Surface excess concentration temperature effect

Note again that surface composition is strongly temperature-dependent. As the temperature increases, the surface excess concentration of the segregating constituent should diminish exponentially if the models expressed by Eqs. 3.48, 3.51, and 3.55 are obeyed. This effect is readily discernible by comparing Figure 3.6a with Figure 3.6b, where the surface excesses of silver in Au-Ag are plotted at two different temperatures. 

Tauber et al. [23] following the same method as Hart et al. but using tert-butanol as the methyl radical source, obtained a temperature of 3,600 K in 10 3 M /(77-butanol and reported, similar to Hart et al. that this temperature decreased with increasing /( / /-butanol concentration. More recently, this method was adopted by Rae et al. [24] and Ciawi et al. [25, 26] in aqueous solutions. Rae et al. examined the effect of concentration of a series of aliphatic alcohols, extrapolating a maximum temperature of about 4,600 K at zero alcohol concentration [24]. They also observed a decrease in temperature with increasing alcohol concentration, which correlated well with the alcohol surface-excess and SL measurements obtained in the same system. Ciawi et al. investigated the effects of ultrasound frequency, solution temperature and dissolved gas on bubble temperature [26],... 

The effect of drying temperature on the surface hydroxyl concentration for Manosil VN3 slurried with 25 ml toluene and treated with excess Zr(7r-allyl)4 is shown in Figure 8. The discrepancy between these results and literature determinations of surface hydroxyl concentrations (20, 49, 50) prompted an investigation of the experimental technique. It was found that the concentration of the silica slurry had a profound effect on the degree of reaction with the organometallic. The results for Aerosil 380 dried at 200°C for 2 hrs under vacuum, slurried with toluene, and allowed to react with excess Zr(7r-allyl)4 or CH3MgI are shown in Figure... 

At least three of the studied blends [16,145] h86 (N86=1520)/d75 (N75=1625, deuteration extent e=0.4),d75/h66 (N66=2030) and h66/d52 (N52=1510 as well as e=0.34) may be described by a rather small Afs driving surface segregation. In an extreme case of the lowest Afs magnitude the enrichment-depletion effect is expected, as observed for the h66/d52 blend (see the next section). Here we characterize this class of mixtures with the results obtained for the h86/d75 blend. Surface excess z has been determined [145] as a function of bulk concentration at two different temperatures the corresponding (f) values are denoted as open circles (O) in the h86/d75 phase diagram (see inset to Fig. 21a). Surface segregation of the h86 component with a local concentration ( >(z) has been stud-... 

Because of the effect of static head, evaporation and cooling occur only in the liquid layer near the magma surface, and concentration and tem wrature gradients near the surface are formed. Also crystals tend to settle to the bottom of the crystallizer, where there may be little or no supersaturation. The crystaUizer will not operate satisfactorily unless the magma is well agitated, to equalize concentration and temperature gradients and suspend the crystals. The simple vacuum crystallizer provides no good method for nucleation control, for classification, or for removal of excess nuclei and very small crystals. 

Based on available results, it can be summarized that the particle size of tantalum powder increases (specific charge decreases) with the increase in temperature, K2TaF7 concentration and excess sodium. In addition, an increase in the specific surface area of the melt and Na/K ratio also leads to the formation of coarser tantalum powder. The most important conclusion is that for the production of finer tantalum powders with higher specific charges, the concentration of K2TaF7 in the melt must be relatively low. This effect is the opposite of that observed in the electrochemical reduction of melts. 

Since the surface properties of the colloid have a strong influence on the photoreduction kinetics, it seemed interesting to elucidate the effect of the added surface-active substances on the kinetic regularities of the reactions photosensitized by semiconductor colloid. The surfactant molecules are known to concentrate near the surface of the colloidal particle, so they may affect strongly the kinetics of photocatalytic reactions proceeding at the particles surface [52,53]. Fig. 2.30 presents the temperature dependencies of the initial rate of the MV photoreduction over colloidal CdS prepared at the excess of the sulfide ions. These dependencies were obtained at the addition of different amounts of PAA. One may see that both the initial rate and the observed activation energy of the methylviologen photoreduction do not depend, within the experimental error, on the concentration of... 

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