(V) Towards Lead-free electroless nickel-boron plating

Electroless nickel-boron coatings present exceptional wear and corrosion resistance but the presence of toxic heavy metals like lead or thallium in most plating baths and the coatings synthesized using them impedes their widespread use. Indeed, environmental legislation such as directives ELV (End of Live Vehicles), RoHS (Restriction of Hazardous Substances), and WEEE (Waste Electrical and Electronic Equipment) or the European Reach directive make the use of such compounds nearly impossible, and with good reason.

However, the role played by those compounds in the plating process, that of stabilizer, is essential because they allow smooth and prolonged operation of the plating bath and make it possible that only the substrate is covered by nickel. Their removal is thus not an easy feat.
In this study, several candidates were investigated and their potential as stabilizing agent was assessed. This allowed us to determine the most important criteria to assess if a metallic ions can act as stabilizing agent in electroless nickel-boron plating: The redox potential of the metal cation/metal pair, The catalytic activity of the metal and The atomic size of the metal atom.