ELEMENT OF THE MONTH
Each month we will explore elements of interest from the periodic table, with a brief history of discovery and development, and a review of uses and applications.
PALLADIUM – ATOMIC NUMBER: 46 – CHEMICAL SYMBOL: PD
Palladium is a relatively hard, silvery-white metallic element, in the platinum group of the periodic table that includes platinum, rhodium, ruthenium, iridium and osmium. It has the lowest density and melting point of elements in that group.
It was discovered in 1803 by William Hyde Wollaston as a residue that remained after dissolving platinum in aqua-regia (a 3:1 molar ratio of hydrochloric acid and nitric acid). Its name was derived from the asteroid Pallas, which itself was named after the Greek goddess of wisdom.
Palladium is corrosion resistant and very ductile at normal temperatures, making it easily worked into jewellery. In its pure or alloyed state, it presents no biological issues and is non-toxic.
The top three producers of palladium worldwide are South Africa, Russia, and Zimbabwe, and its value has increased dramatically in response to an anticipated reduction in supply due to trade and financial sanctions against Russia. However, palladium can be substituted with platinum in its major use as a catalyst.
Palladium is mostly produced as a by-product of nickel refining.
Most palladium is used in automotive catalytic converters that change harmful compounds such as hydrocarbons, carbon monoxide, and nitrogen oxide, into water, carbon dioxide, and nitrogen.
It is also used to produce the best white gold alloys.
WHERE IS PALLADIUM USED?
As a Pure Element
Pure palladium is utilised in electroplated coatings where its corrosion resistance makes for reliable low voltage electrical and electronic contacts. However, its high cost may limit its use to high integrity applications.
As an Alloy
Palladium is alloyed with gold to produce 18 karat white gold for jewellery.
Hallmarking of high palladium content jewellery alloys began in 2009. Typical alloys consist of 95% Pd with 5% other metals such as ruthenium, cobalt, copper, silver, gallium, or indium, either as binary alloys or as a combination of several of these elements.
Electroplated palladium-nickel alloy with a ratio of 80:20 is used in connector manufacture, for wear-resistant electrical or electronic connector pins, and is often over-plated with a very thin layer of gold.
In the manufacture of printed circuit boards, a thin (0.1um) electroless palladium-phosphorous layer is used as a barrier coating to protect the underlying electroless nickel layer from corrosion in the final immersion gold coating of the ENEPIG process.
An alloy of palladium-silver in the ratio 60:40 is tough and wear-resistant and is used in heavy-duty electrical contacts.
As a Compound
Palladium can absorb hydrogen gas like a sponge with a capacity of up to 900 times its own weight. Common applications are as a catalyst in hydrogenation and de-hydrogenation reactions.
Here are some key parameters for Palladium, quantifiable using instruments from Helmut Fischer GmbH
- Thickness and composition of very thin palladium and palladium-nickel coatings on copper-iron integrated circuit lead-frames, in the range 10 to 50 nanometres, measurable with a non-destructive XRF based instrument such as the Fischerscope XDV-SDD
- Composition analysis of Palladium based precious metal alloys to verify fineness prior to hallmarking, using an XRF based instrument such as the XAN 250
- ENIG and ENEPIG thickness testing in PCB manufacture, automated using XRF pattern recognition technology
- Palladium, nickel, cobalt, and other metal concentrations in electroplating or other solutions from grams/litre down to low ppm, using a range of XRF based instruments such as Fischerscope XDAL-SDD