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→Precious Metal Flakes
===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.
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 cm<sup>3</sup> 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).
<table borderfigure id="1" cellspacing="0" style="border-collapsefig: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="s6Solar cell with print pattern of ARGONOR N920">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">4File:Solar cell with print pattern of ARGONOR N920.0 - 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<span class="s8">3</span>jpg|right|thumb|Figure 2: Solar cell with print pattern of ARGONOR N920]</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<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></tablefigure>
While in the past mostly glass ware and ceramics (table china) were coated for decorative purposes with gold or platinum, precious metals have since quite a few years been applied to non-metallic substrates such as ceramics, 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 screen or tampon printing, by spraying, immersion or with a paint brush.
===8.2 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.
<figtable id===8.2.1 Precious Metal "tab:Liquid Silver Preparations for Firing Preparations===Application (ARGONOR)">The firing preparations in liquid or paste form are widely used in electrical and electronic engineering and especially in the thick-film technology <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. 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 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 techniques any shapes of conductive patterns can be created ''(Fig</p></td><td><p class="s6">530 - 650</p></td><td><p class="s6">Viscosity</p><p class="s6">10 – 15. 8.2)'' resulting in conductive paths with 000 mPa·s, good electrical properties and high temperature stability.solderability</p></td><td><p class="s6">65</p></td></tr></table></figtable>
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 (<table border="1" cellspacing="0" stylexr id="border-collapsetab: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 [wt%]</p></td></tr><tr><td><p class="s6">Argonor N92</p></td><td><p class="s6">glassPaints, Conductive Pastes, ceramics</p></td><td><p class=and Conductive Adhesives"s6">paint brush, spray gun</p></td><td><p class="s6">530 !--(Table 8.3)-- 650</p></td><td>). 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 (<p classxr id="s6fig:Flexible keyboard contact pattern printed with AUROMAL 170">Viscosity</p><p class="s6">500 – 1!--(Fig. 8.000 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 3)-- 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 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 of electrical 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 8.2.2 3:-->Silver Paints, Conductive Paints Pastes, and Conductive Adhesives'''</caption>{| class="twocolortable" style=="text-align: left; font-size: 12px"|-!Preparation !Substrate<br />Material!Application by!Drying<br />[°C]!Properties!Usage Amount<br />[g/100 cm<sup>2</sup>]!Area Resistance<br />[Ω/m<sup>2</sup>]|-|AROMAL 38|glass, plastics|spraying, immersion,<br />paint brush|RT,<br />30 min<br />100°C|hard well conducting<br />Ag layer for broad applications|0.5 - 2Conductive paints are precious metal preparations in liquid or paste form|< 0. They contain the metal filler material1|-|AROMAL 50|glass, wax, plastics|spraying, fine silver particles as conductive pigments mostly in flake formimmersion, a <br />paint compound on artificial resin basisbrush|10 min<br />RT|very flat surface, and an organic solvent ''(Table 8<br />especially for electrolytic build-up|0.3)''5 - 2|< 0. The solvent evaporates during drying in air or by aging at slightly elevated temperatures. This allows the silver particles to connect metallically 2|-|AROMAL 70T|plastics|tampon printing|60 min<br />RT|hard and form well conductive paths ''(Figcoating||< 0. 8.3)''1|-|AROMAL 141|plastics,<br />paper- based plastics|screen printing|45 min<br />120°C|mechanically <br />very strong coatings||< 0.05|-|AROMAL 170|plastics|screen printing|30 min<br />100°CConductive adhesives are used mostly |flexible layers,<br />well suited for mechanical bonding with low thermal impactfoil materials||< 0. As the adhesive components high05|-polymer organic substances such |AROMAL K 5 A+B|metal, glass|dispenser,<br />screen printing|24h RT,<br />3h<br />80°C|mechanically very strong<br />bond connection<br />as epoxy resins and mixed polymers are mostly usedalternative to soldering||< 0. They are made electrically filler materials such as flake shaped silver powders (70 – 80 wt%)1|-|AROMAL K 20|metal, plastics,<br />ceramics|dispenser,<br />screen printing|15 min<br />150°C|flexible bonds which help<br />decrease thermal stresses||< 0. 1|-|DOSILAC|colspan="6" |Silver based conductive adhesives are available as single or two component adhesive systems. Both types are hardening without the application paints in spray cans; can be spray painted; properties similar to those of pressure.AUROMAL 50|}</figtable>
The mechanical strength of the bond connections depends mostly on the selected hardening temperature (<table borderxr id="1" cellspacing="0" style="border-collapsefig:collapse"><tr><td><p class="s6Shear force of an adhesive joint">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="s7">[°C]</p></td><td/><td><p class="s6">Amount</p><p class="s7">[g/100 cm²]</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!--(Fig. 8.5 4)-- 2</p></td><td><p class="s7">< 0).1</p></td></tr></table>
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 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. However, in terms of the quantities used, they are of lesser economic importance.Shear force <figure id="fig:SEM photos of an adhesive jointsilver flakes a fine grain b large flat">([[File:SEM photos of silver adhesive AUROMAL K 20) as flakes a function fine grain b large flat.jpg|left|thumb|Figure 5: SEM photos ofsilver flakes (a) fine grain (b) large flat]]the hardening temperature</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"|>>99.0</p></td><td><p class="s6"|>>99.0</p></td><td><p class="s6"|>>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]]