Inorganic salts stabilizers effect in electroless nickel-boron plating: Stabilization mechanism and microstructure modification

Abstract Electroless nickel‑boron coatings present exceptional wear and corrosion resistance, but the presence of toxic heavy metals like Pb or Tl in most plating baths and the coatings synthesized using them impedes their widespread use. In this study, several candidates potential as stabilizing agent were investigated (Pb2+, Ti3+, V3+, Mn2+, Fe3+, Co2+, Cu2+, Zn2+, Ge4+, Zr4+, Nb5+, Mo5+, Ce3+,Ag1+, In3+, Sn2+, W6+and Bi3+). The investigation was based on the fact that stabilizers can stop the deposition in high concentration, once stabilizers also act as inhibitors depending on the concentrations—four distinct groups where observed. In group 1: Cu2+, Zn2+, Ge4+, Ce3+, Zr4+, In3+, Sn2+ and Bi3+, the solution is not decomposed until the end of deposition time (1 h) a deposition take place. Group 2: Ti3+, Mn2+, Fe3+, Co2+, Nb5+ and W6+ causes bath decomposition in less than 5 min. In Group 3: Mo5+, Ag1+ and V3+ the solution decompose in less than 1 min due to the presence of surface activators. Last, group 4: Pb2+ and Tl1+, are toxic stabilizers already studied in the literature. This paper presents a simple way to preselect metallic ions that can act as a stabilizing agent in electroless nickel‑boron plating. The method includes 3 aspects: The redox potential of the cation, the catalytic activity for hydrogenation and the atomic size of the metal. Besides, two green stabilizers were identified: Bi2(WO4)3 and SnCl2 that act as a stabilizer for concentrations of 10−5 mol/L and 10−3 mol/L respectively.