Effects of ligands on electroless Ni–P alloy plating from alkaline citrate–ammonia solution

Electroless Ni–P deposits with a wide range of phosphorus contents (from ∼2 to 13 wt.%) at higher deposition rates have been obtained from alkaline solutions containing tri-sodium citrate and ammonium chloride by controlling the tri-sodium citrate concentration. X-ray fluorescence analysis, XRD, SEM and polarization curves were used to characterize the compositions, structures, morphologies and anti-corrosion properties of these Ni–P coatings, respectively. Systematic UV–Vis absorption measurement shows the presence of a ternary nickel citrate–ammonia complex in alkaline electroless baths, which supports the explanation of a proposed mechanism involving a ternary complex as the discharge species.