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  • 1
    Electronic Resource
    Electronic Resource
    An effect of antiphase boundaries on the kinetics of short-range ordering by a vacancy mechanism (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3227-3229 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In Monte Carlo simulations of chemical short-range ordering on a square lattice, the number of single-atom domains was found to depend on the presence of antiphase boundaries and on the mechanism by which ordering occurred. When antiphase boundaries were present and the ordering occurred by a vacancy mechanism, the number of single-atom domains was found to increase with decreasing temperature, in contrast to thermodynamic predictions. This is understood as a consequence of highly correlated vacancy motions in those regions of the lattice away from antiphase boundaries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453917
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetomechanical effects in textured polycrystalline Tb76Dy24 (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5795-5797 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Uniaxial stress-strain measurements were performed on polycrystalline Tb76Dy24 alloys which exhibit "giant magnetostriction" at cryogenic temperatures. The Young's moduli were reduced by up to a factor of five at 77 K, in comparison to their values at 300 K. We attribute this reduction to a mechanical compliance from domain rotation. Large mechanical hysteresis is also found in nominally elastic stress-strain curves measured below the Curie temperature. Hysteretic curves from 0 to 25 MPa demonstrate up to 19% dissipation of the applied mechanical energy. The anisotropy of thermal expansion was also measured and used as a parameter for the degree of crystallographic texture. This anisotropy was correlated to bulk magnetostriction and to mechanical hysteresis. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372525
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  • 3
    Electronic Resource
    Electronic Resource
    Short-range ordering in face-centered-cubic Ni3Al (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4380-4383 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Films of fcc Ni3Al with suppressed short-range order (SRO) were prepared by physical vapor deposition of Ni3Al onto room-temperature substrates. Extended electron energy-loss fine-structure spectra were obtained from both Al K and Ni L23 edges. After the samples were annealed for various times at 150 °C, a moderate growth of SRO was observed in the first-nearest-neighbor environments of both the Al and Ni atoms. As prepared, these fcc Ni3Al materials, and presumably others having similar heat evolutions as measured by differential scanning calorimetry, have a high degree of chemical disorder. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359463
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  • 4
    Electronic Resource
    Electronic Resource
    Phonon density of states of nanocrystalline Fe prepared by high-energy ball milling (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 8318-8322 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We performed inelastic neutron scattering measurements on nanophase Fe powders prepared by high-energy ball milling. Neutron energy loss spectra were measured for two states of the material: (1) as milled, when the material had a characteristic nanocrystallite size of 12 nm; and (2) annealed, when the material had a characteristic crystallite size of 28 nm. The longitudinal peak in the phonon density of states (DOS) of the nanophase Fe was broadened, compared to that of the annealed material. We attribute this broadening to short phonon lifetimes in nanocrystals. The nanophase material also showed an enhanced density of states at low energies below 15 meV, which may indicate the presence of intercrystallite vibrations. These differences in phonon DOS should have only a small effect on the difference in vibrational entropy of nanocrystalline and larger-grained Fe. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362543
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  • 5
    Electronic Resource
    Electronic Resource
    Average widths of grain boundaries in nanophase alloys synthesized by mechanical attrition (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 3458-3466 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Many binary ferrous alloys were synthesized by mechanical attrition in a high-energy ball mill. X-ray diffractometry and transmission electron microscopy were used to measure grain sizes, which were as small as a few nanometers in several alloys. The nanocrystalline alloys showed new features in their Mössbauer spectra, which we associated with 57Fe atoms at and near grain boundaries. The experimental data on the fraction of 57Fe atoms at and near grain boundaries were correlated to the measured grain sizes to obtain an average width of the grain boundaries. The average grain-boundary widths of the fcc alloys Fe–Mn and Ni–Fe were approximately 0.5 nm, but the average widths of grain boundaries in the bcc alloys Cr–Fe, Mo–Fe, and Fe–Ti were somewhat larger than 1 nm. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358640
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  • 6
    Electronic Resource
    Electronic Resource
