The role of PGMs in modern applications

The six transitional elements that make up the Platinum group metals (PGMs) are used in, or have played a key role in the production of, one-quarter of all manufactured goods. The landscape, and the applications of these materials are explained in this article by Ben Smye, head of growth at materials search engine, MatMatch.

Platinum group metals (PGMs) are often thought of as "exotic". Yet, according to the International Platinum Group Metals Association (IPA), one-quarter of all manufactured goods either contain a PGM or a PGM played a key role in its production. That isn't surprising given that PGMs are the densest known metals. The versatile properties of this unique group of elements are valued in a range of industrial, medical and electronic applications, explains Ben Smye, head of growth at materials search engine Matmatch.

The PGMs are a family of six transitional metal elements that, structurally and chemically, are very similar. They are: platinum, palladium, rhodium, iridium, ruthenium and osmium. Aside from being the densest known materials, PGMs are also highly durable and offer long lifecycles.

All six PGMs are exceptionally rare, costly to produce and expensive to buy. They occur naturally in the same ore bodies and contain the same six elements in varying amounts — predominantly platinum or palladium.

Availability of PGMs

As-mined, platinum group ores contain typically four to five grams per ton of platinum group elements. Demand for PGMs is very high — palladium, for instance, is used in virtually all electronics. So high is this demand that mining alone doesn't produce enough supply, which is why PGMs are often recycled.

Otherwise, they are produced from copper and nickel deposits that contain minor quantities of PGM in the parts per million range. Around 500 tons of PGMs are produced each year. The major producing countries are South Africa and Russia — where they are also mainly found — followed by North America.

Platinum and palladium

Platinum is probably the best known PGM, largely for its use in jewellery making. It is among the densest of the group, along with iridium and osmium, with a high melting point and temperature stability. In fact, platinum is 11 per cent denser than gold and around twice the weight of the same volume of silver or lead. Platinum's stable and rare properties are favoured for electronic devices and applications, and medical uses because of its high biological compatibility.

Platinum is also highly resistant to corrosion oxidation. The element's capabilities as a good oxidation catalyst are the reason behind its popularity in the manufacture of catalytic converters. Indeed, one of the most prominent uses of PGMs is as automotive emission control catalysts — these catalyse nitrogen oxide (NOx) to nitrogen and oxidise carbon monoxide and hydrocarbons. Other automotive applications for platinum include oxygen sensors and spark plugs.

Palladium — a soft, silvery-white metal — is also used in catalytic converters as a substitute for the more expensive platinum. It's known as the most corrosion-resistant pure metal, and can resist salts, oxides and mineral acids but is affected by sodium chloride and sodium cyanide. It also has a high melting point — albeit the lowest of all the PGMs — and a resistance to deformation that makes is very useful for strengthening alloys.

Palladium's unique ability to absorb hydrogen is useful for chemical processes involving hydrogen exchange between two reactants — e.g. to produce the raw materials for synthetic rubber and nylon. Meanwhile, the radioactive isotope of palladium is being tested for the treatment of breast and prostate cancers.

Effective catalysts

Rhodium is another highly active catalyst used in vehicle emission control systems. With a high melting point and temperature stability, rhodium is used to make glass. While it's harder and more difficult to work with than other PGMs, rhodium is favoured in alloy applications for its chemical compounds — this also applies to iridium.

As the rarest and most corrosion-resistant of the PGMs, iridium is also very dense with a high chemical and thermal stability. Like platinum, iridium's biological compatibility suits it to many medical applications, which is why both are used in aural and retinal implants. Iridium is also used to make high-purity crystals for medical, petroleum and security applications.

Ruthenium and osmium are hard and brittle, although with poor resistance to oxidation. Nevertheless, both are valued as alloys additives and, like the other PGMs, have superior catalytic properties. Ruthenium is commonly used as an alloying agent for platinum and palladium. It is relied upon in the electrical and electrochemical industries for its conductive properties and durability.

Osmium is the densest and hardest of the group, overall, and is often alloyed with other PGMs such as platinum and iridium. It's also an excellent conductor of electricity and an effective oxidation catalyst. Common uses for osmium include in fuel cells and for forensic science applications.

Catalytic converters

While the extensive benefits of PGMs as catalysts are clear — for instance, in the petroleum industry — they are not limited to this role. Other uses include as pacemakers; medical implants (this particularly applies to iridium and platinum); staining for fingerprints; DNA applications (osmium); nitric acid production (rhodium); and in chemicals such as cleaning liquids, adhesives and paints (ruthenium).

Given their popularity in catalytic converters, it's not surprising that the growth of the PGM market will be driven primarily by automotive production and consumption — e.g. in Europe and Asia-Pacific (APAC). Mining is another big growth area. PGMs are one of the emerging markets within the mining sector, anticipated to grow at a CAGR of 3.26% between 2019 and 2026.

Finally, beyond the properties of the elements themselves, environmental concerns will majorly drive demand for PGMs. As a vital component of automotive catalytic converters, they will prove critical in reducing vehicle carbon emissions — especially with more stringent government rules in this regard. It's clear that demand will only continue to grow for these unique and "exotic" metals.

Design engineers can use Matmatch's free online database to explore the unique chemical and physical properties of PGMs, and match the right materials and applications. The database features all the PGMs with high purity, high melting points and excellent resistance to corrosion — plus, of course, their exceptional catalytic properties. New suppliers and materials are added regularly.

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