bluuebunny/crossref_metadata_2025_split huggingface dataset:
Low Temperature Synthesis of Lamellar Transition Metal Oxides Containing Surfactant Ions
Authors: Janauer Gerald G. , Chen Rongji , Dobley Arthur D. , Zavalij Peter Y. , Whittingham M. Stanley 
Published: April 2011

ABSTRACTRecently there has been much interest in reacting vanadium oxides hydrothermally with cationic surfactants to form novel layered compounds. A series of new transition metal oxides, however, has also been formed at or near room temperature in open containers. Synthesis, characterization, and proposed mechanisms of formation are the focus of this work. Low temperature reactions of vanadium pentoxide and ammonium (DTA) transition metal oxides with long chain amine surfactants, such as dodecyltrimethylammonium bromide yielded interesting new products many of which are layered phases. DTA4H2V10O28•8H2O, a layered highly crystalline phase, is the first such phase for which a single crystal X-ray structure has been determined. The unit cell for this material was found to be triclinic with space group P1and dimensions a=9.895(1)Å, b=11.596(1)Å, c=21.924(1)Å, α=95.153(2)°, β=93.778(1)°, and γ= 101.360(1)°. Additionally, we synthesized a dichromate phase and a manganese chloride layered phase, with interlayer spacings of 26.8Å, and 28.7Å respectively. The structure, composition, and synthesis of the vanadium compound are described, as well as the synthesis and preliminary characterization of the new chromium and manganese materials.
Computer Simulation of the Structure of Nanocrystals
Authors: Sasajima Y. , Okuda Shigeo 
Published: April 2011

ABSTRACTStructural characteristics of nanocrystals were investigated by molecular dynamics simulation. The structural models were constructed in two dimension, assuming the Lennard-Jones type potential as interaction between atoms. The nanocrystal model consisted of ultra-fine particles as a unit structure, like atoms in normal crystals. In the present study, the diameter of the ultra-fine particles is assumed to be constant and the unit particles are assembled in densely packed structure to form a nanocrystal. The orientations of the unit particles were varied randomly to form various kinds of interfaces between their nearest-neighbor particles. This initial structure was relaxed by the molecular dynamics method with controlling the system temperature by rescaling the velocities of the atoms. The system temperature was set to be so high as to accelerate the relaxation process in the nanocrystal structure. If the diameter of the fine particle is less than 6 (the unit length is nearest-neighbor distance between atoms), the assembled particles were relaxed to form single crystal structure. When the diameter increased larger than 10, the nanocrystal structure was stable and the grain boundaries, vacancies and edge dislocations were remained in the system.
Low Temperature Hydrothermal Synthesis of Nanophase BaTiO3 and BaFe12O19 Powders
Authors: Dogan Fatih , O'rourke Shawn , Qian Mao-Xu , Sarikaya Mehmet 
Published: April 2011

ABSTRACTNanocrystalline powders with an average particle size of 50 nm has been synthesized in two materials systems under hydrothermal conditions below 100°C. Processing variables, such as temperature, concentration and molar ratio of reactants and reaction time were optimized to obtain particles of reduced size and stoichiometric compositions. Hydrothermal reaction takes place between Ba(OH)2 solution and titanium/iron precursors in sealed polyethylene bottles in the BaTiO3 and BaFe12O19 systems, respectively. While crystalline BaTiO3 forms relatively fast within a few hours, formation of fully crystalline and stoichiometric BaFei20i9 require considerably longer reaction times up to several weeks and strongly dependent on the Ba:Fe ratio of the precursors. The structural and compositional evaluation of the nanophase powders were studied by XRD and TEM techniques.
Processing-Property-Microstructure Relationships in Tial-Based Alloys
Authors: Loretto M H , Hu D , Godfrey A 
Published: April 2011

