Palladium Pd

Discovery

In 1802 William Hyde Wollaston dissolved South American platinum ore in aqua regia, separated out the platinum and recovered a new metal from the remaining solution.

Rather than publishing straight away, he arranged in 1803 for samples to be sold anonymously through a London shop as a "new silver". The chemist Richard Chenevix bought some and argued that it was merely an alloy of platinum and mercury, and a public dispute followed.

Wollaston revealed himself as the discoverer in 1805 and formally described the metal's properties. The controversy faded, and palladium was accepted as a genuine element.

Origin of the name

The element is named after the asteroid Pallas, discovered in 1802, which in turn honours Pallas Athena, the Greek goddess of wisdom. Naming elements after newly found celestial bodies was fashionable at the time. The symbol is Pd.

Main uses

• Catalytic converters: palladium is the main metal used to oxidise carbon monoxide and hydrocarbons in the exhaust of petrol vehicles.
• Organic synthesis: palladium-catalysed cross-coupling reactions are essential for making medicines, agrochemicals and display materials. Richard Heck, Ei-ichi Negishi and Akira Suzuki shared the 2010 Nobel Prize in Chemistry for developing them.
• Electronics: palladium is used in electrodes of multilayer ceramic capacitors and in connector plating.
• Dentistry and jewellery: it goes into dental alloys, white gold and palladium jewellery.
• Hydrogen purification: palladium membranes let only hydrogen pass through, producing very pure hydrogen.

Isotopes

Natural palladium has six stable isotopes, palladium-102, -104, -105, -106, -108 and -110, with palladium-106 the most abundant. Palladium-107, a fission product with a half-life of about 6.5 million years, is also used to study the timing of events in the early solar system through meteorites. Palladium-103, with a half-life of about 17 days, is used in brachytherapy seeds implanted directly into tumours such as prostate cancer.

In everyday life

Most palladium comes from Russia and South Africa, often as a by-product of nickel and platinum mining. Demand from the car industry makes its price volatile, and at times it has traded above gold.

The metal is low in toxicity and resists corrosion, though a small number of people are allergic to palladium alloys. Phones and laptops contain small amounts, making palladium an important target of "urban mining" from electronic waste.

In 1989 a claim of room-temperature "cold fusion" using palladium electrodes caused a worldwide sensation, but other laboratories could not reproduce it and the scientific community did not accept it.