scholarly journals Formation of ice particles through nucleation in the mesosphere

2021 ◽  
Author(s):  
Kyoko K. Tanaka ◽  
Ingrid Mann ◽  
Yuki Kimura
Keyword(s):  
Heterogeneous Nucleation ◽  
Amorphous State ◽  
Nucleation Theory ◽  
Molecular Cluster ◽  
Classical Nucleation Theory ◽  
Numerical Density ◽  
Nucleation Process ◽  
Dust Grains ◽  
Atmospheric Conditions ◽  
Ice Particles

Abstract. Observations of polar mesospheric clouds have revealed the presence of solid ice particles in the upper mesosphere at high latitudes; however, their formation mechanism remains uncertain. In this study, we investigated the formation process of ice particles through nucleation from small amounts of water vapor at low temperatures. Previous studies that used classical nucleation theory have shown that amorphous solid water particles can nucleate homogeneously at conditions that are present in the mesosphere. However, the rate predictions for water in classical nucleation theory disagree with experimental measurements by several orders of magnitude. We adopted a semi-phenomenological model for the nucleation process, which corrects the evaluation of the molecular cluster formation energy using the second virial coefficient, which agrees with both experiments and molecular dynamics simulations. To calculate the nucleation process, we applied atmospheric conditions for the temperature, pressure, numerical density of dust grains, and cooling rate. The results indicate that homogeneous water nucleation is extremely unlikely to occur in the mesosphere, while heterogeneous nucleation occurs effectively. Dust grains generated by meteor ablation can serve as nuclei for heterogeneous nucleation. We also showed that the ice can form directly in a crystalline state, rather than an amorphous state.

scholarly journals Nucleation Behavior of a Single Al-20Si Particle Rapidly Solidified in a Fast Scanning Calorimeter

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2920
Author(s):  
Qin Peng ◽  
Bin Yang ◽  
Benjamin Milkereit ◽  
Dongmei Liu ◽  
Armin Springer ◽  
...  
Keyword(s):  
Cooling Rate ◽  
Rapid Solidification ◽  
Heterogeneous Nucleation ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Solidification Behavior ◽  
Nucleation Kinetics ◽  
Nucleation Behavior ◽  
Nucleation Undercooling ◽  
Primary Si

Understanding the rapid solidification behavior characteristics, nucleation undercooling, and nucleation mechanism is important for modifying the microstructures and properties of metal alloys. In order to investigate the rapid solidification behavior in-situ, accurate measurements of nucleation undercooling and cooling rate are required in most rapid solidification processes, e.g., in additive manufacturing (AM). In this study, differential fast scanning calorimetry (DFSC) was applied to investigate the nucleation kinetics in a single micro-sized Al-20Si (mass%) particle under a controlled cooling rate of 5000 K/s. The nucleation rates of primary Si and secondary α-Al phases were calculated by a statistical analysis of 300 identical melting/solidification experiments. Applying a model based on the classical nucleation theory (CNT) together with available thermodynamic data, two different heterogeneous nucleation mechanisms of primary Si and secondary α-Al were proposed, i.e., surface heterogeneous nucleation for primary Si and interface heterogenous nucleation for secondary α-Al. The present study introduces a practical method for a detailed investigation of rapid solidification behavior of metal particles to distinguish surface and interface nucleation.

scholarly journals Multistep nucleation of anisotropic molecules

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Kazuaki Z. Takahashi ◽  
Takeshi Aoyagi ◽  
Jun-ichi Fukuda
Keyword(s):  
Phase Transition ◽  
Materials Science ◽  
Orientational Order ◽  
Functional Materials ◽  
Numerical Approach ◽  
Anisotropic Materials ◽  
Nucleation Theory ◽  
Dynamics Simulation ◽  
Molecular Cluster ◽  
Classical Nucleation Theory

