Passive film methods

Besides the use of anodic polarization with impressed current to achieve passivation, raising the cathodic partial current density by special alloying elements and the use of oxidizing inhibitors (and/or passivators) to assist the formation of passive films can be included in the anodic protection method [1-3]. 

Single Loop EPR Test The single loop method requires the sample to be polished to a 1 tm finish then passivated at -F200 mV (S.C.E.) for 2 min following which the potential is decreased at 1-67 mV s until the corrosion potential of approximately —4(X) mV (S.C.E.) is reached. The reactivation process results in the preferential breakdown of the passive film in the... 

Galvani, measurability of, 7 Potential distribution in passivation, 229 Potential formation as a variation of thickness with passive film, 225 Potential of zero charge, 1, 5-6, 189-192 accuracy of determination, 19 and the adsorption method, 39 at the air-solution interface (Nikitas), 30 and alloys, 142... 

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... 

Nagayama, M. Cohen, M. (1963) Anodic oxidation of Fe in a neutral solution. 1. Nature and composition of the passive film. J. Elec-trochem. Soc. 109 781-790 Nakai, M. Yoshinaga, N. (1980) Fibrous goethite in some soils from Japan and Scotland. Geoderma 24 143-158 Nakazawa, H. Sato, H. Hasebe, S. (1989) Study of the removal of arsenic from hot waste water by the ferrite formation method. Shigento Sozai 105 239-244 Namjesnik-Dejanovic, K. Maurice, P.A. 

Herb Uhlig was the advisor and intellectual father of many U.S. scientists who are at work in numerous companies in the United States. Among the best known of his students were Milton Stern, originator of the Stern-Geary method for the measurement of corrosion, and Winston Revie, who made the first Auger measurements on passive films. 

One of the methods used in corrosion control is anodic inhibition. The method applies in particular to iron and its steels. The electrode is moved in the anodic direction (at first stimulating the corrosion rate), but soon an oxide film forms and reduces the dissolution current. There are certain types of oxide film, passive films, that are particularly protective. Indeed, such films are involved in the way metals preserve themselves in nature. There is much to be found out about these films (why they are so protective) and some of the material that allows us to understand them and their eventual breakdown by aggressive ions such as chloride, has been given in this chapter. 

The analysis of several pure metals and binary alloys yields generally at least a duplex and in some cases a multilayer structure of the passive film, as depicted schematically in Fig. 19. These systems have been examined with surface analytical methods, mainly XPS, but also ISS in some cases. The systematic variation of the electrochemical preparation parameters gives insight to the related changes of layer composition and layer development, and support a reliable interpretation of the results. Usually the lower valent species are found in the inner part and the higher valent species in the outer part of the passive layer. It is a consequence of the applied potential which of the species is dominating. Higher valent species are formed at sufficiently positive potentials only and may suppress the contribution of the lower... 

The direct electrochemical measurement of such low corrosion rates is difficult and limited in accuracy. However, electrochemical techniques can be used to establish a database against which to validate rates determined by more conventional methods (such as weight change measurements) applied after long exposure times. Blackwood et al. (29) used a combination of anodic polarization scans and open circuit potential measurements to determine the dissolution rates of passive films on titanium in acidic and alkaline solutions. An oxide film was first grown by applying an anodic potential scan to a preset anodic limit (generally 3.0 V), Fig. 24, curve 1. Subsequently, the electrode was switched to open-circuit and a portion of the oxide allowed to chemically dissolve. Then a second anodic... 

The test method ASTM F7464 covers the determination of the resistance to either pitting or crevice corrosion of passive metals and alloys from which surgical implants are produced. The resistance of surgical implants to localized corrosion is carried out in dilute sodium chloride solution under specific conditions of potentiodynamic test method. Typical transient decay curves under potentiostatic polarization should monitor susceptibility to localized corrosion. Alloys are ranked in terms of the critical potential for pitting, the higher (more noble) this potential, the more resistant is to passive film breakdown and to localized corrosion. (Sprowls)14... 

Cathodic protection is one of the methods to mitigate the corrosion of steel in concrete Figure 7.24. Some factors to be considered in this connection are remaining service life of the structure should be more than lOyr delamination and spalls should be less than 50% by weight of concrete half-cell potential should be less than —200 mV (indicating breakdown of passive film) the structure should be sound the reinforcing bars should be electrically continuous AC power should be available. 

Thermal oxidation is an old and common method of forming a primary passivating film of Si02 on silicon. The metal is heated in dry oxygen, in wet oxygen, or in steam. A silica layer grows inwardly from the surface by a thermal oxidation mechanism. The silicon wafer is heated to 600-1200°C to achieve 1 pm thick films in about an hour. 

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