Stability of XSH Alacrite mass standards: study of the effect of the BIPM cleaning/washing method

摘要

A gravimetric study of the effect of cleaning XSH Alacrite standards with ethanol and isopropanol showed considerable short-term mass instability after this process, due primarily to the sorption of atmospheric gases and cleaning solvents. A new cleaning method was thus required. The first method investigated is that used currently by the Bureau International des Poids et Mesures (BIPM) for cleaning/washing iridium-platinum standards. Initial results of a gravimetric study and an X-ray photoelectron spectroscopy (XPS) analysis show that this method has a greater cleaning power than that using alcohols and that there is no short-term instability. It was nevertheless found that during the first year following this type of cleaning, the relative mass of the standard increased by about 5 × 10↑(-9) and the reproducibility of the cleaning/washing procedure could not be ensured to better than 4 × 10↑(-9).