A unified statistical model for indentation pop-in: effects of indenter radius and microstructure density on the transition from homogeneous nucleation to heterogeneous nucleation to bulk plasticity

Mullite (3Al2O32SiO2) can be fabricated by transient viscous sintering using composite particles which consist of inner cores of a-alumina and outer coatings of amorphous silica. Powder compacts prepared with these particles are sintered to almost full density at relatively low temperatures (~1300°C) and converted to dense, fine-grained mullite at higher temperatures (>1500°C) by reaction between the alumina core and the silica coating. In order to achieve complete mullitization, optimal conditions for coating alumina particles with amorphous silica must be achieved. Formation of amorphous silica can occur in solution (homogeneous nucleation) or on the surface of alumina (heterogeneous nucleation) depending on the degree of supersaturation of the solvent in which the particles are immersed. Successful coating of silica on alumina occurs when heterogeneous nucleation is promoted and homogeneous nucleation is suppressed. Therefore, one key to successful coating is an understanding of the factors such as pH and concentration that control silica nucleation in aqueous solutions. In the current work, we use TEM to determine the optimal conditions of this processing.

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Direct Nucleation of Crystalline SiGe on Substrates by Reactive Thermal CVD with Si2H6 and GeF4

MRS Proceedings ◽

10.1557/proc-467-349 ◽

1997 ◽

Vol 467 ◽

Cited By ~ 1

Author(s):

Fumio Yoshizawa ◽

Kunihiro Shiota ◽

Daisuke Inoue ◽

Jun-ichi Hanna

Keyword(s):

Growth Rate ◽

Gas Phase ◽

Heterogeneous Nucleation ◽

Homogeneous Nucleation ◽

Film Growth ◽

Early Stage ◽

Gaseous Mixture ◽

The Other ◽

Thermal Cvd ◽

Initial Deposition

ABSTRACTPolycrystalline SiGe (poly-SiGe) film growth by reactive thermal CVD with a gaseous mixture of Si2H6 and GeF4 was investigated on various substrates such as Al,Cr, Pt, Si, ITO, ZnO and thermally grown SiO2.In Ge-rich film growth, SEM observation in the early stage of the film growth revealed that direct nucleation of crystallites took place on the substrates. The nucleation was governed by two different mechanisms: one was a heterogeneous nucleation on the surface and the other was a homogeneous nucleation in the gas phase. In the former case, the selective nucleation was observed at temperatures lower than 400°C on metal substrates and Si, where the activation of adsorbed GeF4 on the surface played a major role for the nuclei formation, leading to the selective film growth.On the other hand, the direct nucleation did not always take place in Si-rich film growth irrespective of the substrates and depended on the growth rate. In a growth rate of 3.6nm/min, the high crystallinity of poly-Si0.95Ge0.05in a 220nm-thick film was achieved at 450°C due to the no initial deposition of amorphous tissue on SiO2 substrates.

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Crystal Nucleation in Submicron Droplets of Pure Elements

MRS Proceedings ◽

10.1557/proc-321-233 ◽

1993 ◽

Vol 321 ◽

Cited By ~ 3

Author(s):

Louis M. Holzman ◽

Thomas F. Kelly ◽

W. N. G. Hitchon

Keyword(s):

Heterogeneous Nucleation ◽

Homogeneous Nucleation ◽

Crystal Nucleation ◽

Droplet Radius ◽

Electrohydrodynamic Atomization ◽

Submicron Droplets ◽

Diffraction Patterns

ABSTRACTLiquid-to-crystal nucleation has been studied extensively through droplet experiments to locate examples of homogeneous nucleation. However, prior to this work very few examples have been found, which implies that the experiments have not been able to isolate heterogeneous nucleants in a small percentage of the droplets as is required. In this research, electrohydrodynamic atomization (EHD) is used to produce sub-Micron droplets of pure elements that are largely free of heterogeneous nucleants.Diffraction patterns of individual EHD-produced droplets are viewed to determine the fraction of crystalline droplets produced as a function of droplet radius. These results are compared to theories for surface and volume heterogeneous nucleation and for homophase nucleation. It is found that Si and Ge nucleate through either homogeneous nucleation or nucleation by homophase impurities. Nucleation results for vanadium and iron were not conclusive.

