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Electrical Contacts β

Platinum Metal Based Materials

The platinum group metals include the elements Pt, Pd, Rh, Ru, Ir, and Os Table 1. 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.

Table 1: Properties, Production Processes, and Application Forms for Platinum Metals
Element Properties Processing Forms of Application
Ru
Ruthenium
Dull grey to silvery white, very hard and brittle,
in the presence of oxygen resistant to acids,
oxidizes during heating in air
Vapor deposition, sputtering, powder metallurgy,
warm-forming only possible at 1200 – 1500°C
Powder; in sheet form, as coatings,
and as wire mostly as alloying component
Rh
Rhodium
Almost silvery white, very hard and brittle, not soluble in acids,
oxidizes in air during red anneal
Electroplating, vapor deposition, sputtering,
after warm-forming at 800 – 1000°C cold working is possible
Coatings (electroplated), alloying component,
in limited form as sheet and wire
Pd
Palladium
Dull white, resistant to most acids,
oxidizes at red anneal
Electroplating, vapor deposition,
sputtering, cold working
Sheet, strip, tubing, wire,
rivets, and coatings
Os
Osmium
Bluish white, hardest platinum metal,
very brittle, resistant against non-oxidizing acids,
oxidizes easily on air
Powder metallurgy Powder, alloying component
Ir
Iridium
Almost silvery white, very hard and brittle,
acid resistant, oxidizes at red anneal
Vapor deposition, sputtering, powder metallurgy,
warm-forming possible at 1200 – 1500°C
Powder, alloying component,
in limited amounts as sheet
Pt
Platinum
Grey white, ductile, acid resistant except for aqua regia,
HBr, and HJ, oxidation resistant at red anneal
Electroplating, vapor deposition,
sputtering, cold working
Sheet, strip, tubing, wire, rivets, coatings


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.

Physical Properties of the Platinum Metals and their Alloys

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 Table 3 und Table 4

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 5. 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 3: Mechanical Properties of the Platinum Metals and their Alloys
MaterialTensile Strength [MPa]Elongation A [%]Vickers Hardness HV 1
soft70% cold worketsoft70% cold worketsoft70% cold worket
Pt (99,95)15036040340120
PtIr526055025285160
PtIr10340570242105210
PtRu106501000242195320
PtNi8640950222200320
PtW5530860212150270
Pd (99,95)2004204224090
PdCu1540078038290220
PdCu40550950352120260
PdNi534070025295200
Pd35AuAgPt420*
Pd44Ag38Cu15 PtAuZn405*
Pd40Co40W20680*
  • maximum hardness

Table 4: Contact and Switching Properties of the Platinum Metals and their Alloys

Material

Properties

Pt

Very high corrosion resistance

PtIr5 - 10

Very high corrosion resistance, low contact resistance

High arc erosion resistance, high hardness

PtRu10

Very high corrosion resistance, low welding tendency

Low contact resistance, very

high hardness

PtNi8

Low material transfer tendency

Very high hardness

PtW5

Low material transfer tendency

High hardness

Pd

Strong tendency to “Brown Powder” formation

Less arc erosion resistant than Pt

PdCu15

PdCu40

Tendency to “Brown Powder” formation

Mostly resistant to material

transfer, high hardness

PdNi5

Strong tendency to “Brown Powder” formation

Low welding tendency

Pd44Ag38Cu15

PtAuZn

High mechanical wear resistance

Standard material for sliding

contact brushes


Table 5: Application Examples and Form of Supply for Platinum Metals and their Alloys

Material

Application Examples

Forms of Supply

Pt (99,95)

Relays

Contact rivets, welded contact parts

PtIr5

PtIr10

PtRu10

PtNi8

PtW5

Relays, sliding contact systems,

automotive ignition breaker points

Semi-finished Contact Materials:

Wire, seam-welded contact profiles

Contact Parts:

Tips, wire-formed parts, solid and composite contact rivets, welded contact parts

Pd (99,95)

