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== Precious Metal Powders==
Precious metal powders are used as raw materials for many technical products as well as for medical and decorative applications. Among these are the manufacture of composite silver materials for electrical contacts (Ag/Ni, Ag/metal oxides, Ag/C, Ag/W, etc), catalysts, electrodes, or dental products. Besides these precious metal powders are used as the base material in preparations as well as conductive paints and adhesives.
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Precious metal powders are produced by various methods, such as for example electrolysis, atomizing from the molten phase, chemical precipitation,
or by cementation with non-precious metals. Depending on the manufacturing process silver powders – as the by far largest volume precious metal powder used – have different properties as shown in <xr id="tab:DifferentTypesofSilverPowders" /> <!--(Tab. 8.1) --> and [[Silver_Based_Materials|Table 2.12]] <!--(Tab. 2.12)-->. Atomizing from a melt results in a powder with high tap density composed of spherical particles. Using electrolytic deposition from a silver salt solution creates randomly shaped dentritic to crystalline particle structures. Chemical processes can result in rather fine particles with a large specific surface area. <xr id="fig:Different shapes of silver powders"/> <!--Fig. 8.1 --> shows typical SEM photo-graphs of atomized silver powder in spherical shapes (a) and a cementation powder composed of rounded crystal agglomerates (b).
<figtable id="tab:DifferentTypesofSilverPowders">
<caption>'''<!--Table 8.1: -->Different Types of Silver Powders'''</caption>
<table class="twocolortable">
<tr><th><p class="s6">Powder type</p></th><th><p class="s6">GE</p></th><th><p class="s6">GN1</p></th><th><p class="s7">ES</p></th><th><p class="s6">V</p></th></tr><tr><td><p class="s6">Manufacturing Process</p></td><td><p class="s6">chemical</p></td><td><p class="s6">chemical</p></td><td><p class="s7">electrolytic</p></td><td><p class="s6">atomized</p></td></tr><tr><td><p class="s6">Particle shape</p></td><td><p class="s6">agglomerated</p></td><td><p class="s6">agglomerated</p></td><td><p class="s7">dentritic</p></td><td><p class="s6">spherical</p></td></tr><tr><td><p class="s6">Avg. particle diameter</p><p class="s6">(median) [µm]</p></td><td><p class="s6">10 - 15</p></td><td><p class="s6">20 - 40</p></td><td><p class="s7">-</p></td><td><p class="s6">32 - 60</p></td></tr><tr><td><p class="s6">Medium particle size</p><p class="s6">(FSS - Fisher Sub Sieve Size) [µm]</p></td><td><p class="s6">-</p></td><td><p class="s6">-</p></td><td><p class="s7">4.0 - 6.0</p></td><td><p class="s6">-</p></td></tr><tr><td><p class="s6">Tap density</p><p class="s6">(DIN/ISO 3953) [g/cm<sup>3</sup>]</p></td><td><p class="s6">0.7 - 1.1</p></td><td><p class="s6">2.0 - 2.5</p></td><td><p class="s7">2.0 - 3.0</p></td><td><p class="s6">4.0 - 6.7</p></td></tr><tr><td><p class="s6">Specific surface area</p><p class="s6">(B.E.T.) [m<sup>2</sup>/g]</p></td><td><p class="s6">0.5 - 0.9</p></td><td><p class="s6">-</p></td><td><p class="s7">-</p></td><td><p class="s6">-</p></td></tr></table>
===Precious Metal Firing Preparations===
The firing preparations in liquid or paste form are widely used in electrical and electronic engineering and especially in the thick-film technology <xr id="tab:Liquid Silver Preparations for Firing Application (ARGONOR)"/> <!--(Table 8.2)-->. The precious metal filler material is mostly pure silver because of its high electrical conductivity. During firing in an oxidizing atmosphere at temperatures between 400 and 850°C a well adhering and highly conductive surface layer is formed.When utilizing screen printing techniques any shapes of conductive patterns can be created <xr id="fig:Solar cell with print pattern of ARGONOR N920"/> <!--(Fig. 8.2) --> resulting in conductive paths with good electrical properties and high temperature stability.
