Loading salts from solutions into nanopores: Model and its test

Farasat, Reza; Yancey, Benjamin; Vyazovkin, Sergey

doi:10.1016/j.cplett.2013.01.009

Cited by 5 publications

(20 citation statements)

References 20 publications

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“…In this case, the effective core radius within which crystallization of water occurs is reduced from R c to a smaller value R sc . From the concomitant decrease of the cross-sectional core area one finds . We infer that the melting point depression of water in the core of the salt-containing pores conforms to a Gibbs–Thomson relation Δ T sc = C / R sc , as in the absence of salt, when Δ T p 0 = C / R c . , Hence, the salt-induced melting point depression will be related to the melting point depression of water/ice in the absence of salt, Δ T p 0 , by …”

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confidence: 83%

Secondary Confinement of Water Observed in Eutectic Melting of Aqueous Salt Systems in Nanopores

Meißner

Prause

Findenegg

2016

J. Phys. Chem. Lett.

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Freezing and melting of aqueous solutions of alkali halides confined in the cylindrical nanopores of MCM-41 and SBA-15 silica was probed by differential scanning calorimetry (DSC). We find that the confinement-induced shift of the eutectic temperature in the pores can be significantly greater than the shift of the melting temperature of pure water. Greatest shifts of the eutectic temperature are found for salts that crystallize as oligohydrates at the eutectic point. This behavior is explained by the larger fraction of pore volume occupied by salt hydrates as compared to anhydrous salts, on the assumption that precipitated salt constitutes an additional confinement for ice/water in the pores. A model based on this secondary confinement effect gives a good representation of the experimental data. Salt-specific secondary confinement may play a role in a variety of fields, from salt-impregnated advanced adsorbents and catalysts to the thermal weathering of building materials.

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confidence: 83%

Secondary Confinement of Water Observed in Eutectic Melting of Aqueous Salt Systems in Nanopores

Meißner

Prause

Findenegg

2016

J. Phys. Chem. Lett.

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“…We also analyze the kinetics of the phase transition in terms of a nucleation model in order to understand the origins of the observed effects. To better highlight the surface effect, our study is conducted in partially filled pores that are naturally accomplished by filling a porous material from a solution. , It should be noted that in fully filled pores only a small fraction of nanocrystals is in direct contact with the surface (Figure A). In this situation, a relative contribution of the surface effect is diminished as compared to the case of partially filled pores (Figure B), in which a much larger fraction of nanocrystals is affected by direct interaction with the surface.…”

Section: Introductionmentioning

confidence: 99%

Nanoconfined Solid–Solid Transitions: Attempt To Separate the Size and Surface Effects

Farasat

Vyazovkin

2015

J. Phys. Chem. C

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The solid–solid phase transitions in ammonium nitrate, ammonium perchlorate, and sodium nitrite confined to native and organically modified silica nanopores are analyzed by differential scanning calorimetry. The study reveals the effect of nanoconfinement on the transition temperature and links it to the kinetic parameters of the process. It is suggested that the effect of nanoconfinement is primarily the surface interaction effect in the native pores and the size effect in organically modified pores. It has been found that in organically modified pores the transition temperature is always depressed relative to the bulk, whereas in the native pores its behavior is generally unpredictable. Kinetic analysis of the transitions in terms of a nucleation model indicates that the experimentally observed shifts in temperature can be explained by a combination of changes in the free energy of nucleation and preexponential factor of the respective processes.

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“…Unlike the transition at −31 °C, the high temperature transition from form II to form I is accompanied by a significant heat of transition, which makes it convenient to study. One of the important reasons to use ammonium chloride is that on heating to 400 °C it decomposes entirely into gases which allows one to employ thermogravimetric analysis for accurate determination of its mass loaded in silica . In addition, this compound is well soluble in water which affords significant variability in terms of the amount loaded into the silica pores.…”

Section: Introductionmentioning

confidence: 99%

High Temperature Solid–Solid Transition in Ammonium Chloride Confined to Nanopores

2013

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This paper describes a calorimetric (DSC) study of the high temperature (∼190 °C) solid−solid phase transition in ammonium chloride in silica nanopores (4− 30 nm) and in bulk. The study focuses on the values of the transition heat and temperature as well as on the transition kinetics. Because ammonium chloride is loaded from a solution, the pores are only filled partially. Thermogravimetric analysis is employed to evaluate the pore fullness, which is further used to estimate the height of ammonium chloride layer deposited inside the pores. With increasing the layer height, the heat of transition increases toward the bulk value. Relative to the bulk value, the transition temperature measured on heating and on cooling respectively increases and decreases with decreasing the layer height. In larger pores (15 and 30 nm), the transition has revealed a second DSC peak that appears above 210 °C on heating and below 100 °C on cooling. The temperature dependencies of the effective activation energy derived from isoconversional kinetic analysis of DSC data have been parametrized in terms of the Turnbull−Fisher model. It is found that the transition in the pores encounters a larger free energy barrier to nucleation.

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Loading salts from solutions into nanopores: Model and its test

Cited by 5 publications

References 20 publications

Secondary Confinement of Water Observed in Eutectic Melting of Aqueous Salt Systems in Nanopores

Secondary Confinement of Water Observed in Eutectic Melting of Aqueous Salt Systems in Nanopores

Nanoconfined Solid–Solid Transitions: Attempt To Separate the Size and Surface Effects

High Temperature Solid–Solid Transition in Ammonium Chloride Confined to Nanopores

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