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David N. Seidman - One of the best experts on this subject based on the ideXlab platform.

  • Solute-atom segregation at internal interfaces on an atomic scale: atom-probe experiments and computer simulations
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1991
    Co-Authors: David N. Seidman
    Abstract:

    Abstract This paper addresses fundamental questions concerning the determination of the chemical compositions of internal interfaces (grain boundaries)—in single-phase f.c.c. or b.c.c. binary alloys—and the relationships of the solute enhancement factor at a grain boundary to its structure. This goal is achieved utilizing three principal techniques: (i) atom-probe field-ion microscopy; (ii) transmission electron microscopy; and (iii) Monte Carlo computer simulations that utilize embedded atom method potentials for f.c.c. alloys. Atom-probe field-ion microscopy is used to determine the chemical composition of an interface, and transmission electron microscopy is employed to determine its five macroscopic degrees of freedom. The Monte Carlo simulations employ the Metropolis et al. algorithm to simulate segregation in the Pt(Au) and Pt(Ni) systems. Detailed experimental and computer simultation results are presented for grain boundaries in Pt(Au), Pt(Ni) and W(Re) Primary Solid-Solution alloys.

Lubomir Kral - One of the best experts on this subject based on the ideXlab platform.

  • alloying of mg mg2ni eutectic by chosen non hydride forming elements relation between segregation of the third element and hydride storage capacity
    Journal of Power Sources, 2012
    Co-Authors: J Cermak, Lubomir Kral
    Abstract:

    Abstract Eutectic mixture Mg–11.3 at.% Ni was modified by elements X from the 13th (Al, Ga, In) and 14th group (Si, Ge, Sn and Pb). Phase analysis and distribution of X between Primary Solid Solution Mg–Ni– X and Mg 2 Ni– X compound was carried out in stabilization annealed samples before hydrogen charging and in hydrided state. In the both states, it was found that X prefers Mg 2 Ni– X to Mg–Ni– X Solid Solution, and that the preference is stronger in the hydrided state. The effect is more pronounced for elements X from the 13th group. Suggested explanation was based on influence of X on the formation enthalpy of hydrides. It was observed that In increases the hydrogen storage capacity of the eutectic mixture. The most likely explanation is based on a strong segregation of In to phase Mg 2 Ni– X , and on a weak tendency of In to form phases with Mg and Ni.

J Corenoalonso - One of the best experts on this subject based on the ideXlab platform.

  • dependence of volume changes during Solid Solution formation and of volume size factor on solute volume group number and crystalline structure
    Intermetallics, 2012
    Co-Authors: O Corenoalonso, J Corenoalonso
    Abstract:

    Abstract This paper describes the dependence of both volume change during Primary Solid Solution formation and that of volume size factor, Vsf on solute mean atomic volume. Our research findings demonstrate a direct relationship between Vsf or volume change and solute atomic volume. For twenty solvent elements, the average linear correlation coefficient between Vsf and solute atomic volume is 0.659. The average correlation coefficient for volume changes is 0.592. Forty-seven systems solute–solvents with the same crystalline structure indicate that the average linear correlation coefficient between Vsf and solute atomic volume is 0.780. The average correlation coefficient between Vsf and solute atomic volume is 0.907 for solute elements from the same group in the Periodic Table. The average correlation coefficient for volume changes is 0.775. Forty-eight systems were analyzed. For fourteen elements, it was found that elements with the same crystalline structure have an average correlation coefficient between Vsf and solvents atomic volume of 0.934. The relationship between volume changes and solvent atomic volume can be expressed with a quadratic model. Then, volume change during Primary Solid Solution depends upon solute volume, group number and crystalline structure.

S. L. Chryssoulis - One of the best experts on this subject based on the ideXlab platform.

  • Gold mineralization in As-rich mesothermal gold ores of the Bogosu-Prestea mining district of the Ashanti Gold Belt, Ghana: remobilization of “invisible” gold
    Mineralium Deposita, 1994
    Co-Authors: A. H. Mumin, M. E. Fleet, S. L. Chryssoulis
    Abstract:

    The Bogosu-Prestea mining district of southwestern Ghana is a 33 km section of the Early Proterozoic Ashanti Gold Belt. Greenschist facies carbonaceous and carbonate-bearing turbidites and greywackes, and mafic dikes host numerous economic mesothermal gold deposits. Structurally higher ores in the Bogosu concession have brittle deformation and consist of disseminated-sulphide lodes in tectonically-disrupted sedimentary rocks and carbonate-altered mafic dikes. Most gold occurs as micrometre-size particles in arsenian pyrite, and as “invisible” gold in arsenian pyrite and arsenopyrite. The structurally deeper ores of the adjoining Prestea concession are associated with brittle-ductile deformation and consist of extensive crack-seal quartz-veins and graphitic shear zones. Only minor amounts of “invisible” gold were detected; in these deeper lodes, gold occurs dominantly as abundant microscopic and larger particles in sulphide/arsenide minerals and in gangue. The gold distribution patterns revealed by SIMS microprobe analysis and ion maps, EMP and colour staining suggest that most of the Primary gold in the Bogosu-Prestea system precipitated in Solid-Solution with sulphide/arsenide minerals. However, post-depositional concentration and redistribution occurred, in increasing degree with: 1) increase in metamorphic/hydrothermal gradients in the gold system (depth), 2) decrease in the refractory properties of the host mineral, and 3) increase in the amount of post-depositional, host-mineral recrystallization and deformation. Gold evolved from Primary Solid-Solution within sulphide/arsenide minerals, to colloidal and micrometre-size particles concentrated in voids, fractures and internal grain boundaries, and finally to microscopic and larger particles at sulphide/arsenide grain margins and in the gangue assemblage. The general conclusions presented here are applicable to As-rich gold deposits of all ages, worldwide. The presence of gold in late fractures is insufficient evidence for late-stage introduction of gold in mesothermal gold systems.

K. Chattopadhyay - One of the best experts on this subject based on the ideXlab platform.

  • Microstructure evolution and thermoelectric properties of Te-poor and Te-rich (Bi,Sb)_2Te_3 prepared via Solidification
    Journal of Materials Science, 2016
    Co-Authors: Olu Emmanuel Femi, N. Ravishankar, K. Chattopadhyay
    Abstract:

    This paper explores in detail, the microstructures and thermoelectric properties of Te-rich and Te-poor (Bi,Sb)_2Te_3 alloys. We show that tuning the composition of ternary Bi–Sb–Te type alloys allows us to synthesize a range of microstructures containing a Primary Solid Solution of (Bi,Sb)_2Te_3 with varying amounts of Te Solid Solution or a (Bi,Sb)Te compound. Te exists as a constituent of the multilayer domain while (Bi,Sb)Te appears in the thin intercellular regions of the (Bi,Sb)_2Te_3 dendritic cells. The presence of Te imparts an n-type behavior to the composite while the (Bi,Sb)_2Te_3 with a small amount of (Bi,Sb)Te exhibits p-type properties. A maximum ZT value of ≈0.4 at 425 K was achieved, opening up the possibility of using these alloys for thermoelectric device applications.