bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface Coating of Hddr Processed and Mechanically Alloyed Powder Based on RE-TM
Authors: Kobe S. , Novak S. , Mcguiness P.J. , Mandrino D , Jenko M. 
Published: April 2011

ABSTRACTChemical surface modification can be used as a method for corrosion protection of sensitive powders based on intermetallic alloys between rare earth and transition metals. Surface coating is used for preventing fine powders, based on Nd-Fe-B, or Sm2Fe17−xTaxN3−δ prepared by HDDR processing and mechanically alloying, from hydrolysis. Powders coated by chemisorbed organic substance, after exposing to a humid atmosphere, do not show any chemical or physical change.Different coating agents were used and the sufficient amount of various materials was optimised with the emphasis on minimising their quantity. Simple experiment shows that the surfactant is successfully chemisorbed on the powder surface and that the coated powders are hydrophobic indefinitely. Magnetic properties were measured on samples after they were exposed to the same corrosion tests. Measurements on coated and bonded samples were compared with the measurements of non-coated and bonded samples. By using Auger electron spectroscopy the thickness of the coating was controlled. In order to distinguish the nature of the bonding between the powder surface and the surface-active substance FT-IR spectroscopy in absorbency and diffuse reflection modes was used. The protection of the fine particles is based on the formation of a covalent bond between the hydroxyl groups at the particle surface and the surface-active substance. The monomolecular layer of organic substance does not damage the magnetic properties of the powder, but successfully protect the powder against humidity.
Synthesis and Characterization of Antiferromagnetic Kmnf3Nanoparticles
Authors: Sangregorio C. , Carpenter E. E. , O'connor C. J. 
Published: April 2011

ABSTRACTThe magnetic properties of nanosized antiferromagnetic particles of KMnF3are presented. The particles were synthesized using the microemulsion technique, i.e. by using the aqueous core of reverse micelles as constrained microreactors for the precipitation of the particles. The structural characterization of the samples, accomplished by TEM and XRD, reveal that the samples consist of cubic-shaped, crystalline KMnF3nanoparticles of uniform size. Control over the average size of the particles was achieved by changing the reaction time. Four different samples of average size in the range 13-35 nm were prepared. DC magnetic susceptibility measurements revealed superparamagnetic behavior of the particles. Hysteresis loops measured after field cooling the samples through TNwere shifted. The shift is ascribed to the exchange coupling between the antiferromagnetic core of the particles and the uncompensated spin shell surrounding it.
Microstructural and Magnetic Studies of Hddr Magnets from High Boron NdFeB(Zr) Alloys
Authors: Brown DN , Williams AJ , Gutfleisch O , Strangwood M , Harris IR 
Published: April 2011

ABSTRACTSome boron-rich (with respect to the Nd 2Fe,4B composition) NdFeB alloys (with and without small additions of zirconium) have been investigated in an attempt to understand the influence of zirconium in the subsequent magnetic properties of HDDR hot pressed magnets. It was found that zirconium additions had a marked influence on the as-cast microstructures with a general refinement of the grain size and evidence of a zirconium-rich phase (probably ZrB2) at the grain boundaries. The magnetic property measurements of fully dense, isotropic HDDR hot pressed magnets indicated that those containing zirconium maintained their coercivity to significantly higher hot pressing temperatures and this was attributed to the pinning of grain boundaries by the zirconium rich phase.
Influence of The Alloy Composition on The Magnetic Properties of Nanocrystalline Fe80M7B12Cu1 (M: Ti, Ta, Nb, Mo)
Authors: Kopcewicz M. , Grabias A. , Idzikowski B. 
Published: April 2011

ABSTRACTFormation of the nanocrystalline bcc Fe phase due to thermal treatment of the amorphous Fe80M7B12Cu1 (M: Ti, Ta, Nb, Mo) precursors is studied by the Mössbauer and differential scanning calorimetry techniques. The dependence of the formation of the bcc Fe phase on the alloy composition is discussed. In order to determine the optimal soft magnetic properties of these nanocrystalline alloys the rf-Mössbauer technique is used in which rf collapse effect induced by a radio-frequency (rf) magnetic field is employed. It was found that anisotropy fields in the nanocrystalline phase were smaller in Nb- and Mo-containing alloys as compared to the alloys which contain Ti or Ta. Variations of the anisotropy field vs. alloy composition and annealing temperature are discussed in detail.
Quantitative Crystallization and Nano-Grain Size Distribution Studies of a Fecunbsib Nanocrystalline Alloy
Authors: Leu M.S. , Chin T.S. 
Published: April 2011

