Silver Based Materials

From Electrical Contacts
Jump to: navigation, search

Pure Silver

Pure silver (also called fine silver) exhibits the highest electrical and thermal conductivity of all metals. It is also resistant against oxidation. Major disadvantages are its low mechanical wear resistance, the low softening temperature, and especially its strong affinity to sulfur and sulfur compounds. In the presence of sulfur and sulfur containing compounds brownish to black silver sulfide layer are formed on its surface. These can cause increased contact resistance or even total failure of a switching device if they are not mechanically, electrically, or thermally destroyed. Other weaknesses of silver contacts are the tendency to weld under the influence of over-currents and the low resistance against material transfer when switching DC loads. In humid environments and under the influence of an electrical field silver can creep (silver migration) and cause electrical shorting between adjacent current paths.

Table 1 shows the typically available quality grades of silver. In certain economic areas, i.e. China, there are additional grades with varying amounts of impurities available on the market. In powder form silver is used for a wide variety of silver based composite contact materials. Different manufacturing processes result in different grades of Ag powder as shown in Table 2. additional properties of silver powders and their usage are described in Precious Metal Powders und Table Different Types of Silver Powders.

Semi-finished silver materials can easily be warm or cold formed and can be clad to the usual base materials. For attachment of silver to contact carrier materials welding of wire or profile cut-offs and brazing are most widely applied. Besides these mechanical processes such as wire insertion (wire staking) and the riveting (staking) of solid or composite contact rivets are used in the manufacture of contact components.

Contacts made from fine silver are applied in various electrical switching devices such as relays, pushbuttons, appliance and control switches for currents < 2 A Table 6. Electroplated silver coatings are widely used to reduce the contact resistance and improve the brazing behavior of other contact materials and components.


Table 1: Overview of the Most Widely Used Silver Grades

Designation

Composition minimum Ag [wt%]

Impurities

[ppm]

Notes on Usage

Spectroscopically

Pure Ag

99.999

Cu < 3

Zn < 1

Si < 1

Ca < 2

Fe < 1

Mg < 1

Cd < 1

Sheets, strips, rods, wires for electronic applications

High Purity Ag, oxygen-free

99.995

Cu < 30

Zn < 2

Si < 5

Ca < 10

Fe < 3

Mg < 5

Cd < 3

Ingots, bars, granulate for alloying

purposes


Table 2: Quality Criteria of Differently Manufactured Silver Powders
Impurities Ag-Chem.* Ag-ES** Ag-V***
Cu ppm < 100 < 300 < 300
Fe ppm < 50 < 100 < 100
Ni ppm < 50 < 50 < 50
Cd ppm < 50
Zn ppm < 10
Na + K + Mg + Ca ppm < 80 < 50 < 50
Ag CI ppm < 500 < 500 < 500
NO3 ppm < 40 < 40
Nh4CI ppm < 30 < 30
Particle Size Distribution (screen analysis)
> 100 μm % 0 0 0
< 100 bis > 63 μm % < 5 < 5 < 15
< 36 μm % < 80 < 90 < 75
Apparent Density g/cm3 1.0 - 1.6 1.0 - 1.5 3 - 4
Tap Density ml/100g 40 - 50 40 - 50 15 - 25
Press/Sintering Behavior
Press Density g/cm3 5.6 - 6.5 5.6 - 6.3 6.5 - 8.5
Sinter Density g/cm3 > 9 > 9.3 > 8
Volume Shrinkage % > 34 > 35 > 0
Annealing Loss % < 2 < 0.1 < 0.1

* Manufactured by chemical precipitation
** Manufactured by electrolytic deposition
*** Manufactured by atomizing of a melt


Figure 1 Strain hardening of Ag 99.95 by cold working

Figure 2 Softening of Ag 99.95 after annealing for 1 hr after different degrees of strain hardening


Figure 1: Strain hardening of Ag 99.95 bei cold working
Figure 2: Softening of Ag 99.95 after annealing for 1 hr after different degrees of strain hardening

Silver Alloys

To improve the physical and contact properties of fine silver melt-metallurgical produced silver alloys are used Table 3. By adding metal components the mechanical properties such as hardness and tensile strength as well as typical contact properties such as erosion resistance, and resistance against material transfer in DC circuits are increased Table 4. On the other hand however, other properties such as electrical conductivity and chemical corrosion resistance can be negatively impacted by alloying Figure 3 and Figure 4.

Table 3: Physical Properties of Silver and Silver Alloys
Material/
DODUCO-
Designation
Silver Content
[wt%]
Density
[g/cm3]
Melting Point
or Range
[°C]
Electrical
Resistivity
[μΩ·cm]
Electrical
Conductivity
[MS/m]
Thermal
Conductivity
[W/mK]
Temp. Coefficient of
the Electr.Resistance
[10-3/K]
Modulus of
Elasticity
[GPa]
Ag 99.95 10.5 961 1.67 60 419 4.1 80
AgNi 0,15
ARGODUR-Spezial
99.85 10.5 960 1.72 58 414 4.0 82
AgCu3 97 10.4 900 - 938 1.92 52 385 3.2 85
AgCu5 95 10.4 910 1.96 51 380 3.0 85
AgCu10 90 10.3 870 2.0 50 335 2.8 85
AgCu28 72 10.0 779 2.08 48 325 2.7 92
Ag98CuNi
ARGODUR 27
98 10.4 940 1.92 52 385 3.5 85
AgCu24,5Ni0,5 75 10.0 805 2.20 45 330 2.7 92
AgCd10 89 - 91 10.3 910 - 925 4.35 23 150 1.4 60
Ag99,5NiMg
ARGODUR 32
Not heat treated
99.5 10.5 960 2.32 43 293 2.3 80
ARGODUR 32
Heat treated
99.5 10.5 960 2.32 43 293 2.1 80

Figure 3 Influence of 1-10 atom% of different alloying metals on the electrical resistivity of silver

Figure 4 Electrical resistivity p of AgCu alloys

Figure 3: Influence of 1-10 atom% of different alloying metals on the electrical resistivity of silver
Figure 4: Electrical resistivity p of AgCu alloys with 0-20 weight% Cu in the soft annealed and tempered stage a) Annealed and quenched b) Tempered at 280°C

Fine-Grain Silver

Fine-Grain Silver (ARGODUR-Spezial) is defined as a silver alloy with an addition of 0.15 wt% of Nickel. Silver and nickel are not soluble in each other in solid form. In liquid silver only a small amount of nickel is soluble as the phase diagram Figure 7 illustrates. During solidification of the melt this nickel addition gets finely dispersed in the silver matrix and eliminates the pronounce coarse grain growth after prolonged influence of elevated temperatures Figure 5 and Figure 6.

Figure 5: Coarse grain micro structure of Ag 99.97 after 80% cold working and 1 hr annealing at 600°C
Figure 6: Fine grain microstructure of AgNi0.15 after 80% cold working and 1 hr annealing at 600°C
Figure 7: Phase diagram of silver nickel

Fine-grain silver has almost the same chemical corrosion resistance as fine silver. Compared to pure silver it exhibits a slightly increased hardness and tensile strength Table 4. The electrical conductivity is just slightly decreased by this low nickel addition. Because of its significantly improved contact properties fine grain silver has replaced pure silver in many applications.

Hard-Silver Alloys

Using copper as an alloying component increases the mechanical stability of silver significantly. The most important among the binary AgCu alloys is that of AgCu3, known in europe also under the name of hard-silver. This material still has a chemical corrosion resistance close to that of fine silver. In comparison to pure silver and fine-grain silver AgCu3 exhibits increased mechanical strength as well as higher arc erosion resistance and mechanical wear resistance Table 4.

