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5.1 Electrode potential is the reversible work that is required to transfer a unit of positive charge between the surface in question and a reference electrode through the electrolyte that is in contact with both electrodes. The sign of the electrode potential is determined by the Gibbs Stockholm Convention described in Practice G3.5.2 The electrode potential of a surface is related to the Gibbs free energy of the oxidation/reduction reactions occurring at the surface in question compared to the Gibbs free energy of the reactions occurring on the reference electrode surface.45.3 Electrode potentials are used together with potential-pH (Pourbaix) diagrams to determine the corrosion products that would be in equilibrium with the environment and the electrode surface.55.4 Electrode potentials are used in the estimation of corrosion rates by several methods. One example is by means of Tafel line extrapolation, see Practices G3 and G102. Polarization resistance measurements are also determined using electrode potential measurements, see Test Method G59 and Guide G96.5.5 Corrosion potential measurements are used to determine whether metal surfaces are passive in the environment in question, see Test Method C876.5.6 Corrosion potential measurements are used in the evaluation of alloys to determine their resistance or susceptibility to various forms of localized corrosion, see Test Methods F746, F2129, G61, and G150.5.7 Corrosion potentials are used to determine the metallurgical condition of some aluminum alloys, see Test Method G69. Similar measurements have been used with hot dipped galvanized steel to determine their ability to cathodically polarize steel. See Appendix X2.5.8 Corrosion potentials are used to evaluate aluminum and magnesium alloys as sacrificial anodes for underground and immersion cathodic protection application, see Test Method G97 and NACE TM0190–2012.5.9 Corrosion potentials are used to evaluate the galvanic performance of alloy pairs for use in seawater and other conductive electrolytes, see Test Method F3044, Guide G71, and Guide G82.5.10 Electrode potential measurements are used to establish cathodic protection levels to troubleshoot cathodic protection systems and to confirm the performance of these systems in soils, concrete, and natural waters, see NACE TM0497, NACE TM0108, and NACE TM0109.5.11 Electrode potential measurements are necessary for the determination of hydrogen overvoltage values in testing for hydrogen embrittlement and related issues with hydrogen cracking. See Appendix X3.1.1 This guide provides guidance on the measurement of electrode potentials in laboratory and field studies both for corrosion potentials and polarized potentials.1.2 The values stated in SI units are to be regarded as standard. Any other units of measurements included in this standard are present because of their wide usage and acceptance.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 appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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5.1 This practice provides nine figures of merit which may be used to estimate the relative thermal hazard of thermally unstable materials. Since numerous assumptions must be made in order to obtain these figures of merit, care must be exercised to avoid too rigorous interpretation (or even misapplication) of the results.5.2 This practice may be used for comparative purposes, specification acceptance, and research. It should not be used to predict actual performance.1.1 This practice covers the calculation of hazard potential figures of merit for exothermic reactions, including:(1) Time-to-thermal-runaway,(2) Time-to-maximum-rate,(3) Critical half thickness,(4) Critical temperature,(5) Adiabatic decomposition temperature rise,(6) Explosion potential,(7) Shock sensitivity,(8) Instantaneous power density, and(9) National Fire Protection Association (NFPA) instability rating.1.2 The kinetic parameters needed in this calculation may be obtained from differential scanning calorimetry (DSC) curves by methods described in other documents.1.3 This technique is the best applicable to simple, single reactions whose behavior can be described by the Arrhenius equation and the general rate law. For reactions which do not meet these conditions, this technique may, with caution, serve as an approximation.1.4 The calculations and results of this practice might be used to estimate the relative degree of hazard for experimental and research quantities of thermally unstable materials for which little experience and few data are available. Comparable calculations and results performed with data developed for well characterized materials in identical equipment, environment, and geometry are key to the ability to estimate relative hazard.1.5 The figures of merit calculated as described in this practice are intended to be used only as a guide for the estimation of the relative thermal hazard potential of a system (materials, container, and surroundings). They are not intended to predict actual thermokinetic performance. The calculated errors for these parameters are an intimate part of this practice and must be provided to stress this. It is strongly recommended that those using the data provided by this practice seek the consultation of qualified personnel for proper interpretation.1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.7 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 appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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