bluuebunny/crossref_metadata_2025 huggingface dataset:
A Tem Study of the Relationship Between Dislocation Structure and the Anomalous Temperature Dependence of the Flow Stress in Ordered Ni3 (Al,1%Ta).
Authors: Mills M. J. , Baluc N. , Karnthaler H. P.
Published: March 2011

The anomalous increase in the yield strength of single crystals of Ni3AI(1%Ta) as a function of temperature has been correlated with the post-deformation substructure using weak beam TEM techniques. At low temperatures (77K), there is evidence for abundant cross-slip between (111) and (111). With increasing temperature, this conventional cross-slip process is gradually replaced by the formation of KW locks--straight screw segments which have crossslipped and completely dissociated on (010). This change in the mode of cross slip corresponds with the onset of the yield strength anomaly. At still higher temperatures (544K and 715K), the KW locks become mobile and bow out on (010). The density of dislocations on the cube plane also increases sharply at higher temperatures, even though deformation occurs principally by glide on the primary (111) based on slip trace analysis. These observations are inconsistent with the widely accepted cross slip pinning model and suggest that deformation occurs primarily by the motion of the non-screw components. A dislocation model is introduced which attempts to account for the observed dislocation configurations while remaining consistent with the yield strength and work hardening behavior of these alloys.
High Temperature Creep Behavior of Single Crystal Gammpraime and Gamm Laloys
Authors: Nathal M. V. , Diaz J. O. , Miner R. V.
Published: March 2011

The creep behavior of single crystals of γ′ and γ alloys were investigated and compared to the response of two phase superalloys tested previously. High temperature deformation in the γ alloys was characteristic of a climb controlled mechanism, whereas the γ′ based materials exhibited glide controlled creep behavior. The superalloys were much more creep resistant than their constituent phases, which indicates the importance of the γ-γ′ interface as a barrier for dislocation motion during creep.
Microstructure and Deformation of Rapidly Solidified TiAl Alloys
Authors: Huang Shyh-Chin , Hall Ernest L.
Published: March 2011

Binary TiAl alloys containing 45–60 at.% Al were studied in detail in order to understand the fundamental deformation behavior and to establish a guideline for advanced alloy design. Because the formation of this compound involves a peritectic reaction, all alloys were processed by the melt spinning technique to minimize segregation. Microstructural and mechanical characterizations were carried out on both the as-solidified and consolidated materials. The results are presented to address the issues of (1) the equilibrium phase relationship, (2) the rapid solidification microstructure, (3) the room temperature deformation behavior, (4) the brittle/ductile transition, (5) the temperature dependence of yield stress, and (6) the implication on alloying effects. Several examples of ternary alloys are given.
Structures and Properties of TiAl-Base Alloys Containing Mn
Authors: Tsujimoto T. , Hashimoto K.
Published: March 2011

Structures and mechanical properties of TiAl-base alloys have been studied, in which Zr, Nb, V or Mn is added as the third element and the Al content is changed. Behavior of the third element in the TiAl-base alloys and effects of various factors on ductility have been discussed. It has been concluded that the Ti-48.4 at% Al-1.0 at% Mn alloy is the optimum composition for obtaining good room temperature ductility.
Powder Processing of High Temperature Aluminides
Authors: German R. M. , Bose A. , Stoloff N. S.
Published: March 2011

This paper reviews the several powder processing techniques that have been applied to the fabrication of both monolithic aluminides and their composites. Attention is given to the active research at Rensselaer on reactive sintering and reactive hot isostatic pressing of elemental powders, hot pressing of prealloyed powders, and molding of powder-fiber-binder slurries. The application of one or more of these techniques to the following monolithic intermetallics is described: NiAl, Ni3Al, TiAl, NbAl3, Ta2Al, and TaAl3. Progress has occurred in fabrication of dense compacts, including some composites, from these aluminides.
Microstructures and Mechanical Behavior of Two-Phase Niobium Silicide-Niobium Alloys
Authors: Mendiratta M. G. , Dimiduk D. M.
Published: March 2011

In the Nb-Si system, it is possible to produce in-situ composites consisting of a brittle Nb5Si3 intermetallic matrix and ductile Nb particles. The two phases are thermochemically stable up to ∼ 1500∼C and are amenable to wide microstructural variations including morphology, volume fraction, and the size of the individual microconstituents. This paper presents microstructures and phase transformations in these composites as a function of composition and heat treatments and bend properties from room-temperature to 1400°C.
The Location of Tantalum Atoms in Ni3Al
Authors: Lin Hui , Pope David P.
Published: March 2011

An X-ray powder diffraction method was used to determine the location of tantalum atoms in Ni3Al. A series of Ni3 (Al,Ta) alloys were produced with tantalum content ranging from 0.1 to 3.0 at%. Fine powders with average particle sizes less than 80 pm were made from melt-spun ribbons by a grinding process. The values of the superlattice peak intensities normalized to the intensity of the (200) fundamental peak agreed with the calculated values assuming that tantalum atoms substitute on aluminum sites, not on nickel sites. Thus it is concluded from our experiments that tantalum atoms substitute for aluminum in Ni3Al, except for Ta contents around 0.2 at% where the data can not be interpreted in terms of a simple substitution scheme.
Compositional Effects on Processing and Properties of Nickel Aluminides
Authors: Sikka Vinod K.
Published: March 2011

