Ceramic separators properties

This chapter is split in two parts. The first part will briefly treat the preparation of flat ceramic membrane supports by colloidal processing. In our laboratory, these supports are used to study stability and gas separation properties of microporous silica membranes because they are easy to prepare and demand less complex testing equipment. 

Most porous membranes used in CMRs are made from oxide materials, although carbon membranes have also been used [1, 14, 22], However, although they possess very good separative properties, they have received less attention in CMR applications, probably due to their limited resistance to oxidative atmospheres. Vycor glass membranes also have certain drawbacks (brittleness, lack of high-temperature resistance) [9] for use in CMRs. Porous membranes in CMRs are, most often, made from ceramic materials or, more recently, from zeolites. 

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. 

Due to the amphoteric behavior of the used oxides, the separative properties of these ceramic nanofilters for ionic solutes in aqueous solutions will depend on both sieving and electrical effects. Complex electrokinetic phenomena occur during the forced flow of the ionic solutions through the confined volume of the micropores because the thickness of the double layer formed on the charged pore surface and the pore size have the same order of magnitude. Figure 25.3 illustrates... 

R.S.A. de Lange, Microporous sol-gel derived ceramic membranes for gas separation, synthesis, gas transport and separation properties, PhD Thesis, University of Twente, Enschede, The Netherlands, 1994. 

C.L. Lin, D.L. Flowers and P.K.T. Liu, Characterization of ceramic membranes. II. Modified commercial membranes with pore size imder 40 A. /. Membr. Sci., 92 (1994) 45. R.J.R. Ulhom, K. Keizer and A.J. Burggraff, Gas transport and separation with ceramic membranes. Part II. Synthesis and separation properties of microporous membranes. /. Membr. Sci., 66 (1992) 271. 

R.J.R. Uhlhom, K. Keizer and A.J. Burggraaf, Gas transport and separation with ceramic membranes. Part II. Synthesis and separation properties of microporous membranes. /. Membr. Sci, 66 (1992) 271-282. 

R. S.A de Lange, Microporous Sol-Gel Derived Ceramic Membranes for gas Separation -Synthesis, Gas Transport and Separation Properties. Thesis, Twente University, 1993. 

It is convenient to consider ceramics that are essentially silicates, called traditional ceramics, separately from all of the others. This latter group comprises engineering ceramics, with important mechanical properties, electroceramics, when... 

M. Moaddeb, W. J. Koros, Effects of colloidal sUica incorporation on oxygen/nitrogen separation properties of ceramic-supported 6FDA-IPDA thin films, J. Membr. ScL, 111, 283 (1996). 

Conventional membranes rely on rigid polymeric, ceramic, or porous stainless steel membranes. These membranes are available in discrete pore sizes and cannot be customized to the characteristics of the feed. Furthermore, once installed on-site it is difficult and costly to modify their separation properties in response to variable feed characteristics. 

An emerging new group of lithium-ion separator comprises of inorganic composite membranes ( ceramic separators ) with their excellent wettability and exceptional thermal stability properties. Most of ceramic separators are porous mats made of ultrafine inorganic particles bonded using a small amount of binder. 

While a battery separator s materials are usually inert and do not influence electrical energy storage or output, its properties can have an important influence on safety. There are three types commonly used [46] (i) high-temperature sohd-polymer electrolytes (SPEs) such as poly(ethylene oxide) (PEO), (ii) microporous shutdown separators, which are composed of poly(ethylene) (PE) or laminates of poly(propylene) (PP) and PE, (iii) gel polymers such as poly(vinyhdene fluoride), PVdF, and (iv) ceramic separators. Table 27.2 shows the types of separators used in secondary Hthium-based batteries. 

The choice of separator affects the abuse tolerance. Ceramic separators are potentially more rugged and maintain high conductivity in the Li-ion battery environment. These were developed by Eedkiw [49] and commercialized at Degussa [50]. D6ring and co-workers studied 8 Ah cells with IiMn204 cathodes that contained a normal polyolefin shutdown separator and a new ceramic separator without shutdown properties. They demonstrated that the thermal runaway produced by overcharge could be avoided with a more stable (ceramic) separator [51]. 

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