Electrochemical test data

Laboratory coupon (including electrochemical tests) data obtained in simulated service conditions... 

Table 4 summarizes electrochemical test data for 316L sintered in hydrogen and under vacuum [24]. In these examples, inferior corrosion resistance, documented also by neutral salt spray data, can be attributed to greater degrees of reoxidation of the surface of a specimen during cooling... 

Electrochemical tests This group includes the various electrochemical tests that have been proposed and used over the last fifty or so years. These tests include a number of techniques ranging from the measurement of potential-time curves, electrical resistance and capacitance to the more complex a.c. impedance methods. The various methods have been reviewed by Walter . As the complexity of the technique increases, i.e. in the above order, the data that are produced will provide more types of information for the metal-paint system. Thus, the impedance techniques can provide information on the water uptake, barrier action, damaged area and delamination of the coating as well as the corrosion rate and corroded area of the metal. However, it must be emphasised that the more comprehensive the technique the greater the difficulties that will arise in interpretation and in reproducibility. In fact, there is a school of thought that holds that d.c. methods are as reliable as a.c. methods. 

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]. 

Electrochemical tests in half-cells allow the preliminary assessment of the WUT carbon as well as of the impact of grinding on the electrochemical performance. The data from the chart on the Figure 5 indicate that the material has high reversible capacity (similar to the capacities of the commercial graphites described earlier). 

The most desirable data are those obtained for the material of interest in the intended conditions of exposure. Such data are not readily available in the literature. Published data on atmospheric corrosion should be used with caution since atmospheric conditions are changing with time, as for example acid rain as a variable factor. Accelerated testing, including electrochemical tests, should have a good link with the natural and practical conditions. Published data should be consulted because they are generally useful. Some published data are mentioned here as examples since they are useful in selecting materials or discussion of case histories ... 

F. Mansfeld, Polarization resistance measurements—experimental procedure and evaluation of test data, in R. Baboian (Ed.), Electrochemical Techniques for Corrosion Engineering, NACE, Houston, 1977, p. 67. 

EDS applications. In addition, new test data from the ACWA Program indicate that polynitroaromatic compounds (e.g., trinitrobenzoic acid and trinitrobenzene) precipitate during treatment of liquid wastes containing explosive residues, which may be present in EDS neutralents (Winkler, 2001). Electrochemical oxidation with Ce(IV) is also dropped from track two, owing to its relative immaturity and the possibility of corrosion and plugging of the electrochemical cells as a result of higher levels of metal ions in the EDS neutralents. 

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. 

Electrochemical test conditions and considerations for data analysis... 

The main variables that are measured in an electrochemical test are the voltage and the current. The goal is to translate this information into a corrosion rate or some other information that describes the corrosion process. ASTM G 3, Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing, provides guidelines for conventions for reporting a myriad of electrochemical data for the more common tests. 

Electrochemical tests are often preferred to mass loss studies as a method of measuring uniform corrosion. Such tests are preferred because in theory they (1) provide a realtime measurement of the metaUic corrosion rate, (2) can provide time-corrosion rate data on a single coupon, and (3) are rapid to perform. Disadvantages of the electrochemical tests include the requirements for comparatively expensive equipment (versus mass loss tests) and higher levels of technical expertise for data analysis. Fmthermore, the data reduction requires the use of conversion-"constants," factors applied to the results of the electrical measurements to convert the data to a corrosion rate. These constants ... 

The corrosion test methods may be any method that can provide corrosion data in the low water environments. This is generally coupon testing, but may include electrochemical tests that are applicable to the high resistivity crude oil continuous environments at low water levels, e.g., electrochemical impedance spectroscopy and electrochemical noise. 

There are several aspects to conducting electrochemical tests in organic liquids that are often not encountered or important while testing in aqueous solutions. These include effects due to low solution conductivities, the importance of the water concentration in the solution, the existence of an extremely wide variety of liquid compositions, the complexity of products from electroactive organic liquids, and a lack of thermodynamic data. 

In vivo electrochemical testing is possible in humans (in the oral cavity) under restricted conditions [77,78]. Open circuit potentials and galvanic currents between dissimilar metals have been measured. Linear polarization and AC impedance tests have been conducted. The paramount concern for these measurements is obtaining accurate data under conditions that present no hazard to the human subjects. 

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