Dispersion Behavior of Al2O3 and SiO2 Nanoparticles in Nickel Sulfamate Plating Baths of Different Compositions

The dispersion behavior of Al2O3 and SiO2 nanoparticles in nickel sulfamate plating baths of different compositions were investigated by Zeta potential measurements and photon correlation spectroscopy (PCS). The Al2O3 particles have a median diameter of 25 nm and are crystallized in the delta- and gamma-phase. The amorphous SiO2 particles have a median diameter of 7 nm. In the case of dispersions with Al2O3 particles it was found by PCS that their agglomeration tendency increases with increasing ion concentration of the bath and therefore obeys qualitatively the Delaguin-Landau-Verwey-Overbeek (DLVO) theory. SiO2 particles in the same electrolytes show a different behavior: At a specific ion concentration the point of zero charge (isoelectric point) is shifted to higher pH values. At the highest ion concentration investigated, the particle charge measurements returned zeta potential values of about + 15 mV and higher even at pH values up to 6. This result could be explained by an adsorption of Ni2+ ions on the SiO2 particle surface. PCS at this dispersion reveals low agglomeration of the SiO2 nanoparticles in the employed plating bath. The results are discussed.