AbstractPhase transition of anisotropic materials is ubiquitously observed in physics, biology, materials science, and engineering. Nevertheless, how anisotropy of constituent molecules affects the phase transition dynamics is still poorly understood. Here we investigate numerically the phase transition of a simple model system composed of anisotropic molecules, and report on our discovery of multistep nucleation of nuclei with layered positional ordering (smectic ordering), from a fluid-like nematic phase with orientational order only (no positional order). A trinity of molecular dynamics simulation, machine learning, and molecular cluster analysis yielding free energy landscapes unambiguously demonstrates the dynamics of multistep nucleation process involving characteristic metastable clusters that precede supercritical smectic nuclei and cannot be accounted for by the classical nucleation theory. Our work suggests that molecules of simple shape can exhibit rich and complex nucleation processes, and our numerical approach will provide deeper understanding of phase transitions and resulting structures in anisotropic materials such as biological systems and functional materials.

Molecular Dynamics Simulation of Nano Cluster-Seed Effects on Heterogeneous Nucleation

2009 ◽  
Author(s):  
Donguk Suh ◽  
Seung-chai Jung ◽  
Woong-sup Yoon
Keyword(s):  
Molecular Dynamics ◽  
Heterogeneous Nucleation ◽  
Three Dimensional ◽  
Seed Mass ◽  
Nucleation Theory ◽  
Dynamics Simulation ◽  
Classical Nucleation Theory ◽  
Supersaturation Ratio ◽  
Order Of Magnitude ◽  
Nano Cluster

A three-dimensional heterogeneous nucleation is simulated by classical molecular dynamics, where the Lennard-Jones gas and solid nano cluster-seed molecules have argon and aluminum properties, respectively. All dimensions of the wall are periodic and a soft core carrier gas within the system controls the temperature rise induced by latent heat of condensation. There are three shapes of cluster-seeds being cube, rod, and sphere, three classes of masses, and the simulation took place under nine supersaturation ratios, making a total of 81 calculations. An analysis of variance was performed under a three-way layout to analyze the cluster-seed and supersaturation ratio effects on the system. For supersaturation ratios above the critical value nucleation rates were evaluated, below growth rates, and overall liquefaction rates were each defined and calculated. Results show that the supersaturation ratio dominantly controls all rates, but seed characteristics are important for the growth of the largest cluster under the critical supersaturation ratio. Overall liquefaction increases subject to an escalation of supersaturation ratio and seed mass. However, the significance of the supersaturation ratio for overall liquefaction suggests that thermal diffusion is more dominant than mass interactions for this system. Homogeneous characteristics are also compared with the heterogeneous system to find that though nucleation may occur for an insufficient supersaturation ratio when a seed is within the system, the addition of a seed does not in fact facilitate the increase in rates of the phenomena at high supersaturation ratios. Finally a comparison with the classical nucleation theory asserts a 3 to 4 order of magnitude difference, which is within the lines of deviation when it comes to theory and molecular simulations.

scholarly journals From molecules to dust grains: The role of alumina cluster seeds

2019 ◽  
Vol 15 (S350) ◽  
pp. 245-248
Author(s):  
David Gobrecht ◽  
John M.C. Plane ◽  
Stefan T. Bromley ◽  
Leen Decin ◽  
Sergio Cristallo
Keyword(s):  
Bulk Material ◽  
Spectral Feature ◽  
Chemical Kinetic ◽  
Asymptotic Giant Branch ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Dust Grains ◽  
Alumina Cluster

