bluuebunny/crossref_metadata_2025 huggingface dataset:
High Tempeature Ordered Compounds for Advanced AERO-Propulsion Applications
Authors: Anton D. L. , Shah D. M.
Published: March 2011

Advanced aero-propulsion engine designs now being considered for implementation require structural materials with high temperature strength and creep properties above 1300°C, in excess of the range where nickel base superalloys are now being used. A number of ordered single phase compounds having melting points above 1500°C have been identified which both hold promise for engine applications and are representative of a number of different crystal structures such as B2, C15 (Laves), A15, C1 and DO19. Elevated temperature characterization has been conducted on these compounds which includes ductile/brittle transition temperature determination, minimum creep rate analysis, elastic modulus, tensile strength and cyclic oxidation testing. The results of these tests have led to insight in the processing methods required for these compounds and selection of compounds based on elemental constituents and crystal structure.
Deformation and its Structure in LloTi-Al-Nb Compound Alloys
Authors: Hahn Yoo-Dong , Whang Sung H.
Published: March 2011

The ternary TiAl-Nb (Llo) alloys stabilized at 1000°C for a week were prepared into miniature specimens for compressive deformation tests. The specimens were deformed in uniaxial compression at room temperature as well as various high temperatures. The yield stress and fracture strain were determined with respect to Nb concentration, and as a function of temperature to investigate positive temperature dependence.

Dislocation structures and other deformation structures of the deformed alloys were studied by TEM.
Accurate Determination of γ′ Solvus in Ni-Al-X Ternary Systems
Authors: Hong Yong Myong , Mishima Yoshinao , Suzuki Tomoo
Published: March 2011

An attempt has been made to determine the γ/γ′ phase boundaries with particular emphasis on the γ′ solvus in ternary Ni-Al-X systems with X being one of the VA or VIA transition metal elements. It is shown that the γ′ solvus in each ternary system can be obtained as a surface with respect to composition and temperature by employing differential thermal analysis (DTA) as a key experimental technique with support from energy dispersive X-ray spectroscopy combined with scanning elecron microscope(SEM-EDX). Also shown is that the DTA results often provide useful information on the phase relation in the vicinity of γ and γ′ phase fields. In the Ni-Al-V ternary system, for example, the pseudo-binary constitution between Ni3Al and Ni3V is suggested. The results presented here are systematic and consistent and therefore are reliable as compared with the previous results reported fragmentarily.
The Tensile Properties and Microstructure of Ti-Tic Composites with Al Additions
Authors: Chen J. , Geng Z. , Chin B. A.
Published: March 2011

The relationship between the tensile properties and microstructure of Ti-TiC composite materials with Al additions was investigated. Composites containing 40–50% TiC by volume were produced using standard casting procedures from the melt. Ultimate tensile strengths of 1113 MPa with 1–2 % ductility were found in these materials. Results show that the tensile properties are controlled by the size and distribution of TiC particles.
Reinforcement/Matrix Interaction in Sic Fiber-Reinforced Ni3a1 Matrix Composites
Authors: Yang J.-M. , Kao W. H. , Liu C. T.
Published: March 2011

The interfacial reaction characteristics of two different types of SiC fibers with Ni3A1 (Ni-Al-Cr-Zr-B) matrix have been investigated. The microstructure and chemical compositions across the reaction zone have been analyzed quantitatively using microscopy and electron probe microanalysis. In both types of SiC/Ni3Al composites, it was found that Ni was the dominant diffusing species responsible for the overall reaction. The C-rich layer outside the SCS-6 fiber provided an incubation period, but could not stop the inward diffusion of Ni. It could, however, effectively stop the diffusion of Al, Zr and Cr. No significant increase in reaction zone thickness after exposure at temperatures below 900 °C for up to 100 hours was observed. When the C-rich layer was depleted, a rapid increase in reaction zone thickness and the formation of multilayer reaction products occurred. In the case of Sigma/Ni3A1 composite, extensive reaction between the fiber and the matrix occurred at all the temperatures studied. Diffusion barrier coating for both types of fibers is required to develop nickel aluminide matrix composites.
An Investigation of the Creep of Ni3Al(B, Hf) Single Crystals at Intermediate Temperatures
Authors: Hemker K. J. , Nix W. D.
Published: March 2011

This study was undertaken to characterize the intermediate temperature creep properties of Ni3Al. Itfocuses on the mechanisms controlling creep deformation and their relationship to the anomalous yielding behavior of this alloy. Constant stress creep tests were conducted for temperatures between 713–973 K, and the following observations were made. The creep curves exhibited two distinct regions. Primary creep was followed by inverse creep. Specimens cooled under constant stress strained an additional 20% during cooling. Temperature drop experiments indicate that Ni3Al is weakened by the addition of creep deformation.

