bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of Cleavage Planes in an Al3Ti-Base Alloy by Electron Channeling in the SEM
Authors: George E. P. , Porter W. D. , Joy D. C.
Published: March 2011

Selected area electron channeling patterns were used to identify the cleavage planes in a polycrystalline Al3Ti-base alloy having the L12 structure. In order to do this unambiguously in the scanning electron microscope (SEM), one needs to know that the cleavage facet from which any given channeling pattern is obtained is indeed normal to the electron beam. We accomplished this by utilizing a recently-developed technique in which an optical microscope with a short depth of focus is inserted in the SEM column and used to measure the elevations of several points on the cleavage facets. By appropriately tilting and rotating the sample, and using the optical microscope to measure elevations, it was possible to orient the facets normal to the beam. The cleavage planes in a cast and extruded alloy having an equiaxed grain structure were compared with those in a directionally-solidified (DS) alloy of the same composition. Of the eight cleavage facets examined in the DS material, six were of the {110} type and two were of the {111} type. Of the six facets examined in the cast and extruded material, two each were of the {110} and {111} types, and one each were of the {100} and {013} types. Although it cannot be said that all possible cleavage planes have been identified in this alloy, the availability of several low-strength cleavage planes apparently exacerbates its brittleness.
Directions in High Temperature Intermetallics Research
Authors: Dimiduk Dennis M. , Miracle Daniel B.
Published: March 2011

Structural intermetallic materials have undergone an evolutionary process whereby some of the materials could provide major payoffs in gas turbine engines. This maturation of select intermetallic systems has provided significant hope for making still greater advances in turbine performance through further developments in other intermetallic materials. The same maturation process has highlighted specific limitations and requirements which are key to the utilization of intermetallic systems. This paper briefly reviews some critical ground rules for high temperature intermetallics development and identifies research directions being pursued by the Air Force for advancing intermetallic materials.
Structure Maps and Phase Stability in AlTi3 Alloyed with Rare-Earth Elements
Authors: Liu C. T. , Horton J. A. , Petitifor D. G.
Published: March 2011

Rare-earth elements including Y, Er and Sc were added to AlTi3 for stabilizing the Ll2 ordered crystal structure, as predicted by the AB3 structure map. The crystal structure and phase composition in the AlTi3 alloys were studied by electron microprobe analysis, X-ray diffraction and TEM. The solubility limit of the rare-earth elements were determined and correlated with the atomic size factor. The results obtained so far indicate that rare-earth additions are unable to change the crystal structure of AlTi3 from DO19 to Ll2. The inability to stabilize the Ll2 structure demonstrates the need to characterize the structure map domains with a further period-dependent parameter.
Investigation of B2 and Related Phases in the Ti-Al-Nb Ternary System
Authors: Bendersky Leonid A. , Boettinger William J.
Published: March 2011

Alloy compositions around Ti2 AINb were studied to establish phase equilibria and transformations during cooling from 1100°C and 1400°C. In addition to general results obtained on a wide range of compositions, which include evidence for a broad B2 phase field, transformation of BCC Ti4 Al3 Nb to a phase with an omega-type structure is reported. Detailed analysis indicates that this phase has the B82 structure after annealing at 700°C.
Recrystallization Behavior of Ni3 AI(B)
Authors: Gottstein G. , Kim W.
Published: March 2011

The recrystallization kinetics, structure development, stored energy of cold work, and rolling and recrystallization textures were studied on boron doped Ni76Al24. The recrystallization kinetics were very slow compared to pure metals or disordered solid solutions, but similar to other intermetallic compounds. The development of the deformed and recrystallized microstructure is similar to metals with intermediate stacking fault energy. Despite a lack of massive deformation twinning the rolling texture is a typical brass type texture. The recrystallization texture is not a brass type recrystallization texture, but consists of components, which are related by a 25°<100> rotation among each other and with the deformation texture. The observed phenomena are attributed to the constraints of grain boundary motion in long range ordered structures. It is further shown that Ni3Al does undergo dynamic recrystallization during high temperature deformation.
Grain Boundary and Cavity Surface Segregation in Crept Ni3Al + 0.2at% B AND Ni3 (AI,Hf) + 0.2at% B
Authors: Au-Yeung Patrick H. , Lukowski John T. , White Calvin L
Published: March 2011

Creep strengths and ductilities of boron-doped nickel aluminides are significantly improved by small additions of hafnium. Since creep failure in these alloys proceeds by growth and coalescence of grain boundary cavities, effects of Hf additions on the compositions of grain boundaries and creep cavity surfaces were examined using Auger electron spectroscopy (AES). In order to facilitate intergranular fracture in the AES analysis chamber, gage sections from creep specimens were hydrogen charged and copper plated.
Grain boundaries in crept specimens were not flat, and the grains did not exhibit a normal polyhedral appearance. The overall levels of boron detected on the fracture surfaces of the creep specimens were significantly higher than those from uncrept specimens. Additionally, boron was found to segregate more strongly to the grain boundaries while higher concentrations of residual sulfur and phosphorus were detected on the cavity surfaces in both alloys. These results are discussed in terms of the effects of impurity segregation on high temperature grain boundary cavitation.
The Effect of Boron on Microhardness in Ni3 Al Polycrystals
Authors: Qian X. R. , Chou Y. T.
Published: March 2011

