Ceramic separators material characteristics

Benefits and Test Results of a Ceramic Separator Component Table 6-1. A comparison of material characteristics of separators... 

The interest in ceramic membranes grew, together with the interest in membrane separation processes, due to their specific properties. They are chemically stable, can withstand high temperatures and are noncompressible. These characteristics made them the only materials available, which could withstand the harsh environment in the isotope separation. On the other hand, the brittleness of most materials is a problem and so is the selectivity. 

Oxide surface materials are widely used in many applications, in particular where chemically modified oxide surfaces are involved. Indeed, in disciplines as separations, catalysis, bioengineering, electronics, ceramics, etc. modified oxide surfaces are very important. In all cases, the knowledge of their chemical and surface characteristics is of great importance for the understanding and eventual improvement of their performances. 

The chapters in this volume present detailed insights into the synthesis-structure-properties relationships of nanostructured materials. In particular, the catalytic and photocatalytic properties of nanoclusters and nanostructured materials with ultrahigh surface-to-volume ratio are demonstrated. The gas absorption characteristics and surface reactivity of nanoporous and nanocrystalline materials are shown for various separation and reaction processes. In addition, the structural manipulation, quantum confinement effects, transport properties, and modeling of nanocrystals and nanowires are described. The biological functionality and bioactivity of nanostructured ceramic implants are also discussed. 

The evaluation of the commercial potential of ceramic porous membranes requires improved characterization of the membrane microstructure and a better understanding of the relationship between the microstructural characteristics of the membranes and the mechanisms of separation. To this end, a combination of characterization techniques should be used to obtain the best possible assessment of the pore structure and provide an input for the development of reliable models predicting the optimum conditions for maximum permeability and selectivity. The most established methods of obtaining structural information are based on the interaction of the porous material with fluids, in the static mode (vapor sorption, mercury penetration) or the dynamic mode (fluid flow measurements through the porous membrane). 

The use of packing instead of trays in multistage separation columns is common for column diameters 3-4 ft or smaller. More recently, packing has been used for larger columns because of its low pressure drops, favorable efficiencies, and high vapor capacity. Packed columns are also the preferred choice where corrosion is a potential problem. The packing material used in these situations is ceramic or polymeric. Another characteristic of packed columns is their low liquid holdup, which could reduce the amounts of off-specification products at startup and shutdown. 

For high-temperature gas separation applications, leak-free sealing of the ITM module components and parts is essential and requires chemically resistant ceramic-metal and ceramic-ceramic seals with similar mechanical, chemical, and expansion characteristics as the membrane material. Little prior art exists for sealing and joining designs for tonnage-quantity ITM modules. ITM ceramics are susceptible to breakage and will have to be joined preferably without any joint interface property difference, possibly as a routine plant maintenance procedure. 

During extrusion laminations basically develop as a result of the combined effect of raw material respectively body-specific characteristics and physical processes caused by transport, homogenisation and shaping operations within the extruder, which may cause shearing, gliding, separation and rejoining effects within the ceramic body. 

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