Cathodic passivation

The major factors probably responsible for the acceleration effect of additives are (1) the charge density of the electron system of the additive and (2) the exchange of electrons between electrode, 7r-bonded additive molecule, and the complexed metal ions in the solution. Inhibition effect and cathodic passivation are explained in terms of blocking of the catalytic surface, which results in a decrease in the available surface area (45). 

Fig. 14.6 (a) Effect of cathodic inhibitor on cathodic poiarization and (b) cathodic passivation in the presence of cathodic inhibitors. 

We can measure the corrosion risk in the cell by introducing an external reference electrode. This is most easily illustrated by a copper/saturated copper sulphate reference electrode moved along the surface of the concrete with a rebar in the concrete which has anodic (corroding) areas and cathodic (passive) areas. 

As a result we see higher potentials (voltages) on our voltmeter in anodic, corroding areas and lower voltages in the cathodic, passive areas. The use and interpretation of reference electrode potential measurements is discussed further in Section 4.8. 

Clarke, M. and Bernie, J.A. (1967) Abnormal high throwing power and cathode passivity in acid tin plating baths. Electrochim. Acta, 12 (2), 205-212. 

Calcium borosilicate is a compiex composite of calcium siiicate avaiiabie commercially in grades differing in borate content and oii absorption value. Its anticorrosive properties are derived from the aikaiinity of the pigment as weii as anodic and cathodic passivation. 

The importance of concrete cracks in rebar corrosion has also been highlighted by Niirnberger. Both carbonation and chloride ion diffusion, two important processes associated with rebar corrosion, can proceed more rapidly into the concrete along the crack faces, compared with uncracked concrete. Niirnberger argued that corrosion in the vicinity of the crack tip could be accelerated further by crevice corrosion effects and galvanic cell formation. The steel in the crack will tend to be anodic relative to the cathodic (passive) zones in uncracked... 

The polymer electrolytes discussed so far suffer from a number of disadvantages. Firstly, they exhibit low conductivities in comparison with liquid or solid (crystalline or glassy) electrolytes at or below room temperature. The best all-amorphous systems have conductivities less than 10 S cm at room temperature. These ambient temperature conductivities may be insufficient in some cases for the power required by a lithium battery. Secondly, the interfacial impedances present at both the lithium anode (passivation) and composite cathode (passivation, contact) are in addition to the ohmic losses in the electrolyte. Thirdly, the lowness of cation transference number, although similar to the values in liquid systems, is a major issue since the total conductivity is lower and could limit the use of solvent-free polymer electrolytes except in the form of extremely thin films or above room temperature. 

Anodic or cathodic passivation (introducing chemicals which change the natural oxide to make it more protective and less active). In cathodic inhibition, inhibitors predominantly form insoluble precipitates or salts due to pH rise during corrosion processes [14]. Anodically active materials [92] promote the adsorption of oxygen at the surface (e.g. chromates, molybdate), or by forming insoluble complex salts with metal ions at the anodic defect sites (e.g. phosphate, borate), known as pore plugging [14]. 

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