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.
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