Silver Plating

Gold plating & Silver plating

Gold plating is a method of depositing a thin layer of gold on the surface of other metal, most often copper or silver.

Gold plating is often used in electronics, to provide a corrosion-resistant electrically conductive layer on copper, typically in electrical connectors and printed circuit boards. With direct gold-on-copper plating, the copper atoms have the tendency to diffuse through the gold layer, causing tarnishing of its surface and formation of an oxide/sulfide layer. A layer of a suitable barrier metal, usually nickel, has therefore to be deposited on the copper substrate, forming a copper-nickel-gold sandwich.

Metals may also be coated with gold for ornamental purposes, using a number of different processes usually referred to as gilding.

 

For less demanding applications in electronics, silver is often used as a cheaper replacement for gold. (Although silver is a better conductor than gold it does oxidize and so gold is better for contacts. However, variable capacitors are considered of the highest quality when they have silver plated plates. In this application there is no make and break contact so gold would not offer any advantage over silver).

Care should be used for parts exposed to high humidity environments. When the silver layer is porous or contains cracks, the underlying copper undergoes rapid galvanic corrosion, flaking off the plating and exposing the copper itself; a process known as red plague.

Historically, silver plate was used to provide a cheaper version of items that might otherwise be made of silver, including cutlery and candlesticks. The earliest kind was Old Sheffield Plate, but in the 19th century new methods of production (including electroplating) were introduced: see Sheffield Plate.

Another method that can be used to apply a thin layer of silver to several objects, such as glass, is the Tollen's Test method, which usually is prepared as follows. Using this method the final reaction can occur by placing Tollen's Reagent in a glass and then adding Glucose/Dextrose and shaking the bottle to perform the reaction.

 

AgNO3 + KOH -> AgOH + KNO3

AgOH + 2NH3 -> [Ag(NH3)2]1+ + [OH]1- (Note: See Tollen's Reagent)

[Ag(NH3)2]1+ + [OH]1- + Aldehyde(Usually Glucose/Dextrose) -> Ag + 2NH3 + H2O

 

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