Passivation surface

Etch primers partially fulfil the roles of both pretreatment and primer. They contain phosphoric acid for surface passivation and are based on polyvinyl butyral ... 

Chromate ions, when used as inhibitors in aqueous solutions, passivate by maintaining a coherent oxide film on the metal surface. Passivation is maintained even in a boiling concentrated chromic acid solution, in which many of the oxides in bulk form are soluble. The passivity breaks down rapidly, however, once the chromate is removed. 

Deterioration of electrode performance due to corrosion of electrode components is a critical problem. The susceptibility of MHt electrodes to corrosion is essentially determined by two factors surface passivation due to the presence of surface oxides or hydroxides, and the molar volume of hydrogen, VH, in the hydride phase. As pointed out by Willems and Buschow [40], VH is important since it governs alloy expansion and contraction during the charge-discharge cycle. Large volume changes... 

Electrode corrosion is the critical problem associated with the use of metal hydride anodes in batteries. The extent of corrosion is essentially determined by two factors alloy expansion and contraction in the charge-discharge cycle, and chemical surface passivation by the formation of corrosion—resistant oxides or hydroxides. 

Both factors are sensitive to alloy composition, which can be adjusted to produce electrodes having an acceptable cycle life. In AB5 alloys the effects of Ce, Co, Mn, and A1 upon cycle life in commercial AB5 -type electrodes are correlated with lattice expansion and charge capacity. Ce was shown to inhibit corrosion even though lattice expansion increases. Co and A1 also inhibit corrosion. XAS results indicate that Ce and Co inhibit corrosion though surface passivation. 

Effective metal waterside surface passivation (using hydrazine, DEHA, tannin, or similar products) remains an essential requirement of higher temperature or pressure system programs. 

Figure 10.1 Types of phosphate structures, (a) Where x = 12 to 14, the structure represents sodium polyphosphate, a phosphate typically used in HW heating and industrial steam boiler formulations. The structure is ill defined and described as glassy rather than crystalline. Where x = 2, it represents sodium tripolyphosphate, (b) This is the structure where effectively, x = 0, and represents trisodium phosphate (sodium orthophosphate), which is commonly supplied in either crystalline or anhydrous powder form and used as an alkalinity booster, boiler boil-out cleaner, and metal surfaces passivator.

Similar effects may exist at other metals. For instance, when the surface of an iron electrode is thermally reduced in hydrogen and then anodically polarized at a current density of 0.01 mA/cm in 0.1 M NaOH solution, passivation sets in after 1 to 2 min (i.e., after a charge flow of about 100 mC/cm ). This amount of charge is much smaller than that required for formation of even a thin phase film. Since prior to the experiment, oxygen had been stripped from the surface, passivation can only be due to the adsorbed layer formed as a result of polarization. 

This chapter presents an overview of the synthesis, ensemble photoluminescence properties and blinking of single CdSe quantum dots. The stress is on (i) widely accepted methods of synthesis, (ii) the origin of photoluminescence and variations of photoluminescence as functions of surface-coating, surface-passivating molecules, chemical environment, and thermal- and photo-activations, and (iii) photolumines-... 

Figure 7.5 Schematic presentation of photoactivation and relaxation processes in a CdSe quantum dot aggregate (a) surface-passivation of photoexcited quantum dots by solvent molecules or dissolved oxygen, (b) thermal activation followed by the formation ofa stabilized state, (c) the formation of deep-trap states, (d) non-radiative relaxation of deep-...

It is evident in Figure 3.5 that the two displayed spectra are slightly different in the band intensities and observed spectral features. This approach is thus suitable for analysing the characteristic band structures to enhance the bio-compatibility of the sapphire lenses, and the surface passivation process enabled more optimized biocompatible lenses to be fabricated. 

All the surface recombination processes, including back reaction, can be incorporated in a heavy kinetic model [22]. The predicted, and experimentally observed, effect of the back reactions is the presence of a maximum in the donor disappearance rate as a function of its concentration [22], Surface passivation with fluoride also showed a marked effect on back electron transfer processes, suppressing them by the greater distance of reactive species from the surface. The suppression of back reaction has been verified experimentally in the degradation of phenol over an illuminated Ti02/F catalyst [27]. 

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