Spherulitic branching in the crystallization of liquid selenium

Bisault, J.; Ryschenkow, G.; Faivre, G

doi:10.1016/0022-0248(91)90647-n

Cited by 81 publications

(106 citation statements)

References 23 publications

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“…a large fragility index); (ii) a fine substructure of the growing crystal (i.e. a rugged interface), which is the case of spherulites 9 . At this stage, our model is consistent with the main experimental facts.…”

Section: Discussionmentioning

confidence: 99%

“…This leads us to question the above simplistic description of a spherulite. Indeed, as documented in detail by Faivre and coworkers 9 , spherulites are compact objects which appear spherical on the optical scale, but are constituted, at smaller scales, of a space-filling accumulation of "sheaves" (of micrometric diameters), themselves constituted of anisotropic single crystals (typical size ∼ 100 nm), growing intermittently via small-and large-angle branching. Therefore, although spherulites of more than micrometric sizes can be viewed on a coarsegrained scale as spherical isotropic elastic inclusions in an amorphous matrix, crystallization actually proceeds via the intermittent growth of fiber-like units (the sheaves).…”

mentioning

confidence: 99%

“…Ediger et al 6 have shown that, as T varies, the growth velocity of the slow (normal) mode scales, not as η −1 , but as D, a result consistent with the idea that crystallization kinetics is controlled by local processes 7 . Moreover, materials exhibiting fast growth share the following common features: molecules are strongly anisotropic (nearly planar); single-crystals grown at small undercoolings are highly facetted -which indicates slow interfacial kinetics; at large undercoolings, crystal growth is spherulitic 8,9 with, in the usual observation domain (spherulite radii ∼ 10's to 100's of microns), a quasi-constant front velocity.…”

mentioning

confidence: 99%

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Ultrafast spherulitic crystal growth as a stress-induced phenomenon specific of fragile glass-formers

Caroli

Lemaı̂tre

2012

The Journal of Chemical Physics

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We propose a model for the abrupt emergence, below temperatures close to the glass transition, of the ultra-fast (GC) steady mode of spherulitic crystal growth in deeply undercooled liquids. We interpret this phenomenon as controlled by the interplay between the generation of stresses by crystallization and their partial release by flow in the surrounding amorphous visco-elastic matrix. Our model is consistent with both the observed ratios (∼ 10 4 ) of fast-to-slow velocities and the fact that fast growth emerges close to the glass transition. It leads us to conclude that the existence of a fast growth regime requires both (i) a high fragility of the glassformer; (ii) the fine sub-structure specific of spherulites. It finally predicts that the transition is hysteretic, thus allowing for an independent experimental test.Upon approaching T g , the rate of crystal growth from deeply supercooled glassformers decreases to very small values -in the 10 −12 m/s range -as appears consistent with the dramatic slowing down of molecular motions. Growth is hence expected to be nearly arrested in the glass phase. This expectation, however, is challenged by a surprising phenomenon identified by Oguni and coworkers in several fragile materials 1,2 and further investigated, more recently, by the groups of Yu and Ediger at Madison 3 . Namely below some temperature T t slightly larger than T g , an ultrafast crystal growth mode (often coined GC, for Glass-Crystal) suddendly emerges. Near T t the ratio of the fast over normal (slow) front velocities, u f and u s , is huge, typically of order 10 4 . Up to now this phenomenon has been observed in 11 one-component molecular glass-formers 3 , which all have high fragility indices, that is, exhibit the so-called decoupling phenomenon 4,5 . Namely, below ∼ 1.2 T g the viscosity η and translational diffusion coefficient D of the SC liquid no longer obey the Stokes-Einstein relation but instead, D ∼ η −ξ , with 0 < ξ < 1. Ediger et al 6 have shown that, as T varies, the growth velocity of the slow (normal) mode scales, not as η −1 , but as D, a result consistent with the idea that crystallization kinetics is controlled by local processes 7 . Moreover, materials exhibiting fast growth share the following common features: molecules are strongly anisotropic (nearly planar); single-crystals grown at small undercoolings are highly facetted -which indicates slow interfacial kinetics; at large undercoolings, crystal growth is spherulitic 8,9 with, in the usual observation domain (spherulite radii ∼ 10's to 100's of microns), a quasi-constant front velocity.To this day, the paradoxical emergence of this fast growth mode near T g largely remains a mystery. A noticeable proposition formulated by Tanaka 10 is that below T g , volume contraction upon crystallization creates in the surrounding glassy matrix a negative pressure, i.e. free-volume; this would increase particle mobility close to the interface, hence accelerate crystallization. Konishi and Tanaka 11 have shown that the values of the velocit...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Ultrafast spherulitic crystal growth as a stress-induced phenomenon specific of fragile glass-formers

