Structure, apatite inducing ability, and corrosion behavior of chitosan/halloysite nanotube coatings prepared by electrophoretic deposition on titanium substrate.

In this study chitosan/halloysite nanotube composite (CS/HNT) coatings were deposited by electrophoretic deposition (EPD) on titanium substrate. Using HNT particles were investigated as new substituents for carbon nanotubes (CNTs) in chitosan matrix coatings. The ability of chitosan as a stabilizing, charging, and blending agent for HNT particles was exploited. Furthermore, the effects of pH, electrophoretic bath, and sonicating duration were studied on the deposition of suspensions containing HNT particles. Microstructure properties of coatings showed uniform distribution of HNT particles in chitosan matrix to form smooth nanocomposite coatings. The zeta potential results revealed that at pH around 3 there is an isoelectric point for HNT and it would have cathodic and anionic states at pH values less and more than 3, respectively. Therefore, CS/HNT composite deposits were produced in the pH range of 2.5 to 3. The apatite inducing ability of chitosan-HNT composite coating assigned that HNT particles were biocompatible because they formed carbonated hydroxyapatite particles on CS/HNT coating in corrected simulated body fluid (C-SBF). Finally, electrochemical corrosion characterizations determined that corrosion resistance in CS/HNT coating has been improved compared to bare titanium substrate.

Effect of cobalt content on wear and corrosion behaviors of electrodeposited Ni-Co/WC nano-composite coatings.

Metal-ceramic composite coatings are widely used in automotive and aerospace industries as well as micro-electronic systems. Electrodeposition is an economic method for application of these coatings. In this research, nickel-cobalt coatings reinforced by nano WC particles were applied on carbon steel substrate by pulse electrodeposition from modified Watts bath containing different amounts of cobalt sulphate as an additive. Saccharin and sodium dodecyl sulphate (SDS) were also added to electroplating bath as grain refiner and surfactant, respectively. The effect of cobalt content on wear and corrosion behavior of the coatings was investigated. Wear and corrosion properties were assessed by pin-on-disk and potentiodynamic polarization methods, respectively. Phase analysis was performed by X-ray diffraction (XRD) using CuK(alpha) radiation and the worn surfaces were studied by means of Scanning Electron Microscopy (SEM). The results showed that the addition of cobalt improved the wear resistance of the coatings. In the presence of 18 g/L cobalt in electrodeposition bath, the wear rate of the coating decreased to 0.002 mg/m and the coefficient of friction reduced to 0.695 while they were 0.004 mg/m and 0.77 in the absence of cobalt, respectively. This improvement in wear properties can be attributed to the formation of hcp phase in metallic matrix. Meanwhile, the corrosion resistance of the coatings slightly reduced because cobalt is more active metal with respect to nickel.

Effect of nano-SiC incorporation on mechanical properties of micro and nano-structured Ni-Co electrodeposits.

Ni-Co/SiC nano-composites were electrodeposited from modified Watts bath containing SiC particles with 50 nm average size, SDS as surfactant and saccharin as grain refiner in appropriate amounts. The effect of grain size and nano-particle incorporation on microstructure and mechanical properties of electrodeposits was investigated. The grain size of the deposits was calculated from X-ray diffraction (XRD) patterns using Williamson-Hall equation and surface morphology of the coatings was studied by means of scanning electron microscopy (SEM). The mechanical properties of electrodeposits were investigated by Vickers microhardness and tensile tests. The results indicated that incorporation of SiC nano-particles increased the microhardness and yield strength of micro-grained deposits due to the change in crystallographic texture, decrease in grain size as well as dispersion hardening. But dispersion hardening mechanism could not be confirmed in nano-structured deposits. Moreover, the increase in the concentration of uniformly dispersed SiC particles initially improved and then decreased the elongation to failure of coarse-grained deposits while a continuous increase was observed for nano-structured deposits.

Corrosion behavior of pulse electrodeposited nanostructure Ni-SiC composite coatings.

Ni-SiC nano-composite coatings with various contents of SiC were prepared by pulse electrodeposition from a modified Watts bath containing SiC nano-particles. The effect of SiC concentration, current density, duty cycle and pulse frequency on the corrosion behavior of the coatings was investigated by means of potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) methods. It has been found that the Ni-SiC composite coatings show better corrosion resistance in a 3.5% NaCI solution than pure nickel. The corrosion resistance of the coatings increases by increasing the amount of embedded SiC particles. This improvement can be attributed to the morphology and the crystallographic texture of the coatings.