Journal articles on the topic 'Nucleation Parameters'
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1
A. Volf, Anna, Elena G. Fominykh, and Mikhail P. Anisimov. "Origin of the Nucleation Rate Empirical Data Inconsistencies for the Vapor-Gas Systems." Siberian Journal of Physics 3, no. 3 (October 1, 2008): 46–52. http://dx.doi.org/10.54362/1818-7919-2008-3-3-46-52.
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Independent results for vapor nucleation rates illustrate the nucleation rates inconsistencies for identical vapor-gas systems at the same conditions. Nature of these inconsistencies is not yet understood enough. Assumption is discussed that a reason for the experimental data inconsistencies is appeared in the result of the carrier gas effects on nucleation. It was supposed for a long time that any carrier gas is an ambient atmosphere to keep the nucleation temperature only. The recent experimental results have shown that a vapor-gas nucleation needs to be treated in approximation of binary solutions, i. e. a composition axis is appeared in addition to axes of nucleation rate versus pressure. Each single line of a nucleation rate isotherm is transformed to surface in a three dimensional space of nucleation parameters. Flow diffusion chamber and expansion Wilson type set up data comparison are discussed on the example of the published empirical data. It was shown using a model system that these two experimental realizations produce the inconsistent trajectories in the space of nucleation parameters. That misfit induces the different origin data inconsistencies and demonstrates relevance of gas treatment as an individual component of a nucleating vapor-gas system.
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Vancleef, Arne, Tom Van Gerven, Leen C. J. Thomassen, and Leen Braeken. "Ultrasound in Continuous Tubular Crystallizers: Parameters Affecting the Nucleation Rate." Crystals 11, no. 9 (September 1, 2021): 1054. http://dx.doi.org/10.3390/cryst11091054.
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Ultrasound has proven to be an important tool for controlling nucleation in continuous tubular crystallizers. However, insufficient information is available about the parameters controlling the nucleation rate in a continuous ultrasonic process. Previous research has studied parameters related to the nucleation rate, but has not measured the nucleation rate directly or continuously. In this work, the nucleation rate is measured continuously and inline to solve this problem and achieve a better process understanding. The results indicate that the ultrasound-assisted nucleation process is presumably dominated by secondary nucleation. Additionally, the supersaturation, residence time and flow rate have a strong influence on the nucleation rate. On the other hand, the influence of the ultrasonic power is crucial but levels off once a certain amount of power is reached. The static pressure in the system determines the effective ultrasonic power and is therefore also important for the nucleation rate. Finally, maintaining an equal power per unit of volume and an equal residence time by increasing the tubing diameter seems to be a good scale-up method. These results will improve understanding of ultrasonic tubular crystallizers and how to control them.
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Chen, J. P., A. Hazra, and Z. Levin. "Parameterizing ice nucleation rates using contact angle and activation energy derived from laboratory data." Atmospheric Chemistry and Physics 8, no. 24 (December 15, 2008): 7431–49. http://dx.doi.org/10.5194/acp-8-7431-2008.
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Abstract. The rate of ice nucleation in clouds is not easily determined and large discrepancies exist between model predictions and actual ice crystal concentration measured in clouds. In an effort to improve the parameterization of ice nucleating in cloud models, we investigate the rate of heterogeneous ice nucleation under specific ambient conditions by knowing the sizes as well as two thermodynamic parameters of the ice nuclei – contact angle and activation energy. Laboratory data of freezing and deposition nucleation modes were analyzed to derive inversely the two thermodynamic parameters for a variety of ice nuclei, including mineral dusts, bacteria, pollens, and soot particles. The analysis considered the Zeldovich factor for the adjustment of ice germ formation, as well as the solute and curvature effects on surface tension; the latter effects have strong influence on the contact angle. Contact angle turns out to be a more important factor than the activation energy in discriminating the nucleation capabilities of various ice nuclei species. By extracting these thermodynamic parameters, laboratory results can be converted into a formulation that follows classical nucleation theory, which then has the flexibility of incorporating factors such as the solute effect and curvature effect that were not considered in the experiments. Due to various uncertainties, contact angle and activation energy derived in this study should be regarded as "apparent" thermodynamics parameters.
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Chen, J. P., A. Hazra, and Z. Levin. "Parameterizing ice nucleation rates for cloud modeling using contact angle and activation energy derived from laboratory data." Atmospheric Chemistry and Physics Discussions 8, no. 4 (July 29, 2008): 14419–65. http://dx.doi.org/10.5194/acpd-8-14419-2008.
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Abstract. The rate of ice nucleation in clouds is not easily determined and large discrepancies exist between model predictions and actual ice crystal concentration measured in clouds. In an effort to improve the parameterization of ice nucleating in cloud models, we investigate the rate of heterogeneous ice nucleation under specific ambient conditions by knowing the sizes as well as two thermodynamic parameters of the ice nuclei – contact angle and activation energy. Laboratory data of freezing and deposition nucleation modes were analyzed to derive inversely the two thermodynamic parameters for a variety of ice nuclei, including mineral dusts, bacteria, pollens, and soot particles. The analysis considered the Zeldovich factor for the adjustment of ice germ formation, as well as the solute and curvature effects on surface tension, the latter effects have strong influence on the contact angle. Contact angle turns out to be a more important factor than the activation energy in discriminating the nucleation capabilities of various ice nuclei species. By extracting these thermodynamic parameters, laboratory results can be converted into a formulation that follows classical nucleation theory, which then has the flexibility of incorporating factors such as the solute effect and curvature effect that were not considered in the experiments.
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Németh, Z., and I. Salma. "Spatial extension of nucleating air masses in the Carpathian Basin." Atmospheric Chemistry and Physics 14, no. 16 (August 27, 2014): 8841–48. http://dx.doi.org/10.5194/acp-14-8841-2014.
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Abstract. Particle number size distributions were measured by differential mobility particle sizer in the diameter range of 6–1000 nm in the near-city background and city centre of Budapest continuously for two years. The city is situated in the middle part of the Carpathian Basin, which is a topographically discrete unit in the southeastern part of central Europe. Yearly mean nucleation frequencies and uncertainties for the near-city background and city centre were (28 + 6/−4) % and (27 + 9/−4) %, respectively. The total numbers of days with continuous and uninterrupted growth process were 43 and 31, respectively. These events and their properties were utilised to investigate the spatial scale of the nucleation in the basin, and whether there are any specific trajectories for the nucleating air masses. Local wind speed and direction data indicated that there seem to be differences between the nucleation and growth intervals and non-nucleation days. For further analysis, backward trajectories were generated by a simple air parcel trajectory model. Start and end time parameters of the nucleation and an end time parameter of the particle growth were derived by a standardised procedure based on examining the channel contents of the contour plots. These parameters were used to specify a segment on each backward trajectory that is associated with the nucleating air mass. The results indicated that regional nucleation happened in the continental boundary layer mostly in the Carpathian Basin but that the most distant trajectories originated outside of the basin. The nucleating air masses were predominantly associated with NW and SE geographical sectors, and some of them were also related to larger forested territories. The results also emphasised indirectly that the regional new particle formation and growth phenomena observable at the fixed location often expand to the bulk of the Carpathian Basin.
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Nisany, Stav, and Dan Mordehai. "A Multiple Site Type Nucleation Model and Its Application to the Probabilistic Strength of Pd Nanowires." Metals 12, no. 2 (February 4, 2022): 280. http://dx.doi.org/10.3390/met12020280.