ABSTRACTA range of TiAl-based alloys have been produced by plasma melting either small buttons (1kg samples) or ingots (up to 50kg). Some of the ingots have been atomised. The influence of thermomechanical processing on the microstructure of these materials has been assessed using optical and electron microscopy and the room temperature mechanical properties and creep strengths determined. It has been found that either through appropriate processing and/or through alloy development, it is possible to obtain alloys with room temperature strengths up to 1000MPa. Elongations of about 1% at room temperature have been obtained for alloys with this strength and this is coupled with significant improvements in creep strength over the reference alloy, Ti-48Al-2Mn-2Nb. The influence of the difficulty of slip transfer between gamma and alpha 2 has been assessed as one of the factors limiting ductility. Regions which are low in aluminium, which are present in the atomised powders initiate fracture at very low strains. These results are discussed in terms of the factors that control the strength and fracture behaviour of TiAl-based alloys.
Deformation of Polysynthetically Twinned (PST) TiAl Crystals at High Strain Rate and High Temperature
Authors: Jin Zhe , Gray George T. , Yamaguchi Masaharu 
Published: April 2011

ABSTRACTDeformation microstructures in a 45°<321> oriented (the lamellar interface was tilted 45° from the loading axis about the <321> direction in the lamellar interface) poly synthetically twinned (PST) TiAl crystal deformed in compression at 3000 s-1 and 800 °C was studied. Deformation of this PST crystal is characterized as follows: 1) Deformation of domains [III] and [IV] is dominated by 1/6 [112] parallel twinning (twinning parallel to lamellar interfaces). Ordinary dislocations observed in these domains are found to be a complementary deformation mode. 2) Deformation of domains [II], [V] and [VI] is controlled by a 1/2<110] ordinary dislocation slip. Complementary deformation modes in these domains are ordinary dislocation slip, superdislocation slip and cross-twinning. 3) Domain [I] is not deformed after the specimen deforms up to ∼7% strain.
The Charpy Impact Behavior of Fe3Al and Fe3Al-20 at % Mn Alloys
Authors: Liu J. N. , Yan W. , Ma J. L. , Wu K. H. 
Published: April 2011

ABSTRACTA series of experiments were conducted to investigate the impact fracture behavior of Fe3Al and Fe3Al-20 Mn alloys. The results of this study indicated that: (i) The addition of Mn introduces an ordered Ll2-type phase in the Fe3Al-based alloys. On the other hand, the addition of Mn decreases the order parameter of the DO3 a phase, (ii) The total- impact energy of an Fe3Al alloy increases with the temperature at the low-temperature range (<600°C), then drops around 700°C, and finally increases again as the temperature further elevates, (iii) The trend of the variation of the impact energy of Fe3Al-20 at % Mn alloy with temperature is the same as that of the Fe3Al alloy, (iv) And the addition of Mn significantly improves the impact energy of the Fe3Al-based alloy, and changes the variation of the crack-growth energy with the testing temperature when the temperature is above 700°C.
The Effect of Ti Addition on Oxidation Behavior of FeAl Intermetallic Alloy
Authors: Li Dingqiang , Lin Dongliang , Lin T. L. 
Published: April 2011

ABSTRACTThe influence of Ti addition on the high temperature oxidation behaviors of FeAl intermetallic alloys in air at 1000°C and 1100°C have been investigated. The oxidation kinetics of FeAl alloys were examined by the weight gain method and oxide products were examined by XRI), SEM, EDS and EPMA. The results showed that the oxidation kinetic curves of both Ti-doped and binary Fe-36.5A1 alloys were described as different parabolas followed the formula: (ΔW/S)2 =Kpt. The parabolic rate constant, Kp values are about 2.4 and 3.3 mg2cm-4h-1 for Fe-36.5A1 alloy and about 1.3 and 2.0 mg2cm-4V-1 for Fe-36.5Al-2Ti alloy when oxidizing at 1000°C and 1100°C respectively. The difference between Fe-36.5Al and Fe-36.5Al-2Ti alloy is not only in the surface morphology but also in the phase components. In the surface there is only α-Al2O3 oxide for the Fe-36.5Al alloy while there are α-Al2O3 and TiO oxide for the Fe-36.5Al-2Ti alloy. The effects of Ti addition on the oxidation resistance of FeAl alloy were discussed based on the micro structural evidence.
Assessment of the Compositional Influences on the Toughness of TiCr2-Base Laves Phase Alloys
Authors: Chen Katherine C. , Allen Samuel M. , Livingston James D. 
Published: April 2011

