PGMs Corrosion Resistance

Tests performed under an inert argon atmosphere 

TaUe 4.107. Corrosion properties of PGMs in several aerated corrosive media between 20°C and 100°C  

Aqua regia HNO,+3HCl RT Attack Attack Attack Attack nil nil nil Shght 

Bromine (moist) Br, RT nil Attack Attack Poor nil nil nil Shght 

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Predominantly rhodium, palladium, iridium, and platinum are used in technical applications. Pure metals and alloys serve as corrosion-resistant materials for melting tubes, laboratory instruments, and spinning jets in synthetic fiber production. Other applications include uses as catalysts in chemical synthesis, in car mufflers, and in the electrotechnical industry. They also find use as alloys in dentistry and orthopedics. These quantities are recycled and serve as a secondary source of PGM. 

Palladium is the second most important PGM. Similar to gold and platinum, it can be beaten into leaf and is easily cold and hot worked. Contamination with low-melting metals causes embrittlement with base metals, hardening and a decrease in corrosion resistance and with silicon, a loss in hot strength. Palladium absorbs over 800 times its volume of hydrogen, which is expelled when heated. The metal also acts as a diffusion barrier for hydrogen purifi-... 

Platinum group metals (PGM) such as Pt, Pd, Rh, Ir, Ru, and Os are extremely corrosion resistant but have poor mechanical properties [Wynblatt, 1986]. They are mainly used as alloys for electrodes such as pacemaker tips because of their high resistance to corrosion and low threshold potentials for electrical conductivity. 

Rhodium has the highest electrical conductivity, thermal conductivity, and reflectivity of any PGM. It is similar to iridium. It is difflcult to fabricate and is resistant to corrosion. The major corrosive agents are moist iodine, NaClO, hot H2SO4, and hot HBr. 

Rhodium is a hard and wear resistant PGM. Advanced optical equipment is plated with thin layers of rhodium in order to get good corrosion and wear protection. Rhodium-alloyed platinum is used in perforated crucibles for making glass fibers. Organic rhodium compounds have been found to be effective catalysts (homogenous) in industrial hydrogenation and in pharmaceutical production of, for instance, the drug L-Dopa for the treatment of Parkinson s disease [32.8]. 

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