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The large discrepancy among the nucleation kinetics extracted from experimental measurements and computer simulations and the prediction of the classical nucleation theory (CNT) has stimulated intense arguments about its origin in the past decades, which is crucially relevant to the validity of the CNT. In this paper, we investigate the atomistic mechanism of the nucleation in liquid Al in contact with amorphous substrates with atomic-level smooth/rough surfaces, using molecular dynamics (MD) simulations. This study reveals that the slightly distorted local fcc/hcp structures in amorphous substrates with smooth surfaces can promote heterogeneous nucleation through a structural templating mechanism, and on the other hand, homogeneous nucleation will occur at a larger undercooling through a fluctuation mechanism if the surface is rough. Thus, some impurities, previously thought to be impotent, could be activated in the homogeneous nucleation experiments. We further find that the initial growth of the nucleus on smooth surfaces of amorphous substrates is one order of magnitude faster than that in homogeneous nucleation. Both these factors could significantly contribute to the discrepancy in the nucleation kinetics. This study is also supported by a recent study of the synthesis of high-entropy alloy nanoparticles assisted with the liquid metal Ga [Cao et al., Nature 619, 73 (2023)]. In this study, we established that the boundary existed between homogeneous and heterogeneous nucleation, i.e., the structural templating is a general mechanism for heterogeneous nucleation, and in its absence, homogeneous nucleation will occur through the fluctuation mechanism. This study provides an in-depth understanding of the nucleation theory and experiments. [ABSTRACT FROM AUTHOR]

We investigate the nucleation dynamics of the three-dimensional random field Ising model under an external field. We use umbrella sampling to compute the free-energy cost of a critical nucleus and use forward flux sampling for the direct estimation of nucleation rates. For moderate to strong disorder, our results indicate that the size of the nucleating cluster is not a good reaction coordinate, contrary to the pure Ising model. We rectify this problem by introducing a coordinate that also accounts for the location of the nucleus. Using the free energy barrier to predict the nucleation rate, we find reasonable agreement, although deviations become stronger as disorder increases. We attribute this effect to cluster shape fluctuations. We also discuss finite-size effects on the nucleation rate. [ABSTRACT FROM AUTHOR]

Zinc–nickel coatings based on the zinc-enriched gamma phase exhibit the maximum corrosion resistance and form the basis of the production of highly electrocatalytically active nanoporous nickel by selective dissolution. The electrodeposition of Zn–Ni alloys is the most widely used method of their preparation which proceeds by the mechanism of anomalous codeposition, where the deposition rate of the electropositive component (nickel) is lower as compared with the electronegative component (zinc). To obtain coatings of the particular morphology, chemical and phase composition, it is necessary to know the kinetics of the cathodic deposition of Zn–Ni alloys in the stage of heterogeneous nucleation, which is the goal of this study. The kinetics of this process is studied in non-stirred ammonium chloride electrolytes using the methods of cyclic voltammetry and chronoamperometry. The mechanism of heterogeneous nucleation at the electrodeposition of zinc and nickel is determined using the approach proposed by Palomar-Pardavé et. al which takes into account the contributions to the total cathodic current made by the parallel reaction of hydrogen reduction and the electric double layer charging. The nucleation mechanism for zinc–nickel coatings is described using the model of Scharifker–Hills for the electrodeposition of binary alloys additionally modified by taking into account the experimentally determined dependence of the composition of zinc–nickel coatings on the time in the stage of cathodic nucleation of the deposit. Using the method of energy-dispersive X-ray spectroscopy, the anomalous character of the deposition of Zn–Ni coatings is confirmed, where the ratio of atomic fractions Ni/Zn turns out to be lower than the ratio of concentrations of ions Ni2+/Zn2+ in the electrolyte. It is found that both during the electrodeposition of zinc and nickel from their individual solutions and during their anomalous codeposition, the nucleation rate constant increases with an increase in the cathodic potential but in average does not exceed 3 s–1, which points to the predominantly progressive nucleation. The growth of the new phase, regardless of its chemical composition, is limited by the 3D-diffusion of zinc and nickel ions to the electrode surface. The nucleation site density depends weakly on the deposition potential, decreasing with the transition from zinc to nickel and zinc–nickel alloys. As expected, the contribution of the side reaction of hydrogen reduction is the maximum for nickel electrocrystallization and decreases with the transition to Zn–Ni alloys and zinc, increasing with an increase in the cathodic potential, in agreement with the values of current efficiency. [ABSTRACT FROM AUTHOR]

Failure initiation and subsequent crack trajectory in heterogeneous materials, such as functionally graded materials and bones, are yet insufficiently addressed. The AT1 phase field model (PFM) is investigated herein in a 1D setting, imposing challenges and opportunities when discretized by h- and p-finite element (FE) methods. We derive explicit PFM solutions to a heterogeneous bar in tension considering heterogeneous E(x) and G Ic (x) , necessary for verification of the FE approximations. G Ic (x) corrections accounting for the element size at the damage zone in h-FEMs are suggested to account for the peak stress underestimation. p-FEMs do not require any such corrections. We also derive and validate penalty coefficient for heterogeneous domains to enforce damage positivity and irreversibility via penalization. Numerical examples are provided, demonstrating that p-FEMs exhibit faster convergence rates comparing to classical h-FEMs. The new insights are encouraging towards p-FEM discretization in a 3D setting to allow an accurate prediction of failure initiation in human bones. [ABSTRACT FROM AUTHOR]

The complex interplay between competing phase stabilities of FCC, L12, BCC, and B2 phases in the Al0.25CoFeNi (7Al-31Co-31Fe-31Ni in at. %) high entropy alloy (HEA) leads to non-classical phase transformation pathways and resultant novel microstructures. Specifically, the competition between the homogenous precipitation of L12 and heterogenous precipitation of BCC/B2 can be studied at a temperature of 500 °C in the Al0.25CoFeNi alloy. Upon isothermally annealing the single FCC phase microstructure of this HEA at 500 °C up to 50 h, the transformation initiates with the formation of a transient ordered L12 phase with minor Ni–Al enrichment, which is far-from equilibrium, as revealed by atom probe tomography, and can be considered non-classical nucleation. The near equilibrium L12 phase eventually replaces the transient L12 during continued annealing at the same temperature. However, the resultant FCC + L12 microstructure is metastable because the true equilibrium for the Al0.25CoFeNi alloy at 500 °C is a mixture of L12 + B2 phases, as revealed by solution thermodynamics modeling. The higher nucleation barrier for the BCC-based ordered B2 phase coupled with the slower kinetics at 500 °C leads to the homogeneous precipitation of L12, while the B2 phase appears to sluggishly grow from grain boundaries acting as heterogeneous nucleation sites. [ABSTRACT FROM AUTHOR]

This diagram depicts the generation process of the core–shell structure Prussian blue material in this paper:Under the influence of introduced H+ ions, Fe(CN) 6 4- decomposes to yield Fe2+, benefiting from the excellent chelating properties of IDHA to protect the generated Fe2+ from oxidation. As the MnHCF surface, is rich in nucleation sites, the ions chelated after nucleation transfer to the MnHCF surface. Upon dissociation under the influence of H+, heterogeneous nucleation occurs on the surface. [Display omitted] In recent years, core–shell structured Prussian Blue Analogues (PBAs) have been considered as highly promising cathode materials for sodium-ion batteries. Reducing production costs and simplifying the preparation method for core–shell PBAs have also become crucial considerations. This paper presents a novel approach for the first time: by acid-treating the as-synthesized solution from a simple coprecipitation reaction, a high-crystallinity, sodium-rich Mn2+-doped iron hexacyanoferrate (Fe/MnHCF) shell material is self-grown on the surface of manganese hexacyanoferrate (MnHCF). This method significantly improves the electrochemical properties of the MnHCF material. The core–shell structured PBA exhibits excellent cycling performance (with a capacity retention of 95.5 % for 400 cycles at 1 A/g) and high rate performance (134.2mAh/g@10 mA/g, 95.2mAh/g@1 A/g). In this article, we explore the growth mechanism of the high-sodium content, high-crystallinity shell structure and introduce a green chelating agent that is better suited for the crystallization of Mn and Fe-type PBA systems. Our study demonstrates that Mn2+ doping enhances the conductivity of the shell material. Meanwhile, the heterojunction structure of MnHCF@Fe/MnHCF conducive to charge separation and migration. This straightforward synthesis strategy offers a novel approach for fabricating high-performance core–shell structured Prussian Blue Analogue materials. [ABSTRACT FROM AUTHOR]

