Comparison of UV/ozone cleaning of platinum/iridium kilogram mass standards with nettoyage-lavage cleaning

A cleaning method using ultraviolet activated ozone has been developed at the National Physical Laboratory (NPL). A comparison to test the effectiveness of this cleaning method with nettoyage-lavage cleaning on platinum–iridium artefacts and kilogram mass standards was undertaken at the Bureau International des Poids et Mesures (BIPM). Three cleaning trials were performed to compare the effectiveness of the two methods at removing natural, medium and heavy levels of surface contamination.Both the ultraviolet light/ozone method and the nettoyage-lavage method successfully removed both natural levels and medium levels of surface contamination. However, in the medium contamination trial nettoyage-lavage cleaning removed additional mass from the Pt/Ir mass standard under test that could not be accounted for in terms of surface contamination.In the heavy contamination trial nettoyage-lavage cleaning successfully removed most of the contamination from the surface of the contaminated Pt/Ir mass standard. The ultraviolet light/ozone method removed about two thirds of the surface contamination and therefore for heavily contaminated mass standards it is advisable to pre-clean them with a solvent before ultraviolet/ozone cleaning.