Evaluation of the localized corrosion on Mg electrode surface by electrochemical noise technique

Nickel or Cobalt-based superalloys represent an important class of engineering materials, finding widespread application in critical components within the gas turbine engines used for jet propulsion and electricity generation. This research aimed at the frequency analysis of transients in electrochemical noise of Waspaloy and Ultimet superalloys, immersed in 3.5 wt.% in H2SO4 and NaCl solutions at two different temperatures, 25 and 60 °C. Localized corrosion behavior of superalloys was assessed using the electrochemical noise technique (EN) according to ASTM-G199 standard. Three different statistical methods filtered the EN signal, and the polynomial method was employed to obtain the noise resistance (Rn), the localization index (LI), skew and kurtosis, and the power spectral density analysis (PSD). Results indicate that the current and potential noise transients have a better behavior with better clarity when a polynomial is used to show a localized corrosion kurtosis for both superalloys.

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ELECTROCHEMICAL NOISE MEASUREMENTS FOR THE STUDY OF LOCALIZED CORROSION AND PASSIVITY BREAKDOWN

Passivity of Metals and Semiconductors ◽

10.1016/b978-0-444-42252-1.50040-0 ◽

1983 ◽

pp. 229-234 ◽

Cited By ~ 4

Author(s):

U. BERTOCCI ◽

J.L. MULLEN ◽

Y-X. Ye

Keyword(s):

Electrochemical Noise ◽

Localized Corrosion ◽

Noise Measurements

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Wavelet Transform Modulus Maxima and Holder Exponents Combined with Transient Detection for the Differentiation of Pitting Corrosion Using Electrochemical Noise

CORROSION ◽

10.5006/2788 ◽

2018 ◽

Vol 74 (9) ◽

pp. 1001-1010 ◽

Cited By ~ 2

Author(s):

A.M. Homborg ◽

P.J. Oonincx ◽

J.M.C. Mol

Keyword(s):

Wavelet Transform ◽

Pitting Corrosion ◽

Electrochemical Noise ◽

Localized Corrosion ◽

General Corrosion ◽

Hölder Exponent ◽

Transient Detection ◽

Time Frequency ◽

Wavelet Transform Modulus Maxima ◽

Modulus Maxima

A potentially powerful tool to detect and classify corrosion mechanisms is the analysis of electrochemical noise (EN). Data analysis in the time-frequency domain using, e.g., continuous wavelet transform (CWT) allows the extraction of localized frequency information, providing information on the type of corrosion, i.e., uniform or localized corrosion, from the EN signal. The CWT provides the opportunity to analyze changes in frequency behavior of EN signals over time. In the presence of transients generated by pitting corrosion that occur only during short instants of time, this is an important property. This paper introduces the combination of automated transient detection with wavelet transform modulus maxima (WTMM) and the Holder exponent. WTMM enhances the determination of transient frequencies by indicating the ridges of a CWT spectrum. The Holder exponent, a measure of singularity of an EN signal, provides a single parameter discrimination tool based on WTMM and serves to differentiate between general corrosion and two types of pitting corrosion of stainless steel Type 304 exposed to aqueous HCl solutions of different concentrations and as such at different pH values.

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