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English Dictionary: iridium by the DICT Development Group
3 results for iridium
From WordNet (r) 3.0 (2006) [wn]:
  1. a heavy brittle metallic element of the platinum group; used in alloys; occurs in natural alloys with platinum or osmium
    Synonym(s): iridium, Ir, atomic number 77
From Webster's Revised Unabridged Dictionary (1913) [web1913]:
   Iridium \I*rid"i*um\, n. [NL., fr. L. iris, iridis, the rainbow.
      So called from the iridescence of some of its solutions. See
      {Iris}.] (Chem.)
      A rare metallic element, of the same group as platinum, which
      it much resembles, being silver-white, but harder, and
      brittle, and indifferent to most corrosive agents. With the
      exception of osmium, it is the heaviest substance known, its
      specific gravity being 22.4. Symbol Ir. Atomic weight 192.5.
      Note: Iridium usually occurs as a native alloy with osmium
               (iridosmine or osmiridium), which may occur alone or
               with platinum. Iridium, as an alloy with platinum, is
               used in bushing the vents of heavy ordnance. It is also
               used for the points of gold pens, and in a finely
               powdered condition (iridium black), for painting
               porcelain black.

From The Elements (22Oct97) [elements]:
   Symbol: Ir
   Atomic number: 77
   Atomic weight: 192.217
   Very hard and brittle, silvery metallic transition element. It has a
   yellowish cast to it. Salts of iridium are highly colored. It is the
   most corrosion resistant metal known, not attacked by any acid, but is
   attacked by molten salts. There are two natural isotopes of iridium, and
   4 radioisotopes, the most stable being Ir-192 with a half-life of 73.83
   days. Ir-192 decays into {platinum}, while the other radioisotopes decay
   into {osmium}. Iridium is used in high temperature apparatus, electrical
   contacts, and as a hardening agent for platinum. Discovered in 1803 by
   Smithson Tennant in England. The name comes from the Greek word iris, which
   means rainbow. Iridium metal is generally non-toxic due to its relative
   unreactivity, but iridium compounds should be considered highly toxic.
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