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Pristine specimens yield plastically under high loads by nucleating dislocations. Since dislocation nucleation is a thermally activated process, the so-called nucleation-controlled plasticity is probabilistic rather than deterministic, and the distribution of the yield strengths depends on the activation parameters to nucleate. In this work, we develop a model to predict the strength distribution in nucleation-controlled plasticity when there are multiple nucleation site types. We then apply the model to molecular dynamics (MD) simulations of Pd nanowires under tension. We found that in Pd nanowires with a rhombic cross-section, nucleation starts from the edges, either with the acute or the obtuse cross-section angles, with a probability that is temperature-dependent. We show that the distribution of the nucleation strain is approximately normal for tensile loading at a constant strain rate. We apply the proposed model and extract the activation parameters for site types from both site types. With additional nudged elastic bands simulations, we propose that the activation entropy, in this case, has a negligible contribution. Additionally, the free-energy barriers obey a power-law with strain, with different exponents, which corresponds to the non-linear elastic deformation of the nanowires. This multiple site type nucleation model is not subjected only to two site types and can be extended to a more complex scenario like specimen with rough surfaces which has a distribution of nucleation sites with different conditions to nucleate dislocations.
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Wang, Chaohong, Jianyang Wu, Hao Wang, and Zhisen Zhang. "Classical nucleation theory of ice nucleation: Second-order corrections to thermodynamic parameters." Journal of Chemical Physics 154, no. 23 (June 21, 2021): 234503. http://dx.doi.org/10.1063/5.0049570.
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Schweitzer, Frank, and Lutz Schimansky-Geier. "Critical parameters for nucleation in finite systems." Journal of Colloid and Interface Science 119, no. 1 (September 1987): 67–73. http://dx.doi.org/10.1016/0021-9797(87)90245-1.
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Hyvönen, S., H. Junninen, L. Laakso, M. Dal Maso, T. Grönholm, B. Bonn, P. Keronen, et al. "A look at aerosol formation using data mining techniques." Atmospheric Chemistry and Physics Discussions 5, no. 4 (August 29, 2005): 7577–611. http://dx.doi.org/10.5194/acpd-5-7577-2005.
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Abstract. Atmospheric aerosol particle formation is frequently observed throughout the atmosphere, but despite various attempts of explanation, the processes behind it remain unclear. In this study data mining techniques were used to find the key parameters needed for atmospheric aerosol particle formation to occur. A dataset of 8 years of 80 variables collected at the boreal forest station (SMEAR II) in Southern Finland was used, incorporating variables such as radiation, humidity, SO2, ozone and present aerosol surface area. Data analysis were done using clustering and classification methods. The aim of this approach was to gain new parameters independent of any subjective interpretation. This resulted in two key parameters, relative humidity and preexisting aerosol particle surface (condensation sink), capable in explaining 88% of the nucleation events. The inclusion of any further parameters did not improve the results notably. Using these two variables it was possible to derive a nucleation probability function. Interestingly, the two most important variables are related to mechanisms that prevent the nucleation from starting and particles from growing, while parameters related to initiation of particle formation seemed to be less important. Nucleation occurs only with low relative humidity and condensation sink values. One possible explanation for the effect of high water content is that it prevents biogenic hydrocarbon ozonolysis reactions from producing sufficient amounts of low volatility compounds, which might be able to nucleate. Unfortunately the most important biogenic hydrocarbon compound emissions were not available for this study. Another effect of water vapour may be due to its linkage to cloudiness which may prevent the formation of nucleating and/or condensing vapours. A high number of preexisting particles will act as a sink for condensable vapours that otherwise would have been able to form sufficient supersaturation and initiate the nucleation process.
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Hyvönen, S., H. Junninen, L. Laakso, M. Dal Maso, T. Grönholm, B. Bonn, P. Keronen, et al. "A look at aerosol formation using data mining techniques." Atmospheric Chemistry and Physics 5, no. 12 (December 14, 2005): 3345–56. http://dx.doi.org/10.5194/acp-5-3345-2005.
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Abstract. Atmospheric aerosol particle formation is frequently observed throughout the atmosphere, but despite various attempts of explanation, the processes behind it remain unclear. In this study data mining techniques were used to find the key parameters needed for atmospheric aerosol particle formation to occur. A dataset of 8 years of 80 variables collected at the boreal forest station (SMEAR II) in Southern Finland was used, incorporating variables such as radiation, humidity, SO2, ozone and present aerosol surface area. This data was analyzed using clustering and classification methods. The aim of this approach was to gain new parameters independent of any subjective interpretation. This resulted in two key parameters, relative humidity and preexisting aerosol particle surface (condensation sink), capable in explaining 88% of the nucleation events. The inclusion of any further parameters did not improve the results notably. Using these two variables it was possible to derive a nucleation probability function. Interestingly, the two most important variables are related to mechanisms that prevent the nucleation from starting and particles from growing, while parameters related to initiation of particle formation seemed to be less important. Nucleation occurs only with low relative humidity and condensation sink values. One possible explanation for the effect of high water content is that it prevents biogenic hydrocarbon ozonolysis reactions from producing sufficient amounts of low volatility compounds, which might be able to nucleate. Unfortunately the most important biogenic hydrocarbon compound emissions were not available for this study. Another effect of water vapour may be due to its linkage to cloudiness which may prevent the formation of nucleating and/or condensing vapours. A high number of preexisting particles will act as a sink for condensable vapours that otherwise would have been able to form sufficient supersaturation and initiate the nucleation process.
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Hauptmann, Marc, Steven Brems, Elisabeth Camerotto, Paul W. Mertens, Marc M. Heyns, Stefan de Gendt, Christ Glorieux, and Walter Lauriks. "Stroboscopic Schlieren Study of Bubble Formation during Megasonic Agitation." Solid State Phenomena 187 (April 2012): 185–89. http://dx.doi.org/10.4028/www.scientific.net/ssp.187.185.
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An important problem in megasonic cleaning is the nucleation process of bubbles, which act as the cleaning agents. A fundamental understanding of this nucleation process will help to optimize the cleaning parameters for future applications to achieve damage free cleaning. In this work, we use quantitative stroboscopic Schlieren imaging to study the interaction of nucleating bubbles with a travelling acoustic wave. The advantage of this method is that it is non-interfering, meaning that it does not disturb the bubble nucleation. It is revealed that nucleation mechanism is a 2 step process, where a regime of slow bubble growth due to rectified diffusion is subsequently followed by a transient cavitation cycle, where bubbles grow explosively. The latter is accompanied by broadband acoustic emission and enhanced thermal dissipation, leading to the occurrence of thermal convection visible in the Schlieren images.
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Németh, Z., and I. Salma. "Source areas and trajectories of nucleating air masses within and near the Carpathian Basin." Atmospheric Chemistry and Physics Discussions 14, no. 7 (April 4, 2014): 9225–47. http://dx.doi.org/10.5194/acpd-14-9225-2014.
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Abstract. Particle number size distributions were measured by differential mobility particle sizer in the diameter range of 6–1000 nm in the near-city background and city centre of Budapest continuously for two years. The city is situated in the middle part of the Carpathian Basin, which is a topographically discrete unit in the southeast Central Europe. Yearly mean nucleation frequencies and uncertainties for the near-city background and city centre were (28+6/−4) % and (27+9/−4) %, respectively. Total numbers of days with continuous and uninterrupted growth process were 43 and 31, respectively. These events and their properties were utilised to investigate if there are any specific tracks and/or separable source regions for the nucleating air masses within or near the basin. Local wind speed and direction data indicated that there seem to be differences between the nucleation and growth intervals and non-nucleation days. For further analysis, backward trajectories were generated by a simple air parcel trajectory model. Start and end time parameters of the nucleation, and end time parameter of the particle growth were derived by a standardized procedure based on examining the channel contents of the contour plots. These parameters were used to specify a segment on each air mass trajectory that is associated with the track of the nucleating air mass. The results indicated that the nucleation events happened in the continental boundary layer mostly within the Carpathian Basin but the most distant trajectories originated outside of the basin. The tracks of the nucleating air masses were predominantly associated with NW and SE geographical fields, while the source areas that could be separated were frequently situated in the NW and NE quarters. Many of them were within or close to large forested territories. The results also emphasize that the new particle formation and growth phenomenon that occurs in the region influences larger territories than the Carpathian Basin.
