ASTM G3-2019 pdf free download

ASTM G3-2019 pdf free download.Standard Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing
1. Scope
1.1 This practice covers conventions for reporting and displaying electrochemical corrosion data. Conventions for potential, current density, electrochemical impedance and admittance, as well as conventions for graphical presentation of such data are included. 1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. See also 7.4. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.4 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
3. Significance and Use
3.1 This practice provides guidance for reporting, displaying, and plotting electrochemical corrosion data and includes recommendations on signs and conventions. Use of this practice will result in the reporting of electrochemical corrosion data in a standard format, facilitating comparison between data developed at different laboratories or at different times. The recommendations outlined in this standard may be utilized when recording and reporting corrosion data obtained from electrochemical tests such as potentiostatic and potentio- dynamic polarization, polarization resistance, electrochemical impedance and admittance measurements, galvanic corrosion, and open circuit potential measurements.
4. Sign Convention for Electrode Potential
4.1 The Stockholm sign invariant convention is recom- mended for use in reporting the results of specimen potential measurements in corrosion testing. In this convention, the positive direction ofelectrode potential implies an increasingly oxidizing condition at the electrode in question. The positive direction has also been denoted as the noble direction because the corrosion potentials of most noble metals, such as gold, are more positive than the nonpassive base metals. On the other hand, the negative direction, often called the active direction, is associated with reduction and consequently the corrosion potentials of active metals, such as magnesium. This conven- tion was adopted unanimously by the 1953 International Union of Pure and Applied Chemistry as the standard for electrode potential (1). 3 4.2 In the context of a specimen electrode of unknown potential in an aqueous electrolyte, consider the circuit shown in Fig. 1 with a reference electrode connected to the ground terminal of an electrometer. If the electrometer reads on scale when the polarity switch is negative, the specimen electrode potential is negative (relative to the reference electrode). Conversely, if the electrometer reads on scale when polarity is positive, the specimen potential is positive. On the other hand, if the specimen electrode is connected to the ground terminal, the potential will be positive if the meter is on scale when the polarity switch is negative, and vice versa.N OTE 1—In cases where the polarity of a measuring instrument is in doubt, a simple verification test can be performed as follows: connect the measuring instrument to a dry cell with the lead previously on the reference electrode to the negative battery terminal and the lead previously on the specimen electrode to the positive battery terminal. Set the range switch to accommodate the dry cell voltage. The meter deflection will now show the direction of positive potential. Also, the corrosion potential of magnesium or zinc should be negative in a 1 N NaCl solution if measured against a saturated standard calomel electrode (SCE).