Corrosion Measurement and Analysis

Successful inhibitor tests require suitable corrosion measurement and analysis techniques that are able to correctly record and interpret corrosion rate data. Many testing and monitoring techniques that were developed initially for the diagnosis and prediction of corrosion have been successful employed in laboratory and field corrosion inhibitor testing and research. These techniques include the use of corrosion coupons, solution analysis, electrical resistance probe, polarization resistance, electrochemical impedance spectroscopy and many other physical, electrical and electrochemical methods. 

The drainage operation is based on controlled removal of stray currents from the underground structure to the source of their formation. The harmful phenomenon of currents outflow from the external surface of structures to the ground is eliminated in this way. Choice and localization of drainage devices should be preceded by determination of the electrolytic corrosion hazard (on the basis of specialist measurements) and analysis of the situation in the field. More information on drainage is given by Chaker and Lindemuth (1994) and Pignatelli (1985). 

Abstract This chapter provides an overview of major corrosion testing and analysis techniques and their applications in corrosion inhibitor research, with a particular focus on electrochemical evaluation of corrosion protection by rare earth metal (REM) compounds. Attempts are made to discuss fundamental issues in inhibitor test design such as limitations in corrosion measurement techniques and challenges that may lead to the reporting of inaccurate corrosion rates and patterns. 

Corrosion behavior of uncoated and Ti02 deposited Ti6A14V was evaluated by Karpagavalli et al. (2007) in freely aerated Hank s solution at 37°C by the measurement and analysis of open circuit potential variation with time, Tafel plots and electrochemical impedance spectroscopy. The electrochemical results indicated that nano Ti02 coated Ti6A14V showed a better corrosion resistance (Table 5.7, Fig. 5.14) in simulated biofluid than uncoated Ti6A14V. 

Electric Breakdown in Anodic Oxide Films Physics and Applications of Semiconductor Electrodes Covered with Metal Clusters Analysis of the Capacitance of the Metal-Solution Interface. Role of the Metal and the Metal-Solvent Coupling Automated Methods of Corrosion Measurement... 

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]. 

Time Constant Analysis, r is the relaxation time of the corrosion process and is dependent on the dielectric properties of the interface. r is given by r = R P, but can be measured independently r = wz"max Since and P vary with surface area in exactly opposite fashion, r (or wzBmax) should be independent of surface area. To verify that this is indeed the case, we examined the corrosion of N80 steel in uninhibited 15% HC1 at 65 C. With increasing exposure time, we observed a continuous decrease in R (hence an increase in corrosion rate) and a concomitant increase in P. And, as expected, wz"max did not vary at all (see Figure 8). 

A different pattern of dissolution was seen with a Zn-Sn alloy containing 26% zinc. In this case the stable dissolution situation established after ca. 90 min showed a ratio of EC to CMT measurements of 1 4. As seen in Fig. 3, this remained fairly constant, though the corrosion potential increased by more than 50 mV. Only selective zinc dissolution took place, and analysis by atomic absorption spectroscopy of the amount of dissolved zinc agreed within 10% with the value according to the titration. This pattern is still difficult to understand. The ratio of ca. 1 4 between EC and CMT measurements could be interpreted in terms of formation of the low-valent zinc species ZnJ, which seems unlikely, or in terms of dissolution of divalent zinc ions accompanied by loss of chunks consisting of precisely three zinc atoms, each time a zinc ion is dissolved. The latter alternative seems to require a more discrete mechanism of dissolution than... 

Z. Nagy and R. F. Hawkins, J. Electrochem. Soc. 138 1047 (1991). Analysis of the correction of the corrosion measurement kinetics for double-layer effects. 

In the laboratory portion of the project, the students quantify iron in real and artificial surface water samples by UV-Vis spectroscopy. The iron is complexed to the o-phenanthroline (phen) ligands in a buffered solution to create a highly colored orange complex, [Fe(phen)3] The intensity of the complex color is proportional to the concentration, following Beer s Law. Students create a standard series and prepare a surface water sample using modified standard protocols (21). We use autodispensers to dispense corrosive reagents and provide the stock iron solutions this equipment reduces exposure and ensures that the experimental work can fit within the three hour laboratory period. Students measure of the absorbance of their standard series as well as their surface water sample on a spectrometer at X = 508 nm. Students complete the experimental write-up, calculations, data analysis, and assessment during the subsequent laboratory period. 

Therefore, the corrosivity of the cabinet was evaluated as v=Am/S g/m2 for 96 h in the eight experiments. The analysis of the main uncertainty sources according to recommendations [6, 7] was performed (Fig. 1) for evaluation of possible value of uncertainty of corrosivity measurement result. Each main source of uncertainty (mass loss Am, surface area S and duration t) was analysed and calculated separately and these components used for combined and expanded uncertainty calculation. 

The analysis of experimental data shows that the average value 111 g/m2 of all corrosivity data (improved by rejecting outliers) corresponds to the value 140 40 g/m2 indicated in the standard. For the evaluation of the expanded combined uncertainty U with factor k=2 the corrosivity measurement gives the value of 215 g/m2 (at 95% confidence). It means that our data uncertainty is five-times higher than that specified in the standard as the data scattering interval 40 g/m2 and seven times as wide compared the statistic confidence interval in our own experimental data corrosivity (Table 2a and 2b). The main components of the combined uncertainty are mass loss and surface area determination. 

The panel addressed three general topics corrosion research and engineering, research on advanced materials, and dissemination of information. The first of these topics focuses on fundamental understanding of corrosion processes, on utilization of measurements and understanding in the engineering systems analysis of corroding systems, and on life prediction. The second examines corrosion of emerging classes of materials. The third addresses education and the transmittal of information on corrosion and corrosion control to the technical community. 

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