bluuebunny/crossref_metadata_2025 huggingface dataset:
Tantalum Nitride Seed Layers for Bcc Tantalum Coatings Deposited on Steel by Magnetron Sputtering
Authors: Patel Anamika , Gladczuk Leszek , Paur Charanjeet Singh , Sosnowski Marek
Published: April 2011

Tantalum, a tough refractory metal with excellent corrosion resistance, is an attractive protective coating material for steel subjected to mechanical wear in harsh chemical environments. The coatings deposited by sputtering usually contain a hard and brittle tetragonal phase mixed with the desirable tough and ductile bcc phase of Ta. One of the methods of promoting the growth of the bcc phase at a moderate substrate temperature is deposition of an interfacial or seed layer of tantalum nitride. Ta coatings were deposited by dc magnetron sputtering in argon, and the interfacial nitride layers by reactive sputtering performed in the same chamber with nitrogen gas added to argon. The critical thickness, stoichiometry, and structure of the seed layer required for bcc Ta growth were studied by scanning electron microscopy and X-ray diffraction. The results of adhesion testing of the Ta coatings deposited on the interfacial layers are also reported.
Laser-Assisted Surface Modification of 4340 Steel with Iron-Aluminum Alloys
Authors: Muralidharan G. , Engleman P. G. , Blue C. A. , Sikka V. K. , Singh A. K. , Khangar A. , Dahotre N. B.
Published: April 2011

High power Nd-YAG laser was used to fuse coatings containing a mixture of FeAl and Al, with 4340 steel. It was observed that good quality coatings could be obtained using this process. Detailed microstructural studies show that Fe aluminides and/or a solid solution of Al in Fe can form within the coating, depending on the processing conditions. Wear measurements show that the best wear properties are obtained in the presence of an aluminide in the coating and that the wear properties significantly degrade when the coating consists primarily of a solid solution of Al in Fe.
Growth of TiN/AlN Superlattice by Pulsed Laser Deposition
Authors: Wang H. , Gupta A. , Tiwari Ashutosh , Zhang X. , Narayan J.
Published: April 2011

TiN-AlN binary-components have attracted a lot of interests in coatings of high speed cutting tools, due to their higher oxidation resistance, higher hardness, lower internal stresses and better adhesion. Especially, nanometer-scale multilayer structures of AlN/TiN show superior structural and mechanical properties due to their tremendous interface area and become one of the promising candidates for superhard coatings. Here we present a novel method to grow highly aligned TiN/AlN superlattice by pulsed laser deposition. In this method TiN and AlN targets are arranged in a special configuration that they can be ablated in sequence, giving alternate layer by layer growth of TiN(1nm)/AlN(4nm). X-ray diffraction and transmission electron microscopy (TEM) analysis showed the structure to be cubic for both TiN and AlN in the nanoscale multilayers. Microstructure and uniformity for the superlattice structure were studied by TEM and Scanning transmission electron microscopy with Z-contrast (STEM). Nanoindentation results indicated a higher hardness for this new structure than pure AlN and rule-of-mixtures value. Four point probe electrical resistivity measurements showed overall insulating behavior.
Hardening Mechanisms of Amorphous / Polycrystalline Nanostructured Multilayer Films: Si3N4/CrN and Si3N4/TiN
Authors: Xu Junhua , Yu Lihua , Azuma Yasushi , Hattori Koichiro , Fujimoto Toshiyuki , Kojima Isao
Published: April 2011

The amorphous/polycrystalline Si3N4/CrN and Si3N4/TiN nano-structured multilayer films have been fabricated by RF reactive magnetron sputtering. The microstructure and properties of these films were measured by XRD, HRTEM and nano-indenter There is no superhardness effect in the Si3N4/CrN multilayers. The hardness values of Si3N4/CrN multilayers are between those of the constituent CrN and Si3N4 films at a substrate temperature of 20∼C, and are a little higher than those of Si3N4 films at a deposition temperature of 500°C. However, the superhardness effect was found in Si3N4/ TiN multilayers. The hardness of Si3N4/ TiN multilayers is affected not only by modulation periods, but also by layer thickness ratio and deposition temperature. The maximum hardness value is about 40% higher than the value calculated from the rule of mixtures at a deposition temperature of 500°C and a layer thickness ratio (lSi3N4/ lTiN) of 3 / 1. Based on experimental results, the hardening mechanisms in these multilayers have been discussed.
Formation and stability of enhanced superhard nanostructured AlN/VN and AlN/TiN superlattice materials
Authors: Stampfl C. , Freeman A. J.
Published: April 2011

Using density functional theory and the full-potential linearized augmented plane wave (FLAPW) method, we investigate the formation and stability, and atomic structure, of rocksalt AlN/TiN and AlN/VN systems, including properties of the clean surfaces of the constituent materials. Calculations of the adlayer formation energy highlights the effect and interplay of the various energetic contributions on the growth of these strained systems, where the so-called “surface-interface” interaction energy is found to be important for the initial stages of AlN epitaxy. A significant strain energy builds up for increasing number of layers, where it is greater in the AlN/TiN system, which limits the thickness of rocksalt AlN regions that can grow before a structural transition to the lower energy wurtzite phase takes place. From our calculations, together with the known experimental critical thicknesses, we can obtain an accurate estimate of the wurtzite/substrate interface energy. That these values are high explains why the metastable rocksalt phase, which has significantly lower interface energies, is stabilized.
Elastic recovery and reloading of hardness impressions with a conical indenter
Authors: Fischer-Cripps A. C.
Published: April 2011

