Electrochemical testing, aluminum

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... 

A library of 35 different catalysts fixed on electrochemically oxidized aluminum either in oxalic acid (Lib 1) or sulfuric add (lib 2) was tested at 450 °C and 1.1 bar. The methane-to-oxygen ratio was set to 1 in order to establish the potential of the catalyst to form intermediates. Figure 3.20 shows experimental results for a residence time of 550 ms and a screening time of 60 s. The conversion rate followed directly the platinum content in the catalysts. The higher the platinum content, the higher is the degree of conversion. Catalyst carrier formed by anodization of... 

R. G. Kelly, J. R. Scully. An evaluation of the susceptibility of laser surface-melted aluminum bronze to dealloying via an accelerated electrochemical test, NSRDC TM-28-83-189. David Taylor Naval Ship R D Center, Annapolis, MD (Sept. 1983). 

Electrochemical tests of aluminum-air battery consisting of 24 cells are made in solution of KOH (20 %). The voltage of battery was 18-20 V, working voltage was 10 V at load current 100-105 A. Aluminum-air battery with power 1 kW was elaborated for electrocar by Rotor (Cherkasy, Ukraine). 

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. 

The results obtained during the electrochemical testing of various faces of aluminum sheet material indicated that short-term EIS measurements could provide good predictions of the general and localized corrosion behavior of this material when exposed to seawater. In fact, the prediction of the localized corrosion behavior with the CPE calculated from the EIS data seemed to agree more closely to the long-term test results than the general corrosion estimation. ... 

The corrosion widths of Prohesion salt spray-tested alloys are calculated and summarized in Figure 32.14. E-coated IVD controls (CC/E), i.e., the combination coating systems of chromate conversion coating with nonchromated E-coat, showed very large corrosion widths for all the IVD Al-coated aluminum alloys. This combination did not provide good corrosion protection, which could be taken as proof that the two completely different approaches (electrochemical corrosion protection and corrosion protection by barrier adhesion principle) should not be mixed. 

In previous work (1), we examined the impact of surface impurities on electrochemical reactions beneath polysiloxane encapsulant coatings. Test specimens consisted of aluminum combs prepared on Si02 by photolithography. Leakage currents were measured as functions of temperature, surface impurity levels, and relative humidity. In all cases, increasing relative humidity, RH, produced a monotonic rise in leakage current, corresponding to increased water... 

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... 

Table 9.1 summarizes environmental alloy combinations that have been shown to produce see. The test temperature accelerates the See for most of the systems listed in Table 9.1. Electrochemical methods and stress corrosion tests should be performed to evaluate possible corrosion environments for a given alloy. More information on these and additional systems may be found in the ASM Metals Handbook [30]. Other significant alloys include nickel alloys [31], austenitic stainless steel [30], carbon steels [32], copper alloys [33], ferritic, martensitic, duplex [31,32], titanium alloys [33], and aluminum alloys [34].

Fig. 6.2 Residual currents measured at 30 and at 60 °C from chronoamperograms of aluminum electrodes as a function of the applied potential. The inset shows the SEM images of the pristine aluminum electrode and aluminum electrodes tested by chronoampeiometry and polarized at 5.30 V in various electrolyte solutions like EC-DMC/1 M IjPF6, EC-DMC/1 M liBOB, and EC-DMC/1 M LiC104 solutions at 60 °C. Reproduced with permission from [20], copyright (2010) The Electrochemical Society...

Another very important fact is the high versatility of this process with makes is very attractive. Indeed, several zincated electrodes with various surface states (more or less oxidized or rough) as well as different substrates (iron, mild steel, aluminum, copper and tin) were tested. In every case, PPy is synthesized without any difficulty with the same electrochemical behavior. 

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