Potentiodynamic polarization resistance measurements ASTM

Standard practice for conducting potentiodynamic polarization resistance measurements. ASTM Standard G-59, ASTM Annual/Book of Standards, ASTM. 

ASTM G59 - 97(2009), Standard Test Method for Conducting Potentiodynamic Polarization Resistance Measurements, ASTM, 2009. 

Linear polarization re.slstance probe.s. LPR probes are more recent in origin, and are steadily gaining in use. These probes work on a principle outlined in an ASTM guide on making polarization resistance measurements, providing instantaneous corrosion rate measurements (G59, Standard Practice for Conducting Potentiodynamic Polarization Resistance Measurements ). 

ASTM G59, Standard Prac tice for Conducting Potentiodynamic Polarization Resistance Measurements, provides instructions for the graphical plotting of data (from tests conducted using the above-noted ASTM Standard G103) as the hnear potential versus current density, from which the polarization resistance can be found. 

ASTM G59 descrihes a method for conducting potentiodynamic polarization resistance measurements [14]. It descrihes a setup for type 430 stainless steel in sulfuric acid, as for ASTM G5 described earher, and the same apparatus is specified. According to this standard, the potential should he scanned from 30 mV negative of the corrosion potential to 30 mV positive of the corrosion potential at a rate of 0.167 mV s . ... 

ASTM G 59, Practice for Conducting Potentiodynamic Polarization Resistance Measurements— The technique of polarization resistance testing is described. This standard conducts electrochemical testing in 1.0 N H2SO4. The apparatus, specimen preparation, and test environment are described. In addition, the equipment, electrochemical test procedure, and standard reference plots are presented. 

Standard test procedures are defined within ASTM standards ASTM G 59, Practice for Conducting Potentiodynamic Polarization Resistance Measurements G 5, "Standard Reference Test Method for Making Potentiostatic and Potentiodynamic Anodic Polarization Measurements G 106, Practice for Verification of Algorithm and Equipment for Electrochemical Impedance Measurements and G 102, Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements. Each of these methods describes a standard procedure or practice for the test method. A complete discussion of the technologies is beyond the scope of the current text. For the current text, the focus is on the application of the most simple and most widely used of these techniques, the polarization resistance measurement, ASTM G 59. The parameters discussed are, however, applicable concerns for all electrochemical tests. 

ASTM G 59 Standard Practice for Conducting Potentiodynamic Polarization Resistance Measurements Provides details on how to conduct DC polarization resistance tests. 

Nickel-base alloys respond well to most electrochemical test techniques and show active-passive behavior in many environments. Due to their rapid repassivation, however, the results obtained with potentiod3mamic techniques can sometimes be affected by scan rate and immersion time prior to starting the test [5,6], Electrochemical techniques are useful for investigating localized corrosion resistance, ASTM G 61, Test Method for Conducting Cyclic Potentio-dynamic Polarization Measurements for Localized Corrosion Susceptibility of Iron-, Nickel-, or Cobalt-Based Alloys, and general corrosion resistance, ASTM G 59, Practice for Conducting Potentiodynamic Polarization Resistance Measurements of nickel alloys. Electrochemical impedance measurement techniques have not been extensively applied to nickel alloys. 

In the LPR technique, a small polarization potential typically of the order of 10-20 mV is applied to a freely corroding electrode and the resulting linear current response is measured. The polarization resistance is the ratio of the applied perturbation potential and the resulting current response. According to the Stem and Geary equation, this resistance is inversely related to the uniform corrosion rate. The fundamentals of the LPR technique and examples of its application have been discussed by Mansfeld. Standard test procedures for conducting potentiodynamic polarization resistance measurements are provided in an ASTM Standard. " LPR is frequently used to determine the rate of uniform corrosion and... 

ASTM standards D-2776 (9) and G-59 (10) describe standard procedures for conducting polarization resistance measurements. Potentiodynamic (11), potential step, and current-step methods (12,13) have all been described to determine the linear E-i behavior of an electrode near Eco . The current step method has been cited to be faster than potentiodynamic methods and less susceptible to errors associated with drift in Econ. This issue will be discussed below. Regardless of the method used, independent determination of pa and pc is still required. 

ASTM G 5, Reference Test Method for Making Potentiostatic and Potentiodynamic Anodic Polarization Measurements ind ASTM G 59, Practice for Conducting Potentiodynamic Poltuization Resistance Measurements. 

Potentiodynamic polarization measurements are quite appropriate for determination of the pitting susceptibility of aluminum coatings, and/or the corrosion current density/ corrosion rate of coated steel products in general. ASTM G 102, Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements, describes the calculation of corrosion rates and other information from electrochemical measurements. Another example of the use of DC electrochemical methods to examine the corrosion performance of coated sheet materials is a study by D. A. Jones et al. [48]. The study used polarization resistance measurements to examine the mechanism of steel and coated sheet degradation under conditions of alternate immersion. Jones compared the polarization resistance of samples of low-carbon steel, unpainted galvanized, aluminum-coated, and Zn-Ni alloy coated steel during continuous immersion and alternate immersion. Alternate immersion cyclic exposure produced a thick oxide that led to significant underfilm attack. Jones found that phosphate pretreatment tends to increase the resistance of these materials to underfilm attack. This study is an excellent example of the way electrochemical measurements can be used as a complement to other techniques to elucidate mechanistic information. 

Cyclic anodic polarization procedures based upon ASTM G5 (Reference Test Method for Making Potentiostatic and Potentiodynamic Anodic Polarization Measurements) have been used to evaluate the localized corrosion resistance of stainless steel alloys in paper machine white waters. The difference between the open circuit or naturally occurring corrosion potential and the pitting breakdown potential of various materials has been reported by many investigators [lO-Id]. Bowers [14] called the difference between the breakdown potential and the potential of the cathodic/anodic current reversal the margin of safety. He also noted the effect of the sulfate to chloride concentration ratio on localized corrosion of Types 304 and 316L stainless steels, These results permitted alternative materials of construction to be ranked and their limits of resistance to be defined. 

The most commonly-used steady state techniques are potentiodynamic tests to determine the corrosion rate in systems that experience a uniform corrosion process. This type of attack can also be studied by measuring resistance to polarization. Cyclical polarization ciurves are also used to study localized corrosion and potentiokinetic reactivation is the most suitable study technique for evaluating intergranular corrosion produced by a sensitization phenomenon following ASTM G108 standard test. 

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