Crystal growth and classical nucleation theory (original) (raw)
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Nucleation in Lithium Disilicate Glass: A Test of Classical Theory by Quantitative Modeling
Journal of the American Ceramic Society, 1991
Published data on the kinetics of crystal nucleation in lithium disilicate glass are analyzed using a numerical simulation based on classical nucleation theory. With a reasonable set of materials parameters, a quantitative fit is possible to all measured data, including those showing transient behavior in single-stage or multistage anneals. The fitting constitutes a comprehensive test of classical nucleation theory, which, even in the simple form used here, is found to be capable of quantitative prediction. The numerical simulation will be of use in developing heat treatments for glassceramics.
New insights on the thermodynamic barrier for nucleation in glasses: The case of lithium disilicate
Journal of Non-Crystalline Solids, 2005
An analysis is performed of the temperature dependence of the thermodynamic barrier to nucleation, W*(T), calculated from a fit of lithium disilicate glass data to the classical theory of nucleation. It is shown that, in order to obtain a satisfactory agreement between experimental and theoretical determinations of W*(T), lower values must be assigned to both the thermodynamic driving force and the surface energy as compared with the corresponding macroscopic values. This finding is consistent with theoretical considerations taking into account the effect that, in general, both the bulk and surface properties of the critical nuclei differ considerably from the respective properties of the newly evolving macroscopic phases. In addition, an anomalous increase of W*(T) with decreasing temperature is found near the glass transition interval. This increase is interpreted as a result of the effect of elastic strain on the thermodynamic driving force. The values of elastic strain energy estimated from the low temperature behavior of W*(T) are congruent with those calculated using the elastic constants of glass and crystal.
TEM and XRD study of early crystallization of lithium disilicate glasses
Journal of Non-Crystalline Solids, 2003
Numerous researchers have speculated the precipitation of metastable phase(s) in the early stages of crystallization of lithium disilicate glass to explain the large discrepancies between the predictions of the classical nucleation theory (CNT) and experimental data. Therefore, we have investigated the early and intermediate stages of crystallization of three glasses on both sides of the stoichiometric composition through direct observations by transmission electron microscopy (TEM)/selected area electron diffraction (SAED) and X-ray diffraction (XRD). In samples heat-treated at T g ¼ 454°C, two distinct crystalline phases, stable lithium disilicate (LS 2 ) and metastable lithium metasilicate (LS) coexist up to 120 h at 454°C (crystalline fraction <1 vol.%). For longer treatments (240-600 h) only the stable phase (LS 2 ) was observed. These results suggest that in the early stages, simultaneous homogeneous nucleation of both LS and LS 2 takes place. As treatment time and crystallized fraction increase, the relative number of LS crystals decreases. Therefore, the precipitation of the LS phase does not disturb the nucleation of the stable LS 2 phase and thus cannot explain the failure of CNT in predicting the nucleation rates in this glass.
Effects of X-rays on Crystal Nucleation in Lithium Disilicate
Crystal Growth & Design, 2011
The use of synchrotron radiation-based X-ray techniques to follow the evolution of materials in time has become quite common in the past decade. The time domains available depend on which specific technique is used, but broadly speaking one can state that the most time-resolved experiments are performed at a rate of around 1À60 s/frame. Obviously, there are experiments where higher time resolution is required and also can be achieved, but these are not numerous. However, in many cases, it is not required or desirable to carry out experiments with too high a time resolution. Common sense tells us that when studying the drying of, for instance, cement, it is not too sensible to take data at a millisecond time frame rate. The same is true for many studies in catalysis or crystallization. Therefore, in many experiments, for example, hydrothermal synthesis of dense metal oxides catalysts at constant temperature or phase transformation during heating at elevated temperatures, is a sample exposed to the X-ray beam in an approximate energy range 5À20 keV for several minutes or hours.
Scientific Reports
Unraveling detailed mechanism of crystal nucleation from amorphous materials is challenging for both experimental and theoretical approaches. In this study, we have examined two methods to understand the initial stage of crystal precipitation from lithium disilicate glasses using molecular dynamics simulations. One of the methods is a modified exploring method to find structurally similar crystalline clusters in the glass models, enabling us to find three different embryos, such as Li2Si2O5 (LS2), Li2SiO3 (LS) and Li3PO4 (LP), in the 33Li2O·66SiO2·1P2O5 glass (LS2P1), in which P2O5 is added as a nucleating agent. Interestingly, LS2 and LP crystals were found inside the LS2P1 glass while LS crystal appeared on the glass surface, which agrees with experimental observations. The other method is free energy calculation using a subnano-scale spherical crystal embedded in the glass model. This method, which we called Free-Energy Seeding Method (FESM), allows us to evaluate free energy cha...
The failure of the Classical Nucleation Theory at low temperatures resolved
arXiv: Soft Condensed Matter, 2019
A relevant observation about crystal nucleation kinetics in glass-forming substances has been a matter of intense debate for several decades. The Classical Nucleation Theory (CNT) allegedly fails to describe the temperature dependence of the homogeneous crystal nucleation rates below the temperature of maximum nucleation rate. This failure was reported for several glass-forming substances and is known as nucleation "breakdown". Some reasonable explanations for this apparent break have been advanced in the literature, however, the simplest hypothesis has never been tested: that this break is a byproduct of nucleation datasets that have not reached the steady-state regime. In this work, we tested this hypothesis by thoroughly analyzing new and published nucleation data for supercooled Li2Si2O5, BaSi2O5, Na4CaSi3O9, and Na2Ca2Si3O9 liquids, using only datasets for which steady-state conditions (likely) have been reached. For that purpose, we used three restraining conditions:...
Normalized Lithium Growth from the Nucleation Stage for Dendrite‐Free Lithium Metal Anodes
Angewandte Chemie International Edition, 2019
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On the persistence of metastable crystal phases in lithium disilicate glass
Journal of Non-Crystalline Solids, 2000
The formation of metastable crystalline phases in lithium disilicate glass has been a subject of controversy for decades. Recent experimental results mainly obtained via the use of electron microscopy have provided strong evidence for the formation of metastable phases during the early stages of crystallization in this composition, and have initiated a re-examination of this topic. Here, we discuss one aspect of this problem relating to the stability of these non-equilibrium phases when glasses are heated for extended time periods (>100 h) at temperatures in the nucleation regime. Recently, we presented experimental evidence obtained via XRD which indicated that metastable phases do not persist at long times in lithium disilicate glass. This ®nding is in direct contradiction to a result reported earlier which suggests that metastable crystalline phases in lithium disilicate glasses are long-lived and can be detected with the aid of XRD. Presented herein are the results of a systematic experimental investigation addressing the potential sources of this discrepancy, namely, glass preparation procedure, glass composition, and water content. Consistent with the results of our previous investigation, in no instance do we ®nd any XRD evidence for the persistence of metastable phases.