Adsorption changes

In Fig. 5.21, from Dawson s paper, the uptake at X for the 250°C-outgassed sample is dose to the calculated value for a monolayer of water with a (H20) = 101 A. Point X has therefore been ascribed to a close-packed monolayer of water on a hydroxylated surface of rutile. The fact that the differential entropy of adsorption relative to the liquid state (calculated from the isosteric heat of adsorption) changes sharply from negative to positive values in this region with A s 0 at X was regarded as supporting evidence. ... 

The amoimt and strength of hydrogen adsorption changed with the adsorption temperature for all catalysts examined. As the adsorption temperature was raised, the amount and strength of adsorption increased. 

We also address the models of adsorption change in electrophysical characteristics of semiconductor adsorbent caused both by diemisorbed charging of the surface due to the charge transition between surface states and volume bands of adsorbent and by local diemical interaction of adsorbate with electrically active defects of semiconductor. 

We consider problems related to electrophysical properties of sintered polycrystalline oxides as well as their adsorption changes. We also analyze the difference in adsorption induced changes of electrophysical characteristics of stoichiometric and non-stoichiometric partially reduced oxide adsorbents. 

Adsorption related charging of surface naturally affects the value of the thermoelectron work function of semiconductor [4, 92]. According to definition the thermoelectron work function is equal to the difference in energy of a free (on the vacuum level) electron and electron in the volume of the solid state having the Fermi energy (see Fig. 1.5). In this case the calculation of adsorption change in the work function Aiqp) in... 

The latter conclusion is reliably confirmed by experimental results [40] in which the studies of effect of the structure on the character of adsorption change in electric conductivity of monocrystal or partially reduced polycrystalline ZnO adsorbents were conducted. The comparative studies of the character and the value of response of electric conductivity in both types of adsorbents on adsorption of various atoms and molecular particles led the authors to conclusion on identical origin of both the mechanisms of electric conductivity and mechanisms of its adsorption induced change. 

Adsorbed layers, thin films of oxides, or other compounds present on the metal surface aggravate the pattern of deactivation of metastable atoms. The adsorption changes the surface energy structure. Besides, dense layers of adsorbate may hamper the approach of metastable atom sufficiently close to the metal to suppress thus the process of resonance ionization. An example can be work [130], in which a transition from a two- to one-electron mechanism during deactivation of He atoms is exemplified by the Co - Pd system (111). The experimental material on the interaction of metastable atoms with an adsorption-coated surface of... 

Surface reconstruction on metal crystals depends on the interior lattice as well as on the nature of the metal, such as Au (100)-(5 x20), Au (lll)-(l x 23) and Pt (llOHl X 2) [Kolb, 1993]. In general, the activation energy of surface reconstruction is relatively great ( 1 eV) on clean metal surfaces so that the reconstruction is frequently suppressed at room temperature. Usually, surface adsorption changes the activation energy that catalyzes or inhibits surface reconstruction. 

The polymers, after adsorption, change in conformation, and thus may increase stability. 

It is possible to calculate the entropies in cases where association or dissociation occurs at the same time as localized adsorption. Chang (17) gave an expression... 

The C.P.D. is obtained directly by the magnetron and the capacitor (or Kelvin) methods. Other methods which have proved successful rely on the variation of anode potential in a diode with constant cathode conditions. In this case, since adsorption changes the effective anode potential, the applied potential necessary to restore the anode current to its original value is equal to the C.P.D. between the two surfaces. As considered in Sec. II, a true average work function is measured in the C.P.D. method when the two conductors are separated by a distance which is much greater than the size of the patches on the surface. These conditions are invariably fulfilled in the capacitor and the space-charge-limited diode methods. 

Ligand effects in adsorption - changing the d band center... 

The transducing mechanism of semiconductor luminescence involves the modification of the semiconductors surface electrical properties through molecular adsorption. Changes in solid-state electro-optical properties result from adsorption of the molecule of interest onto the semiconductor surface. 

Dowden and Reynolds (I) have cited several examples of the parallelism between reaction rates in catalysis and electron density in other adsorbents. Extensive work by Garner and his co-workers (2,3) has shown clearly the intimate relation between adsorption and the conductivity of copper oxide. Clarke (4) and Morrison (5) have shown that adsorption changes the resistance of germanium. In metals, there appears a similar effect, Suhrmann and Schulz (6) have demonstrated the dependence of the conductivity of thin films of nickel on the adsorption of various gases. 

Silanes are commonly used to promote adhesion between inorganic and polymeric materials. Among their applications [1] are to promote adhesion between a polymeric coating and nonpolymeric (ceramic, metal) substrates, or between a filler material and the matrix in reinforced composites. In these applications, it would be very beneficial to know the amount of silane deposited, and how the extent of adsorption changes with their concentration. 

Energy models in these models a constant number of reactive sites is supposed, while the activation energy of adsorption changes with the amount adsorbed. Two models, mathematically equivalent, have been used site heterogeneity and induced heterogeneity. 

The effectiveness of heterogeneous defoaming is determined mainly by two factors the antifoam solubility and its ability to prevent adsorption of the surfactant at the aqueous film/antifoam interface, thus, destabilising the asymmetric aqueous films. The solubility of saturated alcohols in water and in aqueous surfactant solutions decreases with the increase in the molecular mass within the homologous series. The ability of alcohols to prevent adsorption change in the same direction. The difference between the interfacial tensions water/alcohol and aqueous surfactant solution/alcohol can serve as a quantitative measure for the change in the surfactant adsorption at the aqueous solution/alcohol interface... 

The effect of adsorption temperature on metals or supported metals on the mobility of adsorbed probe molecules has not received as much attention as on metal oxides. Gelin and co-workers (96) used adsorption microcalorimetry at 296 and 423 K and IR spectroscopy to study the adsorption of CO on Ir supported on NaY zeolite reduced from 383 to 923 K and on Ir supported on silica. At 296 K it was observed that for intermediate coverages (6 > 0.3) the kinetics of adsorption changed, with the thermograms displaying long tails... 

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