Bulk Nucleation Research Articles

Investigation of halloysite thermal decomposition through differential thermal analysis (DTA): Mechanism and kinetics assessment

The study focused on analysing the kinetics of halloysite decomposition using the differential thermal analysis (DTA) technique. Tests were carried out across a temperature span from ambient temperature to 1673 K, employing heating rates spanning from 5 to 20 °C.min−1. X-ray diffraction and Fourier transform infrared spectroscopy (FT-IR) were utilized to identify the phases formed at different temperatures. Activation energies for halloysite decomposition were determined through isothermal and non-isothermal treatments, yielding values of approximately 151.68 kJ mol−1 and 173.14 kJ mol−1, respectively. The Ligero method's Avrami constant parameter (n) and the Matusita method's numerical factor parameter (m), linked to crystal growth dimensions, were both around 1.5. These findings indicate that the degradation of halloysite is primarily governed by bulk nucleation, succeeded by the 3-dimensional growth of meta-halloysite characterized by polyhedron-like structure, regulated by diffusion from a consistent number of nuclei. The frequency factor for halloysite dehydroxylation was established at 8.48 × 10⁸ s⁻1.

Simulation of Solidification Structure in the Vacuum Arc Remelting Process of Titanium Alloy TC4 Based on 3D CAFE Method

Vacuum arc remelting is the main production method of titanium alloy ingots at present. In order to obtain good quality ingots, it is of great significance to study the formation of the solidification structure of ingots via vacuum arc remelting. In order to select and optimize the nucleation parameters for the solidification microstructure simulation of an ingot, a 3D CAFE model for microstructure evolution during vacuum arc remelting was established, taking into account heat transfer, flow, and solute diffusion. The Gaussian distribution continuous nucleation model and extended KGT model were used to describe the grain nucleation and dendrite tip growth rates, respectively. The multi-point mass source and moving boundary method were used to simulate the ingot growth. The results show that there are three typical crystal regions in the solidification structure of vacuum arc remelting titanium alloy ingots, namely the surface fine crystal region, columnar crystal region, and central equiaxed crystal region. The proportion of the columnar crystal region in the solidification structure of an ingot increases gradually with the increase in the undercooling of the maximum bulk nucleation. With an increase in the maximum bulk nucleation density, the equiaxed grain zone gradually increases, and the grain size gradually decreases. The proportion of the columnar crystal region in the solidification structure of an ingot increases gradually with an increase in the undercooling of the maximum bulk nucleation. The maximum volume nucleation variance has no obvious effect on the change in the solidification structure. When the maximum volume nucleation undercooling is 5.5 K, the maximum volume nucleation standard deviation is 4 K, and the maximum volume nucleation density is 5 × 108. The solidification structure simulation results are in good agreement with the experimental results.

Mechanical and electrical performances of ternary Cu-2.8%Ni-0.7%Si alloy modulated by ultrasonic solidification

One-dimensional (1D) and three-dimensional (3D) ultrasounds were introduced into the solidification process of ternary Cu-2.8wt%Ni-0.7wt%Si alloy together with the in-situ measurements of acoustic fields. In the case of 1D ultrasound, stable cavitation was the main form of acoustic energy transmission. The grain size of α-Cu dendrites was reduced because stable cavitation improved the wetting between impurities and alloy melt, which further promoted nucleation process. When 3D ultrasounds were applied, transient cavitation was the dominant mode of acoustic energy dissipation. This induced local high undercooling in alloy melt, causing a significant increase in bulk nucleation rates and the formation of numerous tiny α-Cu equiaxed grains. Meanwhile, as ultrasonic dimension increased, the strengthened acoustic streaming accelerated solute and thermal diffusion and weakened the preferred orientation of growing α-Cu grains. The proportion of low-angle grain boundaries (LAGBs) increased consequently, which suppressed the nucleation and growth of δ-Ni2Si discontinuous precipitates (DPs) during subsequent annealing treatment. The tensile strength and electrical conductivity of 3D ultrasonically solidified alloy after annealing reached 688.2 MPa and 2.7×107 S/m respectively, showing obvious advantages in synergetic mechanical and electrical performances.