• Limitations of applying theory to predict heterogeneous ice nucleation are discussed. • Models for describing ice nucleation on a surface are reviewed. • Experimental methods for nucleation measurements are analyzed. • Statistical analysis techniques for freezing delay data is discussed. • Machine learning models for heterogeneous ice nucleation are reviewed. The freezing of water on surfaces is an important phase change process with an outsized influence in both natural and engineered systems. Liquid water below the melting temperature can persist for a finite time in a metastable, supercooled state until freezing initiates through nucleation, a process enhanced by the presence of a surface. Despite the importance of this phenomenon, current methods remain inadequate to predict ice nucleation rates across surface types, and experimental data is difficult to compare due to the differing methodologies used, limiting further understanding. This review synthesizes established frameworks modeling ice nucleation and analyzes limitations in applying classical nucleation theory toward quantitative prediction. Simplified, theory-inspired models used to describe the nucleation rate as a function of temperature are discussed. Additionally, models describing how the ice nucleation rate may vary across a surface are compared. Current experimental methods for measuring ice nucleation rates on surfaces are assessed for their ability to produce accurate data that can lead to greater consistency between studies. Variability in results based on factors such as humidity and triple interface effects are discussed. Statistical analysis approaches for experimental freezing data are reviewed. Experimental observations of nonstationary ice nucleation in an unexpectedly large time scale are discussed in the context of experimental methods. Finally, the potential of emerging machine learning techniques to aid in predicting heterogeneous ice nucleation is discussed. [Display omitted] [ABSTRACT FROM AUTHOR]

Simultaneous deoxidation of Al/Ti in steel was performed to analyze the TiS-containing inclusions, TiS single inclusions and Al2O3(or TixOy)-TiS two-layered inclusions were observed in the steel smaple. Density functional theory calculations were performed to study the structures and properties of the intermediate products of TiS before critical nucleation, and the nucleation mechanism of TiS in Al/Ti simultaneously deoxidized steel was discussed based on homogeneous and heterogeneous nucleation modes. The results show that the TiS nucleation is controlled by the formation of (TiS)n clusters; the homogeneous nucleation of TiS inclusions in the steel can only occur using (TiS)n clusters with n ≥ 4, whereas the heterogeneous nucleation of (TiS)n clusters on the surfaces of Al2O3 and Ti2O3 can occur using all the (TiS)n clusters. As a result, the inclusions of Al2O3 and Ti2O3 can act as effective sites to induce the heterogeneous nucleation of TiS inclusions in steel. The Gibbs free energy change values for the (TiS)n clusters formed on the Ti2O3 surface were lower than those on the Al2O3 surface, and the mismatch values of Ti2O3(001)-TiS(001) interface were smaller than those of Al2O3(001)-TiS(001) interface. Thus, TiS inclusions formed more easily on the surface of Ti2O3 than on Al2O3. [ABSTRACT FROM AUTHOR]

Herein origin and nucleation kinetics of transcrystalline layer (TCL) in bamboo fiber deposited with nano‐TiO2 (BF@TiO2)/polypropylene (PP) composite is studied. Firstly, the surface morphology, roughness, and energy, as well as crystalline structure (e. g., crystal face indices (hkl)) of BF@TiO2 are analyzed to clarify the origin of TCL in the composite. Subsequently, the nucleation kinetics of TCL in BF@TiO2/PP composite at different crystallization temperatures (Tc) are investigated through polarized optical microscopy. The results find that the surface roughness and energy of BF@TiO2 increase by 47.55 % and 2.41 % compared with untreated BF, respectively. Interestingly, the mismatch rates (MRs) of hkl(BF) vs. hkl(PP) are >320 %. In comparison, the MRs of (101)(BF@TiO2)TiO2 vs. (hkl)(PP) are dramatically decreased to <25 %, suggesting a similar crystal plane between BF@TiO2 and PP matrix. These results indicate that the TCL formation in the composite is more facile in BF@TiO2 than in the untreated BF. During isothermal crystallization, the nucleation and spherulite growth rates decrease as the Tc increases. The interface free energy difference (▵σ) between BF@TiO2 and PP is calculated based on the heterogeneous nucleation theory. The ▵σ is 1.54±0.11 J cm−2, highlighting that the BF@TiO2 strongly induces the PP nucleation. [ABSTRACT FROM AUTHOR]

The NaP zeolite with excellent crystallinity and adsorption performance was obtained by adopting the Na2SiO3 and NaAlO2 from coal fly ash as the raw materials. As the synthesis condition of aging for 0.5 h at 30ηC and crystalizing for 8 h at 120ηC with n(H2O)/n(SiO2) = 116, n(Na2O)/n(SiO2) = 1.4, and n(SiO2)/n(Al2O3) = 2.8, NaP zeolite owned higher crystallinity (98.98%) and spherical morphology (~2.78 μm). During the crystallization, the nucleation/ growth kinetics was calculated to survey the crystallization mechanism via the theoretical calculation and characterization methods. The diffusion of reactants in the solid--liquid-phase interface was dominant, wherein the heterogeneous nucleation and solid-phase transformation were also proposed based on the fitting results of Avarami--Erofeev and simple kinetic equations. The activation energy results of nucleation (En, 27.67 kJ/mol) and growth (Eg, 13.31 kJ/mol) demonstrated that the induced nucleation period was the critical step during the crystallization. Hence, the method of rapid nucleation was introduced and the induced nucleation time was shortened 50% (from ~2.0 to ~1.0 h) as the crystal seed was added. Moreover, the grain size of NaP-Seed zeolite reduced to ~2.02 μm. Meanwhile, the synthesized NaP zeolite adsorbent was employed for the removal of phenol compound fromthe aqueous solution.Under the synergistic effect of electrostatic interaction and pore filling effect, NaP zeolite exhibited better adsorption with the removal rate of 82.63% (pH = 5.0 and 40 min) and stability in the five consecutive cycles. [ABSTRACT FROM AUTHOR]

Polarization switching in ferroelectric hysteresis of BaTiO3 proceeds by localized nucleation and subsequent growth of domains of reverse polarization. While this process is driven by the applied electric field, thermal activation can play an important role in domain nucleation. As a consequence of the stochastic nature of thermal activation, coercive fields in small systems exhibit a significant scatter. It is demonstrated that the statistics of coercive fields observed in molecular dynamics simulations is consistent with the statistical distribution expected for field-assisted thermally activated nucleation of reverse polarization domains. The excellent quantitative agreement between the simulation data and the theory of thermally activated processes provides strong evidence that polarization switching occurs by nucleation-and-growth rather than loss of the local minimum of the Gibbs free energy function. In a pristine crystal, switching is controlled by the field at which thermal fluctuations can create a critical nucleus in the bulk (homogeneous nucleation). The analysis of crystals with various vacancy-type defects demonstrates that such defects may enable heterogeneous nucleation at reduced fields. In both cases, the statistical analysis gives access to the respective activation energies, their field dependence, and the sizes of the critical nuclei. [ABSTRACT FROM AUTHOR]

Methane hydrate formation is analytically studied in the presence of the water memory effect using the classical nucleation theory. The memory effect is introduced as a change in nucleation site from a three-dimensional heterogenous nucleation on a solid surface with cap-shaped hydrate clusters (3D-HEN) to a two-dimensional nucleation on the solid hydrate residue surface with monolayer disk-shaped hydrate clusters (2D-NOH). The analysis on the stationary nucleation of methane hydrate under isobaric conditions shows that the memory effect caused an average decrease of 4.4 K in metastable zone width, or subcooling. This decrease can be erased at higher dissociation temperatures (ΔT > 17.2 K) due to a decrease in the concentration of 2D-NOH nucleation sites. Moreover, the probability of hydrate formation is estimated for the purpose of quantifying risk associated with methane hydrate formation in the presence of the memory effect. [ABSTRACT FROM AUTHOR]

