===8.1 Precious Metal Powders===Precious metal powders are used as raw materials for many technical products as well as for medical and decorative applications. This includes the production of silver composites 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.

Precious metal powders are used as raw materials for many technical products as well as for medical consist of small particles of approx. 1 – 100 µm diameter, which distinguish themselves by particle shape, particle size and decorative applicationsparticle size distribution. Among these are Depending on the manufacture of composite manufacturing process, silver materials for electrical contacts (Ag/Ni, Ag/metal oxides, Ag/C, Ag/W, etc), catalysts, electrodesparticles may be spherical, crystalline or dental productsdentritic. Besides these precious metal powders are used as the base material in preparations as well as conductive paints and adhesivesSmaller particle size typically leads to a larger surface area.

Precious metal <figure id="fig:Different shapes of silver powders consist "> [[File:Different shapes of small particles of approxsilver powders. jpg|right|thumb|Figure 1 – 100 µm diameter which distinguish themselves by particle shape, particle size and particle size distribution. Depending on the manufacturing process, : Different shapes of silver particles may be powders a) spherical, crystalline, or dentritic. Smaller particle size typically leads to a larger surface area.b) rounded crystal applomerates]]</figure>

The measured densities of powders – both, the apparent density and the tap density – are low , compared to the wrought metals because of the gaps between the particles. They vary in a wide range between 0.5 and 6 g/cm3 cm³ depending on the morphology of the particles and their tendency to agglomeration. Precious metal powders can be compacted by pressing and then sinteredsintering afterwards; a certain amount of porosity is however always retained.

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 – havedifferent properties as shown in (<xr id="tab:DifferentTypesofSilverPowders" /><!--(Tab. 8.1)--> and [[Silver_Based_Materials#label-tab:Quality_Criteria_of_Differently_Manufactured_Silver_Powders|Table Quality Criteria of Differently Manufactured Silver Powders]]<!--(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 photographs of atomized silver powder in spherical shapes (a) and a cementation powder composed of rounded crystal agglomerates (b).

Fig<figtable id="tab:DifferentTypesofSilverPowders"><caption>'''<!--Table 8. 811: -->Different shapes Types of silver powders aSilver 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) spherical b[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/cm³]</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.) rounded crystal applomerates[m²/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></figtable>

Table 8<figure id="fig:Solar cell with print pattern of ARGONOR N920">[[File:Solar cell with print pattern of ARGONOR N920.1jpg|right|thumb|Figure 2: Different Types Solar cell with print pattern of Silver PowdersARGONOR N920]]</figure>

<While in the past mostly glass ware and ceramics (table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s6">Powder type</p></td><td><p class="s6">GE</p></td><td><p class="s6">GN1</p></td><td><p class="s7">ES</p></td><td><p class="s6">V</p></td></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 Sizechina) [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">were coated for decorative purposes with gold or platinum, precious metals have since quite a few years been applied to non-</p></td></tr><tr><td><p class="s6">Tap density</p><p class="s6">(DIN/ISO 3953) [g/cm<span class="s8">3</span>]</p></td><td><p class="s6">0metallic substrates such as ceramics, glass or plastics to make their surfaces electrically conductive.7 - 1To coat these surfaces, fine powders of the precious metal are dispersed in a carrier, containing a paint basis and organic solvents.1</p></td><td><p class="s6">2Such preparations can be applied by screen or tampon printing, by spraying, immersion or with a paint brush.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<span class="s8">2</span>/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>

While in the past mostly glass ware and ceramics <figtable id="tab:Liquid Silver Preparations for Firing Application (table chinaARGONOR) were coated "><caption>'''<!--Table 8.2:-->Liquid Silver Preparations for decorative purposes with gold or platinumFiring 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, precious metals have since quite a few years been applied to nonspray gun</p></td><td><p class="s6">530 -metallic substrates such as ceramics650</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, or plastics to make their surfaces electrically conductive. To coat these surfaces fine powders of the precious metal are dispersed in a carrier containing a paint basis and organic solvents. Such preparations can be applied by </p><p class="s6">ceramics</p></td><td><p class="s6">screen or tampon </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, by spraying, immersion, or with a paint brush.good solderability</p></td><td><p class="s6">65</p></td></tr></table></figtable>

===8.2.1 Precious Metal Firing PreparationsConductive Paints and Adhesives===The firing preparations in liquid or paste form are widely used in electrical and electronic engineering and especially in the thick-film technology ''(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 ''(Fig. 8.2)'' resulting in conductive paths with good electrical properties and high temperature stability.

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 8.23)-->). 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: Liquid Silver Preparations for Firing Application Flexible keyboard contact pattern printed with AUROMAL 170"/><!--(ARGONORFig. 8.3)-->).

