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  • 1
    Electronic Resource
    Electronic Resource
    A cluster model for the viscous flow of glass-forming liquids (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 5002-5006 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model is developed to account for the viscous flow of glass-forming liquids. We consider that a supercooled glass-forming liquid is composed of a liquid phase and some solidlike clusters which have a higher activation energy for viscous flow than the liquid regions. This approach yields a fitting equation for viscosity with a simple form η=η0 exp(E/kBT)exp(ΦT/Tg), where E is the activation energy for viscous flow at low temperatures, and Φ represents the fragility of a glass-forming system. Our results suggest that kinetic viscous flow of glass-forming liquids is closely related to their thermodynamics. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1448494
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  • 2
    Electronic Resource
    Electronic Resource
    A conceptual approach for noncontact calorimetry in space (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 1299-1303 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A concept is developed and described which allows to measure the heat capacity and the effective thermal conductivity of stable and undercooled liquid metals and alloys in an electromagnetic levitation apparatus. We propose to use an ac pulse heating method which is used nowadays as a standard technique for precision measurement of low temperature heat capacities. The ideal process parameters including the drop diameter D, temperature T, and frequency of measurement ω can be optimized when the following relations hold for the external and internal relaxation time constants τ1 and τ2, respectively: ωτ1(approximately-greater-than)10 and ωτ2〈0.1. Then heat capacity data can be obtained with an accuracy of better than 1% with D about 5 to 10 mm, T between 1200 and 1800 K and ω between 0.1 and 1 Hz for typical metals and alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142488
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  • 3
    Electronic Resource
    Electronic Resource
    Structural and thermodynamic properties of heavily mechanically deformed Ru and AlRu (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 305-310 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on high-energy ball milling of Ru and AlRu. The deformation results in a drastic decrease of the crystal size to a nanometer scale and in an increase of atomic-level strain. This is accompanied by a disordering of the crystal lattice as is shown by means of the long-range-order parameter in AlRu. The specific heat increases by more than 15%–20%, indicating large changes in the vibrational and configurational part of the entropy. The stored energy of cold work is up to 6 kJ/mol for AlRu and 10 kJ/mol for Ru. This is almost 40% of the heat of fusion of Ru and exceeds by far the energies stored by other deformation processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342541
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  • 4
    Electronic Resource
    Electronic Resource
    Thermodynamic properties and crystallization kinetics of glass-forming undercooled liquid Au-Pb-Sb alloys (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4494-4502 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The heat capacities of liquid and crystalline Au-Pb-Sb alloys in the glass-forming composition range were measured with droplet emulsion and bulk samples. Based on the measured Cp data, the entropy, enthalpy, and Gibbs free-energy differences between the eutectic solid mixture and undercooled liquid were determined as a function of temperature over ∼60% of the undercooling range below the liquidus temperature and compared with theoretical predictions. The results indicate an isentropic temperature at 313 (±5) K, which agrees well with experimental data for the glass transition. The thermodynamic evaluation was applied further to develop a kinetics analysis of the nucleation undercooling response during cooling. Use of different approximations for the Gibbs free energy leads to a variation of the prefactor terms of six orders of magnitude for classical nucleation theory and, consequently, large variation in calculated transformation diagrams which is more pronounced with increasing undercooling. Extrapolations into the glass-forming temperature range and the effects of viscosity, transient nucleation, and estimated Kauzmann temperatures on the crystallization kinetics at high undercooling have been evaluated. This analysis reveals the importance of using measured values of thermophysical properties, even if they represent a limited temperature range at modest undercooling, rather than model approximations in order to obtain reliable evaluations of crystallization kinetics at high undercooling in the glass-forming temperature range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346200
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  • 5
    Electronic Resource
    Electronic Resource
    Metastable phase formation in the Zr-Al binary system induced by mechanical alloying (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 1744-1748 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the sequence of phase transformations induced in the Zr-Al binary system by mechanical alloying of mixed Zr and Al powders. The structure of these materials has been studied by transmission electron microscopy and by x-ray diffraction measurements. Three different metastable phases have been found experimentally with variation of the initial composition xAl: (1) a nanocrystalline supersaturated solid solution of α-Zr for xAl≤0.15, (2) an amorphous phase for 0.15〈xAl≤0.4, and (3) a metastable face-centered-cubic phase for xAl=0.5 with a grain size of 4 nm. The crystallization reaction of the amorphous phase was monitored by differential scanning calorimetry, and the kinetics of the reaction have been examined as well. A possible explanation based on thermodynamic arguments is given for the defect-driven vitrification of the crystalline Zr phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345624
