Ceramic packing characteristics

Table 24. Geometrical characteristics of ceramic packings with vertical walls...

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. 

Because the ceramic porous structure depends on the shape of individual grains and the way they are packed, different factors can affect the two major characteristics of membrane supports, mechanical strength and porosity. The pseudoplastic behavior of the paste during extrusion is responsible for an exponential dependence of extrusion velocity versus applied pressure. High pressures to increase support permeability and strength have been emphasized in the literature [14]. These can be linked to a better (more dense) particle pack-... 

Metals, both pure and alloyed, consist of atoms held together by the delocalized electrons that overcome the mutual repulsion between the ion cores. Many main-group elements and all the transition and inner transition elements are metals. They also include alloys—combinations of metallic elements or metallic and nonmetallic elements (such as in steel, which is an alloy of primarily Fe and C). Some commercial steels, such as many tool steels, contain ceramics. These are the carbides (e.g., FeaC and WgC) that produce the hardening and enhance wear resistance, but also make it more brittle. The delocalized electrons give metals many of their characteristic properties (e.g., good thermal and electrical conductivity). It is because of their bonding that many metals have close packed structures and deform plastically at room temperature. 

Various additives, generally with very low concentrations, have been used to control the characteristics of the feed materials, in order to achieve desired shapes and control the packing uniformity of the green body of ceramics. For some methods, such as tape casting and injection molding, the use of suitable additives is especially important. The additives can be either organic or inorganic materials. 

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