Nucleation Curves Research Articles

Nucleation Curves of Ice in Dilute Salt Solutions

Nucleation Curves of Ice in Dilute Salt Solutions

Mechanisms of the memory effect of clathrate hydrates

The memory effect in the nucleation of gas hydrates refers to the phenomenon that gas hydrates nucleate easier or faster in the water that has a history of gas hydrate formation than in fresh water that has no such history. Although several hypotheses have been proposed to explain the cause of the memory effect over the last several decades, it remains the longest-standing mystery in the nucleation of gas hydrates. Supersaturation of the guest gas has been considered to occur in a memory system, however, the extent of its impact on the memory effect has been unclear. In the current research, we used linear cooling ramp experiments under isobaric conditions to determine the nucleation curves of CO2 hydrate in quiescent water in a stainless-steel sample cell and in quiescent quasi-free water droplets supported by a bulk liquid of perfluoromethyldecalin contained in a Teflon sample cell. From systematically comparing the nucleation curves of both freshly prepared samples and samples with a history of CO2 hydrate formation in both the stainless-steel sample cell and the quasi-free water droplets, as well as the nucleation curves of methane – propane mixed gas hydrates previously reported, a coherent picture emerged. The impurity imprinting component, with the interfacial gaseous states as the entity of the “impurity”, and the guest supersaturation component, with or without nanobubbles in the bulk water, are comparable in size, albeit the former is the larger one.

Nucleation Curves of Carbon Dioxide Hydrate in the Absence of a Solid Wall

Nucleation kinetics of clathrate hydrate is poorly understood because of the difficulties in determining the essential parameter, nucleation rate. Nucleation rate enables quantitative comparisons of the impacts of various additives and solid walls on nucleation. We made a setup that determines the nucleation curves of structure I─forming CO2 hydrate in quiescent quasi-free water droplets supported by a bulk of liquid perfluoromethyldecalin under isobaric conditions. The results were compared to the nucleation rates of CO2 hydrate in quiescent water that was in direct contact with stainless-steel walls. We assessed the convergence of the nucleation curves with the increasing numbers of nucleation data and compared our results to the nucleation rates of methane/propane mixed gas hydrate in quiescent quasi-free water droplets and the nucleation rates of gas hydrates of various guest types in the presence of solid walls reported in the literature. We found that (1) 400 nucleation events were sufficient to construct a reliable nucleation curve; (2) the addition of stainless-steel walls promoted the nucleation kinetics of CO2 hydrate, as it did to methane/propane mixed gas hydrate; (3) the kinetic parameter was significantly lower than the theoretically expected value, whereas the thermodynamic parameter was comparable to both the theoretically expected value and the experimentally determined value reported in the literature; and (4) CO2 hydrate nucleated over a substantially shallower supercooling range and had higher nucleation rates than those of methane/propane mixed gas hydrate, both in the presence and in the absence of a solid wall.

Study on the nucleation kinetics of DL-methionine based on the metastable zone width of unseeded batch crystallization

The metastable zone width (MSZW) of DL-methionine aqueous solution for unseeded batch crystallization was measured by turbidity method. The spontaneous nucleation curves at different stirring rates (250 rpm, 350 rpm and 450 rpm) and cooling rates (18.0 K/h, 30.0 K/h and 42.0 K/h) were obtained by measuring the nucleation temperatures of solutions with saturation temperatures from 304.3 K to 341.9 K. The results show that the increase in saturation temperature and stirring rate makes the MSZW narrower. This is mainly because the enhanced mass transfer makes solute molecules more likely to collide and thus facilitate nucleation. Also the increase in cooling rate widen the MSZW for there is a time lag between nucleation and turbidity is detected. These data provide the operating boundary of crystallization and are important in production to obtain the desired crystal quality. Meanwhile, the nucleation kinetics is studied based on the MSZW data by five semi-empirical models in this work. And the interfacial energy between DL-methionine and water was determined, which decreases from 1.88 mJ·m2 to 0.99 mJ·m2 when temperature increases from 304.3 K to 341.9 K.

