Kinetics of Materials

Balluffi, R. W.; Allen, Samuel M.; Carter, W. Craig

doi:10.1002/0471749311

Cited by 656 publications

(463 citation statements)

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“…As expected from our discussion, slow cooling leads to much slower solidification than diffusion and, consequently, to a stable nonsupercooled solidification. On the other hand, rapid laser shut-off (shut-off time less than 10 ms) causes the solidification rate to exceed the germanium diffusion rate, which would promote constitutional supercooling (34). In both cases, the experimental results are consistent with the predicted behaviors.…”

Section: Resultssupporting

confidence: 63%

“…In general, constitutional supercooling arises when solute rejection in the liquid creates steep concentration gradients near the solidification front, leading to a situation where the actual temperature ahead of the front is lower than the liquidus temperature near the interface, which drives instability (29,34). This concentration profile occurs if the diffusion of solute in the liquid is slow compared with the solidification velocity, thus resulting in strong gradients at the interface.…”

Section: Resultsmentioning

confidence: 99%

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Confined in-fiber solidification and structural control of silicon and silicon−germanium microparticles

Gumennik

Levy

Grena

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Crystallization of microdroplets of molten alloys could, in principle, present a number of possible morphological outcomes, depending on the symmetry of the propagating solidification front and its velocity, such as axial or spherically symmetric species segregation. However, because of thermal or constitutional supercooling, resulting droplets often only display dendritic morphologies. Here we report on the crystallization of alloyed droplets of controlled micrometer dimensions comprising silicon and germanium, leading to a number of surprising outcomes. We first produce an array of silicon−germanium particles embedded in silica, through capillary breakup of an alloy-core silica-cladding fiber. Heating and subsequent controlled cooling of individual particles with a two-wavelength laser setup allows us to realize two different morphologies, the first being a silicon−germanium compositionally segregated Janus particle oriented with respect to the illumination axis and the second being a sphere made of dendrites of germanium in silicon. Gigapascal-level compressive stresses are measured within pure silicon solidified in silica as a direct consequence of volume-constrained solidification of a material undergoing anomalous expansion. The ability to generate microspheres with controlled morphology and unusual stresses could pave the way toward advanced integrated in-fiber electronic or optoelectronic devices. multimaterial fibers | microparticles | confined solidification | silicon−germanium spheres | stressed silicon C ontrolling the microstructure or state of stress of microparticles and nanoparticles is often key to attaining the desired properties for a specific application (1-5); however, the ability to do so is strongly limited by the synthesis method. For instance, nonspherically symmetric distributions of inorganic materials are difficult to achieve from bottom-up approaches (4-7). Likewise, controlling the state of stress or strain of semiconductor particles is challenging in unconstrained nucleation-and-growth synthesis methods. However, Janus particles of silicon−germanium (SiGe) could potentially find applications as microswimmers or nanoswimmers owing to asymmetric absorption properties (8), as well as in infrared photodetectors or solar cells for increased infrared absorption (9). Stressed silicon particles, on the other hand, could be used for bandgap tunability in photonic or optoelectronic devices (10-12).In the past few years, thermally drawn multimaterial fibers have emerged as a unique platform for top-down scalable fabrication of microparticles to nanoparticles over a broad range of materials, through controlled in-fiber capillary breakup of the fiber components (13-15). In the case of polymers or chalcogenide glasses, structural control of the particle can be achieved by constructing complex cores at the preform level, which is later broken up in the fiber state to form structured particles (13). However, in the case of traditional semiconductor materials such as silicon and germanium, the same...

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Section: Resultssupporting

confidence: 63%

Section: Resultsmentioning

confidence: 99%

Confined in-fiber solidification and structural control of silicon and silicon−germanium microparticles

Gumennik

Levy

Grena

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…where D 0 is the diffusion constant, Q is the activation energy, R is the gas constant, and T is the temperature [24][25][26][27]. Diffusion constant is not dependent on time, hence one diffusion constant was calculated for each temperature.…”

Section: Analytic Model Of Vitamin E Dopingmentioning

confidence: 99%

“…where C 0 is the saturation concentration of the material, x is depth, D is the diffusion coefficient, and t is time [24][25][26][27]. The complementary error function, erfc(z), is simply [1−erf(z)].…”

Section: Analytic Model Of Vitamin E Dopingmentioning

confidence: 99%

Diffusion of vitamin E in ultra-high molecular weight polyethylene

et al. 2007

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Vitamin E-doped, radiation cross-linked ultra-high molecular weight polyethylene (UHMWPE) is developed as an alternate oxidation and wear resistant bearing surface in joint arthroplasty. We analyzed the diffusion behavior of vitamin E through UHMWPE and predicted penetration depth following doping with vitamin E and subsequent homogenization in inert gas used to penetrate implant components with vitamin E. Cross-linked UHMWPE (65-and 100-kGy irradiation) had higher activation energy and lower diffusion coefficients than uncross-linked UHMWPE, but there were only slight differences in vitamin E profiles and penetration depth between the two doses. By using homogenization in inert gas below the melting point of the polymer following doping in pure vitamin E, the surface concentration of vitamin E was decreased and vitamin E stabilization was achieved throughout a desired thickness. We developed an analytical model based on Fickian theory that closely predicted vitamin E concentration as a function of depth following doping and homogenization.

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“…1 In contrast, phase-field models provide a more general, thermodynamically consistent treatment of nucleation and growth without resorting to the artificial placement of phase boundaries. 18,19 Considering the excitement surrounding LiFePO 4 as a phase-separating cathode material, phase-field methods have received relatively little attention. Tang et al modeled phase separation and crystallineto-amorphous transformations in spherical isotropic LiFePO 4 particles with a phase-field model, 20 prompting experiments to seek the predicted amorphous surface layers.…”

mentioning

confidence: 99%

Suppression of Phase Separation in LiFePO₄ Nanoparticles During Battery Discharge

Bai

Cogswell²,

Bazant³

2011

Nano Lett.

453

734

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Using a novel electrochemical phase-field model, we question the common belief that Li x FePO 4 nanoparticles separate into Li-rich and Li-poor phases during battery discharge. For small currents, spinodal decomposition or nucleation leads to moving phase boundaries. Above a critical current density (in the Tafel regime), the spinodal disappears, and particles fill homogeneously, which may explain the superior rate capability and long cycle life of nano-LiFePO 4 cathodes.

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Kinetics of Materials

Cited by 656 publications

References 0 publications

Confined in-fiber solidification and structural control of silicon and silicon−germanium microparticles

Confined in-fiber solidification and structural control of silicon and silicon−germanium microparticles

Diffusion of vitamin E in ultra-high molecular weight polyethylene

Suppression of Phase Separation in LiFePO₄ Nanoparticles During Battery Discharge

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Kinetics of Materials

Cited by 656 publications

References 0 publications

Confined in-fiber solidification and structural control of silicon and silicon−germanium microparticles

Confined in-fiber solidification and structural control of silicon and silicon−germanium microparticles

Diffusion of vitamin E in ultra-high molecular weight polyethylene

Suppression of Phase Separation in LiFePO4 Nanoparticles During Battery Discharge

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Product

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Suppression of Phase Separation in LiFePO₄ Nanoparticles During Battery Discharge