AbstractAsymptotic Giant Branch (AGB) stars contribute a major part to the global dust budget in galaxies. Owing to their refractory nature alumina (stoichiometric formula AlO) is a promising candidate to be the first condensate emerging in the atmospheres of oxygen-rich AGB stars. Strong evidence for that is supplied by the presence of alumina in pristine meteorites and a broad spectral feature observed around ∼ 13 μm. The emergence of a specific condensate depends on the thermal stability of the solid, the gas density and its composition. The evaluation of the condensates is based on macroscopic bulk properties. The growth and size distribution of dust grains is commonly described by Classical Nucleation Theory (CNT). We question the applicability of CNT in an expanding circumstellar envelope as CNT presumes thermodynamic equilibrium and requires, in practise, seed nuclei on which material can condense. However, nano-sized molecular clusters differ significantly from bulk analogues. Quantum effects of the clusters lead to non-crystalline structures, whose characteristics (energy, geometry) differ substantially, compared to the bulk material. Hence, a kinetic quantum-chemical treatment involving various transition states describes dust nucleation most accurately. However, such a treatment is prohibitive for systems with more than 10 atoms. We discuss the viability of chemical-kinetic routes towards the formation of the monomer (Al2O3) and the dimer (Al4O6) of alumina.

scholarly journals Imaging the Homogeneous Nucleation During the Melting of Superheated Colloidal Crystals

Science ◽  
2012 ◽  
Vol 338 (6103) ◽  
pp. 87-90 ◽  
Author(s):  
Ziren Wang ◽  
Feng Wang ◽  
Yi Peng ◽  
Zhongyu Zheng ◽  
Yilong Han
Keyword(s):  
Phase Transitions ◽  
Homogeneous Nucleation ◽  
Critical Size ◽  
Colloidal Crystals ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Nucleation Process ◽  
Particle Exchange ◽  
Superheat Limit ◽  
Shape And Size

The nucleation process is crucial to many phase transitions, but its kinetics are difficult to predict and measure. We superheated and melted the interior of thermal-sensitive colloidal crystals and investigated by means of video microscopy the homogeneous melting at single-particle resolution. The observed nucleation precursor was local particle-exchange loops surrounded by particles with large displacement amplitudes rather than any defects. The critical size, incubation time, and shape and size evolutions of the nucleus were measured. They deviate from the classical nucleation theory under strong superheating, mainly because of the coalescence of nuclei. The superheat limit agrees with the measured Born and Lindemann instabilities.

Concluding remarks

2015 ◽  
Vol 179 ◽  
pp. 543-547 ◽  
Author(s):  
Allan S. Myerson
Keyword(s):  
Crystallization Process ◽  
Crystal Form ◽  
Nucleation Theory ◽  
Crystal Nucleation ◽  
Classical Nucleation Theory ◽  
Nucleation Process ◽  
Nucleation Mechanisms ◽  
Process Work ◽  
And Control ◽  
Crystallization From Solution

Crystallization from solution is a crucial process used in the manufacture of a wide variety of materials. The first step in the crystallization process is the birth of a new crystalline phase, which is known as nucleation. Nucleation plays a key role in determining the results of any crystallization process with respect to the size, shape and crystal form obtained. Classical nucleation theory does not adequately explain the crystal nucleation process. Work described in the literature and at this Faraday Discussion describe more complex nucleation mechanisms which are generally known as two-step nucleation models. In addition, as most nucleation is influenced by dust, dirt and container surfaces, the importance of heterogeneous nucleation and the use of templates to accelerate nucleation and influence crystal form are promising methods for the study and control of nucleation. It is also clear from this Faraday Discussion that interest in this topic has grown, and new and novel experimental and modeling approaches are being used for the study of crystal nucleation from solution.

Thermodynamic and kinetics investigation of homogeneous and heterogeneous nucleation

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Atefeh Khaleghi ◽  
Seyed Mojtaba Sadrameli ◽  
Mehrdad Manteghian
Keyword(s):  
Nucleation Rate ◽  
Heterogeneous Nucleation ◽  
Review Paper ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Homogeneous Part ◽  
Future Studies ◽  
Fundamental Process

AbstractNucleation is a fundamental process widely studied in different areas of industry and biology. This review paper comprehensively discussed the principles of classical nucleation theory (primary homogeneous), and heterogeneous nucleation. In the homogeneous part, the nucleation rate in the transient and intransient state is monitored and also heterogeneous nucleation is covered. Finally, conclusions have been deduced from the collected works studied here, and offers for future studies are proposed.

