Global Blueprints for Reference
In a presentation given by Peter Saunders and Farzana Masouleh of the Measurement Standards Laboratory (MSL) of New Zealand on the 20th of May, 2019, the redefinition of the International System of Units (SI) was discussed. The event, filmed at Unleash Space, Faculty of Engineering, Auckland University, was recorded and later published by Referencing Hub media.
The presentation shed light on the creation of the international prototype kilogram and the international prototype metre, both made from a platinum-iridium alloy. This alloy, typically 90% platinum and 10% iridium, was chosen for its greater stability, hardness, resistance to corrosion, and less porosity compared to pure platinum alone.
One of the key reasons for using this alloy lies in its increased hardness and wear resistance. Pure platinum, while highly resistant to many chemicals, is relatively soft and can be scratched or deformed more easily. The addition of iridium, a harder and more durable metal, produces an alloy that maintains precise dimensions and mass over long periods despite handling and environmental exposure.
The iridium also improves the alloy's chemical stability. While platinum can still be attacked by certain substances and can absorb gases like hydrogen, the iridium improves resistance to chemical attack and oxidation, making the alloy more inert and stable under various conditions.
Moreover, the platinum-iridium alloy is less porous than pure platinum, meaning it absorbs fewer atmospheric contaminants like gases and moisture. This reduces mass changes over time and improves long-term reproducibility of the standard.
The alloy's resistance to corrosion and wear is another significant factor. This alloy withstands mechanical wear and corrosion significantly better, preserving the integrity of the prototypes that define units of measure internationally.
The international prototype kilogram and the international prototype metre, created in 1875, are still in the same vault at the Bureau International des Poids et Mesures (BIPM) today. Thirty length bars and forty standard masses were produced, with one length bar and one mass being randomly selected to become the international prototype kilogram and the international prototype metre. The remaining 30 length bars and 40 standard masses were distributed amongst the member states of the Metric Treaty.
The rights for the video belong to the Measurement Standards Laboratory of New Zealand. The video was filmed at Auckland University, aiming to share the story of metrology development and the importance of these fundamental units underpinning global metrology.
References: [1] NPL. (n.d.). The International Prototype Kilogram. Retrieved from https://www.npl.co.uk/our-science/international-prototypes/the-international-prototype-kilogram [4] NIST. (n.d.). International Prototype Kilogram. Retrieved from https://www.nist.gov/pml/time-and-frequency-division/international-prototype-kilogram-ipk
The presentation at Unleash Space, Faculty of Engineering, Auckland University, on the 20th of May, 2019, highlighted theuse of platinum-iridium alloy in the creation of the international prototype kilogram and metre, citing its stability, hardness, resistance to corrosion, and less porosity as key factors. This technology, with its improved chemical stability and reduced mass changes over time, is essential in maintaining precise measurements for medical-conditions and scientific research.