The present work is concerned with the analysis of elastic unloading data in conventional methods of analysis of nanoindentation test data. Experimental and finite element results are used to show that the reloading of a residual impression with and without the presence of residual stress is an elastic event, and further shows that the estimation of modulus and hardness computed using established techniques is in error due to the assumption the sides of the residual impression are straight. This work calls into question the validity of commonly used methods of test and analysis of instrumented indentation test data that use the elastic unloading data as the basis for the calculation of modulus and hardness of the specimen material.
Planar Extrinsic Biasing Of Thin Film Shape-Memory MEMS Actuators.
Authors: Grummon D. S. , Gotthardt R. , LaGrange T.
Published: April 2011

Although slow and dissipative, sputtered thin-film shape-memory alloys like equiatomic titanium-nickel can exert a large ohmically-excited force displacement product when deployed in photolithographically micromachined actuators. They give energy densities far exceeding those typically produced by competing microactuator materials [1], and their size can probably be scaled down to the nanometer range (where the benefits of high surface to volume ratio are best exploited for speed and efficiency). But a large, energetic, and resettable actuation stroke is possible only if some agency has imparted a non-trivial initial plastic strain, of between one and five percent, to the martensite phase. Is not always obvious how this strain is to be achieved when discrete mechanical manipulation of the active element is difficult. Furthermore, for cyclic actuation, a resetting-force that periodically re-deforms the martensite during the cooling interval must arise naturally from mechanical elements in the design. Here, several methods responding these requirements are discussed in relation to various kinematic themes.
Assessment of aluminium metallisation by nanoindentation
Authors: Soare S. M. , Bull S. J. , Horsfall A. , Dos Santos J. , O'Neill A. G. , Wright N. G.
Published: April 2011

As the trend for miniaturisation in the microelectronics field continues, metallisation connecting components has smaller and smaller dimensions, especially width and thickness. The mechanical properties of the deposited metal are very different from those of the bulk material and it is important to evaluate them accurately if the reliability of the metallisation is to be optimised. The assessment of the mechanical properties of thin aluminium metallisation is possible by nanoindentation but to extract properties useful for lifetime prediction such as yield stress or creep relaxation behaviour additional modelling is necessary using finite elements analysis (FEA). In this study evaporated aluminium layers from 50nm to 600nm thick on (100) silicon were indented to various depths. Proportional loading was used to minimise the effect of creep. The loading curves were then simulated by FEA and the results compared to identify the yield properties of the coating. Modelling data for thicker samples closely follows experimental data but for thinner coatings there is a considerable gradient in properties through the film thickness.
Deformation Microstructure Under Nanoindentations in Cu Using 3D X-Ray Structural Microscopy
Authors: Yang Wenge , Larson B. C. , Pharr G. M. , Ice G. E. , Swadener J. G. , Budai J. D. , Tischler J. Z. , Liu Wenjun
Published: April 2011

We have used a recently developed x-ray structural microscopy technique to make nondestructive, submicron-resolution measurements of the deformation microstructure below a 100mN maximum load Berkovich nanoindent in single crystal Cu. Direct observations of plastic deformation under the indent were obtained using a ∼0.5 μm polychromatic microbeam and diffracted beam depth profiling to make micron-resolution spatially-resolved x-ray Laue diffraction measurements. The local lattice rotations underneath the nanoindent were found to be heterogeneous in nature as revealed by geometrically necessary dislocation (GND) densities determined for positions along lines beneath a flat indent face and under the sharp Berkovich indent blade edges. Measurements of the local rotation-axes and misorientation-angles along these lines are discussed in terms of crystallographic slip systems.
Effect of Crystal Orientation on Microwear of Si Single Crystal and The Wear Structure
Authors: Takagi M. , Arima N. , Iwata H. , Imura T. , Sasaki K. , Saka H.
Published: April 2011

Microtribology of Silicon single crystals is one of the important factors for the practical use of MEMS. In this study, the effect of crystal orientation on microwear of Silicon single crystal and the wear structure were mainly investigated. Microfriction experiments using atomic force / friction force microscope (AFM / FFM) were carried out to investigate the effect of crystal orientation on the microwear depth of Silicon single crystals. In these experiments, the scanning-scratching directions of a tip of AFM / FFM were <100> and <110> on Si(100) surface and <112> on Si(111) surface. As a result, it was found that the depth of the wear marks generated on Silicon surfaces increased in the following order: <112>, <100>, <100>. Cross-sectional TEM observations of the microwear marks were carried out. As a result, it was found that the small dislocation loops were generated in the surface region at the first stage of the microwear, and the size and the number of dislocations increased with the progress of the microwear.
Investigation of Surface Grooves from Migrating Grain Boundaries
Authors: Munoz Nicole E. , Gilliss Shelley R. , Ravishankar N. , Barry Carter C.
Published: April 2011