Nucleation curves of ice in the presence of nucleation promoters

Ice nucleation plays an important role in many fields like global environment, biology, food engineering and so on. It also lays foundation for further studies in the nucleation of clathrate hydrates and other more complex systems. Although the subject of ice nucleation has been studied for decades, several problems remain such as the lack of reliable heterogeneous ice nucleation promoters. For example, both organic and inorganic additives have been reported to be effective ice nucleation promoters but it remains unclear which group is more effective. In this paper, we employed a linear cooling ramp method to determine the nucleation rates of ice in the presence of a range of nucleation promoters, both organic and inorganic, and ranked their efficacy. The additives tested are; silver iodide (AgI), kaolinite, cellulose, cholesterol, steroid and Snomax. We found that the efficacy ranking among the tested additives was; Snomax ≈ AgI ≥ kaolinite > steroid > cholesterol ≈ celluloses ≥ Teflon wall.

Nucleation Curves of Ice in Dilute Salt Solutions

Nucleation Curves of Ice in Dilute Salt Solutions

Consecutive reaction kinetics model reveals the nature of long-term rice amylopectin retrogradation characteristics

Starch retrogradation involves nucleation and crystal growth steps, while their relative contribution to the overall retrogradation kinetics and relations with starch fine molecular structures have not been elucidated. In this study, a consecutive reaction kinetics model (CRK) was developed to fit long-term retrogradation kinetics curves for 10 rice starches with distinct molecular structures. Starch chain-length distributions (CLDs) and melting enthalpy kinetics curves for these starches were obtained from our published data. It was shown that these melting enthalpy kinetics curves can be satisfactorily deconvoluted by the CRK model into a combination of nucleation and crystal growth curves. Correlation analysis between CRK model-fitted parameters with starch CLDs showed that starch retrogradation nucleation and crystal growth steps were controlled by distinct starch fine molecular structures. These results have practical applications, as it enables a separate regulation of nucleation and crystal growth steps during retrogradation process of starch-based foods for desirable nutritional properties.

Optimizing the microstructure of a new machinable bioactive glass-ceramic

ObjectivesThis study aimed to optimize the crystallization process and the microstructure of a new bioactive glass-ceramic (GC) previously developed by our research group to obtain machinable glass-ceramics. MethodsDifferential scanning calorimetry (DSC) analyses were conducted to explore the characteristic temperatures and construct a semi-quantitative nucleation curve. The GC specimens were characterized by X-ray diffraction (XRD) and Rietveld refinement. Their brittleness index (B) and machinability were characterized and compared with IPS e.max-CAD®. Their Young's modulus, fracture toughness, and hardness were assessed. ResultsWe found that the maximum crystal nucleation rate temperature of this GC is ~470 °C. Treatments were designed based on the 1st DSC peak onset (570 °C), 1st peak offset (650 °C), and 2nd peak offset (705 °C) crystallization temperatures of lithium metasilicate (LS, LiSi2O3) and lithium disilicate (LS2, Li2Si2O5). Rietveld refinement indicated an increase in LS2 and a reduction in LS and amorphous phase for increased temperatures and longer treatment times. Their B values indicate good machinability compared with that of the control group based on statistical analyses. As expected, lower levels of LS2 increase the machinability regardless of the rotation speed adopted, leading to a greater depth of cut and reduced Edge Chipping Damage Depth (ECDD). ConclusionThis bioactive GC with optimized microstructure presents high machinability. For treatment temperatures above 570 °C, the number of elongated LS2 crystals increases and decreases the amorphous phase content, which reduce the machinability of the GC, and should therefore be avoided. The best results were obtained using heat treatment at 570 °C, which produces LS crystals embedded in a glassy matrix (67%) with small contents of secondary phases.

Nucleation curves of ice in quasi–free water droplets

Ice nucleation is important in global climate change and could also have implications to nucleation of more complex systems like clathrate hydrates. A new setup for experimental investigations of nucleation of ice that uses linear cooling ramps is described. The nucleation rates of ice in (1) microliter–sized quasi–free water droplets suspended at an interface between an inert fluorocarbon oil, perfluoromethyldecalin, and an inert hydrocarbon oil, squalane, and (2) microliter–sized quasi–free water droplets supported by stable wetting films of squalane, were determined from the procedure that was previously developed for clathrate hydrates. The impact of the number of the data points and the experimental cooling rate was investigated in detail. The nucleation curve of a given system was found to remain largely unchanged with the addition of data after about the first 100 data points. Additional 300 to 400 data points confirmed such convergence. The results also showed that the nucleation rate increased with the system supercooling, as expected, and the whole nucleation curve shifted somewhat downward with the use of a slower cooling rate. The nucleation rates of ice in the water droplets supported by stable wetting films of squalane were broadly similar to but slightly greater than those suspended between two immiscible liquids. We then compared our data to the nucleation rate of ice reported in the literature, which showed broad agreements when the differences in the scales were accounted for. The experimental method described was found to be reliable and the setup provides a basis for future studies on ice nucleation that may involve nucleation promoters, inhibitors or more complex entities.