Previous laboratory measurements suggest that ammonium sulfate crystals (AS, (NH4)2SO4) are efficient ice‐nucleating particles under cirrus conditions. Sulfate particles not completely neutralized by ammonium are less well studied and include two other solids, ammonium bisulfate (AHS, NH4HSO4) and letovicite (LET, (NH4)3H(SO4)2). In this work, we have obtained the first comprehensive data set for the heterogeneous ice nucleation ability of crystallized particles in the AS–LET–AHS system as a function of their degree of neutralization at a temperature of about 220 K. Quantitative data on nucleation onsets, ice‐active fractions, and ice nucleation active surface site densities were derived from expansion cooling experiments in a large cloud chamber and measurements with two continuous flow diffusion chambers. We found a strong dependence of the efficiency and the mode of heterogenous ice nucleation on the degree of neutralization. Ice formation for AS, mixed AS/LET, and LET crystals occurred by the deposition nucleation or pore condensation and freezing mode. The lowest nucleation onset was observed for AS, where 0.1% of the particles became ice‐active at an ice saturation ratio of 1.25. This threshold gradually increased to 1.35 for LET, and abruptly further to 1.45 for mixed LET/AHS crystals, which partially deliquesced and induced ice formation via immersion freezing. Pure AHS crystals did not form due to the inhibition of efflorescence. Our data allow for a more sophisticated treatment of ice formation in the AS–LET–AHS system in future model simulations, which have so far only considered the available data for AS alone. Plain Language Summary: Sulfate particles that are partially or fully neutralized by ammonium are an important component of the atmospheric aerosol. The relative humidity in the environment determines whether they are present as aqueous solution droplets or as solid crystals. Depending on the degree of neutralization, three different crystalline solid phases can form: ammonium sulfate, (NH4)2SO4, letovicite, (NH4)3H(SO4)2, and ammonium bisulfate, NH4HSO4. Knowledge of the phase state of the particles (i.e., aqueous or solid) is required because it affects a variety of important atmospheric processes, including light scattering, chemical reactions, and cirrus cloud formation. Cirrus ice crystals can form heterogeneously on solid particles and homogeneously in supercooled aqueous solution droplets. Heterogeneous ice formation by solid (NH4)2SO4 particles has been well studied in the laboratory, while much less is known about the ice nucleation ability of the other two solids involved. We performed experiments in a large coolable cloud chamber at a temperature of about 220 K to derive a parameterization for the heterogeneous ice nucleation ability of particles in the (NH4)2SO4–(NH4)3H(SO4)2–NH4HSO4 system as a function of their composition. This enables a differentiated treatment of this particle class in future model simulations of cirrus cloud formation. Key Points: The heterogeneous ice nucleation ability of crystalline, ammoniated sulfate particles strongly depends on the degree of neutralizationAmmonium sulfate, letovicite (LET), and their mixtures efficiently form ice by deposition nucleation or pore condensation and freezing at 220 KMixtures of LET and ammonium bisulfate partially deliquesce and nucleate ice less efficiently by immersion freezing at 220 K [ABSTRACT FROM AUTHOR]

The simulation of heat changes resulting from phase transitions can help to interpret differential scanning calorimetry (DSC) measurements, e.g. of metallic alloy systems in which multiple reactions overlap during non-isothermal heat treatments. So far, simulated DSC curves mostly exhibit sharp reaction peaks as commonly just one mean energy value for a certain type of nucleation site is assumed. This work proposes an efficient model for treating heterogeneous nucleation site energy variations within the framework of classical nucleation theory (CNT). The site energies are assumed to vary according to a Rayleigh distribution and a scaling function. The effect on the nucleation behavior of precipitates is studied. A consideration of the distribution of heterogeneous site energies has the potential to significantly smoothen the numerical treatment of precipitation processes compared to the non-distributed case. The comparison to previously published simulations of DSC curves during the cooling of an AA6005 aluminum alloy demonstrates the advantages of this extension, especially for slow cooling rates. [ABSTRACT FROM AUTHOR]

Using a hierarchy of three sigmoid growth models with increasing complexity, i.e., number of parameters, we reanalyzed kinetic data for heterogeneous nucleation—the number of nuclei N(t) vs. time t—from archetypical experiments on the electrodeposition of mercury on platinum by I. Markov and E. Stoycheva, to obtain two scales: Nmax and τ. The universal character of the studied phenomenon was revealed when replotting the original data as α ≡ N(t)/Nmax vs. t/τ. Yet the simplest model, the recently introduced α21 model which is aimed to describe diffusion-limited growth in 2D, α21 = tanh2(2t/τ21), fits all datasets with an R2 ≥ 0.989. This can be rationalized by attracting the non-classical notion of two-step nucleation—the nuclei form in a metastable phase which, in this case, grows on the electrode surface. Beyond the universality, we find the dependence of the two obtained scales on the overvoltage, which is increased systematically from 83 to 88 mV to generate the six N(t) datasets for each of the two electrode types—planar and hemispherical. Surprisingly, for one of them, the planar electrode, there is a discontinuity in the dependence—an almost horizontal jump from 85 to 86 mV, while for the hemispherical electrode, τ decreases smoothly. [ABSTRACT FROM AUTHOR]

Biological ice nucleation plays a key role in the survival of cold-adapted organisms. Several species of bacteria, fungi, and insects produce ice nucleators (INs) that enable ice formation at temperatures above -10 °C. Bacteria and fungi produce particularly potent INs that can promote water crystallization above -5 °C. Bacterial INs consist of extended protein units that aggregate to achieve superior functionality. Despite decades of research, the nature and identity of fungal INs remain elusive. Here, we combine ice nucleation measurements, physicochemical characterization, numerical modeling, and nucleation theory to shed light on the size and nature of the INs from the fungus Fusarium acuminatum. We find ice-binding and ice-shaping activity of Fusarium IN, suggesting a potential connection between ice growth promotion and inhibition. We demonstrate that fungal INs are composed of small 5.3 kDa protein subunits that assemble into ice-nucleating complexes that can contain more than 100 subunits. Fusarium INs retain high ice-nucleation activity even when only the ~12 kDa fraction of size-excluded proteins are initially present, suggesting robust pathways for their functional aggregation in cell-free aqueous environments. We conclude that the use of small proteins to build large assemblies is a common strategy among organisms to create potent biological INs. [ABSTRACT FROM AUTHOR]

A physical understanding of the progression from flow‐driven (quasi‐static) poromechanical deformation to dynamic fault rupture is critical to the resilient operations of several engineering systems. These processes are bridged by a progression from fault reactivation to the spontaneous nucleation of unstable sliding. Toward addressing this challenge, novel automatic time step size control methods are developed to enable accurate and efficient simulation of these dynamics and transitions from the first principles. The controllers combine local models for discretization error and Coulomb failure conditions to automatically adjust the time step size across several orders of magnitude. The methods do not require additional empirical or theoretical input and can resolve the pre‐rupture, interseismic, and seismic periods to the allowed accuracy. The computational results reveal that the proposed methods automatically capture the onset of reactivation and nucleation for homogeneous and heterogeneous fields. Hydrodynamic and structural heterogeneity lead to disparate critical nucleation sizes compared to those predicted by theory. The results highlight its potential in predicting induced seismicity in realistic subsurface engineering systems and at practical scales. Key Points: Automatic time step controller to resolve flow, fault reactivation, and coseismic rupture under geologic complexity from first principlesSimultaneous local error control and monitoring of rupture progression to adapt the simulation time scale across seven orders of magnitudeSimulations (multiphase flow and inertial mechanics) of complex scenarios show alternative approaches can be significantly inaccurate [ABSTRACT FROM AUTHOR]

