Corrosion protection mechanisms

The optimum PVC that provides the best corrosion protection for the substrate is a strong function of the corrosion protecting mechanism. Figs. 8-10 represent primer films based on three different protection mechanisms, and indicate the appropriate formulating windows for each type of primer. 

Two principle mechanisms that are discussed as possible corrosion protection mechanisms on mild steel are discussed in short. ICPs may induce the formation of a passive oxide [206]. The ICP will be reduced as a consequence of passivation and will be reoxidized by oxygen reduction. Consequently, the ICP may promote the cathodic oxygen reduction on the polymer surface rather than at the metal-polymer interface. On the basis of the good corrosion results gained by the combination of a molecular adhesion promoter and the subsequent electrodeposition of the polymethylthiophene film Rammelt and coworkers [207] concluded that the essential aspect of the corrosion protection by ICPs could be the local separation of iron oxidation and oxygen reduction. This would eliminate the local pH increase at the metal surface and subsequent cathodic disbondment. 

Zinc-nickel Zn-Ni alloys with 5 to 15 wt% Ni offer excellent corrosion resistance and are mainly used in the automotive, aerospace, and electronics industries. Above 15% Ni, the alloy coating becomes more noble than steel, and the corrosion-protection mechanism changes from a sacrificial to a pure physical one (comparable to pure Ni coatings, see Sect. 5.5.4.2.2). They can be electrode-posited from acid or alkaline baths. The acid baths are usually based on sulfate, chloride, sulfate-chloride, pyrophosphate, or acetate (Table 15). The system shows anomalous codeposition (see Sect. 5.5.1.2), which has been explained by a hydroxide suppression mechanism [47]. As in the case of Ni-Fe, the alkaline baths must contain complexing agents (see Sect. 5.5.4.6.2). The alloys electroplated from add haths contain approximately 10 to 14% Ni, whereas the alkaline Zn-Ni... 

FIGURE 14.8 Corrosion protection mechanism of (a) PANI/alkyd coatings and (b) PANI/ferrite/alkyd coatings. (Reprinted from Curr. Appl. Phys. 9, J. Alam et al., High Performance Corrosion Resistant Polyaniline/ Alkyd Ecofriendly Coatings, 80, 2009, with permission from Elsevier.)... 

This chapter is aimed to illustrate the most accepted theories concerning corrosion protection mechanisms of conducting polymers and their composites, reporting a wide review of literature on these topics. Firstly, a brief revision of some basic corrosion concepts, as well as of the corrosion prevention and testing methods, is given. 

CPs are redox-active materials having a positive equilibrium potential with respect to those of iron, aluminium and other alloying elements (Table 10.1). This suggests anodic protection as more expected corrosion protection mechanism. For CPs electroactivity, it exists a range of potential values because reduction potential depends on kind and level of doping. 

Since our last review of this topic in 2002 [9,10], several new reports on the use of CPs for corrosion control have appeared in the literature. Many of these recent reports have been discussed in previous sections of this chapter. In this section, we summarize new results (from 2002 to the present) not yet discussed in this chapter, focusing on results published in the refereed literature that address corrosion protection mechanisms. The discussion will be organized into three categories corrosion... 

Torres , R.M., et al. 2005. Galvanic coupling between metal substrate and polyaniline acrylic blends Corrosion protection mechanism. Electrochim Acta 50 (11) 2213. 

There are wide variations in experimental procedures in the literature, such as coating type, substrate, corrosion environment, and test methods. Therefore, various corrosion protection mechanisms for ICPs have been proposed in the past 30 years, and sometimes contradictory viewpoints exist. Till now, thanks to the extensive research on protection mechanisms, we may have a chance to gain a comprehensive understanding of protection mechanism for ICPs or ICP-containing coatings. 

The core issue in corrosion protection mechanism lies in the unique redox property of ICPs as shown in Eqs. (10.1) and (10.2), and the following three important points could be summarized ... 

Sathiyanarayanan, S., (eyaram, R., Muthukrishnan, S., and Venkatachari, G. (2009) Corrosion protection mechanism of polyaniline blended organic coating on steel./. Electrochem. Soc., 156, C127-C134. 

The Corrosion Protective Mechanism of Superprimers Including the Pigments... 

The corrosion protection mechanism of chromatizing layers involves a barrier effect of the oxide film and a chemical effect of the trapped chromates these maintain oxidizing conditions at the surface and thus facilitate passivation of the metal if pores or other defects are present in the film. 

Thorough understanding of corrosion protection mechanisms for nontoxic corrosion inhibitors and conversion-coating procedures. Over the past several years, considerable effort has been spent in replacing chromate coatings, which pose a... 

Changes in both the adhesion values obtained in before-and-after testing and in the failure loci can reveal quite a bit about aging and failure mechanisms. Changes in barrier properties, measured by electrochemical impedance spectroscopy (EIS), are important because the ability to hinder transport of electrolyte in solution is one of the more important corrosion-protection mechanisms of the coating. 

Key words praseodymium, cerium, epoxy polyamide primer, eCoat, phase stability, corrosion protection mechanism. 

Schematic outlining a proposed corrosion protection mechanism of Pr-primers with CrCC on Al 2024-T3. 

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