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A nanonetwork composite coating is prepared for serving as both pH sensor and reservoir for the delivery of functional payload. The composite coating consists in nanofibers containing encapsulated pH‐responsive dye and corrosion inhibitor. The nanofibers are then incorporated in a hydrophobic polymer. While the nanofibers remained intact, they provide additional adhesion strength to the metal substrate. Sensing ability and releasing of active payload are demonstrated by immersing in an artificial corrosive environment and electrochemical impedance spectroscopy measurements. The composite coating can detect the early onset of corrosion and hinders efficiently corrosion compared with passive coatings. This concept paves the way for creating smart coatings that can hinder corrosion progress and allow for an early detection of corrosion before irreversible damages on metallic structures.

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This work studied the corrosion behaviors of 15Ni, 23Ni, 31Ni and 40Ni steels in aerated 3.5% NaCl solutions with various pH levels (2, 7 and 10) at 25ºC. The observed microstructures of 15 and 23 wt.% Ni steels were consisted partially of martensite, while those of 31 and 40 wt.% Ni steels were fully austenitic. Polarization curves of the nickel-containing steels were determined using a potentiodynamic polarization technique. The corrosion potential (Ecorr), corrosion current density (Icorr), corrosion rate (Rmpy), pitting potential (Ep), primary passive potential (Epp) and passive current density (Ip) were evaluated from the polarization curves. The results indicated that an increase in nickel content resulted in an increased corrosion potential, but also a decreased corrosion current density or corrosion rate. Only the solution pH of 10, the passive characteristics of the 23Ni, 31Ni and 40Ni steels were remarkable. As the nickel content of those three nickel-containing steels increased, the primary passive potentials and pitting potentials were increased, but the passive current densities were decreased. Nickel additions improved general corrosion and pitting corrosion resistances of the nickel-containing steels when tested in basic, neutral and acidic 3.5% NaCl solutions. The effects of various nickel contents and solution pHs on general corrosion resistances of nickelcontaining steels were also discussed.

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