Potentiodynamic tests

The potential-independent CPT can be determined by two different electrochemical methods a potentiostatic test method using a sufficiently high potential, and a potentiodynamic test method. The potential-independent CPTs are well-defined, experimental results having a reproducibility of approximately l°Cby potentiodynamic testing and approximately 2°C by potentiostatic testing. 

The o t-a. M-independent CPT determined by the potentiodynamic test method is found to be independent of both the chloride content of the solution in the range of 0.1-5 mole/liter ofNaCl and the pH value (pH 1-7). Testing at different temperatures with different specimens, and evaluating the results from one test temperature before the next temperature is selected, is a time-consuming process. It takes several days to determine a single CPT value. 

The test method ASTM F7464 covers the determination of the resistance to either pitting or crevice corrosion of passive metals and alloys from which surgical implants are produced. The resistance of surgical implants to localized corrosion is carried out in dilute sodium chloride solution under specific conditions of potentiodynamic test method. Typical transient decay curves under potentiostatic polarization should monitor susceptibility to localized corrosion. Alloys are ranked in terms of the critical potential for pitting, the higher (more noble) this potential, the more resistant is to passive film breakdown and to localized corrosion. (Sprowls)14... 

Kim] Modified Huey and potentiodynamic tests, optical microscopy, SEM Stress corrosion cracking of alloy 600, alloy 690, CrioFcioNigo... 

Potentiodynamic tests were initially carried out on WS in 0.1 M Na2S04 -fO. 1 N NaCl having pH 9.5 at scan rate 0.005 mV/s but no sign of passive region was found as per Fig. 4.3 where corrosion rate is very low Icon 32 pA/cm ). 

With the advent of advanced electronics and computerization, electrochemical techniques have evolved rapidly. The most common technologies today are the polarization resistance technique, electrochemical impedance, and Tafel extrapolation. Regardless of the technique used, each relies on the same basic principles in each test, a metallic coupon in an electrolyte is subject to an electrical perturbation. This perturbation is the appUcation of a current from an external source (power supply). This current stimulates the surface corrosion reactions. The voltage (potential) response of the coupon is measured and correlated with the current appUed—a galvanodynamic test. Conversely, the coupon potential is controlled and correlated with the requisite current—a potentiodynamic test. In either case, the resultant current is representative of the rate determining mass transfer or charge transfer rate. This may be related to the corrosion rate. 

The results presented in this study focused on the evaluation of corrosion resistance of two high-Mn steels of the different initial structure in acidic and chloride media. The investigations were carried out on the specimens after the thermo-mechanical rolling and after cold deformation. The results of immersion and potentiodynamic tests as well as structural analysis prove that both examined steels, independent of initial structure, have very low corrosion resistance in acidic medium and low corrosion resistance in chloride solution. In particular it was found that ... 

The most commonly-used steady state techniques are potentiodynamic tests to determine the corrosion rate in systems that experience a uniform corrosion process. This type of attack can also be studied by measuring resistance to polarization. Cyclical polarization ciurves are also used to study localized corrosion and potentiokinetic reactivation is the most suitable study technique for evaluating intergranular corrosion produced by a sensitization phenomenon following ASTM G108 standard test. 

Potentiodynamic tests. As was mentioned earlier, metal corrosion is an electrochemical process comprising oxidation and reduction reactions different from the medium in which the process takes place. It requires anodes and cathodes in electrical contact, as well as an ionic conduction path through an electrolyte. The electron flow between the anodic and cathodic areas quantifies the rates of the oxidation and reduction reactions and the conversion of the reaction rate from current to mass loss is in accordance with Faraday s law. 

ASTM F746-81 test (mV) Scratch test (mV) Potentiodynamic test Current 10 p,A/cm (mV) Repassivation (mV)... 

Garcia, S.J., Muster, T.H., Ozkanat, O., Sherman, N., Hughes, A.E., et al. The influence of pH on corrosion inhibitor selection for 2024-T3 aluminium alloy assessed by high-throughput multielectrode and potentiodynamic testing. ElectrochimicaActa, 2010. 55(7) 2457-2465. 

Potentiodynamic tests for anodic polarizarion curves were carried out at 80 1°C at a scanning rate of 1200 mV/h, starting from—250 mV versus rest potential. The inhibitor concentrations used were 1% for both inhibitors. The experimental apparatus was as reported in ASTM G5-82 standard practice. 

Inhibitor efficiencies were calculated from potentiodynamic tests by determining the corrosion current densities (Table 8.8). Results confirmed good efficiencies at 80 °C of corrosion inhibitors for all the materials. 

DC polarisation tests took place in a three-electrode electrochemical cell where the area of the working electrode (modified Al-2024 T3) exposed to the corrosive solution was 1 cm. For these measurements, a platinum foil and a SCE were used as the counter and the reference electrodes, respectively. Potentiodynamic tests were carried out by scanning the potential between -1 V and 0 V vs SCE at a rate of 1 mV s. The resulting graphics were fitted to the Tafel plots allowing the corrosion current and potential, and the polarisation resistance to be extrapolated. Corrware software was used for fitting. 

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