A Numerical Model of Microstructure Formation Considering Nanoparticle Distribution During Selective Laser Melting Process

Abstract One of the widely used metal additive manufacturing processes, named Selective laser melting (SLM), can facilitate the printing of novel metal matrix nanocomposites through the fusion of metallic powders with nanoparticles. The current study proposes a novel numerical model to simulate microstructure formation considering local nanoparticle distribution during the SLM process. The proposed model formulates a three-dimensional computational fluid dynamics (CFD) model with Lagrangian particle tracking to simulate a single-track, single-layer SLM process of aluminum alloy reinforced with titanium diboride (chemical formula: TiB2) nanoparticles in ANSYS FLUENT. A very low weight fraction (0.0009%) of nanoparticles was considered due to the computational limitations of the software package. The temperature distribution and particle distribution results were first calculated by the 3D CFD model. Then, the results were one-way coupled to a 2D Cellular Automata (CA) model to predict the microstructure evolution using matlab. The coupled CFD-CA model and Lagrangian particle tracking were separately validated in this study. The results showed that the nanoparticles migrate within the recirculation zones formed by both Marangoni and natural convection in the fluid of the molten pool. The microstructure predicted by this model showed that the introduction of the nanoparticles increased bulk nucleation during solidification. The growth of large columnar grains is interrupted by the formation of randomly oriented small equiaxed grains. The average grain diameter decreased by 40% when nanoparticles were present compared to microstructures without nanoparticles.

A comprehensive study on combined organic fouling and gypsum scaling in reverse osmosis: Decoupling surface and bulk phenomena

Reverse osmosis (RO), as an energy efficient desalination technology that is critical to mitigate water scarcity, encounters feedwater containing both organic foulants and inorganic scalants. However, comparing with extensive studies on individual fouling or scaling, our knowledge of the behavior and mechanisms associated with combined organic fouling and mineral scaling is still lacking. Due to the potential occurrence of mineral formation in both bulk solution and on the membrane surface, a complete, mechanistic understanding of combined fouling and scaling requires decoupling of surface and bulk phenomena. Herein, our study employed a comprehensive investigation to delve into the intricate interplay of gypsum scaling and organic fouling in RO process. Our systematic approach is accomplished through three sets of experiments that include static experiments and two types of dynamic experiments (i.e., (1) combined fouling and scaling, and (2) gypsum scaling on foulant-conditioned membranes). A variety of model foulants including humic acid, alginate, bovine serum albumin (BSA), and lysozyme were used to investigate the effects of foulant type. Our results demonstrate that the behavior of combined organic fouling and gypsum scaling aligns more with that of gypsum scaling on foulant-conditioned membranes rather than static experiments where bulk nucleation occurs, indicating the predominance of surface nucleation in RO. BSA exhibited a remarkable hindering effect on gypsum scaling, whereas other foulants displayed an additive effect. The lack of scaling mitigation by lysozyme suggests that molecular properties of protein must play a role in regulating the behavior of combined fouling and scaling. Results from multiple characterization techniques reveal the foulant-scalant interactions by delineating the morphological and chemical features of the fouling/scaling layers. Our study not only elucidates the mechanisms of combined organic fouling and gypsum scaling but also sheds light on potential strategies for membrane scaling control in RO desalination.

Methods to modify supersaturation rate in membrane distillation crystallisation: Control of nucleation and crystal growth kinetics (including scaling)

