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An Investigation on the Pulse Electrodeposition of Ni-TiO2/TiO2 Multilayer Structures

Baradaran Mohajeri, Soha | 2015

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 47144 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Dolati, Abolghasem; Ghorbani, Mohammad
  7. Abstract:
  8. Electrocodeposition of Ni-TiO2 nanocomposite single layers and Ni-TiO2/TiO2 multilayers from Watts bath containing TiO2 sol has been carried out on copper substrate. Cyclic voltammetry and chronoamperometry techniques were applied to study the influence of nickel sulfate and TiO2 sol concentrations on the electrochemical behavior of Ni-TiO2 deposition by direct current. The results clearly showed that at lower sulfate concentrations, the electrodepostion is a diffusion controlled process. Besides, the nucleation mechanism of the nanocomposites at low overpotentials followed the progressive system while at higher overpotentials, it was found to be instantaneous with three-dimensional growth mechanism. XRD results confirmed the presence of anatase phase in the Ni-TiO2 nanocomposite coatings after 3 hours heat treatment at 450°C. The higher sol concentrations in the plating bath led to higher content of TiO2 nanoparticles, reaching 6.23 wt.% for a bath containing 25 mL/L TiO2 sol, under deposition potential of -900 mV. Pulse plating and pulse reverse plating techniques were applied to facilitate higher incorporation of TiO2 nanoparticles in Ni-TiO2 nanocomposite single layers and the results revealed that by prolongation of the current-off durations and the anodic cycles, deposits containing 11.58 wt.% and 13.16 wt.% TiO2 were produced, respectively. The phase structure and surface morphology of the nanocomposite coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM). It was confirmed that the preferred orientations and the crystallite sizes of nickel matrix were influenced by the deposition technique parameters, and higher contents of codeposited TiO2 nanoparticles refined the microstructure. Multilayer coatings which consisted of Ni-TiO2 and TiO2-rich layers were deposited by pulse potential deposition through limiting the nickel deposition by diffusion control mechanism, and cross sectional morphology and line scan of the layers were studied by FESEM. TiO2-rich layers thicknesses and accordingly, the content of TiO2 reinforcement enhanced through limiting the nickel deposition for longer durations, reaching 104 nm and 18.47 wt.%, respectively in the optimum condition. The corrosion behavior of the coatings in 1M NaCl and 0.5M H2SO4 electrolytes were compared by means of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Increase of corrosion resistance and the passivation tendency and the decrease of the double layer capacitance were favored by TiO2 incorporation, while the degree of passivation declined as embedded particles disturbed the continuity of passive layer. The role of TiO2 incorporation on the improvement of mechanical properties including hardness, elasticity, scratch resistance and friction coefficient was investigated by the means of atomic force microscopy (AFM). Hydrophilicity and wettability of the composite coatings were investigated under UV illumination and the water contact angle of the multilayer was reduced to 7.23° after 1 hour of UV irradiation. Furthermore, surface hydroxyl groups density which account for the photoinduced hydrophilicity of the coatings were defined by XPS analysis, before and after UV illumination. The photocatalytic activity of the nanocomposite coatings was characterized by the degradation test of methyl orange and it was confirmed that TiO2 content, irradiation duration and sintering temperature affect the photocatalytic efficiency of the coatings. The multilayer was capable of disintegrating the methyl orange up to 53.64% after 5 hours of UV illumination. The photoelectrocatalytic degradation of phenol using nanocomposite coatings was investigated and the effect of different applied potentials was determined. The results indicated that the amount of phenol degraded by multilayer under the anodic potential of 600 mV along with 2 hours of simultaneous UV illumination was 97.22%
  9. Keywords:
  10. Pulse Current ; Hydrofilicity ; Electrodeposition ; Nanocomposite Multilayer ; Nickel-Titanium Oxide Nanocomposite

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