    Microstructural dependence of vacancy diffusion in ordered alloys (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1467-1472 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dependence of the vacancy diffusional correlation factor on microstructure was investigated by Monte Carlo simulations (MCS). The MCS used activated state rate theory to model the vacancy diffusion. We varied the temperature, size of ordered domains, and the state of order within the domains. Correlations in the vacancy movement were found to vary widely, and numerical values are presented. Two different results were obtained, one for ordering in a homogeneous alloy and another for ordering in an alloy having domains. However, given the existence of domains, the vacancy correlation factor was observed to be independent of domain size. Oscillations in the correlation function were observed, and were attributed to pair trapping of the vacancy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356381
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  • 7
    Electronic Resource
    Electronic Resource
    Phases and phase stabilities of Fe3X alloys (X=Al, As, Ge, In, Sb, Si, Sn, Zn) prepared by mechanical alloying (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5961-5966 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mechanical alloying with a Spex 8000 mixer/mill was used to prepare several alloys of the Fe3X composition, where the solutes X were from groups IIB, IIIB, IVB, and VB of the periodic table. Using x-ray diffractometry and Mössbauer spectrometry, we determined the steady-state phases after milling for long times. The tendencies of the alloys to form the bcc phase after milling are predicted well with the modified usage of a Darken–Gurry plot of electronegativity versus metallic radius. Thermal stabilities of some of these phases were studied. In the cases of Fe3Ge and Fe3Sn, there was the formation of transient D03 and B2 order during annealing, although this ordered structure was replaced by equilibrium phases upon further annealing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358375
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  • 8
    Electronic Resource
    Electronic Resource
    Two-phase coexistence in Fe–Ni alloys synthesized by ball milling (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3946-3955 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We used mechanical alloying with a Spex 8000 mixer/mill to synthesize a series of Fe100−xNix alloys from x=0 to x=49. The Spex mill was modified so that it could also operate at a reduced milling intensity, and we compared the alloys synthesized after long times with the normal and reduced milling intensities. X-ray diffractometry and Mössbauer spectrometry were used to measure the volume fractions of the bcc and fcc phases in the alloys, and to determine the chemical compositions of the individual phases. We found that the composition ranges of the bcc and fcc single phase regions were extended well beyond their equilibrium ranges. At the higher milling intensity, we found that the bcc phase was destabilized with respect to the fcc phase, and the two-phase region shifted to lower Ni concentrations. For those alloys with coexisting bcc and fcc phases, we present evidence that the chemical compositions of the two phases are nearly the same. We explain the destabilization of the bcc with milling intensity as originating with a higher defect density in the bcc alloys than in the fcc alloys. We argue that this defect density is not homogeneous throughout the alloy, however, and the distribution of defect enthalpies can explain the two- phase coexistence in the as-milled alloys. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361821
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  • 9
    Electronic Resource
    Electronic Resource
    Hydrogen adsorption and cohesive energy of single-walled carbon nanotubes (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 2307-2309 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hydrogen adsorption on crystalline ropes of carbon single-walled nanotubes (SWNT) was found to exceed 8 wt. %, which is the highest capacity of any carbon material. Hydrogen is first adsorbed on the outer surfaces of the crystalline ropes. At pressures higher than about 40 bar at 80 K, however, a phase transition occurs where there is a separation of the individual SWNTs, and hydrogen is physisorbed on their exposed surfaces. The pressure of this phase transition provides a tube-tube cohesive energy for much of the material of 5 meV/C atom. This small cohesive energy is affected strongly by the quality of crystalline order in the ropes. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123833
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  • 10
    Electronic Resource
    Electronic Resource
    Hydrogen desorption and adsorption measurements on graphite nanofibers (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3378-3380 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Graphite nanofibers were synthesized and their hydrogen desorption and adsorption properties are reported for 77 and 300 K. Catalysts were made by several different methods including chemical routes, mechanical alloying, and gas condensation. The nanofibers were grown by passing ethylene and H2 gases over the catalysts at 600 °C. Hydrogen desorption and adsorption were measured using a volumetric analysis Sieverts' apparatus, and the graphite nanofibers were characterized by transmission electron microscopy and Brunauer–Emmett–Teller surface area analysis. The absolute level of hydrogen desorption measured from these materials was typically less than the 0.01 H/C atom, comparable to other forms of carbon. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122755
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