Table 4: Mechanical Properties of Silver and Silver Alloys

Material/

DODUCO-Designation

Hardness

Condition

Tensile Strength

Rm [MPa]

Elongation A [%] min.

Vickers Hardness

HV 10

Ag

R 200

R 250

R 300

R 360

200 - 250

250 - 300

300 - 360

> 360

30

8

3

2

30

60

80

90

AgNi 0,15

ARGODUR Special

R 220

R 270

R 320

R 360

220 - 270

270 - 320

320 - 360

> 360

25

6

2

1

40

70

85

100

AgCu3

R 250

R 330

R 400

R 470

250 - 330

330 - 400

400 - 470

> 470

25

4

2

1

45

90

115

120

AgCu5

R 270

R 350

R 460

R 550

270 - 350

350 - 460

460 - 550

> 550

20

4

2

1

55

90

115

135

AgCu10

R 280

R 370

R 470

R 570

280 - 370

370 - 470

470 - 570

> 570

15

3

2

1

60

95

130

150

AgCu28

R 300

R 380

R 500

R 650

300 - 380

380 - 500

500 - 650

> 650

10

3

2

1

90

120

140

160

Ag98CuNi

ARGODUR 27

R 250

R 310

R 400

R 450

250 - 310

310 - 400

400 - 450

> 450

20

5

2

1

50

85

110

120

AgCu24,5Ni0,5

R 300

R 600

300 - 380

> 600

10

1

105

180

AgCd10

R 200

R 280

R 400

R 450

200 - 280

280 - 400

400 - 450

> 450

15

3

2

1

36

75

100

115

Ag99,5NiMg

ARGODUR 32

Not heat treated

R 220

R 260

R 310

R 360

220

260

310

360

25

5

2

1

40

70

85

100

ARGODUR 32 Heat treated

R 400

400

2

130-170


Increasing the Cu content further also increases the mechanical strength of AgCu alloys and improves arc erosion resistance and resistance against material transfer while at the same time however the tendency to oxide formation becomes detrimental. This causes during switching under arcing conditions an increase in contact resistance with rising numbers of operation. In special applications where highest mechanical strength is recommended and a reduced chemical resistance can be tolerated, the eutectic AgCu alloy with 28 wt% of copper Figure 8 is used. AgCu10 also known as coin silver has been replaced in many applications by composite silver-based materials while sterling silver (AgCu7.5) has never extended its important usage from decorative table wear and jewelry to industrial applications in electrical contacts.

Besides these binary alloys, ternary AgCuNi alloys are used in electrical contact applications. From this group the material ARGODUR 27, an alloy of 98 wt% Ag with a 2 wt% Cu and nickel addition has found practical importance close to that of AgCu3. This material is characterized by high resistance to oxidation and low tendency to re-crystallization during exposure to high temperatures. Besides high mechanical stability this AgCuNi alloy also exhibits a strong resistance against arc erosion. Because of its high resistance against material transfer the alloy AgCu24.5Ni0.5 has been used in the automotive industry for an extended time in the North American market. Caused by miniaturization and the related reduction in available contact forces in relays and switches this material has been replaced widely because of its tendency to oxide formation.

The attachment methods used for the hard silver materials are mostly close to those applied for fine silver and fine grain silver.

Hard-silver alloys are widely used for switching applications in the information and energy technology for currents up to 10 A, in special cases also for higher current ranges Table 6.

Dispersion hardened alloys of silver with 0.5 wt% MgO and NiO (ARGODUR 32) are produced by internal oxidation. While the melt-metallurgical alloy is easy to cold-work and form the material becomes very hard and brittle after dispersion hardening. Compared to fine silver and hard-silver this material has a greatly improved temperature stability and can be exposed to brazing temperatures up to 800°C without decreasing its hardness and tensile strength. Because of these mechanical properties and its high electrical conductivity ARGODUR 32 is mainly used in the form of contact springs that are exposed to high thermal and mechanical stresses in relays, and contactors for aeronautic applications.


Figure 8 Phase diagram of silver-copper

Figure 9 Phase diagram of silver-cadmium

Figure 10 Strain hardening of AgCu3 by cold working

Figure 11 Softening of AgCu3 after annealing for 1 hr after 80% cold working

Figure 12 Strain hardening of AgCu5 by cold working

Figure 13 Softening of AgCu5 after annealing for 1 hr after 80% cold working

Figure 14 Strain hardening of AgCu 10 by cold working

Figure 15 Softening of AgCu10 after annealing for 1 hr after 80% cold working

Figure 16 Strain hardening of AgCu28 by cold working

Figure 17 Softening of AgCu28 after annealing for 1 hr after 80% cold working

Figure 18 Strain hardening of AgNi0.15 by cold working

Figure 19 Softening of AgNi0.15 after annealing for 1 hr after 80% cold working

Figure 20 Strain hardening of ARGODUR 27 by cold working

Figure 21 Softening of ARGODUR 27 after annealing for 1 hr after 80% cold working

Figure 8: Phase diagram of silver-copper
Figure 9: Phase diagram of silver-cadmium
Figure 10: Strain hardening of AgCu3 by cold working
Figure 11: Softening of AgCu3 after annealing for 1 hr after 80% cold working
Figure 12: Strain hardening of AgCu5 by cold working
Figure 13: Softening of AgCu5 after annealing for 1 hr after 80% cold working
Figure 14: Strain hardening of AgCu 10 by cold working
Figure 15: Softening of AgCu10 after annealing for 1 hr after 80% cold working
Figure 16: Strain hardening of AgCu28 by cold working
Figure 17: Softening of AgCu28 after annealing for 1 hr after 80% cold working
Figure 18: Strain hardening of AgNiO15 by cold working
Figure 19: Softening of AgNiO15 after annealing
Figure 20: Strain hardening of ARGODUR 27 by cold working
Figure 21: Softening of ARGODUR 27 after annealing for 1 hr after 80% cold working


Table 5: Contact and Switching Properties of Silver and Silver Alloys
Material Properties
Ag
AgNi0,15
ARGODUR-Special
Highest electrical and thermal conductivity, high affinity to sulfur (sulfide formation), low welding resistance, low contact resistance, very good formability Oxidation resistant at higher make currents, limited arc erosion resistance, tendency to material transfer in DC circuits, easy to braze and weld to carrier materials
Ag Alloys Increasing contact resistance with increasing

Cu content, compared to fine Ag higher arc erosion resistance and mechanical strength, lower tendency to material

Good formability, good brazing and welding properties


Table 6: Application Examples and Forms of Supply for Silver and Silver Alloys
Material Application Examples Form of Supply
Ag
AgNi0,15
ARGODUR-Spezial
AgCu3
AgNi98NiCu2
ARGODUR 27
AgCu24,5Ni0,5
Relays,
Micro switches,
Auxiliary current switches,
Control circuit devices,
Appliance switches,
Wiring devices (≤ 20A),
Main switches
Semi-finished Materials:
Strips, wires, contact profiles, clad contact strips, toplay profiles, seam- welded strips
Contact Parts:
Contact tips, solid and composite rivets, weld buttons; clad, welded and riveted contact parts
AgCu5
AgCu10
AgCu28
Special applications Semi-finished Materials:
Strips, wires, contact profiles, clad contact strips, seam-welded strips
Contact parts:
Contact tips, solid contact rivets, weld buttons; clad, welded and riveted contact parts
Ag99, 5NiOMgO
ARGODUR 32
Miniature relays, aerospace relays and contactors, erosion wire for injection nozzles Contact springs, contact carrier parts

Silver-Palladium Alloys

The addition of 30 wt% Pd increases the mechanical properties as well as the resistance of silver against the influence of sulfur and sulfur containing compounds significantly Table 7 and Table 8. Alloys with 40-60 wt% Pd have an even higher resistance against silver sulfide formation. At these percentage ranges however the catalytic properties of palladium can influence the contact resistance behavior negatively. The formability also decreases with increasing Pd contents.

