature. After intercalation, new Raman peaks were observed at low-frequency sides of the high-frequency original Raman peaks and around a rigid-layer mode. This fact indicates the formation of superlattice structure along the c-axis. An intercalation mode in which Li atoms vibrate strongly against the host lattice was observed at about 205 cm−1. Two new broad bands grow in the high-frequency region as the concentration of Li increases. The corresponding peaks were observed by IR absorption. They appears to be caused by vibrations of substitutional defects, in which the Li atoms have substituted for Mo atoms in the host lattice.
Structure and Stability of βAlumina Type Phases
Authors: Petric Anthony , Kirchnerova Jitka , Bale Christopher W. , Pelton Arthur D. 
Published: March 2011

AbstractPolycrystalline β“alumina isomorphs have been produced by ion exchange of Na β“alumina in various molten salts or salt vapors. The exchanged samples were heated to determine their stable structure after thermal decomposition. The stable structures are classified according to the cation on the conduction plane. Cation size and charge are believed to be the critical factors determining the stable structure.