Theory of hydrogen permeability in nonporous silica membranes

Oyama, S. Ted; Lee, D.; Hacarlioglu, P.; Saraf, Ravi F.

doi:10.1016/j.memsci.2004.06.046

Cited by 192 publications

(128 citation statements)

References 36 publications

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“…Although the method can be used for the data obtained here, and gives a reasonable estimate of the pore diameter, if there were pores. Indeed, previous work showed that a critical size cutoff for permeance of molecules of different size was about 0.3 nm 24) . However, for the reasons outlined above, the silica material is best viewed as not containing classical pores.…”

Section: P M M Imentioning

confidence: 99%

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Review on Mechanisms of Gas Permeation through Inorganic Membranes

Oyama

Yamada

Sugawara

et al. 2011

J. Jpn. Petrol. Inst.

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The major mechanisms of gas permeation through solid membranes are described and the applicable equations describing the permeance are presented. The mechanisms depend on the relative size of the permeating molecules and the diameter of the pores. As pore size decreases the operable mechanisms are Hagen-Pouiselle flow, Knudsen diffusion, surface diffusion, gas-translation, and finally solid-state diffusion. The Hagen-Pouiselle mechanism involves flow through large pores, while the Knudsen mechanism involves collision of molecules with the walls of pores of intermediate size. Surface diffusion deals with movement of molecules trapped in the potential field of the walls of pores of relatively small size, while gas-translation involves molecules that can escape the field, but are constrained by the small pores. Finally, solid-state transport comprises dissolution and transport by diffusion within the solid. These mechanisms are illustrated for hydrogen permeance with the use of two membranes, an alumina membrane with intermediate sized pores and a silica on alumina membrane of dense structure. KeywordsPermeation mechanism, Inorganic membrane, Silica membrane, Solid-state diffusion, Glassy membranes mechanism, Hydrogen However, oftentimes the actual selectivity can deviate strongly from that defined above because of interactions between the species with each other or with the walls of the membranes. For example, the preferred adsorption or absorption of one species in the pores of a membrane can block the passage of other species. Thus, single-gas selectivities should be taken as a limiting case approximation.A fundamental expression for transport in membranes is derived from Fick's First Law, which relates the flux of species i to the concentration gradient. The gradient in turn can be related to the concentration in the inlet, cio and outlet, ciL, of a membrane of thickness L:The diffusivity in Fick's first law is the ordinary molecular diffusivity, Di(c) [m 2 ・s-1 ], which may have a concentration dependence. In the case of membranes an effective diffusivity, De,i is used, where the porosity ε and tortuosity τ of the membrane are included. The tortuosity is a factor that accounts for the increased length of a pore by the presence of twists and turns. For example, if a single straight pore is replaced by one having a single 90° turn, the tortuosity would be 2 or 1.4. In an early treatment the relative diameters of the diffusing molecules, dm, and pores, dP, was taken into account through a restrictive factor KrFor many membranes dm/dp is small, so Kr is unity. There have been many proposed mechanisms with a variety of materials based on various interaction and diffusion processes. These mechanisms are in broad terms distinguished by the ratio of pore diameter dp to kinetic diameter dm of the gas molecule. As the pore diameter becomes smaller, that is with increasing value of dm/dp, the interactions between the molecule and the surface become larger in proportion to the ratio of the area of the surface potential fi...