In a recent MRS symposium, the effect of boron on grain boundary hardness (GBH) in Ni3Al was reported. Addition of 0.2 at.% of boron decreased the GBH in all three sets of alloys tested (24, 25, and 26 at.% Al). The present paper summarizes the study of the effect of boron on hardness within grains. Boron-induced softening was again observed in grain interiors. However, it occurred only in alloys with 24 and 25 at.% Al, but not in the alloy with 26 at.% Al. An explanation for this behavior is presented.
The effect of Anti-Phase Domain Size on the Ductility of a Rapidly Solidified Ni3Al-Cr Alloy
Authors: Carro G. , Bertero G. A. , WlTTIG J. E. , Flanagan W. F.
Published: March 2011

Tensile tests on splat-quenched Ni3Al-Cr alloys showed a sharp decrease in ductility with long-time annealing. The growth of the initially very-fine size anti-phase domains showed a tenuous correlation with ductility up to a critical size, where ductility was lost. The grain size was relatively unaffected by these annealing treatments, but the grain-boundary curvature decreased, implying less toughness. An important observation was that for the longest annealing time a chromium-rich precipitate formed, which our data indicate could be a boride. Miniaturized tensile tests were performed on samples which were all obtained from the same splat-quenched foil, and the various domain sizes were controlled by subsequent annealing treatments.
Titanium-Aluminide Alloys Between the Compositions Ti3 Al and TiAl
Authors: Mishurda J. C. , Lin J. C. , Chang Y. A. , Perepezko J. H.
Published: March 2011

Many questions still remain about the Ti-Al phase diagram, particularly for the compositions between the intermetallic compounds Ti3Al and TiAl. In an experimental study of the phase equilibria, titanium-aluminum alloys with 44, 46, 48, 50 at.% aluminum were produced by drop casting, HIP, and a double forging process method. Differential thermal analysis (DTA), optical metallography, and residual oxygen analysis were performed in order to characterize the low and high temperature phase equilibria of the alloys. The experimental results are compared with the calculated Ti-Al phase diagram which is being modeled concurrently. For the bcc, hcp and liquid phases, the Margules type of equations are used to represent the excess Gibbs energies. A maximum of six parameters are used for each of the phases. For the TiAl (Llo) and Ti3Al (D019 ) phases, the Wagner-Schottky type of equations are used to represent the Gibbs energies. All of the other phases are treated as line compounds. Values of the solution parameters were obtained by optimization using existing thermochemical and phase boundary data reported in the literature. The calculated results show that the high temperature hcp phase field is stable between approximately 34 at% Al, in equilibrium with β and α2 up to about 48 at% Al in equilibrium with γ and L and forms from the liquid by a peritectic reaction β+L-α. The experimental results obtained to date for the four alloys are consistent with the calculated equilibria which is being refined and also allows for an estimate of the metastable equilibria.
Improvement of Elevated Temperature Material Properties in Intermetallic Compound Ni3Al
Authors: Fujita Akitsugu , Matsumoto Tatsuki , Nakamura Makoto , Takeda Yorimasa
Published: March 2011

Intermetallic compound Ni3Al(γ′) is one of the major constituents in Ni-base superalloys. But it is not used by itself for structural use because of its low ductility and low strength.

In the present study, the improvement of elevated temperature mechanical properties of Ni3Al intermetallic compound is pursued by addition of such elements as Fe, Ti, Cr, V, Nb, Ta, Mo, W, Zr and Hf. These results show that Ni 3AI which contains some elements substituting for Al has better mechanical properties and creep rupture properties than commercial Inconel 713C.
Corrosion, Wear, and Galling Tests of IC218, a Chromium-Bearing Alloy of Ni3Al
Authors: Dulmaine Bradford A.
Published: March 2011

IC218 contains about 8.4% aluminum and about 7.8% chromium by weight and forms a tenacious alumina scale. In this work the ability of the scale to protect against aqueous corrosion and abrasive and adhesive wear was evaluated. Wrought IC218 was heat treated at 1150°C, yielding a microstructure of ordered FCC islands in a disordered FCC matrix. This material was more resistant to corrosion than common stainless steels in 96% or 98% sulfuric acid and in 5% hydrochloric acid. It was approximately equivalent to stainless steels in 10% sulfuric acid, 50% acetic acid, 50% sodium hydroxide, 5% sodium chloride, and in a sodium chloride + ferric sulfate + hydrochloric acid mixture used to test for pitting resistance. The IC218 performed poorly in 45% sulfuric acid, 20% or 65% nitric acid, 20% phosphoric acid, and in electrolytic 10% oxalic acid. It did not exhibit sensitivity to intergranular corrosion. It resisted stress corrosion cracking at a stress level equal to its yield strength, 645 MPa, in 45% magnesium chloride and in NACE TM0177, a test that simulates an oil well environment. IC218 wore more quickly than austenitic stainless steels do in a dry-sand-rubber-wheel test, but resisted galling as well as or better than most of them do.
Strength and Toughness of Composite Materials Based on Nickel Aluminide Matrices
Authors: Rigney J. D. , Khadkikar P. S. , Lewandowski J. J. , Vedula K.
Published: March 2011

Several nickel aluminide matrix composites were prepared using vacuum hot pressing techniques. The matrix compositions, based on Ni3Al, Ni3Al+B and NiAl, were reinforced with 10 volume % TiB2 particles. Both smooth and notched bend tests were conducted at room temperature on the monolithic as well as the reinforced materials in order to determine the effects of TiB2 reinforcement on both the smooth bend and notched bend properties. TiB2 additions were shown to improve the smooth bend strengths regardless of the matrix composition while notched bend tests, conducted to provide estimates of fracture toughness, revealed somewhat lower values for the composites in comparison to the monolithic materials. Fractographic analyses and in-situ fracture observations of the composites revealed that preferential fracture in regions of clustered TiB2 particles may significantly affect the measured toughnesses.
Improving the Low Temperature Ductility of NiAl
Authors: Guha Sumit , Munroe Paul R. , Baker Ian
Published: March 2011

