Page 309 - Academic Press Encyclopedia of Physical Science and Technology 3rd InOrganic Chemistry

P1: GPA Final Pages Qu: 00, 00, 00, 00
Encyclopedia of Physical Science and Technology EN010b-481 July 14, 2001 18:45

Noble Metals (Chemistry)

Hubert Schmidbaur John L. Cihonski
Technical University of Munich, Garching Engelhard Corporation

I. Occurrence, Properties, and Chemistry
II. Applications
III. Toxicity

GLOSSARY face has been clad mechanically with a coating of gold
or other metal. Rolled gold products carry thinner films
Black Dull black metallic powder obtained by reduction of gold than do gold filled products.
and precipitation from solutions or by condensation Sponge Metal in porous form, usually prepared by reduc-
from the vapor phase. tion without sintering.
Dor´e metal Silver–gold alloy usually derived from noble Sweeps Noble metal wastes from used items or produc-
metal refining. tion scrap.
Filled Product with a gold or gold alloy coating mechan-
ically clad to the surface.
Fineness Term used to define the degree of purity of gold THE NOBLE METALS, or precious metals, consist of
or silver. Fineness is given as parts of the metal con- gold, silver, and the platinum group metals (PGM)—
cerned per 1000 parts by weight. platinum, palladium, iridium, rhodium, osmium, and
Karatage K, term to express the degree of purity of gold. ruthenium. These metals are known for their stability in
The karatage is expressed as pads of gold in 24 pads of corrosive environments, physical beauty, and unique phys-
alloy by weight. Pure gold is 24 karat or 1000 fine. ical and chemical properties. They command a premium
Mud Impure noble metals concentrate produced by re- price because of their low abundance in nature. The noble
moval of base metal from a predominately base metal metals are used in many applications with great success
anode. and often with few, if any, substitutable materials.
Native Term used to describe a metal found as such in
nature in relatively pure form. I. OCCURRENCE, PROPERTIES,
Placer Alluvial,marine,orglacialdepositcontainingpar- AND CHEMISTRY
ticles of valuable minerals, especially gold.
Platinum group metals (PGM) Second and third A. Natural Occurrence
row Group VIII transition metals. These metals—
1. Gold
platinum, palladium, iridium, rhodium, osmium, and
ruthenium—are usually found together in nature. Gold is found in about 3.5 ppb in the earth’s crust, of-
Rolled Rolled gold or other metal product means the sur- ten as 75–90% pure native gold that has been released by

463