Caroli

Lemaı̂tre

2012

The Journal of Chemical Physics

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“…Observation of spherulitic growth in quite pure materials (e.g. Bisault et al 1991) has called into question the need for impurities in spherulitic growth. However, significant impurity concentrations are present in essentially all natural systems, and the formation of spherulites in the absence of impurities does not preclude their importance in most systems of geological interest.…”

Section: Spherulitic Growthmentioning

confidence: 99%

Geological pattern formation by growth and dissolution in aqueous systems

Meakin

Jamtveit

2009

Proc. R. Soc. A.

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Progress towards the development of a better understanding of the formation of geological patterns in wet systems due to precipitation and dissolution is reviewed. Emphasis is placed on the formation of terraces, stalactites, stalagmites and other carbonate patterns due to precipitation from flowing supersaturated solutions and the formation of scallops by dissolution in undersaturated turbulent fluids. In addition, the formation of spherulites, dendrites and very large, essentially euhedral, crystals is discussed. In most cases, the formation of very similar patterns as a result of the freezing/melting of ice and the precipitation/dissolution of minerals strongly suggests that complexity associated with aqueous chemistry, interfacial chemistry and biological processes has only a secondary effect on these pattern formation processes.

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“…This also appears to be the case for other spherulite formers. For instance, pure elemental Se is reported to have a very peculiar molecular structure that is intermediate between polymeric and simple molecular liquids [34].…”

Section: Introductionmentioning

confidence: 99%

Morphology of Spherulites in Rapidly Solidified Ni3Ge Droplets

Haque¹,

Mullis²

2017

Crystals

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Abstract:The congruently melting, single phase, L1 2 intermetallic β-Ni 3 Ge has been subject to rapid solidification via drop-tube processing. Four different cooling rates are used in this process, at very low cooling rates (≥850 µm diameter particles, ≥700 K s −1 ) and slightly higher cooling rates (850-500 µm diameter particles, 700-1386 K s −1 ) the dominant solidification morphology, revealed after etching, is that of isolated spherulites in an otherwise featureless matrix. At higher cooling rates, (500-300 µm diameter particles, 1386-2790 K s −1 and (300-212 µm diameter particles, 2790-4600 K s −1 ) mixed spherulite and dendritic morphologies are observed. Indeed, at the higher cooling rate dendrites with side-branches composed of numerous small spherulites are observed. Selected area diffraction analysis in the TEM indicate that the formation of spherulites is due to an order-disorder transformation. Dark-field TEM imaging has confirmed that the spherulites appear to consist of lamellae of the ordered phase, with disordered material in the space between the lamellae. The lamellar width within a given spherulite is constant, but the width is a function of cooling rate, with higher cooling rates giving finer lamellae. As such, there are many parallels with spherulite growth in polymers.

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Spherulitic branching in the crystallization of liquid selenium

Cited by 81 publications

References 23 publications

Ultrafast spherulitic crystal growth as a stress-induced phenomenon specific of fragile glass-formers

Ultrafast spherulitic crystal growth as a stress-induced phenomenon specific of fragile glass-formers

Geological pattern formation by growth and dissolution in aqueous systems

Morphology of Spherulites in Rapidly Solidified Ni3Ge Droplets

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