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PGMs in oxygen sensors and spark plugs

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Category: Metallurgy

Subject: PGMs in oxygen sensors and spark plugs

Question

How much and what precious metals are used in oxygen sensors and spark plugs?

Answer

Most oxygen sensors include a ceramic bulb coated on both sides with a thin layer of platinum and/or palladium. All catalyst-equipped cars have at least one sensor in the exhaust system. In the USA, and other countries where strict OBD legislation is in place, vehicles have additional sensors downstream of the autocatalyst. A large vehicle may have up to four sensors. The average number of sensors per car has grown steadily in recent years.

Spark plugs may be made from either base metal, platinum or iridium. Palladium, rhodium or ruthenium may also be present as alloying elements. Platinum group metal-based spark plugs are increasingly preferred over their base metal counterparts, due to their superior durability, and iridium is the metal of choice for the most demanding applications. Platinum plugs are fitted on all new vehicles in North America, and it was estimated in 2006 that around 25% of new gasoline cars in Europe and around 50% of Japanese vehicles were fitted with platinum plugs. Around a third of all replacement plugs are platinum-tipped, and this figure is increasing. Diesel vehicles utilise glow plugs, which do not use platinum.

The use of platinum in spark plugs and oxygen sensors together consumed more than 130,000 troy oz of platinum in 2005.

References

Platinum 2006, special chapter: ‘Other Applications for Platinum’

Johnson Matthey Noble Metals: Iridium based spark plug alloys

Answer posted 07 November 2007

Submitted by: Mr Rick Nelson

Answered by: Sara Coles

Affiliation: Platinum Metals Review