Visible-light microscopy (VLM) and atomic-force microscopy (AFM) were used to study the progression of grain-boundary grooving and migration in high-purity alumina (Lucalox™). Groove profiles from the same grain boundaries were revisited using AFM following successive heat-treatments. The grooves measured from migrating grain boundaries were found to have asymmetric partial-angles compared to those measured from boundaries that did not migrate during the experiment. For a moving boundary, the grain with the larger partial-angle was consistently found to grow into the grain with the smaller partial-angle. Migrating boundaries were observed to leave behind remnant thermal grooves. The observations indicate that the boundary may be bowing out during the migration process.
Electron Beam Induced Carbon Depositionand Etching
Authors: Sun Y.-M. , Eklund J. , Wang Q. , Gay D. , White J. M.
Published: April 2011

Electron induced carbon deposition and etching was investigated by Auger electron spectroscopy in a custom designed vacuum system. The Auger electron spectrometer was used to provide a high flux electron beam to induce reactions and to monitor surface composition. During the e-beam induced deposition or etching, the gas phase pressure was 10-4 to 10-5 Torr. Several carbon precursors: benzene, cyclohexane and propane were used for deposition. The deposition rate depended on the precursor sticking coefficient and bonding structure. Among the three precursors tested, the deposition rate of carbon was cyclohexane > benzene > propane. The e-beam induced etching of carbon films was carried out in 1 × 10-4 torr oxygen ambient and the carbon film was prepared by reactive physical vapor deposition. The etching process can be divided into three stages: bulk film, interface, and substrate. For the bulk carbon film, the decrease of film thickness varies linearly with the e-beam flux, while at the interface, the film thickness shows an exponential decay with the electron flux. For the C in the Si substrate, a very slow etching rate was observed. The etching rate for bulk carbon film was ∼ 0.1 nm/min under the experimental conditions, which is equivalent tp 2.4 × 10-27 cm3/electron. At the interfacial region, the cross section of carbon removal by electrons was ∼ 4.6 × 10-21 cm2. Based on the change of the carbon line shape at the interface, we concluded that the etching rate is related to the chemical nature of the carbon species.
Multiple Layers of Copper Thin Films of Alternating Textures
Authors: Huang Hanchen , Wei H. L. , Liang H. Y. , Woo C. H. , Zhang X. X.
Published: April 2011

In this paper, we present a preliminary study of texture development during copper thin film deposition. Using direct current (DC) magnetron sputtering technique, we deposit copper films on a SiO2/Si(111) substrate. A thin layer of copper of <111> texture first develops, and another thin layer of <110> ensues. As deposition continues, a third layer of copper of <111> texture forms on the top, leading to a copper thin film of alternating <111> and <110> textures. The multiple layers of copper thin films of alternating textures form during continuous deposition without changing deposition conditions. The film morphology is characterized with scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the texture with X-ray diffraction (XRD). Based on anisotropic elastic analyses and molecular dynamics simulations, we propose a model of texture evolution during the formation of multilayers, attributing the texture evolution to the competition of surface and strain energies.
Preparation of V-based Alloy Membranes using Chemical Transport Process
Authors: Ozaki Tetsuya , Zhang Yi , Komaki Masao , Nishimura Chikashi
Published: April 2011

Novel preparation process of V-Ni alloys for hydrogen purification membrane using chemical transport was investigated. Vanadium, NH4Cl, and PtCl2 as evaporating source were put in one side of a fused-silica tube, and Ni substrate was put in the other side. The fused-silica tube was sealed in vacuo, and set in a furnace with temperature gradients. Evaporating source temperature was 1173–1273 K. Substrate temperature was 3–100 K higher than the evaporating source temperature. This process consists of formation of HCl from NH4Cl and PtCl2, chemical transport of vanadium under temperature gradient via chlorides in the presence of HCl, and diffusion of the transported V into the Ni substrate. EDX line profile of cross section of the substrates after the process demonstrated that V diffused into the Ni substrates. Distribution of V concentration in the substrates was dependent on the substrate temperature and the temperature difference between the substrate and the evaporating source. Heating condition was optimized to obtain homogeneous V-Ni alloy. When the substrate temperature and evaporating-source temperature were 1228 K and 1223 K, respectively, V diffused homogeneously into the Ni substrate with thickness of 20 μm, and V concentration attained in the substrate was higher than 70at%.
Packed-Bed Reactor Performance Enhancement by Membrane Distributed Feed: The Case of Methanol Oxidative Dehydrogenation
Authors: Diakov Victor , Varma Arvind
Published: April 2011

For methanol oxidative dehydrogenation to formaldehyde, the performance of the packed-bed membrane reactor (PBMR) is compared with that of the conventional fixed-bed reactor (FBR) over a wide range of operating conditions. The reaction was studied in three reactor configurations: the conventional FBR and the packed-bed membrane reactor, with either methanol (PBMR-M) or oxygen (PBMR-O) as the permeating component. The kinetics of methanol and formaldehyde partial oxidation reactions were determined and incorporated in a PBMR model. Both experimental data and model considerations demonstrate that the PBMR enhances reactant conversion and selectivity.

Small oscillations in CO production were observed experimentally. Their amplitude was taken as a basis for comparison of packed-bed operation instability. The likely source of oscillatory behavior is the non-uniformity in reaction conditions along the reactor. It was found that membrane distributed feed, by providing a more uniform reactor operation, is an effective remedy from these instabilities.

