Interference microscopy concentration

Bromination/EDXA (Chap. 4.4) has several disadvantages when compared to the other two techniques. Only relative lignin concentration can be determined directly by this method and a correction factor of 1.7 is required to obtain agreement between techniques (Saka et al. 1982, Donaldson and Ryan 1987). When bromination/EDXA and interference microscopy are used on matched samples, agreement is poor (Donaldson and Ryan 1987) as shown in Table 4.3.2. Not only is there poor quantitative agreement between the two methods, but EDXA data are also much more variable within each specimen. 

Table 4.3.2. Relative lignin concentration (ccml/S2) for two matched samples determined by interference microscopy and bromination/EDXA. (Donaldson and Ryan 1987)...

Boutelje JB (1972) Calculation of lignin concentration and porosity of cell wall regions by interference microscopy Sven Papperstidn 75 683-686... 

Donaldson LA, Ryan KG (1987) A comparison of relative lignin concentration as determined by interference microscopy and bromination/EDXA Wood Sci Technol 21.303-309... 

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. 33 Schematics of interference microscopy, a Two light beams, one passing through the crystal and the other through the simrounding atmosphere, b The interference microscope. c Interference patterns generated due to different optical properties of the media passed hy the two beams, d Concentration profiles calculated from the changes in interference patterns with time...

Finally, one has to mention that interference microscopy is only able to record relative changes in sorbate concentration. Hence, the joint application of interference and IR microscopy turns out to be indispensable for the determination of the absolute loadings under which the experiments are performed. 

Fig. 36 Intracrystalline concentration profiles of isobutane in silicalite-1 along the z direction during adsorption a,b profiles measured by interference microscopy c,d simulated profiles, assuming that the internal interfaces serve only as transport barriers. For the simnlated profiles the time nnit is 10 elementary diffnsion steps. The eqnilibrinm valnes of C(y, z) after the end of adsorption are eqnal to 1...

Fig. 39 The mean concentration integrals I recorded by FTIR (diamonds) and interference microscopy (points) along the y direction for x values between 35 and 55 xm x, y, and z are the crystallographic directions...

The evidence of interference microscopy nicely correlates with the models of crystallization, which in the case of SAPO-5 favor a pencil-like crystallization core [79,80], while in CrAPO-5 crystalUzation proceeds via the formation of dumbbell-shaped structures [81,82]. In no case coifid a nanoporous material with the desired structure of microscopic, ideal macaronis be identified. The appearing dramatic deviation from an ideal channel structure excludes the appHcation of simple model assiunptions for interpretation of the time evolution of the concentration profiles, hi fact, in [83] the experimentally monitored concentration profiles during... 

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...

Fig. 50 Concentration profiles integrated over the z direction observed by interference microscopy during a methanol pressure step from 0 to 1 mbar. a Two-dimensional and b one-dimensional profiles in the crystal center along the x (fair spheres) and y (black spheres) directions. The times after onset of adsorption are indicated in b...

Fig. 29. (a) Ferrierite crystal with a two-dimensional pore structure utilized to determine spatially resolved concentration of methanol, (b) Intercrystalline concentration profiles measured during adsorption hy interference microscopy. Reprinted from 202, cop5rright 2006, with kind permission from American Chemical Society. 

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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