ASTM G220-20

5.1?Electrode potential measurement is an essential step in many electrochemical corrosion test methods and practices.

5.2?The SCE has been widely specified for laboratory tests because it is reliable, accurate, simple to use, and it has been readily available. However, because this device contains mercury, and mercury has recently been banned by some governmental agencies, it may not be available in locations where mercury is banned. As a result, test methods using the SCE may not be possible in locations where mercury is banned. Therefore, it is necessary to establish an alternative reference electrode for these standards.

5.3?The KCl saturated, silver/silver chloride reference electrode, Ag/AgCl (sat KCl), is a satisfactory replacement for the SCE in laboratory test methods and practices. This reference electrode should provide comparable performance and accuracy to the SCE.

5.4 It will be necessary to carry out interlaboratory test programs for each test method where the Ag/AgCl (sat KCl) electrode is specified to replace the SCE, in order to develop the precision of the method using the new reference electrode.

1.1?This practice provides the steps necessary to prepare revisions to standards that specify the saturated calomel reference electrode (SCE) for measuring or controlling electrode potentials.

1.2?The SCE contains mercury and, as a result, it may not be available in locations where mercury has been banned. This practice covers the selection and use of an alternative reference electrode.

1.3?In test methods where the SCE is specified, it will be necessary to develop a new precision statement using the alternative reference electrode.

1.4?This practice will not apply to electrometric pH determinations where the SCE has been used. (Electrometric pH measurement is an analytical method that is covered elsewhere.)

1.5?The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.6?WarningMercury has been designated by many regulatory agencies as a hazardous substance that can cause serious medical issues. Mercury, or its vapor, has been demonstrated to be hazardous to health and corrosive to materials. Use caution when handling mercury and mercury-containing products. See the applicable product Safety Data Sheet (SDS) for additional information. The potential exists that selling mercury or mercury-containing products, or both, is prohibited by local or national law. Users must determine legality of sales in their location.

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.