Relaxation, crystal nucleation, kinetic spinodal and Kauzmann temperature in supercooled zinc selenide

Structural relaxation and crystallization are crucial phenomena in physics, chemistry, and materials science. A thorough study of their relationship could clarify some critical open questions. In this article, we focus on thermodynamic and kinetic properties: the Kauzmann temperature, TK (where the excess entropy tends to zero), the kinetic spinodal temperature, Tks (where the relaxation and crystal nucleation curves cross), and the glass transition temperature, Tg. We used zinc selenide (ZnSe) as a model system for which a reliable potential is available and obtained the self-diffusion coefficient, viscosity, critical nucleus birth times, relaxation times, entropy, Tg, Tks and TK by molecular dynamics (MD) simulations. We confirmed that the Stokes-Einstein equation breaks down in the moderate supercooled regime, impacting the relationships between the dynamic and thermodynamic properties. Two relaxation times were determined in the supercooled liquid (SCL) state: i) using the shear viscosity and the Maxwell equation, τη, and ii) from the self-intermediate scattering function and the Kohlrausch equation, τR. We found that in the whole supercooling regime, τη ≪ τR confirming two recent experimental studies for other substances. The nucleus birth times, τN, were also obtained for two system sizes. The τRT and τNT curves indeedcrossover,confirming the existence of a kinetic spinodal temperature for this system. Hence, for temperatures somewhat above and below the Tks, crystallization of the SCL could be affected by structural relaxation. Finally, our results demonstrate that if the Kauzmann temperature existed, it would be well below the Tks. Hence, crystal nucleation intervenes on the cooling path, and SCL ZnSe cannot reach this temperature, thus averting the paradoxical entropic situation. These findings shed light on some central problems related to supercooled liquids.

Nucleation and Morphology of Cu6Sn5 Intermetallic at the Interface between Molten Sn-0.7Cu-0.2Cr Solder and Cu Substrate

The nucleation kinetics and morphology of Cu6Sn5 IMCs at the interface between a Sn-0.7Cu-0.2Cr solder and Cu substrate were investigated in this study. A Sn-0.7Cu solder was utilized as a reference to elucidate the impact of Cr addition. The mechanical properties of the solder joints were determined via ball-shear tests. Cu coupons were dipped in the molten solders for 1 and 3 s at 240–300 °C, and the morphological analyses were conducted via electron microscopy. Both the solders contained scallop-like Cu6Sn5 IMCs. The smallest Cu6Sn5 IMCs were observed at 260 °C in both the solders, and the particle size increased at 280 and 300 °C. The IMCs in the Sn-0.7Cu-0.2Cr solder were smaller and thinner than those in the Sn-0.7Cu solder at all the reaction temperatures. The thickness of the IMCs increased as the reaction temperature increased. Inverse C-type nucleation curves were obtained, and the maximum nucleation rate was observed at an intermediate temperature. The shear strengths of the Sn-0.7Cu-0.2Cr solder joints were higher than those of the Sn-0.7Cu solder joints. This study will facilitate the application of lead-free solders, such as Sn-0.7Cu-0.2Cr, in automotive electrical components.

Interfacial free energy of a liquid-solid interface: Its change with curvature

We analyze the changes in the interfacial free energy between a spherical solid cluster and a fluid due to the change of the radius of the solid. Interfacial free energies from nucleation studies using the seeding technique for four different systems, being hard spheres, Lennard-Jones, and two models of water (mW and TIP4P/ICE), were plotted as a function of the inverse of the radius of the solid cluster. In all cases, the interfacial free energy was a linear function of the inverse of the radius of the solid cluster and this is consistent with Tolman's equation. This linear behavior is shown not only in isotherms but also along isobars. The effect of curvature on the interfacial free energy is more pronounced in water, followed by hard spheres, and smaller for Lennard-Jones particles. We show that it is possible to estimate nucleation rates of Lennard-Jones particles at different pressures by using information from simple NpT simulations and taking into account the variation of the interfacial free energy with the radius of the solid cluster. Neglecting the effects of the radius on the interfacial free energy (capillarity approximation) leads to incorrect values of the nucleation rate. For the Lennard-Jones system, the homogeneous nucleation curve is not parallel to the melting curve as was found for water in previous work. This is due to the increase in the interfacial free energy along the coexistence curve as the pressure increases. This work presents a simple and relatively straightforward way to approximately estimate nucleation rates.