Glide on the primary octahedral plane appears to be exhausted during primary creep. Slip trace and TEM studies indicate that inverse creep is controlled by slip on the cube cross slip plane and a secondary octahedral plane. Primary octahedral slip is observed in the specimens that are cooled and deformed under constant stress.
Proton Irradiation-induced Disordering Reactions, Ductility and Strengthening of Ni3Al
Authors: Cheng J. , Lee C.-S. , Wagner C. N. J. , Ardell A. J.
Published: March 2011

Ordered Ni3Al containing 24 at.% Al was irradiated by 2 MeV protons at −45 °C to a fluence of 1.34 × 1016 H+/mm2. The induced microstructural changes were investigated by transmission electron microscopy, X-ray diffraction, scanning electron fractography and microhardness measurements. Proton irradiation produced a large volume fraction of small disordered zones residing in the ordered matrix. The morphology of the disordered zones bears some striking similarities to “tweed” microstructures. X-ray diffraction reveals distinct splitting of the higher order fundamental peaks toward low angles, and broadening of the displaced peaks, indicating that the zones observed are small clusters of tetragonally distorted disordered Ni3Al. The microhardness measurements suggest that the disordered zones strengthen the remaining ordered matrix considerably, most likely through a precipitation strengthening mechanism. The fractographic observations suggest that an increase in ductility accompanies disordering, as evidenced by the appearance of dimples, slip markings and river patterns on the fracture surface of the irradiated region of the sample.
Alloying Effect on the Microstructure and Property of Single Crystal Ni3Al Alloys
Authors: Jishan Zhang , Zhiya Zhang , Yajun Tang , Jinghua Zhang , Yang Yu , Yingao Li , Dongsheng Ding , Zhuangqi Hu
Published: March 2011

The alloying effects of Cr, Zr, Ta, Nb and B on the microstructure and properties of single crystal Ni3Al alloys have been studied. The strength of the alloys has been improved markedly with promising plasticity. The 0.2% yield stress of some of these alloys is higher than that of IN713C, a typical cast nickel-base superalloy, in the temperature range from 25 to 950°C and some of them reach the strength level of advanced cast nickel-base alloys such as IN100 in the high temperature range. The creep strength of these alloys is also improved markedly. The single crystal Ni3Al alloy with a high Cr content ( 7 at-%) obviously shows an intermediate temperature low plasticity behavior. Although heat treatment can only slightly improve the strength, it can double the elongation of the alloy from 25% to 50%. In the Ni3Al monocrystal containing 1.2at%Zr there exist great amounts of the low melting point Ni5Zr-γ eutectics around the ordinary γ/γ′ eutectics. This makes it difficult to homogenize the coarse casting structures completely.
Study on Cast Ni3 Al-Base alloys
Authors: Yizhang Zhou , Tianxiang Zhang , Yingjie Tong , Bingda Zhang , Yaoxiao Zhu , Zhuangqi Hu
Published: March 2011

A series of cast Ni3Al-base alloys with the addition of alloying elements, such as Hf, Zr, Ti, Nb etc., have been studied, in which the total amount of Al and alloying elements substituting for Al was controlled in the range of 18 to 23 at%. It was found the alloying elements change remarkably the morphology, distribution and amount of γ phase as well as the morphology and size of primary γ′ intermetallic compound. The size of primary γ′ can be decreased to micron order. The brittle γ′-γ′ boundary (refer to primary γ′) can be substituted by tough γ′-γ-γ′ boundary. As a result, the mechanical properties of the cast Ni3Al-base alloys, especially high temperature ductility, can be enhanced. In addition, the effect of Cr is discussed when tested in air environment, and considered that chromium addition is not very effective to improve the high temperature embrittlement.
Deformation of a NI-AL-FE Gamma/Beta Alloy
Authors: Field R. D. , Krueger D. D. , Huang S. C.
Published: March 2011

Room temperature tensile tests were performed on annealed melt-spun ribbons of a 50Ni-20Al-30Fe alloy. The ribbons were found to possess a duplex structure consisting of fcc γ and B2 β grains and exhibited tensile elongations in excess of 10% while still maintaining good strength. The tested specimens were found to contain high dislocation densities in both the γ and β grains, with no indications of stress-induced martensite formation. Dislocation analysis revealed that the vast majority of dislocations in the β have <100> Burgers vectors; however, <111> dislocations were also observed. Slip transfer was often facilitated by specific orientation relationships between the γ and β grains.
Unlubricated Sliding Wear of Nickel Aluminides at Room Temperature and 400°C
Authors: Bonda N. Rao , Rigney D. A.
Published: March 2011

Unlubricated sliding tests were performed at room temperature and at 400°C on polycrystalline Ni3Al with and without boron and on IC218, an alloy containing nickel plus 8.94 Al, 7.55 Cr, 0.88 Zr, 0.015 B and 0.01 Hf (all in wt. %). A pjn/disk geometry was used with self-mated samples in air and vacuum (1.3×10-3 Pa). Normal load was 1.5 kg (14.7 N), sliding speeds were 15–19 mm/s and sliding distances were 145–175 m.

It had been expected that materials with and without boron would behave differently during sliding because of their well-known differences in ductility and fracture resistance. However, sliding behavior was similar for materials with and without boron. Environmental effects were more dramatic. For tests in vacuum, the friction trace was very noisy and the average coefficient of friction varied erratically during most of each test. Wear debris ranged from 100 μm to 1 mm in size. Wear scars were smooth, but with signs of heavy deformation. All test materials exhibited smoother sliding behavior in air than in vacuum, but the wear rate was usually higher in air. Debris particles were finer, most of them were at least partially oxidized, and they included at least one ferromagnetic component, probably arising from selective oxidation. It is suggested that the increased wear rate in air is related to oxygen-enhanced fracture of these nickel aluminides.
The Effect of Cobalt on Martensitic Toughening Parameters in NiAl
Authors: Russell Scott M. , Law C. C. , Blackburn M. J.
Published: March 2011

