Electroless Plating

December 6, 2002

• Electroplating is a technique for coating an object with metal
  • by an electrochemical reduction
  • making the work piece the cathode in an electrolysis cell

• Electroplating only works when the object is electrically conductive
  • There are some tricks for nonconductive surfaces
    • All tricks involve a thin coating of an electrically conductive material

• Conductive paint is a simple system
  • a paint is prepared with a relatively high concentration of a conductive powder
    • graphite
    • silver
    • brass
    • (aluminum dust is available, but is not useful. Why? See Anodizing Al)
  • the paint is bushed or sprayed on the object and allowed to dry/

• Electroless chemical baths can be used to deposit a thin coating of metal
  • most commonly silver
  • sometimes copper
• These contain the metal ion
  • usually as a complex ion ( Ag(NH₃)₄+ , for example)
  • the solution also contains a reducing agent, such as formaldehyde or glucose
    • the reaction reduces Ag+ (or Cu²⁺) to the metal
    • the metal deposits randomly on surfaces
      • we coat the walls of the beaker as well as the sample
• This is the way mirrors (silver on glass) have been made for several hundred years
  • it's a way to make the inside of Christmas ornaments bright and shiny
  • it can also be used to make a nonmetallic object conductive so it can be electroplated or used for electroforming
    • several companies sell electroformed metallic leaves as jewelry

Experimental--

• wash and rinse a small test tube (metal deposits only on clean surfaces)
  • add a few drops of silvering solution A
  • add an equal volume of silvering solution B
    • these must be mixed at the time of use
  • mix and set aside for about 10-30 minutes
    • leave your glass stirring rod in the tube for an added effect
• we hope to provide comparable solutions for copper deposition