Typical alloy proportions are 90:10 or 70:30 (Pt:Ir). These have the chemical stability of platinum, but increased hardness. The
Vickers hardness of pure platinum is 56 HV while platinum with 50% of iridium can reach over 500 HV.[1][2] This improved hardness has also been considered as beneficial for use in platinum
jewellery, particularly watch cases.
Owing to their high cost, these alloys are rarely used. They have been used for
spinnerets in the manufacture of
synthetic fibres.[3]
The other extremely widespread use for Pt/Ir alloy is fabrication of metal microelectrodes for electrical stimulation of nervous tissue[4] and electrophysiological recordings.[5][6][7] Pt/Ir alloy has an optimal combination of mechanical and electrochemical properties for this application. Pure iridium is very difficult to pull into small diameter wires; at the same time, platinum has a low
Young's modulus which makes pure platinum wires bend too easily during insertion into nervous tissue. Additionally, platinum–iridium alloys containing oxides of both metals can be electro-deposited onto the surface of microelectrodes.[8]
^Egorova, R. V.; Korotkov, B. V.; Yaroshchuk, E. G.; Mirkus, K. A.; Dorofeev N. A.; Serkov, A. T. (1979). "Spinnerets for viscose rayon cord yarn". Fibre Chemistry. 10 (4): 377–378.
doi:
10.1007/BF00543390.
S2CID135705244.
^Cogan, SF; Troyk, PR; Ehrlich, J; Plante, TD (September 2005). "In vitro comparison of the charge-injection limits of activated iridium oxide (AIROF) and platinum-iridium microelectrodes". IEEE Transactions on Bio-Medical Engineering. 52 (9): 1612–4.
doi:
10.1109/tbme.2005.851503.
PMID16189975.
S2CID19297044.
^Stein, Richard B.; Charles, Dean; Gordon, Tessa; Hoffer, Joaquin-Andres; Jhamandas, Jack (November 1978). "Impedance Properties of Metal Electrodes for Chronic Recording from Mammalian Nerves". IEEE Transactions on Biomedical Engineering. BME-25 (6): 532–537.
doi:
10.1109/TBME.1978.326287.
PMID744599.
S2CID7973265.
^Malagodi, Mark S.; Horch, Kenneth W.; Schoenberg, Andrew A. (July 1989). "An intrafascicular electrode for recording of action potentials in peripheral nerves". Annals of Biomedical Engineering. 17 (4): 397–410.
doi:
10.1007/BF02368058.
PMID2774314.
S2CID23762187.