Iridium is the chemical element with atomic number 77. A very hard,
brittle, silvery-white transition metal of the platinum family, iridium
is the second densest element and is the most corrosion-resistant
metal, even at temperatures as high as 2000 °C. Although only certain
molten salts and halogens are corrosive to solid iridium, finely
divided iridium dust is much more reactive and can even be flammable.
Iridium was discovered in 1803 by Smithson Tennant among insoluble
impurities in natural platinum from South America. It is one of the
rarest elements in the Earth's crust, with annual production and
consumption of only three tonnes. However, iridium does find a number
of specialized industrial and scientific applications. Iridium is
employed when high corrosion resistance and high temperatures are
needed, as in spark plugs, crucibles for recrystallization of
semiconductors at high temperatures, electrodes for the production of
chlorine in the chloralkali process, and radioisotope thermoelectric
generators used in unmanned spacecraft. Iridium is found in meteorites
with an abundance much higher than its average abundance in the Earth's
crust. It is thought that due to the high density and siderophilic
("iron-loving") character of iridium, most of the iridium on Earth is
found in the inner core of the planet.
Read the rest of this article:
<http://en.wikipedia.org/wiki/Iridium>
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Today's selected anniversaries:
1734:
A black slave known as Marie-Joseph Angélique, after having been
convicted of setting the fire that destroyed much of Montreal, was
tortured and then hanged in New France.
<http://en.wikipedia.org/wiki/Marie-Joseph_Ang%C3%A9lique>
1813:
Peninsular War: The Marquess of Wellington's combined British,
Portuguese, and Spanish allied army defeated the French near Vitoria,
Spain.
<http://en.wikipedia.org/wiki/Battle_of_Vitoria>
1826:
Greek War of Independence: A combined Egyptian and Ottoman army began
their invasion of the Mani Peninsula, but they were initially held off
by the Maniots at the fortifications of Vergas.
<http://en.wikipedia.org/wiki/Ottoman%E2%80%93Egyptian_Invasion_of_Mani>
1948:
The Manchester Small-Scale Experimental Machine , the world's first
stored-program computer, ran its first computer program.
<http://en.wikipedia.org/wiki/Manchester_Small-Scale_Experimental_Machine>
1973:
The U.S. Supreme Court delivered its decision in the landmark case
Miller v. California, establishing the "Miller test" for determining
what is obscene material.
<http://en.wikipedia.org/wiki/Miller_v._California>
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Wiktionary's word of the day:
spinet (n):
A short, compact harpsichord
<http://en.wiktionary.org/wiki/spinet>
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Wikiquote quote of the day:
Every natural fact is a symbol of some spiritual fact.
--Ralph Waldo Emerson
<http://en.wikiquote.org/wiki/Ralph_Waldo_Emerson>
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