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Zhao, Wei, Xiaofeng Huang, Bingji Yan, Shaoyan Hu, Hongwei Guo, and Dong Chen. "Recycling of Blast Furnace Slag and Fluorite Tailings into Diopside-Based Glass-Ceramics with Various Nucleating Agents’ Addition." Sustainability 13, no. 20 (October 9, 2021): 11144. http://dx.doi.org/10.3390/su132011144.
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Diopside-based glass-ceramics are successfully produced by recycling blast furnace slag and fluorite tailing with the addition of supplementary elements such as TiO2, Fe2O3 and Cr2O3 as nucleation agents, using a conventional melting method. The effects of various nucleating agents on the phase components and structure of the prepared glass-ceramics were evaluated by a differential scanning calorimeter, X-ray diffraction and scanning electron microscope–energy disperse spectrometer methods to determine the optimal dosage of nucleating agents. The results show that, in the preparation of diopside-based glass-ceramics, the suitable percentages of blast furnace and fluorite tailing are 55% and 45%, and the recommended composite nucleating agents consist of 1.5% Cr2O3, 2% TiO2 and 3% Fe2O3. Heat treatment was conducted at a nucleation temperature of 720 °C and a crystallization temperature of 920 °C, and the nucleation and crystallization durations were 1.0 h and 1.5 h, respectively. Under the abovementioned parameters, the obtained diopside-based glass-ceramics displayed a Vickers hardness of 7.12 GPa, density of 2.95 g·cm−3, water absorption of 0.02%, acid resistance of 0.23% and alkali resistance of 0.02%.
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Shi, G., and J. H. Seinfeld. "Transient kinetics of nucleation and crystallization: Part I. Nucleation." Journal of Materials Research 6, no. 10 (October 1991): 2091–96. http://dx.doi.org/10.1557/jmr.1991.2091.
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Analytical results obtained for the transient kinetics of nucleation enable one to interpret N(gd,t), the accumulated number concentration of clusters at the instrumentally detectable size, gd. The new results enable one to extract kinetic and thermodynamic parameters of nucleation from experimentally measured cluster concentrations and to test nucleation theories experimentally. An approach to estimate the mean time to form the first nucleated cluster in a given sample is also presented.
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Zschorsch, Markus, Robert Hölzl, Herbert Rüfer, Hans Joachim Möller, and Wilfried von Ammon. "Optimized Parameters for Modeling Oxygen Nucleation in Silicon." Solid State Phenomena 95-96 (September 2003): 71–76. http://dx.doi.org/10.4028/www.scientific.net/ssp.95-96.71.
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Gravner, Janko, and David Griffeath. "Nucleation Parameters for Discrete Threshold Growth on Z2." Experimental Mathematics 6, no. 3 (January 1997): 207–20. http://dx.doi.org/10.1080/10586458.1997.10504610.
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Shiau, Lie-Ding. "Comparison of the Nucleation Parameters of Aqueous l-glycine Solutions in the Presence of l-arginine from Induction Time and Metastable-Zone-Width Data." Crystals 11, no. 10 (October 12, 2021): 1226. http://dx.doi.org/10.3390/cryst11101226.
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Induction time and metastable-zone-width (MSZW) data for aqueous l-glycine solutions in the presence of l-arginine impurity were experimentally measured using a turbidity probe in this study. The nucleation parameters, including the interfacial free energy and pre-exponential nucleation factor, obtained from induction time data, were compared with those obtained from MSZW data. The influences of lag time on the nucleation parameters were examined for the induction time data. The effects of l-arginine impurity concentration on the nucleation parameters based on both the induction time and MSZW data were investigated in detail.
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Manopradha, N., S. Rama, S. Gowri, K. Kirubavathi, and K. Selvaraju. "Theoretical Investigation on Growth Kinetics and Thermodynamic Properties of Pyridine-2-Carboxylic Acid Crystals." Mechanics and Mechanical Engineering 23, no. 1 (July 10, 2019): 23–27. http://dx.doi.org/10.2478/mme-2019-0004.
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Abstract This work illustrates the significance of kinetic parameters of nucleation and thermal decomposition for Pyridine-2-carboxylic acid crystals. In the interest of maximizing the growth condition for the production of single crystals, nucleation parameters such as interfacial energy (σ), volume free energy (ΔGv), critical energy barrier for nucleation (ΔG*), radius of the critical nucleus (r*) and nucleation rate (J) were determined from the classical nucleation theory of solubility-enthalpy relation. The optimized geometry of the compound was computed from the DFT-B3LYP gradient calculations employing 6-31G(d,p) basis set and its vibrational frequencies were evaluated. Based on the vibrational analysis, the thermodynamic parameters were obtained and the correlative equations between these thermodynamic properties and variation in temperatures were also reported.
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Broerman, Benjamin. "Acoustic response of nuclear recoils in bubble chambers." Journal of Physics: Conference Series 2156, no. 1 (December 1, 2021): 012025. http://dx.doi.org/10.1088/1742-6596/2156/1/012025.
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Abstract The bubble chambers of the PICO collaboration use the acoustic signal generated from nucleations to classify nuclear recoil events from alpha decays in the bulk fluid. The success of these detectors in probing the potential WIMP-proton cross section comes in part from the low energy threshold that can be achieved. This nucleation threshold, based on the Seitz model, is dependent on fluid type, pressure, and temperature. At higher thresholds bubble nucleation does occur but with a significant loss in the measurable acoustic signal. To investigate this, the acoustic response of bulk nuclear recoil events was measured as a function of pressure and temperature and found to depend exponentially on both parameters.
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Azmi, Nik Salwani Md, Nornizar Anuar, Muhamad Fitri Othman, Noor Fitrah Abu Bakar, and Mohd Nazli Naim. "Electric-Potential-Assisted Crystallisation of L-Isoleucine: A Study of Nucleation Kinetics and Its Associated Parameters." Crystals 11, no. 6 (May 31, 2021): 620. http://dx.doi.org/10.3390/cryst11060620.
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The potential of producing L-isoleucine crystals with the aid of electric potential and its effect on the nucleation kinetics of L-isoleucine were probed using polythermal and isothermal crystallisation techniques, assisted with 5 V, 9 V, and 20 V electric potentials. The polythermal experiments were conducted with cooling rates of 0.1 °C/min–0.7 °C/min, whilst isothermal crystallisation was conducted with a supersaturation of 1.30–1.70, and both were carried out in a 200 mL temperature-controlled jacketed reactor. Prediction of the nucleation rate and its associated parameters for isothermal crystallisation was carried out using a molecular dynamics simulation. In both crystallisation techniques, electric potentials increased the nucleation rate, but the intensity of the electric potential had less impact on the measured parameters. Nucleation rates for 5 V isothermal crystallisation were in the order of 1010 higher than for polythermal crystallisation. Electric potential doubled the nucleation rates for polythermal crystallisation and increased the nucleation rates 12-fold in isothermal crystallisation. The isothermal technique produced the form B polymorph, but mixtures of forms A and B were produced in polythermal crystallisation. The predicted critical number of molecules, N*, and the critical radius, r*, were in good agreement with the experimental data, with a higher predicted nucleation rate in the order of 102.
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Korhonen, H., S. L. Sihto, V. M. Kerminen, and K. E. J. Lehtinen. "Evaluation of the accuracy of analysis tools for atmospheric new particle formation." Atmospheric Chemistry and Physics 11, no. 7 (April 1, 2011): 3051–66. http://dx.doi.org/10.5194/acp-11-3051-2011.