ABSTRACTSuperior soft magnetic properties of nanocrystalline two-phase FeCuNbSiB alloy can only be attainable from a suitably nano-crystallized structure in the amorphous matrix. In this study a thermal-cycling-annealing process was adopted to anneal the amorphous specimens. The crystallization fraction of Fe73.5Cu1Nb3Si13 5B9 ribbons after different annealing was quantitatively measured by a DTA method through the integrated crystallization enthalpy from annealed samples versus that of as-cast amorphous specimen. The crystallization fraction was estimated to be 70 % as the specimen was annealed for 550°C×7.63 ks, the optimal annealing condition. Using this method, the crystallization quantity of the crystallized FeCuNbSiB amorphous alloy was accurately estimated and controlled during nano-crystallization processes.Abstact:The nanostructure of the annealed flake were investigated by high resolution TEM. The population of grain size is dominant in the range of 3-9 and 3-11 nm, corresponding to isothermal annealing at 520 and 550 °C, respectively, for 910 s. The average grain size associated with the above two annealing conditions is estimated to be 7 and 8.5 nm, respectively. The portion of nanocrystals with grain size smaller than 10 nm is about 80 % for the annealing at 520°C×910 s and 72 % for the annealing at 550°C×910 s, respectively. However, there is only one α-Fe(Si) phase evidenced in the TEM diffraction patterns.
Rf-Mössbauer Study of the Compositional Dependence of Short Range Order in Amorphous Fe-M-B-Cu Alloys
Authors: Kopcewicz M. , Grabias A. , Idzikowski B. 
Published: April 2011

ABSTRACTThe radio-frequency collapse of the magnetic hyperfine structure in the Mössbauer spectra is employed to study directly the short range order in amorphous Fe-M-B-Cu (M: Zr, Ti, Ta, Nb, Mo) alloys via the electric quadrupole hyperfine interaction. The shape of the quadrupole splitting distributions obtained from the rf collapsed spectra strongly suggests the existence of two short range orders with a high and low local content of iron. The decrease of boron content in FeZrB alloys leads to a more symmetric local structure experienced by Fe atoms.
Effects of Quenching Environment on the Structure of Melt- Spun Nd2Fe14B
Authors: Kramer M. J. , Tang Yali , Dennis K.W. , Mccallum R. W. 
Published: April 2011

ABSTRACTMelt-spun Nd2Fe14B (2–14–1) ribbons were produced under active vacuum and different partial pressures of inert gases of Ar and He. Microstructure and thermal analyses were performed to understand the microstructural evolution and glass formability (GF) of the ribbons. He atmosphere enhances the quenchability of the ribbons over Ar and vacuum. Ribbons made under 250 Torr He have more uniform microstructure and smoother surfaces than those under 760 Torr He. The higher quenchability induced by He, which increases the interfacial heat transfer coefficient between the melt and rotating wheel during melt spinning, is due to its higher thermal conductivity compared to Ar. The lower pressure stabilizes the turbulence between the melt-pool and Cu wheel, enhancing the heat transfer resulting in a more uniform quench. As a result, a more uniform ribbon microstructure can be obtained at relatively low wheel speeds.
Magnetic And Structural Properties Of Laser-Ablated Planar And Cylindrical Co Thin Films
Authors: Madurga V. , Vergara J. , Ortega R. J. , Landazabal I. P. De , Favieres C. 
Published: April 2011

ABSTRACTPlanar and cylindrical Co thin films have been obtained by pulsed laser ablation. X-ray diffractograms have shown no crystalline structure for the as-deposited samples, while the 450 °C annealed samples exhibit Co fcc crystalline peaks. The Scanning Tunnelling Microscopy has revealed a small increase of the surface roughness for the annealed films. The Hall effect has been used to determine the value of the spontaneous magnetization, Ms, at room temperature; Ms, = 14 kgauss for the as-deposited sample and Ms, = 17.6 kgauss for the 450 °C annealed sample. From transverse magnetooptic Kerr effect, it has been found that the as-deposited samples exhibit magnetic bistability, with a coercive field, Hc, = 6 0e. The annealed samples also show a bistable behavior until the annealing temperature is 450 °C. Besides, it has been observed an increase of Hc up to = 50 Oe, when the annealing temperature increases. The vibrating sample magnetometry has confirmed these results, showing that the magnetization participating in the magnetooptic effect for these low fields is the total spontaneous magnetization of these samples. Moreover, the cylindrical films exhibit magnetoelastic behavior when they are subjected to angular deformation. It has been found that the saturation magnetostriction constant is negative.
In-Situ TEM Deformation Studies of Dislocation Generation and Motion in High-Purity MO Single Crystals
Authors: Jouiad M. , Lagow B. W. , Robertson I. M. , Lassila D. H. 
Published: April 2011

