Traditional gold plating solutions contain cyanide, but alternatives like gold nitrides and mechanical plating exist. The plating method and solution used depends on the intended use of the component. Nitride-based solutions are cheaper and more durable than traditional plating, without toxic elements. Research continues to find eco-friendly options.
The gilding solution has typically been composed of liquid galvanic compounds which incorporate the dangerous chemical cyanide bound to gold into the solution. Alternatives to this include the use of gold nitrides which have traditionally proven difficult to synthesize but have now been improved using ion implantation methods. Mechanical barrel and brush plating are further alternatives to the traditionally used electroplating method of plating gold onto a surface.
The method chosen for the plating process and what type of gold plating solution is used is determined by what the component that will be plated is to be used for. Gold tarnishes slowly in the presence of infused copper, silver or nickel atoms which are used as the substrates upon which it is plated. For this reason, for jewelry applications, elements that show the slightest tendency to migrate into the gold and tarnish, such as copper on silver, are immediately plated beneath the gold’s surface. With components used for electrical purposes, where durability is more important, nickel is used as the immediate substrate material to add physical strength to the plating.
Electroplating processes vary greatly in speed, based on both the concentration of gold in the entire electrolyte compound and the actual chemical composition of the plating solution itself. A typical electroplating solution can deposit approximately one micron of gold onto a surface per minute, with layers up to 100 microns thick possible. Conversely, forms of chemical gold plating that immerse the part in a nickel-based solution offer more uniform gold coatings with a much longer shelf life, but a maximum thickness of 10 microns. Immersion solutions also have a much shorter life than typical electroplating solutions, so electroless/immersion technology is typically used to electroplate fine electrical components. Although electroplating has usually required a conductive surface to plate gold, it is now possible to perform the plating process on plastic by first etching the plastic and coating it with palladium metal.
Nitride-based gold compounds are another form of gilding solution. Considered better for electronic applications due to their lower cost and improved durability, gold nitride solutions replace the need to bond gold to toxic elements, such as arsenic and cyanide, and metals such as nickel, cobalt or iron. The nitrides are generated by using an ion gun to implant nitrogen atoms into gold crystals in a high vacuum. The resulting gold coating is harder than traditional industrial plating and contains no toxic elements that can harm the environment when the component is subsequently disposed of. Research into additional types of gold plating solutions continues to develop to eliminate the practice of using toxic metal alloys that can potentially pollute groundwater when old electrical components are disposed of in landfills.
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