Nanostructured ceramics interfaces

To understand the importance of nanostructures in microsieving membranes, the basic structure of nanophased ceramics must be briefly described. Because the particles are extremely small, one to a few tens of nanometers, an important fraction of the atoms is found in or very near the interface between grains, as reported in Table 2 [32]. Figure 11 is a schematic representation of a nanophase material. One can see that individual grains in the 5 nm range induce a biphasic material with an interfacial phase between the grains and a residual nanoporosity, evidenced by positron lifetime spectroscopy [33]. Transmission electron microscopy is also a well-adapted technique for nanoscale structure characterization, as illustrated later. 

Figure 15.22b Erom van Helvoort, A.T.J., Knowles, K.M., and Eernie, J.A. (2003) Characterization of cation depletion in Pyrex during electrostatic bonding, /. Elec-trochem. Soc., 150, G624. By permission of ECS— The Electrochemical Society. And from van Helvoort, A.T.J., Knowles, K.M., and Eernie, J.A. (2003) Nanostructure at electronic bond interfaces, J. Am. Ceram. Soc. 86, 1773. By permission from Blackwell Publishing and the American Ceramic Society.

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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