Nucleation Curve of Carbon Dioxide Hydrate from a Linear Cooling Ramp Method.

Formation of gas hydrate is a first-order phase transition that starts with nucleation. Understanding of nucleation is of interest to many in chemical and petroleum industries, as nucleation, while beneficial in many chemical processes, is detrimentalin flow assurance of oil and natural gas pipelines. A primary difficulty in the investigation of gas hydrate nucleation has been the inability of researchers to compare nucleation rates of gas hydrates across various systems of different scales and complexities, which in turn has been limiting the ability of researchers to study the nucleation process itself. In this study, a first-generation high-pressure automated lag time apparatus (HP-ALTA MkI) was used to determine the nucleation curve of structure I (sI)-forming carbon dioxide hydrate. The instrument subjected a quiescent water sample of well-defined dimensions to a large number of linear cooling ramps under isobaric conditions, and detected and recorded carbon dioxide hydrate formation temperature distributions. A survival curve was constructed from the measured ensemble, and a nucleation curve was derived from the survival curve using the empirical model-independent method we had previously reported. The nucleation rate of carbon dioxide hydrate was found to be significantly greater than that of pure methane hydrate or that of natural gas hydrate over the entire range of subcooling investigated. We provide a new physical interpretation of an experimentally determined nucleation curve and, by doing so, solve one of the outstanding puzzles of the HP-ALTA technology.

Nucleation curve of carbon dioxide hydrate

The first generation High Pressure Automated Lag Time Apparatus (HP-ALTA MkI) was used to measure the nucleation curves of Structure I (sI) – forming carbon dioxide hydrate. The instrument applied a large number of constant cooling ramps to a quiescent water sample contained in a glass sample cell under isobaric conditions and recorded maximum achievable subcooling distributions. A survival curves was constructed from the measured data and a nucleation curve was derived from the survival curve using the model-independent method we had recently reported. It was found that the nucleation rate of carbon dioxide hydrate was significantly greater than that of pure methane hydrate or natural gas hydrates.

Transient Nucleation in Ge–Sb–S Thin Films

The crystal nucleation behavior and kinetics in Ge1.8Sb36.8S61.4 thin films were studied using optical microscopy coupled with a computer-controlled heating stage. The single-stage in situ heat treatment method was chosen for the study of nucleation. In-situ experiments were performed in the temperature range of 236–295 °C. The time evolution of the number of nuclei at various temperatures revealed transient behavior at low nucleation times. The transient nucleation data were described using the Shneidman equation to get values of steady-state nucleation rate, induction period, and time-lag of nucleation for the studied temperatures. On the basis of nucleation experiments, the temperature dependence of crystal–liquid surface energy and decoupling of nucleation rate and viscosity was assessed. The nucleation rate data obtained from microscopy measurements were discussed in terms of classical nucleation theory. It was found that the nucleation curve with the maximum at 288 °C and previously published growth...

Nucleation curves of methane hydrate from constant cooling ramp methods

A High Pressure Automated Lag Time Apparatus (HP-ALTA) was used to measure the nucleation curves of Structure I (sI) – forming methane hydrate. The instrument applied a large number of constant cooling ramps to a quiescent water sample contained in a glass sample cell under isobaric conditions and recorded maximum achievable subcooling distributions. Survival curves were constructed from the measured data and nucleation curves were derived from the survival curves using the model-independent method we had recently devised. The convergence of nucleation rates with the number of experimental runs was observed after approximately 400 runs which suggests that sampling of 400 nucleation events is sufficient for the unambiguous determination of the nucleation curves. The impact of the experimental cooling rates and the approximations used in the derivation of the nucleation curves was also assessed in details. Importantly, the derived nucleation curves continuously covered over a range of 15 K. The obtained nucleation curves were then compared to the nucleation rates of methane hydrate measured at several subcoolings by Makogon and analyzed by Kashchiev and Firoozabadi. Our nucleation curves yielded nucleation rates that were broadly similar to but somewhat lower than those of Makogon and Kashchiev and Firoozabadi at the relevant subcoolings.

