Ceramic membranes porous structure

The vast increase in the application of membranes has expanded our knowledge of fabrication of various types of membrane, such as organic and inorganic membranes. The inorganic membrane is frequently called a ceramic membrane. To fulfil the need of the market, ceramic membranes represent a distinct class of inorganic membrane. There are a few important parameters involved in ceramic membrane materials, in terms of porous structure, chemical composition and shape of the filter in use. In this research, zirconia-coated y-alumina membranes have been developed using the sol-gel technique. 

Catalytic A catalytic-membrane reactor is a combination heterogeneous catalyst and permselective membrane that promotes a reaction, allowing one component to permeate. Many of the reactions studied involve H2. Membranes are metal (Pd, Ag), nonporous metal oxides, and porous structures of ceramic and glass. Falconer, Noble, and Sperry [in Noble and Stern (eds.), op. cit., pp. 669-709] review status and potential developments. 

In this work for the first time magnetron sputtering (technologically effective method) was used for the modification of the tubular a-alumina ceramic support of the composite Pd - membrane. This modification could be realized due to the choice of Ni as hydrogen permeable metal instead of y-Al203 layers. It allows to use total effective cross section of the surface porous structure of the support in high temperature process of hydrogen purification by Pd membrane. 

Tubular composite (X-AI2O3 -based supports for Pd-containing metal membrane have been developed. Their distinction consists in using metal nickel for the modification of the porous structure of ceramic supports. Nickel is analog of palladium in many respects it is also effective catalyst for molecular hydrogen... 

The methods of preparing inorganic membranes with tortuous pores vary enormously. Some use rigid dense solids as the templates for creating porous structures while many others involve the deposition of one or more layers of smaller pores on a premanufactured microporous support with larger pores. Since ceramic membranes have been studied, produced and commercialized more extensively than any other inorganic membrane materials, more references will be made to the ceramic systems. 

Many commercial ceramic membranes nowadays come in the form of a monolith consisting of multiple, straight channels parallel to the axis of the cylindrical structure (Figure 3.6). The surfaces of the open channels are deposited with permselective membranes and possibly one or more intermediate support layers. The porous suppon of these multi-channel structures are produced by extrusion of ceramic pastes described above with a channel diameter of a few millimeters. Their lengths are somewhat limited by the size of the furnaces used to dry, calcine and sinter them and also by such practical considerations as the total compact weights to be supported during heat ueatment and the risk of distortion in the middle section. It should be noted that this type of honeycomb... 

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... 

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... 

The porous structure of ceramic supports and membranes can be first described using the lUPAC classification on porous materials. Thus, macroporous ceramic membranes (pore diameter >50 nm) deposited on ceramic, carbon, or metallic porous supports are used for cross-flow microfiltration. These membranes are obtained by two successive ceramic processing techniques extrusion of ceramic pastes to produce cylindrical-shaped macroporous supports and slip-casting of ceramic powder slurries to obtain the supported microfiltration layer [2]. For ultrafiltration membranes, an additional mesoporous ceramic layer (2 nm<pore diameter <50 nm) is deposited, most often by the solgel process [11]. Ceramic nanofilters are produced in the same way by depositing a very thin microporous membrane (pore diameter <2 nm) on the ultrafiltration layer [4]. Two categories of micropores are distinguished the supermicropores >0.7 nm and the ultramicropores <0.7 nm. 

Microfiltration and ultrafiltration are the two main filtration techniques for which ceramic membranes have been widely used to date. As described in Section 6.2.1.2, MF and UF ceramic membranes exhibit macro- and mesoporous structure, respectively, which result from packing and sintering of ceramic particles. Liquid flow in such porous media is convective in nature and the simplest description of permeation flux, J, is given by the Darcy s equation [20] ... 

A combination of characterization techniques for the pore structure of mesoporous membranes is presented. Equilibrium and dynamic methods have been performed for the characterisation of model membranes with well-defined structure while three-dimensional network models, combined with aspects from percolation theory can be employed to obtain structural information on the porous network topology as well as on the pore shape. Furthermore, the application of ceramic membranes in separations of condensable from noncondensable vapors is explored both theoretically and experimentally. 

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