While water vapour flux is often regarded as the critical parameter in membrane distillation crystallisation (MDC), there are multiple factors that will determine the kinetics of nucleation and crystal growth. A Nývlt-like equation is therefore introduced that can relate how multiple conditional parameters (membrane area, flux, temperature difference, crystalliser volume, magma density) independently modify nucleation rate and supersaturation, enabling a normalising approach for the characterisation of nucleation and crystal growth kinetics within MDC. Each parameter can be modified to increase supersaturation rate, which reduced induction time and broadened the metastable zone width (MSZW) at induction. An increase in supersaturation mitigated scaling and favoured bulk nucleation. This is due to the increase in volume free energy provided by the elevated supersaturation that reduces the critical energy requirement for nucleation to favour a homogeneous primary nucleation mechanism. An increase in temperature difference or magma density narrowed the MSZW. For each parameter, either supersaturation rate, supersaturation or induction time were fixed, while the other two factors were amended. While higher supersaturation rates generally favoured larger crystal sizes with broader size distributions, a high level of supersaturation at a low supersaturation rate increased particle size and narrowed the size distribution. In practice, these factors may be applied collectively and synergistically to deliver strict control over crystal growth, which remains a challenge for current evaporative technology. This was illustrated when facilitating an increase in supersaturation rate with membrane area, where an identical nucleation order was identified between membrane systems, from which it can be implied that MDC affords an inherently scalable solution for crystallisation.

Effects of Carbon on Void Nucleation in Self-Ion–Irradiated Pure Iron

Impurities such as carbon atoms play a significant role in the void swelling of irradiated metals. The phenomenon is important to both materials designs in which impurities are intentionally introduced and accelerator-based ion irradiation testing in which impurities are introduced unintentionally as contaminants. Here, we report rate theory simulations of void nucleation in pure Fe, which are irradiated by 5-MeV Fe ions, as one typical irradiation condition used in nuclear material testing. Based on kinetics obtained previously from ab initio calculations, Multiphysics Object-Oriented Simulation Environment (MOOSE)–based numerical solvers were used to simulate defect distributions and void nucleation. Vacancy-carbon interactions increase the effective migration energies of carbon and decrease the diffusivity prefactors. The vacancy mobility reduction decreases both interstitial flux and vacancy flux. However, the vacancy flux reduction is more significant than that of interstitials, leading to reduced void nucleation in bulk. On the other hand, reduced vacancy flux toward the surface leads to local vacancy pileups, leading to locally enhanced void nucleation. These two combined effects make the void nucleation profile deviate from the displacements per atom (dpa) peak, and void swelling peaks shift to the near-surface region. The transition from deep swelling to near-surface swelling is plotted as a function of dpa rate, carbon concentration, and temperature. The study shows that the swelling peak shifting caused by the carbon effect can be avoided by either reducing dpa rates or increasing irradiation temperatures. The study is important to understand swelling behaviors and to optimize irradiation parameters for accelerator-based swelling testing.

Hydrodynamics (Reynolds number) determine scaling, nucleation and crystal growth kinetics in membrane distillation crystallisation

Reynolds number (Re) has been previously related to several scaling mitigation and crystallisation strategies that offer distinct hypotheses for how Re may regulate the kinetics of nucleation and crystal growth in membrane crystallisation. Such ambiguity has arisen from the present inability to discretely characterise induction time in membrane systems. This study therefore introduces techniques for the detection of induction time, with measurements used to develop a modified power-law relation between nucleation rate and supersaturation to establish how Re can be used to adjust nucleation kinetics. Increasing Re enhanced mass and heat transfer processes which raised permeate flux. The interfacial supersaturation set by the increase in flux, also modified the supersaturation rate at induction for crystals formed in the bulk solution, providing the first direct evidence that it is the supersaturation level set within the boundary layer which controls primary nucleation in the bulk solution. Bulk nucleation rate can therefore be adjusted in proportion to Re. While the extent of scaling was also determined by the interfacial supersaturation set by Re, its formation was shown to be more dependent on the interfacial diffusion coefficient which regulates solute backtransport and the activation energy for nucleation. Through this work we suggest that the nucleation mechanisms underlying scale formation and bulk crystallisation are distinct. The regulation of nucleation rate in the bulk solution by Re is described analytically through classical nucleation theory, while scaling can be mitigated through operation below a critical threshold supersaturation value that determines the rate and type of scaling that prevails. These seemingly distinct strategies can be combined through modifications to T and dT with Re to suppress scaling and offer refined control over the kinetics of nucleation and crystal growth.