Compositional effects on hot and cold workability of ductile-ordered nickel aluminides are described. Compositional effects studied include variations of chromium, aluminum, iron, and zirconium. The hot and cold workability of various nickel-aluminide alloys was ranked with respect to workability of stainless steel. The nickel-aluminide alloy containing chromium and low zirconium (IC-218LZr) had the best combination of hot and cold workability. This alloy also offered a good combination of strength and ductility values over a range of test temperatures.
Extended Solubility and Stability in Vapor Quenched Ni3al-X Intermetallics.
Authors: Wang Rong
Published: March 2011

A series of fine-grain and amorphous Ni3Al-X alloys, where X is a solute of 1 to 45 at.% Hf, C or Hf+C in continuously graded compositions, was formed simultaneously into a 0.2 mm-thick disk by high-rate sputter co-deposition. The as-deposited Ni3Al-X alloys exhibited a disordered Ll2 structure and extended solid solubility limits beyond which amorphous phases were formed. Heat-treatment of the alloys at 900°C resulted in fine grain size of 0.5 to 1.5 μm. Ultra-fine dispersoids less than 500 Å in size were observed and they seemed resistant to coarsening.
Effect of Solutes on Phase Stability in A13 Nb
Authors: Subramanian P. R. , Simmons J. P. , Mendiratta M. G. , Dimiduk D. M.
Published: March 2011

Alloying transition metal trialuminides such as Al3Nb with appropriate ternary elements may stabilize the ordered cubic Ll2 structure relative to the DO22 structure. This may enhance the symmetry related contributions to plastic flow, thereby aiding in overcoming the low ductility in the trialuminide systems. The present investigation was directed towards exploring the potential for obtaining new ternary Al3Nb-based intermetallics with the Ll2 structure. The effects of various ternary elements on the phase stability of A13Nb were studied by SEM, XRD, and EPMA. Results of the A13 Nb-X phase relationship studies are presented. Preliminary microhardness results on the ternary DO22 Al3Nb-X phases are also reported. The predictive capabilities of Pettifor's structural stability scheme are evaluated in the light of the present investigation.
Simultaneous Chromizing-Aluminizing Coating of Nickel and Nickel-Base Superalloys
Authors: Ravi V. A. , Rapp R. A.
Published: March 2011

Ni and Ni-base alloys have been simultaneously chromized-aluminized by a halide-activated pack cementation coating process. The computer program SOLGASMIX was used to calculate the equilibrium partial pressures of the gaseous species. Chloride-activated packs are predicted to be chromizingaluminizing while fluoride-activated packs are not. Codeposition of Cr and Al occurs in packs containing 90–95 w/o Cr in the masteralloy and either NaCl, CrCl2 or NH4 C1 as the halide salt activator at 1273K.
Fatigue/Creep Interactions in Ni3Al-Base Alloys
Authors: Camus G. M. , Duquette D. J. , Stoloff N. S.
Published: March 2011

Stress-controlled fatigue tests and fatigue crack growth rate tests respectively have been carried out on two Ni3Al Cr/Zr alloys, IC 218 at 600°C and 800°C, and IC 221 at 800°C, in vacuum, at various test frequencies. Decreasing the test frequency and/or increasing the temperature leads to a decrease in the number of cycles to failure, and a gradual disappearance of a fatigue fracture zone. In fatigue crack propagation tests, the crack growth rate only decreases at the lowest frequency and remains constant in the major part of the frequency range investigated. The fatigue propagation mode in all cases is intergranular. These trends are shown in both cases to be related to a true creep component but, under fatigue crack growth test conditions, crack blunting intervenes gradually as the frequency is decreased, leading therefore to a less severe frequency effect.
Oxidation Behavior of Ni3Al-8Cr-0.1B Alloy Containing Zr Addition
Authors: Jiangting Guo , Chao Sun , Hui Li , Hengrong Guan
Published: March 2011

The isothermal oxidation behavior of Ni3A1 + 8Cr + 0.1B alloy containing zirconium addition was studied over a temperature range 850 to 1150°C and for periods up to 100 h. The results show that isothermal oxidation kinetics of the alloys at various temperatures obey a parabolic law. The addition of zirconium to Ni3A1-8Cr-0.1B alloy improves oxidation resistance at 850 to 950°C. However, the additive results in a considerable weight gain at 1050 to 1150°C. The structure of scale and phase transformation of the surface zone beneath the scale have been investigated. The addition of zirconium leads to the formation of adherent scale at all temperatures, since the internal oxides, like “tree roots” between the oxide scale and the substrate, are developed during oxidation.
The Tensile Behavior of a Ni3Al-Based Composite with TiC Reinforcement
Authors: Fuchs Gerhard E.
Published: March 2011

The tensile properties of a powder processed intermetallic matrix composite (IMC) and a similarly processed matrix alloy were investigated in the temperature range 298–1273K. The matrix alloy utilized in the study was the advanced nickel-aluminide IC-221 (Ni-16Al-8Cr-1Zr-0.05B). The composites contained 25 vol% TiC particulate reinforcement. The specific modulus of the composites was 20–30% higher than that of typical Ni-base superalloys. The yield strength of the composites were 10–20% greater than that of the matrix at all test temperatures. However, the composites exhibited lower ductility than the matrix. SEM fractography revealed that tensile failure occurred at the matrix/particulate interface. However, remnants of the matrix was observed on TiC particles on the fracture surface, suggesting good matrix/particle bonding. The strengths of the composites were very competitive with Ni-base superalloys.
Effect of Vanadium on Plastic Deformation in Llo TiAl Compound Alloys
Authors: Whang Sung H. , Hahn Yoo-Dong
Published: March 2011

Ternary Ti-Al-V (Llo) alloys containing vanadium up to 10 at.% and aluminum in the range of 50–55 at.% were prepared. Miniature specimens machined from these alloys were deformed in uniaxial compression at room temperature.

