Effects of pretreatment on the structure and properties of electroless nickel coatings
The pretreatment process can significantly affect the corrosion resistance of electroless nickel (EN) coatings. One of the most important reasons is that different pretreatment processes can give different surface morphologies of the substrate. The scanning electron microscope (SEM) and the scanning tunneling microscope (STM) have been used to investigate the structure and properties of EN coatings in the as-plated condition for various deposition times, in relation to different mechanical/chemical pretreatment processes. The morphology of the substrate surface is found to be a key factor in control of the porosity of EN coatings. It can significantly affect the formation of EN deposits, not only in the early stage but also in the morphology/ structure during the continued growth of the deposit
In Situ Scanning Tunneling Microscopy Observation of Electroless-Deposited NiP Film
Preliminary results of an in situ scanning tunneling microscopy (STM) observation of electroless-deposited NiP film as well as that of electrodeposited film were demonstrated. The electroless-deposited film is observed to develop rough features consisting of small grains, suggesting the successive nucleation of the grains and their three-dimensional growth. The electro-deposited film, in contrast, consists of larger grains with smooth features.
Passivation and pitting of electroless nickel surface coatings
Abstract Commercial electroless nickel coatings containing nominally Ni-0.25%B, Ni-10%P and Ni-11.5%P-1%Cu were tested potentiodynamically and examined with a microscope to determine the effect of heat treatment and chloride ion concentration on the passivation and pitting behaviour in 10 vol.% H2SO4. All the electroless nickel coatings had inferior corrosion and pitting resistance compared with commercial nickel. Precipitation hardening or chloride ion concentrations up to 0.005 M did not significantly influence the corrosion. Combined precipitation hardening and the presence of chloride ions greatly increased the corrosion and pitting. The Ni-B coatings had a much higher resistance to corrosion and pitting than the Ni-P coatings had.