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Stability of Reference Masses VIII: X-ray Fluorescence (XRF) as a Noncontact, Nondestructive Measurement Method for Trace Mercury Contamination of Platinum-Group Metal Surfaces

Lookup NU author(s): Professor Peter Cumpson, Dr Naoko Sano



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


We apply X-ray Fluorescence (XRF) to the assessment of contamination on mass standard surfaces for the first time. XRF has a sampling depth suitable for detection of mercury contamination that we previously conjectured would diffuse into surfaces of platinum and platinum-iridium prototypes along defects and grain-boundaries introduced by polishing. XRF shows mercury contamination on a 19th century platinum reference weight of 0.96±0.19µg/cm2, equivalent to around 70µg on a Pt-10%Ir prototype kilogram, confirming that this diffusion into the surface does take place. The mass of contamination does not reach a limit, but continues to increase as the square-root of time since manufacture. We review the implications of mercury accumulation for the study of the stability of platinum-iridium standard weights, in particular the kilogram prototypes that still stand at the heart of the SI, and look at the implications after redefinition of the kilogram when stable transfer standards and stable medium-term storage will be needed.

Publication metadata

Author(s): Cumpson PJ, Li LW, Sano N

Publication type: Article

Publication status: Published

Journal: International Journal of Modern Engineering Research

Year: 2017

Volume: 7

Issue: 1

Pages: 10-20

Online publication date: 01/01/2017

Acceptance date: 30/12/2016

Date deposited: 30/12/2016

ISSN (electronic): 2249-6645

Publisher: International Journal of Modern Engineering Research