Palladium's Properties, Characteristics, and Applications
A Soft, Rare Metal Valued for Its Catalytic Properties
Palladium is a soft, rare, silvery-white metal that is valued for its catalytic properties and shares many of the characteristics common to the platinum group metal (PGM), such as a relatively high melting point and high density. Although high for a metal, palladium's melting point and density are the lowest of the PGMs.
- Atomic Symbol: Pd
- Atomic Number: 46
- Element Category: Transition metal
- Density: 12.02 g/cm³
- Melting Point: 2830 F (1554 C)
- Boiling Point: 5365 F (2963 C)
- Moh's Hardness: 4.75
Palladium, much like platinum, is very resistant to oxidation and corrosion and has excellent catalytic properties. This is mainly due to the fact that palladium has an abnormal - and astounding - ability to absorb hydrogen gas at a rate of 900 times its own volume. Soft and ductile when annealed, palladium increases with strength and hardness when cold annealed. Palladium is also chemically stable and conductive, making it useful for applications in the electronics industry.
In 1803, William Hyde Wollaston was able to isolate palladium from other PGMs by dissolving platinum ore in aqua regia (hydrochloric and nitric acid) mixture along with ammonium chloride and iron.
One of the first unique applications for palladium, which still continues, was in developing photographic prints. The process, known as 'platinotype', which can use either platinum or palladium, was used as early as the late 18th century.
But palladium, like all PGMs, was inhibited by its rarity and high price. This began to change after the discovery of large stores of the metals were discovered in South Africa in the 1920s and Canada in the 1930s. Not long after this, palladium and platinum began to be used in dental alloys.
By the 1960s, research into platinum and palladium's catalytic properties were resulting in new applications in chemical processing, including polyester production and fuel cracking.
The biggest breakthrough for palladium, however, came in the 1970s when automobile emission standards were implemented in the USA. The demand for palladium increased dramatically. Palladium's ability to absorb carbon monoxide and purify hydrogen made it integral to automobile catalytic converters.
The growing interest in palladium as an investment tool has also led to exchange-traded funds, which are backed by physical palladium, being traded on the London and New York Stock Exchanges. Palladium futures are traded on the New York Mercantile Exchange and palladium bullion is also one of only four metals to have an ISO currency code (the others are gold, silver, and platinum).
Palladium is always found alongside other PGMs. PMGs naturally occur in placer deposits found in rocks such as dunite, chromite, and norite. In South Africa's Bushveld complex and a limited number of other ore bodies, PGMs occur in sufficient quantities so as to make it economical to exclusively extract these metals; whereas, at Russia's Norilsk and Canada's Sudbury deposits palladium and other PGMs are extracted as by-products of nickel and copper.
Palladium-containing ores are first crushed and immersed in a reagent containing water; a process known as 'froth flotation'.
Global sales of palladium were estimated to be around 300,000kgs (660,000lbs) in 2010. Autocatalysts are the largest application for the metal, accounting for an estimated 57% of palladium use in 2010.
Other major end-uses for palladium include (approximate percentage global use):
- electronics sector (15%)
- investments (11%)
- jewelry (6.5%)
- dental alloys (6%)
- chemicals (4%).
Some estimate the number of operational automobiles worldwide to be around 450 million. Increasingly stringent emissions controls rely on autocatalysts to reduce carbon monoxide, sulfur dioxide, and hydrocarbons. Palladium plays a crucial role in this process by oxidizing carbon before it is exhausted.
Palladium is primarily used in electronics within multi-layer ceramic capacitors (MLCC), which helps to control the flow of current to various parts of a circuit by storing and releasing charge as required. MLCCs are often made using palladium or an alloy of palladium and silver. Smaller quantities of palladium are used in hybrid integrated circuits and as a plating material.
The use of palladium in the dental industry is a relatively new phenomenon and tends to fluctuate depending on the relative price of gold, platinum, and palladium. Palladium is alloyed with gold or silver, copper and zinc to form dental inlays, crowns, and bridges. The inclusion of PGMs is to increase strength and durability while remaining malleable.
Palladium can also act as an economical substitute for platinum in catalysts that are used to produce a variety of chemicals, in particular, paints, adhesives, fibers, and coatings. Palladium catchment gauzes, which consist of a fine wire mesh, filter gas flows and are used to make nitric acid.
Other uses for palladium are found in:
- Fuel Cells (hydrogen absorption)
- Ethanol fuel production (Wacker Process)
- Oil Refining (catalytic reforming and hydroprocessing)
- Polyester (in the production of purified terephthalic acid, PTA)
- Photography (Platinotype Process)
- Water treatment
- Medicine (palladium -103)