Electrochemical tests electrolytic corrosion test

In view of the electrochemical nature of corrosion, it has seemed reasonable to many investigators to assume that suitable accelerated corrosion tests could be made by observing the response to electrolytic stimulation of the corrosion processes, or by attaching particular significance to the results of quickly made electrode potential and current measurements. 

Electrochemical Testing. Potentlodynamlc polarization measurements provided a sensitive means of evaluating the inhibitors with respect to environmental (Cl ) corrosion protection. The results obtained from anodlcally polarizing polished 7075-T6 A1 samples are presented in Fig. 9. For the control electrolyte (O.IN Na2S0, 0.002N KCl, no inhibitor), pitting was observed almost immediately on the surface, and the aluminum showed no evidence of passivation. The addition of NTMP to the solution did not appear to protect the metal... 

Aqueous solutions were used to simulate specific conditions to carry out electrochemical tests on both field exposed and fresh panels. The test electrolytes are SAEJ 2334 solution (0.25 % NaHCOs -I- 0.5 % NaCl -I- 0.1 % CaCb, pH 9.1) to simulate the atmospheric conditions in the laboratory at 25 3 °C, neutral salt solution (3.5 % NaCl, pH 6.7) and weakly alkaline solution (0.1 M Na2S04 -I-0.1 N NaCl, pH 8.5) to get chloride and sulphate ions in the environment for carrying out tests. Electrolyte used in SAEJ 2334 test was used to determine corrosion performance for coating system as this solution shows a high degree of correlation with field service conditions [5]. 

Electrochemical impedance tests usually investigate the interface between an electrode material and a solution (for example corrosion tests may investigate different coated metals in a salt solution, while battery/fuel cell tests may investigate different electrode materials in an electrolyte). Electrochemical impedance tests provide complementary information to that obtained from dc electrochemical techniques such as cyclic voltammetry, pulse voltammetry, ohmic drop analysis, and chronoamperometry. 

In order to be able to properly design and interpret the results from galvanic corrosion tests, it is necessary to have some appreciation of the electrochemical theory behind galvanic corrosion. Metal corrosion consists of at least two reactions. The first is the metal going into solution in the electrolyte... 

Steppan, J., Roth, J., Hall, L., et al., Review of Corrosion Failure Mechanisms During Accelerated Tests, Electrolytic Metal Migration, Journal of the Electrochemical Society. Vol. 134, No. 1, 1987, p. 175. 

Plastic deformation of metals in electrolytes is accompanied by charge transfer between the solid and electrolyte. There is a lot of data in literature concerning electrochemically controlled stress corrosion, stress corrosion cracking and creep tests performed under a constant load or stress in water solutions on tin and lead single crystals [9] copper and its alloys [16-21] ... 

The composition and concentration of a test solution often affect the electrolyte conductivity, the effectiveness of an electrochemical corrosion cell, and thus the rate of corrosion. In an accelerated inhibitor test, electrolyte concentrations are frequently chosen to allow a sufficient degree of corrosion in a short period of time and yet still allow discrimination of inhibitors effectiveness. For this reason, Blin et for example, chose a 0.01 M sodium chloride solution as the... 

At an electrolyte pH of 8, the passivation region extended for over 0.5 V. Electrochemical tests were performed on acid etched, bare A1 2024-T3 panels with artificial pits as a control experimental to determine if the increased passivation with increasing electrolyte pH was a result of self-passivation of the bare aluminum alloy surface (Fig. 6.12(b)). The polarization curves for the bare A12024-T3 showed no appreciable passivation and no significant difference with pH, indicating that the passivation observed in the primers was not a result of self-passivation of the substrates, but activity from the primer. This behavior provides important clues not only to the inherent electrochemical properties of the initial coatings, but also the mechanisms responsible for corrosion protection. 

In 1980 Bemhardsson et introduced an automated electrochemical method for CPT determination. The specimen is mounted as described in Section IV.2 (ii) using a stream of argon to avoid crevice corrosion and 0.02-5% sodium chloride as electrolyte. The CPT is determined by a potentiostatic test method using an instrument called the Santron CDT 400 for potential control, temperature control, and current measurements. 

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