AgPd alloys are hard, arc erosion resistant, and have a lower tendency towards material transfer under DC loads Table 9. On the other hand the electrical conductivity is decreased at higher Pd contents. The ternary alloy AgPd30Cu5 has an even higher hardness which makes it suitable for use in sliding contact systems.

AgPd alloys are mostly used in relays for the switching of medium to higher loads (> 60V, > 2A) as shown in Table 10. Because of the high palladium price these formerly solid contacts have been widely replaced by multi-layer designs such as AgNi0.15 or AgNi10 with a thin Au surface layer. A broader field of application for AgPd alloys remains in the wear resistant sliding contact systems.


Figure 22 Phase diagram of silver-palladium

Figure 23 Strain hardening of AgPd30 by cold working

Figure 24 Strain hardening of AgPd50 by cold working

Figure 25 Strain hardening of AgPd30Cu5 by cold working

Figure 26 Softening of AgPd30, AgPd50, and AgPd30Cu5 after annealing of 1 hr after 80% cold working

Figure 22: Phase diagram of silver-palladium
Figure 23: Strain hardening of AgPd30 by cold working
Figure 24: Strain hardening of AgPd50 by cold working
Figure 25: Strain hardening of AgPd30Cu5 by cold working
Figure 26: Softening of AgPd30, AgPd50, and AgPd30Cu5 after annealing of 1 hr after 80% cold working


Table 7: Physical Properties of Silver-Palladium Alloys
Material 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 Electr. Resistance
[10-3/K]
AgPd30 30 10.9 1155 - 1220 14.7 6.8 60 0.4
AgPd40 40 11.1 1225 - 1285 20.8 4.8 46 0.36
AgPd50 50 11.2 1290 - 1340 32.3 3.1 34 0.23
AgPd60 60 11.4 1330 - 1385 41.7 2.4 29 0.12
AgPd30Cu5 30 10.8 1120 - 1165 15.6 6.4 28 0.37


Table 8: Mechanical Properties of Silver-Palladium Alloys

Material

Hardness

Condition

Tensile Strength

Rm[MPa]

Elongation A

[%]min.

Vickers Hardness

HV

AgPd30

R 320

R 570

320

570

38

3

65

145

AgPd40

R 350

R 630

350

630

38

2

72

165

AgPd50

R 340

R 630

340

630

35

2

78

185

AgPd60

R 430

R 700

430

700

30

2

85

195

AgPd30Cu5

R 410

R 620

410

620

40

2

90

190


Table 9: Contact and Switching Properties of Silver-Palladium Alloys
Material Properties
AgPd30-60 Corrosion resistant, tendency to Brown Powder formation increases with Pd content, low tendency to material transfer in DC circuits, high ductility Resistant against Ag2S formation, low contact resistance, increasing hardness with higher Pd content, AgPd30 has highest arc erosion resistance, easy to weld and clad
AgPd30Cu5 High mechanical wear resistance High Hardness


Table 10: Application Examples and Forms of Suppl for Silver-Palladium Alloys

Material

Application Examples

Form of Supply

AgPd 30-60

Switches, relays, push-buttons,

connectors, sliding contacts

Semi-finished Materials:

Wires, micro profiles (weld tapes), clad

contact strips, seam-welded strips

Contact Parts:

Solid and composite rivets, weld buttons;

clad and welded contact parts, stamped parts

AgPd30Cu5

Sliding contacts, slider tracks

Wire-formed parts, contact springs, solid

and clad stamped parts

Silver Composite Materials

Silver-Nickel (SINIDUR) Materials

Since silver and nickel are not soluble in each other in solid form and in the liquid phase have only very limited solubility silver nickel composite materials with higher Ni contents can only be produced by powder metallurgy. During extrusion of sintered Ag/Ni billets into wires, strips and rods the Ni particles embedded in the Ag matrix are stretched and oriented in the microstructure into a pronounced fiber structure Figure 31 and Figure 32

The high density produced during hot extrusion aids the arc erosion resistance of these materials Table 11. The typical application of Ag/Ni contact materials is in devices for switching currents of up to 100A Table 14. In this range they are significantly more erosion resistant than silver or silver alloys. In addition they exhibit with nickel contents < 20 wt% a low and over their operational lifetime consistent contact resistance and good arc moving properties. In DC applications Ag/Ni materials exhibit a relatively low tendency of material transfer distributed evenly over the contact surfaces Table 13 .

Typically Ag/Ni (SINIDUR) materials are usually produced with contents of 10-40 wt% Ni. The most widely used materials SINIDUR 10 and SINIDUR 20- and also SINIDUR 15, mostly used in north america-, are easily formable and applied by cladding Figure 27 Figure 28 Figure 29 Figure 30. They can be, without any additional welding aids, economically welded and brazed to the commonly used contact carrier materials. The (SINIDUR) materials with nickel contents of 30 and 40 wt% are used in switching devices requiring a higher arc erosion resistance and where increases in contact resistance can be compensated through higher contact forces.

The most important applications for Ag/Ni contact materials are typically in relays, wiring devices, appliance switches, thermostatic controls, auxiliary switches, and small contactors with nominal currents > 20A Table 14.

Table 11: Physical Properties of Silver-Nickel (SINIDUR) Materials
Material/DODUCOSilver ContentDensityMelting PointElectricalResistivitypElectrical Resistivity (soft)
Designation[wt%][g/cm3][°C][µΩ·cm] [% IACS][MS/m]

Ag/Ni 90/10

SINIDUR 10

89 - 91

10.2 - 10.3

960

1.82 - 1.92

90 - 95

52 - 55

Ag/Ni 85/15

SINIDUR 15

84 - 86

10.1 - 10.2

960

1.89 - 2.0

86 - 91

50 - 53

Ag/Ni 80/20

SINIDUR 20

79 - 81

10.0 - 10.1

960

1.92 - 2.08

83 - 90

48 - 52

Ag/Ni 70/30

SINIDUR 30

69 - 71

9.8

960

2.44

71

41

Ag/Ni 60/40

SINIDUR 40

59 - 61

9.7

960

2.70

64

37


Table 12: Mechanical Properties of Silver-Nickel (SINIDUR) Materials
Material/DODUCO-Designation Hardness Condition Tensile Strength Rm [Mpa] Elongation A (soft annealed) [%] min. Vickers Hardness HV 10
Ag/Ni 90/10
SINIDUR 10
soft
R 220
R 280
R 340
R 400
< 250
220 - 280
280 - 340
340 - 400
> 400
25
20
3
2
1
< 50
50 - 70
65 - 90
85 - 105
> 100
Ag/Ni 85/15
SINIDUR 15
soft
R 300
R 350
R 380
R 400
< 275
250 - 300
300 - 350
350 - 400
> 400
20
4
2
2
1
< 70
70 - 90
85 - 105
100 - 120
> 115
Ag/Ni 80/20
SINIDUR 20
soft
R 300
R 350
R 400
R 450
< 300
300 - 350
350 - 400
400 - 450
> 450
20
4
2
2
1
< 80
80 - 95
90 - 110
100 - 125
> 120
Ag/Ni 70/30
SINIDUR 30
R 330
R 420
R 470
R 530
330 - 420
420 - 470
470 - 530
> 530
8
2
1
1
80
100
115
135
Ag/Ni 60/40
SINIDUR 40
R 370
R 440
R 500
R 580
370 - 440
440 - 500
500 - 580
> 580
6
2
1
1
90
110
130
150


