Influence of bath composition and pH on the electrocodeposition of alumina nanoparticles and nickel

Nanocomposite coatings of nickel and alumina (primary crystallite size 13 nm) were electroplated from an acidic and an alkaline bath. Interestingly the layers from the alkaline bath contained almost three times more particles (4 wt.%) than those deposited from the acidic bath (1.5 wt.%). Measurements of the zeta potential showed that the particles in the acidic bath are positively charged and in the alkaline bath they are negatively charged. A simple electrostatic model is proposed which can explain the preferential codeposition of the negatively charged particles. Furthermore the hardness and the electrical conductivity of the layers were characterized. For the acidic bath the hardness of the layer increased with the particle content. This hardening effect is at least partly caused by a change in the microstructure. Finally, the electrical conductivity can be used as a rough estimate of the particle content of the layers.