<table border="1" cellspacing="0" style="borderConductive adhesives are used mostly for mechanical bonding with low thermal impact. As the adhesive components high-collapse:collapse"><tr><td><p class="s6">Preparation</p></td><td><p class="s6">Substrate</p><p class="s6">Material</p></td><td><p class="s6">Application by</p></td><td><p class="s6">Firing Temperature [°C]</p></td><td><p class="s6">Properties</p></td><td><p class="s6">Silver Content [polymer organic substances such as epoxy resins and mixed polymers are mostly used. They are made of electrical filler materials such as flake shaped silver powders (70 – 80 wt%]</p></td></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). Silver based conductive adhesives are available as single or two component adhesive systems.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 – 15Both types are hardening without the application of pressure.000 mPa·s, good solderability</p></td><td><p class="s6">65</p></td></tr></table>

===8.2.2 Conductive Paints paints and Adhesives===Conductive paints are precious metal preparations adhesives have broad applications in liquid or paste formelectrical and electronic engineering. They contain are used for example for the metal filler materialcontacting of film resistors, fine silver particles as conductive pigments mostly in flake formmounting of terminal wires, a paint compound on artificial resin basis, and an organic solvent ''(Table 8.3)''. The solvent evaporates during drying in air conducting electrostatic electricity or by aging contacting components at slightly elevated low temperatures. This allows the silver particles to connect metallically and form conductive paths ''(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.

Table The mechanical strength of the bond connections depends mostly on the selected hardening temperature (<xr id="fig:Shear force of an adhesive joint"/><!--(Fig. 8.3: Silver Paints, Conductive Pastes, and Conductive Adhesives4)-->).

<table borderfigure id="1" cellspacing="0" style="border-collapsefig:collapse"><tr><td><p class="s6">Preparation</p></td><td><p class="s6">Substrate</p></td><td><p class="s6">Application</p></td><td><p class="s6">Drying</p></td><td><p class="s6">Properties</p></td><td><p class="s6">Usage</p></td><td><p class="s6">Area</p></td></tr><tr><td/><td><p class="s6">Material</p></td><td><p class="s6">by</p></td><td><p class="s7Shear force of an adhesive joint">[°C]</p></td><td/><td><p class="s6">Amount</p><p class="s7">[g/100 cm²File:Shear force of an adhesive joint.jpg|left|thumb|Figure 4: Shear force of an adhesive joint (silver adhesive AUROMAL K 20) as a function of the hardening temperature]</p></td><td><p class="s6">Resistance</p><p class="s7">[<span class="s10">S </span>/m²]</p></td></tr><tr><td><p class="s7">AROMAL 38</p></td><td><p class="s6">glass, plastics</p></td><td><p class="s6">spraying, immersion,</p></td><td><p class="s7">RT,</p><p class="s7">30 min</p></td><td><p class="s6">hard well conducting</p></td><td><p class="s7">0.5 - 2</p></td><td><p class="s7">&lt; 0.1</p></td></tr></tablefigure>

To obtain certain desired physical properties of preparations, the dispersed precious metals in flat flake-like particles (generally called "flakes") are needed. These are produced by milling fine metal powders in the presence of milling additives or agents. The mechanical strength properties of these metal flakes, i.e. silver flakes (ability to disperse easily, flow characteristics, electrical conductivity) are strongly dependent on the bond connections depends mostly particle shape and size as well as on the selected hardening temperature ''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"/><!--(FigTab. 8.4)''-->.Gold and platinum can also be produced as powder flakes. However, in terms of the quantities used, they are of lesser economic 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|left|thumb|Figure 5: SEM photos of silver flakes (a) fine grain (b) large flat]]</figure>

         <table borderfigtable id="1" cellspacing="0" style="border-collapsetab:collapseTypical Commercial Silver Flake Types"><trcaption>'''<td!--Table 8.4:--><p class="s6">Type of Typical Commercial Silver FlakeTypes'''</pcaption></td><td><p  {| class="s6twocolortable">F56</p></td><td><p classstyle="s6text-align: left; font-size: 12px;width:80%">|-!Type of Flake!F56!B190</p></td><td><p class="s6">!ES4</p></td></tr><tr><td><p class="s6">|-|Main characteristics</p></td><td><p class="s6">|Low tap density</p></td><td><p class="s6">|Very fine</p></td><td><p class="s6">|Pure, wide grain size distribution</p></td></tr><tr><td><p class="s6">|-|Silver content [wt%]</p></td><td><p class="s6"|>&gt;99.0</p></td><td><p class="s6"|>&gt;99.0</p></td><td><p class="s6"|>&gt;99.7</p></td></tr><tr><td><p class="s6">|-|Med. Grain size [µmμm] Tap density</p></td><td><p class="s6">|3 - 8</p></td><td><p class="s6">|4 - 6</p></td><td><p class="s6">|9 - 13</p></td></tr><tr><td><p class="s6">|-|DIN/ISO 3953 [g/cm<span class="s8"sup>3</spansup>]</p></td><td><p class="s6">|0.7 - 1.1</p></td><td><p class="s6">|2.1 - 2.7</p></td><td><p class="s6">|2.7 - 3.6</p></td></tr><tr><td><p class="s6">|-|Spec. Surface area B.E.T. [m<span class="s8"sup>2</spansup>/g]</p></td><td><p class="s6">|0.7 - 1.1</p></td><td><p class="s6">|0.3 - 0.7||}</p></td><td/></tr><tr><td/><td/><td/><td/></tr></tablefigtable> [[de:Edelmetallpulver_und_-präparate]]