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Investigation and Fabrication of Cr2O3 Thin Film Coating on Soda Lime and Low Carbon Steel Substrate

Sarhadi, Neda | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46829 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Dolati, Abolghasem
  7. Abstract:
  8. Chromium oxide coatings (Cr2O3) have been widely used due to their remarkable properties in corrosion, wear, optical and mechanical applications. So far, several methods have been used to prepare Cr2O3 thin films. In this study, the chromium oxide was produced by the sol-gel method and dip coated on the low carbon steel and glass substrates. In this context, we encountered with the problem of incoherency of the Cr2O3 ceramic coating to the steel substrates. It is highly likely that this problem be due to causes such as: a) thermal stresses due to the difference between the thermal expansion coefficients of the substrate and the coating, b) incoherent substrate/coating interface due to their different lattice parameters, c) mechanical stresses due to rapid solvent evaporation and d)oxidation of steel substrate during heat treatment. Therefore Using an intermediate layer, controlling heat treatment conditions, using a furnace with inert atmosphere and changing precursor concentration were extremely helpful in order to remove the surface cracks and improve the coatings quality of the steel substrates. After obtaining a cohesive and uniform coating on the substrate, the effect of number of coating layers, sol concentration and heat treatment conditions were studied on the microstructure and crystallite size, optical properties and the corrosion behavior of the coatings. It was observed that increasing the number of coating layers up to 6 caused an 0.07eV drop of the coating band gap, while increasing heat treatment temperature to 400oC could cause 0.4eV drop in coating bang gap. Studding corrosion behavior of produced coating, it was found out that first layer of Cr2O3 thin film increased corrosion current density from 938.45μA/cm2 to 1135.13μA/cm2, while second and third Cr2O3 thin film layers decreased this amount to respectively, 240.64μA/cm2 and 40.58μA/cm2, resulting in improved corrosion properties of the steel samples. The appliation of an intermediate layer of SiO2 coating before applying Cr2O3 layer, lead to a further reduction in the corrosion current density and increased corrosion resistivity, as for the steel samples with 3 layers of Cr2O3 in the presence of SiO2 intermediate layer, corrosion current density decreased to 19.84μA/cm2 which means better corrosion resistance in comparison to samples with no intermediate layer
  9. Keywords:
  10. Corrosion Resistance ; Optical Properties ; Surface Topography Study ; Chromium Oxide Coating ; Cohesive Improvement

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