Figure 27 Strain hardening of Ag/Ni 90/10 by cold working

Figure 28 Softening of Ag/Ni 90/10 after annealing for 1 hr after 80% cold working

Figure 29 Strain hardening of Ag/Ni 80/20 by cold working

Figure 30 Softening of Ag/Ni 80/20 after annealing for 1 hr after 80% cold working

Figure 31 Micro structure of Ag/Ni 90/10 a) perpendicular to the extrusion direction b) parallel to the extrusion direction

Figure 32 Micro structure of Ag/Ni 80/20 a) perpendicular to the extrusion direction b) parallel t o the extrusion direction


Figure 27: Strain hardening of Ag/Ni 90/10 by cold working
Figure 28: Softening of Ag/Ni 90/10 after annealing for 1 hr after 80% cold working
Figure 29: Strain hardening of Ag/Ni 80/20 by cold working
Figure 30: Softening of Ag/Ni 80/20 after annealing for 1 hr after 80% cold working
Figure 31: Micro structure of Ag/Ni 90/10 a) perpendicular to the extrusion direction b) parallel to the extrusion direction
Figure 32: Micro structure of Ag/Ni 80/20 a) perpendicular to the extrusion direction b) parallel to the extrusion direction


Table 13: Contact and Switching Properties of Silver-Nickel (SINIDUR) Materials
Material/DODUCO-Designation Properties
Ag/Ni
SINIDUR
High arc erosion resistance at switching currents up to 100A,
Resistance against welding for starting current up to 100A,
low and over the electrical contact life nearly constant contact resistance for Ag/Ni 90/10 and Ag/Ni 80/20,
ow and spread-out material transfer under DC load,
non-conductive erosion residue on isolating components resulting in only minor change of the dielectric strength of switching devices,
good arc moving properties,
good arc extinguishing properties,
good or sufficient ductility depending on the Ni content,
easy to weld and braze


Table 14: Application Examples and Forms of Supply for Silver-Nickel (SINIDUR) Materials
Material Application Examples Switching or Nominal Current Form of Supply
Ag/Ni 90/10-80/20 Relays
Automotive Relays - Resistive load - Motor load
> 10A
> 10A
Semi-finisched Materials:
Wires, profiles,
clad strips,
Seam-welded strips,
Toplay strips
Contact Parts:
Contact tips, solid
and composite
rivets, Weld buttons,
clad, welded,
brazed, and riveted
contact parts
Ag/Ni 90/10, Ag/Ni 85/15-80/20 Auxiliary current switches ≤ 100A
Ag/Ni 90/10-80/20 Appliance switches ≤ 50A
Ag/Ni 90/10 Wiring devices ≤ 20A
Ag/Ni 90/10 Main switches, Automatic staircase illumination switches ≤ 100A
Ag/Ni 90/10-80/20 Control
Thermostats
> 10A
≤ 50A
Ag/Ni 90/10-80/20 Load switches ≤ 20A
Ag/Ni 90/10-80/20 Contactors circuit breakers ≤ 100A
Ag/Ni 90/10-80/20
paired with Ag/C 97/3-96/4
Motor protective circuit breakers ≤ 40A
Ag/Ni 80/20-60/40
paired with Ag/C 96/4-95/5
Fault current circuit breakers ≤ 100A Rods, Profiles,
Contact tips, Formed parts,
brazed and welded
contact parts
Ag/Ni 80/20-60/40
paired with Ag/C 96/4-95/5
Power switches > 100A

Silver-Metal Oxide Materials Ag/CdO, Ag/SnO2, Ag/ZnO

The family of silver-metal oxide contact materials includes the material groups: silver-cadmium oxide (DODURIT CdO), silver-tin oxide (SISTADOX), and silverzinc oxide (DODURIT ZnO). Because of their very good contact and switching properties like high resistance against welding, low contact resistance, and high arc erosion resistance, silver-metal oxides have gained an outstanding position in a broad field of applications. They mainly are used in low voltage electrical switching devices like relays, installation and distribution switches, appliances, industrial controls, motor controls, and protective devices Table 21.

  • Silver-cadmium oxide (DODURIT CdO) materials

Silver-cadmium oxide (DODURIT CdO) materials with 10-15 wt% are produced by both, internal oxidation and powder metallurgical methods Table 15.

Physical and Mechanical Properties as well as Manufacturing Processes and Forms of Supply of Extruded Silver Cadmium Oxide (DODURIT CdO) Contact Materials

The manufacturing of strips and wires by internal oxidation starts with a molten alloy of silver and cadmium. During a heat treatment below it's melting point in a oxygen rich atmosphere in such a homogeneous alloy the oxygen diffuses from the surface into the bulk of the material and oxidizes the Cd to CdO in a more or less fine particle precipitation inside the Ag matrix. The CdO particles are rather fine in the surface area and are becoming larger further away towards the center of the material Figure 39.

During the manufacturing of Ag/CdO contact material by internal oxidation the processes vary depending on the type of semi-finished material. For Ag/CdO wires a complete oxidation of the AgCd wire is performed, followed by wire-drawing to the required diameter Figure 33 and Figure 34. The resulting material is used for example in the production of contact rivets. For Ag/CdO strip materials two processes are commonly used: Cladding of an AgCd alloy strip with fine silver followed by complete oxidation results in a strip material with a small depletion area in the center of it's thickness and a Ag backing suitable for easy attachment by brazing (sometimes called "Conventional Ag/CdO"). Using a technology that allows the partial oxidation of a dual-strip AgCd alloy material in a higher pressure pure oxygen atmosphere yields a composite Ag/CdO strip material that has besides a relatively fine CdO precipitation also a easily brazable AgCd alloy backing Figure 41. These materials (DODURIT CdO ZH) are mainly used as the basis for contact profiles and contact tips.

During powder metallurgical production the powder mixed made by different processes are typically converted by pressing, sintering and extrusion to wires and strips. The high degree of deformation during hot extrusion produces a uniform and fine dispersion of CdO particles in the Ag matrix while at the same time achieving a high density which is advantageous for good contact properties Figure 40. To obtain a backing suitable for brazing, a fine silver layer is applied by either com-pound extrusion or hot cladding prior to or right after the extrusion Figure 42.

For larger contact tips, and especially those with a rounded shape, the single tip Press-Sinter-Repress process (PSR) offers economical advantages. The powder mix is pressed in a die close to the final desired shape, the "green" tips are sintered, and in most cases the repress process forms the final exact shape while at the same time increasing the contact density and hardness.

Using different silver powders and minor additives for the basic Ag and CdO starting materials can help influence certain contact properties for specialized applications.