The yield stress, and fracture stress and strain were determined with respect to vanadium and aluminum concentration. The deformed alloys were electropolished into thin foils and studied by TEM. In particular, the types of dislocations, stacking faults and twins in the Ti-Al-V alloys were investigated by TEM.
Experimental Determination of the Ti-Nb-Al Phase Diagram At 1200°C.
Authors: Jewett T. J. , Lin J. C. , Bonda N. R. , Seitzman L. E. , Hsieh K. C. , Chang Y. A. , Perepezko J. H.
Published: March 2011

Studies consisting of both bulk sample and diffusion couple experiments have been conducted in order to establish an isothermal section of the Ti-Nb-Al system. Bulk samples were prepared by arc-melting and then annealed in a gettered, flowing, argon atmosphere for extended equilibration periods. The results obtained so far have established the existence of two ternary phases with the following approximate compositions, TI (Ti-18 at% Nb-34 at% Al) and T2 (Ti-ll at% Nb-44 at% Al). Moreover, several of the binary phases were found to have extensive solubilities, including the TiAl phase. The phases TiAl3 and NbAl3 form a continuous solid solution. Several heterogeneous equilibria were also determined. Determination of these phase fields was accomplished through the use of electron microprobe analysis (EMPA), x-ray diffraction, microstructural observations and backscatter electron imaging (BEI).
Annealing Studies of B2 FeAl
Authors: Schmidt Berndt , Nagpal Pavan , Baker Ian
Published: March 2011

Rods of five FeAl alloys whose compositions span the B2 phase field (34–51 at. % Al) were produced by multiple hot extrusions of ingots. Samples of each alloy were annealed in air at 1173K and 1473K in order to study the effect of alloy composition on both the grain growth kinetics and on the rate of oxidation. Little oxidation occurred at 1173K but at 1473K the oxidation rate was found to decrease with increasing aluminum concentration. The predominant oxide was found to be α-A12O3. The grain size was found to increase rapidly during the first hour of annealing at both temperatures after which it increased more slowly. The grain growth rate was found to decrease with increasing aluminum content.

Hardness measurements were made on both as-extruded and annealed samples of FeAl. Hardness increased with increasing aluminum content. The hardness was higher in annealed and air-cooled samples due to vacancy retention. Compression tests of air-cooled, annealed samples also showed higher yield strengths than as-extruded samples. Yield strength and strain hardening rate were found to increase and the ductility was found to decrease with increasing aluminum content.
Effect of Aluminum Level on Boron Clustering in Ni3Al
Authors: Horton J. A. , Miller M. K. , Liu C. T. , George E. P. , Bentley J.
Published: March 2011

In alloys containing 0.24% boron, atom-probe field-ion microscopy (APFIM) revealed the presence of boron clusters in Ni-25 at. % Al and Ni-26 Al but not in Ni-24 Al. The observed boron clusters generally consisted of two to three boron atoms with a maximum size of 10 atoms. Quench rates that ranged from rapid solidification to furnace cooling had little effect on the clustering. The occurrence of the clustering coincides with a higher rate of boron strengthening as measured by an increase in the yield stress per atomic percent boron, and it also coincides with a reduced amount of boron segregation to grain boundaries. The levels of nickel and boron were highly variable on grain boundaries in rapidly solidified material and therefore no consistent indication of nickel enrichment at the grain boundaries associated with boron segregation was found. This result suggests that cosegregation of nickel with boron may not be necessary for the ductilization of Ni3Al by boron, since the rapidly solidified material is also ductilized by boron and exhibits segregation of only boron to the grain boundaries.
Synthesis and Structural Characterization of Rigid Rod-Like Unsubstituted Quinoline Oligomers
Authors: Chiang Long Y. , Kastrup Rodney V. , Hsu Chang S. , Swirczewski John W.
Published: March 2011

The structure of quinoline oligomers synthesized by the catalytic dehydrogenative condensation reaction of 1,2,3,4-tetrahydroquinoline was elucidated on the basis of various spectroscopic data including the 2D COSY 1H NMR. The x-ray crystal structural study of two quinoline dimers successfully isolated from the bulk material resolved the puzzle of ring conjunction positions between quinoline units of the oligomer product. A reaction mechanism is proposed. From this mechanism a delicate balance between dehydrogenation and polymerization activity of the catalyst is required to optimize the yield and the molecular weight of the product.
The Synthesis of Benzothiazole Polymers with Perpendicularly Attached Phenyl Substituents
Authors: Feld William A. , Chang YiHua , Peak John D. , Wierschke Scott G. , Chen Join Pin
Published: March 2011

A series of 2-aryl-4,7-benzothiazoledicarboxylic acids have been synthesized from the corresponding dimethyl derivatives. These derivatives contain the phenyl, and the p-bromo-, mchloro-, p-chloro-, m-methoxy-, and p-methoxyphenyl aryl substituents. The phenyl, pchlorophenyl and p-methoxyphenyl substituted diacids were polymerized with 2,5-diamino-1,4- benzenedithiol dihydrochloride to yield the corresponding poly(benzothiazole)s. The polymers were of low molecular weight (intrinsic viscosity as high as 1.7) and did not show enhanced solubility in common solvents.
An Heterocyclic Aromatic Polymer and Its Mechanical Properties
Authors: Mukai Seiichi , Nozawa S. , Kimura M. , Tayama T.
Published: March 2011

