Bare samples

A comparison of husD and fe/M/t) values for sample 3 are particularly instructive. The heat values for the immersion of monolayer-covered samples in toluene, cyclohexane, and carbon tetrachloride are three to four times less than the heat values for the bare samples and are also significantly less than the surface enthalpies of the respective liquids. Apparently, the attractive forces of the covalent carbon atoms in the surface are highly localized. In addition, the interaction of first-layer molecules with those in the second layer is less than between the liquid molecules in adsorbed monolayer, as indicated by the 7 s (14)- The net energy of adsorption... 

Figure 5. Excess enthalpies during 4-methyl quinoline desorption/decomposition from sample OW-ZSM-5 (a) and from sample 1 OW-ZSM-5 (b). Curves for the bare samples were subtracted.

Four techniques were used to characterize the surface of bare (sample 1) and sized glass fibers (39). The sizes include cationic silane (sample 2), polyethylene dispersion (sample 3), silane/polyurethane dispersion (sample 4), and silane/ep-oxy dispersion (sample 5). Sample 2 shows highest surface free energy by capillary rise method. There is almost 30 mJ/m difference between samples 2 and 4. However, the difference in surface free energy among five samples is nonexis-... 

ICR values were taken with bare samples. If the SS is polarized in simulated PEMFC environments, a passive film forms therefore, the ICR values with passive films are normally higher than those with... 

Fig.6 Spectroscopic data concerning the interaction of ammonia with H-[Al]-MCM-41(28) outgassed at 1073 K in the O - H stretching region, a room temperature IR spectra at increasing ammonia equilibrium pressures, i.e., bare sample (spectrum 1), 0.20 (2), 0.50 (3), 1.00 (4), 3.10 (5), 6.90 (6), 14.6 (7) and 29.3 (8) mbar. b Check of the Langmuir equation (see text for details) and comparison with pure sUica MTS outgassed at the same temperature. In order to allow comparison, spectra have been normalized to the same wafer thickness. 0 is the fraction of Sil species interacting with ammonia...

A possible explanation is as follows. Because of the amorphous nature of the system and the flexibility of Si-O-Si bonds, Bronsted acidic centers responsible for the 3460 cm absorption after interaction may occur in a variety of coordinative environments, so that the corresponding O - H stretch is smeared out and not observed as a definite band in the spectra of the bare sample, nor is it as a negative band in difference spectra like those in section a of Fig. 8. Such is, for instance, the explanation proposed for the species Si(OH)Ga (see Sect. 7). Adsorption would restore homogeneity in the set of the heterogeneously broadened ensemble of acidic species. 

Fig. 12 IR spectra illustrating the conversion of Lewis into Br0nsted sites by adsorption of small doses of water (ca. 0.05 mbar). Left OH stretching region right ammonia deformation region. Lower spectra bare sample as such (spectrum a) and after ammonia adsorption (spectrum b). Upper spectra after chemisorption of a small dose of water (spectrum a) and successive adsorption of ammonia (spectrum b). Sample was H-[A1]-MCM-41(13) outgassed at 1073 K. After [51,52]...

The other three Bronsted sites, hardly detectable in the bare samples, give characteristic (broad, multicomponent) signals centered at 3460 cm (AlOH(II)),3420 cm (AIOH(III)) and 3406 cm (A1 H2O). We propose that these species are all associated with aliuninum atoms partially linked to the silica matrix, because in this way they may be subjected to spatial reorganization upon interaction of an adsorbate molecule (even a weak one like CO), and only this fact can provide an explanation for their "invisibiUty in the bare samples. Also, no comparable acidity is found with alumina particles [67]. 

For a bare sample, a gas permeation membrane, or for an open-circuit fuel ceU or other electrochemical device, the total current is zero. For fuel cells or electrolysers in operation, on the other hand, the current is non-zero. 

According to the Pourbaix diagram, pure aluminium is passive in the pH range of 4 8 [15], however, as shown from Fig. 7.10, the coated sample is stable (10 ohm.cm ), and one order of magnitude higher than that of the bare sample following 2 months of immersion indicating protection of the substrate over this time. 

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