Loading...

Electrodeposition and Characterization of Zn-Ni-P/Zn-Ni Multilayer from Citrate Bath

Ahmadi, Kiumars | 2021

303 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54512 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ghorbani, Mohammad
  7. Abstract:
  8. The aim of this study was electrodeposition of Zn-Ni-P/Zn-Ni multilayer coatings by single-bath method from a citrate bath to produce a sacrificial coating with high barrier properties compared to Zn-Ni monolayer coating. The coatings that were prepared at 10 mA/cm2 was Zn-Ni-P (Ni-rich and percentage of zinc, nickel and phosphorus, respectively: 40, 50 and 10 %), and the alloy deposited in 60 mA/cm2 were practically Zn-Ni (Zn-rich, 85% zinc) and almost phosphorus free. Galvanostatic pulse deposition method through switching of the current density between the two values mentioned in monolayers (10 and 60 mA/cm2) in different time periods to create bilayers corresponding to the monolayers, was applied for deposition of multilayers. Monolayers and multilayers in 2, 4, 6, 8, 10, 16, 20 and 32 layers were prepared and studied. Chemical composition, surface morphology and cross-section of coatings, surface roughness and phase structure were studied by AAS and EDS, SEM, AFM and XRD analysis, respectively. Three-dimensional and pyramidal growth pattern appeared in Zn-Ni layers, and Zn-Ni-P layres had three-dimensional and spherical growth pattern. And the multilayers also included a combination of these two patterns, and as the number of layers increased, it appeared in spherical-cauliflower morphology. The roughness of the Zn-Ni-P and Zn-Ni monolayers were 13.92 nm and 38.38 nm, respectively. The roughness increased by increasing the number of layers and reached to 67.94 nm in 32 layer coating.Structural analysis demonstrated that the Zn-Ni-P layers were amorphous and the Zn-Ni layers exhibited crystallite phase of γ Ni2Zn11 and the multilayers included periodic iteration, nickel-rich amorphous barrier layers and sacrificial of Zn-rich γ phase layers. The corrosion properties of the coatings were studied by polarization and electrochemical impedance tests. The corrosion current densities of Zn-Ni-P and Zn-Ni monolayers were 6.50×10-6 and 6.67×10-4 A/cm2 respectively, and corrosion rate decreased by layering and reached to the optimal value of 1.89×10-5 A/cm2 in the 20 layer coating. The polarization resistance (Rp) of Zn-Ni-P and Zn-Ni monolayers were 2026 and 139.6 Ω.cm2 respectively, and the polarization resistance increased by layering and increasing number of layer and reached to the optimal value of 1460 Ω.cm2 in 20 layer coating
  9. Keywords:
  10. Electrodeposition ; Multi-Layer Coating ; Corrosion ; Citrate Bath ; Zinc-Nickel-Phosphorus Multilayer Coatings ; Single Bath Method

 Digital Object List

 Bookmark

No TOC