Silver, chemical symbol Ag, is one of the best-known metals. Be it the silver cutlery in family possession for over 100 years or silver jewellery that slumbers in a treasure chest. The “silvery”-white metal has been known and appreciated since ancient times. Because it is more common (about 20 times) and because of its lower chemical stability it is not as expensive as gold. The lower chemical stability is illustrated by the fact that silver tarnishes – in most cases this means that silver reacts with sulphur compounds e.g. from perspiration to black silver sulphide. In contrast, gold is so precious that it hardly reacts with “normal” reagents and therefore does not tarnish.
Silver is often mined as metal (called “solid silver”) more seldom in the form of silver salt. It is usually mixed with copper or lead and/or other metals; this is referred to as “association”.
For the chemical industry silver plays only a minor role e.g. as a catalyst. A classical area of application was the traditional photography. Photographic film contained silver salts that were reduced to elemental silver through exposure, thus producing the desired photo.
Film developing in many photo labs lead to unnecessary silver being washed out and ending up in sewage treatment plants (cf. the discussion whether nanosilver is damaging to the sewage treatment plants).
Since the digital camera has reached private and professional households, the contamination of sewage water with silver has to have reduced; the classical (silver) film is today an “endangered species”.
Another important area of application for silver is the electronics industry, as silver has one of the highest conductivities for electrical current and is therefore very important for the electronics industry. Combined with great ductility and the chemical stability described above, silver is a highly demanded material for electronic devices or circuits. Brazing alloys containing silver and other metals are used for brazing joints Silver can play a role in biological systems as well. Already the old Romans knew about the bacteria inhibiting property of silver, they put silver coins in jars that were used for the storage of milk.
The minimal release of silver and thus the release of silver ions lead to a longer preservation of the milk. Because the bactericide (biocidal) effect was only weak, it was possible to drink the dissolved silver without any problems.
For the treatment of warts, which are mostly caused by viruses, silver nitrate is used in the form of a solid stick, the so-called lunar caustic The effect of this stick is commonly described as cauterization, this means the silver nitrate releases corrosive nitric acid when exposed to light and this etches off the wart.
At light, the remaining silver ion is reduced to elemental silver that causes a blackening of the treated skin area. Because the reduction of (atomic) silver ions produces black silver particles ranging in size in the upper nanometer or micrometer scope, there have to exist silver particles with dimensions of a few nanometers at some point in time in between. According to the present definition, the traditional lunar caustic performs a kind of nanotechnology.
In medicine (nano) silver is used as a wound dressing, often the term „collodial“ silver is used – it was called that way before the term nano was in fashion (collides can range in size between nanometers and micrometers). Nanosilver has a better effect compared to coarse silver particles, because it has a larger surface and can be dispersed more finely. Through the larger surface more silver ions are released, that finally have the bactericide (biocidal) effect. Additionally, less of the expensive silver is needed. Because of its bactericide (etc.) effects silver is also used in other products. Often it is not clear whether the attribute “nano” is only used for advertising purposes or if nanoparticles were actually used – that is to say the term nano is not protected.
Furthermore, it can be argued if it makes sense to invest our limited silver supplies in low-odour socks. It is proven that silver is washed off from such textiles and ends up in sewage treatment plants (cf. the above paragraph about photography).
- http://www.nanotechproject.org/inventories/consumer/ (commonly referred to as the Woodrow Wilson Database)
- nanotrust dossier No10: Nanosilber (in German only): http://nanotrust.ac.at/dossiers.html