Stability of nano-/microsized particles in deionized water and electroless nickel solutions

A major problem in the co-deposition of nano- and microsized particles within electroless NiP coatings is particle dispersion in the electroless nickel solution because of the strong tendency of particles toward agglomeration and sedimentation. The stability of colloidal Al2O3, CeO2, and BN particles and Al2O3CeO2 and Al2O3BN particle mixtures in deionized water and electroless nickel solution was investigated by zeta potential measurements and sedimentation tests. Dispersions of Al2O3 and CeO2 particles showed good stability in deionized water with zeta potential values of 55 and 39 mV, respectively. BN dispersion in deionized water was found to be relatively unstable at pH 4 with zeta potential values of −13 mV, but at higher pH (i.e., pH 5.5), the values decreased up to about −40 mV. When the dispersions were made in electroless nickel solution, a significant decrease of the zeta potential values was observed for both single particles and mixtures of particles, indicating a change in the surface charge from high positive to low negative with detrimental effects on dispersion stability. Further, the findings suggested that the stability of particle mixtures is dominated by one type of particle, i.e., the Al2O3CeO2 dispersion is governed by the single CeO2 particles, whereas the Al2O3BN dispersion is governed by the Al2O3 particles. All the zeta potential measurements were in line with the results of the sedimentation tests (i.e., low zeta potential values corresponded to short settling times, whereas high zeta potential values corresponded to long settling times).

Graphical abstractThe stability of single particles and mixtures of particles in deionized water and electroless nickel solution was investigated by zeta potential measurements and sedimentation tests for the synthesis of composite coatings by electroless nickel process.Figure optionsDownload full-size imageDownload as PowerPoint slide