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Sol-gel Derived Nano Structured ZnO-Graphene Thin Film for Corrosion Control Applications

Razavi Zadeh, Omid | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: English
  3. Document No: 52723 (57)
  4. University: Sharif University of Technology, International Campus, Kish Island
  5. Department: Science and Engineering
  6. Advisor(s): Ghorbani, Mohammad; Simchi, Abdolreza
  7. Abstract:
  8. An isopropanol supercritical reducing environment was prepared by fabricating a high temperature, high pressure autoclave, in order to make a hybridized structure of zinc oxide and graphene oxide, entitled as ZnO-G. In this novel structure, the oxygen acts as bridging element between zinc and carbon, that connects a wide band gap semiconductor to a narrow banded one. The hybridization mechanism is studied by FTIR analysis, and morphology is shown by FE-SEM. The micrographs obtained from the thin film show a stacked pile of ZnO-G disks, like a button, dispersed on a crack free layer. In addition, the crystallographic structure was revealed by comparing low angle X-ray diffraction patterns to standard cards.Next, the band gap and photoactive properties of the ZnO-G material were studied by means of UV-Vis and photo-luminescence analysis given away a mix band gap of 1.17eV comprising three electron trapping levels near the Fermi level.Afterwards, the corrosion resistivity and photo-electrochemical (PEC) properties of the ZnO-G thin film on a steel substrate were investigated by Linear Sweep Voltammetry (LSV), Electrochemical Impedance Spectroscopy (EIS) and Mott-Schottky (MS) examination. As a result, hybridized ZnO-G thin film presented 99% lower corrosion rate in 3.5 wt.% NaCl electrolyte than the conventional galvanized steel. Despite the fact that galvanized steel inhibits steel corrosion by sacrificial mechanism, ZnO-G protects the substrate as a solid barrier against invading environment. Likewise, in wet H2S electrolyte, ZnO-G offered 40% lower corrosion rate than the conventional galvanize coating. Moreover, the ability of the ZnO-G thin film as a photo-anode in photo-cathodic protection applications was investigated. ZnO-G thin film effectively protected a stainless steel 304 in darkness, and UV illumination improved the level of protection in the orders of 290 and 390mV via photo-induced current, in 3.5% NaCl and wet H2S electrolytes, respectively. The ZnO-G film slightly accelerated the corrosion of carbon steel St32 under dark condition in 3.5% NaCl electrolyte, but UV illumination led to photo-cathodic protection up to -850 mV vs. SCE. Meanwhile, in wet H2S electrolyte, coupling of carbon steel to ZnO-G photo-anode in darkness had not much effect, while UV illumination caused photo-cathodic protection up to -1050 mV vs. SCE. Finally, the ZnO-G protrusions on the thin film were introduced as a prospecting micro-electrode for sulfidation passive monitoring, as a result of ZnO(1-x)Sx nano-crystals formation
  9. Keywords:
  10. ZINC ; Graphene ; Corrosion ; Photocathodic Protection ; Photoelectrochemical Sensor

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