Figure 33 Strain hardening of internally oxidized Ag/CdO 90/10 by cold working

Figure 34 Softening of internally oxidized Ag/CdO 90/10 after annealing for 1 hr after 40% cold working

Figure 35 Strain hardening of Ag/CdO 90/10 P by cold working

Figure 36 Softening of Ag/CdO 90/10 P after annealing for 1 hr after 40% cold working

Figure 37 Strain hardening of Ag/CdO 88/12 WP

Figure 38 Softening of Ag/CdO 88/12WP after annealing for 1 hr after different degrees of cold working

Figure 39 Micro structure of Ag/CdO 90/10 i.o. a) close to surface b) in center area

Figure 40 Micro structure of Ag/CdO 90/10 P: a) perpendicular to extrusion direction b) parallel to extrusion direction

Figure 41 Micro structure of Ag/CdO 90/10 ZH: 1) Ag/CdO layer 2) AgCd backing layer

Figure 42 Micro structure of AgCdO 88/12 WP: a) perpendicular to extrusion direction b) parallel to extrusion direction

Figure 33: Strain hardening of internally oxidized Ag/CdO 90/10 by cold working
Figure 34: Softening of internally oxidized Ag/CdO 90/10 after annealing for 1 hr after 40% cold working
Figure 35: Strain hardening of Ag/CdO 90/10 P by cold working
Figure 36: Softening of Ag/CdO 90/10 P after annealing for 1 hr after 40% cold working
Figure 37: Strain hardening of Ag/CdO 88/12 WP
Figure 38: Softening of Ag/CdO 88/12WP after annealing for 1 hr after different degrees of cold working
Figure 39: Micro structure of Ag/CdO 90/10 i.o. a) close to surface b) in center area
Figure 40: Micro structure of Ag/CdO 90/10 P: a) perpendicular to extrusion direction b) parallel to extrusion direction
Figure 41: Micro structure of Ag/CdO 90/10 ZH: 1) Ag/CdO layer 2) AgCd backing layer
Figure 42: Micro structure of AgCdO 88/12 WP: a) perpendicular to extrusion direction b) parallel to extrusion direction


  • Silver–tin oxide (SISTADOX) materials

Over the past years, many Ag/CdO contact materials have been replaced by Ag/SnO2 based materials with 2-14 wt% SnO2 because of the toxicity of Cadmium. This changeover was further favored by the fact that Ag/SnO2 contacts quite often show improved contact and switching properties such as lower arc erosion, higher weld resistance, and a significant lower tendency towards material transfer in DC switching circuits Table 20. Ag/SnO2 materials have been optimized for a broad range of applications by other metal oxide additives and modification in the manufacturing processes that result in different metallurgical, physical and electrical propertiesTable 18 und Table 19.

Manufacturing of Ag/SnO2 by internal oxidation is possible in principle, but during heat treatment of alloys containing > 5 wt% of tin in oxygen, dense oxide layers formed on the surface of the material prohibit the further diffusion of oxygen into the bulk of the material. By adding Indium or Bismuth to the alloy the internal oxidation is possible and results in materials that typically are rather hard and brittle and may show somewhat elevated contact resistance and is limited to applications in relays. To make a ductile material with fine oxide dispersion (SISTADOX TOS F) Figure 70 it is necessary to use special process variations in oxidation and extrusion which lead to materials with improved properties in relays. Adding a brazable fine silver layer to such materials results in a semifinished material suitable for the manufacture as smaller weld profiles (SISTADOX WTOS F) Figure 72. Because of their resistance to material transfer and low arc erosion these materials find for example a broader application in automotive relays Table 21.


Powder metallurgy plays a significant role in the manufacturing of Ag/SnO2 contact materials. Besides SnO2 a smaller amount (<1 wt%) of one or more other metal oxides such as WO3, MoO3, CuO and/or Bi2O3 are added. These additives improve the wettability of the oxide particles and increase the viscosity of the Ag melt. They also provide additional benefits to the mechanical and arcing contact properties of materials in this group Table 16 (Table 2.26 als PDF herunterladen: File:Physical Mechanical properties.pdf ).


Physical and Mechanical Properties as well as Manufacturing Processes and Forms of Supply of Extruded Silver-Tin Oxide (SISTADOX) Contact Materials

In the manufacture the initial powder mixes different processes are applied which provide specific advantages of the resulting materials in respect to their contact properties . Some of them are described here as follows:

a) Powder blending from single component powders
In this common process all components including additives that are part of the powder mix are blended as single powders. The blending is usually performed in the dry stage in blenders of different design.
b) Powder blending on the basis of doped powders
For incorporation of additive oxides in the SnO2 powder the reactive spray process (RSV) has shown advantages. This process starts with a waterbased solution of the tin and other metal compounds. This solution is nebulized under high pressure and temperature in a reactor chamber. Through the rapid evaporation of the water each small droplet is converted into a salt crystal and from there by oxidation into a tin oxide particle in which the additive metals are distributed evenly as oxides. The so created doped AgSnO2 powder is then mechanically mixed with silver powder.
c) Powder blending based on coated oxide powders
In this process tin oxide powder is blended with lower meting additive oxides such as for example Ag2 MoO4 and then heat treated. The SnO2 particles are coated in this step with a thin layer of the additive oxide.
d) Powder blending based on internally oxidized alloy powders
A combination of powder metallurgy and internal oxidation this process starts with atomized Ag alloy powder which is subsequently oxidized in pure oxygen. During this process the Sn and other metal components are transformed to metal oxide and precipitated inside the silver matrix of each powder particle.
e) Powder blending based on chemically precipitated compound powders
A silver salt solution is added to a suspension of for example SnO2 together with a precipitation agent. In a chemical reaction silver and silver oxide respectively are precipitated around the additive metal oxide particles who act as crystallization sites. Further chemical treatment then reduces the silver oxide with the resulting precipitated powder being a mix of Ag and SnO2.

Further processing of these differently produced powders follows the conventional processes of pressing, sintering and hot extrusion to wires and strips. From these contact parts such as contact rivets and tips are manufactured. To obtain a brazable backing the same processes as used for Ag/CdO are applied. As for Ag/CdO, larger contact tips can also be manufactured more economically using the press-sinter-repress (PSR) process Table 17.

Figure 43 Strain hardening of Ag/SnO2 92/8 PE by cold working

Figure 44 Softening of Ag/SnO2 92/8 PE after annealing for 1 hr after 40% cold working

Figure 45 Strain hardening of Ag/SnO2 88/12 PE by cold working

Figure 46 Softening of Ag/SnO2 88/12 PE after annealing for 1 hr after 40% cold working

Figure 47 Strain hardening of oxidized Ag/SnO2 88/12 PW4 by cold working

Figure 48 Softening of Ag/SnO2 88/12 PW4 after annealing for 1 hr after 30% cold working

Figure 49 Strain hardening of Ag/SnO2 98/2 PX by cold working

Figure 50 Softening of Ag/SnO2 98/2 PX after annealing for 1 hr after 80% cold working

Figure 51 Strain hardening of Ag/SnO2 92/8 PX by cold working

Figure 52 Softening of Ag/SnO2 92/8 PX after annealing for 1 hr after 40% cold working

Figure 53 Strain hardening of internally oxidized Ag/SnO2 88/12 TOS F by cold working

Figure 54 Softening of Ag/SnO2 88/12 TOS F after annealing for 1 hr after 30% cold working

Figure 55 Strain hardening of internally oxidized Ag/SnO2 88/12P by cold working

Figure 56 Softening of Ag/SnO2 88/12P after annealing for 1 hr after 40% cold working

Figure 57 Strain hardening of Ag/SnO2 88/12 WPC by cold working

Figure 58 Softening of Ag/SnO2 88/12 WPC after annealing for 1 hr after different degrees of cold working

Figure 59 Strain hardening of Ag/SnO2 86/14 WPC by cold working

Figure 60 Softening of Ag/SnO2 86/14 WPC after annealing for 1 hr after different degrees of cold working

Figure 61 Strain hardening of Ag/SnO2 88/12 WPD by cold working

Figure 62 Softening of Ag/SnO2 88/12 WPD after annealing for 1 hr after different degrees of cold working

Figure 63 Softening of Ag/SnO2 88/12 WPX after annealing for 1 hr after different degrees of cold working

Figure 64 Strain hardening of Ag/SnO2 88/12 WPX by cold working

Figure 65 Micro structure of Ag/SnO2 92/8 PE: a) perpendicular to extrusion direction b) parallel to extrusion direction

Figure 66 Micro structure of Ag/SnO2 88/12 PE: a) perpendicular to extrusion direction b) parallel to extrusion direction

