Ceramic membranes porosity

Membrane symmetric or asymmetric microporous. Ceramic, sintered metals, or polymers with pores 0.2 to 1 pm. Symmetric polymers have a porosity of 60 to 85% asymmetric ceramic membranes, porosity 30 to 40%, are used for high pressure and higher temperature <200°C. 

Membrane symmetric or asymmetric microporous. ceramic, sintered metals or polymers with pores 0.2-1 gm. Symmetric polymers have a porosity of 60 to 85% asymmetric ceramic membranes, porosity 30 to 40%, are used for high pressure and higher temperature < 200 °C. Pressure 0.03-0.35 MPa. Pressure 0.3-0.5 MPa for ceramic. Hydraulic permeability. A 70 to 10000 g/s m MPa, capacity/unit 0.001-1 L/s. Liquid permeate flux 0.001-0.2 L/s m with the perme-... 

Various ceramic membranes, for example, possess differing degrees of acid/base resistance, depending on the pH value, particular phase of the membrane material, porosity, contact time and temperature. However, no quantitative data are available on the kinetics of chemical dissolution of ceramic membranes as a guide for chemical corrosion considerations. 

The openness (e.g., volume fraction) and the nature of the pores affect the permeability and permselectivity of porous inorganic membranes. Porosity data can be derived from mercury porosimetry information. Membranes with higher porosities possess more open porous structure, thus generally leading to higher permeation rates for the same pore size. Porous inorganic membranes, particularly ceramic membranes, have a porosity... 

Thermal and hydrothermal exposures can change the ix>re size and its distribution, porosity and tortuosity of a porous membrane which in turn influence the separation properties of the membrane such as permeability and permselectivity. Several ceramic membranes have been investigated for their responses to thermal and hydrothermal environments. 

Non-oxide ceramic materials such as silicon carbide has been used commercially as a membrane support material and studied as a potential membrane material. Silicon nitride has also the potential of being a ceramic membrane material. In fact, both materials have been used in other high-temperature structural ceramic applications. Oxidation resistance of these non-oxide ceramics as membrane materials for membrane reactor applications is obviously very important. The oxidation rate is related to the reactive surface area thus oxidation of porous non-oxide ceramics depends on their open porosity. The generally accepted oxidation mechanism of porous silicon nitride materials consists of two... 

With conventional sol-gel routes, the pore size distribution is usually broad and the tortuosity of the pore network is important with the presence of constrictions. Thus ordered interconnected pore networks with constant pore size are strongly attractive. Hierarchical porosity and adaptive porosity are also fascinating approaches to increase or manage the permeability of ceramic membranes. 

The surface porosity is equal to the ratio of the pore area to membrane area multiplied by the number of pores. In most cases volume flux through ceramic membranes can be best described by the Kozeny-Carman relationship, which corresponds to a system of close packed spheres (see Figure 6.8a) ... 

Basic mechanisms involved in gas and vapor separation using ceramic membranes are schematized in Figure 6.14. In general, single gas permeation mechanisms in a porous ceramic membrane of thickness depend on the ratio of the number of molecule-molecule collisions to that of the molecule-wall collisions. In membranes with large mesopores and macropores the separation selectivity is weak. The number of intermolecular collisions is strongly dominant and gas transport in the porosity is described as a viscous flow that can be quantified by a Hagen-Poiseuille type law ... 

With thin supported ceramic membranes, the pore volume due to the membrane is relatively small and better results are obtained if a major part of the support is scraped off. Specific preparation of samples (e.g. support embedded in a resin) can change the results [39]. If the membrane weight is known and if its pore size can be well differentiated from that of the support the method can be used to determine the porosity of a supported layer. 

The formation of ceramic membranes for microfiltration, ultrafiltration or nanofiltration by association of various granular layers is now a common procedure [10]. Each layer is characterized by its thickness, h, its porosity, 8, and its mean pore diameter, dp. These parameters are controlled by the particle size, d, and the synthesis method. Each layer induces a resistance which may be predicted through the classical Carman-Kozeny model ... 

The amphoteric behaviour of metal oxides in contact with water has thoroughly been described by many authors [22-24]. This basic property results in charged surfaces depending on pH condition. In a first approximation, connected porosity in ceramic membranes can be represented by an array of... 

This chapter focuses on the chemical processing of ceramic membranes, which has to date constituted the major part of inorganic membrane development. Before going further into the ceramic aspect, it is important to understand the requirements for ceramic membrane materials in terms of porous structure, chemical composition, and shape. In separation technologies based on permselective membranes, the difference in filtered species ranges from micrometer-sized particles to nanometer-sized species, such as molecular solutes or gas molecules. One can see that the connected porosity of the membrane must be adapted to the class of products to be separated. For this reason, ceramic membrane manufacture is concerned with macropores above 0.1 pm in diameter for microfiltration, mesopores ranging from 0.1 pm to 2 nm for ultrafiltration, and nanopores less than 2 nm in diameter for nanofiltration, per-vaporation, or gas separation. Dense membranes are also of interest for gas... 

Ceramic membranes normally have an asymmetrical structure composed of at least two, normally three, different porosity levels. Indeed, before applying the active top layer, a mesoporous intermediate layer is often appHed in order to reduce the surface roughness. A macroporous support ensures mechanical stahility. Ceramic membranes generally show a higher chemical, structural and thermal stability. They do not deform under pressure, do not swell and are deaned easily [13]. 

In other respects, we can consider zeolite membranes as pertaining to the ceramic material category. Indeed, zeolites are classified for the most part as microporous, crystalline silicoaluminate structures with different aluminum/silicon ratios. Thus, the chemical compositions are close to those of ceramic oxide membranes, in particular of microporous silica and alumina membranes. On the other hand, zeolites are crystalline materials and they have a structural porosity very different from microporous amorphous silica [167]. Zeolite films can be grown as intergrown layers on porous metallic and ceramic membrane supports. These zeolite films constitute a special type of nanostructured interface capable of very specific interactions with individual molecules so that it can be used as membrane for the selective separation of molecular... 

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