The dehydration of porous glass

Low, M. J. D.; Ramasubramanian, N.

doi:10.1021/j100862a038

Cited by 56 publications

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“…In order to have a realistic description of the surface chemistry, all silicon atoms in an incomplete tetrahedral environment are removed, and all oxygen dangling bonds are saturated with hydrogen atoms placed 1 Å from oxygen perpendicular to the surface. The porosity of the sample is 0.28, the density 1.56 g / cm 3 , the specific surface area 210 m 2 / g, the mean pore diameter 36 Å ͑from chord distribution͒, and OH surface density 7 OH / nm 2 , all in agreement with experimental values: 0.28, 1.50 g / cm 3 , 200 m 2 / g, and around 7 OH / nm 2 if outgassed around 400°C, 15,16 except for the pore size slightly smaller in our pseudo-vycor compared to real one ͑40 Å͒. It has been shown that this numerical sample reproduces quite well micro and meso textural properties of real vycor.…”

Section: Numerical Detailssupporting

confidence: 80%

“…1͒ representing the Gaussian field associated to the volume autocorrelation function of the studied porous structure. 12,13 It has been shown [14][15][16] that this numerical sample reproduces quite well micro-and mesotextural properties of real Vycor, and constitutes an improvement of the topological description of silica mesoporous glasses, because of the presence of disordered and interconnected pores. In order to have a realistic description of the surface chemistry, all silicon atoms in an incomplete tetrahedral environment are removed, and all oxygen dangling bonds are saturated with hydrogen atoms placed 1 Å from oxygen perpendicular to the surface.…”

Section: Numerical Detailsmentioning

confidence: 65%

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Water adsorption in disordered mesoporous silica (Vycor) at 300K and 650K: A Grand Canonical Monte Carlo simulation study of hysteresis

Puibasset

Pellenq

2005

The Journal of Chemical Physics

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This numerical simulation paper focuses on the adsorption/desorption of water in disordered mesoporous silica glasses (Vycor-like). The numerical adsorbent was previously obtained by off lattice method, and was shown to reproduce quite well the micro- and mesotextural properties of real Vycor, as well as morphological (pore size distribution) and topological (pore interconnections) disorder. The water-water interactions are described by the SPC model while water-silica interactions are calculated in the framework of the PN-TrAZ model. The water adsorption/desorption isotherms and the configurational energies are calculated by the Grand Canonical Monte Carlo simulation method. The low pressure results compare well with experiments, showing the good transferability of the intermolecular potential. It is shown that if the hysteresis loop observed in the adsorption/desorption isotherm is considered as a true phase transition (which is actually still an open question in the case of disordered porous materials), then it is possible to calculate the grand potential by applying the thermodynamic integration scheme. The grand potential is shown to be multivalued for low (subcritical) temperature, and continuous for high (supercritical) temperature. A coexistence point is found within the hysteresis loop, actually close to the vertical desorption line. Below the equilibrium chemical potential, the gaslike branch is stable whereas the liquidlike branch is metastable. The situation is reversed above the coexistence point.

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Section: Numerical Detailssupporting

confidence: 80%

Section: Numerical Detailsmentioning

confidence: 65%

Water adsorption in disordered mesoporous silica (Vycor) at 300K and 650K: A Grand Canonical Monte Carlo simulation study of hysteresis

Puibasset

Pellenq

2005

The Journal of Chemical Physics

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“…As in Table 2, the area surfaces are estimated by the Connolly surface which is calculated or measured by a probe of N 2 with a kinetic diameter of 3.64Å. The -OH group density of 6.29 per nm 2 in the present model is close to that of porous silica glass like Vycor [26,27] (5-7 -OH per nm 2 ) and vitreous silica surface [28] (4.5-6.2 -OH per nm 2 ).…”

Section: Structural Properties Of Mcm-41mentioning

confidence: 69%

Analyzing adsorption characteristics of CO2, N2 and H2O in MCM-41 silica by molecular simulation

Chang

Chien

Chen

et al. 2015

Applied Surface Science

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“…Silicate and aluminosilicate are typical examples of systems on which there exist physisorbed and chemisorbed molecules at the same time [2]. It is known that surface hydroxyl groups act as primary centres in the physical adsorption of water [3][4][5]. Zettlemoyer [5] considers the hydroxy !…”

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confidence: 99%

The kinetics of water desorption from porous glasses

Dondur

Fidler

Adnadjević

et al. 1987

Journal of Thermal Analysis

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The kinetics of water desorption from porous glasses silica gel and porous aluminosilicates were followed through the TG and DTG methods.In all cases only one thermodesorption peak appeared. The kinetic parameters were determined by standard nonisothermal methods. The activation energy is constant and independent of the coverage degree and pore diameter in the system porous glass-water. The function E (0) were determined for the silica gel and porous aluminosilicates E = E 0 + a exp ( -bO). The parameters Eo, a and b depend on the SiO2/A1203 ratio and on the distribution of active centers on the surface.Desorption kinetics is most commonly presented by the equation:In which n is the reaction order, A the pre-exponential factor and E the activation energy. In the general case, kinetic parameters depend upon the degree of coverage [1].Such an equation can be applied to high-energy chemisorbed states and to lowenergy physisorbed states. Silicate and aluminosilicate are typical examples of systems on which there exist physisorbed and chemisorbed molecules at the same time [2]. It is known that surface hydroxyl groups act as primary centres in the physical adsorption of water [3][4][5]. Zettlemoyer [5] considers the hydroxy ! groups to be donors and water molecules to be acceptors of hydrogen-bonds. According to the results of Kiselev [6], an adsorptive complex is formed in which approximately two hydroxyl groups correspond to one molecule of water. Dehydroxylation (associative desorption) is preceded by the desorption of physically adsorbed water and, due to the considerable difference in bond energy, it can be expected that these processes take place as two independent consecutive stages. It is probable that John Wiley & Sons, Limited, Chichester AkadOmiai Kiad6, Budapest

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The dehydration of porous glass

Cited by 56 publications

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Water adsorption in disordered mesoporous silica (Vycor) at 300K and 650K: A Grand Canonical Monte Carlo simulation study of hysteresis

Water adsorption in disordered mesoporous silica (Vycor) at 300K and 650K: A Grand Canonical Monte Carlo simulation study of hysteresis

Analyzing adsorption characteristics of CO2, N2 and H2O in MCM-41 silica by molecular simulation

The kinetics of water desorption from porous glasses

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