As part of a study aimed at developing a ductile NiAl-based alloy, ingots of Ni-Fe-Al alloys were cast and hot extruded to rods. The purpose of the iron additions was two-fold viz; to produce a change in the slip vector from <001> to <111> and, in one alloy, to add a L12-structured ductile second phase. Extruded Ni-20A1–3OFe was two-phase, containing a pro-eutectic B2 phase in a fine lamellar structure (< 0.5 μm spacing) of B2+L12phases. Room temperature tensile testing of both single extruded and double extruded alloys resulted in 8% and 22% plastic elongation and yield stresses of 850 and 760 MPa respectively. Fracture in both cases occurred by ductile tearing of the eutectic and transgranular cleavage of the proeutectic phase at 1350 MPa. The ductility in double extruded condition is higher than that reported earlier in rapidly solidified wires by Inoue et al., J. Mat. Sci.,19, (1984), 3097. By comparison, extruded single-phase B2-structured Ni- 30AI-2OFe exhibited a fracture strength of 780 MPa, no plasticity and a mixture of intergranular fracture and transgranular cleavage. This is in contrast to earlier work by Inoue et al. (ibid) where a yield stress of 400 MPa, 5% plastic strain and a mixture of dimple and intergranular fracture was reported.
Strain-Induced Recrystallization of Tial
Authors: Feng C. R. , Michel D. J. , Crowe C. R.
Published: March 2011

Transmission electron microscope investigation of extruded and rolled XD™ titanium aluminide sheet has shown the development of recrystallized TiAl regions adjacent to grains which exhibit submicron scale TiAl twins. Detailed diffraction analysis confirmed that the TiAl twins were separated by a layer of Ti3Al. This is consistent with previous observations of the microstructure of extruded XD™ titanium aluminide. In the extruded material, however, the scale of the twins was larger, but the extent of the recrystallized region was smaller. The evidence suggests that the recrystallization of the TiAl regions may result from the impingement of twins from adjacent grains.
Plastic Deformation of Ti3Al and Ti3Al/TiA1 Polycrystals
Authors: Court S. A. , Löfvander J. P. A. , Stucke M. A. , Kurath P. , Fraser H. L.
Published: March 2011

Samples of polycrystalline Ti3Al-base alloys, and a two phase Ti3Al/TiAl mixture have been deformed at room temperature and at elevated temperatures and examined subsequently by transmission electron microscopy in order to determine the influence of temperature and alloy content on the relative activity of the various slip systems. In particular, the detailed influence of covalent bonding on dislocation mobility in Ti3Al has been identified.
Effects of Structure on Creep of Ti-53.4mol%Al Intermetallics
Authors: Takahashi Tohru , Oikawa Hiroshi
Published: March 2011

Constant stress compression creep behavior at elevated temperature was investigated on Ti-53.4mol%Al polycrystalline intermetallics of gamma single phase in different grain morphologies: coarse columnar grains, fine recrystallized grains and equiaxed grains. The shape of creep curves depended on the applied stress: normal primary transient followed by steady creep was found at higher stresses, but at lower stresses steep acceleration was observed after taking minimum creep rates. This behavior was common to all the grain morphology. The creep rate itself was not greatly different among the three types of structure, and the stress exponent of about 4 and the apparent activation energy of about 340kJ/mol at 0.3 true strain were common to all three types. The shape and size of grains do not affect the essential creep features of this material.
Effect of Hydrogen on the Behavior of Y-TiAl Atomized Powders
Authors: Shong D. S. , Kim Y-W. , Yolton C. F. , Froes F. H.
Published: March 2011

The effect of hydrogen on the phase stability of γ-TiAl and α2-Ti3Al phases was studied, with emphasis on the investigation of decomposition of a metastable α2 phase to a stable γ phase in gamma alloy powders. In this work, progressive decomposition of α2 → γ was observed to occur during aging with increasing temperatures or time under vacuum and under H2. The microstructural analysis indicated that hydrogen may facilitate such decomposition to occur at lower temperatures and shorter aging time.
Electronic Structure and Mechanical Properties of Intermetallics: Apb Energies in Ni-Al-Based Systems
Authors: Hong Tao , Freeman A. J.
Published: March 2011

The possible origin of the high degree of brittleness (i.e., low ductility) of the Ni-Al-based alloys in the B2 structures is investigated by means of all-electron self-consistent total energy LMTO calculations. Using a supercell approach, the energetics of the two simplest anti-phase boundaries (APB) for NiAl in the B2 structure - namely the ½<111> on {110} and ½<111> on {112} - are calculated for the first time assuming no relaxation at the interface. We find APB energies of order of 800 ergs/cm2 for both cases. Since the calculated APB energies are very high, <111> slip is hardly likely to occur - as suggested experimentally. By substituting Ni or Al with V, Cr or Mn at the APB interface plane, remarkably decreased APB energies are obtained. These first results on these simplified model systems may suggest a way to decrease the APB energy contribution to the ductility of NiAl-based alloys.
Stacking Fault Energies, Crystal Elasticity and Their Relation to the Mechanical Properties of L12-Ordered Alloys
Authors: Fu C. L. , Yoo M. H.
Published: March 2011