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Abstract. Several mathematical tools have been developed in recent years to analyze new particle formation rates and to estimate nucleation rates and mechanisms at sub-3 nm sizes from atmospheric aerosol data. Here we evaluate these analysis tools using 1239 numerical nucleation events for which the nucleation mechanism and formation rates were known exactly. The accuracy of the estimates of particle formation rate at 3 nm (J3) showed significant sensitivity to the details of the analysis, i.e. form of equations used and assumptions made about the initial size of nucleating clusters, with the fraction of events within a factor-of-two accuracy ranging from 43–97%. In general, the estimates of the actual nucleation rate at 1.5 nm (J1.5) were less accurate, and even the most accurate analysis set-up estimated only 59% of the events within a factor of two of the simulated mean nucleation rate. The J1.5 estimates were deteriorated mainly by the size dependence of the cluster growth rate below 3 nm, which the analysis tools do not take into account, but also by possible erroneous assumptions about the initial cluster size. The poor estimates of J1.5 can lead to large uncertainties in the nucleation prefactors (i.e. constant P in nucleation equation J1.5 = P × [H2SO4]k). Large uncertainties were found also in the procedures that are used to determine the nucleation mechanism. When applied to individual events, the analysis tools clearly overestimated the number of H2SO4 molecules in a critical cluster for most events, and thus associated them with a wrong nucleation mechanism. However, in some conditions the number of H2SO4 molecules in a critical cluster was underestimated. This indicates that analysis of field data that implies a maximum of 2 H2SO4 molecules in a cluster does not automatically rule out a higher number of molecules in the actual nucleating cluster. Our analysis also suggests that combining data from several new particle formation events to scatter plots of H2SO4 vs formation rates (J1.5 or J3) and determining the slope of the regression line may not give reliable information about the nucleation mechanism. Overall, while the analysis tools for new particle formation are useful for getting order-of-magnitude estimates of parameters related to atmospheric nucleation, one should be very cautious in interpreting the results. It is, for example, possible that the tools may have misdirected our theoretical understanding of the nucleation mechanism.
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Zheng, Dan, Wei Zou, Jie Yan, Chuanfeng Peng, Yuhang Fu, Bo Li, Li Zeng, Tinghong Huang, and Fengzhen Zhang. "Coupling of Contact Nucleation Kinetics with Breakage Model for Crystallization of Sodium Chloride Crystal in Fluidized Bed Crystallizer." Journal of Chemistry 2019 (September 18, 2019): 1–11. http://dx.doi.org/10.1155/2019/2150560.
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There are many nucleation theory-based different mechanisms. These theories mainly focused on production parameters in the crystallization and less on physical properties of crystals. In this research, a new model of contact nucleation theory coupled with the breakage mechanism of crystals is applied to describe the collision process in sodium chloride crystallization. This coupling nucleation model is presented here which relates the number of contact-collision site in nucleation owing to collision rate and the interfacial energy. F2 in the expression of the classic contact nucleation rate is redefined as a power function with the physical properties of crystals and breakage propensity. The experiment results indicate that crystal breakage propensity has a significant influence on the nucleation rate. Finally, analysis of the contact nucleation kinetic model and comparison with experiments reveal that the new nucleation model results are in better agreement with experiments. This new nucleation model is confirmed to represent the time-dependent collision behavior. The parameters of model are strongly related to the physical properties of crystal and fluidization conditions.
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Hoose, Corinna, Jón Egill Kristjánsson, Jen-Ping Chen, and Anupam Hazra. "A Classical-Theory-Based Parameterization of Heterogeneous Ice Nucleation by Mineral Dust, Soot, and Biological Particles in a Global Climate Model." Journal of the Atmospheric Sciences 67, no. 8 (August 1, 2010): 2483–503. http://dx.doi.org/10.1175/2010jas3425.1.
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Abstract An ice nucleation parameterization based on classical nucleation theory, with aerosol-specific parameters derived from experiments, has been implemented into a global climate model—the Community Atmosphere Model (CAM)-Oslo. The parameterization treats immersion, contact, and deposition nucleation by mineral dust, soot, bacteria, fungal spores, and pollen in mixed-phase clouds at temperatures between 0° and −38°C. Immersion freezing is considered for insoluble particles that are activated to cloud droplets, and deposition and contact nucleation are only allowed for uncoated, unactivated aerosols. Immersion freezing by mineral dust is found to be the dominant ice formation process, followed by immersion and contact freezing by soot. The simulated biological aerosol contribution to global atmospheric ice formation is marginal, even with high estimates of their ice nucleation activity, because the number concentration of ice nucleation active biological particles in the atmosphere is low compared to other ice nucleating aerosols. Because of the dominance of mineral dust, the simulated ice nuclei concentrations at temperatures below −20°C are found to correlate with coarse-mode aerosol particle concentrations. The ice nuclei (IN) concentrations in the model agree well overall with in situ continuous flow diffusion chamber measurements. At individual locations, the model exhibits a stronger temperature dependence on IN concentrations than what is observed. The simulated IN composition (77% mineral dust, 23% soot, and 10−5% biological particles) lies in the range of observed ice nuclei and ice crystal residue compositions.
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Boy, M., and M. Kulmala. "Nucleation events in the continental boundary layer: Influence of physical and meteorological parameters." Atmospheric Chemistry and Physics Discussions 1, no. 2 (October 8, 2001): 239–76. http://dx.doi.org/10.5194/acpd-1-239-2001.
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Abstract. The relationship between nucleation events and numerous physical and meteorological parameters was analysed using data collected at the Station for Measuring Forest Ecosystem-Atmosphere Relations (SMEAR II) in Hyytiälä, Finland. To do this, measurements of solar radiation (ultraviolet [UV], global, photosynthetically active radiation [PAR], net, reflected global radiation and reflected PAR), gas concentrations, temperature, humidity, wind direction, horizontal and vertical wind speed, horizontal and vertical wind variances and particle concentrations were collected over a 4 year period. For the year 1999 a detailed analysis of data were completed by examining parameters in order to determine the physical and meteorological conditions favourable to the formation of new particles. A comparison of different wavelength bands during the bursts of new particles led to the suggestion, that UV-A solar radiation seems to be the most probable radiation band concerning the photochemical reactions involved in the production of condensable vapours. Furthermore a high correlation between the daily curves of UV-A irradiance and the concentration of 3–5 nm particles was found throughout the year and examples will be given for two days. During the whole year the concentration of H2O is very low at times nucleation occurs compared to the average of the corresponding month. Especially in June and July many non-event days with high solar irradiance show high amounts of water molecules. To combine these results a "nucleation parameter" was calculated for the year 1999, by dividing UV-A solar radiation by the concentration of H2O and temperature and for clarity all values of the "nucleation parameter" have been divided by the maximum value of the year. Throughout the year nearly all nucleation event days reach a value of 0.2, which means that at this time the "nucleation parameter" reaches 20% of its yearly maximum and non-event days with high values (> 0.1) are mostly accompanied by high concentrations of existing particles.
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Russo, John, and Hajime Tanaka. "Crystal nucleation as the ordering of multiple order parameters." Journal of Chemical Physics 145, no. 21 (December 7, 2016): 211801. http://dx.doi.org/10.1063/1.4962166.
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Nývlt, J. "Effect of the Presence of Crystals on Nucleation Parameters." Crystal Research and Technology 28, no. 2 (1993): 139–43. http://dx.doi.org/10.1002/crat.2170280202.
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Bonn, B., M. Boy, M. Kulmala, A. Groth, K. Trawny, S. Borchert, and S. Jacobi. "A new parametrization for ambient particle formation over coniferous forests and its potential implications for the future." Atmospheric Chemistry and Physics 9, no. 20 (October 27, 2009): 8079–90. http://dx.doi.org/10.5194/acp-9-8079-2009.