Modeling deformation twin nucleation in magnesium has proven to be a challenging task. In particular, the absence of a heterogeneous twin nucleation model which provides accurate energetic descriptions for twin-related structures indicates a need to more deeply understand twin energetics. To address this problem, molecular dynamics simulations are performed to follow the energetic evolution of { 10 1 ‾ 2 } tension twin embryos nucleating from an asymmetrically-tilted grain boundary. The line, surface and volumetric terms associated with twin nucleation are identified. A micromechanical model is proposed where the stress field around the twin nucleus is estimated using the Eshelby formalism, and the contributions of the various twin-related structures to the total energy of the twin are evaluated. The reduction in the grain boundary energy arising from the change in character of the prior grain boundary is found to be able to offset the energy costs of creating the other interfaces. The defect structures bounding the stacking faults that form inside the twin are also found to possibly have significant energetic contributions. These results suggest that both of these effects could be critical considerations when predicting twin nucleation sites in magnesium. [ABSTRACT FROM AUTHOR]

The effect of Ce content (0–1.6 wt.%) on the modification of Mg 2 Si phase in the as-cast Mg-5Al-2Si alloy was investigated. The original Chinese script type Mg 2 Si phase was refined distinctly and transformed to dispersive block shape gradually by adding Ce element. The length of Chinese script type Mg 2 Si phase was reduced from 110 to 50 µm with increasing Ce content to 1.6 wt.%. The results calculated by Pandat software indicated that the added Ce element first combined with Si to form CeSi 2 phase, which could serve as the heterogeneous nucleation of Mg 2 Si phase due to the small lattice mismatch of 7.97%. The modification of Mg 2 Si phase was mainly attributed to the facts that Ce changed the growth steps of Mg 2 Si phase and CeSi 2 promoted the nucleation of Mg 2 Si phase. With increasing Ce content from 0 wt.% to 1.6 wt.%, the YS, UTS and EL at 150 °C were improved from 67.7 MPa, 91.2 MPa and 1.6% to 84.2 MPa, 128 MPa and 7.5%, respectively. [ABSTRACT FROM AUTHOR]

As a new form of energy with substantial potential, natural gas hydrate will play a crucial strategic role in the future due to its vast reserves and broad industrial application prospects. To better comprehend the nucleation and growth mechanism of clathrate hydrate, an enhanced thermodynamic model was proposed based on the wall roughness model and nucleation theory. In general, we discovered that the nucleation of hydrate on a smooth wall surface conforms to the conclusion of classical nucleation theory. However, curvature and surface roughness are frequently characterized by hydrophilicity's inhibition of hydrate and hydrophobicity's enhancement. The specific situation is more complex and requires specific analysis and discussion. Nonetheless, this also explains the uneven distribution of hydrate nucleation induction time. Our research reveals a fundamental method for designing or manipulating the heterogeneous nucleation of hydrates. We foresee promising applications in hydrate‐related technologies based on the fractal structure of the substrate's surface. [ABSTRACT FROM AUTHOR]

Volcanic eruptions are driven by bubbles that form when volatile species exsolve from magma. The conditions under which bubbles form depend mainly on magma composition, volatile concentration, presence of crystals, and magma decompression rate. These are all predicated on the mechanism by which volatiles exsolve from the melt to form bubbles. We critically review the known or inferred mechanisms of bubble formation in magmas: homogeneous nucleation, heterogeneous nucleation on crystal surfaces, and spontaneous phase separation (spinodal decomposition). We propose a general approach for calculating bubble nucleation rates as the sum of the contributions from homogeneous and heterogeneous nucleation, suggesting that nucleation may not be limited to a single mechanism prior to eruption. We identify three major challenges in which further experimental, analytical, and theoretical work is required to permit the development of a general model for bubble formation under natural eruption conditions. We review the mechanisms of bubble formation in magma and summarize the conditions under which the various mechanisms are understood to operate. Bubble formation mechanisms may evolve throughout magma ascent as conditions change such that bubbles may form simultaneously and sequentially via more than one mechanism. Contributions from both homogeneous nucleation and heterogeneous nucleation on multiphase crystal phases can be captured via a single equation. Future work should focus on constraining macroscopic surface tension, characterizing the microphysics, and developing a general framework for modeling bubble formation, via all mechanisms, over natural magma ascent pathways. [ABSTRACT FROM AUTHOR]

The heterogeneous nucleation of ice is an important atmospheric process facilitated by a wide range of aerosols. Drop-freezing experiments are key for the determination of the ice nucleation activity of biotic and abiotic ice nucleators (INs). The results of these experiments are reported as the fraction of frozen droplets fice(T) as a function of decreasing temperature and the corresponding cumulative freezing spectra Nm(T) computed using Gabor Vali's methodology. The differential freezing spectrum nm(T) is an approximant to the underlying distribution of heterogeneous ice nucleation temperatures Pu(T) that represents the characteristic freezing temperatures of all INs in the sample. However, Nm(T) can be noisy, resulting in a differential form nmT that is challenging to interpret. Furthermore, there is no rigorous statistical analysis of how many droplets and dilutions are needed to obtain a well-converged nm(T) that represents the underlying distribution Pu(T). Here, we present the HUB (heterogeneous underlying-based) method and associated Python codes that model (HUB-forward code) and interpret (HUB-backward code) the results of drop-freezing experiments. HUB-forward predicts fice(T) and Nm(T) from a proposed distribution Pu(T) of IN temperatures, allowing its users to test hypotheses regarding the role of subpopulations of nuclei in freezing spectra and providing a guide for a more efficient collection of freezing data. HUB-backward uses a stochastic optimization method to compute nm(T) from either Nm(T) or fice(T). The differential spectrum computed with HUB-backward is an analytical function that can be used to reveal and characterize the underlying number of IN subpopulations of complex biological samples (e.g., ice-nucleating bacteria, fungi, pollen) and to quantify the dependence of these subpopulations on environmental variables. By delivering a way to compute the differential spectrum from drop-freezing data, and vice versa, the HUB-forward and HUB-backward codes provide a hub to connect experiments and interpretative physical quantities that can be analyzed with kinetic models and nucleation theory. [ABSTRACT FROM AUTHOR]

Crystallization initiated at interfaces is a ubiquitous phenomenon, covering both simple liquids and polymer melts. Understanding the physical process underlying interface‐induced crystallization in polymers is of fundamental interest and is relevant for many applications, especially for films of functional semicrystalline polymers. Interface‐induced crystallization of liquids can proceed either by heterogeneous nucleation or by the less explored equilibrium phenomenon of prefreezing. This study reports recent progress in the theoretical and experimental investigation of the effect of substrate‐material interactions on the thermodynamic properties of prefreezing and on the kinetics of heterogeneous nucleation in model polymers on different flat substrates. Through a combination of various microscopy and scattering techniques, supported by theoretical analysis, a detailed picture of the two different phenomena of interface‐induced crystallization in polymers is achieved. [ABSTRACT FROM AUTHOR]

Powder Bed Fusion of Metals using a Laser Beam (PBF-LB/M) has proven to be a competitive manufacturing technology to produce customized parts with a high geometric complexity. Due to process-specific characteristics, such as high cooling rates, the microstructural features can be tailored. This offers the possibility to locally control the mechanical properties. Therefore, the grain structure has to be reliably predicted at first. The starting point of the grain formation and the growth process is characterized by the nucleation. Over the course of this study, various nucleation theories were applied to the PBF-LB/M process and their suitability was evaluated. The two Sc-modified aluminum alloys Scalmalloy® and Scancromal® were processed with a novel experimental PBF-LB/M setup. By performing melt pool simulations based on the Finite Element Method (FEM), the input data for the nucleation models were obtained. The simulatively predicted nucleation zones based on the different theories were compared to real metallographic images and to literature results. It was found that the phenomenological approach should be used whenever no first-time-right prediction of the simulation is necessary. The physically based models with the heterogeneous nucleation should be applied if a first-time-right prediction is striven for. For applications in PBF-LB/M, the nucleation models should be extended in terms of the influence of precipitates and the high cooling rates during the manufacturing process. The presented approach may be used to further assess grain nucleation models for various additive manufacturing processes. [ABSTRACT FROM AUTHOR]