The martensitic transformation and the effect of cobalt additions on important martensitic toughening parameters are being studied as a means of toughening NiAl alloys. Cobalt additions to NiAl martensite are seen to lower the Ms temperature, reduce the transformation strain anisotropy, and reduce the transformation temperature hysteresis (an indicator of interfacial mobility). Optimization of these parameters should allow martensitic transformation toughening processes to aid in overcoming the ambient temperature brittleness of NiAl alloys.
The Deformation Microstructure in NI3Si Polycrystals Strained Over the Range of Temperature of Flow Stress Anomaly
Authors: Tounsia B. , Beauchamp P. , Mishima Y. , Suzuki T. , Veysslière P.
Published: March 2011

In order to correlate the flow stress anomaly of Ni3Si with dislocation properties, a weakbeam study ofpolycrystalline samples deformed between ambient and the peak temperature was carried out. Samples with two extreme Ni/Si ratios were tested.The most frequently activated slip system changes progressively from octahedral to cubic with increasing temperature. The transformation of superdislocations into Kear-Wilsdorf configurations gives rise to screw dislocations that are rectilinear only after deformation at room temperature. The effect of temperature is to gradually promote bending of Kear-Wisdorf configurations in the cube plane, from a few nanometers at 230°C to several tenths of micrometers at intermediate temperature. Cube slip begins to be massively activated a little below the peak temperature. It is suggested that the flow stress anomaly is controlled by progressive exhaustion of octahedral slip by thermally-activated expansion of superdislocations on the cube cross-slip plane.
A Weak-Beam Study of the Microstructure of β-CUZN Deformed in the Domain of Flow Stress Anomaly
Authors: Dirras G. , Beauchamp P. , Veyssière P.
Published: March 2011

β-brass single crystals oriented along <001> were deformed between room temperature and 300°C. The deformation microstructure and dissociation properties were studied by transmission electron microscopy under weak-beam imaging conditions.

Whatever the deformation temperature, superdislocations with <111> Burgers vector and strong edge component dominate within the microstructure. In addition, below the temperature of the flow stress peak (≈ 250°C), the density of screw relative to mixed superdislocations decreases as straining temperature increases. Dissociation does not always occur on the slip plane neither does it proceed exclusively by glide, even in samples deformed at 100°C.
Fracture and Fractography of Ordered Ni4Mo
Authors: Kao H. P. , Brooks C. R. , Sanganeria M.
Published: March 2011

The domain structure of the alloy Ni-20 at. % Mo depends upon the heat treatment below the critical temperature (868°C). Upon aging around 750–850°C, initially a very fine domain structure forms inside the a grains, which then coarsens, and then migration of these boundaries occurs with a coarser domains structure behind them. In the ordered condition, the alloy is very brittle. Fractographs are presented which correlate the fracture morphology to the microstructures of the ordered alloy, showing that fracture occurs along the migrated, former α grain boundaries.
Microstructures and Mechanical Properties of Dual Phase Alloys Consisting of the Intermetallic Phases Ti3 (Al, Si) and Ti5(Si, Al)3
Authors: Wu J. S. , Beaven P. A. , Wagner R. , Hartig Ch. , Seeger J.
Published: March 2011

Alloying additions of silicon to the intermetallic titanium-aluminide Ti4Al lead to two-phase microstructures consisting of α2-Ti3(Al, Si) and Ti5(Si, Al)3.

Although details of the ternary Ti-Al-Si phase diagram are not available, theoretical analysis and experimental screening have indicated the existence of a eutectic line in the Ti-rich region of the Ti3Al + Ti5Si3 two-phase region. The eutectic alloys display dual phase structures with Ti3(Al, Si) being the matrix and Ti5(Si, Al)3 the second phase.

In this paper the microstructures of the eutectic as well as hypoeutectic and hyper-eutectic alloys, which contain additionally primary Ti3(Al, Si) and Ti5(Si, Al)3 needles, respectively, are described. The influence of the particular microstructure on various temperature-dependent mechanical properties such as strength, ductility, creep and fracture behaviour has been investigated. Alloys with hypo-eutectic microstructures show promising high temperature mechanical properties.
Structural Modifications of Rigid-Rod Polymers
Authors: Arnold Fred E.
Published: March 2011

Research in our laboratory on lyotropic liquid crystalline polymers has provided a series of high modulus, high tenacity materials derived from benzobisazole rigid-rod polymers. A number of different structural modifications on these systems have been carried out in our laboratory. This paper will be focused on those structural variations made by maintaining the para-ordered geometry while modifying the structure with pendent groups.
Orientability of Rigid Rodlike Molecules in Solution and Controlled Preparation of Model Systems
Authors: Odell Jeffrey A. , Keller Andrew , Atkins Edward D.T. , Nagy Miklos J. , Feijoo Jose Luis , Ungar Goran
Published: March 2011

