|
Palladium, together with rhodium, ruthenium,
osmium, iridium, and platinum form a group of elements referred to as the
platinum group metals (PGM).
Palladium is a lustrous silver-white metal. It has a face-centered cubic
crystalline structure, at ordinary temperatures it is strongly resistant to corrosion in air and
to the action of acids. It is attacked by hot
acids, and it dissolves in aqua regia. It forms many compounds and
several complex salts. Palladium has a great ability to absorb hydrogen
(up to 900 times its own volume).
Applications
Because of its corrosion resistance, a major use of palladium is in
alloys used in low voltage electrical contacts. When it is finely
divided, palladium forms a good catalyst and is used to speed up
hydrogenation and dehydrogenation reactions.
Palladium is used extensively in jewelry-making in certain alloys
called “white gold.” It may be alloyed with platinum or substituted for
it. It is used in watch bearings, springs, and balance wheels and also
for mirrors in scientific instruments.
In 1990, most catalytic converters relied on platinum to reduce
emissions from car exhausts but, while this metal is still important,
palladium is now the main ingredient because this is even more efficient
at removing unburnt and partially burnt hydrcarbons from the fuel.
Palladium is nowadays more and more used in electrical appliances
such as wide screen televisions, computers and mobile phones, in the
form of tiny multi-layer ceramic capacitors, of which more than 400
billion are made each year.
For use in dentistry it is alloyed with silver, gold, and copper.
Palladium salts are used in electroplating.
Palladium in the environment
Specimen of uncombined palladium are found in Brazil, and there are
some minerals rich in palladium, but most of it is extracted as a
by-product form nickel refining.
Palladium is found as the free
metal associated with platinum and other platinum group metals in
Australia, Brazil, Russia, Ethiopia, and North and South America, as
well as with nickel and copper deposits (from which it is recovered
commercially) in Canada and South Africa.
Palladium is regarded as of low toxicity,
being poorly adsorbed by the body when ingested.
It may cause skin, eye or
respiratory tract irritation, may cause skin sensitisation.
Liquid may cause burns to skin
and eyes. If swallowed, do not induce vomiting, if conscious give water,
milk... In case of contact, flush eyes or skin with plenty of water.
Palladium compounds are
encountered relatively rarely by most people. All palladium compounds
should be regarded as highly toxic and as carcinogenic. Palladium
chloride is toxic, harmful if swallowed, inhaled or absorbed through the
skin. It causes bone marrow, liver and kidney damage in laboratory
animals. Irritant.
However palladium chloride was formerly prescribed as a treatment
for tuberculosis at the rate of 0.065 g per day (approximately 1 mg kg-1)
without too many bad side effects.
Do
not allow material to be released to the environment without proper
environmental permits.
Palladium has little environmental impact. It is present at low levels
in some soils, and the leaves of trees have been found to containg 0.4
ppm. Some plants, such as the water hyacinth, are killed by low levels
of palladium salts but most plants tolerate it, although tests indicate
that their growth is affected at levels above 3 ppm.
Back to chart
periodic table elements.
|