In metal halide perovskites, charge transport in the bulk of the films is influenced by trapping and release and nonradiative recombination at ionic and crystal defects. Thus, mitigating the formation of defects during the synthesis process of perovskites from precursors is required for better device performance. An in-depth understanding of the nucleation and growth mechanisms of perovskite layers is crucial for the successful solution processing of organic–inorganic perovskite thin films for optoelectronic applications. In particular, heterogeneous nucleation, which occurs at the interface, must be understood in detail, as it has an effect on the bulk properties of perovskites. This review presents a detailed discussion on the controlled nucleation and growth kinetics of interfacial perovskite crystal growth. Heterogeneous nucleation kinetics can be controlled by modifying the perovskite solution and the interfacial properties of perovskites adjacent to the underlaying layer and to the air interface. As factors influencing the nucleation kinetics, the effects of surface energy, interfacial engineering, polymer additives, solution concentration, antisolvents, and temperature are discussed. The importance of the nucleation and crystal growth of single-crystal, nanocrystal, and quasi-two-dimensional perovskites is also discussed with respect to the crystallographic orientation. [ABSTRACT FROM AUTHOR]

The isothermal crystallization properties of polypropylene/graphite nanosheet (PP/GN) nanocomposites under supercritical N2 were systematically studied by a self-made in situ high-pressure microscope system. The results showed that the GN caused irregular lamellar crystals to form within the spherulites due to its effect on heterogeneous nucleation. It was found that the grain growth rate exhibits a decreasing and then increasing trend with the enhancement of N2 pressure. Using the secondary nucleation model, the secondary nucleation rate for spherulites of PP/GN nanocomposites was investigated from an energy perspective. The increase in free energy introduced by the desorbed N2 is the essential reason for the increase in the secondary nucleation rate. The results from the secondary nucleation model were consistent with those acquired through isothermal crystallization experiments, suggesting that the model can accurately predict the grain growth rate of PP/GN nanocomposites under supercritical N2 conditions. Furthermore, these nanocomposites demonstrated good foam behavior under supercritical N2. [ABSTRACT FROM AUTHOR]

Submerged arc discharge (SAD) is a simple method to produce carbon nanostructures (CNSs). However, its potential cannot be fully exploited because it generates contaminants and unwanted by-products (CUBPs) that are difficult to eliminate. The formation mechanisms of CNSs and CUBPs were investigated by measuring the correlations between the SAD main parameters (current, voltage, power, anode displacement, and sound emission). It was demonstrated that the SAD takes place in a succession of stable and unstable zones that induce homogeneous and heterogeneous nucleation processes, respectively. In the stable zones, carbon vapor jets are generated and induce the appearance of vortices. Both processes stimulate nucleation. From the measurement of the sound emitted by the jets, the dimensions of the discharge channel were determined. These dimensions match the anode crater size measured by scanning electron microscopy. In the unstable zones, vibrations and thermal stress in the anode intensify. Graphite microparticles are released and act as nucleation centers that induce the formation of CUBPs. While most of the discharge elapses in stable zones, the highest fraction of anode erosion occurs in unstable zones. These results made evident that current theoretical models fail to explain the presence of observed impurities because they do not take into account the influence of vibrations and heterogeneous nucleation. The operation of the synthesis device was simulated, and the results obtained reinforce the aforementioned conclusions. The acoustic emission of the SAD allowed obtaining information on the installation operation for the optimization of its design. Based on this information, recommendations were made for the installation design. [ABSTRACT FROM AUTHOR]

The effect of chemical and structural heterogeneity of the melt on heterogeneous nucleation in crystallization of metallic alloys is considered. The appearance of long-range ordering in the melt in the zone adjoining the substrate gives grounds to expect that the substrate should stimulate heterogeneous nucleation. A principally new mechanism of nucleation not requiring compliance between the lattices of the nucleus and of the substrate is suggested for explaining experimental data that contradict the crystallization theory. It is presumed that nuclei may appear in the region of heterogeneity of the melt around the substrate which absorbs atoms of the components lowering the liquidus temperature. Specifically, this mechanism gives an explanation of initiation of austenite nucleation when the steel is modified with interstitial phases. [ABSTRACT FROM AUTHOR]

A suite of generally applicable statistical methods based on empirical bootstrapping is presented for calculating uncertainty and testing the significance of quantitative differences in temperature and/or ice active site densities between ice nucleation temperature spectra derived from droplet freezing experiments. Such experiments are widely used to determine the heterogeneous ice nucleation properties and ice nucleation particle concentration spectra of different particle samples, as well as in studies of homogeneous freezing. Our methods avoid most of the assumptions and approximations inherent to existing approaches, and when sufficiently large sample sizes are used (approximately >150 droplets and >=1000 bootstrap samples in our system), can capture the full range of random variability and error in ice nucleation spectra. Applications include calculation of accurate confidence intervals and confidence bands, quantitative statistical testing of differences between observed freezing spectra, accurate subtraction of the background filtered water freezing signal, and calculation of a range of statistical parameters using data from a single droplet array freezing experiment if necessary. By providing additional statistical tools to the community, this work will improve the quality and accuracy of statistical tests and representations of uncertainty in future ice nucleation research, and will allow quantitative comparisons of the ice nucleation ability of different particles and surfaces. [ABSTRACT FROM AUTHOR]

Both heterogeneous nucleation and flow‐induced entropy reduction are the two well‐known factors that accelerate polymer crystallization. However, the interplay of nucleation and flow‐induced acceleration is still poorly understood. This work investigates the nucleating effect of carbon nanotubes (CNT) on both the quiescent and flow‐induced crystallization kinetics of polyamide 66 (PA 66). The quiescent crystallization study indicates that CNT acts as a powerful nucleant, as suggested by the fact that the critical cooling rate to bypass crystallization and create the amorphous glassy state changes from 1000 K s−1 in PA 66 neat resin to a rate faster than 4000 K s−1 in the PA 66 nanocomposites. The flow‐induced crystallization study indicates PA 66 onset crystallization time and morphology depend on the shear work introduced by rotational rheometry. A combined acceleration effect from CNT nucleants and flow‐induced crystallization (FIC) persists when the CNT loading is under the saturation limit. However, if CNT loading meets the saturation limit, specific shear work shows no impact on the crystallization time, providing evidence that the role of the FIC acceleration effect no longer exists when nucleant acceleration dominates the crystallization of PA 66. [ABSTRACT FROM AUTHOR]

The regularities of nucleation in a model solution of human synovia under conditions close to physiological have been investigated. The constant of the induction process are determined. It is shown that an increase in supersaturation causes a transition from heterogeneous to homogeneous nucleation of crystallites. The critical nucleus size in the pure model system and in the presence of a number of organic additives is estimated. The series in the retarding effect of impurities on the nucleation in a model synovial solution is found to be as follows: glycine → albumin → proline → glucose → citric acid. [ABSTRACT FROM AUTHOR]

Cirrus clouds related to transported dust layers were identified on 22 occasions with ground-based polarization lidar from December 2012 to February 2018 over Wuhan (30.5°N, 114.4°E), China. All the events occurred in spring and winter. Cirrus clouds were mostly located above 7.6 km on top of the aloft dust layers. In-cloud relative humidity with respect to ice (RHi) derived from water vapor Raman lidar as well as from ERA5 reanalysis data were used as criteria to determine the possible ice nucleation regimes. Corresponding to the two typical cases shown, the observed events can be classified into two categories: (1) category A (3 cases), in-cloud peak RHi ⩾ 150%, indicating competition between heterogeneous nucleation and homogeneous nucleation; and (2) category B (19 cases), in-cloud peak RHi < 150%, revealing that only heterogeneous nucleation was involved. Heterogeneous nucleation generally took place during instances of cirrus cloud formation in the upper troposphere when advected dust particles were present. Although accompanying cloud-top temperatures ranged from −51.9°C to −30.4°C, dust-related heterogeneous nucleation contributed to primary ice nucleation in cirrus clouds by providing ice nucleating particle concentrations on the order of 10−3 L−1 to 102 L−1. Heterogeneous nucleation and subsequent crystal growth reduced the ambient RHi to be less than 150% by consuming water vapor and thus completely inhibited homogeneous nucleation. [ABSTRACT FROM AUTHOR]

