Studies on nucleation phenomena occurring in aqueous solutions supersaturated with calcium sulfate

1978 ◽  
Vol 56 (6) ◽  
pp. 831-838 ◽  
Author(s):  
D. M. Keller ◽  
Ronald E. Massey ◽  
O. E. Hileman Jr.
Keyword(s):  
Aqueous Solutions ◽  
Nucleation Rate ◽  
Calcium Sulfate ◽  
Nucleation Theory ◽  
Critical Parameters ◽  
Classical Nucleation Theory ◽  
In Situ Generation ◽  
Temperature Surface

The results of a set of experiments designed to delineate the nucleation rate, supersaturation, temperature surface for the system CaSO4•2H2O/H2O are reported. The data were obtained using the droplet technique coupled with in situ generation of SO42− under the conditions that dS/dt was large during the early part of the induction period and it was zero during the actual nucleation events. The observed shape of the surface is compared with that suggested by the classical theory of nucleation and differences are commented on. The critical parameters important in classical nucleation theory are reported.

scholarly journals Low-temperature nucleation anomaly in silicate glasses shown to be artifact in a 5BaO·8SiO2 glass

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Xinsheng Xia ◽  
D. C. Van Hoesen ◽  
Matthew E. McKenzie ◽  
Randall E. Youngman ◽  
K. F. Kelton
Keyword(s):  
Nucleation Rate ◽  
Experimental Approach ◽  
Cluster Formation ◽  
Heating Time ◽  
Silicate Glasses ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Real Phenomenon ◽  
Satisfactory Answer ◽  
Over 40 Years

AbstractFor over 40 years, measurements of the nucleation rates in a large number of silicate glasses have indicated a breakdown in the Classical Nucleation Theory at temperatures below that of the peak nucleation rate. The data show that instead of steadily decreasing with decreasing temperature, the work of critical cluster formation enters a plateau and even starts to increase. Many explanations have been offered to explain this anomaly, but none have provided a satisfactory answer. We present an experimental approach to demonstrate explicitly for the example of a 5BaO ∙ 8SiO2 glass that the anomaly is not a real phenomenon, but instead an artifact arising from an insufficient heating time at low temperatures. Heating times much longer than previously used at a temperature 50 K below the peak nucleation rate temperature give results that are consistent with the predictions of the Classical Nucleation Theory. These results raise the question of whether the claimed anomaly is also an artifact in other glasses.

scholarly journals A semi-analytical method for calculating rates of new sulfate aerosol formation from the gas phase

2007 ◽  
Vol 7 (1) ◽  
pp. 2169-2196 ◽  
Author(s):  
J. Kazil ◽  
E. R. Lovejoy
Keyword(s):  
Steady State ◽  
Gas Phase ◽  
Nucleation Rate ◽  
Atmospheric Modeling ◽  
Sulfate Aerosol ◽  
Nucleation Theory ◽  
Rate Coefficients ◽  
Classical Nucleation Theory ◽  
Aerosol Formation ◽  
Aerosol Model

Abstract. The formation of new sulfate aerosol from the gas phase is commonly represented in atmospheric modeling with parameterizations of the steady state nucleation rate. Such parameterizations are based on classical nucleation theory or on aerosol nucleation rate tables, calculated with a numerical aerosol model. These parameterizations reproduce aerosol nucleation rates calculated with a numerical aerosol model only imprecisely. Additional errors can arise when the nucleation rate is used as a surrogate for the production rate of particles of a given size. We discuss these errors and present a method which allows a more precise calculation of steady state sulfate aerosol formation rates. The method is based on the semi-analytical solution of an aerosol system in steady state and on parameterized rate coefficients for H2SO4 uptake and loss by sulfate aerosol particles, calculated from laboratory and theoretical thermodynamic data.

scholarly journals The Effect of Hydrogen on Pore Formation in Aluminum Alloy Castings: Myth Versus Reality

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 368 ◽  
Author(s):  
Murat Tiryakioğlu
Keyword(s):  
Pore Formation ◽  
Liquid Aluminum ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Fundamental Change ◽  
Aluminum Casting ◽  
Solid Aluminum ◽  
Alloy Castings ◽  
Casting Industry

The solubility of hydrogen in liquid and solid aluminum is reviewed. Based on classical nucleation theory, it is shown that pores cannot nucleate either homogeneously or heterogeneously in liquid aluminum. Results of in situ studies on pore formation show that pores appear at low hydrogen supersaturation levels, bypassing nucleation completely. The results are explained based on the bifilm theory introduced by Prof. John Campbell, as this theory is currently the most appropriate, and most likely, the only mechanism for pores to form. Examples for the effect of hydrogen on pore formation are given by using extreme data from the literature. It is concluded that a fundamental change in how hydrogen is viewed is needed in aluminum casting industry.