Investigation of Crystallization Kinetics of Na2ZnP2O7 Glass Using XRD and DTA Analysis

AbstractIn the present investigation, the crystallization kinetics of a glass with a molar composition 25Na2O‐25ZnO‐50P2O5 (NZPO) is studied by means of a non‐isothermal differential thermal analysis (DTA) and X‐ray diffraction (XRD) techniques. XRD pattern of the as‐synthesized glass indicates an amorphous glassy structure without additional crystalline phase. Moreover, the heat‐treated glass sample shows the crystallization of the Na2ZnP2O7 crystalline phase. The glass transition peak temperature increases with increasing heating rates and is ranged from 505.3 to 601.6 K. The crystallization shows the same behavior and the obtained values are ranged from 685.2 to 731.2 K. The activation energies for glass transition and crystallization are determined using different approaches and are in the range of 25.9–30.5 and 82.8–112.0 kJ mol−1, respectively. The n and m kinetic parameters are each close to 3.0, which indicates bulk nucleation process with 3D growth of crystals.

Investigation into Surface Effects on the Crystal Nucleation and Growth of Clotrimazole Polymorphs

Molecules at the surface are spatially different compared to those in the bulk and potentially influence crystallization. In this study, surface effects on crystallization behaviors of two clotrimazole (CMZ) polymorphs were investigated. Form 2 of CMZ is favored to nucleate both at the surface and in the bulk. The nucleation rates of CMZ polymorphs at the surface are vastly accelerated by 5–6.5 orders of magnitude compared to their bulk nucleation rates. The surface-accelerating effect on the nucleation rates for Form 2 is relatively stronger than that for Form 1. The surface molecular structure and surface dynamics exhibit a combined effect on the enhancement of surface nucleation. The surface also enhances growth rates of the two polymorphs while exhibiting a greater accelerating effect on Form 1. The growth rates of Form 2 are higher in the bulk, while they show the opposite order at the surface, with Form 1 growing faster. The classical nucleation theory holds true in the present system both at the surface and in the bulk, and the thermodynamic barriers of the two nucleation processes are similar. This study is relevant for understanding the nucleation and growth kinetics of drug polymorphs at the surface.

Rapid precipitation-free synthesis of zinc oxide nanowire arrays

The microwave-assisted hydrothermal method is cost-effective for rapidly producing zinc oxide (ZnO) nanowire array. However, microwave-assisted heating can make many bulk crystals that may contaminate the nanowire array. The precipitated contamination on the ZnO nanowire array formed using the microwave-assisted hydrothermal method is grossly underreported in the literature. ZnO is usually prepared in a high basic condition to reduce the bulk nucleation, using ammonia or amine complexes. As microwave-assisted synthesis is preferred in open reactors to avoid high-pressure development and design complexity, amine-based components are particularly unsuitable for such reactions due to high volatility. In this work, the ZnO nanowire array was synthesized using the microwave-assisted hydrothermal method in an open reactor using a basic non-volatile compound, Sodium hydroxide (NaOH). Rapid growth of ZnO nanowires was achieved at a rate of 4.6 μm/h without having precipitated materials using NaOH. In contrast, ammonia-assisted synthesis showed a large number of precipitates on the array. High and low-magnified field emission scanning electron microscopy images revealed the formation of pristine ZnO nanowires and debris/contaminant-free arrays using a non-volatile hydrolyzing agent. Speciation data shows that various ionic species of Zn under different basic conditions using ammonia and NaOH can control the bulk nucleation of ZnO.

Surface-enhanced crystal nucleation and polymorph selection in amorphous posaconazole.