Stereocomplexation between enantiomeric poly(l -lactide) (PLLA) and poly(d -lactide) (PDLA) is a promising sustainable approach and gaining momentum to overcome the shortcomings of polylactide (PLA) for its use as a replacement for fossil-based plastics. Filler addition in tailoring the crystallization of stereocomplex PLA (SC-PLA) has attracted extensive attention; however, research has primarily focused on the heterogeneous nucleation effect of filler. The impact of filler on the chain behavior of SC-PLA during crystallization has not been exclusively discussed, and the rigid amorphous fraction (RAF) development remains unknown. In this study, the crystallization of PLLA/PDLA blends was modified by low loading of layered double hydroxide (LDH) (≤ 1 wt%) with the proposed local effect of such filler, and additional RAF development was incurred. In the early stage of crystallization, LDH facilitates the pairing of PLLA and PDLA and arrests the ordered SC pairs during the dynamic balance between the separation and pairing of racemic segments. This explains the severely suppressed homochiral (HC) crystallization, promoted SC crystallization, and additional RAF formation driven by the nucleation-induced chain ordering. This work, for the first time, highlights the role of LDH in creating SC-PLA with tailorable polymorphism and RAF, where the mechanism can be extended to other filler-type nucleator systems. [ABSTRACT FROM AUTHOR]

• We have devised an algorithm for calculating electric field forces in the four-point water molecule model named efieldTIP4P algorithm in LAMMPS. • The formation of cubic ice structures could be a potential reason for extending the nucleation duration. • An electric field of 0.05 V/Å exhibits a substantial capability to realign the water molecules and thus reduce the energy barrier by nearly 50 %. In this study, molecular dynamics simulations on the LAMMPS platform were used to investigate heterogeneous ice nucleation of water molecules based on the TIP4P/Ice-Water molecular model. We have developed a method for calculating electric field force for the TIP4P model, revealing distinct outcomes in the absence and presence of an electric field. In the absence of the electric field, both single and mixed ice structures are observed as final states. In contrast, the introduction of an electric field exclusively leads to the formation of a single ice structure, effectively reducing the energy barrier associated with heterogeneous nucleation. Importantly, this study highlights the significant impact of the electric field, resulting in the controlled formation of a specific ice structure and a pronounced reduction in the energy barrier for non-homogeneous nucleation. These findings provide valuable insights for the freezing industry, offering theoretical guidance for optimizing the freezing process. The developed method for electric field force calculation, specifically tailored to the TIP4P water molecule model, contributes to advancing our understanding of the complex dynamics in ice nucleation and holds promise for practical applications in controlled freezing environments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Surface charge impacts wettability and ice nucleation by regulating interfacial water structure. • Hexagonal rings in the first water layer are key for surface-induced ice nucleation. • Surface ice nucleation rate isn't solely predicted by the order in the first water layer. • Ice nucleation rate relates to the order in the second water layer. Understanding the complex microscopic mechanisms of heterogeneous ice nucleation is crucial across diverse fields from cloud science to microbiology. In this work, we examined the ability of solid surfaces to promote ice nucleation as a function of the structural order of interfacial water, including the first and second hydration layers. Comprehensive all-atom molecular dynamics simulations using the TIP4P/ice water model were conducted on a water film atop a modeled surface inspired by the (0 0 0 1) surface of AgI crystal, with varying surface charges. These simulations revealed non-monotonic nucleation rates. The first hydration layer formed a hexagonal hydrogen-bond network resembling ice structures, exhibiting low mobility essential for inducing ice nucleation. Notably, the second hydration layer, acting as a key-point bridge, displayed varying degrees of orientational preference facilitated by inter-layer hydrogen bonds. The calculation of fluctuation parameters indicated that the greater structural order of the second layer significantly enhances the surface's ice-forming capabilities. Unlike previous studies that focused primarily on the role of the first layer of interfacial water, our findings demonstrate that the second layer provides a more accurate indicator of ice nucleation capabilities. [ABSTRACT FROM AUTHOR]

We investigate the atomization behavior of burning stable water-in-oil microemulsion droplets. The microemulsion compositions are prepared by altering the dispersed phase volume fraction (ϕ) and base oils (dodecane, xylene, and surrogate (90% dodecane and 10% xylene) by weight). The combustion of base oil follows classical droplet combustion, while two-stage combustion, i.e., classical droplet combustion and atomization-dominated combustion, is observed for emulsion droplets. We reveal that vapor bubble formation occurs primarily through heterogeneous nucleation, and the mechanisms leading to bubble formation can be accurately predicted and controlled for distinct, highly stable emulsions. During the initial phase of combustion, water vapor bubbles nucleate, while the nucleation of oil vapor is more prevalent in the later phase of combustion due to the depletion of water content. In both regimes, heterogeneous nucleation ensues due to the agglomeration of surfactant inside the burning droplet. The lower volatility and viscous nature of the oil inhibit the growth rate of the nucleated oil-vapor bubble within the oil–surfactant mixtures. On the contrary, the water vapor bubble exhibits a higher growth rate within the emulsion droplet, attributed to its higher volatility and low viscosity. We show that qualitatively, the global bubble dynamics associated with the emulsion droplets remain substantially consistent regardless of ϕ and the type of base oil. However, it is observed that the onset of nucleation, bubble growth and collapse cycles, and the size of secondary droplets display a strong dependence on the ϕ and the type of base oil. The normalized diameter at the onset of nucleation increases as ϕ increases, exhibiting a logarithmic trend. The optimal dispersed phase volume fraction for effective atomization is found to be ϕ = 0. 2 , regardless of the type of microemulsion. • The atomization behavior of burning stable water-in-oil microemulsion droplets is explored. • The mechanisms associated with the nucleation of vapor bubbles in stable emulsion droplet combustion are revealed. • The effect of dispersed phase volume fraction and type of base oil on the onset of nucleation and bubble dynamics is discussed. [ABSTRACT FROM AUTHOR]

• The puffing phenomenon is discussed in detail by categorizing it into three different modes. • The critical boundary conditions for the different phase transitions of the droplet are analyzed. • An improved vaporization model for the bi-component droplet is developed. • The boiling sub-models consider the effects of fuel viscosity and surface tension. • The model can quantitatively reproduce the bubble number and bubble size within the droplet. With the increasing use of blended fuels, the vaporization process of mixed droplets imposes new requirements on classical droplet vaporization models, highlighting the urgent need for the development of a broadly applicable multi-component fuel droplet vaporization model. In this study, the boiling characteristics of n-heptane/n-hexadecane two-component mixed droplets with different physical properties were experimentally studied under wide ambient temperatures and initial mass fractions. The droplet boiling mainly involves two phenomena, i.e., puffing and micro-explosion. Based on the experimental observations, the puffing phenomenon is further refined and categorized into weak puffing, foam puffing, and strong puffing. Then, the analysis of the influence of initial conditions on the boiling modes was conducted. Furthermore, a droplet vaporization model was constructed according to the experimental data, which includes droplet evaporation, droplet boiling, and bubble point sub-models. The new model considers the effects of fuel viscosity and surface tension and makes improvements to the heterogeneous nucleation and bubble break-up sub-models, reducing the dependence on empirical parameters. The resistance terms were introduced in the heterogeneous nucleation sub-model to prevent the nucleation rate from reaching its upper limit. The relationship between the initial disturbance and the Ohnesorge number in the break-up sub-model was summarized. Based on the above improvements, an updated method for calculating the boiling mass rate was proposed. The results indicate that the vaporization model can effectively replicate droplet lifetime and diameter evolution under different mixing fractions and wide ambient temperatures. [Display omitted] [ABSTRACT FROM AUTHOR]

