Preparation and Characterization of Ni-Cr Nanocomposite Coatings Containing TiO2 Nanoparticles for Corrosion Protection
The paper represents the investigation of the effect of TiO2 particle content on the corrosion behavior if Ni-Cr/TiO2 coatings applied with pulse-reverse electroplating.
In this experiment the Ni-Cr alloy coating and Ni-Cr/TiO2 nanocomposite coatings were deposited on low carbon steel discs with the area of 2 cm2 by the PRC electro-deposition process. The paling solution quantity was 0.5 L. Distilled water and commercial super-grade chemicals were used in order to make up the solution. The TiO2 nanoparticles that were used in the experiment had the average size of about 25 nm. In order to keep the nanoparticles dispersed and to avoid agglomeration and sedimentation in the suspension, the suspension was agitated by an ultrasonic probe for 30 min just prior to electroplating and it was stirred by a magnetic stirrer at rotating speed of 250 rpm during the deposition process. A Pt plate with a size of 20x20 mm was used as the anode.
The electrochemical measurements were done conventional three electrode cell that was open to the air, which contained 500 ml of 0.5 M NaCl as corrosive solution at a temperature of 25 ± 1 oC. The counter electrode and reference electrode were Ag and AgCl electrodes respectively. The potentiodynamic polarization tests were done at potential scanning rate of 0.5 mV/s, with a computer controlled Autolab device. Such corrosion characteristics as corrosion potential (Ecorr), corrosion current density (Icorr) and anodic/cathodic Tafel slopes (βa and βc) were acquired from the intersection of the cathodic and anodic Tafel curve tangents with Tafel extrapolation method.
The Ni-Cr/TiO2 nanocomposite coatings surface showed a better structure that was more uniform and compact in appearance than that of the Ni-Cr alloy coating. This indicates that the co-deposited TiO2 nanoparticles were uniformly distributed in the Ni-Cr matrix of nanocomposite coating. Furthermore, the better structure was achieved by the increase in TiO2 nanoparticle content in coating. The results showed that the corrosion potential of the Ni-Cr/TiO2 nanocomposite coatings was more positive than that of the Ni-Cr alloy coating, also the corrosion current density of Ni-Cr alloy coating was decreased by adding the TiO2 nanoparticles in the coating matrix. This indicated that Ni-Cr/TiO2 nanocomposite coatings had better corrosion resistance than did the Ni-Cr alloy coating. The dependence of the corrosion rate of Ni-Cr/TiO2 nanocomposite coating on the TiO2 nanoparticle content in the coating matrix showed that the corrosion resistance was improved by increasing the content of TiO2 nanoparticles.
The corrosion resistance improvement associated with the addition of the nanoparticles can be considered in two aspects, structural and electrochemical. In the case of structural aspects, a uniform, compact and better surface structure of Ni-CrTiO2 nanocomposite coatings was produced, compared to that of the Ni-Cr alloy coating. On the other hand, the TiO2 nanoparticles embedded in the Ni-Cr matrix filled in crevices, gaps and micro holes and acted as an inert physical barrier to the initiation and development of corrosion defects. …