Electrochemical corrosion resistance evaluation

The corrosion current density icoa is evaluated by the electrochemical polarization resistance method assuming that both the anodic and the cathodic partial currents obey the Tafel relation ... 

Chemical and Corrosion Resistance The corrosion resistance of CCCs depends on thickness and coating age. Corrosion resistance has been observed to scale with total chromium content [153]. Some studies have found that corrosion resistance does scale with Cr(VI) content [154], while others have found no such correlation [155]. Corrosion resistance is evaluated by continuous or cyclic accelerated exposure testing and electrochemical methods. On aluminum alloys, heavy CCCs will resist pitting for as long as 400 to 1000 h [156]. CCC-coated surfaces will exhibit total impedances of 1 to 2 Mf2 cm after exposure to aerated 0.5 M NaCl solution for 24 h. Such coatings can be expected to withstand 168 h of salt spray exposure without serious pitting [157]. CCCs usually perform well in mild neutral environments, but do not fare as well under... 

Electrochemical corrosion techniques are essential in predicting the service hfe ofmetal-hc components used in chemical and construction industries. They measure the corrosion rates, the oxidizing power of the environment, and evaluate the effectiveness of corrosion protection strategies. The following direct current dc electrochemical methods are discussed in this chapter linear polarization technique, Tafel extrapolation, and open circuit potential (OCP) vs. time measurements. Electrochemical impedance spectroscopy (EIS) is introduced as an alternating current technique ac. This technique uses alternating current to measure frequency-dependent processes in corrosion and estimates the change of polarization resistance. 

There are numerous electrochemical approaches to quantitatively assessing the corrosion resistance of bare and painted metallic materials immersed in conductive electrolytes, and they can be very sensitive and relatively easy and rapid to perform (Figure 3.8), either in the laboratory or in the field for corrosion rate monitoring. However, in some environments such as those with high-temperature gases or high-resistivity electrolytes that do not follow classic electrolyte behavior, standard electrochemical approaches either are extremely difficult or fail completely. An important research opportunity is to develop sensitive, quantitative, and accurate methods for evaluating corrosion resistance in these environments. 

Different aging tests (e g. salt spray of intact and scratched samples, immersion in an aerated NaCl 0.5M solution) have been performed by using electrochemical impedance spectroscopy to evaluate both the corrosion resistance and the degree of the degradation of systems studied. Analysis of the impedance spectra has confirmed that the application of a Zr/Ti pre-... 

Tani, G. and Zucchi, F., "Electrochemical Evaluation of the Corrosion Resistance of Commonly Used Metals in Dental Prostheses, Minen>a Stomatology, Vol. 16, 1967, pp. 710-713. 

High-temperature chlorides can require unique chloride resistance testing [9]. In aqueous solutions, it is common to use electrochemical testing to evaluate pitting potential or crevice corrosion. In nonaqueous base solutions, this must usually be evaluated by in-service tests in pilot plants or in existing process equipment. 

Metals are important construction materials, which are classified according to their properties as light or heavy metals (density lower/higher than 4.5 g cm" ), and precious, ferrous, or nonferrous metals. An evaluation of metal corrosion resistance can be derived from the electrochemical potential series. This is valid for metals introduced under standard conditions into an aqueous solution of their ions. Gold is situated at the electronegative end and lithium at the electropositive one. All the other metals, e.g., aluminum, zinc, iron, copper, silver, etc., are situated in-between. Furthermore, with respect to corrosion resistance, the tendency to form passivating layers is important. These are generally thin oxide layers which confer the metals with an apparently more noble position in the potential series than they really have. 

Our own investigations on different cast duplex stainless steels were performed by electrochemical measurements, accompanied by metallographic inspection and chemical analysis of the alloys. At first the influence of different levels of chloride and fluoride, pH, and temperatures, and the combined influence of chloride and fluoride on corrosion resistance were evaluated. Secondly, suitable alloys were identified which would have sufficient corrosion resistance even under extreme conditions. 

It has been demonstrated that BE modeling can accurately predict experimental results. BE methods also can be used to evaluate the effect of a single parameter on system performance. In this way basic understanding of electrochemical corrosion and parameter interactions can be obtained. Several parametric studies have, for example, been published on damage levels in the propeller area, seawater conductivity, and paint resistance effects, as well as on the influence of stray current source on system performance [18]. 

The corrosion resistance of various Al- and Al/Zn-coated AZ91D Mg alloys has been evaluated by salt spray and electrochemical methods. In the following, the results from salt spray test, polarization curve and electrochemical impedance measurements manifesting the benehcial effects of Al and/or Al-Zn coating on AZ91D Mg alloy are demonstrated. 

The most reported application of eiectrodeposited silane sol-gel films has been the corrosion protection of metals. The corrosion resistance of the films is usually evaluated by polarization curves and electrochemical impedance spectroscopy (EIS) measured in corrosive media. Mandler and coworkers [73] reported the electrodeposition of TEOS, MTMS, and PhTMS films on aluminum alloys. They found that all the three eiectrodeposited silane films protected the aluminum alloys, and the PhTMS film provided the highest corrosion resistance due to its hydrophobic aromatic ring. Figure 12.20 shows that the eiectrodeposited PhTMS film performs five orders of magnitude higher in impedance modulus... 

Corrosion behavior of uncoated and Ti02 deposited Ti6A14V was evaluated by Karpagavalli et al. (2007) in freely aerated Hank s solution at 37°C by the measurement and analysis of open circuit potential variation with time, Tafel plots and electrochemical impedance spectroscopy. The electrochemical results indicated that nano Ti02 coated Ti6A14V showed a better corrosion resistance (Table 5.7, Fig. 5.14) in simulated biofluid than uncoated Ti6A14V. 

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