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» وظائف بالكويت مسابقة 2011 2012 للعمل بوزارة التربيه فى جميع التخصصات
History platina: silver , Stylish Motorola KRZR Platinum EmptySun Feb 19, 2012 2:15 pm by محمد السعيد الجيوشي

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 History platina: silver , Stylish Motorola KRZR Platinum

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PostSubject: History platina: silver , Stylish Motorola KRZR Platinum   History platina: silver , Stylish Motorola KRZR Platinum EmptySun Dec 26, 2010 2:49 pm

History


(Sp. platina: silver) Discovered in South America by Ulloa in 1735 and by Wood in 1741. The metal was used by pre-Columbian Indians.Sources


Platinum
occurs natively, accompanied by small quantities of iridium, osmium,
palladium, ruthenium, and rhodium, all belonging to the same group of
metals. These are found in the alluvial deposits of the Ural mountains,
of Columbia, and of certain western American states. Sperrylite,
occurring with the nickel-bearing deposits of Sudbury, Ontario, is the
source of a considerable amount of metal.

The large production of nickel makes up for the fact that is only one part of the platinum metals in two million parts of ore.Properties


Platinum
is a beautiful silvery-white metal, when pure, and is malleable and
ductile. It has a coefficient of expansion almost equal to that of
soda-lime-silica glass, and is therefore used to make sealed electrodes
in glass systems. The metal does not oxidize in air at any temperature,
but is corroded by halogens, cyanides, sulfur, and caustic alkalis.

It is insoluble in hydrochloric and nitric acid, but dissolves when they are mixed as aqua regia, forming chloroplatinic acid.Uses


The
metal is extensively used in jewelry, wire, and vessels for laboratory
use, and in many valuable instruments including therocouple elements. It
is also used for electrical contacts, corrosion-resistant apparatus,
and in dentistry.

Platinum-cobalt
alloys have magnetic properties. One such alloy made of 76.7% Pt and
23.3% Co, by weight, is an extremely powerful magnet that offers a B-H
(max) almost twice that of Alnico V. Platinum resistance wires are used
for constructing high-temperature electric furnaces.

The
metal is used for coating missile nose cones, jet engine fuel nozzles,
etc., which must perform reliably at high temperatures for long periods
of time. The metal, like palladium, absorbs large volumes of hydrogen, retaining it at ordinary temperatures but giving it up when heated.

In
the finely divided state platinum is an excellent catalyst, having long
been used in the contact process for producing sulfuric acid. It is
also used as a catalyst in cracking petroleum products. Much interest
exists in using platinum as a catalyst in fuel cells and in
antipollution devices for automobiles.

Platinum
anodes are extensively used in cathodic protection systems for large
ships and ocean-going vessels, pipelines, steel piers, etc. Fine
platinum wire will glow red hot when placed in the vapor of methyl
alcohol. It acts here as a catalyst, converting the alcohol to
formaldehyde. The phenomenon has been used commercially to produce
cigarette lighters and hand warmers. Hydrogen and oxygen explode in the
presence of platinum.
Costs


The
price of platinum has varied widely. More than a century ago platinum
was used to adulterate gold and was worth nearly eight times more than
gold in 1920. The price in January 1990 was about $500/troy oz.

Title Picture: alchemical symbol for platinum
Stylish Motorola KRZR Platinum


History platina: silver , Stylish Motorola KRZR Platinum Motorola-platinum54545587
Looks
like fans of Motorola will be spoiled again with this exclusive
platinum plated phone from Goldstriker. This elegant and super bling
phone will be released on February 21st. $1200.
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