scholarly journals Heterogeneous Crystal Nucleation from the Melt in Polyethylene Oxide Droplets on Graphite: Kinetics and Microscopic Structure

Crystals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 924
Author(s):  
Muhammad Tariq ◽  
Thomas Thurn-Albrecht ◽  
Oleksandr Dolynchuk
Keyword(s):  
Optical Microscopy ◽  
Polyethylene Oxide ◽  
Heterogeneous Nucleation ◽  
Polarized Light ◽  
Contact Angles ◽  
Nucleation Theory ◽  
Crystal Nucleation ◽  
Classical Nucleation Theory ◽  
Graphite Substrate ◽  
Nucleation Kinetics

It is well known that the crystallization of liquids often initiates at interfaces to foreign solid surfaces. In this study, using polarized light optical microscopy, atomic force microscopy (AFM), and wide-angle X-ray scattering (WAXS), we investigate the effect of substrate–material interactions on nucleation in an ensemble of polyethylene oxide (PEO) droplets on graphite and on amorphous polystyrene (PS). The optical microscopy measurements during cooling with a constant rate explicitly evidenced that the graphite substrate enhances the nucleation kinetics, as crystallization occurred at approximately an 11 °C higher temperature than on PS due to changes in the interactions at the solid interface. This observation allowed us to conclude that graphite induces heterogeneous nucleation in PEO. By employing the classical nucleation theory for analysis of the data with reference to the amorphous PS substrate, the obtained results indicated that the crystal nuclei with contact angles in the range of 100–117° were formed at the graphite interface. Furthermore, we show that heterogeneous nucleation led to a preferred orientation of PEO crystals on graphite, whereas PEO crystals on PS had isotropic orientation. The difference in crystal orientations on the two substrates was also confirmed with AFM, which showed only edge-on lamellae in PEO droplets on graphite compared to unoriented lamellae on PS.

Thermodynamic and Kinetic controls to the ice nucleation rate

2020 ◽  
Author(s):  
Donifan Barahona
Keyword(s):  
Nucleation Rate ◽  
Anthropogenic Activities ◽  
Ice Nucleation ◽  
Nucleation Theory ◽  
Cloud Formation ◽  
Classical Nucleation Theory ◽  
Limited Information ◽  
Atmospheric Conditions ◽  
Theoretical Approaches ◽  
Cloud Models

<p>Ice nucleation is a necessary step for the formation of ice clouds in the atmosphere. It has become clear that its correct representation is critical for the accurate description of atmospheric processes, and for the reliable prediction of the effect of anthropogenic activities on climate. This is accomplished in most cases using empirical models. Although a simple way to parameterize ice nucleation they provide limited information on the nature of ice formation and may not represent all atmospheric conditions.  Theoretical approaches used in cloud models are typically based on the Classical Nucleation Theory (CNT).  There is however a large uncertainty in key parameters of the theory which in most cases are fitted to reproduce observed rates. This talk details recent efforts to go beyond the formulation of CNT to describe ice nucleation. It shows that it is possible to define uncertain parameters like the ice-liquid interfacial tension and the activation energy over a pure thermodynamic basis, hence only as a function of the bulk thermodynamic properties of water. This approach is extended to describe heterogeneous ice nucleation mediated by immersed ice nucleating particles (INPs). It is shown that INPs that significantly reduce the work of ice nucleation also pose strong limitations to the growth of the nascent ice germs. This leads to the onset of a new ice nucleation regime, called spinodal ice nucleation, where the dynamics of ice germ growth instead of the ice germ size determines the nucleation rate. Nucleation in this regime is characterized by an enhanced sensitivity to particle area and cooling rate. Finally a new approach to extract intrinsic nucleation rates from droplet-freezing experiments is used to compare of predicted ice nucleation rates against experimental measurements, for a diverse set of species relevant to cloud formation. This comparison suggests that spinodal ice nucleation may be common in nature, and shows a considerable skill of the new theory in predicting measured ice nucleation rates. </p>

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