Surface Nucleation Rates Research Articles

Effect of Nucleation Heterogeneity on Mineral Precipitation in Confined Environments

AbstractThe formation of new mineral phases in confined environments, especially in porous media, is crucial for various geological processes like mineralization and diagenesis. The nucleation and precipitation of minerals are initiated at the microscale through fluid‐rock interaction, where dissolution of primary phases leads to supersaturated conditions and nucleation and growth of secondary ones. Previous research has focused primarily on either precipitation or nucleation, without fully exploring their combined impact. Our study introduces a computational framework that integrates classical nucleation theory with the micro‐continuum method. We validated our model by comparing with experiments, and discovered that different surface nucleation rate changes the mode of precipitation from a preferential to uniform precipitate textures. Furthermore, our study uncovered that the conventional deterministic precipitation method tends to underestimate the permeability of the porous matrix. In contrast, the new framework significantly improves model accuracy by incorporating preferential precipitation and heterogeneous nucleation.

Atomistic modeling of surface nucleation in anorthite-based glasses

Surface crystallization is one of the most challenging issues in glass research due to the complexity of understanding small length scale phenomena that occur over long time periods. Hence, experimental studies of surface crystallization are difficult and time-consuming. In this report, the surface nucleation rates of a set of glasses in the anorthite (CaO-Al2O3-SiO2) compositional family are predicted using molecular dynamics to simulate the glass/crystal interface. In addition, the Toy Landscape Model is utilized to predict the temperature dependence of nucleation. Furthermore, sodium was added to the base anorthite composition to test the validity of the methods presented here for more complex compositions. Results are verified from both experimental and computational perspectives. The approach proposed in this work can be used to guide commercial glass development more efficiently.

Revisiting fundamental properties of TiO2 nanoclusters as condensation seeds in astrophysical environments

Context. The formation of inorganic cloud particles takes place in several atmospheric environments, including those of warm, hot, rocky, and gaseous exoplanets, brown dwarfs, and asymptotic giant branch stars. The cloud particle formation needs to be triggered by the in situ formation of condensation seeds since it cannot be reasonably assumed that such condensation seeds preexist in these chemically complex gas-phase environments. Aims. We aim to develop a method for calculating the thermochemical properties of clusters as key inputs for modelling the formation of condensation nuclei in gases of changing chemical composition. TiO2 is used as benchmark species for cluster sizes N = 1–15. Methods. We created a total of 90000 candidate (TiO2)N geometries for cluster sizes N = 3−15. We employed a hierarchical optimisation approach, consisting of a force-field description, density-functional based tight-binding, and all-electron density-functional theory (DFT) to obtain accurate zero-point energies and thermochemical properties for the clusters. Results. In 129 combinations of functionals and basis sets, we find that B3LYP/cc-pVTZ, including Grimme’s empirical dispersion, performs most accurately with respect to experimentally derived thermochemical properties of the TiO2 molecule. We present a hitherto unreported global minimum candidate for size N = 13. The DFT-derived thermochemical cluster data are used to evaluate the nucleation rates for a given temperature-pressure profile of a model hot-Jupiter atmosphere. We find that with the updated and refined cluster data, nucleation becomes unfeasible at slightly lower temperatures, raising the lower boundary for seed formation in the atmosphere. Conclusions. The approach presented in this paper allows finding stable isomers for small (TiO2)N clusters. The choice of the functional and basis set for the all-electron DFT calculations has a measurable impact on the resulting surface tension and nucleation rate, and the updated thermochemical data are recommended for future considerations.

