PREPARATION AND CHARACTERIZATION OF ELEC-TROLESS Ni COATING ON THE SURFACE OF MgO WITH POROUS STRUCTURE

Generally,the surface pretreatments such as sensitization and activation are necessary for depositing a nickel metal layer on oxide surface by electroless plating,however,for an oxide surface with porous structure it is possible that the pretreatment is not necessary.In this paper,only by use of the surface activity of porous structure,an electroless plated nickel layer can be prepared on the surface of microarc-oxidation-fabricated porous magnesium oxide film in a conventional electroless nickel plating solution,consisted of nickel sulfate as main salt and sodium hypophosphite as reducing agent.Furthermore,the phase,microstructure,electrical conductivity and corrosion resistance of the obtained nickel layer were characterized.The results indicate that the 5μm-thick nickel layer is composed of fine and homogeneously distributed nickel particles,at the same time the microstructure of nickel layer is dense.Nickel layer spreads into the micropores on the surface of porous magnesium oxide film,so that an interleaving interface is formed at nickel/oxide interface.XRD results reveal that the nickel layer contains crystalline Ni and amorphous Ni-P.Four-point probe measurement indicates that the nickel layer exhibits well electrical conductivity.Meanwhile,polarization curve reveals that corrosion potential elevates notably due to the presence of nickel layer.During electroless nickel plating the nickel ions in solution were reduced and deposited in the micropores of porous magnesium oxide film under the action of reducing agent ions,so as to generate tiny primary nickel particles, subsequently,these primary nickel particles continuously grew and spread,and finally formed an entire nickel layer on oxide surface.