A novel polyimide-based heterocyclic polymer, polyimide benzobisthiazole (PIBT), was prepared from diaminophenylene benzobisthiazole (DAPBT) and pyromellitic acid dianhydride (PMDA). Fibers with tensile modulus of 220 GPa were obtained from PIBT; this modulus value is consistent with the 430 GPa modulus determined by wide-angle x-ray diffraction (WAXD) analysis. Unoriented isotropic films exhibited significantly lower modulus values in the range of 10 GPa. Block copolymers of PIBT with thermoplastic segments were synthesized in an effort to prepare molecular composites. These materials showed a dramatic decrease in melt viscosity and had modulus values lower than observed in isotropic PIBT films.
Lattice Simulation of Mixtures of Flexible and Semi-Flexible Chains
Authors: Cifra P. , Karasz F.E. , Macknight W.J.
Published: March 2011

Miscibility behavior in a binary polymer mixture composed of flexible and semiflexible chains has been examined by Monte Carlo simulations on a cubic lattice. It is shown that as the flexibility of one component in an initially miscible mixture of flexible chains of both kinds is reduced the miscibility of the system is not necessarily lost. In fact, flexible chains in the mixture can adjust to this situation and the equilibrium number of segmental contacts between the blend components is retained. The situation is changed in systems in which the loss of flexibility is coupled with an aggregation tendency of the semiflexible chains. The disparity between blend components due to the presence of orientational correlations between the semiflexible chains to a certain extent drives the system towards demixing. However, the dominant role in miscibility behavior in mixtures of flexible and semiflexible chains is played by intermolecular interactions between blend components.
Film Processing and Applications for Rigid-Rod Polymers
Authors: Lusignea Richard W.
Published: March 2011

High strength, high modulus (2 GPa, 270 GPa, respectively) films have been produced with controllable planar orientation. Films were extruded from high viscosity nematic polymer solutions using rigid-rod aromatic heterocyclic polymers. Novel solution processing and treatment were used to control orientation, microfibrillar structure and texture, and physical properties. The coefficient of thermal expansion of these films was tailored by orientation and addition of secondary materials. This resulted in applications for dimensionally stable electronic substrates and structures for spacecraft. Other applications include high temperature barrier films, thin-walled structures, lightweight capacitors, high temperature insulation and cryogenic tanks.
Some Physical and Mechanical Properties of Pbo Fiber
Authors: Im J. , Percha P.A. , Yeakle D.S.
Published: March 2011

The tensile properties of poly (paraphenylene benzobisoxazole) or PBO fiber strands were studied using two variables: gage length and the number of twists per inch. The gage length was varied from 1 to 10 inches with 2 twists of the fiber per inch. The effect of the number of twists per inch was studied by varying the number of twists from zero to 10 along a 5-inch gage length. The trends of tensile strength and modulus due to these variables were established and appropriate explanations of these behaviors are provided.

The coefficient of thermal expansion (CTE) was studied on bare strands of PBO and Kevlar 49 (a product of Du Pont de Nemours & Co.) fibers, using a Du Pont 943 Thermomechanical Analyzer (TMA) equipped with a film and fiber tension assembly. The axial CTE of both fibers exhibited a dependence on the small dead load employed to keep the fibers straight. Kevlar 49 fiber, when wet, attained a much less negative value of CTE than when dry. In contrast, PBO fiber absorbed very little moisture, and the CTE remained unchanged.
Computational Predictions of the Tensile and Compressive Properties of Rigid-Rod Polymers
Authors: Wierschke Scott G.
Published: March 2011

The Austin Model 1 (AM1) semiempirical molecular orbital method has been used to calculate tensile moduli and molecular tensile and compressive deformation for several rigid-rod polymers and a graphite model. The calculated moduli are an improvement over previous Modified Neglect of Differential Overlap (MNDO) calculations. These are the ultimate moduli or the perfectly aligned bulk systems. By analyzing the deformation of polymer molecules in tension and compression, the failure modes and weak points in the molecules can be determined. In compression, all the heterocyclic rigid-rod polymers exhibit a “bending” failure mode. In tension and compression, the phenyl group in the rods undergoes in-plane deformation more easily than the heterocyclic moiety, thus causing a lowering of the modulus. The hypothetical “ladder” polymer, polyacene, shows higher tensile and compressive resistance than any of the rods, suggesting that further study into the ladder polymers is warranted.
Molecular Packing and Crystalline Order in Polybenzobisoxazole and Polybenzobisthiazole Fibers
Authors: Fratini Albert V. , Lenhert P. Galen , Resch Timothy J. , Adams W. Wade
Published: March 2011

The structures of poly(p-phenylenebenzobisthiazole) (PBZT) and poly(p-phenylenebenzobisoxazole) (PBO) fibers have been investigated by fiber diffraction techniques. d-spacings were obtained from equatorial and meridional scans recorded on a four-circle diffractometer. Intensity data were derived from x-ray rotation patterns taken on Weissenberg and vacuum cylindrical cameras. Unit cells were found to be monoclinic and non-primitive, each containing two chains per cell of dimensions a = 11.79(2), b = 3.539(5), c = 12.514(9) A, γ = 94.0(2)o for PBZT; and = 11.20(1), b = 3.540(2), c = 12.050(3) Å, γ = 101.3(1) for PBO. The fiber axes correspond to c. The conformational torsion angle between the bisthiazole and phenylene units and the orientation of chains within the unit cells were obtained from a ‘linked-atom least-squares’ (LALS)refinement procedure. A packing model is proposed for each polymer in which two independent molecular chains are displaced longitudinally by discrete rather than random increments. Primitive unit cells (Z = 1), besides requiring perfect axial registry of molecular chains, suffer from the occurrence of short intermolecular contacts and are rejected from further consideration.
Structure Analysis of a Rodlike Macromolecule: Poly(2,2'-(p,p'-Biphenyl)−6,6'-bis(4-Phenylquinoline))
Authors: Burkhart Craig W. , Lando Jerome B. , Stille John K.
Published: March 2011