A novel approach for determination of nucleation rates and interfacial energy of metallic magnesium nanoclusters at high temperature using non-isothermal TGA models

The exploration of temperature-dependent nucleation is required to appraise the extent of kinetic and thermodynamic barriers associated with the origin of subatomic size nuclei, which controls the nucleation rate. The precise computation of nucleation rate, thermodynamic parameters, and interfacial surface energy for ultra-small nanoclusters (0.5–2 nm) is still absent in the high-temperature range. Here, apparent activation energy (Ea), thermodynamic parameters (ΔG, ΔH, and ΔS), and pre-exponential kinetic factor were estimated by utmost accurate Vyazovkin advanced, and KAS isoconversional techniques for calculation of nucleation rate and interfacial energy for ultra-small magnesium nanoclusters (∼0.8 ± 0.24 nm), in the temperature range from 555 to 780 K. The master plots propounded the existence of third order random nucleation in magnesium metal matrix over a specified conversion. Based on the above findings, four mathematical models are proposed to compute nucleation rate and interfacial energy in magnesium clusters over respective temperatures and conversions. These models are beneficial for predicting the nucleation rate and interfacial energy over a high range of temperature and specific conversion.

Solid-state reaction process for high-quality organometallic halide perovskite thin film

Recently, a hybrid perovskite material, ABX3 (A= Cs, CH3NH3, NH2CHNH2; B= Pb, Sn; X= Cl, Br, I), has received much attention as an active layer in new-generation solar cells. This material is usually fabricated with either a one-step or a two step process in solution. However, the surface morphology, nucleation rate and grain growth rate of the CH3NH3PbI3 perovskite light absorber prepared by the solution reaction process (SRP) are hard to control. Here, we show a fast solid-solid reaction process (SSRP), to fabricate ultraflat (roughness of approximately 12 nm) CH3NH3PbI3 perovskite thin films with large grain sizes (~947 nm). The SSRP simply involves directly contacting a lead iodide thin film (PbI2) with methylammonium iodide powder (CH3NH3I) without any chemical reagents at 120°C under a normal atmospheric environment. The SSRP reaction dynamics is investigated by an in situ heating scanning electron microscope (SEM) system. This innovative SSRP is an easy approach for the large-scale fabrication of planar heterojunction perovskite solar cells and allows us to demonstrate a power conversion efficiency of approximately 15.27% (active area of 0.16 cm2).

A new hydration kinetics model of composite cementitious materials, Part 2: Physical effect of SCMs

AbstractThis paper is the second part of an overall research project that aims to model the hydration kinetics of composite cementitious materials. The new hydration kinetic model of Portland cement was constructed in the first part of this research project. The aim of this part is to characterize the physical effect of SCMs by modifying some kinetic parameters of the hydration kinetic model of cement. In this paper, the filler effect of SCMs is attributed to the “dilution effect”, “nucleation effect” and “accelerated dissolution effect”. The dilution effect is considered by introducing the actual water/cement ratio into the kinetic model. The nucleation surface area, nucleation and growth rates are modified to account for the nucleation effect and accelerated dissolution effect of fillers. The simulative fit results show that the extra contribution of SCMs due to their filler effect on hydration of cement at early ages has an upper limit: at most 20% extra nucleation surface area, 30% extra nucleation ratio and 40% extra growth ratio of calcium silicate hydrate (CSH). The new modified kinetic model and the value‐taking method of the newly introduced parameters are verified by simulative fitting to the kinetic data from reference. The apparent activation energies of the nucleation rate, growth rate, and diffusion rate are approximately 35 kJ/mol, 36 kJ/mol and 38.5 kJ/mol, which are slightly smaller than those of the pure Portland cement reported in the first part of this research project.

Predictions of homogeneous nucleation rates for n-alkanes accounting for the diffuse phase interface and capillary waves.

