Effect of tin dioxide sol on the peculiarities of electrodeposition and structure of copper and nickel coatings

Abstract

Tin dioxide sol is proposed as the additive in weakly alkaline diphosphate copper and nickel plating electrolytes which provides the deposition on the carbon steel of fine-grained and close-packed coatings with the increased protective ability. It is revealed that nanoparticles of this sol have sizes of 2–5 nm, consist of the SnO2 core and SnO2–x(OH)2x shell, are stabilized to coagulation and dissolution in the electrolytes with the adsorbed copper or nickel diphosphate complex ions, and carry a charge of –(38–42) mV at the pH of the electrolytes within 8.2–8.6. They adsorb both on the initial substrate and on the surface of the growing coating, thus performing the function of nucleation centers in the process of copper and nickel electrodeposition. This happens under certain conditions, which include direct current density of 1.0 A/dm2 and tin dioxide concentration in the electrolyte of 0.5 g/dm3. In these conditions SnO2 sol does not affect the rate of deposition equal to 7−13 μm/h and current efficiency of 68−97%. Tin dioxide has not been detected inside copper and nickel coatings.