Platinum-iridium alloy is a binary platinum-based alloy containing iridium. It is a continuous solid solution at high temperature and decompose in solid phase at 975 ~ 700℃ after slow cooling, but the phase equilibrium process is very slow. Iridium is volatile and oxidized, which significantly improves the corrosion resistance of platinum. There are PTLRL0, PTLR17.5, PTLR25, PTLR30 alloys, with high hardness, high melting point, high corrosion resistance and low contact resistance. The chemical corrosion rate is 58% of that of pure platinum, and the oxidation loss is 2.8mg/g. It is a classic electrical contact material, used for ignition contacts of aero engines, high sensitivity relays and electrical contacts of micromotors. Potentiometers and conducting rings and brushes for precision sensors such as aircraft, missiles and gyroscopes.
Pt-Ir alloy:platinum alloy consisting of platinum as a base and iridium added to it. In the early years, it was believed that the solution was completely solid within the range of all components, and it was confirmed that the high temperature region was a continuous solid solution. Spinodal decomposition occurred below 975℃ : α1=α2+α3, forming an amplitude modulated structure, which expanded to 7% ~ 99%(atomic fraction) iridium wide region at 700℃.
Natural platinum-iridium alloys are often associated with platinum ore and exist in granular form. In 1838, A. Gaudin synthesized PtiR1O alloy pellets for the first time. Iridium was initially considered a harmful element. Extensive research conducted in the mid-to-late 19th century dispelled this misconception. In 1874, PtiR1O alloy ingots weighing 250kg with uniform composition were cast in Paris as the standard material for the manufacture of international meters and kilogram weights. The prototype weights underwent ultra-high pressure tests before being accepted by the International Commission of Metroids. The density values of 11 standard kilogram weights ranged from 21.548 to 21.552g/cm. The standard resistance of platinum-iridium alloy has withstood 67 years of careful examination, and its resistance value has little change.