Uniaxially oriented, crystalline fibers of poly(2,2'-(p,p'-biphenyl)- 6,6'-bis(4-phenylquinoline)) [PBPQ], were subjected to structure analysis via x-ray diffraction and molecular packing analysis. Packing analysis was required due to the sparse and diffuse nature of the fiber diffraction photographs. The combination of the two techniques allowed us to resolve the crystal structure. PBPQ packs in a syn conformation, in a modified herringbone structure. It has a unit cell of a = 16.2Å, b = 5.31Å, c = 21.4Å. There are two independent chains in the unit cell. An overview of the refinement of the crystal structure, the packing analysis and the crystallography are presented.
Concept and Overview of Rigid Rod Molecular Composites
Authors: Hwang Wen-Fang , Helminiak T. E.
Published: March 2011

Recently, the concept of rigid rod molecular composites, originally demonstrated in the Air Force Materials Laboratory, has attracted wide spread attention in the global research community in the hope of creating a new generation of materials for structural and electronic applications in extreme environments. As originally conceived, a molecular composite is a homogeneous, synergistic composite of molecularly dispersed rigid rod polymer molecules (single molecules or small bundles of molecules with a lateral dimension of less than 50 Å) with high aspect ratios in a matrix material. The enhanced and desirable properties, such as superior chemical and environmental resistance, enhanced thermal and thermoxidative stability, toughness, and dimensional stability, resulting from the synergism between the reinforcing rigid rods and the matrix can only be realized in a true molecular composite. Without the development of true rigid rod molecular composite technology, the fundamental detrimental interfacial problems (adhesion, different thermal expansion coefficients, etc.) encountered in conventional fiber composites can not be averted. A truly revolutionary material technology can be developed only if one adheres to the original concept.
The Dynamics of Phase Separation in Rigid-Rod Molecular Composites
Authors: Chuah Hoe Hin , Kyu Thein , Helminiak T. E.
Published: March 2011

The thermally induced phase separation of poly(p-phenylene benzobisthiazole)/ Nylon 66 molecular composites was followed by small-angle light scattering which showed the development of a scattering ring. The intensity increased and the ring moved towards the main beam as a function of time.

The scattering vector qm and intensity maxima Im scaled as qm~t−∝ and Im~tβ with ∝~ 0.33 and β = 0.91-0.95, in close agreement with the cluster dynamics prediction of Binder. However, at longer times, the increase in both qm and Im slowed down dramatically indicating a different mechanism. The structure function S(x) was used to test the validity of universal scaling for a rigid-rod/flexible coil polymer blend. At large x, S(x) scaled to the power of −2.4 in x, which is in between values predicted for systems with one and two-dimensional diffusion.
Orientational Order of α-Helical Poly (γ-Benzyl L-Glutamate) in the Lyotrao-Phiecl Ilciaqlu Idp Oclryy(yS-Tbaelnlziynle Ls-Tate and Conformation of the Pendant Side Chain
Authors: Abe Akihiro , Yamazaki Toshimasa
Published: March 2011

Deuterium NMR studies have been performed on variously labeled PBLG samples in the lyotroplc liquid crystalline state. The orientational orders S of the a-helical backbone were estimated from the observed quadrupolar splittings ∆v of the N-D and Cα-D bond. The values of S decrease gradually by dilution until the upper equilibrium concentration (B-point) is reached. The concentration dependence of Scrit has been compared with those derived from standard theories. The relatlve orientation of side chains with respect to the backbone was elucidated by the rotational isomeric state analysis of the ∆v/S data observed for the γ-, γ-, and ζ-methylene, and p-benzyl deuterons. The results indicate that the steric overlaps between adjacent side chains play an important role in determining the preference of conformations in the PBLG system. A similar analysis has been extended to poly(L-glutamic acid) esters carrying a homologous series of ester residues, -C(O)O(CH2)nC6D5 with n = 2 and 3. A distinct odd-even oscillation was observed for the orientation of the terminal phenyl groups with n.
Distribution and Transport of Charge Carriers in Heterogeneous Electrolyte Systems
Authors: Maier Joachim
Published: March 2011

The thermodynamic point defect concentrations for both ionic (majority) as well as electronic (minority) charge carriers are considered for different types of heterogeneities appearing in ionically conductive solid materials systems. Particularly, the electrical conductivity is discussed for different types of composite electrolytes. Quantitative space charge arguments are shown to be able to explain a variety of different phenomena such as: unusual enhancement of ionic conductivity in two phase samples and in polycrystalline materials, additional conductivity effects in microsized systems; change from cationic to anionic conduction due to heterogeneous doping; simultaneous enhancement of n- and p-conductivity in different electrolyte/ alumina samples, catalytic effects in composite electrolytes as well as chemical interface effects.
Electrical Phenomenon in Membranes
Authors: Pechorin Alentin
Published: March 2011

For some superionic conductive membranes the speed of diffusion of ions is enough to produce a measurable electric field in a magnetic field, which is situated perpendicularly to the di rection of diffusion. This phenomenon may be used in the manufac turing of different kinds of sensors.
Spectroscopic Studies of a Superionic Plastic Phase Crystal: Lithium Sulfate
Authors: Frech Roger
Published: March 2011

Temperature dependent Raman spectroscopic studies of single crystal lithium sulfate are summarized. Coupling between sulfate ion bending modes and the lithium ion translatory modes becomes weaker with increasing temperature until the lithium modes can no longer be observed above 250° C. The temperature interval above 450° in the monoclinic phase is marked by the onset of significant sulfate ion reorientational motion, as evidenced by the bandshape studies of the sulfate ion v1, mode and the librational modes. Bandshape analysis of the v3mode in the plastic phase strongly suggests that the symmetry of the sulfate ion potential energy environment has planar anisotropy.