A survey is presented of our works on orientability of poly(p-phenylene-benzbisthiazole) (PBT) as a model for rigid rods. It starts with the solid state with specific reference to diffraction by the individual molecule. It is followed by behaviour in semidilute solutions, demonstrating increase of orientability with increasing rod alignment, with vastly higher absolute values (as expressed by rotational diffusion coefficient) than anticipated from existing theory. The origin of the discrepancy, as identified by simulations, lies in the inappropriateness of the application of mean constraints, a recognition which should have wider implications. The relaxation from the highly oriented state, also in solution, has been followed and the elementary rotational jump of rods identified, with a new method relying on in situ (synchrotron) X-ray diffraction. As a separate line, we are announcing a new model system, ellipsoidal latices of predesigned axial ratios, with wide ranging potential for the study of rigid rod behaviour in polymer and colloid science.
Formation and Properties of Fiber and Film FROM PBZT
Authors: Chenevey Edwjard C. , Timmons William D.
Published: March 2011

Between 1977 and 1985, the Air Force Materials Laboratory funded a series of contracts, whereby Hoechst Celanese Research, formerly the Celanese Research Company, demonstrated and developed processes for the formation of fibers and films from highly viscous, anisotropic dopes of PBZT polymer. Heat treatment of these products was found to have significant effects on the tensile properties, and comparisons will be shown between asspun fibers and ones heat-treated at up to 1335°F (725°C).

In the later stages of the program, sufficient materials were produced to permit characterization of a broad range of properties. Some data on environmental resistance will be given. Fibers were incorporated into aerospace- grade epoxy resins for measurement of composite properties.

In summary, the results show that PBZT can be processed into fibers and films with improved mechanical properties and environmental resistance compared to aramids. A high degree of orientation of the rigid-rod molecules can be achieved which provides outstanding axial properties but this results in deficiencies in transverse properties and composite compression strength.
An Integrated Laboratory Process for Preparing Rigid Rod Fibers from the Monomers
Authors: Ledbetter Harvey D. , Rosenberg Steven , Hurtig Carl W.
Published: March 2011

The preparation of small, representative research samples of polymers for evaluation in the form of a fiber has been a continuing problem because of the several complex and interrelated steps in going from the monomer to the polymer to the fiber. Such complexity can be magnified in the preparation of rigid rod polymers likecis-PBO, i.e., poly[benzo(1,2-d:5,4-d')-bisoxazole-2,6-diyl-1,4-phenylene]. PBO is a member of the group of high performance polymers generically labeled the PBZ family. With these polymers the additional factors of unreliable mixing, high viscosity, varying morphology, poor solubility, extended polymerization times, etc., present formidable experimental problems. especially when only small quantities of monomers are available.

A new laboratory process has been developed to overcome the difficulties enumerated above so that a dehydrohalogenated monomer mixture in an appropriate solvent can be polymerized rapidly with molecular weight control. The polymer is degassed and otherwise conditioned for spinning, transferred to the spin pump with controlled morphological change, and subjected to dry-jet wet spinning to prepare a fiber representative of the polymer. The spinning operation incorporates features characteristic of both solution processing and thermoplastic extrusion.

Typical fibers of cis-PBO prepared by the process are described.
The Effect of Coagulant on the Structure and Properties of Poly(P-Phenylene Terephthalamide) [PPTA]
Authors: Rakas M.A. , Farris R.J.
Published: March 2011

Poly(p-phenylene terephthalamide) [PPTA] was the first commercially successful lyotropic liquid crystalline polymer to be spun into fibers having excetonally high tensile properties [1,2]. Fibers of PPTA are commonly referred to as Kevlar®, and are a product of the du Pont de Nemours Company, Inc. These fibers are stronger than steel, and have found many applications, including use in sporting goods such as canoes, tires, bullet-proof vests, cables and pressure vessels.
Mechanical Behavior of Rigid Rod Polymeric Fibers
Authors: Allen Steven R. , Farris Richard J.
Published: March 2011

Poly-(p-phenylene benzobisthiazole) fibers provide a model system for the evaluation of structure-property relationships in extended-chain polymeric fibers. Owing to the poorly developed lateral order in as-spun fibers, the enhancement of structural perfection and of mechanical properties may be examined through heat treatment processing more readily than with more crystalline fibers. High tensile modulus (to 300 GPa) and high tensile strength (3 GPa) have been obtained from heat treatment processing of the fibers. The development of tensile modulus and tensile strength depends directly on the enhancement of overall axial molecular orientation. Tensile strength is additionally dominated by the development of stronger lateral molecular interaction. The mechanical properties mimic the inherent chain anisotropy arising from strong primary bonding along the chain and much weaker secondary interactions between chains. Tensile to shear moduli ratios of 200:1, tensile to shear strength ratios of 50:1 and tensile to compressive strength ratios of 10:1 are observed.
Tensile and Compressive Properties of Poly(P-Phenylene Benzobisoxazole) Fiber
Authors: Fawaz S. A. , Palazotto A. N. , Wang C. S.
Published: March 2011

Axial tensile modulus, compressive modulus and compressive strength of poly(p-phenylene benzobisoxazole) fiber were measured with a Tecam Micro-tensile Testing Machine. This machine was configured to allow direct tension and compression testing of a single fiber at extremely small gauge length. The measured tensile and compressive moduli were analyzed for machine compliance corrections and possible gauge length error. Results were discussed for the effects of non-uniform stress distribution and fiber misalignment. By comparing the axial compressive strengths measured from various single fiber characterization techniques, direct compression furnished data closer to that measured from composite compressive tests.
Theoretical Predictions for Side-Chain Liquid-Crystal Polymers and Comparison to Experiment
Authors: Dowell F.
Published: March 2011

