Surface and volume nucleation and growth in TiO2–cordierite glasses

Fokin, Vladimir M.; Zanotto, Edgar Dutra

doi:10.1016/s0022-3093(99)00007-1

Cited by 47 publications

(33 citation statements)

References 17 publications

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“…100 times faster than that of IMC (39). Surface-enhanced crystal growth of organic glasses contrasts the comparable rates of crystal growth at the free surface and in the interior of metallic and silicate glasses (40)(41)(42)(43).…”

Section: Fast Surface Crystal Growthmentioning

confidence: 89%

Stability of Amorphous Pharmaceutical Solids: Crystal Growth Mechanisms and Effect of Polymer Additives

Sun

Zhu

et al. 2012

AAPS J

135

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Abstract. We review recent progress toward understanding and enhancing the stability of amorphous pharmaceutical solids against crystallization. As organic liquids are cooled to become glasses, fast modes of crystal growth can emerge. One such growth mode, the glass-to-crystal or GC mode, occurs in the bulk, and another exists at the free surface, both leading to crystal growth much faster than predicted by theories that assume diffusion defines the kinetic barrier of crystallization. These phenomena have received different explanations, and we propose that GC growth is a solid-state transformation enabled by local mobility in glasses and that fast surface crystal growth is facilitated by surface molecular mobility. In the second part, we review recent findings concerning the effect of polymer additives on crystallization in organic glasses. Low-concentration polymer additives can strongly inhibit crystal growth in the bulk of organic glasses, while having weaker effect on surface crystal growth. Ultra-thin polymer coatings can inhibit surface crystallization. Recent work has shown the importance of molecular weight for crystallization inhibitors of organic glasses, besides "direct intermolecular interactions" such as hydrogen bonding. Relative to polyvinylpyrrolidone, the VP dimer is far less effective in inhibiting crystal growth in amorphous nifedipine. Further work is suggested for better understanding of crystallization of amorphous organic solids and the prediction of their stability.

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Section: Fast Surface Crystal Growthmentioning

confidence: 89%

Stability of Amorphous Pharmaceutical Solids: Crystal Growth Mechanisms and Effect of Polymer Additives

Sun

Zhu

et al. 2012

AAPS J

135

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“…Because the phenomenon occurs in such diverse materials as amorphous silicon and organic glasses, does it also occur in other materials? Why is it considered absent in metallic (12) and silicate (13)(14)(15) glasses? We first note that the surfaces of some solids are so easily oxidized or otherwise chemically altered that surface-enhanced crystallization might not be easily observed.…”

Section: Implications For Current Models Of Surface-enhanced Crystal mentioning

confidence: 99%

“…Fast crystal growth is known for metallic glasses and amorphous silicon, but the abrupt activation of GC growth is reported only for organic glasses. Surface-enhanced crystal growth occurs in amorphous selenium (9) and silicon (10,11), but is considered nonexistent for metallic (12) and silicate (13)(14)(15) glasses.…”

mentioning

confidence: 99%

Glasses crystallize rapidly at free surfaces by growing crystals upward

Sun

Zhu

Kearns

et al. 2011

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

122

137

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The crystallization of glasses and amorphous solids is studied in many fields to understand the stability of amorphous materials, the fabrication of glass ceramics, and the mechanism of biomineralization. Recent studies have found that crystal growth in organic glasses can be orders of magnitude faster at the free surface than in the interior, a phenomenon potentially important for understanding glass crystallization in general. Current explanations differ for surface-enhanced crystal growth, including released tension and enhanced mobility at glass surfaces. We report here a feature of the phenomenon relevant for elucidating its mechanism: Despite their higher densities, surface crystals rise substantially above the glass surface as they grow laterally, without penetrating deep into the bulk. For indomethacin (IMC), an organic glass able to grow surface crystals in two polymorphs (α and γ), the growth front can be hundreds of nanometers above the glass surface. The process of surface crystal growth, meanwhile, is unperturbed by eliminating bulk material deeper than some threshold depth (ca. 300 nm for α IMC and less than 180 nm for γ IMC). As a growth strategy, the upward-lateral growth of surface crystals increases the system's surface energy, but can effectively take advantage of surface mobility and circumvent slow growth in the bulk. C rystallization is a ubiquitous process, producing countless solids in the natural and man-made world. Glasses and amorphous solids are formed by avoiding crystallization while cooling liquids, condensing vapors, or drying solutions. The solidity of a glass might suggest resistance to crystallization; its very existence implies that crystallization is avoidable. And yet glasses can crystallize, sometimes surprisingly fast. The crystallization of glasses is of interest in many fields for understanding the stability of amorphous materials (1), the fabrication of glass ceramics, and the mechanism of biomineralization, for which crystallization of amorphous solid precursors is considered a key step (2).Recent studies have discovered that different modes of crystal growth can emerge as a liquid is cooled to form a glass (3-8), causing crystal growth fronts to advance at velocities much faster than predicted by standard theories. One such growth mode [the glass-to-crystal (GC) mode] exists in the bulk and can cause an increase of crystal growth rate by a factor of 10 4 with a temperature drop by a few kelvin (3, 4). Another new growth mode occurs at the free surface and can lead to much faster crystal growth than in the bulk (5-8). Although these phenomena have been observed prominently in organic glasses, they may be relevant for understanding glass crystallization in general. These phenomena seem to have counterparts in nonorganic glasses, but differences are also evident. Fast crystal growth is known for metallic glasses and amorphous silicon, but the abrupt activation of GC growth is reported only for organic glasses. Surface-enhanced crystal growth occurs in amorphous selenium ...