The lithium ion-sulfate ion interactions are modeled for correlated sulfate ion configurations as a function of lithium ion position. The results support the role of the octahedral site in lithium ion transitions contributing to the ionic conductivity.
Neutron Diffraction in Superionic Glasses
Authors: Börjesson L. , Elmroth M. , Torell L.M. , Howells W.S.
Published: March 2011

Neutron diffraction experiments have been performed on AgI and LiCI doped borate glasses. The experiments reveal a substantial progressive increase of the medium range structural ordering when Agl is introduced into the glass, which is manifested in the appearance of an intense diffraction peak at anomalously low Q-values (0=0.8 Å−1). The observation might be attributed either to density deficits within the boron-oxygen network or to the presence of small clusters of AgI. The conduction path model proposed to explain the high ion conductivity may therefore hold for the AgI doped glasses. In contrast, no additional medium range ordering can be observed when LiCI is used as the dopant salt, which casts some doubts on the microdomain model as an explanation of the high ionic conductivity in superionic glasses.
Polymer Aukali-Metal Polyiodides with Variable Ionic and Electronic Conductivities
Authors: Loye Hans-Conrad Zur , Lyons Leslie J. , Hardy L. Charles , Tonge James S. , Shriver Duward F.
Published: March 2011

Alkali metal polyiodide complexes of polyethers, of the type (polymer)nMIx, [Polymer - poly(ethylene oxide), PEO; poly(propylene oxide), PPO; or poly-(bis(methoxyethoxyethoxy)phosphazene), MEEP, and M - Li or Na] have been prepared and characterized in order to elucidate the nature of the observed ionic and electronic conductivities. Raman spectra of the polyiodide complexes indicate that the relative concentrations of the polyiodide species (such as I3- and higher polyiodides) depend on the salt concentration in the polymer as well as on the iodine to cation ratio. The ionic conduction can best be described by a free volume (VTF) mechanism where both polymer motion and ion mobility are activated processes. The magnitude of the electronic and ionic conductivities are a function of polymer to salt ratio as well as iodine content.
Polymer Electrolytes with Exclusively Cationic Conductivity
Authors: Liu H. , Okamoto Y. , Skotheim T. , Pak Y. S. , Greenbaum S. G. , Adamic K. J.
Published: March 2011

The synthesis of exclusively cation conducting polymer electrolytes based on a nylon-l backbone, ethylene-oxide side chains, and attached dibutyl phenolate anions is described. The tendency for ion pair formation appears to be reduced as the conductivity of the sodium-containing compound reaches −2 × 10−6 S-cm−1 at 50°C. 23Na nuclear magnetic resonance measurements demonstrate: i) motional narrowing of the mobile Na+ resonance above the glass transition temperature; ii) mobile Na+ concentrations of ∼75% at 40°C; iii) insensitivity of the linewidth to applied hydrostatic pressure up to 2 kbar. Similaries between these findings, and those in “conventional” polymer-salt electrolytes are discussed.
Proton Conducting Polymer Electrolytes for Possible Application In Electrochromic Display Devices
Authors: Singh R.P. , Gupta P.N. , Agrawal S.L. , Singh U.P.
Published: March 2011

Proton conduction in polymer composites of PVA+H3PO4 AND PVA+H2SO4 have been investigated. The films protonated by H3PO4 show protonic conductivity between 10−6to 10−3ohm−1cm−1 depending upon the relative ratios and temperature. H2SO4 protonated PVA films also show proton conductance of almost similar magnitude. The ionic transference number has been estimated to be 0.95 for H3PO4 protonated PVA film of ratio 70:30. The frequency and temperature dependence of electrical conductivity has also been carried out. These polymer films have been used to fabricate an electrochromic cell. The colorationtime determined from response time measurement for the system “SnO2|Glass|WO3 film|PVA film|SnO2 Glass” is 2.6 sec for H3PO4 doped films and 6 seconds for H2SO4 doped films.
EXAFS of Polymer Electrolytes
Authors: Cole M. , Latham R.J. , Linford R.G. , Schlindwein W.S. , Sheldon M.H.
Published: March 2011

The technique of EXAFS is reviewed and its application, especially to Ca- and Zn-polymer electrolytes, is considered. The implications of the EXAFS results for the interpretation of the electrochemical properties of these electrolytes are discussed.
The Electronic Transfer and the Formation of Cationic Intercalation Compounds
Authors: Rouxel J.
Published: March 2011

Low-dimensional solids are known to be among the best host structures to practice intercalation chemistry. Besides geometrical aspects which play an important role but are now quite well understood, this paper emphasizes the relationship between chemical reactivity and the electronic structure of the host. A special attention is paid to the nature of redox centers involved in the intercalation process and to the connection between the phase diagram and the band structure of the host material.
Microstructures of The Electron-Beam Evaporated InSb Thin Films
Authors: Cheng D.J. , Yeh S. , Chi G.F.
Published: March 2011

Polycrystalline InSb thin films have been prepared by the two-source electron-beam evaporation method. The InSb films have been grown on both pure Si (100) substrate and on Si (100) substrate which has been thermally oxidized to form a thin amorphous SiOx overlayer. The as-grown thin films have been heat treated under N2 atmosphere which is slightly mixed with air. A thin InOx layer is formed on the top surface of the thin film.