Molecules at a liquid/vapor interface have different organizations and mobilities from those in the bulk. These differences potentially influence the rate of crystal nucleation, but the effect remains imperfectly understood. We have measured the crystal nucleation rates at the surface and in the bulk of amorphous poscaconazole, a rod-like molecule known to have a preferred interfacial orientation. We find that surface nucleation is vastly enhanced over bulk nucleation, by ∼9 orders of magnitude, and selects a different polymorph (II) from bulk nucleation (I). This phenomenon mirrors the recently reported case of D-arabitol and stems from the similarity of anisotropic surface molecular packing to the structure of the surface-nucleating polymorph. In contrast to these two systems, the surface enhancement of nucleation is weaker (though still significant) in acetaminophen and in water and does not select a different polymorph. Together, the systems investigated to date all feature surface enhancement, not suppression, of crystal nucleation, and those showing a polymorphic change feature (1) structural reconstruction at the surface relative to the bulk and (2) existence of a different polymorph that can take advantage of the surface environment to nucleate. These results help predict the effect of a liquid/vapor interface on crystal nucleation and polymorph selection, especially in systems with a large surface/volume ratio, such as atmospheric water and amorphous particles.

Deconvolution of main hydration kinetic peaks in properly sulfated Portland cements with boundary nucleation and growth models and relation to early-age concrete strength development

When the hydration kinetics of properly sulfated Portland cements is monitored by heat flow calorimetry, the initial dissolution peak and the dormant period is followed by the main hydration peak – formation of calcium-silicate-hydrates and portlandite, the so-called silicate peak. This main peak is superimposed by a peak associated to further tricalcium aluminate dissolution and a surge in precipitation of sulfoaluminates (the so-called sulfate depletion peak) right after sulfate added for setting control is depleted in the material system. In this paper strategies for the deconvolution of silicate peak and sulfate depletion peak are presented. Hereby, the boundary nucleation and growth model and the classical bulk nucleation and growth model serve as tools for deconvolution of calorimetric data. We discuss obtained kinetic parameters and their temperature dependency. The boundary nucleation and growth model for constant nucleation rate emerged as the most suitable model for the silicate reaction, the bulk nucleation and growth model with an order of three, indicating site saturation, as adequate for the sulfate depletion peak. The reaction enthalpy for tricalcium silicate hydration was obtained as 503 J/g, remarkably close to literature values. Calorimetric data related to the sulfate depletion peak is corroborated by X-ray diffraction analysis of formation history of crystalline hydration products. Furthermore, the history of the (silicate) degree of reaction as predicted by the boundary nucleation and growth model for different temperature histories is related to experimentally obtained early-age strength histories. • Investigation of hydration kinetics of commercial, well-sulfated Portland cement. • Main peak (C-S-H and portlandite formation) superimposed by sulfate depletion peak. • Strategies for deconvolution of peaks with Avrami–Cahn models as tools for analysis. • Degree of silicate reaction history is linked to early-age strength gain.

Surface Enhancement of Crystal Nucleation in Amorphous Acetaminophen

Crystal nucleation rates have been measured in the bulk and at the surface of acetaminophen melt. Of its six known polymorphs, Form III nucleates in the temperature range investigated (290–333 K), both in the bulk and at the surface. Nucleation is the fastest near 318 K (about 20 K above the bulk glass transition temperature Tg) at a rate of 3 × 106 s–1 m–3 in the bulk and 200 s–1 m–2 on the surface. On the per-molecule basis, surface nucleation outpaces bulk nucleation by 5 orders of magnitude, highlighting the importance of the liquid/vapor interface in crystal nucleation. In contrast to its strong effect on nucleation, the free surface has a weak effect on crystal growth. The observed nucleation kinetics is well described by the Classical Nucleation Theory (CNT) if the crystal growth rate is used to represent the kinetic barrier. Our finding is relevant for understanding the physical stability of amorphous materials for applications in drug delivery and electronics.

