Decrease the surface concentration

For higher amounts of selenium dioxide in the feed (Z > 0.02), while the surface concentration of adsorbed oxygen ions gradually decreases, the surface concentration of adsorbed products becomes significant, and possibly results in the modifier s entering the catalyst lattice substitutionally, rather than interstitially, Cu2+, Cu+, or O" is replaced by selenium, forming a small unit of a covalent compound. Thus, both free... 

All monofunctional modifiers decrease the surface concentration of silanols by 50% (depending on the alkyl ligand) compared to original silica (7.6pmol/m ), while difunctional modifiers only slightly reduces the surface concentration of silanols by 12% and trifunctional modifiers apparently increases the amount of silanols. This reflects actual hydrolysis of nonreacted chlorine groups of the alkyl di- and trifunctional modifiers and their conversion into silanols. 

Chemical annealing steps decrease the surface concentration (E) of electroactive species and improve reversibility. Chemical exchange of electroactive with diluent adsorbate appears to take place at domain boundaries and defect sites. A domains/ defects model of monolayer structure was presented, whereby two populations of electroactive species are present one which is fully desorbed after a few days of exposure to a nonelectroactive solution, and the other which remains unaffected by such chemical annealing for at least 10 days. 

In the original state, amine-, ammonium- and nitrite/nitrate-like coiUKJunds were observed. With increasing the HNO3-exposition-time, the nitrate-contributions increase and the amine/ammonium-contributions decrease. The surface-concentration of oxygen can be enhanced. 

The statistical treatment of the SEM images shows that in the case of the Au/GaAs pair the exposure Ct in the solution (C is the concentration of ions and t is the duration of process) decreases the surface concentration of nanoparticles from 1012 cm"2 to 51O10 cm"2 with an increase of the average size from 5 nm to 50 nm (coalescence). 

In our water effect experiment, a primarily reversible decrease in CO conversion was observed when up to 30 vol% of water was added to the feed for this catalyst [9], With the 0.5% Pt-15%Co/Al203 catalyst, a reversible water effect was obtained at a lower volume percent of water addition but irreversible deactivation occurred at > 25% vol. water addition [7], One possibility for the effect of water is that the amount of catalytic active sites (i.e., surface cobalt metal atoms) available for the FT reaction changes with partial pressure of water, perhaps by a temporary oxidation process for cobalt [9], Alternatively, competitive adsorption of water may decrease the surface concentration of CO and/or H2 [9], Thus, the following equation is proposed to described the reversible impact of water on the CO reaction rate ... 

In a foam where the films ate iaterconnected the related time-dependent Marangoni effect is mote relevant. A similar restoring force to expansion results because of transient decreases ia surface concentration (iacteases ia surface tension) caused by the finite rate of surfactant adsorption at the surface. 

Fig. 6. Top Morphology of FPL surface following fluorine contamination. This is to be compared to the standard FTL morphology of Fig. 14. Middle Climbing drum peel (CDP) strength as a function of F surface concentration. Bottom F concentration on FPL surfaces following doping the FPL etch solution and the rinse water with NaF. The dotted line corresponds to the surface concentration with which the CDP strength began to decrease. Adapted from Ref. [37].

Let us see now what happens in a similar linear scan voltammetric experiment, but utilizing a stirred solution. Under these conditions, the bulk concentration (C0(b, t)) is maintained at a distance S by the stilling. It is not influenced by the surface electron transfer reaction (as long as the ratio of electrode area to solution volume is small). The slope of the concentration-distance profile [(CQ(b, t) — Co(0, /))/r)] is thus determined solely by the change in the surface concentration (Co(0, /)). Hence, the decrease in Co(0, t) duiing the potential scan (around E°) results in a sharp rise in the current. When a potential more negative than E by 118 mV is reached, Co(0, t) approaches zero, and a limiting current (if) is achieved ... 

When a polymer sheet of thickness L is immersed in the gas at a constant pressure, the surface concentration increases instantaneously, to a steady value which is then spread by diffusion throughout the whole bulk of the polymer sheet to finally give a uniform concentration. During the sorption the concentration gradients in the polymer decrease as the time progresses reducing the sorption... 

As shown in Fig. 33, the decreasing mechanism of this fluctuation is summarized as follows At a place on the electrode surface where metal dissolution happens to occur, the surface concentration of the metal ions simultaneously increases. Then the dissolved part continues to grow. Consequently, as the concentration gradient of the diffusion layer takes a negative value, the electrochemical potential component contributed by the concentration gradient increases. Here it should be noted that the electrochemical potential is composed of two components one comes from the concentration gradient and the other from the surface concentration. Then from the reaction equilibrium at the electrode surface, the electrochemical potential must be kept constant, so that the surface concentration component acts to compensate for the increment of the concen-... 