After heat treatment, the InSb films grown on the oxidized Si substrate shows a preferred (111) orientation. While the films grown on Si substrate do not show such preferred orientation as evidenced by the X-ray diffraction patterns.

The TEM cross sectional morphologies of the InSb film grown on oxidized Si substrate shows an ordered arrangement of the grains. While the film grown on the pure Si substrate shows a random arrangement of the grains. The film grown on the oxidized Si substrate also shows the existence of the twin boundary and an ordered arrangement of the precipitation of the second phase.
Structural and Electrical Characteristics of the Thermally Evaporated InSb Thin Films
Authors: Yeh S. , Cheng D. J. , Chi G. F. , Chu M. T.
Published: March 2011

Polycrystalline InSb thin films have been prepared by the two-source thermal co-evaporation method. The InSb films have been grown on both pure Si (100) substrate and on Si (100) substrate which has been thermally oxidized to form a thin amorphous SiOx overlayer. The as-grown films have been heat treated under N2 atmosphere at different temperatures ranged from 520 to 535 C. Both as-grown films have (220) diffraction as the main peak. The heat treated films which have high mobility values show the (111) preferred orientation. For the heat treated film on oxidized Si substrate, the TEM cross sectional morphologies show the existence of the precipitaion of the second phase and the interface diffusion of InSb into the SiOx layer.
Structural Design and Synthesis of H3O+-β”/βAl2O3 and NH4-β”/β-Al2O3 Polycrystals
Authors: Nicholson Patrick S.
Published: March 2011

The synthesis and characterization of H3Oβ”/β-Al2O3 and NH4 + -H3O+β”/β-Al2O3 poly-crystals is described. The role of stress development and control in the intermediate stages of ion-exchange of the NaK-β”/βA12O3 ceramics is analysed and identifies the β-Al2O3 phase as acting as inert reinforcement for the two-phase composite. The Rb + ion-exchange of the intermediate K + β”/β-Al2O3 requisite for NH4+/H3O + ion-exchange to NH4-H3O+β”/βAl2O3 is described as also is the NH4NO3 exchange to the final ceramic. The total weight loss on heating NH4-H3O+β”/βAl2O3 polycrystals to 810°C is 7.4% which agrees with the value expected from the chemical formula. The 25°C conductivity of the grains of NH4 +-H3O + β”/βAl2O3 was 1.7 × 10−4 (ω-cm)−1 and the bulk conductivity was 3 × 10−5(ω-cm)−1.
Complex Defects in Lanthanide ion-Exchanged Beta Aluminas
Authors: Valergai Pedro , Jin Xianglin , Vozzo Frank , Roth Walter L.
Published: March 2011

Na+ beta alumina crystals, ion-exchanged with Eu2+ and Nd3+, were studied using x-ray diffraction and optical spectroscopy. In partially-exchanged crystals, we found different concentrations of sodium and lanthanide ions in the two conduction planes of the unit cell. The results suggest that pairs of sodium ions are rapidly replaced by lanthanide ions in regions of the planes bridged by VAl-Ali-O-Ali-VAl extended defects.
Ion-Implanted Superionic Clusters
Authors: Feng Yiping , Wang Paul W. , Roth Walter L.
Published: March 2011

Ag+ was implanted in silica glass and beta alumina crystal and studied using particle backscattering and optical absorption. We found that Ag aggregates into colloidal metallic particles and when annealed diffuses toward the surface. The activation energy for diffusion is 0.14 eV in silica glass and 0.16 eV in beta alumina. Computer simulations indicate fast Ag+ diffusion is due to large concentrations of vacancies deposited along the track of the implanted ion. The high ionic conductivity of beta alumina promotes uniform spreading of the implanted layer.
Preparation of Thin Film Solid-State Electrochromic Device by Spray Pyrolysis Technique
Authors: Lee T. J. , Fey G. T. K. , Lin W. J. , Yao P.C. , Hsu S. E.
Published: March 2011

in this study we report the use of a self-contained proton conductor, an electrochromic film of PWA, as the coating material for an energy-efficient window. The coating was prepared by spray pyrolysis method. The solar transmittance of the window can vary reversibly between 78% to 8%. The diffusion coefficient of PWA in decoloration is 2.8 × 10−12cm2/sec based on the calculation from the cyclic voltammetric data.
Electrochemical Studies of the Mixed-Conductor System YBa2Cu307-δ
Authors: Holland G.F. , Russek S.L. , Stacy A.M. , Michaels J.N.
Published: March 2011

Oxygen mobility in the system YBa2Cu307-δ (0 ≤ 8 ≤ 1) has been studied by electrochemical methods over the temperature range 500 ≤ T ≤ 800 °C. The experimental cell consisted of a pellet of YBa2Cu307-δ sandwiched between an ionically-blocking Au film electrode and an electronically-blocking yttrium-stabilized zirconia electrolyte/Pt paste electrode. The concentration of mobile oxygen ions, c(02-), and the diffusion coefficient, D, were evaluated from potential step experiments. Coulometric titration studies were used to modify the oxygen content of the oxygen deficient (δ ≥ 0) material. These electrochemically-modified samples were further characterized by magnetic susceptibility measurements to monitor the effect of changes of oxygen content on the width and position of the superconducting transītion.
Macroscopic and Microscopic Aspects of Electron Hopping in Mixed Conductor Membranes using the Quasi-Fermi level
Authors: Buck Richard P.
Published: March 2011