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Abstract. Atmospheric new particle formation is a general phenomenon observed over coniferous forests. So far nucleation is either parameterised as a function of gaseous sulphuric acid concentration only, which is unable to explain the observed seasonality of nucleation events at different measurement sites, or as a function of sulphuric acid and organic molecules. Here we introduce different nucleation parameters based on the interaction of sulphuric acid and terpene oxidation products and elucidate the individual importance. They include basic trace gas and meteorological measurements such as ozone and water vapour concentrations, temperature (for terpene emission) and UV B radiation as a proxy for OH radical formation. We apply these new parameters to field studies conducted at conducted at Finnish and German measurement sites and compare these to nucleation observations on a daily and annual scale. General agreement was found, although the specific compounds responsible for the nucleation process remain speculative. This can be interpreted as follows: During cooler seasons the emission of biogenic terpenes and the OH availability limits the new particle formation while towards warmer seasons the ratio of ozone and water vapour concentration seems to dominate the general behaviour. Therefore, organics seem to support ambient nucleation besides sulphuric acid or an OH-related compound. Using these nucleation parameters to extrapolate the current conditions to prognosed future concentrations of ozone, water vapour and organic concentrations leads to a significant potential increase in the nucleation event number.
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Unno, Joi, and Izumi Hirasawa. "Parameter Estimation of the Stochastic Primary Nucleation Kinetics by Stochastic Integrals Using Focused-Beam Reflectance Measurements." Crystals 10, no. 5 (May 7, 2020): 380. http://dx.doi.org/10.3390/cryst10050380.
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The kinetic parameters of stochastic primary nucleation were estimated for the batch-cooling crystallization of L-arginine. It is difficult for process analytical tools to detect the first nucleus. In this study, the latent period for the total number of crystals to be increased to a predetermined threshold was repeatedly measured with focused-beam reflectance measurements. Consequently, the latent periods were different in each measurement due to the stochastic behavior of both primary and secondary nucleation. Therefore, at first, the distribution of the latent periods was estimated by a Monte Carlo simulation for some combinations of the kinetic parameters of primary nucleation. In the simulation, stochastic integrals of the population and mass balance equations were solved. Then, the parameters of the distribution of latent periods were estimated and correlated with the kinetic parameters of primary nucleation. The resulting correlation was represented by a mapping. Finally, the parameters of the actual distribution were input into the inverse mapping, and the kinetic parameters were estimated as the outputs. The estimated kinetic parameters were validated using statistical techniques, which implied that the observed distribution function of the latent periods for the thresholds used in the estimation coincided reasonably with the simulated one based on the estimated parameters.
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Wagner, Robert, Luisa Ickes, Allan K. Bertram, Nora Els, Elena Gorokhova, Ottmar Möhler, Benjamin J. Murray, Nsikanabasi Silas Umo, and Matthew E. Salter. "Heterogeneous ice nucleation ability of aerosol particles generated from Arctic sea surface microlayer and surface seawater samples at cirrus temperatures." Atmospheric Chemistry and Physics 21, no. 18 (September 21, 2021): 13903–30. http://dx.doi.org/10.5194/acp-21-13903-2021.
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Abstract. Sea spray aerosol particles are a recognised type of ice-nucleating particles under mixed-phase cloud conditions. Entities that are responsible for the heterogeneous ice nucleation ability include intact or fragmented cells of marine microorganisms as well as organic matter released by cell exudation. Only a small fraction of sea spray aerosol is transported to the upper troposphere, but there are indications from mass-spectrometric analyses of the residuals of sublimated cirrus particles that sea salt could also contribute to heterogeneous ice nucleation under cirrus conditions. Experimental studies on the heterogeneous ice nucleation ability of sea spray aerosol particles and their proxies at temperatures below 235 K are still scarce. In our article, we summarise previous measurements and present a new set of ice nucleation experiments at cirrus temperatures with particles generated from sea surface microlayer and surface seawater samples collected in three different regions of the Arctic and from a laboratory-grown diatom culture (Skeletonema marinoi). The particles were suspended in the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud chamber and ice formation was induced by expansion cooling. We confirmed that under cirrus conditions, apart from the ice-nucleating entities mentioned above, also crystalline inorganic salt constituents can contribute to heterogeneous ice formation. This takes place at temperatures below 220 K, where we observed in all experiments a strong immersion freezing mode due to the only partially deliquesced inorganic salts. The inferred ice nucleation active surface site densities for this nucleation mode reached a maximum of about 5×1010 m−2 at an ice saturation ratio of 1.3. Much smaller densities in the range of 108–109 m−2 were observed at temperatures between 220 and 235 K, where the inorganic salts fully deliquesced and only the organic matter and/or algal cells and cell debris could contribute to heterogeneous ice formation. These values are 2 orders of magnitude smaller than those previously reported for particles generated from microlayer suspensions collected in temperate and subtropical zones. While this difference might simply underline the strong variability of the number of ice-nucleating entities in the sea surface microlayer across different geographical regions, we also discuss how instrumental parameters like the aerosolisation method and the ice nucleation measurement technique might affect the comparability of the results amongst different studies.
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Karacs, Gábor, and András Roósz. "Simulation of Isothermal Nucleation of Austenite in Spheroidite Plain Carbon Steels." Materials Science Forum 752 (March 2013): 201–8. http://dx.doi.org/10.4028/www.scientific.net/msf.752.201.
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The austenitization is a solid phase transformation process accompanied by nucleation and nucleus growth controlled by long-range carbon diffusion. In the course of our work, a method was developed by which spheroidite model structures were constructed such a way that their different parameters (the size of ferrite grains, the average value of carbon concentration, the size of cementite spheroids) could be changed optionally. In addition, a nucleation model of free enthalpy base was created by which the difference between the two different places of nucleation can be distinguished on the basis of their free enthalpy. The effects of structure parameters, interface free enthalpies and temperature on the nucleation rate of austenite were investigated by cellular automaton simulations.
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Briard, Mélody, Clément Brandel, Sandrine Morin-Grognet, Gérard Coquerel, and Valérie Dupray. "Potassium Sulfate: A New Candidate to Explore Non-Photochemical Laser-Induced Nucleation Mechanisms." Crystals 11, no. 12 (December 16, 2021): 1571. http://dx.doi.org/10.3390/cryst11121571.
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In this paper, we report a study on the nucleation behavior of potassium sulfate (K2SO4) from aqueous solutions under the influence of unfocused nanosecond laser pulses. The objective is to contribute to the general understanding of the Non-Photochemical Laser-Induced Nucleation (NPLIN) mechanism. First, the influence of several parameters such as supersaturation as well as laser parameters (pulse energy, number of pulses, and laser polarization) on induction time, probability of nucleation and mean number of crystals in comparison with spontaneous nucleation was investigated. Then, we examined the influence of gas composition (i.e., degassing and gas bubbling (CO2 and N2)) of the supersaturated solutions on the NPLIN kinetics, showing no correlation between gas content (or nature) on the crystallization behavior. Our study questions the role of impurities within the solution regarding the mechanism of laser-induced nucleation.
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Zhang, Fajun, José A. Gavira, Geun Woo Lee, and Dirk Zahn. "Nonclassical Nucleation—Role of Metastable Intermediate Phase in Crystal Nucleation: An Editorial Prefix." Crystals 11, no. 2 (February 10, 2021): 174. http://dx.doi.org/10.3390/cryst11020174.
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Classical nucleation theory (CNT), which was established about 90 years ago, represents the most commonly used theory in describing nucleation processes. For a fluid-to-solid phase transition, CNT states that the solutes in a supersaturated solution reversibly form small clusters. Once a cluster reaches its critical size, it becomes thermodynamically stable and is favored for further growth. One of the most important assumptions of CNT is that the nucleation process is described by one reaction coordinate and all order parameters proceed simultaneously. Recent studies in experiments, computer simulations, and theory have revealed nonclassical features in the early stage of nucleation. In particular, the decoupling of order parameters involved during a fluid-to-solid transition leads to the so-called two-step nucleation mechanism, in which a metastable intermediate phase (MIP) exists in parallel to the initial supersaturated solution and the final crystals. These MIPs can be high-density liquid phases, mesoscopic clusters, or preordered states. In this Special Issue, we focus on the role of the various MIPs in the early stage of crystal nucleation of organic materials, metals and alloys, aqueous solutions, minerals, colloids, and proteins, and thus on various scenarios of nonclassical pathways of crystallization.