First-principles calculations of the stacking fault energies of Ni3Al, and the linear elastic constants of Ni3Al and Pt3Al are presented. The anomalous (positive) temperature dependence of flow stress in Ni3Al and its absence in Pt3Al are fully rationalized in terms of the present results and cross-slip pinning mechanism. It is found that the elastic shear anisotropy factor plays an equally (or even more) important role than the anisotropy of antiphase-phase boundary energy in determining the plastic flow behavior of L12-ordered alloys.
Conformational Rearrangement in the Nematic Phase of a Polymer Comprising Rigid and Flexible Sequences in Alternating Succession. II. Theoretical Results and Comparison with Experiments
Authors: Yoon D. Y. , Flory P. J.
Published: March 2011

ABSTRRACT

Theory predicts that the nematic state of a homopolymer comprising rigid and flexible sequences in alternating succession depends critically on the tendency of the flexible units to reconform to ordered extended conformations. When the relative statistical weight s* of such extended conformations is very small (very flexible), the chains undergo only a minor conformational rearrangement in the nematic state. Moreover, the clearing temperature and the orientational order of these nematic polymers are not much different from those of the monomeric liquid crystals. Hlowever, as the value of s* becomes larger than a certain critical value, an ordered (nematic) state exhibiting perfect orientational order and completely rodlike conformations becomes more stable than the state of only partial order. Hlence, an extensive conformational rearrangement is predicted to occur in nematic melts of the polymers when the flexible sequences are niot very flexible. These predictions are in good qualitative agreement with the conclusions from the thermodynamic and NMR measurements on two thermotropic polymers comprising identical rigid groups joined by flexible sequences of substantially different flexibility.
Synthesis of New Nitrogen Substituted Polybenzimidazoles
Authors: Kane James J. , Akmal Naim , Jariwala Chetan , Sinsky Mark
Published: March 2011

N1,N4-diphenyl-1,2,4,5-tetraaminobenzene was condensed with the di-acid chlorides of terephthalic acid, isophthalic acid and 2,5-pyridine-dicarboxylic acid in polar aprotic solvent to give the poly(o-phenylamino)amides which, after cyclodehydration in polyphosphoric, acid gave three new N,N'-diphenyl substituted polybenzimidazoles (PBI). The syntheses and certain of the solution and thermal properties of the PBI's are discussed. The synthesis of three new tetraamine monomers and their related model compounds is also described.
Properties of Solutions of Rodlike Chains from Dilute Solutions to the Nematic State
Authors: Berry Guy C.
Published: March 2011

Certain aspects of the physical chemistry of solutions rodlike polymers are reviewed. The range of concentrations includes infinite dilution ([ŋ]c<<l), dilute solutions ([ŋ,]c<l), moderately concentrated solutions (l<[ŋ]c<[ŋ]cNI), and concentrated solutions (c<cN,), where [ŋ] is the intrinsic viscosity and cNI. is the concentration required for a stable nematic phase. Studies of chain conformation are emphasized at infinite dilution, and rheological behavior is emphasized for more concentrated isotropic and nematic solutions. Both theoretical and experimental considerations are included.
Film Formation by Electrodeposition of Ionized Aramids
Authors: Takayanagi Motowo , Koga Keiko
Published: March 2011

Poly(p-phenylene terephthalamide) (PPTA) recognized as rigid-rod polymer is converted into polyanion by the reagent of sodium methylsulfinylcarbanion in dimethylsulfoxide (DMSO), which is dissolved in DMSO to form a dark red colored homogeneous solution. The electrolysis of PPTA polyanion in DMSO, which has also rigid-rod shape due to resonance effect, gives a PPTA gel swollen by DMSO on the anode. The gel is easily converted to a PPTA film. The structural change during the process was followed by the Xray diffraction. The PPTA film neutralized with acidic water and dried has the hydrogen-bonded sheet in crystal standing perpendicular to the film surface, whereas the same film annealed at temperatures above 300°C has the hydrogen-bonded sheet parallel to the film surface. The latter form is the stable structure. The orientational transition was energetically discussed by taking into the activation energy of the crystalline relaxation. A uniform and homogeneous film was prepared by using a coaxial rotating electrode cell. The modulus was 11 GPa and the strength was 150 MPa. The addition of polyacrylonitrile to the electrolytic solution as the frictionproviding polymer which was removed from the gel after electrolysis, provided the mechanical anisotropy, especially after annealing at 350°C: the modulus along the orientation direction was 14 GPa and the strength was 370 MPa.

The PPTA film unannealed or annealed below 200°C in an unstable orientational tate was used as a matrix of electropolymerization of electroconductive polymers such as polypyrrole, polyaniline and polythiophene, resulting in the electroconductive composite film of PPTA with improved mechanical properties. The PPTA/polyyyrrole with p-toluenesulfonate as a dopant had the conductivity of 50 Scm−1, the modulus of 6.2 GPa and the strength of 140 MPa. The conductivity was stabilized as high as 150°C. The SEM observation and the analysis of dynamic viscoelasticity proved the composite film being composed of two-phase structure.