scholarly journals Analysis of the effect of water activity on ice formation using a new thermodynamic framework

2014 ◽  
Vol 14 (14) ◽  
pp. 7665-7680 ◽  
Author(s):  
D. Barahona
Keyword(s):  
Water Activity ◽  
Nucleation Rate ◽  
Ice Nucleation ◽  
Nucleation Theory ◽  
Cloud Formation ◽  
Classical Nucleation Theory ◽  
Solid Matrix ◽  
Effect Of Water ◽  
Thermodynamic Framework ◽  
New Framework

Abstract. In this work a new thermodynamic framework is developed and used to investigate the effect of water activity on the formation of ice within supercooled droplets. The new framework is based on a novel concept where the interface is assumed to be made of liquid molecules "trapped" by the solid matrix. It also accounts for the change in the composition of the liquid phase upon nucleation. Using this framework, new expressions are developed for the critical ice germ size and the nucleation work with explicit dependencies on temperature and water activity. However unlike previous approaches, the new model does not depend on the interfacial tension between liquid and ice. The thermodynamic framework is introduced within classical nucleation theory to study the effect of water activity on the ice nucleation rate. Comparison against experimental results shows that the new approach is able to reproduce the observed effect of water activity on the nucleation rate and the freezing temperature. It allows for the first time a phenomenological derivation of the constant shift in water activity between melting and nucleation. The new framework offers a consistent thermodynamic view of ice nucleation, simple enough to be applied in atmospheric models of cloud formation.

scholarly journals A semi-analytical method for calculating rates of new sulfate aerosol formation from the gas phase

2007 ◽  
Vol 7 (13) ◽  
pp. 3447-3459 ◽  
Author(s):  
J. Kazil ◽  
E. R. Lovejoy
Keyword(s):  
Steady State ◽  
Gas Phase ◽  
Nucleation Rate ◽  
Atmospheric Modeling ◽  
Sulfate Aerosol ◽  
Nucleation Theory ◽  
Rate Coefficients ◽  
Classical Nucleation Theory ◽  
Aerosol Formation ◽  
Aerosol Model

Abstract. The formation of new aerosol from the gas phase is commonly represented in atmospheric modeling with parameterizations of the steady state nucleation rate. Present parameterizations are based on classical nucleation theory or on nucleation rates calculated with a numerical aerosol model. These parameterizations reproduce aerosol nucleation rates calculated with a numerical aerosol model only imprecisely. Additional errors can arise when the nucleation rate is used as a surrogate for the production rate of particles of a given size. We discuss these errors and present a method which allows a more precise calculation of steady state sulfate aerosol formation rates. The method is based on the semi-analytical solution of an aerosol system in steady state and on parameterized rate coefficients for H2SO4 uptake and loss by sulfate aerosol particles, calculated from laboratory and theoretical thermodynamic data.

scholarly journals Reversible disorder-order transitions in atomic crystal nucleation

Science ◽  
2021 ◽  
Vol 371 (6528) ◽  
pp. 498-503
Author(s):  
Sungho Jeon ◽  
Taeyeong Heo ◽  
Sang-Yeon Hwang ◽  
Jim Ciston ◽  
Karen C. Bustillo ◽  
...  
Keyword(s):  
Early Stage ◽  
Nucleation Theory ◽  
Crystal Nucleation ◽  
Classical Nucleation Theory ◽  
Gold Nanocrystals ◽  
Size Dependent ◽  
In Situ Electron Microscopy ◽  
Nucleation Mechanisms ◽  
Structural Fluctuations

Nucleation in atomic crystallization remains poorly understood, despite advances in classical nucleation theory. The nucleation process has been described to involve a nonclassical mechanism that includes a spontaneous transition from disordered to crystalline states, but a detailed understanding of dynamics requires further investigation. In situ electron microscopy of heterogeneous nucleation of individual gold nanocrystals with millisecond temporal resolution shows that the early stage of atomic crystallization proceeds through dynamic structural fluctuations between disordered and crystalline states, rather than through a single irreversible transition. Our experimental and theoretical analyses support the idea that structural fluctuations originate from size-dependent thermodynamic stability of the two states in atomic clusters. These findings, based on dynamics in a real atomic system, reshape and improve our understanding of nucleation mechanisms in atomic crystallization.