This paper presents results from a unique microscopic molecular theory for side-chain liquid-crystalline polymers (LCPs) in the nematic (N) and multiple smectic-A (SA) LC phases and the isotropic (I) liquid phase. There are no ad hoc or arbitrarily adjustable parameters in this theory. The agreement between the theoretical and experimental values for various properties (including transition temperatures and quadratic characteristic radii) is very good (relative deviations between 0% and less than 6.2%). The theoretical results also show--for the first time--that the N and I phases for these LCPs involve the packing of plate-like sections of backbones and side chains and that the local bilayer SA phase involves packing of side-chains within a plate-like section. This type of packing is predicted to be typical for side-chain LCPs. This theory can predict-- for the first time--whether the side chains of a molecule pack on the same or alternating opposite sides of the backbone and whether side chains on different molecules interdigitate (overlap) with each other.
An Exact Method to Determine the Chain Axis Orientation Distribution in High Performance Fibers from a Single Inter-Chain Reflection
Authors: Saraf Ravi F. , Watson T.J.
Published: March 2011

An exact pole inversion method is used to calculate the complete chain-axis orientation distribution from a single inter-chain reflection. A brief outline of the formulation and computation method is given. This method is demonstrated by comparing the measured chain-axis distribution from a (002) reflection of oriented polyethylene samples, to the calculated distribution from (110) and (200) reflections of the same sample. The error in the Hermans Orientation function is less than 0.5% for the two samples tested.
Structure–Property Relationship of Solution-Spun Ppbt/Peek and Ppbt/Nylon 6,6 Composite Fibers
Authors: Gabriel Carmen A. , Farris Richard J. , Malone Michael F.
Published: March 2011

Previous work investigated the processing/structure/property relationships for solution spun composite fibers of rodlike poly(p-phenylene benzobisthiazole) [PPBT] with nylon 6,6 [N66] and poly(ether ether ketone) [PEEK] [1]. Evidence that these composite fibers were effectively reinforced by a network-like structure of PPBT was given. In the present investigation, the morphology and properties of wet, as-spun, and heattreated PPBT/nylon 6,6 and PPBT/PEEK composite fibers are contrasted to gain insight into the structure/property relations which result from these post-spinning processes. It is concluded that heat-treatment is simply a means of perfecting the network structure, thereby enhancing the tensile properties of the composite fibers.
“In-Situ Network” Composite Fibers of Pbzt/Nylon
Authors: Hwang C. Robin , Malone Michael F. , Farris Richard J. , Martin David C. , Thomas Edwin L.
Published: March 2011

A novel method of preparing PBZT/nylon composite fibers by infiltrating nylon into pure PBZT fiber is described. The pure PBZT fiber formed a microfibrillar network structure during coagulation, which is effective in reinforcing the matrix in the “in-situ network” composite fibers (designated IC). These new composite fibers exhibit nearly indistinguishable mechanical properties as those of “molecular” composite fibers (MC) prepared from isotropic solutions before and after tension heat-treatment (E = 44 GPa, σ = 430 MPa, ε = 1.2 %, σc = 250 MPa, G = 1.75 GPa) for PBZT/nylon weight ratios equal to unity.

The fine structure of pure PBZT and its composite fibers spun from isotropic solutions was characterized using techniques based on nitrogen adsorption, small-angle X-ray scattering, scanning and transmission electron microscopies. The structure of both type of composites was found to be a microfibrillar network of PBZT in a matrix of amorphous nylon. The average diameters of the PBZT microfibrils were in the range of 10 to 20 nm for the IC and 4 nm for the MC.
Processing, Properties and Structure of Bulk Poly(P-Phenylene Benzobisthiazole)/Poly(Ether Ether Ketone) Molecular Composites
Authors: Wang C. S. , Bai S. J.
Published: March 2011

The wet-state-consolidation process was used to fabricate bulk rigid-rod/thermoplastic molecular composites of poly(p-phenylene benzobisthiazole) and poly(ether ether ketone). The composites were molded into bar-shaped specimens. The morphology of those specimens was studied throughout the entire process using X-ray scattering and scanning electron microscopy to correlate processing conditions and properties. The mechanical properties of the bulk composites were comparable to those of other rigid-rod/thermoplastic molecular composite systems.
Theoretical Predictions of Nonlinear Optical Properties of Molecules and Polymers
Authors: Goldfarb Ivan J. , Reale Hector , Wierschke Scott , Medrano Jorge A.
Published: March 2011

The prediction of nonlinear optical properties of molecules and polymers is an important goal toward which a considerable effort has been recently applied. It entails the calculation of the polarizability and first and second hyperpolarizability tensor, for the systems under study, using their quantum wavefunctions. In principle several approaches are possible. The wavefunctions themselves can be calculated at the ab initio or semi-empirical levels of approximation and then the calculations can proceed via the sum over states (SOS) or the finite field (FF) formalisms.

