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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.
<xr id="tab:tab2.11Overview of the Most Widely Used Silver Grades"/> (Table 2.11) 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 <xr id="tab:tab2.12"/> Table 2.12. additional properties of silver powders and their usage are described in [[ Precious Metal Powders and Preparations#Precious_Metal_Powders|Precious Metal Powders ]] und [[Precious_Metal_Powders_and_Preparations|Tab. 8.1]] (Tab. 8.1.)
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.
currents < 2 A <xr id="tab:tab2.16"/> (Table 2.16). Electroplated silver coatings are widely used to reduce the contact resistance and improve the brazing behavior of other contact materials and components.
<figtable id="tab:tab2.11Overview of the Most Widely Used Silver Grades">
'''Table 2.11: Overview of the Most Widely Used Silver Grades'''
<table class="twocolortable">
<xr id="fig:fig2.45Strain hardening of Ag bei cold working"/> Fig. 2.45: Strain hardening of Ag 99.95 by cold working
<xr id="fig:fig2.46Softening of Ag after annealing after different degrees"/> Fig. 2.46: Softening of Ag 99.95 after annealing for 1 hr after different degrees of strain hardening
<div class="multiple-images">
<figure id="fig:fig2.45Strain hardening of Ag bei cold working">
[[File:Strain hardening of Ag bei cold working.jpg|left|thumb|<caption>Strain hardening of Ag 99.95 bei cold working</caption>]]
</figure>
<figure id="fig:fig2.46Softening of Ag after annealing after different degrees">
[[File:Softening of Ag after annealing after different degrees.jpg|left|thumb|<caption>Softening of Ag 99.95 after annealing for 1 hr after different degrees of strain hardening</caption>]]
</figure>
===Silver Alloys===
To improve the physical and contact properties of fine silver melt-metallurgical produced silver alloys are used <xr id="tab:tab2.13Physical Properties of Silver and Silver Alloys"/>(Table 2.13). 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 <xr id="tab:tab2.14"/> (Table 2.14). On the other hand however, other properties such as electrical conductivity and chemical corrosion resistance can be negatively impacted by alloying <xr id="fig:fig2.47"/> (Fig. 2.47) and <xr id="fig:fig2.48"/> (Fig. 2.48).
<figtable id="tab:tab2.13Physical Properties of Silver and Silver Alloys">
'''Table 2.13: Physical Properties of Silver and Silver Alloys'''
</figtable>
<xr id="fig:fig2.47Influence of 1 10 atom of different alloying metals"/> Fig. 2.47: Influence of 1-10 atom% of different alloying metals on the electrical resistivity of silver
<xr id="fig:fig2.48Electrical resistivity p of AgCu alloys"/> Fig. 2.48: Electrical resistivity p of AgCu alloys
<div class="multiple-images">
<figure id="fig:fig2.47Influence of 1 10 atom of different alloying metals">
[[File:Influence of 1 10 atom of different alloying metals.jpg|left|thumb|<caption>Influence of 1-10 atom% of different alloying metals on the electrical resistivity of silver</caption>]]
</figure>
<figure id="fig:fig2.48Electrical resistivity p of AgCu alloys">
[[File:Electrical resistivity p of AgCu alloys.jpg|left|thumb|<caption>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</caption>]]
</figure>
====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 <xr id="fig:fig2.51"/> 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 <xr id="fig:fig2.49Coarse grain micro structure of Ag"/> Fig. 2.49 and <xr id="fig:fig2.50Fine grain microstructure of AgNiO"/>Fig 2.50.
<div class="multiple-images">
<figure id="fig:fig2.49Coarse grain micro structure of Ag">
[[File:Coarse grain micro structure of Ag.jpg|left|thumb|<caption>Coarse grain micro structure of Ag 99.97 after 80% cold working and 1 hr annealing at 600°C</caption>]]
</figure>
<figure id="fig:fig2.50Fine grain microstructure of AgNiO">
[[File:Fine grain microstructure of AgNiO.jpg|left|thumb|<caption>Fine grain microstructure of AgNi0.15 after 80% cold working and 1 hr annealing at 600°C</caption>]]
</figure>