Analytical Investigation on the Homogeneous Nucleation in a Mono-Component and Bi-Component Droplet

2019 ◽  
Author(s):  
Xi Xi ◽  
Hong Liu ◽  
Chang Cai ◽  
Ming Jia ◽  
Weilong Zhang
Keyword(s):  
Nucleation Rate ◽  
Homogeneous Nucleation ◽  
Ambient Pressure ◽  
Analytical Investigation ◽  
Bubble Nucleation ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Liquid Temperature ◽  
Wide Range ◽  
Good Agreement

Abstract The work attempts to analyze the performance of homogeneous nucleation by using the non-equilibrium thermodynamics theory and the classical nucleation theory. A nucleation rate graph was constructed under a wide range of operating temperature conditions. The results indicate that the superheat limit temperature (SLT) estimated by the modified homogeneous nucleation sub-model is in good agreement with the experimental results. The nucleation rate increases exponentially with the liquid temperature rise when the liquid temperature exceeds the SLT under atmospheric pressure. The superheated temperature needed to trigger the bubble nucleation decreases with the elevated ambient pressure.

scholarly journals An aerosol chamber investigation of the heterogeneous ice nucleating potential of refractory nanoparticles

2010 ◽  
Vol 10 (3) ◽  
pp. 1227-1247 ◽  
Author(s):  
R. W. Saunders ◽  
O. Möhler ◽  
M. Schnaiter ◽  
S. Benz ◽  
R. Wagner ◽  
...  
Keyword(s):  
Silicon Oxide ◽  
Cloud Model ◽  
Active Surface ◽  
Accommodation Coefficient ◽  
Contact Angles ◽  
Nucleation Theory ◽  
Cloud Formation ◽  
Classical Nucleation Theory ◽  
Ice Nuclei

Abstract. Nanoparticles of iron oxide (crystalline and amorphous), silicon oxide and magnesium oxide were investigated for their propensity to nucleate ice over the temperature range 180–250 K, using the AIDA chamber in Karlsruhe, Germany. All samples were observed to initiate ice formation via the deposition mode at threshold ice super-saturations (RHithresh) ranging from 105% to 140% for temperatures below 220 K. Approximately 10% of amorphous Fe2O3 particles (modal diameter = 30 nm) generated in situ from a photochemical aerosol reactor, led to ice nucleation at RHithresh = 140% at an initial chamber temperature of 182 K. Quantitative analysis using a singular hypothesis treatment provided a fitted function [ns(190 K)=10(3.33×sice)+8.16] for the variation in ice-active surface site density (ns:m−2) with ice saturation (sice) for Fe2O3 nanoparticles. This was implemented in an aerosol-cloud model to determine a predicted deposition (mass accommodation) coefficient for water vapour on ice of 0.1 at temperatures appropriate for the upper atmosphere. Classical nucleation theory was used to determine representative contact angles (θ) for the different particle compositions. For the in situ generated Fe2O3 particles, a slight inverse temperature dependence was observed with θ = 10.5° at 182 K, decreasing to 9.0° at 200 K (compared with 10.2° and 11.4° respectively for the SiO2 and MgO particle samples at the higher temperature). These observations indicate that such refractory nanoparticles are relatively efficient materials for the nucleation of ice under the conditions studied in the chamber which correspond to cirrus cloud formation in the upper troposphere. The results also show that Fe2O3 particles do not act as ice nuclei under conditions pertinent for tropospheric mixed phase clouds, which necessarily form above ~233 K. At the lower temperatures (<150 K) where noctilucent clouds form during summer months in the high latitude mesosphere, higher contact angles would be expected, which may reduce the effectiveness of these particles as ice nuclei in this part of the atmosphere.

Study Of Nucleation And Growth Ev Al-Zn Alloys Using TEM

1993 ◽  
Vol 321 ◽  
Author(s):  
G. Sundar ◽  
E. A. Kenik ◽  
J. J. Hoyt ◽  
S. Spooner
Keyword(s):  
Completion Time ◽  
Nucleation And Growth ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Initial Value ◽  
Two Phase ◽  
Transmission Electron ◽  
Time Required ◽  
Zn Alloys

ABSTRACTNucleation and growth studies were conducted on Al-Zn alloys at several temperatures using transmission electron Microscopy (TEM) with an in-situ furnace. The value of the critical undercooling was established by noting the lowest temperature at which precipitates were no longer observed, following a quench into the two-phase metastable region. These results were compared with the Langer-Schwartz Model of nucleation and growth in which it is predicted that the half-completion time (i.e, the time required for the supersaturation to reach half its initial value) diverges for initial supersaturations which are higher than those predicted by the classical nucleation theory.

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