Anion structures films

In conclusion, the present discussion of proposed film breakdown and pit initiation mechanisms suggests that several phenomena are responsible for the loss of passivity and the onset of pitting when a metal is polarized to a high potential in presence of aggressive anions. Structural defects in the passive film reflecting those of the metal, anion adsorption on the film and the metal surfaces and the effect of anions on the kinetics of the electrochemical reactions governing oxide formation and metal dissolution are most critical. Practical consequences of these phenomena for pitting corrosion will be discussed in Section 7.3. 

The influence of the dopant anion on film properties was studied by Krivan and Visy [626]. With sodium dodecylsulfate, an increase of redox capacity and a higher doping level were observed. Results obtained with UV-vis spectroscopy and their interpretation indicate that structural changes that result in a decreased hy-drophobicity may be a possible cause. 

Several authors have discussed the ion exchange potentials and membrane properties of grafted cellulose [135,136]. Radiation grafting of anionic and cationic monomers to impart ion exchange properties to polymer films and other structures is rather promising. Thus, grafting of acrylamide and acrylic acid onto polyethylene, polyethylene/ethylene vinyl acetate copolymer as a blend [98], and waste rubber powder [137,138], allows... 

On the other hand, pit initiation which is the necessary precursor to propagation, is less well understood but is probably far more dependent on metallurgical structure. A detailed discussion of pit initiation is beyond the scope of this section. The two most widely accepted models are, however, as follows. Heine, etal. suggest that pit initiation on aluminium alloys occurs when chloride ions penetrate the passive oxide film by diffusion via lattice defects. McBee and Kruger indicate that this mechanism may also be applicable to pit initiation on iron. On the other hand, Evans has suggested that a pit initiates at a point on the surface where the rate of metal dissolution is momentarily high, with the result that more aggressive anions... 

There is a difference in the behavior of benzenediolatoborate and naphthalenedio-latoborate solutions on the one hand, and lithium bis[2,2 -biphenyldiolato(2-)-0,0 ] borate (point 5 in fig. 8) lithium bis[ sali-cylato (2-) Jborate (point 6) or benzene-diolatoborate/phenolate mixed solutions on the other (Fig.8). This can be tentatively explained by the assumption of different decomposition mechanisms due to different structures, which entail the formation of soluble colored quinones from benzenediolatoborate anions and lithium-ion conducting films from solutions of the latter compounds (points 5 and 6) [80], The assumption of a different mechanism and the formation of a lithium-ion conducting, electronically insulating film is supported by... 

In the same year, Fulda and Tieke [75] reported on Langmuir films of monodisperse, 0.5-pm spherical polymer particles with hydrophobic polystyrene cores and hydrophilic shells containing polyacrylic acid or polyacrylamide. Measurement of ir-A curves and scanning electron microscopy (SEM) were used to determine the structure of the monolayers. In subsequent work, Fulda et al. [76] studied a variety of particles with different hydrophilic shells for their ability to form Langmuir films. Fulda and Tieke [77] investigated the influence of subphase conditions (pH, ionic strength) on monolayer formation of cationic and anionic particles as well as the structure of films made from bidisperse mixtures of anionic latex particles. 

MIC depends on the complex structure of corrosion products and passive films on metal surfaces as well as on the structure of the biofilm. Unfortunately, electrochemical methods have sometimes been used in complex electrolytes, such as microbiological culture media, where the characteristics and properties of passive films and MIC deposits are quite active and not fully understood. It must be kept in mind that microbial colonization of passive metals can drastically change their resistance to film breakdown by causing localized changes in the type, concentration, and thickness of anions, pH, oxygen gradients, and inhibitor levels at the metal surface during the course of a... 

There are also models assuming the electrostrictive input of incorporated anions into the breakdown initiation,285,299 ionic drift models,300 and many others reviewed elsewhere.283,293 However, the majority of specialists agree that further work is necessary in order to properly understand the physics of the electric breakdown in growing oxide films and that caused by electric stress in thin-film structures. 

The composition of the film changes with potential and with the incorporation of both anions and cations. EXAFS data on the passive films grown on stainless steel or normal steel with Cr04 show considerable incorporation of Cr into the film with further alterations in bond lengths and covalency parameters. Indeed, as the amount of Cr incorporated increases, so does the flexibility of the structure. It is well known, by contrast, that Cl incorporation leads to poorer quality films and to enhanced rates of corrosion. 

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