PdNi5

Relays

Micro-profiles (weld tapes), contact rivets, welded contact parts

PdCu15

PdCu40

Automotive flasher relays

Micro-profiles, composite contact rivets

Pd35AuAgPt

Pd44Ag38Cu15

PtAuZn

Pd40Co40W20

Potentiometers, slip rings, miniature

DC motors

Wire-formed parts, welded wire segments, multi-arm sliding contact brushes


Figure 1Influence of 1-20 atom% of different additive metals on the electrical resistivity p of platinum (Degussa)

Figure 2 Influence of 1-22 atom% of different additive metals on the electrical resistivity p of palladium

Figure 3Fig. 2.27: Phase diagram of platinum-iridium

Figure 4 Fig. 2.28: Phase diagram of platinum-nickel

Figure 5 Fig. 2.29: Phase diagram of platinum-tungsten

Figure 6 Fig. 2.30: Phase diagram of palladium-copper

Figure 7 Fig. 2.31: Strain hardening of Pt by cold working

Figure 8 Fig. 2.32: Softening of Pt after annealing for 0.5 hrs after 80% cold working

Figure 9 Fig. 2.33: Strain hardening of PtIr5 by cold working

Figure 10 Fig. 2.34: Softening of PtIr5 after annealing for 1 hr after different degrees of cold working

Figure 11Fig. 2.35: Strain hardening of PtNi8 by cold working

Figure 12 Fig. 2.36: Softening of PtNi8 after annealing for 1 hr after 80% cold working

Figure 13Fig. 2.37: Strain hardening of PtW5 by cold working

Figure 14Fig. 2.38: Softening of PtW5 after annealing for 1hr after 80% cold working

Figure 15Fig. 2.39: Strain hardening of Pd 99.99 by cold working

Figure 16Fig. 2.40: Strain hardening of PdCu15 by cold working

Figure 17Fig. 2.41: Softening of PdCu15 after annealing for 0.5 hrs

Figure 18Fig. 2.42: Strain hardening of PdCu40 by cold working

Figure 19Fig. 2.43: Softening of PdCu40 after annealing for 0.5 hrs after 80% cold working

Figure 20Fig. 2.44: Electrical resistivity p of PdCu alloys with and without an annealing step for forming an ordered phase



Figure 1: Influence of 1- 20 atom% of different additive metals on the electrical resistivity p of platinum (Degussa)
Figure 2: Influence of 1-22 atom% of different additive metals on the electrical resistivity p of palladium
Figure 3: Fig. 2.27:Phase diagram of platinum-iridium
Figure 4: Fig. 2.28:Phase diagram of platinum-nickel
Figure 5: Fig. 2.29:Phase diagram of platinum-tungsten
Figure 6: Fig. 2.30: Phase diagram of palladium-copper
Figure 7: Fig. 2.31: Strain hardening of Pt by cold working
Figure 8: Fig. 2.32: Softening of Pt after annealing for 0.5 hrs after 80% cold working
Figure 9: Fig. 2.33: Strain hardening of PtIr5 by cold working
Figure 10: Fig. 2.34: Softening of PtIr5 after annealing for 1 hr after different degrees of cold working
Figure 11: Fig. 2.35: Strain hardening of PtNi8 by cold working
Figure 12: Fig. 2.36: Softening of PtNi8 after annealing for 1 hr after 80% cold working
Figure 13: Fig. 2.37: Strain hardening of PtW5 by cold working
Figure 14: Fig. 2.38: Softening of PtW5 after annealing for 1 hr after 80% cold working
Figure 15: Fig. 2.39: Strain hardening of Pd 99.99 by cold working
Figure 16: Fig. 2.40: Strain hardening of PdCu15 by cold working
Figure 17: Softening of PdCu15 after annealing for 0.5 hrs
Figure 18: Strain hardening of PdCu40 by cold working
Figure 19: Softening of PdCu40 after annealing for 0.5 hrs after 80% cold working
Figure 20: Electrical resistivity p of PdCu alloys with and without an annealing step for forming an ordered phase

References