Sigmoidal Nucleation and Growth Curves Across Nature Fit by the Finke–Watzky Model of Slow Continuous Nucleation and Autocatalytic Growth: Explicit Formulas for the Lag and Growth Times Plus Other Key Insights

Sigmoidal kinetic curves have been reported for a number of cooperative phenomena in nature. These curves may be fit by purely mathematical functions that, however, do not correspond to any physical model. The 1997 Finke–Watzky (F–W) two-step model of slow, continuous nucleation (A → B, rate constant k1) and fast, autocatalytic growth (A + B → 2B, rate constant k2) provides both a physical model and a mathematical solution. As a result, the F–W two-step kinetic model has been successfully applied to a large number of cooperative phenomena throughout nature that display sigmoidal kinetic curves. Herein, we derive formulas for the first, second, and third derivatives of the concentration of product versus time, [B]t, expressed in terms of the F–W parameters k1, k2, and the initial concentration of monomer, [A]0. Mathematical expressions are then derived for key empirical parameters in sigmoidal curves, including the induction period and (maximum) slope, which are then examined under the limit k1 ≪ k2[A]0 wh...

Nucleation kinetics, crystal growth and optical studies on lithium hydrogen oxalate monohydrate single crystal

Semi-organic lithium hydrogen oxalate monohydrate non-linear optical single crystals have been grown by slow evaporation solution technique at 40°C. The nucleation parameters such as critical radius, interfacial tension, and critical free energy change have been evaluated using the experimental data. The solubility and the nucleation curve of the crystal at different temperatures have been analyzed. The crystal has a positive temperature coefficient of solubility. The metastable zone width and induction period have been determined for the aqueous solution growth of lithium hydrogen oxalate monohydrate. The UV–vis–NIR spectrum showed this crystal has high transparency. The photoconductivity studies indicate lithium hydrogen oxalate monohydrate has positive photoconductivity behaviour. The low etch pit density observed on ( 0 0 1) crystal surface and the high resolution x-ray difraction analysis indicate the good quality of the grown crystals

Synthesis of transparent Er-doped fluorotellurite glass–ceramics through controlled crystallization

This work presents a detailed study of the preparation and microstructure of transparent glass–ceramics obtained from a TeO2−ZnO−ZnF2 fluorotellurite glass doped with ErF3. The determination of nucleation and crystal growth rate-like curves allows establishing a narrow temperature range (340–350 °C) for a controlled crystallization. Thereafter, a crystalline phase was grown through a two-step heat treatment: 10–20 h at a temperature slightly above the glass transition temperature, followed by a 2.5–3 h treatment at 340 °C. Structural analysis showed the nucleation of ErF3 nanocrystals (NCs) with a typical size of ≈50 nm that were homogeneously distributed in the glass matrix. The resulting glass–ceramic material remains highly transparent, with a small crystalline to amorphous ratio; yet the presence of ErF3 NCs has a large impact on the photoluminescence response of Er3+ ions. Upconverted visible emission is analyzed under 980 nm excitation: red emission from the 4F9/2 level is dramatically enhanced with respect to green 2H11/2, 4S3/2 → 4I15/2 hypersensitive transitions. The observed behaviour is attributed to the presence of Er3+ ions in the NCs, which are sites with lower phonon energy than the glass matrix. Moreover, the shorter inter-ionic distance between Er3+ ions in the NCs eases energy transfer between them.

Nucleation curves of methane – propane mixed gas hydrates in hydrocarbon oil

The second generation High Pressure Automated Lag Time Apparatus (HP–ALTA MkII) was used to measure the nucleation curves of Structure II (sII)–forming methane–propane mixed gas hydrates on the surface of a quasi–free water droplet suspended in involatile hydrocarbon oil, squalane. The measured nucleation curves were then compared to the previously obtained nucleation curves of the same guest gas hydrate on a quasi–free water droplet supported by perfluorodecalin. The comparison of the two sets of data sets showed that the nucleation rates of the two systems were broadly similar to each other. A simple master nucleation curve was derived for each system as a function of the system subcooling. The model-independent empirical equation that relates the nucleation rate to the system subcooling was Jwater-guest (s−1m−2)=2.38×10−39ΔT26.746 for a quasi-free water droplet suspended in squalane and Jwater-guest (s−1m−2)=7.70×10−11ΔT7.931 for a quasi-free water droplet supported by perfluorodecalin. The nucleation rates predicted by these empirical equations are then compared to the nucleation rates of other relevant systems in the literature. The model-independent analysis method for the derivation of nucleation curves we have developed can be applied to constant cooling ramp data obtained by any experimental techniques.