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  • 6
    Electronic Resource
    Electronic Resource
    Phase separation kinetics of metastable, highly supersaturated Sn-Bi single crystals (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 448-450 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have utilized differential scanning calorimetry to study decomposition of a large number (≈105) of independent, metastable, highly supersaturated Sn63Bi37 single crystals. Three different growth regimes are observed: first, t1/2 diffusion-controlled growth, followed by a t1/3 regime attributed to Lifshitz–Slyozov coarsening [J. Phys. Chem. Solids 19, 35 (1961)] extended to the case of finite volume fraction, and eventually "freezing'' of the growth possibly because of defects. The activation energy of the t1/3 growth is determined to be 0.54±0.05 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99439
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  • 7
    Electronic Resource
    Electronic Resource
    Enhanced microhardness in Zr65.0Al7.5Ni10.0Cu17.5 amorphous rods on coprecipitation of nanocrystallites through supersaturated intermediate solid phase particles (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2825-2827 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous rods of 4 mm diameter of Zr65.0Al7.5Ni10.0Cu17.5 crystallize in a very fine microstructure, with an average size of the crystallites of 19 nm, on an isochronal heating over 655–860 K for a short period of 300 s. The multiple primary crystallization occurs with subsequent precipitation transformation of Zr-rich supersaturated tetragonal Ni11Zr9- type (T phase) and cubic NiZr2- type (I phase) phases to a thermally stable three phase mixture of α-Zr (hexagonal), T and I phase finely dispersed one into another. It results in an enhanced microhardness of 6.9 GPa in the crystallized sample in comparison to 4.6 GPa in the amorphous sample, 5.7 GPa in the well-crystallized bulk ingots, or 1.75 GPa or lower in the pure Zr or other elemental starting components. The results are discussed with the refined microstructure and the formalism of the local precipitations of α-Zr nanocrystallites in the locally phase separated microscopic domains of related supersaturated intermediate phases. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116337
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  • 8
    Electronic Resource
    Electronic Resource
    Glass formation in a multicomponent Zr-based alloy by mechanical attrition and liquid undercooling (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 580-582 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The synthesis of a multicomponent Zr60Al10Ni9Cu18Co3 glass by mechanical alloying has been investigated using thermal and structural analysis and compared with a metallic glass produced by liquid undercooling. The solid-state amorphization reaction is preceded by rapid solution of smaller solute atoms in the Zr matrix with a concomitant reduction in grain size to 10 nm at the amorphization onset. A fully amorphous mechanically alloyed sample shows relaxation compared to a sample synthesized by liquid cooling probably due to removal of residual inhomogeneities on the scale of the nanocrystal size at amorphization. While the kinetic pathways for the two synthesis methods differ, the relaxed amorphous phases from each method exhibit identical thermodynamic properties. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118280
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  • 9
    Electronic Resource
    Electronic Resource
    Power modulation technique for noncontact high-temperature calorimetry (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 3111-3113 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new noncontact calorimetric method has been developed based on inductive heating of a metallic spherical bulk sample by a power-modulated radio-frequency field under ultrahigh vacuum conditions. From the pyrometrically measured temperature response the specimen's external (due to radiative heat loss) and internal relaxation time (due to thermal conductivity) are found to differ by more than two orders of magnitude allowing the specific heat as well as thermal conductivity of the sample to be determined as a function of temperature. The agreement between the measured and predicted temperature response for solid Nb demonstrates the applicability and accuracy of the method which is particularly useful for metastable or chemically reactive samples at high temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109626
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  • 10
    Electronic Resource
    Electronic Resource
    Defect-induced melting and solid-state amorphization (1992)
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 133-135 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A crystal can be 'melted' to an amorphous solid when a thermodynamic driving force for the transition develops and kinetic constraints are maintained (mainly because of the low experimental temperatures) that prevent the establishment of full equilibrium7'8. Such a transition can be described ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/356133a0
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