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Bubbles and element clusters in rock melts: A chicken and egg problem

10.5194/egusphere-egu21-60 ◽

2021 ◽

Author(s):

Renelle Dubosq ◽

Pia Pleše ◽

Brian Langelier ◽

Baptiste Gault ◽

David Schneider

Keyword(s):

Heterogeneous Nucleation ◽

Homogeneous Nucleation ◽

Growth Dynamics ◽

Gas Bubbles ◽

Atom Probe ◽

Bubble Nucleation ◽

Interface Element ◽

Rich Cluster ◽

Heterogeneous Distribution ◽

Rapid Decompression

<p>The nucleation and growth dynamics of gas bubbles and crystals play a vital function in determining the eruptive behaviour of a magma. Their rate and relative timing, among other factors, are controlled by the magma&#8217;s ascent rate. Investigating the kinetics of decompression-induced degassing and crystallization processes can thus give us insight into the rheology of magmas. For example, the rapid decompression of magmas inhibits microlite crystallization and bubble nucleation during ascent leading to crystallization and degassing at shallow levels. This results in a drastic increase in viscosity and an over pressured system, which can lead to violent eruptions. Although many experiments and numerical simulations of magma decompression have been carried out, nascent and initial bubble nucleation remain poorly understood. It is widely accepted that there are two ways bubbles can nucleate within a melt: heterogeneous (on a pre-existing surface) and homogeneous nucleation (within the melt), where homogeneous nucleation requires a higher volatile supersaturation. It has since been tentatively suggested that homogeneous nucleation is simply a variety of heterogeneous nucleation where nucleation occurs on the surface of submicroscopic crystals. However, evidence of these crystals is equivocal. Thus, we have combined novel 2D and 3D structural and chemical microscopy techniques including scanning transmission electron microscopy (STEM), electron energy-loss spectroscopy (EELS) mapping, and atom probe tomography (APT) to investigate the presence of sub-nanometer scale chemical heterogeneities in the vicinity of gas bubbles within an experimental andesitic melt. The combined STEM and EELS data reveal a heterogeneous distribution of bubbles within the melt ranging between 20-100 nm in diameter, some of which have Fe and/or Ca element clusters at the bubble-melt interface. Element clusters enriched in Fe, Ca, and Na are also observed heterogeneously distributed within the melt. The reconstructed APT data reveals bubbles as low ionic density regions overlain by a Na-, Ca-, and K-rich cluster and heterogeneously distributed Fe clusters within the bulk of the melt. Based on these observations, our data demonstrate the existence of nano-scale chemical heterogeneities within the melt and at the bubble-melt interface of bubbles that were previously interpreted to be nucleated homogeneously within the melt, therefore contributing to the proposed hypothesis that homogeneous nucleation could in fact be a variety of heterogeneous nucleation. These results highlight the need to redefine homogeneous nucleation and revisit whether bubbles or crystals occur first within volcanic melts.&#160;</p>

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Desequilibres entre phases solides et fluides mineraux dans la petrogenese

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.s7-iv.2.157 ◽

1962 ◽

Vol S7-IV (2) ◽

pp. 157-164 ◽

Cited By ~ 1

Author(s):

Georges Deicha

Keyword(s):

Crystal Growth ◽

Solid Solutions ◽

Heterogeneous Nucleation ◽

Homogeneous Nucleation ◽

Fluid Solution ◽

Secondary Intervention ◽

The Moment

Abstract The importance of phenomena conditioned by the disequilibrium between gases, liquids, or magmas, and solid minerals is discussed. Four modes of crystal growth are capable of causing the precipitation of a crystalline species in a supersaturated or supercooled fluid solution. In homogeneous nucleation crystallization occurs at the moment when saturation is reached and only in the presence of preformed crystals of the same species. Germinal nucleation occurs when crystallization develops in conditions of disequilibrium causing the formation of minerals of the same composition but of different structure. Crystals of this mode are twinned. Metastable nucleation involves the formation of a species different in structure from the stable crystal which developed after twinning. In heterogeneous nucleation crystallization of a species has its beginning on the surface of another crystal. This introduces impurities which inhibit nucleation and crystal growth. Secondary intervention of liquid or solid solutions in the rocks also produces phenomena equally effected by disequilibrium.

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A model for the simultaneous heterogeneous and homogeneous nucleation of gas bubbles

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1979.0133 ◽

1979 ◽

Vol 368 (1734) ◽

pp. 331-343 ◽

Cited By ~ 3

Keyword(s):

Heterogeneous Nucleation ◽

Homogeneous Nucleation ◽

Bubble Nucleation ◽

Rate Theory ◽

Rare Gases ◽

Bubble Density ◽

Competitive Mechanism ◽

The Matrix ◽

Arrhenius Energy ◽

First Time

Electron microscope observations of cavities in steels have shown that they are often associated with microstructural features as well as occurring randomly in the matrix. Previous theoretical studies of gas bubble nucleation have concentrated on either homogeneous or heterogeneous nucleation. In the present work we extend the homogeneous nucleation rate theory for rare gases in solids to include, for the first time, the competitive mechanism of heterogeneous nucleation. The model indicates that the temperature dependence of the bubble density varies as the binding energy between a trap and a single gas atom is changed, and provides an interpretation of the high Arrhenius energy found from observed cavity densities.