It is found, both by simulations and experimental observations, that relative reactor performance depends strongly on the operating conditions. Using formaldehyde yield as the basis for optimization, optimal reactor performances are determined to be in the order: PBMR-O > FBR > PBMR-M. Further PBMR productivity enhancement is possible by optimizing the membrane feed distribution pattern.
How can Microwave Heating Contribute to the Development of Zeolite Membranes
Authors: Julbe Anne , Motuzas Julius , Charmette Christophe , Guizard Christian
Published: April 2011

In this work the growth of both a zeolite (MFI) and a zeolite-like material (SOD) were investigated in/on αAl2O3 tubular support, using hydrothermal conditions and microwave (MW) heating. The method reveals efficient for the rapid synthesis of MFI/αAl2O3 membranes although gentle conditions were required in order to limit the thermal degradation of the template. Promising results were also obtained for directly growing SOD in/on the support. In both MFI and SOD MW synthesis the chemical dissolution of the αAl2O3 support influences the final membrane characteristics. In the case of SOD synthesis, this phenomena which increases with both temperature and support size, alters the membrane homogeneity (composition and structure). In order to get round it, MWs were used to prepare SOD small crystals which were deposited on/in the αAl2O3 support and submitted to a secondary growth. Homogeneous membranes were then obtained whose ideal selectivities αH2/N2 and αHe/N2 reaches respectively 4.5 at 20°C and 6.2 at 115°C (these selectivities are lower than 2 for a ZSM-5 membrane in similar conditions).
Hydrophilic Surface Modification of Microporous Polymer Membranes Using A Variety of Low-Temperature Plasma Treatments
Authors: Wavhal Dattatray S. , Kull Kristen R. , Steen Michelle L. , Fisher Ellen R.
Published: April 2011

A variety of plasma treatments have been employed to achieve permanent hydrophilic surfaces throughout the membrane structure. Specifically, we have modified microporous polyethersulfone (PES) membranes using H2O, CO2, and N2 plasma treatments to implant polar functional groups; alternatively, Ar-plasma treatment followed by grafting of hydrophilic monomers (acrylic acid and acrylamide) in the vapor phase has also been successful at modifying PES membranes. PES membranes treated with H2O and CO2 plasmas as well as the grafted membranes are found to be permanently hydrophilic (for a minimum of six months), and the entire membrane cross-section is modified. Chemical changes to the modified PES membranes were determined with FTIR and XPS measurements. Furthermore, water bubble point measurements and electron microscopy results reveal that pore sizes of the modified membranes are only slightly affected, depending on the treatment. Incorporation of polar functionalities results in an increase in the glass transition temperature (Tg) and a moderate change in tensile strength of the modified membranes. Most importantly, the surfaces of the modified membrane are less susceptible to absorption by bovine serum albumin (BSA) proteins.
Stochastic Reconstruction and Permeation of Ceramic Membranes Prepared by the Sol-Gel Method
Authors: Kikkinides E. S. , Zaspalis V. T. , Burganos V. N.
Published: April 2011

In the present work we study the relation between structural and permeation properties of ceramic membranes made by the sol-gel process. For this purpose, we have developed γ-Al2O3 mesoporous membranes via the sol-gel route, on top of multi-layer asymmetric α-Al2O3 macroporous supports, to induce mechanical stability. Subsequently, we employ stochastic techniques to generate three-dimensional reconstructions of the membrane and the support that share the basic structural properties of the original materials determined directly from SEM and TEM studies. The permeability of each material is estimated by solving numerically the momentum equation in the void space of the reconstructed images. The very good agreement between predicted and experimentally measured permeability values, without the need to resort to any fitting parameter, renders the proposed reconstruction methodology quite promising for reliable characterization and representation of the pore structure of this type of membranes.
Molecular Modeling of Free Volume Distributions of Amorphous Membrane Polymers
Authors: Hofmann Dieter , Heuchel Matthias , Yampolskii Yuri , Topchiev A. V.
Published: April 2011

The paper deals with important differences in the distribution of free volume in high and low free volume polymers as indicated by a joint investigation utilizing molecular modeling and positron annihilation lifetime (PALS) studies. The main focus of this paper is on the molecular modeling approach. The first set of polymers in question are the ultra-high free volume polymer poly(1–(trimethylsilyl)-1-propyne) (PTMSP) and two polystyrene derivatives containing Si and F. Extended equilibration procedures were necessary to obtain reasonable packing models for the polymers. The transition state Gusev-Suter Monte Carlo method was utilized to prove a reasonable agreement between simulated and measured diffusivity and solubility values for the model structures. The free volume distribution was analyzed for the validated packing models and compared with respective PALS data. In both cases a bimodal distribution of free volume was observed for PTMSP while the polystyrene derivatives as other conventional glassy polymers showed a more or less monomodal behavior. Good qualitative agreement is demonstrated between size distributions of free volume elements in these polymers obtained via molecular computer modeling and PALS experiments. In addition a series of conventional and high performance polyimides was considered. There a major result is that polyimides with conventional permeabilities for small molecules always show just a monomodal distribution of free volume element sizes in the radius range up to about 5 Å, while all polyimides with high permeabilities have a wider, often bimodal, distribution extending up to a radius between 6 and about 8 Å.
Transport Properties of Reconstructed Alumina and Vycor Membranes
Authors: Kainourgiakis M. E. , Kikkinides E. S. , Steriotis Th. A. , Stubos A. K.
Published: April 2011

