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Study of the Effect of Electroplated Nanocrystalline Nickel Grain Size on Corrosion Resistance

Ghorbanpour, Arian | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40139 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Baghalha, Morteza; Kazemeini, Mohammad
  7. Abstract:
  8. In this project, nonocrystalline nickel coatings with grain sizes within the range of 9-27 nanometers were produced on yellow-brass plates by electroplating in a modified Watts bath applying current densities from 2 to 6 A/dm2 and bath stirring speeds from 0 to 400 rpm. To determine crystallite size, X-ray diffraction technique (XRD) was utilized; it was observed that grain size declined continuously with increase in current density and then in bath stirring speed. The experimental results coming from XRD tests were compared with a theoretical model in order to verify their reliability; the obtained curve indicated a good correspondence between the experimental data and the theoretical linear relationship between logarithm of grain size and logarithm of current density. Furthermore, the Tafel slope was calculated at 0.16 V using the line slope, which is a reasonable figure in electrochemical systems. At last, electrochemical behavior of the electrodeposited specimens was evaluated by conducting polarization tests in distilled water. These tests results demonstrated that corrosion rate of the coatings which had been prepared in the stationary system decreased with decrease in grain size. However, by applying turbulence to the bath, the surface became more vulnerable to corrosion and increase in turbulence intensity resulted in a higher corrosion rate in the polarization tests. Moreover, no tangible passivation behavior was observed by raising the potential to values higher than corrosion potential for all the samples, which confirms the weak and defective nature of passive layer forming on electrodeposited nanocrystalline nickel coating
  9. Keywords:
  10. Nickel ; Electroplating ; Grain Size ; Corrosion Rate ; Nanocrystalline Coating

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