Influence of Bath Composition at Acidic pH on Electrodeposition of Nickel-Layered Silicate Nanocomposites for Corrosion Protection

Nickel-layered silicates were electrochemically deposited from acidic bath solutions. Citrate was used as a ligand to stabilize nickel (II) ions in the plating solution. The silicate, montmorillonite, was exfoliated by stirring in aqueous solution over 24 hours. The plating solutions were analyzed for zeta-potential, particle size, viscosity, and conductivity to investigate the effects of the composition at various pHs. The solution particles at pH 2.5 (？22.2？mV) and pH 3.0 (？21.9？mV) were more stable than at pH 1.6 (？10.1？mV) as shown by zeta-potential analysis of the nickel-citrate-montmorillonite plating solution. for the films ranged from ？0.32 to ？0.39？V with varying pH from 1.6 to 3.0. The films were immersed in 3.5% NaCl and the open circuit potential monitored for one month. The coatings deposited at pH 3.0 were stable 13 days longer in the salt solution than the other coatings. X-ray diffraction showed a change in the (111)/(200) ratio for the coatings at the various pHs. The scanning electron microscopy and hardness results also support that the electrodeposition of nickel-montmorillonite at pH 3.0 (234？GPa) had improved hardness and morphology compared to pH 2.5 (174？GPa) and pH 1.6 (147？GPa). 1. Introduction A steady demand for enhanced coatings at a reduced cost has been the main focus in the area of corrosion for many years. Degradation of the coatings takes place because of unfavorable environmental conditions that lead to many types of corrosion [1–4]. Since it is difficult to completely stop corrosion, the best economical idea is to simply reduce the rate at which it occurs [5]. Low cost, convenience, and the ability to work at low temperatures have made electro-deposition one of the more favorable techniques to synthesize coatings [6]. The applied potential, pH, temperature, and current all play a role in determining the morphology, structure, and composition of the coatings [6–8]. One metal commonly used to enhance corrosion resistance is nickel because of its high abundance and capability to protect against common corrosion [1–4]. Nevertheless, corrosion resistance from metal coatings tends to be unsuccessful because of reduced mechanical properties. Forming alloys, with metals such as zinc, seems to be the answer to increasing the corrosion resistance [7]. The alloyed coatings tend to enhance the corrosion resistance properties but possess mechanical properties that are comparable to the individual metals. Ceramic fortification into the metal coatings can improve mechanical properties. To increase the hardness and life of nickel