AbstractThe generation and motion of dislocations in high-purity single crystals of Mo have been observed in real time by deforming electron-transparent samples in-situ in a transmission electron microscope. At 300 K and at low levels of stress, a novel dislocation source was observed that generated a long, straight screw dislocation. The source was a dislocation tangle that existed in the annealed material. An edge dislocation emerged from the tangle, trailing behind it the screw dislocation. These screw dislocations were immobile at this stress level. At higher stresses, the same dislocation tangle generated many dislocations, but now by a pole mechanism. The nature of these tangles and the source operation mechanisms will be described.
The Energetics of Dislocation-Obstacle Interactions by 3-D Quasicontinuum Simulations
Authors: Hardikar Kedar , Phillips R. 
Published: April 2011

AbstractThe goal of this work is to study the interaction of dislocations with local obstacles to glide such as point defects, precipitates and other dislocations. The quasicontinuum method is used as the basis of this study. It is demonstrated that two types of boundary effects are of concern in the calculation of hardening parameters using finite sized simulation cells. A recently developed technique to incorporate periodic boundary conditions in the quasicontinuum method is used to eliminate surface effects which were present in earlier implementations and to simulate a dislocation of infinite extent interacting with an array of obstacles. The second type of boundary effect is due to the boundary conditions on the lateral boundaries. A method based on finite element calculations is proposed for quantifying the effect of lateral boundaries in these simulations. Preliminary results for the validation of the method are presented as well as a simulation of the interaction between a conventional edge dislocation in Al with an array of clusters of Ni atoms.
Atomic-Scale Modeling of the Annihilation of Jogged Screw Dislocation Dipoles
Authors: Vegge T. , Pedersen O. B. , Leffers T. , Jacobsen K. W. 
Published: April 2011

AbstractUsing atomistic simulations we investigate the annihilation of screw dislocation dipoles in Cu. In particular we determine the influence of jogs on the annihilation barrier for screw dislocation dipoles. The simulations involve energy minimizations, molecular dynamics, and the Nudged Elastic Band method. We find that jogs on screw dislocations substantially reduce the annihilation barrier, hence leading to an increase in the minimum stable dipole height.
Damage and Crack Propagation at a Microstructural Scale
Authors: Bouchaud Elisabeth , Paun Florin , Ducourthial Elodie 
Published: April 2011

AbstractA quantitative analysis of the morphology of damage cavities in metallic materials is performed. At larger length scales, the self-affine correlation length of fracture surfaces is shown to be correlated to the grain size. These observations suggest a new scenario for the origin of scaling laws observed on fracture surfaces. It is argued that they reflect strong correlations in damage created prior to fracture during crack propagation.
A Partitioned-Problem Approach to Microstructural Modelling of a Glass-Ceramic
Authors: Fischer-Cripps A.C. 
Published: April 2011

AbstractThe indentation response of a mica-containing glass-ceramic that exhibits yield in an indentation test is interpreted in terms of events occurring on the microstructural scale. This work is unique in that it links the macroscopic and microstructural properties of the specimen material in the indentation process.
Long Distance Fracture Surface Roughness on a Dendritic Aluminum Alloy
Authors: Aldaco J. , Garza F.J. , Hinojosa M. 
Published: April 2011

AbstractThe long distance roughness of the fracture surface of a dendritic aluminum alloy is studied over a wide range of length scales. Self-affinity analysis was performed over samples broken in Charpy impact tests. Simultaneous use of Atomic Force Microscopy, SEM and stylus profilometry allowed us to cover a wide spectrum of length scales, spanning over seven decades, from a few nanometers up to one centimeter. The roughness exponent and correlation length were obtained using the variable bandwidth method. For the roughness exponent, a value of 0.8 was obtained, corresponding to the reported universal exponent. Correlation length was found to correspond well to the characteristic length of the largest heterogeneities in the complex microstructure. Our results provide information that can help to improve our understanding of the role of microstructural parameters on crack propagation mechanisms.
Effect of Precipitate Morphology on the Gradient-Dependent Behaviour of Two-Phase Single Crystals
Authors: Busso E. P. , Meissonnier F. T. , O'Dowd N. P. 
Published: April 2011