A novel aramid, poly(p-phenylene[2,5-bis(4-carboxyphenyl)pyrazine]amide) (PPPA), was synthesized. PPPA is soluble in pure sulfuric acid to form liquid crystal. The X-ray diffraction pattern of the oriented PPPA film predicts that the conformation of the PPPA chain in crystal takes all-trans form, giving the good agreement of the fiber period with the calculated one. It is noticeable that PPPA is dissolved into DMSO with formation of polyanion by the reagent of sodium methylsulfinylcarbanion and the electrolysis of the solution is conducted, resulting in a PPPA film on the anode like PPTA. The aramid copolymer of PPTA forming a molecular coil was unable to be electrodeposited. Thus, it is believed that only the rigid-rod polyelectrolytes are capable of film formation by electrolysis.
X-ray Diffraction Studies of the Axial Tensile Modulus of Rigid-Rod Polymer Fibers
Authors: Lenhert P. Galen , Adams W. Wade
Published: March 2011

We report the design and use of a device to measure the axial tensile modulus of high modulus fibers by following the change in the meridional X-ray spacings as a function of applied tension. The device, which mounts on a Picker 4-circle automated diffractometer, applies tension to the fiber sample by a cantilever arrangement. Tension is measured by a strain gauge bridge on the cantilever arm. The tension is adjusted and read by the control computer, a VAX 11/730. Measurements made on PBZT and PBO fibers before and after heat treatment are reported. For PBZT fibers (as spun, and heat treated at 525° C and 650° C) with tensile moduli of 186, 283 and 290 GPa, the X-ray determined moduli are 348, 385 and 395 GPa. For PBO fibers (as spun and heat treated at 600° C and 665° C) with tensile moduli of 166, 318 and 290 GPa, the X-ray determined moduli are 387, 477 and 433 GPa. These modulus values are to be compared with theoretical values presented by Wierschke in the previous paper and sonic modulus values discussed by Jiang et al in the following paper.
Prediction and Design of First Super-Strong Mostly-Rigid Polymers from Very Molecular Theories for Smectic and Nematic Polymers
Authors: Dowell F.
Published: March 2011

This paper presents a unique microscopic molecular theory for backbone liquid-crystalline polymers (LCPs), side-chain LCPs, and combined 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 thermodynamic and molecular ordering properties for existing LCPs is very good (relative deviations between 0% and less than 6.2%). This theory has been used by this author to predict and design (atom by atom, bond by bond) the first super-strong (SS) LCPs. This paper presents the design of SS mostly-rigid (MR) LCPs.
Deformation Micromechanics in Rigid Rod Fibres and Composites
Authors: Young R.J. , Day R.J. , Zakikhani M.
Published: March 2011

The relationship between structure and mechanical properties in as-spun and heat-treated high modulus poly(p-phenylene benzobisoxazole) (PBO) fibres has been examined using a combination of electron microscopy mechanical testing, and Raman microscopy. The structure of the fibres has been determined by obtaining longitudinal sections and electron diffraction from skin and core regions. Well-defined intense Raman siectra werf obtained from individual fibres and three main bands at 1280cm−1, 1540cm−1 and 1615cm−1 have been indentified. It is shown that shifts in Raman bands during straining are a direct reflection of molecular deformation within the fibres.
Compressive Strength of high Performance Fibers
Authors: Kumar Satish , Helminiak T. E.
Published: March 2011

Significant research efforts have been carried out to improve the tensile modulus and tensile strength of high performance carbon and polymeric fibers. Experimental polymeric fibers (ordered polymer fibers) have been prepared with moduli >50 MPSI and tensile strength approaching one MPSI. However, the benefits of the above improvements in tensile properties for aerospace applications are limited because composites of these fibers have low axial compressive strength, which is a direct result of the poor axial fiber compressive strength. The poor axial fiber compressive strength has usually been attributed to the microfibrillar/fibrillar buckling. However, questions concerning the intrinsic limitations at the molecular level and the effects of intermolecular interactions are also considered important. Better understanding of these aspects will help in determining the theoretically achievable compressive strength and may aid in the development of higher compressive strength high performance fibers. These and other issues related to the compressive strength of high performance polymeric and carbon fibers are discussed in this paper.
The Prime Importance of Second-Order Effects in Rigid-Rod Polymers
Authors: Deteresa Steven J. , Farris Richard J.
Published: March 2011

The torsion modulus of high performance rigid-rod polymer fibers is shown to be dependent on axial tensile stress. This behavior is one of at least second-order elasticity. Fiber ultimate tensile strengths are of the same magnitude as torsion moduli, and increases in torsion moduli in excess of 200% were observed for fibers under tension. Consideration of the effect of an axial compressive stress on fiber torsion modulus leads to a prediction of an elastic shear instability that initiates at a compressive stress approximately equal in magnitude to the zero-stress torsion modulus. Hence, it is concluded that the compressive strengths of high performance polymer fibers are limited by the onset of an elastic microstructural instability.
Thermal Stability Of Rigid-rod Polymers
Authors: Denny Lisa R. , Goldfarb Ivan J. , Soloski Edward J.
Published: March 2011

One of the primary factors influencing the research and development of rigid-rod polymers in the Materials Laboratory has been the excellent environmental resistance of this class of aromatic heterocyclic benzobisazole polymers. Thermal stability of these materials has been determined utilizing thermal analytical, Isothermal Aging and combined Thermal Gravimetric-Mass Spectrometry (TG-MS) techniques. Correlations between the thermal stability and chemical structure, varying substituent groups and processing conditions for these polymers have been observed. An overview of the thermal stability of these rigid-rod polymer systems is presented.
Morphology of Rigid-Rod Polymer Fibers: an Overview
Authors: Martin David C. , Thomas Edwin L.
Published: March 2011