Since we intend to calculate large systems we decided on the semi-empirical MNDO/AMI approaches for the calculation of the wavefunction. We also used the FF approach and numerical methods for finding the necessar) derivatives. The comparison between calculated and available experimental results is very encouraging. We also calculated the tensors for considerably large molecules, providing the first theoretical prediction of these values. The effect of different substituents on a given structure and the result of doping, were also studied. The polarizabilities of some oligomers as functions of the number of repeat units were calculated to assess the convergence properties. Because of the required periodicity of the perturbations, calculations cannot be made for infinite polymers in the same fashion as for small molecules. This problem is currently being addressed.
Theoretical Studies of the Physical Properties of Rodlike and Related Polymers
Authors: Welsh W. J. , Mark J. E. , Yang Y. , Das G. P.
Published: March 2011

This review focuses on a new type of para-catenated aromatic polymer being used in the preparation of high-performance films and fibers of exceptional strength, thermal stability, and environmental resistance, including inertness to essentially all common solvents. Polymers of this type include the cis- and trans-poly(p-phenylene benzobisoxazole) (PBO), the cis- and trans-forms of the corresponding poly(pphenylene benzobisthiazole) (PBT), and the structurally similar poly(5,5ʹ-bibenzoxazole-2.2ʹ-diyl-l,3-phenylene) (AAPBO) and poly(2,5-benzoxazole) (ABPBO) and their sulfurcontaining analogues. Because of their rigidity, these polymers become highly oriented in solution and some display liquid crystalline behavior. The purpose of this paper is to summarize the authorsʹ theoretical work on the structures, conformational energies, intermolecular interactions, electronic properties, electrical conductivity, and electrooptical properties of these chains, including, in some cases, the so-called articulated forms and the protonated forms known to exist in strong acids. The emphasis is on how such studies provide a molecular understanding of the unusual properties and processing characteristics of this new class of materials.
Electric Properties of Ladder Type Polymers BBB and BBL
Authors: Belaish I. , Rettori C. , Davidov D. , Mclean M.R. , Dalton L. , Nalwa H.
Published: March 2011

We report on ESR and electric conductivities of BBB and BBL ladder polymers with emphasis on the former. Both the ESR and the electrical conductivities are strongly anisotropic suggesting that the polymer backbones are plannar. The ESR data implies the existence of two different types of spin species. The hyperfine spectrum of one of these species is analyzed in terms of a Spin Hamiltonian and anisotropic transferred hyperfine interaction with the 14N nuclei (I = 1). We found that “annealing” the BBB and BBL films to high temperatures, To, increase the spin susceptibility for To ≤ 850K (BBB). However annealing to To ≥ 900K results in a dramatic reduction in the spin susceptibility and dramatic incise in the conductivity. The room temperature in-plane conductivity of annealed samples at To ≥ 900K exceeds σ = 1 Ω−1 cm−1. This high intrinsic conductivity is probably associated with the formation of cross-linked condensed aromatic structure. The 'phase transition” temperature to this structure is higher by 50K for BBB compared to BBL. The conductivity versus temperature of annealed samples (700K ≤ To) can be described by the onisotropic version of Mott's law for variable range hopping. We demonstrate that the anisotropic conductivity is due to the anisotropic localization lengths (ξ∥ and ξ⊥) of the wave function of the localized states.
Structural Changes in Fast Ion Conducting Chloride Doped Potassium Borate Glasses
Authors: Fusco F.A. , Massot M. , Oueslati M. , Haro E. , Tuller H.L. , Balkanski M.
Published: March 2011

The effects of halide substitution on ionic conductivity in potassium borate glasses are different from those observed in their Li and Na analogs. Physical property and Raman spectroscopy results suggest that this behavior is associated with differences in the glass network structure induced by the presence of different interstitial alkali cations.
Raman Spectroscopy and Structural Disorder in Gd2(ZrxTi1−x)2O7
Authors: Oueslati M. , Balkanski M. , Moon P.K. , Tuller H.L.
Published: March 2011

Raman measurements on the Gd2(ZrxTi1−x)2O7, solid solution show increasing peak widths as the composition is varied from Gd2Ti2O7, to Gd2Zr2,O7. The increase in peak width is interpreted as reflecting an increase in structural disorder with increasing x in this pyrochlore structure material. Structural disorder occurs readily in such oxides by the formation of cation anti-site defects and anion frenkel defects. We have previously observed that this leads to a marked increase in oxygen ion conduction with increasing x. Preliminary results also indicate that certain peaks in the Raman spectra are characteristic of the end members of the solid solution and may occur at the same frequency independent of composition. The Raman results are discussed in relation to earlier x-ray diffraction and ionic conductivity data obtained in this group.
Studying Ionic Conductivity with Diffraction Techniques an Application to laF3
Authors: Belzner Andreas , Schulz Heinz
Published: March 2011

The LaF3-structure has been reinvestigated using diffraction data measured with twinned crystals.

LaF3 is fluoride ion conductor with essentially 3-dimensional conductivity. The conduction perpendicular to the c-axis is shown to occur on paths which include all three sets of fluorine positions in the structure and which connect symmetrically non-equivalent nearest neighbor positions only. This is confirmed by determination of anharmonic temperature factors. The temperature dependence of the harmonic thermal parameters indicates that thermal vibrations are described rather than static disorder. The magnitude of the temperature factors of fluorine is consistent with an intrinsic activation energy of 0.8 eV for fluorine conduction.
Structural Investigations on Scandium Substituted Nasicons. Order Disorder Effects
Authors: Clearfield A. , Hinson P.G. , Rudolf P.R. , Squattrito P.J.
Published: March 2011

