Effect of the 3,3′-dithiodipropane-1-sulfonic acid disodium salt on the composition, morphology, and corrosion behavior of electroless Ni–P coatings on a copper substrate

The features of the formation of electroless Ni-P coatings in the presence of 3,3dithiodipropane-1-sulfonic acid disodium salt (SPS) have been studied.Introducing SPS into a nickel-plating solution at concentrations up to 3.1610 -5 mol/L accelerates the deposition of Ni-P coating, but at the same time reduces the phosphorus content in it.A further increase in the additive concentration to 110 -4 mol/L leads to inhibition of coating formation until the process is completely stopped.At concentrations of SPS up to 110 -5 mol/L, coatings with a granular surface morphology are formed, but already at an SPS content of 3.1610 -5 mol/L, the coating becomes smooth.The corrosion resistance of Ni-P coatings obtained in the presence of various concentrations of SPS was evaluated using the potentiodynamic polarization method and electrochemical impedance spectroscopy in comparison with the control coating obtained in the absence of SPS.Despite the fact that the control coating manifests itself as more homogeneous, coatings obtained with the additive exhibit higher corrosion resistance, which increases with increasing concentration of the additive in solution.