Corrosion parameters potentiodynamic

Figure 7.59 Potentiodynamic polarisa- The electrochemical corrosion parameters...

Potentiodynamic polarization (LSV and Tafel analysis) Measurement of corrosion parameters fcom lg> g> i p). Additive effects (passivation or stimulation of anodic and cathodic reactions), mass transfer limited effects material removal in ECMP Kallingal et al. (1998), Jiang et al. (2014), Aksu et al. (2003), ASTM (2004)... 

Table 17.6 Measured Vickers hardness (Hy), fracture toughness (/iTic), surface properties (static contact angles measured with water [O ] and glycerol [0 ]), and corrosion parameters calculated from the potentiodynamic measurements for 50-pm-thick pure epoxy and 130-nm silica/epoxy coating... 

The potentiodynamic polarization curves of carbon steel immersed in an aqueous solution containing 60 ppm of d in the absence and presence of adipic acid are shown in Fig. 11.5. The corresponding corrosion parameters are given in Table 11.2. Increase in linear polarization resistance (LPR) and decrease in corrosion current in the presence of adipic acid indicate the corrosion protection nature of SAMs of adipic acid. EIS of carbon steel immersed in an aqueous solution containing 60 ppm of d in the absence and presence of 50 ppm of adipic... 

Figure 3 shows the potentiodynamic curves for the alloys at 37°C. The corresponding corrosion parameters are given in Table 2, and passivation parameters are given in Table 3. 

Mo are single phase, supersaturated solid solutions having an fee structure very similar to that of pure Al. Broad reflection indicative of an amorphous phase appears in deposits containing more than 6.5 atom% Mo. As the Mo content of the deposits is increased, the amount of fee phase in the alloy decreases whereas that of the amorphous phase increases. When the Mo content is more than 10 atom%, the deposits are completely amorphous. As the Mo atom has a smaller lattice volume than Al, the lattice parameter for the deposits decreases with increasing Mo content. Potentiodynamic anodic polarization experiments in deaerated aqueous NaCl revealed that increasing the Mo content for the Al-Mo alloy increases the pitting potential. It appears that the Al-Mo deposits show better corrosion resistance than most other aluminum-transition metal alloys prepared from chloroaluminate ionic liquids. 

Standard test procedures are defined within ASTM standards ASTM G 59, Practice for Conducting Potentiodynamic Polarization Resistance Measurements G 5, "Standard Reference Test Method for Making Potentiostatic and Potentiodynamic Anodic Polarization Measurements G 106, Practice for Verification of Algorithm and Equipment for Electrochemical Impedance Measurements and G 102, Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements. Each of these methods describes a standard procedure or practice for the test method. A complete discussion of the technologies is beyond the scope of the current text. For the current text, the focus is on the application of the most simple and most widely used of these techniques, the polarization resistance measurement, ASTM G 59. The parameters discussed are, however, applicable concerns for all electrochemical tests. 

Nam et al. (2007) combined a chrome plating process with a following thermal nitriding on 316L stainless steel to improve corrosion behavior. The process parameters were chosen to form CrjN on the surface, which decreased corrosion current densities to acceptable values as found in potentiodynamic... 

Rates of corrosion can also be measured using an electrochemical technique known as potentiodynamic polarization. The potential of the test metal electrode relative to a reference electrode (commonly the saturated calomel electrode SCE) is varied at a controlled rate using a potentiostat. The resultant current density which flows in the cell via an auxiliary electrode, typically platinum, is recorded as a function of potential. The schematic curve in fig. 2 is typical of data obtained from such a test. These data can provide various parameters in addition to corrosion rate, all of which are suitable for describing corrosion resistance. The corrosion potential F corr is nominally the open circuit or rest potential of the metal in solution. At this potential, the anodic and cathodic processes occurring on the surface are in equilibrium. When the sample is polarized to potentials more positive than Scon the anodic processes, such as metal dissolution, dominate (Anodic Polarization Curve). With polarization to potentials more negative than Scorr the cathodic processes involved in the corrosion reaction such as oxygen reduction and hydrogen evolution dominate (Cathodic Polarization Curve). These separate halves of the total polarization curve may provide information about the rates of anodic and cathodic processes. The current density at any particular potential is a measure of the... 

Potentiodynamic polarization (intrusive). This method is best known for its fundamental role in electrochemistry in the measurement of Evans diagrams. A three-electrode corrosion probe is used to polarize the electrode of interest. The current response is measured as the potential is shifted away from the free corrosion potential. The basic difference from the LPR technique is that the apphed potentials for polarization are normally stepped up to levels of several hundred millivolts. These polarization levels facihtate the determination of kinetic parameters, such as the general corrosion rate and the Tafel constants. The formation of passive films and the onset of pitting corrosion can also be identified at characteristic potentials, which can assist in assessing the overall corrosion risk. 

---