Electron transport in mixed conductor redox electrolyte membranes: anion/electron charge carriers, and cation/electron charge carriers are analyzed by irreversible thermodynamic methods appropriate to electrolyte transport. The generalized force for electron transport is the gradient of the Fermi level of electrons in electrolyte phases. The generalized force for ion transport is the gradient of the ionic electrochemical potential. New results include current-time, current-voltage, small amplitude and DC bias impedance functions.
Theory of Metal-Solid Electrolyte Interface
Authors: Kim S.I. , Seidl M.
Published: March 2011

A comprehensive time independent theory of the solid electrolyte(SE)–metal electrode interface is presented, using the assumption that cations are the only mobile charge carrier in the electrolyte. The temperature and the dc current across the SE are the only free parameters for the solutions along with three intrinsic parameters which depend on the properties of the particular system. The phenomenological model of the interface double layer is based on the Gouy–Chapman–Stern model.

The numerical solutions of the theory for porous tungstenzeolite system enables us to predict most of the properties in the SE system such as;the current–overpotential characteristics, the capacitances of the double layer, concentration profile in the diffusion layer, the potential profile across the interface, electrochemical exchange current, and the potential of zero charge(PZC) etc. An experimental technique to measure the PZC of SE systems has been also proposed.
Pore Structure Of Hydrated Cement Determined By Mercury Porosimetry And Nitrogen Sorption Techniques.
Authors: Abdel-Jawad Yahia , Hansen Will
Published: March 2011

The pore structure (i.e. total pore volume, surface area and pore-size distribution curves) was measured using mercury porosimetry and nitrogen sorption. Hydrated portland cement (type I) of water-cement (w/c) ratios 0.3, 0.4 and 0.6 by weight was analyzed at three degrees of hydration (i.e., 30%, 50% and 80%; 70% for the 0.3 w/c system) corresponding to low, intermediate and high levels of hydration. The effect of curing temperature (3°, 23°, and 43°C) on pore structure was also studied. The two techniques were evaluated as well on porous Vycor glass, which has a narrow pore size distribution in the size range accessible to both. Results obtained by both techniques on porous Vycor glass agreed well. However neither technique can be used alone to study the entire pore structure in well-hydrated cement due to the wide range in pore sizes and the presence of micropores. Due to the unstable pore structure in cement a specimen treatment procedure such as methanol replacement, combined with volume-thickness (V-t) analysis, is necessary in order to measure the micropores. At low hydration values the pore structure can be estimated by mercury intrusion porosimetry (MIP). At higher hydration values, however, this technique underestimates total pore volume and surface area due to the presence of micropores which MIP cannot determine. In the pore size range of overlap, higher pore volumes were obtained with MIP. Nitrogen V-t analysis shows that micropores are more pronounced with lower w/c ratios. This finding is consistent with pore size distribution curves obtained by MIP. For a given w/c ratio and degree of hydration the total pore volume measured by MIP was found to be independent of curing temperature in the temperature range studied. At any w/c ratio, capillary porosity is controlled by degree of hydration alone.
What Is Needed In A Permeability Test For Evaluation Of Concrete Quality.
Authors: Hooton R. Doug
Published: March 2011

While there is presently a great deal of interest in measurement of permeability, there are a wide variety of non-standard methods reported. The author's experience combined with a critical review of the literature is that:

(a)

results vary with operating variables of each test,

(b)

the coefficient of variation of results is large (typically 30 to 50%),

(c)

most methods cannot provide quantitative results in the range of interest for high strength, concretes and those containing supplementary cementing materials (10−15 m/s or less),

(d)

most methods do not represent the type of boundary conditions experienced by most critical concrete field conditions (i.e. fluid on one side and vapour on the other side),

(e)

Indirect measures of permeability such as rates of absorption, or resistivity measurements are easier to perform and relate directly to permeability.

The activity of research in the area of permeability is similar to that described in the technical literature from the 1920's and 1930's. Much of that early work has abandoned for reason (c) above.

It is attempted to review some of the previous experience, describe the problems and make suggestions for improved measurement of permeability.
Permeability Measurenents On Cement Paste
Authors: Banthia Nenkumar , Mindess Sidiney
Published: March 2011

The permeability of cement paste to water was determined by using a triaxial permeability cell. A new technique of specimen conditioning, based on cyclic flow reversal, was used for the early attainment of equilibrium flow conditions. Effects or cement type, age, and silica fume addition, were investigated. With the specimen conditioning used, equilibrium flow conditions were achieved on the first day of the test itself. The coefficient of permeability was found to decrease with an increase in the degree of hydration. The use of silica fume was found to decrease the permeability However, the permeability did not particularly depend upon the aotunt of silica fume added.
Gas Permeability of Concrete Up Till Pressure Difference of 100 Bar
Authors: Pihlajavaara S. E.
Published: March 2011

In modern society, concrete is one of the materials studied deeply in materials science, and, consequently, it is utilized also in high technology applications. However, the knowledge of gas permeability of concrete seems still to be poor and unreliable. Since 1980, the author has made both theoretical and experimental research to clarify the different aspects of gas permeability of concrete, especially for the applications in nuclear industry. A brief progress report of this work will be presented in this article.