Electrochemical tests films

Use and Uimitations of Electrochemical Techniques A major caution must be noted as to the general, indiscriminate use of all electrochemical tests, especially the use of AC and EIS test techniques, for the study of corrosion systems. AC and EIS techniques are apphcable for the evaluation of very thin films or deposits that are uniform, constant, and stable—for example, thin-film protective coatings. Sometimes, researchers do not recognize the dynamic nature of some passive films, corrosion produc ts, or deposits from other sources nor do they even consider the possibility of a change in the surface conditions during the course of their experiment. As an example, it is note-... 

Environmental tests have been combined with conventional electrochemical measurements by Smallen et al. [131] and by Novotny and Staud [132], The first electrochemical tests on CoCr thin-film alloys were published by Wang et al. [133]. Kobayashi et al. [134] reported electrochemical data coupled with surface analysis of anodically oxidized amorphous CoX alloys, with X = Ta, Nb, Ti or Zr. Brusic et al. [125] presented potentiodynamic polarization curves obtained on electroless CoP and sputtered Co, CoNi, CoTi, and CoCr in distilled water. The results indicate that the thin-film alloys behave similarly to the bulk materials [133], The protective film is less than 5 nm thick [127] and rich in a passivating metal oxide, such as chromium oxide [133, 134], Such an oxide forms preferentially if the Cr content in the alloy is, depending on the author, above 10% [130], 14% [131], 16% [127], or 17% [133], It is thought to stabilize the non-passivating cobalt oxides [123], Once covered by stable oxide, the alloy surface shows much higher corrosion potential and lower corrosion rate than Co, i.e. it shows more noble behavior [125]. 

Wedge test results suggest that the curing process (e.g., percent crosslinking) of the epoxy-polyamide primer system is not affected by the addition of organosilanes, but may be affected by NTMP. The results of substrate surface characterization, adsorption behavior of applied films, and evaluation of candidate inhibitors by chemical, mechanical, and electrochemical test methods are presented. Mechanisms to explain the observed behavior of the various phosphonate and silane polymer systems are discussed. 

The effect of phosphates on SCC susceptibifity ofa-brass was studied by Ashour and Ateya [239]. The results indicated that disodium hydrogen phosphate (DHP) inhibits the SCC in brass by the formation of zinc phosphate. SSRT and electrochemical tests were used to study the SCC properties of H62 brass in Mattsson s solution (MS) containing various concentrations of DHP by Du et al. [240]. MS was used as an accelerated SCC test environment for H62 brass. The susceptibifity of brass to SCC and film-induced stress decreased with increasing DHP concentrations. Electrochemical measurements confirmed that DHP inhibits SCC by forming a copper phosphate and zinc phosphate film on the brass surface. The film inhibits dezincification and decreases film-induced stress and reduces the susceptibility of brass to SCC. As shown in Fig. 9.62a, tarnishing... 

Kotz and Stuck studied the OER activity and stability of 200-nm-thick Ru-lr metallic alloys sputter-deposited on glass [42]. In sulfuric acid, they found that 14 % at. Ir already had produced a substantial stabihzation effect on Ru which is similar to our data for 15 % at. Ir (Fig. 22.12). Based on XPS measurements before and after the electrochemical testing, they concluded that the stabilization is due to the formation of a protective oxide layer with increased Ir content. However, unlike our findings, they saw a steady decrease in the OER current with an increase of Ir content. In addition, our Ru-Ir catalyst, estimated to be only 2 nm thick, has at least an order of magnitude higher OER activity. This obviously points to differences in the structure and the morphology between the two films which could be due to the preparation procedures as well as the substrates. 

Pyrroles have been functionalized at the 3 positions with a carboxyl group which in turn has been functionalized with aminoacids and enzymes by condensation (64). The polymers were produced electrochemically as films and tested for enzyme recognition. Specific recognition was found with carboxypeptidase A [305]. 

After selecting the set of appropriate test conditions, measurements are done to collect information on the electrochemical behaviour of a material fully covered by a passive film. This is done by electrochemical tests in absence of any sliding. After immersion in the electrolyte, the open circuit potential, Eoc is measured versus a reference electrode. In general, a stable value of Eoc is obtained after some time of immersion. From an electrochemical point of view, a stable Eoc is obtained when the long-term fluctuations of Eoc are below 1 mV min-i during a minimum of 1 hour. The time necessary to reach such a stationary open circuit potential in the test electrolyte is an important characteristic of a passivating process, and is called in this protocol as the reaction time characteristic, treac- The evolution of Eoc from immersion time on provides useful information on the electrochemical reactivity of the tested material in the test electrolyte (see Figure 7). 

Sections of the dry reagent films were removed around the perimeter of the IDA electrodes with the use of a micro-manipulator tip and a Cambridge stereo zoom microscope (see below). A Dektak IIA step profiler was used to determine the approximate film thickness of the IDA electrodes. Electrodes were tested for shorts between the electrode fingers using a Fluke 87 multimeter prior to electrochemical testing. 

What is the relationship between the hydrothennal films and films formed in room-temperature water The latter are much more amenable to electrochemical tests which would yield more quantifiable re.sults than surface analysis. 

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