Microscopic origin of coercivity enhancement by dysprosium substitution into neodymium permanent magnets

Neodymium (Nd) magnets (${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$), known as the strongest permanent magnets, are indispensable in realizing high efficiency in energy conversion devices. To enhance their coercivity at high temperatures, the Nd component is substituted with dysprosium (Dy) in the commercial products of the magnet. Surface Dy-rich shells are considered important for enhancing coercivity. However, the underlying microscopic mechanism has not been studied based on atomistic theories. In this study, first, the features and mechanisms of the enhancement were studied using an atomistic model of the Nd magnet. Subsequently, the threshold field (coercive force) for magnetization reversal and the dynamical features at absolute zero and finite temperatures were investigated. The results show that a change from surface to bulk nucleation occurs when the number of substituted layers increases and the anisotropy energy of Dy is resistant to temperature increase, which significantly enhances coercivity, especially at high temperatures.

Effect of Planar Interfaces on Nucleation in Melting and Crystallization.

The effect of planar interfaces on nucleation (namely, on the work of critical cluster formation and their shape) is studied both for crystallization and melting. Advancing an approach formulated about 150 years ago by J. W. Gibbs for liquid phase formation at planar liquid–liquid interfaces, we show that nucleation of liquids in the crystal at crystal–vapor planar interfaces proceeds as a rule with a much higher rate compared to nucleation in the bulk of the crystal. Provided the surface tensions crystal–liquid (), liquid–vapor (), and crystal–vapor () obey the condition , the work of critical cluster formation tends to zero; in the range , it is less than one half of the work of critical cluster formation for bulk nucleation. The existence of a liquid–vapor planar interface modifies the work of critical cluster formation in crystal nucleation in liquids to a much less significant degree. The work of critical crystal cluster formation is larger than one half of the bulk value of the work of critical cluster formation, reaching this limit at . The shape of the critical clusters can be described in both cases by spherical caps with a radius, R, and a width parameter, h. This parameter, h, is the distance from the cutting plane (coinciding with the crystal–vapor and liquid–vapor planar interface, respectively) to the top of the spherical cap. It varies for nucleation of a liquid in a crystal in the range and for crystal nucleation in a liquid in the range . At , the ratio of the critical cluster for nucleation in melting tends to zero (). At the same condition, the critical crystallite has the shape of a sphere located tangentially to the liquid–vapor interface inside the liquid (). We present experimental data which confirm the results of the theoretical analysis, and potential further developments of the theoretical approach developed here are anticipated.

Kinetics of α-cordierite formation from nano-oxide powders

This work reports, for the first time, the kinetics of α-cordierite (Mg2Al4Si5O18) formation from Al2O3, SiO2, and MgO nano-oxide powders. Isothermal and non-isothermal kinetic analysis was performed by Differential Thermal Analysis (DTA) and thermodilatometric analysis (TDA). The thermal measurements were performed at high heating rates (20–70 °C/min) for DTA and low rates (3–9 °C/min) for TDA. Phase transformations leading to the formation of α-cordierite were characterized by x-ray diffraction (XRD). The Kissinger, Boswell, and Ozawa methods were used to calculate the activation energy. The Avrami parameter (n) and dimensionality of crystal growth (m) were calculated using the Augis–Bennett and Matusita equations, respectively. Analysis of samples heated in the DTA equipment or the dilatometer confirmed that the reaction of MgO, Al2O3, and SiO2 led to the formation of enstatite, cristobalite, and metastable μ-cordierite. The later transformed to stable α-cordierite. The activation energy calculated by both isothermal and non-isothermal treatments is 633 and 667 kJ/mol, respectively, for DTA; and is 544 and 646 kJ/mol, respectively, for TDA. The growth morphology parameters n and m, obtained from isothermal and non-isothermal DTA treatments, are both close to 2 indicating that bulk nucleation with constant number of nuclei is dominant in α-cordierite crystallization followed by two-dimensional growth of α-cordierite crystals with plate-like morphology controlled by interface reaction. While those obtained from isothermal and non-isothermal TDA treatments, are both about 1.5 indicating that bulk nucleation is dominant in α-cordierite crystallization followed by three-dimensional growth of α-cordierite crystals with polyhedron-like morphology controlled by diffusion from a constant number of nuclei. A low coefficient of thermal expansion (CTE) of 0.9 × 10−6/°C was measured, in the range 200–1350 °C, for a sample sintered at 1400 °C‏ for 2 h.