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Boy, M., and M. Kulmala. "Nucleation events in the continental boundary layer: Influence of physical and meteorological parameters." Atmospheric Chemistry and Physics 2, no. 1 (January 10, 2002): 1–16. http://dx.doi.org/10.5194/acp-2-1-2002.
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Abstract. The relationship between nucleation events and numerous physical and meteorological parameters was analysed using data collected at the Station for Measuring Forest Ecosystem-Atmosphere Relations (SMEAR II) in Hyytiälä, Finland. To do this, measurements of solar radiation (ultraviolet [UV], global, photosynthetically active radiation [PAR], net, reflected global radiation and reflected PAR), gas concentrations, temperature, humidity, wind direction, horizontal and vertical wind speed, horizontal and vertical wind variances and particle concentrations were collected over a 4 year period. For the year 1999 a detailed analysis of data were completed by examining parameters in order to determine the physical and meteorological conditions favourable to the formation of new particles. A comparison of different wavelength bands during the bursts of new particles led to the suggestion, that UV-A solar radiation seems to be the most probable radiation band concerning the photochemical reactions involved in the production of condensable vapours. Furthermore a high correlation between the daily curves of UV-A irradiance and the concentration of 3 - 5 nm particles was found throughout the year and examples will be given for two days. During the whole year the concentration of H2O is very low at times nucleation occurs compared to the average of the corresponding month. Especially in June and July many non-event days with high solar irradiance show high amounts of water molecules. To combine these results a "nucleation parameter" was calculated for the year 1999, by dividing UV-A solar radiation by the concentration of H2O and temperature. Throughout the year nearly all nucleation event days reach a value of the "nucleation parameter" of at least 5.4 x 10-25 W m molecules-1 K-1. Non-event days with high values (> 2.7 x 10-25 W m molecules-1 K-1) are mostly accompanied by high concentrations of existing particles.
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Gagné, S., T. Nieminen, T. Kurtén, H. E. Manninen, T. Petäjä, L. Laakso, V. M. Kerminen, M. Boy, and M. Kulmala. "Factors influencing the contribution of ion-induced nucleation in a boreal forest, Finland." Atmospheric Chemistry and Physics Discussions 9, no. 6 (December 1, 2009): 25799–838. http://dx.doi.org/10.5194/acpd-9-25799-2009.
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Abstract. We present the longest series of measurements so far (2 years and 7 months) made with an Ion-DMPS at the SMEAR II measurement station in Hyytiälä, Southern Finland. We show that the classification of overcharged (implying some participation of ion-induced nucleation) and undercharged (implying no or very little participation of ion-induced nucleation) days based on Ion-DMPS measurements agrees with the fraction of ion-induced nucleation based on NAIS measurements. We analyzed the influence of different parameters on the contribution of ion-induced nucleation to the total particle formation rate. We found that the fraction of ion-induced nucleation is typically higher on warmer, drier and sunnier days compared to colder days with less solar radiation and a higher relative humidity. Also, we observed that bigger concentrations of new particles were produced on days with a smaller fraction of ion-induced nucleation. Moreover, sulfuric acid concentrations were smaller for days with a bigger fraction of ion-induced nucleation. Finally, we propose tentative explanations on how these different parameters influence the different nucleation mechanisms, and show that the different mechanisms seem to take place at the same time during an event. The relative contribution of the different mechanisms seems to vary depending on the surrounding conditions.
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Ickes, Luisa, André Welti, Corinna Hoose, and Ulrike Lohmann. "Classical nucleation theory of homogeneous freezing of water: thermodynamic and kinetic parameters." Physical Chemistry Chemical Physics 17, no. 8 (2015): 5514–37. http://dx.doi.org/10.1039/c4cp04184d.
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Kulkarni, G., J. Fan, J. M. Comstock, X. Liu, and M. Ovchinnikov. "Laboratory measurements and model sensitivity studies of dust deposition ice nucleation." Atmospheric Chemistry and Physics 12, no. 16 (August 16, 2012): 7295–308. http://dx.doi.org/10.5194/acp-12-7295-2012.
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Abstract. We investigated the ice nucleating properties of mineral dust particles to understand the sensitivity of simulated cloud properties to two different representations of contact angle in the Classical Nucleation Theory (CNT). These contact angle representations are based on two sets of laboratory deposition ice nucleation measurements: Arizona Test Dust (ATD) particles of 100, 300 and 500 nm sizes were tested at three different temperatures (−25, −30 and −35 °C), and 400 nm ATD and kaolinite dust species were tested at two different temperatures (−30 and −35 °C). These measurements were used to derive the onset relative humidity with respect to ice (RHice) required to activate 1% of dust particles as ice nuclei, from which the onset single contact angles were then calculated based on CNT. For the probability density function (PDF) representation, parameters of the log-normal contact angle distribution were determined by fitting CNT-predicted activated fraction to the measurements at different RHice. Results show that onset single contact angles vary from ~18 to 24 degrees, while the PDF parameters are sensitive to the measurement conditions (i.e. temperature and dust size). Cloud modeling simulations were performed to understand the sensitivity of cloud properties (i.e. ice number concentration, ice water content, and cloud initiation times) to the representation of contact angle and PDF distribution parameters. The model simulations show that cloud properties are sensitive to onset single contact angles and PDF distribution parameters. The comparison of our experimental results with other studies shows that under similar measurement conditions the onset single contact angles are consistent within ±2.0 degrees, while our derived PDF parameters have larger discrepancies.
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Yao, X., M. S. Dargusch, A. K. Dahle, C. J. Davidson, and D. H. StJohn. "Investigation into the effect of nucleation parameters on grain formation during solidification using a cellular automaton-finite control volume method." Journal of Materials Research 23, no. 9 (September 2008): 2312–25. http://dx.doi.org/10.1557/jmr.2008.0303.
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A cellular automation (CA) model has successfully been used to model the development of microstructure of an aluminum alloy during solidification to produce detailed structure maps for the solidified alloys. More recently, the application of CA models to practical castings/solidification conditions has attracted increasing research interest. However, the determination of the calculation parameters of any model associated with nucleation is difficult. Accordingly, this work investigates the detailed effect of the six parameters of nucleation on microstructure formation and morphology as well as the grain size by cellular automaton-finite control volume method (CAFVM). The nucleation parameters can be determined or estimated by comparing the calculated and experimental results, which enables a more practical prediction of the microstructure (morphology and grain size).
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Allmendinger, Andrea, Yuen Li Butt, Raphael Mietzner, Felix Schmidt, Joerg Luemkemann, and Carmen Lema Martinez. "Controlling Ice Nucleation during Lyophilization: Process Optimization of Vacuum-Induced Surface Freezing." Processes 8, no. 10 (October 8, 2020): 1263. http://dx.doi.org/10.3390/pr8101263.
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Biopharmaceuticals are often lyophilized to improve their storage stability. Controlling ice nucleation during the freezing step of the lyophilization process is desired to increase homogeneity of product properties across a drug product batch and shorten the primary drying time. The present communication summarizes the process optimization of the freezing process when using vacuum-induced surface freezing to control ice nucleation, in particular for amorphous samples. We characterized freeze-dried samples for solid state properties, and compared these to uncontrolled nucleated samples using bovine serum albumin (BSA) as a model protein. Freezing parameters were optimized to obtain complete nucleation, adequate cake resistance during the subsequent lyophilization cycle, and elegant cakes. We highlight the challenges associated with vacuum-induced surface freezing and propose optimized freezing parameters to control ice nucleation, enabling manufacturing of amorphous samples.
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Kaufmann, Lukas, Claudia Marcolli, Beiping Luo, and Thomas Peter. "Refreeze experiments with water droplets containing different types of ice nuclei interpreted by classical nucleation theory." Atmospheric Chemistry and Physics 17, no. 5 (March 14, 2017): 3525–52. http://dx.doi.org/10.5194/acp-17-3525-2017.
