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School of Materials Science and Engineering

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Author: Ding, Yong × Author: Jin, Z. Q. × search.filters.applied.f.resourcesubtype: Article ×

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    Mechanical behavior and magnetic separation of quasi-one-dimensional SnO₂ nanostructures: A technique for achieving monosize nanobelts/nanowires
    (Georgia Institute of Technology, 2005-03-25) Jin, Z. Q. ; Ding, Yong ; Wang, Z. L. (Zhong Lin)
    The as-synthesized nanowires and nanobelts usually have a large size distribution. We demonstrate here a ball milling technique for narrowing the size distribution of oxide nanobelts and nanowires. High-resolution scanning and transmission electron microscopy reveals that the one-dimensional SnO₂ nanostructures with size >150 nm are sensitive to the milling effect and most of them were fractured into nanoparticles even after a short-time milling. These nanoparticles contain magnetic Fe components, which could be effectively separated from those nanobelts by employing a magnetic field. This feature promises a potentials application in the nanostructured materials separation. It was also found that the dominant size of the survived nanostructures is <100 nm. The good mechanical behavior of the nanostructures are not only related to the superior mechanical toughness due to small size, but also related to the low defect density.
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    Explosive shock processing of Pr₂Fe₁₄B/α–Fe exchange-coupled nanocomposite bulk magnets
    (Georgia Institute of Technology, 2005-03) Jin, Z. Q. ; Thadhani, Naresh N. ; McGill, M. ; Ding, Yong ; Wang, Z. L. (Zhong Lin) ; Chen, M. ; Zeng, Hao ; Chakka, V. M. ; Liu, J. Ping
    Explosive shock compaction was used to consolidate powders obtained from melt-spun Pr₂Fe₁₄B/α–Fe nanocomposite ribbons, to produce fully dense cylindrical compacts of 17–41-mm diameter and 120-mm length. Characterization of the compacts revealed refinement of the nanocomposite structure, with approximately 15 nm uniformly sized grains. The compact produced at a shock pressure of approximately 1 GPa maintained a high coercivity, and its remanent magnetization and maximum energy product were measured to be 0.98 T and 142 kJ/m³, respectively. The compact produced at 4–7 GPa showed a decrease in magnetic properties while that made at 12 GPa showed a magnetic softening behavior. However, in both of these cases, a smooth hysteresis loop implying exchange coupling and a coercivity of 533 kA/m were fully recovered after heat treatment. The results illustrate that the explosive compaction followed by post-shock heat treatment can be used to fabricate exchange-coupled nanocomposite bulk magnets with optimized magnetic properties.
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    Grain size dependence of magnetic properties in shock synthesized bulk Pr₂Fe₁₄B/α-Fe nanocomposites
    (Georgia Institute of Technology, 2004-09-15) Jin, Z. Q. ; Thadhani, Naresh N. ; McGill, M. ; Li, Jing ; Ding, Yong ; Wang, Z. L. (Zhong Lin) ; Zeng, Hao ; Chen, M. ; Cheng, S.-F. ; Liu, J. Ping
    The structural and magnetic properties of the melt-spun Pr₂Fe₁₄B/α-Fe nanocomposite powders consolidated via shock-wave compression and subjected to postshock thermal treatment were investigated. Shock compression results in grain refinement, which leads to a reduction of an effective anisotropy and therefore an increase in the ferromagnetic exchange length, resulting in an enhanced exchange coupling in fully consolidated bulk magnets. A small amount of amorphous phase formed during the shock compression were observed to crystallize into Pr₂Fe₁₄B upon annealing above 600 °C. The heat treatment also results in the recovery of coercivity partially lost during the consolidation, which can be related directly to the dependence of the effective anisotropy on the grain size, as illustrated by the transmission electron microscopy observation of grain refinement in the shock-consolidated bulk samples. A uniform grain morphology is suggested as a means for further increasing the magnetic properties of bulk nanocomposites.
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    Controlling the crystallization and magnetic properties of melt-spun Pr₂Fe₁₄B/α Fe nanocomposites by Joule heating
    (Georgia Institute of Technology, 2004-05-12) Jin, Z. Q. ; Cui, B. Z. ; Liu, J. Ping ; Ding, Yong ; Wang, Z. L. (Zhong Lin) ; Thadhani, Naresh N.
    Pr₂Fe₁₄B/α Fe based nanocomposites have been prepared through crystallization of melt-spun amorphous Pr₇Tb₁Fe₈₅Nb ₀.₅ Zr ₀.₅ B₆ ribbons by means of ac Joule heating while simultaneously monitoring room-temperature electrical resistance R. The R value shows a strong variation with respect to applied current I, and is closely related to the amorphous-to-nanocrystalline phase transformation. The curve of R versus I allows one to control the crystallization behavior during Joule heating and to identify the heat-treatment conditions for optimum magnetic properties. A coercivity of 550 kA/m and a maximum energy product of 128 kJ/m³ have been obtained upon heating the amorphous ribbons at a current of 2.0 A. These properties are around 30% higher than the values of samples prepared by conventionally (furnace) annealed amorphous ribbons.