<figure id="fig:Solar cell with print pattern of ARGONOR N920">
[[File:Solar cell with print pattern of ARGONOR N920.jpg|right|thumb|Solar cell with print pattern of ARGONOR N920]]
<figtable id="tab:Liquid Silver Preparations for Firing Application (ARGONOR)">
<caption>'''<!--Table 8.2: -->Liquid Silver Preparations for Firing Application (ARGONOR)'''</caption>
<table class="twocolortable" style="width:80%">
<tr><th><p class="s6">Preparation</p></th><th><p class="s6">Substrate</p><p class="s6">Material</p></th><th><p class="s6">Application by</p></th><th><p class="s6">Firing Temperature [°C]</p></th><th><p class="s6">Properties</p></th><th><p class="s6">Silver Content [wt%]</p></th></tr><tr><td><p class="s6">Argonor N92</p></td><td><p class="s6">glass, ceramics</p></td><td><p class="s6">paint brush, spray gun</p></td><td><p class="s6">530 - 650</p></td><td><p class="s6">Viscosity</p><p class="s6">500 – 1.000 mPa·s, good solderability</p></td><td><p class="s6">65</p></td></tr><tr><td><p class="s6">Argonor</p></td><td><p class="s6">glass,</p><p class="s6">ceramics</p></td><td><p class="s6">screen</p><p class="s6">printing</p></td><td><p class="s6">530 - 650</p></td><td><p class="s6">Viscosity</p><p class="s6">10 – 15.000 mPa·s, good solderability</p></td><td><p class="s6">65</p></td></tr></table>
=== Conductive Paints and Adhesives===
Conductive paints are precious metal preparations in liquid or paste form. They contain the metal filler material, fine silver particles as conductive pigments mostly in flake form, a paint compound on artificial resin basis, and an organic solvent <xr id="tab:Silver Paints, Conductive Pastes, and Conductive Adhesives"/> <!--(Table 8.3)-->. The solvent evaporates during drying in air or by aging at slightly elevated temperatures. This allows the silver particles to connect metallically and form conductive paths <xr id="fig:Flexible keyboard contact pattern printed with AUROMAL 170"/> <!--(Fig. 8.3)-->.
Conductive adhesives are used mostly for mechanical bonding with low thermal impact. As the adhesive components high-polymer organic substances such as epoxy resins and mixed polymers are mostly used. They are made electrically filler materials such as flake shaped silver powders (70 – 80 wt%). Silver based conductive adhesives are available as single or two component adhesive systems. Both types are hardening without the application of pressure.
<figtable id="tab:Silver Paints, Conductive Pastes, and Conductive Adhesives">
<caption>'''<!--Table 8.3: -->Silver Paints, Conductive Pastes, and Conductive Adhesives'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
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Conductive paints and adhesives have broad applications in electrical and electronic engineering. They are used for example for the contacting of film resistors, mounting of terminal wires, conducting electrostatic electricity, or contacting components at low temperatures.
The mechanical strength of the bond connections depends mostly on the selected hardening temperature <xr id="fig:Shear force of an adhesive joint"/> <!--(Fig. 8.4)-->.
<figure id="fig:Flexible keyboard contact pattern printed with AUROMAL 170">
=== Precious Metal Flakes===
To obtain certain desired physical properties of preparations the dispersed precious metals in flat flake-like particles (generally called “flakes”"flakes") are needed. These are produced by milling fine metal powders in the presence of milling additives or agents. The properties of these metal flakes, i.e. silver flakes (ability to disperse easily, flow characteristics, electrical conductivity) are strongly dependent on the particle shape and size as well as on the type of milling agents used. <xr id="fig:SEM photos of silver flakes a fine grain b large flat"/> <!--Fig. 8.5 --> illustrates through SEM photos a type of rather fine silver flake (medium particle size 4 – 6 µm) (a) and another one with relatively large flat but thin flake shapes (particle size 8 – 11 µm) (b). Typical commercial silver flake types are listed with their respective properties in <xr id="tab:Typical Commercial Silver Flake Types"/> <!--(Tab. 8.4)-->. Gold and platinum can also be produced as powder flakes. By volumes used they are however of lesser commercial importance.
<figure id="fig:SEM photos of silver flakes a fine grain b large flat">
[[File:SEM photos of silver flakes a fine grain b large flat.jpg|right|thumb|SEM photos of silver flakes (a) fine grain (b) large flat]]
<figtable id="tab:Typical Commercial Silver Flake Types">
<caption>'''<!--Table 8.4: -->Typical Commercial Silver Flake Types'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px;width:80%"