Neutron diffraction data were used to refine the structures of three scandium substituted NASICONS: Na2 ZrSc(PO4)3, R3c Na2.5 Zr1.8 Sc0.2 Si1.7 O12 R3c and Na2.7. Zr1.0 Sc0.2Si1.5 P1.5O12, C2/c. The phosphate (compound 1) exhibited oxygen disorder. The second compound exhibited a similar type of oxygen disorder but also an interstitial Na+ position. The oxygen disorder in compound 2 apparently results from the position of the interstitial Nae whereas it is suggested that the Sc site in Na2 ZrSC(PO4)3 is slightly removed from that of the Zr position, requiring a shift of phosphate groups. In contrast the monoclinic phase does not exhibit oxygen disorder and all the sodium ions reside within the cavities.
Solid State NMR Studies of Ionically Conductive Non-Oxide Chalcogenide Glasses
Authors: Eckert Hellmut , Zhang Zhengming , Kennedy J. H.
Published: March 2011

The utility of 29Si, 31 p, and 6.7 Li MAS-NMR at 7.05 T to provide structural information in non-oxide chalcogenide glasses is discussed in connection with experimental results obtained on the systems Li2 S-SiS2, Li2 S-SiS2 -P2S5, and Li2 S-P2 S5-B2 S329Si MAS-NMR data indicate that the principles governing glass formation in these systems are fundamentally different from those applicable to stoichiometry-analog oxide glasses. 31p MAS-NMR can be used to identify microphase-separation in glasses containing two network former constituents. The use of the rare isotope 6 Li instead of 7 Li offers the advantage of significantly improved spectroscopic resolution, enabling the presentation of the first comprehensive lithium NMR chemical shift scale in the solid state.
Ion Association in Polymer Electrolytes; A Raman Study of Poly (Propylene Oxide) Based Complexes
Authors: Kakihana M. , Schantz S. , Torell L.M. , Borjesson L.
Published: March 2011

Raman spectra of a series of PPO-LiClO4 and PPO-NaCF3SO3 complexes have been obtained for different temperatures and salt concentrations to study the various ion associations of the dopant salt. It was found that ion-ion interactions dramatically influenced the internal symmetric stretching modes ν1 of the anions. Splitting of ν1 into a multicomponent band was observed. The intensity profile of the band was found to change rapidly with salt concentration and temperature. A three component band analysis led to the identification of dissociated ions, ion pairs and multiple ion aggregates, respectively. Increased ion association with increased temperature and/or salt concentration was observed for both LiCIO4- and NaCF3SO3- complexes. It is likely to initiate the phase separation and salt precipitation observed in many salt-polymer complexes at higher temperatures. Considerably stronger ion-ion interaction was observed in the NaCF3SO3-system than in the LiCIO4-complex, which may explain the lower conductivities reported for PPO-NaCF3SO3 electrolytes. The drastic conductivity drop observed in both systems at higher salt concentrations can however only partly be due to a decreased concentration of “free” ions, the major effect being attributed to decreased ion mobility.
Ion Transport Through Polyperfluorosulfonic Acid Membranes.
Authors: Nguyen T. , Guante J. , Vanderborgh N.
Published: March 2011

Water transport rates through Dow experimental polyperfluorosulfonic acid membranes were investigated by using dynamic thermogravimetry. A mathematical model was developed to describe water transport rates within the membrane. Values for the diffusion coefficient of water in membrane samples of the same equivalent weight but of three different thicknesses, 265, 4.0, and 7.0 mil, were obtained for temperatures of 60, 80, and 90° C. Results show that the diffusion coefficient of water increases with water content and temperature.
Electrical Properties of Poly(Vinyl Alcohol) Complexed with Phosphoric Acid
Authors: Gong Ke-Cheng , Shou-Cai Huang
Published: March 2011

The electrical properties of poly(vinyl alcohol) complexed with phosphoric acid have been studied. It is found that the conductivity increases with the concentration of the acid, and also increases with time if the sample is exposed to the air, which is interpreted in terms of glass transition temperature. A.C. impedance measurement and polarization experiment show that this proton-conducting polymer is a promising candidate for electrochromic display. It is also found that some plasticizers, such as glycerol and ethylene-glycol are effective for improving its conductivity.
Solid Electrolytes: Jump Relaxation and “Universal” Dynamic Response
Authors: Funke Klaus
Published: March 2011

In solid ionic conductors, the hopping motion of the mobile charged defects is strongly influenced by their mutual repulsive interaction. Therefore, their jump diffusion ist not a random process. Instead, correlated forward-backward hopping sequences are a common phenomenon, constituting the elementary steps of jump relaxation. The microscopic dynamics of the relaxation is described in a simple model which yields the frequency spectrum of the hopping motion. With the help of this function, it is possible to explain experimental spectra displaying the so-called “universal” dynamic response. In particular we reproduce the frequency dependent ionic conductivity of fast ion conductors and the arcs in their complex-conductivity and complex-permittivity planes. The model also explains the non-BPP-type behavior of spin-lattice relaxation times and the broad components of quasielastic neutron scattering spectra. Examples are presented and discussed.
Lithium Electrochemical Investigations of Crystalline Layered Compounds
Authors: Julien C. , Samaras I. , Saikh S.I. , Balkanski M.
Published: March 2011

Electrochemical investigations on lithium insertion in crystalline layered chalcogenide compounds are presented. Systematic and precise studies of the voltage-composition relation were made in single crystals of InSe, In2Se3, MoS2, TiS2 and NiPS3. The stability of the intercalated phases is discussed on bases of electrochemical potential spectroscopy measurements and inverse derivative composition voltage is analysed using the lattice gas model. The chemical diffusion coefficient D and the Darken factor Kt are deduced from the galvanostatic discharge curves of the lithium-solid solution electrode cells. All parameters have been measured as a function of lithium composition.
Plasmon-Phonon Coupling in Li Intercalated InSe
Authors: Burret P.A. , Julien C. , Jouanne M. , Balkanski M.
Published: March 2011

The layered semiconductor InSe which is a potential insertion cathode for thin film batteries can be intercalated with lithium which act as donor in the host. Chemical intercalation in n-butyllithium, leads to a drastic increase of the free carrier density in the host material, InSe single crystal.