A fine and equiaxed solidification process delivers multidimensional benefits to Mg-alloys, such as improved castability, reduced casting defects, enhanced mechanical properties, increased corrosion resistance and potential for increased recycled contents. Despite extensive research on grain refinement of Mg-alloys in the last few decades, currently, there is no effective grain refiner available for refining Mg-Al alloys, and our current understanding of grain refining mechanisms is not adequate to facilitate the development of effective grain refiners. Under the EPSRC (UK) LiME Hub's research program, substantial advances have been made in understanding the early stages of solidification covering prenucleation, heterogeneous nucleation, grain initiation and grain refinement. In this paper, we provide a comprehensive overview of grain refinement of Mg-alloys by native MgO particles. We show that native MgO particles can be made available for effective grain refinement of Mg-alloys by intensive melt shearing regardless of the alloy compositions. More importantly, we demonstrate that (1) the addition of more potent exogenous particles will not be more effective than native MgO; and (2) MgO particles are difficult to be made more impotent for grain refinement through promoting explosive grain initiation. We suggest that the most effective approach to grain refinement of Mg-alloys is to make more native MgO particles available for grain refinement through dispersion, such as by intensive melt shearing. [ABSTRACT FROM AUTHOR]

Large amounts of dust aerosols are lifted to the upper troposphere every year and play a major role in cirrus formation by acting as efficient ice nuclei. However, the relative importance of heterogeneous nucleation and spontaneous homogenous nucleation in dust-related cirrus clouds is still not well evaluated globally. Here, based on spaceborne observations, we propose a method to identify two ice-nucleating regimes of dust-related cirrus clouds, i.e., (1) the sole presence of heterogeneous nucleation and (2) competition between heterogeneous and homogeneous nucleation, by characterizing the relationship between dust ice-nucleating particle concentrations (INPCs) calculated from the Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) using the POlarization LIdar PHOtometer Networking (POLIPHON) method and in-cloud ice crystal number concentration (ICNC) from the DARDAR (lidar–radar) dataset. Two typical cirrus cases over central China are shown as a demonstration. In the first case, the upper part (near the cloud top) of a series of cirrus clouds successfully realized the INPC–ICNC closure, meaning that solely heterogeneous nucleation takes place, while the lower part of cirrus clouds showed the possible competition between heterogeneous and homogeneous nucleation. In the second case, the ICNCs in the cirrus cloud dramatically exceeded the dust INPCs in the vicinity by more than an order of magnitude, revealing that besides dust-induced heterogeneous nucleation, homogeneous nucleation also participated in ice formation and produced additional ice crystals. The proposed identification method is anticipated to apply in the evaluation of the influence of upper-troposphere dust on global cirrus formation and the investigation of the potential positive role of cirrus cloud thinning in the offset of climate warming. [ABSTRACT FROM AUTHOR]

Heterogeneous nucleation and grain initiation are two different processes in early-stage solidification (ESS), although both are deterministic. Heterogeneous nucleation refers to the formation of a 2-dimensional (2D) nucleus (a crystal plane of the solid) that can template further growth, while grain initiation is the formation of a hemispherical cap (3D) from which isothermal growth is possible. It is both theoretically and practically beneficial to separate heterogeneous nucleation from grain initiation. This paper provides an overview of our recent understanding of grain initiation behaviour under different conditions and its consequences on grain refinement. After a brief review of the processes involved in the ESS, we present the grain initiation behaviour on a single substrate. This is followed by grain initiation behaviour in systems with a population of nucleant particles with varying particle types (corresponding to varying nucleation undercoolings), where we give detailed descriptions of progressive grain initiation, explosive grain initiation, hybrid grain initiation, grain initiation maps and grain refinement maps. We then provide a brief introduction to the rules that govern competition for heterogeneous nucleation and grain initiation among multiple types of nucleant particles with varying particles' nucleation undercoolings and sizes. Finally, we present the practical implications of grain refinement maps to grain refinement. A key finding from this work is that more significant grain refinement can be achieved by promoting explosive grain initiation using impotent nucleant particles, which is opposite to the traditional approach for grain refinement where potent particles are used to enhance heterogeneous nucleation. [ABSTRACT FROM AUTHOR]

This paper reviews the role of void nucleation, growth, and coalescence on the spall failure process in light metals. Based on the review of the open literature, the preponderance of evidence show that void nucleation, growth, and coalescence are prevalent in light metals such as HCP magnesium and FCC aluminum alloys. The as-received microstructure and its evolution play a crucial role on how voids nucleate, grow, and coalesce. Nucleation of voids in these light metals and metallic alloys can be either homogeneous and heterogeneous but at high enough stresses, both homogeneous and heterogeneous nucleation can be activated simultaneously. Secondary phase particles and intermetallics can strongly influence spall failure, through matrix-precipitate/intermetallic debonding or precipitate/intermetallic cracking during shock compression. Studying spall failure through modeling has proven to be an invaluable tool in developing a fundamental understanding of void nucleation, growth, coalescence, and consequent spall failure. However, since new alloys are currently been developed, more experimental and modeling research are needed to further understand how spall failure initiate and grow in these new alloys. [ABSTRACT FROM AUTHOR]

Prenucleation refers to the phenomenon of substrate-induced atomic ordering in the liquid adjacent to the liquid/substrate interface at temperatures above the nucleation temperature. We investigated the effects of the physical and chemical properties of the substrate on prenucleation, using the classical molecular dynamics (MD) and ab initio MD simulations. We found that the physical origin of prenucleation is structural templating, which is affected significantly by the lattice misfit between the solid and the substrate, chemical interaction between the solid and the substrate, and the substrate surface roughness at the atomic level. Prenucleation ultimately determines the nucleation potency of a substrate and provides a precursor for heterogeneous nucleation at the nucleation temperature. In this paper, we provide an overview of the recent advances in the understanding of prenucleation made by the LiME Research Hub. After a brief review of the historical research on atomic ordering at the liquid/substrate interface in the literature, we present an overview of the recent advances in understanding prenucleation, covering the concept of prenucleation, the effect of temperature, lattice misfit and substrate chemistry, and substrate surface roughness at the atomic level. Our discussions will be focused on the effect of prenucleation on heterogeneous nucleation and its consequences on grain refinement. [ABSTRACT FROM AUTHOR]

During solidification of metallic materials, heterogeneous nucleation occurs on substrates, either endogenous or exogenous. The potency of the substrates for nucleation is mainly dependent upon the atomic arrangements on the substrate surface, which are affected by the lattice misfit between the substrate and the nucleated solid, the surface roughness at atomic scale, and the chemical interaction between the substrates and the melt. Extensive examinations on metal/substrate (M/S) interfaces at atomic scale by the state-of-the-art aberration (Cs) corrected STEM and associated EDS and EELS have shown that alloying elements in liquid melts tend to segregate at the interfaces, leading to the formation of various 2-dimensional compounds (2DCs) or 2-dimensional solutions (2DSs), depending upon segregation behavior of the elements. For instance, Al3Ti 2DC and Ti2Zr 2DC at the Al/TiB2 interface, Y2O3 2DC at the Mg/MgO interface, and a Si-rich 2DS layer at Al-Si/TiB2 interface have been identified. Such interfacial segregations significantly affect nucleation potency of the substrates, resulting in either promoting or impeding the heterogeneous nucleation process during solidification. In this paper, we present an overview of the current studies of interfacial segregation behavior, the structure and chemistry of interfaces, and their impacts on the subsequent heterogeneous nucleation and grain initiation processes. Our focus is on the advances made in the understanding of the mechanisms for nucleation and grain refinement. It is demonstrated that it is feasible to manipulate heterogeneous nucleation by modifying nucleation potency of a substrate through deliberate interfacial segregation of desirable elements, achieving effective control of the grain structure of cast metallic materials. [ABSTRACT FROM AUTHOR]

