Dispersion Behavior of Al[sub 2]O[sub 3] and SiO[sub 2] Nanoparticles in Nickel Sulfamate Plating Baths of Different Compositions

The dispersion behavior of and nanoparticles in nickel sulfamate plating baths of different compositions were investigated by Zeta potential measurements and photon correlation spectroscopy (PCS). The particles have a median diameter of 25 nm and are crystallized in the δ- and γ-phase. The amorphous particles have a median diameter of 7 nm. In the case of dispersions with 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. 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 ions on the particle surface. PCS at this dispersion reveals low agglomeration of the nanoparticles in the employed plating bath. The results are discussed.