Pd-Free Activation Pretreatment for Electroless Ni-P Plating on NiFe₂O₄ Particles.

A Pd-free activation pretreatment process was developed for electroless Ni-P plating on NiFe₂O₄ particles. The main influencing factors, including NiCl₂·6H₂O concentration, pH of electroless bath and temperature, were investigated. Microstructures of the coating layers were characterized by scanning electron microscopy. It was found that a more uniform and compact Ni-P coating layer was successfully formed by electroless plating via Pd-free activation pretreatment than Pd as sited plating. The coating layers plated by Pd-free activation pretreatment were thicker than those by the sensitization and activation pretreatment on average (9 vs. 5 μm). The new process did not need conventional sensitization or activation pretreatments, because the Ni particles dispersed uniformly on the NiFe₂O₄ substrate became catalytic activation sites for nickel electroless plating. Such improvement was beneficial to shortening the preparation process and reducing the production costs with the use of noble metal Pd.