Surface films compositions

We should point out that at the scale of the whole Caspian Sea the present monitoring results are limited (Bukharitsin and Luneva, 1994 Kuksa, 1996). However, we can conclude that the highest concentrations of DDT in water in the late 1980s were recorded in coastal waters of the Ural and Volga rivers and in the deeper western part of the North Caspian. Taking into account that the maximal content of synthetic surfactants were also observed in the same sea regions, one can postulate that most DDT enters the sea with river discharge in concentrated form, mainly in surface film composition formed by synthetic surfactants. 

Oxidations for varying times showed systematic variations in the U +/U + ratios that fell into three values stable for significant periods of time (Fig. 5). These ratios of U +/U + = 0.5, 1.0 and 2.0 are believed to correspond to the presence of U3O7 (U02 U02 U03), U205 (U02 U03), and U30g (U02-U03-U03), respectively. The surface film composition is controlled by various rates of surface dissolution, oxygen diffusion into the UO2 and precipitation. Film dissolution is believed to occur upon oxidation to UO3. Because no appreciable layer of UO3 was found on the surface, it is concluded that dissolution of UO3 occurs at a rate faster than solid-state oxidation. 

Finally, when an EDX unit is attached to a SEM, it becomes possible to evaluate surface film compositions with high resolution, and produce concentration maps corresponding to the area viewed. Therefore, this is a frequently found addition to a typical SEM installation. 

Metal Solvent system Electrolyte Surface film composition Resistivity Q cm Ref. 

In contrast to the case of lithium, where extensive efforts have been devoted to the study of interfacial phenomena, surface film composition, etc., very little is yet known about the composition and structure of the surface films covering magnesium electrodes in nonaqueous media. In addition, the mechanisms of Mg dissolution and plating in the Grignard solutions are unclear. 

In the case of electrolyte solution with LiPF6 or LiBF4, the surface film composition changed from Al oxide to Al oxide and fluoride [46], Probably, the passivation film becomes more stable by these compositional changes. In nonaqueous electrolyte solutions containing LiCF3S03 or Li(CF3S02)2N, the stability of the passivation... 

Film composition Surface resistivity,Q/sq Triboelectric voltage... 

Characterization. The proper characterization of coUoids depends on the purposes for which the information is sought because the total description would be an enormous task (27). The foUowiag physical traits are among those to be considered size, shape, and morphology of the primary particles surface area number and size distribution of pores degree of crystallinity and polycrystaUinity defect concentration nature of internal and surface stresses and state of agglomeration (27). Chemical and phase composition are needed for complete characterization, including data on the purity of the bulk phase and the nature and quaHty of adsorbed surface films or impurities. 

Alloys having varying degrees of corrosion resistance have been developed in response to various environmental needs. At the lower end of the alloying scale are the low alloy steels. These are kon-base alloys containing from 0.5—3.0 wt % Ni, Cr, Mo, or Cu and controlled amounts of P, N, and S. The exact composition varies with the manufacturer. The corrosion resistance of the alloy is based on the protective nature of the surface film, which in turn is based on the physical and chemical properties of the oxide film. As a rule, this alloying reduces the rate of corrosion by 50% over the fkst few years of atmosphere exposure. Low alloy steels have been used outdoors with protection. 

Biological Corrosion The metabohc activity of microorganisms can either directly or indirectly cause deterioration of a metal by corrosion processes. Such activity can (1) produce a corrosive environment, (2) create electrolytic-concentration cells on the metal surface, (3) alter the resistance of surface films, (4) have an influence on the rate of anodic or cathodic reaction, and (5) alter the environment composition. 

These corrosion parameters have to be modified for time- and place-related reaction velocities [6]. Different local removal rates are in general due to differences in composition or nonuniform surface films, where both thermodynamic and... 

Perhaps the most common use for REELS is to monitor gas—solid reactions that produce surface films at a total coverage of less than a few monolayers. When Eq is a few hundred eV, the surface sensitivity of REELS is such that over 90% of the signal originates in the topmost monolayer of the sample. A particularly powerfiil application in this case involves the determination of whether a single phase of variable composition occurs on the top layer or whether islands occur that is, whether... 

Secondly, crystal defects might be expected to affect the corrosion behaviour of metals which owe their corrosion resistance to the presence of thin passive or thick protective films on their surface. The crystal defects and structural features discussed in Section 20.4 might, in principle, be expected to affect the thickness, strength, adhesion, porosity, composition, solubility, etc. of these surface films, and hence, in turn, the corrosion behaviour of the filmed metal surfaces. Clearly, this is the more common situation in practice. 

While the initial surface species formed on lithium in alkyl carbonates consist of ROC02Li compounds, these species react with water to form Li,CO, C02, and ROH. This reaction gradually changes the composition of the surface films formed on... 

Table 8. Composition of surface films at lithium and lithiated carbons...

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