Transient interference microscopy

Fig. 17 Transient concentration profiles in y-direction (i.e., along 8-ring channels) measured by interference microscopy for a adsorption and b desorption of methanol in a large crystal of ferrierite for pressure steps 5 -> 10 and 10 5 mbar. The form of the profiles shows that both surface resistance and internal diffusion (along the 8-ring chan-...

Fig. 45 Comparison of the transient concentration profiles during methanol uptake by the MOF-type crystal as recorded by interference microscopy (symbols) with the corresponding profiles recalculated from the measured diffusivities with surface permeabilities (full line in Fig. 44) which lead to the best fit to the experimental points...

Various improvements have broadened the research in the field of zeolite membranes and films, such as the development of new synthesis procednres, the use of new supports with specific characteristics (monoliths, foams, etc.), or the use of modified supports by means of masking or grafting techniques, the application of new analytical techniques (isotopic-transient experiments, permporometry, pulsed field gradient nuclear magnetic resonance [NMR], interference microscopy, IR microscopy, etc.), the control of the orientation of the crystals (by means of covalent linkages, synthesis conditions, etc.) and of the thickness of the membranes, and the preparation of new zeolites as membranes or new zeolite-related materials. In addition, a variety of zeolites can now be prepared as colloidal systems with particle dimensions ranging from tens to a few hnndred nanometers. 

A major advantage of the recently developed interference microscopy technique [74, 75] is that in addition to allowing a direct measurement of sorption/desorption rates on the single crystal scale it provides, from the form of the transient concentration profiles, direct experimental evidence concerning the nature of the rate controlling resistances to mass ffansfer. Recent studies by this technique have shown that the influence of sffuctural defects and surface resistance to mass transfer are far more important than has been generally assumed [76-80]. For some systems it appears that sorption rates are controlled by surface resistance while in other cases the profiles suggest a combination of... 

Figure 14. Shape, dimensions and transient concentration profiles during uptake of methanol in a ferrierite crystal measured by interference microscopy, (c) shows the actual profiles along the length of the crystal at the mid point, and (e) shows the same profiles normahzed by subtracting the effect of the roof-hke structures. AQ profiles are at the same times (0, 30, 130 and 370 secs). From Kortunov etal [81].

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