Nucleation and Growth Mechanism of Ni/TiO₂Nanoparticles Electro-Codeposition

Abstract

The mechanism of TiO 2 nanoparticles electro-codeposition with nickel is studied. In-situ different electrochemical techniques such as cyclic voltammetry, electrochemical impedance spectroscopy, chronoamperometry and chronocoulometry are used. The nucleation and growth mechanism of nickel in absence and presence of different nanoparticles concentration are analyzed through a mathematical model. The nucleation process of pure Ni system tends to follow the progressive model with three-dimensional fashion, while Ni/TiO 2 codeposition follows an instantaneous nucleation model. The presence of nanoparticles on the cathode offers many favorable sites for nickel crystallization nucleation, promote electrodeposition process and change the preferred orientation of nickel to a random one. The opportunity to codeposit inert nanoparticles from electrolytic baths has been widely used in metal electrodeposition in order to obtain structured nanocomposite coatings.1 Among the various techniques for producing nanostructured materials, electro-codeposition is technologically feasible and economically superior because this method can easily provide metal matrix nanocomposite coatings on surfaces of different sizes and shapes without porosity, with layer thicknesses from a few nanometers to hundreds of micrometers, or as a multilayer. Also this electrochemical method shows high production efficiency and the technological transfer from the laboratory to the existing infrastructure in the electroplating industry is easy.2 Compared to pure metal coatings, the nanostructured materials exhibit a wide range of new properties, such as increased resistance to wear and corrosion, improved mechanical properties (hardness, tensile strength, yield strength) and good electrocatalytic properties. 1,3Although the electro-codeposition process has aroused over time the interest of researchers for the development and characterization of metal matrix nanocomposites able to meet specific requirements, the theory of particles incorporation mechanisms is not well studied, being yet unclear. In addition such incorporating mechanism depends on each separate system (metal matrix-dispersed phase).In order to improve the properties to microhardness, wear and corrosion of the pure nickel coating, a variety of micro and nanometric sized particles such as Although in the scientific journals, many papers dealing with the electro-codeposition of Ni/TiO 2 composite coatings and their performance 9,11-13 the literature reporting the nucleation and growth mechanisms involved in the electro-codeposition of Ni/nano-TiO 2 layers by electrochemical methods is still scare. Nucleation and growth kinetics of the composite layers are the most important steps that determine the physico-chemical properties of the electrodeposited material and therefore these are crucial issues in understanding and controlling composite coatings. The electrochemical characterization of the nucleation process is generally done by collecting different types of transient current obtained when po...

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