The variation of the free carrier density with intercalation shifts the plasma frequency into the region of the LO-mode vibrations and allows the observation of the plasmon-LO-phonons coupling by light scattering experiments. By varying the sample temperature, it is possible to follow the two branches of the curve ω(q) corresponding to the modes L+ and L-.
Developments in Rechargeable Mno2Electrodes for Lithium Batteries
Authors: Thackeray Michael M
Published: March 2011

Considerable efforts are in progress to develop rechargeable batteries as alternative systems to the nickel-cadmium battery. In this regard, several advances have been made in ambient-temperature lithium battery technology, and specifically in the engineering of rechargeable lithium/manganese dioxide cells. This paper reviews the current state of the art in rechargeable Li/MnO2battery technology; particular attention is paid to the structural features of various MnO2electrode materials which influence their electrochemical and cycling behaviour in lithium cells.
Surface Modification of Solid Electrolytes for Advanced Chemical Sensors.
Authors: Weppner Werner
Published: March 2011

Solid State ion conductors are sucessfully employed in chemical sensors for gases such as oxygen for process control and environmental protection. The application requires elevated temperatures for sufficiently high ionic conductivity and is restricted to a few gases for which suitable solid electrolytes are available.
AC and DC Studies of Non-Exponential Relaxation Processes in Superionic Conductors: Correlation of Conductivity and NMR Studies
Authors: Angell C.A. , Martin S.W.
Published: March 2011

This paper considers the results of NMR relaxation studies of fast ion glasses in the light of variable frequency electrical conductivity measurements. We show that the low activation energy observed for relaxation processes studied at constant frequency below the temperature of the T1minimum is reproduced by the corresponding constant frequency conductivity measurements. Other characteristics of the constant frequency conductivity in this low activation energy regime, such as the unphysically low pre-exponent, match with the corresponding observations for NMR measurements. Since the activation energy observed at constant frequency in the frequency-dependent regime for conductivity depends on the characteristic departure from exponential relaxation for the conductivity process, we conclude that the NMR activation energy is likewise a simple consequence of the nonexponential character of ionic relaxation in the glass. In this case, the low activation energy attributed to processes probed by NMR relaxation is simply a misinterpretation since it is found, in the wide frequency range studies available to admittance bridge measurements, that all elements of the relaxation spectrum have essentially equal activation energies.
Determination Of Water Vapour Permeability In Concrete Under High Moisture Conditions
Authors: Hedenblad Göran
Published: March 2011

With a new method relying on measurements of water vapour flow from a specimen and on measurements of distribution of relative humidity in the specimen at steady state conditions, it is possible to calculate the moisture permeability and to determine its dependence on the relative humidity.
Influence Of Test Conditions On Water Permeability Of Concrete In aTriaxial Cell
Authors: Hooton R. Doug , Wakeley Lillian D.
Published: March 2011

The hydraulic conductivity of three concretes with a high ratio of water to cementitious solids (w/cs) was measured using a test device in which confining and driving pressures are controlled separately (triaxial, or Hassler cell). Test variables included: confining pressure (c), driving pressure (d), ratio of these two pressures (c/d), and sample length. The objective was to determine the effect of these variables on measured permeability (K).

For these concretes, the driving pressure has a strong influence on K values, which generally are significantly higher at lower driving pressures. The c/d ratio controls K to a lesser extent, and not in a consistent direction. K increases as c/d increases for specimen lengths of 3X the maximum aggregate size or longer. For specimens the length of which is closer to the aggregate size, K values decrease with increasing c/d, making specimen length an important variable. Removal of entrapped air from the system and presaturation of the specimens also are important.
Air Permeability Measurement
Authors: Perraton Daniel , Carles-Gibergues André , Aitcin Pierre-Claude , Thenoz Bernard
Published: March 2011

Air permeability was determined for concretes of variable porosity (w/c ratio of 0.33, 0.50, and 0.67). The reproducibility of the test and the ability to characterize the permeability of different concrete were evaluated. Results indicate that air permeability test gives suitable reproducibility with a margin of error of 10%, which tends to improve with increase in w/c ratio. The difference in air permeability of concretes with the w/c ratios investigated are distinguishable by this technique. Furthermore air permeability coefficients used were modified with equations derived in accordance to Darcy's law, and the resulting air permeabilities compared. Data calculated with an air permeability coefficient based on mean radius pore (corrected equation) appears to give a more realistic value with greater differentiation between the ranges. Values were determined on specimens after 28 days, maintained at room temperature (50% RH), then again after an additional 2 days at 60°C in a ventilated oven. Oven-dried specimens exhibit significantly greater air permeability.