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The international prototype of the kilogram (IPK) is an artifact standard of platinum–iridium alloy that was defined as having a mass of exactly one kilogram. Platinum–iridium alloys are alloys of the platinum group precious metals platinum and iridium. Typical alloy proportions are 90:10 or 70:30 (Pt:Ir).
The only three verifications occurred in 1889, 1948, and 1989. For instance, the US owns five 90% platinum / 10% iridium (Pt‑10Ir) kilogram standards, two of which, K4 and K20, are from the original batch of 40 replicas distributed in 1884. [Note 4] The K20 prototype was designated as the primary national standard of mass for the US. Both of ...
Metallic iridium is found with platinum and other platinum group metals in alluvial deposits. [23] Naturally occurring iridium alloys include osmiridium and iridosmine, both of which are mixtures of iridium and osmium. It is recovered commercially as a by-product from nickel mining and processing. [20]
A member of the platinum group metals, iridium is white, resembling platinum, but with a slight yellowish cast. Because of its hardness, brittleness, and very high melting point , solid iridium is difficult to machine, form, or work; thus powder metallurgy is commonly employed instead. [ 12 ]
For more than a century, the kilogram was defined as the mass of a chunk of platinum-iridium alloy housed at the Bureau of Weights and Measures in France.
This page was last edited on 16 November 2024, at 12:16 (UTC).; Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may apply.
The unit of length is the metre, defined by the distance, at 0°, between the axes of the two central lines marked on the bar of platinum–iridium kept at the Bureau International des Poids et Mesures and declared Prototype of the metre by the 1st Conférence Générale des Poids et Mesures, this bar being subject to standard atmospheric ...
Platinum is a chemical element; it has symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish platina, a diminutive of plata "silver". [7] [8] Platinum is a member of the platinum group of elements and group 10 of the periodic table of ...