Figure 67 Micro structure of Ag/SnO2 88/12 PW: a) perpendicular to extrusion direction b) parallel to extrusion direction

Figure 68 Micro structure of Ag/SnO2 98/2 PX: a) perpendicular to extrusion direction b) parallel to extrusion direction

Figure 69 Micro structure of Ag/SnO2 92/8 PX: a) perpendicular to extrusion direction b) parallel to extrusion direction

Figure 70 Micro structure of Ag/SnO2 88/12 TOS F: a) perpendicular to extrusion direction b) parallel to extrusion direction

Figure 71 Micro structure of Ag/SnO2 86/14 WPC: a) perpendicular to extrusion direction b) parallel to extrusion direction, 1) AgSnO2 contact layer, 2) Ag backing layer

Figure 72 Micro structure of Ag/SnO2 92/8 WTOS F: a) perpendicular to extrusion direction b) parallel to extrusion direction,1) AgSnO2 contact layer, 2) Ag backing layer

Figure 73 Micro structure of Ag/SnO2 88/12 WPD: parallel to extrusion direction 1) AgSnO2 contact layer, 2) Ag backing layer

Figure 74 Micro structure of Ag/SnO2 88/12 WPX:parallel to extrusion direction 1) AgSnO2 contact layer, 2) Ag backing layer

Figure 75 Micro structure of Ag/SnO2 86/14 WPX: a) perpendicular to extrusion direction b) parallel to extrusion direction, 1) AgSnO2 contact layer, 2) Ag backing layer

Figure 43: Strain hardening of Ag/SnO2 92/8 PE by cold working
Figure 44: Softening of Ag/SnO2 92/8 PE after annealing for 1 hr after 40% cold working
Figure 45: Strain hardening of Ag/SnO2 88/12 PE by cold working
Figure 46: Softening of Ag/SnO2 88/12 PE after annealing for 1 hr after 40% cold working
Figure 47: Strain hardening of oxidized Ag/SnO2 88/12 PW4 by cold working
Figure 48: Softening of Ag/SnO2 88/12 PW4 after annealing for 1 hr after 30% cold working
Figure 49: Strain hardening of Ag/SnO2 98/2 PX by cold working
Figure 50: Softening of Ag/SnO2 98/2 PX after annealing for 1 hr after 80% cold working
Figure 51: Strain hardening of Ag/SnO2 92/8 PX by cold working
Figure 52: Softening of Ag/SnO2 92/8 PX after annealing for 1 hr after 40% cold working
Figure 53: Strain hardening of internally oxidized Ag/SnO2 88/12 TOS F by cold working
Figure 54: Softening of Ag/SnO2 88/12 TOS F after annealing for 1 hr after 30% cold working
Figure 55: Strain hardening of internally oxidized Ag/SnO2 88/12P by cold working
Figure 56: Softening of Ag/SnO288/12P after annealing for 1 hr after 40% cold working
Figure 57: Strain hardening of Ag/SnO2 88/12 WPC by cold working
Figure 58: Softening of Ag/SnO2 88/12 WPC after annealing for 1 hr after different degrees of cold working
Figure 59: Strain hardening of Ag/SnO2 86/14 WPC by cold working
Figure 60: Softening of Ag/SnO2 86/14 WPC after annealing for 1 hr after different degrees of cold working
Figure 61: Strain hardening of Ag/SnO2 88/12 WPD by cold working
Figure 62: Softening of Ag/SnO2 88/12 WPD after annealing for 1 hr after different degrees of cold working
Figure 63: Softening of Ag/SnO2 88/12 WPX after annealing for 1 hr after different degrees of cold working
Figure 64: Strain hardening of Ag/SnO2 88/12 WPX by cold working
Figure 65: Micro structure of Ag/SnO2 92/8 PE: a) perpendicular to extrusion direction b) parallel to extrusion direction
Figure 66: Micro structure of Ag/SnO2 88/12 PE: a) perpendicular to extrusion direction b) parallel to extrusion direction
Figure 67: Micro structure of Ag/SnO2 88/12 PW: a) perpendicular to extrusion direction b) parallel to extrusion direction
Figure 68: Micro structure of Ag/SnO2 98/2 PX: a) perpendicular to extrusion direction b) parallel to extrusion direction
Figure 69: Micro structure of Ag/SnO2 92/8 PX: a) perpendicular to extrusion direction b) parallel to extrusion direction
Figure 70: Micro structure of Ag/SnO2 88/12 TOS F: a) perpendicular to extrusion direction b) parallel to extrusion direction
Figure 71: Micro structure of Ag/SnO2 86/14 WPC: a) perpendicular to extrusion direction b) parallel to extrusion direction, 1) AgSnO2 contact layer, 2) Ag backing layer
Figure 72: Micro structure of Ag/SnO2 92/8 WTOS F: a) perpendicular to extrusion direction b) parallel to extrusion direction,1) AgSnO2 contact layer, 2) Ag backing layer
Figure 73: Micro structure of Ag/SnO2 88/12 WPD: parallel to extrusion direction 1) AgSnO2 contact layer, 2) Ag backing layer
Figure 74: Micro structure of Ag/SnO2 88/12 WPX:parallel to extrusion direction 1) AgSnO2 contact layer, 2) Ag backing layer
Figure 75: Micro structure of Ag/SnO2 86/14 WPX: a) perpendicular to extrusion direction b) parallel to extrusion direction, 1) AgSnO2 contact layer, 2) Ag backing layer


Table 17: Physical Properties of Powder Metallurgical Silver-Metal Oxide Materials with Fine Silver Backing Produced by the Press-Sinter-Repress Process

Material/

DODUCO- Designation

Additives

Density

[ g/cm3]

Electrical

Resistivity

S ·cm]

Electrical

Conductivity

Vickers

Hardness

HV 10.

[%IACS]

[MS/m]

AgCdO 90/10EP

DODURIT CdO 10EP

10.1

2.08

83

48

60

AgCdO 85/15 EP DODURIT CdO 15EP

9.9

2.27

76

44

65

AgSnO² 90/10 EPX SISTADOX 10EPX

CuO and

Bi² O³

9.8

2.22

78

45

55

AgSnO² 88/12EPX SISTADOX 12EPX

CuO and

Bi² O³

9.6

2.63

66

38

60

Form of Support: formed parts, stamped parts, contact tips
  • Silver–zinc oxide (DODURIT ZnO) materials

Silver zinc oxide (DODURIT ZnO) contact materials with mostly 6 - 10 wt% oxide content including other small metal oxides are produced exclusively by powder metallurgy (Figs. 76 – 81),. Adding Ag2WO4 in the process b) as described in the preceding chapter on Ag/SnO2 has proven most effective for applications in AC relays, wiring devices, and appliance controls. Just like with the other Ag metal oxide materials, semi-finished materials in strip and wire form are used to manufacture contact tips and rivets. Because of their high resistance against welding and arc erosion Ag/ZnO materials present an economic alternative to Cd free Ag-tin oxide contact materials Table 20 and Table 21.