ABSTRACTSystematic studies of alloys based on TiCr2 have been performed in order to improve the toughness of Laves phase intermetallics. The extent to which alloy compositions and annealing treatments influence the toughness was quantified by Vickers indentation. The single-phase Laves behavior was first established by studying stoichiometric and nonstoichiometric TiCr2. Next, alloying effects were investigated with ternary Laves phases based on TiCr2. Different microstructures of two-phase alloys consisting of (Ti,Cr)-bcc+TiCr2 were also examined. Various toughening theories based on vacancies, site-substitutions, crystal structure (C14, C36, or C15) stabilization, and the presence of a second phase were evaluated. The most effective factors improving the toughness of TiCr2 were determined, and toughening mechanisms are suggested.
Ductility Improvement of Direct-Cast Gamma TiAl-Based Alloy Sheet
Authors: Hanamura Toshihiro , Hashimoto Keizo 
Published: April 2011

ABSTRACTFor improving the room temperature tensile ductility of direct-cast gamma TiAl sheets without affecting their high-temperature strength, direct sheet casting with T1B2 particle dispersion is employed and conducted. The T1B2 addition and rapid cooling results in the formation of a fine equiaxed grain microstructure with an average grain size of ∼10μm, contributing to the increase in the room temperature ductility to 2.1% with the high-temperature tensile strength kept at about 200MPa. This improvement of room-temperature ductility is attributable to the following fact. The high oxygen content of this material, about 2500wt. ppm, is not harmful to the tensile ductility when the oxygen is in the solid solution of the 0:2 lamellar phase or in oxide particles, which are fine enough not to cause brittleness to the matrix. From these findings, a principle is proposed that oxygen is not harmful to the ductility of gamma TiAl when its microstructure containing oxygen is fine enough.
Reactive Infiltration Processing of Bulk and Fiber-Reinforced NiAl
Authors: Venkatesh T. A. , Sanmarchi C. W. , Mortensen A. , Dunand D. C. 
Published: April 2011

ABSTRACTReactive infiltration processing was investigated in the NiAl system using nickel-powder and nickel-wire preforms. Inhomogeneous microstructures were often obtained with powder preforms which had high surface-to-volume ratio, low permeability and irregular infiltration paths. Homogenous NiAl could be obtained with nickel-wire preforms which had lower surface-to-volume ratio, higher permeability and regular infiltration paths. NiAl composites reinforced with short molybdenum fibers and long tungsten and sapphire fibers were also fabricated by reactive infiltration.
Key Microstructures Controlling the Mechanical Properties of Two-Phase TiAl Alloys with Lamellar Structures
Authors: Liu C. T. , Maziasz P. J. , Wright J. L. 
Published: April 2011

ABSTRACTThe objective of this study is to identify key microstructural parameters which control the mechanical properties of two-phase γ-TiAl alloys with lamellar structures. TiAl alloys with the base composition of Ti-47Al-2Cr-2Nb (at. %) were prepared by arc melting and drop casting, followed by hot extrusion at temperatures above the oc-transus temperature, Tα. The hot extruded materials were then heat treated at various temperatures above and below Tα in order to control microstructural features in these lamellar structures. The mechanical properties of these alloys were determined by tensile testing at temperatures to 1000° C. The tensile elongation at room temperature is strongly dependent on grain size, showing an increase in ductility with decreasing grain size. The strength at room and elevated temperatures is sensitive to interlamellar spacing, showing an increase in strength with decreasing lamellar spacing. Hall-Petch relationships hold well for the yield strength at room and elevated temperatures and for the tensile elongation at room temperature. Tensile elongations of about 5% and yield strengths around 900 MPa are achieved by controlling both colony size and interlamellar spacing. The mechanical properties of the TiAl alloys with controlled lamellar structures produced directly by hot extrusion are much superior to those produced by conventional thermomechanical treatments.
Simulations of Polymer Blends and Interfaces
Authors: Laasse Martin-D. , Grest Gary S. 
Published: April 2011

AbstractAn efficient continuum-space model for simulating polymer blends and copolymers is presented. In this model, the interactions are short-range and purely repulsive, thus allowing for excellent computational performances. The driving force for phase separation is a difference in the repulsive interaction strength between like and unlike mers. To demonstrate the effectiveness of the model, we study the phase behavior of a symmetric binary blend of polymers as well as the interface between the two immiscible phases. As predicted by theory, we find the critical interaction parameter to scaie with the inverse of the chain length of the polymers. The structure of the interface between two immiscible phases is investigated as a function of chain length and immiscibility. Capillary waves are observed and their measurementallows us to determine the surface tension accurately. Finally, the surface tension is related to the interface width.
Structure Pinning During Phase-Separation of Polyamide/Ionomer Blends
Authors: Weiss R. A. , Feng Y. , Tucker R. , Xie R. , Han C. C. , Karim A. 
Published: April 2011

