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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).
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]
Iridium is extremely brittle, to the point of being hard to weld because the heat-affected zone cracks, but it can be made more ductile by addition of small quantities of titanium and zirconium (0.2% of each apparently works well). [19] The Vickers hardness of pure platinum is 56 HV, whereas platinum with 50% of iridium can reach over 500 HV ...
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 ...
Gold, platinum, and the other platinum group metals (ruthenium, rhodium, palladium, osmium, iridium) are most often so classified. Silver, copper, and mercury are sometimes included as noble metals, but each of these usually occurs in nature combined with sulfur.
Other precious metals include the platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum, of which platinum is the most widely traded. [1] The demand for precious metals is driven not only by their practical use but also by their role as investments and a store of value. Historically, precious metals have commanded ...
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 ...
Iridium is mainly used as a hardening agent for platinum alloys. Iridium is the most corrosion-resistant metal known as it is not attacked by acids, including aqua regia. In the presence of oxygen, it reacts with cyanide salts. Traditional oxidants also react, including the halogens and oxygen at higher temperatures.