Prenucleation refers to the phenomenon of atomic ordering in the liquid adjacent to a liquid/solid interface at temperatures above its nucleation temperature. It produces a precursor for heterogeneous nucleation in the liquid and thus has a strong influence on the nucleation process. Oxide particles, including magnesia, spinel, and alumina, are inevitably formed in the liquid during liquid–metal handling and casting. They may act as nucleation sites for potential grain refinement. Knowledge about prenucleation at liquid–metal/oxide (M(l)/oxide) interfaces is important for an understanding of heterogeneous nucleation during casting. Here, we present an overview of the recent studies on the prenucleation at the M(l)/oxide interfaces using ab initio molecular dynamics simulation techniques. We observed a wide variety of interfacial chemistry and identified the formation of an ordered metal layer terminating the oxide substrates, such as MgO{1 1 1} (denoting MgO with {1 1 1} surface termination), α-Al2O3{0 0 0 1}, MgAl2O4{1 1 1} and γ-Al2O3{1 1 1} in liquid light metals. The terminating metal atoms are positively charged and form topologically rough layers, which strongly impact the prenucleation at the interfaces. We suggest modification of nucleation potency of the substrate surfaces via elemental segregation to manipulate the solidification processes. This is demonstrated by the segregation of La atoms at the Al(l)/γ-Al2O3 interfaces. [ABSTRACT FROM AUTHOR]

Our current understanding of heterogeneous nucleation has been largely confined to the classical nucleation theory (CNT) that was postulated over 100 years ago based on a thermodynamic approach. Further advances in heterogeneous nucleation research requires detailed knowledge of atomistic activities at the liquid/substrate interface. In this work, using a classical molecular dynamics (MD) simulation, we investigated the atomistic mechanisms of heterogeneous nucleation in systems with a large lattice misfit (|f| > 12.5%) demonstrated by the liquid Pb and solid Cu system (denoted as the Pb(l)/Cu(s) system) with a misfit of 27.3%. We found that heterogeneous nucleation in systems with a large misfit takes place in two distinctive steps: (1) Prenucleation creates a coincidence site lattice (CSL) on the substrate surface to accommodate the majority (fcsl) of the initial misfit (f) and (2) Heterogeneous nucleation accommodates the residual misfit fr (fr = misfit − fcsl) at the nucleation temperature to create a plane of the new solid phase (a two-dimensional (2D) nucleus) through either a three-layer dislocation mechanism if fr < 0 or a three-layer vacancy mechanism if fr > 0, such as in the case of the Pb(l)/Cu(s) system. [ABSTRACT FROM AUTHOR]

• The enhanced salinity-gradient solar pond with a nucleation matrix aids crystallization of lithium carbonate. • Influences of matrix materials and spatial distribution on crystallization of lithium carbonate were investigated. • Application of an enhanced salinity-gradient solar pond can improve crystallization efficiency of lithium carbonate. • A nucleation matrix should be made of tumbleweed or a nested three-dimensional space. The utilization of salinity-gradient solar ponds (SGSPs) to extract lithium from salt lake brine is one of the most direct and effective uses of solar energy. The Qinghai-Tibet Plateau in China is rich in unique solar energy resources, as well as various types of salt lakes with abundant lithium resources. Among them, Zabuye salt lake in Tibet is a typical lithium-rich carbonate salt lake, and it has successfully realized the industrialization of lithium extraction from brine for the first time by using the SGSP. In recent years, with the continuous improvement of lithium resource market, the demand for lithium has further grown. There are some bottleneck problems restricting the lithium carbonate production in the lithium extraction technology with traditional SGSPs, which must be overcome, such as the slower heating rate, smaller heating amplitude, longer production cycle, lower crystallization efficiency and so on. From the angle of green environmental protection and high-efficiency technology, this research focused on the temperature field and salinity field distribution of the traditional SGSP and the special crystallization behavior of lithium carbonate, and carried out experimental research on process optimization in Zabuye mining area. Based on the heterogeneous nucleation theory, the use of an enhanced SGSP with a nucleation matrix for assisting the crystallization of lithium carbonate was proposed. The change of crystallization behavior of lithium carbonate, the influence of matrix materials and the spatial distribution on the crystallization effect were investigated. The results show that the enhanced SGSP with the nucleation matrix has a significant effect of increasing the production of lithium carbonate, and the lithium mixed salt attached to the nucleation matrix is of a higher grade and a lower moisture content. The yield per unit area of lithium carbonate on the nucleation matrix made of the gauze and plastic net is equivalent to that on the slope and bottom of the solar pond, and the grade of lithium carbonate approaches 80 %. The yield per unit area of lithium carbonate on the nucleation matrix made of tumbleweed is about four times as much as is achieved with other materials and the crystallization exceeds expectations. It is concluded that the application of the enhanced SGSP with the nucleation matrix can improve the crystallization efficiency, the output and the grade of lithium carbonate to a certain extent and this optimization technique will provide an important theoretical basis and application support for green, efficient development of lithium resources from salt lake brine. [ABSTRACT FROM AUTHOR]

Without the addition of any grain refiner, the inclusion particles in a melt will induce heterogeneous nucleation and grain initiation during the solidification of metallic materials. However, with grain refiner addition, the exogenous particles (from the grain refiner) and the native inclusions (e.g., oxide particles) will co-exist in the melt, and there will be competition for nucleation and grain initiation among different types of solid particles. In this paper, we analyze such competition in Al and Mg alloys using a numerical solidification model that we have developed previously. The numerical calculations show that the competition for nucleation is strongly dependent on nucleation undercooling of the different types of particles, while the competition for grain initiation is closely related to the sizes of solid particles. Based on the numerical results, the general rules of competition for nucleation and grain initiation have been developed: nucleation starts with particles of minimum nucleation undercooling, followed by particles with progressively larger nucleation undercooling; and grain initiation starts with solid particles of the largest size, followed by solid particles with progressively smaller sizes. [ABSTRACT FROM AUTHOR]

Recently, we have proposed a new framework for early stages solidification, in which heterogeneous nucleation and grain initiation have been treated as separate processes. In this paper, we extend our atomic-level understanding of heterogeneous nucleation to spherical cap formation for grain initiation on a single substrate using molecular dynamics calculations. We first show that heterogeneous nucleation can be generally described as a three-layer mechanism to generate a two-dimensional (2D) nucleus under a variety of atomic arrangements at the solid/substrate interface. We then introduce the atomistic concept of spherical cap formation at different grain initiation undercoolings (ΔTgi) relative to nucleation undercooling (ΔTn). When ΔTn < ΔTgi, the spherical cap formation is constrained by the curvature of the liquid/solid interface, produces a dormant cap, and further growth is only made possible by increasing undercooling to overcome an energy barrier. However, when ΔTn > ΔTgi, spherical cap formation becomes barrierless and undergoes three distinctive stages: heterogeneous nucleation to produce a 2D nucleus with radius, rn; unconstrained growth to deliver a hemisphere of rN (substrate radius); and spherical growth beyond rN. This is followed by a theoretical analysis of the three-layer nucleation mechanism to bridge between three-layer nucleation, grain initiation and classical nucleation theory. [ABSTRACT FROM AUTHOR]

We investigate crystallization of Lennard-Jones liquids on substrates under dynamic compression with large-scale molecular dynamics simulations. The substrates examined include single crystals and bicrystals with different crystallographic orientations, and the loading paths include shock and quasi-isentropic loading. Microstructure is characterized with simulated x-ray diffraction and orientation mapping. For shock loading, only heterogeneous nucleation occurs at the simulation scales. Quasi-isentropic loading induces less heating and larger supercooling; as a result, heterogeneous nucleation occurs at low loading strengths, and both heterogeneous and homogeneous nucleation occur at high loading strengths, despite the crystalline substrates. Crystallization depends on the substrate structure (crystal orientation and grain boundary) and loading characteristics. Deformation may induce grain structure change (e.g., reorientation and twinning) of substrates and affect subsequent crystallization. Crystallization rate is anisotropic, inversely proportional to the cosine of the dihedral angle between the substrate plane and a main f111g growth plane. [ABSTRACT FROM AUTHOR]