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Abstract. Homogeneous nucleation of ice in supercooled water droplets is a stochastic process. In its classical description, the growth of the ice phase requires the emergence of a critical embryo from random fluctuations of water molecules between the water bulk and ice-like clusters, which is associated with overcoming an energy barrier. For heterogeneous ice nucleation on ice-nucleating surfaces both stochastic and deterministic descriptions are in use. Deterministic (singular) descriptions are often favored because the temperature dependence of ice nucleation on a substrate usually dominates the stochastic time dependence, and the ease of representation facilitates the incorporation in climate models. Conversely, classical nucleation theory (CNT) describes heterogeneous ice nucleation as a stochastic process with a reduced energy barrier for the formation of a critical embryo in the presence of an ice-nucleating surface. The energy reduction is conveniently parameterized in terms of a contact angle α between the ice phase immersed in liquid water and the heterogeneous surface. This study investigates various ice-nucleating agents in immersion mode by subjecting them to repeated freezing cycles to elucidate and discriminate the time and temperature dependences of heterogeneous ice nucleation. Freezing rates determined from such refreeze experiments are presented for Hoggar Mountain dust, birch pollen washing water, Arizona test dust (ATD), and also nonadecanol coatings. For the analysis of the experimental data with CNT, we assumed the same active site to be always responsible for freezing. Three different CNT-based parameterizations were used to describe rate coefficients for heterogeneous ice nucleation as a function of temperature, all leading to very similar results: for Hoggar Mountain dust, ATD, and larger nonadecanol-coated water droplets, the experimentally determined increase in freezing rate with decreasing temperature is too shallow to be described properly by CNT using the contact angle α as the only fit parameter. Conversely, birch pollen washing water and small nonadecanol-coated water droplets show temperature dependencies of freezing rates steeper than predicted by all three CNT parameterizations. Good agreement of observations and calculations can be obtained when a pre-factor β is introduced to the rate coefficient as a second fit parameter. Thus, the following microphysical picture emerges: heterogeneous freezing occurs at ice-nucleating sites that need a minimum (critical) surface area to host embryos of critical size to grow into a crystal. Fits based on CNT suggest that the critical active site area is in the range of 10–50 nm2, with the exact value depending on sample, temperature, and CNT-based parameterization. Two fitting parameters are needed to characterize individual active sites. The contact angle α lowers the energy barrier that has to be overcome to form the critical embryo at the site compared to the homogeneous case where the critical embryo develops in the volume of water. The pre-factor β is needed to adjust the calculated slope of freezing rate increase with temperature decrease. When this slope is steep, this can be interpreted as a high frequency of nucleation attempts, so that nucleation occurs immediately when the temperature is low enough for the active site to accommodate a critical embryo. This is the case for active sites of birch pollen washing water and for small droplets coated with nonadecanol. If the pre-factor is low, the frequency of nucleation attempts is low and the increase in freezing rate with decreasing temperature is shallow. This is the case for Hoggar Mountain dust, the large droplets coated with nonadecanol, and ATD. Various hypotheses why the value of the pre-factor depends on the nature of the active sites are discussed.
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Lorbiecka, Agnieszka Zuzanna, and Božidar Šarler. "A Sensitivity Study of Grain Growth Model For Prediction of ECT and CET Transformations in Continuous Casting of Steel." Materials Science Forum 649 (May 2010): 373–78. http://dx.doi.org/10.4028/www.scientific.net/msf.649.373.
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A two dimensional model was developed to predict the grain structure (Equiaxed to Columnar Transformation (ECT) and Columnar to Equiaxed Transformation (CET) in the continuous casting of steel. The processes of nucleation, growth and impingement of the grains are modelled as follows: (I) the nucleation is modeled through a continuous dependency of the nucleation density on temperature by the Gaussian distribution. Different nucleation parameters are used at the boundary and in the bulk region. (II) The growth and impingement are modeled by the Kurz, Giovanola, Trivedi (KGT) model. The Cellular Automata (CA) technique is used to solve the model. The CA method is based on the Nastac’s and simplified neighborhoods. Calculations are shown for square billets of the dimension 140 mm. Fixed input parameter of the model represents the macroscopic temperature field obtained from the Štore Steel billet simulation system [1]. All other grain structure physical model parameters are varied, such as: the surface and the bulk area, mean nucleation undercooling, standard deviation of undercooling, maximum density of nuclei. The computational parameters, such as the micro mesh size and the time step are varied as well. The influence of the variation of different parameters on calculated grain structure is shown. Finally, the model parameters are adjusted in order to obtain the experimentally determined actual billet ECT and CET positions for 51CrV4+Mo spring steel (Al: 0.02, Cr: 1.05, Cu: 0.125, Mn: 0.9,Mo: 0.025, Ni: 0.1, Si: 0.275, V: 0.155, C: 0.51, P: 0.0125, S: 0.0275 wt%). A systematic procedure is outlined for adjusting of the model data with the experiment.
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Arnault, J. C., G. Schull, R. Polini, M. Mermoux, and J. Faerber. "Effects of the bias enhanced nucleation hot-filament chemical-vapor deposition parameters on diamond nucleation on iridium." Journal of Applied Physics 98, no. 3 (August 2005): 033521. http://dx.doi.org/10.1063/1.1999027.
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Dobretsov, V. Yu, and V. G. Vaks. "The microscopical theory of homogeneous nucleation in alloys: II. Calculations of nucleation parameters for various alloy models." Journal of Physics: Condensed Matter 10, no. 10 (March 16, 1998): 2275–90. http://dx.doi.org/10.1088/0953-8984/10/10/010.
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Khosrawi, F., J. Ström, A. Minikin, and R. Krejci. "Particle formation in the Arctic free troposphere during the ASTAR 2004 campaign: a case study on the influence of vertical motion on the binary homogeneous nucleation of H<sub>2</sub>SO<sub>4</sub>/H<sub>2</sub>O." Atmospheric Chemistry and Physics Discussions 9, no. 5 (October 20, 2009): 21959–92. http://dx.doi.org/10.5194/acpd-9-21959-2009.
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Abstract. During the ASTAR (Arctic Study of Tropospheric Aerosol and Radiation) campaign nucleation mode particles (4 to 13 nm) were quite frequently observed at altitudes below 4000 m. However, in the upper free troposphere, nucleation mode particles were only observed once, namely during the flight on 24 May 2004 (7000 m). To investigate if vertical motion are the reason for this difference that on one particular day nucleation mode particles were observed but not on the other days we employ a microphysical box model. The box model simulations were performed along air parcel trajectories calculated 6-d backwards based on European Center for Medium-Range Weather Forecasts (ECMWF) meteorological analyses using state parameters such as pressure and temperature in combination with additional parameters such as vertical stability. Box model simulations were performed for the 24 May where nucleation mode particles were observed (nucleation event) as well as for the day with measurements before and after (22 and 26 May) which are representative for no nucleation (none nucleation event). A nucleation burst was simulated along all trajectories, however, in the majority of the simulations the nucleation rate was either too low or too high so that no nucleation mode particles were left at the time were the measurements were performed. Further, the simulation results could be divided into three cases. Thereby, we found that for case 1 the temperature was the only driving mechanism while for case 2 and 3 vertical motion have influenced the formation of new particles. The reason why nucleation mode particles were observed on 24 May, but not on the other day, can be explained by the conditions under which particle formation occurred. On 24 May the particle formation was caused by a slow updraft, while on the other two days the particle formation was caused by a fast updraft.
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Khosrawi, F., J. Ström, A. Minikin, and R. Krejci. "Particle formation in the Arctic free troposphere during the ASTAR 2004 campaign: a case study on the influence of vertical motion on the binary homogeneous nucleation of H<sub>2</sub>SO<sub>4</sub>/H<sub>2</sub>O." Atmospheric Chemistry and Physics 10, no. 3 (February 2, 2010): 1105–20. http://dx.doi.org/10.5194/acp-10-1105-2010.