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“…As far as we know, internal and surface nucleation rates in the same glass have been measured simultaneously only for a cordierite glass containing 8.1 wt% TiO 2 (which serves as a nucleation catalyst) [110]. Nucleation rates of µ-cordierite crystals at diamond-polished surfaces were estimated by Köster's method from size distributions such as those presented in Fig.…”

Section: Comparison Of Surface and Volume Nucleationmentioning

confidence: 99%

Nucleation and Crystallization Kinetics in Silicate Glasses: Theory and Experiment

Fokin

Yuritsyn

Zanotto

2005

Nucleation Theory and Applications

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All truths are easy to understand once they are discovered; the point is to discover them. Galileo GalileiExperimental data on internal homogeneous crystal nucleation in silicate glasses obtained in the last four decades are analyzed in detail in the framework of the classical nucleation theory (CNT). Despite the fact that reasonable qualitative interpretations of the temperature and time dependences of nucleation rates are given by CNT, it meets with serious problems in their quantitative description. Different reasons for this failure are tested and discussed. The main conclusion is that, in contrast to Gibbs' description of heterogeneous systems, the thermodynamic properties of critical nuclei which, to a large extent, govern nucleation kinetics, generally differ from those of the corresponding macrophase. A number of evidences based on the analysis of both crystal nucleation and growth data are given for a decreased thermodynamic driving force for crystallization and critical nuclei/liquid interfacial energy, as compared with the respective properties of the macro-phase. Special attention is devoted to the widespread and practically important type of heterogeneous nucleation -nucleation on glass surfaces. A comparative analysis of available data on surface and bulk nucleation rate data is performed. IntroductionGlasses can be defined as noncrystalline solids that, in the course of their preparation, undergo a process commonly denoted as glass transition. One of the most important (but not the only) ways of vitrification consists in supercooling a liquid suppressing crystallization. When a liquid is cooled down with sufficiently high rates, crystallization may occur to a very limited degree or be completely absent down to temperatures corresponding to very high viscosities in the range η ≥ 10 13 -10 12 Pa · s ∼ = η(T g ), where T g is defined as the glass transition temperature. Below this temperature, the viscosity is so high that large-scale atomic rearrangements in the system are no longer possible within the time-scale of the experiment, and the structure freezes-in, i.e., the structural rearrangements required to retain the liquid in the appropriate metastable equilibrium state cannot follow any more the changes of temperature. This process of freezing-in of the structure of an undercooled liquid is commonly denoted as glass transition and, as a result, the system is transformed into a glass. Typical glass-forming liquids, such as silicate melts, are commonly characterized by: (i) relatively high viscosities (η > 100 Pa · s) at the melting point (or liquidus), and (ii) a steep increase of the viscosity with decreasing temperature. These properties favor the process of transformation of a liquid into a glass. The above mechanism discussed leads to the conclusion that the glass structure is very similar to that of the parent (undercooled) liquid at temperatures near T g .

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Surface and volume nucleation and growth in TiO2–cordierite glasses

Cited by 47 publications

References 17 publications

Stability of Amorphous Pharmaceutical Solids: Crystal Growth Mechanisms and Effect of Polymer Additives

Stability of Amorphous Pharmaceutical Solids: Crystal Growth Mechanisms and Effect of Polymer Additives

Glasses crystallize rapidly at free surfaces by growing crystals upward

Nucleation and Crystallization Kinetics in Silicate Glasses: Theory and Experiment

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