The current state of understanding of the morphology of the rigid-rod polymers PBZT and PBZO is reviewed. The morphology is sensitive to both the structure of the rigid polymer molecules and the nature of processing. Structural models of fiber morphology consistent with experiment are presented. An extensive bibliography is included.
Calculations of the Effects of Substituents on the Conformations of Pbzt and Pbo Model Compounds
Authors: Farmer B. L. , Wierschke Scott G. , Adams W. W.
Published: March 2011

Semiempirical energy calculations have been used to investigate the conformational properties of poly(p-phenylene benzobisthiazole) (PBZT) and poly(p-phenylene benzobisoxazole) (PBO) having various substituents on the phenyl ring. Substituents considered included methyl, ethyl, t-butyl, hydroxyl, phenyl, and benzthiazole groups. The torsional potential for rotation about the backbone bond joining the phenylene and heterocyclic rings has a significant influence on the conformational energies. X-ray structure data and results of semiempirical molecular orbital calculations were used to determine this critical parameter.

The results show that most substituents have surprisingly little influence on the conformations of the molecules. In most cases, the substituent causes a rotation of the backbone rings away from coplanarity, but once the steric interactions are relieved, there is considerable latitude for further rotation. The substituents most effective in locking the molecules into specific conformations were hydroxyl and t-butyl, due, respectively, to the prospect for hydrogen bonding, and non-planarity. In most cases, the conformational freedom is such that packing considerations could significantly influence the conformations of the materials in the solid state.
On the “Lamellar” Morphology of Poly(p-Phenylene Terephthalamide) and Poly(p-Phenylene Benzobisthiazole)
Authors: Roche Eric J.
Published: March 2011

Row-nucleated structures in PPTA and PBZT thin films are compared and their dependence upon quench rate and molecular weight illustrated. It is proposed that the lamellar appearance of the morphology is due to a coherent periodic twisting of fibrillar ribbons. The role of crystallosolvate phases is discussed.
A Rigid-Rod Molecular Composile Processed Directly from the Polymerization Medium
Authors: Haghighat R. Ross , Lusignea Richard L. , Vezie Debora L. , Adams W. Wade
Published: March 2011

The goal of this program was to form and demonstrate improved mechanical properties of biaxially oriented films of 30/70 rod-coil polymer blends of PBZT/ABPBT. These polymeric blends were prepared at three different solids contents CCCR.

Our approach examined PBZT and ABPBT in poly phosphoric acid (PPA) as the common solvent for the first time. Also, we set out to go one step beyond the current state of the art and produce biaxially oriented PBZT reinforced ABPBT molecular composites. Our investigation marked the first time such a study has been attempted. Additionally, fibers of C≳CCR were spun and characterized.
Overview-Rigid Rod Polymers for Nonlinear Optics and Electronics
Authors: Ulrich Donald R.
Published: March 2011

In 1979 the Air Force undertook a program to establish the principles for the design, synthesis, and processing of ultrastructured, electroactive polymers. The promising candidates were determined to be rigid rod polymers. In 1982 this approach was expanded to include the investigation of nonlinear optical properties in rigid rod polymers. The initial results in 1985, demonstrating the concept of multifunctionality, were quite startling. The polymers, PBT and PBO, which were designed as structural polymers with high strength, high modulus, and excellent thermaloxidative stability, were found to possess large nonresonant macroscopic third order optical susceptibilities. Their origin resides in the ultrafast, lossless excitations of highly-charged π- electron states. The state-of-the-art for nonlinear optical rigid rod polymers is reviewed.
Theoretical Studies of the Quadratic Polarizabilities of Rigid-Rod Monomers
Authors: Rondan Nelson G. , Lysenko Zenon , Hwang Wen-Fang
Published: March 2011

One of the requirements in the theoretical determination of optical nonlinearities is the structure of the molecule. Since most of the molecules that we are interested in examining have not been made, we deemed it necessary to determine their molecular geometries. The structures of 2,6-diphenylbenzo[1,2-d:4,5-d']bisoxazole, 2,6-diphenylbenzo[ 1,2-d:5,4-d']bisoxazole, and 2,2'-p-phenylenebisbenzoxazole, and their corresponding donor- and acceptor-substituted derivatives were determined computationally using the AM1 (Austin Model 1) molecular orbital program. The quadratic polarizabilities (β's) of these model compounds were then computed using the CNDO/S (Complete Neglect of Differential Overlap/ Spectroscopy) program and frontier molecular orbital theory. Results from these calculations will be expounded.
Anomalous Dielectric and Non-Linear Optical Response in Main and Side Chain Polymer Nematics and Smectics
Authors: Warner Mark
Published: March 2011

I propose that certain, stereo-regular, main and side chain polymer liquid crystals would have a giant, long-time dielectric susceptibility, χ, of unusual temperature dependence

ϰ ∼ const.. exp{+h/kBT}

with a large ultimate low temperature value χ - χo N where χo is a susceptibility characteristic of a simple dielectric fluid and N the degree of polymerisation. The response would be caused by polarising molecular defects in the nematic ordering; de Gennes hair pins for main chain and torsional defects in side chain polymers. h is the defect energy.

Experimentally χ(2) - χo(2) N is known in the non-linear optical response of PBLG, a limiting case of main chain polymers with no hair pins.

