Copper-graphene oxide composite coatings for corrosion protection of mild steel in 3.5% NaCl

In this paper, the effects of two different types of surfactants on the properties of Ni–P–TiO 2 coating on low carbon steel substrate were investigated. Sodium dodecyl sulphate (SDS) — anionic surfactant and dodecyl trimethyl ammonium bromide (DTAB) — cationic surfactant were used for the deposition. Deposits were characterized by a high resolution scanning electron microscope (HR-SEM), an energy dispersive X-ray spectrometer (EDS), and X-ray diffraction (XRD) to study the surface morphology, composition and crystal structure of the coatings respectively. In addition, the influence of surfactants on the corrosion behaviour of Ni–P–TiO 2 coatings was also examined using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% sodium chloride solution. The results showed that at an optimum concentration of cationic surfactant DTAB, uniform distribution of TiO 2 particles with no defects was observed. The corrosion properties were improved by the incorporation of TiO 2 particles in the Ni–P matrix. The increase in corrosion resistance of the Ni–P-TiO 2 coatings significantly depends on the surfactant and its concentration.

Effect of surfactants on the coating properties and corrosion behaviour of Ni–P–nano-TiO2 coatings

Wear and scratch behaviour of electroless Ni-P-nano-TiO2: Effect of surfactants

Three different types of electroless nickel (EN)-phosphorus plating were applied on AZ31 wrought magnesium alloy. The first type was plain mid-phosphorus coating, the second one was duplex, with the first layer having a mid-phosphorus content and the upper one consisting of high-phosphorus whereas the third type of coating was also duplex with a first mid-phosphorus layer and a second high-phosphorus one with incorporated ceramic TiO 2 and ZrO 2 microparticles. Characterization of deposits by means of scanning electron microscopy and X-ray diffraction analysis proves the production of adherent, defect free coatings with differences in crystallinity depending on P content. Surface roughness was maintained at acceptable levels while a great increase in microhardness was observed that was further enhanced by ceramic microparticles incorporation. Electrochemical testing, that was performed by Tafel polarization in 3.5% NaCl solution, show that all the coatings effectively protect the Mg alloy substrate. Additionally, the composite coatings exceptionally enhance the protective capability of the system after heat treatment at 200 °C.

Characterization and corrosion resistance of duplex electroless Ni-P composite coatings on magnesium alloy

The study of electroless Ni-B coatings is pursued in order to obtain deposits on metal substrates with advanced properties such as high microhardness for particularly demanding engineering uses. In the present study, composite Ni-B coatings enhanced with SiC microparticles on a steel substrate were prepared using the method of electroless plating. Structure characterization was performed by means of X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) in order to draw conclusions concerning the dispersion and incorporation of SiC particles in the Ni-B matrix and how they affect surface roughness measured by a profilometer. Vickers microhardness tests were performed in order to demonstrate the notable increase in microhardness compared to the bare substrate. Furthermore, Tafel electrochemical tests in 3.5% NaCl(aq) were carried out in order to evaluate how the ceramic microparticles affect the behaviour of coatings in the corrosive medium. The results indicate, that improved deposits are obtained capable to withstand very demanding applications where high microhardness along with resistance to corrosion is a prerequisite.

Q. Jiang

Papers

The performance of surfactant on the surface characteristics of electroless nickel coating on magnesium alloy