Aim of the present work is the investigation of the transport properties (Knudsen and molecular diffusivity, permeability) of 3-dimensional binary domains that represent two model mesoporous materials, namely Vycor glass and alumina membrane. A process-based technique producing a random packing of equal spheres is used for the reconstruction of the alumina membrane, while a stochastic reconstruction procedure is employed in the case of Vycor. The comparison between computed and reported transport coefficients confirms that the random sphere pack represents quite well the porous structure of the alumina membrane, while the stochastic reconstruction technique is sufficient for an accurate representation of the porous matrix of Vycor glass.
Mesoscopic modeling of binary diffusion through microporous zeolite membranes
Authors: Snyder Mark A. , Vlachos Dionisios G.
Published: April 2011

The mesoscopic framework describing single-component diffusion through microporous materials is extended here to characterize binary diffusion in the absence of intermolecular forces. Two diffusion mechanisms, single-file diffusion characteristic of confined pore structures and species-species exchange consistent with diffusion modes in less-confined pore topologies, are incorporated at the Master Equation level. Derived fundamentally via rigorous coarse-graining of the underlying Master Equation, the binary mesoscopic relation is validated via direct comparison to gradient continuous time Monte Carlo (G-CTMC) simulations. We further show the capability of this fundamentally derived model to capture the macroscopic diffusion phenomenon of ‘overshoot’ or ‘roll-up’ in the transient uptake and flux. Exploration of the species-species exchange mechanism reveals its strong effect on the transient ‘overshoot’ behavior through relaxation of the constrained single-file diffusion.
Fabrication of Electrochemical Ceramic Membrane with Assistance of Metallization by the Electroless-plating Technique
Authors: Liu Y-Y. , Hong L. , Shao Z-C. , Jiang H-X.
Published: April 2011

This work developed a metal-reinforced ceramic membrane processing approach [by using perovskite La0.2Sr0.8 CoO3-x (LSCO-80) as the model membrane] with the aim of overcoming the membrane-cracking problem. A thin layer of Ag/Pd alloy was incorporated into the LSCO-80 membrane made by dip coating and sintering. It is not viable to obtain a Pd/Ag alloy film using the co-plating method because Ag+ ion strongly inhibits chemical reduction of Pd2+ ion, and the alkaline plating bath causes severe etching of LSCO-80. This obstacle was circumvented through a layer-by-layer deposition procedure, in which Ag and Pd layers were deposited subsequently onto LSCO membrane. The Ag and Pd layers undergo alloying when the laminar structure was subjected to calcinations at 1000°C. It was found that the Pd/Ag alloy drifts beneath into pores in the LSCO layer. The resultant metal-ceramic composite membrane shows excellent structural integrity and free of micro-cracks.
Ion Beam Modification of Matrimid® Gas Separation Membrane—Evolution in Chemical Structure, Microstructure and Gas Permeation Properties
Authors: Xu Xinglong , Hu Ling , Coleman Maria
Published: April 2011

Matrimid® is a widely used polyimide that has both attractive thermal and gas transport properties. In addition, it has been used as a precursor polymer for production of carbon molecular sieving membranes with commercially interesting gas separations. Ion beam irradiation over a wide range of doses was used to modify a series of Matrimid® membranes. A combined analysis of impact of ion irradiation on the chemical structure, microstructure and gas transport properties of Matrimid® will be presented. Specifically, the evolution in gas permeation properties following irradiation over a wide range of doses will be discussed. Ion irradiation resulted in combined increased permeability and permselectivity for several gas pairs of interest.
Use of Electrodialysis to Bentonitics Clays Dispersions
Authors: Amorim L. V. , Gomes C. M. , Silva F. L. H. , França K. B. , Lira H. L. , Ferreira H. C.
Published: April 2011

The aim of this work is to study the uses of electrodialysis to bentonitics clays dispersions from Boa Vista City, PB, to improve the rheological properties. The dispersions were prepared with natural clay in the concentration of 4.86% w/w and submitted to electrodialysis process by using cationic polymeric membranes. Following, the dispersions were treated with Na2CO3. After cure, it was evaluated apparent (AV) and plastic (PV) viscosity and water loss (WL). The tests was setting up according to 22 experimental design, with three measures in the central point, to estimate the best applied voltage and time and the influence on AV, PV and WL. The results showed that variables (voltage and time) have significant influence on the rheological properties. It was observed an increase in PV and decrease in WL, with values that satisfy the specifications for water based drilling fluids.
Organic/inorganic Nanohybrid Membranes for Nanofiltration of Nonaqueous Solutions
Authors: Tsuru Toshinori , Kondo Hiroyasu , Yoshioka Tomohisa , Asaeda Masashi
Published: April 2011

