Artificial spherulites and related aggregates

Morse, Harry W.; Warren, Charles H.; Donnay, J. D. H.

doi:10.2475/ajs.s5-23.137.421

Cited by 62 publications

(21 citation statements)

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“…A second is a high viscosity in the medium being crystallised. The importance of this has been demonstrated unambiguously by Morse et al [27,28] who, in a study of the crystallisation behaviour of inorganic salts, identified around 70 salts that would crystallise in spherulitic form if grown in a gel, but not otherwise. As with polymers, the spherulite morphology observed by Morse et al was that of a single phase of the salt being precipitated, not a eutectic.…”

Section: (A) (C) (B)mentioning

confidence: 91%

Rapid solidification morphologies in Ni 3 Ge: Spherulites, dendrites and dense-branched fractal structures

Haque

Mullis

2016

Intermetallics

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Single-phase -Ni3Ge has been rapidly solidified via drop-tube processing. At low cooling rates (850 -300 m diameter particles, 700 -2800 K s -1 ) the dominant solidification morphology, revealed after etching, is that of isolated spherulites in an otherwise featureless matrix. At higher cooling rates (300 -75 m diameter particles, 2800 -25000 K s -1 ) the dominant solidification morphology is that of dendrites, again imbedded within a featureless matrix. As the cooling rate increases towards the higher end of this range the dendrites display non-orthogonal side-branching and tip splitting. At the highest cooling rates studied (< 75 m diameter particles, > 25000 K s -1 ), dense-branched fractal structures are observed. Selected area diffraction analysis in the TEM reveals the spherulites and dendrites are a disordered variant of -Ni3Ge, whilst the featureless matrix is the ordered variant of the same compound. We postulate that the spherulites and dendrites are the rapid solidification morphology and that the ordered, featureless matrix grew more slowly post-recalescence. Spherulites are most likely the result of kinetically limited growth, switching to thermal dendrites as the growth velocity increases. It is extremely uncommon to observe such a wide range of morphologies as a function of cooling rate in a single material.

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Section: (A) (C) (B)mentioning

confidence: 91%

Rapid solidification morphologies in Ni 3 Ge: Spherulites, dendrites and dense-branched fractal structures

Haque

Mullis

2016

Intermetallics

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“…The second is a high viscosity in the medium being crystallized. Morse et al [29,30] demonstrated this in a comparative study of the crystallisation of 70 salts, showing that crystallization to spherulites only occurred for growth in a gel based media. The requirement for a high viscosity in the melt would be consistent with the propensity for glass forming alloys, but not other metallic melts, to crystallise to spherulitic morphologies.…”

Section: Introductionmentioning

confidence: 89%

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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“…The noise has been discretized as described in Ref 55. Its amplitude scales with the spatial and time steps, with the temperature and the film thickness as follows: 6) where the primed quantities are for the actual simulation, and those without prime belong to a reference state, in which the noise amplitude was ζ.…”

Section: The Noisementioning

confidence: 99%

“…They are observed in a wide range of metallurgical alloys, in pure Se [2,3], in oxide and metallic glasses [4,5], mineral aggregates and volcanic rocks [6,7], polymers [1,8], liquid crystals [9], simple organic liquids [10], and diverse biological molecules [11]. Many everyday materials, ranging from plastic grocery bags to airplane wings and cast iron supporting beams for highway bridges, are fabricated by freezing liquids into polycrystalline solids containing these structures.…”

Section: Introductionmentioning

confidence: 99%

Growth and form of spherulites

et al. 2005

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Many structural materials (metal alloys, polymers, minerals, etc.) are formed by quenching liquids into crystalline solids. This highly non-equilibrium process often leads to polycrystalline growth patterns that are broadly termed 'spherulites' because of their large-scale average spherical shape. Despite the prevalence and practical importance of spherulite formation, only rather qualitative concepts of this phenomenon exist. The present work explains the growth and form of these fundamental condensed matter structures on the basis of a unified field theoretic approach. Our phase field model is the first to incorporate the essential ingredients for this type crystal growth: anisotropies in both the surface energy and interface mobilities that are responsible for needle-like growth, trapping of local orientational order due to either static heterogeneities (impurities) or dynamic heterogeneities in highly supercooled liquids, and a preferred relative grain orientation induced by a misorientation-dependent grain boundary energy. Our calculations indicate that the diversity of spherulite growth forms arises from a competition between the ordering effect of discrete local crystallographic symmetries and the randomization of the local crystallographic orientation that accompanies crystal grain nucleation at the growth front (growth front nucleation or GFN). The large-scale isotropy of spherulitic growth arises from the predominance of GFN.

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Artificial spherulites and related aggregates

Cited by 62 publications

References 0 publications

Rapid solidification morphologies in Ni 3 Ge: Spherulites, dendrites and dense-branched fractal structures

Rapid solidification morphologies in Ni 3 Ge: Spherulites, dendrites and dense-branched fractal structures

Morphology of Spherulites in Rapidly Solidified Ni3Ge Droplets

Growth and form of spherulites

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