D.S. Tsoukleris, E.A. Pavlatou, N. Chronopoulou, A. Karantonis, C. Sarafoglou, D.I. Pantelis
65th Annual Meeting of the International Society of Electrochemistry (2014), 31 August-5 September, Lausanne Switzerland (poster)
The last decades carbon nanotubes (CNTs) have drawn considerable attention in material sciences. CNTs are a kind of allotrope of carbon materials featured with a seamless tubular structure formed by curling-up graphene sheets, which are classified into single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs) according to their layers of graphene sheets. Multi-walled CNTs form 3D networks and are frequently used as thin films in applications such as capacitors, actuators and displays. Nanocomposites of CNT and Ni species are promising for applications in capacitors, hydrogen storage and hydrogenation catalysis. CNT/Ni-species (including Ni, NiO, Ni(OH)2) nanocomposites may be effectively fabricated by electroless plating, electroplating, impregnation and other processes. Pulsed electrodeposition, in which the applied potential is oscillated at high frequencies during deposition of metals, is another strategy to fabricate nanostructured Ni coatings. In this work composite coatings were obtained by electrolytic codeposition of hydride MWCNTs-Al2O3 with Ni matrix from an additive-free Watts type bath, under both direct (DC) and pulse current (PC) conditions. Pure Ni deposits were produced under the same experimental conditions for comparison reasons. The electrodeposition of all deposits was carried out on a rotating disk electrode. The surface morphology and structural characteristics of all coatings were investigated, along with the optimum electroplating conditions concerning the distribution of the embedded hydride particles in the nickel matrix. By utilizing a ball on disc tribometer under dry sliding conditions, wear resistance were studied and correlated with the above mentioned structural characteristics. The corrosion resistance of different deposits was determined in 0.6M NaCl solution by the Tafel method and electrochemical impedance spectroscopy. It was found that the application of high frequency pulse current conditions in combination with low concentrations of MWCNTs in the bath was beneficial for the homogeneous distribution of the hydride MWCNTs in the Ni matrix, both exhibiting a positive effect on the tribological behaviour of the deposits, additionally presenting relatively low corrosion rates. High pulse current frequencies in presence of the hydride particulates resulted in the predominance of a mixed [110+211] orientation for the composites, compared to the pure Ni coatings prepared under the same conditions oriented through the [110] axis.