The effect of nonmetallic element P in electroless Ni-P coating on the passivation process during chemical conversion treatment

Abstract

Pure Ni and electroless Ni-P coating (ENPC) were passivated by a chemical conversion treatment. The passive films formed on pure Ni and ENPCs (with content of P 2.9, 7.2 and 11.7 at.% respectively) were analyzed by X-ray photoelectron spectroscopy (XPS). High-resolution XPS was also used to analyze the chemical states of the elements detected in the passive films. The results indicated that the detected Ni and P were in elemental states, and no compound with Ni and P element was detected in passive film, meaning that Ni and P did not participate in the formation of the passive film. The content of film-forming reaction product in passive film increases with the content of element P in Ni-P coating, suggesting that the nonmetallic P in Ni-P coating played an important role in the formation of the passive film. The XPS results were used to analyze the formation mechanism of the passive film.

Improvement of anti-corrosive and anti-oxidative properties of electroless Ni-P coating

“…In order to enhance the anti-oxidative performance of the ENPC, in the past decades, a chromate conversion treatment using hexavalent chromate as a raw material is widely used because the chromate conversion coating is easy to be obtained and also can improve the anti-corrosive property of the ENPC [19]. Furthermore, in order to alleviate the toxicity of hexavalent chromate, a chromate conversion treatment using trivalent chromate solution as a raw material had also been developed [20].…”

Effect of Cu in electroless Ni–Cu–P coating on passivation process

“…Mu et al concluded that not only Ni but also nonmetallic element P could take part in the passivation reaction. As the content of P increases, Ni–P coating will change from crystalline state to amorphous state, leading Ni and P more difficult to be reacted in passivation solution.…”