Platinum Metal Based Materials

The platinum group metals include the elements Pt, Pd, Rh, Ru, Ir, and Os (Table 2.6). For electrical contacts platinum and palladium have practical significance as base alloy materials and ruthenium and iridium are used as alloying components. Pt and Pd have similar corrosion resistance as gold but because of their catalytical properties they tend to polymerize adsorbed organic vapors on contact surfaces. During frictional movement between contact surfaces the polymerized compounds known as “brown powder” are formed which can lead to significantly increase in contact resistance. Therefore Pt and Pd are typically used as alloys and not in their pure form for electrical contact applications.

Rhodium is not used as a solid contact material but is applied for example as a electroplated layer in sliding contact systems. Ruthenium is mostly used as an alloying component in the material PdRu15. The metals osmium and iridium have no practical applications in electrical contacts.

Since Pd was for the longest time rather stable in price it was looked at as a substitute for the more expensive gold. This was followed by a steep increase in the Pd price which caused a significant reduction in its use in electrical contacts. Today (2011) the Pd price again is lower than that of gold.

Alloys of Pt with Ru, Ir, Ni, and W were widely used in electromechanical components in the telecommunication industry and in heavy duty automotive breaker points (Table 2.7). Today these components have been replaced in many applications by solid state technology and the usage of these materials is greatly reduced. Pd alloys however have a more significant importance. PdCu15 is widely used for example in automotive flasher relays. Because of their resistance to sulfide formation PdAg alloys are applied in various relay designs. The ability to thermally precipitation harden some multi component alloys based on PdAgAuPt they find special usage in wear resistant sliding contact applications. Pd44Ag38Cu15PtAuZn is a standard alloy in this group.

Platinum and palladium alloys are mainly used similar to the gold based materials in the form of welded wire and profile segments but rarely as contact rivets. Because of the high precious metal prices joining technologies are used that allow the most economic application of the contact alloy in the area where functionally needed. Because of their resistance to material transfer they are used for DC applications and due to their higher arc erosion resistance they are applied for medium electrical loads up to about 30W in relays and switches (Table 2.10). Multi-component alloys based on Pd with higher hardness and wear resistance are mainly used as spring arms in sliding contact systems and DC miniature motors.

Table 2.6: Properties, Production Processes, and Application Forms for Platinum Metals

Table 2.7: Physical Properties of the Platinum Metals and their Alloys

Table 2.8: Mechanical Properties of the Platinum Metals and their Alloys

Fig. 2.25: Influence of 1- 20 atom% of different additive metals on the electrical resistivity p of platinum (Degussa)

Fig. 2.26: Influence of 1-22 atom% of different additive metals on the electrical resistivity p of palladium

Fig. 2.27: Phase diagram of platinum-iridium

Fig. 2.28: Phase diagram of platinum-nickel

Fig. 2.29: Phase diagram of platinum-tungsten

Fig. 2.30: Phase diagram of palladium-copper

Fig. 2.31: Strain hardening of Pt by cold working

Fig. 2.32: Softening of Pt after annealing for 0.5 hrs after 80% cold working

Fig. 2.33: Strain hardening of PtIr5 by cold working

Fig. 2.34: Softening of PtIr5 after annealing for 1 hr after different degrees of cold working

Fig. 2.35: Strain hardening of PtNi8 by cold working

Fig. 2.36: Softening of PtNi8 after annealing for 1 hr after 80% cold working

Fig. 2.37: Strain hardening of PtW5 by cold working

Fig. 2.38: Softening of PtW5 after annealing for 1hr after 80% cold working

Fig. 2.39: Strain hardening of Pd 99.99 by cold working

Fig. 2.40: Strain hardening of PdCu15 by cold working

Fig. 2.41: Softening of PdCu15 after annealing for 0.5 hrs

Fig. 2.42: Strain hardening of PdCu40 by cold working

Fig. 2.43: Softening of PdCu40 after annealing for 0.5 hrs after 80% cold working

Fig. 2.44: Electrical resistivity p of PdCu alloys with and without an annealing step for forming an ordered phase

Table 2.9: Contact and Switching Properties of the Platinum Metals and their Alloys

Table 2.10: Application Examples and Form of Supply for Platinum Metals and their Alloys