Silver
Under Silver is understood any technical method that on articles a coating of silver produce. When silvering glass , one also speaks of mirroring .
General
Silver plating only makes sense on largely inelastic materials because the silver layer separates from other materials under mechanical stress.
Metals and alloys such as nickel silver (a nickel-copper-zinc alloy that looks similar to silver ), copper , brass , zinc , tin , lead , iron , steel and nickel , but also non-metallic materials such as glass or plastics are suitable for silvering.
Silver coatings show the following properties:
- very good electrical conductivity, which is important for contacts, wires and waveguides in electrical engineering
- decorative appearance of art , jewelry or everyday objects, e.g. B. Cutlery
- high optical reflectivity used for mirrors and reflectors
- Corrosion protection, e.g. B. in the chemical industry
The layer thicknesses of silver coatings are very different depending on the application. While one to a few µm is often sufficient for electronic parts, up to 120 µm is deposited with cutlery.
- 90s silver plating
The commonly used designation 90 or 100 for cutlery does not refer to the layer thickness of the silver coating, but to its weight in grams on a surface of 24 dm². Usually, this area is given by twelve forks and twelve spoons for cutlery, with a layer thickness of approx. 34 to 37 µm for 90 and 45 µm for 100 silver plating. Often the first indication for the general thickness of the silver plating is followed by a second number, which relates directly to the respective piece of cutlery. A dozen identical pieces of cutlery are used as a basis, so that tablespoons are usually marked with [90] [45]. A common hallmark of [90] [18] on a cake fork indicates that 18 g of silver were necessary to silver-plate twelve cake forks with the same layer thickness as the main cutlery.
Vapor deposition
The vapor deposition of a silver reference as thermal evaporation is the most simple coating technique. The silver is heated to temperatures close to its boiling point by a resistance heater (e.g. a vapor deposition boat made of tungsten or an induction heater with a heat-resistant ceramic crucible) . It evaporates, spreads in gaseous form in the oven or vacuum chamber and condenses on the cooler substrate . The silver vapor forms a thin layer there . The layer thickness depends on the duration of the vapor deposition.
Galvanic silver plating
In galvanic silver plating, the objects are immersed in a silver electrolyte , usually potassium silver cyanide with conductive salts in an alkaline solution, after a pretreatment . When an electrical voltage is applied, a silver coating is deposited on the surface. Post-treatment often follows to improve the surface properties. Little is known that quality goods made from real silver are often given a galvanic coating of fine silver in order to conceal soldered joints and to standardize color differences.
Silver plating is one of the oldest uses in electroplating . On July 24th, 1838 and on March 25th, 1840, GR Elkington and H. Elkington registered the first patents in England under patent number 8447. As early as 1842 there was a connection and license agreement with Charles Christofle & Co, Paris. It was not until the 1870s that electroplating spread among German manufacturers of silver cutlery.
Electroless silver plating
For electroless silver plating, hot cyanide baths with silver nitrate (“brewing process”) or aqueous solutions of silver nitrate, ammonia , hydrazine sulfate and sodium hydroxide are used . To silver or mirror non-metallic objects (mirrors, Christmas balls), the surface must be specially pretreated. In the case of plastics, a copper layer must first be applied.
Fire silver plating
Like fire gilding, fire silver plating is one of the historical processes that are no longer used because of the toxic elements mercury or lead .
See also
Phrase
In a figurative sense, the phrase “silver something” means “turning something into money”. The background to this idiom is the previously widespread use of silver as a material for currency coins (see silver standard ).
Individual evidence
- ↑ silver. code-knacker.de, accessed on September 26, 2010 .
- ↑ types of cutlery. hotelfach.de, accessed on September 26, 2010 .
- ↑ Eduard Vinaricky: Electrical contacts, materials and applications: fundamentals, technologies, test methods . Springer-Verlag, 2013, ISBN 978-3-642-56237-2 ( books.google.com ).
- ^ Alfred Löhr, Electroplating in the Bremen silver goods industry . In: Bremen will be bright, 100 years of living and working with electricity. Bremen 1993, pp. 266-273.
- ↑ CM Baur, Meister & Marken on Old Sheffield Plate and Electro Plate . Munich 2011, p. 5.
- ^ S. Bury, Victorian Electroplate . London 1971, p. 5.