Silica/zirconia (SZ; Si/ Zr molar ratio = 9/1) membranes having pore sizes in the range of 1∼ 3 nm were prepared by the sol-gel process. Organic/ inorganic hybrid membranes were developed by modifying the surface of the silica-zirconia porous membranes via a gas-phase reaction with trimethylchlorosilane (TMCS) to give a surface that was modified with a monolayer of TMCS. Using nanopermporometry, it was found that the inner surface of membrane pores with diameters larger than several nms were successfully modified with TMCS. TMCS-modified membranes showed approximately the same permeability, Lp, irrespective of water concentration (10 and 100 ppm) in hexane. In contrast, an unmodified membrane, showed a decrease in Lp with increasing water concentration, which was pronounced at low permeation temperatures. This suggests that small amounts of water adsorbed to the inner surface of unmodified silica-zirconia membranes and blocked the permeation of hexane.
Interfacial Ion Fluxes at Nanostructured Thin Films
Authors: Kariuki Nancy N. , Luo Jin , Han Li , Maye Mathew M. , Patterson Melissa J. , Moussa Laura , Hepel Maria , Zhong Chuan-Jian
Published: April 2011

Thin films derived from nanocrystal cores and functionalized linkers provide large surface-to-volume ratio and three-dimensional ligand framework. This paper describes the results of an investigation of the interfacial ion fluxes associated with redox reactivity and structural properties of such films using cyclic voltammetry, electrochemical quartz-crystal nanobalance, surface infrared reflection spectroscopy, and X-ray photoelectron spectroscopy. Films from gold nanocrystals of 2 nm core sizes and 11-mercaptoundecanoic acid were studied as a model system. First, the film coated on electrode surface displays redox-like voltammetric waves characteristic of the deprotonation-reprotonation of the carboxylic acid groups in the nanostructured network. This process is accompanied by mass changes. Secondly, the film exhibits capability for the complexation of copper ions via the nanostructured carboxylate framework. This process is also accompanied by interfacial fluxes of electrolyte cations across the electrode | film | electrolyte interface which compensate electrostatically the fixed negative charges in the reduction process.
Hardening by Point Defects and Solutes in B2 Intermetallics
Authors: Pike L. M. , Chang Y. A. , Liu C. T. , Anderson I. M.
Published: April 2011

This paper provides a review of recent progress on point defect and solute hardening in binary and ternary B2 intermetallics. As is the case for disordered metallic solutions, the presence of point defects and solute atoms in ordered intermetallic compounds results in solid solution hardening (SSH). However, factors unique to ordered systems are often responsible for unusual hardening effects. Binary compounds with identical crystal structures can exhibit significantly different hardness behavior. Ternary solute additions to ordered compounds can give rise to apparent solid solution softening as well as unexpectedly rapid hardening. These effects arise from the interaction of multiple defect types as well as the presence of multiple sublattice sites available for solute occupation. Therefore, before the SSH behavior of ordered intermetallics can be properly studied, it is necessary to develop an understanding of the types and quantities of the point defects which are present. Three recent studies by the authors are reviewed. Much of the work was done on NiAl and FeAl in binary form as well as with ternary additions. Defect concentrations over wide ranges in alloy composition and quenching temperature were determined using the ALCHEMI (atom location by channeling enhanced microanalysis) technique combined with vacancy measurements. Hardness values were also measured. It was found that most of the observed SSH effects could be rationalized on the basis of the measured point defect concentrations.
Alignment of the lamellar orientation of multi-component TiAl alloys by directional solidification (DS) and mechanical properties of DS ingots
Authors: Omiya Y. , Muto S. , Yamanaka T. , Johnson D. R. , Inui H. , Yamaguchi M.
Published: April 2011

By using an appropriately oriented seed from the TiAl-Si system (Ti-43Al-3Si), the TiAl/Ti3Al lamellar structure has been successfully aligned parallel to the growth direction for TiAl ingots of the Ti-Al-Nb, Ti-Al-Nb-Si, Ti-Al-Ta-Si systems on the basis of the recently proposed method to predict the appropriate compositions. The Al equivalents for Nb and Ta are reevaluated in order to extend the proposed method to large addition (above a several at. %) of these alloying elements. These DS ingots with the lamellar structure all aligned parallel to the loading axis exhibit creep properties far better than conventionally produced TiAl ingots so far reported.
Microstructural Changes of a γ-TiAl Based Alloy with a Fully Lamellar Microstructure Due to Annealing at Elevated Temperatures
Authors: Beschliesser M. , Appel F. , Kestler H. , Clemens H.
Published: April 2011

The changes of a fully lamellar microstructure caused by annealing at 700 and 800°C for up to 10,000 hours in air have been investigated for a Ti-46.5at.%Al-4at.%(Cr,Nb,Ta,B) sheet material. Changes in morphology as well as in chemical composition and volume fraction of constitutional phases were recorded by means of transmission electron microscopy. Thermodynamic equilibrium calculations performed with the software package ThermoCalc provide baseline information upon both the chemical composition and the amount of constitutional phases of the investigated multi-component alloy. It could be demonstrated that due to high cooling rates which are required to adjust a “defect-free” undisturbed fully lamellar microstructure, composition and amount of the α2 phase are far from the thermodynamic equilibrium. However, during high temperature exposure the composition as well as the amount of α2 phase move towards the values predicted by the calculation. Furthermore, former perfectly shaped γ/α2 lamellae interfaces are disturbed, α2 lamellae decompose and new phases appear instead. Dislocations emitted from dissolving α2 lamellae move into the γ lamellae. Mechanisms responsible for decomposition of lamellae and formation of new phases are explained by thermodynamic equilibrium calculations and diffusion considerations. Finally, results of tensile tests conducted at room temperature and 700°C on long-term annealed specimens are presented and discussed. This work is a basis for understanding microstructural changes and their impact on mechanical properties of γ-TiAl based alloys with a fully lamellar microstructure during service at elevated temperatures.
Effects of the Variation in α-Phase Volume Fraction on the Thermal Stability of TiAl Alloys with Lamellar Microstructures
Authors: Kim S. W. , Lee H. N. , Oh M. H. , Yamaguchi M. , Wee D. M.
Published: April 2011