ABSTRACTBlends of lightly sulfonated polystyrene and poly(N,N'-dimethylethylene sebacamide) (Li-SPS/mPA) are miscible as a result of strong ion-amide complexation. The blends exhibit LCST phase behavior and an increase of the sulfonation level from 4 to 9.5 mol% raises the critical temperature by 150°C. Phase separation may be thermally induced and isthermodynamically reversible. The phase separation kinetics that occur following a temperature-jump deep into the spinodal region of the phase diagram deviate from conventional Cahn-Hilliard theory and the phase separation process stalls after a couple of hours, essentially pinning the structure at that point. The extent of phase-separation that occurs before pinning is temperature-dependent.
Crucible Steel in South India-Preliminary Investigations on Crucibles from Some Newly Identified Sites
Authors: Srinivasan Sharada 
Published: April 2011

ABSTRACTEuropean accounts from the 17th century onwards have referred to the repute and manufacture of “wootz’, a traditional crucible steel made especially in parts of southern India in the former provinces of Golconda, Mysore and Salem. Pliny's Natural History mentions the import of iron and steel from the Seres which have been thought to refer to the ancient southern Indian kingdom of the Cheras. As yet the scale of excavations and surface surveys is too limited to link the literary accounts to archaeometallurgical evidence, although pioneering exploratory investigations have been made by scholars, especially on the pre-industrial production sites of Konasamudram and Gatihosahalli discussed in 18th-19th century European accounts. In 1991–2 during preliminary surveys of ancient base metal mining sites, Srinivasan came across unreported dumps with crucible fragments at Mel-Siruvalur in Tamil Nadu, and Tintini and Machnur in Karnataka and she collected surface specimens from these sites as well as from the known site of Gatihosahalli. She was also given crucible fragments by the Tamil University, Tanjavur, from an excavated megalithic site at Kodumanal, dated to ca 2nd c. Bc, mentioned in Tamil Sangam literature (ca 3rd c. BC-3rd c. AD), and very near Karur, the ancient capital of the Sangam Cheras. Analyses of crucible fragments from the surface collection at Mel-Siruvalur showed several iron prills with a uniform pearlitic structure of high-carbon hypereutectoid steel (∼1–1.5% C) suggesting that the end product was uniformly a high-carbon steel of a structure consistent with those of high-carbon steels used successfully to experimentally replicate the watered steel patterns on ‘Damascus’ swords. Investigations indicate that the process was of carburisation of molten low carbon iron (m.p. 1400° C) in crucibles packed with carbonaceous matter. The fabric of crucibles from all the above mentioned sites appears similar. Preliminary investigations on these crucibles are thus reported to establish their relationship to crucible production of carbon steel and to thereby extend the known horizons of this technology further.
Analyses of Archaeological Ceramics From Classic Period Teotihuacan, Mexico, A.D. 150–750
Authors: Kolb Charles C. 
Published: April 2011

ABSTRACTFrom ca. A.D. 150–750 Classic period civilization in Central Mexico was dominated by the city-state of Teotihuacan, a metropolis of at least 125,000 inhabitants located in a northeastern valley of the Basin of Mexico. This polity exercised economic and religious control over a wide area, regulated obsidian tool resources and production, and locally fabricated and also imported a variety of ceramic artifacts. In this report I shall summarize the status of current and ongoing investigations of Classic Teotihuacan period archaeological ceramics by surveying briefly the regional geology, reviewing previous research employing petrography and INAA, and examining the salient results of the analyses to date on two foreign and seven domestic ceramic wares. Lastly, I consider important research problems and suggest cautions for future investigations of ceramics and clay sources.
Crushed Brick / Lime Mortars of Justinian's Hagia Sophia
Authors: Moropoulou A. , Cakmak A. , Biscontin G. 
Published: April 2011

