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5 definitions found

From: DICT.TW English-Chinese Dictionary 英漢字典

 irid·i·um /ɪˈrɪdiəm/

From: DICT.TW English-Chinese Medical Dictionary 英漢醫學字典

 irid·i·um /ɪrˈɪdɪəm/ 名詞

From: Webster's Revised Unabridged Dictionary (1913)

 i·rid·i·um n.  Chem. A rare metallic element of atomic number 77, of the same group as platinum, which it much resembles, being silver-white and indifferent to most corrosive agents, but harder, more brittle, and with a higher melting temperature (2410° C, versus platinum 1772° C).  With the exception of osmium, it is the heaviest substance known, its specific gravity being 22.4. Symbol Ir. Atomic weight 192.22.
 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: WordNet (r) 2.0

      n : a heavy brittle metallic element of the platinum group; used
          in alloys; occurs in natural alloys with platinum or
          osmium [syn: Ir, atomic number 77]

From: Elements database 20001107

 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.