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Section: P M M Imentioning

confidence: 99%

“…In the case of polyatomic molecules, a rotational factor is also needed to express the state in the solubility site. The final equation is presented below 24) :…”

Section: 1 Glassy Membranes Mechanismmentioning

confidence: 99%

Review on Mechanisms of Gas Permeation through Inorganic Membranes

Oyama

Yamada

Sugawara

et al. 2011

J. Jpn. Petrol. Inst.

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“…Finally, after the 1000˝C-heat treatment, the six-membered Si-O-Si rings remained to form the intrinsic microporosity in amorphous silica. The estimated diameter of the six-membered ring is approximately 0.3 nm [50,51], which is too small for the N 2 probe molecule to access (0.364 nm) [42]. Consequently, the resulting 1000˝C heat-treated sample was characterized as non-porous.…”

Section: R2: 1000°c In Airmentioning

confidence: 99%

Formation of Micro and Mesoporous Amorphous Silica-Based Materials from Single Source Precursors

et al. 2016

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Polysilazanes functionalized with alkoxy groups were designed and synthesized as single source precursors for fabrication of micro and mesoporous amorphous silica-based materials. The pyrolytic behaviors during the polymer to ceramic conversion were studied by the simultaneous thermogravimetry-mass spectrometry (TG-MS) analysis. The porosity of the resulting ceramics was characterized by the N 2 adsorption/desorption isotherm measurements. The Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopic analyses as well as elemental composition analysis were performed on the polymer-derived amorphous silica-based materials, and the role of the alkoxy group as a sacrificial template for the micro and mesopore formations was discussed from a viewpoint to establish novel micro and mesoporous structure controlling technologies through the polymer-derived ceramics (PDCs) route.

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“…Since the membrane permeability is inversely proportional to its thickness [43], these traditional membranes seem inferior to graphene, which is only one-atom thick. However, a perfect graphene is impermeable even to the smallest gas atom, helium, since the densely packed honeycomb crystal lattice is strong enough to prevent atoms and molecules from passing through it [44,45].…”

Section: Gas Separation and Purificationmentioning

confidence: 99%

Porous graphene: Properties, preparation, and potential applications

et al. 2012

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Graphene has recently emerged as an important and exciting material. Inspired by its outstanding properties, many researchers have extensively studied graphene-related materials both experimentally and theoretically. Porous graphene is a collection of graphene-related materials with nanopores in the plane. Porous graphene exhibits properties distinct from those of graphene, and it has widespread potential applications in various fields such as gas separation, hydrogen storage, DNA sequencing, and supercapacitors. In this review, we summarize recent progress in studies of the properties, preparation, and potential applications of porous graphene, and show that porous graphene is a promising material with great potential for future development.graphene, porous graphene, electronic structure, gas separation, DNA sequencing Citation:Xu P T, Yang J X, Wang K S, et al. [9] have made the preparation of large-area graphene feasible. The most intriguing aspect of graphene is its extraordinary properties. Graphene, which is constructed by strong sp 2 covalent bonds, is believed to be the strongest material ever measured [10]. Experiments have revealed that graphene exhibits a high ambipolar electric-field effect at room temperature, better conductivity than any other known material [3], and many other novel properties, including room-temperature quantum Hall effects, mass-less Dirac electrons near the K point, and high mobility of carriers (10 6 m s −1 , close to the speed of light) [11][12][13]. All these properties distinguish graphene from ordinary materials, and make graphene an ideal candidate for the manufacture of electronic devices. To develop a full understanding of its nature and realize the full potential of graphene, extensive investigations have proceeded in various directions. For instance, the electronic and magnetic properties of graphene can be modified by hydrogenation [14] and doping [15]. Another research area, porous graphene, has also attracted increasing attention recently. Porous graphene is a collection of graphene-related materials with nanopores in the plane. Depending on the production techniques used, the pore size ranges from atomic precision to nanoscale. As a result of the nanopores in the graphene plane, porous graphene exhibits properties distinct from those of pristine graphene, leading to its potential applications in numerous

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Theory of hydrogen permeability in nonporous silica membranes

Cited by 192 publications

References 36 publications

Review on Mechanisms of Gas Permeation through Inorganic Membranes

Review on Mechanisms of Gas Permeation through Inorganic Membranes

Formation of Micro and Mesoporous Amorphous Silica-Based Materials from Single Source Precursors

Porous graphene: Properties, preparation, and potential applications

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