Table 18: Physical and Mechanical Properties as well as Manufacturing Processes and Forms of Supply of Extruded Silver-Zinc Oxide (DODURIT ZnO) Contact
Material/
DODUCO-
Designation
Silver Content
[wt%]
Additives Density
[g/cm3]
Electrical
Resistivity
[μΩ·cm]
Electrical
Conductivity
[% IACS] [MS/m]
Vickers
Hardness
Hv1
Tensile
Strength
[MPa]
Elongation
(soft annealed)
A[%]min.
Manufacturing
Process
Form of
Supply
Ag/ZnO 92/8P
DODURIT ZnO 8P
91 - 93 9.8 2.22 78 45 60 - 95 220 - 350 25 Powder Metallurgy
a) indiv. powders
1
Ag/ZnO 94/6PW25
DODURIT ZnO 6PW25
93 - 95 Ag2WO4 9.7 2.0 86 50 60 - 100 200 - 320 30 Powder Metallurgy
c) coated
1
Ag/ZnO 92/8PW25
DODURIT ZnO 8PW25
91 - 93 Ag2WO4 9.6 2.08 83 48 65 - 105 230 - 340 25 Powder Metallurgy
c) coated
1
Ag/ZnO 90/10PW25
DODURIT ZnO 10PW25
89 - 91 Ag2WO4 9.6 2.17 79 46 65 - 100 230 - 350 20 Powder Metallurgy
c) coated
1
Ag/ZnO 92/8WP
DODURIT ZnO 8WP
91 - 93 9.8 2.0 86 50 60 - 95 Powder Metallurgy
with Ag backing a) individ.
2
AgZnO 94/6WPW25
DODURIT ZnO 6WPW25
93 - 95 Ag2WO4 9.7 2.0 86 50 60 - 95 Powder Metallurgy
c) coated
2
Ag/ZnO 92/8WPW25
DODURIT ZnO 8WPW25
91 - 93 Ag2WO4 9.6 2.08 83 48 65 - 105 Powder Metallurgy
c) coated
2
Ag/ZnO 90/10WPW25
DODURIT ZnO 10WPW25
89 - 91 Ag2WO4 9.6 2.7 79 46 65 - 110 Powder Metallurgy
c) coated
2

1 = Wires, Rods, Contact rivets, 2 = Strips, Profiles, Contact tips


Figure 76 Strain hardening of Ag/ZnO 92/8 PW25 by cold working

Figure 77 Softening of Ag/ZnO 92/8 PW25 after annealing for 1 hr after 30% cold working

Figure 78 Strain hardening of Ag/ZnO 92/8 WPW25 by cold working

Figure 79 Softening of Ag/ZnO 92/8 WPW25 after annealing for 1hr after different degrees of cold working

Figure 80 Micro structure of Ag/ZnO 92/8 Pw25: a) perpendicular to extrusion direction b) parallel to extrusion direction

Figure 81 Micro structure of Ag/ZnO 92/8 WPW25:a) perpendicular to extrusion direction b) parallel to extrusion direction, 1) Ag/ZnO contact layer, 2) Ag backing layer

Figure 76: Strain hardening of Ag/ZnO 92/8 PW25 by cold working
Figure 77: Softening of Ag/ZnO 92/8 PW25 after annealing for 1 hr after 30% cold working
Figure 78: Strain hardening of Ag/ZnO 92/8 WPW25 by cold working
Figure 79: Softening of Ag/ZnO 92/8 WPW25 after annealing for 1hr after different degrees of cold working
Figure 80: Micro structure of Ag/ZnO 92/8 Pw25: a) perpendicular to extrusion direction b) parallel to extrusion direction
Figure 81: Micro structure of Ag/ZnO 92/8 WPW25:a) perpendicular to extrusion direction b) parallel to extrusion direction, 1) Ag/ZnO contact layer, 2) Ag backing layer


Table 19: Optimizing of Silver–Tin Oxide Materials Regarding their Switching Properties and Forming Behavior

Material/

Material Group

Special Properties

Ag/SnO2 PE

Especially suitable for automotive relays

(lamp loads)

Good formability (contact rivets)

Ag/SnO2 98/2 PX/PC

Especially good heat resistance

Easily riveted, can be directly welded

Ag/SnO2 TOS F

Especially suited for high inductive

DC loads

Very good formability (contact rivets)

Ag/SnO2 WPC

For AC-3 and AC-4 applications in motor

switches (contactors)

Ag/SnO2 WPD

Especially suited for severe loads (AC-4)

and high switching currents

Ag/SnO2 WPX

For standard motor loads (AC-3) and

Resistive loads (AC-1), DC loads (DC-5)

Ag/SnO2 WTOSF

Especially suitable for high inductive DC

loads


Table 20: Contact and Switching Properties of Silver–Metal Oxide Materials
Material/DODUCO-Designation Properties
Ag/CdO
DODURIT CdO
High resistance against welding during current on switching for currents up to
5kA especially for powder metallurgical materials,

Weld resistance increases with higher oxide contents,
Low and stable contact resistance over the life of the device and good
temperature rise properties,
High arc erosion resistance and contact life at switching currents
of 100A – 5kA,
Very good arc moving properties for materials produced by internal oxidation,
Good arc extinguishing properties,
Formability better than the one of Ag/SnO2 and Ag/ZnO materials,
Use of Ag/CdO in automotive components is prohibited because of Cd toxicity,
Prohibition of use in consumer products and appliances in EU.

Ag/SnO2
SISTADOX
Environmentally friendly materials,

Very high resistance against welding during current on switching,
Weld resistance increases with higher oxide contents,
Low and stable contact resistance over the life of the device and good
temperature rise properties through use of special additives,
High arc erosion resistance and contact life,
Very low and flat material transfer during DC load switching,
Good arc moving and very good arc extinguishing properties

Ag/ZnO
DODURIT ZnO
Environmentally friendly materials,

High resistance against welding during current on switching
(capacitor contactors),
Low and stable contact resistance through special oxide additives,
Very high arc erosion resistance at high switching currents,
Less favorable than Ag/SnO2 for electrical life and material transfer,
With Ag2WO4 additive especially suitable for AC relays


Table 21: Application Examples of Silver–Metal Oxide Materials

Material

Application Examples

Ag/CdO

Micro switches, Network relays, Wiring devices, Appliance switches, Main switches, contactors, Small (main) power switches

Ag/SnO2

Micro switches, Network relays, Automotive relays, Appliance switches,

Main switches, contactors, Fault current protection relays (paired against

Ag/C), (Main) Power switches

Ag/ZnO

Wiring devices, AC relays, Appliance switches, Motor-protective circuit

breakers (paired with Ag/Ni or Ag/C), Fault current circuit breakers paired againct Ag/C, (Main) Power switches

Silver–Graphite (GRAPHOR)-Materials

Ag/C (GRAPHOR) contact materials are usually produced by powder metallurgy with graphite contents of 2 – 5 wt% Table 22. The earlier typical manufacturing process of single pressed tips by pressing - sintering - repressing (PSR) has been replaced in Europe for quite some time by extrusion. In North America and some other regions however the PSR process is still used to some extend mainly for cost reasons.

The extrusion of sintered billets is now the dominant manufacturing method for semi-finished AgC materials . The hot extrusion process results in a high density material with graphite particles stretched and oriented in the extrusion direction (Figs. 86 – 89). Depending on the extrusion method in either rod or strip form the graphite particles can be oriented in the finished contact tips perpendicular (GRAPHOR) or parallel (GRAPHOR D) to the switching contact surface Figure 87 and Figure 88.

Since the graphite particles in the Ag matrix of Ag/C materials prevent contact tips from directly being welded or brazed, a graphite free bottom layer is required. This is achieved by either burning out (de-graphitizing) the graphite selectively on one side of the tips or by compound extrusion of a Ag/C billet covered with a fine silver shell.

Ag/C contact materials exhibit on the one hand an extremely high resistance to contact welding but on the other have a low arc erosion resistance. This is caused by the reaction of graphite with the oxygen in the surrounding atmosphere at the high temperatures created by the arcing. The weld resistance is especially high for materials with the graphite particle orientation parallel to the arcing contact surface. Since the contact surface after arcing consists of pure silver the contact resistance stays consistently low during the electrical life of the contact parts.