AbstractIn this work a recently proposed gradient and rate-dependent crystallographic formulation is used to investigate the macroscopic behaviour of a precipitated single crystal. It relies on strain gradient concepts to account for the additional strengthening mechanism caused by presence of interfacial and geometrically necessary dislocations (GNDs). The total slip resistance is assumed to be due to a mixed population of mobile and sessile forest obstacles arising from both statistically stored dislocations (SSDs) and GNDs. The non-local crystallographic theory is implemented numerically into the finite element method. It requires the calculation of the slip rate gradients at the element level to determine the evolutionary behaviour of the GND densities, and a fully implicit numerical algorithm within a large strain kinematics framework and non-isothermal conditions. The effects of the relevant microstructural features (precipitate size, morphology and volume fraction) and deformation gradient-related length scales on the macroscopic behaviour is investigated and compared with experimental results.
Glass Formation and Nanostructure Development in Al-Based Alloys
Authors: Wu R. I. , Wilde G. , Perepezko J. H. 
Published: April 2011

ABSTRACTAl-Sm and Al-Y-Fe alloys with a high number density of nanocrystalline fcc-Al homogeneously dispersed within the amorphous matrix have been synthesized by devitrifying the precursor metallic glasses produced by rapid solidification. The kinetics of metallic glass formation and the development of the nanostructure during devitrification are discussed in terms of the rate limiting mechanism. The glass transition temperature of the two metallic glasses has been successfully assessed with the application of the modulated-temperature differential scanning calorimetry (DDSC). In addition, the formation of quenched-in nuclei was investigated by a comparison study on the cold-rolled and melt-spun Al92Sm8 amorphous samples. Furthermore, the enhancement of the particle density of the fcc-Al nanocrystals in the amorphous matrix after devitrification has been demonstrated by the incorporation of nanosize Pb particles.
Nanocrystalline Alloys of II-VI Semiconductors from Molecular Multi-Layer Templates
Authors: Cristofolini L. , Facci P. , Fontana M.P. 
Published: April 2011

ABSTRACTWe present the synthesis and characterization of nanocrystalline II-VI semiconductors of mixed composition (CdSe/ZnSe, CdS) grown in fatty acid Langmuir-Schaefer multi-layer templates. The controlled production of i) homogeneous nanocrystalline CdxZn1−xSe alloys and ii) heterogeneous mixtures of different pure composition II-VI semiconductors such as CdSe and ZnSe provides, in addition to the size control, the parameter of the chemical composition for the fine tuning of the electronic properties. The samples are characterized bty optical and quasi-resonance micro-Raman spectroscopy.
Synthesis of Nanostructured WC Films by Supersonic Impaction of Nanoparticle Aerosols
Authors: Nichols W.T. , Malyavanatham G. , Beam M.P. , Henneke D.E. , Brock J.R. , Becker M.F. , Keto J.W. 
Published: April 2011

ABSTRACTTungsten carbide (WC) coatings were prepared using supersonic impaction of nanoparticles produced by pulsed laser ablation of microparticle aerosols. The influence of experimental parameters such as, carrier gas type and impaction velocity on the structure, composition and physical properties of the resultant particles and films were studied. It was found that stoichiometric, crystalline films could be grown. These films pass both the adhesive lift off and scratch tests. TEM investigations indicate that the laser ablation forms individual particles with mean size of 7 ± 3 nm. At the highest aersol pressures small aggregates were also observed, and adjustment of the gas pressure in the laser interaction cell was found to control the degree of aggregation. Upon impaction, the separate particles form dense, self sintering nanocrystalline films, with helium forming the most dense as determined from SEM images.
Formation of Nanocrystalline SiC Powder from Chlorine-Containing Polycarbosilane Precursors
Authors: Mitchell Brian S. , Zhang Haoyue , Ade Martin , Kurtenbach Dirk , Müller Eberhard 
Published: April 2011