The timescale for the response of side chain mesogens is predicted to vary as τ ~ N2.
Non-Linear Optical Polymers for Active Optical Devices
Authors: Demartino R. , Feuer B. , Jacobson S. , Karim D. , Khanarian G. , Stamatoff J. , Teng C. , Yoon H.
Published: March 2011

Second order non-linear optical (NLO) polymers have been the focus of intense research effort in recent years [1]. This effort is justified by the potential value of these materials in a range of attractive optical signal processing applications with lower device costs and enhanced device performance.
Rigid-Rod Polymer Synthesis: Development of Mesophase Polymerization in Strong Acid Solutions
Authors: Wolfe James F.
Published: March 2011

The development of a method for polycondensation of rigid-rod poly(benzazoles) in poly(phosphoric acid) (PPA) in the lyotropic mesophase has led to an understanding of the synthesis variables that determine the important liquid crystalline product characteristics. These product variables, in turn, control processibility and final fiber or film properties. This paper provides a review of the effects of polymer concentration, solvent composition, polymerization temperature, and monomer purity on two liquid crystalline product characteristics: molecular weight achieved during polymerization, and concentrated solution properties, such as rheological and phase behavior. Central to the understanding of these effects are the factors affecting the polymerization rate. The methods for controlling these synthesis variables are also reviewed. Investigation of alternatives to PPA as the polymerization solvent resulted in a method to obtain high molecular weight poly(2,5-benzoxazole) by adding 40-45 wt % of P2O5 to methanesulfonic acid.
Mesophase-Enhanced Polymerization and Chemo-Rheology of Poly(p-Phenylenebenzobisthiazole)
Authors: Chow Andrea W. , Hamlin Richard D. , Sandell Janet F. , Wolfe James F.
Published: March 2011

The phenomenon of mesophase-enhanced polymerization of the rodlike polymer poly(pphenylenebenzobisthiazole) in polyphosphoric acid was investigated. When the polymer concentration was greater than 5 wt%, the reacting mixture became anisotropic at an early stage of the polymerization. The reaction rate increased significantly at the isotropic-nematic phase transition as the rods were aligned in positions more favorable for the condensation reaction to occur. At 4.5 wt% of polymer, the reacting mixture remained isotropic for up to 1500 min of reaction time. The chemo-rheological properties of the 15 wt% reaction mixture indicate the occurrence of the phase change in either the shear viscosity or the first normal stress difference measurements.
Ionic Properties of Oxide Gels
Authors: Livage J. , Barboux P. , Nabavi M. , Judeinstein P.
Published: March 2011

Oxide gels are actually hydrous oxides. Water adsorption and dissociation occur at the surface of the oxide network leading to charged particles surrounded by an acid or basic aqueous medium. They can be considered as particle hydrates. Fast proton conduction is observed arising from proton diffusion through the adsorbed water layers. Proton conductivity is actually strongly related to the water adsorption isotherm.

Ion exchange readily occurs at the oxide-solution interface when the gel is dipped inside an aqueous solution. Some inorganic gels exhibit a layered structure similar to that of sheet silicates. Ion exchange can then be described as an intercalation process. It can be used as a synthetic route toward new compounds.

Electrochemical insertion within the oxide network is highly reversible. This is due to the open structure of the gel and the mixed valence behavior of the transition metal oxide. Reversible cathodes or electrochromic layers have been made from V2 O5, W03or TiO2gels. Thin films or pressed pellets can be easily made from oxide gels. They are therefore good candidates for making "all gel" micro-ionic devices.
Relations Between Structure and Ionic Conductivity of Some Cristobalite-Related Compounds
Authors: Frostiäng Sten , Grîns Jêkabs , Nygren Mats
Published: March 2011

A comparative study of the isotypic Na2BeSiO4, Na1.8[Ga0.2Zn0.8]SiO4 and Na1.8[Ga0.2Zn0.8]Ge04 structures has revealed differences in conduction pathway geometries, and calculations show that the two Na-deficient compounds possess larger “bottlenecks”. A conduction mechanism, with Na ions using interstitial sites during migration is suggested.
In-Situ NMR Studies of Lithium Intercalated Electrode Materials Inside All-Solid-State Electrochemical Cells
Authors: Chabre Y.
Published: March 2011

Preliminary results of in-situ NMR studies on lithium intercalated electrode materials in all solid state electro-chemical cells are presented. We discuss the interest for such measurements which, as far as we know, have never been reported before. The design of the cells is briefly presented and our results are compared with previous studies on compounds chemically intercalated with the n-butyllithium technique.
Molecular Dynamics Simulation of Mass and Charge Transport in Superionic Conductors, and Structural Correlations in Chalcogenide Glasses
Authors: Vashishta P. , Rino José P. , Kalia Rajiv K.
Published: March 2011

Structural properties, single-particle dynamics, and the charge transport are studied in superionic conductor Ag2Se using the molecular dynamics (MD) technique. The calculations are based on a model of interionic potentials in which ions interact through Coulomb interaction, steric repulsion and charge-dipole interaction due to the large electronic polarizability of the selenium ions. Structural and dynamics correlations are studied at five temperatures in the superionic phase. Among the structural correlations the results are presented for partial pair correlation function, coordination numbers, bond angle distributions and wave-vector dependence of the Bragg intensities. Detailed comparison with neutron and x-ray single crystal diffraction experiments. The calculated temperature dependence of the self-diffusion constant of silver is in good agreement with the tracer diffusion measurements. The spectra of velocity autocorrelation functions and the frequency dependent ionic conductivity are calculated. The Haven's ratio is also in good agreement with experiments.

