Design challenges in electrodepositing metal-anionic clay nanocomposites: Synthesis, characterization, and corrosion resistance of nickel-LDH nanocomposite coatings

A method was developed to electrochemically synthesize metal-anionic clay nanocomposite coatings. The coatings consist of Zn-Al layered double hydroxide (LDH) nanoplatelets incorporated into a nickel matrix (NiLDH), and were evaluated for their corrosion resistance versus pure nickel coatings on steel substrates. The LDH nanoplatelets incorporated into the nickel coatings were synthesized from zinc and aluminum nitrate salts using a refluxing coprecipitation method. These nitrate platelets were intercalated with sodium dodecylsulfate, increasing the gallery spacing from 9.06 angstrom to 37.6 angstrom, followed by refluxing in butanol to delaminate the LDH crystal sheets, giving a 1.5 g/L loading of LDH in the continuous phase. The average platelet size was found to be 631 +/- 43 nm. Aliquots of the delaminated LDH colloid were added to a modified nickel bath for electrodeposition. Challenges for electrodepositing these metal anionic clay nanocomposites from an aqueous bath are reviewed and discussed. EDS analysis confirms the presence of the nanoplatelets in the metal coating. The resulting nanocomposite films have a preferred (220) orientation and crystallite sizes ranging from 25 to 60 nm as measured by XRD. Corrosion resistance of the coatings was also improved over the pure nickel coatings and measured in 3.5% NaCl with potentiodynamic polarization and electrochemical impedance spectroscopy. Suggestions for future design and improved properties are discussed for these types of nanocomposite coatings.