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- Type of Document: Ph.D. Dissertation
- Language: Farsi
- Document No: 50609 (46)
- University: Sharif University of Technology
- Department: Institute for Nanoscience and Nanotechnology
- Advisor(s): Dolati, Abolghasem; Ghorbani, Mohammad
- Abstract:
- In this project Ni-SiC nanocomposite coatings were electrodeposited using Watts nickel bath with addition of SiC particles to the bath. Optimization of Ni-SiC electrodeposition parameters was done using Response Surface Methodology (RSM). At specific conditions, 67 Vol% of 10nm SiC is incorporated in nickel electrodeposits which is unique and not yet reported. Study nanomechanical properties of these coatings using Nanoindentation method, it was realized that the dislocation density is increased as force increasing which is in agreement with increasing intensity of (220) and (200) reflections and intensity attenuation of (111) reflection. Nanoscratch tests show that these nano-electrocomposites has adhesive-ploughing behavior and low coefficient of friction. As SDS and CTAB surfactants increased with increasing particle size of SiC, the Vol% of particles increases. The vice versa, increasing PVP with increasing particle size causes decreasing Vol% of SiC particles. Although using surfactants in electrolytic bath increases Vol% of SiC in the coating but corrosion resistance decreases because the grain boundary in coating microstructure is more open in this condition. Hydrodynamic condition affects codeposition of SiC particles with nickel electrodeposits. In low concentration of SiC particles in the bath and in laminar flow on the cathode surface condition, codeposition of SiC particles increases. Particle morphology change from spherical to whisker causes electro-codeposition process and enhances nanomechanical properties of the coating. Mechanism of codeposition of Ni-SiC nanocomposite coatings was studied using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) techniques. It was concluded that (Ni2+-SiCδ-) or/and (Ni(OH)+-SiCδ-) species decrease effective charge density and oxidation number of Ni2+ which are mechanism controller in Ni-SiC electrocodeposition. The results of the kinetic analysis of cyclic voltammograms with non-irreversible system equations indicate that the diffusion coefficient and kinetic constant of the reaction are relatively large and due to increased relative kinetic constant, this kind of diffusion occurs. Also, with increasing particle concentration in the bath, there is an increasing trend for diffusion coefficient and the constant reaction rate, which is the result of the effect of silicon carbide particles in the electrocrystallization of nickel. Pole figure studies were done to characterize the evolved crystallographic texture. The X-ray scans followed by Rietveld analysis using the Rietquan program were used for the determination of texture, lattice parameter, and grain size of the matrix. The Ni/SiC nano-electrocomposites, prepared at 7 A/dm2, exhibited improved properties in comparison to pure nickel electrodeposits. The properties of the composite coatings are associated with structural modifications of the nickel crystallites as well as the morphology of the electrodeposited layers. For the optimum current density, the preferred orientation is ⟨110⟩. Grain refinement is observed for an optimum range of 7–10 A/dm2 associated with the evolution of the ⟨110⟩ texture toward a less marked ⟨210⟩ texture. From pole figure and inverse pole figure studies, a mechanism of crystallographic texture changes as a function of current density and pH values of the electrolyte bath is proposed
- Keywords:
- Electrodeposition ; Mechanism ; Nano-Composite Coating ; Nickel-Silicon Carbide Coating ; Electrochemical Deposition ; Preferred Texture and Orientation
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