The thermal stability of lamellar microstructure in Ti-Al-Mo PST crystals containing C or Si, was investigated. In addition, the variation of α-phase volume fraction in Ti-Al-Mo-(C,Si) systems was investigated at several temperatures. Ti-46Al-1.5Mo-0.2C and Ti-46Al-1.5Mo-1.0Si alloys were found to be very stable during heat treatments at various heating rates and temperatures. Moreover, the α-phase volume fractions of Ti-46Al-1.5Mo-0.2C and Ti-46Al-1.5Mo-1.0Si alloys, which were stable compositions, changed less than those of Ti-47Al and Ti-46–1.5Mo alloys, which were unstable compositions. From these results, it was determined that the instability of the latter alloys was caused by their relatively higher variation of α-phase volume fraction during heating. Therefore, it is suggested that the variation of α-phase volume fraction is an important factor in controlling the thermal stability of lamellar microstructure.
Annealing induced structural changes and microcracking in Mo-Mo3Si
Authors: Wang X.-L. , Schneibel J. H. , Wang Y. D. , Richardson J. W.
Published: April 2011

Cast Mo-Mo3Si intermetallic composites develop microcracks after annealing at high temperature. Neutron diffraction, x-ray diffraction, composition analysis, and scanning electron microscopy have been used to characterize the structural changes induced by annealing of Mo-Mo3Si. It is shown that the observed cracking cannot be attributed to differential thermal stresses that developed on cooling from the annealing temperature. Instead, the experimental data suggest that the cracks were initiated at high temperature, possibly due to diffusion of Si atoms from supersaturated α-Mo to Mo3Si.
Kinetic Calculation of L10 Ordered System Based on Phase Field Methodand Cluster Variation Method
Authors: Ohno M. , Mohri T.
Published: April 2011

During ordering process, anti-site ordering proceeds in atomistic scale and anti-phase domain structure evolves in microstructural scale. In order to describe both the processes, a hybridized calculation of the Phase Field Method(PFM) and Cluster Variation Method(CVM) is attempted. The main objective of the present study is focused on the time evolution of atomic configuration during L10 ordering processes below and above the spinodal ordering temperature and their resultant microstructures. In order to investigate the interplay between atomistic and microstructural processes, we conducted two types of calculations. One is for a homogeneous system without an anti-phase boundary and the other is for an inhomogeneous system in which microstructure is formed by anti-phase domains.

For the homogeneous system, the relaxation curve of Long-Range-Order parameter(LRO) indicates a transient appearance of an L12-like atomic configuration below the spinodal ordering temperature. Such an L12–like state corresponds to a saddle point configuration in the CVM free energy surface. When the composition of an alloy is located near L10 + L12 phase field in the phase diagram, the L12–like phase becomes highly ordered state.

For the inhomogeneous system, it is implied that the appearance of the L12-like phase affects the resultant microstructure by providing the nucleation sites for the L10 ordered phase.
Pulse-Field Activation of Collinear Magnetic Single Crystals
Authors: Jenkins C. A. , O'Handley R. C. , Allen S. M.
Published: April 2011

Single crystals of nickel-manganese-gallium, a ferromagnetic shape memory alloy (FSMA), show up to 10% elongation in response to an applied magnetic field or mechanical stress. The change in dimension is not a result of magnetostriction but of twin boundary motion through the material. The field-induced extension has previously been reversed only by a compressive mechanical stress from a spring or orthogonal field. The use of a second crystal of Ni-Mn-Ga to provide the reset force is unreported.

Data are shown here of the stress and strain behavior of two FSMA crystals connected in series and subjected alternately to a magnetic field. Two samples, one initially in full extension and the other in compression, are arranged in series in a rigid frame such that their total length is held constant. A pulsed magnetic field is alternately applied to the samples, with the output energy of the extending crystal tending to apply a resetting force to the other. This setup shows up to 1.5% resetting strain in single crystal laminates.
Brittle to Ductile Transition in Intermetallic Alloys
Authors: Kysar Jeffrey W.
Published: April 2011

Two distinct approaches are commonly invoked to explain the brittle to ductile transition of a material in the presence of a crack. In one approach, dislocation mobility plays the key role. In the other approach, the competition between crack tip dislocation nucleation and cleavage failure plays the key role. The two approaches are reconciled in the present study.
Evaluation of the Thermodynamic Properties and Phase Equilibria of the Ordered γ’ and Disordered γ Phases in the Ni-Al-Ta System
Authors: Zhou Shihuai , Chen Long-Qing , MacKay Rebecca A. , Li u Zi-Kui
Published: April 2011

