For helicopter sparkplugs.
| Atomic Number: | 77 | Atomic Symbol: | Ir |
| Atomic Weight: | 192.22 | Electron Configuration: | 2-8-18-32-15-2 |
| Shells: | 2,8,18,32,15,2 | Filling Orbital: | 5d7 |
| Melting Point: | 2410oC | Boiling Point: | 4527oC |
| Description: | Heavy brittle white transition metal |
| Uses: | Used for high temp. alloys and pressure bearings.
Very hard and
resists corrosion better than any other |
History
(L. iris, rainbow) Tennant discovered iridium in 1803 in the
residue left when crude platinum is dissolved by aqua regia. The name iridium
is appropriate becayse its salts are highly colored.
Properties
Iridium, a metal of the platinum family, is white, similar to
platinum, but with a slight yellowish cast. Because iridium
is very hard and brittle, it is hard to machine, form, or work.
It is the most corrosion-resistant metal known, and was used in making the
standard meter bar of Paris, which is a 90 percent platinum and 10 percent
iridium alloy. This meter bar was replaced in 1960 as a fundamental unit of
length (see under Krypton).
Iridium is not attacked by any of the acids nor by aqua regia, but is
attacked by molten salts, such as NaCl and NaCN. The specific gravity of iridium
is only very slightly lower than osmium, which is generally credited as the
heaviest known element. Calculations of the densities of iridium and osmium from
the space lattices give values of 22.65 and 22.61 g/cm^3, respectively. These
values may be more reliable than actual physical measurements. At present,
therefore, we know that either iridium or osmium is the densest known element,
but the data do not yet allow selection between the two.
Sources
Iridium occurs uncombined in nature with platinum and other
metals of this family in alluvial deposits. It is recovered as a by-product from
the nickel mining industry.
Uses
Although its principal use is as a hardening agent for platinum,
iridium is also used to make crucibles and devices requiring high temperatures.
It is also used for electrical contacts.
The element forms an alloy with osmium which is used for
tipping pens and compass bearings.
Costs
Iridium costs about $500/troy ounce (as of 1990).