Journal article

Stability of reference masses: VI. Mercury and carbonaceous contamination on platinum weights manufactured at a similar time as the international and national prototype kilograms

Peter J Cumpson, Jose F Portoles, Naoko Sano, Anders J Barlow



The stability of prototype kilogram reference masses has been a long-standing question within the SI, with mass loss or gain at the surface being the principal concern. In papers I, III and IV of this series we showed mercury and organic carbonaceous contamination to be significant in sample surfaces exposed to typical prototype kilogram storage environments. In this work, we have examined the surfaces of six platinum mass standards manufactured in the mid-19th century. We used x-ray photoelectron spectroscopy in order to identify mercury and carbonaceous contamination, and assess the validity of our previous models for the rate of increase. We use white-light interferometry to study surface..

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University of Melbourne Researchers


Funding Acknowledgements

We are very grateful to Dr Keith Moore of the Royal Society and Professor Martyn Poliakoff of Nottingham University for advice, making us aware of the existence of these platinum reference weights, and facilitating their loan from the Royal Society archive. Thanks are also due to Dr Derek Brain and Dr Luke Pomeroy of the London Science Museum for facilitating the loan of SM1, 2, 3 and 4. X-ray photoelectron spectra were obtained at the National EPSRC XPS User's Service (NEXUS) at Newcastle University, an EPSRC Mid-Range Facility. J F Portoles is grateful for the support of the Newcastle/Durham EPSRC Knowledge Transfer Account (KTA). This work is dedicated to Mr Sydney Cumpson (1931-2010), a former president of the North East region of the Institute of British Foundrymen, who would have appreciated both the beauty and metallurgy of these excellent castings.