A disadvantage of the Ag/C materials is their rather high erosion rate. In materials with parallel graphite orientation this can be improved if part of the graphite is incorporated into the material in the form of fibers (GRAPHOR DF), Figure 89. The weld resistance is determined by the total content of graphite particles.

Ag/C tips with vertical graphite particle orientation are produced in a specific sequence: Extrusion to rods, cutting of double thickness tips, burning out of graphite to a controlled layer thickness, and a second cutting to single tips. Such contact tips are especially well suited for applications which require both, a high weld resistance and a sufficiently high arc erosion resistance Table 23. For attachment of Ag/C tips welding and brazing techniques are applied.

welding the actual process depends on the material's graphite orientation. For Ag/C tips with vertical graphite orientation the contacts are assembled with single tips. For parallel orientation a more economical attachment starting with contact material in strip or profile tape form is used in integrated stamping and welding operations with the tape fed into the weld station, cut off to tip form and then welded to the carrier material before forming the final contact assembly part. For special low energy welding the Ag/C profile tapes GRAPHOR D and DF can be pre-coated with a thin layer of high temperature brazing alloys such as CuAgP.

In a rather limited way, Ag/C with 2 – 3 wt% graphite can be produced in wire form and headed into contact rivet shape with low head deformation ratios.

The main applications for Ag/C materials are protective switching devices such as miniature molded case circuit breakers, motor-protective circuit breakers, and fault current circuit breakers, where during short circuit failures highest resistance against welding is required Table 24. For higher currents the low arc erosion resistance of Ag/C is compensated by asymmetrical pairing with more erosion resistant materials such as Ag/Ni and Ag/W.

Figure 82 Strain hardening of Ag/C 96/4 D by cold working

Figure 83 Softening of Ag/C 96/4 D after annealing

Figure 84 Strain hardening of Ag/C DF by cold working

Figure 85 Softening of Ag/C DF after annealing

Figure 86 Micro structure of Ag/C 97/3: a) perpendicular to extrusion direction b) parallel to extrusion direction, 1) Ag/C contact layer, 2) Ag backing layer

Figure 87 Micro structure of Ag/C 95/5: a) perpendicular to extrusion direction b) parallel to extrusion direction, 1) Ag/C contact layer, 2) Ag backing layer

Figure 88 Micro structure of Ag/C 96/4 D: a) perpendicular to extrusion direction b) parallel to extrusion direction, 1) Ag/C contact layer, 2) Ag backing layer

Figure 89 Micro structure of Ag/C DF: a) perpendicular to extrusion direction b) parallel to extrusion direction, 1) Ag/C contact layer, 2) Ag/Ni 90/10 backing layer

Figure 82: Strain hardening of Ag/C 96/4 D by cold working
Figure 83: Softening of Ag/C 96/4 D after annealing
Figure 84: Strain hardening of Ag/C DF by cold working
Figure 85: Softening of Ag/C DF after annealing
Figure 86: Micro structure of Ag/C 97/3: a) perpendicular to extrusion direction b) parallel to extrusion direction, 1) Ag/C contact layer, 2) Ag backing layer
Figure 87: Micro structure of Ag/C 95/5: a) perpendicular to extrusion direction b) parallel to extrusion direction, 1) Ag/C contact layer, 2) Ag backing layer
Figure 88: Micro structure of Ag/C 96/4 D: a) perpendicular to extrusion direction b) parallel to extrusion direction, 1) Ag/C contact layer, 2) Ag backing layer
Figure 89: Micro structure of Ag/C DF: a) perpendicular to extrusion direction b) parallel to extrusion direction, 1) Ag/C contact layer, 2) Ag/Ni 90/10 backing layer
Table 22: Physical Properties of Silver–Graphite (GRAPHOR) Contact Materials
Material/
DODUCO-
Designation
Silver Content
[wt%]
Density
[g/cm3]
Melting Point
[°C]
Electrical Resistivity
[μΩ·cm]
Electrical
Conductivity
[% IACS] [MS/m]
Vickers-Hardnes
HV10
42 - 45
Ag/C 98/2
GRAPHOR 2
97.5 - 98.5 9.5 960 1.85 - 1.92 90 - 93 48 - 50 42 - 44
Ag/C 97/3
GRAPHOR 3
96.5 - 97.5 9.1 960 1.92 - 2.0 86 - 90 45 - 48 41 - 43
Ag/C 96/4
GRAPHOR 4
95.5 - 96.5 8.7 960 2.04 - 2.13 81 - 84 42 - 46 40 - 42
Ag/C 95/5
GRAPHOR 5
94.5 - 95.5 8.5 960 2.12 - 2.22 78 - 81 40 - 44 40 - 60
Ag/C 97/3D
GRAPHOR 3D*)
96.5 - 97.5 9.1 - 9.3 960 1.92 - 2.08 83 - 90 45 - 50 35 - 55
Ag/C 96/4D
GRAPHOR 4D*)
95.5 - 96.5 8.8 - 9.0 960 2.04 - 2.22 78 - 84 43 - 47 35 - 60
AgCDF
GRAPHOR DF**)
95.7 - 96.7 8.7 - 8.9 960 2.27 - 2.50 69 - 76 40 - 44

*) Graphite particles parallel to switching surface
**) Graphite content 3.8 wt%, Graphite particles and fibers parallel to switching surface


Table 23: Contact and Switching properties of Silver–Graphite (GRAPHOR) Contact Materials

Material/

DODUCO-Designation

Properties

Ag/C

GRAPHOR

Highest resistance against welding during make operations at high currents,

High resistance against welding of closed contacts during short circuit,

Increase of weld resistance with higher graphite contents, Low contact resistance,

Low arc erosion resistance, especially during break operations, Higher arc erosion with increasing graphite contents, at the same time carbon build-up on switching chamber walls increases, GRAPHOR with vertical orientation has better arc erosion resistance, parallel orientation has better weld resistance,

Limited arc moving properties, therefore paired with other materials,

Limited formability,

Can be welded and brazed with decarbonized backing, GRAPHOR DF is optimized for arc erosion resistance and weld resistance


Table 24: Application Examples and Forms of Supply of Silver– Graphite (GRAPHOR) Contact Materials

Material/

DODUCO Designation

Application Examples

Form of Supply

Ag/C 98/2

GRAPHOR 2

Motor circuit breakers, paired with Ag/Ni

Contact tips, brazed and welded contact parts, some contact rivets

Ag/C 97/3

GRAPHOR 3

Ag/C 96/4

GRAPHOR 4

Ag/C 95/5

GRAPHOR 5

GRAPHOR 3D GRAPHOR 4D GRAPHOR DF

Circuit breakers, paired with Cu, Motor-protective circuit breakers, paired with Ag/Ni,

Fault current circuit breakers, paired with Ag/Ni, Ag/W, Ag/WC, Ag/SnO2, Ag/ZnO,

(Main) Power switches, paired with Ag/Ni, Ag/W

Contact tips, brazed and welded contact

parts, some contact rivets with

Ag/C97/3

Ag/C 97/3

GRAPHOR 3

Ag/C 96/4

GRAPHOR 4

Ag/C 95/5

GRAPHOR 5

GRAPHOR 3D GRAPHOR 4D GRAPHOR DF

Circuit breakers, paired with Cu, Motor-protective circuit breakers, paired with Ag/Ni,

Fault current circuit breakers, paired with Ag/Ni, Ag/W, Ag/WC, Ag/SnO2, Ag/ZnO,

(Main) Power switches, paired with Ag/Ni, Ag/W

Contact profiles (weld tapes), Contact tips, brazed and welded contact parts

References

References