Corrosion testing impedance

It is preferable to carry out laboratory corrosion tests and to validate the data with service tests for the selection of materials. It is needless to note that the chosen test method be reliable and cost effective. Some of the test methods in use in industry are service tests, field tests, laboratory tests, and rapid electrochemical methods such as potentiodynamic polarization, linear polarization, electrochemical impedance and electrochemical noise. 

Figure 28.25 The impedance modulus at low frequency (IZIo.ihz) dependence on the scribe types and depths and the exposure time in the Prohesion corrosion test chamber.

S. Hamyama and T. Tsum, A Corrosion Monitor Based on Impedance Method, Electrochemical Corrosion Testing, STP 727, F. Mansfeld and U. Bertocci, Ed., ASTM, 1981, p 167-186... 

D.D. Macdonald, M.C.H. Me Kubre, Electrochemical impedance techniques in corrosion science, in F. Mansfeld, U. Bertocci (Eds.), Electrochemical Corrosion Testing, STP 272, ASTM International, Philadelphia, PA, 1981, pp. 110-149. 

There are many different types of electrochemical corrosion tests, but two types, (1) direct current (DC) polarisation methods and (2) electrochemical impedance spectroscopy (EIS) are described in the following because of their relevance and reliability to yield corrosion data in a short time-frame. 

B. Gottis, S.Turgoose, R. Newman, Corrosion Testing Made Easy Impedance and Noise Analysis, NACE International, Houston, Tex., 2000. 

R. Cottis, S. Turgoose, Corrosion Testing Made Easy Electrochemical Impedance and Noise (NACE Intematiraial, Houstrai, 1999)... 

Electrochemical impedance tests usually investigate the interface between an electrode material and a solution (for example corrosion tests may investigate different coated metals in a salt solution, while battery/fuel cell tests may investigate different electrode materials in an electrolyte). Electrochemical impedance tests provide complementary information to that obtained from dc electrochemical techniques such as cyclic voltammetry, pulse voltammetry, ohmic drop analysis, and chronoamperometry. 

D. D. Macdonald and M. C. H. McKubre [1981] Electrochemical Impedance Techniques in Corrosion Science, in Electrochemical Corrosion Testing, ed. Floiian Mansfield and Ugo Bertocci, STP 727, ASTM, Philadelphia. 

In the laboratory, the technique of ac impedance is superseding polarization resistance, because it provides additional information on mechanisms of the processes involved. Guidance on performing corrosion tests in the laboratory in liquids or in soils is provided in ASTM G 31 smd ASTM G 162 [iS,79]. Ac impedance S3 tems are now commercially available, but these units are limited to low polarization currents of 1 A or less, making them unsuitable for most field applications where larger current capabilities (>1 A) are needed. 

Corrosion test methods can be divided into electrochemical and non-electrochemical methods. Among the electrochemical techniques that have been used successfully for corrosion prediction are potentiodynamic polarization scans, electrochemical impedance, corrosion current monitoring, controlled potential tests for cathodic and anodic protection, and the rotating cylinder electrode for studies of velocity effects [3i,32]. Though not literally a test, potential-pH (Pourbaix) diagrams have been used as road maps to help understand the results of other tests. 

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. 

Cottis, R. and Turgoose, S., "Electrochemical Impedance and Noise," Corrosion Testing Made Easy, B. C. Syrett, Series Ed., NACE International, Houston TX, 1997. 

Smyrl, W. H., "Digital Faradaic Impedence Measurements on Corroding Copper in Acid Solutions, Electrochemical Corrosion Testing, ASTM STP 727, 1981, pp. 198-214. 

Electrochemical tests are rapid techniques to determine mechanisms, determine the effect of various parameters on corrosion rate, and screen out a large number of materials [43]. They usually involve measurement of corrosion potentials, corrosion currents, polarization curves, and electrochemical impedance. They are used to evaluate metals and alloys and the behavior of metallic, inorganic, and oiganic coatings. The simplest test involves the measurement of the corrosion potential and its use in conjunction with other measurements. A zero resistance ammeter (ZRA) is commonly used to measure corrosion currents between dissimilar metals and alloys. Controlled potentitd tests and anodic and cathodic polarization curves using potentiostats are the most commonly used electrochemical tests. These are powerful tools for investigating the effect of various parameters on corrosion behavior. These incorporate the use of cycUc polarization and polarization resistance for localized corrosion and corrosion rate measurements. Table 4 lists electrochemical tests that can be used for corrosion tests in the automobile industry. 

The history of airplane corrosion testing includes many successful tests that are now performed routinely, e.g., ASTM G 85 Annex A2 and ASTM G 44. Some other successful tests, such as the wedge test (ASTM D 3762, Test Method for Adhesive-Bonded Surface Durability of Aluminum), discovered as a result of bond line corrosion problems on airplanes, are not described here because they are not strictly corrosion tests. Many of the tests described here are ASTM standards. With others, standardization is being pursued, e.g., electrochemical impedance, or ANCIT (Aluminum-Nitrate Chloride Immersion Test), to replace EXCO [4], Corrosion may never be totally eliminated from an airplane however, further refinements in corrosion testing, made... 

Electrochemical corrosion characteristics of nickel were carried out by potentiodynamic polarization and impedance spectroscopy methods. Corrosion tests of nickel produced by electrocrystallization were ap>plied to its micrometric (Nim) and nanometric (Ni ) crystalline structures and for NiP amorphous alloy of nickel with phosphorus at content of 10.7% by weight (Eftekhari, 2008), (Kowalewska Trzaska, 2006). 

Haynes G. In Corrosion Tests and Standards Apphcation and Interpretation, Baboian R., ed. ASTM Manual Series MNL 20, Philadelphia, PA, 19103, 1995, pp. 91-97 Hirai S., Shimakagen K., Aizawa S. Alkaline corrosion resistance of anodised coated with zirconium oxide by a sol-gel process. J. Am. Ceram. Soc. 1998 81(12) 3087-3092 Hirayama R., Harayama S. Electrochemical impedance for degrades coated steel having pores. Corrosion 1991 47(12) 952-963... 

Haruyama S, Tsuru TA. Corrosion monitor based on impedance method electrochemical corrosion testing. In Mansfeld F, Bertocci U. eds. Computer Modeling in Corrosion [STP 727], Philadelphia, Pa. American Society for Testing and Materials. 1981 167-186. 

For film formation and growth to occur, there must be some corrosion and evidence of this has been noted (Hinton and Amott 1989). However, the extent of corrosion as indicated by corrosion tests, is clearly very small (Hinton 1989, Hinton et al. 1984, 1985, 1988), probably because the rate of corrosion is controlled by the impedance to the cathodic reactions imposed by the presence of the surface film. 

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