Iron dissolution, impedance techniques

Advanced Study of Iron Dissolution by Impedance Techniques Early application of impedance measurement to the anodic dissolution of iron in acidic media demonstrated the inductive character of the iaradic impedances. The reaction scheme initially proposed [13,60] is modified according to ... 

Active and Active-Passive Transition Impedance and Frequency-Resolved RRDE Measurements The assoeiation of impedanee and fiequency-resolved RRDE techniques initially introduced for iron [38,117,197] has been extensively applied to the prepassive and passivation ranges of Fe-Cr alloys with and without chloride added [174,194,195], Of course, the interpretation is more intricate than for pure metals (even with multiple dissolution valences). For kinetic reasons, Cr species are not detectable on the ring. In order to draw unambiguous conclusions, reasonable assumptions had to be made concerning simultaneous alloy dissolution at steady state (see thermodynamics and rate constant approach earlier) and dissolution valences of Cr. 

In anaerobic conditions, some bacteria can reduce the sulfate ion to produce oxygen and the sulfide ion. The sulfide ion then combines with ferrous ions to form iron sulfide, leading to the dissolution of the metal surface. Some other bacteria can directly reduce metal atoms to ions. Impedance spectroscopy is one test technique that is applicable to biocorrosion. Potentiodynamic scans may be used to determine the effect of biofilms in both anodic and cathodic behavior. ... 

In many practical cases of corrosion, the anodic dissolution takes place on a surface partially or totally covered by thick (order of micrometers) solid layers grown by several possible mechanisms (heterogeneous nucleation and growth, dissolution-reprecipitation) and usually regarded as porous. Until the past decade, the mechanism by which this layer interferes, with the anodic dissolution, and particularly the transport phenomena, remained poorly understood. The last developments deal with iron and copper in FFCl solutions and take advantage of steady-state RDE and RRDE associated with AC impedance (EIS and EHD) techniques. Mass transport and solution chemistry [169,170] let to a dissolution model [171] in which the electrochemical monoelectronic surface step... 

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