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 for the reason 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 a significant 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 seen 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 (Dec. 2021) the palladium price is around 2600 Euro/oz.

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).

Table 2: Physical Properties of the Platinum Metals an their Alloys

Material	Platin/Palladium Content [wt.%]	Density [g/cm3]	Melting Point or Range [°C]	Electrical Resistivity [µΩ*cm]	Electrical Conductivity [MS/m]	Thermal Conductivity [W/m*K]	Temp. Coefficient of the Electrical Resistance [103/K]	modulus of Elasticity [Gpa]
Pt (99,95)	>99,95	21,5	1772	10,6	9,5	72	3,9	173
PtIr5	95	21,5	1774 - 1776	22,2	4,5	42		190
PtIr10	90	21,6	1780 - 1785	17,9	5,6	29	2,0	220
PtRu10	90	20,6	ca. 1800	33,3	3,0		0,83	235
PtNi6	92	19,2	1670 - 1710	30	3,3		1,5	180
PtW5	95	21,3	1830 - 1860	43,4	2,3		0,7	185
Pd (99,95)	>99,95	12,0	1554	10,8	9,3	72	3,8	124
PdCu15	85	11,3	1370 - 1400	38,5	2,6	17	0,49	175
PdCu40	60	10,5	1200 - 1230	33,3	3,0	38	0,28	175
PdNi5	95	11,8	1455 - 1485	16,9	5,9		2,47	175

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. With 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 and 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. Due to 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. For reason 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

Material	Tensile Strength [MPa]		Elongation A [%]		Vickers Hardness HV 1
	soft	70% cold worket	soft	70% cold worket	soft	70% cold worket
Pt (99,95)	150	360	40	3	40	120
PtIr5	260	550	25	2	85	160
PtIr10	340	570	24	2	105	210
PtRu10	650	1000	24	2	195	320
PtNi8	640	950	22	2	200	320
PtW5	530	860	21	2	150	270
Pd (99,95)	200	420	42	2	40	90
PdCu15	400	780	38	2	90	220
PdCu40	550	950	35	2	120	260
PdNi5	340	700	25	2	95	200
Pd35AuAgPt						420*
Pd44Ag38Cu15 PtAuZn						405*
Pd40Co40W20						680*

• 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 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

References