Development and evaluation of artefacts suitable to provide maintenance and dissemination of a redefined kilogram:
The aim was to identify materials and production techniques for the new generation of mass artefacts to be used in the watt balances as primary standards. For this purpose METAS analysed the chemical composition of metallic samples such as PtIr, AuPt, iridium, stainless steel, silicon, nickel, electroplated gold and electroplated rhodium using x-ray photoelectron spectroscopy (XPS). Additionally, the surface roughness of the samples was measured.
Development and evaluation of procedures and techniques for the mass transfer be-tween vacuum and air:
The sorption characteristics of mass standards made of different materials using vacuum-air transfers. Measurements by means of XPS, quartz crystal microbalance (QCM) and gravimetric weighings were conducted and correlations were investigated.
Surface effects and dynamic changes on the artefact surface between vauum, air and selected gases:
The aim was to use a range of complementary surface analysis techniques to characterise the surface effects on artefacts stored in and transferred between air, vacuum and inert gas.
For that purpose metallic samples were exposed to cyclic venting with vacuum-N2-vacuum, vacuum-N2-air-vacuum and vacuum-air-vacuum. The effects of the three transfer processes on the surface contamination were investigated by using XPS. In addition, all samples were cleaned by hydrogen plasma, UV/ozone and nettoyage-lavage in order to correlate the influence of the cleaning methods with the materials and transfer processes. Based on these results a ranking list of best materials and processes for future mass standards could be generated.
Evaluation of the mass stability of artefacts with a focus on storage, cleaning and transport methods:
The aim was to address the on-going requirements for improvements and developments to conventional mass standards, storage and transfer methods and cleaning processes. METAS and its JRP partners applied various cleaning techniques to a variety of sample materials to study material-specific (re-)contamination and cleanliness of the surface. Furthermore, different storage conditions for the samples were tested after cleaning. The findings showed significant differences between the efficiency of the cleaning techniques and the achieved cleanliness. It was found that hydrogen plasma was non-abrasive and that UV/ozone oxidized the surface.
Identification and evaluation of the uncertainty components inherent in the mise-en-pratique and in their propagation through the dissemination chain:
One of the aims was to find a mathematical model which can be used to quantify the change in mass of a standard when transferred from air to vacuum and vice versa. For that purpose, surface artefacts of gold, stainless steel and rhodium were exposed to a number of vacuum-air transfers. By means of gravimetric weighings and QCM measurements reversible and irreversible sorption could be distinguished. Mathematically, the change in mass due to sorp-tion effects could be described by a combination of an exponential and a linear term.
