Abstract
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.
Highlights
NiFe2 O4 ceramic is a very promising inert anode for aluminum electrolysis owing to its high thermal stability, chemical stability, and high corrosion resistance against molten cryolite [1,2,3,4,5]
In conventional pretreatment of electroless Ni plating, Sn and Pd are usually deposited on the substrate surface by sensitization and activation treatments [22,23,24]
Pd-free activation was performed by directly inlaying Ni particles on the substrate as catalyst sites for electroless Ni-P plating
Summary
NiFe2 O4 ceramic is a very promising inert anode for aluminum electrolysis owing to its high thermal stability, chemical stability, and high corrosion resistance against molten cryolite [1,2,3,4,5]. A network structure of metallic phase is formed by metal coating on the surface of ceramic particles, where the properties especially conductivity are improved significantly [19,20,21]. In conventional pretreatment of electroless Ni plating, Sn and Pd are usually deposited on the substrate surface by sensitization and activation treatments [22,23,24]. These treatments are limited by many problems, such as the use of highly toxic tin, high cost of noble metal, and uncontrollability which results in the waste of Pd and the failure of plating [25,26]. The effects of deposition conditions on the weight gain rate and morphological properties of the Ni-P coatings were studied
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