Inorganic oxide surface contaminants

Certain inorganic materials can be employed as photocatalysts for the synthesis or degradation of compounds in heterogeneous systems. Relevant devices contain, for example, films incorporating immobilized photocatalyst particles. Typically, titania, Ti02, is used for the treatment of water contaminated with chemical pollutants and/or bacteria [9]. The contaminants are oxidized by reactive species, i.e. hydroxyl and superoxide radicals, generated by reaction of electron/hole pairs with O2 and water adsorbed at the particle surface. Electron/hole pairs are formed when UV light (>, <400 nm) is absorbed by titania (see Scheme 14.5). 

Applications of ISS to polymer analysis can provide some extremely useful and unique information that cannot be obtained by other means. This makes it extremely complementary to use ISS with other techniques, such as XPS and static SIMS. Some particularly important applications include the analysis of oxidation or degradation of polymers, adhesive failures, delaminations, silicone contamination, discolorations, and contamination by both organic or inorganic materials within the very outer layers of a sample. XPS and static SIMS are extremely comple-mentar when used in these studies, although these contaminants often are undetected by XPS and too complex because of interferences in SIMS. The concentration, and especially the thickness, of these thin surfiice layers has been found to have profound affects on adhesion. Besides problems in adhesion, ISS has proven very useful in studies related to printing operations, which are extremely sensitive to surface chemistry in the very outer layers. 

In general, there are two types of surface contamination (1) organic contamination—such as oils, greases, paint coatings etc. and (2) inorganic contamination —such as rust, oxide films, corrosion products, scale, anodic films etc. Although these two types of contaminant can be removed simultaneously, it is simpler to consider the cases separately. 

We construct in this section a model of how inorganic lead reacts as it infiltrates and contaminates an aquifer, and then as the aquifer is flushed with fresh water during pump-and-treat remediation (Bethke, 1997 Bethke and Brady, 2000). We assume groundwater in the aquifer contacts hydrous ferric oxide [Fe(OH)3, for simplicity] which sorbs Pb++ ions according to the surface complexation model of Dzombak and Morel (1990), as discussed in Chapter 10. 

The ISV process uses electricity to heat and melt soil and other earthen materials contaminated with organic, inorganic, and radioactive compounds. Organic compounds undergo pyrolysis (thermal decomposition in the absence of oxygen). The pyrolyzed compounds then migrate to the surface zone, where they are collected and oxidized in a collection hood. Inorganic and radioactive components are incorporated as oxides into a leach-resistant vitrified product. 

This is generally believed to result from the substitution of chloride ions into the surface oxide lattice with subsequent breakdown of the passification of the underlying alloy. The elimination of inorganic chloride contamination from stainless steel components used in nuclear applications has been a goal of designers for many years. 

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