ABSTRACTNanocrystalline β-SiC particulates with a grain size range of 5-20 nm were prepared by heating a pre-pyrolyzed, chlorine-containing polysilane/polycarbosilane (PS/PCS) to 1600°C. The transformation from the pre-pyrolyzed PS/PCS to nanocrystalline SiC was investigated by differential thermal analysis (DTA), thermogravimetric analysis (TGA), X-ray diffraction (XRD), mass-spectrometry and infrared spectroscopy. The results indicated that the nanocrystalline P-SiC was formed by the crystallization of the PS/PCS random network, and crosslinking of Si-Si, Si-Cl, and Si-CH2-Si bonds. The TEM observation showed that SiC particulates consist of equiaxed, randomly oriented, ultrafine grains.
Structure and Composition of Bismuth Nanowire Arrays
Authors: Sander M. S. , Lin Y-M. , Dresselhaus M. S. , Gronsky R. 
Published: April 2011

ABSTRACTArrays of nanowires have attracted considerable recent attention due to their unique electronic and optical properties. While much effort has been directed at fabricating arrays and measuring their properties, much less has been done to characterize these materials. Understanding the structure and composition of the constituents in these arrays is crucial in order to control their properties. In this work, arrays with wire diameters from 35-90nm were fabricated by pressure injecting liquid bismuth into porous alumina templates. Transmission electron microscopy (TEM) and analytical electron microscopy (AEM) were used to characterize the arrays.
Synthesis of Single Crystal Bismuth-Telluride and Lead-Telluride Nanowires for New Thermoelectric Materials
Authors: Wei Q. , Lieber C.M. 
Published: April 2011

ABSTRACTDimensionality can play an important role in determining the properties of materials. In the case of thermoelectric materials, it has been proposed that one-dimensional quantum wires, or nanowires, and two-dimensional superlattices could exhibit substantially higher efficiencies compared to the corresponding bulk, three-dimensional solids. To explore such predictions we have initiated a program directed towards the controlled growth of nanowires, and herein, we report the synthesis of single crystal Bi2Te3 and PbTe nanowires by a pulsed laser ablation method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that Bi2Te3 wires 80 nm to 200 nm in diameter and lengths exceeding 10 microns, and PbTe wires 25 nm to 60 nm in diameter and lengths to 2 microns can be readily produced by the laser ablation method. High-resolution TEM and electron diffraction show that Bi2Te3 nanowires are single crystals with wire axes along the <110> crystal direction. TEM and electron diffraction measurements also show that the PbTe nanowires are single crystals with a <100> growth axis. The transport properties of these new nanowire materials will be discussed.
Oriented Si nanowires grown via an SLS mechanism
Authors: Xing Y. J. , Xi Z. H. , Hang Q. L. , Yan H. F. , Feng S. Q. , Xu J. , Zhang H.Z. , Yu D. P. 
Published: April 2011

ABSTRACTHighly oriented silicon nanowires were grown on Si (111) substrate via a solid-liquid-solid (SLS) mechanism. Unlike the well known vapor-liquid-solid (VLS) mechanism of whisker growth, no gaseous or liquid Si source was supplied during growth. Ni was used as the liquid forming agent and mixture of H2 and Ar was introduced in the experiment. Oriented silicon nanowires grew at 950°C and the ambient pressure kept at about 200 Torr. The oriented silicon nanowires have a length around I il m and uniform diameter about 25nm. Selected area electron diffraction showed that silicon nanowires are completely amorphous. The approach used here is simple and controllable, and may be useful in large-scale synthesis of various nanowires.
Synthesis of Cubic and Rhombohedral Phased Nanocrystalline SnO2 Doped In2O3 [ITO] Powders with Coprecipitation Method
Authors: Kim Bong-Chull , Kim Jeong-Joo , Chang Se-Hong 
Published: April 2011

ABSTRACTNanocrystalline ITO powders have been prepared by a hydroxide coprecipitation method. Through the variation of aging time after precipitation, we have characterized the size, morphology and the structure of the precipitates. It was found that the precipitates are in the state of InOOH at first. Further aging up to 48 h changed it to In(OH)3 structure. After calcinations of the precipitates, rhombohedral nanocrystalline ITO powder with spherical shape was produced from InOOH structured precipitates, while cubic nanocrystalline ITO powder was produced from In(OH)3. Fraction of the rhombohedral ITO powder decreased as the aging time increased. The particle size of the cubic ITO increased with aging time but that of rhombohedral ITO (∼15 nm) was almost invariant.