Design of highly anti-corrosive electroless plated Ni–P/modified halloysite nanotubes nanocomposite coating

Halloysite nanotubes (HNTs) and their modifications with either NH2 (HNT-NH2) or NH2/Polypyrrole (HNT–NH2–PPy) were electroless-deposited into the NiP matrix for the first time to form NiP/HNT, NiP/HNT-NH2 and NiP/HNT–NH2–PPy nanocomposite coatings. The as-prepared nanocomposite coatings were heat-treated at 400 °C for 1 h. The transformation in microstructure, nanoindentation, Vicker's micro-hardness, surface morphology, and anti-corrosive properties of all prepared composite coatings were compared to the HNT-free (NiP) coating. Incorporating HNTs in the NiP coating made an appreciable enhancement in the hardness and corrosion resistance. Using the electrochemical impedance spectroscopy technique (EIS), the NiP/HNT-NH2 and NiP/HNT–NH2–PPy coatings showed more significant levels of enhancement in anticorrosion performance, offering about 16.5% and 25.4%, respectively, an increase in the inhibition efficiency of unmodified one (NiP/HNT), reached to 73 and 82%. Moreover, the modified HNT coatings revealed slightly high levels of betterment in microhardness, about 9% and 5.4% for HNT modification with NH2 and NH2-PPy, respectively. In addition, the heat treatment extra improved the hardness and the corrosion resistance of all HNTs nanocomposite coatings compared to HNT-free coating. Furthermore, the heat-treated NiP/HNT has the highest protection efficiency reached to about 95%, based on the polarization measurements. This momentous improvement in the hardness and electrochemical properties reflects the effect of adding the pristine and the modified HNTs into the NiP matrix, resulting in the development of high-performance NiP/HNT-NH2 and NiP/HNT–NH2–PPy composite coatings facilitating their use in various industries.