THE USE OF UV ACTIVATED OZONE FOR THE CLEANING OF PRIMARY PLATINUM-IRIDIUM KILOGRAM MASS STANDARDS

Abstract: The cleaning of primary platinum-iridium mass standards is traditionally achieved using the nettoyage-lavage process developed at the BIPM. This manual cleaning method is notoriously difficult to reproduce, particularly at laboratories other than the BIPM. An alternative, operator independent, method for the cleaning of primary mass standards, using UV activated ozone, has been investigated and the results are reported. An artefact-based definition thus presents a unique set of problems both to do with the stability of the International Prototype and the national copies, and with the dissemination of the unit of mass worldwide. The only way in which national standard kilograms can be checked is by returning them to the BIPM for calibration. This, combined with the fact that the national prototypes are known to gain between 1 and 5 micrograms every year, makes maintaining the stability of national mass scales a major concern for all national measurement institutes (NMIs) [1]. Figure 2 shows the relative temporal stability of seven of the copies of the International prototype