Crystal grain boundaries

The separation of xylene isomers on MFl zeolite membranes can be considered one example of intracrystaUine size exclusion and competitive adsorption (strongly dependent on coverage). The difference in their kinetic diameters ( 0.58 nm for p-xylene and 0.68 nm for o- and m-xylene) indicates the possibility of an effective separation using MFl membranes (see Table 10.1). The kinetic diameter of p-xylene is close to one of the MFl channels ( 0.55 nm) whereas o- and m-xylene might be excluded. Therefore, MFl zeolite channels and crystal grain boundaries determinate the permeation characteristics [27]. 

Figure 1. Microstructure of a polycrystalline ceramic showing grains (crystals), grain boundaries, and pores.

Read, W.T. and Shockley, W. (1950) Dislocation models of crystal grain boundaries, Phys. Rev. 78(3), 275. A classic readable paper with great diagrams. 

Fig.i. .2-56a-c Scheme of colony and single-crystal grain boundaries proposed for the railway-switch model [2.117] and in a modified picture for the freeway model [2.118]... 

There are various suggested systems for the pre-treatment of stainless steels which consist of treating the metal surface with strong acids to attack crystal grain boundaries in the... 

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