ABSTRACTStructural studies to determine the earthquake worthiness of Hagia Sophia in Istanbul have proved that the monument's static and dynamic behavior depends very strongly on the mechanical and chemical properties of these mortars and bricks used in its masonry. So, the cementrtious nature of the mortars not only explains the fact that the monument still stands but also the very large static deformations which it has undergone, since such mortars have a very long curig period from one to two years. According to the analysis of the dynamic data, the strong motion data from a 4.8R magnitude earthquake about 120 Km south of the building was used to determine the first three natural frequencies of the building. These results show a decrease of about 5–10% in the natural frequencies, as the amplitude of the accelerations increases and returns to their initial values, due to the non-linear nature of the masonry. The above mentioned behavior allows the structure to absorb energy without effecting its material properties, irreversibly. The properties of the mortars and bricks leaded to an extensive study, employing several experimental techniques (FOM, OM, XRD, SEM, TEM, TG/DTA). The results indicated mortars with considerable mechanical strength along with longevity. The model used proved to be resistant to the environmental pollution and to the presence of sah, while the gel phase as binder allows for greater energy absorption and the compatibility of the mortar to the original ones allows continuous stresses and strains. Hence, the recreation of the Hagia Sophia is attempted through a reverse engineering approach to simulate the historical mortars.
Modeling Damage to Limestone Exposed to Atmospheric Pollutants
Authors: Leith S.D. , Reddy M.M. , Ramirez W.F. 
Published: April 2011

ABSTRACTPreservation of building and monument stone exposed to acidic environments relies on the understanding of acidic precipitation deposition processes and damage mechanisms. Presented here is a model which predicts sulfur accumulation in porous limestone subjected to dry deposition of SO2. The model assumes deposition and reaction of SO2 to form a thin gypsum crust on the moist surface of the stone, and subsequent sulfur (as aqueous sulfate) transport and accumulation in the stone interior driven by diurnal wetting and drying of the stone surface. Characterization of the limestone pore structure contributes significantly to the evaluation and interpretation of modeled sulfate transport and accumulation in porous building materials. Predicted sulfur accumulation in the stone interior is dependent on the surface boundary conditions, the stone pore geometry and structure, and the rates and mechanisms of aqueous/solid sulfur partitioning (i.e. adsorption, precipitation and dissolution). Model results are compared to moisture content and sulfur accumulation measured in limestone briquettes exposed to a natural dry deposition environment. The model successfully predicts moisture transport in field-exposed limestone, but overestimates the rate of sulfur accumulation. The model may be improved by quantification of the time dependence of the surface sulfate concentration and better understanding of the sulfate partitioning mechanisms.
The Presence and Role of Paramagnetic Impurities in the Degradation of Paper
Authors: Attanasio Donato , Capitani Donatella , Emanuele Maria C. 
Published: April 2011

ABSTRACTElectron Spin Resonance spectroscopy has been used to carry out a systematic investigation of the paramagnetic impurities present in antique and modern paper. Up to eleven different paramagnetic centres, which include different transition ions (Fe3+, Mn2+, Cu2+), organic free radicals, and paramagnetic point defects have been detected, in concentrations ranging from few ppm to several hundreds. Experiments performed on new and deteriorated samples strongly indicate that some of these impurities participate directly or are produced during the aging and degradation processes. They can be used as quality indicators or probes for quantitative monitoring of the degradation of paper.
The Scattering Distribution from Semiconductors as a Function of Angle and Energy Loss in the Electron Microscope
Authors: Boothroyd C. B. , Dunin-Borkowski R. E. , Walther T. 
Published: April 2011

ABSTRACTWe examine the scattering distribution from thin C, Ge and thick Si specimens as a function of scattering angle and energy loss, in order to gain insight into the relative contributions to both low and high angle annular dark field images from elastically and inelastically scattered elections.
Grain Boundary Dislocation Structure and Motion in an Aluminum Σ=3 [011] Bicrystal
Authors: Medlin D. L. , Foiles S. M. , Carter C. B. 
Published: April 2011

ABSTRACTHigh-resolution transmission electron microscopy (HRTEM) observations are presented of a/3[111] grain-boundary dislocations in an aluminum Σ=3[011] bicrystal. These dislocations are present on both (111) (coherent twin) and (211) (incoherent twin) facets of the bicrystal boundary. The dislocations on the coherent twin facet migrate by a climb process that increases the thickness of the twinned material. These dislocations originate on a Σ=3 (211) incoherent twin boundary where they are closely spaced and dissociated in a wide core configuration. Atomistic calculations of the defect structure and interaction of multiple a/3[111] grain boundary dislocations are discussed.