Evaluate the effect of melt pool convection on grain structure of IN625 in laser melting process using experimentally validated process-structure modeling

During the laser based manufacturing process such as metal additive manufacturing (AM) and laser cladding, enhancing or inhibiting liquid metal flow within the laser-induced melt pool provides a promising approach to tune material microstructure and the resulting mechanical properties. However, the effect of convection flow, specifically the dominant Marangoni convection flow in the melt pool, on the as-solidified material microstructure is still vague. This study aims to reveal convection-modified grain evolution in the laser melting process, e.g., the selective laser melting AM. We use a process-microstructure model and systematically design comparative simulation cases (with and without convection flow) to identify the effects of convection flow on melt pool geometry, solidification conditions, and as-solidified grain structure formation. The model is validated by secondary electron images and electron backscatter diffraction of the laser melted IN625 alloy provided by NIST Additive Manufacturing Benchmark Test Series. It is found that the strong Marangoni convection flow can widen the melt pool and notably affect the solidified microstructure in terms of grain growth directions and bulk nucleation events. This study provides a quantitative basis for controlling the as-solidified microstructure by manipulating the convection flow in the laser-induced melt pool.

Freezing of few nanometers water droplets

Water-ice transformation of few nm nanodroplets plays a critical role in nature including climate change, microphysics of clouds, survival mechanism of animals in cold environments, and a broad spectrum of technologies. In most of these scenarios, water-ice transformation occurs in a heterogenous mode where nanodroplets are in contact with another medium. Despite computational efforts, experimental probing of this transformation at few nm scales remains unresolved. Here, we report direct probing of water-ice transformation down to 2 nm scale and the length-scale dependence of transformation temperature through two independent metrologies. The transformation temperature shows a sharp length dependence in nanodroplets smaller than 10 nm and for 2 nm droplet, this temperature falls below the homogenous bulk nucleation limit. Contrary to nucleation on curved rigid solid surfaces, ice formation on soft interfaces (omnipresent in nature) can deform the interface leading to suppression of ice nucleation. For soft interfaces, ice nucleation temperature depends on surface modulus. Considering the interfacial deformation, the findings are in good agreement with predictions of classical nucleation theory. This understanding contributes to a greater knowledge of natural phenomena and rational design of anti-icing systems for aviation, wind energy and infrastructures and even cryopreservation systems.

A novel, in-situ observation of the initial ice scale layer development on different heat exchanger surfaces during EFC

Ice scale formation is one of the main impediments to the successful implementation of eutectic freeze crystallization (EFC). Controlling the formation of ice scale on heat exchanger (HX) surfaces has been attempted by using mechanical scrapers, with limited success in EFC. Some of these limitations have been associated with the HX surface properties. This has highlighted the requirement to understand the influence of HX surface properties on ice scaling to improve the control of ice scaling. This was achieved by using an augmented differential interference contrast (DIC) technique. The DIC technique allowed the observation of the development of the initial ice scale layer on four different HX surfaces which has not been observed previously. Ice scaling occured through the formation of distinct “ice islands” on the HX surfaces, showing different morphologies. These "ice islands" grew radially, ultimately merging to form the initial ice scale layer that is transparent to the naked eye. It was concluded that in the absence of bulk crystals, ice scaling occurs through heterogeneous nucleation followed by lateral and vertical growth. In the presence of bulk ice crystals, as was observed when a brass HX plate was used, scaling initiated through the adhesion of ice crystals onto the HX surface. Additional bulk ice crystals cohered onto the growing front of the ice scale, ultimately covering the entire HX surface. The scaling rates were influenced by a combination of both the nucleation and growth rates and differed with the HX materials resulting in different ice scaling rates. In conclusion, high scaling rates were attributed to high nucleation rates. When ice scaling was dominated by growth, the scaling rate was reduced. Overall, brass was found to delay scaling and increase the probability of bulk nucleation. SS316 was found to have the highest nucleation rate, resulting in the highest scaling rate of all the materials.