Effective interatomic potentials consisting of two-body (steric effect, charge transfer and charge-dipole interactions) and three-body covalent forces are proposed for GeSe2. Using these interaction potentials in MD simulations, the nature of short-range and medium-range order is investigated in glassy and molten GeSe2. All the features in the static structure factor, S(q), including the first sharp diffraction peak (FSDP), are in good agreement with experiments. The FSDP arises from Ge-Ge and Ge-Se correlations between 4-8Å, and the anomalous decrease in its height on cooling is due to frustration enhanced by the increased density.
Electrical Relaxation Studies in Fluorite Oxides
Authors: Sarkar Partho , Nicholson Patrick S.
Published: March 2011

Electric relaxation in CeO2-M203 (M34 sY3+, La3+) solid solutions has been investigated as a function of temperature (373K-673K) using the electric modulus formalism in the frequency range 5 to 107Hz. Two relaxation processes are observed in dilute solid solutions. The low frequency process is identified as a long range migration of free oxygen-vacancies (Process A) and the high frequency process is due to reorientation relaxation of the (MceVo) charged associates (Process B). The relaxation process is analysed using a non-exponential decay function, ø(t)=exp[-(t/τo)B] for O<β≤1, of the electric field. The observed activation enthalpy minimum as a function of dopant concentration for the Process A is explained using the concept of incomplete dissociation of oxygen-vacancies from (MceVo) defect associates and the formation of higher-order defect clusters at higher mole% M203.
Defect Structure and Ion Transport in PbFCI
Authors: Islam M. Saiful
Published: March 2011

Theoretical techniques are used to examine the energetics of defect formation and ion transport mechanisms in PbFCI. Schottky disorder is found to be the dominant intrinsic defect. The calculated formation energy is in good agreement with experiment. Activation energies for the migration of anion vacancies are presented.
Early History of Solid State Ionics
Authors: T. Takahashi
Published: March 2011

Though the term “Solid State lonics” was named originally by the present author early in the 1960s, solid ionic conductors which are involved in the field of Solid State lonics have been recognized since the mid-nineteenth century. However, room temperature high coniuctivity solid ionic conductors have been studied only after the 1960s. A field of Solid State lonics covers the stuaies of all phenomena of ions in solids, especially solids exhibiting high ionic and electronic-ionic mixed conductivities at fairly low temperatures below their melting points. The applications of these solids are also included in this fiela. Here, only the early history of high conductivity solid ionic conductors which have the longest history in the field of Solid State Ionics is described briefly.
Lithium Insertion Compounds
Authors: Goodenough J.B. , Manthiram A. , James A.C.W.P. , Strobel P.
Published: March 2011

The topotactic insertion/extraction of lithium in layered oxides and sulfides is compared with that in the oxo- and thiospinel frameworks [M2]X4 for both the technical interest of tailoring secondary-battery cathode materials and the scientific interest of exploring narrow-band phenomena and magnetic interactions in compounds and/or phases not accessible by conventional high-temperature techniques. It is pointed out that in layered LiyCoO 2 the higher voltages accessible in oxides is compatible with the higher Li+ -ion mobilities needed in power cells, but that fast three-dimensional Li+ -ion conduction in oxides requires a framework structure such as the monoclinic/orthorhombic Fe2(MO4)3 structure stabilized by M = Mo, W, and S. The influence of the counter cation on the working redox potential is illustrated by a 0.6 eV shift in the Fe3+/2+ redox couple on going from M = Mo or W to M = S.
Sodium and Lithium Intercalation Within The Layered Oxides Na(Li)xMo2O4
Authors: Tarascon J. M. , Colson S.
Published: March 2011

The structural, chemical and electrochemical behavior of the layered molybdate oxides Na(Li)xMo2O4 have been investigated. We found a reversible sodium intercalation process over the range of composition 0.5 < x < 1.9 for the NaxMo2O4 system with 5 single phase domains at x = 0.55, 0.9, 1-1.4, 1.6, and 1.9. We took advantage of the high mobility of sodium diffusion in this compound to exchange sodium for lithium at relatively low temperature (300°C) and to prepare crystallographically pure LixMo2O4. Electrochemical data for the Li system shows that this material, which reversibly intercalates up to 1.7 Li atoms at an average potential of 3.1 volts, is a new promising cathode material for secondary lithium batteries. The ease with which these new molybdate phases can be intercalated is not limited to the alkali metals, since we also were able to intercalate H2O molecules.
Lithium Intercalation in Perovskite and Hexagonal Tungsten Bronze Derivatives
Authors: Delmas C. , Nadiri A. , Flem G. Le , Chang S.H. , Chaminade J.P. , Menetrier M.
Published: March 2011

Lithium has been intercalated chemically and electrochemically in LnNb3O9 (Ln = La, Nd) perovskite-type phases and LiW3O9F which can be considered as a hexagonal tungsten bronze derivative.

The crystallographic formula of the LnNb3O9 starting material is □3/2 (Ln□1/2 )Nb3O9. In both systems, solid solutions are observed in the fir part of the intercalation reaction. While almost all perovskite cavities are filled in the neodymium phases, the higher ionic character of the La-O bonds prevents practically the Li intercalation in the □' sites.

In the LiW3O9F phase two lithium atoms can be electrochemically intercalated via a single phase mechanism. The reaction is completely reversible. For higher amounts of intercalation (x > 3), irreversible structural modifications occur.

In both systems the unit cell parameter variation is negligible during intercalation. This behavior results from the blocking up of the framework by Ln3+ ions in LnNb3O9 phases or by the stacking of the three octahedra triangular arrangement in the hexagonal tungsten bronze structure.