Luo et al. [1,153] used a slurry containing ultra-fine diamond (UFD) powders to polish the surface of HDD sliders. The powders are from 3 nm to 18 nm in diameter and 90 % around 5 nm. They are crystal and sphere-like [154]. The pH value of the slurry is kept in the range from 6.0 to 7.5 in order to avoid the corrosion of read-write heads, especially pole areas. A surface-active agent is added into the slurry to decrease the surface tension of the slurry to 22.5 Dyn/cm, and make it spread on the polish plate equably. An anti-electrostatic solvent is also added to the slurry to avoid the magnetoresistance (MR) head being destroyed by electrostatic discharge. The anion concentration of the slurry is strictly controlled in ppb level so as to avoid the erosion of magnetic heads as shown in Table 5. The concentration of UFDs in the slurry is 0.4 wt %. 

The surface concentration decreases with increasing current density. When the current density has attained a certain critical value. 

When the surface concentration has fallen to zero, further current flow and the associated increase in 5( lead to a decrease in concentration gradient and in current (Fig. 11.3h, the curve for t > Therefore, at f > the original, constant current density can no longer be sustained. It follows that a steady state can only exist under the condition ltr< lim ... 

When an electrode reaction takes place, the applied current is divided between the nonfaradaic components and a faradaic component. Because of the latter, there is a gradual decrease in surface concentration of the reactant [according to Eq. (11.6)]. When the time, required for diffusion to change from transient to steady is large compared to the transition time [Eq. (11.9)], the reactant s surface concentration will fall to zero within the time (see Fig. 11.3). 

A decrease in the surface concentration of strongly chemisorbed C=0 species blocking the snrface (and thus retarding the reaction) or... 

Photoreduction of Si02 doped by six valance molybdenum results in decrease of the surface concentration of Mo ions and, as a consequence, reduces the capability of the sample to emit 2. However, such a treatment does not lead to a complete suppression of emission capability because, according to [96], illumination reduces only 30% of Mo ions in molybdenum oxide catalysts deposited on Si02. 

Figure 5.11 Variation in the catalytic activity of an Mg(0001) surface when exposed to a propene-rich propene- oxygen mixture at room temperature. The surface chemistry is followed by XPS (a), the gas phase by mass spectrometry (b) and surface structural changes by STM (c, d). Initially the surface is catalytically active producing a mixture of C4 and C6 products, but as the surface concentrations of carbonate and carbonaceous CxHy species increase, the activity decreases. STM images indicate that activity is high during the nucleation of the surface phase when oxygen transients dominate. (Reproduced from Ref. 39).

The quantity dyl3 In a2 at the potential of the electrocapillary maximum is of basic importance. As the surface charge of the electrode is here equal to zero, the electrostatic effect of the electrode on the ions ceases. Thus, if no specific ion adsorption occurs, this differential quotient is equal to zero and no surface excess of ions is formed at the electrode. This is especially true for ions of the alkali metals and alkaline earths and, of the anions, fluoride at low concentrations and hydroxide. Sulphate, nitrate and perchlorate ions are very weakly surface active. The remaining ions decrease the surface tension at the maximum on the electrocapillary curve to a greater or lesser degree. 

The number of leaving alkyl groups seems to depend on the degree of hydroxylation of silica. When the silica is heated, water is driven off and the surface concentration of OH groups decreases. At 450°C siloxane bonds are also formed (Scheme 7.8). 

The kinetics of sorption of arsenite and arsenate in the presence of sorbed silicic acid have been only recently examined (Waltham and Eick 2002). These authors demonstrated that the sorption of silicic acid (added 60 h before arsenic) decreased the rate and the total amount of arsenic sorbed. The amount of arsenite sorbed decreased as the surface concentration of silicic acid increased. Furthermore, the inhibition of arsenite sorbed ranged from about 4% at a pH of 6 and 0.1 mM silicic acid up to 40% at a pH of 8 and 1 mol IT1 silicic acid. In contrast, silicic acid reduced the rate of arsenate sorption which decreased by increasing pH and silicic acid concentration, but the total quantity of arsenate sorbed remained nearly constant, indicating that arsenate was able to replace silicate. 

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