Synthesis of Macroporous Silica with Nanometer-sized Continuous Through Pores by Using Denatured Collagen as a Template

General Cluster Sorption Isotherm

10.26434/chemrxiv.12073869.v1 ◽

2020 ◽

Author(s):

Christoph Buttersack

Keyword(s):

Density Functional ◽

Capillary Condensation ◽

Cluster Formation ◽

Full Range ◽

Full Description ◽

Cross Sectional ◽

Macroporous Silica ◽

Isotherm Equation ◽

Type Iv ◽

Classical Thermodynamics

<p>Adsorption isotherms are an essential tool in chemical physics of surfaces. However, several approaches based on a different theoretical basis exist and for isotherms including capillary condensation existing approaches can fail. Here, a general isotherm equation is derived and applied to literature data both concerning type IV isotherms of argon and nitrogen in ordered mesoporous silica, and type II isotherms of disordered macroporous silica. The new isotherm covers the full range of partial pressure (10<sup>-6</sup> - 0.7). It relies firstly on the classical thermodynamics of cluster formation, secondly on a relationship defining the free energy during the increase of the cluster size. That equation replaces the Lennard-Jones potentials used in the classical density functional theory. The determination of surface areas is not possible by this isotherm because the cross-sectional area of a cluster is unknown. Based on the full description of type IV isotherms, most known isotherms are accessible by respective simplifications. </p>

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Phase Behaviour of Methane Hydrates in Confined Media

Crystals ◽

10.3390/cryst11020201 ◽

2021 ◽

Vol 11 (2) ◽

pp. 201

Author(s):

Hao Bian ◽

Lu Ai ◽

Klaus Hellgardt ◽

Geoffrey C. Maitland ◽

Jerry Y. Y. Heng

Keyword(s):

Phase Behaviour ◽

Methane Hydrates ◽

Scanning Calorimetry ◽

Macroporous Silica ◽

Interfacial Energies ◽

Temperature Method ◽

Hydrate Phase ◽

Dissociation Temperature ◽

Confined Media ◽

Decomposition Behaviour

In a study designed to investigate the melting behaviour of natural gas hydrates which are usually formed in porous mineral sediments rather than in bulk, hydrate phase equilibria for binary methane and water mixtures were studied using high-pressure differential scanning calorimetry in mesoporous and macroporous silica particles having controlled pore sizes ranging from 8.5 nm to 195.7 nm. A dynamic oscillating temperature method was used to form methane hydrates reproducibly and then determine their decomposition behaviour—melting points and enthalpies of melting. Significant decreases in dissociation temperature were observed as the pore size decreased (over 6 K for 8.5 nm pores). This behaviour is consistent with the Gibbs–Thomson equation, which was used to determine hydrate–water interfacial energies. The melting data up to 50 MPa indicated a strong, essentially logarithmic, dependence on pressure, which here has been ascribed to the pressure dependence of the interfacial energy in the confined media. An empirical modification of the Gibbs–Thomson equation is proposed to include this effect.

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