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Transient Nucleation in Devitrification

MRS Proceedings ◽

10.1557/proc-321-223 ◽

1993 ◽

Vol 321 ◽

Cited By ~ 2

Author(s):

A. L. Greer

Keyword(s):

Classical Theory ◽

Heterogeneous Nucleation ◽

Glass Formation ◽

Homogeneous Nucleation ◽

Amorphous Solids ◽

Crystal Nucleation ◽

Transient Effects ◽

Interphase Interface ◽

Transient Nucleation ◽

Important Test

ABSTRACTA review is given of transient crystal nucleation in glassy or amorphous solids. The types of behaviour are surveyed. It is shown that the kinetics can be quantitatively modelled and that the matching of experiment and theory provides an important test of the classical theory. Examples are considered of homogeneous nucleation (affecting glass formation), heterogeneous nucleation, and nucleation at an interphase interface. While the emphasis is on transient effects of the kind implicit in the classical theory, it is shown that transients can arise for other reasons as well, thus potentially complicating the interpretation of experiments.

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Non-equilibrium freezing behaviour of aqueous systems

Philosophical Transactions of the Royal Society of London Series B Biological Sciences ◽

10.1098/rstb.1977.0036 ◽

1977 ◽

Vol 278 (959) ◽

pp. 167-189 ◽

Cited By ~ 225

Keyword(s):

Heterogeneous Nucleation ◽

Homogeneous Nucleation ◽

Living Cells ◽

Crystalline Form ◽

Model Systems ◽

Aqueous Systems ◽

Melting Points ◽

Simultaneous Representation ◽

Thermodynamic Factors ◽

Non Equilibrium

The tendencies to non-equilibrium freezing behaviour commonly noted in representative aqueous systems derive from bulk and surface properties according to the circumstances. Supercooling and supersaturation are limited by heterogeneous nucleation in the presence of solid impurities. Homogeneous nucleation has been observed in aqueous systems freed from interfering solids. Once initiated, crystal growth is often slowed and, very frequently, terminated with increasing viscosity. Nor does ice first formed always succeed in assuming its most stable crystalline form. Many of the more significant measurements on a given system can be combined and displayed in the form of a ‘supplemented phase diagram’, the latter permitting the simultaneous representation of thermodynamic and non-equilibrium properties. The diagram incorporates equilibrium melting points, heterogeneous nucleation temperatures, homogeneous nucleation temperatures, glass transition and devitrification temperatures, recrystallization temperatures, and, where appropriate, solute solubilities and eutectic temperatures. Taken together, the findings on model systems aid the identification of the kinetic and thermodynamic factors responsible for the freezing - thawing survival of living cells.

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The Physical Chemistry of Inoculation of Cast Iron

MRS Proceedings ◽

10.1557/proc-34-99 ◽

1984 ◽

Vol 34 ◽

Cited By ~ 2

Author(s):

M. A. Gadd ◽

G. H. J. Bennett

Keyword(s):

Physical Chemistry ◽

Cast Iron ◽

Theoretical Analysis ◽

Heterogeneous Nucleation ◽

Homogeneous Nucleation ◽

Silicate Formation ◽

Graphite Growth

ABSTRACTA theoretical analysis of inoculation shows that homogeneous nucleation of CaO, CaS, Al2O3 and ZrO2 is possible arid subsequent heterogeneous nucleation of silicates yields substrates for graphite growth. Excessive silicate growth leading to separation of nuclei could result in fade.Results show that CaO/CaS embyros are most effective via silicate formation, Zr and Al control fade arido xidation enhances inoculation and fade. Added stable oxides give only limited inoculation.

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Роль гетерогенной нуклеации в активации клеток крови

Физика твердого тела ◽

10.21883/ftt.2020.01.48725.46ks ◽

2020 ◽

Vol 62 (1) ◽

pp. 20

Author(s):

И.В. Приходько ◽

Г.Т. Гурия

Keyword(s):

Heterogeneous Nucleation ◽

Blood Cells ◽

Homogeneous Nucleation ◽

Characteristic Time ◽

Nucleation Theory ◽

Receptor System ◽

Exogenous Ligands ◽

Activation Conditions ◽

Kinetics Of ◽

Theory Framework

The processes of receptors clustering on the surface of blood cells are considered in the nucleation theory framework. In the absence of ligands, the characteristic time of homogeneous nucleation of receptors clustering was assumed to be much longer than a cell's life. By varying the kinetics of the bonds' formation and breaking during receptor clustering, it was possible to describe the activation conditions experimentally observed for several types of blood cells. It was shown that the heterogeneous nucleation characteristic time leading to receptors clustering in the presence of exogenous ligands can be less than one minute. Parametric diagrams are constructed that display the effect of a number of examined ligands on the receptor system. The possible clinical significance of the results is discussed.

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