Homogeneous droplet nucleation has been studied for almost a century but has not yet been fully understood. In this work, we used the density gradient theory (DGT) and considered the influence of capillary waves (CWs) on the predicted size-dependent surface tensions and nucleation rates for selected n-alkanes. The DGT model was completed by an equation of state (EoS) based on the perturbed-chain statistical associating fluid theory and compared to the classical nucleation theory and the Peng-Robinson EoS. It was found that the critical clusters are practically free of CWs because they are so small that even the smallest wavelengths of CWs do not fit into their finite dimensions. The CWs contribute to the entropy of the system and thus decrease the surface tension. A correction for the effect of CWs on the surface tension is presented. The effect of the different EoSs is relatively small because by a fortuitous coincidence their predictions are similar in the relevant range of critical cluster sizes. The difference of the DGT predictions to the classical nucleation theory computations is important but not decisive. Of the effects investigated, the most pronounced is the suppression of CWs which causes a sizable decrease of the predicted nucleation rates. The major difference between experimental nucleation rate data and theoretical predictions remains in the temperature dependence. For normal alkanes, this discrepancy is much stronger than observed, e.g., for water. Theoretical corrections developed here have a minor influence on the temperature dependency. We provide empirical equations correcting the predicted nucleation rates to values comparable with experiments.

New trends in the nucleation research

During the last half of century the most of efforts have been directed towards small molecule system modeling using intermolecular potentials. Summarizing the nucleation theory, it can be concluded that the nowadays theory is far from complete. The vapor-gas nucleation theory can produce values that deviate from the experimental results by several orders of magnitude currently. Experiments on the vapor-gas nucleation rate measurements using different devices show significant inconsistencies in the measured rates as well. Theoretical results generally are quite reasonable for sufficiently low vapor nucleation rates where the capillary approximation is applicable. In the present research the advantages and current problems of the vapor-gas nucleation experiments are discussed briefly and a view of the future studies is presented. Using the brake points of the first derivative for the nucleation rate surface as markers of the critical embryos phase change is fresh idea to show the gas-pressure effect for the nucleating vapor-gas systems. To test the accuracy of experimental techniques, it is important to have a standard system that can be measured over a range of nucleation conditions. Several results illustrate that high-pressure techniques are needed to study multi-channel nucleation. In practical applications, parametric theories can be used for the systems of interest. However, experimental measurements are still the best source of information on nucleation rates. Experiments are labor intensive and costly, and thus, it is useful to extend the value of limited experimental measurements to a broader range of nucleation conditions. Only limited experimental data one needs for use in normalizing the slopes of the linearized nucleation rate surfaces. The nucleation rate surface is described in terms of steady-state nucleation rates. It is supposed that several new measuring systems, such as High Pressure Flow Diffusion Chamber for pressure limit up to 150 bar will be created soon in the frame of the Russian Ministry of Science & Education project under Contract № 14.Z50.31.0041 issued by February 13th of 2017. The Project will provide the nucleation studies for basic problems of theoretical and practical applications. Published under licence in Journal Title by IOP Publishing Ltd.

Kinetic Model for Layer-by-Layer Crystal Growth in Chain Molecules

A kinetic model is proposed to describe the structure and rate of advancement of the growth front during crystallization. Solidification occurs through the mechanisms of surface nucleation and lateral spreading of the solid phase within layers in the vicinity of the growth front. The transformation from liquid to solid within each layer is described by an equation similar to the two-dimensional variant of the Johnson–Mehl–Avrami (JMA) equation, but in which the finite size and shape of the critical nucleus and the dynamic evolution of the solid fraction of the underlying layers are taken into account. Connection to the regime theory of Hoffman and co-workers, for surface nucleation and spreading in one or two dimensions, is also made. Given only molecular level information regarding surface nucleation rates, lateral spreading rates, and critical surface nucleus geometry, the resulting set of coupled nonlinear equations for solidification in each layer is numerically integrated in time to obtain the struct...

Molecular Dynamics Simulation of Surface Nucleation during Growth of an Alkane Crystal

Crystal growth from the melt of n-pentacontane (C50) was studied by molecular dynamics simulation. Quenching below the melting temperature gives rise to propagation of the crystal growth front into the C50 melt from a crystalline polyethylene surface. By tracking the location of the crystal–melt interface, crystal growth rates between 0.02 and 0.05 m/s were observed, for quench depths of 10–70 K below the melting point. These growth rates compare favorably with those from a previous study by Waheed et al. [Polymer 2005, 46, 8689−8702]. Next, surface nucleation was identified with the formation of two-dimensional clusters of crystalline sites within layers parallel to the propagating growth front. Critical nucleus sizes, waiting times, and rates for surface nucleation were estimated by a mean first passage time analysis. A surface nucleation rate of ∼0.05 nm–2 ns–1 was observed, and it was nearly temperature-independent. Postcritical “spreading” of the surface nuclei to form a completely crystallized layer...