The phase equilibria and thermodynamic properties of the ternary Ni-Al-Ta system on Ni-rich side were analyzed. Thermodynamic descriptions of the liquid, γ-fcc, γ'-L12, and π-Ni6AlTa phases were obtained using the CALPHAD (CALculation of PHase Diagrams) technique. The thermodynamics of γ-fcc and γ'-L12 phases were modeled with a single Gibbs energy function taking into account the crystallographic relation between the two phases. The ternary interaction parameters of the liquid and fcc phases were also determined. The calculated phase diagrams of the ternary Ni-Al-Ta system show a good agreement with experimental data.
Vibrational Spectroscopy and MAS NMR Studies of A Cryptomelane Family of Mixed (7Li+, 2 H+) Form Manganic Acids
Authors: Tsuji Masamichi , Paik Younkee , Grey Clare P. , Murao Satoshi
Published: April 2011

Cryptomelane-type manganic acids (CMAs) synthesized by a soft-chemical redox process of KMnO4 with MnSO4 in H2SO4 and α-MnO2s by a decomposition-oxidation process of (CH3)3COK and MnCO3 at 530°C were studied by using the vibrational spectroscopy and 7Li- and 2H-MAS NMR. The infrared absorption bands of the α-MnO2s at 706cm-1 were not changed irrespective of the sort of alkali cations and their uptake amount, while large shifts of this band were observed on the CMA exchanged by alkali cations. Hence, cation-exchange sites of these solids will occupy crystallographically different positions. 7Li-MAS NMR spectra of these manganic acids showed different two chemical shifts depending on their synthetic routes. These findings suggest that different ion-exchange sites are formed at a local level in the 2×2 type tunnel, strongly depending on their synthetic conditions. These are crucial for the control of the cation affinity. These details at a molecular level cannot be obtained by using the conventional XRD analyses.
Surfactant and temperature influence on Co nanocrystal structure and shape
Authors: Puntes V.F. , Zanchet D. , Erdonmez C. K. , Alivisatos A.P.
Published: April 2011

Inorganic nanoparticles of a variety of materials have been obtained by chemical methods. Under the kinetic control, small variations in the synthesis recipe may yield crystals of different sizes, shapes and structures. Co nanocrystals are of particular interest: besides achieving size control, at least three nearly isoenergetic crystal structures (face-centered cubic, hexagonal close-packed and epsilon) can be synthesized, and shape control (spheres, prisms, cubes, rods and disks) is also possible. Although shape and structure should be intrinsically related, the relationship between these two characteristics has not been deeply explored up to this moment. Here, we present our latest results on Co nanoparticles, analyzing the influence of some parameters on particle shape and structure. In particular, the influence of ligand type and temperature has been tackled.
The Migration Concept for Ionic Motion in Materials With Disordered Structures
Authors: Funke K. , Banhatti R. D.
Published: April 2011

The dynamics of the mobile ions in materials with disordered structures are a challengingly complicated many-particle process. In this paper, we consider characteristic frequency-dependent conductivities and permittivities of such materials and show that they can be well reproduced within the framework of the MIGRATION concept. The meaning of the acronym is MIsmatch Generated Relaxation for the Accommodation and Transport of IONs. In the MIGRATION concept, we attempt to grasp the essence of the ion dynamics in a simple set of rules which convey a physical picture of the most relevant elementary processes. The rules are expressed in terms of three coupled rate equations which then form the basis for deriving frequency-dependent model conductivities and permittivities.
Characterization of Multilayer Anodes for SOFC
Authors: Müller Axel C. , Krügel Albert , Weber André , Ivers-Tiffée Ellen
Published: April 2011

SOFC anodes have to combine various tasks. In anode supported single cells a thick anode substrate is used for current collecting and gas distribution whereas a thin functional layer adjacent to the electrolyte is the electrochemically active part of the anode. This functional anode layer is cofired together with the thin film electrolyte to obtain an enhanced interface with low polarisation losses. This multilayer structure was transferred to an electrolyte supported single cell. The electrochemical active Ni/8YSZ anode layer was screen printed onto a 8YSZ electrolyte green tape and subsequently cofired at 1350 °. Mechanical stresses during cofiring due to shrinkage mismatch of anode and electrolyte were avoided by changing the geometry of the anode layer from a continuous layer to a large number of small sized individual areas. Simulations by finite element modeling indicated that a hexagonal pattern similar to honeycombs is preferable. The second layer which adjoins to the fuel gas channels and which is responsible for current collecting and gas distribution was later on screen printed on top and sintered together with the cathode. Single cells with a multilayer anode and different functional layers were electrochemically characterised under realistic operation conditions. The performance and reduction/oxidation stability of this type of anode was investigated. The electrochemically active layer showed only small degradation during redox cycling and long term operation at high fuel utilisation. In contradiction to single layer anodes Nickel agglomeration was not observed in the functional layer.
Characterization of Polymer Clay Nanocomposite Electrolyte Motions via Combined NMR and Neutron Scattering Studies
Authors: Smith Luis J. , Zanotti Jean-Marc , Sandi Giselle , Carrado Kathleen A. , Porion Patrice , Delville Alfred , Price David L. , Saboungi Marie-Louise
Published: April 2011

The activation energies for poly(ethylene oxide) motion in a polymer clay composite are reported for the polymer intercalated and external to the clay. PEO intercalated into the clay is found to have a lower activation energy for motion but also a larger Arrhenius prefactor, by almost two orders of magnitude, than for PEO found external to the clay. Neutron scattering measurements confirm the presence of two environments and the effects of confinement on the mean square displacement of the PEO.