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Formation and Investigation of Zinc-Nickel Two Cathionic Electrophospahte Coating Properties on Galvanized Steel

Barati Darband, Ghasem | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 47516 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Afshar, Abdollah
  7. Abstract:
  8. By using electrophoaphating treatment in the metal coating process, the operating temperature of chemical phosphating bath is decrease and also difficulties with the use of high temperature bath is eliminated. The aim of this study is investigate the effect of operating parameter on coating properties and also investigation the deposition mechanism of Zn-Ni electrophosphate coating. Coating properties such as morphology, corrosion resistance and porosity of the coating characterized using SEM, polarization test and electrochemical method respectively. The values used for pH effect was 1.6,1.8,2 and 2.2 results indicated that by increasing the pH value from 1.6 to 1.8 the icorr decrease from 2.25 to 0.82 µA/cm2. Also increase the pH to 2.2 caused the increase in icorr to 2.83. The used current density values was 5, 15, 25 and 35 mA/cm2. And the results of tests indicated that by increasing the current density from 5 to 15 mA/cm2 the icorr decrease from 3.28 to 2.23µA/cm2. And also by increasing the current density to 35mA/cm2 the icorr was increased to 22.43 µA/cm2 and the coating porosity was increased. By adding the 1g/l Ni(No3)2 to phoaphating bath caused the decrease in icorr from 12.4 to 1µA/cm2 and also the surface of specimen was fully covered by phoaphate crystals. The results also indicated, by increasing the phosphating temperature from 27 to 40 ºC, the icorr decrease from 10.71 to 1.04 µA/cm2 and specimen surface also was covered by phosphate crystals. By increasing the phosphating temperature to 60 ºC the excessive growth of phoaphate crystals cause the increase in coating porosity and thereby reducing the corrosion resistance of the coating. Also results indicated that, by using anodic electrochemical treatments porous coating is formed that compared with the coating formed by cathodic electrochemical method has less corrosion resistance. Also deposition mechanism of Zn-Ni phosphate coating formed by cathodic electrochemical method was investigated in this study
  9. Keywords:
  10. Corrosion Resistance ; Scanning Electron Microscopy (SEM) ; Polarization ; Coating ; Electrophosphating ; Zinc-Nickel Coat

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