HIGH CORROSION RESISTANCE OF NI-P/NANO-SIO₂ ELECTROLESS COMPOSITE COATINGS

The process of electroless plating Ni-P and Ni-P/nano-SiO₂ on API-5L X65 carbon steels was improved. The Ni-P/nano-SiO₂ composite coatings were prepared from the bathes containing different concentrations of nano-SiO₂ particles. The coatings surface and morphologies were observed via scanning electron microscopy (SEM). The chemical compositions were analyzed by EDAX. The corrosion behaviors were evaluated by electrochemical impedance spectroscopy tests. The experimental results indicated that SiO₂ nano-particles co-deposited but some agglomeration occurred. Micro-hardness of electroless Ni-P-SiO₂ composite coatings increased due to the existence of nano-particles. Corrosion tests showed that both electroless Ni-P and Ni-P/nano-SiO₂ composite coatings demonstrated significant improvement of corrosion resistance of substrate in salty atmosphere and latter coating type appeared to offer a better corrosion protection.