| slovo | definícia |
iridium
(encz) | iridium,iridium [chem.] |
iridium
(czen) | iridium,iridium[chem.] |
iridium
(gcide) | iridium \i*rid"i*um\ ([-i]*r[i^]d"[i^]*[u^]m), 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 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[deg] C, versus platinum 1772[deg] C). With the
exception of osmium, it is the heaviest substance known, its
specific gravity being 22.4. Symbol Ir. Atomic weight 192.22.
[1913 Webster +PJC]
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.
[1913 Webster] |
iridium
(wn) | iridium
n 1: a heavy brittle metallic element of the platinum group;
used in alloys; occurs in natural alloys with platinum or
osmium [syn: iridium, Ir, atomic number 77] |
iridium
(elements) | iridium
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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| | podobné slovo | definícia |
osmiridium
(encz) | osmiridium, n: |
Platiniridium
(gcide) | Platiniridium \Plat`i*ni*rid"i*um\, n. (Chem. & Min.)
A natural alloy of platinum and iridium occurring in grayish
metallic rounded or cubical grains with platinum.
[1913 Webster] |
osmiridium
(wn) | osmiridium
n 1: a hard and corrosion resistant mineral that is a natural
alloy of osmium and iridium (usually containing small
amounts of rhodium and platinum); used in needles and pen
nibs etc. [syn: osmiridium, iridosmine] |
platinum-iridium
(foldoc) | platinum-iridium
A standard, against which all others of the same
category are measured. Usage: silly.
The notion is that one of whatever it is has actually been
cast in platinum-iridium alloy and placed in the vault beside
the Standard Kilogram at the International Bureau of Weights
and Measures near Paris, as the bar defining the standard
metre once was.
"This garbage collection algorithm has been tested against
the platinum-iridium cons cell in Paris."
Compare golden.
[Jargon File]
(1997-02-20)
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platinum-iridium
(jargon) | platinum-iridium
adj.
Standard, against which all others of the same category are measured.
Usage: silly. The notion is that one of whatever it is has actually been
cast in platinum-iridium alloy and placed in the vault beside the Standard
Kilogram at the International Bureau of Weights and Measures near Paris.
(From 1889 to 1960, the meter was defined to be the distance between two
scratches in a platinum-iridium bar kept in that same vault — this replaced
an earlier definition as 10^-7 times the distance between the North Pole
and the Equator along a meridian through Paris; unfortunately, this had
been based on an inexact value of the circumference of the Earth. From 1960
to 1984 it was defined to be 1650763.73 wavelengths of the orange-red line
of krypton-86 propagating in a vacuum. It is now defined as the length of
the path traveled by light in a vacuum in the time interval of 1/
299,792,458 of a second. The kilogram is now the only unit of measure
officially defined in terms of a unique artifact. But this will have to
change; in 2003 it was revealed that the reference kilogram has been
shedding mass over time, and is down by 50 micrograms.) “This
garbage-collection algorithm has been tested against the platinum-iridium
cons cell in Paris.” Compare golden.
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