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Abstract. During the ASTAR (Arctic Study of Tropospheric Aerosol and Radiation) campaign nucleation mode particles (4 to 13 nm) were quite frequently observed at altitudes below 4000 m. However, in the upper free troposphere, nucleation mode particles were only observed once, namely during the flight on 24 May 2004 (7000 m). To investigate if vertical motion were the reason for this difference that on one particular day nucleation mode particles were observed but not on the other days we employ a microphysical box model. The box model simulations were performed along air parcel trajectories calculated 6-d backwards based on European Center for Medium-Range Weather Forecasts (ECMWF) meteorological analyses using state parameters such as pressure and temperature in combination with additional parameters such as vertical stability. Box model simulations were performed for the 24 May where nucleation mode particles were observed (nucleation event) as well as for the days with measurements before and after (22 and 26 May) which are representative for no nucleation (non-nucleation event). A nucleation burst was simulated along all trajectories, however, in the majority of the simulations the nucleation rate was either too low or too high so that no nucleation mode particles were left at the time when the measurements were performed. Further, the simulation results could be divided into three cases. Thereby, we found that for case 1 the temperature was the only driving mechanism for the formation of new particles while for case 2 and 3 vertical motion have influenced the formation of new particles. The reason why nucleation mode particles were observed on 24 May, but not on the other days, can be explained by the conditions under which particle formation occurred. On 24 May the particle formation was caused by a slow updraft, while on the other two days the particle formation was caused by a fast updraft.
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Gagné, S., T. Nieminen, T. Kurtén, H. E. Manninen, T. Petäjä, L. Laakso, V. M. Kerminen, M. Boy, and M. Kulmala. "Factors influencing the contribution of ion-induced nucleation in a boreal forest, Finland." Atmospheric Chemistry and Physics 10, no. 8 (April 21, 2010): 3743–57. http://dx.doi.org/10.5194/acp-10-3743-2010.
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Abstract. We present the longest series of measurements so far (2 years and 7 months) made with an Ion-DMPS at the SMEAR II measurement station in Hyytiälä, Southern Finland. We show that the classification into overcharged (implying some participation of ion-induced nucleation) and undercharged (implying no or very little participation of ion-induced nucleation) days, based on Ion-DMPS measurements, agrees with the fraction of ion-induced nucleation based on NAIS measurements. Those classes are based on the ratio of ambient charged particle to steady-state charged particle concentration, known as the charging state. We analyzed the influence of different parameters on the contribution of ion-induced nucleation to the total particle formation rate. We found that the fraction of ion-induced nucleation is typically higher on warmer, drier and sunnier days compared to colder days with less solar radiation and a higher relative humidity. Also, we observed that bigger concentrations of new particles were produced on days with a smaller fraction of ion-induced nucleation. Moreover, sulfuric acid saturation ratios were smaller for days with a bigger fraction of ion-induced nucleation. Finally, we propose explanations on how these different parameters could influence neutral and ion-induced nucleation, and show that the different mechanisms seem to take place at the same time during an event. For example, we propose that these observed differences could be due to high temperature and low vapors' saturation ratios (water and sulfuric acid) increasing the height of the energy barrier a particle has to reach before it can grow and thus limiting neutral nucleation.
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Lacher, Larissa, Martin Steinbacher, Nicolas Bukowiecki, Erik Herrmann, Assaf Zipori, and Zamin Kanji. "Impact of Air Mass Conditions and Aerosol Properties on Ice Nucleating Particle Concentrations at the High Altitude Research Station Jungfraujoch." Atmosphere 9, no. 9 (September 19, 2018): 363. http://dx.doi.org/10.3390/atmos9090363.
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Ice nucleation is the source of primary ice crystals in mixed-phase clouds. Only a small fraction of aerosols called ice nucleating particles (INPs) catalyze ice formation, with their nature and origin remaining unclear. In this study, we investigate potential predictor parameters of meteorological conditions and aerosol properties for INP concentrations at mixed-phase cloud condition at 242 K. Measurements were conducted at the High Altitude Research Station Jungfraujoch (Switzerland, 3580 m a.s.l.), which is located predominantly in the free troposphere (FT) but can occasionally receive injections from the boundary layer (BLI). Measurements are taken during a long-term study of eight field campaigns, allowing for the first time an interannual (2014–2017) and seasonal (spring, summer, and winter) distinction of high-time-resolution INP measurements. We investigate ranked correlation coefficients between INP concentrations and meteorological parameters and aerosol properties. While a commonly used parameterization lacks in predicting the observed INP concentrations, the best INP predictor is the total available surface area of the aerosol particles, with no obvious seasonal trend in the relationship. Nevertheless, the predicting capability is less pronounced in the FT, which might be caused by ageing effects. Furthermore, there is some evidence of anthropogenic influence on INP concentrations during BLI. Our study contributes to an improved understanding of ice nucleation in the free troposphere, however, it also underlines that a knowledge gap of ice nucleation in such an environment exists.
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Alpert, Peter A., and Daniel A. Knopf. "Analysis of isothermal and cooling-rate-dependent immersion freezing by a unifying stochastic ice nucleation model." Atmospheric Chemistry and Physics 16, no. 4 (February 24, 2016): 2083–107. http://dx.doi.org/10.5194/acp-16-2083-2016.
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Abstract. Immersion freezing is an important ice nucleation pathway involved in the formation of cirrus and mixed-phase clouds. Laboratory immersion freezing experiments are necessary to determine the range in temperature, T, and relative humidity, RH, at which ice nucleation occurs and to quantify the associated nucleation kinetics. Typically, isothermal (applying a constant temperature) and cooling-rate-dependent immersion freezing experiments are conducted. In these experiments it is usually assumed that the droplets containing ice nucleating particles (INPs) all have the same INP surface area (ISA); however, the validity of this assumption or the impact it may have on analysis and interpretation of the experimental data is rarely questioned. Descriptions of ice active sites and variability of contact angles have been successfully formulated to describe ice nucleation experimental data in previous research; however, we consider the ability of a stochastic freezing model founded on classical nucleation theory to reproduce previous results and to explain experimental uncertainties and data scatter. A stochastic immersion freezing model based on first principles of statistics is presented, which accounts for variable ISA per droplet and uses parameters including the total number of droplets, Ntot, and the heterogeneous ice nucleation rate coefficient, Jhet(T). This model is applied to address if (i) a time and ISA-dependent stochastic immersion freezing process can explain laboratory immersion freezing data for different experimental methods and (ii) the assumption that all droplets contain identical ISA is a valid conjecture with subsequent consequences for analysis and interpretation of immersion freezing. The simple stochastic model can reproduce the observed time and surface area dependence in immersion freezing experiments for a variety of methods such as: droplets on a cold-stage exposed to air or surrounded by an oil matrix, wind and acoustically levitated droplets, droplets in a continuous-flow diffusion chamber (CFDC), the Leipzig aerosol cloud interaction simulator (LACIS), and the aerosol interaction and dynamics in the atmosphere (AIDA) cloud chamber. Observed time-dependent isothermal frozen fractions exhibiting non-exponential behavior can be readily explained by this model considering varying ISA. An apparent cooling-rate dependence of Jhet is explained by assuming identical ISA in each droplet. When accounting for ISA variability, the cooling-rate dependence of ice nucleation kinetics vanishes as expected from classical nucleation theory. The model simulations allow for a quantitative experimental uncertainty analysis for parameters Ntot, T, RH, and the ISA variability. The implications of our results for experimental analysis and interpretation of the immersion freezing process are discussed.
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Kishore, K., and R. Vasanthakumari. "Nucleation parameters for polymer crystallization from non-isothermal thermal analysis." Colloid & Polymer Science 266, no. 11 (November 1988): 999–1002. http://dx.doi.org/10.1007/bf01428808.
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