scholarly journals Heterogeneous versus homogeneous crystal nucleation of hard spheres

Soft Matter ◽  
2019 ◽  
Vol 15 (47) ◽  
pp. 9625-9631 ◽  
Author(s):  
Jorge R. Espinosa ◽  
Carlos Vega ◽  
Chantal Valeriani ◽  
Daan Frenkel ◽  
Eduardo Sanz
Keyword(s):  
Nucleation Rate ◽  
Heterogeneous Nucleation ◽  
Cell Walls ◽  
Homogeneous Nucleation ◽  
Hard Spheres ◽  
Crystal Nucleation ◽  
Experimental Measurements ◽  
Homogeneous Crystal

Heterogeneous nucleation at the cell walls may at least partly explain the reported discrepancy between experimental measurements and simulation estimates of the homogeneous nucleation rate.

Crystal Nucleation in Submicron Droplets of Pure Elements

1993 ◽  
Vol 321 ◽  
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.

scholarly journals Dependence of homogeneous crystal nucleation in water droplets on their radii and its implication for modeling the formation of ice particles in cirrus clouds

2017 ◽  
Vol 19 (30) ◽  
pp. 20075-20081 ◽  
Author(s):  
Yuri S. Djikaev ◽  
Eli Ruckenstein
Keyword(s):  
Nucleation Rate ◽  
Ice Nucleation ◽  
Cirrus Clouds ◽  
Crystal Nucleation ◽  
Water Droplets ◽  
Ice Particles ◽  
Homogeneous Crystal

Dependence of the ice-nucleation-rate in water droplets on their radii and temperature is determined by taking into account volume-based and surface-stimulated modes.

Transient Nucleation in Devitrification

1993 ◽  
Vol 321 ◽  
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.

scholarly journals Nucleation in novae

1987 ◽  
Vol 122 ◽  
pp. 547-547
Author(s):  
C. M. Callus ◽  
J. S. Albinson ◽  
A. Evans
Keyword(s):  
Nucleation Rate ◽  
Heterogeneous Nucleation ◽  
Homogeneous Nucleation ◽  
Light Curves ◽  
Dust Grains ◽  
Deep Minimum ◽  
Forming Mechanism ◽  
Rapid Formation ◽  
Order Of Magnitude

The observation of a deep minimum in the light curves of some novae, accompanied by a simultaneous rise in the infrared some weeks after outburst, is attributed to the rapid formation and growth of dust grains in the ejecta (Clayton & Wickramasinghe 1976). The observed nucleation rate J(obs) ~ 10−10 cm−3 s−1 for typical dusty novae, whereas the expected homogeneous nucleation rate J(hom) ~ 6 × 10−26 cm−3 s−1. We suggest that heterogeneous nucleation on ions could be a possible grain forming mechanism. In this case J(het) ~ 3.3 × 10−12 cm−3 s−1, which is within an order of magnitude of the observed nucleation rate.

Amorphous silica coating on α-alumina particles

1995 ◽  
Vol 53 ◽  
pp. 210-211
Author(s):  
J. W. Mellowes ◽  
C. M. Chun ◽  
I. A. Aksay
Keyword(s):  
Amorphous Silica ◽  
Heterogeneous Nucleation ◽  
Homogeneous Nucleation ◽  
Silica Coating ◽  
Full Density ◽  
Optimal Conditions ◽  
Fine Grained ◽  
Alumina Particles ◽  
Complete Mullitization ◽  
Powder Compacts

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.

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

1997 ◽  
Vol 467 ◽  
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.

Numerical Simulation of Solidified Structure Formation of Al-Si Alloy Casting Using Cellular Automaton Method

2008 ◽  
Vol 575-578 ◽  
pp. 154-163 ◽  
Author(s):  
Kenichi Ohsasa ◽  
Kiyotaka Matsuura ◽  
Kazuya Kurokawa ◽  
Seiichi Watanabe
Keyword(s):  
Numerical Simulation ◽  
Cellular Automaton ◽  
Structure Formation ◽  
Nucleation Rate ◽  
Heterogeneous Nucleation ◽  
Big Bang ◽  
Grain Structure ◽  
Alloy Casting ◽  
Undercooled Melt ◽  
Columnar To Equiaxed Transition

For the purpose of the prediction of casting structures, heterogeneous nucleation rate in the undercooled melt of solififying Al-Si alloys were evaluated by comparing experimentally observed macrostructures of solidified ingots with numerically simulated ones. Molten alloys were unidirectionally solidified in an adiabatic mold from a steel chill block located at the bottom of the mold. In the experiment, columnar to equiaxed transition (CET) was observed. A numerical simulation for grain structure formation of the sample ingots was carried out using a cellular automaton (CA) method, and heterogeneous nucleation rate in the solidifying alloys were evaluated by producing the similar structures to experimental ones. An attempt was made to predict the grain structure of conventionally cast ingots using the evaluated heterogeneous nucleation rate. However, the simulation could not predict the structure of ingot with low superheat due to crystal multiplication near the mold wall. The crystal multiplication mechanism, so-called "Big Bang mechanism", was introduced into the simulation and the simulation could predict the grain macrostructure composed of columnar and equiaxed crystals that were similar to experimentally observed one.

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