Heterogeneous surface nucleation of lithium disilicate glass: An isothermal DSC study

The paper aims in correlating isothermal DSC signals to the actual nucleation and crystallization processes in a lithium disilicate glass as determined by optical microscopy. The results show that the DSC signal reflects the change from an initial surface nucleation to a site saturation regime (constant number of crystals) leading to a coast-island microstructure in monolithic samples. An isothermal JMAK analysis revealed a maximum of the instantaneous Avrami coefficient at the onset time of saturation (impingement time). Impingement times were used to approximate heterogeneous surface nucleation rates, which were found to be up to 14 orders of magnitude higher than those of homogeneous volume nucleation and correlate positively with temperature in the range 0.64–0.68 Tm.

Crystal nucleation in food colloids

Crystal nucleation in food colloids is considered in the light of recent developments in classical nucleation theory (CNT); it is shown that CNT remains a sound basis upon which to understand nucleation in colloids and in particular nucleation in lipids such as triacylglycerols. Computation of the energy barrier to nucleation for a studied triacylglycerol system (Cocoa butter oil-in-water emulsion) indicates that whilst homogeneous nucleation is unlikely at higher surface energies the addition of surfactant, lowering the interfacial energy may have a dramatic impact on surface nucleation rates. Data is included supporting this contention. The impact of reducing the size of colloidal particles to the point where the interfacial region occupies a significant proportion of the total volume of the dispersed phase is discussed and it is suggested that in these circumstances undercooling may fall significantly in comparison with the undercooling measured in micrometre emulsions.

Does the Homogeneous Ice Nucleation Initiate in the Bulk Volume or at the Surface of Super-Cooled Water Droplets? A Review

The formation of ice in clouds can occur through primary processes, either homogeneously or heterogeneously triggered by aerosol particles called ice nuclei, as well as through secondary processes. The homogeneous ice nucleation process involves only pure water or solution droplets. Homogeneous freezing is crucial for the microphysics in the formation of high-altitude cirrus and polar stratospheric clouds, and also in the glaciation of thunderclouds, at temperatures below about 235 K. Nucleation rates in supercooled water have been measured using different experimental techniques: expansion cloud chambers, water-in-oil emulsions, levitation methods, free falling droplets, supersonic nozzles, field measurements, and molecular dynamics simulations. An important question concerns the possibility that the nucleation process in supercooled water can occur not only in the interior volume of the droplet, but even at or close to its surface. Even if there is no conclusive evidence, the majority of experimental and theoretical results suggest that the contribution of surface nucleation increases with decreasing radius of the supercooled droplets, and the surface (or sub-surface) nucleation rate is prevalent for droplets with radius lower than about 5 μm. If homogeneous freezing initiates at the droplet surface, the freezing rate should depend on the droplet size, and even a slight contamination by molecules within the surface layer could hamper the rate of the nucleation process.

Nucleation Rate Surfaces for Solidphase Polymethylmethacrylate Laser Ablation

Experimental results for laser ablation of polymethylmethacrylate (PMM) by laser pulses are presented in this paper. Schematic construction of nucleation rate surface topology for glass and products under laser ablation is done. It follows from the research results that the using of a single channel version of the nucleation theory is incorrect to describe the nucleation rate in the glass and in the products of ablation, where several channels of nucleation are realized

Eutectic and Peritectic Lines for Diagrams of Quasi Equilibria of Binary Systems with Partially Soluble Components

Topologies of the nucleation rate surfaces over phase equilibria diagrams with eutectic and peritectic points are constructed schematically. Theoretical methods to obtain the topology of these surfaces are not yet available. Individual eutectic and peritectic points, empirically observed previously in non-equilibrium conditions, are following as particular cases of the common results of the present paper. It is shown that there are lines of eutectic and peritectic compositions in general, depending on the mother phase invasion depth into the region of the coupled phase equilibria

Examples of a semiempirical design of nucleation rate surfaces for systems with monotropic polymorphous phase transitions

Examples of the topology of nucleation rate surfaces for systems with monotropic polymorphic transitions constructed using a new concept for the semiempirical design of such surfaces over p-T phase equilibrium diagrams, where p is pressure and T is temperature, are presented. It is shown in these cases that multichannel nucleation corresponding to a set of independent nucleation rate surfaces occurs. Previous attempts to describe such systems in the one-channel approximation of the theory are not valid. We conclude that the obtained topologies of nucleation surfaces can be used as examples that illustrate the generalized rule of the sequence of phases, the first version of which was formulated by Ostwald.

Experimental evidence for surface freezing in supercooled n-alkane nanodroplets

Intermediate chain length (16 ≤i≤ 50) n-alkanes are known to surface freeze at temperatures that are up to three degrees higher than the equilibrium melting point [B. M. Ocko et al., Phys. Rev. E, 1997, 55, 3164-3182]. Our recent experimental results suggest that highly supercooled nanodroplets of n-octane and n-nonane also surface freeze, and subsequently bulk crystallization occurs. The data yield surface and bulk nucleation rates on the order of ~10(15) cm(-2) s(-1) and ~10(22) cm(-3) s(-1), respectively, at temperatures between 180 K and 200 K. Molecular dynamics simulations at the united atom level were used to follow the freezing of a supercooled n-octane drop and show that an ordered monolayer develops on the surface of the droplet almost immediately, and the rest of the droplet then freezes in a layer-by-layer manner.

Vapor Multifold Nucleation Rate Surfaces for Case of the Polimorfous Enantiotropic Phase Transitions of a Condenced Phase

Examples of the nucleation rate topologies for systems which are having the enantiotropy polymorphic phase transitions, using the idea of the nucleation rate surface semiempirical design over the phase equilibria diagrams, are presented. It was shown that multichannel vapor nucleation in according the independent set of the nucleation rate surfaces are realized in these cases. The traditional using for these systems one channel approximations of the nucleation rate theories is wrongful. The nucleation rate surfaces designed can be used as illustration of the phase sequence rule, the first version of which was formulated earlier by Ostwald

Size dependence of volume and surface nucleation rates for homogeneous freezing of supercooled water droplets

Abstract. The relative roles of volume and surface nucleation were investigated for the homogeneous freezing of pure water droplets. Experiments were carried out in a cryogenic laminar aerosol flow tube using supercooled water aerosols with maximum volume densities at radii between 1 and 3 μm. Temperature- and size-dependent values of volume- and surface-based homogeneous nucleation rates between 234.8 and 236.2 K were derived using a microphysical model and aerosol phase compositions and size distributions determined from infrared extinction measurements in the flow tube. The results show that the contribution from nucleation at the droplet surface increases with decreasing droplet radius and dominates over nucleation in the bulk droplet volume for droplets with radii smaller than approximately 5 μm. This is interpreted in terms of a lowered free energy of ice germ formation in the surface-based process. The implications of surface nucleation for the parameterization of homogeneous ice nucleation in numerical models are considered.

Theoretical Study of Phase Transition, Surface Tension, and Nucleation Rate Predictions for Argon

In this work, a weighted density functional theory has been used to study the equilibrium and metastable processes for argon. In the theoretical approach, the two- and three-body interactions of the fluid molecules are considered simultaneously, and the renormalization group transformation is applied to address the long-range fluctuations inside the critical region. The global phase equilibria, planar and curvature-dependent surface tensions, critical radius, and nucleation rates of argon are investigated systematically. The results are in good agreement with the experimental data. Meanwhile, this work applies a methodology for calculating the curved surface tension in local supersaturated environments, showing that the Tolman length is negligible far from the critical region. Near the critical point, however, the Tolman length becomes positive and appears to diverge.